A versatile platform for bioimaging based on colominic acid-decorated upconversion nanoparticles

Non-cytotoxic upconversion nanoparticles decorated with colominic acid exhibit the prolonged circulation time in the bloodstream compared to PEG leading to their effective accumulation in the inflammation site and visualization of blood vessels.

Inadequacy of Colominic Acid as an Absorbent Intended To Facilitate Use of Complement-Preserved Baby Rabbit Serum in the Neisseria meningitidis Serogroup B Serum Bactericidal Antibody Assay

ABSTRACT The surrogate of protection against Neisseria meningitidis serogroup B (MenB) is the serum bactericidal antibody (SBA) assay, which measures the functional activity of antibody by using an exogenous complement source. Despite baby rabbit complement having been used in meningococcal serogroup A, C, Y, and W135 SBA assays, it is not recommended for use in the MenB SBA assay due to elevated SBA titers caused by low-avidity anti-MenB capsular antibody in test sera. Therefore, the possibility of absorbing anti-MenB capsular antibody from test sera to enable the use of baby rabbit complement in the MenB SBA assay was investigated by comparing the results with those gained using human complement. Colominic acid from Escherichia coli K1, which shares the same linkage residue as MenB polysaccharide, was used as an absorbent due to the commercial unavailability of purified MenB polysaccharide. Inclusion of soluble colominic acid as an absorbent with baby rabbit complement resulted in a general reduction in SBA titers compared with those obtained using baby rabbit complement alone. However, these were not comparable to human SBA titers for all samples. Further optimization and investigations demonstrated that for some samples, colominic acid reduced titers to less than those achieved with human complement, and for others, it was not possible to inhibit titers by using colominic acid. The results suggested that the use of colominic acid will not result in the ability to use baby rabbit complement in the MenB SBA assay, thus not alleviating the difficulties in procuring human complement. However, alternative absorbents, such as purified MenB polysaccharide, may warrant further evaluation.

Sulfated Colominic Acid Enhances CXCR4 Function and Promotes Hematopoietic Stem /Progenitor Egress from Bone Marrow.

Hematopoietic progenitors (HPCs) can be mobilized from bone marrow (BM) compartment to the blood by G-CSF. In this process, CXCR4, a cognitive receptor for chemokine SDF-1/CXCL12, and CD26/dipeptidyl peptidase (DPP) IV play critical roles. Colominic acid (CA) is a polymer of N-acetylneuraminic acid, and it has been reported that sulfated colominic acid (SCA) can inhibit HIV entry, the step which requires CXCR4 and CD26 as co-receptors. Thus, we hypothesized that SCA would modulate HPC egress from BM. First, we injected SCA into C57BL/6 mice (100mg/kg, i.v.) and observed rapid HPC mobilization (assessed by CFU-Cs/mL blood, PBS 42±10, SCA 215±50, n=9–12, p<0.01, peaked at 30 min after injection). CA displayed no mobilization, suggesting that the sulfation is critical for its action. G-CSF-induced HPC mobilization was strongly enhanced by the addition of single dose of SCA (CFU-Cs/ml blood, PBS vs SCA: 225±57 vs 1950±485 in 2 day-G-CSF, n=5, p<0.01; 1950±400 vs 8233±1225 in 4 day-G-CSF, respectively, n=6, p<0.001). To evaluate the stem cell activity in mobilized blood by 2 day-G-CSF+SCA, we mixed the same volume of blood from CD45.2 mice treated with 2 day-G-CSF+SCA and CD45.1 mice treated with 4 day-G-CSF, and injected into lethally irradiated CD45.1 mice. The ratio of CFU-C injected (2 day-G-CSF+SCA: 4 day-G-CSF) was 1.12±0.03 and the ratio of peripheral blood leukocytes derived from engrafted stem cells originated from each donor 12 weeks after transplantation was 2.16±0.54, n=3, p=0.11). These results suggest that 2 day administration of G-CSF together with a single dose of SCA may be sufficient for clinical mobilization and that the addition of SCA in full-term G-CSF administration may overcome poor mobilization cases. To elucidate the mechanism of SCA action on HPCs, we first focused on CD26/DPPIV. Pretreatment of mice with a DPPIV inhibitor Diprotin A strongly inhibited the increase of leukocytes but did not alter HPC mobilization. In addition, SCA-induced mobilization in CD26-deficient mice was similar to that in wild-type (WT) controls (WT vs CD26−/−: 356±80 vs 444±86 CFU-Cs/ml blood, n=4). These results suggest that, in contrast to G-CSF-induced mobilization, CD26 is not important for SCA action. We then next evaluated the functional alteration of CXCR4 by SCA. Flow cytometric analyses revealed that SDF-1 bound more efficiently (2.5 times) to HPC cell line FDCP-mix treated with SCA compared to those treated with PBS (n=3, p<0.01). Strikingly, SCA treatment strongly (4.3 times) enhanced FDCP-mix transwell migration toward SDF-1 (n=8, p<0.05) which was completely blocked by a CXCR4 inhibitor. SDF-1 ELISA with K15C as a capture antibody revealed that non-truncated (active) form of SDF-1 was increased 5 times in serum after SCA injection (n=5, p<0.0001) whereas no change was observed in BM extracellular fluid. Together, we propose that SCA induces HPC mobilization by enhancing CXCR4 function and by altering the gradient of its ligand, active SDF-1, toward circulation.