Complexes of rat alpha 1-macroglobulin and subtilisin are endocytosed by parenchymal liver cells

Proteases and protease inhibitors in cerulein-induced acute pancreatitis in rats

BACKGROUND

Proteases and protease inhibitors are important in acute pancreatitis (AP), although little is known about the time course in cerulein-induced AP in the rat.

MATERIALS AND METHODS

AP was induced by supramaximal stimulation of cerulein, 10 microgram/kg/h, and during 72 h we measured lipase, amylase, albumin, prekallikrein, factor X, alpha(1)-protease inhibitor, alpha(1)-macroglobulin, alpha(2)-antiplasmin, antithrombin III (all in plasma) and macroscopic and histologic variables.

RESULTS

Within 12 h an edematous pancreatitis was evident with peak values of peritoneal exudate, pancreatic wet weight ratio, and plasma amylase and lipase activities. Histologically, edema and vacuolization were prominent already after 3 and 6 h, respectively, while inflammation, necrosis, and total histological score gradually increase to reach peak levels at 48 h. Proenzymes and most plasma protease inhibitors decreased to low levels after 6-12 h followed by a gradual increase. The sequential changes over time indicate that kallikrein - kinin activation, and plasminogen activation are probably early events in cerulein-induced AP in rats. alpha(1)-Macroglobulin and alpha(1)-protease inhibitor gradually decreased during the whole study period, probably being "second line" defense inhibitors. Levels above normal were seen for alpha(2)-antiplasmin and factor X at 48 h, normalizing at 72 h.

CONCLUSIONS

These results suggest that protease activation and protease inhibitor consumption occur in cerulein-induced AP in the rat.

Proteases and protease inhibitors in taurocholate-induced acute pancreatitis in rats

CONCLUSION

Taurocholate-induced acute pancreatitis (AP) in the rat mimics early necrotizing human pancreatitis. Protease activation and protease inhibitor consumption occur consistent with a two-stage development, and contact-phase activation is a possible primary event in this model.

BACKGROUND

Proteases and protease inhibitors have been indicated to play an important role in both human and experimental acute pancreatitis, although little is known about them in rats.

METHODS

Three percent sodium taurocholate was infused into the bilio-pancreatic duct to induce AP, and over 0-72 h we measured lipase, amylase, albumin, prekallikrein, factor X, alpha-1-macroglobulin, alpha-2-antiplasmin, antithrombin III, alpha-1-protease inhibitor, and C1-esterase inhibitor (all in plasma) and histologic and macroscopic findings.

RESULTS

A severe necrotizing, nonlethal, AP was induced with an early increase in plasma lipase and alpha-amylase activity levels and peritoneal exudate followed by a return to near control levels after 72 h. Histologic score and pancreatic wet weight ratio increased initially and remained high during the observation period. The protease inhibitors C1-esterase inhibitor, alpha-2-antiplasmin, and antithrombin III decreased early, within 0-6 h, whereafter levels normalized. The protease inhibitors alpha-1-macroglobulin and alpha-1-protease inhibitor later gradually decreased over the 72 h.

Endocytosed ricin and asialoorosomucoid follow different intracellular pathways in hepatocytes

