The Role of Rapamycin in the Preservation of Female Fertility and Ovarian Health

The average age of a first-time mother in the USA and UK is 30 & 31, respectively, with more women leaving it later in life to bear children than ever before. This age is considerably higher than the average age of 21 in the 1970s. There are many reasons why this exponential increase has occurred over the last 50 years. However, it can be largely attributed to (1) the cost of rearing a child [1], (2) education/career aspirations, or (3) failure to meet the right partner. It is also well established that females decline in their ability to successfully bear a child as they age, with a 98% reduction in reproductive cells/egg (termed 'oocytes') from birth to age 37 (~2 million to ~25,000). This is further worsened as oocytes decline to ~1,000 by age 50 and the start of menopause [2].Therefore, several research groups worldwide have sought to determine methods to understand and prolong a woman's reproductive lifespan, enhance ovarian health, and mitigate biological age's detrimental effects on the female reproductive system.One noteworthy therapeutic is rapamycin, a well-established anti-aging & longevity compound. Among the several benefits of rapamycin to human health, recent research has begun to demonstrate that rapamycin may have significant benefits for women's health, particularly in preserving ovarian function, fertility, and delaying menopause.So, what does the science say? In this article, we discuss these exciting findings and how rapamycin may be utilized to enhance reproductive health and longevity in women.

An Overview of Female Reproduction During Ageing

As women age, their bodies undergo a remarkable journey of reproductive aging. Understanding the basic biology behind these changes can empower women to make informed decisions about their reproductive health & well-being.

The Decline of Ovary Health:

The ovaries are central players in a woman's reproductive system and experience significant changes as they age. Evidence shows that women are born with approximately one to two million oocytes (eggs), but by the time they reach puberty, this number decreases to around 300,000 to 500,000 [2]. As a woman approaches her 30s, the decline in egg quantity accelerates, with an estimated 12% reduction per year. By age 35, the decline becomes even steeper, and by 40, only 2% of a woman's original egg supply remains [2].

"Oocytes" refer to the female reproductive cells or eggs found in the ovaries of animals, including humans. These cells are produced and stored within the ovaries and play a crucial role in sexual reproduction. Oocytes are the largest cells in the human body, visible to the naked eye. They are formed during the early stages of fetal development and remain dormant until maturity."

Quality vs Quantity:

While the quantity of oocytes diminishes with age, so does their quality [3]. The molecular decline in oocyte quality results from genome instability, reduced mitochondrial function, increased ROS (Reactive Oxygen Species), and disturbances in chromosome segregation [3]. As a result, the likelihood of conceiving decreases with age, and the risk of chromosomal abnormalities and genetic disorders (i.e., Downs Syndrome) in newborn children increases [4].The primary biological mechanism is thought to be an increase in meiotic nondisjunction, resulting in an increased rate of aneuploidy in the early embryo [5] – Which, in simpler terms, means as women age, there is a higher chance of errors occurring during the division of cells in the early stages of embryo development. This leads to an increased risk of having an abnormal number of chromosomes in the embryo, a condition known as aneuploidy [6].There have been several attempts to restore and maintain oocyte quantity and quality with nutraceutical approaches such as Resveratrol [7], Coenzyme Q10 [8], Vitamin C [9], and NMN [10] to target the increased mitochondrial ROS & DNA damage associated with oocyte aging, albeit with limited effects. Amongst the previously mentioned biological mechanisms, mTOR has an often overlooked role in the activation and dysregulation of ovarian growth signaling of primordial follicles.

"Primordial follicles are the earliest stage of ovarian follicle development and represent the reserve of immature eggs (oocytes)."

It is well established that during aging, cells, and tissues become hyperactive, resulting in dysregulated nutrient sensing, impaired autophagy, and accumulation of senescent cells. This process is largely regulated by hyperactive mTOR-related signaling. Thus, following primordial follicle activation from Follicle stimulating hormone (FSH) and luteinizing hormone (LH), mTOR is crucial in the growth and development of mature follicles. The pharmacological manipulation and reduction in mTOR activity with rapamycin have been proposed as a highly promising strategy to improve oocyte quantity and quality [11].

