Enrique Perez

Alterations in blood-brain barrier permeability to large and small molecules and leukocyte accumulation after traumatic brain injury: effects of post-traumatic hypothermia.

We investigated the temporal and regional profile of blood-brain barrier (BBB) permeability to both large and small molecules after moderate fluid percussion (FP) brain injury in rats and determined the effects of post-traumatic modest hypothermia (33 degrees C/4 h) on these vascular perturbations. The visible tracers biotin-dextrin-amine 3000 (BDA-3K, 3 kDa) and horseradish peroxidase (HRP, 44 kDa) were injected intravenously at 4 h or 3 or 7 days post-TBI. At 30 min after the tracer infusion, both small and large molecular weight tracers were detected in the contusion area as well as remote regions adjacent to the injury epicenter in both cortical and hippocampal structures. In areas adjacent to the contusion site, increased permeability to the small molecular weight tracer (BDA-3K) was evident at 4 h post-TBI and remained visible after 7 days survival. In contrast, the larger tracer molecule (HRP) appeared in these remote areas at acute permeable sites but was not detected at later post-traumatic time periods. A regionally specific relationship was documented at 3 days between the late-occurring permeability changes observed with BDA-3K and the accumulation of CD68-positive macrophages. Mild hypothermia initiated 30 min after TBI reduced permeability to both large and small tracers and the infiltration of CD68-positive cells. These results indicate that moderate brain injury produces temperature-sensitive acute, as well as more long-lasting vascular perturbations associated with secondary injury mechanisms.

Therapeutic hypothermia modulates TNFR1 signaling in the traumatized brain via early transient activation of the JNK pathway and suppression of XIAP cleavage.

Tumor necrosis factor (TNF) plays a critical role in pathomechanisms associated with secondary damage after traumatic brain injury (TBI). The TNF ligand‐receptor system stimulates inflammation by activation of gene transcription through the IκB kinase (IKK)–NF‐κB and c‐Jun NH2‐terminal kinase (JNK)–AP‐1 signaling cascades. TNF signaling following TBI involves both cell survival and apoptotic pathways, but the mechanism that accounts for the dual role of TNF remains unclear. Multiple studies have reported hypothermia to be protective following TBI, but the precise mechanism has not been clearly defined. Here, TNFR1 signaling pathways were investigated in the cerebral cortex of adult male Sprague–Dawley rats subjected to moderate fluid‐percussion TBI and of naïve controls. Another group was subjected to moderate TBI with 30 min of pre‐ and post‐traumatic hypothermia (33 °C). Rapid and marked increases in protein expression of TNFR1 and signaling intermediates in both the IKK–NF‐κB and JNK pathways were induced in traumatized cortices. Hypothermia decreased TNFR1 protein expression acutely in traumatized cortices and stimulated early activation of signaling intermediates in the JNK, but not the IKK–NF‐κB, signaling pathways. Hypothermia promoted a rapid activation of caspase‐3 acutely after injury but suppressed caspase‐3 activation at later time points. Moreover, hypothermia treatment suppressed cleavage of X‐linked inhibitor of apoptosis protein (XIAP) into fragments induced by TBI. These data suggest that hypothermia may regulate both the JNK signaling cascade via XIAP and the preconditioning pathways that activate caspases. Thus, hypothermia mediates TNFR1 responses via early activation of the JNK signaling pathway and caspase‐3, leading to endogenous neuroprotective events.

