Sickle-cell anemia: molecular and cellular bases of therapeutic approaches (first of three parts)

Sickle Cell Hemoglobin "Drugged" with Cyclic Peptides Is Aggregation Incompetent

Sickle cell disease (SCD) is a monogenic blood disorder associated with a mutation in the hemoglobin subunit β gene encoding for the β-globin of normal adult hemoglobin (HbA). This mutation transcribes into a Glu-β6 → Val-β6 substitution in the β-globins, inducing the polymerization of this hemoglobin form (HbS) when in the T-state. Despite advances in stem cell and gene therapy, and the recent approval of a new antisickling drug, therapeutic limitations persist. Herein, we demonstrate through molecular dynamics and umbrella sampling, that (unrestrained) blockage of the hydrophobic pocket involved in the lateral contact of the HbS fibers by 5-mer cyclic peptides, recently proposed as SCD aggregation inhibitors (Neto, V.; J. Med. Chem. 2023, 66, 16062-16074), is enough to turn the dimerization of HbS thermodynamically unfavorable. Among these potential drugs, some exhibit an estimated pocket abandonment probability of around 15-20% within the simulations' time frame, and an impressive specificity toward the mutated Val-β6. Additionally, we show that the dimerization can be thermodynamically unfavored by blocking a nearby region while the pocket remains vacant. These results are compared with curcumin, an antisickling molecule and a pan-assay interference compound, with a good binding affinity for different proteins and protein domains. Our results confirm the potential of some of these cyclic peptides as antisickling drug candidates to reduce the concentration of aggregation-competent HbS.

Cyclic Peptides as Aggregation Inhibitors for Sickle Cell Disease

Sickle cell disease is a missense genetic disorder characterized by the aggregation of deoxy-HbS into helical fibers that distort erythrocytes into a sickle-like shape. Herein, we investigate, through molecular dynamics, the effect of nine 5-mer cyclic peptides (CPs), tailor-designed to block key lateral contacts of the fibers. Our results show that the CPs bind orthogonally to the main HbS pocket involved in the latter contacts, with some revealing exceedingly long residence times. These CPs display moderate to high specificity, exhibiting molecular recognition events even at a HbS/CP (1:1) ratio. A much lower HbS-CP binding free energy, longer residence times, and higher specificity are also found relative to a previously reported CP with modest in vitro antisickling activity. These results indicate that some of these CPs have the potential to reduce the concentration of aggregation-competent deoxy-HbS, precluding or delaying the formation of lateral contact at the homogeneous nucleation stage.

Sickle cell disease: Contributing factors and radiological assessments

Sickle Cell Disease (SCD) is genetically described as an autosomal blood disorder resulting from the presence of a mutated form of hemoglobin. Morbidity, frequency of crisis, degree of anemia, and organ systems involved vary considerably per patient. Dental health professionals and other specialists commonly request comprehensive medical consultations prior to performing complex periodontal, endodontic, and surgical procedures. In order to have successful dental outcomes and minimize posttreatment dental complications, relevant disease indicators are noted. This review is to raise awareness of the impact of oral diseases in patients with sickle cell disease and to emphasize the importance of full medical disclosure, radiographic interpretation, and a well-documented medical history, and a well-written consultation which can guide treatment planning and greatly improve the course of dental treatment.

Antioxidant-Rich Nutraceutical as a Therapeutic Strategy for Sickle Cell Disease

Sickle cell disease (SCD) is a genetically inherited disease in which the "SS" individual possesses two copies of the abnormal beta-globin gene. This disease is one of the most dominant genetic diseases in the world. SCD is marked by the propensity of red cell hemoglobin to polymerize and distort the red cell from a biconcave disk shape into a sickle shape, resulting in a typical vaso-occlusive episode and accelerated hemolysis. Plants are rich sources of bioactive compounds that are promising anti-sickling agents to scavenge free radicals, thereby ensuring oxidative balance. The current review highlights the potential therapeutic benefits of antioxidant-rich nutraceutical in the treatment and management of sickle cell disease. The anti-sickling potential of nutraceutical is attributed to the presence of antioxidant bioactive chemicals such as alkaloids, polyphenols, vitamins, and minerals, which acts as scavengers of free radicals that prevent oxidative damage of the hemoglobin and prevent hemolysis, facilitating longer erythrocyte lifespan. The challenges of current therapies for SCD and future directions are also discussed.KEY TEACHING POINTSSickle cell disease is a genetically inherited disease in which SS individuals possess two copies of the abnormal beta-globin gene.Oxidative stress contributes to the pathophysiology of secondary dysfunction in sickle cell patients.Antioxidants can play a vital role in maintaining a balance between oxidant and antioxidant defense systems.Nutraceutical rich in antioxidants such as alkaloids, polyphenols, vitamins, and minerals is potential therapeutic agents for sickle cell disease.An antioxidant-rich nutraceutical may act to reduce vaso-occlusive crises.

