Hamish Richardson

Coronary Arterial 18F-Sodium Fluoride Uptake : A Novel Marker of Plaque Biology

OBJECTIVES With combined positron emission tomography and computed tomography (CT), we investigated coronary arterial uptake of 18F-sodium fluoride (18F-NaF) and 18F-fluorodeoxyglucose (18F-FDG) as markers of active plaque calcification and inflammation, respectively. BACKGROUND The noninvasive assessment of coronary artery plaque biology would be a major advance particularly in the identification of vulnerable plaques, which are associated with specific pathological characteristics, including micro-calcification and inflammation. METHODS We prospectively recruited 119 volunteers (72 ± 8 years of age, 68% men) with and without aortic valve disease and measured their coronary calcium score and 18F-NaF and 18F-FDG uptake. Patients with a calcium score of 0 were used as control subjects and compared with those with calcific atherosclerosis (calcium score >0). RESULTS Inter-observer repeatability of coronary 18F-NaF uptake measurements (maximum tissue/background ratio) was excellent (intra-class coefficient 0.99). Activity was higher in patients with coronary atherosclerosis (n = 106) versus control subjects (1.64 ± 0.49 vs. 1.23 ± 0.24; p = 0.003) and correlated with the calcium score (r = 0.652, p < 0.001), although 40% of those with scores >1,000 displayed normal uptake. Patients with increased coronary 18F-NaF activity (n = 40) had higher rates of prior cardiovascular events (p = 0.016) and angina (p = 0.023) and higher Framingham risk scores (p = 0.011). Quantification of coronary 18F-FDG uptake was hampered by myocardial activity and was not increased in patients with atherosclerosis versus control subjects (p = 0.498). CONCLUSIONS 18F-NaF is a promising new approach for the assessment of coronary artery plaque biology. Prospective studies with clinical outcomes are now needed to assess whether coronary 18F-NaF uptake represents a novel marker of plaque vulnerability, recent plaque rupture, and future cardiovascular risk. (An Observational PET/CT Study Examining the Role of Active Valvular Calcification and Inflammation in Patients With Aortic Stenosis; NCT01358513).

Assessment of Valvular Calcification and Inflammation by Positron Emission Tomography in Patients With Aortic Stenosis

Background— The pathophysiology of aortic stenosis is incompletely understood, and the relative contributions of valvular calcification and inflammation to disease progression are unknown. Methods and Results— Patients with aortic sclerosis and mild, moderate, and severe stenosis were compared prospectively with age- and sex-matched control subjects. Aortic valve severity was determined by echocardiography. Calcification and inflammation in the aortic valve were assessed by 18F-sodium fluoride (18F-NaF) and 18F-fluorodeoxyglucose (18F-FDG) uptake with the use of positron emission tomography. One hundred twenty-one subjects (20 controls; 20 aortic sclerosis; 25 mild, 33 moderate, and 23 severe aortic stenosis) were administered both 18F-NaF and 18F-FDG. Quantification of tracer uptake within the valve demonstrated excellent interobserver repeatability with no fixed or proportional biases and limits of agreement of ±0.21 (18F-NaF) and ±0.13 (18F-FDG) for maximum tissue-to-background ratios. Activity of both tracers was higher in patients with aortic stenosis than in control subjects (18F-NaF: 2.87±0.82 versus 1.55±0.17; 18F-FDG: 1.58±0.21 versus 1.30±0.13; both P<0.001). 18F-NaF uptake displayed a progressive rise with valve severity (r2=0.540, P<0.001), with a more modest increase observed for 18F-FDG (r2=0.218, P<0.001). Among patients with aortic stenosis, 91% had increased 18F-NaF uptake (>1.97), and 35% had increased 18F-FDG uptake (>1.63). A weak correlation between the activities of these tracers was observed (r2=0.174, P<0.001). Conclusions— Positron emission tomography is a novel, feasible, and repeatable approach to the evaluation of valvular calcification and inflammation in patients with aortic stenosis. The frequency and magnitude of increased tracer activity correlate with disease severity and are strongest for 18F-NaF. Clinical Trial Registration— http://www.clinicaltrials.gov. Unique identifier: NCT01358513.

