Investigating the metabolic and antioxidative pharmacological potential of ellagitannins obtained from pomegranate fruit peel in fructose-fed experimental rats

Abstract

Background The increasing prevalence of obesity, and some unhealthy lifestyle factors such as physical inactivity and unhealthy dieting, has exacerbated the prevalence of metabolic and cardiovascular diseases. Specifically, chronic consumption of added sugars such as sucrose and fructose has been implicated in metabolic and cardiovascular impairments, including insulin resistance and dyslipidaemia. Pomegranate fruit is a fruit that is beneficial to oxidative and vascular health, largely attributed to its constituent ellagitannins. Increasing evidence indicates that the peel is particularly rich in ellagitannins and possesses antioxidant, glycaemic control, and anti-dyslipidaemic potentials. However, the ameliorative potential of pomegranate peel or its ellagitannins on metabolic disorders associated with chronic consumption of added sugars remains poorly investigated or understood. Therefore, this study was undertaken to investigate the effect of an ellagitannins-rich fraction obtained from pomegranate peel on selected metabolic alterations in rats induced by high fructose consumption. Methodology Class 1 grade of pomegranate fruit (Var. “Wonderful) was bought from a local fruit packaging company (Sonlia Fruit Packhouse, Wellington, Western Cape Province, South Africa). The peel was removed and extracted with distilled water to obtain the crude water extract. An ellagitannins-rich fraction was obtained from the crude extract using an Amberlite® XAD16N resin. The phytochemicals in the fractions were determined and quantified using liquid chromatography-mass spectrometry (LC-MS). For the animal experiment, eighteen 14 weeks old Sprague-Dawley rats were procured and allowed to acclimatize for 1 week. The animals were then divided into three groups, namely “Normal Control”, “Fructose”, and “Fructose + Ellagitannins” groups. The “Normal Control” received normal drinking water. The “Fructose” group received 20% fructose solution instead of drinking water. The last group, “Fructose + Ellagitannins” received 20% fructose solution containing 200 mg/kg body weight of the fraction in place of drinking water. The treatments lasted for 6 weeks, during which body weight and food intake were measured weekly. In the last week of the experiment, oral glucose tolerance test (OGTT) was carried out, while fasting (FBG) and non-fasting (NFBG) blood glucose were measured. At the end of the 6-week experimental period, the blood lipids (triglycerides, total cholesterol, LDL-cholesterol and HDL-cholesterol) levels were measured. The animals were then euthanized, and blood and liver tissue were collected. Serum and liver homogenates were prepared from the blood and liver tissue, respectively. Liver glycogen content and lipid peroxidation level was determined, while serum insulin, liver total and phospho Akt, and liver interleukin 1β (IL-1β) levels were measured using commercial ELISA kits. Catalase and superoxide dismutase (SOD) activities were measured using commercial colorimetric assay kits. Liver histology was examined microscopically, and the homeostatic model assessment of insulin resistance (HOMA-IR) was calculated. Results Fructose consumption suppressed food intake but increased weight gain. It also elevated insulin levels, impaired glucose tolerance (AUC = 246 vs 208 mg.h/dL), reduced insulin sensitivity (HOMA-IR = 5.8 vs 2.0), and altered blood lipid profiles (triglycerides = 4.2 vs 1.7 mmol/L; LDL-cholesterol = 3.0 vs 1.4 mmol/L; HDL-cholesterol 0.4 vs 0.8 mmol/L). In addition, it caused vacuolar hepatopathy, induced hepatic inflammation (IL-1β elevation), and increased both hepatic and systemic oxidative stress. Treatment with ellagitannins treatment improved glucose tolerance (AUC = 230 mg.h/dL), insulin resistance (HOMA-IR = 4.0; with improved hepatic Akt phosphorylation), blood lipids (triglycerides, LDL-cholesterol and HDL-cholesterol = 3.7, 1.9, and 0.6 mmol/L, respectively), hepatic histology, inflammation, and antioxidant status (reduced lipid peroxidation and increased catalase and SOD enzyme activity). LC-MS showed the presence of bioactive ellagitannins (punicalagin, corilagin, and pendunculagin) and catechins, with punicalagin being the most predominant. Conclusion Ellagitannins from pomegranate peel exerted ameliorative effects on fructose-induced metabolic alterations, such as impaired glycaemic control, dyslipidaemia, inflammation and oxidative stress in rats. Ellagitannins from pomegranate peels may therefore be useful dietary polyphenols capable of preventing or managing sugar-induced metabolic, cardiovascular, and oxidative disorders.