Olezarsen for Hypertriglyceridemia in Patients at High Cardiovascular Risk

BACKGROUND

Reducing the levels of triglycerides and triglyceride-rich lipoproteins remains an unmet clinical need. Olezarsen is an antisense oligonucleotide targeting messenger RNA for apolipoprotein C-III (APOC3), a genetically validated target for triglyceride lowering.

METHODS

In this phase 2b, randomized, controlled trial, we assigned adults either with moderate hypertriglyceridemia (triglyceride level, 150 to 499 mg per deciliter) and elevated cardiovascular risk or with severe hypertriglyceridemia (triglyceride level, ≥500 mg per deciliter) in a 1:1 ratio to either a 50-mg or 80-mg cohort. Patients were then assigned in a 3:1 ratio to receive monthly subcutaneous olezarsen or matching placebo within each cohort. The primary outcome was the percent change in the triglyceride level from baseline to 6 months, reported as the difference between each olezarsen group and placebo. Key secondary outcomes were changes in levels of APOC3, apolipoprotein B, non-high-density lipoprotein (HDL) cholesterol, and low-density lipoprotein (LDL) cholesterol.

RESULTS

A total of 154 patients underwent randomization at 24 sites in North America. The median age of the patients was 62 years, and the median triglyceride level was 241.5 mg per deciliter. The 50-mg and 80-mg doses of olezarsen reduced triglyceride levels by 49.3 percentage points and 53.1 percentage points, respectively, as compared with placebo (P<0.001 for both comparisons). As compared with placebo, each dose of olezarsen also significantly reduced the levels of APOC3, apolipoprotein B, and non-HDL cholesterol, with no significant change in the LDL cholesterol level. The risks of adverse events and serious adverse events were similar in the three groups. Clinically meaningful hepatic, renal, or platelet abnormalities were uncommon, with similar risks in the three groups.

CONCLUSIONS

In patients with predominantly moderate hypertriglyceridemia at elevated cardiovascular risk, olezarsen significantly reduced levels of triglycerides, apolipoprotein B, and non-HDL cholesterol, with no major safety concerns identified. (Funded by Ionis Pharmaceuticals; Bridge-TIMI 73a ClinicalTrials.gov number, NCT05355402.).

Olezarsen, Acute Pancreatitis, and Familial Chylomicronemia Syndrome

BACKGROUND

Familial chylomicronemia syndrome is a genetic disorder associated with severe hypertriglyceridemia and severe acute pancreatitis. Olezarsen reduces the plasma triglyceride level by reducing hepatic synthesis of apolipoprotein C-III.

METHODS

In a phase 3, double-blind, placebo-controlled trial, we randomly assigned patients with genetically identified familial chylomicronemia syndrome to receive olezarsen at a dose of 80 mg or 50 mg or placebo subcutaneously every 4 weeks for 53 weeks. There were two primary end points: the difference between the 80-mg olezarsen group and the placebo group in the percent change in the fasting triglyceride level from baseline to 6 months, and (to be assessed if the first was significant) the difference between the 50-mg olezarsen group and the placebo group. Secondary end points included the mean percent change from baseline in the apolipoprotein C-III level and an independently adjudicated episode of acute pancreatitis.

RESULTS

A total of 66 patients underwent randomization; 22 were assigned to the 80-mg olezarsen group, 21 to the 50-mg olezarsen group, and 23 to the placebo group. At baseline, the mean (±SD) triglyceride level among the patients was 2630±1315 mg per deciliter, and 71% had a history of acute pancreatitis within the previous 10 years. Triglyceride levels at 6 months were significantly reduced with the 80-mg dose of olezarsen (-43.5%; 95% confidence interval [CI], -69.1 to -17.9; P<0.001) but not with the 50-mg dose (-22.4%; 95% CI, -47.2 to 2.5; P = 0.08). The difference in the mean percent change in the apolipoprotein C-III level from baseline to 6 months in the 80-mg group as compared with the placebo group was -73.7% (95% CI, -94.6 to -52.8) and between the 50-mg group as compared with the placebo group was -65.5% (95% CI, -82.6 to -48.3). By 53 weeks, 11 episodes of acute pancreatitis had occurred in the placebo group, and 1 episode had occurred in each olezarsen group (rate ratio [pooled olezarsen groups vs. placebo], 0.12; 95% CI, 0.02 to 0.66). Adverse events of moderate severity that were considered by a trial investigator at the site to be related to the trial drug or placebo occurred in 4 patients in the 80-mg olezarsen group.

