Presence and activity of Fibrinogen like protein 2 in platelets

BACKGROUND

Fibrinogen-like protein 2 (FGL2) is a serine protease capable of converting prothrombin into thrombin (i.e., prothrombinase-like activity) while bypassing the classic coagulation cascade. It has been reported to be expressed by mononuclear blood cells and endothelial cells. There are multiple reports that FGL2 supports tumor development and metastasis. However, in the blood, the origin and functional significance of FGL2 has not been established.

OBJECTIVE

To determine if FGL2, a malignancy related enzyme, is present in platelets.

METHODS

Peripheral blood samples were collected in K2 EDTA tubes. Blood cells and platelets were separated and thoroughly washed to produce plasma-free samples. Procoagulant activity was measured in the cell lysates using a thrombin generation test or an adjusted prothrombin time (PT) test in plasma deficient of factor X. The findings were further supported by confocal microscopy, immunoprecipitation, flow cytometry, enzyme-linked immunosorbent assays and specific inhibition assays.

RESULTS

FGL2 protein was readily detected in platelets. Also, despite being expressed by lymphocytes, FGL2 prothrombinase-like activity was solely detected in platelet samples, but not in white blood cell samples. Quiescent platelets were shown to contain the FGL2 protein in an active form. Upon activation, platelets secreted the active FGL2 into the milieu.

CONCLUSIONS

Active FGL2 is found in platelets. This suggests another role for the involvement of platelets in malignancies.

Comparison of a modified flow cytometry osmotic fragility test with the classical method for the diagnosis of hereditary spherocytosis

BACKGROUND

Hereditary spherocytosis (HS) is the most common inherited hemolytic anemia. The flow cytometric test using eosin-5'maleimide (EMA) is a well-established diagnostic method. However, in order to improve HS detection, it is recommended that EMA and an osmotic fragility test (OFT) both be performed. OFT is time consuming and labor intensive. We used a flow cytometric (FOFT) adaptation of the classical OFT reported by Yamamoto. We compare the FOFT to the classical OFT including practical data and propose options for simplifying this method.

METHODS

Suspected and known HS patients and controls were tested by the following methods: EMA, OFT, and FOFT including some modifications.

RESULTS

The FOFT method is robust and correlates to loss of red blood cells. OFT and FOFT gave similar results in healthy controls and four HS patients. Normal range for FOFT in 70 adults is shown and can be used as a reference value. Neonates should have their own normal range defined. Overnight sample incubation at 37°C did not add information to the FOFT results.

CONCLUSION

Our modified Yamomoto FOFT can replace the classic OFT as the addition to EMA for the diagnosis of HS. The use of flow cytometry in both these methods requires small sample volume, is reproducible, simpler, and produces results more rapidly.

Leukemic Phase of Histiocytic Sarcoma of the Digestive System: A Rare Manifestation of a Rare Disease

Histiocytic sarcoma (HS) is a rare, malignant, and aggressive subtype of histiocytosis. We present an unusual case of aggressive HS presenting in the gastrointestinal tract and gallbladder that progressed after several lines of chemotherapy with a leukemic phase. We review the clinical, pathological, and molecular characteristics of HS in this case and review the literature on HS involving the digestive system as well as on overt leukemic phase of this disease. HS is often diagnosed at an advanced stage, and mortality is high. We discuss the therapeutic approach to patients with HS. We highlight the role of overexpression and somatic alterations in the RAF-MEK-ERK pathway in the pathogenesis of HS and discuss potential targeted approaches to treat these rare tumors.

Genomic analysis of metastatic rhabdomyosarcoma masquerading as acute leukemia

Blast appearing cells in the peripheral blood and bone marrow may occasionally arise from non-hematopoietic tissues. We present a 58 year old female who presented at our emergency room with symptomatic pancytopenia. Several months earlier she was diagnosed and treated for rhabdomyosracoma of the nasopharynx and entered remission. When we examined the bone-marrow aspirate we estimated the number of blasts at 25 %. Based on this evaluation, a provisional diagnosis of acute leukemia was made. However, immunohistochemistry and flow cytometry analysis revealed that the cells presumed to be blasts were in fact rhabdomyosarcoma cells masquerading as leukemia. The mutational landscapes of the primary tumor and the bone marrow metastasis had similar yet distinct profiles. Annotation analysis suggested that the primary and metastatic tumors use alternate mutations to activate the RAS/AKT signaling pathways. In this case, looking beyond the mutational profiling revealed an additional layer of similarity between both the original and metastatic samples, exposing a common and possibly targetable pathway. Application of annotation tools in clinical practice could enable extraction of valuable information from somatic mutational gene panels.

[THE EFFECT OF INFECTIOUS AND AUTOIMMUNE DISEASES ON PROCOAGULANT ACTIVITY OF FIBRINOGEN-LIKE PROTEIN 2 IN THE PERIPHERAL BLOOD]

AIMS

In this article we address the effect of bacterial or viral infections as well as autoimmune diseases on FGL2 activity in the blood.

BACKGROUND

Fibrinogen-like protein 2 (FGL2) is a novel prothrombinase capable of initiating thrombin generation independent of the classical coagulation pathway. FGL2 is involved in immune-coagulation response. Considering the tight relationship between coagulation and cancer, FGL2 had been suggested to be utilized as a potential biomarker for cancer. Recently, we have shown that FGL2 activity is increased in blood of B-cell lymphoma patients and decreased during remission. However, it is unclear whether FGL2 activity is simultaneously affected by the presence of conditions other than cancer.

METHODS

FGL2 procoagulant activity levels were examined in peripheral blood cell samples of 93 patients with clinical diagnosis of various bacterial or viral infections or autoimmune diseases, and 39 healthy controls. Activity was determined according to clotting time measurements. Clinical and demographic data was collected.

RESULTS

FGL2 activity in peripheral blood samples of healthy individuals and patients was rather similar. Moreover, no significant correlation was detected between measured FGL2 activity and clinical or demographic data of the patients. The range of activities was rather broad, indicating high variance (up to 2.5-fold from average) in the basal activity levels in the population.

CONCLUSIONS

The presence of infectious/autoimmune diseases does not significantly alter FGL2 activity in the peripheral blood.

DISCUSSION

While FGL2 activity in the blood is affected by malignancies such as lymphomas, the presence of inflammatory/infectious diseases does not significantly influence basal FGL2 activity. The broad range of FGL2 activities in tested samples indicates that FGL2 is a better marker for follow up implications than diagnostic screening.

