RUNX3 levels in human hematopoietic progenitors are regulated by aging and dictate erythroid-myeloid balance

Healthy bone marrow progenitors yield a co-ordinated balance of hematopoietic lineages. This balance shifts with aging toward enhanced granulopoiesis with diminished erythropoiesis and lymphopoiesis, changes which likely contribute to the development of bone marrow disorders in the elderly. In this study, RUNX3 was identified as a hematopoietic stem and progenitor cell factor whose levels decline with aging in humans and mice. This decline is exaggerated in hematopoietic stem and progenitor cells from subjects diagnosed with unexplained anemia of the elderly. Hematopoietic stem cells from elderly unexplained anemia patients had diminished erythroid but unaffected granulocytic colony forming potential. Knockdown studies revealed human hematopoietic stem and progenitor cells to be strongly influenced by RUNX3 levels, with modest deficiencies abrogating erythroid differentiation at multiple steps while retaining capacity for granulopoiesis. Transcriptome profiling indicated control by RUNX3 of key erythroid transcription factors, including KLF1 and GATA1 These findings thus implicate RUNX3 as a participant in hematopoietic stem and progenitor cell aging, and a key determinant of erythroid-myeloid lineage balance.

Requirements for Aggregation of Washed Human Platelets Suspended in Buffered Salt Solutions

With the use of washed human platelets suspended in a buffered salt solution, we have studied the factors capable of acting directly at the platelet plasma membrane to produce aggregation as opposed to those which produce the platelet release reaction and secondary aggregation. Platelet aggregation was measured in an aggregometer and the release reaction followed by assays of the release products.

Ca and fibrinogen will not independently induce aggregation in washed human platelets suspended in a buffered salt solution. However, in their absence ADP-, 5HT-and epinephrine-mediated aggregation will not proceed. Of particular interest was the finding that in the presence of Ca, threshold doses of thrombin will produce aggregation earlier if μg amounts of fibrinogen are added. Ca and fibrinogen therefore appear to be absolutely required for aggregation, whether the aggregation is produced by the addition or by the release of required components.

If either ADP, 5HT or epinephrine is added singly to buffer-suspended platelets in the presence of Ca and fibrinogen, 10–20% aggregation is observed. The combination of either ADP-5HT, ADP-epinephrine or 5HT-epinephrine produces 60–70% aggregation. The addition of ADP, 5HT and epinephrine together produces 80–90% aggregation.

No release reaction is produced by the addition of ADP or 5HT alone or in combination. A new finding in this study therefore is that 5HT and ADP can act directly at the platelet plasma membrane to produce extensive aggregation in the absence of any release reaction.

Epinephrine does produce a small release reaction, and may therefore produce its enhancement of aggregation either by acting directly at the platelet plasma membrane or by the release of something other than Ca, fibrinogen, ADP, 5HT, or epinephrine.

In this study using washed human platelets suspended in a buffered salt solution, no evidence was found for the requirement of a plasma protein other than fibrinogen in platelet aggregation.

Association of Testosterone Levels With Anemia in Older Men: A Controlled Clinical Trial

IMPORTANCE

In one-third of older men with anemia, no recognized cause can be found.

OBJECTIVE

To determine if testosterone treatment of men 65 years or older with unequivocally low testosterone levels and unexplained anemia would increase their hemoglobin concentration.

DESIGN, SETTING, AND PARTICIPANTS

A double-blinded, placebo-controlled trial with treatment allocation by minimization using 788 men 65 years or older who have average testosterone levels of less than 275 ng/dL. Of 788 participants, 126 were anemic (hemoglobin ≤12.7 g/dL), 62 of whom had no known cause. The trial was conducted in 12 academic medical centers in the United States from June 2010 to June 2014.

INTERVENTIONS

Testosterone gel, the dose adjusted to maintain the testosterone levels normal for young men, or placebo gel for 12 months.

MAIN OUTCOMES AND MEASURES

The percent of men with unexplained anemia whose hemoglobin levels increased by 1.0 g/dL or more in response to testosterone compared with placebo. The statistical analysis was intent-to-treat by a logistic mixed effects model adjusted for balancing factors.

RESULTS

The men had a mean age of 74.8 years and body mass index (BMI) (calculated as weight in kilograms divided by height in meters squared) of 30.7; 84.9% were white. Testosterone treatment resulted in a greater percentage of men with unexplained anemia whose month 12 hemoglobin levels had increased by 1.0 g/dL or more over baseline (54%) than did placebo (15%) (adjusted OR, 31.5; 95% CI, 3.7-277.8; P = .002) and a greater percentage of men who at month 12 were no longer anemic (58.3%) compared with placebo (22.2%) (adjusted OR, 17.0; 95% CI, 2.8-104.0; P = .002). Testosterone treatment also resulted in a greater percentage of men with anemia of known cause whose month 12 hemoglobin levels had increased by 1.0 g/dL or more (52%) than did placebo (19%) (adjusted OR, 8.2; 95% CI, 2.1-31.9; P = .003). Testosterone treatment resulted in a hemoglobin concentration of more than 17.5 g/dL in 6 men who had not been anemic at baseline.

CONCLUSIONS AND RELEVANCE

Among older men with low testosterone levels, testosterone treatment significantly increased the hemoglobin levels of those with unexplained anemia as well as those with anemia from known causes. These increases may be of clinical value, as suggested by the magnitude of the changes and the correction of anemia in most men, but the overall health benefits remain to be established. Measurement of testosterone levels might be considered in men 65 years or older who have unexplained anemia and symptoms of low testosterone levels.

TRIAL REGISTRATION

clinicaltrials.gov Identifier: NCT00799617.

Age-associated changes in human hematopoietic stem cells

Aging has a broad impact on the function of the human hematopoietic system. This review will focus primarily on the effect of aging on the human hematopoietic stem cell (HSC) population. With age, even though human HSCs increase in number, they have decreased self-renewal capacity and reconstitution potential upon transplantation. As a population, human HSCs become more myeloid-biased in their differentiation potential. This is likely due to the human HSC population becoming more clonal with age, selecting for myeloid-biased HSC clones. The HSC clones that come to predominate with age may also contain disease-causing genetic and epigenetic changes that confer an increased risk of developing into an age-associated clonal hematopoietic disease, such as myelodysplastic syndrome, myeloproliferative disorders, or leukemia. The selection of these aged human HSC clones may be in part due to changes in the aging bone marrow microenvironment. While there have been significant advances in the understanding of the effect of aging on mouse hematopoiesis and mouse HSCs, we have comparatively less detailed analyses of the effect of aging on human HSCs. Continued evaluation of human HSCs in the context of aging will be important to determine how applicable the findings in mice and other model organisms are to the human clinical setting.

