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C C Willhite

Publications and source records attributed to C C Willhite.

At least 19 recordsLinked to original sources
PubMed1997

Embryonic delivered dose of isotretinoin (13-cis-retinoic acid) and its metabolites in hamsters.

All-trans-retinoic acid (all-trans-RA) is required in normal embryogenesis and both deficiency and excess are teratogenic. Isotretinoin (13-cis-RA) is teratogenic in all species examined; based on administered dose, humans appear most sensitive, followed by (in order or decreasing sensitivity) monkey, rabbit, hamster, mouse, and rat. Identification of the teratogenic threshold in these species is difficult because RAs are normal physiologic constituents. The rabbit no-observed-adverse-effect-level (NOAEL) and lowest-observed-adverse-effect-level (LOAEL) administered doses (3 and 15 mg/kg/day, respectively, on gestation Days 8-11) are less than the corresponding values in hamster (7.5 and 37.5 mg/kg/day, respectively, on gestation Days 7 and 8), but drawing conclusions from administered dose alone ignores differences in absorbed, metabolized, and embryonic delivered dose. Therefore, distribution and metabolism studies of 13-cis-RA at the NOAEL and LOAEL in pregnant hamsters were performed and plasma and tissue concentrations of parent compound and metabolites were compared to those found in rabbits. Metabolites of 13-cis-RA common to all species include three RAs (all-trans-RA, all-trans-4-oxoRA, 13-cis-4-oxoRA) and the glucuronide conjugate of 13-cis-RA (13-cis-RAG). As in rabbits, we found 13-cis-4-oxoRA also to be the major metabolite of 13-cis-RA in hamster plasma, peripheral tissues, and embryo. Of maternal tissues, peak 13-cis-RA concentrations were highest in liver. Total concentration of RA (13-cis-RA + 13-cis-4-oxoRA + all-trans-RA + all-trans-4-oxoRA) per gram of wet tissue was greatest in maternal liver, followed by that in lung, adipose tissue, muscle, kidney, and brain. At the NOAEL, total RA plasma Cmax in hamster was 6 times that in rabbit; at the LOAEL, hamster plasma total RA Cmax was 4 times that in rabbit. Hamster absorbed and metabolized dose (as AUC of plasma total RA) at the NOAEL and LOAEL was 2.6 and 2.4 times that in rabbit, respectively. In the embryo, hamster total RA Cmax was 2.7 times (at NOAEL) and 2.6 times (at LOAEL) that in rabbit. However, embryonic delivered dose (total RA AUC in hamster and rabbit embryo, respectively) at the NOAEL (2.08 and 2.14 microg . hr.g-1) and LOAEL (5.34 and 5.54 microg . hr . g-1) was virtually identical. Embryonic AUCs in hamster and rabbit for all-trans-RA and all-trans-4-oxoRA, metabolites which transactivate directly the nuclear RA receptors (RARs), were also very similar at the NOAEL (0.66 and 0.81 microg . hr g-1) and at the LOAEL (1.14 and 1.32 microg . hr g-1). Based on embryonic delivered dose, we suggest that 13-cis-RA is an equipotent teratogen in hamster and rabbit.

Abnormalities, Drug-Induced↗
PubMed1995

Comparative disposition, receptor affinity, and teratogenic activity of sulfon arotinoids.

