Evaluation of the protective effects of curcumin-rich turmeric (Curcuma longa) extract against isotretinoin-induced liver damage in rats

AIM

The aim of this study was to evaluate the protective effect of curcumin-rich turmeric (CRT) extract against isotretinoin (ISO)-induced liver damage through routine biochemical parameters and oxidative stress parameters that indicate liver damage.

MATERIAL AND METHOD

42 albino Wistar rats of 200 g were randomly grouped as Group I: Healthy control, Group II: Sunflower oil, Group III: Curcumin 200 mg/kg, Group IV: ISO control groups (7.5 mg/kg), Group V: Curcumin 50 mg/kg + ISO 7.5 mg/kg, Group VI: Curcumin 100 mg/kg + ISO 7.5 mg/kg, Group VII: Curcumin 200 mg/kg + ISO 7.5 mg/kg. At the end, after the rats were killed, their blood and liver tissues were collected. ALT and AST levels in serum; superoxide dismutase activity (SOD), GSH, and MDA levels in liver tissue were determined.

RESULTS

Our results showed that ALT, AST, and MDA levels increased, and SOD and GSH levels decreased in the ISO-administered group compared to the healthy control group. CRT 50, 100, and 200 mg/kg groups were compared to ISO group. A dose-dependent increase in protective effect was observed. A decrease in ALT, AST, and MDA levels, and an increase in SOD and GSH levels were determined. A protective effect was found at all doses. The best protective effect was in the CRT 200 mg/kg group.

CONCLUSION

CRT extract can be considered a candidate herbal medicine for the elimination of liver damage in individuals using ISO. However, further experimental and clinical validation should be studied.

Assessment of the In Vivo Reprotoxicity of Isotretinoin in Sprague-Dawley Male Rat

BACKGROUND

Isotretinoin (ISO) belongs to a family of drugs called retinoids. It is the most effective drug prescribed by dermatologists for the treatment of the inflammatory disease, acne vulgaris. A significant barrier to the use of ISO has worries regarding its adverse effect profile. Despite the well-recognized reproductive toxicity and teratogenicity in females, there is no warning related to the use by male patients in the medication prospectus. Current data on the effects on human male fertility is contradictory and inconclusive.

OBJECTIVES

This study was undertaken to investigate the potential effects of ISO oral doses in the Sprague-Dawley male rat germ cells using the sperm morphology assay. Also, the serum levels of the follicle-stimulating hormone (FSH), luteinizing hormone (LH), and testosterone were measured.

METHODS

The rat groups were given varying ISO doses via gastric gavage for seven consecutive days. The epididymis sperm specimens were microscopically examined for the following reproductive toxicity parameters: sperm concentration, examined viability, motility, and morphology. The serum FSH, LH, and testosterone levels were measured by using the corresponding enzyme-linked immunosorbent assay (ELISA) kit. The data were analyzed statistically by one-way analysis of variance (ANOVA) followed by the Tukey test at P ≤ 0.05 significance level.

RESULTS

The results indicated that the drug did not significantly increase the sex hormone levels but notably affected both the sperm quantity and quality.

CONCLUSION

These observations suggest that ISO was reprotoxic, and future therapies should be further reassessed.

Toxicity, Genotoxicity, and Carcinogenicity of Isotretinoin

BACKGROUND

Acne is a chronic inflammatory disease mainly observed in adolescence, but it can also be seen during the neonatal, infantile, pre-pubertal, and adult periods. Isotretinoin (13-cis-retinoic acid) is a first-generation retinoid and is the most effective treatment for acne vulgaris.

OBJECTIVE

The present study has been systematically designed to figure out the toxic, genotoxic, and carcinogenic activities of isotretinoin.

METHODS

In this study, a systematic approach was followed by focusing on the possible links between these topics. The search of the databases was carried out author in accordance with the guidelines of the Centre for Reviews and Dissemination (2009) developed by York University National Institute of Health Research. The search was concentrated on the Web of Science, PubMed, Science Direct, Scopus, EBSCO Host, and Google Scholar databases.

RESULTS

Isotretinoin was found as a toxic agent in all studies. All researchers proposed that apoptosis is the only pathway of adverse effects of isotretinoin. However, genotoxicity, teratogenicity, and carcinogenicity information of isotretinoin is very limited and controversial.

CONCLUSION

More detailed studies need to clarify the genotoxic and carcinogenic potential of isotretinoin. Patients should be informed correctly, the risks of treatment should be explained, and awareness should be raised.

