Nath, Karl A.

Abstract Abstract 1318 Previous studies have demonstrated that heme-oxygenase-1 (HO-1), the rate limiting enzyme in the catabolism of heme, is a regulator of the balance between hematopoiesis and stem cell preservation under stress. HO-1−/− mice display oxidative stress, anemia, and leukocytosis with chronic inflammation. We hypothesize that therapy with inhaled carbon monoxide (CO), a by-product of HO-1 activity with antioxidant and anti-apoptotic properties; will reduce stress hematopoiesis in HO-1−/− mice, reducing inflammation and redistributing hematopoietic potential. In order to test this hypothesis we treated 25 week old HO-1−/− mice and HO-1+/+ mice (n=7/strain) with 250 ppm inhaled CO for 1 h/day, 3 days/week for eight weeks and compared them to an equal number of untreated HO-1−/− and HO-1+/+ mice. After 8-weeks of treatment the mice were sacrificed and flow cytometry was performed on bone marrow to assess hematopoietic potential. Cell cycle analysis of the bone marrow demonstrates that untreated HO-1−/− mice have a significantly decreased percent of cells in S-phase compared to untreated HO-1+/+ mice. Treatment with CO significantly (p<0.05) increases the percent of cells in S-phase in HO-1−/− mice but not HO-1+/+ mice. Reactive oxygen species (ROS) production in lineage−, c-kit+, Sca-1+ (KLS) cell population was assessed using 5-(and 6-)-chloromethyl-2',7'-dichlorodihydrofluorescein diacetate dye. HO-1−/− mice have a significantly (p<0.001) increased proportion of ROS positive KLS cells compared with HO-1+/+ mice. Analysis of long-term (LT), short-term, and multipotent (MPP) progenitor cell populations was conducted. Treatment with CO significantly (p<0.05) increases the percent of LT-HSC and MPP progenitor cells in HO-1−/− mice but not HO-1+/+ mice. Concordantly, the total white blood cell count of the CO-treated mice increased significantly. The differential of the mature blood cells demonstrates significant shift in cell maturation, with significant increase in red blood cells, platelets, and lymphocytes and a significant decrease in monocytes. Combined this data indicates that CO therapy is able to modify the hematopoietic potential of HO-1−/− mice leading to a change in mature cell populations. We propose a model in which CO-mediated signaling initiates a homeostatic conditioning program in stem cells to balance hematopoiesis and stem cell preservation, ultimately leading to a change in the inflammatory milieu of the mice. Disclosures: Belcher: Sangart, Inc: Research Funding. Vercellotti:Sangart, Inc: Research Funding.

Abstract The kidney is the most common organ involved in systemic light-chain amyloidosis (AL), seen in up to 40% of patients. Renal involvement can result in proteinuria and/or renal insufficiency. The mechanism of renal injury in amyloidosis remains unclear. We present data supporting a central role for oxidative stress in amyloid-induced renal damage. Soluble free light chains(LCs) were isolated from plasma of AL and myeloma patients obtained at the time of stem cell collection. LCs were purified by liquid-phase iso-electric fractionation of pooled plasma samples from each patient. Purified LC were incubated with cultured rat renal epithelial cells, both wild-type and heme oxygenase-1 (HO-1) over-expressing, for 16 hours. Macrophage chemoattractant protein-1 (MCP-1) induction was measured in the media by ELISA. LC from myeloma patients were used as negative controls. Significant induction of MCP-1, a sensitive indicator of oxidative stress, was seen in 4/5 patients with lambda light-chain amyloidosis and 0/4 kappa light-chain amyloidosis patients. Induction of MCP-1 was seen in only 1/8 myeloma patients tested (4 lambda and 4 kappa). Induction of MCP-1 was reduced in the presence of HO-1 overexpression, implicating oxidative stress as a critical pathway of toxicity of amyloidogenic lambda light chains in this system. These results suggest that lambda and kappa light chains may cause renal injury through distinct pathways in the kidney.

