Effects of atorvastatin and diet interventions on atherosclerotic plaque inflammation and [18F]FDG uptake in Ldlr-/-Apob100/100 mice.

BACKGROUND AND AIMS: Uptake of the positron emission tomography (PET) tracer 2-deoxy-2-[18F]-fluoro-d- glucose ([18F]FDG) into macrophages is a sensitive marker of inflammation in atherosclerosis. To assess the anti-inflammatory effects of statins, we studied whether atorvastatin therapy reduces aortic [18F]FDG uptake in hypercholesterolemic mice deficient in low-density lipoprotein receptor (Ldlr), and expressing only apolipoprotein B-100 (Ldlr-/-Apob100/100). METHODS: Thirty-six Ldlr-/-Apob100/100 mice were fed a high-fat diet (HFD) for 12 weeks and then allocated to receive a HFD (n = 13), chow diet (Chow, n = 12), or HFD with added atorvastatin (HFD + A, n = 11), for another 12 weeks. In addition to aortic histopathology, [18F]FDG uptake was studied in vivo using PET/computed tomography (CT), and ex vivo by gamma counting of excised aorta. RESULTS: Total cholesterol levels were lower in the Chow and HFD + A groups than in the HFD group (10 ± 3.2, 23 ± 4.9 and 34 ± 9.2 mmol/l, respectively), with the Chow group also showing a lower plaque burden and lower numbers of macrophages in the lesions. Compared to the HFD group, [18F]FDG uptake in the aorta (normalized for blood) was lower in the Chow group in both in vivo (2.1 ± 0.21 vs. 1.7 ± 0.25, p = 0.018) and ex vivo (5.2 ± 2.3 vs. 2.8 ± 0.87, p = 0.011) analyses, whereas atorvastatin had no effect on uptake (2.1 ± 0.42 in vivo and 3.9 ± 1.8 ex vivo). [18F]FDG uptake correlated with plasma total cholesterol levels. CONCLUSIONS: Atorvastatin therapy did not show cholesterol-independent effects on inflammation in atherosclerotic lesions in Ldlr-/-Apob100/100 mice, as determined by histology and [18F]FDG PET, whereas a cholesterol-lowering diet intervention was effective.

Human Cathelicidin Compensates for the Role of Apolipoproteins in Hepatitis C Virus Infectious Particle Formation.

UNLABELLED: Exchangeable apolipoproteins (ApoA, -C, and -E) have been shown to redundantly participate in the formation of infectious hepatitis C virus (HCV) particles during the assembly process, although their precise role in the viral life cycle is not well understood. Recently, it was shown that the exogenous expression of only short sequences containing amphipathic α-helices from various apolipoproteins is sufficient to restore the formation of infectious HCV particles in ApoB and ApoE double-gene-knockout Huh7 (BE-KO) cells. In this study, through the expression of a small library of human secretory proteins containing amphipathic α-helix structures, we identified the human cathelicidin antimicrobial peptide (CAMP), the only known member of the cathelicidin family of antimicrobial peptides (AMPs) in humans and expressed mainly in bone marrow and leukocytes. We showed that CAMP is able to rescue HCV infectious particle formation in BE-KO cells. In addition, we revealed that the LL-37 domain in CAMP containing amphipathic α-helices is crucial for the compensation of infectivity in BE-KO cells, and the expression of CAMP in nonhepatic 293T cells expressing claudin 1 and microRNA miR-122 confers complete propagation of HCV. These results suggest the possibility of extrahepatic propagation of HCV in cells with low-level or no expression of apolipoproteins but expressing secretory proteins containing amphipathic α-helices such as CAMP. IMPORTANCE: Various exchangeable apolipoproteins play a pivotal role in the formation of infectious HCV during the assembly of viral particles, and amphipathic α-helix motifs in the apolipoproteins have been shown to be a key factor. To the best of our knowledge, we have identified for the first time the human cathelicidin CAMP as a cellular protein that can compensate for the role of apolipoproteins in the life cycle of HCV. We have also identified the domain in CAMP that contains amphipathic α-helices crucial for compensation and show that the expression of CAMP in nonhepatic cells expressing claudin 1 and miR-122 confers complete propagation of HCV. We speculate that low levels of HCV propagation might be possible in extrahepatic tissues expressing secretory proteins containing amphipathic α-helices without the expression of apolipoproteins.

Angiopoietin-2 blocking antibodies reduce early atherosclerotic plaque development in mice.

