The requirement of both intracellular reactive oxygen species and intracellular calcium elevation for the induction of heparin-binding EGF-like growth factor in vascular endothelial cells and smooth muscle cells

The initiation of oxidative stress and therapeutic strategies in wound healing

When the production of reactive oxygen species (ROS) is overloaded surpassing the capacity of the reductive rheostat, mammalian cells undergo a series of oxidative damage termed oxidative stress (OS). This phenomenon is ubiquitously detected in many human pathological conditions. Wound healing program implicates continuous neovascularization, cell proliferation, and wound remodeling. Increasing evidence indicates that reactive oxygen species (ROS) have profound impacts on the wound healing process through regulating a series of the physiological and pathological program including inflammatory response, cell proliferation, angiogenesis, granulation as well as extracellular matrix formation. In most pathological wound healing processes, excessive ROS exerts a negative role on the wound healing process. Interestingly, the moderate increase of ROS levels is beneficial in killing bacteria at the wound site, which creates a sterile niche for revascularization. In this review, we discussed the physiological rhythms of wound healing and the role of ROS in this progress, aim to explore the potential manipulation of OS as a promising therapeutic avenue.

Role of Heparin-Binding Epidermal Growth Factor-Like Growth Factor in Oxidative Stress-Associated Metabolic Diseases

Heparin-binding EGF-like growth factor (HB-EGF) is an EGF family member that interacts with epidermal growth factor receptor (EGFR) and ERBB4. Since HB-EGF was first identified as a novel growth factor secreted from a human macrophage cell line, numerous pathological and physiological functions related to cell proliferation, migration, and inflammation have been reported. Notably, the expression of HB-EGF is sensitively upregulated by oxidative stress in the endothelial cells and functions for auto- and paracrine-EGFR signaling. Overnutrition and obesity cause elevation of HB-EGF expression and EGFR signaling in the hepatic and vascular systems. Modulations of HB-EGF signaling showed a series of protections against phenotypes related to metabolic syndrome and advanced metabolic diseases, suggesting HB-EGF as a potential target against metabolic diseases.

High levels of HB-EGF and interleukin-18 are associated with a high risk of in-stent restenosis

Objective:

To explore the clinical significance of heparin-binding epidermal growth factor-like growth factor (HB-EGF), interleukin-18 (IL-18), and interleukin-10 (IL-10) in restenosis after percutaneous coronary intervention (PCI).

Methods:

A total of 198 patients with acute coronary syndrome underwent coronary drug-eluting stent implantation and were divided into the restenosis group and non-restenosis group on the basis of second coronary angiography. Biological parameters and HB-EGF, IL-18, and IL-10 levels were measured. Patients in the restenosis group were further divided into 3 subgroups according to Gensini score: group A (Gensini score of <20), group B (Gensini score of >20 but <40), and group C (Gensini score of >40).

Results:

Compared with the non-restenosis group, HB-EGF and IL-18 levels were significantly higher but serum IL-10 levels were significantly lower in the restenosis group. Furthermore, HB-EGF levels increased with the Gensini score among the 3 subgroups. Spearman’s correlation analysis showed that HB-EGF levels were associated with IL-18 levels and the number of diseased vessels. Multivariate logistic regression analysis showed that diabetes, HB-EGF, and IL-18 were risk factors for restenosis [odds ratio with 95% confidence interval: 3.902 (1.188-4.415), 2.185 (1.103-4.014), and 2.079 (1.208-4.027), respectively].

Conclusion:

The present study has demonstrated that HB-EGF may be used to evaluate the severity of restenosis and coronary artery lesion and that inflammatory responses may be involved in the process of restenosis.