Optimizing Isotretinoin Treatment of Acne: Update on Current Recommendations for Monitoring, Dosing, Safety, Adverse Effects, Compliance, and Outcomes

Acne vulgaris is the most common skin disease treated by dermatologists. It can be severe and result in permanent scars. Isotretinoin is the most effective treatment for acne and has the potential for long-term clearance. Prescribing and monitoring protocols can vary widely among prescribers. Recent studies, reports, and consensus statements help shed light on optimizing the use of isotretinoin for acne. A recent literature review is summarized in this article to help the practitioner optimize isotretinoin use for acne. The article outlines the advantages and disadvantages of standard, high-dose, and low-dose isotretinoin regimens; discusses the current status of controversies surrounding isotretinoin (including depression/suicide, pregnancy, and inflammatory bowel disease); reviews monitoring recommendations and treatment for hypertriglyceridemia and elevated transaminase levels; and discusses common adverse effects seen with isotretinoin, along with their treatment and prevention.

The effects of microduplication 1q21.1 and in-utero isotretinoin exposure

The impact of in-utero isotretinoin exposure has been widely reported, with many affected pregnancies failing to reach term.^{1 2} Due to the low numbers of in-utero isotretinoin exposed pregnancies, the interactions between this drug and rare genetic defects such as microduplication 1q21.1 are unclear, particularly how they might manifest phenotypically. We present this case of in-utero isotretinoin exposure occurring in a child with microduplication 1q21.1. The child was born with congenital abnormalities which did not fit into a single syndrome. Regrettably in-utero exposure to isotretinoin continues to occur. We hope this case will trigger further discussion on the dangers of dispensing Isotretinoin without ensuring stringent pregnancy testing and its potential interaction with genetic abnormalities, in particular with microduplication 1q21.1.

Developmental Neurotoxic Effects of Percutaneous Drug Delivery: Behavior and Neurochemical Studies in C57BL/6 Mice

Dermatosis often as a chronic disease requires effective long-term treatment; a comprehensive evaluation of mental health of dermatology drug does not receive enough attention. An interaction between dermatology and psychiatry has been increasingly described. Substantial evidence has accumulated that psychological stress can be associated with pigmentation, endocrine and immune systems in skin to create the optimal responses against pathogens and other physicochemical stressors to maintain or restore internal homeostasis. Additionally, given the common ectodermal origin shared by the brain and skin, we are interested in assessing how disruption of skin systems (pigmentary, endocrine and immune systems) may play a key role in brain functions. Thus, we selected three drugs (hydroquinone, isotretinoin, tacrolimus) with percutaneous excessive delivery to respectively intervene in these systems and then evaluate the potential neurotoxic effects. Firstly, C57BL/6 mice were administrated a dermal dose of hydroquinone cream, isotretinoin gel or tacrolimus ointment (2%, 0.05%, 0.1%, respectively, 5 times of the clinical dose). Behavioral testing was performed and levels of proteins were measured in the hippocampus. It was found that mice treated with isotretinoin or tacrolimus, presented a lower activity in open-field test and obvious depressive-like behavior in tail suspension test. Besides, they damaged cytoarchitecture, reduced the level of 5-HT-5-HT1A/1B system and increased the expression of apoptosis-related proteins in the hippocampus. To enable sensitive monitoring the dose-response characteristics of the consecutive neurobehavioral disorders, mice received gradient concentrations of hydroquinone (2%, 4%, 6%). Subsequently, hydroquinone induced behavioral disorders and hippocampal dysfunction in a dose-dependent response. When doses were high as 6% which was 3 times higher than 2% dose, then 100% of mice exhibited depressive-like behavior. Certainly, 6% hydroquinone exposure elicited the most serious impairment of hippocampal structure and survival. The fact that higher doses of hydroquinone are associated with a greater risk of depression is further indication that hydroquinone is responsible for the development of depression. These above data demonstrated that chronic administration of different dermatology drugs contributed into common mental distress. This surprising discovery of chemical stressors stimulating the hippocampal dysfunction, paves the way for exciting areas of study on the cross-talk between the skin and the brain, as well as is suggesting how to develop effective and safe usage of dermatological drugs in daily practice.

Short term 13-cis-retinoic acid treatment at therapeutic doses elevates expression of leptin, GLUT4, PPARgamma and aP2 in rat adipose tissue

Temporary defects in the plasma lipid and glucose homeostasis are frequent complication accompanying chronic treatment with 13-cis-retinoic acid (13cRA). White adipose tissue acts as an endocrine organ producing a variety of hormones (adipocytokines) including leptin, adiponectin, tumor-necrosis factor alpha (TNFalpha) and angiotensin II (Ang II), which influence lipid metabolism, systemic insulin sensitivity and inflammation. To study the effect of a short-term 13cRA administration on metabolism of epididymal fat tissue, we treated Wistar rats with five identical therapeutic doses of 13cRA (0.8 mg/kg b.w.) by gavage during a period of 10 days. Expression of adiponectin, leptin, TNFalpha and selected proteins such as adipocyte fatty acid binding protein (aP2), insulin-dependent glucose transporter GLUT4, peroxisome proliferator-activated receptor gamma (PPARgamma) and retinoid X receptors (RXRs) was investigated using RT-PCR. Short-term treatment with therapeutic doses of 13cRA caused significant increase of the aP2, PPARgamma and moderately RXRalpha gene expression. Similarly, the relative amount of mRNA for leptin and GLUT4 was increased, while the TNFa transcript was decreased after treatment with 13cRA. The gene expression and plasma concentration of adiponectin were without any significant changes. Since local adipose renin-angiotensin system (RAS) has been presumed to be involved in the regulation of fat tissue metabolism, we also investigated the gene expression of RAS components in epididymal fat depot. Our data has shown that 13cRA elevated Ang II receptor type 1 (AT(1) receptor)--at both, mRNA and protein level. Thus, our results demonstrate that short-term 13cRA treatment is inducing alterations in fat tissue metabolism in relation to stimulated adipogenesis.

