title: Optimal temperature for whole-body hypothermia in the newborn: an in vitro study using foreskin mitochondrial oxygen consumption.
abstract: OBJECTIVE
  Whole-body hypothermia (to 33.5 ± 0.5°C) is a therapeutic modality that reduces risks of death and neurodevelopmental disability in neonates subjected to hypoxic-ischemic insults. This in vitro study was designed to determine changes in neonatal cellular metabolism with temperature. Its main aim was to compare the metabolic rate at ≤33°C with that at ≥35°C.
  
  
  METHODS
  Foreskin specimens were used as a source of neonatal tissue. Cellular respiration (mitochondrial O2 consumption) was used as a surrogate biomarker for the metabolic rate. Foreskin specimens from healthy newborns were collected immediately after circumcision and processed within one hour for measuring the rate of O2 consumption at various temperatures (±0.5°C). O2 consumption was determined as function of time from the phosphorescence decay of Pd (II) meso-tetra-(4-sulfonatophenyl)-tetrabenzoporphyrin.
  
  
  RESULTS
  In a vial sealed from air and containing foreskin specimen in phosphate-buffered saline supplemented with 5 mM glucose, [O2] decreased linearly with time, confirming its zero-order kinetics. The rate of O2 consumption (μM O2.min-1), thus, was the negative of the slope of [O2] vs. time. Cyanide inhibited O2 consumption, confirming the oxidation occurred in the respiratory chain. Cellular respiration at ≤33°C (n = 25) significantly differed from that at ≥35°C (n = 24), p < 0.001. The rate (μM O2.min-1.mg-1) at 25°C was 0.034 ± 0.006 (n = 11, p = 0.044), at 33°C was 0.029 ± 0.008 (n = 14, reference temperature), at 35°C was 0.062 ± 0.020 (2-fold higher, n = 18, p < 0.001), and at 37°C was 0.061 ± 0.009 (2-fold higher, n = 6, p < 0.001).
  
  
  CONCLUSIONS
  Neonatal foreskin cellular respiration is highly sensitive to critical temperatures (33°C vs. 35°C).
authors.affiliation: Department of Pediatrics, Tawam Hospital, Al Ain, United Arab Emirates.
authors.forename: A
authors.initials: A
authors.lastname: Al Zaabi
authors.affiliation: Department of Pediatrics, Tawam Hospital, Al Ain, United Arab Emirates.
authors.forename: A Y
authors.initials: AY
authors.lastname: Rahmani
authors.affiliation: Department of Pediatrics, United Arab Emirates University, College of Medicine and Health Sciences, Al Ain, United Arab Emirates.
authors.forename: A
authors.initials: A
authors.lastname: Souid
mesh_terms: D019069:Cell Respiration; D003080:Cold Temperature; D052816:Foreskin; D006801:Humans; D007036:Hypothermia, Induced / Q000379:methods*; D066298:In Vitro Techniques; D007231:Infant, Newborn; D008297:Male; D008928:Mitochondria / Q000378:metabolism*; D010101:Oxygen Consumption
keywords: Cellular respiration; bioenergetics; hypothermia; metabolism; mitochondria; neonates