13-cis-Retinoic acid alters neural crest cells expressing Krox-20 and Pax-2 in macaque embryos

This study investigates hindbrain and associated neural crest (NCC), otocyst, and pharyngeal arch development in monkey embryos following teratogenic exposure to 13-cis-retinoic acid (cRA). cRA was orally administered (5 mg/kg) to pregnant long-tailed macaques (Macaca fascicularis) between gestational days (GD) 12 and 27. Embryos were surgically collected at desired stages during treatment, analyzed for external morphological changes, and processed for immunohistochemistry. Two transiently expressed nuclear proteins, Krox-20 and Pax-2, were used as markers for the target cellular and anatomical structures. Rhombomere (r) expression patterns of Pax-2 (r4/r6) and Krox-20 (r3/r5) were maintained after cRA treatment, but r4 and r5 were substantially reduced in size. In untreated embryos, Krox-20 immunoreactive NCC derived from r5 migrated caudally around the developing otocyst to contribute to the third pharyngeal arch mesenchyme. In cRA-treated embryos, a subpopulation of NCC rostral to the otocyst also showed Krox-20 immunoreactivity, but there was a substantial reduction in Krox-20 post-otic NCC. Pax-2 immunoreactive NCC migrating from r4 to the second pharyngeal arch were substantially reduced in numbers in treated embryos. Alteration in the otic anlage included delayed invagination, abnormal relationship with the adjacent hindbrain epithelium, and altered expression boundaries for Pax-2. cRA-associated changes in the pharyngeal arch region due to cRA included truncation of the distal portion of the first arch and reduction in the size of the second arch. These alterations in hindbrain, neural crest, otic anlage, and pharyngeal arch morphogenesis could contribute to some of the craniofacial malformations in the macaque fetus associated with exposure to cRA.

Isotretinoin alters morphology, polarity, and motility of neural crest cells in culture

Migrating neural crest cells (NCCs) contribute to a diverse array of vertebrate head and neck structures. Retinoids are proven human and animal teratogens. To elucidate isotretinoin's effects, cranial and trunk neural folds were microdissected from chick embryos and cultured. Image analysis and immunostaining were used to quantitate cell behavior. We found that a higher proportion of Stage 8, 9, and 10 treated NCCs were rounded and clustered. Medians and means for cell area, perimeter, and elongation index were lower for treated cells from Stage 9 and 10 embryos, but not from Stage 8. Cumulative medians and means for changes in area and perimeter, and cell migration were similarly lower. Thus interference with the transitory basal activity of the cytoskeleton that adjusts and determines cell-substratum adhesion, spreading, elongation, and migration may be the mechanism by which isotretinoin acts on NCCs in slightly older embryos.

Effects of 13-cis-retinoic acid on hindbrain and craniofacial morphogenesis in long-tailed macaques (Macaca fascicularis)

Hindbrain and craniofacial development during early organogenesis was studied in normal and retinoic acid-exposed Macaca fascicularis embryos. 13-cis-retinoic acid impaired hindbrain segmentation as evidenced by compression of rhombomeres 1 to 5. Immunolocalization with the Hoxb-1 gene product along with quantitative measurements demonstrated that rhombomere 4 was particularly vulnerable to size reduction. Accompanying malformations of cranial neural crest cell migration patterns involved reduction and/or delay in pre- and post-otic placode crest cell populations that contribute to the pharyngeal arches and provide the developmental framework for the craniofacial region. The first and second pharyngeal arches were partially fused and the second arch was markedly reduced in size. The otocyst was delayed in development and shifted rostrolaterally relative to the hindbrain. These combined changes in the hindbrain, neural crest, and pharyngeal arches contribute to the craniofacial malformations observed in the retinoic acid malformation syndrome manifested in the macaque fetus.