18F-Sodium Fluoride Uptake Is a Marker of Active Calcification and Disease Progression in Patients With Aortic Stenosis

Background—18F-Sodium fluoride (18F-NaF) and 18F-fluorodeoxyglucose (18F-FDG) are promising novel biomarkers of disease activity in aortic stenosis. We compared 18F-NaF and 18F-FDG uptake with histological characterization of the aortic valve and assessed whether they predicted disease progression. Methods and Results—Thirty patients with aortic stenosis underwent combined positron emission and computed tomography using 18F-NaF and 18F-FDG radiotracers. In 12 patients undergoing aortic valve replacement surgery (10 for each tracer), radiotracer uptake (mean tissue/background ratio) was compared with CD68 (inflammation), alkaline phosphatase, and osteocalcin (calcification) immunohistochemistry of the excised valve. In 18 patients (6 aortic sclerosis, 5 mild, and 7 moderate), aortic valve computed tomography calcium scoring was performed at baseline and after 1 year. Aortic valve 18F-NaF uptake correlated with both alkaline phosphatase (r=0.65; P=0.04) and osteocalcin (r=0.68; P=0.03) immunohistochemistry. There was no significant correlation between 18F-FDG uptake and CD68 staining (r=−0.43; P=0.22). After 1 year, aortic valve calcification increased from 314 (193–540) to 365 (207–934) AU (P<0.01). Baseline 18F-NaF uptake correlated closely with the change in calcium score (r=0.66; P<0.01), and this improved further (r=0.75; P<0.01) when 18F-NaF uptake overlying computed tomography–defined macrocalcification was excluded. No significant correlation was noted between valvular 18F-FDG uptake and change in calcium score (r=−0.11; P=0.66). Conclusions—18F-NaF uptake identifies active tissue calcification and predicts disease progression in patients with calcific aortic stenosis. Clinical Trial Registration—URL: http://www.clinicaltrials.gov. Unique identifier: NCT01358513.

18F-NaF Uptake Is a Marker of Active Calcification and Disease Progression in Patients with Aortic Stenosis

Background—18F-Sodium fluoride (18F-NaF) and 18F-fluorodeoxyglucose (18F-FDG) are promising novel biomarkers of disease activity in aortic stenosis. We compared 18F-NaF and 18F-FDG uptake with histological characterization of the aortic valve and assessed whether they predicted disease progression. Methods and Results—Thirty patients with aortic stenosis underwent combined positron emission and computed tomography using 18F-NaF and 18F-FDG radiotracers. In 12 patients undergoing aortic valve replacement surgery (10 for each tracer), radiotracer uptake (mean tissue/background ratio) was compared with CD68 (inflammation), alkaline phosphatase, and osteocalcin (calcification) immunohistochemistry of the excised valve. In 18 patients (6 aortic sclerosis, 5 mild, and 7 moderate), aortic valve computed tomography calcium scoring was performed at baseline and after 1 year. Aortic valve 18F-NaF uptake correlated with both alkaline phosphatase (r=0.65; P=0.04) and osteocalcin (r=0.68; P=0.03) immunohistochemistry. There was no significant correlation between 18F-FDG uptake and CD68 staining (r=−0.43; P=0.22). After 1 year, aortic valve calcification increased from 314 (193–540) to 365 (207–934) AU (P<0.01). Baseline 18F-NaF uptake correlated closely with the change in calcium score (r=0.66; P<0.01), and this improved further (r=0.75; P<0.01) when 18F-NaF uptake overlying computed tomography–defined macrocalcification was excluded. No significant correlation was noted between valvular 18F-FDG uptake and change in calcium score (r=−0.11; P=0.66). Conclusions—18F-NaF uptake identifies active tissue calcification and predicts disease progression in patients with calcific aortic stenosis. Clinical Trial Registration—URL: http://www.clinicaltrials.gov. Unique identifier: NCT01358513.

A Randomized Controlled Trial of Peripheral Blood Mononuclear Cell Depletion in Experimental Human Lung Inflammation

