Pharmacological profile of mifentidine: a novel H2-receptor antagonist

Genome-wide association study of intracranial aneurysms identifies 17 risk loci and genetic overlap with clinical risk factors

Rupture of an intracranial aneurysm leads to subarachnoid hemorrhage, a severe type of stroke. To discover new risk loci and the genetic architecture of intracranial aneurysms, we performed a cross-ancestry, genome-wide association study in 10,754 cases and 306,882 controls of European and East Asian ancestry. We discovered 17 risk loci, 11 of which are new. We reveal a polygenic architecture and explain over half of the disease heritability. We show a high genetic correlation between ruptured and unruptured intracranial aneurysms. We also find a suggestive role for endothelial cells by using gene mapping and heritability enrichment. Drug-target enrichment shows pleiotropy between intracranial aneurysms and antiepileptic and sex hormone drugs, providing insights into intracranial aneurysm pathophysiology. Finally, genetic risks for smoking and high blood pressure, the two main clinical risk factors, play important roles in intracranial aneurysm risk, and drive most of the genetic correlation between intracranial aneurysms and other cerebrovascular traits.

Inhibitory effects of H2-receptor antagonists on cytochrome P450 in male ICR mice

1. The present study was undertaken to examine the effects of H2-receptor antagonists including newly developed mifentidine derivatives, IY-80843 and IY-80845, on cytochrome P450(P450) in vitro and in vivo. 2. Initially, 3-methylcholanthrene-, phenobarbital-, ethanol- and dexamethasone-induced liver microsomes were prepared from male ICR mice to study in vitro effects of above chemicals on ethoxyresorufin O-deethylase(EROD), pentoxyresorufin O-dealkylase(PROD), p-nitrophenol hydroxylase and erythromycin N-demethylase(ERDM) activities, respectively. It was found that histamine, cimetidine and famotidine were not inhibitory to four enzyme activities. Meanwhile, mifentidine slightly inhibited EROD and PROD activities and its derivatives IY-80843 and IY-80845 strongly inhibited PROD, EROD and ERDM activities. 3. Prolongation of hexobarbital-induced sleeping time was determined in male ICR mice to confirm in vitro inhibitory effects of mifentidine and its derivatives in vivo. It was observed that cimetidine, mifentidine, IY-80843 and IY-80845 caused dose-dependent increases in the sleeping time, indicating the inhibition of P450 responsible for hexobarbital metabolism. 4. It was concluded that mifentidine and its derivatives are P450 inhibitors and that our newly synthesized IY-80843 is most inhibitory. 5. The present results indicate that mifentidine and its derivatives not only antagonise the H2-receptor but also inhibit P450 enzymes.

Mechanism of action of H2-antagonists on histamine- or dimaprit-stimulated H2-receptors of spontaneously beating guinea-pig atrium

Cimetidine, ranitidine and famotidine are antagonists of the histamine H2-receptors on the spontaneously beating right atrium of the guinea pig. When analyzed by the classical Schild method their pA2-values are respectively: 6.3, 6.8 and 7.7 with dimaprit as agonist and 5.8, 6.5 and 7.7 with histamine as agonist. Radioligand-displacement studies with [3H]-tiotidine as radioligand resulted in pKd values for cimetidine, ranitidine and famotidine of 6.3; 6.9 and 8.2 respectively. In dimaprit-stimulated atria all antagonists added at concentrations above their Kd values depressed the maximal increase in frequency. In the presence of histamine this effect was much less pronounced and only visible at concentrations of ranitidine and famotidine around 10.Kd. The rightward shift of the curves as well as the decrease in Emax are reversible but the dissociation constants of the antagonists are small (less than 10(-3) s-1). The spontaneously beating right atrium showed receptor reserve for histamine and virtually no receptor reserve for dimaprit. The results have been interpreted in a model in which H2-antagonists act mainly by competing with the agonist for the histamine receptor site but have in addition a distinct affinity for a secondary site on the receptor. Occupation of this site by the antagonist prevents building up of the stimulus elicited by the agonist and thus decreases the Emax. In systems with receptor reserve (histamine) the effect of antagonist binding to the secondary binding site is seen only at high concentration of antagonist while in absence of receptor reserve (dimaprit) the depression of Emax is directly visible. Simulations of the model show that the affinity of this secondary binding site is 50-(famotidine) to 100-(cimetidine and ranitidine) fold lower than for the agonist binding site.

