Loss of SIRT1 inhibits hematopoietic stem cell aging and age-dependent mixed phenotype acute leukemia

Aging of hematopoietic stem cells (HSCs) is linked to various blood disorders and malignancies. SIRT1 has been implicated in healthy aging, but its role in HSC aging is poorly understood. Surprisingly, we found that Sirt1 knockout improved the maintenance of quiescence of aging HSCs and their functionality as well as mouse survival in serial bone marrow transplantation (BMT) recipients. The majority of secondary and tertiary BMT recipients of aging wild type donor cells developed B/myeloid mixed phenotype acute leukemia (MPAL), which was markedly inhibited by Sirt1 knockout. SIRT1 inhibition also reduced the growth and survival of human B/myeloid MPAL cells. Sirt1 knockout suppressed global gene activation in old HSCs, prominently the genes regulating protein synthesis and oxidative metabolism, which may involve multiple downstream transcriptional factors. Our results demonstrate an unexpected role of SIRT1 in promoting HSC aging and age-dependent MPAL and suggest SIRT1 may be a new therapeutic target for modulating functions of aging HSCs and treatment of MPAL.

Abstract 4403: Antitumor properties of ouabain in lipid double emulsion integrated with tumor cell membrane fractions

Cell membrane proteins such as integrins are crucial for cell-cell recognition, binding and communication, cell-stromal interaction and adhesion, tumor invasion and metastasis. It was reported that cell-size hydrophobic beads coated with tumor membrane molecules could stimulate the lymphokine activated killer (LAK) cells to release IFN-alpha and TNF-alpha, and interrupted the recognition between LAK cells and tumor cells (Chong AS, 1988, 1991). Lipid double emulsion is a convenient formulation method to integrate lipid materials, hydrophilic and hydrophobic drugs in uniformed particles to achieve combinational chemotherapy. However the nonspecific uptake of double emulsion particles in vivo limits its targeting therapeutic potential. In current study, we sought to coat double emulsion particles with tumor cell membrane fraction to mimic the tumor cell surface in order to enhance the interaction and uptake of emulsion particles into tumor cells. Canine osteosarcoma cells and lymphoma cells were chosen for this study because canine cancers develop in immunocompetent environments and share many similar features observed in human cancers, such as long periods of latency for initiation, progression and development, metastasis, acquired drug resistance and recurrence. We use ouabain as therapeutic warhead in the emulsion particles because ouabain is known to have extremely high anticancer potential at nanomolar concentration level from our previous studies. The major obstacle of applying ouabain in vivo therapy is that the therapeutic dose window of ouabain is very narrow. Therefore in an attempt to mitigate such narrow therapeutic margin of safety, ouabain was formulated in lipid double emulsion by using microfluidic synthesis method and membrane emulsification method. The double emulsion particles were further coated with osteosarcoma cell membrane fraction. Our preliminary results showed enhanced antitumor activities of ouabain in tumor cell mimic-double emulsion or nanoemulsion against canine osteosarcoma cells and lymphoma cells in vitro and in orthotopic xenograft models in vivo, suggesting a promising therapeutic benefit in canine cancer targeting therapy.

Citation Format: Jun Wu, Mariele Mondala, Meng-Yin Hsieh, Eugene Roberts, Richard Ermel. Antitumor properties of ouabain in lipid double emulsion integrated with tumor cell membrane fractions. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 4403. doi:10.1158/1538-7445.AM2015-4403

Effects of a new advanced glycation inhibitor, LR-90, on mitigating arterial stiffening and improving arterial elasticity and compliance in a diabetic rat model: aortic impedance analysis

BACKGROUND AND PURPOSE

We determined the effects of treatment with LR-90, an inhibitor of advanced glycation end products, on the mechanical properties of the arterial system in streptozotocin (STZ)-induced diabetic Sprague Dawley rats, using aortic impedance analysis, and further investigated the effects of LR-90 on the progression of aortic pathology.

EXPERIMENTAL APPROACH

STZ-induced diabetic rats were treated with or without LR-90 (50 mg L(-1) in drinking water) for 8 weeks and compared with control groups. Arterial BP measurements, various metabolic parameters, aortic histopathology, collagen cross-linking, AGE accumulation, and RAGE protein expression in aortic tissue were determined. Pulsatile parameters were evaluated using a standard Fourier series expansion technique and impulse response function of the filtered aortic input impedance spectra.

KEY RESULTS

LR-90 reduced glycated haemoglobin and triglycerides levels, although it had no effect on the glycaemic status. LR-90 did not affect arterial BP, but prevented the diabetes-induced increase in peripheral resistance and variations in aortic distensibility, as it reduced aortic characteristic impedance by 21%. LR-90 also prevented the elevation in wave reflection factor, as indicated by a 22.5% reduction and an associated increase of 23.5% in wave transit time, suggesting it prevents the augmentation of the systolic load of the left ventricle. Moreover, LR-90 inhibited collagen cross-linking and the accumulation of AGE and RAGE in the vasculature of diabetic rats.

CONCLUSIONS AND IMPLICATIONS

Treatment with LR-90 may impart significant protection against diabetes-induced aortic stiffening and cardiac hypertrophy and provides an additional therapeutic option for treatment of AGE associated diabetic complications.

