Photoaging: pathogenesis, prevention, and treatment

Premature skin aging, or photoaging, results largely from repeated exposure to ultraviolet (UV) radiation from the sun. Photoaging is characterized clinically by wrinkles, mottled pigmentation, rough skin, and loss of skin tone; the major histologic alterations lie in dermal connective tissue. In recent years, a great deal of research has been done to explain the mechanism by which UV induces dermal damage. This research has enabled the identification of rational targets for photoaging prevention strategies. Moreover, studies that have elucidated photoaging pathophysiology have produced significant evidence that topical tretinoin (all-trans retinoic acid), the only agent approved so far for the treatment of photoaging, also works to prevent it. This article summarizes evidence mainly from studies of human volunteers that provide the basis for the current model of photoaging and the effects of tretinoin.     

Retinoids and interferon: a new promising combination?

The retinoids: all-transretinoic acid (tretinoin), 13-cis retinoic acid (isotretinoin) and the aromatic retinoids etretinate and acitretin have a preventive and therapeutic effect on chemically-induced tumours. Clinically, retinoids have shown variable effectiveness in therapy and/or prevention of oncological diseases of skin, head and neck, lung, bladder, vulva and bone marrow, With a few exceptions, monotherapy with retinoids has not been satisfactory. Similarly, monotherapy with interferon alpha has been used successfully only for some specific indications. Retinoids have a marked differentiation-inducing effect which may contribute to their therapeutic effect. Experiments were carried out in transformed cell lines to test the combination of retinoids with interferon alpha and other cytokines on differentiation. In HL-60 cells, an acute promyelocytic leukaemia cell line, induction of differentiation was determined by induction of an oxidative burst potential. Retinoids showed the following order of activity: tretinoin > isotretinoin > acitretin. Cytokines had no differentiation-inducing effect by themselves. However, the addition of the following cytokines to retinoids potentiated the retinoid-induced differentiation: IFNα, IFNβ, IFNγ, TNFα, G-CSF, IL-1α and IL-4. In experiments with HL-60 or other cell lines, the pattern of differentiation-induction was always dependent on the particular retinoid/cytokine combination. IFNα provoked a marked potentiation of retinoid-induced differentiation. The combination of the antipro-liferative and differentiation-inducing effect of the retinoids together with the antiproliferative, immunostimulatory and differentiation-potentiating effects of IFNα suggests that this combination might be a particularly promising treatment for neoplastic diseases.     

An overview of the retinoids

The retinoids, a group of compounds consisting of vitamin A and its derivatives, have been the subject of intense investigation over the past 30 years. These molecules have shown beneficial effects in the areas of acne, psoriasis, neoplastic processes and, most recently, reversal of extrinsically aged skin. Additional retinoids are currently under development. Adverse reactions to these drugs include mucocutaneous irritation, hyperlipidemia, and profound teratogenicity. Appropriate patient selection is imperative before beginning therapy with these medications. An overview of retinoid metabolism and the currently available compounds is presented. The newest class of retinoids, the arotinoids, is also discussed.     

Retinoids as preventive and therapeutic anticancer agents (Part I)