Photocarcinogenesis of topical tazarotene and isotretinoin alone and in combination with valproic acid in hairless mice

Retinoids and the histone deacetylase inhibitor valproic acid have shown anticancer properties, but the photocarcinogenic or photoprotective effect is unclear. Therefore, we investigated whether a topical formulation of valproic acid is photocarcinogenic or photoprotective in hairless female C3.Cg/TifBomTac immunocompetent mice exposed to simulated solar radiation (SSR) and whether valproic acid changes the effect of the retinoids: tazarotene and isotretinoin. The products were applied on the dorsal skin of 400 mice (five times weekly) followed by SSR (three times weekly) 3-4 h after the application. This was performed during 12 months or until death. Tumors appeared sooner in groups treated with tazarotene and isotretinoin compared with that of the group treated with valproic acid and the control group. The present study shows that valproic acid alone is not photocarcinogenic or photoprotective in hairless mice. When valproic acid is combined with tazarotene or isotretinoin, it does not change their photocarcinogenicity significantly.

Sequence-dependent antitumor effects of differentiation agents in combination with cell cycle-dependent cytotoxic drugs

PURPOSE

Combination of two differentiation agents such as phenylbutyrate (PB) and 13-cis-retinoic acid (CRA) has been shown to have an additive inhibitory effect on tumor growth in preclinical studies. In this report we explored the hypotheses that these "cytostatic" agents may have a greater antitumor activity in combination with "cytotoxic" compounds and their biological effect may be sequence-dependent.

METHODS

The antitumor activity of combination of PB and CRA with paclitaxel (TX ) and doxorubicin (DOXO) on human prostate and colon carcinoma cell lines was assessed both in vitro and in vivo. The effect on cell cycle, apoptotic rate, cyclin expression and induction of p21 expression was also determined.

RESULTS

Following treatment of tumor cells with PB + CRA + TX or DOXO, inhibition of tumor cell growth was greatly enhanced as compared to PB + CRA, TX or DOXO alone, with >90% growth inhibition. However, when the cells were pretreated with PB + CRA followed by TX or DOXO, the enhanced inhibition was abolished suggesting a protective effect to this sequence. Interestingly treatment with PB + CRA restored sensitivity to DOXO in PC-3 human prostate cancer cell line. PB + CRA induced p21 expression and cell-cycle arrest in G1 phase, while TX and DOXO induced G2/M arrest. p21 and p53-deficient colon carcinoma cell lines were more sensitive to the effect of PB + CRA and TX as single agents and in combination, as compared to the wild type cells. When p21-deficient cells were pretreated with PB + CRA followed by TX the protective effect was still observed. Treatment of tumor cells with combination of these drugs induced cell cycle delay at multiple mitotic checkpoints before undergoing apoptosis. Tumor growth was significantly inhibited and delayed in animals treated with either TX or concomitantly with TX and PB + CRA as compared to control. Animals treated with all three agents demonstrated further growth inhibition or delay than the TX alone or PB + CRA arm.

CONCLUSIONS

These results suggest a rational therapeutic approach for combination of differentiation-inducing agents with cytotoxic drugs given concomitantly, but not sequentially.

Serum levels of albumin, triglycerides, total protein and glucose in rats are altered after oral treatment with low doses of 13-cis-retinoic acid or all-trans-retinoic acid

Currently used to treat severe acne, 13-cis-retinoic acid (13-cis-RA) is under investigation for its anticancer effects as is the isomer, all-trans-retinoic acid (all-trans-RA). Here, the effects of oral 13-cis-RA or all-trans-RA treatment on serum chemistry, leptin and adiponectin levels were evaluated. Adult Sprague-Dawley rats were gavaged once daily for 7 consecutive days with 13-cis-RA (7.5 or 15 mg kg(-1)), all-trans-RA (10 or 15 mg kg(-1)) (n=24/sex/dose), or soy oil (n=16/sex) and blood was sampled 30-480 min after the last gavage. The body weight was unaffected; however, the liver/body weight ratios were increased by both doses of all-trans-RA. Sex differences were noted for levels of cholesterol, creatine, triglycerides, albumin, alanine aminotransferase and total protein. Both doses of all-trans-RA reduced albumin levels to approximately 90% of the control and total protein levels to approximately 93% of the control while substantially elevating triglyceride levels to approximately 66%-99% above the control. Additionally, triglyceride levels of the 15 mg kg(-1) 13-cis RA group were approximately 62% higher than the controls and total protein levels were approximately 5% less. Glucose levels were affected by sex and RA treatment in that males treated with 15 mg kg(-1) of 13-cis-RA or 10 mg kg(-1) all-trans-RA had lower (13%-19%) levels than the same-sex controls; however, females were not similarly affected. Neither 13-cis-RA nor all-trans-RA treatment had significant effects on the levels of blood urea nitrogen, aspartate amino transferase, leptin or adiponectin. On a mg kg(-1) basis, all-trans-RA was more potent than 13-cis-RA. These results replicate previous findings of RA-induced increased triglyceride levels. Additionally, several new findings indicate there may be sex-specific effects of RA treatment. Finally, neither treatment appeared to alter the typical diurnal cycles of these endpoints.

