Mevalonate supplementation in pregnant rats suppresses the teratogenicity of mevinolinic acid, an inhibitor of 3-hydroxy-3-methylglutaryl-coenzyme a reductase

Embryonic lethality and defective neural tube closure in mice lacking squalene synthase

Squalene synthase (SS) catalyzes the reductive head-to-head condensation of two molecules of farnesyl diphosphate to form squalene, the first specific intermediate in the cholesterol biosynthetic pathway. We used gene targeting to knock out the mouse SS gene. The mice heterozygous for the mutation (SS+/-) were apparently normal. SS+/- mice showed 60% reduction in the hepatic mRNA levels of SS compared with SS+/+ mice. Consistently, the SS enzymatic activities were reduced by 50% in the liver and testis. Nevertheless, the hepatic cholesterol synthesis was not different between SS+/- and SS+/+ mice, and plasma lipoprotein profiles were not different irrespective of the presence of the low density lipoprotein receptor, indicating that SS is not a rate-limiting enzyme in the cholesterol biosynthetic pathway. The mice homozygous for the disrupted SS gene (SS-/-) were embryonic lethal around midgestation. E9.5-10.5 SS-/- embryos exhibited severe growth retardation and defective neural tube closure. The lethal phenotype was not rescued by supplementing the dams either with dietary squalene or cholesterol. We speculate that cholesterol is required for the development, particularly of the nervous system, and that the chorioallantoic circulatory system is not mature enough to supply the rapidly growing embryos with maternal cholesterol at this developmental stage.

Preclinical safety evaluation of cerivastatin, a novel HMG-CoA reductase inhibitor

Cerivastatin is a new but structurally distinct 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitor ("statin"). It effectively decreases low-density lipoprotein (LDL) cholesterol at 1% of the doses of other currently available statins. The toxicology of cerivastatin was evaluated in a comprehensive program of studies including: (1) single- and multiple-dose toxicity studies in rats, mice, minipigs, dogs, and monkeys; (2) reproductive toxicity studies in rats and rabbits; (3) in vitro and in vivo mutagenicity assays in rats and mice; and (4) carcinogenicity studies in rats and mice. In addition, studies were undertaken to investigate the effects of cerivastatin on lens opacity, testicular tissue, and hemorrhage in dogs. Oral administration of single and multiple doses of cerivastatin over periods ranging from 4 weeks to 24 months was generally well tolerated. Adverse effects were similar to those observed with other statins and primarily involved the liver and muscle tissue. At the high doses used in the toxicologic studies, cerivastatin caused elevations in serum transaminases and creatine phosphokinase levels as well as some degeneration of muscle fibers in rats, mice, dogs, and minipigs. In dogs, the species most sensitive to statins, cerivastatin caused erosions and hemorrhages in the gastrointestinal tract, bleeding in the brain stem with fibroid degeneration of vessel walls in the choroid plexus, and lens opacity. Apart from minor morphologic changes in the testicular tissue of dogs--the only organ for which a comparably low margin of safety was observed--cerivastatin had no significant effects on the male or female reproductive system. Cerivastatin also caused no primary embryotoxic or teratogenic effects. With the exception of cerivastatin-induced effects on the eyes and testicles, administration of mevalonic acid reversed the toxicologic effects of cerivastatin, indicating that the toxic effects were related to its mode of action and not to any intrinsic toxicity of the molecule itself. There was no evidence that cerivastatin had any mutagenic effects and, in contrast to other statins, high doses of cerivastatin did not induce tumors in rats. The main metabolite of cerivastatin was well tolerated systemically in all animals, including dogs. Overall, cerivastatin has a similar toxicologic profile to other statins and is a well-tolerated HMG-CoA reductase inhibitor.

Cholesterol metabolism and embryogenesis

Although cholesterol has long been known to be an essential component of cell membranes in vertebrate organisms, recent studies have suggested that cholesterol plays a crucial role in specific processes during embryonic development, including the covalent modification of Hedgehog proteins. Here we review the overlapping developmental phenotypes associated with pharmacologically or genetically induced defects in cholesterol biosynthesis, embryonic cholesterol transport and Hedgehog proteins. Shared aspects of these phenotypes suggest that common mechanisms underlie impaired central nervous system development associated with cholesterol deficiency.

