Basic types of bioassays for testing of phytochemicals

Question 1

In vitro assays with purified proteins

Answer 1

High throughput; no cell culture or animal facilities necessary.

Prone to irrelevant hits (compounds with low bioavailability unable to reach the respective target in intact cells or in vivo).

Question 2

In vitro cell-based target-oriented assays

Answer 2

Medium- to high-throughput; demonstrate efficacy of the hits at the cellular level; the affected molecular target is known, saving further work for mechanism of action studies.

Require access to cell culture facility; do not assure efficacy in vivo (e.g., identified hits may not reach their site of in vivo action, for example as a result of rapid catabolism in the liver).

Question 3

In vitro phenotypic cell-based assays

Answer 3

Medium- to high-throughput; demonstrate efficacy of the hits at the cellular level; useful for addressing the underlying mechanism of action, whereby such investigations might lead to the discovery of new molecular targets or pathways affecting the respective phenotype.

Require access to cell culture facility; great effort might be needed to identify the affected molecular target(s) underlying the changed phenotype; do not assure efficacy in vivo (e.g., identified hits may not reach their site of in vivo action, for example as a result of rapid catabolism in the liver).

Question 4

In situ / ex vivo assays with isolated tissues or organs

Answer 4

High pathophysiological relevance; some of the applications allow reduction of the number of used animals and offer higher throughput in comparison to rodent models.

Lower throughput in comparison to cell-based assays; ethical concerns related to the use of animals; short ex vivo half-life of the isolated tissues and organs.

Question 5

In vivo rodent models

Answer 5

High pathophysiological relevance demonstrating activity of hits on the level of a whole organism; reasonably high homology in genomes and similarity in physiology to humans; possibility to generate transgenic models.

Low throughput; ethical considerations; need access to an animal facility; require higher amount of the tested substances; possibility of existence of species-related differences (the observed effects might not be relevant for humans); require a great amount of follow-up work to identify the affected molecular targets.

Question 6

In vivo models in zebrafish and C. elegans

Answer 6

Medium- to high-throughput due to the possibility to implement automation; pathophysiological relevance due to pharmacological testing in a whole organism; possibility to generate transgenic models; lower price compared to rodent models; requires lower amount of the tested substances in comparison to rodent models.

Increased possibility of species-related differences (the observed effects might not be relevant for humans); ethical considerations; require a great amount of follow-up work to identify the affected molecular target.