Oral treatment with retinoic acid decreases bone mass in rats

13-cis-retinoic acid (13-cis-RA, isotretinoin) is used to treat severe recalcitrant acne. Other retinoids have adverse effects on bone. Recent studies of human patients treated with 13-cis-RA have had varying results, perhaps because of variability among patients and the lack of control groups. The effects of retinoids have been studied in rodents, but little information is available regarding the effects of clinically relevant retinoid doses as evaluated by use of bone densitometric techniques. We treated rats for 15 or 20 wk with 13-cis-RA, all-trans-RA, or soybean oil (control) by gavage. We used dual-energy X-ray absorptiometry, histomorphometry, and histologic evaluation to evaluate effects on bone. Spontaneous long bone fractures occurred in some rats treated with 15 mg/kg all-trans-RA daily. Bone mineral density, bone mineral content, bone diameter, and cortical thickness of the femur were reduced in rats treated daily with 10 or 15 mg/kg all-trans-RA or 30 mg/kg 13-cis-RA. The lumbar spine was not affected. Although the effects of 13-cis-RA were not as dramatic as those of all-trans-RA, further study of the effects of 13-cis-RA on long bones is warranted.

Coping with the isotretinoin registry

The isotretinoin registry has arrived. It has a lofty goal of preventing all isotretinoin pregnancies. How we got to this point and what the registry means to prescribers and patients have many dermatologists confused and concerned. Will it be burdensome, will it preclude the use in most offices of this most important drug? Will it breed a new group of "isotretinologists" who are willing to take on the challenge? This article endeavors to answer these questions and to put most concerns at rest. The new system seems ultimately to have few changes compared to the risk management program we are already (technically) following. The difference is that compliance with all the rules will be monitored and mandatory. The system seems user friendly, is accessible to the computer-savvy as well as those of us still addicted to telephone, and may well turn out to be much fuss made over minimal hassle. What is clear is that this is likely our last chance to save this wonderful drug from oblivion. It is time for dermatologists to step to the plate and do what is in the best interest of their patients.

Four weeks of oral isotretinoin treatment causes few signs of general toxicity in male and female Sprague–Dawley rats

Despite widespread use of isotretinoin for its anti-acne effects and its current evaluation in clinical trials as a cancer treatment, little is known about its general toxicity in adult nonpregnant animals, particularly after oral administration which mimics the human route. Here, adult male and female Sprague-Dawley rats were gavaged daily with 0 (soy oil), 7.5, or 15 mg/kg isotretinoin for 28 days during which time body weight, food/water intake, and estrous phase were measured. At sacrifice, organ weights were collected and concentrations of dopamine (DA), serotonin and metabolites were measured in frontal cortex, striatum, hippocampus, and diencephalon. Food intake was mildly decreased in both treated groups (approximately 15% in males and 7% in females); however, body weight and water consumption were unaffected. The estrous cycle appeared slightly affected (i.e., lengthened by 15 mg/kg, and both treated groups appeared to have less time in diestrus and more time in estrus). Kidney/body weight ratio was decreased by 7.5 and 15 mg/kg isotretinoin and spleen/body weight ratio was increased in the 7.5 mg/kg group. Males of the 7.5 mg/kg group exhibited significantly higher gonad/body weight ratios than did same-sex controls. Concentrations of monoamine and metabolites in the frontal cortex and diencephalon were unaffected. Nor were striatal DA and DOPAC concentrations affected; however, there were isolated effects on striatal HVA and 5-HIAA. Hippocampal DA concentrations were marginally increased. These data indicate mild effects resulting from oral isotretinoin treatment at doses which likely produce serum levels within the range of humans.

