Hepatic Cytochrome P450 Activity and Nitric Oxide Production During Multiple Ovalbumin Challenges.

BACKGROUND AND OBJECTIVES: Mast cell-mediated allergic diseases are a significant global health problem. Nitric oxide (NO) produced by acute type 1 allergies greatly suppresses hepatic cytochrome P450 (CYP) metabolism. A recent in vitro study demonstrated that repeated FcεRI-mediated activation intrinsically modulates mast cell function. We investigated the effect of ovalbumin (OVA) challenges on CYP activity and NO production under real immune responses. METHODS: After repeated sensitization with OVA once a week, serum nitrate plus nitrite (NOx) and total plasma immunoglobulin E concentrations were measured using commercially available kits. Hepatic microsomal CYP-specific activities and protein expression were determined using typical substrates and by western blot, respectively. In the liver, the levels of inducible NO synthase (iNOS), F4/80, and c-kit mRNA were determined by real-time polymerase chain reaction. Hepatic total NOS activity was measured using a colorimetric assay kit. RESULTS: When mice received multiple OVA challenges, the 11th sensitization elevated NOx concentrations in serum and suppressed the activities of five major CYPs without altering protein expression levels. After the 7th, 11th, and 15th sensitizations, F4/80-positive Kupffer cell and hepatic c-kit-dependent mast cell mRNA levels were similar to those of the control. The 7th and 11th sensitizations increased hepatic iNOS mRNA expression to 15-fold and threefold above control levels, respectively, but did not enhance the total NOS activity in the liver. CONCLUSIONS: Multiple OVA challenges, unlike acute sensitization, greatly reduced serum NOx levels. The challenge-suppressed hepatic CYP metabolism was likely related to the increased serum NOx. Serum NOx may be an endogenous marker for CYP metabolism inhibition in type 1 allergic diseases.

Hepatic cytochrome P450 metabolism suppressed by mast cells in type 1 allergic mice.

Mast cells and Kupffer cells secrete interleukin (IL)-1ß, interferon (IFN)-γ, and tumor necrosis factor (TNF)-α, which stimulate excess nitric oxide (NO) producing-inducible NO synthase (iNOS). Unlike Kupffer cells, immunoglobulin E-sensitized mast cells elicit sustained NO production. We investigated the participation of mast cell-released NO and cytokine-derived iNOS activation in type 1 allergy-suppressed hepatic cytochrome P450 (CYP) metabolism. Aminoguanidine, a selective iNOS inhibitor, completely suppressed serum nitrate plus nitrite (NOx) concentrations after primary and secondary sensitization of ICR mice and markedly attenuated allergy-suppressed hepatic CYP1A2, CYP2C, CYP2E1, and CYP3A activities. In the liver, primary and secondary sensitization enhanced iNOS-stimulating IFN-γ (5-15-fold) and TNF-α (3-5-fold) mRNA levels more than IL-1ß (2-fold) and F4/80-positive Kupffer cell (2-fold) mRNA levels. When mast cell-deficient (-/-) mice were sensitized, hepatic CYP activities were not suppressed. Serum NOx levels in the sensitized -/- mice were similar with those in saline-treated ICR and -/- mice. In the liver of -/- mice, secondary sensitization markedly enhanced mRNA expression of iNOS (20-fold), IFN-γ (15-fold), and TNF-α (3-fold). However, hepatic total NOS activities in -/- mice were not significantly different between saline treatment and sensitization. Similarly, primary and secondary ICR mice did not significantly enhance total NOS activities in the liver and hepatocytes. The total NOS activities observed did not relate to the high levels of iNOS, IFN-γ, and TNF-α mRNA in the liver. Hepatic c-kit-positive mast cells in sensitized ICR mice were maintained at control levels. Therefore, our data suggest that mast cell-released NO participates in type 1 allergy-suppressed CYP1A2, CYP2C, CYP2E1, and CYP3A metabolism.

Hepatic Flavin-Containing Monooxygenase 3 Enzyme Suppressed by Type 1 Allergy-Produced Nitric Oxide.

Flavin-containing monooxygenases (FMOs) are major mammalian non-cytochrome P450 oxidative enzymes. T helper 2 cell-activated allergic diseases produce excess levels of nitric oxide (NO) that modify the functions of proteins. However, it remains unclear whether allergy-induced NO affects the pharmacokinetics of drugs metabolized by FMOs. This study investigated alterations of hepatic microsomal FMO1 and FMO3 activities in type 1 allergic mice and further examined the interaction of FMO1 and FMO3 with allergy-induced NO. Imipramine (IMP; FMO1 substrate) N-oxidation activity was not altered in allergic mice with high serum NO and immunoglobulin E levels. At 7 days after primary sensitization (PS7) or secondary sensitization (SS7), benzydamine (BDZ; FMO1 and FMO3 substrate) N-oxygenation was significantly decreased to 70% of individual controls. The expression levels of FMO1 and FMO3 proteins were not significantly changed in the sensitized mice. Hepatic inducible NO synthase (iNOS) mRNA level increased 5-fold and 15-fold in PS7 and SS7 mice, respectively, and hepatic tumor necrosis factor-α levels were greatly enhanced. When a selective iNOS inhibitor was injected into allergic mice, serum NO levels and BDZ N-oxygenation activity returned to control levels. NO directly suppressed BDZ N-oxygenation, which was probably related to FMO3-dependent metabolism in comparison with IMP N-oxidation. In hepatic microsomes from PS7 and SS7 mice, the suppression of BDZ N-oxygenation was restored by ascorbate. Therefore, type 1 allergic mice had differentially suppressed FMO3-dependent BDZ N-oxygenation. The suppression of FMO3 metabolism related to reversible S-nitrosyl modifications of iNOS-derived NO. NO is expected to alter FMO3-metabolic capacity-limited drug pharmacokinetics in humans.