Amanda B. Campaña

Metabolic Disorders and Adipose Tissue Insulin Responsiveness in Neonatally STZ-Induced Diabetic Rats Are Improved by Long-Term Melatonin Treatment

Diabetes mellitus is a product of low insulin sensibility and pancreatic β-cell insufficiency. Rats with streptozotocin-induced diabetes during the neonatal period by the fifth day of age develop the classic diabetic picture of hyperglycemia, hypoinsulinemia, polyuria, and polydipsia aggravated by insulin resistance in adulthood. In this study, we investigated whether the effect of long-term treatment with melatonin can improve insulin resistance and other metabolic disorders in these animals. At the fourth week of age, diabetic animals started an 8-wk treatment with melatonin (1 mg/kg body weight) in the drinking water at night. Animals were then killing, and the sc, epididymal (EP), and retroperitoneal (RP) fat pads were excised, weighed, and processed for adipocyte isolation for morphometric analysis as well as for measuring glucose uptake, oxidation, and incorporation of glucose into lipids. Blood samples were collected for biochemical assays. Melatonin treatment reduced hyperglycemia, polydipsia, and polyphagia as well as improved insulin resistance as demonstrated by constant glucose disappearance rate and homeostasis model of assessment-insulin resistance. However, melatonin treatment was unable to recover body weight deficiency, fat mass, and adipocyte size of diabetic animals. Adiponectin and fructosamine levels were completely recovered by melatonin, whereas neither plasma insulin level nor insulin secretion capacity was improved in diabetic animals. Furthermore, melatonin caused a marked delay in the sexual development, leaving genital structures smaller than those of nontreated diabetic animals. Melatonin treatment improved the responsiveness of adipocytes to insulin in diabetic animals measured by tests of glucose uptake (sc, EP, and RP), glucose oxidation, and incorporation of glucose into lipids (EP and RP), an effect that seems partially related to an increased expression of insulin receptor substrate 1, acetyl-coenzyme A carboxylase and fatty acid synthase. In conclusion, melatonin treatment was capable of ameliorating the metabolic abnormalities in this particular diabetes model, including insulin resistance and promoting a better long-term glycemic control.

High Sodium Intake Enhances Insulin‐stimulated Glucose Uptake in Rat Epididymal Adipose Tissue

Objective: This study investigated the effect of different sodium content diets on rat adipose tissue carbohydrate metabolism and insulin sensitivity.

Chronic glucocorticoid treatment enhances lipogenic activity in visceral adipocytes of male Wistar rats

Glucocorticoid (GC) in excess promotes the redistribution of adipose tissue from peripheral to central sites of the body. In this study, we characterized an experimental condition of prolonged GC excess and investigated its effect on the lipogenic metabolism in white adipose tissue.

Pinealectomy interferes with the circadian clock genes expression in white adipose tissue.

Melatonin, the main hormone produced by the pineal gland, is secreted in a circadian manner (24‐hr period), and its oscillation influences several circadian biological rhythms, such as the regulation of clock genes expression (chronobiotic effect) and the modulation of several endocrine functions in peripheral tissues. Assuming that the circadian synchronization of clock genes can play a role in the regulation of energy metabolism and it is influenced by melatonin, our study was designed to assess possible alterations as a consequence of melatonin absence on the circadian expression of clock genes in the epididymal adipose tissue of male Wistar rats and the possible metabolic repercussions to this tissue. Our data show that pinealectomy indeed has impacts on molecular events: it abolishes the daily pattern of the expression of Clock, Per2, and Cry1 clock genes and Pparγ expression, significantly increases the amplitude of daily expression of Rev‐erbα, and affects the pattern of and impairs adipokine production, leading to a decrease in leptin levels. However, regarding some metabolic aspects of adipocyte functions, such as its ability to synthesize triacylglycerols from glucose along 24 hr, was not compromised by pinealectomy, although the daily profile of the lipogenic enzymes expression (ATP‐citrate lyase, malic enzyme, fatty acid synthase, and glucose‐6‐phosphate dehydrogenase) was abolished in pinealectomized animals.

Metabolic recovery of adipose tissue is associated with improvement in insulin resistance in a model of experimental diabetes.

