A novel prophylactic strategy to minimize stem cell transplantation-related complications

Abstract

Hematopoietic stem cell transplantation (HSCT) is a curative treatment and sometimes is the only option for patients with hematological malignancies and some types of solid tumors. It is also the first-line treatment for several severe genetic and metabolic disorders. The annual numbers of HSCT are continuously increasing, among which around 40% are allogeneic transplantations. However, the survival and life quality of those patients are largely compromised by transplantation-related complications, including acute graft-versus-host disease (aGvHD) and cardiovascular diseases. Oxidative stress is ubiquitously implied in the pathogenesis of these conditions and can thus serve as a treatment target. The present thesis provides a systematic investigation of a new prophylactic strategy employing antioxidants to combat HSCT-related complications.

Using a mouse model, we found that the onset of aGvHD is associated with intensive renal injury manifested by neutrophil gelatinase-associated lipocalin upregulation, hetero-lysosomes accumulation in the renal proximal tubular epithelial cells, and especially αKlotho depletion and increased circulatory FGF23. These findings suggest the important role of oxidative stress in the pathogenesis of aGvHD. Thereafter, two antioxidants N-acetylcysteine (NAC) and Nacetylcysteine amide (NACA) were investigated thoroughly in respect of their therapeutic potentials.

In order to compare the pharmacokinetic-pharmacodynamic properties and the mechanisms of action of NACA and NAC, we developed a new liquid chromatography-mass spectrometry method that could quantify both compounds in biological samples. We found that in relation to NAC, NACA has a higher oral bioavailability and superior capability to replenish glutathione.

In the aGvHD mouse model, NACA, but not NAC, was shown to ameliorate disease burden and prolong survival. Mechanistic studies demonstrated that the protective role of NACA was mediated by its antioxidative, anti-inflammatory and immuno-modulatory effects. Importantly, NACA did not negatively affect the engraftment efficiency in transplanted mice.

In addition to the prophylactic ability against aGvHD, NACA also exhibited a cardioprotective effect. We observed that NACA significantly attenuated the endothelial injuries induced by cyclophosphamide treatment. NACA preserved the integrity of the vascular endothelium in vivo, while reduced intracellular oxidative stress and cell death in vitro. Moreover, NACA assisted in maintaining the endothelial hemostasis and angiogenesis. Yet, NAC was relatively less efficient compared to NACA.

Taken together, the results obtained in the present thesis provide experimental evidence that the novel antioxidant, NACA, is a promising candidate for prophylaxis of HSCT-related complications. Further investigations are warranted to optimize the treatment regimen and to evaluate the influence of NACA on the clinical outcome of HSCT.