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Biomedical subjects

G C White

Publications and source records attributed to G C White.

At least 109 records · Page 6Linked to original sources
PubMed1988

Cellular immune response to viral peptides in patients exposed to HIV.

In efforts to identify B cell and T cell epitopes of HIV-1 structural components, serum as well as lymphocytes from HIV-1-seropositive individuals were reacted with several recombinant and native peptides representing defined viral gag and env determinants. Several areas of discordance between humoral and cellular reactivity were identified. Specifically, the principal neutralizing site within HIV-1, the major envelope glycoprotein gp120, failed to elicit detectable cellular reactivities. The carboxyl portion of gp120 and the transmembrane gp41 region were uniformly recognized by patient antibodies but did not produce significant lymphocyte blastogenesis. However, the amino half of gp120 elicited cellular responses in a majority of the immunocompetent individuals tested, despite its extremely low reactivity with patient sera. Last, the major HIV-1 structure component p24 was found to be the most consistent T cell activation antigen among the panel tested.

Acquired Immunodeficiency Syndrome↗
PubMed1988

Enzymatic amplification of platelet-specific messenger RNA using the polymerase chain reaction.

Human platelets are derived from megakaryocytes as anucleate cells, and thus contain only vestigial amounts of RNA capable of being transcribed into protein. This has greatly hampered efforts to study directly platelet-specific gene products and their associated polymorphisms. In this report, we describe direct amplification, using the polymerase chain reaction, of platelet-derived mRNA in amounts sufficient to permit detailed analysis, such as restriction mapping and nucleotide sequencing. The ability to generate large amounts of cDNA from platelet-specific mRNA sequences should make possible direct molecular characterization of normal platelet proteins, and facilitate the investigation of a wide variety of inherited platelet disorders.

Blood Platelets↗
PubMed1988

The use of high-dose intravenous gamma-globulin in acquired von Willebrand syndrome.

Acquired von Willebrand syndrome has been reported in patients with a variety of primary diseases, many immunologic in nature. Usually, an autoantibody to von Willebrand factor can be identified. These patients often experience severe hemorrhages requiring large doses of cryoprecipitate or factor VIII concentrates, thus exposing them to viral and allergic complications. The success of intravenous gamma-globulin in the treatment of other autoimmune diseases prompted us to treat two patients with acquired von Willebrand syndrome with high-dose intravenous gamma-globulin. Two days after initiation of therapy, von Willebrand factor and factor VIII rose to normal levels in both patients. Patient 1 underwent dental surgery, and patient 2 underwent a splenectomy without increased bleeding and without additional factor coverage or desmopressin acetate therapy. Thus, intravenous gamma-globulin is efficacious for acquired von Willebrand syndrome and obviates the need for replacement therapy with its attendant complications.

Aged↗
PubMed1987

Partial purification and characterization of thrombolamban, a 22,000 dalton cAMP-dependent protein kinase substrate in platelets.

In preparations of human platelet microsomes, cyclic AMP-dependent protein kinase induced the rapid phosphorylation of a single protein that was electrophoretically identical to the 22,000 dalton protein (P22) phosphorylated by cAMP in intact platelets. Phosphorylation of the microsomal protein was maximal at one minute and was followed by slow dephosphorylation. Although the protein was associated with a microsomal fraction, it could be separated from the membrane by 2 M NaCl indicating that it was a peripheral protein. Molecular weight was estimated by NaDodSO4-PAGE and by gel filtration chromatography. The molecular weight estimated by NaDodSO4-PAGE was 22,400 daltons and was somewhat larger than the 16,000 molecular weight estimated by gel filtration in the presence of NaDodSO4. In the absence of NaDodSO4, the protein chromatographed as a 36,000 dalton form. The presence of the 36,000 dalton form was not dependent on the phosphorylation state of the protein. The partially purified protein contained phosphoserine, but no phosphothreonine or phosphotyrosine. Two dimensional NaDodSO4-PAGE and isoelectric focusing of the phosphorylated protein revealed isomers with pl values of 5.9 and 6.3. These studies indicate that the 22 kDa microsomal protein and P22 in intact platelets are the same protein and that the 22 kDa protein is tightly bound to the microsomal membrane although the nature of this binding and the microsomal component(s) to which it is bound remain to be determined. We conclude that the 22 kDa protein in platelet microsomes is structurally distinct from, but functionally similar to, phospholamban, the cAMP-dependent protein kinase substrate in muscle, and may play a similar role in calcium transport. Based on this similarity, it is proposed that the 22 kDa protein in platelets be called thrombolamban.