Zinc pretreatment inhibits isotretinoin teratogenicity and induces embryonic metallothionein in CD-1 mice

Isotretinoin (ITR), a teratogen in many species, is associated with increased oxidative stress. Metallothionein (MT) is an important tissue antioxidant whose concentrations are induced by zinc. To study the role of supplemental Zn as an inducer of embryonic MT, we injected pregnant CD-1 mice subcutaneously with saline vehicle, or 20 or 40 mg/kg Zn on gestational day (GD) 6.5. After 48 h, embryonic MT concentrations increased in a dose-related manner (r = 0.64, P < 0.05) with Zn treatment. The possible protective role of Zn pretreatment against ITR teratogenicity was investigated in vivo and in vitro. CD-1 mice were pretreated with saline or Zn (20 and 40 mg/kg) on GD 8.5 and 9.5. ITR was administered to both groups of mice via three intragastric intubations of 100 mg ITR/kg at 4 h intervals on GD 10.5. On GD 18.5, Zn pre-treated mice demonstrated decreased ITR-mediated growth retardation, cleft palates and postpartum mortality. A reduction in embryonic MT concentrations was observed in mice exposed to ITR. Mouse embryos cultured on GD 8.5 with an addition of 15 micromol/L Zn for 48 h had a sixfold greater MT concentration (688 microg/g protein) than controls. The Zn pretreatment of cultured embryos prevented malformations and lessened growth retardation caused by 24 h exposure to 17 micromol/L ITR. These results suggest that Zn-mediated induction of MT in mouse embryos could protect against ITR teratogenicity.

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.

State of differentiation affects the response of endometrial adenocarcinoma cells to retinoic acid

BACKGROUND

Patients with poorly differentiated endometrial cancers have a worse prognosis than patients with well-differentiated endometrial cancers. If poorly differentiated cells in endometrial cancers could be induced to differentiate, they would be more responsive to hormonal manipulation, and survival rates would be increased. We set up an in vitro model system to examine the effects of retinoic acid on human endometrial adenocarcinoma cells at three states of differentiation.

METHODS

Cells were treated with pharmacological doses of 13-cis or all-trans retinoic acid (0.5 microM, 1 microM or 5 microM), and stained for mucins or actin filaments.

RESULTS

Untreated undifferentiated (KLE) cells lack organized actin filaments and cytoplasmic mucins. Treatment with 5 microM retinoic acid caused some reorganization of actin filaments, but cytoplasmic mucins remained absent. Moderately differentiated (RL95-2) cells differentiated the most with retinoic acid treatment evidenced by a dramatic reorganization of actin filaments and an increase in cytoplasmic mucins. Untreated or treated well differentiated (Ishikawa) cells possessed well organized actin filaments and exhibit positive staining for cytoplasmic mucins.

CONCLUSION

Retinoic acid causes cellular differentiation in less differentiated human endometrial adenocarcinoma cells.

A risk assessment of topical tretinoin as a potential human developmental toxin based on animal and comparative human data

BACKGROUND

Although topically applied all-trans-retinoic acid (tretinoin) undergoes minimal absorption and adds negligibly to normal endogenous levels, its safety in humans is occasionally questioned because oral ingestion of retinoids at therapeutic levels is known to entail teratogenic risks.

OBJECTIVE

To assess the actual potential for developmental toxicity from treatment with topical tretinoin.

METHODS

Risk assessments were conducted on four known human developmental toxicants (valproic acid, methotrexate, thalidomide, and isotretinoin) and a potential developmental toxicant (acetylsalicylic acid). The margin of safety for each chemical was calculated from the ratio of animal no-observed adverse effect levels to human lowest-observed adverse effect levels or estimated exposure doses.

RESULTS

The derived safety margin of more than 100 for topical tretinoin (with 2% absorption) contrasted sharply with the near unity values for valproic acid, methotrexate, thalidomide, and isotretinoin and was larger than that for acetylsalicylic acid.

CONCLUSION

These data support other epidemiologic and animal data that topical tretinoin is not a potential human developmental toxicant.

