Inhibition of bovine adrenocortical mitochondrial cytochrome P-450(11)beta-mediated reactions by imidazole derivatives and mineralocorticoid analogs

Antifungal therapy with azoles and the syndrome of acquired mineralocorticoid excess

The syndromes of mineralocorticoid excess describe a heterogeneous group of clinical manifestations leading to endocrine hypertension, typically either through direct activation of mineralocorticoid receptors or indirectly by impaired pre-receptor enzymatic regulation or through disturbed renal sodium homeostasis. The phenotypes of these disorders can be caused by inherited gene variants and somatic mutations or may be acquired upon exposures to exogenous substances. Regarding the latter, the symptoms of an acquired mineralocorticoid excess have been reported during treatment with azole antifungal drugs. The current review describes the occurrence of mineralocorticoid excess particularly during the therapy with posaconazole and itraconazole, addresses the underlying mechanisms as well as inter- and intra-individual differences, and proposes a therapeutic drug monitoring strategy for these two azole antifungals. Moreover, other therapeutically used azole antifungals and ongoing efforts to avoid adverse mineralocorticoid effects of azole compounds are shortly discussed.

Effect of Angiotensin II and ACTH on Adrenal Blood Flow in the Male Rat Adrenal Gland In Vivo

Angiotensin II (Ang II) and adrenocorticotropic hormone (ACTH) regulate adrenal vascular tone in vitro through endothelial and zona glomerulosa cell-derived mediators. The role of these mediators in regulating adrenal blood flow (ABF) and mean arterial pressure (MAP) was examined in anesthetized rats. Ang II (0.01 to 100 ng/kg) increased ABF [maximal increase of 97.2 ± 6.9 perfusion units (PUs) at 100 ng/kg] and MAP (basal, 115 ± 7 mm Hg; Ang II, 163 ± 5 mm Hg). ACTH (0.1 to 1000 ng/kg) also increased ABF (maximum increase of 91.4 ± 10.7 PU) without changing MAP. ABF increase by Ang II was partially inhibited by the nitric oxide (NO) synthase inhibitor N-nitro-l-arginine methyl ester (L-NAME) (maximum increase of 72.9 ± 4.2 PU), the cytochrome P450 inhibitor miconazole (maximum increase of 39.1 ± 6.8 PU) and the epoxyeicosatrienoic acid (EET) antagonist 14,15-epoxyeicosa-5(Z)-enoic acid (14,15-EEZE) (maximum increase of 56.0 ± 13.7 PU) alone, whereas combined administration of miconazole and L-NAME (maximum increase of 16.40 ± 8.98 PU) ablated it. These treatments had no effect on MAP. Indomethacin did not affect the increase in ABF or MAP induced by Ang II. The ABF increase by ACTH was partially ablated by miconazole and 14,15-EEZE but not by L-NAME. Steroidogenic stimuli such as Ang II and ACTH increase ABF to promote oxygen and cholesterol delivery for steroidogenesis and aldosterone transport to its target tissues. The increases in ABF induced by Ang II are mediated by release of NO and EETs, whereas ABF increases with ACTH are mediated by EETs only.

A review of etomidate for rapid sequence intubation in the emergency department

Currently, there is no one drug that is the agent of choice for induction in rapid sequence intubation in the emergency department (ED). All agents currently used as induction agents in the ED offer distinct advantages for various clinical conditions, but each has a significant side effect profile and specific contraindications that limit its use in many common clinical settings. A review of the data available from the anesthesia literature suggests that etomidate possesses many properties that may make it the agent of choice for rapid sequence intubations in the ED. These advantages include excellent pharmacodynamics, protection from myocardial and cerebral ischemia, minimal histamine release, and a hemodynamic profile that is uniquely stable. Disadvantages include a lack of blunting of sympathetic response to intubation, a high incidence of myoclonus, prominent nausea and vomiting, potential activation of seizures in patients with epileptogenic foci, and impaired glucocorticoid response to stress. Further studies are needed to evaluate the advantages and disadvantages of the use of etomidate for rapid sequence intubation in the ED.

