Difference in metabolic profile of potassium canrenoate and spironolactone in the rat: mutagenic metabolites unique to potassium canrenoate

Genotoxic and mutagenic studies of teratogens in developing rat and mouse

In this review, genotoxic and mutagenic effects of teratogenic chemical agents in both rat and mouse have been reviewed. Of these chemicals, 97 are drugs and 33 are pesticides or belong to other groups. Large literature searches were conducted to determine the effects of chemicals on chromosome abnormalities, sister chromatid exchanges, and micronucleus formation in experimental animals such as rats and mice. In addition, studies that include unscheduled DNA synthesis, DNA adduct formations, and gene mutations, which help to determine the genotoxicity or mutagenicity of chemicals, have been reviewed. It has been estimated that 46.87% of teratogenic drugs and 48.48% of teratogenic pesticides are positive in all tests. So, all of the teratogens involved in this group have genotoxic and mutagenic effects. On the other hand, 36.45% of the drugs and 21.21% of the pesticides have been found to give negative results in at least one test, with the majority of the tests giving positive results. However, only 4.16% of the drugs and 18.18% of the pesticides were determined to give negative results in the majority of the tests. Among tests with major negative results, 12.50% of the teratogenic drugs and 12.12% of the teratogenic pesticides were negative in all conducted tests.

30 YEARS OF THE MINERALOCORTICOID RECEPTOR: Mineralocorticoid receptor antagonists: 60 years of research and development

The cDNA of the mineralocorticoid receptor (MR) was cloned 30 years ago, in 1987. At that time, spirolactone, the first generation of synthetic steroid-based MR antagonists (MRAs), which was identified in preclinical in vivo models, had already been in clinical use for 30 years. Subsequent decades of research and development by Searle & Co., Ciba-Geigy, Roussel Uclaf and Schering AG toward identifying a second generation of much more specific steroidal MRAs were all based on the initial 17-spirolactone construct. The salient example is eplerenone, first described in 1987, coincidentally with the cloning of MR cDNA. Its launch on the market in 2003 paralleled intensive drug discovery programs for a new generation of non-steroidal MRAs. Now, 30 years after the cDNA cloning of MR and 60 years of clinical use of steroidal MRAs, novel non-steroidal MRAs such as apararenone, esaxerenone and finerenone are in late-stage clinical trials in patients with heart failure, chronic kidney disease (CKD), hypertension and liver disease. Finerenone has already been studied in over 2000 patients with heart failure plus chronic kidney disease and/or diabetes, and in patients with diabetic kidney disease, in five phase II clinical trials. Here, we reflect on the history of the various generations of MRAs and review characteristics of the most important steroidal and non-steroidal MRAs.

Clinically insignificant negative interferences of spironolactone, potassium canrenoate, and their common metabolite canrenone in new dimension vista LOCI digoxin immunoassay

Spironolactone, a potassium-sparing diuretic metabolized to canrenone is often used with digoxin to treat various conditions including congestive heart failure. Potassium canrenoate is a similar drug, which is also metabolized to canrenone. Due to reported both positive and negative interference of spironolactone, potassium canrenoate, and their common metabolite canrenone with digoxin immunoassays, we investigated potential interference of these compounds with the new homogenous sequential chemiluminescent assay for digoxin based on the luminescent oxygen channeling technology (LOCI digoxin) for application on the Dimension and Vista platform. When aliquots of a drug-free serum pool were supplemented with various amounts of spironolactone, potassium canrenoate, or canrenone and apparent digoxin values were measured using Dimension Vista LOCI digoxin assay, we observed no detected value except when aliquots were supplemented with very high amounts of potassium canrenoate or canrenone. However, we observed that apparent digoxin concentrations were very low. When aliquots of a serum digoxin pool (prepared by pooling specimens from patients receiving digoxin), were further supplemented with various amounts of spironolactone, potassium canrenoate, or canrenone and serum digoxin concentrations were remeasured using the LOCIdigoxin assay, only statistically significant falsely lower digoxin values (negative interference) were observed in specimens containing very high amounts of canrenone or potassium canrenoate. However, such small bias may not have any clinical significance. We conclude that new Dimension Vista LOCI digoxin assay is virtually free from interferences of spironolactone, potassium canrenoate, and their common metabolite canrenone.

