Accumulating evidence indicates that the adolescent hippocampus is highly susceptible to alcoholinduced structural damage and behavioral deficits. Microglia are vitally important brain constituents needed to support and maintain proper neural function; however, alcohol's effects on microglia have only recently gained attention. The microglial response to alcohol during adolescence has yet to be studied; therefore, we examined hippocampal microglial activation in an adolescence binge alcohol exposure model. Adolescent male Sprague-Dawley rats were administered ethanol 3 times/day for 4 days and were sacrificed 2, 7, and 30 days later. Bromodeoxy-Uridine was injected 2 days after ethanol exposure to label dividing cells. Microglia morphology was scored using the microglia marker Iba-1, while the extent of microglial activation was examined with ED-1, major histocompatability complex-II (MHC-II), and tumor necrosis factor (TNF)-α expression. Ethanol induced significant morphological change in hippocampal microglia, consistent with activation. In addition, ethanol increased the number of BrdU+ cells throughout all regions of the hippocampus 2 days after the last dose. Confocal microscopy showed that the proliferating BrdU+ cells in each region were Iba-1+ microglia. Importantly, newly born microglia survived and retained their morphological characteristics 30 days after ethanol exposure. Ethanol did not alter hippocampal ED-1, MHC-II, or TNF-α expression, suggesting that a single period of binge ethanol exposure does not induce a full microglial-driven neuroinflammatory response. These results establish that ethanol triggers partial microglial activation in the adolescent hippocampus that persists through early adulthood, suggesting that alcohol exposure during this unique developmental time period has long-lasting consequences.

Myeloid differentiation factor-2 (MD-2) binds lipopolysaccharide (LPS) and initiates toll-like receptor-4 (TLR4) pro-inflammatory signaling. Heme also activates TLR4 signaling, but it is unknown if heme interacts with MD-2. Therefore, we examined MD-2 for a potential heme activation site. Heme-agarose and biotin-heme/streptavidin-agarose pulled down recombinant MD-2, which was inhibited by excess free heme. UV/visible spectroscopy confirmed MD-2-heme binding. To determine whether MD-2 was required for heme-mediated TLR4 signaling, HEK293 cells were transfected with MD-2, TLR4, CD14, and an NF-κB luciferase reporter, and then stimulated with heme or LPS. Heme or LPS treatment elicited robust reporter activity. Absence of MD-2, TLR4 or CD14 plasmid abolished NF-κB reporter responses to heme or LPS. In silico analysis identified two potential heme docking sites on MD-2 near conserved amino acids W23/S33/Y34 and Y36/C37/I44. Heme-induced NF-κB activity was reduced by 39 and 78% in HEK293 cells transfected with MD-2 mutants W23A and Y34A, respectively, compared to WT-MD-2. NF-κB activation by LPS was not affected by the same mutants. Biotinyl-heme/streptavidin-agarose pulled down 68% less W23A and 80% less W23A/S33A/Y34A mutant MD-2 than WT-MD-2. In contrast, at the Y36/C37/I44 MD-2 site, heme-induced NF-κB activity was significantly increased by mutants Y36A (191% of WT-MD-2) and unchanged by mutants C37A and I44A (95 and 92%, respectively, of WT-MD-2). In conclusion, these data suggest that heme binds and activates TLR4 signaling at amino acids W23 and Y34 on MD-2.

