Tetrahydrobiopterin Protects Soluble Guanylate Cyclase against Oxidative Inactivation

Abstract

Tetrahydrobiopterin (BH4) is a major endogenous vasoprotective agent that improves endothelial function by increasing nitric oxide (NO) synthesis and scavenging of superoxide and peroxynitrite. Therefore, administration of BH4 is considered a promising therapy for cardiovascular diseases associated with endothelial dysfunction and oxidative stress. Here we report on a novel function of BH4 that might contribute to the beneficial vascular effects of the pteridine. . Whereas scavenging of superoxide and/or peroxynitrite with superoxide dismutase, tiron, Mn(III)tetrakis(4-benzoic acid)porphyrin, and urate had no protective effects, supplementation of the cells with BH4, either by application of BH4 directly or of its precursors dihydrobiopterin or sepiapterin, completely prevented the inhibition of NO-induced cGMP accumulation by GTN and ODQ. Tetrahydroneopterin had the same effect, and virtually identical results were obtained with RFL-6 fibroblasts, suggesting that our observation reflects a general feature of tetrahydropteridines that is unrelated to NO synthase function and not limited to endothelial cells. Protection of sGC against oxidative inactivation may contribute to the known beneficial effects of BH4 in cardiovascular disorders associated with oxidative stress.

The Role of Nitric Oxide Synthase Uncoupling in Tumor Progression

“…Oral SP inhibited expression of inflammatory cytokines (IL-1β, IL-6, IL-17A), reduced infiltration of inflammatory cells (neutrophils and macrophages), and significantly inhibited the increased protein Tyr nitration in the diseased colons. These results are consistent with DSS/chronic inflammation induced uncoupling of NOS although we could not eliminate that BH4 or SP also protect sGC from oxidative inactivation (20). …”

“…SP is an antioxidant and shown to possibly protect sGC from oxidant-inactivation (20). To rule out this role in the cytotoxic activity of SP, cells were incubated with, tetrahydroneopterin (NHP4), a biopterin with equivalent free radical scavenging activity as SP but unable to participate as a cofactor for NOS (20).…”

“…To rule out this role in the cytotoxic activity of SP, cells were incubated with, tetrahydroneopterin (NHP4), a biopterin with equivalent free radical scavenging activity as SP but unable to participate as a cofactor for NOS (20). As shown in Figure 4C, NHP4 at concentrations equal to those used with SP is not cytotoxic.…”

Chronic β1-adrenergic blockade enhances myocardial β3-adrenergic coupling with nitric oxide-cGMP signaling in a canine model of chronic volume overload: new insight into mechanisms of cardiac benefit with selective β1-blocker therapy

“…BAY60) can stimulate sGC cyclase activity independent of NO or heme; oxidized sGC has a relatively potentiated response to sGC activators [24]. Thus, differential cyclase response of sGC to BAY60 versus NO-donor DEA/NO can reveal its redox state [48]. We previously showed that while NLR-localized sGC becomes oxidized in the volume-overloaded heart, caveolae-localized sGC does not [29].…”

Cell type-specific recycling of tetrahydrobiopterin by dihydrofolate reductase explains differential effects of 7,8-dihydrobiopterin on endothelial nitric oxide synthase uncoupling

“…Intracellular levels of pteridines were quantified by HPLC analysis using a method adapted from Fukushima and Nixon [20] as described previously [21]. Briefly, cells grown in petri dishes (diameter 90 mm) were harvested (∼5 × 10 6 per petri dish), washed, and resuspended in either 0.1 ml of PBS containing 1 mM DTT (for quantifying biopterin), 0.1 ml of alkaline oxidant solution (0.02 M KI/I 2 in 0.1 M NaOH; for quantifying biopterin plus BH2), or 0.1 ml of acidic oxidant solution (0.02 M KI/I 2 in 0.1 M HCl; for quantifying biopterin plus BH2 plus BH4).…”