Understanding HDL Metabolism and Biology Through In Vivo Tracer Kinetics

Radiolabeling lipoproteins to study and manage disease

PURPOSE

Lipoproteins are endogenous nanoparticles with essential roles in lipid transport and inflammation. Lipoproteins are also valuable in diagnosing and treating disease. For instance, certain lipoproteins are overexpressed in patients with atherosclerotic cardiovascular disease, and reconstituted lipoproteins have been extensively used for drug delivery. Radiolabeling has proven an especially powerful approach for studying and therapeutically exploiting lipoproteins. This review details how radiochemistry and nuclear imaging can facilitate the study of lipoproteins in health and disease. Among other topics, we discuss approaches for radiolabeling lipoproteins and detail how these have helped advance our understanding of lipoprotein biology and the diagnosis and treatment of diseases, including atherosclerosis, cancer, and hypercholesteremia.

METHODS

We performed an extensive literature search on all peer-reviewed studies involving radiolabeled lipoproteins and selected representative examples to provide a high-level overview of the most important discoveries and technological advancements.

RESULTS

More than 200 peer-reviewed papers involved radiolabeled lipoproteins, spanning mechanistic, diagnostic, and therapeutic studies across a wide range of diseases.

CONCLUSION

Radiolabeling has been critical in advancing our understanding of lipoprotein biology and leveraging these nanomaterials for diagnosing and treating disease.

Long-term trajectories of apolipoprotein A1 and major adverse cardiovascular events and mortality in a community cohort

BACKGROUND

Apolipoprotein A1 (ApoA1) is a major component of high-density lipoprotein cholesterol and plays a critical role in reverse cholesterol transport. Dynamic changes in ApoA1 levels may be associated with major adverse cardiovascular events. This study aimed to evaluate the impact of ApoA1 trajectories over three early assessments.

METHODS

Participants in the Chin-Shan Community Cardiovascular Cohort with dyslipidemia and receiving three early ApoA1 assessments were enrolled. Group-based multivariate trajectory modeling was used to classify participants into distinct trajectories after multivariable adjustment. The follow-up duration was from April 1990 to August 2022, and the long-term outcomes of major adverse cardiovascular events (MACE) and death outcomes were evaluated.

RESULTS

A total of 1,080 participants were included (median [interquartile range] age 66.14 [57.93-75.04] years, 43.2% males). Participants were classified into four ApoA1 trajectories: Trajectory 1 (low-level persistence pattern); Trajectory 2 (fall-then-rise pattern); Trajectory 3 (rise-then-fall pattern); and Trajectory 4 (elevated stable pattern). The cumulative incidence of MACE was ranked as Trajectory 4 (7.9%) < Trajectory 2 (9.3%) < Trajectory 3 (9.4%) < Trajectory 1 (12.7%). Comparing to Trajectory 4, both Trajectory 1 and Trajectory 2 had significantly higher risks of MACE (Trajectory 1: hazard ratio [HR] = 2.06, 95% confidence interval [CI] 1.10-3.86; Trajectory 2: HR = 2.38, 95% CI 1.03-5.48). For cardiovascular death, similar results were present. There were no significant differences in composite outcome, all-cause death, non-cardiovascular death across ApoA1 trajectories.

CONCLUSION

The trajectory changes of ApoAI levels significantly influences MACE risk during long-term follow-up, particularly in the low-stable and J-shaped trajectories. Dynamic monitoring of ApoAI may serve as a valuable tool for early risk stratification in high-risk populations, facilitating more individualised interventions.

New perspectives on the high-density lipoprotein system and its role in the prevention and treatment of atherosclerotic cardiovascular disease

PURPOSE OF REVIEW

The causal role of high-density lipoprotein (HDL) in atherosclerotic cardiovascular disease (CVD) remains debated. Considering recent evidence, the purpose of this review is to a provide a focused update and new perspectives on HDL and CVD.

RECENT FINDINGS

A Mendelian randomization study demonstrated an increased risk of CVD when HDL-cholesterol was predominantly transported in larger HDL particles and a decreased risk of CVD when HDL-cholesterol was predominantly transported in smaller HDL particles. Moreover, another Mendelian randomization study demonstrated that concentration and content of medium HDL particles is associated with CVD. A Mendelian randomization study that utilized stratified analyses demonstrated that individuals with HDL-cholesterol 50 mg/dl or less were at increased risk of CVD. Lastly, the AEGIS-II trial demonstrated that CSL112, a human apolipoprotein A-I that increases cholesterol efflux, did not significantly reduce cardiovascular events in patients at very high risk. Exploratory analyses showed that patients treated with CSL112 had numerically lower rates of cardiovascular events.