Bulk volume susceptibility difference between deoxyhemoglobin and oxyhemoglobin for HbA and HbS: A comparative study

PURPOSE

Sickle cell anemia is a blood disorder that alters the morphology and the oxygen affinity of the red blood cells. Cerebral oxygen extraction fraction measurements using quantitative BOLD contrast have been used for assessing inadequate oxygen delivery and the subsequent risk of ischemic stroke in sickle cell anemia. The BOLD signal in MRI studies relies on Δ χ do , the bulk volume susceptibility difference between fully oxygenated and fully deoxygenated blood. Several studies have measured Δ χ do for normal hemoglobin A (HbA). However, it is not known whether the value is different for sickle hemoglobin. In this study, Δ χ do was measured for both HbA and sickle hemoglobin.

METHODS

Six sickle cell anemia patients and 6 controls were recruited. Various blood oxygenation levels were achieved through in vivo manipulations to keep the blood close to its natural state. To account for the differences in oxygen affinity, Hill's equations were used to translate partial pressure of oxygen to oxygen saturation for HbA, sickle hemoglobin, and fetal hemoglobin (HbF) separately. The pH and PCO₂ corrections were performed. Temperature and magnetic field drift were controlled for. A multivariate generalized linear mixed model with random participant effect was used.

RESULTS

Assuming that Δ χ do is similar for HbA and HbF and that Δ χ metHb is 5/4 of Δ χ do for HbA, it was found that the Δ χ do values for HbA and sickle hemoglobin were not statistically significantly different from each other.

CONCLUSION

The same Δ χ do value can be used for both types of hemoglobin in quantitative BOLD analysis.

Diagnosing sickle cell disease and iron deficiency anemia in human blood by Raman spectroscopy

This work proposed the diagnosis of iron deficiency anemia (IDA) and sickle cell disease (SCD) in human blood caused by iron deficiency and hemoglobin S (HbS), which are among the most common anemias, by means of Raman spectroscopy. Whole blood samples from patients diagnosed with IDA and HbS, as well as from normal subjects (HbA), were obtained and submitted to Raman spectroscopy (830 nm, 150 mW, 400-1800 cm^-1 spectral range, 4 cm^-1 resolution). Difference spectra of IDA-HbA showed spectral features of hemoglobin with less intensity in the IDA, whereas the difference spectra of SCD-HbA showed spectral features of deoxyhemoglobin increased and of oxyhemoglobin decreased in SCD. An exploratory analysis by principal components analysis (PCA) showed that the peaks referred to oxy- and deoxyhemoglobin markedly differentiated SCD and HbA, as well as the increased amount of hemoglobin features in the SCD group, suggesting increased erythropoiesis. The IDA group showed hemoglobin features with lower intensities as well as peaks referred to the iron bonding to the porphyrin ring with reduced intensities when compared to the HbA. Discriminant analysis based on partial least squares (PLS-DA) and PCA (PCA-DA) showed that the IDA and SCD anemias could be discriminated from the HbA spectra with 95.0% and 93.8% of accuracy, for the PLS and PCA respectively, with sensitivity/specificity of 93.8%/95.7% for the PLS-DA model. The iron depletion and the sickling of erythrocytes could be identified by Raman spectroscopy and a spectral model based on PLS accurately discriminated these IDA and SCD samples from the normal HbA.

From fiction to science: clinical potentials and regulatory considerations of gene editing

Gene editing technologies such as CRISPR/Cas9 have emerged as an attractive tool not only for scientific research but also for the development of medicinal products. Their ability to induce precise double strand breaks into DNA enables targeted modifications of the genome including selective knockout of genes, correction of mutations or precise insertion of new genetic material into specific loci. Gene editing-based therapies hold a great potential for the treatment of numerous diseases and the first products are already being tested in clinical trials. The treatment indications include oncological malignancies, HIV, diseases of the hematopoietic system and metabolic disorders. This article reviews ongoing preclinical and clinical studies and discusses how gene editing technologies are altering the gene therapy landscape. In addition, it focusses on the regulatory challenges associated with such therapies and how they can be tackled during the drug development process.

"Sickling" in vertebrates: Animal studies vs. sickle cell disease

Before the description of sickled cells in humans, erythrocytes of normal deer were found to deform, or sickle in vitro. Sickling required oxygenation and alkalization; human erythrocytes sickle because their abnormal sickle hemoglobin (HbS) polymerizes following deoxygenation in vivo and in vitro. HbS and some deer hemoglobins polymerize because of specific amino acid contacts between hemoglobin beta-globin chains, although different amino acid residues form the contact points of the polymer. Hemoglobin precipitation is found in other vertebrates. Most often it is a benign in vitro phenomenon. Natural selection established the balanced polymorphism accounting for the high prevalence of HbS where malaria is endemic. A similar selective advantage for "sickling" animal hemoglobins is unproven. The mean corpuscular hemoglobin concentration is about 30 to 35 g/dL. Perhaps during in vitro studies of susceptible animal hemoglobins, minor changes in buffer pH, osmolality and the ligand state of the molecule increases mean cell hemoglobin concentration beyond its solubility limit allowing precipitation.

