Grape constituents for protection against photodamage to skin

Abstract

Cutaneous overexposure to ultraviolet radiation has a variety of deleterious effects. The extent to which dietary factors are effective at moderating UV damage is a significant issue. Grapes contain phytochemicals that protect against excessive UV damage. Components of grapes, in particular resveratrol, proanthocyanidins, and cyanidin‐3‐glucoside, are receiving considerable attention for their photoprotective actions because of their lack of toxicity, abundance, and low cost. Resveratrol and proanthocyanidins are potent antioxidants that interfere with signal transduction and immunosuppressive pathways activated by UV radiation, which are responsible for its harmful effects. Studies in humans provide a rationale for their further development as a novel method of photoprotection.

Excessive exposure to solar ultraviolet radiation has a major negative impact on the health of skin. It causes sunburn, photoaging, keratinocyte carcinomas, and melanomas. Current methods of prevention have failed to stem the incidence of these adverse effects. Grapes are natural products that are being investigated as preventive agents that can impede these deleterious effects. Components of grapes, in particular resveratrol, proanthocyanidins, and cyanidin‐3‐glucoside, are potent antioxidants that interfere with signal transduction and immunosuppressive pathways activated by UV radiation, which are responsible for its harmful effects. Studies in humans provide a rationale for their further development as a novel method of photoprotection.

Abbreviations

BCC

basal cell carcinoma

COX‐2

cyclooxygenase‐2

CPD

cyclobutane pyrimidine dimers

CYP1A1

cytochrome P450, family 1, subfamily A, polypeptide 1

GSP

grape seed proanthocyanidin

IL‐10

interleukin‐10

IL‐12

interleukin‐12

IV

intravenous

KC

keratinocyte carcinoma

MAPK

mitogen‐activated protein kinase

MED

minimal erythema dose

PCNA

proliferating cell nuclear antigen

PGE2

prostaglandin E2

ROI

reactive oxygen intermediates

SCC

squamous cell carcinoma

SHH

sonic hedgehog

TGF‐β

transforming growth factor‐beta

TGP

table grape powder

TSLP

thymic stromal lymphopoietin

UVR

ultraviolet radiation

VEGF

vascular endothelial growth factfactor

INTRODUCTION

Excessive ultraviolet radiation exposure contributes to premature aging of the skin, suppression of immune responses, and triggering of selected infections, such as herpes simplex virus. It is also a contributing factor to a variety of skin malignancies, including melanomas, ¹ Merkel cell carcinomas, and cutaneous squamous cell (SCC) and basal cell (BCC) carcinomas, grouped together under the term keratinocyte carcinomas (KCs). ² , ³ BCC and SCC are the most common malignancies in the United States, with an estimated 5.4 million new cases diagnosed each year. ² , ³ Although their mortality is low, the continuing rise in their incidence, and their occurrence in younger and younger age groups, makes BCC and SCC a significant clinical concern. ⁴ Government agencies and healthcare organizations worldwide have implemented public health programs directed at avoiding excessive UV exposure. Despite these measures, the incidence of KCs continues to rise. The reasons for this include increased time spent in outdoor leisure activities, persistent practice of indoor tanning for cosmetic purposes, increase in the proportion of older people in the population, and increase in the prolonged use of photosensitizing pharmaceuticals, which have been identified as a risk factor in KCs. ⁴ , ⁵ The cost of diagnosis and treatment of KCs and their precursors places a heavy burden on healthcare systems worldwide. In the United States alone, the expenditure exceeds 8 billion dollars annually. ²

Prevention of KCs has relied primarily on treatment of actinic keratoses (precursors of SCC), avoidance of excessive sun exposure, and the use of sunscreens and photoprotective clothing. ⁶ Noteworthy is the mention of some systemic beneficial health effects of ultraviolet radiation B (UVB), independent from production of vitamin D. ⁷ UVB is necessary for the cutaneous production of vitamin D and its photoderivatives, which, after enzymatic activation, also show photoprotective effects. ⁸ Notwithstanding, the frequency of KCs continues to mount. Thus, there is great interest in identifying additional dietary and pharmaceutical compounds that inhibit, slow, or reverse the molecular and biochemical changes involved in cutaneous carcinogenesis and cancer progression while at the same time having minimal toxicity and low cost. ⁹

