HDL-S1P protects endothelial function and reduces lung injury during sepsis in vivo and in vitro.

OBJECTIVE: In sepsis, the protection of the vascular endothelium is essential and the maintenance of its function is critical to prevent further deterioration. High-density lipoprotein (HDL)-associated sphingosine-1-phosphate (S1P) is a bioactive lipid in plasma and its role in sepsis has not been extensively studied. This study aimed to investigate the effects of HDL-S1P on sepsis in cellular and animal models, as well as human plasma samples. MEASUREMENTS: We established an animal model of sepsis with different severities achieved by caecal ligation and puncture (CLP) and lipopolysaccharide (LPS) injection, and then explored the relationship between HDL-S1P and lung endothelial dysfunction in vivo. To determine the effects of HDL-S1P in the pulmonary endothelium of septic rats, we then injected HDL-S1P into septic rats to find out if it can reduce the lung injury caused by sepsis. Further, we explored the mechanism in vitro by studying the role of S1P-specific receptor agonists and inhibitors in LPS-stimulated human umbilical vein endothelial cells. We also explored the relationship between plasma HDL-S1P content and sepsis severity in septic patients by analysing their plasma samples. RESULTS: HDL-S1P concentrations in plasma were negatively correlated with endothelial functional damage in sepsis, both in the animal model and in the septic patients in our study. In vivo, HDL-S1P injection significantly reduced pulmonary oedema and endothelial leakage in septic rats. In vitro, cell experiments showed that HDL-S1P effectively protected the proliferation and migration abilities of endothelial cells, which could be partly explained by its biased activation of the S1P receptor 1. CONCLUSION: Our study preliminary explored the function of HDL-S1P in sepsis in cellular and animal models, as well as human subjects. The results indicate HDL-S1P protected endothelial functions in septic patients. Thus, it has therapeutic potential and can be used for the clinical treatment of sepsis.

Effects of Replacing Dietary Monounsaturated Fat With Carbohydrate on HDL (High-Density Lipoprotein) Protein Metabolism and Proteome Composition in Humans.

OBJECTIVE: Clinical evidence has linked low HDL (high-density lipoprotein) cholesterol levels with high cardiovascular disease risk; however, its significance as a therapeutic target remains unestablished. We hypothesize that HDLs functional heterogeneity is comprised of metabolically distinct proteins, each on distinct HDL sizes and that are affected by diet. Approach and Results: Twelve participants were placed on 2 healthful diets high in monounsaturated fat or carbohydrate. After 4 weeks on each diet, participants completed a metabolic tracer study. HDL was isolated by Apo (apolipoprotein) A1 immunopurification and separated into 5 sizes. Tracer enrichment and metabolic rates for 8 HDL proteins-ApoA1, ApoA2, ApoC3, ApoE, ApoJ, ApoL1, ApoM, and LCAT (lecithin-cholesterol acyltransferase)-were determined by parallel reaction monitoring and compartmental modeling, respectively. Each protein had a unique, size-specific distribution that was not altered by diet. However, carbohydrate, when replacing fat, increased the fractional catabolic rate of ApoA1 and ApoA2 on alpha3 HDL; ApoE on alpha3 and alpha1 HDL; and ApoM on alpha2 HDL. Additionally, carbohydrate increased the production of ApoC3 on alpha3 HDL and ApoJ and ApoL1 on the largest alpha0 HDL. LCAT was the only protein studied that diet did not affect. Finally, global proteomics showed that diet did not alter the distribution of the HDL proteome across HDL sizes. CONCLUSIONS: This study demonstrates that HDL in humans is composed of a complex system of proteins, each with its own unique size distribution, metabolism, and diet regulation. The carbohydrate-induced hypercatabolic state of HDL proteins may represent mechanisms by which carbohydrate alters the cardioprotective properties of HDL.

Dihydro-sphingosine 1-phosphate interacts with carrier proteins in a manner distinct from that of sphingosine 1-phosphate.

