Neuroprotective effects of NV-31, a bilobalide-derived compound: evidence for an antioxidative mechanism

The Use of Ginkgo Biloba L. as a Neuroprotective Agent in the Alzheimer's Disease

Alzheimer's disease, a neurodegenerative disease, is one of the most common causes of dementia if elderly people worldwide. Alzheimer's disease leads to the alienation of individuals and their exclusion from social and professional life. It is characterized mainly by the degradation of memory and disorientation, which occurs as a result of the loss of neuronal structure and function in different brain areas. In recent years, more and more attention has been paid to use in the treatment of natural bioactive compounds that will be effective in neurodegenerative diseases, including Alzheimer's disease. G. biloba L. and its most frequently used standardized extract (EGb 761), have been used for many years in supportive therapy and in the prevention of cognitive disorders. The paper presents an overview of reports on the pathogenesis of Alzheimer's disease, as well as a summary of the properties of G. biloba extract and its effects on the possible pathogenesis of the disease. By exploring more about the pathogenesis of the disease and the benefits of G. biloba extract for patients with Alzheimer's disease, it will be possible to create an individualized therapeutic protocol to optimize the treatment.

Neuroprotective effect of intravitreal cell-based glucagon-like peptide-1 production in the optic nerve crush model

PURPOSE

To examine the effect of intraocularly produced glucagon-like peptide-1 (GLP-1) on the survival rate of retinal ganglion cells in an optic nerve crush model.

METHODS

Forty-one Sprague--Dawley rats were divided into a study group (21 animals) in which 4 beads with 3000 genetically modified cells to produce GLP-1 were intravitreally implanted into the right eye; a saline control group (n = 12) with intravitreal saline injection; and a GLP-1 negative bead control group (n = 8) in which 4 beads with 3000 cells without GLP-1 production were intravitreally implanted. The right optic nerves of all animals were crushed in a standardized manner. After labeling the retinal ganglion cells by injecting 3% fluorogold into the superior colliculus, the animals were sacrificed, and the ganglion cells were counted on retinal flat mounts.

RESULTS

The retinal ganglion cell density of the right eyes was significantly higher in the study group (median: 2081 cells/mm(2) ; range: 1182-2953 cells/mm(2) ) than in the GLP-1 bead negative control group (median: 1328 cells/mm(2) ; range: 1007-2068 cells/mm(2) ; p = 0.002) and than in the saline control group (median: 1777 cells/mm(2) ; range: 1000-2405 cells/mm(2) ; p = 0.07). Correspondingly, the survival rate (ratio of retinal ganglion cell density of right eye/left eye) was significantly higher in the study group (median: 0.72; range: 0.40-1.04) than in the GLP-1 bead negative control group (median: 0.44; range: 0.36-0.68; p = 0.003) and than in the saline control group (median: 0.56; range: 0.36-0.89; p = 0.03).

CONCLUSION

Glucagon-like peptide-1 produced by intravitreally implanted cell beads was associated with a higher survival rate of retinal ganglion cells after an experimental optic nerve crush in rats.

The effect of ginkgo biloba on the rat retinal ganglion cell survival in the optic nerve crush model

PURPOSE

To investigate the effect of ginkgo biloba on the retinal ganglion cell survival in a rat optic nerve crush model.

METHODS

Twenty-four Sprague-Dawley rats were divided randomly into a study group of 12 animals receiving intraperitoneal injections of ginkgo biloba and a control group of 12 animals receiving intraperitoneal saline injections. All injections were performed 1 hr before the optic nerve crush and daily afterwards. For each animal, the right optic nerve was crushed closely behind the globe for 60 seconds using a microclip with 40 g power. The left optic nerve was kept intact. At 23 days after the optic nerve crush, the retinal ganglion cells were labelled retrogradely by injecting 3% fluorogold into both sides of the superior colliculus of the brain. At 4 weeks after the optic nerve crush, the animals were killed. Photographs taken from retinal flat mounts were assessed for the number and density of the retinal ganglion cells.

RESULTS

The survival rate, defined as the ratio of the retinal ganglion cell density in the right eye with the optic nerve crush divided by the retinal ganglion cell density in left eye without an optic nerve trauma, was significantly (p=0.035) higher in the study group with ginkgo biloba than in the control group (60.0+/-6.0% versus 53.5+/-8.0%).

CONCLUSION

The results suggest that intraperitoneal injections of a ginkgo biloba extract given prior to and daily after an experimental and standardized optic nerve crush in rats were associated with a higher survival rate of retinal ganglion cells.

