The dietary supplement Ginkgo biloba (Gb), a mixture of flavonoids and terpenoids, is a pluripotent radical scavenger and inhibitor of protein kinases including protein kinase C (PKC). These properties suggest that Gb has the capacity to modulate enzymes that are regulated by reactive oxygen species and protein kinases. Enzymes that are susceptible to these regulatory mechanisms include angiotensin converting enzyme (ACE), nitric oxide synthase (NOS), and superoxide dismutase (SOD). These enzymes occur in endothelial cells and play key roles in orchestrating the profile of vasoactive factors that mediate endothelial function and dysfunction. Upregulated ACE has been implicated in the pathology of hypertension and heart failure, and may play a role in human cancers. Since PKC activates ACE, we hypothesize that Gb has the capacity to induce a beneficial downregulation of ACE. Nitric oxide generated from iNOS mediates bactericidal activity whereas that from eNOS mediates vasorelaxation. However, excessive iNOS activity is detrimental. Conditions that shift the total NOS equilibrium to favor eNOS over iNOS are likely to be beneficial. Such conditions have the potential to preserve eNOS mediated cellular communication without excessive nitric oxide spillover from iNOS during inflammation. Because PKC upregulates NOS and downregulates eNOS, we hypothesize that Gb can induce this favorable NOS equilibrium shift. SOD is a cellular defense against the damaging effects of superoxide and peroxynitrite (that forms when superoxide combines with nitric oxide). Gb has been shown to increase SOD levels in rat heart, liver, and kidney. We hypothesize that Gb will increase SOD in endothelial cells. This proposal seeks to examine the effect of Gb on ACE, NOS, and SOD in endothelial cells.
The specific aims are: 1. To determine if Ginkgo biloba regulates baseline expression of ACE, NOS, or SOD. 2. To determine if Ginkgo biloba regulates activated expression of ACE, NOS, or SOD. 3. To determine if the putative effects of Ginkgo biloba on ACE, NOS, or SOD occur at the level of transcription. 4. To determine the effect of Ginkgo biloba on endothelial cell protein kinases. We anticipate that these experiments will provide meaningful data with respect to how Gb modulates key endothelial cell enzymes and, as a consequence, to how Gb may play a beneficial role in protecting against the adverse effects of endothelial dysfunction. These data should establish core findings that can be extrapolated to encompass a more complete understanding of how Gb induces physiological effects deemed to be beneficial.
