Preconditioning effects of steroids and hyperoxia on cardiac ischemia-reperfusion injury and vascular reactivity.

OBJECTIVE: Corticosteroids and hyperoxia protect the heart against ischemia-reperfusion injury and may attenuate vascular reactivity. We hypothesized that (1) combining these two pretreatments induces an additive cardioprotection, (2) protection depends on activation of survival kinases and/or heat shock proteins, and (3) these interventions would change vascular reactivity into a more relaxed state. METHODS: Male rats were randomized (n=10 in each group): 1. control, 2. dexamethasone (3mg/kg) injected 24 and 12 h before harvesting the hearts, 3. 60 min of hyperoxia (90-95% O(2)) immediately before harvest, 4. combination of dexamethasone and hyperoxia as in groups 2 and 3. The hearts were Langendorff-perfused and exposed to 30 min of global ischemia and reperfused for 120 min. Cardiac function was monitored and infarct size determined. Isometric tension to vasoconstrictive and vasodilatory agents was measured in femoral artery rings. Phosphorylation of survival kinases (protein kinase B/AKT, extracellular signal-regulated kinases (ERK1/2), the stress-activated/c-Jun NH2 terminal kinases (SAPK/JNK) and p38 MAPK), adenosine monophosphate dependent kinase (AMPK) and expression of heat shock protein 72 (HSP72) in hearts was evaluated by immunoblotting. RESULTS: Infarct size was attenuated in all pretreated groups versus controls: 29% reduction in the combined group (p<0.01), 23% in hyperoxia group (p<0.05) and 31% in dexamethasone group (p<0.01). There was no significant difference between the treated groups. Combined pretreatment improved postischemic left ventricular end diastolic pressure compared to all other groups (p<0.001 vs controls, p=0.002 vs dexamethasone, p=0.005 vs hyperoxia). Combined pretreatment improved left ventricular developed pressure and coronary flow compared to controls (p<0.001 for both) and hyperoxia (p=0.0047 and p=0.0024, respectively). Combined pretreatment enhanced endothelium-independent relaxation (p=0.0032) compared to controls. Excepting ERK1/2 phosphorylation in the combined group during early reperfusion, there was no increased phosphorylation of the survival kinases AKT, p38, JNK, or AMPK and no increase of HSP72 expression. CONCLUSION: Combined pretreatment by hyperoxia and dexamethasone improved postischemic heart function, but did not reduce infarct size compared to single pretreatment groups. Except of a possible role of ERK1/2, protection depended neither on survival kinases nor heat shock protein 72.     

Pre-treatment with hyperoxia before coronary artery bypass grafting - effects on myocardial injury and inflammatory response

BACKGROUND: In experimental studies, exposure to hyperoxia for a limited time before ischaemia induces a low-grade systemic oxidative stress and evokes an (ischaemic) preconditioning-like effect of the myocardium. We hypothesised that hyperoxia before cardioplegia could protect the myocardium against necrosis and stunning caused by ischaemia-reperfusion. METHODS: Forty patients undergoing coronary artery bypass grafting were randomly exposed to an oxygen fraction of 0.4 or > 0.96 in inspired air on an average of 120 min before cardioplegia. Blood for troponin I, creatine kinase-MB, lactate, glutathione and interleukin-6 was sampled from arterial and coronary sinus cannulae during 20 min of reperfusion. Additional arterial samples were drawn 60 min after declamping and in the first post-operative morning. The cardiac index and right and left ventricular stroke work indices were measured before sternotomy and up to 12 h post-operatively. RESULTS: Troponin I, creatine kinase-MB and lactate did not differ between the groups. Hyperoxic pre-treatment had no impact on the post-operative haemodynamic indices measured with the thermodilution pulmonary artery catheter. More oxidised glutathione was released in the hyperoxia group in the first minute of reperfusion (P = 0.015). Hyperoxic pre-treatment abolished the myocardial release of interleukin-6 during 20 min of reperfusion (P = 0.021 vs. controls). In the first post-operative morning, interleukin-6 was higher in the hyperoxia group [127.0 (86.0-140.0) vs. 85.2 pg/ml (66.6-94.5 pg/ml); P = 0.016]. Conclusions: Exposure to >96% oxygen before cardioplegia did not attenuate ischaemia-reperfusion injury of the heart in patients undergoing coronary artery bypass grafting. The only potentially beneficial effect observed was the decreased transmyocardial release of interleukin-6.     

