Screening for drug-induced alterations in the production and release of steroid hormones by porcine adrenocortical cells in vitro

High risk of adrenal toxicity of N1-desoxy quinoxaline 1,4-dioxide derivatives and the protection of oligomeric proanthocyanidins (OPC) in the inhibition of the expression of aldosterone synthetase in H295R cells

Quinoxaline 1,4-dioxide derivatives (QdNOs) with a wide range of biological activities are used in animal husbandry worldwide. It was found that QdNOs significantly inhibited the gene expression of CYP11B1 and CYP11B2, the key aldosterone synthases, and thus reduced aldosterone levels. However, whether the metabolites of QdNOs have potential adrenal toxicity and the role of oxidative stress in the adrenal toxicity of QdNOs remains unclear. The relatively new QdNOs, cyadox (CYA), mequindox (MEQ), quinocetone (QCT) and their metabolites, were selected for elucidation of their toxic mechanisms in H295R cells. Interestingly, the results showed that the main toxic metabolites of QCT, MEQ, and CYA were their N1-desoxy metabolites, which were more harmful than other metabolites and evoked dose and time-dependent cell damage on adrenal cells and inhibited aldosterone production. Gene and protein expression of CYP11B1 and CYP11B2 and mRNA expression of transcription factors, such as NURR1, NGFIB, CREB, SF-1, and ATF-1, were down regulated by N1-desoxy QdNOs. The natural inhibitors of oxidant stress, oligomeric proanthocyanidins (OPC), could upregulate the expression of diverse transcription factors, including CYP11B1 and CYP11B2, and elevated aldosterone levels to reduce adrenal toxicity. This study demonstrated for the first time that N1-desoxy QdNOs have the potential to be the major toxic metabolites in adrenal toxicity, which may shed new light on the adrenal toxicity of these fascinating compounds and help to provide a basic foundation for the formulation of safety controls for animal products and the design of new QdNOs with less harmful effects.

Combined Use of Etomidate and Dexmedetomidine Produces an Additive Effect in Inhibiting the Secretion of Human Adrenocortical Hormones

Background

The direct effects of etomidate were investigated on the secretion of cortisol and its precursors by dispersed cells from the adrenal cortex of human of animals. Dexmedetomidine (DEX) is an anesthetic agent that may interfere with cortisol secretion via an unknown mechanism, such as involving inhibition of 11β-hydroxylase and the cholesterol side-chain cleavage enzyme system. The aim of this study was to determine whether dexmedetomidine (DEX) has a similar inhibitory effect on adrenocortical function, and whether combined use of etomidate (ETO) and DEX could produce a synergistic action in inhibiting the secretion of human adrenocortical hormones.

Material/Methods

Human adrenocortical cells were exposed to different concentrations of ETO and DEX. The dose-effect model between the ETO concentration and the mean secretion of cortisone (CORT) and aldosterone (ALDO) per hour was estimated.

Results

Hill’s equation well-described the dose-effect correlation between the ETO concentration and the amount of ALDO and CORT secretion. When the DEX concentration was introduced into the model by using E₀ (basal secretion) as the covariate, the goodness of fit of the ETO-CORT dose-effect model was improved significantly and the objective function value was reduced by 4.55 points (P<0.05). The parameters of the final ETO-ALDO pharmacodynamics model were EC₅₀=9.74, E_max=1.20, E₀=1.33, and γ=18.5; the parameters of the final ETO-CORT pharmacodynamics model were EC₅₀=9.49, E_max=8.16, E₀=8.57, and γ=37.0. In the presence of DEX, E₀ was 8.57–0.0247×(CDEX–4.6), and the other parameters remained unchanged. All parameters but γ were natural logarithm conversion values.

Conclusions

Combined use of DEX and ETO reduced ETO’s inhibitory E₀ (basal secretion) of CORT from human adrenocortical cells in a dose-dependent manner, suggesting that combined use of ETO and DEX produced an additive effect in inhibiting the secretion of human adrenocortical hormones.

Acute and subchronic toxicological evaluation of Mequindox in Wistar rats

We studied an acute and subchronic oral toxicity of Mequindox (MEQ), a quinoxaline 1,4-dioxide antimicrobial promoter, in Wistar rats according to OECD guidelines. For acute toxicity study, single doses of MEQ at 175, 550 and 2000 mg/kg b.w. were administered to rats by oral gavage. The calculated LD(50) was 550 mg/kg b.w. In subchronic study, rats were fed diets containing 0, 55, 110 or 275 mg MEQ/kg. There was a reduction in body weight of rats fed 275 mg MEQ/kg diet. At 90 days autopsy, a significant decrease in the kidney weight was observed in males while an increase in relative liver and adrenal weights were observed in females fed 275 mg MEQ/kg diet. There was a significant increased in alanineaminotransferase (ALT) and malondialdehyde (MDA) concentrations in males, superoxide dismutase (SOD) activities in females, and aspartateaminotransferase (AST) levels in serum of both genders fed 275 mg MEQ/kg diet. Other toxic effects of 275 mg MEQ/kg diet included significant decrease in sodium and significant increase in potassium concentrations in serum in both genders. We may conclude that MEQ can induce hepatic and adrenal histological changes as well as leaking of different serum constituents in Wistar rats.

