Cellular phosphate metabolism in patients receiving bisphosphonate therapy

Area of Science:

• Biochemistry
• Nephrology
• Pharmacology

Background:

• Paget's disease of bone is a condition affecting bone turnover.
• Disodium dihydrogen ethylidene-1-hydroxy-1,1-bisphosphonate (EHBP) is used to treat Paget's disease.
• EHBP is known to influence renal tubular reabsorption of orthophosphate (Pi).

Purpose of the Study:

• To investigate the effect of EHBP on plasma and cellular phosphate levels.
• To determine the mechanism and time course of EHBP's action on phosphate regulation.

Main Methods:

• Patients with Paget's disease were treated with oral and intravenous EHBP.
• Plasma and erythrocyte orthophosphate (Pi) concentrations were measured.
• Cellular Pi levels in blood platelets and leukocytes were assessed.

Main Results:

• Oral EHBP treatment increased plasma Pi from 1.02 to 1.67 mmol/l after 2 weeks.
• Intravenous EHBP led to a rapid increase in plasma Pi, peaking 7-11 days later.
• Erythrocyte Pi increased by 31% after 2 weeks of oral EHBP, while plasma Pi increased by 64%.

Conclusions:

• EHBP effectively increases plasma orthophosphate levels in patients with Paget's disease.
• The delayed peak in plasma Pi suggests the effect is not an immediate interaction with the renal transporter.
• EHBP influences the distribution of Pi between plasma and erythrocytes without altering key cellular metabolites or membrane properties.