Effects of fish oil on serum lipids in men during a controlled feeding trial.

Effects of fish-oil (FO) feeding on serum lipids were investigated in a 42-d controlled diet study. Fifteen healthy male college students were assigned to one of three groups: control (0 g FO); 5 g FO, supplying 2 g n - 3 (omega-3) fatty acids (FAs); or 20 g FO, supplying 8 g n - 3 FAs. In an initial 7-d period subjects consumed a basal diet with no FO. Then FO replaced an equivalent amount of margarine for 5 wk. FO feeding significantly (p less than 0.05) decreased the serum n - 6 FAs, linoleic acid, eicosatrienoic acid, and arachidonic acid. A significant increase in the n - 3 FAs, eicosapentaenoic acid and docosahexaenoic acid, was noted in serum, platelet, and neutrophil phospholipids. The 20-g-FO group showed a 30% decrease (p less than 0.01) in triglycerides after 2 wk FO with no further decrease observed. Thus, 20 g FO produced changes in both FA patterns and triglyceride concentrations whereas 5 g FO produced changes in FA patterns only. Neither FO amount resulted in significant changes in total or HDL cholesterol, apolipoprotein A-I, or apolipoprotein B-100.

Thrombospondin forms complexes with single-chain and two-chain forms of urokinase.

Thrombospondin (TSP), an adhesive glycoprotein found in platelets and extracellular matrix, has been shown previously to interact with plasminogen and tissue plasminogen activator, resulting in efficient plasmin generation. We now demonstrate specific complex formation of TSP with both the single-chain and two-chain forms of urokinase (scuPA and uPA). Binding of uPA and scuPA to immobilized TSP was detected and quantified using colorimetric immunoassays and a functional amidolytic assay. Binding was time and concentration dependent with apparent affinity constants of 40-50 nM. Binding was not affected by serine protease inhibitors, EDTA, or epsilon-aminocaproic acid. scUPA and uPA bound to TSP retained functional activity. Using a sensitive amidolytic assay we found that TSP. scuPA complexes were efficiently converted to TSP. uPA by catalytic plasmin concentrations. Additionally, TSP.uPA complexes were found to have plasminogen-activating activity equivalent to fluid-phase uPA and to be protected from inhibition by plasminogen activator inhibitor type 1, the major plasma and matrix plasminogen activator inhibitor. Using immunohistochemical techniques, we also demonstrated co-distribution of TSP and uPA in normal and malignant breast tissue. Complex formation of TSP with uPA may serve to localize, concentrate, and protect these enzymes on cell surfaces and within the extracellular matrix, thereby providing a reservoir of plasminogen activator activity.

Characterization of purified pp60c-src protein tyrosine kinase from human platelets.

Intact pp60c-src, the cellular homologue of the transforming protein of Rous sarcoma virus, was purified from human platelets. The purified fractions also contained small amounts of a 54-kDa proteolytic degradation product of pp60c-src. We investigated some of the biochemical and kinetic properties of pp60c-src protein tyrosine kinase. Maximum kinase activity occurred at pH 6.5 and required a mixture of 2 mM Mn2+/Mg2+ as divalent cations. The enzyme most strongly phosphorylated casein, followed by enolase and alcohol dehydrogenase. The Km value for ATP was 4 microM for substrate phosphorylation and for autophosphorylation. Using casein, we determined a Vmax for substrate phosphorylation by pp60c-src in the range of 1.9-3.4 nmol.min-1.mg-1. Since the Vmax value for the purified 54-kDa fragment of pp60c-src was also included in this value, we conclude that proteolytic degradation of a 6-kDa fragment from the N-terminus of pp60c-src did not affect its kinase activity. Tryptic phosphopeptide analysis identified Tyr-416 as the major autophosphorylation site. Preincubation of purified pp60c-src with ATP increased the amount of autophosphorylation accompanied by an increase in Vmax, whereas the Km values were not altered. Our data directly demonstrate that autophosphorylation at Tyr-416 exerts, in contrast to phosphorylation at Tyr-527, a positive regulatory effect on the pp60c-src kinase activity.

