Distribution and composition of acid mucopolysaccharides in normal and atherosclerotic human aortas

Is There Enough Evidence to Support the Role of Glycosaminoglycans and Proteoglycans in Thoracic Aortic Aneurysm and Dissection?—A Systematic Review

Altered proteoglycan (PG) and glycosaminoglycan (GAG) distribution within the aortic wall has been implicated in thoracic aortic aneurysm and dissection (TAAD). This review was conducted to identify literature reporting the presence, distribution and role of PGs and GAGs in the normal aorta and differences associated with sporadic TAAD to address the question; is there enough evidence to establish the role of GAGs/PGs in TAAD? 75 studies were included, divided into normal aorta (n = 51) and TAAD (n = 24). There is contradictory data regarding changes in GAGs upon ageing; most studies reported an increase in GAG sub-types, often followed by a decrease upon further ageing. Fourteen studies reported changes in PG/GAG or associated degradation enzyme levels in TAAD, with most increased in disease tissue or serum. We conclude that despite being present at relatively low abundance in the aortic wall, PGs and GAGs play an important role in extracellular matrix maintenance, with differences observed upon ageing and in association with TAAD. However, there is currently insufficient information to establish a cause-effect relationship with an underlying mechanistic understanding of these changes requiring further investigation. Increased PG presence in serum associated with aortic disease highlights the future potential of these biomolecules as diagnostic or prognostic biomarkers.

Elastic tissue disruption is a major pathogenic factor to human vascular disease

Elastic fibers are essential components of the arterial extracellular matrix. They consist of the protein elastin and an array of microfibrils that support the protein and connect it to the surrounding matrix. The elastin gene encodes tropoelastin, a protein that requires extensive cross-linking to become elastin. Tropoelastin is expressed throughout human life, but its expression levels decrease with age, suggesting that the potential to synthesize elastin persists during lifetime although declines with aging. The initial abnormality documented in human atherosclerosis is fragmentation and loss of the elastic network in the medial layer of the arterial wall, suggesting an imbalance between elastic fiber injury and restoration. Damaged elastic structures are not adequately repaired by synthesis of new elastic elements. Progressive collagen accumulation follows medial elastic fiber disruption and fibrous plaques are formed, but advanced atherosclerosis lesions do not develop in the absence of prior elastic injury. Aging is associated with arterial extracellular matrix anomalies that evoke those present in early atherosclerosis. The reduction of elastic fibers with subsequent collagen accumulation leads to arterial stiffening and intima-media thickening, which are independent predictors of incident hypertension in prospective community-based studies. Arterial stiffening precedes the development of hypertension. The fundamental role of the vascular elastic network to arterial structure and function is emphasized by congenital disorders caused by mutations that disrupt normal elastic fiber production. Molecular changes in the genes coding tropoelastin, lysyl oxidase (tropoelastin cross-linking), and elastin-associated microfibrils, including fibrillin-1, fibulin-4, and fibulin-5 produce severe vascular injury due to absence of functional elastin.

Cardiovascular Risk and Serum Hyaluronic Acid: A Preliminary Study in a Healthy Population of Low/Intermediate Risk

BACKGROUND

Hyaluronic acid (HA) has been found to be an important trigger of atherosclerosis. In this study, we investigate the possible association of serum HA with cardiovascular disease risk in a population of low/intermediate risk for cardiovascular events.

METHODS

We enrolled 200 subjects with low/intermediate risk for developing cardiovascular disease. High specific C-reactive protein (hsCRP) was used as an indicator of preclinical atherosclerosis. The Framingham score was used to calculate the cardiovascular risk.

RESULTS

Participants with dyslipidemia had significantly higher levels of serum HA than those without dyslipidemia (t-test, P = 0.05), higher levels of hsCRP (Kruskal-Wallis test, P = 0.04), and higher cardiovascular risk according to the Framingham score (Kruskal-Wallis test, P = 0.05). Serum HA concentration correlated significantly with the Framingham score for risk for coronary heart disease over the next 10 years (Spearman r = 0.152, P = 0.02). Diabetic volunteers had significantly higher HA than those without diabetes (t-test, P = 0.02). Participants with metabolic syndrome had higher serum HA levels and higher hsCRP (Kruskal-Wallis test, P = 0.01) compared to volunteers without metabolic syndrome (t-test, P = 0.03).

