In the absence of the low density lipoprotein receptor, human apolipoprotein C1 overexpression in transgenic mice inhibits the hepatic uptake of very low density lipoproteins via a receptor-associated protein-sensitive pathway

M2 macrophage exosome-derived Apoc1 promotes ferroptosis resistance in osteosarcoma by inhibiting ACSF2 deubiquitination

Osteosarcoma (OS) is the most common primary malignant tumor of bone. The aim of this study was to investigate the regulatory mechanisms of M2 macrophage exosomes (M2-Exos) in ferroptosis in OS. A mouse model was established to investigate the in vivo role of M2-Exos. We investigated their effects on ferroptosis in OS using erastin, a ferroptosis activator, and deferoxamine mesylate, an iron chelator. In vitro, we investigated whether the Apoc1/Acyl-CoA Synthetase Family Member 2 (ACSF2) axis mediates these effects, using shApoc1 and shACSF2. The mechanisms whereby Apoc1 regulates ACSF2 were examined using cyclohexanone, a protein synthesis inhibitor, and MG132, a proteasomal inhibitor. M2-Exos reversed the inhibitory effects of erastin on OS cells, thus enhancing their viability, migration, invasion, proliferation, and reducing ferroptosis. Apoc1 was highly expressed in M2-Exos, and interfering with this expression reversed the effects of M2-Exos on OS cells. ACSF2 mediated the effects of M2-Exos-derived Apoc1. Apoc1 interacted with ACSF2, which, in turn, interacted with USP40. Apoc1 overexpression increased ACSF2 ubiquitination, promoting its degradation, whereas USP40 overexpression inhibited ACSF2 ubiquitination and promoted its expression. Apoc1 overexpression inhibited ACSF2 binding to USP40. M2-Exos-derived Apoc1 promoted ferroptosis resistance by inhibiting USP40 binding to ACSF2 and promoting ACSF2 ubiquitination and degradation, thus enhancing OS development.

Circadian Regulation of Apolipoproteins in the Brain: Implications in Lipid Metabolism and Disease

The circadian rhythm is a 24 h internal clock within the body that regulates various factors, including sleep, body temperature, and hormone secretion. Circadian rhythm disruption is an important risk factor for many diseases including neurodegenerative illnesses. The central and peripheral oscillators' circadian clock network controls the circadian rhythm in mammals. The clock genes govern the central clock in the suprachiasmatic nucleus (SCN) of the brain. One function of the circadian clock is regulating lipid metabolism. However, investigations of the circadian regulation of lipid metabolism-associated apolipoprotein genes in the brain are lacking. This review summarizes the rhythmic expression of clock genes and lipid metabolism-associated apolipoprotein genes within the SCN in Mus musculus. Nine of the twenty apolipoprotein genes identified from searching the published database (SCNseq and CircaDB) are highly expressed in the SCN. Most apolipoprotein genes (ApoE, ApoC1, apoA1, ApoH, ApoM, and Cln) show rhythmic expression in the brain in mice and thus might be regulated by the master clock. Therefore, this review summarizes studies on lipid-associated apolipoprotein genes in the SCN and other brain locations, to understand how apolipoproteins associated with perturbed cerebral lipid metabolism cause multiple brain diseases and disorders. This review describes recent advancements in research, explores current questions, and identifies directions for future research.

APOC1 promotes the progression of osteosarcoma by binding to MTCH2

Osteosarcoma is the most prevalent primary malignant bone cancer worldwide. Apolipoprotein C1 (APOC1) and mitochondrial carrier homolog 2 (MTCH2) have been identified to be upregulated during the oncogenesis and metastasis of osteosarcoma. The aim of the present study was to explore the role of APOC1 in osteosarcoma progression and the mechanisms associated with MTCH2. APOC1 and MTCH2 expression in osteosarcoma cells was assessed by reverse transcription-quantitative PCR and western blotting. Then, APOC1 was silenced to detect its effect on cell viability, proliferation and apoptosis using Cell Counting Kit-8, a colony formation assay and TUNEL staining, respectively. Transwell and wound healing assays were used to evaluate cell invasion and migration. The interaction between APOC1 and MTCH2 as predicted by the Biological General Repository for Interaction Datasets and the Search Tool for the Retrieval of Interacting Genes/Proteins databases was verified by co-immunoprecipitation assay. Subsequently, rescue experiments were performed to analyze the regulatory effects of APOC1 on MTCH2 in the biological behavior and Warburg effect of osteosarcoma cells. Significantly upregulated APOC1 and MTCH2 expression was found in osteosarcoma SAOS-2 cells. APOC1 silencing attenuated cell viability, inhibited proliferation and promoted cell apoptosis, coupled with the decreased Bcl-2 expression and increased Bax and cleaved-caspase 3 expression. The invasive and migratory capacities of SAOS-2 cells were also suppressed following APOC1 knockdown. Moreover, APOC1 was confirmed to interact with MTCH2 in osteosarcoma cells. MTCH2 upregulation inhibited the impacts of APOC1 deletion on the malignant behavior of osteosarcoma cells. APOC1 silencing-induced oxidative phosphorylation elevation and Warburg effect decrease were partially restored by MTCH2 upregulation. In sum, APOC1 promoted progression of osteosarcoma by binding to MTCH2, suggesting that targeting the APOC1/MTCH2 axis may be a potential treatment of osteosarcoma.

Role of apolipoprotein C1 in lipoprotein metabolism, atherosclerosis and diabetes: a systematic review

Apolipoprotein C1 (apoC1) is a small size apolipoprotein whose exact role is not totally clarified but which seems to modulate significantly the metabolism of lipoproteins. ApoC1 is involved in the metabolism of triglyceride-rich lipoproteins by inhibiting the binding of very low density lipoproteins (VLDL) to VLDL-receptor (VLDL-R), to low density lipoprotein receptor (LDL-R) and to LDL receptor related protein (LRP), by reducing the activity of lipoprotein lipase (LPL) and by stimulating VLDL production, all these effects leading to increase plasma triglycerides. ApoC1 takes also part in the metabolism of high density lipoproteins (HDL) by inhibiting Cholesterol Ester Transfer Protein (CETP). The functionality of apoC1 on CETP activity is impaired in diabetes that might account, at least in part, for the increased plasma CETP activity observed in patients with diabetes. Its different effects on lipoprotein metabolism with a possible role in the modulation of inflammation makes the net impact of apoC1 on cardiometabolic risk difficult to figure out and apoC1 might be considered as pro-atherogenic or anti-atherogenic depending on the overall metabolic context. Making the link between total plasma apoC1 levels and the risk of cardio-metabolic diseases is difficult due to the high exchangeability of this small protein whose biological effects might depend essentially on its association with VLDL or HDL. The role of apoC1 in humans is not entirely elucidated and further studies are needed to determine its precise role in lipid metabolism and its possible pleiotropic effects on inflammation and vascular wall biology. In this review, we will present data on apoC1 structure and distribution among lipoproteins, on the effects of apoC1 on VLDL metabolism and HDL metabolism and we will discuss the possible links between apoC1, atherosclerosis and diabetes.

Apolipoprotein C1 promotes glioblastoma tumorigenesis by reducing KEAP1/NRF2 and CBS-regulated ferroptosis

Glioblastoma (GBM), a malignant brain tumor, is a world-wide health problem because of its poor prognosis and high rates of recurrence and mortality. Apolipoprotein C1 (APOC1) is the smallest of apolipoproteins, implicated in many diseases. Recent studies have shown that APOC1 promotes tumorigenesis and development of several types of cancer. In this study we investigated the role of APOC1 in GBM tumorigenesis. Using in silico assays we showed that APOC1 was highly expressed in GBM tissues and its expression was closely related to GBM progression. We showed that APOC1 protein expression was markedly increased in four GBM cell lines (U251, U138, A172 and U87) compared to the normal brain glia cell lines (HEB, HA1800). In U251 cells, overexpression of APOC1 promoted cell proliferation, migration, invasion and colony information, which was reversed by APOC1 knockdown. APOC1 knockdown also markedly inhibited the growth of GBM xenografts in the ventricle of nude mice. We further demonstrated that APOC1 reduced ferroptosis by inhibiting KEAP1, promoting nuclear translocation of NRF2 and increasing expression of HO-1 and NQO1 in GBM cells. APOC1 also induced ferroptosis resistance by increasing cystathionine beta-synthase (CBS) expression, which promoted trans-sulfuration and increased GSH synthesis, ultimately leading to an increase in glutathione peroxidase-4 (GPX4). Thus, APOC1 plays a key role in GBM tumorigenesis, conferring resistance to ferroptosis, and may be a promising therapeutic target for GBM.

