Early and Long-term Undernutrition in Female Rats Exacerbates the Metabolic Risk Associated with Nutritional Rehabilitation.

Human studies have suggested that early undernutrition increases the risk of obesity, thereby explaining the increase in overweight among individuals from developing countries who have been undernourished as children. However, this conclusion is controversial, given that other studies do not concur. This study sought to determine whether rehabilitation after undernutrition increases the risk of obesity and metabolic disorders. We employed a published experimental food-restriction model. Wistar female rats subjected to severe food restriction since fetal stage and controls were transferred to a moderately high-fat diet (cafeteria) provided at 70 days of life to 6.5 months. Another group of undernourished rats were rehabilitated with chow. The energy intake of undernourished animals transferred to cafeteria formula exceeded that of the controls under this regime and was probably driven by hypothalamic disorders in insulin and leptin signal transduction. The cafeteria diet resulted in greater relative increases in both fat and lean body mass in the undernourished rats when compared with controls, enabling the former group to completely catch up in length and body mass index. White adipose tissues of undernourished rats transferred to the high-lipid regime developed a browning which, probably, contributed to avoid the obesigenic effect observed in controls. Nevertheless, the restricted group rehabilitated with cafeteria formula had greater accretion of visceral than subcutaneous fat, showed increased signs of macrophage infiltration and inflammation in visceral pad, dyslipidemia, and ectopic fat accumulation. The data indicate that early long-term undernutrition is associated with increased susceptibility to the harmful effects of nutritional rehabilitation, without causing obesity.

Resveratrol treatment restores peripheral insulin sensitivity in diabetic mice in a sirt1-independent manner.

SCOPE: Mice with deletion of insulin receptor substrate (IRS) 2 develop hyperglycaemia, impaired hepatic insulin signaling and elevated gluconeogenesis. Protein tyrosine phosphatase 1B (PTP1B) inhibition by resveratrol improves peripheral insulin sensitivity of these mice. Although resveratrol activates Sirtuin1 (Sirt1), the mechanisms underlying its beneficial effects are not totally elucidated. In this study, we have investigated whether Sirt1 mediates the effects of resveratrol in controlling insulin resistance in diabetic mice. METHODS AND RESULTS: We attempted to ameliorate peripheral insulin resistance in two diabetic models, Irs2-deficient (Irs2(-/-)) mice and streptozotocin (STZ)-injected mice by resveratrol treatment or Sirt1 overexpression. Resveratrol improved systemic insulin sensitivity of Irs2-deficient mice. Irs2-deficient mice are characterized by high levels of PTP1B expression in liver and muscle. Interestingly, resveratrol decreased PTP1B in both tissues, thereby restoring IRS1-mediated insulin signaling. Moreover, resveratrol also restored insulin sensitivity and hepatic insulin signaling in STZ-diabetic mice. In contrast, moderate overexpression of Sirt1 neither normalized PTP1B levels nor restored insulin signaling in Irs2-deficient mice or STZ-diabetic mice. CONCLUSION: Resveratrol improves peripheral insulin signaling independently of Sirt1 in diabetic mice in association with the inhibition of PTP1B and, therefore, this polyphenol could be an effective adjuvant for the treatment of diabetes.

Involvement of protein tyrosine phosphatases and inflammation in hypothalamic insulin resistance associated with ageing: effect of caloric restriction.

