| Obesity is the result of energy imbalance within an organism, that is, energy intake exceeds energy expenditure, characterized with excessive accumulation of fat mass or the higher proportion of adipose tissue to body weight. During the past decades, a large number of researches have been focused on the genetic etiology and the pathological basis of environmental factors of obesity. Obesity-prone (OP) and obesity-resistant (OR) phenomena are two body weight phenotypes among animals within the same strain which are fed with identical diet. The OP and OR phenotypes are interactive results of both genetic and environmental factors. As a result, the comprehensive study on OP and OR rats would facilitate the elucidation of mechanism of obesity, and the obese-related metabolic disorders. Currently, there is no report on comparison of metabolic and transcript profiles between OP and OR rats with metabonomic and transcriptomic approaches. Therefore, we intend to compare the metabolic and transcript profiles between OP and OR rats with the approaches of metabonomics, transcriptomics and molecular biology in this study. The main results are as following:⑴Pharmaco-metabonomic study on different responses to high fat diet feeding in rats We have detected characterized urinary metabolic profiles of OP and OR rats before high fat diet feeding. These differences between OP and OR rats included structure of gut microflora and energy metabolism, which were relative with body weight gain after high fat diet feeding. Additionally, we also validated the pharmaco-metabonomic concept in streptozotocin (STZ)-induced diabete model, which revealed that the predose unrinary metabolic profile was predictive for the increasing extent of postdose blood glucose.⑵The comparisons of biochemistry between OP and OR rats The differences between OP and OR rats included not only body weight, but lipids metabolism and insulin sensitivity as well, characterized with insulin resistance, increasing in serum free fatty acids and ketone body, and hepatic TC and TG in OP rats. However, no significant differences were observed in serum TG, TC, LDL, HDL and fasting glucose between OP and OR rats.⑶Comparisons of metabolites in serum, urine and liver tissue between OP and OR rats①There were significant differences in amino acids concentration between OP and OR rats,especially in liver tissue, such as high concentrations in ketogenic and glucogenic amino acids in OP rats, suggesting differences in amino acids metabolism;② The different metabolites between OP and OR rats included increasing of various saturated fatty acids and decreasing of polyunsaturated fatty acids in OP rats;③The urinary metabolites analysis indicated that different structure or metabolism of gut microflora might exist between the two phenotypes, which probably influenced the regulation of body weight gain;④The end-products of catecholamines in urine and intermediates of krebs cycle in serum in OP rats were all up-regulated, suggesting that the activity of sympatheic nervous system and energy metabolism was higher in OP rats than OR rats.⑷Transcriptomic comparisons between OP and OR rats Nearly 80 differently expressed hepatic genes were found between OP and OR rats (more than 1.5 fold ratio). These genes were involved in pathways of lipids metabolism, ketone body production, enzymatic and transcriptional regulation, most of which were consistent with results of metabonomic investigation. Combined with real time RT-PCR, we found that genes such as Ephx2, Nr3c2, Igfals, Pparg, Apoa4 and Hmgcs1were up-regulated in OP rats. The differentially expressed genes and metabolites partly explained the metabolic processes to metabolic disorders among obese subjects.Our study discloses the relationship between pre-dose metabolic profiles and body weight increasing (or blood glucose rising) through analysis of urine samples before high fat diet feeding (or STZ injection), which provides experimental evidence for application of metabonomics in pharmacological evaluation in the future. The metabonomic investigation indicates that the global metabolic patterns between OP and OR rats are different, including sympathetic nervous system, energy metabolism, fatty acid metabolism, amino acid metabolism and gut microflora. The comparative transcript profiles between OP and OR rats reveal some differentially expressed genes involved in lipids metabolism, ketone body production, blood pressure regulation and adipoctyes differentiation processes.The combined strategy of metabonomics and transcriptomics provides comprehensive information of metabolic characters of obesity and corresponding mechanisms to obese-related metabolic disorders from a systematic view, e.g. gut microflora-involved body weight regulation, Ephx2 gene in catecholamines metabolism pathway, and Pparg in hepatic lipids transport. Therefore, this study provides practical reference for integration of different"omics"in research of complex diseases. |
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