Association of lipid metabolism-related gene promoter methylation with risk of coronary artery disease

BACKGROUND

Coronary artery disease (CAD) is a complex disease that is influenced by environmental and genetic factors. Lipid levels are regarded as a major risk factor for CAD, and epigenetic mechanisms might be involved in the regulation of CAD development. This study was designed to investigate the association between the DNA methylation status of 8 lipid metabolism-related genes and the risk of CAD in the Chinese Han population.

METHODS

A total of 260 individuals were sampled in this study, including 120 CAD cases and 140 normal healthy controls. DNA methylation status was tested via targeted bisulfite sequencing.

RESULTS

The results indicated a significant association between hypomethylation of the APOC3, CETP and APOC1 gene promoters and the risk of CAD. Individuals with higher methylation levels of the APOA5 and LIPC gene promoters had increased risks for CAD. In addition, ANGPTL4 methylation level was significantly associated with CAD in males but not females. There were no significant differences in the methylation levels of the APOB and PCSK9 gene promoters between CAD patients and controls.

CONCLUSIONS

The methylation status of the APOC3, APOA5, LIPC, CETP and APOC1 gene promoters may be associated with the development of CAD.

The BET Inhibitor JQ1 Augments the Antitumor Efficacy of Gemcitabine in Preclinical Models of Pancreatic Cancer

Gemcitabine is used to treat pancreatic cancer (PC), but is not curative. We sought to determine whether gemcitabine + a BET bromodomain inhibitor was superior to gemcitabine, and identify proteins that may contribute to the efficacy of this combination. This study was based on observations that cell cycle dysregulation and DNA damage augment the efficacy of gemcitabine. BET inhibitors arrest cells in G1 and allow increases in DNA damage, likely due to inhibition of expression of DNA repair proteins Ku80 and RAD51. BET inhibitors (JQ1 or I-BET762) + gemcitabine were synergistic in vitro, in Panc1, MiaPaCa2 and Su86 PC cell lines. JQ1 + gemcitabine was more effective in vivo than either drug alone in patient-derived xenograft models (P < 0.01). Increases in the apoptosis marker cleaved caspase 3 and DNA damage marker γH2AX paralleled antitumor efficacy. Notably, RNA-seq data showed that JQ1 + gemcitabine selectively inhibited HMGCS2 and APOC1 ~6-fold, compared to controls. These proteins contribute to cholesterol biosynthesis and lipid metabolism, and their overexpression supports tumor cell proliferation. IPA data indicated that JQ1 + gemcitabine selectively inhibited the LXR/RXR activation pathway, suggesting the hypothesis that this inhibition may contribute to the observed in vivo efficacy of JQ1 + gemcitabine.

Human apolipoprotein C1 transgenesis reduces atherogenesis in hypercholesterolemic rabbits

BACKGROUND AND AIMS

Apolipoprotein (apo) C1 is a 6.6 kDa protein associated with HDL and VLDL. ApoC1 alters triglyceride clearance, and it also favors cholesterol accumulation in HDL, especially by inhibiting CETP in human plasma. Apart from studies in mice, which lack CETP, the impact of apoC1 on atherosclerosis in animal models expressing CETP, like in humans, is not known. This study aimed at determining the net effect of human apoC1 on atherosclerosis in rabbits, a species with naturally high CETP activity but with endogenous apoC1 without CETP inhibitory potential.

METHODS

Rabbits expressing a human apoC1 transgene (HuApoC1Tg) were generated and displayed significant amounts of human apoC1 in plasma.

RESULTS

After cholesterol feeding, atherosclerosis lesions were significantly less extensive (-22%, p < 0.05) and HDL displayed a reduced ability to serve as CETP substrates (-25%, p < 0.05) in HuApoC1Tg rabbits than in WT littermates. It was associated with rises in plasma HDL cholesterol level and PON-1 activity, and a decrease in the plasma level of the lipid oxidation markers 12(S)-HODE and 8(S)HETE. In chow-fed animals, the level of HDL-cholesterol was also significantly higher in HuApoC1Tg than in WT animals (0.83 ± 0.11 versus 0.73 ± 0.11 mmol/L, respectively, p < 0.05), and it was associated with significantly lower CETP activity (cholesteryl ester transfer rate, -10%, p < 0.05; specific CETP activity, -14%, p < 0.05).

CONCLUSIONS

Constitutive expression of fully functional human apoC1 in transgenic rabbit attenuates atherosclerosis. It was found to relate, at least in part, to the inhibition of plasma CETP activity and to alterations in plasma HDL.

Apolipoprotein C1 stimulates the malignant process of renal cell carcinoma via the Wnt3a signaling

Background

Renal cell carcinoma (RCC) is a clinically common tumor in the urinary system, showing an upward trend of both incidence and mortality. Apolipoprotein C1 (APOC1) has been identified as a vital regulator in tumor progression. This study aims to uncover the biological function of APOC1 in RCC process and the underlying mechanism.

Methods

Differential levels of APOC1 in RCC samples and normal tissues in a downloaded TCGA profile and clinical samples collected in our center were detected by quantitative reverse transcription PCR (qRT-PCR). The prognostic value of APOC1 in RCC was assessed by depicting Kaplan–Meier survival curves. After intervening APOC1 level by transfection of sh-APOC1 or oe-APOC1, changes in phenotypes of RCC cells were examined through CCK-8, colony formation, Transwell assay and flow cytometry. Subsequently, protein levels of EMT-related genes influenced by APOC1 were determined by Western blot. The involvement of the Wnt3a signaling in APOC1-regulated malignant process of RCC was then examined through a series of rescue experiments. Finally, a RCC xenograft model was generated in nude mice, aiming to further clarify the in vivo function of APOC1 in RCC process.

Results

APOC1 was upregulated in RCC samples. Notably, its level was correlated to overall survival of RCC patients, displaying a certain prognostic value. APOC1 was able to stimulate proliferative, migratory and invasive abilities in RCC cells. The Wnt3a signaling was identified to be involved in APOC1-mediated RCC process. Notably, Wnt3a was able to reverse the regulatory effects of APOC1 on RCC cell phenotypes. In vivo knockdown of APOC1 in xenografted nude mice slowed down the growth of RCC.

Conclusions

APOC1 stimulates the malignant process of RCC via targeting the Wnt3a signaling.

Apolipoprotein C1: Its Pleiotropic Effects in Lipid Metabolism and Beyond

Apolipoprotein C1 (apoC1), the smallest of all apolipoproteins, participates in lipid transport and metabolism. In humans, APOC1 gene is in linkage disequilibrium with APOE gene on chromosome 19, a proximity that spurred its investigation. Apolipoprotein C1 associates with triglyceride-rich lipoproteins and HDL and exchanges between lipoprotein classes. These interactions occur via amphipathic helix motifs, as demonstrated by biophysical studies on the wild-type polypeptide and representative mutants. Apolipoprotein C1 acts on lipoprotein receptors by inhibiting binding mediated by apolipoprotein E, and modulating the activities of several enzymes. Thus, apoC1 downregulates lipoprotein lipase, hepatic lipase, phospholipase A2, cholesterylester transfer protein, and activates lecithin-cholesterol acyl transferase. By controlling the plasma levels of lipids, apoC1 relates directly to cardiovascular physiology, but its activity extends beyond, to inflammation and immunity, sepsis, diabetes, cancer, viral infectivity, and-not last-to cognition. Such correlations were established based on studies using transgenic mice, associated in the recent years with GWAS, transcriptomic and proteomic analyses. The presence of a duplicate gene, pseudogene APOC1P, stimulated evolutionary studies and more recently, the regulatory properties of the corresponding non-coding RNA are steadily emerging. Nonetheless, this prototypical apolipoprotein is still underexplored and deserves further research for understanding its physiology and exploiting its therapeutic potential.

A Novel Genes Signature Associated with the Progression of Polycystic Ovary Syndrome

To identify genes involving in the pathogenesis of polycystic ovary syndrome (PCOS). In this study, the comprehensive analysis of GSE8157 was downloaded. Overlapping genes of differentially expressed genes (DEGs) were identified, and enrichment analysis for these genes was performed. A modular network of differentially expressed genes was constructed by weighted gene co-expression network analyses (WGCNA), and a total of 322 differentially expressed genes in 5 stable modules were screened. The correlations of genes of the stable modules in BioGRID 3.4, STRING 10.5, HPRD9 databases were screened, and the interaction network of 104 DEGs was constructed. In addition, some genes and the key words were searched in CTD. A total of 596 differentially expressed genes were screened, including 379 genes that were up-regulated in case group and down-regulated in control group and treat group, and 217 genes that were down-regulated in case group and up-regulated in control group and treat group. The differentially expressed genes were enriched in PPAR signaling pathway, Neuroactive ligand-receptor interaction, cAMP signaling pathway, of which pathways were involved in the cancer development. Finally, 7 important target genes were identified, such as APOC3 was interacted with pioglitazone, ADCY2 involved in cAMP signaling pathway, and the genes (C3AR1, HRH2, GRIA1, MLNR and TAAR2) involved in neuroactive ligand-receptor interaction. In addition, the important target genes were significantly differential expression. These results implied that the 7 important target genes were played an important role in the development and progression of PCOS. Our study implied that genes had played a key role in the development and progression of PCOS, the results showed that microarray can be use as a method for the discovery of new biomarkers and therapeutic targets for PCOS.

