The Relationship between Type 2 Diabetes Mellitus and Related Thyroid Diseases

Microcystin-LR induced thyroid dysfunction and metabolic disorders in mice

There is growing evidence that microcystins (MCs) act as hazardous materials and can disrupt the endocrine systems of animals. However, the response of thyroid function and the related energy metabolism following MCs exposure is still unknown. In the present study, mice were injected intraperitoneally (i.p.) with doses of either 5 or 20 μg/kg MC-LR for 4 weeks. We report, for the first time, that mice exposed to 20 μg/kg MC-LR showed disrupted glucose, triglyceride and cholesterol metabolism with obvious symptoms of hyperphagia, polydipsia, and weight loss. The circulating thyroid hormone (TH) levels in mice following MC-LR exposure were detected. Significantly increased free triiodothyronine (FT3) and decreased free thyroxin (FT4) were largely responsible for the physiological aberrations and metabolic disorders observed in mice after the 20 μg/kg MC-LR exposure. Increased expression of TH receptor (Trα) and mTOR expression in the brain after the 20 μg/kg MC-LR exposure suggests that the increased FT3 enhanced mTOR signaling subsequently led to hyperphagia and elevated energy expenditure in mice. Furthermore, several genes involved in glucose homeostasis and lipid metabolism, which have been identified affected by TH, were also differentially expressed after MC-LR exposure. The above results clearly showed that mice exposed to MC-LR experienced thyroid dysfunction and its downstream functional changes, and are useful to better understand the endocrine toxicity of MC-LR to mammals or even humans.

Influence of high-normal serum TSH levels on major cardiovascular risk factors and Visceral Adiposity Index in euthyroid type 2 diabetic subjects

Although several observations indicate that serum TSH levels in the high normal range are related to cardiovascular (CVD) risk factors in the general population, similar data are limited in diabetic subjects. The aim of this study was to investigate the potential associations between TSH serum levels within the normal range and major metabolic and non-metabolic CVD risk factors in a cohort of euthyroid type 2 diabetic subjects. Thyroid hormones, TSH levels, anthropometric parameters, lipid profile, glucose control, and blood pressure were measured in 490 euthyroid type 2 diabetic subjects, consecutively attending two outpatient diabetic units in Southern Italy. In all subjects, we also calculated the Visceral Adiposity Index (VAI), an obesity-related index associated with CVD risk. Diabetic women showed higher mean serum TSH levels and lower FT4 concentration than diabetic men, while FT3 levels were comparable in the two genders. Stratifying the study population according to quartiles of TSH levels, subjects in the highest TSH quartile were more likely to be female and younger, with higher values of BMI and waist circumference (P = 0.05 both), higher triglycerides (P = 0.002) and non-HDL cholesterol concentrations (P = 0.01), higher VAI values (P = 0.02), and lower FT4 levels (P = 0.05), when compared to those in the lowest quartile. At multivariate analysis, a younger age, female gender, triglycerides levels, and waist circumference were independently associated with higher TSH levels. In conclusion, in type 2 diabetic subjects with no evidence of thyroid disease, higher TSH concentrations within the normal range were more frequent in women and in younger subjects, and they were associated with visceral obesity and higher triglycerides concentrations, two well-known CVD risk factors.

Postnatal exposure to a high-carbohydrate diet interferes epigenetically with thyroid hormone receptor induction of the adult male rat skeletal muscle glucose transporter isoform 4 expression

