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Special Feature: Oral Presentations

NOVEL APPLICATIONS & PERFLUOROCHEMICAL-ASSOCIATED DRUG DELIVERY

Wolfson, Marla R. PhD

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This presentation was divided into two parts. First, the concept of perfluorochemical applications for selective cerebral hypothermia for neuroprotection was developed. Cerebral hypoxic-ischemic events are the leading cause of acute neurological injury at birth, and, cause of long-term disability across age worldwide. A 2–5oC reduction in brain temperature after this event can improve neuropathological, cerebral energetic, and electrophysiological outcomes. The neuroprotective efficacy of cerebral hypothermia has been linked to how rapidly cooling is initiated, how quickly the brain is cooled, and the extent of tissue that reaches the therapeutic hypothermic zone. Whole body surface (WBS) or intravascular methods for brain cooling are encumbered by equipment, systemic hypothermia, slow response, and concomitant systemic instability. Selective head cooling by circulating cold water cap shows promise, although regional gradients in brain temperature remain. Due to proximity to the cerebral circulation, the nasopharynx is uniquely suited for selective and homogenous brain cooling; however, nasopharyngeal (NP) cooling with oxygen or liquid is limited by low heat capacity and/or respiratory compromise. As an alternative, the favorable distribution and rapid evaporative properties of nasopharyngeal delivered perfluorochemical (PFC) increase the heat capacity of respired gas, thus should facilitate rapid induction and maintenance of global brain cooling without substantial compromise in systemic temperature. The theoretical basis for PFC nasopharyngeal cooling includes: (1) latent heat of vaporization in which the phase change of PFC liquid to PFC vapor and the endothermic reaction contribute to the change in heat which is proportional to the PFC flow, specific heat, and surface area contact; (2) hematogenous cooling; and, (3) conductive cooling commensurate with structural cooling. To compare regional cooling rates and cardiopulmonry function in juvenile sheep during WBS or NP-PFC cooling, anesthetized and ventilated young sheep, instrumented with multiple temperature probes and vascular catheters, were randomized to WBS (cold H2O blanket) or NP-PFC aerosol (PFC/O2spray device; BeneChill, Inc.) cooling. Temperatures, blood pressure, cardiac output and blood chemistry were measured for up to 2 h. Cooling rates were evaluated (ANOVA) as a function of method (WBS vs NP-PFC), PFC/O2flow (0.50 – 2.0 mL/kg/min; 0.20 – 2 L/kg/min), and time to reach the brain THZ (- 3oC below baseline).

Table
Table:
Cooling Rates (°C/hr) X ± SE

Independent of flow and region, cooling was faster (*p<0.001) during NP-PFC vs WBS. With WBS, brain vs systemic cooling rates were not different and brain THZ was not reached by 2 hr. With NP-PFC independent of flow, brain>vascular>rectal rates (**p<0.001) and brain THZ was reached in 24.2 ± 3.3 SE min. Brain cooling rates increased (p<0.001) with PFC and O2 flow; brain to systemic temperature gradient increased (p<0.001) with PFC flow. Blood pressure and cardiac output decreased with cooling during WBS and remained stable during NP-PFC. Gas exchange was stable with both methods. Summarily, NP-PFC aerosol cooling provides rapid and preferential brain hypothermia without cardiovascular compromise or cumbersome equipment. Second, the presentation reviewed the fundamental principles of using perfluorochemical liquids as an adjunct for selective pulmonary delivery of biological agents. Late-breaking in vitro and in vivo data were presented to demonstrate efficacy as an adjunct to induce gene expression and confer lung protection against hyperoxia. Perfluorochemicals (PFC) have been shown to recruit lung volume and facilitate distribution of antibiotics and proteins. In addition, pulse-chase delivery of recombinant adenovirus (rAd) with PFCs markedly improves distribution to the distal airways of the lung. To assess a novel PFC combination, PP2/PP9 (F2, Ltd) as a vehicle to deliver rAd to the lung, compare the efficiency of PFC/rAd suspensions to the pulse-chase method and examine the ultrastructural effects of PFC suspensions on alveolar type II cells. rAd-LacZ in saline (2 mL/kg) or PFC (PP2/PP9, 25/75 v/v, 10 mL/kg) were administered by tracheal puncture to mice. μ-galactosidase activity was assessed after 72 h on whole lungs, and subsequently embedded and sectioned. Spatial and temporal distribution of PFC-augmented rAd gene expression was examined non-invasively using rAd-Luc over 94 d, and expression was determined using the IVIS 50 system and associated software (Living Image, Xenogen Corp). Finally, A549 cells were transduced with rAd-LacZ suspended in PFC or medium for 2 h then prepared for electron microscopy. Delivery of PFC/rAd suspension demonstrated marked improvement in expression in the distal portion of the lung and specifically in alveolar type II cells compared to saline and pulse-chase delivery. rAd-Luc/PFC suspension induced expression as early as 24 h post-administration, peaked 3–4 d and was detectable up to 94 d. The pattern and distribution of expression was more consistent when rAd was delivered with PFC. EM of A549 cells revealed multivesicular bodies and viral particles aggregating on the cell surface and in vacuoles only in the PFC/rAD-treated cells. These data demonstrate that this method: (1) enhances rAd-mediated gene expression in the alveolar air space; (2) reduces variability associated with rAd-mediated gene expression and extends the duration of expression; and, (3) induces a receptor-independent method of entry for rAd into cells.

Copyright © 2006 by the American Society for Artificial Internal Organs