Depletion of liver regulatory heme in benzene exposed rats

Tryptophan metabolism in alcoholism

Acute and chronic alcohol (ethanol) intake and subsequent withdrawal exert major effects on tryptophan (Trp) metabolism and disposition in human subjects and experimental animals. In rats, activity of the rate-limiting enzyme of Trp degradation, liver Trp pyrrolase (TP), is enhanced by acute, but inhibited after chronic, ethanol administration, then enhanced during withdrawal. These changes lead to alterations in brain serotonin synthesis and turnover mediated by corresponding changes in circulating Trp availability to the brain. A low brain-serotonin concentration characterizes the alcohol-preferring C57BL/6J mouse strain and many alcohol-preferring rat lines. In this mouse strain, liver TP enhancement causes the serotonin decrease. In man, acute ethanol intake inhibits brain serotonin synthesis by activating liver TP. This may explain alcohol-induced depression, aggression and loss of control in susceptible individuals. Chronic alcohol intake in dependent subjects may be associated with liver TP inhibition and a consequent enhancement of brain serotonin synthesis, whereas subsequent withdrawal may induce the opposite effects. The excitotoxic Trp metabolite quinolinate may play a role in the behavioural disturbances of the alcohol-withdrawal syndrome. Some abstinent alcoholics may have a central serotonin deficiency, which they correct by liver TP inhibition through drinking. Further studies of the Trp and serotonin metabolic status in long-term abstinence in general and in relation to personality characteristics, alcoholism typology and genetic factors in particular may yield important information which should facilitate the development of more effective screening, and preventative and therapeutic strategies in this area of mental health.

Release of iron from ferritin by metabolites of benzene and superoxide radical generating agents

The release of iron from ferritin in the presence of benzene metabolites, viz. phenol (P), catechol (CT), hydroquinone (HQ) and superoxide radical generating compounds, viz. pyrogallol (PL), phloroglucinol (PG), phenylhydrazine (PH) or phenylenediamine (PD) was studied in acetate buffer, pH 5.6. Monitoring the formation of the iron-ferrozine complex quantitated the release of iron from ferritin. The presence of P (125 microM) did not result in the release of iron from ferritin, whereas the same concentration of CT, HQ, PL, PH or PD resulted in the release of significant amounts of iron from ferritin and a marginal amount of iron in the presence of PG, CT, HQ, PL, PH or PD concentration and time-dependent increase in iron release from ferritin were observed although the increase was not linear as a function of time and concentration of the compounds studied. The presence of superoxide dismutase inhibited significantly the release of iron from ferritin by CT, HQ, PL, PH or PD. The iron released from ferritin by CT, HQ, PL, PH or PD enhanced lipid peroxidation in rat brain homogenate and released aldehydic products from bleomycin-dependent degradation of DNA and also caused single strand nicks to pUC18 DNA. These studies indicate that CT and HQ, the two principal polyphenolic metabolites of benzene and PL, PH or PD, the superoxide radical generating compounds were capable of reducing ferric iron from ferritin and also mobilizing and releasing iron from ferritin core. The release of iron from ferritin by these compounds is a result of direct reduction of ferritin iron by electron transfer and also reduction via superoxide radical. The release of iron from ferritin by CT and HQ may have toxicological implications in relation to benzene toxicity. The release of iron by superoxide radical generating agents suggests that oxidative stress may play a role as this could lead to disruption of intracellular iron homeostasis.

Modulation of benzene induced toxicity by protein A

Administration of benzene (i.p. 1.0 mL/kg body weight) for 3 consecutive days produced leucopenia and lymphocytopenia in female albino rats. In addition, the total iron content, lipid peroxidation and superoxide dismutase activity of the liver and bone marrow were significantly (P < 0.001) increased. Low molecular weight (LMW) bleomycin-detectable iron accumulated only in bone marrow. Prior administration of Protein A (PA), a multipotent immunostimulant and interferon inducer (60 micrograms/kg body weight, i.v. twice weekly for 2 weeks), ameliorated most of the adverse effects of benzene. PA restored the changes in hepatic histological architecture, reversed leucopenia and superoxide dismutase activity, lipid peroxidation, total iron content and LMW iron content of bone marrow were normalized. Isozymes of glutathione-S-transferase (alpha, pi, mu) which decreased following benzene exposure increased in PA pretreated benzene exposed rats. This study suggests that pretreatment with PA modulates the toxicity of benzene.

Liver delta-aminolevulinate dehydratase activity in amitriptyline- or chlorpromazine-treated rats

Amitriptyline (AMT) and chlorpromazine (CPZ) (0.5 mg per animal, i.p.) were injected into rats separately for 30 days and their effects on heme metabolism in liver were examined. Significant decreases in the delta-aminolevulinate dehydratase activity were observed following the administration of both drugs (mean value of AMT-group: 6.58 U/g tissue; and CPZ-group: 7.04 U/g tissue) in comparison to that of controls (11.71 U/g tissue); however total liver heme content was not altered. When 24-h urinary excretions of delta-aminolevulinate (ALA) and porphobilinogen (PBG) were measured on the last day of the experiment, a slight (AMT-group: 38.40 micrograms/day) to distinct (CPZ-group: 59.11 micrograms/day) increase of urinary ALA was observed, while PBG excretion tended to decline only moderately under CPZ (3.52 micrograms/day), but significantly in presence of AMT (2.16 micrograms/day). Mean values obtained from control group were 32.12 micrograms/day for ALA and 4.25 micrograms/day for PBG.

Accumulation of low molecular weight (bleomycin detectable) iron in bone marrow cells of rats after benzene exposure

An accumulation of low molecular weight (LMW) bleomycin detectable iron in the bone marrow was observed after administration of benzene (IP 0.5 ml/kg, daily) for 5 and 10 days in female albino rats. However, this LMW iron was not detectable in the bone marrow of rats from the control group. Studies of bone marrow fractionation showed that the maximum accumulation of this LMW iron was in the mitochondrial fraction. An increase in the activity of superoxide dismutase and lipid peroxidation was also noticed in the benzene exposed groups.