Introduction
Ganoderma lucidum (Curtis) P. Karst (commonly known as Reishi) is a medicinal mushroom belonging to the Agaricomycetes class, Polyporales order, and the Ganodermataceae family. Reishi is best known for boosting the immune system and being extremely important in treating and preventing many diseases. This mushroom has been used for medicinal and therapeutic purposes for many years in Asian countries. Research in the field of modern food chemistry has discovered about 400 bioactive compounds from the groups of polyphenols, polysaccharides, steroids, triterpenoids, nucleotides, amino acids, nutritious minerals, trace elements, and various vitamins in fruits (sporophores), mycelia, and spores of reishi [1]. Some of these bioactive compounds, including polysaccharides, triterpenes, and peptides, have anti-aging properties. Previous studies have paid their most attention to ethanol and aqueous extracts of fruiting bodies, mycelium extracts, and spore extracts of reishi to study their anti-aging effects [2]. This study aims to review the anti-aging effects of reishi and its possible mechanisms at the cellular and molecular level. 

Methods
This is a review study. Relevant articles in Persian or English published from 1989 to 2023 were searched in databases such as PubMed, Scopus, Google Scholar, SID, and Magiran using the following keywords: Reishi, G. lucidum, anti-aging properties, antioxidant properties, free radicals, and neurodegenerative diseases/disorders. Emphasis was placed on selecting original research articles rather than review studies. 

Results
Aging has been shown to be one of the most important risk factors for impaired immune system. With aging, the efficiency of T lymphocytes and their ability to produce cytokines decrease, leading to a decrease in the thymus. This problem is the main cause of weakened immunity in the elderly. With aging, the bone marrow’s ability to regulate the function of B lymphocytes and the ability of these lymphocytes to secrete immunoglobulins also decreases. In-vitro and in-vivo studies have shown the effectiveness of Reishi in improving the cognitive function and oxidative stress response, and increasing immune activity [3]. Evidence showed that the extracts of Reishi can protect the heart, liver and brain of normal mice against aging, mainly due to their antioxidant nature.
Aging and subsequent changes are also important risk factors for common neurocognitive or neurodegenerative disorders such as mild cognitive impairment, Alzheimer’s disease, cerebrovascular disease, and Parkinson’s disease. G. lucidum polysaccharides are one of the promising compounds for the treatment of neurodegenerative diseases [4]. In fact, the effect of G. lucidum extracts or compounds on treating or preventing neurodegenerative diseases is directly related to the prevention of aging process. According to studies, Reishi avoids the activation of the core protein kappa B (NF-κB), preventing endotoxin from binding to its cellular receptor TLR4 and initiating inflammatory pathways [5]. Reishi’s extracts have also been shown to reduce the expression of a set of genes associated with Alzheimer’s and Parkinson’s disease in mice’s microglial cells stimulated with bacterial endotoxin [6]. However, there are still limited animal studies on the effectiveness of Reishi extract in preventing brain tissue damage and preventing neurodegenerative diseases. 
One concern with Reishi and other herbal compounds is their unknown adverse effects on normal cells and possible interference with chemotherapeutic drugs. In this regard, one of the interesting assumptions is that the anti-aging and anti-cancer properties of G. lucidum compounds are applied by protecting rather than damaging cellular DNA, while chemotherapeutic drugs work by damaging cellular DNA [7].

Conclusion
In summary, this review study showed that various extracts of Reishi or G. lucidum have measurable anti-aging properties, especially in three tissues: Heart, liver and brain. These effects are primarily attributed to modulation of the immune system, antioxidant activity and free radicals scavenging, the increase of mitochondrial dehydrogenases, and the prevention of oxidative stress-induced neurodegeneration. However, still more clinical trials on human models are needed to fully explain the mechanisms underlying the anti-aging properties of Reishi.

Ethical Considerations
Compliance with ethical guidelines
In this study, no experiments were conducted on animal or human models. In this regard, no ethical considerations were needed.

Funding
This research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors.

Authors' contributions
Data collection and search in databases: Sharareh Rezaeian; Writing and editing: Hamid Reza Pourianfar; Final approval: The both authors.

Conflicts of interest
The authors declared no conflict of interest.


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