Enhanced estradiol-induced vasorelaxation in aortas from type 2 diabetic mice may reflect a compensatory role of p38 MAPK-mediated eNOS activation

Impact of different hormones on the regulation of nitric oxide in diabetes

Polymetabolic syndrome achieved pandemic proportions and dramatically influenced public health systems functioning worldwide. Chronic vascular complications are the major contributors to increased morbidity, disability, and mortality rates in diabetes patients. Nitric oxide (NO) is among the most important vascular bed function regulators. However, NO homeostasis is significantly deranged in pathological conditions. Additionally, different hormones directly or indirectly affect NO production and activity and subsequently act on vascular physiology. In this paper, we summarize the recent literature data related to the effects of insulin, estradiol, insulin-like growth factor-1, ghrelin, angiotensin II and irisin on the NO regulation in physiological and diabetes circumstances.

Downregulation of the expression of galanin impairs erectile function in hypoandrogenic rats

Background

The relationship between galanin and erectile function under low androgen levels is still unclear.

Aim

To explore whether a low testosterone level damages the erection of a rat by regulating the expression of galanin and GalR in penile cavernous tissue.

Methods

Thirty-six male Sprague-Dawley rats, 8 weeks of age, were randomly grouped as follows (n = 6): control, castration, castration + testosterone replacement, control + transfection, castration + transfection, and castration + empty transfection. At 4 weeks after castration, rats in the transfection group were injected with lentivirus carrying the targeting galanin gene (2 × 10⁸ TU/mL, 10 μL) in the corpus cavernosum. After 1 week of injection, the intracavernosal pressure (ICP), mean arterial blood pressure (MAP), nitric oxide (NO), serum testosterone concentration, galanin, GalR1-3, ROCK1, ROCK2, and p-eNOS/eNOS in the rat penile tissues were evaluated.

Outcomes

ICPmax/MAP and the expression of galanin in the corpus cavernosum in castrated rats were obviously decreased as compared with those in the control rats.

Results

The castrated rats showed remarkably lower ICPmax/MAP, galanin, GalR1-3, p-eNOS/eNOS, and NO content and markedly higher ROCK1 and ROCK2 in penile tissues than the control group (P < .05). The transfected rats administrated with LV Gal had obviously higher ICPmax/MAP, p-eNOS/eNOS, and NO content and less ROCK1 and ROCK2 protein expression in the corpus cavernosum when compared with the castration group (P < .05).

Clinical Translation

Upregulating the expression of galanin in the penile corpus cavernosum might be a novel method of treating erectile dysfunction caused by a low androgen level.

Strengths and Limitations

The conclusions obtained in the animal experiments need to be confirmed in human data.

Conclusion

The erectile function of hypoandrogen rats might be inhibited by downregulating the level of galanin and GalR1-3, upregulating ROCK1 and ROCK2 levels, and inhibiting the eNOS/NO signaling pathway in penile corpus cavernosum.

In utero hypoxia attenuated acetylcholine-mediated vasodilatation via CHRM3/p-NOS3 in fetal sheep MCA: role of ROS/ERK1/2

