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PubMed1988

[Crohn's disease and enteral feeding: comparative nutritional efficacy of elemental and polymeric nutritive mixtures].

The nutritional development with three types of enteral diets during 28 days, was compared in 45 patients with malnutrition presenting an active Crohn's disease. Enteral feeding consisted of a polymeric mixture (Realmentyl) administered in addition to a normal oral diet in 11 patients; the same mixture was administered alone exclusively to 9 patients, and an elemental diet (Vivonex HN) administered exclusively to 25 patients. The total caloric intake reached, in the three groups, the mean values of 60.2, 36.9 and 33.8 kcal/kg of ideal weight/day, respectively. 33 patients also received steroids. At the end of 28 days of enteral diet, the improvement in the weight and the anthropometric measurements (muscle circumference, triceps skinfold) was significantly more marked (gain of 6.5 kg) with the supplemental polymeric mixture than with exclusive enteral diet, polymeric diet (+/- 2.0 kg) or basic (+1.2 kg). Transferrin and albumin plasma levels increased in all 3 groups, but much faster with the exclusive elemental feeding, in spite of a higher urinary urea excretion in these patients. The overall nutritional development was significantly better with supplemental polymeric feeding, and was identical in the two other groups. These results confirm that the supplemental polymeric enteral feeding is more effective, from the nutrition standpoint. With an exclusive enteral feeding, the nutritional result is appreciably the same, whether the mixture consists of polymers or basic elements.

Adult↗
PubMed1987

Actin polymerization and its relationship to locomotion and chemokinetic response in maturing human promyelocytic leukemia cells.

We studied actin polymerization in the HL-60 human promyelocytic leukemia cell line during induced myeloid maturation and its relationship to the rate of locomotion (ROL). The percent G-actin (of total actin) was measured by DNAase I inhibition, F-actin was determined by fluorescence-activated cell sorter (FACS) analysis of nitrobenzoxadiazol (NBD)-phallacidin-stained cells, and ROL was measured by computer-assisted analysis of the tracks of individual cells. Uninduced HL-60 cells moved slowly (2.3 +/- 1.0 microns/min) and showed no change in ROL or in the state of actin polymerization when stimulated by formyl-methionyl-leucyl-phenylalanine (fMLP). Nonstimulated cells induced to differentiate with dimethylformamide had no change in the degree of actin polymerization but exhibited a mean (m) ROL similar to normal human polymorphonuclear leukocytes (PMN) (8.6 +/- 1.4 micron/min [HL-60 cells] v 7.8 +/- 1.8 microns/min [PMN]. When induced HL-60 cells were stimulated with fMLP, actin polymerization occurred. The F-actin content increased, as determined by FACS analysis of NBD-phallacidin-stained cells, and the percentage of G-actin decreased, as determined by a 24.5% decrease in DNAase I inhibitory activity. However, induced HL-60 cells stimulated with fMLP did not increase their mROL. These studies show that, unlike normal human PMN, chemotactic peptides can cause an intracellular biochemical change that is not associated with a chemokinetic response in induced HL-60 cells. The HL-60 cell line may be a useful model to study the development of chemotactic peptide-mediated actin polymerization during myeloid cell maturation.

Actins↗
PubMed1986

Disulfide-bonded polymerization of plasma fibronectin in the presence of metal ions.

