The Remnant Lipoprotein Hypothesis of Diabetes-Associated Cardiovascular Disease

The residual risk of inflammation and remnant cholesterol in acute coronary syndrome patients on statin treatment undergoing percutaneous coronary intervention

BACKGROUND

Residual risk assessment for acute coronary syndrome (ACS) patients after sufficient medical management remains challenging. The usefulness of measuring high-sensitivity C-reactive protein (hsCRP) and remnant cholesterol (RC) in assessing the level of residual inflammation risk (RIR) and residual cholesterol risk (RCR) for risk stratification in these patients needs to be evaluated.

METHODS

Patients admitted for ACS on statin treatment who underwent percutaneous coronary intervention (PCI) between March 2016 and March 2019 were enrolled in the analysis. The included patients were stratified based on the levels of hsCRP and RC during hospitalization. The primary outcome was ischemic events at 12 months, defined as a composite of cardiac death, myocardial infarction, or stroke. The secondary outcomes included 12-month all-cause death and cardiac death.

RESULTS

Among the 5778 patients, the median hsCRP concentration was 2.60 mg/L and the median RC concentration was 24.98 mg/dL. The RIR was significantly associated with ischemic events (highest hsCRP tertile vs. lowest hsCRP tertile, adjusted hazard ratio [aHR]: 1.52, 95% confidence interval [CI]: 1.01-2.30, P = 0.046), cardiac death (aHR: 1.77, 95% CI:1.02-3.07, P = 0.0418) and all-cause death (aHR: 2.00, 95% CI: 1.24-3.24, P = 0.0048). The RCR was also significantly associated with these outcomes, with corresponding values for the highest tertile of RC were 1.81 (1.21-2.73, P = 0.0043), 2.76 (1.57-4.86, P = 0.0004), and 1.72 (1.09-2.73, P = 0.0208), respectively. The risks of ischemic events (aHR: 2.80, 95% CI: 1.75-4.49, P < 0.0001), cardiac death (aHR: 4.10, 95% CI: 2.18-7.70, P < 0.0001), and all-cause death (aHR: 3.00, 95% CI, 1.73-5.19, P < 0.0001) were significantly greater in patients with both RIR and RCR (highest hsCRP and RC tertile) than in patients with neither RIR nor RCR (lowest hsCRP and RC tertile). Notably, the RIR and RCR was associated with an increased risk of ischemic events especially in patients with adequate low-density lipoprotein cholesterol (LDL-C) control (LDL-C < 70 mg/dl) (Pinteraction=0.04). Furthermore, the RIR and RCR provide more accurate evaluations of risk in addition to the GRACE score in these patients [areas under the curve (AUC) for ischemic events: 0.64 vs. 0.66, P = 0.003].

CONCLUSION

Among ACS patients receiving contemporary statin treatment who underwent PCI, high risks of both residual inflammation and cholesterol, as assessed by hsCRP and RC, were strongly associated with increased risks of ischemic events, cardiac death, and all-cause death.

APOC3 siRNA and ASO therapy for dyslipidemia

PURPOSE OF REVIEW

The aim of this review is to present the clinical indications of apolipoprotein C-III (apoC3) inhibition in the therapeutic arsenal for the treatment of lipid disorders and associated risks and to compare the most advanced modalities of apoC3 inhibition currently available or in development, specifically APOC3 antisense oligonucleotides (ASO) and small interfering RNA (siRNA).

RECENT FINDINGS

ApoC3 inhibition significantly decreases triglyceride levels by mechanisms coupling both lipoprotein lipase (LPL) upregulation and LPL-independent mechanisms. The main apoC3 inhibitors in advanced clinical development are the GalNAc-ASO olezarsen and the GalNAc-siRNA plozasiran. Clinical studies conducted with volanesorsen, the olezarsen precursor, showed a favorable effect on hepatic steatosis (nonalcoholic fatty liver disease, NAFLD). Olezarsen does not appear to be associated with the main side effects attributed to volanesorsen including thrombocytopenia. Plozasiran is in advanced clinical development and requires subcutaneous injection every 3 months and present to-date an efficacy and safety profile comparable to that of the monthly ASO.

SUMMARY

Inhibition of apoC3 is effective across all the spectrum of hypertriglyceridemia, might have a favorable effect on hepatic steatosis (NAFLD) and the effect of apoC3 inhibition on cardiovascular risk is not limited to its effect on plasma triglycerides. APOC3 GalNAc-conjugated ASO and siRNA are both effective in decreasing plasma apoC3 and triglyceride levels.

