The Endothelin Receptor Antagonist CPU0213 is More Effective Than Aminoguanidine to Attenuate Isoproterenol-induced Vascular Abnormality by Suppressing Overexpression of NADPH Oxidas, ETA, ETB, and MMP9 in the Vasculature

Argirein alleviates stress-induced and diabetic hypogonadism in rats via normalizing testis endothelin receptor A and connexin 43

AIM

Argirein (rhein-arginine) is a derivative of rhein isolated from Chinese rhubarb (Rheum Officinale Baill.) that exhibits antioxidant and anti-inflammatory activities. In the present study we investigated the effects of argirein on stress-induced (hypergonadotrophic) and diabetic (hypogonadotrophic) hypogonadism in male rats.

METHODS

Stress-induced and diabetic hypogonadism was induced in male rats via injection of isoproterenol (ISO) or streptozotocin (STZ). ISO-injected rats were treated with argirein (30 mg·kg(-1)·d(-1), po) or testosterone replacement (0.5 mg·kg(-1)·d(-1), sc) for 5 days, and STZ-injected rats were treated with argirein (40-120 mg·kg(-1)·d(-1), po) or aminoguanidine (100 mg·kg(-1)·d(-1), po) for 4 weeks. After the rats were euthanized, blood samples and testes were collected. Serum hormone levels were measured, and the expression of endothelin receptor A (ETA), connexin 43 (Cx43) and other proteins in testes was detected. For in vitro experiments, testis homogenate was prepared from normal male rats, and incubated with ISO (1 μmol/L) or high glucose (27 mmol/L).

RESULTS

ISO injection induced hyper-gonadotrophic hypogonadism characterized by low testosterone and high FSH and LH levels in the serum, whereas STZ injection induced hypogonadotrophic hypogonadism as evidenced by low testosterone and low FSH and LH levels in the serum. In the testes of ISO- and STZ-injected rats, the expression of ETA, MMP-9, NADPH oxidase and pPKCε was significantly increased, and the expression of Cx43 was decreased. Administration of argirein attenuated both the abnormal serum hormone levels and the testis changes in ISO- and STZ-injected rats, and aminoguanidine produced similar actions in STZ-injected rats; testosterone replacement reversed the abnormal serum hormone levels, but did not affect the testis changes in ISO-injected rats. Argirein (0.3-3 μmol/L) exerted similar effects in testis homogenate incubated with ISO or high glucose in vitro.

CONCLUSION

Two types of hypogonadism of male rats exhibit increased expression of ETA and depressed expression of Cx43 in testes, despite different patterns of serum FSH and LH. Argirein alleviates the two types of male hypogonadism via normalizing ETA and Cx43 in testes.

Isoproterenol induces vascular oxidative stress and endothelial dysfunction via a Giα-coupled β2-adrenoceptor signaling pathway

OBJECTIVE

Sustained β-adrenergic stimulation is a hallmark of sympathetic hyperactivity in cardiovascular diseases. It is associated with oxidative stress and altered vasoconstrictor tone. This study investigated the β-adrenoceptor subtype and the signaling pathways implicated in the vascular effects of β-adrenoceptor overactivation.

METHODS AND RESULTS

Mice lacking the β1- or β2-adrenoceptor subtype (β1KO, β2KO) and wild-type (WT) were treated with isoproterenol (ISO, 15 μg.g(-1) x day(-1), 7 days). ISO significantly enhanced the maximal vasoconstrictor response (Emax) of the aorta to phenylephrine in WT (+34%) and β1KO mice (+35%) but not in β2KO mice. The nitric oxide synthase (NOS) inhibitor L-NAME abolished the differences in phenylephrine response between the groups, suggesting that ISO impaired basal NO availability in the aorta of WT and β1KO mice. Superoxide dismutase (SOD), pertussis toxin (PTx) or PD 98,059 (p-ERK 1/2 inhibitor) incubation reversed the hypercontractility of aortic rings from ISO-treated WT mice; aortic contraction of ISO-treated β2KO mice was not altered. Immunoblotting revealed increased aortic expression of Giα-3 protein (+50%) and phosphorylated ERK1/2 (+90%) and decreased eNOS dimer/monomer ratio in ISO-treated WT mice. ISO enhanced the fluorescence response to dihydroethidium (+100%) in aortas from WT mice, indicating oxidative stress that was normalized by SOD, PTx and L-NAME. The ISO effects were abolished in β2KO mice.

CONCLUSIONS

The β2-adrenoceptor/Giα signaling pathway is implicated in the enhanced vasoconstrictor response and eNOS uncoupling-mediated oxidative stress due to ISO treatment. Thus, long-term β2-AR activation might results in endothelial dysfunction.

