Ultrastructural Damage to the Malaria Parasite in the Sickled Cell

The process by which malaria parasites are killed in sickled erythrocytes was studied by electron microscopy. In vitro cultures of Plasmodium falciparum in sickle cell hemoglobin (HbS) homozygous (SS) and heterozygous (SA) red cells were deoxygenated for up to 6 h and fixed under anaerobic conditions. Parasites in SS cells appeared to be disrupted by intrusions of needle-like deoxyHbS aggregates; disintegration of cytoplasm and membranes followed. In SA red cells, the parasites were generally not disrupted. Instead, extensive vacuolization occurred, a sign of metabolic inhibition. The resistance of HbS gene carriers to malaria results partly from these causes of intracellular parasite death.     

Potential of isoquercitrin as antisickling agent: a multi-spectroscopic,thermophoresis and molecular modeling approach

Abstract

Sickle cell disease is an inherited disease caused by point mutation in hemoglobin (β-globin gene). Under oxygen saturation, sickle hemoglobin form polymers, leading to rigid erythrocytes. The transition of the blood vessels is altered and initiated by the adhesion of erythrocytes, neutrophils and endothelial cells. Sickle Hemoglobin (HbS) polymerization is a major cause in red blood cells (RBC), promoting sickling and destruction of RBCs. Isoquercitrin, a medicinal bioactive compound found in various medicinal plants, has multiple health benefits. The present study examines the potential of isoquercitrin as an anti-sickle agent, showing a significant decrease in the rate of polymerization as well as sickling of RBCs. Isoquercitrin-induced graded alteration in absorbance and fluorescence of HbS, confirmed their interaction. A negative value of ΔG° strongly suggests that it is a spontaneous exothermic reaction induced by entropy. Negative ΔH° and positive ΔS° predicted that hydrogen and hydrophobic binding forces interfered with a hydrophobic microenvironment of β6Val leading to polymerization inhibition of HbS. HbS-Isoquercitrin complex exhibits helical structural changes leading to destabilization of the HbS polymer as confirmed by CD spectroscopy. MST and DSC results indicate greater changes in thermophoretic mobility and thermal stability of sickle hemoglobin in the presence of isoquercitrin, respectively. These findings were also supported by molecular simulation studies using DOCK6 and GROMACS. Hence, we can conclude that isoquercitrin interacts with HbS through hydrogen bonding, which leads to polymerization inhibition. Consequently, isoquercitrin could potentially be used as a medication for the treatment of sickle cell disease.

Communicated by Ramaswamy H. Sarma     

Design,synthesis, and optimization of a series of 2-azaspiro[3.3]heptane derivatives as orally bioavailable fetal hemoglobin inducers

Pharmacological reactivation of the γ-globin gene for the production of fetal hemoglobin (HbF) is a promising approach for the management of β-thalassemia and sickle cell disease (SCD). We conducted a phenotypic screen in human erythroid progenitor cells to identify molecules that could induce HbF, which resulted in identification of the hit compound 1. Exploration of structure–activity relationships and optimization of ADME properties led to 2-azaspiro[3.3]heptane derivative 18, which is more rigid and has a unique structure. In vivo using cynomolgus monkeys, compound 18 induced a significant dose-dependent increase in globin switching, with developable properties. Moreover, compound 18 showed no genotoxic effects and was much safer than hydroxyurea. These findings could facilitate the development of effective new therapies for the treatment of β-hemoglobinopathies, including SCD.     

Nitric oxide reduces sickle hemoglobin polymerization: potential role of nitric oxide-induced charge alteration in depolymerization

We previously demonstrated that inhaling nitric oxide (NO) increases the oxygen affinity of sickle red blood cells (RBCs) in patients with sickle cell disease (SCD). Our recent studies found that NO lowered the P₅₀ values of sickle hemoglobin (HbS) hemolysates but did not increase methemoglobin (metHb) levels, supporting the role of NO, but not metHb, in the oxygen affinity of HbS. Here we examine the mechanism by which NO increases HbS oxygen affinity. Because anti-sickling agents increase sickle RBC oxygen affinity, we first determined whether NO exhibits anti-sickling properties. The viscosity of HbS hemolysates, measured by falling ball assays, increased upon deoxygenation; NO treatment reduced the increment. Multiphoton microscopic analyses showed smaller HbS polymers in deoxygenated sickle RBCs and HbS hemolysates exposed to NO. These results suggest that NO inhibits HbS polymer formation and has anti-sickling properties. Furthermore, we found that HbS treated with NO exhibits an isoelectric point similar to that of HbA, suggesting that NO alters the electric charge of HbS. NO–HbS adducts had the same elution time as HbA upon high performance liquid chromatography analysis. This study demonstrates that NO may disrupt HbS polymers by abolishing the excess positive charge of HbS, resulting in increased oxygen affinity.     

