Investigation of the Mechanism of False Positive 125I-Labelled Fibrinogen Scans

S ummary . When ¹²⁵I-fibrinogen scanning is used for the early detection of venous thrombosis, comparison with venography has shown a small percentage of abnormal scans associated with normal venograms. The mechanism of this discrepancy was investigated in an experimental model. Venous thrombosis was produced in 56 dogs using stasis and local thrombin. The data obtained from scanning and venography were validated by direct vein examination. ¹²⁵I scanning agreed in 96% with venography when thrombus was present, but when thrombus lysed or embolized scans continued to read positive even though venograms were negative. Deliberate embolization of thrombi showed that these false positive scans continued for up to 48 hr owing to activity persisting in the vein wall. This was shown on histology to be related to fibrin deposition in the sub-endothelial and adventitial layers with inflammatory changes.     

How we diagnose and treat deep vein thrombosis

Making a diagnosis of deep vein thrombosis (DVT) requires both clinical assessment and objective testing because the clinical features are nonspecific and investigations can be either falsely positive or negative. The initial step in the diagnostic process is to stratify patients into high-, intermediate-, or low-risk categories using a validated clinical model. When the clinical probability is intermediate or high and the venous ultrasound result is positive, acute symptomatic DVT is confirmed. Similarly, when the probability is low and the ultrasound result is normal, DVT is ruled out. A low clinical probability combined with a negative D-dimer result can also be used to rule out DVT, thereby obviating the need for ultrasonography. In contrast, when the clinical assessment is discordant with the results of objective testing, serial venous ultrasonography or venography is required to confirm or refute a diagnosis of DVT. Once a patient is diagnosed with an acute DVT, low-molecular-weight heparin (LMWH) is the agent of choice for initial therapy and oral anticoagulant therapy is the standard for long-term secondary prophylaxis. Therapy should continue for at least 3 months; the decision to continue treatment beyond 3 months is made by weighing the risks of recurrent thrombosis and anticoagulant-related bleeding, and is influenced by patient preference. Screening for associated thrombophilia is not indicated routinely, but should be performed in selected patients whose clinical features suggest an underlying hypercoagulable state. Several new anticoagulants with theoretical advantages over existing agents are undergoing evaluation in phase 3 studies in patients with venous thromboembolism.     

The emerging role of low-molecular-weight heparin in cardiovascular medicine

Although unfractionated heparin is widely used in the treatment of acute coronary syndromes, it has several pharmacokinetic, biophysical, and biological limitations. The practical advantages and success of low-molecular-weight heparin administered subcutaneously without laboratory monitoring for the treatment of venous thromboembolism have prompted a number of randomized studies investigating the efficacy and safety of these agents in patients with acute coronary syndromes. This article will review the limitations of unfractionated heparin and the mechanisms by which low-molecular-weight heparin overcomes these limitations, as well as the results of recent trials involving low-molecular-weight heparin in the management of patients with acute coronary syndromes.     

Acquisition, storage and release of iron by cultured human hepatoma cells.

BACKGROUND/AIMS: The recovery from iron overload is hampered by the limited number of pathways and therapeutic agents available for the augmentation of iron secretion/excretion. The present study was aimed to investigate the process of iron storage and release by cultured human hepatoma cells, the role of transferrin receptors and ferritin in this process as well as the effect of iron chelators. METHODS: We followed the acquisition, storage and release of iron by cultured cells HepG2 and Hep3B by biochemical means and electron microscopy. RESULTS: The uptake of iron from diferric transferrin (Trf) was extremely low, while iron as ferric-ammonium-citrate (FAC) was taken up readily, especially by Hep3B cells. Up to 80% of the iron taken up by hepatoma cells was released to the medium. The rate of spontaneous iron release depended on the extent of iron loading. ApoTrf and deferoxamine facilitated release after 1- and 7-day iron-exposure. Up to a third of the radio-iron released from the cells was associated with ferritin. The release of ferritin-iron was not enhanced by either deferoxamine or Trf. CONCLUSIONS: Ferritin-iron release appeared to be an important mechanism of iron discarding in cultured human hepatoma cells, independent of the activity of chelating agents.     

Is impaired renal function a contraindication to the use of low-molecular-weight heparin?

BACKGROUND: Because of the risk of accumulation of anticoagulant effect, it has been suggested that patients with a creatinine clearance of 30 mL/min or less (< or =0.50 mL/s) should be excluded from treatment with low-molecular-weight (LMW) heparin, or have anti-factor Xa heparin level monitoring performed. OBJECTIVE: To assess the appropriateness of this recommendation. METHODS: We performed a systematic search of MEDLINE, EMBASE, and International Pharmaceutical Abstracts to identify prospective articles comparing differences in the pharmacokinetics of LMW heparins in nondialyzed patients with varying degrees of renal function. Reference lists of retrieved reports were checked for additional articles. RESULTS: Three single-dose pharmacokinetic trials and 2 multiple-dose deep vein thrombosis (treatment trials met our selection criteria. The 3 trials that could address our primary objective did not support the use of a 30-mL/min (0.50-mL/s) cutoff of creatinine clearance to select individuals at risk of accumulation when LMW heparin is used. Four of the 5 trials support the notion that anti-factor Xa activity of some LMW heparin preparations accumulates in patients with impaired creatinine clearance. Tinzaparin sodium, an LMW heparin with a higher-than-average molecular weight distribution, appears to be the exception, since it did not exhibit accumulation in patients with creatinine clearances as low as 20 mL/min (0.33 mL/s). CONCLUSIONS: The use of a 30-mL/min (0.50-mL/s) cutoff is not justified, on the basis of currently available evidence, to select individuals at increased risk of accumulation when LMW heparin is used. The pharmacokinetic response to impaired renal function may differ among LMW heparin preparations.     

