Assessment of Aloe vera (L.) genotoxic potential on Escherichia coli and plasmid DNA
Introduction
The use of phytotherapeutic products by the world population has greatly increased in the last decades (Briskin, 2000, Ang-Lee et al., 2001, Chan, 2003). As they used to be generally classified as “natural”, these products are considered to be harmless. However, several studies show that many of those products present undesirable action when ingested or applied on the skin (Joshi and Kaul, 2001, Chan, 2003, Gilbert and Alves, 2003).
The Aloe vera (L.) Burm.f., popularly known in Brazil as babosa, is a tropical or sub-tropical plant from North Africa, with turgid lace-shaped green leaves with jagged edges and sharp points (Okiar et al., 2001). The plant is a member of the lily family (Liliaceae), not the cactus family, as many would believe from the rosette-like arrangement of the long, spiked leaves on the central stem (Grindlay and Reynolds, 1986). Historically, Muslims considered it as a sacred plant, which could keep malignant influences away from home (Zeilmann et al., 2003). There are over 300 species of Aloe known, but Aloe vera L. is recognized as the “true Aloe vera” for its widespread use and purported healing powers.
It has been demonstrated that a large part of the pharmacological activity of this plant is due to polysaccharides, which makes up the majority of the mucilaginous Aloe vera gel (t’Hart et al., 1989). Furthermore, the refined polysaccharide has been shown to act as an immunostimulant, displaying adjuvant activity on specific antibody production (t’Hart et al., 1989) and enhancing the release of interleukin-1, interleukin-6, tumor necrosis factor-a and interferon-c (Peng et al., 1991). Release of these cytokines stimulates an increase in the replication of fibroblasts in tissue culture and proliferation of fibroblasts is known to be responsible for healing burns, ulcers and other wounds of the skin and gastrointestinal lining (Kahlon et al., 1991, Yates et al., 1992).
People use the Aloe vera orally or topically and the latter is believed to promote cellular regeneration (Yagi et al., 2002), healing of burns (Somboonwong et al., 2000), act in dermatitis, skin irritation after shaving and after exposure to the sun, flabbiness, scalp irritations, fungi infections and hair loss (Choi et al., 2001). By acting in this way, it is frequently added to soap, toilet paper, shampoo, conditioning and moisturizing creams (Reynolds and Dweck, 1999). Besides, the aloe extract is indicated for patients submitted to radiotherapy treatment to minimize the burn and skin lesions induced by this kind of procedure (Olsen et al., 2001). In spite of its wide pharmaceutical use, there are few data on aloe toxicity.
Sunlight has many components, including the near ultraviolet (near-UV) light, which is in the range between 290 and 400 nm, reaching the earth's surface. This radiation can be divided in UVA (320–400 nm) and UVB (290–320 nm). In this study, UVA (365 nm) was used, as the most abundant solar UV component that reaches the surface of our planet (Kuluncsics et al., 1999). Near-UV can produce lesions in different cell structures, for instance, enzymes, DNA and cellular membranes, with the participation of endogen sensibilizators (Peak, 1970). In Escherichia coli, the generation of this kind of damage only occurs in aerobic conditions, contributing to the induction of SOS response (Favre et al., 1986), conferring to it a mutagenic potentiality (Caldeira-de-Araújo and Favre, 1986). In sub-letal doses, below 200 kJ/m2, the UVA is capable to induce, in Escherichia coli, a temporary blockage in growth and cellular division (Favre et al., 1985).
Since Aloe vera is a tropical plant, it receives much UVA radiation from sunlight. Also, its extract has a wide spread topical use, leading people to expose themselves to sunlight, with residual extract on the body.
Thus, the aim of this work was to evaluate the toxicity of Aloe vera extract, either alone or associated with UVA radiation.
Section snippets
Preparation of Aloe vera extract
Aloe vera (babosa) leaves were collected and processed from a single garden plant, to obtain a fresh extract for each experiment during this work. The extract was prepared by using 3 g from the vegetable leaf pulp, mixing it with 5 mL of 0.9% NaCl solution in order to carry out the bacterial inactivation assays or solved in the same volume of Milli-Q water (Millipore Corp., Bedford, MA, USA), to proceed to DNA electrophoresis and bacterial transformation experiments. The solution was then
Results and discussion
The ability of Aloe vera to decrease Escherichia coli survival was first evaluated and, as it can be seen in Fig. 1, panels A–D, the Aloe vera extract was not capable of inducing Escherichia coli inactivation, in a significant way, in all strains tested, neither alone nor associated with a sub-lethal dose of UVA. These results pointed either to a Aloe vera absence of cytotoxic activity or to a lack of its entry into the cells.
In order to better understand this point, transformation efficiency
Conclusion
From the experiments, we can conclude that Aloe vera has no cytotoxicity, whether associated or not with UVA, in the conditions tested, because the values encountered in all the mutants were similar and near the control level. However, it has a genotoxic action, mainly at high concentrations, as shown in the results of transformation and electrophoresis. The transformation assays also shows that the cellular mechanisms most effective against lesions induced by Aloe vera seem to be base excision
Acknowledgements
This work was supported by CNPq, FAPERJ and UERJ
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