Induction of inducible nitric oxide synthase gene expression by Pokeweed mitogen

Ovariectomy provokes inflammatory and cardiovascular effects of endotoxemia in rats: Dissimilar benefits of hormonal supplements

The female gender is protected against immunological complications of endotoxemia. Here we investigated whether gonadal hormone depletion by ovariectomy (OVX) uncovers inflammatory and cardiovascular effects of endotoxemia and whether these effects are reversed by hormone replacement therapies. Changes in inflammatory cytokines, blood pressure (BP), left ventricular (LV) function, and cardiac autonomic activity caused by lipopolysaccharide (LPS) in conscious female rats with different hormonal states were determined. In contrast to no effects in sham-operated females, treatment of OVX rats with LPS (i) decreased BP, (ii) increased spectral low-frequency/high-frequency ratio of HRV, denoting enhanced cardiac sympathetic dominance, (iii) attenuated reflex tachycardic responses to sodium nitroprusside, and (iv) increased systolic contractility (dP/dt_max). The developed hypotension was (i) fully eliminated in estrogen (E₂)-pretreated OVX rats, (ii) partially counteracted after selective activation of estrogen receptor-α (PPT) or β (DPN). All estrogenic compounds abrogated LPS enhancement of cardiac sympathetic drive. However, PPT was more successful than E2 or DPN in compromising LPS depression in baroreflex activity and elevation in dP/dt_max. Molecular studies showed that PPT was most effective in attenuating the upregulated myocardial expressions of NF-κB and iNOS in endotoxic OVX rats. Myocardial expression of the defensive HSP70 was comparably increased by all estrogenic products. Except for improved cardiac spectral activity, none of these functional or molecular entities was affected by medroxyprogesterone acetate (MPA). Overall, our data suggest diverse therapeutic advantages for gonadal hormones in the worsened endotoxic complications in rats with surgical menopause, with probably more favorable role for ERα agonism within this context.

Inflammatory effect of endosulfan via NF-κB activation in macrophages

Macrophages are essential for the inflammatory response process because they release a wide variety of proinflammatory mediators. Endosulfan is extremely toxic to invertebrates and has been implicated in various mammalian toxicities. However, its influence on production of cytokine or on the functions of macrophages is unclear. This study examined the effects of endosulfan on the production of nitric oxide (NO) and proinflammatory cytokines (IL-1beta, IL-6, TNF-alpha), and examined the molecular mechanism in macrophages. Exposing macrophages to endosulfan induced the production of NO and proinflammatory cytokines and the expression of these genes. The transient transfection and electrophoretic mobility shift assays with the NF-kappaB binding sites showed that the NF-kappaB transcription factor mediated the endosulfan-induced increase in the expression levels of iNOS and proinflammatory cytokines. These results show that endosulfan stimulates the production of NO and proinflammatory cytokines and can up-regulate the gene expression levels through NF-kappaB transactivation. Overall, these results suggest that endosulfan has inflammatory potential.

Endotoxin contamination in commercially available pokeweed mitogen contributes to the activation of murine macrophages and human dendritic cell maturation

Commercially available pokeweed mitogen (PWM) has been reported to activate macrophages, leading to production of proinflammatory cytokines and nitric oxide (NO). However, we found that polymyxin B (PMB), a specific inhibitor of endotoxin activity, inhibited the PWM-induced expression of proinflammatory cytokines and NO and the activation of Toll-like receptor 4 (TLR4). A kinetic-turbidimetric Limulus amebocyte lysate assay demonstrated that commercial PWM contained substantial endotoxin, over 10(4) endotoxin units/mg of the PWM. A PWM repurified by PMB-coupled beads no longer induced the expression of proinflammatory cytokines, TLR4 activation, or dendritic cell maturation. However, the repurified PWM remained able to induce proliferation of human lymphocytes, which is a representative characteristic of PWM. These results suggest that commercial PWM might be contaminated with a large amount of endotoxin, resulting in the attribution of misleading immunological properties to PWM.

The coffee diterpene kahweol suppress the inducible nitric oxide synthase expression in macrophages

Excessive nitric oxide production by inducible nitric oxide synthase (iNOS) in stimulated inflammatory cells is thought to be a causative factor of cellular injury in cases of inflammation. In recent studies, it has been shown that kahweol, coffee-specific diterpene, exhibit chemoprotective effects. In this study, we investigated the effects of kahweol on the production of and the expression of inducible nitric oxide synthase (iNOS) in lipopolysaccharide (LPS)-activated RAW 264.7 macrophages. The nitrite production induced by LPS was markedly reduced in a dose-dependent manner. In addition, kahweol suppressed the expression of iNOS protein and iNOS mRNA. Since iNOS transcription has been shown to be under the control of the transcription factor, NF-kappaB, the effects of kahweol on NF-kappaB activation were examined. Transient transfection experiments showed that kahweol inhibited NF-kappaB-dependent transcriptional activity. Moreover, electrophoretic mobility shift assay experiments indicated that kahweol blocked the LPS-induced activation of NF-kappaB. The results of these studies suggest that the suppression of the transcriptional activation of iNOS by kahweol might be mediated through the inhibition of NF-kappaB activation. Taken together, the results of our study provide evidence that kahweol possess an anti-inflammatory potential, which constitutes a previously unrecognized biologic activity, and which may provide new insights into the inflammatory process.