Involvement of reactive oxygen species in stimuli-induced shedding of heparin-binding epidermal growth factor-like growth factor

Heparin-binding epidermal growth factor-like growth factor (HB-EGF) is a critical growth factor for a number of physiological and pathological processes, such as wound healing, atherosclerosis and cancer proliferation. HB-EGF is synthesized as a membrane form (proHB-EGF), and is shedded at the cell surface to yield soluble HB-EGF, resulting in making it active. In this study, the involvement of reactive oxygen species (ROS) in stimuli-induced shedding of HB-EGF was investigated using monkey kidney Vero cells overexpressing HB-EGF (Vero-H cells). 12-O-tetradecanoylphorbol-13-acetate (TPA), lysophosphatidic acid (LPA) as a ligand for seventransmembrane G protein coupled receptors (GPCR) and sorbitol as stress induced shedding of HB-EGF mediated protein kinase C (PKC)-δ, mitogen-activated protein kinase (MAPK) and p38MAPK, respectively. These stimuli-induced sheddings of HB-EGF were inhibited by N-acetyl-L-cysteine (NAC), suggesting the involvement of ROS. As specific inhibitors of these protein kinases inhibited the shedding of HB-EGF, these signaling pathways seem to be independent, respectively. In contrast, γ-ray irradiation did not induce shedding although it did increase intracellular ROS levels. Taken together, these results suggest that the synergistic generation of ROS and the activation of protein kinase are required to promote stimuli-induced shedding of HB-EGF.

Early growth response protein 1 promotes restenosis by upregulating intercellular adhesion molecule-1 in vein graft

OBJECTIVES

To verify the relationship between Egr-1 and vein graft restenosis and investigate the related mechanisms.

METHODS

Mouse vein graft models were established in Egr-1 knockout (KO) and wild-type (WT) mice. The vein grafts in the mice were taken for pathological examination and immunohistochemical analysis. The endothelial cells (ECs) were stimulated by using a computer-controlled cyclic stress unit. BrdU staining and PCR were used to detect ECs proliferation activity and Egr-1 and ICAM-1 mRNA expression, respectively. Western-blot analysis was also used to detect expression of Egr-1 and intercellular adhesion molecule-1 (ICAM-1) proteins.

RESULTS

The lumens of vein grafts in Egr-1 KO mice were wider than in WT mice. ECs proliferation after mechanical stretch stimulation was suppressed by Egr-1 knockout (P < 0.05). Both in vein grafts and ECs from WT mice after mechanical stretch stimulation, mRNA expression and protein of Egr-1 and ICAM-1 showed increases (P < 0.05). However, ICAM-1 expression was significantly suppressed in ECs from Egr-1 knockout mice (P < 0.05).

CONCLUSIONS

Egr-1 may promote ECs proliferation and result in vein graft restenosis by upregulating the expression of ICAM-1. As a key factor of vein graft restenosis, it could be a target for the prevention of restenosis after CABG surgery.

The protective effect of Bcl-xl overexpression against oxidative stress-induced vascular endothelial cell injury and the role of the Akt/eNOS pathway

Restenosis after intraluminal or open vascular reconstruction remains an important clinical problem. Vascular endothelial cell (EC) injury induced by oxidative stress plays an important role in the development of intimal hyperplasia. In this study, we sought to evaluate the protective effects of Bcl-xl overexpression in vitro on oxidative stress-induced EC injury and the role of the Akt/endothelial nitric oxide synthase (eNOS) pathway. Human umbilical vein endothelial cells (HUVECs) exposed to hydrogen peroxide (H₂O₂, 0.5 mM) were used as the experimental oxidative stress model. The Bcl-xl gene was transferred into HUVECs through recombinant adenovirus vector pAdxsi-GFP-Bcl-xl before oxidative treatment. Cell apoptosis was evaluated by Annexin V/propidium iodide and Hoechst staining, caspase-7 and PARP cleavage. Cell viability was assessed using the cell counting kit-8 assay, proliferating cell nuclear antigen (PCNA) immunocytochemical detection and the scratching assay. Expressions of Akt, phospho-Akt and eNOS were detected by Western blotting. Our results showed that H₂O₂ induced apoptosis and decreased the cell viability of HUVECs. Bcl-xl overexpression significantly protected cells from H₂O₂-induced cell damage and apoptosis and maintained the cell function. Furthermore, the level of phospho-Akt and eNOS protein expression was significantly elevated when pretreated with Bcl-xl gene transferring. These findings suggest that Bcl-xl overexpression exerts an anti-apoptotic and protective effect on EC function. The Akt/eNOS signaling pathway is probably involved in these processes.

