Subcutaneous Adipose Tissue Type II Deiodinase Gene Expression Reduced in Obese Individuals with Metabolic Syndrome

Understanding the Roles of Selenium on Thyroid Hormone-Induced Thermogenesis in Adipose Tissue

Brown adipose tissue (BAT) and white adipose tissue (WAT) are known to regulate lipid metabolism. A lower amount of BAT compared to WAT, along with adipose tissue dysfunction, can result in obesity. Studies have shown that selenium supplementation protects against adipocyte dysfunction, decreases WAT triglycerides, and increases BAT triiodothyronine (T3). In this review, we discuss the relationship between selenium and lipid metabolism regulation through selenoprotein deiodinases and the role of deiodinases and thyroid hormones in the induction of adipose tissue thermogenesis. Upon 22 studies included in our review, we found that studies investigating the relationship between selenium and deiodinases demonstrated that selenium supplementation affects the iodothyronine deiodinase 2 (DIO2) protein and the expression of its associated gene, DIO2, proportionally. However, its effect on DIO1 is inconsistent while its effect on DIO3 activity is not detected. Studies have shown that the activity of deiodinases especially DIO2 protein and DIO2 gene expression is increased along with other browning markers upon white adipose tissue browning induction. Studies showed that thermogenesis is stimulated by the thyroid hormone T3 as its activity is correlated to the expression of other thermogenesis markers. A proposed mechanism of thermogenesis induction in selenium supplementation is by autophagy control. However, more studies are needed to establish the role of T3 and autophagy in adipose tissue thermogenesis, especially, since some studies have shown that thermogenesis can function even when T3 activity is lacking and studies related to autophagy in adipose tissue thermogenesis have contradictory results.

The role of the thyroid in polycystic ovary syndrome

Polycystic ovary syndrome (PCOS) is the most common endocrine and metabolic disease in women of childbearing age and can cause metabolic disorder, infertility, and increased anxiety and depression; as a result, it can seriously affect the physical and mental health of fertile women. PCOS is a highly clinically heterogeneous disease with unclear etiology and pathogenesis, which increases the difficulty of treatment. The thyroid gland has complex regulatory effects on metabolism, reproduction, and emotion, and produces hormones that act on almost all cells of the human body. The clinical manifestations of PCOS are similar to some thyroid diseases. Furthermore, some thyroid diseases, such as subclinical hypothyroidism (SCH), not only increase the incidence rate of PCOS, but also exacerbate its associated metabolic abnormalities and reproductive disorders. Interestingly, PCOS also increases the incidence of some thyroid diseases. However, the role of the thyroid in PCOS remains unclear. This review is intended to thoroughly explore the critical role of the thyroid in PCOS by summarizing the comorbidity of PCOS and thyroid diseases and their combined role in metabolic disorders, related metabolic diseases, and reproductive disorders; and by analyzing the potential mechanism through which the thyroid influences the development and progression of PCOS and its symptoms. We hope this review will provide a valuable reference for the role of the thyroid in PCOS.

Selenium and Selenoproteins in Adipose Tissue Physiology and Obesity

Selenium (Se) homeostasis is tightly related to carbohydrate and lipid metabolism, but its possible roles in obesity development and in adipocyte metabolism are unclear. The objective of the present study is to review the current data on Se status in obesity and to discuss the interference between Se and selenoprotein metabolism in adipocyte physiology and obesity pathogenesis. The overview and meta-analysis of the studies on blood Se and selenoprotein P (SELENOP) levels, as well as glutathione peroxidase (GPX) activity in obese subjects, have yielded heterogenous and even conflicting results. Laboratory studies demonstrate that Se may modulate preadipocyte proliferation and adipogenic differentiation, and also interfere with insulin signaling, and regulate lipolysis. Knockout models have demonstrated that the selenoprotein machinery, including endoplasmic reticulum-resident selenoproteins together with GPXs and thioredoxin reductases (TXNRDs), are tightly related to adipocyte development and functioning. In conclusion, Se and selenoproteins appear to play an essential role in adipose tissue physiology, although human data are inconsistent. Taken together, these findings do not support the utility of Se supplementation to prevent or alleviate obesity in humans. Further human and laboratory studies are required to elucidate associations between Se metabolism and obesity.

