Glucose & energy homeostasis: Lessons from animal studies.

Glucose in our body is maintained within a narrow range by the humoral control and a 'lipostat' system regulated by leptin from adipose tissues, which keep our accumulated fat stores in check. Any disturbance in this delicately poised homeostasis could be disastrous as it can lead to obesity and its associated metabolic manifestations. Laboratory animals, especially rodents, have contributed to our knowledge in understanding this physiological mechanism through an array of genetic and non-genetic animals developed over the years. Two rat mutant obese models-Wistar inbred at National Institute of Nutrition (WNIN)/Ob-obese rats with normal glucose levels and WNIN/GR-Ob-obese with impaired glucose tolerance were developed in the National Centre for Laboratory Animal Sciences (Now ICMR-National Animal Resource Facility for Biomedical Research) at Hyderabad, India. These animals are unique, as, unlike the earlier models, they show all types of degenerative disorders associated with obesity, within a single system. Thus they show impairment in all the major organs of the body - liver, pancreas, kidney, bones, muscles, gonads, brain, eyes, and are sensitive to diet manipulations, have compromised immunity, often develop tumours and have reduced life span. One may argue that there are limitations to one's interpretations from animal studies to human application, but then one cannot shut one's eyes to the new lessons they have taught us in modifying our life styles.

Interleukin-18-induced atherosclerosis involves CD36 and NF-κB crosstalk in Apo E-/- mice.

OBJECTIVE: Interleukin (IL)-18 is a pleotropic cytokine involved in various inflammatory disorders. The transcription factor, nuclear factor kappa-B (NF-κB), is thought to play an important role in IL-18 signaling. The present study proposes a novel role for IL-18 in cholesterol efflux and plaque stability and demonstrates that pyrrolidine dithiocarbamate (PDTC), a NF-κB inhibitor blocks IL-18 signaling in apolipoprotein (Apo) E-/- mice. METHODS: Three groups of normal chow-diet-fed, male Apo E-/- mice, aged 12 weeks (n=6/group) were employed: Gp I, PBS (2mo); Gp II, recombinant (r)IL-18 (1mo) followed by PBS (1mo); Gp III, rIL-18 (1mo) followed by PDTC (1mo). RESULTS: Significantly augmented expression of IL-18 receptor (R)α by fluorescence-activated cell sorting analysis and plasma IL-18 was observed in Gp II. There was a significant increase in total cholesterol and low-density lipoprotein cholesterol whereas high-density lipoprotein cholesterol was significantly decreased in Gp II. However, this pattern was reversed in Gp III. Significantly augmented mRNA expression of IL-18, CD36, matrix metalloproteinase (MMP)-9, and NF-κB was observed in Gp II but liver X receptor alpha (LXR-α) gene was significantly reduced. A significant increase in frequency of atherosclerotic lesions was observed in Gp II animals, whereas there was a significant decrease in the Gp III. CONCLUSION: IL-18 administration initiates inflammatory cascade by binding with IL-18 Rα via NF-κB which is involved in progression and destabilization of atherosclerotic plaques in Apo E-/- mice. This study also reveals that NF-κB blockade with PDTC, blocks IL-18 signaling through down-regulation of IL-18, IL-18 Rα, CD36, and MMP-9, thus reducing inflammation and restoring plaque instability via upregulation of LXR-α.

Altered ubiquitin-proteasome system leads to neuronal cell death in a spontaneous obese rat model.