Carbon monoxide (CO) at low, non-toxic concentrations has been previously demonstrated to exert anti-inflammatory protection in murine models of sickle cell disease (SCD). However CO delivery by inhalation, CO-hemoglobin infusion or CO-releasing molecules presents problems for daily CO administration. Oral administration of a CO-saturated liquid avoids many of these issues and potentially provides a platform for self-administration to SCD patients. To test if orally-delivered CO could modulate SCD vaso-occlusion and inflammation, a liquid CO formulation (HBI-002) was administered by gavage (10 ml/kg) once-daily to NY1DD and Townes-SS transgenic mouse models of SCD. Baseline CO-hemoglobin (CO-Hb) levels were 1.6% and 1.8% in NY1DD and Townes-SS sickle mice and 0.6% in Townes-AS control mice. CO-Hb levels reached 5.4%, 4.7% and 3.0% within 5 minutes in NY1DD, SS and AS mice respectively after gavage with HBI-002. After ten treatments, each once-daily, hemoglobin levels rose from 5.3g/dL in vehicle-treated Townes-SS mice to 6.3g/dL in HBI-002-treated. Similarly, red blood cell (RBC) counts rose from 2.36 x 106/μL in vehicle-treated SS mice to 2.89 x 106/μL in HBI-002-treated mice. In concordance with these findings, hematocrits rose from 26.3% in vehicle-treated mice to 30.0% in HBI-002-treated mice. Reticulocyte counts were not significantly different between vehicle and HBI-002-treated SS mice implying less hemolysis and not an increase in RBC production. White blood cell counts decreased from 29.1 x 103/μL in vehicle-treated versus 20.3 x 103/μL in HBI-002-treated SS mice. Townes-SS mice treated with HBI-002 had markedly increased Nrf2 and HO-1 expression and decreased NF-κB activation compared to vehicle-treated mice. These anti-inflammatory effects were examined for the ability of HBI-002 (administered orally once-daily for up to 5 days) to inhibit vaso-occlusion induced by hypoxia-reoxygenation. In NY1DD and Townes-SS sickle mice, HBI-002 decreased microvascular stasis in a duration-dependent manner. Collectively, these findings support HBI-002 as a useful anti-inflammatory agent to treat SCD and warrants further development as a therapeutic.

Heme, released from red blood cells in sickle cell disease (SCD), interacts with toll-like receptor 4 (TLR4) to activate NF-κB leading to the production of cytokines and adhesion molecules which promote inflammation, pain, and vaso-occlusion. In SCD, TLR4 inhibition has been shown to modulate heme-induced microvascular stasis and lung injury. We sought to delineate the role of endothelial verses hematopoietic TLR4 in SCD by developing a TLR4 null transgenic sickle mouse. We bred a global Tlr4-/- deficiency state into Townes-AA mice expressing normal human adult hemoglobin A and Townes-SS mice expressing sickle hemoglobin S. SS-Tlr4-/- had similar complete blood counts and serum chemistries as SS-Tlr4+/+ mice. However, SS-Tlr4-/- mice developed significantly less microvascular stasis in dorsal skin fold chambers than SS-Tlr4+/+ mice in response to challenges with heme, lipopolysaccharide (LPS), and hypoxia/reoxygenation (H/R). To define a potential mechanism for decreased microvascular stasis in SS-Tlr4-/- mice, we measured pro-inflammatory NF-κB and adhesion molecules in livers post-heme challenge. Compared to heme-challenged SS-Tlr4+/+ livers, SS-Tlr4-/- livers had lower adhesion molecule and cytokine mRNAs, NF-κB phospho-p65, and adhesion molecule protein expression. Furthermore, lung P-selectin and von Willebrand factor immunostaining was reduced. Next, to establish if endothelial or hematopoietic cell TLR4 signaling is critical to vaso-occlusive physiology, we created chimeric mice by transplanting SS-Tlr4-/- or SS-Tlr4+/+ bone marrow into AA-Tlr4-/- or AA-Tlr4+/+ recipients. Hemin-stimulated microvascular stasis was significantly decreased when the recipient was AA-Tlr4-/-. These data demonstrate that endothelial, but not hematopoietic, TLR4 expression is necessary to initiate vaso-occlusive physiology in SS mice.

