Effects of single intraperitoneal injections of an extract of Ginkgo biloba (EGb 761) and its terpene trilactone constituents on barbital-induced narcosis in the mouse

Herbal Approaches in the Management of Mental Depression

BACKGROUND

Human's existence has become more stressful these days, most likely for the sake of improving one's lifestyle and fulfilling one's aspirations and needs. Depression is the most frequent neurological disorder, which affects millions of individuals worldwide. In clinical research, depression is the second most frequent chronic disease. A variety of herbal medications thought to have antidepressant-like effects have been reported in ancient pharmacopoeias from around the world. These provide several prospective chemicals that could be developed into modern mental medications while also causing no noticeable negative effects.

OBJECTIVE

The review is written to provide herbal treatment and comprehensive information about depression.

METHODS

Plants and plant formulations that were found effective in the treatment of depression are thoroughly reviewed. The antidepressant efficacies of medicinal plants, as well as their dosages, are investigated using experimental models. The review article contains 140 plants possessing antidepressant properties, 11 commercial formulations, and 25 active/isolated ingredients, as well as their chemical structure, which have been thoroughly reviewed with antidepressant activity after studying 283 references.

RESULTS

Literature revealed that a variety of medicinal plants are effective for the treatment of depression such as Hypericum perforatum, Catha edulis, Tinospora cordifolia, Curcuma longa, Ferula foetida, Rhodio larosea, Glycyrrhiza glabra, Crocus sativus, Ocimumba silicum and Embelica officinalis.

CONCLUSION

Potential compounds isolated from medicinal plants for the treatment of depressive disorders need to be established and herbal plant research could aid in this endeavour.

Pharmacologic treatments in preclinical tinnitus models with special focus on Ginkgo biloba leaf extract EGb 761®

Tinnitus is defined as the perception of sound in the absence of external acoustic stimuli. Frequent comorbidities or associated factors are depression, anxiety, concentration problems, insomnia, resignation, helplessness, headache, bruxism, or social isolation, just to name a few. Although many therapeutic approaches have already been tested with varying success, there still is no cure available for tinnitus. The search for an effective treatment has been hampered by the fact that the mechanisms of tinnitus development are still not fully understood, although several models are available and discussed in this review. Our review will give a brief overview about preclinical models, presenting the heterogeneity of tinnitus sub-types depending on the different inner ear and brain structures involved in tinnitus etiology and pathogenesis. Based on these models we introduce the different target structures and transmitter systems implicated in tinnitus development and provide an extensive overview on preclinical drug-based therapeutic approaches that have been explored in various animal models. As the special extract from Ginkgo biloba leaves EGb 761® has been the most widely tested drug in both non-clinical tinnitus models as well as in clinical trials, a special focus will be given to EGb 761®. The efficacy of terpene lactones, flavone glycosides and proanthocyanidines with their distinct contribution to the overall efficacy profile of the multi-constituent drug EGb 761® will be discussed.

Intraperitoneal injection of ginkgolide B, a major active compound of Ginkgo biloba, dose-dependently increases the amount of wake and decreases non-rapid eye movement sleep in C57BL/6 mice

The terpene lactones of Ginkgo biloba extract, namely ginkgolides (A, B, and C) and bilobalide, possess antioxidant, anti-inflammatory, and neuroprotective effects. They are widely prescribed for the treatment of cerebral dysfunctions and neurological impairments. In addition, they demonstrate antagonistic action at the gamma-aminobutyric acid type A and glycine receptors, which are members of the ligand-gated ion channel superfamily. In the present study, the effects of ginkgolides (A, B, and C) and bilobalide on sleep in C57BL/6 mice were investigated. Ginkgolide B was found to dose-dependently increase the amount of wake and decrease that of non-rapid eye movement sleep without changes in the electroencephalography power density of each sleep/wake stage, core body temperature and locomotor activity for the first 6 h after intraperitoneal injection. Of note, the amount of wake after injection of 5 mg/kg of ginkgolide B showed a significant increase (14.9 %) compared with that of vehicle (P = 0.005). In contrast, there were no significant differences in the amount of sleep, core body temperature, and locomotor activity in the mice injected with ginkgolide A and C. Bilobalide briefly induced a decrease in locomotor activity but did not exert significant effects on the amounts of sleep and wake. The modes of action of the wake-enhancing effects of ginkgolide B are unknown. However, it may act through the antagonism of gamma-aminobutyric acid type A and glycine receptors because it is established that these inhibitory amino acids mediate sleep and sleep-related physiology. It is of interest to further evaluate the stimulant and awaking actions of ginkgolide B on the central nervous system in clinical and basic research studies.