Chronic Oral Treatment with 13-cis-Retinoic Acid (Isotretinoin) or all-trans-Retinoic Acid Does Not Alter Depression-Like Behaviors in Rats

Oral treatment with the anti-acne drug Accutane (isotretinoin, 13-cis-retinoic acid) has been associated with suicide ideation and depression. Here, depression-like behaviors (i.e., behavioral despair and anhedonia) were quantified in adult Sprague-Dawley rats gavaged daily beginning at postnatal day (PND) 82 with 13-cis-RA (7.5 or 22.5 mg/kg) or all-trans-retinoic acid (10 or 15 mg/kg ). Tested at PND 130-131 in the Forced Swim Test, 7.5 mg/kg 13-cis-RA marginally decreased immobility and slightly increased climb/struggle durations whereas neither all-trans-retinoic acid group differed from controls. Voluntary saccharin solution (0.03%) intake at PND 102-104 and PND 151-153 was not different from controls in any treated group, although all RA-treated groups had lower intakes. Swim speed in a water maze at PND 180 was similar across groups, indicating no RA-induced differences in physical ability. Open field activity was mildly decreased at PND 91 in 7.5 mg/kg-treated males only, but it was within the control range at PND 119, 147, and 175. Thus, at serum levels similar to those in humans receiving the drug, chronic 13-cis-RA treatment did not severely affect depression-like behaviors in rats. These data do not substantiate the hypothesis of 13-cis-RA-induced depression.

Isotretinoin and fenofibrate induce adiposity with distinct effect on metabolic profile in a rat model of the insulin resistance syndrome

OBJECTIVE

To investigate the effect of transcription-modulating drugs, fenofibrate and isotretinoin, on metabolic profile, insulin sensitivity of adipose and muscle tissues and gene expression in a genetic model of insulin resistance syndrome, polydactylous rat strain (PD/Cub).

DESIGN

Administration of fenofibrate (100 mg/kg/day), isotretinoin (30 mg/kg/day) or vehicle to adult male PD/Cub rats fed standard laboratory chow for 15 days.

MEASUREMENTS

Parameters of lipid and carbohydrate metabolism-oral glucose tolerance test, serum concentrations of insulin, triglycerides (TG), free fatty acids (FFA), glycerol, total cholesterol (CH); morphometric variables, in vitro insulin sensitivity of adipose and muscle tissues, catecholamine-stimulated lipolysis and the expression of ApoC-III and Hnf-4 genes in liver.

RESULTS

Both experimental groups displayed an increase in adiposity with contrasting effects on TG (lowered by fenofibrate and increased by isotretinoin) and gene expression (no change in fibrate-treated rats and increased expression of ApoC-III and Hnf-4 in isotretinoin-treated group). Fenofibrate-treated rats also showed decreased concentrations of FFA and CH with concomitant decrease of catecholamine-induced lipolysis in adipocytes, but also hyperinsulinemia and the highest insulin/glucose ratio. Isotretinoin increased glycerol concentrations and decreased the insulin sensitivity of peripheral tissues.

CONCLUSION

The PD/Cub rat showed a distinct pharmacogenetic reaction to fenofibrate and isotretinoin administration. Several lines of evidence now implicate specific variant(s) of ApoC-III and/or ApoA-V alleles as responsible for the dyslipidemia observed in this genetic model. The PD/Cub strain may also serve as a pharmacogenetic model for dissection of the retinoid-induced hypertriglyceridemia.

The nonhuman primate as a model of developmental immunotoxicity

Macaques are well suited for preclinical testing of biopharmaceutics due to reproductive and developmental similarities with humans. In order to characterize ontogeny of the immune system in this model, we studied lymphocyte and antigen-presenting cell populations in developing lymphoid tissues of rhesus macaque fetuses during the second and third trimesters [gestation days (GD) 75-145, term 165 days]. Systemic lymphoid tissues (thymus, spleen and lymph nodes, and intestinal tissue) were examined for morphology and cell surface markers by immunohistochemistry. Lymphocytes were further characterized by flow cytometry for differentiation markers. Splenic tissue from early second trimester fetuses was populated mainly by CD20+ B cells while the thymus contained large numbers of CD3+ T cells. In the late second trimester (day 80), approximately equal populations of B and T cells were present in both tissues and numerous dendritic cells (p55+) were present in the intestinal lamina propria. By the second trimester, the rhesus macaque fetal lymphoid system is well developed. Analysis of lymphoid organs from retinoic acid-treated fetuses indicated that the T-cell (thymus)-dependent compartment of the spleen white pulp in specimens with thymic aplasia showed a reduction in size and proportion of CD3+ T cells compared to controls. Our findings indicate that RA-induced thymic defects result in disrupted development of the splenic T-cell-dependent compartment.

Effect of isotretinoin on tooth germ and palate development in mouse embryos

Vitamin A and its derivatives, retinoic acid, tretinoin and isotretinoin, are currently used in dermatological treatments. The administration of high doses of this vitamin provokes congenital malformations in mice: cleft palate, maxillary and mandibular hypoplasia and total or partial fusion of the maxillary incisors. This study compares the tooth germs of the first maxillary and mandibular molars of fetal mice submitted to isotretinoin during organogenesis. Twelve 60-day-old female Mus musculus were divided into two groups on the 7th day of pregnancy: treated group--1 mg isotretinoin per kg body weight, dissolved in vegetable oil, was administered from the 7th to the 13th day of pregnancy; control group--vegetable oil in equivalent volume was administered orally for the same period. On the 16th day of pregnancy, the females were sacrificed, the fetuses were removed and their heads amputated. After standard laboratory procedures, 6-micron thick serial slices were stained with hematoxylin and eosin for optical microscopy examination. The results showed that both groups had closed palates with no reminiscence of epithelial cells; however, the first molar germs of the isotretinoin-treated animals showed delayed development compared to the control animals.

