Potency ranking of valproic acid analogues as to inhibition of cardiac differentiation of embryonic stem cells in comparison to their in vivo embryotoxicity.

The embryonic stem cell test (EST) is one of the more promising and extensively studied tests in the field of developmental toxicology. We evaluated the effect of a series of structurally related valproic acid analogues on cardiomyocyte differentiation in the EST. The goal of the present study was to determine the applicability of the EST by potency ranking within this chemical class. Cardiomyocyte differentiation was evaluated by morphological scoring as well as by gene expression analysis of cardiac markers using RT-PCR. All VPA analogues tested inhibited cardiomyocyte differentiation, with the exception of (±)-2-ethyl-4-methyl pentanoic acid, which correlates to their known in vivo developmental toxicity. Effects were also evident on gene expression of cardiomyocyte differentiation-regulated genes, such as MHC and Nkx2.5. Overall, the present results indicate that the assay can be a valuable screening tool in potency ranking of structurally related compounds.

Modulation of synaptic transmission and analysis of neuroprotective effects of valproic Acid and derivates in rat embryonic motoneurons.

Amyotrophic lateral sclerosis is a devastating motoneuron disorder for which no effective treatment exists. There is some evidence for neuroprotective effects of valproic acid (VPA). The beneficial effects, however, are limited due to the adverse effects of VPA. To overcome this problem, a number of VPA derivates with fewer side effects have been synthesized. In the present study, we investigated the viability of highly purified embryonic motoneurons cultured on glial feeder layers, composed of either astrocytes or Schwann cells, or in monoculture, in presence of VPA and its three derivates 3-propyl-heptanoic acid (3-PHA), PE-4-yn enantiomers (R- and S-PE-4-yn). An excitotoxic stimulus, kainate (KA), was added at day in vitro 9 (DIV9) and the neuroprotective effect of either simultaneous incubation (DIV9) or pre-incubation (DIV1) of VPA and its derivates was tested. The survival of motoneurons under simultaneous application of KA and VPA derivates was not remarkably increased. Pre-incubation with VPA and even more with the derivates before the addition of KA, however, significantly reduced their vulnerability against the KA-induced neurotoxic effect. Our data suggest that the neuroprotective capacities of VPA and its three derivates tested here drastically increase when they are added several days before KA. Most prominent neuroprotective effects were seen for the PE-4-yn enantiomers. Patch-clamp experiments revealed an antiexcitotoxic effect of the S-PE-4-yn enantiomer that reduces the frequency of postsynaptic currents and enhances the inhibitory postsynaptic transmission dependent on the co-culture condition.

Detection of estrogenically active substances in diets for sows by an in vitro bioassay supported by HPLC analysis.

There is considerable evidence that exogenous estrogenic compounds can have adverse effects on fertility. The main reason cited in literature for hyperestrogenism in pigs is contamination of feedstuffs by the mycotoxin zearalenone (Boehm, 2000), but further estrogenically active substances might also be involved in cases of impaired fertility with symptoms like enlarged, red-coloured vulvae in piglets, irregular estrus cycles and anestrus of sows (Bennetts et al., 1946; Drane et al., 1981). It is well known that soy used in diets for pigs as a main protein source contains phytoestrogens. Amongst them, isoflavones like genistein and daidzein are of particular interest. Aim of this study was to optimize and use an established bioassay (Kluczka, 2003) to determine estrogenic activity in feedstuffs for pigs related to isoflavones and further substances with estrogenic potential. This bioassay is a reporter gene assay based on stably transfected human embryonal kidney cells (HEK 293) that contains either alpha or beta estrogen receptor (alpha- or beta-HEK). The estrogenic activity measured in the luciferase assay was expressed in estradiol-equivalents (EEQ) and the results were compared with the isoflavone content (genistein, daidzein) obtained by chemical analysis using high performance liquid chromatography-Ultraviolet (HPLC-UV). Mean estrogenic activity in diets fed to sows in herds with altered fertility was 275.8 microg EEQ/kg feed in alpha-HEK cells and 295.0 microg EEQ/kg feed in beta-HEK cells. Feedstuffs from herds without any altered fertility showed an average estrogenic activity of 204.9 microg EEQ/kg feed in alpha-HEK and 213.3 microg EEQ/kg feed in beta-HEK. The estrogenic activity was strongly related to the concentration of the isoflavones (alpha-HEK, r(2)=0.9488; beta-HEK, r(2)=0.9427). Clinically relevant zearalenone concentrations (>50-150 microg/kg feed) displayed estrogenic effects in the bioassay that did not differ significantly from those caused by high isoflavone concentration because of the use of soy as protein source.

