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 biological activities 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/prooxidant 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, discrepancies 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.

Antimicrobial activity and toxicity of Syzygium australe and Syzygium leuhmannii fruit extracts

“…[13] Antioxidants have been associated with the prevention of cancer, cardiovascular disease and neurological degenerative disorders. [14][15][16] They are also linked with antidiabetic bioactivities and have been associated with the reduction of obesity. Antioxidants can directly scavenge free radicals, protecting cells against oxidative stress related damage to proteins, lipids and nucleic acids.…”

The safe usage of herbal medicines: counterindications, cross-reactivity and toxicity

“…[111] Unripe bitter melon (Momordica charantia) 112 and Gymnema sylvestre 113 were used in traditional Asian medicinal systems as remedies for diabetes. Similarly, several Aloe species including Aloe vera 12,73 and fenugreek (Trigonella foenum-graecum) 111 were used in the Middle East as anti-diabetes drugs. In Latin American regions, the pads and fruit of prickly pears (Opuntia spp.)…”

“…Other medications contain phytochemicals which may not cause tissue damage in infants, yet still make them ill. Aloe vera for example contains anthraquinones which may induce colic and diarrhoea in infants. 12,111,143,144 Black snakeroot (Fucus vesiculosus), 136 male fern (Dryopteris filix-mas, 111 elecampane (Inula helenium), 111,137 rhubarb (Rheum officinale) 111 and senna (Senna alexandrina) 52 should all be avoided by breastfeeding women for similar reasons. Medications with immunosuppressive effects (e.g.…”

“…Aloe emodin, barbaloin) without fully detailing the levels of other important components. As the levels and ratios of various components in Aloe vera juices have profound effects on their bioactivity, 12 it is important that the levels of these components are known.…”

Acai, cacao and maca extracts: Anticancer activity and growth inhibition of microbial triggers of selected autoimmune inflammatory diseases

“…Some antioxidant compounds may function as either an antioxidant or an oxidant, with their action being dependent upon their concentration. 9 For example, the Aloe vera (L.) Brum.f. anthraquinone aloe emodin exerts antioxidant behaviour at lower concentrations, yet acts as a pro-oxidant at high concentrations.…”