Decreased deiodinase activity after glucose load could lead to atherosclerosis in euthyroid women with polycystic ovary syndrome

OBJECTIVE

Glucose and lipid disturbances, as well as higher tendency to atherosclerosis, are observed in women with polycystic ovary syndrome (PCOS). Thyroid hormones action has long been recognized as an important determinant of glucose and lipid homeostasis. Some studies suggest that even in euthyroid subjects, thyroid function may affect atherosclerosis risk factors. The aim of this study was to evaluate the relationships between thyroid hormonal status and glucose and lipid profile before and after oral glucose tolerance test (OGTT) in PCOS women in comparison to the control group.

PATIENTS AND METHODS

The study group included 98 women-60 women with PCOS and 38 women matched for age and BMI as a control group. OGTT with estimation of plasma glucose and lipids, as well as serum insulin and thyroid hormones (TH) concentrations was performed. Activity of peripheral deiodinases at baseline (SPINA-GD1) and at the 120 min of OGTT (SPINA-GD2) was calculated according to the formula by Dietrich et al. as a measure of T4-T3 conversion efficiency. Delta GD was estimated as SPINA-GD1-SPINA-GD2, and delta fT3 was calculated as a difference between fT3 before and after OGTT.

RESULTS

We did not find differences in TH, SPINA-GDs, and plasma lipid concentrations between PCOS and control group before and after OGTT. Glucose load resulted in a decrease of level TSH, TC, TG, HDL-C, and LDL-C concentrations in women with PCOS, as well as in the control group (all p < 0.05). We found that GD (p = 0.01) and serum fT3 concentration (p = 0.0008) decreased during glucose load only in the PCOS group. We observed a positive relationship between delta fT3 and plasma TG concentration (r = 0.36, p = 0.004), delta GD and plasma TG concentration after glucose load (r = 0.34, p = 0.007), only in the PCOS group. We also found negative relationship between SPINA-GD2 and plasma TC concentration (r = -0.29, p = 0.02) after glucose load and positive relationship between delta GD and insulin at the 60 min of OGTT (r = 0.29, p = 0.02), only in the PCOS women.

CONCLUSIONS

These data showed insufficient conversion of fT4 to fT3, as well as a relationship of SPINA-GDs with insulin, TC and TG in PCOS women after glucose load. It may suggest that disturbances in deiodinase activity after glucose load might promote atherosclerosis in PCOS women.

Lipoprotein(a)-activated immunity, insulin resistance and new-onset diabetes

OBJECTIVES

Some evidence suggests that serum lipoprotein[Lp](a) may be inversely linked to type-2 diabetes. We aimed to determine in nondiabetic people the relationship of serum [Lp](a) with insulin resistance and new-onset diabetes (NOD).

MATERIALS AND METHODS

Population-based middle-aged adults (n = 1685) were categorized by fasting glucose and stratified to gender, having excluded prevalent diabetic subjects. NOD (n = 90) occurred over a median 5 years' follow-up.

RESULTS

Subjects that subsequently developed NOD, derived both from the normoglycemia and impaired fasting glucose (IFG) groups,were distinguished, among others, primarily by significantly elevated serum gamma glutamyltransferase, reduced Lp(a) (by 31%) and, compared to IFG, by low total cholesterol levels. Partial correlation of Lp(a) with homeostatic model assessment (HOMA) was inverse in normoglycemic men; such correlation, neutral in normoglycemic women, proved inverse in IFG (r = -0.17). Circulating Lp(a) in individuals with paired measures increased significantly (1.55-fold) in the period from baseline up to NOD. Multivariable-adjusted logistic regression analysis for NOD in combined sexes indicated independent and additive prediction by serum Lp(a), albeit inverse in direction (RR 0.84, [95%CI 0.72; 0.97]).

CONCLUSION

Lp(a) is significantly reduced in the period preceding NOD and is inversely associated with HOMA index, observations consistent with underlying autoimmune activation.