CONCLUSIONS

In patients with familial chylomicronemia syndrome, olezarsen may represent a new therapy to reduce plasma triglyceride levels. (Funded by Ionis Pharmaceuticals; Balance ClinicalTrials.gov number, NCT04568434.).

RANK ligand converts the NCoR/HDAC3 co-repressor to a PGC1β- and RNA-dependent co-activator of osteoclast gene expression

The nuclear receptor co-repressor (NCoR) complex mediates transcriptional repression dependent on histone deacetylation by histone deacetylase 3 (HDAC3) as a component of the complex. Unexpectedly, we found that signaling by the receptor activator of nuclear factor κB (RANK) converts the NCoR/HDAC3 co-repressor complex to a co-activator of AP-1 and NF-κB target genes that are required for mouse osteoclast differentiation. Accordingly, the dominant function of NCoR/HDAC3 complexes in response to RANK signaling is to activate, rather than repress, gene expression. Mechanistically, RANK signaling promotes RNA-dependent interaction of the transcriptional co-activator PGC1β with the NCoR/HDAC3 complex, resulting in the activation of PGC1β and inhibition of HDAC3 activity for acetylated histone H3. Non-coding RNAs Dancr and Rnu12, which are associated with altered human bone homeostasis, promote NCoR/HDAC3 complex assembly and are necessary for RANKL-induced osteoclast differentiation in vitro. These findings may be prototypic for signal-dependent functions of NCoR in other biological contexts.

APOC3 inhibition with volanesorsen reduces hepatic steatosis in patients with severe hypertriglyceridemia

ApoC-III inhibits lipoprotein lipase and hepatic uptake of triglyceride-rich lipoproteins. It is unknown whether targeting apoC-III affects hepatic steatosis in patients with hypertriglyceridemia. We studied the effect of volanesorsen, a potent antisense oligonucleotide targeting APOC3 mRNA, on hepatic fat fraction (HFF) assessed by MRI in patients with severe hypertriglyceridemia (SHTG, triglycerides ≥500 mg/dL), familial partial lipodystrophy (FPL, triglycerides ≥200 mg/dL) and familial chylomicronemia syndrome (FCS, triglycerides ≥750 mg/dL). The data were evaluated individually in COMPASS (SHTG), APPROACH (FCS), and BROADEN (FPL) trials. The baseline absolute HFF were elevated in all three trials and ranged from 6.3-18.1%. In COMPASS, compared to placebo, volanesorsen significantly reduced the absolute HFF by -3.02% (95% CI, (-5.60, -0.60), p = 0.009) (placebo-adjusted % change from baseline -24.2%, p = 0.034) from baseline to 6 months. In APPROACH a non-significant absolute -1.0% (95% CI, -2.9, 0.0, p = 0.13) reduction in HFF was noted from baseline to 12 months (placebo-adjusted % change from baseline -37.1%, p = 0.20). In BROADEN volanesorsen significantly reduced the absolute HFF by -8.34% (95% CI, -13.01, -3.67, p = 0.001) from baseline to 12 months (placebo-adjusted % change from baseline -52.7%, p = 0.004). In all 3 trials individually, a strong inverse correlation was present between the baseline HFF and the change in HFF in the volanesorsen groups, but not in the placebo groups. In conclusion, apoC-III inhibition with volanesorsen has favorable effects in HFF in patients with different etiologies of hypertriglyceridemia.