Deficiency of lncRNA MERRICAL abrogates macrophage chemotaxis and diabetes-associated atherosclerosis

Diabetes-associated atherosclerosis involves excessive immune cell recruitment and plaque formation. However, the mechanisms remain poorly understood. Transcriptomic analysis of the aortic intima in Ldlr-/- mice on a high-fat, high-sucrose-containing (HFSC) diet identifies a macrophage-enriched nuclear long noncoding RNA (lncRNA), MERRICAL (macrophage-enriched lncRNA regulates inflammation, chemotaxis, and atherosclerosis). MERRICAL expression increases by 249% in intimal lesions during progression. lncRNA-mRNA pair genomic mapping reveals that MERRICAL positively correlates with the chemokines Ccl3 and Ccl4. MERRICAL-deficient macrophages exhibit lower Ccl3 and Ccl4 expression, chemotaxis, and inflammatory responses. Mechanistically, MERRICAL guides the WDR5-MLL1 complex to activate CCL3 and CCL4 transcription via H3K4me3 modification. MERRICAL deficiency in HFSC diet-fed Ldlr-/- mice reduces lesion formation by 74% in the aortic sinus and 86% in the descending aorta by inhibiting leukocyte recruitment into the aortic wall and pro-inflammatory responses. These findings unveil a regulatory mechanism whereby a macrophage-enriched lncRNA potently inhibits chemotactic responses, alleviating lesion progression in diabetes.

Apolipoprotein C3: form begets function

Increased circulating levels of apolipoprotein C3 (APOC3) predict cardiovascular disease (CVD) risk in humans, and APOC3 promotes atherosclerosis in mouse models. APOC3's mechanism of action is due in large part to its ability to slow the clearance of triglyceride-rich lipoproteins (TRLs) and their remnants when APOC3 is carried by these lipoproteins. However, different pools and forms of APOC3 exert distinct biological effects or associations with atherogenic processes. Thus, lipid-free APOC3 induces inflammasome activation in monocytes whereas lipid particle-bound APOC3 does not. APOC3-enriched LDL binds better to the vascular glycosaminoglycan biglycan than does LDL depleted of APOC3. Patterns of APOC3 glycoforms predict CVD risk differently. The function of APOC3 bound to HDL is largely unknown. There is still much to learn about the mechanisms of action of different forms and pools of APOC3 in atherosclerosis and CVD, and whether APOC3 inhibition would prevent CVD risk in patients on LDL-cholesterol lowering medications.

D-β-Hydroxybutyrate Dehydrogenase Mitigates Diabetes-Induced Atherosclerosis through the Activation of Nrf2

BACKGROUND

 We aimed to investigate the role and mechanism of β-hydroxybutyrate dehydrogenase 1 (Bdh1) in regulating macrophage oxidative stress in diabetes-induced atherosclerosis (AS).

METHODS

 We performed immunohistochemical analysis of femoral artery sections to determine differences in Bdh1 expression between normal participants, AS patients, and patients with diabetes-induced AS. Diabetic Apoe-/- mice and high-glucose (HG)-treated Raw264.7 macrophages were used to replicate the diabetes-induced AS model. The role of Bdh1 in this disease model was determined by adeno-associated virus (AAV)-mediated overexpression of Bdh1 or overexpression or silencing of Bdh1.

RESULTS

 We observed reduced expression of Bdh1 in patients with diabetes-induced AS, HG-treated macrophages, and diabetic Apoe-/- mice. AAV-mediated Bdh1 overexpression attenuated aortic plaque formation in diabetic Apoe-/- mice. Silencing of Bdh1 resulted in increased reactive oxygen species (ROS) production and an inflammatory response in macrophages, which were reversed by the ROS scavenger N-acetylcysteine. Overexpression of Bdh1 protected Raw264.7 cells from HG-induced cytotoxicity by inhibiting ROS overproduction. In addition, Bdh1 induced oxidative stress through nuclear factor erythroid-related factor 2 (Nrf2) activation by fumarate acid.

CONCLUSION

 Bdh1 attenuates AS in Apoe-/- mice with type 2 diabetes, accelerates lipid degradation, and reduces lipid levels by promoting ketone body metabolism. Moreover, it activates the Nrf2 pathway of Raw264.7 by regulating the metabolic flux of fumarate, which inhibits oxidative stress and leads to a decrease in ROS and inflammatory factor production.

Quartet of APOCs and the Different Roles They Play in Diabetes

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.

Hematopoietic NLRP3 and AIM2 Inflammasomes Promote Diabetes-Accelerated Atherosclerosis, but Increased Necrosis Is Independent of Pyroptosis

Serum apolipoprotein C3 (APOC3) predicts incident cardiovascular events in people with type 1 diabetes, and silencing of APOC3 prevents both lesion initiation and advanced lesion necrotic core expansion in a mouse model of type 1 diabetes. APOC3 acts by slowing the clearance of triglyceride-rich lipoproteins, but lipid-free APOC3 has recently been reported to activate an inflammasome pathway in monocytes. We therefore investigated the contribution of hematopoietic inflammasome pathways to atherosclerosis in mouse models of type 1 diabetes. LDL receptor-deficient diabetes mouse models were transplanted with bone marrow from donors deficient in NOD, LRR and pyrin domain-containing protein 3 (NLRP3), absent in melanoma 2 (AIM2) or gasdermin D (GSDMD), an inflammasome-induced executor of pyroptotic cell death. Mice with diabetes exhibited inflammasome activation and consistently, increased plasma interleukin-1β (IL-1β) and IL-18. Hematopoietic deletions of NLRP3, AIM2, or GSDMD caused smaller atherosclerotic lesions in diabetic mice. The increased lesion necrotic core size in diabetic mice was independent of macrophage pyroptosis because hematopoietic GSDMD deficiency failed to prevent necrotic core expansion in advanced lesions. Our findings demonstrate that AIM2 and NLRP3 inflammasomes contribute to atherogenesis in diabetes and suggest that necrotic core expansion is independent of macrophage pyroptosis.

