PURPOSE: We reported that polyethylene glycol (PEG) modified albumin at multiple(6-8)sites using PEG-Alb5000 has superior plasma expansion properties compared to albumin and crystalloid . Recently we modified albumin at one site using PEG 40.000Daltons. It is hypothesized that PEG-Alb’s improved effect is a result of increased intravascular retention of the larger PEG-Alb (16 times the size of albumin), but this Hypothesis has not been objectively demonstrated.
METHODS: We applied a novel double-chromophore technique to quantify the relative albumin versus PEG-Alb40.000 retention times in 10 septic (cecal ligation and puncture) and 11 control rats. Albumin and PEG-Alb40.000 were tagged with one of two spectroscopically distinct chromophores (Fluorescein or Texas Red) injected in tracer amounts. Intravascular Albumin and PEG-Alb concentrations were derived by fluorometric measurements from 10-12 serum samples drawn 15 minutes to 144 hours after injection.
RESULTS: Albumin and PEG-Alb-40.000 concentrations decreased as a function of time (fig 1). All elimination half-lives were consistently and significantly greater for PEG-Alb-40.000 in both control [66.9±12 (PEG-Alb) vs. ± and 15.47±5 hours (Albumin)] and sepsis [47±6 hours (PEG-Alb) vs. 11 ± 5hours (Albumin)] rats. These findings were further corroborated via evidence of isolated extravasation of albumin(red) in lung tissue specimens (fluorescence microscopy) fig 2.
CONCLUSION: We report evidence supporting our hypothesis that modification of albumin using PEG 40.000 Daltons at one site resulted in increase albumin retention time at least four times in both control and septic rats. This explains the improved resuscitation properties of PEG-Alb in sepsis or capillary leak conditions.
CLINICAL IMPLICATIONS: We described an experimental method that 1) allows for the simultaneous (i.e., in same subject) assessment of albumin and PEG-Alb intravascular retention times and 2) provides visualization of extravascular (or leaked) albumin and PEG-Alb. Importantly, this technique may be applied to other proteins combinations, and developing it may allow the early detection and quantification of capillary leak which is a known marker preceding the overt development of organ injury by at least two to three days.
DISCLOSURE: Ragheb Assaly, Product/procedure/technique that is considered research and is NOT yet approved for any purpose. Three of the authors (Ragheb Assaly MD, Joseph Shapiro MD and David Dignam PhD), Together with the Medical University of Ohio, have filed a patent for PEG-Alb (US patent number 101106,793).