Effect of the steroid K-canrenoate on hsp70 expression and tissue damage in transgenic Drosophila melanogaster (hsp70-lacZ) Bg9

In the present study the effect of 0.1, 0.2, 0.4, 0.8, and 1.0 µL/mL of the steroid K-canrenoate was evaluated in the third instar larvae of transgenic Drosophila melanogaster (hsp70-lacZ) Bg(9) for 6, 24, and 48 hours of duration. The treatment of 0.1, 0.2, and 0.4 µL/mL of K-canrenoate did not induce the activity of hsp70 significantly compared to the control. The treatments of 0.8 and 1.0 µL/mL of K-canrenoate not only caused tissue damage but also induced a significant increase in the expression of hsp70 for the different durations of exposure. The results of the present study suggest that the K-canrenoate at 0.8 and 1.0 µL/mL is cytotoxic and caused tissue damage in the third instar larvae of transgenic D. melanogaster (hsp70-lacZ) Bg(9).

Abbott ARCHITECT clinical chemistry and immunoassay systems: digoxin assays are free of interferences from spironolactone, potassium canrenoate, and their common metabolite canrenone

Spironolactone, which is metabolized to canrenone, is often used in combination with digoxin. Potassium canrenoate is a similar drug that is also metabolized to canrenone. As a result of reported interference of spironolactone, potassium canrenoate, and their common metabolite canrenone with digoxin immunoassays, we investigated potential interference of these compounds with two relatively new digoxin assays for application on ARCHITECT clinical chemistry platforms (cDig, particle-enhanced turbidimetric inhibition immunoassay) and ARCHITECT immunoassay platforms (iDig, chemiluminescent microparticle immunoassay), both from Abbott Diagnostics. When aliquots of drug-free serum pool were supplemented with various amounts of spironolactone, potassium canrenoate, and canrenone, no apparent digoxin concentration was observed using cDig assay on ARCHITECT c4000, c8000, and c16000 or iDig assay on i1000SR and i2000SR analyzers. In addition, we observed no false increase in serum digoxin value when aliquots of a digoxin pool were further supplemented with various amounts of spironolactone, potassium canrenoate, or canrenone. We conclude that both the cDig and iDig assays on the ARCHITECT analyzers are free from interferences by spironolactone, potassium canrenoate, and canrenone.

A core in vitro genotoxicity battery comprising the Ames test plus the in vitro micronucleus test is sufficient to detect rodent carcinogens and in vivo genotoxins

In vitro genotoxicity testing needs to include tests in both bacterial and mammalian cells, and be able to detect gene mutations, chromosomal damage and aneuploidy. This may be achieved by a combination of the Ames test (detects gene mutations) and the in vitro micronucleus test (MNvit), since the latter detects both chromosomal aberrations and aneuploidy. In this paper we therefore present an analysis of an existing database of rodent carcinogens and a new database of in vivo genotoxins in terms of the in vitro genotoxicity tests needed to detect their in vivo activity. Published in vitro data from at least one test system (most were from the Ames test) were available for 557 carcinogens and 405 in vivo genotoxins. Because there are fewer publications on the MNvit than for other mammalian cell tests, and because the concordance between the MNvit and the in vitro chromosomal aberration (CAvit) test is so high for clastogenic activity, positive results in the CAvit test were taken as indicative of a positive result in the MNvit where there were no, or only inadequate data for the latter. Also, because Hprt and Tk loci both detect gene-mutation activity, a positive Hprt test was taken as indicative of a mouse-lymphoma Tk assay (MLA)-positive, where there were no data for the latter. Almost all of the 962 rodent carcinogens and in vivo genotoxins were detected by an in vitro battery comprising Ames+MNvit. An additional 11 carcinogens and six in vivo genotoxins would apparently be detected by the MLA, but many of these had not been tested in the MNvit or CAvit tests. Only four chemicals emerge as potentially being more readily detected in MLA than in Ames+MNvit--benzyl acetate, toluene, morphine and thiabendazole--and none of these are convincing cases to argue for the inclusion of the MLA in addition to Ames+MNvit. Thus, there is no convincing evidence that any genotoxic rodent carcinogens or in vivo genotoxins would remain undetected in an in vitro test battery consisting of Ames+MNvit.

