Citrus surprise: Vitamin C boosts the reprogramming of adult cells into stem cells

December 24, 2009

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Famous for its antioxidant properties and role in tissue repair, vitamin C is touted as beneficial for illnesses ranging from the common cold to cancer and perhaps even for slowing the aging process. Now, a study published online on December 24th by Cell Press in the journal Cell Stem Cell uncovers an unexpected new role for this natural compound: facilitating the generation of embryonic-like stem cells from adult cells.

Over the past few years, we have learned that adult cells can be reprogrammed into cells with characteristics similar to embryonic stem cells by turning on a select set of genes. Although the reprogrammed cells, called induced pluripotent stem cells (iPSCs), have tremendous potential for regenerative medicine, the conversion is extremely inefficient.

"The low efficiency of the reprogramming process has hampered progress with this technology and is indicative of how little we understand it. Further, this process is most challenging in human cells, raising a significant barrier for producing iPSCs and serious concerns about the quality of the cells that are generated," explains senior study author Dr. Duanqing Pei from the South China Institute for Stem Cell Biology and Regenerative Medicine at the Guangzhou Institutes of Biomedicine and Health, Chinese Academy of Sciences.

Dr. Pei and colleagues measured the production of reactive oxygen species or ROS during reprogramming and discovered a potential link between high ROS and low reprogramming efficiency. They became particularly interested in antioxidants, hypothesizing that they might suppress ROS and cell senescence, which seems to be a major roadblock for the generation of iPSCs.

The researchers found that adding vitamin C, an essential nutrient that is abundant in citrus fruits, enhanced iPSC generation from both mouse and human cells. Vitamin C accelerated gene expression changes and promoted a more efficient transition to the fully reprogrammed state. Somewhat to their surprise, they found that other antioxidants do not have the same effect, but vitamin C does seem to act at least in part through slowing cell senescence.

"Our results highlight a simple way to improve iPSC generation and provide additional insight into the mechanistic basis of reprogramming," concludes Dr. Pei. "It is also of interest that a vitamin with long-suspected anti-aging effects has such a potent influence on reprogramming, which can be considered a reversal of the aging process at the cellular level. It is likely that our work may stimulate further research in this area as well."

More information: Esteban et al.: “Report: Vitamin C Enhances the Generation of Mouse and Human Induced Pluripotent Stem Cells.” Publishing in Cell Stem Cell, January 8, 2010. http://www.cellstemcell.com

Source: Cell Press

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Targeted Nanoparticles Deliver Therapeutic DNA to Cancer Cells

12/25/2008 11:22:47 PM

Given that cancer is a disease caused by gene mutations, cancer researchers have been striving to develop gene therapies aimed at correcting these mutations. However, these efforts have been hobbled by the difficulty in safely and efficiently delivering anticancer genes to tumors. Nanoparticles, however, may solve these delivery issues, and two recently published studies, using two different types of nanoparticles, lend credence to that hypothesis.

Miqin Zhang, Ph.D., PI of the Nanotechnology Platform for Pediatric Brain Cancer Imaging and Therapy project at the University of Washington in Seattle, led a group of researchers that developed a targeted polymer nanoparticle that efficiently delivered a model gene into two types of cancer cells. More importantly, the gene functions properly once it enters the targeted cells. In the second study, Mansoor Amiji, Ph.D., PI of the Nanotherapeutic Strategy for Multidrug Resistant Tumors Platform Partnership at Northeastern University, and doctoral student Padmaja Magadala, M.S., used gelatin-based nanoparticles and a different targeting agent to efficiently deliver the same model gene to human pancreatic tumor cells. As in the first study, the delivered gene functioned properly inside the tumor cells.

The nanoparticle developed by Dr. Zhang’s group was made of two polymers—polyethyleneimine (PEI) and polyethylene glycol (PEG)—linked to chlorotoxin, a small protein isolated from scorpion venom. Previous research by several research teams had shown that chlorotoxin binds many types of tumors, including gliomas and medulloblastomas, two types of brain cancer. PEI forms stable nanoparticles that bind deoxyribonucleic acid (DNA), but the resulting nanoparticles can be toxic. Adding PEG to the nanoparticles provides a biocompatible surface that greatly reduces the toxicity of PEI.

As a test, Dr. Zhang and her colleagues used these nanoparticles to deliver DNA that codes for green fluorescent protein (GFP), which is used widely to study gene expression. When added to tumor cells expressing the chlorotoxin receptor, the nanoparticles were quickly taken up by the cells. The cells also turned green, thanks to the expression of GFP. In contrast, nanoparticles lacking chlorotoxin were not taken up by the cells, and tumor cells lacking the chlorotoxin receptor did not take up the nanoparticles.

(The three scientists credited with discovering and developing GFP as a critical research tool were awarded the 2008 Nobel Prize in Chemistry. One of those scientists, Roger Tsien, Ph.D., is an investigator at NCI’s Center of Nanotechnology for Treatment, Understanding, and Monitoring of Cancer at the University of California, San Diego.)

Dr. Amiji’s approach differed, in that he used a peptide that targets the epidermal growth factor receptor that is overexpressed by several types of tumors, including pancreatic cancer. He also used a nanoparticle constructed from negatively charged gelatin, which readily incorporates DNA and other nucleic acids, which are positively charged at normal physiological pH. The structure of the nanoparticle material also promotes DNA to take on a supercoiled structure that is efficiently taken up and transported to the cell’s nucleus, a critical factor for gene expression to occur. To improve the biocompatibility of these nanoparticles, Dr. Amiji also used PEG to coat the nanoparticles.

When added to pancreatic cells, nearly half of the administered dose of these engineered, targeted nanoparticles were taken up by pancreatic tumor cells, a remarkably high value. More importantly, a large percentage of the transfected cells subsequently expressed GFP. In addition, the nanoparticles were not toxic to the cells, an important finding given that they did not contain any therapeutic agent.

The work from Dr. Zhang’s group, which was detailed in the paper “A ligand-mediated nanovector for targeted gene delivery and transfection in cancer cells,” was supported by the NCI Alliance for Nanotechnology in Cancer, a comprehensive initiative designed to accelerate the application of nanotechnology to the prevention, diagnosis, and treatment of cancer. An abstract of this paper is available at the journal’s Web site.

View abstract

The study headed by Dr. Amiji, which was described in the paper “Epidermal growth factor receptor-targeted gelatin-based engineered nanocarriers for DNA delivery and transfection in human pancreatic cancer cells,” was also supported by the NCI Alliance for Nanotechnology in Cancer. An abstract of this paper is available at the journal’s Web site.

View abstract.

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