LDL-receptors expression in HIV-infected patients: relations to antiretroviral therapy, hormonal status, and presence of lipodystrophy

BACKGROUND

Abnormalities in lipid levels and lipodystrophy (LD) have been commonly reported after commencement of highly active antiretroviral therapy (HAART). A major mechanism by which plasma low-density lipoprotein (LDL) cholesterol levels may be influenced is via the regulation of hepatic LDL receptor expression. The activity of LDL receptors is under hormonal control. Moreover, HIV infection and HAART are associated with important modifications of hormonal status. As the cause of these adverse reactions is unknown, the effects of HAART and lipodystrophy on LDL receptors were evaluated.

MATERIALS AND METHODS

Thirty-nine HIV treated patients (21 with a protease inhibitor (PI) containing regimen, 18 without PI use) and 22 control subjects were tested for insulin resistance (HOMA model assessment), lipid profile, serum concentration of dehydroepiandrosterone (DHEA) and LDL-R expression. LDL-R on mononuclear cells were quantified by flow cytrometry.

RESULTS

Among the 39 HIV infected patients, 14 patients had a lipodystrophy (LD). Patients with LD had significantly higher levels of triglyceride (TG) and insulin resistance compared to patients without LD. There was no significant difference in LDL-R count between patients with or without PI use. In contrast, LDL-R count was significantly lower in patients with LD compared with those without (8504 +/- 3901 vs. 13 200 +/- 4532, P = 0.001). There was no difference in LDL-R count between patients without LD and control subjects. Patients with LD had lower levels of DHEA compared to patients without LD. In HIV-infected patients, we found a significant correlation between LDL-R expression and TG (r = -0.32; P = 0.04) and LDL cholesterol (r = -0.33; P = 0.04). In contrast, we did not observe a correlation between DHEA level and LDL-R count or LDL cholesterol level.

CONCLUSIONS

HIV-lipodystrophy is associated with a lower expression of LDL-R. This decreased expression of LDL-R seems independent of DHEA or insulin secretion.

Increased plasma apoA-IV level is a marker of abnormal postprandial lipemia: a study in normoponderal and obese subjects

Plasma apolipoprotein A-IV (apoA-IV) levels are found elevated in hypertriglyceridemic patients. However, the relationship between plasma apoA-IV level and postprandial lipemia is not well known and remains to be elucidated. Thus, our objective was to study the relationship between plasma apoA-IV and postprandial TG after an oral fat load test (OFLT). Plasma apoA-IV was measured at fast and during an OFLT in 16 normotriglyceridemic, normoglucose-tolerant android obese subjects (BMI = 34.6 +/- 2.9 kg/m(2)) and 30 normal weight controls (BMI = 22.2 +/- 2.3 kg/m(2)). In spite of not statistically different fasting plasma TG levels in controls and obese patients, the former group showed an altered TG response after OFLT, featuring increased nonchylomicron TG area under the curve (AUC) compared with controls (516 +/- 138 vs. 426 +/- 119 mmol/l x min, P < 0.05). As compared to controls, obese patients showed increased apoA-IV levels both at fast (138.5 +/- 22.4 vs. 124.0 +/- 22.8 mg/l, P < 0.05) and during the OFLT (apoA-IV AUC: 79,833 +/- 14,281 vs. 68,176 +/- 17,463 mg/l x min, P < 0.05). Among the whole population studied, as among the control and obese subgroups, fasting plasma apoA-IV correlated significantly with AUC of plasma TG (r = 0.60, P < 0.001), AUC of chymomicron TG (r = 0.45, P < 0.01), and AUC of nonchylomicron TG (r = 0.62, P < 0.001). In the multivariate analysis, fasting apoA-IV level constituted an independent and highly significant determinant of AUC of plasma TG, AUC of chymomicron TG, AUC of nonchylomicron TG, and incremental AUC of plasma TG. In conclusion, we show a strong link between fasting apoA-IV and postprandial TG metabolism. Plasma fasting apoA-IV is shown to be a good marker of TG response after an OFLT, providing additional information on post-load TG response in conjunction with other known factors such as fasting TGs.

