Some organic acids attenuate the effects of furosemide on the endocochlear potential

Drug repurposing for cardiovascular diseases: New targets and indications for probenecid

The available pharmacological options in the management of cardiovascular diseases such as ischaemic heart disease and subsequent heart failure are effective in slowing the progression of this condition. However, the long-term prognosis is still poor, raising the demand for new therapeutic strategies. Drug repurposing is a time- and cost-effective drug development strategy that offers approved and abandoned drugs a new chance for new indications. Recently, drugs used for the management of gout-related inflammation such as canakinumab or colchicine have been considered for drug repurposing in cardiovascular indications. The old uricosuric drug, probenecid, has been identified as a novel therapeutic option in the management of specific cardiac diseases as well. Probenecid can modulate myocardial contractility and vascular tone and exerts anti-inflammatory properties. The mechanisms behind these beneficial effects might be related inhibition of inflammasomes, and to modulation purinergic-pannexin-1 signalling and TRPV2 channels, which are recently identified molecular targets of probenecid. In this review, we provide an overview on repurposing probenecid for ischaemic heart disease and subsequent heart failure by summarizing the related experimental and clinical data and propose its potential repurposing to treat cardiovascular diseases.

Ototoxicity in dogs and cats

A variety of drugs in veterinary use have side effects that can potentially damage the senses of hearing or balance in animals. A large body of literature exists on the incidence and mechanisms of ototoxicity in experimental animals and in humans, but little is documented in domestic dogs and cats. However, the generality of these adverse actions across species allows one to extrapolate and provide the veterinarian with insight into possible complications of chemotherapy.

Combined effects of salicylic acid and furosemide and noise on hearing

Background

A major cause of the hearing loss following exposure to intense noise involves release of free radicals resulting from the elevated metabolism. The free radicals induce damage to several of the components of the cochlear amplifier including the outer hair cells and indirectly to the transduction currents. Salicylic acid induces a reversible hearing loss since it binds to the motor protein prestin in the outer hair cells, reducing electromotility. Furosemide also induces a reversible hearing loss since it reduces the endocochlear potential which is a major component of the cochlear transduction currents. On the other hand, each of these drugs also provides protection from a noise induced hearing loss if they are injected just before a noise exposure, probably as a result of the decreased metabolism induced in their presence, with release of lower levels of free radicals. In this study, both drugs were administered in order to assess whether their protective effects would be additive.

Methods

The study was conducted on normal hearing albino mice of the Sabra strain. They were injected with either salicylic acid alone (N = 11), or furosemide alone (N = 14), or both together (N = 14), or with saline control (N = 11) and exposed to broad band noise for 3.5 hours. An additional group of 9 mice was injected with both salicylic acid and furosemide, but not exposed to noise. The degree of the resulting hearing loss was assessed by recording thresholds of the auditory nerve brainstem evoked responses to broad band clicks before the injections and noise, and 7, 14 and 21 days after.

Results

The noise induced hearing loss in the mice injected with salicylic acid alone or furosemide alone was smaller than in those injected with saline, i.e. these drugs provided protection, as in previous studies in this laboratory. There was no threshold elevation after two weeks in the mice injected with both drugs without noise exposure, i.e. the effects of the two drugs given together was reversible. On the other hand, there was a significant hearing loss (i.e. threshold elevation) in the group which received both drugs and was also exposed to noise, with mean threshold elevations of 38.8 ± 19.0 dB and 28.3 ± 11.7 dB 7 days after noise exposure.

Conclusions

This result is very surprising, if not paradoxical. Drugs which provide protection from a noise induced hearing loss when administered alone, not only do not provide protection when given together, but also induce a greater hearing loss when accompanied by noise. This observation may be related to the finding that the depression of the endocochlear potential normally caused by furosemide is reduced in the presence of salicylic acid, so that the protection usually provided by furosemide is not present when it is administered together with salicylic acid. Thus it seems that each drug may interfere with the protective action of the other when coupled with noise.

