Ascorbate enhances iNOS activity by increasing tetrahydrobiopterin in RAW 264.7 cells

Antioxidant and Anti-Inflammatory Activities of Lindera glauca Extracts

INTRODUCTION

The current study investigated the antioxidant and anti-inflammatory effects of ethanol extracts from Lindera glauca twig (LGT) and leaf/stem (LGLS).

METHODS

The antioxidant activities were measured by total content of polyphenol and flavonoid, DPPH radical scavenging, and ABTS+ radical scavenging activity. To evaluate the anti-inflammatory effect in the LPS-induced RAW 264.7 cells, protein and mRNA expression of major inflammatory factors were analyzed using Western blot analysis and RT-PCR.

RESULTS

The total polyphenol content of LGT and LGLS was 88.45 ± 11.74 and 115.75 ± 7.87 GA mg/g, respectively. The total flavonoid content was 66 ± 2.89 and 74.33 ± 2.89 QE mg/g. Both LGT and LGLS showed high DPPH and ABTS+ radical scavenging activities. Neither LGT nor LGLS was cytotoxic to RAW 264.7 cells. The anti-inflammatory activities were measured by LPS-induced RAW 264.7 cells. LGT and LGLS showed inhibition of the LPS-induced production of nitric oxide (NO), inducible NO synthase, cyclooxygenase-2 at the protein and mRNA levels, as determined by Western blotting and RT-PCR, respectively. In addition, the release of tumor necrosis factor-α and interleukin-6 mRNA expression levels of these cytokines was reduced by LGT and LGLS.

CONCLUSION

These results suggest that LGT and LGLS extracts have potential for use as a functional antioxidant and anti-inflammatory ingredient in cosmetic industry.

What Are Reactive Oxygen Species, Free Radicals, and Oxidative Stress in Skin Diseases?

Oxygen in the atmosphere is a crucial component for life-sustaining aerobic respiration in humans. Approximately 95% of oxygen is consumed as energy and ultimately becomes water; however, the remaining 5% produces metabolites called activated oxygen or reactive oxygen species (ROS), which are extremely reactive. Skin, the largest organ in the human body, is exposed to air pollutants, including diesel exhaust fumes, ultraviolet rays, food, xenobiotics, drugs, and cosmetics, which promote the production of ROS. ROS exacerbate skin aging and inflammation, but also function as regulators of homeostasis in the human body, including epidermal keratinocyte proliferation. Although ROS have been implicated in various skin diseases, the underlying mechanisms have not yet been elucidated. Current knowledge on ROS-related and oxidative stress-related skin diseases from basic research to clinical treatment strategies are discussed herein. This information may be applied to the future treatment of skin diseases through the individual targeting of the ROS generated in each case via their inhibition, capture, or regulation.

Multiple roles of macrophage in skin

More than 100 years have passed since Elie Metchnikoff discovered macrophage. Over the recent decade, attracting information about macrophage polarization have been reported. This is because many molecules have been identified as markers of macrophage polarization. Additionally, mechanistic insights have been demonstrated by experiments with various stimuli-induced macrophage polarization. Historically and simply, macrophages are divided into M1 (classically activated) and M2 (alternatively activated). However, some of them are not specific yet. Studies in the field of cardiology revealed the plasticity of macrophages and their subsets are divided into details: Mhem, MHb, Mox and M4 macrophages. M2 macrophages were further divided in M2a, M2b, M2c and M2d. There appears to be more phenotypes of macrophages. However, there still lack studies in dermatological field. This review summarizes the spectrum of macrophage activation and finding about various roles of macrophages in the dermatological field.

Jak2/Stat1 pathway mediated tetrahydrobiopterin up-regulation contributes to nitric oxide overproduction in high-glucose cultured rat mesangial cells

Nitric oxide (NO) is crucial for the progression of early diabetic nephropathy (DN). It is important to clarify the mechanism for the production of NO in mesangial cells (MCs). In this study, the amounts/activities of related factors such as reactive oxygen species (ROS), NO, 3 isoforms of nitric oxide synthase (NOS), tetrahydrobiopterin (BH4), GTP cyclohydrolase I (GTPCH I), Jak2, and Stat1 were determined using high-glucose cultured rat MCs. The results showed that the production of BH4 under oxidative stress was strongly stimulated by its rate-limiting enzyme GTP cyclohydrolase, which increased the expression and activity of inducible NOS to facilitate NO synthesis. Furthermore, the relative quantities of activated-Jak2 and activated-Stat1 were increased. Therefore, Jak2/Stat1 pathway mediated BH4 up-regulation can contribute to excessive NO in high-glucose cultured MCs. Our results will be helpful for screening new targets to improve the therapy for early DN.

