Regulation of 3β-hydroxysteroid dehydrogenase and sulphotransferase 2A1 gene expression in primary porcine hepatocytes by selected sex-steroids and plant secondary metabolites from chicory (Cichorium intybus L.) and wormwood (Artemisia sp.)

In pigs the endogenously produced compound androstenone is metabolised in the liver in two steps by 3β-hydroxysteroid dehydrogenase (3β-HSD) and sulphotransferase 2A1 (SULT2A1). The present study investigated the effect of selected sex-steroids (0.01–1 μM androstenone, testosterone and estradiol), skatole (1–100 μM) and secondary plant metabolites (1–100 μM) on the expression of 3β-HSD and SULT2A1 mRNA. Additionally the effect of a global methanolic extract of dried chicory root was investigated and compared to previous obtained in vivo effects. Primary hepatocytes were isolated from the livers of piglets (crossbreed: Landrace × Yorkshire and Duroc) and cultured for 24 h before treatment for an additionally 24 h. RNA was isolated from the hepatocytes and specific gene expression determined by RT-PCR using TaqMan probes. The investigated sex-steroids had no effect on the mRNA expression of 3β-HSD and SULT2A1, while skatole decreased the content of SULT2A1 30% compared to control. Of the investigated secondary plant metabolites artemisinin and scoparone (found in Artemisia sp.) lowered the content of SULT2A1 by 20 and 30% compared to control, respectively. Moreover, we tested three secondary plant metabolites (lactucin, esculetin and esculin) found in chicory root. Lactucin increased the mRNA content of both 3β-HSD and SULT2A1 by 200% compared to control. An extract of chicory root was shown to decrease the expression of both 3β-HSD and SULT2A1. It is concluded that the gene expression of enzymes with importance for androstenone metabolism is regulated by secondary plant metabolites in a complex manner.     

Positive and Negative Allosteric Modulation of an α1β3γ2 γ-Aminobutyric Acid Type A (GABAA) Receptor by Binding to a Site in the Transmembrane Domain at the γ+-β? Interface

In the process of developing safer general anesthetics, isomers of anesthetic ethers and barbiturates have been discovered that act as convulsants and inhibitors of γ-aminobutyric acid type A receptors (GABA_ARs) rather than potentiators. It is unknown whether these convulsants act as negative allosteric modulators by binding to the intersubunit anesthetic-binding sites in the GABA_AR transmembrane domain (Chiara, D. C., Jayakar, S. S., Zhou, X., Zhang, X., Savechenkov, P. Y., Bruzik, K. S., Miller, K. W., and Cohen, J. B. (2013) J. Biol. Chem. 288, 19343–19357) or to known convulsant sites in the ion channel or extracellular domains. Here, we show that S-1-methyl-5-propyl-5-(m-trifluoromethyl-diazirynylphenyl) barbituric acid (S-mTFD-MPPB), a photoreactive analog of the convulsant barbiturate S-MPPB, inhibits α1β3γ2 but potentiates α1β3 GABA_AR responses. In the α1β3γ2 GABA_AR, S-mTFD-MPPB binds in the transmembrane domain with high affinity to the γ⁺-β⁻ subunit interface site with negative energetic coupling to GABA binding in the extracellular domain at the β⁺-α⁻ subunit interfaces. GABA inhibits S-[³H]mTFD-MPPB photolabeling of γ2Ser-280 (γM2–15′) in this site. In contrast, within the same site GABA enhances photolabeling of β3Met-227 in βM1 by an anesthetic barbiturate, R-[³H]methyl-5-allyl-5-(m-trifluoromethyl-diazirynylphenyl)barbituric acid (mTFD-MPAB), which differs from S-mTFD-MPPB in structure only by chirality and two hydrogens (propyl versus allyl). S-mTFD-MPPB and R-mTFD-MPAB are predicted to bind in different orientations at the γ⁺-β⁻ site, based upon the distance in GABA_AR homology models between γ2Ser-280 and β3Met-227. These results provide an explanation for S-mTFD-MPPB inhibition of α1β3γ2 GABA_AR function and provide a first demonstration that an intersubunit-binding site in the GABA_AR transmembrane domain binds negative and positive allosteric modulators.