Effect of brimonidine on retinal ganglion cell survival in an optic nerve crush model

PURPOSE

To investigate the effect of brimonidine on the retinal ganglion cell survival in an optic nerve crush model.

DESIGN

Experimental animal study.

METHODS

Twenty-four Sprague-Dawley rats were divided into a study group of eight animals receiving intraperitoneal injections of brimonidine (1 mg/kg) and into a control group of 12 animals receiving intraperitoneal saline injections. All injections were performed one hour before the optic nerve crash and daily afterwards. For each animal, the right optic nerve was crushed for 60 seconds by a microclip with 40-g power. At 23 days after the optic nerve crush, the retinal ganglion cells were retrogradely labeled by injecting 3% fluorogold into both sides of the superior colliculus of the brain. At four weeks after the optic nerve crush, the animals were sacrificed. Photographs taken from retinal flat mounts were assessed for number and density of the retinal ganglion cells.

RESULTS

The retinal ganglion cell density of the right eyes with an optic nerve lesion was statistically significantly (P = .02) higher in the brimonidine study group (1281 +/- 189 cells/mm(2)) than in the control group (1060 +/- 148 cells/mm(2)). Correspondingly, the survival rate (ratio of retinal ganglion cell density in the right eye divided by cell density in the left eye) was statistically significantly (P = .027) higher in the study group than in the control group (61.0% +/- 6.0% vs 53.5+/-8.0%).

CONCLUSION

Intraperitoneal injections of brimonidine given prophylactically prior to and posttreatment daily after an experimental and standardized optic nerve crush in rats were associated with a higher survival rate of retinal ganglion cells.

Subunit-specific potentiation of recombinant glycine receptors by NV-31, a bilobalide-derived compound

Bilobalide, a major bioactive component of Ginkgo biloba herbal extracts, exhibits neuroprotective and anti-ischaemic activity. However, its therapeutic potential is limited because of its instability. Attempts to synthesise a more stable analogue culminated in the development of NV-31. This compound recapitulates some aspects of bilobalide pharmacology. However, although bilobalide inhibits recombinant glycine receptor Cl channels (GlyRs), NV-31 potentiates hippocampal neuron GlyRs. Because of the possible therapeutic relevance of this effect, the present study investigated the molecular mechanism and subunit specificity of NV-31 actions at recombinantly expressed alpha1, alpha1beta, alpha2 and alpha3 GlyRs. NV-31 potentiated alpha1 GlyRs by approximately 135% with an EC50 near 170 nM. Its potentiating effect was observed only at low (EC10) glycine concentrations. The magnitude of its potentiating effect was reduced at alpha1beta GlyRs and it had no effect at all at alpha2 and alpha3 GlyRs. NV-31 was unlikely to bind at the bilobalide pore-binding site as its efficacy was not affected by the alpha1 subunit G2'A and T6'S mutations. However, the S15'C mutation to the alcohol-binding site abolished its effects, suggesting that NV-31 modulates the GlyR via a specific (steric or allosteric) interaction with S15'. GlyRs are potential therapeutic targets for chronic anti-inflammatory pain and movement disorders. NV-31, as a positive modulator of these receptors, thus remains viable as a therapeutic candidate for these disorders.

Ginkgo biloba extract EGb 761 attenuates hippocampal neuronal loss and cognitive dysfunction resulting from chronic restraint stress in ovariectomized rats

We have recently found that a combination of ovariectomy (OVX) and chronic restraint stress causes cognitive dysfunction and reduces hippocampal CA3 neurons in female rats and that estrogen replacement suppresses the OVX/stress-induced behavioral and morphological changes. In this study, we examined the effect of Ginkgo biloba extract (EGb 761), a popular herbal supplement, on the cognitive dysfunction and neuromorphological change in OVX/stress-subjected rats. Female Fisher 344 rats were randomly divided into three groups: vehicle-treated OVX, EGb 761 (50 mg/kg) -treated OVX and vehicle-treated sham-operated control groups. Two months after ovariectomy, all animals received restraint stress for 21 days (6 h/day), and were then subjected to a novel object recognition test followed by morphological examination by Nissl staining. EGb 761 was orally administered once daily until the behavioral analysis was done. Treatment with EGb 761 improved memory impairment and neuronal loss of hippocampus in the OVX/stress-subjected group in the same ways as 17beta-estradiol. On the other hand, EGb 761 did not affect the loss of bone mineral density and increase in body weight after OVX, although 17beta-estradiol attenuated them. These results have important implications for neuroprotective and cognition enhancing effects of EGb 761 in postmenopausal women and suggest that the effects are mediated by a different mechanism from estrogen.