Preliminary Evidence That High-Dose Vitamin C has a Vascular Disrupting Action in Mice

High intravenous doses of vitamin C (ascorbic acid) have been reported to benefit cancer patients, but the data are controversial and there is incomplete knowledge of what physiological mechanisms might be involved in any response. Vitamin C is taken up efficiently by cells expressing SVCT2 transporters and since vascular endothelial cells express SVCT2, we explored the hypothesis that administration of high-dose vitamin C (up to 5 g/kg) to mice might affect vascular endothelial function. A single administration of vitamin C to mice induced time- and dose-dependent increases in plasma concentrations of the serotonin metabolite 5-hydroxyindole acetic acid (5-HIAA), a marker for vascular disrupting effects. Responses were comparable to those for the tumor vascular disrupting agents, vadimezan and fosbretabulin. High-dose vitamin C administration decreased tumor serotonin concentrations, consistent with the release of serotonin from platelets and its metabolism to 5-HIAA. High-dose vitamin C also significantly increased the degree of hemorrhagic necrosis in tumors removed after 24 h, and significantly decreased tumor volume after 2 days. However, the effect on tumor growth was temporary. The results support the concept that vitamin C at high dose increases endothelial permeability, allowing platelets to escape and release serotonin. Plasma 5-HIAA concentrations could provide a pharmacodynamic biomarker for vitamin C effects in clinical studies.

Does vitamin C enhance nitric oxide bioavailability in a tetrahydrobiopterin-dependent manner? In vitro, in vivo and clinical studies

Ascorbate (Asc) has been shown to increase nitric oxide (NO) bioavailability and thereby improve endothelial function in patients showing signs of endothelial dysfunction. Tetrahydrobiopterin (BH₄) is a co-factor of endothelial nitric oxide synthase (eNOS) which may easily become oxidized to the inactive form dihydrobiopterin (BH₂). Asc may increase NO bioavailability by a number of mechanisms involving BH₄ and eNOS. Asc increases BH₄ bioavailability by either reducing oxidized BH₄ or preventing BH₄ from becoming oxidized in the first place. Asc could also increase NO bioavailability in a BH₄-independent manner by increasing eNOS activity by changing its phosphorylation and S-nitrosylation status or by upregulating eNOS expression. In this review, we discuss the putative mechanisms by which Asc may increase NO bioavailability through its interactions with BH₄ and eNOS.

Guinea pig ascorbate status predicts tetrahydrobiopterin plasma concentration and oxidation ratio in vivo

Tetrahydrobiopterin (BH₄) is an essential co-factor of nitric oxide synthases and is easily oxidized to dihydrobiopterin (BH₂) which promotes endothelial nitric oxide synthase uncoupling and deleterious superoxide production. Vitamin C has been shown to improve endothelial function by different mechanisms, some involving BH₄. The hypothesis of the present study was that vitamin C status, in particular low levels, influences biopterin redox status in vivo. Like humans, the guinea pig lacks the ability to synthesize vitamin C and was therefore used as model. Seven day old animals (n = 10/group) were given a diet containing 100, 250, 500, 750, 1000, or 1500 ppm vitamin C until euthanasia at age 60-64 days. Blood samples were drawn from the heart and analyzed for ascorbate, dehydroascorbic acid (DHA), BH₄ and BH₂ by high-performance liquid chromatography. Plasma BH₄ levels were found to be significantly lower in animals fed 100 ppm vitamin C compared to all other groups (P < .05 or less). BH₂ levels were not significantly different between groups but the BH₂-to-BH₄ ratio was higher in the group fed 100 ppm vitamin C (P < .001 all cases). Significant positive correlations between BH4 and ascorbate and between BH₂-to-BH₄ ratio and DHA were observed (P < .0001 both cases). Likewise, BH₂-to-BH₄ ratio was negatively correlated with ascorbate (P < .0001) as was BH₄ and DHA (P < .005). In conclusion, the redox status of plasma biopterins, essentially involved in vasodilation, depends on the vitamin C status in vivo. Thus, ingestion of insufficient quantities of vitamin C not only leads to vitamin C deficiency but also to increased BH₄ oxidation which may promote endothelial dysfunction.

