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D R Borges

Publications and source records attributed to D R Borges.

At least 37 records · Page 2Linked to original sources
PubMed1992

The recognition site for hepatic clearance of plasma kallikrein is on its heavy chain and is latent on prokallikrein.

We partially purified the glycoproteins prokallikrein and kallikrein from rat plasma. The purification of rat plasma kallikrein may result in two forms: an intact form (alpha, M(r) 84-87 kDa) and a partially degraded form (beta, M(r) 46-51 kDa). The alpha-form is composed of a heavy chain (M(r) 50 kDa) and a light chain (M(r) 34-37 kDa) linked by a disulfide bond. The catalytic site is found on the light chain. The beta-form has a partially degraded heavy chain (M(r) 28 kDa). Using a preparation of exsanguinated and perfused rat liver, we verified that rat plasma prokallikrein is not activated by the liver and that neither the proenzyme nor the light chain is removed by the organ. Both forms (alpha and beta) of the active enzyme are similarly removed from the perfusate. We also observed that the clearance of plasma kallikrein is temperature-dependent, and not affected by substances that inhibit binding to galactosyl-, mannosyl-, fucosyl- or phosphomannosyl-specific lectins, but inhibited by beta-galactosides. We suggest that: (a) the binding site to hepatocytes is latent on prokallikrein and is located on its heavy chain, more specifically on the 28-kDa fragment still present in the beta form of the active enzyme and (b) plasma kallikrein is recognized by an S-type lectin.

Amides↗
PubMed1991

Native plasma kallikrein is cleared at similar rates by mammalian and avian livers.

Rat plasma kallikrein (RPK) is a serine protease that circulates as an inactive precursor, prokallikrein, and once activated is efficiently cleared by the liver by a carbohydrate-dependent, Ca(2+)-independent mechanism. Seven hepatic lectin systems have been described for mammals but not all of these animal lectins are expressed in the avian liver. Using a liver perfusion system we compared the plasma kallikrein clearance of rats (N = 10) and pigeons (N = 4). Our results show that the lectin responsible for the hepatic clearance of plasma kallikrein is also present in pigeon liver and that this organ clears the enzyme with an efficiency (11.4 +/- 1.3 pmol/g, 20 min) similar to that of the rat liver (10.0 +/- 0.7 pmol/g, 20 min).

Animals↗
PubMed1990

Chronic administration of ethanol does not alter plasma kallikrein hepatic clearance.

1. The clearance of plasma kallikrein by the isolated and perfused liver of rats chronically intoxicated with ethanol was studied. Alcohol was added to the diet as 36% of total calories, and the animals were kept on this diet for 5-7 weeks. 2. The hepatic clearance of plasma kallikrein by these rats (uptake half-life, 15 +/- 2 min; N = 3) was similar to that observed in the control groups (normal diet, uptake half-life, 14 +/- 2 min; N = 5, or normal diet with sucrose added as 36% of total calories, uptake half-life, 16 +/- 3 min; N = 4). 3. These results provided indirect evidence that the endocytosis mechanism of plasma kallikrein by the liver differs from that described for glycoproteins which use the galactosyl receptor, since liver endocytosis via this latter system is reduced by chronic alcohol intoxication.

Alcohol Drinking↗
PubMed1990

Plasma kallikrein clearance by the liver in food-restricted rats.

We measured the clearance rate of plasma kallikrein by the liver in three groups of rats: one recently weaned, and two seven weeks old (control and food-restricted groups). The clearance rates were similar in the three groups when expressed as units/g liver. The livers of the recently weaned and food-restricted rats were, however, smaller than those of the controls and consequently their livers cleared plasma kallikrein less efficiently.

Animals↗
PubMed1989

Identification of receptors in the liver that mediate endocytosis of circulating tissue kallikreins.

