Marfan's syndrome: structural, biochemical, and mechanical studies of the aortic media.

An intrinsic defect in the aortic media in six patients with Marfan's syndrome, who died of cardiovascular complications of the disease at an average age of 32 years, has been delineated by correlated morphologic, biochemical, and mechanical studies. The findings in the Marfan aortas have been compared with those in age- and sex-matched controls, who died of unrelated diseases without significant aortic lesions, and in three patients with dissecting aneurysms of non-Marfan origin. The results showed that there was a significant reduction in the tensile strength of the aorta in Marfan's syndrome. This finding was correlated by scanning electron microscopy with structural alterations of the medial elastic fibers, including enlarged interlaminar spaces and loss of interlaminar elastic fibrils. No structural alterations were identified in collagen fibers. Biochemical analyses of the aortic media revealed a substantial reduction in aortic elastin content. Furthermore, the desmosine content of the isolated elastin was reduced by approximately 50%. No changes were detected in the composition or solubility of the medial collagen. In contrast to Marfan aortas, the elastin and collagen contents of the dissecting aneurysms of non-Marfan origin were similar to those of the controls. These findings suggest that the vascular complications in Marfan's syndrome may be based on a genetic abnormality affecting elastin fibrillogenesis.

Marfan syndrome. Demonstration of abnormal elastin in aorta.

Aortae from three patients with classic presentation of Marfan syndrome, who died of vascular complications, were subjected to biochemical analyses of the connective tissue; for comparison, aortae from eight age-matched controls, without evidence of connective tissue abnormalities, were examined. Elastin was prepared from the aortae by two techniques. First, the tissues were extracted with 5 M guanidine-HCl, bacterial collagenase digestion and reduction with dithiothreitol (elastin I preparation). Secondly, this material was further purified by extraction with 0.1 M NaOH at 99 degrees C (elastin II preparation). Amino acid analyses of both elastin preparations indicated that the values for desmosine and isodesmosine were reduced in Marfan cases to approximately one-half of the control values. A corresponding increase in lysyl residues was noted in elastin II preparations. Also, the concentration of elastin per milligram dry weight of tissue was reduced in Marfan cases. The hydroxyproline content of elastin was increased in two cases with the Marfan syndrome. Recoveries indicated that the alkali treatment solubilized 46.2% of the elastin I preparations in Marfan aortae compared with 23.7% in controls. In contrast to elastin, the concentration and solubility of collagen were unchanged; the amino acid composition and the genetic types of insoluble collagen isolated by limited pepsin proteolysis were the same in both Marfan and control aortae. The results of our study demonstrate that the cross-linking of aortic elastin is reduced in the three patients with Marfan syndrome. Thus, a defect in elastin could explain the vascular fragility observed clinically in these patients.

Effects of pulse cyclophosphamide on NZB/W disease.

Induced IgM anti-ss-DNA antibodies in NZB/W female mice did not alter the time of onset nor the course of nephritis. Monthly pulse doses of cyclophosphamide suppressed the mortality of these mice, and also prevented a switch of anti-ss-DNA from IgM to IgG class. The production of IgM anti-SRBC was markedly reduced in old NZB/W mice, but IgG anti-SRBC was only moderately reduced and this hyporesponsiveness towards SRBC could be reversed by CPA treatment. These observations are discussed in relation to cyclophosphamide as an effective therapeutic agent for the murine lupus syndrome.

Chromatographic purification of soluble elastin.

An improved method for extraction and purification of soluble elastin from aortas of copper-deficient swine has been devised. It depends upon the use of both acidic and neutral protease inhibitors during preparation. Collagen is first precipitated with acetic acid. A two-step separation and purification of elastin from the collagen-free extract is based on absorption of the acidic proteins on DEAE-cellulose and gel filtration through agarose. The protein recovered is homogeneous by gel electrophoresis. It has the molecular weight (75,000) and amino acid composition of the soluble elastin from the same source prepared by repeated coacervation.

Isolation of a cross-linked dimer of elastin.

Salt-soluble elastin, isolated by coacervation from extracts of copper-deficient pig aorta, contains a minor protein component separable by gel electrophoresis in 6 M urea. This protein has a molecular weight of 150,000 compared to 75,000 of the major component. The amino acid analyses of both proteins are typical of elastin but the higher molecular weight component has a significantly lower lysine content and lysine-derived cross-links that are lacking from the major component. The proteins were labeled by incubation of the fresh aortic tissue with [14C]lysine. The acid hydrolysate of the borohydride-reduced higher molecular weight protein contained a labeled amino acid eluting at a time identical to standard merodesmosine and a trace of radioactivity corresponding to lysinonorleucine. We conclude that the higher molecular weight protein is a cross-linked dimer of the previously identified soluble elastin.

Inhalation anthrax in a home craftsman.

Inhalation anthrax with complicating subarachnoid hemorrhage due to simultaneous infection with two capsular biotypes of Bacillus anthracis of different virulence for the mouse is reported. The patient, a home craftsman, acquired his infection from imported animal-origin yarn.

Studies of the biosynthesis of a soluble precursor of elastin.

A salt soluble protein, isolated from the aortas of copper-deficient swine, has been characterized as a precursor of elastin by its amino acid composition and its incorporation into insoluble aortic elastin in vitro.

The biosynthesis of elastin by an aortic medial cell culture.

A long term culture of aortic medial cells, derived from newborn pig aorta, has been established. The ability of these cells to synthesize soluble elastin has been demonstrated by isolation and characterization of the radioactively labeled protein, using soluble elastin of copper-deficient pig aorta as the carrier. The synthesis of corsslinked elastin was shown by the isolation and identification of the lysine-derived crosslinks after incubating the cultures with [14C]-labeled lysine. The precursor relationship of soluble to insoluble elastin was demonstrated by incubating the [3H]-labeled soluble elastin from copper-deficient pig aorta with the culture and isolating labeled crosslinks from the insoluble elastin residue.