Sickle Cell Hemoglobin in the Ferryl State Promotes βCys-93 Oxidation and Mitochondrial Dysfunction in Epithelial Lung Cells (E10)

Polymerization of intraerythrocytic deoxyhemoglobin S (HbS) is the primary molecular event that leads to hemolytic anemia in sickle cell disease (SCD). We reasoned that HbS may contribute to the complex pathophysiology of SCD in part due to its pseudoperoxidase activity. We compared oxidation reactions and the turnover of oxidation intermediates of purified human HbS and HbA. Hydrogen peroxide (H₂O₂) drives a catalytic cycle that includes the following three distinct steps: 1) initial oxidation of ferrous (oxy) to ferryl Hb; 2) autoreduction of the ferryl intermediate to ferric (metHb); and 3) reaction of metHb with an additional H₂O₂ molecule to regenerate the ferryl intermediate. Ferrous and ferric forms of both proteins underwent initial oxidation to the ferryl heme in the presence of H₂O₂ at equal rates. However, the rate of autoreduction of ferryl to the ferric form was slower in the HbS solutions. Using quantitative mass spectrometry and the spin trap, 5,5-dimethyl-1-pyrroline-N-oxide, we found more irreversibly oxidized βCys-93in HbS than in HbA. Incubation of the ferric or ferryl HbS with cultured lung epithelial cells (E10) induced a drop in mitochondrial oxygen consumption rate and impairment of cellular bioenergetics that was related to the redox state of the iron. Ferryl HbS induced a substantial drop in the mitochondrial transmembrane potential and increases in cytosolic heme oxygenase (HO-1) expression and mitochondrial colocalization in E10 cells. Thus, highly oxidizing ferryl Hb and heme, the product of oxidation, may be central to the evolution of vasculopathy in SCD and may suggest therapeutic modalities that interrupt heme-mediated inflammation.     

A recombinant human hemoglobin with anti-sickling properties greater than fetal hemoglobin

A new recombinant, human anti-sickling beta-globin polypeptide designated beta(AS3) (betaGly(16) --> Asp/betaGlu(22) --> Ala/betaThr(87) --> Gln) was designed to increase affinity for alpha-globin. The amino acid substitutions at beta22 and beta87 are located at axial and lateral contacts of the sickle hemoglobin (HbS) polymers and strongly inhibit deoxy-HbS polymerization. The beta16 substitution confers the recombinant beta-globin subunit (beta(AS3)) with a competitive advantage over beta(S) for interaction with the alpha-globin polypeptide. Transgenic mouse lines that synthesize high levels of HbAS3 (alpha(2)beta(AS3)(2)) were established, and recombinant HbAS3 was purified from hemolysates and then characterized. HbAS3 binds oxygen cooperatively and has an oxygen affinity that is comparable with fetal hemoglobin. Delay time experiments demonstrate that HbAS3 is a potent inhibitor of HbS polymerization. Subunit competition studies confirm that beta(AS3) has a distinct advantage over beta(S) for dimerization with alpha-globin. When equal amounts of beta(S)- and beta(AS3)-globin monomers compete for limiting alpha-globin chains up to 82% of the tetramers formed is HbAS3. Knock-out transgenic mice that express exclusively human HbAS3 were produced. When these mice were bred with knock-out transgenic sickle mice the beta(AS3) polypeptides corrected all hematological parameters and organ pathology associated with the disease. Expression of beta(AS3)-globin should effectively lower the concentration of HbS in erythrocytes of patients with sickle cell disease, especially in the 30% percent of these individuals who coinherit alpha-thalassemia. Therefore, constructs expressing the beta(AS3)-globin gene may be suitable for future clinical trials for sickle cell disease.     

Ultrastructural damage to the malaria parasite in the sickled cell.

