SCHOOL OF INDUSTRIAL SCIENCE AND TECHNOLOGY
Evaluation of anti-obesity properties of Mangifera indica leaves for potential incorporation into an anti-obesity remedy
By Deon T Mageza (h140254w)
HIT 400 PROJECT (CAPSTONE DESIGN)
SUPERVISED BY MR CHUMA
A DISSERTATION SUBMITTED IN PARTIAL FULFILMENT OF THE
REQUIREMENTS FOR THE BACHOLORS OF PHARMACY HOUNOURS DEGREE OF
The prevalence of obesity is increasing at a frightening rate, but, sadly, only few medications are currently on the market. Currently it is estimated that there are more than 1.9 billion adults aged 18 years and older are overweight and 650 million adults obese. Overweight and obesity is the risk factor for many health problems like diabetes, heart disease, osteoarthritis and certain cancers. Obesity is largely regarded as lipid metabolism disorder and enzymes involved in this process can be selectively targeted to develop anti-obesity drugs. However, most of the anti-obesity drugs that were approved on the market have now been withdrawn due to serious adverse effects. Available approaches for the treatment of obesity involve inhibition of dietary triglyceride absorption via inhibition of pancreatic lipase (PL) as this is the major source of excess calories and natural products have a potential to provide a vast pool of PL inhibitors that can possibly be developed into clinical products. In this project the inhibitory effect of on lipase enzyme was determined using titration techinique. The % inhibition of the extracts was found to be 40 %.The lipase enzyme inhibition effect of Mangifera indica leaves ethanol extract was ascribed to be due to the presents of phytochemials such as phenolic compounds like flavonoids, phenolic acid and polyphenols which were conformed to be present by phytochemical analysis performed.
Obesity, Inhibition, absorption, extracts, metabolism, Lipid
The capstone design project is my original work except where source have been acknowledged. This work has never been submitted to any university for any degree and is not being concurrently submitted for any degree.
Student’s Signature: ………………………………..Date: …………………
(Deon T Mageza)
Supervisor’s Signature: ……………………………. Date: …………………
(Mr D F Chuma)
Supervisor’s Signature: ……………………………. Date: …………………
(Proff B M Gundidza)
All rights reserved. No part of this research project may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, recording or otherwise without prior permission of the author or of the Harare Institute of Technology on behalf of the author.
This project is lovingly dedicated to my father Mr Lucklips Mageza and my mother Mrs Cecilia Mageza who are my constant joy and inspiration. I would also like to dedicate this project to my brother Guidance T Mageza and my two young sisters Persistance T Mageza and Viennah T Mageza for constantly bringing out the best in me. I only hope that I am able to bring out the best in them.
You cannot depend on your eyes when
your imagination is out of focus.
— Mark Twain
Throughout this project, it becomes increasingly ostensible that its success depends on so many other people’s effort in addition to mine. As the adage goes, to go too fast you go alone but to go to fast you go together. While the list is endless I am indebted to them all. For space limitation this document will include few names. I would like to thank my core supervisors Mr D.F Chuma for his patient and kind supervision and also Professor B M Gundidza for their unwavering support throughout the year to make this project a success and not forgetting Mr Chaweza the laboratory technician for his unconditional input throughout the project. I also want to acknowledge my family and friends for providing moral and financial support. Last but not least I want to thank the Almighty God for everything to make this project a success. While these contributions were of great assistance, mistakes herein are my own faults.
List of acronyms
BMI ………………………………………..Body Mass Index
BMR…………………………………………..Basal Metabolic Rate
CB1………………………………………….. Cannabinoid -1 receptors
CB2……………………………………………Cannabinoid -2 receptors
FAS…………………………………………Fatty Acid Synthase
FTC…………………………………………….Ferric Thiocyanate Test
HFD ……………………………………………High Fat Diet
MAO………………………………………….. Monoamine Oxidase
MIC …………………………………………….Minimum Inhibitory Concentration
MILE……………………………………………Mangifera indica leaves extract
PAL……………………………………………..Physical Activity Level
WHO………………………………………..World Health Organisation
Definition of terms
Adipose tissue is a type of connective tissue consisting of adipose cells, which are specialized to produce and store large fat globules. These globules are composed mainly of glycerol esters of oleic, palmitic, and stearic acids. Adipose tissue is the main reservoir of fat in animals.
Adiposity is a condition of being severely overweight, or obese.
Fatty Acid is a carboxylic acid with a long aliphatic chain, which is either saturated or unsaturated. Most naturally occurring fatty acids have an unbranched chain of an even number of carbon atoms, from 4 to 28.
Fats also known as triglycerides are esters of three fatty acid chains and the alcohol glycerol.
Inhibitor is a substance which slows down or prevents a particular chemical reaction or other process or which reduces the activity of a particular reactant, catalyst, or enzyme.
Inhibition concentration is the concentration of a chemical which prevents or inhibit the enzyme activity.
Lipase inhibitors are substances used to reduce the activity of lipases found in the intestine. Lipases are secreted by the pancreas when fat is present. The primary role of lipase inhibitors is to decrease the gastrointestinal absorption of fats.
Lipolysis is the breakdown of fats and other lipids by hydrolysis to release fatty acids.
Metabolism is the set of life-sustaining chemical transformations within the cells of organisms. The three main purposes of metabolism are the conversion of food/fuel to energy to run cellular processes, the conversion of food/fuel to building blocks for proteins, lipids, nucleic acids, and some carbohydrates, and the elimination of nitrogenous wastes. These enzyme-catalyzed reactions allow organisms to grow and reproduce, maintain their structures, and respond to their environments. The word metabolism can also refer to the sum of all chemical reactions that occur in living organisms, including digestion and the transport of substances into and between different cells, in which case the set of reactions within the cells is called intermediary metabolism or intermediate metabolism.