Incubation of human plasma fibronectin in the presence of low concentrations of FeCl3 or CuSO4 led to the formation of disulfide-bonded multimers as revealed by analysis in sodium dodecyl sulfate-polyacrylamide gel electrophoresis under nonreducing or reducing conditions. The polymers induced by FeCl3 did not enter the spacer gel, and those induced by CuSO4 migrated to the top of the running gel, indicating that the former polymers were larger than the latter, which in gel filtration experiments appeared to be larger than Mr 670,000. The polymerization occurred between pH 7 and 9 and more rapidly at 22 or 37 degrees C than at 4 degrees C and was inhibited by metal-chelating reagents. NaCl, heparin, spermine, urea, or guanidine hydrochloride did not appreciably affect the reaction, whereas dithioerythritol enhanced the CuSO4-induced polymerization of fibronectin. When incubated in the presence of FeCl3, the Mr 30,000 NH2-terminal, Mr 40,000 gelatin-binding, and the Mr 120,000-140,000 COOH-terminal fragments of fibronectin formed disulfide-bonded polymers, whereas only the Mr 140,000 fragment was polymerized in the presence of CuSO4. Disulfide-bonded polymers were also formed in the presence of FeCl3 but not CuSO4 when the free sulfhydryl groups of fibronectin were blocked by N-ethylmaleimide. The results suggest that in the presence of CuSO4, disulfide-bonded polymerization of fibronectin may involve predominantly the free sulfhydryl groups, whereas in the presence of FeCl3, also the intramolecular disulfides may exchange to form disulfides between separate fibronectin molecules. Thus, under different conditions, different parts of fibronectin may be susceptible to disulfide-bonded polymerization.

Chelating Agents↗
PubMed1986

N-ethylmaleimide cannot inhibit actin polymerization in platelets.

We investigated the effects of the N-ethylmaleimide (NEM), a sulfhydryl(SH) radical blocker, on platelet activation. Platelet aggregation and ATP release was suppressed by 0.2 mM NEM during ADP (20 microM) stimulation and by 0.5 mM NEM during A23187 (4 microM) stimulation. However the agent had no effect on actin polymerization in stimulated platelets. In the absence of a stimulant, NEM (over 1 mM) induced shape changes and slight (5%) actin polymerization, but not aggregation or ATP release. Although platelet aggregation and ATP release were suppressed by the addition of 1 mM NEM during the process of both reactions, the amount of polymerized actin was not influenced by the addition. The reconstructed system consisting of actin and partially purified regulatory proteins without myosin showed a dose-dependent increase in turbidity by the addition of NEM. From these findings, we concluded that NEM enhances actin polymerization, although actin molecules contain SH-radicals, and that actin polymerization has little affect on aggregation and release reaction.

Actins↗
PubMed1985

The membrane attack complex of complement: C5b-8 complex as accelerator of C9 polymerization.

Polymerization of C9 occurs spontaneously or can be induced by the tetramolecular complex C5b-8. Spontaneous C9 (0.15 mg/ml) polymerization required more than 3 days at 37 degrees C. In the presence of C5b-8, C9 polymerization was complete within 10 min. The molar C9:C5b-8 ratio determined the extent of tubular poly C9 formation by C5b-8-bearing phospholipid vesicles. When this ratio was 9:1 or 12:1, 72% of complex-bound C9 was present as SDS resistant tubular poly C9 (Mr = 1.1 X 10(6]. At lower C9:C5b-8 ratios, poly C9 was bound primarily in nontubular form. Tubular poly C9, as part of C5b-9, could also be generated on rabbit erythrocytes by using whole human serum as a complement source. At limiting serum concentration (molar C9 to C8 ratio approximately 2), no SDS-resistant tubular poly C9 was detected. At high serum concentration or when using serum that was supplemented with C9, up to 40% of the C9 was SDS-resistant tubular poly C9, and the rest was poly C9, which was incompletely polymerized. It is suggested that the C5b-8 complex acts as an accelerator of C9 polymerization, and that its relative concentration to C9 determines the ultrastructure of the C5b-9 complex.

Animals↗
PubMed1979

Use of a GTP photoaffinity probe to resolve aspects of the mechanism of tubulin polymerization.

8-Azidoguanosine 5'-triphosphate (8-N3GTP) was used in a photoactivatable probe to examine the role of GTP in microtubule assembly. 8-N3GTP was able to substitute for GTP in the promotion of tubulin polymerization and was hydrolyzed at 37 degrees C in the presence or absence of colchicine or calcium. Photolysis of the analog in the presence of microtubular protein resulted in its covalent incorporation onto a GTP-specific site of the beta monomer. The efficiency of this incorporation was different when 8-N3GDP (which does not affect polymerization) was used in place of 8-N3GTP, implying a different orientation of the nucleoside diphosphate within the receptor site. During microtubule assembly, 8-N3GTP was hydrolyzed in situ at the tubulin-GTP exchangeable site in a process that was dependent upon polymerization. The use of [beta, gamma-32P]8-N3GTP and [gamma-32P]8-N3GTP indicated that this hydrolysis occurred concurrently with polymerization and that only nucleoside diphosphate remained bound to the polymerized tubulin.

