Optical Properties of Europium Tetracycline Complexes in the Presence of High-Density Lipoproteins (HDL) Subfractions.

Standard lipoprotein measurements of triglycerides, total cholesterol, low-density lipoproteins (LDL), and high-density lipoproteins (HDL) fail to identify many lipoprotein abnormalities that contribute to cardiovascular heart diseases (CHD). Studies suggested that the presence of CHD is more strongly associated with the HDL subspecies than with total HDL cholesterol levels. The HDL particles can be collected in at least three subfractions, the HDL2b, HDL2a, and HDL3. More specifically, atherosclerosis is associated with low levels of HDL2. In this work, the optical spectroscopic properties of europium tetracycline (EuTc) complex in the presence of different HDL subspecies was studied. The results show that the europium spectroscopic properties in the EuTc complex are influenced by sizes and concentrations of subclasses. Eu3+ emission intensity and lifetime can discriminate the subfractions HDL3 and HDL2b.

Fluorescent lifetime imaging microscopy using Europium complexes improves atherosclerotic plaques discrimination.

The objective of this study is to characterize arterial tissue with and without atherosclerosis by fluorescence lifetime imaging microscopy (FLIM) using Europium Chlortetracycline complex (EuCTc) as fluorescent marker. For this study, twelve rabbits were randomly divided into a control group (CG) and an experimental group (EG), where they were fed a normal and hypercholesterolemic diet, respectively, and were treated for 60 days. Cryosections of the aortic arch specimens were cut in a vertical plane, mounted on glass slides, and stained with Europium (Eu), Chlortetracycline (CTc), Europium Chlortetracycline (EuCTc), and Europium Chlortetracycline Magnesium (EuCTcMg) solutions. FLIM images were obtained with excitation at 405 nm. The average autofluorescence lifetime within plaque depositions was ~1.36 ns. Reduced plaque autofluorescence lifetimes of 0.23 and 0.31 ns were observed on incubation with EuCTc and EuCTcMg respectively. It was observed a quenching of collagen, cholesterol and TG emission spectra increasing EuCTc concentration. The drastic reduction in fluorescence lifetimes is due to a resonant energy transfer between collagen, triglycerides, cholesterol and europium complexes, quenching fluorescence.

Aminolevulinic acid with gold nanoparticles: a novel theranostic agent for atherosclerosis.

In this study, 5-aminolevulinic acid (ALA) gold nanoparticles (ALA:AuNPs) functionalized with polyethylene glycol (PEG) were synthesized and administered to rabbits to evaluate their use in clinical practice as theranostic agents for atherosclerosis. This was done by measuring the porphyrin fluorescence extracted from the rabbits' blood and feces. An increase in blood and feces porphyrin emission after ALA:AuNP administration suggests that ALA was incorporated by gold nanoparticles, its structure was preserved, and a rapid conversion into endogenous porphyrins occurred, overloading the synthetic pathway that led to protoporphyrin IX (PPIX) accumulation. This finding indicated that this method can aid in the early diagnosis and therapy of atherosclerosis with high sensitivity.

Liquid biopsy of atherosclerosis using protoporphyrin IX as a biomarker.

Protoporphyrin IX (PPIX), a derivative of hematoporphyrin, can accumulate in rapidly growing tissues, including tumors and atherosclerotic plaques. The objective of this study is to employ PPIX fluorescence to detect the changes in blood caused by the formation of atheromatous plaques in arteries; this measurement can function as a liquid biopsy. For this purpose twenty four rabbits were randomly divided into groups: control group (CG)--fed with a normal diet, and an experimental group (EG)--fed with a hypercholesterolemic diet (1% cholesterol). Blood samples were collected before (0 time) and after 22, 43, 64 days to measure biochemical factors. The aortas were removed after 22, 43 and 64 days to assess the atherosclerotic plaques. PPIX was extracted from the blood and fluorescence was measured in the 550-750 nm range from samples that were excited at 405 nm. Aminolevulinic acid (ALA) was administered intravenously to increase the PPIX fluorescence intensity in the arteries and consequently in the liquid biopsy of the atherosclerotic plaques. The results have shown that the PPIX fluorescence increased as the atheromatous plaques grew. The aorta fluorescence and the PPIX fluorescence increased in the animals in the experimental group that received ALA. PPIX that accumulates in atheromatous plaques transfers to the blood and can be analyzed by extracting porphyrin from total blood. Therefore, this method can aid in the early diagnosis of atherosclerosis with high sensitivity.

Study of tryptophan lifetime fluorescence following low-density lipoprotein modification.

In this paper we report the effects of the irradiation of low-density lipoprotein (LDL) by ultra-short laser pulses to obtain in vitro alterations mimicking proatherogenic modifications occurring in vivo in LDL. The modifications by metallic ions (copper and iron) and ultra-short laser pulses were studied by fluorescence steady state and time-resolved lifetime measurements. The results demonstrate that the modifications caused by ultra-short laser pulses and by iron affect the tryptophan residues of apolipoprotein B-100 (Apo-B), slightly decreasing fluorescent lifetimes, with almost no modifications in pre-exponential factors, indicating preservation of structural properties around the fluorophore. On the other hand, oxidation by copper strongly affects the Apo-B protein associated with LDL. We describe a fast, inexpensive, and nondestructive fluorescence-based method that is readily accessible to provide the LDL particle characterization.