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Biomedical subjects

Ronald L Nagel

Publications and source records attributed to Ronald L Nagel.

At least 19 recordsLinked to original sources
PubMed2003

Expression of HbC and HbS, but not HbA, results in activation of K-Cl cotransport activity in transgenic mouse red cells.

Elevation of K-Cl cotransport in patients with homozygous hemoglobin (Hb) S or HbC increases red cell mean corpuscular hemoglobin concentration (MCHC) and contributes significantly to pathology. Elucidation of the origin of elevated K-Cl cotransport in red cells with mutant hemoglobins has been confounded by the concomitant presence of reticulocytes with high K-Cl cotransport. In red cells of control mice (C57BL), transgenic mice that express only human HbA, and transgenic mice that express both mouse globins and human HbS, volume stimulation is weak and insensitive to NO3- and dihydroindenyl-oxy-alkanoic acid (DIOA). DIOA and NO3- are inhibitors in all other mammalian red cells. In contrast, in knock-out mice expressing exclusively human hemoglobin HbC or HbS+ gamma, replacement of isotonic Cl- media by hypotonic Cl- resulted in strong volume stimulation and sensitivity to DIOA, okadaic acid, and NO3-. In summary, we find that HbC, under all conditions, and HbS+ gamma, in the absence of mouse globins, have significant quantitative and qualitative effects on K-Cl cotransport in mouse red cells and activate mouse K-Cl. We conclude that human globins are able to stimulate the activity and/or regulation of K-Cl cotransport in mouse red cells. These observations support the contention that HbS and HbC stimulate K-Cl cotransport in human red cells.

Animals↗
PubMed2003

The paradox of hemoglobin SC disease.

Homozygous HbC gene results only in mild hemolytic anemia. In HbSC disease red cells contain equal levels of HbS and HbC. It is a paradox that HbSC exhibit a moderately severe phenotype in spite of being a mixture of HbS trait and HbC trait, neither of which has significant pathology. Why does the combination of these two Hbs result in a serious disease? The short answer is that HbC enhances, by dehydrating the SC red cell, the pathogenic properties of HbS, resulting in a clinically significant disorder, but somewhat milder that sickle cell anemia (SCA). Nevertheless, retinnitis proliferans, osteonecrosis, and acute chest syndrome have equal or higher incidence in HbSC disease compared to SCA. This pathogenic trick is accomplished by HbC inducing, by mechanisms not fully understood, an increase in the activity of K:Cl cotransport that induces the lost of K(+) and consequently of intracellular water. This event creates a sufficient increase of MCHC, so that the lower levels of HbS found in SC red cells can polymerize rapidly and effectively. This situation offers a unique opportunity: if we could inhibit the effect of HbC on K(+) transport we can cure the disease.

Anemia, Sickle Cell↗
PubMed2003

Beta7E-beta132K salt bridge and sickle haemoglobin stability and conformation.

The liganded (R-state) form of sickle cell haemoglobin (HbS) is of particular relevance at non-polymerizing concentrations as oxy HbS exhibits unusual properties compared with oxy HbA: mechanical precipitability (resulting from surface denaturation), greater unfolding at an air-water interface and a tendency to oxidize more readily. In human haemoglobins, the beta7 (A4) Glu residue forms an intrachain salt bridge with beta132 (H10) Lys in both liganded and deoxy structures. In the present study, recombinant haemoglobins with substitutions in the beta7 and beta132 sites were studied in order to determine the role of the beta7-beta132 salt bridge on Hb conformational integrity and stability. The elimination of this interhelix bridge correlates with enhanced surface denaturation and conformational alterations in the central cavity 2,3-diphosphoglycerate (DPG) cleft and alpha1beta2 interface. The A-helix beta7 Ala substitution generates a class of conformational change at the DPG pocket and alpha1beta2 interface that is distinct from that dictated by the H-helix beta132 Ala substitution. These results are significant with regard to the communication pathway between the alpha1beta1 and alpha1beta2 interfaces, and the new understanding of Hb allostery dependent upon tertiary structural constraints caused by effector binding to the R-state.

