Effects of disulfiram, cyanamide and 1-aminocyclopropanol on the aldehyde dehydrogenase activity in human erythrocytes and leukocytes

The effects of the aldehyde dehydrogenase (ALDH; EC 1.2.1.3) inhibitors disulfiram, cyanamide and 1-aminocyclopropanol (ACP) on the ALDH activities in human erythrocytes and leukocytes were studied. Assays were performed by incubating intact or sonicated blood cells in the presence of different concentrations of the inhibitors, using 3,4-dihydroxyphenylacetaldehyde, the aldehyde derived from dopamine oxidation, as the substrate. The amount of acid metabolite formed was measured using high-performance liquid chromatography with electrochemical detection. The erythrocyte ALDH was extremely sensitive to disulfiram, and only about 0.5 microM was needed to cause a 50% inhibition of the activity. The leukocyte activity was less sensitive, and showed a similar degree of inhibition at an 100-fold higher concentration of disulfiram. Cyanamide and ACP were both potent inactivators of the leukocyte ALDH activity, giving a 50% inhibition at concentrations of 10 and 50 microM, respectively, whereas the erythrocyte activity was much less affected. Diethyldithiocarbamate, the reduced metabolite of disulfiram, and coprine, from which ACP is derived, were much less effective inhibitors of the erythrocyte and leukocyte ALDH activities than were disulfiram and ACP.     

Inactivation of aldophosphamide by human aldehyde dehydrogenase isozyme 3

Tumors resistant to chemotherapeutic oxazaphosphorines such as cyclophosphamide often overexpress aldehyde dehydrogenase (ALDH), some isozymes of which catalyze the oxidization of aldophosphamide, an intermediate of cyclophosphamide activation, with formation of inert carboxyphosphamide. Since resistance to oxazaphosphorines can be produced in mammalian cells by transfecting them with the gene for human ALDH isozyme 3 (hALDH3), it seems possible that patients receiving therapy for solid tumors with cyclophosphamide might be protected from myelosuppression by their prior transplantation with autologous bone marrow that has been transduced with a retroviral vector causing overexpression of hALDH3. We investigated whether retroviral introduction of hALDH3 into a human leukemia cell line confers resistance to oxazaphosphorines. This was examined in the polyclonal transduced population, that is, without selecting out high expression clones. hALDH3 activity was 0.016 IU/mg protein in the transduced cells (compared with 2x10(-5) IU/mg in untransduced cells), but there was no detectable resistance to aldophosphamide-generating compounds (mafosfamide or 4-hydroperoxycyclophosphamide). The lack of protection was due, in part, to low catalytic activity of hALDH3 towards aldophosphamide, since, with NAD as cofactor, the catalytic efficiency of homogeneous, recombinant hALDH3 for aldophosphamide oxidation was shown to be about seven times lower than that of recombinant hALDH1. The two polymorphic forms of hALDH3 had identical kinetics with either benzaldehyde or aldophosphamide as substrate. Results of initial velocity measurements were consistent with an ordered sequential mechanism for ALDH1 but not for hALDH3; a kinetic mechanism for the latter is proposed, and the corresponding rate equation is presented.     

Effect of flavin adenine dinucleotide on ultraviolet B induced damage in cultured human corneal epithelial cells

This study evaluated the effects of flavin adenine dinucleotide (FAD) on ultraviolet B (UV-B)-induced damage in cultured human corneal epithelial (HCE-T) cells. The cultured HCE-T cells were treated with 0.003125-0.05% FAD before exposure to 80 mJ/cm² UV-B. Cell viability was measured 24 h after UV-B irradiation using the MTS assay. Reactive oxygen species (ROS) were detected 30 min after UV-B irradiation using 5-(and-6)-chloromethyl-2',7'-dichlorodihydrofluorescein diacetate acetyl ester. Apoptosis was evaluated 4 h after UV-B irradiation in the caspase-3/7 activity assay. UV-B irradiation reduced cell viability and stimulated ROS production and caspase-3/7 activity in HCE-T cells. Pretreatment of UV-B irradiated HCE-T cells with FAD significantly attenuated cell viability reduction and inhibited the stimulation of both ROS production and caspase-3/7 activity due to UV-B exposure compared with those with vehicle (0% FAD). These results clarified that FAD inhibits ROS-mediated apoptosis by UV-B irradiation in HCE-T cells and suggest that FAD may be effective as a radical scavenger in UV-B-induced corneal damage.     

