Effect of Obestatin and its Fragment Analog Nt8U on the Epididymal and Brain Tissue of DIO-C57BL/6 Mice

Imbalance in energy intake and energy expenditure due to change in lifestyles and genetic issues results in obesity which is a serious health problem. The entero‐endocrine system plays a major role in nutrient signaling. Appetite inducing signals and satiety peptides in the entero‐endocrine system have a definite role in management of obesity. Obestatin, a relatively new gastro‐peptide produced post translationally from preproghrelin gene and its N‐terminal fragment analog Nt8U (13 amino acids) have been shown to reduce food intake, gain in body weight, fat pads and also circulating lipids in normal adult male mice. In the present study, it is aimed to study the effect of these peptides on the epididymal and brain tissue of diet induced obese (DIO) mice. In an attempt to decipher their mechanism of action, it is intended to explore the changes these peptides bring about in the mouse brain at the genomic level. Mice fed with 60% (calorie by fat) high fat diet for a period of 19 weeks were administered obestatin and Nt8U intraperitoneally for 8 days and the mice maintained on HFD for 3 more weeks. Food intake and gain in bodyweight were monitored daily. Blood lipid parameters, plasma proteins and serum leptin levels were estimated after the administration regimen. No reduction in food intake or significant reduction in weight gain upon administration of the peptides. The leptin levels were drastically reduced from 21.7ng/dL in the saline treated mice to 10.4 and 8.9ng/dL in obestatin and Nt8U treated mice respectively. Triglyceride, cholesterol and HDL‐C levels were not altered after 8 days injection period but there was decrease in triglyceride levels by 30% in the Nt8U administered group and by 11% in the obestatin administered group 3 weeks after the treatment. Obestatin and Nt8U reduced epididymal fat by 7.5%. Estimation of serum enzymes SGPT, SGOT, ALP and LDH, weight and appearance of the organs showed the vital organs were unaffected by the treatment. mRNA from epididymal and brain tissue were extracted and subjected to Next Generation Sequencing (NGS). Analysis of NGS data revealed that, the genes Olr1, Alox 15, Gykl1 were upregulated in epididymal tissue and Cbr2, Btk in brain tissue. And, the genes Casq 1, Slc6a2, AldoB and Omp were down regulated in brain tissue. These differentially regulated genes modulate enzymes mainly involved in lipolysis and sequestration of triglycerides in the adipose tissue. In conclusion, administration of obestatin and Nt8U has a definite fat lowering effect as seen from reduced leptin levels. Reduction in triglycerides and the set of genes being differentially regulated strongly imply that there is alteration in lipid metabolism. Support or Funding Information This research is funded by Council of Scientific and Industrial Research (CSIR) India, Department of Biotechnology (DBT), India. The presenting author is grateful to Indian Council of Medical Research (ICMR), India for providing Senior Research Fellowship.