Hypercholesterolemia abrogates late preconditioning via a tetrahydrobiopterin-dependent mechanism in conscious rabbits

Institute of Molecular Cardiology, University of Louisville, The Jewish Hospital Heart and Lung Institute, Louisville, KY, USA.
Circulation (Impact Factor: 14.95). 11/2005; 112(14):2149-56. DOI: 10.1161/CIRCULATIONAHA.105.566190
Source: PubMed

ABSTRACT Although the late phase of ischemic preconditioning (PC) is known to confer cardioprotection in healthy animal models, it is unknown whether this phenomenon exists in the presence of hypercholesterolemia. The goal of this study was to determine whether the infarct-sparing effect of late PC is affected by hypercholesterolemia and, if so, whether a tetrahydrobiopterin (BH4)-dependent mechanism is responsible for the loss of late PC.
Conscious rabbits fed a normal diet or a 1% cholesterol diet for 6 weeks were subjected to ischemic PC (six 4-minute coronary occlusion/4-minute reperfusion cycles) and, 24 hours later, underwent a 30-minute occlusion followed by 3 days of reperfusion. A total of 125 rabbits were used. In normocholesterolemic rabbits, ischemic PC reduced infarct size, an effect that was abrogated by administration of the BH4 synthesis inhibitor N-acetylserotonin (15 mg/kg IV) before the 30-minute occlusion. In hypercholesterolemic rabbits, however, ischemic PC failed to reduce infarct size. Myocardial BH4 levels in the ischemic zone increased 24 hours after ischemic PC in normocholesterolemic rabbits but not in hypercholesterolemic rabbits. In addition, in normocholesterolemic rabbits, pretreatment with N-acetylserotonin completely abolished the ischemic PC-induced increase in myocardial BH4 levels.
This study demonstrates that (1) hypercholesterolemia abrogates both the infarct-sparing effect of late PC and the concomitant upregulation of myocardial BH4, and (2) inhibition of myocardial BH4 synthesis in the absence of hypercholesterolemia is sufficient to abolish the infarct-sparing effect of late PC. The results support the concept that hypercholesterolemia abrogates late PC by preventing the upregulation of BH4, an essential cofactor for inducible nitric oxide synthase.

