Involvement of cytochrome P-450IIIA in metabolism of potassium canrenoate to an epoxide: mechanism of inhibition of the epoxide formation by spironolactone and its sulfur-containing metabolite

In vitro metabolism studies of potassium canrenoate (PC) were conducted to examine whether spironolactone (SP) and/or its sulfur-containing metabolites inhibit the PC metabolic pathways to mutagenic metabolites and to elucidate the mechanism for any observed inhibitory effect. The mechanistic study was conducted using liver microsomes prepared from male and female rats with and without pretreatment of a cytochrome (Cyt) P-450IIIA inducer [pregnenolone-16 alpha-carbonitrile (PCN) or dexamethasone (DEX)] and with and without a Cyt P-450IIIA inhibitor, triacetyloleandomycin (TAO). The present study demonstrates that SP and its sulfur-containing metabolite 7 alpha-thio-spirolactone substantially inhibited the formation of promutagen 6 beta, 7 beta-epoxycanrenone (6 beta, 7 beta-epoxy-CAN) from PC. The sulfur-containing metabolite of SP that inhibit promutagen formation were not formed from PC, although a glutathione conjugate of PC was formed. The formation rate of 6 beta, 7 beta-epoxy-CAN was greater in liver microsomes prepared from rats pretreated with a Cyt P-450IIIA inducer (PCN or DEX) than in liver microsomes prepared from the untreated rats. The formation rate of the epoxide metabolite was lower after in vitro addition of TAO. Pretreatment of animals with TAO 4 hr before sacrifice produced similar results. Erythromycin, which is N-demethylated by Cyt P-450IIIA, also reduced the formation rate of 6 beta, 7 beta-epoxy-CAN. Inhibition of PC metabolism to 6 beta, 7 beta-epoxy-CAN by TAO and erythromycin, and its induction by DEX and PCN, suggest involvement of Cyt P-450IIIA, which is in turn inhibited by SP and 7 alpha-thio-spirolactone.

Pharmacokinetics of a novel antiarrhythmic drug, actisomide

The pharmacokinetics of a novel antiarrhythmic drug, actisomide, were examined in the rat, dog, monkey, and human. The terminal half-life of actisomide was similar (1.15-1.89 hr) across species, regardless of dose. The total plasma clearance was higher in the monkey (13.5-16.4 mL/min/kg) than in the dog (9.01-9.32 mL/min/kg), rat (8.6-9.8 mL/min/kg), or human (6.79 +/- 1.07 mL/min/kg). Excretion of the parent drug was higher in urine than in feces in the dog and rat, whereas in the monkey and human, urinary and fecal excretions of actisomide were similar. In humans, atypical plasma concentration-time curves with double peak concentrations were observed following oral doses. Systemic availability of actisomide was higher in the dog than in the rat, monkey, and human. Further, the systemic availability appeared to increase with dose in the rat and monkey. The species-dependent systemic availability appeared to be due primarily to species-dependent absorption of actisomide, and not to species-dependent first-pass metabolism, biliary excretion, and/or renal elimination. The absorption of actisomide in the rat and its in vitro uptake in CaCo-2 cells were pH dependent. The higher systemic availability of actisomide observed in the dog may be due partly to the higher pH in the gastrointestinal (GI) tract of the dog. However, the pH differences in the GI tract of the different species alone did not appear to be enough to explain the difference in systemic availability of actisomide.

