Hydroquinone: genotoxicity and prevention of genotoxicity following ingestion.

Plant-derived polyphenolics and other chemicals with antioxidant properties have been reported to inhibit the expression of genotoxic activity by pro-oxidant chemicals (Sai et al., 1992, 1994; Teel and Castonguay, 1992). In vitro and in vivo studies with ionizing radiation suggest that hydroquinone (HQ) may have similar protective effects (Babaev et al., 1994). The present study was conducted to determine whether HQ is capable of inhibiting the induction of micronuclei in the bone marrow of mice following exposure to an oxidant, potassium bromate or KBrO3 (Nakajima et al., 1989; Sai et al., 1992, 1994). To be able to interpret the results of this work, it was also necessary to determine whether HQ is itself genotoxic when fed in the diet. HQ diets (0.8%) fed to mice for 6 days reduced the background incidence of micronuclei compared with the basal diet. KBrO3 dosed ip (12.5-100 mg/kg) produced a dose-dependent increase in micronuclei as reported by others. Mice fed 0.8% HQ diets 6 days, and then dosed intraperitoneally with KBrO3, showed a 36% reduction in micronuclei across the range of KBrO3 dose levels. This effect was associated with a reduction in the background micronucleus response as well as a reduction in response to KBrO3. Statistical significance (P < or = 0.05), observed at a dose of 25 mg/kg KBrO3 in the mice fed the control diet, was abolished in the group fed 0.8% HQ. When mice were given 50 mg HQ/kg by oral gavage and then given 50 mg KBrO3/kg ip 20 min later, the micronucleus response induced by KBrO3, was lower in animals given HQ. The results of this study demonstrate that large doses of HQ may be given orally without induction of micronuclei or bone marrow depression, that HQ reduces the background micronucleus response in animals fed a basal diet, and that the HQ reduces the micronucleus response to KBrO3 as well as background incidence of micronuclei in KBrO3-dosed animals. The protective effect of HQ may be due to enzyme induction or a direct antioxidant effect of HQ against oxidants commonly present in the diet.

Prevention of renal injury after induction of ozone tolerance in rats submitted to warm ischaemia.

On the basis that ozone (O3) can upregulate cellular antioxidant enzymes, a morphological, biochemical and functional renal study was performed in rats undergoing a prolonged treatment with O3 before renal ischaemia. Rats were divided into four groups: (1) control, a medial abdominal incision was performed to expose the kidneys; (2) ischaemia, in animals undergoing a bilateral renal ischaemia (30 min), with subsequent reperfusion (3 h); (3) O3 + ischaemia, as group 2, but with previous treatment with O3 (0.5 mg/kg per day given in 2.5 ml O2) via rectal administration for 15 treatments; (4) O2 + ischaemia, as group 3, but using oxygen (O2) alone. Biochemical parameters as fructosamine level, phospholipase A, and superoxide dismutases (SOD) activities, as well as renal plasma flow (RPF) and glomerular filtration rate (GFR), were measured by means of plasma clearance of p-amino-hippurate and inulin, respectively. In comparison with groups 1 and 3, the RPF and GFR were significantly decreased in groups 2 and 4. Interestingly, renal homogenates of the latter groups yielded significantly higher values of phospholipase A activity and fructosamine level in comparison with either the control (1) and the O3 (3) treated groups. Moreover renal SOD activity showed a significant increase in group 3 without significant differences among groups 1, 2 and 4. Morphological alterations of the kidney were present in 100%, 88% and 30% of the animals in groups 2, 4 and 3, respectively. It is proposed that the O3 protective effect can be ascribed to the substantial possibility of upregulating the antioxidant defence system capable of counteracting the damaging effect of ischaemia. These findings suggest that, whenever possible, ozone preconditioning may represent a prophylactic approach for minimizing renal damage before transplantation.

Posttranslational regulation of Ty1 retrotransposition by mitogen-activated protein kinase Fus3.

Ty1 retrotransposons in Saccharomyces cerevisiae are maintained in a state of transpositional dormancy. We isolated a mutation, rtt100-1, that increases the transposition of genomic Ty1 elements 18- to 56-fold but has little effect on the transposition of related Ty2 elements. rtt100-1 was shown to be a null allele of the FUS3 gene, which encodes a haploid-specific mitogen-activated protein kinase. In fus3 mutants, the levels of Ty1 RNA, protein synthesis, and proteolytic processing were not altered relative to those in FUS3 strains but steady-state levels of TyA, integrase, and reverse transcriptase proteins and Ty1 cDNA were all increased. These findings suggest that Fus3 suppresses Ty1 transposition by destabilizing viruslike particle-associated proteins. The Fus3 kinase is activated through the mating-pheromone response pathway by phosphorylation at basal levels in naive cells and at enhanced levels in pheromone-treated cells. We demonstrate that suppression of Ty1 transposition in naive cells requires basal levels of Fus3 activation. Substitution of conserved amino acids required for activation of Fus3 derepressed Ty1 transposition. Moreover, epistasis analyses revealed that components of the pheromone response pathway that act upstream of Fus3, including Ste4, Ste5, Ste7, and Ste11, are required for the posttranslational suppression of Ty1 transposition by Fus3. The regulation of Ty1 transposition by Fus3 provides a haploid-specific mechanism through which environmental signals can modulate the levels of retrotransposition.