Pharmacological adrenalectomy with mitotane

The potential of mitotane (ortho, para'-DDD, commonly used to treat adrenal carcinomas in humans and dogs) was investigated as an alternative to surgical adrenalectomy in birds, salamanders, and lizards. House sparrows (Passer domesticus) were injected twice daily with vehicle or one of two doses of mitotane (225 or 450 mg/kg), and basal and stress-induced levels of corticosterone (CORT) were measured 3 and 5 days after injections. Mitotane reduced basal CORT levels to nondetectable and abolished stress-induced CORT increases by the 3rd day of treatment. In another study, a single injection of mitotane was effective in lowering endogenous CORT levels 36 h later, but levels had apparently recovered by 10 days after the injection. Mitotane did not effect testicular weights and had no detectable effect on testosterone levels. In contrast to its effects on house sparrows, mitotane did not lower endogenous CORT levels in either tiger salamanders (Ambystoma tigrinum) or tree lizards (Urosaurus ornatus), even at doses much higher than those used in house sparrows.

Feed Additives: Do They Add to Animal Welfare? An Evaluation

The welfare of farm animals is strongly influenced by the man-made environment. Welfare problems also arise from reduced homeostatic capacities in animals. Feed additives, used to promote growth or to prevent diseases can alter the animals' self-regulating capacities thus affecting their welfare. The EU regulates the use of these additives within specified groups of Directive 70/524/EEC. Although these feed additives can be regarded as prescription-free veterinary drugs, critical remarks on their desired and adverse effects have received little attention.

A survey of the available literature shows that about one-third of licensed feed additives alter adrenal function in vitro. Reports of the adverse effects of anticoccidial additives in vivo suggest they can be classified under three headings: (i) substances with a very narrow safety margin (the difference between the permitted dose and the dose with adverse effects) and often irreversible effects on growth and feed conversion; (ii) substances with a narrow safety margin and largely reversible effects; (iii) substances with an adequate safety margin. The growth promoters (including antibiotic growth promoters) can - on the basis of their adverse effects - be classified into two groups: (i) substances with a very narrow safety margin; and (ii) substances with an adequate safety margin.

On the one hand, animal welfare considerations require use of disease-preventing additives, but on the other hand, they also demand discontinuation of current practices. Judicious use of additives can add to animal welfare. However, their unlimited use to obscure defects in husbandry is detrimental to animal welfare. A major obstacle to the judicious use of feed additives, is the lack of published, unbiased information on their efficacy and safety for farm animals.

Effects of atipamezole, detomidine and medetomidine on release of steroid hormones by porcine adrenocortical cells in vitro

The 4-substituted imidazole type alpha2-adrenoceptor ligands atipamezole, detomidine, and medetomidine were screened for actions on the release of aldosterone by a suspension of porcine adrenocortical cells with deoxycorticosterone (1 microM) as substrate. Progesterone, pregnenolone or corticosterone (all at 1 microM) were also used as substrates. With pregnenolone as substrate, drug-induced effects on the output of nine steroids (aldosterone, corticosterone, cortisol, deoxycortisol, testosterone, progesterone, 17alpha-hydroxyprogesterone, androstenedione, dehydroepiandrosterone) were monitored simultaneously. The alpha2-adrenoceptor antagonist atipamezole was a potent inhibitor of aldosterone release (range 10-1000 nM). The sedative alpha2-adrenoceptor agonists medetomidine and detomidine also inhibited aldosterone release (range 10-1000 nM). With pregnenolone as substrate, the inhibition induced by 4-substituted imidazoles of the release of corticosterone and cortisol was more pronounced than that of aldosterone. Androstenedione and deoxycortisol release was enhanced. The 4-substituted imidazoles atipamezole, detomidine, and medetomidine inhibited mitochondrial cytochrome P450(11beta/18) in vitro. This inhibition was unrelated to their alpha2-adrenoceptor actions. The 4-substituted imidazole type alpha2-adrenoceptor ligands used to control sedation/anaesthesia can alter the steroid-based defence mechanisms of the body.

Differential effects of nitrofurans on the production/release of steroid hormones by porcine adrenocortical cells in vitro

Changes in the biogenesis of corticosteroids caused by nitrofurans were studied. The three nitrofurans used: furazolidone, furaltadone and nitrofurantoin, altered the steroid production/release by porcine adrenocortical cells in vitro during 1 h incubations. With pregnenolone as a substrate the nitrofurans inhibited aldosterone production/release. Although the nitrofurans differed in potency (nitrofurantoin > furazolidone > furaltadone) maximum inhibition occurred at 100 microM. In this concentration the nitrofurans changed also the release/production of other corticosteroids. The output of corticosterone and cortisol decreased by 50%. The production/release of deoxycortisol stayed the same. In contrast the output of progesterone and 17alpha-hydroxyprogesterone increased to more than 200% of control. The nitrofurans slightly reduced the output of androstenedione. No significant increases of the production/release of other steroids (testosterone, dehydroepiandrosterone, estradiol-17beta and estrone) by the cell suspension could be observed. The profile of the nitrofuran-induced changes lead to the conclusion that nitrofurans interfere with mitochondrial enzymes. These enzymes, presumably cytochrome P450(11,18) mediate the hydroxylation and the oxidation at C11 and C18, the final steps in the biogenesis of aldosterone, corticosterone and cortisol. The rapid and reversible fall in the output of these steroids occurs in vitro at concentrations which are below therapeutic blood concentrations seen in vivo. At higher concentrations the nitrofurans hinder the biogenesis of androgens. Thus nitrofurans can also affect steps in the steroid biogenesis located in the endoplasmatic reticulum.