Eric D. Morrell

High passage number of stem cells adversely affects stem cell activation and myocardial protection.

ABSTRACT Progenitor cell plasticity enhances positive remodeling of damaged tissue. We and others have previously shown that progenitor cells may limit apoptosis and modulate inflammation in part by the production of growth factors. However, recent studies suggest that progenitor cells senesce and lose their differentiation potential with increasing time in culture and passage. We hypothesize that murine bone marrow mesenchymal stem cells (MSCs) are cardioprotective against ischemia/reperfusion injury in the isolated perfused rat heart, and that passage number has an adverse effect on MSC activation and cardioprotection. Adult male and female Sprague-Dawley rat hearts were isolated, perfused via Langendorff model, and subjected to ischemia/reperfusion. Mouse MSCs were harvested, cultured, suspended in perfusate, and infused before global index ischemia. Hearts were assigned to controls or infusion with passage 3, 5, or 10 MSCs. In addition, MSCs in culture were stressed by hypoxia and increasing doses of endotoxin (lipopolysaccharide). Mesenchymal stem cell activation was determined by measuring vascular endothelial growth factor production with enzyme-linked immunosorbent assay. All data are reported as mean ± SEM and were analyzed with 2-way analysis of variance. Differences are considered significant if P < 0.05. Passage 3 murine MSC infusion in hearts before ischemia reduced the depression of left ventricular developed pressure, attenuated the increase of end-diastolic pressure, and reduced the depression of +dP/dT and −dP/dT. However, the MSC protective effect disappeared in hearts infused with passage 5 and passage 10 MSCs. Although hypoxia and lipopolysaccharide resulted in significant activation of MSCs, passage 3 MSCs demonstrated significantly greater vascular endothelial growth factor release than passage 5 and 10 MSCs. Acute murine MSC infusion confers protection in isolated rat hearts. However, high passage number has an adverse effect on MSC activation and protection. This portends limited ex vivo expansion before possible therapeutic use.

Sex dimorphisms in activated mesenchymal stem cell function

ABSTRACT The plasticity of bone marrow-derived stem cells (BMSCs) has resulted in positive remodeling and the regeneration of viable tissues. However, BMSC release of growth factors, which limit apoptosis and inflammation, may play an important role in conferring organ protection. Recent studies also indicate that those patients with higher circulating BMSC counts may be more resistant to septic and traumatic insults. There are clear sex differences in response to such insults. Within the population of BMSC, mesenchymal stem cells (MSCs) may have clinical advantages. Therefore, we hypothesize that sex differences in the MSC paracrine response to acute injury exist. Mesenchymal stem cells were obtained from male and female mice. One million MSCs per well (triplicate wells per group) were stressed by hypoxia and increasing doses of endotoxin (lipopolysaccharide [LPS]) and hydrogen peroxide. Mesenchymal stem cell activation was determined by measuring vascular endothelial growth factor (VEGF) and tumor necrosis factor &agr; production by enzyme-linked immunosorbent assay. Differences were considered significant if P < 0.05. Results Lipopolysaccharide resulted in significant activation of both male and female MSCs. However, LPS provoked significantly more VEGF production in female MSCs versus male MSCs at all LPS doses. Hypoxia of 1 h and hydrogen pyroxide exposure also caused significantly more VEGF production in female MSCs versus male MSCs. Female MSCs expressed significantly less tumor necrosis factor &agr; than male MSCs after acute LPS and hypoxia. Conclusion This study constitutes the first demonstration that sex differences exist in activated MSC function. Sex differences in progenitor cell function may have important implications in understanding the observed sex differences in the hosts response to injury.

Experimental therapies for hypoxia-induced pulmonary hypertension during acute lung injury.

ABSTRACT Hypoxic pulmonary vasoconstriction (HPV) and pulmonary hypertension present a common and formidable clinical problem for practicing thoracic, transplant, and trauma surgeons. The recent discovery of efficacious drugs that are selective for the pulmonary vasculature has brought about the potential for very powerful therapeutic agents. Inhaled nitric oxide (NO) therapy has already found broad clinical utility, yet its use is limited by potential toxicities. Rho kinase (ROK) has been discovered to play a very central role in the formation of hypoxia induced pulmonary hypertension, and the advent of very specific ROK inhibitors has shown positive clinical results. Finally, phosphodiesterase-5 inhibitors have been found to selectively vasodilate the pulmonary vasculature in the midst of HPV. The purposes of this review are to: 1) discuss the advantages and disadvantages of inhaled preparations of NO; 2) address experimental alternatives to inhaled preparations of NO to treat HPV; 3) explore potential therapeutic avenues associated with inhibition of Rho-kinase; and, 4) examine the use of phosphodiesterase-5 (PDE-5) inhibitors and combination therapy in the treatment of HPV.