Fluorometry↗
PubMed2003

Origin of Hb A2' (Hb B2) [delta16(A13)Gly --> Arg (GGC --> CGC)].

On a field trip to the Dogon country (le Pays Dogon) in central Mali, we detected a high frequency of the Hb A2 abnormality, reaching higher numbers among blacksmiths (up to 12.4%) living in the same villages. In this report, by direct nucleotide sequencing and employing a polymerase chain reaction-restriction fragment length polymorphism approach, we show that the Hb A2 variant observed in the Dogon population is indeed Hb A2', also called Hb B2, and that in all of the cases the abnormal delta-globin gene is linked to a unique haplotype. The same haplotype was found linked to Hb A2' in the Herero population belonging to the South African Bantu-speaking Blacks from Namibia. Although the unique origin of this mutation in Africa is a possibility, a recurrent mutational event cannot be excluded because the linked beta cluster haplotype is one of the two major haplotypes found in all African populations. A study of populations from other regions of Africa is required to clarify this issue.

Amino Acid Substitution↗
PubMed2003

Hemoglobinopathies.

The outlook for patients with sickle cell disease has improved steadily during the last two decades. In spite of these improvements, curative therapies are currently available only to a small minority of patients. The main theme of this chapter is to describe new therapeutic options that are at different stages of development that might result in further improvements in the outlook for patients with these disorders. Dr. Joseph DeSimone and his colleagues had previously made the important observation that the hypomethylating agent 5-azacytidine can reverse the switch from adult to fetal hemoglobin in adult baboons. Although similar activity was demonstrated in patients with sickle cell disease and beta-thalassemia, concern about the toxicity of 5-azacytidine prevented its widespread use in these disorders. In Section I, Dr. DeSimone discusses the role of DNA methylation in globin gene regulation and describe recent clinical experience with decitabine (an analogue of 5-azacytidine) in patients with sickle cell disease. These encouraging studies demonstrate significant fetal hemoglobin inducing activity of decitabine in patients who fail to respond to hydroxyurea. In Section II, Dr. George Atweh continues the same theme by describing recent progress in the study of butyrate, another inducer of fetal hemoglobin, in patients with sickle cell disease and beta-thalassemia. The main focus of his section is on the use of a combination of butyrate and hydroxyurea to achieve higher levels of fetal hemoglobin that might be necessary for complete amelioration of the clinical manifestations of these disorders. Dr. Atweh also describes novel laboratory studies that shed new light on the mechanisms of fetal hemoglobin induction by butyrate. In Section III, Dr. Ronald Nagel discusses the different available transgenic sickle mice as experimental models for human sickle cell disease. These experimental models have already had a significant impact on our understanding of the pathophysiology of sickle cell disease. Dr. Nagel describes more recent studies in which transgenic sickle mice provide the first proof of principle that globin gene transfer into hematopoietic stem cells inhibits in vivo sickling and ameliorates the severity of the disease. Although stroke in adult patients with sickle cell disease is not as common as in children, adult hematologists, like their pediatric colleagues, need to make management decisions in adult patients with a stroke or a history of stroke. Dr. Robert Adams has led several large clinical studies that investigated the role of transfusions in the prevention of stroke in children with sickle cell disease. Much less is known, however, about the prevention of first or subsequent strokes in adult patients with sickle cell disease. In Section IV, Dr. Adams provides some general guidelines for the management of adult patients with stroke while carefully distinguishing between recommendations that are evidence-based and those that are anecdotal in nature.

Animals↗
PubMed2003

Human genetic polymorphisms and asymptomatic Plasmodium falciparum malaria in Gabonese schoolchildren.