Hypoxia can lead to adult middle cerebral artery (MCA) dysfunction and increase the risk of cerebrovascular diseases. It is largely unknown whether intrauterine hypoxia affects fetal MCA vasodilatation. This study investigated the effects and mechanisms of intrauterine hypoxia on fetal MCA vasodilatation. Near-term fetal sheep were exposed to intrauterine hypoxia. Human umbilical vein endothelial cells (HUVECs) were exposed to hypoxia in cellular experiments. Vascular tone measurement, molecular analysis, and transmission electron microscope (TEM) were utilized to determine vascular functions, tissue anatomy, and molecular pathways in fetal MCA. In fetal MCA, acetylcholine (ACh) induced reliable relaxation, which was markedly attenuated by intrauterine hypoxia. Atropine, P-F-HHSiD, L-NAME, and u0126 blocked most ACh-mediated dilation, while AF-DX 116 and tropicamide partially inhibited the dilation. Indomethacin and SB203580 did not significantly change ACh-mediated dilation. Tempol and PS-341 could restore the attenuated ACh-mediated vasodilatation following intrauterine hypoxia. The mRNA expression levels of CHRM2 and CHRM3 and the protein levels of CHRM3, p-NOS3, SOD2, ERK1/2, p-ERK1/2, MAPK14, and p-MAPK14 were significantly reduced by intrauterine hypoxia. The dihydroethidium assay showed that the production of ROS was increased under intrauterine hypoxia. TEM analysis revealed endothelial cells damaged by intrauterine hypoxia. In HUVECs, hypoxia increased ROS formation and decreased the expression of CHRM3, p-NOS3, SOD1, SOD2, SOD3, ERK1/2, p-ERK1/2, and p-MAPK14, while tempol and PS-341 potentiated p-NOS3 protein expression. In conclusion, in utero hypoxia reduced ACh-mediated vasodilatation in ovine MCA predominantly via decreased CHRM3 and p-NOS3, and the decreased NOS3 bioactivities might be attributed to ROS and ERK1/2.

Bufalin inhibits peritoneal dissemination of gastric cancer through endothelial nitric oxide synthase-mitogen-activated protein kinases signaling pathway

Peritoneal dissemination threatens the survival of patients with gastric cancer (GC). Bufalin is an extract of traditional Chinese medicine, which has been proved to have anticancer effect. The target of bufalin in suppressing gastric cancer peritoneal dissemination (GCPD) and the underlying mechanism are still unclear. In this research, GC cell line MGC-803 and high-potential peritoneal dissemination cell line MKN-45P were treated with bufalin or L-NAME. Malignant biological behavior and protein level of GC cell lines were detected with MTT, wound healing, transwell, adhesion, and western blotting. Bioinformatics analysis and patient tissues were used to verify the role of endothelial nitric oxide synthase (NOS3) in GC. Mice model was used to assess the effect of bufalin and role of NOS3 in vivo. We found that bufalin inhibited the proliferation, invasion, and migration in GC cell lines. NOS3, which was an independent prognostic factor of GC patients, was predicted to be a potential target of bufalin. Further experiments proved that bufalin reduced the phosphorylation of NOS3, thereby inhibiting the mitogen-activated protein kinase (MAPK) signaling pathway, and ultimately suppressed GCPD by inhibiting EMT process. In conclusion, NOS3 was a potential therapeutic target and prognostic biomarker of GC. Bufalin could suppress GCPD through NOS3-MAPK signaling pathway, which provided more evidence support for intraperitoneal perfusion of bufalin to treat GCPD.

Impairment of Protease-Activated Receptor 2-Induced Relaxation of Aortas of Aged Spontaneously Hypertensive Rat

Hypertension is one of the most prevalent diseases worldwide and can cause harmful complications within the vascular system. Further research on vascular responsiveness to different ligands and diverse receptors in various arteries is required to understand the mechanisms underlying the development of these vascular complications. Here, we investigated the vasorelaxant effect of the protease-activated receptor 2 (PAR2) agonist 2-furoyl-LIGRLO-amide (2-Fly) and two commonest agents, namely endothelium-dependent dilator acetylcholine (ACh) and endothelium-independent dilator sodium nitroprusside (SNP), on the thoracic aorta isolated from aged spontaneously hypertensive rats (SHR) (age, 52±1 weeks). The effects of these agents were compared between aortas isolated from SHR and age-matched normotensive Wistar Kyoto (WKY) rats. Compared with the WKY group, in the SHR group, 2-Fly-induced relaxation was impaired, ACh-induced relaxation was slightly decreased at low concentrations, and SNP-induced relaxation was similar. In addition, 2-Fly-induced aortic relaxation was largely decreased by a PAR2 antagonist (FSLLRY), endothelial denudation, and a nitric oxide (NO) synthase inhibitor N^G-nitro-L-arginine (L-NNA) but not by an Akt inhibitor. These results suggested that PAR2-induced relaxations of aortas of aged SHR was impaired, and this impaired aortic relaxation may be attributed to decreased NO bioavailability rather than altered NO sensitivity unrelated to the Akt activity.