Apolipoprotein C1 (APOC1) promotes tumor progression via MAPK signaling pathways in colorectal cancer

Aim: Identifying high-efficiency prognostic markers for colorectal cancer (CRC) is necessary for clinical practice. Increasing evidence demonstrates that apolipoprotein C1 (APOC1) promotes carcinogenesis in some human cancers. However, the expression status and biological function of APOC1 in CRC remain unclear.

Materials and methods: We detected the association between APOC1 expression and clinicopathological features in 140 CRC patients by immunohistochemistry. Small interfering RNA (siRNA) technology was used to downregulate APOC1 expression in CRC cells. Cell proliferation was estimated by CCK8 and clonogenic assays. The cell cycle and apoptosis were analyzed by flow cytometry. Cell migration and invasion were examined by a transwell assay. Gene set enrichment analysis (GSEA) and protein expression of signaling pathways were used to suggest the possible APOC1-associated pathways in CRC.

Results: APOC1 was highly expressed in CRC tissues. High immunohistochemistry (IHC) expression of APOC1 was correlated with the N stage, M stage and TNM stage. High IHC APOC1 expression in CRC tissues was associated with poor prognosis. Univariate and multivariate Cox regression analyses showed that APOC1 was an independent risk factor for OS. Cell proliferation of CRC cell lines was inhibited by the downregulation of APOC1. Moreover, si-APOC1 transfection induced cell cycle arrest but low apoptosis increases by regulating the expression of related proteins. Cell migration and invasion were also inhibited by the downregulation of APOC1. The Cancer Genome Atlas Colorectal Adenocarcinoma (TCGA COAD-READ) dataset analyzed by GSEA showed that APOC1 might be involved in the mitogen-activated protein kinase (MAPK) signaling pathway, which was further preliminarily confirmed by Western blotting.

Conclusion: APOC1 was overexpressed in CRC tissues, and a high level of APOC1 contributed to a poor prognosis. APOC1 expression influenced the cell proliferation ability and motility capacity of CRC via the MAPK pathway. APOC1 could act as a novel prognostic biomarker in CRC.

Apolipoprotein profiling as a personalized approach to the diagnosis and treatment of dyslipidaemia

An elevated low-density lipoprotein cholesterol concentration is a classical risk factor for cardiovascular disease. This has led to pharmacotherapy in patients with atherosclerotic heart disease or high heart disease risk with statins to reduce serum low-density lipoprotein cholesterol. Even in patients in whom the target levels of low-density lipoprotein cholesterol are reached, there remains a significant residual cardiovascular risk; this is due, in part, to a focus on low-density lipoprotein cholesterol alone and neglect of other important aspects of lipoprotein metabolism. A more refined lipoprotein analysis will provide additional information on the accumulation of very low-density lipoproteins, intermediate density lipoproteins, chylomicrons, chylomicron-remnants and Lp(a) concentrations. Instead of measuring the cholesterol and triglyceride content of the lipoproteins, measurement of their apolipoproteins (apos) is more informative. Apos are either specific for a particular lipoprotein or for a group of lipoproteins. In particular measurement of apos in atherogenic particles is more biologically meaningful than the measurement of the cholesterol concentration contained in these particles. Applying apo profiling will not only improve characterization of the lipoprotein abnormality, but will also improve definition of therapeutic targets. Apo profiling aligns with the concept of precision medicine by which an individual patient is not treated as 'average' patient by the average (dose of) therapy. This concept of precision medicine fits the unmet clinical need for stratified cardiovascular medicine. The requirements for clinical application of proteomics, including apo profiling, can now be met using robust mass spectrometry technology which offers desirable analytical performance and standardization.

Effects of apoC1 genotypes on the hormonal levels, metabolic profile and PAF-AH activity in Chinese women with polycystic ovary syndrome

Background

Elevated serum levels of apolipoprotein (apo) C1 may be an early protein marker of metabolic abnormality in women with polycystic ovary syndrome (PCOS). It is not clear, however, whether there are any relationships between the apoC1 rs4420638A/G and -317deletion (H1)/insertion (H2) polymorphisms and PCOS. We investigated the relationship between these two variants and the risk of PCOS, evaluated the genotypic effects on clinical, hormonal and metabolic indexes and plasma platelet-activating factor acetylhydrolase (PAF-AH) activity, and defined the association of apoC1 gene variants with apoE ε2/ε3/ε4 polymorphisms.

Methods

This is a cross-sectional study of 877 women with PCOS and 761 controls. The apoC1 rs4420638A/G genotype was determined by a Taqman real-time PCR allelic discrimination assay. The apoC1–317H1/H2 and apoE ε2/ε3/ε4 genotypes were measured using PCR and restriction fragment length polymorphism analysis. The clinical, hormonal and metabolic parameters and PAF-AH activity were measured.

Results

The frequencies of apoC1 rs4420638A/G and -317H1/H2 genotypes and alleles were similar between PCOS and control groups (P > 0.05). However, the rs4420638 G allele was related to increased serum luteinizing hormone, cholesterol and apoB levels, and the ratio of apoB to apoA1 (P < 0.05), and the -317H1H1 genotype was associated with a higher acne grade score and a higher ratio of apoB-PAF-AH to H-PAF-AH activity (P < 0.05) in patients with PCOS. We also demonstrated that the apoC1 rs4420638A/G and -317H1/H2 gene variants existed in moderate to reasonably high linkage disequilibrium with apoE ε2/ε3/ε4 polymorphisms in Chinese women.

Conclusion

The apoC1 rs4420638A/G and -317H1/H2 gene variants might be involved in endocrine abnormalities of reproductive axis, metabolic abnormalities and chronic inflammation in PCOS, although no association was observed between the apoC1 genetic variants and the risk of PCOS in Chinese women.

Apolipoprotein C-I plays a role in the pathogenesis of glomerulosclerosis

Diabetic nephropathy is the leading cause of end-stage renal disease. Diabetic patients have increased plasma concentrations of apolipoprotein C-I (apoCI), and meta-analyses found that a polymorphism in APOC1 is associated with an increased risk of developing nephropathy. To investigate whether overexpressing apoCI contributes to the development of kidney damage, we studied renal tissue and peritoneal macrophages from APOC1 transgenic (APOC1-tg) mice and wild-type littermates. In addition, we examined renal material from autopsied diabetic patients with and without diabetic nephropathy and from autopsied control subjects. We found that APOC1-tg mice, but not wild-type mice, develop albuminuria, renal dysfunction, and glomerulosclerosis with increased numbers of glomerular M1 macrophages. Moreover, compared to wild-type macrophages, stimulated macrophages isolated from APOC1-tg mice have increased cytokine expression, including TNF-alpha and TGF-beta, both of which are known to increase the production of extracellular matrix proteins in mesangial cells. These results suggest that APOC1 expression induces glomerulosclerosis, potentially by increasing the cytokine response in macrophages. Furthermore, we detected apoCI in the kidneys of diabetic patients, but not in control kidneys. Moreover, patients with diabetic nephropathy have significantly more apoCI present in glomeruli compared to diabetic patients without nephropathy, suggesting that apoCI could be involved in the development of diabetic nephropathy. ApoCI co-localized with macrophages. Therefore, apoCI is a promising new therapeutic target for patients at risk of developing nephropathy. Copyright © 2016 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Plasma apolipoprotein C1 concentration is associated with plasma triglyceride concentration, but not visceral fat, in patients with type 2 diabetes

INTRODUCTION

Apolipoprotein C1 (apoC1) is likely to play an important role in triglyceride (TG) metabolism. Mice overexpressing human apoC1 present decreased adipose tissue stores. This study aimed to determine whether apoC1 concentration influences fat mass and distribution and liver fat content (LFC) in patients with type 2 diabetes (T2D).

METHODS

ApoC1 concentrations were measured by ELISA in 113 T2D patients and 56 normolipidaemic-normoglycaemic subjects. Visceral and subcutaneous fat areas were determined by single-slice axial T1-weighted magnetic resonance imaging (MRI), while LFC was measured by hydrogen-1 ((1)H) MR spectroscopy.

