Oxidative stress mediates monocrotaline-induced alterations in tenascin expression in pulmonary artery endothelial cells

Role of oxidative stress versus lipids in monocrotaline-induced pulmonary hypertension and right heart failure

Pulmonary hypertension (PH) is a global health issue with a prevalence of 10% in ages >65 years. Right heart failure (RHF) is the main cause of death in PH. We have previously shown that monocrotaline (MCT)-induced PH and RHF are due to an increase in oxidative stress. In this study, probucol (PROB), a strong antioxidant with a lipid-lowering property, versus lovastatin (LOV), a strong lipid-lowering drug with some antioxidant effects, were evaluated for their effects on the MCT-induced RHF. Rats were treated (I.P.) with PROB (10 mg/kg ×12) or LOV (4 mg/kg ×12), daily 6 days before and 6 days after a single MCT injection (60 mg/kg). Serial echocardiography was performed and at 4-week post-MCT, lung wet-to-dry weight, hemodynamics, RV glutathione peroxidase (GSHPx), superoxide dismutase (SOD), catalase, lipid peroxidation, and myocardial as well as plasma lipids were examined. MCT increased RV systolic and diastolic pressures, wall thickness, RV end diastolic diameter, mortality, and decreased ejection fraction as well as pulmonary artery acceleration time. These changes were mitigated by PROB while LOV had no effect. Furthermore, PROB prevented lipid peroxidation, lowered lipids, and increased GSHPx and SOD in RV myocardium. LOV did decrease the lipids but had no effect on antioxidants and lipid peroxidation. A reduction in oxidative stress and not the lipid-lowering effect of PROB may explain the prevention of MCT-induced PH, RHF, and mortality. Thus targeting of oxidative stress as an adjuvant therapy is suggested.

HMGB1 is mechanistically essential in the development of experimental pulmonary hypertension

Pulmonary hypertension (PH) is a mortal disease featuring pulmonary vascular constriction and remodeling, right heart failure, and eventual death. Several reports showed that high-mobility group box 1 (HMGB1) appears to be critical for the development of PH; the underlying mechanism, however, has not been revealed. Experiments in the present study demonstrated that HMGB1 levels were elevated in the lung tissue and blood plasma of rats after chronic hypoxia exposure and monocrotaline treatment. HMGB1 was originally located within the nucleus and translocated to the cytoplasm of pulmonary artery smooth muscle cells (PASMCs) upon hypoxia exposure, a process that appeared to be mediated by endogenous H₂O₂. Exposure to HMGB1 mobilized calcium signaling in PASMCs, a response that was attenuated by extracellular Ca²⁺ removal, Toll-like receptor 4 (TLR4) inhibition by TAK-242, or transient receptor potential channel (TRPC) suppression with 2-aminoethoxydiphenyl borate (2-APB) and SKF-96365. The sustained phosphorylation of the Akt pathway modulated HMGB1-induced migration of PASMCs. The blockage of HMGB1 with glycyrrhizin or anti-HMGB1 neutralizing antibody attenuated lung inflammation and PH establishment in rats after hypoxia exposure and monocrotaline treatment. The above findings reveal the mechanistic importance of HMGB1 in PH through TLR4- and TRPC-associated Ca²⁺ influx and Akt phosphorylation-driven PASMC migration.

Hypoxia and Redox Signaling on Extracellular Matrix Remodeling: From Mechanisms to Pathological Implications

SIGNIFICANCE

The extracellular matrix (ECM) is an essential modulator of cell behavior that influences tissue organization. It has a strong relevance in homeostasis and translational implications for human disease. In addition to ECM structural proteins, matricellular proteins are important regulators of the ECM that are involved in a myriad of different pathologies. Recent Advances: Biochemical studies, animal models, and study of human diseases have contributed to the knowledge of molecular mechanisms involved in remodeling of the ECM, both in homeostasis and disease. Some of them might help in the development of new therapeutic strategies. This review aims to review what is known about some of the most studied matricellular proteins and their regulation by hypoxia and redox signaling, as well as the pathological implications of such regulation.

CRITICAL ISSUES

Matricellular proteins have complex regulatory functions and are modulated by hypoxia and redox signaling through diverse mechanisms, in some cases with controversial effects that can be cell or tissue specific and context dependent. Therefore, a better understanding of these regulatory processes would be of great benefit and will open new avenues of considerable therapeutic potential.

