Quantitative and comparative studies of the vocal fold extracellular matrix - I: Elastic fibers and hyaluronic acid

Objectives: This study examines the elastic fiber and hyaluronic acid (HA) content of the midmembranous vocal fold laminae propriae (LPs) of humans, dogs, pigs, and ferrets. Methods: Lamina propria elastin was quantified by measuring the amino acid desmosine, and HA was measured by an enzyme-linked immunosorbent assay-based technique. Quantitative histology was used to evaluate elastin and HA levels in specific LP regions. The distributions of fibrillin-1, a primary microfibrillar component of elastic fibers, and of tropoelastin, an indicator of elastin synthesis, were immunohistochemically analyzed. Results: Elastin and HA constituted 8.5% 2.1% and 0.82% 0.11% of human LP, respectively, relative to tissue total protein. Although the mean LP desmosine levels were similar across species, the mean HA levels in canine (p < 3.1 x 10(-5)), porcine (p < 1.5 x 10(-5)), and ferret (p < 6.6 x 10(-4)) LPs were 3 to 4 times higher than that in humans. Marked interspecies differences in elastin, fibrillin-1, tropoelastin, and HA distributions were observed histologically. Conclusions: The elastin content of the human LP is roughly twice that of the dermis, whereas the HA content of the human LP is similar to that of the dermis. Although all species had similar levels of desmosine, histologic evaluation indicates that the porcine elastin distribution is most similar to that of the human LP. Fibrillin-1 staining suggests that stress in the human LP may be particularly high in the superior superficial layer, and tropoelastin staining indicates that the rate of LP elastin turnover may vary spatially.