13-cis-retinoic acid causes patterning defects in the early embryonic rostral hindbrain and abnormal development of the cerebellum in the macaque

BACKGROUND

We have previously reported that exposure of embryos to 13-cis-retinoic acid (cRA) results in an abnormal phenotype of the fetal cerebellum. In this study, we analyzed early changes in the cerebellar anlagen (midbrain-hindbrain junction) as well as lesions of the fetal cerebellar vermis after a teratogenic dosing regimen of cRA in the macaque model.

METHODS

We examined embryo coronal sections of the midbrain-hindbrain junction immunostained for Pax-2, Engrailed-2 (En-2) and Krox-20. To characterize the cerebellum foliation and fissure formation processes, we analyzed vermal cortical cell layer development and the number and depth of the major fissures on sagittal sections of fetal vermis. We also examined Purkinje cell development in vermal sections immunostained for CD3.

RESULTS

Compared with controls, there was a consistent truncation of the midbrain-hindbrain region of early embryos exposed to cRA. The cRA-induced fetal vermis lesions included inhibition in its anteroposterior growth, altered folial patterning, a general loss of prominence of the fissures accompanied by a total loss of sublobular fissures, and changes in cortical cell layer development. CD3(+) Purkinje cells were abnormally dispersed deep into the molecular layer in the vermis.

CONCLUSIONS

Our findings indicate that the effects of cRA on the developing cerebellum involve interference with the hierarchy of complex cellular and genetic interactions that lead to the growth and subdivision of the cerebellum into smaller units. The regional vermal defects may be related to early postnatal functional deficits.

The vitamin A analogues: 13-cis retinoic acid, 9-cis retinoic acid, and Ro 13-6307 inhibit neuroblastoma tumour growth in vivo

BACKGROUND

Neuroblastoma, a childhood tumour of the sympathetic nervous system, may undergo spontaneous differentiation or regression due to apoptosis after no or minimal therapy. However, the majority of neuroblastomas are diagnosed as metastatic tumours with a poor prognosis in spite of intensive multimodal therapy. Vitamin A and its analogues (retinoic acid, RA) play an important role in normal cel lular differentiation and programmed cell death. RA regulates neuroblastoma growth and differentiation in vitro, and has shown activity against human neuroblastoma in vivo.

PROCEDURE

Recently, 9-cis RA was shown to induce apoptosis in vitro in neuroblastoma using a 5 days short-term treatment and subsequent washout. In the present study, nude rats with human neuroblastoma SH-SY5Y xenografts were treated with 13-cis RA (4 mg po daily), 9-cis RA (5 mg po daily) or the novel analogue Ro 13-6307 (0.3 mg po daily) using either a continuous or short-term schedule.

RESULTS

ALL three different retinoids decreased neuroblastoma growth significantly in terms of tumour weight after 8-12 days when compared to untreated controls (P < 0.05). Minor signs of toxicity in 13-cis RA treated rats were observed. However, severe toxicity with significant weight loss was seen in all rats treated with 9-cis RA and Ro 13-6307. Toxicity was more pronounced with the continuous regimen.

CONCLUSIONS

We conclude that different retinoids reduce neuroblastoma tumour growth in vivo. Drug scheduling and dosage may affect both therapeutic efficacy and toxic side effects. Further in vivo studies are warranted, including pharmacokinetic and molecular analyses, before clinical trials with promising retinoids like 9-cis RA and Ro 13-6307 can be started in children with neuroblastoma.

Pulmonary availability of isotretinoin in rats after inhalation of a powder aerosol

Repeated oral administration of chemopreventive retinoids such as isotretinoin over extended periods of time is associated with intolerable systemic toxicity. Here isotretinoin was formulated as a powder aerosol, and its delivery to the lungs of rats was studied with the aim to explore the possibility of minimizing adverse effects associated with its oral administration. Rats received isotretinoin orally (0.5, 1 or 10 mg kg(-1)) or by inhalation (theoretical dose approximately 1 or approximately 10 mg kg(-1)) in a nose-only inhalation chamber. Isotretinoin was quantitated by high-pressure liquid chromatography in plasma and lung tissue. The ratios of mean area of concentration-vs-time curve (AUC) values in the lungs over mean AUCs in the plasma for isotretinoin following single or repeated aerosol exposure surpassed those determined for the oral route by factors of between two (single low-dose) and five (single high-dose). Similarly, the equivalent ratios for the maximal peak concentrations in lungs and plasma obtained after aerosol exposure consistently exceeded those seen after oral administration, suggesting that lungs were exposed to higher isotretinoin concentrations after aerosol inhalation than after oral administration of similar doses. Repeated high doses of isotretinoin by inhalation resulted in moderate loss of body weight, but microscopic investigation of ten tissues including lung and oesophagus did not detect any significant aerosol-induced damage. The results suggest that administration of isotretinoin via powder aerosol inhalation is probably superior to its application via the oral route in terms of achieving efficacious drug concentrations in the lungs.

