Pentoxifylline increases cochlear blood flow while decreasing blood pressure in guinea pigs

Use of the guinea pig in studies on the development and prevention of acquired sensorineural hearing loss, with an emphasis on noise

Guinea pigs have been used in diverse studies to better understand acquired hearing loss induced by noise and ototoxic drugs. The guinea pig has its best hearing at slightly higher frequencies relative to humans, but its hearing is more similar to humans than the rat or mouse. Like other rodents, it is more vulnerable to noise injury than the human or nonhuman primate models. There is a wealth of information on auditory function and vulnerability of the inner ear to diverse insults in the guinea pig. With respect to the assessment of potential otoprotective agents, guinea pigs are also docile animals that are relatively easy to dose via systemic injections or gavage. Of interest, the cochlea and the round window are easily accessible, notably for direct cochlear therapy, as in the chinchilla, making the guinea pig a most relevant and suitable model for hearing. This article reviews the use of the guinea pig in basic auditory research, provides detailed discussion of its use in studies on noise injury and other injuries leading to acquired sensorineural hearing loss, and lists some therapeutics assessed in these laboratory animal models to prevent acquired sensorineural hearing loss.

Ginkgo biloba extract EGb 761® versus pentoxifylline in chronic tinnitus: a randomized, double-blind clinical trial

Background Ginkgo biloba extract EGb 761^® and pentoxifylline are frequently prescribed for the treatment of tinnitus. Objective To compare the treatment effects of Ginkgo biloba extract EGb 761R and pentoxifylline. Setting The study was performed at Department of Otorhinolaryngology of University Hospital Královské Vinohrady and 3rd Medical Faculty, Charles University in Prague. Method Patients with sub-chronic or chronic tinnitus were enrolled in double-blind trial and randomized to receive 120 mg EGb 761^® or 600 mg pentoxifylline, each twice a day and in double-dummy fashion over a 12-week period. Main outcome measure changes in 11-Point Box Scales for tinnitus loudness and annoyance, the abridged Tinnitus Questionnaire (Mini-TQ), the Hospital Anxiety and Depression Scale (HADS), and the Sheehan Disability Scale (SDS). Results Full analysis set for efficacy analysis comprised 197 patients (EGb 761^®, 99; pentoxifylline 98). For both treatment groups, significant improvements were observed in the Mini-TQ, the 11-Point Box Scales for tinnitus loudness and annoyance, the HADS anxiety score and the SDS. There was no relevant difference with regard to tinnitus-related outcomes between the two treatment groups. 20 adverse events were documented in EGb 761^® group and 36 adverse events were reported for pentoxifylline group. No serious adverse event was reported during the study. Conclusion EGb 761^® and pentoxifylline were similarly effective in reducing the loudness and annoyance of tinnitus as well as overall suffering of the patients. The incidence of adverse events was lower in the EGb 761^® group.

Intratympanic Dexamethasone and Hyaluronic Acid in Patients with Low-Frequency and Ménière's-Associated Sudden Sensorineural Hearing Loss

BACKGROUND

Steroids are widely used for the treatment of cochleovestibular disorders. Direct steroid application in the middle ear cavity, when combined with a round window membrane permeability-modulating substance, increases the level of the steroid reaching the target cells. We measured hearing in patients with idiopathic isolated low-frequency sensorineural hearing loss and in patients with sudden sensorineural hearing loss and a history of Ménière's disease. Contradictory reports about effectiveness of intratympanic steroid therapy on vertigo control and hearing improvement in patients with Ménière's disease exist in the literature.

METHODS

Eighteen patients with isolated low-frequency idiopathic sudden sensorineural hearing loss and 21 patients with sudden sensorineural hearing loss and a history of Ménière's disease were prospectively evaluated. The acute effect of the intratympanic application of dexamethasone with hyaluronic acid on hearing outcome after failure of an initial standard treatment with intravenous steroid and vasoactive substances was assessed. Evaluation was based on standard pure-tone audiometry findings.

RESULTS

After intratympanic injection of dexamethasone and hyaluronic acid, 14 of the 18 patients with isolated low-frequency sensorineural hearing loss showed a significant improvement in hearing. After intratympanic therapy, 15 patients with a previous history of Ménière's disease and idiopathic isolated low-frequency sensorineural hearing loss showed an improvement in hearing on pure-tone audiometry, four remained unchanged, and two showed a tendency toward a slight deterioration.

CONCLUSION

Intratympanic combined dexamethasone/hyaluronic acid application provides a reliable and safe therapeutic option for improvement of hearing in patients with isolated low-frequency idiopathic sudden sensorineural hearing loss or sensorineural hearing loss resulting from Ménière's disease who have failed intravenous steroid and vasoactive treatments.

Idiopathic sudden sensorineural hearing loss in children

OBJECTIVE

Although idiopathic sudden sensorineural hearing loss (ISSHL) is a frequent disease in adults, less is known about incidence and treatment of ISSHL in children.