OBJECTIVE: Angiopoietin-2 (Ang-2) blocking agents are currently undergoing clinical trials for use in cancer treatment. Ang-2 has also been associated with rupture-prone atherosclerotic plaques in humans, suggesting a role for Ang-2 in plaque stability. Despite the availability of Ang-2 blocking agents, their clinical use is still lacking. Our aim was to establish if Ang-2 has a role in atheroma development and in the transition of subclinical to clinically relevant atherosclerosis. We investigated the effect of antibody-mediated Ang-2 blockage on atherogenesis after in a mouse model of atherosclerosis. METHODS: Hypercholesterolemic (low-density lipoprotein receptor(-/-) apolipoprotein B(100/100)) mice were subjected to high-cholesterol diet for eight weeks, one group with and one group without Ang-2 blocking antibody treatment during weeks 4-8.To enhance plaque development, a peri-adventitial collar was placed around the carotid arteries at the start of antibody treatment. Aortic root, carotid arteries and brachiocephalic arteries were analyzed to evaluate the effect of Ang-2 blockage on atherosclerotic plaque size and stable plaque characteristics. RESULTS: Anti-Ang-2 treatment reduced the size of fatty streaks in the brachiocephalic artery (-72%, p < 0.05). In addition, antibody-mediated Ang-2 blockage reduced plasma triglycerides (-27%, p < 0.05). In contrast, Ang-2 blockage did not have any effect on the size or composition (collagen content, macrophage percentage, adventitial microvessel density) of pre-existing plaques in the aortic root or collar-induced plaques in the carotid artery. CONCLUSIONS: Ang-2 blockage was beneficial as it decreased fatty streak formation and plasma triglyceride levels, but had no adverse effect on pre-existing atherosclerosis in hypercholesterolemic mice.

Molecular characterization of Tunisian families with abetalipoproteinemia and identification of a novel mutation in MTTP gene.

BACKGROUND: Abetalipoproteinemia (ABL; OMIM 200100) is a rare monogenic disorder of lipid metabolism characterized by reduced plasma levels of total cholesterol (TC), low density lipoprotein-cholesterol (LDL-C) and almost complete absence of apolipoprotein B (apoB). ABL results from genetic deficiency in microsomal triglyceride transfer protein (MTP; OMIM 157147). In the present study we investigated two unrelated Tunisian patients, born from consanguineous marriages, with severe deficiency of plasma low-density lipoprotein (LDL) and apo B. METHODS: Intestinal biopsies were performed and The MTTP gene was amplified by Polymerase chain reaction then directly sequenced in patients presenting chronic diarrhea and retarded growth. RESULTS: First proband was homozygous for a novel nucleotide deletion (c. 2611delC) involving the exon 18 of MTTP gene predicted to cause a non functional protein of 898 amino acids (p.H871I fsX29). Second proband was homozygous for a nonsense mutation in exon 8 (c.923 G > A) predicted to cause a truncated protein of 307 amino acids (p.W308X), previously reported in ABL patients. CONCLUSIONS: We discovered a novel mutation in MTTP gene and we confirmed the diagnosis of abetalipoproteinemia in new Tunisian families. VIRTUAL SLIDES: The virtual slide(s) for this article can be found here: http://www.diagnosticpathology.diagnomx.eu/vs/8134027928652779.

Pioglitazone attenuates valvular calcification induced by hypercholesterolemia.

OBJECTIVE: Development of calcific aortic valve stenosis involves multiple signaling pathways, which may be modulated by peroxisome proliferator-activated receptor-γ). This study tested the hypothesis that pioglitazone (Pio), a ligand for peroxisome proliferator-activated receptor-γ, inhibits calcification of the aortic valve in hypercholesteremic mice. METHODS AND RESULTS: Low density lipoprotein receptor(-/-)/apolipoprotein B(100/100) mice were fed a Western-type diet with or without Pio (20 mg/kg per day) for 6 months. Pio attenuated lipid deposition and calcification in the aortic valve, but not aorta. In the aortic valve, Pio reduced levels of active caspase-3 and terminal deoxynucleotidyl transferase dUTP nick end labeling staining. Valve function (echocardiography) was significantly improved by Pio. To determine whether changes in gene expression are associated with differential effects of Pio on aortic valves versus aorta, Reversa mice were fed Western diet with or without Pio for 2 months. Several procalcific genes were increased by Western diet, and the increase was attenuated by Pio, in aortic valve, but not aorta. CONCLUSIONS: Pio attenuates lipid deposition, calcification, and apoptosis in aortic valves of hypercholesterolemic mice, improves aortic valve function, and exhibits preferential effects on aortic valves versus aorta. We suggest that Pio protects against calcific aortic valve stenosis, and Pio or other peroxisome proliferator-activated receptor-γ ligands may be useful for early intervention to prevent or slow stenosis of aortic valves.

Regulation of endothelial lipase and systemic HDL cholesterol levels by SREBPs and VEGF-A.