Preconditioning with oxygen attenuates rat renal ischemia-reperfusion injury

BACKGROUND: Short time pretreatment with oxygen is reported to be protective against subsequent ischemia-reperfusion (IR) injury of heart and spinal cord in some animal models. The purpose of this study was to investigate the effects of pre-exposure to hyperoxic environment on rat renal IR injury for the first time. MATERIALS AND METHODS: The effects of 1 h/d pretreatment with oxygen (>or=95%) for 5 days on a right nephrectomized rat model of renal IR injury was investigated by comparing creatinine clearance, fractional excretion of sodium, plasma creatinine, blood urea nitrogen, and histological injury scores among three groups: IR (40 min ischemia-24 h reperfusion), sham (no IR), and hyperoxia (5 days intermittent pretreatment with oxygen + IR). RESULTS: Intermittent pretreatment with oxygen resulted in significant improvement of creatine clearance and fractional excretion of sodium (P 相似文献   

Preconditioning protects the severely atherosclerotic mouse heart

BACKGROUND: Coronary atherosclerosis has profound effects on vascular and myocardial biology, and it has been speculated that the atherosclerotic heart does not benefit from ischemic preconditioning. METHODS: To investigate if atherosclerosis would influence the preconditioning response, Apolipoprotein E/low density lipoprotein (LDL) receptor double knockout mice (ApoE/LDLr-/-) were fed an atherogenic diet (21% fat, 0.15% cholesterol) for 6 to 8 months. At that time, extensive atherosclerotic lesions throughout the coronary tree were seen in transverse sections stained with Oil Red-O. Hearts of ApoE/LDLr-/- mice were Langendorff-perfused with 40 minutes of global ischemia and 60 minutes reperfusion, and compared with C57BL/6 controls. Preconditioning with two episodes of 2 minutes of ischemia and 5 minutes reperfusion, or exposing the mice to a hyperoxic environment (O2 > 98%) for 60 minutes before heart perfusion, was performed. RESULTS: Hearts of mice with coronary atherosclerosis had worse postischemic function, and increased infarct size and troponin T release compared to hearts of C57BL/6 mice. Ischemic preconditioning improved postischemic ventricular function, and reduced myocardial infarct size and troponin T release in both normal and ApoE/LDLr-/- mice. The effects were most pronounced in ApoE/LDLr-/- hearts. Exposure to hyperoxia exerted a similar protection of function and cell viability of ApoE/LDLr-/- mice hearts. CONCLUSIONS: These findings suggest that the severely atherosclerotic heart may be protected by preconditioning induced by ischemia or hyperoxia.     

Myocardial protection with intermittent cross-clamp fibrillation: does preconditioning play a role?

