MK-447

Evidence for the O-sulfo derivative of MK-447 as active metabolite of MK-447

In contrast with furosemide (and other sulfamoylbenzoic and aryloxyacetic acids loop diuretics), MK-447 was unable to inhibit the [Na+,K+,Cl-] cotransport system in human red blood cells. Indeed, this compound was a very poor ion transport inhibitor (inactive on Ca(2+)-sensitive K+ channels, the Ca2+ pump, the Na+:Mg2+ exchange, the Na+:Li+ countertransport system and the [K+,Cl-] cotransport system, and only inhibiting the [Cl-/HCO3-] exchanger and the Na+,K+ pump at high concentrations). Conversely, its urinary metabolite (O-sulfo)-MK-447 was a very potent inhibitor of the [Na+,K+,Cl-] cotransport system (IC50 of 1.6 +/- 0.5 x 10(-6) M; mean +/- S.D. of four experiments). This compound was a much more potent [Na+,K+,Cl-] cotransport inhibitor than furosemide, and almost as active as bumetanide. In addition, (O-sulfo)-MK-447 was a moderate inhibitor of the [Cl-/HCO3-] exchanger (IC50 of 6 +/- 3 x 10(-5) M, n = 3), its potency being intermediate between that of xipamide and that of furosemide. Interestingly, it exhibited some inhibitory activity against Ca(2+)-sensitive K+ channels but only at high concentrations (it had no effect on the [K+,Cl-] cotransport system, the Ca2+ pump or the Na+:Mg2+ exchanger). The results suggest strongly that the O-sulfo derivative of MK-447 is an active natriuretic metabolite of MK-447. This metabolite may be responsible for the salidiuretic action of MK-447.

Effects of MK-447 on thrombin-induced aggregation, secretion of ATP, and [Ca2+]i mobilization in rabbit platelets

Aim: To study the effects of MK-447 on aggregation release reaction and intracellular calcium mobilization by thrombin.
Methods: Aggregation and release reaction were assessed by light transmission and ATP content in rabbit citrate platelet-rich plasma (PRP), and cytosolic-free calcium was measured by fluorescence and imaging.
Results: MK-447 (2-aminomethyl-4-t-butyl-6-iodophenol hydrochloride) induced a decrease in light transmission (DLT), so called platelet shape change, without detectable aggregation and secretion of ATP, and increased intracellular calcium concentration ([Ca2+]i) slightly in washed single platelet loaded with Fura 2, the peak value being about 160 nmol.L-1. These effects were not inhibited by egtazic acid 3 mmol.L-1 or indometacin 3 mumol.L-1. The pretreatment of PRP with MK-447 700 mumol.L-1 reduced the DLT by thrombin, potentiated and enhanced thrombin-induced aggregation and secretion of ATP in a concentration-dependent manner. Thrombin-induced [Ca2+]i mobilization (peak value: 369 +/- 45 nmol.L-1) was further enhanced by the administration of MK-447 at 2 min before the addition of thrombin, and the peak value reached 623 +/- 121 nmol.L-1 (P < 0.01).
Conclusion: MK-447-induced platelet shape change was involved in intracellular calcium release in this preparation. MK-447 enhanced thrombin-induced aggregation and release reaction and these effects of MK-447 on aggregation and release reaction by thrombin might result from the synergistic effect of intracellular calcium mobilization.

Effects of 2-aminomethyl-4-t-butyl-6-iodophenol (MK-447) on granulomatous inflammation: lack of correlation with changes in levels of prostaglandin-like material

MK-447, administered locally to carrageenan-soaked sponges implanted in the backs of rats, either on the day of implantation (day 1) or on days 4-7, exhibited a weak, dose-related inhibition of subsequent granuloma formation. With the later treatment period, prostaglandin (PG)-like material in day 8 exudates was increased at all doses, but with MK-447 treatment on day 1, levels of PG-like material after 24 h were unaffected. Thus, inhibition of granuloma formation was unrelated to local levels of PG-like material. Following treatment with low doses of MK-447 on implantation, mononuclear cell counts in 24 h exudates were reduced. Similar results were obtained with PGE1. Higher doses of MK-447 did not alter monuclear cell counts, but both high and low doses of MK-447 markedly increased polymorphonuclear cell counts in 24-h exudates. The results do not permit the conclusion that the anti-granuloma action of MK-447 is necessarily related to alteration of stable PG level at the inflamed site. Therefore, MK-447 cannot be used unequivocably as a tool to investigate the role of endogenous stable PGs during granulomatous inflammation.

Dual effects of a basic anti-inflammatory agent, 2-aminomethyl-4-t-butyl-6-iodophenol hydrochloride (MK-447), on biosynthesis of prostaglandin endoperoxides

Effects of MK-447 on prostaglandin (PG) endoperoxide formation from arachidonic acid by bovine seminal vesicle microsomes in the presence of cofactors (hemoglobin and tryptophan) were studied by cascade superfusion on rabbit aorta and mesenteric artery and rat stomach and colon. In the presence of hemoglobin (0.2 muM), MK-447 (up to 30 muM) accelerated PG endoperoxide formation, as tryptophan did, whereas higher concentrations of MK-447 lost the acceleration effect and finally inhibited the PG endoperoxide formation. Increased concentration of hemoglobin (2 muM) shifted the dose of MK-447 for peak generation from 30 to 100 muM. Thus, MK-447 shows dual action, acceleration and inhibition, on the PG endoperoxide formation.

Diuretic and haemodynamic effects of MK 447 in normotensive and hypertensive sheep

The short term effects of the novel diuretic MK 447 were examined in both normotensive and hypertensive (ACTH treated) conscious sheep. The drug had profound diuretic, natriuretic and kaliuretic effects in both groups. Plasma sodium was unchanged but plasma potassium fell and haematocrit increased. Plasma renin concentration increased with MK 447 in the normotensive but not the hypertensive sheep. In the normotensive sheep cardiac output fell, peripheral resistance increased and blood pressure was unchanged. In the hypertensive ACTH treated sheep cardiac output and blood pressure fell but resistance was unchanged.