Background on Rapamycin

Rapamycin is a macrolide compound that has been shown to have a wide range of biological effects, including immunosuppressive, anti-cancer, and longevity properties [12]. Notably, rapamycin was 1 of only 10 (out of 64) therapeutics tested so far as part of the Interventions Testing Programme (ITP) at the National Institute on Aging (NIA) that improved lifespan [13]. Other successful therapeutics were Acarbose [14], Aspirin [15], Canagliflozin [16], Glycine [17], Protandim [18], 17α-estradiol [14] and nordihydroguaiaretic acid [15]. Since then, several research groups from around the world have begun to demonstrate that the off-label repurposing of rapamycin may also serve the potential as a therapeutic to prevent many non-communicable diseases [12].The primary mechanism in which rapamycin has a beneficial therapeutic effect is by inhibiting the activity of the mammalian target of rapamycin (mTOR), a key regulator of cellular metabolism, growth, and proliferation. Specifically, rapamycin binds to a protein called FK506-binding protein 12 (FKBP12), which then dephosphorylates mTOR, thereby 'turning off' downstream growth signals such as P70S6K & ribosomal complexes needed for cellular growth [19].

Chronic overactivation of mTOR is at the foundation of many age-related diseases. As we get older, mTOR may stay active all the time—opening the door to out-of-control cell growth that can lead to cancer and closing the door on cell repair. It is a driver of toxic cellular hyperactivity, leading to the decline of healthy tissue.

By inhibiting mTOR, rapamycin can reduce cellular growth (improved proteostasis), increase mitochondrial function (reduced ROS production) [20], increase autophagy [21], and enhance overall metabolic health [22], which has been shown to have a wide range of therapeutic effects.

An Overview of the Established Effects of Rapamycin

• Longevity

  : Perhaps the most well-studied effect of rapamycin is its ability to enhance longevity in a variety of model organisms, including mice, flies, and worms. In these models, treatment with rapamycin has been shown to extend lifespan by up to 30% or more. However, the original ITP NIA longevity study on rapamycin conducted by Professor David Harrison at The Jackson Laboratory showed a 9-14% increase in lifespan [13].

• Cancer:

   

  Rapamycin has shown promising benefits in cancer treatment. Cancer cells display increased activation of mTOR and metabolic reprogramming, making them highly glycolytic, resulting in rapid tumour growth. Rapamycin can inhibit the growth and proliferation of cancer cells by blocking mTOR and minimizing tumour growth. Furthermore, recent evidence suggests it processes anti-vascular effects, reducing vascular endothelial growth factors in tumours [23]. Additionally, rapamycin has demonstrated the ability to enhance the effectiveness of other anti-cancer therapies and reduce drug resistance [24].

• Neurological Disease:

   

  Rapamycin has been shown to have potential as a therapeutic for neurodegenerative diseases such as Alzheimer's disease [25]. This effect is thought to be due to the ability of rapamycin to enhance autophagy, which can help to reduce amyloid-β deposition [26], prevent tau-induced neuronal loss [27], and improve cognitive function [26]. Overall, drastically rapamycin drastically improves spatial learning and memory in older mice. Although there is no direct human evidence to date, Professor Mitzi Gonzales 

  of the University of Texas, San Antonio, is currently running a 12-month clinical trial

  into the effects of daily rapamycin (1mg dose) to determine its effect on brain volume, cerebral metabolism, and functional cognitive testing

  in patients with diagnosed Alzheimer's – We are very much looking forward to seeing the data on this in the future.

Can Rapamycin Improve Female Reproductive Health?

Unlocking the potential of rapamycin as a therapeutic intervention to prevent menopause and enhance ovarian health in women has become an increasingly popular avenue of research for longevity researchers. The shift in the hormonal environment during menopause brings about a significant shift in a woman's reproductive health, often accompanied by a decline in ovarian function. Recent studies have shed light on rapamycin's ability to extend ovarian lifespan, enhance oocyte quality, and delay reproductive senescence. Exploring the benefits of rapamycin as a therapeutic agent holds promise for preserving fertility and improving women's overall youthfulness into older age. Here we delve into the emerging evidence and discuss the potential of rapamycin as a game-changer in women's reproductive health.