Localization of fibrinogen during ADP- or thrombin-induced aggregation of washed rabbit platelets.

In contrast to human platelets, which aggregate poorly in response to ADP unless fibrinogen is present in the external medium, washed rabbit platelets form large aggregates in response to ADP without fibrinogen in the suspending medium. Addition of fibrinogen to the suspending medium of rabbit platelets frequently has little or no effect on the extent of ADP-induced platelet aggregation. We examined washed rabbit platelets by immunocytochemistry during ADP-induced aggregation and deaggregation and during thrombin-induced aggregation when the external medium did not contain added fibrinogen to determine if (a) fibrinogen was expressed on the surface of rabbit platelets that could support aggregation when the platelets were stimulated, or (b) fibrinogen secreted from the alpha granules supports platelet aggregation. Glutaraldehyde-fixed samples were prepared at different times after addition of ADP or thrombin, embedded in Lowicryl K4M, sectioned, incubated with sheep anti-rabbit fibrinogen, washed, reacted with gold-labeled anti-sheep IgG, and prepared for electron microscopy. The alpha granules of rabbit platelets were heavily labeled with immunogold; the platelet membrane was not labeled. During platelet aggregation and deaggregation in response to ADP, fibrinogen was not detectable on the platelet surface. In response to thrombin, large aggregates formed before fibrinogen was secreted from the alpha granules; fibrinogen was detectable focally at sites of granule discharge by 30-60 sec and fibrin formed by 3 min. Therefore, stimulated washed rabbit platelets can adhere to each other without large amounts of fibrinogen taking part in the close platelet-to-platelet contact, since aggregation occurs before detectable secretion, and large areas where the platelets are in contact are devoid of fibrinogen between the adherent membranes. Adhesion mechanisms not involving fibrinogen may support the aggregation of washed rabbit platelets.

Preliminary studies of a platelet function disorder in Simmental cattle.

A bleeding disorder due to abnormal platelet function occurs in Simmental cattle. Whole blood from these animals underwent good clot retraction. Platelet aggregation in response to adenosine diphosphate (ADP) and collagen in a whole blood aggregation system was markedly impaired. Normal bovine platelets in a whole blood aggregation system showed very little aggregation in response to epinephrine and arachidonic acid. Aggregation in platelet-rich plasma was negligible in response to ADP, collagen and thrombin. Dense granule release of radiolabelled serotonin from the platelets of one affected cow was similar to that of normal bovine platelets. Platelet membrane glycoprotein electrophoresis with the platelets of one affected cow revealed no quantitative abnormalities. These findings reveal similarities and differences in thrombopathic Simmental platelet function when compared to human Glanzmann's thrombasthenia and Basset Hound thrombopathia.

Purification and enzymatic characterization of pp60c-src from human platelets.

The purification of pp60c-src has been hampered by the low levels of protein it represents in most cells and its tendency to undergo proteolysis during purification. The discovery that the platelet expresses unusually high levels of pp60c-src has made large-scale purification from a normal source feasible. We have developed a method for the purification of intact pp60c-src to near homogeneity from human platelets and have determined the enzymatic properties of this purified protein in vitro. Rapid, high yield purification of pp60c-src from isolated platelet membranes was achieved in a two-step protocol involving sequential chromatography on an anti-pp60c-src immunoaffinity matrix and phenyl-Sepharose. This protocol yielded 0.5 mg of pp60c-src from 30 units of platelets. Using enolase as an exogenous substrate, the specific activity of the enzyme was 25 nmol P.min-1.mg-1. The Km for MnATP2- for enolase phosphorylation (2.2 microM) was higher than for the autophosphorylation of pp60c-src (0.6 microM). Maximal enzyme activity required either Mn2+ or Mg2+, and both ATP and GTP could be utilized as the phosphate donor. Evidence is shown which indicate that the autophophorylation of pp60c-src in vitro occurs through an intramolecular mechanism and that this reaction is reversible.