Abstract Abstract SCI-26 The kidney is often the target of injury by heme proteins and states of iron overload. Exogenous heme proteins, such as hemoglobin delivered to the kidney in hemolytic states, or myoglobin imposed upon the kidney following rhabdomyolysis, can injure the kidney via pathways that include vasoconstriction, direct cytotoxicity, and tubular cast formation. The former two pathways critically involve the heme prosthetic group: heme can bind vasodilator gases such as nitric oxide and carbon monoxide, while free heme can be cytotoxic because it is lipophilic, lipid membrane-transmissible, lipid membrane-destabilizing, prooxidant, and proinflammatory. Renal injury can also arise from endogenous heme proteins, such as cytochrome P450 enzymes, which can be destabilized by ischemic and nephrotoxic insults; such destabilization leads to the release of heme and incurs heme-dependent injury. The toxicity of heme may also reflect, at least in part, the release of iron and the attendant increase in labile cellular iron, the latter representing a potent catalyst for oxidative stress; increased levels of cellular iron may also originate from intracellular nonheme sources. Heme-iron can not only induce acute kidney injury, but also can provoke chronic kidney disease by virtue of its proinflammatory and profibrotic effects. Mechanisms that protect against heme-dependent and iron-dependent toxicity include heme oxygenase (HO), the rate-limiting enzyme in heme degradation, and increased synthesis of ferritin. Induction of HO-1, the inducible HO isoform, is protective against renal injury because of the following mechanisms: 1) the prevention of acute elevation in cellular heme concentrations otherwise incurred by cell injury; 2) the safe sequestration of iron in iron-binding proteins such as ferritin, or the cellular extrusion of iron by iron-exporting proteins; 3) the generation of antioxidant, anti-inflammatory metabolites such as bile pigments; and 4) the generation of carbon monoxide which is an antiapoptotic, anti-inflammatory, and vasorelaxant gas. Carbon monoxide can also be cytoprotective by binding cytochrome P450 enzymes, and thereby preventing their destabilization and the release of heme that subsequently occurs. In addition to these areas, this presentation discusses the pathobiologic and clinical significance of the siderophore-binding protein, NGAL (Neutrophil gelatinase-associated lipocalin): NGAL protects against renal ischemic injury through mechanisms that require the induction of HO-1; NGAL is increasingly utilized as a biomarker of acute kidney injury. The presentation concludes by discussing the use of iron supplementation in the treatment of anemia of chronic kidney disease and therapeutic strategies that may be designed from understanding endogenous and adaptive mechanisms that protect against the toxicity of heme-iron. Disclosures: No relevant conflicts of interest to declare.

Abstract Abstract 4767 Previous studies have demonstrated that heme-oxygenase-1 (HO-1), the rate limiting enzyme in the catabolism of heme, is a regulator of the balance between hematopoiesis and stem cell preservation under stress. HO-1 produces three by-products, carbon monoxide, biliverdin/bilirubin, and iron/ferritin, all of which have demonstrated antioxidant and anti-apoptotic properties. HO-1-/- mice display oxidative stress, anemia, and leukocytosis with chronic inflammation. We hypothesize that therapy with inhaled carbon monoxide (CO) may reduce stress hematopoiesis in HO-1-/- mice, restoring them to normal hematopoiesis. We have previously reported that treatment with 250 ppm CO for 1 h raises mouse carboxyhemoglobin to 14–20% which returns to baseline within 24 hours. Therefore, in order to test this hypothesis we treated 25 week old HO-1-/- mice and HO-1+/+ mice (n=7/strain) with 250 ppm inhaled CO for 1 h/day, 3 days/week for eight weeks and compared them to an equal number of untreated HO-1-/- and HO-1+/+ mice. We demonstrate that after four weeks, CO-treated HO-1-/- mice have a total white blood cell count of 11.9 ± 3.2 K/μ L compared to 22.6 ± 3.2 K/μ L in untreated HO-1-/- mice (p<0.05), with HO-1+/+ mice having no treatment effect. After 8-weeks of treatment the mice were sacrificed and methylcellulose colony-forming unit assays and flow cytometry were performed on bone marrow to assess their hematopoietic potential. Total methylcellulose colony-forming units were similar in both HO-1-/- and HO-1+/+ mice with CO-treatments significantly (p<0.05) increasing the total number of colonies per animal. Of note, in both the CO-treated HO-1-/- and HO-1+/+ mice the CFU-GM were not significantly affected. Cell cycle analysis of the bone marrow using propidium iodide demonstrates that untreated HO-1-/- mice have a significantly decreased percent of cells in S-phase compared to untreated HO-1+/+ mice. Treatment with CO significantly (p<0.05) increases the percent of cells in S-phase in HO-1-/- mice but not HO-1+/+ mice. Similarly, untreated HO-1-/- mice have a lower frequency of cells in sub-G1 phase compared to untreated HO-1+/+ mice, however CO-treatments significantly (p<0.01) increase this frequency in HO-1-/- mice to levels comparable with untreated and CO-treated HO-1+/+ mice. Reactive oxygen species (ROS) production in lineage-, c-kit+, Sca-1+ (KLS) cell population was assessed using 5-(and 6-)-chloromethyl-2′,7′-dichlorodihydrofluorescein diacetate dye. HO-1-/- mice have a significantly (p<0.001) increased proportion of ROS positive KLS cells compared with HO-1+/+ mice. Interestingly, the CO-treated HO-1-/- mice had a significantly higher proportion of KLS cells staining positive for ROS, but the mean fluorescent intensity of this population was significantly (p<0.05) decreased compared to untreated HO-1-/- mice. This indicates that there is an overall decrease in ROS in the KLS cells of CO-treated HO-1-/- mice compared to untreated HO-1-/- mice. Analysis of long-term, short-term, and multipotent progenitor cell populations was conducted and reveals significant changes at the level of the short-term hematopoietic progenitor population (ST-HSC). Specifically, untreated HO-1-/- mice have a significantly increased percent of ST-HSC cells compared to untreated HO-1+/+ mice. Treatment with CO significantly (p<0.05) decreases the percent of ST-HSC cells in HO-1-/- mice but not HO-1+/+ mice. Combined this data indicates that CO therapy is able to modify the hematopoietic potential of HO-1-/- mice. We propose a model in which CO-mediated signaling initiates a homeostatic conditioning program in stem cells to balance hematopoiesis and stem cell preservation. Disclosures: Belcher: Sangart: Research Funding. Vercellotti:Sangart: Consultancy, Research Funding.