Positive human health effects of dust suppression with canola oil in swine barns.

A crossover trial was conducted to evaluate the acute human health effects of a dust control technology in a swine confinement facility. Twenty lifetime nonsmoking male subjects, with no evidence of allergy or asthma and no previous swine barn exposure, participated in the study, which included a laboratory session (baseline), 5-h exposure in a swine room sprinkled with canola oil (treatment) and 5-h exposure in a traditional swine room (control). Mean values of inhalable dust concentrations and endotoxin levels in the control room were significantly greater than those observed in the treatment room. Mean shift changes in FEV1 from preexposure to end of exposure were 1.1% (standard error, 0.63%) on baseline day, -1.9% (0.63%) on treatment day, and -9.9% (1.12%) on control day; the differences in the shift changes were statistically significant. Mean value of methacholine concentration that reduced the FEV1 by 20% (PC20) in bronchoprovocation tests on baseline day was significantly different from that on treatment day (p = 0.04) and that on control day (p < 0.001). Significant increases were also observed in white blood cell counts and nasal lavage cell counts on the control day in comparison with the other two days. Blood neutrophil counts after control room exposure were twice those observed on baseline and after exposure to the treatment room. Significant differences were also observed in IL-1 beta, IL-6, and IL-8 nasal lavage cytokines and in IL-6 serum cytokine. These results suggest that the canola oil dust control method is effective in improving indoor air quality in swine barns and reducing acute health effects in naive healthy subjects.

L-arginine supplementation improves venous endothelial cell but not smooth muscle cell dysfunction induced by prolonged diet-induced hypercholesterolemia.

Hypercholesterolemia induces venous vasomotor dysfunction. This study examines the endothelial and smooth muscle cell vasoreactivity of external jugular veins from rabbits fed either a normal or a 1% cholesterol diet for 8 weeks with and without L-arginine supplementation (2 g/kg day-1 orally for the last 5 weeks). Isometric tension studies were performed on harvested jugular veins. Concentrations of serum cholesterol were 20-fold higher than controls and serum L-arginine twofold higher than untreated animals. Hypercholesterolemia induced hypersensitivity to norepinephrine (p < .05), bradykinin (p < .05), and histamine (p < .05) with a contractile response to serotonin compared to controls. L-Arginine supplementation decreased bradykinin hypersensitivity but had no effect on the changes in norepinephrine serotonin and histamine responses compared to controls. Hypercholesterolemia interfered with relaxation induced by acetylcholine but with L-arginine, normal acetylcholine-induced, endothelium-dependent relaxation returned (54 +/- 10%, compared to 40 +/- 14% in control veins; p > .05). Non-endothelium-dependent relaxation to sodium nitroprusside of precontracted veins was unaffected by the presence of high cholesterol concentrations. This study suggests that L-arginine therapy may ameliorate hypercholesterolemia-induced functional abnormalities in endothelial cells.

Adaptive regulation of neutral amino acid transport System A in rat H4 hepatoma cells.

Substrate regulation of System A transport activity in rat H4 hepatoma cells is described. The uptake of several amino acids was tested in the presence of system-specific inhibitors. System A activity was increased in a RNA- and protein synthesis-dependent manner by amino acid deprivation of the cells (adaptive regulation), whereas transport by Systems ASC, N, y+, and L was unaffected. Unlike human fibroblasts, the H4 cells did not require serum to exhibit the depression of System A. At cell densities between 88 X 10(3) and 180 X 10(3) cells/cm2, the degree of adaptive regulation was inversely related to cell density. Both transport of AIB and adaptive regulation of System A were nearly abolished if either K+ or Li+ was substituted for Na+ in the medium. The presence of cycloheximide or tunicamycin blocked further increases in starvation-induced activity within 1 hr of addition, suggesting the involvement of a plasma membrane glycoprotein. In contrast, if the medium was supplemented with actinomycin after the stimulation of System A had begun, the activity continued to increase for an additional 2 hr before being slowed by the inhibitor. The contributions of trans-inhibition and repression to the amino acid-induced decay of System A activity were estimated for several representative amino acids. In general, the System A activity in normal rat hepatocytes was much less sensitive to trans-inhibition than the corresponding activity in H4 hepatoma cells. The half-life values for the amino acid-dependent decay of System A ranged from 0.5 to 2.0 hr.