The effects of vitamin A derivative etretinate on the skin of MRL mice

MRL/Mp-lpr/lpr (MRL/lpr) mice are characterized by the disorder of apoptosis due to defects in Fas antigens and autoimmune symptoms including spontaneous lupus erythematosus (LE)-like skin lesions. MRL/Mp- +/+ (MRL/n) mice do not carry the defect of lpr mutation nor do they exhibit skin disorders during the first six months of life. Retinoids are known to inhibit the proliferation of skin fibroblasts, collagen synthesis, modulate immune responses, and apoptosis by Fas ligand upregulation in skin fibroblasts. We examined changes in dermal thickness and appearance of skin disorders in five months old MRL/lpr mice by oral treatment with etretinate, a retinoic acid derivative. Etretinate treated MRL/lpr mice did not have skin lesions or dermatopathological characteristics including an increase in cells infiltrating the dermis. The mean dermal thickness of MRL/lpr and MRL/n mice treated with etretinate decreased significantly and apoptotic cells density in the dermis of MRL/lpr mice with etretinate was significantly higher compared with the control group (P, 0.05) although MRL/lpr mice have a defect within the Fas antigen. We assumed that etretinate reduced dermal thickness, and suppressed the appearance of skin lesions by inducting apoptosis and perhaps regulation of cytokine expression.

Comparison of the in vitro and in vivo effects of retinoids either alone or in combination with cisplatin and 5-fluorouracil on tumor development and metastasis of melanoma

PURPOSE

Retinoids have previously been reported to inhibit proliferation of melanoma cell lines in vitro. However, the relative antimetastatic efficacy of various retinoids on melanoma in vivo is unknown. Therefore, we investigated the effects of different retinoids on the invasion and metastasis of murine melanoma B16-F10 cells in vitro and in vivo. Based on the findings, the antitumor effects of a selected retinoid either alone or in combination with cisplatin were also investigated in a preclinical mouse melanoma model.

METHODS

Cell proliferation and invasion analyses of murine melanoma B16-F10 cells were assessed in the presence of different retinoids, either alone or in combination with cisplatin (CDDP) or 5-fluorouracil (5-FU). Experimental lung metastasis assay was performed in this study to investigate the antimetastatic efficacy of retinoids. Additionally, a mouse melanoma model was used to assess the antitumor efficacy of a selected retinoid in combination with cisplatin.

RESULTS

Retinoids showed significant antiproliferation and anti-invasion effects on murine melanoma B16-F10 cells. Pretreatment with retinoids increased the sensitivity to CDDP but not to 5-FU in in-vitro. Moreover, the number of metastatic colonies formed in the lungs of mice injected intravenously with B16-F10 cells was significantly reduced by injecting the respective retinoid once a day for 10 days. Treatment with a combination of cisplatin and 13-cis-retinoic acid resulted in a significant reduction in primary tumor size and the number of lung metastatic nodules in melanoma-bearing mice.

CONCLUSION

These results suggest that retinoids not only exhibit antimetastatic effect, but also enhance the antitumor activity of cisplatin in vivo.

In vivo and in vitro influence of etretinate on erythrocyte membrane fluidity

The molecular mechanisms underlying the action of synthetic retinoids have been studied intensively, but they are not fully understood yet. It is well known that retinoids exert their effects on gene expression via the retinoic acid receptor. Some observations suggest that the main aromatic retinoid etretinate (Tigason) exerts its therapeutic effect in psoriasis also through an action on the cell membrane. In this paper, we present the results of previously unreleased experiments (when Tigason was still in use) concerning the in vivo and in vitro influence of etretinate on erythrocyte membrane fluidity in psoriatic patients. Erythrocytes from healthy subjects and topically treated psoriatics were chosen as control groups. Membrane fluidity was measured by the electron paramagnetic resonance (EPR) spin-labelling technique. Erythrocytes from psoriatic patients had lower membrane fluidity, a lower antioxidant activity and a greater susceptibility to peroxidation than those from healthy subjects. After treatment with etretinate, a significant increase in erythrocyte membrane fluidity and in antioxidant activity as well as a decrease in lipid peroxidation were observed in erythrocytes from patients. Local therapy of psoriatic lesions had no influence on the improvement in membrane fluidity and antioxidant activity of erythrocytes. Incubation of erythrocytes from healthy controls and topically treated psoriatics with etretinate in vitro confirmed its fluidizing effect on erythrocyte membranes. These data may indicate that two mechanisms lead to an increase in erythrocyte membrane fluidity in psoriatic patients treated with Tigason: the first one, indirect, by improvement of the antioxidant defence system and cell protection against lipid peroxidation, and the second one, by a direct fluidizing effect of etretinate on the erythrocyte membrane.

Etretinate augments interferon beta-1b effects on suppressor cells in multiple sclerosis

BACKGROUND

Interferon beta treatment is only partially effective in multiple sclerosis (MS) suggesting a potential role for adjunctive therapies. Retinoids can augment the clinical efficacy of type 1 interferons in patients with cancer. We reasoned that the same might hold in MS. Interferon beta-1b added to peripheral blood mononuclear cells in vitro partially reverses the CD8 suppressor cell defect of patients with MS. All-trans retinoic acid added to peripheral blood mononuclear cells from untreated patients with MS or from controls potentiates this ability of interferon beta-1b to augment CD8 suppressor cell function in vitro.

OBJECTIVE

To determine whether retinoid administration to patients with MS who are being treated with interferon beta-1b augments their CD8 suppressor cell function.

SETTING

A university hospital MS clinic.

PARTICIPANTS

Patients with MS who were being treated with interferon beta-1b, 14 patients with secondary progressive MS and 3 patients with relapsing remitting MS.

RESULTS

Seventeen patients with MS received etretinate treatment for up to 6 months. Planned dosing was 10 mg 3 times daily for the first month, 25 mg twice daily for the second and third months, and 10 mg twice daily thereafter. The 25-mg twice daily dose was not well tolerated and of the 14 patients who remained in the phase 1 clinical trial through month 3 dose reduction to 10 mg thrice daily was required in 1 patient and to 10 mg twice daily in 4 patients. Eleven patients completed the trial. Etretinate treatment significantly augmented suppressor function over baseline values at 1, 3, and 6 months. No meaningful change was noted in disability or quality of life over the course of the phase 1 clinical trial. Neuropsychological testing of completers suggested improvement on selected aspects of verbal memory at 6 months compared with baseline values.

CONCLUSIONS

Etretinate treatment at a dose of 10 mg twice or three times daily augments suppressor cell function in patients with MS receiving interferon beta-1b. Higher dose etretinate treatment (25 mg twice daily) is poorly tolerated by patients with MS. Even at 10 mg twice daily adverse experiences involving the mucous membranes and the skin become troublesome for some, but not all, patients. Whether pulse therapy or administration of retinoid restricted to the day of interferon beta dosing will also augment suppressor function, while being better tolerated, remains to be determined.