To investigate the relationship between sulfon arotinoid biotransformation and teratogenic activity, the potency of the ethyl (Ro 15-1570) and methyl (Ro 14-9706) arotinoid sulfones and their in vivo disposition in pregnant hamsters were studied. Administration of Ro 15-1570 was teratogenic, but Ro 14-9706 showed no such activity. Total absorbed doses of the ethyl and methyl sulfones (measured as maternal plasma AUC) were very similar. Total delivered dose of Ro 14-9706 to liver and lung was 120-160% that of Ro 15-157, and Ro 14-9706 was transferred in greater amounts to the embryo as well. Placenta AUC for parent sulfon arotinoids was 160-250% that in the embryo. Plasma analyses by HPLC suggested that the ethyl sulfone was oxidized and appeared in maternal plasma as the corresponding sulfinic (Ro 14-9572) and sulfonic (Ro 14-3899) acids, amounting to 10% and 16%, respectively, of the mean maternal ethyl sulfone Cmax value. The concentrations of sulfinic and sulfonic metabolites were always less than the analytical limit of detection in placenta and embryo after maternal ethyl sulfone intubation. Neither the sulfinic nor the sulfonic acid were ever detected in maternal circulation, placenta, or embryo after methyl sulfone intubation. Comparisons of their binding affinities found that neither the ethyl nor the methyl arotinoid sulfone could act as a ligand for cellular retinoic acid-binding protein (CRABP), nor could these compounds bind retinoid nuclear receptors (RAR). Transcriptional activation of RARs was weak and similar for both compounds. The sulfinic and sulfonic acid arotinoids bind and transactivate RARs, and bind CRABP with efficiencies similar to all-trans-retinoic acid. Furthermore, they are active in cultured limb bud chondrocytes. The results suggest that the methyl sulfone (in accord with its lack of activity in cultured limb bud chondrocytes) is of no toxicologic significance in hamster embryo--even after relatively high delivered dose. Teratogenicity of the ethyl sulfone (which shows marked inhibition of chondrogenesis in cultured limb bud) does not appear to depend on measurable concentrations of these sulfinic/sulfonic acid metabolites in the hamster embryo.

Abnormalities, Drug-Induced↗
PubMed1994

Selenium kinetics, placental transfer, and neonatal exposure in cynomolgus macaques (Macaca fascicularis).

Forty pregnant cynomolgus macaques were treated daily from gestational day 20 to 50 by nasogastric intubation of 0, 25, 150, or 300 micrograms selenium as L-selenomethionine/kg body weight. In each group, 7-8 pregnancies were terminated by hysterotomy at gestational day 100 +/- 2 and the fetuses were examined, while 2-3 pregnancies in each group were allowed to proceed to term. Selenium and soluble glutathione peroxidase were measured in: maternal, neonatal, and fetal plasma and erythrocytes; fetal kidney, liver, muscle, and placenta; and maternal breast milk. The area under the multidose maternal plasma selenium concentration:time curve, the maximum maternal plasma selenium concentration, and the maternal urinary selenium excretion rates were proportional to the L-selenomethionine dose. Selenium concentrations in all fetal and neonatal, tissues were also proportional to maternal L-selenomethionine dose. Glutathione peroxidase was affected only in maternal erythrocytes, fetal kidney, and neonatal plasma. The selenium concentration in fetal plasma was an average 33% of that in maternal plasma. Although selenium concentrations in macaque milk were doubled by the highest dose, intrauterine selenium accumulation accounted for the majority of the neonatal selenium body burden. Despite the elevated selenium concentrations in fetal tissues, neonatal blood, and milk, no deleterious effects on neonates were observed. These results suggest that primate fetuses are well protected against selenium toxicity arising from high maternal L-selenomethionine intakes.

Animals↗
PubMed1993

Incorporation of a micronucleus study into a developmental toxicology and pharmacokinetic study of L-selenomethionine in nonhuman primates.

Concomitant to a developmental toxicology study of selenium in long-tailed macaques (Macaca fascicularis), a transplacental bone marrow micronucleus assay was conducted in the fetuses of treated animals. Selenium was administered as L-selenomethionine by nasogastric intubation at 0, 150 or 300 micrograms/kg-day to pregnant macaques daily throughout organogenesis (gestation days 20-50). Pregnancy was terminated on gestation day 100 +/- 2 and fetuses were obtained by hysterotomy. Selenium concentrations in maternal blood were monitored throughout pregnancy and selenium concentrations in fetal blood were measured at hysterotomy. Maternal circulating selenium did not exceed 4 ppm in plasma or 3.7 ppm in erythrocytes. Selenium in cord blood was < or = 0.1 ppm in plasma and < or = 1.1 ppm in erythrocytes at 300 micrograms/kg-day. Fetal bone marrow smears were prepared from the humerus and micronucleated polychromatic erythrocytes were scored. No increase of micronucleus frequency was detected in any dose group, although signs of maternal selenosis were obvious. This finding is compared to the previous observation that micronuclei were induced in the bone marrow of adult nonpregnant macaques treated at 600 micrograms/kg-day, a lethal dose yielding blood selenium levels to 7.3 ppm in plasma and 5.7 ppm in erythrocytes after 15 days of daily treatment, when death occurred. These data demonstrate that measurement of circulating xenobiotics can be useful for the interpretation of genetic toxicology results.

