Vanesa Jiménez-Ortega

Melatonin effect on plasma adiponectin, leptin, insulin, glucose, triglycerides and cholesterol in normal and high-fat fed rats.

Abstract:  Melatonin effect on body weight progression, mean levels and 24‐hr pattern of circulating adiponectin, leptin, insulin, glucose, triglycerides and cholesterol were examined in rats fed a normal or a high‐fat diet. In experiment 1, rats fed a normal diet were divided into two groups: receiving melatonin (25 μg/mL drinking water) or vehicle for 9 wk. In experiment 2, animals were divided into three groups: two fed with a high‐fat diet (35% fat) and melatonin (25 μg/mL) or vehicle in drinking water for 11 wk, while a third group was given a normal diet (4% fat). At the end of experiments, groups of eight rats were killed at six different time intervals throughout a 24‐ hr period. Melatonin administration for 9 wk decreased body weight gain from the 3rd wk on without affecting food intake. A significant reduction in circulating insulin, glucose and triglyceride mean levels and disrupted daily patterns of plasma adiponectin, leptin and insulin were observed after melatonin. In high fat–fed rats, melatonin attenuated body weight increase, hyperglycemia and hyperinsulinemia, as well as the increase in mean plasma adiponectin, leptin, triglycerides and cholesterol levels. The high‐fat diet disrupted normal 24‐ hr patterns of circulating adiponectin, insulin and cholesterol, the effects on insulin and cholesterol being counteracted by melatonin. Nocturnal plasma melatonin concentration in control and obese rats receiving melatonin for 11 wk attained values 21–24‐fold greater than controls. The results indicate that melatonin counteracts some of the disrupting effects of diet‐induced obesity in rats.

Effect of a high-fat diet on 24-h pattern of circulating levels of prolactin, luteinizing hormone, testosterone, corticosterone, thyroid-stimulating hormone and glucose, and pineal melatonin content, in rats

Circadian rhythmicity is affected in obese subjects. This article analyzes the effect of a high-fat diet (35% fat) on 24-h changes circulating prolactin, luteinizing hormone (LH), testosterone, corticosterone, thyroid-stimulating hormone (TSH) and glucose, and pineal melatonin content, in rats. When body weight of rats reached the values of morbid obesity, the animals were sacrificed at six different time intervals throughout a 24-h cycle, together with age-matched controls fed a normal diet (4% fat). Plasma hormone levels were measured by specific radioimmunoassays and glucose concentration by an automated glucose oxidase method. In rats under a high-fat diet, a significant disruption of the 24-h pattern of plasma TSH, LH, and testosterone and a slight disruption of prolactin rhythm were found. Additionally, high-fat fed rats showed significantly lower total values of plasma TSH and testosterone and absence of correlation between testosterone and circulating LH levels. Plasma corticosterone levels increased significantly in high-fat fed rats and their 24-h variation became blunted. In obese animals, a significant hyperglycemia developed, individual plasma glucose values correlating with circulating corticosterone in high-fat fed rats only. The amplitude of the nocturnal pineal melatonin peak decreased significantly in high-fat fed rats. The results underlie the significant effects that obesity has on circadian organization of hormone secretion.

Effects of caloric restriction on insulin pathway gene expression in the skeletal muscle and liver of normal and long-lived GHR-KO mice.

Growth hormone receptor/binding protein knockout (GHR-KO) mice are characterized by resistance to growth hormone (GH), reduced insulin like growth factor 1 (IGF1) levels and enhanced insulin sensitivity and markedly increased lifespan. Findings in these and other long-lived mutant mice, and in normal animals subjected to caloric restriction (CR) indicate that insulin signaling is importantly involved in the control of longevity. We have examined the mRNA expression level of genes involved in insulin/IGF1 action in the skeletal muscle and liver of normal and GHR-KO mice fed ad libitum or subjected to long term 30% CR. The levels of IR, IRS1, IRS2, GLUT4 and IGF1 message in the skeletal muscle were reduced by CR in both normal and GHR-KO mice. In the liver, the results indicate that in GHR-KO mice mRNA expression of genes related to early steps of insulin signaling is up-regulated in the liver but not in the muscle. The results also show that improved insulin sensitivity in response to CR is not due to increased mRNA expression of the above genes in either normal or GHR-KO animals.

