N,N'-diacetyl-L-cystine (DiNAC), the disulphide dimer of N-acetylcysteine, inhibits atherosclerosis in WHHL rabbits: evidence for immunomodulatory agents as a new approach to prevent atherosclerosis.

Oxidation of lipoprotein-derived lipids is generally accepted to be important in atherogenesis, and lipophilic antioxidants have been suggested as potential antiatherosclerotic agents. The antiatherogenic effects observed by certain antioxidants, especially probucol, in different animal models support this suggestion. There are however also cases where other lipophilic antioxidants have not been able to support this hypothesis. This has raised the question whether the effects of probucol and similar compounds are mainly due to some other property, unrelated to their antioxidant efficacy. For example, probucol is shown to possess immunomodulatory properties. Immune reactions are known to occur during atherogenesis. We therefore tested the dimer of N-acetylcysteine, DiNAC, which is a disulfide with immunomodulating properties and enhances oxazolone-induced contact sensitivity (CS) reactions in mice, for effects on atherosclerosis. When given to male heritable hyperlipidemic rabbit (WHHL) rabbits from 10 to 22 weeks of age, this compound reduced by 50% thoracic aorta atherosclerosis (p < 0.05), without affecting plasma lipid levels. Here we also show that probucol and a close chemical analog, both known to prevent atherosclerosis in WHHL rabbits, enhance the CS reaction in mice, while two other related antioxidants did not affect the CS reaction. At least one of these is also without effect on atherosclerosis in WHHL rabbits. The results show that DiNAC might represent a new treatment modality for atherosclerosis-related disease, and suggest that some antioxidants may have antiatherosclerotic properties more related to "immunomodulatory" properties than to antioxidant properties in general.

N,N'-Diacetyl-L-cystine-the disulfide dimer of N-acetylcysteine-is a potent modulator of contact sensitivity/delayed type hypersensitivity reactions in rodents.

Oral N-acetyl-L-cysteine (NAC) is used clinically for treatment of chronic obstructive pulmonary disease. NAC is easily oxidized to its disulfide. We show here that N,N'-diacetyl-L-cystine (DiNAC) is a potent modulator of contact sensitivity (CS)/delayed type hypersensitivity (DTH) reactions in rodents. Oral treatment of BALB/c mice with 0.003 to 30 micromol/kg DiNAC leads to enhancement of a CS reaction to oxazolone; DiNAC is 100 to 1000 times more potent than NAC in this respect, indicating that it does not act as a prodrug of NAC. Structure-activity studies suggest that a stereochemically-defined disulfide element is needed for activity. The DiNAC-induced enhancement of the CS reaction is counteracted by simultaneous NAC-treatment; in contrast, the CS reaction is even more enhanced in animals treated with DiNAC together with the glutathione-depleting agent buthionine sulfoximine. These data suggest that DiNAC acts via redox processes. Immunohistochemically, ear specimens from oxazolone-sensitized and -challenged BALB/c mice treated with DiNAC display increased numbers of CD8(+) cells. DiNAC treatment augments the CS reaction also when fluorescein isothiocyanate is used as a sensitizer in BALB/c mice; this is a purported TH2 type of response. However, when dinitrofluorobenzene is used as a sensitizer, inducing a purported TH1 type of response, DiNAC treatment reduces the reaction. Treatment with DiNAC also reduces a DTH footpad-swelling reaction to methylated BSA. Collectively, these data indicate that DiNAC in vivo acts as a potent and effective immunomodulator that can either enhance or reduce the CS or DTH response depending on the experimental conditions.

Alpha1-microglobulin and bikunin in rats with collagen II-induced arthritis: plasma levels and liver mRNA content.