B-1b Cells Have Unique Functional Traits Compared to B-1a Cells at Homeostasis and in Aged Hyperlipidemic Mice With Atherosclerosis

Immunoglobulin M (IgM) to oxidation specific epitopes (OSE) are inversely associated with atherosclerosis in mice and humans. The B-1b subtype of B-1 cells secrete IgM to OSE, and unlike B-1a cells, are capable of long-lasting IgM memory. What attributes make B-1b cells different than B-1a cells is unknown. Our objectives were to determine how B-1b cells produce more IgM compared to B-1a cells at homeostatic condition and to see the differences in the B-1a and B-1b cell distribution and IgM CDR-H3 sequences in mice with advanced atherosclerosis. Here, in-vivo studies demonstrated greater migration to spleen, splenic production of IgM and plasma IgM levels in ApoE^-/-Rag1^-/- mice intraperitoneally injected with equal numbers of B-1b compared to B-1a cells. Bulk RNA seq analysis and flow cytometry of B-1a and B-1b cells identified CCR6 as a chemokine receptor more highly expressed on B-1b cells compared to B-1a. Knockout of CCR6 resulted in reduced B-1b cell migration to the spleen. Moreover, B-1b cell numbers were significantly higher in spleen of aged atherosclerotic ApoE^-/- mice compared to young ApoE^-/- mice. Single cell sequencing results of IgHM in B-1a and B-1b cells from peritoneal cavity and spleen of atherosclerotic aged ApoE^-/- mice revealed significantly more N additions at the V-D and D-J junctions, greater diversity in V region usage and CDR-H3 sequences in B-1b compared to B-1a cells. In summary, B-1b cells demonstrated enhanced CCR6-mediated splenic migration, IgM production, and IgM repertoire diversification compared to B-1a cells. These findings suggest that potential strategies to selectively augment B-1b cell numbers and splenic trafficking could lead to increased and more diverse IgM targeting OSE to limit atherosclerosis.

Systematic analysis of naturally occurring insertions and deletions that alter transcription factor spacing identifies tolerant and sensitive transcription factor pairs

Regulation of gene expression requires the combinatorial binding of sequence-specific transcription factors (TFs) at promoters and enhancers. Prior studies showed that alterations in the spacing between TF binding sites can influence promoter and enhancer activity. However, the relative importance of TF spacing alterations resulting from naturally occurring insertions and deletions (InDels) has not been systematically analyzed. To address this question, we first characterized the genome-wide spacing relationships of 73 TFs in human K562 cells as determined by ChIP-seq (chromatin immunoprecipitation sequencing). We found a dominant pattern of a relaxed range of spacing between collaborative factors, including 45 TFs exclusively exhibiting relaxed spacing with their binding partners. Next, we exploited millions of InDels provided by genetically diverse mouse strains and human individuals to investigate the effects of altered spacing on TF binding and local histone acetylation. These analyses suggested that spacing alterations resulting from naturally occurring InDels are generally tolerated in comparison to genetic variants directly affecting TF binding sites. To experimentally validate this prediction, we introduced synthetic spacing alterations between PU.1 and C/EBPβ binding sites at six endogenous genomic loci in a macrophage cell line. Remarkably, collaborative binding of PU.1 and C/EBPβ at these locations tolerated changes in spacing ranging from 5 bp increase to >30 bp decrease. Collectively, these findings have implications for understanding mechanisms underlying enhancer selection and for the interpretation of non-coding genetic variation.

Publisher Correction: Oxidized phospholipids are proinflammatory and proatherogenic in hypercholesterolaemic mice

In this Letter, affiliation number 1 was originally missing from the HTML; the affiliations were missing for author Ming-Yow Hung in the HTML; and the Fig. 4 legend erroneously referred to panels a-h, instead of a-g. These errors have been corrected online.

Oxidized phospholipids are proinflammatory and proatherogenic in hypercholesterolaemic mice

