The influence of neonatal intake of curcumin on lipid metabolism : implication on obesity model

PhD (Science with Biochemistry), North-West University, Mahikeng Campus

The high prevalence of obesity and related metabolic disorders due to increased consumption of fructose-rich diet is a serious global threat to the public’s health among children and adolescents. Obesity is associated with several metabolic disorders including, type-2 diabetes, insulin resistance, inflammation, and oxidative stress. Furthermore, obesity is characterised by impaired lipid metabolism in key tissues such as the liver and adipose tissue. Curcumin, a hydrophobic polyphenol extracted from Curcuma longa (turmeric), possesses anti-obesity, anti-diabetic, anti-inflammatory, and antioxidant effects. Although curcumin has been reported to possess a range of biological activities, molecular targets of curcumin are not fully elucidated. The present study was also motivated by evidence suggesting that curcumin may regulate lipid metabolism, which plays a central role in the development of obesity and its complications. Therefore, the first objective of the present study reported the effect of neonatal intake of curcumin on key molecular biomarkers associated with lipid metabolism in the liver, namely, LKB-1, AMPK, CPT-1, and ACC-1. Likewise, the second objective reported the effect of neonatal intake of curcumin on key molecular biomarkers associated with glucose metabolism in the liver, namely, AKT-1, GLUT-2, GP, and PGM (AKT-1 was also considered as the biomarker for insulin resistance in this study). The third objective reported the effect of neonatal intake of curcumin on inflammatory biomarkers in the liver, viz., TNF-α and IL-6. Furthermore, the fourth objective reported the effect of neonatal intake of curcumin on oxidative stress by determining the antioxidant status of curcumin in the liver using FRAP and TEAC assays, as well as the antioxidant scavenging activity of curcumin using DPPH assay and the antioxidant enzyme activity of the SOD. Finally, the fifth objective reported the effect of neonatal intake of curcumin on levels of liver metabolites as well as the concentration of the lipid-bound fatty acids detected as fatty acid methyl esters in adipose tissues. In this study, forty male Sprague Dawley rats were divided into four groups and administered with either a 0.5% dimethyl sulfoxide (vehicle control), 500 mg.kg-1 body mass of curcumin, fructose (20%, w/v) or a combination of curcumin and fructose. The study was conducted in two phases, the first phase was the pre-weaning which began from postnatal day 6 to day 21, and the second phase was the post-weaning which began from postnatal day 21 to day 63. At the end of the treatments on postnatal day 63, rats were euthanized. Then the liver and visceral fat tissues were collected for further molecular analysis. Gene expression was analysed using real-time quantitative polymerase chain reaction while protein expression was analysed using western blot. The antioxidant status was determined using the FRAP and TEAC assays while the antioxidant scavenging activity was determined using the DPPH radical scavenging and SOD activity assays. The concentration levels of hepatic metabolites and the adipose tissue lipid-bound fatty acids were assessed using gas-chromatography-mass spectrometry. Results showed upregulation in the expression of genes and proteins associated with lipid metabolism when the high fructose diet was administered. These include AMPK and its direct activator LKB-1, as well as subsequent target molecules ACC-1 and CPT-1 in the liver tissues. Treatment with curcumin showed to reverse the adverse effects of high fructose diet by upregulating the expression of genes and proteins analysed in the lipid metabolism. This study found that high fructose diet feeding altered hepatic insulin signalling target molecule AKT-1 by downregulating its gene and protein expression. In comparison, treatment with curcumin upregulated the expression of AKT-1. On the one hand, the upregulation of GP and PGM gene and protein expression in the high fructose diet group suggest that hepatic glucose production was promoted. On the other hand, treatment with curcumin suppressed hepatic glucose production by downregulating the expression of GP and PGM. In this study, it was also noted that the administration of curcumin downregulated the gene and protein expression of TNFα and IL-6 whereas the high fructose diet abnormally upregulated their expression. Furthermore, treatment with curcumin showed to enhance hepatic antioxidant status. This was observed by the increase in FRAP and TEAC values, as well as in DPPH level and SOD activity. Finally, it was noted that hepatic carbohydrate metabolite and hepatic organic acids were reduced in the high fructose diet group compared to the control group, while treatment with curcumin showed no significant difference. In the adipose tissue fatty acids levels analysis, results showed an increase in concentration level in the high fructose diet group of all SFA analysed, whereas the opposite had been observed in some of the MUFA and PUFA. Treatment with curcumin showed a decrease in the elevated concentration level of SFA respectively. Moreover, treatment with curcumin increased the concentration level of omega-3 PUFA (EPA and clupanodonic acid), though with no significant difference. The study concluded that curcumin elicits beneficial effects to ameliorate obesity and its related metabolic disorders by regulating molecular biomarkers associated with lipid metabolism through AMPK activation and its subsequent target molecules such as ACC-1 and CPT-1 in the liver tissues. In glucose metabolism, we concluded that curcumin suppressed hepatic glucose production by regulating GP and PGM which are key hepatic glucose production biomarkers. The regulation of an insulin signalling biomarker (AKT-1) by curcumin could also be an alternative therapeutic target to alleviate obesity and its related metabolic disorders. We further confirmed that curcumin possesses anti-inflammatory potential by reducing key inflammatory biomarkers such as TNF-α and IL-6. Finally, using the FRAP and TEAC assays, we further confirmed that curcumin possesses antioxidant capacity in the liver. Similarly, DPPH and SOD activity assays confirmed the antioxidant scavenging activity of curcumin. Therefore, the present study demonstrated that neonatal intake of curcumin could prevent and protect against high fructose diet-induced obesity and its related metabolic disorders such as type-2 diabetes, inflammation, and oxidative stress.

Doctoral