A prospective randomized wait list control trial of intravenous iron sucrose in older adults with unexplained anemia and serum ferritin 20-200 ng/mL

Anemia is common in older persons and is associated with substantial morbidity and mortality. One third of anemic older adults have unexplained anemia of the elderly (UAE). We carried out a randomized, wait list control trial in outpatients with UAE and serum ferritin levels between 20 and 200 ng/mL. Intravenous iron sucrose was given as a 200-mg weekly dose for 5 weeks either immediately after enrollment (immediate intervention group) or following a 12-week wait list period (wait list control group). The primary outcome measure was changed in 6-minute walk test (6MWT) distances from baseline to 12 weeks between the two groups. Hematologic, physical, cognitive, and quality of life parameters were also assessed. The study was terminated early after 19 subjects enrolled. The distance walked in the 6MWT increased a mean 8.05±55.48 m in the immediate intervention group and decreased a mean 11.45±49.46 m in the wait list control group (p=0.443). The hemoglobin increased a mean 0.39±0.46 g/dL in the immediate intervention group and declined a mean 0.39±0.85 g/dL in the wait list control group (p=0.026). Thus, a subgroup of adults with UAE may respond to intravenous iron. Enrollment of subjects into this type of study remains challenging.

Prognostic impact of KMT2E transcript levels on outcome of patients with acute promyelocytic leukaemia treated with all-trans retinoic acid and anthracycline-based chemotherapy: an International Consortium on Acute Promyelocytic Leukaemia study

The KMT2E (MLL5) gene encodes a histone methyltransferase implicated in the positive control of genes related to haematopoiesis. Its close relationship with retinoic acid-induced granulopoiesis suggests that the deregulated expression of KMT2E might lead acute promyelocytic leukaemia (APL) blasts to become less susceptible to the conventional treatment protocols. Here, we assessed the impact of KMT2E expression on the prognosis of 121 APL patients treated with ATRA and anthracycline-based chemotherapy. Univariate analysis showed that complete remission (P = 0·006), 2-year overall survival (OS) (P = 0·005) and 2-year disease-free survival (DFS) rates (P = 0·037) were significantly lower in patients with low KMT2E expression; additionally, the 2-year cumulative incidence of relapse was higher in patients with low KMT2E expression (P = 0·04). Multivariate analysis revealed that low KMT2E expression was independently associated with lower remission rate (odds ratio [OR]: 7·18, 95% confidence interval [CI]: 1·71-30·1; P = 0·007) and shorter OS (hazard ratio [HR]: 0·27, 95% CI: 0·08-0·87; P = 0·029). Evaluated as a continuous variable, KMT2E expression retained association with poor remission rate (OR: 10·3, 95% CI: 2·49-43·2; P = 0·001) and shorter survival (HR: 0·17, 95% IC: 0·05-0·53; P = 0·002), while the association with DFS was of marginal significance (HR: 1·01; 95% CI: 0·99-1·02; P = 0·06). In summary, low KMT2E expression may predict poor outcome in APL patients.

Evaluation and management of anemia in the elderly

Anemia is now recognized as a risk factor for a number of adverse outcomes in the elderly, including hospitalization, morbidity, and mortality. What constitutes appropriate evaluation and management for an elderly patient with anemia, and when to initiate a referral to a hematologist, are significant issues. Attempts to identify suggested hemoglobin levels for blood transfusion therapy have been confounded for elderly patients with their co-morbidities. Since no specific recommended hemoglobin threshold has stood the test of time, prudent transfusion practices to maintain hemoglobin thresholds of 9-10 g/dL in the elderly are indicated, unless or until evidence emerges to indicate otherwise.

The role of oxidant injury in the pathophysiology of human thalassemias

The anemia in beta-thalassemia major is caused by a combination of hemolysis and ineffective erythropoiesis, with the latter being more important. Studies of the underlying cause of the hemolysis have indicated that oxidant injury to circulating red blood cells (RBCs) was of critical importance, with evidence of oxidant damage to RBC membrane proteins 4.1 and band 3. Therefore, it seemed reasonable that oxidant damage to thalassemic erythroid precursors would cause their accelerated apoptosis and ineffective erythropoiesis. However, direct analysis showed that the apoptotic programs turned on in thalassemics were not those triggered by oxidative damage but were dependent on activation of FAS/FAS-Ligand interaction. Thus, destruction of thalassemic erythroid precursors may involve different mechanisms from those that cause RBC hemolysis.

Lenalidomide, melphalan and dexamethasone in a population of patients with immunoglobulin light chain amyloidosis with high rates of advanced cardiac involvement

Immunoglobulin light chain amyloidosis remains incurable despite recent therapeutic advances, and is particularly difficult to treat in patients with amyloid cardiomyopathy. Based on evidence of activity in multiple myeloma, we designed a pilot study of an oral regimen of lenalidomide in combination with dexamethasone and low-dose melphalan in order to evaluate its safety and efficacy in patients with amyloidosis, including those with advanced cardiac involvement. Twenty-five patients were enrolled. Ninety-two percent of patients had cardiac involvement by amyloidosis, and 36% of patients met the criteria for Mayo Clinic cardiac stage III disease. Patients received up to nine cycles of treatment, consisting of lenalidomide 10 mg/day orally on days 1 - 21 (28-day cycle); melphalan 0.18 mg/kg orally on days 1-4; and dexamethasone 40 mg orally on days 1, 8, 15, and 22. High rates (33%) of cardiac arrhythmias and low rates of treatment completion (12.5%) were observed. Ten patients died during the study, all within the first several months of treatment due to acute cardiac events. The overall hematologic response rate was 58%, however organ responses were seen in only 8% of patients. The overall survival rate at 1 year was 58%. While we confirmed the hematologic response rates observed with similar regimens, front-line treatment with melphalan, lenalidomide and dexamethasone was toxic, ineffective, and did not alter survival outcomes for patients with high-risk cardiac disease. Our data highlight the importance of developing novel treatment approaches for amyloid cardiomyopathy. This trial was registered at www.clinicaltrials.gov (NCT00890552).

The prognostic value of diagnosing concurrent multiple myeloma in immunoglobulin light chain amyloidosis

The prevalence and prognostic value of a concomitant diagnosis of symptomatic or asymptomatic multiple myeloma (MM), as defined by the current International Myeloma Working Group (IMWG) criteria, in patients with immunoglobulin light chain amyloidosis (AL), are unknown. We studied 46 consecutive patients with AL who underwent quantification of serum M-protein and clonal bone marrow plasma cells, as well as a comprehensive evaluation for end organ damage by MM. Using standard morphology and CD138 immunohistochemical staining, 57% and 80% of patients were found to have concomitant MM, respectively. Nine patients exhibited end organ damage consistent with a diagnosis of symptomatic MM. While overall survival was similar between AL patients with or without concurrent myeloma (1-year overall survival 68% vs. 87%; P = 0.27), a diagnosis of symptomatic myeloma was associated with inferior outcome (1-year overall survival 39% vs. 81%; P = 0.005). Quantification of bone marrow plasma cells by both standard morphology and CD138 immunohistochemistry identified a much higher prevalence of concurrent MM in patients with AL than previously reported. Evaluation of bone marrow plasma cell infiltration and presence of myeloma associated end organ damage could be clinically useful for prognostication of patients with AL.