Abnormal cholesterol biosynthesis as in Smith-Lemli-Opitz syndrome disrupts normal skeletal development in the rat

Smith-Lemli-Opitz syndrome (SLOS) in human infants is a common autosomal recessive malformation syndrome (estimated incidence, 1:20,000). It is characterized clinically by congenital anomalies, especially craniofacial and limb defects, and biochemically by a defect in 7-dehydrocholesterol-delta7-reductase activity (7DHC-reductase), the final enzyme in cholesterol biosynthesis. In previous studies, early administration of the 7DHC-reductase inhibitor AY9944 to pregnant rats resulted in a high frequency of holoprosencephaly, relevant to craniofacial anomalies of SLOS. In order to test the effect of AY9944 on limb development, we treated dams on gestation day 7 (GD7), which delays the biochemical defect to about GD13 to GD14. Sera were sampled on GD12, GD14, and GD21 and cholesterol and dehydrocholesterols (7DHC and 8DHC) were measured by gas-chromatography-mass spectrometry (GC-MS), as for the diagnosis of SLOS. GD21 fetuses were examined for gross malformations and skeletal development. In treated dams, the SLOS biochemical marker 7DHC accounted for one fourth and one third of total sterols, respectively, on GD12 and GD14, and cholesterolemia on these two gestation days was reduced by 50% and 43%, respectively, as compared with control values. This maternal metabolic defect was associated with decrease in fetal weight and delayed ossification. In addition, scapular malformations were observed in four fetuses from three litters. The malformations could have been caused by the same mechanism as holoprosencephaly after early treatment with AY9944. These cholesterol-deficiency-based malformations could have a common cause in the abnormal expression of Hedgehog or other developmental gene proteins, and may thus explain various congenital polymalformative syndromes in humans, including SLOS.

Probing cataractogenesis associated with mevalonic aciduria

PURPOSE

Mevalonic aciduria in humans results from a genetic deficiency of mevalonate kinase and is characterized by very high plasma mevalonic acid levels, developmental malformations and cataracts. This study tested the possibility that the cataracts could result from direct toxicity of the accumulated mevalonate.

METHODS

Young rat lenses were cultured for up to 4 days in medium TC199 containing 1 to 5 mM mevalonic acid. Changes in the water, sodium and potassium content of the lens were followed; electrolytes were measured by atomic absorption spectroscopy. The identities of proteins leaked from the lens were determined by sodium dodecylsulfate polyacrylamide electrophoresis and isoelectric focusing. Changes in cation flux were measured by 86Rb uptake. Lens concentrations of mevalonic acid were measured from uptake of 3H-mevalonolactone.

RESULTS

Culture of young rat lenses with 3 to 5 mM mevalonic acid produced lens opacification and nuclear cataracts starting within 1 to 2 days of culture. Mevalonic acid did not concentrate in the lens. Treated lenses accumulated water and sodium and lost potassium and soluble gamma crystallin proteins. These changes were preceded by a loss of the len's capacity to concentrate 86Rb, a potassium analogue. The loss of 86Rb uptake might have been due to a slow poisoning of the cation pump, direct effects on membrane integrity or both.

CONCLUSIONS

The results show that chronic exposure of the lens to mevalonic acid can induce cataracts, which appear caused by a progressive increase in the permeability of lens cell membranes. The cataracts associated with mevalonic aciduria could be due to toxicity from mevalonic acid.

Postmarketing surveillance of lovastatin and simvastatin exposure during pregnancy

Pregnancy outcomes in women with inadvertent exposure to lovastatin and simvastatin during pregnancy have been examined based on reports submitted to the manufacturer as part of worldwide postmarketing surveillance. There were 134 reports of exposure during pregnancy in which pregnancy outcome was known. Among prospectively followed pregnancies with known outcome, the proportion of normal outcomes was 85%, congenital anomalies 4.0%, spontaneous abortions 8.0%, fetal deaths/stillbirths 1.0%, and miscellaneous adverse outcomes 2.0%. While the number of prospective reports available for evaluation were only sufficient to rule out a three- to fourfold increase in the overall frequency of congenital anomalies, these proportions do not exceed what would be expected in the general population. Based on findings from this interim evaluation, there is no relationship between exposure to therapeutic doses of these agents during pregnancy and the occurrence of adverse pregnancy outcomes.