Evaluating platelet function disorders in children with bleeding tendency - A single center study

Platelet function disorders (PFDs) are a common cause of mild bleeding tendency. However, they cannot be recognized by standard screening studies. The gold standard test for PFD is platelet aggregation, performed by light transmission aggregometry (LTA). A newer and less validated method is the closure time (CT), performed by the platelet function Analyzer 100 (PFA-100). Data regarding the validity of these tests in children are limited. The aim of this study was to evaluate the usefulness of LTA and PFA-100 for the diagnosis of pediatric patients with bleeding tendency. This retrospective study included patients one month-18 year old that had LTA tests performed at the coagulation laboratory of Rabin Medical Center between the years 2006-2015. Bleeding severity was assessed using a pediatric bleeding score. Patients were excluded from analysis if they had thrombocytopenia, thrombocytosis or coagulation factors deficiencies. One hundred and thirty-seven (137) patients were included in the analysis. The median age was 7.5 years (range one month-18 years). Most patients (93%) had a bleeding score of 2 or more. Abnormal LTA was found in 40% and prolonged CT in 23% of the patients. Abnormal LTA was significantly more common in patients with a bleeding score of 2 or more compared to patients with a lower bleeding scores (P = 0.04). No significant correlation was found between the bleeding severity and the number of agonists which induced abnormal responses (p = 0.52) or the CT (p = 0.35). Furthermore, no correlation was found between abnormal LTA and prolonged CT. To conclude, we were able to diagnose 40% of children who presented with bleeding tendency with platelet aggregation defects by LTA. Abnormal LTA was significantly more prevalent in patients with a bleeding score of 2 and above. In contrast, CT was not found to be sensitive as a screening tool for PFD. Therefore, our data extend the validity of the use of LTA for the evaluation of pediatric patients with bleeding tendency.

Lymphocyte Subset Reference Ranges in Healthy Israeli Adults

BACKGROUND

Reference ranges for adult peripheral blood lymphocyte subsets have been established in a few countries. To the best of our knowledge no broad lymphocyte subset analysis of the Israeli population has been reported.  Objectives: To establish reference ranges for healthy adults in Israel and to describe age- and gender-specific differences, if present.

OBJECTIVES

To establish reference ranges for healthy adults in Israel and to describe age- and gender-specific differences, if present.

METHODS

Lymphocyte subsets CD3, CD3/CD4, CD3/CD8, CD3-/CD16+/CD56+, CD3/TCRαβ, CD3/TCRγδ, and CD19 were examined by flow cytometry in 326 subjects. Samples were subdivided according to age and gender.

RESULTS

Women of all ages had a significantly higher percentage and absolute counts of CD3/CD4 cells than their male counterparts. Higher CD3/CD4 cells were observed also in the older population (> 50 years). CD3/CD8 and CD3-/CD16+/CD56+ were higher in males. Older males had a lower total lymphocyte percentage and CD19 cells compared to younger men. No significant gender-related differences were observed in percent and number of CD19, CD3/TCRαβ or CD3/TCRγδ at all ages.

CONCLUSIONS

These reference values could be useful in further studies for assessing changes that occur in different populations in human pathology.

Adult pre B-cell acute lymphoblastic leukemia with unusually large proportion of bone marrow CD45 bright/high SSc blasts

BACKGROUND

We present a pre B-ALL patient with the rare clinical manifestation of extramedullary disease, and a normal hemogram. This patient's blasts expressed bright CD45 and high side scatter (SSc) placing the cells in the monocyte gate.

METHODS

Samples from peripheral blood and bone marrow (BM) aspirate from a 50-year-old female patient were immunophenotyped by multiparametric flow cytometry.

RESULTS

Flow cytometry studies of the BM aspirate showed a large monocyte gate with 90-95% of the cells expressing an abnormal B cell phenotype. Peripheral white blood cells count was normal and cytogenetic analysis of the BM revealed a normal karyotype.

CONCLUSION

It was not possible, based on CD45/SSc to identify a lymphoblast population in this pre B-ALL patient. Although bright expression of CD45 B-ALL blasts has been associated with poor prognosis to the best of our knowledge, the combination of bright CD45 blasts with high SSc has not been reported. As CD45 expression vs. SSc is routinely measured in the diagnostics of acute leukemias, a possible association between CD45 bright positivity and extramedullary disease or prognosis warrants further exploration. © 2015 International Clinical Cytometry Society.

Acute promyelocytic leukemia with isochromosome 17q and cryptic PML-RARA successfully treated with all-trans retinoic acid and arsenic trioxide

Acute promyelocytic leukemia (APL) is a subtype of acute leukemia that is characterized by typical morphology, bleeding events and distinct chromosomal aberrations, usually the t(15;17)(q22;q21) translocation. Approximately 9% of APL patients harbor other translocations involving chromosome 17, such as the t(11;17)(q23;q21), t(5;17)(q35;q12-21), t(11;17)(q13;q21), and der(17). All-trans retinoic acid (ATRA) and arsenic trioxide (ATO) have specific targeted activities against the PML-RARA fusion protein. The combination of ATRA and ATO is reportedly superior to chemotherapy and ATRA as induction therapy for APL. The clinical significance of non-t(15:17) APL-related aberrations is controversial, with conflicting reports regarding sensitivity to modern, targeted therapy. Isochromosome 17q (iso(17q)) is rarely associated with APL and usually occurs concurrently with the t(15:17) translocation. No published data is available regarding the efficacy of ATO-based therapy for APL patients who harbor iso(17q). We report on an APL patient with iso(17q) as the sole cytogenetic aberration and a cryptic PML-RARA transcript, who was treated with ATRA and ATO after failure of chemotherapy and achieved complete remission. To our knowledge, this is the first published report of APL associated with iso(17q) as the sole cytogenetic aberration, which was successfully treated with an ATO containing regimen.