Alteration of Vascular Responsiveness to Uridine Adenosine Tetraphosphate in Aortas Isolated from Male Diabetic Otsuka Long-Evans Tokushima Fatty Rats: The Involvement of Prostanoids

We investigated whether responsiveness to dinucleotide uridine adenosine tetraphosphate (Up₄A) was altered in aortas from type 2 diabetic Otsuka Long-Evans Tokushima Fatty (OLETF) rats compared with those from age-matched control Long-Evans Tokushima Otsuka (LETO) rats at the chronic stage of disease. In OLETF aortas, we observed the following: (1) Up₄A-induced contractions were lower than those in the LETO aortas under basal conditions, (2) slight relaxation occurred due to Up₄A, but this was not observed in phenylephrine-precontracted LETO aortas, (3) acetylcholine-induced relaxation was reduced (vs. LETO), and (4) prostanoid release (prostaglandin (PG)F_2α, thromboxane (Tx)A₂ metabolite, and PGE₂) due to Up₄A was decreased (vs. LETO). Endothelial denudation suppressed Up₄A-induced contractions in the LETO group, but increased the contractions in the OLETF group. Under nitric oxide synthase (NOS) inhibition, Up₄A induced contractions in phenylephrine-precontracted aortas; this effect was greater in the LETO group (vs. the OLETF group). The relaxation response induced by Up₄A was unmasked by cyclooxygenase inhibitors, especially in the LETO group, but this effect was abolished by NOS inhibition. These results suggest that the relaxant component of the Up₄A-mediated response was masked by prostanoids in the LETO aortas and that the LETO and OLETF rats presented different contributions of the endothelium to the response.

Effect of Long-Term Diabetes on Serotonin-Mediated Contraction in Carotid Arteries from Streptozotocin-Induced Diabetic Male and Female Rats

An accumulating body of evidence suggests that males and females differ in vascular function in arteries under pathophysiological states. In this study, we tested whether there was a sex difference associated with serotonin (5-hydroxytryptamine, 5-HT)-mediated contraction in the carotid arteries of long-term streptozotocin (STZ)-induced diabetic rats [viz. 23 or 24 weeks after STZ (65 mg/kg, intravenously (i.v.)) injection starting at 8 weeks old of rats]. In the control group, the 5-HT- and high-K⁺-induced contractions were greater in females than in males. In both sexes, treatment with STZ led to a decrease of 5-HT-induced contraction in carotid arteries compared to controls. In STZ-induced diabetic rats, the carotid arterial 5-HT-induced contraction was greater in female rats than in diabetic male rats. The high-K⁺-induced contraction was greater in diabetic female rats than in either age-matched female controls or diabetic male rats. Expression of the 5-HT_2A receptor, which is the main receptor for 5-HT-induced contraction in rat carotid arteries, was similar among the four groups. These results suggest that decreased 5-HT-induced carotid arterial contraction is seen in both sexes under long-term STZ-induced diabetic conditions. Further, this reduction seems to be weaker in females than in males. This alteration of 5-HT-induced contraction may be partly associated with increased voltage-dependent Ca²⁺ channel activity.

