Regulation of circulating thyroid hormone levels by hypothalamic tanycytes and hypophysial pars tuberalis-specific cells and their morphological and gene- and protein-expression changes under different photoperiods

Thyroid hormone in the hypothalamus acts as a key determinant of seasonal transitions. Thyroid hormone-levels in the brain are mainly regulated by the hypothalamic tanycytes and pituitary pars tuberalis (PT)-specific cells. TSHβ produced by the PT-specific cells stimulates Dio2 expression and decreases Dio3 expression of the tanycytes. Both tanycytes and PT-specific cells in photosensitive animals exhibit remarkable changes of morphological appearance and expressions of genes and proteins under different photoperiods. Long photoperiods induce increased gene- and protein-expressions and active features. Short photoperiods cause the decreased gene- and protein-expressions and inactive features. In the PT, expressions of TSHβ, common α-subunit of glycoprotein hormones (α-GSU), and MT1 receptor of melatonin receptors and eyes absent 3 change under different photoperiods. Diurnal rhythms of α-GSU mRNA expression are observed in the PT of Djungarian hamsters. Hes1, Nkx2.1, and LIM homeodomain gene 2 (Lhx2) are involved in the differentiation of PT. In the hypothalamic tanycytes, expressions of Dio2, Dio3, vimentin, serine/threonine kinase 33, GPR50, Nestin, Retinoid signaling genes (retinaldehyde dehydrogenase 1, cellular retinol binding protein 1, and Stra6), monocarboxylate transporter 8, and neural cell adhesion molecule change under different photoperiods. Rax, Lhx2, Nfia/b/x, and fibroblast growth factor 10 are involved in the differentiation of tanycytes.

Is beta-carotene consumption associated with thyroid hormone levels?

The thyroid hormones play a pivotal role in various physiological processes, including growth, metabolism regulation, and reproduction. While non-modifiable factors are known to impact thyroid function, such as genetics and age, nutritional factors are also important. Diets rich in selenium and iodine are conventionally acknowledged to be beneficial for the production and release of thyroid hormones. Recent studies have suggested a potential link between beta-carotene, a precursor to vitamin A (retinol), and thyroid function. Beta-carotene is known for its antioxidant properties and has been shown to play a role in the prevention of various clinical conditions such as cancer and cardiovascular and neurological diseases. However, its impact on thyroid function is still unclear. Some studies have suggested a positive association between beta-carotene levels and thyroid function, while others have found no significant effect. Conversely, the hormone produced by the thyroid gland, thyroxine, enhances the conversion of beta-carotene to retinol. Furthermore, vitamin A derivatives are being explored as potential therapeutic options for thyroid malignancies. In this review, we highlight the mechanisms through which beta-carotene/retinol and thyroid hormones interact and review the findings of clinical studies examining the association between beta-carotene consumption and thyroid hormone levels. Our review underscores the need for further research to clarify the relationship between beta-carotene and thyroid function.

Association between thyroid hormone levels and frailty in an older inpatient cohort: a cross-sectional study

BACKGROUND

Frailty is a common biological syndrome in elderly people, and the aging process regulates thyroid function. The present study aimed to determine the prevalence of frailty in an older inpatient cohort using the FRAIL scale and to evaluate the association of frailty with thyroid hormone levels.

METHODS

This cross-sectional study was performed in the Department of Geriatrics, Sichuan Provincial People's Hospital, University of Electronic Science and Technology of China. From November 2019 to April 2020, 146 inpatients aged ≥65 years were recruited for the study and demographic data, frailty, geriatric assessment, and thyroid hormone levels were evaluated. Frailty was determined by the FRAIL scale, and geriatric assessment was based on activities of daily living (ADL) and instrumental activities of daily living (IADL). The data were analyzed using appropriate parametric and nonparametric statistical tests.