Heme oxygenase (HO) activity is exhibited by inducible (HO-1) and constitutive (HO-2) proteins. HO-1 protects against ischemic and nephrotoxic acute kidney injury (AKI). We have previously demonstrated that HO-2 protects against heme protein-induced AKI. The present study examined whether HO-2 is protective in ischemic AKI. Renal ischemia was imposed on young and aged HO-2+/+ and HO-2−/− mice. On days 1 and 2 after renal ischemia, there were no significant differences in renal function between young male HO-2+/+ and HO-2−/− mice, between young female HO-2+/+ and HO-2−/− mice, or between aged female HO-2+/+ and HO-2−/− mice. However, in aged male mice, HO-2 deficiency worsened renal function on days 1 and 2 after ischemic AKI, and, on day 2 after ischemia, such deficiency augmented upregulation of injury-related genes and worsened histological injury. Renal HO activity was markedly decreased in unstressed aged male HO-2−/− mice and remained so after ischemia, despite exaggerated HO-1 induction in HO-2−/− mice after ischemia. Such exacerbation of deficiency of HO-2 protein and HO activity may reflect phosphorylated STAT3, as activation of this proinflammatory transcription factor was accentuated early after ischemia in aged male HO-2−/− mice. This exacerbation may not reflect impaired induction of nephroprotectant genes, since the induction of HO-1, sirtuin 1, and β-catenin was accentuated in aged male HO-2−/− mice after ischemia. We conclude that aged male mice are hypersensitive to ischemic AKI and that HO-2 mitigates such sensitivity. We speculate that this protective effect of HO-2 may be mediated, at least in part, by suppression of phosphorylated STAT3-dependent signaling.