Heparin-binding epidermal growth factor-like growth factor is a potent neurotrophic factor for PC12 cells

Heparin-binding epidermal growth factor EGF-like growth factor (HB-EGF) is a member of the epidermal growth factor family that is expressed in many cell types. We have previously reported the effects of HB-EGF on intestinal epithelial cells and endothelial cells after exposure to ischemia/reperfusion in vivo or anoxia/reoxygenation injury in vitro. However, the effect of HB-EGF on neuronal cells is largely unexplored. In this study, we examined the effect of HB-EGF on neurite outgrowth in pheochromocytoma (PC12) cells as well as the neuroprotective effect of HB-EGF on injured PC12 cells exposed to oxygen and glucose deprivation (OGD), which mimics ischemic conditions. We found that HB-EGF significantly promotes PC12 cell neurite outgrowth and that this effect was blocked by EGF receptor (EGFR) inhibition or mitogen-activated protein kinase (MAPK) inhibition, but not by tyrosine kinase inhibition. In the face of OGD injury, HB-EGF preserves cell viability and decreases apoptosis and LDH release in PC12 cells. HB-EGF-mediated cytoprotection was abolished by EGFR inhibition and MAPK inhibition. We conclude that HB-EGF, through its interaction with the EGF receptor, activates the MAPK signaling pathway in PC12 cells under basal or injury conditions, leading to enhanced neurite outgrowth and neuroprotection against ischemic injury.

An oxidized extracellular oxidation-reduction state increases Nox1 expression and proliferation in vascular smooth muscle cells via epidermal growth factor receptor activation

OBJECTIVE

To examine the effect of an oxidized extracellular oxidation-reduction (redox) state (E(h)) on the expression of NADPH oxidases in vascular cells.

METHODS AND RESULTS

The generation of reactive oxygen species by NADPH oxidase (Nox)-based NADPH oxidases activates redox-dependent signaling pathways and contributes to the development of "oxidative stress" in vascular disease. An oxidized plasma redox state is associated with cardiovascular disease in humans; however, the cellular mechanisms by which the extracellular redox state may cause disease are not known. Aortic segments and cultured aortic smooth muscle cells were exposed to E(h) between -150 mV (reduced) and 0 mV (oxidized) by altering the concentration of cysteine and its disulfide, cystine, the predominant redox couple in plasma. A more oxidized E(h) increased the expression of Nox1 and resulted in Nox1-dependent proliferation of smooth muscle cells. Oxidized E(h) rapidly induced epidermal growth factor receptor phosphorylation via shedding of epidermal growth factor-like ligands from the plasma membrane and caused extracellular signal-regulated kinase 1/2-dependent phosphorylation of the transcription factors activating transcription factor-1 and cAMP-response element-binding protein. Inhibition of epidermal growth factor receptor or extracellular signal-regulated kinase 1/2 activation, or addition of small interference RNA to activating transcription factor-1, prevented the increase in Nox1 expression.

CONCLUSIONS

Our results identify a novel mechanism by which extracellular oxidative stress increases expression and activity of Nox1 NADPH oxidase and contributes to vascular disease.