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    • "In fact, recent studies have shown that BH4 has a protective effect against I–R injury in various organs, such as heart and stomach (Ishii et al. 2000; Yamashiro et al. 2002; Tiefenbacher et al. 2003; Wajima et al. 2006), although whether BH4 changes are related to the late IPC effect was not elucidated. Tang et al. (2005) recently described that brief I–R for late IPC increases BH4 levels in the rabbit heart, and hypercholesterolaemia abrogates late IPC by preventing the upregulation of BH4 as a cofactor for iNOS. Thus, the increase in BH4 levels appears to be involved in late IPC; however, the underlying mechanism for stimulating BH4 synthesis during late IPC is unknown. "
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    ABSTRACT: The goal of this study was to elucidate whether there is an increase in myocardial tetrahydrobiopterin (BH4), which is a cofactor for nitric oxide synthase, during the late phase of ischaemic preconditioning (IPC) leading to cardioprotection against myocardial infarction and, if so, to examine the induction mechanisms of BH4 synthesis. Rats were preconditioned with four cycles of 3 min left main coronary artery (LCA) occlusion followed by 10 min reperfusion. Twenty-four hours later, the rats were subjected to 20 min ischaemia by LCA ligation and 2 h reperfusion, and the infarct size was determined by 2,3,5-triphenyltetrazolium chloride staining. The IPC protocol reduced the infarct size, and increased the BH4 content and expression of GTP-cyclohydrolase I (GTPCH), which is the rate-limiting enzyme for BH4 synthesis. Administration of a GTPCH inhibitor attenuated both the reduction in infarct size and the increase in BH4 levels. Moreover, the increase in BH4 content was reduced by administration of catalase or a Janus tyrosine kinase-2 (JAK2) inhibitor. These observations suggest that upregulation of BH4 synthesis in the heart contributes to an acquisition of ischaemic tolerance in late IPC, and the increase in myocardial BH4 content seems to be mediated by the induction of GTPCH via the H(2)O(2)-JAK2 pathway.
    Experimental physiology 02/2010; 95(5):609-21. DOI:10.1113/expphysiol.2009.051417 · 2.87 Impact Factor
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    • "The underlying mechanisms by which hyperlipidaemia prevents the protective effect of pre-and post-conditioning are not known. The impairment might occur through down-regulation of NO synthesis, disruption of sGC activity or decreased PKG expression/activation (Ueda et al., 1999; Tang et al., 2005). Despite the well-recognized impairment of the NO–cGMP pathway in hyperlipidaemia, it is not known if the alternative NPR–cGMP system, activated by natriuretic peptides, remains effective. "
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    ABSTRACT: Hyperlipidaemia interferes with cardioprotective mechanisms, but the cause of this phenomenon is largely unknown, although hyperlipidaemia impairs the cardioprotective NO-cGMP system. However, it is not known if natriuretic peptide-cGMP-protein kinase G (PKG) signalling is affected by hyperlipidaemia. Therefore, we investigated the cardioprotective efficacy of cGMP-elevating agents in hearts from normal and hyperlipidaemic rats. Male Wistar rats were rendered hyperlipidaemic by feeding with 2% cholesterol-enriched chow for 12 weeks. Hearts isolated from normal and hyperlipidaemic rats were perfused (Langendorff mode) and subjected to 30 min occlusion of the left main coronary artery, followed by 120 min reperfusion. 8-Br-cGMP (CG, 10 nM), B-type natriuretic peptide-32 (BNP, 10 nM), S-nitroso-N-acetyl-penicillamine (SNAP, 1 microM) were perfused from 10 min prior to coronary occlusion until the 15th min of reperfusion. Infarct size (% of ischaemic risk zone) was determined by triphenyltetrazolium staining. Treatment with CG, SNAP or BNP decreased infarct size significantly in normal hearts from its control value of 41.6 +/- 2.9% to 15.5 +/- 2.4%, 23.3 +/- 3.0% and 25.3 +/- 4.6%, respectively (P < 0.05). Protection by BNP was abolished by co-perfusion of PKG inhibitors KT5823 (600 nM) or Rp-8pCPT-PET-cGMPs (1 microM), confirming its PKG dependence. In hearts from hyperlipidaemic rats, CG, SNAP or BNP failed to decrease infarct size. Hyperlipidaemia did not alter basal myocardial PKG content, but decreased its activity as assessed by phosphorylation of cardiac troponin I. This is the first demonstration that defects in the cardioprotective cGMP-PKG system could be a critical biochemical anomaly in hyperlipidaemia.
    British Journal of Pharmacology 11/2009; 158(6):1495-502. DOI:10.1111/j.1476-5381.2009.00424.x · 4.99 Impact Factor
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    ABSTRACT: Although NO donors have been shown to confer late preconditioning (PC) against myocardial ischemia/reperfusion injury in healthy rabbits, it is unknown whether concurrent systemic disorders affect NO donor-induced cardioprotection. Since many patients with coronary artery disease have hypercholesterolemia (HC), we examined the effect of this condition on late PC induced by the NO donor diethylenetriamine/nitric oxide (DETA/ NO). Chronically instrumented rabbits were fed a normal diet (normocholesterolemia, NC) or a diet enriched with 1% cholesterol (HC) for 4 weeks. Plasma cholesterol levels were significantly elevated and the arterial pressure response to the endothelium-dependent vasodilator bradykinin was blunted in cholesterol diet-fed rabbits. Conscious rabbits underwent a 30-minute coronary occlusion followed by 3 days of reperfusion. When NC rabbits were pretreated with DETA/NO (0.1 mg/kg, i. v. x 4, group II, n = 7) 24 hours before the 30-minute occlusion, infarct size was reduced by 52% (29.7 +/- 3.4% versus 62.4 +/- 4.0% of the region at risk in NC controls [group I, n = 5], P < 0.05), indicating that DETA/NO induced a late PC effect against myocardial infarction. In contrast, when HC rabbits were pretreated with the same dose of DETA/NO (group IV, n = 6), infarct size was not significantly reduced (61.0 +/- 5.7% versus 68.1 +/- 4.5% of the region at risk in HC [group III, n = 5], P = NS), suggesting that DETA/NO failed to induce a delayed cardioprotective effect. These data demonstrate, for the first time, that HC blunts NO donor-induced late PC against myocardial infarction, implying that the inhibitory effects of HC on ischemia-induced and NO donor-induced late PC are caused by disruption of biochemical pathways distal to the generation of NO that triggers these adaptations.
    Archiv für Kreislaufforschung 11/2004; 99(6):395-403. DOI:10.1007/s00395-004-0485-4 · 5.96 Impact Factor
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