Age-related changes in composition and mechanical properties of the tunica media of the upper thoracic human aorta.

Abstract

A cylindrical segment, free of complex atherosclerotic lesions, was resected at autopsy from each of 59 descending human thoracic aortas by cutting just below the level of the first pair of intercostal arteries and 35 mm distal to this incision. Each isolated tunica media was defatted and subjected to successive treatment with EDTATris, 5 M guanidine hydrochloride-Tris, 5 M guanidine hydrochloride-Tris-DTE, collagenase and either trypsin or hot alkali. After each extraction or digestion, the dimensions and weight of the segments were measured and the extracted materials were analyzed and quantltated. This allowed the total content of the various components of the tunica media to be assessed by both gravimetric and analytical means. An agerelated rise was observed in the total content of the following components: proteins and glycoproteins soluble in chaotropic solvents (ranging from 24 mg/cm in the youngest samples to 46 mg/cm in the oldest) and collagen (38 mg/cm to 69 mg/cm).In contrast, the total content of elastin remained constant at 70 mg/cm at all ages, but its concentration decreased due to the rise in the concentration of the other tissue components as the tunica media thickened with age. It was also noted that with increasing age there was an accumulation of protein(s) which could not be solubilized by extraction with chaotropic agents or with collagenase, but which could be removed by treatment with either trypsin or hot alkali. Mechanical measurements conducted before and after trypsin digestion on samples previously subjected to purification with the first four agents used suggest that this accumulated protein(s) influenced the elastic response of the tissue to the applied stress by increasing the incremental modulus, the breaking stress, and the hysteresis. After the removal of this additional protein(s), the mechanical behavior of the elastin component was found to be Identical in all samples, irrespective of age. It is therefore proposed that the morphological changes and the stiffening observed in the aging aortic wall are not due to degradation of its elastin network but to variations in the supramolecular organization of connective tissue components. (Arteriosclerosis 3:64-76, January/February 1983) W ith advancing age, the human aorta dilates and becomes stiffer at physiological pressures. To date, investigations aimed at the identification of compositional or structural changes of the wall components responsible for these alterations have produced rather conflicting results. 6 " 9 This probably reflects differences in sampling or in the methodologies adopted for the isolation and quantitation of ma- trix components, complicated by the use of relative, rather than absolute, concentrations in the expression of the results. 10 In addition, it is not yet known whether the mechanical properties of the aortic collagen fibers change with aging, while data relating to the dynamics of the elastin component, which is responsible for the long-range reversible extensibility of the vessel, are largely u...

Soluble Elastin Fragments in Serum Are Elevated in Acute Aortic Dissection

“…15,16 With aging, the structure of the aortic wall is altered: it dilates and becomes thicker with fragmentation and/or the calcification of elastin fibers. 17,19,22,26 In accordance with such pathological developments, the sELAF levels in sera from healthy subjects gradually increase as the subjects progress from their teens to old age (Figure 1). …”

“…16,17,19,20,22 In contrast, the interlaminar elastic fibers become irregular in arrangement and shape and decrease in number in AAD patients. 19,20 This disarrangement and decrease of interlaminar elastic fibers may result in medial instability and weakness against various forces, especially against the force that dissects the media.…”

“…[12][13][14][15][16][17][18] Mature elastin is composed of soluble elastin subunits, which are intermolecularly cross-linked into a fibrous network (desmosine and isodesmosine formation) and thus construct a highly polymerized insoluble protein.…”

Female Vascular Senescence

“…In parallel, there is a marked increase on collagen fibers, mucinous substrate, and calcification of the intercellular substrates begins (Toda et al, 1980). Biochemical studies have shown that the content of elastin in human aorta decreases with age (Spina et al, 1983). Large amounts of elastin are produced during the fetal or neonatal period but not later (Godfrey et al, 1993).…”

“…During infancy or early childhood, collagen fibers are absent in the aorta and begin to accumulate with age; this process is known as fibrosis or sclerosis. Most studies have shown an age-related increase in the collagen content in the aorta (Spina et al, 1983) and increase in the number of collagen cross-links (Watanabe et al, 1996). Both an increase in the collagen content and the number of cross-links contributes significantly to the stiffening of the elastic arteries, namely atherosclerosis.…”