Cholelithiasis and its complications in sickle cell disease in a university hospital

INTRODUCTION

The clinical manifestations of sickle cell disease are related to the polymerization of hemoglobin S. The chronic hemolysis caused by this condition often causes the formation of gallstones that can migrate and block the common bile duct leading to acute abdomen.

OBJECTIVE

This study aimed to evaluate the profile of patients with sickle cell disease and cholelithiasis.

METHODS

Patients with sickle cell disease were separated into groups according to the presence or absence of cholelithiasis. Socioepidemiological and clinical characteristics, such as gender, age, use of hydroxyurea and the presence of other hemoglobinopathies were researched in the medical records of patients.

RESULTS

A hundred and seven patients with sickle cell anemia were treated at the institution. Of these, 27 (25.2%) had cholelithiasis. The presence of cholelithiasis was higher in the 11-29 age group than in younger than 11 years and over 29 years. No association was found for the presence of cholelithiasis with gender, use of hydroxyurea or type of hemoglobinopathy (hemoglobin SS, hemoglobin SC or sickle beta-thalassemia). Sixteen of the patients had to be submitted to cholecystectomy with 14 of the surgeries being performed by laparoscopy. Complications were observed in three patients and one patient died for reasons unrelated to the surgery.

CONCLUSION

A quarter of patients with sickle cell disease had gallstones, more commonly in the 11- to 29-year age range. Patients should be monitored from childhood to prevent cholelithiasis with preoperative, intra-operative and postoperative care being crucial to reduce the risk of complications in these patients.

Dynamic deformability of sickle red blood cells in microphysiological flow

In sickle cell disease (SCD), hemoglobin molecules polymerize intracellularly and lead to a cascade of events resulting in decreased deformability and increased adhesion of red blood cells (RBCs). Decreased deformability and increased adhesion of sickle RBCs lead to blood vessel occlusion (vaso-occlusion) in SCD patients. Here, we present a microfluidic approach integrated with a cell dimensioning algorithm to analyze dynamic deformability of adhered RBC at the single-cell level in controlled microphysiological flow. We measured and compared dynamic deformability and adhesion of healthy hemoglobin A (HbA) and homozygous sickle hemoglobin (HbS) containing RBCs in blood samples obtained from 24 subjects. We introduce a new parameter to assess deformability of RBCs: the dynamic deformability index (DDI), which is defined as the time-dependent change of the cell's aspect ratio in response to fluid flow shear stress. Our results show that DDI of HbS-containing RBCs were significantly lower compared to that of HbA-containing RBCs. Moreover, we observed subpopulations of HbS containing RBCs in terms of their dynamic deformability characteristics: deformable and non-deformable RBCs. Then, we tested blood samples from SCD patients and analyzed RBC adhesion and deformability at physiological and above physiological flow shear stresses. We observed significantly greater number of adhered non-deformable sickle RBCs than deformable sickle RBCs at flow shear stresses well above the physiological range, suggesting an interplay between dynamic deformability and increased adhesion of RBCs in vaso-occlusive events.

Musculoskeletal Manifestations of Sickle Cell Disease: A Review

Sickle cell disease (SCD) is an inherited disorder of abnormal haemoglobin commonly encountered in the West African sub-region. It has varied osteoarticular and non-osseous complications that mimic some surgical conditions. The most common orthopaedic complications include avascular necrosis, osteomyelitis, septic arthritis, etc. A cautious and painstaking evaluation is required in handling these patients. Acute care and anaesthetic precautions are vital in ensuring an uneventful postoperative period.

Protein carbamylation in kidney disease: pathogenesis and clinical implications

Carbamylation describes a nonenzymatic posttranslational protein modification mediated by cyanate, a dissociation product of urea. When kidney function declines and urea accumulates, the burden of carbamylation naturally increases. Free amino acids may protect proteins from carbamylation, and protein carbamylation has been shown to increase in uremic patients with amino acid deficiencies. Carbamylation reactions are capable of altering the structure and functional properties of certain proteins and have been implicated directly in the underlying mechanisms of various disease conditions. A broad range of studies has demonstrated how the irreversible binding of urea-derived cyanate to proteins in the human body causes inappropriate cellular responses leading to adverse outcomes such as accelerated atherosclerosis and inflammation. Given carbamylation's relationship to urea and the evidence that it contributes to disease pathogenesis, measurements of carbamylated proteins may serve as useful quantitative biomarkers of time-averaged urea concentrations while also offering risk assessment in patients with kidney disease. Moreover, the link between carbamylated proteins and disease pathophysiology creates an enticing therapeutic target for reducing the rate of carbamylation. This article reviews the biochemistry of the carbamylation reaction, its role in specific diseases, and the potential diagnostic and therapeutic implications of these findings based on recent advances.

