The link between inflammation and atherosclerotic cardiovascular disease (ASCVD) is well established.¹ Recently, studies have highlighted a molecularly defined subgroup of individuals in whom inflammation may play a particularly strong role in promoting ASCVD.² Clonal hematopoiesis of indeterminate potential (CHIP), the presence of somatic changes in the nuclear genome of human blood cells, is an age-related process detected in 10-20% of individuals >70 years of age.³ In a case-control study published in 2017, individuals with CHIP were found to be at increased risk not only of myeloid malignancies but also coronary artery disease (CAD), at a rate 1.9 times greater than that of noncarriers.³ CHIP was also associated with a fourfold increase in the incidence of early onset myocardial infarction.

Although complete understanding of the cellular pathways underlying the relationship between CHIP and ASCVD remains aspirational, genetic studies have demonstrated a multifaceted interplay between mutant CHIP clones, immune effector cells, and inflammatory genes and proteins.⁴ Achieving further clarity on the molecular crosslinks between these clonally mutated lines, the inflammatory cascade, and cardiovascular (CV) health will be essential to reducing the risk of cardiovascular disease (CVD).

Mechanisms of Heightened Inflammation in CHIP

The biologic underpinnings of ASCVD in CHIP are complex and depend on the specific mutated gene. For example, ten-eleven translocation methylcytosine dioxygenase 2 (TET2) deficiency in mice results in upregulation of inflammatory mediators and manifests with more severe inflammatory phenotypes than in wild-type control mice.⁵ Mechanistically, TET2-deficient macrophages manifest an elevated inflammatory state because of the lack of TET2 inhibition of interleukin-1 beta (IL-1 beta) and interleukin-6 (IL-6) expression.⁶ TET2 deficiency, generated by bone marrow reconstitution with TET2-deficient cells,results in increased "NOD-like" receptor family pyrin domain containing 3 (NLRP3) inflammasome-mediated IL-1 beta secretion and plaque size in atherogenic chimeric mice compared with that of wild-type control mice.⁷ In humans, the presence of TET2 clones was shown to predict the response to IL-1 beta inhibition in the CANTOS (Canakinumab Anti-Inflammatory Thrombosis Outcomes Study) trial data.⁸

The Janus kinase 2 (JAK2) V617F mutation portends the greatest risk of CAD among all CHIP mutations and is characterized by elevated cytokine levels, including IL-1 beta and IL-6. Pharmacologic inhibition of IL-1 beta in atherogenic transgenic mice expressing the JAK2 V617F mutation leads to plaque stabilization.⁹ JAK2 V617F accelerates atherogenesis by activation of the NLRP3 and absent in melanoma 2 (AIM2) inflammasomes, leading to an abundance of inflammatory myeloid cells and prominent formation of a necrotic core in atherosclerotic lesions seen in mice expressing JAK2 V617F in macrophages.¹⁰

DNA methyltransferase 3 alpha (DNMT3A) gene alterations, the most prevalent among individuals with CHIP, are also notable for their proinflammatory milieu, with a higher expression of IL-6, chemokine (C-X-C motif) ligand (Cxcl) 1, and Cxcl2 by murine macrophages. In a transcriptome analysis of monocytes and T cells of patients with heart failure (HF) and DNMT3A mutations, inflammatory genes (including IL-1 beta, IL-6, interleukin-8, and NLRP3) were upregulated, consistent with a potential role of DNMT3A mutations in individuals with CHIP and ASCVD.¹¹ Similarly, CHIP-harboring mutations in additional sex combs like transcriptional regulator 1 (ASXL1), a commonly mutated gene in myeloid malignancies, have also been shown to promote HF by proinflammatory mechanisms leading to cytokine overproduction by myeloid cells.¹²

CHIP and CVD: Therapeutic Hypotheses

Given mounting evidence that proinflammatory cytokines might represent the biologic link between clonal hematopoiesis and ASCVD, it is natural to posit that decreasing inflammation by targeting different aspects of the CHIP-inflammation cascade could ameliorate atherogenesis and reduce myocardial and cerebrovascular complications (Table 1).

Table 1: Therapeutic Hypotheses for Reducing Inflammation to Lower CVD Risk in Individuals With CHIP

First, inflammasome activity could be modulated, for example, with specific inhibitors of NLRP3 or AIM2. Several compounds that target NLRP3 deubiquitination are under development. Thiolutin, a zinc chelator, has been shown to inhibit NLRP3 deubiquitination and suppress IL-1 beta production. An ongoing phase 1c, multicenter, randomized study (GC43343) is evaluating NLRP3 inhibition with selnoflast in patients with CAD and elevated high-sensitivity C-reactive protein (hs-CRP) levels.¹³ A substudy is focused on individuals with pathogenic TET2 CHIP. The primary objective is to evaluate the medication's safety, and secondary (hs-CRP) and exploratory (IL-1 beta) endpoints will shed light on the agent's effects on systemic and pathologic inflammation. Importantly, NLRP3 inhibition is expected to be less immunosuppressive than anti-IL-1 beta therapy given that IL-1 beta is also produced by other inflammasomes. Inhibition of the AIM2 inflammasome similarly shares the potential for reducing CVD risk, and preliminary data have demonstrated improvements in plaque vulnerability in mice treated with AIM2-antagonizing synthetic oligonucleotides.

An alternative strategy involves antagonism of cellular mediators downstream of inflammasomes, thus exploiting signaling pathways with a postulated role in plaque development and progression. For example, inhibitors to IL-6 using monoclonal antibodies, such as ziltivekimab, are currently in development with the goal of reducing the risk of ASCVD. Similarly, pharmacologic inhibition of inflammatory and proatherogenic cytokines that are elevated in individuals with CHIP, such as IL-1 beta and interleukin-18, might ameliorate development of coronary heart disease. Interestingly, patients with rheumatoid arthritis treated with tocilizumab, a humanized monoclonal antibody against the IL-6 receptor, developed elevated triglyceride and non-high-density lipoprotein cholesterol levels.¹⁴ Additional work is needed to develop specific compounds with anti-inflammatory activity and no deleterious effects on lipid and hepatic profiles.

A third category of interventions involves the use of CHIP mutation-specific therapies. Hypomethylating agents such as azacytidine and decitabine have demonstrated efficacy in individuals with TET2-mutant myeloid malignancies and could be evaluated for their antiatherogenic effects in individuals with CHIP. Vitamin C has been shown to mimic TET2 restoration, enhance tumor sensitivity to DNA damage, and suppress leukemia progression of TET2-deficient mouse hematopoietic stem and progenitor cells.¹⁵ Similarly, JAK2 inhibitors could be exploited to target JAK2 V617F mutations. Indeed, ruxolitinib, a Janus kinase 1 (JAK1) and JAK2 inhibitor, has been shown to reduce atherosclerotic plaque size in mice with JAK2 V617F-dependent atherosclerosis, whereas fedratinib, a selective JAK2 inhibitor, has the potential to spare off-target effects. Medications targeting splicing factor mutations (e.g., splicing factor 3b subunit 1 [SF3B1] modulators) and mutant tumor protein P53 (TP53) also deserve detailed evaluation in individuals with CHIP and residual inflammatory risk.

Clinicians are just beginning to appreciate the complicated interplay between mutant CHIP clones, immune pathways, and chronic inflammation. Understanding these processes and their influence on atherosclerosis will be critical to identifying patients at high risk, developing preventive and therapeutic strategies, and improving the long-term CV outcomes of individuals with CHIP.

References

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