20-HETE-mediated vasoconstriction by hemoglobin-O2 carrier in Sprague-Dawley but not Wistar rats

Microvascular and Systemic Impact of Resuscitation with PEGylated Carboxyhemoglobin-Based Oxygen Carrier or Hetastarch in a Rat Model of Transient Hemorrhagic Shock

BACKGROUND

Hemorrhage is the leading cause of preventable, traumatic death. Currently, prehospital resuscitation fluids provide preload but not oxygen-carrying capacity-a critical blood function that mitigates microvascular ischemia and tissue hypoxia during hemorrhagic shock. Solutions containing polymerized hemoglobin have been associated with vasoactive and hypertensive events. A novel hemoglobin-based oxygen carrier, modified with PEGylation and CO moieties (PEG-COHb), may overcome these limitations.

OBJECTIVES

To evaluate the systemic and microcirculatory effects of PEG-COHb as compared with the 6% hetastarch in a rat model of hemorrhagic shock.

METHODS

Male Sprague Dawley rats (N = 20) were subjected to severe, controlled, hemorrhagic shock. Animals were randomized to 20% estimated blood-volume resuscitation with either 6% hetastarch or PEG-COHb. Continuous, invasive, cardiovascular measurements, and arterial blood gases were measured. Microcirculatory measurements of interstitial oxygenation (PISFO2) and vasoactivity helped model oxygen delivery in the spinotrapezius muscle using intravital and phosphorescence quenching microscopy.

RESULTS

Hemorrhage reduced mean arterial pressure (MAP), arteriolar diameter, and PISFO2, and increased lactate 10-fold in both groups. Resuscitation with both PEG-COHb and hetastarch improved cardiovascular parameters. However, PEG-COHb treatment resulted in higher MAP (P < 0.001), improved PISFO2 (14 [PEG-COHb] vs. 5 [hetastarch] mmHg; P < 0.0001), lower lactate post-resuscitation (P < 0.01), and extended survival from 90 to 142 min (P < 0.001) as compared with the hetastarch group.

CONCLUSIONS

PEG-COHb improved MAP PISFO2, lactate, and survival time as compared with 6% hetastarch resuscitation. Importantly, hypertension and vasoactivity were not detected in response to PEG-COHb resuscitation supporting further investigation of this resuscitation strategy.

Determination of major UDP-glucuronosyltransferase enzymes and their genotypes responsible for 20-HETE glucuronidation

The compound 20-HETE is involved in numerous physiological functions, including blood pressure and platelet aggregation. Glucuronidation of 20-HETE by UDP-glucuronosyltransferases (UGTs) is thought to be a primary pathway of 20-HETE elimination in humans. The present study identified major UGT enzymes responsible for 20-HETE glucuronidation and investigated their genetic influence on the glucuronidation reaction using human livers (n = 44). Twelve recombinant UGTs were screened to identify major contributors to 20-HETE glucuronidation. Based on these results, UGT2B7, UGT1A9, and UGT1A3 exhibited as major contributors to 20-HETE glucuronidation. The Km values of 20-HETE glucuronidation by UGT1A3, UGT1A9, and UGT2B7 were 78.4, 22.2, and 14.8 μM, respectively, while Vmax values were 1.33, 1.78, and 1.62 nmol/min/mg protein, respectively. Protein expression levels and genetic variants of UGT1A3, UGT1A9, and UGT2B7 were analyzed in human livers using Western blotting and genotyping, respectively. Glucuronidation of 20-HETE was significantly correlated with the protein levels of UGT2B7 (r(2) = 0.33, P < 0.001) and UGT1A9 (r(2) = 0.31, P < 0.001), but not UGT1A3 (r(2) = 0.02, P > 0.05). A correlation between genotype and 20-HETE glucuronidation revealed that UGT2B7 802C>T, UGT1A9 -118T9>T10, and UGT1A9 1399T>C significantly altered 20-HETE glucuronide formation (P < 0.05-0.001). Increased levels of 20-HETE comprise a risk factor for cardiovascular diseases, and the present data may increase our understanding of 20-HETE metabolism and cardiovascular complications.