PXR Mediated Protection against Liver Inflammation by Ginkgolide A in Tetrachloromethane Treated Mice

The pregnane X receptor (PXR), a liver and intestine specific receptor,, has been reported to be related with the repression of inflammation as well as activation of cytochromosome P450 3A (CYP3A) expression. We examined the effect of PXR on tetrachloromethane (CCl4)-induced mouse liver inflammation in this work. Ginkgolide A, one main component of Ginkgo biloba extracts (GBE), activated PXR and enhanced PXR expression level, displayed both significant therapeutic effect and preventive effect against CCl4-induced mouse hepatitis. siRNA-mediated decrease of PXR expression significantly reduced the efficacy of Ginkgolide A in treating CCl4-induced inflammation in mice. Flavonoids, another important components of GBE, were shown anti-inflammatory effect in a different way from Ginkgolide A which might be independent on PXR because flavonoids significantly inhibited CYP3A11 activities in mice. The results indicated that anti-inflammatory effect of PXR might be mediated by enhancing transcription level of IκBα through binding of IκBα. Inhibition of NF-κB activity by NF-κB-specific suppressor IκBα is one of the potential mechanisms of Ginkgolide A against CCl4-induced liver inflammation.

Summative interaction between astaxanthin, Ginkgo biloba extract (EGb761) and vitamin C in suppression of respiratory inflammation: a comparison with ibuprofen

In this study, combinations of Ginkgo biloba leaf extract (EGb761) plus the carotenoid antioxidant astaxanthin (ASX) and vitamin C were evaluated for a summative dose effect in the inhibition of asthma-associated inflammation in asthmatic guinea-pigs. Ovalbumin-sensitized Hartley guinea-pigs challenged with ovalbumin aerosol to induce asthma, were administered EGb761, ASX, vitamin C or ibuprofen. Following killing, bronchoalveolar lavage (BAL) fluid was evaluated for inflammatory cell infiltrates and lung tissue cyclic nucleotide content. Each parameter measured was significantly altered to a greater degree by drug combinations, than by each component acting independently. An optimal combination was identified that included astaxanthin (10 mg/kg), vitamin C (200 mg/kg) and EGb761 (10 mg/kg), resulting in counts of eosinophils and neutrophils each 1.6-fold lower; macrophages 1.8-fold lower, cAMP 1.4-fold higher; and cGMP 2.04-fold higher than levels in untreated, asthmatic animals (p < 0.05). In conclusion, EGb761, ASX and vitamin C are shown here to interact summatively to suppress inflammation with efficacy equal to or better than ibuprofen, a widely used non-steroidal antiinflammatory drug (NSAID). Such combinations of non-toxic phytochemicals constitute powerful tools for the prevention of onset of acute and chronic inflammatory disease if consumed regularly by healthy individuals; and may also augment the effectiveness of therapy for those with established illness.

Role of GABAergic antagonism in the neuroprotective effects of bilobalide

Bilobalide, a constituent of Ginkgo biloba, has neuroprotective properties. Its mechanism of action is unknown but it was recently found to block GABA(A) receptors. The goal of this study was to test the potential role of a GABAergic mechanism for the neuroprotective activity of bilobalide. In rat hippocampal slices exposed to NMDA, release of choline indicates breakdown of membrane phospholipids. NMDA-induced choline release was almost completely blocked in the presence of bilobalide (10 microM) and under low-chloride conditions. Bicuculline (100 microM), a competitive antagonist at GABA(A) receptors, reduced NMDA-induced choline release to a small extent (-23%). GABA (100 microM) partially antagonized the inhibitory action of bilobalide. Exposure of hippocampal slices to NMDA also caused edema formation as measured by increases of tissue water content. NMDA-induced edema formation was suppressed by bilobalide and by low-chloride conditions. Bicuculline exerted partial protection (by 30%) while GABA reduced bilobalide's effect by about one third. To investigate bilobalide's interaction with GABA(A) receptors directly, we measured binding of [(35)S]-TBPS to rat cortical membranes. TBPS binding was competitively inhibited by bilobalide in the low micromolar range (IC(50)=3.7 microM). As a functional test, we determined (36)chloride flux in rat corticohippocampal synaptoneurosomes. GABA (100 microM) significantly increased (36)chloride flux (+65%), and this increase was blocked by bilobalide, but with low potency (IC(50): 39 microM). We conclude that, while antagonism of GABA(A) receptors may contribute to bilobalide's neuroprotective effects, additional mechanisms must be postulated to fully explain bilobalide's actions.