Determination of phoxim residues in eggs by using high-performance liquid chromatography diode array detection after treatment of stocked housing facilities for the poultry red mite (Dermanyssus gallinae).

The poultry red mite Dermanyssus gallinae is the most important ectoparasite of poultry in several European countries. Phoxim is a well-known antiparasitic agent in wide use. Initial studies indicated that this compound could successfully be applied to eliminate D. gallinae in egg-laying birds and in henhouses by treating the cages and the equipment with it. In order to investigate whether phoxim residues are present in eggs from laying hens, we developed a selective and sensitive high-performance liquid chromatography method employing a simple water/acetonitrile gradient system. The amount of phoxim was determined by UV detection at 281 nm, and the presence of the residue was confirmed by diode array detection. The eggs were homogenized for sample pretreatment and extracted with acetonitrile and partitioned with n-hexane. The acetonitrile extract was further purified with silica gel column chromatography. Recovery rates (performed at the 5-120 microg kg(-1) level) were in the range of 86.0-92.1% with relative standard deviations between 3.1% and 16.3%. Based on a signal to noise ratio of 3, the limit of detection of the assay was approximately 2 microg kg(-1). The day-to-day variation in the concentration of phoxim in four contaminated eggs (5.7-51.6 microg kg(-1)) was generally less than 20%. The decision limit (CCalpha) and the detection capability (CCbeta) were 62.0 and 68.7 microg kg(-1), respectively. The applicability of the method was demonstrated in eggs from three clinical trials and from a field study. In these investigations, all animals were kept in conventional battery cages. No sample was found containing more than the maximum residue level of 60 microg kg(-1) for phoxim in eggs as given in Annex I of Council Regulation (EEC) No. 2377/90.

[Impacts and impact mechanisms of "dioxins" in humans and animals]. / Wirkungen und Wirkungsmechanismen von "Dioxinen" im menschlichen und tierischen Organismus.

"Dioxins" are used to specify polychlorinated dibenzo-p-dioxins (PCDD), dibenzo-furanes (F) and dioxin-like polychlorinated biphenyls (PCB's). Many of the congeners proved to be highly toxic; 2,3,7,8-tetrachloro-dibenzo-p-dioxin (TCDD) is the most toxic congener, and probably the most toxic compound ever synthesized by man (the natural occurance of this substance is very low). The total concentration/-toxicity of a mixture of congeners (WHO-PCDD/F-TEQ, or including the PCB's WHO-PCDD/F-PCB-PCB-TEQ) is calculated by addition of the individual concentrations multiplied by respective toxicity equivalence factors TEF; the most toxic congener TCDD is defined as 1. The tolerable weekly intake TWI set by the European Commission is 14pg WHO-PCDD/F-TEQ/kg bw. The "body burden" of adults in industrial countries is about 2-6 ng WHO-PCDD/F-TEQ/kg bw., or about double this value if PCB's are also considered. There is a very broad range of toxic effects of "dioxins". Many of the congeners can induce toxic responses at very low "body burdens". The most sensitive effects are immunosuppression, developmental and reproductive toxicity, as well as neurological behavioral effects. These effects occur at "body burdens" whih are close to background exposure of the human. Cancerogenic effects are induced at higher exposure (Seveso, industrial exposure). TCDD was considered a "complete carcinogen" by the IARC (Group 1). There is a broad range of carcinogenic effects, and there is no "hallmark" effect. Most toxic effects induced by TCDD are mediated by binding to the Ah-receptor (Ah-R) which binds together with a second protein, ARNT, to the respone elements of a number of target genes, and thus modulates gene expression. "Dioxins" are strong promotors, but weak initiators. The multitude of interactions of the Ah-R and ARNT ("receptor cross-talk") results in numerous molecular and cellular effects. The TCDD-Ah-R complex can also bind to the response element of the estrogen receptor, and thus can block the effects of es-trogens. This explains the fact that TCDD can be an estrogen antagonist reducing or preventing mamma carcinoma. Other Ah-R ligands occur in vegetables (e.g. indoles, flavones) and will possibly be developed in the future as functional substances. PCB's have similar properties to TCDD if they can exist in a planar configuration (dioxin-like PCB's). The non-dioxin-like PCB's always occur together with "dioxins"; their toxixty cannot be adequately determined although they occur in high concenrations. The consumption of food contaminated with "dioxins" need not directly lead to a toxic effect. Due to the continous cumulation of "dioxins" repeated ingestion of contaminated food could result in an increase of the "body burden" and thus chronic toxicity. This shows that the exposure of the human to dioxins should be minimized wherever possible.

