Decreased expression of phospholipase C-beta 2 isozyme in human platelets with impaired function

Platelets from a patient with a mild inherited bleeding disorder and abnormal platelet aggregation and secretion show reduced generation of inositol 1,4,5-trisphosphate, mobilization of intracellular Ca2+, and phosphorylation of pleckstrin in response to several G protein mediated agonists, suggesting a possible defect at the level of phospholipase C (PLC) activation (see accompanying report). A procedure was developed that allows quantitation of platelet PLC isozymes. After fractionation of platelet extracts by high-performance liquid chromatography, 7 out of 10 known PLC isoforms were detected by immunoblot analysis. The amount of these isoforms in normal platelets decreased in the order PLC- gamma 2 > PLC-beta 2 > PLC-beta 3 > PLC-beta 1 > PLC-gamma 1 > PLC- delta 1 > PLC-beta 4. Compared with normal platelets, platelets from the patient contained approximately one-third the amount of PLC-beta 2, whereas PLC-beta 4 was increased threefold. These results suggest that the impaired platelet function in the patient in response to multiple G protein mediated agonists is attributable to a deficiency of PLC-beta 2. They document for the first time a specific PLC isozyme deficiency in human platelets and provide an unique opportunity to understand the role of different PLC isozymes in normal platelet function.     

Characterization of platelets from normal mink and mink with the Chediak-Higashi syndrome

Bleeding times of mink with the Chediak-Higashi (CH) syndrome was markedly prolonged. Platelet counts were normal but there was an impaired platelet aggregation response to collagen. The metabolic adenine nucleotide pool of platelets from normal and CH mink was labeled with 14C-adenine and the platelets were gel-filtered. Gel-filtered platelets (GFP) from CH mink contained only 37.9% of the adenosine triphosphate (ATP) and 9.6% of the adenosine diphosphate (ADP) found in normal platelets and the ATP/ADP ratio was similar to the 14C-ATP/14C-ADP ratio. Platelet content of Ca2+, Mg2+, and in particular 5-hydroxytryptamine was decreased. When GFP were incubated with thrombin to induce maximal secretion, only negligible amounts of ATP and ADP were released. The specific activity of the extracellular nucleotides approximated that within the platelet. These findings suggest that the stored nucleotide pool in CH platelets is virtually absent and that the abnormalities in platelet function may be due, in part, to the essential absence of secretable ADP and serotonin. The release of Ca2+ and Mg2+ by CH platelets was 56% and 27.8% of normal, respectively.     

Platelet function in the Chediak-Higashi syndrome.

Platelet function studies were performed on two patients with the Chediak-Higashi syndrome, one of whom had a history of easy bruising unrelated to thrombocytopenia. Both patients had prolonged bleeding times, abnormal platelet aggregation, and a defect of platelet storage granules, manifested by reduced platelet ADP, an increased ATP/ADP ratio, increased adenine nucleotide specific radioactivity after 3H-adenine labeling, and decreased platelet uptake of radioactive 5-hydroxytryptamine. These findings confirm preliminary data in animals with the Chediak-Higashi syndrome, provide and explanation for impaired primary hemostasis in these patients, and illustrate another disorder in which platelet storage-pool deficiency occurs.     

Decreased supportive function of platelets from patients with SLE on human endothelial cells

Platelets show a supportive effect on human endothelial cells in culture. Platelets of patients with systemic lupus erythematosus showed a significantly reduced growth stimulation as demonstrated by reduced DNA synthesis of the endothelial cells.     

Evidence for a storage pool defect in platelets from cirrhotic patients with defective aggregation.

