A Potent Inhibitor of Aminopeptidase P2 Reduces Reperfusion Injury in Models of Myocardial Infarction and Stroke.

During a myocardial infarction or ischemic stroke, blood flow to the heart or brain is partially blocked. This results in reduced delivery of oxygen and nutrients and, ultimately, tissue damage. Initial treatment involves removing the clot and restoring blood flow (reperfusion). However, this treatment is not as effective as one would hope because the reperfusion process itself can cause a different type of damage (reperfusion injury) that contributes up to 50% of the total damage. Bradykinin is an autocoid that is released from blood vessel endothelial cells during ischemia and reperfusion and has the potential to prevent reperfusion injury. However, bradykinin is rapidly inactivated by enzymes on endothelial cells, limiting its beneficial effects. One of these enzymes is aminopeptidase P2. We designed a potent and specific inhibitor of aminopeptidase P2 called ST-115, [(S)-2-mercapto-4-methylpentanoyl]-4(S)-fluoro-Pro-Pro-3(R)-beta-Pro. When ST-115 is administered intravenously at the start of reperfusion, it reduces bradykinin degradation. This increases bradykinin's concentration in the capillaries and enhances its protective effects. We tested ST-115 in a mouse model of myocardial infarction and found that the damaged area of the heart was reduced by 58% compared with mice given saline. In a rat model of ischemic stroke, ST-115 reduced functional deficits in a skilled walking test by 60% and reduced brain edema by 51%. It reduced brain infarct size by 48% in a major subset of rats with small strokes. The results indicate that ST-115 can ameliorate reperfusion injury and can ultimately serve as a therapeutic for acute myocardial infarction and ischemic stroke. SIGNIFICANCE STATEMENT: We have shown that our aminopeptidase P2 inhibitor, ST-115, can reduce tissue injury caused by episodes of ischemia followed by reperfusion. It was successful in rodent models of myocardial infarction and stroke. The clinical use would involve the intravenous administration of ST-115 at the induction of reperfusion. In the case of stroke, the successful technique of thrombectomy could be combined with ST-115 administration to simultaneously reduce both ischemic and reperfusion injury.

Cardioprotection via the skin: nociceptor-induced conditioning against cardiac MI in the NIC of time.

Timely reperfusion is still the most effective approach to limit infarct size in humans. Yet, despite advances in care and reduction in door-to-balloon times, nearly 25% of patients develop heart failure postmyocardial infarction, with its attendant morbidity and mortality. We previously showed that cardioprotection results from a skin incision through the umbilicus in a murine model of myocardial infarction. In the present study, we show that an electrical stimulus or topical capsaicin applied to the skin in the same region induces significantly reduced infarct size in a murine model. We define this class of phenomena as nociceptor-induced conditioning (NIC) based on the peripheral nerve mechanism of initiation. We show that NIC is effective both as a preconditioning and postconditioning remote stimulus, reducing infarct size by 86% and 80%, respectively. NIC is induced via activation of skin C-fiber nerves. Interestingly, the skin region that activates NIC is limited to the anterior of the T9-T10 vertebral region of the abdomen. Cardioprotection after NIC requires the integrity of the spinal cord from the region of stimulation to the thoracic vertebral region of the origin of the cardiac nerves but does not require that the cord be intact in the cervical region. Thus, we show that NIC is a reflex and not a central nervous system-mediated effect. The mechanism involves bradykinin 2 receptor activity and activation of PKC, specifically, PKC-α. The similarity of the neuroanatomy and conservation of the effectors of cardioprotection supports that NIC may be translatable to humans as a nontraumatic and practical adjunct therapy against ischemic disease. NEW & NOTEWORTHY This study shows that an electrical stimulus to skin sensory nerves elicits a very powerful cardioprotection against myocardial infarction. This stimulus works by a neurogenic mechanism similar to that previously elucidated for remote cardioprotection of trauma. Nociceptor-induced conditioning is equally potent when applied before ischemia or at reperfusion and has great potential clinically.

Manganese(III) tetrakis(1-methyl-4-pyridyl) porphyrin, a superoxide dismutase mimetic, reduces disease severity in in vitro and in vivo models for dry-eye disease.

PURPOSE: To determine the efficacy of the superoxide dismutase mimetic, manganese(III) tetrakis(1-methyl-4-pyridyl) porphyrin (Mn-TM-2-PyP), in vitro in human corneal epithelial (HCE-T) cells and in vivo in a preclinical mouse model for dry-eye disease (DED). METHODS: In vitro, HCE-T cultures were exposed either to tert-butylhydroperoxide (tBHP) to generate oxidative stress or to hyperosmolar conditions modeling cellular stress during DED. Cells were pre-treated with Mn-TM-2-PyP or vehicle. Mn-TM-2-PyP permeability across stratified HCE-T cells was assayed. In vivo, Mn-TM-2-PyP (0.1% w/v in saline) was delivered topically as eye drops in a desiccating stress/scopolamine model for DED. Preclinical efficacy was compared to untreated, vehicle- and ophthalmic cyclosporine emulsion-treated mice. RESULTS: Mn-TM-2-PyP protected HCE-T cells in a dose-dependent manner against tBHP-induced oxidative stress as determined by calculating the IC50 for tBHP in the resazurin, MTT and lactate dehydrogenase release cell viability assays. Mn-TM-2-PyP did not protect HCE-T cells from hyperosmolar insult. Its permeability coefficient across a barrier of HCE-T cells was 1.1 ±â€¯0.05 × 10-6 cm/s and the mass balance was 62 ±â€¯0.6%. In vivo, topical dosing with Mn-TM-2-PyP resulted in a statistically significant reduction of corneal fluorescein staining, similar to ophthalmic cyclosporine emulsion. Furthermore, Mn-TM-2-PyP significantly reduced leukocyte infiltration into lacrimal glands and prevented degeneration of parenchymal tissue. No protective effect against loss of conjunctival goblet cells was observed. Notably, Mn-TM-2-PyP did not produce ocular toxicity when administered topically. DISCUSSION: Our data suggest that Mn-TM-2-PyP, a prototypic synthetic metalloporphyrin compound with potent catalytic antioxidant activity, can improve signs of DED in vivo by reducing oxidative stress in corneal epithelial cells.