Novel valproic acid derivatives with hemoglobin F inducing activity.

Pharmacological induction of hemoglobin F expression may be a promising approach for the treatment of beta-thalassemia and sickle cell disease. Valproic acid, a drug frequently used for the treatment of seizure disorders, has been shown to enhance fetal hemoglobin synthesis in erythroid cells. However, this effect is only modest and requires relative high concentrations. Therefore, the drug appears not to be applicable for the treatment of beta-globin chain disorders. Here, we describe the identification of novel valproic acid derivatives with potent hemoglobin F inducing activities at concentrations that presumably can be obtained in vivo.

Differential teratogenesis of all-trans-retinoic acid administered on gestational day 9.5 to SWV and C57BL/6N mice: emphasis on limb dysmorphology.

BACKGROUND: Mouse strain differences in teratologic response are well documented. However, because retinoids cause similar malformation syndromes across many species, the strain differences may be predicted to be minimal. The goals of this study were to characterize and explain the differences between the C57BL/6N and SWV mouse strains in terms of all-trans-retinoic acid (RA)-induced teratologic effects at the time of gestation that cause postaxial forelimb ectrodactyly. METHODS: Visceral and skeletal malformations were determined by Wilson's sectioning and double-staining techniques, respectively; developmental staging was performed according to the somite count; and retinoid concentrations were assessed by HPLC. RESULTS: C57BL/6N mice were more susceptible than SWV mice to induction of embryolethality, cardiovascular defects, and forelimb ectrodactyly, whereas the opposite was true for the induction of ear, thymus, and tail agenesis, and cleft palate, gastroschisis, and anal atresia. As determined by somite counts, 1 strain intercross was developmentally advanced compared to the parental strains and the reciprocal cross. Retinoid susceptibility was equivalent between the reciprocal crosses for some malformations and determined by the maternal genotype for others. Toxicokinetic experiments showed that whole-embryo peak retinoid concentrations did not differ between the strains, but the area under the curve (AUC) for all-trans-RA was 1.3 times higher in C57BL/6N than in SWV embryos. CONCLUSIONS: The malformation spectrum induced by RA was strain-specific, and the strain sensitivity for forelimb ectrodactyly was consistent with all previously tested teratogenic agents (i.e., C57BL/6N was more sensitive than SWV). The strain differences in teratologic effects were not explained by developmental timing differences or toxicokinetic differences at the whole-embryo level.

Repeated topical treatment, in contrast to single oral doses, with Vitamin A-containing preparations does not affect plasma concentrations of retinol, retinyl esters or retinoic acids in female subjects of child-bearing age.

BACKGROUND: Vitamin A is widely used in cosmetic preparations. Given that oral Vitamin A and its metabolites present a potential reproductive risk, the present study investigated the effect of topical Vitamin A on human endogenous plasma levels of Vitamin A and its metabolites. METHODS: Two groups of 14 female volunteers of child-bearing age were kept on a Vitamin A-poor diet and treated topically for 21 days with creams containing 0.30% retinol or 0.55% retinyl palmitate on approximately 3000 cm2 of their body surface area, amounting to a total of approximately 30,000 IU Vitamin A/subject/day. After a 12-day wash-out period, the study groups received single oral doses of 10,000 IU or 30,000 IU retinyl palmitate (RP), corresponding to the maximal EU allowance during pregnancy or three-times higher, respectively. Blood samples were collected over 24h on study days -3 (pre-study), 1, 21 (first and last days of topical treatment) and 34 (oral administration) at 0, 1, 2, 4, 6, 8, 12, 14-16 h and 24 h after treatment for determination of plasma concentrations of retinol (REL), retinyl palmitate (RP), oleate (RO) and stearate (RS), 9-cis-, 13-cis-, all-trans- (AT), 13-cis-4-oxo- or AT-4-oxo-retinoic acids (RAs). RESULTS: With the exception of transient mild (RP-group) to moderate (REL-group) local irritation on the treatment sites, no adverse local or systemic effects were noted. On days 1 or 21 of topical treatment, no changes were measured in individual or group mean plasma Cmax, AUC0-24 h or other pharmacokinetic parameters of REL, retinyl esters or RAs relative to pre-study data. In contrast, single oral doses of RP at 10,000 IU or 30,000 IU produced dose-related and sustained increases in Cmax and AUC0-24 h values of plasma RP, RO, RS, 13-cis- and 13-cis-4-oxo-RAs, as well as a transient increase in AT-RA. In conclusion, our results provide evidence that human topical exposure to retinol- or retinyl ester-containing cosmetic creams at 30,000 IU/day and maximal use concentrations do not affect plasma levels of retinol, retinyl esters or RAs, whereas single oral doses at 10,000 IU or 30,000 IU produce significant increases in plasma retinyl esters and RAs.