Effect of spironolactone, potassium canrenoate, and their common metabolite canrenone on Dimension Vista Digoxin Assay

Spironolactone, a potassium sparing diuretic metabolized to canrenone, is often used with digoxin to treat various conditions including congestive heart failure. Potassium canrenoate is a similar drug that is also metabolized to canrenone. Due to reported interference of spironolactone, potassium canrenoate, and their common metabolite canrenone with digoxin immunoassays, we investigated potential interference of these compounds with Dimension Vista Digoxin immunoassay using Flex reagent cartridge. Aliquots of a drug-free serum pool were supplemented with various amounts of spironolactone, potassium canrenoate, or canrenone and apparent digoxin values were measured using Dimension Vista digoxin assay, we observed none-detected value except when aliquots were supplemented with higher amounts of spironolactone or canrenone. Similarly, when aliquots of a serum digoxin pool (prepared by pooling specimens from patients receiving digoxin) where further supplemented with various amounts of spironolactone, potassium canrenoate, or canrenone, we observed moderately falsely elevated digoxin values only in specimens containing higher amounts of spironolactone or canrenone. We conclude that spironolactone and canrenone but not potassium canrenoate may cause modest interference with Dimension Vista digoxin assay but such interferences may not be clinically significant except with very high amounts of canrenone.

A new enzyme-linked chemiluminescent immunosorbent digoxin assay is virtually free from interference of spironolactone, potassium canrenoate, and their common metabolite canrenone

Spironolactone and potassium canrenoate (aldosterone antagonist diuretics) are sometimes used in conjunction with digoxin for patient management. Spironolactone, potassium canrenoate, and their common metabolite canrenone interfere with serum digoxin measurement using various immunoassays. Recently a new enzyme-linked chemiluminescent immunosorbent digoxin assay (ECLIA-Digoxin) became commercially available for application on the ADVIA IMS 800i modular system (Bayer HealthCare, Tarrytown, NY). We investigated the potential interference of spironolactone and related compounds in this assay by comparing the results with the fluorescence polarization immunoassay (FPIA), which is known to have significant cross-reactivity with these compounds as well as a turbidimetric assay for digoxin with no known cross-reactivity with spironolactone and related compounds. Aliquots of drug free serum were supplemented with therapeutic and above therapeutic concentrations of spironolactone, canrenone, and potassium canrenoate, and apparent digoxin concentrations were measured. No apparent digoxin concentration was observed using the ECLIA-Digoxin or turbidimetric assay. When serum pools prepared from patients receiving digoxin were further supplemented with these compounds, we observed no significant change in digoxin concentrations in the presence of these compounds with the ECLIA-Digoxin. We conclude that this assay is virtually free from interferences from spironolactone, potassium canrenoate and their common metabolite canrenone.

Potassium Canrenoate, an Aldosterone Receptor Antagonist, Reduces Isoprenaline-Induced Cardiac Fibrosis in the Rat

The purpose of the present study was to determine whether the administration of an antagonist of aldosterone could prevent the fibrosis induced by an acute injection of isoprenaline. Male Wistar rats were submitted to one subcutaneous injection of isoprenaline (400 mg/kg) and were simultaneously treated with potassium canrenoate in drinking water (20 mg/kg/day) started 5 days before the injection of isoprenaline. Two months later, echocardiographic and hemodynamic measurements were performed. Then, the heart was prepared for morphometric histology and quantification of fibrosis in the left ventricle. Heart and left ventricular weights were increased significantly by isoprenaline. Potassium canrenoate attenuated this increase. The administration of isoprenaline increased significantly end diastolic diameter and end systolic volume compared with control. These changes were increased further with the addition of potassium canrenoate. In contrast, the fibrosis induced by isoprenaline was reduced significantly by potassium canrenoate at the three section levels. Potassium canrenoate attenuated the fibrosis but not the enhanced dilatation of the left ventricle induced by isoprenaline.

