Icariin modulates eNOS activity via effect on post-translational protein-protein interactions to improve erectile function of spontaneously hypertensive rats

3-Hydroxy-3-methylglutaryl-CoA synthase 2 facilitates erectile dysfunction via inhibiting autophagy by enhancing the mammalian target of rapamycin pathway in type 1 diabetic mellitus rats

BACKGROUND

The relationship between erectile dysfunction (ED) and type 1 diabetes mellitus (T1DM) is currently a hot topic of medical research. It has been reported that autophagy plays a crucial role in causing erectile dysfunction in T1DM. Recent research has shown that mitochondrial 3-hydroxy-3-methylglutaryl-CoA synthase 2 (HMGCS2) is strongly linked to the development of T1DM. However, the specific mechanism by which it regulates the erectile function is not yet fully understood.

OBJECTIVES

To investigate whether HMGCS2 affects erectile function in type 1 diabetic rats by regulating autophagy in corpus cavernosum endothelial cells (CCECs).

MATERIALS AND METHODS

First, the rat model of T1DM was established. Then, the ratio of maximum penile intracavernous pressure (ICPmax) and mean arterial pressure (MAP) was detected to assess the erectile function in various groups, and the protein expression of HMGCS2, mTOR and p-mTOR was evaluated by western blot (WB) and immunohistochemistry (IHC). To explore the relationship between HMGCS2 and the mTOR signaling pathway in T1DM ED rats, we silenced the expression of HMGCS2 and activated the mTOR signaling pathway with MHY1485 in CCECs and then assessed the expression of beclin1, P62, LC3, autophagosome, endothelial nitric oxide synthase (eNOS), phosphorylation of eNOS (p-eNOS), and nitric oxide (NO) to evaluate autophagy and the erectile function by reverse transcription quantitative polymerase chain reaction and western blot.

RESULTS

The study conducted on T1DM ED rats showed that the expression of HMGCS2 was significantly increased, while the autophagy was suppressed. Additionally, the mTOR signaling pathway was highly activated. In contrast, when HMGCS2 was silenced in vitro, p-mTOR/mTOR was reduced, and autophagy was improved. These effects were accompanied by the enhanced activity of eNOS. Furthermore, when HMGCS2 was silenced and the mTOR signaling pathway was simultaneously activated, the results revealed a decrease in autophagy as well as a reduction in activity of eNOS in comparison to just silencing HMGCS2 alone.

DISCUSSION AND CONCLUSION

HMGCS2 upregulation in T1DM rats inhibited autophagy and eNOS activity by activating the mTOR pathway and led to a decrease in the erectile function.

"NO" controversy?: A controversial role in insulin signaling of diabetic encephalopathy

Insulin, a critical hormone in the human body, exerts its effects by binding to insulin receptors and regulating various cellular processes. While nitric oxide (NO) plays an important role in insulin secretion and acts as a mediator in the signal transduction pathway between upstream molecules and downstream effectors, holds a significant position in the downstream signal network of insulin. Researches have shown that the insulin-NO system exhibits a dual regulatory effect within the central nervous system, which is crucial in the regulation of diabetic encephalopathy (DE). Understanding this system holds immense practical importance in comprehending the targets of existing drugs and the development of potential therapeutic interventions. This review extensively examines the characterization of insulin, NO, Nitric oxide synthase (NOS), specific NO pathway, their interconnections, and the mechanisms underlying their regulatory effects in DE, providing a reference for new therapeutic targets of DE.

