Enantiomers of indacrinone: a new approach to producing an isouricemic diuretic

Cochlear effects of indacrinone are not altered by penicillin

Indacrinone is a loop diuretic structurally related to ethacrynic acid. Indacrinone is a racemic mixture. Previous studies have shown that the (-) enantiomer caused reduction of endocochlear potential (EP) and elevation of compound action potential (CAP) threshold (Rybak and Whitworth, 1987a). It has been demonstrated that organic acids such as penicillin, probenecid and sodium salicylate prevent the reduction of EP normally observed after furosemide administration (Rybak et al., 1992a). The present study was designed to determine whether penicillin pretreatment could prevent changes in EP and CAP threshold in (-)-indacrinone treated chinchillas. Adult chinchillas were anesthetized with ketamine and pentobarbital. A microelectrode was advanced into the scala media using the round window approach, and CAP responses to clicks were measured. One group was treated with (-)-indacrinone 100 mg/kg via the jugular vein. A second group of animals received penicillin 50 mg/kg i.v. thirty minutes before (-)-indacrinone. The mean EP change in the indacrinone-treated animals was 38.38 +/- 19.32 millivolts (mv). The reduction of EP in the group receiving penicillin was 24.43 +/- 20.74 mv (P > 0.09). The mean CAP threshold changes in animals receiving indacrinone was 20 +/- 14.14 dB whereas those pretreated with penicillin showed a threshold shift of 21.43 +/- 20.35 dB (P > 0.05). These findings are consistent with previous studies which showed that the effect of ethacrynic acid on the EP and CAP was not changed by the pretreatment with penicillin (Rybak et al., 1990).

Comparative acute ototoxicity of loop diuretic compounds

A microelectrode was used to measure endocochlear potentials (EP) in adult chinchillas and to study the effects of a series of loop diuretics. EP was measured before, during and for several hours after the intravenous injection of the following loop diuretics: furosemide, piretanide, bumetanide, ethacrynic acid, indacrinone stereoisomers and ozolinone. The first four loop diuretics caused a substantial dose-related reduction of EP. The (-) isomer of indacrinone was found to cause a dose-related reduction of EP to a moderate degree. The (+) isomer of indacrinone and ozolinone caused very little change of EP, even in very high doses. Findings are consistent with data on the mechanism of action of these agents in the kidney.

Determination of the optical purity of indacrinone by proton nuclear magnetic resonance spectroscopy using chiral lanthanide chelates

A simple, specific and reliable 1H-NMR spectroscopic method for the quantitative determination of the optical purity of indacrinone is described. After conversion of the S(+)- and R(-)-enantiomers to their methyl ester derivatives, they were coordinated with chiral europium(III) or praseodymium(III) shift reagents in CCl4/C2HCl3 (2:1). The optical purity was calculated from the relative intensities of the enantiomeric resonance signals for the protons of the methyl groups at position C(2) of the indanone ring. Mean +/- SD (n = 6) recoveries of S(+)-indacrinone from synthetic enantiomeric mixtures amounted to 99.75 +/- 0.63% when using europium(III) and 100.01 +/- 0.55% when using praseodymium(III).

Ototoxicity of indacrinone is stereospecific

Indacrinone (MK-196) is a loop diuretic which consists of a racemic mixture. The purpose of this study was to evaluate the individual enantiomers in the chinchilla model to determine whether these compounds affect auditory function and whether a difference in ototoxic potency exists. Very little change of endocochlear potential (EP) or compound action potential (CAP) was noted in animals receiving the (+)-enantiomer. On the other hand, chinchillas injected with the (-)-enantiomer were found to have a dose related reduction in both CAP and EP. These findings suggest the possibility that the diuretic receptor in the kidney and the receptor mediating ototoxicity in the cochlea, may have similar steric requirements for interacting with loop diuretics.

Antihypertensive and biochemical effects of indacrinone enantiomers

The enantiomers of indacrinone (I), an investigational loop diuretic, have different pharmacologic activity. The (-) enantiomer is natriuretic, and the (+) enantiomer is uricosuric. To determine the antihypertensive effects and an isouricemic ratio of indacrinone enantiomers, 37 patients with sitting diastolic blood pressure (BP) between 90 and 104 mm Hg, after a 4-week placebo washout, randomly received one of the ratios of I enantiomers, namely -2.5/+80 mg (A), -5/+80 mg (B), -10/+80 mg (C) or placebo (P), once daily for 12 weeks in a double-blind, parallel study. The mean reductions (baseline-end of treatment) in BP of 23/8, 20/10 and 25/10 mm Hg with treatments A, B and C respectively were greater (p less than 0.01) than that on P (0/3). Initially, serum uric acid decreased with treatments A and B but not with C. Mean changes in serum uric acid were -0.3, -0.4, 0.2 and 0.3 mg/dl respectively with treatments A, B, C and P. The ratio of -10/+80 mg produced least variation in serum uric acid. Reduction in serum K+ and Cl- appeared to be dose related to (-) enantiomer. No serious adverse effects were reported. A 1:9 ratio of I enantiomers intended for wide-scale use as a diuretic also showed good antihypertensive activity, a favorable uric acid profile and absence of hepatic toxicity in 14 patients.