Tretinoin: a review of the nonclinical developmental toxicology experience

Tretinoin has been thoroughly evaluated for its potential as an embryofetal developmental toxicant. Oral tretinoin produces developmental anomalies in animal models; the minimal teratogenic dose is consistently 2.5 to 10 mg/kg. In contrast, topical application does not induce developmental malformations in laboratory animals. A structurally related compound, isotretinoin, is a potent toxicant in humans and animals; the lowest systemic dose that induces fetal anomalies varies more than 100-fold depending on the model. Oral isotretinoin is a more potent developmental toxicant than oral tretinoin in monkeys. Between-drug differences in the metabolism and transplacental transfer of the two retinoids account for the differences in toxicant potency. Pharmacokinetic studies reveal that absorption of tretinoin from the skin is poor and yields maternal plasma concentrations below the developmentally toxic threshold established after oral administration. Analysis of outcomes of developmental toxicology and pharmacokinetic studies suggests that the human risk of fetal anomalies is negligible after therapeutic application of topical tretinoin.

Similarities in genetic mental retardation and neuroteratogenic syndromes

Principles and mechanisms of neurobehavioral teratogenesis are used to show commonalities between manifestations of abnormal development consequent to genetic abnormality or teratogenic exposure. A comparison and contrast of both the neuropathological and neuropsychological characteristics of children with early embryonic exposure to isotretinoin (Accutane) or with selected mental retardation syndromes is presented. Putative mechanisms of retinoid teratogenesis through the disruption of normal retinoid-triggered embryogenesis and the alteration of homeobox gene expression are discussed. Interference with homeobox gene expression as an avenue to the perturbation of early developmental processes and the production of hindbrain and craniofacial abnormalities is then proposed as a common basis for the translation and expression of several genetic mental retardation syndromes. Finally, dose-response effects and other modulators of vulnerability to abnormal development are used to provide a conceptual framework for the understanding of variability in the expression of genetically caused abnormalities.

Retinoid-induced hypertriglyceridemia in rats is mediated by retinoic acid receptors

Retinoids in clinical use today are known to induce hypertriglyceridemia as one of their major side effects. The purpose of the present study was to determine, in an appropriate animal model, if retinoid-induced hypertriglyceridemia is mediated by retinoic acid receptors (RARs) and/or by retinoid X receptors (RXRs). Oral gavage of male Fischer rats with 13-cis-retinoic acid for 6 days caused a rapid and sustained increase in serum triglycerides that was reversible within 4 days posttreatment. In subsequent experiments, rats were treated by gavage once daily for 3 days with various retinoids, and serum triglyceride levels were determined 24 hr after the last treatment without fasting. All-trans- and 13-cis-retinoic acid, which can be converted to both RAR and RXR agonists, and 9-cis-retinoic acid, an RAR/RXR pan-agonist, caused dose-dependent increases in serum triglycerides at doses that did not cause weight loss or mucocutaneous toxicity. Ro 13-6298 and AGN 190121, two RAR-specific agonists, caused dose-dependent increases in serum triglycerides, although Ro 13-6298 only induced hypertriglyceridemia at weight-suppressive doses. Two RXR-selective agonists, LG100268 and AGN 191701, failed to induce hypertriglyceridemia or weight loss up to the highest doses tested. A structural isomer of AGN 190121 that does not activate RARs or RXRs, AGN 190727, did not induce hypertriglyceridemia. Hypertriglyceridemia induced by AGN 190121 was significantly inhibited by cotreatment with an RAR-selective antagonist, AGN 193109. Taken together, these data provide strong evidence that retinoid-induced hypertriglyceridemia is mediated, at least in part, by RARs. These data also suggest that RXR-specific agonists may have reduced potential to induce hypertriglyceridemia relative to RAR-active retinoids.

Retinoic acid embryopathy: case report and review of literature

Isotretinoin use as a treatment for acne has increased tremendously and, with it, the problems of associated birth defects. We feel that pathologists should be familiar with isotretinoin embryopathy and its pathogenesis in order to assist in differentiating this syndrome from other genetic syndromes that involve branchial arch defects, such as DiGeorge syndrome or velocardiofacial syndrome. Although selected autopsy findings have been presented in epidemiologic reports, to our knowledge a detailed autopsy report has not been published. We therefore wish to present a complete case study of isotretinoin embryopathy that illustrates the pathologic diagnostic criteria and correlates these with the clinical findings. Although the syndrome's major features are explained by the drug's effect on neural crest cells, it has been postulated that isotretinoin also affects other cells in the central nervous system. Our current case supports this theory and shows that these changes in the nervous system may present significant functional impairment, while not presenting visible anatomic changes on either imaging studies or routine histologic examinations.