Identification of new agents for skin cancer prevention has relied on our understanding of the mechanistic basis by which these tumors arise. UV‐induced BCC and SCC develop through several distinct steps. ² In the first stage, termed initiation, UV‐induced cyclobutane pyrimidine dimers cause mutations in the p53 tumor suppressor gene that are found in both BCC and SCC. Pathological activation of the sonic hedgehog (SHH) pathway represents a crucial step in BCC development. These mutations result in populations of keratinocytes amenable to further damage. Repeated UV exposure during the second phase, termed promotion, leads to the generation of reactive oxygen intermediates (ROI) and non‐specific inflammatory changes that augment the proliferation of mutant keratinocytes. ² These biochemical changes ultimately result in pre‐cancerous actinic keratoses. ² Further genetic and biochemical changes facilitate the evolution of AKs into SCCs during the progression phase of UV carcinogenesis. Events that occur during the progression phase include increased cyclooxygenase‐2 (COX‐2) expression and transforming growth factor‐β (TGF‐β) activity, which, in turn, result in epithelial– mesenchymal transition and increased angiogenesis. ² In addition to the mutational changes in keratinocytes, UV radiation induces a variety of immunosuppressive mediators in the skin, ¹⁰ , ¹¹ suppressing local and systemic host immune responses. As a result, mutant keratinocytes are either not identified and eliminated or not neutralized prior to their transition to malignancy. ¹² SCCs arise when both mutant keratinocytes and immune suppression are present. Furthermore, tumor cells, in cooperation with recruited stroma cells, can autoregulate their environment, protecting them from host responses that have evolved to protect them from tumor development. ¹³

Careful elucidation of the molecular and biochemical events in UV carcinogenesis has been the basis for introducing new agents that protect against the generation of KCs. Systemic administration of niacinamide, a vitamin B3 analogue, promotes repair of UV‐induced DNA damage and causes a reduction of KCs in non‐organ transplant patients, but not in organ transplant recipients. ¹⁴ , ¹⁵ The cyclooxygenase inhibitor, celecoxib, which blocks the enzyme COX‐2, has also been found to effectively reduce KCs in prospective, randomized clinical trials. ¹⁶ , ¹⁷ Combined topical application of 5‐fluorouracil, an inhibitor of DNA replication, and of the vitamin D analogue, calcipotriene, which augments immune responses by enhancing the production of thymic stromal lymphopoietin (TSLP), ¹⁸ prevents KCs from developing as well. ¹⁹ Furthermore, diverse vitamin D and lumisterol hydroxyderivatives ⁸ , ²⁰ as well as melatonin and its metabolites, ²¹ , ²² all considered natural products, ²³ show radioprotective and anticancer properties in preclinical models.

In addition to pharmacologic agents, there is mounting interest in the use of natural products, especially plant phytochemicals, which will prevent or delay the onset of KCs as well as block the onset of a variety of other diseases. ⁴ , ⁹ , ²⁴ , ²⁵ UV radiation causes extensive damage to nucleic acids in plants; however, these obligate phototrophs require sunlight for photosynthesis. This method of energy production exposes plants to high levels of genotoxic stress that affect their physiology and survival. Plants have evolved a variety of protective mechanisms to survive, including physical barriers (e.g., skin, hair, and wax), activation of DNA damage repair enzymes, and the synthesis of UVB filtering polyphenols. ²⁶ These phytochemicals are essential for plant survival, are a means of communication with other plants, and protect against the harmful effects of external physical and chemical agents, including UV radiation. Without protective phytochemicals, solar UV exposure would be lethal to plants. The mechanisms that protect plants from excessive UV exposure are being exploited to prevent KCs.

Constituents of green tea, pomegranate, broccoli, golden serpent fern (Polypodium leucotomos), turmeric (curcumin), and grapes, to name a few, are being examined in this regard. ⁹ Previous research had considered proanthocyanidins as a potential novel therapeutic agent for psoriasis because of their ability to reduce oxidative stress. ²⁷ Because non‐specific inflammation and oxidative stress are involved in UV‐induced skin damage, grape constituents have been evaluated for their potential to prevent the adverse effects of UV on the skin of mice.

