Small Arms Fire-like noise: Effects on Hearing Loss, Gap Detection and the Influence of Preventive Treatment.

A noise-induced loss of inner hair cell (IHC) - auditory nerve synaptic connections has been suggested as a factor that can trigger the progression of maladaptive plastic changes leading to noise-induced tinnitus. The present study used a military relevant small arms fire (SAF)-like noise (50 biphasic impulses over 2.5 min at 152 dB SPL given unilaterally to the right ear) to induce loss (∼1/3) of IHC synaptic ribbons (associated with synapse loss) in rat cochleae with only minor (less than 10%) loss of outer hair cells. Approximately half of the noise-exposed rats showed poorer Gap Detection post-noise, a behavioral indication suggesting the presence of tinnitus. There was significantly greater loss of IHC ribbons in noise-exposed rats with reduced Gap Detection compared to noise-exposed rats retaining normal Gap Detection. We have previously shown systemic administration of piribedil, memantine, and/or ACEMg significantly reduced loss of IHC ribbons induced by a 3 h 4 kHz octave band 117 dB (SPL) noise. The present study examined if this treatment would also reduce ribbon loss from the SAF-like noise exposure and if this would prevent the reduced Gap Detection. As in the previous study, piribedil, memantine, and ACEMg treatment significantly reduced the noise-induced loss of ribbons, such that it was no longer significantly different from normal. However, it did not prevent development of the reduced Gap Detection indication of tinnitus in all treated noise-exposed rats, reducing the incidence but not reaching significance.

Treatment with Piribedil and Memantine Reduces Noise-Induced Loss of Inner Hair Cell Synaptic Ribbons.

Noise overstimulation can induce loss of synaptic ribbons associated with loss of Inner Hair Cell - Auditory Nerve synaptic connections. This study examined if systemic administration of Piribedil, a dopamine agonist that reduces the sound evoked auditory nerve compound action potential and/or Memantine, an NMDA receptor open channel blocker, would reduce noise-induced loss of Inner Hair Cell ribbons. Rats received systemic Memantine and/or Piribedil for 3 days before and 3 days after a 3 hour 4 kHz octave band noise at 117 dB (SPL). At 21 days following the noise there was a 26% and 38% loss of synaptic ribbons in regions 5.5 and 6.5 mm from apex, respectively, elevations in 4-, 8- and 20 kHz tonal ABR thresholds and reduced dynamic output at higher intensities of stimulation. Combined treatment with Piribedil and Memantine produced a significant reduction in the noise-induced loss of ribbons in both regions and changes in ABR sensitivity and dynamic responsiveness. Piribedil alone gave significant reduction in only the 5.5 mm region and Memantine alone did not reach significance in either region. Results identify treatments that could prevent the hearing loss and hearing disorders that result from noise-induced loss of Inner Hair Cell - Auditory Nerve synaptic connections.

ACEMg Diet Supplement Modifies Progression of Hereditary Deafness.

Dietary supplements consisting of beta-carotene (precursor to vitamin A), vitamins C and E and the mineral magnesium (ACEMg) can be beneficial for reducing hearing loss due to aminoglycosides and overstimulation. This regimen also slowed progression of deafness for a boy with GJB2 (CONNEXIN 26) mutations. To assess the potential for treating GJB2 and other forms of hereditary hearing loss with ACEMg, we tested the influence of ACEMg on the cochlea and hearing of mouse models for two human mutations: GJB2, the leading cause of childhood deafness, and DIAPH3, a cause of auditory neuropathy. One group of mice modeling GJB2 (Gjb2-CKO) received ACEMg diet starting shortly after they were weaned (4 weeks) until 16 weeks of age. Another group of Gjb2-CKO mice received ACEMg in utero and after weaning. The ACEMg diet was given to mice modeling DIAPH3 (Diap3-Tg) after weaning (4 weeks) until 12 weeks of age. Control groups received food pellets without the ACEMg supplement. Hearing thresholds measured by auditory brainstem response were significantly better for Gjb2-CKO mice fed ACEMg than for the control diet group. In contrast, Diap3-Tg mice displayed worse thresholds than controls. These results indicate that ACEMg supplementation can influence the progression of genetic hearing loss.

Disposition of WR-1065 in the liver of tumor-bearing rats following regional vs systemic administration of amifostine.

PURPOSE: Amifostine is a prodrug in which selectivity is largely determined by the preferential formation and uptake of its cytoprotective metabolite, WR-1065, in normal tissues as a result of differences in membrane-bound alkaline phosphatase activity. It was hypothesized that amifostine may be a good candidate for regional drug delivery to the liver because of its large hepatic extraction and total body clearance. METHODS: Rat livers were implanted with Walker-256 tumors. The tumor-bearing rats received 15 min infusions of amifostine (200 mg/kg) via the portal vein or the femoral vein. WR-1065 concentrations in the blood, liver and tumor were measured at various times. RESULTS: The WR-1065 tumor portal dosing AUC15-60 was 40% of systemic dosing, and tumor concentrations following portal dosing were one-fifth of that following systemic dosing. The portal dosing WR-1065 liver AUC15-60 was 60% higher than the values for systemic dosing. The liver/tumor concentration ratios of WR-1065 following portal dosing were up to 8-fold higher than the ratio following systemic administration. Unfortunately, systemic exposure to WR-1065 was greater following portal vs systemic amifostine. CONCLUSIONS: Amifostine may provide increased liver protection and decreased tumor protection from radio- or chemotherapy when administered by the portal vein. However, portal dosing also increases systemic exposure to WR-1065, which is associated with hypotension.

