Interaction of psychotropic drugs with phospholipids

The interactions of psychotropic drugs with phospholipids, including lysophosphatidylcholine, phosphatidylinositol, and lysophosphatidylserine, were studied using calmodulin-dependent cyclic nucleotide phosphodiesterase partially purified from the cortex of hog brain. All the compounds used inhibited both calmodulin- and phospholipid-stimulated phosphodiesterase activity but not the basal activity. Fluphenazine was confirmed by kinetic analysis to be a competitive inhibitor, with both calmodulin and phospholipid. Using fluphenazine-Sepharose affinity chromatography, it was demonstrated that fluphenazine did not interact with the enzyme. The potencies of antipsychotics such as fluphenazine in inhibiting the various phospholipid-dependent activations decreased in the following order: lysophosphatidylcholine-, phosphatidylinositol-, and lysophosphatidylserine-dependent activation. On the other hand, antidepressant drugs exhibited similar inhibitory potencies towards lysophosphatidylcholine- and phosphatidylinositol-dependent activation. Antipsychotic and antidepressant drugs appear to have different characteristics with regard to lipid-drug interaction.     

Interaction of kanamycin A and kanamycin B with phospholipids

It has been suggested that the aminoglycoside drugs are ototoxic because they contain amine groups that interact with membrane phospholipids. The interaction of kanamycin A and kanamycin B with vesicles containing various phospholipids was assessed from studies of vesicle aggregation and of the fluorescence of the probes 1-anilino-8-naphthalene sulfonic acid (ANS) and 1,6-diphenyl-1,3,5-hexatriene (DPH) added to the system. Kanamycin B, with 5 amino groups, showed a stronger interaction with the acidic phospholipids than kanamycin A, with only 4 amino groups. The evidence indicated that the interaction was an ionic one involving the charged groups of both components with penetration of the hydrocarbon interior of the bilayers. Of all the phospholipids tested polyphosphoinositide showed the greatest ability to interact with the kanamycins, supporting the proposal that interaction with this phospholipid may be the basis of the ototoxicity of aminoglycosides.     

Inhibition of alpha-chymotrypsin by dibenamine

α-Chymotrypsin is rapidly inhibited by an acid solution of dibenamine in an irreversible manner when the reactants are mixed in a buffer at near neutral pH. The degree of inhibition depends on the molar ratio of the reactants. The alkylating species is probably the ethyl-eniminium ion from dibenamine, this ion being present at a higher level in the acid media than in the near neutral media used here.     

Inhibition of the muscarinic receptor by dibenamine

The rate of reaction of a group at the muscarinic receptor of isolated guineapig ileum and rat jejunum with the ethyleniminium ion derived from dibenamine is independent of pH over the range 6.9–8.9. This group may be either a carboxyl group or an imidazole residue. The muscarinic receptor is not identical with the active site of acetylcholinesterase as proposed since the enzyme reacts in a different manner with dibenamine over this pH range.     

Interaction of the diuretics torasemide and U-37883A with the KATP channel in rat isolated aorta

