Cytotoxicity
As a routine part of our anti-infective agent investigations, we have begun includ-
ing cytotoxicity studies to rule out false positive bioactivity results ensuing from a
general toxic effect of a plant extract [70]. The brine shrimp assay [85] involves in-
cubating test substances with freshly hatched brine shrimp larvae and examining
5.16 Cytotoxicity 115
the larvae for mortality after incubation. This assay has been frequently used to de-
tect in vitro cytotoxic or pharmacological effects [85], but does not detect activity in
those compounds requiring metabolic activation. We have found that few extracts
of plants known to be toxic to livestock animals displayed activity in the brine
shrimp assay [69]. Therefore it would appear that this cytotoxicity assay has limited
applicability in detecting toxic effects of plant extracts.
At present we are employing a cell-line cytotoxicity assay, where viable cell
growth after incubation with test compound is determined spectrophotometrically
using a tetrazolium-based colorimetric assay [86]. The LC50 values are calculated as
the concentration of test compound resulting in a 50% reduction of absorbance
compared to untreated cells. A number of different cell lines are suitable for use in
the assay.
Several other approaches have been taken in the assessment of the toxicity of
medicinal plants, including testing for genotoxic effects using in vitro bacterial and
mammalian cell assays such as the Ames test, micronucleus test, and comet assay
[3]. The genotoxicity of various South African medicinal plants has been reported
As a routine part of our anti-infective agent investigations, we have begun includ-
ing cytotoxicity studies to rule out false positive bioactivity results ensuing from a
general toxic effect of a plant extract [70]. The brine shrimp assay [85] involves in-
cubating test substances with freshly hatched brine shrimp larvae and examining
5.16 Cytotoxicity 115
the larvae for mortality after incubation. This assay has been frequently used to de-
tect in vitro cytotoxic or pharmacological effects [85], but does not detect activity in
those compounds requiring metabolic activation. We have found that few extracts
of plants known to be toxic to livestock animals displayed activity in the brine
shrimp assay [69]. Therefore it would appear that this cytotoxicity assay has limited
applicability in detecting toxic effects of plant extracts.
At present we are employing a cell-line cytotoxicity assay, where viable cell
growth after incubation with test compound is determined spectrophotometrically
using a tetrazolium-based colorimetric assay [86]. The LC50 values are calculated as
the concentration of test compound resulting in a 50% reduction of absorbance
compared to untreated cells. A number of different cell lines are suitable for use in
the assay.
Several other approaches have been taken in the assessment of the toxicity of
medicinal plants, including testing for genotoxic effects using in vitro bacterial and
mammalian cell assays such as the Ames test, micronucleus test, and comet assay
[3]. The genotoxicity of various South African medicinal plants has been reported
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