Retinoids, the synthetic and natural analogs of vitamin A, frequently block the phenotypic expression of cancer in vitro; they also inhibit growth and induce differentiation in many animal and human malignant cell types. Only recently has it become possible to propose a unifying mechanism of retinoid action, which involves the protein kinase-C cascade system. This system may mediate retinoids' many diverse actions, including their effects on enzyme synthesis, membrane properties, growth factors, binding proteins, genomic and postgenomic expression, the extracellular matrix, and immunologic responses. Ongoing in vitro studies of retinoid structure-activity relationships, effects on oncogene expression, reversal of drug-resistance, and, especially, the protein kinase-C cascade system should help clarify the precise mechanism of their anticancer action. Many in vitro and in vivo assay systems are available for testing the 2000 + synthetic retinoids. These assays indicate specific drug sensitivities, which may help focus future clinical trials. In human cancer prevention, retinoids have been most effective for skin diseases, including actinic keratosis, keratoacanthoma, and basal cell carcinoma; however, nondermatologic premalignancies, such as oral leukoplakia, bronchial metaplasia, laryngeal papillomatosis, cervical dysplasia, myelodysplastic syndromes, and the urinary bladder, also respond to retinoid therapy. Significant therapeutic advances are also occurring with this class of drugs in refractory malignancies, including advanced cutaneous squamous and basal cell cancer, mycosis fungoides, and acute promyelocytic leukemia. Newer third-generation retinoids, such as the highly potent retinoidal benzoic acid derivatives, are demonstrating therapeutic indexes far higher than earlier-generation retinoids. Current in vitro testing is also demonstrating that retinoids have synergistic activity in combination with other agents (eg, biologic modifiers, hormones, and DNA synthesis inhibitors) and treatment modalities (eg, irradiation). Notwithstanding the progress already made with retinoids in human cancer, many in vitro questions remain, and clinical work is just beginning.     

Pathways of vitamin A delivery to the embryo: insights from a new tunable model of embryonic vitamin A deficiency

Circulating retinoids (vitamin A and its derivatives) are found predominantly as retinol bound to retinol-binding protein (RBP), which transports retinol from liver stores to target tissues, or as retinyl ester incorporated in lipoproteins of dietary origin. The transport of retinoids from maternal to fetal circulation is poorly understood, especially under conditions of inadequate dietary vitamin A intake. Here we present RBP-/- mice as a tunable model of embryonic vitamin A deficiency. This model has enabled us to analyze metabolic links between maternal nutrition and retinoid delivery to the fetus. Our data show that retinol-RBP is the primary contributor to fetal development, whereas retinyl ester are largely responsible for accumulation of fetal retinoid stores. Furthermore, these studies indicate the importance of embryonic RBP in distributing vitamin A to certain developing tissues under restrictive diets. We also show differences among developing tissues in their dependency on the embryonic retinol-RBP pathway. Finally, we demonstrate that accumulation of embryonic vitamin A stores does not depend on the expression of RBP in the fetal liver.     

Photoaging. Manifestations, prevention, and treatment

In recent years there has been an increasing awareness that many of the so-called attributes of aging skin are, instead, a reflection of environmental assault upon exposed areas of the body. Of special import are the deleterious effects of solar radiation on dermal connective tissue, leading to the visible manifestations of photoaging. Often termed "premature aging," the salient features of the process are distinctly different from those found in normal intrinsic aging. In general, chronically irradiated skin is metabolically hyperactive with epidermal hyperplasia and neoplasia, increased production of elastic fibers, GAGs, accelerated breakdown and synthesis of collagen, and enhanced inflammatory processes. In contrast, protected aged skin is usually characterized by a slow decline in many of these components. Experimental studies with animal models have confirmed the notion that the shorter, more energetic portion of the ultraviolet spectrum (UVB) is responsible for the dermal connective tissue destruction observed in photoaged skin. More recently, it has been shown that UVA and infrared radiation contribute significantly to photoaging, producing, among other changes, severe elastosis. Because the three broad wavebands are inseparably linked in terrestrial sunlight, all are of concern in the photoaging of human skin. Photoaged skin has been thought to be irreversibly damaged. However, our findings indicate that destruction and repair go on simultaneously under continued assault by actinic radiation. The balance is shifted toward repair when the radiation stress is relieved. Both epidermis and dermis are capable of moderate self-restoration when exogenous injury ceases, either by avoidance of sunlight or by the use of broad-spectrum, high-SPF sunscreens. Repair of the dermis, characterized by broad regions of new collagen deposited subepidermally, can be pharmacologically enhanced by topical application of retinoic acid. Although early protection from sunlight, before severe photodamage occurs, is most desirable, it is deemed advisable to counsel even older persons with photoaged skin to adopt protective measures, thereby allowing repair processes to occur.     