FUTURE DIRECTIONS

Characterizing the specific molecular mechanisms that modulate matricellular proteins in pathological processes that involve hypoxia and redox signaling warrants additional consideration to harness the potential therapeutic value of these regulatory proteins. Antioxid. Redox Signal. 27, 802-822.

Expression of key enzymes in the mevalonate pathway are altered in monocrotaline-induced pulmonary arterial hypertension in rats

Pulmonary arterial hypertension (PAH) is a serious pulmonary vascular disease. The changes in the structure, function and metabolism of endothelial cells are some of the important features of PAH. Previous studies have demonstrated that the mevalonate pathway is important in cardiovascular remodeling. However, whether the mevalonate pathway is involved in the development of PAH remains to be elucidated. The present study aimed to investigate the expression pattern of mevalonate pathway-related enzymes in monocrotaline (MCT)-induced PAH. F344 rats were randomly divided into two groups (n=6/group): Control group rats were injected with a single dose of saline, and MCT group rats were injected with a single dose of MCT (60 mg/kg). After 4 weeks, the right ventricular systolic pressure (RVSP) was measured, and lung and pulmonary artery tissue samples were collected. It was demonstrated that the RVSP increased and pulmonary vascular remodeling was detected in the PAH group. The expression levels of the enzymes farnesyldiphosphate synthase farnesyltransferase α and geranylgeranyltransferase type I increased in the PAH group, which suggested that the mevalonate pathway may be involved in the pathological development of PAH.

Monocrotaline Induces Endothelial Injury and Pulmonary Hypertension by Targeting the Extracellular Calcium-Sensing Receptor

BACKGROUND

Monocrotaline has been widely used to establish an animal model of pulmonary hypertension. The molecular target underlying monocrotaline-induced pulmonary artery endothelial injury and pulmonary hypertension remains unknown. The extracellular calcium-sensing receptor (CaSR) and particularly its extracellular domain hold the potential structural basis for monocrotaline to bind. This study aimed to reveal whether monocrotaline induces pulmonary hypertension by targeting the CaSR.

METHODS AND RESULTS

Nuclear magnetic resonance screening through WaterLOGSY (water ligand-observed gradient spectroscopy) and saturation transfer difference on protein preparation demonstrated the binding of monocrotaline to the CaSR. Immunocytochemical staining showed colocalization of monocrotaline with the CaSR in cultured pulmonary artery endothelial cells. Cellular thermal shift assay further verified the binding of monocrotaline to the CaSR in pulmonary arteries from monocrotaline-injected rats. Monocrotaline enhanced the assembly of CaSR, triggered the mobilization of calcium signaling, and damaged pulmonary artery endothelial cells in a CaSR-dependent manner. Finally, monocrotaline-induced pulmonary hypertension in rats was significantly attenuated or abolished by the inhibitor, the general or lung knockdown or knockout of CaSR.

CONCLUSIONS

Monocrotaline aggregates on and activates the CaSR of pulmonary artery endothelial cells to trigger endothelial damage and, ultimately, induces pulmonary hypertension.

Naringenin adds to the protective effect of L-arginine in monocrotaline-induced pulmonary hypertension in rats: favorable modulation of oxidative stress, inflammation and nitric oxide

The present study was directed to investigate the possible modulatory effect of naringenin when co-administered with L-arginine in monocrotaline-induced pulmonary hypertension in rats. Pulmonary hypertension was induced by a single subcutaneous injection of monocrotaline (60 mg/kg). L-arginine (500 mg/kg) and naringenin (50 mg/kg) were orally administered daily, alone and in combination, for 3 weeks. Mean arterial blood pressure, electrocardiography and echocardiography were then recorded and rats were sacrificed and serum was separated for determination of total nitrate/nitrite level. Right ventricles and lungs were isolated for estimation of oxidative stress markers, tumor necrosis factor-alpha, total nitrate/nitrite and transforming growth factor-beta. Myeloperoxidase and caspase-3 activities in addition to endothelial and inducible nitric oxide synthase protein expression were also determined. Moreover, histological analysis of pulmonary arteries and cardiomyocyte cross-sectional area was performed. Combined therapy provided a significant improvement in L-arginine protective effect toward preserving hemodynamic changes and alleviating oxidative stress, inflammatory and apoptotic markers induced by monocrotaline treatment. Furthermore, combined therapy prevented monocrotaline-induced changes in endothelial and inducible nitric oxide synthase protein expression as well as histological analysis compared with either treatment alone. In conclusion, naringenin significantly adds to the protective effect of L-arginine in pulmonary hypertension induced by monocrotaline in rats.

