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The lipolytic processing of triglyceride-rich lipoproteins (TRLs) by lipoprotein lipase (LPL) is crucial for the delivery of dietary lipids to the heart, skeletal muscle, and adipose tissue. The processing of TRLs by LPL is regulated in a tissue-specific manner by a complex interplay between activators and inhibitors. Angiopoietin-like protein 4 (ANGPTL4) inhibits LPL by reducing its thermal stability and catalyzing the irreversible unfolding of LPLs α/β-hydrolase domain. We previously mapped the ANGPTL4 binding site on LPL and defined the downstream unfolding events resulting in LPL inactivation. The binding of LPL to glycosylphosphatidylinositol-anchored high-density lipoprotein-binding protein 1 protects against LPL unfolding. The binding site on LPL for an activating cofactor, apolipoprotein C2 (APOC2), and the mechanisms by which APOC2 activates LPL have been unclear and controversial. Using hydrogen-deuterium exchange/mass spectrometry, we now show that APOC2s C-terminal α-helix binds to regions of LPL surrounding the catalytic pocket. Remarkably, APOC2s binding site on LPL overlaps with that for ANGPTL4, but their effects on LPL conformation are distinct. In contrast to ANGPTL4, APOC2 increases the thermal stability of LPL and protects it from unfolding. Also, the regions of LPL that anchor the lid are stabilized by APOC2 but destabilized by ANGPTL4, providing a plausible explanation for why APOC2 is an activator of LPL, while ANGPTL4 is an inhibitor. Our studies provide fresh insights into the molecular mechanisms by which APOC2 binds and stabilizes LPL-and properties that we suspect are relevant to the conformational gating of LPLs active site.

Apolipoproteins (apo) C-I and C-II are key regulators of triglyceride and HDL metabolism. Both exist as full-size native and truncated (apoC-I'; apoC-II') posttranslational proteoforms. However, the determinants and the role of these proteoforms in lipid metabolism are unknown. Here, we measured apoC-I and apoC-II proteoforms by mass spectrometry immunoassay in baseline and 10-year follow-up plasma samples from the Multi-Ethnic Study of Atherosclerosis. We found that baseline total apoC-I (mean = 9.2 mg/dl) was lower in African Americans (AA), Chinese Americans (CA), and Hispanics (by 1.8; 1.0; 1.0 mg/dl vs. whites), higher in women (by 1.2 mg/dl), and positively associated with plasma triglycerides and HDL. Furthermore, we observed that the truncated-to-native apoC-I ratio (apoC-I'/C-I) was lower in CA, negatively associated with triglycerides, and positively associated with HDL. We determined that total apoC-II (8.8 mg/dl) was lower in AA (by 0.8 mg/dl) and higher in CA and Hispanics (by 0.5 and 0.4 mg/dl), positively associated with triglycerides, and negatively associated with HDL. In addition, apoC-II'/C-II was higher in AA and women, negatively associated with triglycerides, and positively associated with HDL. We showed that the change in triglycerides was positively associated with changes in total apoC-I and apoC-II and negatively associated with changes in apoC-I'/C-I and apoC-II'/C-II, whereas the change in HDL was positively associated with changes in total apoC-I and apoC-II'/C-II and negatively associated with change in total apoC-II. This study documents racial/ethnic variation in apoC-I and apoC-II plasma levels and highlights apolipoprotein posttranslational modification as a potential regulator of plasma lipids.

