Topical retinoids: in vivo predictive assays

The Pharmacology of a Novel Topical Retinoid, BMY 30123: Comparison with Tretinoin

Preclinical studies pertaining to the pharmacology and toxicology of BMY 30123 (4-acetamidophenyl retinoate) are reported. BMY 30123 is a novel compound which has topical retinoid activity. This compound exhibits lower toxicity, both local and systemic, than other clinically used topical retinoids such as tretinoin (all-trans retinoic acid) in animal models. BMY 30123 is effective in a number of retinoid sensitive skin models including the rhino mouse utriculi reduction assay, the mouse epidermal hyperplasia model and in the suppression of DNA synthesis in mouse skin stimulated with phorbol ester. BMY 30123 was equipotent with tretinoin in these topical models. In the rhino mouse model the ED30 values for BMY 30123 and tretinoin were 0·037 and 0·015 Mm, respectively. In addition, BMY 30123 was active in the UVB-induced photodamaged mouse model, another retinoid sensitive model. One of the problems associated with topically applied tretinoin is local irritation. Therefore, for topical therapy to be optimal, it is important to reduce or minimize local irritation. Repeated applications of BMY 30123 to rabbit skin resulted in low skin irritation. The first perceptible signs of skin irritation produced by BMY 30123 occurred at a dose 10 times higher than that observed for tretinoin. BMY 30123 also exhibits low retinoid activity after oral or i.p. administration in mice and produced no signs of hypervitaminosis A-related toxicity at twenty times the no effect dose of tretinoin. Because retinoids are effective modulators of epidermal growth and differentiation, this compound should be useful for the treatment of cutaneous disorders that exhibit altered epidermal differentiation such as acne, psoriasis, ichthyosis and epithelial tumours. While BMY 30123 and tretinoin are shown here to be equipotent in animal efficacy models, the low skin irritation activity gives BMY 30123, at a minimum, a 10-fold enhancement in the therapeutic index relative to tretinoin and suggests that retinoid efficacy and skin irritation are separable phenomena.

Tocoretinate inhibited the contraction of collagen gel matrices by human dermal fibroblasts with tenascin-C expression

Retinoids are strong tissue modifiers and have been used to treat severe acne, keloids and photo-aged skin. Tocoretinate (TR), ester bound retinoic acid and tocopherol, has been topically applied for skin ulcers and, more recently, for sclerotic skin diseases. To clarify the mechanism of tissue softening by retinoids and TR, we investigated their effects on the contraction of hydrated type-1 collagen gel matrices by human dermal fibroblasts and on tenascin-C expression. TR, 13-cis-retinoic acid/isotretinoin and all trans-retinoic acid significantly inhibited collagen gel matrices contraction at concentrations from 10(-4) to 10(-8) M without significant changes of the fibroblast growth. TR and the other two retinoids dose-dependently induced tenascin-C expression in the fibroblasts. Since tenascin-C is involved in cellular detachment and tissue remodeling, these results suggest that TR and other retinoids down-regulated the tensile tension of fibroblasts in collagen gel matrices by the induction of tenascin-C.

Topical tocoretinate improved hypertrophic scar, skin sclerosis in systemic sclerosis and morphea

Four patients with systemic scleroderma (SSc), 4 patients with morphea, and 4 patients with hypertrophic scar were treated with topical tocoretinate for 6 months to 3 years and studied clinically and histopathologically. Clinically, all of the lesions responded to this therapy. The stiffness of the skin lesions, glossy appearance of the lesions, and telangiectasia improved. Histopathologically, the proliferated collagen fibers decreased in thickness, and the inter-fiber spaces increased. Immunoreactive tenascin-C expressed in the proliferated deep dermal fibers of the SSc and hypertrophic scar lesions was markedly decreased compared with the level before the topical tocoretinate therapy. Topical tocoretinate has been used for the treatment of ulcers; it is also a potent treatment for sclerotic skin diseases.

