Interferon increases serum thrombopoietin in patients with chronic hepatitis C

Hepatitis C virus-related thrombocytopenia: clinical and laboratory characteristics compared with chronic immune thrombocytopenic purpura

Thrombocytopenia can be a complication of hepatitis C viral (HCV) infection. However, there is little published data regarding the clinical and laboratory manifestations of HCV-related thrombocytopenia (HCV-TP) compared with adult chronic immune thrombocytopenic purpura (CITP). We reviewed the medical records for all patients evaluated for chronic thrombocytopenia by the Haematology Service between January 1996 and June 2000. All patients were screened for HCV infection at the time of initial diagnosis. Of 250 patients who fulfilled American Society of Hematology criteria for CITP, 76 (30%) were HCV seropositive. HCV-TP patients were older [mean age (+/-SD) 54.9 +/- 8 years vs. 40.3 +/- 8 years, P </= 0.001] and equally distributed between both sexes. HCV-TP patients had less severe thrombocytopenia, defined as platelet count </=10 x 10(9)/l (4% vs. 46% for CITP, P </= 0.001). However, 56 (74%) had a platelet count </=50 x 10(9)/l. Symptoms and signs of thrombocytopenia were less frequent in HCV-TP, but major bleeding was more frequent (25% vs. 10%, P = 0.0059). Serum cryoglobulins and anticardiolipin antibodies were more frequent in HCV-TP (90% and 62% respectively), but rare in CITP (7% and 15%, P </= 0.001 compared with HCV-TP). HCV infection can be associated with significant thrombocytopenia and appears to be a distinct clinical entity.

The role of thrombopoietin in the thrombocytopenia of patients with liver cirrhosis

OBJECTIVES

Thrombocytopenia is a common disorder among cirrhotics that has been traditionally explained by splenic platelet pooling and destruction. Thrombopoietin (TPO), the main stimuli for thrombopoiesis is produced primarily in the liver and degraded by circulating platelets, but its role in the thrombocytopenia of liver cirrhosis is not well understood. The main goal of this study is to clarify the role of TPO in the pathogenesis of thrombocytopenia in cirrhosis.

METHODS

The relation among TPO, platelet count, spleen size, portal hypertension, and liver function was studied in 33 cirrhotic patients before and after either partial splenic embolization or liver transplantation.

RESULTS

Cirrhotics with thrombocytopenia had lower serum TPO levels than healthy controls (median values (interquartile range: ICR) were 120.7 (42.0-191.6) vs 756.4 (527.0-965.1) pg/mL, respectively; p<0.001). Among cirrhotics with thrombocytopenia, serum TPO was related to spleen size (rho=-0.387, p=0.046), but not to platelet count as occurs physiologically. After partial splenic embolization, TPO and platelet count increased significantly and the physiological relation between TPO and platelet count was restored (rho=-0.665, p=0.026). Similar results were observed after liver transplantation.

CONCLUSIONS

Our results suggest that besides impaired production in the failing liver, an increased TPO degradation by platelets sequestered in the congested spleen may contribute to thrombocytopenia in cirrhotic patients.

Thrombopoietin production in human hepatic cell cultures (HepG2) is resistant to IFN-alpha, IFN-beta, and IFN-gamma treatment

Thrombocytopenia is an important complication of interferon (IFN) therapy for chronic viral hepatitis. To study whether IFN interferes with hepatic thrombopoietin (TPO) synthesis, we used the human hepatoma cell line HepG2. Our results show that IFN-alpha, IFN-beta, or IFN-gamma did not impair TPO mRNA expression, as determined by quantitative RT-PCR, even when high IFN doses (up to 5000 U/ml) or long-term incubations (up to 14 days) were applied. Neither was the rate of secretion of immunoreactive TPO reduced on IFN treatment. These findings support the concept that IFNs primarily mediate effects on megakaryocytic cells and platelets rather than on TPO-producing hepatocytes.

Role of blood platelets in infection and inflammation

Blood platelets are here presented as active players in antimicrobial host defense and the induction of inflammation and tissue repair in addition to their participation in hemostasis. Megakaryopoiesis is inhibited after acute infection with viruses or bacteria. In contrast, chronic inflammation is often associated with reactive thrombocytosis. Platelets can bind and internalize pathogens and release microbicidal proteins that kill certain bacteria and fungi. By making cell-cell contacts with leukocytes and endothelial cells, platelets assist white blood cells in rolling, arrest and transmigration. On stimulation by bacteria or thrombin, platelets release the content of their alpha-granules, which include an arsenal of bioactive peptides, such as CC-chemokines and CXC-chemokines and growth factors for endothelial cells, smooth muscle cells and fibroblasts. Thus, integral to innate immunity, the tiny little platelets may become bombshells when irritated by pathogens.

