The Role of Regulatory Proteins and S‐nitrosylation of Endothelial Nitric Oxide Synthase in the Human Clitoris: Implications for Female Sexual Function

Effect of folic acid on the sexual function of postmenopausal women: a triple-blind randomized controlled trial

BACKGROUND

There are reports of sexual dysfunction in postmenopausal women, and several treatment recommendations are available.

AIM

To investigate the effect of folic acid on postmenopausal women's sexual function.

METHODS

This triple-blind randomized controlled trial was conducted in Tehran, Iran, in 2020. A sample of 100 postmenopausal women was recruited from comprehensive health centers affiliated with the Shahid Beheshti University of Medical Sciences. Eligible women were randomly assigned to receive folic acid (5 mg) or placebo on an empty stomach every day for 8 weeks. Women were assessed at 3 time points: baseline and 4 and 8 weeks after the intervention.

OUTCOME

Sexual function was the main outcome, as measured by the Female Sexual Function Index.

RESULTS

The mean ± SD age of participants in the folic acid and placebo groups was 53.2 ± 3.84 and 54.4 ± 4.05 years, respectively (P = .609). The results obtained from mixed effects analysis of variance revealed a statistically significant difference between baseline and posttreatment scores and the interaction between time and group for desire, orgasm, satisfaction, arousal, pain, and total sexual function score, with the folic acid group improving more than control group. Lubrication was the only domain that showed no significant difference for the interaction between time and group.

CLINICAL IMPLICATIONS

Folic acid may beneficially affect sexual function in postmenopausal women.

STRENGTHS AND LIMITATIONS

Strengths include the novelty of the subject, the triple-blind design, the block randomization, the administration of a standard scale for sexual function (Female Sexual Function Index), and the affordability and availability of folic acid. This study was conducted with a small sample size and short follow-up time; therefore, interpretation of the results requires great caution.

CONCLUSION

The findings suggest that folic acid possibly improves sexual function in postmenopausal women. Larger studies are needed to confirm the findings.

TRIAL REGISTRATION

IRCT20150128020854N8; August 2, 2020. Iranian Registry of Clinical Trials; https://en.irct.ir/user/trial/48920/view.

NADPH diaphorase detects S-nitrosylated proteins in aldehyde-treated biological tissues

NADPH diaphorase is used as a histochemical marker of nitric oxide synthase (NOS) in aldehyde-treated tissues. It is thought that the catalytic activity of NOS promotes NADPH-dependent reduction of nitro-blue tetrazolium (NBT) to diformazan. However, it has been argued that a proteinaceous factor other than NOS is responsible for producing diformazan in aldehyde-treated tissues. We propose this is a NO-containing factor such as an S-nitrosothiol and/or a dinitrosyl-iron (II) cysteine complex or nitrosated proteins including NOS. We now report that (1) S-nitrosothiols covalently modify both NBT and TNBT, but only change the reduction potential of NBT after modification, (2) addition of S-nitrosothiols or β- or α-NADPH to solutions of NBT did not elicit diformazan, (3) addition of S-nitrosothiols to solutions of NBT plus β- or α-NADPH elicited rapid formation of diformazan in the absence or presence of paraformaldehyde, (4) addition of S-nitrosothiols to solutions of NBT plus β- or α-NADP did not produce diformazan, (5) S-nitrosothiols did not promote NADPH-dependent reduction of tetra-nitro-blue tetrazolium (TNBT) in which all four phenolic rings are nitrated, (6) cytoplasmic vesicles in vascular endothelial cells known to stain for NADPH diaphorase were rich in S-nitrosothiols, and (7) procedures that accelerate decomposition of S-nitrosothiols, markedly reduced NADPH diaphorase staining in tissue sections subsequently subjected to paraformaldehyde fixation. Our results suggest that NADPH diaphorase in aldehyde-fixed tissues is not enzymatic but is due to the presence of NO-containing factors (free SNOs or nitrosated proteins such as NOS), which promote NADPH-dependent reduction of NBT to diformazan.

Protective effects of irbesartan and benazepril against vaginal vascular remodeling and fibrosis in female spontaneously hypertensive rats

Objective

To compare the potential beneficial effects of the angiotensin converting enzyme inhibitor (ACEI) benazepril and the angiotensin II receptor 1 blocker (ARB) irbesartan on vaginal vascular remodeling and fibrosis in female spontaneously hypertensive rats (SHRs).

