Role of endogenous reactive oxygen derived species and cyclooxygenase mediators in 5-hydroxytryptamine-induced contractions in rat aorta: relationship to nitric oxide

Deoxynivalenol Induces Drp-1-Mediated Mitochondrial Dysfunction via Elevating Oxidative Stress

Mitochondrial dysfunction is often linked to neurotoxicity and neurological diseases and stems from oxidative stress, yet effective therapies are lacking. Deoxynivalenol (DON or vomitoxin) is one of the most common and hazardous type-B trichothecene mycotoxins, which contaminates crops used for food and animal feed. Despite the abundance of preliminary reports, comprehensive investigations are scarce to explore the relationship between these fungal metabolites and neurodegenerative disorders. The present study aimed to elucidate the precise role of DON in mitochondrial dynamics and cell death in neuronal cells. Excessive mitochondrial fission is associated with the pathology of several neurodegenerative diseases. Human SH-SY5Y cells were treated with different concentrations of DON (250-1000 ng/mL). Post 24 and 48 h DON treatment, the indexes were measured as follows: generation of reactive oxygen species (ROS), ATP levels, mitochondrial membrane potential, calcium levels, and cytotoxicity in SH-SY5Y cells. The results showed that cytotoxicity, intracellular calcium levels, and ROS in the DON-treated group increased, while the ATP levels and mitochondrial membrane potential decreased in a dose-dependent manner. With increasing DON concentrations, the expression levels of P-Drp-1, mitochondrial fission proteins Mff, and Fis-1 were elevated with reduced activities of MFN1, MFN2, and OPA1, further resulting in an increased expression of autophagic marker LC3 and beclin-1. The reciprocal relationship between mitochondrial damage and ROS generation is evident as ROS can instigate structural and functional deficiencies within the mitochondria. Consequently, the impaired mitochondria facilitate the release of ROS, thereby intensifying the cycle of damage and exacerbating the overall process. Using specific hydroxyl, superoxide inhibitors, and calcium chelators, our study confirmed that ROS and Ca2+-mediated signaling pathways played essential roles in DON-induced Drp1 phosphorylation. Therefore, ROS and mitochondrial fission inhibitors could provide critical research tools for drug development in mycotoxin-induced neurodegenerative diseases.

Protective effects and plausible mechanisms of antler-velvet polypeptide against hydrogen peroxide induced injury in human umbilical vein endothelial cells

Antler velvet polypeptide (VAP) is a prominent bioactive component of antler velvet. Whereas uncharacterized crude extracts have typically been used in pharmacological studies, in this study, the velvet polypeptide was isolated and purified by acid water extraction, ethanol precipitation, ammonium sulfate fractionation and precipitation, and chromatography, progressively. Human umbilical vein endothelial cells (HUVECs) were induced with H₂O₂ followed purified polypeptide treatment. Cell viability was evaluated by MTT assay. The apoptosis of cells was detected by fluorescence microscopy and flow cytometry. A cell analyzer was used to measure the mitochondrial membrane potential. The intracellular reactive oxygen species (ROS) levels were determined by flow cytometry. Oxidative stress related biochemical parameters were detected, and the expression of apoptosis-related proteins was examined by Western blot analysis. The results indicated that a 7.0 kDa polypeptide (VAP II) was isolated from antler velvet. VAP II enhanced cell viability, decreased cell apoptosis, reversed depolarization of mitochondrial membrane potential, decreased ROS levels, inhibited oxidative stress, and regulated the downstream signaling apoptotic cascade expression caused by H₂O₂. The protective effects of VAP II on HUVECs suggests a potential strategy for the treatment of cardiovascular disease.

Vasomodulatory effect of novel peroxovanadate compounds on rat aorta: Role of rho kinase and nitric oxide/cGMP pathway