BACKGROUND: Obesity is associated with various progressive age-related diseases, including neurological disorders. However, underlying molecular basis for increased risk of neurodegeneration in obesity is unknown. A suitable animal model would immensely help in understanding the obesity-linked neurological problems. METHODS: A spontaneously developed obese rat (WNIN/Ob) which is highly vulnerable for a variety of degenerative diseases was isolated from the existing WNIN stock rats. Ultrastructure of neurons in the cerebral cortex of 12-month old obese rats was evaluated by transmission electron microscopy. qRT-PCR and immunoblotting of ubiquitin C-terminal hydrolases (UCHs), ubiquitin, proteasomal sub-units, markers of ER stress and apoptosis were performed in the cerebral cortex. Proteasome activity was assayed by fluorometric method. Immunohistochemistry was performed for mediators of apoptosis, which was further confirmed by TUNEL assay. These investigations were also carried in high-fat diet-induced obese rat model. RESULTS: Neurons in the cerebral cortex of 12-month obese rats showed swollen mitochondria, disrupted ER and degenerating axons, nucleus and finally neurons. Results showed altered UPS, existence of ER stress, up-regulation of apoptotic markers and apoptosis in the cerebral cortex of obese rats. It appears that UCHL-1 mediated apoptosis through stabilizing p53 might play a role in neuronal cell death in obese rat. Similar changes were observed in the brain of diet-induced obese WNIN rats. CONCLUSION: Altered UPS could be one of the underlying mechanisms for the neuronal cell death in obese conditions. GENERAL SIGNIFICANCE: This is the first report to highlight the role of altered UPS in neurodegeneration due to obesity.

Increased macromolecular damage due to oxidative stress in the neocortex and hippocampus of WNIN/Ob, a novel rat model of premature aging.

Wistar of the National Institute of Nutrition obese (WNIN/Ob) is a unique rat strain isolated and established at NIN, Hyderabad, India, in 1996, from its existing stock of Wistar rat colony (WNIN). This animal model exhibits all traits of metabolic syndrome and has a remarkably reduced lifespan (1.5 years as compared to 3 years in parental WNIN rats), albeit, the factors associated with premature aging are not well understood. Considering that oxidative stress and DNA damage are crucial players associated with senescence, we analyzed oxidative stress markers like lipid peroxidation and protein oxidation; DNA damage in terms of both single-stranded and double-stranded breaks and the activity of antioxidant enzymes: superoxide dismutase and catalase in brain regions of these animals. Our study revealed that the magnitude of oxidative stress and DNA damage in the neocortex and hippocampus of 3-month-old WNIN/Ob obese rats is as high as that seen in 15-month-old parental WNIN control rats. Concurrently, the antioxidant enzyme activity was significantly decreased. From these results, it can be concluded that increased oxidative stress-induced damage of macromolecules, probably due to reduced activity of antioxidant enzymes, is associated with premature aging in WNIN/Ob obese rats.

Genetic & epigenetic approach to human obesity.

Obesity is an important clinical and public health challenge, epitomized by excess adipose tissue accumulation resulting from an imbalance in energy intake and energy expenditure. It is a forerunner for a variety of other diseases such as type-2-diabetes (T2D), cardiovascular diseases, some types of cancer, stroke, hyperlipidaemia and can be fatal leading to premature death. Obesity is highly heritable and arises from the interplay of multiple genes and environmental factors. Recent advancements in Genome-wide association studies (GWAS) have shown important steps towards identifying genetic risks and identification of genetic markers for lifestyle diseases, especially for a metabolic disorder like obesity. According to the 12th Update of Human Obesity Gene Map there are 253 quantity trait loci (QTL) for obesity related phenotypes from 61 genome wide scan studies. Contribution of genetic propensity of individual ethnic and racial variations in obesity is an active area of research. Further, understanding its complexity as to how these variations could influence ones susceptibility to become or remain obese will lead us to a greater understanding of how obesity occurs and hopefully, how to prevent and treat this condition. In this review, various strategies adapted for such an analysis based on the recent advances in genome wide and functional variations in human obesity are discussed.

WNIN/GR-Ob - an insulin-resistant obese rat model from inbred WNIN strain.