Objective: Previously, we showed intermittent cross-clamp fibrillation afforded equivalent protection to cardioplegia. This study examined whether protection induced by intermittent cross-clamp fibrillation involves an ischemic preconditioning mechanism. Methods: Isolated Langendorff-perfused rat hearts were subjected to three different studies to determine: Study 1, whether a single intermittent cross-clamp fibrillation episode (10 min) and reperfusion (10 min) before prolonged ischemia acts as a preconditioning trigger for protection; Study 2, whether cardioprotection induced by intermittent cross-clamp fibrillation alone (no prolonged ischemia) involves a preconditioning mechanism; Study 3, whether intermittent cross-clamp fibrillation cardioprotection can be prevented by targeting putative components of the preconditioning mechanism (protein kinase C or the mitochondrial ATP-sensitive potassium (K_ATP) channel). Hearts were reperfused (60 min) and recovery of function (left ventricular developed pressure measured using an intraventricular balloon) and myocardial injury (creatine kinase leakage) were measured. Results: In Study 1, recovery of function in the single intermittent cross-clamp fibrillation hearts was 61 ± 3% (mean ± SEM) (p < 0.05) compared to 41 ± 2% in control group; glibenclamide (a non-specific ATP-sensitive potassium (K_ATP)-channel blocker) prevented this preconditioning protection (37 ± 4%). In Study 2, recovery of function in intermittent cross-clamp fibrillation hearts (62 ± 3%) was significantly (p < 0.05) higher than intermittent cross-clamp fibrillation hearts treated with glibenclamide (33 ± 2%) and ischemia hearts (30 ± 5%). In Study 3, protection by intermittent cross-clamp fibrillation (60 ± 3%; p < 0.05) was attenuated by protein kinase C inhibition (chelerythrine, 34 ± 3%) and mitochondrial K_ATP-channel blockade (5-hydroxydecanoate, 27 ± 4%) to levels not significantly different from that of ischemia hearts (25 ± 4%). Conclusions: The cardioprotective efficacy of intermittent cross-clamp fibrillation was attenuated by protein kinase C inhibition or K_ATP-channel blockade. Involvement of these putative preconditioning cascade components in association with cardioprotection induced by intermittent cross-clamp fibrillation, suggests a role for the ischemic preconditioning mechanism.     

Aerobic interval training improves VO2peak in coronary artery disease patients; no additional effect from hyperoxia

Objectives. To investigate whether hyperoxic aerobic interval training improves training quality in coronary artery disease patients. Design. Twenty-one stable coronary artery disease patients were recruited to hyperoxic (n=10) and normoxic (n=11) groups (age: 62.4±6.8 years). Patients underwent 30 supervised 4×4 minutes interval training sessions using treadmill walking, at 85–95% of peak heart rate. Results. Arterial saturation was significantly increased by 3% at pretest from normoxic to hyperoxic testing conditions. Peak oxygen uptake and stroke volume increased significantly by 16% and 17% (p<0.05) and by 16% and 18% (p<0.05) in the hyperoxic and normoxic training groups respectively. No difference was revealed between groups for peak oxygen uptake and stroke volume. Blood volumes were unchanged from pre to post training. Peak oxygen uptake measured in normoxia and hyperoxia in the hyperoxia training group revealed no difference. Conclusion. The present study shows that breathing 100% oxygen enriched air during aerobic interval training in stable coronary artery disease patients does not improve peak oxygen uptake above the level attained with normoxic training.     

The effect of anaesthetics on the myocardium--new insights into myocardial protection

A variety of laboratory and clinical studies clearly indicate that exposure to anaesthetic agents can lead to a pronounced protection of the myocardium against ischaemia-reperfusion injury. Several changes in the protein structure of the myocardium that may mediate this cardioprotection have been identified. Ischaemia-reperfusion of the heart occurs in a variety of clinical situations including transplantations, coronary artery bypass grafting or vascular surgery. Ischaemia may also occur during a stressful anaesthetic induction. Early restoration of arterial blood flow and measures to improve the ischaemic tolerance of the tissue are the main therapeutic options (i.e. cardioplegia and betablockers). There exists increasing evidence that anaesthetic agents interact with the mechanisms of ischaemia-reperfusion injury and protect the myocardium by a 'preconditioning' and a 'postconditioning' mechanism. Hence, the anaesthesiologist may substantially influence the critical situation of ischaemia-reperfusion during surgery by choosing the appropriate anaesthetic agent. This review summarizes the current understanding of the mechanisms of anaesthetic-induced myocardial protection. In this context, three time windows of anaesthetic-induced cardioprotection are discussed: administration (1) during ischaemia, (2) after ischaemia-during reperfusion (postconditioning) and (3) before ischaemia (preconditioning). Possible clinical implications of these interventions will be reviewed.     