SUMMARY

Qualitative markers of HDL may be causally related to CVD. There is a need for ongoing research into HDL therapeutics that promote the biological properties of HDL. The optimal cohort or disease state that will benefit from these therapies needs to be identified.

Quo Vadis after AEGIS: New Opportunities for Therapies Targeted at Reverse Cholesterol Transport?

PURPOSE OF REVIEW

High-density lipoprotein (HDL) is integral to reverse cholesterol transport (RCT), a process considered to protect against atherosclerotic cardiovascular disease (ASCVD). We summarise findings from the recent AEGIS-II trial and discuss new opportunities for HDL therapeutics targeted at RCT.

RECENT FINDINGS

Mendelian randomisation studies have suggested a causal association between the functional properties of HDL and ASCVD. However, the AEGIS-II trial of CSL112, an apolipoprotein A-I therapy that enhances cholesterol efflux, did not meet its primary endpoint. Exploratory analyses demonstrated that CSL112 significantly reduced ASCVD events among participants with a baseline low-density lipoprotein (LDL)-cholesterol ≥ 100 mg/dL, suggesting that RCT may depend on LDL-cholesterol levels. The role of HDL therapeutics in patients with familial hypercholesterolaemia, inherited low HDL-cholesterol and impaired HDL function, especially with inadequately controlled LDL-cholesterol, merits further investigation. The treatment of patients with monogenic defects in HDL metabolism remains a significant gap in care that needs further research.

Molecular profiling unveils pyroptosis markers in preterm birth

Through a comprehensive examination of pyroptosis-related differential expressed genes (PRDEGs), this work investigates the molecular complexities of spontaneous preterm birth (SPTB), also known as premature delivery, before the due date. Through the process of merging and correcting batch effects in the GSE120480 and GSE73714 datasets, we were able to identify 36 PRDEGs that exhibited significant expression differentiation in SPTB. Through functional enrichment and pathway analysis, their importance in amino acid transport and cytokine receptor interaction has been highlighted. Among the genes that have emerged as crucial, CEBPA, APOA1, and CEP55 have been identified. The relevance of these molecules was demonstrated using experimental knockdowns, which also suggested that they could be used as molecular biomarkers and therapeutic targets for SPTB.

The functions of apolipoproteins and lipoproteins in health and disease

Lipoproteins and apolipoproteins are crucial in lipid metabolism, functioning as essential mediators in the transport of cholesterol and triglycerides and being closely related to the pathogenesis of multiple systems, including cardiovascular. Lipoproteins a (Lp(a)), as a unique subclass of lipoproteins, is a low-density lipoprotein(LDL)-like particle with pro-atherosclerotic and pro-inflammatory properties, displaying high heritability. More and more strong evidence points to a possible link between high amounts of Lp(a) and cardiac conditions like atherosclerotic cardiovascular disease (ASCVD) and aortic stenosis (AS), making it a risk factor for heart diseases. In recent years, Lp(a)'s role in other diseases, including neurological disorders and cancer, has been increasingly recognized. Although therapies aimed at low-density lipoprotein cholesterol (LDL-C) and high-density lipoprotein cholesterol (HDL-C) have achieved significant success, elevated Lp(a) levels remain a significant clinical management problem. Despite the limited efficacy of current lipid-lowering therapies, major clinical advances in new Lp(a)-lowering therapies have significantly advanced the field. This review, grounded in the pathophysiology of lipoproteins, seeks to summarize the wide-ranging connections between lipoproteins (such as LDL-C and HDL-C) and various diseases, alongside the latest clinical developments, special emphasis is placed on the pivotal role of Lp(a) in cardiovascular disease, while also examining its future potential and mechanisms in other conditions. Furthermore, this review discusses Lp(a)-lowering therapies and highlights significant recent advances in emerging treatments, advocates for further exploration into Lp(a)'s pathogenic mechanisms and its potential as a therapeutic target, proposing new secondary prevention strategies for high-risk individuals.

The predictive value of cumulative atherogenic index of plasma (AIP) for cardiovascular outcomes: a prospective community-based cohort study

BACKGROUND

Atherogenic index of plasma (AIP) has been reported as a critical predictor on the risks and clinical outcomes of cardiovascular diseases (CVDs), and we aimed to explore the potential predictive value of cumulative AIP on major adverse cardiac events (MACE), stroke, myocardial infarction (MI) and cardiovascular mortality.

