Histology and ultrastructure of liver and kidney following blood exchange with ultrapurified, polymerised bovine hemoglobin in comparison with hydroxyethyl starch

Because of their oxygen binding capacity, cell-free hemoglobin solutions are promising blood substitutes. However, their clinical use has so far been limited by toxic side effects on liver and kidney until ultrapurification and chemical modifications have been established in the production process of hemoglobin-based oxygen carriers. The present study has been designed to examine structural changes of liver and kidney by light and electron microscopy after complete isovolemic blood exchange with a new ultrapurified bovine hemoglobin solution (UPBH-2) in eight beagle dogs. The results have been compared with a sham-operated control and eight animals having undergone blood exchange with hydroxyethyl starch (HES), a clinically used colloidal volume substitute. In the kidney, no changes were observed after blood exchange with UPBH-2 as compared with the sham control. These findings indicate sufficient tissue oxygenation and lack of renal toxicity. In contrast, histological signs of severe proximal tubular damage, eg, wide lumina, cytoplasmic protrusions, brush-border defects, and tubular necroses, were seen after blood exchange with HES. These changes are consistent with hypoxic tissue damage. In the liver, a slight increase in the number of single cell necroses was observed after UPBH-2 treatment as well as after blood exchange with HES. At the ultrastructural level, partial loss of microvilli and cytoplasmic protrusions of hepatocytes as well as swelling of endothelial cells were present in both groups, but slightly more pronounced in the UPBH-2 group. In all UPBH-2-treated animals, a marked diminution of glycogen-granula in hepatocytes was observed indicating an influence of UPBH- 2 upon glycogen metabolism. Whereas the alterations of hepatocytes after nearly complete blood exchange with HES can be interpreted as a consequence of tissue hypoxia, the ultrastructural changes after UPBH-2 treatment cannot be attributed to hypoxic conditions, because improved tissue oxygenation has been demonstrated during treatment with UPBH-2. Hepatocyte damage was very discrete and comparable with the alterations observed after HES treatment. Hence, major hepatotoxicity can be excluded. The absence of significant adverse effects on the ultrastructural integrity of the kidney indicates that UPBH-2, owing to ultrapurification and polymerization, is an oxygen-carrying hemoglobin without acute renal toxicity.