Topical all-trans retinoic acid augments ultraviolet radiation-induced increases in activated melanocyte numbers in mice

Cosmetic retinoid use in photoaged skin: A review of the compounds, their use and mechanisms of action

The inevitable attrition of skin due to ultraviolet radiation, termed photoaging, can be partially restored by treatment with retinoid compounds. Photoaged skin in lightly pigmented individuals, clinically presents with the appearance of wrinkles, increased laxity, and hyper- and hypopigmentation. Underlying these visible signs of ageing are histological features such as epidermal thinning, dermal-epidermal junction flattening, solar elastosis and loss of the dermal fibrillin microfibrillar network, fibrillar collagen and glycosaminoglycans. Retinoid compounds are comprised of three main generations with the first generation (all-trans retinoic acid, retinol, retinaldehyde and retinyl esters) primarily used for the clinical and cosmetic treatment of photoaging, with varying degrees of efficacy, tolerance and stability. All-trans retinoic acid is considered the 'gold standard' for skin rejuvenation; however, it is a prescription-only product largely confined to clinical use. Therefore, retinoid derivatives are readily incorporated into cosmeceutical formulations. The literature reported in this review suggests that retinol, retinyl esters and retinaldehyde that are used in many cosmeceutical products, are efficacious, safe and well-tolerated. Once in the skin, retinoids utilize a complex signalling pathway that promotes remodelling of photoaged epidermis and dermis and leads to the improvement of the cutaneous signs of photoaging.

The immunomodulatory effects of lactoferrin and its derived peptides on NF-κB signaling pathway: A systematic review and meta-analysis

BACKGROUND

Lactoferrin is a versatile protein with important modulatory functions in inflammation and immune response. This glycoprotein can bind and sequester iron and LPS, thereby intervening in certain signaling pathways and biological processes. In the present meta-analysis, we aimed to pool experimental data regarding the immunomodulatory effects of lactoferrin and its derived peptides on the NF-κB signaling pathway.

MATERIALS

We searched PubMed, Google Scholar, and Web of Science databases and obtained all related articles published before April 2022. Finally, 25 eligible studies were selected, and their reports were analyzed.

METHODS

We used Review Manager Version 5.2 to compute the standardized mean difference (SMD) and its 95% confidence interval. In addition, the source of heterogeneity was explored using meta-regression and sensitivity analysis. The symmetry of the funnel plot and Egger's test were also used to evaluate publication bias utilizing Comprehensive Meta-Analysis Version 2.

RESULTS

Comparing the group of cells and animals exposed to lipopolysaccharide alone with the group that received pretreatment with lactoferrin and its derivatives, we observed significant reductions in TNF-α, IL-1 beta, and IL-6 levels by 8.73 pg/mL, 2.21 pg/mL, and 3.24 pg/mL, respectively, in the second group. Additionally, IKK-β, p-IκB, and NF-κB (p65) levels were significantly lower by 7.37-fold, 15.02-fold, and 3.88-fold, respectively, in various cells and tissues.

CONCLUSION

Based on the results of this meta-analysis, lactoferrin and its derived peptides can be considered potent prophylactic and therapeutic candidates against inflammation-associated diseases by targeting the NF-kB pathway.

9-cis retinoic acid is the ALDH1A1 product that stimulates melanogenesis

Aldehyde dehydrogenase 1A1 (ALDH1A1), an enzyme that catalyses the conversion of lipid aldehydes to lipid carboxylic acids, plays pleiotropic roles in UV-radiation resistance, melanogenesis and stem cell maintenance. In this study, a combination of RNAi and pharmacologic approaches were used to determine which ALDH1A1 substrates and products regulate melanogenesis. Initial studies revealed that neither the UV-induced lipid aldehyde 4-hydroxy-2-nonenal nor the ALDH1A1 product all-trans retinoic acid appreciably induced melanogenesis. In contrast, both the ALDH1A1 substrate 9-cis retinal and its corresponding product 9-cis retinoic acid potently induced the accumulation of MITF mRNA, Tyrosinase mRNA and melanin. ALDH1A1 depletion inhibited the ability of 9-cis retinal but not 9-cis retinoic acid to stimulate melanogenesis, indicating that ALDH1A1 regulates melanogenesis by catalysing the conversion of 9-cis retinal to 9-cis retinoic acid. The addition of potent ALDH1A inhibitors (cyanamide or Angeli's salt) suppressed Tyrosinase and MITF mRNA accumulation in vitro and also melanin accumulation in skin equivalents, suggesting that 9-cis retinoids regulate melanogenesis in the intact epidermis. Taken together, these studies not only identify cyanamide as a potential novel treatment for hyperpigmentary disorders, but also identify 9-cis retinoic acid as a pigment stimulatory agent that may have clinical utility in the treatment of hypopigmentary disorders, such as vitiligo.

