Bone alkaline phosphatase in rheumatic diseases

Area of Science:

• Biochemistry
• Rheumatology
• Immunology

Background:

• Elevated total alkaline phosphatase (TAP) is common in active rheumatoid arthritis (RA) and ankylosing spondylitis (AS).
• The origin of elevated TAP (bone vs. liver) in these inflammatory rheumatic diseases is not fully understood.

Purpose of the Study:

• To investigate whether elevated total alkaline phosphatase (TAP) in active rheumatoid arthritis (RA) and ankylosing spondylitis (AS) originates from bone or liver.
• To assess the correlation between bone alkaline phosphatase (BAP), TAP, and disease activity in RA and AS.

Main Methods:

• A double monoclonal immunoradiometric assay specific for bone alkaline phosphatase (BAP) was employed.
• Fifty-eight RA patients, 14 AS patients, and 14 non-inflammatory rheumatic disease (NI) patients were studied.
• Disease activity was assessed using plasma viscosity; liver function was monitored via aspartate transaminase and gamma-glutamyl transferase (GGT).

Main Results:

• Elevated BAP concentrations were found in a small subset of patients (7/86), with only two also having abnormal TAP.
• Abnormal TAP activities were observed in only three RA patients.
• BAP did not correlate with disease activity in RA or AS, whereas TAP and GGT correlated with plasma viscosity in RA.

Conclusions:

• The elevated TAP often seen in active RA and AS is unlikely to be primarily derived from bone.
• While TAP and GGT correlate with disease activity in RA, BAP does not show this correlation.
• Further investigation is needed to explain the complex relationships observed between TAP, BAP, GGT, and disease activity in inflammatory rheumatic diseases.