Inhibition of 7-dehydrocholesterol reductase by the teratogen AY9944: a rat model for Smith-Lemli-Opitz syndrome

Our aim is to verify the validity of a rat model proposed for Smith-Lemli-Opitz (SLO) syndrome, a developmental disorder characterized by a defect in 7-dehydrocholesterol-delta 7 (7DHC)-reductase and by facial dysmorphism close to the holoprosencephaly caused by the teratogen AY9944. We investigated the sterol profile in rats treated with AY9944 blocking 7DHC-reductase. AY9944 was given orally to rats on gestation day 3 (D3). The sera were sampled for kinetic data on D3, D6, D9, D12, and D21. Cholesterol was measured in parallel by the routine enzymatic method and by the gas chromatography/mass spectrometry (GC-MS) procedure used in SLO diagnosis. In addition to sterols, we dosed steroid hormones punctually on D4 and on D10, and examined D21 fetuses in other animals. The enzymatic method was not specific for cholesterol, and measured 70% pure 7DHC added to a normal serum. On D21, 77% live fetuses showed pituitary agenesis. Cholesterol was rapidly reduced by more than 50% on D6 involving an accumulation of 7DHC, 8DHC, and trienols, as identified in SLO-affected children. The most abundant 7DHC reached a maximum from D9 to D12, equaling cholesterol on D9 (11 mg/dl). On D10, the magnitudes of hypocholesterolemic and of 7DHC accumulation were found to be dose-dependent. Progesterone was reduced as early as 24 hr after treatment and dropped to 40% of the levels in the controls on D10, correlating to the decrease in cholesterolemia. This rat model reproduces the same biochemical perturbations as seen in SLO, strongly suggesting that aberrant sterols (7DHC, 8DHC, or nortrienol) may contribute to the developmental defects.

Developmental toxicity of the HMG-CoA reductase inhibitor, atorvastatin, in rats and rabbits

The developmental toxicity of the 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase inhibitor, atorvastatin, was investigated in pregnant rats and rabbits given daily oral doses during organogenesis. Rats received 0, 10, 100, or 300 mg/kg on days 6-15 of gestation, and rabbits received 0, 10, 50, or 100 mg/kg on days 6-18 of gestation. Maternal and fetal parameters were evaluated on day 20 (rats) or 29 (rabbits) of gestation. Live fetuses were examined for external, visceral, and skeletal malformations and variations. At 300 mg/kg in rats, 1 treatment-related death occurred on day 12 of gestation, and maternal body weight gain and food consumption were decreased during treatment (43% and 23%, respectively). In addition, 1 animal at 300 mg/kg had total litter resorption. Increased postimplantation loss (not statistically significant) and slightly decreased fetal body weight (statistically significant only in males) were also observed at 300 mg/kg. There were no significant differences between treated and control groups in the incidence of fetal malformations or variations. No maternal or developmental toxicity was observed in rats at 10 or 100 mg/kg. In rabbits, marked maternal toxicity (7 deaths, body weight loss during and after treatment, and decreased food consumption) and abortion occurred at 100 mg/kg. At 50 mg/kg, maternal toxicity (2 deaths and 72% body weight gain suppression) and abortion also occurred. There were no treatment-related effects on live litter size or sex ratio. At 50 and 100 mg/kg, nonstatistically significant increases in postimplantation loss and decreases in gravid uterine weight were observed, and at 100 mg/kg, decreases in fetal body weight were observed relative to controls.(ABSTRACT TRUNCATED AT 250 WORDS)

Prevention of fluvastatin-induced toxicity, mortality, and cardiac myopathy in pregnant rats by mevalonic acid supplementation

