Effect of cooling on lung secretory phospholipase A2 activity in vitro, ex vivo and in vivo.

BACKGROUND: Hypothermia can modify surfactant composition and function. Secretory phospholipase A2 (sPLA2) hydrolyses surfactant phospholipids and is important in the pathobiology of several critical respiratory disorders. We hypothesize that sPLA2 activity might be influenced by the temperature partially explaining surfactant changes. This study aims to comprehensively evaluate the effect of hypothermia on sPLA2 activity.

METHODS: We measured sPLA2 activity, at different temperatures, alone or combined with bile acids, in vitro(incubating human recombinantsPLA2-IIA and porcine sPLA2-IB), ex vivo(by cooling bronchoalveolar lavage samples from neonates with respiratory distress syndrome or no lung disease) and in vivo(using lavage samples obtained before and after 72h of whole body cooling in neonates with hypoxic-ischaemic encephalopathy). We also measured concentrations of various sPLA2 subtypes and natural sPLA2 inhibitors in in vivocooled samples. Results were corrected for protein content and dilution.

RESULTS: In vitrocooling did not show any effect of hypothermia on sPLA2. Ex vivocooling did not alter total sPLA2 activity and the addition of bile acids increased sPLA2 activity, irrespective of the temperature and the type of sampled patient. In vivo hypothermia reduced median sPLA2 activity from 16.6 [15.2-106.7]IU/mg to 3.3 [2.7-8.5]IU/mg ( p=0.026) and mean sPLA2-IIA from 1.1 (0.8)pg/mg to 0.6 (0.4)pg/mg ( p=0.047), while increased dioleylphosphatidylglycerol from 8.3 (3.9)% to 12.8 (5.1)% ( p=0.02).

CONCLUSIONS: Whole body hypothermia decreases in vivoglobal sPLA2 activity in broncho-alveolar lavage fluids through the reduction of sPLA2-IIA and increment of dioleylphosphatidylglycerol. This effect is absent during in vitroor ex vivohypothermia.