METHODS

A large-scale community-based prospective cohort was established from December 2011 to April 2012 and followed up in May to July 2014. The endpoint outcomes were obtained before December 31, 2021. AIP was calculated as the logarithmically transformed ratio of triglyceride (TG) to high-density lipoprotein cholesterol (HDL-c) and cumulative AIP was the average value of AIP in 2012 and 2014.

RESULTS

An overall of 3820 participants (36.1% male) with mean (SD) age of 59.1 (8.7) years, were enrolled. Within a median follow-up of 7.5 years, a total of 371 (9.7%) participants were documented with MACE, 293 (7.7%) participants developed stroke, 68 (1.8%) suffered from MI and 65 (1.7%) experienced cardiovascular mortality. Multivariable Cox regression analysis revealed significant associations between cumulative AIP and the risk of MACE, stroke and MI. Regarding MACE, individuals with one higher unit of cumulative AIP were associated with 75% increment on the incidence of going through MACE in fully adjusted model, while categorizing participants into four groups, individuals in the highest cumulative AIP quartile were significantly associated with increased incidence of MACE (HR = 1.76, 95%CI: 1.27-2.44, p < 0.001 in fully adjusted model), stroke (HR = 1.69, 95%CI: 1.17-2.45, p = 0.005) and MI (HR = 2.82, 95%CI: 1.18-6.72, p = 0.019). But not a significant association was observed between cumulative AIP and cardiovascular mortality. In subgroup analysis, the association of cumulative AIP and the incidence of stroke was more pronounced in the elderly (HR: 0.89 vs. 2.41 for the age groups < 65 years and ≥ 65 years, p for interaction = 0.018).

CONCLUSIONS

A higher cumulative AIP was significantly associated with an increased risk of MACE, stroke and MI independent of traditional cardiovascular risk factors in a community-based population, and the association of cumulative AIP and stroke was particularly pronounced in the elderly population.

Lipoprotein Particles in Cerebrospinal Fluid

The brain is the most lipid-rich organ in the body, and the intricate interplay between lipid metabolism and pathologies associated with neurodegenerative disorders is being increasingly recognized. The brain is bathed in cerebrospinal fluid (CSF), which, like plasma, contains lipid-protein complexes called lipoproteins that are responsible for extracellular lipid transport. Multiple CSF lipoprotein populations exist, some of which are produced de novo in the central nervous system and others that appear to be generated from protein constituents that are produced in the periphery. These CSF lipoproteins are thought to play key roles in maintaining lipid homeostasis in the central nervous system, while little else is known due to their limited accessibility and their low abundance in CSF. Recent work has provided new insights into the compositional complexity of CSF lipoprotein families and their metabolism in cerebral circulation. The purpose of this review is to summarize our current state of knowledge on the composition, origin, and metabolism of CSF lipoproteins.

High-Density Lipoprotein Is Located Alongside Insulin in the Islets of Langerhans of Normal and Rodent Models of Diabetes

Recent studies have implicated pre-beta and beta lipoproteins (VLDL and LDL) in the etiopathogenesis of complications of diabetes mellitus (DM). In contrast, alpha lipoprotein (HDL) is protective of the beta cells of the pancreas. This study examined the distribution of HDL in the islets of Langerhans of murine models of type 1 diabetic rats (streptozotocin (STZ)-induced DM in Wistar rats) and type 2 models of DM rats (Goto-Kakizaki (GK), non-diabetic Zucker lean (ZL), and Zucker diabetic and fatty (ZDF)). The extent by which HDL co-localizes with insulin or glucagon in the islets of the pancreas was also investigated. Pancreatic tissues of Wistar non-diabetic, diabetic Wistar, GK, ZL, and ZDF rats were processed for immunohistochemistry. Pancreatic samples of GK rats fed with either a low-fat or a high-fat diet were prepared for transmission immune-electron microscopy (TIEM) to establish the cytoplasmic localization of HDL in islet cells. HDL was detected in the core and periphery of pancreatic islets of Wistar non-diabetic and diabetic, GK, ZL, and ZDF rats. The average total of islet cells immune positive for HDL was markedly (<0.05) reduced in GK and ZDF rats in comparison to Wistar controls. The number of islet cells containing HDL was also remarkably (p < 0.05) reduced in Wistar diabetic rats and GK models fed on high-fat food. The co-localization study using immunofluorescence and TIEM techniques showed that HDL is detected alongside insulin within the secretory granules of β-cells. HDL did not co-localize with glucagon. This observation implies that HDL may contribute to the metabolism of insulin.