Bortezomib induces thrombocytopenia by the inhibition of proplatelet formation of megakaryocytes

Bortezomib is a potent proteasome inhibitor that has been extensively used to treat multiple myeloma. One of the most common grade 3 adverse events is cyclic thrombocytopenia. In this study, we studied the mechanism by which bortezomib induces thrombocytopenia in a mouse model. After the intravenous administration of bortezomib (2.5 mg/kg) via tail vein, platelet counts significantly decreased on days 2–4 and recovered to the normal range on day 6. Bortezomib (2.5 mg/kg) injected into mice in vivo did not affect colony‐forming unit‐megakaryocytes (CFU‐Mk) or megakaryocytes in the bone marrow. However, proplatelet formation (PPF) significantly decreased on days 2 and 4, after bortezomib administration to mice. Meanwhile, CFU‐Mk formation and the ploidy distribution of cultured megakaryocytes in vitro were not affected by bortezomib used at concentrations of ≤1 ng/mL. The PPF of megakaryocytes in vitro significantly decreased with 0.1, 1, 10, and 100 ng/mL bortezomib. Considering the bortezomib concentration in clinical studies, these data strongly suggest that decreased PPF activity induces thrombocytopenia. To elucidate the mechanism behind decreased PPF, Western blot was performed. Activated Rho expression increased after the incubation of murine platelets with bortezomib. Decreased PPF activity was eliminated by the addition of Y27632, a Rho kinase inhibitor, in vitro. Given that the Rho/Rho kinase pathway is a negative regulator of PPF, bortezomib increases activated Rho, inducing decreased PPF, which results in decreased platelet count.     

Anti-c-Mpl (thrombopoietin receptor) autoantibody-induced amegakaryocytic thrombocytopenia in a patient with systemic sclerosis

Amegakaryocytic thrombocytopenia (AMT) associated with systemic sclerosis (SSc) has been described in several case reports, but the underlying mechanisms have not been identified. Here we describe a rare case of SSc accompanied by thrombocytopenia and megakaryocytic hypoplasia, in which autoantibody against thrombopoietin receptor (c-Mpl) was detected. A 61-year-old woman with limited SSc was admitted to our hospital because of severe thrombocytopenia (platelet count 0.2 x 10(4)/mm(3)) with gingival bleeding. Her bone marrow was hypocellular with absent megakaryocytes, consistent with AMT. Treatment with corticosteroids and intravenous immunoglobulin infusions resulted in an increased platelet count, and she sustained a remission over a 1-year period, with a platelet count averaging 10.0 x 10(4)/mm(3). Her serum was strongly positive for anti-c-Mpl antibody, and IgG fraction purified from her serum inhibited thrombopoietin-dependent cell proliferation in vitro. Our case report suggests that AMT in patients with SSc could be mediated by the anti-c-Mpl antibody, which functionally blocks an interaction between thrombopoietin and c-Mpl.     

Anti–c‐Mpl (thrombopoietin receptor) autoantibody–induced amegakaryocytic thrombocytopenia in a patient with systemic sclerosis

Amegakaryocytic thrombocytopenia (AMT) associated with systemic sclerosis (SSc) has been described in several case reports, but the underlying mechanisms have not been identified. Here we describe a rare case of SSc accompanied by thrombocytopenia and megakaryocytic hypoplasia, in which autoantibody against thrombopoietin receptor (c‐Mpl) was detected. A 61‐year‐old woman with limited SSc was admitted to our hospital because of severe thrombocytopenia (platelet count 0.2 × 10⁴/mm³) with gingival bleeding. Her bone marrow was hypocellular with absent megakaryocytes, consistent with AMT. Treatment with corticosteroids and intravenous immunoglobulin infusions resulted in an increased platelet count, and she sustained a remission over a 1‐year period, with a platelet count averaging 10.0 × 10⁴/mm³. Her serum was strongly positive for anti–c‐Mpl antibody, and IgG fraction purified from her serum inhibited thrombopoietin‐dependent cell proliferation in vitro. Our case report suggests that AMT in patients with SSc could be mediated by the anti–c‐Mpl antibody, which functionally blocks an interaction between thrombopoietin and c‐Mpl.     