RESULTS

ApoC1 concentrations were higher in T2D patients than in normolipidaemic-normoglycaemic subjects (P<0.0001), and did not correlate with visceral or subcutaneous fat areas, but significantly correlated with TG (P<0.0001) and LFC (P=0.02) in T2D patients. However, the correlation between apoC1 and LFC was lost after adjusting for TG. ApoC1 concentration was also significantly higher in T2D patients with TG<1.5mmol/L than in control subjects (P<0.0001), although both groups had similar TG levels. On multivariate analysis performed in T2D patients with TG<1.5mmol/L and control subjects, apoC1 concentration was independently and positively associated with type 2 diabetes (P<0.0001) and TG levels (P=0.03).

CONCLUSION

This study reports, for the first time, that apoC1 is increased in T2D patients and is significantly correlated with TG, whereas no association was found between apoC1 and adipose tissue. This indicates that, in T2D, apoC1 may play a role in TG metabolism, but is unlikely to modulate fat mass and distribution. This increased apoC1 concentration in T2D patients is not only explained by the increased TG level in T2D patients.

The potential of cholesteryl ester transfer protein as a therapeutic target

INTRODUCTION

Over recent decades, attempts to ascertain the pro-atherogenic nature of plasma cholesteryl ester transfer protein (CETP) and to establish the relevance of its pharmacological blockade as a promising high density lipoproteins-raising and anti-atherogenic therapy have been disappointing.

AREAS COVERED

The current review focuses on CETP as a multifaceted protein, on genetic variations at the CETP gene and on their possible consequences for cardiovascular risk in human populations. Specific attention is given to physiological modulation of endogenous CETP activity by the apoC1 inhibitor. Finally, the rationale behind the need for selection of patients to treat is discussed in the light of recent studies.

EXPERT OPINION

At this stage one can only speculate on the clinical outcome of pharmacological CETP inhibitors in high-risk populations, but recent advances give cause to adjust the expectations from now on. The CETP effect is probably largely influenced by the overall metabolic state, and whether CETP blockade may be relevant or not in promoting cholesterol disposal is still questioned. The possible need for a careful stratification of patients to treat with CETP inhibitors is outlined. Finally, manipulation of CETP activity should be considered with caution in the context of sepsis and infectious diseases.

Glycation of apolipoprotein C1 impairs its CETP inhibitory property: pathophysiological relevance in patients with type 1 and type 2 diabetes

OBJECTIVE Apolipoprotein (apo)C1 is a potent physiological inhibitor of cholesteryl ester transfer protein (CETP). ApoC1 operates through its ability to modify the electrostatic charge at the lipoprotein surface. We aimed to determine whether the inhibitory ability of apoC1 is still effective in vivo in patients with diabetes and whether in vitro glycation of apoC1 influences its electrostatic charge and its CETP inhibitory effect. RESEARCH DESIGN AND METHODS ApoC1 concentrations and CETP activity were measured in 70 type 1 diabetic (T1D) patients, 113 patients with type 2 diabetes, and 83 control subjects. The consequences of in vitro glycation by methylglyoxal on the electrostatic properties of apoC1 and on its inhibitory effect on CETP activity were studied. An isoelectric analysis of apoC1 was performed in patients with T1D and in normolipidemic-normoglycemic subjects. RESULTS An independent negative correlation was found between CETP activity and apoC1 in control subjects but not in patients with diabetes. HbA1c was independently associated with CETP activity in T1D patients. In vitro glycation of apoC1 modified its electrostatic charge and abrogated its ability to inhibit CETP activity in a concentration-dependent manner. The isoelectric point of apoC1 in T1D patients was significantly lower than that in control subjects. CONCLUSIONS The ability of apoC1 to inhibit CETP activity is impaired in patients with diabetes. Glycation of apoC1 leads to a change in its electrostatic properties that might account, at least in part, for a loss of constitutive CETP inhibition and an increase in plasma CETP activity in patients with diabetes.

Corticosterone regulation of ovarian follicular development is dependent on the energy status of laying hens

Glucocorticoids participate in the arousal of stress responses and trigger physiological adjustments that shift energy away from reproduction toward survival. Ovarian follicular development in avians is accompanied by the supply of yolk precursors, which are mainly synthesized in the liver. Therefore, we hypothesized energy status and hepatic lipogenesis are involved in the induction of reproductive disorders by glucocorticoids in laying hens. The results show that corticosterone decreased the laying performance by suppressing follicular development in energy-deficit state, rather than in energy-sufficient state. In corticosterone-treated hens, the suppressed follicular development was associated with the reduced availability of yolk precursor, indicated by the plasma concentration of VLDL and vitellogenin and the decreased proportion of yolk-targeted VLDL (VLDLy). Corticosterone decreased the expression of apolipoprotein B and apolipoprotein VLDL-II in the liver. A drop in VLDL receptor content and an increase in the expression of tight junction proteins occludin and claudin1 were also observed in hierarchical follicles. The results suggest corticosterone-suppressed follicular development is energy dependent. The decreased apolipoprotein synthesis and VLDLy secretion by liver are responsible for the decreased availability of circulating yolk precursor, and the upregulation of occludin and claudin expression further prevents yolk deposition into oocytes.

Constitutive inhibition of plasma CETP by apolipoprotein C1 is blunted in dyslipidemic patients with coronary artery disease

Plasma cholesteryl ester transfer protein (CETP) promotes the cholesterol enrichment of apoB-containing lipoproteins (VLDL and LDL) at the expense of HDL. Recent studies demonstrated that apoC1 is a potent CETP inhibitor in plasma of healthy, normolipidemic subjects. Our goal was to establish whether the modulation of CETP activity by apoC1 is influenced by dyslipidemia in patients with documented coronary artery disease (CAD). In the total CAD population studied (n = 240), apoC1 levels correlated negatively with CETP activity, independently of apoE-epsilon, CETP-Taq1B, and apoC1-Hpa1 genotypes. In multivariate analysis, the negative relationship was observed only in normolipidemic patients, not in those with hypercholesterolemia, hypertriglyceridemia, or combined hyperlipidemia. In the normolipidemic subjects, apoC1 levels were positively associated with higher HDL- to LDL-cholesterol ratio (r = 0.359, P < 0.001). It is concluded that apoC1 as a CETP inhibitor no longer operates on cholesterol redistribution in high-risk patients with dyslipidemia, probably due to increasing amounts of VLDL-bound apoC1, which is inactive as a CETP inhibitor. Patients with dyslipidemia could experience major benefits from treatment with pharmacological CETP inhibitors, which might compensate for blunted endogenous inhibition.

Aspirin reduces hypertriglyceridemia by lowering VLDL-triglyceride production in mice fed a high-fat diet

Systemic inflammation is strongly involved in the pathophysiology of the metabolic syndrome, a cluster of metabolic risk factors that includes hypertriglyceridemia. Aspirin treatment lowers inflammation via inhibition of NF-κB activity but also reduces hypertriglyceridemia in humans. The aim of this study was to investigate the mechanism by which aspirin improves hypertriglyceridemia. Human apolipoprotein CI (apoCI)-expressing mice (APOC1 mice), an animal model with elevated plasma triglyceride (TG) levels, as well as normolipidemic wild-type (WT) mice were fed a high-fat diet (HFD) and treated with aspirin. Aspirin treatment reduced hepatic NF-κB activity in HFD-fed APOC1 and WT mice, and in addition, aspirin decreased plasma TG levels (-32%, P < 0.05) in hypertriglyceridemic APOC1 mice. This TG-lowering effect could not be explained by enhanced VLDL-TG clearance, but aspirin selectively reduced hepatic production of VLDL-TG in both APOC1 (-28%, P < 0.05) and WT mice (-33%, P < 0.05) without affecting VLDL-apoB production. Aspirin did not alter hepatic expression of genes involved in FA oxidation, lipogenesis, and VLDL production but decreased the incorporation of plasma-derived FA by the liver into VLDL-TG (-24%, P < 0.05), which was independent of hepatic expression of genes involved in FA uptake and transport. We conclude that aspirin improves hypertriglyceridemia by decreasing VLDL-TG production without affecting VLDL particle production. Therefore, the inhibition of inflammatory pathways by aspirin could be an interesting target for the treatment of hypertriglyceridemia.

The apolipoprotein C-I content of very-low-density lipoproteins is associated with fasting triglycerides, postprandial lipemia, and carotid atherosclerosis

Background. Experimental studies in animals suggest that apolipoprotein (apo) C-I is an important regulator of triglycerides in fasting and postprandial conditions and associated with carotid atherosclerosis. Methods. A cross-sectional study was conducted with 81 subjects, aged 56–80 years recruited from a population health survey. The participants underwent a fat tolerance test (1 g fat per Kg body weight) and carotid atherosclerosis was determined by ultrasound examination. VLDL particles, Sf 20–400, were isolated and their lipid composition and apoC-I content determined. Results. The carotid plaque area increased linearly with the number of apoC-I molecules per VLDL particles (P = 0.048) under fasting conditions. Fasting triglycerides increased across tertiles of apoC-I per VLDL particle in analyses adjusted for apoC-II and -C-III, apoE genotype and traditional cardiovascular risk factors (P = 0.011). The relation between apoC-I in VLDL and serum triglycerides was conveyed by triglyceride enrichment of VLDL particles (P for trend <0.001. The amount of apoC-I molecules per VLDL was correlated with the total (r = 0.41, P < 0.0001) and incremental (r = 0.35, P < 0.001) area under the postprandial triglyceride curve. Conclusions. Our findings support the concept that the content of apoC-I per VLDL particle is an important regulator of triglyceride metabolism in the fasting and postprandial state and associated with carotid athrosclerosis.