Triglycerides are an ester derived from glycerol and three fatty acids (from tri- and glyceride).
Table of contents
CHAPTER 1: INTRODUCTION 1
Problem statement 1
Aims and objectives 5
CHAPTER 2: LITRITURE REVIEW 6
2.0 OBESITY 6
2.1 EDEMIOLOGY 9
2.2 CAUSES OF OBESITY 10
2.2.1Energy Balance in the Development of Obesity 10
2.2.2 High fat diets 12
2.2.3 Energy dense foods and drinks 13
Physical Activity 13
Weight gain secondary to medical conditions 14
2.2 Pathophysiological futures of obesity 15
2.2.1 Anatomical Effects 15
2.2.2 Metabolic and Physiological Effects 16
2.2.3 Psychological Effects 17
Clinical presentation and diagnosis 18
Different ways to treat obesity 18
Appetite Regulation 18
Inhibitors of Adipogenesis 20
Inhibition of Fat Absorption 21
Plant used: Mangifera indica 30
Habitat and description of the plant 30
Other pharmacological uses 34
CHAPTER 3: Materials and Methodology 37
Plant extractions 37
Pancreatic Lipase Inhibition Assay 37
Oral acute toxicity test 38
CHAPTER 4: EXPERIMENTAL RESULTS AND ANALYSIS 40
Extraction of Mangifera indica leaves 40
Table 2 Phytochemical constituent screening of Mangifera indica leaves 41
Pancreatic Lipase Inhibition Assay 43
Calculation of % inhibition 46
Oral Acute Toxicity of Mangifera indica leaves extract 47
CHAPTER 5: DISCUSSION 49
CHAPTER 6: Conclusion 51
CHAPTER 7: RECOMENTATIONS AND SUGGESTION FOR FUTHER STUDIES. 52
Table of figure
Figure 1 shows how adiposity due to obesity contribute to a number of complications 8
Figure 2 shows how net energy stores are determined by various inputs and outputs. Obesity occurs when imbalance occurs between energy intake and expenditure 12
Figure 3 stacture of orlistat 26
Figure 4 33
Figure 5 fig mango fruits and a mango tree 33
Figure 6 structure of magifen the major bio-active constituent of Mangifera indica 34
Figure 7 shows the internal organs of a mouse during oral acute studies 48
Figure 8 internal parts of a mouse during oral acute studies 49
Consents of tables
Table 1: Quantities of initial plant material and the crude and purified extracts 41
Table 2 Phytochemical constituent screening of Mangifera indica leaves 42
Table 3 Titration of free fatty acids produced form a mixture lipase enzyme, Mangifera indica leaves extracts and olive oil with 0.1mol/LNaOH 44
Table 4 Titration of free fatty acids produced from a mixture of lipase and olive oil with 0.1mol/L NaOH 44
Table 5 Titration of olive oil without either enzyme or MIE with 0.1mol/L NaOH 45
CHAPTER 1: INTRODUCTION
Obesity is a rapidly growing epidemic worldwide, presenting an increase in the risk of morbidity and mortality in many countries across the world (1). Today more than 1.9 billion people are overweight worldwide and 650 million are classified as obese. The incidence of obesity is rising at a frightening rate and obesity is becoming a major public health concern with incalculable social costs (1). Changes in food consumption, socioeconomic and demographic factors and physical activity may be important factors that contribute to the increase prevalence of the condition. World Health Organization (WHO) defines obesity as an abnormal or excessive fat accumulation detrimental to human health. Obesity is a complex disease caused by the interaction of a myriad of genetic, dietary, lifestyle, and environmental factors, which favours a chronic positive energy balance, and leads to increased body fat mass (2). Obesity is a risk factor for the development of metabolic disorders such as diabetes, hypertension, and cardiovascular diseases in addition to chronic diseases such as stroke, osteoarthritis, sleep apnea, some cancers, and inflammation-based pathologies (3).Since obesity is associated with a number of complications there is need to come up with long-term solutions for weight management and control. Obesity is also defined as an increased adipose tissue mass, which is the result of an enlargement in fat cells and/or an increase in their number. A crude measure of obesity is the Body Mass Index (BMI), calculated as body weight in kilogram divided by the square of height in meters. Being overweight is defined as a BMI of 25.0–29.9?kg?m?2, and a BMI exceeding 30?kg?m?2 is considered as obese. An extreme obesity is defined as a BMI of greater than 40?kg?m?2. (3)
Pancreatic lipase inhibition is classified as one of the best approaches to treat obesity because more that 50-70 % total dietary fat hydrolysis are performed by pancreatic lipase 4. Besides, pancreatic lipase inhibition does not alter any central mechanism; make it an ideal approach for obesity treatment 5. Search for potent lipase inhibitors from plant extracts is one of the screening strategies used in the discovery of anti-obesity drugs .Plants have been used as traditional natural medicines for healing many diseases. In particular, various oriental medicinal plants are reported to have biological activity 6. In this study Mangifera indica crude extracts will be evaluated as potential anti-obesity agents by monitoring their anti-lipase activity.
Mangifera indica (mango) is one of the widely consumed tropical fruits in the world (8).Different parts of mango tree are shown to have medicinal properties.The leaves are astringent and odontalgic. An infusion of leaves extracts is drunk to reduce blood pressure and as a treatment for conditions such as angina, asthma, coughs and diabetes. Externally, the leaves are used in a convalescent bath. A mouthwash made from the leaves is effective in hardening the gums and helping to treat dental problems. The leaves are used to treat skin irritations (9).