β-Cryptoxanthin suppresses UVB-induced melanogenesis in mouse: involvement of the inhibition of prostaglandin E2 and melanocyte-stimulating hormone pathways

Objective

β-cryptoxanthin (β-CPX) is a carotenoid that is widely contained in the fruits of citrus plants. We evaluated the effect of β-CPX on UVB-induced pigmentation and mRNA expression related to melanogenesis in mouse skin. In addition, changes in melanogenic molecules were evaluated in cultured melanocytes stimulated with prostaglandin (PG) E2, melanocyte-stimulating hormone (MSH) and endothelin (ET)-1.

Methods

Mice were irradiated with UVB and were given β-CPX (0.1, 1 and 10 mg/kg) orally for 14 days. Pigmentation was evaluated by skin colour change and microscopic observation. Total RNA was obtained from the skin and the expression of melanogenic mRNA was evaluated by RT-PCR. In cell culture studies, human melanocytes were cultured with β-CPX and melanogenic stimulants (PGE2, MSH and ET-1) for 6–10 days. Melanin contents, dendricity, melanogenic mRNA and phosphorylation of cyclic AMP response element-binding protein (CREB) were evaluated.

Key findings

β-CPX (10 mg/kg) significantly suppressed skin pigmentation and mRNA expression of cyclooxygenase-2, ET-1 receptors, low-affinity neurotrophin receptor, PGE2 receptor (EP1), melanocortin 1 receptor (MC1R), tyrosinase (Tyr), tyrosinase-related protein (Tyrp) 1 and microphthalmia transcription factor. β-CPX (10 µg/ml) suppressed melanogenesis induced by PGE2, MSH and ET-1. In the PGE2-stimulated melanocytes, mRNA expressions of EP-1, Tyr and Tyrp1 and phosphorylation of CREB protein were suppressed. In the ET-1-stimulated cells, only expression of CREB protein was suppressed. In the MSH-induced cells, mRNA expression of MC1R and Tyrp1 and protein expression of CREB were suppressed.

Conclusion

Oral administration of β-CPX was found to suppress UVB-induced melanogenesis. Suppression of melanogenic enzymes, receptors of melanogenic stimulators, expression and phosphorylation of CREB are thought to be involved in the mechanism.

All Trans-Retinoic Acid (ATRA) Elevated Eukaryotic Translation Initiation Factor 4A1 (eIF4A1) mRNA in ATRA-Responsive Vitiliginous Epidermis

Chronic skin disorders that require long-term treatment with corticosteroids, such as vitiligo, may use a combination of topical corticosteroids and topical all-trans-retinoic acid (ATRA) to prevent corticosteroid-induced skin atrophy. Besides protecting against the side effects of corticosteroids, ATRA produces a better clinical outcome in some patients. This study examined whether ATRA influences the expression of mRNAs responsible for the clinical correlation. Differential display was performed using kits incorporating an annealing control primer. Epidermis from suction blisters taken from six patients diagnosed with a generalized type of vitiligo, who were included in a placebo-controlled paired-comparison left-right study using ATRA and vehicle for 3-6 months, were used. Ten differentially expressed mRNAs were identified in those six patients. Expression levels were restored to normal particularly in four types of mRNAs, which were matched with sequences encoding eukaryotic translation initiation factor 4A1 (eIF4A1), ribosomal protein L13, mediator of RNA polymerase to transcription (MRT) and ribosomal phosphoprotein PO. Of those mRNAs, the level of eIF4A1 mRNA showed a clinical correlation; The expression of eIF4A1 mRNA, examined by real-time PCR, was elevated in four patients who showed a favorable clinical response to ATRA, whereas no change or a decrease occurred in three patients whose clinical responses did not differ between ATRA and vehicle treatment. The eIF4A1 protein expression from the other two patients, one of them with a favorable response to ATRA, also showed a clinical correlation. Therefore, eIF4A1 mRNA may be an important gene related to ATRA effects, although further studies are required.