Caveolae and caveolin-1 as targets of dietary polyphenols for protection against vascular endothelial dysfunction

Caveolae, consisting of caveolin-1 proteins, are ubiquitously present in endothelial cells and contribute to normal cardiovascular functions by acting as a platform for cellular signaling pathways as well as transcytosis and endocytosis. However, caveolin-1 is thought to have a proatherogenic role by inhibiting endothelial nitric oxide synthase activity and Nrf2 activation, or by promoting inflammation through NF-κB activation. Dietary polyphenols were suggested to exert anti-atherosclerotic effects by a mechanism involving the inhibition of endothelial dysfunction, by which they can regulate redox-sensitive signaling pathways in relation to NF-κB and Nrf2 activation. Some monomeric polyphenols and microbiota-derived catabolites from monomeric polyphenols or polymeric tannins might be responsible for the inhibition, because they can be transferred into the circulation from the digestive tract. Several polyphenols were reported to modulate caveolin-1 expression or its localization in caveolae. Therefore, we hypothesized that circulating polyphenols affect caveolae functions by altering its structure leading to the release of caveolin-1 from caveolae, and attenuating redox-sensitive signaling pathway-dependent caveolin-1 overexpression. Further studies using circulating polyphenols at a physiologically relevant level are necessary to clarify the mechanism of action of dietary polyphenols targeting caveolae and caveolin-1.

Methylation of eNOS in the rat penile corpus cavernosum under different pathological states and its relationship with erectile function

BACKGROUND

It has been shown that methylation in the promoter region of eNOS can downregulate eNOS expression resulting in the endothelial dysfunction. However, it is unclear whether low androgen levels and type 1 diabetes cause ED by methylating the promoter region of eNOS in the penile corpus cavernosum.

OBJECTIVE

To clarify the effects of type 1 diabetes and hypo-androgen status on the methylation level of the promoter region of the eNOS gene in penile cavernous tissue and their relationship with the erectile function.

METHODS

Fifty-eight eight-week-old male Sprague-Dawley rats were randomly divided into six groups (n = 6): sham operation group, castration group, castration+testosterone (cast+T) group, normoglycemia group, diabetic group, and diabetic+methyltransferase inhibitor (5-aza-dc, 1.5 mg/kg) group. The ICPmax/MAP, serum T, the concentration of nitric oxide (NO), the expression of DNMT1, DNMT3a, DNMT3b, and eNOS, and the methylation level of the eNOS promoter region in penile corpus cavernosum of rat were examined 4 weeks after surgery in the sham-operated group, the castration group, and the castration + testosterone replacement group. Those tests were examined after 6 weeks using of methylation inhibitors in the normoglycemic group, the diabetic group, and the diabetic + methylation inhibitor group.

RESULTS

ICPmax/MAP, DNMT1, DNMT3a, DNMT3b, eNOS, and NO levels were significantly lower in castrated rats than in sham and cast+T rats (P < 0.05). ICPmax/MAP, eNOS, and NO levels were lower, and DNMT1, DNMT3a, and DNMT3b expression levels were significantly increased in the diabetic group compared with the normoglycemic and diabetic+methyltransferase inhibitor groups (P < 0.05). There was no significant difference in the methylation level of the promoter region of eNOS in penile cavernous tissue of castrated rats compared with the sham group or the testosterone replacement group. The methylation level of the promoter region of eNOS in penile cavernous tissue was significantly higher in the diabetic group than in the normoglycemic group and diabetic+methyltransferase inhibitor group (P < 0.05).

CONCLUSION

Although low androgen status inhibited the level of methyltransferase in rat penile cavernous tissue, did not affect the level of methylation in the promoter region of eNOS. Hyperglycemia inhibits the NO level in the penile cavernous tissue and the erectile function of rats by upregulating the methyltransferase level in the penile cavernous tissue and the methylation level in the promoter region of eNOS. Methylation inhibitors can partly improve the erectile function in type 1 diabetic rats.

Low testosterone state inhibits erectile function by downregulating the expression of GIT1 in rat penile corpus cavernosum

Background

The mechanism of erectile dysfunction (ED) caused by a low androgen level is still not clear.

Aim

To explore the influence of the low testosterone state on G protein-coupled receptor kinase interactor 1 (GIT1) and its contact to erectile function.

