High-Density Lipoprotein Alterations in Type 2 Diabetes and Obesity

Alterations affecting high-density lipoproteins (HDLs) are one of the various abnormalities observed in dyslipidemia in type 2 diabetes mellitus (T2DM) and obesity. Kinetic studies have demonstrated that the catabolism of HDL particles is accelerated. Both the size and the lipidome and proteome of HDL particles are significantly modified, which likely contributes to some of the functional defects of HDLs. Studies on cholesterol efflux capacity have yielded heterogeneous results, ranging from a defect to an improvement. Several studies indicate that HDLs are less able to inhibit the nuclear factor kappa-B (NF-κB) proinflammatory pathway, and subsequently, the adhesion of monocytes on endothelium and their recruitment into the subendothelial space. In addition, the antioxidative function of HDL particles is diminished, thus facilitating the deleterious effects of oxidized low-density lipoproteins on vasculature. Lastly, the HDL-induced activation of endothelial nitric oxide synthase is less effective in T2DM and metabolic syndrome, contributing to several HDL functional defects, such as an impaired capacity to promote vasodilatation and endothelium repair, and difficulty counteracting the production of reactive oxygen species and inflammation.

Normal HDL Cholesterol Efflux and Anti-Inflammatory Capacities in Type 2 Diabetes Despite Lipidomic Abnormalities

OBJECTIVE

To assess whether, in type 2 diabetes (T2D) patients, lipidomic abnormalities in high-density lipoprotein (HDL) are associated with impaired cholesterol efflux capacity and anti-inflammatory effect, 2 pro-atherogenic abnormalities.

DESIGN AND METHODS

This is a secondary analysis of the Lira-NAFLD study, including 20 T2D patients at T0 and 25 control subjects. Using liquid chromatography/tandem mass spectrometry, we quantified 110 species of the main HDL phospholipids and sphingolipids. Cholesterol efflux capacity was measured on THP-1 macrophages. The anti-inflammatory effect of HDL was measured as their ability to inhibit the tumor necrosis factor α (TNFα)-induced expression of vascular cell adhesion molecule-1 (VCAM-1) and intercellular cell adhesion molecule-1 (ICAM-1) on human vascular endothelial cells (HUVECs).

RESULTS

The cholesterol-to-triglyceride ratio was decreased in HDL from T2D patients compared with controls (-46%, P = 0.00008). As expressed relative to apolipoprotein AI, the amounts of phosphatidylcholines, sphingomyelins, and sphingosine-1-phosphate were similar in HDL from T2D patients and controls. Phosphatidylethanolamine-based plasmalogens and ceramides (Cer) were, respectively, 27% (P = 0.038) and 24% (P = 0.053) lower in HDL from T2D patients than in HDL from controls, whereas phosphatidylethanolamines were 41% higher (P = 0.026). Cholesterol efflux capacity of apoB-depleted plasma was similar in T2D patients and controls (36.2 ± 4.3 vs 35.5 ± 2.8%, P = 0.59). The ability of HDL to inhibit the TNFα-induced expression of both VCAM-1 and ICAM-1 at the surface of HUVECs was similar in T2D patients and controls (-70.6 ± 16.5 vs -63.5 ± 18.7%, P = 0.14; and -62.1 ± 13.2 vs -54.7 ± 17.7%, P = 0.16, respectively).

CONCLUSION

Despite lipidomic abnormalities, the cholesterol efflux and anti-inflammatory capacities of HDL are preserved in T2D patients.

HDL functionality in type 1 diabetes: enhancement of cholesterol efflux capacity in relationship with decreased HDL carbamylation after improvement of glycemic control

Background

Reduced cholesterol efflux capacity (CEC) of HDLs is likely to increase cardiovascular risk in type 1 diabetes (T1D). We aimed to assess whether improvement of glycemic control in T1D patients is associated with changes in CEC in relation with changes in carbamylation of HDLs.

Methods

In this open-label trial, 27 uncontrolled T1D patients were given a three-month standard medical intervention to improve glycemic control. HDL fraction was isolated from plasma, and CEC was measured on THP-1 macrophages. Carbamylation of HDLs was evaluated by an immunoassay. Control HDLs from healthy subjects were carbamylated in vitro with potassium cyanate.

Results

HbA_1c decreased from 11.4% [10.2–12.9] (median [1st–3rd quartiles]) at baseline to 8.1% [6.6–9.0] after the three-month intervention (P < 0.00001). The CEC of HDLs increased after intervention in 19 (70%) patients (P = 0.038). At the same time, the carbamylation of HDLs decreased in 22 (82%) patients after intervention (P = 0.014). The increase in CEC significantly correlated with the decrease in carbamylated HDLs (r = −0.411, P = 0.034), even after adjustment for the change in HbA_1c (β = −0.527, P = 0.003). In vitro carbamylation of control HDLs decreased CEC by 13% (P = 0.041) and 23% (P = 0.021) using 1 and 10 mmol/L of potassium cyanate, respectively.

Conclusions

The improvement of CEC in relation to a decrease in the carbamylation of HDLs may likely contribute to the beneficial cardiovascular effect of glycemic control in T1D patients.

Trial registration: NCT02816099 ClinicalTrials.gov.

The dysregulated innate immune response in severe COVID-19 pneumonia that could drive poorer outcome

Background

Although immune modulation is a promising therapeutic avenue in coronavirus disease 2019 (COVID-19), the most relevant targets remain to be found. COVID-19 has peculiar characteristics and outcomes, suggesting a unique immunopathogenesis.

Methods

Thirty-six immunocompetent non-COVID-19 and 27 COVID-19 patients with severe pneumonia were prospectively enrolled in a single center, most requiring intensive care. Clinical and biological characteristics (including T cell phenotype and function and plasma concentrations of 30 cytokines) and outcomes were compared.

Results

At similar baseline respiratory severity, COVID-19 patients required mechanical ventilation for significantly longer than non-COVID-19 patients (15 [7–22] vs. 4 (0–15) days; p = 0.0049). COVID-19 patients had lower levels of most classical inflammatory cytokines (G-CSF, CCL20, IL-1β, IL-2, IL-6, IL-8, IL-15, TNF-α, TGF-β), but higher plasma concentrations of CXCL10, GM-CSF and CCL5, compared to non-COVID-19 patients. COVID-19 patients displayed similar T-cell exhaustion to non-COVID-19 patients, but with a more unbalanced inflammatory/anti-inflammatory cytokine response (IL-6/IL-10 and TNF-α/IL-10 ratios). Principal component analysis identified two main patterns, with a clear distinction between non-COVID-19 and COVID-19 patients. Multivariate regression analysis confirmed that GM-CSF, CXCL10 and IL-10 levels were independently associated with the duration of mechanical ventilation.

Conclusion

We identified a unique cytokine response, with higher plasma GM-CSF and CXCL10 in COVID-19 patients that were independently associated with the longer duration of mechanical ventilation. These cytokines could represent the dysregulated immune response in severe COVID-19, as well as promising therapeutic targets.

ClinicalTrials.gov: NCT03505281.

Professional drivers and cardiovascular risk: APPTIV cohort

Background

Professional drivers have a high risk of morbidity, including myocardial infarction. Bus, taxi and truck drivers have most often constituted the studied populations. However, if the transport sector faces road risk, 70% of employees in all activity sectors are exposed to this risk in France. Most often studied by the analysis of global working time, the real driving time and the distance travelled are rarely taken into account, whereas they are potentially modifiable factors.

Purpose

To assess the associations between exposure to road risk by taking into account driving time and the number of kilometers travelled professionally and certain cardiovascular risk factors, in different sectors of professional activity.

Method

Based on the APPTIV cohort, data from 984 men and women employees from 94 companies in France was collected from 2018 to 2019, during occupational health medical visits focused on road risk. The number of Kms / month (&lt;400 (ref); &lt;1600; ≥1600) and the duration of driving (hours / d &lt;1 (ref); &lt;4; ≥4) were studied according to the respective tertiles. A variable with 9 classes was created. Logistic regressions adjusted for age, gender and activity sectors were carried out to explain the associations with certain cardiovascular factors (Hypertension, overweight (≥25 kg/m2), obesity (30 kg/m2) Hypertriglyceridemia (≥1.7 mmol/l), Hypercholesterolemia, HypoHDLemia).

