A hypothesis of synergism: the interrelationship of T3 and insulin to disturbances in metabolic homeostasis

Insulin resistance, leptin and adiponectin in lean and hypothyroid children and adolescents with obesity

BACKGROUND

Obesity usually complicates hypothyroidism. Adipokines like leptin and adiponectin secreted by adipose tissue modulate insulin resistance (IR), appetite, and obesity. The association between adipokines, IR, and thyroid hormone has not been sufficiently studied in children. We investigated leptin and adiponectin as well as IR and their association with thyroid hormone in both lean and hypothyroid children and adolescents with obesity.

METHODS

The study included 30 lean hypothyroid, 30 hypothyroid children and adolescents with obesity, and 30 healthy lean children as the control group. Serum thyroid-stimulating hormone (TSH), free triiodothyronine (fT3), free thyroxine (fT4), fasting blood glucose, fasting insulin, homeostatic model assessment method of insulin resistance (HOMA-IR), leptin, and adiponectin levels were estimated in all participants.

RESULTS

Fasting insulin, HOMA-IR, and leptin levels were significantly elevated in hypothyroid children compared to the control group; more in hypothyroid children with obesity. In contrast, adiponectin levels were significantly lower in the hypothyroid children with obesity compared to the lean hypothyroid children and controls. HOMA-IR was positively correlated to TSH and BMI but inversely correlated with fT3 and fT4 in hypothyroid children. There was no correlation between IR and either leptin or adiponectin levels. Leptin and adiponectin levels correlated well with BMI in hypothyroid children and adolescents with obesity.

CONCLUSION

Insulin resistance and leptin levels are increased in hypothyroid children and adolescents; more in those with obesity. IR is not related to leptin and adiponectin levels, however, leptin and adiponectin levels correlate well with BMI in hypothyroid children and adolescents with obesity.

IMPACT

Insulin resistance (IR) and leptin levels increase in hypothyroid children and adolescent; more with obesity. IR is not related to leptin and adiponectin levels, however leptin and adiponectin levels correlated well with BMI in hypothyroid children and adolescents with obesity.

Association between thyroid dysfunction and type 2 diabetes: a meta-analysis of prospective observational studies

BACKGROUND

Diabetes mellitus and thyroid disease are two areas of broad interest in the field of endocrinology and metabolism. Variation of thyroid hormone concentration, even within the normal range, may portend the onset of type 2 diabetes mellitus (T2DM), especially among those with prediabetes. However, current evidence is mixed.

METHODS

Prospective studies which assessed diabetes incidence were identified using a database search of MEDLINE and Embase through May 1, 2021. The Sidik-Jonkman random-effects model and cubic spline model were used to evaluate the associations and dose-response relationships between thyroid function/hormone levels and risk of T2DM and cardiovascular disease (CVD) risk among T2DM patients.

RESULTS

A total of 12 prospective studies were included. We found that high baseline TSH levels were related to a 17% higher risk of T2DM (RR 1.17, 95% CI 1.01, 1.36; I²=78%, P<0.01), compared with normal TSH levels. Low FT3 (RR 1.40, 95% CI 1.09, 1.80; I²=59%, P=0.03) and low FT4 (RR 1.33, 95% CI 1.04, 1.71; I²=62%, P=0.02) levels were significantly associated with risk of T2DM. The cubic spline model indicated a J-shaped relationship with TSH, but inverted-J-shaped relationships with FT3 and FT4. CVD events and all-cause deaths were prospectively evaluated in four studies, but were not associated with abnormal thyroid function.

CONCLUSIONS

Our meta-analysis determined that abnormal thyroid hormone level is associated with an increased risk of T2DM, showing a J-shaped relationship with TSH and inverted-J-shaped relationships with FT3 and FT4.

TRIAL REGISTRATION

Registered number in PROSPERO: CRD42021225695 .

Zanthoxylum alkylamides ameliorate protein metabolism in type 2 diabetes mellitus rats by regulating multiple signaling pathways

Type 2 diabetes mellitus (T2DM) can easily induce insulin resistance (IR) in skeletal muscle, causing protein metabolism disorder and inflammation. The present study aimed to investigate whether Zanthoxylum alkylamides (ZA) could ameliorate T2DM through regulating protein metabolism disorder by using a rat model of T2DM. The predominant bioactive constituents found in ZA were hydroxyl-α-sanshool, hydroxyl-β-sanshool and hydroxyl-γ-sanshool. The results showed that ZA improved a series of biochemical indices associated with protein metabolism and inflammation in T2DM rats. Our mechanistic finding indicated that ZA promoted protein anabolism in T2DM rats by up-regulating the phosphoinositide 3-kinase (PI3K)/protein kinase B (Akt)/mammalian target of rapamycin (mTOR) signaling pathway. ZA also promoted glucose transportation in skeletal muscle to ameliorate skeletal muscle IR and energy metabolism through regulating the AMP-activated protein kinase (AMPK) signaling pathway. Moreover, ZA inhibited protein degradation and improved protein catabolism disorder in T2DM rats by down-regulating the PI3K/Akt/forkhead box O (FoxO) signaling pathway, and ZA further ameliorated inflammation to inhibit protein catabolism via regulating the tumor necrosis factor α (TNF-α)/nuclear factor κB (NF-κB) pathway in the skeletal muscle of T2DM rats. Collectively, the ameliorating effect of ZA on protein metabolism disorder in T2DM rats was the common result of regulating multiple signaling pathways. ZA decreased skeletal muscle IR to promote protein anabolism and inhibit protein catabolism for improving protein metabolism disorder, thus ultimately ameliorating T2DM. In sum, our findings demonstrated that ZA treatment could effectively ameliorate T2DM through improving protein metabolism, providing a new treatment target for T2DM.