Activity profiles of antimutagens: in vitro and in vivo data

In this review, retinol, chlorophyllin, and N-acetylcysteine are examined and compared with regard to their antimutagenic activity against some promutagens and a group of direct-acting alkylating agents. The promutagens included aflatoxin B1, certain polycyclic aromatic hydrocarbons (e.g., benzo[a]pyrene), and certain heterocyclic amines (e.g., food pyrolysates). Results of antimutagenicity testing selected from data surveyed in the published literature are displayed graphically as activity profiles of antimutagens showing both the doses tested and the extent of inhibition or enhancement of mutagenic activity. All three antimutagens are discussed in terms of their putative mechanisms of action in vitro and in vivo with emphasis on the xenobiotic metabolizing enzyme systems.

Dry and photo-aged skin: manifestations and management

A review is presented on the causes and management of dry and photo-aged skin. The causative factors discussed range from adverse weather conditions to serious dermatological disease. The potential use of moisturizers in certain clinical cutaneous disorders. The main types of skin moisturizers and anti-ageing substances currently available are reviewed with particular emphasis on the rationale behind their development.

Regulation of ornithine decarboxylase gene expression, polyamine levels, and DNA synthetic rates by all-trans-retinoic acid in cultured human keratinocytes

Regulation of ornithine decarboxylase (ODC) gene expression and cell growth by all-trans-retinoic acid in the presence and absence of exogenous putrescine were examined in normal keratinocyte cultures maintained in serum-free medium containing 0.15 mM Ca++. Putrescine and the higher polyamines are negative feedback regulators of ODC synthesis and are essential for cell growth. Human keratinocytes were incubated with and without 1 microM putrescine and the effects of 5 x 10(-7) M retinoic acid on ODC mRNA levels, ODC activity, polyamine levels, and DNA synthetic rates were determined. Northern blot analysis of total RNA isolated from breast reduction keratinocytes treated with retinoic acid up to 24 h showed a time-dependent suppression of ODC mRNA levels that was unaffected by putrescine. ODC activity was suppressed more rapidly in keratinocytes grown in the absence of putrescine; however, at 24 h, ODC activity was suppressed to an equal extent under both culture conditions. The effect of retinoic acid on polyamine levels was determined in the absence of exogenous putrescine. Retinoic acid treatment markedly suppressed putrescine and N1-acetylspermidine levels, whereas spermidine and spermine levels were relatively unaffected. The effect of retinoic acid on DNA synthetic rates, as measured by 3H-thymidine incorporation, was variable. Retinoic acid either stimulated or had little effect on keratinocyte DNA synthetic rates in cells derived from breast reductions and cultured in the absence of putrescine; these effects were not opposed by the presence of exogenous putrescine. In contrast, DNA synthesis in keratinocytes derived from neonatal foreskins was consistently suppressed by retinoic acid, independent of the polyamine status. Our data, therefore, suggest that the effect of retinoic acid on cell growth, as indicated by DNA synthetic rates, does not necessarily parallel its effect on ODC activity and mRNA levels.

Suppression of ornithine decarboxylase gene expression by retinoids in cultured human keratinocytes

Modulation of ornithine decarboxylase (ODC) gene expression by retinoids was analyzed in human keratinocyte cultures maintained in serum-free medium containing 0.15 mM Ca++. Cells were incubated with all-trans-retinoic acid, 13-cis-retinoic acid or arotinoid Ro15-0778 (10(-10) to 10(-5) M), total RNA was isolated, and mRNA transcripts for ODC were analyzed by Northern and slot blot hybridizations with a human ODC cDNA. Treatment of cells for 24 h resulted in a dose-dependent decrease in ODC mRNA levels, with an estimated IC50 of approximately 1 X 10(-8) M for all-trans- and 13-cis-retinoic acid, while Ro15-0778 was somewhat less effective (IC50 approximately 1-5 X 10(-7) M). The suppression of ODC mRNA levels by retinoids was detectable at approximately 3 h of incubation, with essentially a maximal inhibition at 12 h. Reduced ODC mRNA levels noted after 24 h of incubation with 5 X 10(-7) M all-trans-retinoic acid were accompanied by a reduction in ODC enzyme activity. To determine if all-trans-retinoic acid was regulating ODC gene expression directly, or if protein synthesis was required, ODC expression was analyzed in cultures treated with protein synthesis inhibitors. In the presence of cycloheximide or puromycin, all-trans-retinoic acid did not suppress ODC mRNA levels. These findings suggest that suppression of ODC gene expression is not a direct effect of all-trans-retinoic acid, but depends on ongoing protein synthesis.