GRAPE CONSTITUENTS

Grapes are among the most popular fruits worldwide. Production was estimated to be over 80 million tons in 2022. ²⁸ Grape skin and seeds have high concentrations of polyphenols such as phenolic acids, flavonoids, stilbenoids, proanthocyanidins, and anthocyanins, all of which have been evaluated for their health benefits (Table 1). ²⁹

TABLE 1.

Polyphenols.

Number of carbons	Class	Examples	Basic structure
6	Simple phenol
7	Phenolic acid	Gallic acid Caffeic acid ferulic acid
14	Stilbenoid	Resveratrol
15	Flavonoid	Flavones Flavanones Flavonol Flavanonol Flavanols Anthocyanidins Anthocyanins

Polyphenols

In addition to grapes, polyphenols are found in fruits, vegetables, tea, nuts, seeds, flowers, tree bark, coffee, and chocolate, and are essential for their physiology. ³⁰ They provide plants with yellow, red, or purple pigments. They are also involved in plant growth, reproduction, and host defenses against pathogens by increasing astringency or acting as phytoalexins (antimicrobial compounds that inhibit the growth of microbes). ³⁰

Polyphenolic compounds were originally studied for taxonomy as they are ubiquitous constituents of plants, and they differ in chemical properties within the same species. ³⁰ They exist in plants as glycosides with sugar units such as acylated sugars with a common polyphenol skeleton that can range from simple aromatic compounds to complex polymers. ³¹ , ³² Scientists have identified over 8000 different classes of polyphenols based on the number and organization of their carbon atoms. ³² Simple phenols, phenolic acids, stilbenoids, and flavonoids are a few of the more common classes. Polyphenols also have antioxidant, anti‐inflammatory, and antineoplastic properties.

Phenolic acids

The majority of polyphenols produced in plants are phenolic acids, that is, phenols attached to a carboxylic acid group. They are primarily found in their bound forms, which can be released through enzymatic reactions and acid or alkaline hydrolysis. ³¹ , ³³ This class can be further divided into benzoic acids and cinnamic acids based on their structural backbone (Figure 1A and Table 1). ³¹

FIGURE 1.

Grape Polyphenols. (A) Structural backbones of phenolic acids. (B) Stilbene and resveratrol. (C) Flavonoids.

Stilbenoids

Stilbenoids are a class of polyphenols found in grapes, red wine, mulberries, and peanuts (Figure 1B and Table 1). They are synthesized by plants in response to stress and serve as phytoalexins against bacteria, fungi, and viruses. ³⁴ They share a common stilbene backbone. ³⁵ Stilbenes (C6‐C2‐C6) have two phenyl groups linked by a trans‐ethene bond. They are produced from phenylalanine, acetyl‐CoA, and 3 malonyl‐CoAs. ³² Methylation, glycosylation, and prenylation of the stilbene backbone allow for subclassification. ³⁵ Resveratrol (trans‐3,5,4′ trihydroxystilbene) is the stilbenoid that has received the greatest attention as a health promoter. ³⁶ Resveratrol prevents damage from ROS and inhibits the carcinogen‐activating enzyme CYP1A1. ³⁷ , ³⁸ It also arrests the cell cycle at the G₀/G₁ phase and activates p53‐dependent pathways. ³⁸ In addition, resveratrol promotes apoptosis in human cancer cell lines. ³⁶ Despite its potent anticancer properties, the poor bioavailability of resveratrol is an impediment to its potential therapeutic uses. The unstable hydroxyl groups and C‐C double bond make it sensitive to light, alkaline pH, and temperature. ³⁹ A study on the bioavailability of oral and IV‐administered ¹⁴C‐labeled resveratrol showed rapid and extensive metabolism of the compound. ³⁶ Plasma levels of unmetabolized resveratrol were beneath the level of detection (<5 ng/mL) at all time points in a study of six healthy human volunteers given an oral dose of 25 mg, although its sulfate and glucuronic acid metabolites were found in urine. ³⁶ Similarly, non‐metabolized resveratrol was not detected in plasma past 30 min after a 0.2 mg IV dose in all three volunteers. ³⁶ Attempts to circumvent this problem have been addressed by using resveratrol‐loaded nanoemulsions, which can be applied topically. These formulations have been successful in increasing its bioavailability and have shown efficacy in protecting against the adverse effects of UVR in animal models. ⁴⁰ , ⁴¹