Vitamin D and iodine status was associated with the risk and complication of type 2 diabetes mellitus in China

The purpose of this study was to assess the relationship between 25-hydroxyvitamin D (25(OH)D), urinary iodine concentration (UIC), and type 2 diabetes mellitus (T2DM) risk and complications and to establish a model to predict T2DM in the general population. A total of 567 adults (389 T2DM patients and 178 controls) were enrolled, and the levels of 25(OH)D, iodine, and blood biochemical parameters were measured. Pearson’s correlation analysis showed an inverse correlation between 25(OH)D level, UIC, and T2DM risk. Low 25(OH)D level was a risk factor for developing T2DM (OR, 0.81; 95% CI, 1.90–2.63; P = 0.043) after adjustment for multiple risk factors. 25(OH)D level and UIC were inversely correlated with short-term and long-term glucose levels. 25(OH)D deficiency was also associated with a high incidence of T2DM complicated with thyroid dysfunction. A prediction model based on 25(OH)D, iodine status, and other risk factors was established and recommended to screen high-risk T2DM in the general population and provide early screening and timely treatment for them.

Correlation Between Insulin Levels and Thyroid Hormones in Diabetic Animals After Caffeine Consumption Associated with Exercise

Introduction:

Thyroid hormones (TH) are important determinants of glucose homeostasis, and in contrast, insulin is the first hormone responsible for glycemic control.

Objective:

The objective of the present study was to correlate the levels of insulin and thyroid hormones in diabetic animals after caffeine consumption associated with physical exercise.

Methods:

A total of 48 animals, 60 days old were allocated in eight experimental groups: Control, Diabetic, Exercise, Diabetes + exercise, Caffeine, Diabetes + Caffeine, Caffeine + Exercise, and Diabetes + Exercise + Caffeine. Diabetes model was induced by intraperitoneal administration of 120 mg/kg of alloxan. On the test day, 6 mg/kg of caffeine was administrated 30 minutes before physical exercise. After, animals performed a 60 minutes’ session of predominantly aerobic exercise, using an overload of 6% of their body’s weight. Blood has been collected by a caudal puncture to future insulin, TSH, T3, and T4 analyses.

Results:

After caffeine treatment and training, insulin values were higher for the control groups (231%) when compared to the diabetic groups. A significant increase in plasmatic insulin concentration was found in caffeine group (95%) and Exercise+Caffeine group (56%) when compared to Control and Exercise groups. TSH values were increased for Diabetes, Diabetes+Caffeine and Diabetes+ Exercise+Caffeine groups (30%) compared to the other groups. A reduction in T4 values occurred in the animals of groups Diabetes+Exercise and Diabetes +Caffeine (66%) compared to the Control group. T3 values were significantly increased for the Diabetes+Exercise group (70%) when compared to the Diabetes+Exercise+Caffeine group.

Conclusion:

Physical exercise and caffeine consumption were able to promote hormonal changes in diabetic animals after 30 days of training. The study showed a reduction in the serum concentration of thyroid hormones, but insulin levels were higher.

Variation in the Level of Thyroid Markers in Association with Inflammation in Patients with Type 2 Diabetes

BACKGROUND

A possible relationship between thyroid hormones and glucose metabolism in diabetes has already been established.

OBJECTIVES

We aimed to evaluate the thyroid function markers and their relationship with inflammation, which is considered as a pathogenic condition of diabetes.

METHODS

This cross-sectional study included 276 patients with type 2 diabetes. Serum levels of thyroid (TSH, FT4, and FT3) and inflammatory markers (CRP, IL-6, and TNF-α) were measured.

RESULTS

The mean age of the subjects was 55.2 years and mean diabetes duration of 16.8 years. The inflammatory markers showed significant differences with the tertiles of TSH and thyroid hormones. TSH was significantly correlated with inflammatory markers, IL-6 (r = 0.13, P = 0.020) and TNF-α (r = 0.17, P = 0.003), while FT4 had a correlation only with TNF-α (r = 0.25, P = <0.001). FT3 was negatively correlated with inflammatory marker IL-6 (r = -0.14, P = 0.020), HbA1c (r = -0.12, P = 0 .040), and HOMA-IR (r = -0.17, P = 0.010).

CONCLUSION

Abnormalities in the thyroid hormone metabolism are related to the increased inflammatory activity as well as insulin resistance, and are associated with the disorders of glucose metabolism.