Animals↗
PubMed1992

Inner ear malformations induced by isotretinoin in hamster fetuses.

Inner ear malformations induced in anotic hamster fetuses following maternal treatment with 50 mg/kg isotretinoin (13-cis-retinoic acid) on gestational day 8 are described. Computer-assisted three dimensional reconstruction was used. Two general types of defective vestibulocochlear development were seen. Defects were bilateral and correlated with extent of middle ear deficiency and severity of mandibular defects. In the more severely affected fetuses the inner ear was limited to an epithelial sac with occasional small projections, no apparent innervation and a correspondingly reduced otic capsule. In most of the fetuses examined the inner ear was less severely affected and was characterized by a reduction in the number of semicircular ducts and alterations in the size and shape of the cochlear duct. These defects are similar to those seen in a child with the isotretinoin embryopathy. Pathogenesis may result from a direct effect on otic epithelium or from faulty inductive interactions with the rhombencephalon or with periotic neural crest cells.

Abnormalities, Drug-Induced↗
PubMed1992

Effects of excess selenomethionine on selenium status indicators in pregnant long-tailed macaques (Macaca fascicularis).

Forty pregnant long-tailed macaques were treated daily for 30 d with 0, 25, 150, or 300 micrograms selenium as L-selenomethionine/kg body weight. Erythrocyte and plasma selenium and glutathione peroxidase specific activities, hair and fecal selenium, and urinary selenium excretion were increased by and were linearly related to L-selenomethionine dose. Hair selenium was most sensitive to L-selenomethionine dose, with an 84-fold increase in the 300 micrograms selenium/(kg-d) group relative to controls (r = 0.917). Daily urinary selenium excretion (80-fold, r = 0.958), plasma selenium (22-fold, r = 0.885), erythrocyte selenium (24-fold, r = 0.920), and fecal selenium (18-fold, r = 0.911) also responded strongly to L-selenomethionine. Erythrocyte and plasma glutathione peroxidase specific activities increased 154% and 69% over controls, respectively. Toxicity was associated with erythrocyte selenium > 2.3 micrograms/mL, plasma selenium > 2.8 micrograms/mL, and hair selenium > 27 micrograms/g. Plasma, erythrocyte, and hair selenium concentrations may be useful for monitoring and preventing the toxicity of L-selenomethionine administered to humans in cancer chemoprevention trials.

Analysis of Variance↗
PubMed1992

Structure-affinity relationships of retinoids with embryonic cellular retinoic acid-binding protein.

Separation and quantitation of cellular retinoic acid-binding protein (CRABP) in embryonic and fetal hamster tissues was accomplished with high-performance size-exclusion chromatography. Binding affinity of 26 retinoids was established by in vitro displacement of high specific activity all-trans-[3H2]retinoic acid from fetal CRABP. The CRABP concentration in presomite-to-early somite (Day 8) hamster embryos was 1.9 pmol/mg cytosolic protein and increased to 7.5 pmol/mg protein in Day 13 fetuses; CRABP concentrations subsequently declined as gestation progressed. CRABP was located primarily in fetal brain and skin (5.8 +/- 0.3 and 2.2 +/- 0.1 pmol/mg protein, respectively), whereas only trace concentrations were found in fetal liver, placenta, and maternal uterus. Retinoids that could displace all-trans-retinoic acid from CRABP had a free acid at the polar terminus (or were carboxylate esters that were readily hydrolyzed to the corresponding free acid) and had a hydrophobic ring at the distal position. The ligand specificity of the CRABP studied here suggests that this protein was analogous to the CRABP I isoform. The in vitro binding affinities of teratogenic retinoids that competed for embryonic CRABP failed to correlate directly with relative teratogenic potency. In some instances, the latter observation can be related to extensive in vivo biotransformation of retinoids to multiple teratogenic metabolites and to retinoid persistence in the embryo. Three analogs containing a free carboxy terminus, SRI 5898-21, SRI 7323-78, and SRI 6153-40, were identified with high teratogenic potency but failed to bind fetal hamster CRABP. The structure-activity and binding data of the analogs studied here indicate that many, if not most, teratogenic retinoids (or their acidic metabolites) bind with embryonic/fetal CRABP, but the present data question the role for CRABP in their teratogenic mechanism of action.