The present study was undertaken to assess the role of reactive oxygen species (ROS) in rat aortic ring vasoreactivity and integrity by using various peroxovanadate (pV) compounds. All the pV compounds (1nM-300 μM) used in the present study exerted concentration-dependent contractions on endothelium intact rat aortic rings. All compounds with an exception of DPV-asparagine (DPV-asn) significantly altered vascular integrity as shown by diminished KCl responses. Phenylephrine (PE)-mediated contractions (3nM-300 μM) were unaltered in the presence of these compounds. Acetylcholine (Ach)-mediated relaxation in PE (1μM) pre-contracted rings was significantly reduced in presence of diperoxovanadate (DPV), poly (sodium styrene sulfonate-co-maleate)-pV (PSS-CoM-pV) and poly (sodium styrene 4-sulfonate)-pV (PSS-pV). However, no significant change in Ach-mediated responses was observed in the presence of poly (acrylate)-pV (PAA-pV) and DPV-asn. DPV-asn was thus chosen to further elucidate mechanism involved in peroxide mediated modulation of vasoreactivity. DPV-asn (30nM - 300 μM) exerted significantly more stable contractions, that was found to be catalase (100U/ml) resistant in comparison with H(2)O(2) (30nM-300 μM) in endothelium intact aortic rings. These contractile responses were found to be dependent on extracellular Ca(2+) and were significantly inhibited in presence of ROS scavenger N-acetylcysteine (100 μM). Intracellular calcium chelation by BAPTA-AM (10μM) had no significant effect on DPV-asn (30nM-300 μM) mediated contraction. Pretreatment of aortic rings by rho-kinase inhibitor Y-27632 (10μM) significantly inhibited DPV-asn-mediated vasoconstriction indicating role of voltage-dependent Ca(2+) influx and downstream activation of rho-kinase. The small initial relaxant effect obtained on addition of DPV-asn (30nM-1 μM) in PE (1 μM) pre-contracted endothelium intact rings, was prevented in the presence of guanylate cyclase inhibitor, methylene blue (10 μM) and/or nitric oxide synthase (NOS) inhibitor, l-NAME (100 μM) suggesting involvement of nitric oxide and cGMP. DPV-asn, like H(2)O(2), exerted a response of vasoconstriction in normal arteries and vasodilation at low concentrations (30nM-1 μM) in PE-pre contracted rings with overlapping mechanisms. These findings suggest usefulness of DPV-asn having low toxicity, in exploring the peroxide-mediated effects on various vascular beds. The present study also convincingly demonstrates role of H(2)O(2) in the modulation of vasoreactivity by using stable peroxide DPV-asn and warrants future studies on peroxide mediated signaling from a newer perspective.

Reactive oxygen species are messengers in maintenance of human and guinea pig gallbladder tonic contraction

The tonic contraction of human and guinea pig gallbladder (GB) is dependent on basal levels of PGE(2) and thromboxane A(2) (TxA(2)). The pathway involved in the genesis of these prostaglandins has not been elucidated. We aimed to examine the source of reactive oxygen species (ROS) and whether they contribute to the genesis of GB tonic contraction by generating basal prostaglandin levels. Tonic contraction was studied in human and guinea pig GB muscle strips treated with ROS scavengers (Tiron and catalase), apocynin (an inhibitor of NADPH oxidase), and NOX-1 small interference RNA (siRNA). The subunits of NADPH oxidase and their functional roles were determined with specific antibodies in GB muscle cells. ROS scavengers reduced the GB tonic contraction and H(2)O(2) and PGE(2) levels. Apocynin also inhibited the tonic contraction. Antibodies against subunits of NADPH oxidase present in GB muscle cells lowered H(2)O(2) and PGE(2) levels. NOX-1 siRNA transfection reduced the tonic contraction, NOX-1 expression, and levels of H(2)O(2) and PGE(2). Tiron and apocynin inhibited the expected increase in tension and H(2)O(2) levels induced by stretching of muscle strips. H(2)O(2) increased the levels of PGE(2) and TxA(2) by increasing platelet-activating factor-like lipids that phosphorylate p38 and cPLA(2) sequentially. H(2)O(2) generated by NADPH oxidase participates in a signal transduction pathway that maintains the GB tonic contraction by activating PAF, p38, and cPLA(2) to generate prostaglandins.

Role of NADPH oxidase and iNOS in vasoconstrictor responses of vessels from hypertensive and normotensive rats

BACKGROUND AND PURPOSE

To analyse the influence of hypertension in the modulation induced by inducible NOS (iNOS)-derived NO and superoxide anion (O(2) (*-)) of vasoconstrictor responses and the sources of O(2) (*-) implicated.

EXPERIMENTAL APPROACH

Vascular reactivity experiments were performed in segments of aorta from normotensive, Wistar Kyoto (WKY) and spontaneously hypertensive rats (SHR); protein and mRNA expressions were respectively measured by western blot and quantitative reverse transcription-polymerase chain reaction and O(2) (*-) production was evaluated by ethidium fluorescence.