The process by which malaria parasites are killed in sickled erythrocytes was studied by electron microscopy. In vitro cultures of Plasmodium falciparum in sickle cell hemoglobin (HbS) homozygous (SS) and heterozygous (SA) red cells were deoxygenated for up to 6 h and fixed under anaerobic conditions. Parasites in SS cells appeared to be disrupted by intrusions of needle-like deoxyHbS aggregates; disintegration of cytoplasm and membranes followed. In SA red cells, the parasites were generally not disrupted. Instead, extensive vacuolization occurred, a sign of metabolic inhibition. The resistance of HbS gene carriers to malaria results partly from these causes of intracellular parasite death.     

Hemoglobin switching in sheep: commitment of erythroid stem cells to expression of the betaC-globin gene and accumulation of betaC-globin mRNA

The switch from HbA (α₂β₂^A) to HbC (α₂β₂^C) synthesis was induced by injection of erythropoietin into a lamb homozygous for HbA. Serial samples of bone marrow were analyzed to detect the initial commitment of erythroid stem cells (CFU-E) to form colonies which made HbC in vitro, and to detect the initial accumulation of β^C-globin mRNA and the onset of HbC synthesis in erythroblasts in vivo. CFU-E-derived erythroid colonies were formed in plasma clot culture at a low erythropoietin concentration, and the relative amounts of β^A- and β^C-globin synthesized were determined after a 24 hr pulse of ³H-leucine, added after 84 hr in culture. RNA was extracted from nuclei and cytoplasm of “early” and “late” populations of bone marrow erythroblasts which had been fractionated by Ficoll-Hypaque density centrifugation. The concentration of β^A- and β^C-globin mRNA was determined by annealing to purified synthetic DNAs (cDNAs) complementary to β^A and β^C mRNA. No β^C-globin was synthesized in erythroblasts or in CFU-E-derived erythroid colonies prior to the injection of erythropoietin. An increase in the concentration of CFU-E in the bone marrow and the appearance of β^C-globin synthesis in CFU-E-derived colonies were detected 12 hr after the erythropoietin injection. In contrast, β^C mRNA was not detected in either “early” or “late” erythroid cells until 36 hr later. The first measurable β^C-globin mRNA was accompanied by the appearance of β^C-globin synthesis in bone marrow erythroblasts. Our results suggest that the accumulation of β^C-globin mRNA is a relatively late event following induction of HbA to HbC switching by erythropoietin. The expansion of the compartment of erythroid stem cells and the commitment of CFU-E to β^C-globin synthesis appear to precede the detectable accumulation of β^C mRNA by 24–36 hr.     

Na+/H+ exchange is increased in sickle cell anemia and young normal red cells

Summary Red cell volume regulation is important in sickle cell anemia because the rate and extent of HbS polymerization are strongly dependent on initial hemoglobin concentration. We have demonstrated that volume-sensitive K:Cl cotransport is highly active in SS whole blood and is capable of increasing MCHC. We now report that Na⁺/H⁺ exchange (Na/H EXC), which is capable of decreasing the MCHC of erythrocytes with pH_i<7.2, is also very active in the blood of patients homozygous for HbS. The activity of Na/H EXC (maximum rate) was determined by measuring net Na⁺ influx (mmol/liter cell·hr=FU) driven by an outward H⁺ gradient in oxygenated, acidloaded (pH_i 6.0), DIDS-treated SS cells. The Na/H EXC activity was 33±3 FU (mean±se) (n=19) in AA whites, 37±8 FU (n=8) in AA blacks, and 85±15 FU (n=14) in SS patients (P<0.005). Separation of SS cells into four density-defined fractions by density gradient revealed mean values of Na/H EXC four to five times higher in reticulocytes (SS1), discocytes (SS2) and dense discocytes (SS3), than in the fraction containing irreversibly sickled cells and dense discocytes (SS4). In contrast to K:Cl cotransport, which dramatically decreases after reticulocyte maturation, Na/H EXC persists well after reticulocyte maturation. In density-defined, normal AA red cells, Na/H EXC decreased monotonically as cell density increased. In SS and AA red cells, the magnitude of stimulation of Na/H EXC by cell shrinkage varied from individual to individual. We conclude that Na/H EXC is highly expressed in SS and AA young red cells and decays slowly after reticulocyte maturation.     

