Circulating glucagon to ghrelin ratio as a determinant of insulin resistance in hyperthyroidism

Exploring the association between triglyceride-glucose index and thyroid function

BACKGROUND

Thyroid dysfunction is associated with abnormal glucose-insulin homeostasis, and the triglyceride-glucose (TyG) index has been recommended as a convenient surrogate of insulin resistance (IR). This study aimed to investigate the relationship between TyG and thyroid function in the US population.

METHODS

 We analyzed data from the National Health and Nutrition Examination Survey (NHANES) conducted from 2007 to 2012 in a cross-sectional manner. Aside from conventional thyroid parameters, our study evaluated the central sensitivity to thyroid hormones (THs) using the thyroid feedback quantile-based index (TFQI), thyrotropin resistance index (TT4RI), and thyrotropin index (TSHI). To evaluate peripheral sensitivity to THs, we calculated the ratio of free triiodothyronine (FT3) to free thyroxine (FT4) and the sum activity of peripheral deiodinases (SPINA-GD). In the 1848 adults, multivariable linear regression, subgroup, and interaction analyses were employed to estimate the association between TyG and thyroid parameters. The nonlinear relationship was addressed by smooth curve fittings and generalized additive models.

RESULTS

After adjusting covariates, we demonstrated a significant negative association between TyG and FT4 (β = - 0.57, p < 0.001), and a positive relationship between TyG and thyroid-stimulating hormone (β = 0.34, p = 0.037), as well as TgAb (β = 17.06, p = 0.005). Subgroup analysis indicated that the association between TyG and TgAb was more pronounced in the female subjects (β = 32.39, p < 0.001, p for interaction = 0.021). We also confirmed an inverse correlation between TyG and central sensitivity to THs, as assessed by TSHI and TT4RI (βTSHI = 0.12, p < 0.001; βTT4RI = 2.54, p = 0.023). In terms of peripheral sensitivity to THs, we found a significant positive correlation between TyG and FT3/FT4 (β = 0.03, p = 0.004), and SPINA-GD (β = 2.93, p = 0.004).

CONCLUSION

The present study established a noteworthy association between TyG and thyroid parameters, indicating a strong link between IR and thyroid dysfunction. Further investigations are warranted to validate these results.

HbA1c: an independent risk factor for dysthyroid optic neuropathy

Background

We aimed to explore the frequencies of islet β-cell autoantibodies and insulin resistance (IR) in thyroid-associated ophthalmopathy (TAO) and identify specific diabetes mellitus (DM) indicators as early predictors for dysthyroid optic neuropathy (DON).

Methods

Ninety-eight TAO patients (57 DON and 41 non-DON patients) and 48 healthy control (HC) participants were recruited for this prospective cross-sectional study. Serum thyroxine, serum thyroid autoantibodies, serum humoral immune markers against islet β-cell, fasting plasma glucose (FPG), fasting serum insulin (FINS), fasting c-peptide (FCP), and glycosylated hemoglobin A1 (HbA1c) were measured. Logistic regression analysis was used to evaluate the correlation of patients' age, body mass index (BMI), FPG, HbA1c, and related indexes of islet β-cell function to the occurrence of DON.

Results

The DON group had higher FPG (P<0.001, 0.016) and HbA1c (P<0.0001, P<0.001) levels than the HC and non-DON groups. The homeostasis model assessment (HOMA)-IR level was the highest in the DON group (HC 2.15 ± 0.89, non-DON 2.41 ± 1.24, and DON 2.82 ± 2.65), while the HOMA-β level was the lowest (HC 101.8 ± 44.75%, non-DON 102.9 ± 54.61%, and DON 88.29 ± 52.75%), with no significant differences (P=1, P>0.05). On univariate analysis, age (P=0.006), BMI (P=0.022), history of steroid use (P=0.014), FPG (P=0.013), and HbA1c (P=0.001) levels were significantly associated with the presence/absence of DON. In addition, after adjusting for potential confounds, the HbA1c level was an independent factor associated with DON (P=0.009, OR=4.012).

Conclusions

HbA1c is an independent risk factor for DON. Given the interconnected link between thyroid dysfunction and DM, the use of HbA1c as a potential biomarker for DON warrants further investigation.

Thyroid dysfunction in young, first-episode and drug-naïve patients with major depressive disorder: prevalence and associated clinical factors

Objective

The incidence of thyroid dysfunction (TD) and major depressive disorder (MDD) is increasing year by year in the general population. However, the prevalence and correlates of TD in first-episode drug-naive (FEDN) MDD patients have not been explored. This study sought to fill this gap and examine the association between TD and MDD.

Methods

We recruited 1,289 FEDN MDD patients aged 18 ~ 45 years. A total of 1,289 FEDN MDD outpatients were recruited. Demographical and suicide data were collected for each patient, and lipid profiles, thyroid function, and fasting blood glucose (FBG) levels were measured. The Hamilton Depression Scale 17 (HAMD-17) was assessed for depression.

