Kroon, Jeffrey

Abstract Background Patients with cancer treated with immune checkpoint inhibitors are at increased risk of myocardial infarction and ischemic stroke. The mechanism is incompletely understood but may involve accelerated atherosclerosis due to plaque inflammation. Pre-clinical studies may provide insight in these mechanisms. Aim To assess the effects of modulating co-inhibitory immune checkpoint proteins on atherosclerosis progression in animal models. Methods A systematic review was performed in MEDLINE, Embase, Web of Science, and Scopus up to September 2023. Animal studies were included if the effect of modulation of programmed cell death protein 1 (PD-1), programmed death-ligand 1 (PD-L1), cytotoxic T-lymphocyte associated protein 4 (CTLA-4), and/or lymphocyte-activation gene 3 (LAG-3) on atherosclerotic plaque size was evaluated. Secondary outcomes were plaque composition and systemic inflammation. The ratios of means (RoM) across the studies were pooled in a random effects meta-analysis. Results 1,655 studies were identified of which twelve were included. All studies used an atherosclerotic mouse model (Apoe-/-, Ldlr-/-, or ApoE3*Leiden) and either evaluated pharmacological or genetic modulation of co-inhibitory immune checkpoint proteins. Upon inhibition, atherosclerotic plaque size in the aorta was 49% higher in exposed mice compared to control mice (RoM, 1.49; 95% CI, 1.12-1.82; I2=86%). Plaque composition was predominantly characterized by a greater abundance of CD4+ T cells, CD8+ T cells, and macrophages. Studies stimulating co-inhibitory immune checkpoint proteins corroborated these findings and demonstrated that atherosclerotic plaque size was reduced by 28% in treated mice compared to controls (RoM, 0.72; 95% CI, 0.65-0.80; I2=85%). This reduction was paralleled by a decrease in the number of macrophages and T cells in plaques. Conclusion Immune checkpoint inhibition leads to plaque inflammation and a significant increase in murine atherosclerotic plaque size. These changes may reflect the cause of the increased risk of myocardial infarction and ischemic stroke in patients treated with immune checkpoint inhibitors.

Background: The importance of protein glycosylation in regulating lipid metabolism is becoming increasingly apparent. We set out to further investigate this by studying patients with type I congenital disorders of glycosylation (CDGs) with defective N-glycosylation. Methods: We studied 29 patients with the 2 most prevalent types of type I CDG, ALG6 (asparagine-linked glycosylation protein 6)–deficiency CDG and PMM2 (phosphomannomutase 2)–deficiency CDG, and 23 first- and second-degree relatives with a heterozygous mutation and measured plasma cholesterol levels. Low-density lipoprotein (LDL) metabolism was studied in 3 cell models—gene silencing in HepG2 cells, patient fibroblasts, and patient hepatocyte-like cells derived from induced pluripotent stem cells—by measuring apolipoprotein B production and secretion, LDL receptor expression and membrane abundance, and LDL particle uptake. Furthermore, SREBP2 (sterol regulatory element-binding protein 2) protein expression and activation and endoplasmic reticulum stress markers were studied. Results: We report hypobetalipoproteinemia (LDL cholesterol [LDL-C] and apolipoprotein B below the fifth percentile) in a large cohort of patients with type I CDG (mean age, 9 years), together with reduced LDL-C and apolipoprotein B in clinically unaffected heterozygous relatives (mean age, 46 years), compared with 2 separate sets of age- and sex-matched control subjects. ALG6 and PMM2 deficiency led to markedly increased LDL uptake as a result of increased cell surface LDL receptor abundance. Mechanistically, this outcome was driven by increased SREBP2 protein expression accompanied by amplified target gene expression, resulting in higher LDL receptor protein levels. Endoplasmic reticulum stress was not found to be a major mediator. Conclusions: Our study establishes N-glycosylation as an important regulator of LDL metabolism. Given that LDL-C was also reduced in a group of clinically unaffected heterozygotes, we propose that increasing LDL receptor–mediated cholesterol clearance by targeting N-glycosylation in the LDL pathway may represent a novel therapeutic strategy to reduce LDL-C and cardiovascular disease.