Association between apolipoprotein ε4 allele,factor V Leiden,and plasma lipid and lipoprotein levels with sickle cell disease in southern Iran

To investigate whether there is any association between various APOE alleles and factor V Leiden (FVL) with lipid profiles and sickle cell disease (SCD) in Southern Iran. 65 SCD patients consisting of 35 sickle cell anemia homozygous (SS), 15 sickle cell heterozygous (AS) and 15 sickle cell/βThalassemia (S/βthal) patients and 68 healthy individuals with normal hematological indices were studied. APOE and FVL polymorphisms were detected by PCR–RFLP and serum lipid level was measured enzymatically. The frequencies of FVL and APOE-ε4 allele were significantly higher in SCD patients than in control (15.4 vs. 4.4 and 13.7% vs. 3.3%, respectively). The distributions of APOE ε3ε3, ε2ε3 and ε2ε4 + ε3ε4 alleles in SCD patients were significantly different from those in the control group. The SCD subjects particularly SS/S βthal (SS + S/βthal) and SS patients have significantly lower frequency of APOE ε3ε3 allele (P < 0.05) whereas SCD, SS patients and AS individuals have a significantly higher frequency of APOE ε4 allele (ε2ε4 + ε3ε4; P = 0.003, P = 0.011 and P = 0.035, respectively) compared to the control group. The LDL-C (P = 0.006) and total cholesterol (P < 0.001) levels in SCD subjects were found to be significantly lower than those in the control group. In addition, the presence of non-APOE ε4 allele (ε2ε3 + ε3ε3) resulted in a significant decrease in the level of LDL-C and total cholesterol in SCD subjects in general and in SS and SS/S βthal patients in particular compared to controls. Furthermore, the presence of APOE ε4 allele (ε2ε4 + ε3ε4) was found to be associated with the risk of sickle cell anemia [OR = 4.1, P = 0.04]. The presence of either FVL mutation (OR = 4.6; CI: 0.91–24, P = 0.07) or APOE-ε4 allele (OR = 4.07; CI: 1.01–16.4, P = 0.048) is associated with the risk of sickle cell disease in Southern Iran. This data suggest that the activation of coagulation system enhances thrombus generation and decreases antioxidant activity in SCD patients from Southern Iran.     

Erythroid-specific expression of β-globin from Sleeping Beauty-transduced human hematopoietic progenitor cells

Gene therapy for sickle cell disease will require efficient delivery of a tightly regulated and stably expressed gene product to provide an effective therapy. In this study we utilized the non-viral Sleeping Beauty (SB) transposon system using the SB100X hyperactive transposase to transduce human cord blood CD34(+) cells with DsRed and a hybrid IHK-β-globin transgene. IHK transduced cells were successfully differentiated into multiple lineages which all showed transgene integration. The mature erythroid cells had an increased β-globin to γ-globin ratio from 0.66±0.08 to 1.05±0.12 (p=0.05), indicating expression of β-globin from the integrated SB transgene. IHK-β-globin mRNA was found in non-erythroid cell types, similar to native β-globin mRNA that was also expressed at low levels. Additional studies in the hematopoietic K562 cell line confirmed the ability of cHS4 insulator elements to protect DsRed and IHK-β-globin transgenes from silencing in long-term culture studies. Insulated transgenes had statistically significant improvement in the maintenance of long term expression, while preserving transgene regulation. These results support the use of Sleeping Beauty vectors in carrying an insulated IHK-β-globin transgene for gene therapy of sickle cell disease.     

O2 dependence of K+ transport in sickle cells: the effect of different cell populations and the substituted benzaldehyde 12C79.

The molecular basis of sickle cell disease (SCD) is well known but the pathophysiology is poorly understood. It remains intractable to therapy. Hyperactivity of several membrane transport systems, including the K+-Cl- cotransporter (termed KCC), cause HbS-containing red cells (termed HbS cells) to dehydrate and sickle, leading to the development of sickle cell crises (SCCs). Contrary to normal red cells (HbA cells), KCC in HbS cells is active at low O2 tensions (PO2s), remaining responsive to low pH or urea. Since these stimuli are usually encountered in hypoxic regions, the abnormal O2 dependence increases the contribution of KCC to dehydration, and hence development of SCCs. These differences with HbA cells may be due to the younger population of cells or to polymerization of HbS. We used 86Rb+ as a K+ congener to investigate the activity of KCC at different PO2s, and density gradient separation to investigate different red cell fractions. We found no correlation of O2 dependence with cell fractions. We also used the substituted benzaldehyde 12C79 to increase the O2 affinity of HbS and found that its effect on HbS O2 saturation and cell sickling correlated with that on both Cl--independent and Cl--dependent K+ transport, implying that, at low PO2s, KCC activity correlated with HbS polymerization. The importance of these results to understanding the pathophysiology of SCD, and for the design of chemotherapeutic agents to ameliorate or prevent SCC, is discussed.     

