The relationship between chemerin, bone metabolism, the RANKL/RANK/OPG system, and bone mineral density in girls with anorexia nervosa

Abstract

Based on recent studies in humans, chemerin has been classified as an adipokine that might be associated with osteoporosis and BMD. Bone loss is common in adolescents with anorexia nervosa (AN). Moreover, dysfunction in the production of chemerin has also been shown. Therefore, we carried out a comparative analysis between chemerin, bone metabolism, the RANKL/RANK/OPG system, and BMD in girls with AN. Plasma chemerin, OC, CTx, OPG, and sRANKL were determined by ELISA in 75 girls with AN aged 12.6-17.8 years. BMD was assessed by DXA and expressed as Z-score according to the lumbar spine (s) and total body (TB) sites. According to the s-BMD- and TB-BMD Z-score, girls with AN were divided into two subgroups with parallel analyses used: normal (Z-score > -2.0) and low (Z-score ≤ -2.0) s-BMD, and normal (Z-score > -2.0) and low (Z-score ≤ -2.0) TB-BMD. Mean OC and the OPG/sRANKL ratio were markedly lower in the low s-BMD subgroup compared to the normal s-BMD subgroup. The s-Z-score values (both low and normal) correlated significantly and positively with the OPG/sRANKL ratio. Only in the low s-BMD subgroup did chemerin correlate significantly and positively with all nutritional indices and the OPG/sRANKL ratio. In the low TB-BMD subgroup the mean OC and the OPG/sRANKL ratio were lower than in the normal TB-BMD subgroup. The TB-Z-score values (both normal and low) correlated significantly and positively with all nutritional indices and the OPG/sRANKL ratio. The low TB-Z-score values correlated significantly and positively also with chemerin. In the low TB-BMD subgroup chemerin correlated significantly and positively with weight and BMI (expressed as absolute values), Cole index, the duration of the disease, and OPG/sRANKL ratio while its correlation with age was negative. Undernutrition and associated deficit of adipose tissue may result in inadequate chemerin production and skeletal disorders in girls with AN. Chemerin acts as a coordinator of the dynamic balance between bone metabolism and the OPG/RANK/RANKL system and, in turn, may contribute to the loss of bone mass in girls with AN. The cortical bone site seems to be more severely responsive to chemerin actions than the trabecular bone site.