Affinity Labels↗
PubMed1981

Characterization of the interaction between polymerized human albumin and hepatitis B surface antigen.

The interaction of polymerized human albumin with hepatitis B surface antigen was characterized utilizing a solid-phase radioimmunoassay. The interaction was specific as shown by quantitative inhibition of binding by soluble polymerized human albumin. The interaction was species restricted in that hepatitis B surface antigen did not bind nonhuman polymerized albumins. The albumin polymer size was critical to the binding reaction as was the concentration of hepatitis B surface antigen; the interaction was also temperature, ionic strength, and pH dependent. Hepatitis B e antigen positive sera possessed greater polyalbumin binding reactivity than hepatitis B e antigen negative sera. This interaction was shown to be inhibited by normal human serum which suggested that the polyalbumin receptor on hepatitis B surface antigen may be a host rather than viral component. In view of our previous observation that polymerized human albumin binds human C1q, the interactions between polymerized human albumin, hepatitis B surface antigen, and human C1q may be relevant to hepatitis B virus-host receptor mechanisms.

Animals↗
PubMed1982

Kinetics of the polymerization of hemoglobin in high and low phosphate buffers.

Diluted solutions of deoxyhemoglobin S in concentrated phosphate buffer form aggregates or gels with a clear exhibition of a delay time. The aggregates can be liquified by cooling, bubbling with O2 or CO gas, or the dilution of phosphate buffer with water. These properties can be used as a simple method for studying the mechanism of polymerization and depolymerization of hemoglobins. The advantages of this method are: 1) The amount of hemoglobin sample required is only 1% to 5% of that required for the gelation of deoxy-Hb S in low phosphate buffer. 2) The kinetics can be measured turbidimetrically using an ordinary spectrophotometer. 3) The solubility of hemoglobin can be directly determined by taking the absorption spectrum of the supernatant solution after polymerization. 4) The polymer phase can be easily separated from the solution so that the amount and composition of the polymers can be analyzed. 5) The volume of the polymer phase is so small that excluded volume effect can be neglected. 6) The method can be applied to the study of polymerization of non-sickle hemoglobins and that of mixtures of sickle and non-sickle hemoglobins. The major question is whether the polymerization of hemoglobin in concentrated phosphate buffer is the same as that of deoxy-Hb S in low phosphate buffer. To answer this question, we studied the polymerization of Hb S, Hb A, Hb C Harlem, and Hb C in phosphate buffers of different molarities. We also studied the mechanism of the conversion of gels of these hemoglobins into crystals.

Buffers↗
PubMed1983

A hepatitis B surface antigen polypeptide (P31) with the receptor for polymerized human as well as chimpanzee albumins.

Hepatitis B virus, and hepatitis B surface antigen particles co-occurring with hepatitis B e antigen, have the receptor for polymerized human and chimpanzee albumins that may be involved in the hepatotropism of hepatitis B virus. We identified the receptor on a hepatitis B surface antigen polypeptide with a molecular size of 31,000 daltons (P31). P31 bound to polymerized albumins from human and chimpanzee, but did not react with polymerized albumins from the experimental animals without susceptibility to hepatitis B virus. P31 was composed of the major polypeptide of hepatitis B surface antigen with a molecular size of approximately 22,000 daltons (P22) and additional 55 amino acid residues coded by the pre-S region in the hepatitis B virus-specific deoxyribonucleic acid. Because P22 did not react with polymerized albumin, the sequence of 55 amino acid residues in the pre-S region appeared to bear the receptor. Polypeptides with the receptor for polymerized albumin may make an efficacious hepatitis B vaccine, because they could raise antibodies against the putative site on hepatitis B virus capable of binding with hepatocytes to initiate the infection.