The cell-membrane prothrombinase, fibrinogen-like protein 2, promotes angiogenesis and tumor development

The aim of the study was to further investigate the role of fibrinogen-like protein 2 (FGL-2), a transmembrane prothrombinase that directly cleaves prothrombin to thrombin, in angiogenesis and tumor development and the mechanism(s) underlying these processes. To study angiogenesis HUVEC clones with decreased fgl-2 mRNA were generated by specific siRNA. To study tumorigenesis SCID mice were implanted with intact (wild type) and fgl-2-silenced PC-3 clones. IFN-γ treated HUVEC expressing increased fgl-2 mRNA exhibited significant capillary sprouting that was not inhibited by hirudin, whereas fgl-2 silencing completely inhibited blood-vessel formation. Tumors (poorly differentiated carcinoma) developed in all 12 mice injected with wild type PC-3 compared with 8/12 mice injected with the fgl-2-silenced PC-3 clone. The tumors developed by fgl-2-silenced PC-3 clones were smaller and less aggressive and contained significantly fewer blood vessels (p<0.05). All tumors' sections were negative for thrombin staining, indicating that FGL-2-induced tumorigenesis was not mediated by thrombin. In fgl-2-silenced tumors there was a decrease in fgl-2 mRNA (p=0.02) and ERK1/2 phosphorylation (p<0.05) by 80% and a 20%, respectively. The mechanism underlying these processes, studied in PC-3 clones, revealed that fgl-2 silencing was associated with a 65% decrease in FGF-2 mRNA (p<0.01) and a 30% down regulation of ERK1/2 phosphorylation (p<0.05). Together, these results suggest that FGL-2 mediates angiogenesis and tumorigenesis not by thrombin-mediated mechanism but rather through FGF-2/ERK signaling pathway. FGL-2 may serve as a valuable therapeutic target in the future.

Increased activity of cell membrane-associated prothrombinase, fibrinogen-like protein 2, in peripheral blood mononuclear cells of B-cell lymphoma patients

Fibrinogen-like protein 2, FGL-2, was reported to be overexpressed in various cancer tissues, where it acts as a transmembrane prothrombinase. This study aims to determine the prothrombinase activity of FGL-2 in peripheral blood mononuclear cells (PBMC) of patients with B-cell lymphoma. FGL-2 activity was determined in patients with B-cell lymphoma (n = 53), and healthy controls (n = 145). FGL-2 activity in patients at diagnosis increased 3±0.3 fold (p<0.001). Sensitivity and specificity of the test was established at 73.6% and 80.7%, respectively, using a cutoff of 150% activity over control. Moreover, FGL-2 activity in 10 of 11 patients in remission decreased by 76%. In contrast, no significant difference was observed in expression levels of fgl-2 gene in patients and controls. Taken together, our study indicates that FGL-2 prothrombinase activity in PBMC of lymphoma patients is increased in active disease and normalizes during remission, thus being a potential marker for follow up of lymphoma patients.

Historical data decrease complete blood count reflex blood smear review rates without missing patients with acute leukaemia

INTRODUCTION

The availability of historical data decreases the rate of blood smear review rates in outpatients, but we are unaware of studies done at referral centres. In the following study, we determined the effect of historical data on the rates of peripheral blood smears over a 3-month period and then the detection rate of patients with acute leukaemia.

METHODS

All results of complete blood counts (CBCs) tested on three ADVIA 120 analyzers at the regional Rabin Medical Centre, Beilinson Campus over a 3-month period were accessed on a computerised laboratory information system. Over a 3-month period, we determined the proportion of total CBC and patients with criteria for a manual differential count and the actual number of peripheral blood smears done. Finally, we determined the proportion of 100 consecutive patients with acute leukaemia detected using our criteria that included limiting reflex testing according to historical data.

RESULTS

Over the 3-month period, there were 34,827 tests done in 12,785 patients. Without historical data, our smear rate would have been 24.5%, but with the availability of historical data, the blood smear review rate was 5.6%. The detection rate for cases of acute leukaemia was 100%.

CONCLUSIONS

We conclude that the availability of previous test results significantly reduces the need for blood smear review without missing any patients with acute leukaemia.

Butyrate-induced differentiation in leukemic myeloid cells - in-vitro and in-vivo studies

A study of the effects of three differentiating agents, butyric acid, retinoic acid and cytosine arabinoside on proliferation and differentiation of primary cultures, obtained from sixteen patients with myelo-proliferative disorder was conducted. The results showed that BA was an effective inhibitor of cell proliferation and inducer of cytodifferentiation. An acute non-lymphoblastic leukemia patient was treated with sodium butyrate. A temporary increase in differentiation-associated parameters were noted. However, the effects of SB were short-lived. The lack of clinical response led to the development of a BA prodrug pivaloyloxymethylbutyrate (AN-9). This prodrug was more potent in vitro than BA in the induction of cytodifferentiation and inhibition of cell proliferation.

Rituximab associated neutropenia: description of three cases and an insight into the underlying pathogenesis

BACKGROUND

To describe Rituximab associated neutropenia (RAN), and to explore its underlying mechanism.

CASE REPORT

We describe three patients with RAN. The effect of patient's plasma on colony forming unit, Granulocyte-Monocyte (CFU-GM) was measured by the addition of plasma to the culture of a healthy bone-marrow. Repeated tests were performed after recovery of white count. In the leukopenic period the patient's plasma inhibited CFU growth completely. Control plasma did not have such an effect. Addition of patient's cell supernatant to bone marrow cells did not change the number of CFU. The same effect was demonstrated in normal control. After recovery the patient's plasma did not inhibit colony formation, similar to control.

CONCLUSIONS

RAN is a clinically significant side effect. It may take place during treatment or several months afterwards. Circulating antibodies in the plasma may be responsible for this unique BM toxicity.

Effect of imatinib on the signal transduction cascade regulating telomerase activity in K562 (BCR-ABL-positive) cells sensitive and resistant to imatinib

OBJECTIVE

Imatinib mesylate (IM) is a tyrosine kinase inhibitor selective for BCR-ABL and indicated for the treatment of chronic myeloid leukemia. It has recently been demonstrated that IM also targets other cellular components. Considering the significant role of telomerase in malignant transformation, we studied the effect of IM on telomerase activity (TA) and regulation in BCR-ABL-positive and -negative cells, sensitive and resistant to IM.

MATERIALS AND METHODS

Through combining telomeric repeat amplification protocol for detecting TA, reverse transcription polymerase chain reaction and Western blots for detecting RNA and protein levels of telomerase regulating proteins and fluorescence-activated cell sorting analysis, we showed that IM targets telomerase and the signal transduction cascade upstream of it.

RESULTS

IM significantly inhibited TA in BCR-ABL-positive and -negative cells and in chronic myeloid leukemia patients. TA inhibition was also observed in BCR-ABL positive cells resistant to IM at drug concentrations that did not lead to a reduction in BCR-ABL expression. In addition, a reduction in phosphorylated AKT and phosphorylated PDK-1 was also detected following IM incubation.