Oxidized phospholipids (OxPL) are ubiquitous, are formed in many inflammatory tissues, including atherosclerotic lesions, and frequently mediate proinflammatory changes ¹ . Because OxPL are mostly the products of non-enzymatic lipid peroxidation, mechanisms to specifically neutralize them are unavailable and their roles in vivo are largely unknown. We previously cloned the IgM natural antibody E06, which binds to the phosphocholine headgroup of OxPL, and blocks the uptake of oxidized low-density lipoprotein (OxLDL) by macrophages and inhibits the proinflammatory properties of OxPL^2-4. Here, to determine the role of OxPL in vivo in the context of atherogenesis, we generated transgenic mice in the Ldlr^-/- background that expressed a single-chain variable fragment of E06 (E06-scFv) using the Apoe promoter. E06-scFv was secreted into the plasma from the liver and macrophages, and achieved sufficient plasma levels to inhibit in vivo macrophage uptake of OxLDL and to prevent OxPL-induced inflammatory signalling. Compared to Ldlr^-/- mice, Ldlr ^-/- E06-scFv mice had 57-28% less atherosclerosis after 4, 7 and even 12 months of 1% high-cholesterol diet. Echocardiographic and histologic evaluation of the aortic valves demonstrated that E06-scFv ameliorated the development of aortic valve gradients and decreased aortic valve calcification. Both cholesterol accumulation and in vivo uptake of OxLDL were decreased in peritoneal macrophages, and both peritoneal and aortic macrophages had a decreased inflammatory phenotype. Serum amyloid A was decreased by 32%, indicating decreased systemic inflammation, and hepatic steatosis and inflammation were also decreased. Finally, the E06-scFv prolonged life as measured over 15 months. Because the E06-scFv lacks the functional effects of an intact antibody other than the ability to bind OxPL and inhibit OxLDL uptake in macrophages, these data support a major proatherogenic role of OxLDL and demonstrate that OxPL are proinflammatory and proatherogenic, which E06 counteracts in vivo. These studies suggest that therapies inactivating OxPL may be beneficial for reducing generalized inflammation, including the progression of atherosclerosis, aortic stenosis and hepatic steatosis.

Massively Parallel Sequencing of Peritoneal and Splenic B Cell Repertoires Highlights Unique Properties of B-1 Cell Antibodies

B-1 cells are a unique subset of B cells that are positively selected for expressing autoreactive BCRs. We isolated RNA from peritoneal (B-1a, B-1b, B-2) and splenic (B-1a, marginal zone, follicular) B cells from C57BL/6 mice and used 5'-RACE to amplify the IgH V region using massively parallel sequencing. By analyzing 379,000 functional transcripts, we demonstrate that B-1a cells use a distinct and restricted repertoire. All B-1 cell subsets, especially peritoneal B-1a cells, had a high proportion of sequences without N additions, suggesting predominantly prenatal development. Their transcripts differed markedly and uniquely contained V_H11 and V_H12 genes, which were rearranged only with a restricted selection of D and J genes, unlike other V genes. Compared to peritoneal B-1a, the peritoneal B-1b repertoire was larger, had little overlap with B-1a, and most sequences contained N additions. Similarly, the splenic B-1a repertoire differed from peritoneal B-1a sequences, having more unique sequences and more frequent N additions, suggesting influx of B-1a cells into the spleen from nonperitoneal sites. Two CDR3s, previously described as Abs to bromelain-treated RBCs, comprised 43% of peritoneal B-1a sequences. We show that a single-chain variable fragment designed after the most prevalent B-1a sequence bound oxidation-specific epitopes such as the phosphocholine of oxidized phospholipids. In summary, we provide the IgH V region library of six murine B cell subsets, including, to our knowledge for the first time, a comparison between B-1a and B-1b cells, and we highlight qualities of B-1 cell Abs that indicate unique selection processes.

Abstract 221: B-1b Cells Produce IgM to Malondialdehyde-Modified Low Density Lipoprotein in Perivascular Adipose Tissue in Response to Immunization And Attenuate Diet Induced Atherosclerosis

Background: B-1b cells are capable of long-lasting IgM memory and secrete more IgM, particularly malondialdehyde-modified low density lipoprotein (MDA-LDL) specific IgM than B-1a cells after transfer into hyperlipidemic Rag1 -/- mice. Id3 is a basic helix-loop-helix protein and dominant negative inhibitor of E proteins. B cell specific Id3 deficiency (Id3 BKO ) increases B-1b cell numbers systemically and provides atheroprotection. Adipose tissue is a source of B-1b-derived IgM and regulates inflammatory cytokine production from M1 macrophages locally. Perivascular adipose tissue (PVAT) has been implicated in regulation of atherosclerosis. However, the effect of B cell specific Id3 deficiency on B-1 cell responses in PVAT is not yet known. Also, whether these B-1b cells respond to MDA-LDL immunization is unknown.