Inhibition of gene expression of heparin-binding epidermal growth factor-like growth factor by extracellular superoxide dismutase in rat aortic smooth muscle cells

Both extracellular superoxide dismutase (EC-SOD) and heparin binding EGF like growth factor (HB-EGF) are produced in smooth muscle cells of the arterial wall, and are thought to play pathological roles in atherosclerosis with heparin binding characteristics. EC-SOD treatment clearly reduced the H2O2 induced expression of HB-EGF in rat aortic smooth muscle cells (RASMC). EC-SOD also inhibited the induction of HB-EGF by 12-O-tetradecanoylphorbol-13-acetate (TPA) in RASMC by 60%. Both H2O2 and TPA increased intracellular ROS levels, and EC-SOD inhibited ROS generation only for the case of H2O2 but not TPA. Treatment of the cells with heparin alone decreased HB-EGF expression by 20%, whereas EC-SOD alone and a co-incubation with EC-SOD and heparin suppressed the induction by 60 and 70%, respectively. These results suggest that EC-SOD is related to the EGF signaling in two ways, competition for HSPG with HB-EGF and as an ROS scavenger.

Concentration dependent dual effect of thrombin in endothelial cells via Par-1 and Pi3 Kinase

Disruption of endothelial barrier is a critical pathophysiological factor in inflammation. Thrombin exerts a variety of cellular effects including inflammation and apoptosis through activation of the protease activated receptors (PARs). The activation of PAR-1 by thrombin is known to have a bimodal effect in endothelial cell permeability with a low concentration (pM levels) eliciting a barrier protective and a high concentration (nM levels) eliciting a barrier disruptive response. It is not known whether this PAR-1-dependent activity of thrombin is a unique phenomenon specific for the in vitro assay or it is part of a general anti-inflammatory effect of low concentrations of thrombin that may have a physiological relevance. Here, we report that low concentrations of thrombin or of PAR-1 agonist peptide induced significant anti-inflammatory activities. However, relatively high concentration of thrombin or of PAR-1 agonist peptide showed pro-inflammatory activities. By using function-blocking anti-PAR-1 antibodies and PI3 kinase inhibitor, we show that the direct anti-inflammatory effects of low concentrations of thrombin are dependent on the activation of PAR-1 and PI3 kinase. These results suggest a role for cross communication between PAR-1 activation and PI3 kinase pathway in mediating the cytoprotective effects of low concentrations of thrombin in the cytokine-stimulated endothelial cells. J. Cell. Physiol. 219: 744-751, 2009. (c) 2009 Wiley-Liss, Inc.

Activation of NADPH oxidase by transforming growth factor-beta in hepatocytes mediates up-regulation of epidermal growth factor receptor ligands through a nuclear factor-kappaB-dependent mechanism

The TGF-beta (transforming growth factor-beta) induces survival signals in foetal rat hepatocytes through transactivation of EGFR (epidermal growth factor receptor). The molecular mechanism is not completely understood, but both activation of the TACE (tumour necrosis factor alpha-converting enzyme)/ADAM17 (a disintegrin and metalloproteinase 17; one of the metalloproteases involved in shedding of the EGFR ligands) and up-regulation of TGF-alpha and HB-EGF (heparin-binding epidermal growth factor-like growth factor) appear to be involved. In the present study, we have analysed the molecular mechanisms that mediate up-regulation of the EGFR ligands by TGF-beta in foetal rat hepatocytes. The potential involvement of ROS (reactive oxygen species), an early signal induced by TGF-beta, and the existence of an amplification loop triggered by initial activation of the EGFR, have been studied. Results indicate that DPI (diphenyleneiodonium) and apocynin, two NOX (NADPH oxidase) inhibitors, and SB431542, an inhibitor of the TbetaR-I (TGF-beta receptor I), block up-regulation of EGFR ligands and Akt activation. Different members of the NOX family of genes are expressed in hepatocytes, included nox1, nox2 and nox4. TGF-beta up-regulates nox4 and increases the levels of Rac1 protein, a known regulator of both Nox1 and Nox2, in a TbetaR-I-dependent manner. TGF-beta mediates activation of the nuclear factor-kappaB pathway, which is inhibited by DPI and is required for up-regulation of TGF-alpha and HB-EGF. In contrast, EGFR activation is not required for TGF-beta-induced up-regulation of those ligands. Considering previous work that has established the role of ROS in apoptosis induced by TGF-beta in hepatocytes, the results of the present study indicate that ROS might mediate both pro- and anti-apoptotic signals in TGF-beta-treated cells.

