Neural stem/progenitor cells damaged by reactive oxygen species evolved in photosensitizing reaction

We want to know how the growth of neural stem/progenitor cells and their differentiation are affected by reactive oxygen species evolved in photosensitizing reaction, because of the similarity between the stem cells and the tumor cells in central nervous system. We investigated the effects of two photosensitizers (rhodamine 123 and hematoporphyrin) on the mouse neural stem/progenitor cells cultured in vitro under the illumination. ABC transporters were expressed in the cells, and could pump rhodamine 123 and hematoporphyrin out of the cells. Under the illumination of strong actinic light with those photosensitizers, reactive oxygen species was evolved to injure the cells. Number of viable cells decreased under illumination through apoptosis and necrosis. Those cell-killing activities were not clearly dependent on the presence of inhibitors for ABC transporters. Immunocytochemical staining with showed that immature cells with markers of neural stem/progenitor cells (Sox 2, CD133, nestin) were more sensitive to the reactive oxygen species than the differentiated cells.

Cell viability of the mouse neural stem/progenitor cells (NSPC) measured by the WST-method at 24 h (A) after the illumination with photosensitizers. Open bar (20 μM RH without CsA), black filled bar (20 μM RH with 20 μM CsA), bar with hatched stripe (8 μM HP without FTC) and dotted bar (8 μM HP with 8 μM FTC) show each data in (D). Ratio of the Annexin V-positive/PI-unstained cells as apoptotic cells (A+P−) at 24 h (bar with vertical stripe), that of Annexin V-negative/PI-stained cells as necrotic cells (A−P+) at 24 h (bar with horizontal stripe), that of Annexin V-negative/PI-unstained cells as undamaged intact cells (A−P−) at 24 h (dotted bar), A+P− apoptotic cells at 48 h (open bar), A−P+ necrotic cells at 48 h (filled bar), A−P− undamaged intact cells at 48 h (bar with hatched stripe) after the illumination with photosensitizers are shown in (B). Apoptotic cells (striped bars) and necrotic cells (dotted bars) at 48 h are also shown in (B). Symbols shows the condition of each sample, RH(+); rhodamine 123, illuminated for 10 min, RH(−); rhodamine 123, unilluminated, HP(+); hematoporphyrin, illuminated, HP(−); hematoporphyrin, unilluminated for 10 min. We showed that illumination with strong actinic light evolve the ROS and then killed the NSPCs. However cell-killing activity of photosensitizers on NSPCs did not clearly depend on the presence of ABC-transporter inhibitors.Figure optionsDownload high-quality image (66 K)Download as PowerPoint slideResearch highlights
► ABC transporters were expressed in the mouse neural stem progenitor cells (NSPCs).
► ABC transporters pumped out photosensitizers (PS), rhodamine 123 and hematoporphyrin.
► Reactive oxygen species (ROS) evolved by PS injured the NSPCs under illumination.
► The cell-killing activity of PS did not depend on inhibitors for ABC transporters.
► Immature (Sox 2, CD133, nestin-positive) NSPCs were sensitive to ROS.