Retinoids induced t-PA synthesis by C6 glioma cells--role in tumoral haemorrhagic necrosis

Treatment of rat C6 glioma with high doses of 13 cis-retinoic acid (cRA) was responsible for death related to haemorrhagic necrosis localized to the tumor. Our aim was to explore this adverse effect of retinoid treatment. We show that cRA-treated C6 glioma at 25 mg/kg/day for 18 days exhibits in vivo an increase T-PA activity, which is responsible for a localized tumor fibrinolytic activity. Production of t-PA is supported by specific enhancement of gene expression, as was shown by the increase in t-PA mRNA (x 2.3). This production is a direct effect of cRA when treating the tumor, since tumor cells themselves do not produce enough t-PA and treatment of control rats does not increase the t-PA level. T-PA production by rat C6 glioma is in vivo related to the specific synthesis of t-PA by the C6 cell-line. The stimulation of C6 cell-line by cRA in vitro is dose-dependent and reached a maximum for 3 and 30 microM at the 72nd h. So cRA-treated C6 glioma cells produce t-PA which appears to be the major species associated with the fibrinolytic activity-induced intra-tumoral haemorrhage after exposure to retinoid treatment.

[Feasibility study: concurrent 13-cis-retinoic acid, alfa-2a interferon and radiotherapy in the treatment of 23 patients with advanced cervix uteri epidermoid carcinoma]

The important therapeutic activity of 13-cRA and IFN-alpha-2a in carcinoma of squamous cells, cervical, without previous treatment, is confirmed. An unexpected result was the early toxicity of the biologic agents on the colon mucosa when they are combined with radiotherapy.

Placental transfer and developmental effects of 9-cis retinoic acid in mice

9-cis retinoic acid (RA) is a naturally occurring isomer of all-trans RA. While both isomers can bind with high affinity and activate RA receptors, only 9-cis RA is the specific ligand for the retinoid X receptors. 9-cis RA has also been shown to be much more potent than all-trans RA in inducing digit duplication in the chick embryo wing bud. To gain further insight into its mechanisms, here we investigated the teratogenic activity in pregnant mice of 9-cis RA and compared it with those of all-trans RA and 13-cis RA. Using frequency and severity of limb reduction defects as well as palatal clefts in the resultant fetuses as indicators, we found that orally administered 9-cis RA was one-half as potent a teratogen as all-trans RA. That 9-cis RA was intrinsically less active than all-trans RA was deduced by comparing the inhibitory activities of the two retinoids in the limb bud mesenchymal cell micromass cultures using chondrogenesis as an end-point. Since placental transfer of cis isomers of RA is generally poor, we monitored the identities and amounts of retinoids in the embryo after administration of 9-cis RA to the mother. We found that 9-cis RA undergoes extensive metabolism and isomerization during absorption resulting in a number of metabolites in the maternal circulation within 30 min after administration. Although some of these metabolites remain to be identified, the most abundant RA isomers in the plasma coeluted with 13-cis RA.(ABSTRACT TRUNCATED AT 250 WORDS)

Maternal toxicokinetics, metabolism, and embryo exposure following a teratogenic dosing regimen with 13-cis-retinoic acid (isotretinoin) in the cynomolgus monkey

