Resveratrol inhibited hydroquinone-induced cytotoxicity in mouse primary hepatocytes

Hydroquinone (1,4-benzenediol) has been widely used in clinical situations and the cosmetic industry because of its depigmenting effects. Most skin-lightening hydroquinone creams contain 4%–5% hydroquinone. We have investigated the role of resveratrol in prevention of hydroquinone induced cytotoxicity in mouse primary hepatocytes. We found that 400 µM hydroquinone exposure alone induced apoptosis of the cells and also resulted in a significant drop of cell viability compared with the control, and pretreatment of resveratrol to a final concentration of 0.5 mM 1 h before hydroquinone exposure did not show a significant improvement in the survival rate of the hepatocytes, however, relatively higher concentrations of resveratrol (≥1 mM) inhibited apoptosis of the mouse primary hepatocytes and increased cell viability in a dose-dependent manner, and in particular the survival rate of the hepatocytes was recovered from 28% to near 100% by 5 mM resveratrol. Interestingly, pretreatment with resveratrol for longer time (24 h), even in very low concentrations (50 µM, 100 µM), blocked the damage of hydroquinone to the cells. We also observed that resveratrol pretreatment suppressed hydroquinone-induced expression of cytochrome P450 2E1 mRNA dose-dependently. The present study suggests that resveratrol protected the cells against hydroquinone-induced toxicity through its antioxidant function and possibly suppressive effect on the expression of cytochrome P450 2E1.

Syntheses of hydroxy substituted 2-phenyl-naphthalenes as inhibitors of tyrosinase

Oxyresveratrol and resveratrol, with hydroxy substituted trans-stilbene structure, exert potent inhibitory effects on cyclooxygenase, rat liver mitochondrial ATPase activity, and tyrosinase. As the isosteres of oxyresveratrol, a new family of hydroxyl substituted phenyl-naphthalenes were synthesized to show excellent inhibition of mushroom tyrosinase. Compound 10, which is isostere of resveratrol, showed IC50 value of 16.52 microM in mushroom tyrosinase activity. As compared to this, the reference compound, resveratrol, showed IC50 value of 55.61 microM. Compound 4, which is isostere of oxyresveratrol, showed IC50 value of 0.49 microM. Among the other three derivatives, compound 13 showed IC50 value of 0.034 microM.

Fluorinated quinoid inhibitor: possible "pure" arylator predicted by the simple theoretical calculation

We report on the fluorinated form of Cpd 5 as a cell growth inhibitor. This compound is 3-fold more potent than the parent Cpd 5 and is predicted, using the semi-empirical AM1 method to be only an arylator of cysteine-containing proteins, without generating reactive oxygen species.

Ceramide, an apoptotic rheostat, inhibits CCAAT/enhancer binding protein-beta and NF-E2-related factor-2 activation: the role in glutathione S-transferase A2 gene repression

Ceramide is a sphingolipid that acts as a second messenger in signaling systems. Sphingomyelinase generates ceramide in response to cytotoxic stimuli. CCAAT/enhancer binding protein-beta (C/EBPbeta) and NF-E2-related factor-2 (Nrf2) are both involved in the regulation of the genes encoding phase II detoxification enzymes including glutathione S-transferase (GST). In the present study, we examined the effects of ceramide on C/EBPbeta or Nrf2 activation and on the inducible GSTA2 gene transactivation. C2-ceramide (C2), a cell-permeable analog, inhibited GSTA2 induction by oltipraz or tert-butylhydroquinone (t-BHQ) in H4IIE cells, whereas dihydro-C2-ceramide (dihydro-C2), an inactive analog, had no effect. Immunoblot analysis revealed that C2 prevented increase in the level of nuclear C/EBPbeta by oltipraz, whereas the level of C/EBPbeta in total cell lysates was not changed. Increase in nuclear Nrf2 by t-BHQ was also prevented by C2 treatment. Decreases in nuclear C/EBPbeta and Nrf2 by C2 were reversed by treatment of cells with N-benzoyloxycarbonyl (Z)-Leu-Leu-leucinal (MG132), a proteasome inhibitor, verifying the previous observations that the transcription factors were degraded by the proteasome system. In another study, we found that ceramide decreased nuclear hepatic nuclear factor-1 (HNF1), whose binding to the HNF1-response element in the GSTA2 gene was responsible for the constitutive and inducible gene expression. To define the role of C/EBPbeta or Nrf2 repression in GST expression under the condition excluding the negative regulation by C2-mediated HNF1 suppression, luciferase activity was determined in the cells transfected with DeltaHNF-pGL-1651 plasmid lacking the HNF1-response element. In the cells transfected with DeltaHNF-pGL-1651, C2 decreased the luciferase induction by oltipraz or t-BHQ. Thus, ceramide inhibits C/EBPbeta or Nrf2 activation, which contributes to repression of GSTA2 gene transactivation.