BACKGROUND & OBJECTIVES: WNIN/GR-Ob is a mutant obese rat strain with impaired glucose tolerance (IGT) developed at the National Institute of Nutrition (NIN), Hyderabad, India, from the existing 80 year old Wistar rat (WNIN) stock colony. The data presented here pertain to its obese nature along with IGT trait as evidenced by physical, physiological and biochemical parameters. The study also explains its existence, in three phenotypes: homozygous lean (+/+), heterozygous carrier (+/-) and homozygous obese (-/-). METHODS: Thirty animals (15 males and 15 females) from each phenotype (+/+, +/-, -/-) and 24 lean and obese (6 males and 6 females) rats were taken for growth and food intake studies respectively. Twelve adult rats from each phenotype were taken for body composition measurement by total body electrical conductivity (TOBEC); 12 rats of both genders from each phenotype at different ages were taken for clinical chemistry parameters. Physiological indices of insulin resistance were calculated according to the homeostasis model assessment for insulin resistance (HOMA-IR) and also by studying U¹4C 2-deoxy glucose uptake (2DG). RESULTS: WNINGR-Ob mutants had high growth, hyperphagia, polydipsia, polyurea, glycosuria, and significantly lower lean body mass, higher fat mass as compared with carrier and lean rats. These mutants, at 50 days of age displayed abnormal response to glucose load (IGT), hyperinsulinaemia, hypertriglyceridaemia, hypercholesterolaemia and hyperleptinaemia. Basal and insulin-stimulated glucose uptakes by diaphragm were significantly decreased in obese rats as compared with lean rats. INTERPRETATION & CONCLUSIONS: Obese rats of the designated WNIN/GR-Ob strain showed obesity with IGT, as adjudged by physical, physiological and biochemical indices. These indices varied among the three phenotypes, being lowest in lean, highest in obese and intermediate in carrier phenotypes thereby suggesting that obesity is inherited as autosomal incomplete dominant trait in this strain. This mutant obese rat model is easy to propagate, and can easily be transformed to frank diabetes model by dietary manipulation and thus can be used for screening anti-diabetic drugs.

Vitamin A improves insulin sensitivity by increasing insulin receptor phosphorylation through protein tyrosine phosphatase 1B regulation at early age in obese rats of WNIN/Ob strain.

To test the hypothesis that early intervention of vitamin A-enriched diet contains the development of obesity and improves insulin resistance, 50-day-old male lean and obese rats of WNIN/Ob strain were given either stock diet (2.6 mg vitamin A/kg diet) or vitamin A-enriched diet (129 mg vitamin A/kg diet) for 3 months. Compared with stock diet-fed obese rats, vitamin A-enriched diet-fed obese rats had reduced body weight gain, visceral adiposity and improved insulin sensitivity as evidenced by decreased fasting plasma insulin and unaltered glucose levels, which could possibly be due to higher phosphorylation of soleus muscle insulin receptor. This in turn is explained by decreased protein tyrosine phosphatase 1B (PTP1B) levels. Most of these changes were not observed in lean rats. In conclusion, chronic feeding of vitamin A-enriched diet to obese rats at an early age ameliorates visceral adiposity and improves the insulin sensitivity, possibly by decreasing soleus muscle PTP1B levels.

Simple synthesis and spectroscopic studies on cobalt added ZnO nanocrystals.

Cobalt doped zinc oxide nanoparticles were prepared through simple wet chemical method. X-ray diffraction studies confirm the prepared particles are in wurtzite structure. Scanning Electron Microscopy studies show the shape and morphology of the particles. To identify the presence of cobalt in ZnO, Energy Dispersive X-ray analysis was done. Optical absorption measurements show the presence of exciton peak at 375 nm. Photoluminescence studies were done with the excitation wavelength of 330 nm, which shows the emission because of exciton recombination and oxygen vacancy.

Prenatal and perinatal zinc restriction: effects on body composition, glucose tolerance and insulin response in rat offspring.

Maternal undernutrition increases the risk of adult chronic diseases, such as obesity and type 2 diabetes. This study evaluated the effect of maternal zinc restriction in predisposing the offspring to adiposity and altered insulin response in later life. Seventy-day-old female Wistar/NIN rats received a control (ZnC) or zinc-restricted (ZnR) diet for 2 weeks. Following mating with control males, a subgroup of the ZnR dams were rehabilitated with ZnC diet from parturition. Half the offspring born to the remaining ZnR dams were weaned onto the ZnC diet and the other half continued on the ZnR diet throughout their life. Body composition, glucose tolerance, insulin response and plasma lipid profile were assessed in male and female offspring at 3 and 6 months of age. The ZnR offspring weighed less than control offspring at birth and weaning and continued so until 6 months of age. Rehabilitation regimens corrected the body weights of male but not female offspring. Maternal zinc restriction increased the percentage of body fat and decreased lean mass, fat-free mass and fasting plasma insulin levels in both male and female offspring at 6 months of age. Also, glucose-induced insulin secretion was decreased in female but not male offspring. Despite the differences in fasting insulin and the area under the curve for insulin, the fasting glucose and the area under the curve for glucose were in general comparable among offspring of different groups. Rehabilitation from parturition or weaning partly corrected the changes in the percentage of body fat but had no such effect on other parameters. Changes in plasma lipid profile were inconsistent among the offspring of different groups. Thus chronic maternal zinc restriction altered the body composition and impaired the glucose-induced insulin secretion in the offspring.