The effect of Ginkgo biloba on the cerebellum of aging SAMP mouse--a TUNEL, bcl-2, and fMRI study

EGb 761, an extract from Ginkgo biloba that possesses neuroprotective properties, was fed to a strain of fast aging mice (SAMP-8) beginning at 3 weeks of age until they were sacrificed at 3 months and 11 months, respectively, along with an age-matched control group without herbal feeding. The aim of the study was to determine (1) the status of apoptosis and the status of bcl-2, a molecule involved in the fate of cells following injury, in the cerebella of these mice and (2) to analyze the functional changes as shown by fMRI images. The data indicated that there were no differences in apoptosis between the mice fed with EGb 761 and the control group at the two time points of 3 and 11 months of age. For bcl-2 positive cells, there was a decrease in density only in the cerebella of 11-month-old mice fed with the herbal extract when compared with controls. Functional studies indicated that while no changes were observed in the 3-month-old mice fed with Ginkgo biloba, an expansion of activated sites, possibly related to "synaptic reorganization and pathway alteration," was observed in the 11-month-old mice.

Evaluation of the effect of Ginkgo biloba extract (EGb 761) on the myenteric plexus of the small intestine of Wistar rats

BACKGROUND

The aging process causes a reduction in the myenteric neuronal population, related to oxidative stress, resulting in malfunctioning of the digestive tract. The purpose of this study was to evaluate the action of Ginkgo biloba extract (EGb 761), an important antioxidant drug, on the myenteric plexus of the jejunum and ileum of rats after treatment for 120 days.

METHODS

Fragments of the jejunum and ileum were collected from three groups of rats: a 90-day-old group (group Y), a 210-day-old group (group A), and a 210-day-old group treated daily with the extract EGb 761 (50 mg/kg body weight) (group TA). The analysis was carried out by using the myosin-V immunohistochemical technique. Neuronal densities were estimated, and a study of the neuronal profile area of 500 neurons from each group was carried out.

RESULTS

In the jejunum, there was a significant neuronal population reduction of 17% only in group A compared with group Y. In the ileum, there was a significant neuronal reduction of 36% in group A compared with group Y, and a significant reduction in group TA of 20%. The difference in the reduction between groups A and TA in the ileum was also significant. In the jejunum, only group A showed a significant increase in neuronal profile area, but in the ileum, there was a significant increase in both groups A and TA.

CONCLUSIONS

A daily dose of 50 mg/kg body weight of Ginkgo biloba extract has a significant neuroprotector effect on the myenteric plexus of the ileum during the aging process in rats.

Application of reverse-flow micellar electrokinetic chromatography for the simultaneous determination of flavonols and terpene trilactones in Ginkgo biloba dosage forms

A reverse-flow micellar electrokinetic chromatographic (RF-MEKC) method was developed for the simultaneous qualitative determination of 10 components consisting of the flavonol glycosides, rutin and quercitrin, the flavonol aglycones, isorhamnetin, kaempferol and quercetin, the terpene trilactones, ginkgolides A, B, C and J and the sesquiterpene, bilobalide. This method was used to fingerprint Ginkgo biloba solid oral dosage forms and validated for the quantitation of the marker compounds, rutin and quercetin in some commercial products. In addition to the usual variables, the influence of some essential background electrolyte (BGE) components such as sodium dodecyl sulphate (SDS) and <beta>-cyclodextrin concentrations were investigated. A polyimide fused-silica square capillary column (75 microm I.D. x 360 microm O.D.) with a total length of 60.0 cm and effective length of 45.0 cm was used for the separation. The final BGE consisted of 20 mM phosphoric acid, 40 mM SDS and 12 mM <beta>-cyclodextrin (pH 2.2) using reverse polarity with a voltage of -17.5 kV. Samples were injected electrokinetically at -5 kV for 3 s for the qualitative analysis and hydrodynamically at 20 mbar for 0.6 s for the quantitative assay. The total run time was 22 min and the limits of detection were 3.13 microg/ml and 1.88 microg/ml for rutin and quercetin, respectively. Fingerprint profiles of the solid oral dosage forms and the results of the quantitative analysis indicated that there were major discrepancies in the marker content between products and illustrates the value of this method for use as a procedure to assess product quality of commercially available Ginkgo biloba products.

