Nathan J Cherrington

PMID: 9711811;Abstract:

1. The mouse and rat exhibit substantial differences in the gender expression of flavin-containing monooxygenase (FMO) forms. Hepatic FMO1 is gender-dependent in both species, selective to the male in rat, female in mouse. Human FMO1 is nearly undetectable. FMO3 in mouse is gender-specific to the female, but gender-independent in rat and man. FMO5 is gender-independent for mouse, rat and man. 2. Gender differences in substrate metabolism do not reflect overall FMO or isoform differences. Methimazole, imipramine and thiobenzamide are much better substrates for FMO1 than for FMO3 or FMO5. 3. Activities of microsomal samples toward these substrates reflect the relative abundance of FMO1. Hepatic samples show a 3-fold greater activity toward methimazole in the female mouse and male rat. Human microsomal samples show minimal activity. 4. Developmentally, FMO1 and FMO5 are expressed in foetuses as early as gestation days 15 and 17 and equally between genders until puberty. FMO3 is not found until 2 weeks post-partum and is found equally in the male and female until 6 weeks post-partum when it becomes undetectable in the male. 5. An event takes place after birth but before puberty that confers the ability to produce FMO3. The developmental pattern observed for mouse FMO3 is similar to human FMO3.

Drug-metabolizing enzymes and membrane transporters are responsible for the detoxication and elimination of xenobiotics from the body. The goal of this study was to identify alterations in mRNA expression of various transport and detoxication proteins in mouse liver after administration of the hepatotoxicants, acetaminophen or carbon tetrachloride. Therefore, male C57BL/6 J mice received acetaminophen (APAP, 200, 300, or 400 mg/kg, ip) or carbon tetrachloride (CCl4, 10 or 25 microl/kg, ip). Plasma and liver samples were collected at 6, 24, and 48 h for assessment of alanine aminotransferase (ALT) activity, total RNA isolation, and histopathological analysis of injury. Heme oxygenase-1 (Ho-1), NAD(P)H quinone oxidoreductase-1 (Nqo1), organic anion-transporting polypeptides (Oatp1a1, 1a4 and 1b2), sodium/taurocholate-cotransporting polypeptide (Ntcp), and multidrug resistance-associated protein (Mrp 1-6) mRNA levels in liver were determined using the branched DNA signal amplification assay. Hepatotoxic doses of APAP and CCl4 increased Ho-1 and Nqo1 mRNA levels by 22- and 2.5-fold, respectively, and reduced Oatp1a1, 1a4, and Ntcp mRNA levels in liver. By contrast, expression of Mrps 1-4 was increased after treatment with APAP and CCl4. Notably, a marked elevation of Mrp4 mRNA expression was observed 24 h after APAP 400 mg/kg (5-fold) and CCl4 25 microl/kg (37-fold). Collectively, these expression patterns suggest a coordinated regulation of both transport and detoxification genes during liver injury. This reduction in expression of uptake transporters, as well as enhanced transcription of detoxication enzymes and export transporters may limit the accumulation of potentially toxic products in hepatocytes.

Uptake of drugs and other xenobiotics from the nasal cavity and into either the brain or systemic circulation can occur through several different mechanisms, including paracellular transport and movement along primary olfactory nerve axons, which extend from the nasal cavity to the olfactory bulb of the brain. The present study was conducted to expand knowledge on a third means of uptake, namely the expression of drug transporters in the rat nasal epithelium. We used branched DNA technology to compare the level of expression of nine transporters [(equilibrative nucleoside transporters (ENT)1 and ENT2; organic cation transporter (OCT)1, 2, and 3; OCTN1; organic anion-transporting polypeptide (OATP)3; and multidrug resistance (MRP)1 and MRP4] in nasal respiratory mucosa, olfactory mucosa, and olfactory bulb to the level of expression of these transporters in the liver and kidney. Transporters with high expression in the nasal respiratory mucosa or olfactory tissues were immunolocalized by immunohistochemistry. ENT1 and ENT2 expression was relatively high in nasal epithelia and olfactory bulb, which may explain the uptake of intranasally administered nucleoside derivatives observed by other investigators. OATP3 immunoreactivity was high in olfactory epithelium and olfactory nerve bundles, which suggests that substrates transported by OATP3 may be candidates for intranasal administration.

The molecular mechanisms behind the transition from simple steatosis to nonalcoholic steatohepatitis (NASH) in nonalcoholic fatty liver disease (NAFLD) are not clearly understood. This hinders development of effective therapies for treatment and prevention of NASH. In this study expression profiling data from normal, steatosis, and NASH human livers were used to predict transcription factors that are misregulated as mechanistic features of NAFLD progression. Previously-published human NAFLD gene expression profiling data from normal, steatosis, and NASH livers were subjected to transcription factor binding site enrichment analysis. Selected transcription factors that bind enriched transcription factor binding sites were analyzed for changes in expression. Distinct transcription factor binding sites were enriched in genes significantly up- or down-regulated in NASH livers. Those enriched in up-regulated genes were bound by transcription factors such as FOXA, CEBP, and HNF1 family members, while those enriched in down-regulated genes were bound by nuclear receptors involved in xenobiotic sensing and lipid metabolism. Levels of mRNA and protein for selected transcription factors were significantly changed during disease progression. The study indicates that NAFLD progression involves changes in activity or expression of transcription factors that regulate genes involved in hepatic processes known to be altered in NASH. Transcription factors such as PPAR receptors, FoxA family members, and HNF4A might be targeted therapeutically to prevent NAFLD progression.

PMID: 17442726;Abstract:

An electroneutral organic cation (OC)/proton exchanger in the apical membrane of proximal tubules mediates the final step of renal OC excretion. Two members of the multidrug and toxin extrusion family, MATE1 and MATE2-K, were recently identified in human and rodent kidney and proposed to be the molecular basis of renal OC/H⁺ exchange. To take advantage of the comparative value of the large database on the kinetic and selectivity characteristics of OC/H⁺ exchange that exists for rabbit kidney, we cloned rbMATE1 and rbMATE2-K. The rabbit homologs have 75% (MATE1) and 74% (MATE2-K) amino acid identity to their human counterparts (and 51% identity with each other). rbMATE1 and rbMATE2-K exhibited H⁺ gradient-dependent uptake and efflux of tetraethylammonium (TEA) when expressed in Chinese hamster ovary cells. Both transporters displayed similar affinities for selected compounds [IC 50 values within 2-fold for TEA, 1-methyl-4-phenylpyridinium, and quinidine] and very different affinities for others (IC50 values differing by 8- to 80-fold for choline and cimetidine, respectively). These results indicate that rbMATE1 and rbMATE2-K are multispecific OC/H⁺ exchangers with similar, but distinct, functional characteristics. Overall, the selectivity of MATE1 and MATE2-K correlated closely with that observed in rabbit renal brush-border membrane vesicles. Copyright © 2007 the American Physiological Society.