Biomedical subjects

M I Gyongyossy-Issa

Publications and source records attributed to M I Gyongyossy-Issa.

13 recordsLinked to original sources

PubMed2001

Generation of reticulated platelets in response to whole blood donation or plateletpheresis.

BACKGROUND: There are few reports about thrombopoietic responses in whole blood (WB) and platelet-pheresis donors. This study compares the thrombopoietic responses of such donors and their platelet values. STUDY DESIGN AND METHODS: The effect of WB donation or selective platelet loss (plateletpheresis) was evaluated prospectively. WB and platelet donor samples before donation and for 7 days thereafter were assessed for platelet count, mean platelet volume, and platelet reticulocytes. RESULTS: Reticulated platelets appeared in the circulation of plateletpheresis donors by 24 hours. The proportion of reticulated platelets was highest on Day 2, and above-normal levels of reticulated platelets persisted until Day 7. The mean platelet volume was high on Days 2 and 3, which corresponded with the appearance of reticulated platelets. After plateletpheresis, platelet counts were higher than could be accounted for by new platelets, which suggested the release of sequestered platelets. WB donors manifested no changes in platelet counts but had a peak of circulating platelet reticulocytes 2 days after the donation. CONCLUSION: The thrombopoietic peak in WB and plateletpheresis donors occurs 2 days after donation, and the response level is related to the amount of platelets lost. The impact of platelet loss on the number of circulating platelets is modulated by the release of platelets from the spleen.

Benzothiazoles↗

PubMed2000

Incorporation of an Asp-Ser sequence to form an RGDS-like motif in hirutonin: the effect on in vitro platelet function.

We investigated the effect on in vitro platelet function of hirutonin, a modified hirutonin with an RGD-like motif, a pseudo-RGDS peptide and a linear RGDS peptide. Inhibition of expression of surface fibrinogen on ADP-activated platelets with 40 microM of the peptide was as follows: hirutonin 10+/-3%, modified chimeric peptide 26+/-5%, pseudo-RGDS 66+/-11% and linear RGDS 93+/-13%. Both hirutonin and the chimeric peptide significantly inhibited ADP-induced platelet activation as detected by CD62 expression. Unlike the RGDS and pseudo-RGDS controls, neither the chimeric peptide nor the parent hirutonin inhibited ADP-induced platelet aggregation even at 140 microM. The chimeric hirutonin peptide reduced ATP release from ADP-stimulated platelets by 40+/-4%. This inhibition was stronger than that caused by hirutonin (23+/-13%), but less than the RGDS (90+/-2%) and pseudo RGDS-peptides (59+/-11%). Primary platelet haemostasis was slightly but not significantly affected by the peptide at 40 and 80 microM. However, shear-induced platelet adhesion to vWF and especially subsequent aggregate formation was interrupted after the addition of the chimeric peptide. Similar results were obtained with hirutonin. This inhibition was not as marked as with the RGDS- and pseudo-RGDS peptides. Both the parent hirutonin and the chimeric peptide caused prolongation of the clinical coagulation assays aPTT and TT. In conclusion, the chimeric hirutonin peptide with introduction of the RGD motif retained its anticoagulant effect but had little formal disintegrin activity. Instead, it appeared to have novel anti-platelet effects that may be of therapeutic use.

Adenosine Triphosphate↗

PubMed1999

Effects of prestorage white cell reduction on platelet aggregate formation and the activation state of platelets and plasma enzyme systems.

BACKGROUND: The introduction of prestorage white cell (WBC) reduction in random-donor platelet concentrates in Canada has increased the occurrence of particulate material in PCs. The effects of filtration on platelet activation state and the activation of plasma enzyme systems were assessed. STUDY DESIGN AND METHODS: Particulate material was examined by light microscopy, electron microscopy, protein electrophoresis, and biochemical analysis. Thirty PCs (10 unfiltered, 20 filtered) were examined during processing and 5-day storage for pH, platelet count and mean volume, morphology, activation marker expression, and hypotonic shock response. Complement activation, thrombin generation, and fibrinolysis were assessed by using specific enzyme immunoassays or chromogenic assays. RESULTS: By all analyses, the particulate material appeared to be platelet aggregates. Platelets exposed to WBC-reduction filters expressed a significantly higher level of activation markers CD62 and CD63, altered morphology, and increased platelet microparticles throughout the storage period than did unfiltered platelets. Complement activation at the C3 level was significantly increased in filtered units with little evidence of coagulation or fibrinolytic system activation. CONCLUSION: Exposure of platelets to filters during prestorage WBC reduction increased platelet activation and mildly increased complement activation over the levels during the storage period. These alterations can contribute to the formation of irreversible platelet aggregates during processing.