The plasma proteins alpha1-microglobulin (alpha1-m) and bikunin are synthesized in the liver as a common precursor which is cleaved just before secretion. Half of plasma alpha1-m is covalently linked to fibronectin and alpha1-inhibitor-3, and more than 95% of bikunin is part of pre-alpha-inhibitor, inter-alpha-inhibitor and related large molecules. Both alpha1-m and bikunin have been shown to be involved in inflammation, but the regulation of their synthesis is not clear. The authors have measured the plasma and urinary concentrations of alpha1-m and bikunin as well as their hepatic mRNA levels in rats during the development of collagen-induced arthritis. Also, the plasma concentrations of acknowledged acute-phase proteins were measured. The results suggested a biphasic inflammatory reaction: an early response after 1 week, represented by an elevated fibronectin level; and a late response after 3 weeks, represented by elevated alpha1-acid glycoprotein and decreased albumin and alpha1-inhibitor-3 levels. The alpha1-m-bikunin mRNA content in liver was slightly reduced after 1 week and elevated after 3 weeks, but the total concentrations of free and bound alpha1-m and bikunin in plasma were unchanged. The free bikunin fraction as well as the fibronectin/alpha1-m complex in plasma, however, were elevated after 1 week. Urinary bikunin levels were also elevated after 1 week, whereas urinary alpha1-m levels remained unchanged. The results thus suggest that free bikunin in plasma is increased and excreted in the urine at an early stage during the development of collagen-induced arthritis. Later, when the synthesis rate of alpha1-m-bikunin is elevated, both proteins are most likely directed to other locations in the body.

Effects of N-acetylcysteine stereoisomers on oxygen-induced lung injury in rats.

The effects of the stereoisomers of N-acetylcysteine (L-NAC and D-NAC) on oxygen-induced lung oedema have been studied in rats. The NAC-isomers were given by an osmotic minipump in order to attain continuous administration, either intravenously or intragastrically. In some experiments, plasma concentrations of NAC, cysteine and glutathione (total concentrations, i.e., concentrations obtained after reduction of the samples with dithiothreitol) were recorded. Exposure to oxygen induced an almost two-fold increase of the lung wet weight. When L-NAC or D-NAC were given intravenously, in dose of 1.1 mmol/day/kg body weight, the increase of lung wet weight was prevented by 40-50%. The plasma concentrations were approximately 40 microM (L-NAC) and approximately 90 microM (D-NAC). Following intragastrical administration of the same doses, plasma concentrations of L-NAC and D-NAC reached approximately 3 and approximately 60 microM, respectively. Using this method of administration, only D-NAC significantly diminished the increase of the lung wet weight. The difference in plasma concentrations of the NAC isomers, particularly after intragastric administration, most likely reflects the fact that L-NAC is effectively hydrolysed in most tissues, while D-NAC is resistant to enzymatic hydrolysis, thus penetrating largely intact into the systemic circulation. The data presented shows that NAC, regardless of stereoconfiguration, will protect the lung against oxygen toxicity, provided sufficient systemic levels are obtained. Since D-NAC is not a precursor of L-cysteine, formation of glutathione cannot explain the protective effects of this isomer. L- and D-NAC may therefore act via direct antioxidant/radical scavenging mechanisms and not necessarily as precursors of glutathione in this model.

Immune-inflammatory functions of fibroblasts.

Inflammation is a response that has evolved over millions of years to become an extremely complex process. This complexity reflects the host's need to deal effectively with a wide variety of potentially injurious agents, as well as the need to incorporate an adequate set of checks and balances. An inappropriately checked response, which occurs rarely, results in disease, either acute or chronic. However, in most instances, inflammation is a beneficial response, essential for survival. Inflammation comprises an extensive network of cellular interactions implemented by an overwhelming number of molecules. One category of signal includes soluble products, such as neuropeptide, lipid mediators, cytokines and growth factors, most of which can be produced by inflammatory/haemopoietic cells. However, resident structural cells can also produce many of these products and, on this basis only, fibroblasts, epithelial, endothelial and smooth muscle cells should be considered as active contributors to the regulation of the inflammatory response. Extracellular matrix (ECM) proteins comprise another category of signals. Whilst the most recognized activities of these proteins are those concerned with providing structural tissue integrity, it is clear that they also have powerful inductive effects. Indeed, ECM proteins can influence the shape, movement and state of activation of inflammatory cells in the tissue. Recent evidence indicates that these signals may also play substantial roles in homing of inflammatory cells to certain sites and in the handling of a number of cytokines and growth factors. In so far as fibroblasts are the main producers of ECM proteins, these new data establish an indirect but important role for fibroblasts in the regulation of the inflammatory response.

