Pharmacokinetics of the PDGF-antagonist trapidil in patients with and without renal impairment

The pharmacokinetics of the PDGF-antagonist trapidil and its major metabolite desethyl-trapidil (M 1) were studied in patients with and without renal failure after a single dose of 200 mg and following 4-day treatment with 200 mg t.i.d. Twenty patients were classified according to their renal function as assessed by creatinine clearance (C(Cr)) in group A: 133.7 +/- 30.3 ml/min (n = 8), group B: 63.6 +/- 15.4 ml/min (n = 6) and group C: 17.9 +/- 6.1 ml/min (n = 6), patients on hemodialysis were not enrolled. After the first dose maximal plasma concentrations of trapidil with 5.99 +/- 1.60 (A), 5.76 +/- 1.46 (B) and 5.63 +/- 1.53 micrograms/ml (C) were not different between groups, but somewhat lower on day 4 with 4.96 +/- 0.78 (A), 5.78 +/- 1.78 (B) and 5.47 +/- 1.42 micrograms/ml (C). Similarly, AUC0-infinity-values on day 1 with 16.9 +/- 4.8 (A), 20.2 +/- 6.7 (B) and 22.2 +/- 11.2 micrograms/ml x h (C) showed only modest (NS) differences between groups, but decreased markedly on day 4 to 10.8 +/- 1.8 (A), 13.6 +/- 5.8 (B) and 14.4 +/- 4.3 micrograms/ml x h (C). Linear regression analysis between AUC and C(Cr) demonstrated no relationship between these parameters. For plasma concentrations of M 1 no significant differences were seen between groups. At steady state maximal plasma concentrations of M 1 occurred earlier and were slightly increased. In one patient (group B) receiving tamoxifen comedication markedly elevated plasma concentrations of trapidil and desethyltrapidil occurred, suggesting a pharmacokinetic interaction. Trapidil may be safely given to patients with impaired renal function, the apparent decrease of trapidil plasma concentrations may suggest autoinduction of metabolizing enzymes.

Zinc, cadmium, and mercury complexes of 5,7-dimethyl-[1,2,4]triazolo[1,5-a]pyrimidine (dmtp). Preparation, spectroscopic characterization, and biological activity. X-ray crystal structures of [Zn(dmtp)2Br2], [Hg(dmtp)2Cl2], and [Hdmtp]2[CdBr4]. 2H2O

The preparation and spectroscopic characterization of a series of dmtp complexes of Zn, Cd, and Hg, where dmtp is 5,7-dimethyl[1,2,4]triazolo[1,5-a]pyrimidine, is reported. Crystal structure analyses of [Zn(dmtp)2Br2] and [Hg(dmtp)2Cl2] reveal distorted tetrahedral geometries about the central atoms and the dmtp ligands to coordinate via the N(3) atom exclusively. In the X-ray structure of [Hdmtp]2[CdBr4].2H2O, the [Hdmtp]+ cation is protonated at the N(3) atom, there being no significant interaction between Hdmtp and cadmium. A study of the antimicrobial activity of the complexes shows that the [Cd(dmtp)X2(OH2)] (X = Cl, Br) compounds display activity against two strains.

Influence of trapidil and derivatives on cholesterol synthesis and esterification in cultured cells

The effect of trapidil (Rocornal) and its derivatives AR 12456 and AR 12463 on endogenous cholesterol synthesis and on cholesterol esterification rate was studied in human skin fibroblasts (HSF), in human hepatoma cell line Hep G2 and in primary culture of peritoneal macrophages from mouse (PMM). The cholesterol esterification rate was not influenced by the drugs in the tested cell lines. The incorporation of [14C]acetate into cholesterol in HSF was inhibited by AR 12463 and AR 12456, but not by trapidil. The inhibitory potency of AR 12456 in HSF was enhanced after preincubation of the drug with Hep G2 and removal of the medium to HSF, suggesting that the formed metabolite(s) are more potent inhibitors than the parent substance. The metabolite(s) formed seem(s) to influence the first steps in the endogenous formation of cholesterol, because the incorporation of [14C]mevalonate into cholesterol was not significantly inhibited. These findings suggest that the demonstrated inhibition of the endogenous cholesterol synthesis by AR 12456, especially after transformation into a probably more active substance(s), together with the recently described enhanced expression of LDL receptors in Hep G2 cells may partially explain the hypocholesterolaemic activity of AR 12456.

The trapidil derivative AR 12456 protects against serum hyperlipidemia in guinea pigs

The administration of the trapidil derivative AR 12465 (5 mg/kg body weight) intraperitoneally to hypercholesterolemic guinea pigs caused a stronger reduction in serum total cholesterol (TC) than trapidil (20 mg/kg, i.p.) or a vehicle injection (saline with 5% ethanol i.p.). The stronger reduction of TC is caused by a lower level in the sum of all beta-migrating lipoproteins and an enhanced level of high-density lipoprotein. The levels of free and esterified cholesterol were not changed in kidney and left cardiac ventricle, but significantly enhanced (P less than 0.05) in the liver of all groups fed a cholesterol-rich diet. The elevation in liver cholesterol was higher in the group treated with AR 12456 than in the group treated with trapidil or with vehicle. The treatment with AR 12456 diminished the ratio TXB2/6-keto-PGF1 alpha for the capacity of aorta to form these prostanoids. In conclusion, our data show that AR 12456 has a strong antilipidemic action in guinea pigs fed a cholesterol-rich diet.

