ELECTROPHORETIC STUDY OF THE PHYSICOCHEMICAL CHARACTERISTICS OF BENCE-JONES PROTEINURIA AND ITS ASSOCIATION WITH KIDNEY DAMAGE

Aim-To identify a physico-chemical criterion, or set of criteria, expl aining and possibly predicting the nephrotoxic behaviour of Bence-Jone s proteins (BJP). Methods-The electrophoretic mobility and isoelectric point (pI) of 92 BJP isolates were determined using various electroph oresis procedures on polyacrylamide gel. The proportions of monomers a nd dimers were determined using sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS PAGE) in 58 cases. PAGE data for 10 BJP isol ates were used to construct Ferguson plots and titration curves. Resul ts-The distribution of electrophoretic mobility and pI values was bimo dal and showed a positive correlation when the pI was above 6. The val ues of these two parameters in 22 patients with renal impairment were not significantly different from those in the patients without renal i mpairment, and the statistical analysis showed no predictive value for the onset of renal impairment. However, patients excreting the lambda light chain isotype had a 2.8-fold higher risk of developing renal im pairment compared with the other patients. Studies of the charge varia tion of the protein with pH indicated three types of behaviour, sugges ting that the charge of BJP is highly variable at physiological pH.Con clusion-It is important to study not only the positivity or negativity of the BJP charge at a given pH, but also its intensity. The study of the BJP titration curves in patients with renal impairment suggests t hat a low charge at physiological urinary pH could predict renal impai rment.