血小板生成素在慢性乙型肝炎血小板减少症中的作用

目的：探讨血小板生成素在慢性乙型肝炎血小板减少症患者中的作用。方法：对76例慢性乙型肝炎血小板减少症患者进行血清血小板生成素水平、凝血酶原活动度、骨髓巨核细胞计数检查。结果：血小板生成素水平与凝血酶原活动度、骨髓巨核细胞计数、外周血小板计数相关（r分别为0．423、0.396、0．297，P〈0．05）；76例患者标本中有22例骨髓巨核细胞计数〈7（个／4．5cm^2），占20％；巨核细胞成熟障碍29例，占38％。结论：血小板生成素在慢性乙型肝炎血小板减少症的发病机制中起一定作用。     

Liver cirrhosis with marked thrombocytopenia and highly elevated serum thrombopoietin levels.

Three patients with liver cirrhosis (LC) and a bleeding tendency due to marked thrombocytopenia of less than 20 x 10(9)/l were admitted to our hospital for further examination. Bone marrow examination revealed megakaryocytic hypoplasia in all three patients. All patients exhibited amegakaryocytic thrombocytopenic purpura, myelodysplastic syndrome, or bone marrow hypoplasia. 111In-labeled platelet kinetic studies revealed decreased platelet production in all patients. Although serum thrombopoietin (sTPO) levels are usually within the normal level in patients with LC, the sTPO levels of our patients were about 10 times higher than the levels of normal subjects (1.22 +/- 0.37 fmol/ml): 13.34, 16.79, and 10.46 fmol/ml, respectively. These sTPO data supported our findings of decreased megakaryopoiesis. Our findings suggest that examination of sTPO levels is useful in determining the etiology of marked thrombocytopenia in LC patients.     

Cyclic thrombocytopenia complicated with Sjögren syndrome and the mechanism of periodic platelet count fluctuation

Cyclic thrombocytopenia is a rare disorder with periodic changes of the platelet count. We experienced a patient with cyclic thrombocytopenia and Sj?gren syndrome (SS), and studied the mechanism of the cyclic changes of the platelet count. The patient, a 75-year-old woman, was referred to our hospital because of dry mouth, dry eyes, and severe thrombocytopenia. Her platelet count varied from 0.2 x 10(4)/microl to 22.7 x 10(4)/microl in 14-28-day cycles. Anti-SS-A/Ro antibody and Schirmer's test were positive. Histological examination of the salivary glands revealed infiltration of inflammatory cells, leading to the diagnosis of SS. There was an inverse relation between the platelet count and serum levels of PA-IgG. When the platelet count was low, the number of bone marrow megakaryocytes and the colony counts of CFU-Meg decreased. The serum thrombopoietin level increased at the nadir of the platelet count and decreased as platelets increased. After prednisolone therapy, her platelet count increased along with the improvement of sicca symptoms. These findings suggest that platelet fluctuation is due to the periodic increase of platelet destruction, as well as periodic failure of platelet production.     

Characterisation of haematological profiles and low risk of thromboembolic events with bortezomib in patients with relapsed multiple myeloma

Haematological toxicities and thromboembolic (TE) events are common complications of myeloma therapy. TE risk may be elevated with combination regimens, notably thalidomide/lenalidomide plus high-dose dexamethasone; concomitant erythropoietin appears to further increase the risk with lenalidomide-dexamethasone. We characterised thrombocytopenia and neutropenia in the phase 3 APEX (Assessment of Proteasome Inhibition for Extending Remissions) study of bortezomib versus high-dose dexamethasone in relapsed myeloma, and calculated the incidences of deep-vein thrombosis (DVT)/pulmonary embolism (PE) with: bortezomib or dexamethasone +/- erythropoietin in APEX; bortezomib +/- dexamethasone +/- erythropoietin in two phase 2 studies of relapsed/refractory myeloma. Bortezomib-associated thrombocytopenia and neutropenia were transient, predictable and manageable; mean platelet and neutrophil counts followed a cyclical pattern, and improved over the treatment course. Grade 3/4 thrombocytopenia incidence was higher with bortezomib versus dexamethasone (26%/4% vs. 5%/1%), but significant bleeding events were comparable (4% vs. 5%). DVT/PE incidence was low (< or =3.1%) in all analyses; addition of dexamethasone/erythropoietin did not affect TE risk. In APEX, TE risk appeared lower with bortezomib versus dexamethasone. Bortezomib caused transient and cyclical thrombocytopenia and was not associated with elevated TE risk, alone or with dexamethasone +/- erythropoietin. Preliminary data suggest bortezomib may reduce the thrombogenic potential of combination regimens via inhibition of platelet function or other mechanism-specific effects on coagulation.     

