We recently demonstrated that a variant allele of CYP3A5 (CYP3A5*3) confers low CYP3A5 expression as a result of improper mRNA splicing. In this study, we further evaluated the regulation of CYP3A5 in liver and jejunal mucosa from white donors. For all tissues, high levels of CYP3A5 protein were strongly concordant with the presence of a wild-type allele of the CYP3A5 gene (CYP3A5*1). CYP3A5 represented greater than 50% of total CYP3A content in nearly all of the livers and jejuna that carried the CYP3A5*1 wild-type allele. Overall, CYP3A5 protein content accounted for 31% of the variability in hepatic midazolam hydroxylation activity. Improperly spliced mRNA (SV1-CYP3A5) was found only in tissues containing a CYP3A5*3 allele. Properly spliced CYP3A5 mRNA (wt-CYP3A5) was detected in all tissues, but the median wt-CYP3A5 mRNA was 4-fold higher in CYP3A5*1/*3 livers compared with CYP3A5*3/*3 livers. Differences in wt-CYP3A5 and CYP3A4 mRNA content explained 53 and 51% of the interliver variability in CYP3A5 and CYP3A4 content, respectively. Hepatic CYP3A4 and CYP3A5 contents were not correlated when all livers were compared. However, for CYP3A5*1/*3 livers, levels of the two proteins were strongly correlated (r ϭ 0.93) as were wt-CYP3A5 and CYP3A4 mRNA (r ϭ 0.76). These findings suggest that CYP3A4 and CYP3A5 genes share a common regulatory pathway for constitutive expression, possibly involving conserved elements in the 5Ј-flanking region.CYP3A contributes to the metabolism of numerous therapeutic agents and endogenous molecules. Substrates of CYP3A include benzodiazepines, hydroxymethyl glutarylCoA reductase inhibitors, dihydropyridine calcium channel blockers, human immunodeficiency virus protease inhibitors, antiepileptics, chemotherapeutics, and immunosuppressants (Guengerich, 1999). Interindividual differences in the oral bioavailability and systemic clearance of CYP3A substrates can be attributed in large part to variable expression of CYP3A in the liver (Thummel et al., 1994) and mucosal epithelium of the small intestine (DeWaziers et al., 1990;Paine et al., 1996Paine et al., , 1997. CYP3A4 is the dominant CYP3A isoform in the liver and small intestine of most white adults, whereas CYP3A7 is primarily a fetal enzyme (Kitada and Kamataki, 1994). More recently, human CYP3A43 has been identified and cloned , although its contribution to hepatic or extrahepatic CYP3A-dependent drug clearance is thought to be negligible (Westlind et al., 2001). CYP3A5 is also found in the liver and intestinal mucosa (Wrighton et al., 1990;Paine et al., 1997) and other extrahepatic tissues, including the kidney (Haehner et al., 1996), lung (Kivistö et al., 1996), and prostate gland (Yamakoshi et al., 1999). Its expression is polymorphic, with readily detectable levels in 25 to 30% and very low or undetectable levels in 70 to 75% of livers and small intestines examined (Wrighton et al., 1990;Paine et al., 1997;Tateishi et al., 1999).The genetic basis for polymorphic CYP3A5 expression was first examined by Jounä idi et al....

Thyroid hormone is essential for normal brain development. Therefore, it is a genuine concern that thyroid function can be altered by a very large number of chemicals routinely found in the environment and in samples of human and wildlife tissues. These chemicals range from natural to manufactured compounds. They can produce thyroid dysfunction when they are absent from the diet, as in the case of iodine, or when they are present in the diet, as in the case of thionamides. Recent clinical evidence strongly suggests that brain development is much more sensitive to thyroid hormone excess or deficit than previously believed. In addition, recent experimental research provides new insight into the developmental processes affected by thyroid hormone. Based on the authors' research focusing on the ability of polychlorinated biphenyls to alter the expression of thyroid hormone-responsive genes in the developing brain, this review provides background information supporting a new way of approaching risk analysis of thyroid disruptors. endemias occurring in different parts of the world have led to the proposal that the various symptoms of the two forms of cretinism arise from thyroid hormone deficits occurring at different developmental windows of vulnerability (15,17,49). Therefore, thyroid hormone appears to play an important role in fetal brain development, perhaps before the onset of fetal thyroid function.The second type of pathological situation is that of subtle, undiagnosed maternal hypothyroxinemia. The concept and definition of maternal hypothyroxinemia were developed in a series of papers by . Low thyroid hormone was initially defined empirically-those pregnant women with the lowest butanol-extractable iodine among all pregnant women (55,57). This work was among the first to document an association between subclinical hypothyroidism in pregnant women and neurological function of the offspring. After the development of radioimmunoassay for thyroid hormone, Pop et al. (58) found that the presence of antibodies to thyroid peroxidase in pregnant women, independent of thyroid hormone levels per se, is associated with significantly lower IQ in the offspring. Subsequent studies have shown that children born to women with thyroxine (T 4 ) levels in the lowest 10 th percentile of the normal range had a higher risk of low IQ and attention deficit (25). Excellent recent reviews discuss these studies in detail (24,57,59). Taken together, these studies present strong evidence that maternal thyroid hormone plays a role in fetal brain development before the onset of fetal thyroid function, and that thyroid hormone deficits in pregnant women can produce irreversible neurological effects in their offspring (18,19,22,37,(60)(61)(62). Thyroid Hormone and Brain Development in Experimental AnimalsConsiderable research using experimental animals has provided important insight into the mechanisms and consequences of thyroid hormone action in brain development. The body of this work is far too extensive to review here but has been rev...

