Biochemical basis for the difference between normal and atherosclerotic arterial fluorescence.

Abstract

The observation that laser-induced fluorescence (LIF) spectra of atherosclerotic and normal artery are different has been proposed as the basis for guiding a "smart" laser angioplasty system. The purpose of this study was to investigate the causes of this difference in LIF. Helium-cadmium laser-induced (325 nm) fluorescence was recorded from pure samples of known constituents of normal and atherosclerotic artery including collagen, elastin, calcium, cholesterol, and glycosaminoglycans. Similarities between the LIF spectra of atherosclerotic plaque and collagen and normal aorta and elastin were noted. LIF spectroscopy was then performed on specimens of atherosclerotic aortic plaque (n=9) and normal aorta (n=13) and on their extracted lipid, collagen, and elastin. Lipid extraction did not significantly alter atherosclerotic plaque or normal aortic LIF, suggesting a minor contribution of lipid to arterial LIF. The LIF spectra of normal aorta wall was similar to the spectra of the extracted elastin, whereas the LIF spectra of atherosclerotic aortic plaque was similar to the spectra of the extracted collagen. These observations are consistent with the reported relative collagen-to-elastin content ratio of 0.5 for normal arterial wall and 7.3 for atherosclerotic plaque. A classification algorithm was developed to discriminate normal and atherosclerotic aortic spectra based on an elastin and collagen spectral decomposition. A discriminant score was formed by the difference of elastin and collagen (E-C) coefficients and used to classify 182 aortic fluorescence spectra. The mean E-C value was +0.83±0.04 for normal and -0.48±0.07 for atherosclerotic aorta (p<0.001). Classification accuracy was 92%. With 325-nm excitation, collagen and elastin are therefore the major fluorophores of aortic atherosclerotic plaque and normal aortic wall, respectively, and the difference between normal and atherosclerotic arterial fluorescence appears to be due to differences in relative collagen and elastin content. Consistent with this observation, a classification algorithm based on a collagen and elastin spectral decomposition can accurately classify normal and atherosclerotic aortic fluorescence spectra. Other laser lines may excite different chromophores. These findings will require validation for muscular arteries. (Circulation 1989;80:1893-1901 The difference between the laser-induced fluorescence spectra of atherosclerotic plaque and normal arterial wall has been well established1-5 and has been proposed as the basis

Discrimination of Human Coronary Artery Atherosclerotic Lipid-Rich Lesions by Time-Resolved Laser-Induced Fluorescence Spectroscopy

“…8,15 Calcium exhibits sharp fluorescence peaks in the 350-to 650-nm range on 308-nm excitation, 28 but its emission on longer excitation wavelengths (325 nm) was not reliably detected. 25 Consequently, these components are less likely to significantly influence the fluorescence characteristics reported in our study (excitation 337 nm).…”

“…8,15 Calcium exhibits sharp fluorescence peaks in the 350-to 650-nm range on 308-nm excitation, 28 but its emission on longer excitation wavelengths (325 nm) was not reliably detected. 25 Consequently, these components are less likely to significantly influence the fluorescence characteristics reported in our study (excitation 337 nm).Early work reported a penetration depth of irradiation at Ϸ337 nm of 150 to 200 m. 8 Therefore, the fluorescence of normal-wall and type I specimens in our study is likely to originate not only from intima but also from media (Figure 1), whereas the fluorescence of advanced lesions originates entirely from diseased intima. Furthermore, the fluorescence of type IV lesions is likely to be generated by both the thin cap and the top layers of the lipid-rich core, in contrast to type V a lesions, in which the emission may be yielded only by the thick collagenous cap.…”

“…The main fluorescent components of normal and diseased arterial wall, together with their emission characteristics, are depicted in Table II (http://atvb.ahajournals.org). [25][26][27][28][29][30][31][32] The fluorescence of the structural proteins elastin and collagen was related primarily to artery fluorescence. Previous research 8,25 demonstrated that the fluorescence of elastic fibers within the internal lamina or media predominates over the emission of normal coronary artery or aorta, respectively, whereas the fluorescence of collagen (30% to 60% dry weight 3 ) prevails over the emission of advanced collagenous lesions (type V a or fibrous plaques).…”

“…Chondroitin sulfate 340 -600 / 405 / 55 -325 Laifer et al 25 Hyaluronic acid 340 -600 / 405 / 55 -325 Laifer et al 25 Heparan sulfate 340 -600 / 400 / 55 -325 Laifer et al 25 i…”

Differential Expression of Connexin43 and Desmin Defines Two Subpopulations of Medial Smooth Muscle Cells in the Human Internal Mammary Artery

“…A third channel corresponding to FITC fluorescence was used to record autofluorescent signal that mainly derives from elastic fibers. 28 In addition, phase-contrast imaging was used, where appropriate, to enhance visualization of general tissue architecture. The images were taken by using singleor simultaneous dual-/triple-channel scanning; some were transformed into projection views by using sets of consecutive single optical sections.…”