The mechanisms underlying the defective platelet function in cirrhotic patients were investigated. Eleven cirrhotic patients with mild disease (group 1), 20 patients with severe cirrhosis (group 2), and 31 controls were studied. Platelet aggregation was significantly reduced in cirrhotics compared with controls. Compared with controls, cirrhotic patients in group 2 showed a significant reduction in the total content of adenosine triphosphate (57.8 +/- 7.8 vs. 26.1 +/- 6.3 mumol/10(11) platelets; P less than 0.05), 5-hydroxytryptamine (285 +/- 26 vs. 104 +/- 38 nmol/10(11) platelets; P less than 0.05), beta-thromboglobulin (2129 +/- 120 vs. 1223 +/- 161 ng/10(8) platelets; P less than 0.01), and platelet factor 4 (1389 +/- 108 vs. 805 +/- 176 ng/10(8) platelets; P less than 0.05). In patients with severe disease, an increase in plasma beta-thromboglobulin-platelet factor 4 ratio, an index of in vivo platelet activation, was observed (controls, 3.50 +/- 0.50; group 1, 4.02 +/- 0.80; and group 2, 6.59 +/- 1.15). Our data indicate the existence of a platelet storage pool defect, which may favor the bleeding tendency of cirrhotic patients.     

Correction of symptoms of platelet storage pool deficiency in animal models for Chediak-Higashi syndrome and Hermansky-Pudlak syndrome

Two human diseases of platelet storage pool deficiency (SPD), Hermansky- Pudlak syndrome and Chediak-Higashi syndrome, are recessively inherited disorders characterized by hypopigmentation, prolonged bleeding, and normal platelet counts accompanied by a reduction in dense granule number. We have recently described seven independent recessive mutations in the mouse regulated by separate genes which are likely animal models for human SPD. Reciprocal bone marrow transplants were carried out between normal C57BL/6J mice and two of these mutants, beige and pallid, in order to test whether the platelet defects are due to a defect in platelet progenitor cells or to humoral factors. Normal and congenic mutant mice were transplanted with marrow after 950 rad whole body radiation. The long bleeding times and low serotonin concentrations of the two mutants were converted to normal values after transplantation with normal marrow. Likewise, normal mice displayed symptoms of SPD when transplanted with mutant marrow. These studies demonstrate that with each of the two mutations, platelet SPD results from a defect in bone marrow precursor cells. Also, the studies suggest that in severe cases, platelet SPD may be successfully treated by bone marrow transplantation.     

Defective mononuclear leukocyte chemotaxis in the Chediak-Higashi syndrome of humans, mink, and cattle

Chemotaxis of mononuclear leukocytes from humans, mink, and cattle was evaluated in vitro using a morphologic Boyden chamber technique and a new 51-Cr-labeled mononuclear radioassay with a double micropore filter system. Significantly decreased mononuclear leukocyte chemotactic response were noted when human, mink, or cattle Chediak-Higashi cells were tested using autologous serum or endotoxin-activated autolotous serum. A similar Chediak-Higashi mononuclear leukocyte defect was noted in humans when kallikrein or dialyzable transfer factor were used as the chemotactic stimulus. Studies using smaller pore filters in the chemotactic chamber exaggerated the chemotactic defect. Serum from Chediak-Higashi subjects had normal chemotactic activity. Additional studies on the spontaneous (random) locomotion of Chediak-Higashi mononuclear leukocytes revealed normal results when a capillary tube assay system was used, but abnormal results were obtained when a Boyden chamber micropore filter assay was used, demonstrating fundamental differences in these two assays of random locomotion. It is clear from these studies that defective mononuclear leukocyte chemotaxis is another feature of the imparied host defenses in the Chediak-Higashi syndrome that may contribute to the marked susceptibility to pyogenic infections so characteristic of this dease.     

Microtubule organization of unstimulated and stimulated adherent human neutrophils in Chediak-Higashi syndrome

The numbers and length of centriole-associated microtubules of two patients with Chediak-Higashi syndrome (CHS) were examined. Detergent- extracted whole-mount preparations of adherent cells were studied by stereo high-voltage electron microscopy. Under conditions of random migration, neutrophils from both patients had a microtubule organization similar to that of the control; microtubule numbers (28 +/- 3) and length (7.0 +/- 2.8 micron) were within normal range. When cells were treated with phorbol myristate acetate (PMA), differences in the response of the two patients were noted. Neutrophils from patient No. 2 and the control showed a significant rise in numbers (38 +/- 5) and length (9.5 +/- 3.6 micron) of microtubules. In contrast, neutrophils from patient No. 1 were unresponsive to PMA treatment. Because vitamin C is used therapeutically in CHS patients and has been shown to correct microtubule-related cell function, neutrophils were exposed to ascorbic acid. A significant increase in microtubule numbers (35 +/- 6) was observed in cells from the control and patient No. 2 after ascorbate treatment; neutrophils from patient No. 1 showed no increase in microtubule numbers. While ascorbic acid did not affect microtubule length in the control cells, it caused a significant increase in microtubule length in neutrophils from both patients. Results suggest that adherent CHS neutrophils contain centriole-associated microtubules which are normal in number and length. However, differences between patients are observed regarding neutrophil responsiveness to stimuli which induce microtubule polymerization.     