[Implication and mode of action of infectious agents in the formation of atheromatous plaques. Infection and atherosclerosis]

Different kinds of infectious agents seem to be implied in the atherosclerotic process. Indeed, some bacteria and viruses have been identified in atherosclerotic lesions: Chlamydia pneumoniae, Helicobacter pylori, Streptococcus sanguis, Porphyromonas gingivalis, herpes simplex viruses type 1 and 2, coxsakievirus B and hepatitis virus A. By their ability to induce antigenic and functional changes in the cells of the vascular wall (endothelial cells, smooth muscle cells, monocytes/macrophages, and fibroblasts) and to stimulate immune response as well as oxidative stress, it is more and more tempting to speculate that infectious agents probably play key roles in the initiation and in the formation of atherosclerotic plaques in certain patients.

Efficiency of homocysteine plus copper in inducing apoptosis is inversely proportional to gamma-glutamyl transpeptidase activity

Hyperhomocysteinemia represents an independent risk factor for atherosclerosis, but the mechanisms leading to cellular dysfunctions remain unknown. Using ECV304 cells, we found that homocysteine (Hcy) plus copper (Cu2+) induced cytotoxic effects: loss of cell adhesion, increased permeability to PI, and the occurrence of morphologically apoptotic cells. This form of apoptosis, inhibited by Z-VAD-fmk, was associated with a loss of mitochondrial potential, a cytosolic release of cytochrome c, activation of caspase-3, degradation of poly(ADP-ribose)polymerase, and internucleosomal DNA fragmentation. However, the ability of Hcy plus Cu2+ to induce apoptosis decreased when the pretreatment culture time increased. As a positive correlation was found between the length of time of culture before treatment and the enhancement of gamma-glutamyl transpeptidase (gamma-GT) activity, we asked whether gamma-GT was involved in the control of Hcy plus Cu2+-induced apoptosis. Therefore, ECV304 cells were treated with either acivicin or dexamethasone, inhibiting and stimulating gamma-GT, respectively. In ECV304 cells and human umbilical venous endothelial cells, acivicin favored Hcy plus Cu2+-induced apoptosis whereas dexamethasone counteracted the apoptotic process. As acivicin and dexamethasone were also capable of modulating cell death in ECV304 cells treated with antitumoral drugs, our data emphasize that the involvement of gamma-GT in the control of apoptosis is not restricted to Hcy but also concerns other chemical compounds.

Confocal image characterization of human papillomavirus DNA sequences revealed with Eu in HeLa cell nuclei stained with Hoechst 33342

OBJECTIVE

To visualize and localize specific viral DNA sequences revealed with Eu by fluorescence in situ hybridization, confocal laser scanning microscopy (CLSM) and factor analysis of biomedical image sequences (FAMIS).

STUDY DESIGN

Human papillomavirus DNA (HPV-DNA) was identified in HeLa cells with biotinylated DNA probes recognizing HPV-DNA types 16/18. DNA-DNA hybrids were revealed by a three-step immunohistochemical amplification procedure involving an antibiotin mouse monoclonal antibody, a biotinylated goat antimouse polyclonal antibody and streptavidin-Eu. Cell nuclei were counterstained with Hoechst 33342. Image sequences were obtained using a CLSM that made possible ultraviolet excitation. The location of fluorescent signals inside cellular preparations was determined by FAMIS and selection of filters at emission. Image sequences were summarized into a reduced number of images, or factor images, and curves, or factors. Factors estimate spectral or temporal patterns and depth emission profiles. Factor images correspond to spatial distributions of the different factors.

RESULTS

We distinguished between Eu corresponding to HPV-DNA hybridization signals and nuclear staining by taking into account differences in their spectral and temporal patterns and (using their decay rates).

CONCLUSION

FAMIS, together with CLSM and Eu, made possible the detection and characterization of viral papillomavirus DNA sequences in HeLa cells.