Clinical Use and Molecular Mechanisms of Action of Extract of Ginkgo biloba Leaves in Cardiovascular Diseases

Ginkgo biloba is one of the oldest living tree species that has been referred to as a living fossil. Extract from Ginkgo biloba leaves (GBE) is among the most commonly used herbal drugs and is popularized for its alleged tonic effect and possible curative and restorative properties. There is an increasing evidence of the potential role of GBE in treating cardiovascular diseases. We examined the history of GBE usage and reviewed the literature on its effects on the cardiovascular system. In the extensive studies involving cell cultures and animal models, GBE has been shown to exert its action through diverse mechanisms. GBE has been reported to have antioxidatant properties, to modify vasomotor function, to reduce adhesion of blood cells to endothelium, to inhibit activation of platelets and smooth muscle cells, to affect ion channels, and to alter signal transduction. In addition, relevant clinical trials with CBE are being carried out, particularly in the treatment of arterial and venous insufficiency and in the prevention of thrombosis. Finally, the controversial clinical findings and the possible adverse interactions between GBE and other drugs are discussed. This review underscores the potential benefits of Ginkgo biloba in cardiovascular diseases, highlights the gaps in our current research, and suggests the necessity for more rigorous systematic investigation of cardiovascular properties of CBE.

Determination of terpene trilactones in Ginkgo biloba solid oral dosage forms using HPLC with evaporative light scattering detection

A reversed phase high performance liquid chromatographic method with evaporative light scattering detection (RP-HPLC-ELSD) was developed for the quantitative determination of the terpene trilactones, ginkgolide A, B, C and J and the sesquiterpene, bilobalide in Ginkgo biloba solid oral dosage forms. Separation was achieved using a minibore Phenomenex Luna (5 microm) C18 column with dimensions 250 mm x 2.00 mm maintained at a temperature of 45 degrees C. A simple gradient method using a mobile phase of methanol:water and a flow rate of 350 microl/min facilitated baseline separation of the selected marker compounds within 14 min. The ELSD parameters affecting the detector response were optimized prior to the validation. The limits of detection and quantification were 31.25 and 62.50 ng, respectively. The percentage relative errors of the recovery ranged between -3.16 and +1.88 and both intra-day and inter-day percentage standard deviations were all better than 6%. This method was used to assay commercially available Ginkgo biloba products and proved to be suitable for the routine analysis of such products for quality control purposes.

Antioxidative and neuroprotective activities of extracts from the fruit hull of mangosteen (Garcinia mangostana Linn.)

OBJECTIVE

The aim of this study was to investigate the antioxidative and neuroprotective activities of various extracts from the fruit hull of mangosteen (Garcinia mangostana Linn., GM).

MATERIALS AND METHODS

Four extracts: water, 50% ethanol, 95% ethanol and ethyl acetate, were used. The antioxidative activity was evaluated using 2,2-diphenyl-1-picrylhydrazyl free-radical scavenging assay at extract concentrations of 1, 10, 50 and 100 microg/ml. Based on the free radical scavenging activity of the extracts, two (water and 50% ethanol) were selected for their protective activity in NG108-15 neuroblastoma cells against H(2)O(2)-induced oxidative stress and for cell viability using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay.

RESULTS

All extracts exhibited antioxidative activity. The water and 50% ethanol extracts showed high free-radical scavenging activity with IC(50) values of 34.98 +/- 2.24 and 30.76 +/- 1.66 microg/ml, respectively. Both water and 50% ethanol extracts exhibited neuroprotective activity on NG108-15 cells. The highest activity was observed at the concentration of 50 microg/ml for both the water and 50% ethanol extracts. For cytotoxicity test, none of the extracts was toxic to the cells except at the high concentration of 100 microg/ml.

CONCLUSIONS

These results suggest that the water and 50% ethanol extracts from the fruit hull of GM may be potent neuroprotectants.