The maternal pharmacokinetics, metabolism, and placental transfer of 13-cis-retinoic acid (isotretinoin) have been determined in the cynomolgus monkey using a dosing regimen which had been previously shown to result in retinoid-specific teratogenic effects [Hummler et al. (1990) Teratology 42:263-272]. The drug (2.5 mg/kg body weight) was administered by nasogastric intubation once a day between gestational days (GD) 16-26, and twice a day between GD 27-31. Maternal plasma kinetics were determined following dosing on GD 26 and GD 31, and placental transfer was studied following the last dose on GD 31. The plasma half life of 13-cis-retinoic acid in the monkey (13.2 h) was comparable to that in the human. The main plasma metabolite in the monkey was the 13-cis-4-oxo-retinoic acid which occurred at levels lower or comparable to those of the administered drug. During multiple dosing, this metabolite accumulated to the same degree as the parent drug. All-trans-retinoic acid was present in maternal plasma in very low concentrations (2% of 13-cis-retinoic acid). The beta-glucuronides of all-trans- and 13-cis-retinoic acid were further minor plasma metabolites. 13-cis-retinoic acid and its 4-oxo-metabolite reached the monkey embryo slowly but extensively during organogenesis and reached 24 h-AUC values of 956 and 590 ng.h/g embryo wet weight, resulting in embryo/maternal plasma concentration ratios of 0.41 and 0.33, respectively. The AUC value of all-trans-retinoic acid (316 ng.h/g) was only raised approximately 40% above the endogenous AUC level (225 ng.h/g); only at two time periods examined were the embryonic all-trans-retinoic acid concentrations above endogenous levels (at 4 h and 8 h; P < 0.01 and < 0.05, respectively; Student's t-test). The beta-glucuronides of all-trans- and 13-cis-retinoic acid were not detected in the embryo. Accumulation of 13-cis-retinoic acid and the 4-oxo-metabolite during the twice-per-day dosing regimen was apparent both in maternal plasma and embryo. An interspecies comparison suggests that the half life as well as the metabolic pattern of 13-cis-retinoic acid in plasma were similar in monkey and human: 13-cis-4-oxo-retinoic acid was the main metabolite in both species and the beta-glucoronides as well as all-trans-retinoic acid were minor metabolites. However, the plasma AUC values of the administered drug and particularly the 4-oxo-metabolite were found to be lower in the monkey as compared to the human.(ABSTRACT TRUNCATED AT 400 WORDS)

Comparative teratology and transplacental pharmacokinetics of all-trans-retinoic acid, 13-cis-retinoic acid, and retinyl palmitate following daily administrations in rats

The retinoids are teratogenic in a wide variety of species. In the rat, 13-cis-retinoic acid and retinyl palmitate are significantly less potent teratogens than all-trans-retinoic acid. This investigation questioned whether differing teratogenic potencies of these moieties can be correlated with the concentrations of these drugs and/or metabolites in the embryonic compartment. Approximately equipotent teratogenic doses of these three retinoids were administered and the pharmacokinetics in maternal plasma and embryo of the most prevalent vitamin A metabolites were measured. The glucuronides of the respective retinoids were the predominant metabolites in the maternal plasma, but were not detected in the embryo. Also, the transport of 13-cis-retinoic acid across the placenta occurred to a much lesser extent than the transport of all-trans-retinoic acid. Administration of either all-trans- or 13-cis-retinoic acid causes a depression in the endogenous retinol concentration. This depression is more pronounced in the maternal plasma than in the embryo. The depression of the retinol level in both plasma and embryo after 13-cis-retinoic acid administration (75 mg/kg/day) was greater than the depression after all-trans-retinoic acid (6 mg/kg/day), corroborating the inferential teratological data that the 13-cis-retinoic acid dose was more embryotoxic than the all-trans-retinoic acid dose. Although the dose of all-trans-retinoic acid was less embryotoxic than that of either 13-cis-retinoic acid or retinyl palmitate, the embryonic exposure to all-trans-retinoic acid was considerably larger, as determined by maximum concentration or area under the concentration-versus-time curve, after administration of all-trans-retinoic acid than after either retinyl palmitate or 13-cis-retinoic acid application. These results suggest that embryonic retinoids other than all-trans-retinoic acid--including the administered substances themselves--are important in the teratogenic process induced by 13-cis-retinoic acid and retinyl palmitate.

