Aortic acid mucopolysaccharides and collagen in scorbutic guinea pigs

Hyperglycemia-induced latent scurvy and atherosclerosis: the scorbutic-metaplasia hypothesis

Latent scurvy is characterized by a reversible atherosclerosis that closely resembles the clinical form of this disease. Acute scurvy is characterized by microvascular complications such as widespread capillary hemorrhaging. Vitamin C (ascorbate) is required for the synthesis of collagen, the protein most critical in the maintenance of vascular integrity. We suggest that in latent scurvy, large blood vessels use modified LDL--in particular lipoprotein(a)--in addition to collagen to maintain macrovascular integrity. By this mechanism, collagen is spared for the maintenance of capillaries, the sites of gas and nutrient exchange. The foam-cell phenotype of atherosclerosis is identified as a mesenchymal genetic program, regulated by the availability of ascorbate. When vitamin C is limited, foam cells develop and induce oxidative modification of LDL, thereby stabilizing large blood vessels via the deposition of LDL. The structural similarity between vitamin C and glucose suggests that hyperglycemia will inhibit cellular uptake of ascorbate, inducing local vitamin C deficiency.

Ascorbic acid and atherosclerotic cardiovascular disease

In this chapter, we have briefly reviewed the current scientific knowledge of the role of vitamin C in the prevention of atherosclerosis and its associated clinical manifestations. There is good evidence from animal studies that vitamin C can slow the progression of experimental atherosclerosis. Most of these studies, however, were done either in guinea pigs, using ascorbic acid depletion, or in cholesterol-fed rabbits, using ascorbic acid supplementation. Both animal models have limitations, as guinea pigs are not a well-established (nor well-studied) model of atherosclerosis, and rabbits develop atherosclerosis at high serum beta-VLDL cholesterol levels, and in addition can synthesize ascorbic acid. In contrast, humans develop atherosclerosis spontaneously and readily at moderately elevated serum LDL cholesterol levels and have lost the ability to synthesize ascorbic acid. Thus, the animal studies discussed, although quite promising and suggestive of an anti-atherogenic effect of ascorbic acid, need to be expanded to primates before more definitive conclusions can be drawn. Similar to the animal data, the current evidence from epidemiological studies on the role of vitamin C in the prevention of CVD is inconclusive, with some studies showing a very strong correlation between increased vitamin C intake and incidence of CVD events and other studies showing no correlation at all. Studies on CVD risk factors indicate that vitamin C may moderately decrease total serum cholesterol levels, increase HDL levels, and exert a hypotensive effect. These findings are particularly intriguing and should be pursued vigorously in basic research studies to elucidate biological mechanisms. In addition, it appears that large placebo-controlled, double-blind, randomized trials of vitamin C supplementation (without simultaneous supplementation with vitamin E) in populations with a wide range of vitamin C body levels are needed in order to confirm or refute a role for vitamin C in the prevention of CVD. Unfortunately, no such trials are currently being conducted. The possible mechanisms by which ascorbic acid may affect the development of atherosclerosis and the onset of acute coronary events include effects on arterial wall integrity related to biosynthesis of collagen and GAGs, altered cholesterol metabolism mediated by vitamin C-dependent conversion of cholesterol to bile acids, and effects on triglyceride levels via modulation of lipoprotein lipase activity. A particularly intriguing possible mechanism for the anti-atherogenic effect of vitamin C is prevention of atherogenic, oxidative modification of LDL. Numerous in vitro studies have demonstrated that ascorbic acid strongly inhibits LDL oxidation by a variety of mechanisms. The potential effects of ascorbic acid on platelet function and EDRF metabolism are particularly intriguing, as they might have widespread consequences for the prevention of atherosclerotic lesion development as well as acute clinical events. Thus, both metabolic and antioxidant functions may contribute to the possible reduction of CVD risk by vitamin C.

