Retinoic acid receptors regulate expression of retinoic acid 4-hydroxylase that specifically inactivates all-trans retinoic acid in human keratinocyte HaCaT cells.

Tissue levels of all-trans retinoic acid (RA) are maintained through coordinated regulation of biosynthesis and breakdown. The major pathway for all-trans RA inactivation is initiated by 4-hydroxylation. A novel cytochrome P-450 (CYP26) that catalyzes 4-hydroxylation of all-trans RA has recently been cloned. We have investigated regulation and properties of RA 4-hydroxylase in immortalized human keratinocyte HaCaT cells. In the absence of added retinoid, RA 4-hydroxylase (CYP26) mRNA and protein were minimally detected. Addition of all-trans RA rapidly induced RA 4-hydroxylase mRNA (within 2 h) and activity (within 6 h). Induction of both mRNA and activity was transient, returning to baseline within 48 h, and completely dependent on mRNA synthesis (i.e., blocked by actinomycin D). The synthetic retinoid CD367, which specifically activates nuclear RA receptors, also rapidly induced RA 4-hydroxylase activity. This induction, however, unlike that of all-trans RA, was long-lived (>48 h). This difference was attributable to lack of metabolic inactivation of CD367 in HaCaT cells. CD2665, which inhibits RA receptor-dependent gene transcription, blocked retinoid induction of RA 4-hydroxylase, indicating that it is mediated by RA receptors. Addition of excess unlabeled substrates specific for 10 distinct mammalian P-450 subfamilies did not compete with all-trans RA for RA 4-hydroxylase activity. RA 4-hydroxylase did not hydroxylate 9-cis RA or 13-cis RA. Inhibition of RA 4-hydroxylase activity by ketoconazole potentiated activation of RA receptors by all-trans RA. In summary, RA 4-hydroxylase is a unique, highly specific cytochrome P-450 isoenzyme, whose expression is regulated by its natural substrate, all-trans RA, through activation of RA receptors. RA 4-hydroxylase functions to limit the levels, and thereby the biologic activity of all-trans RA in HaCaT cells.

Unoccluded retinol penetrates human skin in vivo more effectively than unoccluded retinyl palmitate or retinoic acid.

The formation of all-trans retinoic acid is an oxidative process whereby retinol is converted to retinaldehyde and then to retinoic acid. Because retinol causes qualitative molecular changes similar to those produced by retinoic acid, we compared potency of retinol, retinaldehyde, and retinyl palmitate to retinoic acid and assessed the effects of occlusion. Retinoids were prepared in an experimental vehicle of 95% ethanol:propylene glycol (7:3) with anti-oxidant. Induction of retinoic acid 4-hydroxylase activity was the end point for comparison. Retinoic acid concentrations from 0.001% to 0.05% under occlusion produced a linear dose-response induction of 4-hydroxylase activity. The concentrations of the other retinoids under occlusion required to achieve significant induction of enzyme activity were 0.6% retinyl palmitate, 0.025% retinol, and 0.01% retinaldehyde. The linear dose-response was lost with retinoid concentrations in excess of 0.25% retinol or 0.5% retinaldehyde. Statistical analyses showed no difference in 4-hydroxylase activity between unoccluded and occluded retinol treated sites. By contrast, however, unoccluded sites treated with retinoic acid or retinyl palmitate had less induction of 4-hydroxylase activity than occluded sites. Retinol, retinaldehyde, and retinyl palmitate did not produce erythema but did increase epidermal thickness. Although retinol is a weaker retinoid than retinoic acid, the increased penetration of unoccluded retinol in comparison to unoccluded retinoic acid with this prototypic vehicle confers on retinol a more effective delivery of a retinoidal effect than unoccluded retinoic acid. Retinol at 0.25% may be a useful retinoid for application without occlusion because it does not irritate but does induce cellular and molecular changes similar to those observed with application of 0.025% retinoic acid.

The retinoid X receptor agonist 9-cis-retinoic acid and the 24-hydroxylase inhibitor ketoconazole increase activity of 1,25-dihydroxyvitamin D3 in human skin in vivo.