Mevalonic acid is a product of the enzyme HMG-CoA reductase which is essential for cholesterol biosynthesis. Fluvastatin (Sandoz compound XU 62-320) is a potent inhibitor of this enzyme and, hence, mevalonic acid production. In three separate studies, oral administration of fluvastatin at 12 and 24 mg/kg/day to mated rats from day 15 of gestation through weaning resulted in unanticipated maternal mortality at the time of parturition and during lactation. Microscopic evaluations performed in two studies revealed significant cardiac myopathy in the dying animals. Drug-related clinical signs, significant maternal body weight loss, and an increase in stillborn pups and neonatal mortality were also noted at one or both dose levels. Supplementation of fluvastatin administration with 500 mg/kg b.i.d. of mevalonic acid completely blocked and/or ameliorated the mortality, cardiac myopathy, and other adverse effects. These studies indicate that the adverse maternal effects observed with fluvastatin before or following parturition resulted from exaggerated pharmacologic activity at the dose levels administered, i.e., inhibition of the enzyme HMG-CoA reductase, its immediate product mevalonic acid, and cholesterol biosynthesis.

HMG-CoA reductase mRNA in the post-implantation rat embryo studied by in situ hybridization

3-Hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase (EC 1.1.1.34) is the rate limiting step in the mevalonate pathway that produces isoprenoids and cholesterol. Inhibitors of HMG-CoA reductase are teratogenic in vivo and induce neural tube defects in rat embryo culture, effects which appear unrelated to cholesterol deficiency. This study is the first to localize HMG-CoA reductase mRNA by in situ hybridization (ISH). Expression of reductase mRNA was examined in post-implantation rat embryos, and for control purposes in rat liver and UT-1 cells, using a digoxigenin-11 (dig-11) labelled cRNA probe. Eighteen-day fetal liver showed heavy but patchy hybridization, and adult rat liver showed strong hybridization only on some periportal hepatocytes, which was absent in livers of fasted animals. UT-1 cells stimulated to overexpress HMG-CoA reductase mRNA were strongly positive with the same probe. Control hybridizations with sense strand RNA probe, or with cRNA probe on pre-RNased tissue were negative. Strong hybridization signal for HMG-CoA reductase mRNA was observed in all tissues of the post-implantation rat embryo, from egg cylinder to 30 somite stages (7 to 12 days). Heavy signal was noted in primitive ectoderm and neural tube. The wide embryonic and extraembryonic distribution and abundance of HMG-CoA reductase mRNA may reflect developmental requirements for products of the mevalonate pathway, e.g., isoprenoids for post-translational farnesylation of p21ras.

Facts and artefacts in mevalonic aciduria: development of a stable isotope dilution GCMS assay for mevalonic acid and its application to physiological fluids, tissue samples, prenatal diagnosis and carrier detection

A stable isotope dilution assay using D3-mevalonic acid was developed and applied to the study of mevalonic aciduria. The method also appears to be suitable for the evaluation of different therapeutic regimens in patients with hypercholesterolemia. Mevalonic acid was isolated by liquid partition chromatography and quantified as the underivatized lactone by means of ammonia chemical ionization selected ion monitoring capillary gas chromatography-mass spectrometry. In heterozygotes there was significantly greater urinary excretion of mevalonic acid, while the range of enzymatic activity of mevalonate kinase showed an overlap with that of controls. The analysis of amniotic fluids of two pregnancies at risk for mevalonic aciduria showed a 3277-fold elevation as compared to controls in the first case, diagnostic of an affected fetus, and a normal value in the second one. Mevalonic acid concentration was much increased in tissues of the affected and aborted fetus. Concentrations ranged from 840 to 1120 mumol/kg in various tissues and were as high as 1810 mumol/kg in brain. Concentrations in control fetal tissues were approximately 1 mumol/kg.

Preclinical evaluation of lovastatin

Administration of lovastatin to animals at high dosage levels produces a broad spectrum of toxicity. This toxicity is expected based on the critical nature of the target enzyme (HMG CoA reductase) and the magnitude of the dosage levels used. The information reviewed in this paper demonstrates that these adverse findings in animals do not predict significant risk in humans. The reason for this derives from the fact that all the available evidence suggests that the adverse effects observed are produced by an exaggeration of the desired biochemical effect of the drug at high dosage levels. The presence of clear and high no-effect doses for these toxic effects along with the fact that most of the changes observed are clearly mechanism-based (directly attributable to inhibition of mevalonate synthesis) indicate that it is unlikely that similar changes will be observed at the therapeutic dosage levels in humans. This hypothesis is supported by the extensive human safety experience described by Tobert in the following report.

