Growth hormone/insulin-like growth factor-1/PTH axis in bone

Geriatric nutritional risk index as a predictor for fragility fracture risk in elderly with type 2 diabetes mellitus: A 9-year ambispective longitudinal cohort study

BACKGROUND & AIMS

The elderly are prone to fragility fractures, especially those suffering from type 2 diabetes mellitus (T2DM) combined with osteoporosis. Although studies have confirmed the association between GNRI and the prevalence of osteoporosis, the relationship between GNRI and fragility fracture risk and the individualized 10-year probability of osteoporotic fragility fractures estimated by FRAX remains unclear. This study aims to delve into the association between the GNRI and a fragility fracture and the 10-year probability of hip fracture (HF) and major osteoporotic fracture (MOF) evaluated by FRAX in elderly with T2DM.

METHODS

A total of 580 patients with T2DM aged ≥60 were recruited in the study from 2014 to 2023. This research is an ambispective longitudinal cohort study. All participants were followed up every 6 months for 9 years with a median of 3.8 years through outpatient services, medical records, and home fixed-line telephone interviews. According to the tertiles of GNRI, all subjects were divided into three groups: low-level (59.72-94.56, n = 194), moderate-level (94.56-100.22, n = 193), and high-level (100.22-116.45, n = 193). The relationship between GNRI and a fragility fracture and the 10-year probability of HF and MOF calculated by FRAX was assessed by receiver operating characteristic (ROC) analysis, Spearman correlation analyses, restricted cubic spline (RCS) analyses, multivariable Cox regression analyses, stratified analyses, and Kaplan-Meier survival analysis.

RESULTS

Of 580 participants, 102 experienced fragile fracture events (17.59%). ROC analysis demonstrated that the optimal GNRI cut-off value was 98.58 with a sensitivity of 75.49% and a specificity of 47.49%, respectively. Spearman partial correlation analyses revealed that GNRI was positively related to 25-hydroxy vitamin D [25-(OH) D] (r = 0.165, P < 0.001) and bone mineral density (BMD) [lumbar spine (LS), r = 0.088, P = 0.034; femoral neck (FN), r = 0.167, P < 0.001; total hip (TH), r = 0.171, P < 0.001]; negatively correlated with MOF (r = -0.105, P = 0.012) and HF (r = -0.154, P < 0.001). RCS analyses showed that GNRI was inversely S-shaped dose-dependent with a fragility fracture event (P < 0.001) and was Z-shaped with the 10-year MOF (P = 0.03) and HF (P = 0.01) risk assessed by FRAX, respectively. Multivariate Cox regression analysis demonstrated that compared with high-level GNRI, moderate-level [hazard ratio (HR) = 1.950; 95% confidence interval (CI) = 1.076-3.535; P = 0.028] and low-level (HR = 2.538; 95% CI = 1.378-4.672; P = 0.003) had an increased risk of fragility fracture. Stratified analysis exhibited that GNRI was negatively correlated with the risk of fragility fracture, which the stratification factors presented in the forest plot were not confounding factors and did not affect the prediction effect of GNRI on the fragility fracture events in this overall cohort population (P for interaction > 0.05), despite elderly females aged ≥70, with body mass index (BMI) ≥24, hypertension, and with or without anemia (all P < 0.05). Kaplan-Meier survival analysis identified that the lower-level GNRI group had a higher cumulative incidence of fragility fractures (log-rank, all P < 0.001).

CONCLUSION

This study confirms for the first time that GNRI is negatively related to a fragility fracture and the 10-year probability of osteoporotic fragility fractures assessed by FRAX in an inverse S-shaped and Z-shaped dose-dependent pattern in elderly with T2DM, respectively. GNRI may serve as a valuable predictor for fragility fracture risk in elderly with T2DM. Therefore, in routine clinical practice, paying attention to the nutritional status of the elderly with T2DM and giving appropriate dietary guidance may help prevent a fragility fracture event.