1,25-Dihydroxyvitamin D3 [1,25(OH)2D3] transactivates its target genes via the vitamin D receptor (VDR). VDR functions in physiology as a dimer complexed with retinoid X receptor (RXR), whose natural ligand is 9-cis-retinoic acid (9-c-RA). Inactivation of 1,25(OH)2D3 occurs through a cytochrome P-450 24-hydroxylase (OHase). The promoter of the human 24-OHase gene contains a 1,25(OH)2D3-responsive enhancer element (VDRE). We have used this VDRE containing gene as an endogenous reporter for vitamin D3-mediated gene activation in vivo. Normal adult human skin was keratomed after a 2-d exposure to 1,25(OH)2D3, 9-c-RA, all-trans-RA, and ketoconazole. 1,25(OH)2D3 caused a concentration-dependent increase in 24-OHase mRNA expression as determined by northern blot analysis. The activity of epidermal 24-OHase was also induced by 1,25(OH)2D3. Compared with vehicle, neither of the RA isomers nor ketoconazole alone induced 24-OHase mRNA. Addition of 9-c-RA or t-RA to 1,25(OH)2D3, however, caused a synergistic increase in 24-OHase mRNA. Similarly, 1,25(OH)2D3 plus ketoconazole increased 24-OHase mRNA synergistically. Ketoconazole inhibited ex vivo 1,25(OH)2D3-induced epidermal 24-OHase activity. Thus, 24-OHase mRNA induction is a sensitive reporter of 1,25(OH)2D3 activity in vivo; RXR bound to VDR is not a silent partner in vivo, because 9-c-RA enhances 1,25(OH)2D3-liganded RXR/VDR stimulation of the VDRE containing 24-OHase gene; ketoconazole inhibition of 24-OHase enhances 1,25(OH)2D3 activity by impeding its breakdown. Thus, the synergistic response of human skin to topical 1,25(OH)2D3 and/or 1,25(OH)2D3 analogs plus RXR retinoids and/or ketoconazole may be exploited to give a desired biologic/therapeutic response with less 1,25(OH)2D3, minimizing the potential calcemic risk from systemic absorption of 1,25(OH)2D3.

Liarozole inhibits human epidermal retinoic acid 4-hydroxylase activity and differentially augments human skin responses to retinoic acid and retinol in vivo.

Metabolic inactivation of all-trans retinoic acid to 4-hydroxy retinoic acid occurs via a cytochrome P-450 enzyme. We investigated the effects of liarozole on the retinoic acid 4-hydroxylase activity of human epidermis and its ability to modify in vivo human skin responses to retinoic acid and all-trans retinol. Retinoic acid 4-hydroxylase activity induced in vivo by 4 d treatment with retinoic acid (0.1%) was inhibited in vitro by liarozole in a concentration-dependent manner. Comparable micromolar concentrations of liarozole were extracted from stratum corneum-free epidermis treated with 3% liarozole. Retinoic acid levels in liarozole-treated skin increased to 19 +/- 5 ng/g wet wt (mean +/- SEM, p < 0.002, n = 17) at 18 h and to 6 +/- 2 ng/g wet wt (p = 0.38, n = 17) at 48 h as compared to vehicle (not detectable). At 48 h, retinoic acid 4-hydroxylase activity was induced 9-fold over vehicle (p < 0.03, n = 8). At 96 h, no significant erythema or increased epidermal thickness was found when either retinoic acid (0.001%), all-trans retinol (0.0250%), or liarozole (3%) was applied individually, but when 0.001% retinoic acid and 3% liarozole were applied together, both erythema and increased epidermal thickness occurred. In contrast, 0.025% all-trans retinol and 3% liarozole together caused increased epidermal thickness but no erythema. These data demonstrate that, at doses used here, liarozole, although an effective inhibitor of retinoic acid 4-hydroxylase, cannot function alone like a retinoid in vivo, probably because of retinoic acid 4-hydroxylase induction. In the presence of a low dose retinoic acid or all-trans retinol, however, liarozole can amplify human skin responses to each retinoid in a manner characteristic of the retinoid at a higher dose (erythema and hyperplasia with retinoic acid; no erythema but hyperplasia with all-trans retinol).

Extraction of human epidermis treated with retinol yields retro-retinoids in addition to free retinol and retinyl esters.