CONCLUSIONS

We demonstrate an inhibitory effect of IM on TA and on the AKT/PDK pathway. Because this effect was observed in cell expressing the BCR-ABL protein as well as cells not expressing it, and in cells sensitive as well as resistant to IM, it is reasonable to assume that the inhibitory effect of IM on TA is not mediated through known IM targets. The results of this study show that cells resistant to IM with regard to its effect on BCR-ABL could still be sensitive to IM treatment regarding other cellular components.

A proof of concept study: human C48-placenta immunoregulatory factor is an effective, single therapeutic agent enabling allogeneic, nonmanipulated murine bone marrow transplantation

OBJECTIVE

Cloned placenta immunoregulatory ferritin (PLIF) contains a novel, nonferritin bioactive domain (C-48) with immunodulatory activity. We documented that treatment of whole human bone marrow cells with PLIF and its subcloned C48 proteins resulted in myeloid progenitor cell growth and differentiation and T-cell suppression via an effect on the cytokine network. We tested whether this differential effect supports allogeneic bone marrow transplantation with long-lasting tolerance without any further treatments.

MATERIALS AND METHODS

Splenocyte-enriched C3H (H2(k)) whole bone marrow was transplanted into C57Bl (H2(b)) recipients after total body irradiation. Recipients were injected with recombinant C48 (3 mg/kg, intraperitoneal) for 21 days or with glutathione S-transferase. Animals were monitored for survival, chimerism, and clinical signs of graft-vs-host disease (GVHD). Next, chimera whole bone marrow was transplanted to secondary myeloablated C57Bl (H2(b)) hosts without treatment.

RESULTS

Mice that received C48 treatment following allogeneic splenocyte-enriched bone marrow transplantation demonstrated full-donor chimerism without GVHD mortality, and normal blood cell counts in 75% of recipients. Secondary transplants from the full chimera to myeloblated C57Bl hosts showed 100% engraftment, no GVHD mortality, and no impairment in the long-term hematopoietic reconstitution potential. Allogeneic response of spleen cells from secondary chimeras against donor C3H (H2(k)) and recipient C57Bl (H2(b)) were similar to syngeneic response, whereas reactivity to third party (DBA H2(d)) was significantly enhanced.

CONCLUSIONS

Findings of this study provide the proof of concept that C48-a novel, single, bifunctional therapeutic modality enabled successful allogeneic, unmanipulated bone marrow transplantation without GVHD, and with lasting specific tolerance.

Follicular lymphoma with extensive gastrointestinal tract involvement: follow-up by capsule endoscopy

Follicular lymphoma with gastrointestinal tract involvement is rare. We describe the case of a young woman with follicular lymphoma with multiple nodular lesions involving segments of the proximal jejunum and terminal ileum. The presenting symptom was chronic diarrhea. The diagnosis was made by endoscopy with histologic examination of the mucosal lesions of the proximal and distal small intestine, immunohistochemical staining, and molecular analysis. The initial spread and pattern of the small bowel involvement, as well as treatment response, were evaluated by videocapsule endoscopy. The application of molecular analysis along with immunophenotypic evaluation has made it possible to precisely diagnose follicular lymphoma. In the present case, the use of capsule endoscopy improved the evaluation of the extent of small bowel involvement prior to and following treatment.

Pivanex, a histone deacetylase inhibitor, induces changes in BCR-ABL expression and when combined with STI571, acts synergistically in a chronic myelocytic leukemia cell line

Chronic myelogenous leukemia (CML) is associated with the high TK activity chimeric protein BCR-ABL, known to contribute to cell tumorogenicity, resistance to apoptosis and differentiation. STI571, the TK inhibitor, is the current treatment for CML. One possible approach to overcome STI571 resistance appearing in some cases, involves the combination of histone deacetylase inhibitors (HDI) and STI571. We demonstrated that in K562, the CML cell line, pivaloyloxymethyl butyrate (Pivanex)-induced apoptosis, differentiation and reduced BCR-ABL protein levels and that the combination of Pivanex with STI571 acted synergistically. These data suggest the possible benefit of combining this HDI with STI571 for treatment of CML.

A family with hereditary thrombocythaemia and normal genes for thrombopoietin and c-Mpl

Hereditary thrombocythaemia (HT) is an inherited autosomal dominant disorder. Recent studies reported six different mutations, four within the thrombopoietin (TPO) gene and two within c-Mpl (TPO receptor) gene in six unrelated families with HT. This study investigated the molecular basis of hereditary thrombocythaemia in an Israeli-Jewish family. We screened the genes for TPO and c-Mpl by amplification and sequencing of all the corresponding exons including exon/intron boundaries and promoters. In addition, plasma levels of TPO and erythropoietin (EPO) were measured. No abnormality in the TPO/c-Mpl genes has been identified in affected HT family members. Plasma TPO and EPO levels were found to be normal/low or normal respectively in the individuals affected. In conclusion, lack of a molecular lesion within either TPO or cMpl genes indicate that HT may be caused by factors other than TPO-cMpl axis in this family.

Nucleated Red Blood Cells in Uncomplicated Prolonged Pregnancy

OBJECTIVE

Elevated counts of nucleated red blood cells (NRBCs), as well as prolongation of pregnancy, have been suggested as predictors of adverse perinatal outcome. However, the association between these 2 variables has received only minimal attention. We sought to evaluate fetal NRBCs in prolonged pregnancies.

METHODS

Umbilical cord blood was prospectively collected at delivery from 75 prolonged (at or beyond 287 days) pregnancies. One hundred and fifty term deliveries (260-286 days) served as controls. All pregnancies were accurately dated with the use of first-trimester sonography. Fetal biophysical profile testing was initiated at 40 weeks of gestation. Patients were delivered if they were in spontaneous labor or the biophysical profile was nonreassuring or by 42 weeks of gestation. Nucleated red blood cell counts were expressed per 100 white blood cells (WBC). Umbilical artery pH studies, as well as other demographic and clinical variables, were obtained.

RESULTS

Prolonged pregnancy was associated with a significantly increased incidence of induction of labor and a greater birth weight. There were no other differences between the study group and controls. The median NRBCs per 100 WBCs in prolonged pregnancy was not significantly elevated over the term values (median 3, range 0-35 versus median 3, range 0-34, respectively; P =.25). Neonatal outcome was also comparable between groups. The univariate regression analysis demonstrated a significant association between elevated NRBC counts and low arterial cord blood pH (P <.008, R = 0.175), elevated base excess (P =.02, R = 0.149), low platelet counts (P =.046, R = 0.134), and male gender (P =.028). Stepwise regression analysis revealed that low arterial cord blood pH and male gender were the only independent variables predicting elevated NRBC counts at birth.