Relationship of one form of human histamine-releasing factor to connective tissue activating peptide-III.

We have previously reported purification of three forms of histamine-releasing factors (HRFs) from mixtures of streptokinase-streptodornase stimulated human mononuclear cells and platelets with apparent molecular masses of 10-12, 15-17, and 40-41 kD (1989. J. Clin. Invest. 83:1204-1210). We have also prepared mouse MAbs against the 10-12-kD HRF (1989. J. Allergy Clin. Immunol. 83:281). Affinity-purified 10-12-kD HRF appears as a broad band upon polyacrylamide gel electrophoresis in the presence of SDS. We determined the NH2-terminal amino acid sequence of the top and bottom halves of this broad band. Sequence analysis revealed striking homology between this HRF and connective tissue activating peptide-III (CTAP-III), a platelet-derived 8-10-kD protein known to cause mitogenesis and extracellular matrix formation in fibroblast cultures. 19 of 21 NH2-terminal residues in the top half of the HRF band were identical to the NH2-terminal sequence of CTAP-III. 20 of 21 NH2-terminal residues in the bottom half were identical to the NH2-terminal sequence of neutrophil-activating peptide-2, which is derived from CTAP-III by proteolytic cleavage between residues 15 and 16. Purified CTAP-III also released histamine from basophils. Rabbit antiserum raised against either native or recombinant CTAP-III recognized affinity-purified HRF in immunodot blot assays, and MAb against HRF recognized CTAP-III in both dot blot and microtiter plate based immunoassays. These data demonstrate the first structural, functional, and immunologic relationship between one form of human HRF and a previously described cell product.

[A rapid method of isolation of platelet membranes for radioligand and enzymatic assays]. / Bystryi metod polucheniia kletochnykh membran trombotsitov dlia radioligandnykh i énzimaticheskikh issledovanii.

A simple and rapid procedure for isolation of the total platelet membrane fraction by chromatography on Sepharose CL 6B has been developed. This method allows a rapid (25-30 min) one-step separation of the membrane fraction on 26 x 150 mm columns with a 20-21 mg recovery. The high degree of purity of membrane preparations was confirmed by a radioligand assay using [3H]adenosine and L-[3H]glutamic acid. The purity of membrane preparations is comparable with that of membrane fractions obtained by standard ultracentrifugation methods. The homogeneity of the membrane fraction was demonstrated by using marker enzymes of plasma, microsomal and mitochondrial membranes. This finding is very important in that it allows the isolation of fractions differing in their protein content with no effect on the method reproducibility. The high utility of the membrane preparations in receptor studies was demonstrated for high affinity binding sites for [3H]adenosine and L-[3H]glutamic acid.

The surgical implications of purpura fulminans.

Purpura fulminans is an uncommon catastrophic syndrome that occurs in children, typically one to four weeks after a seemingly benign infectious process. The child usually presents with a high fever, purpuric ecchymosis, hypotension, disseminated intravascular coagulation, and gangrene of the extremities. We have recently treated six children, whose mean age was 22 months; three were male and three were female. Five of the six had a change of mental status upon initial examination. Their mean temperature was 104 degrees F. All six children had purpuric involvement of their extremities; three had involvement of their hands, two had involvement of their faces, and two had involvement of their trunks. All had absent palpable pulses and sluggish capillary refill in the involved hands and feet. Two patients died shortly after admission as a result of severe end-stage sepsis. The platelet counts in these two patients, and the white blood cell counts were markedly depressed. The mean platelet count of the survivors was 370,000 and the mean white blood cell count was 25,000. Lumbar punctures were positive for bacterial meningitis in five patients and viral meningitis in one patient. All patients were treated with intravenous heparin. Of the four survivors, two lost significant tissue and required multiple plastic reconstructive procedures, and two improved on heparin alone with no tissue loss. In addition to systemic support and intravenous antibiotics, the mainstay of treatment is one of immediate heparinization and a continuous heparin drip. Heparin prevents subsequent small vessel thrombosis and limits tissue loss due to ongoing purpura. Conservative management of the purpuric lesions is the treatment of choice until final demarcation occurs.

