13-cis Retinoic acid ameliorates benzoyl peroxide-induced oxidative stress and hyperproliferative response in murine skin: a chemopreventive study

The Use of Retinoids for the Prevention and Treatment of Skin Cancers: An Updated Review

Retinoids are natural and synthetic vitamin A derivatives that are effective for the prevention and the treatment of non-melanoma skin cancers (NMSC). NMSCs constitute a heterogenous group of non-melanocyte-derived skin cancers that impose substantial burdens on patients and healthcare systems. They include entities such as basal cell carcinoma and cutaneous squamous cell carcinoma (collectively called keratinocyte carcinomas), cutaneous lymphomas and Kaposi’s sarcoma among others. The retinoid signaling pathway plays influential roles in skin physiology and pathology. These compounds regulate diverse biological processes within the skin, including proliferation, differentiation, angiogenesis and immune regulation. Collectively, retinoids can suppress skin carcinogenesis. Both topical and systemic retinoids have been investigated in clinical trials as NMSC prophylactics and treatments. Desirable efficacy and tolerability in clinical trials have prompted health regulatory bodies to approve the use of retinoids for NMSC management. Acceptable off-label uses of these compounds as drugs for skin cancers are also described. This review is a comprehensive outline on the biochemistry of retinoids, their activities in the skin, their effects on cancer cells and their adoption in clinical practice.

Clinical implications of lipid peroxidation in acne vulgaris: old wine in new bottles

Acne vulgaris is a common dermatological disorder, one that is frequently associated with depression, anxiety and other psychological sequelae. In recent years there has been an increasing focus on the extent to which oxidative stress is involved in the pathophysiology of acne. Emerging studies have shown that patients with acne are under increased cutaneous and systemic oxidative stress. Indeed, there are indications that lipid peroxidation itself is a match that lights an inflammatory cascade in acne. The notion that lipid peroxidation is a 'starter gun' in acne is not a new one; here we review the nearly 50-year-old lipid peroxidation theory and provide a historical perspective to the contemporary investigations and clinical implications.

In addition, we present a novel hypothesis in which lipid peroxidation may be priming an increased susceptibility to co-morbid depression and anxiety in those with acne. The emerging research on the systemic burden of oxidative stress in acne sheds further light on the brain-skin axis. The recent findings also suggest potential avenues of approach for the treatment of acne via specific nutrients, dietary modifications, oral and topical interventions.

Free Radical Oxidation of (E)-Retinoic Acid by the Fenton Reagent: Competing Epoxidation and Oxidative Breakdown Pathways and Novel Products of 5,6-Epoxyretinoic Acid Transformation

The nature of the products formed by reaction of all-trans retinoic acid (1) and its major metabolite, 5,6-epoxyretinoic acid (2), with the Fenton reagent was investigated. Oxidation of 1 in a vigorously stirred biphasic medium (0.1 M phosphate buffer, pH 7.4/ethyl acetate 5:1 v/v) with Fe2+/EDTA complex (2 mol equiv) and a 10-fold excess of H2O2 proceeded smoothly to give a very complex mixture of products. Repeated TLC fractionation of the reaction mixture after methylation allowed isolation of the main products which were identified as 2 methyl ester, (7E)-7,8-epoxyretinoic acid methyl ester (6), all-(E)-2,6-dimethyl-8-(2,6,6-trimethyl-2-cyclohexen-1-ylidene)-2,4,6-octatrienal (11), the novel (9E)-5,6,9,10-diepoxyretinoic acid methyl ester (7), and (9Z)-5,6,9,10-diepoxyretinoic acid methyl ester (8) (1:1 mixture of syn/anti isomers each), 5,6-epoxy-beta-ionone (9), 5,6-epoxy-beta-ionylideneacetaldehyde (10), and trace amounts of beta-ionone (12), beta-ionylideneacetaldehyde (13), and 4-oxoretinoic acid (3) methyl ester. When the oxidation was carried out with the substrate and the Fenton reagent at concentrations as low as 10 microM, the main detectable products were 2 methyl ester, 11, and 7/8. Under similar conditions, the epoxide 2 gave mainly products 7-10. A less efficient conversion of 1 and 2 but similar product patterns were observed with other oxidizing systems such as peroxidase/H2O2 and 13-hydroperoxyoctadecadienoic acid in the presence of Fe(II). Besides providing the first detailed insight into the products formed by reaction of a retinoid with the Fenton reagent, the results of this study disclose a novel nonenzymatic route from 1 to the epoxide 2 and offer an improved chemical basis to inquire into the mechanism of the antiinflammatory, antimutagenic, and cancer chemopreventive action of these retinoids.