Fetal alcohol syndrome and fatty acid ethyl esters

Fetal alcohol syndrome is the leading known cause of mental retardation. The syndrome, defined as growth retardation, midface hypoplasia, and neurologic dysfunction, represents only part of the spectrum of fetal alcohol effects. The biochemical mechanism of teratogenesis is unknown. In adults, metabolites of ethanol, FAEE, are known to accumulate in major organs. The formation of FAEE is catalyzed by a family of enzymes, FAEE synthases. Our hypothesis is that accumulation of FAEE in the embryo results in fetal alcohol syndrome. We have developed assays for FAEE and FAEE synthase activity using mg of tissue. Using these assays, we have shown the following: Human placenta, mouse placenta, heart, and liver are active in catalyzing the formation of FAEE. One h after maternal ethanol administration on gestational d 14, mouse placenta and fetuses accumulated significant quantities of FAEE. The fatty acid incorporated into FAEE was tissue dependent. Tissues from pregnant animals given ethanol on gestational d 7 showed persistence of FAEE on gestational d 14. We conclude that: 1) human and mouse placentas have significant FAEE synthase activity, 2) mouse heart, liver, placenta, and fetal tissues accumulate significant amounts of FAEE after maternal ethanol exposure, 3) there is tissue specificity for the fatty acid incorporated into FAEE, and 4) FAEE may persist for 7 d in placentas. These results provide a basis for further research into the role of FAEE in the development of fetal alcohol syndrome.

Metabolism of actisomide in the dog, monkey and man: a novel rearrangement of N-dealkylated metabolites

The metabolism of actisomide, a novel antiarrhythmic agent, was studied in the dog, monkey and man and was found to be more extensive in the monkey than in the dog or man. The major metabolites identified were a piperidinyl hydroxylated metabolite, the mono-N-dealkylated, cyclized and piperidine hydroxylated metabolite, and the cyclized and mono-N-dealkylated metabolite. Excretion of the parent drug was higher in urine than in feces in the dog, but in the monkey and man, urinary and fecal excretion of actisomide was similar. In all species the metabolites were primarily excreted in feces.

Use of biometry and keratometry for determining optimal power for intraocular lens implants in dogs

Axial length and corneal curvature were determined by use of A-scan ultrasonography and keratometry on both eyes of dogs of various breeds, sizes, and ages. Mean axial length was 20.43 +/- 1.48 mm; axial length was not related to age or sex, but was significantly greater (P = 0.047) in dogs of larger breeds. Mean corneal curvature was 39.94 +/- 2.61 diopters. Dogs of large breeds had significantly (P less than 0.001) flatter corneas. Mild, roughly symmetric astigmatism was detected in a majority of dogs. Use of mean values in a theoretic artificial intraocular lens power equation suggests that aphakic dogs require an implant of approximately 40 diopters to achieve emmetropia.

RPE dysplasia with retinal duplication in a mutant mouse strain

An autosomal dominant mutation was produced by quadruple gonadal exposure of a male (C3H x 101)F1 mouse to 500 rad of X-irradiation. This mutation is maintained by the mating of affected heterozygous males to normal (C3H x C57B1)F1 females. Clinically apparent abnormalities were limited to the eyes and, in the affected adults, ranged from apparent anophthalmia to globes that were enlarged and exhibit large uveoscleral colobomas. Sequential evaluations of the embryogenesis of this condition have identified abnormal differentiation of the outer layer of the optic cup (presumptive retinal pigment epithelium-RPE) into a second layer of neural retina. The abnormality is identified as early as day 10 of gestation, during invagination of the optic cup and lens placode. The area of RPE dysplasia may be diffuse or regional with an abrupt transition from normal RPE and often demonstrates excessive and uncontrolled proliferation. The two symmetrical, apposed layers of photoreceptors fail to differentiate and begin to degenerate prenatally. Absence of normal RPE leads to failure of induction of adjacent choroid and sclera, resulting in a posterior segment consisting of a large neuroepithelial-lined cyst. Radiation-induced ocular malformations of this type have not been previously described. In addition, this model presents a unique opportunity to examine the processes leading to differentiation of a single, continuous epithelial layer into tissues as anatomically and functionally distinct as neural retina and RPE.

Metabolism and pharmacokinetics of nufenoxole in animals and humans: an example of stereospecific hydroxylation of an isoquinuclidine ring

1. Nufenoxole, a novel antidiarrhoeal agent, was well absorbed in rat, monkey and human after oral administration. Systemic availability of nufenoxole was 85% in monkey and 102% in man. 2. The elimination rate was much faster in rat (t1/2 of 1.8 h) and monkey (t1/2 of 4.9 h) compared with human (t1/2 of 35.8 h). 3. After oral and i.v. 14C-nufenoxole, concentrations of 14C in human erythrocytes and saliva were approx. 3- and 4-fold lower, respectively, than plasma concentrations. 4. Nufenoxole was metabolized to metabolites hydroxylated on the methyl substituent and isoquinuclidine ring in rat and monkey. The isoquinuclidine ring hydroxylation, a major pathway in human, was stereospecific. 5. Following oral doses of 14C-nufenoxole the urinary excretion of radioactivity (about 8%) was less than the faecal excretion (66.6%) in rat, while urinary excretion was the major route of drug elimination (about 60%) in man. In monkey, urinary and faecal excretion were equally important.

