Elastin fluorescence

Tissue also contains some endogenous species that exhibit fluorescence, such as aromatic amino acids present in proteins (phenylalanine, tyrosine, and tryptophan), pyridine nucleotide enzyme cofactors (e.g., oxidized nicotinamide adenine dinucleotide, NADH pyridoxal phosphate flavin adenine dinucleotide, FAD), and cross-links between the collagen and the elastin in extracellular matrix.100 These typically possess excitation maxima in the ultraviolet, short natural lifetimes, and low quantum yields (see Table 10.1 for examples), but their characteristics strongly depend on whether they are bound to proteins. Excitation of these molecules would elicit background emission that would contaminate the emission due to implanted sensors, resulting in baseline offsets or even major spectral shifts in extreme cases therefore, it is necessary to carefully select fluorophores for implants. It is also noteworthy that the lifetimes are fairly short, such that use of longer lifetime emitters in sensors would allow lifetime-resolved measurements to extract sensor emission from overriding tissue fluorescence. 

Aortic samples, free of atherosclerotic lesions, were obtained from haemodialysis patients with end-stage renal disease and from age-matched controls.437 The media, but not the intima, proved positive immunohistochemically for pentosidine, which was observed along and between elastic fibres. In both groups, pentosidine-linked fluorescence was higher in elastin than in collagen, and the HPLC level of pentosidine was higher in the elastin from patients than in that from the controls. 

In the work of Loomeijer and work on similar lines carried out in the author s laboratory no evidence was found for the presence in important amounts of the common fatty esters, phospholipids, or steroids in purified preparations of elastin in these circumstances there seems to be little reason to classify elastin with the lipoproteins. The uptake of lipophilic dyes, which has been mentioned by several authors as indicating a lipoprotein character, can as well be explained by the presence of massive nonpolar radicals in the fluorescent prosthetic group, as described by Loomeijer, or to interactions with lipophilic sections of the peptide chain due to the large concentrations of nonpolar amino acids such as valine, the leucines, and phenylalanine. 

The soluble proteins derived from elastin retain the yellow color of the fibrous protein, and also its strong blue-white fluorescence, and the pigment cannot be removed by further mild hydrolysis and exhaustive dialysis or repeated precipitation with alcohol. It thus appears that a fluores-... 

Blomfiel J, Farrar JF (1969) Fluorescent properties of maturing arterial elastin. Cardiovasc Res 3 161-170... 

Purified elastin has a pale yellow color and a bluish fluorescence in uv light. Resists acid and alkaline hydrolysis. Practically insol in a wide range of hydrogen-bond-breaking solvents at temps up to 100° and swells, but does uot dissolve, in phenolic solvents. It appears practically impossible to bring elastin into oln except by hydrolytic reagents capable of rupturing peptide bonds. Elastin is one of only a few polymeric substances which, in the presence of water, exist in a form with rubber-Like extensibility and low modulus of elasticity. Enzymes which dissolve fibers of the insol protein... 

The dermis follows the epidermis and has a thickness of 1 to 2 mm. It is a complex structure and consists of cells including fibroblasts, mast cells, endothelial cells, blood cells, and nerve cells. Fluorescence microscopy suggests that the dermis is filled with a gel containing oriented tropocollagen (polypeptide) macromolecules. The network or gel structure is responsible for the elastic properties of the skin. An approximate composition of the dermis includes collagen (75%), elastin (4%), reticulin (0.4%), and ground... 

S. Sharpe, K. Simonetti, J. Yau, P. Walsh, Solid-state NMR characterization of auto-fluorescent fibrils formed by the elastin-derived peptide GVGVAGVG, Biomacromolecrfles 12 (2011) 1546—1555. 

Some of the fluorophores native to cells are NADH, flavins and aromatic aminoacids constituents of proteins (e.g., tryptophan, tyrosine, phenylalanine). Various porphyrins and lipopigments such as ceroids, lipofuscin, which are end products of lipid metabolism, also fluoresce. In addition, some important endogenous fluorophores are present in the extracellular structures of tissues. For example, collagen and elastin, present in the extracellular matrix (ECM), fluoresce as a result of cross-linking between amino acids. The absorption and emission spectra of some endogenous fluorophores are shown in Figure 3 (Katz and Alfano, 2000). 

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