Transfer of Phosphatidylethanol Between Lipoproteins

Infrared analysis of lipoproteins in the detection of alcohol biomarkers

Background:

Alcoholism is a major public health problem. Alcohol causes modifications in the composition and concentration of lipoproteins and influences the enzymes and transfer proteins that transform lipoproteins in plasma. Alcohol is associated with the presence of alcohol biomarkers (fatty acid ethyl esters [FAEEs] and phosphatidylethanol [PEth]) in lipoproteins. We explore the possibilities of detecting alcohol biomarkers in non-high-density-lipoproteins (non-HDLs) precipitated from serum using attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR).

Methods:

Analyzes were carried out on stored serum samples, with known % carbohydrate-deficient transferrin (CDT) values, included in a driver’s license regranting program under the control of the Belgian Institute of Road Safety. The study consisted of 127 control samples (CDT≤1.3%) and 114 alcoholic samples (CDT>1.3%). Liver enzymes, CRP, triglycerides, total, HDL- and LDL-cholesterol values were determined. Non-HDLs were precipitated with sodium phosphotungstate and MgCl2 and analyzed using ATR-FTIR in the range from 4500 cm−1 to 450 cm−1 using a Perkin Elmer ATR-FTIR Spectrometer Two.

Results:

The area under the curve of the 1130–990 cm−1 region (AUC1130−990 cm−1) was able to discriminate controls from alcoholics (p<0.0001) due to the presence of FAEEs in lipoproteins. Multiple regression analysis significantly predicted the AUC1130−990 cm−1 (adj. r2=0.13, p<0.0001). Significant correlations were found between AUC1130−990 cm−1 and CDT values (r=0.32, p<0.0001), AST/ALT ratio (r=0.21, p=0.001). GGT showed no significant correlation.

Conclusions:

Infrared analysis of lipoproteins is a potential tool in the detection of alcohol biomarkers.

Phosphatidyl alcohols: effect of head group size on domain forming properties and interactions with sterols

In this study, we have examined the membrane properties and sterol interactions of phosphatidyl alcohols varying in the size of the alcohol head group coupled to the sn-3-linked phosphate. Phosphatidyl alcohols of interest were dipalmitoyl derivatives with methanol (DPPMe), ethanol (DPPEt), propanol (DPPPr), or butanol (DPPBu) head groups. The Phosphatidyl alcohols are biologically relevant, because they can be formed in membranes by the phospholipase D reaction in the presence of alcohol. The melting behavior of pure phosphatidyl alcohols and mixtures with 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) or cholesterol was assessed using high sensitivity differential scanning calorimetry (DSC). DPPMe had the highest melting temperature ( approximately 49 degrees C), whereas the other phosphatidyl alcohols had similar melting temperatures as DPPC ( approximately 40-41 degrees C). All phosphatidyl alcohols, except DPPMe, also showed good miscibility with DPPC. The effects of cholesterol on the melting behavior and membrane order in multilamellar bilayer vesicles were assessed using steady-state anisotropy of 1,6-diphenyl-1,3,5-hexatriene (DPH) and DSC. The ordering effect of cholesterol in the fluid phase was lower for all phosphatidyl alcohols as compared to DPPC and decreased with increasing head group size. The formation of ordered domains containing the phosphatidyl alcohols in complex bilayer membranes was determined using fluorescence quenching of DPH or the sterol analogue cholesta-5,7,(11)-trien-3-beta-ol (CTL). The phosphatidyl alcohols did not appear to form sterol-enriched ordered domains, whereas DPPMe, DPPEt appeared to form ordered domains in the temperature window examined (10-50 degrees C). The partitioning of CTL into bilayer membranes containing phosphatidyl alcohols was to a small extent increased for DPPMe and DPPEt, but in general, sterol interactions were weak or unfavorable for the phosphatidyl alcohols. Our results show that the biophysical and sterol interacting properties of phosphatidyl alcohols, having identical acyl chain structures, are markedly dependent on the size of the head group.

Phosphatidylethanol mediates its effects on the vascular endothelial growth factor via HDL receptor in endothelial cells

BACKGROUND

Previous epidemiological studies have shown that light to moderate alcohol consumption has protective effects against coronary heart disease but the mechanisms of the beneficial effect of alcohol are not known. Ethanol may increase high density lipoprotein (HDL) cholesterol concentration, augment the reverse cholesterol transport, or regulate growth factors or adhesion molecules. To study whether qualitative changes in HDL phospholipids mediate part of the beneficial effects of alcohol on atherosclerosis by HDL receptor, we investigated whether phosphatidylethanol (PEth) in HDL particles affects the secretion of vascular endothelial growth factor (VEGF) by a human scavenger receptor CD36 and LIMPII analog-I (CLA-1)-mediated pathway.