Earlier studies have suggested that fluid phase endocytosis in rat hepatocytes takes place via a clathrin-independent mechanism [1,2]. This observation suggests that a relatively large amount of plasma membrane outside coated pits may be involved in hepatic endocytosis. Ricin, which binds to galactose residues on glycoproteins and glycolipids, has, in this report, been used as a general marker for the plasma membrane of hepatocytes. The endocytosis of ricin was compared with that of asialoorosomucoid (AOM) which is taken up exclusively via clathrin-coated pits. Hypertonic medium has been shown to inhibit uptake via coated pits more effectively than clathrin-independent uptake [3-5]. It was found, in this study, that the addition of 100 mM sucrose to the incubation medium inhibited the uptake of 125I-tyramine-cellobiose-asialoorosomucoid (125I-TC-AOM) more extensively than that of 125I-tyramine-cellobiose-ricin (125I-TC-ricin), compatible with the notion that the two probes are internalised via different mechanisms. Subcellular fractionation experiments indicated that 125I-TC-ricin entered a denser endocytic organelle than that receiving 125I-TC-AOM. To determine whether the separation of the two probes was due to a different transport kinetics (i.e. that 125I-TC-ricin is transported more rapidly to a later, denser compartment than 125I-TC-AOM) the cells were incubated at 18 degreesC to allow a slower internalisation/transport of the labelled probes. The results obtained showed, again, that the early endosomes containing 125I-TC-ricin were significantly denser than those containing 125I-TC-AOM. We also employed the horseradish peroxidase (HRP)-diaminobenzidine (DAB) density shift technique of Courtoy et al. [6] to determine whether 125I-TC-ricin and 125I-TC-AOM were in separate endosomes early after their uptake. The results showed that early endosomes containing 125I-TC-AOM were density shifted whereas those containing 125I-TC-ricin were unaffected by the density shift procedure. The use of probes labelled with 125I-TC allowed us to identify compartments involved in the degradation of 125I-TC-AOM and 125I-TC-ricin, by measuring acid soluble radioactivities in the gradient fractions. It was found that 125I-TC-ricin was degraded mainly in endosomes, whereas 125I-TC-AOM, as expected, was degraded mainly in lysosomes.

The isolation and partial characterization of alpha 2-macroglobulin from the serum of the ostrich (Struthio camelus

1. alpha 2-Macroglobulin (alpha 2M) activity is present in the serum of the ostrich, Struthio camelus. The chromogenic synthetic peptide substrates BAPNA and ATNA were hydrolysed by trypsin and chymotrypsin, respectively, in the presence of ostrich serum and the alpha 2 M in ostrich serum protected trypsin from being inhibited by soybean trypsin inhibitor. Ostrich alpha 2M proved to be a potent inhibitor of bovine pancreatic trypsin and chymotrypsin. 2. alpha 2M was purified to apparent homogeneity by PEG precipitation, DEAE-Toyopearl 650M, Bio-Gel A-5m and Zn(2+)-affinity chromatography. 3. Ostrich alpha 2M migrated as a single band (M(r) 779,000 during non-denaturing gradient gel electrophoresis and showed increased mobility after reaction with trypsin. Denaturation dissociated ostrich alpha 2M into half-molecules. Denaturation with reduction further dissociated the protein into quarter-subunits. 4. Isoelectric focusing revealed a pI of 5.3. 5. The amino acid composition of ostrich alpha 2M is typical of an alpha 2M, comparing favourably with those of other animal species. The carbohydrate composition of the purified protein, in percentage dry weight of the molecule, was galactose: mannose (1:1), 4.55; N-acetylglucosamine 2.35; N-acetylneuraminic acid, 0.58; and fucose, 0.77. 6. alpha 2M was assessed immunologically by Ouchterlony double-diffusion and Western blot analysis with polyvalent antisera directed against ostrich alpha 2M. 7. Ostrich alpha 2M seems to show many physical, chemical and kinetic properties similar to those of other known alpha 2M(s), but is expected to differ from other alpha Ms when considering the primary structure of the bait region, the area differing among alpha Ms from different species and determining its specificity.

Comparison between clearance rates of plasma kallikrein and of plasma kallikrein-alpha-macroglobulin complexes by the liver

1. alpha-Macroglobulins (alpha Ms) were isolated from the serum of injured rats through a two-stage method: gel filtration and ultracentrifugation. 2. The clearance rates of rat plasma kallikrein (RPK) and alpha Ms-RPK complexes were compared in an isolated rat liver perfusion system: the alpha Ms-RPK complexes are cleared at a much slower rate (half-life ranging from 24 to > 120 min) than does RPK itself (half-life ranging from 13 to 18 min).

