Tissue-specific and developmental stage-dependent expression of a novel rat Dopa/tyrosine sulfotransferase

Spinal interneurons of the lower urinary tract circuits

The storage and elimination of urine requires coordinated activity between muscles of the bladder and the urethra. This coordination is orchestrated by a complex system containing spinal, midbrain and forebrain networks. Normally there is a reciprocity between patterns of activity in urinary bladder sacral parasympathetic efferents and somatic motoneurons innervating the striatal external urethral sphincter muscle. At the spinal level this reciprocity is mediated by ensembles of excitatory and inhibitory interneurons located in the lumbar-sacral segments. In this review I will present an overview of currently identified spinal interneurons and circuits relevant to the lower urinary tract and will discuss their established or hypothetical roles in the cycle of micturition. In addition, a recently discovered auxiliary spinal neuronal ensemble named lumbar spinal coordinating center will be described. Sexual dimorphism and developmental features of the lower urinary tract which may play a significant role in designing treatments for patients with urine storage and voiding dysfunctions are also considered. Spinal cord injuries seriously damage or even eliminate the ability to urinate. Treatment of this abnormality requires detailed knowledge of supporting neural mechanisms, therefore various experiments in normal and spinalized animals will be discussed. Finally, a possible intraspinal mechanism will be proposed for organization of external urethral sphincter (EUS) bursting which represents a form of intermittent EUS relaxation in rats and mice.

Establishment of metabolism and transport pathways in the rodent and human fetal liver

The ultimate fate of drugs and chemicals in the body is largely regulated by hepatic uptake, metabolism, and excretion. The liver acquires the functional ability to metabolize and transport chemicals during the perinatal period of development. Research using livers from fetal and juvenile rodents and humans has begun to reveal the timing, key enzymes and transporters, and regulatory factors that are responsible for the establishment of hepatic phase I and II metabolism as well as transport. The majority of this research has been limited to relative mRNA and protein quantification. However, the recent utilization of novel technology, such as RNA-Sequencing, and the improved availability and refinement of functional activity assays, has begun to provide more definitive information regarding the extent of hepatic drug disposition in the developing fetus. The goals of this review are to provide an overview of the early regulation of the major phase I and II enzymes and transporters in rodent and human livers and to highlight potential mechanisms that control the ontogeny of chemical metabolism and excretion pathways.

Tissue Distribution and Ontogeny of Sulfotransferase Enzymes in Mice

Sulfotransferases (Sults) are phase-II conjugation enzymes that catalyze the transfer of a sulfonate group from 3'-phosphoadenosine 5'-phosphosulfate (PAPS) to target endo and xenobiotics. PAPS is formed from inorganic sulfate by the action of the enzyme PAPS synthase (PAPSs). In the present study, the tissue distribution and developmental changes in the mRNA expression of 11 Sult isozymes and 2 PAPSs isoforms in mice were quantified. Sult1a1, 1b1, 1c1, 1c2, 1d1, 1e1, 2a1/2, 2b1, 3a1, 4a1, 5a1, PAPSs1, and PAPSs2 mRNA expression was quantified in 14 tissues from male and female mice using the branched DNA signal amplification assay. Sult2a1/2 and 3a1 expression were highest in liver; Sult1b1, 2b1, and PAPSs2 in small intestine; Sult1a1 in large intestine; Sult1c2 in stomach; Sult1d1 in kidney; Sult1e1 in placenta; and Sult4a1 in brain. Sult1c1, 5a1, and PAPSs1 were ubiquitously expressed in most tissues. These enzymes demonstrated three different ontogenic expression patterns in liver. Sult1a1, 1c2, 1d1, 2a1/2, and PAPSs2 hepatic expression gradually increased from birth until about 3 weeks of age and then declined somewhat thereafter, Sult1c1 expression was highest before birth and declined after that, and Sult3a1 mRNA expression was very low in fetal livers and remained low until 30 days of age, when expression in females dramatically increased, whereas it never increased in males. The organ-specific distribution of Sults as well as the different expression of the Sults in young animals may affect the pharmacokinetic behavior and organ-specific toxicity of xenobiotics.