CONCLUSION

The findings of this study suggest that elevated NRBC counts are associated with specific pregnancy complications rather than uncomplicated prolonged pregnancies in general.

All three receptors for vascular endothelial growth factor (VEGF) are expressed on B-chronic lymphocytic leukemia (CLL) cells

B-chronic lymphocytic leukemia (B-CLL) cells have a long survival owing to an alteration in the normal pathways of apoptosis. CLL cells have been found to produce and secrete vascular endothelial growth factor (VEGF). In addition to its major role in angiogenesis, VEGF affects cell survival by interfering with apoptosis. The aim of the present study was to investigate the expression of the VEGF receptors VEGFR-1, VEGFR-2, and VEGFR-3 on B-CLL cells, singly and combined. B-CLL cells were isolated from peripheral blood drawn from patients with CLL. Total VEGF receptor, examined in 13 samples by flow cytometry was present in all cases with mean CD19+/VEGF+ expression of 76% (range 52-92%). Specific receptor expression, examined in 27 samples by immunocytochemical methods, was positive for VEGFR-1 in all 27 patients and for VEGFR-2 and VEGFR-3 in 26 (96%). These findings suggest that the VEGF transduction pathway may be very active in CLL cells, and both its paracrine and autocrine pathways may contribute to their enhanced survival.

Expression of adhesion molecules on leukemic B cells from chronic lymphocytic leukemia patients with predominantly splenic manifestations

BACKGROUND

The highly tissue-specific trafficking of normal and malignant lymphocytes to particular organs is mediated by adhesion molecules, or "homing receptors." Among our patients with B cell chronic lymphocytic leukemia 15% demonstrate predominantly splenic manifestations and are classified as stage II(S).

OBJECTIVE

To investigate whether expression of cell surface adhesion molecules can distinguish stage II(S) patients from stage 0 or stage 0 and I CLL patients.

METHODS

Expression of adhesion molecules belonging to different families was studied in CD19-positive cells isolated from the blood of 42 patients by dual color flow cytometry. The families included: immunoglobulin superfamily (CD54, CD58), integrin family (beta1, beta2 and beta3 chains, CD11a, CD11c, CD49d), selectin family (L-selectin), and lymphocyte homing receptor family (CD44).

RESULTS

The average percentage of leukemic cells expressing CD11c in the 23 patients with stage II(S) was 25.7 compared with 13.2% in the 14 patients with stage 0 disease (P = 0.047). The average percentage of leukemic cells expressing CD44 in patients with stage II(S) was 90.5 compared with 77.2% in patients with stage 0 (P = 0.007) and 80% in patients with stages 0 and I together (n = 19, P = 0.008). Other adhesion molecules tested did not show a statistically significance difference in expression between the different disease stages.

CONCLUSIONS

The higher expression of CD44 and CD11c in cells of CLL patients with predominantly splenic manifestations may account for the tendency of their lymphocytes to home to the spleen.

Expression of basic fibroblast growth factor is associated with poor outcome in non-Hodgkin's lymphoma

It is now clear that angiogenesis and angiogenesis factors are important in the pathogenesis of haematological malignancies. High pretreatment levels of serum basic fibroblast growth factor have been shown to be associated with poor prognosis in patients with non-Hodgkin's lymphoma. The aim of this study was to evaluate whether non-Hodgkin's lymphoma cells express basic fibroblast growth factor and/or its receptor (fibroblast growth factor receptor-1) and whether basic fibroblast growth factor expression correlates with basic fibroblast growth factor serum levels, intratumoral microvessel density, and patient outcome. We measured basic fibroblast growth factor by enzyme-linked immunosorbent assay in sera taken from 58 patients with non-Hodgkin's lymphoma before treatment and in 19 of them also after treatment. Pathological specimens at diagnosis were evaluated by immunohistochemistry staining using polyoclonal antibody against factor-VIII-related antigen, basic fibroblast growth factor and fibroblast growth factor receptor-1 to determine the expression of the microvessel count and basic fibroblast growth factor and fibroblast growth factor receptor-1. The lymphoma specimens demonstrated positive staining for basic fibroblast growth factor (in 23%) and fibroblast growth factor receptor-1 (in 58.5%). The patients who expressed basic fibroblast growth factor had a significantly worse progression-free and overall survival than those who did not (P=0.003 and P=0.03 respectively), while patients expressing fibroblast growth factor receptor-1 were less likely to achieve complete remission than those lacking the receptor (33% vs 65%, P=0.047). There was no correlation of basic fibroblast growth factor staining with either serum basic fibroblast growth factor levels or microvessel count. Basic fibroblast growth factor serum levels did not change significantly after treatment These results suggest that non-Hodgkin's lymphoma specimens express basic fibroblast growth factor and its receptor (fibroblast growth factor receptor-1) and this expression is associated with poor patient outcome.

Bcl-2 expression correlates positively with serum basic fibroblast growth factor (bFGF) and negatively with cellular vascular endothelial growth factor (VEGF) in patients with chronic lymphocytic leukaemia

A large proportion of B-chronic lymphocytic leukaemia (B-CLL) cells express the anti-apoptotic protein Bcl-2. Basic fibroblast growth factor (bFGF) has been shown to upregulate the expression of Bcl-2 in B-CLL cell lines. Vascular endothelial growth factor (VEGF) has been shown to enhance the survival of endothelial cells by upregulating the expression of Bcl-2. In the present study, we measured serum and cellular levels of bFGF and VEGF in 85 patients with CLL using a commercial quantitative sandwich enzyme immunoassay technique. Levels of Bcl-2 were also assayed concomitantly using Western blot analysis. The mean serum level of bFGF was 53.4 pg/ml (range 0-589) and that of VEGF 459.2 pg/ml (range 33-1793). The mean cellular level of bFGF was 158.3 pg/2 x 105 cells (range 0.8-841) and VEGF, 42.4 pg/2 x 105 cells (range 0-244). A high correlation was found between serum and cellular bFGF levels (P < 0.001), but not between the corresponding VEGF levels. Twenty-nine of 69 patients (42%) evaluated for Bcl-2 level, expressed it. The Bcl-2 level was positively correlated with the serum bFGF level (P = 0.007). However, surprisingly there was a negative correlation between Bcl-2 expression and intracellular VEGF level (P = 0.003). A positive correlation was also found between serum bFGF and disease follow-up time and log white blood cell count. These findings indicate that in CLL there is a correlation between angiogenesis-related factors and apoptosis-related protein expression, and elevated bFGF levels may account for the elevated Bcl-2 levels.