The Combined Effects of Extracts Containing Carotenoids and Vitamins E and C on Growth and Pigmentation of Cultured Human Melanocytes

In the present study, we investigated the effects of tomato extract (TE) containing lycopene and palm fruit extract (PE) rich in carotenoids on the growth and pigmentation of melanocyte cultures of Caucasian origin. The extracts were tested at different concentrations and in combination with vitamins E and C. Melanocytes with basic and increased (tyrosine-induced) pigmentation were treated in short-term and long-term experiments. Prevention of UVA-induced DNA damage was studied by using the comet assay. Melanocytes with stimulated melanin production showed reduced growth. Incubation of the cells with TE/PE (20/4 microg/ml) in combination with 35 microM vitamin E and 100 microM vitamin C (COMB 20/4) reduced this growth inhibition, especially in the long-term cultures. Increased production of melanin pigment was obtained when the cells were treated with 2.5 x and 10 x higher concentrations of the TE/PE and the same concentration of vitamins E and C (COMB 50/10 and 200/40). Reduced DNA damage was found after UVA irradiation in cells preincubated with COMB 50/10. The results indicate that the presence of carotenoids from TE and PE in combination with vitamins E and C may influence growth and pigmentation in melanocyte monocultures. Depending on the concentration of the carotenoid mixtures, their presence may provide some protection against the melanogenic intermediates and/or exogenous DNA damage.

Photoreaction, phototoxicity, and photocarcinogenicity of retinoids

Sunlight is a human carcinogen. Many retinoid-containing cosmetics are used to protect damages caused by sunlight irradiation. Since retinol is thermally unstable and retinyl palmitate (RP) s relatively more stable, RP is also widely used as an ingredient in cosmetic formulations. In general, little is known about the photodecomposition of retinoids and the toxicity of retinoids and their photodecomposition products on the skin's responses to sunlight. This review focuses on the update information on photoreactions, phototoxicity, and photocarcinogenicity of the natural retinoids including retinol, retinal, retinoid acid (RA), retinyl acetate, and RP.

All-trans retinoic acid induces differentiation and apoptosis of murine melanocyte precursors with induction of the microphthalmia-associated transcription factor

The effects of all-trans retinoic acid on the differentiation and proliferation of immature melanocyte precursors were studied. NCC-melb4 cells are an immortal cloned cell line established from mouse neural crest cells using a single-cell cloning method. These cells were positive for tyrosinase-related protein 1, tyrosinase-related protein 2 and KIT, but were negative for tyrosinase and had no dihydroxyphenylalanine reaction. They contained only stage I melanosomes without any melanosomes in more advanced stages. After treatment with all-trans retinoic acid, many of the cells became tyrosinase- and dihydroxyphenylalanine-reaction-positive, changed from polygonal to dendritic in shape, and had stage III to IV melanosomes. These findings indicate that treatment with all-trans retinoic acid induced the differentiation of NCC-melb4 cells. Reverse transcription polymerase chain reaction analysis revealed a marked increase in expression of microphthalmia-associated transcription factor mRNA after all-trans retinoic acid treatment, suggesting that microphthalmia-associated transcription factor may be the key molecule in this event. Enhanced expression of protein kinase Calpha following treatment with all-trans retinoic acid was also demonstrated. The proliferation of NCC-melb4 cells was inhibited by all-trans retinoic acid in a dose-dependent manner. Increased apoptosis after all-trans retinoic acid treatment was observed by electron microscopy, the TUNEL method, DNA fragmentation assay, and flow cytometry. All-trans retinoic acid upregulated caspase-3 and downregulated bcl-2. Electron microscopy showed that apoptotic cells contained melanosomes of advanced stages, suggesting that mature melanocytes may tend to undergo apoptosis after all-trans retinoic acid treatment. This study provides important clues towards understanding the roles and working mechanisms of retinoic acids in melanocyte development and melanogenesis.