Hypothesis: B-1b cells are present in PVAT and produce MDA-LDL specific IgM in PVAT, and immunization with MDA-LDL can enhance B-1b-mediated atheroprotection.

Methods and Results: Flow Cytometry and Enzyme-Linked ImmunoSpot (ELISPOT) analysis of PVAT of normal chow diet fed young mice demonstrated that ApoE.Id3 BKO mice have significantly higher numbers of B-1b cells and IgM secreting cells but not B-2 and B-1a cell numbers in PVAT compared to ApoE.Id3 WT mice. ELISPOT demonstrated that the % of MDA-LDL specific IgM of total IgM secreting cells was significantly greater in PVAT, but not in spleen or bone marrow, of ApoE.Id3 BKO mice compared to ApoE.Id3 WT mice, suggesting that modified lipids such as MDA-LDL in plaques and PVAT may stimulate local B-1b cells to secrete MDA-LDL specific IgM. Adoptive transfer of B-1b cells into ApoE.Rag1 -/- mice followed by MDA-LDL+PPS3 (pneumococcal polysaccharide) immunization, increased plasma IgM to MDA-LDL after 2 weeks and significantly attenuated atherosclerosis after 16 weeks of Western diet compared to PBS injected mice and B-1b cells transferred mice with PBS immunization.

Conclusion: B-1b cells produce IgM to MDA-LDL in PVAT. MDA-LDL immunization increased IgM to MDA-LDL after two weeks and attenuated diet-induced atherosclerosis. Taken together, results suggest that B-1b cells may regulate atherosclerosis through both local and systemic IgM production.

Abstract 361: Oxidized Phospholipids Are Proinflammatory and Proatherogenic

Oxidized phospholipids (OxPL) are ubiquitously generated during inflammation, and found on apoptotic cells, OxLDL, and Lp(a). They facilitate uptake of OxLDL by macrophages (Mac) and mediate cellular inflammatory responses. The E06 natural IgM binds to the PC of OxPL, neutralizing biological effects and inhibiting OxLDL uptake by Mac. To determine the role of OxPL in atherogenesis, we generated transgenic mice expressing a single chain variant (scFv) of E06 in Ldlr background (E06-Tg). E06-scFv was secreted into plasma, bound to OxLDL and had sufficient titer to inhibit OxLDL uptake into Mac. E06-Tg or Ldlr mice were fed 1% Chol diet for 4, 7 or 12 months (n=12-15 mice/group). Plasma Chol was ~ 1600 mg/dL in all mice. Atherosclerosis decreased in E06-Tg mice: En face lesions decreased 57%, 34% and 28%, and aortic root lesions decreased 55%, 41% and 26% at 4, 7 and 12-months, respectively. OxLDL uptake by Macs was decreased: Thus, in E06-Tg mice, the uptake by peritoneal Mac of fluorescently-labeled OxLDL injected ip was decreased ~ 50%, as was peritoneal Mac Chol content. As Macs secrete E06-scFv, we performed BMT from E06-Tg donors into irradiated Ldlr recipients (n=10-12): This also decreased lesions 31% compared to BMT from control donors, even though plasma titers of E06-scFv were ~10% of Tg mice. Overexpression of E06-scFv was anti-inflammatory: Thus, in E06-Tg mice, both peritoneal and aortic wall resident macrophages exhibited decreased inflammatory gene expression, and phenotypic switches from M1 to M2 analyzed by RNAseq and FACS. Further, in E06-Tg mice, plasma SAA levels were reduced 32%, and hepatic steatosis was also decreased (-50% in both TG and Chol), as was hepatic inflammatory gene expression. Finally, E06-scFv attenuated both a progressive increase in aortic valve gradient (via echocardiography) and calcification in aged Ldlr mice. The E06-scFv lacks functional effects of an intact antibody other than the ability to “neutralize” OxPL. Thus, these data demonstrate that OxPL are profoundly proatherogenic and proinflammatory, which E06 counteracts in vivo . Neutralizing OxPL may therefore reduce the progression of atherosclerosis and cardiovascular events and more generally, represents a novel strategy to safely attenuate inflammation.