Dexamethasone inhibits invasion of murine T cells through cultured fibroblastic monolayers

Despite the wide clinical use of glucocorticoids in the chemotherapy of leukaemia and lymphoma, there have been limited efforts at understanding the effects of these hormones on metastasis formation. The purpose of this study was to investigate the effects of glucocorticoids on the tissue-infiltrating capability of lymphoid cells. Using an in vitro invasion assay, we found that dexamethasone, a synthetic glucocorticoid analogue, inhibited the invasion of a murine T-cell hybridoma through a monolayer of fibroblast-like cells. Even low doses of dexamethasone were effective at inhibiting cellular transmigration (EC50 = 0.4 nM). A maximal decrease was observed after an overnight culture in the presence of dexamethasone. The effect persisted for at least 24 h after removal of the drug and required the binding of the hormone to its intracellular glucocorticoid receptor. Our results suggest that the decreased invasiveness of dexamethasone-treated cells is not the consequence of reduced motility or deficient production of an autocrine factor required for cell migration. This in vitro study suggests that glucocorticoids may act to reduce dissemination of lymphoma cells in vivo.     

Inhibition of human erythrocyte and leukocyte aldehyde dehydrogenase activities by diethylthiocarbamic acid methyl ester. An in vivo metabolite of disulfiram

The inhibitory effects of diethylthiocarbamic acid methyl ester (DTC-Me), an in vivo metabolite of disulfiram (Antabuse), on the aldehyde dehydrogenase (ALDH; EC 1.2.1.3) activities in human erythrocytes and leukocytes were studied. ALDH assays were performed by incubating intact isolated blood cells in the presence of different concentrations of DTC-Me, using 3,4-dihydroxy-phenylacetaldehyde, the aldehyde derived from dopamine, as the substrate. DTC-Me was more selective as inhibitor of the leukocyte ALDH activity (which resembles the liver "mitochondrial" low Km ALDH), whereas both disulfiram and diethyldithiocarbamic acid, the reduced monomer of disulfiram, were more selective for the erythrocyte ALDH (which is similar to the "cytosolic" high-Km ALDH). Diethylthiocarbamic acid, the free acid of DTC-Me, was less potent than DTC-Me, and caused similar inactivation of the erythrocyte and leukocyte ALDH activities. The inhibition of ALDH by DTC-Me could not be completely restored by extensive dilution of intact or sonicated blood cell samples, which indicated that ALDH was irreversibly inhibited. Since the inhibition patterns with DTC-Me agrees with the previously reported patterns of inhibition of the high-Km and low-Km isozymes after the administration of disulfiram, the results suggest that DTC-Me might be the active in vivo inhibitory metabolite of disulfiram.     

Studies in vitro on the inactivation of mitochondrial rat-liver aldehyde dehydrogenase by the alcohol-sensitizing compounds cyanamide, 1-aminocyclopropanol and disulfiram

The inhibition of the low-K_m, rat-liver mitochondrial aldehyde dehydrogenase (ALDH) by the alcohol-sensitizing agents cyanamide, 1-aminocyclopropanol (ACP) and disulfiram was studied in vitro. All three compounds caused a progressive decline in the enzyme activity. Restoration of activity could not be achieved by gel-filtration, dilution or by the addition of excess thiol. High concentrations of acetaldehyde partly restored the activity of the cyanamide-inactivated enzyme but had no effects on the disulfiram- or ACP-inactivated enzyme. In the presence of saturating concentrations of the coenzyme (NAD⁺), the inactivation process followed first-order kinetics at fixed concentrations of the inhibitors. Plots of the apparent first-order rate constants against inhibitor concentration were curved, suggesting the formation of saturable, reversible holoenzyme-inhibitor complexes prior to the covalent reactions. In the absence of NAD⁺, the rate of inactivation by disulfiram was biphasic and considerably higher than that in the presence of NAD⁺. In contrast, no inactivation was obtained with cyanamide in the absence of NAD⁺. Likewise, the presence of NAD⁺ greatly promoted the inactivation by ACP. The esterase activity of the enzyme was also affected by the inhibitors, although to a lesser extent than was the dehydrogenase activity. The results obtained suggest that all three inhibitors inactivate the enzyme through covalent reactions with the thiol groups at the active site. It is proposed that binding of NAD⁺ limits access of disulfiram to the thiols at the active site but provides a situation that favours an electrophilic attack of cyanamide and ACP on the thiol groups.     