Antigens, CD↗

PubMed1998

The covalent coupling of Arg-Gly-Asp-containing peptides to liposomes: purification and biochemical function of the lipopeptide.

With the advent of liposomes as drug carriers, there arises a need for efficient targeted delivery in vivo. Proteins coupled to liposomes usually yield heterogeneous products that are ill-defined both chemically and in terms of spatial orientation. We now report on the disulfide linkage to the surface of intact liposomes of a peptide representing one-half of a ligand-receptor pair. An RGD-motif-containing peptide was coupled to the phospholipid PDP-DOPE of the liposomes by a thiol-disulfide exchange. The resulting lipopeptides were amenable to definition by TLC, HPLC, and MS and found to be in a functional orientation allowing biochemical interaction with their receptor, the integrin glycoprotein IIb-IIIa.

1,2-Dipalmitoylphosphatidylcholine↗

PubMed1994

Complement activation in platelet concentrates is surface-dependent and modulated by the platelets.

Activation of platelets during storage may contribute to the loss of function and viability known as the platelet storage lesion. We investigated the role of complement activation as a possible mediator of the platelet storage lesion. We studied platelet bags stored up to 5 days under standard blood bank conditions and monitored the generation of several complement activation fragments from both the classical and alternative pathways. To assess the role of noncellular artificial surfaces in the activation of complement, parallel bags were prepared containing platelet-poor plasma. The levels of C4d and C3a increased steadily over time in storage, as did the level of the inactivated membrane attack complex SC5b-9. Generation of C4d, C5a, and SC5b-9 was greater in the absence of platelets than when platelets were present in the container. C5a levels in both groups were low and remained so during storage, suggesting that the C5a generated became surface associated. Using flow cytometry we detected C3 and C3a, but not C9, on the platelet surface. The percentage of C3-positive platelets peaked at the third day of storage; by day five platelet-associated C3 had declined. Decay accelerating factor expression on the platelet surface increased with time in storage and in parallel with CD63 expression. Based on the C4d levels, complement activation proceeded via the classical pathway; minimal generation of the alternative pathway activation fragment. Bb was seen in either the presence or absence of platelets. As an indirect measure of the activation of C1, the functional level of C1 esterase inhibitor (C1INH) was determined. C1INH levels declined over time in storage in bags containing only plasma; however, in the presence of platelets, the levels remained constant presumably because of release of C1INH from the alpha-granules of activated platelets.

Blood Platelets↗

PubMed1989

Species-specific hemolysis of erythrocytes by T-2 toxin.

The tricothecene mycotoxin, T-2 toxin interacts differently with mammalian erythrocytes. Pig, man, rabbit, guinea pig, horse, dog, rat, and mouse erythrocytes are all lysed to a varying degree by T-2 toxin. But cow, sheep, goat, buffalo, and deer erythrocytes are all resistant to hemolysis by T-2 toxin. Since erythrocytes from ruminant animals contain little or no phosphatidylcholine, perhaps the presence of phosphatidylcholine in the membrane is required for the hemolytic action of T-2 toxin. Sheep erythrocytes were used to encapsulate T-2 toxin further confirming the resistance of erythrocytes from animals with ruminant physiology to T-2 toxin lysis.

Animals↗

PubMed1986

Changes induced by T-2 toxin in the erythrocyte membrane.

The interaction of the trichothecene mycotoxin T-2 with guinea-pig erythrocytes was studied. In a time- and dose-dependent manner, T-2 toxin showed a protective antihaemolytic effect in hypotonic solutions. In isotonic environments, T-2 toxin caused membrane changes resulting in an increase in cell volume and a dramatic alteration in red-cell morphology from the biconcave disc to an echinocyte. These results demonstrate that T-2 toxin, in line with other amphipaths, distributes into the outer half of the cell membrane's phospholipid bilayer. This constitutes the first direct demonstration of an initially amphipathic mechanism of action for this toxin. Therefore, it is suggested that the degree of the final toxic effect of T-2 may be influenced by the targeted cell's membrane.

Animals↗

PubMed1986

Prehemolytic erythrocyte deformability changes caused by trichothecene T-2 toxin: an ektacytometer study.

