Animal models ischemia-reperfusion injury

Apart from these two Vertex compounds, only one other caspase inhibitor, BDN-6556, has been used in clinical trials. This compound belongs to the class of oxamyl dipeptides and was originally developed by Idun Pharmaceuticals (taken over by Pfizer). It is the only pan-caspase inhibitor that has been evaluated in humans. BDN-6556 displays inhibitory activity against all tested human caspases. It is also an irreversible, caspase-specific inhibitor that does not inhibit other major classes of proteases, or other enzymes or receptors. The therapeutic potential of BDN-6556 was first evaluated in several animal models of liver disease because numerous publications suggested that apoptosis contributes substantially to the development of some hepatic diseases, such as alcoholic hepatitis, hepatitis B and C (HBV, HCV), non-alcoholic steato-hepatitis (NASH), and ischemia/reperfusion injury associated with liver transplant. Accordingly, BDN-6556 was tested in a phase I study. The drug was safe and... 

Recently, monoclonal antibodies were attached to gas-filled microbubbles using this spacer coupHng technology. Testing in vitro, in a cell culture system, demonstrated selective accumulation of decafluorobutane-based lipid shell MP1950 microbubbles with covalently attached anti-lCAM-1 antibodies, onto the surface of activated endotheUum [8]. Anti-P-selectin antibodies attached to such microbubbles via an avidin-biotin scheme showed selective accumulation in the areas of inflammation and ischemia/reperfusion injury in an animal model [93]. In the latter example, biotin was also connected to the microbubble surface via a flexible polymer spacer arm. 

Studies in various animal models and in human hearts suggest that apoptosis does occur in ischemia/reperfusion injury of the heart, though the relative contribution of apoptosis in comparison with necrosis to cell loss in ischemia/ reperfusion injury is still controversial. Cardiomyocyte apoptosis was first reported by Gottlieb et al. [107], who studied the ischemia/reperfusion in rabbit hearts and found the hallmark of apoptosis in ischemic/reperfused hearts but not in the normal or ischemic-only rabbit hearts. Identification of apoptosis was based on the presence of fragmented DNA in electrophoretic gels, on in situ nick end-labeling assays, and on electron microscopy. They concluded that apoptosis may be a specific feature of reperfusion injury in cardiac myocytes. Subsequent studies have shown that apoptosis probably occurs both in ischemia and reperfusion [108], It appears that apoptosis is more prominent after ischemia followed by reperfusion than after ischemia alone [109, 110],... 

Superoxide dismutases are a class of oxido-reductase enzymes which contain either Cu, Fe, or Mn at the active site and catalyze the dismutation of superoxide (1), the one-electron reduction product of molecular oxygen (Eqs. 1 and 2, where M" is the metalloenzyme in the reduced state and M" is the enzyme in the oxidized state) to oxygen and hydrogen peroxide. The SOD enzymes have been shown to have efficacy in animal models of disease states proposed to be, in part, mediated by superoxide, such as myocardial ischemia-reperfusion injury, " inflammation, and cerebral ischemia-reperfusion injury. Evidence for superoxide as a mediator... 

The observed stability of this complex was thus adequate to assess this synthetic SOD mimic in a variety of in vitro and in vivo models of superoxide-mediated injury. Most notably this complex exhibits efficacy in in vitro and in vivo models of inflammation, myocardial ischemia-reperfusion injury, " and vascular relaxation and restenosis. In addition, this and other complexes of this class of SOD mimetics derived from I have superior properties to the SOD enzymes in regard to their normal dose-response curve (no deleterious effects observed at high doses in animal models), cellular permeability (dependent on the nature of the R groups), extended in vivo stability, nonimmunogenicity, and projected lower cost. 

A partial form of recombinant human PSGL-1 has been covalently linked to IgG to give rPSGL-Ig (47). This fusion peptide is active as a competitive inhibitor of PSGL-1, and in an animal model, pretreatment with rPSGL-Ig reduces both the thrombo-inflam-matory and neointimal proliferative responses (48). As an inhibitor of neutrophil-endothelial cell adherence, rPSGL-Ig was in early clinical development for the treatment of ischemia-reperfusion injury. 

Renal ischemia/ reperfusion injiuy in vivo activates caspase-1 and caspase-3 [58,67]. In a murine model of ischemia/reperfusion injury, ZVAD-fmk, a pancaspase inhibitor, was shown to attenuate reperfusion-induced DNA damage (as determined by TUNEL assay) and inflammation [67]. Recent studies by Edelstein et al. [62, 62a] help establish a link between the inflammatory aspects of the ischemic/reperfusion injury and caspase activation. In these studies it was observed that caspase 1 deficient mice were protected from ischemia-reperfusion injury. Aware that IL-18 is expressed after several cell stresses and is activated by caspase-1, the authors observed that IL-18 expression is increased in ischemia-reperfusion and caspase-1 converts IL-18 precursor to its active form. Furthermore in caspase-defi-cient mice the activity of IL-18 does not increase and the use of a neutralizing antibody to IL-18 offers protection in wild-type animals. The authors also demonstrate reduced leukocyte infiltration in caspase-1 deficient mice, completing a loop between cell injury, initiation of inflammation, and caspase-1 activation. Another study has demonstrated that caspase-3 activation during ischemia/reperfusion injury may be involved in the downregulation of calpastatin, an inhibitor of calpain [68] indicating a role of caspases for calpain activation during renal injury. 