A review of tazarotene in the treatment of photodamaged skin

Chronic sun exposure leads to photodamage, which is characterized clinically by fine and coarse wrinkles, dyspigmentation, telangiectasia, laxity, roughness and a sallow appearance. Many treatments claim to reduce the signs of photodamage, however evidence from randomized controlled trials (RCT) to support these claims is limited. The use of topical retinoids, particularly tretinoin, isotretinoin and tazarotene, has been shown to significantly reduce signs of photodamage both clinically and histologically. Over recent years a number of RCTs, have affirmed that topical tazarotene is an effective and safe treatment for photodamaged skin.     

Retinoid concentrations in the mouse during postnatal development and after maternal vitamin A supplementation

BACKGROUND: Vitamin A (VA) and its derivates (retinoids) are important nutritional substances, which mediate their biological activity mainly via nuclear retinoid receptors. Maternal VA intake during lactation influences the VA content in milk and the VA status of the progeny. We investigated the effects of maternal supplementation during lactation and direct supplementation to the pups after weaning on the retinoid concentration in serum and liver of neonatal mice using high doses of VA. METHODS: Dams were fed a basal (4,500 retinol equivalents/kg diet) or a VA-supplemented (324,000 retinol equivalents/kg diet) diet during lactation. Pups kept receiving the same diet after weaning. Serum and liver samples of the pups were collected during lactation at days 1, 3, 5, 7, and 14 and post-weaning at days 21 and 65 after birth. Samples were analysed for retinoids by high-performance liquid chromatography. RESULTS: Maternal VA supplementation resulted in significantly higher concentrations of retinol, retinyl palmitate and retinyl stearate in serum of mice neonates at days 5, 7, 14, 21 and 65 after birth in comparison to the basal diet, whereas significantly higher concentrations were observed in liver at days 5, 14, 21 and 65 after birth. At day 7 after birth, a decrease in the liver retinoid concentrations occurred in the VA-supplemented diet. CONCLUSION: Our results show for the first time that supplementation with high doses of VA during the lactation period in mice can affect serum retinol concentrations in the neonates and report that day 7 after birth is a critical time in the tissue distribution of retinoids during postnatal development.     

Clinical trials with retinoids for breast cancer chemoprevention

Retinoids have been studied as chemopreventive agents in clinical trials due to their established role in regulating cell growth, differentiation and apoptosis in preclinical models. Experimental evidence suggests that retinoids affect gene expression both directly, by activating and/or repressing specific genes, and indirectly, by interfering with different signal transduction pathways. Induction of apoptosis is a unique feature of fenretinide, the most widely studied retinoid in clinical trials on breast cancer chemoprevention due to its selective accumulation in breast tissue and to its favourable toxicological profile. In a phase III breast cancer prevention trial, fenretinide showed a durable trend to a reduction of second breast malignancies in premenopausal women. This pattern was associated with a favourable modulation of circulating IGF-I and its main binding protein (IGF-binding protein-3, IGFBP-3), which have been associated with breast cancer risk in premenopausal women in different prospective studies. In a subsequent biomarker study on premenopausal women who had participated in the phase III trial, high IGF-I and low IGFBP-3 baseline levels were found to predict second breast cancer risk, although the magnitude of their changes during treatment did not fulfil the requirements for suitable surrogate end-point biomarkers. In postmenopausal women, fenretinide did not reduce second breast cancer incidence, nor did it induce significant modulation of the IGF system. Similarly, fenretinide was not found to affect risk biomarkers significantly in early postmenopausal women on hormone replacement therapy, who are at increased risk of developing breast cancer. Biomarker studies of fenretinide alone or in combination with different nuclear receptor ligands are being conducted. In particular, clinical trials of fenretinide and tamoxifen have proved to be feasible, and this combination appears to be safe and well tolerated in high-risk women, especially when low-dose tamoxifen is employed. Novel retinoid X receptor-selective retinoids, or rexinoids, have been shown to suppress the development of breast cancer in several animal models with minimal toxicity, and are being intensively studied either alone or in combination with selective oestrogen receptor modulators, both in vitro and in vivo. The rexinoid, bexarotene, has recently been approved for the treatment of patients with cutaneous T-cell lymphoma, and a biomarker trial with bexarotene in women with high breast cancer risk is currently underway.     

