Extracts from a number of Aloe species are widely regarded as having therapeutic dermatologic properties useful in the treatment of sunburn and mild thermal injury (Heggers etal., 1993). These properties seem to be separate from aloe's laxative activity, anti-gastrointestinal ulcer activity and from efficacy in the treatment of severe thermal burns and wound-healing activity (Pelley and Heggers, unpublished observations). The popular recognition of aloe as a dermatologic has led to the widespread incorporation of aloe extracts in healthcare and cosmetic products.
Development of Aloe Research Foundation (ARF) standard samples
Scientific evidence for aloe's efficacy is limited and studies using commercial 'Aloe vera' have been extremely difficult to reproduce. Probably the best example of this is in the area of the treatment of radiation dermatitis. During the 1930s there were reports of treating radiation-induced skin lesions with crude extracts of Aloe vera (reviewed in Grindlay and Reynolds, 1986). Subsequent publications were divided in their findings with the more rigorous clinical investigations failing to show a beneficial effect (Aleshkina and Rostotskii, 1957; Ashley etal, 1957; Rovatti and Brennan, 1959; Rodriguez-Bigas etal, 1988; Williams etal, 1996). One factor in this lack of repro-ducibility is undoubtedly the fraud, adulteration of feed stocks, and misrepresentation that is currently widespread in the 'Aloe vera' industry (Pelley etal., 1998). Active ingredients are also commonly destroyed by routine industrial processing (Waller etal, 1994; Pelley etal, 1998, and most recently Waller etal. in this volume). Given the lack of knowledge of proper processing on the part of academic investigators, the lack of scientific expertise on the part of commercial entrepreneurs, and the difficulty of obtaining fresh, undegraded aloe gel, it is remarkable that any positive results were attained at all during this era.
We began our studies by developing standardized Aloe barbadensis gel materials (Aloe Research Foundation Standard Samples) with uniform chemical and biological properties (Pelley etal, 1993; Waller etal, 1994). The ARF Process 'A' materials used in most experiments with unfractionated aloe represent depulped aloe gel fillets produced under conditions of rigorous sanitation not usual to the industry and lyophilized extremely rapidly, within hours of harvest. ARF materials (Processes B, C, D and E) were also produced approximating to the various processes, pasteurization, filtration, absorption with activated charcoal, treatment with cellulase, and concentration by rising/ falling thin film evaporation, employed in the industry. The ARF Process A material corresponds to no commercial product in current existence and its production is not economically feasible. These ARF materials were produced at several commercial sites by Todd A. Waller and R.P. Pelley, chemically characterized by RPP and distributed to three groups of investigators who characterized the biological activities therein. The first was the late Robert H. Davis at the University of Pennsylvania's College of Podiatric Medicine who was, for many years, one of the few investigators publishing controlled experiments on biological properties of A. barbadensis in peer reviewed journals (Davis etal, 1986; Davis etal, 1987). Davis examined the anti-inflammatory activities of ARF materials in the phorbal ester-induced foot pad swelling assay. A second investigator was at the University of Wisconsin in Madison. Dr Sheffield's laboratory was working on mammary gland ductal epithelium and its response to physical injury and injury by activated phagocytes. Lastly, the laboratory of F.M. Strickland at the University of Texas, M.D. Anderson Cancer clinic, examined the effect of UVB radiation on the skin immune system of mice. The ability to concordantly assay materials of known provenance and chemically defined composition with highly standardized assays has led us to realize that: (i) multiple biologically active substances are present in crude extracts of A. barbadensis; (ii) these materials are differentially labile: and, (iii) the biologically active molecules are variably present in authentic commercial materials. We further realized that the biologically active molecules were not being measured by existing methods of commercial chemical detection. For a more complete discussion of these concepts the reader is referred to the accompanying article (Waller etal., Chapter 8, this volume).
Effects of crude A. barbadensis gel on numbers and morphology of dendritic T cells and Langerhans cells in UV exposed mice
UVB irradiation decreases the number of immune cells in the skin (Toews etal, 1980; Lynch etal, 1981). In the epidermis, the outer most of the three layers of the skin, these immune cells are of two types (Table 12.3). One type is the Langerhans cells, a cell that processes antigen into a form in which it can trigger the immune response. The second type is the dendritic thymus-derived lymphocyte. The skin dentritic T cell recognizes processed antigen and regulates the immune response. Low doses of UV
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