The liver plays an important role in the clearance, by receptor-mediated endocytosis, of circulating glycoproteins. It has been demonstrated that tissue kallikreins, which are acid glycoproteins, circulate in plasma, where they are poorly inhibited by plasma proteins. We have shown that the liver is the main organ that clears tissue kallikreins from the circulation. We now report the identification of receptors involved in this clearance. Using a perfused rat-liver system, and as models, pig pancreatic (PPK) and horse urinary (HoUK) kallikreins, we have found that: (a) the binding of PPK to the perfused liver was inhibited by 50 mM methyl alpha-D-mannoside and 20 microM mannan, was partially inhibited by 50 mM mannose and was unaffected by 1.5 microM asialofetuin; (b) binding of HoUK to the perfused liver was inhibited by 1.5 microM asialofetuin, 50 mM galactose and 50 mM lactose and was unaffected by 50 mM mannose; (c) the clearance rate of both kallikreins followed the equation y = a.xb; (d) their binding was Ca2+-dependent and their clearance was inhibited by 3 mM chloroquine and 10 mM methylamine. Using isolated liver cells and tritiated HoUK, we calculated that 500,000 receptors/cell were present and the Scatchard plot showed that there were two apparent affinity constants: 0.24.10(9) l/M) (high-affinity) and 0.3.10(8) l/M (low-affinity). These results show that PPK is recognized by a liver mannose receptor and HoUK by the galactose receptor. The liver uptake of native and circulating tissue kallikreins thus emerges as a mechanism by which their levels in plasma are regulated.

Animals↗
PubMed1989

Plasma kallikrein clearance by the liver of normal and injured rats.

We report the clearance of rat plasma kallikrein (RPK) by the perfused livers of normal rats and from others at 2 and 4 days after subcutaneous injection of turpentine oil. RPK removal from the perfusate follows a logarithmic curve (y = a+b lnx) and from this equation its half-life of removal can be calculated. RPK clearance rate followed the potential equation y = axb. Both the half-life of RPK removal and RPK clearance rates were similar in the 3 groups of perfused livers. We conclude that, at the initial concentration of RPK used (approximately 3 nM), its liver clearance is not affected during the acute-phase response to inflammation.

Animals↗
PubMed1987

Protein C deficiency in the compensated form of hepatosplenic schistosomiasis.

Plasma levels of protein C (enzyme immunoassay), albumin (electrophoresis), and transthyretin (radial immunodiffusion) were measured in 15 patients with the compensated hepatosplenic form of schistosomiasis and in 10 healthy volunteers. Plasma levels of protein C were below normal in 47% of the schistosomiasis patients; this deficiency could be explained by diminished hepatic synthesis since it occurred in conjunction with low plasma levels of albumin and/or transthyretin. In 33% of the schistosomiasis patients, plasma levels of protein C were below 0.5 U/ml, a value which has been associated with thrombotic disease. Protein C deficiency may explain the unexpectedly low incidence of hemorrhagic episodes, as well as the occurrence of portal vein thrombosis that is not infrequent in these patients.

Adolescent↗
PubMed1987

Purification and characterization of the alpha form of rat plasma kallikrein.

A four-step procedure was used to purify rat plasma kallikrein (RPK) with a relative molecular mass (Mr) of 87 kD (obtained both by gel filtration and SDS-PAGE), which indicates the purification of an alpha (intact) kallikrein, in contrast to previously described RPK preparations which had lower Mr (beta or degraded form). RPK is a neutral (pI 6.7) serine proteinase glycoprotein (15% carbohydrates) and contains (residues/mol): galactose (27), N-acetylglucosamine (24), mannose (13), glucose (13) and fucose (7). This purified alpha form of RPK has properties very similar to those of pure human and bovine kallikreins.

Animals↗
PubMed1986

Receptor-mediated clearance of tissue kallikreins by rat liver.