Heart transplantation and cardiac amyloidosis: approach to screening and novel management strategies

Limited data exist regarding screening methods and outcomes for orthotopic heart transplantation (OHT) in cardiac amyloidosis. As a result, uncertainty exists over the best approach to OHT for cardiac amyloidosis and for the timing of critical post-transplant therapies. This article reviews 6 patients who underwent OHT for cardiac amyloidosis at the Stanford University Amyloid Center from 2008 to present. All patients with light-chain amyloidosis received chemotherapy in the interval between OHT and autologous hematopoietic stem cell transplant. Five patients remain alive up to 25 months after OHT, without evidence of recurrent cardiac amyloid deposition. A novel strategy of OHT, followed by light-chain suppressive chemotherapy before autologous hematopoietic stem cell transplant, is feasible for patients with light-chain amyloidosis.

Anemia in older persons: etiology and evaluation

The aim of this study was to prospectively determine the etiology of anemia in a cohort of community-dwelling older outpatients with a comprehensive hematologic evaluation. Participants were men and women age 65 and older with anemia as defined by World Health Organization criteria recruited from outpatient hematology clinics at Stanford Hospital and Clinics (SHC) and Veterans Affairs Palo Alto Health Care System (VAPAHCS). Each participant underwent a history and physical examination, followed by a comprehensive hematologic evaluation, which in all participants included complete blood count, red cell indices, review of the blood smear, and assessment of vitamin B12, folate, iron status and renal function. Additional evaluation was obtained by clinical providers as per their discretion. 190 participants enrolled and completed the evaluation. Twelve percent of participants had iron deficiency anemia. Of those with iron deficiency in whom there was follow-up information, half normalized their hemoglobin in response to iron repletion, and half did not. Thirty-five percent of participants had unexplained anemia. Those with unexplained anemia had mildly increased inflammatory markers compared to non-anemic controls, and, at the lower hemoglobin ranges had relatively low erythropoietin levels. Sixteen percent of participants were categorized as being "suspicious for myelodysplastic syndrome." Thus, even with comprehensive hematologic evaluation, unexplained anemia is common in older anemic outpatients. Iron deficiency anemia is also common and can be difficult to diagnose, and frequently the anemia is not fully corrected with iron repletion.

Pitting of malaria parasites and spherocyte formation

BACKGROUND

A high prevalence of spherocytes was detected in blood smears of children enrolled in a case control study conducted in the malaria holoendemic Lake Victoria basin. It was speculated that the spherocytes reflect intraerythrocytic removal of malarial parasites with a concurrent removal of RBC membrane through a process analogous to pitting of intraerythrocytic inclusion bodies. Pitting and re-circulation of RBCs devoid of malaria parasites could be a host mechanism for parasite clearance while minimizing the anaemia that would occur were the entire parasitized RBC removed. The prior demonstration of RBCs containing ring-infected erythrocyte surface antigen (pf 155 or RESA) but no intracellular parasites, support the idea of pitting.

METHODS

An in vitro model was developed to examine the phenomenon of pitting and spherocyte formation in Plasmodium falciparum infected RBCs (iRBC) co-incubated with human macrophages. In vivo application of this model was evaluated using blood specimens from patients attending Kisumu Ditrict Hospital. RBCs were probed with anti-RESA monoclonal antibody and a DNA stain (propidium iodide). Flow cytometry and fluorescent microscopy was used to compare RBCs containing both the antigen and the parasites to those that were only RESA positive.

RESULTS

Co-incubation of iRBC and tumor necrosis factor-alpha activated macrophages led to pitting (14% +/- 1.31% macrophages with engulfed trophozoites) as opposed to erythrophagocytosis (5.33% +/- 0.95%) (P < 0.01). Following the interaction, 26.9% +/- 8.1% of the RBCs were spherocytes as determined by flow cytometric reduction in eosin-5-maleimide binding which detects RBC membrane band 3. The median of patient RBCs with pitted parasites (RESA+, PI-) was more than 3 times (95,275/muL) that of RESA+, PI+ RBCs (28,365/muL) (P < 0.01). RBCs with pitted parasites showed other morphological abnormalities, including spherocyte formation.

CONCLUSION

It is proposed that in malaria holoendemic areas where prevalence of asexual stage parasites approaches 100% in children, RBCs with pitted parasites are re-circulated and pitting may produce spherocytes.

VEGF modulates erythropoiesis through regulation of adult hepatic erythropoietin synthesis

Vascular endothelial growth factor (VEGF) exerts crucial functions during pathological angiogenesis and normal physiology. We observed increased hematocrit (60-75%) after high-grade inhibition of VEGF by diverse methods, including adenoviral expression of soluble VEGF receptor (VEGFR) ectodomains, recombinant VEGF Trap protein and the VEGFR2-selective antibody DC101. Increased production of red blood cells (erythrocytosis) occurred in both mouse and primate models, and was associated with near-complete neutralization of VEGF corneal micropocket angiogenesis. High-grade inhibition of VEGF induced hepatic synthesis of erythropoietin (Epo, encoded by Epo) >40-fold through a HIF-1alpha-independent mechanism, in parallel with suppression of renal Epo mRNA. Studies using hepatocyte-specific deletion of the Vegfa gene and hepatocyte-endothelial cell cocultures indicated that blockade of VEGF induced hepatic Epo by interfering with homeostatic VEGFR2-dependent paracrine signaling involving interactions between hepatocytes and endothelial cells. These data indicate that VEGF is a previously unsuspected negative regulator of hepatic Epo synthesis and erythropoiesis and suggest that levels of Epo and erythrocytosis could represent noninvasive surrogate markers for stringent blockade of VEGF in vivo.

New Strategies in the Treatment of the Thalassemias

In addition to the severe beta thalassemias, hematologists have begun to recognize the more severe forms of alpha thalassemia, namely hemoglobin (Hb) H disease and Hb H/Hb Constant Spring, as well as the beta compound heterozygote, beta thalassemia/HbE. Clinically, variably severe anemia becomes apparent in the first year accompanied by occasionally massive expansion of erythropoiesis. The most anemic patients require regular red blood cell transfusions to avoid death from cardiac failure. However, the inevitable iron accumulation leads to dysfunction, primarily involving the heart, liver, and endocrine system; thus, regularly transfused patients require iron chelation. A major discovery was that allogeneic bone marrow (stem cell) transplantation in severely affected subjects with both alpha and beta thalassemia could result in cure. Current work deals with specific complications, such as iron overload and endocrine, cardiopulmonary, thrombophilic, and osteopenic problems. The thalassemias are likely to benefit in the future from specific gene therapy. There are also important advances in genetic counseling based on results of early fetal diagnosis.

