Evidence that triiodothyronine decreases rat serum leptin concentration by down-regulation of leptin gene expression in white adipose tissue

Limits to sustained energy intake. XXXIII. Thyroid hormones play important roles in milk production but do not define the heat dissipation limit in Swiss mice

The limits to sustained energy intake set physiological upper boundaries that affect many aspects of human and animal performance. The mechanisms underlying these limits, however, remain unclear. We exposed Swiss mice to either supplementary thyroid hormones (THs) or the inhibitor methimazole during lactation at 21 or 32.5°C, and measured food intake, resting metabolic rate (RMR), milk energy output (MEO), serum THs and mammary gland gene expression of females, and litter size and mass of their offspring. Lactating females developed hyperthyroidism following exposure to supplementary THs at 21°C, but they did not significantly change body temperature, asymptotic food intake, RMR or MEO, and litter and mass were unaffected. Hypothyroidism, induced by either methimazole or 32.5°C exposure, significantly decreased asymptotic food intake, RMR and MEO, resulting in significantly decreased litter size and litter mass. Furthermore, gene expression of key genes in the mammary gland was significantly decreased by either methimazole or heat exposure, including gene expression of THs and prolactin receptors, and Stat5a and Stat5b. This suggests that endogenous THs are necessary to maintain sustained energy intake and MEO. Suppression of the thyroid axis seems to be an essential aspect of the mechanism by which mice at 32.5°C reduce their lactation performance to avoid overheating. However, THs do not define the upper limit to sustained energy intake and MEO at peak lactation at 21°C. Another, as yet unknown, factor prevents supplementary thyroxine exerting any stimulatory metabolic impacts on lactating mice at 21°C.

Triiodothyronine modulates the expression of leptin and adiponectin in 3T3-L1 adipocytes

Objective

To study the effect of different doses of triiodothyronine on gene expression of the adipokines leptin and adiponectin, at different times, and to evaluate the difference in expression between the two adipokines in each group.

Methods

3T3-L1 adipocytes were incubated with triiodothyronine at physiological dose (10nM) and supraphysiological doses (100nM or 1,000nM), or without triiodothyronine (control, C) for 0.5, 6, or 24 hours. Leptin and adiponectin mRNA was detected using real-time polymerase chain reaction (RT-PCR). One-way analyses of variance, Tukey’s test or Student’s t test, were used to analyze data, and significance level was set at 5%.

Results

Leptin levels decreased in the 1,000nM-dose group after 0.5 hour. Adiponectin levels dropped in the 10nM-dose group, but increased at the 100nM dose. After 6 hours, both genes were suppressed in all hormone concentrations. After 24 hours, leptin levels increased at 10, 100 and 1,000nM groups as compared to the control group; and adiponectin levels increased only in the 100nM group as compared to the control group.

Conclusion

These results demonstrated fast actions of triiodothyronine on the leptin and adiponectin expression, starting at 0.5 hour, at a dose of 1,000nM for leptin and 100nM for adiponectin. Triiodothyronine stimulated or inhibited the expression of adipokines in adipocytes at different times and doses which may be useful to assist in the treatment of obesity, assuming that leptin is increased and adiponectin is decreased, in obesity cases.

Triiodothyronine increases mRNA and protein leptin levels in short time in 3T3-L1 adipocytes by PI3K pathway activation

