Cathepsin K in treatment monitoring following intravenous zoledronic acid

Association Between CTSK Gene Polymorphisms and Response to Alendronate Treatment in Postmenopausal Chinese Women with Low Bone Mineral Density

Purpose

The aim of this study was to explore the association between CTSK polymorphisms and the response to alendronate treatment in postmenopausal Chinese women with low bone mineral density.

Patients and Methods

In this study, 460 postmenopausal women from Shanghai were included. All of them were treated with weekly oral alendronate 70 mg, daily calcium 600 mg and vitamin D 125 IU for a year. Four tag single nucleotide polymorphisms (SNPs) in CTSK gene were genotyped. Bone mineral densities of lumbar spine (L1-L4), femoral neck and total hip were measured at baseline and after 12 months of treatment, respectively.

Results

After 1-year of treatment, there was no significant differences in BMI between baseline and follow-up. After alendronate treatment, the BMD of L1-4, femoral neck and total hip all increased significantly (all P < 0.001), with average increases of 4.33 ± 6.42%, 1.85 ± 4.20%, and 2.36 ± 3.79%, respectively. There was no significant difference in BMD at L1-L4, the femoral neck and total hip between different genotype groups at baseline (P>0.05). After 1-year treatment with alendronate, rs12746973 and rs10847 were associated with the % change of BMD at L1-L4 (P=0.038) and % change of BMD at femoral neck (P=0.038), respectively. Furthermore, rs10847 was associated with BMD response at femoral neck (P=0.013). However, the associations were not significant after Bonferroni correction.

Conclusion

We concluded that the common variations of CTSK gene were potentially associated with the therapeutic response to alendronate treatment in Chinese women with low bone mineral density. However, further validation is needed.

Relation of Bone Mineral Density with Homocysteine and Cathepsin K levels in Postmenopausal Women

BACKGROUND

Homocysteine (HCY) interferes with collagen cross-linking in bones and stimulates osteoclast activity. The activated osteoclasts secrete cathepsin K (CathK), a cysteine protease, in eminent quantity during bone resorption. Hyperhomocysteinemia may effect bone mineral density (BMD) through CathK. We, therefore, examined the relation between HCY and BMD along with CathK, 25-hydroxyvit-D (25[OH]D), intact parathyroid hormone (iPTH), and Vitamin B12.

MATERIALS AND METHODS

We recruited a total of 93 postmenopausal women between the age group of 45-60 years, attending the Endocrinology outpatient department at King George's Medical University, Lucknow. BMD was done by DXA scan using Hologic QDR1000 system. Based on the WHO criteria, patients were segregated into three groups as follows; normal bone mass, osteopenia, and osteoporosis. All women underwent routine biochemical laboratory parameters, HCY, Vitamin B12, and CathK levels.

RESULTS

Among 93 postmenopausal women, 56% (52) had osteoporosis. Nineteen percent (18) had normal BMD (mean age, 53.22 ± 8.5 years) and 23 (25%) had osteopenia (mean age 52.86 ± 6.67 years). The mean age in the osteoporetic group was 56.2 ± 6.9 years. The median (interquartile range) levels of HCY in the three groups were 14.5 μmol/L (12.2-24.7), 15.05 μmol/L (12.1-19.9) and 13.2 μmol/L (10.3-17.0), respectively. CathK levels were similar in three groups 7.6 ng/ml (7.0-80.5), 8.3 ng/ml (7.3-8.5), and 8.6 ng/ml (7.2-8.9). Both HCY and CathK were found positively associated with serum phosphorus (r = 0.584, P < 2.01 and r = 0.249, P < 0.05, respectively). Levels of HCY positively correlate with PTH (r = 0.303, P < 0.01) and inversely with Vitamin B12 (r = -0.248, P < 0.05). No significant association was seen between CathK level and 25(OH) D, iPTH, serum calcium.

CONCLUSION

Low bone mass by DXA is a significant problem in postmenopausal females. HCY and CathK do not reliably correlate with bone loss in postmenopausal women although phosphorus metabolism may play a role.