In situ hybridization detection of single-copy human papillomavirus on isolated cells, using a catalyzed signal amplification system: GenPoint

The performance and drawbacks of GenPoint, which is a catalyzed signal amplification system for immunohistochemistry, have been evaluated for its ability to reveal human papillomavirus (HPV) DNA detected by in situ hybridization with biotinylated DNA probes. For this aim, formalin-fixed cell deposits from carcinoma cells of the uterine cervix, CaSki, SiHa, and HeLa, containing, respectively, 600 copies of HPV DNA type 16, 1-2 copies of HPV DNA type 16, and 10-50 copies of HPV DNA type 18, were used, and the GenPoint method (consisting of successive incubations with peroxidase-conjugated streptavidin, biotinyl tyramide, and peroxidase-conjugated streptavidin) was compared to immunoenzymatic revelation procedures involving either a one-step reaction (streptavidin-alkaline phosphatase or streptavidin-peroxidase), or a three-step reaction (anti-biotin mouse monoclonal antibody, rabbit anti-mouse antiserum, and mouse APAAP complex). In these conditions, after analysis with a bright-field microscope, GenPoint appeared the most sensitive method of revelation, easily allowing detection of 1-2 copies of HPV DNA on isolated cells by in situ hybridization.

Confocal analysis of phosphatidylserine externalization with the use of biotinylated annexin V revealed with streptavidin-FITC, -europium, -phycoerythrin or -Texas Red in oxysterol-treated apoptotic cells

OBJECTIVE

To analyze externalization of phosphatidylserine via annexin V on apoptotic cells by laser scanning confocal microscopy and factor analysis of biomedical image sequences (FAMIS).

STUDY DESIGN

Streptavidin-fluorescein isothiocyanate (FITC), -europium (Eu), -phycoerythrin (PE) and -Texas Red (TR) were chosen to reveal the binding of biotinylated annexin V on apoptotic U937 human leukemic cells and ECV-304 human endothelial cells induced under treatment with 7-ketocholesterol or 7 beta-hydroxycholesterol. Excitation of each fluorochrome was obtained by selection of specific lines (351 + 364 nm, 488 nm) of the argon laser of a confocal microscope. Temporal and spectral series were performed to characterize each fluorochrome. FAMIS was applied to these series to estimate images corresponding to stains.

RESULTS

Each fluorochrome was clearly distinguished, and images showed localization of phosphatidylserine, which was improved by image analysis.

CONCLUSION

On apoptotic cells it is possible to analyze differences in the improved visualization of phosphatidylserine in series processed by FAMIS with the use of biotinylated annexin V revealed with streptavidin-FITC, -Eu, -PE or -TR.

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.

Human apolipoprotein C-I accounts for the ability of plasma high density lipoproteins to inhibit the cholesteryl ester transfer protein activity

The aim of the present study was to identify the protein that accounts for the cholesteryl ester transfer protein (CETP)-inhibitory activity that is specifically associated with human plasma high density lipoproteins (HDL). To this end, human HDL apolipoproteins were fractionated by preparative polyacrylamide gradient gel electrophoresis, and 30 distinct protein fractions with molecular masses ranging from 80 down to 2 kDa were tested for their ability to inhibit CETP activity. One single apolipoprotein fraction was able to completely inhibit CETP activity. The N-terminal sequence of the 6-kDa protein inhibitor matched the N-terminal sequence of human apoC-I, the inhibition was completely blocked by specific anti-apolipoprotein C-I antibodies, and mass spectrometry analysis confirmed the identity of the isolated inhibitor with full-length human apoC-I. Pure apoC-I was able to abolish CETP activity in a concentration-dependent manner and with a high efficiency (IC(50) = 100 nmol/liter). The inhibitory potency of total delipidated HDL apolipoproteins completely disappeared after a treatment with anti-apolipoprotein C-I antibodies, and the apoC-I deprivation of native plasma HDL by immunoaffinity chromatography produced a mean 43% rise in cholesteryl ester transfer rates. The main localization of apoC-I in HDL and not in low density lipoprotein in normolipidemic plasma provides further support for the specific property of HDL in inhibiting CETP activity.

Co-incubation of native and oxidized low-density lipoproteins: potentiation of relaxation impairment

The influence of native low-density lipoprotein (LDL) on the inhibition of endothelium-dependent relaxation previously induced by oxidized LDL was investigated with intact rabbit aortic rings. We also tried to assess oxysterol involvement in the native lipoprotein effects. Lipoprotein fractions (1 mg protein/ml) were tested for their ability to inhibit the vasorelaxation induced by acetylcholine in aorta rings previously precontracted by noradrenaline vs. that in control strips in Krebs buffer. Co-incubation of oxidized and native LDL reinforced the oxidized LDL-induced inhibition, compared to the impairment evoked by oxidized LDL alone (E(max)=43.3+/-6.7% and 61. 4+/-5.4%, respectively; P<0.05). Finally, smaller amounts of 7-oxy-cholesterols were recovered in organ baths after co-incubation of native and oxidized LDL than after incubation of oxidized LDL alone. Conversely, more oxy-cholesterols were found in the strip vessels under the same conditions (% of oxysterol incorporation: 0. 05158 vs. 0.10199, r=0.703). Together these results suggest that the strengthening of oxidized LDL-induced inhibition by native LDL is dependent on an oxysterol effect on arterial wall cells. Mechanisms involved in this phenomenon remain to be investigated.