Early life nutritional intervention causes adult-onset insulin resistance and obesity in rats. Thyroid hormone receptor (TR), in turn, transcriptionally enhances skeletal muscle Glut4 expression. We tested the hypothesis that reduced circulating thyroid-stimulating hormone and T4 concentrations encountered in postnatal (PN4-PN24) high-carbohydrate (HC) milk formula-fed versus the mother-fed controls (MF) would epigenetically interfere with TR induction of adult (100 days) male rat skeletal muscle Glut4 expression, thereby providing a molecular mechanism mediating insulin resistance. We observed increased DNA methylation of the CpG island with enhanced recruitment of Dnmt3a, Dnmt3b and MeCP2 in the glut4 promoter region along with reduced acetylation of histone (H)2A.Z and H4 particularly at the H4.lysine (K)16 residue, which was predominantly mediated by histone deacetylase 4 (HDAC4). This was followed by enhanced recruitment of heterochromatin protein 1β to the glut4 promoter with increased Suv39H1 methylase concentrations. These changes reduced TR binding of the T3 response element of the glut4 gene (TREs; -473 to -450 bp) detected qualitatively in vivo (electromobility shift assay) and quantified ex vivo (chromatin immunoprecipitation). In addition, the recruitment of steroid receptor coactivator and CREB-binding protein to the glut4 promoter-protein complex was reduced. Co-immunoprecipitation experiments confirmed the interaction between TR and CBP to be reduced and HDAC4 to be enhanced in HC versus MF groups. These molecular changes were associated with diminished skeletal muscle Glut4 mRNA and protein concentrations. We conclude that early postnatal exposure to HC diet epigenetically reduced TR induction of adult male skeletal muscle Glut4 expression, uncovering novel molecular mechanisms contributing to adult insulin resistance and obesity.

Different levels of thyroid hormones between impaired fasting glucose and impaired glucose tolerance: free T3 affects the prevalence of impaired fasting glucose and impaired glucose tolerance in opposite ways

CONTEXT

There is an association between thyroid disorders and diabetes mellitus.

OBJECTIVE

To investigate thyroid hormone levels in different glucose metabolic statuses, analyse relationships between thyroid hormone levels and different categories of prediabetes and metabolic parameters within a large euthyroid nondiabetic population.

METHODS

A total of 3328 subjects without diabetes or thyroid dysfunction were included in this cross-sectional study. Subjects were divided in to four groups [normal glucose tolerance (NGR), impaired fasting glucose (IFG), impaired glucose tolerance (IGT) and combined glucose intolerance (CGI)] according to the results of oral glucose tolerance test. Participants were then divided into four groups according to the quartile of free T3 (FT3) in their blood.

RESULTS

Subjects with IFG had higher levels of FT3 and ratio of FT3 to FT4 (FT3/FT4), but lower level of free T4 (FT4) than subjects with IGT. FT3/FT4 was negatively associated with postprandial plasma glucose (PPG) [standardized β (β) = -0·087; P < 0·001]. The prevalence of IFG and CGI was increased with the level of FT3, while the prevalence of IGT was decreased with the level of FT3 (P for trend: <0·001, 0·003 and <0·001, respectively). FT3 was negatively associated with the risk of IGT (OR = 0·409, 95% CI 0·179-0·935), whereas FT4 was positively associated with the risk of IGT (OR = 1·296, 95% CI 1·004-1·673).

CONCLUSIONS

Free thyroid hormone levels were different between subjects with IFG and IGT. FT3 affects the prevalence of IFG and IGT in opposite ways. The difference in thyroid hormone levels may play an important role in the different pathological mechanisms of IFG and IGT.

Association between the serum concentration of triiodothyronine with components of metabolic syndrome, cardiovascular risk, and diet in euthyroid post-menopausal women without and with metabolic syndrome

PURPOSE

To determine the association between the serum concentration of triiodothyronine (T3) with components of metabolic syndrome (MetS), cardiovascular risk (CVR), and diet in euthyroid post-menopausal women without and with MetS.

METHODS

A cross-sectional study was performed in 120 voluntary women of an indigenous population from Tlaxcala-México. Euthyroid status was assessed measuring the serum concentration of thyrotropin (TSH) and thyroid hormones, while that of estradiol was measured to confirm the postmenopausal condition. MetS was diagnosed using the American Heart Association/National Heart, Lung, and Blood Institute Scientific Statement (AHA/NHLBI) criterion. Estimation of CVR was calculated based on the Framingham scale. Diet components were evaluated based on survey applications. Correlations, logistic regression analyses, ANOVA or Kruskall-Wallis, and chi-square tests were used to determine significant differences (P ≤ 0.05) between women without MetS and women with MetS having different serum concentrations of T3.