Vitamin A, all-trans-retinol, is metabolized to retinoic acid in vivo by a tightly controlled two-step conversion. Retinoic acid then binds to nuclear receptors and modulates cellular proliferation and differentiation. Because only a small fraction of retinol applied topically can be metabolized to retinoic acid, alternative pathways of retinol metabolism in skin were investigated. Retinol (0.4%) was applied to adult human skin under occlusion for 6 h to 4 d. The conversion of retinol into various metabolites such as 14-hydroxy-4,14-retro-retinol, anhydroretinol, 4-oxo-retinol, retinyl esters, and retinyl glucuronides was investigated. The level of 14-hydroxy-retro-retinol was increased from undetectable at time 0 to 326 ng/g wet weight of tissue at 6 h (6% of the retinol level) and maintained approximately the same concentration at 24 h to 409 ng/g wet weight (1.9% of the retinol level); it decreased to 48 ng/g wet weight of tissue (12% of its maximum level) by 4 d. Anhydroretinol was undetectable at time 0, increased only slightly at 6 h, and remained at the same level. We did not detect 4-oxo-retinol. Because 14-hydroxy-retro-retinol was found in the retinol-treated areas, its effects on epidermis were compared with those of retinol. Topical application of trans-retinol (0.3%) significantly increased both epidermal thickness and cellular retinoic acid binding protein II mRNA, whereas 14-hydroxy-4,14-retro-retinol (0.3%) did not increase either of these well-characterized cutaneous retinoid responses. Retinol, when applied topically in pharmacologic doses to human epidermis, remained as free retinol, was metabolized primarily to retinol ester, and was metabolized to a lesser extent to retro-retinoids and didehydroretinol.

Auto-regulation of retinoic acid biosynthesis through regulation of retinol esterification in human keratinocytes.

In this report, we describe an auto-regulatory loop in human keratinocytes, whereby all-trans retinoic acid (retinoic acid) regulates its own biosynthesis from all-trans retinol (retinol) through regulation of retinol esterification. Retinol esterification activity was low in normal proliferating human keratinocytes, cultured in retinoid-free media. Treatment of keratinocytes with retinoic acid induced retinol esterifying activity (8-fold). Induction of retinol esterifying activity was blocked by either actinomycin D or cycloheximide. Based on substrate specificity and inhibitor sensitivity, lecithin:retinol acyltransferase (LRAT) was identified as the retinoic acid-inducible retinol esterifying enzyme. Induction of LRAT by retinoic acid reduced conversion of retinol to retinoic acid by 50%. This reduction in retinoic acid synthesis resulted from sequestration of retinol as retinyl esters, since inhibition of LRAT restored retinoic acid synthesis to control levels. In normal human skin, undifferentiated keratinocytes, in the lowest cell layer, esterified retinol 4 times greater, than differentiating keratinocytes, in upper cell layers, reflecting an induced state, under conditions of retinol sufficiency. Regulation of LRAT activity by retinoic acid provides a novel mechanism through which retinoic acid can regulate its own level by controlling availability of retinol for conversion to retinoic acid. In human skin in vivo, retinyl esters synthesized in basal keratinocytes could undergo hydrolysis during differentiation and thus serve as a source of retinol for keratinocytes in upper layers of skin.

Retinoic acid isomers applied to human skin in vivo each induce a 4-hydroxylase that inactivates only trans retinoic acid.

Application of all-trans retinoic acid to human skin for 4 d under occlusion produces a marked increase in retinoic acid 4-hydroxylase activity. In this study, the possible induction of other hydroxylase in response to 9-cis and 13-cis retinoic acid application to adult human skin in vivo was determined. Application of 0.1% all-trans, 0.1% 9-cis, and 0.1% 13-cis retinoic acid to human skin for 2 d resulted in induction of only all-trans retinoic acid 4-hydroxylase activity. The 4-hydroxylase activity in microsomes from the treated tissue ranged from 838 +/- 46 to 531 +/- 59 pg of 4- hydroxy all-trans retinoic acid formed/min/mg protein (n=6). These same preparations were unable to use 9-cis or 13-cis retinoic acid as substrate for the hydroxylation reaction. Extraction of the retinoic acid isomers from epidermis 48 h after application of 0.1% solution of each isomer yielded significant amounts of all-trans retinoic acid (36-72%) regardless of the isomer applied. The all-trans isomer produced by isomerization of both 9-cis and 13-cis retinoic acids is the likely inducer of the 4-hydroxylase. All-trans retinol and all-trans retinal were unable to compete with all-trans retinoic acid as substrate for 4-hydroxylase enzyme. The 4-hydroxylase induced in response to pharmacological doses of retinoic acids is specific for the all-trans isomer. The inability of 9-cis or 13-cis retinoic acid to induce their own hydroxylation and inactivation or act as substrate for the 4-hydroxylase in skin may have considerable implications in light of the clinical use of retinoids in the treatment of various diseases including cancers.

Application of retinol to human skin in vivo induces epidermal hyperplasia and cellular retinoid binding proteins characteristic of retinoic acid but without measurable retinoic acid levels or irritation.