In this study we have investigated the interaction of the loop diuretics torasemide and furosemide and of the eukalemic diuretic U-37883A (4-morpholinocarboximidine-N–1-adamantyl-N’-cyclohexylhydrochloride) with the ATP-sensitive K⁺ channel (K_ATP channel) in rat aortic rings. Torasemide contains a sulphonylurea group which might enable the compound to interfere with K_ATP channels; this group is lacking in furosemide. U-37883A blocks several types of K_ATP channels. The interaction with the vascular K_ATP channel was probed in binding studies, ⁸⁶Rb⁺ efflux experiments and vasorelaxation assays. Torasemide inhibited the binding of the K_ATP channel inhibitor [³H]glibenclamide and of the opener [³H]P1075 with IC₅₀ values of 19 and 45 μM, respectively; furosemide and U-37883A were inactive or interfered with binding in a nonspecific way. In ⁸⁶Rb⁺ efflux experiments, the loop diuretics, at μM concentrations, inhibited basal tracer efflux to 50% whereas U-37883A had no effect. P1075-stimulated ⁸⁶Rb⁺ efflux, a qualitative measure of K_ATP channel opening, was inhibited by U-37883A and torasemide with IC₅₀ values of 0.06 and 130 μM, respectively; furosemide induced only a small (23%) inhibition. In experiments measuring isometric force, torasemide and furosemide partially relaxed endothelium-denuded aortic rings precontracted with noradrenaline or KCl with EC₅₀ values between 6 and 10 μM. The vasorelaxant effect of P1075 was inhibited in a noncompetitive manner by torasemide (300 μM) but unaffected by furosemide. U-37883A increased noradrenaline-induced force and inhibited the vasorelaxant effect of P1075 in an apparently competitive manner with an inhibition constant of 0.4 μM. The data show that torasemide interferes specifically with the binding of the K_ATP channel modulators [³H]glibenclamide and [³H]P1075 and with the K_ATP channel opening and vasorelaxant effects of P1075 whereas furosemide is inactive. This suggests that the interaction of torasemide with the vascular K_ATP channel is due to the sulphonylurea group present in torasemide. U-37883A, which does not inhibit P1075 binding, is one of the most potent blockers of P1075-induced ⁸⁶Rb⁺ efflux yet described but is relatively weak as an inhibitor of P1075-mediated vasorelaxation. The opposite vascular actions of torasemide and U-37883A are expected to contribute to the renal effects of these drugs. Received: 28 January 1998 / Accepted: 20 April 1998     

Inhibition of acetylcholinesterase by dibenamine and dibenzyline

Dibenamine and dibenzyline are irreversible inhibitors of acetylcholinesterase (AChE). Kinetic studies show that at pH 9.5 a fast reaction occurs between a group on the enzyme with pK_a 9.1 and the ethyleniminium ion derived from the inhibitor. Either the ε-amino-group of a lysine residue is alkylated or else a lysine residue catalyses the alkylation of a non-ionisable group (e.g. hydroxyl). At pH 6.5 there is a slow reaction between a carboxyl anion on the enzyme and the ethyleniminium ion. Studies of the alkylation reactions in the presence of the reversible competitive inhibitor of the enzyme, tetramethylammonium ion, show that alkylation occurs at some distance from the anionic site and probably on the borders of the active site.     

Interaction of BKCa channel modulators with adrenergic agonists in the rat aorta is influenced by receptor reserve

Our main objective was to study the interaction of BKCa channel modulators with adrenergic agonists UK 14304 and noradrenaline (NA), acting on alpha1-adrenoceptors, in the rat aorta and how this is affected by receptor reserve. NA and UK 14304 evoked concentration-dependent contractions of the rat aorta. UK 14304 was a partial agonist relative to NA in this preparation. The BK(Ca) channel blocker tetraethylammonium (TEA, 1 mM) and opener NS 1619 (3 x 10(-5) M) modulated NA- and UK 14304-induced contractions, and were more effective on UK 14304-induced contractions. TEA (1 mM) increased the maximum response to NA and UK 14304 by about 13% and 300%, respectively, while NS 1619 (3 x 10(-5) M) reduced the maximum response to UK 14304 by about 81% compared to 31% for noradrenaline. The effect of TEA on the noradrenaline concentration-response curve was increased after treatment of the aorta with phenoxybenzamine (PBZ), an irreversible alpha1-adrenoceptor antagonist, to reduce receptor reserve. We concluded that the interaction of BKCa channel modulators with alpha1-adrenergic agonists in the rat aorta was influenced by receptor reserve.     

Reduction by pretreatment with dibenamine of hepatotoxicity induced by carbon tetrachloride, thioacetamide or dimethylnitrosamine

Pretreatment with dibenamine (25 mg/kg sc 48 and 24 hr before the administration of a hepatotoxic agent) protected rats against the hepatotoxicity of CCl₄, thioacetamide, or dimethylnitrosamine, but not against allyl alcohol or bromobenzene. Protection was evident from reduced activity of plasma glutamic-pyruvic transaminase and reduced liver necrosis as demonstrated by histologic evaluations. In rats pretreated with dibenamine, LD50 values for CCl₄ and thioacetamide were elevated and liver triglycerides after CCl₄ and dimethylnitrosamine were reduced. Dibenamine protection against hepatotoxicity did not correlate with alpha-adrenergic receptor blockade. Similar pretreatment with 3 other alpha-adrenergic blocking agents, tolazoline, phenoxybenzamine, and EEDQ (N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline), failed to protect rats against CCl₄-induced hepatotoxicity.     