Rapamycin and Fertility

As women age, their ovaries begin to produce fewer oocytes, which can lead to infertility and other reproductive issues [28]. Recent studies have shown that rapamycin can improve ovarian function and increase the number of eggs produced by the ovaries.In one study published in Aging Cell titled 'Short‐term rapamycin treatment increases ovarian lifespan in young and middle‐aged female mice', female mice treated with rapamycin had a significantly greater egg quality [29]. In particular, across the lifespan of a mouse, from 4.5 months to 12 months (equivalent human age of 25 & 45 years), the number of oocytes decreased by ~75%, with 20% and 42% of oocytes expressing abnormalities.

"Primordial follicles are the earliest stage of follicular development. They consist of a primary oocyte surrounded by a single layer of flat granulosa cells. Following activation, they transition to primary follicles, in which the oocyte is still surrounded by a single layer of granulosa cells, but these cells have become more cuboidal in shape. Additionally, a specialized layer called the zona pellucida starts forming around the oocyte. The last phase of development is the tertiary follicles. These are the most advanced stage of follicular development before ovulation and have a large antrum filled with fluid and are surrounded by several layers of granulosa cells. Tertiary follicles eventually undergo ovulation, where the mature oocyte is released from the ovary, ready for fertilization."

Although the rapamycin-treated mice observed a similar decline in oocyte number to the placebo, there was a large reduction in the number of oocyte abnormalities, with only 10% & 20% of oocytes at 4.5 months and 12 months of age displaying abnormalities [29]. This may be attributed to the ~26% greater abundance of primordial follicles in the rapamycin-treated group compared to placebo.

The expression of the active protein involved in mTOR & cell growth, rpS6, was reduced by >85% [29]. Overall, showing rapamycin has the potential to preserve primordial follicles and enhance egg quality via the reduction in mTOR activity, which may result in increased chances of a successful pregnancy.

Rapamycin and Menopause

Menopause is a natural process that occurs in women at approximately 50 years of age, although it can develop <40 years of age (termed 'early menopause'), and it is deemed the end of a women's ovarian lifespan [28].The end of a woman's fertility window is a result of empty follicle pool reserves, in which no primordial follicles remain. A measurement of primordial follicle reserve can be established via an invasive ovarian biopsy; however, the levels of anti-müllerian hormone give a detailed non-invasive quantification.The treatment of rapamycin has been shown to increase anti-müllerian hormone by >100% following a treatment regime of 4mg/kg/EOD for three months [30]. Interestingly, rapamycin did not alter the total number of follicles, but compared to placebo, rapamycin modified the number of primordial (+83%), primary (-57%), and tertiary follicles (-37%) [30].

Overall, rapamycin has the capability of altering follicle development to maintain a higher follicular reserve, thereby extending a women's reproductive lifespan and offsetting menopause by potentially years or even decades.

Future Research on Rapamycin and Ovarian Aging

The University of Columbia, New York, recently have begun recruitment on a world-first study investigating the effects of 12 weeks of rapamycin on delaying the start of menopause. The study is being conducted by Professor Zev Williams, an Associate Professor of Women's Health and the Chief of the Division of Reproductive Endocrinology and Infertility of Columbia University's Irving Medical Centre. In short, the primary objective of the 12-week long study is looking to determine the effects of a normal 5mg/week dose can improve ovarian reserve measured via transvaginal ultrasound. Other secondary outcomes include evaluating the levels of anti-müllerian hormone, estradiol, follicle stimulating hormone, and levels of Klotho. As the study has recently begun recruitment in April 2023, we eagerly await results from this clinical trial in the coming years – If you're local to Columbia University and are interested in taking part, please find more details here.

"anti-müllerian hormone has clinical significance as a fertility biomarker for assessing ovarian reserve, which refers to the quantity and quality of a woman's remaining eggs."

To Wrap it up - What does all this mean?

Rapamycin has shown significant promise for improving women's health in preclinical models. From improving ovarian function and menopause symptoms to preventing uterine fibroids, rapamycin has the potential to help women live healthier, more fulfilling lives as they age.While more research is needed to fully understand the benefits of rapamycin in humans, the current evidence suggests that it could be a valuable tool for improving women's reproductive health, allowing them to have children later in life, and delaying the side effects associated with menopause and hormonal replacement therapy.