Laser-induced fluorescence detection of cardiovascular atherosclerotic deposits via their natural emission and hypocrellin (HA) probing

Fluorescence lifetime in cardiovascular diagnostics

We review fluorescence lifetime techniques including time-resolved laser-induced fluorescence spectroscopy (TR-LIFS) and fluorescence lifetime imaging microscopy (FLIM) instrumentation and associated methodologies that allow for characterization and diagnosis of atherosclerotic plaques. Emphasis is placed on the translational research potential of TR-LIFS and FLIM and on determining whether intrinsic fluorescence signals can be used to provide useful contrast for the diagnosis of high-risk atherosclerotic plaque. Our results demonstrate that these techniques allow for the discrimination of important biochemical features involved in atherosclerotic plaque instability and rupture and show their potential for future intravascular applications.

Classification of atherosclerotic rabbit aorta samples by mid-infrared spectroscopy using multivariate data analysis

Atherosclerotic and normal rabbit aorta samples show a marked difference in chemical composition governed by the water, lipid, and protein content. The strongly overlapping infrared absorption features of the different constituents, and the complexity of the tissue matrix, render tissue classification by direct evaluation of molecular spectroscopic characteristics obtained from IR reflectance or attenuated total reflectance (ATR) measurements virtually impossible. We apply multivariate analysis and classification techniques based on partial least squares regression (PLS) and linear discriminant analysis to IR spectroscopic data obtained by IR-ATR measurements and reflectance IR microscopy with high predictive accuracy during blind testing. Training data are collected from atherosclerotic and normal rabbit aorta samples. These results demonstrate the potential of IR spectroscopy combined with multivariate classification strategies for the in-vitro identification of normal and atherosclerotic aorta tissue. The prospect for future in-vivo measurement concepts is also discussed.

Artificial neural networks for discriminating pathologic from normal peripheral vascular tissue

The identification of the state of human peripheral vascular tissue by using artificial neural networks is discussed in this paper. Two different laser emission lines (He-Cd, Ar+) are used to excite the chromophores of tissue samples. The fluorescence spectrum obtained, is passed through a nonlinear filter based on a high-order (HO) neural network neural network (NN) [HONN] whose weights are updated by stable learning laws, to perform feature extraction. The values of the feature vector reveal information regarding the tissue state. Then a classical multilayer perceptron is employed to serve as a classifier of the feature vector, giving 100% successful results for the specific data set considered. Our method achieves not only the discrimination between normal and pathologic human tissue, but also the successful discrimination between the different types of pathologic tissue (fibrous, calcified). Furthermore, the small time needed to acquire and analyze the fluorescence spectra together with the high rates of success, proves our method very attractive for real-time applications.

Spectroscopic characterisation of carotid atherosclerotic plaque by laser induced fluorescence

BACKGROUND AND OBJECTIVE

An effort has been made to distinguish the composition of carotid atherosclerotic plaques (CAP) from patients undergoing carotid endarterectomy, by laser induced fluorescence spectroscopy.

STUDY DESIGN/MATERIALS AND METHODS

Different excitation wavelengths were used: 476, 488, and 458 nm of a continuous wave krypton/argon ion laser, and 337 nm of a pulsed nitrogen laser. Twenty-three CAP samples from different patients were investigated and several spectra from each plaque were obtained.

RESULTS

Results were crossed-examined with conventional histologic techniques, which showed three areas of different composition on the pathologic samples: fibrous tissue, lipid constituents, and calcified plaque. Gaussian fittings were performed to reproduce the fluorescence spectra as a correlation of multiple Gaussian curves.

CONCLUSION

The accuracy for discrimination of the heterogeneous composition of the atherosclerotic plaque is still limited, due to superposition of the fluorescence emission of various plaque components.

Single and double wavelength excitation of laser-induced fluorescence of normal and atherosclerotic peripheral vascular tissue

Laser-induced fluorescence spectra were recorded from the exposure of peripheral vascular tissue to both helium-cadmium and argon-ion laser radiation. Spectral analysis was based on simple algebraic expressions constructed using the intensity difference of the various spectral regions. The above methods were developed in order to determine the degree of atherosclerosis according to the laser-induced fluorescence signal. Similar results with single wavelength excitation were observed during in vivo irradiation of peripheral vessels.