Currently drugs available in the market for treatment of obesity can be divided into two major classes one being orlistat, which reduces fat absorption through inhibition of pancreatic lipase and the second is subutramine which is an anorectic or appetite suppressant. These drugs both have adverse effects including increased blood pressure, headache, dry mouth, insomnia, and constipation which limit their use. Also there use of medicinal plants in the management of obesity have no enough evidence based results to support their efficacy as well as well as understanding of their mechanism of action which this project seeks to address.
Mangifera indica leaves extract have lipase inhibition activity.
Aims and objectives
To evaluate anti-obesity properties of Mangifera indica leaves extracts
To extract crude extracts from Mangifera indica using ethanol.
To do phytochemical analysis of Mangifera indica leaves crude extracts.
To determine the lipase inhibition activity of Mangifera indica leaves crude extracts.
To do acute oral toxicity using mice.
CHAPTER 2: LITRITURE REVIEW
Obesity is chronic metabolic disorder that is determined by multiple biological and environmental factors, a sedentary lifestyle, and a genetic predisposition (11).It is characterised by an abnormal increase in body weight due to excessive fat deposition. It is a condition in which excess body fat has accumulated to the extent that they may have adverse health effects which leads to reduction in life expectancy and / or increased health problems. If the daily caloric intake is in perfect balance with the energy requirements, mature healthy individuals maintain a constant body weight (12).
A convenient and reliable indicator of the body fat is the body mass index (BMI) which is body weight in kilograms divided by the square of height in meters. BMI Values above 25 are abnormal. Individuals with BMI values between 25 and 30 are overweight and those with values greater than 30 are obese (13). These markers provide common benchmarks for assessment, but the risks of disease in all populations can increase progressively from lower BMI levels.
Measurement of waist circumference (WC) is used to assess for increased abdominal fat accumulation and to determine health risk. Waist circumference measurements greater than 102 cm in men and 88 cm in women have been proposed as markers for increased risk of metabolic diseases. Increased WC, independent of BMI classification, has been shown to predict obesity-related diseases which include diabetes, hypertension, dyslipidemia, and cardiovascular disease. Therefore, WC measurement is useful in identifying individuals that are normal weight or overweight with health risk due to increased abdominal fat accumulation (12, 13).
Obesity increases the chances of a range of diseases, like heart disease, type 2 diabetes, breathing difficulties during sleep, certain types of cancer, and osteoarthritis (2).
Figure 1 shows how adiposity due to obesity contribute to a number of complications
Obesity is a major public health concern worldwide and is
the leading cause of numerous medical conditions like cardiovascular disease, hypertension, dyslipidemia, diabetes, sleep
apnea and premature death. According to recent WHO global estimates in 2016, more than 1.9 billion adults aged 18 years and older were overweight. Of these over 650 million adults were obese. In 2016, 39% of adults aged 18 years and over were overweight and about 13% of the world’s adult population was obese in 2016(14).
The worldwide prevalence of obesity has tripled between 1975 and 2016.An estimate 41 million children under the age of 5 years were overweight or obese in 2016. Obesity and overweight were historically considered a high-income country problems but are now are also on the rise in low-income country and middle-income countries, mainly in urban settings. In Africa, the number of overweight children below the age of 5 has increased by nearly 50 per cent since 2000. Nearly half the number of children under 5 who were overweight or obese in 2016 lived in Asia. Over 340 million children and adolescents aged 5-19 were overweight or obese in 2016.The prevalence of overweight and obesity among children and adolescents aged 5-19 has risen spectacularly from just 4% in 1975 to over 18% in 2016. The rise has occurred similarly among both boys and girls: in 2016 18% of girls and 19% of boys were overweight (15).
Overweight and obesity are linked to more deaths worldwide than underweight (16). Globally there are more people who are obese than underweight. This occurs in every region except parts of sub-Saharan Africa and Asia (17).
CAUSES OF OBESITY
Obesity is a result of an imbalance of energy intake and energy
expenditure. Body fat accumulation will occur when an individual consumes more calories than are burned. This can easily
occur with very small differences over long periods of time (12).
The exact cause of obesity in most individuals is rarely established. Obesity is a complex trait whose etiology is multifactorial in origin, with genetic, environmental, and physiologic factors contributing to various degrees in different individuals. (12)
Energy Balance in the Development of Obesity
Obesity can be caused by a minor energy imbalance, which leads to a gradual persistent weight gain over a considerable period of time. Some researchers proposed that energy imbalance is caused by inherited metabolic characteristics whereas others believe it is caused by poor eating and lifestyle habits (18).
Positive energy balance occurs when energy intake is greater than energy expenditure and promotes weight gain (Figure 2). Conversely, negative energy balance promotes decrease in body fat stores and weight loss. Body weight is regulated by a number of physiological processes, which have the ability to maintain weight within a relatively narrow range. It is thought that the body exerts a stronger defence against under nutrition and weight loss than it does against over-consumption and weight gain (19).
Figure 2 shows that positive weight and energy balance are predisposed by powerful societal and environmental forces which may overwhelm the physiological regulatory mechanisms that operate to keep weight stable. These include increasing automation, lack of recreational facilities and opportunities, increase in food variety and availability. Moreover, the vulnerability of individuals to these influences is affected by genetic and other biological factors such as sex, age and hormonal activities, over which they have little or no control.