METHODS

Human EA.hy 926 endothelial cells were incubated in the presence of native HDL or PEth-HDL. VEGF concentration and CLA-1 protein expression were measured. Human CLA-1 receptor-mediated mechanisms in endothelial cells were studied using CLA-1 blocking antibody and protein kinase inhibitors.

RESULTS

Phosphatidylethanol-containing HDL particles caused a 6-fold increase in the expression of CLA-1 in endothelial cells compared with the effect of native HDL. That emergent effect was mediated mainly through protein kinase C and p44/42 mitogen-activated protein kinase pathways. PEth increased the secretion of VEGF and that increase could be abolished by a CLA-1 blocking antibody.

CONCLUSIONS

High density lipoprotein particles containing PEth bind to CLA-1 receptor and thereby increase the secretion of VEGF from endothelial cells. Ethanol-induced protective effects against coronary heart disease may be explained, at least partly, by the effects of PEth-modified HDL particles on VEGF via CLA-1-mediated mechanisms in endothelial cells.

Effects of phosphatidylethanol on mouse adipocyte differentiation and expression of stearoyl-CoA desaturase 1

BACKGROUND

Phosphatidylethanol (PEth) is an aberrant phospholipid formed in vivo only in the presence of ethanol. In circulation PEth is associated with lipoproteins and is transferred from one lipoprotein to another. Lipoprotein-associated PEth affects endothelial and smooth muscle cells of blood vessels, but its effects on other cell types have not been explored. Adipocytes have a central role in metabolic syndrome and obesity. In this study we tested whether lipoprotein-associated PEth affects stearoyl-CoA desaturase 1 (SCD1) which plays a major role in lipid-mediated signaling in the differentiation of adipocytes.

METHODS

Mouse 3T3-L1 preadipocytes were differentiated to adipocytes in the presence of high-density lipoproteins (HDL) isolated from the plasma of healthy volunteers or PEth-containing HDL modified in vitro. After incubation, fat accumulation, SCD1 mRNA expression, SCD1 protein content, and fatty acid composition of adipocytes were determined.

RESULTS

Phosphatidylethanol-containing HDL particles inhibited adipocyte differentiation and decreased the 18:1/18:0 ratio of cellular fatty acids by 28% compared with native HDL particles. Moreover, PEth-containing HDL reduced the SCD1 protein content by 39%.

CONCLUSIONS

Lipoprotein-associated PEth may mediate the effects of ethanol on SCD1 and differentiation of preadipocytes to adipocytes.

Lipoprotein-associated proteins involved in platelet signaling

Platelets and lipoproteins are both key elements in the development of atherosclerosis and thrombosis. Based on their density, five classes of lipoproteins have been identified which all influence platelets via distinct mechanisms. The activation of platelets starts with binding of apolipoproteins to different platelet receptors and is followed by the activation of signaling pathways resulting in activation or inhibition of platelet functions like aggregation or secretion. In addition to apolipoproteins, lipoproteins are also associated to a large amount of proteins, enzymes and lipids that also can induce platelet activation or inhibition. This review provides a summary of the activation of signaling pathways after platelet-lipoprotein interactions initiated by lipoprotein-associated proteins and lipids.

From alcohol toxicity to treatment

This article presents the proceedings of a symposium held at the meeting of the International Society for Biomedical Research on Alcoholism in Mannheim, Germany, in October 2004. This symposium was dedicated to Charles S. Lieber in recognition of his contribution in alcohol research over the last 50 years. It was divided into two parts, namely effects of alcohol on the gastrointestinal tract and effects of alcohol on the liver. Major emphasis was given to recent discoveries elucidating mechanisms of alcohol-associated carcinogenesis. M. Salaspuro (Finland) discussed the role of acetaldehyde in the saliva and in the large intestine with respect to its role in the pathogenesis of alcohol-associated cancer, and H. K. Seitz (Germany) presented new data identifying individuals homozygous for the ADH1C&1 allele as high on risk for alcohol-associated upper aerodigestive tract cancer. M. Savolainen (Finland) discussed the role phosphatidylethanol as a bioactive lipid that can mediate beneficial and harmful effects of alcohol drinking. In the second part of the symposium, alcoholic liver disease was discussed. P. Haber (Australia) presented new data on hepatic transcriptome in alcoholic liver disease with the identification of new genes possibly involved in alcohol-initiated fibrogenesis of the liver, and H. Moshage (The Netherlands) described survival mechanisms of the cholestatic hepatocytes with implications for therapy in cholestatic liver disease. The role of the hepatic microsomal ethanol oxidizing system in the metabolism of alcohol in alcoholic liver disease was summarized by R. Teschke (Germany). H. Ishii (Japan) discussed the current status and treatment of alcoholic hepatitis in Japan. Finally, in a state-of-the-art lecture, Charles S. Lieber (USA) discussed the development of the understanding of the pathophysiology of alcoholic liver disease in the last 50 years. He emphasized the role of pathophysiology as an important prerequisite for better treatment strategies.