Alpha-macroglobulin secreted by alveolar macrophages serves as a binding protein for a macrophage-derived homologue of platelet-derived growth factor

Evidence is presented to support our hypothesis that an alpha-macroglobulin (alpha M) produced by lung macrophages serves as a specific binding protein for platelet-derived growth factor (PDGF) from these same macrophages. Culture medium "conditioned" by alveolar macrophages was fractionated by gel filtration according to molecular weight. Proteins larger than 200 kD were bound to greater than 50% of the macrophage-derived PDGF (MD-PDGF) that was extractable by 1 M acetic acid. Another approximately 25% was bound to fractions at approximately 150 kD, and approximately 20% remained unbound. The two high molecular weight fractions inhibited approximately 40% of specific [125I]PDGF binding to rat lung fibroblasts, whereas other fractions did not block PDGF binding to its receptor. Only the greater than 200 kD fractions inhibited the binding of PDGF antisera to purified human PDGF by 20% of control and exhibited specific complex formation and coelution on a gel filtration column with [125I]PDGF. The macrophage-derived alpha M (MD-alpha M) was separated from other macrophage-derived proteins by nickel-affinity chromatography and exhibited clear characteristics of alpha Ms, i.e., cross-reactivity with antibodies to human alpha 2-macroglobulin (alpha 2M) on immunoblots as well as gel migration corresponding to the electrophoretic mobility of the protease-bound "fast" and protease-unbound "slow" forms of human alpha 2M. Nickel-bound protein identified as an alpha M was bound to greater than 50% of the acid-extractable MD-PDGF in macrophage-conditioned medium, supporting the view that the greater than 200 kD protein separated by gel filtration is an alpha M.(ABSTRACT TRUNCATED AT 250 WORDS)

Biosynthesis and regulation of rat alpha 1-inhibitor3, a negative acute-phase reactant of the macroglobulin family

The biosynthesis of rat alpha 1-inhibitor3, a negative acute-phase reactant specifically found in rodents, was studied in vitro in a cell-free translation system from rabbit reticulocytes, in rat hepatocyte primary cultures and in vivo by immunocytochemistry using normal and turpentine-injected rats. By sucrose-gradient centrifugation and subsequent translation of the fractionated RNA in vitro it was found that the mRNA coding for alpha 1-inhibitor3 exhibited a size of about 28S. For the alpha 1-inhibitor3 translated in vitro an apparent Mr of 155,000 was determined. A continuous decrease in the level of alpha 1-inhibitor3 in serum during experimental inflammation induced by turpentine injection was demonstrated by means of quantitative 'rocket' immunoelectrophoresis. This result agrees with the observation by immunocytochemistry of a drastic decrease in alpha 1-inhibitor3 levels in hepatocytes 24 h after turpentine injection. At that time alpha 1-inhibitor3 is mainly located in the Golgi apparatus, whereas it is also present in the membranes of the rough and smooth endoplasmic reticulum when normal liver is used. All hepatocytes, but no other hepatic cells, contain alpha 1-inhibitor3. When hepatocyte primary cultures were labelled with [35S]methionine and alpha 1-inhibitor3 was immunoprecipitated from the hepatocyte medium and the supernatant of homogenized cells, two different forms of alpha 1-inhibitor3 were found. The intracellular form of alpha 1-inhibitor3, with an apparent Mr of 173,000, is characterized by oligosaccharide side chains of the high-mannose type. The form of alpha 1-inhibitor3 in the medium exhibited an Mr of 186,000 and carried carbohydrate side chains of the complex type. After labelling hepatocytes with radioactive sugars, [3H]mannose was found in both forms of alpha 1-inhibitor3, whereas [3H]fucose and [3H]galactose were incorporated only into the form found in the medium. In the presence of tunicamycin an unglycosylated alpha 1-inhibitor3 with an apparent Mr of 154,000 was found in cells and in the medium. In a pulse-chase experiment it was shown that inhibition of glycosylation by tunicamycin resulted in a marked delay of secretion of alpha 1-inhibitor3. Thus the oligosaccharide side chains of alpha 1-inhibitor3 play an important role during its transport into the medium.