METHOD

A retrospective chart analysis was performed to evaluate the frequency of ISSHL in children aged under 18 years between 2000 and 2003, who were treated in our department. Children received prednisolone intravenously at an initial dose of 3mg/kg bodyweight. Prednisolone dose was reduced to half every second day. The medication was given for a maximum of 14 days or finished 2 days after the hearing normalized in pure-tone audiometry. The follow-up was continued between 3 and 14 months.

RESULTS

The complete recovery rate was 57%, and the partial recovery was 36%. Initial hearing loss of 50dB and more was predictive for poor outcome in children (p=0.028). Presence of tinnitus was without relevance for the outcome. The incidence of ISSHL in the local area of about 250,000 inhabitants was 1/10,000 in children.

CONCLUSION

ISSHL seems to be a less frequent disease in children than in adults. Severe initial hearing loss is coupled with poor outcome. Under treatment with prednisolone hearing improvement was found in 13 of 14 patients.

Intratympanic dexamethasone with hyaluronic acid in the treatment of idiopathic sudden sensorineural hearing loss after failure of intravenous steroid and vasoactive therapy

The purpose of this prospective study was to test whether intratympanic application of dexamethasone/hyaluronic acid improves hearing outcome in patients with pantonal idiopathic sudden sensorineural hearing loss (ISSHL), in patients with sudden deafness or sudden profound SHL and in patients with predominant high-frequency ISSHL who are refractory to intravenous steroid and vasoactive therapy. The study took place in an academic tertiary referral hospital involving 21 patients with pantonal ISSHL, 10 patients with sudden deafness or sudden profound SHL and 9 patients with a high-frequency ISSHL. Intratympanic dexamethasone/hyaluronic acid was administered in the affected ear. Hearing was evaluated by means of standard pure-tone audiometry. The differences between pure-tone hearing thresholds by air conduction before intravenous therapy and before the beginning of the intratympanic therapy, as well as before and after intratympanic therapy, were calculated. Statistical analysis was performed by means of the Wilcoxon's test for paired samples. Intratympanic injection of dexamethasone/hyaluronic acid results in a significant global (pantonal) improvement in hearing in patients with pantonal ISSHL. It also effects improvement in hearing at selected frequencies (namely at 1.5 and 3 kHz) in patients with a predominant high-frequency ISSHL and at selected frequencies (namely at 0.5, 0.75 and 1 kHz) in patients with sudden deafness or sudden profound SHL. Neither systemic nor local side effects were observed. Intratympanic administration of dexamethasone/hyaluronic acid provides a safe and efficacious therapeutic option for the treatment of patients with pantonal and high-frequency ISSHL who don't respond to intravenous steroid and vasoactive therapy.

The effect of blood flow promoting drugs on cochlear blood flow, perilymphatic pO(2) and auditory function in the normal and noise-damaged hypoxic and ischemic guinea pig inner ear

The effect of blood flow promoting drugs, such as hydroxyethyl starch (HES) either of low or high molecular weight (HES 70, HES 200), pentoxifylline, ginkgo biloba, naftidrofuryl and betahistine, and various combinations of the drugs was studied in unexposed and noise-exposed (broad-band noise, bandwidth 1-12 kHz, 106 dB SPL, 30 min) guinea pigs. The results were compared without therapy and placebo (isotonic saline, NaCl). The cochlear blood flow (CoBF) and the partial pressure of oxygen in the perilymph (PL-pO(2)) were continuously and simultaneously recorded over a period of 210 min. In addition, cochlear microphonics (CMs), compound action potentials of the auditory nerve (CAPs) and auditory brain stem responses (ABRs) were registered. Noise-induced hearing loss (NIHL) paralleled a decrease of PL-pO(2). Both were found to occur before evidence of reduced CoBF. PL-pO(2) and CoBF declined progressively post-exposure, while CMs, CAPs and ABRs showed no further deterioration or signs of recovery up to 180 min after cessation of noise. Treatment started 60 min post-exposure, respectively after 90 min, without manipulation in unexposed animals, and was then studied for a further 120 min. In unexposed animals, CoBF increased significantly during infusion of HES 70, HES 200, pentoxifylline and betahistine. NaCl, ginkgo biloba and naftidrofuryl did not alter CoBF. PL-pO(2) decreased significantly during infusion of all administered drugs and combinations, except for NaCl. CMs, CAPs and ABRs remained constant, with the exception of increased ABRs after infusion of HES 70 and HES 200. In noise-exposed animals, a sustained therapeutic effect on cochlear ischemia was achieved only by HES 200 and pentoxifylline. HES 70, betahistine and ginkgo biloba compensated cochlear ischemia only during infusion; however, 30-60 min after termination of therapy, no significant difference of values for CoBF was observed compared to the untreated noise-exposed groups. NaCl and naftidrofuryl showed no effect on CoBF. None of the applied drugs had a sustained compensatory effect on cochlear hypoxia. CMs, CAPs and ABRs improved significantly after HES 70, HES 200 and betahistine, resulting in partial recovery of CMs, and partial (betahistine) or even full (HES 70 and HES 200) recovery of CAPs and ABRs. In contrast, NaCl, pentoxifylline, ginkgo biloba and naftidrofuryl had no therapeutic effect on NIHL.