[The protective effect of amifostine on hydroquinone-induced apoptosis in bone marrow]

OBJECTIVE

To evaluate the protective effect of amifostine on hydroquinone-induced apoptosis of bone marrow mononuclear cells in vitro.

METHODS

The mononuclear cells were separated and divided into four groups: blank control, amifostine group, hydroquinone group, amifostine + hydroquinone group. The cell apoptotic rate was examined in separated group at different time point, and apoptosis was detected by HT stain, then cell morphology was observed under fluorescent microscope and DNA fragments was tested by agarose gel electrophoresis. In addition, apoptotic and necrotic rate was detected by flow cytometer.

RESULTS

After 10 hour culture, DNA ladder was detected in the hydroquinone group, but not in other groups. The apoptotic rate was not significantly different between amifostine group and blank control group at different culture time (P > 0.05). After 8 - 12 hour culture, the apoptotic rate in amifostine + hydroquinone group was significantly lower than that in the group of hydroquinone alone (P < 0.01). After 18 - 48 hour culture, the necrotic rate in amifostine + hydroquinone group was lower than that in the group of hydroquinone alone (P < 0.05).

CONCLUSION

Amifostine can protect cell from hydroguinone-induced bone marrow damage through inhibition on cell apoptosis, and decrease in cell necrosis.

Aspirin potently inhibits oxidative DNA strand breaks: implications for cancer chemoprevention

Epidemiological studies have suggested that the use of aspirin is associated with a decreased incidence of human malignancies, particularly colorectal cancer. Since reactive oxygen species (ROS) are critically involved in multistage carcinogenesis, this study was undertaken to examine the ability of aspirin to inhibit ROS-mediated DNA damage. Hydrogen peroxide (H2O2)+Cu(II) and hydroquinone (HQ) + Cu(II) were used to cause oxidative DNA strand breaks in phiX-174 plasmid DNA. We demonstrated that the presence of aspirin at concentrations (0.5-2 mM) compatible with amounts in plasma during chronic anti-inflammatory therapy resulted in a marked inhibition of oxidative DNA damage induced by either H2O2/Cu(II) or HQ/Cu(II). The inhibition of oxidative DNA damage by aspirin was exhibited in a concentration-dependent manner. Moreover, aspirin was found to be much more potent than the hydroxyl radical scavengers, mannitol and dimethyl sulfoxide, in protecting against the H2O2/Cu(II)-mediated DNA strand breaks. Since the reduction of Cu(II) to Cu(I) is crucially involved in both H2O2/Cu(II)- and HQ/Cu(II)-mediated formation of hydroxyl radical or its equivalent, and the subsequent oxidative DNA damage, we examined whether aspirin could inhibit this Cu(II)/Cu(I) redox cycle. It was observed that aspirin at concentrations that showed the inhibitory effect on oxidative DNA damage did not alter the Cu(II)/Cu(I) redox cycle in either H2O2/Cu(II) or HQ/Cu(II) system. In addition, aspirin was not found to significantly scavenge H2O2. This study demonstrates for the first time that aspirin potently inhibits both H2O2/Cu(II)- and HQ/Cu(II)-mediated oxidative DNA strand breaks most likely through scavenging the hydroxyl radical or its equivalent derived from these two systems. The potent inhibition of oxidative DNA damage by aspirin may thus partially contribute to its anticancer activities observed in humans.

