Human Tissue Kallikrein 1 Improves Erectile Dysfunction of Streptozotocin-Induced Diabetic Rats by Inhibition of Excessive Oxidative Stress and Activation of the PI3K/AKT/eNOS Pathway

Objective. To investigate the protective effects and mechanisms of human tissue kallikrein 1 (hKLK1) on type 1 diabetes mellitus- (DM-) induced erectile dysfunction in rats. Materials and Methods. The homozygous transgenic rats (TGR) harboring the hKLK1 gene and age-matched wild-type Sprague Dawley rats (WTR) were involved, and intraperitoneal injection of streptozotocin was utilized to induce diabetes in rats. Forty-eight-week-old male rats were randomly divided into a WTR group, TGR group, diabetic WTR group (WTDM), diabetic TGR group (TGDM), and TGDM with HOE140 group (TGDMH), with eight rats in each group. Twelve weeks later, the erectile response of all rats was detected by cavernous nerve electric stimulation, and corpus cavernosums were harvested to evaluate the levels of cavernous oxidative stress (OS), apoptosis, fibrosis, and involved pathways. Moreover, cavernous smooth muscle cells (CSMC) and endothelial cells (EC) were primarily isolated to build a coculture system for a series of in vitro verification. Results. The hKLK1 gene only existed and was expressed in TGR. Compared to the WTR group, the WTDM group showed a lower erectile response, overactivated OS and apoptosis, inhibited PI3K/AKT/eNOS pathway, and aggravated cavernous fibrosis. However, hKLK1 in the TGDM group could improve these pathological changes induced by DM, while its protective effects could be weakened by HOE140 in the TGDMH group. In the coculture system, hKLK1 could induce CSMC relaxation through activating PI3K/eNOS/cGMP signaling and inhibiting calcium ion influx under physiological condition. It could also resist the increased reactive oxygen species, apoptosis level, and reduced cGMP level in CSMC under high-glucose condition. Conclusions. hKLK1 preserves erectile function of DM rats through its antitissue excessive OS, apoptosis, and fibrosis effects, as well as activation of the PI3K/AKT/eNOS/cGMP pathway in the penis. Moreover, hKLK1 promotes relaxation and prevents high glucose-induced injuries of CSMC mediated by EC-CSMC crosstalk.

Losartan Preserves Erectile Function by Suppression of Apoptosis and Fibrosis of Corpus Cavernosum and Corporal Veno-Occlusive Dysfunction in Diabetic Rats

Background/Aims: Transforming growth factor-β1 (TGF-β1) plays important roles in penile corporal fibrosis and veno-occlusive dysfunction (CVOD). Angiotensin II (Ang II) is critically involved in erectile dysfunction, and blocking of Ang II is more important than inhibition of TGF-β in non-penile tissue fibrosis. However, the role of Ang II in corporal fbrosis and CVOD in a diabetic condition has not been investigated. Methods: Diabetic rats were treated with sildenafil or losartan (an Ang II antagonist) alone or in combination. Intracavernosal pressure, dynamic infusion cavernosometry, and histological and molecular alterations of the corpus cavernosum were examined. Results: Diabetic rats exhibited decreases in erectile response, severe CVOD, apoptosis, fibrosis, and activation of the TGF-β1 pathway. Treatment with sildenafil had a modest effect on erectile response and an insignificant suppressive effect on CVOD, apoptosis, fibrosis, and the TGF-β1 pathway. Although losartan greatly improved the histological and molecular changes and CVOD as compared with sildenafil, its effect on erectile response was low. The combination of sildenafil and losartan had superior effects on these parameters than did either compound alone. Conclusion: Ang II activation may be involved in apoptosis and fibrosis of the corpus cavernosum through Smad and non-Smad pathways, resulting in CVOD and ED. The low efficacy of sildenafil in a diabetic ED rat model was at least partly due to its inadequate effects on apoptosis, fibrosis, and CVOD.

Analysis of erectile responses to H2S donors in the anesthetized rat

Hydrogen sulfide (H2S) is a biologically active endogenous gasotransmitter formed in penile tissue that has been shown to relax isolated cavernosal smooth muscle. In the present study, erectile responses to the H2S donors sodium sulfide (Na2S) and sodium hydrosulfide (NaHS) were investigated in the anesthetized rat. Intracavernosal injections of Na2S in doses of 0.03–1 mg/kg increased intracavernosal pressure and transiently decreased mean arterial pressure in a dose-dependent manner. Blood pressure responses to Na2S were rapid in onset and short in duration. Responses to Na2S and NaHS were similar at doses up to 0.3 mg/kg, after which a plateau in the erectile response to NaHS was reached. Increases in intracavernosal pressure in response to Na2S were attenuated by tetraethylammonium (K+ channel inhibitor) and iberiotoxin (large-conductance Ca2+-activated K+ channel inhibitor), whereas glybenclamide [ATP-sensitive K+ (KATP) channel inhibitor] and inhibitors of nitric oxide (NO) synthase, cyclooxygenase, and cytochrome P-450 epoxygenase had no effect. These data indicate that erectile responses to Na2S are mediated by a tetraethylammonium- and iberiotoxin-sensitive mechanism and that KATP channels, NO, or arachidonic acid metabolites are not involved. Na2S did not alter erectile responses to sodium nitroprusside (NO donor) or cavernosal nerve stimulation, indicating that neither NO nor cGMP metabolism are altered. Thus, Na2S has erectile activity mediated by large-conductance Ca2+-activated K+ channels. It is suggested that strategies that increase H2S formation in penile tissue may be useful in the treatment of erectile dysfunction when NO bioavailability, KATP channel function, or poor responses to PGE1 are present.