Thrombopoietic status of patients on haemodialysis

Thrombocytopenia is a potential dialysis‐related treatment complication. Developments in bio‐compatible dialyser membranes have decreased the occurrence of thrombocytopenia. We investigated whether thrombopoiesis is impaired in haemodialysis patients by measuring the thrombopoietin level and absolute immature platelet number (AIPN) in the blood of patients undergoing haemodialysis. Samples were collected from the dialysis tubing pre‐ and post‐ haemodialysis in a cohort of 45 well‐characterized haemodialysis patients. Thrombopoietin levels and AIPN increased following haemodialysis, despite no change in platelet count. Observed increase in release of immature platelets from the bone marrow following haemodialysis indicates possible complement activation secondary to interaction between blood constituents and the dialysis membrane.     

Evaluation of platelet kinetics in patients with liver cirrhosis: similarity to idiopathic thrombocytopenic purpura

BACKGROUND: Thrombocytopenia is a common manifestation of liver cirrhosis (LC), but its underlying mechanism is not fully understood. The purpose of the present paper was to evaluate the platelet kinetics in LC patients by examining several non-invasive convenient markers. METHODS: Fifty-seven LC patients, 32 patients with idiopathic thrombocytopenic purpura (ITP), 12 with aplastic anemia (AA), and 29 healthy individuals were studied. Plasma thrombopoietin was measured by enzyme-linked immunosorbent assay. Absolute reticulated platelet (RP) count and plasma glycocalicin were used as indices for thrombopoiesis, and the indices for platelet turnover were the RP proportion and the plasma glycocalicin normalized to the individual platelet count (GCI). RESULTS: There was no difference in thrombopoietin levels between LC patients and healthy controls. The RP proportion and GCI were significantly higher and the absolute RP count and glycocalicin significantly lower in LC patients than in healthy controls. These markers in ITP and LC patients were comparable, but significantly different from those in AA patients. The bone marrow megakaryocyte density in LC and ITP patients was similar, and significantly higher than in AA patients. CONCLUSIONS: Cirrhotic thrombocytopenia is a multifactorial condition involving accelerated platelet turnover and moderately impaired thrombopoiesis. Thrombopoietin deficiency is unlikely to be the primary contributor to cirrhotic thrombocytopenia.     

Graft-v-host disease is associated with autoimmune-like thrombocytopenia [see comments]

Persistent thrombocytopenia after allogeneic marrow transplantation is associated with poor patient survival. To identify the mechanisms of the thrombocytopenia, we studied platelet and fibrinogen kinetics and antiplatelet antibodies in 20 patients between 60 and 649 days (median 90) after transplantation. Seventeen patients had isolated thrombocytopenia (less than 100 X 10(9) platelets/L): the marrow cellularity was normal in five patients and slightly reduced in 12, and there was no discrepancy between thrombopoiesis and myeloerythropoiesis. Three patients had pancytopenia following marrow graft rejection (two) and relapse of leukemia (one). Only three patients had evidence of increased platelet production, indicating that in most cases there is a poor marrow response to thrombocytopenia early after marrow grafting. There was no correlation between platelet count and splenic pooling, suggesting that hypersplenism was an unlikely mechanism of the thrombocytopenia. Although there was a direct relationship between platelet count and platelet survival, the reduction in platelet survival was greater than what could be explained by the fixed platelet removal found in thrombocytopenic patients; this suggests increased platelet destruction. Seven patients had intercurrent infections that reduced both platelet and fibrinogen survivals. In addition, platelet antibodies bound to autologous or marrow donor platelets were present in five of the 12 patients studied. Patients with antiplatelet antibodies had lower platelet counts (30 +/- 10 X 10(9)/L v. 49.1 +/- 28.7 X 10(9)/L, P less than 0.05) and platelet survivals (1.32 +/- 0.92 days v. 3.58 +/- 2.02 days, P less than 0.05) than patients without antiplatelet antibodies. Furthermore, platelet- bound autoantibodies were present in five of six patients with grade II- IV acute or chronic graft-versus-host disease (GVHD), but were not present in six patients free of GVHD (P less than 0.01). We conclude that persistent thrombocytopenia after marrow transplantation is most often secondary to increased platelet destruction mediated by multiple mechanisms and that platelet autoantibodies are found in patients with acute or chronic GVHD.     

