Increased Phospholipid Transfer Protein Activity Is Associated With Markers of Enhanced Lipopolysaccharide Clearance in Human During Cardiopulmonary Bypass

Introduction: Lipopolysaccharide (LPS) is a component of gram-negative bacteria, known for its ability to trigger inflammation. The main pathway of LPS clearance is the reverse lipopolysaccharide transport (RLT), with phospholipid transfer protein (PLTP) and lipoproteins playing central roles in this process in experimental animal models. To date, the relevance of this pathway has never been studied in humans. Cardiac surgery with cardiopulmonary bypass is known to favor LPS digestive translocation. Our objective was to determine whether pre-operative PLTP activity and triglyceride or cholesterol-rich lipoprotein concentrations were associated to LPS concentrations in patients undergoing cardiac surgery with cardiopulmonary bypass.Methods: A post-hoc analysis was conducted on plasma samples obtained from patients recruited in a randomized controlled trial.Total cholesterol, high density lipoprotein cholesterol (HDLc), low density lipoprotein cholesterol (LDLc), triglyceride and PLTP activity were measured before surgery. LPS concentration was measured by mass spectrometry before surgery, at the end of cardiopulmonary bypass and 24 h after admission to the intensive care unit.Results: High PLTP activity was associated with lower LPS concentration but not with inflammation nor post-operative complications. HDLc, LDLc and total cholesterol were not associated with LPS concentration but were lower in patients developing post-operative adverse events. HDLc was negatively associated with inflammation biomarkers (CRP, PCT). Triglyceride concentrations were positively correlated with LPS concentration, PCT and were higher in patients with post-operative complications.Conclusion: Our study supports the role of PLTP in LPS elimination and the relevance of RLT in human. PLTP activity, and not cholesterol rich lipoproteins pool size seemed to be the limiting factor for RLT. PLTP activity was not directly related to post-operative inflammation and adverse events, suggesting that LPS clearance is not the main driver of inflammation in our patients. However, HDLc was associated with lower inflammation and was associated with favorable outcomes, suggesting that HDL beneficial anti-inflammatory effects could be, at least in part independent of LPS clearance.

The Systemic Redox Status Is Maintained in Non-Smoking Type 2 Diabetic Subjects Without Cardiovascular Disease: Association with Elevated Triglycerides and Large VLDL

Decreased circulating levels of free thiols (R-SH, sulfhydryl groups) reflect enhanced oxidative stress, which plays an important role in the pathogenesis of cardiometabolic diseases. Since hyperglycemia causes oxidative stress, we questioned whether plasma free thiols are altered in patients with type 2 diabetes mellitus (T2DM) without cardiovascular disease or renal function impairment. We also determined their relationship with elevated triglycerides and very low density lipoproteins (VLDL), a central feature of diabetic dyslipidemia. Fasting plasma free thiols (colorimetric method), lipoproteins, VLDL (nuclear magnetic resonance spectrometry), free fatty acids (FFA), phospholipid transfer protein (PLTP) activity and adiponectin were measured in 79 adult non-smoking T2DM subjects (HbA1c 51 ± 8 mmol/mol, no use of insulin or lipid lowering drugs), and in 89 non-smoking subjects without T2DM. Plasma free thiols were univariately correlated with glucose (r = 0.196, p < 0.05), but were not decreased in T2DM subjects versus non-diabetic subjects (p = 0.31). Free thiols were higher in subjects with (663 ± 84 µmol/L) versus subjects without elevated triglycerides (619 ± 91 µmol/L; p = 0.002). Age- and sex-adjusted multivariable linear regression analysis demonstrated that plasma triglycerides were positively and independently associated with free thiols (β = 0.215, p = 0.004), FFA (β = 0.168, p = 0.029) and PLTP activity (β = 0.228, p = 0.002), inversely with adiponectin (β = −0.308, p < 0.001) but not with glucose (β = 0.052, p = 0.51). Notably, the positive association of free thiols with (elevated) triglycerides appeared to be particularly evident in men. Additionally, large VLDL were independently associated with free thiols (β = 0.188, p = 0.029). In conclusion, circulating free thiols are not decreased in this cohort of non-smoking and generally well-controlled T2DM subjects. Paradoxically, higher triglycerides and more large VLDL particles are likely associated with higher plasma levels of thiols, reflecting lower systemic oxidative stress.

