Genetic and Environmental Factors in Autoimmune Thyroid Disease: Exploring Associations with Selenium Levels and Novel Loci in a Latvian Cohort.

The interplay of genetic, immune and environmental factors strongly contributes to the development of autoimmune thyroid disease (AITD), which can be classified as Graves' disease (GD) or Hashimoto thyroiditis (HT). One of the most studied exogenous factors in the pathogenesis of AITD is selenium, which, in the form of selenoproteins, strengthens the antioxidative defence system of thyroid cells against superoxide production. Furthermore, it modulates inflammatory cytokine release and autoantibody production. The aim of this study was to assess the associations of genetic factors with selenium levels in a cohort of adults with HT and GD and healthy controls from Latvia. A total of 148 GD patients, 102 HT patients and 2442 control participants were included in the study. The genotypes were determined using genome-wide genotyping; imputation was carried out using the TOPMed r2 imputation panel; and association analysis was performed with PLINK v1.90b7. We found three loci associated with GD (LSAMP, HNRNPA3P5, and NTN1) and one locus associated with HT (VAT1L); furthermore, one locus was associated with a serum selenium concentration > 80 µg/L (LINC01544/RNF152/PIGN). The detected associations could be attributed to population-specific effects or unknown stratification in our cohort, and further assessment of these results is required to explain the relationships of genetic traits with AITD and other phenotypes.

Stress-Related Immune Response and Selenium Status in Autoimmune Thyroid Disease Patients.

Autoimmune thyroid disease (AITD), including Graves' disease (GD) or Hashimoto's thyroiditis (HT), occurs due to genetic susceptibility and environmental factors, among which the role of stressful events remains controversial. This study investigated the relationship between the number and impact of stressful life events in AITD patients with selenium status, and the Th1/Th2/Th17 immune response. The study population included three groups: HT (n = 47), GD (n = 13), and a control group (n = 49). Thyroid function parameters, autoantibody levels, and the plasma levels of cytokines, selenium, selenoprotein P (SeP), and glutathione peroxidase 3 (GPx) activity were measured. Participants filled out the Life Experiences Survey. No significant differences in the number of stressful life events were found among the patients with HT, GD, and the controls. A higher (median (interquartile range)) negative stress level (8 (4-12)) than a positive stress level (3 (1-9)) was found in the HT group. The HT group showed a correlation between SeP and the positive stress level: rs = -0.296, p = 0.048, and the GD group between GPx and the negative stress level (rs = -0.702, p = 0.011). Significant positive correlations between thyroid peroxidase antibody level and the total number of major life events (p = 0.023), the number of major life events in the last 7-12 months, and the number of major life events with no impact and a negative stress level were found. We suggest that the measurements of Th2-related cytokines and selenoproteins could be used as biomarkers for the development of AITD in cases where stress is considered a component cause of the pathogenic mechanism of the disease.

Fasting-Mimicking Diet Reduces Trimethylamine N-Oxide Levels and Improves Serum Biochemical Parameters in Healthy Volunteers.

Elevated plasma levels of trimethylamine N-oxide (TMAO) have been proposed as a diet-derived biomarker of cardiometabolic disease risk. Caloric restriction is the most common dietary intervention used to improve cardiometabolic health; however, novel trends suggest a fasting-mimicking diet (FMD) as a more feasible alternative. FMD is a variation of intermittent fasting, based on caloric restriction and limitation of protein sources of animal origin, applied in daily cycles during a 5-day period. As TMAO is intensively produced by gut microbiota after the consumption of animal-derived products, we aim to investigate whether a 5-day FMD affects plasma TMAO levels and markers of metabolic health. To investigate whether an increase in vegetable intake possesses similar effects on TMAO levels and metabolic parameters, healthy volunteers (n = 24) were subjected to a 5-day FMD and 19 volunteers served as a reference group (VEG). This group of volunteers consumed an additional four servings of vegetables per day, but otherwise stayed on their usual diet. FMD resulted in a twofold decrease in plasma TMAO levels, which was not evident in the volunteers from the VEG group. Moreover, FMD led to a weight loss of 2.8 ± 0.2 kg and a subsequent reduction in BMI compared to baseline. The FMD group exhibited a significant elevation in plasma ketone bodies (14-fold compared to baseline) and a decrease in IGF-1 levels by 37 ± 8 ng/mL. Since fasting glucose and C-peptide levels decreased, all volunteers in the FMD group showed improved insulin sensitivity and a decreased HOMA-IR index. In contrast, in the VEG group, only a slight reduction in plasma levels of fasting glucose and triglycerides was noted. In conclusion, we show that FMD is a viable strategy to reduce plasma levels of TMAO by limiting caloric intake and animal-derived protein consumption. The reduction in the level of TMAO could be an additional benefit of FMD, leading to a reduced risk of cardiometabolic diseases.