Methods

Thirty male Sprague-Dawley rats aged 8 weeks were distributed at random into 5 groups: control (sham operated), castration, testosterone supplement after castration, castration + vacant lentiviral transfection, and castration + lentiviral transfection. The testis and epididymis were removed through a scrotal incision to develop castrated rats. Four weeks after castration, a lentivirus carrying the GIT1 gene was injected into the middle of rat penile corpus cavernosum. One week after transfection, maximum intracavernous pressure/mean arterial pressure (ICPmax/MAP), serum testosterone, nitric oxide, GIT1, endothelial nitric oxide synthase (eNOS), phospho-eNOS (p-eNOS), p-eNOS/eNOS, and the interaction between eNOS and GIT1 were assessed in the rats.

Outcomes

The levels of GIT1 in the penile cavernous tissue of castrated rats are significantly lower than that of controls.

Results

GIT1 was expressed in the cytoplasm and cell membrane of vascular endothelial cells and smooth muscle cells in rat penile tissue. In comparison with normal rats, the castrated rats showed lower levels of GIT1 expression, GIT1 and eNOS interaction, p-eNOS/eNOS, nitric oxide, and ICPmax/MAP (P < .01). Overexpression of GIT1 can intensively enhance the expression level of GIT1, the interaction between GIT1 and eNOS, p-eNOS/eNOS, nitric oxide, and ICPmax/MAP in rats (P < .01).

Clinical Translation

Modulating the interaction between eNOS and GIT1 might be a novel method of treating ED caused by a low androgen level.

Strengths and Limitations

The impact of GIT1 phosphorylation on the activity of eNOS and its possible mechanisms affecting erectile function require further study.

Conclusion

A low testosterone state inhibits erectile function in rats by reducing the expression of GIT1 and the protein interaction between GIT1 and eNOS.

Inhibition of multidrug resistance proteins by MK571 restored the erectile function in obese mice through cGMP accumulation

BACKGROUND

Intracellular levels of cyclic nucleotides can also be controlled by the action of multidrug resistance protein types 4 (MRP4) and 5 (MRP5). To date, no studies evaluated the role of their inhibition in an animal model of erectile dysfunction (ED).

OBJECTIVES

To evaluate the effect of a 2-week treatment with MK571, an inhibitor of the efflux of cyclic nucleotides in the ED of obese mice.

MATERIALS AND METHODS

Mice were divided in three groups: (i) lean, (ii) obese, and (iii) obese + MK571. The corpus cavernosum (CC) were isolated, and concentration-response curves to acetylcholine (ACh), sodium nitroprusside (SNP), and tadalafil in addition to electrical field stimulation (EFS) were carried out in phenylephrine pre-contracted tissues. Expression of ABCC4 and ABCC5, intracellular levels of cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP), the protein levels for pVASP^Ser157 and pVASP^Ser239 , and the intracavernous pressure (ICP) were also determined. The intracellular and extracellular (supernatant) ratios in CC from obese and lean stimulated with a cGMP-increasing substance (BAY 58-2667) in the absence and presence of MK571 (20 μM, 30 min) were also assessed.

RESULTS

The treatment with MK571 completely reversed the lower relaxing responses induced by EFS, ACh, SNP, and tadalafil observed in obese mice CC in comparison with untreated obese mice. Cyclic GMP and p-VASP^Ser239 expression were significantly reduced in CC from obese groups. MK571 promoted a sixfold increase in cGMP without interfering in the protein expression of p-VASP^Ser239 . Neither the cAMP levels nor p-VASP^Ser157 were altered in MK571-treated animals. The ICP was ∼50% lower in obese than in the lean mice; however, the treatment with MK571 fully reversed this response. Expressions of ABCC4 and ABCC5 were not different between groups. The intra/extracellular ratio of cGMP was similar in CC from obese and lean mice stimulated with BAY 58-2667.

CONCLUSIONS

The MRPs inhibition by MK571 favored the accumulation of cGMP in the smooth muscle cells, thus improving the smooth muscle relaxation and the erectile function in obese mice.