CONCLUSIONS

Serum HA should be explored as an early marker of atheromatosis and cardiovascular risk.

The differential distribution of hyaluronic acid in the layers of human atheromatic aortas is associated with vascular smooth muscle cell proliferation and migration

Vascular smooth muscle cells (VSMC), under conditions of induced proliferation, similar to those involved in atherosclerosis, secrete an acidic glycan, 82% of which exhibits structural homology with hyaluronic acid (HA), has a molecular mass of 340 kDa (HA-340) and inhibits VSMC proliferation in vitro. In this study, the expression of glycans was investigated in human atheromatic aortas and evidence is presented that a HA molecule, similar to HA-340, is distinctly expressed in all aortic layers. The isolation of the glycans from human aortas was performed after homogenization of the individual aortic layers (atheromatic plaque, tunica intima, tunica media and tunica adventitia), by lipid extraction and extensive digestion with pronase and DNase. The total glycans were purified from the digestion products by gel filtration on Sephadex G-25 and fractionated on a Superose 6 column. Enzymatic treatment of the ensuing glycan fractions with all known glycosaminoglycan-degrading enzymes, followed by electrophoresis on polyacrylamide gradient gels and cellulose acetate membranes, revealed that, in addition to HA, the tunica intima and the atheromatic plaque also contained dermatan sulfate, while the tunica media and the tunica adventitia also contained chondroitin sulfates and heparan sulfate. The highest concentration of the human aorta HA was found in the tunica media, exhibiting a negative concentration gradient from the tunica media to the atheromatic plaque. Investigation of the biological function of the human aorta HA revealed that this molecule acts as a negative regulator on the PDGF-induced VSMC proliferation and as a positive regulator on the PDGF-induced VSMC migration. The differential expression of HA within the aortic layers correlates with the biological function attributed to this acidic glycan and associates it with key events in the progression of atherogenesis.

Glycosaminoglycans in the human aorta in diabetes mellitus: a study of tunica media from areas with and without atherosclerotic plaque

Alterations in the connective tissue of the arterial wall have been suggested to play a role in the development of macrovascular disease in diabetes mellitus. The present study deals with changes in the content of GAG in aortic tunica media in human diabetes by separately analysing normal areas and areas with fibrous plaques. The thoracic aorta from 15 diabetic patients (7 with IDDM, 8 with NIDDM), and 30 sex- and age-matched non-diabetic subjects were collected at autopsy. Tunica intima was removed and GAG were isolated from the dried defatted and pulverized tunica media. GAG were quantified by uronic acid analysis and characterized by electrophoresis on cellulose acetate. Results showed that IDDM patients had a relative and absolute increase in hyaluronic acid in normal tunica media compared to non-diabetic subjects. There was a significant positive correlation between hyaluronic acid content of normal tunica media and duration of diabetes, but not between hyaluronic acid content and age. When tunica media from plaque areas was compared to normal areas the same pattern was evident in diabetic patients as in non-diabetic patients--significantly increased proportion of dermatan sulphate and reduced hyaluronic acid. The data agree with the notion that the arterial wall is subject to different pathological processes in diabetes, one of classical atherosclerosis with changes in GAG similar to non-diabetic subjects, and the other seen in areas without plaques with dissimilar alterations in GAG. These data therefore support the concept of the presence of a macrovascular disease in diabetes different from atherosclerosis.

