Intrinsic Fluorescence and Diffuse Reflectance Spectroscopy Identify Superficial Foam Cells in Coronary Plaques Prone to Erosion

Abstract

Objective-Foam cells perform critical functions in atherosclerosis. We hypothesize that coronary segments with superficial foam cells (SFCs) situated in a region of interest with a depth of 200 m can be identified using intrinsic fluorescence spectroscopy (IFS) and diffuse reflectance spectroscopy (DRS). This is a key step in our ongoing program to develop a spectroscopic technique for real-time in vivo diagnosis of vulnerable atherosclerotic plaque. Methods and Results-We subjected 132 human coronary segments to in vitro IFS and DRS. We detected SFCs in 13 thick fibrous cap atheromas and 8 pathologic intimal thickening (PIT) lesions. SFCs colocalized with accumulations of smooth muscle cells and proteoglycans, including hyaluronan (PϽ0.001). Two spectroscopic parameters were generated from analysis of IFS at 480 nm excitation and DRS. A discriminatory algorithm using these parameters identified specimens with SFC area Ͼ40%, 20%, 10%, 5%, 2.5%, and 0% of the region of interest with 98%, 98%, 93%, 94%, 93%, and 90% accuracy, respectively. Key Words: foam cells Ⅲ spectroscopy Ⅲ atherosclerosis Ⅲ coronary artery disease Ⅲ human A s a continuation of our work of arterial fluorescence and Raman spectroscopy, 1 we developed an ongoing program targeting the diagnosis of vulnerable atherosclerotic plaques. The main objective of the current study was to demonstrate that a combination of intrinsic fluorescence spectroscopy (IFS) and diffuse reflectance spectroscopy (DRS) can accurately detect human coronary superficial foam cells (SFCs), a potential marker of vulnerable atherosclerotic plaques. Conclusion-Our combined IFS and DRS technique accurately detectsFibrous cap rupture and plaque erosion are the 2 main causes of coronary thrombosis. 2 Eroded plaques are responsible for at least a third of sudden cardiac deaths, with increased prevalence among young subjects. 2,3 Several studies have demonstrated the presence of macrophages and foam cells in ruptured and eroded vulnerable plaques. [3][4][5] Eroded plaques accumulate in their superficial layers macrophages, proteoglycans, smooth muscle cells (SMCs), and extracellular lipids. 2-7 However, whereas ruptured plaques feature a necrotic core and thin fibrous cap, these 2 structures are not necessarily present in eroded plaques. 2,3,6,7 Hence, an ideal technique for diagnosis of vulnerable plaques prone to rupture or erosion should be able to accurately identify macrophages and macrophage-derived foam cells.Although existing invasive diagnostic techniques such as intravascular ultrasound, elastography, and intravascular MRI can identify subsurface plaque features such as fibrous cap and necrotic core, it is only thermography and more recently optical coherence tomography that can identify areas of increased macrophage density. 8 However, none of these methods have focused specifically on foam cells, which, through their interaction with oxidized low-density lipoprotein (LDL) particles and complex inflammatory and plaque degrading functions, play a critical role in the vuln...

Fluorescence lifetime in cardiovascular diagnostics

“…[23][24][25][26][27][28][29][30][31][32][33][34] Fluorescence spectroscopy techniques have been shown to detect elastin, collagen, lipids, and other sources of autofluorescence in normal and diseased arterial walls as well as to characterize the biochemical composition of atherosclerotic plaques both ex vivo and in vivo. 19,22,24,[35][36][37][38][39][40][41] More recently, a few studies have reported the application of fluorescence techniques to the identification of plaque disruption, 39 detection of plaques with thin fibrous cap, 40 discrimination of lipid-rich lesions, 42 and detection of macrophage infiltration. 41,[43][44][45] All of these are considered features associated with plaque vulnerability.…”

“…19,22,24,[35][36][37][38][39][40][41] More recently, a few studies have reported the application of fluorescence techniques to the identification of plaque disruption, 39 detection of plaques with thin fibrous cap, 40 discrimination of lipid-rich lesions, 42 and detection of macrophage infiltration. 41,[43][44][45] All of these are considered features associated with plaque vulnerability. 1 Fluorescence measurements can be conducted as either steady state ͑spectrally resolved͒ or time resolved.…”

Multimodal spectroscopy detects features of vulnerable atherosclerotic plaque

“…Moreover, there is sound physical basis and justification for the agreement between spectroscopy and histology rather than simply statistical correlations. The algorithm for detecting NC /SFCs is consistent with previously published work, in which β-carotene from DRS was used to detect SFCs, 12 and the Raman contribution 9, 13, 24 was used to detect lipid pools. However, this is the first time that such an algorithm is proposed that utilizes both DRS and Raman spectral parameters in a joint classification.…”

“…9 Independently, we have also shown the potential of diffuse reflectance spectroscopy (DRS) and intrinsic fluorescence spectroscopy (IFS) to detect plaque vulnerability features such as superficial foam cells. 12 By combining DRS, IFS, and Raman spectroscopy, a methodology we call multimodal spectroscopy (MMS), we can obtain even more detailed information about the disease state of the plaque. 13 The spectroscopic information provided by the three components of MMS is complementary and depth sensitive.…”

Histological Characteristics of Glistening Yellow Coronary Plaques Seen on Angioscopy - With Special Reference to Vulnerable Plaques -

“…17 Angheloiu et al observed superficial foam cells in erosion-prone plaque. 18 Although depostion of proteoglycans and hyaluronan were not examined, frequent deposition of MF in the superficial layer indicates that the superficial lipid deposition group and the calcified cap subtype of yellow plaques were a pre-stage of erosion.…”