Inhibitory effect of retinoid on esophageal carcinogenesis in rats induced by N-nitroso-N-methylbutylamine in relation to cellular retinoic acid-binding protein

The inhibitory effect of a synthetic retinoid, ethyl alltrans-9-(4-methoxy-2, 3, 6-trimethyl-phenyl)-3, 7-dimethyl-2, 4, 6, 8-nonatetraenoate (Tigason), on esophageal carcinogenesis in F344 rats induced by N-nitroso-N-methylbutylamine (NMBA) was evaluated. The animals were given NMBA daily in their drinking water for 21 weeks at a concentration of 15 mg per liter ad libitum starting at 8 weeks of age. One week before the beginning of NMBA treatment, the rats were divided randomly into Tigason-fed and -unfed groups. Thirty-five rats were fed a diet supplemented with Tigason at a concentration of 30 mg per kg of diet, and 80 rats were given a basal diet alone. In NMBA-treated rats, multiple papillomas were seen 11 weeks after NMBA treatment and squamous cell carcinoma developed 12 weeks after NMBA; the tumors increased in number thereafter, and the numbers of papillomas and carcinomas were the same at 17 and 21 weeks after NMBA. At 21 weeks after NMBA treatment, the number of papillomas was similar, regardless of the dietary Tigason supplement, however, the number of esophageal squamous cell carcinomas was significantly lower in the Tigason-fed rats than in -unfed animals (p < 0.025). In normal esophageal tissues, a small amount of cellular retinoic acid-binding protein (cRABP) was detected throughout the experimental period, while during carcinogenesis, the levels of cRABP increased continuously until 16 weeks after NMBA; the cRABP level was higher in papillomas than in squamous cell carcinomas. As Tigason specificially blocked the progression of papillomas to carcinomas, it may be a promising candidate chemopreventive agent in esophageal carcinogenesis.

Intervention studies on cancer

This paper (and an extensive supplementary report) considers how far cancer/risk factor associations based on epidemiology have been confirmed by evidence from 226 studies involving interventions other than smoking. Many are small, uncontrolled, of unrepresentative populations, concern cancer markers not cancer, and may involve combinations of agents. Many agents suspected of causing cancer are untested by intervention trials. For seven of 16 agents tested (fibre, folic acid, low-fat diet, riboflavin, zinc, vitamin Bs, and vitamin D), the evidence is clearly inadequate to confirm or deny the epidemiology, while the evidence relating to calcium only concerns biomarkers. For other agents, the evidence relating to cancer itself is weak. In studies where cancer is the endpoint, only three effects have been replicated: (a) selenium supplementation and decreased liver cancer incidence, (b) treatment by the retinoid etretinate and reduced bladder tumours in susceptible individuals, and (c) beta-carotene supplementation and increased lung cancer incidence. Studies involving pre-cancerous conditions as the endpoint, which have a number of practical advantages, more frequently report benefits of intervention. Thus, oral pre-cancerous lesions can certainly be reduced by beta-carotene, vitamin A, and other retinoids, and possibly by vitamin E. It also seems that retinoids can reduce pre-cancerous cervix, skin and lung lesions, that vitamin C and the NSAID sulindac can reduce colonic polyps, and that sunscreens can reduce solar keratoses. Our findings clearly show that the great majority of causal relationships suggested by epidemiology have not been validated by intervention trials. This may be partly due to lack of suitable studies of adequate size or duration, or to using single dietary compounds as agents that are by themselves not responsible for the epidemiologically-observed associations between diet and cancer. However, this lack of validation must cause concern in view of the markedly conflicting evidence on beta-carotene and lung cancer between epidemiological and intervention studies. More intervention studies are needed, but in their absence, caution in interpreting epidemiological findings is warranted.

Expression and function of beta 2 integrin CD11B/CD18 on leukocytes from patients with psoriasis

The expression of beta 2 integrin CD11b on granulocytes and monocytes from patients with psoriasis vulgaris and pustular psoriasis was examined by flow cytometry. The amount of CD11b expressed on both granulocytes and monocytes was greater in 4 patients with pustular psoriasis than in 16 patients with psoriasis vulgaris. Its expression correlated with the development of pustules on the skin. No difference was seen between healthy blood donors and patients with active psoriasis vulgaris. Three patients with pustular psoriasis were followed during retinoid treatment. Granulocytes and monocytes showed a decrease in CD11b expression after administration of retinoids, in parallel with clearing of the skin. The adherence of granulocytes isolated from psoriasis patients was tested on cultured human umbilical vein endothelium. No significant difference in adherence was observed between control cells and cells from patients with active psoriasis vulgaris. These data indicate that the development of microabscesses in the dermis in psoriasis vulgaris is not related to enhanced beta 2 integrin function. The increased CD11b expression found in patients with pustular psoriasis may, however, serve as a triggering factor for pustule formation in pustular psoriasis.

Differential effect of etretinate on proliferation and extracellular matrix metabolism of human dermal fibroblasts from elderly and young individuals in a novel three-dimensional culture

The effect of etretinate on proliferation and biosynthesis of collagens and glycosaminoglycans (GAGs) were investigated using human dermal fibroblasts in a novel three-dimensional culture supplemented with L-ascorbic acid 2-phosphate. Fibroblasts from two young and two elderly individuals were studied at different concentrations of etretinate, 0.25, 1.0 and 2.5 microg/ml. Collagens (hydroxyproline) and GAGs (disaccharide units) extracted from the cell layer were analyzed and quantified biochemically by high-performance liquid chromatography (HPLC). Etretinate showed no significant effect on fibroblast proliferation either in the monolayer or the three-dimensional culture. Etretinate increased the collagen or GAGs content in the cell layer, which was prominent at etretinate concentrations of 1.0 and 2.5 or 0.25 microg/ml, respectively in fibroblasts from the elderly (P < 0.05). This effect was not seen in dermal fibroblast from the young. These results suggest that etretinate may have the differential effect on collagen and GAG metabolisms depending on the donor age of the cultured fibroblasts.

In vitro effects of retinoids on mitogen-induced peripheral blood leucocyte responses

The aim of the present study was to investigate the influence of three different retinoids, isotretinoin, etretinate and acitretin, on the mitogenic response of peripheral blood mononuclear cells (PBMCs) to PHA and PMA in vitro. All three retinoids at high concentrations (10(-4)M) significantly inhibited the mitogenic response of PBMCs to these mitogens. At lower concentrations (10(-5) M and 10(-6) M) none of the three retinoids had any effect on PBMC proliferation in response to PHA. Interestingly, isotretinoin and etretinate significantly enhanced the PMA-induced stimulation of proliferation, whereas acitretin at 10(-5) M failed to influence the mitogenic response to PMA but enhanced it at 10(-6) M. The enhancing effects of retinoids on the proliferative response of PMA-stimulated PBMCs were reversed by rapamycin (10 ng/ml), an immunosuppressant known to inhibit the phorbol ester-induced protein kinase C pathway of lymphocyte activation. In conclusion, our study indicates that retinoids directly trigger the PMA-induced protein kinase C pathway of lymphocyte activation in a concentration-dependent manner. This observation could explain the findings of previous studies showing an in vivo immunopotentiating effect of retinoids on certain immune functions.