Protection of oral hydrogen water as an antioxidant on pulmonary hypertension

This study aimed to explore the protective effect of hydrogen as an antioxidant on monocrotaline (MCT)-induced pulmonary hypertension (PH). Forty-eight SD rats were equally randomized into four groups: SHAM group, MCT group, MCT+Oral-H₂ group and MCT+Inj-H₂ group. The results showed that the mean pulmonary arterial pressure, right ventricle weight and right ventricular hypertrophy index in MCT group were significant higher than those in SHAM group; pulmonary inflammatory response, atrial natriuretic factor, 3-nitrityrosine and intercellular adhesion molecule-1 were also increased significantly in MCT group. These indexes were decreased significantly in both MCT+Oral-H₂ group and MCT+Inj-H₂ group, which indicate Oral-H₂ and Inj-H₂ have similar effects of preventing the development of PH and mitigating RV hypertrophy. The protective effect of hydrogen is associated with its antioxidative ability and action of reducing pulmonary inflammatory response. While Oral-H₂ is more convenient than Inj-H₂, Oral-H₂ may be ideal for clinical use in future.

Endothelium-specific GTP cyclohydrolase I overexpression attenuates blood pressure progression in salt-sensitive low-renin hypertension

BACKGROUND

Tetrahydrobiopterin (BH4) is an essential cofactor of endothelial nitric oxide synthase (eNOS). When BH4 levels are decreased, eNOS becomes uncoupled to produce superoxide anion (O2(-)) instead of NO, which contributes to endothelial dysfunction. Deoxycorticosterone acetate (DOCA)-salt hypertension is characterized by a suppressed plasma renin level due to sodium retention but manifests in eNOS uncoupling; however, how endogenous BH4 regulates blood pressure is unknown. GTP cyclohydrolase I (GTPCH I) is the rate-limiting enzyme for de novo BH4 synthesis. This study tested the hypothesis that endothelium-specific GTPCH I overexpression retards the progression of hypertension through preservation of the structure and function of resistance mesenteric arteries.

METHODS AND RESULTS

During 3 weeks of DOCA-salt treatment, arterial blood pressure was increased significantly in wild-type mice, as determined by radiotelemetry, but this increase was attenuated in transgenic mice with endothelium-specific GTPCH I overexpression (Tg-GCH). Arterial GTPCH I activity and BH4 levels were decreased significantly in wild-type DOCA-salt mice, but both were preserved in Tg-GCH mice despite DOCA-salt treatment. Significant remodeling of resistance mesenteric arteries (approximately 100-microm outside diameter) in wild-type DOCA-salt mice exists, evidenced by increased medial cross-sectional area, media thickness, and media-lumen ratio and overexpression of tenascin C, an extracellular matrix glycoprotein that contributes to hypertrophic remodeling; all of these effects were prevented in DOCA-salt-treated Tg-GCH mice. Furthermore, NO-mediated relaxation in mesenteric arteries was significantly improved in DOCA-salt-treated Tg-GCH mice, in parallel with reduced O2(-) levels. Finally, phosphorylation of eNOS at serine residue 1177 (eNOS-S1177), but not its dimer-monomer ratio, was decreased significantly in wild-type DOCA-salt mice compared with sham controls but was preserved in DOCA-salt-treated Tg-GCH mice.

CONCLUSIONS

These results demonstrate that endothelium-specific GTPCH I overexpression abrogates O2(-) production and preserves eNOS phosphorylation, which results in preserved structural and functional integrity of resistance mesenteric arteries and lowered blood pressure in low-renin hypertension.

Dietary fish oil protects against lung and liver inflammation and fibrosis in monocrotaline treated rats