Dietary intake and physical activity are important risk factors in the development of obesity (18). If calorie intake is in excess of requirement it will be stored mainly as body fat. If the stored body fats are not utilised over time, it will cause overweight or obesity (20).
Inter-individual variations among people in energy intake, basal metabolic rate, spontaneous physical activity, the relative rates of carbohydrate-to-fat oxidation, and the degree of insulin sensitivity seem to be closely involved in energy balance and in determining body weight in some individuals (18, 20).
Figure 2 shows how net energy stores are determined by various
inputs and outputs. Obesity occurs when imbalance occurs between energy intake and expenditure
High fat diets
Foods or meals that are high in fat are smaller in weight or volume than high carbohydrate foods or meals of similar energy content. Dietary fat content is directly correlated with energy intake, produces only weak satiation in comparison with protein and carbohydrate, and is thought to be processed efficiently by the body. A number of studies found that individuals on a high-fat diet are more prone to become overweight (21).
Energy dense foods and drinks
It is clear that caloric intake in excess of habitual energy
expenditure is a prerequisite to weight gain and obesity even though not all individuals with high caloric intake gain weight. Consuming too much or too often high calorie foods and drinks may increase the total calories and thus lead to obesity (20, 21, and 22). Examples of commonly eaten high calorie foods are nuts, seeds, dark chocolate, dried fruit, avocados, whole grains, milk, dairy, eggs, fish, and meats.
The energy density of foods may be contributed by its macronutrient contents. A high fat food will often be labelled as energy-dense. However, sugars for example table sugar, honey, syrups also contribute to energy density. Extra sugars added to low fat confectionaries, cakes or desserts will increase the calorie content of the food. Low fat food products may also be high in calories and therefore should not be eaten in excess. Beverages containing substantial amounts of sugar or alcohol can also contribute to excessive calorie intake (20).
Generally increased physical activity is important in the management of obesity. On the other side a sedentary lifestyle predisposes to weight gain and obesity. Studies show that obesity is associated with lower levels of physical activity (23).There is credible evidence which support that regular physical activities are protective against unhealthy weight gain whereas sedentary lifestyles, particularly sedentary occupations and inactive recreation such as watching television, promote it. Modern life is becoming increasingly sedentary and has been associated with an increased risk of obesity. Most modern jobs can be done with less physical effort due to technical progress, urbanization, transport and availability of a large range of domestic electrical appliances resulting in substantial decline in the energy spent in these activities (22, 24).
Weight gain secondary to medical conditions
In some cases patients present with obesity secondary to an identifiable acquired medical condition. Weight gain is often associated with hypothyroidism, although the majority of patients presenting with hypothyroidism are not overweight. Some of these patients lose weight within weeks of thyroxin-replacement therapy (20).
Cushing’s syndrome is another cause of obesity seen most
commonly in patients receiving exogenous glucocorticoid therapy.
Glucocorticoids are mainly prescribed for chronic conditions like
chronic obstructive pulmonary disease, organ transplantation, and
arthritis. Idiopathic Cushing’s disease caused by excess endogenous
steroid secretion is very rare. In both iatrogenic and
idiopathic Cushing’s disease, the weight gain is partly a result of fluid
retention, as well as of increased adiposity. The adiposity associated
with glucocorticoid excess has a particular body distribution in that
it is central with relative loss of body muscle mass and thinning of the skin, leading to the characteristic purple skin striae and a buffalo
hump behind the neck (12, 20).
Some medications are associated with weight gain for example medication for diabetes, notably insulin, sulfonylureas, and thiazolidinediones. Some of the weight gain associated with diabetic treatments is thought to be caused by appetite-stimulated transient hypoglycemia, but it is likely that other mechanisms are also involved. Also weight gain is associated with a number of psychiatric medicines used for treatment of psychosis, mood disorders, and depression, and with several anticonvulsants. The pharmacologic mechanism responsible for the weight gain in patients who are receiving
atypical and other antipsychotics, as well as most anticonvulsants has not been determined, but does not seem to be related to dopamine blockade (20).
Pathophysiological futures of obesity
Usually excess adiposity typically evolves slowly over time, with a long term positive energy balance. Accumulation of lipids, mainly triglycerides, in the adipose tissue occurs in conjunction with volume increases in skeletal muscle, liver, and other organs and tissues (24).Excess weight in individuals who are overweight or obese includes variable proportions of these organs and tissues. An obese person with stable weight, as compared with a person without overweight or obesity, thus has larger fat and lean mass, along with higher resting energy expenditure, cardiac output, and blood pressure and greater pancreatic ?-cell mass. Insulin secretion in the fasting state and after a glucose load increases linearly with the BMI (24).
With weight gain over time, excess lipids are distributed to many body compartments. Subcutaneous adipose tissue holds most of the stored lipids at a variety of anatomical sites that differ in metabolic and physiological characteristics (24, 25) .Most of the adipocytes in subcutaneous adipose tissue are white owing to stored triglycerides; relatively small and variable amounts of thermogenic brown and beige adipocytes are also present in adults (24,26).
Obesity is accompanied by increases in macrophages and other immune cells in adipose tissue because of tissue remodelling in response to adipocyte apoptosis. These immune cells secrete proinflammatory cytokines, which contribute to the insulin resistance that is often present in patients with obesity (24).
Obesity is usually accompanied by an increase in pharyngeal soft tissues, which may block airways during sleep and lead to obstructive sleep apnoea. Excess adiposity can imposes a mechanical load on joints which makes obesity a risk factor for the development of osteoarthritis. An increase in intraabdominal pressure purportedly accounts for the elevated risks of gastroesophageal reflux disease, Barrett’s esophagus, and esophageal adenocarcinoma among persons who are overweight or obese (24).