Aims Apolipoprotein C-II (ApoC-II) is thought to activate lipoprotein lipase (LPL) and is therefore a possible target for treating hypertriglyceridemia. Its relationship with cardiovascular risk has not been investigated in large-scale epidemiologic studies, particularly allowing for apolipoprotein C-III (ApoC-III), an LPL antagonist. Furthermore, the exact mechanism of ApoC-II–mediated LPL activation is unclear. Methods and results ApoC-II was measured in 3141 LURIC participants of which 590 died from cardiovascular diseases during a median (inter-quartile range) follow-up of 9.9 (8.7–10.7) years. Apolipoprotein C-II–mediated activation of the glycosylphosphatidylinositol high-density lipoprotein binding protein 1 (GPIHBP1)–LPL complex was studied using enzymatic activity assays with fluorometric lipase and very low-density lipoprotein (VLDL) substrates. The mean ApoC-II concentration was 4.5 (2.4) mg/dL. The relationship of ApoC-II quintiles with cardiovascular mortality exhibited a trend toward an inverse J-shape, with the highest risk in the first (lowest) quintile and lowest risk in the middle quintile. Compared with the first quintile, all other quintiles were associated with decreased cardiovascular mortality after multivariate adjustments including ApoC-III as a covariate (all P < 0.05). In experiments using fluorometric substrate-based lipase assays, there was a bell-shaped relationship for the effect of ApoC-II on GPIHBP1–LPL activity when exogenous ApoC-II was added. In ApoC-II-containing VLDL substrate-based lipase assays, GPIHBP1–LPL enzymatic activity was almost completely blocked by a neutralizing anti-ApoC-II antibody. Conclusion The present epidemiologic data suggest that increasing low circulating ApoC-II levels may reduce cardiovascular risk. This conclusion is supported by the observation that optimal ApoC-II concentrations are required for maximal GPIHBP1–LPL enzymatic activity. [ABSTRACT FROM AUTHOR]

Background: This study aimed at finding the diagnostic and prognostic possibilities of determining apoC-II, as a serological marker for MM in early gestation. Methods and Results: The study included 182 pregnant women aged between 18 and 45 years at gestational age under 11 weeks. All women were divided into 3 groups. Group 1 (Gr1) included 90 women with MM; Group 2 (Gr2) included 52 women with spontaneous miscarriage; Group 3 included 40 women without pathology (control group [CG]). Lipid metabolism disorders were diagnosed according to the Russian national recommendations of the VII revision(the Russian Society of Cardiologists [RSC, 2020]), considering the European recommendations (2019). Proteomic analysis of the blood serum was performed using LC-MS. Abnormalities in the lipid profile were more common in patients with MM and spontaneous abortions: 62.2% and 59.7% of cases, respectively, which correlates with the identified marker apoC-II in Gr1 and Gr2. Conclusion: ApoC-II can be considered as the most promising serologic marker for MM in the early gestation period for women with dyslipidemia.

Mortality rates due to lung cancer are high worldwide. Although PD-1 and PD-L1 immune checkpoint inhibitors boost the survival of patients with non-small-cell lung cancer (NSCLC), resistance often arises. The Warburg Effect, which causes lactate build-up and potential lysine-lactylation (Kla), links immune dysfunction to tumor metabolism. The role of non-histone Kla in tumor immune microenvironment and immunotherapy remains to be clarified. Here, global lactylome profiling and metabolomic analyses of samples from patients with NSCLC is conducted. By combining multi-omics analysis with in vitro and in vivo validation, that intracellular lactate promotes extracellular lipolysis through lactyl-APOC2 is revealed. Mechanistically, lactate enhances APOC2 lactylation at K70, stabilizing it and resulting in FFA release, regulatory T cell accumulation, immunotherapy resistance, and metastasis. Moreover, the anti-APOC2 K70-lac antibody that sensitized anti-PD-1 therapy in vivo is developed. This findings highlight the potential of anti lactyl-APOC2-K70 approach as a new combination therapy for sensitizing immunotherapeutic responses., (© 2024 The Author(s). Advanced Science published by Wiley‐VCH GmbH.)

Hypertriglyceridemia is an independent risk factor for cardiovascular disease. Apolipoprotein C-II (APOC2) is an obligatory cofactor for lipoprotein lipase (LPL), the major enzyme catalyzing plasma triglyceride hydrolysis. We have created an apoc2 knockout zebrafish model, which mimics the familial chylomicronemia syndrome (FCS) in human patients with a defect in the APOC2 or LPL gene. In this study, we measured plasma levels of free cholesterol (FC) and cholesterol esters (CE) and found that apoc2 mutant zebrafish have a significantly higher FC to CE ratio (FC/CE), when compared to the wild type. Feeding apoc2 mutant zebrafish a low-fat diet reduced triglyceride levels but not the FC/CE ratio. In situ hybridization and qPCR results demonstrated that the hepatic expression of lecithin-cholesterol acyltransferase (lcat), the enzyme responsible for esterifying plasma FC to CE, and of apolipoprotein A-I, a major protein component of HDL, were dramatically decreased in apoc2 mutants. Furthermore, the FC/CE ratio was significantly increased in the whole plasma and in a chylomicron-depleted fraction of human FCS patients. The FCS plasma LCAT activity was significantly lower than that of healthy controls. In summary, this study, using a zebrafish model and human patient samples, reports for the first time the defect in plasma cholesterol esterification associated with LPL deficiency.