Mutations of conserved arginines in the membrane domain of erythroid band 3 lead to a decrease in membrane-associated band 3 and to the phenotype of hereditary spherocytosis

To elucidate the molecular basis of band 3 deficiency in a recently defined subset of patients with autosomal dominant hereditary spherocytosis (HS), we screened band 3 cDNA for single-strand conformation polymorphism (SSCP). In 5 of 17 (29%) unrelated HS subjects with band 3 deficiency, we detected substitutions R760W, R760Q, R808C, and R870W that were all coinherited with the HS phenotype. The involved arginines are highly conserved throughout evolution. To examine whether or not the product of the mutant allele is inserted into the membrane, we studied one HS subject who was doubly heterozygous for the R760Q mutation and the K56E (band 3sMEMPHIS) polymorphism that results in altered electrophoretic mobility of the band 3 Memphis proteolytic fragments. We detected only the band 3MEMPHIS in the erythrocyte membrane indicating that the protein product of the mutant, R760Q, band 3 allele is absent from the red blood cell membrane. These findings suggest that the R760Q substitution, and probably the other arginine subsitutions, produce band 3 deficiency either by precluding incorporation of the mutant protein into the red blood cell membrane or by leading to loss of mutant protein from differentiating erythroid precursors.     

A role for ciliary neurotrophic factor as an inducer of reactive gliosis, the glial response to central nervous system injury.

Within the central nervous system (CNS) ciliary neurotrophic factor (CNTF) is expressed by astrocytes where it remains stored as an intracellular protein; its release and function as an extracellular ligand are thought to occur in the event of cellular injury. We find that overexpression of CNTF in transgenic mice recapitulates the glial response to CNS lesion, as does its injection into the uninjured brain. These results demonstrate that CNTF functions as an inducer of reactive gliosis, a condition associated with a number of neurological diseases of the CNS.     

Normal cellular counterparts of B cell chronic lymphocytic leukemia

In an attempt to compare B cell chronic lymphocytic leukemia (B-CLL) with its normal cellular counterpart, the cell surface phenotype of 100 cases of B-CLL was determined by using a panel of monoclonal antibodies (MoAbs) directed against B cell-restricted and -associated antigens. The majority of B-CLL cells expressed Ia, B4 (CD19), B1 (CD20), B2 (CD21), surface immunoglobulin (sIg), and T1 (CD5) but lacked C3b (CD35) receptors. In contrast, the overwhelming majority of small unstimulated B cells expressed Ia, B4, B1, B2, sIg, and C3b receptors but lacked detectable T1. Small numbers of weakly sIg+ cells could be identified in peripheral blood and tonsil that coexpressed the B1 and T1 antigens. Approximately 16% of fetal splenocytes coexpressed B1, T1, weak sIg, B2, and Ia but lacked C3b receptors and therefore closely resembled most B-CLL cells. With the phenotypic differences between the majority of small unstimulated B cells and B-CLL cells, we examined normal in vitro activated B cells and B-CLL cells for the expression of B cell-restricted and -associated activation antigens. Of 20 cases examined, virtually all expressed B5, and approximately 50% of the cases expressed interleukin-2 receptors (IL-2R) and Blast-1. Normal B cells were activated with either anti-Ig or 12-0-tetradecanoylphorbol- beta-acetate (TPA) and then were examined for coexpression of B1, T1, and the B cell activation antigens B5 and IL-2R. Only cells activated with TPA coexpressed B1 and T1 as well as B5 and IL-2R. B cells activated with either anti-Ig or TPA proliferated in the presence of IL- 2, whereas B-CLL cells did not, although they all expressed the identical 60-kilodalton proteins by immunoprecipitation. These studies are consistent with the notion that B-CLL resembles several minor subpopulations of normal B cells including a population of B cells that are activated in vitro directly through the protein kinase C pathway.     

Bone marrow transplantation for patients with Philadelphia chromosome- positive acute lymphoblastic leukemia

We report the treatment outcome of allogeneic bone marrow transplantation in ten patients with Philadelphia chromosome-positive acute lymphoblastic leukemia. Six patients are alive and well for 6 to 30 months (median 19 months) after transplantation. Four patients died with transplant related complications. In view of the poor prognosis associated with this disease, marrow ablation followed by allogeneic or syngeneic marrow grafting may be the preferred treatment modality if a suitable marrow donor is available.