The impact of oleanolic acid on lipid metabolism and mitochondrial biogenesis in fructose-induced neonatal metabolic derangement model

Abstract

Metabolic syndrome is a health condition emanating from a combination of metabolic disorders, which include diabetes, hypertension, dyslipidemia, insulin resistance and obesity. These metabolic disorders are commonly referred to as life-style or non-communicable diseases in some quarters. These conditions have become the leading cause of death in the recent years. The prevalence of metabolic syndrome is at an alarming rate in both the developing and developed countries across the globe. There is an overwhelming strain in the national health budget because of non-communicable diseases, big chunk of moneys are allocated in trying to address them. Metabolic diseases are attributed to a combination of contributing factors such as the type of food consumed, life style activities and genetic inheritance. These contributing factors are responsible for aggravating metabolic diseases. Diabetes and cardiovascular diseases are increasingly becoming silent killers among both young and older population. Obesity is another condition which is having devastating consequences in human health. Individuals gain an excessive amount of fat around the adnominal area, which end up tempering with the functions of vital organs such as the liver, heart and kidneys. The metabolic diseases are caused by a number factors. One of the possible causes of metabolic diseases is genetic inheritance, this involves genetic materials in the form of DNA being passed form parents to their offspring. Individuals coming from families with history of metabolic disorders are susceptible to developing such diseases. There is undisputed evidence suggesting an increase of fructose consumption in food intake. This increase intake of fructose is marred with a lot of controversies and it is correlated to the rise in metabolic disorders and other related complications. Fructose and its metabolism form the cornerstone of this study. Fructose has been viewed as having metabolic programming effects. Metabolic programming is the window period of early health status, which is very delicate and can affect the state of health in adulthood life. In order to address the rapid increase of metabolic diseases, plants are commonly used as alternative or complementary remedy for chronic diseases, especially in African and Asian countries. Oleanolic acid (OA) is a plant phytochemical with many therapeutic potentials in several foods and medicinal plants. Therefore, OA has been used in this scientific research to determine its impact in lipid metabolism and mitochondrial biogenesis. In this study, one week old neonatal experimental animals (Sprague Dawley rats) were subjected to different treatments for seven consecutive days with 10 mℓ/kg body mass of: DMSO with 0.5% (v/v) as Control, Oleanolic Acid (OA) with 60 mg/kg, High Fructose (HF) with 20% w/v, Oleanolic Acid + High Fructose (OA+HF) and Metformin + High Fructose (MET+HF) with 60 mg/kg. The pups were raised until they reached their adulthood life, fasted on 111ᵗʰ day and were sacrificed on 112ᵗʰ day. The Snowrex Electronic and Clover scales were used to measure the weekly weights of rats and the Contour Plus glucometer was used to determine the blood glucose levels. The skeletal muscle and liver samples were harvested from the sacrificed rats. The Gas Chromatography-Mass Spectrometry (GC-MS) was used to determine the levels of different fatty acids and Real Time quantitative Polymerase Chain Reaction (RT-qPCR) was used to evaluate the expression of genes related to lipid metabolism, mitochondrial biogenesis and inflammatory responses. Western blot was used for protein analysis while ChIP assay was used to assess protein-DNA interactions of MEF-2A to NRF-1 genes. The results showed increased percentage weight gain and fasting blood glucose in high fructose-fed rats, while oleanolic acid and metformin treatments showed no significant differences when compared with the untreated controls. The concentration levels of omega 3 polyunsaturated fatty acids (docosahexaenoic, eicosapentaenoic, alpha linoleic acid) and omega 6 polyunsaturated fatty acid (eicosadienoic, calendic and gamma linoleic acid) in high fructose-fed rats were not significantly increased when compared with the normal control. However, high fructose-fed rats treated with oleanolic acid or metformin showed significantly increased concentration of these fatty acids. A similar result was also observed in the concentration levels of monounsaturtaed fatty acids (MUFA) in the high fructose-fed rats. The treatment of high fructose-fed rats with oleanolic acid showed increased significant levels of MUFA. Lipid oxidation associated genes assessed in this study were CPT-1, NRF-1, GLUT-4 and MEF-2A and were highly expressed when high fructose-fed rats were treated with oleanolic acid and metformin when compared with the control. Similarly, mitochondrial associated genes such as TIM, TOM, TFAM, PGC-1 and COX-2, also were highly expressed when the high fructose-fed rats were treated with oleanolic acid or metformin. On the contrary, lipid synthesis associated genes such as FAS, ACC-1 and SREBP-1c were highly expressed on the rats fed with high fructose alone. The insulin related genes such as IRS-1and PPARγ were highly expressed on the rats treated with oleanolic acid. These results indicated that, oleanolic acid possesses ability to alleviate metabolic dysfunctions and their related complications.