Obesity and insulin resistance are highly correlated with metabolic disturbances. Both the excess and lack of adipose tissue can lead to severe insulin resistance and diabetes. Adipose tissue plays an active role in energy homeostasis, hormone secretion, and other proteins that affect insulin sensitivity, appetite, energy balance, and lipid metabolism. Rats with streptozotocin-induced diabetes during the neonatal period develop the classic diabetic picture of hyperglycemia, hypoinsulinemia, and insulin resistance in adulthood. Low body weight and reduced epididymal (EP) fat mass were also seen in this model. The aim of this study was to investigate the glucose homeostasis and metabolic repercussions on the adipose tissue following chronic treatment with antidiabetic drugs in these animals. In the 4th week post birth, diabetic animals started an 8-week treatment with pioglitazone, metformin, or insulin. Animals were then killed, EP fat pads were excised, and blood samples were collected for biological and biochemical assays. Pioglitazone and insulin treatments, but not metformin, reduced hyperglycemia, polydipsia, and polyphagia. Although all antidiabetic therapies improved insulin sensitivity, this was particularly noteworthy in the pioglitazone-treated rats. Furthermore, a recovery of adipose mass and insulin levels were observed in pioglitazone- and insulin-, but not metformin-treated animals. Treatments with insulin or pioglitazone were able to correct significantly, but not completely, the metabolic abnormalities, parallel to full recovery of adipose mass, indicating that not only the low insulin levels but also the lack of adipose tissue might play a significant role on the pathophysiology of this particular diabetes model.

Kinin B1 Receptor in Adipocytes Regulates Glucose Tolerance and Predisposition to Obesity

Background Kinins participate in the pathophysiology of obesity and type 2 diabetes by mechanisms which are not fully understood. Kinin B1 receptor knockout mice (B1 −/−) are leaner and exhibit improved insulin sensitivity. Methodology/Principal Findings Here we show that kinin B1 receptors in adipocytes play a role in controlling whole body insulin action and glucose homeostasis. Adipocytes isolated from mouse white adipose tissue (WAT) constitutively express kinin B1 receptors. In these cells, treatment with the B1 receptor agonist des-Arg9-bradykinin improved insulin signaling, GLUT4 translocation, and glucose uptake. Adipocytes from B1 −/− mice showed reduced GLUT4 expression and impaired glucose uptake at both basal and insulin-stimulated states. To investigate the consequences of these phenomena to whole body metabolism, we generated mice where the expression of the kinin B1 receptor was limited to cells of the adipose tissue (aP2-B1/B1 −/−). Similarly to B1 −/− mice, aP2-B1/B1 −/− mice were leaner than wild type controls. However, exclusive expression of the kinin B1 receptor in adipose tissue completely rescued the improved systemic insulin sensitivity phenotype of B1 −/− mice. Adipose tissue gene expression analysis also revealed that genes involved in insulin signaling were significantly affected by the presence of the kinin B1 receptor in adipose tissue. In agreement, GLUT4 expression and glucose uptake were increased in fat tissue of aP2-B1/B1 −/− when compared to B1 −/− mice. When subjected to high fat diet, aP2-B1/B1 −/− mice gained more weight than B1 −/− littermates, becoming as obese as the wild types. Conclusions/Significance Thus, kinin B1 receptor participates in the modulation of insulin action in adipocytes, contributing to systemic insulin sensitivity and predisposition to obesity.

Cessation of physical exercise changes metabolism and modifies the adipocyte cellularity of the periepididymal white adipose tissue in rats

All of the adaptations acquired through physical training are reversible with inactivity. Although significant reductions in maximal oxygen uptake (Vo2max) can be observed within 2 to 4 wk of detraining, the consequences of detraining on the physiology of adipose tissue are poorly known. Our aim was therefore to investigate the effects of discontinuing training (physical detraining) on the metabolism and adipocyte cellularity of rat periepididymal (PE) adipose tissue. Male Wistar rats, aged 6 wk, were divided into three groups and studied for 12 wk under the following conditions: 1) trained (T) throughout the period; 2) detrained (D), trained during the first 8 wk and detrained during the remaining 4 wk; and 3) age-matched sedentary (S). Training consisted of treadmill running sessions (1 h/day, 5 days/wk, 50-60% Vo2max). The PE adipocyte size analysis revealed significant differences between the groups. The adipocyte cross-sectional area (in μm(2)) was significantly larger in D than in the T and S groups (3,474 ± 68.8; 1,945.7 ± 45.6; 2,492.4 ± 49.08, respectively, P < 0.05). Compared with T, the isolated adipose cells (of the D rats) showed a 48% increase in the ability to perform lipogenesis (both basal and maximally insulin-stimulated) and isoproterenol-stimulated lipolysis. No changes were observed with respect to unstimulated lipolysis. A 15% reduction in the proportion of apoptotic adipocytes was observed in groups T and D compared with group S. The gene expression levels of adiponectin and PPAR-gamma were upregulated by factors of 3 and 2 in D vs. S, respectively. PREF-1 gene expression was 3-fold higher in T vs. S. From these results, we hypothesize that adipogenesis was stimulated in group D and accompanied by significant adipocyte hypertrophy and an increase in the lipogenic capacity of the adipocytes. The occurrence of apoptotic nuclei in PE fat cells was reduced in the D and T rats; these results raise the possibility that the adipose tissue changes after detraining are obesogenic.