CYP3A-mediated apoptosis of dauricine in cultured human bronchial epithelial cells and in lungs of CD-1 mice

Dauricine is the major bioactive component isolated from the root of Menispermum dauricum DC and has shown promising pharmacologic activities with a great potential for clinical use. Recently, we found that intraperitoneal exposure of dauricine produced selective pulmonary injury in mice. A quinone methide metabolite of dauricine was identified and is suggested to be associated with the pulmonary toxicity of dauricine. The present study evaluated the apoptotic effect of dauricine in cultured cells and mice, determined the change in cellular glutathione (GSH) contents after exposure to dauricine, investigated the role of GSH depletion in dauricine-induced cytotoxicity and apoptosis, and examined the role of CYP3A in dauricine-induced GSH depletion and apoptosis. Dauricine was found to induce apoptosis in NL-20 cells. Additionally, intraperitoneal administration of dauricine caused GSH depletion and apoptosis in lungs of mice. Treatment with ketoconazole, an inhibitor of CYP3A, reversed cellular GSH depletion in lungs of mice given dauricine and showed protective effect on dauricine-induced apoptosis in lungs of mice. This indicates that metabolic activation is involved in dauricine-induced GSH-depletion, cytotoxicity and apoptosis. The glutathione depletor l-buthionine sulfoximine showed potentiating effect on cytotoxicity and apoptosis induced by dauricine. We propose that dauricine is metabolized to a quinone methide intermediate which depletes cellular GSH, and the depletion of GSH may trigger and/or intensify the cytotoxicity and apoptosis induced by dauricine.     

Diethylthiocarbamic acid methyl ester. A potent inhibitor of aldehyde dehydrogenase found in rats treated with disulfiram or diethyldithiocarbamic acid methyl ester

Rats were treated with disulfiram (Antabuse, DSF) or its metabolite diethyldithiocarbamic acid methyl ester (Me-DDC) and challenged with ethanol. The blood pressure response to ethanol was followed and blood was analyzed for DSF, Me-DDC and diethyldithiocarbamic acid (DDC). The rat liver aldehyde dehydrogenase (ALDH) isozyme activities were measured 2 hr after the ethanol challenge. Both treatments produced a significant fall in the blood pressure when challenged with ethanol, probably caused by a marked decrease in hepatocyte low Km and high Km activities. The mean plasma concentration ranges of Me-DDC and DDC were found to be 49-1241 nmol/l and 182-841 nmol/l, respectively, whereas DSF was undetectable. In addition, it was found that inactivation of hepatocyte low Km ALDH activity was dependent on preoxidation of Me-DDC by the microsomal cytochrome P-450 mixed function oxidases. Me-DDC was found to be oxidized under aerobic conditions in the presence of NADP to form diethylthiocarbamic acid methyl ester (Me-DTC). The structure was confirmed from its MS/EI fragmentation spectrum. Me-DTC was found to be a potent inhibitor of low Km ALDH when added to rat liver homogenate. The compound was also identified as a metabolite in rat blood collected from the DSF and Me-DDC treated rats, and in blood from human alcoholics on DSF treatment. Me-DTC appears to be more selective for the low Km isozymes whereas the opposite seems to be the case for the hydrolytic product, DTC.     

pH-dependent transport of procainamide in cultured renal epithelial monolayers of OK cells: consistent with nonionic diffusion.

1. Previous studies suggest that procainamide is a substrate for organic cation/proton antiport. In order to study the coupling between procainamide flux and proton flux in greater detail we investigated the effects of extracellular procainamide addition upon intracellular pH in cultured monolayers of renal OK cells. Intracellular pH was monitored by use of BCECF as a probe. 2. Apical addition of procainamide (10 mM) caused a significant alkalinisation of intracellular pH. Basolateral addition of procainamide was equally effective in raising intracellular pH. A similar alkalinisation was found in two other renal cell lines: MDCK strain 1 and LLCPK1. 3. In contrast, both tetraethylammonium and N-methylnicotinamide, archetypal substrates for organic cation/proton antiport were without effect upon intracellular pH. 4. At physiological pH values, procainamide exists as a neutral weak base (B) and its conjugate weak acid (BH+). To test which species of procainamide was responsible for the alkalinisation, experiments in which [B] was kept constant whilst [BH+] was varied from 1.15 mM to 7.25 mM were performed. The results suggested that the neutral weak base (B) was the permeant species. 5. Procainamide efflux from procainamide-loaded cell monolayers resulted in a significant acidification of intracellular pH. As with procainamide uptake, this result could be ascribed to the movement of neutral weak base. 6. These effects of procainamide upon intracellular pH are consistent with nonionic diffusion of procainamide rather than an interaction of procainamide with the organic cation/proton antiporter. In addition, the results suggest that organic cation/proton antiport is not highly expressed in OK cells.     

