Selenoneine is an organic compound containing selenium, and is also an analogue of ergothioneine, a naturally occurring amino acid. It is said to have strong antioxidant properties, and is the major form of organic selenium in the blood, muscles, and other tissues in tuna.
Researchers at Okayama University, Nutrition Act Co. Ltd, the National Research Institute of Fisheries Science, and National Fisheries University conducted a study using a mouse model to determine if an STDME-rich diet could exert enough antioxidant activity to prevent carcinogenesis in two types of colorectal cancer.
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Induction and supplementation
The researchers used six-week old female mice and randomly placed them into two groups: one on an STDME-enriched standard rodent diet, and the other on a standard diet alone, both for one week.
The mice were then intraperitoneally injected with the carcinogen azoxymethane (AOM) to induce colorectal carcinogenesis. Five days later, they were given dextran sodium sulfate (DSS) in drinking water for the next five days, followed by 16 days of regular water.
This cycle was repeated three times, with the mice's body weight and dietary intake measured every two to three days throughout the process.
After this, the researchers assessed the incidence of macroscopic polyps and performed a functional analysis of immune cells from the spleen. They also studied tumour formation rates and median survival after a colorectal cancer cell line had been subcutaneously implanted.
They later reported that the mice in the control group exhibited significant weight loss, bleeding and diarrhoea after the third round of DSS treatment, while the mice in the STDME-supplemented group gained a significant amount of weight, and saw their bleeding and diarrhoea alleviated.
Furthermore, despite the mice's colon length being similar in both groups, the supplemented group experienced a lower incidence of tumours, and a shorter maximal cross-sectional diameter in macroscopic polyps.
At the same time, daily STDME administration produced no observable toxicity or disorders, and "inhibited the accumulation of myeloid-derived suppressor cells (MDSCs) while also inhibiting the down-regulation of interferon gamma (IFNγ) production during carcinogenesis".
The researchers noted previous reports that had shown that ROS (reactive oxygen species) production by cancer cells had both tumour-promoting and anti-tumour properties.
There have been instances whereby antioxidant dietary supplements have helped to lower cancer risk, while in other cases, such supplements are said to have both harmful and beneficial effects.
As such, the effect of dietary antioxidants on cancer "remains controversial".
However, they also said that since selenoneine's antioxidant properties are more powerful than other types of selenium supplementation, an STDME diet might have a stronger impact on cancer prevention.
In conclusion, they wrote: "We showed that an STDME diet protects against colorectal cancer. The underlying mechanism may involve the suppression of the splenic MDSC accumulation that promotes cancer progression by attenuation of anti-tumour activity.
"Moreover, selenoneine also affected the cells directly to inhibit in vitro carcinogenesis. Since selenoneine is highly concentrated in cells…STDME might be effective as a dietary antioxidant.
"We anticipate that STDME will emerge as a functional food with excellent antioxidant properties, while further research to clarify the physiological roles of selenoneine to prevent carcinogenesis or tumour growth should be still required."
"Dietary Supplementation of Selenoneine-Containing Tuna Dark Muscle Extract Effectively Reduces Pathology of Experimental Colorectal Cancers in Mice"
Authors: Junko Masuda, et al.