Skeletal scintigraphy manifestations of hematologic disorders

Skeletal manifestations are common in hematologic disorders. Benign entities such as Sickle cell disease develop microvascular embolization causing skeletal crisis. Leukemia, acute myeloblastic or lymphoblastic may develop bone marrow infarcts. Compromised immunity makes them susceptible to secondary infection leading to osteomyelitis or septic arthritis. Exposure to steroids may lead to osteonecrosis in these cases. Presented here is an atlas of various scintigraphic skeletal manifestations encountered over the past 10 years, in hematologic disorders.

REALISTIC PATTERNS OF INHERITANCE OF SICKLE-CELL ANEMIA GENE: A THEORETICAL APPROACH

We derive equations which describe the reproductive interactions of human individuals in a population governed by their genotype structure. The model assumes reproduction within a specified age interval and the approach is basically theoretical. Some fundamental properties of the renewal equations as well as the interaction function are listed. It is significant that genetic screening prior to marriage still remains the principal preventive measure in order to avoid an increase in the population of those suffering from genetic defects.

Theoretical population dynamics model of a genetically transmitted disease: sickle-cell anaemia

We formulate a realistic demographic model that captures the pattern of inheritance of the S gene, which is responsible for the most common genetic defect, namely, sickle-cell anaemia (SCA), using general pair formations. The model equation is implicitly solved via the Laplace transform technique, while the existence of a unique solution is proved by applying the contraction mapping principle. One of the main results is the boundedness of the solution. A fundamental reason for the persistence of SCA is probably due to the role played by the selective advantage of the abnormal S gene over the normal haemoglobin A in tropical regions, and the fact that carriers are more fertile and survive longer (a property known as hybrid vigor), because they are essentially asymptomatic. We also discuss possible public health policies.

Retinopathy in sickle cell trait: does it exist?

BACKGROUND

Patients with sickle cell trait and concomitant systemic disease are known to be at risk for proliferative retinopathy. However, there are reports of retinopathy in patients with sickle cell trait without systemic disease. There are no population-based studies addressing the risk of sickle cell retinopathy in this group. We performed a study to clarify the relation between sickle cell trait and retinopathy in healthy subjects.

METHODS

We reviewed the medical records of 100 children with sickle cell disease who attended the Sickle Cell Clinic at the Hospital for Sick Children, Toronto. We then contacted 200 parents with sickle cell trait, of whom 32 agreed to participate in the study. All participants were proven to have hemoglobin AS status with prior hemoglobin electrophoresis. An ophthalmologic history was obtained, and a complete ophthalmologic examination was performed. We defined sickle cell retinopathy as any salmon patch hemorrhages, iridescent spots, black sunbursts, retinal neovascularization or retinal detachment. The evaluation also included attempts to identify the more subtle signs of sickle cell retinopathy, such as optic nerve head vascular changes, vascular tortuosity, macular changes (e.g., microaneurysms and vascular loops) and peripheral arteriovenous anastamoses. Blood samples were obtained for complete blood count, reticulocyte count and smear.

RESULTS

We found no cases of sickle cell retinopathy among the 32 subjects. Ten of 30 subjects had a high reticulocyte count (greater than 120 x 10(9)/L); however, there were no associated eye findings in this subgroup.

INTERPRETATION

Our results indicate that there is no increased risk of retinopathy in healthy people with sickle cell trait.

Erythrocyte-active agents and treatment of sickle cell disease

The sickle hemoglobin (HbS)-containing erythrocyte and its membrane represent a logical target for sickle cell disease therapy. Several antisickling agents which interfere with HbS polymerization have been studied over the last 30 years, but none has overcome the challenge of delivering high concentrations inside the sickle red blood cell without toxicity. The sickle erythrocyte membrane has also been targeted for therapeutic developments. Prevention of sickle cell dehydration by use of specific blockers of ion transport pathways mediating potassium loss from the sickle erythrocyte has been shown to be a feasible strategy in vitro, in vivo in transgenic sickle mice, and in patients. Other approaches have focused on improving the hemorheology of sickle erythrocytes and reducing their abnormal adhesion to endothelial cells. These potential treatments could be used alone or in combination with other approved therapies, such as hydroxyurea.

In vivo blood flow abnormalities in the transgenic knockout sickle cell mouse

The accepted importance of circulatory impairment to sickle cell anemia remains to be verified by in vivo experimentation. Intravital microscopy studies of blood flow in patients are limited to circulations that can be viewed noninvasively and are restricted from deliberate perturbations of the circulation. Further knowledge of sickle blood flow abnormalities has awaited an animal model of human sickle cell disease. We compared blood flow in the mucosal-intestinal microvessels of normal mice with that in transgenic knockout sickle cell mice that have erythrocytes containing only human hemoglobin S and that exhibit a degree of hemolytic anemia and pathological complications similar to the human disease. In sickle cell mice, in addition to seeing blood flow abnormalities such as sludging in all microvessels, we detected decreased blood flow velocity in venules of all diameters. Flow responses to hyperoxia in both normal and sickle cell mice were dramatic, but opposite: Hyperoxia promptly slowed or halted flow in normal mice but markedly enhanced flow in sickle cell mice. Intravital microscopic studies of this murine model provide important insights into sickle cell blood flow abnormalities and suggest that this model can be used to evaluate the causes of abnormal flow and new approaches to therapy of sickle cell disease.

