Hydroxyl radical generation in oxygen-treated infants.
OBJECTIVE
Because the hydroxyl radical is capable of oxidizing phenylalanine to O-tyrosine, we sought to determine whether increased levels of O-tyrosine are found in urine of infants treated with supplemental oxygen.


METHODS
A total of 39 consecutively admitted neonates to an intensive care unit were included. Twenty-seven received supplemental oxygen therapy for respiratory disease, and 12 did not. Urinary O-tyrosine levels were determined on two or more occasions using high-performance liquid chromatography with results expressed as a percentage of the urinary phenylalanine concentration. Using simple and stepwise multiple linear regression analyses, urinary O-tyrosine was examined for associations with relevant clinical conditions and laboratory measurements.


RESULTS
Infants supplemented with oxygen showed significantly higher mean +/- SEM urinary O-tyrosine levels (0.40% +/- 0.028) compared with those remaining in room air (0.18% +/- 0.012). Mean daily FIO2 was the clinical and laboratory variable most highly correlated with urinary O-tyrosine (r = 0.66). In the stepwise regression, significant associations were also found for renal fractional sodium excretion and Apgar score at 5 minutes.


CONCLUSIONS
Hydroxylation at the O position of phenylalanine, a specific direct marker for the hydroxyl radical attack, was strongly associated with oxygen treatment in neonates. This finding increases our understanding of the pathogenesis of oxygen injury and suggests a basis for developing therapeutic approaches.
Lubec
G
G
Department of Pediatrics, Division of Neonatology, University of Vienna, Vienna, Austria.
Widness
J A
JA
Hayde
M
M
Menzel
D
D
Pollak
A
A
D001034:Apgar Score; D004305:Dose-Response Relationship, Drug; D006801:Humans; D017665:Hydroxyl Radical / Q000378:metabolism*; D007231:Infant, Newborn / Q000378:metabolism* / Q000652:urine; D007232:Infant, Newborn, Diseases / Q000378:metabolism / Q000628:therapy* / Q000652:urine; D010100:Oxygen / Q000008:administration & dosage / Q000378:metabolism; D010102:Oxygen Inhalation Therapy; D010649:Phenylalanine / Q000378:metabolism / Q000652:urine; D012044:Regression Analysis; D014443:Tyrosine / Q000652:urine*
D017665:Hydroxyl Radical; D014443:Tyrosine; D010649:Phenylalanine; D010100:Oxygen