[Biotransformation of the trapidil (rocornal) derivative AR 12463 in the rat]

After p.o. administration of 5-piperidino-7-[N-pentyl-N-(beta- hydroxyethyl)]amino-s-triazolo[1,5-a]pyrimidine (1; AR 12463) more than 15 metabolites were isolated from urine and feces of male Wistar rats. Only small amounts of unchanged 1 were observed. The structure of 12 metabolites was elucidated or proposed on the basis of UV-, 13C NMR- and mass spectra. Main metabolites are 5-piperidin-4'-olyl-7-[N-pentyl-N-(beta- hydroxyethyl)]amino-s-triazolo[1,5-a]pyrimidine and 5-piperidin-4'-olyl-7-[N-pent-4-olyl-N-(beta-hydroxyet hyl)]amino-s- triazolo[1,5-a]pyrimidine. The other metabolites are mainly hydroxy- or ketopentyl derivatives and piperidinoles or piperidinones, respectively. Conjugates of most of the metabolites were identified, but the ratio phase-I/II metabolites was about 3:1. In contrast to trapidil, 5-methyl-7-diethylamino-s- triazolo[1,5-a]pyrimidine, no hydroxy derivatives of the bicyclic system were observed. The major part of unchanged 1 and metabolites is excreted via kidneys.

Trapidil derivatives and low density lipoprotein metabolism by human skin fibroblasts and by human hepatoma cell line Hep G2

The effect of trapidil (RocornalR) and some of its newly developed derivatives (AR 12456, AR 12463, AR 12465, AR 12464) on the receptor-mediated low density lipoprotein (LDL) binding, uptake and degradation was studied in human skin fibroblasts (HSF) and in human hepatoma cell line Hep G2. Compound AR 12456 influenced this pathway in a selective way: it enhanced the uptake and degradation of 125I-LDL by Hep G2 cells in a dose-dependent manner, but inhibited it in HSF. Scatchard analysis of the saturable LDL binding in Hep G2 indicates that the effect of compound AR 12456 is the result of an increased number of LDL binding sites. Compound AR 12465 was less effective on LDL catabolism. Trapidil and the other derivatives were inactive under the same experimental conditions. When Ar 12456 was preincubated with Hep G2 cells and then the incubation medium was transferred to HSF, a stimulation of specific LDL pathway occurred also in this cell line. These findings suggest that a metabolite(s) of AR 12456 might be responsible for the enhanced expression of LDL receptors in cultured human cells.

Effects of trapidil-derivatives on calcium channel currents in isolated ventricular cells from mice

A single glass micropipette voltage clamp technique with intracellular dialysis was used to study the effects of the trapidil derivatives AR 12-456 and AR 12-463 on Ca channel currents carried by Ba2+ in isolated ventricular cells from mice hearts. Inspite of a more potent inhibition of the cAMP phosphodiesterase from heart (Bartel et al. 1985) a reversible Ca channel blocking action of both compounds could be observed. The concentration of half maximal block was calculated to about 50 mumol/l for both derivatives tested. Neither a shift in the current-voltage relationships nor a significant change in the potential for half maximal activation was found. The maximal Ba2+-conductance was reduced. The steady state inactivation was shifted towards more negative potentials by application of 100 mumol/l AR 12-463. The decay of the Ba currents was accelerated in the range of the applied test potentials between -20 and +20 mV. It is concluded that the new trapidil derivatives with more potent inhibitory action on cardiac phosphodiesterase than trapidil can block myocardial Ca channels.

Inhibition of thromboxane B2 formation of blood platelets by trapidil and other s-triazolo(1,5-a)pyrimidine derivatives

Trapidil and some other 5,7-disubstituted s-triazolo(1,5-a)pyrimidine derivatives (TPDs) which were shown to have potent actions against platelet aggregation also inhibited in vitro platelet thromboxane A2 (TXA2) biosynthesis in clotting human and rabbit whole blood as well as in arachidonic acid-activated platelet-rich human plasma. The inhibitory potency of TPDs on TXB2 formation paralleled the antiaggregatory effectiveness to a certain extent and decreased in the following order: AR 12456 greater than AR 12463 approximately AR 12464 approximately AR 12465 greater than trapidil. When TPDs were administered orally to rabbits and blood was taken 2 hours later, no changes of serum TXB2 level were observed. After i.v. injection of TPDs in rabbits, the most active TPDs AR 12456 and AR 12463 led to a short-lasting reduction of serum TXB2 by 61.4 and 49.4% resp.. The TXB2 levels returned nearly to pre-treatment level after 80 min. The possibility is discussed that TPDs mainly prevent platelet TXA2 formation by inhibiting phosphodiesterase activity.

