Effect of dietary restriction on benzo[a]pyrene (BaP) metabolic activation and pulmonary BaP-DNA adduct formation in mouse

Caloric restriction attenuates C57BL/6 J mouse lung injury and extra-pulmonary toxicity induced by real ambient particulate matter exposure

Background

Caloric restriction (CR) is known to improve health and extend lifespan in human beings. The effects of CR on adverse health outcomes in response to particulate matter (PM) exposure and the underlying mechanisms have yet to be defined.

Results

Male C57BL/6 J mice were fed with a CR diet or ad libitum (AL) and exposed to PM for 4 weeks in a real-ambient PM exposure system located at Shijiazhuang, China, with a daily mean concentration (95.77 μg/m³) of PM_2.5. Compared to AL-fed mice, CR-fed mice showed attenuated PM-induced pulmonary injury and extra-pulmonary toxicity characterized by reduction in oxidative stress, DNA damage and inflammation. RNA sequence analysis revealed that several pulmonary pathways that were involved in production of reactive oxygen species (ROS), cytokine production, and inflammatory cell activation were inactivated, while those mediating antioxidant generation and DNA repair were activated in CR-fed mice upon PM exposure. In addition, transcriptome analysis of murine livers revealed that CR led to induction of xenobiotic metabolism and detoxification pathways, corroborated by increased levels of urinary metabolites of polycyclic aromatic hydrocarbons (PAHs) and decreased cytotoxicity measured in an ex vivo assay.

Conclusion

These novel results demonstrate, for the first time, that CR in mice confers resistance against pulmonary injuries and extra-pulmonary toxicity induced by PM exposure. CR led to activation of xenobiotic metabolism and enhanced detoxification of PM-bound chemicals. These findings provide evidence that dietary intervention may afford therapeutic means to reduce the health risk associated with PM exposure.

The MDT-15 subunit of mediator interacts with dietary restriction to modulate longevity and fluoranthene toxicity in Caenorhabditis elegans

Dietary restriction (DR), the limitation of calorie intake while maintaining proper nutrition, has been found to extend life span and delay the onset of age-associated disease in a wide range of species. Previous studies have suggested that DR can reduce the lethality of environmental toxins. To further examine the role of DR in toxin response, we measured life spans of the nematode Caenorhabditis elegans treated with the mutagenic polyaromatic hydrocarbon, fluoranthene (FLA). FLA is a direct byproduct of combustion, and is one of U.S. Environmental Protection Agency's sixteen priority environmental toxins. Treatment with 5 µg/ml FLA shortened the life spans of ad libitum fed nematodes, and DR resulted in increased sensitivity to FLA. To determine the role of detoxifying enzymes in the toxicity of FLA, we tested nematodes with mutations in the gene encoding the MDT-15 subunit of mediator, a transcriptional coactivator that regulates genes involved in fatty acid metabolism and detoxification. Mutation of mdt-15 increased the life span of FLA treated animals compared to wild-type animals with no difference observed between DR and ad libitum fed mdt-15 animals. We also examined mutants with altered insulin-IGF-1-like signaling (IIS), which is known to modulate life span and stress resistance in C. elegans independently of DR. Mutation of the genes coding for the insulin-like receptor DAF-2 or the FOXO-family transcription factor DAF16 did not alter the animals' susceptibility to FLA compared to wild type. Taken together, our results suggest that certain compounds have increased toxicity when combined with a DR regimen through increased metabolic activation. This increased metabolic activation appears to be mediated through the MDT-15 transcription factor and is independent of the IIS pathway.

Effects of benzo[a]pyrene on tissue activities of metabolizing enzymes and antioxidant system in normal and protein-malnourished rats

The effects of benzo[a]pyrene (B[a]P) on some drug-metabolizing and antioxidant systems in liver, lung, and stomach were investigated in normal and protein malnutrition (PM) rats. PM significantly inhibited tissue glutathione (GSH) content and increased hepatic lipid peroxidation. Cytochrome P450 isoform CYP1A1 was significantly increased in various tissues (42-73%). Also, lung glutathione S-transferase (GST) activity was significantly decreased (19%) in PM rats. On the other hand, B[a]P significantly induced tissue GSH of control and PM rats. Also, hepatic lipid peroxidation were significantly increased in control rats treated with B[a]P. Superoxide dismutase (SOD) activity was decreased by B[a]P treatment in PM rat stomach. B[a]P significantly induced both quinone reductase (QR) (in all tissues) and hepatic GST of control and PM rats. GST activity in PM rat liver was significantly higher than that of control rat liver after B[a]P treatment. Also, B[a]P induced hepatic CYP1A1 by 32-fold and 27-fold (P < or = 0.05) in control and PM rats, respectively. Stomach and hepatic UDP-glucuronosyltransferase activities were significantly decreased (34%) and increased (74%), respectively by B[a]P in PM rats. The results suggest that PM status has a modifying effect on the response of some antioxidant and metabolizing systems to a well-known carcinogen risk.

Protective effect of Cassia occidentalis extract on chemical-induced chromosomal aberrations in mice

This study was conducted to determine the antimutagenic potential of aqueous extract of Cassia occidentalis against the chromosomal aberrations (CA) produced in vivo by benzo[a]pyrene (B[a]P) and cyclophosphamide (CP) in mice. Animals (male mice) were treated with three doses of plant extract (50 mg/kg, 250 mg/kg and 500 mg/kg) for 7 days prior to the administration of single dose of mutagens (B[a]P 125 mg/kg oral; CP 40 mg/kg i.p.). The results indicated that C. occidentalis was not genotoxic per se and exerted no other toxic signs and symptoms in treated animals. The chromosomal aberrations produced by B[a]P and CP were significantly reduced (p < 0.001) by C. occidentalis pre-treatment. Furthermore, animals treated with plant extract showed a reduced level of cytochrome P 450 (Cyt P 450) and elevated levels of glutathione S-transferase (GST) activity and glutathione content in the liver. It seems that C. occidentalis exerts its antimutagenic activity by modulating the xenobiotic activation and detoxification mechanisms.