Characterization of the aortic collagens in guinea pigs with chronic vitamin C deficiency

Marginal vitamin C deficiency lasting 19 weeks caused hypercholesterolemia and hypertriglyceridemia in guinea pigs. In the thoracic aorta of deficient animals a moderate decline of type I and an increase of type III collagen was observed. Both types of collagen isolated from deficient aortas proved to be slightly underhydroxylated.

Ascorbic acid and glycosaminoglycan and lipid metabolism in guinea pigs fed normal and atherogenic diets

The effect of low and high doses of ascorbic acid on glycosaminoglycan and lipid metabolism was studied in guinea pigs fed both normal and atherogenic diets. The high dose of ascorbic acid (25 mg/100 g body weight/day) decreased the cholesterol level in the liver and aorta but not in the serum in animals fed the normal diet in comparison with those fed the low dose of ascorbic acid (0.1 mg/100 g body weight/day). In animals fed the atherogenic diet, cholesterol decreased in the serum and liver, but not in the aorta. Serum triglycerides were not affected by the dose of ascorbic acid in the group on the normal diet, but in the animals receiving the atherogenic diet, the high dose of ascorbic acid caused serum triglycerides to decrease when compared with the low dose. Hepatic and aortic triglycerides decreased in groups on normal and atherogenic diets receiving the high dose of ascorbic acid. Lipoprotein lipase activity was not affected in the aorta by the dose of ascorbic acid either in the normal or atherogenic diet group. It was increased in the liver and heart in both the groups receiving the low dose of ascorbic acid but decreased in the high dose group. The concentration of all the glycosaminoglycans significantly increased in the aorta of animals on normal diet receiving the high dose of ascorbic acid when compared with the low dose group. In the group on the atherogenic diet, hyaluronic acid was not affected, but all the sulphated glycosaminoglycans increased in the animals receiving the high dose when compared with those receiving the low dose. In the liver all the sulphated glycosaminoglycans increased while hyaluronic acid decreased in both the normal and atherogenic diet groups receiving the high rather than the low dose of ascorbic acid. L-Glutamine:D-fructose-6-phosphate aminotransferase and UDPG dehydrogenase, two key enzymes in the biosynthesis of precursors of glycosaminoglycans, were studied in relation to the dose of ascorbic acid. Hepatic aminotransferase activity was higher both in the normal and atherogenic diet groups when receiving the high rather than the low dose of ascorbic acid. UDPG dehydrogenase was not affected by the dose of ascorbic acid. The activities of the degrading enzymes -- hyaluronidase, beta-glucuronidase, beta-hexosaminidase and aryl sulphatase -- significantly increased both in the normal and atherogenic diet groups when receiving the low rather than the high dose of ascorbic acid. The concentration of PAPS, sulphate activity and sulphotransferase activity were all increased in both the normal and atherogenic diet groups receiving the high dose of ascorbic acid.

Tissue changes induced by marginal vitamin C deficiency

Chronic marginal vitamin C deficiency in guinea pigs results in alterations in certain tissues that are quite different from those observed following acute deficiency. In autonomic ganglia, although changes observed in the organelles of some cells are similar to those seen in acute deficiency, the specific changes are the presence of large numbers of cilia in the cytoplasm of both ganglion cells and their associated neuroglia and the marked proliferation of collagen fibers in the extracellular spaces. The evidence presented points to a link between vitamin C and arteriosclerosis. One mode of interaction may be the effect of latent vitamin C deficiency on cholesterol metabolism. The data presented indicate important changes in the liver with marked increases of agranular endoplasmic reticulum. Together with the liver cholesterol studies, the indications suggest an increased cholesterol deposition in the liver. Light-microscopic sections of the aorta reveal alterations in many of these vessels ranging from endothelial proliferation to large, well-formed musculofibrotic arteriosclerotic plaques.

Copper deficiency in chicks: effects of ascorbic acid on iron, copper, cytochrome oxidase activity, and aortic mucopolysaccharides

1. Copper deficiency was induced in newly hatched chicks by feeding on a milk-based diet for 12 d; effects of supplementation with ascorbic acid were studied.