Anemia in the elderly: a public health crisis in hematology

Over 3 million people in the United States aged 65 years and older are anemic. This condition is associated with significant functional impairment and, perhaps, increased mortality. In March 2004, the American Society of Hematology (in conjunction with the National Institute of Aging) convened a "blue ribbon" panel of twenty physicians who are experts on various aspects of this topic. This paper highlights important consensus concepts resulting from that meeting. In particular, four areas of thought are shared. First, the epidemiology of anemia in the elderly is reviewed, including its definition, its expression in different racial groups, and its wide-ranging manifestations. Second, the pathophysiology of anemia in the elderly is reviewed as pertains to three general etiological categories (nutritional, chronic diseases, and so-called "unexplained" anemias). Particular emphasis is given to pathophysiologic mechanisms of anemia that are potentially unique to this age group. Third, a practical approach to the diagnosis and management of anemia for this patient population for the practicing hematologist is provided. Finally, the public health implications of anemia in the elderly for key stakeholder constituencies will be discussed in the oral presentation.

The FIP1L1-PDGFRalpha fusion tyrosine kinase in hypereosinophilic syndrome and chronic eosinophilic leukemia: implications for diagnosis, classification, and management

Idiopathic hypereosinophilic syndrome (HES) and chronic eosinophilic leukemia (CEL) comprise a spectrum of indolent to aggressive diseases characterized by unexplained, persistent hypereosinophilia. These disorders have eluded a unique molecular explanation, and therapy has primarily been oriented toward palliation of symptoms related to organ involvement. Recent reports indicate that HES and CEL are imatinib-responsive malignancies, with rapid and complete hematologic remissions observed at lower doses than used in chronic myelogenous leukemia (CML). These BCR-ABL-negative cases lack activating mutations or abnormal fusions involving other known target genes of imatinib, implicating a novel tyrosine kinase in their pathogenesis. A bedside-to-benchtop translational research effort led to the identification of a constitutively activated fusion tyrosine kinase on chromosome 4q12, derived from an interstitial deletion, that fuses the platelet-derived growth factor receptor-alpha gene (PDGFRA) to an uncharacterized human gene FIP1-like-1 (FIP1L1). However, not all HES and CEL patients respond to imatinib, suggesting disease heterogeneity. Furthermore, approximately 40% of responding patients lack the FIP1L1-PDGFRA fusion, suggesting genetic heterogeneity. This review examines the current state of knowledge of HES and CEL and the implications of the FIP1L1-PDGFRA discovery on their diagnosis, classification, and management.

A tyrosine kinase created by fusion of the PDGFRA and FIP1L1 genes as a therapeutic target of imatinib in idiopathic hypereosinophilic syndrome

BACKGROUND

Idiopathic hypereosinophilic syndrome involves a prolonged state of eosinophilia associated with organ dysfunction. It is of unknown cause. Recent reports of responses to imatinib in patients with the syndrome suggested that an activated kinase such as ABL, platelet-derived growth factor receptor (PDGFR), or KIT, all of which are inhibited by imatinib, might be the cause.

METHODS

We treated 11 patients with the hypereosinophilic syndrome with imatinib and identified the molecular basis for the response.

RESULTS

Nine of the 11 patients treated with imatinib had responses lasting more than three months in which the eosinophil count returned to normal. One such patient had a complex chromosomal abnormality, leading to the identification of a fusion of the Fip1-like 1 (FIP1L1) gene to the PDGFRalpha (PDGFRA) gene generated by an interstitial deletion on chromosome 4q12. FIP1L1-PDGFRalpha is a constitutively activated tyrosine kinase that transforms hematopoietic cells and is inhibited by imatinib (50 percent inhibitory concentration, 3.2 nM). The FIP1L1-PDGFRA fusion gene was subsequently detected in 9 of 16 patients with the syndrome and in 5 of the 9 patients with responses to imatinib that lasted more than three months. Relapse in one patient correlated with the appearance of a T674I mutation in PDGFRA that confers resistance to imatinib.

CONCLUSIONS

The hypereosinophilic syndrome may result from a novel fusion tyrosine kinase - FIP1L1-PDGFRalpha - that is a consequence of an interstitial chromosomal deletion. The acquisition of a T674I resistance mutation at the time of relapse demonstrates that FIP1L1-PDGFRalpha is the target of imatinib. Our data indicate that the deletion of genetic material may result in gain-of-function fusion proteins.

Pathophysiology of thalassemia

Despite discoveries concerning the molecular abnormalities that led to the thalassemic syndromes, it still is not known how accumulation of excess unmatched alpha-globin in beta thalassemia and beta-globin in alpha thalassemia leads to red blood cell hemolysis in the peripheral blood, and in the beta thalassemias particularly, premature destruction of erythroid precursors in marrow (ineffective erythropoiesis). Oxidant injury may cause hemolysis, but there is no evidence that it causes ineffective erythropoiesis. Hemoglobin E/beta thalassemia is now a worldwide clinical problem. The reasons underlying the heterogeneity and occasional severity of the syndrome remain obscure. Ineffective erythropoiesis now appears to be caused by accelerated apoptosis, in turn caused primarily by deposition of alpha-globin chains in erythroid precursors. However, it is not clear how alpha-globin deposition causes apoptosis. The author uses new observations on the control of erythropoiesis to provide a framework for studying the enhanced thalassemic erythroid apoptosis.

The importance of erythroid expansion in determining the extent of apoptosis in erythroid precursors in patients with beta-thalassemia major

Beta-thalassemia major is characterized by ineffective erythropoiesis leading to severe anemia and extensive erythroid expansion. The ineffective erythropoiesis is in part due to accelerated apoptosis of the thalassemic erythroid precursors; however, the extent of apoptosis is surprisingly variable. To understand this variability as well as the fact that some patients undergoing allogeneic marrow transplantation are resistant to the myeloablative program, we attempted more quantitative analyses. Two groups of patients totaling 44 were studied, along with 25 healthy controls, and 7 patients with hemolysis and/or ineffective erythropoeisis. By 2 flow cytometric methods, thalassemic erythroid precursors underwent apoptosis at a rate that was 3 to 4 times normal. Because thalassemic marrow has between 5- to 6-fold more erythroid precursors than healthy marrow, this translated into an absolute increase in erythroid precursor apoptosis of about 15-fold above our healthy controls. In searching for the causes of the variability in thalassemic erythroid precursor apoptosis, we discovered tight direct correlations between the relative and absolute extent of apoptosis and the extent of erythroid expansion as measured either by the absolute number of marrow erythroid precursors or by serum soluble transferrin receptor levels. These results could mean that the most extreme rates of erythroid proliferation lend themselves to cellular errors that turn on apoptotic programs. Alternatively, extreme rates of erythroid hyperplasia and apoptosis might be characteristic of more severely affected patients. Lastly, extreme erythroid hyperplasia could generate such numbers of apoptotic erythroid precursors that marrow macrophages are overwhelmed, leaving more apoptotic cells in the sample.