Retinoids irreversibly inhibit in vitro growth of Epstein-Barr virus-immortalized B lymphocytes

Natural and synthetic retinoids have proved to be effective in the treatment and prevention of various human cancers. In the present study, we investigated the effect of retinoids on Epstein-Barr virus (EBV)-infected lymphoblastoid cell lines (LCLs), since these cells closely resemble those that give rise to EBV-related lymphoproliferative disorders in the immunosuppressed host. All six compounds tested inhibited LCL proliferation with no significant direct cytotoxicity, but 9-cis-retinoic acid (RA), 13-cis-RA, and all-trans-RA (ATRA) were markedly more efficacious than Ro40-8757, Ro13-6298, and etretinate. The antiproliferative action of the three most effective compounds was confirmed in a large panel of LCLs, thus appearing as a generalized phenomenon in these cells. LCL growth was irreversibly inhibited even after 2 days of treatment at drug concentrations corresponding to therapeutically achievable plasma levels. Retinoid-treated cells showed a marked downregulation of CD71 and a decreased S-phase compartment with a parallel accumulation in Gzero/ G1 phases. These cell cycle perturbations were associated with the upregulation of p27 Kip1, a nuclear protein that controls entrance and progression through the cell cycle by inhibiting several cyclin/cyclin-dependent kinase complexes. Unlike what is observed in other systems, the antiproliferative effect exerted by retinoids on LCLs was not due to the acquisition of a terminally differentiated status. In fact, retinoid-induced modifications of cell morphology, phenotype (downregulation of CD19, HLA-DR, and s-Ig, and increased expression of CD38 and c-Ig), and IgM production were late events, highly heterogeneous, and often slightly relevant, being therefore only partially indicative of a drug-related differentiative process. Moreover, EBV-encoded EBV nuclear antigen-2 and latent membrane protein-1 proteins were inconstantly downregulated by retinoids, indicating that their growth-inhibitory effect is not mediated by a direct modulation of viral latent antigen expression. The strong antiproliferative activity exerted by retinoids in our experimental model indicates that these compounds may represent a useful tool in the medical management of EBV-related lymphoproliferative disorders of immunosuppressed patients.

Production and secretion of platelet-derived growth factor AB by cultured human keratinocytes: regulatory effects of phorbol 12-myristate 13-acetate, etretinate, 1,25-dihydroxyvitamin D3, and several cytokines

Platelet-derived growth factor (PDGF) is a potent mitogen for several mesenchymal cells and plays an important role in wound repair. Three PDGF isoforms, PDGF-AA, PDGF-BB, and PDGF-AB, have been found to be generated in various tissues. PDGF-AB production by normal human keratinocytes (NHKs), by human squamous cell carcinoma cell line (HSC-1) cells, and by human dermal fibroblasts (HDFs) was studied in the presence of agents which influence cell growth. Both NHKs and HSC-1 cells spontaneously produced and secreted PDGF-AB. NHKs grown in keratinocyte growth medium produced more PDGF-AB than did those grown in keratinocyte basic medium. Phorbol 12-myristate 13-acetate inhibited PDGF-AB production in NHKs but promoted its production in HSC-1 cells. 1,25-dihydroxyvitamin D3 up-regulated PDGF-AB production, whereas etretinate did not. High levels of calcium in the culture medium induced little change in cellular PDGF-AB levels. Prostaglandin E1 slightly inhibited PDGF-AB production, transforming growth factor beta 1 promoted PDGF-AB production and interferon-gamma, interleukin-1 alpha, and tumor necrosis factor-alpha failed to exert any influence at all. Cultured HDFs did not produce any detectable PDGF-AB. These results suggest that keratinocytes are a major source of cutaneous PDGF and that this factor may therefore play an important role in wound repair and in certain proliferative skin diseases.

Modulation of collagen synthesis and cell proliferation by retinoids in human skin fibroblasts

The effect of the retinoids, 13-cis-retinoic acid (-RA), etretinate and all-trans-RA on collagen synthesis and cell proliferation of human skin fibroblasts was studied. These compounds all inhibited collagen synthesis at concentrations between 10(-8) and 10(-5) M after 48 h treatments. The inhibitory effect of 13-cis-RA was the most pronounced. Both all-trans-RA and etretinate inhibited DNA synthesis, to 60% and 53% of control value, respectively, at 10(-5) M. In contrast, 13-cis-RA did not show any significant effect on DNA synthesis at the concentrations used. 13-cis-RA appears to be a unique drug showing a pronounced inhibitor effect on collagen synthesis without affecting DNA synthesis and may prove a useful tool for the treatment of fibrotic diseases.

The effect of topical retinoic acid (Etretinate) on mouse conjunctival Langerhans cells

Four groups of BALB/c mice were treated locally with different concentrations (0.1-1.0%) of retinoic acid (Etretinate) ointment for a period of one to four weeks. A fifth group was treated with the ointment base only. Ia-positive dendritic cells were identified by an indirect immunofluorescence technique which was confirmed by ADPase staining. Quantitative counts of Langerhans cells were performed for each group. After four weeks, the 0.1 and 0.2% Etretinate-treated conjunctiva showed no significant reduction in Langerhans cell concentration. However, following 0.5 and 1.0% Etretinate treatment for four weeks, the concentration of Langerhans cells was significantly reduced, and the cells showed morphologic changes, consisting mainly of loss of dendritic processes. Between one and two weeks of therapy at these two high concentrations, no significant changes were found. Light microscopy of the conjunctival epithelium showed marked atrophic changes following four weeks of 0.5 and 1.0% Etretinate treatment compared to no changes with 0.1 and 0.2% Etretinate treatment.

Low-dose short-term cyclosporine versus etretinate in psoriasis: improvement of skin, nail, and joint involvement

BACKGROUND

High-dose cyclosporine therapy significantly alleviates psoriasis within 2 to 4 weeks but is associated with a high rate of side effects. Reports are conflicting on the frequency and promptness of relapse after discontinuation of cyclosporine therapy.

OBJECTIVE

Our purpose was to compare the efficacy and safety of low-dose cyclosporine with that of etretinate and the stability of remission after replacing cyclosporine therapy with topical anthralin during tapering of cyclosporine.