Developmental neurotoxicity induced by therapeutic and illicit drugs

The developmental neurotoxicity of phenytoin, isotretinoin, and methamphetamine has been reviewed to illustrate effects from both therapeutic and illicit drugs to which people are exposed and which either induce or show the potential for inducing learning disabilities following in utero exposure. In each case both human and experimental animal data are presented and compared where possible. The findings point to several conclusions. First, some drugs in current use induce developmental neurotoxicity, and it cannot safely be assumed that there are not more as yet unidentified. Second, of the types of neurotoxicity induced by drugs, learning disabilities figure prominently. Third, the effects observed are dependent on both the drug's mechanism of action and the period of brain development during which exposure occurs. Fourth, with the exception of CNS teratogens, it is not yet possible to predict which periods of brain development are the most vulnerable for the induction of learning disabilities, as seen by the different patterns of critical periods for phenytoin and isotretinoin compared to methamphetamine. Fifth, as seen with isotretinoin, existing drugs that cause developmental neurotoxicity are not the only problem; new drugs with such effects are still being introduced. Sixth, only a small fraction of the drugs currently in use have ever been examined for developmental neurotoxicity; hence, the full scope of the problem cannot even be accurately estimated based on current information. It is concluded that prevention of new cases caused by drugs such as isotretinoin should be a high priority for future regulatory action.

Retinoid chemoprevention studies in upper aerodigestive tract and lung carcinogenesis

Chemoprevention is a clinical strategy to block or reverse carcinogenesis before the development of invasive cancer. Studies of chemoprevention in the lungs and upper aerodigestive tract have relied on the field carcinogenesis hypothesis, which predicts that diffuse epithelial injury will result from exposure of that epithelium to carcinogens. This hypothesis is supported by the frequent occurrence of multiple primary tumors within the exposed field. In addition, the understanding of carcinogenesis as a multistep process supports the use of interventions in damaged epithelium before the development of clinically invasive cancer. Current efforts are focused on applying to chemoprevention studies the increasing knowledge of the molecular events in carcinogenesis. In our program, clinical trials in lung and head and neck chemoprevention have focused on individuals with evidence of field carcinogenesis, i.e., a history of previous epithelial cancer or the presence of premalignant lesions. These trials include studies to develop clinically applicable intermediate markers of carcinogenesis and large Phase III trials to evaluate the efficacy of the retinoid isotretinoin in preventing second primary tumors following head and neck or lung cancers.

Teratogenicity and transplacental pharmacokinetics of 13-cis-retinoic acid in rabbits

No embryotoxic or teratogenic effects, considered to be treatment related, were observed in rabbits after daily oral doses of 3 mg/kg of 13-cis-retinoic acid (13-cis-RA) from Day 8 to Day 11 of gestation. In contrast, treatment with 15 mg/kg/day significantly increased the rate of fetal resorptions (22%) and 13 out of 68 surviving fetuses (16%) were malformed. Pharmacokinetic studies with both dosing regimens of 13-cis-RA in pregnant rabbits showed that on Day 11 of gestation, high concentrations of parent compound, 13-cis-RA, and its major metabolite, 13-cis-4-oxoRA, existed in maternal plasma. Much lower concentrations were found for all-trans-4-oxoRA and all-trans-RA. The area under the concentration-time curve (AUC) of all-trans-RA following the 15 mg/kg/day dosing regimen of 13-cis-RA was only 1.2% that of parent compound 13-cis-RA. At this dose, embryo levels of 13-cis-RA, 13-cis-4-oxoRA, and all-trans-4-oxoRA were 2.5-, 4.7-, and 3.6-fold higher by AUC comparison (24-hr period of Day 11) compared with the dose of 3 mg/kg. However, embryo levels of all-trans-RA were virtually identical at both doses and were, in fact, somewhat lower than endogenous concentrations measured in untreated rabbit embryos. In contrast to mice, where isomerization from 13-cis- to all-trans-RA was suggested to be crucial for the teratogenic action of 13-cis-RA, we found that the teratogenic action of 13-cis-RA (15 mg/kg/day) in rabbits is characterized by increased whole embryo concentrations of 13-cis-RA, 13-cis-4-oxoRA, and all-trans-4-oxoRA, but not of all-trans-RA.