Direct inhibitions of the activities of steroidogenic cytochrome P-450 mono-oxygenase systems by anticonvulsants

The effects of anticonvulsants on the activities of cytochromes P-450(17alpha,lyase) (CYP17), P-450arom (CYP19), P-450C21 (CYP21), P-450SCC (CYP11A1), and P-450(11beta) (CYP11B1) mono-oxygenase systems were studied using rat testicular microsomes, human placental microsomes, bovine adrenocortical microsomes, bovine adrenocortical mitochondria and purified cytochrome P-450(11beta). Phenytoin, clonazepam and carbamazepine inhibited the steroidogenesis catalysed by these cytochrome P-450 mono-oxygenase systems and the Ki values for each anticonvulsant were determined. Neither hydantoin nor sodium valproate inhibited the activities of steroidogenic cytochromes P-450. When the activities of cytochromes P-450arom and P-450C21 were measured in the presence of anticonvulsants, the Ki values (0.15 mM) for phenytoin were close to the plasma concentration of phenytoin under therapeutic conditions. Phenytoin, clonazepam and carbamazepine directly inhibited the monooxygenase activities of cytochromes P-450, because they did not affect the activities of NADPH-cytochrome P-450 reductase, NADPH-adrenoferredoxin reductase and adrenoferredoxin.

Inhibition of bovine cytochrome P-450(11 beta) by 18-unsaturated progesterone derivatives

The last step of aldosterone biosynthesis, an 11 beta-hydroxylation followed by two 18-hydroxylations, are catalyzed, in the bovine system, by the same enzyme, the cytochrome P-450(11 beta) (deoxycorticosterone (DOC)-->corticosterone-->18-hydroxycorticosterone-->aldosterone). The 11 beta- and 18-hydroxylase activities were studied separately with a reconstituted enzymic system, using 11-deoxy[14C]corticosterone and [3H]corticosterone, respectively, as substrates. The inhibition of 11 beta-hydroxylase activity by corticosterone was competitive (Ki = 60 microM) showing that transformation of both substrates occurs at the same site. Double-label/double-substrate experiments, using an equimolar mixture of 11-deoxy[14C]corticosterone and [3H]corticosterone, suggested that 18-hydroxycorticosterone is directly formed from 11-deoxycorticosterone without the intermediate corticosterone leaving the enzyme. Inhibitions by 18-vinylprogesterone and 18-ethynylprogesterone, potent inhibitors of aldosterone biosynthesis [Viger, A., Coustal, S., Pérard, S., Piffeteau, A. & Marquet, A. (1989) J. Steroid Biochem. 33, 119-124], were characterized for both activities (11 beta- and 18-hydroxylase). The value of reversible Ki for the 18-hydroxylation (Ki = 5 microM for 18-vinylprogesterone and 30 microM for 18-ethynylprogesterone) is lower than that for the 11 beta-hydroxylation (30 microM and 100-150 microM, respectively); the former inhibitor is stronger than the latter for both steps. The binding of substrates and inhibitors to the active site was also examined by difference absorption spectroscopy. 18-Vinylprogesterone gave rise to a type I spectrum with a Ks value of 35 microM close to that of progesterone, while 18-ethynylprogesterone showed a reverse type I spectrum with a much higher Ks value (140 microM). Based on these results, a hypothetical model, involving a conformational change of the enzyme for the second step, is proposed.