A single-nucleotide polymorphism (A6986G) in the cytochrome p-450 3A5 (CYP3A5) gene distinguishes an expressor (*1) and a reduced-expressor (*3) allele and largely predicts CYP3A5 content in liver and intestine. CYP3A5 is the prevailing CYP3A isoform in kidney. We report that, among renal microsomes from 21 organ donors, those from *1/*3 individuals had at least eightfold higher mean kidney microsomal CYP3A5 content and 18-fold higher mean CYP3A catalytic activity than did those from *3/*3 individuals (P = 0.0001 and P = 0.0137, respectively). We also report significant associations between the A6986G polymorphism and systolic blood pressure (P = 0.0007), mean arterial pressure (P = 0.0075), and creatinine clearance (P = 0.0035) among 25 healthy African-American adults. These associations remained significant when sex, age, and body mass index were taken into account. The mean systolic blood pressure of homozygous CYP3A5 expressors (*1/*1) exceeded that of homozygous nonexpressors (*3/*3) by 19.3 mmHg. We speculate whether a high CYP3A5 expressor allele frequency among African-Americans may contribute to a high prevalence of sodium-sensitive hypertension in this population.

Down syndrome (DS) is the most common genetic cause of intellectual disability in children, and the number of adults with DS reaching old age is increasing. By the age of 40 years, virtually all people with DS have sufficient neuropathology for a postmortem diagnosis of Alzheimer disease (AD). Trisomy 21 in DS leads to an overexpression of many proteins, of which at least two are involved in oxidative stress and AD: superoxide dismutase 1 (SOD1) and amyloid precursor protein (APP). In this study, we tested the hypothesis that DS brains with neuropathological hallmarks of AD have more oxidative and nitrosative stress than those with DS but without significant AD pathology, as compared with similarly aged-matched non-DS controls. The frontal cortex was examined in 70 autopsy cases (n=29 control and n=41 DS). By ELISA, we quantified soluble and insoluble Aβ40 and Aβ42, as well as oligomers. Oxidative and nitrosative stress levels (protein carbonyls, HNE-bound proteins, and 3-nitrotyrosine) were measured by slot-blot. We found that soluble and insoluble Aβ and oligomers increase as a function of age in DS frontal cortex. Of the oxidative stress markers, HNE-bound proteins were increased overall in DS. Protein carbonyls were correlated with Aβ40 levels. These results suggest that oxidative damage, but not nitrosative stress, may contribute to the onset and progression of AD pathogenesis in DS. Conceivably, treatment with antioxidants may provide a point of intervention to slow pathological alterations in DS.

Despite clinical evidence that thyroid hormone is essential for brain development before birth, effects of thyroid hormone on the fetal brain have been largely unexplored. One mechanism of thyroid hormone action is regulation of gene expression, because thyroid hormone receptors (TRs) are ligand-activated transcription factors. We used differential display to identify genes affected by acute T 4 administration to the dam before the onset of fetal thyroid function. Eight of the 11 genes that we identified were selectively expressed in brain areas known to contain TRs, indicating that these genes were directly regulated by thyroid hormone. Using in situ hybridization, we confirmed that the cortical expression of both neuroendocrine-specific protein (NSP) and Oct-1 was affected by changes in maternal thyroid status. Additionally, we demonstrated that both NSP and Oct-1 were expressed in the adult brain and that their responsiveness to thyroid hormone was retained. These data are the first to identify thyroid hormone-responsive genes in the fetal brain.