Results

The population studied came from 23.30% of the transport sector, 23.30% of the construction sector, 26.75 of the public administration and 4.78% of the trade sector. After adjustments, the estimated risks of hypertension according to the driving time or the number of km travelled are not significant. Driving between 1 and 4 hours and more than 4 hours per day increases the risk of obesity, by: OR: 1.85 (1.22–2.80); 1.85 (1.19–2.86), the risk of hypertriglyceridemia of 1.39 (1.0–1.95); 1.54 (1.09–2.18). Traveling more than 1600 km / m increases the risk of hypertriglyceridemia by 1.5. People driving between 400 and 1600 km / m with a driving time between 1 and 4 h / d or those covering more than 1600 km with long driving times (&gt;4 h / d) have an estimated risk of obesity at 1.82 (1.05–3.14) and 1.87 (1.13–3.11) respectively. Those traveling over 1600 km / m with long driving times (&gt;4 hrs / day) have a 1.5 times risk of hypertriglyceridemia.

Conclusion

Taking into account the number of hours of driving and the kilometers travelled professionally, this study highlighted some employee profiles with high cardiovascular risk, accessible to medical and professional prevention measures.

Funding Acknowledgement

Type of funding source: None

Small dense HDLs display potent vasorelaxing activity, reflecting their elevated content of sphingosine-1-phosphate

The functional heterogeneity of HDL is attributed to its diverse bioactive components. We evaluated whether the vasodilatory effects of HDL differed across HDL subpopulations, reflecting their distinct molecular composition. The capacity of five major HDL subfractions to counteract the inhibitory effects of oxidized LDL on acetylcholine-induced vasodilation was tested in a rabbit aortic rings model. NO production, an essential pathway in endothelium-dependent vasorelaxation, was studied in simian vacuolating virus 40-transformed murine endothelial cells (SVECs). Small dense HDL3 subfractions displayed potent vasorelaxing activity (up to +31% vs. baseline, P < 0.05); in contrast, large light HDL2 did not induce aortic-ring relaxation when compared on a total protein basis. HDL3 particles were enriched with sphingosine-1-phosphate (S1P) (up to 3-fold vs. HDL2), with the highest content in HDL3b and -3c that concomitantly revealed the strongest vasorelaxing properties. NO generation was enhanced by HDL3c in SVECs (1.5-fold, P < 0.01), a phenomenon that was blocked by the S1P receptor antagonist, VPC 23019. S1P-enriched reconstituted HDL (rHDL) was a 1.8-fold (P < 0.01) more potent vasorelaxant than control rHDL in aortic rings. Small dense HDL3 particles displayed potent protective effects against oxidative stress-associated endothelium dysfunction, potentially reflecting their elevated content of S1P that might facilitate interaction with S1P receptors and ensuing NO generation.

Impairment of the Ability of HDL From Patients With Metabolic Syndrome but Without Diabetes Mellitus to Activate eNOS

Objective—

High-density lipoprotein (HDL) from nondiabetic patients with metabolic syndrome (MetS) displays abnormalities in their lipidome, such as triglyceride enrichment and sphingosine-1-phosphate depletion. We hypothesized that these abnormalities could impair the ability of HDL to stimulate endothelial nitric oxide synthase (eNOS).

Approach and Results—

Compared with HDL from control subjects, HDL from normoglycemic patients with MetS was 39% richer in triglycerides ( P <0.01) and 15% poorer in sphingosine-1-phosphate ( P <0.05; n=23 in each group). eNOS activity, assessed by the conversion of L-[ 3 H]arginine to L-[ 3 H]citrulline, was 69% lower in human umbilical vein endothelial cells incubated with HDL from MetS patients than in cells incubated with HDL from controls ( P <0.0001). In addition, the activating phosphorylation of eNOS at serine (Ser) 1177 and of Akt (protein kinase B) at Ser473 was 37% ( P <0.001) and 39% ( P <0.05) lower, respectively, with HDL from MetS patients. Sphingosine-1-phosphate enrichment of HDL from MetS patients restored their ability to stimulate eNOS activity ( P <0.05), in relation with a significant increase in eNOS phosphorylation at Ser1177 ( P <0.05) and in Akt phosphorylation at Ser473 ( P =0.05). By contrast, triglyceride enrichment of HDL from control subjects did not modify eNOS activity ( P =0.90) and phosphorylation at Ser1177 ( P =0.87).

Conclusions—

We provide evidence that the activation of eNOS by HDL is decreased in MetS patients before the appearance of diabetes mellitus and that sphingosine-1-phosphate depletion of HDL is the main factor responsible for this defect. This has important consequences on the impairment of HDL functionality and antiatherogenic properties in these patients.

No improvement of high-density lipoprotein (HDL) vasorelaxant effect despite increase in HDL cholesterol concentration in type 2 diabetic patients treated with glitazones

CONTEXT

High-density lipoproteins (HDLs) from type 2 diabetic patients are unable to counteract the inhibitory effect of oxidized low-density lipoproteins (ox-LDLs) on vasorelaxation. We hypothesized that glitazones, which improve glycemic control and dyslipidemia, could correct this abnormality.

OBJECTIVES AND DESIGN

We compared the ability of HDL from controls (n = 12) and from type 2 diabetic patients before and after 6 months of treatment with either rosiglitazone (n = 11) or pioglitazone (n = 8) to counteract the inhibitory effect of ox-LDL on vasodilatation of rabbit aorta rings.

RESULTS

Rosiglitazone induced a decrease in hemoglobin A1c (7.7% ± 1.1% vs 9.8% ± 1.0%, P = .003) and an increase in HDL cholesterol (1.14 ± 0.32 vs 0.98 ± 0.24 mmol/L, P = .033). Pioglitazone induced a decrease in hemoglobin A1c (8.3% ± 2.5% vs 9.5% ± 3.2%, P = .068) and serum triglycerides (1.58 ± 0.89 vs 2.03 ± 0.70 mmol/L, P = .069) and an increase in HDL cholesterol (1.39 ± 0.22 vs 1.14 ± 0.22 mmol/L, P = .018). The triglyceride content of HDL was unchanged by rosiglitazone and was decreased by 25% (P = .068) by pioglitazone. HDL from controls counteracted the inhibitory effect of ox-LDL on vasodilatation (maximal relaxation [Emax] = 74.4% ± 3.5% vs 51.9% ± 3.3%, P = .0029), whereas HDL from type 2 diabetic patients did not (Emax = 51.7% ± 5.8% vs 52.3% ± 4.6% [P = .66] and 52.7% ± 5.5% vs 51.9% ± 4.5% [P = .78] for the rosiglitazone and pioglitazone group, respectively). Rosiglitazone or pioglitazone did not improve Emax (58.6% ± 5.9% vs 52.3% ± 4.6% [P = .15] and 49.3% ± 6.5% vs 51.9% ± 4.5% [P = .48], respectively).

CONCLUSION

Glitazones increased the concentration of HDL cholesterol without restoring the ability of HDL particles to protect the endothelium from oxidative stress-induced dysfunction, meaning that HDL remained dysfunctional with impaired antiatherogenic properties.

Deleterious effect of glycation on the ability of HDL to counteract the inhibitory effect of oxidized LDL on endothelium-dependent vasorelaxation

BACKGROUND

Contrary to high-density lipoprotein (HDL) from normolipidaemic and normoglycaemic subjects, HDL from diabetic patients loses its ability to reverse the inhibition of vasorelaxation induced by oxidized low-density lipoprotein (LDL). The aim of this study was to analyze the role of glycation, a major abnormality observed in diabetes, on the impairment of the vasorelaxant effect of HDL.

METHODS

HDL from healthy subjects was glycated in vitro by incubation in glucose 200 mmol/L for 3 days. Vasoreactivity was evaluated by the relaxation response to acetylcholine of rabbit aorta rings pre-contracted with noradrenaline, before and after 2 h incubation with or without different lipoprotein fractions (Krebs buffer, oxidized LDL, normal or glycated HDL alone and with oxidized LDL).