ARTICLE HIGHLIGHTS

The contribution of hematopoietic cell inflammasome activation to atherosclerosis associated with type 1 diabetes is unknown. The goal of this study was to address whether hematopoietic NOD, LRR, and pyrin domain-containing protein 3 (NLRP3), absent in melanoma 2 (AIM2) inflammasomes, or the pyroptosis executioner gasdermin D (GSDMD) contributes to atherosclerosis in mouse models of type 1 diabetes. Diabetic mice exhibited increased inflammasome activation, with hematopoietic deletions of NLRP3, AIM2, or GSDMD causing smaller atherosclerotic lesions in diabetic mice, but the increased lesion necrotic core size in diabetic mice was independent of macrophage pyroptosis. Further studies on whether inflammasome activation contributes to cardiovascular complications in people with type 1 diabetes are warranted.

Inflammasomes and Atherosclerosis: a Mixed Picture

The CANTOS (Canakinumab Anti-inflammatory Thrombosis Outcome Study) and colchicine trials suggest an important role of inflammasomes and their major product IL-1β (interleukin 1β) in human atherosclerotic cardiovascular disease. Moreover, studies in mouse models indicate a causal role of inflammasomes and IL-1β in atherosclerosis. However, recent studies have led to a more granular view of the role of inflammasomes in atherosclerosis. Studies in hyperlipidemic mouse models suggest that prominent activation of the NLRP3 inflammasome requires a second hit such as defective cholesterol efflux, defective DNA repair, clonal hematopoiesis or diabetes. Similarly in humans some mutations promoting clonal hematopoiesis increase coronary artery disease risk in part by promoting inflammasome activation. Recent studies in mice and humans point to a wider role of the AIM2 (absent in melanoma 2) inflammasome in promoting cardiovascular disease including in some forms of clonal hematopoiesis and diabetes. These developments suggest a precision medicine approach in which treatments targeting inflammasomes or IL-1β might be best employed in clinical settings involving increased inflammasome activation.

Remnant cholesterol in patients admitted for acute coronary syndromes

BACKGROUND

Remnant cholesterol has been identified as one of leading lipid values associated with the incidence of coronary heart disease. There is scarce evidence on its distribution and prognostic value in acute coronary syndrome (ACS) patients.

METHODS AND RESULTS

We included all consecutive patients admitted for ACS in two different centres. Remnant cholesterol was calculated by the equation: total cholesterol minus LDL cholesterol minus HDL cholesterol, and values ≥30 were considered high. Among the 7479 patients, median remnant cholesterol level was 28 mg/dL (21-39), and 3429 (45.85%) patients had levels ≥30 mg/dL. Age (r: -0.29) and body mass index (r: 0.44) were the variables more strongly correlated. At any given age, patients with overweigh or obesity had higher levels. In-hospital mortality was 3.75% (280 patients). Remnant cholesterol was not associated to higher in-hospital mortality risk (odds ratio: 0.89; P = 0.21). After discharge (median follow-up of 57 months), an independent and linear risk of all-cause mortality and heart failure (HF) associated to cholesterol remnant levels was observed. Remnant cholesterol levels >60 mg/dL were associated to higher risk of mortality [hazard ratio (HR): 1.49 95% CI 1.08-2.06; P = 0.016], cardiovascular mortality (HR: 1.49 95% CI 1.08-2.06; P = 0.016), and HF re-admission (sub-HR: 1.55 95% CI 1.14-2.11; P = 0.005).

CONCLUSIONS

Elevated remnant cholesterol is highly prevalent in patients admitted for ACS and is inversely correlated with age and positively with body mass index. Remnant cholesterol levels were not associated to higher in-hospital mortality risk, but they were associated with higher long-term risk of mortality and HF.

Application of optical tweezers in cardiovascular research: More than just a measuring tool

Recent advances in the field of optical tweezer technology have shown intriguing potential for applications in cardiovascular medicine, bringing this laboratory nanomechanical instrument into the spotlight of translational medicine. This article summarizes cardiovascular system findings generated using optical tweezers, including not only rigorous nanomechanical measurements but also multifunctional manipulation of biologically active molecules such as myosin and actin, of cells such as red blood cells and cardiomyocytes, of subcellular organelles, and of microvessels in vivo. The implications of these findings in the diagnosis and treatment of diseases, as well as potential perspectives that could also benefit from this tool, are also discussed.