Caloric Restriction and Growth Hormone Receptor Knockout: Effects on Expression of Genes Involved in Insulin Action in the Heart

Blockade of growth hormone (GH), decreased insulin-like growth factor-1 (IGF1) action and increased insulin sensitivity are associated with life extension and an apparent slowing of the aging process. We examined expression of genes involved in insulin action, IR, IRS1, IRS2, IGF1, IGF1R, GLUT4, PPARs and RXRs in the hearts of normal and GHR-/- (KO) mice fed ad libitum or subjected to 30% caloric restriction (CR). CR increased the cardiac expression of IR, IRS1, IGF1, IGF1R and GLUT4 in normal mice and IRS1, GLUT4, PPARalpha and PPARbeta/delta in GHR-KO animals. Expression of IR, IRS1, IRS2, IGF1, GLUT4, PPARgamma and PPARalpha did not differ between GHR-KO and normal mice. These unexpected results suggest that CR may lead to major modifications of insulin action in the heart, but high insulin sensitivity of GHR-KO mice is not associated with alterations in the levels of most of the examined molecules related to intracellular insulin signaling.

Melatonin normalizes clinical and biochemical parameters of mild inflammation in diet-induced metabolic syndrome in rats

The objective of this study was to evaluate the efficacy of melatonin to affect mild inflammation in the metabolic syndrome (MS) induced by a high‐fat diet in rats. Adult Wistar male rats were divided into four groups (n = 16/group): (i) control diet (3% fat); (ii) high‐fat (35%) diet; (iii) high‐fat diet + melatonin; and (iv) melatonin. Rats had free access to high‐fat or control chow and one of the following drinking solutions for 10 wk: (a) tap water; (b) 25 μg/mL of melatonin. Plasma interleukin (IL)‐1β, IL‐4, IL‐6, IL‐10, tumor necrosis factor (TNF)‐α, interferon (IFN)‐γ, and C‐reactive protein (CRP) were measured at two time intervals, that is, the middle of daylight period and the middle of the scotophase. In addition, a number of somatic and metabolic components employed clinically to monitor the MS were measured. Melatonin decreased the augmented circulating levels of IL‐1β, IL‐6, TNF‐α, IFN‐γ, and CRP seen in obese rats and restored the depressed levels of IL‐4 and IL‐10. Rats fed with the high‐fat diet showed significantly higher body weights and augmented systolic blood pressure from the third and fourth week onwards, respectively, melatonin effectively preventing these changes. In high‐fat‐fed rats, circulating low‐density lipoprotein‐cholesterol, total cholesterol, and triglyceride concentration augmented significantly, melatonin being effective to counteract these changes. Melatonin‐treated rats showed a decreased insulin resistance, the highest values of plasma high‐density lipoprotein‐cholesterol, and the lowest values of plasma uric acid. The results indicate that melatonin is able to normalize the altered biochemical pro‐inflammatory profile seen in rats fed with a high‐fat diet.

24-Hour variation in gene expression of redox pathway enzymes in rat hypothalamus: effect of melatonin treatment

