Citations

Importance Elevated low-density lipoprotein cholesterol (LDL-C) is a modifiable risk factor for cardiovascular disease, the leading cause of premature death worldwide. Assessing the LDL-C–related burden is critical for guiding prevention and treatment strategies. Objectives To estimate the global, regional, and national burden of ischemic heart disease and ischemic stroke attributable to elevated LDL-C (relative to 35-54 mg/dL) from 1990 to 2023 and to quantify the contributions of population growth, aging, risk-deleted burden, and exposure changes to burden trends. Design, Setting, and Population This comparative risk assessment, part of the Global Burden of Disease Study 2023, estimated population-level LDL-C exposure and associated health loss in 204 countries and territories. Mean LDL-C levels were estimated using spatiotemporal gaussian process regression based on 806 studies across 161 countries. Relative risks were derived from meta-analyses of 38 randomized clinical trials. Population-attributable fractions for deaths and disability-adjusted life-years (DALYs) were estimated by age and sex for adults aged 25 years or older from 1990 to 2023, with 95% uncertainty intervals. Exposure Population-level LDL-C concentrations. Main Outcomes and Measures Population-attributable fractions, counts, and rates (all ages and age standardized per 100 000) of LDL-C–attributable deaths and DALYs from ischemic heart disease and ischemic stroke, with uncertainty intervals. Results In 2023, elevated LDL-C accounted for 3.6 million deaths (95% uncertainty interval, 2.2-5.4 million; 6.0% of global mortality) and 90.7 million DALYs (95% uncertainty interval, 58.9-123.3 million; 3.2% of DALYs). Although global all-ages rates remained stable, age-standardized death and DALY rates decreased by 45.6% and 39.5%, respectively, since 1990. In 2023, age-standardized LDL-C–attributable DALY rates were highest in Eastern Europe and lowest in high-income Asia-Pacific. One-third of the global LDL-C burden occurred in India and China. Population growth and aging drove the increasing burden, with notable regional disparities in LDL-C exposure and risk-deleted DALY rates shifting toward middle-sociodemographic settings. Conclusions and Relevance Despite declining age-standardized rates, the absolute LDL-C burden has increased since 1990 due to demographic changes and has shifted toward middle-sociodemographic countries. Measurement and surveillance gaps persist. Strengthened prevention, diagnosis, and treatment access strategies are essential to mitigate the health burden of LDL-C.

Abstract The hallmark of heparin-induced thrombocytopenia (HIT) is the presence of immunoglobulin G (IgG) antibodies against platelet factor 4/heparin (PF4/H) complexes, typically detected by PF4/H enzyme-linked immunosorbent assay (ELISA); thus, negative ELISA results are commonly used to exclude this diagnosis. Here, we report a prevalent yet previously unrecognized subset of antibodies that are undetectable by PF4/H ELISA (ELISA−) but activate platelets in the PF4-dependent P-selectin expression assay (PEA+). In 11 patients with clinically confirmed HIT who tested positive in both PF4/H ELISA and platelet activation assays, ELISA−PEA+ antibodies accounted for 65% ± 19% of total platelet-activating IgG activity and coexisted with ELISA+PEA+ antibodies. Consistent with this finding, single-cell cloning from 7 patients with HIT identified 23 PEA+ antibody-producing B-cell clones, of which 17 were ELISA−, outnumbering the ELISA+ clones. Functionally, ELISA−PEA+ antibodies closely resembled ELISA+PEA+ antibodies: platelet binding and activation required exogenous PF4 and were inhibited by FcγRIIA blockade, high-dose heparin, or Fab fragments made from ELISA+PEA+ antibodies. Importantly, these antibodies induced thrombocytopenia in a humanized mouse model of HIT. Despite lacking PF4/H reactivity in ELISAs, they recognize PF4 on platelets and showed no appreciable binding to neutrophil-activating peptide-2, interleukin-8, or PF4 alone. Structurally, these antibodies were heterogeneous, with a subset sharing heavy-chain features with ELISA+PEA+ antibodies. Collectively, our findings demonstrate that ELISA−PEA+ antibodies are a common, previously unrecognized feature of HIT, with functional relevance, supporting the possibility that they play an important, perhaps even central, role in HIT pathogenesis. Defining their prevalence, kinetics, and clinical impact deserves high priority for further investigation.