Inefficiency of insulin therapy to correct apolipoprotein A-I metabolic abnormalities in non-insulin-dependent diabetes mellitus

Non-insulin-dependent diabetes mellitus (NIDDM) is associated with low high density lipoprotein (HDL) cholesterol and apoA-I, related to an increased apoA-I fractional catabolic rate. This stable isotope kinetic experiment, using L-[1-(13)C] leucine, was designed to study the effect of insulin therapy on HDL apoA-I and A-II metabolism in poorly controlled NIDDM patients. A kinetic study was performed in five control subjects and in six NIDDM patients before and two months after the introduction of insulin therapy. ApoA-I and A-II were modelled using a monoexponential function. Insulin treatment was able to correct neither the low HDL apoA-I concentration observed in NIDDM patients (1.14+/-0.19 vs. 1.16+/-0. 12 g l(-1) (controls: 1.33+/-0.14)), nor the HDL apoA-I hypercatabolism (0.39+/-0.11 vs. 0.34+/-0.05 pool d(-1), (controls: 0.23+/-0.01, P< 0.01)). HDL apoA-I production rate was increased in NIDDM patients compared to control subjects and was not modified by insulin (0.45+/-0.12 vs. 0.39+/-0.08 g d(-1) l(-1), (controls: 0. 31+/-0.04, P< 0.05)). HDL apoA-II kinetic parameters were initially not significantly different between NIDDM patients and control subjects, and were not modified by insulin. The decreased insulin sensitivity, assessed by the insulin suppressive test, was not modified by insulin therapy in NIDDM patients. HDL apoA-I fractional catabolic rate was significantly correlated to HDL triglyceride/cholesteryl ester and triglyceride/protein ratios, which were significantly higher in NIDDM patients than in controls and were not modified by insulin therapy. The persistence of insulin resistance and of high neutral lipid exchanges between triglyceride rich lipoproteins and HDL in insulin-treated NIDDM patients probably explain the inefficiency of insulin therapy to correct HDL apoA-I metabolic abnormalities.

Metabolic abnormalities of apolipoprotein B-containing lipoproteins in non-insulin-dependent diabetes: a stable isotope kinetic study

BACKGROUND

Kinetic abnormalities of apolipoprotein B (apoB)-containing lipoproteins in noninsulin-dependent diabetes mellitus (NIDDM) remain poorly understood. To get further insight into these abnormalities we performed a stable isotope kinetic experiment comparing the metabolism of apoB-containing lipoproteins in moderately severe NIDDM patients and healthy control subjects.

METHODS

The study was performed in the fed state. Subjects underwent a primed infusion of 0.7 mg kg(-1) of L-[1-(13)C]leucine followed by a 16-h constant infusion of 0.7 mg kg(-1) h(-1). [13C]Leucine enrichment in apoB was measured by gas chromatography/combustion/isotope ratio mass spectrometry.

RESULTS

In NIDDM patients, we observed a 3.49- and 4.52-fold increase of very-low-density lipoprotein (VLDL) and intermediate-density lipoprotein (IDL) apoB plasma concentrations, respectively (P<0.01). VLDL apoB production was increased by 41% (P<0.05) and fractional catabolic rate towards IDL and low-density lipoprotein (LDL) was decreased by 61% (P<0.05). The increased IDL apoB plasma concentration was also related to a major catabolic defect (-78%; P<0.01). For most patients, plasma LDL apoB concentration was comparable to that of controls. Nevertheless, LDL apoB metabolism was impaired in NIDDM subjects, with both a decreased LDL catabolic rate (-28%; P<0.05) and a trend towards a diminished synthesis.