Valproic acid induces extracellular signal-regulated kinase 1/2 activation and inhibits apoptosis in endothelial cells.

The histone deacetylase (HDAC) inhibitor valproic acid (VPA) was recently shown to inhibit angiogenesis, but displays no toxicity in endothelial cells. Here, we demonstrate that VPA increases extracellular signal-regulated kinase 1/2 (ERK 1/2) phosphorylation in human umbilical vein endothelial cells (HUVEC). The investigation of structurally modified VPA derivatives revealed that the induction of ERK 1/2 phosphorylation is not correlated to HDAC inhibition. PD98059, a pharmacological inhibitor of the mitogen-activated protein kinase kinase 1/2, prevented the VPA-induced ERK 1/2 phosphorylation. In endothelial cells, ERK 1/2 phosphorylation is known to promote cell survival and angiogenesis. Our results showed that VPA-induced ERK 1/2 phosphorylation in turn causes phosphorylation of the antiapoptotic protein Bcl-2 and inhibits serum starvation-induced HUVEC apoptosis and cytochrome c release from the mitochondria. Moreover, the combination of VPA with PD98059 synergistically inhibited angiogenesis in vitro and in vivo.

Molecular and cellular effects of cis-9, trans-11-conjugated linoleic acid in enterocytes: effects on proliferation, differentiation, and gene expression.

It has been hypothesized that dietary conjugated linoleic acids (CLA) may inhibit colon tumorigenesis. The aim of our study was to investigate the cellular and molecular effects of cis-9 (9Z), trans-11 (11E)-CLA on the proliferation, differentiation, interaction with peroxisome proliferator-activated receptors (PPARs), and expression of genes relevant in the APC-beta-catenin-TCF4 signalling pathway in human HT-29 and Caco-2 colon cells. We found that 9Z,11E-CLA inhibited the proliferation of HT-29 and Caco-2 cells. Trans-vaccenic acid (VA) showed no antiproliferative effects at all. We determined that 9Z,11E-CLA induced cell differentiation as measured by intestinal alkaline phosphatase (IAP) enzyme activity in Caco-2 cells, mRNA expression of IAP, and activation of a 5' flanking region of IAP. The 9Z,11E-CLA activated human PPARdelta as measured in a reporter gene assay. Treatment of HT29 cells in the poliferation phase with 9Z,11E-CLA repressed mRNA-expression of proliferation genes such as c-myc, cyclin D1 and c-jun in a concentration dependent manner. The promoter activities of c-myc and AP1 were also inhibited after incubation with 9Z,11E-CLA. beta-Catenin mRNA and protein expression was also repressed by the treatment with 9Z,11E-CLA. In addition, the mRNA expression of PPARdelta was repressed by treatment of the HT-29 cells with 9Z,11E-CLA. We conclude that 9Z,11E-CLA has an antiproliferative effect at the cellular and molecular levels in human colon cells. The results indicate that the preventive effects of CLA in the development of colon cancer may be due to their downregulation of some target genes of the APC-beta-catenin-TCF-4- and PPARdelta signalling pathway.

Effects of valproic acid derivatives on inositol trisphosphate depletion, teratogenicity, glycogen synthase kinase-3beta inhibition, and viral replication: a screening approach for new bipolar disorder drugs derived from the valproic acid core structure.