Enhanced Adherence of Sickle Erythrocytes to Thrombin-Treated Endothelial Cells Involves Interendothelial Cell Gap Formation

The adherence of sickle erythrocytes to vascular endothelium has the capacity to initiate vasoocclusion. The known effects of thrombin on endothelial cell function and the increased activity of thrombin in sickle cell disease led us to examine the effect of thrombin on the adhesivity of cultured endothelial cells for sickle erythrocytes. In particular, we studied whether the effect of thrombin on interendothelial cell gap formation (ICGF) was involved in endothelial cell adhesivity for sickle erythrocytes. Those endothelial cell monolayers stimulated by thrombin to maximal levels of static sickle erythrocyte adherence also underwent striking cell contraction and enlargement of interendothelial cell gaps. Adhesivity also increased when gaps were induced with antilaminin antibodies or EDTA. Maximally adhesogenic thrombin conditions failed to increase adhesivity when gap formation was prevented by pretreatment of the monolayers with 8-bromo-cyclic adenosine monophosphate (bromo-cAMP) or glutaraldehyde, agents that respectively inhibit actin-myosin–dependent cell contraction or cross-link adjacent cells in the monolayer. The influence of these two agents on EDTA-enhanced adhesivity was linked to their ability to prevent gap formation. Glutaraldehyde prevented both increased adherence and gap formation; bromo-cAMP prevented neither. Interendothelial cell gap formation may contribute to vasoocclusion by facilitating sickle erythrocyte adherence.

© 1998 by The American Society of Hematology.

Enhanced Adherence of Sickle Erythrocytes to Thrombin-Treated Endothelial Cells Involves Interendothelial Cell Gap Formation

The adherence of sickle erythrocytes to vascular endothelium has the capacity to initiate vasoocclusion. The known effects of thrombin on endothelial cell function and the increased activity of thrombin in sickle cell disease led us to examine the effect of thrombin on the adhesivity of cultured endothelial cells for sickle erythrocytes. In particular, we studied whether the effect of thrombin on interendothelial cell gap formation (ICGF) was involved in endothelial cell adhesivity for sickle erythrocytes. Those endothelial cell monolayers stimulated by thrombin to maximal levels of static sickle erythrocyte adherence also underwent striking cell contraction and enlargement of interendothelial cell gaps. Adhesivity also increased when gaps were induced with antilaminin antibodies or EDTA. Maximally adhesogenic thrombin conditions failed to increase adhesivity when gap formation was prevented by pretreatment of the monolayers with 8-bromo-cyclic adenosine monophosphate (bromo-cAMP) or glutaraldehyde, agents that respectively inhibit actin-myosin–dependent cell contraction or cross-link adjacent cells in the monolayer. The influence of these two agents on EDTA-enhanced adhesivity was linked to their ability to prevent gap formation. Glutaraldehyde prevented both increased adherence and gap formation; bromo-cAMP prevented neither. Interendothelial cell gap formation may contribute to vasoocclusion by facilitating sickle erythrocyte adherence.

© 1998 by The American Society of Hematology.

N-ethylmaliemide (NEM)-stimulated potassium transport in camel erythrocytes

In this study N-ethylmaliemide (NME)-stimulated, ouabain-resistant potassium influx in camel erythrocytes was measured using the radioactive rubidium tracer 86Rb+. The results showed that camel erythrocytes responded to NEM pretreatment by a threefold increase in influx which was Cl- dependent. The anion dependence of K+ influx in pre-treated cells was Br- > Cl- > NO3-. The pH dependence curve for NEM-stimulated K+ influx and the combination between volume and NEM stimulation in camel erythrocytes were determined. The findings indicated that the camel erythrocytes potassium transport system has many similarities to that of other mammalian species.

Trimidox-mediated morphological changes during erythroid differentiation is associated with the stimulation of hemoglobin and F-cell production in human K562 cells

Trimidox (3,4,5-trihdroxybenzamidoxime) has been shown to reduce the activity of ribonucleotide reductase with accompanied growth inhibition and differentiation of mammalian cells. Hydroxyurea (HU) is the only ribonucleotide reductase inhibitor in clinical use for the treatment and management of sickle cell anemia, since this compound increases fetal hemoglobin (Hb F) production: a potent inhibitor of sickle hemoglobin (Hb SS) polymerization. However, the main limitations of HU is its lack of potency, myelosuppression and short half life. These studies investigated the effects of trimidox on the induction of hemoglobin and F-cells production in K562 erythroleukemia cells. Our study reveals that trimidox exhibits concentration dependent inhibitory effect on K562 cells with increase in benzidine positive normoblasts and F-cells production as well as morphological changes typical of erythroid differentiation. These findings provide the first evidence that the growth inhibitory differentiation of cells induced by trimidox enhance hemoglobin and F-cells production.