Skin pigmentation enhancers

The highest incidences of cancer are found in the skin, but endogenous pigmentation is associated with markedly reduced risk. Agents that enhance skin pigmentation have the potential to reduce both photodamage and skin cancer incidence. The purpose of this review is to evaluate agents that have the potential to increase skin pigmentation. These include topically applied substances that simulate natural pigmentation: dihydroxyacetone and melanins; and substances that stimulate the natural pigmentation process: psoralens with UVA (PUVA), dimethylsulfoxide (DMSO), L-tyrosine, L-Dopa, lysosomotropic agents, diacylglycerols, thymidine dinucleotides, DNA fragments, melanocyte stimulating hormone (MSH) analogs, 3-isobutyl-1-methylxanthine (IBMX), nitric oxide donors, and bicyclic monoterpene (BMT) diols. These agents are compared with regards to efficacy when administered to melanoma cells, normal human epidermal melanocytes, animal skin, and human skin. In addition, mechanisms of action are reviewed since these may reveal issues related to both efficacy and safety. Both dihydroxyacetone and topically applied melanins are presently available to the consumer, and both of these have been shown to provide some photoprotection. Of the pigmentation stimulators, only PUVA and MSH analogs have been tested extensively on humans, but there are concerns about the safety and side effects of both. At least some of the remaining pigmentation stimulators under development have the potential to safely induce a photoprotective tan.

Effects of all-trans retinoic acid on melanogenesis in pigmented skin equivalents and monolayer culture of melanocytes

The effects of all-trans retinoic acid (RA) on melanogenesis and the mechanism of its action in topical treatment have not been elucidated. The purpose of this study was to determine the effects of RA on melanogenesis in the pigmented skin equivalent as well as in monolayer culture of melanocytes, and to determine whether RA, hydroquinone (HQ), and hydrocortisone (HC) show synergistic depigmenting effects in combined treatments of each other. The suppressing effect of RA on melanogenesis was not observed in pigmented skin equivalents and monolayer culture of murine and human melanocytes, although HQ showed strong inhibition of melanogenesis. The synergistic effects between RA, HQ, and HC were not particularly seen. The results suggested that RA neither has direct inhibitory effects on melanogenesis of melanocytes, nor influences the cell-cell interactions between melanocytes, keratinocytes and fibroblasts, such as paracrine actions with regard to melanin production. The role of RA in bleaching treatments appears to be in other specific actions, such as promotion of keratinocytes proliferation and acceleration of epidermal turnover.

Topical retinoic acid enhances, and a dark tan protects, from subedemal solar-simulated photocarcinogenesis

Studies into the effects of topical retinoic acid on photocarcinogenesis have yielded ambiguous findings. This may be due to different Experimental protocols and ultraviolet spectra. Retinoic acid is commonly used for a range of dermatologic conditions, and therefore it is important to resolve whether it affects skin tumor formation. To address this issue we used a protocol to mimic as closely as possible human use of retinoic acid. Two mouse strains were used: Skh:HR-1 (albino) and Skh:HR-2 (lightly pigmented). The pigmented mice more closely resemble Caucasian skin as they develop a light tan in response to ultraviolet radiation. This tan is greatly augmented by retinoic acid. As these are congenic mice, any differences can be attributed to the development of a tan. Mice were exposed to solar-simulated ultraviolet radiation, followed by treatment with 0.05% retinoic acid. This modeled exposure to sunlight during the day followed by retinoic acid treatment and a night-time period in the absence of sunlight. As it is recommended that ultraviolet exposure is minimized when using topical retinoic acid, the mice were only exposed to one-third of minimal edemal dose of ultraviolet radiation per day. This retinoic acid protocol augmented photocarcinogenesis. Retinoic acid decreased the latency period, reduced the probability that a mouse would survive without a tumor, and increased the number of tumors per mouse. All tumors induced were squamous cell carcinomas, and the skin between the tumors on mice treated with retinoic acid was found to contain carcinoma in situ upon histologic diagnosis. The light tan of the solvent-treated pigmented mice did not provide any protection, whereas the dark tan, which developed in Skh:HR-2 mice in response to retinoic acid, reduced photocarcinogenesis but did not overcome the augmenting effect of retinoic acid. Thus, using this experimental design, topical retinoic acid augmented photocarcinogenesis, and the ability to develop a dark but not light tan provided some, but limited, protection.