2. Cu deficiency alone resulted in 30% mortality from aortic rupture. This was associated with a 20% increase in total acid mucopolysaccharides in the aorta, manifested as an increase in chondroitin sulphate and a relative decrease in hyaluronic acid. Cytochrome oxidase activity of liver and heart was less than half that of the controls.

3. Supplementing the Cu-deficient diet with 0.5 % L-ascorbic acid increased mortality to 40%, raised total aortic acid mucopolysaccharides to a higher level, and increased liver iron by 36%.

4. Supplementing the control diet with ascorbic acid decreased liver Cu by 30% and significantly reduced total aortic acid mucopolysaccharides.

5. The enhancement of the Cu-deficiency effect by ascorbic acid probably results from interactions between ascorbic acid and absorption or metabolism of Cu; untoward effects of supplementing the control diet with ascorbic acid may be interpreted as manifestations of ascorbic acid toxicityper se.

The effect of scurvy on glycosaminoglycans of granulation tissue and costal cartilage

1. The effect of ascorbic acid deficiency on glycosaminoglycans of granulation tissue and cartilage of guinea pigs was investigated by determination of the changes in the glucosamine and galactosamine contents 12 days after tendonectomy. 2. In normal granulation tissue, the glucosamine and galactosamine contents rose to a peak at 5 and 10 days respectively, whereas the hydroxyproline and proline contents continued to rise throughout the 20 days after tendonectomy. 3. The galactosamine in scorbutic granulation tissue, but not in that of pair-fed controls, decreased significantly in absolute amount and relatively to glucosamine, which remained practically unchanged; the cartilage galactosamine did not decrease during the 22 days of deficiency owing to the presence of excess of preformed galactosaminoglycans, which masked the small amount of newly formed glycosaminoglycans. 4. The chemical results were confirmed by radioactivity studies in vivo of incorporation of [U-(14)C]glucose into galactosamine and glucosamine of scorbutic granulation tissue and cartilage. The incorporation of (14)C into galactosamine decreased significantly in scurvy in both tissues. 5. The results indicated in both tissues a decreased formation of galactosamine during scurvy, although an increased degradation of polymerized glycosaminoglycans could not be entirely ruled out. It is concluded that, if lack of ascorbic acid causes an impaired galactosamine formation, the most likely position for the block may be in the UDP-N-acetylglucosamine 4-epimerase reaction.

Ascorbic acid deficiency in cultured human fibroblasts

Fibroblasts grown in medium containing less than 1 microg of ascorbic acid per milliliter showed evidence of ascorbic acid deficiency when compared with cells grown in medium containing 50 microg of ascorbic acid per milliliter. This was manifested morphologically by dilated endoplasmic reticulum, a decrease in number, size, and intensity of staining of the mitochondria, by defective intercellular fibril formation, and by easy disaggregation of the cells from the intercellular matrix after treatment with pronase. When 50 microg per milliliter of ascorbic acid was incorporated into the medium, the altered morphology was corrected, banded fibrils were produced which were organized into bundles, and the cells were tightly bound in a matrix which was resistant to disaggregation with a variety of proteolytic enzymes. Collagen and sulfated glycosaminoglycan synthesis were less in the control than in the ascorbic acid supplemented cells. Similar morphological and chemical changes have been reported in the connective tissue of scorbutic animals. The effects of low ascorbic acid concentration on fibroblasts in culture indicate that these cells require ascorbic acid to maintain connective tissue functions.

Vitamin C-induced increase of dermatan sulfate in cultured Hurler's fibroblasts

In fibroblasts taken from patients witli Hurler's syndromne and grown in cultlure, dermatan sulfate constituted a larger percentage of the total sulfated glycosaminoglycans than it did in cultured fibroblasts from unaffected individuals. Moreover, the addition of ascorbic acid (vitamnin C) to the culture medium markedly increased the concentration of dermatan sulfate in the Hurler's fibroblasts but not in the normal fibroblasts. The biochemical phenotype of the Hurler's cells persisted during 28 weeks of serial culture.