Experimental granulomatous alveolitis in rat. Effect of antigen manipulation, smoke exposure and route of administration.

When Sephadex beads (0.45mg/kg b.w) are instilled intratracheally into rats, a granulomatous alveolitis with giant cell formation and fibrosis occurs. Moreover, the events in the alveolar region are paralleled by an eosinophil-dominated peribronchitis/bronchiolitis and perivasculitis. Bronchoalveolar lavage (BAL) shows a very distinct feature with an early pronounced neutrophil increase, followed by an increase of eosinophils and lymphocytes. BAL findings returned to normal after 1-2 weeks, but tissue morphology showed persistent inflammation with large numbers of eosinophils and to a lesser degree mononuclear cells, peribronchially and perivascularly several weeks after the instillation. Fragmentation of the Sephadex beads by ultrasonication dramatically diminished the response, giving a transient neutrophil alveolitis, without eosinophils and with no granuloma formation. On the other hand, when the Sephadex dose was divided into three, given 10 days apart, a more pronounced fibrosing activity occurred, with mast cells appearing in the collagen rich granulomas. Finally, smoke exposure had a significant suppressive effect upon the response. The numbers of cells in the interstitium as well as in the peribronchial and perivascular tissue were markedly decreased in the smoke exposed group compared to the controls. This decrease was mainly due to decreased numbers of mononuclear cells, while the numbers of eosinophils remained unchanged.

Sephadex-induced granulomatous alveolitis in rat: effects of antigen manipulation.

A granulomatous alveolitis, with multinuclear cell formation combined with an eosinophilic peribronchiolitis, was achieved in rats by intratracheal administration of sephadex beads (G-200, Pharmacia, Sweden). The pattern of inflammation and the degree of postgranulomatous fibrosis were substantially dampened when the particles were dispersed by ultrasonification. The animals were analyzed with bronchoalveolar lavage and tissue morphology.

Altered expression of small proteoglycans, collagen, and transforming growth factor-beta 1 in developing bleomycin-induced pulmonary fibrosis in rats.

The development of bleomycin-induced pulmonary fibrosis in rats was studied over a period of 21 d after an intratracheal instillation of bleomycin. The expression of three small proteoglycans (biglycan, decorin, and fibromodulin), collagen III and TGF-beta 1 was studied by RNA-transfer blot analysis. The proteoglycans were also studied by SDS-polyacrylamide gel electrophoresis and Western blots. TGF-beta 1 mRNA increased threefold already on day 3 and remained elevated until day 10. After the increase of TGF-beta 1 mRNA the messages for biglycan and collagen III steadily increased to reach a maximum 10 d after bleomycin instillation. The mRNA for biglycan increased maximally fourfold and that of collagen III 2.5-fold. Decorin mRNA, in contrast to biglycan decreased and reached 20% of control on day 10. The message for fibromodulin remained constant throughout the study period. The amounts of biglycan and decorin in the tissue changed in accordance with the mRNA levels. The results corroborate and extend previous in vitro studies concerning the effect of TGF-beta 1 on the metabolism of small proteoglycans and show that these macromolecules are regulated differently also in vivo. The marked alterations of biglycan and decorin during the development of fibrosis suggests that these proteoglycans have a regulating role in this process.

Eosinophil cationic protein alters proteoglycan metabolism in human lung fibroblast cultures.