Animals↗
PubMed1992

Absorption, distribution and elimination of selenium as L-selenomethionine in non-human primates.

20 adult female macaques (Macaca fascicularis) were given oral doses of L-selenomethionine (L-SeMet) equivalent to 0, 25, 150, 300 and 600 micrograms selenium (Se)/kg body weight, and plasma, erythrocyte, hair, faecal and urine Se concentrations were determined. The macaques were scheduled for 30 daily oral doses of L-SeMet, but systemic toxicity necessitated dose reduction in several animals; two macaques given 600 micrograms Se/kg body weight/day for 10-15 days died, and the concentration of Se in their tissues was determined and compared with Se concentrations in tissues collected from one untreated animal. Circulating and urinary Se concentrations in control macaques were within the normal human ranges. Plasma, erythrocyte, hair and urinary Se concentrations were generally dependent on the dose of L-SeMet administered. Plasma Se reflected more immediately exposure to L-SeMet, whereas erythrocyte Se concentrations increased and decreased more slowly. In some cases, erythrocyte Se was still increasing or showed a plateau after L-SeMet treatment was discontinued. Plasma Se concentrations of 6.7-7.3 ppm were observed in the two animals that died due to acute toxicity to L-SeMet. Neither plasma nor erythrocyte GPx activity was influenced by a single L-SeMet dose, but an increase in erythrocyte GPx activity occurred with continuous exposure. Total tissue Se increased 13-28-fold in macaques given 600 micrograms Se/kg body weight/day for 10-15 days, with the liver and kidneys containing the the highest Se concentrations.

Absorption↗
PubMed1991

Temporal distribution of retinoic acid and cellular retinoic acid-binding protein (CRABP) in the fetal hamster.

The temporal relationship between the distribution of retinoic acid, a known human and rodent teratogen, and that of cellular retinoic acid-binding protein (CRABP) was investigated from Day 11 to Day 14 of hamster prenatal development. The 11,12-(3)H2 and 15(-14C) forms of all-trans-retinoic acid were used for quantitative distribution studies and autoradiography, respectively, and were evaluated 15 min after a single intravenous injection. Radioactivity was detected in all fetal tissues examined (brain, liver, heart, spinal cord, limb, and skin), and at Day 14, approximately 66% of the total radioactivity was present as parent all-trans-retinoic acid. High concentrations of total radioactivity were observed by autoradiography in the midbrain and hindbrain (mesencephalon, metencephalon, and myelencephalon) and spinal cord, but not in the forebrain. At the earliest time studied, limb buds showed relatively high concentrations of radioactivity. Levels of radioactivity were also high in portions of the developing face, nose, and tongue. Immunohistochemical analyses indicated that the amount of CRABP in Day 14 tissues was the highest in spinal cord followed by limb and skin; heart and liver contained only relatively small amounts of this protein. From Day 11 to Day 14, the amount of CRABP, as measured by high-performance size-exclusion liquid chromatography, in the whole body decreased as gestation progressed. Microscopic immunohistochemical localization of CRABP found the highest concentration in the ventral midbrain and in the ventral and lateral sides of the hindbrain and spinal cord; CRABP was also abundant in tongue, limb, and skin. The distribution of CRABP-positive cells in the central nervous system was similar to the distribution of retinoic acid. The data presented here indicate that fetal CRABP appears to play a role in differential accumulation of retinoic acid in certain structures of the developing hamster. The patterns of tissue retinoid and CRABP distribution observed here are consistent with the patterns of congenital malformations induced by prenatal retinoid exposure.

Animals↗
PubMed1991

Developmental toxicity of L-selenomethionine in Macaca fascicularis.

