Mangosteen (Garcinia mangostana) flesh supplementation attenuates biochemical and morphological changes in the liver and kidney of high fat diet-induced obese rats

Obesity appeared to be a leading health challenge over the past century in both developed and developing countries. According to World Health Organization [1], the prevalence of worldwide obesity tripled between 1975 and 2016 with the current statistics showed 13% of adults aged 18 and above were obese and 39% were overweight. Obesity is characterized by excess accumulation of fat that lead to increase body weight [1]. It is associated with adverse health problems with fatal complications including insulin resistance, enhanced inflammatory marker expression, obstructive sleep apnoea syndrome and increased oxidative stress. Consequently, the number of people with hypertension, diabetes mellitus and cardiovascular diseases are proportionally increase with the growing prevalence of obesity [2]. The aetiology of obesity is very complex involving genetic, environmental and psychosocial factors acting through the physiological mediators of energy intake and expenditure [3]. Data from several studies suggest that increase consumption of high-calorie foods coupled with reduce intake of fruits and vegetables favour a positive energy balance which set the foundation for obesity epidemic [4‐7]. On the contrary, diet rich in vegetables and fruits can decrease the risk for chronic diseases through the beneficial combinations of fibers, micronutrients, and phytochemicals [8, 9].

The economic burden of obesity including the tangible and intangible cost is projected to increase every year [1]. Therefore, the development of novel natural therapy that is safe and effective is very critical in order to alleviate the global public health crisis of obesity and its related co-morbidities. To date, only few prescription drugs available and approved by Food and Drug Administration (FDA) for obesity treatments [10]. However, the use of anti-obesity drugs produces only small and inconsistent weight loss with severe adverse effects including abdominal pain, faecal urgency and incontinence [11]. Alternatively, dietary intervention including the use of plant based extract could produce a consistent decrease in obesity and its co-morbid diseases with less side effects.

Garcinia mangostana or known as mangosteen is a dark purple fruit with slightly acidic and sweet flavour flesh. The fruit is commonly found in the Asian region like Malaysia, India and Thailand. The fruit pericarps have been traditionally used to treat various medical conditions such as abdominal pain, wounds and skin infection since ancient time [12]. Numerous bioactive compounds have been isolated from different parts of mangosteen [13]. Among them are xanthones derivatives which are the major constituent in the pericarp. Extensive research has been carried out on the mangosteen pericarp, and demonstrated a wide range of activities including antifungal, antioxidant, antiobesity and antidiabetic [14].

The ethanolic extract of G. mangostana has been reported to exhibit potent hypoglycemic effect in streptozotocin-induced diabetic rats [15]. It is hypothesized that the positive effects were due to inhibition of α-glucosidase and α-amylase activity, which are the enzymes that responsible for carbohydrate digestion [16]. In an in-vitro study, the major component of G. mangostana extract, α-mangostin and γ-mangostin showed inhibition toward the production of pro-inflammatory markers in RAW.264.7 macrophage cells [17]. Moreover, Bumrungpert et al. [18] demonstrated that xanthones from mangoesteen ameliorated inflammation in primary human adipocytes by decreasing the expression of inflammatory mediators. Further clinical research exploring the effect of mangosteen juice blend supplementation in 40 subjects for 8 weeks found a reduction in body mass index (BMI) and c-reactive protein (CRP) levels [19]. Inflammation has been implicated in various chronic diseases including obesity. Despite of numerous reports on anti-inflammatory activities of mangosteen, to the best of our knowledge, no single study exists that examine the effect of mangosteen flesh on obesity. Hence, the present study was carried out to investigate the potential of Garcinia mangostana flesh (GMF) in attenuating the metabolic and structural changes in high fat diet-induced obese rats. In this study, Sprague Dawley rats were used because they produced neural and microvascular abnormalities which are a more-human like model after induction with high fat diet [20]. Besides, diet-induced model was found to be the closest model that have comparable aetiology of obesity as well as the pathophysiology changes that occur in obese human [21, 22].

The role of dietary fats in developing obesity is well established [24]. In this study, high-fat diet-induced obese rats were used as an experimental model for obesity. The experimental model produce obesity complications similar to human as obesity is developed from excess intake of calories which closely mimics the human diet. The high percentage of fat in the diet (40% in HFD compared to 30% in normal diet) provides excess calories intake [25] and resulted in the accumulation of body fat [7]. Consequently, HFD used in the present study successfully developed obesity in rats as evidenced from higher BMI compared to the rats fed with normal diet. Moreover, the HFD produced changes in metabolic parameters, as well as kidney and liver architectures. In the present study, the obese rats showed elevated level of plasma glucose and LDL-cholesterol level after 10 weeks of HFD induction. Similarly, Sprague-Dawley rats that were given 32% kcal of fat for 10 weeks showed significant increase in plasma LDL-cholesterol level as early as 3 weeks of induction period [26]. In addition, the obese rats in the present study developed dyslipidaemia which is characterized by the increased in triglyceride, total cholesterol and reduced HDL-cholesterol level after 17 weeks of HFD. This outcome is contrary with Poudyal et al. [27] and Ramli et al. [21] who found dyslipidaemia in high fat and high carbohydrate diet-induced obese rats after 8 weeks of induction. A possible explanation for this might be that the combination of excess carbohydrate and fat in the diet leads to higher rate of lipogenesis.