Assessment of Iodine and Selenium Nutritional Status in Women of Reproductive Age in Latvia.

Background and Objectives: Adequate dietary intake of iodine and selenium is essential during pregnancy. While iodine is vital for maternal thyroid function and fetal development, selenium contributes to the regulation of thyroid function and thyroid autoimmunity. This study aimed to assess the consumption of iodine- and selenium-containing products by women of reproductive age and the iodine and selenium nutritional status of pregnant women in Latvia. Materials and Methods: Population health survey (2010-2018) data were used to characterize dietary habits in women of reproductive age. Additionally, 129 pregnant women in the first trimester were recruited; they completed a questionnaire and were tested for thyroid function, urinary iodine concentration (UIC), and serum selenium and selenoprotein P levels. Results: The use of some dietary sources of iodine (e.g., milk and dairy products) and selenium (e.g., bread) has decreased in recent years. Less than 10% of respondents reported the use of iodized salt. The use of supplements has become more common (reported by almost 50% of respondents in 2018). Dietary habits were similar in pregnant women, but the use of supplements was even higher (almost 70%). Nevertheless, most supplements used in pregnancy had insufficient contents of iodine and selenium. Thyroid function was euthyreotic in all women, but 13.9% of participants had a thyroid peroxidase antibodies (TPO-ab) level above 60 IU/mL. The median UIC (IQR) was 147.2 (90.0-248.1) µg/gCr, and 52.8% of pregnant women had a UIC below 150 µg/gCr. The mean selenium (SD) level was 101.5 (35.6) µg/L; 30.1% of women had a selenium level below 80 µg/L. The median selenoprotein P level was 6.9 (3.1-9.0) mg/L. Conclusions: Iodine nutrition in Latvian population of pregnant women was near the lower limit of adequate and a third of the population had a selenium deficiency. Supplements were frequently used, but most did not contain the recommended amounts of iodine and selenium.

Plasma levels of Th17-associated cytokines and selenium status in autoimmune thyroid diseases.

INTRODUCTION: The contribution of Th17 cytokines to autoimmune thyroid disease (AITD) is generally accepted. However, the roles of Th17 cells in the initiation and progression of Hashimoto's thyroiditis (HT) and Graves' disease (GD) remain unclear. Selenium deficiency, along with genetic predisposition and environmental factors, may have a role in thyroid autoimmunity. AIM: We aimed to assess (1) the Th17 immune response by measuring plasma levels of Th17- and Treg-associated cytokines and (2) the selenium status in treatment-naïve Latvian patients with newly diagnosed GD or HT. METHODS: Eleven GD patients, 41 HT patients, and 26 healthy subjects were recruited for this study. Plasma levels of IL-17a, IL-22, IL-23, IL-6, and IL-10 were detected by xMAP technology, while selenium was detected fluorometrically. RESULTS AND CONCLUSIONS: No significant differences in IL-17a, IL-22, IL-23, IL-6, or IL-10 levels were found among the HT patients, GD patients, and controls. In the HT patients, IL-17a levels were positively correlated with IL-22, IL-23, IL-6, and IL-10, while IL-22 was correlated with IL-6, IL-23, and IL-10. In the GD patients, IL-17a levels were positively correlated with IL-22, IL-23, and IL-10; IL-22 was positively correlated with IL-23, IL-6, and IL-10; FT3 was positively correlated with IL-17a, IL-23, and IL-10; and FT4 was positively correlated with IL-17a and IL-10 levels. Plasma selenium levels were negatively correlated with antithyroid peroxidase antibody titers in the HT patients. Although no difference in selenium levels was observed between the AITD patients and controls, the selenium status of the Latvian patients with GD or HT was at a suboptimal level.