Effect of antioxidants on radical intensity and cytotoxicity of hydroquinone

Hydroquinone (HQ) dose-dependently reduced the viable cell number of oral tumor cell lines (HSC-2, HSG). HQ induced internucleosomal DNA fragmentation in human promyelocytic leukemic HL-60 cells, but not in HSC-2 nor HSG cells. Cytotoxic activity of HQ was slightly reduced by catalase, but was enhanced by superoxide dismutase, suggesting the possible involvement of hydrogen peroxide in HQ-induced cytotoxicity. This was supported by slight increase or decrease of cytotoxicity of HQ in the presence of Cu2+ and Fe3+, respectively. Lower concentrations of sodium ascorbate, ascorbic acid and ascorbic acid 6-palmitate reduced both the radical intensity and cytotoxic activity of HQ, more efficiently than ascorbic acid 2,6-dipalmitate, in contrast to the cytotoxic action of these ascorbates at higher (millimolar) concentrations. Popular antioxidants such as N-acetyl-L-cysteine and cysteine also reduced the radical intensity and cytotoxic activity of HQ. The present study suggests that cytotoxic activity of HQ is generated by radical-mediated oxidation mechanism.

Protection by desferrioxamine and other hydroxamic acids against tetrachlorohydroquinone-induced cyto- and genotoxicity in human fibroblasts

Tetrachlorohydroquinone (TCHQ) has been identified as a major toxic metabolite of the widely used wood preservative pentachlorophenol and has also been implicated in its genotoxicity. We have recently demonstrated that protection by the trihydroxamate iron chelator desferrioxamine (DFO) on TCHQ-induced single-strand breaks in isolated DNA was not the result of its chelation of iron but rather of its efficient scavenging of the reactive tetrachlorosemiquinone (TCSQ) radical. In this study, we extended our research from isolated DNA to human fibroblasts. We found that DFO provided marked protection against both the cyto- and genotoxicity induced by TCHQ in human fibroblasts when it was incubated simultaneously with TCHQ. Pretreatment of the cells with DFO followed by washing also provided marked protection, although less efficiently compared with the simultaneous treatment. Similar patterns of protection were also observed for three other hydroxamic acids (HAs): aceto-, benzo-, and salicylhydroxamic acid. Dimethyl sulfoxide, an efficient hydroxyl radical scavenger, provided only partial protection even at high concentrations. In vitro studies showed that the HAs tested effectively scavenged the reactive TCSQ radical and enhanced the formation of the less reactive and less toxic 2,5-dichloro-3, 6-dihydroxy-1,4-benzoquinone (chloranilic acid). The results of this study demonstrated that the protection provided by DFO and other HAs against TCHQ-induced cyto- and genotoxicity in human fibroblasts is mainly through scavenging of the observed reactive TCSQ radical and not through prevention of the Fenton reaction by the binding of iron in a redox-inactive form.

The inhibition of phenylhydroquinone-induced oxidative DNA cleavage by constituents of Moutan Cortex and Paeoniae Radix

Moutan Cortex (root cortex of Paeonia suffruticosa ANDREWS) and Paeoniae Radix (root of Paeonia lactiflora PALLAS) are crude drugs used in many traditional prescriptions and have constituents in common. We studied the effects of extracts of these crude drugs and their constituents on oxidative DNA damage caused by phenylhydroquinone (PHQ), a major metabolite of o-phenylphenol. Both drugs suppressed the cleavage of pUC18 DNA induced by PHQ, and scavenged the superoxide and hydroxy radical generated by the chemical. They also inhibited the oxidative DNA cleavage by tert-butylhydroquinone (TBHQ), one of the major metabolites of butylated hydroxyanisole. When constituents were examined with the same system, galloylpaeoniflorin and 1,2,3,4,6-penta-O-galloyl-beta-D-glucose (PGG) were found to be the most potent inhibitors of the DNA cleavage. These constituents had oxygen radical scavenging activity. Paeonol also attenuated the DNA cleavage. Paeoniflorin and albiflorin had relatively small inhibitory effects on DNA cleavage. However, catechin enhanced the PHQ-induced DNA cleavage. The suppression of oxidative DNA damage by Moutan Cortex and Paeoniae Radix might be attributable to the additive effects of galloylpaeoniflorin, PGG and other constituents.