CONCLUSION

NIDDM is associated with multiple apoB metabolism abnormalities that are potentially atherogenic. In addition to the increased number of circulating VLDL and IDL particles, the increased residence time observed on all apoB-containing lipoproteins may promote the development of atherosclerotic lesions, by potentiating their oxidizability.

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)(*).

Significant improvement of apolipoprotein B-containing lipoprotein metabolism by insulin treatment in patients with non-insulin-dependent diabetes mellitus

AIMS/HYPOTHESIS

Patients with Type II (non-insulin-dependent) diabetes mellitus have multiple abnormalities in apolipoprotein B (apoB)-containing lipoprotein metabolism. These abnormalities are likely to play an important part in the development of premature atherogenesis in these patients. This stable isotope kinetic experiment was designed to study the effect of insulin therapy on apoB metabolism in poorly controlled Type II diabetic patients.

METHODS

Using L-[1-13C] leucine, we studied apoB metabolism in five control subjects without insulin resistance and in six poorly controlled Type II diabetic patients before and 2 months after the introduction of insulin therapy.

RESULTS

Insulin treatment induced a decrease of very low density lipoprotein apoB plasma concentration [121 +/- 42 vs 158 +/- 91 mg.l-1, p < 0.05 (control subjects: 48 +/- 20)], related to an increased catabolism of very low density lipoprotein towards intermediate density lipoprotein or low density lipoprotein [0.20 +/- 0.08 vs 0.14 +/- 0.07 pool.h-1, p < 0.05 (control subjects: 0.36 +/- 0.10)]. On the other hand, insulin treatment induced an acceleration of intermediate density lipoprotein apoB turn-over without changing its plasma concentration [77 +/- 37 vs 61 +/- 18 mg.l-1, (control subjects: 17 +/- 3)], by increasing both its production rate [22.6 +/- 9.2 vs 18.2 +/- 9.6 mg.l-1.h-1, p < 0.05 (control subjects: 18.4 +/- 3.2)] and its catabolic rate towards low density lipoprotein [0.34 +/- 0.22 vs 0.22 +/- 0.16 pool.h-1, p < 0.05 (control subjects: 1.02 +/- 0.13)]. Likewise, insulin treatment increased low density lipoprotein apoB production rate [20.2 +/- 7.4 vs 16.9 +/- 7.7 mg.l-1.h-1, p < 0.05 (control subjects: 16.9 +/- 2.3)] and restored a normal low density lipoprotein apoB fractional catabolic rate [0.022 +/- 0.004 vs 0.018 +/- 0.004 pool.h-1, p < 0.05 (control subjects: 0.025 +/- 0.004)], resulting in a constant low density lipoprotein apoB plasma concentration [965 +/- 485 vs 984 +/- 558 mg.l-1 (control subjects: 699 +/- 106)].

CONCLUSION/INTERPRETATION

Insulin treatment in Type II diabetes induces profound metabolic modifications of lipoprotein, resulting in significant decrease of the intravascular residence time of very low density lipoprotein, intermediate density lipoprotein and low density lipoprotein particles. This is likely to make these particles less harmful.

Impairment of endothelium-dependent arterial relaxation by high-fat feeding in ApoE-deficient mice: toward normalization by human ApoA-I expression

BACKGROUND

Atherogenic lipoproteins can impair the endothelium-dependent arterial relaxation, and circumstantial evidence suggests a beneficial role of plasma high density lipoproteins and apolipoprotein (apo) A-I in counteracting the endothelium dysfunction. In the present study, vascular reactivity was determined in control, apoE-deficient mice (apoE-KO mice), and apoE-deficient mice expressing human apoA-I (apoE-KO/HuAITg mice).

METHODS AND RESULTS

In the first part of the study, control and apoE-KO mice were fed a low-fat or a high-fat diet for 23 weeks, and the vasoactive responses of isolated thoracic aortic segments to norepinephrine, sodium nitroprusside, and acetylcholine (ACh) were determined. Whereas norepinephrine, sodium nitroprusside, and ACh evoked similar vascular responses in control and apoE-KO mice fed the low-fat diet, high-fat feeding in apoE-KO mice produced a significant 3-fold increase in the mean concentration required to produce a half-maximal relaxing effect (EC(50)) of ACh as compared with control mice. This reflects a weaker sensitivity to ACh of the aortic segments from the apoE-deficient animals. In the second part of the study, the mean EC(50) for ACh after high-fat feeding was found to be 4.4-fold lower in apoE-KO/HuAITg mice than in apoE-KO mice, indicating that the reduced sensitivity to ACh of the thoracic aorta from the apoE-KO mice fed the high-fat diet is improved by the expression of human apoA-I.