Pentoxifylline maintains cochlear microcirculation and attenuates temporary threshold shifts following acoustic overstimulation

The etiology of noise-induced hearing loss is poorly understood despite years of clinical experience and experimental investigations. One potential mechanism which may contribute to noise-induced temporary threshold shifts (TTS) are vascular pathologies in the microcirculation of the cochlea. Several studies have demonstrated histologic evidence of reduced cochlear blood flow following noise exposure. Recent studies utilizing intravital microscopy (IVM) complement these histologic studies and furthermore demonstrate localized ischemia during noise exposure. The purpose of the current study was to attempt to maintain cochlear blood flow during noise exposure by treating with pentoxifylline, a xanthine derivative which promotes blood flow in capillary beds. The possibility that preserved cochlear microcirculation with pentoxifylline treatment attenuates noise-induced TTS was also examined in this study. The results show treatment with pentoxifylline maintains cochlear microcirculation as assessed by continuous red blood cell movement through capillaries. Pentoxifylline treatment did not prevent vasoconstriction or increased permeability often observed in the cochlear microvasculature during noise. Treatment with this drug reduced noise-induced TTS.

Effects of vasodilating agents on cochlear blood flow in mice

The mouse has several distinct advantages as an experimental model for study of the cochlear blood flow (CBF) in the mammal, particularly for studies involving genetic manipulation, development and aging factors. In this investigation we evaluated the effects of selected vasodilating agents on CBF using laser-Doppler flowmetry. Sodium nitroprusside, hydralazine and pentoxifylline were applied topically on the round window (RW) or systemically by a subcutaneous injection. Topical application of sodium nitroprusside and hydralazine elevated CBF significantly, while systemic administrations of these two drugs failed to elevate CBF consistently. Pentoxifylline did not change CBF following topical application but increased CBF slightly following systemic administration. Age and gender did not influence the CBF response to topical application of sodium nitroprusside.

Brain angiotensin receptor subtypes in the control of physiological and behavioral responses

This review summarizes emerging evidence that supports the notion of a separate brain renin-angiotensin system (RAS) complete with the necessary precursors and enzymes for the formation and degradation of biologically active forms of angiotensins, and several binding subtypes that may mediate their diverse functions. Of these subtypes the most is known about the AT1 site which preferentially binds angiotensin II (AII) and angiotensin III (AIII). The AT1 site appears to mediate the classic angiotensin responses concerned with body water balance and the maintenance of blood pressure. Less is known about the AT2 site which also binds AII and AIII and may play a role in vascular growth. Recently, an AT3 site was discovered in cultured neoblastoma cells, and an AT4 site which preferentially binds AII(3-8), a fragment of AII now referred to as angiotensin IV (AIV). The AT4 site has been implicated in memory acquisition and retrieval, and the regulation of blood flow. In addition to the more well-studied functions of the brain RAS, we review additional less well investigated responses including regulation of cellular function, the modulation of sensory and motor systems, long term potentiation, and stress related mechanisms. Although the receptor subtypes responsible for mediating these physiologies and behaviors have not been definitively identified research efforts are ongoing. We also suggest potential contributions by the RAS to clinically relevant syndromes such as dysfunctions in the regulation of blood flow and ischemia, changes in cognitive affect and memory in clinical depressed and Alzheimer's patients, and angiotensin's contribution to alcohol consumption.

Effects of hydroxyethyl starch, nimodipine, and propylene glycol on cochlear blood flow

A primary goal of pharmacologic treatment for otopathologies of vascular origin is to elevate cochlear blood flow (CoBF), thus facilitating the transport of oxygen and nutrients without compromising perfusion pressure in other tissues. In the present investigation, significant increases in CoBF were measured during intra-arterial infusion of the plasma expanding agent, hydroxyethyline starch (HES), and the vasodilator nimodipine, in anesthetized adult male guinea pigs. There were no changes in systemic blood pressure during the infusion of HES or nimodipine. Intra-arterial infusion of propylene glycol (PG), which is used as a nonaqueous solvent, produced inconsistent CoBF effects accompanied by initial decreases in systemic blood pressure with subsequent increases. It is concluded that nimodipine and HES are very promising agents for inducing increases in CoBF, whereas PG produced inconsistent effects on CoBF while elevating blood pressure, thus compromising its potential usefulness in the treatment of otopathologies.