Gene activation by recruitment of the RNA polymerase II holoenzyme

The single amino acid "P" (potentiator) mutation in the holoenzyme component GAL11 creates an interaction between that protein and the dimerization region of GAL4. That interaction triggers strong gene activation when the GAL4 fragment is tethered to DNA. Here we show that, among a series of variants of the GAL4 dimerization region and different GAL11P alleles, the strength of the interaction as quantitated in vitro correlates with the degree of activation in vivo; swapping the protein fragments bearing the GAL4 dimerization region and the GAL11P mutation such that the latter is tethered to DNA and the former is attached to the holoenzyme does not diminish gene activation; gene activation in this system is squelched by overproduction of either a fragment bearing the GAL4 dimerization region or a fragment of GAL11 bearing a P mutation; and neither GAL11 nor GAL11P is a target of an acidic activating region. These results argue that the GAL4-GAL11P interaction triggers gene activation simply by recruiting the holoenzyme to DNA. Consistent with this view, we also show that fusion of LexA to another holoenzyme component, SRB2, creates an activator, and that an SRB2 mutant predicted on genetic grounds to interact especially efficiently with a holoenzyme containing a specific mutant form of polymerase also activates more efficiently when tethered to DNA.

Pharmacokinetics and pharmacodynamics of tucaresol, an antisickling agent, in healthy volunteers

1. Tucaresol is an orally administered antisickling agent which increases the oxygen affinity of haemoglobin. 2. The pharmacokinetics, effects on moderate graded exercise and psychometric performance of tucaresol were examined in a double-blind, placebo-controlled, parallel groups study in 12 healthy men. 3. Three doses of tucaresol were given at 48 h intervals intended to modify 15, 25 and 32.5% of a subject's haemoglobin to a high affinity form (%MOD). 4. Mean peak %MOD was 34%. Mean Cmax values in plasma and erythrocytes were 81.4 and 1459 micrograms ml-1, respectively. 5. Heart rate, compared with baseline, increased in the tucaresol group with the greatest changes at the highest %MOD and workload. There were no differences between groups in psychometric test performance. 6. Three volunteers on active drug developed fever, rash and tender cervical lymphadenopathy with onset 7-10 days from the start of dosing, suggesting an immune mechanism. 7. The acute increase in oxygen affinity with tucaresol is physiologically well-tolerated, but the utility of tucaresol in the management of sickle cell disease will depend on the identification of a dosing regimen with a lower incidence of drug allergy.

Sickle myonecrosis revisited

This review focuses on the classification of sickle myonecrosis in the context of sickle cell vaso-occlusive crisis. Further, the potential and novel use of magnetic resonance imaging to further clarify the nature of sickle crisis is discussed.

Measurement of fluxes through the pentose phosphate pathway in erythrocytes from individuals with sickle cell anemia by carbon-13 nuclear magnetic resonance spectroscopy

Erythrocytes from individuals with sickle cell anemia have previously been shown to have increased levels of intracellular oxidants and increased oxidative damage. Oxidative damage has been implicated in the events leading to the painful crises and hemolytic anemia found in sickle cell anemia. Since the pentose phosphate pathway (PPP) is an important source of reducing capacity in erythrocytes, we have investigated the fluxes through the PPP in normal and sickle cell erythrocytes using [2-13C]D-glucose and carbon-13 nuclear magnetic resonance (NMR) spectroscopy. Our results indicate that sickle cell erythrocytes have a flux through the PPP of 0.13 +/- 0.02 mumol/h per ml erythrocytes that is comparable to that in normal erythrocytes, 0.21 +/- 0.02 mumol/h per ml erythrocytes. However, when stimulated with methylene blue, sickle cell erythrocytes show a decreased response, 0.59 +/- 0.10 mumol/h per ml erythrocytes, compared to normal erythrocytes, 1.64 +/- 0.10 mumol/h per ml erythrocytes. When homogeneous populations of sickle cell erythrocytes are isolated by density gradient centrifugation, the rate of flux through the PPP in methylene blue-stimulated sickle cell erythrocytes, 1.16 +/- 0.16 mumol/h per ml erythrocytes, approaches that in methylene blue-stimulated normal erythrocytes. In addition, by analyzing the dose response to methylene blue, we have found that the decreased stimulation of the PPP by methylene blue in heterogeneous populations of sickle cell erythrocytes is a failure of methylene blue to stimulate the PPP rather than a deficiency in the PPP in sickle cell erythrocytes.