CONCLUSIONS

The present study demonstrates that the endothelium-dependent arterial relaxation is impaired in apoE-KO mice fed the high-fat diet. The endothelium dysfunction tends to be normalized by human apoA-I expression.

Plasma phospholipid transfer protein prevents vascular endothelium dysfunction by delivering alpha-tocopherol to endothelial cells

alpha-tocopherol, the most potent antioxidant form of vitamin E, is mainly bound to lipoproteins in plasma and its incorporation into the vascular wall can prevent the endothelium dysfunction at an early stage of atherogenesis. In the present study, the plasma phospholipid transfer protein (PLTP) was shown to promote the net mass transfer of alpha-tocopherol from high density lipoproteins (HDL) and alpha-tocopherol-albumin complexes toward alpha-tocopherol-depleted, oxidized low density lipoproteins (LDL). The facilitated transfer reaction of alpha-tocopherol could be blocked by specific anti-PLTP antibodies. These observations indicate that PLTP may restore the antioxidant potential of plasma LDL at an early stage of the oxidation cascade that subsequently leads to cellular damages. In addition, the present study demonstrated that the PLTP-mediated net mass transfer of alpha-tocopherol can constitute a new mechanism for the incorporation of alpha-tocopherol into the vascular wall in addition to the previously recognized LDL receptor and lipoprotein lipase pathways. In ex vivo studies on rabbit aortic segments, the impairment of the endothelium-dependent arterial relaxation induced by oxidized LDL was found to be counteracted by a pretreatment with purified PLTP and alpha-tocopherol-albumin complexes, and both the maximal response and the sensitivity to acetylcholine were significantly improved. We conclude that PLTP, by supplying oxidized LDL and endothelial cells with alpha-tocopherol through a net mass transfer reaction may play at least two distinct beneficial roles in preventing endothelium damage, i.e., the antioxidant protection of LDL and the preservation of a normal relaxing function of vascular endothelial cells.

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.

Plasma lipoprotein distribution and lipid transfer activities in patients with type IIb hyperlipidemia treated with simvastatin

The aim of the present study was to search in type IIb hyperlipidemic patients for putative concomitant effects of simvastatin on the physicochemical characteristics of low density lipoproteins (LDL) and high density lipoproteins (HDL), as well as on the activities of the cholesteryl ester transfer protein (CETP) and the phospholipid transfer protein (PLTP) that were determined in both endogenous lipoprotein-dependent and endogenous lipoprotein-independent assays. In a double-blind, randomized trial, patients received either placebo (one tablet/day; n = 12) or simvastatin (20 mg/day; n = 12) for a period of 8 weeks after a 5-week run-in period. Simvastatin, unlike placebo, reduced the lipid and apolipoprotein B contents of the most abundant LDL-1, LDL-2, and LDL-3 subfractions without inducing significant changes in the overall size distribution of LDL and HDL. Whereas simvastatin significantly increased PLTP activity in an endogenous lipoprotein-dependent assay (P < 0.01), no variation was observed in a lipoprotein-independent assay. Simvastatin significantly decreased plasma CETP activity in an endogenous lipoprotein-dependent assay (P < 0.01), and the reduction in plasma cholesteryl ester transfer rates was explained by a 16% drop in CETP mass concentration (P < 0.01). In contrast, the specific activity of CETP was unaffected by the simvastatin treatment reflecting at least in part the lack of significant alteration in plasma triglyceride-rich lipoprotein acceptors. The simvastatin-induced changes in plasma CETP mass levels correlated positively with changes in plasma CETP activity (r = 0.483, P = 0.0561), in total cholesterol levels (r = 0.769; P < 0.01), and in LDL-cholesterol levels (r = 0.736; P < 0.01). Whereas the observations suggest that simvastatin might exert concomitant beneficial effects on plasma CETP and LDL levels, neither plasma cholesteryl ester transfer activity nor plasma phospholipid transfer activity appeared as the main determinants of the LDL and HDL distribution profiles in type IIb hyperlipidemic patients.

