Marlys Laverne Koschinsky

Elevated levels of lipoprotein(a) (Lp(a)) are an independent risk factor for the development of atherothrombotic diseases. However, it is unknown if Lp(a) directly promotes thrombus formation, inhibits thrombus clearance, or merely accelerates the underlying atherosclerotic processes that culminate in plaque rupture. While numerous studies indicate that the apolipoprotein(a) (apo(a)) component of Lp(a) can inhibit plasminogen activation and fibrinolysis, recent evidence suggests that these effects may not be retained in Lp(a). An alternative mechanism through which Lp(a) may promote atherothrombotic events is by impacting platelet function. However, the effects of Lp(a) on platelet function and thrombosis have never been directly assessed in blood clots formed from flowing whole blood. Using a transgenic mouse model expressing high plasma concentrations of apo(a), we showed using a laser-induced mesenteric vessel injury model employing intravital microscopy that apo(a) increased platelet and fibrin volumes in the thrombi without affecting fibrinolysis. In a ferric chloride-induced mouse carotid artery thrombosis model, we found that apo(a) substantially reduced occlusion times and led to more stable thrombi; importantly, we also demonstrated that the effects of Lp(a) could be mitigated by low-dose aspirin therapy. We evaluated the prothrombotic potential of Lp(a) in human blood clots formed under arterial flow conditions using a Chandler loop apparatus. In these studies, we showed that the presence of Lp(a) during thrombogenesis inhibited lysis of the thrombi, without directly impacting fibrinolysis. Lp(a) promoted platelet accumulation in the Chandler thrombi and facilitated the development of fibrin networks that displayed features of fibrinolysis resistance. In an analysis of the UK Biobank, participants with Lp(a) ≥125 nmol/L had a higher risk for arterial thrombosis of non-atherosclerotic etiology but not a higher risk for venous thromboembolism. Collectively, these findings demonstrate that Lp(a) is inherently prothrombotic and likely promotes arterial thrombosis in vivo in part through promoting platelet activation. These findings explain how elevated Lp(a) is an important risk factor for arterial thrombosis either with or without an atherosclerotic etiology as well as observational primary prevention data suggesting that aspirin reduces atherothrombotic risk specifically in patients with elevated Lp(a).

Elevated plasma concentration of lipoprotein(a) is a highly prevalent, independent, and causal risk factor for the development of numerous cardiovascular diseases. This review summarizes the key clinical evidence for elevated lipoprotein(a) as a risk factor for atherosclerotic cardiovascular disease, aortic stenosis, and abdominal aortic aneurysm. These data are specifically linked to ongoing developments in understanding the pathophysiological mechanisms of lipoprotein(a) in these contexts. Highly potent lipoprotein(a)-lowering therapies are being studied in cardiovascular outcomes trials for their ability to prevent major adverse coronary events and aortic stenosis progression, potentially ushering in a new era of clinical management of lipoprotein(a).

Elevated plasma concentrations of Lp(a) (lipoprotein(a)) are an independent and causal risk factor for the development of atherosclerotic cardiovascular diseases, including peripheral artery disease (PAD). Although proatherosclerotic, proinflammatory, procalcific, and prothrombotic effects have been attributed to Lp(a), the precise pathogenic mechanisms by which Lp(a) contributes to these disorders are unclear. Moreover, whether Lp(a) contributes in different ways to atherosclerotic cardiovascular diseases in different vascular sites has not been explored. In particular, PAD involves atherosclerotic plaque rupture and subsequent thrombosis in vessels above the knee, but medial arterial calcification leading to vessel stiffness and thrombosis below the knee; the significance of Lp(a) in these contexts is unclear. Elevated Lp(a) is associated with the spectrum of PAD outcomes, including incident claudication, PAD progression, lower limb revascularization, restenosis, major adverse leg events, including limb amputation, and death and hospitalization due to PAD. Overall, elevated Lp(a) is as potent a risk factor for PAD as it is for coronary artery disease. Reducing Lp(a) to mitigate risk of PAD and to treat patients with PAD, therefore, remains a substantial unmet clinical need, although studies are underway to assess the efficacy of RNA-directed Lp(a)-lowering therapies in preventing atherosclerotic cardiovascular disease events. Mounting clinical trials of these therapies to specifically address their effect on PAD events is the next key step.