The trichothecene mycotoxin, T-2, is responsible for a wide range of human diseases and animal toxicoses and is known to cause hemolysis of erythrocytes, over time. In order to determine the initial, prehemolytic effect of T-2 toxin on the red cell, we analysed the osmotic deformability pattern using the ektacytometer. After a lag period of 10-60 minutes, hemolysis of T-2 treated red cells is associated with a loss of deformability. During this lag phase there is echinocytosis but no hemolysis. Concurrent with production of echinocytosis there is an initial left shift of the osmotic deformability profile so that the points of maximum and minimum deformability occur in solutions of lower osmolality than normal. The elongation index is also increased. This pattern, one of increased surface area and/or reduced volume (cellular dehydration), represents the initial effect of T-2 toxin on the red cell and is transient. Very quickly, the deformability profile returns to normal, then shifts to the right with a subsequent decrease in elongation index as hemolysis ensues. These changes are independent of the presence of Ca++ and Mg++ and reduced cellular levels of ATP. The findings are consistent with T-2 toxin interacting directly with the cell membrane.

Adenosine Triphosphate↗

PubMed1985

Interaction of T-2 toxin and murine lymphocytes and the demonstration of a threshold effect on macromolecular synthesis.

Although T-2 toxin intoxications have been described as radiomimetic, we find that T-2 toxin does not preferentially affect multiplying cells. Among the targets of T-2 toxin toxicity, DNA, RNA and protein synthesis inhibition are analysed. All three types of macromolecular syntheses are affected by a threshold dose of T-2 toxin which corresponds to the interaction of approx. 1 X 10(5) T-2 toxin molecules with the same number of T-2 toxin receptors (Gyongyossy-Issa, M.I.C. and Kachatourians, G.G. (1984) Biochim. Biophys. Acta 803, 197-202). Since toxic effects occur faster at higher toxin concentrations than at lower levels, the time-toxic effect relationship may be defined by a constant. Based on these observations, we hypothesize that complete receptor-occupation is the critical first step in the course of T-2 toxin toxicity events.

Animals↗

PubMed1985

Characterisation of hemolysis induced by T-2 toxin.

The erythrocyte constitutes a good model system for the study of membrane-associated toxicity events caused by the trichothecene mycotoxin, T-2. This study confirms that T-2 has a direct lytic effect on erythrocytes. Lysis of guinea pig red cells requires approx. 10(10) molecules/cell and reaches plateau values after 4-6 h. An activation energy, Ea approximately equal to 4.5 kcal was derived from the Arrhenius equation. By use of osmotic blockers of differing Stokes' radii, the functional size of the membrane lesion caused by T-2 toxin was shown to be smaller than 5.5 A. It is concluded that T-2 toxin may exert its toxic effects via the cell membrane.

Carbohydrates↗

PubMed1985

Tumour minicells: single, large vesicles released from cultured mastocytoma cells.

We describe a new type of cell fragmentation in P815Y mastocytoma cells yielding one, large, enucleated 'minicell' at a time per parent tumour cell. These tumour minicells (TMC) arise spontaneously in semi-synthetic medium during early stationary phase of the growth curve. Their diameter comprises 21-30% of that of the parent cell line. Separated from parent tumour cells, they are non-tumorigenic. TMC can induce cytotoxic T cell activity against the parent tumour cell line greater cytotoxicity being observed against the P815Y line than an H-2-identical line, L1210. TMC may provide a new tool adaptable to the study of host-tumour relationships, cell size regulation or the mechanistic aspects of cell membrane function.

Animals↗

PubMed1984

Interaction of T-2 toxin with murine lymphocytes.

T-2 toxin is taken up by lymphocytes in 10-15 min in a saturable manner. Uptake is dependent on temperature and partially on the availability of energy. Approx. 10(5) molecules of T-2 toxin are bound per cell, having a mean affinity constant, Ka = 1.6 X 10(7) M-1. The toxin is rapidly dissociated from the cell to leave approx. 10-15% of the original loading in 1 h. It is concluded that T-2 toxin uptake and release do not follow conventional mechanisms.

Animals↗

PubMed1984

Charge-shift electrophoretic behavior of T-2 toxin in agarose gels.

We report the use of charge-shift electrophoresis to define the behavior of the trichothecene mycotoxin T-2 in aqueous solutions. We found that T-2 behaves in a hydrophobic manner and that this technique can be adapted for the separation of small hydrophobic molecules such as T-2 and cholesterol.

Buffers↗