Neonatal myocardium resists reperfusion injury

The response of neonatal myocardium to ischemia and reperfusion was observed in an isolated working heart model using neonatal rabbits and compared to that of the adult rabbit heart. Lipid peroxidation occurring during ischemia and that occurring during reperfusion were evaluated separately. Malondialdehyde (MDA) in heart tissue was measured as an index of lipid peroxidation, and the occurrence of oxygen free radical damage was assessed by the effects of the scavengers, superoxide dismutase and catalase, on MDA production. Baseline MDA levels were similar in neonatal and adult hearts, were changed little by treatment with normoxic cardioplegia, and were elevated in both groups by treatment with hyperoxic cardioplegia. Thus, the degree of lipid peroxidation during ischemia is similar in neonatal and adult hearts. After 10 min of retrograde reperfusion subsequent to treatment with anoxic cardioplegia, the MDA content of adult hearts was significantly greater than that of similarly treated neonatal hearts. Addition of free radical scavengers to the reperfusion medium lowered the MDA content of adult hearts significantly, but not to the level of neonatal hearts. After 60 min of reperfusion subsequent to hyperoxic cardioplegia, adult hearts had higher MDA than neonates; addition of scavengers to the cardioplegia did not lower the MDA significantly in either group. Only 5 of 12 adult hearts recovered function after hyperoxic cardioplegia, while all 12 neonatal hearts recovered. Our results indicate that neonatal myocardium suffers less damage from oxygen-centered free radicals during reperfusion than does adult myocardium.     

Membrane perturbations in myocardium: oxygen radicals mediate injuries in experiments

Experiments were undertaken on rats and dogs to study the range of endogenous lipid peroxidation (measured by formation of malondialdehyde in heart tissue) and to analyse the effects of hyperoxic, hypoxic and ischaemic influences. The acute hyperoxia caused a moderate increase in lipid peroxidation. The malondialdehyde formation was perceptibly higher in hypoxia, while the highest values were found in ischaemic hearts. It can be concluded that the cytotoxic oxygen metabolites cause unfavourable influences on heart structure and function, for this reason an antioxidant therapy is to be recommended.     

Effects of hydrogen sulphide on ischaemia–reperfusion injury and ischaemic preconditioning in the isolated, perfused rat heart

OBJECTIVE: Hydrogen sulphide (H(2)S) protects the heart against ischaemia-reperfusion injury caused by low flow or local ischaemia. We hypothesised that: (1) H(2)S protects against global ischaemia-reperfusion injury of the heart, (2) H(2)S plays a mechanistic role in ischaemic preconditioning, and (3) H(2)S acts by phosphorylation of protein kinases. METHODS: Isolated, perfused rat hearts were used in two series. Series 1: group 1.1 (n=10), 40 min of ischaemia and 120 min of reperfusion, group 1.2 (n=7), like 1.1 except that 40 microM NaHS was added to the perfusate during stabilisation and throughout the experiment. Group 1.3 (n=10), like 1.1, but endogenously produced H(2)S was blocked by D,L-propargylglycine. Series 2: group 2.1 (n=10) control, 30 min of ischaemia followed by 120 min of reperfusion. Group 2.2 (n=10) ischaemic preconditioning before sustained ischaemia and 120 min of reperfusion. Group 2.3 (n=10) like 2.2 except of D,L-propargylglycine treatment like in group 1.3. Mitogen activated protein kinases including extracellular signal-regulated kinases (ERK 1/2), the stress-activated/c-Jun NH2 terminal kinases (JNK), P38, as well as protein kinase B/AKT (AKT), adenosine monophosphate dependent protein kinase (AMPK) and the inducible heat shock protein 72 were measured by Western blotting. Adenine nucleotides (ATP, ADP, and AMP) were measured by high-pressure liquid chromatography and energy charge was calculated. RESULTS: Infarct size was increased by D,L-propargylglycine (40+/-6 vs 27+/-10% in controls, p=0.03, Bonferroni post hoc test). There was a non-significant decrease in infarct size in the NaHS group (to 20+/-13%). Western blot analysis indicated an upregulation of heat shock protein 72 in the NaHS treated group and a reduced phosphorylation of AKT in the D,L-propargylglycine group. D,L-propargylglycine had no effect on ischaemic preconditioning or on phosphorylation of protein kinases (ERK, AKT, P38, JNK and AMPK) in preconditioned hearts. No difference in energy charge was found between groups, although ADP was increased in the NaHS-treated group. CONCLUSION: Endogenous H(2)S production protects against global ischaemia, and H(2)S may be a part of the endogenous cell defence. However, endogenous H(2)S did not appear to be important in ischaemic preconditioning, and protein kinases were not important for the effect of H(2)S. Exogenous H(2)S may provide myocardial protection, possibly acting by expression of heat shock protein 72.     

