Differential susceptibity of transgenic mice lacking one or both apolipoprotein alleles to folate and vitamin E deprivation

The E4 allele of apolipoprotein E (ApoE) is associated with neurodegeneration in part due to increased oxidative stress. Transgenic mice lacking ApoE (-/-) represent a model for the consequences of deficiencies in ApoE function. Dietary deficiency in folate and vitamin E has previously been shown to potentiate the impact of ApoE deficiency; ApoE-/- mice deprived of folate and vitamin E for 1 month demonstrated increased oxidative damage in brain tissue and impaired cognitive performance as compared to ApoE+/+ mice. Since individuals homozygous for E4 can demonstrate more increased risk for neurodegeneration and an earlier age of onset than individuals heterozygous for E4, we tested the impact of folate and vitamin E deprivation on ApoE+/- mice. Thiobarbituric acid-reactive substances in brain tissue of ApoE+/- were significantly increased compared to ApoE+/+ mice, but this increase was less than that observed in ApoE-/- mice. By contrast, livers of ApoE+/- and -/- mice displayed an identical increase over that of +/+ mice. ApoE-/- mice, but not +/- or +/+ mice, exhibited impaired cognitive performance in maze trials when deprived of folate and vitamin E. These findings support the notion that homozygous deficiency of ApoE function can be more severe than heterozygous deficiency. They further suggest that the impact of partial deficiency in ApoE function may present a latent risk that may manifest only when compounded by other factors such as dietary deficiency.