Doxorubicin and a butyric acid derivative effectively reduce levels of BCL-2 protein in the cells of chronic lymphocytic leukemia patient

B-chronic lymphocytic leukemia (B-CLL) is a disease caused primarily by defects in the apoptosis mechanism. AN-9, a butyric acid (BA) derivative, is a potent differentiating and an anti-cancer drug that induces apoptosis in HL-60 cells. Herein we show the affect of AN-9, alone and in combination with doxorubicin, on cell cultures from B-CLL patients. Cells from 17 patients were cultured and tested for viability, apoptosis, bcl-2 and bax protein expression. Exposure of B-CLL cell cultures to AN-9 was accompanied by apoptosis and a marked viability loss (up to 46%, p=0.0017). AN-9 reduced up to 51% (p=0.0017) the levels of bcl-2 in 57% of the cultures that express bcl-2. The combination of low concentrations of AN-9 and doxorubicin more than additively enhanced apoptosis and reduced bcl-2 levels in B-CLL cultures which were resistant to AN-9. AN-9 enhanced bax expression up to 58%(p=0.008) in cultures from 53% of the patients, but had no effect on bax levels when combined with doxorubicin. In conclusion, AN-9 alone reduced bcl-2 and enhanced bax expression in cultures from B-CLL patients, and the reduction of bcl-2 levels in combination with doxorubicin was greater than additive. These results may be beneficial in possible future combination therapy with AN-9 in B-CLL.

Uptake of pivaloyloxymethyl butyrate into leukemic cells and its intracellular esterase-catalyzed hydrolysis

Pivaloyloxymethyl butyrate (AN-9), a butyric acid (BA) prodrug, exhibited low toxicity and significant anticancer activity in vitro and in vivo. The purpose of this study was to elucidate the basis for AN-9 increased anticancer activity compared to BA, by studying the uptake of BA and AN-9 into the cells.

METHODS

The uptake rate and level of [14C]-AN-9 and [14C]-BA, labeled on the carboxylic moiety of BA, into HL-60 and MEL leukemic cell lines was measured. The cells were filtered and the retained radioactivity was determined. The dependence of the uptake on the activity of cellular esterases and membrane fluidity was investigated.

RESULTS

The uptake level in cells incubated with [14C]-AN-9 increased rapidly, peaked after 30 min in MEL and 1 h in HL-60 cells, and declined thereafter. This decline could be attributed to the hydrolysis of AN-9 by cellular esterases and catabolism of the released BA to CO2. In cells pretreated with an esterase inhibitor and incubated with [14C]-AN-9, the reduction of radioactivity was less precipitous. In cells exposed to [14C]-BA, the intracellular radioactivity level was low and unaffected by treatment with an esterase inhibitor. The uptake of [14C]-AN-9 decreased significantly at 4 degrees C compared to that at 37 degrees C.

CONCLUSION

The higher potency of AN-9 compared to BA could be at least partially attributed to the more rapid uptake of the lipophilic AN-9 and the release of BA in the cells.

Microvessel density in chemosensitive and chemoresistant diffuse large B-cell lymphomas

Preliminary reports involving a number of different kinds of tumors have indicated that microvessel quantification may be useful in predicting disease outcome. The aim of this study was to examine the relationship between microvessel density (MVD) as a parameter of tumor angiogenesis and the response to chemotherapy in diffuse large B-cell (DLBC) lymphomas. A total of 36 DLBC lymphoma patients were evaluated, 23 of them with a chemosensitive; responsive disease (median survival 8y) and 13 with a chemoresistant, refractory disease (median survival 8 months). Microvessel quantification was performed by immunohistochemical staining, using monoclonal antibodies against factor VIII related antigen (F8RA) and against platelet/endothelial cell adhesion molecule-CD31. We found that F8RA stained a significantly higher number of blood vessels (about 2.5 times more) than CD-31; 7 samples were not stained with CD-31 but were positive for F8RA. There was no significant difference between the density of microvessel staining of the two groups. In the chemosensitive DLBC lymphomas positive for F8RA, the mean number of microvessels stained was 54.5 +/- 36.1 per microscopic field (200x) examined (range 6-149) whereas in the chemoresistant group the corresponding mean number was 43.1 +/- 25.5 (range 11-94). F8RA appears to be more sensitive for staining DLBC lymphomas microvessels than CD-31. Our data demonstrate that there is no correlation between tumor MVD and response to chemotherapy in patients with DLBC lymphomas.

Expression of bcl-2 and bax in cells isolated from B-chronic lymphocytic leukemia patients at different stages of the disease

B-Chronic lymphocytic leukemia (B-CLL) is an example of a human malignancy caused by alterations in the pathways of programmed cell death. In this disease the anti-apoptotic protein, bcl-2, is overexpressed and may lead to the prolonged survival of a malignant CLL clone. In the present study we examined the expression of bcl-2 and bax, which has an antagonistic role against the function of bcl-2, in cells from CLL patients at different stages of the disease, by immunoblot analysis. A direct association between the stage of the disease and the level of bcl-2 in the patients' cells was observed. At stages A and B, 33% and 29% of patients, respectively, expressed high levels of bcl-2, as opposed to 80% of patients at stage C (p= 0.019). Bax level was not significantly associated with the stage of the disease, although patients at stage C had higher levels of bax. In this study we found a trend of association between bcl-2 and bax levels. Analysis including all patients revealed that 65% of the patients who expressed high levels of bcl-2 had high levels of bax (p = 0.058). Of patients in stage C, 45% expressed high levels of both bcl-2 and bax while 50% and 42% of patients at stages A and B had low levels of both proteins.