Amino Acids↗
PubMed1981

Localization of a fibrin polymerization site.

The formation of a fibrin clot is initiated after the proteolytic cleavage of fibrinogen by thrombin. The enzyme removes fibrinopeptides A and B and generates fibrin monomer which spontaneously polymerizes. Polymerization appears to occur though the interaction of complementary binding sites on the NH2-terminal and COOH-terminal (Fragment D) regions of the molecule. A peptide has been isolated from the gamma chain remnant of fibrinogen Fragment D1 which has the ability to bind to the NH2-terminal region of fibrinogen as well as to inhibit fibrin monomer polymerization. The peptide reduces the maximum rate and extent of the polymerization of thrombin or batroxobin fibrin monomer and increases the lag time. The D1 peptide does not interact with disulfide knot, fibrinogen, or Fragment D1, but it binds to thrombin-treated disulfide knot with a Kd of 1.45 X 10(-6) M at approximately two binding sites per molecule of disulfide knot. Fibrin monomer formed either by thrombin or batroxobin binds approximately two molecules of D1 peptide per molecule of fibrin monomer, indicating that the complementary site is revealed by the loss of fibrinopeptide A. The NH2-terminal sequence (Thr-Arg-Trp) and COOH-terminal sequence (Ala-Gly-Asp-Val) of the D1 peptide were determined. Therefore the gamma 373-410 region of fibrinogen contains a polymerization site which is complementary to the thrombin-activated site on the NH2-terminal region of fibrinogen.

Amino Acids↗
PubMed1982

The regulation of actin polymerization and the inhibition of monomeric actin ATPase activity by Acanthamoeba profilin.

Profilin inhibits the rate of nucleation of actin polymerization and the rate of filament elongation and also reduces the concentration of F-actin at steady state. Addition of profilin to solutions of F-actin causes depolymerization. The same steady state concentrations of polymerized and nonpolymerized actin are reached whether profilin is added before initiation of polymerization or after polymerization is complete. The KD for formation of the 1:1 complex between Acanthamoeba profilin and Acanthamoeba actin is in the range of 4 to 11 microM; the KD for the reaction between Acanthamoeba profilin and rabbit skeletal muscle actin is about 60 to 80 microM, irrespective of the concentrations of KCl or MgCl2. The critical concentration of actin for polymerization and the KD for the actin-profilin interaction are independent of each other; therefore, a change in the critical concentration of actin alters the amount of actin bound to profilin at steady state. As a consequence, the presence of profilin greatly amplifies the effects of small changes in the actin critical concentration on the concentration of F-actin. Profilin also inhibits the ATPase activity of monomeric actin, the profilin-actin complex being entirely inactive.

Actins↗
PubMed1983

The regulation of actin polymerization by the 88K protein/actin complex and cytochalasin B.

The action of the 88K protein/actin complex (88K/A) and cytochalasin B on various aspects of actin polymerization kinetics was investigated, and the results were interpreted in terms of the condensation polymerization and treadmilling mechanism for actin polymerization. A substoichiometric concentration of 88K/A promotes actin nucleation under physiological salt conditions, especially in the presence of Ca2+. In addition, it reduces both the elongation rate and the depolymerization rate by up to 70% and inhibits annealing of the actin filaments. As a consequence, the average length of actin filaments polymerized with 88K/A becomes less than that of a control. These data indicate that 88K/A caps one end of actin filaments or actin oligomers where in the absence of 88K/A the rates for both association and dissociation of monomers are faster than at the other end. In a KCl/MgCl2 medium, 88K/A increases the steady state monomer concentration (the critical concentration) to a limited extent. This is explained by assuming that 88K/A caps the lengthening end (in treadmilling) of actin filaments, where the critical concentration is lower than at the other end (the shortening end). Moreover, cytochalasin B which has been shown to bind to the barbed end of actin filaments does not affect the 88K/A-nucleated actin polymerization. Therefore, it is strongly suggested that 88K/A caps the barbed end of actin filaments and that the barbed end is the lengthening end as well as the rapidly growing and rapidly depolymerizing end. The result obtained in the study on the action of cytochalasin B was consistent with this suggestion.