METHODS

In a multicenter study 210 patients with moderate to severe chronic plaque-type psoriasis were randomly assigned to treatment with cyclosporine or etretinate. The initial dosages were 2.5 mg/kg/day for cyclosporine and 0.5 mg/kg/day for etretinate, which could be individually adjusted to 5.0 and 0.75 mg/kg/day, respectively. After a treatment phase of 10 weeks (phase 1) patients receiving cyclosporine were again randomly assigned to a group in which cyclosporine was replaced by topical dithranol (anthralin), or to another group in which the drug was tapered during the next 12 weeks (phase 2). All patients treated with etretinate discontinued therapy after 10 weeks and used topical dithranol.

RESULTS

Mean Psoriasis Area and Severity Index decreased by 71% in the cyclosporine group and by 47% in the etretinate group during phase 1. After 10 weeks of treatment 47% of the patients treated with cyclosporine and 10% of those treated with etretinate showed a reduction of more than 80% in skin involvement. Sixty-four percent of the cyclosporine group and 48% of the etretinate group did not require an increase in the initial dosage, resulting in a mean daily dose of 3.0 and 0.53 mg/kg, respectively. There was significant alleviation of nail involvement and joint complaints in both groups. In phase 2 the increase in mean Psoriasis Area and Severity Index and the incidence of relapse were significantly higher in patients in whom cyclosporine was discontinued and replaced by dithranol than in patients in whom cyclosporine was tapered or who were pretreated with etretinate. During treatment four patients from the cyclosporine group and three patients of the etretinate group discontinued the study because of side effects.

CONCLUSION

Low-dose short-term cyclosporine therapy for psoriasis is, in comparison with etretinate, highly effective and well tolerated. Individually adjusted cyclosporine therapy allows the majority of patients to continue the low dosage of 2.5 mg/kg/day and still achieve a good clinical response. Remission can be better preserved by tapering the drug than by discontinuing treatment abruptly.

Etretinate administration reduces serum propeptide of type I procollagen level in patients with psoriasis

The serum carboxyterminal propeptide of type I procollagen (PICP) level in 26 patients with psoriasis was significantly lower than in control subjects (124 +/- 47 and 224 +/- 78 ng/ml, respectively; P < 0.001). The patients were divided into two groups, those treated with etretinate and untreated patients. PICP levels in the treated group were significantly lower than those in the untreated group (P < 0.001), but there was no difference between the control and untreated groups. In addition, there was a negative correlation between PICP levels and the serum etretinate concentration in treated patients (r = -0.622, P < 0.05). There was no difference between procollagen type III aminoterminal propeptide (PIIIP) levels in patients and controls, nor was there any significant difference between etretinate-treated and untreated patients. In cell culture studies, etretinate dose-dependently (from 10(-9) to 10(-5) M) decreased the PICP concentration in the medium of fibroblasts from both healthy subjects and patients. In osteoblast cell culture, PICP levels were reduced only in a high concentration of etretinate (10(-5) M). However, no change was observed in preadipose cells. Our in vivo and in vitro observations indicated that psoriasis per se did not affect either serum PICP or PIIIP levels, but that etretinate had an inhibitory effect on collagen synthesis by fibroblasts. Hence, the administration of etretinate to psoriatic patients is, at least in part, responsible for the reduction of serum PICP levels in these patients.

Effects of etretinate on keratinocyte proliferation and secretion of interleukin-1 alpha (IL-1 alpha) and IL-8

Etretinate has proven to be effective in the treatment of psoriasis. Since abnormal proliferation and cytokine secretion are well-known features of psoriatic epidermis, we studied the in vitro effects of etretinate on these two processes using human keratinocytes. Etretinate promoted proliferation of normal human keratinocytes (NHKs) grown in keratinocyte growth medium (KGM) but not in growth factor-deficient keratinocyte basic medium (KBM). Moreover, etretinate partly overcame growth inhibition by PMA. Etretinate was shown to have an effect on either IL-1 alpha or IL-8 secretion in unstimulated NHKs. In HSC-1, a human squamous cell carcinoma cell line cultured in 20% FCS/DMEM, inhibited IL-1 alpha secretion and enhanced IL-8 secretion. These results indicate that the effects of etretinate on keratinocyte proliferation and cytokine secretion may depend on cell type and culture conditions. Stimulation of NHKs with PMA significantly enhanced IL-1 alpha and IL-8 secretion, and these effects were inhibited by etretinate. However, etretinate failed to inhibit rTNF alpha-induced IL-8 secretion, suggesting that etretinate regulation of NHK cytokine secretion may also depend on the stimulus. As treatment of keratinocytes or epidermis with PMA can induce psoriasis-like changes, so might the experimental "anti-PMA" activity of etretinate be related to its therapeutic benefit in the treatment of psoriasis.

Gestational-age-dependent effects of retinoids on HCG secretion by placental explants

Vitamin A (VITA) is considered to be an essential nutrient in both pregnant and non-pregnant states. It has been suggested that VITA, among others, is involved in the process of morphogenesis. In contrast, synthetic derivatives of VITA, specifically Tigasone (etretinate, TIG) and Roaccutane (isotretinoin, ROA), are regarded as major teratogens. Therefore, in the present study we have examined the effect of VITA and other retinoids on human chorionic gonadotrophin (HCG) secretion by placental explants in the first trimester. Results show that, at 7-9 gestational weeks, all three compounds had a significant inhibitory effect on HCG secretion. In the case of VITA, this inhibition was time-dependent. A biphasic maximal inhibition was present at 1 microM concentrations when the retinoids VITA, TIG and ROA were added for 16 h (52, 58 and 57%, respectively; P < 0.01 by one-way analysis of variance). In contrast, the addition of the three retinoids at 1 microM concentrations for 16 h had no significant effect on HCG secretion by placental explants of 11-13 weeks gestational age. In conclusion, both natural and synthetic retinoids demonstrate a significant inhibitory effect on HCG secretion by the early placenta (pre-HCG peak). VITA may be involved in causing a plateau and the later decline in HCG secretion. Inhibition of HCG secretion by retinoids may contribute either directly or indirectly to their teratogenicity.

Modulation of in vitro T cell alloreactivity by synthetic retinoids

Diversity of the effects of retinoids on virtually all components of the immune system makes them important immunomodulators. We recently suggested the mechanism of the inhibitory effect of some synthetic retinoids on lectin-induced T cell proliferation, acting predominantly on events occurring after the interaction of IL-2 and its receptor. To identify further immunomodulatory effects, two synthetic retinoids, etretinate and tretinoin, have been studied in a model of the in vitro proliferative response of rat T lymphocytes to alloantigens. Both retinoids, present at non-toxic concentrations, significantly decreased the lymphocyte proliferation in the unidirectional mixed lymphocyte reaction. In experiments designed to examine whether decreased proliferative response to alloantigens is a result of the reduced antigen presenting properties of stimulator cells caused by retinoids, it was shown that preincubation of allogeneic stimulator cells with either etretinate, or tretinoin enhanced rather than reduced their capacity to stimulate fresh responder lymphocytes. Finally, examination of the effect of retinoids on the generation of non-specific suppressor T cells by Con A showed that tretinoin and etretinate potentiated the induction of cells which inhibit alloantigen-stimulated proliferation of fresh responder cells. Thus, our results strongly support the concept that, besides a direct inhibitory effect of synthetic retinoids on alloresponsive T cells, an additional indirect mechanism may exist, which involves potentiation of the induction of suppressor T cells.