Targeting mitochondria to overcome conventional and bortezomib/proteasome inhibitor PS-341 resistance in multiple myeloma (MM) cells

Bortezomib (PS-341), a selective inhibitor of proteasomes, induces apoptosis in multiple myeloma (MM) cells; however, prolonged drug exposure may result in cumulative toxicity and the development of chemoresistance. Here we show that combining PK-11195 (PK), an antagonist to mitochondrial peripheral benzodiazepine receptors (PBRs), with bortezomib triggers synergistic anti-MM activity even in doxorubicin-, melphalan-, thalidomide-, dexamethasone-, and bortezomib-resistant MM cells. No significant cytotoxicity was noted in normal lymphocytes. Low-dose combined PK and bortezomib treatment overcomes the growth, survival, and drug resistance conferred by interleukin-6 or insulin growth factor within the MM bone marrow milieu. The mechanism of PK + bortezomib-induced apoptosis includes: loss of mitochondrial membrane potential; superoxide generation; release of mitochondrial proteins cytochrome-c (cyto-c) and Smac; and activation of caspases-8/-9/-3. Furthermore, PK + bortezomib activates c-Jun NH2 terminal kinase (JNK), which translocates to mitochondria, thereby facilitating release of cyto-c and Smac from mitochondria to cytosol. Blocking JNK, by either dominant-negative mutant (DN-JNK) or cotreatment with a specific JNK inhibitor SP600125, abrogates both PK + bortezomib-induced release of cyto-c/Smac and induction of apoptosis. Together, these preclinical studies suggest that combining bortezomib with PK may enhance its clinical efficacy, reduce attendant toxicity, and overcome conventional and bortezomib resistance in patients with relapsed refractory MM.     

Thrombocytopenia after liver transplantation: Should we care?

Transient thrombocytopenia is a common phenomenon after liver transplantation. After liver transplantation(LT), platelet count decreases and reaches a nadir on postoperative days 3-5, with an average reduction in platelet counts of 60%; platelet count recovers to preoperative levels approximately two weeks after LT. The putative mechanisms include haemodilution, decreased platelet production, increased sequestration, medications, infections, thrombosis, or combination of these processes. However, the precise mechanisms remain unclear. The role of platelets in liver transplantation has been highlighted in recent years, and particular attention has been given to their effects beyond hemostasis and thrombosis. Previous studies have demonstrated that perioperative thrombocytopenia causes poor graft regeneration, increases the incidence of postoperative morbidity, and deteriorates the graft and decreases patient survival in both the short and long term after liver transplantation. Platelet therapies to increase perioperative platelet counts, such as thrombopoietin, thrombopoietin receptor agonist, platelet transfusion, splenectomy, and intravenous immunoglobulin treatment might have a potential for improving graft survival, however clinical trials are lacking. Further studies are warranted to detect direct evidence on whether thrombocytopenia is the cause or result of poor-graft function and postoperative complications, and to determine who needs platelet therapies in order to prevent postoperative complications and thus improve post-transplant outcomes.     