Capecitabine in the treatment of metastatic renal cell carcinoma

To evaluate the therapeutic effects and systemic toxicities of a capecitabine-based home therapy regimen in patients with metastatic renal cell carcinoma, 30 patients were enrolled in a phase II clinical trial. Treatment consisted of oral capecitabine combined with subcutaneous recombinant human interferon-alpha 2a, recombinant human interleukin-2 and oral 13-cis-retinoic acid. There were two (7%) complete responses (CRs) and eight (27%) partial remissions (PRs), for an overall objective response rate of 34% (95% CI 17-53%). Except one, all responses are ongoing, with a median duration of 9+ and 8+ months for CRs and PRs, respectively. Additionally, 12 patients (40%) reached stable disease. Eight patients (27%) showed continued disease progression despite treatment. Therapy was well tolerated and was given in the outpatient setting. Capecitabine-related World Health Organization (WHO) grade 2 and 3 toxicities were observed in five and two patients respectively, and were limited to fatigue, nausea/vomiting, diarrhoea, stomatitis, dermatitis and hand-and-foot syndrome. The substitution of capecitabine for 5-FU in the pre-existing biochemotherapy regimen did not result in a reduced therapeutic efficacy and showed significant anti-tumour activity in patients with advanced renal cell carcinoma.

Inhaled isotretinoin (13-cis retinoic acid) is an effective lung cancer chemopreventive agent in A/J mice at low doses: a pilot study

In previously treated head-and-neck cancer patients, p.o. administered isotretinoin (13-cis retinoic acid) reduced the occurrence of second aerodigestive tumors, including lung tumors, but side effects made chronic therapy problematic. We reasoned that inhaled isotretinoin might provide sufficient drug to the target cells for efficacy while avoiding systemic toxicity, and we proceeded with the pilot study reported here. Male A/J mice were given single i.p. doses of urethane, a common experimental lung carcinogen, or benzo[a]pyrene (BaP) or 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), putative major carcinogens in tobacco smoke. The following day, exposures to isotretinoin aerosols for 45 min daily at 1.3, 20.7, or 481 microg/l were initiated. After 2 weeks, the high dose caused severe toxicity on the snout skin, necessitating a reduction of dose frequency to twice a week. As a precaution, the mid dose was reduced to three exposures per week. The weekly total deposited doses after the dose frequency reductions were calculated to be 0.24, 1.6, and 24.9 mg/kg for the low, mid, and high doses, of which 16% was estimated to be deposited in the lungs. The weekly deposited pulmonary drug doses were calculated to be 0.01, 0.07, and 1.1% of a previously reported ineffective oral dose in urethane-treated A/J mice. After 10-16 weeks, mice were sacrificed to count areas of pulmonary hyperplasia and adenomas. For all carcinogens, the mice exposed to the high isotretinoin dose showed reductions of tumor multiplicity ranging from 56 to 80% (P < 0.005). The mid dose was associated with reductions of tumor multiplicity by 67 and 88% (P < 0.005) in BaP- and NNK-treated mice, respectively, and was tolerated until approximately 12 weeks, when both these and the high-dose mice began losing weight. The low-dose mice had nonsignificant reductions of 30% (P < 0.13) and 16% (P < 0.30) for BaP- and NNK-treated mice, respectively without any evidence of side effects. For BaP- and NNK-treated mice, numbers of hyperplastic areas directly correlated to dose level and inversely to tumor number, suggesting arrested progression. Inhaled mid-dose isotretinoin caused up-regulation of lung tissue nuclear retinoic acid receptors (RARs) relative to vehicle-exposed mice, RARalpha (3.9-fold vehicle), RARbeta (3.3-fold), and RARgamma (3.7-fold), suggesting that these receptors may be useful biomarkers of retinoid activity in this system. The encouraging results from this pilot study suggest that inhaled isotretinoin merits evaluation in people at high risk for lung cancer.