Laminin and fibronectin in retinoid-induced keratolenticular dysgenesis

Acute embryonic exposure to isotretinoin during gastrulation (gestational day 7) in the mouse results in delay or failure of separation of the lens vesicle from the surface ectoderm. During normal lens vesicle detachment, laminin is localized within the lens, keratolenticular stalk and adjacent surface ectoderm. The mesenchyme surrounding the stalk stains positively for fibronectin. In contrast, isotretinoin-exposed embryos at the same stage of gestation exhibit reduced staining for both extracellular matrix components. Persistent keratolenticular attachment observed later in gestation in the exposed embryos is associated with increased production of laminin by the keratolenticular stalk and anterior lens epithelium. A delay in the sequence of production of extracellular matrix may be causally associated with persistence of the keratolenticular stalk.

Pharmacokinetics of disopyramide in the dog. Importance of mono-N-dealkylated metabolite kinetics in assessing pharmacokinetic modeling of the parent drug

The antiarrhythmic drug disopyramide (DP) is metabolized to the mono-N-dealkylated compound (MND) and to the pyrrolidone derivative (PYR). This study examines the detailed pharmacokinetic characteristics of DP and MND when given simultaneously or separately to dogs. DP and MND were both relatively well absorbed and showed similar pharmacokinetic characteristics. However, the amount of PYR relative to MND as judged by the area under the plasma concentration-time curves (AUC) following oral or iv administration was much greater with DP than with MND. These findings were also supported by the urinary excretion values where the PYR/MND ratio with DP was much greater than with the MND administration. For an explanation of this phenomenon, plasma concentration-time curves for DP, MND, and PYR were simultaneously analyzed assuming various pharmacokinetic models. The plasma levels of these compounds were best described when nonlinear kinetics were assumed for conversion of MND to PYR.

Experimental models of anterior segment dysgenesis

Normal anterior segment embryogenesis is summarized followed by a review of syndromes of spontaneous and inherited conditions of abnormal development in humans and animals. The study of teratogen-induced malformations in animal models has provided valuable information about critical periods during gestation for the initiation of anterior segment dysgenesis. Although the major developmental events leading to iridocorneal angle formation occur during the third trimester, it appears that embryonic insult much earlier in human gestation (during the first three to five weeks post fertilization) can induce an abnormal sequence of events leading to anterior segment dysgenesis.

Teratogens and craniofacial malformations: relationships to cell death

Environmental agents including ethanol, 13-cis retinoic acid (RA, Accutane®), the antimetabolite methotrexate, periods of hypoxia, ionizing radiation or hyperthermic stress, when administered acutely to pregnant experimental animals, induce stage-dependent craniofacial malformations comparable to those in corresponding human teratogen syndromes. Acute treatment regimens have allowed analysis of cell populations initially affected and subsequent dysmorphogenetic sequences as well as speculation relative to mechanisms of teratogenesis. In rodent models, ethanol and RA appear to affect similar cell populations and comparable malformations can be induced by both agents. When administered during gastrulation they cause a major insult to the anterior neural plate which results in characteristic ocular, brain and facial malformations comparable to those seen in the fetal alcohol syndrome. Exposure to these drugs at a time just prior to and during neural crest cell migration into the craniofacial and cervical regions results in malformations comparable to those seen in the Di-George sequence and/or retinoic acid embryopathy. Slightly later, at the time that the epibranchial placodes are active, insult results in mandibulofacial dysostosis-like syndromes. We propose that the pattern of these malformations is related to the particular vulnerability of cells in the vicinity of normal programmed cell death. Cell death is also associated with ionizing radiation and hyperthermia-induced malformations. Both of these teratogens are particularly damaging to the early development of the eye and central nervous system. Teratogenic temperature elevations result in arrest of mitotic activity and death of cells in mitosis. Hypoxia is also associated with cell death in specific regions and subsequent malformation. For example, death of cells in the invaginating olfactory placode has recently been associated with cleft lip formation. The relationship of hypoxiainduced cell death to energy requirements is being explored. Acute treatment with methotrexate results in frontonasal dysplasia (median facial clefts). Combined effects of fluid imbalance, lack of proliferation or death of frontonasal mesenchyme appear to be involved. Although the mechanisms of craniofacial malformation are complex, a common feature for many is excessive cell death for which the embryo may be unable to compensate. Excessive cell death in regions of programmed cell death represents an important, yet little appreciated, mechanism of teratogenesis.