Aims: Lipoprotein(a) [Lp(a)] is a causal risk factor for atherosclerotic cardiovascular disease (ASCVD); however, the relationship between Lp(a) and the capacity for vascular repair remains unclear. Depletion of vascular regenerative (VR) progenitor cells has been shown to be a novel indicator of compromised vascular repair in people living with cardiometabolic disorders. The purpose of this study was to determine if elevated levels of Lp(a) modify VR cell content properties. Methods and results: The cross-sectional, multi-site Lipoprotein(a) and Vascular Regenerative Cell Content CardioLink-16 [Lp(a)-VRCE] study enrolled 40 individuals—20 with Lp(a) ≥100 nmol/L and 20 with Lp(a) <100 nmol/L. Isolated peripheral blood mononuclear cells were analysed by multi-parameter flow cytometry. VR progenitor cells were identified based on high aldehyde dehydrogenase (ALDH) activity, in combination with primitive vs. mature lineage-specific cell surface markers. The Lp(a) ≥100 nmol/L group exhibited baseline characteristic differences compared with the Lp(a) <100 nmol/L group such as lower estimated glomerular filtration rate (86.9 vs. 100.1 mL/min/1.73 m2), lower total cholesterol (4.0 vs. 4.8 mmol/L), greater statin use (90 vs. 60%), and a higher prevalence of ASCVD (60 vs. 25%). The Lp(a) ≥100 nmol/L group had lower frequencies of pro-angiogenic ALDHhiSSClowCD133+ (P = 0.0008) and ALDHhiSSClowCD34+CD133+ (P = 0.005) progenitor cells with pro-angiogenic secretory function. Compared with those in the Lp(a) <100 nmol/L group, individuals in the Lp(a) ≥100 nmol/L group demonstrated a higher frequency of M1-polarized pro-inflammatory monocytes (ALDHhiSSCmidCD86+CD163−; P = 0.007) and a lower frequency of ALDHhiSSChiCD49d+ granulocyte precursor cells (P = 0.04) that are involved in vessel repair. Conclusion: In this translational study, people with an Lp(a) ≥100 nmol/L had fewer VR cells and more pro-inflammatory polarized monocyte precursor cells than those with Lp(a) levels <100 nmol/L. These findings suggest that vessel repair activities may be compromised in individuals with elevated Lp(a) levels. Registration: Lp(a)-VRCE ClinicalTrials.gov: NCT06626659

Purpose of review: Elevated plasma lipoprotein(a) (Lp(a)) is a causal and independent risk factor for atherosclerotic cardiovascular disease; therefore, understanding the fundamental mechanisms underlying Lp(a)-mediated pathogenesis is of significant clinical importance. This review summarizes recent advances in understanding the precise cellular targets of Lp(a) in atherogenesis, uncovering potential therapeutic avenues worth exploring. Recent findings: Genetic evidence reveals that Lp(a) is six-fold more atherogenic per particle than LDL, and clinical imaging studies show increased atherosclerotic plaque burden and severity in patients with elevated Lp(a). A novel study using human monocytes uncovered diacylglycerols and lysophosphatidic acid as lipid species that contribute to the pro-inflammatory impacts of Lp(a), independent of the known pro-inflammatory oxidized phospholipids. The identification of a novel cell-surface receptor on endothelial cells involved in Lp(a) uptake offers another exploratory direction in vascular cells involved in atherosclerosis. Several studies have also pointed to accelerated coagulation as a potential target of Lp(a), involving Lp(a)-mediated impacts on platelet aggregation and monocyte tissue factor expression. Summary: An understanding of these cell-specific targets of Lp(a) in atherogenesis will aid the Lp(a) field in identifying novel therapeutic targets for patients with elevated Lp(a), for whom few available therapeutic strategies currently exist.