Medin-amyloid: a recently characterized age-associated arterial amyloid form affects mainly arteries in the upper part of the body.

Amyloid deposition occurs commonly in the aging aortic media. We recently found that a 50 amino acid amyloid fibril protein, which we called medin, forms the fibrils of this amyloid form. Medin is an internal fragment of the 364 long precursor lactadherin, which is expressed by several kinds of cells including vascular smooth muscle cells. With the use of specific antibodies we have now studied the vascular distribution of medin (AMed) amyloid in a series of 18 individuals, 57 years of age and older. All individuals had widely spread AMed amyloid in the media of the thoracic aorta while this type of amyloid occurred less commonly in the abdominal aorta. In 8 of the 18 individuals, AMed-amyloid was also found in the basilar artery while the frequency was lower in other studied arteries. Amyloid was usually seen in close association with the internal elastic lamina. Analysis of proteins extracted from amyloid-rich aortic media showed presence of both lactadherin and medin. This study shows that AMed amyloid is not restricted to the aorta and the temporal artery but also occurs in other arteries, mainly in the upper part of the body. AMed amyloid has to be added to the forms of amyloid that may be seen in intracranial vessels.