KEY RESULTS

The contractile responses to phenylephrine (1 nM-30 microM) and 5-hydroxytryptamine (0.1-100 microM) were greater in aortic segments from SHR than WKY. The selective iNOS inhibitor, 1400W (10 microM), increased the phenylephrine contraction only in WKY segments; however, iNOS protein and mRNA expressions were greater in aorta from SHR than WKY. Superoxide dismutase (SOD, 150 U ml(-1)) reduced phenylephrine and 5-hydroxytryptamine responses only in aorta from SHR; the NAD(P)H oxidase inhibitor apocynin (0.3 mM) decreased phenylephrine and 5-hydroxytryptamine responses more in vessels from SHR than WKY. Co-incubation with SOD plus 1400W potentiated the phenylephrine and 5-hydroxytryptamine responses more in segments from SHR than WKY. O(2) (*-) production was greater in aorta from SHR than WKY; apocynin abolished this difference.

CONCLUSIONS AND IMPLICATIONS

Increased O(2) (*-) formation from NADP(H) oxidase in vessels from hypertensive rats contributes to the vasoconstrictor responses and counteract the increase of NO from iNOS and the consequent modulation of these responses.

Activation of protein kinase B/Akt and endothelial nitric oxide synthase mediates agmatine-induced endothelium-dependent relaxation

The ability of agmatine, formed from L-arginine by the enzyme arginine decarboxylase (ADC), to modulate vasomotor function in rat aorta was investigated in the present study. Agmatine-mediated modulation of vasomotor tone was studied in organ chambers, protein expression quantified by Western blot analysis and cyclic guanosine 5'-monophosphate (cGMP) levels measured by radioimmunoassay. Agmatine (10(-10) to 10(-3) M) produced concentration-dependent relaxations (82+/-5%) in phenylephrine-contracted endothelium intact rat aorta. Relaxations to agmatine were diminished on denudation of endothelium and nitric oxide synthase (NOS) inhibition by L-Nomega-nitro arginine or soluble guanylate cyclase inhibition by 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (P<0.001) abolished agmatine-mediated relaxations, while relaxations were insensitive to inducible NOS inhibition by 1400W. Agmatine-treated aorta demonstrated increased protein expression of phosphorylated S473-Akt and phosphorylated S1177-endothelial nitric oxide synthase (eNOS), and elevated the levels of cyclic GMP (P<0.01). Agmatine-mediated potentiation of relaxations and elevation of cGMP levels was sensitive to phosphatidylinositol 3'-kinase inhibitor, wortmannin. Relaxations to agmatine were also affected by pre-treatment with tetraethylammonium (P<0.01) or apamin (P<0.05), and were not affected by charybdotoxin. Relaxations to agmatine were partially affected by pre-treatment of aortic rings with barium chloride (P<0.05), and glybenclamide (P<0.05). Results obtained suggest that agmatine activates protein kinase B/Akt to phosphorylate eNOS and elevate cyclic GMP levels to produce vasodilatation of aorta. Agmatine-mediated relaxations in rat aorta seems to be mediated mainly by endothelial NO-mediated activation of small conductance Ca2+-activated K+ channels, and partly by ATP-sensitive and inward rectifying K+ channels.

Consomic strategies to localize genomic regions related to vascular reactivity in the Dahl salt-sensitive rat

Chromosomal substitution strains afford the opportunity to discover regions of the rat genome that contain genes related to cardiovascular traits with the long-range goal of linking these genes to physiological function. PhysGen (Programs for Genomic Applications) created a consomic panel of rats derived from the introgression of a single chromosome (> or =95% of the BN chromosome, one at a time) of the Brown Norway (BN/NHsdMcwi) rat onto the homogeneous genetic background of the Dahl salt-sensitive rat (SS/JrHsdMcwi). For 3 wk before the experiment, the rats were maintained on a low-salt diet (0.4% NaCl). The dose response of aortic rings from each strain of rat to phenylephrine, acetylcholine, sodium nitroprusside, and three different levels of tissue bath hypoxia (10, 5, and 0% O2) was measured and compared with the parental SS rat. To maximize the possibility that differences among the strains would become apparent, each strain of rat including the parental SS and BN was also studied after being maintained on a high-salt diet (4.0% NaCl) for 3 wk. If the response of the aortic ring from a consomic strain to these vasoactive substances was different from that of the SS parental strain, it was concluded that the introgressed chromosome contained a gene or genes that contributed to that difference. Because the BN chromosome is removed from its native background and the SS rat loses a native chromosome, it is also necessary to consider the contribution of changes in gene-to-gene interaction.