The present study aimed to examine the effects of thyroid hormone (TH), more precisely triiodothyronine (T3), on the modulation of leptin mRNA expression and the involvement of the phosphatidyl inositol 3 kinase (PI3K) signaling pathway in adipocytes, 3T3-L1, cell culture. We examined the involvement of this pathway in mediating TH effects by treating 3T3-L1 adipocytes with physiological (P=10nM) or supraphysiological (SI=100 nM) T3 dose during one hour (short time), in the absence or the presence of PI3K inhibitor (LY294002). The absence of any treatment was considered the control group (C). RT-qPCR was used for mRNA expression analyzes. For data analyzes ANOVA complemented with Tukey’s test was used at 5% significance. T3 increased leptin mRNA expression in P (2.26 ± 0.36, p< 0.001), SI (1.99 ±0.22, p< 0.01) compared to C group (1± 0.18). This increase was completely abrogated by LY294002 in P (1.31±0.05, p< 0.001) and SI (1.33±0.31, p< 0.05). Western blotting confirmed these results at protein level, indicating the PI3K pathway dependency. To examine whether leptin is directly induced by T3, we used the translation inhibitor cycloheximide (CHX). In P, the presence of CHX maintained the levels mRNA leptin, but was completely abrogated in SI (1.14±0.09, p> 0.001). These results demonstrate that the activation of the PI3K signaling pathway has a role in TH-mediated direct and indirect leptin gene expression in 3T3-L1 adipocytes.

A comparative genotoxicity study of a supraphysiological dose of triiodothyronine (T₃) in obese rats subjected to either calorie-restricted diet or hyperthyroidism

This study was designed to determine the genotoxicity of a supraphysiological dose of triiodothyronine (T₃) in both obese and calorie-restricted obese animals. Fifty male Wistar rats were randomly assigned to one of the two following groups: control (C; n = 10) and obese (OB; n = 40). The C group received standard food, whereas the OB group was fed a hypercaloric diet for 20 weeks. After this period, half of the OB animals (n = 20) were subjected to a 25%-calorie restriction of standard diet for 8 weeks forming thus a new group (OR), whereas the remaining OB animals were kept on the initial hypercaloric diet. During the following two weeks, 10 OR animals continued on the calorie restriction diet, whereas the remaining 10 rats of this group formed a new group (ORS) given a supraphysiological dose of T₃ (25 µg/100 g body weight) along with the calorie restriction diet. Similarly, the remaining OB animals were divided into two groups, one that continued on the hypercaloric diet (OB, n = 10), and one that received the supraphysiological dose of T₃ (25 µg/100 g body weight) along with the hypercaloric diet (OS, n = 10) for two weeks. The OB group showed weight gain, increased adiposity, insulin resistance, increased leptin levels and genotoxicity; T₃ administration in OS animals led to an increase in genotoxicity and oxidative stress when compared with the OB group. The OR group showed weight loss and normalized levels of adiposity, insulin resistance, serum leptin and genotoxicity, thus having features similar to those of the C group. On the other hand, the ORS group, compared to OR animals, showed higher genotoxicity. Our results indicate that regardless of diet, a supraphysiological dose of T₃ causes genotoxicity and potentiates oxidative stress.

Impacts of the coexistence of diabetes and hypothyroidism on body weight gain, leptin and various metabolic aspects in albino rats

The present study was conducted to assess the interrelationship and the influence of the coexistence of diabetes and hypothyroidism on thyroid hormone levels, insulin levels and biochemical variables related to carbohydrate, lipid and protein metabolism in addition to thyroid gland and Islets of Langerhans histological changes and antioxidant defense system. Diabetes mellitus was induced by intraperitoneal injection of streptozotocin to fasting albino rats at dose level of 45 mg/kg b. w. Hypothyroidism in diabetic and normal rats was induced by adding methimazole in drinking water (0.02% w/v) for 4 weeks. The obtained results revealed that hypothyroidism interacts with diabetes in a way that prevents the progress of the hyperglycemic state. This may be due to the increase in the insulin secretory response in diabetic hypothyroid than diabetic rats. Serum T3 level decreased in order in diabetic (-26.63%), hypothyroid (-61.89%) and diabetic hypothyroid (-65.69%) rats while T4 level was increased in diabetic rats and decreased in hypothyroid ones. The decrease in T3 level in diabetic animals in spite of T4 increase may be attributed to the decrease in conversion of T4 to T3 as a result of hepatic 5'-DI decreased activity. Liver glycogen content was three-fold decreased in diabetic rats and was not significantly altered in both hypothyroid and diabetic hypothyroid rats. The serum leptin level and body weight gain were decreased in diabetic and diabetic hypothyroid rats; the leptin level was more deteriorated in diabetic hypothyroid rats while body weight gain was more affected in diabetic rats. Serum triglycerides level was more increased in diabetic rats than in diabetic hypothyroid ones on one hand, while total lipids, total cholesterol, LDL-cholesterol levels as well as cardiovascular indices were more deteriorated in diabetic hypothyroid rats than diabetic ones on the other hand. Serum total protein and globulin levels were decreased in diabetic rats and were increased in hypothyroid and diabetic hypothyroid rats. Hepatic total thiols and glutathione contents and catalase and peroxidase activity were profoundly decreased in diabetic rats while they (except glutathione) were increased in hypothyroid and diabetic hypothyroid rats. In conclusion, the hypothyroidism may have a counteracting effect on the hyperglycemic state and the elevated serum T4 level as well as the deteriorated antioxidant defense system found in diabetes mellitus, but both experimentally-induced diseases may synergize in inducing more elevation of serum total lipids, total cholesterol and LDL-cholesterol and more decrease in leptin levels.