We investigated the clinical, histologic, and molecular responses of normal human skin to all-trans-retinol (ROL) application, compared to those induced by topical all-trans-retinoic acid (RA), and measured ROL-derived metabolites. Up to 1.6% ROL, 0.025% RA in vehicle (70% ethanol/30% propylene glycol), or vehicle alone were applied in a double-blind fashion to normal buttock skin and occluded for 4 d. ROL produced from none to only trace erythema, which was clinically and statistically insignificant, whereas RA induced a significant 3.7-fold increase in erythema score compared to vehicle (n = 10, p < 0.01). However, ROL induced significant epidermal thickening (1.5-fold at 1.6% ROL, p < 0.01), similar to RA (1.6-fold at 0.025% RA, p < 0.01), relative to the vehicle. ROL, compared with vehicle, also increased mRNA levels of cellular retinoic acid binding protein (CRABP-II) and cellular retinol binding protein (CRBP) genes as determined by Northern analysis (5-6-fold and 6-7-fold, respectively) and riboprobe in situ hybridization. CRABP-II and CRBP protein levels were also higher following ROL than vehicle treatment, as measured by ligand binding (3.2-fold, p < 0.001; n = 7) and Western analysis (3.6-fold, p < 0.003; n = 6), respectively. Epidermal retinyl ester (RE) content, measured after removal of stratum corneum, rose 240-fold (p < 0.005, n = 5) by 24 h of ROL occlusion. RA content, however, was undetectable or detectable only at trace amounts in all samples obtained at 0, 6, 24, and 96 h after ROL occlusion. Detectability of RA was not correlated with ROL treatment (compared to untreated normal skin, p = 0.86) or baseline skin ROL levels (average r = -0.1, p > 0.3). These data demonstrate that ROL application 1) produces trace erythema not significantly different from vehicle, whereas RA causes erythema; 2) induces epidermal thickening and enhances expression of CRABP-II and CRBP mRNAs and proteins as does RA; 3) causes marked accumulation of retinyl ester; and 4) does not significantly increase RA levels. Taken together, the data are compatible with the idea that ROL may be a prohormone of RA, because it produces changes in skin similar to those produced by RA but without measurable RA or irritation.

Retinoic acid antagonizes basal as well as coal tar and glucocorticoid-induced cytochrome P4501A1 expression in human skin.

Cytochrome P4501A1 is known to be expressed in skin and thus has been implicated in the pathogenesis of skin cancer due to certain environmental carcinogens. Retinoic acid (RA) has been used in chemoprevention of certain skin and other epithelial cancers. Therefore, we used Northern and Western analysis to determine the effect of externally applied RA on basal P4501A1 expression. RA reduced basal levels of P4501A1 mRNA and protein by 68 (n = 14, P = 0.005) and 75% (n = 7, P = 0.04) respectively. RA application also reduced basal levels of P4501A2 (another P4501A1 subfamily member) mRNA by 93% (n = 7, P = 0.001) as determined by reverse transcription-polymerase chain reaction. Interestingly, P4501A1 mRNA expression induced by coal tar or glucocorticoid (clobetasol) was reduced 46 (n = 10, P = 0.003) and 69% (n = 5, P < 0.05) respectively by RA co-application. Downregulation of basal P4501A1 expression and antagonism of coal tar mediated P4501A1 induction by RA may be a mechanism involved in chemo-prevention of skin and other epithelial cancer by RA.

Biological activity of all-trans retinol requires metabolic conversion to all-trans retinoic acid and is mediated through activation of nuclear retinoid receptors in human keratinocytes.

