Hydrochlorothiazide inhibits osteoclastic bone resorption in vitro

Area of Science:

• Pharmacology
• Bone Biology
• Mineral Metabolism

Background:

• Long-term thiazide diuretic use is linked to improved bone mineral density and reduced hip fracture risk.
• This effect is thought to be mediated by increased serum calcium and reduced parathyroid hormone activity, leading to decreased bone resorption.

Purpose of the Study:

• To investigate the direct effect of hydrochlorothiazide (HCTZ) on bone resorption by osteoclasts.
• To determine the concentration-dependent efficacy and potential cytotoxicity of HCTZ on bone cells.

Main Methods:

• In vitro bone slice assay using isolated rat osteoclasts.
• Assessment of osteoclast survival and osteoblast proliferation (UMR-106 rat osteoblasts).
• Dose-response analysis to determine the IC50 for HCTZ inhibition of bone resorption.

Main Results:

• Hydrochlorothiazide (HCTZ) dose-dependently inhibited bone resorption by isolated rat osteoclasts with an IC50 of approximately 20 microM.
• HCTZ did not affect osteoclast survival or osteoblast proliferation at tested concentrations (1-100 microM), indicating no cytotoxicity.
• Therapeutic concentrations of HCTZ in humans are significantly lower than those showing in vitro effects on bone resorption.

Conclusions:

• In vitro, HCTZ directly inhibits osteoclast-mediated bone resorption.
• The observed in vitro effects may not be clinically relevant in humans due to low achievable concentrations.
• The mechanism may involve the inhibition of osteoclast carbonic anhydrase.