Volume-dependent potassium transport in camel red blood cells

In this study the volume-dependent, ouabain-resistant K+ influx and efflux in camel red blood cells were measured with the tracer 86Rb+. The results showed that the camel erythrocytes do not have the Na(+)-K+ cotransport. The cell swelling increases a ouabain-resistant K+ influx and shrinkage decreases it nearly two-fold. The swelling-stimulated K+ influx and efflux were chloride dependent. The anion dependence of K+ influx in swollen cells was as follows: Br- > Cl- > NO3. The pH-dependent curve for swelling-stimulated potassium influx, and the active K+ influx in camel erythrocytes were determined. The findings indicate that camel erythrocytes' potassium transport system has many similarities to other mammalian species.

The pharmacokinetics, tolerability and pharmacodynamics of tucaresol (589C80; 4[2-formyl-3-hydroxyphenoxymethyl] benzoic acid), a potential anti-sickling agent, following oral administration to healthy subjects

1. Tucaresol (589C80; 4[2-formyl-3-hydroxyphenoxymethyl] benzoic acid) interacts stoichiometrically with haemoglobin to increase oxygen affinity. By decreasing the proportion of insoluble deoxy sickle haemoglobin at capillary oxygen concentrations, tucaresol may be of therapeutic benefit in sickle cell anaemia. 2. In this study, which involved the first administration to man, the pharmacokinetics and pharmacodynamics of tucaresol were studied in healthy male volunteers following oral doses of 200-3600 mg. 3. Peak drug concentrations in plasma and erythrocytes were linearly related to dose; mean (s.d.) values were 95.8 (26.1) and 1035 (67) micrograms ml-1, respectively, at the highest dose. Median tmax in plasma was 6.5 h and in erythrocytes 24.5 h, when approximately 60% of the administered dose was in the target tissue. Plasma drug concentrations fell biexponentially with commencement of the apparent terminal elimination phase at approximately 24 h. The terminal elimination half-life from plasma increased with dose (r = 0.77; P < 0.0001) from 133-190 h at 400 mg to a mean (s.d.) of 289 (30) h at 3600 mg. Erythrocyte drug concentrations declined mono-exponentially with a half-life that was always shorter than the apparent terminal half-life in plasma: overall mean (95% CI) of t1/2 erythrocyte/t1/2 plasma ratio was 0.57 (0.53, 0.61). The erythrocyte AUC/plasma AUC ratio increased with dose (r = 0.67; P < 0.001). 4. The proportion of haemoglobin modified to a form with high oxygen affinity (%MOD) increased in a dose-related manner above doses of 800 mg reaching 19-26% after the 3600 mg dose.(ABSTRACT TRUNCATED AT 250 WORDS)

Sickle cell disease pathophysiology

The primary pathophysiological event in the erythrocytes of individuals with the various sickle syndromes is the intracellular aggregation or polymerization of sickle haemoglobin (HbS). The extent of polymerization is determined by the intracellular haemoglobin composition (% HbS and % HbS A, A2 and F), concentration (MCHC and % of dense cells) and oxygen saturation, as well as minor factors such as intracellular pH and DPG concentration. Intracellular HbS polymerization leads to a marked decrease in the flexibility or rheological properties of the sickle erythrocytes and obstruction in various microcirculatory beds, as well as chronic anaemia. Other abnormalities in the properties of the sickle erythrocytes, including membrane abnormalities, changes in ion fluxes and volume and endothelial adhesion, result from acute and chronic oxygen-linked polymerization events and may, in turn, modify polymerization. However, within a good approximation, many aspects of sickle cell disease pathophysiology--for example variations in anaemia among the different sickle syndromes--can be explained in terms of differences in polymerization tendency. Thus, the effects of alpha-thalassaemia can be explained with reference to changes in MCHC and syndromes with high HbF are understandable in terms of the sparing effect of HbF on polymerization. Recent therapeutic approaches to sickle cell disease focus on attempts to reduce intracellular HbS polymerization by altering the haemoglobin molecules, erythrocyte properties, or the distribution of intracellular haemoglobin species. The last, through pharmacological elevation of HbF, has become the central focus of much laboratory and clinical research in recent years. Agents such as hydroxyurea (with or without recombinant erythropoietin) and butyrate compounds elevate HbF (and reduce HbS) in a majority of sickle erythrocytes, thus decreasing intracellular polymerization. Current prospective protocols are designed to see if these changes cause clinical improvement at acceptable doses. Other treatment strategies, including bone marrow transplantation and possible gene replacement therapies, are also under active clinical or laboratory investigation.

Emergency department analgesia without narcotics for adults with acute sickle cell pain crisis: case reports and review of crisis management

Vaso-occlusive crises are one of the most debilitating features of sickle cell disease. There appears to be no standardization of care for adults with pain crisis, and some commonly utilized regimens, such as those employing intramuscular meperidine, are pharmacologically unsound. Parenteral narcotic use may be associated with respiratory compromise acutely and with dependence over the long term, but nonopioid preparations are often unsatisfactory in relieving pain. We have recently enjoyed success with a combination of a parenteral nonsteroidal anti-inflammatory medication and an oral tricyclic antidepressant. We report four representative cases and review the salient points of the management of pain crisis in adult patients in the emergency department.