Age-Dependent Changes in Glucose Homeostasis in Male Deiodinase Type 2 Knockout Zebrafish

Thyroid hormones (THs) are crucial regulators of glucose metabolism and insulin sensitivity. Moreover, inactivating mutations in type 2 deiodinase (DIO2), the major TH-activating enzyme, have been associated with type 2 diabetes mellitus in both humans and mice. We studied the link between Dio2 deficiency and glucose homeostasis in fasted males of two different Dio2 knockout (KO) zebrafish lines. Young adult Dio2KO zebrafish (6 to 9 months) were hyperglycemic. Both insulin and glucagon expression were increased, whereas β and α cell numbers in the main pancreatic islet were similar to those in wild-types. Insulin receptor expression in skeletal muscle was decreased at 6 months, accompanied by a strong downregulation of hexokinase and pyruvate kinase expression. Blood glucose levels in Dio2KO zebrafish, however, normalized around 1 year of age. Older mutants (18 to 24 months) were normoglycemic, and increased insulin and glucagon expression was accompanied by a prominent increase in pancreatic islet size and β and α cell numbers. Older Dio2KO zebrafish also showed strongly decreased expression of glucagon receptors in the gastrointestinal system as well as decreased expression of glucose transporters GLUT2 and GLUT12, glucose-6-phosphatase, and glycogen synthase 2. This study shows that Dio2KO zebrafish suffer from transient hyperglycemia, which is counteracted with increasing age by a prominent hyperplasia of the endocrine pancreas together with decreases in hepatic glucagon sensitivity and intestinal glucose uptake. Further research on the mechanisms allowing compensation in older Dio2KO zebrafish may help to identify new therapeutic targets for (TH deficiency-related) hyperglycemia.

Thyroid Dysfunction and Diabetes Mellitus: Two Closely Associated Disorders

Thyroid dysfunction and diabetes mellitus are closely linked. Several studies have documented the increased prevalence of thyroid disorders in patients with diabetes mellitus and vice versa. This review critically discusses the different underlying mechanisms linking type 1 and 2 diabetes and thyroid dysfunction to demonstrate that the association of these two common disorders is unlikely a simple coincidence. We assess the current state of knowledge on the central and peripheral control of thyroid hormone on food intake and glucose and lipid metabolism in target tissues (such as liver, white and brown adipose tissue, pancreatic β cells, and skeletal muscle) to explain the mechanism linking overt and subclinical hypothyroidism to type 2 diabetes and metabolic syndrome. We also elucidate the common susceptibility genes and the pathogenetic mechanisms contributing to the autoimmune mechanism involved in the onset of type 1 diabetes mellitus and autoimmune thyroid disorders. An untreated thyroid dysfunction can impair the metabolic control of diabetic patients, and this association can have important repercussions on the outcome of both of these disorders. Therefore, we offer recommendations for the diagnosis, management, and screening of thyroid disorders in patients with diabetes mellitus, including the treatment of diabetic patients planning a pregnancy. We also discuss the major causes of failure to achieve an optimal management of thyroid dysfunction in diabetic patients and provide recommendations for assessing and treating these disorders during therapy with antidiabetic drugs. An algorithm for a correct approach of these disorders when linked is also provided.

MORPHOBIOCHEMICAL FUNCTIONS OF THE SHEEP ORGANISM AND THEIR ADJUSTMENT IN THE CONDITIONS OF IODINE DEFICIENCY

Aim.Widespread iodine deficiency causing endemic diseases in the highlands of the North Caucasus relate to the iodine epidemic. This type of pathology causes economic damage to the livestock industry, including sheep. In this regard, the aim of this work was to study morphobiochemical changes, hormonal (thyroid) background, immune reactivity in Karachai sheep during ontogenesis in different ecological zones with different iodine availability levels as well as to consider the effect of exogenous hormone (thyroxine) on the immune status of young stock under conditions of iodine deficiency and determine promising ways of developing an effective method of prevention and treatment against the pathology.

Methods.We conducted an analysis of the blood of lambs aged 1, 2, 3, 4 and 8 months kept in conditions of unequal iodine provision. The serum concentration of thyroid hormones (T3, T4) was evaluated by the results of an enzyme immunoassay, morphobiochemical status and immune reactivity by hematological, biochemical analysis, correction of iodine deficiency by intramuscular injections of thyroxine at a dose of 1 mg/kg with an interval of 2-3 months.

Results.The ontogenetic features of the formation of morphobiochemical systems, hormonal background, immune status in sheep kept in different climatic zones with different iodine provision were established.

Conclusion.Disorders of hematopoietic function, differences in hematological parameters, hypoproteinemia, changes in hormonal levels, low levels of immunocompetent T and B cells in the blood of sheep from different zones were detected. It was established that the metabolic response to exogenous thyroxine contributed to the normalization of metabolic processes and activation of cellular immunity.

