Halothane and isoflurane increase pulmonary artery endothelial cell sensitivity to oxidant-mediated injury

Volatile anesthetics inhibit phagocytic cell function, yet little is known about their effects on target tissues or on the target tissue response to stimulated phagocytes. Experiments were performed to determine how exposure to halothane and isoflurane changes rat pulmonary artery endothelial cell (RPAEC) viability in response to the toxic oxygen metabolites produced by stimulated phagocytic cells. RPAECs were grown in monolayer culture. The monolayers were treated with phorbol myristate acetate (PMA) -stimulated human neutrophils at an effector-to-target ratio of 20:1 after equilibration with 0.4% or 1.7% halothane or 0.7% or 2.8% isoflurane. As measured by percent-specific release of incorporated ⁵¹Cr label (mean ± SE), cytotoxicity in the presence of 1.7% halothane (75.3 ± 3.4%) was significantly greater (P < 0.02) than cytotoxicity in 5% CO₂ in air (44.7 ± 3.3%) and in 0.4% halothane (57.3 ± 4.7%). Also, cytotoxicity in 1.7% halothane was significantly greater than in 0.4% halothane (P < 0.02). The authors found that RPAECs incubated in isoflurane exhibited significantly greater release of ⁵¹Cr than cells incubated in the MAC equivalent concentrations of halothane: 78.2 ± 2.6% in 0.7% isoflurane (P = 0.0004) and 83.8 ± 1% in 2.8% isoflurane (P = 0.005). Because early neutrophil cytotoxicity has been found to be mediated primarily by hydroxyl radical (HO·) and hydrogen peroxide (H₂O₂), the authors measured H₂O₂ production by similar numbers of PMA-stimulated neutrophils under similar exposure conditions. In carrier gas, PMA-stimulated neutrophils produced 20.5 ± 1.3 nmol H₂O₂·10⁶ cells^-1·h^-1. At the higher concentrations of halothane, H₂O₂ production actually was inhibited in comparison with carrier gas (15.4 ± 1.4 nmol H₂O₂·10⁶ cells^-1·h^-1 in 1.7% halothane and 16.8 ± 0.8 in 2.8% halothane), but the degree of inhibition did not reach statistical significance. In isoflurane, however, H₂O₂ production was not different from that seen in carrier gas. In other experiments, the monolayers were treated with 0, 200, 500, and 1,000 μM H₂O₂ after equilibration with 0.4%, 1.7%, and 2.8% halothane or 0.7%, 2.8%, and 5% isoflurane in 5% CO₂ in air. Efficiency of replating was used to measure degree of injury. Both halothane and isoflurane enhance the sensitivity of the RPAEC monolayers to injury by H₂O₂. The sensitizing effect of halothane was reversed by removing the anesthetic. Halothane and isoflurane thus enhance RPAEC sensitivity to injury by both H₂O₂ and PMA-stimulated neutrophils. In increasing RPAEC sensitivity to injury by oxygen metabolites, halothane and isoflurane may be inhibiting processes involved in intracellular antioxidant defenses. Use of volatile anesthetics in patients at risk for oxidant-mediated end-organ injury thus may enhance the magnitude of such injuries.