The popular recognition of the Aloe barbadensis Miller (Aloe vera) plant as a therapeutic dermatologic agent has led to the widespread incorporation of Aloe vera leaf extracts in skincare products. Studies have suggested that Aloe vera in skincare preparations may enhance the induction of skin cancer by ultraviolet radiation. A 1-year study was conducted in mice to determine whether the topical application of creams containing Aloe vera plant extracts (aloe gel, whole leaf, or decolorized whole leaf) or creams containing aloe-emodin would enhance the photocarcinogenicity of simulated solar light (SSL).
One-year study
Groups of 36 male and 36 female Crl:SKH-1 (hr -/hr -) hairless mice received topical applications of control cream or creams containing 3% or 6% (w/w) aloe gel, whole leaf, or decolorized whole leaf or 7.46 or 74.6 µg/g aloe-emodin to the dorsal skin region each weekday morning. The mice were irradiated with SSL emitted from filtered 6 kW xenon arc lamps each weekday afternoon. The topical applications of creams and irradiance exposures were conducted 5 days per week for a period of 40 weeks. A 12-week recovery/observation period followed the 40-week treatment/exposure period. Additional groups of 36 male and 36 female mice received no cream and were exposed to 0.00, 6.85, 13.70, or 20.55 mJ⋅CIE/cm2 SSL per day.
Mice that received no cream treatment and were exposed to increasing levels of SSL showed significant SSL exposure-dependent decreases in survival and significant increases in the in-life observations of skin lesion onset, incidence, and multiplicity, and significant SSL exposure-dependent increases in the incidences and multiplicities of histopathology-determined squamous cell nonneoplastic skin lesions (squamous hyperplasia and focal atypical hyperplasia) and squamous cell neoplasms (papilloma, carcinoma in situ, and/or carcinoma). Squamous cell neoplasms were not detected in mice that received no SSL exposure.
The topical treatment with the control cream of mice that were exposed to SSL did not impart a measurable effect when compared with comparable measurements in mice that received no cream treatment and were exposed to the same level of SSL, suggesting that the control cream used in these studies did not alter the efficiency of the SSL delivered to mice or the tolerability of mice to SSL.
The application of aloe gel creams to mice had no effect on body weights, survival, or the in-life observations of skin lesion onset, incidence, or multiplicity. The administration of aloe gel creams to male mice had no effect on the incidences or multiplicities of histopathology-determined squamous cell nonneoplastic skin lesions or neoplasms. Female mice treated with aloe gel creams (3% and 6%) had significantly increased multiplicities of squamous cell neoplasms.
There were no treatment-related effects on body weights, survival, or the in-life observations of skin lesion onset, incidence, or multiplicity in mice treated with the whole leaf creams. In male mice exposed to SSL and treated with the 6% whole leaf cream, a significant increase was observed in the multiplicity of squamous cell neoplasms. Female mice exposed to SSL and treated with the 3% whole leaf creams had significantly decreased multiplicity of squamous cell nonneoplastic lesions and significantly increased multiplicity of squamous cell neoplasms. Female mice exposed to SSL and treated with the 6% whole leaf cream had significantly decreased multiplicity of squamous cell nonneoplastic lesions.
The application of decolorized whole leaf creams to mice had no effect on body weights, survival, or the in-life observations of skin lesion onset, incidence, or multiplicity. Male mice administered the 3% decolorized whole leaf cream had significantly increased multiplicity of squamous cell neoplasms. Female mice administered the 3% decolorized whole leaf cream had significantly decreased multiplicity of squamous cell nonneoplastic skin lesions and significantly increased multiplicity of squamous cell neoplasms. In female mice that received the 6% decolorized whole leaf cream, there was a significant increase in the multiplicity of squamous cell neoplasms.
As with the Aloe vera plant extracts, the application of aloe-emodin creams to mice had no measurable effect on body weights, survival, or the in-life observations of skin lesion onset, incidence, or multiplicity. The administration of aloe-emodin creams to male mice had no effect on the incidence or multiplicity of histopathology-determined nonneoplastic skin lesions or squamous cell neoplasms. Female mice treated with the 74.6 µg/g aloe-emodin cream had significantly decreased multiplicity of histopathology-determined squamous cell nonneoplastic skin lesions and significantly increased multiplicity of squamous cell neoplasms.
Conclusions
These experiments investigated the potential of topical application of creams containing extracts of Aloe barbadensis Miller plant (aloe gel, whole leaf, or decolorized whole leaf) or aloe-emodin to alter the photocarcinogenic activity of filtered xenon arc simulated solar light (SSL) in male and female SKH-1 hairless mice. Data on skin lesions were collected both on digital images during the in-life phase and by histopathologic evaluation at necropsy. No effects of creams upon SSL-induced skin lesions were identified from data collected during the in-life phase.
Aloe gel or aloe-emodin
Under the conditions of these studies, there was a weak enhancing effect of aloe gel or aloe-emodin on the photocarcinogenic activity of SSL in female but not in male SKH-1 mice based on an increase in the multiplicity of histopathologically-determined squamous cell neoplasms.
Aloe whole leaf or decolorized whole leaf
Under the conditions of these studies, there was a weak enhancing effect of aloe whole leaf or decolorized whole leaf on the photocarcinogenic activity of SSL in both male and female SKH-1 mice based on an increase in the multiplicity of histopathologically-determined squamous cell neoplasms.