DISTINCT ROLE OF BILOBALIDE AND GINKGOLIDE A IN THE MODULATION OF RAT CYP2B1 AND CYP3A23 GENE EXPRESSION BY GINKGO BILOBA EXTRACT IN CULTURED HEPATOCYTES

In the present study, primary cultures of rat hepatocytes were treated for 48 h with one of several extracts of Ginkgo biloba (10, 100, or 1000 microg/ml). Maximal increase in CYP2B1 and CYP3A23 mRNA levels was obtained at 100 microg/ml. This concentration of G. biloba extract also increased CYP3A2 and CYP3A18 mRNA expression in addition to CYP2B-mediated 7-benzyloxyresorufin O-dealkylation (BROD) and CYP3A-mediated testosterone 6beta-hydroxylation. In other experiments, cultured hepatocytes were treated for 48 h with bilobalide, ginkgolide A, ginkgolide B, ginkgolide C, ginkgolide J, kaempferol, quercetin, isorhamnetin, or a flavonol diglycoside at a concentration that represented the level present in a 100 microg/ml concentration of an extract. Only bilobalide (2.8 microg/ml) increased CYP2B1 mRNA expression, and the -fold increase (7.9 +/- 0.5; mean +/- S.E.M.) was similar to that (8.3 +/- 1.7) by the extract. By comparison, only ginkgolide A (1.1 microg/ml) increased CYP3A23 mRNA expression, but the extent (2.6 +/- 0.5-fold) was less than the 5.3 +/- 1.7-fold increase by the extract. A greater concentration (5 microg/ml) of ginkgolide A was required to elevate CYP3A2 and CYP3A18 mRNA expression. Over the range of 1 to 5 microg/ml, bilobalide increased CYP2B1 mRNA and BROD, but not CYP3A23 mRNA or testosterone 6beta-hydroxylation, whereas ginkgolide A increased CYP3A23 mRNA and testosterone 6beta-hydroxylation, but not CYP2B1 mRNA or BROD. Overall, our novel results indicate a distinct role of bilobalide and ginkgolide A in the modulation of CYP2B1 and CYP3A23 gene expression and enzyme activities by G. biloba extract in primary cultures of rat hepatocytes.

Ginkgolides, diterpene trilactones of Ginkgo biloba, as antagonists at recombinant α1β2γ2L GABAA receptors

Ginkgolides A, B, and C are diterpene trilactones and active constituents of the 50:1 Ginkgo biloba leaf extract widely used in the symptomatic treatment of mild to moderate dementia. Using the two-electrode voltage clamp methodology, these ginkgolides were found to be moderately potent antagonists at recombinant human alpha(1)beta(2)gamma(2L) GABA(A) receptors expressed in Xenopus oocytes. Ginkgolides A, B, and C inhibited the direct action of gamma-aminobutyric acid (GABA) with K(i) values of 14.5+/-1.0, 12.7+/-1.7, and 16.3+/-2.4 microM respectively. Antagonism by these ginkgolides at alpha(1)beta(2)gamma(2L) GABA(A) receptors appears to be noncompetitive as indicated by the nonparallel right shift and reduced maximal GABA response in their GABA concentration-effect curves.

An anxiolytic-like effect of Ginkgo biloba extract and its constituent, ginkgolide-A, in mice