Thioredoxin-linked mitigation of allergic responses to wheat

Thioredoxin, a ubiquitous 12-kDa regulatory disulfide protein, was found to reduce disulfide bonds of allergens (convert S-S to 2 SH) and thereby mitigate the allergenicity of commercial wheat preparations. Allergenic strength was determined by skin tests with a canine model for food allergy. Statistically significant mitigation was observed with 15 of 16 wheat-sensitive animals. The allergenicity of the protein fractions extracted from wheat flour with the indicated solvent was also assessed: the gliadins (ethanol) were the strongest allergens, followed by glutenins (acetic acid), albumins (water), and globulins (salt water). Of the gliadins, the alpha and beta fractions were most potent, followed by the gamma and omega types. Thioredoxin mitigated the allergenicity associated with the major protein fractions-i.e, the gliadins (including the alpha, beta, and gamma types) and the glutenins-but gave less consistent results with the minor fractions, the albumins and globulins. In all cases, mitigation was specific to thioredoxin that had been reduced either enzymically by NADPH and NADP-thioredoxin reductase or chemically by dithiothreitol; reduced glutathione was without significant effect. As in previous studies, thioredoxin was particularly effective in the reduction of intramolecular (intrachain) disulfide bonds. The present results demonstrate that the reduction of these disulfide bonds is accompanied by a statistically significant decrease in allergenicity of the active proteins. This decrease occurs alongside the changes identified previously-i.e., increased susceptibility to proteolysis and heat, and altered biochemical activity. The findings open the door to the testing of the thioredoxin system in the production of hypoallergenic, more-digestible foods.

IgG3 reactive rheumatoid factor in rheumatoid arthritis: etiologic and pathogenic considerations

Rheumatoid factor (RF) is a polyclonal autoantibody directed against the Fc portion of IgG. Although the role of RF in patients with rheumatoid arthritis (RA) is unclear, immune complexes that form between RF and IgG can activate the classical complement (C) pathway, leading to pathogenic outcomes involving inflammatory events and tissue damage. The specificity of serum RF and RF produced by rheumatoid synovial cells (RSC) is different. Serum RF has specificity for rabbit IgG and human IgG subclasses IgG1, 2, and 4, but binds poorly to IgG3. The affinity of serum RF for IgG Fc is low, having an association constant of 10(4)-10(5) M-1. RSC RF, however, has specificity for human IgG and high avidity for IgG3. Because of this greater specificity and avidity for IgG3, and because RSC RF may be pathogenically more important than serum RF, an important role for IgG3-reactive RF in RA may exist. Binding of RF to IgG may be dependent on the allotype and glycosylation of IgG. Infectious agents present in RA patients may directly or indirectly induce the production of certain RF. In this communication, we review and expand on several observations examining the role of IgG3-reactive RF in RA including: 1) binding differences between RF derived from RSC and serum; 2) glycosylation characteristics of IgG and its interaction with RF; 3) apparent allotype dependent binding of IgG3-reactive RF; and 4) possible relationship between infectious agents and the production of IgG3-reactive RF. Taken together, these observations suggest an important role for IgG3-reactive RF in better understanding the etiology and pathogenesis of RA.

Human monoclonal rheumatoid factor derived from rheumatoid synovial cells monospecific for rabbit IgG

Rheumatoid factors (RF) in rheumatoid arthritis (RA) are polyclonal autoantibodies directed against antigenic epitopes located in the Fc portion of the IgG molecule. Hybridoma technology has overcome the difficulty of their polyclonality, so that monoclonal RF (mRF) can be examined for their individual binding specificities and genetics. We isolated a monoclonal IgM RF secreting hybridoma (designated H4) from the rheumatoid synovial cells (RSC) of a patient with RA. H4 bound specifically with rabbit IgG (RIgG) and had no human IgG (HIgG) reactivity. By direct binding ELISA and absorption experiments, 6% of the RIgG reactive RSC RF in this patient with RA was monospecific for RIgG. H4 was tested against RIgG F(ab')2 and pFc' fragments, and bound only to the pFc' fragment (CH3 domain). Moreover, H4 mRF had high avidity for RIgG in a capture ELISA. Total RNA was extracted and the variable region heavy (VH) and light (VL) chain cDNA were amplified using polymerase chain reaction technology. Sequence analysis of the IgM RF VH and VL chain genes indicated usage of the VH26 germline gene (VhIII gene family) and a new V lambda germline gene. Our results suggest preferential use of restricted germline genes in the formation of autoantibodies in human autoimmune diseases. The pathological significance of RIgG specific RF is still unclear. However, this finding suggests that all RSC RF production may not necessarily be induced by autologous IgG.

Allotype-dependent stimulation of peripheral blood and synovial lymphocytes by IgG3 in rheumatoid arthritis

The immunopathologic process of rheumatoid arthritis (RA) is primarily expressed in the synovium where rheumatoid factor (RF) synthesis is concentrated. We hypothesized that RF synthesized by rheumatoid synovial cells (RSC) may be driven via a T cell-mediated immune response developed against IgG3 epitopes. To identify and characterize specific RSC RF epitopes and T cell antigens, two 28 amino acid peptides homologous with the C-terminus of IgG1 (P1) and IgG3 [G3m(5)] (P3) were synthesized and used in RF-binding studies and lymphocyte proliferation assays. Our results indicate that (i) the C-terminus of the CH3 domain contains epitopes for IgG3-reactive RSC RF; (ii) IgG3-reactive RSC RF binds primarily to IgG3 [G3m(5)]; (iii) P3 stimulated proliferation of T lymphocytes from both RA peripheral blood and RSC; and (iv) RF production was enhanced by P3 in selected RA cell cultures. These observations suggest that the C-terminus of IgG3 allotype G3m(5) may be important in T cell activation and RF production in RA.