Cytoprotection by Achyrocline satureioides (Lam) D.C. and some of its main flavonoids against oxidative stress

Epidemiological studies indicate that dietary antioxidants can influence the incidence of neurodegenerative diseases. Among them flavonoids have been proposed to be effective cytoprotectors. Consequently, herbs with a high concentration of these compounds such as Achyrocline satureioides, Ginkgo biloba and Epilobium parviflorum are of special interest. In this context a comparative study of the cytoprotective capacity of infusions from the three plants against an oxidative insult was performed. Hence, the cytoprotective activity of each infusion against H2O2 injury to PC12 cells was tested and the antioxidant capacity was assessed by the ABTS*+ radical bleaching assay. Free and glycosylated flavonoids contained in the infusions were identified by HPLC and the cytoprotective effect of some of these individual flavonoids was tested. The analysis of the flavonoid content of the infusions revealed different profiles. Epilobium parviflorum infusion showed the highest antioxidant capacity but only Achyrocline satureioides infusion proved to be cytoprotective. Moreover, the free flavonoids quercetin and luteolin contained in this infusion were also cytoprotective. In conclusion, the free radical scavenger capacity did not correlate with the cytoprotective profile of the infusions. The special mixture of unglycosylated Achyrocline satureioides flavonoids could be a clue to explain the unique effect of this plant.

Effect of bilobalide on peripheral nerve regeneration

The present study provides in vivo trials of silicone rubber chambers filled with different concentrations of bilobalide (0, 50, 100, 200, 400 microM) to bridge a 15 mm sciatic nerve defect in rats. Collagen was also filled in the chambers to prevent the bilobalide from leakage. Histological and electrophysiological techniques were used to evaluate the functional recovery of the nerve. At the conclusion of 8 weeks, animals from the group treated with the bilobalide, especially at the concentration of 200 microM, had a higher rate (40%) of successful regeneration across the wide gap and a significantly larger number of myelinated axons (4094 +/- 1555), compared to only 10% and 2485 in the control group. However, the high dose bilobalide (400 microM) completely reversed this positive effect of growth-promoting capability and inhibited nerve regeneration. Only 10% of the animals treated with the high dose bilobalide had regenerated cables within the silicone rubber chambers. These results indicated that bilobalide could be involved in both positive and negative effects on regenerating nerves. Therefore, whether a proper dosage of bilobalide is used or not plays a critical factor in deciding if it can sustain nerve regeneration over long gaps.

Some aspects of the in vivo neuroprotective capacity of flavonoids: bioavailability and structure-activity relationship

On the basis of previous work showing that flavonoids structurally related to quercetin are neuroprotective for cells in culture, this work was directed towards determining if several flavonoids (quercetin, fisetin and catechin) could acutely and by an intraperitoneal (IP) route reach significant cerebral concentrations and either prevent or facilitate recovery from a brain lesion induced by focal ischemia in rats. Aqueous and liposomal preparations of quercetin, fisetin and catechin were administered IP in a single dose and assessed in the brain by HPLC at 30 min, 1 h, 2 h and 4 h. Ischemic damage from focal middle cerebral artery occlusion was assessed spectrophotometrically with 2,3,5,-triphenylltetrazolium chloride (TTC). Infarct volume was assessed by an image analysis system following perfusion with TTC. The status of the cerebral tissue was evaluated by hematoxylin-eosin. Flavonoids administered in aqueous preparations were undetected in the brain. Cerebral concentrations of catechin (10.5 ng/g), fisetin (8.23 ng/g) and quercetin (509 ng/g) were detected in the brain only after IP injection of the liposomal preparations. Spectrophotometric analysis of brain tissue with the TTC-technique showed that liposomal quercetin reduced ischemic damage and infarct volume after permanent occlusion of the middle cerebral artery (ischemic: 41.3 mm3 vs liposomal quercetin: 17 mm3). In liposomal quercetin-treated animals there was also recovery of the cytoarchitecture in ischemic areas of striatum and cortex. Although a liposomal preparation of fisetin had similar effects, catechin failed to protect brain tissue. In conclusion, early administration of liposomal preparations of quercetin and structurally related flavonoids are beneficial and neuroprotective in experimental focal ischemia.