聚乙二醇修饰聚酰胺-胺的合成、表征及其人角膜上皮细胞毒性

目的:研究不同相对分子质量聚乙二醇(PEG)修饰不同代数树枝状大分子聚酰胺-胺(PAM-AM)得到的产物,测定其对人体角膜上皮细胞(HCECs)的毒性。方法:采用硝基苯氯甲酸酯(p-NPC)将单甲氧基聚乙二醇(mPEG,相对分子质量为750,2 000,5 000)活化成PEG碳酸酯,对第4,5代PAMAM大分子进行修饰;目标产物用FT-IR、1H-NMR进行结构表征;采用WST-8法考察PEG修饰对PAMAM的人角膜上皮细胞(HCECs)毒性的影响。结果:PAMAM经较低浓度PEG修饰后,对HCECs的毒性减弱不明显,经较高浓度PEG修饰后,对HCECs减毒明显减弱,不同相对分子质量的PEG修饰对PAMAM的减毒作用无明显差异。结论:经PEG修饰后,可以降低PAMAM对HCECs的毒性,作为新型眼部给药载体具有良好的前景。     

Diesel exhaust particle-induced cell death of cultured normal human bronchial epithelial cells

We investigated the effect of diesel exhaust particles (DEPs) on normal human bronchial epithelial (NHBE) cells. Inclusion of DEPs in culture media was lethal to NHBE cells. NHBE cells are more susceptible to DEPs than other normal human lung cells, normal human pulmonary artery endothelial cells and normal human embryonic lung fibroblasts. DEP-induced cell death was mainly due to necrosis. Using the fluorescence probes diacetoxymethyl 6-carboxy-3',6'-diacetoxy-2',7'-dichloro-3',6'-dideoxydihydrofluorescinate and 4,5-diaminofluorescein diacetate, it was observed that hydrogen peroxide and nitrogen monoxide, respectively, were generated within DEP-exposed NHBE cells. DEP cytotoxicity increased or decreased with an increase or decrease in the cellular level of reduced glutathione (GSH) by treatment with L-buthionine-(R,S)-sulfoximine or ethyl reduced glutathionate, respectively. In addition, DEPs themselves decreased the cellular level of GSH in a dose-dependent manner. Upon exposure of NHBE cells to high concentrations of DEPs, their cellular GSH was depleted almost throughout. Further, the following agents decreased DEP cytotoxicity: 1) antioxidants 2,2,5,7,8-pentamethylchroman-6-ol, ebselen, and N,N'-bis(salicylidene)ethylenediaminomanganese(II) dihydrate (EUK-8); 2) iron ion-chelating agents disodium bathophenanthrolinedisulfonate and desferrioxamine mesylate; 3) nitrogen monoxide synthase inhibitors N(G)-nitro-L-arginine methyl ester hydrochloride and N(G)-methyl-L-arginine acetate salt; and 4) an endocytosis inhibitor quinacrine. On the basis of these observations, the mechanism of DEP cytotoxicity toward NHBE cells is discussed.     

Mediation of cimetidine secretion by P-glycoprotein and a novel H(+)-coupled mechanism in cultured renal epithelial monolayers of LLC-PK1 cells.