High-level co-expression of complement regulators on vascular endothelium in transgenic mice: CD55 and CD59 provide greater protection from human complement-mediated injury than CD59 alone

Abstract: High-level endothelial expression of the human complement regulatory factor CD59 has been shown to protect transgenic mouse hearts from human complement-mediated injury in an ex vivo perfusion model. In this study we examine whether co-expression of CD55 provides additional protection. CD55/CD59 double-transgenic mice were generated by co-injection of CD55 and CD59 expression constructs driven by the human intercellular adhesion molecule 2 (ICAM-2) promoter. A line was established from one mouse that exhibited strong expression of CD55 and CD59 on vascular endothelium in the heart and other transplantable organs. An ex vivo perfusion model was used to compare hearts from these CD55/CD59 mice with hearts from a previously established line, which expressed CD59 at a similar level to the double transgenic line. CD59 hearts displayed prolonged survival compared to wild-type hearts during perfusion with 40% human plasma and maintained approximately 20% maximum work after 60 min. CD55/CD59 hearts were further protected, with work maintained at 35% of the maximum level after 60 min. The data demonstrate that high-level endothelial co-expression of CD55 and CD59 provides greater protection from human complement-mediated injury in this model than expression of CD59 alone.     

Xenon - noble gas with organprotective properties

Besides it's anaesthetic properties, xenon may induce biological effects that may protect various organs from ischaemia-reperfusion injury. Xenon is an antagonist of the NMDA-receptor and reduces the neuronal injury mediated via these receptors. In contrast to other NMDA-receptor antagonists, xenon has no neurotoxic side effects. Xenon also protects the heart in ischaemia-reperfusion situations. Xenon reduces the post-ischaemic reperfusion injury and offers cardioprotection by inducing pharmacological preconditioning. These organ protective properties of xenon might be useful in special clinical situations.     

Hyperoxia-Induced Protection against Rat's Renal Ischemic Damage: Relation to Oxygen Exposure Time

Background. Pre-exposure to hyperoxic gas (≥ 95%) has been shown to protect the heart and central nervous system from ischemia-reperfusion injury. In the present study, we investigated whether oxygen pretreatment induces delayed renal protection in rats. The possible role of some renal antioxidant agents was also investigated. Materials and methods. Adult male Wistar rats were kept in a hyperoxic (HO) (≥ 95% O₂) environment for 0.5 h, 1 h, 2 h, 3 h, 6 h, and 2 h/day for three consecutive days and 4 h/day for six consecutive days, and control group (IR) animals were kept in the cage with no HO, one day before subjecting their kidney to 40 minutes of ischemia and 24h of reperfusion. Renal function was assessed by comparing plasma creatinine (Cr), blood urea nitrogen (BUN), creatinine clearance (CLCr), and fractional excretion of sodium (FENa%). Histopathological injury score was also determined according to the Jablonski method. To examine the antioxidant system induction by hyperoxia, we measured renal catalase and superoxide dismutase activity, and renal glutathione and malondialdehyde content. Results. Our data demonstrated that only in 4 h/day HO for six consecutive days, the renal function tests (Cr, CLCr, BUN, and FENa%) and Jablonski histological injury were better than control group (p < 0.05). The beneficial effect of oxygen pretreatment in this group was associated with increased renal catalase activity compared with those obtained from control group (p < 0.05). Conclusion. The present study demonstrates that repeated exposure to hyperoxic (≥ 95% O₂) environment can reduce subsequent rat's renal ischemia-reperfusion damage. Induction of endogenous antioxidant system may partially explain this beneficial effect of hyperoxic preconditioning.     