Down-regulation of c-jun N-terminal kinase-activator protein-1 signaling pathway by Ginkgo biloba extract in human peripheral blood T cells

The activation of T lymphocytes contributes to inflammatory process of cardiovascular and cerebrovascular diseases. We investigated the effects of the extract of Ginkgo biloba (EGb), an ancient plant preserving antioxidant property, on phorbol 12-myristate 13-acetate+ionomycin or anti-CD3+anti-CD28 monoclonal antibodies-activated T cells. Human peripheral blood T cells were negatively selected from whole blood. Cytokines were measured by ELISA, cell surface markers by flow cytometry and the activities of transcription factors and kinases were determined by electrophoresis mobility shift assays, kinase assays and transfection assays. We showed that EGb inhibited several cytokines, including tumor necrosis factor-alpha, interleukin (IL)-2, IL-4 and interferon-gamma production from activated T cells. Electrophoresis mobility shift assay analysis indicated that EGb down-regulated activator protein-1 (AP-1) but not nuclear factor kappa B DNA-binding activity. In addition, EGb inhibited c-jun N-terminal kinase but not extracellular signal regulated protein kinase activity. The inhibitory specificity on AP-1 by EGb was also demonstrated in transfection assays. The inhibition of AP-1 signaling pathway in T cells by EGb provides a support for its efficacy in cardiovascular and cerebrovascular diseases and raises a therapeutic potential for this drug in activated T cell-mediated pathologies.

Protective effect of ginkgo biloba extract on endothelial cell against damage induced by oxidative stress

The viability of bovine aortic endothelial cells (BAECs) treated with 0.1 m H O was decreased by 39.8%, and 100 mg/l EGb761 increased the viability by 20.6%. Exposure BAECs to H O for 6 min resulted in a significant elevation in the intracellular free Ca. Pretreatment of BAECs with 10 mg/l and 100 mg/l EGb761 for 10 min showed a decrease in the intracellular free Ca, 4.5% and 20.6%, respectively. The apoptotic rate of BAECs measured by propidium iodide (PI) staining was (38.1 +/- 2%) after 18 h of treatment with H O. Pretreatment of BAECs with 100 mg/l EGb761 for 1 h reduced the apoptotic rate to 27 +/- 1%. In addition, there were about 5-7% of cells stained positive measured by TUNEL assay. When BAECs were exposed to 0.1 m H O for 18 h, the number of TUNEL-positive cells increased to 37-44%. When 10 mg/l EGb761 and 100 mg/l EGb761 were used, the TUNEL-positive cells decreased to 26.5 +/- 3.1% and 17.5 +/- 1.7%, respectively. Furthermore, EGb761 also inhibited caspase-3 activity induced by H O. It is concluded that EGb761 has protective effect on bovine vascular endothelial cells against damage induced by H O. Further studies are needed to clarify the mechanisms of action of EGb761.

Bilobalide and neuroprotection

In vivo studies have indicated that systemically administered bilobalide, a sesquiterpene trilactone constituent of Ginkgo biloba leaf extracts, can reduce cerebral edema produced by triethyltin, decrease cortical infarct volume in certain stroke models, and reduce cerebral ischemia. In vitro and ex vivo studies indicate that bilobalide has multiple mechanisms of action that may be associated with neuroprotection, including its preservation of mitochondrial ATP synthesis, its inhibition of apoptotic damage induced by staurosporine or by serum-free medium, its suppression of hypoxia-induced membrane deterioration in the brain, and its actions of increasing the expression of the mitochondrial DNA-encoded COX III subunit of cytochrome c oxidase and the ND1 subunit of NADH dehydrogenase. As multiple modes of action may apply to bilobalide, it could be useful in developing therapy for disorders involving cerebral ischemia and neurodegeneration.

Release of cytochrome c into the extracellular space contributes to neuronal apoptosis induced by staurosporine

The mitochondrial protein cytochrome c has been identified as one of the key signalling molecules of apoptosis. In the present study, we used primary neuronal cultures to investigate whether cytochrome c was released from the mitochondria into the cytosol and subsequently into the culture medium during staurosporine-induced apoptosis and whether extracellular cytochrome c modulates the degree of damage caused by staurosporine. We found the cytochrome c content in the mitochondria decreased 24 h after and increased in the cytosol 8 h after staurosporine was added to the culture medium. The cytochrome c content of the culture medium increased from 8 h up to 24 h after starting the staurosporine treatment. In parallel with the release of cytochrome c into the culture medium, membrane leakage occurred as determined by the release of LDH. Addition of cytochrome c accelerated, whereas the addition of anti-cytochrome c antibodies reduced staurosporine-induced neuronal death suggesting a pro-apoptotic role of cytochrome c released into the culture medium. Under control conditions, extracellularly added cytochrome c (25 ng/ml), which was in the range of the amount of cytochrome c released from staurosporine-treated neurons into the culture medium, increased the percentage of apoptotic neurons to 30% compared with 18% in vehicle-treated controls. Our results suggest that the release of cytochrome c into the extracellular space contributes to neuronal apoptosis induced by staurosporine.