Protein kinase C agonist and antagonist effects in normal human epidermal keratinocytes

Several lines of evidence implicate protein kinase C (PKC) in the development of basal cell and squamous cell carcinomas, tumors which originate from epidermal keratinocytes. To examine PKC in a model relevant to human skin, we exposed normal human epidermal keratinocytes (NHEK) in serum-free media to a variety of PKC agonists and antagonists. NHEK PKC activity increased up to 10-fold within the 1st hour of exposure to tetradecanoyl phorbol acetate (TPA), and gradually returned to control values within 72 h. TPA-induced PKC activity was enhanced by pretreatment of cultures with protein and RNA synthesis inhibitors. TPA-induced growth arrest and differentiation was antagonized by staurosporine. Down-regulation by bryostatin pretreatment blocked TPA-stimulated differentiation. Our overall conclusion is that activation of PKC in cultured human keratinocytes is required for differentiation. These results are crucial to the analysis of compounds suspected of promoting or inhibiting epidermal tumors.

The effects of retinoids and terbinafine on the human hepatic microsomal metabolism of cyclosporin

Following the observation of increased trough whole blood cyclosporin A (CyA) concentrations and reduced renal function in a patient with recalcitrant generalized pustular psoriasis treated with a combination of CyA and etretinate, the effect of vitamin A analogues on human microsomal cytochrome P450-dependent CyA metabolism was investigated in vitro. In addition, the effect of terbinafine, a new allylamine antifungal agent, was also tested. Etretinate, its major metabolite acitretin, and isotretinoin, each at a single concentration of 100 microM, inhibited total hepatic microsomal CyA metabolism to a similar extent (33-45%, compared with control values). The generation of total primary and total secondary CyA metabolites was also inhibited to a similar extent by each of the retinoids. Conversely, terbinafine was without significant effect on CyA metabolism in vitro. The results, which suggest that inhibition of hepatic CyA metabolism by retinoids may contribute to increased circulating CyA concentrations, are discussed in relation to other potential drug interactions, and to the use of etretinate in reducing the CyA administered dose.

Roferon-A (interferon alpha 2a) combined with Tigason (etretinate) for treatment of cutaneous T cell lymphomas

Many treatments are used for epidermotropic cutaneous T cell lymphomas (CTCL) such as mycosis fungoides (MF) and Sézary syndrome (SS). All pretend to be effective, but none is really curative. As single drug therapy provides a response rate of about 55% with interferon alpha and about 45% with etretinate, we studied the effectiveness of combining these two drugs for immunomodulatory therapy in epidermotropic CTCL. A review of four reports, including a multicenter study performed in 45 patients, indicates a response rate of 56%, with better results for MF than SS. Side effects are generally moderate when low doses are used. The mechanism of action of this combined therapy on cutaneous lesions remains unclear. In vitro, a synergistic effect of retinoids on interferon alpha antiviral activity has been demonstrated, and in vivo an immunohistochemical study showed that the combined therapy modulates antigens expressed by keratinocytes and increases cytotoxic cells in dermis without modifying the number of Langerhans cells in epidermis.

Effect of etretinate on cyclosporin metabolism in vitro

Cyclosporin (CyA) is an effective treatment for psoriasis, including cases unresponsive to other therapies. The major side-effect of CyA treatment is dose-related nephrotoxicity. Combinations of CyA and etretinate (Et) have been tested with a view to reducing CyA dose requirements, and therefore minimizing adverse effects. We have studied the effect of Et on the cytochrome P-450-mediated metabolism of CyA. Microsomes prepared from histologically normal human (obtained from four cadaver kidney transplant donors; all male; age range 21-56) were incubated with CyA and various concentrations of Et. Metabolism was quantified by high-performance liquid chromatography with radiometric detection, and metabolites tentatively identified from the retention times of authentic standards. After 30 min incubation of CyA and microsomal protein at 37 degrees C, 10.1 +/- 3.0% (mean +/- SD) 3H-CyA was converted to the monohydroxylated metabolites M1 and M17, and 3.3 +/- 0.8% to the N-demethylated metabolite M21. At an Et concentration of 100 microM inhibition of CyA hydroxylase and N-demethylase was < 20%. This study indicates that there is no metabolic interaction between CyA and Et in vitro; it is likely that the two drugs are metabolized by different P-450 isoenzymes.

Acitretin and etretinate. How and when they should be used

Nearly two decades after the advent of synthetic retinoids for the treatment of many severe and incapacitating dermatologic conditions, the usefulness of these drugs is not universally accepted. The safety profile is well established. Other than teratogenicity, which can be avoided if the recommended precautions for use are followed, serious or unexpected adverse reactions rarely occur. This article concisely addresses some questions about etretinate and acitretin therapy that are most pertinent for the dermatologist.

Pharmacokinetics and drug interactions of etretinate and acitretin

Acitretin, the metabolite of etretinate, is eliminated far more rapidly from the human body than is etretinate. It had therefore been suggested that only a short period of contraception would be required after the cessation of long-term therapy with acitretin. However, recent studies have demonstrated the presence of etretinate in the plasma of patients who were treated with acitretin. In this article we provide results from a study in our center and discuss earlier data in light of the recently discovered metabolic pathways for acitretin. Reesterification of acitretin to etretinate, however, results in a loss of the metabolic advantages of acitretin. Because of this situation the recommended contraception period after acitretin therapy has been lengthened to 2 years.

Functional assessment of the stratum corneum under the influence of oral aromatic retinoid (etretinate) in guinea-pigs and humans. Comparison with topical retinoic acid treatment

Clinically we have noted that the skin of patients treated with long-term oral etretinate becomes uniformly soft and smooth to touch, like facial skin that becomes smoother and less wrinkled following treatment with topical tretinoin. This suggests that retinoids, whether used systemically or topically, alter the physical properties of the skin, particularly of the stratum corneum (SC). To study the influence of retinoids on the SC, we serially assessed the functional properties of the SC non-invasively in retinoid-treated humans and experimental animals. SC hydration and barrier function were assessed by measurement of high-frequency conductance and transepidermal water loss (TEWL), respectively. Daily application of topical retinoic acid creams was found to rapidly induce a time- and dose-dependent, linear increase in SC hydration of the forearm skin of healthy adults over a 2-week period and to compromise its water barrier function in a similar fashion. Systemic administration of high-dosage etretinate, 4 or 8 mg/kg/day, to guinea-pigs also induced dose-dependent increases in both SC hydration and TEWL measured on the plantar skin after 1 month. Moreover, in the animals given etretinate 4 mg/kg/day we confirmed a slight but significant decrease in the number of cell layers of the plantar SC. Likewise, patients with various dermatoses began to show similar functional changes of the SC in the uninvolved skin of the flexor surface of the forearms 3 weeks after the start of oral etretinate treatment, consisting of 50 mg daily for 2 weeks, followed by gradual dose tapering.(ABSTRACT TRUNCATED AT 250 WORDS)