Ascorbate in aqueous humor augments nitric oxide production by macrophages

Immunosuppressive molecules within the aqueous humor (AqH) are thought to preserve ocular immune privilege by inhibiting proinflammatory NO production by macrophages (MΦs). Consistent with previous observations, we observed that although MΦs stimulated in the presence of AqH expressed NO synthase 2 (NOS2) protein, nitrite concentrations in culture supernatants, an indirect measure of NO production, did not increase. Interestingly, NOS2 enzymatic activity, as measured by the conversion of L-arginine (L-Arg) into L-citrulline, was augmented in lysates of MΦs stimulated in the presence of AqH. These data suggested that intracellular L-Arg may have been limited by AqH. However, we observed increased mRNA expression of the L-Arg transporter, cationic amino acid transporter 2B, and increased L-Arg uptake in MΦs stimulated in the presence of AqH. Arginases were expressed by stimulated Ms, but competition for L-Arg with NOS2 was excluded. Expression of GTP cyclohydrolase, which produces tetrahydrobiopterin (H(4)B), an essential cofactor for NOS2 homodimerization, increased after M stimulation in the presence or absence of AqH and NOS2 homodimers formed. Taken together, these data provided no evidence for inhibited NOS2 enzymatic activity by AqH, suggesting that a factor within AqH may have interfered with the measurement of nitrite. Indeed, we observed that nitrite standards were not measurable in the presence of AqH, and this effect was due to ascorbate in AqH. Controlling for interference by ascorbate revealed that AqH augmented NO production in MΦs via ascorbate, which limited degradation of H(4)B. Therefore, AqH may augment NO production in macrophages by stabilizing H(4)B and increasing intracellular L-Arg.

Intravenous ascorbic acid to prevent and treat cancer-associated sepsis?

The history of ascorbic acid (AA) and cancer has been marked with controversy. Clinical studies evaluating AA in cancer outcome continue to the present day. However, the wealth of data suggesting that AA may be highly beneficial in addressing cancer-associated inflammation, particularly progression to systemic inflammatory response syndrome (SIRS) and multi organ failure (MOF), has been largely overlooked. Patients with advanced cancer are generally deficient in AA. Once these patients develop septic symptoms, a further decrease in ascorbic acid levels occurs. Given the known role of ascorbate in: a) maintaining endothelial and suppression of inflammatory markers; b) protection from sepsis in animal models; and c) direct antineoplastic effects, we propose the use of ascorbate as an adjuvant to existing modalities in the treatment and prevention of cancer-associated sepsis.

Regulation of endothelial cell tetrahydrobiopterin pathophysiological and therapeutic implications

Tetrahydrobiopterin (BH(4)) is a critical cofactor for the nitric oxide synthases. In the absence of BH(4), these enzymes become uncoupled, fail to produce nitric oxide, and begin to produce superoxide and other reactive oxygen species (ROS). BH(4) levels are modulated by a complex biosynthetic pathway, salvage enzymes, and by oxidative degradation. The enzyme GTP cyclohydrolase-1 catalyzes the first step in the de novo synthesis of BH(4) and new evidence shows that this enzyme is regulated by phosphorylation, which reduces its interaction with its feedback regulatory protein (GFRP). In the setting of a variety of common diseases, such as atherosclerosis, hypertension, and diabetes, reactive oxygen species promote oxidation of BH(4) and inhibit expression of the salvage enzyme dihydrofolate reductase (DHFR), promoting accumulation of BH(2) and NOS uncoupling. There is substantial interest in therapeutic approaches to increasing tissue levels of BH(4), largely by oral administration of this agent. BH(4) treatment has proved effective in decreasing atherosclerosis, reducing blood pressure, and preventing complications of diabetes in experimental animals. While these basic studies have been very promising, there are only a few studies showing any effect of BH(4) therapy in humans in treatment of these common problems. Whether BH(4) or related agents will be useful in treatment of human diseases needs additional study.