Immunotactoid glomerulopathy

During the past 10 years, immunotactoid glomerulopathy has become recognized with increasing frequency. The lesion is characterized histologically by highly organized ultrastructural deposits that appear to be composed of immunoglobulin and complement and are negative for amyloid by Congo red stain. Clinically and/or serologically, patients have no evidence of cryoglobulinemia, amyloidosis, systemic lupus erythematosus, or a paraproteinemia, disorders associated with glomerular deposits, which also have a highly organized tactoidal or fibrillar characteristic. Immunotactoid glomerulopathy does not appear to be a multisystemic disease process and thus may represent a primary glomerulopathy. Patients with immunotactoid glomerulopathy present with proteinuria (nephrotic range in more than 60%) and over half of the patients have hypertension, hematuria, and renal insufficiency. Progression to end stage renal disease has occurred in more than 40% of patients reported to date. The experience in treating this disorder using prednisone and/or immunosuppression is limited and has not been impressive. Four patients have successfully undergone renal transplantation, but proteinuria recurred in two and was associated with the recurrence of immunotactoid glomerulopathy in the renal allograft. Although we have gained insight into the clinical course and histopathology of this disorder over the past few years, we still know little about its pathogenesis, an area for further research.

QSAR and molecular shape analysis of aryl-substituted alanine analogs as antigelling agents

Quantitative structure activity relationship (QSAR) analyses have been performed to analyze the basis for the antigelling activity of a series of aryl-substituted alanine analogs, including both phenylalanine and tryptophan analogs. We find that these two groups of compounds should be treated separately, probably due to the difference in shape between the phenyl and indole rings in the respective side chains. For the phenylalanine analogs, the hydrophobicity of the side chain, as measured by the pi constants of the aromatic ring and their substituents, explains about 50% of the variance in antigelling activity. The square of the aromatic dipole moment and the steric overlap volume, as obtained from three dimensional molecular shape analysis, account for an additional 20% and 10% of the variance, respectively. For the tryptophan analogs, the majority of the variance is explained either by the square of the aromatic dipole moment (70%) or by the steric overlap volume (60%), with the two descriptors being highly correlated. This result suggests that the tryptophan analogs exhibit a relatively tight steric fit within their binding sites. The separate QSAR's of phenylalanine and tryptophan analogs also suggest that these two groups of compounds may bind to hemoglobin through different mechanisms or at different sites. For phenylalanine analogs, the hydrophobic interaction is dominant, and the dipole-dipole interaction and steric effects contribute to lesser extents. For the tryptophan analogs, the dipole-dipole interaction prevails with a high degree of steric shape complimentarity, but without any significant contribution from hydrophobic interactions. This information should assist in the future development of more specific and effective agents.

Volume-dependent K+ transport in rabbit red blood cells comparison with oxygenated human SS cells

In this study the volume-dependent or N-ethylmaleimide (NEM)-stimulated, ouabain-insensitive K+ influx and efflux were measured with the tracer 86Rb+ in rabbit red blood cells. The purpose of the work was to examine the rabbit as a potential model for cell volume regulation in human SS red blood cells and also to investigate the relationship between the NEM-reactive sulfhydryl group(s) and the signal by which cell swelling activates the transport. Ouabain-resistant K+ efflux and influx increase nearly threefold in cells swollen hypotonically by 15%. Pretreatment with 2 mM NEM stimulates efflux 5-fold and influx 10-fold (each measured in an isotonic medium). The ouabain-resistant K+ efflux was dependent on the major anion in the medium. The anion dependence of K+ efflux in swollen or NEM-stimulated cells was as follows: Br- greater than Cl- much greater than NO3- = acetate. The magnitudes of both the swelling- and the NEM-stimulated fluxes are much higher in young cells (density separated but excluding reticulocytes) than in older cells. Swelling- or NEM-stimulated K+ efflux in rabbit red blood cells was inhibited 50% by 1 mM furosemide, and the inhibitory potency of furosemide was enhanced by extracellular K+, as is known to be true for human AA and low-K+ sheep red blood cells. The swelling-stimulated flux in both rabbit and human SS cells has a pH optimum at approximately 7.4. We conclude that rabbit red blood cells are a good model for swelling-stimulated K+ transport in human SS cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Sickle cell anemia and mitral valve replacement. Case report

An 8-year-old black boy with sickle cell disease and severe hemolytic anemia crisis (95% hemoglobin S) also had mitral incompetence due to rheumatic valve disease. A 27 mm monostrut Björk-Shiley valve prosthesis was implanted after partial exchange transfusions had reduced the hemoglobin S to less than 40%. High-flow normothermic perfusion was used during extracorporeal circulation, with care taken to avoid hypoxia and acidosis. Postoperative recovery was uneventful.