Effect of Thyroid Hormones onFlavin-containing Monooxygenase Activity in Co-cultured Adult Rat Hepatocytes

Identification of longevity-associated genes in long-lived Snell and Ames dwarf mice

Recent landmark molecular genetic studies have identified an evolutionarily conserved insulin/IGF-1 signal transduction pathway that regulates lifespan. In C. elegans, Drosophila, and rodents, attenuated insulin/IGF-1 signaling appears to regulate lifespan and enhance resistance to environmental stress. The Ames (Prop1 (df/df)) and Snell (Pit1 (dw/dw)) hypopituitary dwarf mice with growth hormone (GH), thyroid-stimulating hormone (TSH), and prolactin deficiencies live 40-60% longer than control mice. Both mutants are resistant to multiple forms of environmental stress in vitro. Taken collectively, these genetic models indicate that diminished insulin/IGF-l signaling may play a central role in the determination of mammalian lifespan by conferring resistance to exogenous and endogenous stressors. These pleiotropic endocrine pathways control diverse programs of gene expression that appear to orchestrate the development of a biological phenotype that promotes longevity. With the ability to investigate thousands of genes simultaneously, several microarray surveys have identified potential longevity assurance genes and provided information on the mechanism(s) by which the dwarf genotypes (dw/dw) and (df/df), and caloric restriction may lead to longevity. We propose that a comparison of specific changes in gene expression shared between Snell and Ames dwarf mice may provide a deeper understanding of the transcriptional mechanisms of longevity determination. Furthermore, we propose that a comparison of the physiological consequences of the Pit1dw and Prop1df mutations may reveal transcriptional profiles similar to those reported for the C. elegans and Drosophila mutants. In this study we have identified classes of genes whose expression is similarly affected in both Snell and Ames dwarf mice. Our comparative microarray data suggest that specific detoxification enzymes of the P(450) (CYP) family as well as oxidative and steroid metabolism may play a key role in longevity assurance of the Snell and Ames dwarf mouse mutants. We propose that the altered expression of these genes defines a biochemical phenotype which may promote longevity in Snell and Ames dwarf mice.

Cell-, tissue-, sex- and developmental stage-specific expression of mouse flavin-containing monooxygenases (Fmos)

The cell-, tissue-, sex- and developmental stage-specific expression profiles of five members of the flavin-containing monooxygenase (FMO) family, FMO1, 2, 3, 4 and 5, were investigated in 129/SV mice, using isoform-specific antisense RNA probes. In situ hybridization localized FMO1 and 5 mRNAs to the perivenous, and FMO 2, 3 and 4 mRNAs to the periportal, regions of the liver. In kidney, each FMO mRNA is localized to the distal and proximal tubules and collecting ducts; FMO1 mRNA is present also in the glomerulus. In lung, FMO1 and 3 mRNAs are expressed in the terminal bronchiole, and FMO1 mRNA also in the alveoli. FMO1 mRNA is present in neurons of the cerebrum and in the choroid plexus. RNase protection assays showed that the most abundant isoform in newborn liver, lung, kidney and brain, and in adult lung and kidney is FMO1, but in adult liver FMO5 is present in greatest amounts. In liver, lung and kidney, expression of Fmo1, 3 and 5 peaks at 3 or 5 weeks of age, but in the brain, Fmo1 expression is greatest in newborns. In the kidney, FMO5 mRNA abundance is fourfold greater in males than in females, at all stages of development. Our results demonstrate that Fmo1, 2, 3, 4 and 5 exhibit distinct cell-, tissue-, sex- and developmental stage-specific patterns of expression.

Hydroxypropyl-beta-cyclodextrin as delivery system for thyroid hormones, regulating glutathione S-transferase expression in rat hepatocyte co-cultures

Thyroid hormones play a role in the regulation of glutathione S-transferase (GST) expression. Here, co-cultures of rat hepatocytes with bile duct epithelial cells have been used to study the direct effects of both triiodothyronine (T3) and thyroxine (T4) on GST activities and proteins. Because T3 and T4 are poorly water soluble and organic solvents used to dissolve them often interfere with biotransformation pathways, an alternative delivery system namely hydroxypropyl-beta-cyclodextrin (HPBC) has been applied. Appropriate control cultures contained either 0.02 or 0.10% (w/v) HPBC, the concentrations necessary to supply T3 and T4 (10(-9) to 10(-5) M) to the cells, respectively. No effect of the vehicle HPBC on the different GST isoenzyme activities and proteins could be observed. On the contrary, after 10 days of co-culture, T3 and T4 decreased GST protein concentrations as well as GST activities measured by 1-chloro-2,4-dinitrobenzene (broad spectrum), 1,2-dichloro-4-nitrobenzene (Mu class M1/M2-specific) and 7-chloro-4-nitrobenzo-2-oxa-1,3-diazole (Alpha class A1/2-specific) in a concentration-dependent manner. The Alpha class subunits A1/2 and A3, and the Mu class subunit M2 were mostly affected. No effect was observed on the Pi class enzyme. These findings indicate that a combination of co-cultured hepatocytes with an HPBC-based delivery system for hydrophobic compounds represents a powerful in vitro tool in drug development.