Inositol-1,4,5-trisphosphate (InsP3) depletion has been implicated in the therapeutic action of bipolar disorder drugs, including valproic acid (VPA). It is not currently known whether the effect of VPA on InsP3 depletion is related to the deleterious effects of teratogenicity or elevated viral replication, or if it occurs via putative inhibitory effects on glycogen synthase kinase-3beta (GSK-3beta). In addition, the structural requirements of VPA-related compounds to cause InsP3 depletion are unknown. In the current study, we selected a set of 10 VPA congeners to examine their effects on InsP3 depletion, in vivo teratogenic potency, HIV replication, and GSK-3beta activity in vitro. We found four compounds that function to deplete InsP3 in the model eukaryote Dictyostelium discoideum, and these drugs all cause growth-cone enlargement in mammalian primary neurons, consistent with the effect of InsP3 depletion. No relationship was found between InsP3 depletion and teratogenic or elevated viral replication effects, and none of the VPA congeners were found to affect GSK-3beta activity. Structural requirements of VPA congers to maintain InsP3 depletion efficacy greater than that of lithium are a carboxylic-acid function without dependence on side-chain length, branching, or saturation. Noteworthy is the enantiomeric differentiation if a chiral center exists, suggesting that InsP3 depletion is mediated by a stereoselective mode of action. Thus, the effect of InsP3 depletion can be separated from that of teratogenic potency and elevated viral replication effect. We have used this to identify two VPA derivatives that share the common InsP3-depleting action of VPA, lithium and carbamazepine, but do not show the side effects of VPA, thus providing promising novel candidates for bipolar disorder treatment.

Potentiation of the teratogenic effects induced by coadministration of retinoic acid or phytanic acid/phytol with synthetic retinoid receptor ligands.

Previous studies in our laboratory identified retinoid-induced defects that are mediated by RAR-RXR heterodimerization using interaction of synthetic ligands selective for the retinoid receptors RAR and RXR in mice (Elmazar et al. 1997, Toxicol Appl Pharmacol 146:21-28; Elmazar et al. 2001, Toxicol Appl Pharmacol 170:2-9; Nau and Elmazar 1999, Handbook of experimental pharmacology, vol 139, Retinoids, Springer-Verlag, pp 465-487). The present study was designed to investigate whether these RAR-RXR heterodimer-mediated defects can be also induced by interactions of natural and synthetic ligands for retinoid receptors. A non-teratogenic dose of the natural RXR agonist phytanic acid (100 mg/kg orally) or its precursor phytol (500 mg/kg orally) was coadministered with a synthetic RARalpha-agonist (Am580; 5 mg/kg orally) to NMRI mice on day 8.25 of gestation (GD8.25). Furthermore, a non-teratogenic dose of the synthetic RXR agonist LGD1069 (20 mg/kg orally) was also coadministered with the natural RAR agonist, all- trans-retinoic acid (atRA, 20 mg/kg orally) or its precursor retinol (ROH, 50 mg/kg orally) to NMRI mice on GD8.25. The teratogenic outcome was scored in day-18 fetuses. The incidence of Am580-induced resorptions, spina bifida aperta, micrognathia, anotia, kidney hypoplasia, dilated bladder, undescended testis, atresia ani, short and absent tail, fused ribs and fetal weight retardation were potentiated by coadministration of phytanic acid or its precursor phytol. Am580-induced exencephaly and cleft palate, which were not potentiated by coadministration with the synthetic RXR agonists, were also not potentiated by coadministration with either phytanic acid or its precursor phytol. LGD1069 potentiated atRA- and ROH-induced resorption, exencephaly, spina bifida, aperta, ear anotia and microtia, macroglossia, kidney hypoplasia, undescended testis, atresia ani, tail defects and fetal weight retardation, but not cleft palate. These results suggest that synergistic teratogenesis can be induced by coadministration of a natural RXR ligand (phytanic acid) with a synthetic RAR agonist (Am580). Thus, certain potentially useful therapeutic agents or nutritional factors such as phytanic acid should be tested for teratogenic risk by coadministration with other retinoid receptor agonists.

[Effects of animal housing facilities on residues and contaminants in food]. / Einfluss der Tierhaltung auf Rückstände und Kontaminanten in Lebensmitteln.