Global proteomic profiling reveals altered proteomic signature in schizophrenia serum

Schizophrenia is one of the most severe psychiatric disorders affecting 1% of the world population. There is yet no empirical method to validate the diagnosis of the disease. The identification of an underlying molecular alteration could lead to an improved disease understanding and may yield an objective panel of biomarkers to aid in the diagnosis of this devastating disease. Presented is the largest reported liquid chromatography-mass spectrometry-based proteomic profiling study investigating serum samples taken from first-onset drug-naive patients compared with samples collected from healthy volunteers. The results of this large-scale study are presented along with enzyme-linked immunosorbent assay-based validation data.

Metabolism of very-low-density lipoprotein and low-density lipoprotein containing apolipoprotein C-III and not other small apolipoproteins

OBJECTIVE

We aimed to clarify the influence of apolipoprotein C-III (apoCIII) on human apolipoprotein B metabolism.

METHODS AND RESULTS

We studied the kinetics of 4 very-low-density lipoprotein (VLDL), intermediate-density lipoprotein (IDL), and low-density lipoprotein (LDL) types containing: (1) otherApos-CIII-: none of apoCIII, apoAII, apoCI, apoCII, or apoE; (2) otherApos+CIII-: no apoCIII but at least one of the others; (3) otherApos-CIII+: apoCIII, but not any others; and (4) otherApos+CIII+: apoCIII and at least one other. VLDL and IDL otherApos-CIII+ and otherApos-CIII- had similar rates of lipolytic conversion to smaller particles. However, light LDL otherApos-CIII+ compared with otherApos-CIII- had much faster conversion to dense LDL as did light LDL otherApos+CIII+ compared with otherApos+CIII-. VLDL and IDL otherApos-CIII+ had minimal direct removal from circulation, whereas VLDL and IDL otherApos+CIII-, rich in apoE, showed fast clearance. Lipoproteins in fraction otherApos+CIII+ also rich in apoE had very low clearance.

CONCLUSIONS

The results suggest that apoCIII strongly inhibits hepatic uptake of VLDL and IDL overriding the opposite influence of apoE when both are present. The presence of apoCIII on dense VLDL is not associated with slow conversion to IDL, a lipoprotein lipase-dependent process; but when on light LDL, apoCIII is associated with enhanced conversion to dense LDL, a process involving hepatic lipase.

The use of network analyses for elucidating mechanisms in cardiovascular disease

Systems biology offers the potential to provide new insights into our understanding of the pathogenesis of complex diseases such as atherosclerosis. It seeks to comprehend the system properties of the non-linear interactions of the multiple biomolecular components that characterize a living organism. An important component of this research approach is identifying the biological networks that connect the differing elements of a system and in the process describe the characteristics that define a shift in equilibrium from a healthy to a diseased state. The utility of this method becomes clear when applied to multifactorial diseases with complex etiologies such as inflammatory-related diseases, herein exemplified by cardiovascular disease. In this study, the application of network theory to systems biology is described in detail and an example is provided using data from a clinical biobank database of carotid endarterectomies from the Karolinska University Hospital (Biobank of Karolinska Endarterectomies, BiKE). Data from 47 microarrays were examined using a combination of Bioconductor modules and the Cytoscape resource with several associated plugins to analyze the transcriptomics data and create a combined gene association and correlation network of atherosclerosis. The methodology and workflow are described in detail, with a total of 43 genes found to be differentially expressed on a gender-specific basis, of which 15 were not directly linked to the sex chromosomes. In particular, the APOC1 gene was 2.1-fold down-regulated in plaques in women relative to men and was selected for further analysis based upon a purported role in cardiovascular disease. The resulting network was identified as a scale-free network that contained specific sub-networks related to immune function and lipid biosynthesis. These sub-networks link atherosclerotic-related genes to other genes that may not have previously known roles in disease etiology and only evidence small alterations, which are challenging to find by statistical and comparison-based methods. A number of Gene Ontology (GO), BioCarta and KEGG pathways involved in the atherosclerotic process were identified in the constructed sub-network, with 19 GO pathways related to APOC1 of which 'phospholipid efflux' evidenced the strongest association. The utility and functionality of network analysis and the different Cytoscape plugins employed are discussed. Lastly, the applications of these methods to cardiovascular disease are discussed with focus on the current limitations and future visions of this emerging field.

APOC1 T45S polymorphism is associated with reduced obesity indices and lower plasma concentrations of leptin and apolipoprotein C-I in aboriginal Canadians

Apolipoprotein (apo) C-I is a constituent of chylomicrons, very low density lipoprotein, and high density lipoprotein. The role of apo C-I in human metabolism is incompletely defined. We took advantage of a naturally occurring amino acid polymorphism that is present in aboriginal North Americans, namely apo C-I T45S. We assessed the hypothesis that metabolic traits, including obesity-related and lipoprotein-related traits, would differ between carriers and noncarriers of apo C-I T45S. A genotyping assay was developed for APOC1 T45S and genotypes were determined in a sample of 410 Canadian Oji-Cree subjects. The allele frequency of the apo C-I S45 allele was approximately 8% in this sample. We observed the apo C-I S45 allele was significantly associated with 1) lower percent body fat (P < 0.05), 2) lower waist circumference (P = 0.058), 3) lower serum leptin levels (P < 0.05), and 4) lower plasma apo C-I levels (P < 0.0001), using a newly developed ELISA-based method. Taken together, these results suggest that at the whole human phenotype level, apo C-I is associated with the complex metabolic trait of obesity as well as with serum leptin levels.

Apolipoprotein CI is a physiological regulator of cholesteryl ester transfer protein activity in human plasma but not in rabbit plasma

Plasma cholesteryl ester transfer protein (CETP) activity is high in rabbits, intermediate in humans, and nondetectable in rodents. Human apolipoprotein CI (apoCI) was found to be a potent inhibitor of CETP. The aim of this study was to compare the ability of rabbit and human apoCI to modulate the interaction of CETP with HDLs and to evaluate to which extent apoCI contributes to plasma cholesteryl ester transfer rate in normolipidemic humans and rabbits. Rabbit apoCI gene was cloned and sequenced, rabbit and human apoCI were purified to homogeneity, and their ability to modify the surface charge properties and the CETP inhibitory potential of HDL were compared. It is demonstrated that unlike human apoCI, rabbit apoCI does not modulate cholesteryl ester transfer rate in total plasma. Whereas both human and rabbit apoCI readily associate with HDL, only human apoCI was found to modify the electrostatic charge of HDL. In humans, both CETP and apoCI at normal, physiological levels contribute significantly to the plasma cholesteryl ester transfer rate. In contrast, CETP is the sole major determinant of cholesteryl ester transfer in normolipidemic rabbit plasma as a result of the inability of rabbit apoCI to change HDL electronegativity.

Can serum apolipoprotein C-I demonstrate metabolic abnormality early in women with polycystic ovary syndrome?

OBJECTIVE

To evaluate the role of apolipoprotein C-I (apoC-I) levels and assess relationships between apoC-I and clinical features in women with polycystic ovary syndrome (PCOS).

DESIGN

Prospective study.

SETTING

Reproductive Center of Peking University Third Hospital.

PATIENT(S)

Thirty patients with PCOS with insulin resistance, 30 patients with PCOS without insulin resistance, and 30 control individuals.

INTERVENTION(S)

Fasting serum samples.

MAIN OUTCOME MEASURE(S)

Measures of serum apoC-I, androgens, total cholesterol, triglycerides, high-density lipoprotein cholesterol, low-density lipoprotein cholesterol, apoA1, apoB, heat-shock C-reactive protein, glucose, and homeostasis model assessment of insulin resistance (HOMA-IR).

RESULT(S)

We found differentially expressed proteins by use of the surface-enhanced laser adsorption/ionization (SELDI) protein chip in the serum of women with PCOS and controls. Of these, apoC-I, was highly up-regulated. ApoC-I is associated with glycometabolism and lipid metabolism, but its role in PCOS has been unknown. The serum levels of apoC-I in the patients with PCOS were statistically significantly elevated compared with those of controls, especially in women with insulin resistance. The lean PCOS women had higher apoC-I levels than controls. In patients with PCOS and without any abnormal serum lipid index, apoC-I levels were still higher than in controls. Analysis showed that apoC-I correlated with body mass index, triglycerides, high-density lipoprotein cholesterol, apoA1, and HOMA-IR.