The interaction of penicillins with phospholipids

The interaction of the antibiotics, penicillin G and ampicillin, with sonicated sols of phosphatidylcholine, lysophosphatidylcholine, phosphatidylethanolamine, phosphatidylinositol and phosphatidylserine has been examined by Sephadex gel nitration and dynamic dialysis. Nuclear magnetic resonance spectroscopy provided evidence of a predominantly hydrophobic interaction between the antibiotics and the phospholipids, phosphatidylserine and phosphatidylcholine. Confirmation of hydrophobic interaction was provided by a rheological investigation of the effects of urea and guanidine hydrochloride on the antibiotic-phospholipid complex. Penicillin G was found to interact to a greater degree than ampicillin, a result which is of interest in the light of present knowledge of in vivo activity of these antibiotics.     

NMR-Studies on the molecular basis of drug-induced phospholipidosis—II. Interaction between several amphiphilic drugs and phospholipids

NMR binding measurements have been performed in order to analyze the molecular mechanism underlying the drug-induced phospholipidosis. The dependency of the T₂ relaxation rates of the various spin systems of the drug molecules on structure, type of lipid, concentrations of interacting species, and ionic strength has been evaluated. Increasing lipophilicity is correlated with an increase in binding for this type of amphiphilic drugs. The degree of signal broadening is determined by the ratio of drug/lipid concentration. Strong interaction occurs with phospholipids, like phosphatidylcholine or phosphatidylethanolamine, whereas less polar lipids, like diacylglycerole or digalactosyldiglyceride, show no interaction with the drugs. Cholesterol antagonizes the phospholipid/drug interaction.     

Reversal by pronethalol of dibenamine blockade: A study on the seminal vesicle of the guinea-pig

1. The guinea-pig seminal vesicle has been shown to be a very suitable test object for the study of mechanisms involving alpha-adrenoceptive receptors, because no beta-receptors were found in this preparation.2. Adrenaline, noradrenaline and phenylephrine were directly acting agonists, their ED50 values being 7.1 x 10(-6)M, 1.5 x 10(-5)M and 2.7 x 10(-5)M, respectively.3. Pretreatment with reserpine had no influence on the contractions caused by adrenaline, noradrenaline and phenylephrine but abolished or greatly reduced the contractions caused by dopamine. Cocaine enhanced the effects of adrenaline, noradrenaline and phenylephrine and reduced those of dopamine.4. Pronethalol (6.8 x 10(-5)M) reversed the alpha-receptor blockade by dibenamine, ergotamine and phentolamine of responses to adrenaline, noradrenaline and phenylephrine; it did not affect the blockade by dibenamine of responses to histamine.5. Reversal of the blockade by dibenamine was observed only when its concentration was such that it caused a parallel shift of the dose-effect curves of the agonists to the right; higher concentrations, which caused an unsurmountable depression of the maximal contraction, were not antagonized by pronethalol.6. It is assumed that the reversal is dependent on a direct action on alpha-receptors, "spare receptors" being probably involved.     

Radiospectroscopic research on the interaction of the pyrazole molecule with phospholipids

By using the NMR spectroscopy it was shown that hydrogen bond is formed during the interaction between pyrazole molecule and iecithin. The hydrogen bond formation is probably one of the manifestations of the biological activity of pyrazole.     

Inhibition of cholecystokinin response in the gallbladder by dibenamine and its protection by benzodiazepines

The contractile response of the guinea-pig gallbladder to cholecystokinin (CCK) and acetylcholine (ACh) was irreversibly inhibited by 5 X 10(-5) M dibenamine, and the dibenamine-induced inhibition in the CCK response was prevented by 10(-4) M chlordiazepoxide (CDP) and diazepam (DZP), but not by 10(-2) M proglumide or 10(-6) M atropine. The dibenamine-induced inhibition in the ACh response was prevented by 10(-6) M atropine, but not by 10(-4) M CDP. These findings suggest that the binding of CCK to the CCK receptor can be inhibited by benzodiazepines.