Increased Risk Of Bone Loss In Patients With Kidney Deficiency:A Cross Sectional Study With Rheumatoid Arthritis

ObjectiveThe aim of our study was to investigate the association between kidney deficiency and bone turnover biomarkers in rheumatoid arthritis(RA),and to explore the potential mechanisms of kidney deficiency linked to bone metabolism disorders in rheumatoid arthritis.MethodsThe present study was a cross-sectional study.We enrolled 70 patients with established RA in our Rheumatology department of the First Affiliated Hospital of Guangzhou University of Chinese Medicine.Clinical parameters were recorded including age,gender,age of onset,disease duration,menopausal status,history uses of DMARDs,swelling joint counts,tender joint counts,levels of bone mineral density,titers of rheumatoid factors,titers of anti-CCP antibodies,levels C-reactive proteins,erythrocyte sedimentation rates,etc.Also,we collected 5 ml of peripheral blood from RA patients,and serum levels of bone turnover biomarkers were measured by enzyme-linked immunosorbent assay(Elisa): N-MID Osteocalcin(N-MID-OT),procollagen I N-terminal peptide(PINP),cross-linked Carboxyterminal telopeptide of type I collagen(CTX-I).Results1.No significant differences were noted between kidney deficiency group and nonkidney deficiency group regarding clinical parameters like age,sex,disease duration,disease activity,tilters of autoantibodies,proportions of postmenopausal patients,history of glucocorticoid use,DMARDs use(P>0.05).2.No significant difference was found in BMD measurements of the lumbar spine,the femoral neck and the total hip between kidney deficiency group and non-kidney deficiency group(P>0.05)。3.RA patients with kidney deficiency tend to have lower median values of bone formation markers of N-MID-OT(14.52(10.25-22.50)ng/ml vs 21.31(15.85-34.09)ng/ml,P=0.003<0.05)and PINP(7.10(5.91-8.83)ng/ml vs 7.79(6.83-10.20),compared with patients with non-kidney deficiency.4.No significant difference was found for CTX-I values in two groups(3.68(2.56-6.12)ng/ml vs 3.68(2.56-6.12)ng/ml,P=0.814>0.05).5.Spearman correlation analysis suggested that serum CTX-I levels in rheumatoid arthritis patients correlated with DAS28 scores(r=0.281,P=0.021<0.05),also with the tender joint counts(r=0.281,P=0.021<0.05),as well as with DMARD uses before(r=-0.322,P=0.012<0.05).6.Spearman correlation analysis suggested that,for RA patients,PINP(r=-0.261,P=0.041<0.05)and N-MID-OT levels(r=-0.360,P=0.003<0.05)were negatively correlated with kidney deficiency.PINP levels were also negatively correlated with lumbar spine BMD levels(r=-0.360,P=0.003<0.05).Conclusion1.Levels of serum bone formation markers like N-MID-OT and PINP in kidneydeficiency group of RA patients were significantly lower than non-kidney deficiency group.Levels of the bone resorption marker of CTX-1 were consistent in the two groups.2.Kidney deficiency syndrome was significantly associated with disorders of bone metabolism in rheumatoid arthritis.Kidney deficiency syndrome was associated with the inhibition of bone formation.No correlation was found between kidney-deficiency syndrome and status of bone resorption in rheumatoid arthritis.3.The RA patients with kidney deficiency syndrome may have a faster rate of bone loss compared to the patients without kidney deficiency syndrome.RA patients with kidney deficiency syndrome may have a higher risk of secondary osteoporosis compared to the patients without kidney deficiency syndrome.