Potential Atheroprotective Effects of Ixmyelocel-T Cellular Therapy Kelly J. Ledford, Nikki Murphy, Frank Zeigler, Ronnda L. Bartel 1
Ixmyelocel-T, an expanded, autologous multicellular therapy cultured from bone marrow mononuclear cells, contains a M2-like population of macrophages Alternatively activated macrophages (M2 macrophages) promote the resolution of inflammation by secreting antiinflammatory cytokines and removing tissue debris. Therefore, delivering increased numbers of this macrophage population to ischemic tissues may limit tissue injury and promote repair. The purpose of this study was to investigate a novel population of alternatively activated, M2 macrophages, a major component of ixmyelocel-t therapy, which are potentially beneficial in the treatment of atherosclerotic diseases.
Atherosclerosis is a multi-factorial disease of the vessel wall Libby P. Nature 42, 868-874(19 December 22) Atherosclerosis is complex disease involving several different factors including: Chronic Inflammation Cellular Death Lipid Accumulation An ideal therapy should address all components of this multifactorial disease in order to really be efficacious 3
Atherosclerosis- Role of the Macrophage Macrophages are a key cell type involved in atherosclerosis-lipid accumulation, inflammation, efferocytosis Efferocytosis- In early atherosclerotic lesions- macrophages remove dying foam cells, decreased plaque progression. In advanced lesions, macrophages do not function properly leading to necrosis, lipid accumulation, and a pro-inflammatory state Maintaining Cholesterol Homeostasis- Accumulation of lipid loaded macrophage foam cells is a central feature in the formation of atherosclerosis. Maintaining macrophage cholesterol homeostasis (uptake vs. efflux) is essential in preventing the pathogenesis of atherosclerosis An imbalance between cholesterol uptake by scavenger receptors and efflux in macrophages is widely recognized as an underlying mechanism progression atherosclerosis In disease states where alternatively activated macrophages promote tissue repair or limit injury it might be beneficial to enhance their activity. Thorp E, Tabas I. J Leukoc Biol. 29 Nov;86(5):189-95. Ixmyelocel-T Macrophages
Cytokine Secretion (pg/ml) Ixmyelocel-T Macrophages Secretes Anti- Inflammatory Cytokines 45 4 35 3 25 2 15 1 5 IL-1 IL-1ra TNFα IL-1β IL-12 Basal +LPS IL-1, IL-r1a, TNFα, IL-1β, and IL-12 were quantified in MACS sorted CD14+ sorted ixmyelocel-t supernatants treated with and without LPS (n > 3). Ixmyelocel-T macrophages secrete elevated levels of anti-inflammatory cytokines, before and after LPS stimulation, while pro-inflammatory cytokine secretion remains minimal. P <.5 vs. basal, P <.1 vs. basal 5
Ixmyelocel-T Macrophages Express Surface Receptors of Alternative Activation and Scavenger Receptors Involved in Lipid and Apoptotic Cell Uptake Flow cytometry revealed that ixmyelocel-t macrophages express surface receptors of alternative activation, CD26 and CD163, and scavenger receptors involved in lipid and apoptotic cell uptake: CD36, LDLR, CD91, MSR1, and MerTK.
