Study explores health benefits of selenium and zinc-enriched eggs

By Dr. Sushama R. Chaphalkar, PhD.Reviewed by Danielle Ellis, B.Sc.Feb 15 2024

In a recent study published in Nutrients, researchers investigated the effect of a diet of selenium- and/or zinc-enriched eggs (SZE) on oxidative stress, cognitive impairment, and intestinal flora in D-galactose-induced aging mice. They found that the SZE diet could reduce organ damage and improve cognitive function in mice models by modulating oxidative stress, inflammation, and gut microbiota.

Background

The aging process involves an irreversible structural and functional decline influenced by genetics and the environment. It is characterized by an imbalance in reactive oxygen species (ROS), leading to cellular aging and age-related diseases. The essential trace elements selenium (Se) and zinc (Zn) have shown anti-aging effects linked to their roles in reducing ROS and combating oxidative stress. Although the individual roles and pathways of Se and Zn have been studied in mitigating the effects of aging, their combined effects of Se and Zn remain underexplored.

Eggs, recognized for their high nutritional value, contain essential nutrients like proteins, fatty acids, vitamins, and trace minerals, contributing significantly to the human diet and health. SZE represents an innovative approach to enhance mineral potency, with potential health benefits attributed to active substances like ovalbumin, ovoglobulin, and phosphatide. However, our understanding of SZE's nutritional functions and biological activities is currently limited. Therefore, researchers in the present study aimed to explore the chemical composition of SZE and assess their potential efficacy in mitigating aging-related oxidative stress and inflammation, and promoting gut health in model mice.

About the study

Egg powders were developed from SZE and normal eggs (NE), and their composition was analyzed. Mineral content in the eggs was determined using inductively coupled plasma mass spectrometry (ICP-MS). In the in vivo analysis, 70 male Kunming mice were randomized into seven groups (n = 10 each). The groups were as follows: the control group (Con) was given 0.9% saline, the model group (Mod) given 0.9% saline, the low-dose SZE group (SZLE), the high-dose SZE group (SZHE), the ordinary eggs group (OE), the DL-Selenomenthionine group (SeM), and the ZnSO4 group (ZnSO4). All groups except Con were injected with D-galactose to induce aging.

Maze-based spontaneous alternation and cognitive function tests were conducted on the mice. Blood samples were collected and analyzed for levels of total superoxide dismutase (SOD), malondialdehyde (MDA), alanine transaminase (ALT), aspartate amino transferase (AST), and glutathione peroxidase (GSH-Px) were measured.

After an 8-week intervention, behavioral analysis, fasting, and euthanasia, tissues of the brain, liver, and duodenum, as well as cecum contents, were collected and analyzed. The organ index was calculated as the weight of the organ divided by body weight. Se and Zn content of the organs was measured.

Acetylcholine (Ach), acetylcholinesterase (AChE), and protein concentrations were measured in the brain tissue. Interleukin (IL)-6, IL-1β, and tumor necrosis factor α (TNF-α) levels were measured in the liver tissue using enzyme-linked immunosorbent assay (ELISA). Genomic DNA was extracted from the cecum contents, and the V3-V4 region of the bacterial 16S ribosomal ribonucleic acid (16S rRNA) region was amplified.

Results and discussion

While the moisture, lipid, and ash content were found to be similar in SZE and NE, the protein, sugar, Se, Zn, iron, manganese, molybdenum, magnesium, and phospholipid content of SZE was found to be higher than NE. Total cholesterol and other heavy metals were found to be lower in SZE than NE. Se was majorly enriched in the albumen, while Zn was enriched in the yolk.

In the in vivo analysis, researchers found that although the body weight of mice in Con and Mod groups increased initially, at the end of eight weeks, Mod mice showed reduction in organ index, indicating organ atrophy. This effect was attenuated in the groups SZE, OE, SeM, ZnSO₄, SZLE, and SZHE groups.

Se and Zn were majorly enriched in the brains of all the mice, and the levels varied across groups. The Mod group had significantly low levels of SOD and GSH-Px and significantly higher levels of MDA as compared to Con. The alternation rate and dwelling time in the new maze-arm were found to be significantly lower in the Mod groups as compared to Con. As measured by Ach and AChE levels, SZE was found to improve brain dysfunction induced by D-galactose. Similarly, based on interleukin, AST, and ALT levels, SZE intervention was also found to lower D-galactose-induced hepatic impairment and inflammation.

Further, the microbiota of all the groups was found to be very different. SZE helped maintain the balance of intestinal flora by significantly increasing the ratio of Firmicutes and Bacteroidota. The levels of Blautia were found to correlate with inflammatory markers and antioxidant levels.

Conclusion

The findings of the study demonstrate the promising role of SZE diet in mice, alleviating oxidative stress and improving gut microbiota balance. Further research exploring the therapeutic application of SZE diet in humans is warranted.