RESULT

The fructosamine/apolipoprotein AI ratio was significantly increased in glycated HDL compared with native HDL (53.63 ± 7.91 vs 18.51 ± 4.10 µmol/g; p < 0.05). Oxidized LDL inhibited endothelium-dependent vasodilation compared with Krebs buffer [maximal relaxation (Emax) = 53.15 ± 6.50 vs 98.67 ± 2.07%, p < 0.001]. Native HDL was able to counteract the oxidized LDL-induced inhibition of vasorelaxation (Emax = 76.93 ± 5.41 vs 53.15 ± 6.50%, p < 0.001). On the other hand, glycated HDL had no effect on oxidized LDL-induced inhibition of endothelium vasorelaxation compared with incubation with oxidized LDL alone (Emax = 52.98 ± 2.07 vs 53.15 ± 6.50%, not significant).

CONCLUSION

Glycation of HDL induces the loss of the ability of HDL to counteract the inhibitory effect of oxidized LDL on endothelium-dependent vasorelaxation, this is likely contributing to the impairment of antiatherogenic properties of HDL in diabetic patients.

Plasma phospholipid transfer protein deficiency in mice is associated with a reduced thrombotic response to acute intravascular oxidative stress

OBJECTIVE

Earlier in vitro studies suggested a putative role for the plasma phospholipid transfer protein (PLTP) in the modulation of blood coagulation. The effect of PLTP expression on blood coagulation under both basal and oxidative stress conditions was compared here in wild-type and PLTP-deficient (PLTP-/-) mice.

METHODS AND RESULTS

Under basal conditions, PLTP deficiency was associated with an extended tail bleeding time despite a significant depletion of vascular α-tocopherol content and an impairment of endothelial function. When acute oxidative stress was generated in vivo in the brain vasculature, the steady state levels of oxidized lipid derivatives, the extent of blood vessel occlusion, and the volume of ischemic lesions were more severe in wild-type than in PLTP-/- mice.

CONCLUSIONS

In addition to its recognized hyperlipidemic, proinflammatory, and proatherogenic properties, PLTP increases blood coagulation and worsens the extent of ischemic lesions in response to acute oxidative stress. Thus, PLTP arises here as a cardiovascular risk factor for the late thrombotic events occurring in the acute phase of atherosclerosis.

7-ketocholesterol incorporation into sphingolipid/cholesterol-enriched (lipid raft) domains is impaired by vitamin E: a specific role for alpha-tocopherol with consequences on cell death

Cholesterol oxides, in particular 7-ketocholesterol, are proatherogenic compounds that induce cell death in the vascular wall when localized in lipid raft domains of the cell membrane. Deleterious effects of 7-ketocholesterol can be prevented by vitamin E, but the molecular mechanism involved is unclear. In this study, unlike gamma-tocopherol, the alpha-tocopherol vitamin E form was found to prevent 7-ketocholesterol-mediated apoptosis of A7R5 smooth muscle cells. To be operative, alpha-tocopherol needed to be added to the cells before 7-ketocholesterol, and its anti-apoptotic effect was reduced and even suppressed when added together or after 7-ketocholesterol, respectively. Both pre- and co-treatment of the cells with alpha-tocopherol resulted in the redistribution of 7-ketocholesterol out of the sphingolipid/cholesterol-enriched (lipid raft) domains. In turn, fewer amounts of alpha-tocopherol associated with lipid rafts on 7-ketocholesterol-pretreated cells compared with untreated cells, with no prevention of cell death in this case. In further support of the implication of lipid raft domains, the dephosphorylation/inactivation of Akt-PKB was involved in the 7-ketocholesterol-induced apoptosis. Akt-PKB dephosphorylation was prevented by alpha-tocopherol, but not gamma-tocopherol pretreatment.

Effects of 20 mg rosuvastatin on VLDL1-, VLDL2-, IDL- and LDL-ApoB kinetics in type 2 diabetes

AIMS/HYPOTHESIS

In addition to its efficacy in reducing LDL-cholesterol, rosuvastatin has been shown to significantly decrease plasma triacylglycerol. The use of rosuvastatin may be beneficial in patients with type 2 diabetes, who usually have increased triacylglycerol levels. However, its effects on the metabolism of triacylglycerol-rich lipoproteins in type 2 diabetic patients remains unknown.

METHODS

We performed a randomised double-blind crossover trial of 6-week treatment with placebo or rosuvastatin 20 mg in eight patients with type 2 diabetes who were being treated with oral glucose-lowering agents. In each patient, an in vivo kinetic study of apolipoprotein B (ApoB)-containing lipoproteins with [13C]leucine was performed at the end of each treatment period. A central randomisation centre used computer-generated tables to allocate treatments. Participants, caregivers and those assessing the outcomes were blinded to group assignment.

RESULTS

Rosuvastatin 20 mg significantly reduced plasma LDL-cholesterol, triacylglycerol and total ApoB. It also significantly reduced ApoB pool sizes of larger triacylglycerol-rich VLDL particles (VLDL1; p = 0.011), smaller VLDL particles (VLDL2; p = 0.011), intermediate density lipoprotein (IDL; p = 0.011) and LDL (p = 0.011). This reduction was associated with a significant increase in the total fractional catabolic rate of VLDL1-ApoB (6.70 +/- 3.24 vs 4.52 +/- 2.34 pool/day, p = 0.049), VLDL2-ApoB (8.72 +/- 3.37 vs 5.36 +/- 2.64, p = 0.011), IDL-ApoB (7.06 +/- 1.68 vs 4.21 +/- 1.51, p = 0.011) and LDL-ApoB (1.02 +/- 0.27 vs 0.59 +/- 0.13, p = 0.011). Rosuvastatin did not change the production rates of VLDL2-, IDL- or LDL-, but did reduce VLDL1-ApoB production rate (12.4 +/- 4.5 vs 19.5 +/- 8.4 mg kg(-1) day(-1), p = 0.035). No side effects of rosuvastatin were observed during the study.

CONCLUSIONS/INTERPRETATION

In type 2 diabetic patients rosuvastatin 20 mg not only induces a significant increase of LDL-ApoB catabolism (73%), but also has favourable effects on the catabolism of triacylglycerol-rich lipoproteins, e.g. a significant increase in the catabolism of VLDL1-ApoB (48%), VLDL2-ApoB (63%) and IDL-ApoB (68%), and a reduction in the production rate of VLDL1-ApoB (-36%). The effects of rosuvastatin on the metabolism of triacylglycerol-rich lipoproteins may be beneficial for prevention of atherosclerosis in type 2 diabetic patients.

Effect of plasma phospholipid transfer protein deficiency on lethal endotoxemia in mice

Lipopolysaccharides (LPS) are components of Gram-negative bacteria. The cellular response from the host to LPS is mediated through stepwise interactions involving the lipopolysaccharide-binding protein (LBP), CD14, and MD-2, which produces the rearrangement of TLR4. In addition to LBP, the lipid transfer/lipopolysaccharide-binding protein gene family includes the phospholipid transfer protein (PLTP). Here we show that the intravascular redistribution of LPS from the plasma lipoprotein-free fraction toward circulating lipoproteins is delayed in PLTP-deficient mice. In agreement with earlier in vitro studies, which predicted the neutralization of the endotoxic properties of LPS when associated with lipoproteins, significant increases in the plasma concentration of proinflammatory cytokines were found in PLTP-deficient as compared with wild type mice. Similar inflammatory damage occurred in tissues from wild type and PLTP-deficient mice 24 h after one single intraperitoneal injection of LPS but with a more severe accumulation of red blood cells in glomeruli of LPS-injected PLTP-deficient mice. Complementary ex vivo experiments on isolated splenocytes from wild type and PLTP-deficient mice further supported the ability of cell-derived PLTP to prevent LPS-mediated inflammation and cytotoxicity when combined with lipoprotein acceptors. Finally, PLTP deficiency in mice led to a significant increase in LPS-induced mortality. It is concluded that increasing circulating levels of PLTP may constitute a new and promising strategy in preventing endotoxic shock.