Amino Acids↗
PubMed1987

An investigation of functional similarities between the sarcoplasmic reticulum and platelet calcium-dependent adenosinetriphosphatases with the inhibitors quercetin and calmidazolium.

The platelet and skeletal sarcoplasmic reticulum calcium-dependent adenosinetriphosphatases (Ca2+-ATPases) were functionally compared with respect to substrate activation by steady-state kinetic methods using the inhibitors quercetin and calmidazolium. Quercetin inhibited platelet and sarcoplasmic reticulum Ca2+-ATPase activities in a dose-dependent manner with IC50 values of 25 and 10 microM, respectively. Calmidazolium also inhibited platelet and sarcoplasmic reticulum Ca2+-ATPase activities, with half-maximal inhibition measured at 5 and 4 microM, respectively. Both inhibitors also affected the calcium transport activity of intact platelet microsomes at concentrations similar to those which reduced Ca2+-ATPase activity. These inhibitors were then used to examine substrate ligation by the platelet and sarcoplasmic reticulum calcium pump proteins. For both Ca2+-ATPase proteins, quercetin has an affinity for the E-Ca2 (fully ligated with respect to calcium at the exterior high-affinity calcium binding sites, unligated with respect to ATP) conformational state of the protein that is approximately 10-fold greater than for other conformational states in the hydrolytic cycle. Quercetin can thus be considered a competitive inhibitor of the calcium pump proteins with respect to ATP. In contrast to the effect of quercetin, calmidazolium interacts with the platelet and sarcoplasmic reticulum Ca2+-ATPases in an uncompetitive manner. The dissociation constants for this inhibitor for the different conformational states of the calcium pump proteins were similar, indicating that calmidazolium has equal affinity for all of the reaction intermediates probed. These observations indicate that the substrate ligation processes are similar for the two pump proteins. This supports the concept that the hydrolytic cycles of the two proteins are comparable.

Animals↗
PubMed1987

Platelet factor 4 enhances fibrin fiber polymerization.

In order to further examine the role of platelet secretory products on fibrin assembly, we have examined the effects of purified platelet factor 4 (PF4) on fibrin formation in vitro. The kinetics of fibrin formation and the structural properties of the resulting fibrin gel are strongly affected by PF4. In the presence of 7.6 ng/mL PF4, the fibrin fiber mass-length ratio increases from 3.5 X 10(12) daltons/cm. These results emphasize the importance of the local microenvironment in clot structure and its subsequent fate at the site of vascular injury.

Fibrin↗
PubMed1987

Prolonged neonatal alloimmune thrombocytopenic purpura associated with anti-Bak(a). Two cases in siblings.

Two cases of prolonged neonatal alloimmune thrombocytopenic purpura in siblings due to anti-Bak(a) are reported. The first case was complicated by an intracranial hemorrhage due to severe thrombocytopenia, but the second case had no untoward complications. Delivery by cesarean section and immediate platelet support from "compatible" (nonmaternal) donors may have contributed to the more favorable outcome in the second case. An analysis of the gene frequencies of platelet-specific antigens suggests that factors other than the potential for maternal exposure to antigen determine the incidence of affected births. Knowledge of gene frequencies may, however, permit a priori prenatal calculation of the probability of an affected birth for couples with a previously affected child even if the genotype of the father is unknown.

Acute Disease↗
PubMed1987

A conserved region at the COOH terminus of human immunodeficiency virus gp120 envelope protein contains an immunodominant epitope.

A highly immunogenic epitope from a conserved COOH-terminal region of the human immunodeficiency virus (HIV) gp120 envelope protein has been identified with antisera from HIV-seropositive subjects and a synthetic peptide (SP-22) containing 15 amino acids from this region (Ala-Pro-Thr-Lys-Ala-Lys-Arg-Arg-Val-Val-Gln-Arg-Glu-Lys-Arg). Peptide SP-22 absorbed up to 100% of anti-gp120 antibody reactivity from select HIV+ patient sera in immunoblot assays and up to 79% of serum anti-gp120 antibody reactivity in competition RIA. In RIA, 45% of HIV-seropositive subjects had antibodies that bound to peptide SP-22. Human anti-SP-22 antibodies that bound to and were eluted from an SP-22 affinity column reacted with gp120 in RIA and immunoblot assays but did not neutralize HIV or inhibit HIV-induced syncytium formation in vitro, even though these antibodies comprised 70% of all anti-gp120 antibodies in the test serum. In contrast, the remaining 30% of SP-22 nonreactive anti-gp120 antibodies did not react with gp120 in immunoblot assays but did not react in RIA and neutralized HIV in vitro. Thus, approximately 50% of HIV-seropositive patients make high titers of nonneutralizing antibodies to an immunodominant antigen on gp120 defined by SP-22. Moreover, the COOH terminus of gp120 contains the major antigen or antigens identified by human anti-gp120 antibodies in immunoblot assays.