A correlation of erythrokinetics, ineffective erythropoiesis, and erythroid precursor apoptosis in thai patients with thalassemia

The variety of patients with thalassemia in Thailand offers an opportunity to fully characterize the kinetic causes of the anemia and to study apoptosis of marrow erythroid precursors as a possible factor contributing to its severity. Kinetic studies showed that in hemoglobin H (HbH) disease, the extent of hemolysis, as well as the minimally ineffective erythropoiesis, usually falls within the compensatory capacity of normal erythropoiesis; therefore, anemia in patients with HbH partly represents a failure to expand erythropoiesis adequately. Hemoglobin Constant Spring (HbCS), a common variant of alpha thalassemia in Bangkok, causes more severe hemolysis and a distinct increase in ineffective erythropoiesis. Ineffective erythropoiesis plays a much more prominent role in beta thalassemia/hemoglobin E (beta-thal/HbE) disease, in which the variability of the anemia is puzzling. We compared mild and severe cases and found that patients with severe disease had a maximal marrow erythropoietic response that failed to compensate for very short survival of red blood cells and a marked quantitative increase in ineffective erythropoiesis. Analysis of apoptosis of marrow erythroid precursors done both on shipped samples and in Bangkok showed a moderate increase in HbH disease, consistent with the small increase in ineffective erythropoiesis. In patients with homozygous HbCS, there was a further increase in apoptosis, consistent with the additional increase in ineffective erythropoiesis. Patients with beta-thal/HbE disease had the most ineffective erythropoiesis and the most erythroid apoptosis. Thus, it appears that alpha-chain deposition in erythroid precursors, either alpha(A) or alpha(cs), leads to accelerated apoptosis and ineffective erythropoiesis.

Membrane phospholipid asymmetry in human thalassemia

Phospholipid asymmetry in the red blood cell (RBC) lipid bilayer is well maintained during the life of the cell, with phosphatidylserine (PS) virtually exclusively located in the inner monolayer. Loss of phospholipid asymmetry, and consequently exposure of PS, is thought to play an important role in red cell pathology. The anemia in the human thalassemias is caused by a combination of ineffective erythropoiesis (intramedullary hemolysis) and a decreased survival of adult RBCs in the peripheral blood. This premature destruction of the thalassemic RBC could in part be due to a loss of phospholipid asymmetry, because cells that expose PS are recognized and removed by macrophages. In addition, PS exposure can play a role in the hypercoagulable state reported to exist in severe beta-thalassemia intermedia. We describe PS exposure in RBCs of 56 comparably anemic patients with different genetic backgrounds of the alpha- or beta-thalassemia phenotype. The use of fluorescently labeled annexin V allowed us to determine loss of phospholipid asymmetry in individual cells. Our data indicate that in a number of thalassemic patients, subpopulations of red cells circulate that expose PS on their outer surface. The number of such cells can vary dramatically from patient to patient, from as low as that found in normal controls (less than 0.2%) up to 20%. Analysis by fluorescent microscopy of beta-thalassemic RBCs indicates that PS on the outer leaflet is distributed either over the entire membrane or localized in areas possibly related to regions rich in membrane-bound alpha-globin chains. We hypothesize that these membrane sites in which iron carrying globin chains accumulate and cause oxidative damage, could be important in the loss of membrane lipid organization. In conclusion, we report the presence of PS-exposing subpopulations of thalassemic RBC that are most likely physiologically important, because they could provide a surface for enhancing hemostasis as recently reported, and because such exposure may mediate the rapid removal of these RBCs from the circulation, thereby contributing to the anemia.

Removal of erythrocyte membrane iron in vivo ameliorates the pathobiology of murine thalassemia

Abnormal deposits of free iron are found on the cytoplasmic surface of red blood cell (RBC) membranes in beta-thalassemia. To test the hypothesis that this is of importance to RBC pathobiology, we administered the iron chelator deferiprone (L1) intraperitoneally to beta-thalassemic mice for 4 wk and then studied RBC survival and membrane characteristics. L1 therapy decreased membrane free iron by 50% (P = 0.04) and concomitantly improved oxidation of membrane proteins (P = 0.007), the proportion of RBC gilded with immunoglobulin (P = 0.001), RBC potassium content (P < 0.001), and mean corpuscular volume (P < 0.001). Osmotic gradient ektacytometry confirmed a trend toward improvement of RBC hydration status. As determined by clearance of RBC biotinylated in vivo, RBC survival also was significantly improved in L1-treated mice compared with controls (P = 0.007). Thus, in vivo therapy with L1 removes pathologic free iron deposits from RBC membranes in murine thalassemia, and causes improvement in membrane function and RBC survival. This result provides in vivo confirmation that abnormal membrane free iron deposits contribute to the pathobiology of thalassemic RBC.

Pathophysiology of the thalassemias. The Albion Walter Hewlett Award presentation

The Albion Walter Hewlett Award (named for Professor of Medicine and Chair of the Stanford Department of Medicine 1916-1925) recognizes a role model, accomplished in discovery of the biological sciences and at the same time a consummate and compassionate physician. In introductory remarks, Dr. Stanley L. Schrier, Professor of Medicine (Hematology), the tenth recipient of the Award, indicated that the person so identified is no longer a viable model in academic medicine. The loss of this sort of person is serious because this appropriately trained physician-investigator was uniquely positioned to study pathophysiology, defined as the processes by which disordered biology produces disease. He used his own studies on the clinical manifestations of the thalassemias to clarify what he meant by pathophysiology. Thus he and his colleagues first defined membrane material properties of alpha and beta thalassemic RBC membranes and the states of hydration of alpha and beta thalassemic RBC and found them to be strikingly divergent. The biochemical counterparts of these alterations proved to be the accumulation of the excess unmatched partially oxidized globin chains on the membrane skeleton. In vitro studies with chemical oxidants selectively oxidized alpha and beta globin chains which then attached to the RBC membrane skeleton and reproduced the membrane material properties characteristic of beta and alpha thalassemia respectively. Many of these alterations had occurred prior to the reticulocyte stage so that pursuit of pathophysiology shifted to studies of marrow erythroid precursors, and it was shown that in beta thalassemia major there was accelerated programmed cell death as well as defective assembly of the membrane skeleton.