Protective Role for B-1b B Cells and IgM in Obesity-Associated Inflammation, Glucose Intolerance, and Insulin Resistance

OBJECTIVE

Little is known about the role(s) B cells play in obesity-induced metabolic dysfunction. This study used a mouse with B-cell-specific deletion of Id3 (Id3(Bcell KO)) to identify B-cell functions involved in the metabolic consequences of obesity.

APPROACH AND RESULTS

Diet-induced obese Id3(Bcell KO) mice demonstrated attenuated inflammation and insulin resistance in visceral adipose tissue (VAT), and improved systemic glucose tolerance. VAT in Id3(Bcell KO) mice had increased B-1b B cells and elevated IgM natural antibodies to oxidation-specific epitopes. B-1b B cells reduced cytokine production in VAT M1 macrophages, and adoptively transferred B-1b B cells trafficked to VAT and produced natural antibodies for the duration of 13-week studies. B-1b B cells null for Id3 demonstrated increased proliferation, established larger populations in Rag1(-/-) VAT, and attenuated diet-induced glucose intolerance and VAT insulin resistance in Rag1(-/-) hosts. However, transfer of B-1b B cells unable to secrete IgM had no effect on glucose tolerance. In an obese human population, results provided the first evidence that B-1 cells are enriched in human VAT and IgM antibodies to oxidation-specific epitopes inversely correlated with inflammation and insulin resistance.

CONCLUSIONS

NAb-producing B-1b B cells are increased in Id3(Bcell KO) mice and attenuate adipose tissue inflammation and glucose intolerance in diet-induced obese mice. Additional findings are the first to identify VAT as a reservoir for human B-1 cells and to link anti-inflammatory IgM antibodies with reduced inflammation and improved metabolic phenotype in obese humans.

B-1b Cells Secrete Atheroprotective IgM and Attenuate Atherosclerosis

RATIONALE

B cells contribute to atherosclerosis through subset-specific mechanisms. Whereas some controversy exists about the role of B-2 cells, B-1a cells are atheroprotective because of secretion of atheroprotective IgM antibodies independent of antigen. B-1b cells, a unique subset of B-1 cells that respond specifically to T-cell-independent antigens, have not been studied within the context of atherosclerosis.

OBJECTIVE

To determine whether B-1b cells produce atheroprotective IgM antibodies and function to protect against diet-induced atherosclerosis.

METHODS AND RESULTS

We demonstrate that B-1b cells are sufficient to produce IgM antibodies against oxidation-specific epitopes on low-density lipoprotein both in vitro and in vivo. In addition, we demonstrate that B-1b cells provide atheroprotection after adoptive transfer into B- and T-cell deficient (Rag1(-/-)Apoe(-/-)) hosts. We implicate inhibitor of differentiation 3 (Id3) in the regulation of B-1b cells as B-cell-specific Id3 knockout mice (Id3(BKO)Apoe(-/-)) have increased numbers of B-1b cells systemically, increased titers of oxidation-specific epitope-reactive IgM antibodies, and significantly reduced diet-induced atherosclerosis when compared with Id3(WT)Apoe(-/-) controls. Finally, we report that the presence of a homozygous single nucleotide polymorphism in ID3 in humans that attenuates Id3 function is associated with an increased percentage of circulating B-1 cells and anti-malondialdehyde-low-density lipoprotein IgM suggesting clinical relevance.

CONCLUSIONS

These results provide novel evidence that B-1b cells produce atheroprotective oxidation-specific epitope-reactive IgM antibodies and protect against atherosclerosis in mice and suggest that similar mechanisms may occur in humans.

Abstract 21: B-1b Cells Secrete Atheroprotective IgM and Attenuate Atherosclerosis

Rationale: B cells contribute to atherosclerosis through subset specific mechanisms. Whereas some controversy exists about the role of B-2 B cells, B-1a B cells are atheroprotective. The function of B-1b B cells, a unique subset of B-1 cells that can produce T cell-independent (TI) memory, has not been studied within the context of atherosclerosis.