The high sensitivity of the rabbit to the teratogenic effects of 13-cis-retinoic acid (isotretinoin) is a consequence of prolonged exposure of the embryo to 13-cis-retinoic acid and 13-cis-4-oxo-retinoic acid, and not of isomerization to all-trans-retinoic acid

Previous studies suggested that the rabbit is much more susceptible to the teratogenic action of 13-cis-retinoic acid (13-cis-RA) than the mouse or the rat, while the teratogenicity of all-trans-RA was comparable in these species. In the present study we investigated if pharmacokinetics can explain these species- and structure-related differences. The embryotoxic and teratogenic potential of all-trans-retinoic acid (all-trans-RA) and 13-cis-RA were evaluated in the Swiss hare rabbit after oral administration of daily doses of the two drugs throughout organogenesis, from gestation day (GD) 6 to 18 (plug day = GD 0). All-trans-RA was given at dose levels of 0.7, 2 or 6 mg/kg body weight per day and 13-cis-RA at 3, 7.5 or 10 mg/kg per day. The doses needed to elicit a minimum teratogenic response were found to be 6 mg/kg per day for all-trans-RA and 10 mg/kg per day for 13-cis-RA. Using these doses, transplacental pharmacokinetics of all-trans- and 13-cis-RA were performed. Pregnant rabbits were treated once daily from GD 7 to 12 and plasma and embryo samples were collected for HPLC analysis at various time intervals after the final dose. The main plasma metabolites of all-trans- and 13-cis-RA were all-trans-beta-glucuronide (all-trans-RAG) and 13-cis-4-oxo-RA, respectively. The elimination of 13-cis-RA and its metabolites from maternal plasma were much slower than of all-trans-RA resulting in accumulation of the 13-cis-isomers in plasma. Marked differences in the placental transfer of the two drugs and their metabolites were observed. All-trans-RA and all-trans-4-oxo-RA were efficiently transferred to the rabbit embryo, reaching concentrations similar to the plasma levels. On the contrary, the 13-cis-isomers reached the embryo to a lesser extent. Despite its limited placental transfer, a considerable embryonic exposure to 13-cis-RA and 13-cis-4-oxo-RA was noticed after treatment with isotretinoin, as indicated by their area-under-the-concentration-time-curve (AUC) values in the embryo, which were in the same range as the corresponding AUC value of all-trans-RA after treatment with the all-trans-isomer.(ABSTRACT TRUNCATED AT 400 WORDS)

Toxic effects of systemic retinoids on meibomian glands

Systemic use of retinoids is common in the treatment of various dermatological disorders. Blepharitis and conjunctivitis have been reported in 20-45% of the patients following systemic treatment with 13-cis-retinoic acid. Our purpose was to study the histopathological changes in the eyelids caused by long-term systemic treatment of female New Zealand rabbits with isotretinoin (2 mg/kg) and etretinate (2 mg/kg). The histopathological evaluation showed degenerative changes in the meibomian gland acini, leading to cell necrosis and a decrease in the basaloid cells lining the acini walls. No evidence of acute or chronic inflammatory reaction was noted.

13-cis-retinoic acid plus interferon-alpha: a phase II clinical study in squamous cell carcinoma of the lung and the head and neck

Retinoids and interferon-alpha (IFN-alpha) have been shown to have a synergetic antiproliferative and differentiative effect on many cell lines, and in combination they have already been tested with some success in the treatment of some tumors. We investigated the tolerance and efficacy of high dose 13-cis-retinoic acid (2 mg/kg/day) and IFN-alpha in the treatment of advanced squamous cell carcinoma of the lung and of the head and neck. No partial or complete response was observed in the 10 patients treated. The toxicity was unusual and mild to moderate considering the dose of retinoid given. This observation leads us to suspect that IFN-alpha may alleviate some of the side effects of the retinoid, and is of interest in the design of future clinical trials.