Experimental hyperthyroidism decreases gene expression and serum levels of adipokines in obesity

Aims. To analyze the influence of hyperthyroidism on the gene expression and serum concentration of leptin, resistin, and adiponectin in obese animals. Main Methods. Male Wistar rats were randomly divided into two groups: control (C)—fed with commercial chow ad libitum—and obese (OB)—fed with a hypercaloric diet. After group characterization, the OB rats continued receiving a hypercaloric diet and were randomized into two groups: obese animals (OB) and obese with 25 μg triiodothyronine (T₃)/100 BW (OT). The T₃ dose was administered every day for the last 2 weeks of the study. After 30 weeks the animals were euthanized. Samples of blood and adipose tissue were collected for biochemical and hormonal analyses as well as gene expression of leptin, resistin, and adiponectin. Results. T₃ treatment was effective, increasing fT₃ levels and decreasing fT₄ and TSH serum concentration. Administration of T₃ promotes weight loss, decreases all fat deposits, and diminishes serum levels of leptin, resistin, and adiponectin by reducing their gene expression. Conclusions. Our results suggest that T₃ modulate serum and gene expression levels of leptin, resistin, and adiponectin in experimental model of obesity, providing new insights regarding the relationship between T₃ and adipokines in obesity.

Endocrine factors in the hypothalamic regulation of food intake in females: a review of the physiological roles and interactions of ghrelin, leptin, thyroid hormones, oestrogen and insulin

Controlling energy homeostasis involves modulating the desire to eat and regulating energy expenditure. The controlling machinery includes a complex interplay of hormones secreted at various peripheral endocrine endpoints, such as the gastrointestinal tract, the adipose tissue, thyroid gland and thyroid hormone-exporting organs, the ovary and the pancreas, and, last but not least, the brain itself. The peripheral hormones that are the focus of the present review (ghrelin, leptin, thyroid hormones, oestrogen and insulin) play integrated regulatory roles in and provide feedback information on the nutritional and energetic status of the body. As peripheral signals, these hormones modulate central pathways in the brain, including the hypothalamus, to influence food intake, energy expenditure and to maintain energy homeostasis. Since the growth of the literature on the role of various hormones in the regulation of energy homeostasis shows a remarkable and dynamic expansion, it is now becoming increasingly difficult to understand the individual and interactive roles of hormonal mechanisms in their true complexity. Therefore, our goal is to review, in the context of general physiology, the roles of the five best-known peripheral trophic hormones (ghrelin, leptin, thyroid hormones, oestrogen and insulin, respectively) and discuss their interactions in the hypothalamic regulation of food intake.