Interplay between CaSR and PTH1R signaling in skeletal development and osteoanabolism

Parathyroid hormone (PTH)-related peptide (PTHrP) controls the pace of pre- and post-natal growth plate development by activating the PTH1R in chondrocytes, while PTH maintains mineral and skeletal homeostasis by modulating calciotropic activities in kidneys, gut, and bone. The extracellular calcium-sensing receptor (CaSR) is a member of family C, G protein-coupled receptor, which regulates mineral and skeletal homeostasis by controlling PTH secretion in parathyroid glands and Ca(2+) excretion in kidneys. Recent studies showed the expression of CaSR in chondrocytes, osteoblasts, and osteoclasts and confirmed its non-redundant roles in modulating the recruitment, proliferation, survival, and differentiation of the cells. This review emphasizes the actions of CaSR and PTH1R signaling responses in cartilage and bone and discusses how these two signaling cascades interact to control growth plate development and maintain skeletal metabolism in physiological and pathological conditions. Lastly, novel therapeutic regimens that exploit interrelationship between the CaSR and PTH1R are proposed to produce more robust osteoanabolism.

A prospective study of plasma 25-hydroxyvitamin D concentration and prostate cancer risk

Mechanistic hypotheses suggest that vitamin D and the closely related parathyroid hormone (PTH) may be involved in prostate carcinogenesis. However, epidemiological evidence is lacking for PTH and inconsistent for vitamin D. Our objectives were to prospectively investigate the association between vitamin D status, vitamin D-related gene polymorphisms, PTH and prostate cancer risk. A total of 129 cases diagnosed within the Supplémentation en Vitamines et Minéraux Antioxydants cohort were included in a nested case-control study and matched to 167 controls (13 years of follow-up). 25-Hydroxyvitamin D (25(OH)D) and PTH concentrations were assessed from baseline plasma samples. Conditional logistic regression models were computed. Higher 25(OH)D concentration was associated with decreased risk of prostate cancer (ORQ4 v. Q1 0·30; 95 % CI 0·12, 0·77; P trend=0·007). PTH concentration was not associated with prostate cancer risk (P trend=0·4) neither did the studied vitamin D-related gene polymorphisms. In this prospective study, prostate cancer risk was inversely associated with 25(OH)D concentration but not with PTH concentration. These results bring a new contribution to the understanding of the relationship between vitamin D and prostate cancer, which deserves further investigation.

A comparative study of the bone metabolic response to dried plum supplementation and PTH treatment in adult, osteopenic ovariectomized rat

Dried plum has been reported to have potent effects on bone in osteopenic animal models, but the mechanisms through which bone metabolism is altered in vivo remain unclear. To address this issue, a study comparing the metabolic response of dried plum to the anabolic agent, parathyroid hormone (PTH), was undertaken. Six month-old female Sprague Dawley rats (n=84) were sham-operated (SHAM) or ovariectomized (OVX) and maintained on a control diet for 6wks until osteopenia was confirmed. Treatments were initiated consisting of a control diet (AIN-93M) supplemented with dried plum (0, 5, 15 or 25%; w/w) or a positive control group receiving PTH. At the end of 6wks of treatment, whole body and femoral bone mineral density (BMD) were restored by the two higher doses of dried plum to the level of the SHAM group. Trabecular bone volume and cortical thickness were also improved with these two doses of dried plum. Dried plum suppressed the OVX-induced increase in bone turnover as indicated by systemic biomarkers of bone metabolism, N-terminal procollagen type 1 (P1NP) and deoxypyridinoline (DPD). Dynamic bone histomorphometric analysis of the tibial metaphysis revealed that dried plum restored the OVX-induced increase in cancellous bone formation rate (BFR) and mineralizing surface (MS/BS) to the SHAM group, but some doses of dried plum increased endocortical mineral apposition rate (MAR). As expected, PTH significantly increased endocortical MAR and BFR, periosteal BFR, and trabecular MAR and BFR beyond that of the OVX and maintained the accelerated rate of bone resorption associated with OVX. Dried plum up-regulated bone morphogenetic protein 4 (Bmp4) and insulin-like growth factor 1 (Igf1) while down-regulating nuclear factor T cell activator 1 (Nfatc1). These findings demonstrate that in the adult osteopenic OVX animal, the effects of dried plum differ from that of PTH in that dried plum primarily suppressed bone turnover with the exception of the indices of bone formation at the endocortical surface.

Pathophysiology of Bone Remodelling and Current Therapeutic Approaches

Different metabolic bone parameters such as RANK (receptor activator of nuclear factor-κB), RANK ligand (receptor activator of nuclear factor-κB ligand) and OPG (osteoprotegerin) control physiological bone remodelling. The pathophysiology of these factors in bone diseases and osseous metastases is becoming clearer. In metastatic breast cancer, osteolytic bone metastases are the result of increased osteoclastic activity caused either by increased RANK ligand or decreased OPG expression of metastatic osseous tumour cells. These findings may lead to new therapeutic options for the treatment of breast cancer patients. The aim of this work is to provide an overview of physiological bone remodelling and of the interaction between tumour cells and bone environment. Current therapy approaches and the mechanisms of action of drugs are described.