Objective: To determine whether B-1b cells produce atheroprotective IgM antibodies and function to protect against diet induced atherosclerosis.

Methods and Results: We demonstrate that B-1b cells are sufficient to produce IgM antibodies against oxidation specific epitopes (OSE) on LDL in vitro in response to activating stimulation. Additionally, we demonstrate that B-1b cells provide direct atheroprotection after adoptive transfer into B and T cell deficient (Rag1-/-Apoe-/-) hosts. To support these findings, we utilize a B cell specific Id3 knockout mouse model (Id3BKO), which develops increased numbers of B-1b cells systemically, to demonstrate that these mice develop attenuated atherosclerosis and increased OSE IgM antibodies compared to wild-type controls (Id3WT) after being fed a Western diet for 16 weeks. Finally, we report that the presence of a functionally relevant homozygous SNP in ID3 in humans associates with increased proportion of circulating B-1 cells and anti-MDA-LDL IgM and that the percentage of circulating B-1 cells is directly associated with the amount of anti-MDA-LDL IgM suggesting clinical relevance.

Conclusions: These results provide novel evidence that B-1b B cells produce atheroprotective OSE IgM antibodies and protect against atherosclerosis in mice, and suggest that similar mechanisms may occur in humans.

Circulating microparticles carry oxidation-specific epitopes and are recognized by natural IgM antibodies

Oxidation-specific epitopes (OSEs) present on apoptotic cells and oxidized low density lipoprotein (OxLDL) represent danger-associated molecular patterns that are recognized by different arcs of innate immunity, including natural IgM antibodies. Here, we investigated whether circulating microparticles (MPs), which are small membrane vesicles released by apoptotic or activated cells, are physiological carriers of OSEs. OSEs on circulating MPs isolated from healthy donors and patients with ST-segment elevation myocardial infarction (STE-MI) were characterized by flow cytometry using a panel of OSE-specific monoclonal antibodies. We found that a subset of MPs carry OSEs on their surface, predominantly malondialdehyde (MDA) epitopes. Consistent with this, a majority of IgM antibodies bound on the surface of circulating MPs were found to have specificity for MDA-modified LDL. Moreover, we show that MPs can stimulate THP-1 (human acute monocytic leukemia cell line) and human primary monocytes to produce interleukin 8, which can be inhibited by a monoclonal IgM with specificity for MDA epitopes. Finally, we show that MDA⁺ MPs are elevated at the culprit lesion site of patients with STE-MI. Our results identify a subset of OSE⁺ MPs that are bound by OxLDL-specific IgM. These findings demonstrate a novel mechanism by which anti-OxLDL IgM antibodies could mediate protective functions in CVD.

Interaction of protein C inhibitor with the type II transmembrane serine protease enteropeptidase

The serine protease inhibitor protein C inhibitor (PCI) is expressed in many human tissues and exhibits broad protease reactivity. PCI binds glycosaminoglycans and certain phospholipids, which modulate its inhibitory activity. Enteropeptidase (EP) is a type II transmembrane serine protease mainly found on the brush border membrane of epithelial cells in the duodenum, where it activates trypsinogen to initiate the digestion of food proteins. Some active EP is also present in duodenal fluid and has been made responsible for causing pancreatitis in case of duodeno-pancreatic reflux. Together with its substrate trypsinogen, EP is furthermore present in the epidermis and in some cancer cells. In this report, we show that PCI inhibited EP with an apparent 2nd order rate constant of 4.48 × 10(4) M(-1) s(-1). Low molecular weight (LMWH) and unfractionated heparin (UFH) slightly reduced the inhibitory effect of PCI. The SI (stoichiometry of inhibition) value for the inhibition of EP by PCI was 10.8 in the absence and 17.9 in the presence of UFH (10 U/ml). By inhibiting trypsin, chymotrypsin, and additionally EP, PCI might play a role in the protection of the pancreas from autodigestion. Furthermore the interaction of PCI with EP may influence the regulation of epithelial differentiation.