The biological activity of all-trans retinol, in human keratinocytes, was investigated through metabolic and functional analyses that assessed the capacity for retinol uptake and metabolism and the mechanism of retinol-induced activation of gene transcription. Human keratinocytes converted all-trans retinol predominantly to retinyl esters, which accounted for 60 and 90% of cell-associated radiolabel after a 90-min pulse and a 48-h chase, respectively. Human keratinocytes also metabolized all-trans retinol to low levels of all-trans retinoic acid (11.47-131.3 ng/mg of protein) in a dose-dependent manner, between 0.3 and 10 microM added retinol. Small amounts of 13-cis retinoic acid (5.47-8.62 ng/mg of protein) were detected, but 9-cis retinoic acid was detected only when keratinocytes were incubated with radiolabeled retinol. There was no accumulation of the oxidized catabolic metabolites 4-hydroxy- or 4-oxoretinoic acid; however, 5,6-epoxy retinoic acid was detected at pharmacological levels (10 and 30 microM) of added retinol. Biological activity of retinol was assessed through analysis of two known retinoic acid-mediated responses: 1) reduction of type I epidermal transglutaminase and 2) activation of a retinoic acid receptor-dependent reporter gene, beta RARE3-tk-CAT. Both all-trans retinol and all-trans retinoic acid reduced type I epidermal transglutaminase in a dose-dependent manner; however, the ED50 for all-trans retinol (10 nM) was 10 times greater than for all-trans retinoic acid (1 nM). All-trans retinol also stimulated beta RARE3-tk-CAT reporter gene activity in a dose-dependent manner. Half-maximal induction was observed at 30 nM retinol, which was again 10-fold greater than observed with all-trans retinoic acid. Cotransfection of human keratinocytes with expression vectors for dominant negative mutant retinoic acid and retinoid X receptors reduced retinol-induced beta RARE3-tk-CAT reporter gene activation by 80%. Inhibition of conversion of all-trans retinol or all-trans retinaldehyde to all-trans retinoic acid by citral reduced beta RARE3-tk-CAT activity 98 and 86%, respectively. These data demonstrate that retinol-induced responses in human keratinocytes are mediated by its tightly regulated conversion to retinoic acid, which functions as a ligand to activate nuclear retinoic acid receptors.

A retinoic acid-inducible skin-specific gene (RIS-1/psoriasin): molecular cloning and analysis of gene expression in human skin in vivo and cultured skin cells in vitro.

A retinoic acid (RA) inducible skin-specific gene transcript (RIS-1) was isolated by differential hybridization screening of a RA-treated human skin cDNA library. The library was constructed from pooled RNA derived from normal adult human skin treated with all trans-RA for 4 h (n = 6) and 12 h (n = 6) in vivo. RIS-1 cDNA corresponded to a 0.6 kb transcript that was barely detectable in normal adult human skin but was significantly induced by 8 h in RA-treated compared to vehicle-treated skin (range 1.1-3.6 fold). Prolonged RA treatment for up to 24 h further increased relative RIS-1 mRNA levels by 1.3-5.5 fold. HPLC analysis of the RA content of 0.1% RA-treated skin in vivo revealed significant levels at 6 h (18.8-120.6 ng RA/g wet weight tissue; approximately 240 nM), immediately preceding the time point at which the increased RIS-1 mRNA level was first seen. This concentration of RA also induced the mRNA levels for cellular RA binding protein II (1.6-19 fold), a marker of RA activity in human skin. RIS-1 mRNA was detected by Northern and dot blotting only in normal skin but not in any other normal human tissues examined, indicating a tissue-specific pattern of gene expression. RIS-1 transcripts were detected at very low levels in untreated cultured human epidermal keratinocytes, while no expression was seen in dermal fibroblasts and melanocytes, the other major cell types in skin. Southern analysis of human and mouse DNA indicated the existence of evolutionarily conserved sequences for RIS-1 between these two species. The polypeptide sequence derived from the partial RIS-1 cDNA was found to be identical to the calcium binding domain found in 'psoriasin', a gene whose expression appears to be increased in the skin of psoriasis patients.

In vitro model of essential fatty acid deficiency.

The polyunsaturated fatty acids linoleic acid (18:2, n-6) and arachidonic acid (20:4, n-6) are essential for normal skin function and structure, both as eicosanoid precursors and as components of lipids forming cell membranes. Adult human keratinocytes grow optimally in serum-free medium (MCDB 153) that contains no fatty acids. These keratinocytes expand rapidly and produce normal epidermis upon in vivo grafting. Analysis of lipid extracts of epidermis and of cultured keratinocytes was done to determine the fatty acid composition of cells grown in essential fatty acid (EFA)-deficient medium. Gas chromatography and high-performance liquid chromatography analyses were done of the fatty acids in the entire cell and in a thin-layer chromatography separated fraction containing those lipids that form cellular membranes. Comparison of snap-frozen epidermis and epidermal basal cell suspensions to passage 1 to 4 cultures shows that the cells are in an extreme essential fatty acid-deficient state by the first passage. The amount of the saturated fatty acids 16:0, 18:0, and 14:0 is unchanged by culture. The polyunsaturated fatty acids are found to be significantly decreased, the cells balancing their lack with a significant increase in the relative abundance of the monounsaturated fatty acids, 18:1 and 16:1. Greater than 85-90% of the fatty acids was found in lipids associated with membranes and no unusual fatty acids were detected. Because the serum-free medium is fatty acid free and the cells cannot synthesize essential fatty acids, the rapid division of the cells results in the predominance of an extreme EFA-deficient cell type. The essential fatty acid-deficient keratinocyte is an excellent adult, normal epidermal cell model that can be used to study EFA deficiency and the effect of the eicosanoid and fatty acids on cell function and structure.