A tier system for developmental toxicity evaluations based on considerations of exposure and effect relationships

The backlog of untested chemicals and the rate at which new substances enter the marketplace exceed our capacity for developmental effects testing by standard in vivo methods. However, conservative use of two observations in a manner consistent with present day understanding of abnormal developmental biology can more accurately focus attention and resources on those agents in greatest need of complex testing for effects on in utero development. These two observations are 1) most chemicals are no more toxic to embryonic development than they are to adult homeostasis and 2) most human exposure to chemicals is de minimus, i.e., so small that it is inconsequential. Recently devised in vitro assays to quantitatively rank chemicals according to their developmental hazard index, when used in conjunction with more conventional in vivo methods and appropriate considerations of exposure, permit evaluation of a significantly larger number of chemicals than is currently achieved. The methods described apply a tier approach to establish testing priorities that markedly reduce the time, cost, and number of laboratory animals needed for evaluation of developmental toxicity.

Mevalonic aciduria--an inborn error of cholesterol and nonsterol isoprene biosynthesis

A two-year-old boy presented with severe failure to thrive, developmental delay, anemia, hepatosplenomegaly, central cataracts, and dysmorphic features. Quantitative analyses of urinary organic acids revealed massive excretion of mevalonic acid, a metabolic precursor of cholesterol and nonsterol isoprenes: 46,000 to 56,200 mmol per mole of creatinine, as compared with 0.2 to 0.3 mmol per mole in normal children. The mevalonic acid concentration in plasma was also greatly increased at 440 mumol per liter (normal, less than 0.05). The activity of mevalonate kinase, the enzyme that catalyzes the first step in mevalonate metabolism, was severely deficient in the patient's fibroblasts, lymphocytes, and lymphoblasts. In the subsequent pregnancy of the patient's mother, gas chromatography-mass spectrometry demonstrated a marked elevation of mevalonic acid in the mother's urine and a 3000-fold elevation, as compared with control levels in the amniotic fluid, suggesting that the fetus was affected. The diagnosis was confirmed by demonstration of the deficiency of mevalonate kinase in amniocytes and ultimately in liver from the abortus. Intermediate activities of the enzyme in both parents indicated an autosomal recessive mode of inheritance. These observations identify an inherited disorder of cholesterol and nonsterol isoprene biosynthesis in humans.

Maternal toxicity: a possible etiological factor in embryo-fetal deaths and fetal malformations of rodent-rabbit species

Data from animal teratology studies were surveyed to determine whether embryo-fetal mortality and fetal malformations result from a primary action of the agent on the conceptus or if they are secondary to maternal toxicity--a consequence of administration with high dose levels of test chemicals. A fairly strong association between embryo-fetal mortality and maternal toxicity was revealed by analysis of data from hamsters, mice, rats, and rabbits in 234 studies of chemical and physical agents, of which 83 were conducted at both maternotoxic and nonmaternotoxic doses, 94 only at maternotoxic doses, and 49 at nonmaternotoxic doses. In the above studies, only nine chemicals (four each in hamsters and rabbits and one in rats) were reported to induce embryo-fetal deaths at apparently nonmaternotoxic doses. These findings tend to suggest a contributory role for maternal toxicity in the induction of embryo-fetal deaths. The previously reported hypothesis that certain fetal defects in mice may perhaps be caused by maternal toxicity was also found to be true in a review of data on hamsters, rats, and rabbits. Salient maternal toxicity-associated fetal malformations were exencephaly, encephalocele, micro- or anophalmia, and fused ribs in hamsters and defective (fused, missing, or extra) ribs, vertebrae, and sternebrae, ex-, an-, or microphthalmia, and cleft palate in rats and rabbits. These malformations occurred at low frequencies, generally with no readily apparent dose-response relationship. Presumptive evidence indicates that embryo-fetal deaths, and the above-mentioned fetal malformations in experimental animals, which in published literature are presently attributed to chemical induction for a large number of chemicals, may be a consequence of maternal toxicity per se.