Immune response of rabbits to native G-actins.

Actins are highly conserved proteins and are therefore claimed to be not very immunogenic without prior denaturation or chemical modification. We have obtained in rabbits high-titered antibodies to "native" G-actins from chicken and man, and assayed their cross-reaction using an enzyme immunoassay, Western blotting and immunohistochemistry. The antigens differ in their ability to induce antibody formation (chicken gizzard actin [(beta), gamma] greater than chicken skeletal actin [alpha] = human platelet actin [beta, (gamma)]). Antibodies to skeletal actin [alpha] are muscle-specific and mainly directed against the homologous region comprising the N-terminus (residues 1-226). Antibodies to gizzard actin [(beta), gamma] cross-react, to a lesser extent, with the alpha and beta, (gamma) isoforms. They show no regional specificity within the homologous antigen. Antibodies to the tryptic core fragment (residues 69-374) of skeletal actin react with fragments comprising the C-terminal part of muscular actins. Antibodies to platelet actin [beta, (gamma)] cross-react with muscular actins, recognizing not the native, but slightly degraded molecules. Platelet actin induces the formation of high-titered albumin antibodies for hitherto unknown reasons.

Enrichment of (n-3) fatty acids of suckling rats by maternal dietary menhaden oil.

The study was undertaken to determine whether the content of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) in neonatal rats can be increased through milk provided by lactating mothers fed a diet containing 20% menhaden oil (experimental group), in comparison with a group fed a 20% corn oil diet (control group). The test diets were isocaloric and provided 41% of total energy as fat. Coinciding with 3-9% higher maternal body weight gain throughout the lactation period with the menhaden oil diet, the suckling rats in the experimental group at the ages of 3-9 d gained 5-10% more weight than did their control counterparts. When compared with corn oil, maternal dietary menhaden oil induced not only a higher weight percentage but also higher concentrations (microgram/mL) of EPA, DHA and total (n-3) fatty acids in milk, plasma, platelets and erythrocytes of neonates. These changes were accompanied by lower arachidonic and linoleic acid levels. EPA and DHA were detected in all three blood components of the control group, whose corn oil diet contained linolenic acid but not longer chain (n-3) fatty acids. This finding, together with the higher DHA to EPA ratios found in the three blood components than in the milk of the experimental group, suggests that neonatal rats possess the enzymes necessary for producing DHA from EPA and linolenate by desaturation and elongation mechanisms.

Comparison and functional characterization of C-CAM, glycoprotein IIb/IIIa and integrin beta 1 in rat platelets.

Three adhesion-related proteins in rat platelets were compared, namely C-CAM, gpIIb/IIIa, and integrin beta 1. These three proteins behaved as distinct components as judged by both biochemical and immunological analyses. GpIIb/IIIa bound to a GRGDSPC-peptide, but neither beta 1-containing integrins nor C-CAM had any affinity either for this peptide or for a large cell-binding fragment of fibronectin. C-CAM and integrin beta 1 behaved differently when platelets were labeled with 125I, solubilized by detergent, and immunoprecipitated. Significant amounts of labeled C-CAM was precipitated when the platelets were first solubilized with detergent and then 125I-labeled. Almost no labeled C-CAM could be precipitated when intact platelets, that were unactivated or activated by ADP, were labeled. In contrast, labeled integrin beta 1 was immunoprecipitated when unactivated platelets were surface-labeled. However, when platelets that were activated by ADP and calcium ions were labeled almost no labeled integrin beta 1 could be immunoprecipitated. These data indicate 1) that C-CAM in intact platelets is inaccessible to surface-labeling and 2) that beta 1 integrin is less accessible to surface-labeling after platelet activation in the presence of calcium ions.

