Blockade of peroxynitrite-induced neural stem cell death in the acutely injured spinal cord by drug-releasing polymer

Abstract

Therapeutic impact of neural stem cells (NSCs) for acute spinal cord injury (SCI) has been limited by the rapid loss of donor cells. Neuroinflammation is likely the cause. As there are close temporal-spatial correlations between the inducible nitric oxide (NO) synthase expression and the donor NSC death after neurotrauma, we reasoned that NO-associated radical species might be the inflammatory effectors which eliminate NSC grafts and kill host neurons. To test this hypothesis, human NSCs (hNSCs: 5 × 104 to 2 × 106 per milliliter) were treated in vitro with "plain" medium, 20 μM glutamate, or donors of NO and peroxynitrite (ONOO-; 100 and 400 μM of spermine or DETA NONOate, and SIN-1, respectively). hNSC apoptosis primarily resulted from SIN-1 treatment, showing ONOO --triggered protein nitration and the activation of p38 MAPK, cytochrome c release, and caspases. Therefore, cell death following post-SCI (p.i.) NO serge may be mediated through conversion of NO into ONOO-. We subsequently examined such causal relationship in a rat model of dual penetrating SCI using a retrievable design of poly-lactic-co-glycolic acid (PLGA) scaffold seeded with hNSCs that was shielded by drug-releasing polymer. Besides confirming the ONOO--induced cell death signaling, we demonstrated that cotransplantation of PLGA film embedded with ONOO- scavenger, manganese (III) tetrakis (4-benzoic acid) porphyrin, or uric acid (1 μmol per film), markedly protected hNSCs 24 hours p.i. (total: n = 10). Our findings may provide a bioengineering approach for investigating mechanisms underlying the host microenvironment and donor NSC interaction and help formulate strategies for enhancing graft and host cell survival after SCI. © AlphaMed Press.