Metabolic and Physiological Effects
Adipocytes synthesize adipokines which are cell-signalling proteins and hormones whose secretion rates and effects are influenced by the distribution and amount of adipose tissue present. Excessive secretions of proinflammatory adipokines by adipocytes and macrophages within adipose tissue cause low-grade systemic inflammatory state in some individuals with obesity.
Hydrolysis of triglycerides within adipocytes releases free fatty acids, which are then transported in plasma to sites where they may be useful metabolically. Plasma free fatty acid levels are usually high in patients with obesity, reflecting several sources like enlarged adipose tissue mass. In addition to being found in adipose tissue, lipids are also found in liposomes, which are small cytoplasmic organelles in proximity to the mitochondria in many types of cells. Having excess adiposity, liposomes in hepatocytes can increase in size forming large vacuoles that are accompanied by a series of pathological states like non-alcoholic fatty liver disease, steatohepatitis, and cirrhosis. Accumulation of excess lipid intermediates like ceramides in some nonadipose tissues can cause lipotoxicity with cellular dysfunction and apoptosis (24).
Elevated levels of free fatty acids, inflammatory cytokines, and lipid intermediates in nonadipose tissues contribute to impaired insulin signalling and the insulin-resistant state that occurs in many individuals who are overweight or obese. Insulin resistance is again strongly linked with excess intraabdominal adipose tissue. This constellation of metabolic and anatomical findings is one of several pathophysiological mechanisms underlying the dyslipidemia of obesity, type 2 diabetes, obesity-related liver disease, and osteoarthritis. Elevated bioavailable levels of insulin-like growth factor 1 and other tumour promoting molecules have been implicated in the development of some cancers (28, 29).
Chronic over activity of the sympathetic nervous system is present in some patients with obesity and may account for multiple pathophysiological processes like high blood pressure. Heart diseases, stroke, and chronic kidney diseases all have as their main pathophysiological mechanisms high blood pressure and the cluster of findings associated with insulin resistance, obesity-associated dyslipidemia, and type 2 diabetes. Figure 1 shows some of the pathways by which the mechanical, metabolic, and physiological effects of excess adiposity lead to coexisting chronic diseases.
Obesity is associated with increased prevalence of mood, anxiety, and other psychiatric disorders, particularly among individuals with severe obesity and those seeking bariatric surgery. Causal pathways between obesity and psychiatric disorders may be bidirectional. Moreover, medications used to treat bipolar disorder, major depression, and some psychotic disorders may be associated by substantial weight gain (12, 20, and 24)
Clinical presentation and diagnosis
Excessive body fat can be determined by skinfold thickness, body density using underwater body weight, bioelectrical impedance and conductivity, dual-energy x-ray absorptiometry, computed axial tomography scan, and magnetic resonance imaging. Unfortunately, many of these methods are too expensive and time consuming for routine use (12).
Body mass index (BMI) and waist circumference (WC) are recognized,
acceptable markers of excess body fat, which independently predict disease risk. WC is the most practical method of characterizing central adiposity.WC is the narrowest circumference between the last rib and top of the iliac crest (12).
Different ways to treat obesity
A number of approaches have been applied to develop anti-obesity agents including increase in energy expenditure by blocking adipogenesis or inducing lipolysis followed by fat oxidation and reduction of energy intake by suppressing appetite and delaying or inhibiting absorption of nutrition (30,31). In this project Mangifera indica leaves extracts were analyzed for their potential lipase inhibition property.
Appetite control is the first line for obesity management. Regulation of body weight by appetite suppression is a multifactorial action which results from hormonal and neurological interrelationships (32). It is well known that dopamine, histamine, serotonin, and their related receptor activities are correlated with regulation of satiety. A complex control of human appetite and satiety is made up of about 40 orexigenic and anorexigenic hormones, enzymes, neuropeptides, other cell signaling molecules, and their receptors .Hunger and satiety signaling molecules are produced in the brain and in liver, digestive tract, and adipose tissue. The hypothalamus arcuate nucleus is the most important area of the brain which plays a key role in appetite regulation. Appetite can be regulated by neural and endocrine signaling from gastrointestinal tract for short term, while the information about adiposity level and acute nutritional status, from peripheral hormones, can be received and translated by the arcuate nucleus and brainstem neurons (33).
Substances like beta-adrenergic agonists are known to enhance hepatic fatty acid oxidation and decrease voluntary food intake in rats. Ingredients which enhance hepatic fatty acid oxidation such as consumption of 1,3-diacylglyceride oil and medium-chain fatty acids lead to reduction of food intake in human subjects (34).
The mechanism of appetite suppression in the brain is generally by affecting hunger control centers and is related with a feeling of fullness. On the other side reduction of food intake may increase ghrelin secretion in the stomach of humans which leads to stimulation of increased intake hence ghrelin antagonism might reduce the increased appetite which possibly happens with reduced feeding. Thus ghrelin can be considered an important target for treatment of obesity (31, 34) Also Melanin-Concentrating Hormone receptor antagonism can be considered a potential target for treatment of obesity by appetite regulation.