Improved perfusion with rt-PA and hirulog in a rabbit model of embolic stroke

We conducted a study using diffusion-weighted (DWI) and perfusion-weighted (PWI) magnetic resonance imaging (MRI) to evaluate the efficacy of thrombolysis in an embolic stroke model with recombinant tissue plasminogen activator (rt-PA) and hirulog, a novel direct-acting antithrombin. DWI can identify areas of ischemia minutes from stroke onset, while PWI identifies regions of impaired blood flow. Right internal carotid arteries of 36 rabbits were embolized using aged heterologous thrombi. Baseline DWI and PWI scans were obtained to confirm successful embolization. Four animals with no observable DWI lesion on the initial scan were excluded; therefore, a total of 32 animals were randomized to one of three treatment groups: rt-PA (n = 11), rt-PA plus hirulog (n = 11), or placebo (n = 10). Treatment was begun 1 h after stroke induction. Intravenous doses were as follows: rt-PA, 5 mg/kg over 0.5 h with 20% of the total dose given as a bolus; hirulog, 1 mg/kg bolus followed by 5 mg/kg over 1 h. MRI was performed at 2, 3, and 5 h following embolization. Six hours after embolization, brains were harvested, examined for hemorrhage, then prepared for histologic analysis. The rt-PA decreased fibrinogen levels by 73%, and hirulog prolonged the aPTT to four times the control value. Posttreatment areas of diffusion abnormality and perfusion delay were expressed as a ratio of baseline values. Significantly improved perfusion was seen in the rt-PA plus hirulog group compared with placebo (normalized ratios of the perfusion delay areas were as follows: placebo, 1.58, 0.47-3.59; rt-PA, 1.12, 0.04-3.95; rt-PA and hirulog, 0.40, 0.02-1.08; p < 0.05). Comparison of diffusion abnormality ratios measured at 5 h showed trends favoring reduced lesion size in both groups given rt-PA (normalized ratios of diffusion abnormality areas were as follows: placebo, 3.69, 0.39-15.71; rt-PA, 2.57, 0.74-5.00; rt-PA and hirulog, 1.95, 0.33-6.80; p = 0.32). Significant cerebral hemorrhage was observed in one placebo, two rt-PA, and three rt-PA plus hirulog treated animals. One fatal systemic hemorrhage was observed in each of the rt-PA groups. We conclude that rt-PA plus hirulog improves cerebral perfusion but does not necessarily reduce cerebral injury. DWI and PWI are useful methods for monitoring thrombolysis.

The unusual pathobiology of hemoglobin constant spring red blood cells

Hemoglobin Constant Spring (HbCS) is the most common nondeletional alpha-thalassemic mutation and is an important cause of HbH-like disease in Southeast Asia. HbCS variants have an almost normal mean cell volume (MCV) and the anemia is more severe when compared with other alpha-thalassemic variants. We explored the pathobiology of HbCS red blood cells (RBCs) because the underlying cause(s) of this MCV "normalizing" effect of HbCS and the more severe anemia are not fully explained. HbCS containing RBCs are distinctly overhydrated relative to deletional alpha-thalassemia variants, and the derangement of volume regulation and cell hydration occurs early in erythroid maturation and is fully expressed at the reticulocyte stage. Furthermore, the membrane rigidity and membrane mechanical stability of HbCS containing RBCs is increased when compared with HbH and alpha-thalassemia-1 trait RBCs. In seeking the cause(s) underlying these cellular alterations we analyzed membranes from HbCS and deletional alpha-thalassemic variants and found that in addition to oxidized beta-globin chains, oxidized alpha cs-globin chains are also associated with the membranes and their skeletons in HbCS containing RBCs. We propose that the membrane pathology of HbCS variants is caused by combination of the deleterious effects induced by membrane-bound oxidized alpha cs- and beta-globin chains. The membrane alterations induced by alpha cs chains are more akin to those induced by beta A-globin chains than those induced by the alpha A-globin chains that accumulate in the beta-thalassemias. Thus, each globin chain, alpha cs, alpha A, beta A, appears to produce its own form of membrane perturbation.

Pathobiology of thalassemic erythrocytes

Although study of the thalassemias has focussed on possible cure or amelioration by genetic techniques, considerable progress has been made in understanding the underlying pathobiology of these diseases. Better control of childhood infectious diseases has led to a clearer understanding of the frequency and clinical severity of some of these disorders. The striking differences between alpha- and beta-thalassemia are now well documented and the role of oxidant attack in the pathobiology is becoming clearer. Some authors believe that severe beta-thalassemia induces a hypercoagulable state that could be partially caused by scrambling of the phospholipid bilayer of affected erythrocytes. There is growing appreciation that double heterozygosity for hemoglobin E/beta-thalassemia, while causing variable anemia, can produce a clinical condition as severe as Cooley's anemia (beta-thalassemia major). Anemia severity may be related to the extent of oxidant attack on the unstable hemoglobin E. Studies of the hemoglobin Constant Spring variants demonstrate the consequences of accumulating excess unmatched beta globin as well as the unique alpha CS. Studies on marrow erythroid precursors in the beta-thalassemias have already shown accelerated programmed cell death and abnormal assembly of membrane proteins. Such studies in the future will likely further delineate the underlying differences between alpha- and beta-thalassemias.

Abnormal assembly of membrane proteins in erythroid progenitors of patients with beta-thalassemia major

The life threatening anemia in beta-thalassemia major (Cooley's anemia) is characterized by profound intramedullary lysis, the cause of which is incompletely understood. Using marrow obtained from beta thalassemia major patients undergoing allogeneic bone marrow transplantation in Pesaro Italy, it became possible to directly study the mechanism of the intramedullary hemolysis. Based on our previous studies, we hypothesized that the unmatched alpha globin chains would interfere with normal assembly of erythroid precursor membrane proteins. Patient and control erythroid precursors were reacted with monospecific polyclonal rabbit antibodies directed against spectrin, band 3, and band 4.1 and with a monoclonal anti-alpha globin chain antibody. Using laser confocal fluorescence microscopy, normal erythroid precursors show no alpha globin chain accumulation and exhibited uniformly smooth rim fluorescence of the three membrane proteins. In some thalassemic precursors, spectrin appeared to interact with large alpha globin accumulations, and in many of these cells the spectin appeared clumped and discontinuous. Band 4.1 interacted strongly with accumulations of alpha globin in thalassemic precursors to produce bizarrely clumped zones of abnormal band 4.1 distribution. Band 3 was incorporated smoothly into thalassemic erythroblast membranes. However, the proerythroblasts and basophilic erythroblasts were significantly deficient in band 3. Thus, accumulations of alpha globin in beta-thalassemia major colocalized with and disrupt band 4.1 and spectrin assembly into the membrane. The cause of deficient band 3 incorporation into thalassemic proerythroblast membranes remains unknown. These profound membrane alterations would likely contribute to the intramedullary lysis seen in Cooley's anemia.

