At the time of tissue injury, the eicosanoid cascade is initiated by platelets and the primary mediator of progressive tissue loss is the potent vasoconstrictor, thromboxane
Table 10.3 Bactericidal Effects of 70% concentration of gel.
Gram negative organisms Gram positive organisms
Escherichia coli Stapylococcush. Aureus
Enterobacter sp. Streptococcus. Pyogenes
Citrobacter sp. S. agalactiae
Serratia marcescens S. sp., group D enterococci Klebsiella sp. Pseudomonas aeruginosa
A2 (Rosenburg and Gallin, 1999). Aloe acts as a thromboxane A2 synthetase inhibitor, preventing its production and maintaining a balanced equilibrium between PGE2 and PGF2a (Heggers and Robson, 1989). Aloe gel's anti-thromboxane properties have been shown to dilate arteries and enhance local blood flow (Davis etal, 1986; Robson etal, 1979, 1980).
Aloe gel can block vasoactive substances responsible for inflammation, can constrict small blood vessels, can block PMN (polymorphonuclear leucocyte) infiltration, can inhibit the production of oxygen free radicals and can dilate capillaries allowing for increased blood supply to damaged tissue (Davis etal., 1987; DelBeccaro etal., 1978; Heggers etal., 1985). These properties have given aloe the ability to reverse progressive tissue necrosis in partially damaged tissue (Zawacki, 1974). The plant hormones called gibberellins and auxins and the group of substances related to aspirin, known as the salicylates, seem to be the mediators of this response (Davis etal., 1991). In addition, there are organic compounds in aloe such as emolin, barbaloin and emodin that can be broken down by the Kolbe reaction into salicylates (t'Hart etal, 1988). The anti-thromboxane effect of these compounds may be due to enzymatic substrate competition. Aloe gel contains an abundance of fatty acids that allow for competitive inhibition of thromboxane production through stereochemical means, while also supplying the necessary nutrient precursors such as triglycerides and cholesterol for the initiation of the remaining arachidonic cascade (t'Hart etal, 1988). This allows for inhibition of inflammatory mediators while supplying the cell with the important constituents to maintain cellular integrity and normal tissue maturation (Brasher etal, 1969; Fujita etal, 1978).
Purified glucomannans have also shown impressive anti-inflammatory activity when separated from other aloe constituents (Davis etal., 1991). This concept has been supported by research in which the administration of mannans prevented arthritic flares in rats (Moreland, 1999). Also, mannose inhibits free radical production by neutrophils, limiting tissue damage (Rest etal, 1988). This is important since the neutrophil is the hallmark cell of inflammation and its presence is crucial to the inflammatory response (Kuby, 1997). Furthermore, polymannose can inhibit the initial step in the migration of neutrophils out of the blood stream and can aid in the clearance of certain pathogens through the presence of cell surface carbohydrate-receptor interactions (Lefkowitz etal., 1999).
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