Bcl-2, Bcl-X, Bax, and Bak expression in short- and long-lived patients with diffuse large B-cell lymphomas

Long-term cure is now possible for approximately 50% of all patients with aggressive non-Hodgkin's lymphoma (NHL). Apoptosis-related proteins play an important role in the chemosensitivity or chemoresistance of tumors. We examined the role of Bcl-2 family proteins in aggressive NHL. We retrospectively selected two groups of patients by clinical outcome: 24 patients with chemoresponsive disease and long survival (median, 88 months); and 20 patients with chemoresistant disease and short survival (median, 8 months). The expression of the apoptosis-regulating proteins, Bcl-2, Bcl-X, Bax, and Bak, in the initial biopsy samples was examined with immunohistochemical methods. Specimens containing >10% immunostained tumor cells were considered immunopositive. An inverse association was found between length of patient survival and expression of Bcl-2, Bcl-X, and Bax. Bcl-2 was expressed in 75% of short-lived patients but in only 42% of the long-lived ones (P = 0.026). Bcl-X expression was also higher in the short-lived patients (40% versus 12.5%; P = 0.036). Unexpectedly, Bax expression was strongly associated with short survival (60% versus 21%; P = 0.008). Several combinations of protein expression, i.e., Bcl-2 with Bax, Bcl-2 with Bcl-X, and Bcl-X with Bax, were different between the groups: a positive expression of these proteins was found in the short-lived patients. Furthermore, a strong association was found between the expression of Bcl-2 and Bcl-X, suggesting that Bcl-X potentiates rather than replaces the effect of Bcl-2 in NHL. In diffuse large B-cell NHL, Bcl-2, Bcl-X, and Bax expression alone or in combination is associated with chemoresistance and shortterm survival.

Effect of the cytostatic butyric acid pro-drug, pivaloyloxymethyl butyrate, on the tumorigenicity of cancer cells

Previously we have shown that pivaloyloxymethyl butyrate (AN-9), a pro-drug of butyric acid (BA), is a differentiation-inducing agent in a variety of cells. In this report, we demonstrate that AN-9 is a cytostatic but not cytotoxic agent in a myelomonocytic cell line (WEHI); thus, the cells were growth-arrested and differentiated. These late changes in the cells were preceded by changes in the expression of the early regulatory genes, c-myc and c-jun. Although initiation of all these events had already occurred after 1 h exposure to AN-9, the tumorigenicity of these cells tested in Balb/c mice was not affected. A marked reduction in the tumorigenicity of AN-9-treated cells was observed after 4 h of exposure. Exposure of the highly metastatic subclone of Lewis lung carcinoma (3LLD122) to AN-9 resulted in a very pronounced effect on the tumorigenicity of these cells tested in C57BL mice. Unlike WEHI cells, the tumorigenicity of 3LLD122 was almost completely diminished after 1 h of exposure. In both cell types a 10-fold higher concentration of BA did not affect the tumorigenicity of the cells as did AN-9.

Esterase inhibitors diminish the modulation of gene expression by butyric acid derivative, pivaloyloxymethyl butyrate (AN-9)

Pivaloyloxymethyl butyrate (AN-9) belongs to the family of acyloxyalkyl ester prodrugs of carboxylic acids which undergo intracellular hydrolysis to yield butyric acid (BA). We have previously shown that AN-9 and BA reduce the level of c-myc and enhance c-jun transcripts in HL-60 cells, and that the differentiation of these cells, induced by AN-9, is dependent on the presence of intracellular esterases. In this study we show that esterase inhibitors abolish the changes induced by AN-9 on c-myc and c-jun expression. In contrast, esterase inhibitors do not change the effects of BA on c-myc or c-jun. Interestingly, these inhibitors affect the modulation induced by both AN-9 and BA on the retinoblastoma tumor suppressor gene. These data suggest that AN-9 is indeed a prodrug of BA and that prior intracellular hydrolysis by esterases is material for AN-9 activity.

Rapid alteration of c-myc and c-jun expression in leukemic cells induced to differentiate by a butyric acid prodrug

The novel prodrug of butyric acid (BA), pivaloyloxymethyl butyrate, has been shown, in vitro, to induce differentiation and inhibit leukemic cell proliferation. The prodrug affects the cells in vitro at lower concentration and at least 100 times faster than does (BA). We have compared the ability of BA with that of its prodrug AN-9 to modulate the expression of the early regulating genes, c-myc and c-jun, in HL-60 cells. Exposure of HL-60 cells to the prodrug resulted in a decrease of c-myc and an increase of c-jun expression. The prodrug elicited this effect at lower concentrations and at least 100 times faster than BA. Since changes in the expression of c-myc and c-jun occur minutes after exposure of the cells to the prodrug, these genes are likely to play a major role in the early stages of the differentiation pathway.

Novel anticancer prodrugs of butyric acid. 2

The antitumor activity of novel prodrugs butyric acid was examined. The in vitro effect of the compounds on induction of cytodifferentiation and on inhibition of proliferation and clonogenicity showed that (pivaloyloxy)methyl butyrate (1a) (labeled AN-9) was the most active agent. SAR's suggested that its activity stemmed from hydrolytically released butyric acid. In vivo, 1a displayed antitumor activity in B16F0 melanoma primary cancer model, manifested by a significant increase in the life span of the treated animals. Murine lung tumor burden, induced by injection of the highly metastatic melanoma cells (B16F10.9), was decreased by 1a. It also displayed a significant therapeutic activity against spontaneous metastases which were induced by 3LL Lewis lung carcinoma cells. Moreover, 1a has the advantage of low toxicity, with an acute LD50 = 1.36 +/- 0.1 g/kg (n = 5). These results suggest that 1a is a potential antineoplastic agent.

Derivatives of butyric acid as potential anti-neoplastic agents

A novel derivative of butyric acid, pivalyloxymethyl butyrate (AN-9) has been shown, in vitro, to: (a) induce cytodifferentiation and inhibit the proliferation of leukemic cells; (b) inhibit the growth and formation of Lewis lung carcinoma colonies in semi-solid agar. AN-9 affect cells at about 10-fold lower concentration and at a faster rate than does butyric acid. The pivalyloxymethyl esters of propionic, isobutyric and valeric acids do not elicit effects similar to those of AN-9, while the isobutyryloxymethyl butyrate does, which strongly suggests that the activity of AN-9 stems from intracellular metabolic degradation of the pro-drug to butyric acid. In vivo, AN-9, increased the survival of mice in Lewis lung carcinoma primary cancer model and significantly decreased the number of lung lesions of the animals inoculated with highly metastatic cells, but did not affect their life span. Acute LD50 studies have shown that AN-9 possesses low toxicity. These results suggest that AN-9 is a potential anti-neoplastic agent as well as a tool for investigation of the differentiation induction mechanism.