Pharmacokinetics of mifentidine after single and multiple oral administration to healthy volunteers

1. The pharmacokinetics of mifentidine, a new long acting histamine H2-receptor antagonist, were studied using two protocols. 2. In one study, on 5 different days six normal male subjects were given 2.5, 5, 10, or 20 mg mifentidine or placebo orally 60 min before starting a 3 h continuous gastric aspiration during which time blood samples were taken for measurement of mifentidine concentration. 3. The area under the curves of mifentidine plasma levels (AUC) vs time for the four doses was linearly related to the dose for each individual subject (r = 0.972, P less than 0.001). After doses of 2.5, 5, 10 and 20 mg, mifentidine reduced hydrogen ion output by respectively 36, 37, 60 and 75% and secretory volume by 1, 17, 40, and 47%. The effects at the two highest doses were statistically significant. AUC was correlated positively with the percentage reduction in hydrogen ion output (r = 0.802, P less than 0.001) and volume (r = 0.834, P less than 0.001) over a 3 h period. 4. In the second study, the pharmacokinetics were evaluated after once-daily treatment for 14 days in seven subjects given 10 mg and in seven others subjects given 20 mg. 5. After multiple dosing, renal clearance was similar for the two doses (11.6 +/- 2.11 l h-1 for the low dose and 17.0 +/- 2.0 l h-1 for the high dose). Plasma half-life (t1/2 lambda 2) was 16.0 +/- 3.0 h after the 10 mg dose and 11.9 +/- 1.2 h after 20 mg.(ABSTRACT TRUNCATED AT 250 WORDS)

Action of mifentidine on the secretory response to sham feeding and pentagastrin and on serum gastrin in duodenal ulcer patients

A study has been done in 10 duodenal ulcer patients of the effect of a single oral dose of 10 mg mifentidine on the acid and pepsin responses to sham feeding after 1 h 30 min and to pentagastrin after 4 h 15 min. The study followed a double-blind, randomized, placebo-controlled, cross-over design. Gastric juice was collected for 5 h 15 min after treatment. Blood was sampled for up to 3 h 30 min to determine the effects of mifentidine on serum gastrin. Mifentidine suppressed basal acid output by 77% and sham feeding-stimulated acid output by 71% vs the placebo values. Pentagastrin-stimulated acid output was inhibited by 30% throughout the pentagastrin infusion. The suppressant effect of the drug on pepsin output was not as marked as on acid secretion. Mifentidine did not affect the serum gastrin level during the basal and sham feeding phases. No untoward effects were reported by the patients. The results show that 10 mg mifentidine p.o. produced a large reduction in the acid output in response to sham feeding and pentagastrin without affecting the serum gastrin responses.

Evaluation of novel compounds interacting with H2-histamine receptors: effect on histamine-sensitive adenylate cyclase activity in guinea-pig gastric mucosa

The activity of a number of compounds belonging to the novel class of N-imidazolylphenyl-N'-alkyl-formamidines on histamine-sensitive adenylate cyclase was evaluated. All substances inhibited histamine-dependent adenylate cyclase activation. The compounds which were investigated in a wider concentration range, i.e. DA 4360, DA 4577, and DA 4626, behaved as simple competitive antagonists, yielding apparent KB values comparable with those estimated in conventional H2-receptor assays. These results provide further evidence for the highly selective H2-receptor antagonism of these new molecules, and confirm the suitability of the histamine-stimulated adenylate cyclase assay in guinea-pig gastric cells as a functionally reduced system for the study of H2 antagonists.