Amplification of Cardioprotective Response of Remote Ischemic Preconditioning in Rats by Quercetin: Potential Role of Activation of mTOR-dependent Autophagy and Nrf2

OBJECTIVES

Noninvasive remote ischemic preconditioning (RIPC) is a practical, acceptable, and feasible conditioning technique reported to provide cardioprotection in myocardial ischemia-reperfusion injury (MIRI). It has been well-reported that quercetin possesses antioxidant and anti-inflammatory properties. This study investigates the modification of the cardioprotective response of RIPC by quercetin.

METHODS

Adult Wistar rats were randomized into 12 groups of six animals each. MIRI was induced by subjecting the isolated hearts of Wistar rats to global ischemia for 30 min, succeeded by reperfusion of 120 min after mounting on the Langendorff PowerLab apparatus. Hind limb RIPC was applied in four alternate cycles of ischemia and reperfusion of 5 min each by tying the pressure cuff before isolation of hearts.

RESULTS

MIRI was reflected by significantly increased infarct size, LDH-1, and CK-MB, TNF-α, TBARS, and decreased GSH, catalase, and hemodynamic index, and modulated Nrf2. Pretreatment of quercetin (25 and 50 mg/kg; i.p.) significantly attenuated the MIRI-induced cardiac damage and potentiated the cardioprotective response of RIPC at the low dose. Pretreatment of ketamine (10 mg/kg; i.p.), an mTOR-dependent autophagy inhibitor, significantly abolished the cardioprotective effects of quercetin and RIPC.

CONCLUSIONS

The findings highlight the modification of the cardioprotective effect of RIPC by quercetin and that quercetin protects the heart against MIRI through multiple mechanisms, including mTOR-dependent activation of autophagy and Nrf-2 activation.

Limbic-predominant age-related TDP-43 encephalopathy (LATE-NC): Co-pathologies and genetic risk factors provide clues about pathogenesis

Limbic-predominant age-related TDP-43 encephalopathy neuropathologic change (LATE-NC) is detectable at autopsy in more than one-third of people beyond age 85 years and is robustly associated with dementia independent of other pathologies. Although LATE-NC has a large impact on public health, there remain uncertainties about the underlying biologic mechanisms. Here, we review the literature from human studies that may shed light on pathogenetic mechanisms. It is increasingly clear that certain combinations of pathologic changes tend to coexist in aging brains. Although "pure" LATE-NC is not rare, LATE-NC often coexists in the same brains with Alzheimer disease neuropathologic change, brain arteriolosclerosis, hippocampal sclerosis of aging, and/or age-related tau astrogliopathy (ARTAG). The patterns of pathologic comorbidities provide circumstantial evidence of mechanistic interactions ("synergies") between the pathologies, and also suggest common upstream influences. As to primary mediators of vulnerability to neuropathologic changes, genetics may play key roles. Genes associated with LATE-NC include TMEM106B, GRN, APOE, SORL1, ABCC9, and others. Although the anatomic distribution of TDP-43 pathology defines the condition, important cofactors for LATE-NC may include Tau pathology, endolysosomal pathways, and blood-brain barrier dysfunction. A review of the human phenomenology offers insights into disease-driving mechanisms, and may provide clues for diagnostic and therapeutic targets.

Cerebral Ischemic Preconditioning Aggravates Death of Oligodendrocytes

Neurodegeneration can benefit from ischemic preconditioning, a natural adaptive reaction to sublethal noxious stimuli. Although there is growing interest in advancing preconditioning to preserve brain function, preconditioning is not yet considered readily achievable in clinical settings. One of the most challenging issues is that there is no fine line between preconditioning stimuli and lethal stimuli. Here, we show deleterious effect of preconditioning on oligodendrocyte precursor cells (OPCs). We identified Bcl-2/adenovirus E1B 19-kDa interacting protein 3 (BNIP3), a mitochondrial BH3-only protein specifically involved in OPCs loss after preconditioning. Repeated ischemia stabilized BNIP3 and increased the vulnerability of OPCs to subsequent ischemic events. BNIP3 became mitochondrial-bound and was concurrent with the dysfunction of monocarboxylate transporter 1 (MCT1). Inhibition of BNIP3 by RNAi or necrostatin-1 (Nec-1) and knocking out of BNIP3 almost completely prevented OPCs loss and preserved white matter integrity. Together, our results suggest that the unfavorable effect of BNIP3 on OPCs should be noted for safe development of ischemic tolerance. BNIP3 inhibition appears to be a complementary approach to improve the efficacy of preconditioning for ischemic stroke.