Distribution of glycosaminoglycans in the intima of human aortas: changes in atherosclerosis and diabetes mellitus

Arterial glycosaminoglycans are considered to be important in atherogenesis due to their ability to trap lipid inside the vessel wall and to influence cellular migration and proliferation. Atherosclerotic lesions have displayed an altered glycosaminoglycan content and distribution. Diabetes is a recognized risk factor for atherosclerosis, but no information is available on the arterial glycosaminoglycans in human diabetes. We examined glycosaminoglycans in normal and atherosclerotic intima of non-diabetic and Type 2 (non-insulin-dependent) diabetic patients. Intima was stripped from autopsy samples of thoracic aortas; normal and plaque areas were separated. Glycosaminoglycans were isolated by delipidation, proteolytic digestion, and precipitation and characterized by quantitation of total glycosaminoglycan and evaluation of glycosaminoglycan distribution by electrophoresis and densitometry. Results indicate a significant decrease in total glycosaminoglycan and significant changes in their distribution in atherosclerotic plaques: a relative decrease in heparan sulphate, a relative increase in dermatan sulphate and thus a decrease in the ratio of heparan sulphate to dermatan sulphate. A similar but less marked change in the ratio was found in normal intima of diabetic subjects, while in their plaques this change was more pronounced. This suggests that changes in arterial glycosaminoglycans (especially the ratio of heparan sulphate to dermatan sulphate) precede the development of lesions in diabetes and may be important in atherogenesis.

Collagen types I and III, collagen content, GAGs and mechanical strength of human atherosclerotic plaque caps: span-wise variations

Measurements of total collagen, of the ratio of collagen types III/(I+III) and of sulphated glycosaminoglycans (GAGs) were compared with mechanical strength for individual ulcerated and non-ulcerated human aortic plaque caps and with intima adjacent to the plaques. The distributions of the collagen type ratio were similar for both ulcerated and non-ulcerated plaque caps but different from that of the adjacent intima. The proportions of different collagen types were not related to fracture stress and are thus unlikely to affect the potential to ulcerate. The distributions of the sulphated GAGs showed lower amounts for the plaque caps compared with the nearby intima, with the centres of ulcerated plaque caps having the lowest values. Total collagen had higher values in the peripheries of plaque caps compared with the nearby intima, but was distinctly lower in the centres of ulcerated plaque caps. Plaque caps appeared to require a higher collagen content than adjacent intima to support a given level of mechanical strength, suggesting that while collagen production had occurred in the plaque caps it was not as efficiently organized to resist fracture as a similar amount of collagen in the adjacent intima. Ulcerated plaque caps are notable for much larger transverse (centre vs. periphery) gradients of connective tissue constituents than for non-ulcerated plaque caps. The development of these transverse gradients may be a critical aspect in determining the propensity of a plaque to ulcerate.

Composition of proteoglycans from human atherosclerotic lesions

Proteoglycans from human atherosclerotic lesions and from uninvolved aortic intima were isolated and their composition was studied. The tissues were sequentially extracted by guanidine hydrochloride followed by hydrolysis of the tissue by elastase. Chondroitin sulfate/dermatan sulfate proteoglycans were predominant in guanidine hydrochloride extracts of the tissue. Most of the heparan sulfate proteoglycans were released from the tissue by hydrolysis with elastase. The content of proteoglycan material, measured as uronate per unit weight of wet tissue, was lower in fatty streaks and fibrous plaques than in uninvolved tissue (0.58 and 0.48 mg vs. 0.7 mg/g wet tissue). The distribution of different glycosaminoglycans in guanidine hydrochloride-extracted proteoglycans was similar among the lesions and uninvolved tissue, but varied in the elastase-hydrolyzed extracts. Gel filtration studies suggested that the major proteoglycan material, chondroitin sulfate proteoglycans, from lesions had greater molecular weight than proteoglycans from uninvolved tissue. The studies indicate that alteration in intrinsic composition and molecular size of proteoglycans occurs in atherosclerotic lesions.

Effects of mesoglycan sulfate on the arterial elastic module

Ten patients with peripheral obstructive arterial disease (POAD) in stages I and II according to Leriche-Fontaine, were subjected to therapy with mesoglycan sulfate (60 mg/day for twenty days), to evaluate the effect of the drug on the elastic module of the arterial wall. The wall elasticity was deduced from some Doppler velocitographic indices (arterial dynamics index, resistance index, perfusion pressure index, tibial distensibility index); from the analysis of systolic, protodiastolic, and end diastolic velocity variations; and from computerized analysis of the Doppler sound spectrum. The results show a significant improvement of arterial wall elasticity, which suggests a rational use for the drug in the initial stages of peripheral obstructive arterial disease.