Characterization of rat iodothyronine sulfotransferases

Sulfation appears to be an important pathway for the reversible inactivation of thyroid hormone during fetal development. The rat is an often used animal model to study the regulation of fetal thyroid hormone status. The present study was done to determine which sulfotransferases (SULTs) are important for iodothyronine sulfation in the rat, using radioactive T4, T3, rT3, and 3,3'-T2 as substrates, 3'-phosphoadenosine-5'-phosphosulfate (PAPS) as cofactor, and rat liver, kidney and brain cytosol, and recombinant rat SULT1A1, -1B1, -1C1, -1E1, -2A1, -2A2, and -2A3 as enzymes. Recombinant rat SULT1A1, -1E1, -2A1, -2A2, and -2A3 failed to catalyze iodothyronine sulfation. For all tissue SULTs and for rSULT1B1 and rSULT1C1, 3,3'-T2 was by far the preferred substrate. Apparent Km values for 3,3'-T2 amounted to 1.9 microM in male liver, 4.4 microM in female liver, 0.76 microM in male kidney, 0.23 microM in male brain, 7.7 microM for SULT1B1, and 0.62 microM for SULT1C1, whereas apparent Km values for PAPS showed less variation (2.0-6.9 microM). Sulfation of 3,3'-T2 was inhibited dose dependently by other iodothyronines, with similar structure-activity relationships for most enzymes except for the SULT activity in rat brain. The apparent Km values of 3,3'-T2 in liver cytosol were between those determined for SULT1B1 and -1C1, supporting the importance of these enzymes for the sulfation of iodothyronines in rat liver, with a greater contribution of SULT1C1 in male than in female rat liver. The results further suggest that rSULT1C1 also contributes to iodothyronine sulfation in rat kidney, whereas other, yet-unidentified forms appear more important for the sulfation of thyroid hormone in rat brain.

Molecular cloning, expression, and characterization of a canine sulfotransferase that is a human ST1B2 ortholog

Sulfation is an important conjugation pathway in deactivating thyroid hormones, keeping the proper hormonal balance, and increasing the rate of thyroid hormone metabolism. We have identified, cloned, and characterized a sulfotransferase (SULT) that is capable of thyroid hormone conjugation in the dog. This enzyme, designated cSULT1B1, displays a strong identity (>84%) to the human ST1B2 enzyme. However, cSULT1B1 displays less identity, about 73%, to mouse and rat orthologs. In addition, the canine enzyme is three amino acids shorter than the rodent ones but has the same length as the human ortholog, 296 amino acids. The bacterial expressed and partial purified cSULT1B1 enzyme sulfates p-nitrophenol and 1-naphtol, but not dopamine. The thyroid hormones 3,3'-diiodothyronine and 3,5,3'-triiodothyronine are efficiently sulfated. 3,3',5'-Triiodothyronine is sulfated to lesser degree while sulfation of 3,5'-diiodothyronine and 3,3',5,5'-tetraiodothyronine cannot be detected. The cSULT1B1 is found in the colon (highest level), kidney and small intestine in dogs, but surprisingly not in the male dog liver although low levels of immunoreactivity were detected in the female dog liver. The male dog expresses more of SULT1B1 enzyme in the lower part of the small intestine while the female dog displays an opposite pattern of expression. These results describe the cloning and characterization of a canine thyroid hormone sulfating enzyme that is more closely related to the human ortholog than to the rodent thyroid sulfating enzymes.