Heparin-induced thrombocytopenia (HIT) is a severe complication of heparin therapy, driven by IgG antibodies (Abs) that target platelet factor 4 (PF4) bound to heparin, resulting in platelet activation and a pro-thrombotic state. The PF4/Heparin (PF4/H) ELISA is the most commonly used screening assay for HIT due to its wide accessibility and high sensitivity. Despite its limited specificity, resulting in only a small fraction of positive cases progressing to actual HIT, PF4/H ELISA remains a critical tool in initial diagnostics. It is generally believed that HIT patients produce two types of Abs - those that bind to PF4/H and may or may not activate platelets. However, there are documented but rare HIT cases with an atypical profile: Abs testing negative in the PF4/H ELISA (ELISA-) but capable of platelet activation, suggesting the presence of a third type of Abs - those that activate platelets but can't recognize PF4/H complex. Since a PF4/H ELISA- result typically excludes an HIT diagnosis, overseeing these cases could lead to the resumption of heparin, potentially resulting in life-threatening thrombosis. Additionally, in HIT cases with a positive ELISA test profile, or classic HIT cases, levels of platelet-activating Abs and PF4/H-reactive Abs are not always correlated, suggesting the presence of ELISA- platelet-activating Abs. We thus investigated whether ELISA- platelet-activating Abs are present in classic HIT. To identify and characterize ELISA- Abs at the serological level, we firstly purified IgG Abs from the plasma of 5 healthy donors (HD) and 8 HIT patients using protein A beads, followed by the depletion of PF4/H-binding Abs using PF4/H-coated Sepharose beads. The efficiency of IgG purification and PF4/H-specific IgG depletion was confirmed by IgG and PF4/H ELISA. P-selectin expression assay (PEA) was conducted to evaluate the platelet activating ability of purified IgG pre and post depletion of PF4/H-specific Abs. We found that variable, but significant levels of platelet-activating Abs exist in the PF4/H non-reactive IgG portion in all 8 HIT samples, but none of the HD samples. Closely resembling those found in the PF4/H-reactive Abs in HIT patients' plasma, platelet activation induced by post-depletion Abs relied on exogenous PF4 and FcγRIIa and was inhibited by high-dose heparin. These data demonstrate that PF4/H non-reactive IgG Abs coexist with PF4/H-reactive Abs and may contribute to platelet activation in HIT patients. To verify these findings at the clonal level, we conducted single B-cell culture to induce antibody secretion by the cultured B cells from patients experiencing clinical manifestations of HIT. We screened clonal Abs made by 1506 single IgG1+ B cells isolated from peripheral blood mononuclear cells (PBMCs) of seven HIT patients and identified 18 clones capable of platelet activation. Of these, 13 were unable to bind to PF4/H. The functionality of these Abs was confirmed by recombinant Abs derived from single B-cell clones. This finding suggests that PF4/H non-reactive platelet-activating Abs exist at a higher frequency than those that bind to PF4/H. Interestingly, even though these Abs tested negative in the PF4/H ELISA, they were able to bind to the surface of PF4-treated platelets, and their platelet activation ability correlated with platelet binding affinity, suggesting a potential method for their detection. In summary, our study identified a novel group of potentially pathogenic Abs in HIT that, while unable to recognize the PF4/H complex, can bind to the PF4-coated platelet surface. These Abs frequently coexist with PF4/H-binding pathogenic Abs and may contribute to HIT pathogenesis. These insights will enrich our understanding of HIT pathogenesis and may pave the way for more advanced diagnostic and therapeutic strategies.