In Vivo Coronary 18F-Sodium Fluoride Activity: Correlations With Coronary Plaque Histological Vulnerability and Physiological Environment

Discovery of σ2R/TMEM97 as a Novel Biomarker for Atherosclerotic Plaques: A PET Imaging and Validation Study

BACKGROUND

The aims of this study were to evaluate σ2R (sigma-2 receptor)/TMEM97 (transmembrane protein 97) expression in atherosclerotic plaques, and assess the feasibility of in vivo atherosclerotic plaques imaging using the σ2R/TMEM97 targeting probe 1-(4-(5,6-dimethoxyisoindolin-2-yl)butyl)-3-(2-[18F]fluoroethyl)-1,3-dihydro-2H-benzo[d]imidazol-2-one ([18F]SYB-NF) developed in our laboratory.

METHODS

Hematoxylin and eosin and immunohistochemical staining were performed on both human coronary endarterectomy specimens and mouse samples. The expression of σ2R/TMEM97 in RAW264.7 cells incubated with ox-LDL (oxidized low-density lipoprotein) was analyzed using western blot analysis. Positron emission tomography imaging with [18F]SYB-NF, [18F]NaF, and [18F]fluoro-2-deoxy-d-glucose was conducted in wide-type C57BL/6 and ApoE-/- mice. Specific binding was evaluated by coinjecting [18F]SYB-NF with the σ2R/TMEM97 antagonist CM398. Autoradiography and Oil Red O staining were performed on harvested aortas and corresponding sections.

RESULTS

Staining results demonstrated significant upregulation of σ2R/TMEM97 expression during both early plaque formation and atherosclerosis progression. Western blot analysis indicated that incubation of macrophages with ox-LDL led to increased σ2R/TMEM97 expression. [18F]SYB-NF specifically accumulated in the aortic arch of ApoE-/- mice. Treatment with CM398 significantly reduced the standardized uptake value in the aortic arch of ApoE-/- mice. [18F]SYB-NF exhibited a higher standardized uptake value in the aortic arch (0.67±0.09 versus 0.51±0.07) and higher aortic arch-to-heart ratio (2.58 versus 0.56) in ApoE-/- mice compared with [18F]fluoro-2-deoxy-d-glucose, and a higher aortic arch-to-bone ratio (2.24 versus 0.44) compared with [18F]NaF. Autoradiography analysis revealed a strong correlation between the positive area in Oil Red O staining and autoradiography (Pearson correlation coefficient=0.993; P=0.001), further supporting the association between elevated σ2R/TMEM97 expression and plaque formation.

CONCLUSIONS

σ2R/TMEM97 may serve as a potential biomarker for atherosclerotic plaques, and σ2R/TMEM97 positron emission tomography imaging may be used to monitor plaque formation and progression, as well as the efficacy of emerging therapeutic strategies for atherosclerotic plaques.

Advances in the application of 18F-sodium fluoride PET in the assessment of atherosclerosis

Atherosclerosis serves as the primary cause of cardiovascular diseases (CVDs), with its pathological processes encompassing lipid deposition, inflammatory responses, and calcification. Traditional imaging techniques, such as computed tomography angiography and MRI, are primarily utilized for detecting arterial stenosis and calcified plaques, yet they face challenges in accurately assessing plaque activity and instability. 18F-sodium fluoride PET (18F-NaF PET) offers a novel approach for plaque activity and stability assessment by labeling and quantifying arterial wall calcification. This article reviews the advances in the application of 18F-NaF PET in the assessment of atherosclerosis.

Estimating inflammatory risk in atherosclerotic cardiovascular disease: plaque over plasma?

Inflammation is an important driver of disease in the context of atherosclerosis, and several landmark trials have shown that targeting inflammatory pathways can reduce cardiovascular event rates. However, the high cost and potentially serious adverse effects of anti-inflammatory therapies necessitate more precise patient selection. Traditional biomarkers of inflammation, such as high-sensitivity C-reactive protein, show an association with cardiovascular risk on a population level but do not have specificity for local plaque inflammation. Nowadays, advancements in non-invasive imaging of the vasculature enable direct assessment of vascular inflammation. Positron emission tomography (PET) tracers such as 18F-fluorodeoxyglucose enable detection of metabolic activity of inflammatory cells but are limited by low specificity and myocardial spillover effects. 18F-sodium fluoride is a tracer that identifies active micro-calcification in plaques, indicating vulnerable plaques. Gallium-68 DOTATATE targets pro-inflammatory macrophages by binding to somatostatin receptors, which enhances specificity for plaque inflammation. Coronary computed tomography angiography (CCTA) provides high-resolution images of coronary arteries, identifying high-risk plaque features. Measuring pericoronary adipose tissue attenuation on CCTA represents a novel marker of vascular inflammation. This review examines both established and emerging methods for assessing atherosclerosis-related inflammation, emphasizing the role of advanced imaging in refining risk stratification and guiding personalized therapies. Integrating these imaging modalities with measurements of systemic and molecular biomarkers could shift atherosclerotic cardiovascular disease management towards a more personalized approach.

