[Pharmacologic actions of Ginkgo biloba extract and contents]

[Role of energy metabolism in retinal pigment epithelium]

The universal energy source adenosine triphosphate (ATP)is reduced by approximately 30 % in the retinal pigment epithelium (RPE) of elderly persons. Increased oxidative stress and decreased antioxidative capacity, such as glutathione in aging eyes cause impairment of energy-dependent RPE processes and lead to loss of visual function. We developed a cell culture model of aging RPE using atractyloside to inhibit mitochondrial ATP synthesis and tert-butyl hydroperoxide as oxidant. The ATP levels were reduced by 30 % and oxidative damaged proteins and DNA increased whereas antioxidative glutathione decreased. Autophagy as an internal cellular repair mechanism and phagocytosis of photoreceptors were impaired. Antioxidative and mitochondria-activating Ginkgo biloba extract EGb 761 increased the intracellular ATP level and antioxidative glutathione. This cell culture model seems to be suitable to investigate in vitro the effect of protective substances and their compounds on aging processes in RPE.

Proanthocyanidins from Ginkgo biloba leaf extract and their radical scavenging activity

CONTEXT

Ginkgo biloba L (Ginkgoaceae) is a traditional herbal medicinal plant for the treatment of mild to moderate cognitive disorders, tinnitus, and dementia. These uses may be correlated with the presence of radical scavenging compounds.

OBJECTIVE

The chemical composition and the 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity of the flavan-3-ols and proanthocyanidins from G. biloba were studied.

MATERIAL AND METHODS

The compounds have been isolated using column chromatography on Sephadex LH-20 and MCI gel and the structures were determined on the basis of 1D- and 2D-NMR (HSQC, HMBC) experiments of their peracetylated derivatives, MALDI-TOF-MS and by acid-catalyzed degradation with phloroglucinol. The DPPH radical scavenging activities of the compounds were investigated.

RESULTS

The new trimeric prodelphinidin, epigallocatechin-(4β→8)-epigallocatechin-(4β→8)-catechin (compound 7), has been isolated from the air-dried leaves of the title plant, in addition to catechin, epigallocatechin, gallocatechin, and three dimeric proanthocyanidins. The dimeric prodelphinidin epigallocatechin-(4β→8)-epigallocatechin (compound 6) showed the strongest DPPH radical scavenging activity, with IC(50) 1.7 μg/mL, 10 times more active than the positive control, BHT (IC(50) 17.3 µg/mL), followed by the new trimeric proanthocyanidin epigallocatechin-(4β→8)-epigallocatechin-(4β→8)-catechin with IC(50) 2.1 µg/mL. The crude extract exhibited high DPPH radical scavenging activity with IC(50) 15.5 µg/mL comparable with that of BHT.

DISCUSSION AND CONCLUSION

The results showed that all the isolated compounds from the tannin fraction exhibited potent free radical scavenging activities, which were higher than that of BHT, suggesting that the condensed tannins from G. biloba leaves strongly contribute to the overall antioxidant effects.

Does Ginkgo biloba Special Extract EGb??761?? Provide Additional Effects on Coagulation and Bleeding when Added to Acetylsalicylic Acid 500mg Daily?

OBJECTIVE

The aim of this study was to determine whether Ginkgo biloba special extract EGb 761 amplifies the known effects of acetylsalicylic acid (ASA) on platelet aggregation, bleeding time or other coagulation parameters in healthy subjects.

METHODS

In a double-blind, double-dummy procedure, 50 healthy male subjects (20-44 years) were randomly allocated in equal numbers to one of two possible treatment sequences, i.e. ASA followed by ASA + EGb 761 or ASA + EGb 761 followed by ASA. Each treatment lasted 7 days; the washout period between treatments was 3 weeks. Study medication was taken twice daily (ASA group: ASA 500 mg tablet + placebo-coated tablet in the morning and placebo tablet + placebo-coated tablet in the evening; ASA + EGb 761 group: ASA 500 mg tablet + EGb 761 120 mg-coated tablet in the morning and placebo tablet + EGb 761 120 mg-coated tablet in the evening), resulting in a daily dose of ASA 500 mg in the ASA group and 500 mg ASA + 240 mg EGb 761 in the ASA + EGb 761 group. Bleeding time, coagulation parameters and platelet activity in response to various agonists were determined. In addition, adverse events, laboratory variables and vital signs were measured. The primary variable bleeding time was assessed in confirmatory analysis, all other variables were evaluated descriptively. The coagulation variables were analysed by ANOVA under the crossover model.

RESULTS

ASA given alone clearly prolonged bleeding time. ASA and the combination of ASA + EGb 761 exerted quite similar effects on all coagulation parameters measured, including bleeding time (ASA alone: 4.1 min before therapy, 6.2 min after therapy; ASA + EGb 761: 4.2 min before therapy, 6.3 min after therapy; ratio of means: 1.01, 90% CI 0.86, 1.19) and agonist-induced platelet aggregation (collagen-induced platelet aggregation - ASA: 84.5% before therapy, 81.0% after therapy; ASA + EGb 761: 86.6% before therapy, 81.0% after therapy; ratio of means: 1.00, 90% CI 0.95, 1.05; adenosine diphosphate-induced platelet aggregation - ASA: 72.6% before therapy, 47.2% after therapy; ASA + EGb 761: 71.7% before therapy, 44.8% after therapy; ratio of means: 0.95, 90% CI 0.85, 1.06). Both treatments were well tolerated, and both the number and nature of adverse events in the two groups were similar.

