No abstract

Background Excessive pro-inflammatory activation following trauma plays a role in late morbidity and mortality including the development of multiple organ dysfunction syndrome (MODS). To date, identification of patients at risk has been challenging. Results from animal and human studies suggest that circulating IL-6, may serve as a biomarker for excessive inflammation. The purpose of this analysis was to determine the association of IL-6 to outcome in a multi-center developmental cohort and in a single-center validation cohort. Methods Severely injured patients with shock due to hemorrhage were evaluated within a multi-center developmental cohort (n=79). All had blood drawn within 12 hours of injury. Plasma IL-6 was determined by multiplex proteomic analysis. Clinical and outcome data were prospectively obtained. Within this developmental cohort, a plasma IL-6 level was determined for the subsequent development of MODS by developing a receiver operating curve (ROC) and defining the optimal IL-6 level using the Youden index. This IL-6 level was then evaluated within a separate validation cohort (n=56). Results A receiver operating curve was generated for IL-6 and MODS development with an IL-6 level of 350 pg/ml having the highest sensitivity and specificity within the developmental cohort. IL-6 was associated with MODS after adjusting for APACHE II, ISS, male gender and blood transfusions with an odds ratio of 3.9 [95% CI: 1.33–11.19]. An IL-6 level greater than 350 pg/ml within the validation cohort was associated with an increase in MODS score, MODS development, ventilator days, ICU length of stay (LOS), and hospital LOS. However, this IL-6 level was not associated with either the development of nosocomial infection or mortality. Conclusion Elevation in plasma IL-6 appears to correlate with a poor prognosis. This measurement may be useful as a biomarker for prognosis and serve to identify patients at higher risk of adverse outcome that would benefit from novel therapeutic interventions.

In addition to its effect on high density lipoprotein (HDL) cholesteryl ester (CE) uptake, scavenger receptor BI (SR-BI) was recently reported to stimulate free cholesterol (FC) flux from Chinese hamster ovary (CHO) cells stably expressing mouse SR-BI, a novel function of SR-BI that may play a role in cholesterol removal from the vessel wall where the receptor can be found. It is possible that SR-BI stimulates flux simply by tethering acceptor HDL particles in close apposition to the cell surface thereby facilitating the movement of cholesterol between the plasma membrane and HDL. To test this, we used transiently transfected cells and compared the closely related class B scavenger receptors mouse SR-BI and rat CD36 for their ability to stimulate cholesterol efflux as both receptors bind HDL with high affinity. The results showed that, although acceptor binding to SR-BI may contribute to efflux to a modest extent, the major stimulation of FC efflux occurs independently of acceptor binding to cell surface receptors. Instead our data indicate that SR-BI mediates alterations to membrane FC domains which provoke enhanced bidirectional FC flux between cells and extracellular acceptors. -de la Llera-

A key cellular event in atherogenesis is the interaction of macrophages with lipoproteins in the subendothelium. In vivo, these lipoproteins are bound to matrix and often aggregated, yet most cell-culture experiments explore these events using soluble monomeric lipoproteins. We hypothesized that the internalization and degradation of matrix-retained and aggregated low density lipoprotein (LDL) by macrophages may involve the actin-myosin cytoskeleton in a manner that distinguishes this process from the endocytosis of soluble LDL. To explore these ideas, we plated macrophages on sphingomyelinase-aggregated LDL bound to smooth muscle cellderived matrix in the presence of lipoprotein lipase. The macrophages internalized and degraded the LDL, which was mediated partially by the LDL receptor-related protein. Cytochalasin D and latrunculin A, which block actin polymerization, markedly inhibited the uptake and degradation of matrix-retained LDL but not soluble LDL. Inhibition of Rho family GTPases by Clostridium difficile toxin B blocked the degradation of matrix-retained and aggregated LDL by >90% without any inhibition of soluble LDL degradation. However, specific inhibition of Rho had no effect, suggesting the importance of Rac1 and Cdc42. Degradation of matrix-retained, but not soluble, LDL was also blocked by inhibitors of tyrosine kinase, phosphatidylinositol 3-kinase, and myosin ATPase. These findings define fundamental cytoskeletal pathways that may be involved in macrophage foam cell formation in vivo but have been missed by the use of previous cell culture models.

HDL-phospholipids are determinants in reverse cholesterol transport. They are mostly derived from triacylglycerol (TG)-rich lipoproteins. Chylomicron size is important, therefore, because it is related to the ratio surface phospholipids: core TG and, thus, determines the availability of postprandial phospholipids for transfer to HDL. Eleven healthy young women each ingested four different fat loads supplemented with retinyl palmitate and containing 60 g sunflower oil (SO), oleicsunflower oil (OSO), mixed oil (MO; (g/kg) linoleic acid 480, oleic acid 380, linolenic acid 13) or beef tallow (BT). At the peak of TG absorption for all loads (4 h) chylomicron diameters, determined by agarose-gel filtration, were larger after SO compared with OSO (i><0-05) and BT (i>=006) and after MO compared with BT (P < 0-05). At 6 h chylomicron size was larger after the vegetable oils compared with BT (P < 0 05 in each case). After each fat load chylomicron size decreased at 6 and 8h compared with that at 4h (P<005) except for OSO. Retinyl ester and TG concentrations were lower in chylomicrons after BT than after the other fats but not in the chylomicron-free serum (containing chylomicron remnants), suggesting absorption in the form of very small particles. Compared with the fasting value, the concentration of the Svedberg unit of flotation 20-400 fraction, which contains VLDL and chylomicron remnants, was lower 8 h after MO, the only fat to contain significant amounts of linolenic acid. We conclude that chylomicron size is dependent on the fatty acid composition of ingested fats and the time-course of digestion, being larger for polyunsaturated fatty acid-rich fats and in the early phase of digestion. On the basis of retinyl ester concentration there were no differences between fats in chylomicron-remnant clearance.