Assessment by c-Fos immunostaining of changes in brain neural activity induced by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and leptin in rats

Effect of tocopherol and acetylsalicylic acid on the biochemical indices of blood in dioxin-exposed rats

New sources of dioxins and increased dioxin concentrations in the environment, coupled with their increased bioavailability along the food chain and accumulation in adipose tissues, contribute to various adverse long-term biological effects. The purpose of the study was to determine whether tocopherol protects the CNS by decreasing the pro-inflammatory influence of free radicals generated by TCDD; whether acetylsalicylic acid inhibits the production of inflammatory mediators; and whether the combined administration of tocopherol and acetylsalicylic acid to TCDD-exposed rats has a potential CNS-protective effect. The study included 117 rats divided into 8 groups: 75 female and 12 male Buffalo rats aged 8-10 weeks, weighing 140-160 g; as well as 30 female rats aged 6 weeks and weighing 120 g, which were the offspring of females from each study group. In the experiment, the following substances were used: 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), dosed at 5 μg/kg BW and 12.5 μg/kg BW, diluted in a 1% DMSO solution at the concentration of 1 μg/ml; α-tocopherol acetate, dosed at 30 mg/kg BW, in 0.2 ml of oil solution; and acetylsalicylic acid, 50mg/kg BW, suspended in 0.5 ml of starch solution, administered orally using a feeding tube. Pleurisy was induced by an injection of 0.15 ml of 1% carrageenin solution. The use of tocopherol reduces the adverse effects of the inflammatory reaction induced by TCDD. Administering tocopherol improves protein metabolism by reducing protein catabolism, and raises γ-globulin fraction levels. Combined acetylsalicylic acid and tocopherol suppress catabolic processes accompanying inflammation.

Developmental exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin alters DNA methyltransferase (dnmt) expression in zebrafish (Danio rerio)

DNA methylation is one of the most important epigenetic modifications involved in the regulation of gene expression. The DNA methylation reaction is catalyzed by DNA methyltransferases (DNMTs). Recent studies have demonstrated that toxicants can affect normal development by altering DNA methylation patterns, but the mechanisms of action are poorly understood. Hence, we tested the hypothesis that developmental exposure to TCDD affects dnmt gene expression patterns. Zebrafish embryos were exposed to 5nM TCDD for 1h from 4 to 5h post-fertilization (hpf) and sampled at 12, 24, 48, 72, and 96 hpf to determine dnmt gene expression and DNA methylation patterns. We performed a detailed analysis of zebrafish dnmt gene expression during development and in adult tissues. Our results demonstrate that dnmt3b genes are highly expressed in early stages of development, and dnmt3a genes are more abundant in later stages. TCDD exposure upregulated dnmt1 and dnmt3b2 expression, whereas dnmt3a1, 3b1, and 3b4 are downregulated following exposure. We did not observe any TCDD-induced differences in global methylation or hydroxymethylation levels, but the promoter methylation of aryl hydrocarbon receptor (AHR) target genes was altered. In TCDD-exposed embryos, AHR repressor a (ahrra) and c-fos promoters were differentially methylated. To characterize the TCDD effects on DNMTs, we cloned the dnmt promoters with xenobiotic response elements and conducted AHR transactivation assays using a luciferase reporter system. Our results suggest that ahr2 can regulate dnmt3a1, dnmt3a2, and dnmt3b2 expression. Overall, we demonstrate that developmental exposure to TCDD alters dnmt expression and DNA methylation patterns.

Association of dioxin and other persistent organic pollutants (POPs) with diabetes: epidemiological evidence and new mechanisms of beta cell dysfunction

The worldwide explosion of the rates of diabetes and other metabolic diseases in the last few decades cannot be fully explained only by changes in the prevalence of classical lifestyle-related risk factors, such as physical inactivity and poor diet. For this reason, it has been recently proposed that other "nontraditional" risk factors could contribute to the diabetes epidemics. In particular, an increasing number of reports indicate that chronic exposure to and accumulation of a low concentration of environmental pollutants (especially the so-called persistent organic pollutants (POPs)) within the body might be associated with diabetogenesis. In this review, the epidemiological evidence suggesting a relationship between dioxin and other POPs exposure and diabetes incidence will be summarized, and some recent developments on the possible underlying mechanisms, with particular reference to dioxin, will be presented and discussed.

Bifunctional modulating effects of an indigo dimer (bisindigotin) to CYP1A1 induction in H4IIE cells

In this study, we measured and characterized the bifunctional effects of a newly identified natural compound-bisindigotin (SLY-1), isolated from leaf extracts of Isatis indigotica, to CYP1A1/EROD activities in H4IIE cells. The compound, SLY-1 (1muM) elicited a transitory and significant induction of CYP1A1 RNA/protein levels and EROD activities in the cells. Maximum levels of CYP1A1 expression and EROD induction were attained at 8 and 12h of post-treatment, respectively. Thereafter the induction decreased significantly. Similar profile of CYP1A2 and CYP1B1 mRNA induction was observed. In contrast TCDD elicited CYP1A1/EROD induction was persistent. The transitory effect by SLY-1 is most likely due to the clearance of SLY-1 by cellular metabolism. Taken together the observation indicated that SLY-1 is an Ah receptor agonist for CYP1A1/CYP1A2/CYP1B1/EROD induction. Interestingly in the TCDD/SLY-1 cotreatment study, although synergistic effects on CYP1A1 expression and EROD induction were observed at 4-8h, significant inhibitory effects to TCDD induced CYP1A1 protein and EROD activity were detected at 12-24h of post-treatment. Because there was no significant reduction of CYP1A1, CYP1A2 or CYP1B1 transcript levels between TCDD- and TCDD/SLY-1 treated cells, the data pointed to the translational and/or post-translational inhibitory effect. The cellular signal transduction system may be modulated following exposure to SLY-1. To investigate the possible mechanisms involved, various specific kinase inhibitors or activators (chelerythrin, PD98059, U0126, ZM336372, SB202190, PKA inhibitor PKI (6-22) amide, and dbcAMP) were used for the assessment. Chelerythrine, PD98059 or dbcAMP treatment in TCDD induced cells showed significant inhibitory effects on CYP1A1 mRNA/protein expressions and EROD activities. U0126 had no observable EROD inhibitory effect. ZM336372 or SB202190 showed inhibition only at EROD activities. The results indicated that the SLY-1 inhibitory effect was possibly not mediated by the cAMP/PKA, PKC or MEK pathways. Nevertheless our results indicate that SLY-1 is not only an inducer of the CYP1A1 system, but also a potent inhibitor of CYP1A1 enzyme.