Bortezomib-induced tumor lysis syndrome with a remarkable elevation of LDH in a case of relapsed and therapy-resistant multiple myeloma

A 60-year-old female patient with a therapy-resistant Bence-Jones (BJ) lambda-type multiple myeloma was treated with bortezomib. She had been treated with tandem autologous stem cell transplantations and achieved complete remission before her disease relapsed. Sixteen hours after the first administration of bortezomib, an episode of fever, slight consciousness disturbance and vomiting occurred, which was accompanied by a remarkable elevation of LDH (3608 IU/l). Serum levels of creatinine, uric acid, and AST were also transiently elevated. Serum interleukin-6 level was also increased after the administration of bortezomib. The symptoms disappeared rapidly within 48 hours. Bortezomib at a 25%-reduced dose was administered again along with dexamethasone 26 days later, which caused a moderate increase in LDH levels, but no other symptoms. Further treatment caused no increase in LDH. The treatment was very effective and eradicated both urinary BJ protein and bone marrow myeloma cells after 8 sessions of bortezomib administration. These findings suggest that a bortezomib-induced rapid reduction in tumor burden led to tumor lysis syndrome, for which caution is needed when treating myeloma patients with this very effective agent.     

Acquired amegakaryocytic thrombocytopenia previously diagnosed as idiopathic thrombocytopenic purpura in a patient with hepatitis C virus infection

We report the first case of a patient with hepatitis C virus(HCV) infection and idiopathic thrombocytopenic purpura(ITP), who later developed acquired amegakaryocytic thrombocytopenia(AAMT), with autoantibodies to the thrombopoietin(TPO) receptor(c-Mpl). A 64-year-old woman, with chronic hepatitis C, developed severe thrombocytopenia and was diagnosed with ITP. She died of liver failure. Autopsy revealed cirrhosis and liver carcinoma. In the bone marrow, a marked reduction in the number of megakaryocytes was observed, while other cell lineages were preserved. Therefore, she was diagnosed with AAMT. Additionally, autoantibodies to c-Mpl were detected in her serum. Autoantibodies to c-Mpl are one of the causes of AAMT, acting through inhibition of TPO function, megakaryocytic maturation, and platelet formation. HCV infection induces several autoantibodies. HCV infection might also induce autoantibodies to c-Mpl, resulting in the development of AAMT. This mechanism may be one of the causes of thrombocytopenia in patients with HCV infection.     

Cyclic thrombocytopenia and polycythemia vera

A periodic fall of platelet number characterizes an acquired pathological condition named cyclic thrombocytopenia. We describe an unusual case of polycythemia vera in which the episodes of thrombocytopenia were followed regularly by thrombocytosis. The period of platelet count fluctuation was about 50 days, with the counts ranging from 34 to 820 x 10(9)/l. Bone marrow megakaryocytes were decreased in number during platelet nadir. Circulating thrombopoietin levels fluctuated out of phase with the platelet count. We suggest that at least some cases of polycythemia vera may have an unstable hematopoietic stem cell pool in nature, which could contribute to the development of unprovoked cyclic thrombocytopenia.     

Variation in platelet size during recovery from thrombocytopenia following extracorporeal circulation

Summary. Serial platelet counts and measurements of mean platelet volume have been performed on patients who became thrombocytopenic during open heart surgery. The results show that large platelets are released from the bone marrow during the 48 hours following the operation as a primary response to an acute increase in demand. During this period there is only a gradual recovery of the platelet count. In the subsequent days there is an acceleration of platelet production and a simultaneous reduction in platelet volume. These results suggest a change in the nature of the stimulus following the initial postoperative period, indicating a close relationship between platelet size and the total platelet count. Platelet size, therefore, may not be wholly dependent upon either megakaryocytic heterogeneity or platelet age.     

Dietary flavonoids inhibit the anticancer effects of the proteasome inhibitor bortezomib

Dietary flavonoids have many health-promoting actions, including anticancer activity via proteasome inhibition. Bor-tezomib is a dipeptide boronate proteasome inhibitor that has activity in the treatment of multiple myeloma but is not effective in chronic lymphocytic leukemia (CLL). Although CLL cells are sensitive in vitro to bortezomib-induced apoptosis when cultured in medium, the killing activity was blocked when cultured in 50% fresh autologous plasma. Dietary flavonoids, quercetin and myricetin, which are abundant in plasma, inhibited bortezomib-induced apoptosis of primary CLL and malignant B-cell lines in a dose-dependent manner. This inhibitory effect was associated with chemical reactions between quercetin and the boronic acid group, -RB(OH)2, in bortezomib. The addition of boric acid diminished the inhibitory effect of both quercetin and plasma on bortezomib-induced apoptosis. The protective effect was also reduced when myeloma cell lines, but not B-cell lines, were preincubated with quercetin, indicating a direct effect of quercetin on myeloma cells. At high doses, quercetin itself induced tumor cell death. These data indicate that dietary flavonoids limit the efficacy of bortezomib, whereas supplemental inorganic boric acid is able to reverse this. The complex interactions between quercetin, tumor cells, and bortezomib mean caution is required when giving dietary advice to patients.     