CONCLUSION(S)

ApoC-I may have an important role in glucose and lipid metabolism, and may be useful for early demonstration of metabolic abnormality in women with PCOS.

ApoE and ApoC-I polymorphisms: association of genotype with cardiovascular disease phenotype in African Americans

Apolipoproteins (apo) E and C-I are components of triglyceride (TG)-rich lipoproteins and impact their metabolism. Functional polymorphisms have been established in apoE but not in apoC-I. We studied the relationship between apoE and apoC-I gene polymorphisms and plasma lipoproteins and coronary artery disease (CAD) in 211 African Americans and 306 Caucasians. In African Americans but not in Caucasians, apoC-I H2-carriers had significantly lower total and LDL cholesterol and apoB levels, and higher glucose, insulin, and HOMA-IR levels compared with H1 homozygotes. Differences across CAD phenotypes were seen for the apoC-I polymorphism. African-American H2-carriers without CAD had significantly lower total cholesterol (P < 0.001), LDL cholesterol (P < 0.001), and apoB (P < 0.001) levels compared with H1 homozygotes, whereas no differences were found across apoC-I genotypes for African Americans with CAD. Among African-American apoC-I H1 homozygotes, subjects with CAD had a profile similar to the metabolic syndrome (i.e., higher triglyceride, glucose, and insulin) compared with subjects without CAD. For African-American H2-carriers, subjects with CAD had a pro-atherogenic lipid pattern (i.e., higher LDL cholesterol and apoB levels), compared with subjects without CAD. ApoC-I genotypes showed an ethnically distinct phenotype relationship with regard to CAD and CAD risk factors.

Apolipoprotein CI inhibits scavenger receptor BI and increases plasma HDL levels in vivo

Apolipoprotein CI (apoCI) has been suggested to influence HDL metabolism by activation of LCAT and inhibition of HL and CETP. However, the effect of apoCI on scavenger receptor BI (SR-BI)-mediated uptake of HDL-cholesteryl esters (CE), as well as the net effect of apoCI on HDL metabolism in vivo is unknown. Therefore, we evaluated the effect of apoCI on the SR-BI-mediated uptake of HDL-CE in vitro and determined the net effect of apoCI on HDL metabolism in mice. Enrichment of HDL with apoCI dose-dependently decreased the SR-BI-dependent association of [(3)H]CE-labeled HDL with primary murine hepatocytes, similar to the established SR-BI-inhibitors apoCIII and oxLDL. ApoCI deficiency in mice gene dose-dependently decreased HDL-cholesterol levels. Adenovirus-mediated expression of human apoCI in mice increased HDL levels at a low dose and increased the HDL particle size at higher doses. We conclude that apoCI is a novel inhibitor of SR-BI in vitro and increases HDL levels in vivo.

A two step fractionation approach for plasma proteomics using immunodepletion of abundant proteins and multi-lectin affinity chromatography: Application to the analysis of obesity, diabetes, and hypertension diseases

Plasma is an important biological material for biomarker discovery. However, the wide dynamic range in protein concentration remains a major challenge. In this paper, we introduce the development of a proteomic platform for analysis of plasma samples. The method utilizes a double fractionation approach which combines the MARS immunodepletion column with multi-lectin affinity chromatography, M-LAC, to deplete the most abundant proteins in plasma, the majority of which are glycosylated. To determine the suitability of this methodology, we applied the workflow described in this study to a sample set composed of four groups: a control pool and three different disease pools: obesity, diabetes, and hypertension. We were able to identify changes in the level of several proteins; for example, a protein such as angiotensinogen was found to be present at high levels in patients with obesity plus diabetes and hypertension. On the other hand, apolipoprotein CI was shown to be elevated in all disease groups. A review of the literature supported our observation. The methodology presented in this report was shown to be effective for profiling changes in the plasma proteome of subjects with obesity and its associated complications such as diabetes and hypertension.

Defective lipid delivery modulates glucose tolerance and metabolic response to diet in apolipoprotein E-deficient mice

OBJECTIVE

Apolipoprotein E (ApoE) regulates plasma lipid levels via modulation of lipolysis and serving as ligand for receptor-mediated clearance of triglyceride (TG)-rich lipoproteins. This study tested the impact of modulating lipid delivery to tissues on insulin responsiveness and diet-induced obesity.

RESEARCH DESIGN AND METHODS

ApoE(+/+) and apoE(-/-) mice were placed on high-fat-high-sucrose diabetogenic diet or control diet for 24 weeks. Plasma TG clearance, glucose tolerance, and tissue uptake of dietary fat and glucose were assessed.

RESULTS

Plasma TG clearance and lipid uptake by adipose tissue were impaired, whereas glucose tolerance was improved in control diet-fed apoE(-/-) mice compared with apoE(+/+) mice after an oral lipid load. Fat mass was reduced in apoE(-/-) mice compared with apoE(+/+) mice under both dietary conditions. The apoE(-/-) mice exhibited lower body weight and insulin levels than apoE(+/+) mice when fed the diabetogenic diet. Glucose tolerance and uptake by muscle and brown adipose tissue (BAT) was also improved in mice lacking apoE when fed the diabetogenic diet. Indirect calorimetry studies detected no difference in energy expenditure and respiratory quotient between apoE(+/+) and apoE(-/-) mice on control diet. Energy expenditure and uncoupling protein-1 expression in BAT were slightly but not significantly increased in apoE(-/-) mice on diabetogenic diet.

CONCLUSIONS

These results demonstrated that decreased lipid delivery to insulin-sensitive tissues improves insulin sensitivity and ameliorates diet-induced obesity.

Apolipoprotein C1 and apolipoprotein E are differentially expressed in atheroma of the carotid and femoral artery

BACKGROUND

A number of the genes and proteins as the causes of carotid atherosclerotic disease have been recently reported, but the major factors for atherosclerosis have still not been identified.

METHODS

The atherosclerotic atheromas were obtained during endarterectomy for each of 10 cases of diseased carotid and femoral arteries. As the nonatherosclerotic arteries, the iliac arteries were obtained during organ harvest from five cases of brain-dead donors, and the leg arteries were obtained during leg amputation from five cases of Buerger's disease. The total RNAs and proteins were isolated from the atheromas and arteries. The annealing control primer method was used to screen the differentially expressed mRNAs. To identify if the mRNA expression of screened gene was associated with the protein expression, we performed an immunohistochemical analysis.

RESULTS

We found that the apolipoprotein C1 (apo C1) gene was prominently expressed in the atheroma of the carotid and femoral arteries, as compared to the nonatherosclerotic arteries. Immunohistochemical analysis showed the high expression of apo C1 protein in the atheromas of the carotid and femoral arteries. Apo E protein was also highly expressed in atheromas compared with the nonatherosclerotic arteries, but there was no difference for apo C2 protein between those four groups of arteries.

DISCUSSION

The expression of apo C1 and apo E are closely associated with the susceptibility to the pathogenesis of atherosclerosis. This study suggests that these factors might play important roles in the future to screen for preventing atherosclerosis and for diagnostic testing of patients.

Apolipoprotein C-I binds free fatty acids and reduces their intracellular esterification

Mice that overexpress human apolipoprotein C-I (apoC-I) homozygously (APOC1(+/+) mice) are protected against obesity and show cutaneous abnormalities. Although these effects can result from our previous observation that apoC-I inhibits FFA generation by LPL, we have also found that apoC-I impairs the uptake of a FFA analog in adipose tissue. In this study, we tested the hypothesis that apoC-I interferes with cellular FFA uptake independent of LPL activity. The cutaneous abnormalities of APOC1(+/+) mice were not affected after transplantation to wild-type mice, indicating that locally produced apoC-I prevents lipid entry into the skin. Subsequent in vitro studies with apoC-I-deficient versus wild-type macrophages revealed that apoC-I reduced the cell association and subsequent esterification of [(3)H]oleic acid by approximately 35% (P < 0.05). We speculated that apoC-I binds FFA extracellularly, thereby preventing cell association of FFA. We showed that apoC-I was indeed able to mediate the binding of oleic acid to otherwise protein-free VLDL-like emulsion particles involving electrostatic interaction. We conclude that apoC-I binds FFA in the circulation, thereby reducing the availability of FFA for uptake by cells. This mechanism can serve as an additional mechanism behind the resistance to obesity and the cutaneous abnormalities of APOC1(+/+) mice.