RATIONALE Depletion of monocytes reduces LPS-induced lung inflammation in mice, suggesting monocytes as potential therapeutic targets in acute lung injury. OBJECTIVES To investigate whether depletion of circulating blood monocytes has beneficial effects on markers of systemic and pulmonary inflammation in a human model of acute lung inflammation. METHODS A total of 30 healthy volunteers were enrolled in a randomized controlled trial. Volunteers inhaled LPS at baseline, and were randomized to receive active mononuclear cell depletion by leukapheresis, or sham leukapheresis, in a double-blind fashion (15 volunteers per group). Serial blood counts were measured, bronchoalveolar lavage (BAL) was performed at 9 hours, and [(18)F]fluorodeoxyglucose positron emission tomography at 24 hours. The primary endpoint was the increment in circulating neutrophils at 8 hours. MEASUREMENTS AND MAIN RESULTS As expected, inhalation of LPS induced neutrophilia and an up-regulation of inflammatory mediators in the blood and lungs of all volunteers. There was no significant difference between the depletion and sham groups in the mean increment in blood neutrophil count at 8 hours (6.16 × 10(9)/L and 6.15 × 10(9)/L, respectively; P = 1.00). Furthermore, there were no significant differences in BAL neutrophils or protein, positron emission tomography-derived measures of global lung inflammation, or cytokine levels in plasma or BAL supernatant between the study groups. No serious adverse events occurred, and no symptoms were significantly different between the groups. CONCLUSIONS These findings do not support a role for circulating human monocytes in the early recruitment of neutrophils during LPS-mediated acute lung inflammation in humans.

18F-NAF IS A PREDICTOR OF PROGRESSION AND OUTCOME IN AORTIC VALVE DISEASE

Calcification is a key process in the pathogenesis of aortic stenosis and its activity in the valve can be measured using the positron-emission-tomography (PET) tracer 18F-sodium fluoride (18F-NaF). We sought to assess whether 18F-NaF PET predicts progression and outcomes in aortic stenosis. We

Reply: The alveolar macrophage and acute respiratory distress syndrome: a silent actor?

We are grateful to Dr. Mokart and colleagues for their interest in our article (1) and for their stimulating comments. We entirely agree that the pathogenesis of acute lung injury (ALI) is complex and that many cell types are likely to be involved. In many respects, our purpose was to stimulate the process of taking a systematic experimental approach from in vivo models to the more relevant human situation. In this setting, and at this very early stage, experimental considerations led us to try to change as few variables as possible (in this case attempting to target circulating monocytes by mononuclear cell leukapheresis). Equally, ethical considerations clearly impacted which cell types we could deplete, and a comprehensive assessment of the role of alveolar macrophages in the human situation was always going to be beyond the scope of our study. Having said this, and in keeping with findings elsewhere (2, 3), our in vivo work showed that prior depletion of alveolar macrophages (with preservation of blood monocytes) did not influence the progression of ALI (4). In contrast, depletion of monocytes after the delivery of intratracheal LPS significantly reduced lung inflammation, despite the preservation of alveolar macrophages (4). The correspondents also make interesting points in relation to the setting of neutropenia. We completely agree that ALI occurs in this context. However, our specific intention was to study the influence of monocytes in a neutrophil-dependent model of lung inflammation. As the authors imply, the pathogenesis of ALI associated with neutropenia is likely to be quite different from “usual” ALI. The authors correctly point out that we depleted monocytes after administration of LPS. However, we have performed similar in vivo experiments in which monocytes were depleted before LPS administration (Dhaliwal and colleagues, unpublished data). Prior monocyte depletion also significantly reduced acute lung inflammation. In our human study, we chose to deplete monocytes after LPS inhalation because physicians are far more commonly faced with established ALI than with the opportunity to prevent it. We accept that “prophylactic” monocyte depletion might potentially have yielded a different outcome from the one we observed in our human study, and this deserves further exploration. We also accept that our model of human inflammation attempts to mimic “subclinical” ALI— monocytes undoubtedly play a role in established ALI. Furthermore, our in vivo model had an endpoint at 48 hours, with optimal monocyte depletion at 18 hours, which was sustained to the end of the study period. This is different from our human model, in which we temporally depleted mononuclear cells within 2 hours of LPS, with a recrudescence before 24 hours. It was not our intention to draw conclusions about “the role of monocytes in ARDS pathophysiology.” In keeping with logistical and ethical constraints, our intention was to evaluate the potential influence of circulating mononuclear cells on subclinical LPS-induced (i.e., neutrophil-dependent) acute lung inflammation in humans. Ultimately, we believe our study highlights the feasibility of evaluating the pathophysiology of (and new interventions for) acute lung inflammation in humans. However, it simultaneously emphasizes difficulties in attempting to replicate experimental conditions and responses between rodents and humans, and the challenges inherent in influencing leukocyte populations in human studies. As Mokart and colleagues imply, experimental and interventional studies of human acute lung inflammation are at an early stage and have a long way to go. n