The instability of the membrane skeleton in thalassemic red blood cells

The thalassemias are a heterogeneous group of disorders characterized by accumulation either of unmatched alpha or beta globin chains. These in turn cause the intramedullary and peripheral hemolysis that leads to varying anemia. A partial explanation for the hemolysis came our of our studies on material properties that showed that beta-thalassemia (beta-thal) intermedia ghosts were very rigid but unstable. A clue to this instability came from the observation that the spectrin/band 3 ratio was low in red blood cells (RBCs) of splenectomized beta-thal intermedia patients. The possible explanations for the apparent decrease in spectrin content included deficient or defective spectrin synthesis in thalassemic erythroid precursors or globin chain-induced membrane changes that lead to spectrin dissociation from the membrane during ghost preparation. To explore the latter alternative, samples from different thalassemic variants were obtained, ie, beta-thal intermedia, HbE/beta-thal, HbH (alpha-thal-1/alpha-thal-2), HbH/Constant Spring (CS), and homozygous HbCS/CS. We searched for the presence of spectrin in the first lysate of the standard ghost preparation. Normal individuals and patients with autoimmune hemolytic anemia, sickle cell anemia, and anemia due to chemotherapy served as controls. Using gradient sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis, no spectrin was detected in identical aliquots of the supernatants of normals and these control samples. Varying amounts of spectrin were detected in the first lysate supernatants of almost all thalassemic patients. The identification of spectrin was confirmed by Western blotting using an affinity-purified, monospecific, rabbit polyclonal antispectrin antibody. Relative amounts of spectrin detected were as follows in decreasing order: splenectomized beta-thal intermedia including HbE/beta-thal; HbCS/CS; nonsplenectomized beta-thal intermedia, HbH/CS; and, lastly, HbH. These findings were generally confirmed when we used an enzyme-linked immunosorbent assay technique to measure spectrin in the first lysate. Subsequent analyses showed that small amounts of actin and band 4.1 also appeared in lysates of thalassemic RBCs. Therefore, the three major membrane skeletal proteins are, to a varying degree, unstably attached in severe thalassemia. From these studies we could postulate that membrane association of abnormal or partially oxidized alpha-globin chains has a more deleterious effect on the membrane skeleton than do beta-globin chains.

Defective assembly of membrane proteins in erythroid precursors of beta-thalassemic mice

beta-Thalassemic mice provide a useful model for studying the pathophysiology of human beta-thalassemia in that one can perform experiments that are difficult to perform in humans. The ease of access to beta-thalassemic mouse marrow provided the opportunity to explore the cause of the ineffective erythropoiesis that characterizes severe beta-thalassemia in mouse and man. We hypothesized that the accumulation of excess alpha-globin might interfere with the normal assembly of red blood cell (RBC) membrane proteins, thus contributing to the severe intramedullary lysis. Femoral marrow was obtained from normal and beta-thalassemic mice, and RBC precursors were purified (> 90%) by panning and harvesting CD45- cells. The assembly of RBC membrane proteins was assessed by observing immunofluorescence patterns obtained on fixed permeabilized precursors using rabbit polyclonal antibodies directed against human spectrin, and band 4.1, and murine band 3. The distribution of the proteins was shown with a fluorescein-tagged goat antirabbit antibody. In contrast to normal mice, about 30% of intermediate and late stage erythroblasts in beta-thalassemic mice appear abnormal. Neither spectrin nor band 4.1 formed crisp rim fluorescence in these erythroid precursors of thalassemic mice, whereas assembly of band 3 appeared normal. Therefore, the assembly of membrane skeletal proteins is abnormal in murine beta-thalassemic erythroid precursors perhaps because of the deposition of unmatched alpha-globin chains.

Thalassemia: pathophysiology of red cell changes

The thalassemias are extremely heterogeneous in terms of their clinical severity, and their underlying pathophysiology relates directly to the extent of accumulation of excess unmatched globin chains: alpha in beta thalassemia and beta in the alpha thalassemias. However, the accumulation of each separate globin chain affects red cell membrane material properties and the state of red cell hydration very differently. These observations presumably account for the varying extent of ineffective erythropoiesis and peripheral blood hemolysis in the major variants of thalassemia. The thalassemias are a worldwide group of inherited disorders of globin-chain synthesis that developed in multiple geographic regions, probably because they provided partial protection against malaria. In normal assembly of adult hemoglobin (HbA-alpha 2 beta 2), alpha and beta globin are synthesized by genes on different chromosomes, whereas heme is synthesized primarily on mitochondria. The synthesis of these chains is very tightly coordinated so that the ratio of alpha globin to beta globin (beta in this case including the beta-like globins delta and gamma) is normally 1 +/- 0.05. Furthermore, specific erythroid proteases are designed to attack and destroy excess alpha or beta globin chains, demonstrating the deleterious impact of the accumulation of excess unmatched globin chains. In beta thalassemia, production of beta globin decreases and excess alpha globin accumulates. In alpha thalassemia, on the other hand, this process occurs in reverse. Perhaps in these disorders more than any others, molecular biologists have documented the deletional and transcriptional events leading to diminished synthesis of specific classes of globin chains.(ABSTRACT TRUNCATED AT 250 WORDS)

Accelerated programmed cell death (apoptosis) in erythroid precursors of patients with severe beta-thalassemia (Cooley's anemia)

The profound and life-threatening anemia in patients with Cooley's anemia is ascribed primarily to intramedullary hemolysis (ineffective erythropoiesis), the cause of which is obscure. Based on prior morphologic data showing nuclear abnormalities, we hypothesized that accelerated apoptosis could occur in these erythroid precursors. The highly successful bone marrow (BM) transplantation program for patients with Cooley's anemia provided us with a unique opportunity to test this hypothesis. We obtained pretransplantation BM aspiration samples from patients undergoing BM transplantation in Pesaro, Italy and from their allogeneic donors. The erythroid precursors were isolated using ficoll sedimentation and then panning selecting fro CD45- cells. Cytospin and Giemsa staining showed that the separation provided greater than 90% erythroblasts. Five million of these erythroblasts were lysed and their DNA was isolated. There were obvious ladder patterns of DNA breakdown products in beta-thalassemia major samples, with less occurring in beta-thalassemia trait. Normal individuals showed only a slight smear of breakdown of DNA. These results indicate there is enhanced apoptosis in the erythroblasts in the BMs of Cooley's anemia patients. This finding might partially explain why most of these erythroblasts never survive to become mature erythrocytes.