Teratogenicity of 13-cis retinoic acid and phenobarbital sodium in CF-1 mice

The teratogenicity of 13-cis-retinoic acid (RA) either administered alone or following pretreatment with phenobarbital sodium (PB), was assessed. Groups of gravid CF-1 mice were administered dosages of either 10, 100, 200, or 400 mg/kg of RA orally on either days 11, 12 or 13 of gestation, in order to determine structural alterations. In addition, separate groups of mice were orally pretreated with 80 mg/kg/day of PB on days 7 through 10 of gestation prior to the administration of RA. Skeletal alterations attributed to maternal administration of either 100, 200 or 400 mg/kg of RA on days 11-13 included delayed ossification of the limbs and supraoccipital bone, the presence of extra ribs, and various sternebral defects. Soft tissue alterations included cleft palate and dilation of the renal pelves which occurred following maternal exposure on days 11 and 12-13, respectively. Significant decreases in the incidence of cleft palate and delayed ossification of the limbs were observed in those dams administered RA on days 11 or 12, respectively, following prior treatment with PB. These data suggest that administration of PB, a prototypical hepatic microsomal enzyme inducer, may partially antagonize the teratogenicity of RA.

Hypercalcemia: a dose-limiting toxicity associated with 13-cis-retinoic acid

PURPOSE

13-cis-Retinoic acid (cis-RA) has efficacy in the treatment and prevention of certain malignancies. In vitro effects against neuroblastoma include induction of differentiation, inhibition of proliferation, and decreased N-myc expression. We hypothesized that cis-RA may be effective against minimal residual disease in neuroblastoma patients. A phase I trial to determine the maximal tolerated dosage and toxicity of cis-RA in pediatric patients with neuroblastoma after bone marrow transplantation was initiated.

PATIENTS AND METHODS

Forty-nine pediatric patients (status post-bone marrow transplant for neuroblastoma) were treated for 14 days with oral cis-RA in escalating doses from 100 to 200 mg/m2/day followed by a 14-day rest period for up to 12 months.

RESULTS

In three of 39 patients (7.7%) evaluable for calcium levels, hypercalcemia (12.6-18.7 mg/dl) was the dose-limiting toxicity. Grade 1-3 hypercalcemia occurred in nine of 39 patients (23%). The overall incidence of hypercalcemia was 31% (12 of 39). Only one patient was symptomatic due to the hypercalcemia, with arthralgias and myalgias. The hypercalcemia resolved with temporary discontinuation of the drug and a 25% dose reduction for subsequent courses.

CONCLUSIONS

Hypercalcemia is a novel dose-limiting toxicity for cis-RA. Patients receiving high doses of cis-RA should have monitoring of serum calcium levels.

13-cis-retinoic acid and hepatic steatosis in rats

The effect of administration of 13-cis-retinoic acid (100 mg/kg diet) on lipid metabolism was examined in male rats fed either a 20% casein + 0.3% methionine diet, a 20% casein diet, a 10% casein + 0.3% methionine diet, or a 10% casein + 0.6% methionine diet for 10 days. Hepatic triglyceride concentrations of rats fed either 10% casein diet were 3-fold greater than animals receiving diets containing 20% casein. The addition of 13-cis-retinoic acid to the diet further increased the total hepatic lipid (43-56%) and triglyceride (approximately 2-fold) concentrations in rats fed the 10% casein diets. 13-cis-Retinoic acid supplementation did not alter the total liver lipid or triglyceride concentrations in rats fed either of the 20% casein diets. Thus, under specific dietary conditions, the administration of 13-cis-retinoic acid resulted in a marked accumulation of hepatic lipids which did not appear to be related to the total methionine content of the diet nor to the hepatic concentrations of S-adenosylmethionine and glutathione. In addition, all four groups of 13-cis-retinoic acid-fed rats exhibited elevations in the concentration of serum triglycerides, and 10-20% reductions in serum cholesterol concentrations.