The purpose of the present study was to evaluate the effectiveness of fish oil in preventing tissue pathologies associated with monocrotaline (MCT) toxicity. Twenty-four weanling rats were randomly assigned to one of two groups: (1) 12 to a group fed a diet containing 15% (w/w) corn oil (control) and (2) 12 to a group fed a diet containing fish oil (13%) and corn oil (2%) as the source of fat. Rats were fed for 4 weeks prior to MCT treatment. Six rats in each group were subcutaneously injected with MCT and six injected with its vehicle (water) and all were continued on their respective diets. All rats were sacrificed 3 weeks after injection. In rats receiving MCT, we observed severe interstitial pneumonia, septal fibrosis, vasculitis with virtual obliteration of the lumen of the small arteries and arterioles, right ventricular hypertrophy (RVH), and hepatomegaly and hepatocyte vacuole formation. Dietary fish oil significantly reduced septal fibrosis and development of pneumonia. There was a slight, but statistically insignificant decrease in vasculitis and fish oil did not prevent RVH (pulmonary hypertension). In addition, fish oil effectively protected the MCT-treated rats from development of hepatocyte vacuoles (steatosis), hepatic inflammation and vasculitis, increased presence of fibroblasts and collagen deposition in the centrilobular and, to a lesser extent, in the periportal spaces. These results suggest that lung parenchymal inflammation can be attenuated without altering the course of development of pulmonary hypertension in the MCT model. These results also indicate that fish oil protects against inflammation and fibrosis in the lung and liver, and against hepatocyte vacuole formation in MCT-treated rats.

Effects of monocrotaline on endothelial nitric oxide synthase expression and sulfhydryl levels in rat lungs

The nitric oxide-cyclic guanosine monophosphate signal-transduction mechanism plays a key role in the regulation of vascular tone and structure. Monocrotaline-induced pulmonary hypertension is associated with low bioavailability of nitric oxide. To characterize the mechanism(s) involved in this dysfunction, rats received a single subcutaneous injection of monocrotaline, normal saline (control), or monocrotaline plus daily L-arginine, a precursor of nitric oxide, in drinking water. Pulmonary artery pressure and right ventricular hypertrophy were assessed 2 weeks later. In addition, the authors evaluated the expression of endothelial nitric oxide synthase messenger RNA, endothelial nitric oxide synthase protein, cyclic guanosine monophosphate, and sulfhydryl levels in the lungs. Sulfhydryls are needed for the dynamic modulation of soluble guanylate cyclase by nitric oxide, which results in cyclic guanosine monophosphate formation. L-arginine treatment did not attenuate monocrotaline-induced pulmonary hypertension or right ventricular hypertrophy. Monocrotaline did not alter the expression of endothelial nitric oxide synthase messenger RNA or endothelial nitric oxide synthase protein in the lungs. Protein-bound sulfhydryls (28 +/- 5 vs. 75 +/- 16 pmol/microg protein) and cyclic guanosine monophosphate (0.63 +/- 0.05 vs. 1.06 +/- 0.017 pmol/microg protein) levels in the monocrotaline group were significantly low compared with controls. The low sulfhydryl levels, an indicator of oxidant stress, may account for the impaired availability of bioactive nitric oxide and low cyclic guanosine monophosphate levels. These results suggest that oxidative stress may, in part, contribute to the pathogenesis of pulmonary hypertension in the monocrotaline model.

Blockade of alpha 5 beta 1 integrins reverses the inhibitory effect of tenascin on chemotaxis of human monocytes and polymorphonuclear leukocytes through three-dimensional gels of extracellular matrix proteins

Tenascin is an extracellular matrix protein found in adults in T cell-dependent areas of lymphoid tissues, sites of inflammation, and tumors. We report here that it inhibited chemotaxis of chemoattractant-stimulated human monocytes and chemoattractant-stimulated polymorphonuclear leukocytes (PMN) through three-dimensional gels composed of collagen I or Matrigel, and chemotaxis of leukotriene B4-stimulated PMN through fibrin gels. The inhibitory effect of tenascin on monocyte or PMN chemotaxis through these matrices was reversed by Abs directed against alpha5beta1 integrins or by a peptide (GRGDSP) that binds to beta1 integrins. Tenascin did not affect leukotriene B4- or fMLP-stimulated expression of beta1 or beta2 integrins, but did exert a small inhibitory effect on PMN adhesion and closeness of apposition to fibrin(ogen)-containing surfaces. Thus, alpha5beta1 integrins mediate the inhibitory effect of tenascin on monocyte and PMN chemotaxis, without promoting close apposition between these leukocytes and surfaces coated with tenascin alone or with tenascin bound to other matrix proteins. This contrasts with the role played by alpha5beta1 integrins in promoting close apposition between fMLP-stimulated PMN and fibrin containing surfaces, thereby inhibiting chemotaxis of fMLP-stimulated PMN through fibrin gels. Thus, chemoattractants and matrix proteins regulate chemotaxis of phagocytic leukocytes by at least two different mechanisms: one in which specific chemoattractants promote very tight adhesion of leukocytes to specific matrix proteins and another in which specific matrix proteins signal cessation of migration without markedly affecting strength of leukocyte adhesion.