Apolipoprotein CI aggravates atherosclerosis development in ApoE-knockout mice despite mediating cholesterol efflux from macrophages

OBJECTIVE

Apolipoprotein CI (apoCI) is expressed in the liver and in macrophages, and has several roles in lipid metabolism. Since macrophage apoCI expression might affect macrophage lipid homeostasis and atherosclerotic lesion development locally in the arterial wall, we investigated the effect of both systemic and macrophage apoCI on atherosclerotic lesion development.

METHODS AND RESULTS

To investigate whether physiological expression levels of apoCI affect atherosclerosis development, we first assessed the effect of systemic endogenous apoCI expression on atherosclerosis in apoe-/- apoc1+/+ as compared to apoe-/- apoc1-/- mice at 26 weeks of age. ApoCI expression increased plasma levels of triglycerides (TG) (+70%; P<0.01) and cholesterol (+30%; P<0.05), and increased the atherosclerotic lesion area in the aortic root (+87%; P<0.05). Paradoxically, incubation of apoc1+/+ and apoc1-/- murine peritoneal macrophages with AcLDL (50 microg/mL; 48 h) revealed that macrophage apoCI decreased the accumulation of cellular cholesteryl esters (CE) relatively to free cholesterol (-22%; P<0.05). Accordingly, exogenous human apoCI increased cholesterol efflux from AcLDL-laden wild-type macrophages, and to a similar extent as apoAI and apoE. To evaluate whether atherosclerosis development would be affected by macrophage apoCI expression in vivo, we assessed atherosclerotic lesion development at 16 weeks after transplantation of bone marrow from apoe-/- apoc1-/- or apoe-/- apoc1+/+ mice to apoe-/- apoc1+/+ mice. However, in the situation wherein the liver and adipose tissue still produce apoCI, macrophage apoCI expression did not affect plasma lipid levels or the atherosclerotic lesion area.

CONCLUSIONS

Systemic apoCI increases atherosclerosis, probably by inducing hyperlipidemia. Despite decreasing macrophage lipid accumulation in vitro, apoCI production by macrophages locally in the arterial wall does not affect atherosclerosis development in vivo.

High-density lipoprotein and transport of cholesterol and triglyceride in blood

High-density lipoproteins (HDL) contain approximately 25% of the cholesterol and <5% of the triglyceride in the plasma of human blood. However, the dynamic exchange of lipids and lipid-binding proteins is not revealed by simply considering the mass of material at any point in time. HDL are the most complex of lipoprotein species with multiple protein constituents, which facilitate cholesterol secretion from cells, cholesterol esterification in plasma, and transfer of cholesterol to other lipoproteins and to the liver for excretion. They also play a major role in triglyceride transport by providing for activation of lipoprotein lipase, exchange of triglyceride among the lipoproteins, and removal of triglyceride rich remnants of chylomicrons and very-low-density lipoproteins after lipase action. In addition, antioxidative enzymes and phospholipid transfer proteins are important components of HDL. Many of the proteins of HDL are exchangeable with other lipoproteins, including chylomicrons and very-low-density lipoproteins. The constantly changing content of lipids and apolipoproteins in HDL particles generate a series of structures that can be analyzed by using separation techniques that depend on size or charge of the particles. Interaction of these various structures can be very different with cell surfaces depending on the size or apolipoprotein content. A series of different transport proteins preferentially exchange lipids with specific structures among the HDL but interact poorly or not at all with others. The role of these differing forms of HDL and their interactions with cells and other lipoprotein species in plasma is the subject of intense study stimulated by the potential for reducing atherogenesis. The strength of this is only partially indicated by the correlation of higher total levels of the HDL particles with reduced incidence of vascular disease in various clinical trials and epidemiological studies.

Apolipoprotein CI stimulates the response to lipopolysaccharide and reduces mortality in Gram‐negative sepsis

Gram-negative sepsis is a major death cause in intensive care units. Accumulating evidence indicates the protective role of plasma lipoproteins such as high-density lipoprotein (HDL) in sepsis. It has recently been shown that septic HDL is almost depleted from apolipoprotein CI (apoCI), suggesting that apoCI may be a protective factor in sepsis. Sequence analysis revealed that apoCI possesses a highly conserved consensus KVKEKLK binding motif for lipopolysaccharide (LPS), an outer-membrane component of gram-negative bacteria. Through avid binding to LPS involving this motif, apoCI improved the presentation of LPS to macrophages in vitro and in mice, thereby stimulating the inflammatory response to LPS. Moreover, apoCI dose-dependently increased the early inflammatory response to Klebsiella pneumoniae-induced pneumonia, reduced the number of circulating bacteria, and protected mice against fatal sepsis. Our data support the hypothesis that apoCI is a physiological protector against infection by enhancing the early inflammatory response to LPS and suggest that timely increase of apoCI levels could be used to efficiently prevent and treat early sepsis.

Phenotype characterisation using integrated gene transcript, protein and metabolite profiling

Multifactorial diseases present a significant challenge for functional genomics. Owing to their multiple compartmental effects and complex biomolecular activities, such diseases cannot be adequately characterised by changes in single components, nor can pathophysiological changes be understood by observing gene transcripts alone. Instead, a pattern of subtle changes is observed in multifactorial diseases across multiple tissues and organs with complex associations between corresponding gene, protein and metabolite levels. This article presents methods for exploratory and integrative analysis of pathophysiological changes at the biomolecular level. In particular, novel approaches are introduced for the following challenges: (i) data processing and analysis methods for proteomic and metabolomic data obtained by electrospray ionisation (ESI) liquid chromatography-tandem mass spectrometry (LC/MS); (ii) association analysis of integrated gene, protein and metabolite patterns that are most descriptive of pathophysiological changes; and (iii) interpretation of results obtained from association analyses in the context of known biological processes. These novel approaches are illustrated with the apolipoprotein E3-Leiden transgenic mouse model, a commonly used model of atherosclerosis. We seek to gain insight into the early responses of disease onset and progression by determining and identifying--well in advance of pathogenic manifestations of disease--the sets of gene transcripts, proteins and metabolites, along with their putative relationships in the transgenic model and associated wild-type cohort. Our results corroborate previous findings and extend predictions for three processes in atherosclerosis: aberrant lipid metabolism, inflammation, and tissue development and maintenance.

LDL receptor cooperates with LDL receptor–related protein in regulating plasma levels of coagulation factor VIII in vivo

Low-density lipoprotein (LDL) receptor (LDLR) and LDLR-related protein (LRP) are members of the LDLR family of endocytic receptors. LRP recognizes a wide spectrum of structurally and functionally unrelated ligands, including coagulation factor VIII (FVIII). In contrast, the ligand specificity of LDLR is restricted to apolipoproteins E and B-100. Ligand binding to the LDLR family is inhibited by receptor-associated protein (RAP). We have previously reported that, apart from LRP, other RAP-sensitive mechanisms contribute to the regulation of FVIII in vivo. In the present study, we showed that the extracellular ligand-binding domain of LDLR interacts with FVIII in vitro and that binding was inhibited by RAP. The physiologic relevance of the FVIII–LDLR interaction was addressed using mouse models of LDLR or hepatic LRP deficiency. In the absence of hepatic LRP, LDLR played a dominant role in the regulation and clearance of FVIII in vivo. Furthermore, FVIII clearance was accelerated after adenovirus-mediated gene transfer of LDLR. The role of LDLR in FVIII catabolism was not secondary to increased plasma lipoproteins or to changes in lipoprotein profiles. We propose that LDLR acts in concert with LRP in regulating plasma levels of FVIII in vivo. This represents a previously unrecognized link between LDLR and hemostasis.

Apolipoprotein CI overexpression is not a relevant strategy to block cholesteryl ester transfer protein (CETP) activity in CETP transgenic mice

ApoCI (apolipoprotein CI) is a potent inhibitor of plasma CETP [CE (cholesteryl ester) transfer protein]. The relevance of apoCI overexpression as a method for CETP blockade in vivo was addressed in the present study in CETPTg/apoCITg mice (mice expressing both human CETP and apoCI). Despite a significant reduction in specific CETP activity in CETPTg/apoCITg mice compared with CETPTg mice [transgenic mouse to human CETP; 46.8+/-11.1 versus 101.8+/-25.7 pmol x h(-1).(mug of plasma CETP)(-1) respectively; P<0.05], apoCI overexpression increased both the CETP mass concentration (3-fold increase; P<0.05) and the hepatic CETP mRNA level (4-fold increase, P<0.005), leading to an increase in total plasma CE transfer activity (by 39%, P<0.05). The ratio of apoB-containing lipoprotein to HDL (high-density lipoprotein) CE was 10-fold higher in CETPTg/apoCITg mice than in apoCITg mice (P<0.0005). It is proposed that the increased CETP expression in CETPTg/apoCITg mice is a direct consequence of liver X receptor activation in response to the accumulation of cholesterol-rich apoB-containing lipoproteins. In support of the latter view, hepatic mRNA levels of other liver X receptor-responsive genes [ABCG5 (ATP-binding cassette transporter GS) and SREBP-1c (sterol-regulatory-binding protein-1c)] were higher in CETPTg/apoCITg mice compared with CETPTg mice. In conclusion, overexpression of apoCI, while producing a significant inhibitory effect on specific CETP activity, does not represent a suitable method for decreasing total CE transfer activity in CETPTg/apoCITg mice, owing to an hyperlipidaemia-mediated effect on CETP gene expression.