Cell surface expression of LDL receptor in chronic hepatitis C: correlation with viral load

The LDL receptor (LDL-R) has been proposed as the viral receptor for Hepatitis C virus (HCV). This hypothesis has been based exclusively on in vitro studies. In human mononuclear cells, LDL-R gene expression has been demonstrated to be parallel and be coordinately regulated to gene expression in the human liver. The purpose of the current study was to determine the mononuclear cell surface expression of the LDL receptor in patients with HCV chronic infection according to viral load. Sixty-eight consecutive untreated chronic hepatitis C patients were studied to determine the mononuclear cell surface expression of the LDL-R. LDL-Rs were quantified at the surface of mononuclear cells in fresh blood samples taken after fasting using flow cytometry. LDL-R expression was significantly associated with LDL-cholesterol (r = -0.25; P = 0.03) and HCV-viral load (r = 0.37, P = 0.002). In multivariate analysis, the LDL-R expression was significantly associated with HCV viral load, whereas genotype, age, body mass index, and fibrosis were not. In conclusion, our data provided by a human study, suggest that the LDL-R may be one of the receptors implicated in HCV replication.

7-Ketocholesterol-induced apoptosis. Involvement of several pro-apoptotic but also anti-apoptotic calcium-dependent transduction pathways

Oxysterols, and particularly 7-ketocholesterol, appear to be strongly involved in the physiopathology of atherosclerosis. These molecules are suspected to be cytotoxic to the cells of the vascular wall and monocytes/macrophages, particularly by inducing apoptosis. Previous studies have demonstrated that 7-ketocholesterol-induced apoptosis is triggered by a sustained increase of cytosolic-free Ca2+, which elicits the mitochondrial pathway of apoptosis by activation of the calcium-dependent phosphatase calcineurin, leading to dephosphorylation of the 'BH3 only' protein BAD. However, thorough study of the results suggests that other pathways are implicated in 7-ketocholesterol-induced cytotoxicity. In this study, we demonstrate the involvement of two other calcium-dependent pathways during 7-ketocholesterol-induced apoptosis. The activation of the MEK-->ERK pathway by the calcium-dependent tyrosine kinase PYK 2, a survival pathway which delays apoptosis as shown by the use of the MEK inhibitor U0126, and a pathway involving another pro-apoptotic BH3 only protein, Bim. Indeed, 7-ketocholesterol treatment of human monocytic THP-1 cells induces the release of Bim-LC8 from the microtubule-associated dynein motor complex, and its association with Bcl-2. Therefore, it appears that 7-ketocholesterol-induced apoptosis is a complex phenomenon resulting from calcium-dependent activation of several pro-apoptotic pathways and also one survival pathway.

Effect of age on salivary flow obtained under feeding and non-feeding conditions

Age, health status and disease treatments are thought to influence salivary flow. In this study, age effect on salivation was compared in non-feeding (at rest and during parafilm chewing) and feeding (during meat chewing) conditions for two groups of healthy subjects, 25 young subjects (mean age 27.4 years) and 20 old subjects (mean age 71.2 years). In non-feeding conditions, parotid flow was assessed at rest (3 min) and during parafilm chewing (1 min) from the absorptive capacity of a cotton roll placed in front of the upper duct apertures. Remaining saliva emanating mainly from the submandibular/sublingual glands was determined at rest by a sublingual cotton roll. In order not to impede in the chewing process during parafilm chewing, no cotton roll was placed in the lower part of the mouth and the remaining saliva was simply spit out for evaluation. Assessments were made under feeding conditions during the mastication of meat of different textures. The saliva content of the bolus was evaluated at different stages of the chewing process by weighing the mouth contents after spitting. No direct age effect was found on the different salivary flow rates measured during different conditions of stimulation. However, a significant correlation was found between the salivary flow rates at rest and those obtained during meat chewing in the elderly group but not in the young group. In elderly adults, rest salivary flow rate appears as a good predictor of salivary flow during the consumption of food. Within each group, significant correlations were found between salivation elicited by meat and by parafilm chewing. These results confirm the lack of direct global age effect on salivary flow rate by chewing in the 3 min after the stimulation, although adaptations to the measurement conditions are different between both groups of subjects.

Involvement of a calcium-dependent dephosphorylation of BAD associated with the localization of Trpc-1 within lipid rafts in 7-ketocholesterol-induced THP-1 cell apoptosis

7-Ketocholesterol is a component of oxidized LDL, which plays a central role in atherosclerosis. It is a potent inducer of cell death towards a wide number of cells involved in atherosclerosis. In this study, it is reported that 7-ketocholesterol treatment induces an increase of cytosolic-free Ca(2+) in THP-1 monocytic cells. This increase is correlated with the induction of cytotoxicity as suggested from experiments using the Ca(2+) channel blockers verapamil and nifedipine. This 7-ketocholesterol-induced apoptosis appears to be associated with the dephosphorylation of serine 75 and serine 99 of the proapoptotic protein Bcl-2 antagonist of cell death (BAD). We demonstrated that this dephosphorylation results mainly from the activation of calcium-dependent phosphatase calcineurin by the oxysterol-induced increase in Ca(2+). Moreover, this Ca(2+) increase appears related to the incorporation of 7-ketocholesterol into lipid raft domains of the plasma membrane, followed by the translocation of transient receptor potential calcium channel 1, a component of the store operated Ca(2+) entry channel, to rafts.

[Microspheres, nanospheres and flow cytometry: from cellular to molecular analysis]

Micro- and nanospheres are tightly associated with the development of flow cytometry. They are indispensable tools to optimize diffraction and fluorescence signals as well as for fluorescence calibration and cellular purification (magnetic micro- and nanospheres). They are also usefull to evaluate phagocytosis and to detect slightly expressed antigens. Recently, developments of microspheres-based flow cytometric assays have raised to quantify soluble analytes in biological fluids, cellular and tissue samples. The technology utilizes spectrally distinct fluorescent microspheres as a solid support for a conventional immunoassay, affinity assay or DNA hybridisation assay which is subsequently analyzed on a flow cytometer. Several multiplexed bead systems are now available facilitating the development of multiplexed assays that simultaneously measure many different analytes in few microliters of sample. Some recent applications with fluorescent microspheres coated with antibodies or oligonucleotides include cytokines and PCR products quantitation and single nucleotide polymorphism genotyping. Thus, multiplex assays using microspheres and flow cytometry technologies are exciting techniques which have the potential to contribute to the development of efficient diagnostic and research methods.

Cell surface expression of LDL receptor is decreased in type 2 diabetic patients and is normalized by insulin therapy

OBJECTIVE

In type 2 diabetic patients with poor metabolic control, kinetic studies have demonstrated that LDL fractional catabolic rate (FCR) is slowed down, whereas it is normalized on insulin therapy. This study was designed to analyze whether variations in the expression of LDL receptors at the cell surface could explain the results observed in kinetic studies.

RESEARCH DESIGN AND METHODS

LDL receptors were quantified at the surface of mononuclear cells in fresh fasting blood samples by a flow cytometry method in 21 control subjects and 21 type 2 diabetic patients before and 3 months after the introduction of insulin therapy and concomitant removal of oral antidiabetic drugs.

RESULTS

Before insulin treatment, monocyte LDL receptor expression was reduced by 41% (6,439 +/- 2,310 vs. 10,846 +/- 2,764 receptors per monocyte, P < 0.001) in type 2 diabetic patients compared with control subjects. It increased by 57% after 3 months of insulin therapy (10,096 +/- 5,657 vs. 6,439 +/- 2,310, P < 0.01) and was similar to that observed in control subjects.

CONCLUSIONS

Our results suggest that insulin plays an important role in the in vivo expression of LDL receptors. Moreover, modulations in the expression of LDL receptors in type 2 diabetic patients either with poor metabolic control or on insulin therapy are likely to contribute to the variations of LDL FCR demonstrated by kinetic studies under those circumstances.