Molecular insights into the irreversible mechanical behavior of sickle hemoglobin

Sickle cell disease is caused by the amino acid substitution of glutamic acid to valine, which leads to the polymerization of deoxygenated sickle hemoglobin (HbS) into long strands. These strands are responsible for the sickling of red blood cells (RBCs), making blood hyper-coagulable leading to an increased chance of vaso-occlusive crisis. The conformational changes in sickled RBCs traveling through narrow blood vessels in a highly viscous fluid are critical in understanding; however, there are few studies that investigate the origins of the molecular mechanical behavior of sickled RBCs. In this work, we investigate the molecular mechanical properties of HbS molecules. A mechanical model was used to estimate the directional stiffness of an HbS molecule and the results were compared to adult human hemoglobin (HbA). The comparison shows a significant difference in strength between HbS and HbA, as well as anisotropic behavior of the hemoglobin molecules. The results also indicated that the HbS molecule experienced more irreversible mechanical behavior than HbA under compression. Further, we have characterized the elastic and compressive properties of a double stranded sickle fiber using six HbS molecules, and it shows that the HbS molecules are bound to each other through strong inter-molecular forces.     

Molecular Determination of Vascular Endothelial Growth Factor,miRNA-423 Gene Abnormalities by Utilizing ARMS-PCR and Their Association with Fetal Hemoglobin Expression in the Patients with Sickle Cell Disease

Recent studies have indicated that microRNA and VEGF are considered to be genetic modifiers and are associated with elevated levels of fetal haemoglobin HbF, and thus they reduce the clinical impact of sickle haemoglobin (HbS) patients. This cross-sectional study was performed on clinical confirmed subjects of SCD cases. miR-423-rs6505162 C>T and VEGF-2578 C>A genotyping was conducted by ARMS-PCR in SCD and healthy controls. A strong clinical significance was reported while comparing the association of miR-423 C>T genotypes between SCD patients and controls (p = 0.031). The microRNA-423 AA genotype was associated with an increased severity of SCD in codominant model with odd ratio (OR = 2.36, 95% CI, (1.15–4.84), p = 0.018) and similarly a significant association was observed in recessive inheritance model for microRNA-423 AA vs (CC+CA) genotypes (OR = 2.19, 95% CI, (1.32–3.62), p < 0.002). The A allele was associated with SCD severity (OR = 1.57, 95% CI, (1.13–2.19), p < 0.007). The distribution of VEGF-2578 C>A genotypes between SCD patients and healthy controls was significant (p < 0.013). Our results indicated that in the codominant model, the VEGF-2578-CA genotype was strongly associated with increased SCD severity with OR = 2.56, 95% CI, (1.36–4.82), p < 0.003. The higher expression of HbA1 (65.9%), HbA2 (4.40%), was reported in SCD patients carrying miR-423-AA genotype than miR-423 CA genotype in SCD patients carrying miR-423 CA genotype HbA1 (59.98%), HbA2 (3.74%) whereas SCD patients carrying miR-423 CA genotype has higher expression of HbF (0.98%) and HbS (38.1%) than in the patients carrying AA genotype HbF (0.60%), HbS (36.1%). ARMS-PCR has been proven to be rapid, inexpensive and is highly applicable to gene mutation screening in laboratories and clinical practices. This research highlights the significance of elucidating genetic determinants that play roles in the amelioration of the HbF levels that is used as an indicator of severity of clinical complications of the monogenic disease. Further well-designed studies with larger sample sizes are necessary to confirm our findings.     

Human globin knock-in mice complete fetal-to-adult hemoglobin switching in postnatal development

Elevated levels of fetal γ-globin can cure disorders caused by mutations in the adult β-globin gene. This clinical finding has motivated studies to improve our understanding of hemoglobin switching. Unlike humans, mice do not express a distinct fetal globin. Transgenic mice that contain the human β-globin locus complete their fetal-to-adult hemoglobin switch prior to birth, with human γ-globin predominantly restricted to primitive erythroid cells. We established humanized (100% human hemoglobin) knock-in mice that demonstrate a distinct fetal hemoglobin (HbF) stage, where γ-globin is the dominant globin chain produced during mid- to late gestation. Human γ- and β-globin gene competition is evident around the time of birth, and γ-globin chain production diminishes in postnatal life, with transient production of HbF reticulocytes. Following completion of the γ- to-β-globin switch, adult erythroid cells synthesize low levels of HbF. We conclude that the knock-in globin genes are expressed in a pattern strikingly similar to that in human development, most notably with postnatal resolution of the fetal-to-adult hemoglobin switch. Our findings are consistent with the importance of BCL11A in hemoglobin switching, since removal of intergenic binding sites for BCL11A results in human γ-globin expression in mouse definitive erythroid cells.     