Keratolenticular dysgenesis (Peters' anomaly) as a result of acute embryonic insult during gastrulation

Keratolenticular dysgenesis (Peters' anomaly) was induced in mice by exposure to the human teratogens, ethanol or 13-cis retinoic acid (isotretinoin, Accutane). Acute teratogen exposure on the seventh day of gestation (corresponding to the third week of human gestation) resulted in an eye malformation incidence of 46% to 100% in day 14 fetuses. Of the abnormal eyes, 10% to 29% demonstrated failure of detachment of the lens from the surface ectoderm. Delayed lens detachment was seen as anterior lenticonus in 33% to 35% of the abnormal eyes. Abnormal lens detachment appeared to result in mechanical interference with neural crest migration to form the corneal stroma and endothelium, and iris stroma. This secondary effect on neural crest derivatives is exhibited in the adult animals as corneal opacities associated with defects in Descemet's membrane and endothelium, and anterior polar cataracts.

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

The metabolic fates of potassium canrenoate (PC) and spironolactone (SP) were compared for the rat in vivo and in vitro. Approximately 18% of an in vivo dose of SP was metabolized to canrenone (CAN) and related compounds in the rat. In vitro, 20-30% of SP was dethioacetylated to CAN and its metabolites by rat liver 9000 g supernatant (S9). Thus, the major route of SP metabolism is via pathways that retain the sulfur moiety in the molecule. PC was metabolized by rat hepatic S9 to 6 alpha, 7 alpha- and 6 beta, 7 beta-epoxy-CAN. The beta-epoxide was further metabolized to its 3 alpha- and 3 beta-hydroxy derivatives as well as its glutathione (GSH) conjugate. Both 3 alpha- and 3 beta-hydroxy-6 beta, 7 beta-epoxy-CAN were shown to be direct acting mutagens in the mouse lymphoma assay, whereas 6 alpha, 7 alpha- and 6 beta, 7 beta-epoxy-CAN were not. These mutagenic metabolites, their precursor epoxides and their GSH conjugates were not formed from SP under identical conditions. The above findings appear to be due to inhibition of metabolism of CAN formed from SP by SP and/or its S-containing metabolites, since the in vitro metabolism of PC by rat hepatic microsomes was appreciably reduced in the presence of SP. The hypothesized mechanism(s) for this inhibition is that SP and its S-containing metabolites specifically inhibit an isozyme of hepatic cytochrome P-450 or SP is a preferred substrate over PC/CAN for the metabolizing enzymes. Absence of the CAN epoxide pathway in the metabolism of SP provides a possible explanation for the observed differences in the toxicological profiles of the two compounds.

Fetal alcohol syndrome. Eye malformations in a mouse model

Acute maternal ethanol administration on gestational day 7 (gastrulation stage) in C57Bl/6J mice results in a spectrum of ocular malformations. A deficiency in the anterior neural plate observable within 24 hours of exposure results in corresponding defects in the optic sulcus and subsequent optic vesicle. Deficiency in the size of the lens vesicle induced by a small optic vesicle is demonstrable as microphakia in older embryos. Delayed detachment of the lens vesicle from the surface ectoderm manifests in the live offspring as progressive corneal opacification and vascularization related to defects in corneal endothelium and Descemet's membrane. Anterior segment dysgenesis results in persistent iridocorneal adhesions, dyscoria, and abnormal formation of the anterior chamber. In contrast, ethanol exposure on day 8 of gestation did not result in eye malformations. Thus, it appears that many of the ocular abnormalities associated with fetal alcohol syndrome may result from an acute insult to the optic primordia during a very specific period that corresponds to the third week after fertilization in the human.

