Hyperoxia depletes (6R)-5,6,7,8-tetrahydrobiopterin levels in the neonatal retina

Implications for nitric oxide synthase function in retinopathy

Kevin S. Edgar, Nuria Matesanz, Tom A. Gardiner, Zvonimir S Katusic, Denise M. McDonald

Research output: Contribution to journalArticle

8 Citations (Scopus)

Abstract

Retinopathy of prematurity is a sight-threatening complication of premature birth caused by nitro-oxidative insult to the developing retinal vasculature during therapeutic hyperoxia exposure and later ischemia-induced neovascularization on supplemental oxygen withdrawal. In the vasodegenerative phase, during hyperoxia, defective endothelial nitric oxide synthase (NOS) produces reactive oxygen and nitrogen free radicals rather than vasoprotective nitric oxide for unclear reasons. Crucially, normal NOS function depends on availability of the cofactor (6R)-5,6,7,8-tetrahydrobiopterin (BH4). Because BH4 synthesis is controlled enzymatically by GTP cyclohydrolase (GTPCH), we used GTPCH-depleted mice [hyperphenylalaninemia strain (hph1)] to investigate the impact of hyperoxia on BH4 bioavailability and retinal vascular pathology in the neonate. Hyperoxia decreased BH4 in retinas, lungs, and aortas in all experimental groups, resulting in a dose-dependent decrease in NOS activity and, in the wild-type group, elevated NOS-derived superoxide. Retinal dopamine levels were similarly diminished, consistent with the dependence of tyrosine hydroxylase on BH4. Despite greater depletion of BH4, the hph<sup>+/-</sup> and hph1<sup>-/-</sup> groups did not show exacerbated hyperoxia-induced vessel closure, but exhibited greater vascular protection and reduced progression to neovascular disease. This vasoprotective effect was independent of enhanced circulating vascular endothelial growth factor (VEGF), which was reduced by hyperoxia, but to local retinal ganglion cell layer-derived VEGF. In conclusion, a constitutively higher level of VEGF expression associated with retinal development protects GTPCH-deficient neonates from oxygen-induced vascular damage.

Original languageEnglish (US)
Pages (from-to)1769-1782
Number of pages14
JournalAmerican Journal of Pathology
Volume185
Issue number6
DOIs
StatePublished - Jun 1 2015

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Hyperoxia
Nitric Oxide Synthase
Retina
GTP Cyclohydrolase
Vascular Endothelial Growth Factor A
Oxygen
Blood Vessels
Retinal Vessels
Retinopathy of Prematurity
Phenylketonurias
Retinal Ganglion Cells
Nitric Oxide Synthase Type III
Premature Birth
Tyrosine 3-Monooxygenase
Superoxides
Biological Availability
Free Radicals
Aorta
sapropterin
Dopamine

ASJC Scopus subject areas

  • Pathology and Forensic Medicine

Cite this

Hyperoxia depletes (6R)-5,6,7,8-tetrahydrobiopterin levels in the neonatal retina : Implications for nitric oxide synthase function in retinopathy. / Edgar, Kevin S.; Matesanz, Nuria; Gardiner, Tom A.; Katusic, Zvonimir S; McDonald, Denise M.

In: American Journal of Pathology, Vol. 185, No. 6, 01.06.2015, p. 1769-1782.

Research output: Contribution to journalArticle

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abstract = "Retinopathy of prematurity is a sight-threatening complication of premature birth caused by nitro-oxidative insult to the developing retinal vasculature during therapeutic hyperoxia exposure and later ischemia-induced neovascularization on supplemental oxygen withdrawal. In the vasodegenerative phase, during hyperoxia, defective endothelial nitric oxide synthase (NOS) produces reactive oxygen and nitrogen free radicals rather than vasoprotective nitric oxide for unclear reasons. Crucially, normal NOS function depends on availability of the cofactor (6R)-5,6,7,8-tetrahydrobiopterin (BH4). Because BH4 synthesis is controlled enzymatically by GTP cyclohydrolase (GTPCH), we used GTPCH-depleted mice [hyperphenylalaninemia strain (hph1)] to investigate the impact of hyperoxia on BH4 bioavailability and retinal vascular pathology in the neonate. Hyperoxia decreased BH4 in retinas, lungs, and aortas in all experimental groups, resulting in a dose-dependent decrease in NOS activity and, in the wild-type group, elevated NOS-derived superoxide. Retinal dopamine levels were similarly diminished, consistent with the dependence of tyrosine hydroxylase on BH4. Despite greater depletion of BH4, the hph+/- and hph1-/- groups did not show exacerbated hyperoxia-induced vessel closure, but exhibited greater vascular protection and reduced progression to neovascular disease. This vasoprotective effect was independent of enhanced circulating vascular endothelial growth factor (VEGF), which was reduced by hyperoxia, but to local retinal ganglion cell layer-derived VEGF. In conclusion, a constitutively higher level of VEGF expression associated with retinal development protects GTPCH-deficient neonates from oxygen-induced vascular damage.",
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