Photoaging as a consequence of natural and therapeutic ultraviolet irradiation--studies on PUVA-induced senescence-like growth arrest of human dermal fibroblasts

Premature aging of the skin is a prominent side effect of psoralen photoactivation, a therapy widely and successfully used for different skin disorders. Recently, we demonstrated that treatment of fibroblasts with 8-methoxypsoralen and ultraviolet A irradiation resulted in growth arrest with morphological and functional changes reminiscent of replicative senescence. In this minireview we will focus on the similarities between intrinsic and extrinsic aging and PUVA-induced senescence-like growth arrest both resulting in the loss of the structural integrity of the dermal connective tissue as a hallmark of intrinsic aging and photoaging (extrinsic aging) of the skin, and we will discuss the important role of oxidative stress related telomere attrition in the PUVA-induced phenotype of dermal fibroblasts. With the PUVA-induced growth arrest of fibroblasts a new model has been added to the growing number of in vitro models with longterm growth arrest upon exposure to sublethal stressors (i.e. hyperoxia, hydrogen peroxide, ethanol), which are characterized by morphological and functional changes common for cellular senescence. This model may be particularly suited for further studies addressing mechanisms of stress-induced senescence-like growth arrest in vitro and in vivo, since many dermatological patients are treated with PUVA allowing the analysis of putative stress-induced premature senescence in vivo.     

Photoaging as a consequence of natural and therapeutic ultraviolet irradiation—studies on PUVA-induced senescence-like growth arrest of human dermal fibroblasts

Premature aging of the skin is a prominent side effect of psoralen photoactivation, a therapy widely and successfully used for different skin disorders. Recently, we demonstrated that treatment of fibroblasts with 8-methoxypsoralen and ultraviolet A irradiation resulted in growth arrest with morphological and functional changes reminiscent of replicative senescence. In this minireview we will focus on the similarities between intrinsic and extrinsic aging and PUVA-induced senescence-like growth arrest both resulting in the loss of the structural integrity of the dermal connective tissue as a hallmark of intrinsic aging and photoaging (extrinsic aging) of the skin, and we will discuss the important role of oxidative stress related telomere attrition in the PUVA-induced phenotype of dermal fibroblasts.With the PUVA-induced growth arrest of fibroblasts a new model has been added to the growing number of in vitro models with longterm growth arrest upon exposure to sublethal stressors (i.e. hyperoxia, hydrogen peroxide, ethanol), which are characterized by morphological and functional changes common for cellular senescence. This model may be particularly suited for further studies addressing mechanisms of stress-induced senescence-like growth arrest in vitro and in vivo, since many dermatological patients are treated with PUVA allowing the analysis of putative stress-induced premature senescence in vivo.     

Rat hepatic stellate cells become retinoid unresponsive during activation.

Hepatic stellate cells (HSC) play an essential role in fibrogenesis. Many stimuli cause HSC to activate, lose their Vitamin A and produce collagen. It is unclear whether Vitamin A loss causes activation, potentiates it or is simply an event in the cascade of activation changes. We determine if exogenous retinoids prevent the activation of freshly isolated rat HSC activated by plating on plastic. We also determine if retinoids: (1) reverse HSC activation; (2) maintain/restore HSC intracellular retinoid levels; (3) maintain expression of HSC nuclear receptors for retinoic acid (RAR) in HSC that are becoming activated or are chronically activated. Markers of activation in freshly isolated HSC were decreased by either retinol or retinoic acid without increases in HSC retinoid concentration. mRNA levels for RAR-alpha, RAR-beta and RAR-gamma, the nuclear receptors for retinoic acid, decreased during activation of freshly isolated HSC even with retinoid supplementation. RAR-alpha, RAR-beta and RAR-gamma mRNA and RAR-beta protein was undetectable in chronically activated HSC and remained absent after retinoic acid supplementation. Activation markers in chronically activated HSC were only slightly decreased after retinoid exposure. We conclude that exposure of HSC to extracellular retinoids diminishes some markers of activation but does not prevent HSC activation.     