OBJECTIVE: Endothelial lipase (EL) regulates HDL cholesterol levels and in inflammatory states, like atherosclerosis, EL expression is increased contributing to low HDL cholesterol. The regulation of EL expression is poorly understood and has mainly been attributed to inflammatory stimuli. As sterol regulatory element binding proteins (SREBPs) are regulators of genes involved in lipid metabolism, we hypothesized that EL is regulated by SREBPs and that EL expression is modified by the SREBP activator vascular endothelial growth factor A (VEGF-A). METHODS: and results: Quantitative PCR and Western blot results demonstrated that starvation increased EL expression in human umbilical vein endothelial cells (HUVECs) and human aortic endothelial cells (HAECs). Also, 25-hydroxycholesterol (25HC), an inhibitor of SREBP activation inhibited EL expression. With siRNA-mediated inhibition of SREBPs the effect of starvation was shown to be SREBP-2 dependent. VEGF-A decreased EL expression in both endothelial cell lines used, most likely via inhibition of SREBP-2 binding determined by chromatin immunoprecipitation (ChIP). Furthermore, in atherosclerosis prone LDLR(-/-)ApoB(100/100) mice, systemic adenoviral gene transfer with human VEGF-A decreased EL mRNA in peripheral tissues and increased plasma HDL cholesterol. CONCLUSIONS: These results identify SREBPs as novel regulators of EL expression. VEGF-A as an endogenous EL inhibitor could be therapeutically relevant in atherosclerosis by increasing systemic HDL cholesterol levels.

Vascular endothelial growth factor (VEGF)-D stimulates VEGF-A, stanniocalcin-1, and neuropilin-2 and has potent angiogenic effects.

OBJECTIVE: The mature form of human vascular endothelial growth factor-D (hVEGF-D(ΔNΔC)) is an efficient angiogenic factor, but its full mechanism of action has remained unclear. We studied the effects of hVEGF-D(ΔNΔC) in endothelial cells using gene array, signaling, cell culture, and in vivo gene transfer techniques. METHODS AND RESULTS: Concomitant with the angiogenic and proliferative responses, hVEGF-D(ΔNΔC) enhanced the phosphorylation of VEGF receptor-2, Akt, and endothelial nitric oxide synthase. Gene arrays, quantitative reverse transcription-polymerase chain reaction, and Western blot revealed increases in VEGF-A, stanniocalcin-1 (STC1), and neuropilin (NRP) 2 expression by hVEGF-D(ΔNΔC) stimulation, whereas induction with hVEGF-A(165) altered the expression of STC1 and NRP1, another coreceptor for VEGFs. The effects of hVEGF-D(ΔNΔC) were seen only under high-serum conditions, whereas for hVEGF-A(165), the strongest response was observed under low-serum conditions. The hVEGF-D(ΔNΔC)-induced upregulation of STC1 and NRP2 was also evident in vivo in mouse skeletal muscle treated with hVEGF-D(ΔNΔC) by adenoviral gene delivery. The importance of NRP2 in hVEGF-D(ΔNΔC) signaling was further studied with NRP2 small interfering RNA and NRP antagonist, which were able to block hVEGF-D(ΔNΔC)-induced survival of endothelial cells. CONCLUSIONS: In this study, the importance of serum and upregulation of NRP2 and STC1 for VEGF-D(ΔNΔC) effects were demonstrated. Better knowledge of VEGF-D(ΔNΔC) signaling and regulation is valuable for the development of efficient and safe VEGF-D(ΔNΔC)-based therapeutic applications for cardiovascular diseases.

Detection of hypoxia by [18F]EF5 in atherosclerotic plaques in mice.

OBJECTIVE: Atherosclerotic plaques with large lipid cores and inflammation contain regions of hypoxia. We examined the uptake of 2-(2-nitro-1H-imidazol-1-yl)-N-(2,2,3,3,3-pentafluoropropyl) acetamide ([18F]EF5), a specific marker of hypoxia labeled for positron emission tomography, in mouse atherosclerotic plaques. METHODS AND RESULTS: Atherosclerotic mice of 2 different genetic backgrounds (low-density lipoprotein receptor-/- apolipoprotein B100/100 and insulin-like growth factor II/low-density lipoprotein receptor-/- apolipoprotein B100/100) were first fed a Western diet to induce development of plaques with variable phenotypes and then injected with [18F]EF5. C57BL/6N mice served as controls. Aortas were dissected for biodistribution studies, autoradiography, histology, and immunohistochemistry. Uptake of [18F]EF5 was significantly higher in the aortas of mice with large atherosclerotic plaques than in the C57BL/6N controls. Furthermore, autoradiography demonstrated, on average, 2.0-fold higher [18F]EF5 uptake in atherosclerotic plaques than in the adjacent normal vessel wall. Hypoxia in plaques was verified by using an EF5 adduct-specific antibody and pimonidazole. The blood clearance of [18F]EF5 was slow, with blood radioactivity remaining relatively high up to 180 minutes after injection. CONCLUSIONS: Large atherosclerotic plaques in mice contained hypoxic areas and showed uptake of [18F]EF5. Despite its slow blood clearance, the high uptake of [18F]EF5 in plaques suggested that plaque hypoxia is a potential target for identifying high-risk plaques noninvasively.