Experimental and/or genetically controlled alterations of the renal microsomal cytochrome P450 epoxygenase induce hypertension in rats fed a high salt diet

Excess dietary salt induces a cytochrome P450 arachidonic acid epoxygenase isoform in rat kidneys (Capdevila, J. H., S. Wei, J. Yang, A. Karara, H. R. Jacobson, J. R. Falck, F. P. Guengerich, and R. N. Dubois. 1992. J. Biol. Chem. 267:21720-21726). Treatment of rats on a high salt diet with the epoxygenase inhibitor, clotrimazole, produces significant increases in mean arterial blood pressure (122 +/- 2 and 145 +/- 4 mmHg for salt and salt- and clotrimazole-treated rats, respectively). The salt- and clotrimazole-dependent hypertension is accompanied by reductions in the urinary excretion of epoxygenase metabolites and by a selective inhibition of the renal microsomal epoxygenase reaction. The prohypertensive effects of clotrimazole are readily reversed when either the salt or clotrimazole treatment is discontinued. The indication that a salt-inducible renal epoxygenase protects against hypertension, are supported by studies with the Dahl rat model of genetic salt-sensitive hypertension. Dahl resistant animals responded to excess dietary salt by inducing the activity of their kidney microsomal epoxygenase(s) (0.102 +/- 0.01 and 0.240 +/- 0.04 nmol of products formed/min per mg of microsomal protein for control and salt-treated rats, respectively). Despite severe hypertension during excess dietary salt intake (200 +/- 20 mmHg), Dahl salt-sensitive rats demonstrated no increase in renal epoxygenase activity. These studies indicate that acquired or inherited abnormalities in renal epoxygenase activities and/or regulation can be related to salt-sensitive hypertension in rodents. Studies on the human renal epoxygenase and its relationship to salt hypertension may prove useful.

Different inhibitory effect of etomidate and ketoconazole on the human adrenal steroid biosynthesis

The narcotic agent etomidate and the antimycotic drug ketoconazole are known to block steroid biosynthesis in man. To study the different effects of these imidazole derivatives on human adrenal steroid biosynthesis we incubated slices of human adrenal glands with 3H-labeled precursors and increasing concentrations of etomidate or ketoconazole (0-2000 microM). After extraction the labeled metabolites were separated by thin-layer chromatography and quantified by scintillation counting. Etomidate inhibited most potently 11 beta-hydroxylase activity by suppressing the formation of corticosterone from 11-deoxycorticosterone to 1% of control [50% inhibitory concentration (IC50) 0.03 microM] while ketoconazole suppressed 11 beta-hydroxylase to only 39% of control activity (IC50 15 microM). Ketoconazole however, most potently blocked the conversion of 17 alpha-hydroxy-progesterone to androstenedione by C17,20-desmolase to about 15% of control activity (IC50 1 microM) while etomidate showed a much weaker effect on this enzyme with a suppression to 50% of C17,20-desmolase control activity at a concentration of 380 microM. Both imidazole drugs showed a similar strong inhibitory effect on the activity of 17 alpha-hydroxylase (IC50 6-18 microM) and 16 alpha-hydroxylase (IC50 4-8 microM) and did not affect 21-hydroxylase. These in vitro data indicate a predominant inhibitory effect of etomidate on corticosteroid biosynthesis by relative selective inhibition of 11 beta-hydroxylase and of ketoconazole on the adrenal androgen biosynthesis by a predominant inhibition of C17,20-desmolase. This differential inhibitory effect of etomidate and ketoconazole on human steroid biosynthesis may be of clinical importance for a possible therapeutic use of these imidazole derivatives in endocrine disorders.

Photoaffinity labeling of cytochrome P-45011 beta with methyltrienolone as a probe for the substrate binding region