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Lipopolysaccharide (LPS), the first-identified TLR4 agonist, binds myeloid differentiation factor-2 (MD-2) in association with TLR4 to initiate TLR4 signaling. LPS binds to a large hydrophobic pocket in MD-2 and directly bridges the MD-2/TLR4 heterodimer. The MD-2/TLR4 complex also recognizes a diverse number of endogenous molecules released from injured cells called damage-associated molecular patterns or DAMPs. One such DAMP is heme. Large amounts of heme can be released intravascularly by trauma, sepsis, malaria and red blood cell disorders such as sickle cell disease (SCD). Recent studies underscore the importance of heme-mediated MD-2/TLR4 activation in inflammation, vessel occlusion, lethality and pulmonary injury in SCD. Therefore, we examined human MD-2 for potential heme activation sites. Recombinant MD-2 (rMD-2) was produced by transfecting Chinese hamster ovary (CHO) cells with human MD-2 plasmids. After 72 hours, Western blots of the CHO-conditioned media demonstrated soluble rMD-2 was present. Heme was shown to bind rMD-2 using pull-down assays utilizing heme-agarose or biotin-heme with streptavidin-agarose coupled with MD-2 Western blots of the pellet. These pull-down assays of rMD2 were inhibited by excess heme, indicating specific binding of heme to rMD-2. UV/visible scanning spectroscopy (250 - 550 nm) of purified rMD-2 in the presence or absence of heme, confirmed specific rMD-2-heme binding. In silico analyses combining both structure and sequence-based methods, identified two potential heme docking sites on MD-2 near conserved amino acids W23/S33/Y34 and Y36/C37/I44 (Figure 1). To determine whether MD-2 mutations at these two sites affect heme-MD-2/TLR4 signaling, HEK293 cells were transfected with plasmids encoding human MD-2, TLR4, CD14 and an NF-κB luciferase reporter. After 24 hours, transfected cells were stimulated with heme (10 μM) or LPS (10 ng/ml) for 6 hours and NF-κB luciferase reporter activity was measured. Heme or LPS treatment elicited robust luciferase activity. The addition of both heme and LPS had an additive effect on NF-κB luciferase activity. Absence of an MD-2, TLR4 or CD14 plasmid abolished NF-κB luciferase reporter responses to heme and/or LPS. When plasmids encoding MD-2 point mutants W23A or Y34A were introduced into MD-2, heme-induced NF-κB luciferase activity was inhibited 91-92% compared to WT-MD-2. The S33A MD-2 mutant stimulated NF-κB luciferase activity by 40%. NF-κB activation by LPS was marginally affected by the same mutants. Biotin-heme/streptavidin-agarose pulled down 68% less W23A mutant MD-2 and 80% less W23A/S33A/Y34A mutant MD-2 than WT-MD-2. In contrast, at the other potential heme binding site, heme-induced NF-κB luciferase activity was increased in mutants Y36A (120%), C37A (121%) and I44A (230%) compared to WT-MD-2. These data suggest that amino acids W23 and Y34 on MD-2 are specific for heme binding and TLR4 signaling. This heme activation site was targeted for potential inhibitors using virtual screening. The virtual screen identified 60 potential inhibitors for screening in heme-stimulated primary human umbilical vein endothelial cells (HUVEC) and a human U-937 monocyte cell line. Four of these molecules inhibited Weibel-Palade body P-selectin and von Willebrand factor expression in HUVEC and IL-8 secretion by U-937 cells stimulated with heme. We conclude that heme activates MD-2/TLR4 signaling at residues W23 and Y34 on MD-2, which might be a drugable target in SCD and other hemolytic diseases. Disclosures Belcher: Mitobridge, an Astellas Company: Consultancy, Research Funding. Vercellotti:Mitobridge, an Astellas Company: Consultancy, Research Funding.

BackgroundChronic inflammation is a characteristic of sickle cell disease (SCD), and is invariably associated with vascular endothelial injury. Hydroxyurea (HU), a naturally cytotoxic chemotherapeutic agent, is the only FDA drug approved for SCD, and is therefore naturally cytotoxic. Quercetin (QCT) is a dietary flavonoid found ubiquitously in plants and foods that have anti-oxidative and anti-inflammatory characteristics. Our hypothesis is that dietary QCT will decrease cytotoxic effects of lipopolysaccharide (LPS) and HU induced vascular cell damage.MethodsLipopolysaccharide (LPS) was used to induce inflammation in immortalized mouse aortic endothelial cells (iMAECs), providing an in vitro model of inflamed endothelial cells. The cells were exposed to LPS throughout the entire experiment. Interventions included treating the LPS exposed cells with QCT, HU, or QCT + HU over 50 hours. The 50-hour period included 24 hours of varying treatments, followed by two hours of hypoxic exposure and then 24 hours under normal aerobic exposure.ResultsLDH level was significantly higher for LPS treated versus untreated cells (P = 0.0004). LPS plus 30 micromole QCT reduced the LDH (p = 0.1, trend), whereas LPS plus 100 micromoles HU, significantly increased LDH (p = 0.0004). However, LPS plus treatment with 30 micromoles QCT/100 micromoles HU, significantly reduced LDH, compared with HU alone (p = 0.0002).DiscussionThese results suggest that quercetin may be effective against vascular endothelial cell damage for iMAECs in vitro. In particular, it shows promise in preventing HU-induced cytotoxicity, surprisingly found from these results. This latter finding is important, and should be given more consideration, since HU is the only FDA-approved drug for treating sickle cell patients, and its use is rapidly increasing.