Impairment of the cytotoxic and oxidative activities of 7 beta-hydroxycholesterol and 7-ketocholesterol by esterification with oleate

Atherosclerosis involves inflammatory processes, as well as cytotoxic and oxidative reactions. In atherosclerotic plaques, these phenomena are revealed by the presence of dead cells, oxidized lipids, and oxidative DNA damage, but the molecules triggering these events are still unknown. As 7 beta-hydroxycholesterol and 7-ketocholesterol, which are present at elevated concentrations in atherosclerotic lesions, are strongly cytotoxic and pro-oxidative, their effects were determined on cell death, superoxide anion and nitric oxide production, lipid peroxidation, and oxidative DNA damage. 7-Ketocholesterol- and 7 beta-hydroxycholesterol-induced cell death leads to a loss of mitochondrial potential, to increased permeability to propidium iodide, and to morphological nuclear changes (swelling, fragmentation, and/or condensation of nuclei). These effects are preceded by the formation of cytoplasmic monodansylcadaverine-positive structures and are associated with a rapid enhancement of cells overproducing superoxide anions, a decrease in cells producing nitric oxide, lipid peroxidation (formation of malondialdehyde and 4-hydroxynonenal adducts, low ratio of [unsaturated fatty acids]/[saturated fatty acids]) as well as oxidative DNA damage (8-oxoguanine formation). Noteworthy, none of the cytotoxic features previously observed with 7 beta-hydroxycholesterol and 7-ketocholesterol were noted with cholesterol, 7 beta-hydroxycholesteryl-3-oleate and 7-ketocholesteryl-3-oleate, with the exception of a slight increase in superoxide anion production with 7 beta-hydroxycholesteryl-3-oleate. This finding supports the theory that 7 beta-hydroxycholesterol and 7-ketocholesterol could induce cytotoxic and oxidative processes observed in atherosclerotic lesions and that esterification of these compounds may contribute to reducing atherosclerosis progression.

Chronology of cellular alterations during 7-ketocholesterol-induced cell death on A7R5 rat smooth muscle cells: analysis by time lapse-video microscopy and conventional fluorescence microscopy

BACKGROUND

Time-lapse video microscopy was used to determine whether mitochondrial and nuclear changes (decrease in mitochondrial transmembrane potential, condensation, and/or fragmentation of the nuclei, morphologic features typical of apoptosis) occurring during 7-ketocholesterol-induced cell death on A7R5 rat smooth muscle cells took place before or after the loss of cell adhesion. In addition, changes in actin organization were followed by conventional fluorescence microscopy.

METHODS

Morphologic, functional, and spatial changes at the mitochondrial level were investigated with 3,3'-dihexyloxacarbocyanine iodide and/or MitoTracker Red, and nuclear morphology was characterized by staining with Hoechst 33342. Actin fibers, which are major components of the filament network of the cytoskeleton, were visualized with phalloidin linked to fluorescein. The numbers of adherent and nonadherent cells were determined by cell counting.

RESULTS

7-Ketocholesterol-induced cell death was associated with a rapid alteration of actin fibers, a loss of intercellular junctions, and cell shape modifications. Analysis of mitochondrial transmembrane potential showed successively a hyperpolarization and a more or less pronounced progressive decrease followed by a dramatic drop associated with an increase in Hoechst 33342 staining, reflecting chromatin condensation and morphologic changes in the nuclei.

CONCLUSIONS

During cell death induced by 7-ketocholesterol in A7R5 rat smooth muscle cells, the different methods of microscopy allowed us to establish that alterations of actin fibers and mitochondrial dysfunctions occurred before condensation and/or fragmentation of the nuclei, which preceded the loss of cell adhesion.

Flow cytometry and factor analysis evaluation of confocal image sequences of morphologic and functional changes occurring at the mitochondrial level during 7-ketocholesterol-induced cell death

OBJECTIVE

To analyze functional and morphologic alterations that occur at the mitochondrial level by flow cytometry and laser scanning confocal microscopy (CLSM) combined with factor analysis of biomedical image sequences (FAMIS).

STUDY DESIGN

Under treatment of U937 cells with 7-ketocholesterol, functional alterations that occur at the mitochondrial level (especially loss of transmembrane mitochondrial potential [delta psi m]) were assessed with 3,3'-dihexyloxacarbocyanine iodide (DiOC6(3)) and mitotracker red (CMXRos), whereas morphologic changes were analyzed with nonyl acridine orange (NAO). By flow cytometry, these different dyes were excited at 488 nm, whereas on CLSM, excitation of NAO and CMXRos was performed by lines of an argon laser. By CLSM, spectral sequences were performed to characterize NAO and CMXRos. FAMIS was used to transform the image sequences in factor images.

RESULTS

By flow cytometry, rapid loss of delta psi m induced by 7-ketocholesterol was detected with both DiOC6(3) and CMXRos, which gave similar results. Morphologic alterations of mitochondria were revealed with NAO. The factor images obtained from confocal image sequences confirmed these results.

CONCLUSION

The simultaneous use of NAO, CMXRos and FAMIS constitutes a new method to detect morphologic and functional alterations occurring at the mitochondrial level during cell death.

The impairment of endothelium-dependent arterial relaxation by 7-ketocholesterol is associated with an early activation of protein kinase C

Among components of oxidized low density lipoproteins, cholesterol derivatives oxidized in position 7 inhibit endothelium-dependent arterial relaxation by decreasing the release of the main endothelium-derived relaxing factor, nitric oxide (NO). The aim of the present study was to bring new insights into the molecular mechanism by which 7-ketocholesterol can block the endothelium-dependent arterial relaxation. Superoxide dismutase did not prevent the inhibitory effect of 7-ketocholesterol on endothelium-dependent relaxation, and consistent observations were made whether superoxide dismutase was conjugated or not to polyethylene glycol. In addition, neither glutathione supplementation, nor oxypurinol, i.e. a xanthine oxidase inhibitor could reverse the effect of 7-ketocholesterol, indicating that NO was not inactivated by superoxide anion. A direct alteration of the activity of the calcium-dependent NO synthase could also be ruled out, since identical relaxing effects of the calcium ionophore A23187 were observed whether arterial rings were treated or not with 7-ketocholesterol. 4 Whereas the above observations come in support of an early, inhibitory action of 7-ketocholesterol, the specific blockade of one given subtype of membrane receptors could be discarded, and similar inhibitions were observed when either muscarinic or purinergic receptors were stimulated. Finally, the blockade of protein kinase C activity by chelerythrine arose as the sole relevant tool in preventing the effect of 7-ketocholesterol on the endothelium-dependent relaxation of rabbit aortic rings. In addition, complementary studies on cultured bovine aortic endothelial cells came in direct support of the ability of 7-ketocholesterol to activate PKC. In conclusion, 7-ketocholesterol that is present in human hypercholesterolaemic plasma, in atherosclerotic arteries, and in many processed foods can block the release of NO by vascular endothelial cells through its ability to activate PKC.

Analysis of oxidative processes and of myelin figures formation before and after the loss of mitochondrial transmembrane potential during 7beta-hydroxycholesterol and 7-ketocholesterol-induced apoptosis: comparison with various pro-apoptotic chemicals

Among oxysterols oxidized at C7 (7alpha-, 7beta-hydroxycholesterol, and 7-ketocholesterol) 7beta-hydroxycholesterol and 7-ketocholesterol are potent inducers of cell death and probably play central roles in atherosclerosis. As suggested by our previous investigations, 7-ketocholesterol might be a causative agent of vascular damage by inducing apoptosis and enhancing superoxide anion (O2*-) production. To determine the precise relationships between cytotoxicity and oxidative stress, the ability of oxysterols oxidized at C7 to induce apoptosis, to stimulate O2*- production and to promote lipid peroxidation was compared with different pro-apoptotic chemicals: antitumoral drugs (VB, Ara-C, CHX, and VP-16) and STS. All compounds, except 7alpha-hydroxycholesterol, induced apoptosis characterized by the occurrence of cells with fragmented and/or condensed nuclei, loss of mitochondrial potential, caspase-3 activation, PARP degradation, and internucleosomal DNA fragmentation. The highest proportion of apoptotic cells was found with antitumoral drugs and STS, whereas the highest overproduction of O2*- detected before and after the loss of mitochondrial potential was obtained with 7beta-hydroxycholesterol and 7-ketocholesterol. Overproduction of O2*- was always correlated with enhanced lipid peroxidation. Vit E was only capable to significantly counteract apoptosis and oxidative stress induced by 7beta-hydroxycholesterol, 7-ketocholesterol, VB and STS. By electron and fluorescence microscopy, myelin figures evocating autophagic vacuoles were barely observed under treatment with 7beta-hydroxycholesterol and 7-ketocholesterol, and their formation occurring before the loss of mitochondrial potential was reduced by Vit E. In the presence of 7alpha-hydroxycholesterol, no enhancement of O2*- production, no lipid peroxidation, and no formation of myelin figures were observed. Collectively, our data demonstrate, that there can be a more or less important stimulation of oxidative stress during apoptosis. They also suggest that enhancement of O2*- production associated with lipid peroxidation during 7beta-hydroxycholesterol and 7-ketocholesterol-induced apoptosis could contribute to in vivo vascular injury, and that myelin figures could constitute suitable markers of oxysterol-induced cell death.