There are--especially in the case of food of animal origin--only a few well-controlled studies available comparing organically and conventionally produced food with a focus on residues and contaminants. The differences found seemed to be much lower than expected, and the amounts of residues and contaminants were mostly below regulatory maximum residue levels. In the case of organically and conventionally produced milk there have been slight but usually not significant differences reported. One important observation is, that conventionally produced milk contains aflatoxin M1 more frequently than biologically produced milk. The investigation of eggs from different housing systems for laying hens showed in the case of dioxins the highest concentrations in free range eggs. In contrast, propoxur, an insecticide used against the poultry red mite, was found in eggs from battery cages in higher amounts than in those from enriched cages and in eggs obtained from an aviary system. Further research in this field is highly recommended, but there should be more sophisticated evaluation of the data sets from national and international monitoring programs.

Phytanic acid and docosahexaenoic acid increase the metabolism of all-trans-retinoic acid and CYP26 gene expression in intestinal cells.

Retinoids are essential for growth and cell differentiation of epithelial tissues. The effects of the food compounds phytol, the phytol metabolite phytanic acid, and the fatty acid docosahexaenoic acid (DHA) on the retinoid signaling pathway in intestinal cells were studied. Phytol inhibited the formation of all-trans-retinoic acid (RA) from dietary retinol in intestinal cells. Phytanic acid, a known retinoic X receptor (RXRalpha) and peroxisome proliferator activating receptor (PPARalpha) activator, also activated PPARdelta, and to a lesser degree PPARgamma, in a transactivation assay. Phytanic acid had no effect on intestinal RA hydroxylase CYP26 (also named P450RAI) gene expression and metabolism of all-trans-RA in intestinal Caco-2 cells. However, in combination with retinoic acid receptor (RAR)-ligands (all-trans-RA or synthetic Am580) phytanic acid enhanced the induction of CYP26 and RA-metabolism in comparison to treatments with all-trans-RA or Am580 alone. Also treatment with DHA did not affect CYP26 gene expression and RA-metabolism but cotreatment of the cells with DHA and all-trans-RA or Am580 enhanced the induction of CYP26, in comparison to the induction caused by all-trans-RA or Am580 alone. This study indicates that food compounds such as phytanic acid and DHA that are RXR-agonists and have an impact on intestinal CYP26 gene expression and metabolism of all-trans-RA in intestinal cells.

Peroxisome proliferator-activated receptor delta is a specific sensor for teratogenic valproic acid derivatives.

The antiepileptic drug valproic acid (2-propylpentanoic acid) is a potent teratogen in both humans and mice. Valproic acid can induce differentiation of F9 teratocarcinoma cells and stimulate peroxisome proliferator-activated receptor (PPAR) activity. In this study, the structure-activity relationship between valproic acid, its teratogenic and non-teratogenic analogues (branched small- and medium chain fatty acids) and the three PPAR subtypes alpha, gamma or delta was investigated. PPAR-alpha and PPAR-gamma were activated by some valproic acid-derivatives; however, no correlation between teratogenicity and receptor activation could be observed. In contrast, only valproic acid and exclusively its teratogenic analogues were able to activate PPAR-delta in different cellular systems. However, valproic acid appears not to be a direct ligand of PPAR-delta, since in contrast to carbaprostacyclin (cPGI), valproic acid showed not to be able to induce complex formation of PPAR-delta-retinoid X receptor (RXR) heterodimers on DNA. In conclusion, in contrast to PPAR-alpha and PPAR-gamma, PPAR-delta shows to be a specific sensor for teratogenic valproic acid-derivatives.

Teratogenicity of isotretinoin revisited: species variation and the role of all-trans-retinoic acid.

This paper reviews the teratogenicity of isotretinoin in regard to aspects of species variation, toxicokinetics, and metabolism. Particular emphasis is given to the hypothesis that most effects of isotretinoin (13-cis-retinoic acid) are mediated by isomerization to the all-trans-retinoic acid. This mechanism of action would provide a basis for the understanding of species differences and the extrapolation of experimental results to the human situation and thus improve drug development. The insensitive species (rat, mouse) eliminate the drug rapidly through detoxification to the beta-glucuronide; also, placental transfer is limited in these species. On the other hand, in sensitive species (primates), the drug is predominantly metabolized to the active 13-cis-4-oxo-retinoic acid; placental transfer is more extensive here. The beta-glucuronides showed limited placental transfer in all species examined; these metabolites exhibited very low, if any, measurable concentrations in the human. The 13-cis-retinoic acid is not appreciably bound to cellular retinoid-binding proteins or nuclear receptors and exhibits low tissue distribution and placental transfer. Its access to the nucleus may be extensive. Because of the long half life of 13-cis-retinoic acid, continuous isomerization results in significant area under the concentration-time curve levels of all-trans-retinoic acid in the mouse, monkey and the human; the all-trans-retinoic acid formed is extensively distributed across the placenta and may be an important factor that contributes to the teratogenic potency of 13-cis-retinoic acid. Isomerization cannot explain the teratogenic effects of 13-cis-retinoic acid in the rat and rabbit. It is concluded that the high teratogenic activity of isotretinoin in sensitive species (human, monkey) is related to slow elimination of the 13-cis-isomer, to metabolism to the 4-oxo-derivative, to increased placental transfer, to continuous isomerization and significant exposure of the target tissue to all-trans-retinoic acid; and to lack of binding to cytoplasmic retinoid binding proteins that could possibly result in ready access to the nucleus.