Gabriel D Pinilla-Monsalve,1,* Juliana Lores,1,2,* Harry Pachajoa,1,2 Juan D López-Ponce de León,1,3 Alejandro López,1,4 Lisa X Rodríguez-Rojas,1,2 José A Nastasi-Catanese1,2 1Faculty of Health Sciences, Universidad Icesi, Cali 760032, Colombia; 2Department of Genetics, Fundación Valle del Lili, Cali 760032, Colombia; 3Department of Cardiology, Fundación Valle del Lili, Cali 760032, Colombia; 4Department of Endocrinology, Fundación Valle del Lili, Cali 760032, Colombia*These authors contributed equally to this workCorrespondence: José A Nastasi-Catanese Cra. 98 No. 18-49, Cali 760032, ColombiaTel +57 323 514-7106Fax +57 2 3319090Email jose.nastasi@fvl.org.coAbstract: Hypertriglyceridemia is a common disease with only 2% of cases exhibiting monogenic mutations. Familial chylomicronemia syndrome (FCS) is a rare genetic condition associated with recurrent and severe episodes of pancreatitis and is mainly caused by mutations in the LPL gene, with few cases related to abnormal function of apolipoprotein C-II. This is a 50-year-old female with a past medical history of arterial hypertension, miscarriage and recurrent pancreatitis. In the last four years, her triglycerides and lipase concentration reached > 3000 mg/dL and > 700 U/L, respectively. The patient was not responsive to statins, fibrates, or tetrahydrolipstatin. A novel homozygous frameshift mutation on exon 3 of the APOC2 gene was detected, c.133_134delTC. Subsequent Sanger sequencing confirmed that three first-degree relatives were carriers of the same mutation. To the best of our knowledge, we are reporting the first Colombian patient with FCS due to an APOC2 mutation. We propose that this mutation caused recurrent hypertriglyceridemic pancreatitis.Keywords: hypertriglyceridemia, hyperlipoproteinemia type I, apolipoprotein C-II, pancreatitis

In this clinical case report, we present a rare subtype of amyloidosis, apolipoprotein CII (apo CII), which was diagnosed through a renal biopsy and subsequently confirmed by identifying the p.K41T mutation via germline DNA sequencing. Upon reviewing the literature, five patients exhibiting identical mutation were identified via renal biopsy, while an additional patient was diagnosed through biopsies of the fat pad and bone marrow. Notably, our patient is the youngest recorded case. We pioneered the application of immunofluorescence and immunogold electron microscopy techniques for apo CII evaluation. Our report provides a detailed description of this case, supplemented by an extensive review encompassing apo CII, documented instances of apo CII amyloidosis with renal or systemic involvement, and potential underlying mechanisms.

Elevated plasma triglyceride (TG) levels are associated with higher risk of atherosclerotic cardiovascular disease. One way to reduce plasma TG is to increase the activity of lipoprotein lipase (LPL), the rate limiting enzyme in plasma TG metabolism. An apolipoprotein (apo) C-II mimetic peptide (18A–CII–a) has been recently developed that stimulated LPL activity in vitro and decreased plasma TG concentration in animal models for hypertriglyceridemia. Since this peptide can serve as a new therapeutic approach for treatment of hypertriglyceridemia, we investigated how 18A–CII–a peptide influences LPL activity in human plasma. We used recently described isothermal titration calorimetry based approach to assess the peptide, which enables the analysis in nearly undiluted human plasma. The 18A–CII–a peptide was 3.5-fold more efficient in stimulating LPL activity than full-length apoC-II in plasma sample from normolipidemic individual. Furthermore, 18A–CII–a also increased LPL activity in hypertriglyceridemic plasma samples. Unlike apoC-II, high concentrations of the 18A–CII–a peptide did not inhibit LPL activity. The increase in LPL activity after addition of 18A–CII–a or apoC-II to plasma was due to the increase of the amount of available substrate for LPL. Measurements with isolated lipoproteins revealed that the relative activation effects of 18A–CII–a and apoC-II on LPL activity were greater in smaller size lipoprotein fractions, such as remnant lipoproteins, low-density lipoproteins and high-density lipoproteins. In summary, this report describes a novel mechanism of action for stimulation of LPL activity by apoC-II mimetic peptides. • Calorimetry enables to test apoC-II mimetic peptides in undiluted human plasma. • ApoC-II mimetic peptide, 18A–CII–a, is an efficient LPL activator in human plasma. • Unlike apoC-II, high concentrations of 18A–CII–a do not inhibit LPL activity. • 18A–CII–a and apoC-II increase the amount of available substrate for LPL in plasma. • Effect of 18A–CII–a on LPL activity is more pronounced in smaller size lipoproteins. [ABSTRACT FROM AUTHOR]

