Effects of intensive glycemic control on serum levels of insulin-like growth factor-I and dehydroepiandrosterone sulfate in Type 2 diabetes mellitus

Connecting the Dots Between the Gut-IGF-1-Prostate Axis: A Role of IGF-1 in Prostate Carcinogenesis

Prostate cancer (PCa) is the most common malignancy in men worldwide, thus developing effective prevention strategies remain a critical challenge. Insulin-like growth factor 1 (IGF-1) is produced mainly in the liver by growth hormone signaling and is necessary for normal physical growth. However, several studies have shown an association between increased levels of circulating IGF-1 and the risk of developing solid malignancies, including PCa. Because the IGF-1 receptor is overexpressed in PCa, IGF-1 can accelerate PCa growth by activating phosphoinositide 3-kinase and mitogen-activated protein kinase, or increasing sex hormone sensitivity. Short-chain fatty acids (SCFAs) are beneficial gut microbial metabolites, mainly because of their anti-inflammatory effects. However, we have demonstrated that gut microbiota-derived SCFAs increase the production of IGF-1 in the liver and prostate. This promotes the progression of PCa by the activation of IGF-1 receptor downstream signaling. In addition, the relative abundance of SCFA-producing bacteria, such as Alistipes, are increased in gut microbiomes of patients with high-grade PCa. IGF-1 production is therefore affected by the gut microbiome, dietary habits, and genetic background, and may play a central role in prostate carcinogenesis. The pro-tumor effects of bacteria and diet-derived metabolites might be potentially countered through dietary regimens and supplements. The specific diets or supplements that are effective are unclear. Further research into the "Gut-IGF-1-Prostate Axis" may help discover optimal diets and nutritional supplements that could be implemented for prevention of PCa.

Obesity and Bone Health: A Complex Link

So far, the connections between obesity and skeleton have been extensively explored, but the results are inconsistent. Obesity is thought to affect bone health through a variety of mechanisms, including body weight, fat volume, bone formation/resorption, proinflammatory cytokines together with bone marrow microenvironment. In this review, we will mainly describe the effects of adipokines secreted by white adipose tissue on bone cells, as well as the interaction between brown adipose tissue, bone marrow adipose tissue, and bone metabolism. Meanwhile, this review also reviews the evidence for the effects of adipose tissue and its distribution on bone mass and bone-related diseases, along with the correlation between different populations with obesity and bone health. And we describe changes in bone metabolism in patients with anorexia nervosa or type 2 diabetes. In summary, all of these findings show that the response of skeleton to obesity is complex and depends on diversified factors, such as mechanical loading, obesity type, the location of adipose tissue, gender, age, bone sites, and secreted cytokines, and that these factors may exert a primary function in bone health.

Diabetes Mellitus-induced Bone Fragility

Accumulating evidence has shown that the risk of osteoporotic fractures is increased in patients with diabetes mellitus (DM). Thus, DM-induced bone fragility has been recently recognized as a diabetic complication. Because the fracture risk is independent of the reduction in bone mineral density, deterioration of the bone quality may be the main cause of bone fragility. Although its mechanism remains poorly understood, accumulated collagen cross-links of advanced glycation end-products (AGEs) and dysfunctions of osteoblast and osteocyte may be involved. Previous studies have suggested that various diabetes-related factors, such as chronic hyperglycemia, insulin, insulin-like growth factor-I, AGEs, and homocysteine, are associated with the risk of bone fragility caused by impaired bone formation and bone remodeling. Furthermore, several anti-diabetic drugs are known to affect bone metabolism and fracture risk. We herein review the association between DM and fracture risk as well as the mechanism of DM-induced bone fragility based on recent evidence.

Decreased Serum Insulin-like Growth Factor-I is a Risk Factor for Non-vertebral Fractures in Diabetic Postmenopausal Women

Objective Previous studies have shown that serum insulin-like growth factor-I (IGF-I) is involved in diabetes-related bone fragility. Although lower serum levels of IGF-I are reported to be associated with a higher risk of vertebral fractures in patients with type 2 diabetes, it is unknown whether or not the serum level of IGF-I is associated with the incidence of non-vertebral fractures. Methods We investigated the relationships between the serum levels of IGF-I and the incidence of non-vertebral osteoporotic fractures in 188 men and 168 postmenopausal women with type 2 diabetes. Results A multiple logistic regression analysis adjusted for age, duration of diabetes, observation period, body mass index, HbA1c, serum creatinine, and the bone mineral density at the lumbar spine showed that the serum IGF-I level was significantly and inversely associated with the incidence of non-vertebral osteoporotic fractures in postmenopausal women (odds ratio =0.48, 95% confidential interval [CI] 0.23-0.99 per SD increase; p=0.047), but not in men. Moreover, the inverse association between the serum IGF-I level and the incidence of non-vertebral fractures remained significant after additional adjustment for insulin use, and the serum calcium and phosphate levels (odds ratio =0.48, 95% CI 0.23-0.99 per SD increase; p=0.046). Conclusion This is the first study to show that decreased serum IGF-I levels are associated with a higher risk of non-vertebral osteoporotic fractures in postmenopausal women with type 2 diabetes. Serum IGF-I could be a useful marker for assessing the incidence of osteoporotic fractures.

Dehydroepiandrosterone sulfate (DHEAS) as an endocrine marker of aging in calorie restriction studies

The adrenal steroid, dehydroepiandrosterone sulfate (DHEAS), is generally regarded as being a reliable endocrine marker of aging, because in humans and nonhuman primates its circulating concentrations are very high during young adulthood, and the concentrations then decline markedly during aging. Despite promising results from early studies, we were recently surprised to find that caloric restriction (CR) did little to prevent or delay the decline of DHEAS concentrations in old rhesus macaques. Here we summarize the use of circulating DHEAS concentrations as a biomarker of aging in CR studies and suggest reasons for its limited value. Although DHEAS can reliably predict aging in animals maintained on a standard diet, dietary manipulations may affect liver enzymes involved in the metabolism of steroid hormones. Consequently, in CR studies the reliability of using DHEAS as a biomarker of aging may be compromised.