Aged Wistar rats present central insulin resistance associated with ageing. Several steps of the insulin signaling pathway have been described to be impaired in aged rats at hypothalamic level. In the present article we have explored possible alterations in protein tyrosine phosphatases (PTPs) involved in insulin receptor dephosphorylation, as well as pro-inflammatory pathways and serine kinases such as inhibitory kappa ß kinase-nuclear factor kappa-B (IKKß-NFκB), p38 mitogen-activated protein kinase (p38) and protein kinase C θ (PKCθ) that may also be involved in the decreased insulin signaling during ageing. We detected that ageing brings about a specific increase in insulin receptor tyrosine phosphatase activity and PTP1B serine phosphorylation. Increased association of PTP1B and leukocyte common antigen-related tyrosine protein phosphatase (LAR) with insulin receptor was also observed in hypothalamus from aged rats. Besides these mechanisms, increased activation of the IKKß-NFκB pathway, p38 and PKCθ serine/threonine kinases were also detected. These data contribute to explain the hypothalamic insulin resistance associated with ageing. Caloric restriction ameliorates most of the effects of ageing on the above mentioned increases in PTPs and serine/threonine kinases activities and points to age-associated adiposity and inflammation as key factors in the development of age-associated insulin resistance.

Age-associated development of inflammation in Wistar rats: Effects of caloric restriction.

CONTEXT: Insulin resistance and type 2 Diabetes have been associated to a low grade of inflammation and their prevalence increase with ageing. OBJECTIVE: To analyse the development of inflammation in adipose tissue, liver, muscle and hypothalamus during ageing and the effects of caloric restriction. MATERIALS AND METHODS: We have analysed the expression of inflammatory cytokines (TNFα, IL1-ß, IL-12B and IL-6), proteins involved in macrophage recruitment (MCP-1, CCR2), TLR4 and macrophage markers (CD11c, CD11b and arginase1). Immunohistochemistry of macrophages has also been performed. RESULTS: All studied tissues present signs of inflammation during ageing, but with different pattern and intensity. Caloric restriction decreases the expression of most of inflammatory markers. DISCUSSION AND CONCLUSIONS: These data indicate a role of adiposity in the development of inflammation and insulin resistance during ageing. Dietetic intervention could be a useful tool to ameliorate the development of inflammation and insulin resistance associated with ageing.

Leptin accumulation in hypothalamic and dorsal raphe neurons is inversely correlated with brain serotonin content.

Food intake and energy balance are among the functions regulated by serotonin in the brain. Recent studies have shown an interaction of serotonergic system with leptin, a protein released from adipose tissue that inhibits feeding behavior and increases fuel expenditure. In this study, leptin labeled with digoxigenin was injected in the lateral cerebral ventricle of 5 young adult rats (4months old) and 5 aged rats (24months old) to assess the effect of aging on the accumulation of exogenous leptin by raphe and hypothalamic neurons. Four aged rats showed an intense leptin accumulation in neuronal cell bodies, mainly at the level of the dorsal raphe nucleus. In contrast, only one young rat showed neuronal accumulation of leptin in dorsal raphe and hypothalamus. Low brain serotonin immunoreactivity was found in all animals with high neuronal leptin accumulation at the raphe nucleus, independently of their age. In contrast, high brain serotonin immunoreactivity was accompanied by a low neuronal accumulation of leptin. To determine whether differences in serotonin content were the cause of the differences in leptin accumulation an inhibitor of serotonin synthesis, p-chlorophenylalanine, was administered to young rats. Serotonin depletion resulted in an enhanced accumulation of leptin in raphe as well as in hypothalamic neurons. These findings indicate that serotonin regulates leptin uptake by neuronal cell bodies of the dorsal raphe and hypothalamus, this suggests that at least part of the effects of serotonin may be mediated by the regulation of neuronal trafficking in the brain.

Changes in the neuroendocrine control of energy homeostasis by adiposity signals during aging.

