Ascorbic acid and tetrahydrobiopterin potentiate the EDHF phenomenon by generating hydrogen peroxide

Garry, Ambroise; Edwards, David Hughes; Fallis, Ian A.; Jenkins, Robert L.; Griffith, T. M.

doi:10.1093/cvr/cvp235

Cited by 39 publications

(34 citation statements)

References 40 publications

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“…Hydrogen peroxide has been shown to induce EDHF like relaxations, and promotes endothelium dependent and independent relaxations (Ozkor et al, 2011) (Rubanyi et al, 1986). BH4 can react with molecular oxygen producing hydrogen peroxide, thereby offering an additional pathway to promote vascular relaxation within resistance vessels (Garry et al, 2009) (Starr et al, 2013). Thus, the improved ACh induced relaxations by L-phe in mesenteric arteries may have also been mediated by an improvement of EDHF-like signalling.…”

Section: Oral L-phe Leads To a Rise In Aortic Bh4 Levels And Improvedmentioning

confidence: 99%

Investigating the interaction between GTP-cyclohydrolase1 and its feedback regulatory protein

et al. 2012

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GTP-cyclohydrolase-1 (GTPCH1) catalyses the rate-limiting step in the biosynthesis of tetrahydrobiopterin (BH4), an essential cofactor for enzymes including aromatic amino acid hydroxylases and nitric oxide synthases. Strategies that increase vascular BH4 biosynthesis represent a promising therapeutic approach for the treatment of endothelial dysfunction. GTPCH1 is subject to feedback and feed-forward regulation by BH4 and L-phenylalanine (L-phe) respectively, via an allosteric protein interaction with GTPCH1 feedback regulatory protein (GFRP). The aim of this thesis was to investigate the GTPCH1-GFRP interaction using recombinant proteins, and to validate the functional significance of the interaction in the vasculature using animal models. Human GTPCH1 and GFRP proteins were recombinantly expressed. Studies compared the activity and protein interactions of native GTPCH1 with a truncated mutant. A kinetic GTPCH1 activity assay was modified to enable a high-throughput screen of a fragment library. GTPCH1-GFRP interactions were assessed using surface plasmon resonance (SPR). Finally, in-vivo and ex-vivo functional studies in rodents investigated the effects of L-phe on vascular function and BH4 levels. Studies using recombinant proteins revealed the activity of truncated GTPCH1 exceeds that of native GTPCH1. A high-throughput screen successfully identified four compounds that modulate GTPCH1 activity. Biophysical analysis (SPR) demonstrated that both native and truncated GTPCH1 bind to GFRP in the absence of natural ligands. The kinetics and binding rate constants have been reported for the first time. In functional studies, oral L-phe supplementation in rodents led to a rise of BH4 levels within aortic tissue, and reversed vascular dysfunction observed in vessels obtained from spontaneously hypertensive rats. This thesis demonstrates that modulation of the GTPCH1-GFRP interactions represents a novel therapeutic target to regulate endogenous BH4 levels. SPR data suggests that GTPCH1 and 2 GFRP are constitutively bound in-vivo and indicate that the N-terminal region of GTPCH1 may directly interact with GFRP and modulate basal enzyme activity. The functional effects of L-phe on vascular BH4 levels and function, validate the potential of the GTPCH1-GFRP pathway as a therapeutic target for cardiovascular disease. 3

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Section: Oral L-phe Leads To a Rise In Aortic Bh4 Levels And Improvedmentioning

confidence: 99%

Investigating the interaction between GTP-cyclohydrolase1 and its feedback regulatory protein

et al. 2012

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“…Catalase inhibited BH 4 induced vasorelaxation in mouse cerebral arteries [24] and rabbit iliac arteries, and inhibited the vasodilatory effect of BH 4 on HPV in WT mice in our study. The mechanism by which H 2 O 2 produces its vasorelaxant effects includes activation of soluble guanylate cyclase [29], stimulating the production of prostanoids [30] and sarcoplasmic endoplasmic reticulum Ca 2+ ATPase [16].…”

Section: Pulmonary Vascular Disease Bn Francis Et Almentioning

confidence: 99%

“…As a result, there is interest in using exogenous BH 4 therapeutically in pulmonary hypertension to restore tissue levels and promote NO production from NOS. Recent studies suggest that BH 4 may also act independently of NO, generating hydrogen peroxide, another molecule with vasorelaxant properties [16,17].…”