Transmembrane redistribution of phospholipids of the human red cell membrane during hypotonic hemolysis

The transmembrane distribution of spin-labeled phospholipids was measured in human erythrocytes before and after hypotonic hemolysis by electron paramagnetic resonance. With a first series of partially water soluble probes a complete randomization of phosphatidylcholine, phosphatidylethanolamine, phosphatidylserine and sphingomyelin analogues was achieved when cells were resealed in the absence of Mg-ATP or when the aminophospholipid translocase was inhibited by vanadate or calcium. If the ghosts were resealed with Mg-ATP inside, the transmembrane asymmetry of the aminophospholipids was reestablished. With long chain insoluble spin-labeled lipids complete randomization was obtained with the phosphatidylcholine analogue but even in the presence of vanadate only a small percentage (approx. 15%) of the spin-labeled phosphatidylserine flopped to the outer monolayer and comparable percentage of the spin-labeled sphingomyelin flipped to the inner monolayer, indicating a hierarchy in the phospholipid redistribution for these water insoluble lipids during hemolysis. The mechanism by which a selective randomization takes place is not known. It may involve phosphatidylserine-protein interactions in the inner leaflet and sphingomyelin-cholesterol or sphingomyelin-sphingomyelin interaction in the outer leaflet.

Globin-chain specificity of oxidation-induced changes in red blood cell membrane properties

We have previously shown that excess unpaired alpha- and beta-globin chains in severe alpha- and beta-thalassemia interacting with the membrane skeleton induce different changes in membrane properties of red blood cells (RBCs) in these two phenotypes. We suggest that these differences in membrane material behavior may reflect the specificity of the membrane damage induced by alpha- and beta-globin chains. To further explore this hypothesis, we sought in vitro models that induce similar membrane alterations in normal RBCs. We found that treatment of normal RBCs with phenylhydrazine produced rigid and mechanically unstable membranes in conjunction with selective association of oxidized alpha-globin chains with the membrane skeleton, features characteristic of RBCs in severe beta-thalassemia. Methylhydrazine, in contrast, induced selective association of oxidized beta-globin chains with the membrane skeleton and produced rigid but hyperstable membranes, features that mimicked those of RBCs in severe alpha-thalassemia. These findings suggest that consequences of oxidation induced by globin chains are quite specific in that those agents that cause alpha-globin chain accumulation at the membrane produce rigid but mechanically unstable membranes, whereas membrane accumulation of beta-globin chains results in rigid but mechanically stable membranes. These in vitro experiments lend further support to the hypothesis that membrane-associated alpha- and beta-chains induce oxidative damage to highly specific different skeletal components and that the specificity of this skeletal damage accounts for the differences in material membrane properties of these oxidatively attacked RBCs and perhaps of alpha- and beta-thalassemic RBCs as well.

Characterization and comparison of the red blood cell membrane damage in severe human alpha- and beta-thalassemia

The aim of the present work was to understand the pathophysiology of the severe human thalassemias as represented by beta-thalassemia intermedia and hemoglobin (Hb) H (alpha-thalassemia) disease. We have previously shown that the material properties of the red blood cell (RBC) and its membrane differ in severe alpha- and beta-thalassemia, and we now show that this difference is probably caused by accumulation of alpha-globin chains at the cytoskeleton in beta-thalassemia, whereas beta-globin chains are associated with the cytoskeleton in alpha-thalassemia. In both alpha- and beta-thalassemia, some of these globin chains have become oxidized as evidenced by loss of the free thiols. Furthermore, there is similar evidence of oxidation of protein 4.1 in beta-thalassemia, whereas beta-spectrin appears to be subject to oxidation in alpha-thalassemia. These observations support the idea that the association of partly oxidized globin chains with the cytoskeleton results in oxidation of adjacent skeletal proteins. The abnormality of protein 4.1 in beta-thalassemia is consistent with a prior observation, and is also in accord with the known importance of protein 4.1 in maintenance of membrane stability, a property that is abnormal in beta-thalassemic membranes.

Oxidative red blood cell membrane injury in the pathophysiology of severe mouse beta-thalassemia

In severe human beta-thalassemia, the pathophysiology relates to accumulation of excess alpha-globin chains at the membrane. One hypothesis is that membrane-associated alpha-globin by virtue of it's iron or hemichromes produces oxidation of adjacent membrane proteins. The availability of a mouse model of severe beta-thalassemia, as well as a transgenic (thalassemic-sickle) mouse that expresses 12% of human beta s-chain, has allowed us to study the effect of graded accumulation of alpha-chains at the red blood cell (RBC) membrane on the clinical status of the animal and on the material properties of its RBCs. Proteins from control, beta-thalassemic, and transgenic mouse RBC membranes were analyzed for evidence of oxidation, as measured by thiol-disulfide exchange chromatography, which detects intramolecular sulfhydryl oxidation. Ratios of oxidized globin to protein 7 were calculated and increased amounts were seen in thalassemic mice as compared with control mice and transgenic mice. Furthermore, there were increased amounts of thiol-free protein 4.1 in the thalassemic mice, compared with very small amounts in the control mice and intermediate amounts in the transgenic mice. Membrane mechanical stability as assessed by ektacytometry showed that the thalassemic mouse RBCs were markedly unstable. Transgenic mouse RBCs showed intermediate levels of membrane instability compared with the controls. We propose that this oxidized globin, in conjunction with oxidized protein 4.1, accounts (at least in part) for membrane instability. A 12% increase in beta s-globin chain synthesis (by decreasing excess globin available) confers considerable protection against both oxidative damage and the consequent membrane instability.

Mechanisms of amphipath-induced stomatocytosis in human erythrocytes

We studied stomatocytosis induced in human red blood cells (RBC) by vinblastine and chlorpromazine, monitoring the movements of spin-labeled phosphatidylcholine (PC*) and sphingomyelin (SM*) by electron spin resonance (ESR) spectroscopy. This technique allows determination of the fraction of labeled lipids, respectively, on the external leaflet, on the cytosol face, or trapped in endocytic vacuoles. Both vinblastine and chlorpromazine produce a time- and concentration-dependent stomatocytic shape change, which is paralleled by a shift of approximately 10% to 33% of outer leaflet SM* and PC* inward. Of this amount, 8% to 12% was trapped in endocytic vacuoles and 8% to 19% had flipped to the inner leaflet. Vanadate, while inhibiting the stomatocytosis, did not block the flip of either SM* or PC* to the inner leaflet. To explain the inhibiting effect of vanadate, as well as the adenosine triphosphate (ATP) requirement for drug-induced stomatocytosis, we propose the following model: (1) addition of amphipath partially scrambles the bilayer; and (2) the flop of phosphatidylserine (PS) and phosphatidylethanolamine (PE) to the outer leaflet provides substrate for the aminophospholipid translocase (APLT), which flips back PS and PE inward faster than PC or SM can diffuse outward--thereby producing inner layer expansion or stomatocytosis. This role of APLT accounts for the vanadate inhibition of amphipath stomatocytosis. However, the vanadate effect can be overcome by increasing the amphipath concentration, which at such levels probably passively expands the inner leaflet.