Plasma thrombopoietin in patients with cavernous transformation of the portal vein

Thrombopoietin (TPO), the primary regulator of thrombopoiesis, is produced mainly in the liver. Previous studies investigating blood TPO in chronic liver diseases revealed conflicting results. It has been suggested that hepatic TPO production is regulated by the portal blood supply to the liver. However, the role of TPO in the pathobiological basis of idiopathic portal vein thrombosis (PVT) and cavernous transformation of the portal vein (CTPV) has not been elucidated. The objective of this study is to assess plasma TPO concentrations in patients with CTPV. Eleven patients (4 men and 7 women, aged 38+/-12 years) with CTPV were studied. Sixteen healthy adults served as the control group (8 men and 8 women, aged 34+/-12 years). Median plasma TPO concentration was 326 pg/mL (range, 15-1402 pg/mL) in the patients with CTPV and 62.65 pg/mL (range, 38.5-102 pg/mL) in the control group (P = .003). In this study, we found significantly higher TPO concentrations in the plasma of patients with CTPV. The higher concentrations could be a result of the altered portal hemodynamics due to thrombosis. Moreover, TPO release by activated platelets might lead to the subsequent propagation of thrombosis in PVT.

Treatment of hepatitis C related thrombocytopenia with interferon alpha

Thrombocytopenia is a common extrahepatic manifestation of hepatitis C (HCV) infection. Treatment with steroids may be effective, but can exacerbate the viral infection. Interferon alpha (INF) has documented efficacy in the treatment of HCV, but its use in the treatment of HCV thrombocytopenia is controversial. We treated eight patients with HCV-related thrombocytopenia, who had platelet counts of fewer than 50 x 10(9)/l (range: 16 to 46 x 10(9)/L) with INF 3 MU SQ three times a week. Planned duration of treatment was 24 weeks. Five patients had no evidence of hepatic cirrhosis, three had cirrhosis, and two had palpable splenomegaly. Only three patients tolerated the full course of treatment, and all three had improvement in their platelet counts to greater than 50 x 10(9)/l. Two other patients had improvement in platelet counts to more than 50 x 10(9)/l with shorter duration of treatment (six and 16 weeks, respectively). The mean increase in platelet count in the five responders was 44 x 10(9)/lL (range: 28 to 90 x 10(9)/l). The average peak platelet count in the responders was 81 x 10(9)/l (range: 62 to 136 x 10(9)/l). Duration of response ranged from four to 18+ months, with the shortest responses observed in the two patients treated with a shorter course of INF. Response was independent of the presence of cirrhosis. Responding patients had improvement in hepatic transaminases, reduction in cryoglobulin and anticardiolipin antibodies, and HCV plasma RNA when tested. Relapse was associated with an increase in these laboratory markers of HCV infection. We conclude that INF can be an effective treatment in patients with HCV-related thrombocytopenia.

The role of the liver in the production of thrombopoietin compared with erythropoietin

The liver plays an important role in the production of haemopoietic hormones. It acts as the primary site of synthesis of erythropoietin (EPO) in the fetal stage, and it is the predominant thrombopoietin (TPO)-producing organ for life. In contrast to that of EPO and other liver proteins, the hepatic synthesis of TPO is influenced little by external signals. Hepatocytes express the TPO gene in a constitutive way, i.e. irrespective of the level of platelets in blood. Megakaryocytes and platelets remove the hormone from blood by means of their high-affinity TPO receptors. Normally, the plasma level of TPO is relatively low ( approximately 10(-12) mol/l). However, in thrombocytopenic states due to marrow failure or bleeding, the concentration of circulating TPO may increase greatly. The simple feedback regulation by TPO and its target cells is efficient in maintaining constant platelet numbers in healthy people. Persisting thrombocytopenia develops only in severe liver or marrow failure. On the other hand, an increase in circulating TPO and interleukin 6 (IL-6) may cause reactive thrombocytosis in inflammatory diseases, including cancer. The indications for recombinant human thrombopoietin (rHuTPO) therapy and its impact on transfusion medicine are still under investigation.

Plasma thrombopoietin levels in liver cirrhosis and kidney failure

BACKGROUND

Recently, c-Mpl ligand (thrombopoietin, TPO) has been cloned by several groups and found to be a primary regulator of thrombopoiesis. Its mRNA expression has been detected in several organs including kidneys, bone marrow stroma cells, muscles, and is very strongly expressed in the liver.

OBJECTIVE

To clarify thrombopoiesis and the regulation of TPO in severe liver and renal failure.

DESIGN

We analysed plasma TPO levels in patients with biopsy verified liver cirrhosis (n = 18; mean platelet count 115 +/- 54 x 109 L-1), in patients on chronic haemodialysis as a result of end-stage renal failure (n = 20; mean platelet count 295 +/- 94 x 109 L-1), and in healthy individuals (n = 20; mean platelet count 250 +/- 40 x 109 L-1). Plasma was prepared from EDTA-anticoagulated whole blood and a commercially available ELISA kit was used for the analysis.

RESULTS

The mean plasma TPO concentration amongst the normal individuals was 50 +/- 14 pg mL-1. In the patients with liver cirrhosis and in patients on haemodialysis the mean TPO levels were 62 +/- 19 pg mL-1 and 46 +/- 17 pg mL-1, respectively. The mean plasma TPO concentration for the cirrhotic patients was significantly higher than the mean recorded for the healthy volunteers (P = 0.031), whereas no statistically significant differences in plasma TPO were seen between the group of end-stage renal failure and normals.

CONCLUSION

Our results suggest that TPO production is maintained in liver cirrhosis and in renal failure, and that the thrombocytopenia in liver cirrhosis is not due to an impaired TPO production.