Heparin-binding EGF-like growth factor (HB-EGF) and necrotizing enterocolitis

Necrotizing enterocolitis (NEC) is a common and devastating gastrointestinal disease that occurs predominantly in premature infants. Despite various advances in management, the mortality of this disease remains high. During the last decade, studies from our laboratory have shown that heparin-binding epidermal growth factor-like growth factor (HB-EGF), a member of the epidermal growth factor (EGF) family, can protect intestinal epithelial cells (IEC) from various forms of injury in vitro. Furthermore, we have used both an intestinal I/R injury model in adult rats, and a neonatal rat pup model of NEC, to show that HB-EGF can protect the intestines from injury. On administration of HB-EGF in the neonatal rat model, the incidence of NEC is reduced from 65% to 27.3% (P < 0.05), and the histological injury score is decreased from 2 to 1.1 (P < 0.05). In addition, the survival rate is increased from 25% to 63.6% and the survival time extended from 59 hours to 73 hours (P < 0.05). In addition, using human specimens from newborns undergoing bowel resection for NEC, we found that the expression of endogenous HB-EGF mRNA in normal areas of the intestine at the resection margins was higher than that of the intestine afflicted with acute NEC. Endogenous HB-EGF may be involved in epithelial cell repair, proliferation, and regeneration during recovery from injury. Exogenous administration of HB-EGF potentiates recovery from intestinal injury in vitro and in vivo. Taken together, these results support a potential therapeutic role for HB-EGF in the treatment of NEC in the future.

The role of transforming growth factor β1 in the vascular system

The transforming growth factor beta (TGFbeta) family of cytokines exert pleiotropic effects upon a wide variety of cell types. TGFbeta1 has been demonstrated to be of fundamental importance in the development, physiology and pathology of the vascular system. As the role of TGFbeta1 in these processes becomes clearer, influencing its activity for therapeutic benefit is now beginning to be investigated. This review presents an overview of the role of TGFbeta1 in the vasculature. The cellular and extracellular biology of the TGFbeta family is first addressed, followed by an overview of the function of TGFbeta1 during vascular development, atherogenesis, hypertension, and vessel injury.

The effect of hyperbaric oxygen therapy on the adverse effects of octreotide on wound healing

OBJECTIVE

Octreotide, a long-acting somatostatin analogue, has been used in the treatment of various disorders. Octreotide has significant detrimental impacts upon wound healing. We tested the hypothesis that hyperbaric oxygen therapy may overcome octreotide-mediated suppression of wound healing.

DESIGN

Prospective, randomised, parallel-group animal study.

METHODS

Operated rats were divided into four groups: (1) controls, (2) octreotide therapy, (3) hyperbaric oxygen therapy and (4) combination of octreotide and hyperbaric oxygen therapy. Wound healing was assessed by breaking-strength measurements, hydroxyproline levels and fibrosis scores.

RESULTS

Octreotide decreased the breaking-strength measurements, hydroxyproline levels and fibrosis scores to 72%, 88% and 55%, respectively, of the control group. In the combination group, hyperbaric oxygen therapy increased breaking-strength measurements and hydroxyproline levels to 137% and 126%, respectively, of the control group. In the combination group, hyperbaric oxygen therapy tended to increase the fibrosis scores to 111% of the control group, but without statistical significance.

CONCLUSION

Hyperbaric oxygen therapy tends to reverse the octreotide-induced impairment of wound healing.