Molecular mechanisms regulating the pharmacological actions of icariin with special focus on PI3K-AKT and Nrf-2 signaling pathways

Icariin is a primary active component of the traditional Chinese medicinal plant Epimedium grandiflorum. A range of pharmacological effects of icariin has been researched by modern science to explain its traditional medicinal uses. Attributing to the wide range of pharmacological properties like anti-osteoporosis, anti-inflammation, anti-oxidative stress, anti-depression, and anti-tumor property possessed by icariin, it is now being considered a potential therapeutic agent for a wide variety of disorders ranging from neoplasm, neurodegenerative disorders, osteoporosis, and cardiovascular diseases. Various signaling pathways including NFκB/NALP3, IGF-1, MiR-223-3p/ NALP3, TLR4/ NFκB, and WNT1/β-catenin are involved in the different biological actions exerted by icariin. Apart from these pathways, PI3K-AKT (Phosphoinositide 3 kinase-Protein kinase B) and Nrf-2 (nuclear erythroid 2-related factor 2) signaling pathways are two important pathways that form the fundamental basis for the pharmaceutical efficacy of icariin. This review gives an overview of previous in vitro and in vivo studies that investigated the potential role of icariin via PI3K-AKT and Nrf-2 signaling pathways to provide greater insights into its potential clinical use in a variety of disorders.

Vitamin C Lowers Blood Pressure in Spontaneously Hypertensive Rats by Targeting Angiotensin-Converting Enzyme I Production in a Frequency-Dependent Manner

The lowering blood pressure effect of vitamin C (VC) has been evaluated in various models. As VC has a fast degradation rate in the body after consumption, a study of the frequency-dependent manner of VC is essential for the sustained antihypertension effect of VC. In this study, we investigated the frequency and dose dependency of vitamin C (VC) on blood pressure reduction in spontaneously hypertensive rats (SHRs). Wistar–Kyoto rats (WKYs) and SHRs were orally administered tap water or VC (250, 500, 1000, and 2000 mg/60 kg/day). Blood pressures were measured using the tail-cuff method, and thoracic aortas, liver, and blood were harvested from sacrificed rats after 8 weeks to measure angiotensinogen, angiotensin-converting enzyme (ACE) I, endothelial nitric oxide synthase (eNOS), and total nitric oxide (NOx) concentration. VC decreased blood pressure from the fourth week with no significant differences between doses. The twice-a-day administration of VC decreased blood pressure from the second week, and the blood pressure in these groups was close to that of the WKY group in the eighth week. Treatment with once a day VC decreased ACE I production which was further significantly reduced in twice a day groups. Angiotensinogen and eNOS production were increased upon VC treatment but were not significant among groups. The NOx content was decreased by VC treatment. These results suggest that VC lowers blood pressure in SHRs by directly targeting ACE I production in a frequency-dependent manner and may improve endothelial function depending on the frequency of administration.

Icariin inhibits the formation of mitochondria-associated membranes (MAMs) and improves erectile function in rats treated with prostate radiation

BACKGROUND

Erectile function is usually impaired after radiation therapy in prostate cancer patients. eNOS is a key enzyme in the process of erection. Mitochondria-associated membranes (MAMs) are closely contacted with the production and bioactivity of eNOS.

OBJECTIVE

To study the mechanism of icariin improves the erectile function of rats treated with prostate radiation by controling the expression of MAMs in penile corpus cavernosum.

METHODS

Twenty 8-week-old healthy male SD rats were randomized to four groups: control group, radiation therapy (RT) group, icariin (10 mg/kg/d gavage) group, and RT + icariin (10 mg/kg/d gavage) group (n = 5). In RT group and RT + icariin group, rats were irradiated with X-rays to the prostate region (total dose 37.5 gray; 7.5 gray/day for 5 days). The ICPmax/MAP, NO concentration and the level of IP₃ R1, PACS2, FACL4, nNOS, p-eNOS, and eNOS in rats' penile cavernous tissue was determined 9 weeks after radiation therapy.

RESULTS

Compared with the control group and the RT + icariin group, the ICPmax/MAP of the RT group was remarkably reduced (P<0.05). The levels of p-eNOS/eNOS, nNOS and the concentration of NO in the penile cavernous tissue of the penis in the RT group were remarkably decreased compared to the control group and the RT + icariin group (P<0.05). The levels of IP₃ R1, PACS2, and FACL4 in penile cavernous tissue of the RT group were significantly higher than those in the control group and the RT + icariin group (P<0.05).