RESULTS

At enrollment, 31 (21.23%) of the total participants were robust, 31 (21.23%) were pre-frail, and 84 (57.53%) were frail. The frail patients were significantly older than the robust patients and pre-frail patients (P<0.001 for both). The percentages of ADL disability differed significantly among the patients for frail versus robust, frail versus pre-frail, and pre-frail versus robust, as did the percentages of IADL disability among patients for frail versus robust and frail versus pre-frail (P<0.01 for all). In binary logistic regression analyses adjusted for age, sex, body mass index, HbA1c (%), and smoking, frailty was significantly associated with serum thyroid stimulating hormone (TSH) concentration [odds ratio (OR): 1.704], T3 concentration (OR: 0.102), ADL score (OR: 0.793), and IADL score (OR: 0.413).

CONCLUSIONS

In our study population, the prevalence of frailty was higher in older geriatric inpatients in China than other studies. Inpatients with high TSH levels were at increased risk of frailty. Conduction of future longitudinal studies is warranted to determine the relationship between thyroid hormone levels and frailty.

Pre-contrast CT attenuation of the thyroid gland is lower in brachycephalic dogs versus non-brachycephalic dogs

Computed tomography has been used in human medicine to evaluate the thyroid gland functional status by means of Hounsfield units (HU). Studies describing attenuation value abnormalities, other than those in thyroid neoplasia, lack in veterinary medicine. The authors have observed a subjective reduction in thyroid attenuation in some patients undergoing CT for reasons other than thyroid disease. This finding has been identified more frequently in brachycephalic breeds compared to non-brachycephalic breeds. In order to determine the thyroid gland attenuation variability on CT, a retrospective and prospective, analytical, cross-sectional study was performed. The thyroid attenuation values of 65 client-owned dogs were assessed using a 16-slice helical CT scanner. Differences in attenuation between brachycephalic and non-brachycephalic dogs were estimated by Welch's t-test. Serum TT4 and TSH levels were available in 26 patients. Statistically significant differences were observed in the pre-contrast attenuation value ranges between brachycephalic and non-brachycephalic dogs (P = .04). The pre-contrast attenuation value range for the brachycephalic group was 69.1-108 HU while being 75.8-121 HU for the non-brachycephalic group. No significant correlation was found between thyroid attenuation and serum thyroid hormone levels in our population (P > .6). All patients with hypoattenuating thyroid were brachycephalic and reported euthyroid. In conclusion, brachycephalic dogs seem to have a pre-contrast attenuation thyroid gland range lower than non-brachycephalic dogs. The present study contributes to the veterinary literature by providing a new thyroid attenuation value range for brachycephalic breeds. Additionally, hypoattenuating thyroid glands may be found in dogs with normal TT4 and TSH values.

Evaluation of the Relationship Between Ischemia-Modified Albumin Levels and Thyroid Hormone Levels

BACKGROUND

A novel ischemia marker named ischemia modified albumin was previously considered as an early marker of myocardial ischemia, however due to recent reports, its contribution was demonstrated in different pathologies such as oxidative stress, diabetes, stroke and cancer. We aimed to investigate the relation between oxidative stress and thyroid dysfunctions determining IMA levels since IMA is closely related with increased oxidative stress.

METHODS

A total of 88 individuals were participated in this study: 34 cases in hypothyroid, 27 cases in hyperthyroid and 27 cases in euthyroid group. Ischemia-modified albumin levels were measured by albumin cobalt binding test and thyroid hormone levels were determined with electrochemiluminescent method.

RESULTS

Ischemia modified albumin levels were significantly decreased in hypothyroid group compared to hyperthyroid and euthyroid groups (p < 0.001). In hyperthyroid individuals ischemia modified albumin levels were higher compared to euthyroid ones (p < 0.001). Ischemia modified albumin was negatively correlated with TSH levels (r = -0.473, p < 0.001), and positively correlated with FT4 and FT3 levels (r = 0.496, p < 0.001 and r = 0.275, p = 0.010, respectively).

CONCLUSION

We suggest that albumin adjusted IMA levels are significantly lower in hypothyroid group than hyperthyroid and euthyroid groups.