Hyperthyroidism and Wnt Signaling Pathway: Influence on Bone Remodeling

Graves' disease is an autoimmune disease of the thyroid gland, characterized by increased production of thyroid hormones, which can affect many different organ systems in the body. Among other problems, it can cause disorders of the skeletal system, shortening the bone remodeling cycle and causing a decrease in bone density. The Wnt cascade signaling pathway and the β-catenin, as a part of the canonical Wnt pathway, also play roles in maintaining bone mass. Inhibition of the Wnt pathway can cause bone loss, and its stimulation can increase it. The Wnt signaling pathway influences the effectiveness of thyroid hormones by affecting receptors for thyroid hormones and deiodinase, while thyroid hormones can change levels of β-catenin within the cell cytoplasm. This indicates that the Wnt pathway and thyroid hormone levels, including hyperthyroidism, are linked and may act together to change bone density. In this review article, we attempt to explain the interplay between thyroid hormones and the Wnt pathway on bone density, with a focus on directions for further research and treatment options.

IMPACT OF GRAVES' DISEASE AND ANTITHYROID DRUG THERAPY ON BONE MINERAL DENSITY - PATHOPHYSIOLOGICAL MECHANISMS AND CLINICAL RELEVANCE

Graves' disease is an autoimmune disease characterized by excessive thyroid hormone production. One of the consequences of that state can be a decrease in bone mineral density (BMD). Graves' disease is often treated with antithyroid drugs (ATD) as first line therapy, which can lead to disease remission. Moreover, recent data show that improvement in BMD can be expected. However, vitamin D deficiency can coexist along with Graves' disease, which is also involved in the process of bone remodeling. It is still not known whether lower values of vitamin D can contribute to onset of Graves' disease and if its supplementation might be helpful in therapy for hyperthyroidism. In the past couple of decades, osteopenia and osteoporosis have become a major health burden not only in post-menopausal women but also as a result of other diseases, leading to extensive research into various pathophysiological mechanisms responsible for bone remodeling. The Wnt (wingless integrated) signaling pathway is a very important factor in bone homeostasis, especially the canonical pathway. Present data indicate that stimulation of the Wnt pathway leads to bone mass increase and, in contrast, its inhibition leads to bone mass decrease. Hence, inhibitors of the canonical Wnt pathway became the focus of interest, in particular sclerostin and dickkopf 1 (DKK1). Hyperthyroidism and osteopenia/osteoporosis are quite common today and can coexist together or as separate entities. In this article, we aimed to give an overview of possible associations and potential mutual pathophysiological mechanisms.

Hypothyroidism and Nonalcoholic Fatty Liver Disease: Pathophysiological Associations and Therapeutic Implications

Nonalcoholic fatty liver disease (NAFLD) is a complex clinical entity which can be secondary to many other diseases including hypothyroidism, characterized by lowering of thyroid hormones and increased thyroid stimulating hormone (TSH). A lot of emerging data published recently advocates the hypothesis that hypothyroid induced NAFLD could be a separate clinical entity, even suggesting possible treatment options for NAFLD involving substitution therapy for hypothyroidism along with lifestyle modifications. In addition, a whole new field of research is focused on thyromimetics in NAFLD/NASH treatment, currently in phase 3 clinical trials. In this critical review we summarized epidemiological and pathophysiological evidence linking these two clinical entities and described specific treatment options with the accent on promising new agents in NAFLD treatment, specifically thyroid hormone receptor (THR) agonist and its metabolites.

Biochemical bone turnover markers: significance in patients with osteoporosis

Osteoporosis is a systemic disease, which is characterized by reduced bone mass and microarchitectural deterioration of the bone tissue, resulting in an increased risk of fracture. Since osteoporosis is today a disease with high incidence rate, the aim of this study was to determine a correlation between bone mass density (BMD) and concentration of biochemical bone turnover markers--deoxypyridinoline (DPD) as a marker of bone resorption, and osteocalcin (OC) as a marker of bone formation. The study included 70 women between 33 and 76 years of age. In all women BMD was measured by Dual X-ray Absorptiometry (DXA) as a T-score. T-score was defined as the number of standard deviations of the bone mass density from the maximum bone mass density in young adults. According to T-score, patients were divided into three groups: patients with osteoporosis, patients with osteopenia and control group consisting of patients with normal T-score. DPD in urine and OC in serum were measured by a routine procedure.

RESULTS

a negative correlation between BMD and concentration of bone turnover marker was discovered. One-way analysis of variance and Pearson correlation were used for statistical analysis, with a P value < 0.05 being considered significant. Although a negative correlation was discovered, we concluded that both procedures have a significant role in diagnosis and follow-up of patients with osteoporosis.