Pentyl-4-yn-valproic acid enhances both spatial and avoidance learning, and attenuates age-related NCAM-mediated neuroplastic decline within the rat medial temporal lobe.

2-N-Pentyl-4-pentynoic acid [pentyl-4-yn-valproic acid (VPA)] is an analogue of valproic acid that induces neuritogenesis and increases neural cell adhesion molecule (NCAM) prevalence in cultured neural cells. As memory consolidation involves synapse growth, aided by cell adhesion molecule function, we determined whether or not pentyl-4-yn-VPA had cognition-enhancing properties. Pentyl-4-yn-VPA (16-85 mg/kg) significantly improved water maze learning and task retention when given prior to each training session. Acute administration of pentyl-4-yn-VPA also influenced memory consolidation processes as, when given at 3 h post-passive avoidance training, the amnesia induced by scopolamine given 6 h post-training was prevented in a dose-dependent manner. Chronic administration of pentyl-4-yn-VPA (16.8 or 50.4 mg/kg) also significantly reduced escape latencies in the water maze task, 24 h following the last drug administration. This improved spatial learning was accompanied by enhanced neuroplasticity as the expression of NCAM polysialylated neurons in the infragranular zone of the dentate gyrus and in layer II of the perirhinal and piriform cortex was increased significantly following chronic drug treatment. The cognition-enhancing qualities of pentyl-4-yn-VPA, combined with its ability to attenuate the age-related loss of the NCAM polysialylation state, suggest that it may effectively slow the onset of cognitive decline.

Embryonic subcellular distribution of 13-cis- and all-trans-retinoic acid indicates differential cytosolic/nuclear localization.

Isotretinoin (13-cis-retinoic acid [13CRA], Accutane) is used for the treatment of dermatological diseases. Isotretinoin is, however, teratogenic in animals and humans. The mechanism of action of its teratogenicity is still not clearly identified. It has little or no binding properties to cytosolic retinoid-binding proteins or nuclear retinoid receptors (RAR, RXR). One hypothesis is that the teratogenicity of 2 approximately equipotent teratogenic doses of 13CRA and all-trans-retinoic acids (ATRA) could mainly be correlated to ATRA in the nuclei, where the retinoic acid receptors (RARs) are located. To test this hypothesis, female mice at gestational day 11 were treated with approximately equipotent teratogenic doses of 13-cis-retinoic acid (100 mg/kg orally) or all-trans-retinoic acid (10 mg/kg orally) and sacrificed 1 h and 4 h after administration. Embryos were homogenized and centrifuged into 4 fractions, and the purity of the fractions was tested by quantification of marker constituents for various cell compartments. We analyzed, by RP-HPLC, nuclear, mitochondrial, microsomal, and cytosolic fractions, as well as embryo homogenate and maternal plasma. After treatment with 13-cis-retinoic acid, this substance was mainly located in the nuclear fraction of the embryo (approximately 82%), whereas all-trans-retinoic acid, after ATRA treatment, was mainly located in the cytosolic supernatant (approximately 64%). The binding to cellular retinoid-binding protein (CRABP) may limit the access of ATRA to the nucleus, in contrast to 13CRA, which does not bind to CRABP. The concentration of ATRA in the nuclear fraction was similar after administration of either 13CRA or ATRA. The teratogenic activity of 13-cis-retinoic acid could therefore be explained by its access to the nucleus and its possible conversion to all-trans-retinoic acids, which will interact with the nuclear retinoid receptors.