In vivo [31P]NMR assessment of early hepatocellular dysfunction during endotoxemia

Hepatocellular dysfunction, as a result of sepsis or endotoxemia, plays a critical role in the pathogenesis of multiple systems organ failure. Conventional methods to assay hepatic ATP require large tissue samples, making repeat measurements in the same animal impossible, and are unable to detect the minimal changes in metabolism consistent with early or reversible cellular injury. 31P NMR is a modality available for the in vivo measurement of high energy phosphates. Inorganic phosphate (Pi) and phosphomonoester (PME) ratios (markers of cellular metabolism and viability) as well as fractionated ATP may be repeatedly quantitated. To assess the early effects of endotoxemia on hepatic function, phosphorus spectra of the liver were obtained using a 1.7-cm surface coil in six rats after the ip administration of 4 mg/kg Escherichia coli lipopolysaccharide. Conventional assay was performed on 24 matched controls. Pi, PME, alpha-, beta-, and gamma-ATP peaks (expressed as percentage total signal area) were collected over 20 min, integrated, and analyzed. Pi/beta-ATP decreased over time until 6 hr reflecting ongoing uptake of inorganic phosphate and continued cellular metabolism. PME/beta-ATP ratios, which indicate cellular viability, became significantly elevated at 6 hr. Using 31P NMR, beta-ATP best reflected the early subtle energy changes present prior to cell death and subsequent organ failure with significant decreases at 2, 4, and 6 hr. Conventional assay for ATP confirmed similar trends. We conclude that 31P NMR is a valuable tool for the study of reversible hepatic energy changes during early endotoxemia.