Eosinophil cationic protein (ECP), a highly basic protein secreted from eosinophilic granulocytes, has been shown to take part in the inflammatory reaction. The involvement of ECP in fibroblast activation was therefore investigated in cell culture. Production of proteoglycans, hyaluronan and collagen in the presence of ECP was measured after incorporation of radioactive precursors and separation into different proteoglycan classes using gel and ion exchange chromatography and hydrophobic interaction chromatography. Proteoglycan accumulation in the cell layer was increased two- to fivefold at an ECP-concentration of 10 micrograms/ml. No effect on collagen, other proteins or hyaluronan was noted. Furthermore, no effect was observed on cell proliferation. The increased proteoglycan accumulation could be inhibited by addition of heparin or of antibodies to ECP. The effect could not be mimicked by the two basic peptides protamine and poly-L-lysine, speaking in favor of specificity. The increase in proteoglycan material was seen exclusively in the intracellular pool. No change of proteoglycans in the medium or the cell surface-associated pool was noted. The increase in the cell layer was accounted for by a two- to fivefold increase in free chains of heparan sulfate and dermatan sulfate. No change was seen in the proteoglycan pattern. No effect on proteoglycan synthesis or on endocytosis was noted. The increased accumulation of polysaccharide was caused by inhibited degradation of glycosaminoglycans. The half-lives of large and small heparan sulfate proteoglycans/glycosaminoglycans and dermatan sulfate proteoglycans/glycosaminoglycans in the cell layer are increased four- to sevenfold. We conclude that ECP inhibits proteoglycan degradation in fibroblasts, which indicates a role for the eosinophil in generation of fibrosis.

Radiation-induced increase in hyaluronan and fibronectin in bronchoalveolar lavage fluid from breast cancer patients is suppressed by smoking.

Bronchoalveolar lavage (BAL) fluid was analysed from 21 patients with breast cancer, stage T1N0M0, who had undergone tumour resection and post-operative local irradiation (accumulated dose 56 Gy). The lavage was performed two months after radiotherapy, in the anterior part of the lingula (left side) or of the right middle lobe (right side), depending on which side had been exposed to radiation. The patients had significantly increased concentrations of fibronectin (FN) (p less than 0.001), hyaluronan (HA) (p less than 0.01) and albumin (p less than 0.05) in BAL fluid compared with the healthy controls (n = 19). However, when the patients were separated, according to smoking history, it was obvious that the inflammatory reaction occurred entirely in the nonsmoking patient group (n = 10), whilst no difference could be found between the smoking patients (n = 11) and the controls. In the nonsmoking patient group, there was a sevenfold increase in BAL concentrations of FN and a threefold increase in HA. Moreover, four patients had detectable levels of procollagen III peptide in BAL, all were nonsmokers. The smoking habits of the controls had no influence on the BAL measurements. These findings indicate that smoking interferes with the radiation-induced early inflammatory connective tissue reaction of the lung. Finally, the results justify further investigation of interaction of smoking with cancer treatment, both from the view of therapy effectiveness and reduction of adverse effects.

Transforming growth factor-beta induces selective increase of proteoglycan production and changes in the copolymeric structure of dermatan sulphate in human skin fibroblasts.