CONCLUSIONS

After prostate X-ray radiotherapy in rats, the formation of MAMs may be increased by increased expression of IP₃ R1, PACS2, and FACL4 in penile cavernous tissue, resulting in impaired erectile function. Icariin might increase p-eNOS/eNOS and improve erectile function in rats after prostate radiotherapy by inhibiting the expression of IP₃ R1, PACS2, and FACL4. This article is protected by copyright. All rights reserved.

Comparative Efficacy of Antihypertensive Agents in Flow-Mediated Vasodilation of Patients with Hypertension: Network Meta-Analysis of Randomized Controlled Trial

Hypertension induces both structural and functional changes in blood vessels, thereby increasing endothelial dysfunction, which in turn, contributes to an increase in blood pressure. A popular and widely used noninvasive tool, flow-mediated dilation (FMD), is used to examine peripheral artery endothelium-dependent dilation. This study aimed to compare the efficacies of different classes of antihypertensive agents based on their effects on FMD. PubMed, Embase, and Cochrane Library were queried till November 1, 2020. Comparative studies on the efficacies of two or more antihypertensive agents or placebos for hypertensive patients were included. The outcomes were variations in mean systolic and diastolic blood pressure. Two reviewers independently reviewed and filtered the literature and extracted the data; the Cochrane “risk of bias” method was used to evaluate the methodological quality of the randomized controlled trials. A network meta-analysis was performed using Stata 15.0 software with a total of 49 studies. Subgroup analysis based on age and duration of treatments was performed. As compared to the placebo group, patients receiving the antihypertensive drugs exhibited significantly enhanced FMD (ARB + CCB: 4.01%, 95% CI, 0.92–7.11%, p < 0.001; ACEI + ARB: 2.81%, 95% CI, 1.19–4.43%, p < 0.001; ACEI: 2.55%, 95% CI, 1.34–3.77%, p < 0.001; ARB: 2.22%, 95% CI, 1.05–3.38%, p < 0.001; β-blocker: 2.23%, 95% CI, 0.93–3.52%, p < 0.001). In the SUCRA curve for network meta-analysis, the combination of CCB and ARB was found to be the most effective in increasing FMD (SUCRA = 89.0%), followed by ACEI monotherapy (SUCRA = 74.2%). ARB combined with CCB was superior in improving the endothelial function measured as the FMD; ACEI monotherapy was the most effective treatment among the antihypertension medications. There were no significant differences between antihypertensive drug-based monotherapies.

Diabetes associated with hypertension exacerbated oxidative stress-mediated inflammation, apoptosis and autophagy leading to erectile dysfunction in rats

BACKGROUND

Diabetes or hypertension contributes to erectile dysfunction (ED). We hypothesized that excess reactive oxygen species (ROS) production evoked by diabetes combined with hypertension may further suppress endothelial nitric oxide (NO) expression/activity and promote oxidative stress in the ED penis.

METHODS

Twenty-four adult male Wistar Kyoto rats (WKY) and spontaneously hypertensive rats (SHR) were divided into four groups: normal WKY, diabetic WKY, normal SHR and diabetic SHR. Intraperitoneal streptozotocin (65 mg/kg) was applied to induce type I diabetes. After 4-week diabetes and/or hypertension induction, we determined the intra-cavernous pressure (ICP) using electrical stimulation of cavernous nerves, intra-cavernosum NO amount using an electrochemical NO probe, and blood ROS using an ultrasensitive chemiluminescence-amplified analyzer. Western blot analysis and immunohistochemistry were used to explore the pathophysiologic mechanisms of inflammation, apoptosis and autophagy in the penis. A novel NO donor, CysaCysd Lu-5 (CCL5, (RCH2CH2S)(R'R"CHCH2S)Fe(NO)2, 1-4 µg), was intravenously administered to these ED rats for evaluating their ICP responses.