Also fatty acid synthase (FAS) is the protein in human genome produced from acetyl coenzyme A and malonyl-CoA, which catalyze the reductive synthesis of long chain fatty acids. Researches show that inhibition of FAS in mice treated with FAS inhibitors resulted in reduction of food intake and hence reduce body weight. Thus suppression of FAS can be potential therapeutic target to inhibit appetite to inducing weight loss (33)
Inhibitors of Adipogenesis
Adipocytes, also known as fat cells and lipocytes, play a major role in the regulation of energy balance and lipid homeostasis, by storing triglycerides and releasing free fatty acids in response to changing energy needs. However their long-term increased intake is related with progression of obesity and result in serious comorbidities. Adiposity mass and size are considered as important indicators of obesity. There are two types of obesity in which the first is the result of increase in adipocyte number (hyperplasic) and the second one due to increase in adipocyte volume (hypertrophic). Hyperplasia has a strongest correlation relation with obesity severity and is most obvious in severely obese individuals. However, hypertrophy, to a certain degree, is characteristic of all overweight and obese individuals (31, 33, 34).
The same as adipose tissue and muscles, peripheral tissues deal with energy production as well as nutrient metabolism although the central nervous system specifically the hypothalamus, integrates and regulates energy expenditure and food intake .Treatment which regulate the number and size of the adipocytes and the expression of signals related to energy balance and enhancement or inhibition of especial adipokines has been suggested to express anti-obesity related bioactivities. However latest research findings showed that inhibition of adipose tissue or adipogenesis expansion is associated with diabetes type 2 and metabolic disorders, like atherosclerosis.
Inhibition of Fat Absorption
Digestion and absorption of nutrients can be decreased to reduce energy intake. As fat contributes more than protein or carbohydrate to unwanted calories deposition, inhibition of fat absorption can be considered the most appropriate target to decrease energy intake. Among the currently existing treatments for obesity, development of nutrient digestion and absorption inhibitors is considered important strategies in the effort to decrease energy intake via gastrointestinal mechanisms. Inhibition of digestion and absorption of dietary lipids by inhibiting the action of pancreatic lipase can be targeted for development of anti-obesity drugs (31).
Pancreatic lipase an enzyme which catalyzes the digestion of dietary triglycerides is an important lipolytic enzyme which is synthesized and secreted through the pancreas. In humans, pancreatic lipase encoded by the PNLIP gene, plays a major role in dietary triacylglycerol absorption, hydrolyzing triacylglycerols to monoacylglycerols and fatty acids. Pancreatic lipase is responsible for the hydrolysis of 50–70% of total dietary fats and is secreted into the duodenum through the duct system of the pancreas. Pancreatic acinar cells secrete pancreatic lipase which releases fatty acids from the triglyceride skeleton at the C-1 and C-3 position. These fatty acids are incorporated into bile acid-phospholipid micelles and further absorbed at the level of the brush border of the small intestine, to finally enter the peripheral circulation as chylomicrons. Interference with fat hydrolysis results in decreased usage of ingested lipids. Thus lipase inhibition reduces fat absorption from the intestines (30,31,32,34).
Management and treatment
Obesity is a chronic disease that requires lifelong effort for successful treatment. Treatment of obesity involves a multidisciplinary approach including the expertise of a general practitioner, dietician, pharmacist, psychiatrist, or surgeon depending on the specific needs of the individual. The goals of therapy involve weight loss or weight maintenance to improve or eliminate obesity-related medical complications (12, 20).
Treatments should be aligned with the severity of overweight, associated coexisting chronic diseases, and functional limitations. The major treatment options with available for obesity sufficient evidence-based support are lifestyle intervention, pharmacotherapy, and bariatric surgery (12).
Lifestyle interventions designed to modify eating habits and physical activity are the first option for weight management considering their low cost and the minimum risk of complications (22, 36).The aim for patients who are overweight or obese is to improve health and quality of life by achieving and maintaining moderate weight loss. Less-intensive lifestyle counselling is an option for preventing additional weight gain in patients who are at low risk for disease or who choose not to participate in a high-intensity program.
Behavioural modification programs using support groups, a balanced diet, and exercise are most effective for mild obesity (20% to 40% overweight). Behavioural modification programs including nutritional education, exercise, cognitive restructuring, self monitoring are the most effective for overweight children and help to motivate parents and children to alter their lifestyles (12). Supportive family therapy is desirable, mainly for obese children. Obesity can be related to cultural attitudes, family eating behaviours, and social events involving food. Relapse prevention should identify high-risk situations or events that may cause weight gain so that the person can learn new coping strategies to avoid overeating.
Weight regain is common after a patient completes a lifestyle intervention program. The most effective behavioural method for preventing weight regain is continued support on an every-other week or monthly basis, whether in person or by telephone. Although long-term behavioural counselling is effective, it is not widely available. Moreover, when this approach fails to produce the additional weight loss that patient’s desire, it is challenging to persuade the patients to remain in counselling to maintain the smaller weight loss they have achieved (12, 36,37).
Pharmacotherapy is indicated in combination to reduced-calorie diet and increased physical exercises for long-term weight management. Medications may be considered in adults who have a BMI of 30 or higher or a BMI of 27 to 29 with at least one weight-related coexisting condition. Pharmacotherapy and lifestyle intervention resulted in additive weight loss and must be used together. Pharmacotherapy with lifestyle intervention may also be of benefit in facilitating the maintenance of reduced weight.(12,20)
Orlistat is an example. Orlistat a lipase inhibitor is a synthetic derivative of lipstatin is natural produced by Streptomyces toxytricini. Orlistat is minimally absorbed and is a potent inhibitor of gastric and pancreatic lipase. Lipase inhibition results in decreased formation of free fatty acids from dietary triglyceride (38). Additionally, lower luminal free fatty acid concentrations result in malabsorption of cholesterol. Orlistat induces weight loss by a continual lowering of dietary fat absorption (39).