Results

The prevalence of TD in young FEDN MDD patients was 64.86%. Compared with those without TD, patients with TD had longer duration of illness, greater HAMD score, higher BMI, TG, TC, and LDL-C levels, and higher suicide attempt rates, but lower HDL-C and FBG levels. Further logistic regression indicated that duration of illness, HAMD score, TC, HDL-C, BMI, and FBG levels were significantly associated with TD.

Limitations

No causal relationship can be drawn due to the cross-sectional design.

Conclusion

TD is common in young FEDN MDD patients. So clinicians should monitor thyroid function in patients with MDD.

Selenium and Selenoproteins at the Intersection of Type 2 Diabetes and Thyroid Pathophysiology

Type 2 diabetes (T2D) is considered one of the largest global public-health concerns, affecting approximately more than 400 million individuals worldwide. The pathogenesis of T2D is very complex and, among the modifiable risk factors, selenium (Se) has recently emerged as a determinant of T2D pathogenesis and progression. Selenium is considered an essential element with antioxidant properties, and is incorporated into the selenoproteins involved in the antioxidant response. Furthermore, deiodinases, the enzymes responsible for homeostasis and for controlling the activity of thyroid hormones (THs), contain Se. Given the crucial action of oxidative stress in the onset of insulin resistance (IR) and T2D, and the close connection between THs and glucose metabolism, Se may be involved in these fundamental relationships; it may cover a dual role, both as a protective factor and as a risk factor of T2D, depending on its basal plasma concentration and the individual’s diet intake. In this review we discuss the current evidence (from experimental, observational and randomized clinical studies) on how Se is associated with the occurrence of T2D and its influence on the relationship between thyroid pathophysiology, IR and T2D.

Association of decreased muscle mass with reduced bone mineral density in patients with Graves' disease

AIM

This study aimed to determine the association of decreased muscle mass with reduced bone mineral density in patients with Graves' disease.

METHODS

A total of 758 patients with Graves' disease at diagnosis (mean age 41.2 years) were enrolled for a cross-sectional study; of these, 287 were enrolled for a cohort study with a median follow-up of 24 months. Meanwhile, 1164 age- and sex-matched healthy controls were recruited. All participants underwent dual-energy x-ray absorptiometry and muscle mass index (ASMI) measurements. The changes in ASMI and bone mineral density (BMD) were calculated from the measurements made at a gap of 2 years.

RESULTS

The BMD of patients with Graves' disease was still significantly lower after normalizing serum thyroid hormone levels compared with that of healthy controls. ASMI positively correlated with BMD in patients with Graves' disease (lumbar BMD, r = 0.210; femoral neck BMD, r = 0.259; hip BMD, r = 0.235; P < 0.001), and this relationship persisted after successful anti-thyroid therapy (lumbar BMD, r = 0.169; femoral neck BMD, r = 0.281; hip BMD, r = 0.394; P < 0.001). Low muscle mass was associated with low BMD (OR, 1.436; 95% CI, 1.026-2.010). Improving the muscle mass led to changes in the bone mass of the femoral neck (OR, 0.420; 95% CI, 0.194-0.911) and hip (OR, 0.217; 95% CI, 0.092-0.511) during the follow-up. However, this phenomenon was not observed in lumbar and bone turnover markers.

CONCLUSIONS

The recovery of bone mass might be related to the recovery of the muscle mass. Patients with Graves' disease should be helped to regain their muscle mass and thus accelerate the recovery of bone mass while administering anti-thyroid therapy.

A longitudinal study of thyroid markers during pregnancy and the risk of gestational diabetes mellitus and post-partum glucose metabolism

AIMS

To determine the relationship between thyroid markers during pregnancy and gestational diabetes mellitus (GDM) or post-partum glucose metabolism.

MATERIALS AND METHODS

Based on pregnancy 75-g oral glucose tolerance test (OGTT) results, 1467 subjects were grouped into normal glucose tolerance (NGTp; n = 768) and GDM (n = 699) groups. Furthermore, based on post-partum 75-g OGTT results, 286 GDM subjects, screened for glucose metabolism after delivery, were grouped into NGTd (n = 241) and abnormal glucose tolerance (AGT; n = 45) groups.

RESULTS

Maternal age, family history of diabetes, acanthosis nigricans, previous adverse pregnancy outcomes and caesarean section incidence, and thyroid positive antibody rates were higher in the GDM group than in the NGTp group. In the first trimester, free triiodothyronine (FT3), thyroid peroxidase antibody (TPOAb) and thyroglobulin antibody (TgAb) levels were higher in the GDM group than in the NGTp group. In the second trimester, free thyroxine (FT4) levels were lower and TPOAb and TgAb levels were higher in the GDM group than in the NGTp group. After adjusting for confounding factors, FT3, TPOAb and TgAb (first trimester), and FT4, TPOAb and TgAb (second trimester) were risk factors for GDM. TPOAb and TgAb levels were higher in the AGT group than in the NGTd group and were potential predictors of abnormal post-partum glucose tolerance.