Modulation of Nitric Oxide Synthase Activity in Brain, Liver, and Blood Vessels of Spontaneously Hypertensive Rats by Ascorbic Acid: Protection from Free Radical Injury

End organ damage in essential hypertension has been linked to increased oxygen free radical generation, reduced antioxidant defense, and/or attenuation of nitric oxide synthase (NOS) activity. Ascorbic acid (AA), a water-soluble antioxidant, has been reported as a strong defense against free radicals in both aqueous and nonaqueous environment. In this study we examined the hypothesis that antioxidant ascorbic acid may confer protection from increased free radical activity in brain, liver, and blood vessels of spontaneously hypertensive rats (SHR). Male SHRs were divided into groups: SHR + AA (treated with AA, 1 mg/rat/day; for 12 weeks) or SHR (untreated). Wister-Kyoto rats (WKY) served as the control. Mean systolic blood pressure (SBP) in treated and untreated SHR was 145 +/- 7 mmHg and 142 +/- 8 mmHg, respectively. AA treatment prevented the increase in systolic blood pressure in SHR by 37 +/- 1% (p < 0.05). NOS activity in the brain, liver, and blood vessels of WKY rat was 1.82 +/- 0.02, 0.14 +/- 0.003, and 1.54 +/- 0.06 pmol citruline/mg protein, respectively. In SHR, total NOS activity was significantly reduced by 52 +/- 1%, 21 +/- 3%, and 44 +/- 4%, respectively. AA increased NOS activity in brain, liver, and blood vessels of SHR from 0.87 +/-.03, 0.11 +/-.01, and 0.87 +/-.08 pmol citruline/mg protein to 0.93 +/- 0.01, 0.13 +/- 0.001, and 1.11 +/- 0.03 pmol citruline/mg protein (p < 0.05), respectively. Lipid peroxides in the brain, liver, and blood vessels from WKY rats were 0.87 +/- 0.06, 0.11 +/- 0.005, and 0.47 +/- 0.04 nmol MDA equiv/mg protein, respectively. In SHR, lipid peroxides in brain, liver, and blood vessels were significantly increased by 40 +/- 3%, 64 +/- 3%, and 104 +/- 13%, respectively. AA reduced lipid peroxidation in liver and blood vessels by 17 +/- 1% and 34 +/- 3% but not in brain. Plasma lipid peroxides were almost doubled in SHR (p < 0.01) together with a reduction in total antioxidant status (6 +/- 0.1%; p < 0.05), nitrite (53 +/- 2%; p < 0.05) and superoxide dismutase (SOD) activity (36 +/- 2%; p < 0.05). AA treatment reduced plasma lipid peroxide (p < 0.001), and increased TAS (p < 0.001), nitrite (p < 0.001), and SOD activity (p < 0.001). From this study, we conclude that brain, liver, and blood vessels in SHR are susceptible to free radical injury, which reduces the availability of NO either by scavenging it or by reducing its production via inhibiting NOS. In addition, brain, liver, and blood vessels in SHR; may be protected by antioxidant, which improves total antioxidant status, and SOD thus may prevent high blood pressure and its complications.

Ascorbate sustains neutrophil NOS expression, catalysis, and oxidative burst

Previous studies from this lab have demonstrated that in vitro ascorbate augments neutrophil nitric oxide (NO) generation and oxidative burst. The present study was therefore undertaken in guinea pigs to further assess the implication of ascorbate deficiency in vivo on neutrophil ascorbate and tetrahydrobiopterin content, NOS expression/activity, phagocytosis, and respiratory burst. Ascorbate deficiency significantly reduced ascorbate and tetrahydrobiopterin amounts, NOS expression/activity, and NO as well as free radical generation in neutrophils from scorbutics. Ascorbate and tetrahydrobiopterin supplementation in vitro, though, significantly enhanced NOS catalysis in neutrophil lysates and NO generation in live cells, but could not restore them to control levels. Although phagocytic activity remained unaffected, scorbutic neutrophils were compromised in free radical generation. Ascorbate-induced free radical generation was NO dependent and prevented by NOS and NADPH oxidase inhibitors. Augmentation of oxidative burst with dehydroascorbate (DHA) was counteracted in the presence of glucose (DHA uptake inhibitor) and iodoacetamide (glutaredoxin inhibitor), suggesting the importance of ascorbate recycling in neutrophils. Ascorbate uptake was, however, unaffected among scorbutic neutrophils. These observations thus convincingly demonstrate a novel role for ascorbate in augmenting both NOS expression and activity in vivo, thereby reinforcing oxidative microbicidal actions of neutrophils.