Heparin-binding epidermal growth factor-like growth factor and intestinal ischemia-reperfusion injury

Intestinal ischemia/reperfusion (I/R) injury affects patients of different ages, especially premature babies and the elderly. The outcome after intestinal I/R is often dismal, which may be attributed to loss of the barrier and immune functions of the intestines, as well as development of secondary injury in remote organs. The available treatment for advanced gut ischemia mandates extensive resection, which may cause growth retardation in infants and nutritional problems in the elderly. Throughout the past decade we have been investigating the potential therapeutic role of heparin-binding epidermal growth factor-like factor (HB-EGF) in intestinal I/R. The mitogenic and chemoattractant functions of HB-EGF formed the initial rationale for our investigations. In addition, HB-EGF is a potent antiapoptotic protein that enables cells and tissues exposed to different apoptotic stimuli to survive hypoxic, oxidative, and nutritional stresses. HB-EGF is known to have a vital role in wound healing and postischemic regeneration in different organs. In the current review, we summarize the results of our findings of the beneficial effects of HB-EGF in intestinal I/R, supported by additional evidence from the literature and an explanation of different possible mechanisms of its actions. Collectively, the data strongly suggest a potential therapeutic role for the use of HB-EGF to treat intestinal ischemic diseases such as I/R and necrotizing enterocolitis.

Vanadium-induced HB-EGF expression in human lung fibroblasts is oxidant dependent and requires MAP kinases

Vanadium pentoxide (V(2)O(5)) is a transition metal derived from the burning of petrochemicals that causes airway fibrosis and remodeling. Vanadium compounds activate many intracellular signaling pathways via the generation of hydrogen peroxide (H(2)O(2)) or other reactive oxygen species. In this study, we investigated the regulation of heparin-binding epidermal growth factor-like growth factor (HB-EGF) in human lung fibroblasts after V(2)O(5) treatment. V(2)O(5)-induced HB-EGF mRNA expression was abolished by N-acetyl-l-cysteine, suggesting an oxidant-mediated effect. Exogenous H(2)O(2) (>10 microM) mimicked the effect of V(2)O(5) in upregulating HB-EGF expression. Fibroblasts spontaneously released low levels of H(2)O(2) (1-2 microM), and the addition of V(2)O(5) depleted the endogenous H(2)O(2) pool within minutes. V(2)O(5) caused a subsequent increase of H(2)O(2) into the culture medium at 12 h. However, the burst of V(2)O(5)-induced H(2)O(2) occurred after V(2)O(5)-induced HB-EGF mRNA expression at 3 h, indicating that the V(2)O(5)-stimulated H(2)O(2) burst did not mediate HB-EGF expression. Either V(2)O(5) or H(2)O(2) activated ERK-1/2 and p38 MAP kinase. Inhibitors of the ERK-1/2 pathway (PD-98059) or p38 MAP kinase (SB-203580) significantly reduced either V(2)O(5)- or H(2)O(2)-induced HB-EGF expression. These data indicate that vanadium upregulates HB-EGF via ERK and p38 MAP kinases. The induction of HB-EGF is not related to a burst of H(2)O(2) in V(2)O(5) treated cells, yet the action of V(2)O(5) in upregulating HB-EGF is oxidant dependent and could be due to the reaction of V(2)O(5) with endogenous H(2)O(2).

Selective interleukin-12 synthesis defect in 12/15-lipoxygenase-deficient macrophages associated with reduced atherosclerosis in a mouse model of familial hypercholesterolemia