Auditory sensori-neural alterations induced by salicylate

Early after the development of aspirin, almost 150 years ago, its auditory toxicity has been associated with high doses employed in the treatment of chronic inflammatory diseases. Tinnitus, loss of absolute acoustic sensitivity and alterations of perceived sounds are the three auditory alterations described by human subjects after ingestion of large doses of salicylate. They develop over the initials days of treatment but may then level off, fluctuate or decrease, and are reversible within a few days of cessation of treatment. They may also occur within hours of ingestion of an extremely large dose. Individual subjects vary notably as to their susceptibility to salicylate-induced auditory toxicity. Tinnitus may be the first subjective symptom, and is often described as a continuous high pitch sound of mild loudness. The hearing loss is slight to moderate, bilaterally symmetrical and affects all frequencies with often a predominance at the high frequencies. Alterations of perceived sounds include broadening of frequency filtering, alterations in temporal detection, deterioration of speech understanding and hypersensitivity to noise. Behavioral conditioning of animals provides evidence for mild and reversible hearing loss and tinnitus, similar to those observed in humans. Anatomical examinations revealed significant alterations only at outer hair cell lateral membrane. Electrophysiological investigations showed no change in endocochlear resting potential, and small changes in the compound sensory potentials, cochlear microphonic and summating potential, at low acoustic levels. Measures of cochlear mechanical responses to sounds indicated a clear loss of absolute sensitivity and an associated broadening of frequency filtering, both of a magnitude similar to audiometric alterations in humans, but at extremely high salicylate levels. Otoacoustic emissions demonstrated changes in the mechano-sensory functioning of the cochlea in the form of decrease of spontaneous emissions and reduced nonlinearities. In vitro measures of isolated outer hair cells showed reduction of their fast motile responses which are thought to be at the origin of cochlear absolute sensitivity and associated fine filtering. Acoustically evoked neural responses from the eighth nerve to the auditory cortex showed reversible and mild losses of absolute sensitivity and associated broadening of frequency filtering. There is no evidence of a direct alteration of cochlear efferent innervation. Evidence was obtained for decreases in cochlear blood supply under control of autonomous innervation. Spontaneous neural activity of the auditory nerve revealed increases in firings and/or in underlying temporal synchronies. Similar effects were found at the inferior colliculus, mostly at the external nucleus, and at the cortex, mostly at the anterior and less at the secondary auditory cortex but not at the primary auditory cortex. These changes in spontaneous activity might underlie tinnitus as they affect mostly neural elements coding high frequencies, can occur without a loss of sensitivity, are dose dependent, develop progressively, and are reversible. Biochemical cochlear alterations are poorly known. Modifications of oxydative phosphorylation does not seem to occur, involvement of inhibition of prostaglandin synthesis appears controversial but could underlie changes in blood supply. Other biochemical alterations certainly also occur at outer hair cells and at afferent nerve fibers but remain unknown.

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).

Effects of organic acids on the edema of the stria vascularis induced by furosemide

Furosemide is a loop diuretic which is ototoxic. Investigations have shown the stria vascularis to be the target tissue of this ototoxic drug. The purpose of the present study was to investigate the effects of furosemide on the stria vascularis in chinchillas, in controls and in animals pretreated with the above organic acids. Control animals were injected with 0.5 ml alkalinized saline followed by furosemide IV 30 min later. Experimental animals received probenecid, penicillin or sodium salicylate IV. Thirty minutes later, furosemide was injected in the same dose as in the controls. The basal turn of the stria vascularis was rapidly removed at various times from 10 to 30 min after furosemide administration and processed for transmission electron microscopy. Control animals were found to have reversible edema of the stria vascularis. Experimental animals had variable findings. Those animals pretreated with penicillin had virtually no edema of the stria vascularis at any time. Salicylate and probenecid pretreated animals had significantly less edema from one to 10 min after furosemide injection, but more edema than controls at later times. These findings suggest a discrepancy between ultrastructural pathology and functional status of the cochlea in experimental animals pretreated with probenecid or sodium salicylate followed by furosemide. On the other hand, good structure function correlations were seen in controls and in experimental animals pretreated with penicillin.

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.

Organic acids do not alter the cochlear effects of ethacrynic acid

Previous studies have shown a reduction of the ototoxicity of furosemide in chinchillas pretreated with organic acid transport inhibitors. The current studies were designed to investigate whether such a protective effect could be observed in chinchillas receiving ethacrynic acid. Chinchillas weighing 400-600 g were injected with saline followed by ethacrynic acid 12.5 mg/kg i.v. (controls) or one of three organic acids (probenecid, penicillin G and or sodium salicylate) 50 mg/kg i.v., thirty minutes prior to ethacrynic acid injection (experimentals). Endocochlear potential (EP) and compound action potential of the eighth nerve (CAP) elicited by click stimuli were simultaneously monitored before and after injection in both groups. The mean change in EP and CAP findings are consistent with observations by other investigators of the actions of these loop diuretics in the isolated loop of Henle. In the latter tissues, the 'furosemide-like loop diuretics' appear to have a different mechanism of action than does ethacrynic acid. It appears from the findings of the present study that the actions of furosemide and ethacrynic acid on the cochlea are by different mechanisms as well.