Abstract The 24-h changes in medial basal hypothalamic (MBH) gene expression of redox pathway enzymes nitric oxide synthase (NOS)-1 and NOS-2, heme oxygenase (HO)-1 and HO-2, Cu/Zn- and Mn-superoxide dismutases (SOD) and catalase were examined in adult male Wistar rats kept under an alternating regimen of light/dark. Half of the animals received melatonin (∼60 μg/day) in the drinking water. After 1 month, rats were killed at six different time intervals, throughout a 24-h cycle. MBH mRNA levels were measured by real-time PCR analysis. In controls, gene expression of NOS-2 and HO-2 peaked at the early light phase while that of HO-1 showed a maximum at the middle of the dark phase. None of MBH mRNAs encoding NOS-1, Cu/Zn-SOD, Mn-SOD and catalase exhibited significant 24-h variations in control rats. Melatonin administration decreased significantly mRNAs for NOS-1, NOS-2, HO-1 and HO-2 as well as changed their 24-h profile. Melatonin augmented gene expression of the antioxidant enzymes Cu/Zn-SOD, Mn-SOD or catalase at certain time intervals only. The results are compatible with the view that the principal indirect (i.e. gene expression of redox pathway enzymes) effect of melatonin on redox pathway in the hypothalamus is mainly exerted via down-regulation of pro-oxidant enzyme mRNAs.

Cadmium as an endocrine disruptor: Correlation with anterior pituitary redox and circadian clock mechanisms and prevention by melatonin

To examine the effect of a low dose of cadmium (Cd) as an endocrine disruptor, male Wistar rats received CdCl2 (5ppm Cd) in drinking water or drinking water alone. After 1 month, the rats were euthanized at one of six time intervals around the clock and the 24-h pattern of adenohypophysial prolactin (PRL) synthesis and release, lipid peroxidation, and redox enzyme and metallothionein (MT) gene expression was examined. Cd suppressed 24-h rhythmicity in expression of the PRL gene and in circulating PRL by increasing them at early photophase only, in correlation with an augmented pituitary lipid peroxidation and redox enzyme expression. CdCl2 treatment effectively disrupted the 24-h variation in expression of every pituitary parameter tested except for MT-3. In a second experiment the effect of melatonin (3μg/ml in drinking water) was assessed at early photophase, the time of maximal endocrine-disrupting effect of Cd. Melatonin treatment blunted the effect of Cd on PRL synthesis and release, decreased Cd-induced lipid peroxidation, and counteracted the effect of Cd on expression of most redox enzymes. A third experiment was performed to examine whether melatonin could counteract Cd-induced changes in the 24-h pattern of pituitary circadian clock gene expression and plasma PRL, luteinizing hormone (LH), thyrotropin (TSH), and corticosterone levels. Rats receiving CdCl2 exhibited a suppressed daily rhythm of Clock expression and a significant disruption in daily rhythms of pituitary Bmal1, Per1, Per2, Cry1, and Cry2. The coadministration of melatonin restored rhythmicity in Clock and Bmal1 expression but shifted the maxima in pituitary Per1, Cry1, and Cry2 expression to the scotophase. Melatonin also counteracted the effect of Cd on 24-h rhythmicity of circulating PRL, LH, TSH, and corticosterone. The results highlight the occurrence of a significant endocrine disruptor effect of a low dose of Cd. Generally melatonin counteracted the effects of Cd and ameliorated partially the circadian disruption caused by the pollutant.

Cadmium-Induced Disruption in 24-h Expression of Clock and Redox Enzyme Genes in Rat Medial Basal Hypothalamus: Prevention by Melatonin.