Down-regulation of inducible nitric oxide synthase and tumor necrosis factor-alpha expression by bisphenol A via nuclear factor-kappaB inactivation in macrophages

Bisphenol A [BPA, 2,2bis(4hydroxyphenyl)propane] is reported to have estrogenic activity; however, its influence on cytokine production or immune system function remains unclear. In this study, we investigated the effects of BPA on the production of nitric oxide (NO) and tumor necrosis factor-alpha (TNF-alpha), and on the level of inducible nitric oxide synthase (iNOS) and TNF-alpha gene expression in mouse macrophages. BPA alone did not affect NO or TNF-alpha production. In contrast, BPA inhibited lipopolysaccharide (LPS)-induced NO and TNF-alpha production, and the levels of iNOS and TNF-alpha mRNA in a dose-dependent manner. Treatment with ICI 182.780, an estrogenreceptor antagonist, inhibited the suppressive effects of BPA. Transient expression and electrophoretic mobility shift assays with NF-kappaB binding sites revealed that BPA reduced the levels of the LPS-induced NF-kappaB transcription factor complex. These results demonstrate that BPA may affect the regulation of the immune system function by reducing NO and TNF-alpha production via the inhibition of NF-kappaB transactivation mediated through the estradiol receptor.

Suppression of inducible nitric oxide synthase and tumor necrosis factor-alpha expression by 4-nonylphenol in macrophages

4-Nonylphenol (NP) is reported to have estrogenic activity; however, its influence on cytokine production or immune system function remains unclear. In this study we investigated the effects of NP on the production of nitric oxide (NO) and tumor necrosis factor-alpha (TNF-alpha), and on the level of inducible nitric oxide synthase (iNOS) and TNF-alpha gene expression in mouse macrophages. NP alone did not affect NO or TNF-alpha production. In contrast, NP inhibited lipopolysaccharide (LPS)-induced NO and TNF-alpha production, and the levels of iNOS and TNF-alpha mRNA in a dose-dependent manner. Treatment with ICI 182.780, an estrogen-receptor antagonist, inhibited the suppressive effects of NP. NF-kappaB sites have been identified in the promoter of the iNOS and TNF-alpha genes. Transient expression and electrophoretic mobility shift assays with NF-kappaB binding sites revealed that NP reduced the levels of the LPS-induced NF-kappaB transcription factor complex. These results demonstrate that NP may affect the regulation of the immune system function by reducing NO and TNF-alpha production via the inhibition of NF-kappaB transactivation mediated through the estradiol receptor.

Induction of inducible nitric oxide synthase expression by 18beta-glycyrrhetinic acid in macrophages

Glycyrrhizin (GL), a triterpenoid saponin fraction of licorice, is reported to have anti-viral and anti-tumor activities and is metabolized to 18beta-glycyrrhetinic acid (GA) in the intestine by intestinal bacteria. However, the mechanism underlying its effects is poorly understood. To further elucidate the mechanism of GA, the aglycone of GL, we investigated the effects of GA on the release of nitric oxide (NO) and at the level of inducible NO synthase (iNOS) gene expression in mouse macrophages. We found that GA elicited a dose-dependent increase in NO production and in the level of iNOS mRNA. Since iNOS transcription has been shown to be under the control of the transcription factor nuclear factor kappaB (NF-kappaB), the effects of GA on NF-kappaB activation were examined. Transient expression assays with NF-kappaB binding sites linked to the luciferase gene revealed that the increased level of iNOS mRNA, induced by GA, was mediated by the NF-kappaB transcription factor complex. By using DNA fragments containing the NF-kappaB binding sequence, GA was shown to activate the protein/DNA binding of NF-kappaB to its cognate site, as measured by electrophoretic mobility shift assay. These results demonstrate that GA stimulates NO production and is able to up-regulate iNOS expression through NF-kappaB transactivation in macrophages.