The exsanguinated, isolated and perfused rat liver clears from the perfusate, at comparable rates, some native tissue kallikreins: human and horse urinary as well as hog pancreatic; the clearance rates were dependent on the initial enzyme concentration in the perfusing fluid. Contrary-wise, rat urinary kallikrein was cleared at negligible rates. Neuraminidase pretreatment of these four kallikreins did not alter their clearance rates. Horse urinary kallikrein binding to isolated prefixed hepatocytes was calcium-dependent and inhibited by asialofetuin (but not by fetuin) and some sugars; these characteristics are compatible with the interpretation that this native tissue kallikrein is recognized by the hepatocyte asialoglycoprotein-receptor. It was calculated that there are about 300,000 receptor sites per cell either using perfusion experiments at 4 degrees C or isolated hepatocytes.

Animals↗
PubMed1985

Rat plasma kallikrein clearance by perfused rat liver.

Previous studies have shown that perfused rat liver in situ is able to clear recirculating rat plasma kallikrein (RPK) in two phases: an initial clearance lasting a few minutes, followed by a slow exponential phase. Using purified RPK preparations we now show that: RPK is a glycoprotein; clearance was inhibited by human serum against blood group B and 0.1 M melibiose but was not affected by human serum against blood group A, 0.1 M lactose, 0.1 M mannose, 0.05 M N-acetyl galactosamine, 0.05 M galactose or 15 microM asialofetuin. Prolonged incubation of RPK with alpha-galactosidase reduced RPK clearance. Oligosaccharide structures in RPK may have terminal galactose units since treatment of RPK with neuraminidase did not affect the clearance rate; RPK clearance occurs in the absence of added Ca2+, with either EDTA or EGTA in the perfusion fluid; the exponential phase is reversibly inhibited by the addition of NH4Cl or chloroquine to the perfusion fluid. This observation, along with experiments using liver homogenates, suggests that RPK catabolism is carried out by lysosomal enzymes, probably cathepsin B of possible hepatocyte origin.

Animals↗
PubMed1984

Kinin-inactivating endopeptidase from rat liver.

A kinin-inactivating serine-endopeptidase from rat liver was purified to an activity of 912 mU/mg of protein, when measured on bradykinin. The endopeptidase molecular weight, estimated by gel filtration, was 68,000. Its isoelectric point was close to pH 4.9. Vm for the hydrolysis of bradykinin, was 1.25 mumol/min/mg protein; Km was 28 microM. The two hydrolysis products from bradykinin were the pentapeptide Arg1-Phe5 and the tetrapeptide Ser6-Arg9.

Amino Acid Sequence↗
PubMed1983

Lysosome injury by perfusion of the isolated rat liver with ethanol or a molasses distillate (cachaça).

An isolated rat liver perfusion model was used to study the effects of acute exposure of the organ to either ethanol or a molasses distillate (cachaça). When ethanol (72 mM) or a molasses distillate (68 mM ethanol) was added to the perfusion fluid, lysosomal injury was indicated by the increased release of tartrate-inhibited acid phosphatase activity at the end of a 3 h period of perfusion. Other cellular compartments were not significantly damaged in these acute experiments, as judged by the release of aspartate and alanine aminotransferases, lactate dehydrogenase and alkaline phosphatase. The behavior of both ethanol itself and the alcoholic beverage was similar as far as enzyme release is concerned but only the molasses distillate caused significant acidosis (a decrease in perfusate pH) at the end of a 3 h period of perfusion. These data may be of importance for a better understanding of the hepatic damage caused by alcohol abuse and useful for laboratory investigation of alcohol intoxication.

Alcoholic Intoxication↗
PubMed1983

Exocrine pancreatic hypersecretion in Brazilian alcoholics.

Thirty percent of alcoholic patients without clinical evidence of pancreatic or hepatic disease showed hypersecretion of pancreatic bicarbonate in all three test periods after stimulation with secretin and secretin-cholecystokinin, and an increased amount of protein in the duodenal aspirate of the first test period, probably due to ductal wash-out. This hypersecretion must be taken into account when the secretion or secretin-cholecystokinin tests of alcoholics are interpreted, and, indeed, may be useful in identifying possible early pancreatic dysfunction that precedes insufficiency and clinical symptoms.

Adult↗