Methods

Twelve-week-old female SHRs were treated with irbesartan or benazepril for 12 weeks. Vaginal renin angiotensin system (RAS) components were detected by polymerase chain reaction and western blot and vaginal α-smooth muscle actin (α-SMA), endothelial nitric oxide synthase (eNOS), and collagen III (Col III) were analyzed by western blot. Vaginal tissue sections were examined by hematoxylin and eosin staining, Masson trichrome staining, and immunohistochemical analysis of α-SMA and Col III.

Results

Irbesartan and benazepril had different impacts on vaginal RAS components. Both agents decreased vaginal α-SMA and Col III and increased eNOS expression in SHR. The wall/lumen thickness ratio of vaginal arterioles was similarly decreased following irbesartan and benazepril treatment. Both drugs also decreased collagen deposition in SHRs. There was no difference in vaginal vascular remodeling or fibrosis between the two groups.

Conclusions

Irbesartan and benazepril have different effects on vaginal RAS expression but similar positive effects against vaginal vascular remodeling and fibrosis.

Transnitrosylation: A Factor in Nitric Oxide-Mediated Penile Erection

INTRODUCTION

Nitric oxide (NO) signaling can be mediated not only through classic 3',5'-cyclic guanosine monophosphate but also through S-nitrosylation. However, the impact of S-nitrosylation on erectile function and in NO regulation and oxidative stress in the penis remains poorly understood.

AIMS

To characterize the role of S-nitrosoglutathione reductase (GSNOR), a major regulator of S-nitrosylation homeostasis, on erection physiology and on endothelial NO synthase (eNOS) function and oxidative-nitrosative stress in the penis.

METHODS

Adult GSNOR-deficient and wild-type (WT) mice were used. Erectile function was assessed in response to electrical stimulation of the cavernous nerve. Total NO in penile homogenates was measured by Griess reaction. Protein S-nitrosylation, eNOS phosphorylation on Ser-1177 (positive regulatory site), eNOS uncoupling, and markers of oxidative stress (4-hydroxy-2-nonenal, malondialdehyde, and nitrotyrosine) in the penis were measured by western blot.

MAIN OUTCOME MEASURES

Erectile function, eNOS function, and oxidative stress in the penis of GSNOR-deficient mice.

RESULTS

Erectile function was intact in GSNOR-deficient mice. Total S-nitrosylated proteins were increased (P < .05) in the GSNOR(-/-) compared with WT mouse penis. Although eNOS phosphorylation on Ser-1177 did not differ between the GSNOR(-/-) and WT mouse penises at baseline, electrical stimulation of the cavernous nerve increased (P < .05) phosphorylated eNOS in the WT mouse penis but failed to increase phosphorylated eNOS in the GSNOR(-/-) mouse penis. Total NO production was decreased (P < .05), whereas eNOS uncoupling, 4-hydroxy-2-nonenal, malondialdehyde, and nitrotyrosine were increased (P < .05) in the GSNOR-deficient mouse penis compared with the WT mouse penis.

CONCLUSION

Transnitrosylation mechanisms play an important role in regulating NO bioactivity in the penis. Deficiency of GSNOR leads to eNOS dysfunction and increased oxidative damage, suggesting that homeostatic eNOS function in the penis is governed by transnitrosylation.

Flibanserin for hypoactive sexual desire disorder: place in therapy

The pathophysiology, diagnosis and treatment of female sexual interest in pre- and post-menopausal women present a complex arena for patients and physicians to navigate. Flibanserin was the first pharmacologic treatment, approved by the United States Food and Drug Administration in August 2015, for hypoactive sexual desire disorder (HSDD) in premenopausal women. Side effects, contraindications and lack of approval in postmenopausal women are all limitations, as are issues surrounding patient and physician knowledge and access. Testosterone, buspirone, sildenafil, bupropion, bremelanotide, as well as herbal medications (Herbal vX or Tribulus terrestris) have demonstrated some clinical benefit in women with sexual dysfunction disorders however, trials have significant design, dosing or generalizability limitations. Nonpharmaceutical cognitive behavioral therapy, mindfulness meditation, pelvic floor therapy, and clitoral stimulators are also interventions women may pursue. This manuscript will explore the clinical data regarding these therapeutic modalities so as to bring attention to this issue of female HSDD, to offer an overview of current research, and to incite providers to initiate discussion among themselves and their patients.