Flavonoids

Flavonoids are found in the leaves and skin of fruits. They are responsible for the red color in wine. There are 13 subclasses of over 5000 compounds. ³⁰ , ³² Their chemical structure is comprised of two phenyl rings connected by a heterocyclic ring (C6‐C3‐C6) ³⁰ (Table 1 and Figure 1C). Variability in the heterocyclic ring and hydroxylation allows for the diverse number of flavonoid compounds. ³¹ Polymeric flavanols are also commonly known as proanthocyanidins, as their two isomers of flavanols can produce anthocyanidins through acid‐catalyzed cleavage of the polymeric chains (Figure 1C). ³¹ , ³² Their biochemical properties have been exploited in the production industry for paint, cosmetics, tanning agents, perfumes, pesticides, herbicides, and paper. ³⁰ , ³² They are also used in the food industry as food coloring and preservatives. ³⁰

Anthocyanins are another class of flavonoids (Figure 1C). Cyanidin‐3‐glucoside, for example, is found in grapes, blackberries, raspberries, black soybeans, common beans, cowpeas, and lentils, and has been investigated for its photoprotective properties. ⁴² , ⁴³

BIOCHEMICAL EFFECTS OF GRAPE CONSTITUENTS

Protection against DNA damage

One of the major direct biochemical effects of UV radiation on cells is damage to DNA, primarily in the form of cyclobutane pyrimidine dimers (CPDs). In vitro experiments have demonstrated that GSPs diminish CPDs produced by UVR. ⁴⁴ When UVR‐induced DNA damage occurs, it is repaired by activation of nucleotide excision repair enzymes. In in vivo experiments in mice in which GSPs were placed in drinking water, UV‐induced CPDs were reduced, and nucleotide excision repair enzymes were enhanced. ⁴⁴ Similarly, resveratrol has been shown to augment UVC‐induced DNA damage repair enzymes in in vitro experiments using the A549 cell line. ⁴⁵

Antioxidant effects

Previous research had examined grape constituents as potential novel therapeutic agents for psoriasis because of their ability to reduce oxidative stress. ²⁷ Because UVR increases ROI (i.e., hydrogen peroxide, lipid peroxidation, protein oxidation) and reactive nitrogen intermediates, ⁴⁶ grape constituents were examined for their ability to interfere with UVR‐induced increases in these moieties and to help prevent and induce repair of UV‐induced damage to skin cells, proteins, lipids, and DNA. As a consequence, grape constituents might protect against UVR‐induced carcinogenesis, premature skin aging, and other detrimental effects of chronic sun exposure. In fact, grape seed proanthocyanidins (GSPs), resveratrol, and cyanidin‐3‐O‐glucoside were all found to mitigate the activity of ROIs. ⁴⁶ , ⁴⁷ , ⁴⁸

Oral GSPs given as a dietary supplement prevent UVB‐induced oxidative stress by having an antagonistic effect on the depletion of antioxidant enzymes produced by keratinocytes, including catalase, glutathione peroxidase, and glutathione. ⁴⁹ Also, in vitro studies in UVR‐irradiated keratinocytes and in vivo experiments in UVR‐irradiated SKH‐1 hairless mice found that pretreatments with resveratrol attenuate the generation of ROI by activating and increasing superoxide dismutase and glutathione peroxidase, directly scavenging free radicals, and inhibiting oxidation and degradation of cell membrane lipids. ⁴⁷ Similarly, cyanidin‐3‐O‐glucoside inhibits oxidative damage in vitro and in vivo. ⁴⁸ , ⁵⁰ By reducing oxidative stress through multiple mechanisms, resveratrol, grape proanthocyanidins, and cyanidin‐3‐O‐glucoside prevent UVR‐induced damage to cell membranes, proteins, lipids, and DNA, potentially helping to prevent premature skin aging, UV‐induced skin cancer, and other detrimental effects of chronic sun exposure.