[Effect of etretinate on the activity of intestinal disaccharidases]

The retinoid etretinate influences the proliferation and differentiation of epithelial cells. Therefore, the activity of disaccharidases maltase and sucrase was measured in duodenum and jejunum after oral retinoid application to female mice. The enzymes are localized in the brush border of differentiating mucosal cells. The etretinate dose ranged from 0.1 to 1 mg/kg. The treatment with etretinate induced a decrease of the duodenal and jejunal disaccharidase activity. A correlation between the influence in intestinal enzyme activity and undesired gastrointestinal side effects which were described by GOLD et al. (1988) is supposed.

Mouse conceptuses have a limited capacity to elevate the mRNA level of cellular retinoid binding proteins in response to teratogenic doses of retinoic acid

In these studies, we wished to determine the effect of teratogenic doses of retinoic acid on the expression of cellular retinoic acid binding protein I (CRABP-I) mRNA, cellular retinoic acid binding protein II (CRABP-II) mRNA, cellular retinol binding protein I (CRBP-I) mRNA, and cellular retinol binding protein II (CRBP-II) mRNA in mouse conceptuses. Levels of CRABP-II mRNA and CRBP-I mRNA were modestly elevated (2.5-fold and 1.5-fold, respectively) in 9-day gestation conceptuses following treatment of dams with 100 mg/kg b.w. of retinoic acid. These levels were elevated by 6 hr following treatment and remained elevated until 48 and 24 hr, respectively. Two other retinoids, etretinate and retinoyl beta-glucuronide, also moderately elevated CRABP-II mRNA and CRBP-I mRNA levels in conceptuses. In contrast, the levels of CRABP-I mRNA in the conceptuses remained unaffected by treatment with any of these three retinoids. These results demonstrate that conceptuses have a limited capacity to elevate the cellular retinoid binding proteins mRNA levels and presumably the synthesis of their respective proteins in response to high, teratogenic doses of retinoic acid. As a result, an excess of free retinoic acid becomes available to the nuclear retinoic acid receptors, which may lead to inappropriate gene expression and eventual maldevelopment.

Etretinate or cyclosporin-A treatment normalizes the enhanced respiratory burst of polymorphonuclear leukocytes in psoriasis

During a therapeutic trial to treat psoriasis with either etretinate or cyclosporin A (CyA) we measured the respiratory burst activity of polymorphonuclear leukocytes (PMN). Six patients received 0.5-0.75 mg/kg etretinate and 14 patients 2.5-5.0 mg/kg CyA over a period of 10 weeks. The extent of psoriasis was graded by the psoriasis area-and-severity index (PASI score). The respiratory burst of PMN isolated from the peripheral blood was measured employing luminol-enhanced chemiluminescence at weeks 0, 3 and 10 and compared with that of 26 healthy control individuals. PMN were stimulated with zymosan particles, aggregated immunoglobulin (aggIg) and concanavalin A (ConA). Both treatment regimens improved psoriasis; at 10 weeks there was an approximate 40% PASI score reduction under etretinate and an 80% improvement under CyA. Before treatment the respiratory burst was abnormally high under stimulation with the three stimuli in patients (p = 0.021 to less than 0.0001). After 3 to 10 weeks PMN activity normalized in all patients and even tended to drop below values correlating with an improvement in skin lesions. We conclude that the elevated respiratory burst of PMN in psoriasis normalizes under treatment with both etretinate and CyA.

In vitro effects of retinoid RO 10-9359 on lectin-induced activation and proliferation of T-lymphocytes

RO 10-9359 has been shown to cause a dose-dependent (0.05-50 micrograms/ml) inhibition of proliferation of rat thymocytes after in vitro activation by PHA and Con A. In experiments designed to dissect the effects of the drug on various aspects of proliferation it was demonstrated that RO 10-9359 did not inhibit IL1 production by macrophages, nor the IL1-dependent events of T-cell activation, i.e. the IL2 production and the acquisition of IL2-receptors. However, the capacity of exogenously supplied IL2 to stimulate the proliferation of T-cells that had previously acquired IL2-receptors was suppressed by RO 10-9359 in a dose-dependent manner. Thus, it appears that retinoid RO 10-9359 does not interfere with the early events of T-cell activation, but inhibits lectin-induced proliferation by affecting the later phase of proliferative activity after T-cell triggering.

Retinoid augmentation of bioactive interleukin-1 production by murine keratinocytes

The effect of retinoids on the production of interleukin-1 (IL-1) by murine epidermal keratinocytes was investigated. Freshly isolated keratinocytes were cultured in the presence of etretinate, acitretin, all-trans retinoic acid or 13-cis retinoic acid at concentrations of 8 x 10(-9)-8 x 10(-6) mol/l. Exposure of keratinocytes to retinoids increased IL-1 bioactivity in culture supernatants and cell extracts at concentrations as low as 8 x 10(-9) mol/l, as assessed by T-cell proliferation. Prolongation of the culture period enhanced the augmentative effect of retinoids. All-trans retinoic acid and 13-cis retinoic acid had a greater ability to induce IL-1 production than the two aromatic retinoids, etretinate and acitretin. Treatment with 8-methoxypsoralen plus ultraviolet A radiation and treatment with triamcinolone acetonide both reduced the effect of retinoids on the production of bioactive IL-1.

Effects of retinoids on endothelial cell proliferation, prostacyclin production and platelet aggregation

In addition to their anti-inflammatory and anti-cancer activities, retinoids have been shown to affect angiogenesis, endothelial proliferation and the process of wound healing. While peripheral vascular occlusion has not been observed as an adverse effect clinically, the effects of retinoids on prostacyclin production in endothelial cells and platelet aggregation are not known. We examined the effects of tretinoin, isotretinoin and etretinate (3.3 x 10(-8) to 3.3 x 10(-5) M) on cytotoxicity by 51Cr-release assay, growth and prostacyclin in bovine carotid endothelial cell cultures, and the aggregation of human platelets induced by ADP. All retinoids showed either no or only small effects on cytotoxicity and human platelet aggregation. Prostacyclin production was not significantly affected except for tretinoin and isotretinoin at 3.3 x 10(-5) M. Endothelial proliferation was affected by all three retinoids in a dose-dependent fashion; for tretinoin and isotretinoin an inhibitory trend was noted as the concentration increased but the reverse was true for etretinate. Retinoids at 3.3 x 10(-5) M induced alterations of typical endothelial morphology; the cells became fibroblastoid. The results of prostacyclin production and platelet aggregation in the present study are consistent with the absence of peripheral vascular occlusion as a side effect clinically.

