Aging of proteins: immunological detection of a glucose-derived pyrrole formed during maillard reaction in vivo.

Recent work from this laboratory revealed that glucose-derived pyrroles can form with model amines under physiological conditions (Niroge, F. G., Sayre, L. M., and Monnier, V. M. (1987) Carbohydr. Res. 167, 211-220). The major extractable product, 5-hydroxymethyl-1-alkylpyrrole-2-carbaldehyde (named by us pyrraline) was labile to acid hydrolysis. To allow its detection in proteins undergoing advanced glycosylation, an enzyme-linked immunosorbent assay was developed. An immunogen consisting of epsilon-caproyl pyrraline (hapten) was linked onto poly-L-lysine (114:1) and used to raise polyclonal antibodies in the rabbit. High antibody titers were obtained 16 weeks after immunization. The antibody cross-reacted with butyl pyrraline (88%), propyl pyrraline (8%), lysyl pyrraline (2%), and neopentyl pyrraline (1.3%). A time-related increase in pyrraline immunoreactivity was observed in bovine serum albumin incubated with glucose (1000 mM), glycated lysine (50 mM), and 3-deoxyglucosone (50 mM) which reached 25, 300, and 350 pmol/mg, respectively, after 30 days. Mean level of protein pyrraline immunoreactivity were 27.0 +/- 7.2 and 43.3 +/- 11.7 pmol/mg in serum albumin from control and diabetic subjects, respectively (p less than 0.001). The pathobiological relevance of pyrraline may relate to its reported antiproteolytic and mutagenic properties. In addition, glucose-derived pyrroles may play a role in diabetic neuropathy in analogy to pyrroles formed during hexane-induced neuropathy.