CONCLUSIONS

Our findings suggest that co-administration of ASA and EGb 761 does not constitute a safety risk, including in an elderly patient population undergoing treatment with EGb 761.

Analysis of ginkgolides and bilobalide in Ginkgo biloba L. extract injections by high-performance liquid chromatography with evaporative light scattering detection

A RP-HPLC method with evaporative light scattering detection (ELSD) was developed for the determination of ginkgolides and bilobalide in Ginkgo biloba L. extract injections. The samples were extracted with ethyl acetate and the resulting extract was purified by aluminum oxide column. The resultant solution was determined by HPLC on a C(18) column with methanol-water (33:67, v/v) as eluent. The optimum ELSD parameters were set. The recovery of the method was between 98.3 and 102.1%. The method is suitable for routine quantitation of terpenes in Ginkgo biloba L. extract injections.

Properties and interaction of heterologously expressed glutamate decarboxylase isoenzymes GAD(65kDa) and GAD(67kDa) from human brain with ginkgotoxin and its 5'-phosphate

Two isoforms of glutamate decarboxylase (GAD(65kDa) and GAD(67kDa)) from human brain, which had previously been overexpressed in Escherichia coli as fusion proteins containing a glutathione-S-transferase domain, were purified by affinity chromatography on glutathione Sepharose 4B. Both isoforms were also expressed in Saccharomyces cerevisiae. After modification of a HPLC based assay, the enzymes were characterized with respect to their biochemical properties. Comparison of kinetic data, pH, and temperature optima as well as of the mode of interaction with pyridoxal phosphate as a cofactor revealed several significant differences between the two isoenzymes reflecting their somewhat different physiological and molecular features. Investigation of the influence of 4'-O-methylpyridoxine (ginkgotoxin) (1), a neurotoxin occurring in Ginkgo biloba L., on the different isoenzymes, indicates that the phosphorylated form of the toxin, 4'-O-methylpyridoxine-5'-phosphate (2), decreases GAD(65kDa) activity, although in unphysiologically high concentrations, whereas GAD(67kDa) activity seems to be hardly affected.

The effect of blood flow promoting drugs on cochlear blood flow, perilymphatic pO(2) and auditory function in the normal and noise-damaged hypoxic and ischemic guinea pig inner ear

The effect of blood flow promoting drugs, such as hydroxyethyl starch (HES) either of low or high molecular weight (HES 70, HES 200), pentoxifylline, ginkgo biloba, naftidrofuryl and betahistine, and various combinations of the drugs was studied in unexposed and noise-exposed (broad-band noise, bandwidth 1-12 kHz, 106 dB SPL, 30 min) guinea pigs. The results were compared without therapy and placebo (isotonic saline, NaCl). The cochlear blood flow (CoBF) and the partial pressure of oxygen in the perilymph (PL-pO(2)) were continuously and simultaneously recorded over a period of 210 min. In addition, cochlear microphonics (CMs), compound action potentials of the auditory nerve (CAPs) and auditory brain stem responses (ABRs) were registered. Noise-induced hearing loss (NIHL) paralleled a decrease of PL-pO(2). Both were found to occur before evidence of reduced CoBF. PL-pO(2) and CoBF declined progressively post-exposure, while CMs, CAPs and ABRs showed no further deterioration or signs of recovery up to 180 min after cessation of noise. Treatment started 60 min post-exposure, respectively after 90 min, without manipulation in unexposed animals, and was then studied for a further 120 min. In unexposed animals, CoBF increased significantly during infusion of HES 70, HES 200, pentoxifylline and betahistine. NaCl, ginkgo biloba and naftidrofuryl did not alter CoBF. PL-pO(2) decreased significantly during infusion of all administered drugs and combinations, except for NaCl. CMs, CAPs and ABRs remained constant, with the exception of increased ABRs after infusion of HES 70 and HES 200. In noise-exposed animals, a sustained therapeutic effect on cochlear ischemia was achieved only by HES 200 and pentoxifylline. HES 70, betahistine and ginkgo biloba compensated cochlear ischemia only during infusion; however, 30-60 min after termination of therapy, no significant difference of values for CoBF was observed compared to the untreated noise-exposed groups. NaCl and naftidrofuryl showed no effect on CoBF. None of the applied drugs had a sustained compensatory effect on cochlear hypoxia. CMs, CAPs and ABRs improved significantly after HES 70, HES 200 and betahistine, resulting in partial recovery of CMs, and partial (betahistine) or even full (HES 70 and HES 200) recovery of CAPs and ABRs. In contrast, NaCl, pentoxifylline, ginkgo biloba and naftidrofuryl had no therapeutic effect on NIHL.