Na+/H+ antiporter gene expression increases during retinoic acid-induced granulocytic differentiation of HL60 cells

During differentiation of human leukemic HL60 cells into granulocytes, sustained increases in intracellular pH and Na+/H+ antiporter activity have been observed. In the present study we report that retinoic acid (RA)-induced granulocytic differentiation of HL60 cells causes an approximately 18-fold increase in the steady-state mRNA levels for the Na+/H+ antiporter. This was due to an increase in the rate of Na+/H+ antiporter gene transcription as measured by nuclear run-on analysis. Antiporter protein synthesis increased by seven-fold during RA-induced granulocytic differentiation of HL60 cells as measured by immunoprecipitation of 35S-methionine-labeled proteins with the RP1-c28 Na+/H+ antiporter antibody. No increase in antiporter mRNA was observed in response to etretinate, an analogue of retinoic acid, which did not induce differentiation. Thus, Na+/H+ antiporter gene expression is associated with RA-induced granulocytic differentiation of HL60 cells. The present findings and our previous data (Rao et al., 1991) demonstrate that Na+/H+ antiporter gene expression is a generalized feature of HL60 cell differentiation.

Antitumor action of retinoids: inhibition of tumor cell line-induced angiogenesis and prevention of tumors in mice

Acitretin was shown to inhibit angiogenic response to the tumorigenic SKV cell line bearing HPV16 genome and to sarcoma L-1 cell line, both in vitro and in vivo systems. The lowered angiogenic response to tumor cells was independent of duration and timing of the application of acitretin to animals. Acitretin, but not etretinate, was also found to be effective in the prevention of sarcoma tumors in mice.

Retinoic acid decreases thyroid hormone receptor expression in pituitary GH1 cells

Retinoic acid produced a time and dose-dependent depletion of thyroid hormone receptors in GH1 cells without modifying their affinity for triiodothyronine (T3). A maximal decrease (50-70%) was obtained after 24-48 h incubation with 5-10 microM retinoic acid. Treatment with 0.8 nM T3 for 24 h caused a similar reduction and did not potentiate the decrease produced by these concentrations of retinoic acid. However, the combination of sub-maximally effective doses of both ligands had an additive effect on receptor levels. The reduction of receptor caused by retinoic acid is accompanied by a decreased expression of c-erbA alpha 1 and alpha 2 mRNAs, but the retinoid did not reduce the abundance of c-erbA beta mRNA. In contrast, T3 decreased the levels of both alpha and beta transcripts.

Histological changes of the bladder mucosa following the administration of BCG adriamycin and RO 10-9359

Three groups of Wistar rats have been treated with intravesical Adriamycin and BCG and oral retinoids. The main effect on the bladder seen on histological sections was mononuclear infiltration in the Adriamycin group, polymorphonuclear infiltration in the BCG group and minimal mononuclear and polymorphous infiltration in the retinoid group. The results are discussed in relation to the existing theories on the protective action of these agents against bladder tumour recurrences.

Effects of a synthetic retinoid, etretinate (RO 10-9359), on the peripheral metabolism of thyroid hormones in rats

Male Wistar rats were administered a synthetic vitamin A compound, etretinate, at various doses, including levels exceeding recommended therapeutic doses. At 2 mg/kg body weight/day given intragastrically, no effects were detected with respect to serum retinol or thyroid hormones after 15 days of treatment. At 5 mg/kg/day only a slight decrease in serum triiodothyronine was detected. In contrast, the dose of 20 mg/kg/day for 15 days resulted in relatively severe effects: body weight was decreased by 23% in comparison with the controls, serum retinol was decreased by 62% (while liver stores of vitamin A were unaffected), and serum thyroxine and triiodothyronine levels were, respectively, 24 and 29% lower than in the controls. A kinetic study demonstrated that the biological half-life of serum thyroxine decreased by 62% and that of serum triiodothyronine by 24%, suggesting increased peripheral metabolism of the thyroid hormones. The two main metabolic pathways (i.e. hepatic 5'-monodeiodination and glucuronide conjugation) were not significantly affected by etretinate treatment and do not account for the apparent metabolic loss of the thyroid hormones. This experiment demonstrates that etretinate doses beyond the therapeutic range are required to imbalance thyroid hormone homoeostasis. Possible mechanisms relating to increased hormonal clearance in rats treated with high doses of etretinate are discussed.

Cultivation of human dermal microvascular endothelial cells in vitro: immunocytochemical and ultrastructural characterization and effect of treatment with three synthetic retinoids

A new reliable and reproducible technique to culture endothelial cells from the small vessels and capillaries of human skin is introduced, and proliferation and differentiation of the growing cells are characterized. The endothelial origin of the culture cells was confirmed by light- and electron microscopy and by labelling with Ulex europaeus Agglutinin I and an antibody against Factor VIII-related antigen. Further immunocytochemical characterization showed that 92-100% of the cells were positive for beta 2-microglobulin and the entire cell population expressed vimentin, whereas cytokeratins, desmin, HLA-DR antigen, Leu 6 and S 100 protein, could not be detected. As vascular endothelium is a common site of inflammation and retinoids have been shown to be of good clinical efficacy in some chronic inflammatory skin diseases, we investigated the influence of etretinate, etretin and isotretinoin on proliferation and antigen expression of our culture cells. All retinoids applied inhibited proliferation of endothelial cells in a dose- and time-dependent manner whereas they induced neither HLA-DR nor intercellular adhesion molecule-1 (ICAM-1). Furthermore, none of the retinoids applied influenced the gamma-interferon-induced expression of these surface antigens on endothelial cells. Our results suggest that the action of retinoids in skin inflammation is not mediated by modulation of HLA-DR or ICAM-1. The cell culture technique described here is an interesting and reliable model for studying the influence of drugs on endothelial cell growth and differentiation in vitro.

Acitretin decreases tumor cell-induced angiogenesis

The effects of acitretin and etretinate on angiogenesis induced in Balb/c mice by intradermal injection of keratinocyte tumor cell lines were evaluated. It was shown that both retinoids are capable of inhibiting angiogenesis evoked by a human epidermoid carcinoma cell line (A431). Acitretin, but not etretinate, inhibited also angiogenesis induced by the spontaneously transformed murine keratinocyte cell line Pam 212 and by the established tumorigenic SKv cell line harboring the HPV16 genome. We suggest that inhibition of blood vessel formation may be one of the mechanisms responsible for the anticancerogenic effect of retinoids.