18F-NaF uptake on vascular PET imaging in symptomatic versus asymptomatic atherosclerotic disease: A meta-analysis

INTRODUCTION

18F-sodium fluoride (NaF) positron-emission tomography (PET) is increasingly being used to measure microcalcification in atherosclerotic disease in vivo. Correlations have been drawn between sodium fluoride uptake and the presence of high-risk plaque features, as well as its association with clinical atherosclerotic sequelae. The aim of this study was to perform a meta-analysis of NaF uptake on PET imaging and its relation to symptomatic and asymptomatic disease.

METHODS

A systematic review was performed according to PRISMA guidelines, via searching the Ovid MEDLINE, Ovid Embase, Cochrane Library, PubMed, Scopus, and Web of Science Core Collection databases up to May 2024. The search strategy included the terms 'NaF', 'PET', and 'plaque', and all studies with data regarding the degree of microcalcification, as measured by 18F-NaF uptake in symptomatic and asymptomatic atherosclerotic plaques, were included. Analysis involved calculating mean differences between uptake values and comparison using a random-effects model.

RESULTS

A total of 16 articles, involving 423 participants, were included in the meta-analysis (10 carotid artery studies, five coronary artery studies, and one in peripheral vascular disease). Comparing 18F-NaF uptake in symptomatic versus asymptomatic atherosclerotic plaques, a mean difference of 0.43 (95% CI 0.29 to 0.57; p < 0.0001, I2 = 65%) was noted in studies comparing symptomatic and asymptomatic plaques in the same participant, with a significant difference in effect based on arterial territory studied (χ2 = 12.68, p = 0.0018). In studies of participants with and without symptomatic disease, there was no significant difference between symptomatic and asymptomatic plaques (mean difference 0.27, 95% CI -0.26 to 0.80, p = 0.28, I2 = 85%).

CONCLUSIONS

PET imaging using 18F-NaF can detect differences in microcalcification between symptomatic and asymptomatic atherosclerotic plaques within, but not between, individuals, and thus, is a marker of symptomatic disease. The standardization of 18F-NaF PET imaging protocols, and its future use as a risk stratification tool or outcome measure, requires further study. (PROSPERO Registration ID: CRD42023451363).

Coronary sodium [18F]fluoride activity predicts outcomes post-CABG: a comparative evaluation with conventional metrics

PURPOSE

The value of preoperative multidisciplinary approach remains inadequately delineated in forecasting postoperative outcomes of patients undergoing coronary artery bypass grafting (CABG). Herein, we aimed to ascertain the efficacy of multi-modality cardiac imaging in predicting post-CABG cardiovascular outcomes.

METHODS

Patients with triple coronary artery disease underwent cardiac sodium [18F]fluoride ([18F]NaF) positron emission tomography/computed tomography (PET/CT), coronary angiography, and CT-based coronary artery calcium scoring before CABG. The maximum coronary [18F]NaF activity (target-to-blood ratio [TBR]max) and the global coronary [18F]NaF activity (TBRglobal) was determined. The primary endpoint was perioperative myocardial infarction (PMI) within 7-day post-CABG. Secondary endpoint included major adverse cardiac and cerebrovascular events (MACCEs) and recurrent angina.

RESULTS

This prospective observational study examined 101 patients for a median of 40 months (interquartile range: 19-47 months). Both TBRmax (odds ratio [OR] = 1.445; p = 0.011) and TBRglobal (OR = 1.797; P = 0.018) were significant predictors of PMI. TBRmax>3.0 (area under the curve [AUC], 0.65; sensitivity, 75.0%; specificity, 56.8%; p = 0.036) increased PMI risk by 3.661-fold, independent of external confounders. Kaplan-Meier test revealed a decrease in MACCE survival rate concomitant with an escalating TBRmax. TBRmax>3.6 (AUC, 0.70; sensitivity, 76.9%; specificity, 73.9%; p = 0.017) increased MACCEs risk by 5.520-fold. Both TBRmax (hazard ratio [HR], 1.298; p = 0.004) and TBRglobal (HR = 1.335; p = 0.011) were significantly correlated with recurrent angina. No significant associations were found between CAC and SYNTAX scores and between PMI occurrence and long-term MACCEs.

