Evidence for specific interactions between kavain and human cortical neurons monitored by fluorescence correlation spectroscopy

Specific interactions between a tetramethylrhodamine-labeled kavain derivative and human cortical neurons were found for the first time using fluorescence correlation spectroscopy (FCS). Human cortical neurons, cultivated in Nunc chambers, were incubated with 1 nM of the dye-labeled kavain derivative. A total binding of 0.55 nM was found after an incubation period of 60 min. 50% of the total binding was specifically displaced in the presence of 1 microM non-labeled (+)-kavain. Evidence for these specific interactions was verified by a saturation experiment. Both the non-linear Scatchard plot and the n value of 1.58 +/- 0.07 in the sigmoid Hill plot indicate binding sites with different binding affinities.

The alternatively spliced CD64 transcript FcgammaRIb2 does not specify a surface-expressed isoform

Three highly homologous genes (A, B and C) and six transcripts have been identified for the class I human IgG receptor (CD64). The hFcgammaRIa1 isoform encodes the prototypic high-affinity receptor for IgG. The alternatively spliced hFcgammaRIb2 transcript was postulated to exist as a second surface-expressed CD64 isoform on myeloid cells. In this report we assessed this proposed role for hFcgammaRIb2 in detail. As CD64 monoclonal antibodies might not recognize hFcgammaRIb2, we tagged the receptor with an hemagglutinin tag and transfected hFcgammaRIb2tag in the presence of FcR gamma-chain into IIA1.6 cells. Both transcript and protein of hFcgammaRIb2tag were clearly present in transfectants. However, in contrast to the (control) hFcgammaRIa1tag, no surface expression of hFcgammaRIb2tag was detectable with a tag-specific monoclonal antibody. Confocal scan laser microscopy revealed hFcgammaRIb2tag to be retained in the endoplasmic reticulum, resulting in absent plasma membrane expression. These results show hFcgammaRIb2 neither to be surface expressed, nor to represent a separate CD64 isoform. This finding, furthermore, implicates that other FcR transcripts defined at the mRNA level may not represent true FcR isoforms either.

In vivo effects of the kavapyrones (+)-dihydromethysticin and (+/-)-kavain on dopamine, 3,4-dihydroxyphenylacetic acid, serotonin and 5-hydroxyindoleacetic acid levels in striatal and cortical brain regions

The in vivo effect of a single oral dose of 100 mg (+)-dihydromethysticin/kg body weight on striatal and cortical tissue concentrations of dopamine, serotonin, 3,4-dihydroxyphenylacetic acid and 5-hydroxyindoleacetic acid, as well as the dopamine and serotonin turnover, was tested in rats. Additionally, other rats were fed with a (+/-)-kavain containing food over a period of 78 days in order to calculate the influence of a chronic treatment with kavapyrones on the neurotransmitters. The results of the present in vivo study clearly demonstrate that neither (+)-dihydromethysticin in a high single dose, nor (+/-)-kavain chronically administered, altered the dopaminergic or serotonergic tissue levels in rats significantly.

Influence of genuine kavapyrone enantiomers on the GABA-A binding site

The influence of kavapyrones from Piper methysticum Forst. on the GABAA receptor was demonstrated using radioreceptor assays. Both the dienolide yangonin and the genuine enolide enantiomers (+)-kavain, (+)-dihydrokavain, (+)-methysticin, and (+)-dihydromethysticin enhanced the specific binding of [3H]bicuculline methochloride ([3H]BMC). The kavapyrones have been investigated at assay concentrations between 100 microM and 10 nM. (+)-Kavain, (+)-methysticin and (+)-dihydromethysticin showed maximal enhancements of 18% to 28% at a concentration of 0.1 microM, whereas a 100-fold concentration of (+)-dihydrokavain revealed a similar modulatory activity of 22%. In the presence of 1 microM yangonin an increase of about 21% of the specific [3H]BMC binding was observed. Desmethoxyyangonin did not alter the binding behavior of the GABAA-receptor. A structure comparison of desmethoxyyangonin and yangonin indicated that the aromatic methoxy group was of particular importance for the modulatory activity. In contrast, the substitution pattern of the aromatic ring did not influence the modulatory activity of the enolides in a decisive manner. A structure comparison of desmethoxyyangonin and (+)-kavain revealed that an angular lactone ring was an important structure requirement. Both the enolides and the dienolides did not inhibit the specific binding of [3H]flunitrazepan. Thus, the influence on the GABAA receptor was not based upon an interaction of these kavapyrones with the benzodiazepine receptor.

In vivo microdialysis study of (+/-)-kavain on veratridine-induced glutamate release

This is the first microdialysis study to address the effects of (+/-)-kavain on veratridine-induced glutamate release in freely moving rats. (+/-)-Kavain (100 mg/kg, p.o.) significantly reduced veratridine-induced glutamate release compared with that of vehicle-treated controls. Maximum extracellular glutamate levels were obtained 20-40 min after veratridine stimulation (500 microM, added to the perfusate). In the control group the increase was 301% and in the (+/-)-kavain group the increase was significantly reduced to 219% (the basal value was 100%). These results demonstrate that (+/-)-kavain reduces veratridine-induced glutamate release in vivo, which confirms previous in vitro data.

