Molecular regulation of plasma lipid levels during systemic inflammation and sepsis.

PURPOSE OF REVIEW: Sepsis is a common syndrome of multiorgan system dysfunction caused by a dysregulated inflammatory response to an infection and is associated with high rates of mortality. Plasma lipid and lipoprotein levels and composition change profoundly during sepsis and have emerged as both biomarkers and potential therapeutic targets for this condition. The purpose of this article is to review recent progress in the understanding of the molecular regulation of lipid metabolism during sepsis. RECENT FINDINGS: Patients who experience greater declines in high-density lipoprotein during sepsis are at much greater risk of succumbing to organ failure and death. Although the causality of these findings remains unclear, all lipoprotein classes can sequester and prevent the excessive inflammation caused by pathogen-associated lipids during severe infections such as sepsis. This primordial innate immune function has been best characterized for high-density lipoproteins. Most importantly, results from human genetics and preclinical animal studies have suggested that several lipid treatment strategies, initially designed for atherosclerosis, may hold promise as therapies for sepsis. SUMMARY: Lipid and lipoprotein metabolism undergoes significant changes during sepsis. An improved understanding of the molecular regulation of these changes may lead to new opportunities for the treatment of sepsis.

A novel type hypertriglyceridemia observed in FLS mice.

The unique inborn hypertriglyceridemia seen in FLS (fatty liver Shionogi) mice was relieved by the administration of purified apolipoprotein (apo) C-II. Lipoprotein lipase (LPL) and its cofactor, apoC-II, play a pivotal role in VLDL metabolism. Therefore, we investigated the genetic background involved in this hypertriglyceridemia. Plasma levels of TG and total cholesterol as well as LPL activity were measured in male FLS mice and C57/BL6J mice. Agarose gel electrophoresis and fast protein liquid chromatography were used to analyze the lipoprotein profile. A cross experiment was done to determine the genetic background of hypertriglyceridemia observed in FLS mice. cDNA sequences of apoC-II and apoC-III of FLS mice were determined. Prealpha-lipoprotein was the predominant lipoprotein class in FLS mouse plasma. LPL activity remained in the range observed in C57/BL6J mice, and purified apoC-II transiently relieved FLS mice from hypertriglyceridemia. Prealpha-lipoproteinemia was inherited in an autosomal recessive manner. ApoC-III appeared to be a causal factor for this unique hypertriglyceridemia. Microsatellite analysis, however, revealed that the responsible chromosome was not 7; rather, apoC-III mapped onto chromosome 9. Therefore, we suggest apoC-III as a candidate causative factor for the hypertriglyceridemia observed in FLS mice because an excessive amount of apoC-III attenuates LPL activity in vivo and in vitro.

Apolipoprotein C-II deficiency syndrome. Clinical features, lipoprotein characterization, lipase activity, and correction of hypertriglyceridemia after apolipoprotein C-II administration in two affected patients.

Two patients (brother and sister, 41 and 39 yr of age, respectively) have been shown to have marked elevation of plasma triglycerides and chylomicrons, decreased low density lipoproteins (LDL) and high density lipoproteins (HDL), a type I lipoprotein phenotype, and a deficiency of plasma apolipoprotein C-II (apo C-II). The male patient had a history of recurrent bouts of abdominal pain often accompanied by eruptive xanthomas. The female subject, identified by family screening, was asymptomatic. Hepatosplenomegaly was present in both subjects. Analytical and zonal ultracentrifugation revealed a marked increase in triglyceride-rich lipoproteins including chylomicrons and very low density lipoproteins, a reduction in LDL, and the presence of virtually only the HDL3 subfraction. LDL were heterogeneous with the major subfraction of a higher hydrated density than that observed in plasma lipoproteins of normal subjects. Apo C-II levels, quantitated by radioimmunoassay, were 0.13 mg/dl and 0.12 mg/dl, in the male and female proband, respectively. A variant of apo C-II (apo C-IIPadova) with lower apparent molecular weight and more acidic isoelectric point was identified in both probands by two-dimensional gel electrophoresis. The marked hypertriglyceridemia and elevation of triglyceride-rich lipoproteins were corrected by the infusion of normal plasma or the injection of a biologically active synthesized 44-79 amino acid residue peptide fragment of apo C-II. The reduction in plasma triglycerides after the injection of the synthetic apo C-II peptide persisted for 13-20 d. These results definitively established that the dyslipoproteinemia in this syndrome is due to a deficiency of normal apo C-II. A possible therapeutic role for replacement therapy of apo C-II by synthetic or recombinant apo C-II in those patients with severe hypertriglyceridemia and recurrent pancreatitis may be possible in the future.