1. Previous studies have shown that the weak base, cimetidine, is actively secreted by the renal proximal tubule. In this study we have examined the transport of cimetidine by renal LLC-PK1 epithelial cell monolayers. 2. In LLC-PK1 cell monolayers the basal-to-apical flux of cimetidine was significantly greater than the apical-to basal flux, consistent with net secretion of cimetidine in a basal-to-apical direction. 3. Net secretion of cimetidine was significantly (70%) reduced by the addition of either 100 microM verapamil or 100 microM nifedipine to the apical membrane. The reduction in net secretion was the result of an inhibition of basal-to-apical flux; these agents had no effect upon flux in the apical-to-basal direction. These results suggest that cimetidine secretion is mediated primarily by P-glycoprotein located in the apical membrane. In addition we found no evidence of a role for organic cation antiport in the secretion of cimetidine. 4. In the presence of an inwardly directed proton gradient across the apical membrane (pH 6.0), cimetidine secretion was significantly reduced compared to that measured at an apical pH of 7.4. The reduction in net secretion at pH 6.0 was the result of a stimulation of cimetidine uptake across the apical membrane. This pH-dependent uptake mechanism was sensitive to inhibition by DIDS (100 microM). 5. Experiments with BCECF (2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein) loaded monolayers demonstrated that cimetidine influx across the apical membrane was associated with proton flow into the cell and was sensitive to inhibition by DIDS. 6. These results suggest that net secretion of cimetidine across the apical membrane is a function of the relative magnitudes of cimetidine secretion mediated by P-glycoprotein and cimetidine absorption mediated by a novel proton-coupled, DIDS-sensitive transport mechanism.     

Exposure to chrysotile asbestos causes carbonylation of glucose 6-phosphate dehydrogenase through a reaction with lipid peroxidation products in human lung epithelial cells

Exposure to asbestos is known to lead to a reduction in glucose 6-phosphate dehydrogenase (G6PDH) activity and to cause oxidative damage to cells. In the present study, we exposed the human lung carcinoma cell line A549 to chrysotile. We observed an increase in the production of thiobarbituric acid-reactive substances (TBARS, the breakdown products of lipid peroxide) along with a significant decrease in G6PDH activity. Alternatively, when chrysotile was added directly to the cell extract obtained by removing the cell membrane, no loss of G6PDH activity was observed. To elucidate the mechanism of G6PDH inactivation due to exposure to chrysotile, we focused on the TBARS responsible for protein modification via carbonylation. When malondialdehyde or 4-hydroxy-2-nonenal was added to a membrane-free A549 cell extract, G6PDH activity was reduced markedly. However, when t-butylhydroperoxide was added to the extract, there was no significant decrease in G6PDH activity. Western blot analysis and immunoprecipitation of the carbonylated proteins in the A549 cell lysate that was prepared after exposure to chrysotile demonstrated that G6PDH had been carbonylated. Our findings indicate that the decrease in G6PDH activity that occurs after exposure of the cultured cells to chrysotile results from the carbonylation of G6PDH by TBARS.     

Induction of micronuclei in cultured human bronchial epithelial cells by direct-acting carcinogens

The sensitivity of human bronchial epithelial cells to induction of micronuclei was determined in cultures derived from seven different donors. Two direct-acting carcinogens, dl-7,8-dihydroxy-9,10-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene and N-methyl-N′-nitro-N-nitrosoguanidine were used to induce micronuclei. Both agents increased the incidence of micronuclei in a concentration-dependent fashion in cells from most donors, event at concentrations that did not produce appreciable cytotoxicity; there were considerable variations in the responses of different donors. Cytokinesis was blocked with cytochalasin B so that micronuclei were counted only in binucleate cells, thereby decreasing the total number of cells that needed to be examined and also eliminating variations due to possible differences in cell growth rates. The results demonstrate the potential usefulness of the micronucleus assay as a sensitive measure of genetic damage in human epithelial cells from the lung.     

Ability of 1-methyltetrazole-5-thiol with microsomal activation to inhibit aldehyde dehydrogenase

Antibiotics that contain the 1-methyltetrazole-5-thiol (MTT) leaving group are associated with an adverse effect when alcohol is ingested after their administration. Therefore, the ability of MTT to inhibit an enzyme in alcohol metabolism, aldehyde dehydrogenase (ALDH), was examined. In the absence of microsomes, MTT did not inhibit ALDH obtained from either yeast or rat liver. In the presence of rat hepatic microsomes, MTT was able to inhibit the enzyme from both sources. The characteristics of the inhibition were studied, using the yeast enzyme, and found to be dependent upon the length of incubation with the hepatic microsomes and upon the concentration of MTT. Inhibition required the presence of NADH and was not detected if the microsomes were heat treated. Dilution did not reverse the inhibition. Intact antibiotics which contain the MTT moiety did not cause an inhibition of yeast ALDH unless the antibiotics were first treated with potassium hydroxide and then incubated with microsomes. Inhibition of ALDH activity measured in the mitochondrial plus microsomal fractions of rat liver also required NADH and was prevented by glutathione and heat treatment of the microsomes. These results indicate that microsomal activation of MTT is necessary for inhibition of aldehyde dehydrogenase. The behavior of MTT described here may explain the adverse effect observed if alcohol is ingested following administration of MTT-containing antibiotics.     