Response of the canine corneal endothelium to intraocular irrigation with saline solution, balanced salt solution, and balanced salt solution with glutathione

The right or left anterior chamber of 12 dogs (ie, 24 eyes) was irrigated with 100 ml of 0.9% saline solution, balanced salt solution, or balanced salt solution with glutathione (8 eyes/solution) for 22 minutes. Changes in endothelial cell density and corneal thickness from pretreatment values were evaluated immediately after, and at 2 and 7 days after irrigation. Using specular microscopy and scanning and transmission electron microscopy, corneas were examined immediately after and at 2, 7, and 14 days after irrigation. Changes were not seen in endothelial cell density after irrigation with any of the solutions evaluated. Corneal thickness increased 4% immediately after irrigation with 0.9% saline solution and returned to normal by 1 week after irrigation; treatment with 0.9% saline solution was not associated with visible corneal edema. Ultrastructural changes attributable to differences in irrigating solution composition were not observed. The difference between the endothelium's response to limited irrigation with saline solution, balanced salt solution, and balanced salt solution with glutathione was small and irrigation with these solutions was not associated with permanent endothelial damage.

Clinical and pathologic evaluation of a flexible silicone posterior chamber lens design in a rabbit model

Flexible silicone posterior chamber intraocular lenses made of a proprietary formulation were implanted in rabbits following planned extracapsular lens extraction. The lenses were of three designs: unfenestrated, partially fenestrated, and fully fenestrated haptics. Biostability and tissue reactivity of the silicone lenses and another manufacturer's polymethylmethacrylate lenses appeared equivalent as evaluated clinically by slitlamp biomicroscopy and by light microscopy. The frequency and distribution of lens precipitates were evaluated grossly and by scanning electron microscopy and appeared notably less prominent on the surfaces of the hydrophobic silicone lenses.

Copper exchanges and toxicity in the rabbit lens in vitro

Lenses (in vitro) exposed to 10(-4) M Cu for 24 hr gained an excess of Na and lost K. Incubation for 7 days with 10(-5) M Cu had a similar toxic effect. Threonine, which is present in aqueous humor, increased sensitivity of lenses to Cu, and also uptake of 64Cu. Uptake of 64Cu commenced reaching tissue saturation levels in 5 hr at 10(-7) M Cu. At higher concentrations, uptake was greater (1263 X for a 1000-fold rise in concentration from 10(-7) -10(-4) M) and saturation was not seen in this time. Autoradiography of sections of such lenses suggested that accumulation of the 64Cu occurred principally within the region of the cells of the anterior epithelium and capsule and lens bow. Efflux of accumulated 64Cu occurred more rapidly when copper was present in the external media suggesting the presence of 'specific' binding sites for copper. Percentage retention of accumulated 64Cu was greater in lenses loaded in 10(-6) M than 10(-5) M Cu. It is suggested that copper can enter lenses, possibly facilitated by threonine, and can bind to two types of sites: one with a high affinity but low capacity for the metal ion, the other with a lower affinity but larger capacity. The former may be concerned with the physiological roles and normal metabolism of copper and the latter with its toxic actions.

Experimental hypercupremia does not result in increases in copper in lens, iris, or ocular fluids

Rabbits were continuously administered copper sulfate via subcutaneously implanted osmotic pumps. After one month, plasma, liver, ocular tissues and fluids were analyzed for copper by atomic absorption spectrophotometry. No elevation in copper content of the ocular fluids, lens or iris was noted although, dose-related increases were seen in the plasma and liver indicating that the copper was absorbed and disseminated systemically. It is likely that excess copper, like that which is normally ingested and absorbed, is largely protein-bound in the circulation, preventing crossing of the blood-ocular barrier.

