1. Adipose derived stem cells (ADSCs), transfected to overexpress hepatic growth factor (HGF) or to silence HGF expression, were injected into irradiated rats to examine their ability to protect against radiation-induced liver damage.
2. The HGF-overexpressing ADSCs appeared to mitigate liver damage, increasing liver cell proliferation and reducing liver cell apoptosis, fibrotic scarring, and serum levels of radiation-induced enzymes.
Evidence Rating Level: 3 (Average)
Study Rundown: Radiation is used commonly in cancer treatment, but can also cause off-target damage in surrounding healthy tissues. In particular, radiation-induced liver damage (RILD) sometimes leads to liver failure and resulting death, and unfortunately no widely accepted treatment plan is currently available.
In the past, ADSCs have been shown to improve the outcomes of some liver injuries. Additionally, HGF promotes hepatocyte regeneration, and prevents the cell death and fibrotic scarring typical of liver damage. Researchers in this study built on such previous research to hypothesize that ADSCs overexpressing HGF would ameliorate the damaging effects of RILD. Isolated ADSCs were transfected with lentiviruses containing no additional gene sequence, an HGF-expressing gene (ADSCs+HGF), or shRNA that silences HGF production (ADSCs+shHGF). These ADSCs were then injected into rats immediately following high-dose irradiation. ADSCs+HGF most significantly lowered hepatocyte apoptosis and scarring, and promoted hepatocyte regeneration. Mice injected with ADSCs+shHGF demonstrated reduced liver protection when compared with those injected with control ADSCs or ADSCs overexpressing HGF.
Taken together, this work points to important roles for both ADSCs and HGF in mitigating RILD. More research is needed to apply this work to human medicine, which usually uses high doses of radiation localized to tumor areas rather than the whole-liver irradiation used in this study. This system can be easily translatable to the clinical setting, and suggests that ADSCs overexpressing HGF may be instrumental to preventing RILD in clinical applications.
In-Depth [animal study]: ADSCs were isolated from rat adipose tissue. Fluorescence-activated cell sorting analysis verified the ADSCs phenotype, showing that 99% of cells expressed the cell surface protein CD90, and <1% expressed CD34, CD45, or CD31. ADSCs were transfected with lentiviruses encoding GFP alone, HGF-GFP, or shHGF-GFP, and transfection was shown to be 100% effective by ADSC fluorescence. RT-PCR demonstrated, as compared to the ADSC group, HGF levels were higher in the HGF group (p<0.05), and lower in the shHGF group (p<0.05).
A total of 70 Sprague-Dawley rats were used, with 10 serving as no-radiation controls. The remaining 60 were given 60Gy of whole liver irradiation, and then immediately injected with multiple doses of saline (RILD, n=15), ADSCs (n=15), ADSCs+HGF (n=15), or ADSCs+shHGF (n=15). Two weeks after transplantation, ELISA experiments showed that compared to the ADSC control groups, HGF liver levels were higher in the ADSCs+HGF group (p<0.05), and lower in the ADSCs+shHGF group (p<0.05).
The TUNEL assay showed the ADSCs+HGF group most significantly lowered the increased hepatocyte apoptosis featured in the RILD group (p<0.05), followed by ADSCs alone (p<0.05) and then ADSCs+shHGF. Histological examination and western blotting showed that RILD-mediated increases in collagen-I levels, indicative of fibrosis, were lowered in the ADSCs+HGF group (p<0.05). The number of cells positive for the antigen ki-67, an indicator of cell proliferation, was most increased in the ADSCs+HGF group (p<0.05), with ADSCs and ADSCs+shHGF also exhibiting pronounced, though decreased, proliferative effects (p<0.05). Finally, serum levels of the enzymes alanine aminotransferase (ALT) and aspartate aminotransferase (AST), which were raised in the RILD group, indicating liver damage, were lowered 2 days post irradiation in the ADSCs+HGF group (p<0.05 for both enzymes).
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