Age-Related Reduction of Contractile Responses to Urotensin II Is Seen in Aortas from Wistar Rats but Not from Type 2 Diabetic Goto-Kakizaki Rats

Vascular dysfunction is a common finding in type 2 diabetes, although the response to urotensin II (UII), a potent vasoconstrictor peptide, remains unclear. We investigated whether a UII-induced contraction was increased in the aortas from type 2 diabetic Goto-Kakizaki (GK) rats at the chronic stage. At 36 or 37 weeks of age (older group), a UII-induced contraction was seen in GK rats and was reduced by a Rho kinase inhibitor or urotensin receptor (UT) antagonist, whereas UII failed to induce a contraction in aortas from age-matched Wistar rats. In UII-stimulated aortas, the expression of Rho kinases, Rho A, and phosphorylated myosin phosphatase target subunit 1 did not change between the two groups; however, phosphorylation of extracellular-regulated kinase 1/2 and p38 mitogen-activated protein kinase (MAPK) was greater in GK than in Wistar rats. Compared to intact aortas, UII-induced contractions were slightly, but not significantly, increased by endothelial denudation of the aortas of Wistar rats at 24 weeks of age. At 6 weeks of age (young group), the UII-induced contractions were seen in GK and Wistar groups. The total expression and the membrane-to-cytosol ratio of the UT protein slightly decreased in Wistar aortas with aging but not in GK aortas. These results demonstrate that the UII-induced contraction gradually decreased with aging in Wistar rats and was preserved in type 2 diabetes. Although alterations of UII-induced contractions during aging and type 2 diabetes may be associated with kinase activities (MAPKs or Rho kinase) or receptor profiles, further investigations are necessary to clarify the mechanisms.

Glucose and angiotensin II-derived endothelial extracellular vesicles regulate endothelial dysfunction via ERK1/2 activation

In various diseases, including diabetes, extracellular vesicles (EVs) have been detected in circulation and tissues. EVs are small membrane vesicles released from various cell types under varying conditions. Recently, endothelial cell-derived EVs (EEVs) were identified as a marker of endothelial dysfunction in diabetes, but the ensuing mechanisms remain poorly understood. In this study, we dissected the ensuing pathways with respect to nitric oxide (NO) production under the condition of type 2 diabetes. Human umbilical vein endothelial cells (HUVECs) were stimulated with glucose alone and with glucose in combination with angiotensin II (Ang II) for 48 h. In supernatants from glucose + Ang II-stimulated HUVECs, release of EEVs was assessed using Western blotting with an anti-CD144 antibody. EEV release was significantly increased after stimulation of HUVECs, and high glucose + Ang II-derived EEVs impaired ACh-induced vascular relaxation responses and NO production in mice aortic rings. Furthermore, high glucose + Ang II-derived EEVs induced ERK1/2 signalling and decreased endothelial NO synthase (eNOS) protein expression in mice aortas. Furthermore, in the presence of the MEK/ERK1/2 inhibitor PD98059, high glucose plus Ang II treatment stimulated EEVs in HUVECs and those EEVs prevented the impairments of ACh-induced relaxation and NO production in mice aortas. These data strongly indicate that high glucose and Ang II directly affect endothelial cells and the production of EEVs; the resultant EEVs aggravate endothelial dysfunction by regulating eNOS protein levels and ERK1/2 signalling in mice aortas.

Differential Effects of E2 on MAPK Activity in the Brain and Heart of Aged Female Rats

Aging and the coincident loss of circulating estrogens at menopause lead to increased risks for neurological and cardiovascular pathologies. Clinical studies show that estrogen therapy (ET) can be beneficial in mitigating these negative effects, in both the brain and heart, when it is initiated shortly after the perimenopausal transition. However, this same therapy is detrimental when initiated >10 years postmenopause. Importantly, the molecular mechanisms underlying this age-related switch in ET efficacy are unknown. Estrogen receptors (ERs) mediate the neuroprotective and cardioprotective functions of estrogens by modulating gene transcription or, non-genomically, by activating second messenger signaling pathways, such as mitogen activated protein kinases (MAPK). These kinases are critical regulators of cell signaling pathways and have widespread downstream effects. Our hypothesis is that age and estrogen deprivation following menopause alters the expression and activation of the MAPK family members p38 and ERK in the brain and heart. To test this hypothesis, we used a surgically induced model of menopause in 18 month old rats through bilateral ovariectomy (OVX) followed by an acute dose of 17β-estradiol (E2) administered at varying time points post-OVX (1 week, 4 weeks, 8 weeks, or 12 weeks). Age and E2 treatment differentially regulated kinase activity in both the brain and heart, and the effects were also brain region specific. MAPK signaling plays an integral role in aging, and the aberrant regulation of those signaling pathways might be involved in age-related disorders. Clinical studies show benefits of ET during early menopause but detrimental effects later, which might be reflective of changes in kinase expression and activation status.