Targeted gene disruption or overexpression of 12/15-lipoxygenase in mice on the genetic background of apolipoprotein E or low density lipoprotein-receptor (LDL-R) deficiency has implicated 12/15-lipoxygenase in atherogenesis. The data support indirectly a role for 12/15-lipoxygenase in the oxidative modification of low density lipoprotein. In this study we set out to explore other potential mechanisms for 12/15-lipoxygenase in atherosclerosis using apolipoprotein B mRNA editing catalytic polypeptide-1/LDL-R double-deficient mice, a model highly related to the human condition of familial hypercholesterolemia. 12/15-Lipoxygenase deficiency in this strain led to approximately 50% decrease in aortic lesions in male and female mice at 8 months on a chow diet in the absence of cholesterol differences. While studying 12/15-lipoxygenase-deficient macrophages in culture, we discovered a remarkable selective defect (75-90% decrease) in interleukin-12 production but not in tumor necrosis factor-alpha or nitric oxide release, in response to lipopolysaccharide in the presence or absence of interferon-gamma priming. The lipopolysaccharide/interferon-gamma response was associated with a 33-50% decrease in nuclear interferon consensus sequence-binding protein, which is consistent with interferon consensus sequence-binding protein containing protein complex-dependent regulation of the interleukin-12 p40 gene. The decrease in interleukin-12 production was recapitulated in vivo in mouse aortas of the triple knockout group and was reflected in a marked decrease in interferon-gamma expression. The data provide support for a novel mechanism linking the 12/15-lipoxygenase pathway to a known immunomodulatory Th1 cytokine in atherogenesis.

Complement c3a and c5a induce different signal transduction cascades in endothelial cells

In leukocytes, C3a and C5a cause chemotaxis in a G(i)-dependent, pertussis toxin (PT)-sensitive fashion. Because we found that HUVECs and immortalized human dermal microvascular endothelial cells express small numbers of C3aRs and C5aRs, we asked what the function of these receptors was on these cells. Activation of the C3aR caused transient formation of actin stress fibers, which was not PT-sensitive, but depended on rho activation implying coupling to G(alpha12) or G(alpha13). Activation of the C5aR caused a delayed and sustained cytoskeletal response, which was blocked by PT, and resulted in cell retraction, increased paracellular permeability, and facilitated eosinophil transmigration. C5a, but not C3a, was chemotactic for human immortalized dermal microvascular endothelial cells. The response to C5a was blocked by inhibitors of phosphatidylinositol-3-kinase, src kinase, and of the epidermal growth factor (EGF) receptor (EGFR) as well as by neutralizing Abs against the EGFR and heparin-binding EGF-like factor. Furthermore, immune precipitations showed that the EGFR was phosphorylated following stimulation with C5a. The C5aR in endothelial cells thus uses a signaling cascade-transactivation of the EGFR-that does not exist in leukocytes, while the C3aR couples to a different G protein, presumably G(alpha12/13).

Oxygen, oxidants, and antioxidants in wound healing: an emerging paradigm

Disrupted vasculature and high energy-demand by regenerating tissue results in wound hypoxia. Wound repair may be facilitated by oxygen therapy. Evidence supporting the mode of action of hyperbaric oxygen in promoting wound healing is sketchy, however. Topical oxygen therapy involves local administration of pure oxygen. The advantages of topical oxygen therapy include low cost, the lack of systemic oxygen toxicity, and possibility of home treatment. While this modality of wound care is of outstanding interest, it clearly lacks the support of mechanism-oriented studies. The search for mechanisms by which oxygen supports wound healing has now taken another step. Respiratory burst-derived oxidants support healing. Oxidants serve as cellular messengers to promote healing. Although this information is of outstanding significance to the practice of oxygen therapy, it remains largely unexplored. The search for "natural remedies" has drawn attention to herbals. Proanthocyanidins or condensed tannins are a group of biologically active polyphenolic bioflavonoids that are synthesized by many plants. Proanthocyanidins and other tannins facilitate wound healing. A combination of grape seed proanthocyanidin extract and resveratrol facilitates inducible VEGF expression, a key element supporting wound angiogenesis. Strategies to manipulate the redox environment in the wound are likely to be of outstanding significance in wound healing.