Enhancement of myeloid cell growth by benzene metabolites via the production of active oxygen species

In low concentrations, benzene and its metabolite hydroquinone are known to have diverse biological effects on cells, including the synergistic stimulation with GM-CSF of hematopoietic colony formation in vitro, stimulation of granulocytic differentiation in vitro and in vivo, and general suppression of hematopoiesis in vivo. These chemicals are also known to be active in the induction of active oxygen species. We used several assays to determine the effects of benzene metabolites (hydroquinone, benzenetriol, benzoquinone) and active oxygen species (xanthine/xanthine oxidase) on cell growth and cell cycle kinetics of the human myeloid cell line HL-60. HL-60 cells treated with these chemicals for 2 h in PBS showed increased growth over untreated controls in a subsequent 18h growth period in complete media. Incorporation of 3H-thymidine was also increased proportionately by these treatments. Catalase treatment abrogated the increased cell growth of all chemicals, suggesting an oxidative mechanism for the effect of all treatments alike. Cell cycle kinetics assays showed that the growth increase was caused by an increased recruitment of cells from G0/G1 to S-phase for both hydroquinone and active oxygen, rather than a decrease in the length of the cell cycle. Benzene metabolite's enhancement of growth of myeloid cells through an active oxygen mechanism may be involved in a number of aspects of benzene toxicity, including enhanced granulocytic growth and differentiation, stimulation of GM-CSF-induced colony formation, apoptosis inhibition, and stimulation of progenitor cell mitogenesis in the bone marrow. These effects in sum may be involved in the benzene-induced "promotion" of a clonal cell population to the fully leukemic state.

Ca2+-ATPase inhibitor induces IL-4 and MCP-1 production in RBL-2H3 cells

The effects of a Ca2(+)-ATPase inhibitor, cyclopiazonic acid (CPA), and two hydroquinone-antioxidants, 2,5-di-(tert-butyl)-1,4-hydroquinone (DTBHQ) and 2,5-di-(tert-amyl)-1,4-hydroquinone (DTAHQ) on the release of IL-4 and MCP-1 from RBL-2H3 cells were investigated. CPA, DTBHQ and DTAHQ, all of which induce intracellular free Ca2+ concentration ([Ca2+]i) increase, induced IL-4 and MCP-1 release in a dose-dependent manner. The release of TNF-alpha required both a Ca2(+)-ATPase inhibitor and 12-O-tetradecanoylphorbol-13-acetate (TPA). However, the Ca2(+)-ATPase inhibitors induced IL-4 and MCP-1 production without TPA. The release of IL-4 and MCP-1 reached a maximum at 9 and 6 h, respectively. IL-4 and MCP-I release was inhibited by treatment with the immunosuppressant FK-506 and actinomycin D. Therefore, in our system IL-4 and MCP-1 release involves Ca2(+)-dependent and FK-506-sensitive signaling pathways. This is the first report about Th-2 type cytokine and chemokine production in RBL-2H3 cells.

[8-(N,N-diethylamino)-n-octyl-3,4,5-trimethoxybenzoate(TMB-8) reduced the elevation of [Ca2+]i induced by BHQ, NE and KCl in cultured single smooth muscle cells of the calf basilar artery]

The effect of 8-(N, N-diethylamino)-n-octyl-3,4,5-trimethoxybenzoate (TMB-8) on the elevation of [Ca2+]i induced by 2, 5-di (tert-butyl)-1, 4-benzohydroquinone (BHQ), norepinephrine (NE), KCl in cultured single smooth muscle cells of the calf basilar artery was studied by a system of measurement of AR-CM-MIC, using Fura-2/AM as a fluoresent indicator. In the presence of extracellular Ca2+ 1.3 mmol.L-1, the resting [Ca2+]i was not changed by TMB-8 (10, 30 and 100 mumol.L-1), but the elevation of [Ca2+]i induced by BHQ, NE and KCl were reduced by TMB-8 (30 mumol.L-1) significantly. In Ca2+ free Hank's solution containing EGTA 0.1 mmol.L-1, the resting [Ca2+]i was markedly reduced by TMB-8 (10, 30 and 100 mumol.L-1), and the increase of [Ca2+]i evoked by BHQ and NE was blocked completely by TMB-8 (30 mumol.L-1). The result suggested that TMB-8 inhibited the Ca2+ release from intracellular stores or increased the up-take of Ca2+ into sarcoplasmic reticulum and the inhibition of Ca(2+)-influx from extracellular site may be an indirect machanism.