Human embryonic skin fibroblasts were pretreated with transforming growth factor-beta (TGF-beta) for 6 h and then labeled with [35S]sulphate and [3H]leucine for 24 h. Radiolabeled proteoglycans from the culture medium and the cell layer were isolated and separated by isopycnic density-gradient centrifugation, followed by gel, ion-exchange and hydrophobic-interaction chromatography. The major proteoglycan species were examined by polyacrylamide gel electrophoresis in sodium dodecyl sulphate before and after enzymatic degradation of the polysaccharide chains. The results showed that TGF-beta increased the production of several different 35S-labelled proteoglycans. A large chondroitin/dermatan sulphate proteoglycan (with core proteins of approximately 400-500 kDa) increased 5-7-fold and a small dermatan sulphate proteoglycan (PG-S1, also termed biglycan, with a core protein of 43 kDa) increased 3-4-fold both in the medium and in the cell layer. Only a small effect was observed on another dermatan sulphate proteoglycan, PG-S2 (also named decorin). These observations are generally in agreement with results of other studies using similar cell types. In addition, we have found that the major heparan sulphate proteoglycan of the cell layer (protein core approximately 350 kDa) was increased by TGF-beta treatment, whereas all the other smaller heparan sulphate proteoglycans with protein cores from 250 kDa to 30 kDa appeared unaffected. To investigate whether TGF-beta also influences the glycosaminoglycan (GAG) chain-synthesizing machinery, we also characterized GAGs derived from proteoglycans synthesized by TGF-beta-treated cells. There was generally no increase in the size of the GAG chains. However, the dermatan sulphate chains on biglycan and decorin from TGF-beta treated cultures contained a larger proportion of D-glucuronosyl residues than those derived from untreated cultures. No effect was noted on the 4- and 6-sulphation of the GAG chains. By the use of p-nitrophenyl beta-D-xyloside (an initiator of GAG synthesis) it could be demonstrated that chain synthesis was also enhanced in TGF-beta-treated cells (approximately twofold). Furthermore, the dermatan sulphate chains synthesized on the xyloside in TGF-beta-treated fibroblasts contained a larger proportion of D-glucuronosyl residues than those of the control. These novel findings indicate that TGF-beta affects proteoglycan synthesis both quantitatively and qualitatively and that it can also change the copolymeric structure of the GAG by affecting the GAG-synthesizing machinery. Altered proteoglycan structure and production may have profound effects on the properties of extracellular matrices, which can affect cell growth and migration as well as organisation of matrix fibres.

Alveolar accumulation of fibronectin and hyaluronan precedes bleomycin-induced pulmonary fibrosis in the rat.

The development of bleomycin-induced pulmonary fibrosis in rats was studied over a period of 30 days after an intratracheal instillation of bleomycin. Fibronectin was visualized in histological sections and quantified in bronchoalveolar lavage fluid (BALF) and related to simultaneous measurements of hyaluronan, collagen and albumin in BALF and/or lung tissue extracts. An increase in BALF fibronectin levels was noted after 3 days and the peak value a sixty fold increase was noted at day 7. Thereafter, the fibronectin levels declined and reached control values on day 21. A pronounced, patchily distributed staining for fibronectin appeared in the injured alveolar tissue parallel to the increased lavage fluid fibronectin levels on days 3-7. A fainter, streakily distributed fibronectin staining remained within the alveolar walls in areas with proliferating fibroblasts on days 14-30. Albumin in BALF increased to a peak level, 20 times control values, after 3 days and then rapidly declined. Thus, the ratio of fibronectin to albumin increased to a peak value of 43 times control values on day 7, indicating that plasma leakage cannot be the only source of the observed increase in lavage fibronectin. Lung tissue hydroxyproline increased between days 7 and 30, whereas extractable hyaluronan in lung tissue and bronchoalveolar lavage fluid peaked on days 3-7 and then gradually declined towards normal values on days 21-30. These data demonstrate that fibronectin accumulates in the alveolar tissue during the early inflammatory phase of the bleomycin-induced lung injury, parallelling hyaluronan accumulation and preceding the development of pulmonary fibrosis.

Oral N-acetylcysteine reduces bleomycin-induced collagen deposition in the lungs of mice.