In obesity, the elevated levels of abdominal adipose tissues produces abundance of free fatty acid (FFA) released to the liver. These non-esterified fatty acids (NEFA) caused excessive production of triglyceride-rich lipoprotein (TG) particles like very low-density lipoprotein (VLDL). Consequently, liver, skeletal muscle and heart were exposed to the lipotoxic state and cause impairment to insulin-dependent metabolic process [28]. Increased VLDL is associated with increased synthesis of atherogenic LDL. High density lipoprotein cholesterol (HDL) can protect against development of atherosclerosis by reverse cholesterol transport from the vessel wall back to the liver and lessen inflammation by protecting LDL from being oxidized [29]. However, in obesity HDL decreased [30]. This is due to a reduction in lipolysis and hindered clearance of triglyceride-rich lipoprotein. Hence, this condition induces hyperinsulinemia, glucose intolerance and low plasma HDL levels [31, 32].

Besides, obesity leads to overproduction of reactive oxygen species from the increasing mechanical load and myocardial metabolism which eventually increased oxygen consumption. As a result, the balance between oxidant and antioxidant in the biological system is disrupted. The endogenous antioxidant defence system is reduced as the system is in favour of the oxidants [33]. As a result, the cell structure of lipids, proteins and DNA are damaged. In addition, the enlargement of adipocytes in obese people cause excess production of macrophage, a scavenging moribund adipocytes which is responsible for the production of inflammatory cytokines such as inducible nitric oxide synthase (iNOS) and interleukin-6 (IL-6) [34]. It was reported that the obese rats fed with high fat diet for 10 weeks had decreased their glutathione peroxidase (GPx) and superoxide dismutase (SOD) level [35]. Similarly, the current study found that obese rats had reduced plasma GPx and SOD as markers of antioxidant enzymes, as well as elevated level of plasma TNF-α and IL-6 as the pro-inflammatory markers. Therefore, our HFD-induced model showed metabolic and structural abnormalities that mimic human obesity.

Histopathological examination of liver and kidney in obese rats revealed comparable findings with previous research whereby dilation was observed in the hepatic central vein and branches of portal vein in rat fed with HFD (30%) for 8 to 12 weeks [36]. The finding suggests that HFD may act as major cause of liver steatosis. Additionally, results from the present study are in accordance with the previous study indicating that the kidney of rats that were given HFD for 3 months showed dilated blood vessels and Bowman’s capsule, mononuclear cell infiltration and degeneration in nephrons [37]. Human studies also demonstrated glomerular hypertrophy and glomerular capillary dilation in obese subjects [38]. It is suggested that the dilation of glomerulus after HFD is due to increase in metabolic demands in obese rats which consequently lead to glomerular hyperfiltration [39]. This finding broadly supports the work of other studies in this area linking obesity and glomerular size [40, 41] and adiposity and glomerular hyperfiltration [42].

With the exception of increased level of plasma glucose, GMF supplementation attenuated metabolic abnormalities and structural changes due to high fat feeding. GMF-supplemented rats reduced body weight and inflammation, improved lipid profile with no changes in HDL-cholesterol, enhanced antioxidant defence system and decreased hepatic fat accumulation and ameliorated renal abnormalities. Nevertheless, the most notable result from our study is the reduction of body weight and food intake while improving some signs of metabolic syndrome. GMF supplementation decreased food intake and total energy intake causing a reduction in body weight and other cardio-metabolic risk factors. We observed that GMF supplemented groups showed the lowest weight gain compared to control rats between week 17 and week 10. Similar results had been reported by Azman et al. [35] whereby obese rats supplemented with Tamarindus indica pulp at 25 mg/kg and 50 mg/kg showed a reduction in their body weight. The report also revealed that total food intake of the animals did not relate to total dietary caloric consumed. Our data provides us with the fact that supplementation of GMF in obese rats reduced the amount of food and total dietary calorie consumed and subsequently suppressed the excessive body weight gain due to HFD. This observations support the hypothesis that G. mangostana possesses weight reducing properties.