Several studies have focused their attention on the relationship between host genetic factors and susceptibility/resistance to severe malaria. However, there is a paucity of information concerning the role of host genetic factors in asymptomatic malaria, a form of low-grade Plasmodium falciparum infection without clinical symptoms. We investigated in this study the potential relationship between the host (human) genetic polymorphisms (glucose-6-phosphate dehydrogenase [G6PD], mannose binding lectin [MBL], tumor necrosis factor alpha [TNFalpha](-308) and (-238), and nitric oxide synthase 2 [NOS2](-954)) and the prevalence and profile of asymptomatic P. falciparum infection in 158 Gabonese schoolchildren. We found that G6PD A- heterozygous females (18 of 74) have a low prevalence of asymptomatic malaria (38.9% versus 67.3%; P = 0.03, by chi-square test). Children heterozygous for TNFalpha(-238) (25 of 156) carry high number of diverse infecting parasite genotypes (2.5 versus 1.99; variance F = 3.05). No statistically significant association was found between MBL, TNFalpha(-308), or NOS2 polymorphisms and asymptomatic malaria. Upon combining our data on asymptomatic forms with those from the literature for others forms, we conclude that G6PD A- heterozygous females are protected against all forms of P. falciparum malaria, and that the TNFalpha(-238A) allele confers protection against clinical malaria.

Adolescent↗
PubMed2002

Conformational changes in hemoglobin S (betaE6V) imposed by mutation of the beta Glu7-beta Lys132 salt bridge and detected by UV resonance Raman spectroscopy.

The impact upon molecular structure of an additional point mutation adjacent to the existing E6V mutation in sickle cell hemoglobin was probed spectroscopically. The UV resonance Raman results show that the conformational consequences of mutating the salt bridge pair, betaGlu(7)-betaLys(132), are dependent on which residue of the pair is modified. The betaK132A mutants exhibit the spectroscopic signatures of the R --> T state transition in both the "hinge" and "switch" regions of the alpha(1)beta(2) interface. Both singly and doubly mutated hemoglobin (Hb) betaepsilon7Alpha exhibit the switch region signature for the R --> T quaternary state transition but not the hinge signature. The absence of this hinge region-associated quaternary change is the likely origin of the observed increased oxygen binding affinity for the Hb betaepsilon7Alpha mutants. The observed large decrease in the W3 alpha14beta15 band intensity for doubly mutated Hb betaepsilon7Alpha is attributed to an enhanced separation in the A helix-E helix tertiary contact of the beta subunits. The results for the Hb A betaGlu(7)-betaLys(132) salt bridge mutants demonstrate that attaining the T state conformation at the hinge region of the alpha(1)beta(2) dimer interface can be achieved through different intraglobin pathways; these pathways are subject to subtle mutagenic manipulation at sites well removed from the dimer interface.

Dimerization↗
PubMed2002

Structure of mutant human carbonmonoxyhemoglobin C (betaE6K) at 2.0 A resolution.

Previous studies have demonstrated that in vitro crystallization of R-state liganded hemoglobin C (HbC), a naturally occurring mutant human hemoglobin (betaE6K), in high-phosphate buffer solutions provides a potential model system for the intracellular crystallization of HbC associated with chronic hemolytic anemia in CC disease. The first high-resolution crystal structure of liganded HbC is reported here. HbC was crystallized from high phosphate and the structure of the carbonmonoxy-liganded R-state form was refined at 2.0 A resolution. Crystals exhibit diffraction consistent with the tetragonal space group P4(1)2(1)2, with unit-cell parameters a = 54.16, c = 195.30 A. The structure was solved by difference Fourier techniques and refinement by simulated annealing and restrained least-squares yielded a final R of 0.183 and an R(free) of 0.238 for all 19,382 unique reflections. The side chain of betaK6 exhibits very weak electron density consistent with significant mobility within the crystalline lattice. The highly dynamic nature of the side chain could potentially support a number of specific polar interactions that might reduce the barrier to crystallization and thus result in enhanced crystallization kinetics for HbC relative to HbA. Specifically, the NZ atom of the BK6 side chain could participate in an amino-aromatic hydrogen bond with the pi-electron cloud of betaH116 in a symmetry-related tetramer. BetaK6 NZ might also interact with the main-chain carbonyl O atom of betaH117 and the carboxylate group of betaE22 from a symmetry-related tetramer.