N-acetylcysteine (NAC) has been employed in the treatment of acute lung injury but its therapeutic value is as yet unproven. In the present study we examined the effect of both L- and D-forms of NAC as inhibitors of bleomycin-induced fibrosis in mice. We hypothesized that, because of the D-form is not metabolized, it may be more effective than the L-form in ameliorating lung injury and fibrosis. Both drugs were given daily in the drinking water at a dose of approximately 400 mg.kg-1 body weight commencing one week prior to a single intratracheal instillation of bleomycin at a dose of 6 mg.kg-1 body weight. Lung injury was assessed 35 days later by measuring total lung collagen content, lung wet weight and examination of tissues by light and electron microscopy. Total collagen content and lung wet weight of animals receiving bleomycin together with L-NAC were 2.90 +/- 0.03 mg and 0.23 +/- 0.01 g, respectively. The values for collagen content, but not wet weight, were significantly less (p less than 0.05) than those given for bleomycin alone (3.90 +/- 0.02 mg and 0.260 +/- 0.005 g, respectively), but greater than (p less than 0.05) controls (2.10 +/- 0.01 mg and 0.160 +/- 0.002 g, respectively). Values for collagen content and wet weight of animals given bleomycin together with D-NAC (3.10 +/- 0.02 mg and 0.21 +/- 0.01 mg, respectively) were both significantly greater than values for control animals but lower than animals given bleomycin alone.(ABSTRACT TRUNCATED AT 250 WORDS)

TGF-beta enhances the production of hyaluronan in human lung but not in skin fibroblasts.

Transforming growth factor-beta (TGF-beta) enhances the production of extracellular matrix components, such as type I and type III collagen, fibronectin, proteoglycans, in various cell types. The effect on hyaluronan synthesis in relation to proteoglycan synthesis has not been investigated. Human lung or skin fibroblast cultures were treated with TGF-beta in serum-free medium for various periods of time. 35SO4 or [3H]glucosamine was then added to the cultures in the absence of TGF-beta for up to 48 h. Hyaluronan and proteoglycans were isolated by ion-exchange chromatography and quantitated. TGF-beta induced a three- to fourfold increase in hyaluronan production by lung cells but had no effect on skin fibroblasts. In contrast, proteoglycan synthesis was enhanced in both cell types, although skin fibroblasts responded at lower concentrations of TGF-beta. Increased accumulation of hyaluronan was noted only in the cell medium, whereas proteoglycan accumulation was observed both in the medium and in the cell layer. The ED50 for TGF-beta on hyaluronan accumulation in lung cells was the same as that for proteoglycan accumulation, i.e., 40 pM. In skin fibroblasts the ED50 was considerably lower (4 pM). The induction time needed to attain full effect of TGF-beta was 6 h for both hyaluronan and proteoglycan synthesis. These results indicate that TGF-beta has tissue-specific effects on matrix production which may be of importance for control of cell proliferation in various disease states.

Prospects for future topical glucocorticoid development.

Current glucocorticoids are inactivated mainly in the liver. Results from studies of their catabolism; their concentration gradients in epidermis and upper and lower dermis after topical application to intact and injured skin; and the concentration needed to inhibit synthesis of human connective tissue by skin fibroblasts; suggest that their systemic and local adverse reactions would logically be reduced further by adding a rapid extrahepatic biotransformation. An ideal glucocorticoid should be locally inactivated during, or immediately after, absorption. The data available for three glucocorticoids with some extrahepatic metabolism suggest that such relatively labile steroids may have a more autoregulating absorption than that of the conventional, more stable, steroids. This means that in skin areas with a damaged stratum corneum, the balance between steroid influx and inactivation may favour anti-inflammatory activity, while that balance is insufficient in intact skin for a triggering of glucocorticosteroid activity. When the skin lesions heal, and the high influx rate tapers off, corticosteroid activity in the epidermis and dermis may be better cut off than with the conventional, metabolically stable, corticosteroids. The compounds subject to local metabolism available today appear to have only moderate topical corticosteroid activity. There are still no valid data to support a claim that their catabolic effects on the connective tissue of diseased skin are less than those of conventional topical steroids. However, novel glucocorticosteroids with a still better relation between high intrinsic glucocorticosteroid activity and rapid metabolic turnover in skin should be designed and tested.

Glucocorticoids change the nucleotide and sugar nucleotide pool sizes in cultured human skin fibroblasts.