Acquired Immunodeficiency Syndrome↗
PubMed1987

Sigmoid growth and the assessment of hormesis: a case for caution.

Recent advances in procedures for the analysis of sigmoid curves have provided some sensitive methods of detecting and evaluating hormesis in the growth responses of organisms exposed to a variety of stressors. Based on a reparameterized Richards process error model, these procedures allow the quantification and independent evaluation of the three major properties of a sigmoid growth curve: size: a measure of the asymptote approached by the growth process, rate: a measure of the approximate amount of time required to complete growth, and shape: a quantity which indicates the specific path or trajectory taken by the growth process to approach the asymptote within the time constraints of the growing period. When applied to growth data for cypress tree seedlings and two species of waterfowl exposed chronically to low levels of a variety of stressors, these analyses revealed that curve shape was more likely to change in response to stress than were either asymptotic size or growth rate. The types of changes observed suggested that growth size, rate and curve shape may respond independently and in some cases, in opposite directions. Thus, while one aspect of growth may change in a fashion suggestive of hormesis (e.g. larger asymptote or faster growth rate), other aspects of the same growth function may be changing in a way suggestive of a stress response. Thus, studies designed to reveal growth hormesis should be specific with respect to which particular mathematical model is chosen, as well as with respect to which aspect of the growth response is being considered.

Animals↗
PubMed1986

PCB intake and the growth of waterfowl: multivariate analyses based on a reparameterized Richards sigmoid model.

Multivariate analyses of the parameters of a modified Richards growth model were used to determine the effects of sex and varying levels of dietary intake of PCB's (0-50 ppm), on the asymptotic size (W infinity), total growing time (T) and shape (m) of the growth curves of game farm mallards (Anas platyrhynchos) and wild wood ducks (Aix sponsa) raised under laboratory conditions. Level of PCB intake did not affect any of the growth parameters of the wood ducks, while sex affected both m and W infinity, with males of this species growing to greater body weights and showing slightly lower shape parameters than females. Growth characteristics of the mallards on the other hand, did not differ between the sexes. PCB intake however, had a significant effect on the shape of the mallard growth curve, but did not affect either W infinity or T. All interactions between sex and PCB treatment level were non-significant in both species. The growth responses of game-farm mallards to PCB intake cannot be assumed to typify that of other wild waterfowl species without additional evidence from comparative studies.

Aging↗
PubMed1986

Hemophilic patients with an inhibitor to factor VIII treated with high dose factor VIII concentrate. Results of a collaborative study for the evaluation of factor VIII inhibitor titer, recovery and half life of infused factor VIII.

The long term treatment of hemophilic patients with an inhibitor to Factor VIII has been difficult although some success with immunosuppressive agents has been reported. Eighteen hemophilic patients, mainly from Bonn in Germany, but also from other countries, have completed a high dose Factor VIII treatment in an attempt to reduce their inhibitor titer and induce "immune tolerance" to Factor VIII. Plasma samples from the 18 patients collected before and after infusion of 50 units Factor VIII/kg body weight were sent to five laboratories to evaluate inhibitor titer, Factor VIII recovery and half life. This collaborative study demonstrated a close correlation from one laboratory to another concerning inhibitor titration and Factor VIII recovery. The conclusion of the study is that all patients treated with this protocol showed an undetectable or low inhibitor titer against Factor VIII indicating that they can be efficiently treated with Factor VIII.

Adolescent↗
PubMed1986

Sigmoid growth analyses of wood ducks: the effects of sex, dietary protein and cadmium on parameters of the Richards model.

Growth analyses were conducted for 194 captive-reared wood ducks, using a reparameterized Richards process error model which provided estimates of: asymptotic size (W infinity); an approximation of the amount of time required to complete the growing period (T); and the Richards shape parameter (m). Multivariate analysis of variance indicated that growth was affected by sex and the level of cadmium in the diet on which the birds were reared (0-100 ppm). Crude protein in the diet (high = 30%; low = 18%) did not affect growth. Univariate analyses indicated that the growth of the sexes differed only with respect to W infinity, with males growing to larger body weights than females. Cadmium, however, altered both T and m, with longer times being required to complete growth in both controls which received no cadmium, and at higher levels of cadmium intake. Intermediate treatment levels completed growth in the shortest periods of time. Increasing cadmium intake altered the shape of the growth curve by progressively delaying the time at which maximum growth rate occurred.