Carboxyhemoglobin↗
PubMed2002

Permanent and panerythroid correction of murine beta thalassemia by multiple lentiviral integration in hematopoietic stem cells.

Achieving long-term pancellular expression of a transferred gene at therapeutic level in a given hematopoietic lineage remains an important goal of gene therapy. Advances have recently been made in the genetic correction of the hemoglobinopathies by means of lentiviral vectors and large locus control region (LCR) derivatives. However, panerythroid beta globin gene expression has not yet been achieved in beta thalassemic mice because of incomplete transduction of the hematopoietic stem cell compartment and position effect variegation of proviruses integrated at a single copy per genome. Here, we report the permanent, panerythroid correction of severe beta thalassemia in mice, resulting from a homozygous deletion of the beta major globin gene, by transplantation of syngeneic bone marrow transduced with an HIV-1-derived [beta globin gene/LCR] lentiviral vector also containing the Rev responsive element and the central polypurine tract/DNA flap. The viral titers produced were high enough to achieve transduction of virtually all of the hematopoietic stem cells in the graft with an average of three integrated proviral copies per genome in all transplanted mice; the transduction was sustained for >7 months in both primary and secondary transplants, at which time approximately 95% of the red blood cells in all mice contained human beta globin contributing to 32 +/- 4% of all beta-like globin chains. Hematological parameters approached complete phenotypic correction, as assessed by hemoglobin levels and reticulocyte and red blood cell counts. All circulating red blood cells became and remained normocytic and normochromic, and their density was normalized. Free alpha globin chains were completely cleared from red blood cell membranes, splenomegaly abated, and iron deposit was almost eliminated in liver sections. These findings indicate that virtually complete transduction of the hematopoietic stem cell compartment can be achieved by high-titer lentiviral vectors and that position effect variegation can be mitigated by multiple events of proviral integration to yield balanced, panerythroid expression. These results provide a solid foundation for the initiation of human clinical trials in beta thalassemia patients.

3T3 Cells↗
PubMed2002

Expression of a human beta-globin transgene in erythroid cells derived from retrovirally transduced transplantable human fetal liver and cord blood cells.

Transfer of therapeutic genes to human hematopoietic stem cells (HSCs) using complex vectors at clinically relevant efficiencies remains a major challenge. Recently we described a stable retroviral vector that sustains long-term expression of green fluorescent protein (GFP) and a human beta-globin gene in the erythroid progeny of transduced murine HSCs. We now report the efficient transduction of primitive human CD34(+) fetal liver or cord blood cells with this vector and expression of the beta-globin transgene in the erythroid progeny of these human cells for at least 2 months. After growth factor prestimulation and then a 2- to 3-day exposure to the virus, 35% to 55% GFP(+) progeny were seen in assays of transduced colony-forming cells, primitive erythroid precursors that generate large numbers of glycophorin A(+) cells in 3-week suspension cultures, and 6-week long-term culture-initiating cells. In immunodeficient mice injected with unselected infected cells, 5% to 15% of the human cells regenerated in the marrow (including the erythroid cells) were GFP(+) 3 and 6 weeks after transplantation. Importantly, the numbers of GFP(+) human lymphoid and either granulopoietic or erythroid cells in individual mice 6 weeks after transplantation were significantly correlated, indicative of the initial transduction of human multipotent cells with in vivo repopulating activity. Expression of the transduced beta-globin gene in human cells obtained directly from the mice or after their differentiation into erythroid cells in vitro was demonstrated by reverse transcriptase-polymerase chain reaction using specific primers. These experiments represent a significant step toward the realization of a gene therapy approach for human beta-globin gene disorders.