Abstract The apolipoprotein family is a set of highly conserved proteins characterized by the presence of amphipathic α-helical sequences that mediate lipid binding. Paradoxically, this family of proteins is also prominent among the proteins known to form amyloid fibrils, characterized by extensive cross-β structure. Several apolipoproteins including apolipoprotein (apo) A-I, apoA-II and apoC-II accumulate in amyloid deposits of atherosclerotic lesions. This review illustrates the role of lipid-apolipoprotein interactions in apolipoprotein folding and aggregation with a specific focus on human apoC-II, a well-studied member of the family. In the presence of high concentrations of micellar lipid mimetics apoC-II adopts a stable and predominantly α-helical structure, similar to other members of the family and presumed to be the structure of apoC-II in circulating plasma lipoproteins. In contrast, lipid-free apoC-II aggregates to form long amyloid fibrils with a twisted ribbon-like morphology. Detailed structural analyses identify a letter G-like conformation as the basic building block within these fibrils. Phospholipids at submicellar concentrations accelerate apoC-II fibril formation by promoting the formation of a discrete tetrameric intermediate. Conversely, several small molecule lipid-mimetics inhibit apoC-II fibril formation at submicellar concentrations, inducing well-defined dimers unable to further aggregate. Finally, low concentrations of phospholipid micelles and bilayers induce the slow formation of amyloid fibrils with distinct rod-like fibril morphology. These studies highlight the diversity of lipid effects on apolipoprotein amyloid formation and reveal a conformational adaptability that could underlie the widespread occurrence of apolipoproteins in amyloid deposits and atheroma. Highlights • Apolipoproteins are prominent in the list of proteins known to form amyloid in vivo. • Lipids alter the rate of formation and final structure of apolipoprotein amyloid. • These effects may play roles in pathology of atherosclerosis and systemic amyloidoses. • We review the complex effects of lipid on amyloid formation by apolipoprotein C-II. [ABSTRACT FROM AUTHOR]

Apolipoprotein C-II (APOC2) is an obligatory activator of lipoprotein lipase. Human patients with APOC2 deficiency display severe hypertriglyceridemia while consuming a normal diet, often manifesting xanthomas, lipemia retinalis and pancreatitis. Hypertriglyceridemia is also an important risk factor for development of cardiovascular disease. Animal models to study hypertriglyceridemia are limited, with no Apoc2-knockout mouse reported. To develop a genetic model of hypertriglyceridemia, we generated an apoc2 mutant zebrafish characterized by the loss of Apoc2 function. apoc2 mutants show decreased plasma lipase activity and display chylomicronemia and severe hypertriglyceridemia, which closely resemble the phenotype observed in human patients with APOC2 deficiency. The hypertriglyceridemia in apoc2 mutants is rescued by injection of plasma from wild-type zebrafish or by injection of a human APOC2 mimetic peptide. Consistent with a previous report of a transient apoc2 knockdown, apoc2 mutant larvae have a minor delay in yolk consumption and angiogenesis. Furthermore, apoc2 mutants fed a normal diet accumulate lipid and lipid-laden macrophages in the vasculature, which resemble early events in the development of human atherosclerotic lesions. In addition, apoc2 mutant embryos show ectopic overgrowth of pancreas. Taken together, our data suggest that the apoc2 mutant zebrafish is a robust and versatile animal model to study hypertriglyceridemia and the mechanisms involved in the pathogenesis of associated human diseases.