Signal transduction pathways

The pro‐oxidant properties of UVR modulate the actions of signal transduction pathways (Figure 2). MAPK (ERK1/2, JNK, p38) and NF‐κB pathways are both important for photocarcinogenesis and UV‐induced photodamage. ⁴ These pathways regulate cellular proliferation, differentiation, apoptosis, inflammation, and host antitumor immune responses. In keratinocytes, UVB is particularly effective at activating JNK and p38, whereas UVA preferentially targets ERK. ⁵¹ The addition of GSPs to human epidermal keratinocytes in vitro diminishes UVR‐induced MAPK activation, thereby abrogating the pro‐proliferative and antiapoptotic effects on cancer cells. Resveratrol also inhibits UVR‐induced activation of the ERK1/2, JNK, and p38 MAPK subfamilies. ⁵² , ⁵³ By inhibiting ERK1/2, JNK, and p38, the activity of the downstream molecules PI‐3K/Alt is also diminished. ⁵⁴ Inactivation of PI‐3 K by resveratrol is associated with inhibition of markers of cellular proliferation (PCNA, cyclin D1) and cyclooxygenase 2, the rate‐limiting enzyme in prostaglandin E2 synthesis, both of which are important events in UVR‐induced carcinogenesis. ⁵⁴ , ⁵⁵ , ⁵⁶ In the same way, cyanidin‐3‐O‐glucoside‐induced inhibition of UV‐induced generation of ROIs regulates the MAP kinase signaling pathway in SKH‐1 hairless mice. ⁴⁸

FIGURE 2.

Pathways in skin affected by UV radiation. COX‐2, cyclooxygenase‐2; PGE2, prostaglandin E2; ROI, reactive oxygen intermediates.

NF‐κB is an important regulator of inflammatory and immune responses that are activated in keratinocytes by UV exposure. ⁵⁷ Resveratrol reduces NF‐κB activation by a complex process that involves inhibition of UVB‐mediated phosphorylation and degradation of IκBα, a protein that keeps NF‐κB inactive in the cytoplasm. ⁵⁸ These effects have been demonstrated in in vitro studies using human epidermal keratinocytes and in vivo studies in the skin of mice. ⁴⁶ The actions on NF‐κB attenuate the non‐specific inflammatory response that promotes UVR‐induced skin carcinogenesis and inhibit the tumor‐specific immunosuppressive actions of UV radiation. Cyanidin‐3‐O‐glucoside has also been shown to inhibit the NF‐κB signaling pathway in vivo. ⁴⁸

Other signaling pathways

The addition of resveratrol to cultures of squamous cell carcinoma cell lines inhibits their growth and enhances apoptosis. ⁵⁹ This is associated with enhanced Axin2 activity, which in turn results in a reduction in gene and protein expression of Wnt2. Wnt signaling is important for the development of cutaneous SCCs, and its inhibition abrogates cyclin D1 and vascular endothelial growth factor (VEGF), both of which are involved in photocarcinogenesis.

Survivin expression is enhanced in many types of cancer, including SCCs of the skin. It enhances cell proliferation and inhibits apoptosis by blocking caspase activation. ⁶⁰ Phosphorylation of survivin is necessary for its binding to Smac/DIABLO, which is required for the antiapoptotic activity of survivin. In mice subjected to a UVR skin carcinogenesis protocol, topical application of resveratrol inhibits phosphorylation of survivin and suppresses Smac/DIABLO expression. As a result, resveratrol increases apoptosis, decreases tumor cell proliferation, and inhibits photocarcinogenesis. ⁶¹

Resveratrol has been shown to inhibit SHH signaling in prostate, acute myeloid leukemia, and chronic myeloid leukemia. ⁶² , ⁶³ , ⁶⁴ , ⁶⁵ , ⁶⁶ This pathway is important for the generation of BCCs. It is interesting to speculate that resveratrol may inhibit BCC generation through interactions with the SHH pathway. However, until now, grape constituents have not been examined as chemopreventive agents for BCCs.