Background: Stroke prevention using warfarin is challenging in AF patients with CKD, due to high bleeding risk and difficulties in the INR control. NOACs provide alternative options, but all have greater degrees of renal clearance. This study aimed to compare the outcomes of apixaban, dabigatran, rivaroxaban, and warfarin across the range of kidney function in patients with AF. Methods: Using a US administrative database including private insurance or Medicare Advantage patients with linked claims and laboratory data, we identified 34,569 new users of oral anticoagulants with AF and eGFR ≥15 between 10/1/2010-11/29/2017. Stabilized IPTW balanced four treatment groups on 66 baseline characteristics. The primary outcomes included stroke, major bleeding, and mortality. Weighted Cox proportional hazards models compared treatments in the overall population and in each eGFR subgroup, with mortality as a competing risk for stroke and major bleeding. Results: The proportion of patients using warfarin increased as the kidney function declined - 26.5%, 30.4%, 34.6%, 40.5%, and 55.0% of patients were prescribed warfarin in eGFR ≥90, 60-90, 45-60, 30-45, 15-30 groups, respectively. In comparison to warfarin, apixaban was associated with a lower risk of stroke, major bleeding, and mortality; dabigatran was associated with a similar risk of stroke, and a lower risk of major bleeding and mortality; rivaroxaban was associated with a lower risk of stroke, major bleeding, and mortality (Figure). When comparing one NOAC to another NOAC, apixaban and dabigatran were associated with a lower risk of major bleeding than rivaroxaban (HR 0.61 [0.51-0.73], p<0.001 for apixaban versus rivaroxaban; HR 0.67 [0.50-0.90], p=0.007 for dabigatran versus rivaroxaban); dabigatran was associated with a higher risk of stroke than apixaban (HR 1.65 [1.11-2.46], p=0.01); there was no difference in mortality. There was no significant interaction between treatment and eGFR categories for any outcome, but the number of patients with low eGFR was small. Conclusions: In practice, relative to warfarin, NOACs are progressively less commonly used with increasing degree of renal dysfunction. However, each NOAC was consistently associated with at least equivalent effectiveness and safety compared with warfarin across the range of kidney function.

Background The endothelial glycocalyx is a vasoprotective barrier between the blood and endothelium. We hypothesized that glycocalyx degradation is present in preeclampsia, a pregnancy‐specific hypertensive disorder characterized by endothelial dysfunction and activation. Methods and Results We examined the sublingual glycocalyx noninvasively using sidestream dark field imaging in the third trimester among women with normotensive pregnancies (n=73), early (n=14) or late (n=29) onset preeclampsia, or gestational diabetes mellitus (n=21). We calculated the width of the glycocalyx that was permeable to red blood cells (called the perfused boundary region , a measure of glycocalyx degradation) and the percentage of vessels that were filled with red blood cells ≥50% of the time (a measure of microvascular perfusion). In addition, we measured circulating levels of glycocalyx components, including heparan sulfate proteoglycans, hyaluronic acid, and SDC1 (syndecan 1), in a subset of participants by ELISA . Repeated‐measures ANOVA was performed to adjust for vessel diameter and caffeine intake. Women with early onset preeclampsia showed higher glycocalyx degradation, indicated by a larger perfused boundary region (mean: 2.14 [95% CI, 2.05–2.20]), than the remaining groups (mean: normotensive: 1.99 [95% CI, 1.95–2.02], P =0.002; late‐onset preeclampsia: 2.01 [95% CI, 1.96–2.07], P =0.024; gestational diabetes mellitus: 1.97 [95% CI, 1.91–2.04], P =0.004). The percentage of vessels that were filled with red blood cells was significantly lower in early onset preeclampsia. These structural glycocalyx changes were accompanied by elevated plasma concentrations of the glycocalyx components, heparan sulfate proteoglycans and hyaluronic acid, in early onset preeclampsia compared with normotensive pregnancy. Conclusions Glycocalyx degradation and reduced microvascular perfusion are associated with endothelial dysfunction and activation and vascular injury in early onset preeclampsia.

There is no therapy that promotes maturation and functionality of a dialysis arteriovenous fistula (AVF). The search for such therapies largely relies on evaluation of vascular responses and putative therapies in experimental AVFs. We studied an AVF in mice with chronic kidney disease (CKD). We demonstrate numerous stressors in the vein of the AVF-CKD group, including pathological shear, mitogenic, inflammatory, and hypoxia-reoxygenation stress. Because stress promotes premature senescence, we examined whether senescence is induced in the vein of the AVF-CKD model. We demonstrate a senescence phenotype in the AVF-CKD model, as indicated by increased expression of p16Ink4a, p21Cip1, and p53 and expected changes for certain senescence-associated microRNAs. RNA-sequencing analysis demonstrated differential expression of ~10,000 genes, including upregulation of proinflammatory and proliferative genes, in the vein of the AVF-CKD group. The vein in the AVF-CKD group exhibited telomere erosion and increased senescence-associated β-galactosidase activity and staining. Senescence was induced in the artery of the AVF-CKD group and in the vein of the AVF without CKD. Finally, given the rapidly rising clinical interest in senolytics, we provide proof of concept of senolytics as a therapeutic approach by demonstrating that senolytics decrease p16Ink4a expression in the AVF-CKD model. This study introduces a novel concept underlying the basis for maturational and functional failure in human dialysis AVFs and identifies a new target for senolytic therapy.