Sera from patients with heparin-induced thrombocytopenia generate platelet-derived microparticles with procoagulant activity: an explanation for the thrombotic complications of heparin-induced thrombocytopenia

Heparin-induced thrombocytopenia is characterized by moderate thrombocytopenia and thrombotic complications, whereas quinine/quinidine-induced thrombocytopenia usually presents with severe thrombocytopenia and bleeding. Using flow cytometry and assays of procoagulant activity, we investigated whether sera from patients with these immune drug reactions could stimulate normal platelets to generate platelet-derived microparticles with procoagulant activity. Sera or purified IgG from patients with heparin-induced thrombocytopenia stimulated the formation of platelet-derived microparticles in a heparin-dependent fashion. Further studies showed that heparin-induced thrombocytopenia sera also produced a marked increase in procoagulant activity. In contrast, sera from patients with quinine- or quinidine-induced thrombocytopenia did not generate platelet-derived microparticles nor generate increased procoagulant activity. However, quinine/quinidine-induced thrombocytopenia sera produced a significant increase in the binding of IgG to platelets in a drug-dependent fashion, whereas sera from patients with heparin-induced thrombocytopenia demonstrated no drug-dependent binding of IgG to platelets. We also observed increased levels of circulating microparticles in patients with acute heparin-induced thrombocytopenia compared with control patients. Our observations indicate that the generation of procoagulant platelet-derived microparticles in vivo is a plausible explanation for the thrombotic complications observed in some patients with heparin-induced thrombocytopenia.     

Pancreas and islet cell transplantation

Currently, for the patient with type 1 diabetes, a definitive treatment without resorting to the use of exogenous insulin can be achieved only with pancreas or islet cell transplantation. These means of restoring beta-cell mass can completely maintain essentially normal long-term glucose homeostasis, although the need for powerful immunosuppressive regimens limits their application to only a subgroup of adult patients. Apart from the shortage of donors that has limited all kinds of transplantation, however, the widespread use of beta-cell replacement has been precluded until recently by the drawbacks associated with both organ and islet cell transplantation. Although the study of recurrence of diabetes has generated attention, the fundamental obstacle to pancreas and islet transplantation has been, and remains, the alloimmune response. With a better elucidation of the mechanisms of alloengraftment achieved during the last 3 years, the stage has been set for further advances.     

Donor gender does not affect liver transplantation outcome in children

The liver is recognized as a sex hormone-responsive organ. Gender-specific differences in liver function are known to exist. Recently, a higher failure rate for organs transplanted in adults from female donors to male recipients has been reported. This increased failure rate of livers obtained from adult females and transplanted into adult males is thought to occur, at least in part, as a result of intrinsic gender-specific differences in hepatocyte cell surface expression and to alterations in the hormonal milieu of the donor liver in the recipient. To determine whether the same graft-recipient gender-determined failure rates pertain in the pediatric liver transplant population, the outcome of 335 primary liver transplants performed in children at the University of Pittsburgh Medical Center was examined. No difference in transplant outcome was demonstrated in children based on the gender pairings between the donor and recipient whether or not variables such as the age, etiology of the liver disease, and the blood group of the recipient were included in the data analysis. Thus, in contrast, to the situation in adults, the gender of the donor does not influence the outcome of liver transplantation in children and should not be used as a criterion for donor selection. This difference between adults and children may be due, at least in part, to gender differences in hepatocyte phenotypic expression induced as a consequence of puberty.Supported by Research Grants from the Veterans Administration Project grant DK 29961 from the National Institutes of Health NIDDK 32556.     