l-Leucine Supplementation Worsens the Adiposity of Already Obese Rats by Promoting a Hypothalamic Pattern of Gene Expression that Favors Fat Accumulation

Several studies showed that l-leucine supplementation reduces adiposity when provided before the onset of obesity. We studied rats that were exposed to a high-fat diet (HFD) for 10 weeks before they started to receive l-leucine supplementation. Fat mass was increased in l-leucine-supplemented rats consuming the HFD. Accordingly, l-leucine produced a hypothalamic pattern of gene expression that favors fat accumulation. In conclusion, l-leucine supplementation worsened the adiposity of rats previously exposed to HFD possibly by central mechanisms.

Combined treatment with melatonin and insulin improves glycemic control, white adipose tissue metabolism and reproductive axis of diabetic male rats

Aims: Melatonin treatment has been reported to be capable of ameliorating metabolic diabetes‐related abnormalities but also to cause hypogonadism in rats. We investigated whether the combined treatment with melatonin and insulin can improve insulin resistance and other metabolic disorders in rats with streptozotocin‐induced diabetes during neonatal period and the repercussion of this treatment on the hypothalamic‐pituitary‐gonadal axis. Main methods: At the fourth week of age, diabetic animals started an 8‐wk treatment with only melatonin (0.2 mg/kg body weight) added to drinking water at night or associated with insulin (NHP, 1.5 U/100 g/day) or only insulin. Animals were then euthanized, and the subcutaneous (SC), epididymal (EP), and retroperitoneal (RP) fat pads were excised, weighed and processed for adipocyte isolation for morphometric analysis as well as for measuring glucose uptake, oxidation, and incorporation of glucose into lipids. Hypothalamus was collected for gene expression and blood samples were collected for biochemical assays. Key findings: The treatment with melatonin plus insulin (MI) was capable of maintaining glycemic control. In epididymal (EP) and subcutaneous (SC) adipocytes, the melatonin plus insulin (MI) treatment group recovered the insulin responsiveness. In the hypothalamus, melatonin treatment alone promoted a significant reduction in kisspeptin‐1, neurokinin B and androgen receptor mRNA levels, in relation to control group. Significance: Combined treatment with melatonin and insulin promoted a better glycemic control, improving insulin sensitivity in white adipose tissue (WAT). Indeed, melatonin treatment reduced hypothalamic genes related to reproductive function.

Fat gain with physical detraining is correlated with increased glucose transport and oxidation in periepididymal white adipose tissue in rats

As it is a common observation that obesity tends to occur after discontinuation of exercise, we investigated how white adipocytes isolated from the periepididymal fat of animals with interrupted physical training transport and oxidize glucose, and whether these adaptations support the weight regain seen after 4 weeks of physical detraining. Male Wistar rats (45 days old, weighing 200 g) were divided into two groups (n=10): group D (detrained), trained for 8 weeks and detrained for 4 weeks; and group S (sedentary). The physical exercise was carried out on a treadmill for 60 min/day, 5 days/week for 8 weeks, at 50-60% of the maximum running capacity. After the training protocol, adipocytes isolated from the periepididymal adipose tissue were submitted to glucose uptake and oxidation tests. Adipocytes from detrained animals increased their glucose uptake capacity by 18.5% compared with those from sedentary animals (P<0.05). The same cells also showed a greater glucose oxidation capacity in response to insulin stimulation (34.55%) compared with those from the S group (P<0.05). We hypothesize that, owing to the more intense glucose entrance into adipose cells from detrained rats, more substrate became available for triacylglycerol synthesis. Furthermore, this increased glucose oxidation rate allowed an increase in energy supply for triacylglycerol synthesis. Thus, physical detraining might play a role as a possible obesogenic factor for increasing glucose uptake and oxidation by adipocytes.