Comparison of packing material in an animal model of middle ear trauma

PURPOSE To compare the performance of absorbable gelatin sponge (AGS) with polyurethane foam (PUF) as middle ear packing material after mucosal trauma. MATERIALS AND METHODS Using a randomized, controlled and blinded study design fifteen guinea pigs underwent middle ear surgery with mucosal trauma performed on both ears. One ear was packed with either PUF or AGS while the contralateral ear remained untreated and used as non-packed paired controls. Auditory brainstem response (ABR) thresholds were measured pre-operatively and repeated at 1, 2, and 6weeks postoperatively. Histological analysis of middle ear mucosa was done in each group to evaluate the inflammatory reaction and wound healing. Another eighteen animals underwent middle ear wounding and packing in one ear while the contralateral ear was left undisturbed as control. Twelve guinea pigs were euthanized at 2weeks postoperatively, and six were euthanized at 3days post-operatively. Mucosal samples were collected for analysis of TGF-β1 levels by enzyme-linked immunosorbent assay. RESULTS ABR recordings demonstrate that threshold level changes from baseline were minor in PUF packed and control ears. Threshold levels were higher in the AGS packed ears compared with both control and PUF packed ears for low frequency stimuli. Histological analysis showed persistence of packing material at 6weeks postoperatively, inflammation, granulation tissue formation, foreign body reaction and neo-osteogenesis in both AGS and PUF groups. TGF-β1 protein levels did not differ between groups. CONCLUSION PUF and AGS packing cause inflammation and neo-osteogenesis in the middle ear following wounding of the mucosa and packing.

Trauma, Inflammation, Cochlear Implantation Induced Hearing Loss and Otoprotective Strategies to Limit Hair Cell Death and Hearing Loss

Hair cells are highly sensitive units that in response to trauma, inflammation, and cochlear implantation activate different signaling pathways leading to hair cell death and hearing impairment. In this chapter we discuss the most recent literature regarding signaling pathways of hair cell loss, mechanisms and inflammatory responses after noise exposure and electrode insertion, and otoprotective strategies that can limit hair cell death and hearing loss.

Comparison of Packing Material in Middle Ear Mucosal Trauma

Objective: To compare absorbable gelatin sponge (AGS) with polyurethane foam (PUF) as middle ear packing material after mucosal trauma. Method: Controlled animal experiment. Thirty-six guinea pigs underwent middle ear surgery with mucosal trauma performed on both ears. One ear was packed with either PUF or AGS. Contralateral ears were used as nonpacked paired controls. Auditory brainstem response (ABR) thresholds were measured preoperatively and repeated at 1, 2, and 6 weeks postoperatively. Histological analysis was done by a pathologist blinded to the type of packing using hematoxylin and eosin staining to measure inflammatory reaction and trichome staining to measure fibrosis in each group. Results: ABR recordings demonstrates that threshold level changes from baseline were minor in the PUF and the control groups. Threshold levels were higher in the AGS group compared with both control groups and the PUF group for the 1 KHz and 0.5 KHz frequencies. Macoscopic analysis showed no tympanic membrane perforation and packing material was absorbed in all groups at 6 weeks postoperatiely. The histological analysis showed normal mucosal healing in the PUF and control groups. There was more packing retention, inflammation, and osteoneogenesis in the AGS group than the PUF or either control group. Conclusion: Following surgical trauma, the middle ear mucosa healed well without packing or with PUF packing material, and hearing was not affected. In contrast AGS packing material showed hearing loss at low frequencies and osteogenesis.

Local drug delivery for inner ear therapy

This review of local drug delivery for inner ear therapy covers the topics of: noise-induced hearing loss (NIHL); vibration-induced hearing loss (VHL); cisplatin ototoxicity; aminoglycoside ototoxicity; and mechanical trauma-induced hearing loss that can occur during the process of cochlear implantation. The cellular, biochemical and molecular mechanisms involved in the causation of the hearing losses that result from exposure to these diverse traumas to the cochlea and its auditory sensory epithelium are explored as well as the efficacy of different drug therapies in their ability to either prevent or lessen the damage to the cochlear sensory epithelium and ameliorate the level of hearing loss. This review concludes with a section that explores future strategies for unique methods of drug delivery to the cochlea (e.g. biorelease from hydrogels via the round window membrane) and the development of novel inner ear therapies (e.g. short interfering ribonucleic acids, siRNAs) to conserve hearing against trauma associated losses and/or to restore hearing (e.g. stem cell therapy) following trauma-initiated losses of hair cells and hearing.