Partial separation of platelet and placental adenosine receptors from adenosine A2-like binding protein.

The ubiquitous adenosine A2-like binding protein obscures the binding properties of adenosine receptors assayed with 5'-N-[3H]ethylcarboxamidoadenosine [( 3H]NECA). To solve this problem, we developed a rapid and simple method to separate adenosine receptors from the adenosine A2-like binding protein. Human platelet and placental membranes were solubilized with 1% 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate. The soluble platelet extract was precipitated with polyethylene glycol and the fraction enriched in adenosine receptors was isolated from the precipitate by differential centrifugation. The adenosine A2-like binding protein was removed from the soluble placental extract with hydroxylapatite and adenosine receptors were precipitated with polyethylene glycol. The specificity of the [3H]NECA binding is typical of an adenosine A2 receptor for platelets and an adenosine A1 receptor for placenta. This method leads to enrichment of adenosine A2 receptors for platelets and adenosine A1 receptors for placenta. This provides a useful preparation technique for pharmacologic studies of adenosine receptors.

Determination of epsilon (gamma-glutamyl)lysine crosslink in proteins using phenylisothiocyanate derivatization and high-pressure liquid chromatographic separation.

A sensitive, reproducible high-performance liquid chromatographic method is reported for the determination of the epsilon (gamma-glutamyl)lysine isopeptide bond, which is usually formed by protein-crosslinking transglutaminases between polypeptide chains. The procedure is based on the separation and quantitation of epsilon (gamma-glutamyl)lysine isodipeptide following exhaustive proteolytic digestion of the crosslinked peptide. It involves preliminary separation steps on a cation exchanger resin and a silica HPLC column, precolumn derivatization with phenylisothiocyanate, and reversed-phase high-pressure liquid chromatographic separation on a C18 column. The derivatized isodipeptide gave a linear concentration-response relationship, with a detection limit of 10 pmol/mg of protein. The combination of the preliminary separation steps and the sensitive detection system permits the determination of the epsilon (gamma-glutamyl)lysine crosslink in complex biological systems including total tissue homogenates.

Extraction of protein-bound ATP and ADP from human platelets in plasma.

Actin is the major ATP and ADP binding protein in platelets, 0.9-1.3 nmol/10(8) cells, 50-70% in the unpolymerized state. The goal of these experiments was to develop a method for extracting all protein-bound ATP and ADP from undisturbed platelets in plasma. Extraction of actin-bound ADP is routine while extraction of actin-bound ATP from platelets in buffer has been unsuccessful. Prior to extraction the platelets were exposed to 14-C adenine, to label the metabolic and actin pools of ATP and ADP. The specific activity was determined from the actin-bound ADP in the 43% ethanol precipitate. Sequential ethanol and perchlorate extractions of platelet rich plasma, and the derived supernatants and precipitates were performed. ATP concentrations were determined with the luciferase assay, and radioactive nucleotides separated by TLC. A total of 1.18 nmol/10(8) cells of protein-bound ATP and ADP was recovered, 52% ATP (0.61 nmol). The recovery of protein-bound ADP was increased from 0.3 to 0.57 nmol/10(8) cells. This approach for the first time successfully recovered protein bound ATP and ADP from platelets in a concentration expected for actin.

Precise quantitation of PAIgG: a new radiometric microtechnique.