Contribution to the quantitative and enantioselective determination of kavapyrones by high-performance liquid chromatography on ChiraSpher NT material

A simultaneous HPLC separation of the enantiomers of kavain, dihydrokavain, methysticin and dihydromethysticin, as well as the achiral dienolides yangonin and desmethoxyyangonin was carried out on a ChiraSpher NT column. For quantitative determinations, calibration curves with correlation coefficients between 0.9982 and 0.9996 were established for the genuine kavapyrones. Detection limits between 0.25 microg and 0.5 microg per injection were measured at 240 nm. The defined scopes of work corresponded with the different kavapyrone amounts, depending on growth factors of distinct plant locations. The precision of the method was verified by analysing a phytopharmacon with a nominal value of 40 mg kavapyrones per tablet. The evaluation revealed 39.62 mg per tablet by the sum of single calculated kavapyrones. Relative standard deviations between 1.06% and 2.39% were found for the compounds under investigation. The accuracy of the method was proved by a recovery of 99.7%. To simplify the determination of the total kavapyrone amount, response factors and correlation factors for (+)-dihydrokavain, (+)-methysticin, (+)-dihydromethysticin, yangonin and desmethoxyyangonin were calculated relative to (+)-kavain.

Piper methysticum: enantiomeric separation of kavapyrones by high performance liquid chromatography

A simultaneous separation of the enantiomers of kawain, dihydrokawain, methysticin, and dihydromethysticin as well as the achiral dienolides yangonin and demethoxyyangonin was carried out on a ChiraSpher NT column. This HPLC method can be used for the investigation of the enantiomeric purity of plant material and herbal medicines. The influence of temperature and flow rate are discussed in respect to the chromatographic resolution of the enantiomers. All tested enolide racemates can be preparatively separated on ChiraSpher NT.

Chelidonium majus L.: components with in vitro affinity for the GABAA receptor. Positive cooperation of alkaloids

The influence of an ethanolic dry extract of Chelidonii herba on the GABAA receptor has been studied in vitro. In the presence of 90 micrograms/assay a positive cooperation was induced for [3H]muscimol accompanied by an increase of the specific binding (115%) while 160 micrograms/assay exerted a 50% inhibition of the specific binding of the radioligand [3H]muscimol. The quantitative determination of the Chelidonium alkaloids by HPLC together with the evaluation of the radioreceptor assays of the pure alkaloids revealed that the allosteric modulation of the GABAA receptor is mainly due to protopine. The small amounts of allocryptopine and stylopine assumingly support the action of protopine. Protopine, stylopine, and allocryptopine do not influence the specific binding of [3H]flunitrazepam. Thus, the positive cooperative modulation of the GABAA receptor is not based on an interaction of these alkaloids with the benzodiazepine receptor. The specific [3H]muscimol binding was inhibited only by chelerythrine and sanguinarine with IC50 values of 25 microM and 39 MicroM, respectively. The content of chelerythrine and sanguinarine in the ethanolic dry extract of Chelidonii herba is 500 or even 1000 times too low to account for the observed interference with GABAA receptor activity. Thus, the alkaloids are not responsible for the inhibitory action on the GABAA receptor at higher concentrations of the ethanolic dry extract.

Degranulation of individual mast cells in response to Ca2+ and guanine nucleotides: an all-or-none event

Widespread experience indicates that application of suboptimal concentrations of stimulating ligands (secretagogues) to secretory cells elicits submaximal extents of secretion. Similarly, for permeabilized secretory cells, the extent of secretion is related to the concentration of applied intracellular effectors. We investigated the relationship between the extent of secretion from mast cells (assessed as the release of hexosaminidase) and the degranulation (exocytosis) responses of individual cells. For permeabilized mast cells stimulated by the effector combination Ca2+ plus GTP-gamma-S and for intact cells stimulated by the Ca2+ ionophore ionomycin, we found that exocytosis has the characteristics of an all-or-none process at the level of the individual cells. With a suboptimal stimulus, the population comprised only totally degranulated cells and fully replete cells. In contrast, a suboptimal concentration of compound 48/80 applied to intact cells induced a partial degree of degranulation. This was determined by observing the morphological changes accompanying degranulation by light and electron microscopy and also as a reduction in the intensity of light scattered at 90 degrees, indicative of a change in the cell-refractive index. These results may be explained by the existence of a threshold sensitivity to the combined effectors that is set at the level of individual cells and not at the granule level. We used flow cytometry to establish the relationship between the extent of degranulation in individual rat peritoneal mast cells and the extent of secretion in the population (measured as the percentage release of total hexosaminidase). For comparison, secretion was also elicited by applying the Ca2+ ionophore ionomycin or compound 48/80 to intact cells. For permeabilized cells and also for intact cells stimulated with the ionophore, levels of stimulation that generate partial secretion gave rise to bimodal frequency distributions of 90 degrees light scatter. In contrast, a partial stimulus to secretion by compound 48/80 resulted in a single population of partially degranulated cells, the degree of degranulation varying across the cell population. The difference between the all-or-none responses of the permeabilized or ionophore-treated cells and the graded responses of cells activated by compound 48/80 is likely to stem from differences in the effective calcium stimulus. Whereas cell stimulated with receptor-directed agonists can undergo transient and localized Ca2+ changes, a homogeneous and persistent stimulus is sensed at every potential exocytotic site in the permeabilized cells.