Effects of dexamethasone or celecoxib on biliary toxicity after hepatic arterial infusion of 5-fluorodeoxyuridine in a canine model.

Previous work has shown that in humans the dose-limiting toxicity for fluorodeoxyuridine [2-fluoro-5'-deoxyuridine (FdUrd)] when administered by hepatic arterial infusion is biliary sclerosis. The current study was undertaken to attempt to modify this toxicity in a canine model that has been demonstrated to closely mimic the clinical situation. Unlike previous studies using this model, in which animals were sacrificed after extensive fibrosis had already occurred, the current experiments were designed so that observations of pathology were made at an earlier time, when the initial inflammatory injury underlying the fibrotic process was still taking place. Implantable pumps were used to deliver FdUrd into the hepatic artery of animals at a rate of 0.3 mg/kg/day in the presence or absence of 10 mg/week dexamethasone or 100 mg/day of celecoxib for 35 days, at which time the animals were beginning to show signs of toxicity. After evaluation for radiological evidence of biliary obstruction, the animals were sacrificed and portions of their livers were processed for examination of microscopic pathology and 2-bromo-5'deoxyuridine labeling index. Dexamethasone treatment protected the animals from biliary sclerosis determined radiologically, further validating this model as being representative of the response in humans. Similarly the Cox-2 inhibitor, celecoxib, appeared to provide protection against radiological changes of biliary stricture, although possibly to a lesser degree than the resultant from dexamethasone. In addition, FdUrd treatment caused elevation of the DNA 2-bromo-5'deoxyuridine labeling index above control levels in biliary epithelial cells. Dexamethasone and celecoxib each significantly attenuated the FdUrd-induced elevation of DNA labeling index in biliary epithelium. These findings demonstrate the usefulness of this canine model for studying the mechanisms of drug-induced biliary sclerosis and reinforce the hypothesis that blocking inflammation may retard the progression of injury that eventually leads to fibrosis. This study suggests that clinical testing of celecoxib as a preventive for hepatic arterial-FdUrd induced biliary damage could prove valuable.

Regional delivery and selective expression of a high-activity yeast cytosine deaminase in an intrahepatic colon cancer model.

A major potential limitation to the success of enzyme prodrug gene therapy is the toxicity that could result from gene expression in normal tissues. In this study, we investigated the use of an enhanced human carcinoembryonic antigen (CEA) promoter for yeast cytosine deaminase (yCD), which converts 5-fluorocytosine to 5-fluorouracil, to increase targeting while maintaining activity both in cell culture and in nude rats bearing intrahepatic xenografts. We found that an enhanced CEA-yCD adenoviral vector can achieve significantly greater yCD expression in CEA-expressing colon carcinoma cell lines (LoVo, HT29, and CaCo2) compared with a nonspecific Rous sarcoma virus-yCD virus. In contrast, infection with CEA-yCD led to lower or equivalent yCD expression in normal hepatocytes or fibroblasts compared with that produced by the RSV-yCD. Adenovirus administered in the portal vein or the hepatic artery of nude rats bearing intrahepatic LoVo colon carcinomas could mediate beta-galactosidase expression equally in liver and tumors under the control of cytomegalovirus, a nonspecific promoter. However, infusion of CEA-yCD virus markedly increased yCD expression in tumors over normal liver (>4-fold) measured both by levels of mRNA and yCD activity. Moreover, the efficiency of 5-fluorocytosine conversion into 5-fluorouracil in tumors was significantly higher than that in normal liver ( approximately 3-fold) in rats receiving portal venous viral infusion of CEA-yCD and subsequent 5FC treatment. Thus, an enhanced CEA promoter can preferentially stimulate yCD gene expression in CEA-expressing cells in vivo. Such tumor-specific expression should prove useful in colorectal cancer gene therapy to achieve selective prodrug conversion in tumors.

Regional pharmacokinetics of amifostine in anesthetized dogs: role of the liver, gastrointestinal tract, lungs, and kidneys.

Amifostine is a prodrug in which selectivity is largely determined by the preferential formation and uptake of its cytoprotective metabolite, WR-1065, in normal tissues as a result of differences in membrane-bound alkaline phosphatase activity. In this study, we characterized the sites and extent of organ-specific activation by the liver, gastrointestinal tract, lungs, and kidneys after systemic administrations of amifostine. A total of 10 dogs were infused via the cephalic vein using sequential dose rates of drug at 0.125, 0.500, and 1.00 micro mol/min/kg. Infusion of each dose rate lasted 2 h, at which time steady-state plasma concentrations were obtained (i.e., portal vein, carotid artery, hepatic vein, pulmonary artery, and renal vein). The hepatic arterial, portal venous, and renal arterial blood flows, and cardiac output, were measured. The hepatic and splanchnic extraction of amifostine remained high at 90%, whereas gastrointestinal extraction decreased from 43 to 12 to 15% with increasing dose. Pulmonary extraction of amifostine was low at 7%, whereas renal extraction was intermediate at 57%. Because blood flow measurements were relatively constant during the drug infusions, clearance parameters paralleled that of organ extraction. As a result, saturability was observed in the gastrointestinal blood clearance (i.e., from 9.8 to 2.8-3.3 ml/min/kg) and total body plasma clearance of amifostine (i.e., from 52.6 to about 37.3 ml/min/kg), as the doses increased. Due to the drug's high activation in liver, these findings suggest that amifostine may offer good protection of this organ against the toxicities of chemotherapy and radiation.