L-ascorbic acid enhances apoptosis in human gastric carcinoma cell line AZ-521 cells infected with Mycoplasma hyorhinis

Mycoplasma hyorhinis (M. hyorhinis) exerts multiple effects on cell metabolisms including apoptosis mediated by their endonucleases and nitric oxide production in vitro. Although AsA is preferable to health in general because of its reactive oxygen species scavenging activity, we found that in a human carcinoma cell line AZ-521 infected with M. hyorhinis, apoptosis was enhanced by addition of L-ascorbic acid (AsA) to the cell cultures. No significant differences were evident between the AZ-521 cells with and without AsA (AsA-) after 24 hr of incubation in the mitochondrial fluorescence. M. hyorhinis-infected AZ-521 cells treated with AsA (AsA +) have developed distinct DNA ladders as compared to the control cells AsA- after 24 hr of incubation. Marked cytopathic effects were rather apparent in AsA-treated cells than in control cells AsA- after 24 hr. Our data demonstrate that AsA addition to cell cultures enhances apoptosis induced by M. hyorhinis infection. We suggest that the presence of another external apoptotic pathway by M. hyorhinis infection.

Phosphoinositide 3-kinase in nitric oxide synthesis in macrophage: critical dimerization of inducible nitric-oxide synthase

Phosphoinositide 3-kinase (PI3K) has important functions in various biological systems, including immune response. Although the role of PI3K in signaling by antigen-specific receptors of the adaptive immune system has been extensively studied, less is known about the function of PI3K in innate immunity. In the present study, we demonstrate that macrophages deficient for PI3K (p85alpha regulatory subunit) are impaired in nitric oxide (NO) production upon lipopolysaccharide and interferon-gamma stimulation and thus vulnerable for intracellular bacterial infection such as Chlamydophila pneumoniae. Although expression of inducible nitric-oxide synthase (iNOS) is induced normally in PI3K-deficient macrophages, dimer formation of iNOS protein is significantly impaired. The amount of intracellular tetrahydrobiopterin, a critical stabilizing cofactor for iNOS dimerization, is decreased in the absence of PI3K. In addition, induction of GTP cyclohydrolase 1, a rate-limiting enzyme for biosynthesis of tetrahydrobiopterin, is greatly reduced. Our current results demonstrate a critical role of class IA type PI3K in the bactericidal activity of macrophages by regulating their NO production through GTP cyclohydrolase 1 induction.

Ascorbate uptake and antioxidant function in peritoneal macrophages

Since activated macrophages generate potentially deleterious reactive oxygen species, we studied whether ascorbic acid might function as an antioxidant in these cells. Thioglycollate-elicited murine peritoneal macrophages contained about 3 mM ascorbate that was halved by culture in ascorbate-free medium. However, the cells took up added ascorbate to concentrations of 6-8 mM by a high-affinity sodium-dependent transport mechanism. This likely reflected the activity of the SVCT2 ascorbate transporter, since its message and protein were present in the cells. Activation of the cells by phagocytosis of latex particles depleted intracellular ascorbate, although not below the basal levels present in the cells in culture. Glutathione (GSH) was unaffected by phagocytosis, suggesting that ascorbate was more sensitive to the oxidant stress of phagocytosis than GSH. Phagocytosis induced a modest increase in reactive oxygen species as well as a progressive loss of alpha-tocopherol, both of which were prevented in cells loaded with ascorbate. These results suggest that activated macrophages can use ascorbate to lessen self-generated oxidant stress and spare alpha-tocopherol, which may protect these long-lived cells from necrosis or apoptosis.