ESR and UV-Vis studies of semiquinone radical anion and hydroquinone generated by irradiation of 15-deacetyl-13-glycine substituted hypocrellin B

15-Deacetyl-13-glycine substituted hypocrellin B (GDHB) is a new type of hypocrellin derivative with enhanced red absorption longer than 600 nm and water solubility. When an anaerobic DMSO or DMSO-buffer (pH 7.4) solution of GDHB was illuminated with >470 nm light, a strong electron spin resonance (ESR) signal was formed. The ESR signal was assigned to the semiquinone anion radical of GDHB (GDHB*-) based on a series of experiments. GDHB*- was predominantly photoproducted via the self-electron transfer between the excited- and ground-state species. Decay of this species, both in the presence and absence of electron donor, was consistent with second-order kinetics. In aqueous solution, the TEMPO counter-spin experiment indicated the formation of GDHB*- that could not be detected by ESR method directly. The formation of GDHB*- and hydroquinone of GDHB (GDHBH*-) was also confirmed by spectrometric method. These findings suggested that GDHB was at least a favorable type I phototherapeutic agent.

Glycoconjugated hypocrellin: synthesis of [(beta-D-glucosyl)ethylthiyl]hypocrellins and photosensitized generation of singlet oxygen

In order to improve the water solubility and specific affinity for malignant tumors of hypocrellin, glycoconjugated hypocrellins have been synthesized using an improved Königs-Knörr reaction from mercaptoethanol substituted hypocrellin B and 2,3,4,6-tetra-O-acetyl-alpha-D-glucopyranosyl bromide precursors. Deprotection of glucose moieties allows the production of derivatives which had improved solubility in neutral aqueous solution and covered a range of amphiphilic character. The structures of these new protected and unprotected compounds were characterized by UV-Vis, IR, 1H-NMR and MS data. The present strategy should prove applicable to the synthesis of other glycoconjugated perylenequinone compounds. In addition, the quantum yield of singlet oxygen generation photosensitized by these glycoconjugated hypocrellins has been determined.

Spectral variations of laser-induced tissue emission during in vivo detection of malignancies in the female genital tract

A laser-based fluorescence-guided biopsy system has been developed for the screening and early detection of malignancies in the female inner/outer genital tract. Fluorescence spectra were recorded during in vivo exposure of normal and malignant tissue to He-Cd laser (442 nm) radiation. Spectral distribution of tissue natural fluorescence allowed for the development of simple algorithms, based on spectral intensity variations. A subsequent index of discrimination between normal and various malignant tissues has been calculated. This study focuses on the variability of the experimental data and the possible sources of spectral variations. These results suggest that monitoring of this index during colposcopy could enhance selective detection of the malignant tissue, reducing the risk of leaving pathologic tissue untreated during standard exploratory surgical procedures.

Novel therapeutic and diagnostic applications of hypocrellins and hypericins

Hypocrellins and hypericins, structurally related plant pigments isolated from Hypocrella bambuase and Hypericum respectively, are known photodynamic agents. This review summarizes certain significant advances in the photophysics, photochemistry and photobiology of these pigments in the last 2 years and discusses their prospects as novel therapeutic and diagnostic agents in the future. Recently, certain unique properties of hypocrellins and hypericins have been explored for a variety of therapeutic and diagnostic applications. In particular, substantial progress has been made in both anticancer and antiviral applications (especially anti-human immunodeficiency virus). The promising anticancer and antiviral results obtained both in vitro and in vivo have led to intensive investigation into their photo-physical and photochemical processes, especially kinetic studies of their intramolecular proton transfer. These compounds offer the potential for a highly sensitive fluorescent redox sensor for investigation of a variety of cellular events. The biomedical advances of hypocrellins and hypericins have been further promoted by significant progress in their chemical synthesis and the recent commercialization of hypocrellins A and B and hypericin.

Malignancies and atherosclerotic plaque diagnosis--is laser induced fluorescence spectroscopy the ultimate solution?

A non-invasive diagnostic tool that can identify diseased tissue sites in situ and in real time could have a major impact on the detection and treatment of cancer and atherosclerosis. A review of the research performed on the utilization of laser induced fluorescence spectroscopy (LIFS) as a means of diseased tissue diagnosis is presented. Special emphasis is given to problems which were raised during clinical trials and recent experimental studies. The common origin and possible solution of these problems are shown to be related to, firstly, the identification of the fluorescent chemical species, secondly, the determination of the excitation/collection geometry and its effect to the method and, finally, the further elaboration on the laser-tissue interaction.