Overall, results from clinical trials shows that orlistat effectively increases the amount of weight lost and decreases the amount of weight regained during medically supervised weight-loss programs. Significant improvements in lipid profile, glucose control, and other markers of metabolism are seen in spite of the elatively small 2- to 4-kg differences in weight lost when using orlistat in addition to diet. In patients with impaired glucose tolerance, weight loss using orlistat significantly decreased the rate of conversion to type 2 diabetes. Glycemic control can be improved in patients with type 2 diabetes by inducing or increasing weight loss with orlistat in addition to diet management. Also in some cases, dosages or the number of agents required for glucose lowering may be deceased in patients who use orlistat .Orlistat is the first agent of choice for the chronic treatment of obesity.
Orlistat have adverse effects which include liquid stools, steatorrhea, abdominal cramping and fat-soluble vitamin deficiencies, faecal urgency, incontinence, flatulence. These unpleasant gastrointestinal side effects limit its clinical use.
Figure 3 stacture of orlistat
Sibutramine is an example of noradrenergic–Serotonergic Agents available on the market. Sibutramine is a centrally acting phenethylamine class of drug currently approved for long-term treatment of obesity in adults. It reduces food intake by selective inhibition of reuptake of noradrenaline, serotonin and dopamine and stimulation of sympathetic nervous system, resulting in thermogenesis and lipolysis.
Baseline blood pressure should be established before beginning therapy, and close monitoring is required when using this agent. Sibutramine product labeling indicates that it should not be used in patients with a history of coronary artery disease, stroke, congestive heart failure, or arrhythmias. Like other centrally acting appetite suppressants, sibutramine should not be used in patients receiving monoamine oxidase (MAO) inhibitor therapies.
Side effects of sibutramine are due to activation of sympathetic nervous system like dry mouth, insomnia, constipation, headache, anorexia, hypertension and palpitation (37).
Endocannabinoid System Agents
A complex regulatory relationship exists between the endocannabinoid system, energy regulatory hormones, and neuropeptides. The endocannabinoid system appears to be overactive in states of overweight and obesity.
Rimonabant is an example of endocannabinoids system agents which regulate appetite. Its appetite regulation involves cannabinoid-1 (CB1) receptor which on stimulation increases demand of food. Rimonabant reduces food intake by blocking CB1 receptors and enhances thermogenesis. Its side effects include mood changes, nausea and vomiting, diarrhea, headache, dizziness and anxiety (20).
Phentermine.Phentermine is structurally similar to amphetamine,
though it has less-severe CNS stimulation and lower potential for abuse. Its mechanism of action is related to enhance NE and dopamine
Evening or nighttime dosing should be avoided because of insomnia.
Significant increases in blood pressure, palpitations, and arrhythmias
are a side effect associated with phentermine use.Use of phentamine is not advisable in hypertensive patients and those with unstable cardiovascular function. The potential for hypertensive crisis with coadministration of phentermine and MAO inhibitors is noted in product labelling because of the documented cases of this syndrome seen with coadministration of amphetamine or noradrenergic derivatives and MAO
inhibitors. Complexities surrounding the prescribing of phentermine, has led some professional groups to discourage long-term use of phentermine.
Amphetamines .Amphetamines has appetite suppressant effects. Amphetamines activate central noradrenergic receptor systems as well as dopaminergic pathways at higher doses, by stimulating neurotransmitter release. Increases in blood pressure and mild bronchodilation are attributed to peripheral ?- and ?-receptor activation. The powerful stimulant and addictive potential of the amphetamines relative to other available agents has resulted in its limited use in the treatment of obesity (20).
Mazindol .It is chemically distinct from amphetamines and phentermine. Mazindol’s tricyclic structure resulted in amphetamine-like appetite suppression. Although mazindol demonstrated efficacy as a short term therapy for weight reduction it is longer available in the market due to severe side effects.
Diethylpropion Diethylpropion stimulates norepinephrine release from presynaptic storage granules which increase adrenergic neurotransmitter concentrations and activate hypothalamic centres, which result in decreased appetite and food intake. Side effects of diethylpropion include insomnia, CNS stimulation and hypoglycaemia in diabetic patients. Diethylpropion is contraindicated in patients with severe hypertension or significant cardiovascular disease.
Serotonin is an important neurotransmitter involved in a number of
human physiologic systems like sleep–wake cycles, sensitivity to pain,
blood pressure, mood, and eating behaviours .Increasing central serotonin levels decreases the amount of food consumed and prolongs the time between food intake. Some serotonergic agents increase central serotonin concentrations via stimulating release of presynaptic stores and/or inhibition of reuptake into storage granules (20, 39)
Lorcaserin is an example of selective 5-HT2C receptor agonist which has serotonergic properties and acts as an anorectic. 5-HT2C receptors are located in various parts of the brain and their activation leads to proopiomelanocortin production .and results in the weight loss through hypophagia.
Surgery should only be used for morbidly obese individuals with BMI
?40, or ?35 kg/m2 with comorbid conditions when behavioural or pharmacologic treatments have failed. For severely obese patients with more than 100% normal weight the most effective treatment is a surgical procedure to reduce the size of the stomach. Although surgery is more effective than lifestyle and pharmacologic interventions, the procedure is associated with greater risks. Bariatric surgical procedures reduce the
absorptive surface of the GI tract resulting in malabsorption, or
reduce the stomach volume so that the person feels full after a
smaller meal. (13)
Main types of bariatric surgery currently performed are gastric banding,
vertical banded gastroplasty, Roux-en-Y gastric bypass, and biliopancreatic diversion .These procedures are effective but they cause different degree of weight loss and their complications may differ as well .Gastric bypass have shown to produce a greater weight loss compared to gastroplasty procedures. Laparoscopic is preferred than open surgical approaches for reducing postoperative complications and hospital stay (12, 13).