[Effect of TMB-8 on the increase of intracellular free Ca2+ induced by NE and BHQ in dissociated single rat brain cell]

The inhibitory effect and mechanism of 8-(N, N'-diethylamino) octyl 3, 4, 5-trimethoxybenzoate hydrochloride (TMB-8) on the elevation of single intracellular free Ca2+ concentration ([Ca2+]i) induced by High K+, Norepinephrine(NE) and 2, 5-Di(tert-butyl)-1, 4-benzohydroquinone (BHQ) in dissociated single rat brain cells were studied. The changes of [Ca2+]i were reflected by the fluorescent indicator, Fura-2/AM, employed. In the absence of extracellular Ca2+, Ca-free Hank's solution, preincubation with TMB-8 (10, 30 mumol.L-1) for 20 min significantly decreased the resting [Ca2+]i from 79 +/- 13 nmol.L-1 to 65 +/- 11 and 61 +/- 6 nmol.L-1, respectively. [Ca2+]i were markedly increased by NE and BHQ and reduced significantly to control level by TMB-8. On the other hand, when the cells were incubated in Hank's solution containing Ca2+ 1.3 mmol.L-1, TMB-8(30, 100 mumol.L-1) suppressed the increase of [Ca2+]i induced by NE (0.0001-0.1 mumol.L-1). TMB-8 showed no significant effect on [Ca2+]i elevation induced by KCl and BHQ in Hank's solution containing Ca2+ 1.3 mmol.L-1. These results indicate that TMB-8 reduced [Ca2+]i via increase of the sarcoplasmic reticulum (SR) sequestration, which blocked the release of intracellular store from the SR. However, the inhibitory effect of TMB-8 on Ca-influx from extracellular medium seems to be an indirect action from the saturation of SR with calcium.

Differential inhibition of DNA synthesis in human T cells by the cigarette tar components hydroquinone and catechol

Hydroquinone (HQ), catechol, and phenol exist in microgram quantities in cigarette tar and represent the predominant form of human exposure to benzene. Exposure of human T lymphoblasts (HTL) in vitro to 50 microM HQ or 50 microM catechol decreased IL-2-dependent DNA synthesis and cell proliferation by >90% with no effect on cell viability. Phenol had no effect on HTL proliferation at concentrations up to 1 mm. The addition of HQ or catechol to proliferating HTL blocked 3H-TdR uptake by >90% within 2 hr without significantly affecting 3H-UR uptake, suggesting that both compounds inhibit a rate-limiting step in DNA synthesis. However, the effects of HQ and catechol appear to involve different mechanisms. Ferric chloride (FeCl3) reversed the inhibitory effect of catechol, but not HQ, corresponding with the known ability of catechol to chelate iron. HQ, but not catechol, caused a decrease in transferrin receptor (TfR, CD71) expression, comparable to the level observed in IL-2-starved cells. HQ also inhibited DNA synthesis in cultures of transformed Jurkat T lymphocytes, primary and transformed fibroblasts, and mink lung epithelial cells, indicating that its antiproliferative effect was not restricted to IL-2 mediated proliferation. However, DNA synthesis by primary lymphocytes was more sensitive to HQ (IC50 = 6 microM) than that of the transformed Jurkat T cell line (IC50 = 37 microM) or primary human fibroblasts (IC50 = 45 microM), suggesting that normal lymphocytes may be particularly sensitive to HQ. The effects of HQ and catechol on DNA synthesis could be partially reversed by a combination of adenosine deoxyribose and guanosine deoxyribose, suggesting that both compounds may inhibit ribonucleotide reductase.