Insulin resistance and diabetes in hyperthyroidism: a possible role for oxygen and nitrogen reactive species

In addition to insulin, glycemic control involves thyroid hormones. However, an excess of thyroid hormone can disturb the blood glucose equilibrium, leading to alterations of carbohydrate metabolism and, eventually, diabetes. Indeed, experimental and clinical hyperthyroidism is often accompanied by abnormal glucose tolerance. A common characteristic of hyperthyroidism and type 2 diabetes is the altered mitochondrial efficiency caused by the enhanced production of reactive oxygen and nitrogen species. It is known that an excess of thyroid hormone leads to increased oxidant production and mitochondrial oxidative damage. It can be hypothesised that these species represent the link between hyperthyroidism and development of insulin resistance and diabetes, even though direct evidence of this relationship is lacking. In this review, we examine the literature concerning the effects of insulin and thyroid hormones on glucose metabolism and discuss alterations of glucose metabolism in hyperthyroid conditions and the cellular and molecular mechanisms that may underline them.

Exogenous thyroxine improves glucose intolerance in insulin-resistant rats

Both hypothyroidism and hyperthyroidism are associated with glucose intolerance, calling into question the contribution of thyroid hormones (TH) on glucose regulation. TH analogues and derivatives may be effective treatment options for glucose intolerance and insulin resistance (IR), but their potential glucoregulatory effects during conditions of impaired metabolism are not well described. To assess the effects of thyroxine (T4) on glucose intolerance in a model of insulin resistance, an oral glucose tolerance test (oGTT) was performed on three groups of rats (n = 8): (1) lean, Long Evans Tokushima Otsuka (LETO), (2) obese, Otsuka Long Evans Tokushima Fatty (OLETF) and (3) OLETF + T4 (8.0 µg/100 g BM/day × 5 weeks). T4 attenuated glucose intolerance by 15% and decreased IR index (IRI) by 34% in T4-treated OLETF compared to untreated OLETF despite a 31% decrease in muscle Glut4 mRNA expression. T4 increased the mRNA expressions of muscle monocarboxylate transporter 10 (Mct10), deiodinase type 2 (Di2), sirtuin 1 (Sirt1) and uncoupling protein 2 (Ucp2) by 1.8-, 2.2-, 2.7- and 1.4-fold, respectively, compared to OLETF. Activation of AMP-activated protein kinase (AMPK) and insulin receptor were not significantly altered suggesting that the improvements in glucose intolerance and IR were independent of enhanced insulin-mediated signaling. The results suggest that T4 treatment increased the influx of T4 in skeletal muscle and, with an increase of DI2, increased the availability of the biologically active T3 to upregulate key factors such SIRT1 and UCP2 involved in cellular metabolism and glucose homeostasis.

Association Between Changes in Thyroid Hormones and Incident Type 2 Diabetes: A Seven-Year Longitudinal Study

BACKGROUND

Thyroid hormones are important regulators of glucose homeostasis. However, the association between thyroid hormones within the reference range and type 2 diabetes mellitus (T2DM) remains unclear. The aim of this study was to clarify the incidence of T2DM according to the baseline levels and changes of thyrotropin (TSH) and thyroid hormones (free thyroxine and triiodothyronine) in euthyroid subjects.

METHODS

Among the participants who consecutively underwent thyroid function tests between 2006 and 2012 through a yearly health checkup program, 6235 euthyroid subjects (3619 men and 2616 women) without T2DM were enrolled in the study. The change in each hormone was calculated by subtracting the baseline value from the level at the end of follow-up or one year before the diagnosis of diabetes.

RESULTS

During 25,692 person-years of follow-up, there were 229 new cases of T2DM. After full adjustment for potential confounders including HbA1c and fasting glucose in Cox proportional hazards models, the individuals in the highest tertile of TSH change (2.5-4.2 μIU/mL) had a greater risk of incident T2DM (hazard ratio [HR] = 1.44 [confidence interval (CI) 1.04-1.98], p = 0.027) in comparison with individuals in the lowest tertile (-4.1 to -0.5 μIU/mL). Simultaneously, the highest tertile of triiodothyronine change (16.3-104.7 ng/dL) and free thyroxine change (0.2-1.6 ng/dL) conferred protective effects against diabetes (HR = 0.60 [CI 0.43-0.85], p = 0.002, and HR = 0.34 [CI 0.24-0.48], p < 0.001, respectively) compared with those in the lowest tertile (-76.5 to -1.8 ng/dL and -0.6 to 0.0 ng/dL, respectively). These associations remained significant when each of the hormones was analyzed as a continuous variable. However, baseline levels or tertiles of TSH and thyroid hormones were not associated with the risk of diabetes.

CONCLUSIONS

Individual changes in TSH and thyroid hormones, even within the normal reference range, were an additional risk factor of incident T2DM.

Novel Clinical Evidence of an Association between Homocysteine and Insulin Resistance in Patients with Hypothyroidism or Subclinical Hypothyroidism

Objective

Hypothyroidism (HO) can induce significant metabolic dysfunction and increase cardiovascular disease risk. In the present study, we investigated the relationship between homocysteine (Hcy) and insulin resistance (IR) in patients with HO or subclinical hypothyroidism (SHO).

Methods

A total of 270 subjects were enrolled. All subjects were divided into the following three groups: HO, SHO and control. Plasma levels of Hcy were measured, and each patient’s homeostatic index of insulin resistance (HOMA-IR) was calculated. Statistical analyses were carried out to evaluate the correlations among groups and to determine the predictors of IR in patients with HO or SHO.

