FORT LAUDERDALE, FLA. — Serum cathepsin K levels could be used to measure treatment response in patients with Paget's disease of bone, Dr. Daniela Merlotti said at a meeting sponsored by the Paget Foundation for Paget's Disease of Bone and Related Disorders.
Cathepsin K, a cysteine protease enzyme, is the most abundantly synthesized protein of the resorbing osteoclast and plays a role in the degradation of organic matrix in the bone, noted Dr. Merlotti of the University of Siena, Italy.
At baseline, serum cathepsin K levels were significantly higher in 60 Paget's disease patients, compared with 50 age-matched controls, and were higher in patients with polyostotic disease than in those with monostotic disease. Baseline cathepsin K correlated positively with cross-linked telopeptide of type I collagen (sCTX) and urinary calcium, but not with total or bone-specific alkaline phosphatase (ALP).
Overall, intravenous bisphosphonate treatment reduced cathepsin K levels by 28% at 3 days, 34% at 30 days, 45% at 3 months, 29% at 6 months, and 32% at 1 year. For the group as a whole, serum ALP dropped by 33% at 30 days and 24% at 90 days, then increased slightly thereafter up to 1 year.
Cathepsin K levels at 3 months predicted treatment response: Patients whose cathepsin K was decreasing at 3 months had an 18% reduction in total serum ALP levels at 6 months. Those whose cathepsin K was rising at 3 months showed a 5% increase in total serum ALP at 6 months.