8-(N,N-diethylamino)-n-octyl-3,4,5-trimethoxybenzoate actions on calcium dynamics in cultured vascular smooth muscle cells

AIM

To study 8-(N,N-Diethylamino)n-octyl-3,4,5-trimethoxybenzoate (TMB), a potent Ca(2+)-antagonist, actions on cellular calcium dynamics in vascular smooth muscle cell (VSMC) cultures.

METHODS

A7r5 VSMC were cultured with Fura-2 measurements of intracellular Ca2+ concentration, [Ca2+]i.

RESULTS

TMB reduced [Ca2+]i from control levels and blocked [Ca2+]i increase caused by norepinephrine (NE) and 2,5-di (t-butyl)-1,4-benzohydroquinone (BHQ). [Ca2+]i reduction by TMB was further enhanced by ryanodine.

CONCLUSION

TMB is an effective agent for blocking the [Ca2+]i increase caused by NE and BHQ and for enhancing the [Ca2+]i reduction caused by ryanodine.

Inhibition of 1,2,4-benzenetriol-generated active oxygen species and induction of phase II enzymes by green tea polyphenols

Autooxidation of polyphenolic metabolites of benzene, such as hydroquinone (HQ), catechol (CT), 1,2,4-benzenetriol (BT) and pyrogallol (PG), produced several kinds of active oxygen species (AOS). BT and PG induced DNA breaks in the absence of metal ions, especially when producing AOS such as H2O2, O2-, HO. or 1 delta gO2. HQ and CT did not result in double-strand DNA breaks, except when ferrous ion was added, indicating the participation of the Fenton reaction. Polyphenolic fractions isolated from green tea (GTP) exerted inhibitory effects on the autooxidation of BT and suppressive effects on H2O2 or HO. generated from phenolic metabolites of benzene in the presence of S9 or an in vivo system. Additionally, although the activities of antioxidant and phase II enzymes were elevated by both GTP and phenolic metabolites of benzene, GTP counteracted the lowering GSH caused by phenolic metabolites of benzene in rat liver. The above results suggest that GTP and phenolic metabolites of benzene are antagonistic in their response to AOS, especially hydroxyl radical.

Eicosanoids released following inhibition of the endoplasmic reticulum Ca2+ pump stimulate Ca2+ efflux in the perfused rat liver

In the isolated perfused rat liver 2,5-di(tert-butyl)hydroquinone (tBuHQ), a selective inhibitor of the endoplasmic reticulum Ca2+ pump, induces a prolonged glucose output and stimulates Ca2+ efflux. The present study shows that tBuHQ depleted the hormone-sensitive Ca2+ pool in the perfused liver, abolishing the vasopressin- or phenylephrine-induced Ca2+ efflux. The effects of tBuHQ were reversible, since the response to these agonists gradually returned within 1 hr of perfusion, and protein synthesis was not required for this recovery. Since tBuHQ does not cause Ca2+ efflux from isolated hepatocytes, we examined the mechanism responsible for the tBuHQ-induced Ca2+ efflux observed in the intact liver. The cyclooxygenase inhibitor indomethacin prevented the Ca2+ extrusion stimulated by tBuHQ, but not that induced by vasopressin. During infusion of tBuHQ there was a 9-fold increase in the concentration of thromboxane B2 in the perfusate. The Ca2+ efflux response to tBuHQ was inhibited by the thromboxane/prostaglandin endoperoxide receptor antagonist, L-655,240 (3-[1-(4-chlorobenzyl)-5-fluoro-3-methyl-indol-2-yl]2,2-dimethylpropa noic acid) in the absence of any effect on thromboxane B2 release. Thus, the inhibition of the endoplasmic reticulum Ca2+ pump by tBuHQ results in a rise in the cytosolic Ca2+ concentration in non-parenchymal cells, leading to the formation of cyclooxygenase products. The released eicosanoids, in turn, stimulate Ca2+ efflux from hepatocytes.