Iodothyronine Interactions with the System L1 Amino Acid Exchanger in 3T3-L1 Adipocytes

Thyroid hormones enter isolated white adipocytes largely by a System L1-type amino acid transporter en route to exerting genomic actions. Differentiated 3T3-L1 mouse adipocytes in culture express mRNA for LAT1 (the catalytic subunit of high-affinity System L1). L-[¹²⁵I]-T₃ uptake into 3T3-L1 adipocytes included a substantial saturable component inhibited by leucine. L-[³H]phenylalanine uptake into 3T3-L1 cells was saturable (K_m of 31 μM), competitively inhibited by T₃ (K_i of 1.2 μM) and blocked by leucine, BCH, and rT₃ as expected for substrate interactions of System L1. Efflux of preloaded L-[³H]phenylalanine from 3T3-L1 adipocytes was trans stimulated by external leucine, demonstrating the obligatory exchange mechanism of System L1 transport. T₃ (10 μM) did not significantly trans stimulate L-[³H]phenylalanine efflux, but did competitively inhibit the trans stimulatory effect of 10 μM leucine. The results highlight strong competitive interactions between iodothyronines (T₃, rT₃) and amino acids for transport by System L1 in adipocytes, which may impact cellular iodothyronine exchanges during altered states of protein nutrition.

Effects of escin mixture from the seeds of Aesculus hippocastanum on obesity in mice fed a high fat diet

Escins, a triterpene glycoside mixture obtained from the ethanol extract of Aesculus hippocastanum L. (Hippocastanaceae) seed, was evaluated for its in vivo effects on the plasma levels of some hormones (leptin, insulin, FT(3), FT(4)) and biochemical parameters (glucose, triglyceride, total cholesterol, HDL-C, LDL-C concentrations) in mice fed with a high fat diet for 5 weeks. A high fat diet induced a remarkable increment in the plasma leptin (p <0.01), total cholesterol (p <0.01) and LDL-C (p <0.001) concentrations compared to control group animals. Combined administration of a high-fat diet with escins decreased leptin (31.6%) (p<0.05) and FT(4) (36.0%) (p<0.05) levels, increased HDL-C concentration (17.0%), while remained ineffective on LDL-C concentration in mice. Results have shown that escins may have beneficial effects in the understanding of obesity.

Administration of physiologic levels of triiodothyronine increases leptin expression in calorie-restricted obese rats, but does not influence weight loss

Obesity has become a major public health problem, most commonly treated via dietary restriction to promote weight loss. Although leptin and thyroid hormones are involved in the regulation of energy balance, the role of these hormones after the stabilization of weight loss remains unclear. This study was designed to analyze the effect of thyroid hormone on sustained weight loss and leptin gene expression in obese animals after a loss of 5% to 10% of body weight. Thirty-day-old male Wistar rats were separated into 4 groups: control, obese, calorie restriction (CR), and calorie restriction with triiodothyronine administration (CRT). The obese group had increased weight and adiposity, leptin and insulin levels, and leptin gene expression. Dietary restriction in the CR group resulted in decreased body weight and adiposity, diminished leptin, and increased thyroid hormone receptor beta expression. The CRT group, submitted to dietary restriction with concomitant administration of a physiologic triiodothyronine dose, had thyroid hormone receptor beta expression at levels comparable with those observed in the control group and simultaneously increased leptin expression as compared with that in the CR group, suggesting that thyroid hormone modulates leptin expression under conditions of calorie restriction. Increased leptin expression in the CRT group did not result in increased circulating leptin or a statistically significant reduction in body weight during the treatment period. These data provide impetus for further study, as a longer treatment period may result in increased circulating leptin and, thus, further reduction in body weight during calorie restriction in an obesity model.

Effects of thyroid hormone on the adaptation in short bowel syndrome

BACKGROUND

Thyroid hormone acts on structural and functional maturation of the mammalian small intestine, mitochondrial pathways, and several protein-gene interactions. Therefore, it is one of the most important regulators of intestinal epithelial differentiation. The aim of the study was to evaluate the effects of thyroid hormone on the adaptation in an experimental model of short bowel syndrome.

METHODS

Rats were divided into three groups: sham (bowel transection and anastomosis), short bowel syndrome-saline (75% bowel resection and anastomosis), and short bowel syndrome-thyroid hormone (75% bowel resection and anastomosis, and was administered triiodothyronine). The evaluation of adaptation parameters, histopathological and biochemical analysis were performed in all groups.