Actins↗
PubMed1983

Delayed clearance of specific polymeric IgA immune complexes in patients with IgA nephropathy.

The presence of multimeric (polymeric and monomeric) IgA immune complexes (IC), detected by Raji cell assay and by the inhibition binding assay, as well as the specific polymeric IgA-IC were examined before and after the ingestion of 100 g protein. A rise in multimeric IgA-IC occurred in three out of seven controls with a peak at two to four hours after the meal, being cleared thereafter. The amount of multimeric IC present at fasting in four of six patients diminished at two to four hours after food challenge reaching a new peak around six hours. In both controls and patients, IC containing antibodies against diet antigens (e.g. ovalbumin) paralleled those of multimeric IgA-IC. In controls the specific polymeric IgA-IC presented a maximal peak with distribution similar to multimeric IgA-IC, but with a faster disappearance from the circulation. By contrast, polymeric IgA-IC remained elevated 24 hours after food ingestion in most patients. These results suggest that a defect in the hepatic clearance of circulating polymeric IgA-IC exists in patients with IgA nephropathy.

Adult↗
PubMed1982

Tissue origins of human polymeric and monomeric IgA.

Human tissues were examined for their ability to produce monomeric and polymeric forms of IgA in vitro. Mononuclear cells were examined for the presence of cytoplasmic immunoglobulins and J chain (by immunofluorescence) and for the amounts and molecular forms of intracellular and secreted IgA (by radioimmunoassay). Cultured bone marrow cells were the largest producers of total IgA, and approximately 90% of the secreted IgA was monomeric. Spleen cells also produced predominantly monomeric IgA. Intestinal lamina propria cells secreted the greatest amounts of polymeric IgA, but also produced significant amounts of monomeric IgA. Tonsillar, lymph node, and peripheral blood cells produced approximately equal proportions of monomeric and polymeric IgA. These results suggested that bone marrow may be a major source of serum monomeric IgA, and that lymphoid tissues associated with secretory surfaces may provide a greater proportion of polymeric IgA than other lymphoid tissues. There was a positive correlation between the production of polymeric IgA and the presence of cytoplasmic J chain; tissues that produced predominantly monomeric IgA generally displayed fewer cells containing cytoplasmic J chain.

Blood Cells↗
PubMed1982

Feedback regulation of granulopoiesis: polymerization of lactoferrin abrogates its ability to inhibit CSA production.

Neutrophil extracts were prepared from the peripheral blood of 40 normal volunteers and tested for their ability to inhibit CSA production by mononuclear leukocytes. Highly dilute neutrophil extracts inhibited CSA production/release, while extracts selectively depleted of lactoferrin by antibody affinity chromatography did not. In addition, higher concentrations of neutrophil extracts and higher doses of lactoferrin (10(-9)-10(-6) M) failed to inhibit CSA production/release. We found no evidence of CSA or CSA-enhancing factors in either our lactoferrin or our neutrophil extracts. However, using gel chromatography and rate zonal density sedimentation, we noted that lactoferrin undergoes concentration-dependent polymerization at 10(-9)-10(-10) M in tissue culture medium and that while monomeric lactoferrin effectively inhibits CSA production/release in vitro, the polymeric form does not. Thus, while we have confirmed that lactoferrin is the activity in neutrophil extracts that inhibits CSA production, we have also found that lactoferrin undergoes reversible polymerization at physiologic concentrations and that the polymerized molecule is inactive. The tendency of lactoferrin to polymerize in tissue culture medium and in vivo should be taken into account in any studies on its potential role as a physiologically relevant regulator of granulopoiesis.

Centrifugation, Density Gradient↗
PubMed1982

Detection of monomeric and polymeric IgA containing immune complexes in serum and kidney from patients with alcoholic liver disease.