Inhibition of thromboxane A2 production by trapidil and trapidil derivatives in the arachidonic acid-injected rat

Trapidil and four selected 5,7-disubstituted s-triazolo (1,5-a)pyrimidine derivatives (AR 12456, AR 12463, AR 12464, AR 12465) which have already been shown to possess inhibitory effects on arachidonic acid(AA)-induced aggregation and thromboxane A2(TXA2) formation in human and rabbit platelets in vitro diminished the AA-stimulated TXA2 production in murine blood in vivo. The inhibitory effects of the derivatives were generally stronger than those of trapidil. The strongest inhibitor of TXA2 formation was the derivative AR 12456. These in vivo results correspond well with our previous in vitro findings.

[Thromboxane A2 antagonistic effect of antiangina drugs, with special reference to trapidil and trapidil derivatives]

In isolated perfused guinea pig hearts and in the cardiocirculatory system of anaesthetized rabbits the thromboxane A2-agonist U 46619 shows cardiodepressive effects. The contraction force of isolated auricle preparations from guinea pigs was enhanced. Antianginous drugs (dipyridamole, propranolol, verapamil, nitroglycerin and trapidil) induced a significant inhibition of the U 46619 effects. Oxyfedrine remained ineffective. The efficiency of some derivatives of trapidil was markedly diminished or abolished in comparison with the original substance. Because of the different chemical structure of the active drugs the TXA2-antagonism is regarded to be caused by a functional influence on the cellular membrane and the calcium transport. Nevertheless the inhibition of the TXA2-effects by antianginous drugs seems to be a factor for the therapeutic use of these substances.

Gas chromatographic evaluation of trapidil and its desethyl metabolite in biological fluids for pharmacokinetic and bioavailability investigations

This paper describes a suitable and cost-saving method for quantitative analysis of trapidil (5-methyl-7-diethylamino-s-triazolo [1,5-a]pyrimidine) and its desethyl metabolite in plasma and urine for pharmacokinetic and bioavailability investigations. Trapidil and desethyl-trapidil were extracted from plasma, concentrated and injected into the gas chromatography without any derivatization process. The authors suggest a series of internal standards. A thermoionic specific detector enables high sensitivity to be achieved, i.e. 20 ng/ml, and good specificity. The method is cost-saving in that it allows about 30 analyses a day to be performed without automatic integrators, and about 50 analyses a day with these integrators.

[The effectiveness of trapidil and trapidil derivatives on drug-induced heart arrhythmias in the rat and guinea pig]

Trapidil and some selected derivatives of trapidil were investigated in ouabain induced arrhythmia in guinea-pigs and in aconitine induced arrhythmia in rats. In both models trapidil exerted a marked antiarrhythmic effect. Investigations on ouabain induced arrhythmia showed that three derivatives were more effective than trapidil concerning the threshold for premature ventricular beats and flutter. One derivative only was able to decrease the sensitivity for fibrillation in the same order of magnitude as trapidil. On aconitine induced arrhythmia all derivatives of trapidil were less effective in elevating the threshold of arrhythmia than trapidil itself, but three derivatives showed antiarrhythmic properties.

[The effectiveness of trapidil and some derivatives on heart function under in vitro and in vivo conditions]

Cardiac and coronary effects of trapidil (Rocornal) and some derivatives were investigated in isolated heart preparations and rabbit hearts in vivo. All substances showed a comparable increase of the coronary flow. Contrary to the cardiotonic influence of trapidil the trapidil derivates induced a negative inotropic effect, possibly due to a weak calcium antagonism. Heart rate was slightly diminished, but in some cases higher doses caused an acute tachycardia. I.v. application of the substances to rabbits in doses of 10 mg/kg and 30 mg/kg induced an initial depression of blood pressure normalizing within 3-5 min. An increase of the myocardial prostacyclin biosynthesis is only demonstrable under trapidil. The results indicate that the cardiac effects of trapidil derivatives are possibly caused by a direct influence on the contractile system and the membrane potential of the cardiac muscle cell.

[The effect of trapidil and the trapidil derivative AR 12463 on blood pressure and thromboxane formation in spontaneously hypertensive rats]

The trapidil derivative AR 12463 has a much more stronger inhibiting effect than trapidil on different atherosclerotic parameters of the cell cultures obtained from normal intima and fatty streaks of human aorta, on thromboxane (TX) formation and on the aggregation of human platelets in vitro, and on the activity of phosphodiesterase. In addition to these present results, AR 12463 reduced significantly the mean arterial blood pressure of spontaneously hypertensive rats (at a dosage of 20 mg/kg/d administered orally for 2 weeks) in contrast to the same dosage of trapidil. Simultaneously, TX formation is significantly reduced in serum by 48% in aorta thoracica by 29%, and in aorta abdominalis by 19%. Due to these properties, AR 12463 seems to be suitable for a therapeutic and prophylactic strategy in chronic ischemic diseases.