RESULTS

Triiodothyronine treatment resulted in a significant increase in adaptation parameters, villus height-crypt depth, and enterocyte proliferation, whereas significant decrease was seen in apoptotic index in jejunum. Enterocyte proliferation and most of the adaptation parameters changed significantly in ileum following the treatment with triiodothyronine as in jejunum. The changes in ileal villus height-crypt depth and apoptotic index were not statistically significant. Serum levels of free triiodothyronine were lower in the short bowel syndrome-saline group.

CONCLUSIONS

Our results suggest that thyroid hormone treatment in the hypothyroid phase of SBS enhances intestinal adaptive response.

Possible implications of leptin, adiponectin and ghrelin in the regulation of energy homeostasis by thyroid hormone

Thyroid hormone plays a critical role in energy homeostasis through mechanisms, which are not fully understood. In the present study, we investigated possible alterations of important energy regulators such as leptin, adiponectin, and ghrelin in relation to changes in thyroid hormones. Thyroid hormone (250 microg/kg) was administered in male Wistar rats for 2 weeks (THYR), while hypothyroidism (HYPO) was induced by propylthiouracil administration (0.05% in drinking water) for 3 weeks. Untreated animals served as controls (NORM). Leptin and adiponectin were measured in plasma by ELISA, while total ghrelin was measured with RIA. Body weight was significantly reduced both in THYR and HYPO rats, while food intake was significantly increased in THYR and decreased in HYPO. This response was associated with various changes in leptin, adiponectin, and ghrelin in plasma. In fact, in THYR rats, leptin levels (mean +/- SEM) were 240 +/- 55 pg/ml as compared to 819 +/- 70 pg/ml in untreated rats (P < 0.05), while no changes were observed in ghrelin and adiponectin. In HYPO rats, leptin levels were 1400 +/- 200 pg/ml vs. 819 +/- 70 pg/ml in untreated rats (P < 0.05), while ghrelin and adiponectin were significantly increased in HYPO rats as compared to untreated rats (P < 0.05). Furthermore, T(3) and T(4) levels were inversely correlated to leptin (P = 0.014), while ghrelin and adiponectin were inversely correlated to weight changes (P = 0.05 and P = 0.03, respectively). In conclusion, leptin seems mainly to be involved in the thyroid hormone effects on energy homeostasis. Ghrelin and adiponectin may serve a compensatory physiological role in hypothyroidism.

Developmental control of plasma leptin and adipose leptin messenger ribonucleic acid in the ovine fetus during late gestation: role of glucocorticoids and thyroid hormones

In developed countries, the increasing incidence of obesity is a serious health problem. Leptin exposure in the perinatal period affects long-term regulation of appetite and energy expenditure, but control of leptin production in utero is unclear. This study investigated perirenal adipose tissue (PAT) and placental leptin expression in ovine fetuses during late gestation and after manipulation of plasma glucocorticoid and thyroid hormone concentrations. Between 130 and 144 d of gestation (term at 145 +/- 2 d), plasma leptin and PAT leptin mRNA levels increased in association with increments in plasma cortisol and T(3). Fetal adrenalectomy prevented these developmental changes, and exposure of intact 130 d fetuses to glucocorticoids, by cortisol infusion or maternal dexamethasone treatment, caused premature elevations in plasma leptin and PAT leptin gene expression. Fetal thyroidectomy increased plasma leptin and PAT leptin mRNA abundance, whereas intravenous T(3) infusion to intact 130 d fetuses had no effect on circulating or PAT leptin. Leptin mRNA expression was low in the ovine placenta. Therefore, in the sheep fetus, PAT appears to be a primary source of leptin in the circulation, and leptin gene expression is regulated by both glucocorticoids and thyroid hormones. Developmental changes in circulating and PAT leptin may mediate the maturational effects of cortisol in utero and have long-term consequences for appetite regulation and the development of obesity.