Effects of repeated treatments with an extract of Ginkgo biloba (EGb 761), bilobalide and ginkgolide B on the electrical activity of pancreatic beta cells of normal or alloxan-diabetic mice: an ex vivo study with intracellular microelectrodes

Beneficial effects of Ginkgo biloba extract on insulin signaling cascade, dyslipidemia, and body adiposity of diet-induced obese rats

Ginkgo biloba extract (GbE) has been indicated as an efficient medicine for the treatment of diabetes mellitus type 2. It remains unclear if its effects are due to an improvement of the insulin signaling cascade, especially in obese subjects. The aim of the present study was to evaluate the effect of GbE on insulin tolerance, food intake, body adiposity, lipid profile, fasting insulin, and muscle levels of insulin receptor substrate 1 (IRS-1), protein tyrosine phosphatase 1B (PTP-1B), and protein kinase B (Akt), as well as Akt phosphorylation, in diet-induced obese rats. Rats were fed with a high-fat diet (HFD) or a normal fat diet (NFD) for 8 weeks. After that, the HFD group was divided into two groups: rats gavaged with a saline vehicle (HFD+V), and rats gavaged with 500 mg/kg of GbE diluted in the saline vehicle (HFD+Gb). NFD rats were gavaged with the saline vehicle only. At the end of the treatment, the rats were anesthetized, insulin was injected into the portal vein, and after 90s, the gastrocnemius muscle was removed. The quantification of IRS-1, Akt, and Akt phosphorylation was performed using Western blotting. Serum levels of fasting insulin and glucose, triacylglycerols and total cholesterol, and LDL and HDL fractions were measured. An insulin tolerance test was also performed. Ingestion of a hyperlipidic diet promoted loss of insulin sensitivity and also resulted in a significant increase in body adiposity, plasma triacylglycerol, and glucose levels. In addition, GbE treatment significantly reduced food intake and body adiposity while it protected against hyperglycemia and dyslipidemia in diet-induced obesity rats. It also enhanced insulin sensitivity in comparison to HFD+V rats, while it restored insulin-induced Akt phosphorylation, increased IRS-1, and reduced PTP-1B levels in gastrocnemius muscle. The present findings suggest that G. biloba might be efficient in preventing and treating obesity-induced insulin signaling impairment.

Inhibition of cPLA2 activation by Ginkgo biloba extract protects spinal cord neurons from glutamate excitotoxicity and oxidative stress-induced cell death

Ginkgo biloba extract (EGb761) has been shown to be neuroprotective; however, the mechanism by which EGb761 mediates neuroprotection remains unclear. We hypothesized that the neuroprotective effect of EGb761 is mediated by inhibition of cytosolic phospholipase A(2) (cPLA(2)), an enzyme that is known to play a key role in mediating secondary pathogenesis after acute spinal cord injury (SCI). To determine whether EGb761 neuroprotection involves the cPLA(2) pathway, we first investigated the effect of glutamate and hydrogen peroxide on cPLA(2) activation. Results showed that both insults induced an increase in the expression of phosphorylated cPLA(2) (p-cPLA(2)), a marker of cPLA(2) activation, and neuronal death in vitro. Such effects were significantly reversed by EGb761 administration. Additionally, EGb761 significantly decreased prostaglandin E(2) (PGE(2)) release, a downstream metabolite of cPLA(2). Moreover, inhibition of cPLA(2) activity with arachidonyl trifluromethyl ketone improved neuroprotection against glutamate and hydrogen peroxide-induced neuronal death, and reversed Bcl-2/Bax ratio; notably, EGb761 produced greater effects than arachidonyl trifluromethyl ketone. Finally, we showed that the extracellular signal-regulated kinase 1/2 signaling pathway is involved in EGb761's modulation of cPLA(2) phosphorylation. These results collectively suggest that the protective effect of EGb761 is mediated, at least in part, through inhibition of cPLA(2) activation, and that the extracellular signal-regulated kinase 1/2 signaling pathway may play an important role in mediating the EGb761's effect.

Ginkgo biloba leave extract: biological, medicinal, and toxicological effects

Ginkgo biloba leave extract is among the most widely sold herbal dietary supplements in the United States. Its purported biological effects include: scavenging free radical; lowering oxidative stress; reducing neural damages, reducing platelets aggregation; anti-inflammation; anti-tumor activities; and anti-aging. Clinically, it has been prescribed to treat CNS disorders such as Alzheimer's disease and cognitive deficits. It exerts allergy and changes in bleeding time. While its mutagenicity or carcinogenic activity has not been reported, its components, quercetin, kaempferol and rutin have been shown to be genotoxic. There are no standards or guidelines regulating the constituent components of Ginkgo biloba leave extract nor are exposure limits imposed. Safety evaluation of Ginkgo biloba leave extract is being conducted by the U.S. National Toxicology Program.

Potential role for Ginkgo biloba extract in the treatment of glaucoma

Glaucoma is becoming recognized as a condition for which not only elevated intraocular pressure, but also non-pressure-dependent risk factors are responsible. New avenues of treatment into which investigations are being initiated include agents which could possibly improve blood flow to the eye and neuroprotective drugs. Only calcium channel blockers are presently available for such treatment in glaucoma, and these have not been widely adopted, in contrast to clinical trials involving a number of neuroprotectants in other neurologic disorders. Ginkgo biloba extract is freely available and has several biological actions which combine to make it a potentially important agent in the treatment of glaucoma: improvement of central and peripheral blood flow, reduction of vasospasm, reduction of serum viscosity, antioxidant activity, platelet activating factor inhibitory activity, inhibition of apoptosis, and inhibition of excitotoxicity. The effect of Ginkgo biloba extract as a potential antiglaucoma therapy deserves intensive scrutiny.

The effects of an extract of Ginkgo biloba, EGb 761, on cognitive behavior and longevity in the rat

Extracts of the leaves of the Ginkgo biloba tree are widely used throughout the world for their purportedly beneficial effects on brain function. In the present investigation, a standardized extract, EGb 761, was self-administered orally by male Fischer 344 rats that were then tested in an eight-arm radial maze. The tasks employed were a) continuous learning and b) delayed nonmatching to position. Chronic postsession administration of EGb 761 at a dose of 50 mg/kg had no effect on continuous learning but the same dose given presession resulted in a trend toward fewer sessions to reach criterion performance as well as fewer errors. In addition, it was observed that rats chronically treated with EGb 761 lived significantly longer than vehicle-treated subjects. In a delayed nonmatching to position task using a 30-min delay in 20-month-old rats. EGb 761 administered presession produced a dose-related decrease in total, retroactive, and proactive errors; a repeated-measures design was used, with subjects serving as their own controls. Following the dose-response determination, the group, now 26 months of age, was divided in two with half receiving EGb 761 at a dose of 200 mg/kg presession and the other half vehicle (sweetened condensed milk). A statistically significant positive effect of treatment with EGb-761 was observed. The present data are consistent with the beneficial effects on cognitive performance which have been widely reported in human subjects. In addition, the data suggest that the methods employed, i.e., continuous learning and delayed nonmatching to position tasks in aged rats, are capable of detecting drugs of possible value in the treatment of human cognitive impairment. Finally, the present results encourage a search for the pharmacologically active principles of EGb 761 and for their mechanisms of action.