Energy balance in mammals is modulated by peripheral signals that inform the brain about the magnitude of fat stores, the amount of food in the gastrointestinal tract, and the level of nutrients such as glucose in the circulation. Among these, insulin and leptin are considered adiposity signals involved in the long-term maintenance of fat stores. Here we review the mechanisms of action of leptin and insulin in the hypothalamus and how these mechanisms are altered during aging in rat models. Aged rats are characterized by increased fat mass, central leptin and insulin resistance, and hyperleptinemia. Leptin resistance is manifested by its failure to inhibit food intake, deplete fat stores, down regulate its own expression in adipose tissue, and increase energy expenditure. Moreover, leptin and insulin signaling are decreased in hypothalamus from aged rats. Calorie restriction and fasting studies provide controversial data on the cause-effect interrelationship between increased adiposity and development of central leptin resistance. Although in the absence of obesity leptin resistance seems to be a characteristic of aged animals, adiposity could either reinforce it or cause an early onset of this resistance. More studies are necessary to clarify the role of the hypothalamus in the development of age-associated obesity and insulin resistance.

Effects of chronic acarbose treatment on adipocyte insulin responsiveness, serum levels of leptin and adiponectin and hypothalamic NPY expression in obese diabetic Wistar rats.

1. Inhibitors of intestinal glucosidases have been shown to improve glycaemic control in diabetic and obese humans and animals. In the present study, we have investigated the effect of 3 months treatment with acarbose on adiposity, food intake and the modulation of hypothalamic neuropeptide Y (NPY) in obese diabetic Wistar (WDF) rats and the possible correlation between changes in overall insulin sensitivity and the level of circulating adipokines, leptin and adiponectin. In addition, we investigated the effect of acarbose on adipocyte insulin signalling. 2. Mature male WDF rats were randomly distributed to one of three treatment groups (no acarbose or 20 or 40 mg of acarbose/100 g diet). After 3 months, blood glucose, cholesterol, triglyceride, insulin, leptin and adiponectin were analysed. Insulin signalling was determined in isolated adipocytes as the stimulation of mitogen-activated protein kinase (MAPK) and Akt phosphorylation; the level of hypothalamic NPY was assessed by immunohistochemistry. 3. Acarbose-treated rats had lower levels of blood glucose, cholesterol, triglyceride, insulin and leptin and an increase in adiponectin compared with untreated animals. There were no changes in bodyweight and adiposity. Stimulation of adipocyte MAPK activity by insulin was higher in rats treated with both doses of acarbose, whereas higher stimulation of Akt phosphorylation was observed with the highest dose of acarbose. Although food intake was not significantly reduced in rats treated with acarbose, the acarbose-treated rats had lower NPY expression in the arcuate nucleus. 4. We conclude that the improvement in overall insulin sensitivity in WDF rats after prolonged acarbose treatment is paralleled by increases in circulating adiponectin and adipocyte insulin responsiveness. Acarbose neither decreases food intake nor reverts obesity, but decreases leptin levels and the expression of the orexigenic NPY in the hypothalamus.

Impaired central insulin response in aged Wistar rats: role of adiposity.

Insulin, like leptin, is considered as a lipostatic signal acting at a central level. Aging and age-associated adiposity have been related to the development of leptin resistance in Wistar rats. In the present article, hypothalamic insulin response during aging has been studied in Wistar rats. Thus, the effects of intracerebroventricular infusion of insulin during a week on food intake and body weight as well as insulin signal transduction after acute intracerebroventricular insulin administration have been studied in 3-, 8-, and 24-month-old rats. To explore the possible role of age-associated adiposity, these experiments were also performed in 8- and 24-month-old rats after 3 months of food restriction to reduce visceral adiposity index to values below those of young animals. Intracerebroventricular administration of insulin during a week was more efficient at reducing food intake and body weight in 3-month-old rats than in 8- and 24-month-old rats. Hypothalamic insulin-stimulated insulin receptor, GSK3, AKT, and p70S6K phosphorylation decreased with aging. Insulin receptor and IRS-2 phosphoserine was increased in 24-month-old rats. Food restriction improved both insulin responsiveness and insulin signaling. These data suggest that Wistar rats develop hypothalamic insulin resistance with aging. This can be explained by alterations of the signal transduction pathway. The fact that food restriction improves central insulin response and signal transduction points to the age-associated adiposity as a key player in the development of central insulin resistance.