Fibroblasts in culture were treated with the glucocorticoid budesonide. The nucleotide and sugar nucleotide pools were quantitated after separation by isotachophoresis. Steroid treatment induced a 40% increase of the UDP-N-acetylhexosamine pool and a 30% increase of the UDP-glucuronic acid pool whereas the UTP pool was diminished. These effects became apparent after 24 h of incubation and a new steady state was attained after 48 h of incubation. The 3'-phosphoadenosine-5'-phosphosulfate pool was probably not influenced by the glucocorticoid treatment. The half-life of the UDP-N-acetylhexosamine pool was considerably longer in treated than in control cells. The efflux from the UDP-N-acetylhexosamine pool was also lowered in the treated cells. The changed efflux may be due to a decreased glycoconjugate synthesis induced by glucocorticoid treatment. The rate of equilibration of [14C]glucose and [3H]glucosamine with the UDP-N-acetylhexosamine pool was changed by glucocorticoid treatment; especially that of [3H]glucosamine was decreased.

Biochemical characterization and tissue distribution of the scleredema in a case of Buschke's disease.

Biopsies from a patient with a longstanding form of scleredema adultorum Buschke were analysed for morphological and biochemical changes in the dermal connective tissue. By light microscopy the tissue changes were located to the deep part of the reticular dermis. Therefore dermal tissue was separated into a superficial and a deep part and analysed biochemically. By this procedure it was possible to show that the concentration of hyaluronan in the deep part of the dermis was increased. The urinary excretion of methylimidazole acetic acid, an indicator of the mast cell mass in the body, was also elevated.

Equilibration of [3H]glucosamine and [35S]sulfate with intracellular pools of UDP-N-acetylhexosamine and 3'-phosphoadenosine-5'-phosphosulfate (PAPS) in cultured fibroblasts.

Nucleotides and sugar nucleotides were extracted from cultures of human fibroblasts with perchloric acid, separated by isotachophoresis, and quantified by uv absorption analysis at 254 nm. ATP (936 pmol/micrograms DNA) was, as expected, the dominating nucleotide pool. The energy charge was estimated to 0.9. The UDP-N-acetylhexosamine pool was also a very prominent compound (596 pmol/micrograms DNA). After incubation of fibroblasts with [3H]glucosamine, more than 95% of the acid-soluble radioactivity was found in the UDP-N-acetylhexosamine pool. Incubation with [35S]sulfate resulted in the incorporation of [35S]sulfate into 3'-phosphoadenosine-5'-phosphosulfate (PAPS). The latter could, however, only be measured as radioactivity, as the amount was too small to be quantified as total mass. Pulse-labeling of fibroblasts with [35S]sulfate and [3H]glucosamine from 5 min to 16 h showed that [35S]PAPS was equilibrated in less than 10 min, while [3H]glucosamine required a longer time, 2-4 h, to attain a steady state with UDP-N-acetylhexosamine. [14C]Glucose required approximately the same time as [3H]glucosamine to reach steady state with UDP-acetylhexosamine, which suggests that the reason for the long equilibration time is the slow turnover of this pool.

Biosynthesis and secretion of dermatan sulphate proteoglycans in cultures of human skin fibroblasts.

Fibroblasts in culture were incubated with [3H]leucine and [35S]sulphate for 1-24 h. A large glucuronic acid-rich and a small iduronic acid-rich dermatan sulphate proteoglycan were isolated with the use of isopycnic density-gradient centrifugation, ion-exchange and gel chromatography. After 3 h the accumulation in the cell layer of the small proteoglycan reached a steady state, whereas the large one continued to increase, albeit more slowly. In the medium both proteoglycans accumulated 'linearly', although the large one appeared somewhat later than the small one. The composition of the polysaccharide chains and the size of the protein cores did not vary during the experiment. The two proteoglycans were synthesized at approximately similar rates, but were distributed differently in the culture. The small proteoglycan was mainly confined to the medium, whereas the large one was found in the medium as well as in a cell-associated pool. There was an intracellular accumulation of iduronic acid-rich dermatan sulphate as free polysaccharides.