| Summary: | <p>Abstract</p> <p>Background</p> <p>The early stages of Alzheimer's disease (AD) are closely associated with the production of the Aβ<sub>1–42 </sub>peptide, loss of synapses and gradual cognitive decline. Since some epidemiological studies showed that EGb 761, an extract from the leaves of the <it>Ginkgo biloba </it>tree, had a beneficial effect on mild forms of AD, the effects of some of the major components of the EGb 761 extract (ginkgolides A and B, myricetin and quercetin) on synapse damage in response to Aβ<sub>1–42 </sub>were examined.</p> <p>Results</p> <p>The addition of Aβ<sub>1–42 </sub>to cortical or hippocampal neurons reduced the amounts of cell associated synaptophysin, a pre-synaptic membrane protein that is essential for neurotransmission, indicating synapse damage. The effects of Aβ<sub>1–42 </sub>on synapses were apparent at concentrations approximately 100 fold less than that required to kill neurons; the synaptophysin content of neuronal cultures was reduced by 50% by 50 nM Aβ<sub>1–42</sub>. Pre-treatment of cortical or hippocampal neuronal cultures with ginkgolides A or B, but not with myrecitin or quercetin, protected against Aβ<sub>1–42</sub>-induced loss of synaptophysin. This protective effect was achieved with nanomolar concentrations of ginkgolides. Previous studies indicated that the ginkgolides are platelet-activating factor (PAF) receptor antagonists and here we show that Aβ<sub>1–42</sub>-induced loss of synaptophysin from neuronal cultures was also reduced by pre-treatment with other PAF antagonists (Hexa-PAF and CV6209). PAF, but not lyso-PAF, mimicked the effects Aβ<sub>1–42 </sub>and caused a dose-dependent reduction in the synaptophysin content of neurons. This effect of PAF was greatly reduced by pre-treatment with ginkgolide B. In contrast, ginkgolide B did not affect the loss of synaptophysin in neurons incubated with prostaglandin E<sub>2</sub>.</p> <p>Conclusion</p> <p>Pre-treatment with ginkgolides A or B protects neurons against Aβ<sub>1–42</sub>-induced synapse damage. These ginkgolides also reduced the effects of PAF, but not those of prostaglandin E<sub>2</sub>, on the synaptophysin content of neuronal cultures, results consistent with prior reports that ginkgolides act as PAF receptor antagonists. Such observations suggest that the ginkgolides are active components of <it>Ginkgo biloba </it>preparations and may protect against the synapse damage and the cognitive loss seen during the early stages of AD.</p>
|
|---|