CONCLUSIONS

GDM risk significantly increased with increased FT3 (first trimester), TPOAb and TgAb (first and second trimesters) or with decreased FT4 (second trimester). Presence of thyroid antibodies predicted post-partum glucose abnormalities in subjects with GDM.

High T3 Induces β-Cell Insulin Resistance via Endoplasmic Reticulum Stress

Hyperthyroidism can cause glucose metabolism disorders and insulin resistance. Insulin resistance in muscle and adipose tissues has been extensively studied, whereas investigations on β-cell insulin resistance are limited. This study preliminarily explored the effects of high T3 levels on β-cell line (MIN6) insulin resistance, as well as the roles of endoplasmic reticulum stress (ERS). In this study, we treated β-cell line with T3, with or without an inhibitor of phosphotyrosine phosphatases (PTPs, sodium vanadate) or ERS inhibitor (4-PBA). The results indicated that high levels of T3 significantly inhibited insulin secretion in β-cell line. In addition, we observed an upregulation of p-IRS-1^ser307 and downregulation of Akt. These results can be corrected by sodium vanadate. Moreover, high T3 levels upregulate the ERS-related proteins PERK, IRE1, ATF6, and GRP78, as well as ERS-related apoptosis CHOP and caspase-12. Similarly, this change can be corrected by 4-PBA. These results suggest that high T3 levels can induce insulin resistance in β-cell line by activating ERS and the apoptotic pathway.

Effects of Excessive Iodine Intake on Blood Glucose, Blood Pressure, and Blood Lipids in Adults

To understand the effects of excess iodine intake on blood glucose, blood pressure, and blood lipids in adults. We selected three villages from Shanxi Province to conduct cross-sectional survey: Maxi [median water iodine concentration (MWIC) 6.3 μg/L, median urinary iodine concentration (MUIC) 126.6 μg/L, 320 adults]; Xiwenzhuang (MWIC 79.8 μg/L, MUIC 221.2 μg/L, 264 adults); and Gaoche (MWIC 506.0 μg/L, MUIC 421.3 μg/L, 241 adults). According to the urinary iodine levels in adults, the three villages were defined as iodine-adequate, iodine-sufficient, and iodine-excess. Urinary iodine, water iodine, thyroid function, blood glucose, blood pressure, and blood lipids were measured. Compared with the iodine-adequate area, blood glucose and systolic and diastolic pressure of adults in iodine-sufficient and iodine-excess areas increased and high-density lipoprotein-cholesterol decreased (all P < 0.001). Urinary iodine, thyroid-stimulating hormone, and free thyroxine have a nonlinear correlation with blood glucose (R² = 0.8174, 0.8264, and 0.8520, respectively). Excessive iodine intake may result in elevated blood glucose and blood pressure and has some influence on blood lipids, and may increase the risk of hypertension and diabetes.

Thyroid Nodules in Type 2 Diabetes Mellitus

The present analysis aims to investigate the prevalence of thyroid nodules in type 2 diabetes mellitus (T2DM) population. We searched PubMed, EMBASE, and Web of Science from inception to the March 1, 2018. The studies were selected to estimate the prevalence of thyroid nodules in T2DM subjects and to compare the prevalence of thyroid nodules in different glucose tolerance status. The random effects model was used, and the outcome was presented as a pooled prevalence proportion with 95% confidence interval (95% CI) or a summary odds ratio (OR) with 95% CI. In the end, 9 studies met the inclusion criteria and were included in the analysis. The pooled prevalence of thyroid nodules was 60% (95% CI: 0.52, 0.68) for T2DM 2 diabetes patients, 50% (95% CI: 0.48, 0.51) for pre-diabetes, and 43% (95% CI: 0.34, 0.52) for normal glucose tolerance population. Compared with patients without diabetes, diabetes subjects are more likely to develop thyroid nodules, adjusted OR for thyroid nodule was 1.78 (95% CI: 1.25, 2.55). Insulin resistance might be involved in thyroid nodule development.

Thyroid Hormone Regulation and Insulin Resistance: Insights From Animals Naturally Adapted to Fasting

The contribution of thyroidal status in insulin signaling and glucose homeostasis has been implicated as a potential pathophysiological factor in humans, but the specific mechanisms remain largely elusive. Fasting induces changes in both thyroid hormone secretion and insulin signaling. Here, we explore how mammals that undergo natural, prolonged bouts of fasting provide unique insight into evolved physiological adaptations that allow them to tolerate such conditions despite intermittent states of reversible insulin resistance. Such insights from nature may provide clues to better understand the basis of thyroidal involvement in insulin dysregulation in humans.