Cell Percentage (%) Efferocytosis: Ixmyelocel-T alternatively activated macrophages readily phagocytize apoptotic cells 7 6 5 ixmyelocel-t Apoptotic Cells ixmyelocel-t + Apoptotic Cells Enlarged 4 3 2 1 CD14 CD14 + Apoptotic Cells ixmyelocel-t PKH26 Apoptotic Cells ixmyelocel-t + PKH26 Apoptotic Cells Efferocytosis was measured by microscopy and flow cytometry. 6% of ixmyelocel-t CD14+ cells efferocytosed apoptotic cells (n > 5). P <.1 vs. CD14. Magnification: 6X
SCARB1 (Fold Change) CD36 (Fold Change) Ixmyelocel-T Macrophages as less likely to become overladen with modified lipids- Reduced Scavenger Receptor Expression THP-1 IXT 1.4 1.2 1.8.6.4 -Ac-LDL +Ac-LDL.2 THP-1 IXT Fluorescent microscopy images of ixmyelocel-t and THP-1 macrophages loaded with Dil-Ac-LDL. Magnification: 4X. 2 1.5 Quantitative real-time PCR gene expression analysis of scavenger receptors normalized to GAPDH, the relative control (n > 5). Expression of (A) CD36 and (B) SCARB1 in THP-1 and ixmyelocel-t macrophages before and after lipid loading. Values are presented as mean ± SEM relative to control, p <.1 vs. THP-1 Ac-LDL, p <.1 vs. THP-1 Ac-LDL. 1.5 THP-1 IXT -Ac-LDL +Ac-LDL
Apoptosis (Relative to Control) Ixmyelocel-T is not sensitive to modified cholesterol-induced lipotoxicity 14 12 1 8 6 -AcLDL +AcLDL 4 2 THP-1 IXT To determine if lipid loading resulted in apoptosis, both ixmyelocel-t and THP-1 macrophages were loaded with 1 μg/ml Ac-LDL for 24 hours. Apoptosis was then analyzed using a luminometric caspase 3/7 assay, which examines activation of caspases-3 and -7. THP-1 macrophages exhibited a statistically significant higher level of Ac-LDL induced apoptosis than ixmyelocel-t. Values are presented as mean ± SEM, p <.1 vs. THP -Ac LDL.
Ixmyelocel-T Macrophages Display Enhanced Cholesterol Efflux Capacity- Cholesterol Transport Genes Quantitative real-time PCR gene expression analysis of scavenger receptors normalized to GAPDH, the relative control (n > 5). Expression of ABCA1, ABCG1, ACAT1, and CEH in THP-1 and ixmyelocel-t macrophages before and after lipid loading. Values are presented as mean ± SEM relative to control, p <.5, p <.1, p <.1 vs. THP-1 Ac-LDL; #p <.5, ##p <.1 vs. IXT Ac-LDL.
Cholesterol Efflux (%) Ixmyelocel-T Displays Enhanced Cholesterol Efflux Capacity 18 16 14 12 1 8 6 4 2 ApoA-I HDL3 THP-1 ixmyelocel-t The ability of ixmyelocel-t to efflux cholesterol was measured with an in vitro cholesterol efflux assay. Ixmyelocel-T and THP-1 cells were loaded with free cholesterol using radiolabeled acetylated LDL ( 3 H- cholesterol-acldl). Ixmyelocel-T demonstrated a robust increase in ABCA1-mediated cholesterol efllux, as seen by the increase in efflux to apoa-i. (n=4) p <.1, p<.1 vs. THP-1
RCT to Liver (% injected cpm) RCT to Feces (% injected cpm) RCt to Serum (% injected cpm) Ixmyelocel-T Effluxes Cholesterol In Vivo (Reverse Cholesterol Transport Assay) 4.5 4 3.5 3 2.5 2 J774 1.5 IXT 1.5 7 6 5 4 3 2 1 24 48 Time (hrs) 6 4 3 2 1 J774 IXT 5 J774 IXT Reverse cholesterol transport comprises all the different steps in cholesterol metabolism between cholesterol efflux from macrophage foam cells and the final excretion of cholesterol into the feces either as neutral sterols or after metabolic conversion into bile acids. In vivo cholesterol efflux was examined in scid mice after intraperitoneal injections of either 3 H-cholesterol-loaded J774 cells of ixmyelocel-t. Plasma 3 H-cholesterol levels after 24 and 48 hours, 3 H-tracer found in the liver, and 3 H-tracer found in the feces after 48 hours (n > 3 per group). Values are presented as mean ± SEM relative to control, p <.5 vs. J774
Collectively this data suggests ixmyelocel-t therapy might be beneficial for the treatment of atherosclerotic diseases Immunomodulation: Anti-inflammatory cytokine secretion Tissue Remodeling/Phagocytosis of necrotic tissue Modified Cholesterol Uptake/Efflux: Enhanced cholesterol uptake could protect the vasculature by removing atherogenic lipoproteins which elicit strong pro-inflammatory responses. Cholesterol efflux would allow cholesterol to be disposed of preventing more inflammation, as well as cell death Libby P. Nature 42, 868-874(19 December 22) These potential MOA of ixmyelocel-t would address several of the components of this multifactorial disease, potentially making ixmyelocel-t not only an ideal therapy but an efficacious one.