Dihydro-sphingosine 1-phosphate (DH-S1P) is an analog of sphingosine 1-phosphate (S1P), which is a potent lysophospholipid mediator. DH-S1P has been proposed to exert physiological properties similar to S1P. Although S1P is known to be carried on HDL via apolipoprotein M (apoM), the association between DH-S1P and HDL/apoM has not been fully elucidated. Therefore, in the present study, we aimed to elucidate this association and to compare it with that of S1P and HDL/apoM. First, we investigated the distributions of S1P and DH-S1P among lipoproteins and lipoprotein-depleted fractions in human serum and plasma samples and observed that both S1P and DH-S1P were detected on HDL; furthermore, elevated amounts of DH-S1P in serum samples were distributed to the lipoprotein-depleted fraction to a greater degree than to the HDL fraction. Concordantly, a preference for HDL over albumin was only observed for S1P, and not for DH-S1P, when the molecules were secreted from platelets. Regarding the association with HDL, although both S1P and DH-S1P prefer to bind to HDL, HDL preferentially accepts S1P over DH-S1P. For the association with apoM, S1P was not detected on HDL obtained from apoM knockout mice, while DH-S1P was detected. Moreover, apoM retarded the degradation of S1P, but not of DH-S1P. These results suggest that S1P binds to HDL via apoM, while DH-S1P binds to HDL in a non-specific manner. Thus, DH-S1P is not a mere analog of S1P and might possess unique clinical significance.

Correlation Between Apolipoprotein M and Inflammatory Factors in Obese Patients.

BACKGROUND The aim of this study was to observe apolipoprotein M (ApoM) level in obese patients and to explore its correlation with inflammatory factors. MATERIAL AND METHODS A total number of 96 participants were recruited and divided into 2 groups: the control group (or healthy group) whose participants had normal body weight (n=58), and the obese group with all its participants diagnosed with obesity (n=38). Data on blood pressure, body weight, height, body mass index, diastolic function of brachial artery endothelium, fasting venous blood glucose, blood lipids, plasmatic ApoM, interleukin-6 (IL-6), C-reactive protein (CRP), tumor necrosis factor-α (TNF-α), fasting insulin, and adiponectin levels were collected for both groups. RESULTS In the obese group, the levels of plasmatic ApoM, high-density lipoprotein cholesterol (HDL-C), and plasmatic adiponectin were significantly (p<0.05) decreased compared to the control group, and the levels of IL-6, TNF-α, CRP, and fasting insulin were significantly increased (p<0.05) compared to the control group. For the obese group, plasmatic ApoM level was positively correlated with HDL-C level and negatively correlated with levels of IL-6, TNF-α, CRP, insulin, and insulin resistance index. However, no significant correlations were revealed between plasmatic ApoM and the diastolic function of brachial artery endothelium, adiponectin level, blood pressure, and blood glucose level. CONCLUSIONS Obese patients showed significantly lower plasmatic ApoM levels than people with normal body weight, and ApoM level showed a strong correlation with CRP, TNF-α, and IL-6 levels, which indicated that ApoM might be regulated by these inflammatory factors.

Increased apolipoprotein M induced by lack of scavenger receptor BI is not activated via HDL-mediated cholesterol uptake in hepatocytes.

BACKGROUND: Scavenger receptor BI (SR-BI) is a classic high-density lipoprotein (HDL) receptor, which mediates selective lipid uptake from HDL cholesterol esters (HDL-C). Apolipoprotein M (ApoM), as a component of HDL particles, could influence preß-HDL formation and cholesterol efflux. The aim of this study was to determine whether SR-BI deficiency influenced the expression of ApoM. METHODS: Blood samples and liver tissues were collected from SR-BI gene knockout mice, and serum lipid parameters, including total cholesterol (TC), triglyceride (TG), high and low-density lipoprotein cholesterol (HDL-C and LDL-C) and ApoM were measured. Hepatic ApoM and ApoAI mRNA levels were also determined. In addition, BLT-1, an inhibitor of SR-BI, was added to HepG2 cells cultured with cholesterol and HDL, under serum or serum-free conditions. The mRNA and protein expression levels of ApoM were detected by RT-PCR and western blot. RESULTS: We found that increased serum ApoM protein levels corresponded with high hepatic ApoM mRNA levels in both male and female SR-BI-/- mice. Besides, serum TC and HDL-C were also significantly increased. Treatment of HepG2 hepatoma cells with SR-BI specific inhibitor, BLT-1, could up-regulate ApoM expression in serum-containing medium but not in serum-free medium, even in the presence of HDL-C and cholesterol. CONCLUSIONS: Results suggested that SR-BI deficiency promoted ApoM expression, but the increased ApoM might be independent from HDL-mediated cholesterol uptake in hepatocytes.