Dexmedetomidine Provides Cardioprotection During Early or Late Reperfusion Mediated by Different Mitochondrial K+-Channels

BACKGROUND

Cardioprotective interventions-such as pharmacological postconditioning-are a promising strategy to reduce deleterious consequences of ischemia and reperfusion injury (I/RI) in the heart, especially as timing and onset of myocardial infarction are unpredictable. Pharmacological postconditioning by treatment with dexmedetomidine (Dex), an α2-adrenoreceptor agonist, during reperfusion protects hearts from I/RI, independently of time point and duration of application during the reperfusion phase. The mitochondrial ATP-sensitive K (mKATP) and mitochondrial large-conductance calcium-sensitive potassium channel (mBKCa) play a pivotal role in mediating this cardioprotective effect. Therefore, we investigated whether Dex-induced cardioprotection during early or late reperfusion is mediated variously by these mitochondrial K-channels.

METHODS

Hearts of male Wistar rats were randomized into 8 groups and underwent a protocol of 15 minutes adaption, 33 minutes ischemia, and 60 minutes reperfusion in an in vitro Langendorff-system. A 10-minute treatment phase was started directly (first subgroup, early reperfusion) or 30 minutes (second subgroup, late reperfusion) after the onset of reperfusion. Control (Con) hearts received vehicle only. In the first subgroup, hearts were treated with 3 nM Dex, 100 µM mKATP-channel blocker 5-hydroxydecanoate (5HD) or 1 µM mBKCa-channel blocker Paxilline (Pax) alone or with respective combinations (5HD + Dex, Pax + Dex). Hearts of the second subgroup received Dex alone (Dex30') or in combination with the respective blockers (5HD + Dex30', Pax + Dex30'). Infarct size was determined with triphenyltetrazoliumchloride staining. Hemodynamic variables were recorded during the whole experiment.

RESULTS

During early reperfusion (first subgroup), the infarct size reducing effect of Dex (Con: 57% ± 9%, Dex: 31% ± 7%; P< .0001 versus Con) was completely abolished by 5HD and Pax (52% ± 6%; Pax + Dex: 53% ± 4%; each P< .0001 versus Dex), while both blockers alone had no effect on infarct size (5HD: 54% ± 8%, Pax: 53% ± 11%). During late reperfusion (second subgroup) the protective effect of Dex (Dex30': 33% ± 10%, P< .0001 versus Con) was fully abrogated by Pax (Pax + Dex30': 58% ± 7%, P < .0001 versus Dex30'), whereas 5HD did not block cardioprotection (5HD + Dex30': 36% ± 7%). Between groups and within each group throughout reperfusion no significant differences in hemodynamic variables were detected.

CONCLUSIONS

Cardioprotection by treatment with Dex during early reperfusion seems to be mediated by both mitochondrial K-channels, whereas during late reperfusion only mBKCa-channels are involved.

Remote ischemic postconditioning as well as blood plasma from double-conditioned donor ameliorate reperfusion syndrome in skeletal muscle

The aim of this study was to verify the possibility of preparation and effectiveness of the use of blood plasma containing an effector of ischemic tolerance activated by applying two sublethal stresses to a donor. As sublethal stresses, two periods of 20-minute hindlimb ischemia were used with a two-day interval between them. Active plasma was isolated six hours after the second hindlimb ischemia. The effectiveness of active plasma as well as remote postconditioning was tested after three hours of tourniquet-induced ischemia on the gastrocnemius muscle. The wet/dry ratio of gastrocnemius muscle (degree of tissue oedema), nitroblue tetrazolium reduction (tissue necrosis), and CatWalk test (hind limb functionality) were evaluated 24 h after the end of ischemia. Three hours of ischemia increased muscle oedema and necrosis in comparison to control by 26.72% (p < 0.001) and 41.58% (p < 0.001) respectively. Remote ischemic postconditioning as well as injection of conditioned blood plasma significantly prevented these changes, even when they were applied one or three hours after the end of ischemia. Equally effective double-conditioned plasma appears to have better prospects in life-threatening situations such as stroke and myocardial infarction.