Tetrahydrobiopterin modulates cyclooxygenase-2 expression in human mesangial cells

Intraplantar injection of tetrahydrobiopterin induces nociception in mice

Tetrahydrobiopterin (BH4) is implicated in the development and maintenance of chronic pain. After injury/inflammation, the biosynthesis of BH4 is markedly increased in sensory neurons, and the pharmacological and genetic inhibition of BH4 shows analgesic effects in pre-clinical animal pain models. Intrathecal injections of BH4 have been shown to induce and enhance pain-like behaviours in rats, suggesting that under chronic pain conditions BH4 may act by facilitating central sensitisation. So far it is unknown whether BH4 acts on peripheral sites of the somatosensory system or whether BH4 per se provokes nociceptive pain behaviours. The purpose of this study was therefore to investigate the acute nociceptive effects of intraplantar injection of BH4. BH4 was found to induce dose-dependent licking/biting of the paw lasting 5 min, which was not observed following an injection of biopterin (inactive BH4 metabolite). Paw swelling, measured as paw thickness and weight, was not observed after BH4 injection. To explore possible mechanisms of action of BH4, the effect of local pre-treatment with indomethacin, Nω-nitro-L-arginine methyl ester, Nω-nitro-L-arginine, capsazepine and ruthenium red was tested. Morphine served as a positive control. Intraplantar pre-injection of morphine dose-dependently inhibited BH4-induced nociception, while none of the other compounds showed any statistical significant antinociception. These results suggest that BH4 exhibits nociceptive properties at peripheral sites of the somatosensory system, proposing an as yet unexplored involvement of BH4 in peripheral nociceptive processes. However, this appears not to be mediated through nitric oxide and prostaglandin release or by activation of the transient receptor potential vanilloid 1.

Activation of phosphoinositide 3-kinase in response to inflammation and nitric oxide leads to the up-regulation of cyclooxygenase-2 expression and subsequent cell proliferation in mesangial cells

In this study, we showed that nitric oxide (NO) donors induced the mesangial cell proliferation and cyclooxygenase-2 (COX-2) protein expression in murine mesangial cells. An inflammatory condition [lipopolysaccharide (LPS) plus interferon-gamma (IFN-gamma)] could also induce cell proliferation and significantly enhance inducible nitric oxide synthase (iNOS) and COX-2 expression. Phosphoinositide 3-kinase (PI3K) inhibitor, LY294002, inhibited these responses. LPS/IFN-gamma-induced COX-2 expression in mesangial cells could be inhibited by iNOS inhibitor, aminoguanidine. Selective COX-2 inhibitor, NS398, was capable of inhibiting NO donor- or LPS/IFN-gamma-induced mesangial cell proliferation. Both NO donor and LPS/IFN-gamma markedly activated the PI3K activity and the phosphorylation of Akt and nuclear factor (NF)-kappaB DNA binding activity in mesangial cells, which could be inhibited by LY294002 and transfection of dominant-negative vectors of PI3K/p85 and Akt. These results indicate that a PI3K/Akt-dependent pathway involved in the NO-regulated COX-2 expression and cell proliferation in mesangial cells under inflammatory condition.

Interleukin-1beta-induced nitric oxide production and inhibition of insulin secretion in rat islets of langerhans is dependent upon the nitric oxide synthase cofactor tetrahidrobiopterin

Interleukin (IL)-1 beta-induced inhibition of glucose-stimulated insulin secretion in rat islets of Langerhans is mediated in part by nitric oxide (NO). The NO synthase cofactor 5,6,7,8-tetrahydrobiopterin (BH(4)) supports NO synthesis in many cell types and IL-1 beta-induced NO generation and inhibition of insulin secretion have been previously correlated with intracellular BH(4 )levels in rat insulinoma cells. Using rat islets and the beta cell line BRIN-BD11, we have investigated whether synthesis of BH(4) limits IL-1beta-induced NO generation and inhibition of glucose-induced insulin secretion. IL-1 beta-induced NO generation by BRIN cells and islets was reduced by 2,4-diamino-6-hydroxypyrimidine (DAHP), an inhibitor of de novo BH(4) synthesis. Sepiapterin, the substrate for salvage pathway BH(4) synthesis, reversed this inhibitory effect of DAHP in islets but not BRIN cells. DAHP reversed IL-1 beta-induced inhibition of islet insulin secretion, an effect prevented by sepiapterin. We conclude that BH(4) generation is necessary for IL-1 beta-induced NO generation in rat islets and BRIN cells. While a contribution of non-NO mediators cannot be excluded, our results support the proposal that IL-1 beta-induced, NO-mediated inhibition of insulin secretion in rat islets is dependent on the NOS cofactor BH(4).

Regulation of cyclooxygenase-2 expression by nitric oxide in cells

Two different cyclooxygenases (COXs) are functional in mammals: COX-1 and COX-2. COX-2 is mainly an inducible isoform that shares significant features with inducible nitric oxide synthase (iNOS) in terms of its tissue distribution and participation in pathophysiological phenomena. Furthermore, the product of iNOS catalysis, nitric oxide (NO), is an important regulator of COX-2 activity and expression, and the products of COX-1 and COX-2 (diverse prostanoids) may also influence iNOS expression. Both positive and negative effects of NO on COX-2 expression have been encountered in experimental systems, showing that the outcome of the NO-COX-2 interaction is exquisitely dependent upon the temporal frame and the cell type studied. The pathophysiological significance of NO-COX cross-talk also arises from in vivo studies, in which most evidence points to a positive effect of NO on COX-2 activity and/or expression. This emphasizes the need to understand the underlying mechanisms. Among these, the capacity of NO and its effector cyclic GMP to modulate the function of several target proteins, including transcription factors such as nuclear factor-kappaB and activator protein-1, appears as the key pathway by which NO may regulate COX-2 expression. Given the capacity of some prostanoids to modulate the inflammatory response, the interplay between NO synthase and COX pathways stands at the center of the pathophysiological basis of inflammatory diseases.