Simultaneous Quantification of Various Retinoids by High Performance Liquid Chromatography: Its Relevance to Alcohol Research

Background: We established a high performance liquid chromatography system that allowed simultaneous quantification of various retinoids. Methods: We applied the retinoids to a high performance liquid chromatography system with a silica gel absorption column. Samples were separated by the system with a binary multistep gradient with two kinds of solvent that contained n-Hexan, 2-propanol, and glacial acetic acid in different ratios. Each retinoid was detected at a wavelength of 350 nm. Results: This condition allowed separation of 13-cis-retinoic acid, 9-cis-retinoic acid, all-trans-retinoic acid, 13-cis-retinol, all-trans-retinol, all-trans-4-oxo-retinoic acid, and 13-cis-4-oxo-retinoic acid as distinct single peaks. Each retinoid was also analyzed separately and its retention time determined. To ascertain the reliability of this system for retinoid quantification, retinoids at various concentrations were applied to the system. We observed the linearities between the concentration and area under the curve of the peak for each retinoid by linear least-squares regression analysis up to 2.5 ng/ml for all retinoic acids and up to 5 ng/ml for all retinols. There was no significant scattering in tests of within-day reproducibility or day-to-day reproducibility. Using this system, we examined effects of light exposure on isomerization of retinoids. When retinoids were exposed to room light for 2 hr, the amounts of all but 13-cis-retinol changed significantly. In particular, the amounts of all-trans-retinoic acid and 9-cis-retinoic acid were reduced by 40% and 60%, respectively. Conclusion: The HPLC system established in this study should be useful for studying the oxidation pathway of retinol to retinoic acid. A light-shielded condition is required when particular retinoic acids are analyzed.     

Modulation of endothelial cell shape and growth by retinoids

Physiologic concentrations of retinol (1 X 10(-6) M) caused capillary and aortic endothelial cells (EC) to undergo a morphologic change, characterized by a rounder cell body, increased refractility at cell edges, and longer cytoplasmic processes distributed in a bipolar fashion. Computer image analysis of retinoid-treated EC revealed that both retinoic acid and retinol affected cellular area. Twenty-four hours following retinoic acid treatment, EC occupied a greater area than control (P less than 0.03) or retinol-treated EC (P less than 0.02). By Day 7, however, retinoic acid-treated EC occupied equivalent cellular areas as compared to control cells (P = 0.8). In contrast, by Day 7, retinol-treated EC occupied a smaller cellular area than control (P less than 0.002) or retinoic acid-treated EC (P less than 0.001). Proliferation studies revealed that within the first 72 hr of retinol treatment, basal EC growth was inhibited by 33% and the cells exhibited a lowered responsiveness to basic fibroblast growth factor (bFGF). In contrast, EC treated with retinoic acid and pericytes treated with each of the retinoids were not inhibited. The inhibitory effect of the 72 hr retinol treatment was reversible. Following 3 days exposure to retinol, EC given fresh media without retinoid underwent a population doubling in a subsequent 3-day period. However, in the continued presence of retinol, EC were 100% growth-inhibited. After a 3-day pretreatment with retinol, with or without continued retinol treatment, EC were refractile to the mitogenic action of bFGF in a subsequent 3-day period. These results demonstrate that retinol inhibits the basal and growth factor-stimulated growth of EC and causes a significant shape alteration of EC, supporting our hypothesis that vitamin A may be one of the signals that modify the growth and phenotype of EC.     