Methyltrienolone, a synthetic steroid, was used as a photoaffinity ligand for steroid-binding proteins. The enzymatic activity of bovine adrenocortical cytochrome P-450(11) beta was inhibited by methyltrienolone in a competitive manner without exposure to light and cytochrome P-450(11) beta was photolabeled with methyltrienolone after irradiation with UV light. The addition of 11-deoxycorticosterone during photolabeling protected cytochrome P-450(11) beta from photolabeling. Photolabeled cytochrome P-450(11) beta was digested with TPCK-treated trypsin and the peptide fragments were separated with a reverse-phase HPLC system. The labeled peptide was analyzed and its amino acid sequence was determined to be Trp428-Leu429-Asp430-Arg431. Alignment of the primary structure of cytochrome P-450(11) beta with that of cytochrome P-450cam revealed that the identified sequence corresponds to the region between the beta 3-sheet and L-helix of cytochrome P-450cam. This region of mammalian cytochromes P-450 shows poor homology with that of cytochrome P-450cam, but is well-conserved, especially at Trp-428 and preceding amino acids, as the aromatic region. The present results demonstrate that the labeled sequence contributes in part to the formation of the substrate binding pocket of cytochrome P-450(11) beta which was not expected from the results of the primary sequence alignment with cytochrome P-450cam.

Steroid 11ß-hydroxylation by a fungal microsomal cytochrome P450

The steroid 11ß-hydroxylase activity of the fungus Cochliobolus lunatus was increased about 100-fold by cultivation of mycelia for 4-5 h with 20-hydroxymethyl-1,4-pregnadien-3-one. Cell-free extracts revealed a maximum activity of 45 nmol 11ß-hydroxyprogesterone/h·mg protein in the 100,000 g pellet fraction. The 11ß-hydroxylation was dependent on NADPH. The formation of 11ß-hydroxyprogesterone correlated linearly with the cytochrome P450 concentration. The fungal 11ß-hydroxylase transformed both 21-methyl and 21-hydroxymethyl steroids. The enzyme showed a broader substrate specificity and lower regioselectivity as compared with the adrenal cytochrome P45011ß system. The fungal cytochrome P450 was partially purified to a specific content of 700 pmol P450/mg protein. Western blots showed that polyclonal antibodies against cytochrome P45011α from Rhizopus nigricans cross-react with a 60 kD protein of partially purified fractions. The NADPH-cytochrome c reductase was enriched up to a specific activity of 20 U/mg protein. Polyclonal antibodies against NADPH-cytochrome P450 reductases from Candida maltosa and rat liver cross-reacted with the fungal reductase. It is concluded that the 11ß-hydroxylase of Cochliobolus lunatus represents a microsomal two-component monooxygenase system which is composed of a cytochrome P450 (M(r) 60 kD) and a NADPH-cytochrome P450 reductase (M(r) 79 kD).

Inhibition mechanism of reconstituted cytochrome P-450scc-linked monooxygenase system by antimycotic reagents and other inhibitors

The effects of various antimycotic reagents and some other reagents on a cytochrome P-450-linked monooxygenase system were investigated with respect to the activities of NADPH-ferricyanide reductase. NADPH-cytochrome c reductase of NADPH-adreno-ferredoxin reductase from NADPH to cytochrome c via adreno-ferredoxin, NADPH-cytochrome P-450-phenylisocyanide complex reductase, and the cholesterol side chain cleavage of the cytochrome P-450scc-linked monooxygenase system. No reagents inhibited the NADPH-ferricyanide reductase activity. Only cloconazole inhibited about 50% of NADPH-cytochrome c reductase activity. Cloconazole, econazole, clotrimazole, etomidate and ketoconazole inhibited both NADPH-cytochrome P-450-phenylisocyanide complex reductase and the side chain cleavage activity of cholesterol of the cytochrome P-450scc-linked monooxygenase system. Cloconazole, econazole, etomidate and ketoconazole behaved like non-competitive inhibitors for NADPH-cytochrome P-450-phenylisocyanide reductase activities and their Ki values were 10(-4)-10(-6) M. Cloconazole was a non-competitive inhibitor of NADPH-cytochrome c reductase and its Ki value was 8.3 x 10(-4) M. Cloconazole, clotrimazole, econazole, etomidate, ketoconazole and mitotane completely inhibited the side chain cleavage activity of cholesterol.