RESULTS

In the baseline status, the lucigenin- and luminol-amplified blood ROS were significantly enhanced in the diabetic SHR rats vs normal WKY rats. Significantly decreased ICP, eNOS expression and NO amount were found in the normal SHR, diabetic WKY, and diabetic SHR vs normal WKY rats. Intravenous NO donor L-Arginine markedly increased ICP and NO amount, whereas eNOS inhibitor, Nω-Nitro-L-Arginine methyl ester hydrochloride depressed ICP in all four groups. Diabetes and/or hypertension alone increased fibrosis, proinflammatory NF-kB/ICAM-1 expression, mast cell numbers, CD68 expression and infiltration, Caspase 3-mediated apoptosis, Beclin-1/LC3-II-mediated autophagy and mild Nrf-2/HO-1 expression and depressed eNOS expression in the ED penis. The novel NO donor, CCL5, was more efficient than L-arginine to improve diabetes and/or hypertension-induced ED by the significant increase of ICP.

CONCLUSION

Diabetes combined with hypertension synergistically exacerbated ED through enhanced oxidative stress, inflammation, apoptosis and autophagy and depressed eNOS activity and NO production.

Effect of the icariin on endothelial microparticles, endothelial progenitor cells, platelets, and erectile function in spontaneously hypertensive rats

OBJECTIVES

To investigate the effect of icariin on endothelial microparticles, endothelial progenitor cells, platelets, and erectile function in spontaneously hypertensive rats.

MATERIALS AND METHODS

Twelve 8-week-old healthy male Wistar-Kyoto rats and 12 spontaneously hypertensive rats were randomly divided into four following groups: Wistar-Kyoto control group (normal saline 1 ml/d given by gavage), Wistar-Kyoto + icariin group (icariin 10 mg/kg × d dissolved in 1 ml normal saline and given by gavage), spontaneously hypertensive rats control group (normal saline 1 ml/d given by gavage), and spontaneously hypertensive rats + icariin group (icariin 10 mg/kg × d dissolved in 1 ml normal saline and given by gavage). Four weeks later, the maximum intracavernous pressure/mean arterial pressure, platelet count, mean platelet volume, platelet distribution width, endothelial microparticles, endothelial progenitor cells, and vitronectin receptor were measured in each group.

RESULTS

Under 3 or 5 V electrical stimulation, the maximum intracavernous pressure/mean arterial pressure in the spontaneously hypertensive rats + icariin group (0.23 ± 0.03, 0.38 ± 0.02) was significantly higher compared to the spontaneously hypertensive rats control group (0.12 ± 0.02, 0.20 ± 0.02) (p<0.05). Platelet count, mean platelet volume, and platelet distribution width in the spontaneously hypertensive rats + icariin group (1103.67 ± 107.70 × 10⁹ /L, 9.08 ± 0.50 fl, 11.87 ± 0.45%) were significantly lower than those in the spontaneously hypertensive rats control group (1298.00 ± 89.54 × 10⁹ /L, 9.72 ± 0.44 fl, 13.03 ± 0.59%) (all p < 0.05). Endothelial microparticles, endothelial progenitor cells, and vitronectin receptor in the spontaneously hypertensive rats + icariin group (1.01 ± 0.28%, 1.53 ± 0.65%, 2.13 ± 0.53%) were significantly lower than those in the spontaneously hypertensive rats control group (1.58 ± 0.19%, 2.71 ± 0.64%, 3.76 ± 0.52%) (all p < 0.05). Moreover, maximum intracavernous pressure/mean arterial pressure was strongly negatively correlated with platelet distribution width and vitronectin receptor (r > 0.7), and maximum intracavernous pressure/mean arterial pressure was moderately negatively correlated with mean platelet volume, endothelial microparticles, and endothelial progenitor cells (0.5 < r<0.7).

CONCLUSION

Icariin may improve erectile function in spontaneously hypertensive rats by reducing the content of endothelial microparticles in blood and inhibiting the activation of the platelets. Endothelial microparticles, endothelial progenitor cells, and platelet activation-related (mean platelet volume, platelet distribution width, and vitronectin receptor) can be used as indicators for icariin to improve erectile function in spontaneously hypertensive rats.