Ceramide generation occurring during 7beta-hydroxycholesterol- and 7-ketocholesterol-induced apoptosis is caspase independent and is not required to trigger cell death

Biological activities of oxysterols seem tightly regulated. Therefore, the ability to induce cell death of structurally related oxysterols, such as those oxidized at C7(7alpha-, 7beta-hydroxycholesterol, and 7-ketocholesterol), was investigated on U937 cells at different times of treatment in a concentration range of 5-80 microg/ml. Whereas all oxysterols accumulate inside the cells, strong inhibition of cell growth and increased permeability to propidium iodide were observed only with 7beta-hydroxycholesterol and 7-ketocholesterol, which trigger an apoptotic process characterized by the occurrence of cells with fragmented and/or condensed nuclei, and by various cellular dysfunctions: loss of mitochondrial transmembrane potential, cytosolic release of cytochrome c, activation of caspase-9 and -3 with subsequent enhanced activity of caspase-3, degradation of poly(ADP-ribose) polymerase, and increased accumulation of cellular C16 : 0 and C24 : 1 ceramide species. This ceramide generation is not attributed to caspase activation since inhibition of 7beta-hydroxycholesterol- and 7-ketocholesterol-induced apoptosis by Z-VAD-fmk (100 microM), a broad spectrum caspase inhibitor, did not reduce C16 : 0 and C24 : 1 ceramide species accumulation. Conversely, when U937 cells were treated with 7beta-hydroxycholesterol and 7-ketocholesterol in the presence of fumonisin B1 (100 microM), a specific inhibitor of ceramide synthase, C16 : 0 and C24 : 1 ceramide species production was completely abrogated whereas apoptosis was not prevented. Noteworthy, 7alpha-hydroxycholesterol induced only a slight inhibition of cell growth. Collectively, these results are consistent with the notion that the alpha or beta hydroxyl radical position of oxysterols oxidized at C7 plays a key role in the induction of the apoptotic process. In addition, our findings demonstrate that 7beta-hydroxycholesterol- and 7-ketocholesterol-induced apoptosis involve the mitochondrial signal transduction pathway and they suggest that C16 : 0 and C24 : 1 ceramide species generated through ceramide synthase play a minor role in the commitment of 7beta-hydroxycholesterol- and 7-ketocholesterol-induced cell death.

Impairment with various antioxidants of the loss of mitochondrial transmembrane potential and of the cytosolic release of cytochrome c occuring during 7-ketocholesterol-induced apoptosis

Previous investigations of our laboratory have shown that 7-ketocholesterol was a potent inducer of apoptosis involving a release of cytochrome c into the cytosol, and a lipid peroxidation process that could be the consequence of a production of radical oxygen species. According to these considerations, we asked whether some antioxidants were able to counteract 7-ketocholesterol-induced apoptosis, and whether prevention of cell death was associated with the impairment of mitochondrial events implied in the commitment to apoptosis, i.e., opening of the mitochondrial megachannels leading to the loss of the mitochondrial transmembrane potential (DeltaPsim), and release of cytochrome c from mitochondria into the cytosol. To this end, we studied the effects of glutathione (15 mM), N-acetylcysteine (15 mM), vitamin E (100 microM), vitamin C (50 microM) and melatonin (1 mM) on U937 cells treated with 7-ketocholesterol (40 microg/ml). Only glutathione, N-acetylcysteine, and vitamin E prevented apoptosis measured by the occurrence of cells with condensed and/or fragmented nuclei, as well as the loss of DeltaPsim, and the release of cytochrome c. However, all the antioxidants used were potent inhibitors of the production of O(2)(*) occuring under treatment with 7-ketocholesterol. Collectively, our data demonstrate that impairment of apoptosis by glutathione, N-acetylcysteine, and vitamin E correlates with the prevention of mitochondrial dysfunctions, and they underline that the ability of antioxidants to counteract 7-ketocholesterol-induced apoptosis does not only depend on their capability to inhibit the production of O(2)(*).

Characterization and comparison of the mode of cell death, apoptosis versus necrosis, induced by 7beta-hydroxycholesterol and 7-ketocholesterol in the cells of the vascular wall

Oxidized low density lipoproteins (LDLs) play a central role in atherosclerosis, and their toxicity is due, at least in part, to the formation of oxysterols that have been shown to induce apoptosis in various cell types. As 7beta-hydroxycholesterol and 7-ketocholesterol are the major oxysterols found in oxidized LDLs, we have investigated and compared the mode of cell death, apoptosis versus necrosis, that they induce in the cells of the vascular wall, ie, endothelial cells, smooth muscle cells, and fibroblasts. To this end, human vascular endothelial cells from umbilical cord veins (HUVECs), human artery smooth muscle cells, A7R5 rat smooth muscle cells, MRC5 human fibroblasts, and human fibroblasts isolated from umbilical cord veins were taken at confluence and incubated for 48 hours with 7beta-hydroxycholesterol or 7-ketocholesterol (concentration range, 5 to 80 microg/mL). In all cells, both 7beta-hydroxycholesterol and 7-ketocholesterol exhibited toxic effects characterized by a loss of cell adhesion and an increased permeability to propidium iodide. In oxysterol-treated endothelial and smooth muscle cells, typical features of apoptosis were revealed: condensed and/or fragmented nuclei were detected by fluorescence microscopy after staining with Hoechst 33342, oligonucleosomal DNA fragments were visualized in situ in the cell nuclei by the TdT-mediated dUTP-biotin nick-end labeling (TUNEL) method, and internucleosomal DNA fragmentation was found on agarose gel. In contrast, in oxysterol-treated fibroblasts, fragmented and/or condensed nuclei were never revealed, and no DNA fragmentation was observed either by the TUNEL method or by DNA analysis on agarose gel, indicating that these oxysterols induced necrosis in these cells but not apoptosis. In addition, acetylated Asp-Glu-Val-L-aspartic acid aldehyde (an inhibitor of Asp-Glu-Val-L-aspartic acid-sensitive caspases) prevented 7beta-hydroxycholesterol- and 7-ketocholesterol-induced cell death in HUVECs and smooth muscle cells but not in fibroblasts. Thus, 7beta-hydroxycholesterol and 7-ketocholesterol have dual cytotoxic effects on the cells of the vascular wall by their ability to induce apoptosis in endothelial and smooth muscle cells and necrosis in fibroblasts.

Different patterns of IL-1beta secretion, adhesion molecule expression and apoptosis induction in human endothelial cells treated with 7alpha-, 7beta-hydroxycholesterol, or 7-ketocholesterol

Among oxysterols oxidized at C7 (7alpha-, 7beta-hydroxycholesterol, and 7-ketocholesterol), 7beta-hydroxycholesterol and 7-ketocholesterol involved in the cytotoxicity of oxidized low density lipoproteins (LDL) are potent inducers of apoptosis. Here, we asked whether all oxysterols oxidized at C7 were able to trigger apoptosis, to stimulate interleukin (IL)-Ibeta and/or tumor necrosis factor (TNF)-alpha secretion, and to enhance adhesion molecule expression (intercellular adhesion molecule-1 (ICAM-1), vascular cell adhesion molecule-1 (VCAM-1), and E-selectin) on human umbilical venous endothelial cells (HUVECs). Only 7beta-hydroxycholesterol and 7-ketocholesterol were potent inducers of apoptosis and of IL-1beta secretion. TNF-alpha secretion was never detected. Depending on the oxysterol considered, various levels of ICAM-1, VCAM-1 and E-selectin expression were observed. So, oxysterols oxidized at C7 differently injure and activate HUVECs, and the alpha- or beta-hydroxyl radical position plays a key role in apoptosis and IL-1beta secretion.