Apolipoprotein CII (ApocII) plays a key role in regulating lipoprotein lipase (LPL) in lipid metabolism and transport. Numerous polymorphisms within APOCII are reportedly associated with type 2 diabetes mellitus (T2DM), dyslipidemia, and aberrant plasma lipid levels. Few studies have investigated sequence variants at APOCII loci and their association with metabolic disorders. This study aimed to identify and characterize genetic variants by sequencing the full APOCII locus and its flanking sequences in a sample of the Kuwaiti Arab population, including patients with T2DM, hypertriglyceridemia, non-Arab patients with T2DM, and healthy Arab controls. A total of 52 variants were identified in the noncoding sequences: 45 single nucleotide polymorphisms, wherein five were novel, and seven insertion deletions. The minor allele frequency (MAF) of the 47 previously reported variants was similar to the global MAF and to that reported in major populations. Sequence variant analysis predicted a conserved role for APOCII with a potential role for rs5120 in T2DM and rs7133873 as an informative ethnicity marker. This study adds to the ongoing research that attempts to identify ethnicity-specific variants in the apolipoprotein gene loci and associated LPL genes to elucidate the molecular mechanisms of metabolic disorders.

Ischemic stroke is a disease with a very high incidence in the clinic, and hypertension is the most important variable risk factor of ischemic stroke. Studies have shown that intestinal microbes are involved in the occurrence and development of various diseases. This study aims to explore whether intestinal microbes play an important role in the pathogenesis of ischemic stroke in a hypertensive population. In this study, the inpatients in the Department of Neurology and Cardiology of the Second Affiliated Hospital of Shandong First Medical University in April 2021 were selected, including seven patients with hypertension complicated with ischemic stroke and only seven patients with hypertension. After collecting the stool samples of patients, the gene sequence of the samples was detected by 16S rRNA sequencing technology, and the double-ended 2 × 150 bp sequencing was carried out. After sequencing, the results were analyzed by diversity analysis, species difference analysis, species function difference analysis, and other bioinformatics tests. According to the test results, serum proteomics and biochemical blood tests were carried out to verify. There was no significant difference in α diversity and β diversity between hypertension complicated with the cerebral infarction and hypertension groups. LEfSe analysis showed that at the genus level, compared with the hypertension group, Bacteroides, UCG&#95;009, and Eisenbergiella had significantly increased relative abundance. The genera with relatively significantly reduced abundance are Ruminococcus&#95;gnavus&#95;group, Sutterellaceae, Burkholderia, and Prevotella and the LDA score of Prevotella is <  - 4, which indicates that there are significant differences. Compared with the blood biochemical indexes, the results showed that the level of APOA1 in hypertensive patients with ischemic stroke was significantly higher than that in hypertensive patients (p < 0.05), but there was no significant difference in total cholesterol (CHOL), triglyceride (TG), high-density lipoprotein (HDL), low-density lipoprotein (LDL), apolipoprotein B (APOB), and free fatty acid (NEFA). Proteomic analysis showed that there were 89 up-regulated genes and 51 down-regulated genes in the serum of the two groups, and the expression of APOC2 and APOC3 in the cerebral infarction group with hypertension was significantly higher than that in the hypertension group (p < 0.05). The intestinal diversity of patients with hypertension complicated with stroke is similar to that of patients with hypertension, but there are differences in microbiota, among which Prevotella is the most significant. Prevotella could affect lipid metabolism so that APOC2 and APOC3 in the blood are significantly increased, leading to cerebral artery atherosclerosis and, finally, ischemic stroke. This provides a new idea for preventing and treating ischemic stroke in patients with hypertension, but the mechanism of Prevotella acting on apolipoprotein needs further verification by basic medical research., (© 2023. The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.)