The purpose of this study was to characterize circulating IgA and the IgA deposited in the glomeruli of patients with alcoholic liver disease. In the 6 patients studied there was an increased proportion in monomeric IgA (3.5 fold) and IgA between 9-13S (8.94 fold), 13-17S (4.49 fold) and 17-21S (1.63 fold) fractions on 5-40% sucrose density gradient ultracentrifugation at physiological pH. All fraction between 9.12S decreased at acid pH, however a 3.28 fold increase in fractions where polymeric IgA is expected to appear. IgG eluted at acid pH from autopsy kidney was studied by the same procedures. At pH 7.4 about 55% of that IgA have a molecular weight comprised between 9-12S, decreasing to around 25% at acid pH. The existence of true polymeric IgA in serum and kidney was based on the capacity of high molecular weight IgA to bind human secretory component. The amount of immune complexes with monomeric IgA were higher than those with polymeric IgA in serum as well as in kidney. However, the percentage of heavy IgA (probably polymeric IgA) in kidney were, in each patient, higher than those observed in serum. Our results show the presence of high amounts of monomeric and polymeric IgA, both partially as immune complexes, in serum and kidneys of patients with alcoholic liver disease and IgA glomerulonephritis. Furthermore, our data suggest a role for human liver in the clearance of serum IgA such as has been demonstrated in the some animal species, especially in rats.

Antigen-Antibody Complex↗
PubMed1982

Ultrastructural events in the translocation of polymeric IgA by rat hepatocytes.

It has been proposed that polymeric IgA is translocated from plasma to bile across hepatocytes of the rat liver by a secretory component-mediated, vesicular transport. To define the ultrastructural details of the proposed transport mechanism, we employed peroxidase-labeled antibody immunocytochemistry to localize secretory component in the rat liver and monitor the hepatic translocation of homologous myeloma polymeric IgA infused i.v. Secretory component was found associated with the endoplasmic reticulum, Golgi complexes, cytoplasmic vesicles, and plasma membranes of the sinusoidal and canalicular surfaces of hepatocytes; secretory component at the sinusoidal surface was most prominent in micropinocytic invaginations or pits. Livers were examined for the sites of polymeric IgA 5, 15, and 30 min after infusion. Evidence was obtained that polymeric IgA is translocated across hepatocytes by a series of events: 1) polymeric IgA binds selectively to secretory component on the external surface of the sinusoidal plasma membrane; 2) secretory component-IgA complexes are internalized in endocytic vesicles; 3) the vesicles migrate through the cytoplasm without association with lysosomes or Golgi complexes; 4) the vesicles fuse with the cytoplasmic surface of the bile canalicular membrane, where secretory component-IgA complexes are released into bile by exocytosis.

Animals↗
PubMed1982

Increased rates of polymeric IgA synthesis by circulating lymphoid cells in IgA mesangial glomerulonephritis.

Recently we have described the existence of high levels of polymeric IgA, partially as immune complexes, in the serum and kidney from patients with IgA mesangial glomerulonephritis. As these patients often have macroscopic haematuria, following upper respiratory tract infections, our working hypothesis in this paper was that circulating lymphocytes from secretory tissues after viral stimulus could produce in these patients a large amount of polymeric IgA. To test it, peripheral blood lymphocytes (PBL) from patients and controls were cultured for seven days in the presence or absence of pokeweed mitogen (PWM). In cell culture supernatants immunoglobulin synthesis was measured by RIA and the proportion of polymeric and monomeric IgA was determined on Ultrogel Ac A22 column. There was no difference in spontaneous production of immunoglobulins between patients and controls. On the contrary, the IgA synthetized by PWM-stimulated PBL was significantly higher in patients than in controls. The percentages of IgA with molecular weight between 600,000 and 250,000 after supernate fractionation were significantly higher in patients than in controls. The true nature of polymeric IgA was confirmed by their ability to bind secretory component, the existence of covalent structures, and the decrease of the larger forms of IgA after reduction and alkylation. The percentage of IgA producing cells binding secretory component was significantly higher in patients than in controls (69 +/- 21 versus 44 +/- 27) after seven days of culture. IgM and IgG produced in patient culture were similar to controls. These results show that mitogen stimulated PBL from patients with Berger's disease synthetized a large amount of true polymeric IgA. It is suggested that a similar situation could occur in vivo after viral of other stimuli.

Cells, Cultured↗