Copper concentration in cornea, iris, normal, and cataractous lenses and intraocular fluids of vertebrates

A method using electrothermal atomic absorption spectroscopy was developed for the determination of copper (Cu) concentration in the cornea, iris, and lens of a variety of species, including dog, cat, rabbit, horse, and toad. Previously described methods were used to determine Cu in aqueous and vitreous humor. There was little difference between copper levels in the same tissue or fluid across the species. However, there were age and pathology-related changes in Cu concentration of the aqueous humor, cornea, and lens. In the groups of older dogs, the Cu concentration of the aqueous humor and cornea is significantly lower than the two younger groups. In both the dog and rabbit, lenses from young animals have the lowest copper concentration which increases and then finally decreases with age. Canine hypermature cataracts have a significantly higher copper concentration than control dogs of all age groups. There was no correlation between Cu concentration in the intraocular fluids and the cataractous lenses taken from the same eye. The role such an increase in lenticular Cu concentration may play in cataractogenesis needs to be explored.

Idiopathic hyperaldosteronism in a dog

Idiopathic hyperaldosteronism was diagnosed in an 8-year-old castrated male Yorkshire Terrier, based on increased concentration of plasma aldosterone, hypertension, hypernatremia, decreased natriuresis, hypokalemia, and hyperkaluria. Unilateral adrenalectomy was performed after visualization of a nodule on the right adrenal gland. Hyperplasia of the zona glomerulosa and increased postoperative aldosterone concentrations supported the diagnosis of idiopathic hyperaldosteronism.

Malignant melanoma of the conjunctiva in a cat

A conjunctival melanoma was diagnosed in an adult domestic cat. The neoplasm was excised without further complications. It is important to differentiate conjunctival melanoma from other types of pigmented ocular neoplasia. In man, conjunctival melanomas are often malignant tumors with potential for metastatic behavior. Although this neoplasm had histologic features of malignancy, no evidence of local recurrence or metastasis has been apparent during the 11-month follow-up period.

Metastatic ocular squamous cell carcinoma in a cat

Bilateral ocular metastatic squamous cell carcinoma was diagnosed in a cat. Ophthalmic signs included bilaterally swollen optic discs, choroidal pallor, and retinal vascular engorgement. A retinal detachment was apparent in the left eye and retinal edema and hemorrhage in the right eye. Systemic signs of progressive visual impairment, ataxia, and weakness were noted. The patient's condition continued to deteriorate despite therapy with systemic antibiotics and corticosteroids, and euthanasia was performed. The diagnosis was made upon histologic examination that revealed metastasis of malignant squamous cells to both globes, the brain, and lungs.

Photosynthesis in Encelia farinosa Gray in Response to Decreasing Leaf Water Potential

Photosynthetic responses of intact leaves of the desert shrub Encelia farinosa were measured during a long term drought cycle in order to understand the responses of stomatal and nonstomatal components to water stress. Photosynthetic rate at high irradiance and leaf conductance to water vapor both decreased linearly with declining leaf water potential. The intercellular CO(2) concentration (c(i)) remained fairly constant as a function of leaf water potential in plants subjected to a slow drought cycle of 25 days, but decreased in plants exposed to a 12-day drought cycle. With increasing water stress, the slope of the dependence of photosynthesis on c(i) (carboxylation efficiency) decreased, the maximum photosynthetic rates at high c(i) became saturated at lower values, and water use efficiency increased. Both the carboxylation efficiency and photosynthetic rates were positively correlated with leaf nitrogen content. Associated with lower leaf conductances, the calculated stomatal limitation to photosynthesis increased with water stress. However, because of simultaneous changes in the dependence of photosynthesis on c(i) with water stress, increased leaf conductance alone in water-stressed leaves would not result in an increase in photosynthetic rates to prestressed levels. Both active osmotic adjustment and changes in specific leaf mass occurred during the drought cycle. In response to increased water stress, leaf specific mass increased. However, the increases in specific leaf mass were associated with the production of a reflective pubescence and there were no changes in specific mass of the photosynthetic tissues. The significance of these responses for carbon gain and water loss under arid conditions are discussed.