Human apolipoprotein (apo) C‐II is one of several plasma apolipoproteins that form amyloid deposits in vivo and is an independent risk factor for cardiovascular disease. Lipid‐free apoC‐II readily self‐assembles into twisted‐ribbon amyloid fibrils but forms straight, rod‐like amyloid fibrils in the presence of low concentrations of micellar phospholipids. Charge mutations exerted significantly different effects on rod‐like fibril formation compared to their effects on twisted‐ribbon fibril formation. For instance, the double mutant, K30D‐D69K apoC‐II, readily formed twisted‐ribbon fibrils, while the rate of rod‐like fibril formation in the presence of micellar phospholipid was negligible. Structural analysis of rod‐like apoC‐II fibrils, using hydrogen–deuterium exchange and NMR analysis showed exchange protection consistent with a core cross‐β structure comprising the C‐terminal 58–76 region. Molecular dynamics simulations of fibril arrangements for this region favoured a parallel cross‐β structure. X‐ray fibre diffraction data for aligned rod‐like fibrils showed a major meridional spacing at 4.6 Å and equatorial spacings at 9.7, 23.8 and 46.6 Å. The latter two equatorial spacings are not observed for aligned twisted‐ribbon fibrils and are predicted for a model involving two cross‐β fibrils in an off‐set antiparallel structure with four apoC‐II units per rise of the β‐sheet. This model is consistent with the mutational effects on rod‐like apoC‐II fibril formation. The lipid‐dependent polymorphisms exhibited by apoC‐II fibrils could determine the properties of apoC‐II in renal amyloid deposits and their potential role in the development of cardiovascular disease. [ABSTRACT FROM AUTHOR]

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APOA1 and APOB are the structural proteins of high-density lipoprotein and APOB-containing lipoproteins, such as low-density lipoprotein and very low-density lipoprotein, respectively. The 4 smaller APOCs (APOC1, APOC2, APOC3, and APOC4) are exchangeable apolipoproteins; they are readily transferred among high-density lipoproteins and APOB-containing lipoproteins. The APOCs regulate plasma triglyceride and cholesterol levels by modulating substrate availability and activities of enzymes interacting with lipoproteins and by interfering with APOB-containing lipoprotein uptake through hepatic receptors. Of the 4 APOCs, APOC3 has been best studied in relation to diabetes. Elevated serum APOC3 levels predict incident cardiovascular disease and progression of kidney disease in people with type 1 diabetes. Insulin suppresses APOC3 levels, and accordingly, elevated APOC3 levels associate with insulin deficiency and insulin resistance. Mechanistic studies in a mouse model of type 1 diabetes have demonstrated that APOC3 acts in the causal pathway of diabetes-accelerated atherosclerosis. The mechanism is likely due to the ability of APOC3 to slow the clearance of triglyceride-rich lipoproteins and their remnants, thereby causing an increased accumulation of atherogenic lipoprotein remnants in lesions of atherosclerosis. Less is known about the roles of APOC1, APOC2, and APOC4 in diabetes., Competing Interests: Disclosures Dr Bornfeldt serves on the scientific advisory board of Esperion Therapeutics. The other authors report no conflicts.

The article discusses the case of a juvenile-onset systemic lupus erythematosus (SLE) patient, who developed severe hypertriglyceridemia from anti-apolipoprotein C (apoC)-II autoantibodies. The patient has a history of malarrash and polyarthralgia and was observed to have hypertriglyceridemia, low high-density lipoprotein cholesterol (HDL-C), and low-density lipoprotein cholesterol (LDL-C). The patient was treated with diet therapy, bezafibrate, and mycophenolate mofetil.

Background: Amyloid signature proteins such as serum amyloid P component, apolipoprotein E (ApoE), and ApoA-IV generally co-localise with amyloid, regardless of the types of amyloid precursor protein or the organs. Most of these proteins derive from serum and have reportedly been involved in amyloid fibril formation and stabilisation, as well as in excretion and degradation of amyloid precursor proteins. However, the processes and mechanisms by which these specific proteins deposit together with amyloid fibrils have not been clarified., Methods: We analysed the binding of serum proteins to amyloid fibrils derived from amyloid β and insulin in vitro by using liquid chromatography-tandem mass spectrometry (LC-MS/MS)., Results: Specific serum proteins including ApoA-I, ApoE, ApoA-IV, ApoC-III and vitronectin adhered to amyloid fibrils at high concentrations in vitro . In addition, the profile of these proteins commonly occurred in both amyloid β and insulin amyloid fibrils and was mostly consistent with the composition of amyloid signature proteins. We also showed that high concentrations of serum proteins can adhere to amyloid fibrils in a short time., Conclusions: Our in vitro results suggest that amyloid signature proteins coexist with amyloid primarily dependent on the binding of each serum protein, in the extracellular fluid, to amyloid fibrils.