Results

The HOMA-IR value was significantly higher in the HO group than in the SHO and control groups. Plasma levels of Hcy were markedly increased in the HO group compared with those of the SHO group and controls. In addition, plasma levels of Hcy were positively correlated with the HOMA-IR values in both the HO and SHO groups. Multiple linear regression models showed that plasma levels of Hcy and free thyroxine (FT4) were the only predictors of HOMA-IR in patients with HO or SHO.

Conclusions

Plasma levels of Hcy and HOMA-IR were increased in patients with HO or SHO. Our results suggest that HO and SHO may increase the risk for atherogenesis and cardiovascular disease by increased IR. The increased IR induced by hyperhomocysteinemia in patients with HO or SHO may partially explain this adverse effect.

The rs225017 polymorphism in the 3'UTR of the human DIO2 gene is associated with increased insulin resistance

The Thr92Ala (rs225014) polymorphism in the type 2 deiodinase (DIO2) gene has been associated with insulin resistance (IR) and decreased enzyme activity in human tissues but kinetic studies failed to detect changes in the mutant enzyme, suggesting that this variant might be a marker of abnormal DIO2 expression. Thus, we aimed to investigate whether other DIO2 polymorphisms, individually or in combination with the Thr92Ala, may contribute to IR. The entire coding-region of DIO2 gene was sequenced in 12 patients with type 2 diabetes mellitus (T2DM). Potentially informative variants were evaluated in 1077 T2DM patients and 516 nondiabetic subjects. IR was evaluated using the homeostasis model assessment (HOMA-IR) index. DIO2 gene sequencing revealed no new mutation but 5 previously described single nucleotide polymorphisms (SNPs). We observed that all T2DM patients displaying high HOMA-IR index (n = 6) were homozygous for the rs225017 (T/A) polymorphism. Further analysis showed that the median fasting plasma insulin and HOMA-IR of T2DM patients carrying the T/T genotype were higher than in patients carrying the A allele (P = 0.013 and P = 0.002, respectively). These associations were magnified in the presence of the Ala92Ala genotype of the Thr92Ala polymorphism. Moreover, the rs225017 and the Thr92Ala polymorphisms were in partial linkage disequilibrium (|D'| = 0.811; r2 = 0.365). In conclusion, the rs225017 polymorphism is associated with greater IR in T2DM and it seems to interact with the Thr92Ala polymorphism in the modulation of IR.

Relationship between thyroid hormones, resting energy expenditure and cardiometabolic risk factors in euthyroid subjects

BACKGROUND & AIMS

Whereas hypothyroid subjects have a decreased resting energy expenditure (REE), it is unknown whether REE is associated with TSH in euthyroid subjects. It is also uncertain whether there is an association between cardiometabolic risk factors and TSH among euthyroid subjects. The primary aim was to test whether REE and TSH are associated in euthyroid subjects. The second aim was to evaluate the association between TSH and cholesterol, HDL-cholesterol, triglycerides, glucose and blood pressure.

METHODS

885 Caucasian euthyroid subjects (75% women) aged 18-79 years and with a median body mass index of 28.6 kg/m(2) were consecutively studied at our Research Center. REE was measured using a canopy-equipped indirect calorimeter. Multivariable regression of 25(th), 50(th) and 75(th) percentiles was used to evaluate the association between the outcomes (REE, cholesterol, HDL-cholesterol, triglycerides, glucose and blood pressure) and the predictors (TSH, FT4 and FT3) controlling by gender, age and body mass index.

RESULTS

REE was not associated with TSH, FT4 and FT3 at any percentile. On the contrary, a positive association between TSH and triglycerides was evident at all percentiles. A positive association between FT3 and HDL-cholesterol was also present but only at the 75(th) percentile.

CONCLUSIONS

REE is not associated with TSH in euthyroid subjects. It is however positively associated with triglycerides confirming the findings of recent population studies.

Visfatin, Leptin, and TNF-α: Interrelated Adipokines in Insulin-Resistant Clinical and Subclinical Hypothyroidism

PURPOSE

This study is designed to evaluate the interrelationships among adipokines-visfatin, leptin, and tumor necrosis factor-α (TNF-α)- and insulin resistance (IR) in overt (n = 40) and subclinic hypothyroid (n = 25) patients and compare our findings with sex and body mass index-matched healthy controls (n = 25).

METHODS

Serum visfatin, leptin, and TNF-α levels were measured by enzyme-linked immunosorbent assay and C-reactive protein by immunoturbidimetry. Thyroid status (TSH, FT3, FT4) and lipid status (triglyceride, low-density lipoprotein-cholesterol, high-density lipoprotein-cholesterol, total cholesterol) parameters were measured. IR was determined by homeostatic model assessment (HOMA-IR) and McAuley (McA) indices.

RESULTS

HOMA-IR (p < 0.05) and McA indices (p < 0.01) revealed the presence of IR in overt hypothyroid patients. C-reactive protein, TNF-α, leptin, and visfatin levels were significantly higher (p < 0.01, p < 0.01, p < 0.001, and p < 0.001) in overt hypothyroid patients than euthyroid control group. Subclinic hypothyroid patients were observed to have significantly higher leptin and visfatin levels (p < 0.05) than euthyroid control group. In overt hypothyroid patients, we found plasma visfatin to be significantly positively correlated with HOMA-IR index (r = 0.336, p < 0.05) and body mass index (r = 0.445, p < 0.01) and negatively correlated with McA index (r = -0.574, p < 0.01).