Human skin levels of retinoic acid and cytochrome P-450-derived 4-hydroxyretinoic acid after topical application of retinoic acid in vivo compared to concentrations required to stimulate retinoic acid receptor-mediated transcription in vitro.

Metabolism of retinoic acid to a less active metabolite, 4-hydroxyretinoic acid, occurs via cytochrome P-450 isozyme(s). Effect of a pharmacological dose of retinoic acid on the level of retinoic acid in skin and on cytochrome P-450 activity was investigated. A cream containing 0.1% retinoic acid or cream alone was applied topically to adult human skin for four days under occlusion. Treated areas were removed by a keratome and a microsomal fraction was isolated from each biopsy. In vitro incubation of 3H-retinoic acid with microsomes from in vivo retinoic acid treated sites resulted in a 4.5-fold increase (P = 0.0001, n = 13) in its transformation to 4-hydroxyretinoic acid in comparison to in vitro incubations with microsomes from in vivo cream alone treated sites. This cytochrome P-450 mediated activity was oxygen- and NADPH-dependent and was inhibited 68% by 5 microM ketoconazole (P = 0.0035, n = 8) and 51% by carbon monoxide (P = 0.02, n = 6). Cotransfection of individual retinoic acid receptors (RARs) or retinoid X receptor-alpha (RXR-alpha) and a chloramphenicol acetyl transferase (CAT) reporter plasmid containing a retinoic acid responsive element into CV-1 cells was used to determine the ED50 values for stimulation of CAT activity by retinoic acid and its metabolites. Levels of all trans and 13-cis RA in RA-treated tissues were greater than the ED50 values determined for all three RARs with these compounds. Furthermore, the level of all trans RA was greater than the ED50 for RXR-alpha whereas the 4-OH RA level was greater than the ED50 for RAR-beta and RAR-gamma but less than for RAR-alpha and RXR-alpha. These data suggest that there are sufficient amounts of retinoic acid in treated skin to activate gene transcription over both RARs and RXR-alpha.

Arachidonic acid metabolites: effects on inflammation of fetal rabbit excisional wounds.

Uncovered fetal rabbit excisional wounds do not exhibit any classic signs of healing; wounds covered with an impermeable cover do contract, reepithelialize, and exhibit inflammation. Prostaglandin E2 (PGE2) is elevated in amniotic fluid, acting as an immunosuppressant at the maternal-fetal interface. Full-thickness excisional wounds were made on 25-day gestational age rabbit fetuses. Half the wounds were covered with an impermeable cover. Tissue from covered, uncovered, and nonwounded fetuses was examined 72 h after wounding for arachidonic acid metabolites. Uncovered wounds had significantly (P less than or equal to 0.05) elevated levels of PGE2, PGF2 alpha, and 12-HETE versus covered wounds and control tissue. Covered wounds had significantly elevated levels of 15-HETE compared to uncovered and control tissue. The elevated PGE2 in uncovered wounds may act as a fetal immunosuppressant; covered wounds (lower PGE2) developed cellular inflammation. Further investigations of these interactions may permit modulation of adult inflammation.

Cyclosporine metabolism by P450IIIA in rat enterocytes--another determinant of oral bioavailability?

Cyclosporine is converted to its major metabolites (M-17, M-1, and M-21) in human liver by enzymes belonging to the P450IIIA subfamily. These enzymes are also present in rat and human enterocytes; however, the possibility that CsA is metabolized in enterocytes has not been previously investigated. We therefore directly compared metabolism of 3H-CsA in microsomes prepared from liver and jejunal enterocytes. M-17, M-1, and M-21 were the major CsA metabolites produced by enterocyte microsomes. This metabolism appeared to be catalyzed by P450IIIA, because pretreatment of rats with the P450IIIA inducer dexamethasone significantly increased the rate of CsA metabolism in enterocyte microsomes and preincubation of enterocyte microsomes with anti-P450IIIA IgG inhibited the production of CsA metabolites by greater than 95%. To determine if enterocyte P450IIIA metabolizes CsA in vivo, rats were pretreated with the P450IIIA inducer dexamethasone, the P450IIIA inhibitor erythromycin, or vehicle alone. At laparotomy, 2 mg/kg of 3H-CsA was injected into a sealed loop of jejunum, and after collection of the mesenteric venous blood draining this segment for 45 min, the production of M-17 and M-1 was measured. In the control group, a mean of 3.9% of the recovered radioactivity was found as M-1 and M-17. In the rats pretreated with dexamethasone, a mean of 8.4% of the radioactivity was found as M-1 and M-17 (P less than 0.05 relative to control) and this decreased to 2.3% in the group pretreated with erythromycin (P = 0.08 relative to control). We conclude that P450IIIA in jejunal enterocytes readily metabolizes CsA. Furthermore, the metabolism of CsA by enterocytes in vivo is substantial and likely contributes to "first pass metabolism" of orally administered CsA. Our observations provide novel hypotheses to explain some important drug interactions and interpatient differences in CsA dosing requirements.