IMMUNOLOGICAL EFFECTS

UVB exposure has suppressive effects on the immune system through stimulation of immunosuppressive cytokines or other mediators of which peptides derived from proopiomelanocortin are examples. ⁸ , ¹⁰ This also includes decreased IL‐12 and increased IL‐10 levels. ¹² The role of GSPs in preventing UVB‐induced immune suppression has been evaluated in mice. ⁴⁴ Studies have found that GSPs show chemopreventive properties by stimulating IL‐12 production, which then activates nucleotide excision repair and in turn limits UVB‐induced DNA damage. ⁴⁴ This repair of DNA damage in epidermal Langerhans cells is postulated to reverse the immunosuppressive effect of UVR. ⁴⁴ This occurs by activating CD8 effector T cells, reducing immunosuppressive cytokines, such as TGF‐β and IL10, and increasing the immunostimulatory cytokine IFN‐γ. ⁶⁷

GRAPE PHOTOPROTECTION IN HUMANS

The photoprotective effect of grape powder and its constituents on skin in healthy human volunteers has been evaluated in prospective studies. ⁶⁸ , ⁶⁹ , ⁷⁰ , ⁷¹ When freeze‐dried table grape powder (TGP), comprised of a mixture of red and white seeded and seedless varieties, was applied topically 30 min prior to a two minimal erythema dose (MED) of UVB radiation, ⁶⁸ skin biopsies showed fewer sunburn and mutant p53‐positive keratinocytes and more Langerhans cells compared with biopsies from skin sites that were UV‐irradiated but were not pretreated with TGP, supporting their role as a potential photoprotective agent. ⁶⁸

To determine whether oral consumption of dietary table grapes could protect humans from ultraviolet photodamage, a prospective single‐group, open‐label intervention study was conducted. ⁶⁹ The participants consisted of 19 healthy human volunteers aged 19 years and older and Fitzpatrick sun reactive skin types I‐III. ⁶⁹ Volunteers were instructed to consume TGP (25 g, 3× per day in water, equivalent to three servings per day of table grapes) for 14 days. ⁶⁹ Changes in the MED were measured before and after the indicated treatment. ⁶⁹ [The MED is the smallest amount of ultraviolet radiation that will give a uniform area of redness to the entire surface of UV‐irradiated skin 24 h after exposure.] There was an overall mean increase of 75% in the MED (i.e., there was greater photoprotection) which was statistically significant. ⁶⁹ Also, skin biopsies were taken before and after TGP treatment to evaluate biomarker changes. ⁷⁰ There was a decrease in biomarkers of UV‐induced DNA damage and inflammation, and an increase in biomarkers associated with apoptosis (Figure 3). ⁷⁰

FIGURE 3.

Changes in UV‐irradiated human skin altered by oral administration of grape constituents.

In a subsequent study of 29 healthy volunteers who were given the equivalent of three servings of table grapes for 2 weeks, nine experienced significantly greater resistance to UV than those who did not. ⁷¹ In microbiome and metabolome studies, individuals who developed UV resistance with grape consumption had significant changes in their gut microbiome, which correlated with the cutaneous photoprotective efficacy of orally administered grapes. Although the data support the beneficial effect of orally administered grape constituents on photodamage to the skin, further randomized placebo‐controlled trials are needed to determine their efficacy in preventing photoaging and KCs in humans.

CONCLUSION

KCs continue to increase in incidence, with an estimated 5.4 million cases treated annually, placing them higher in incidence than cancers of all other organs combined. ²⁷ Diagnoses of KCs also have been appearing more frequently and in younger age groups. ²⁷ Chronic UV exposure is the main environmental factor causing KCs. There have been multiple efforts toward improving sunscreen knowledge and reducing sun exposure. However, sunscreens are not entirely effective in the prevention of UV‐induced photodamage, and the cost of treating KCs and their precursors represents a significant financial burden on healthcare systems. Therefore, an agent that can prevent, slow, or reverse the UV‐induced photodamage and photocarcinogenesis is an appropriate area for future research.

The use of grape constituents in the chemoprevention of KCs shows promise in preventing this public health concern. Grape constituents are ideal in their role as chemopreventive agents due to their tolerability, low toxicity, low cost, and availability as dietary supplements. Clinical trials and research should further explore different agents to find the safest and most effective compound for the chemoprevention of KCs.

FUNDING INFORMATION

This research did not receive any specific grant from funding agencies in the public, commercial, or not‐for‐profit sectors.

THEORY AND CALCULATION

This is a review and therefore the large majority of the manuscript is theory and calculation.

Kwon Y, Shafi R, Oak A, Athar M, Slominski A, Elmets CA. Grape constituents for protection against photodamage to skin. Photochem Photobiol. 2025;101:1392‐1401. doi: 10.1111/php.14110

DATA AVAILABILITY STATEMENT

The manuscript is a review and therefore there is no original data.