The effect of haemodynamic stress on the glycosaminoglycan content of blood vessel walls of experimental aneurysms and arteriovenous fistulae

The glycosaminoglycan content of experimental saccular aneurysms and arteriovenous fistulae of sheep has been measured. In the experimental aneurysm hyaluronic acid, heparan sulphate, dermatan sulphate, chondroitin sulphate and total glycosaminoglycans were all elevated above control tissue levels with increases most striking for dermatan sulphate and chondroitin sulphate. In the anastomosed vein of the arteriovenous fistulae, total glycosaminoglycans were also significantly raised but which individual glycosaminoglycans were responsible was not clearly established. In the arteries feeding the fistulae, increased chondroitin sulphate in the proximal arterial segment was the only significant change observed. The changes were attributed to altered haemodynamic stresses and are similar to those reported for animal models of hypertension and early human atherosclerosis.

Heterogeneity in the composition and aggregation patterns of coronary intima acid mucopolysaccharides (glycosaminoglycans)

The thickened intima of human coronary arteries included acid mucopolysaccharides (glycosaminoglycans) with a large variety of patterns of composition and aggregation. This heterogeneity, detectable with histochemical methods, was related in our material to age, branching anatomical pattern, size of vessel, collateral or terminal character of the vessel, bifurcations, intimal histology, internal elastic membrane alterations, as well as to the onset of fatty streaks, gelatinous plaques and incorporated microthrombi.

Histochemical study on the glycosaminoglycans (acid mucopolysaccharides) of the human coronary arteries

Investigations carried out on fetuses, children, adolescents and young adults showed that a particular histochemical pattern of the coronary intima glycosaminoglycans existed in each group of age. Beginning with childhood, a subendothelial "ground substance-rich layer" could be more clearly and constantly delineated in the thickened coronary intima. It exhibited a different chemical composition and macromolecular structural stability of its glycosaminoglycans as compared to those of the elastic hyperplastic and musculo-elastic layers. The presence of a "ground substance-rich layer" including dermatan sulfate and glycosaminoglycans resistant to hyaluronidases and chondroitinases appeared in our material as a prerequisite for the development of fatty dots and streaks. During the onset of fibrous plaques, the progressive blockade of the glycosaminoglycan acidic groups by basic proteins and the occurrence of numerous saline linkages between intimal macromolecular aggregates were the prevalent histochemical changes.

The ground substance of the arterial wall. Part 1. Extractability of glycosaminoglycans and the isolation of a proteoglycan from bovine aorta

Water and glycosaminoglycan contents were measured in upper and lower thoracic aortas of claves and steers. The ability of various molarities of guanidine hydrochloride to extract glycosaminoglycans from these tissues was assessed. Some glycosaminoglycans seem to be more resistant to extraction than others. A procedure is described for the isolation of a proteoglycan. The molecule appears to contain both dermatan sulfate and chondroitin sulfate. It also seems to be less dense than cartilage proteoglycans extracted by similar methods as assessed by its behavior in centrifugal fields. The properties, locus and biological activities of this molecule are currently being studied.

The contents of acid glycosaminoglycans in the aortic wall of newborns, small children, and older adults

The contents of acid glycosaminoglycans (aGAG) was determined in the inner and medial layers of aortae from 13 newborns, 9 small children (1-5 years of age), and 10 older adults (7th decade of life). The total aGAG contents was expressed in mug hexuronic acid/100 mg dry weight. Newborns and older adults showed similiar contents of aGAG in their aortae (275.5 plus or minus 27.9 and 313.4 plus or minus 46.7, respectively). Small children had significantly less aGAG in their aortae (202.1 plus or minus 21.5). The aGAG material from aortae was fractionated by a microcolumn chromatographic procedure on cetylpyridinium chloride cellulose. No significant differences of the aGAG fractions were found in aortae of newborns and children. In both groups of children the percentage of hyaluronic acid was significantly increased and dermatan sulfate was significantly decreased when compared with aortae from older adults. The increased contents of acid glycosaminoglycans (aGAG) in aortae of human newborns is possibly caused by the concentrated hormonal environment (especially estrogens) to which the fetus is exposed in utero.