Hypoxia/oxidative stress alters the pharmacokinetics of CPU86017-RS through mitochondrial dysfunction and NADPH oxidase activation

AIM

Hypoxia/oxidative stress can alter the pharmacokinetics (PK) of CPU86017-RS, a novel antiarrhythmic agent. The aim of this study was to investigate the mechanisms underlying the alteration of PK of CPU86017-RS by hypoxia/oxidative stress.

METHODS

Male SD rats exposed to normal or intermittent hypoxia (10% O2) were administered CPU86017-RS (20, 40 or 80 mg/kg, ig) for 8 consecutive days. The PK parameters of CPU86017-RS were examined on d 8. In a separate set of experiments, female SD rats were injected with isoproterenol (ISO) for 5 consecutive days to induce a stress-related status, then CPU86017-RS (80 mg/kg, ig) was administered, and the tissue distributions were examined. The levels of Mn-SOD (manganese containing superoxide dismutase), endoplasmic reticulum (ER) stress sensor proteins (ATF-6, activating transcription factor 6 and PERK, PRK-like ER kinase) and activation of NADPH oxidase (NOX) were detected with Western blotting. Rat liver microsomes were incubated under N2 for in vitro study.

RESULTS

The Cmax, t1/2, MRT (mean residence time) and AUC (area under the curve) of CPU86017-RS were significantly increased in the hypoxic rats receiving the 3 different doses of CPU86017-RS. The hypoxia-induced alteration of PK was associated with significantly reduced Mn-SOD level, and increased ATF-6, PERK and NOX levels. In ISO-treated rats, the distributions of CPU86017-RS in plasma, heart, kidney, and liver were markedly increased, and NOX levels in heart, kidney, and liver were significantly upregulated. Co-administration of the NOX blocker apocynin eliminated the abnormalities in the PK and tissue distributions of CPU86017-RS induced by hypoxia/oxidative stress. The metabolism of CPU86017-RS in the N2-treated liver microsomes was significantly reduced, addition of N-acetylcysteine (NAC), but not vitamin C, effectively reversed this change.

CONCLUSION

The altered PK and metabolism of CPU86017-RS induced by hypoxia/oxidative stress are produced by mitochondrial abnormalities, NOX activation and ER stress; these abnormalities are significantly alleviated by apocynin or NAC.

Current status of NADPH oxidase research in cardiovascular pharmacology

The implications of reactive oxygen species in cardiovascular disease have been known for some decades. Rationally, therapeutic antioxidant strategies combating oxidative stress have been developed, but the results of clinical trials have not been as good as expected. Therefore, to move forward in the design of new therapeutic strategies for cardiovascular disease based on prevention of production of reactive oxygen species, steps must be taken on two fronts, ie, comprehension of reduction-oxidation signaling pathways and the pathophysiologic roles of reactive oxygen species, and development of new, less toxic, and more selective nicotinamide adenine dinucleotide phosphate (NADPH) oxidase inhibitors, to clarify both the role of each NADPH oxidase isoform and their utility in clinical practice. In this review, we analyze the value of NADPH oxidase as a therapeutic target for cardiovascular disease and the old and new pharmacologic agents or strategies to prevent NADPH oxidase activity. Some inhibitors and different direct or indirect approaches are available. Regarding direct NADPH oxidase inhibition, the specificity of NADPH oxidase is the focus of current investigations, whereas the chemical structure-activity relationship studies of known inhibitors have provided pharmacophore models with which to search for new molecules. From a general point of view, small-molecule inhibitors are preferred because of their hydrosolubility and oral bioavailability. However, other possibilities are not closed, with peptide inhibitors or monoclonal antibodies against NADPH oxidase isoforms continuing to be under investigation as well as the ongoing search for naturally occurring compounds. Likewise, some different approaches include inhibition of assembly of the NADPH oxidase complex, subcellular translocation, post-transductional modifications, calcium entry/release, electron transfer, and genetic expression. High-throughput screens for any of these activities could provide new inhibitors. All this knowledge and the research presently underway will likely result in development of new drugs for inhibition of NADPH oxidase and application of therapeutic approaches based on their action, for the treatment of cardiovascular disease in the next few years.