Introduction Sickle cell anemia (SCA) is caused by the homozygous inheritance of the βS allele (HbSS). SCA's destructive pathogenesis drives a state of continual oxidative stress and vascular inflammation due to accelerated auto-oxidation, iron de-compartmentalization, and inflammatory cell-derived oxidants. Continuous oxidative stress and vascular inflammation bolsters vaso-occlusion and ischemia-reperfusion cycling, impacting the functionality of multiple organ systems. The auditory system is particularly vulnerable to vaso-occlusive events as an end organ system. Repetitive damage secondary to recurrent SCA crises presents phenotypically as sensorineural hearing loss (SNHL), negatively impacting many children and adults living with SCA. A SCA crisis leads to stasis of the labyrinthine artery which supplies the inner ear, leading to hypoxia of the Organ of Corti and the Stria Vascularis within the cochlea and causing death of outer hair cells--important for amplification of sound. This results in permanent inner ear damage and hearing loss. Hearing loss in children has a documented negative effect on academic performance, speech and language development as well as self-image. For adults, hearing loss can have significant impact on career choices and effective communication in the workplace. Previous studies estimating the rate of SNHL in SCA suffer from significant design flaws, making broad application difficult. The major design flaws were: 1) no matched control population, 2) varying definitions of what qualifies as SNHL, and 3) absence of defined demographics within SCA and control groups. To address these flaws, a strict meta-analysis of the literature was performed comparing the prevalence of hearing loss in SCA and the general population. Methods & Results A comprehensive-- SCOPUS, PubMed, Google Scholar, and Medline--literature search was conducted to identify the prevalence of SCA pediatric SNHL, published between January 1970 and December 2018. Data was extracted by two reviewers per the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines, whereby there was no blinding to authors, journals of publication, or the results of the studies. Conference abstracts, posters, and single patient case reports were not excluded. Inclusion criteria included studies that examined exclusively SCA populations and rate of SNHL with a clearly defined threshold for hearing loss. Additionally, papers needed to include distinctly defined age ranges and a non-SCA control population. The initial search yielded 49 studies, with 21 studies meeting the inclusion criteria. Of the 21 studies identified, only 6 exclusively examined pediatric patients while the remaining were mixed adult/pediatric studies. To perform the analysis, we conducted a random effect (DerSimonian-Laird) meta-analysis. A Haldane-Anscombe correction was used to account for cases of no hearing loss within certain groups with small samples. The log odds ratio (LogOR) for SNHL in the mixed adult/pediatric population was 1.9 (95% CI 1.33 - 2.4) and the LogOR for SNHL in the pediatric only population was 1.4 (95% CI 0.781 - 2.1). These results indicate a strong association between SNHL and SCA in the adult and pediatric population. Conclusions SNHL among children can have deleterious impacts on their development, this meta-analysis showed a significant association between SCA and the development SNHL. The stronger association between SNHL in AN adult population compared to A pediatric population showed that there is worsening of SNHL over time secondary to SCA. At present, the data implies there should be an increase in audiological testing and screening in all patients diagnosed with SCA. (add in all forms of SCD) Clinical care providers should also make themselves aware of this under-reported and severe pathology in their patient population. The research community must also make efforts to standardize their approaches to measuring and observing this phenomenon to make certain that all future studies are clinically applicable and translatable. Figure Disclosures Vercellotti: Mitobridge, an Astellas Company: Consultancy, Research Funding.