Abstract
Autofluorescence (AF) of crude serum was investigated with reference to the potential of its intrinsic AF biomarkers for the noninvasive diagnosis of liver injury. Spectral parameters of pure compounds representing retinol (vitamin A) and fluorescing free fatty acids were characterized by spectrofluorometry, to assess spectral parameters for the subsequent AF analysis of serum, collected from rats undergoing liver ischemia/reperfusion (I/R). Differences in AF spectral profiles detected between control and I/R were due to the increase in the AF components representing fatty acids in I/R serum samples. No significant changes occurred for retinol levels, consistently with the literature reporting that constant retinol levels are commonly observed in the blood, except for malnutrition or chronic severe liver disease. Conversely, fatty acids, in particular arachidonic and linoleic acid and their derivatives, act as modulating agents in inflammation, representing both a protective and damaging response to stress stimuli. The biometabolic and pathophysiological meaning of serum components and the possibility of their direct detection by AF spectrofluorometry open up interesting perspectives for the development of AF serum analysis, as a direct, cost effective, supportive tool to assess liver injury and related systemic metabolic alterations, for applications in experimental biomedicine and foreseen translation to the clinics.
Highlights
The development of optical biopsy for multipurpose diagnostic applications in biomedicine relies on the presence of numerous types of biomolecules acting as endogenous fluorophores (EFs) [1,2,3]
Changes in the contribution of fluorescing lipids to the overall liver tissue AF were suggested to depend on the intrinsic metabolic properties of normal and fatty livers, rather than on functional alteration induced by external interferences, in a likely agreement with the metabolic plasticity of liver engaged in the maintenance of its own and whole organism homeostasis [14,15]
The analyses addressed the choice of the excitation wavelengths at 310 nm and 366 nm, the latter matching with excitation wavelength previously applied by us to investigate AF of liver tissue, ex vivo and in vivo [4,42]
Summary
The development of optical biopsy for multipurpose diagnostic applications in biomedicine relies on the presence of numerous types of biomolecules acting as endogenous fluorophores (EFs) [1,2,3]. Arachidonic acid has been considered to represent fluorescing lipids contributing to the overall AF of liver tissue. Changes in the contribution of fluorescing lipids to the overall liver tissue AF were suggested to depend on the intrinsic metabolic properties of normal and fatty livers, rather than on functional alteration induced by external interferences, in a likely agreement with the metabolic plasticity of liver engaged in the maintenance of its own and whole organism homeostasis [14,15]. Subsequent work on pure compounds and lipid extract solutions from liver tissue showed the AF ability to discriminate arachidonic acid from other fluorescing free fatty acids, such as linoleic and oleic acids [16,17]. The semi quantitative analysis of the AF contribution of these lipid components, in parallel with mass spectrometry data, showed changes in the balance between arachidonic acid and a miscellanea of the other fluorescing free fatty acids in two different models of fatty liver, genetic or induced by a methyl-choline deficient (MCD)
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