Ursolic acid enhances nitric oxide and tumor necrosis factor-alpha production via nuclear factor-kappaB activation in the resting macrophages

Ursolic acid (UA), a pentacyclic triterpene acid, is reported to have anti-tumor activities; however, the mechanism underlying its anti-tumorigenic effects is poorly understood. To further determine the mechanism of UA, we investigated the effects of UA on the release of nitric oxide (NO) and tumor necrosis factor-alpha (TNF-alpha), and on the level of inducible nitric oxide synthase (iNOS) and TNF-alpha gene expression in mouse resting macrophages. We found that UA elicited a dose-dependent increase in NO and TNF-alpha production, and the level of iNOS and TNF-alpha mRNA. Transient expression and electrophoretic mobility shift assays with nuclear factor-kappaB (NF-kappaB) binding sites revealed that the increased level of iNOS mRNA and TNF-alpha mRNA induced by UA were mediated by the NF-kappaB transcription factor complex. These results demonstrate that UA stimulates NO and TNF-alpha release and is able to upregulate iNOS and TNF-alpha expression through NF-kappaB transactivation in the resting macrophages.

Nitric oxide and tumor necrosis factor-alpha production by oleanolic acid via nuclear factor-kappaB activation in macrophages

Oleanolic acid (OA), a pentacyclic triterpene acid, is reported to have antitumor activities; however, the mechanism underlying its antitumorigenic effects is poorly understood. To further determine the mechanism of OA, we investigated the effects of OA on the release of nitric oxide (NO) and tumor necrosis factor-alpha (TNF-alpha) and on the level of inducible nitric oxide synthase (iNOS) and TNF-alpha gene expression in mouse macrophages. We found that OA elicited a dose-dependent increase in NO and TNF-alpha production. Reverse transcription-polymerase chain reaction showed that the increased NO and TNF-alpha secretion were due to an increase in iNOS mRNA and TNF-alpha mRNA, respectively. Since iNOS and TNF-alpha transcription have recently been shown to be under the control of the NF-kappaB transcription factor, the effects of OA on NF-kappaB activation were examined using a transient transfection assay and an electrophoretic mobility shift assay (EMSA). Transient expression assays with NF-kappaB binding sites linked to the luciferase gene revealed that the increased levels of iNOS mRNA and TNF-alpha mRNA induced by OA were mediated by the NF-kappaB transcription factor complex. Using DNA fragments containing the NF-kappaB binding sequence, OA was shown to activate the protein/DNA binding of NF-kappaB to its cognate site as measured by EMSA. These results demonstrate that OA stimulates NO and TNF-alpha release and is able to upregulate iNOS and TNF-alpha expression through NF-kappaB transactivation, which may be the mechanism whereby OA elicits its biological effects.

The effects of pokeweed mitogen (PWM) and phytohemagglutinin (PHA) on bovine oocyte maturation and embryo development in vitro

The effects of two commonly used cell culture mitogens, pokeweed (PWM) and phytohemagglutinin (PHA) on bovine oocyte maturation in vitro (IVM) and preimplantation embryo development in vitro were evaluated by randomized complete block experimental design with three treatments. Effects were measured by quantifying subsequent embryo development. Oocyte maturation was adversely affected by PWM-containing medium as indicated by a decrease in cleavage rate and subsequent embryo development to morula and blastocyst stages. Embryo developmental competence was also adversely affected by PWM. Development in PHA-containing medium was significantly better (P<0.05) than in the PWM treatment, although there was no difference (P>0.05) when compared to Control. We conclude that there are no beneficial effects in adding mitogenic agents to culture medium to enhance in vitro embryo production and development.

Cytokine-mediated suppression of cytochrome P450 1A1 in Hepa-1c1c7 cells by pokeweed mitogen

This study investigated the effects of pokeweed mitogen (PWM) on the regulation of cytochrome P450 (P450) 1A1 expression in an in vitro model, using murine hepatoma cell line Hepa-1c1c7 and murine macrophage cell line RAW 264.7 cell cultures. PWM added directly to Hepa-1c1c7 cells had no effect on 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)-induced P450 1A1-specific 7-ethoxyresorufin O-deethylase (EROD) activity. However, TCDD-induced EROD activity and P450 1A1 mRNA levels were markedly suppressed when Hepa-1c1c7 cells were cultured with PWM-treated conditioned media from RAW 264.7 in a dose-dependent manner. Concomitant treatment with PWM and pentoxifylline, a TNFalpha synthesis inhibitor, to RAW 264.7 cells decreased the suppressive effects of PWM on TCDD-induced EROD activity. In PWM-exposed RAW 264.7 cell cultures, TNFalpha and IL-6 levels increased in a dose-dependent fashion. When antibodies to TNFalpha or/and IL-6 were added to PWM-treated conditioned media from RAW 264.7, the suppression of EROD activity was inhibited. These results suggested the suppression of P450 1A1 by PWM was mediated exclusively by TNFalpha and IL-6, released from macrophages.