Forty pregnant long-tailed macaques were dosed via nasogastric intubation with 0, 25, 150, or 300 micrograms/kg of L-selenomethionine (Se) daily during organogenesis [Gestational Day (GD) 20-50]. Clinical examination of the dams, maternal body weights, sonographic evaluations, clinical chemistry screens, and measures of serum progesterone and urinary estrone conjugates were used as indicators of maternal and fetal status in all animals. The pregnancies of two to three dams from each dose group were followed until term (approximately GD 165); the remainder (N = 7/dose group) were scheduled for hysterotomy on GD 100 +/- 2. A standard teratologic evaluation was performed including visceral and skeletal examinations. Fetal liver, kidney, skin, and smooth, cardiac, and skeletal muscles were examined by light microscopy; heart muscle was also evaluated by transmission electron microscopy. Neonates delivered at term remained with the dams and were removed periodically for morphometric, neurologic, behavioral, and ophthalmologic assessments on Days 1, 8, 15, 22, and 30 of age. Dose-dependent maternal toxicity as evidenced by anorexia, vomiting, and a significant reduction in body weight increased with increasing duration of Se exposure. One growth-retarded fetus was recovered on GD 131 from a compromised dam exposed to 25 micrograms/kg-day; one early embryonic death (GD 35) and two fetal deaths [GD 68 (followed by maternal death) and GD 123] occurred among animals dosed with 300 micrograms/kg-day. Pregnancy loss among treated animals was not significantly different from concurrent or historical controls. No statistically significant treatment-related effects were observed at necropsy on GD 100 +/- 2. One infant exposed to 150 micrograms/kg-day prenatally exhibited a unilateral cortical cataract, which may have been a spontaneous occurrence. The limited developmental effects observed and reported teratogenesis in nonmammalian species suggest that comparative pharmacokinetic studies are required before the full public health significance of elevated Se is understood.

Animals↗
PubMed1990

Dithiocarbamates and prevention of cadmium teratogenesis in the hamster.

Certain dithiocarbamates (DTC) have been reported to protect against cadmium (Cd)-induced lethality and to decrease Cd body burden. The present study evaluated the influence of sodium N-benzyl-D-glucamine dithiocarbamate, sodium N-di(hydroxyethyl)amine dithiocarbamate, sodium 4-carboxyamidopiperidine-N-dithiocarbamate, and sodium N-methyl-D-glucamine dithiocarbamate on Cd-induced teratogenesis in the hamster. When given as a single ip injection at 2.2 mmol/kg 15 min prior to iv CdCl2 (2 mg/kg), all of the DTC afforded significant protection against Cd-induced developmental toxicity and reduced kidney [Cd] in the dam. Maternal liver [Cd] was reduced with the glucamine and dihydroxyethyl amine analogs, but treatment with the piperidine failed to influence hepatic [Cd]. Pretreatment of the dams with DTC 24 hr prior to Cd challenge failed to protect against Cd-induced embryotoxicity, and provided minimal, if any, reduction in renal or hepatic [Cd]. Pretreatment with the N-methyl-D-glucamine congener 24 hr prior to Cd exposure increased embryolethality. The dose-time relationships found here suggest that pharmacologically effective levels of these DTC decline within 24 hr of treatment and that induction of metallothionein does not play a major role in DTC antagonism of Cd poisoning.

Animals↗
PubMed1990

Route-dependent pharmacokinetics, distribution, and placental permeability of organic and inorganic selenium in hamsters.