Cellular, immunologic and biochemical characterization of topical retinoic acid-treated human skin.

Histologic and clinical improvement of sun-exposed skin following topical treatment with retinoic acid has been reported. Daily application of retinoic acid typically results within 2-5 d in an erythematous scaling reaction, which lessens with continued usage. The cellular, immunologic, and biochemical basis of this retinoid reaction and its role in the repair of photodamaged skin are not known. To investigate the retinoid reaction in man, we have treated non-sun-exposed skin with 0.1% retinoic acid cream (Retin-A, Ortho Pharmaceutical Corporation, Raritan, NJ) under occlusion for 4 d to induce erythema and then examined changes in 1) histology, 2) expression of cell-surface molecules, 3) the enzymes and second messengers of the phospholipase C/protein kinase C signal-transduction system, 4) levels of eicosanoids, and 5) levels of interleukin-1 protein and mRNA. These parameters were chosen for measurement both because they are indicators of epidermal function and previous studies suggest they may be responsive to retinoic acid treatment. Epidermal cell growth as judged by increased epidermal thickness and mitotic figures was significantly increased in retinoic acid-treated skin compared to vehicle-treated controls. Increased numbers of CD4+ T cells accompanied by prominence of dermal dendrocytes in the papillary dermis and focal keratinocyte expression of intercellular adhesion molecule-1 were observed in retinoic acid-treated biopsies. Phosphoinositide-specific phospholipase C activity and 1,2-diacylglycerol content were also elevated in retinoic acid-treated epidermis. Protein kinase C activity was reduced by one third in both the soluble and membrane fraction, suggesting down-regulation. Surprisingly, in view of the inflammatory nature of the retinoid reaction, no increases were observed in arachidonic acid, its metabolites, interleukin-1 alpha, or interleukin-1 beta. To examine the specificity of the retinoid reaction, subjects were treated with the irritant sodium lauryl sulfate, under conditions that resulted in a reaction clinically similar to that observed with retinoic acid. The histologic alterations induced by sodium lauryl sulfate were found to be indistinguishable from those induced by retinoic acid. These data indicate that, although a wide range of cellular and molecular alterations occur in retinoic acid-treated skin, these changes may not be necessarily specific or unique for retinoic acid.

Effect of topical cyclosporine rinse on oral lichen planus. A double-blind analysis.

BACKGROUND: Oral lichen planus is a relatively common disorder of the mouth that can be debilitating. It is frequently palliated with topical or systemic corticosteroids and retinoids. These treatments require prolonged use, however, and are not always effective. METHODS: In a double-blind trial, 16 patients with symptomatic oral lichen planus were randomly assigned to receive either topical cyclosporine or its vehicle. The patients swished and expectorated 5 ml of medication (containing 100 mg of cyclosporine per milliliter) three times daily. RESULTS: After eight weeks, the eight recipients of cyclosporine had marked improvement in erythema (P = 0.003), erosion (P = 0.02), reticulation (presence of white lacelike lesions; P = 0.007), and pain (P = 0.002), whereas the eight recipients of vehicle had no change or minimal improvement. After a switch to cyclosporine for eight weeks, the vehicle-treated patients had improvement similar to that seen in the patients who initially received cyclosporine. There were no systemic side effects. In most cases blood cyclosporine levels were low or undertectable. Cyclosporine levels present in specimens of oral mucosa at the end of therapy four hours after the patients swished were similar to the levels previously reported in psoriatic lesions after treatment with systemic cyclosporine (14 mg per kilogram of body weight per day). CONCLUSIONS: As a topical preparation, cyclosporine may be useful in the treatment of oral lichen planus and possibly other cutaneous disorders.