We report the development of a radiometric assay for platelet-bound IgG that is both sensitive and quantitative. The assay utilized 96-well millititer plates incorporating a 0.2 microns filter membrane in the bottom. A 125I-labeled monoclonal antihuman IgG, as a secondary antibody, detected the platelet-bound human IgG. Since 5 x 10(6) platelets were used for each assay, tests for platelet-bound IgG can be performed on persons with severe thrombocytopenia. For the detection of circulating antiplatelet alloantibodies, as little as 10 microliters of platelet-free plasma per assay is required. Antiplatelet IgG was quantitated by using anti-PIA1 antibody that was purified with affinity and elution and DEAE chromatography. This purified antiplatelet antibody was labeled with 125I and was used to determine the binding ratio of secondary antibody to primary antibody. Under our standard conditions, this ratio was found to be stable at approximately 0.35 over the sensitivity range of the assay. The assay can detect approximately 200 molecules of human IgG per platelet (0.1 ng of secondary antibody bound per 5 x 10(6) platelets). It has a linear range from 0 to 7,000 molecules per platelet. Quantitation of anti-PIA1 binding for platelets stored for up to 6 months under refrigeration showed no change in number of PIA1 binding sites. Clinical studies showed that 18 of 19 ITP patients had an increased number of IgG molecules per platelet as did patients with malignancy and drug-induced immune thrombocytopenia. Patients who had received multiple platelet transfusions had antiplatelet antibody in their plasma. Normal amounts of PAIgG were observed in platelets and plasma of patients with nonimmune thrombocytopenia. The advantages of this method are that it is: 1) a more precise quantitation of PAIgG via direct measurement of binding ratio with PIA1 antibody; 2) performed with small amounts of platelets and plasma; 3) both sensitive and specific; and 4) reliably reproducible with both fresh and stored platelets.

Platelets mediate glomerular cell proliferation in immune complex nephritis induced by anti-mesangial cell antibodies in the rat.

We investigated whether platelets, which are rich in growth factors, could mediate glomerular cell proliferation in immune complex glomerulonephritis (GN) in the rat induced with an antibody directed against the Thy-1 antigen present on mesangial cells. Rats were depleted of platelets (mean platelet count less than 20,000/mm3) with goat anti-rat platelet IgG before induction of GN and platelet depletion was maintained for 48 hours. At 72 hours sections were immunostained for cyclin, an S-phase-related nuclear antigen, to identify proliferating cells, and for the common leukocyte antigen (CD45) to identify infiltrating leukocytes. Platelet depleted rats had fewer proliferating resident glomerular cells (CD45-, cyclin+) compared to controls (0.8 +/- 0.5 vs. 2.8 +/- 1.4 cells/glom cross section, P less than 0.01) and better renal function (creatinine 1.07 +/- 0.12 vs. 1.27 +/- 0.15 mg/dl, P less than 0.05). These effects were not due to changes in circulating or glomerular leukocyte counts, complement, or glomerular antibody binding. These studies provide the first direct evidence that platelets mediate glomerular (probably mesangial cell) proliferation in antibody-mediated GN.

[Effects of the administration of urinary trypsin inhibitor on the morphology and function of platelets in the rat septic models].

Effects of urinary trypsin inhibitor (UTI) on the number, morphology and function of platelets under septic state were studied in rat models of cecal ligation and puncture (CLP). At formation of CLP, 5,000 U/kg/h of UTI was serially administered intraperitoneally and blood was sampled after 16 hours. Comparative study among sham-operation group, CLP group, and CLP + UTI group revealed: 1) inhibition of the platelets of platelet counts and appearance of large-sized, active platelets by UTI in the CLP + UTI group, 2) increase of platelet maximum aggregation rate (MAR) by ADP and increase of collagen in the CLP group, while inhibition in the CLP + UTI group and 3) by HPLC evaluation of adenine nucleotide in the platelet, increased levels of total ATP and ADP in the CLP group, particularly, increases of ATP in the metabolic pool and ADP in the granular pool. CLP + UTI group did not show these changes in the adenylate pool. UTI was thus considered to stabilize the platelet cycle in sepsis. Platelets under septic state might be hyperactive, and thrombosis is easy to occur. UTI administration might work for maintaining constancy of the platelet internal environment and improve septic state because adenine nucleotide level in the platelet did not change in the CLP + UTI group through changed in the CLP group.