Inorganic selenium (Se) salts (selenite and selenate oxyanions) and the organic selenoamino acids (selenomethionine and seleniferous grains) are teratogenic and embryolethal in domestic and wild birds. Selenium bioaccumulation has been held responsible for reproductive failure among waterfowl at the Kesterson Reservoir (California), the Ouray and Stewart Lake Wildlife Refuges (Utah), and the Carson Sink (Nevada). Anecdotal field and controlled laboratory reports have implicated Se exposure in mammalian embryotoxicity (including human), but developmental toxicity studies in hamsters failed to demonstrate an adverse response, except at maternally toxic doses (Ferm et al., Reprod. Toxicol., in press). Uptake, distribution, and elimination of Se after a single bolus equimolar dose (60 mumol/kg) of selenate or selenomethionine by oral or intravenous administration were compared using day 8 pregnant hamsters. Intravenous selenate was eliminated ten times more rapidly from maternal plasma than oral selenate, but concentrated in liver, kidney, and placenta to the same degree. Intravenous (iv) L-selenomethionine achieved lower maximum circulating total [Se], but it was eliminated more slowly than iv selenate. Larger areas under the plasma and peripheral tissue [Se]:time curve (AUC) after oral or parenteral selenomethionine than after equimolar selenate were consistent with previous studies in rodents and in humans. Embryonic [Se] plateaued at 3 nmol/g after selenate, but embryonic [Se] after selenomethionine continued to accumulate (80 nmol/g) as gestation progressed. The lack of a teratogenic response in hamsters at doses of either selenate or selenomethionine less than those associated with maternal intoxication cannot be attributed to lack of Se accumulation in early embryonic and placental tissue.

Animals↗
PubMed1990

Structure-activity relationships of retinoids in developmental toxicology. IV. Planar Cisoid conformational restriction.

To evaluate the influence of the three-dimensional configuration of retinoids on teratogenic activity, 14 retinoids were studied in hamsters. Retinoids with a conformational restriction of the retinoic acid polyene chain adjacent to the beta-cyclogeranylidene ring showed increased teratogenic potency and retinoids with aromatic conformational restriction adjacent to the polar terminus showed potency equivalent to retinoic acid. Conformational restriction of the polyene chain that permits rotation of the bond adjacent to the beta-cyclogeranylidene ring abolished teratogenic activity. Incorporation of dimethyl substituents at positions corresponding to C1 and C4 positions of retinoic acid enhanced teratogenic potency. Elimination of the twist chair conformation of gem-dimethyl substituents via incorporation of a benzothiopyran or substituted planar aromatic ring decreased teratogenic potency. Planar cisoid conformational restriction alone was insufficient to confer teratogenic activity in that elimination of the polar terminus abolished teratogenic activity. That an acidic polar terminus, as contrasted to a carboxyl residue per se, was required for teratogenic activity was illustrated by administration of a retinoidal phenyl sulfone which was metabolized to the corresponding teratogenic sulfonic acid. Retinoid teratogenicity in hamsters depends upon the assumption of a 10,11 cisoid and/or 12,13 cisoid rotameric form by a conjugated spacer greater than five carbon atoms in length located between a hydrophobic ring system and an acidic terminus, ionized at physiologic pH. Comparison of the relative teratogenic potencies of this series of conformationally restricted retinoids with their activities in assays for chemoprevention activity showed that those analogs with high intrinsic control of epithelial or mesenchymal cell differentiation were also the more potent teratogens. The results suggest that those biochemical mechanisms responsible for retinoid control of normal adult or neoplastic cell differentiation also mediate retinoid-induced teratogenesis.

Abnormalities, Drug-Induced↗
PubMed1990

Chlorine dioxide and hemodialysis.

In the United States chlorination of potable water supplies has been the standard method of disinfection for about 75 years. In recent times concern has been raised about the propensity of chlorination to introduce potentially carcinogenic trihalomethanes (THM) such as chloroform into finished water. The levels of THM introduced depend on many factors including the quality of the raw water. Numerous community water treatment facilities are experiencing difficulty in meeting current U.S. Environmental Protection Agency standards, and it is likely that the permissible levels may be lowered in the future. An alternative to chlorination which does not generate THM during disinfection is chlorine dioxide, but there are concerns about the acute and chronic toxicity of ClO2 and its disinfection by-products, chlorite and chlorate. Deleterious effects of moderately high levels of these oxychlorines have been demonstrated experimentally on red blood cells, thyroid function, and development in laboratory animals. Adverse effects in controlled prospective studies in humans and in actual use situations in community water supplies have as yet failed to reveal clear evidence of adverse health effects. Among groups who may be at special risk from this suggested alternative are patients who must undergo chronic extracorporeal hemodialysis. The special needs, precautions, and experience to date in regard to finished water are reviewed. Again, very limited human experience has failed to reveal adverse health effects. Further study, caution, and extreme vigilance are indicated, but dialysis patients in carefully controlled facilities may be at no greater risk than the general population.

Animals↗