title: Impaired systemic tetrahydrobiopterin bioavailability and increased dihydrobiopterin in adult falciparum malaria: association with disease severity, impaired microvascular function and increased endothelial activation.
abstract: Tetrahydrobiopterin (BH₄) is a co-factor required for catalytic activity of nitric oxide synthase (NOS) and amino acid-monooxygenases, including phenylalanine hydroxylase. BH4 is unstable: during oxidative stress it is non-enzymatically oxidized to dihydrobiopterin (BH₂), which inhibits NOS. Depending on BH₄ availability, NOS oscillates between NO synthase and NADPH oxidase: as the BH₄/BH₂ ratio decreases, NO production falls and is replaced by superoxide. In African children and Asian adults with severe malaria, NO bioavailability decreases and plasma phenylalanine increases, together suggesting possible BH₄ deficiency. The primary three biopterin metabolites (BH₄, BH₂ and B₀ [biopterin]) and their association with disease severity have not been assessed in falciparum malaria. We measured pterin metabolites in urine of adults with severe falciparum malaria (SM; n=12), moderately-severe malaria (MSM, n=17), severe sepsis (SS; n=5) and healthy subjects (HC; n=20) as controls. In SM, urinary BH₄ was decreased (median 0.16 ¼mol/mmol creatinine) compared to MSM (median 0.27), SS (median 0.54), and HC (median 0.34)]; p<0.001. Conversely, BH₂ was increased in SM (median 0.91 ¼mol/mmol creatinine), compared to MSM (median 0.67), SS (median 0.39), and HC (median 0.52); p<0.001, suggesting increased oxidative stress and insufficient recycling of BH2 back to BH4 in severe malaria. Overall, the median BH₄/BH₂ ratio was lowest in SM [0.18 (IQR: 0.04-0.32)] compared to MSM (0.45, IQR 0.27-61), SS (1.03; IQR 0.54-2.38) and controls (0.66; IQR 0.43-1.07); p<0.001. In malaria, a lower BH₄/BH₂ ratio correlated with decreased microvascular reactivity (r=0.41; p=0.03) and increased ICAM-1 (r=-0.52; p=0.005). Decreased BH4 and increased BH₂ in severe malaria (but not in severe sepsis) uncouples NOS, leading to impaired NO bioavailability and potentially increased oxidative stress. Adjunctive therapy to regenerate BH4 may have a role in improving NO bioavailability and microvascular perfusion in severe falciparum malaria.
authors.affiliation: Global and Tropical Health Division, Menzies School of Health Research and Charles Darwin University, Darwin, Northern Territory, Australia; Lee Kong Chian School of Medicine, Nanyang Technological University, Singapore; Institute of Infectious Disease and Epidemiology, Tan Tock Seng Hospital, Singapore.
authors.forename: Tsin W
authors.initials: TW
authors.lastname: Yeo
authors.affiliation: Menzies School of Health Research-National Institute of Health Research and Development Research Program, and District Ministry of Health, Timika, Papua, Indonesia.
authors.forename: Daniel A
authors.initials: DA
authors.lastname: Lampah
authors.affiliation: Menzies School of Health Research-National Institute of Health Research and Development Research Program, and District Ministry of Health, Timika, Papua, Indonesia.
authors.forename: Enny
authors.initials: E
authors.lastname: Kenangalem
authors.affiliation: National Institute of Health Research and Development, Jakarta, Indonesia.
authors.forename: Emiliana
authors.initials: E
authors.lastname: Tjitra
authors.affiliation: Global and Tropical Health Division, Menzies School of Health Research and Charles Darwin University, Darwin, Northern Territory, Australia; Centre for Tropical Medicine, Nuffield Department of Clinical Medicine, University of Oxford, Oxford, United Kingdom.
authors.forename: Ric N
authors.initials: RN
authors.lastname: Price
authors.affiliation: Duke University and VA Medical Centers, Durham, North Carolina, United States of America.
authors.forename: J Brice
authors.initials: JB
authors.lastname: Weinberg
authors.affiliation: Medical Neurogenetics LLC, Atlanta, Georgia, United States of America.
authors.forename: Keith
authors.initials: K
authors.lastname: Hyland
authors.affiliation: Division of Infectious Diseases, University of Utah and Veterans Affairs Medical Center, Salt Lake City, Utah, United States of America.
authors.forename: Donald L
authors.initials: DL
authors.lastname: Granger
authors.affiliation: Global and Tropical Health Division, Menzies School of Health Research and Charles Darwin University, Darwin, Northern Territory, Australia; Division of Medicine, Royal Darwin Hospital, Darwin, Northern Territory, Australia.
authors.forename: Nicholas M
authors.initials: NM
authors.lastname: Anstey
mesh_terms: D000328:Adult; D001708:Biopterins / Q000031:analogs & derivatives* / Q000652:urine; D003404:Creatinine / Q000097:blood / Q000652:urine; D004727:Endothelium / Q000378:metabolism* / Q000473:pathology; D005260:Female; D006801:Humans; D016778:Malaria, Falciparum / Q000097:blood / Q000628:therapy / Q000652:urine*; D008297:Male; D008833:Microcirculation; D009569:Nitric Oxide / Q000097:blood; D018805:Sepsis / Q000097:blood / Q000652:urine*; D012720:Severity of Illness Index
chemical_list: D001708:Biopterins; D009569:Nitric Oxide; D003404:Creatinine; C003402:sapropterin