Retinoid metabolism in the small intestine during development of liver cirrhosis

Background and Aims:  Retinoids are important mediators of cellular differentiation and proliferation in various epithelia of the body including the small intestine. Though alterations in intestinal epithelial cell proliferation have been noted in liver cirrhosis, mechanisms involved in the process are not well understood. This study examined the levels of various retinoids and retinoid-metabolizing enzymes in the small intestine during development of liver cirrhosis.
Methods:  Four groups of animals were used (control, phenobarbitone control, thioacetamide and carbon tetrachloride treatment). Twice-weekly intragastric or i.p. administration of carbon tetrachloride or thioacetamide, respectively, produced liver cirrhosis after 3 months, which was confirmed through histology and serum markers. Retinoid levels were measured by high-performance liquid chromatography.
Results:  A decrease in the levels of retinal, retinoic acid and retinol was evident in the intestine by 3 months, when cirrhosis was evident histologically, and these remained low until 6 months. A decrease in the activities of retinaldehyde oxidase, retinaldehyde reductase and retinol dehydrogenase was also seen in intestine from cirrhotic rats.
Conclusion:  These results suggest that altered retinoid metabolism in the intestine of cirrhotic rats might have an influence on changes in intestinal epithelial cell differentiation, seen in liver cirrhosis.     

Retinoids and retinol differentially regulate steroid biosynthesis in ovarian theca cells isolated from normal cycling women and women with polycystic ovary syndrome

CONTEXT: Polycystic ovary syndrome (PCOS) is characterized by ovarian androgen excess and infertility. Recent experiments have suggested that several genes involved in retinoic acid synthesis may be differentially expressed in PCOS theca cells and may contribute to excessive theca-derived androgen production. OBJECTIVE: The study was performed to examine whether there are differential effects of retinol and retinoids on normal and PCOS theca cell function. DESIGN: We used in vitro assays. SETTING: The study was conducted at the university laboratory. PATIENTS: We studied theca interna cells isolated from normal-cycling women and women with PCOS. INTERVENTIONS: Theca cells were treated with all-trans-retinoic acid (atRA), 9-cis retinoic acid (9-cis RA), or the retinoic acid precursor retinol. MAIN OUTCOME MEASURE(S): We measured dehydroepiandrosterone, testosterone, and progesterone biosynthesis as well as cytochrome P450 17alpha-hydroxylase (CYP17), cytochrome P450 cholesterol side-chain cleavage, and steroidogenic acute regulatory protein mRNA abundance and promoter function. RESULTS: Dehydroepiandrosterone production was increased by atRA and 9-cis RA in normal cells and by atRA, 9-cis RA, and retinol in PCOS. Testosterone production was increased by atRA in normal and by atRA, 9-cis RA, and retinol in PCOS. Progesterone production was not altered by retinoid treatment. Retinoids stimulated mRNA abundance and promoter function for CYP17 and steroidogenic acute regulatory protein in both cell types and cytochrome P450 cholesterol side-chain cleavage in normal cells. Retinol stimulated CYP17 mRNA accumulation and promoter function in PCOS but not normal theca cells. P < 0.05 was considered statistically significant. CONCLUSIONS: Differential responses to retinol and retinoids in normal and PCOS theca suggest that altered retinoic acid synthesis and action may be involved in augmented CYP17 gene expression and androgen production in PCOS.     

Liver retinoids and retinol esterification in fetal and pregnant rats at term

Retinol esterification in fetal rats and their mothers at term was studied in liver microsomes. The esterification rate was 0.28 +/- 0.05 nmol ester formed per milligram protein per minute, a value somewhat lower than that found in their mothers (0.44 +/- 0.11). The fetuses had significant amounts of liver retinoids. Analysis by high-performance liquid chromatography showed that the retinoid store consisted mainly of retinyl ester both in fetal and adult rat livers, but the fetal livers had higher percentages of free retinol and retinyl oleate than the adult livers. The presence of retinol esterification and a retinyl ester store in fetal rat liver at term is in accordance with the view that retinol brought to liver on retinol-binding protein can be taken up and retained there.