Glutathione is implied in the control of 7-ketocholesterol-induced apoptosis, which is associated with radical oxygen species production

In a number of experimental systems, inhibition of apoptosis by antioxidants has led to the production of radical oxygen species (ROS) in certain apoptotic forms of cell death. Since antioxidant therapies can reduce vascular dysfunctions in hypercholesterolemic patients who frequently have increased plasma levels of oxysterols constituting potent inducers of apoptosis, we speculate that oxysterol-induced apoptosis could involve oxidative stress. Here, we tested the protective effects of the aminothiols glutathione (GSH) and N-acetylcysteine (NAC), which are two potent antioxidants, on apoptosis induced by 7-ketocholesterol in U937 cells, and we present evidence indicating that oxidative processes are involved in 7-ketocholesterol-induced cell death. Thus, GSH and NAC prevented phenomenona linked to apoptosis such as reduction of cell growth, increase cellular permeability to propidium iodide, and occurrence of nuclear condensation and/or fragmentation, and they delayed internucleosomal DNA fragmentation. In addition, cell treatment with GSH impaired cytochrome c release into the cytosol and degradation of caspase-8 occurring during cell death. During 7-ketocholesterol-induced apoptosis, we also observed a rapid decrease in cellular GSH content, oxidation of polyunsaturated fatty acids, and a production of ROS by flow cytometry with the use of the dye 2', 7'-dichlorofluorescin-diacetate; both phenomena were inhibited by GSH. Prevention of cell death by GSH and NAC does not seem to be a general rule since these antioxidants impaired etoposide (but not cycloheximide) -induced apoptosis. Taken together, our data demonstrate that GSH is implied in the control of 7-ketocholesterol-induced apoptosis associated with the production of ROS.

Overexpression of the ARF1 exchange factor ARNO inhibits the early secretory pathway and causes the disassembly of the Golgi complex

The small GTPase ARF1 is a key regulator of intracellular membrane traffic. In its active, GTP-bound form, ARF1 is associated with Golgi membranes and promotes the recruitment of the cytosolic coat protein complex, which will result in membrane budding and vesicle formation. ARNO (ARF nucleotide site opener) has been shown to act in vitro as a GTP exchange factor for ARF1. Here, we have investigated the function of ARNO in vivo. By immunofluorescence and cell fractionation, ARNO was found to be mostly cytosolic in HeLa cells. Its overexpression led to a strong inhibition of the secretion of SEAP (secreted form of alkaline phosphatase). Newly synthesized SEAP failed to acquire endoglycosidase H resistance, indicating a block in the early secretory pathway. This effect on secretion was accompanied by a disassembly of the Golgi complex and a redistribution of Golgi resident proteins into the endoplasmic reticulum (ER). On the other hand, ARNO overexpression did not affect the early endocytic pathway. These results show that ARNO functions in vivo in Golgi to ER transport. Its behavior is then consistent with ARNO being an exchange factor for ARF1.

ARNO3, a Sec7-domain guanine nucleotide exchange factor for ADP ribosylation factor 1, is involved in the control of Golgi structure and function

Budding of transport vesicles in the Golgi apparatus requires the recruitment of coat proteins and is regulated by ADP ribosylation factor (ARF) 1. ARF1 activation is promoted by guanine nucleotide exchange factors (GEFs), which catalyze the transition to GTP-bound ARF1. We recently have identified a human protein, ARNO (ARF nucleotide-binding-site opener), as an ARF1-GEF that shares a conserved domain with the yeast Sec7 protein. We now describe a human Sec7 domain-containing GEF referred to as ARNO3. ARNO and ARNO3, as well as a third GEF called cytohesin-1, form a family of highly related proteins with identical structural organization that consists of a central Sec7 domain and a carboxy-terminal pleckstrin homology domain. We show that all three proteins act as ARF1 GEF in vitro, whereas they have no effect on ARF6, an ARF protein implicated in the early endocytic pathway. Substrate specificity of ARNO-like GEFs for ARF1 depends solely on the Sec7 domain. Overexpression of ARNO3 in mammalian cells results in (i) fragmentation of the Golgi apparatus, (ii) redistribution of Golgi resident proteins as well as the coat component beta-COP, and (iii) inhibition of SEAP transport (secreted form of alkaline phosphatase). In contrast, the distribution of endocytic markers is not affected. This study indicates that Sec7 domain-containing GEFs control intracellular membrane compartment structure and function through the regulation of specific ARF proteins in mammalian cells.

Inhibition by cholesterol oxides of NO release from human vascular endothelial cells

Recent studies have demonstrated that, unlike cholesterol, cholesterol oxidized at position 7 can reduce the maximal endothelium-dependent relaxation of isolated rabbit aortas (Circulation. 1997;95:723-731). The aim of the current study was to determine whether cholesterol oxides reduce the release of nitric oxide (NO) from human umbilical vein endothelial cells (HUVECs). The amount of NO released by histamine-stimulated HUVECs was determined by differential pulse amperometry using a nickel porphyrin- and Nafion-coated carbon microfiber electrode. The effects of cholesterol (preserved from oxidation by butylated hydroxytoluene), 7-ketocholesterol, 7beta-hydroxycholesterol, 5alpha,6alpha-epoxycholesterol, 19-hydroxycholesterol (60 microg/mL), and alpha-lysophosphatidylcholine (10 microg/mL) were compared. Pretreatment of HUVECs with cholesterol, 5alpha,6alpha-epoxycholesterol, or 19-hydroxycholesterol did not alter histamine-activated NO production. In contrast, pretreatment with 7-ketocholesterol or 7beta-hydroxycholesterol significantly decreased NO release. The inhibitory effect of 7-ketocholesterol was time and dose dependent and was maintained in the presence of L-arginine. In the absence of serum, lysophosphatidylcholine also reduced NO production. In ionomycin-stimulated cells, pretreatment with 7-ketocholesterol did not inhibit NO release. These results demonstrate that cholesterol derivatives oxidized at the 7 position, the main products of low density lipoprotein oxidation, reduce histamine-activated NO release in HUVECs. Such an inhibitory effect of cholesterol oxides may account, at least in part, for the ability of oxidized low density lipoprotein to reduce the endothelium-dependent relaxation of arteries.

Induction of apoptosis and of interleukin-1beta secretion by 7beta-hydroxycholesterol and 7-ketocholesterol: partial inhibition by Bcl-2 overexpression

The oxysterols, 7beta-hydroxycholesterol and 7-ketocholesterol, are involved in the cytotoxicity of oxidized LDL. To elucidate their molecular mechanisms, the human promonocytic leukemia cells U937 and U4 were used. U4 cells overexpressing Bcl-2 were obtained by transfection of U937 cells. 7Beta-hydroxycholesterol and 7-ketocholesterol induced nuclear condensation and/or fragmentation, internucleosomal DNA fragmentation, and IL-1beta secretion, which were partially inhibited by Bcl-2 overexpression. These findings underline that these oxysterols could constitute major risk factors in atherosclerosis by their cytotoxicity and their ability to induce IL-1beta release which might favor the recruitment of immunocompetent cells in the atherosclerotic plaque.