Aging↗
PubMed1985

Evidence that platelet and skeletal sarcoplasmic reticulum Ca2+-ATPase are structurally distinct.

Proteolytic digestion and indirect immunostaining were used to compare the platelet and sarcoplasmic reticulum Ca2+-ATPase proteins. When the platelet and sarcoplasmic reticulum Ca2+-ATPase proteins were digested in the native state with trypsin, the platelet Ca2+-ATPase, which had an apparent undigested molecular mass of 103 kDa, yielded 78-kDa and 25-kDa fragments. Calcium transport activity depended on the integrity of the 103-kDa protein, while the digested protein had residual ATPase activity. Tryptic digestion of the sarcoplasmic reticulum pump protein, which also had an undigested molecular mass of 103 kDa, yielded products with apparent molecular masses of 55 kDa, 36 kDa, and 26 kDa. Distinct patterns were also observed when the platelet and sarcoplasmic reticulum calcium pump proteins were digested with chymotrypsin and Staphylococcus aureus protease in the presence of sodium dodecyl sulfate. Chymotrypsin digestion of the platelet protein resulted in the appearance of products with apparent molecular masses of 70 kDa, 39 kDa, and 31 kDa, while a similar digestion of the sarcoplasmic reticulum calcium pump protein yielded 54-kDa, 52.5-kDa, 46-kDa, 41-kDa, and 36-kDa fragments. Exposure of the sarcoplasmic reticulum and platelet Ca2+-ATPase proteins to S. aureus protease also yielded dissimilar fragmentation patterns. These results indicate that the Ca2+-ATPases from platelets and sarcoplasmic reticulum are distinct proteins.

Animals↗
PubMed1985

Glycoprotein V hydrolysis by thrombin. Lack of correlation with secretion.

Platelet membrane glycoprotein V (GPV) was hydrolyzed during thrombin-induced platelet aggregation releasing a fragment GPVfl into the supernatant. Hydrolysis of GPV required catalytically active thrombin and was diminished by chemical modification of the fibrinogen binding site of thrombin. Half-maximal liberation of GPVfl occurred at a 10-fold higher concentration of thrombin than was required for half-maximal release. Time course studies at several thrombin concentrations showed disparate release of GPVfl and thrombospondin. These results emphasize the complexity of the initial events in thrombin-induced platelet activation.

Binding Sites↗
PubMed1985

Ozone inhibits prostacyclin synthesis in pulmonary endothelium.

The effects of ozone on lung arachidonate metabolism in-vitro were studied in cultured bovine pulmonary endothelial cells exposed for 2 hours to ozone in concentrations up to 1.0 ppm. A concentration-dependent decrease in prostacyclin synthesis was found (90% decrease at the highest ozone level of 1.0 ppm). The inhibition of prostacyclin synthesis was not due to a decreased release of arachidonic acid from membrane lipids. We also examined the hypoxic pulmonary vasoconstrictive response to 10% oxygen inhalation in anesthetized dogs in-vivo after exposure to 1.0 ppm ozone for 1 hour. Pulmonary vascular resistance was significantly increased after ozone exposure, similar to the findings in dogs given indomethacin (15 mg/kg). The percentage change in the hypoxic pulmonary pressor response was similar between the ozone exposure and indomethacin-treated groups, although due to the variance of the pulmonary vascular resistance values during hypoxia the results did not reach statistical significance. These results suggest that ozone inhalation affects pulmonary endothelial arachidonate metabolism in-vivo as well as in-vitro.

Animals↗
PubMed1985

Effect of active site-modified thrombin on the hydrolysis of platelet-associated glycoprotein V by native thrombin.

To determine the relationship between equilibrium binding of thrombin to sites on the platelet surface and the cleavage of membrane glycoprotein V (GPV) by thrombin, we examined the effect of active site-modified thrombin (1-chloro-3-tosylamido-7-amino-L-2-heptanone thrombin toslysCH2-thrombin) on the binding of native thrombin to platelets and on the hydrolysis of GPV by native thrombin. ToslysCH2-thrombin inhibited binding of native thrombin to high affinity sites on the platelet surface. In contrast, hydrolysis of GPV by native thrombin, even at threshold thrombin concentrations, was not inhibited by pretreatment with toslysCH2-thrombin at concentrations up to 210 nmol/L. ToslysCH2-thrombin also had no appreciable effect on platelet aggregation or release of 14C-serotonin induced by native thrombin. Because toslysCH2-thrombin does not inhibit platelet release, aggregation, or GPV hydrolysis by native thrombin but does inhibit high affinity surface binding by native thrombin, these results indicate that thrombin binding and hydrolysis of GPV are separate and unrelated events.

Binding Sites↗