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 tertbutylhydroperoxide (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 tBHPinduced oxidative stress as determined by calculating the IC 50 for tBHP in the resazurin, MTT and lactate dehydrogenase release cell viability assays. Mn-TM-2-PyP did not protect HCE-T cells
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.
ΔAbs, the difference between the two absorbances; ACE, angiotensin converting enzyme; B 2 : bradykinin B 2 receptor; (a number [95.0%CI number, number]): effect size, 95.0% confidence interval, width lower bound, upper bound]); CCA, common carotid arteries; DTNB, 5,5'-dithio-bis-(2-nitrobenzoic acid); GMP, Good Manufacturing Practices; IC 50, the concentration of an inhibitor that inhibits the enzyme activity by 50% relative to control activity; K i , the dissociation equilibrium constant of an enzyme-inhibitor complex; K m , Michaelis constant (the concentration of the substrate at which the enzyme is at half maximal velocity); LAD, left anterior descending coronary artery; MCA, middle cerebral artery; eNOS, endothelial nitric oxide synthase; RRR, Relative Risk Reduction; tMCAO, transient middle cerebral artery occlusion; ST-115, [(S)-2-mercapto-4-methylpentanoyl]-4(S)-fluoro-Pro-Pro-3(R)-beta-Pro; tPA, tissue plasminogen activator; TTC, triphenyltetrazolium chloride.
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