CONCLUSION

Quantification of coronary microcalcification activity via [18F]NaF PET displayed a strong ability to predict early and long-term post-CABG cardiovascular outcomes, thereby outperforming conventional metrics of coronary macrocalcification burden and stenosis severity.

TRIAL REGISTRATION

The trial was registered with the Chinese Clinical Trial Committee (number: ChiCTR1900022527; URL: www.chictr.org.cn/showproj.html?proj=37933 ).

Computed Tomography Angiography Characteristics of Thin-Cap Fibroatheroma in Patients With Diabetes

BACKGROUND

It was recently reported that thin-cap fibroatheroma (TCFA) detected by optical coherence tomography was an independent predictor of future cardiac events in patients with diabetes. However, the clinical usefulness of this finding is limited by the invasive nature of optical coherence tomography. Computed tomography angiography (CTA) characteristics of TCFA have not been systematically studied. The aim of this study was to investigate CTA characteristics of TCFA in patients with diabetes.

METHODS AND RESULTS

Patients with diabetes who underwent preintervention CTA and optical coherence tomography were included. Qualitative and quantitative analyses were performed for plaques on CTA. TCFA was assessed by optical coherence tomography. Among 366 plaques in 145 patients with diabetes, 111 plaques had TCFA. The prevalence of positive remodeling (74.8% versus 50.6%, P<0.001), low attenuation plaque (63.1% versus 33.7%, P<0.001), napkin-ring sign (32.4% versus 11.0%, P<0.001), and spotty calcification (55.0% versus 34.9%, P<0.001) was significantly higher in TCFA than in non-TCFA. Low-density noncalcified plaque volume (25.4 versus 15.7 mm3, P<0.001) and remodeling index (1.30 versus 1.20, P=0.002) were higher in TCFA than in non-TCFA. The presence of napkin-ring sign, spotty calcification, high low-density noncalcified plaque volume, and high remodeling index were independent predictors of TCFA. When all 4 predictors were present, the probability of TCFA increased to 82.4%.

CONCLUSIONS

The combined qualitative and quantitative plaque analysis of CTA may be helpful in identifying TCFA in patients with diabetes.

REGISTRATION INFORMATION

URL: https://www.clinicaltrials.gov; Unique identifier: NCT04523194.

Induction of Arterial Inflammation by Immune Checkpoint Inhibitor Therapy in Lung Cancer Patients as Measured by 2-[18F]FDG Positron Emission Tomography/Computed Tomography Depends on Pre-Existing Vascular Inflammation

BACKGROUND

Immune checkpoint inhibitors (ICI) are one of the most effective therapies in oncology, albeit associated with various immune-related adverse events also affecting the cardiovascular system.

METHODS

We aimed to investigate the effect of ICI on arterial 2-[18F]FDG uptake by using 2-[18F]FDG PET/CT imaging pre/post treatment in 47 patients with lung cancer. Maximum 2-[18F]FDG standardized uptake values (SUVmax) and target-to-background ratios (TBRs) were calculated along six arterial segments. We classified the arterial PET lesions by pre-existing active inflammation (cut-off: TBRpre ≥ 1.6). 2-[18F]FDG metabolic activity pre/post treatment was also quantified in bone marrow, spleen, and liver. Circulating blood biomarkers were additionally collected at baseline and after immunotherapy.

RESULTS

ICI treatment resulted in significantly increased arterial inflammatory activity, detected by increased TBRs, in all arterial PET lesions analyzed. In particular, a significant elevation of arterial 2-[18F]FDG uptake was only recorded in PET lesions without pre-existing inflammation, in calcified as well as in non-calcified lesions. Furthermore, a significant increase in arterial 2-[18F]FDG metabolic activity after immunotherapy was solely observed in patients not previously treated with chemotherapy or radiotherapy as well as in those without CV risk factors. No significant changes were recorded in either 2-[18F]FDG uptake of bone marrow, spleen and liver after treatment, or the blood biomarkers.