In a previous study we reported that a low daily p.o. dose of cadmium (Cd) disrupted the circadian expression of clock and redox enzyme genes in rat medial basal hypothalamus (MBH). To assess whether melatonin could counteract Cd activity, male Wistar rats (45 days of age) received CdCl2 (5 ppm) and melatonin (3 μg/mL) or vehicle (0.015% ethanol) in drinking water. Groups of animals receiving melatonin or vehicle alone were also included. After 1 month, MBH mRNA levels were measured by real-time PCR analysis at six time intervals in a 24-h cycle. In control MBH Bmal1 expression peaked at early scotophase, Per1 expression at late afternoon, and Per2 and Cry2 expression at mid-scotophase, whereas neither Clock nor Cry1 expression showed significant 24-h variations. This pattern was significantly disrupted (Clock, Bmal1) or changed in phase (Per1, Per2, Cry2) by CdCl2 while melatonin counteracted the changes brought about by Cd on Per1 expression only. In animals receiving melatonin alone the 24-h pattern of MBH Per2 and Cry2 expression was disrupted. CdCl2 disrupted the 24-h rhythmicity of Cu/Zn- and Mn-superoxide dismutase (SOD), nitric oxide synthase (NOS)-1, NOS-2, heme oxygenase (HO)-1, and HO-2 gene expression, most of the effects being counteracted by melatonin. In particular, the co-administration of melatonin and CdCl2 increased Cu/Zn-SOD gene expression and decreased that of glutathione peroxidase (GPx), glutathione reductase (GSR), and HO-2. In animals receiving melatonin alone, significant increases in mean Cu/Zn and Mn-SOD gene expression, and decreases in that of GPx, GSR, NOS-1, NOS-2, HO-1, and HO-2, were found. The results indicate that the interfering effect of melatonin on the activity of a low dose of CdCl2 on MBH clock and redox enzyme genes is mainly exerted at the level of redox enzyme gene expression.

Neuroendocrine-immune correlates of circadian physiology: studies in experimental models of arthritis, ethanol feeding, aging, social isolation, and calorie restriction

Virtually all neuroendocrine and immunological variables investigated in animals and humans display biological periodicity. Circadian rhythmicity is revealed for every hormone in circulation as well as for circulating immune cells, lymphocyte metabolism and transformability, cytokines, receptors, and adhesion molecules. Clock genes, notably the three Period (Per1/Per2/Per3) genes and two Cryptochrome (Cry1/Cry2) genes, are present in immune and endocrine cells and are expressed in a circadian manner in human cells. This review discusses the circadian disruption of hormone release and immune-related mechanisms in several animal models in which circulating cytokines are modified including rat adjuvant arthritis, social isolation in rats and rabbits and alcoholism, the aging process and calorie restriction in rats. In every case the experimental manipulation used perturbed the temporal organization by affecting the shape and amplitude of a rhythm or by modifying the intrinsic oscillatory mechanism itself.

Melatonin counteracts changes in hypothalamic gene expression of signals regulating feeding behavior in high-fat fed rats

Abstract Background: Previous studies indicate that the administration of melatonin caused body weight and abdominal visceral fat reductions in rodent models of hyperadiposity. The objective of the present study performed in high-fat fed rats was to evaluate the activity of melatonin on gene expression of some medial basal hypothalamus (MBH) signals involved in feeding behavior regulation, including neuropeptide Y (NPY), proopiomelanocortin (POMC), prolactin-releasing peptide (PrRP), leptin- and insulin-receptors (R) and insulin-R substrate (IRS)-1 and -2. Blood levels of leptin and adiponectin were also measured. Methods: Adult Wistar male rats were divided into four groups (n=16 per group): (i) control diet (3% fat); (ii) high-fat (35%) diet; (iii) high-fat diet+melatonin; (iv) control diet+melatonin. Rats had free access to high-fat or control chow and one of the following drinking solutions: (a) tap water; (b) 25 μg/mL of melatonin. Results: After 10 weeks, the high-fat fed rats showed augmented MBH mRNA levels of NPY, leptin-R, PrRP, insulin-R, IRS-1 and IRS-2. The concomitant administration of melatonin counteracted this increase. Feeding of rats with a high-fat diet augmented expression of the MBH POMC gene through an effect insensitive to melatonin treatment. The augmented levels of circulating leptin and adiponectin seen in high-fat fed rats were counteracted by melatonin as was the augmented body weight: melatonin significantly attenuated a body weight increase in high-fat fed rats without affecting chow or water consumption. Melatonin augmented plasma leptin and adiponectin in control rats. Conclusions: The results indicate that an effect on gene expression of feeding behavior signals at the central nervous system (CNS) may complement a peripheral rise of the energy expenditure produced by melatonin to decrease body weight in high-fat fed rats.