ADVANCED GLYCATION END-PRODUCTS IN HUMAN PENIS - ELEVATION IN DIABETIC TISSUE, SITE OF DEPOSITION, AND POSSIBLE EFFECT THROUGH INOS OR ENOS

Objectives. We hypothesized that advanced glycation end product (AGE) formation contributes to erectile dysfunction (ED) by quenching nitric oxide. Our first goal was to identify the specific AGE pentosidine in the diabetic human penis. Because AGE-mediated effects may involve in ducible nitric oxide synthase (iNOS), we performed immunohistochemical and Western blot analysis of diabetic and nondiabetic human penile ti ssue for iNOS. Finally, because AGEs may act intracellularly to affect proteins, we set out to identify endothelial NOS (eNOS) in the human penis as an initial step in examining a possible intracellular interac tion between eNOS and AGEs. Methods. We performed high-performance liq uid chromatographic analysis of diabetic human penile corpus cavernosu m and serum for pentosidine and performed immunohistochemical, electro n microscopic (EM), and Western blot analysis of the diabetic and nond iabetic penile corpus cavernosum and tunica for pyrraline, iNOS, and e NOS (and neural NOS [nNOS] for comparative purposes) via standard meth ods. Results. We found a significant elevation of pentosidine in the p enile tissue but not the serum of diabetic patients (average age 55.6 +/- 2.3 years) compared with that of nondiabetic patients (average age 61.8 +/- 3.6 years). Pentosidine was 117.06 +/- 9.19 pmol/mg collagen in the diabetic tunica versus 77.58 +/- 5.5 pmol/mg collagen in the n ondiabetic tunica (P < 0.01) and 74.58 +/- 8.49 pmol/mg collagen in th e diabetic corpus cavernosum versus 46.59 +/- 2.53 pmol/mg collagen in the nondiabetic corpus cavernosum (P < 0.01), suggesting a tissue-spe cific effect of the AGEs. We localized the site of deposition of the s pecific AGE pyrraline to the human penile tunica and the penile corpus cavernosum collagen. Immunohistochemical and EM analysis localized eN OS and iNOS to the cavernosal endothelium and smooth muscle. Western b lot analysis in 6 patients revealed the following: iNOS, but no eNOS, in penile tissue from 1 insulin-dependent diabetic man; eNOS only in 1 man after radical prostatectomy; both eNOS and iNOS in 2 men with Pey ronie's disease, as well as in 2 other men with impotence and hyperten sion. Finally, the specific iNOS inhibitor PNU-19451A significantly au gmented relaxation of precontracted human cavernosal tissue, from 64.7 % +/- 5.58 to 80.03% +/- 4.55 at 10 mu M acetylcholine and 65.06% +/- 2.84 to 86.16% +/- 3.96 at 0.1 mM acetylcholine (n = 4, P < 0.002 and P < 0.02, respectively). Conclusions. AGEs are elevated in diabetic hu man penile tissue, but not in serum, and are localized to the collagen of the penile tunica and corpus cavernosum. We identified eNOS and iN OS in the human penile cavernosal smooth muscle and endothelium. The a ugmentation of cavernosal relaxation with a specific iNOS inhibitor, c ombined with the identification of iNOS protein, but not eNOS, in a pa tient with severe diabetes and ED, allows for speculation of a pathoph ysiologic mechanism for AGE-mediated ED via upregulation of iNOS and d ownregulation of eNOS. These data provide further insight into the mec hanisms of advanced glycation end product-mediated ED and provide a fo undation for further study. (C) 1997, Elsevier Science Inc. All rights reserved.