Beneficial effects of aminoguanidine on skin flap survival in diabetic rats

Random flaps in DM patients have poor reliability for wound coverage, and flap loss remains a complex challenge. The protective effects of aminoguanidine (AG) administration on the survival of dorsal random flaps and oxidative stress were studied in diabetic rats. Two months after the onset of DM, dorsal McFarlane flaps were raised. Forty rats were divided into four groups: (1) control, (2) AG, (3) DM, and (4) DM + AG groups. Flap viability, determined with the planimetric method, and free-radical measurements were investigated. In addition, HbA1c and blood glucose levels, body weight measurements, and histopathological examinations were evaluated. The mean flap necrotic areas (%) in Groups I to IV were 50.9 ± 13.0, 32.9 ± 12.5, 65.2 ± 11.5, and 43.5 ± 14.7, respectively. The malondialdehyde (MDA) and nitric oxide (NO) levels were higher in the DM group than in the nondiabetic group, while the reduced glutathione (GSH) levels and superoxide dismutase (SOD) activity were reduced as a result of flap injury. In the diabetic and nondiabetic groups, AG administration significantly reduced the MDA and NO levels and significantly increased GSH content and SOD enzyme activity. We concluded that AG plays an important role in preventing random pattern flap necrosis.

Argirein alleviates corpus cavernosum dysfunction by suppressing pro-inflammatory factors p66Shc and ER stress chaperone Bip in diabetic rats

Objectives

The aim was to investigate whether argirein, which releases rhein and l-arginine after medication, could improve erectile dysfunction (ED) in diabetic rats through normalising the abnormalities of nitric oxide synthase (NOS), p66Shc and immunoglobulin heavy-chain binding protein (Bip), in the corpus cavernosum (CC).

Methods

SD rats were randomly divided into six groups. Except for the control group, rats were injected with streptozotocin (STZ) (60 mg/kg, i.p.) once. During weeks 5–8 following STZ injection, except for STZ-injected untreated rats, others were treated with aminoguanidine (AMG; 100 mg/kg/day, i.g.), or argirein at three doses (50, 100 and 200 mg/kg/day, i.g.). The vascular activity and biomarkers of the cavernosum were examined.

Key findings

Constrictive and dilative activity was abnormal in the CC, associated with decreased nitric oxide (NO) in serum in the diabetic (DM) group. Increased expression of p66Shc, Bip and inducible nitric oxide synthase (iNOS) and decreased endothelial nitric oxide synthase (eNOS) in the CC were significant in DM rats. Argirein and AMG improved these abnormities significantly.

Conclusions

We concluded that vascular activity of the cavernosal tissue was impaired due to upregulated p66Shc and Bip in the diabetic CC. Argirein alleviates the vascular dysfunction of the CC by suppressing these upregulated pro-inflammatory proteins caused by diabetic lesions.

Sildenafil improves diabetic vascular activity through suppressing endothelin receptor A, iNOS and NADPH oxidase which is comparable with the endothelin receptor antagonist CPU0213 in STZ-injected rats

OBJECTIVES

Abnormal vascular activity in diabetes is related not only to impaired nitric oxide bioavailability but also to inflammatory cytokines, endothelin A receptor (ET(A) ) activation and NADPH oxidase in the vasculature. The potential role of sildenafil in improving vascular function was investigated. Its action was likely blocking upregulated ET(A) and NADPH oxidase, and was compared with the endothelin receptor antagonist CPU0213.

METHODS

Diabetes was induced by single-dose administration of streptozotocin (65 mg/kg, i.p.) to rats and the vascular activity of the thoracic aorta was measured.

KEY FINDINGS

An increase in contractile tone to phenylephrine and a decrease in relaxant tone to acetylcholine was found in the thoracic aorta. Oxidative stress was evident by increased malondialdehyde and reduced glutathione peroxidase levels in serum and upregulation of ET(A), MMP-9 (matrix metalloproteinase-9), inducible nitric oxide synthase and NADPH oxidase p67(phox) were found in the vascular wall. The vascular abnormalities and abnormal biomarkers were attenuated significantly by either sildenafil or CPU0213 along with an improvement of nitric oxide bioavailability and vascular activity.

CONCLUSIONS

Improvement of diabetic vascular abnormal activity by sildenafil results from its suppression of activation of ET(A) and NADPH oxidase in the vasculature, and these actions are comparable with those of the endothelin receptor antagonist CPU0213.