Eltrombopag in chronic hepatitis C

Chronic hepatitis C is a public health problem worldwide. Unfortunately, not all patients may benefit from antiviral therapy due to thrombocytopenia. Its causes are represented by portal hypertension and platelet sequestration in the spleen, decreased serum levels or activity of thrombopoietin, the bone marrow suppression induced by hepatitis C virus and a possible adverse effect of interferon. Thrombopoietin receptor analogs may contribute to increase platelet counts in these patients. Eltrombopag binds to another region of the thrombopoietin receptor compared to endogenous thrombopoietin and stimulates the proliferation and maturation of megakaryocytes and the platelet production in a dose-dependent manner. Eltrombopag has proven its effectiveness for the treatment of patients with primary immune thrombocytopenia. Its indication for other hemopathies or situations (like thrombocytopenia secondary to chemo- or radiotherapy, acute leukemia, myelodysplastic syndroms, acquired and hereditary bone marrow failure, and platelet donors) is under study. Eltrombopag may be particularly useful in patients with advanced chronic hepatitis or liver cirrhosis who require antiviral treatment. We present a minireview on the results of treatment with eltrombopag in patients chronically infected with hepatitis C virus, highlighting the benefits and mentioning possible adverse effects. In some studies eltrombopag increased the number of virological responses after clasical antiviral treatment of patients with chronic hepatitis C and reduced the transfusional requirements of those who had to be subjected to invasive surgery. Eltrombopag is a solution for many of these patients, which allows them receiving antiviral therapy and sometimes getting a sustained virological response, but they must be well monitored to prevent possible thromboembolic or bone marrow complications or liver failure occurrence.     

Platelet count increase following phlebotomy in iron overloaded patients with liver cirrhosis

Thrombocytopenia is a frequent hematological complication in patients with liver cirrhosis, but its pathogenesis is not clearly understood. We evaluated the effect of iron depletion by phlebotomy on platelet count in 62 consecutive iron overloaded patients with liver cirrhosis and thrombocytopenia. After a median follow-up of 30.2 months we observed a significant increase of platelet count in all patients (from mean baseline levels of 110.1 up to 168.22109/l at the end of follow-up, P<0.001) with platelet count normalization in 42 of them (67.7%). In addition, we observed a significant improvement of serum ALT levels (from pretreatment mean values of 126.7 up to 59.7 U/l at the end of follow-up, P<0.001) along with the reduction of serum ferritin levels and transferrin saturation during phlebotomy. Different pathogenetic mechanisms involving both humoral (erythropoietin and thrombopoietin, TPO) and physical (portal hypertension and hypersplenism) factors are here discussed to explain the platelet count increase following phlebotomy. Our results show that phlebotomy is effective not only in lowering iron overload, but also in improving liver function and thrombocytopenia in patients with liver cirrhosis.     

Thrombocytosis-induced suppression of small acetylcholinesterase- positive cells in bone marrow of rats

Transfusion of platelet concentrates was used to establish a thrombocytosis of approximately three times normal platelet levels in male rats. This thrombocytosis resulted in a rebound thrombocytopenia to 60% of normal counts. Examination of the small acetylcholinesterase (ACh-E) positive cells of the marrow at this time showed a reduction to 50% of normal levels without significant changes in control animals. A second group of experiments indicated that this suppression developed as early as the third day posttransfusion, persisted until day 7, and returned to baseline levels by day 9. Incorporation of 75SeM indicated that the reduction in platelet count was due to decreased platelet production. Little or no changes were observed in the hematocrit or WBC. This evidence supports the hypothesis that these cells are early cells in the megakaryocytic series. They are the earliest cells of the series seen to be affected by thrombocytosis. Feedback control by platelets or platelet extracts of this cell population may represent one level of regulation of megakaryopoiesis.