Vascular smooth muscle growth: autocrine growth mechanisms

Vascular smooth muscle cells (VSMC) exhibit several growth responses to agonists that regulate their function including proliferation (hyperplasia with an increase in cell number), hypertrophy (an increase in cell size without change in DNA content), endoreduplication (an increase in DNA content and usually size), and apoptosis. Both autocrine growth mechanisms (in which the individual cell synthesizes and/or secretes a substance that stimulates that same cell type to undergo a growth response) and paracrine growth mechanisms (in which the individual cells responding to the growth factor synthesize and/or secrete a substance that stimulates neighboring cells of another cell type) are important in VSMC growth. In this review I discuss the autocrine and paracrine growth factors important for VSMC growth in culture and in vessels. Four mechanisms by which individual agonists signal are described: direct effects of agonists on their receptors, transactivation of tyrosine kinase-coupled receptors, generation of reactive oxygen species, and induction/secretion of other growth and survival factors. Additional growth effects mediated by changes in cell matrix are discussed. The temporal and spatial coordination of these events are shown to modulate the environment in which other growth factors initiate cell cycle events. Finally, the heterogeneous nature of VSMC developmental origin provides another level of complexity in VSMC growth mechanisms.

Reactive oxygen species in cell signaling

Reactive oxygen species (ROS) are generated as by-products of cellular metabolism, primarily in the mitochondria. When cellular production of ROS overwhelms its antioxidant capacity, damage to cellular macromolecules such as lipids, protein, and DNA may ensue. Such a state of "oxidative stress" is thought to contribute to the pathogenesis of a number of human diseases including those of the lung. Recent studies have also implicated ROS that are generated by specialized plasma membrane oxidases in normal physiological signaling by growth factors and cytokines. In this review, we examine the evidence for ligand-induced generation of ROS, its cellular sources, and the signaling pathways that are activated. Emerging concepts on the mechanisms of signal transduction by ROS that involve alterations in cellular redox state and oxidative modifications of proteins are also discussed.

Modulation of protein kinase activity and gene expression by reactive oxygen species and their role in vascular physiology and pathophysiology

Emerging evidence indicates that reactive oxygen species, especially superoxide and hydrogen peroxide, are important signaling molecules in cardiovascular cells. Their production is regulated by hormone-sensitive enzymes such as the vascular NAD(P)H oxidases, and their metabolism is coordinated by antioxidant enzymes such as superoxide dismutase, catalase, and glutathione peroxidase. Both of these reactive oxygen species serve as second messengers to activate multiple intracellular proteins and enzymes, including the epidermal growth factor receptor, c-Src, p38 mitogen-activated protein kinase, Ras, and Akt/protein kinase B. Activation of these signaling cascades and redox-sensitive transcription factors leads to induction of many genes with important functional roles in the physiology and pathophysiology of vascular cells. Thus, reactive oxygen species participate in vascular smooth muscle cell growth and migration; modulation of endothelial function, including endothelium-dependent relaxation and expression of a proinflammatory phenotype; and modification of the extracellular matrix. All of these events play important roles in vascular diseases such as hypertension and atherosclerosis, suggesting that the sources of reactive oxygen species and the signaling pathways that they modify may represent important therapeutic targets.

Production of hydrogen peroxide by serum and its involvement in cell proliferation in ROS 17/2.8 osteoblasts

The effects of hydrogen peroxide, which fetal bovine serum (FBS) releases, on proliferation have been studied in ROS 17/2.8 osteoblasts. Cell proliferation, when activated by FBS, was inhibited by catalase in ROS 17/2.8 osteoblasts, but did not in primary osteoblast-like cells. Serum-induced extracellular signal-regulated kinase(ERK) activity was reduced by the pretreated catalase in ROS 17/2.8 osteoblasts. In addition, the present studies demonstrate that addition of FBS led to an increase of fluorescence of dihydrorhodamine 123, indicating formation of free radicals including hydrogen peroxide in ROS 17/2.8 osteoblasts, but not in primary osteoblast-like cells. These phenomena may account for the generation of reactive oxygen species during cellular proliferation in ROS 17/2.8 osteoblasts.