Cytotoxic effects of phenyl-hydroquinone and some hydroquinones on isolated rat hepatocytes

The cytotoxic effects of phenyl-hydroquinone (PHQ) and some other hydroquinones on freshly isolated rat hepatocytes were investigated. Addition of PHQ (0.5 or 0.75 mM) to the hepatocytes elicited dose-dependent cell death accompanied by losses of intracellular glutathione (GSH), protein thiols and ATP. These effects were related to both PHQ loss and phenyl-benzoquinone (PBQ) formation in the cell suspension. The cytotoxicity of PHQ was prevented by sulphydryl compounds such as cysteine and GSH. In Krebs-Henseleit buffer without cells, loss of PHQ (0.5 mM; initial concentration) and formation of PBQ, monitored by spectral measurements, were inhibited by addition of 50 microM GSH. Further, the oxygen consumption owing to autoxidation of PHQ (0.5 mM) in Krebs-Henseleit buffer without cells was depressed by addition of 50 microM GSH. Among all the hydroquinones tested (at 0.5 mM), tert-butyl-hydroquinone and PHQ were most toxic, followed by hydroquinone and 2,5-di(tert-butyl)-1,4-benzohydroquinone. However, accumulation of cellular malondialdehyde was not affected by these hydroquinones. The toxicity was related to the rate of oxygen consumption by each hydroquinone in the buffer. These results suggest that hydroquinone-induced cytotoxicity is dependent on the rate of oxidation of these compounds as well as the loss of protein thiols.

Vasoconstriction and bronchoconstriction induced by 2,5-di-(tert-butyl)1,4-benzohydroquinone, an endoplasmic reticular Ca2+-ATPase inhibitor, in isolated and perfused rat lung

The microsomal Ca(2+)-ATPase inhibitor 2,5-di-(tert-butyl)-1,4-benzohydroquinone (tBuBHQ) induced bronchoconstriction and vasoconstriction in the isolated perfused and ventilated rat lung. These effects were accompanied by increased levels of thromboxane and prostacyclin in the effluent perfusate. The effect of tBuBHQ was inhibited by L-655,240, a thromboxane receptor antagonist, indicating thromboxane-A2-mediated bronchoconstriction and vasoconstriction. Accordingly, the cyclooxygenase inhibitor indomethacin largely blocked the effects of tBuBHQ. The involvement of a phospholipase in the generation of thromboxane A2(TXA2) was supported by dibucaine protection on tBuBHQ effects. The results from this study indicate that tBuBHQ, probably by inhibiting the microsomal Ca(2+)-ATPase, can trigger the arachidonic acid cascade leading to the formation of TXA2, which in turn causes bronchoconstriction and vasoconstriction in rat lung.

Suppression of bone marrow stromal cell function by benzene and hydroquinone is ameliorated by indomethacin

Administration of benzene to mice will inhibit bone marrow stromal cell-supported hemopoiesis in culture. Hydroquinone, a major metabolite of benzene, will cause a similar inhibition of stromal cell function in vitro. Stromal cells produce both an inducer (colony-stimulating factor) and an inhibitor (prostaglandin E2; PGE2) of hemopoiesis. This research was conducted to determine if prostaglandin synthesis is involved in the suppression of stromal cell function by benzene and hydroquinone. Male B6C3F1 mice were administered benzene (100 mg/kg), indomethacin (1 mg/kg), or benzene plus indomethacin twice a day for 4 consecutive days. On Day 5 bone marrow cells were removed to determine the effect of treatment. In a second series of experiments mouse bone marrow stromal cells in culture were treated with hydroquinone (10(-7) to 10(-4) M), indomethacin (10(-6) M), or a combination of hydroquinone plus indomethacin. Stromal cell function was based on the ability of the treated stromal cells to support granulocyte/monocyte colony development in coculture. The results demonstrated that preadministration of indomethacin in vivo ameliorated benzene-induced inhibition of bone marrow stromal cell function. In vitro, indomethacin ameliorated hydroquinone toxicity to stromal cell function. Benzene administration in vivo induced elevated PGE2 in bone marrow samples which were prevented by preadministration of indomethacin. However, hydroquinone in vitro did not induce a consistent increase in PGE2 levels. These results suggested that toxicity to stromal cells was not due solely to increased prostaglandin synthetase activity.

Urinary indole profile of Bufo melanostictus during hydroquinone-induced leucoderma and its regeneration

The abnormal urinary indole profile induced by hydroquinone has been found to be reversed by psoralene, a pigmentogenic drug in vitiligo.