Biological assays commonly just referred to as bioassays are biological standardisation measures used to determine biological activity, purity and concentrations of constituents in a sample. In plant biotechnology, especially under ethno-pharmacology, the activity of plants on particular biological organisms or processes, have to be determined. When studying medicinal plants for instance, it is important to determine whether they do have biological activity against pathogens or irritants that the plant extracts are traditionally used for. In most African cultures, or even different cultures across the world, decoctions were used from plants known by reputable herbalists or traditional doctors to treat different ailments. Just like in modern medicine where different drugs are used for treatment of different ailments, the same is true for traditional healing as different plants and their extracts or paste were used to treat different health conditions.
A good example of such medicinal plants is plants of the genus Salvia. Salvia plants are known the world over for their culinary and medicinal properties. Traditional uses of this plant that appears across cultures include boiling the plants as tea and using that to treat respiratory ailments, gynecological problems, stomach ache, and the paste which is used and applied to infected areas to treat wounds, shave rash and related conditions. Scientists had to study extracts of these plants to see what is in them that makes them to be able to treat all these conditions, and most successfully at that.
The constituents of some of the Salvia species have been identified and quantified and their biological activities have been determined. In South Africa most research on these plants is done by Kamatou and his colleagues. Different established biological assays are used to further characterise extracts of these plants. Biological activities tested include anti-oxidant, anti-inflammants, anti-microbial, anti-malarial and anti-cancer activities. These same assays can be used in studies of any other plant's extracts. The different bioassays in regard to the above biological activities are discussed. Anti-oxidant and anti-inflammatory assays will be discussed.
Anti-oxidant activity: DPPH (2, 2-diphenyl-1-picrylhadrazyl) assay is used. Oxidation reactions produce free radicals which can lead to reactions in the cells that are detrimental to cells thus killing them. In human health free radicals are associated with health problems such as cancer, ageing and heart diseases. Thus to stop activity of these free radicals antioxidants thus inhibits oxidation by scavenging for the free radicals. Radical scavenging properties of extracts are tested against DPPH which is a free radical, thus anything that can inhibit its activity, has antioxidant properties. A solution of DPPH, where it is dissolved in HPLC grade methanol, is purple, but when it is neutralised by free radical scavenging molecules in gets neutralised to a pale yellow colour. The number of free radicals of DPPH scavenged can be determined by spectrophotometric readings at wavelengths of 517nm as the absorptivity of DPPH has been shown to reduce as the free electron reacts with antioxidants. Thus a measure of activity of antioxidant activity of plant extracts at different concentrations can be determined.
Anti-inflammatory activity: 5-lipozygenase (5-LOX) assays and cyclooxygenase (COX) assays are used. 5-LOX is involved in the production of leukotrienes which are fatty molecules that are involved in inflammation. Thus anything that can inhibit the activity of 5-LOX results in these inflammants not being produced. COX is an enzyme that catalyses the production of prostanoids which include prostaglandins which are mediates inflammatory reactions. Thus inhibiting the activity of COX will result in this inflammants not being produced. Therefore if plant extracts can inhibit the activity of 5-LOX and COX it has anti-inflammatory bioactivity. Different concentrations of plant extracts are tested and the concentrations needed to inhibit 50% of the enzyme are determined as a measure of anti-inflammatory activity.
These two bio-activities have been measured in various Salvia species and indeed plant extracts from the different Salvia species did show or display anti-oxidant and anti-inflammatory activities. Thus this shows that as much as traditional healers do not know why and how the plant extract can treat the different ailments or conditions, science has proven that they are indeed justified to use these plant extracts to treat those conditions.
Ethno-pharmacology and biotechnology are important fields of study that works together very well. This is because in determining the bioactivity of plant constituents by ethno-pharmacologists, bio-technologists under genetic engineering can then manipulate the genetic makeup of the plants in order to increase the production of plant constituents that are involved.
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