Nevertheless, Benton and Young [43] reported that the decreasing in body weight due to reduction in energy intake is a short term effect. Energy balance is a complex system and involves the interactions of many factors other than energy intake and energy expenditure [44]. Therefore, it is important to emphasize the physiological and psychological factors including satiating effect which may influence the amount of foods consumed. Among the contribution factors are cognitive, sensory and physiological signals during consumption and the macronutrients components of foods [45]. GMF contain 5.1% fiber in the flesh [46, 47]. The high level of fiber in GMF might contribute to satiety effects. Dietary fiber especially soluble fiber that present in significant amount in fruit have been shown to improve post-prandial satiety and reduce subsequent hunger in short term studies [48]. In fact, previous research showed the potential role of whole fruit in reducing obesity symptoms from its relatively low level of energy density and high content of dietary fiber [49]. It can thus be suggested that the mechanism of body weight reduction is due to the metabolic effects of fiber which increase the nutrient breakdown and release from the foods and contribute to satiating effect [50] as shown in our previous study [51].

In addition to the metabolic effects elicited by dietary fiber, the bioactive compounds in G. mangostana such as xanthones, anthocyanin and phenolic acids [52] may play a pivotal role in normalizing the metabolic abnormalities in obese rats. Available evidences suggested that the polyphenols from mangoesteen extract including its xanthones exerted good pharmacological effects in animal model of metabolic syndromes, diabetes and obesity [53, 54]. The most abundant xanthones in the pericarp of mangosteen is α-mangostin which has been shown to possess strong cardioprotective, antioxidant, anti-inflammatory and anti-obesity agents [55]. These beneficial effects are clearly seen in the present study whereby the antioxidant enzymes and total antioxidant capacity (TAC) increases while total cholesterol, LDL-cholesterol and triglyceride level in obese rats decreases following GMF supplementation. Our results are consistent with those of Choi et al. [56] and Chae et al. [57] who found a reduction of free fatty acids (FFA), total cholesterol and LDL-cholesterol in obese mouse supplemented with 50 mg/kg α-mangostin or 200 mg/kg peel extract. Previous study has shown that the supplementation of α-mangostin in obese mice reduced their body weight through the regulation of SirT-1-AMPK (Sirtuin 1–5’AMP-activated protein kinase) and PPARγ (peroxisome proliferator-activated receptor-γ) pathways [56]. Based on the studies, it is proposed that the antiobesity effect of GMF is associated with the increase in lipid metabolism that lead to the reduction in body fat mass and other related metabolic complications. It is possible; therefore, the combined effect of α-mangostin and fiber may be responsible for the GMF-induced reduction of body weight and the improvement of lipid profile in the present study. Thus, the limitation of the present study is the lack of capacity to determine the effect of specific compounds in GMF that mediate the observed positive results.

In the present study, GMF was observed to enhance endogenous antioxidant system as evidenced from the elevated level of antioxidant enzymes. These effects suggest the ability of GMF to scavenge the free radicals generated from HFD and illustrate the efficiency of GMF in the deactivation of hydrogen peroxide in biological system. In addition, the reductions of TNF-α and IL-6 levels after GMF supplementation reflect inflammation decreased in obese rats. A comparable finding was reported by Bumrungpert et al. [18] whereby human adipocytes treated with α-mangostin showed a decreased in the expression of inflammatory genes. Besides, daily consumption of mangosteen-based drink for 30 days in healthy adult demonstrated 46% reduction of inflammatory markers [58]. A part from that, the treatment with 800 mg/kg ethanolic extract of mangosteen pericarp induced protection from atherosclerosis in hypercholestromic rats by maintaining the expression of eNOS (endothelial nitric oxide synthase) and reducing hydrogen peroxide and HIF-1α (hypoxia-inducible factor 1-alpha) that eventually leads to reduce vasa vasorum angiogenesis [13, 59]. On the contrary, α-mangostin was unable to scavenge hydrogen peroxide; instead, the compound ameliorated 3-nitropropionic acid-induced reactive oxygen species formation and provides renoprotective effects against cisplatin (cDDP; cis-diamminedichloroplatinum II)-induced nephrotoxicity in rats [60]. Nevertheless, the inhibition of lipid peroxidation and enhancement of antioxidant defence system shown in injury-induced myocardial infarction in rats following α-mangostin pre-treatment could reflect the potent antioxidant and anti-inflammatory action of this xanthones [61]. It can thus be proposed that GMF has the potential to attenuate abnormalities caused by high fat diet-induced obesity in rats based on the positive results observed from the present study.

The results of this study demonstrate that supplementation of GMF in high fat diet-induced obese rats reduced body weight and attenuated the metabolic and structural changes in liver and kidney of obese rats. Therefore, GMF may have potential to ameliorate the complications related to high fat diet-induced obesity in rats. However, the results warrant further research on pharmacokinetics and pharmacodynamic, as well as the underlying mechanism using molecular approach, especially on the effects of specific bioactive compounds in GMF on obesity. Furthermore, it is also crucial to determine the effect GMF on pancreatic lipase activity as the inhibition of its activity may reduce fat absorption, and possess beneficial effects on obesity.