Evaluation of Expression Level of Apolipoprotein M as a Diagnostic Marker for Primary Venous Thromboembolism.

Recently, decreased levels of apolipoprotein M (ApoM) were shown to be associated with higher risk of recurrent venous thromboembolism (VTE) in male patients. However, the role of ApoM in primary VTE is unknown. We aimed in our study to analyze the plasma levels of ApoM in patients with VTE in order to evaluate the diagnostic importance of ApoM in primary VTE. A total of 357 patients with suspected first episode of VTE were recruited prospectively in the SCORE study. Plasma samples from 307 patients were available for quantifying the plasma levels of ApoM in patients with VTE using sandwich enzyme-linked immunosorbent assay method. Among the whole population, plasma levels (mean [standard deviation]) of ApoM were not significantly different between patients with VTE (0.72 [0.20]) and non-VTE patients (0.72 [0.16]), P = .99. Similarly, in regression analyses, no significant association of ApoM plasma levels with the risk of VTE was found on univariate (odds ratio [OR] =1.0, 95% confidence interval [CI] 0.21-4.84, P = .99) and multivariate analysis (OR = 1.25, 95% CI = 0.19-8.34, P = .819) after adjusting for age, body mass index, and smoking. Moreover, results did not differ significantly after stratification of data according to sex ( P > .05). In this study, our results do not suggest a diagnostic role for ApoM plasma levels in patients with primary VTE. Moreover, the current study suggests that role of ApoM as a risk factor may differ for primary VTE and recurrent VTE in male patients.

Vehicle-dependent Effects of Sphingosine 1-phosphate on Plasminogen Activator Inhibitor-1 Expression.

AIM: Sphingosine 1-phosphate (S1P) has been suggested to be a positive regulator of plasminogen activator inhibitor 1 (PAI-1) in adipocytes, while some studies are not consistent with this prothrombotic property of S1P. Since S1P is bound to apolipoprotein M (apoM) on HDL or to albumin in plasma, we compared the properties of these two forms on the PAI-1 induction. METHODS: We investigated the associations of S1P, apoM, and PAI-1 concentrations in the plasma of normal coronary artery (NCA), stable angina pectoris (SAP), and acute coronary syndrome (ACS) subjects (n=32, 71, and 38, respectively). Then, we compared the effects of S1P with various vehicles on the PAI-1 expression in 3T3L1 adipocytes. We also investigated the modulation of the PAI-1 levels in mice infected with adenovirus coding apoM. RESULTS: Among ACS subjects, the PAI-1 level was positively correlated with the S1P level, but not the apoM level. In adipocytes, S1P bound to an apoM-rich vehicle induced PAI-1 expression to a lesser extent than the control vehicle, while S1P bound to an apoM-depleted vehicle induced PAI-1 expression to a greater extent than the control vehicle in 3T3L1 adipocytes. Additionally, apoM overexpression in mice failed to modulate the plasma PAI-1 level and the adipose PAI-1 expression level. S1P bound to albumin increased PAI-1 expression through the S1P receptor 2-Rho/ROCK-NFκB pathway. CONCLUSION: S1P bound to albumin, but not to apoM, induces PAI-1 expression in adipocytes, indicating that S1P can exert different properties on the pathogenesis of vascular diseases, depending on its vehicle.