Enhanced plasminogen-activator production by leukocytes in the human and murine Chediak-Higashi syndrome

We have studied the coagulation status of eight patients with the Chediak-Higashi syndrome (CHS), both in the chronic and the accelerated phase of the disease. It has been shown that during the accelerated phase there are coagulation abnormalities. These abnormalities include a peripheral thrombocytopenia, minor alterations of liver clotting factors, and mainly a profound hypofibrinogenemia and hypoplasminogenemia, which cause life-threatening bleedings. These disorders are of complex origin, but a fibrinolytic process, possibly primary, appears to play a significant role, since the present evidence for intravascular coagulation is not definitive. The accelerated phase of the CHS is characterized by a visceral infiltration by macrophages and lymphocytes. Therefore, we have investigated the possible role of the macrophages in the fibrinolytic process. We have found an excessive plasminogen activator (PA) production by CHS mononuclear cells in the accelerated phase and to a lesser extent in the chronic phase, except in one patient in whom no anomaly was found. Single-cell studies revealed an increased number of PA-producing cells among the monocyte- macrophage lineage rather than a higher level of production per cell. Polymorphonuclear cells (PMN) from patients with CHS were also shown to contain more PA. Slight but significant abnormalities in PA production were observed in obligatory heterozygotes (five out of nine), indicating the inherited nature of the excessive PA production. Finally, an enhanced PA production was similarly demonstrated using beige mice macrophages. The exacerbated production of PA by macrophages in the accelerated phase of the CHS can account to some extent for the coagulation abnormalities that have been observed.     

Increase in density and accumulation of serotonin by human aging platelets

⁵¹Cr-labeled autologous platelets were infused into splenectomized subjects and the specific radioactivities of high-density (HD) and low-density (LD) platelet subpopulations were determined sequentially in postinfusion samples. A rapid decrease in the specific radioactivity of LD cohorts (T 1/2 = 2.5 days) was observed, but the specific radioactivity of HD platelets remained constant or increased slightly during the first 4 days and then gradually declined for the next 5 days. No experimental artifacts during the platelet-labeling steps that could account for these results were demonstrated. These findings confirm previous observations in eusplenic individuals and support the hypothesis that human LD platelets are, on the average, younger than HD platelets. LD platelets contain 33.8 ± 13.5 ng serotonin (5HT)/10⁸ platelets and HD platelets 76.8 ± 9.5 ng 5HT/10⁸ platelets (P < 0.001). Sequential measurements of 5HT in PRP platelets were performed during the recovery phase of thrombocytopenia following splenectomy in patients with idiopathic thrombocytopenic purpura (ITP), a condition associated with aging of platelets in circulation. Presplenectomy platelet 5HT was 17.7 ng/10⁸ platelets and on days 1, 6, and 12 after surgery it increased to 18.1, 37.8, and 61.0 ng/10⁸ platelets (n = 7). When three healthy volunteers were given aspirin (500 mg/day) for up to 15 days, no significant change in the 5HT content of circulating platelets was observed. If aspirin blocks, at least partially, the secretory process in vivo without interfering the 5HT uptake by the platelets, this finding stands against the possibility that a net depletion of 5HT occurs during the life-span of normal human platelets. The observation that human HD platelets, enriched with older cells, contain more 5HT than LD platelets taken together with the parallel increase in platelet 5HT and age during the recovery from thrombocytopenia in ITP patients and the lack of effect of aspirin on platelet 5HT content, provides initial evidence that human platelets accumulate 5HT during their life-span in circulation.     