18F-SODIUM FLUORIDE IS A MARKER OF ACTIVE CALCIFICATION AND DISEASE PROGRESSION IN PATIENTS WITH AORTIC STENOSIS

results: Over 1 year aortic valve calcification increased (469±479 vs 580±576 p<0.01) in patients with a range of disease severity (6 sclerosis; 5 mild, 7 moderate, 2 severe stenosis). 18FNaF uptake correlated with disease progression: both in terms of the calcium score (r2=0.44 p<0.01) and aortic valve area (r2=0.24 P=0.03). When 18FNaF overlying existing calcium on the CT was excluded, the correlation improved further (r2= 0.64 p<0.01). There were no associations between 18FFDG uptake and CT or echo measures of disease progression (r2=0.02 p=0.55). There was a good correlation between in vivo 18FNaF uptake and both alkaline phosphatase (n=7; r2=0.79 P<0.01) and osteocalcin staining (n=5; r2=0.43 P=0.22) of the excised tissue.

CORONARY ARTERIAL 18F-NAF UPTAKE: A NOVEL MARKER OF PLAQUE BIOLOGY

Results: Repeatability statistics for the measurement of the coronary 18F-NaF uptake (max TBR) were excellent (intra-class coeficient 0.99). Activity was higher in patients with coronary atherosclerosis versus controls (1.64±0.49 vs 1.23±0.24; p 1000 displayed normal uptake. Patients with increased coronary 18F-NaF (n=40) had higher rates of prior cardiovascular events (P=0.02) and angina (p=0.02) and higher Framingham risk scores (P=0.01). By contrast quantiication of coronary 18F-FDG activity was hampered by myocardial uptake and not increased in those with atherosclerosis versus controls (p=0.50). Conclusion: 18F-NaF is a promising new approach for the assessment of coronary plaque biology and appears to be a novel marker of vulnerability, recent plaque rupture and cardiovascular risk

B Assessment of valvular calcification and inflammation by positron emission tomography

Background The pathophysiology of aortic stenosis is incompletely understood and the relative contributions of valvular calcification and inflammation to disease progression are unknown. Methods Patients with aortic sclerosis and mild, moderate and severe stenosis were prospectively compared to age and sex-matched control subjects. Aortic valve severity was determined by echocardiography. Calcification and inflammation in the aortic valve were assessed by sodium 18-fluoride (18F-NaF) and 18-fluorodeoxyglucose (18F-FDG) uptake using positron emission tomography. Histological analysis was performed on the valves of five patients who subsequently underwent aortic valve replacement. Results 121 subjects (20 controls; 20 aortic sclerosis; 25 mild, 33 moderate and 23 severe aortic stenosis) were administered both 18F-NaF and 18F-FDG. Quantification of tracer uptake within the valve demonstrated excellent inter-observer repeatability with no fixed or proportional biases and limits of agreement of ±0.21 (18F-NaF) and ±0.13 (18F-FDG) for maximum tissue-to-background ratios. Activity of both tracers was higher in patients with aortic stenosis than control subjects (18F-NaF: 2.87±0.82 vs 1.55±0.17; 18F-FDG: 1.58±0.21 vs 1.30±0.13; both p<0.001). 18F-NaF uptake displayed a progressive rise with valve severity (r2=0.540, p<0.001) and colocalised to osteocalcin staining on histology. Uptake was observed both in the presence and absence of underlying calcium on CT with the latter predominating. 18F-FDG displayed a more modest increase in activity with valve severity (r2=0.218; p<0.001) and mapped to areas of macrophage accumulation. Among patients with aortic stenosis, 91% had increased 18F-NaF (>1.97) and 35% increased 18F-FDG (>1.63) uptake. A weak correlation between the activities of these tracers was observed (r2=0.174, p<0.001) and while 18F-NaF activity was higher in the aortic valve than aortic atheroma (2.68±0.84 vs 2.07±0.30; p<0.001) the reverse was true for 18F-FDG (1.56±0.21 vs 1.80±0.25; p<0.001). Conclusions Positron emission tomography is a novel, feasible and repeatable approach to the evaluation of valvular calcification and inflammation in patients with aortic stenosis. Calcification appears to be the predominant process that is particular to the valve and disproportionate to the degree of inflammation, indicating it to be a more attractive target for therapeutic intervention.