Often, the complex nature of extract products and the possible synergistic effects of their components make detailed analysis difficult. This is certainly the case for one of the more high-profile herbal varieties, Ginkgo biloba extract (GBE), which is commonly taken for its reported neurological effects, such as memory enhancement or to combat Alzheimer’s disease.

Recently, an international group of researchers applied high-density oligonucleotide microarrays to probe specific biochemical events that result from the regular use of GBE (Proc. Natl. Acad. Sci. U.S.A. 2001, 98, 6577–6580).

The scientists put a group of mice on a diet supplemented with the herb, alongside a control group with no supplement, for four weeks. Then they dissected the cortex and hippocampus of each mouse and extracted and labeled the total RNA for subsequent array hybridization.

The study used chips containing about 12,000 mouse full-length genes and expressed sequence tags, which allowed for genomewide determination of GBE-induced expression changes. Expression level differences of threefold or more between the control and experimental groups were considered to be significant effects. Ten distinct genes, one from the hippocampus and nine from the cortex, showed increased expression levels at or above this threshold.

Upregulation was highest in the one hippocampus gene, which showed a 16-fold increase. This gene encodes the transthyretin protein, which has a role in regulating neuronal proliferation and outgrowth, as well as in sequestering the Alzheimer’s-relevant amyloid- protein. Several of the GBE-enhanced cortex proteins have been previously studied for their neuronal activity, such as tyrosine/threonine phosphatase 1 (7-fold increase), which may restrict neurofibrillary tangle lesions in Alzheimer’s formation, and microtubule-associated (3–4-fold increase), which could lead to neuropathological accumulations. Other upregulated proteins, such as purinergic-region binding protein , have not yet been investigated in detail.

The researchers believe that further investigation of these genes will lead to more in-depth knowledge of the mechanism of action of GBE and its overall effects on brain function. Moreover, the study has demonstrated the utility of the microarray experimental approach for exploration of the activities of complex extracts, which could raise confidence in the effectiveness and safety of herbal supplements on the market.