Sulfasalazine improves psoriasis. A double-blind analysis.

In an 8-week double-blind trial of sulfasalazine for the treatment of moderate-to-severe psoriasis, 23 and 27 patients received the active and placebo tablets, respectively. At the end of the double-blind phase, there were 17 assessable patients receiving sulfasalazine; 7 (41%) had marked improvement, 7 (41%) had moderate improvement, and 3 (18%) demonstrated minimal change. Only 1 patient receiving placebo demonstrated moderate improvement, whereas the rest had minimal improvement or worsening of psoriasis. When the randomization code was broken, patients receiving sulfasalazine were allowed to continue therapy for an additional 4 weeks in an open manner, while those using placebo left the study. Six of 23 patients discontinued sulfasalazine therapy during the double-blind phase because of side effects, 4 due to the development of a cutaneous eruption and 2 due to nausea. Fourteen of 17 patients, who were assessable at the end of the 8-week double-blind phase, completed the additional 4 weeks of sulfasalazine therapy. Of these 14 patients, marked improvement occurred in 8 (57%), moderate improvement in 2 (14%), and minimal improvement in 4 (29%), compared with pretherapy. The low incidence of severe side effects makes sulfasalazine a consideration for oral therapy in patients whose disease severity does not justify use of methotrexate, etretinate, or psoralen plus UV-A, but whose disease severity is too widespread for safe and practical use of topical corticosteroids.

Topical cyclosporine A inhibits the phorbol ester induced hyperplastic inflammatory response but not protein kinase C activation in mouse epidermis.

Cyclosporine A (CsA) is efficacious in the treatment of psoriasis. Although CsA is known to inhibit T-lymphocyte proliferation in vitro, whether this is its mode of action in psoriasis is uncertain. 12-0-tetradecanoylphorbol-13-acetate (TPA) induces an inflammatory, hyperplastic response in mouse skin, with many of the biochemical and histologic aberrations that occur in psoriatic epidermis. Protein kinase C is the major cellular phorbol ester receptor, and most responses of cells to TPA are mediated by PK-C, which is directly activated by TPA. We therefore have investigated the effects of CsA on pleiotypic responses induced by TPA and whether CsA acts in vivo as a direct inhibitor of PK-C. Simultaneous application of CsA (1.7 mumol) and TPA (10 nmol) to mouse skin significantly reduced inflammatory cell infiltration and increased epidermal thickness induced by TPA treatment alone. CsA had to be applied within 30 min of TPA application in order to have a significant inhibitory effect. Optimal doses of CsA inhibited TPA-induced ODC activity, TGase activity, arachidonic acid release, and interleukin-1 beta (IL-1 beta) mRNA to the same degree (approximately 80%), despite measurement at widely different times (30 min-12 h) required to obtain maximal induction by TPA. CsA did not, however, directly inhibit activation of PK-C by TPA. These data demonstrate that CsA blocks the pleiotypic responses of mouse skin to TPA treatment involving biochemical events, inflammatory cell infiltration, and epidermal hyperplasia. The molecular site(s) of action of CsA appears to be distal to the initial activation of PK-C by TPA and clearly inhibits PK-C inducible events. Furthermore, the above data suggest that CsA may directly affect keratinocytes in vivo.

Determination of 5,12, and 15-lipoxygenase products in keratomed biopsies of normal and psoriatic skin.

Keratomed epidermal tissue from normal individuals and from the lesional and non-lesional skin of psoriasis patients served as source materials for the extraction, separation, and quantitation of eicosanoids that may be important to cutaneous function and pathophysiology. The eicosanoids were extracted in ethanol and buffer, partially purified on SEP-PAKs, separated by reverse phase microbore high-performance liquid chromatography, and quantitated by radioimmunoassay or integration of absorbency peaks obtained by high performance liquid chromatography. The involved areas from psoriasis patients contained a statistically significant seven- to 11-fold increase in the levels of leukotriene B4, 13-hydroxyoctadecadienoic acid-like compound, 15-hydroxyeicosatetraenoic acid compound and 12-hydroxyeicosatetraenoic acid in comparison to normal samples and a three- to sevenfold increase in comparison to uninvolved tissue. The uninvolved areas contained 40% to 100% increases in the levels of these compounds in comparison to normal tissue; these increases were statistically significant except for 13-hydroxyoctadecadienoic acid-like compound. From a single keratome biopsy, multiple eicosanoids can be separated and quantitated; in addition, levels before, during, and after therapy for psoriasis may be compared.