Drug-induced ototoxicity. Pathogenesis and prevention

Ototoxicity is a disabling adverse effect of several widely used classes of drugs, such as diuretics, anti-inflammatory agents, antineoplastic agents and aminoglycoside antibiotics. High-dose therapy with either diuretics or anti-inflammatory agents is primarily associated with acute and transient impairment of hearing or tinnitus. In contrast, long term treatment with antineoplastic agents or aminoglycoside antibiotics is typically associated with delayed and irreversible loss of hearing; lesion in the organ of Corti include the destruction of auditory sensory cells. Vestibular function can also be compromised by ototoxic drugs. Occasional cases of ototoxicity have been reported for a variety of other therapeutic compounds and environmental toxins. In addition, the simultaneous administration of multiple agents which are potentially ototoxic can lead to synergistic loss of hearing. Exposure to loud noise may also potentiate the hearing loss due to cochleotoxic drugs. Ototoxic agents can impair the sensory processing of sound at many cellular or subcellular sites. However, the molecular mechanisms of ototoxicity have not been established for most of these drugs, and structure-toxicity relationships have not been determined. It has therefore been difficult to predict the ototoxic potential of new drugs, and rational approaches to the prevention of ototoxicity are still lacking. The clinical and experimental features of ototoxicity are reviewed for several classes of drugs, with an emphasis on current knowledge of the mechanism and the possibilities for the prevention of ototoxicity for each.

The time-course of furosemide-induced strial changes in guinea pigs after pretreatment with daltroban

It was shown previously (Ernst et al., 1989) that pretreatment of guinea pigs with a thromboxane (TX) receptor antagonist attenuates the decline of the endocochlear potential (EP) induced by furosemide. The present paper is aimed at investigating a possible correlation between the electrophysiological data and ultrastructural changes of the stria vascularis by electron microscopy. The dosages of 40, 60, and 80 mg/kg furosemide were injected after the pretreatment with the TX receptor antagonist daltroban and compared to controls which were injected with furosemide only. It was found at all furosemide concentrations that the strial changes 10 min after injection were nearly unchanged against controls. 30 min after furosemide injection, the most pronounced changes were seen when pretreating the animals: a clear reduction of the marginal cell swelling and edema in general were observed at 40 and 60 mg/kg furosemide. The guinea pigs injected with 80 mg/kg furosemide after pretreatment displayed nearly the same changes as controls.

Arachidonate metabolites change furosemide-induced cochlear potentials

Furosemide-induced changes of cochlear potentials were used as a model to study the influence of arachidonic acid metabolites on ion movements within the cochlea. No influence was exerted by the drugs Esculetin - blocking the synthesis of lipoxygenase products - and Dazoxiben - suppressing thromboxane A2 levels within the cochlea. A weakening of the furosemide-induced changes of the endocochlear potential was found when infusing the thromboxane (TX) receptor antagonists BM 13,505 and BM 13,177 before furosemide was given. This effect was also observed when pre-treating the guinea pig with a specific platelet-activating factor receptor antagonist, BN 52,021, before the diuretics was given. Summating potential and cochlear microphonics remained insignificantly changed against controls. The results suggest that a TX receptor contributes to the control of ion movements within the cochlea. A possible involvement of loop diuretics' receptors is discussed.

Quinine reduces noxious cochlear effects of furosemide and ethacrynic acid

Endocochlear potential (EP) and eighth nerve action potential (AP) were measured in chinchillas. We investigated the interaction of quinine with the loop diuretics furosemide and ethacrynic acid to determine whether the cochlear effects of these agents are attenuated by pretreatment with quinine. Animals were injected with either furosemide, 25 mg/kg intravenously (IV), or ethacrynic acid, 15 mg/kg IV. Control animals injected without pretreatment were found to have a large decrease in EP, with a decrease of compound action potentials (CAP) amplitude and an elevation of CAP threshold. Animals pretreated with quinine, 25 mg/kg, were found to have a significantly smaller reduction of EP and CAP amplitude following injection of either diuretic. No significant differences in urine volumes were noted between experimental and control groups. Quinine is known to cause nonspecific changes in the membranes of epithelial cells, which may cause alterations of the transport of organic anions by such tissues. Such an effect on epithelial cells in the cochlea may cause reduced uptake of loop diuretics in this organ, resulting in reduced toxicity.

Dazoxiben-induced changes in the thromboxane/prostacyclin balance in the lateral cochlear wall of the guinea pig

Dazoxiben, a thromboxane synthetase inhibitor, was infused i.v. in a first group of guinea pigs. Saline was given to a second group of animals as controls. Subsequently, the lateral cochlear walls of each animal were prepared and analyzed for thromboxane (TXA) and prostacyclin (PGI) using radioimmunoassay. These studies showed that dazoxiben crosses the blood-labyrinth barrier and shifts the TXA2/PGI2 balance in favor of the latter. The effects demonstrated are discussed with respect to the relevance of prostanoids in cochlear physiology.