Catechin treatment improves cerebrovascular flow-mediated dilation and learning abilities in atherosclerotic mice.

Severe dyslipidemia and the associated oxidative stress could accelerate the age-related decline in cerebrovascular endothelial function and cerebral blood flow (CBF), leading to neuronal loss and impaired learning abilities. We hypothesized that a chronic treatment with the polyphenol catechin would prevent endothelial dysfunction, maintain CBF responses, and protect learning abilities in atherosclerotic (ATX) mice. We treated ATX (C57Bl/6-LDLR(-/-)hApoB(+/+); 3 mo old) mice with catechin (30 mg · kg(-1) · day(-1)) for 3 mo, and C57Bl/6 [wild type (WT), 3 and 6 mo old] mice were used as controls. ACh- and flow-mediated dilations (FMD) were recorded in pressurized cerebral arteries. Basal CBF and increases in CBF induced by whisker stimulation were measured by optical coherence tomography and Doppler, respectively. Learning capacities were evaluated with the Morris water maze test. Compared with 6-mo-old WT mice, cerebral arteries from 6-mo-old ATX mice displayed a higher myogenic tone, lower responses to ACh and FMD, and were insensitive to NOS inhibition (P < 0.05), suggesting endothelial dysfunction. Basal and increases in CBF were lower in 6-mo-old ATX than WT mice (P < 0.05). A decline in the learning capabilities was also observed in ATX mice (P < 0.05). Catechin 1) reduced cerebral superoxide staining (P < 0.05) in ATX mice, 2) restored endothelial function by reducing myogenic tone, improving ACh- and FMD and restoring the sensitivity to nitric oxide synthase inhibition (P < 0.05), 3) increased the changes in CBF during stimulation but not basal CBF, and 4) prevented the decline in learning abilities (P < 0.05). In conclusion, catechin treatment of ATX mice prevents cerebrovascular dysfunctions and the associated decline in learning capacities.

New mutations in APOB100 involved in familial hypobetalipoproteinemia.

Familial hypolipoproteinemia (FHBL) is characterized by an inherited low plasma level of apolipoprotein B containing lipoproteins. FHBL may be caused by mutations of APOB. Individuals with FHBL typically have intestinal malabsorption and frequently suffer from a deficiency of fat-soluble vitamins. Most mutations that cause FHBL are APOB truncating mutations. Here we describe a patient with FHBL caused by a novel truncating mutation together with a novel missense mutation.

Evaluation of alphavbeta3 integrin-targeted positron emission tomography tracer 18F-galacto-RGD for imaging of vascular inflammation in atherosclerotic mice.

BACKGROUND: (18)F-Galacto-RGD is a positron emission tomography (PET) tracer binding to alpha(v)beta(3) integrin that is expressed by macrophages and endothelial cells in atherosclerotic lesions. Therefore, we evaluated (18)F-galacto-RGD for imaging vascular inflammation by studying its uptake into atherosclerotic lesions of hypercholesterolemic mice in comparison to deoxyglucose. METHODS AND RESULTS: Hypercholesterolemic LDLR(-/-)ApoB(100/100) mice on a Western diet and normally fed adult C57BL/6 control mice were injected with (18)F-galacto-RGD and (3)H-deoxyglucose followed by imaging with a small animal PET/CT scanner. The aorta was dissected 2 hours after tracer injection for biodistribution studies, autoradiography, and histology. Biodistribution of (18)F-galacto-RGD was higher in the atherosclerotic than in the normal aorta. Autoradiography demonstrated focal (18)F-galacto-RGD uptake in the atherosclerotic plaques when compared with the adjacent normal vessel wall or adventitia. Plaque-to-normal vessel wall ratios were comparable to those of deoxyglucose. Although angiogenesis was not detected, (18)F-galacto-RGD uptake was associated with macrophage density and deoxyglucose accumulation in the plaques. Binding to atherosclerotic lesions was efficiently blocked in competition experiments. In vivo imaging visualized (18)F-galacto-RGD uptake colocalizing with calcified lesions of the aortic arch as seen in CT angiography. CONCLUSIONS: (18)F-Galacto-RGD demonstrates specific uptake in atherosclerotic lesions of mouse aorta. In this model, its uptake was associated with macrophage density. (18)F-Galacto-RGD is a potential tracer for noninvasive imaging of inflammation in atherosclerotic lesions.