Hyperoxia and angiogenesis

We hypothesized that tissue hyperoxia would enhance and hypoxia inhibit neovascularization in a wound model. Therefore, we used female Swiss-Webster mice to examine the influence of differential oxygen treatment on angiogenesis. One milliliter plugs of Matrigel, a mixture of matrix proteins that supports but does not itself elicit angiogenesis, were injected subcutaneously into the mice. Matrigel was used without additive or with added vascular endothelial growth factor (VEGF) or anti-VEGF antibody. Animals were maintained in hypoxic, normoxic, or one of four hyperoxic environments: hypoxia -- 13 percent oxygen at 1 atmosphere absolute (ATA); normoxia -- 21 percent oxygen at 1 ATA; hyperoxia -- (groups a-d) 100 percent oxygen for 90 minutes twice daily at the following pressures: Group a, 1 ATA; Group b, 2 ATA; Group c, 2.5 ATA; Group d, 3.0 ATA. Subcutaneous oxygen tension was measured in all groups. The Matrigel was removed 7 days after implantation. Sections were graded microscopically for the extent of neovascularization. Angiogenesis was significantly greater in all hyperoxic groups and significantly less in the hypoxic group compared with room air-exposed controls. Anti-VEGF antibody abrogated the angiogenic effect of both VEGF and increased oxygen tension. We conclude that angiogenesis is proportional to ambient pO(2) over a wide range. This confirms the clinical impression that angiogenesis requires oxygen. Intermittent oxygen exposure can satisfy the need for oxygen in ischemic tissue.     

Protective effects of prostaglandin I2 analogues on CPK release in rat’s heart-lung preparation

The effects of prostaglandin I₂ analogues (PGI₂-a: op-41483 and op-2507) on oxygen toxicity during hyperoxic perfusion were evaluated in an experiment on isolated rat heart lung preparation, with the release of creatine phosphokinase (CPK) in the perfusate blood. There were no significant differences in heart rate and right atrial pressure between PGI₂-a treated and untreated hearts. The CPK release from the heart with oxygen was significantly higher than that of the air (P < 0.001). However, the CPK release from the PGI₂-a treated hearts was significantly less than that from the untreated hearts (P < 0.05). These results indicate that PGI₂-a may prevent cell damage which was induced by hyperoxia.(Kashimoto S, Nakamura T, Oguchi T, et al.: Protective effects of prostaglandin I₂ analogues on CPK release in rats heart-lung preparation. J Anesth 5: 359–362, 1991)     

Effects of hyperoxia on neonatal myocardial energy status and response to global ischemia

Background. This study examines the effect of neonatal exposure to clinically relevant hyperoxia levels on both in vivo myocardial metabolism and the subsequent metabolic response to global ischemia.

Methods. Three-day-old pigs were ventilated to normoxia (80 mm Hg, 2 or 5 hours, N = 11), mild hyperoxia (250 mm Hg, 2 hours, N = 9), or severe hyperoxia (500 mm Hg, 5 hours, N = 14). Ventricular biopsies obtained at the end of the ventilation period, and at early and late ischemia were analyzed for ATP, ADP, AMP, creatine phosphate, glycogen, and lactate.