Liver transplantation in the treatment of primary liver cancer

One hundred and fifteen patients underwent orthotopic liver transplantation (OLT) for primary liver malignancy. Overall survivals of these patients were significantly lower than those of patients with non-malignant diseases (5-year survival rates 37% and 65%, respectively). Hepatocellular carcinoma (HCC) was the most common malignancy among our patients (n = 80). Fibrolamellar HCC (n = 9) was associated with better survival than non-fibrolamellar HCC (N = 71) among the lesions greater than or equal to 5 cm in diameter. More frequent recurrence was noted in patients with large tumors (greater than or equal to 5 cm), multiple tumors, and gross vascular involvement. A significant lower survival rate was observed in patients with bile duct cancer (n = 19) than in those with HCC or epithelioid hemangioendothelioma (n = 8). Careful patient selection and effective adjuvant anti-cancer therapy are needed to improve the results of OLT for primary liver malignancy.     

Immunoglobulin G from patients with heparin-induced thrombocytopenia binds to a complex of heparin and platelet factor 4

Heparin-induced thrombocytopenia (HIT) is an important complication of heparin therapy. Although there is general agreement that platelet activation in vitro by the HIT IgG is mediated by the platelet Fc receptor, the interaction among the antibody, heparin, and platelet membrane components is uncertain and debated. In this report, we describe studies designed to address these interactions. We found, as others have noted, that a variety of other sulfated polysaccharides could substitute for heparin in the reaction. Using polysaccharides selected for both size and charge, we found that reactivity depended on two independent factors: a certain minimum degree of sulfation per saccharide unit and a certain minimum size. Hence, highly sulfated but small (< 1,000 daltons) polysaccharides were not reactive nor were large but poorly sulfated polysaccharides. The ability of HIT IgG to recognize heparin by itself was tested by Ouchterlony gel diffusion, ammonium sulfate and polyethylene glycol precipitation, and equilibrium dialysis. No technique demonstrated reactivity. However, when platelet releasate was added to heparin and HIT IgG, a 50-fold increase in binding of radio-labeled heparin to HIT IgG was observed. The releasate was then depleted of proteins capable of binding to heparin by immunoaffinity chromatography. Only platelet factor 4-immunodepleted releasate lost its reactivity with HIT IgG and heparin. Finally, to determine whether the reaction occurred on the surface of platelets or in the fluid phase, washed platelets were incubated with HIT IgG or heparin and after a wash step, heparin or HIT IgG was added, respectively. Reactivity was only noted when platelets were preincubated with heparin. Consistent with these observations was the demonstration of the presence of PF4 on platelets using flow cytometry. These studies indicate that heparin and other large, highly sulfated polysaccharides bind to PF4 to form a reactive antigen on the platelet surface. HIT IgG then binds to this complex with activation of platelets through the platelet Fc receptors.     

Tacrolimus (FK 506), a Treatment for Primary Sclerosing Cholangitis: Results of an Open-Label Preliminary Trial

Primary sclerosing cholangitis (PSC) is a chronic inflammatory disease of the liver that is characterized by progressive cholestasis and the development of secondary biliary cirrhosis. There is no widely recognized therapy for this disease, although anti-inflammatory agents (steroids), immunosuppressive agents (methotrexate), anti-fihrotics (colchicine), and choleretic agents (ursodeoxycholic acid) have been used in various small series. In the present study, Tacrolimus (FK 506), a new and powerful immunosuppressive macrolide antibiotic, has been used to treat 10 patients with PSC. Each subject had a liver biopsy, ERCP with visualization of the intra-and extrahepatic biliary tree, and a panel of hcmatological, serological, and biochemical laboratory tests before the initiation of the FK 506 therapy. The FK 506 was administered orally at 12-h intervals and was monitored by serial plasma FK 506 trough levels. After 360 days of treatment, the median serum bilirubin level was reduced by 75%, and the serum alkaline phosphatase was reduced by 70%. Moreover, the serum ALT and AST levels were reduced by 80 and 86%, respectively. No change in the serum level of BUN and creatinine levels occurred as a consequence of the FK 506 treatment. These data demonstrate that: 1) FK 506 can be used to treat PSC; 2) the response to FK 506 by patients with PSC is rapid; and, 3) no adverse effect on the serum BUN and creatinine levels was observed. It is anticipated that FK 506 will become an important agent for the treatment of patients with PSC because of its powerful immunosuppressive activity.