Pancreatic Lipase Inhibitors from Natural Products
Pancreatic lipase inhibitory properties have been extensively examined in the past two decades to determine the potential effect of natural products as antiobesity agents. Due to the huge success of natural products in the management of obesity, more researches have been focused on the identification of newer pancreatic lipase inhibitors with less unpleasant adverse effects. A number of natural products have been reported to pancreatic lipase inhibition property including protamine, ?-polylysine, polysaccharides like chitosan, dietary fibers from wheat bran and cholestyramine, soya proteins and synthetic compounds (30, 33, 34)
Plant used: Mangifera indica
Habitat and description of the plant
Mangifera indica L.also known as mango is a juicy stone fruit belongs to the family of Anacardiaceae in the order of Sapindales and is grown in many parts of the world, particularly in tropical countries. Over 1000 mango varieties are available worldwide. Among available varieties, only a few are grown on commercial scales for traded (40). Mango is currently grown for commercially purpose in nearly more than 87 countries (41). Currently, mango is cultivated on an area of approximately 3.7 million ha worldwide. In Zimbabwe, almost every homestead in the rural areas has a mango tree.
The Mangifera indica tree is medium to large (10-40 m in height) and evergreen with symmetrical, rounded canopy ranging from low and dense to upright and open. Bark is usually dark grey-brown to black, rather smooth, superficially cracked or inconspicuously fissured, peeling off in irregular, rather thick pieces. The tree has a long unbranched long tap root (up to 6-8 m) and dense mass of superficial feeder roots. Effective root system of an 18- year old mango tree may observe a 1.2 m depth with lateral spread as far as 7.5m (42). The leaves are arranged simply and are 15-45 cm in length. The petioles vary in length from 1 to 12 cm and are always swollen at the base. Leaves are variable in different shapes like oval-lanceolate, lanceolate, oblong, linear-oblong, ovate, obovate-lanceolate or roundishoblong (43). The upper surfaceof the leaves are shine and dark green while the lower is glabrous light green. Hermaphrodite and male flowers are produced in the same panicle, usually with a larger number of male flowers. The size of male and hermaphrodite flowers differs from 6 to 8 mm in diameter. They are subsessile, rarely pedicellate and have a sweet smell. The pollen grains have variable shapes and the size varying from 20 to 35 micron (46, 47). The mango fruit is more or less compressed, fleshy drupe, varies considerably in size, shape, colour, presence of fibre, flavour, taste and several other characters.
Figure 4 Shows mango fruit and a mango tree
Chemical constituents of Mangifera indica are always of an interest since there are number of medicinal claim for the plant. Researchers want to know phytochemicals responsible for the pharmacodynamic effects of the plant .The different chemical constituents of the plant are polyphenolics, flavonoids, triterpenoids. Mangiferin is a xanthone glycoside and the major bio-active constituent, isomangiferin, tannins ; gallic acid derivatives. The of mango tree bark is reported to contain protocatechic acid, catechin, mangiferin ,alanine, glycine, ?-aminobutyric acid, kinic acid, shikimic acid and the tetracyclic triterpenoids cycloart-24-en-3?,26diol, 3-ketodammar-24 (E)-en-20S,26-diol, C-24 epimers of cycloart-25 en 3?,24,27-triol and cycloartan-3?,24,27-triol (48,49).
Figure 5 structure of magifen the major bio-active constituent of Mangifera indica
Lipase inhibition and anti-obesity effects
In a study undertaken to test whether Mangifera indica Bark extracts and leaves extracts reduce body weight of normal rats receiving a high-fat diet shows that both extracts increase focal fat without significantly affecting food intake indicating that the extracts may be useful in body weight control. Rats fed with high-fat diet provide an animal model for the study of human diet-induced obesity.
In a study to investigate the anti-obesity effects of mango seeds extracts extracted with hot water in a high fat diet (HFD)-induced obesity rat model showed a significant decrease in the activity of glycerol-2-phosphate dehydrogenase in 3T3-L1 adipocytes without eliciting cell cytotoxicity and inhibited cellular lipid accumulation through down-regulation of transcription factors. In the animal model, rats fed an HFD containing 1% Mangifera indica seeds extract gained less weight than rats fed on HFD alone. The visceral fat mass in rats fed on HFD containing 1% Mangifera indica seeds extracts tended to be lower than that in rats fed on HFD alone. The study concluded that Mangifera indica seeds extract provides a novel preventive potential against obesity 29.
The study by D George et al show that ethanolic Mangifera indaca leaves extracts cause a significant reduction in body weight, Triglycerides, total cholesterol, LDL, blood glucose levels, organ and fat pad weights and increase in HDL level in rats fed with HFD.
Other pharmacological uses
Mangifera indica fruit peel extracts have anticancer effects. The anticancer properties of polyphenolic extracts from several mango varieties in cancer lines Molt-4 leukemia, A-549lung, MDA-MB-231 breast, LnCap prostate, SW-480 colon cancer cells and non-cancer colon cell line CCD-18Co were compared.Again it was also discovered that ethanol extracts of mango fruit peel had significant cytotoxicity to HeLa cells. The bioactive fraction from the ethanol extract had anti-proliferative effects with an IC50 value of