Energy deprivation and a deficiency in downstream metabolic target genes during the onset of embryonic heart failure in RXRalpha-/- embryos.

RXRalpha null mutant mice display ocular and cardiac malformations, liver developmental delay, and die from cardiac failure around embryonic day (E) 14.5 pc. To dissect the molecular basis of the RXRalpha-associated cardiomyopathy, we performed subtractive hybridization and systematically characterized putative downstream target genes that were selectively lacking in the mutant embryos, both at early (E10.5) and late (E13.5) stages of mouse embryonic development. Approximately 50% of the subtracted clones (61/115) encoded proteins involved in intermediary metabolism and electron transport, suggesting an energy deficiency in the RXRalpha-/- embryos. In particular, clone G1, which encodes subunit 14.5b of the NADH-ubiquinone dehydrogenase complex, displayed a dose-dependent expression in the wild-type, heterozygous and RXRalpha mutant mice. This gene was also downregulated in a retinoid-deficient rat embryo model. ATP content and medium Acyl-CoA dehydrogenase mRNA were lower in RXRalpha mutant hearts compared to wild-type mice. Ultrastructural studies showed that the density of mitochondria per myocyte was higher in the RXRalpha mutant compared to wild-type littermates. We propose a model whereby defects in intermediary metabolism may be a causative factor of the RXRalpha-/- phenotype and resembles an embryonic form of dilated cardiomyopathy.

A long-term study of the absorption of large oral doses of folic acid.

Large daily doses of oral folic acid ranging from 25 to 1,000 mg and totalling between 1,875 and 16,000 mg per course of treatment were well tolerated without any evidence of toxic effects by four hyperuricemic men of the ages of 26, 38, 46 and 50 years. The minimum folate absorption in the gut as measured by urinary excretion ranged from 10.1 to 45.7 percent. The percentage of absorption within a give patient remained similar in successive courses and there was no evidence of saturation of the absorption process related to dose or time. The pattern of urinary excretion of folates did not indicate that appreciable fractions relative to the large folate doses were retained by the patients. Serum, erythrocyte, and urine folates returned to pretreatment levels within 120 days after treatment. These findings suggest that the folate stores of the body do not expand by orders of magnitude even when megadoses of folates are absorbed in the gut. The rise of the folate levels in erythrocytes was gradual and continuous during treatment and is best explained by postulating that incorporation of folate into red cell takes place mostly at the precursor and reticulocyte stages. The decrease of erythrocyte folate values seen 40 to 66 days after folate treatment indicates that the folate content of erythrocytes diminishes during their life span.