Resolvins (Rv) are derivatives of EPA and/or DHA and are now well-established as exhibiting anti-inflammatory or pro-resolving properties. They were first identi-hed in a murine air pouch model by Serhan in 2000 (Serhan et al. 2000), and since then have been both applied and detected in various animal inflammatory disease models (i.e., colitis, ischemia-reperfusion injury, wound healing) and human nutritional intervention/disease studies (Kasuga et al. 2008 Bento et al. 2011 Norling et al. 2011 Giera et al. 2012 Mas et al. 2012). 

This condition is referred to as ischemia-reperfusion injury. Several studies in animal models of ischemia-reperfusion injury have shown that the principal cause of cellular death is necrosis (11-13). However, other smdies have shown that cellular death consisted of a necrotic core surrounded by a peri-necrotic area that displayed properties consistent with apoptosis (11,14-18). Therefore, it is likely that cellular death resulting from ischemia-reperfusion injury can consist of a mixture of apoptosis and necrosis, depending on the extent and duration of the ischemia prior to reperfusion. Other disease conditions where evidence demonstrating both apoptosis and necrosis occur includes diabetic cardiomyopathy, sepsis, stroke, and the neurodegenerative disorders Alzheimer s disease and Parkinson s disease. The development of a noninvasive imaging technique capable of measuring apoptosis and necrosis independently could provide valuable information on the balance between apoptosis and necrosis, and if there is a temporal shift in the balance of these mechanisms of cellular death, in a wide variety of pathological conditions. 

Although several potential therapeutic agents have been tested in animal models of ischemia/reperfusion heart injury with some success, nearly none of the specific antiapoptotic agents have reached the stage of clinical research [172]. The studies which have examined the effect of caspase inhibitors on ischemia/reperfusion models are summarized in Table 2. Broad-spectrum caspase inhibitors have been shown in many studies to reduce cardiomyo-cyte apoptosis, to reduce the size of MI, and to preserve heart function after MI [173-175, 178, 181]. The protective effect of caspase inhibitors can be seen when these agents are administered before or after the onset of ischemia but are most prominent when introduced before the onset of reperfusion [172, 175, 178]. Selective caspase inhibitors, on the other hand, have been reported to have varying effect they have been found to reduce cardiomyocytes apoptosis, but the infarct size remained unchanged [177, 178, 181],... 

Two waves of apoptosis during the reperfusion phase after ischemic AKl have been described. The first coincides with a maximum proliferative activity that is at 2-3 days post-injury. The second occurs on day 7-8 following injury [53]. Other investigators have demonstrated that apoptosis peaks between 4 and 14 days of post-ischemia [10]. The discrepancy may be due to different methods used to detect and quantify apoptosis or different animal models of ischemic AKI. 

Much controversy seems to exist as to whether the diabetic heart is more or less sensitive to ischemic injury. A large number of studies using animal models of experimental diabetes (induced by streptozotocin or alloxan) report no change, increased or decreased sensitivity to ischemia and reperfusion. Differences in the experimental design in relation to metabolic and ion changes that occur in diabetic heart might be the basis of such discrepancies. Short-term diabetes is associated with decreased sensitivity to zero-flow ischemia and reperfusion injury. This beneficial effect disappears with increased duration or severity of diabetes. The diabetic heart appears to be more vulnerable in low-flow ischemia and in the presence of elevated fatty acids in the perfusate. Furthermore, hearts from Zucker diabetic fatty and lean Goto-Kakizaki Type-2 diabetic rats are resistant to reperfusion injury.205... 

Using an animal model of ischemia and reperfusion injury, A. M. Lefer etal. (1993) recently showed that sydnonimine C87-3754 infusion, initiated 10 min prior to reperfusion, attenuated myocardial necrosis, prevented neutrophil adherence to the endothelium, and reduced the neutrophil release of damaging superoxide radicals. These effects appear to be related to pharmacological NO donation, since a non-NO compound with a similar chemical structure had no effect in this animal model. Antineutrophil and myocardial protective actions of an experimental NO donor (SPM-5185, a cysteine-containing mononitrate that releases NO) have also been shown in a dog model of myocardial infarction (D. J. Lefer et al., 1993), and in vitro studies have shown that NO donors inhibit activation of human polymorphonuclear leukocytes (Moilanen et al., 1993). 

In support of the antioxidant activity of resveratrol, a number of studies have demonstrated protective effects on oxidative cardiovascular injury." - In animal models, preinfusion of resveratrol prevents reperfusion-induced arrhythmias and mortality due to its antioxidant, free radical-scavenging activity as well as its ability to increase NO release. " These in vivo findings are supported by in vitro observations indicating that resveratrol significantly inhibits the ischemia/reperfusion-induced leukocyte recruitment and superoxide-related microvascular barrier dys-... 

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