Proliferation-associated changes of Ca2+ transport in myeloid leukemic cell lines

Proliferation-associated changes in calcium metabolism were investigated employing the promyelocytic HL-60 and monoblastic U-937 cell lines. The cells were stimulated to proliferate employing mitogenic factors as follows. 1) Transferrin or insulin: HL-60 cells were adjusted for growth in serum-free medium, and 24 h prior to the experiment, the cells were deprived of transferrin or insulin. The re-addition of either one of them stimulated cell proliferation as was evident by increased [3H]-tymidine incorporation activity. Cell proliferation was associated with an enhanced Ca2+ influx rate, measured by 45Ca2+ uptake activity. 2) Granulocyte-monocyte colony-stimulating factor (GM-CSF): addition of GM-CSF to proliferating or quiescent HL-60 cells resulted in increased cell proliferation, which was also accompanied by increased rate of Ca2+ influx. 3) Serum: HL-60 and U-937 were grown for 24 h in serum-depleted medium. Re-addition of serum to the cells was not associated with immediate or delayed change in calcium influx rate but rather with an immediate increase in the cytosolic free calcium concentration, measured employing the fluorescent probe, fura-2AM. This increase was independent of extracellular calcium, unaffected by verapamil, diltiazem, and lanthanum, and associated with enhanced 45Ca2+ efflux. Thus, in all three cases evoked cell proliferation was accompanied by quantitative changes in Ca2+ metabolism. While the transferrin-, insulin-, and GM-CSF-stimulated cell proliferation was accompanied by delayed increases in 45Ca2+ influx, the serum-stimulated cell proliferation was accompanied by an immediate elevation of free cytosolic Ca2+.

The role of calcium in differentiation of leukemic cell lines

Increased calcium influx associated with differentiation of four human myeloid leukemic cell lines: HL-60, KG-1, U-937 and K-562, to either monocytic or granulocytic direction was demonstrated. Calcium influx was measured employing two methods; measurement of radioactive calcium influx rate at 4 degrees C and employing the fluorescent probe, fura-2 acetoxymethyl ester. The increase in Ca2+ influx was demonstrated with three chemically unrelated differentiation inducers: retinoic acid, 1 alpha, 25 dihydroxy vitamin D3 and dimethyl sulfoxide. Inhibitors of calcium uptake such as verapamil diltiazem and cromolyn, partially reduced differentiation, suggesting that differentiation of myeloid leukemic cell lines is dependent on the availability of extracellular calcium.

Disintegration of red cell membrane cytoskeleton by hemin

Spectrin and actin were isolated and their oligomeric state after association with hemin at various conditions was studied. Intact cytoskeletons were prepared by Triton X-100 extraction of red blood cells and incubated with hemin and their stability analyzed by the appearance of dissociated proteins in the supernatant. The cytoskeletons dissociated in a time, temperature and hemin concentration-dependent manner. Following 18 hours incubation in the presence of 0.3 mM hemin there was no dissociation at 4 degrees C, while at the same hemin concentration after 2 hours complete dissociation of the cytoskeletons occurred at 37 degrees C. Microscopy indicated that the cytoskeletons incubated with hemin lost their "cell like" shapes in a time dependent manner. Hemin applied to intact cells also caused dissociation of their cytoskeletons as judged by the failure to separate integer cytoskeletons from red cells treated with hemin. From hemin-induced dissociation profiles of separated actin, spectrin and whole cytoskeletons under various conditions, a mechanism of cytoskeleton breakdown was analyzed, as a release of band 4.1 in the first step which is followed by spectrin dimerization and eventually dissociation of the entire cytoskeletons.

Accumulation and drainage of hemin in the red cell membrane

The subject of hemin intercalation in red cell membranes and the correlation of the accumulated hemin level with the membrane pathology was studied. Methods which made use of dioxan and octan-2-ol mixtures to quantitate small amounts of hemin in membranes were developed. Applying these methods, hemin levels were measured in the cytoskeleton and the remaining lipid core of various red cell membranes. The amount of hemin, in both membrane fractions, was higher in pathological cells of sickle cell anemia and beta-thalassemia as compared to normal circulating cells. Correlation exists between the amount of the membrane-accumulated hemin and the severity of the disease. The level of hemin in the membrane was found to be age dependent, old cells in circulation accumulating more hemin than young cells. The level of hemin in all cells tested was much lower than the amount found previously to cause immediate hemolysis when applied externally (Kirschner-Zilber, I., Rabizadeh, E. and Shaklai, N. (1982) Biochim. Biophys. Acta 690, 20-30). This was explained by the differences between the process leading to immediate lysis and membrane changes recognized as pathological by the in-vivo sequestration mechanism. In search of a physiological mechanism which may drain the cell membrane from the hazardeous hemin, albumin, the main serum protein, was found capable of serving as an efficient agent for extracting hemin trapped in red cell membranes. It is suggested that under normal conditions albumin extracts enough hemin to leave the erythrocyte with unharmful hemin amounts, however, under pathological conditions greater amounts accumulate leading to a shorter cell life span.

Interaction of spectrin with hemin disaggregates spectrin associations

Crude spectrin preparations were extracted from red cell membranes either in dimeric or tetrameric forms and incubated at 4 degrees C with hemin. The mixtures were subjected immediately or after 18 hours to nondenaturing electrophoresis. It was found that immediately after addition of 0.3 mM hemin, the fraction of spectrin complexed with other skeletal proteins, disaggregated to tetramer and dimer forms. After incubation for 18 hours at 4 degrees C most of the spectrin appeared in two additional bands which contained more hemin and migrated on the gels as molecular weight forms smaller than the dimers. Since SDS electrophoresis showed that spectrin subunits retained their integrity in these mixtures, it was concluded that hemin bound spectrin dissociates with time into monomers. It is suggested that there are pathophysiological implications to the disaggregation of spectrin complexes in the cytoskeleton by hemin.

The interaction of hemin and bilirubin with the human red cell membrane

The incubation of 0.5% suspension of fresh normal erythrocytes with hemin or bilirubin resulted in substantial hemolysis. The amount of hemolysis achieved depended on the concentration of the lytic agents. In each concentration maximum hemolysis was reached within half an hour. The hemolytic effect was somewhat dependent on temperature. Comparison with the hemolytic effect of hemin on mice (Chau, A.C. and Fitch, C.D. (1980) J. Clin. Invest. 66, 856-858) showed that although both cells undergo hemolysis by hemin, the behaviour of each red cell type is different. Centrifugation and fluorescence quenching of membrane embedded probe revealed that both hemin and bilirubin bind to the red cell membrane, hemin having higher affinity. The reaction was found to be hydrophobic and therefore independent of ionic strength. The high affinity of the membrane for hemin was shown by its ability to compete successfully with globin for hemin. Electron microscopy of the red cells which underwent hemolysis indicated cell damage and some membrane destruction. Red cell ghosts were totally disrupted when saturated with hemin. These results suggest an explanation for hemolytic events occurring in cases such as elevation of serum bilirubin or abnormalities leading to hemin release by hemoglobin.