The aortic glycosaminoglycans in arteriosclerosis induced by systemic hypoxia

Early signs of atherosclerosis in obstructive sleep apnea

BACKGROUND

Obstructive sleep apnea (OSA) is associated with several cardiovascular diseases. However, the mechanisms are not completely understood. Recent studies have shown that OSA is associated with multiple markers of endothelial damage. We hypothesized that OSA affects functional and structural properties of large arteries, contributing to atherosclerosis progression.

METHODS AND MEASUREMENTS

Twelve healthy volunteers, 15 patients with mild to moderate OSA, and 15 with severe OSA matched for age, sex, and body mass index were studied by using (1) full standard overnight polysomnography; (2) carotid-femoral pulse wave velocity with a noninvasive automatic device; and (3) a high-definition echo-tracking device to measure intima-media thickness, diameter, and distensibility. All participants were free of hypertension, diabetes, and smoking, and were not on any medications. Patients with OSA were naive to treatment.

MAIN RESULTS

Significant differences existed between control subjects and patients with mild to moderate and severe OSA (apnea-hypopnea index, 3.1 +/- 0.3, 16.2 +/- 1.7, and 55.7 +/- 5.9 events/hour, respectively) in pulse wave velocity (8.7 +/- 0.2, 9.2 +/- 0.2, and 10.3 +/- 0.2 m/second; p < 0.0001), intima-media thickness (604.4 +/- 25.2, 580.2 +/- 29.0, and 722.2 +/- 35.2 microm; p = 0.004), and carotid diameter (6,607.8 +/- 126.7, 7,152.3 +/- 114.4, and 7,539.9 +/- 161.2 microm; p < 0.0001). Multivariate analyses showed that the apnea-hypopnea index correlated independently with pulse wave velocity and intima-media thickness variability (r = 0.61, p < 0.0001, and r = 0.44, p = 0.004, respectively), whereas minimal oxygen saturation correlated with the carotid diameter (r = -0.60, p < 0.0001).

CONCLUSIONS

Middle-aged patients with OSA who are free of overt cardiovascular diseases have early signs of atherosclerosis. All vascular abnormalities correlated significantly with the severity of the OSA, which further supports the hypothesis that OSA plays an independent role in atherosclerosis progression.

General mechanism of chronic diseases

In a human, the cells function adequately to the needs of the organism, and to their own needs. Consequently, adequate cell function is comprised of the organism-oriented, and cell-oriented functions. It is suggested that an independent stage in the pathogenesis of a chronic disease exists which so far has not been considered. This is the disturbance of the cell-oriented function of the cells involved. This initial stage may last for years and decades, whereas function of the organ remains preserved. Organism-oriented cellular function appears to become involved in the pathologic process long after the disease has actually started. At this time the cells themselves are severely impaired, and as a result a disease acquires its progressive, irreversible course. Pathogenesis of atherosclerosis is considered as an example of the above-mentioned developments.

Immune-induced vascular connective tissue alterations in rabbits chronically immunized with bovine serum albumin: biochemical studies on collagen, glycosaminoglycans, RNA, and DNA in normal and injured aorta

Repeated intravenous injections of bovine serum albumin in rabbits caused a significant reduction in the aortic in vivo biosynthesis of chondroitin-4,6-sulfate, whereas no changes were observed in the synthesis of other glycosaminoglycans nor in the content of collagen. This contrasts the biochemical changes generally seen in acute vascular injury. When experimentally elicited vascular injury and repair processes were induced in chronically immunized rabbits, the proliferative response was greatly inhibited, as reflected by a significant diminution of the DNA amount. Also, the vascular connective tissue matrix repair was restrained: the aortic content of collagen and the collagen type III/I ratio was repressed, and the in vivo biosynthesis of sulfated glycosaminoglycans was markedly reduced. All immunized rabbits developed antibodies to bovine albumin, but in only a few were circulating immune complexes detected. The inhibitory effect of persistent immunostimulation on the nonspecific processes of repair in vascular connective tissue may be of significance as to chronicity of vasculitis, as well as inflammation and repair in general, in inflammatory connective tissue diseases.

Glucocorticoid and starvation effect on glycosaminoglycans in vascular connective tissue. Biochemical studies on repair processes in rabbit aorta

Male rabbits were injured by a single mechanical dilatation injury of aorta and then injected with prednisone 2 mg/kg or saline for 14 days or subjected to starvation. The biosynthesis of the sulfated glycosaminoglycans as evaluated by the uptake of 35S-sulfate and the content of the glycosaminoglycans were measured on the intima-media layer of the descending thoracic aorta. The results indicate that prednisone may inhibit the biosynthesis of heparan and/or dermatan sulfate while starvation increases the biosynthesis of all the sulfated glycosaminoglycans. No alterations were observed in the total amount of glycosaminoglycans in aorta following glucocorticoid injection or starvation. The metabolism of aortic glycosaminoglycans during repair is less sensitive to the action of prednisone than in undamaged aorta. This contrasts with the effect of prednisone on the metabolism of aortic collagen.