Role of endothelin receptor A and NADPH oxidase in vascular abnormalities

Vascular dilatation is critically impaired in many diseases and is encountered by an upregulated endothelin receptor A (ETA) in the vasculature in association with a decline in nitric oxide bioavailability. Diabetic vasculopathy is characterized as a compromised vascular dilatation, implicated in many diabetic complications. It appears to be activated ETA and NADPH (nicotinamide adenine dinucleotide phosphate) oxidase in the vasculature. Glucose-lowering agents do not always blunt these changes, as these changes may be progressive leading to the end stage of renal disease. The vascular insults by hypertension, hyperglycemia and aging may share the changes with diabetic vascular beds. Endothelin receptor antagonist CPU0213 and ingredients from plant origins such as CPU86017, p-benzyl-tetra-hydro-berberine are effective in attenuating vascular abnormality by normalizing changes of biomarkers in the vascular wall. The early sign of subclinical atherosclerosis presented as an intima media thickness in the carotid may indicate endothelium dysfunction. The reduced ABI (ankle brachial index) has been taken to predict patients at risk for cardiovascular and cerebrovascular events, and an increased risk of mortality from all causes and cardiovascular disease. An application of agents which suppress the activated ET-NADPH oxidase in the vascular wall is beneficial to attenuate vascular abnormalities. It is worth testing the activity of these agents further for the potential in relieving abnormal vascular activity, reducing the risk of morbidity and mortality in patients at risk.

Hypercholesterolaemia induces early renal lesions characterized by upregulation of MMP-9 and iNOS and ETAR: alleviated by a dual endothelin receptor antagonist CPU0213 and simvastatin

Objectives

We aimed to investigate hypercholesterolaemia-induced early renal lesions which result in abnormal expression of endothelin A receptor (ETAR), induced nitric oxide synthase (iNOS) and matrix metalloproteinase 9 (MMP-9). We hypothesized that this is due to an upregulated endothelin (ET) pathway consequent to hypercholesterolaemia and that CPU0213, a dual ET antagonist, could mitigate these changes.

Methods

Rats were randomly divided into four groups: (1), control; (2), high-fat diet for 60 days (HFD); HFD rats medicated in the last 15 days with either (3) CPU0213 (30 mg/kg daily, s.c.) or (4) simvastatin (4 mg/kg daily, p.o.).

Key findings

Body weight, serum triglycerides, total cholesterol and low-density-lipoprotein cholesterol were significantly increased, whereas high-density lipoprotein cholesterol decreased in the HFD group, relative to normal. Meanwhile, these changes were associated with upregulation of mRNA and protein of ETAR, iNOS and MMP-9 in the kidney. The lipid-lowering effect of simvastatin was predominant, lessening abnormal expression of these molecules in the kidney dramatically. Interestingly, CPU0213 significantly normalized expression of mRNA and protein of ETAR, iNOS and MMP-9, comparable with simvastatin, leaving no changes in hyperlipidaemia.

Conclusions

CPU0213 relieves renal lesions by blunting hypercholesterolaemia caused by the upregulated ET system, iNOS and MMP-9 in the kidney. This indicates that CPU0213 is promising in treating patients with end stage renal disease.

Stress-induced cardiac insufficiency relating to abnormal leptin and FKBP12.6 is ameliorated by CPU0213, an endothelin receptor antagonist, which is not affected by the CYP3A suppressing effect of erythromycin

Objectives

Cardiac injury induced by isoprenaline produces stress. This stress can be mediated by the activated endothelin and leptin pathway; thus, the endothelin receptor antagonist CPU0213 may reverse these changes. CPU0213 is metabolized mainly by cytochrome P450 (CYP)3A, thus, erythromycin, an inhibitor of CYP3A, could affect its effects by raising its plasma levels.

Methods

Forty rats were divided into five groups. Group 1 rats were normal. Group 2 rats were administered isoprenaline (1 mg/kg, s.c.) for 10 days. Groups 3, 4 and 5 were administered isoprenaline, but group 3 was given erythromycin (100 mg/kg, p.o.) alone on days six to ten, group 4 was given CPU0213 20 mg/kg (s.c.) on days six to ten, whilst group 5 received erythromycin plus CPU0213 on days six to ten. Measurements were conducted to observe changes in the haemodynamics, cardiac weight index, serum lactate dehydrogenase and creatine kinase levels, and expression of endothelin receptor A (ETa), leptin and its OBRb receptor.

Key findings

In isoprenaline-treated rats, cardiac hypertrophy and dysfunction were found. This was associated with upregulated myocardial leptin protein and OBRb receptor mRNA. Immunohistochemical assay of ETa was upregulated, accompanied with downregulation of FKBP12.6 (calstabin 2) in isoprenaline-treated rats. These effects were significantly reversed by CPU0213. HPLC assay presented an increased plasma level of CPU0213 by erythromycin, but no change in its effects.

Conclusions

CPU0213 improved isoprenaline-induced cardiomyopathy by modulating ETa, leptin and FKBP12.6. However, erythromycin increased plasma levels but did not change its effects.