Selective reduction of serotonin storage and ATP release in chronic renal failure patients platelets

Hemorrhagic complications, as monitored by skin bleeding times, occur in a significant number of chronic renal failure (CRF) patients. The etiology of hemostatic defects in these patients is complex and ill defined. Our studies demonstrate, for the first time, that activated platelets, derived from CRF patients, release significantly (P less than .001) less ATP than controls while the percent of releasable serotonin (5HT), assumed to be co-stored with ATP, is unaltered. Analysis of the CRF-derived platelets reflects a selective acquired storage pool defect with significantly (P less than .001) reduced 5HT levels while their dense granule contents of ATP and ADP are normal. The comparison of ATP release from platelets derived from CRF patients whose bleeding times were less than 9 min to those with bleeding times of 9 min or greater was significantly different (P less than .02). This report demonstrates for the first time that there is a statistically significant correlation of ATP release and 5HT content to bleeding times (P less than .001). The perturbation of platelet 5HT uptake, 5HT dense granule content, and ATP release appears to result from newly described altered plasma factors, detected by our in vitro mixing studies. It is proposed that the reduced level of releasable platelet 5HT and ATP contributes to bleeding disorders commonly encountered in CRF patients.     

Restoration of neutrophil and platelet function in feline Chediak-Higashi syndrome by bone marrow transplantation

Allogeneic bone marrow transplantation (BMT) was successfully performed in four Chediak-Higashi (CHS) syndrome affected cats. Preparatory regimens included selective intestinal flora decontamination, fractionated total body irradiation for myeloablation, and prophylactic treatment for graft-versus-host disease with cyclosporin A. Neutrophil chemotaxis under-agarose and whole-blood platelet aggregation/secretion were characterized prior to BMT and after engraftment of donor-origin marrow cells. Liver and kidney biopsies were obtained and evaluated by light and electron microscopy before, and at 6 months post-BMT to determine what effect BMT might have on abnormal lysosome fusion in hepatocytes and renal tubule cells. The platelet storage pool defect was resolved by day 40 post-BMT. In vitro neutrophil migration in all cats appeared to improve with time after BMT and complete restoration was evident by day 175 post-BMT. No apparent differences were evident in either the liver or the kidney at 6 months post-BMT. One cat developed seizures and one developed posterior paresis 5 months post-BMT; neurologic impairment ultimately resulted in death of two cats at 6 and 8 months post-BMT, respectively. Neurologic lesions in both cats were characterized by non-suppurative encephalitis. Allogeneic BMT successfully corrected the neutrophil migration defect and platelet storage pool deficiency but had no effect on lysosome distribution in liver and kidney cells of CHS cats.     

Storage pool deficiency in cattle with the Chediak-Higashi syndrome results from an absence of dense granule precursors in their megakaryocytes

Platelets from cattle with the Chediak-Higashi syndrome (CHS) have a storage pool deficiency and virtual absence of platelet dense granules. Megakaryocytes (MKs) from five control (n = 135) and five CHS (n = 133) cattle were evaluated using standard transmission electron microscopy. Osmiophilic dense granules were not observed in control or CHS MKs. In MKs from normal cattle, clear vesicles of 200- to 650-nm diameter bounded by a sharp membrane were observed. They were easily differentiated from the demarcation membrane system, endoplasmic reticulum, and alpha granules. The clear vesicles were virtually absent in MKs from CHS cattle at all stages of maturation. MKs in bone marrow samples from two control (n = 91) and two CHS (n = 61) cattle that had been processed for the uranaffin reaction were also evaluated. The clear vesicles were replaced by uranaffin-positive granules in MKs from control cattle, but positive uranaffin granules were not observed in CHS MKs. These findings indicate that the platelet dense granule storage pool deficiency in CHS cattle results from an anatomic absence of dense granule precursors in maturing and mature CHS MKs.     