A new turbidometric digoxin immunoassay on the ADVIA 1650 analyzer is free from interference by spironolactone, potassium canrenoate, and their common metabolite canrenone

Spironolactone and potassium canrenoate (aldosterone antagonist diuretics) are often used with digoxin in clinical practice. It has been well documented in the literature that spironolactone, potassium canrenoate, and their common metabolite canrenone cross-react with the fluorescence polarization immunoassay (FPIA) for digoxin and falsely elevate measured serum digoxin concentrations. Recently a new turbidometric assay for digoxin became commercially available from Bayer Diagnostic for application on the ADVIA 1650 Chemistry analyzer. We studied the potential interference of these compounds in this new digoxin assay. Aliquots of drug-free serum were supplemented with therapeutic and above-therapeutic concentrations of spironolactone, canrenone, and potassium canrenoate, and apparent digoxin concentrations were measured. We observed apparent digoxin concentrations with the FPIA digoxin assay as expected but observed no apparent digoxin levels with the new turbidometric immunoassay. When serum pools prepared from patients receiving digoxin were supplemented with these compounds in concentrations expected in serum in patients receiving these medications, we observed falsely elevated digoxin levels with the FPIA digoxin assay, but no statistically significant change was observed with the new turbidometric assay. We conclude that the new turbidometric assay for digoxin is free from interference by spironolactone, potassium canrenoate, and their common metabolite canrenone.

Are some progestins genotoxic liver carcinogens?

Progestins (progestogens) are classified by the International Agency for Research on Cancer (IARC) as possibly carcinogenic to humans. In the last decade evidence has shown that a synthetic drug of this family, cyproterone acetate, is activated to a reactive species by the liver, and forms DNA adducts and elicits DNA repair in hepatocytes from both rats and humans. The response is similar in humans of both genders but markedly higher in female than in male rats. The promutagenic character of DNA lesions is indicated by the increase in liver of female rats of the frequency of micronucleated cells, of mutations, and of enzyme-altered preneoplastic foci. Two other synthetic progestins, chlormadinone acetate and megestrol acetate, and an aldosterone antagonist, potassium canrenoate, share with cyproterone acetate the 17-hydroxy-3-oxopregna-4,6-diene structure. While less extensively studied, results so far obtained indicate that they are capable of inducing genotoxic effects qualitatively similar to those of cyproterone acetate. The majority of progestins have not been systematically tested for genotoxicity and the generally negative responses obtained with the standard battery of genotoxicity tests might be the consequence of the use of inappropriate target cells and/or metabolic activation systems. Cyproterone acetate, is activated by the hepatocytes to reactive species of such short half-life that they react only with the DNA of the cell in which are formed. Therefore, it cannot be excluded a priori that other progestins will not display genotoxic effects when tested adequately. This hypothesis is supported by the knowledge that estrogen-progestin combinations used as oral contraceptives are classified by the IARC as carcinogenic to humans due to the increased risk of hepatocellular carcinoma. This risk should probably be ascribed to the progestin component, since estrogens are carcinogenic to humans due to the increased risk of endometrial and possibly of breast cancer but not liver cancer.

Digoxin Assays: Frequent, Substantial, and Potentially Dangerous Interference by Spironolactone, Canrenone, and Other Steroids

Background: A case of digoxin toxicity resulted from falsely low values with the MEIA II assay for digoxin (AxSYM®; Abbott). The low results were caused by negative interference from canrenone and spironolactone, the latter of which has recently been advocated for the treatment of severe heart failure. Analytical interference from spironolactone has been reported, but little information is available for this effect with newer digoxin assays.

Methods: We examined nine assays (AxSYM, IMx®, TDx®, Emit®, Dimension®, aca®, TinaQuant®, Elecsys®, and Vitros®) for interference by spironolactone, canrenone, and three metabolites. Additionally, all routine digoxin measurements (AxSYM) over a period of 16.5 months (n = 3089) were monitored for interference.

