TNF-alpha and IL-1beta separately and synergistically depress human myocardial function. Sphingosine likely participates in the TNF-alpha and IL-1beta signal leading to human myocardial functional depression. Therapeutic strategies to reduce production or signaling of either TNF-alpha or IL-1beta may limit myocardial dysfunction in sepsis.

The purpose of this study was to determine whether isolated renal ischemia and reperfusion (I/R) induces renal tumor necrosis factor (TNF) mRNA production, TNF protein expression, or TNF bioactivity and, if so, whether local/early TNF production acts as mediator of ischemia-induced, neutrophil-mediated renal injury. After rats were anesthetized, varying periods of renal ischemia, with or without reperfusion, were induced. Kidney mRNA content (RT-PCR), TNF protein expression (ELISA), TNF bioactivity (WEHI-164 cell clone cytotoxicity assay), and neutrophil infiltration [myeloperoxidase (MPO) assay] were determined. In other animals, renal MPO and serum creatinine were assessed after TNF was neutralized [binding protein (TNF-BP)]. Thirty minutes of ischemia induced renal TNF mRNA. TNF protein expression and bioactivity peaked after 1 h ischemia and 2 h reperfusion, whereas neutrophil infiltration peaked at 4 h reperfusion. TNF-BP neutralized TNF bioactivity, reduced neutrophil infiltration, and protected postischemic function. These results constitute the initial demonstration that 1) early renal tissue TNF expression contributes to neutrophil infiltration and injury after I/R and 2) TNF-BP may offer a new adjunctive therapy in renal preservation prior to planned ischemic insults.

The proinflammatory cytokine IL-18 was investigated for its role in human myocardial function. An ischemia͞reperfusion (I͞R) model of suprafused human atrial myocardium was used to assess myocardial contractile force. Addition of IL-18 binding protein (IL-18BP), the constitutive inhibitor of IL-18 activity, to the perifusate during and after I͞R resulted in improved contractile function after I͞R from 35% of control to 76% with IL-18BP. IL-18BP treatment also preserved intracellular tissue creatine kinase levels (by 420%). Steady-state mRNA levels for IL-18 were elevated after I͞R, and the concentration of IL-18 in myocardial homogenates was increased (control, 5.8 pg͞mg vs. I͞R, 26 pg͞mg; P < 0.01). Active IL-18 requires cleavage of its precursor form by the IL-1␤-converting enzyme (caspase 1); inhibition of caspase 1 also attenuated the depression in contractile force after I͞R (from 35% of control to 75.8% in treated atrial muscle; P < 0.01). Because caspase 1 also cleaves the precursor IL-1␤, IL-1 receptor blockade was accomplished by using the IL-1 receptor antagonist. IL-1 receptor antagonist added to the perifusate also resulted in a reduction of ischemia-induced contractile dysfunction. These studies demonstrate that endogenous IL-18 and IL-1␤ play a significant role in I͞R-induced human myocardial injury and that inhibition of caspase 1 reduces the processing of endogenous precursors of IL-18 and IL-1␤ and thereby prevents ischemia-induced myocardial dysfunction.

Renal ischemia-reperfusion injury induces a cascade of events leading to cellular damage and organ dysfunction. Tumor necrosis factor-alpha (TNF), a potent proinflammatory cytokine, is released from the kidney in response to, and has been implicated in the pathogenesis of, renal ischemia-reperfusion injury. TNF induces glomerular fibrin deposition, cellular infiltration and vasoconstriction, leading to a reduction in glomerular filtration rate (GFR). The signaling cascade through which renal ischemia-reperfusion induces TNF production is beginning to be elucidated. Oxidants released following reperfusion activate p38 mitogen activated protein kinase (p38 MAP kinase) and the TNF transcription factor, NFkappaB, leading to subsequent TNF synthesis. In a positive feedback, proinflammatory fashion, binding of TNF to specific TNF membrane receptors can reactivate NFkappaB. This provides a mechanism by which TNF can upregulate its own expression as well as facilitate the expression of other genes pivotal to the inflammatory response. TNF receptor binding can also induce renal cell apoptosis, the major form of cell death associated with renal ischemia-reperfusion injury. Anti-TNF strategies targeting p38 MAP kinase, NFkappaB, and TNF itself are being investigated as methods of attenuating renal ischemic injury. The control of TNF production and activity represents a realistic goal for clinical medicine.

Preconditioning may find ready applicability in humans facing scheduled global cardiac ischemiareperfusion (IR) during bypass or transplantation, where such a maneuver is feasible before arrest. Our objective was to delineate and exploit the endogenous preconditioning mechanism triggered by transient ischemia (TI) and thereby attenuate myocardial postischemic mechanical dysfunction by clinically acceptable means. Preconditioning by 2 minutes of TI followed by 10 minutes of normal perfusion protected isolated rat left ventricle function assessed after 20 minutes of global, 37°C ischemia and 40 minutes of reperfusion. Final recovery of developed pressure (DP) was improved (91.5±l.9%o of equilibration DP versus unconditioned IR control, 57.4+2.4%, P<.01) and was accompanied by increased contractility (±dP/dt). Norepinephrine release increased after TI, and reserpine pretreatment abolished TI preconditioning. This suggests that endogenous norepinephrine mediates functional preconditioning in rat. Brief pretreatment (2 minutes) with exogenous norepinephrine reproduced the protection (89.1+1.4%) of postischemic function. Functional protection persisted after the hemodynamic effects had resolved. Norepinephrine-induced preconditioning was simulated by phenylephrine and blocked by al-adrenergic receptor antagonist. TI preconditioning was similarly lost after selective ovl-adrenergic receptor blockade. We conclude that transient ischemic preconditioning is mediated by the sympathetic neurotransmitter release and at,-adrenergic receptor stimulation. Although the postreceptor mechanism remains unclear, functional protection after IR does not seem related to the magnitude of ATP depletion and elevation of resting pressure during ischemia. Rather, the endogenous mechanisms facilitate both recovery of mechanical function and ATP repletion during reperfusion. (Circ Res. 1993;73:656-670.) KEY WoRDs * adaptation * preconditioning mechanism * myocardial function * norepinephrine * cl-adrenergic receptors * ATP * rat heart T he high rate of energy turnover in myocardial tissue renders the heart very susceptible to ischemia.' Although perfusion must be restored to preserve myocardial function and viability, reperfusion can itself be deleterious.12 Yet, the 150 000 cardiopulmonary bypass and 1000 heart transplantation operations performed annually necessitate extended periods of myocardial ischemia with subsequent reperfusion. Although myocardial dysfunction becomes progressively irreversible with extended ischemia, brief periods of myocardial ischemia trigger an adaptive response that protects the heart against sustained ischemia and reperfusion.2-4 This "preconditioning" phenomenon suggests that transient ischemia (TI) induces intrinsic changes within the myocardium, thereby enhancing its resistance to subsequent ischemia-reperfusion (IR) injury. These protective changes appear effective against a range of post-IR pathophysiology, including stunning, arrhythmias, and infarction. If this preconditioning effect