Novel biomarkers for prediction of outcome in hip fracture patients-An exploratory study

Effect of age and gender on serum growth differentiation factor 15 and its relationship to bone density and bone turnover

Senescent cells and senescence-associated secretory phenotype (SASP) proteins are involved in age-related bone loss. Growth differentiation factor 15 (GDF 15), a stress-responsive cytokine member of the transforming growth factor-β (TGF-β) superfamily, is one of the key SASP proteins. It is strongly associated with age and higher levels correlate with frailty and are detected in several conditions and diseases. It also modulates appetite and body weight through the binding to its receptor glial cell- derived neurotrophic factor family receptor alpha- like (GFRAL) in the brainstem. The GDF 15 involvement in bone metabolism has been studied in several murine models, however, it is still unclear in humans. Therefore, this study aims to determine whether GDF 15 is associated with bone mineral density (BMD) and bone turnover, and to establish the effect of age and gender on its levels. Serum GDF 15 was measured with an ELISA from R&D Systems in 180 healthy women and men from the "XtremeCT study", divided into three age groups which represent different stages of skeletal development (16-18, 30-32, over 70 years). We also measured bone resorption marker C-terminal telopeptide of type I collagen (CTX) and bone formation markers N-terminal propeptide of type I collagen (PINP), osteocalcin (OC) and bone alkaline phosphatase (BAP) using iSYS-IDS analyser. Parathyroid hormone (PTH), 25hydroxyvitamin D (25OH-vitamin D), Insulin-like Growth Factor I (IGF-1), estradiol and testosterone were measured using the Cobas automated analyser (Roche Diagnostics). We assessed BMD at spine and total hip by dual-energy x-ray absorptiometry (DXA) and high resolution peripheral quantitative computed tomography (HRpQCT) of the radius and tibia. Univariate analysis of variance with the post-hoc Sheffe test and multiple linear regression has been used to assess the effect of age and gender. Spearman's rank correlation was used to evaluate the associations between GDF 15 and the other variables. We found GDF 15 levels significantly associated with age (p < 0.001) and gender (p = 0.008), with a significant gender ∗ age interaction (p < 0.001). Significantly higher levels of GDF 15 were found in subjects aged over 70 compared with the younger people (p < 0.001) and significantly higher levels were detected in men. We did not find any significant correlation between GDF 15 and bone turnover markers (BTMs), BMD, HRpQCT measures and hormones in any of the age groups. In conclusion, age and gender are determinants of GDF15 and much higher levels are found in older people and in men. Since no association was found between GDF 15 and bone health measures, we hypothesize that the effect of GDF 15 on bone might be exert by other tissue, such as muscle.

Elevated gamma-glutamyl transpeptidase level is associated with an increased risk of hip fracture in postmenopausal women

The aim of this study was to evaluate the association between gamma-glutamyl transferase (GGT) levels and the risk of hip fracture among middle-aged women by using the Korean National Health Insurance Service claims database from 2002 to 2015. After exclusion of those with any chronic liver disease, heavy alcohol consumption, any missing values required for our analysis, or GGT levels less than 1 or greater than 99 percentile, we classified subjects into three groups according to baseline GGT levels. A total of 127,141 women aged 50 years or older were included for analysis (GGT range: 8–106 U/L). During an average 12.1 years of follow-up, 2758 patients sustained hip fractures (2.17%). Compared with the group in the lowest tertile, the group in the highest tertile had the highest cumulative incidence of hip fracture. One log-unit increase in GGT was associated with a 17% increased risk of hip fracture. Subgroup analysis by BMI (≥ 25 vs. < 25 kg/m²), presence of diabetes, levels of other liver enzymes, and alcohol consumption level did not show significant effect modification. In summary, elevated baseline GGT level was associated with an increased risk of hip fracture in postmenopausal women, independent of alcohol consumption and chronic liver disease.