Mixed gelation theory. Kinetics, equilibrium and gel incorporation in sickle hemoglobin mixtures.

This paper outlines a theoretical formalism for describing the gelling behavior of sickle cell hemoglobin in mixtures with other hemoglobin and non-hemoglobin proteins. Experimental applications are reported for hybridized and unhybridized mixtures of HbS (sickle hemoglobin), HbA (adult hemoglobin), HbF (fetal hemoglobin), and HbC Harlem. The theory is a general one based on a modification of the sol—gel phase equilibrium equation to take into account the varying tendencies of different hemoglobin species to promote gelation, and specific hemoglobin interactions are encoded in gelling coefficients which quantify gelling capability. Gelling coefficients for the hemoglobin species dealt with here are evaluated by measuring incorporation into the polymer phase in S-A, S-F, and S-C_H mixtures. Given this information, the theory is found to provide accurate prodictions for the equilibrium gelling behavior of the calibrating pairs themselves when they are hybridized or unhybridized, for gelation kinetics in diverse mixtures of these species taken two, three and four at a time, for the anomalous equilibrium and kinetic gelling behavior of A- C_H mixtures, and it also accounts for a variety of results previously published by others. Apparently, given the gelling coefficients for any mutant hemoglobin, one can compute gelling behavior (equilibrium, kinetics, incorporation, etc.) in any specified mixture with any other known hemoglobin(s). The gelling coefficients for any mutant hemoglobin depend upon, and therefore provide information about, gel interactions at the mutant site. From the gelling coefficients one can also obtain the change in free energy of interaction in the gel due to the altered residue. Experimental approaches are described which allow an analysis for the gelling coefficients of any mutant hemoglobin to be performed in a few hours.     

Role of age and neuroinflammation in the mechanism of cognitive deficits in sickle cell disease

This study aims to determine whether sickle cell mice could recapitulate features of cognitive and neurobehavioral impairment observed in sickle cell patients and whether neuroinflammation could be a potential therapeutic target as in other non-sickle cell disease-related cognitive dysfunction. Cognitive (learning and memory) and behavioral (anxiety) deficits in 13- and later 6-month-old male Townes humanized sickle cell (SS) and matched control (AA) mice were evaluated using novel object recognition (NOR) and fear conditioning tests. Immunohistochemistry was performed to quantify peripheral immune cell (CD45⁺) and activated microglia (Iba1⁺) as markers of neuroinflammation in the dentate and peri-dentate gyrus areas. We evaluated cell fate by measuring 5''-bromodeoxyuridine and doublecortin fluorescence and phenotyped proliferating cells using either glial fibrillary acid protein (GFAP⁺), neuronal nuclei (NeuN⁺), CD45⁺, and Iba1⁺. In addition, Golgi-Cox staining was used to assess markers of neuroplasticity (dendritic spine density and morphology and density of dendrite arbors) on cortical and hippocampal pyramidal neurons. Compared to matched AA controls, 13-month-old SS mice showed significant evidence of cognitive and behavioral deficit on NOR and fear conditioning tests. Also, SS mice had significantly higher density of CD45⁺ and activated microglia cells (i.e. more evidence of neuroinflammation) in the dentate and peri-dentate gyrus area. Additionally, SS mice had significantly lower dendritic spine density, but a higher proportion of immature dendritic spines. Treatment of 13-month-old SS mice with minocycline resulted in improvement of cognitive and behavioral deficit compared to matched vehicle-treated SS mice. Also, treated SS mice had significantly fewer CD45⁺ and activated microglia cells (i.e. less evidence of neuroinflammation) in the dentate and peri-dentate gyrus, as well as a significant improvement in markers of neuroplasticity.Impact statementThis study provides crucial information that could be helpful in the development of new or repurposing of existing therapies for the treatment of cognitive deficit in individuals with sickle cell disease (SCD). Its impact is in demonstrating for the first time that neuroinflammation and along with abnormal neuroplasticity are among the underlying mechanism of cognitive and behavioral deficits in SCD and that drugs such as minocycline which targets these pathophysiological mechanisms could be repurposed for the treatment of this life altering complication of SCD.