CONCLUSION

This study demonstrates the presence of IR in overt hypothyroid patients by HOMA and McA indices. Increased levels of visfatin, leptin, and TNF-α in overt and subclinic hypothyroid patients and the correlations among these adipokines highlighten their crucial role in the IR-associated disorders.

Hyperinsulinemia and insulin resistance is associated with low T₃/T₄ ratio in pre diabetic euthyroid Pakistani subjects

OBJECTIVE

To investigate the relationship of thyroid hormones in glucose homeostasis in impaired glucose-tolerant subjects with normal thyroid functions.

METHODS

Cross-sectional analysis was carried out in (n=260) impaired glucose-tolerant (IGT) and normal glucose-tolerant (NGT) subjects. Thyrotropin (TSH), total triiodothyronine (TT₃), total thyroxin (TT₄) free T₃ (fT₃), free T₄ (fT₄), and insulin were assessed by enzyme-linked immunoassays (ELISA). Fasting plasma glucose (FPG) and HbA1c were measured by glucose oxidase and low-pressure cation exchange chromatography. Homeostasis model of assessment (HOMA-IR) was employed to assess the level of insulin resistance; fT₃/fT₄ ratio was calculated. Anthropometric measurement and habits were recorded.

RESULTS

Marked hyperinsulinemia and insulin resistance were observed in IGT subjects. Serum TT₃ and fT₃ levels were significantly low in the IGT as compared to normal glucose-tolerant (NGT) controls. TT₄ and TSH were higher in IGT subjects as compared to control subjects. There was a significant positive correlation of TSH with BMI only in the control group (r=0.351; P<0.05). Correlation of insulin with TT₃, fT₃,and TSH was significant (P<0.05) in IGT subjects. A significant low fT₃/fT₄ ratio was observed in IGT subjects as compared to NGT subjects (P<0.01). In multiple regression analysis, TSH, TT₄ and fT₃ contributed significantly to the variance of fasting insulin and insulin resistance in IGT subjects.

CONCLUSION

Hyperinsulinemia and insulin resistance are associated with low T₃/T₄ ratio in pre-diabetic euthyroid Pakistani subjects.

Association analyses of variants in the DIO2 gene with early-onset type 2 diabetes mellitus in Pima Indians

BACKGROUND

The type 2 deiodinase gene (DIO2) encodes a deiodinase that converts the thyroid prohormone, thyroxine, to the biologically active triiodothyronine. Thyroid hormones regulate energy balance and may also influence glucose metabolism. Therefore, we hypothesized that variations in DIO2 could contribute to obesity or type 2 diabetes mellitus (T2DM) in Pima Indians.

METHODS

Sequencing of the DIO2 gene in DNA from 83 Pima Indians identified 12 single-nucleotide polymorphisms (SNPs). Several of these SNPs were in perfect genotypic concordance among the 83 samples that were sequenced, and all 12 could be divided into five linkage disequilibrium groups. One representative SNP from each group (Thr92Ala, rs225011, rs225015, rs6574549, and a rare 5' flanking SNP) was selected for further genotyping for association analyses. In this study, the five selected variants in DIO2, as described above, were genotyped in three groups of Pima Indians: (i) a case (n=150)/control (n=150) group for early-onset T2DM (onset age <25 years); (ii) a case (n=362)/control (n=127) group for obesity; (iii) a large (n=1,311, cases n=810/controls n=501) family-based group, of which 256 nondiabetic subjects had undergone detailed metabolic phenotyping.

RESULTS

The Thr92Ala variant common in Pima Indians, rs225011, and rs225015 were modestly associated with early-onset T2DM (p=0.01-0.04) in the case-control study, but were not associated with obesity in the obesity case-control study, nor associated with T2DM (at any age) or body-mass index (BMI; as a quantitative trait) in the family-based analysis. Thr92Ala, rs225011, rs225015, and rs6574549 were also nominally associated with hepatic glucose output (p=0.02). rs6574549 was associated with fasting insulin (p=0.02), insulin action (p=0.04), and energy expenditure (p=0.02). None of these nominal associations remained statistically significant after corrections for multiple testing.

CONCLUSIONS

We propose that variation in DIO2 may have a subtle role in altering metabolic processes that lead to early-onset T2DM, but this gene does not have a large impact on T2DM at older ages, nor does DIO2 influence BMI in the Pima Indian population.