Variations in serum cholesteryl ester transfer and phospholipid transfer activities in healthy women and men consuming diets enriched in lauric, palmitic or oleic acids

Cholesteryl ester transfer protein (CETP) and phospholipid transfer protein (PLTP) activities were measured in sera from 32 normolipidemic women and men consuming diets enriched in lauric, palmitic, or oleic acids. Serum CETP activity, measured as the rate of radiolabeled cholesteryl esters transferred from HDL toward serum apo B-containing lipoproteins, was higher with the palmitic acid diet (25.1+/-2.5%) than with the lauric acid (23.7+/-2.4%) and the oleic acid (24.0+/-2.7%) diets (P = 0.0028 and 0.0283, respectively). CETP mass concentrations, as measured with an enzyme-linked immunosorbent assay were increased after the lauric acid diet (2.57+/-0.63 mg/l) and the palmitic acid diet (2.49+/-0.64 mg/l) as compared with the oleic acid diet (2.34+/-0.45 mg/l) (P = 0.0035 and 0.0249, respectively). In contrast with CETP, serum PLTP activity, as measured as the rate of radiolabeled phosphatidylcholine transferred from liposomes toward serum HDL, was significantly higher with the lauric acid diet (23.5+/2.6%) than with the palmitic acid diet (22.5+/-2.5%) (P = 0.0013), while no significant differences were noted when comparing the saturated diets versus the oleic acid diet (23.0+/-2.3%). No significant alterations in the mean apparent diameter of LDL, and in the relative proportions of individual HDL subpopulations were observed from one dietary period to another. Nevertheless, lipid transfer activities correlated significantly with the relative abundance of HDL2b, HDL2a, HDL3b, and HDL3c, with opposite tendencies being observed for cholesteryl ester transfer and phospholipid transfer activities. In general, serum CETP activity correlated negatively with HDL cholesterol, but positively with triglyceride concentrations after the dietary interventions, and the relations with serum lipids were just the opposite for PLTP activity. In addition, CETP and PLTP activities correlated negatively when subjects consumed the standardized diets (P < 0.05 in all cases), but not when subjects consumed their habitual diet. It is concluded that serum lipid transfer activities in normolipidemic subjects can be significantly affected by the fatty acid content of the diet, with differential effects on CETP and PLTP activities.

Mass concentration of plasma phospholipid transfer protein in normolipidemic, type IIa hyperlipidemic, type IIb hyperlipidemic, and non-insulin-dependent diabetic subjects as measured by a specific ELISA

Mean plasma phospholipid transfer protein (PLTP) concentrations were measured for the first time by using a competitive enzyme-linked immunosorbent assay. PLTP mass levels and phospholipid transfer activity values, which were significantly correlated among normolipidemic plasma samples (r=0.787, P<0.0001), did not differ between normolipidemic subjects (3.95+/-1.04 mg/L and 575+/-81 nmol. mL-1. h-1, respectively; n=30), type IIa hyperlipidemic patients (4. 06+/-0.84 mg/L and 571+/-43 nmol. mL-1. h-1, respectively; n=36), and type IIb hyperlipidemic patients (3.90+/-0.79 mg/L and 575+/-48 nmol. mL-1. h-1, respectively; n=33). No significant correlations with plasma lipid parameters were observed among the various study groups. In contrast, plasma concentrations of the related cholesteryl ester transfer protein (CETP) were higher in type IIa and type IIb patients than in normolipidemic controls, and significant, positive correlations with total and low density lipoprotein cholesterol levels were noted. Interestingly, plasma PLTP mass concentration and plasma phospholipid transfer activity were significantly higher in patients with non-insulin-dependent diabetes mellitus (n=50) than in normolipidemic controls (6.76+/-1. 93 versus 3.95+/-1.04 mg/L, P<0.0001; and 685+/-75 versus 575+/-81 nmol. mL-1. h-1, P<0.0001, respectively). In contrast, CETP levels did not differ significantly between the 2 groups. Among non-insulin-dependent diabetes mellitus patients, PLTP levels were positively correlated with fasting glycemia and glycohemoglobin levels (r=0.341, P=0.0220; and r=0.382, P=0.0097, respectively) but not with plasma lipid parameters. It is proposed that plasma PLTP mass levels are related to glucose metabolism rather than to lipid metabolism.

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.