Results. Hyperoxia did not significantly alter in vivo metabolism. During early ischemia, hearts exposed to severe hyperoxia had better ATP and glycogen preservation (p < 0.003). These hearts exhibited almost complete (92%) creatine phosphate depletion, in contrast to incomplete creatine phosphate use in all other neonatal hearts, even in the face of 30% ATP reductions. However, hearts exposed to severe hyperoxia also had a higher incidence of fibrillation during ischemia, which accelerated ATP and glycogen degradation.

Conclusions. Although severe hyperoxia provided an energy-sparing effect during early ischemia, it also increased the incidence of ventricular fibrillation, which negated this beneficial effect.     

Hyperbaric oxygen therapy suppresses osteoclast formation and bone resorption

The cellular and molecular mechanism through which hyperbaric oxygen therapy (HBO) improves osteonecrosis (ON) is unclear. The present study therefore examined the effect of HBO, pressure and hyperoxia on RANKL‐induced osteoclast formation in RAW 264.7 cells and human peripheral blood monocytes (PBMC). Daily exposure to HBO (2.4 ATA, 97% O₂, 90 min), hyperbaric pressure (2.4 ATA, 8.8% O₂, 90 min) or normobaric hyperoxia (1 ATA, 95% O₂, 90 min) significantly decreased RANKL‐induced osteoclast formation and bone resorption in normoxic conditions. HBO had a more pronounced anti‐osteoclastic effect than hyperoxia or pressure alone and also directly inhibited osteoclast formation and resorption in hypoxic conditions a hallmark of many osteolytic skeletal disorders. The suppressive action of HBO was at least in part mediated through a reduction in RANK, NFATc1, and Dc‐STAMP expression and inhibition of hypoxia‐induced HIF‐1α mRNA and protein expression. This data provides mechanistic evidence supporting the use of HBO as an adjunctive therapy to prevent osteoclast formation and bone loss associated with low oxygen partial pressure. © 2013 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 31:1839–1844, 2013     

The pig analogue of CD59 protects transgenic mouse hearts from injury by human complement

BACKGROUND: It has been proposed that hyperacute rejection (HAR) of pig-to-primate vascularized xenografts is due in large part to ineffective regulation of recipient complement by pig complement regulatory proteins (CRPs), and indeed transgenic expression of human CRPs in pigs can prevent hyperacute rejection. However, at least one pig CRP (CD59) efficiently regulates human complement in vitro, suggesting that it is the level of expression of a particular CRP(s) rather than cross-species incompatibility that explains the HAR of porcine xenografts. We investigated the relative effectiveness of transgenically expressed pig and human CD59 in providing protection of mouse hearts from human complement in an ex vivo setting. METHODS: Transgenic mice expressing pig CD59 or human CD59 under the control of the human ICAM-2 promoter, which restricts expression in tissues to vascular endothelium, were used. Hearts from mice expressing similar levels of pig CD59 or human CD59 were perfused ex vivo with 10% human plasma and heart function was monitored for 60 min. Sections of perfused hearts were examined for deposition of the membrane attack complex (MAC). RESULTS: Control nontransgenic hearts (n=5) were rapidly affected by the addition of human plasma, with mean function falling to less than 10% of the initial level within 15 min. In contrast, hearts expressing either pig CD59 (n=6) or human CD59 (n=8) were protected from plasma-induced injury, maintaining 31 and 35% function, respectively, after 60 min of perfusion. MAC deposition was markedly reduced in both pig CD59 and human CD59 transgenic hearts compared to nontransgenic control hearts. CONCLUSIONS: When highly expressed on endothelium in transgenic mice, pig CD59 provided equivalent protection to human CD59 in a model of human complement-mediated xenograft rejection. Thus supranormal expression of endogenous porcine CRPs may be a feasible alternative to the expression of human CRPs in preventing HAR of pig-to-primate xenografts.