Hydrogen peroxide is an endothelium-dependent contracting factor in rat renal artery

In addition to endothelium-derived relaxing factor and hyperpolarizing factor, vascular endothelium also modulates smooth muscle tone by releasing endothelium-derived contracting factor(s) (EDCF), but the identity of EDCF remains obscure. We studied here the involvement of hydrogen peroxide (H2O2) in endothelium-dependent contraction (EDC) of rat renal artery to acetylcholine (ACh). ACh (10(-6), 10(-5), and 10(-4) M) induced a transient contraction of rat renal artery with intact endothelium in a concentration-related manner, but not in the artery with endothelium removed. In phenylephrine-precontracted renal arteries, ACh induced an endothelium-dependent relaxation response at lower concentrations (10(-8)-10(-6) M), and a relaxation followed by a contraction at higher concentrations (10(-5) M). Inhibition of nitric oxide synthase by N(omega)-nitro-L-arginine (10(-4) M) enhanced the EDC to ACh. Catalase (1000 U ml(-1)) reduced the EDC to ACh. H2O2 (10(-6), 10(-5), and 10(-4) M) induced a similar transient contraction of the renal arteries as ACh, but in an endothelium-independent manner. Inhibition of NAD(P)H oxidase and cyclooxygenase by diphenylliodonium chloride and diclofenac greatly attenuated ACh-induced EDC, while inhibition of xanthine oxidase (allopurinol) and cytochrome P450 monooxygenase (17-octadecynoic acid) did not affect the contraction. Antagonist of thromboxane A2 and prostaglandin H2 receptors (SQ 29548) and thromboxane A2 synthase inhibitor (furegrelate) attenuated the contraction to ACh and to H2O2. In isolated endothelial cells, ACh (10(-5) M) induced a transient H2O2 production detected with a fluorescence dye sensitive to H2O2 (2',7'-dichlorofluorescein diacetate). The peak concentration of H2O2 was 5.1 x 10(-4) M at 3 min and was prevented by catalase. Taken together, these results show that ACh triggers H2O2 production through NAD(P)H oxidase activation in the endothelial cells, and that ACh and H2O2 share the same signaling pathway in causing smooth muscle contraction. Therefore, H2O2 is most likely the EDCF in rat renal artery in response to ACh stimulation.

Acute and chronic effects of free radicals on α1-adrenergic-induced vasoconstriction in mesenteric beds of spontaneously hypertensive rats

OBJECTIVE

To determine whether free radicals participate in the increased sensitivity of the alpha-adrenergic pathway in mesenteric arteries from spontaneously hypertensive rats (SHRs).

METHODS AND RESULTS

SHRs are characterized by a greater vasoconstriction (P < 0.001) in response to phenylephrine in isolated and perfused mesenteric arteries. Deferoxamine (DFX) produced a significant increase in the phenylephrine-induced vasoconstriction in isolated mesenteric beds from both SHRs (P < 0.001) and Wistar-Kyoto (WKY) rats (P < 0.05), but with a greater magnitude in SHRs (P < 0.01). Acutely, activation of the hypoxanthine-xanthine oxidase (HX-XO) system produced an endothelium- and NO-dependent vasoconstriction at low concentration (P < 0.01), followed by an endothelium-independent vasorelaxation at greater concentrations in phenylephrine-preconstricted mesenteric beds (P < 0.01). Catalase and SOD (P < 0.01) prevented this endothelium-dependent response, whereas the endothelium-independent vasorelaxation induced by HX-XO was blocked by catalase, SOD and DFX (P < 0.01). Chronic administration of a diet deficient in selenium and vitamin E decreased the glutathione peroxidase activity in erythrocytes and plasma from SHRs and WKY rats (P < 0.001). Moreover, the deficient diet significantly increased the sensitivity of mesenteric arteries to phenylephrine in SHRs (P < 0.001) and WKY rats (P < 0.05), whereas it decreased acetylcholine-induced vasodilatation in SHRs only (P < 0.05). The KCl-induced vasoconstriction in response to oxygen radicals was enhanced only in mesenteric bed from SHRs.

CONCLUSION

Free radicals seem to potentiate the alpha-adrenergic pathway acutely in low concentrations and to sensitize this pathway chronically in SHRs. These observations may explain the potentiated response to alpha-adrenergic agonists observed in SHRs.