Microalbuminuria (MA) is an independent risk factor for atherosclerosis in patients with type 2 diabetes mellitus (T2DM). Postprandial lipemia is also associated with excess cardiovascular risk. However, the association between MA and postprandial lipemia in diabetes has not been investigated. A total of 64 patients with T2DM, 30 with and 34 without MA, were examined. Plasma total triglycerides (TGs), triglycerides contained in chylomicrons (CM-TG), and TGs in CM-deficient plasma were measured at baseline and every 2 h for 6 h after a mixed meal. Postheparin LPL and HL activities were also determined. Plasma levels of apolipoprotein A-V (apoA-V), apoC-II, and apoC-III were measured in the fasting state and 2 h postprandially. Patients with MA had higher postprandial total TG levels than those without MA (P < 0.001); this increase been attributed mainly to CM-TG. LPL activity and fasting concentrations of the measured apolipoproteins were not different between the studied groups, whereas HL activity was higher in the patients with MA. ApoC-II and apoC-III levels did not change postprandially in either study group, whereas apoA-V increased more in the patients with MA. These data demonstrate for the first time that MA is characterized by increased postprandial lipemia in patients with T2DM and may explain in part the excess cardiovascular risk in these patients.

Background Experimental data suggest that apolipoprotein (apo) C- II and C- III regulate triglyceride-rich lipoprotein ( TRL) metabolism, but there are limited studies in humans. We investigated the metabolic associations of TRLs with apoC- II and apoC- III concentrations and kinetics in women. Material and methods The kinetics of plasma apoC- II, apoC- III and very low-density lipoprotein ( VLDL) apoB-100 and triglycerides were measured in the postabsorptive state using stable isotopic techniques and compartmental modelling in 60 women with wide-ranging body mass index (19·5-32·9 kg/m2). Results Plasma apoC- II and apoC- III concentrations were positively associated with the concentrations of plasma triglycerides, VLDL1- and VLDL2-apoB-100 and triglyceride (all P < 0·05). ApoC- II production rate ( PR) was positively associated with VLDL1-apoB-100 concentration, VLDL1 triglyceride concentration and VLDL1 triglyceride PR, while apoC- II fractional catabolic rate ( FCR) was positively associated with VLDL1 triglyceride FCR (all P < 0·05). No significant associations were observed between apoC- II and VLDL2 apoB-100 or triglyceride kinetics. ApoC- III PR, but not FCR, was positively associated with VLDL1 triglyceride, and VLDL2-apoB-100 and triglyceride concentrations (all P < 0·05). No significant associations were observed between apoC- III and VLDL-apoB-100 and triglyceride kinetics. In multivariable analysis, including homoeostasis model assessment score, menopausal status and obesity, apoC- II concentration was significantly associated with plasma triglyceride, VLDL1-apoB-100 and VLDL1 triglyceride concentrations and PR. Using the same multivariable analysis, apoC- III was significantly associated with plasma triglyceride and VLDL1- and VLDL2-apoB-100 and triglyceride concentrations and FCR. Conclusions In women, plasma apoC- II and apoC- III concentrations are regulated by their respective PR and are significant, independent determinants of the kinetics and plasma concentrations of TRLs. [ABSTRACT FROM AUTHOR]

Backgrounds Familial apolipoprotein (apo) C-II deficiency is a very rare inherited disorder characterized by chylomicronemia. Since the discovery in 1978, reports on apo C-II deficient patients have been limited and only 13 different mutations in APOC2 , a gene encoding apo C-II protein, were identified. Objectives The objective is to investigate the biochemical and genetic features of a 3-month-old Bosniak girl with chylomicronemia whose apo C-II protein was undetectable in her plasma. Methods APOC2 , LPL , APOA5 , and GPIHBP1 were sequenced. Isoelectrofocusing and immunoblotting of chylomicrons and VLDL fraction from the patient were performed. Results Sequence analysis demonstrated a large deletion of 2978 base pairs in APOC2 , which encompassed exons 2, 3, and 4. The patient was homozygous for the deletion. The 5′ part of the breakpoint was located in an Alu Sx repetitive element in intron 1 of APOC2 , whereas the 3′ part of the breakpoint was in another Alu Sx between APOC2 and CLPTM1 , a gene flanking APOC2 . We speculate that the deletion was caused by a homologous recombination between two Alu Sx elements. No mutations were detected in LPL , APOA5 , and GPIHBP1 . Isoelectrofocusing and immunoblotting confirmed the absence of apo C-II protein. Conclusions We diagnosed the patient as having apo C-II deficiency and designated the novel large deletion as apo C-II Tuzla . This is the first description of apo C-II deficiency caused by Alu-Alu recombination in APOC2 . [ABSTRACT FROM AUTHOR]

