Recombinant human activated protein C attenuates cardiovascular and microcirculatory dysfunction in acute lung injury and septic shock

Abstract

Introduction: This prospective, randomized, controlled, experimental animal study looks at the effects of recombinant human activated protein C (rhAPC) on global hemodynamics and microcirculation in ovine acute lung injury (ALI) and septic shock, resulting from smoke inhalation injury.

Methods: Twenty-one sheep (37 ± 2 kg) were operatively prepared for chronic study and randomly allocated to either the sham, control, or rhAPC group (n = 7 each). The control and rhAPC groups were subjected to insufflation of four sets of 12 breaths of cotton smoke followed by instillation of live Pseudomonas aeruginosa into both lung lobes, according to an established protocol. Healthy sham animals were not subjected to the injury and received only four sets of 12 breaths of room air and instillation of the vehicle (normal saline). rhAPC (24 μg/kg/hour) was intravenously administered from 1 hour post injury until the end of the 24-hour experiment. Regional microvascular blood flow was analyzed using colored microspheres. All sheep were mechanically ventilated with 100% oxygen, and fluid resuscitated with lactated Ringer's solution to maintain hematocrit at baseline levels.

Results: The rhAPC-associated reduction in heart malondialdehyde (MDA) and heart 3-nitrotyrosine (a reliable indicator of tissue injury) levels occurred parallel to a significant increase in mean arterial pressure and to a significant reduction in heart rate and cardiac output compared with untreated controls that showed a typical hypotensive, hyperdynamic response to the injury (P < 0.05). In addition, rhAPC significantly attenuated the changes in microvascular blood flow to the trachea, kidney, and spleen compared with untreated controls (P < 0.05 each). Blood flow to the ileum and pancreas, however, remained similar between groups. The cerebral blood flow as measured in cerebral cortex, cerebellum, thalamus, pons, and hypothalamus, was significantly increased in untreated controls, due to a loss of cerebral autoregulation in septic shock. rhAPC stabilized cerebral blood flow at baseline levels, as in the sham group.

Conclusions: We conclude that rhAPC stabilized cardiovascular functions and attenuated the changes in visceral and cerebral microcirculation in sheep suffering from ALI and septic shock by reduction of cardiac MDA and 3-nitrotyrosine.

Figure 1

Changes in global hemodynamics. Changes in (a) mean arterial pressure (mmHg), (b) heart rate (bpm), (c) cardiac output (l/minute), and (d) regional microvascular blood flow (RMBF) in kidney cortex (percentage of baseline). Data expressed as mean ± standard error of the mean of seven animals per group. Significance P < 0.05: #versus baseline (BL = 0 hours); †versus sham; *versus control. rhAPC, recombinant human activated protein C.

Figure 2

Regional microvascular blood flow. Microvascular blood flow (RMBF) in the (a) trachea, (b) cerebral cortex, (c) spleen, and (d) cerebellum (percentage of baseline). Data expressed as mean ± standard error of the mean of seven animals per group. Significance P < 0.05: #versus baseline (BL = 0 hours); †versus sham; *versus control. rhAPC, recombinant human activated protein C.

Figure 3

Tissue analysis. Levels of (a) heart malondialdehyde (MDA, μM/ml/mg) and (b) heart 3-nitrotyrosine (3-NT, nM/ml/mg protein). Data expressed as mean ± standard error of the mean of seven animals per group. Significance P < 0.05: †versus sham; *versus control. rhAPC, recombinant human activated protein C.