Reactive oxygen species and substance P in monocrotaline-induced pulmonary hypertension

We attempted to evaluate whether the antioxidants 1,3-dimethyl-2-thiourea (DMTU) and hexa(sulfobutyl)fullerenes (FC(4)S) attenuate monocrotaline (MCT)-induced pulmonary hypertension (PH) by lowering lung substance P (SP) in Wistar rats. Sixty-three rats weighing 297 +/- 8 g were divided into six groups: control; MCT; capsaicin + MCT; MCT + DMTU-1; MCT + DMTU-2; and MCT + FC(4)S. Three weeks before the functional study, saline was injected into each control rat, whereas each MCT rat received 60 mg/kg sc MCT. Rats in the third group received capsaicin pretreatment followed by MCT. A 3-day injection of DMTU was performed during the early (DMTU-1) or the late (DMTU-2) post-MCT period. For the last group, each MCT-treated rat received a daily FC(4)S injection until the commencement of the functional study. Compared to the control group, MCT caused significant increases in pulmonary arterial pressure (Ppa), right ventricular hypertropy, pulmonary arterial medial thickness, lung SP level, and luminol-enhanced chemiluminescence counts in bronchoalveolar lavage. Both capsaicin and antioxidants significantly attenuated the above MCT-induced alterations. SP-induced acute increase in Ppa was exaggerated in MCT-treated rats. These results suggest that oxygen radicals play an important role in MCT-induced PH via elevating lung SP level.

Dietary beta-carotene protects lung and liver parenchyma of rats treated with monocrotaline

Some studies have indicated that the injury induced by the hepato- and pneumotoxin monocrotaline (MCT) is in part mediated by oxidation. Because beta-carotene is a potent antioxidant, we hypothesized that it would protect the lung and liver parenchyma against MCT-induced injury. Twenty rats were assigned randomly to four groups. All rats were fed a standard AIN93G diet with or without beta-carotene. After 1 week on the purified diets, half of the rats fed the control (standard) diet and half of the rats fed the beta-carotene-supplemented diet were injected subcutaneously with 60 mg MCT/kg body weight or its vehicle (water). All rats were sacrificed at 4 weeks. Histological examination showed that beta-carotene alone did not affect lung or liver structure. On the other hand, lungs of MCT-treated rats had severe focal pneumonia, extensive deposition of collagen in the septa, marked inflammation of the small arteries and arterioles, and arterialization of the small venules. Livers of MCT-treated rats showed some fatty infiltration and diffuse hemorrhages, more prominent sometimes in the centrilobular area and sometimes in the periportal region. Concomitant treatment with beta-carotene protected the lung parenchyma from the inflammatory reaction and the septal fibrosis, but did not prevent cardiac right ventricular hypertrophy and only slightly reduced the thickening of the wall of small arteries and arterioles. Incidence of steatosis and hemorrhages was decreased in the liver. These results indicate that MCT-induced pulmonary vascular remodeling occurs in the absence of inflammatory cell infiltration. Furthermore, beta-carotene prevented inflammation and protected the lung and liver parenchyma of MCT-treated rats.

Arachidonic acid-induced oxidative injury to cultured spinal cord neurons

Spinal cord trauma can cause a marked release of free fatty acids, in particular, arachidonic acid (AA), from cell membranes. Free fatty acids, and AA by itself, may lead to secondary damage to spinal cord neurons. To study this hypothesis, cultured spinal cord neurons were exposed to increasing concentrations of AA (0.01-10 microM). AA-induced injury to spinal cord neurons was assessed by measurements of cellular oxidative stress, intracellular calcium levels, activation of nuclear factor-KB (NF-kappaB), and cell viability. AA treatment increased intracellular calcium concentrations and decreased cell viability. Oxidative stress increased significantly in neurons exposed to 1 and 10 microM AA. In addition, AA treatment activated NF-kappaB and decreased levels of the inhibitory subunit, IKB. It is interesting that manganese superoxide dismutase protein levels and levels of intracellular total glutathione increased in neurons exposed to this fatty acid for 24 h, consistent with a compensatory response to increased oxidative stress. These results strongly support the hypothesis that free fatty acids contribute to the tissue injury observed following spinal cord trauma.