Results: Suppression of the expected values by canrenone (3125 μg/L) was observed for the AxSYM (42% of expected value), IMx (51%), and Dimension (78%) assays. A positive bias was observed for the aca (0.7 μg/L), the TDx (0.62 μg/L), and the Elecsys (>0.58 μg/L). Twenty-five of 669 routinely monitored patients had falsely low results. Nineteen of these had potentially toxic concentrations of digoxin (Emit; >2.0 μg/L), although the AxSYM assay indicated therapeutic or less severe toxic concentrations (Δmax = 7.1 μg/L). Except for two unresolved cases, this was attributable to spironolactone, canrenone, hydrocortisone, or prednisolone. Standard doses of spironolactone (up to 50 mg/day) in patients with heart failure displayed inhibition <11%.

Conclusions: The frequency and magnitude of the false-negative results particularly compromise the use of both microparticle enzyme immunoassays. Not only may toxic concentrations remain unidentified, but intoxication could occur should dosage be increased because of falsely low results. With 11 million digoxin tests/year ordered in the US, conceivably many patients could be adversely affected.

DNA damage in tissues of rat treated with potassium canrenoate

Potassium canrenoate (PC), a competitive aldosterone antagonist previously found to increase tumor incidence in rats and to produce genotoxic effects in in vitro systems, was examined in rats to acquire information on its genotoxic activity in vivo. Intragastric administration of 1/2 LD50 produced, as revealed by the Comet assay, a modest but statistically significant increase in the frequency of DNA lesions in liver but not in thyroid and bone marrow of male rats, and in thyroid and bone marrow but not in liver of female rats. In contrast with the frankly positive responses observed in primary cultures of rat hepatocytes (Martelli et al., Mutagenesis 14 (1999) 463-472) any evidence of DNA repair and micronuclei formation was absent in liver of rats treated with 1/2 LD50, and initiation of enzyme-altered liver preneoplastic lesions did not occur in the liver of rats given 100 mg/kg PC once a week for 6 successive weeks. A high and dose-dependent frequency of DNA lesions was found to occur in testes and ovaries of rats given single doses ranging from 1/8 to 1/2 LD50.

Stereoselectivity in S- and N-oxygenation by the mammalian flavin-containing and cytochrome P-450 monooxygenases

In general, the use of stereoselectivity studies in examining the contribution of monooxygenases or other catalysts to the N- and S-oxidation of drugs, xenobiotics and endogenous substrates provides a useful method to distinguish enzymatic from nonenzymatic processes. Recent developments in this active area of research have been rapid, presumably due to advances in bioanalytical chemistry, chiral stationary-phase HPLC, and attendant breakthroughs in the instruments to measure centers of chirality. This research area has also been aided by the availability of enzymes and other catalysts. In light of the ever-increasing necessity for new single-isomer drugs, metabolites, and other chiral drug market materials, the demand for stereoselectivity information in the drug development business should continue to expand. In the future, demand for enantiomeric intermediates and metabolites to be studied in their own right for pharmacological activity will undoubtedly increase. Finally, technologies related to the creation or characterization of enantiomerically pure drugs or their metabolites presumably will grow because of the increased number of compounds entering the drug development pipeline due to combinatorial chemistry.

Small doses of canrenone block the effects of ouabain on the mechanical activity of the heart and vessels of the rat

Canrenone has been described as an antihypertensive drug that blocks endogenous ouabain effects in volume-dependent hypertensive models. Considering that some canrenone metabolites may be putative mutagenic factors, therapeutic dose reduction might be advantageous if the blockade of ouabain effects is maintained. In this study, the effects of low doses or concentrations of canrenone were investigated in rats by using isolated papillary muscles, Langendorff-perfused hearts, perfused rat-tail vascular bed, and anesthetized animals. Canrenone (0.5, 1, 2, and 5 mg/ml) produced a dose-dependent negative inotropic effect in papillary muscles contracting isometrically and blocked the positive inotropic effect produced by 660 microM ouabain. In Langendorff-perfused hearts beating spontaneously, a low concentration of canrenone (10 microg/ml) increased the isovolumic systolic pressure obtained at several diastolic pressures. Higher concentrations of canrenone (20, 30 microg/ml) brought the isovolumic pressure toward control values, and 100 microg/ml canrenone produced an isovolumic pressure reduction. In these preparations, 20 microg/ml canrenone reduced significantly the positive inotropic effects of 100 microM ouabain. Investigating the vascular smooth muscle reactivity to phenylephrine (PE; 0.5, 1, and 2 microg bolus injections) in the perfused rat-tail vascular bed, it was observed that canrenone blocked completely the enhancement of PE pressor effect produced by 1-h treatment with 100 microM ouabain. Similar results were obtained with the arterial blood pressure reactivity to PE in anesthetized rats. In these animals, canrenone (1 mg/kg) blocked the sensitizing effect of 18 microg/kg ouabain on PE reactivity. In conclusion, results presented here suggest that canrenone may block ouabain effects at very low concentrations. It blocked myocardial positive inotropic effects of ouabain on both papillary muscle and perfused hearts, and the sensitization of PE pressor effects. The results also suggest that canrenone at very small doses might be used to reduce arterial blood pressure in hypertensive conditions accompanied by increased ouabain plasma levels as the main therapeutic procedure or as an adjunct treatment to prevent ouabain sensitizing effects on pressor responses.