Effect of ascorbate on abnormal neutrophil, platelet and lymphocytic function in a patient with the Chediak-Higashi syndrome

A diminished chemotactic response was observed with the neutrophils of a patient with the Chediak-Higashi syndrome, who was not in the accelerated phase of the disease. An abnormally low release of myeloperoxidase from these cells during phagocytosis was also noted; this resulted in a decreased iodination capacity and probably also caused the defect in the intracellular killing of bacteria by the neutrophils. The level of cyclic AMP in these cells was elevated, but decreased after treatment with ascorbate either in vitro or in vivo. During ascorbate therapy, the bactericidal activity of the neutrophils normalized, whereas the chemotactic response remained low. Nevertheless, the patient had significantly less infections during ascorbate therapy. The bleeding tendency, due to a storage-pool disorder of the Chediak-Higashi platelets, was unaffected by treatment with ascorbate. The patient's lymphocytes did not display any activity in antibody-dependent lymphocytotoxicity. This defect was not affected by treatment with ascorbate either.     

Phosphotyrosine proteins in platelets from patients with storage pool disease: direct relation between granule defects and defective signal transduction

BACKGROUND AND OBJECTIVES: Storage pool diseases (SPD) are heterogeneous disorders associated with an abnormal presence of intraplatelet granules, which cause mild to moderate bleeding diathesis. We investigated signaling through tyrosine phosphorylation of proteins occurring in platelets with total or partial absence of dense- and alpha-granules in response to activation. DESIGN AND METHODS: We included a patient with severe delta-SPD, a patient with severe alpha-SPD or gray platelet syndrome, and six patients with partial deficiency of dense or a-granules. SPD was confirmed by electron microscopy evaluation of platelet ultrastructure. Platelet function was evaluated by bleeding time determination and conventional aggregometry. Platelet suspensions were activated with collagen and thrombin to analyze changes in tyrosine phosphorylation of proteins by electrophoresis and Western-blotting. RESULTS: Bleeding times were prolonged in all the patients included. Aggregation responses were slightly decreased in delta-SPD and normal in the rest of patients. Tyrosine phosphorylation in platelets from patients with partial forms of SPD was equivalent to that observed in control platelets, absent in response to collagen and thrombin activation in delta-SPD, and deficient only to thrombin activation in alpha-SPD. INTERPRETATION AND CONCLUSIONS: Tyrosine phosphorylation of proteins in activated platelets is highly dependent on the substances contained in the dense-granules and moderately dependent on those contained in the alpha-granules. A minimum amount of intraplatelet granules ensures signaling through tyrosine phosphorylation of proteins.     

Storage of platelets: effects associated with high platelet content in platelet storage containers

Background

A major problem associated with platelet storage containers is that some platelet units show a dramatic fall in pH, especially above certain platelet contents. The aim of this study was a detailed investigation of the different in vitro effects occurring when the maximum storage capacity of a platelet container is exceeded as compared to normal storage.

Materials and methods

Buffy coats were combined in large-volume containers to create primary pools to be split into two equal aliquots for the preparation of platelets (450–520×10⁹ platelets/unit) in SSP+ for 7-day storage in two containers (test and reference) with different platelet storage capacity (n=8).

Results

Exceeding the maximum storage capacity of the test platelet storage container resulted in immediate negative effects on platelet metabolism and energy supply, but also delayed effects on platelet function, activation and disintegration.

Conclusion

Our study gives a very clear indication of the effects in different phases associated with exceeding the maximum storage capacity of platelet containers but throw little additional light on the mechanism initiating those negative effects. The problem appears to be complex and further studies in different media using different storage containers will be needed to understand the mechanisms involved.     

Acquired "storage pool disease" of platelets associated with circulating antiplatelet antibodies

This study reports the first example of acquired “storage pool disease” in a patient with nephritis, polyarthralgia, chondritis, thrombophlebitis, Raynaud's phenomenon and circulating antiplatelet antibodies. Studies of platelet function showed a long bleeding time, decreased aggregation to collagen, thrombin and adenosine diphosphate (ADP), and depleted platelet stores of ADP and serotonin. These findings are similar to those found in a congenital disorder of platelets characterized by a deficiency of the storage pool of adenine nucleotides and serotonin. It is suggested that in this patient the circulating antibodies induced a release of the storage pools of adenine nucleotides and serotonin of the circulating platelets, leading to a state of defective hemostasis. The patient responded well to steroid therapy, and platelet function returned to normal concomitant with the disappearance of the antiplatelet antibodies. It is possible that “storage pool disease” with or without a thrombotic tendency may occur in other acquired disorders, especially the myeloproliferative disorders and those associated with circulating antibody.