The gender differences in the inhibitory action of UVB-induced melanocyte activation by the administration of tranexamic acid

BACKGROUND

Tranexamic acid has an inhibitory action on ultraviolet (UV) B-induced melanocyte activation. This study examined the sex differences in the inhibitory action of tranexamic acid on UVB-induced melanocyte activation.

METHODS

We irradiated the eye and ear of male and female mice with UVB at a dose of 1.0 kJ/m(2) using a 20SE sunlamp. We orally administered tranexamic acid (750 mg/kg/day) at 30 min before UVB exposure.

RESULTS

Tranexamic acid inhibited the UVB-induced epidermal melanocyte activation, and the effect was more remarkable under UVB eye irradiation than under UVB ear irradiation. Furthermore, the melanocyte activity suppression effect was stronger in female mice than in male mice. Following the administration of tranexamic acid, the female displayed increased blood levels of β-endorphin and μ-opioid receptor and estradiol receptor β expression in comparison with the male. Furthermore, the effect of melanocyte activity suppression in the female mice was decreased by the administration of tamoxifen (antagonist of estrogen receptor) or naltrexone (antagonist of μ-opioid receptor).

CONCLUSIONS

These results suggest that the suppression by tranexamic acid of the UVB-induced melanocyte activation (UVB sensitivity) is stronger in female mice than in male mice and that female hormones and β-endorphin play an important role in this sex difference.

Tissue-specific up-regulation of arginase I and II induced by p38 MAPK mediates endothelial dysfunction in type 1 diabetes mellitus

BACKGROUND AND PURPOSE

Emerging evidence suggests a selective up-regulation of arginase I in diabetes causing coronary artery disease; however, the mechanisms behind this up-regulation are still unknown. Activated p38 MAPK has been reported to increase arginase II in various cardiovascular diseases. We therefore tested the role of p38 MAPK in the regulation of arginase I and II expression and its effect on endothelial dysfunction in diabetes mellitus.

EXPERIMENTAL APPROACH

Endothelial function was determined in septal coronary (SCA), left anterior descending coronary (LAD) and mesenteric (MA) arteries from healthy and streptozotocin-induced diabetic Wistar rats by wire myographs. Arginase activity and protein levels of arginase I, II, phospho-p38 MAPK and phospho-endothelial NOS (eNOS) (Ser(1177) ) were determined in these arteries from diabetic and healthy rats treated with a p38 MAPK inhibitor in vivo.

KEY RESULTS

Diabetic SCA and MA displayed impaired endothelium-dependent relaxation, which was prevented by arginase and p38 MAPK inhibition while LAD relaxation was not affected. Arginase I, phospho-p38 MAPK and eNOS protein expression was increased in diabetic coronary arteries. In diabetic MA, however, increased expression of arginase II and phospho-p38 MAPK, increased arginase activity and decreased expression of eNOS were observed. All these effects were reversed by p38 MAPK inhibition.

CONCLUSIONS AND IMPLICATIONS

Diabetes-induced activation of p38 MAPK causes endothelial dysfunction via selective up-regulation of arginase I expression in coronary arteries and arginase II expression in MA. Therefore, regional differences appear to exist in the arginase isoforms contributing to endothelial dysfunction in type 1 diabetes mellitus.