Abstract 330: Liver-Specific Phospholipids Transfer Protein Activity Has Significant Contribution in Hepatocyte Apob-Containing Lipoprotein Production and in Plasma Lipoprotein Metabolism

Atherosclerosis is the leading cause of death in western countries. Lipoprotein metabolism is closely related with the disease. ApoB-containing lipoproteins (BLp) are atherogenic particles, while, high density lipoproteins (HDL) are anti-atherogenic. Phospholipids Transfer Protein (PLTP) activity has important impact on BLp and HDL homeostasis. Animal studies, including general knock out (KO) and transgenic approaches, have shown pro-atherogenic properties for PLTP. However, the tissue specific function of PLTP remains mostly unknown. To address the impact of liver-specific expression of PLTP on lipoprotein metabolism, we have created two mouse models which either express PLTP specifically in the liver on a PLTP-null background or do not express PLTP in the liver (liver-specific PLTP KO) in a wild type background. In both models, our findings show that liver-specific PLTP is responsible for 25-30% of total plasma PLTP activity. Moreover, liver-specific PLTP expression model shows a remarkable increase in plasma levels of BLp, whereas liver-specific PLTP KO mice show significant reduction of BLp in plasma in compare to control group. These results further show the significant contribution of PLTP in BLp production. We also found that HDL levels are slightly increased in the first model, while in liver-specific PLTP KO animals HDL levels are significantly decreased. In order to unravel the mechanism, we evaluated the apoB and triglyceride production rates after blocking the clearance of the particles. We found that liver-specific PLTP increases apoB (both apo48 and apoB100) and triglyceride (TG) secretion rates. Additionally, the study of the hepatocyte microsomal luminal content lipidation in the first model showed that in the presence of PLTP BLp lipidation, which reflects as higher level of TG in microsomal luminal content, is significantly higher than the control group. Our results indicate that liver-generated PLTP promotes atherogenic lipoprotein production and provides a rationale for liver-specific PLTP inhibition as a therapeutical approach for the treatment of atherosclerosis.

Abstract 167: PLTP Acts in Concert with SAA to Reduce Plasma HDL Levels in Mice and Modulates Nascent HDL Formation in Hepatocytes

Phospholipid transfer protein (PLTP), which binds phospholipids and facilitates their transfer between lipoproteins in plasma, plays a key role in lipoprotein remodeling. PLTP levels increase during acute inflammation and increased PLTP activity is associated with the inflammatory markers C-reactive protein (CRP) and serum amyloid A (SAA) as seen in patients with type 2 diabetes and cardiovascular disease. SAA, an HDL apolipoprotein, is highly induced during inflammation. In this study we investigated whether HDL remodeling by PLTP is affected by SAA, and the significance of PLTP on HDL biogenesis. Over-expression of PLTP in mice using an adenoviral vector reduced HDL-C and phospholipid (PL) in a dose dependent manner with the liberation of lipid-poor apoA-I. Co-expression of PLTP and SAA produced a significantly greater reduction in HDL-C and PL than expression of either PLTP or SAA alone. Studies were carried out to examine the lipidation of apoA-I and formation of nascent HDL particles by primary mouse hepatocytes. Over-expression of PLTP in hepatocytes markedly affected the levels as well as the species of nascent HDL particles produced by cells. Although the formation of smaller nascent HDLs was reduced by PLTP, the formation of the larger HDLs was increased. PLTP expression in hepatocytes did not change ABCA1 levels. Co-expression of SAA with PLTP exerted only a modest effect on the levels and types of HDL generated in the presence of PLTP. Our findings suggest that the remodeling of plasma HDL by PLTP and SAA contributes to the reduced HDL-C levels observed during inflammation. PLTP also significantly affects apoA-I lipidation and nascent HDL biogenesis in hepatocytes.