Induction of beta-retinoic acid receptor mRNA by teratogenic doses of retinoids in murine fetuses

Retinoic acid is required for normal growth and development, however excessive doses are teratogenic. Recently several nuclear retinoic acid receptors (RAR) have been identified and postulated to mediate the response of retinoic acid at the gene level. We wished to determine if alpha-RAR mRNA or beta-RAR mRNA levels are modulated by teratogenic doses of retinoic acid in vivo. We have found that beta-RAR mRNA levels in 9-day-gestation mouse conceptuses are increased as early as 3 h after administration of a completely teratogenic dose of retinoic acid (100 mg/kg body weight; b.w.) and reach a maximum of approximately sixfold after 6 h of treatment. Maternal liver and maternal kidney demonstrated a similar pattern of increase in beta-RAR mRNA, however this was only approximately threefold. Retinoic acid dose-response experiments demonstrated a reduced increase of beta-RAR mRNA levels with 10 mg/kg b.w. (minimally teratogenic dose), and no increase with a more-physiological dose of 1 mg/kg b.w. in the conceptuses. beta-RAR mRNA levels were elevated in 18-day-gestation fetuses to a similar extent to that observed in the 9-day-gestation conceptuses. Therefore, the twofold difference in the extent to which beta-RAR mRNA levels increase does not occur because the fetuses are at a developmental stage that is sensitive to the teratogenic effects of retinoic acid. Finally, treatment with another teratogenic retinoid, etretinate, and a nonteratogenic retinoid, retinoyl beta-glucuronide, both resulted in increase in the level of beta-RAR mRNA in the conceptuses and the maternal tissues. Therefore, an increase in beta-RAR mRNA levels caused by treatment with retinoids does not necessarily commit a fetus to undergo an abnormal pattern of development characteristic of teratogenic retinoids.

Interaction of etretinate with methotrexate pharmacokinetics in psoriatic patients

Combined treatment of psoriasis with methotrexate and etretinate may be associated with hepatoxicity. This study investigated the potential effects of steady state etretinate administration on methotrexate pharmacokinetics in six psoriatic patients. When compared with a matched group a significantly higher mean value for the maximum plasma concentration Cmax (992 nmol/L +/- 94 SE vs 721 nmol/L +/- 35 SE) for methotrexate was found (P less than .05) after intramuscular administration of 0.2 mg/kg body weight of the drug. In accordance with this finding mean values of the time (tmax) to reach Cmax, half-life of the absorption (t1/2ka) and the apparent volume of distribution at steady state Vss were also lower than in the control groups but did not deviate significantly. Total clearance differed very little and insignificantly between the two groups. Absorption and disposition rates of etretinate during combined treatment with methotrexate were not significantly altered compared with previous results in psoriatic patients only receiving etretinate. Overall, these results indicate that the apparently increased risk for developing hepatotoxic reactions during coadministration of methotrexate and etretinate cannot be explained by drug accumulation due to pharmacokinetic interaction. A possible influence on potential hepatotoxicity of an increase of Cmax for methotrexate cannot be excluded.

Effects of retinoids on DNA synthesis of pig epidermis: its relation to epidermal beta-adrenergic adenylate cyclase response and to epidermal superoxide dismutase activity

It has been suggested that the epidermal beta-adrenergic adenylate cyclase response and the epidermal superoxide dismutase (SOD) activity is inversely associated with keratinocyte cell proliferation. Effects of various retinoids on the thymidine incorporation of pig epidermis were compared with their effects on the beta-adrenergic response and the SOD activity. Following 24 h incubation with synthetic retinoids (etretin and E-5166 (3,7,11,15-tetramethyl-2,4,6,10,14-hexadecapentaenoic acid)), thymidine incorporation of epidermis was significantly decreased. The effect of etretin was more potent than that of E-5166; the former revealed the inhibitory effect at lower concentrations than the latter. The effect of etretinate was not statistically significant. Following the 24 h incubation with the synthetic retinoids, the epidermal beta-adrenergic adenylate cyclase responses were increased. Etretin was again more potent than E-5166, while etretinate showed also little effect on the beta-adrenergic response of epidermis. Thus the inhibitory effect on the thymidine incorporation was inversely correlated with the beta-adrenergic augmentation effect among these synthetic retinoids. On the other hand, physiologic retinoids (retinol and retinoic acid) revealed no correlation between these two parameters; whereas both compounds decreased the thymidine incorporation to a similar extent, only retinoic acid revealed a marked beta-adrenergic augmentation effect. Decreased SOD activity has been observed in various hyperproliferative epidermis. The SOD activity, however, was totally unaffected by the retinoid-treatments.

Retinoid effects on sebocyte proliferation

The human sebocyte model offers several advantages over the current animal models. Foremost among these is the correlation of in vitro activity with clinical results, which was not true for arotinoids in the animal models. It is also possible to study several parameters (total cell number, [3H]thymidine uptake, protein and lipid composition/synthesis, hormone response, receptor regulation, etc.) in the same system. The proliferation of isolated sebocytes is inhibited by retinoids, such as isotretinoin and tretinoin, which are known to be clinically active in human acne. Sebocytes are not responsive to the arotinoid temarotene, which is active in the aforementioned animal models and against dimethylbenz[a]anthracene (DMBA)-induced rat mammary carcinoma but inactive clinically in acne. Additionally, this model is not responsive to etretinate, a compound known to be active in psoriasis but inactive in acne. The in vitro model is, therefore, more predicative of clinical efficacy than the animal models alone.

Effect of etretinate on peripheral T lymphocytes in psoriatic patients before, during and after 6 months of therapy

Total peripheral T lymphocytes, OKT4 helper/inducer cells and OKT8 suppressor/cytotoxic cells, as well as T lymphocyte function determined by the local xenogeneic graft-versus-host reaction (GVHR), were investigated in 14 psoriatic patients prior to institution of treatment with etretinate, during the course of treatment and 6 months after its initiation. After approximately 2 months of treatment, there was a significant increase in the number of E-rosette-forming lymphocytes and OKT4 subpopulations with a return to normal levels after 6 months of treatment. The GVHR was positive in only 5/11 patients prior to therapy but in 9/11 patients after 2 and 6 months. Our results indicate that etretinate has a stimulatory effect on T lymphocytes and their subset counts.

[Effect of etretinate treatment on fluidity and lipid composition of the erythrocyte membrane in patients with psoriasis]

The effect of etretinate (Ro 10-9359) treatment, at low daily dose (0.3 mg/kg), on erythrocyte membrane and physico-chemical state in psoriatic patients has been studied. The results have shown that etretinate induces a significant increase of erythrocyte membrane fluidity, as shown by a decrease of fluorescence polarization. In fact the values of 1,6-diphenyl-1,3,5-hexatriene (DPH) fluorescence polarization were significantly decreased after therapy in comparison with the values observed at the beginning of the study. The modifications of membrane fluidity were associated with modifications of lipid composition. In fact the study of membrane composition has revealed a decrease of the cholesterol to protein ratio and slight but not significant changes of phospholipid fatty acid composition.