Effect of Chronic Administration of Estradiol on Responsiveness of Isolated Systemic and Pulmonary Blood Vessels from Ovariectomized Wistar Rats with Hypoxic Pulmonary Hypertension

The long-term (4 weeks) administration of estradiol (15 μg/kg/day) to ovariectomized female Wistar rats induced hypoxic pulmonary hypertension and significantly (p<0.05) diminished relaxation of perfused serotonin-preconstricted isolated vascular segments of the pulmonary artery in response to estradiol (10(-6) M). At the same time, the isolated segments of systemic popliteal artery demonstrated a diminished response to serotonin and increased relaxation induced by acetylcholine (10(-5) M) or estradiol (10(-5) M) in comparison with preconstricted control vessels. Moderation of responsiveness to estradiol in pulmonary circulation can be one of the factors underlying the pro-hypertensive action of estradiol in female rats with hypoxic pulmonary hypertension.

Regulation of endothelial nitric oxide synthase and high-density lipoprotein quality by estradiol in cardiovascular pathology

Estrogens have been recognized, in the last 3 decades, as important hormones in direct and indirect modulation of vascular health. In addition to their direct benefit on cardiovascular health, the presence of esterified estrogen in the lipid core of high-density lipoprotein (HDL) particles indirectly contributes to atheroprotection by significantly improving HDL quality and functionality. Estrogens modulate their physiological activity via genomic and nongenomic mechanisms. Genomic mechanisms are thought to be mediated directly by interaction of the hormone receptor complex with the hormone response elements that regulate gene expression. Nongenomic mechanisms are thought to occur via interaction of the estrogen with membrane-bound receptors, which rapidly activate intracellular signaling without binding of the hormone receptor complex to its hormone response elements. Estradiol in particular mediates early and late endothelial nitric oxide synthase (eNOS) activation via interaction with estrogen receptors through both nongenomic and genomic mechanisms. In the vascular system, the primary endogenous source of nitric oxide (NO) generation is eNOS. Nitric oxide primarily influences blood vessel relaxation, the heart rate, and myocyte contractility. The abnormalities in expression and/or functions of eNOS lead to the development of cardiovascular diseases, both in animals and in humans. Although considerable research efforts have been dedicated to understanding the mechanisms of action of estradiol in regulating cardiac eNOS, more research is needed to fully understand the details of such mechanisms. This review focuses on recent findings from animal and human studies on the regulation of eNOS and HDL quality by estradiol in cardiovascular pathology.

Enhanced uridine adenosine tetraphosphate-induced contraction in renal artery from type 2 diabetic Goto-Kakizaki rats due to activated cyclooxygenase/thromboxane receptor axis

The dinucleotide uridine adenosine tetraphosphate (Up4A), which has both purine and pyrimidine moieties, was reported as a novel endothelium-derived contracting factor. Recently, growing evidence has suggested that Up4A plays an important role in regulation of the cardiovascular function. We previously demonstrated that Up4A-induced vasoconstrictions are altered in arteries from DOCA-salt hypertensive rats. We have assessed responses to Up4A shown by renal arteries from type 2 diabetic Goto-Kakizaki (GK) rats (42-46 weeks old) and identified the molecular mechanisms involved. Concentration-dependent contractions to Up4A were greater in renal arterial rings from the GK than age-matched control Wistar group. In both groups, the inhibition of nitric oxide synthase (with N (G)-nitro-L-arginine) increased the response to Up4A, whereas the inhibition of cyclooxygenase (COX) (with indomethacin) decreased the response. Specific inhibitors of COX-1 (valeroyl salicylate) and COX-2 (NS398), a thromboxane (TX) receptor (TP) antagonist (SQ29548), and P2 receptor antagonist (suramin) also decreased the response to Up4A. Protein expressions of COXs in renal arteries were greater in the GK than Wistar group. The production of TXB2 (a metabolite of TXA2) by Up4A did not differ between these groups. Concentration-dependent contractions to U46619, an agonist of the TP receptor, were greater in renal arteries from the GK than Wistar group. The expression of P2X1 and P2Y2 receptors did not differ between these groups. These results suggest that enhancement of the Up4A-induced contraction in renal arteries from GK rats may be attributable to the increased activation of COXs/TP receptor signaling.