Induction of similar features of apoptosis in human and bovine vascular endothelial cells treated by 7-ketocholesterol

Cholesterol oxides have numerous cytotoxic effects and those oxidized in the C7 position have been shown to induce apoptosis in bovine aortic endothelial cells (BAEC). The aim of the present study was to determine whether apoptosis also occurs in human vascular endothelial cells (HUVEC) treated with 7-ketocholesterol. To this end, cultured BAEC and HUVEC were incubated for 48 h with 7-ketocholesterol (concentration range 5-80 micrograms/ml) and the characteristics of cell death were assessed by various methods: counting of adherent and non-adherent cells; analysis of DNA fragmentation pattern; and morphological study by light, fluorescence, and electron microscopy. The 7-ketocholesterol treatment was accompanied by a decrease in the number of adherent cells and an increase in the number of non-adherent cells. Apoptotic cells, recognized by fragmented and/or condensed nuclei after staining with Hoechst 33342 or Giemsa, were mainly detected among non-adherent cells, and agarose gel electrophoresis revealed a typical internucleosomal DNA fragmentation among 7-ketocholesterol-treated cells. The DNA fragmentation was no longer detected when HUVEC and BAEC were simultaneously incubated with 0.5 mmol/l zinc chloride, which is known to inhibit Ca2+/Mg(2+)-dependent endonucleases. Finally, the ultrastructural abnormalities observed by electron microscopy in both 7-ketocholesterol-treated HUVEC and BAEC were remarkably similar and were mainly characterized by condensed chromatin, altered mitochondria, disturbed organization of the cytoskeleton, and vacuoles containing myelin figures and/or cell debris; apoptotic bodies were also frequently detected. It is concluded that 7-ketocholesterol constitutes a potent inducer of apoptosis in endothelial vascular cells of both bovine and human origin, suggesting that cholesterol oxides may be involved in the early steps of the atherosclerotic process in humans.

[Flow cytometry measurement of DNA fragmentation in the course of cell death via apoptosis. New techniques for evaluation of DNA status for the pathologist]

Cell death by apoptosis is characterized by DNA fragmentation in 200-250 and/or 30-50 kb followed or not by internucleosomal DNA fragmentation in 180-200 pb. Such characteristics have been used to distinguish between necrotic and apoptotic cells, and also to identify and quantify apoptotic cells by flow cytometry. In the case of internucleosomal DNA fragmentation, the analysis of DNA content constitutes the easiest method to identify apoptotic cells giving an hypoploid cell population commonly called "Sub G1". The identification of the "Sub G1" does not depend on the dyes used; however according to the method of cell fixation and permeabilization, of the divalent cations (Ca2+, Mg2+) present in the staining buffers and of the use of trypsin, the "Sub G1" population may be more or less difficult to identify. To detect apoptotic cells whatever the pattern of DNA fragmentation, the most commonly used methods are either in situ nick-translation or TUNEL (TdT dUTP Nick End Labelling). Thus, flow cytometry offers a wide range of attractive techniques to characterize apoptotic cells but it requires the use of methodological controls for validating results.

[Observation of illicit or misused psychotropic drugs (O.P.P.I.D.U.M.): five years of surveillance of products consumed by drug addicts at Marseille]

The aim of O.P.P.I.D.U.M. is the survey of products used by drug addicts. A five year survey, based on regular pools, has provided interesting results. 1,283 patients (80 per cent men, about 27 years old, 1/4 employed) used 2,241 drugs. The most frequent was heroin, followed by benzodiazepines, cannabis and cocaine. Flunitrazepam was the most commonly misused product, taken by users who started consumption earlier, with a higher rate of unemployment and imprisonment. Cocaine was as often taken intravenously as by sniffing, and most often used before imprisonment. Ecstasy (M.D.M.A.) has appeared recently. Codeine taken alone was used by subjects older than the heroin users, more frequently employed and virtually never prison inmates: this suggests the existence of an unofficial detoxication and substitution process. Confidence of clinicians needs anonymity of the records and return of information. Such a campaign is about to be launched.

Oligomerization of VIP21-caveolin in vitro is stabilized by long chain fatty acylation or cholesterol

VIP21-caveolin is one of the components which form the cytoplasmic surface of caveolae. In vivo, this integral membrane protein is found in homo-oligomers with molecular masses of approximately 200, 400 and 600 kDa. These oligomers are also formed by the addition of cytosol to the in vitro synthesized and membrane inserted VIP21-caveolin. Here we show that long chain fatty acyl coenzyme A esters can completely substitute for cytosol in inducing 200 kDa and 400 kDa complexes, whereas 25-hydroxy-cholesterol can produce the 200 kDa oligomer. In order to understand whether acylation of VIP21-caveolin itself is a prerequisite for oligomerization, we studied a mutant protein lacking all three cysteines. When analyzed by velocity sucrose gradient centrifugation in the presence of the non-ionic detergent octylglucoside, both palmitoylated and non-palmitoylated VIP21-caveolin formed oligomers that were indistinguishable. However, only the oligomers of the non-palmitoylated protein are disrupted when analyzed by SDS-PAGE without boiling. These data suggest that the protein domains of VIP21-caveolin are the primary determinants of oligomerization, but that palmitoylation of cysteine residues can increase the stability of the oligomers.

VIP21-caveolin, a membrane protein constituent of the caveolar coat, oligomerizes in vivo and in vitro

VIP21-caveolin is a membrane protein, proposed to be a component of the striated coat covering the cytoplasmic surface of caveolae. To investigate the biochemical composition of the caveolar coat, we used our previous observation that VIP21-caveolin is present in large complexes and insoluble in the detergents CHAPS or Triton X-114. The mild treatment of these insoluble structures with sodium dodecyl sulfate leads to the detection of high molecular mass complexes of approximately 200, 400, and 600 kDa. The 400-kDa complex purified to homogeneity from dog lung is shown to consist exclusive of the two isoforms of VIP21-caveolin. Pulse-chase experiments indicate that the oligomers form early after the protein is synthesized in the endoplasmic reticulum (ER). VIP21-caveolin does indeed insert into the ER membrane through the classical translocation machinery. Its hydrophobic domain adopts an unusual loop configuration exposing the N- and C-flanking regions to the cytoplasm. Similar high molecular mass complexes can be produced from the in vitro-synthesized VIP21-caveolin. The complex formation occurs only if VIP21-caveolin isoforms are properly inserted into the membrane; formation is cytosol-dependent and does not involve a vesicle fusion step. We propose that high molecular mass oligomers of VIP21-caveolin represent the basic units forming the caveolar coat. They are formed in the ER and later, between the ER and the plasma membrane, these oligomers could associate into larger detergent-insoluble structures.

Growth factor activity of IL-6 in the synovial fluid of patients with rheumatoid arthritis

OBJECTIVE

We set out to determine whether the ability of synovial fluids (SF) in patients with rheumatoid arthritis (RA) to facilitate the proliferation of synovial tissue-derived fibroblastic cell lines was related to the presence of growth factors and/or cytokines.

METHODS

The growth factor activity of 20 RA SF was measured by their ability to induce anchorage-independent growth of the rat NRK-49F (49F) fibroblastic strain. The presence of transforming growth factor-beta (TGF-beta) and platelet-derived growth factor (PDGF) was also assessed using neutralising anti-TGF-beta or anti-PDGF-AB mAbs. Cytokines were measured by functional assays or ELISA:

RESULTS

We observed a correlation between growth factor activity and the IL-6 levels in SF. Both were correlated to the erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) levels in SF and serum. IL-6 (at concentrations above 10(4) U/ml), synergized with growth factors in the induction of the anchorage independent (AI) growth of 49F cells. Pretreatment of SF with a neutralising anti-IL-6 mAb substantially reduced the capacity of these SF to induce AI growth of 49F cells, confirming the growth factor activity of IL-6 in this test. In contrast, IL-6 alone or in association with PDGF, epidermal growth factor (EGF) or TGF-beta had no effect on the anchored growth of synovial tissue-derived fibroblasts, and treatment of SF with a neutralising anti-IL-6 mAb did not affect their ability to increase the growth rate of synovial tissue-derived fibroblasts.

CONCLUSIONS

These results strongly suggest that IL-6 is responsible for the observed correlation between the growth factor activity of SF and inflammatory indexes such as ESR and CRP. However, neither IL-6 nor PDGF were responsible for the observed positive effect of SF on synovial fibroblastic cell lines.

Jacalin, a lectin that inhibits in vitro HIV-1 infection, induces intracellular calcium increase via CD4 in cells lacking the CD3/TcR complex

The lectin jacalin interacts with the CD4 cell surface antigen; this lectin inhibits in vitro infection by human immunodeficiency virus type 1 without preventing virus binding on the host cell. The infection process is known to involve cellular events triggered by the binding of the viral external glycoprotein gp120 to CD4. Herein we demonstrate that jacalin induces cell signaling directly through the CD4 antigen and that independently of the CD3/TcR complex. The capacity of jacalin to trigger cell signals through the CD4 molecule is discussed in relation to its ability to inhibit HIV infection.