Vitamin A teratogenicity and risk assessment in the macaque retinoid model

Studies were performed in the cynomolgus monkey (Macaca fascicularis) to provide risk assessment information on safe dose levels of Vitamin A during human pregnancy. Vitamin A palmitate was orally administered at 7500 IU/kg (2.25 mg/kg) to 80 000 IU/kg (24 mg/kg) body weight during early pregnancy (gestation day [GD] 16-27). The results indicated a dose-related increase in exposure (AUC) to retinyl esters and retinoic acids (RA) (all-trans-RA, all-trans-4-oxo-RA, 13-cis-RA, 13-cis-4-oxo-RA). There was also a dose-related increase in abortion and malformation that affected typical retinoid target tissues in the embryo, including the craniofacial region, heart, and thymus. The NOAEL and LOAEL for structural malformations were 7500 IU/kg and 20 000 IU/kg (6 mg/kg), respectively. A companion study involving oral administration of 13-cis-RA during the same gestational period established the NOAEL for malformations at 0.5 mg/kg/day, which is close to the human therapeutic dose range (0.5 to 1.5 mg/kg/day) associated with retinoid embryopathy. Based on the known similarities in teratogenic susceptibility to 13-cis-RA, the monkey NOAEL for Vitamin A (7500 IU/kg) was used to estimate safe levels of this nutrient in humans applying a safety factor of 10. This approach yielded safe levels of Vitamin A during human pregnancy in the range of approximately 25 000 to 37 000 IU/day.

Distribution, teratogenicity, and embryonic delivered dose of retinoid Ro 23-9223

Ro 23-9223 is a highly lipophilic aromatic retinoid with antiproliferative and sebum supressive effects in preclinical disease models of acne. To investigate the relation between Ro 23-9223 developmental toxicity, drug distribution, and transplacental transfer, groups of pregnant hamsters were given oral doses of 50-500 mg/kg Ro 23-9223 on days 8 and 9 of gestation. The teratogenic phenotype induced at doses greater than 125 mg/kg per day was similar to that found after exposure to doses of 13-cis-retinoic acid (isotretinoin, Accutane) greater than 37.5 mg/kg per day. Oral bioavailability of Ro 23-9223 was very low compared to 13-cis-retinoic acid. The highest concentrations of Ro 23-9223 were found in maternal liver, lung, adipose tissue, cardiac muscle, and placenta, whereas only little of the compound crossed the blood-brain barrier. Based on embryo AUC, Ro 23-9223 had a 30- to 50-fold greater embryo:maternal concentration ratio than 13-cis-retinoic acid plus its bioactive metabolites following similar doses of the two retinoids. In preclinical pharmacology studies, oral doses of Ro 23-9223 (5 mg/kg per day) and 13-cis-retinoic acid (10 mg/kg per day) produced comparable gland size reductions in the hamster ear sebaceous gland reduction assay. Under these conditions, Ro 23-9223 plasma AUC was 40 times smaller than that of 13-cis-retinoic acid plus its bioactive metabolites. Assuming that the near linear dose-exposure relationship of Ro 23-9223 extends beyond the dose range of this study, embryo AUCs of Ro 23-9223 and 13-cis-retinoic acid (plus metabolites) would be near identical following pharmacologically equivalent doses. A comparison of embryo retinoid AUCs suggests a 4-fold lower teratogenic potency of Ro 23-9223 compared to with 13-cis-retinoic acid. Despite high embryo levels in hamsters, the data suggest an improved therapeutic index for Ro 23-9223 compared with 13-cis-retinoic acid in a preclinical acne disease model.

Carboplatin, vindesine, 5-fluorouracil-leucovorin and 13-cis retinoic acid in the treatment of advanced non-small cell lung cancer. A phase II study

PURPOSE

Carboplatin, vindesine and 5-fluorouracil/leucovorin are drugs active in the treatment of non-small cell lung cancer (NSCLC) and they can be administered in an outpatient setting. Retinoids, which are widely used agents in chemoprevention, have been reported to exert (in vitro models) growth inhibitory effects of synergistic type with chemotherapy, and differentiating effects on NSCLC cells.

PATIENTS AND METHODS

28 patients with advanced NSCLC with measurable disease were entered into the trial. Eligibility criteria included performance status < or = 3 and adequate renal and liver function. Patients with brain metastases were not excluded. Treatment was as follows: Carboplatin (CBCDA) 300 mg/m2 day 1, Vindesine (VDS) 3 mg/m2 days 1 and 5, leucovorin (L) 100 mg/m2, 5-fluorouracil (5-FU) 370 mg/m2 for 5 days and 13-cis retinoic acid (R) 1 mg/kg, administered between chemotherapy courses. After 6 courses of chemotherapy responders were maintained with R, until progression.

RESULTS

120 courses of chemotherapy have been delivered (median 4 courses per patient, range 1 to 6). All patients were evaluable for response and toxicity. Objective responses: 2 complete responses (CR) (7%), 9 partial responses (PR) (32%), 9 stable disease (SD) (32%), 8 progressive disease (PD) (29%). (Response rate 39%, 95% CI: 22% to 60%). Median time to progression was 7.7 months (range 3.4-22) and median survival was 9.7 months (range 0.5-27) with 40% of patients alive after one year. Toxicity WHO: hematological grade 3-4 in 46% of patients, grade 2 diarrhea in 21% of patients, ileus in 14% of patients, Neurologic grade 2 in 11% of patients.

CONCLUSIONS

The addition of RA to CBDCA, VDS, FU, L, R represents an effective treatment in NSCLC, with manageable toxicity.

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.