Effects of dehydroepiandrosterone on mitogen-activated protein kinase in human aortic smooth muscle cells

The objective of the present study was to determine whether dehydroepiandrosterone (DHEA) modifies growth factor-induced mitogen-activated protein kinase (MAPK) activation, based on our previous study demonstrating that DHEA attenuates fetal calf serum-induced proliferation in human male aortic smooth muscle cells (human male aortic SMCs). Human male aortic SMCs were used for this study. Platelet-derived growth factor-BB (PDGF-BB), epidermal growth factor (EGF), and basic fibroblast growth factor (bFGF), but not insulin-like growth factor-1 (IGF-1), stimulated MAPK activity. Only MAPK activation induced by PDGF-BB was reduced by pretreatment with DHEA, although DHEA did not affect the MAPK activation induced by EGF or bFGF. The basal and PDGF-stimulated MAPK activity were decreased by two types of cyclic AMP (cAMP) elevating agents and increased by cAMP-dependent protein kinase (PKA) inhibitor in human male aortic SMCs, suggesting that cAMP regulates MAPK negatively. The intracellular cAMP was increased by PDGF-BB. The increase of cAMP by PDGF-BB was augmented by pretreatment with DHEA, although DHEA alone did not affect cAMP. Neither EGF nor bFGF affected cAMP with and without DHEA pretreatment. Secretion of PGE2 induced by PDGF was augmented by pretreatment with DHEA. Stimulatory effects of DHEA on the production of PGE2 and cAMP were partially canceled by aromatase inhibitor and completely canceled by indomethacin or selective inhibitor of cyclooxygenase-2. These results suggest that DHEA inhibited MAPK activation induced by PDGF-BB via PGE2 overproduction and subsequent cAMP-dependent pathway in human male aortic SMCs.

Dual effect of nitric oxide donors on cyclooxygenase-2 expression in human mesangial cells

Nitric oxide (NO) is emerging as a key regulator of gene expression, capable of playing either positive or negative roles. The results of this study indicate that NO exerts a dual effect on cyclooxygenase-2 (COX-2) expression in human mesangial cells (HMC). Treatment of HMC with NO synthase inhibitors attenuated interleukin-1beta (IL-1beta/tumor necrosis factor-alpha (TNF-alpha)-elicited COX-2 protein and mRNA expression, suggesting a positive role of endogenous NO on COX-2 induction. However, NO donors (sodium nitroprusside [SNP] and S-nitroso-N-acetylpenicillamine [SNAP]) amplified cytokine-elicited COX-2 expression at early time points of treatment (up to 8 h for mRNA and up to 24 h for protein expression), but were inhibitory at later times. Oligonucleotide decoy experiments confirmed the importance of nuclear factor kappaB (NF-kappaB) activation for COX-2 induction by IL-1beta/TNF-alpha. Treatment with N(G)-nitro-L-arginine methyl ester (L-NAME) did not affect initial activation of NF-kappaB by IL-1beta/TNF-alpha, but unveiled an inhibitory effect of NO generation on NF-kappaB activity after 4 h. In HMC supplemented with SNP, cytokine-induced NF-kappaB activation was potentiated at early times of induction (5 to 15 min), but inhibited at later times (1 to 4 h), suggesting a dual effect of NO donors on NF-kappaB activation. Interestingly, IkappaBalpha protein levels followed a reciprocal pattern of expression: IkappaBalpha levels were lower at early times of induction in NO donor-supplemented cells; however, after 1 h of treatment, IkappaBalpha levels became higher than in cells treated only with cytokines. In the presence of SNP, cytokine-elicited IkappaBalpha mRNA induction was initially delayed, but was amplified at later times. These changes in IkappaBalpha expression could contribute to the dual effects of NO donors on NF-kappaB activation and COX-2 expression in HMC.

Regulation of cyclooxygenase-2 expression in human mesangial cells--transcriptional inhibition by IL-13

Activated mesangial cells may play an important part in glomerulonephritis. Cytokines can modulate the release of prostanoids by human mesangial cells (HMC). We have investigated the effects of pro-inflammatory stimuli on COX-2 expression in HMC and its potential modulation by interleukin (IL)-13. HMC released increased amounts of prostaglandin E2 (PGE2) after treatment with several combinations of IL-1 beta, tumor necrosis factor (TNF)-alpha and/or lipopolysaccharide. Increases in PGE2 correlated with the induction of COX-2 protein expression. The accumulation of PGE2 elicited by a combination of IL-1 beta/TNF-alpha correlated closely with the temporal pattern of COX-2 protein expression, which reflected the induction of COX-2 mRNA. IL-13 inhibited IL-1 beta/TNF-alpha-elicited PGE2 production, as well as COX-2 protein and mRNA expression in a concentration-dependent fashion. With 50 ng.mL-1 IL-13 these parameters were inhibited by 90, 80 and 84%, respectively. In HMC transfected with the 5' regulatory region of the COX-2 gene, IL-13 suppressed cytokine-induced promoter activation. Our results suggest that COX-2 expression is a major target for IL-13-mediated abrogation of prostaglandin release by HMC and support that this process takes place by transcriptional inhibition of the COX-2 gene.