Effect of Chronic Cadmium Exposure on Brain and Liver Transporters and Drug-Metabolizing Enzymes in Male and Female Mice Genetically Predisposed to Alzheimer's Disease.

Cadmium (Cd) exposure is associated with increased Alzheimer's disease (AD) risks. The human Apolipoprotein E (ApoE) gene encodes a lipid-transporting protein that is critical for brain functions. Compared with ApoE2 and E3, ApoE4 is associated with increased AD risk. Xenobiotic biotransformation-related genes have been implicated in the pathogenesis of AD. However, little is known about the effects of Cd, ApoE, and sex on drug-processing genes. We investigated the Cd-ApoE interaction on the transcriptomic changes in the brains and livers of ApoE3/ApoE4 transgenic mice. Cd disrupts the transcriptomes of transporter and drug-processing genes in brain and liver in a sex- and ApoE-genotype-specific manner. Proinflammation related genes were enriched in livers of Cd-exposed ApoE4 males, whereas circadian rhythm and lipid metabolism related genes were enriched in livers of Cd-exposed ApoE3 females. In brains, Cd up-regulated the arachidonic acid-metabolizing Cyp2j isoforms only in the brains of ApoE3 mice, whereas the dysregulation of cation transporters was male-specific. In livers, several direct target genes of the major xenobiotic-sensing nuclear receptor pregnane X receptor were uniquely upregulated in Cd-exposed ApoE4 males. There was a female-specific hepatic upregulation of the steroid hormone-metabolizing Cyp2 isoforms and the bile acid synthetic enzyme Cyp7a1 by Cd exposure. The dysregulated liver transporters were mostly involved in intermediary metabolism, with the most significant response observed in ApoE3 females. In conclusion, Cd dysregulated the brain and liver drug-processing genes in a sex- and ApoE-genotype specific manner, and this may serve as a contributing factor for the variance in the susceptibility to Cd neurotoxicity. SIGNIFICANCE STATEMENT: Xenobiotic biotransformation plays an important role in modulating the toxicity of environmental pollutants. The human ApoE4 allele is the strongest genetic risk factor for AD, and cadmium (Cd) is increasingly recognized as an environmental factor of AD. Very little is known regarding the interactions between Cd exposure, sex, and the genes involved in xenobiotic biotransformation in brain and liver. The present study has addressed this critical knowledge gap.