Induction of rat hepatic aryl sulfotransferase (SULT1A1) gene expression by triamcinolone acetonide: impact on minoxidil-mediated hypotension

The hypotensive agent minoxidil (6-imino-1, 2-dihydro-1-hydroxy-2-imino-4-piperidinopyrimidine) depends upon aryl sulfotransferase (SULT1)-catalyzed sulfation for its bioactivation. Previous reports suggest that glucocorticoids induce class-specific SULT1 and isoform-specific SULT1A1 gene expression in rat liver. In the present study, rats were treated with the glucocorticoid triamcinolone acetonide (TA, 5 mg/kg/day i.p. x 3 days) or its vehicle, 2% Tween-20, prior to minoxidil, and subsequent effects on mean arterial pressure (MAP), heart rate (HR), and hepatic SULT1 gene expression were characterized. Minoxidil treatment (1.5 mg/kg) resulted in a steady decline in MAP values of 16.3 to 18.6% relative to basal control levels at 35 to 60 min following minoxidil injection. Pentachlorophenol (PCP, 40 micromol/kg i.p.), an inhibitor of SULT1 enzyme activity, effectively ablated the hypotensive effects of minoxidil. By contrast, pretreatment with TA significantly enhanced minoxidil-induced hypotension. Relative to vehicle-treated controls, TA-treated rats displayed a steeper rate of decline in MAP and more profound levels of hypotension with decreases in MAP following minoxidil administration of 27.8%. TA also produced significant increases in hepatic SULT1 mRNA expression (of 271%) and SULT1A1 immunoreactive protein levels (of 273%), relative to vehicle-treated controls. These results provide physiological evidence to support the biological relevance of SULT1A1 induction by glucocorticoids. The data indicate that steroid treatment induces SULT1A1 gene expression and, as a consequence, accentuates the hypotensive effects of minoxidil.

In vitro inhibition of thyroid hormone sulfation by hydroxylated metabolites of halogenated aromatic hydrocarbons

Earlier studies in our laboratory showed that hydroxylated metabolites of polychlorinated biphenyls (PCBs), dibenzo-p-dioxins (PCDDs), and dibenzofurans (PCDFs) competitively inhibit thyroxine (T4) binding to transthyretin (TTR) and type I deiodinase (D1) activity. In this study, we investigated the possible inhibitory effects of hydroxylated metabolites of polyhalogenated aromatic hydrocarbons (PHAHs) on iodothyronine sulfotransferase activity. Rat liver cytosol was used as a source of sulfotransferase enzyme in an in vitro assay with 125I-labeled 3,3'-diiodothyronine (T2) as a model substrate. Increasing amounts of hydroxylated PCBs, PCDDs, or PCDFs or extracts from incubation mixtures of PHAHs and induced liver microsomes were added as potential inhibitors of T2 sulfotransferase activity. Hydroxylated metabolites of PCBs, PCDDs, and PCDFs were found to be potent inhibitors of T2 sulfotransferase activity in vitro with IC50 values in the low micromolar range (0.2-3.8 microM). The most potent inhibitor of T2 sulfotransferase activity in our experiments was the PCB metabolite 3-hydroxy-2,3',4, 4',5-pentachlorobiphenyl with an IC50 value of 0.2 microM. A hydroxyl group in the para or meta position appeared to be an important structural requirement for T2 sulfotransferase inhibition by PCB metabolites. Ortho hydroxy PCBs were much less potent, and none of the parent PHAHs was capable of inhibiting T2 sulfotransferase activity. In addition, the formation of T2 sulfotransferase-inhibiting metabolites of individual brominated diphenyl ethers and nitrofen as well as from some commercial PHAH mixtures (e.g., Bromkal, Clophen A50, and Aroclor 1254) was also demonstrated. These results indicate that hydroxylated PHAHs are potent inhibitors of thyroid hormone sulfation. Since thyroid hormone sulfation may play an important role in regulating free hormone levels in the fetus, and PCB metabolites are known to accumulate in fetal tissues after maternal exposure to PCBs, these observations may have implications for fetal thyroid hormone homeostasis and development.