Vitamin A regulates obesity in WNIN/Ob obese rat; independent of stearoyl-CoA desaturase-1.

Stearoyl-CoA desaturase 1 (SCD1), an important enzyme involved in monounsaturated fatty acid biosynthesis is a key player in energy homeostasis. Here, we tested the impact of vitamin A on hepatic and adipose tissue SCD1 expression and adiposity per se, using an obese mutant rat strain namely, WNIN/Ob developed at National Center for Laboratory Animal Sciences of National Institute of Nutrition, India. Seven months-old 24 male lean and obese rats of WNIN/Ob strain were divided into two groups; each group was subdivided into two subgroups having 6 lean and 6 obese rats and received diets containing either 2.6mg or 129mg vitamin A/kg diet for two months. Feeding of high (but non-toxic) doses of vitamin A resulted in significant reduction in body weight gain, and retroperitoneal white adipose tissue weight (RPWAT) in obese rats. Further, vitamin A feeding resulted in augmented expression of SCD1 in liver and RPWAT of lean rats, while no such effect was seen in obese rats. Taken together, the present data suggest that vitamin A decreases body weight gain in obese rat model independent of SCD1 gene regulation.

Vitamin A supplementation induces adipose tissue loss through apoptosis in lean but not in obese rats of the WNIN/Ob strain.

Vitamin A is a known regulator of adipose tissue growth. In this paper, we report the possible role of dietary vitamin A supplementation in the regulation of adipose tissue mass, using a novel obese rat model of the WNIN/Ob strain developed at the National Centre for Laboratory Animal Sciences of the National Institute of Nutrition, India. Twenty-four male lean and obese rats of the WNIN/Ob strain were broadly divided into two groups at 7 months of age; each group was subdivided into two subgroups consisting of six lean and six obese rats and they were given diets containing either 2.6 mg or 129 mg vitamin A/kg diet for 2 months. Feeding a high but non-toxic dose of vitamin A (129 mg/kg diet) resulted in a significant reduction in the adiposity index and retroperitoneal white adipose tissue (RPWAT) weight in obese rats while a marginal reduction was observed in lean rats. Further, this treatment resulted in a significantly increased RPWAT apoptotic index and Bax protein expression and a decreased expression of Bcl2 in the lean rats. However, no such changes were observed in the RPWAT of the obese rats subjected to identical treatment. Thus, our data suggests that chronic dietary vitamin A supplementation at a high dose effectively regulates adipose tissue mass both in the lean and obese phenotypes of the WNIN/Ob rat strain, perhaps through different mechanisms.

Animal models of obesity & their usefulness in molecular approach to obesity.

Obesity, a multifactorial nutrition disorder, is no longer the problem of the affluent West; it has been slowly gaining entry in to developing countries as well. Ever since the first demonstration of an experimental hypothalamic obese rat model, laboratory animals have been in the forefront of basic research concerned with this important metabolic disease. Apart from nongenetic models, an array of genetic murine models of obesity is now available. Over the years the obese loci in these mutants were localised, and most of them have been cloned. Among them leptin and its receptor--the first gene products to be identified, have revolutionised the field, and the possibility of a 'lipostat' mechanism operating in the body is no longer in the realm of imagination. Studies are now on, to identify the murine obese genes in the human population with a view to understand the problem and intervene therapeutically. We have recently developed a new rat model of obesity in our animal facilities, which has several advantages over the existing Western models. It is hoped, that this new model will strengthen and expand our knowledge on obesity--an interesting but complex syndrome.