Progenitor cell therapy for traumatic brain injury: effect of serum osmolarity on cell viability and cytokine production

Abstract

Introduction: The potential translation of mesenchymal stem cell (MSC) therapy into a multimodal protocol for traumatic brain injury requires evaluation of viability and cytokine production in a hyperosmolar environment. Optimization of MSC therapy requires delivery to the target area without significant loss of cellular function or viability. No model evaluating the potential efficacy of MSC therapy at varying osmolarities currently exists.

Methods: Rat MSCs were characterized with flow cytometric immunophenotyping. MSCs (passage 3) were placed in culture with multipotent adult progenitor cell media at varying osmolarities (250, 270, 290, 310, 330, 350 and 370 mOsm) potentially found with hypertonic saline infusion. After culture for 24 h, cellular viability was measured using flow cytometry (n = 6). Next, brain tissue supernatant was harvested from both normal rat brains and injured brains 6 h after cortical injury. Subsequently, MSCs were placed in culture with multipotent adult progenitor cell media +/- 20% normal brain or injured brain supernatant (at the aforementioned osmolarities) and allowed to remain in culture for 24 h (n = 11). At this point, media supernatant cytokine levels were measured using a multiplex cytokine assay system.

Results: MSCs showed no clinically significant difference in viability at 24 h. MSCs cultured with 20% injured brain supernatant showed an decrease in proinflammatory cytokine production (IL-1alpha and IL-1beta) with increasing osmolarity. No difference in anti-inflammatory cytokine production (IL-4 and IL-10) was observed.

Conclusion: Progenitor cell therapy for traumatic brain injury may require survival and activity in a hyperosmolar environment. Culture of MSCs in such conditions shows no clinically significant effect on cell viability. In addition, MSC efficacy could potentially be enhanced via a decrease in proinflammatory cytokine production. Overall, a multimodal traumatic brain injury treatment protocol based upon MSC infusion and hypertonic saline therapy would not negatively affect progenitor cell efficacy and could be considered for multicenter clinical trials.

Figure 1. Mesenchymal stem cell viability measured after 24 h in multipotent adult progenitor cell media of varying osmolarities

Fractional viability values observed from 0.914 to 0.939 indicate that while there are statistically significant differences, adequate mesenchymal stem cell viability is observed under all culture conditions. *Statistical significance (one-way ANOVA with Dunnett’s post-hoc) compared with control osmolarity (290 mOsm) (p < 0.05).