Ultrastructural effects of intravascularly injected polyethylene glycol-hemoglobin in intestinal mucosa

Design of recombinant hemoglobins for use in transfusion fluids

Molecular biology has been applied to the development of hemoglobin-based oxygen carrier (HBOC) proteins that can be expressed in bacteria or yeast. The transformation of the hemoglobin molecule into an HBOC requires a variety of modifications for rendering the acellular molecule of hemoglobin physiologically acceptable when transfused in circulation. Hemoglobins with different oxygen affinities can be obtained by introducing mutations at the heme pocket, the site of oxygen binding, or by introducing surface mutations that stabilize the hemoglobin molecule in the low-oxygen-affinity state. Modification of the size of the heme pocket is also used to hinder nitric oxide depletion and associated vasoconstriction. Introduction of cysteine residues on the hemoglobin surface allows formation of intermolecular bonds and formation of polymeric HBOCs. These polymers of recombinant hemoglobin have the characteristics of molecular size, molecular stability, and oxygen delivery to hypoxic tissue suitable for an HBOC.

Differential effects of sodium selenite in reducing tissue damage caused by three hemoglobin-based oxygen carriers

Three “blood substitutes,” a diaspirin cross-linked human hemoglobin (DBBF-Hb), a bovine polymerized hemoglobin (PolyHbBv), and a human polymerized hemoglobin ( O-R-PolyHbA0), that have undergone clinical trials are used in this study. Previously, we showed in the rat that coadministration of sodium selenite (Na2SeO3) and DBBF-Hb significantly decreased mesenteric venular leakage and epithelial disruption produced by DBBF-Hb alone but did not reduce mast cell degranulation unless given orally. The purpose of this study was to determine whether Na2SeO3 produced similar beneficial responses when used with PolyHbBv and O-R-PolyHbA0. In anesthetized Sprague-Dawley rats, the mesenteric microvasculature was perfused with PolyHbBv or O-R-PolyHbA0, with and without Na2SeO3 in the perfusate and suffusate, for 10 min, followed by FITC-albumin for 3 min, and then fixed for microscopy. Na2SeO3 did not reduce leak number or area in preparations perfused with PolyHbBv and only reduced leak number (but not significantly) in preparations perfused with O-R-PolyHbA0. Na2SeO3 significantly increased mesenteric mast cell degranulation and impaired epithelial integrity in animals treated with PolyHbBv. In vitro, Na2SeO3 significantly reduced the oxidation rate of DBBF-Hb in the presence of oxidants, had little effect on PolyHbBv, and increased the oxidation rate of O-R-PolyHbA0. These results suggest that Na2SeO3 moderates hemoglobin-induced damage, at least partly, through its redox interactions with the heme sites in the hemoglobin molecules studied and that accessibility of the heme site to Na2SeO3 governs those interactions.

Comparison of effects of two hemoglobin-based O(2) carriers on intestinal integrity and microvascular leakage

Two "blood substitutes," a diaspirin cross-linked human hemoglobin [bis(3,5 dibromosalicyl)fumarate, DBBF-Hb] and a bovine polymerized hemoglobin (PolyHbBv), advanced to clinical trials, are used in this study. Previously, we have shown that injection of DBBF-Hb into the rat circulation produces venular leakage and intestinal epithelial disruption. The purpose of this study was to determine whether PolyHbBv, currently approved for veterinary use in the United States, shows similar effects. In anesthetized Sprague-Dawley rats, the mesenteric microvasculature was perfused with DBBF-Hb (n = 6), PolyHbBv (n = 5), cyanomet Hb (CNmet-DBBF-Hb), or HEPES-buffered saline with 0.5% bovine serum albumin (HBS-BSA) (controls, n = 7) for 10 min, followed by FITC-albumin for 3 min, and then fixed for microscopy. For DBBF-Hb, the mean leak number per micrometer venule length [2.41 +/- 0.33 (+/-SE) x 10(-3)] was significantly greater than for PolyHbBv (0.53 +/- 0.14 x 10(-3)), CNmet-DBBF-Hb (0.36 +/- 0.14 x 10(-3)), and HBS-BSA (0.12 +/- 0.08 x 10(-3)) (P < 0.01). Corresponding quantities for leak area were 0.10 +/- 0.03, 0.010 +/- 0.003, 0.005 +/- 0.003, and 0.02 +/- 0.02 microm(2)/microm. In rats injected with DBBF-Hb (n = 8), intestinal epithelial integrity was significantly compromised compared with those injected with PolyHbBv (n = 5) or saline (n = 6). These results indicate that intravascular PolyHbBv produces significantly less disruption of the intestinal exchange barrier than does DBBF-Hb, probably because the heme is not so easily oxidized.