The anxiolytic-like effects of Ginkgo biloba extract (GBE) and its four terpenoid components (ginkgolide-A, ginkgolide-B, ginkgolide-C, and bilobalide) were assessed using the elevated plus-maze test in mice. Administration of GBE as a single oral dose (0.5 or 1 g/kg, po) caused a state of suppressed motor activity and, thus, shortened the time spent in the open-sided arms. However, when GBE (0.063-1 g/kg, po) was administered daily for 7 days and the plus-maze test was carried out 24 h after the final administration, the time spent in the open-sided arms was prolonged, with the peak anxiolytic-like effect at 0.125 g/kg. A combination of seven-day administration of GBE (0.125 g/kg) and a single dose of diazepam (1 mg/ kg, po, 10 min before testing) enhanced the anxiolytic-like effect. Flumazenil (0.3 mg/kg, ip, 10 min before testing) blocked the effect of diazepam, but not of GBE. Daily administration of ginkgolide-A (1 or 2 mg/kg, po) resulted in an anxiolytic-like effect by the third treatment, with the maximal effect observed after the fifth administration. Neither ginkgolide-B, ginkgolide-C, nor bilobalide produced any anxiolytic-like effects. At doses higher than 0.5 g/kg, GBE not only inhibited motor activity but also suppressed active avoidance behavior, reduced caffeine-induced stimulation, and enhanced pentobarbital-induced sleep, while ginkgolide-A (up to 20 mg/kg) did not exhibit these effects. Diazepam (1 mg/kg) is known to enhance pentobarbital-induced sleep. These results suggest that GBE produces a significant anxiolytic-like effect following repeated administration and that ginkgolide-A is most likely responsible for this effect. There are also indications that although GBE exerts a sedative effect at comparatively higher doses, ginkgolide-A has a relatively weak tendency to produce benzodiazepine-like side effects.

Inactivation of the hepatic cytochrome P450 system by conditional deletion of hepatic cytochrome P450 reductase

Cytochrome P450 (CYP) monooxygenases catalyze the oxidation of a large number of endogenous compounds and the majority of ingested environmental chemicals, leading to their elimination and often to their metabolic activation to toxic products. This enzyme system therefore provides our primary defense against xenobiotics and is a major determinant in the therapeutic efficacy of pharmacological agents. To evaluate the importance of hepatic P450s in normal homeostasis, drug pharmacology, and chemical toxicity, we have conditionally deleted the essential electron transfer protein, NADH:ferrihemoprotein reductase (EC, cytochrome P450 reductase, CPR) in the liver, resulting in essentially complete ablation of hepatic microsomal P450 activity. Hepatic CPR-null mice could no longer break down cholesterol because of their inability to produce bile acids, and whereas hepatic lipid levels were significantly increased, circulating levels of cholesterol and triglycerides were severely reduced. Loss of hepatic P450 activity resulted in a 5-fold increase in P450 protein, indicating the existence of a negative feedback pathway regulating P450 expression. Profound changes in the in vivo metabolism of pentobarbital and acetaminophen indicated that extrahepatic metabolism does not play a major role in the disposition of these compounds. Hepatic CPR-null mice developed normally and were able to breed, indicating that hepatic microsomal P450-mediated steroid hormone metabolism is not essential for fertility, demonstrating that a major evolutionary role for hepatic P450s is to protect mammals from their environment.

Intraocular pressure in genetically distinct mice: an update and strain survey

BACKGROUND

Little is known about genetic factors affecting intraocular pressure (IOP) in mice and other mammals. The purpose of this study was to determine the IOPs of genetically distinct mouse strains, assess the effects of factors such as age, sex and time of day on IOP in specific strain backgrounds, and to assess the effects of specific candidate gene mutations on IOP.

RESULTS

Based on over 30 studied mouse strains, average IOP ranges from approximately 10 to 20 mmHg. Gender does not typically affect IOP and aging results in an IOP decrease in some strains. Most tested strains exhibit a diurnal rhythm with IOP being the highest during the dark period of the day. Homozygosity for a null allele of the carbonic anhydrase II gene (Car2n) does not alter IOP while homozygosity for a mutation in the leptin receptor gene (Leprdb) that causes obesity and diabetes results in increased IOP. Albino C57BL/6J mice homozygous for a tyrosinase mutation (Tyrc-2J) have higher IOPs than their pigmented counterparts.

CONCLUSIONS

Genetically distinct mouse strains housed in the same environment have a broad range of IOPs. These IOP differences are likely due to interstrain genetic differences that create a powerful resource for studying the regulation of IOP. Age, time of day, obesity and diabetes have effects on mouse IOP similar to those in humans and other species. Mutations in two of the assessed candidate genes (Lepr and Tyr) result in increased IOP. These studies demonstrate that mice are a practical and powerful experimental system to study the genetics of IOP regulation and disease processes that raise IOP to harmful levels.