Thyroid function in childhood obesity and metabolic comorbidity

Childhood obesity is a worldwide health problem and its prevalence is increasing steadily and dramatically all over the world. Obese subjects have a much greater likelihood than normal-weight children of acquiring dyslipidemia, elevated blood pressure, and impaired glucose metabolism, which significantly increase their risk of cardiovascular and metabolic diseases. Elevated TSH concentrations in association with normal or slightly elevated free T4 and/or free T3 levels have been consistently found in obese subjects, but the mechanisms underlying these thyroid hormonal changes are still unclear. Whether higher TSH in childhood obesity is adaptive, increasing metabolic rate in an attempt to reduce further weight gain, or indicates subclinical hypothyroidism or resistance and thereby contributes to lipid and/or glucose dysmetabolism, remains controversial. This review highlights current evidence on thyroid involvement in obese children and discusses the current controversy regarding the relationship between thyroid hormonal derangements and obesity-related metabolic changes (hypertension, dyslipidemia, hyperglycemia and insulin resistance, nonalcoholic fatty liver disease) in such population. Moreover, the possible mechanisms linking thyroid dysfunction and pediatric obesity are reviewed. Finally, the potential role of lifestyle intervention as well as of therapy with thyroid hormone in the treatment of thyroid abnormalities in childhood obesity is discussed.

Thyroid hormones are positively associated with insulin resistance early in the development of type 2 diabetes

Thyroid hormones have generally been found normal in diabetic patients. The question of whether variation within the euthyroid range influences insulin sensitivity in type 2 diabetes remains to be established. To investigate this, a meal was given to four groups: 17 healthy volunteers (controls), 22 first-degree relatives of type 2 diabetic subjects (relatives), 15 subjects with impaired glucose tolerance (IGT), and 24 subjects with overt type 2 diabetes (DM). Blood was drawn for 360 min for measurements of glucose and insulin. Plasma-free-T4(FT4) and plasma-free-T3(FT3) levels were measured. Fasting and postprandial insulin resistance was assessed by HOMA-IR and ISI indices, respectively. FT4 levels were found to be lower in controls (13.73 ± 0.48 pmol/l) than relatives, IGT, and DM (15.33 ± 0.52, 16.13 ± 0.65, and 17.7 ± 0.85 pmol/l, respectively, P = 0.007). FT3 levels were lower in controls (3.68 ± 0.09 pmol/l) than in relatives, IGT, and DM (4.35 ± 0.1, 4.8 ± 0.067, and 4.87 ± 0.11 pmol/l, respectively, P = 0.001). HOMA-IR was positively associated with FT4 and FT3 levels (β-co-efficient = 1.876 ± 0.476, P = 0.001; and 0.406 ± 0.090, P = 0.001, respectively). ISI was negatively associated with FT4 and FT3 levels (β-co-efficient = -0.051 ± 0.009, P = 0.001 and -0.009 ± 0.002, P = 0.001, respectively). In conclusion, increases of thyroid hormone levels within the normal range associate positively with insulin resistance. These data suggest that thyroid hormones may be part of the pathogenetic mechanism to explain metabolic derangement early in the development of type 2 diabetes.

Insulin action in hyperthyroidism: a focus on muscle and adipose tissue

Hyperthyroidism leads to an enhanced demand for glucose, which is primarily provided by increased rates of hepatic glucose production due to increased gluconeogenesis (in the fasting state) and increased Cori cycle activity (in the late postprandial and fasting state). Adipose tissue lipolysis is increased in the fasting state, resulting in increased production of glycerol and nonesterified fatty acids. Under these conditions, increased glycerol generated by lipolysis and increased amino acids generated by proteolysis are used as substrates for gluconeogenesis. Increased nonesterified fatty acid levels are necessary to stimulate gluconeogenesis and provide substrate for oxidation in other tissues (such as muscle). In the postprandial period, insulin-stimulated glucose uptake by the skeletal muscle has been found to be normal or increased, mainly due to increased blood flow. Under hyperthyroid conditions, insulin-stimulated rates of glycogen synthesis in skeletal muscle are decreased, whereas there is a preferential increase in the rates of lactate formation vs. glucose oxidation leading to increased Cori cycle activity. In hyperthyroidism, the Cori cycle could be considered as a large substrate cycle; by maintaining a high flux through it, a dynamic buffer of glucose and lactate is provided, which can be used by other tissues as required. Moreover, lipolysis is rapidly suppressed to normal after the meal to facilitate the disposal of glucose by the insulin-resistant muscle. This ensures the preferential use of glucose when available and helps to preserve fat stores.

Oxidative DNA damage: the thyroid hormone-mediated effects of insulin on liver tissue

Thyroid hormone affects glucose homeostasis with its actions between the skeletal muscle and liver and the altered oxidative and non-oxidative glucose metabolism. In our study three chemicals are considered biomarkers associated with oxidative stress for protein modifications were measured; 8-hydroxy-2-deoxyyguanosine (8-OHdG), a major lesion that can be generated by reactive oxygen species for DNA damage, protein carbonyl content (PCO), products of protein oxidation and advanced oxidation protein products (AOPPs) a dithyrosine containing cross-linked protein products. The purpose of the recent study was to determine the effects of insulin and T4 or their combination in diabetic, thyroidectomized, or diabetic-thyroidectomized rats and possible relations with oxidative DNA and protein damages. For this purpose, rats were assigned to eight groups: Group 1; control, Group 2; diabetes, Group 3; diabetes+insulin, Group 4; surgically thyroidectomized control, Group 5; thyroidectomized+diabetes, Group 6; thyroidectomized+diabetes+insulin, Group 7; thyroidectomized+diabetes+insulin+thyroid hormone, levothyroxin sodium, 2.5 μg/kg and Group 8; thyroidectomized+diabetes+insulin+thyroid hormone, levothyroxin sodium, 5.0 μg/kg for 5 weeks. After the genomic DNA of liver tissues was extracted, the ratio of 8-OHdG to deoxyguanosine and liver tissue protein oxidation markers was determined. The main findings of our recent study were the increased 8-OHdG levels during the diabetes, hypothyroidism, and hypothyroidism with diabetes, which can be regulated in different percentages with the treatment of 2.5 and 5.0 μg/kg doses of thyroid hormone and the altered protein carbonyl and AOPP levels of liver tissue. Consequently, it was observed that the DNA and protein damage induced by oxidative stress in diabetes could be regulated by dose-dependent thyroid hormone-mediated effects to insulin treatment.