CONCLUSIONS

ICI induces vascular inflammation in lung cancer patients lacking pre-existing arterial inflammation.

Osteopontin Activation and Microcalcification in Venous Grafts Can Be Modulated by Dexamethasone

BACKGROUND

Osteopontin has been implicated in vascular calcification formation and vein graft intimal hyperplasia, and its expression can be triggered by pro-inflammatory activation of cells. The role of osteopontin and the temporal formation of microcalcification in vein grafts is poorly understood with a lack of understanding of the interaction between haemodynamic changes and the activation of osteopontin.

METHODS

We used a porcine model of vein interposition grafts, and human long saphenous veins exposed to ex vivo perfusion, to study the activation of osteopontin using polymerase chain reaction, immunostaining, and 18F-sodium fluoride autoradiography.

RESULTS

The porcine model showed that osteopontin is active in grafts within 1 week following surgery and demonstrated the presence of microcalcification. A brief pretreatment of long saphenous veins with dexamethasone can suppress osteopontin activation. Prolonged culture of veins after exposure to acute arterial haemodynamics resulted in the formation of microcalcification but this was suppressed by pretreatment with dexamethasone. 18F-sodium fluoride uptake was significantly increased as early as 1 week in both models, and the pretreatment of long saphenous veins with dexamethasone was able to abolish its uptake.

CONCLUSIONS

Osteopontin is activated in vein grafts and is associated with microcalcification formation. A brief pretreatment of veins ex vivo with dexamethasone can suppress its activation and associated microcalcification.

Coronary Atherosclerotic Plaque Activity and Future Coronary Events

Importance

Recurrent coronary events in patients with recent myocardial infarction remain a major clinical problem. Noninvasive measures of coronary atherosclerotic disease activity have the potential to identify individuals at greatest risk.

Objective

To assess whether coronary atherosclerotic plaque activity as assessed by noninvasive imaging is associated with recurrent coronary events in patients with myocardial infarction.

Design, Setting, and Participants

This prospective, longitudinal, international multicenter cohort study recruited participants aged 50 years or older with multivessel coronary artery disease and recent (within 21 days) myocardial infarction between September 2015 and February 2020, with a minimum 2 years' follow-up.

Intervention

Coronary 18F-sodium fluoride positron emission tomography and coronary computed tomography angiography.

Main Outcomes and Measures

Total coronary atherosclerotic plaque activity was assessed by 18F-sodium fluoride uptake. The primary end point was cardiac death or nonfatal myocardial infarction but was expanded during study conduct to include unscheduled coronary revascularization due to lower than anticipated primary event rates.

Results

Among 2684 patients screened, 995 were eligible, 712 attended for imaging, and 704 completed an interpretable scan and comprised the study population. The mean (SD) age of participants was 63.8 (8.2) years, and most were male (601 [85%]). Total coronary atherosclerotic plaque activity was identified in 421 participants (60%). After a median follow-up of 4 years (IQR, 3-5 years), 141 participants (20%) experienced the primary end point: 9 had cardiac death, 49 had nonfatal myocardial infarction, and 83 had unscheduled coronary revascularizations. Increased coronary plaque activity was not associated with the primary end point (hazard ratio [HR], 1.25; 95% CI, 0.89-1.76; P = .20) or unscheduled revascularization (HR, 0.98; 95% CI, 0.64-1.49; P = .91) but was associated with the secondary end point of cardiac death or nonfatal myocardial infarction (47 of 421 patients with high plaque activity [11.2%] vs 19 of 283 with low plaque activity [6.7%]; HR, 1.82; 95% CI, 1.07-3.10; P = .03) and all-cause mortality (30 of 421 patients with high plaque activity [7.1%] vs 9 of 283 with low plaque activity [3.2%]; HR, 2.43; 95% CI, 1.15-5.12; P = .02). After adjustment for differences in baseline clinical characteristics, coronary angiography findings, and Global Registry of Acute Coronary Events score, high coronary plaque activity was associated with cardiac death or nonfatal myocardial infarction (HR, 1.76; 95% CI, 1.00-3.10; P = .05) but not with all-cause mortality (HR, 2.01; 95% CI, 0.90-4.49; P = .09).

Conclusions and Relevance

In this cohort study of patients with recent myocardial infarction, coronary atherosclerotic plaque activity was not associated with the primary composite end point. The findings suggest that risk of cardiovascular death or myocardial infarction in patients with elevated plaque activity warrants further research to explore its incremental prognostic implications.