RESULTS

Triiodothyronine was positively correlated with insulin but negatively correlated with glucose, high-density lipoprotein cholesterol (HDL-C), and CVR. Compared to women without MetS, women with MetS and low-normal T3 concentration showed a high risk for hyperglycemia and moderate/high risk for CVR. In contrast, a high-normal T3 concentration increased the risk to have a big waist circumference, a high concentration of HDL-C, and insulin resistance. Diet analysis showed a high grade of malnutrition in women from all groups. The intake of calories was positively affected by the T3 concentration, albeit it did not affect the extent of malnutrition.

CONCLUSIONS

In contrast to concentrations of TSH, total thyroxin (T4), and free T4, the concentration of serum T3 was strongly correlated with cardio-metabolic variables in euthyroid postmenopausal women. In comparison to women without MetS, a high-normal serum concentration of T3 in women with MetS is positively associated with reduced glycaemia and CVR but negatively related to body mass index (BMI), insulin, insulin resistance, and HDL-C. Although the analyzed population had a nutritional deficiency, both calories and iron intake were positively affected by the T3 concentration. Our results suggest the necessity of health programs monitoring T3 in old people in order to treat hyperglycemia, cardio-metabolic components, and the ageing anorexia.

Dyslipidemia and serum mineral profiles in patients with thyroid disorders

OBJECTIVES

To investigate changes in serum lipid profile, levels of serum minerals associated with thyroid disorders, and to compare these with the serum lipid and mineral profiles in hypothyroid patients receiving thyroxine therapy.

METHODS

A cross-sectional study was conducted in King Khaled Hospital, Hail, Saudi Arabia. The patient database was searched for new patients with thyroid dysfunction between January 2011 and June 2012. They were classified into 5 groups: 1) subclinical-hypothyroid (SHY), 2) overt-hypothyroid (OHY), 3) subclinical-hyperthyroid (SHE), 4) overt-hyperthyroid (OHE), 5) patients under thyroxine therapy (EU), and normal controls.

RESULTS

The OHY group showed impaired renal function; whereas, the kidney function of the SHE, OHE, and EU groups was normal. The OHY and OHE groups exhibited elevated serum glucose. The OHY group showed elevated serum cholesterol, triglyceride, and low-density lipoprotein cholesterol, and decreased high-density lipoprotein cholesterol. Serum lipids were reduced in the OHE group, and no different in the EU group compared with controls. The serum calcium and phosphate were reduced in the OHY group, whereas, in the OHE group, the phosphate was increased while magnesium and potassium were reduced.

CONCLUSION

Hypothyroidism caused impaired renal function, glucose intolerance, hyperlipidemia, and reduction in serum phosphate. Hyperthyroidism caused a reduction in serum lipids, magnesium, and potassium. Thyroxine therapy normalized the deranged lipids and minerals, but not glucose. RESULTS indicate that thyroid function tests should be considered when diagnosing those metabolic disorders. 

Risk Factors for Thyroid Dysfunction among Type 2 Diabetic Patients in a Highly Diabetes Mellitus Prevalent Society

Diabetes and thyroid dysfunction found to exist simultaneously. In this regard, the present study looked into the prevalence of different forms of thyroid dysfunction and their risk factors among Type 2 diabetic Saudi patients. Methodology. A cross-sectional retrospective randomized hospital-based study of 411 Type 2 diabetic Saudi patients of >25 years of age was conducted to test the prevalence of different types of thyroid dysfunction and their risk factors. Results. The prevalence of different types of thyroid dysfunction is 28.5%, of which 25.3% had hypothyroidism, where 15.3%, 9.5%, and 0.5% are clinical, subclinical, and overt hypothyroidism, respectively. The prevalence of hyperthyroidism is 3.2%, of which subclinical cases accounted for 2.7% and overt hyperthyroidism accounted for 0.5%. Risk factors for thyroid dysfunction among Saudi Type 2 diabetic patients are family history of thyroid disease, female gender, and duration of diabetes of >10 years, while the risk was not significant in patients with history of goiter and patients aged >60 years. Smoking and parity show a nonsignificant reduced risk. Conclusion. Thyroid dysfunction is highly prevalent among Saudi Type 2 diabetic patients, and the most significant risk factors are family history of thyroid disease, female gender, and >10 years duration of diabetes.