Water-soluble beta-cyclodextrins in paediatric oral solutions of spironolactone: preclinical evaluation of spironolactone bioavailability from solutions of beta-cyclodextrin derivatives in rats

Water-soluble derivatives of beta-cyclodextrin have been considered for solubilization of spironolactone in the formulation of a safe liquid preparation for premature infants. The oral absorption of spironolactone was studied in rats to evaluate the need to adjust spironolactone dosage in prospective clinical studies. Spironolactone was administered in solutions of sulphobutyl ether beta-cyclodextrin (SBE7) or dimethyl-beta-cyclodextrin (DM-beta-CyD) and also as spironolactone-containing powder papers (reference preparation). Spironolactone in SBE7 solution was administered intravenously to assess the extent of intestinal absorption from the different formulations. Spironolactone and the metabolites 7alpha-thiospirolactone, 7alpha-thiomethylspirolactone and canrenone were determined in rat serum after intravenous administration of spironolactone. Half-lives for spironolactone, 7alpha-thiomethylspirolactone and canrenone were 0.72 +/- 0.17, 1.5 +/- 0.3 and 2.2 +/- 0.3 h, respectively. Although, according to Cmax values, 7alpha-thiomethylspirolactone was the major serum metabolite in rats, higher AUC (area under the serum concentration-time curve) values were obtained for canrenone. After oral administration of spironolactone the bioavailabilities evaluated from the AUC values of 7alpha-thiomethylspirolactone were 27.5 +/- 9.3%, 81.3 +/- 28.8% and 82.8 +/- 28.6% for powder papers, DM-beta-CyD and SBE7 solutions, respectively. The oral absorption of spironolactone by rats was better after administration of spironolactone in SBE7 and DM-beta-CyD solutions than after administration as powder papers. Both cyclodextrin formulations enhanced spironolactone bioavailability to a similar extent despite some deacetylation of spironolactone in the presence of SBE7. A reduction of spironolactone dosage would be recommended during clinical studies with premature infants. These results indicate that SBE7 could be a safe and suitable excipient for the solubilization of spironolactone in paediatric formulations.

Improved bioavailability from a spironolactone beta-cyclodextrin complex

The relative bioavailabilty of spironolactone from a complex with beta-cyclodextrin has been evaluated. Capsules containing 100 mg micronised spironolactone powder were compared with 100 mg spironolactone beta-cyclodextrin complex in 8 healthy volunteers by a single dose, double blind, crossover pharmacokinetic study. Subjects were randomly allocated to each preparation and crossed over after 2 weeks. Relative bioavailability was assessed by the measurement of serum canrenone concentrations. The mean relative bioavailability of the spironolactone cyclodextrin complex, compared to the micronised spironolactone powder, was 233%. Statistical analysis (Wilcoxon signed rank test) revealed that this difference was significant with a mean area under the serum concentration time curve of 3.90 and 1.88 mg.h.l-1 for the complex and micronised spironolactone powder, respectively. Four of the volunteer also received a 100 mg spironolactone tablet (Aldactone) under identical conditions. Pharmacokinetic analysis revealed that the mean relative bioavailability of the spironolactone beta cyclodextrin complex and micronised powder when compared with spironolactone tablets (Aldactone) was 252% and 124%, respectively. There was no change in the canrenone elimination half lives of each subject.