Methods for the differential integrative omic analysis of plasma from a transgenic disease animal model

Multitiered quantitative analysis of biological systems is rapidly becoming the desired approach to study hierarchical functional interactions between proteins and metabolites. We describe here a novel systematic approach to analyze organisms with complex metabolic regulatory networks. By using precise analytical methods to measure biochemical constituents and their relative abundance in whole plasma of transgenic ApoE*3-Leiden mice and an isogenic wild-type control group, simultaneous snapshots of metabolic and protein states were obtained. Novel data processing and multivariate analysis tools such as Impurity Resolution Software (IMPRESS) and Windows-based linear fit program (WINLIN) were used to compare protein and metabolic profiles in parallel. Canonical correlations of the resulting data show quantitative relationships between heterogeneous components in the TG animals. These results, obtained solely from whole plasma analysis allowed us, in a rapid manner, to corroborate previous findings as well as find new events pertaining to dominant and peripheral events in lipoprotein metabolism of a genetically modified mammalian organism in relation to ApoE3, a key mediator of lipoprotein metabolism.

The common insertional polymorphism in the APOC1 promoter is associated with serum apolipoprotein C-I levels in Hispanic children

We examined the effect of APOC1-317insCGTT allele status (HpaI RFLP, deletion [H1] and insertion [H2] alleles) on serum apolipoprotein (apo) C-I level in 362 Hispanic children in the Columbia University BioMarkers Study. The H2 allele was present in 147 subjects (40.6%). Serum apoC-I was 20% lower in the presence of the H2 allele in APOE epsilon3/epsilon3 homozygotes (P=0.003) but did not differ by H2 status in epsilon4 carriers. Insufficient numbers of epsilon2 carriers (N=45) were present for analysis. In multivariate analysis in the epsilon3/epsilon3 context, after adjusting for potential covariate effects and familial aggregation, the mean effect of H2/* versus H1/H1 on apoC-I level, was estimated to be 2.15+/-0.55mg/dl (P<0.0025). Plasma triglyceride level was weakly correlated with serum apoC-I level (Pearson's r=0.17, P<0.001) but was highly correlated with serum apoC-III (Pearson's r=0.74, P<0.0001). Nevertheless, presence of the H2 allele was not significantly associated with serum apoC-III level. Thus, the effect of APOC1 genotype on serum apoC-I level was not due to apoC-I level serving as a surrogate for triglyceride level. The APOC1-317insCGTT allele is a commonly polymorphic genetic marker that is associated with serum apoC-I level in the APOE epsilon3/epsilon3 context. These findings suggest that the mechanism of the previously described association with plasma TG is, at least in part, related to the correlation of the polymorphism with the level of expression of apoC-I.

Effects of subchronic clozapine administration on serum glucose, cholesterol and triglyceride levels, and body weight in male BALB/c mice

Atypical antipsychotics, like clozapine, have fewer extrapyramidal side effects compared with typical antipsychotics, however, such treatment is associated with several adverse metabolic effects such as weight gain, hyperglycemia and hyperlipidemia in patients with schizophrenia. In this study, we investigated the effects of 30-day clozapine treatment on weight change, and serum fasting glucose, cholesterol and triglyceride levels in male BALB/c mice. The results demonstrate that 10.0 mg/kg clozapine group gained significantly less weight but had higher cholesterol compared with controls and the 2.0 mg/kg clozapine group. Our findings indicate the possibility of using mice to study the mechanisms of body weight change and lipid dysregulations induced by clozapine.

Severe hypertriglyceridemia in human APOC1 transgenic mice is caused by apoC-I-induced inhibition of LPL

Studies in humans and mice have shown that increased expression of apolipoprotein C-I (apoC-I) results in combined hyperlipidemia with a more pronounced effect on triglycerides (TGs) compared with total cholesterol (TC). The aim of this study was to elucidate the main reason for this effect using human apoC-I-expressing (APOC1) mice. Moderate plasma human apoC-I levels (i.e., 4-fold higher than human levels) caused a 12-fold increase in TG, along with a 2-fold increase in TC, mainly confined to VLDL. Cross-breeding of APOC1 mice on an apoE-deficient background resulted in a marked 55-fold increase in TG, confirming that the apoC-I-induced hyperlipidemia cannot merely be attributed to blockade of apoE-recognizing hepatic lipoprotein receptors. The plasma half-life of [3H]TG-VLDL-mimicking particles was 2-fold increased in APOC1 mice, suggesting that apoC-I reduces the lipolytic conversion of VLDL. Although total postheparin plasma LPL activity was not lower in APOC1 mice compared with controls, apoC-I was able to dose-dependently inhibit the LPL-mediated lipolysis of [3H]TG-VLDL-mimicking particles in vitro with a 60% efficiency compared with the main endogenous LPL inhibitor apoC-III. Finally, purified apoC-I impaired the clearance of [3H]TG-VLDL-mimicking particles independent of apoE-mediated hepatic uptake in lactoferrin-treated mice. Therefore, we conclude that apoC-I is a potent inhibitor of LPL-mediated TG-lipolysis.

Post-transcriptional regulation of apoC-I synthesis and secretion in human HepG2 cells

ApoC-I plays an important role in controlling plasma lipid metabolism, however little is known about factors regulating the hepatic synthesis and secretion of this apolipoprotein. In the present study, we have carried out experiments with human hepatoma (HepG2) cells, in order to determine the effect of different tissue culture conditions on cellular lipid levels and on the production of apoC-I (and apoE) at the protein and mRNA level. Cells incubated for 48 h with 10% human serum had significantly higher cellular triglyceride (22%, P<0.05) and cholesterol levels (19%, P<0.01), higher medium apoC-I and apoE levels (2.6- and 2.9-fold, respectively), but similar levels of apoC-I and apoE mRNA, compared to cells incubated with 10% human lipoprotein-deficient serum (LPDS). Serum containing only HDL, or containing HDL with LDL, also increased cellular lipids and increased secreted apoC-I and apoE levels without altering apoC-I and apoE mRNA levels. Incubation of cells with Intralipid triglyceride (625 microM), increased cellular triglyceride (2.8-fold, P<0.001), decreased cellular cholesterol (32%, P<0.01), decreased cellular and medium apoC-I (24 and 26%, P<0.01) and had no effect on apoC-I mRNA levels. Additional experiments in which cells were loaded with cholesterol (incubation with 10 microg/ml cholesterol plus 1 microg/ml 25-hydroxycholesterol) or depleted of cholesterol (statin treatment) confirmed that secretion of apoC-I by HepG2 cells was dependent on cellular cholesterol levels and independent of changes in apoC-I mRNA levels. These results demonstrate that cellular cholesterol rather than triglyceride levels play a role in controlling apoC-I production by HepG2 cells and that this regulation occurs at a post-transcriptional level.

Grape seed procyanidins improve atherosclerotic risk index and induce liver CYP7A1 and SHP expression in healthy rats

Moderate consumption of red wine reduces risk of death from cardiovascular disease. The polyphenols in red wine are ultimately responsible for this effect, exerting antiatherogenic actions through their antioxidant capacities and modulating intracellular signaling pathways and transcriptional activities. Lipoprotein metabolism is crucial in atherogenesis, and liver is the principal organ controlling lipoprotein homeostasis. This study was intended to identify the primary effects of procyanidins, the most abundant polyphenols in red wine, on both plasma lipoprotein profile and the expression of genes controlling lipoprotein homeostasis in the liver. We show that procyanidins lowered plasma triglyceride, free fatty acids, apolipoprotein B (apoB), LDL-cholesterol and nonHDL:nonLDL-cholesterol levels and slightly increased HDL-cholesterol. Liver mRNA levels of small heterodimer partner (SHP), cholesterol 7alpha-hydroxylase (CYP7A1), and cholesterol biosynthetic enzymes increased, whereas those of apoAII, apoCI, and apoCIII decreased. Lipoprotein lipase (LPL) mRNA levels increased in muscle and decreased in adipose tissue. In conclusion, procyanidins improve the atherosclerotic risk index in the postprandial state, inducing in the liver the overexpression of CYP7A1 (suggesting an increase of cholesterol elimination via bile acids) and SHP, a nuclear receptor emerging as a key regulator of lipid homeostasis at the transcriptional level. These results could explain, at least in part, the beneficial long-term effects associated with moderate red wine consumption.