Lipoprotein lipase (LPL) hydrolyzes triacylglycerol (TG) of TG-rich lipoproteins. We investigated the effects of sphingomyelin (SM) and cholesterol (Chol) on the lipolysis of lipid emulsions by LPL using human apolipoprotein C-II (apoC-II) or plasma as an activator. Kinetic studies of the lipolysis rates clearly demonstrated that the primary effect of the activator on the LPL reaction was not to increase the affinity of LPL for the emulsion surface, but to enhance LPL catalytic activity. Incorporation of SM into the emulsion surface caused increases in Km(app) and decreases in Vmax(app), indicating that SM inhibited lipolysis by decreasing both affinity for substrates and catalytic activity of LPL. SM was also found to affect possible factors related to the lipolysis rates; that is, SM increased TG solubility in surface layers and decreased apoC-II binding to the emulsion surface. Interestingly, Chol did not affect the lipolysis rates even though it decreased TG solubility and apoC-II binding. These results indicated that neither TG solubility nor amount of apoC-II binding were determinate factors in LPL-mediated lipolysis under physiological conditions. Our results suggest that the content of SM in the lipoprotein surface plays an important role by controlling lipoprotein lipase-mediated lipolysis, and that cholesterol enrichment in the lipoprotein surface has no influence on lipolysis, but may affect other metabolic processes such as uptake by the liver through the selectivity of apolipoprotein binding.—Arimoto, I., H. Saito, Y. Kawashima, K. Miyajima, and T. Handa. Effects of sphingomyelin and cholesterol on lipoprotein lipase-mediated lipolysis in lipid emulsions. J. Lipid Res. 1998. 39: 143–151.

[Display omitted] • Small heat-shock proteins populate a monomer–dimer-oligomer equilibrium. • The alpha-crystallin domain binds at fibril ends to inhibit elongation. • Chaperone-activity is inhibited by disulfide crosslinking at the dimer interface. • Monomers of the alpha-crystallin domain are proposed to interact with fibril ends. Small heat-shock proteins (sHSPs) are ubiquitously expressed molecular chaperones present in all kingdoms of life that inhibit protein misfolding and aggregation. Despite their importance in proteostasis, the structure–function relationships of sHSPs remain elusive. Human sHSPs are characterised by a central, highly conserved α-crystallin domain (ACD) and variable-length N- and C-terminal regions. The ACD forms antiparallel homodimers via an extended β-strand, creating a shared β-sheet at the dimer interface. The N- and C-terminal regions mediate formation of higher order oligomers that are thought to act as storage forms for chaperone-active dimers. We investigated the interactions of the ACD of two human sHSPs, αB-crystallin (αB-C) and Hsp27, with apolipoprotein C-II amyloid fibrils using analytical ultracentrifugation and nuclear magnetic resonance spectroscopy. The ACD was found to interact transiently with amyloid fibrils to inhibit fibril elongation and naturally occurring fibril end-to-end joining. This interaction was sensitive to the concentration of fibril ends indicating a 'fibril-capping' interaction. Furthermore, resonances arising from the ACD monomer were attenuated to a greater extent than those of the ACD dimer in the presence of fibrils, suggesting that the monomer may bind fibrils. This hypothesis was supported by mutagenesis studies in which disulfide cross-linked ACD dimers formed by both αB-C and Hsp27 were less effective at inhibiting amyloid fibril elongation and fibril end-to-end joining than ACD constructs lacking disulfide cross-linking. Our results indicate that sHSP monomers inhibit amyloid fibril elongation, highlighting the importance of the dynamic oligomeric nature of sHSPs for client binding. [ABSTRACT FROM AUTHOR]