Problems of Reproducibility and Efficacy of Bioassays Using Crude Extracts, with reference to Aloe vera

Abstract

Aloe vera has a long history of medicinal usage and its therapeutic properties have been well documented in a variety of bioassays. However, isolated Aloe vera leaf components generally do not display the same bioactivities, or have lower efficacies than crude juice/extracts. It is likely that several components work in a synergistic manner in the crude mixture, resulting in increased bioactivities. Furthermore, different laboratories often report varying bioactivities using the same extraction procedure on plant material from the same species. Individual Aloe vera cultivars may have widely varying levels of the bioactive phytochemicals. Due to the structure and chemical nature of many of the Aloe vera phytochemicals, it is likely that many of its reported medicinal properties are due to anti-oxidant or pro-oxidant effects. The anti-oxidant/pro-oxidant activities of many of Aloe vera's phytochemicals is dependent not only on their individual levels, but also on the ratios of various components, and on their individual redox states. Therefore, discrepencies between bioactivity studies are likely when using different crude mixtures. The potential differences between these crude mixtures need to be taken into account when analysing the reproducibility and efficacy of bioassays of crude extracts.