Animals↗
PubMed2002

Liquid-liquid separation in solutions of normal and sickle cell hemoglobin.

We show that in solutions of human hemoglobin (Hb)--oxy- and deoxy-Hb A or S--of near-physiological pH, ionic strength, and Hb concentration, liquid-liquid phase separation occurs reversibly and reproducibly at temperatures between 35 and 40 degrees C. In solutions of deoxy-HbS, we demonstrate that the dense liquid droplets facilitate the nucleation of HbS polymers, whose formation is the primary pathogenic event for sickle cell anemia. In view of recent results that shifts of the liquid-liquid separation phase boundary can be achieved by nontoxic additives at molar concentrations up to 30 times lower than the protein concentrations, these findings open new avenues for the inhibition of the HbS polymerization.

Buffers↗
PubMed2002

Arginine supplementation of sickle transgenic mice reduces red cell density and Gardos channel activity.

Nitric oxide (NO), essential for maintaining vascular tone, is produced from arginine by nitric oxide synthase. Plasma arginine levels are low in sickle cell anemia, and it is reported here that low plasma arginine is also found in our sickle transgenic mouse model that expresses human alpha, human beta(S), and human beta(S-Antilles) and is homozygous for the mouse beta(major) deletion (S+S-Antilles). S+S-Antilles mice were supplemented with a 4-fold increase in arginine that was maintained for several months. Mean corpuscular hemoglobin concentration (MCHC) decreased and the percent high-density red cells was reduced. Deoxy K(+) efflux is characteristic of red cells in sickle cell disease and contributes to the disease process by increasing the MCHC and rendering the cells more susceptible to polymer formation. This flux versus the room air flux was reduced in S+S-Antilles red cells from an average value of 1.6 +/- 0.3 mmol per liter of red cells x minute (FU) in nonsupplemented mice to 0.9 +/- 0.3 FU (n = 4, P < .02, paired t test) in supplemented mice. In room air, V(max) of the Ca(++)-activated K(+) channel (Gardos) was reduced from 4.1 +/- 0.6 FU (off diet) to 2.6 +/- 0.4 FU (n = 7 and 8, P < .04, t test) in arginine-supplemented mice versus clotrimazole. In conclusion, the major mechanism by which arginine supplementation reduces red cell density (MCHC) in S+S-Antilles mice is by inhibiting the Ca(++)-activated K(+) channel.

Anemia, Sickle Cell↗
PubMed2002

Feasibility of using autologous transplantation to evaluate hematopoietic stem cell-based gene therapy strategies in transgenic mouse models of human disease.

Histoincompatibility between murine donors and recipients of bone marrow (BM) transplants reduces engraftment, and this compromises assessment of hematopoietic stem cells (HSCs) in certain transgenic mice. To study HSCs in the S+S-Antilles mouse model of human sickle cell disease (SCD), we developed an autotransplant protocol. Initial experiments showed no differences between S+S-Antilles mice and normal C57BL/6 (+/+) mice in their radiosensitivity or baseline hematopoietic progenitor numbers. The kinetics of red blood cell (RBC) replacement post-transplant in +/+ recipients of mixtures of transgenic and +/+ BM cells also showed no competitive advantage of the +/+ cells. BM cells were then aspirated from mice 4 days after 5-fluorouracil treatment, transduced with a green fluorescent protein (GFP)-encoding retrovirus, and transplanted into the same recipients that, just before transplant, were irradiated with 800 cGy. We subsequently detected high levels of GFP(+) RBCs (21-79%) and white blood cells (WBCs; 35-88%) in the blood for 11 months and showed that transduced HSCs regenerated in the primary mice also repopulated secondary mice. These findings provide a generally applicable protocol for performing autotransplants in mice and forecast the potential utility of this approach in assessing HSC-based gene therapy protocols in transgenic mouse models of many human diseases.

Anemia, Sickle Cell↗