Studies of insulin resistance in patients with clinical and subclinical hypothyroidism

OBJECTIVE

Although clinical hypothyroidism (HO) is associated with insulin resistance, there is no information on insulin action in subclinical hypothyroidism (SHO).

DESIGN AND METHODS

To investigate this, we assessed the sensitivity of glucose metabolism to insulin both in vivo (by an oral glucose tolerance test) and in vitro (by measuring insulin-stimulated rates of glucose transport in isolated monocytes with flow cytometry) in 21 euthyroid subjects (EU), 12 patients with HO, and 13 patients with SHO.

RESULTS

All three groups had comparable plasma glucose levels, with the HO and SHO having higher plasma insulin than the EU (P<0.05). Homeostasis model assessment index was increased in HO (1.97+/-0.22) and SHO (1.99+/-0.13) versus EU (1.27+/-0.16, P<0.05), while Matsuda index was decreased in HO (3.89+/-0.36) and SHO (4.26+/-0.48) versus EU (7.76+/-0.87, P<0.001), suggesting insulin resistance in both fasting and post-glucose state. At 100 microU/ml insulin: i) GLUT4 levels on the monocyte plasma membrane were decreased in both HO (215+/-19 mean fluorescence intensity, MFI) and SHO (218+/-24 MFI) versus EU (270+/-25 MFI, P=0.03 and 0.04 respectively), and ii) glucose transport rates in monocytes from HO (481+/-30 MFI) and SHO (462+/-19 MFI) were decreased versus EU (571+/-15 MFI, P=0.04 and 0.004 respectively).

CONCLUSIONS

In patients with HO and SHO: i) insulin resistance was comparable; ii) insulin-stimulated rates of glucose transport in isolated monocytes were decreased due to impaired translocation of GLUT4 glucose transporters on the plasma membrane; iii) these findings could justify the increased risk for insulin resistance-associated disorders, such as cardiovascular disease, observed in patients with HO or SHO.

A novel hemostatic model with triple protective functions

While the role of hemostatic activity is well established, the importance of infection prevention in the wound has not been addressed. Based on the available evidence from disinfection and infection prevention, essential oils are attractive candidates for antimicrobial drugs. Therefore, we hypothesize to design a novel hemostatic model with triple protective functions through coordinating essential oils to hematostatic ingredients. The hematostatic ingredients play their roles in hemostasis when hemorrhage occurs. Simultaneously, the essential oils evaporate naturally to form a protective layer around the wound, which can help to prevent pathogenic bacteria from infecting the wound. What more, most plant essential oils possess antibacterial activity. Thus, the essential oils can be used as an accessory treatment for infection once the wound infected by pathogenic bacteria. So the novel hematostatic model with triple protective functions will have broader utility in therapy of out-wound bleeding than current hemostatic drugs.

Lower serum free thyroxine levels are associated with metabolic syndrome in a Chinese population

Thyroid hormones play an important role in regulating energy homeostasis and lipid and glucose metabolism. This study assessed the relationship between free thyroxine and clinical features of metabolic syndrome (MS). A total of 4,938 Taiwanese subjects (2,891 men and 2,047 women with a mean age of 50.1+/-12.6 years) with normal serum free thyroxine levels were enrolled. A modified National Cholesterol Education Program definition of MS was adopted substituting body mass index (BMI) for waist circumference. Serum free thyroxine concentrations were determined by immunoassay. Overall, 14% of subjects had a high fasting glucose, 27% had high blood pressure, 14% had high serum total triglyceride, 8% had low high-density lipoprotein cholesterol, and 18% were obese. The serum free thyroxine concentrations showed a statistically significant correlation with triglyceride and body mass index, respectively (P<.01), but not with blood pressure, glucose level, or high-density lipoprotein cholesterol level. According to the presence of 0, 1, 2, and 3 or more features of MS, age and sex-adjusted means of serum free thyroxine were 17.8+/-3.7, 17.6+/-3.7, 17.5+/-3.7, and 17.1+/-3.3 pmol/L, respectively, with a modest, but statistically significant, decreasing trend (P<.05). When comparing subjects in the highest and lowest quartile of free thyroxine, the former group demonstrated a 2-fold decrease in the odds ratio for MS with 3 or more metabolic features. Low circulating free thyroxine levels, albeit normal, were associated with MS in a Chinese population. Further study is necessary to document the role of thyroid hormones in metabolic abnormalities of MS.