Nathan J Cherrington

PMID: 12695343;Abstract:

Messenger RNA levels of rat organic anion transporter 1 (Oat1; Slc22a6) and Oat2 (Slc22a7) in kidney and Oat3 (Slc22a8) in liver are gender-predominant. Oat1 and Oat3 are male-predominant, whereas Oat2 is female-predominant. Gonadectomized and hypophysectomized (HX) rats were studied to determine whether sex steroids and/or growth hormone (GH) are responsible for these gender-divergent patterns. GH was administered to HX rats by two daily injections (simulating male secretion) or continuous infusion (simulating female secretion). Oat1 mRNA levels, normally higher in male than female kidney, were lowered by gonadectomy and HX in male rats, but not in females. Additionally, GH injections or infusion did not alter Oat1 levels in HX rats. Oat2 mRNA levels, typically much higher in female than in male kidney, were unaffected by gonadectomy. However, HX dramatically decreased Oat2 in female kidney without altering male levels. GH administered by continuous infusion increased Oat2 in kidneys of both HX male and female rats, whereas injections had no affect. Gonadectomy reduced Oat3 mRNA levels in male livers without affecting levels in female livers. In contrast, HX decreased male and elevated female Oat3 mRNA. GH injections did not significantly change Oat3 mRNA levels in HX rats, but infusion decreased Oat3 mRNA in liver. In conclusion, androgens, but not GH, are responsible for the Oat1 mRNA gender difference in kidney; the female GH secretion pattern is responsible for the Oat2 mRNA gender difference in kidney; and both androgens and the female GH secretion pattern are responsible for the Oat3 mRNA gender difference in liver.

Garlic oil (GO) contains several linear sulfur compounds, including diallyl sulfide (DAS), diallyl disulfide (DADS), and diallyl trisulfide (DATS), that induce drug-metabolizing enzymes such as CYP2B and NAD(P)H quinone oxidoreductase 1 (NQO1). CYP2B and NQO1 are primarily regulated by constitutive androstane receptor (CAR) and nuclear factor E2-related factor 2 (Nrf2) transcription factors, respectively. The purpose of this study was to determine whether GO and its specific constituents induce these two enzymes via CAR and Nrf2 activation. Female Wistar-Kyoto (WKY) rats express little CAR protein and exhibit less induction of CYP2B1/2 than males. GO, DAS, and DADS, but not DATS, induced CYP2B1/2 mRNA levels to a greater extent in WKY males than in females, suggesting CAR activation. Conversely, DAS induced NQO1 levels equally in WKY males and females, indicating CAR-independent induction in rats. DAS, but not GO, DADS, or DATS, induced CYP2B10 mRNA levels 530-fold in wild-type (WT) mice, whereas this induction was attenuated in CAR(-/-) mice. DAS induced NQO1 in WT and CAR(-/-) mice equally, suggesting CAR-independent induction in mice. DAS induced NQO1 5-fold in WT mice, whereas induction was completely absent in Nrf2(-/-) mice, indicating DAS also activates Nrf2. DAS induction of CYP2B10 mRNA was independent of Nrf2 presence or absence. In in vivo transcription assays, DAS activated the human CYP2B6 promoter, and the antioxidant response element of the human NQO1 promoter, respectively. These studies indicate that GO constituents, particularly DAS, activate CAR and Nrf2 to induce drug-metabolizing enzymes.

PMID: 14570762;Abstract:

We previously demonstrated that multidrug resistance protein 3 (Mrp3/ABCC3) is induced in rat liver by phenobarbital (PB) and several other microsomal enzyme inducers that induce cytochrome P450 2B (CYP2B). CYP2B is induced by constitutive androstane receptor (CAR)-retinoid X receptor (RXR) heterodimer binding to a phenobarbital-responsive promoter element in the CYP2B promoter. Hepatic mRNA levels of CYP2B and Mrp3 were measured in three models of altered CAR activity to determine whether CAR is also involved in the induction of Mrp3. In Wistar Kyoto rats, where males express higher CAR protein levels than females, the induction of CYP2B1/2 was significantly higher in males than in females by PB, diallyl sulfide, and trans-stilbene oxide but not oltipraz. Mrp3 was induced by each of these treatments, but in contrast to CYP2B1/2, to a similar magnitude in males and females. In male hepatocyte-specific RXRα^-/- mice, CYP2B10 was not induced by diallyl sulfide or oltipraz but remained inducible by PB and trans-stilbene oxide after considering the decrease in basal CYP2B10 expression. Mrp3, however, was induced by PB, diallyl sulfide, trans-stilbene oxide and oltipraz in both wild-type and RXRα^-/- mice. Additionally, constitutive expression of Mrp3 was significantly reduced in RXRα^-/- mice. In CAR^-/- mice, the robust induction of CYP2B10 by PB was completely absent. However, Mrp3 was equally induced both in wild-type and CAR ^-/- mice by PB. These data clearly demonstrate that induction of hepatic Mrp3 by PB and other microsomal enzyme inducers is CAR-independent and implies a role for RXRα in the constitutive expression of Mrp3.