Skeletal health of children and adolescents with inflammatory bowel disease

Current evidence points to suboptimal bone health in children and adolescents with inflammatory bowel disease (IBD) when compared with their healthy peers. This compromise is evident from diagnosis. The clinical consequences and long-term outcome of this finding are still unknown. The mechanism of suboptimal bone health in children and adolescents with IBD lays mainly in reduced bone formation, but also reduced bone resorption, processes necessary for bone growth. Factors contributing to this derangement are inflammation, delayed growth and puberty, lean mass deficits, and use of glucocorticoids. We recognize that evidence is sparse on the topic of bone health in children and adolescents with IBD. In this clinical guideline, based on current evidence, we provide recommendations on screening and monitoring bone health in children and adolescents with IBD, including modalities to achieve this and their limitations; monitoring of parameters of growth, pubertal development, and reasons for concern; evaluation of vitamin D status and vitamin D and calcium intake; exercise; and nutritional support. We also report on the current evidence of the effect of biologics on bone health in children and adolescents with IBD, as well as the role of bone active medications such as bisphosphonates. Finally, we summarize the existing numerous gaps in knowledge and potential subjects for future research endeavors.

The role of liver-derived insulin-like growth factor-I

IGF-I is expressed in virtually every tissue of the body, but with much higher expression in the liver than in any other tissue. Studies using mice with liver-specific IGF-I knockout have demonstrated that liver-derived IGF-I, constituting a major part of circulating IGF-I, is an important endocrine factor involved in a variety of physiological and pathological processes. Detailed studies comparing the impact of liver-derived IGF-I and local bone-derived IGF-I demonstrate that both sources of IGF-I can stimulate longitudinal bone growth. We propose here that liver-derived circulating IGF-I and local bone-derived IGF-I to some extent have overlapping growth-promoting effects and might have the capacity to replace each other (= redundancy) in the maintenance of normal longitudinal bone growth. Importantly, and in contrast to the regulation of longitudinal bone growth, locally derived IGF-I cannot replace (= lack of redundancy) liver-derived IGF-I for the regulation of a large number of other parameters including GH secretion, cortical bone mass, kidney size, prostate size, peripheral vascular resistance, spatial memory, sodium retention, insulin sensitivity, liver size, sexually dimorphic liver functions, and progression of some tumors. It is clear that a major role of liver-derived IGF-I is to regulate GH secretion and that some, but not all, of the phenotypes in the liver-specific IGF-I knockout mice are indirect, mediated via the elevated GH levels. All of the described multiple endocrine effects of liver-derived IGF-I should be considered in the development of possible novel treatment strategies aimed at increasing or reducing endocrine IGF-I activity.

Factors associated with elevated or blunted PTH response in vitamin D insufficient adults

OBJECTIVES

The purpose of this study was to examine factors associated with high or low parathyroid hormone (PTH) levels in relationship to vitamin D insufficiency.

DESIGN

This was a cross-sectional study consisting of 516 healthy men and women, aged 30-85, all Caucasians with vitamin D insufficiency [serum 25(OH)D<45 nmol L(-1)]. The group was divided into quartiles by PTH levels and the highest and lowest quartiles were compared with regard to various factors likely to affect calcium metabolism. We used stepwise multivariable logistic regression to determine the independent association between PTH levels and other variables for men and women separately.

RESULTS

We found that men in the lowest PTH quartile were significantly younger, had less energy intake, lower body mass index (BMI) and better kidney function compared with the highest PTH quartile. They had also higher ionized calcium, insulin-like growth factor (IGF1) and testosterone and were more likely to smoke. Women within the lowest PTH quartile were younger, had lower BMI and magnesium values and higher IGF1 levels and were more likely to smoke. Stepwise multivariate regression showed that IGF1, testosterone and BMI were significantly associated with PTH in men (R(2)=0.472) but smoking, BMI and kidney function in women (R(2)=0.362).

CONCLUSIONS

Our results indicate that during vitamin D insufficiency, factors other than calcium and vitamin D may modify PTH response. These factors may be different between sexes and we have identified novel factors, IGF1 and testosterone in men which may be compensatory in nature and confirmed previous factors such as smoking, BMI and kidney function in women.