Effect of selected substances on heat-induced aggregation of albumin, IgG and lysozyme

Compounds capable of inhibiting protein aggregation may find pharmacologica l applications in the treatment of a number of diseases called protein cond ensation diseases [Benedek (1997)], which include cataract, biliary and uri nary lithiasis and certain rheumatic diseases. We examined the effect of se lected compounds on heat-induced aggregation human serum albumin (HSA), IgG and lysozyme. HSA (0.2% w/v in 0.066 M sodium phosphate pH 5.3 at 22 degre es C), IgG (0.5% w/v in 0.066 M Tris pH 8.0 at 22 degrees C), and L (0.2 % w/v in 0.066 M CAPS pH 11.0 at 22 degrees C) were heated for 30 min at 70 d egrees C in the presence or absence of different concentrations of the subs tance under examination and heat-induced aggregation of 100 mu l aliquots w as evaluated by measuring the absorbance at 595 nm using an automatic micro plate reader. In these conditions, inhibition of aggregation could be due t o an anti-denaturant effect or to interferences with the aggregation of den atured molecules, as previously described [Saso, Casini ef al. (1998)]. How ever, this distinction may not be pharmacologically relevant when the targe t of the therapy is the prevention of abnormal phenomena of protein aggrega tion. Inorganic salts like NaCl and CaCl2 were active on the three proteins (IgG > HSA > L) but many ligands of HSA such as tryptophan, N-acetyl-trypt ophan, caprylic acid, capric acid, cholic acid, deoxycholic acid, chenodeox ycholic acid, lithocholic acid and bendazac were active on their carrier bu t not on IgG and L, indicating that the latter proteins are more difficult to protect and that specific anti-denaturant and/or anti-aggregant compound s should be developed.