应用A549细胞单层模型研究蛋白多肽类药物肺部吸收的特性应用A549细胞单层模型研究蛋白多肽类药物肺部吸收的特性

药物通过呼吸进行吸收的路径依次为气管→支气管→肺泡,其中通过肺泡上皮细胞吸收占90％以上。由于肺泡上皮细胞使大分子的蛋白多肽类药物不易通过,是它们渗透的主要屏障,因此对肺泡膜屏障特性、药物透过过程及渗透特性的研究有助于更     

Dose dependent cytotoxicity of pranoprofen in cultured human corneal endothelial cells by inducing apoptosis

Pranoprofen (PPF), a non-steroidal anti-inflammatory drugs (NSAIDs), is often used in keratitis treatment in clinic. Several studies have assessed in vitro the cytotoxicity of topical NSAIDs to corneal epithelial cells due to its importance for predicting human corneal toxicity. Damage by cytotoxic drugs can result in excessive loss of human corneal endothelial (HCE) cells which lead to decompensation of the endothelium and eventual loss of visual acuity. However, the endothelial cytotoxicity of PPF has not yet been reported using an in vitro model of HCE cells. This study assessed the cytotoxicity of PPF to HCE cells and its underlying mechanism. Cellular viability was determined using inverted phase contrast light microscopy, and plasma membrane permeability, genomic DNA fragmentation, and ultrastructure were detected by acridine orange/ethidium bromide staining, DNA agarose gel electrophoresis, and transmission electron microscopy (TEM), respectively. The results on cellular viability showed that PPF at concentrations ranging from 0.0625 to 1.0?g/l had poignant cytotoxicity to HCE cells, and the extent of its cytotoxicity was dose- and time-dependent. Further characterization indicated that PPF induced plasma membrane permeability elevation, DNA fragmentation, and apoptotic body formation, proving its apoptosis inducing effect on HCE cells. In conclusion, PPF above 0.0625?g/l has poignant cytotoxicity on HCE cells in vitro by inducing cell apoptosis, and should be carefully employed in eye clinic.     

UVB light regulates expression of antioxidants and inflammatory mediators in human corneal epithelial cells

The cornea is highly sensitive to ultraviolet B (UVB) light-induced oxidative stress, a process that results in the production of inflammatory mediators which have been implicated in tissue injury. In the present studies, we characterized the inflammatory response of human corneal epithelial cells to UVB (2.5–25 mJ/cm²). UVB caused a dose-dependent increase in the generation of reactive oxygen species in the cells. This was associated with increases in mRNA expression of the antioxidants Cu,Zn superoxide dismutase (SOD), Mn-SOD, catalase and heme oxygenase-1 (HO-1), as well as the glutathione S-transferases (GST), GSTA1-2, GSTA3, GSTA4, GSTM1, and mGST2. UVB also upregulated expression of the proinflammatory cytokines, IFNγ, IL-1β, TGFβ and TNFα, and enzymes important in prostaglandin (PG) biosynthesis including cyclooxygenase-2 (COX-2) and the PG synthases mPGES-2, PGDS, PGFS and thromboxane synthase, and in leukotriene biosynthesis including 5-lipoxygenase (5-LOX), 15-LOX-2, and the epidermal and platelet forms of 12-LOX. UVB was found to activate JNK and p38 MAP kinases in corneal epithelial cells; ERK1/2 MAP kinase was found to be constitutively active, and its activity increased following UVB treatment. Inhibition of p38 blocked UVB-induced expression of TNFα, COX-2, PGDS and 15-LOX-2, while JNK inhibition suppressed TNFα and HO-1. These data indicate that UVB modulates corneal epithelial cell expression of antioxidants and proinflammatory mediators by distinct mechanisms. Alterations in expression of these mediators are likely to be important in regulating inflammation and protecting the cornea from UVB-induced oxidative stress.