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confidence: 99%

Tetrahydrobiopterin and the regulation of hypoxic pulmonary vasoconstriction

2010

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Tetrahydrobiopterin (BH 4 ) is an essential cofactor for nitric oxide synthases (NOS). This study investigated the effect of increasing BH 4 levels on hypoxia-induced pulmonary vasoconstriction (HPV).Sprague Dawley rats and hph-1 (BH 4 deficient) mice were given BH 4 before and during HPV in an isolated perfused lung preparation. BH 4 inhibited HPV in a concentration-dependent manner and increased NO metabolites in the perfusate. Bradykinin-induced reductions in HPV were blunted in hph-1 mice and pre-administration of BH 4 restored the response. The effect of BH 4 was attenuated by L-NAME (NOS inhibitor), PTIO (NO scavenger), and catalase (H 2 O 2 catalyser) administered prior to HPV but enhanced by MnTMPyP (superoxide dismutase mimetic). The effect of BH 4 on HPV was partially recapitulated by NH 4 , a stereoisomer that shares antioxidant properties with BH 4 but is not a NOS cofactor.The bioavailability of BH 4 is an important determinant of the pulmonary vascular response to hypoxia. Its effects are mediated via nitric oxide, hydrogen peroxide and its antioxidant properties, and are attenuated by oxidant stress. Pharmacological administration of BH 4 may have therapeutic potential in pulmonary hypertension.

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“…Consequently, pharmacological (e.g., antioxidants, tetrahydrobiopterin; Refs. 21,22,27,30,58,65,67) and/or nonpharmacological (e.g., exercise training; Refs. 13, 17, 46, 58 -60, 64) interventions aiming at improving endothelial function and/or NO bioavailability could mitigate age-related blood flow redistribution and increase exercise capacity.…”

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confidence: 99%

Aging alters the contribution of nitric oxide to regional muscle hemodynamic control at rest and during exercise in rats

Hirai

Copp

Hageman³

et al. 2011

Journal of Applied Physiology

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Advanced age is associated with altered skeletal muscle hemodynamic control during the transition from rest to exercise. This study investigated the effects of aging on the functional role of nitric oxide (NO) in regulating total, inter-, and intramuscular hindlimb hemodynamic control at rest and during submaximal whole body exercise. We tested the hypothesis that NO synthase inhibition (N(G)-nitro-l-arginine methyl ester, l-NAME; 10 mg/kg) would result in attenuated reductions in vascular conductance (VC) primarily in oxidative muscles in old compared with young rats. Total and regional hindlimb muscle VCs were determined via radiolabeled microspheres at rest and during treadmill running (20 m/min, 5% grade) in nine young (6-8 mo) and seven old (27-29 mo) male Fisher 344 × Brown Norway rats. At rest, l-NAME increased mean arterial pressure (MAP) significantly by ∼17% and 21% in young and old rats, respectively. During exercise, l-NAME increased MAP significantly by ∼13% and 19% in young and old rats, respectively. Compared with young rats, l-NAME administration in old rats evoked attenuated reductions in 1) total hindlimb VC during exercise (i.e., down by ∼23% in old vs. 43% in young rats; P < 0.05), and 2) VC in predominantly oxidative muscles both at rest and during exercise (P < 0.05). Our results indicate that the dependency of highly oxidative muscles on NO-mediated vasodilation is markedly diminished, and therefore mechanisms other than NO-mediated vasodilation control the bulk of the increase in skeletal muscle VC during the transition from rest to exercise in old rats. Reduced NO contribution to vasomotor control with advanced age is associated with blood flow redistribution from highly oxidative to glycolytic muscles during exercise.

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Ascorbic acid and tetrahydrobiopterin potentiate the EDHF phenomenon by generating hydrogen peroxide

Cited by 39 publications

References 40 publications

Investigating the interaction between GTP-cyclohydrolase1 and its feedback regulatory protein

Investigating the interaction between GTP-cyclohydrolase1 and its feedback regulatory protein

Tetrahydrobiopterin and the regulation of hypoxic pulmonary vasoconstriction

Aging alters the contribution of nitric oxide to regional muscle hemodynamic control at rest and during exercise in rats

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