Chlorogenic Acid Protects Transplanted Spermatogonial Stem Cells in Torsion-Induced Azoospermia Models

A compound found in coffee, fruit and vegetables may help protect the stem cells needed to make sperm from the damaging effects of deep freezing, according to a new study in mice. Researchers report that adding chlorogenic acid to the preservation medium used for spermatogonial stem cells improved the cells’ survival, proliferation and differentiation after transplantation into testes rendered infertile by testicular torsion. The findings raise the possibility of making fertility-preservation procedures more reliable for boys who cannot yet produce and bank mature sperm, although the work remains firmly at the preclinical stage and does not demonstrate that the approach is ready for human treatment.

Spermatogonial stem cells, or SSCs, sit at the foundation of sperm production. In the adult testis, a small population of these cells continually renews itself while producing descendants that enter the long process of spermatogenesis. Prepubertal boys do not yet have mature spermatozoa, so children facing treatments such as chemotherapy or radiotherapy have limited fertility-preservation options. One experimental strategy is to collect testicular tissue, isolate or enrich SSCs, freeze them for years and later return them to the patient’s testes. If the transplanted cells successfully colonize the seminiferous tubules and resume development, they could potentially restore sperm production using the patient’s own genetic material.

Freezing, however, is not biologically neutral. As cells cool, water shifts and ice formation can disrupt membranes, proteins and organelles. The thawing process creates another threat: sudden changes in temperature and osmotic pressure can injure membranes and disturb cellular metabolism. Cryopreservation can also increase the production of reactive oxygen species, chemically reactive molecules that damage lipids, proteins and DNA when antioxidant defenses are overwhelmed. This condition, known as oxidative stress, may push vulnerable stem cells toward apoptosis, a regulated form of cell death. The challenge is therefore not simply to keep SSCs frozen, but to preserve cells capable of surviving, settling into their new environment and generating the descendants required for spermatogenesis.

In the new work, Sareh Khoshbakht, Azim Hedayatpour and colleagues at institutions in Iran tested chlorogenic acid, a plant-derived phenolic compound with antioxidant and anti-inflammatory properties. The researchers used a mouse model in which testicular torsion was followed by detorsion, recreating the ischemia–reperfusion injury that occurs when a twisted testis is deprived of blood and then suddenly reperfused. This procedure produced an azoospermia model, meaning that sperm production was effectively absent. The animals were then assigned to experimental groups receiving fresh SSCs, SSCs preserved with chlorogenic acid, SSCs preserved in a basal cryopreservation medium, or no cell transplantation. A control group provided a comparison with animals that had not undergone the same infertility-inducing process.

The investigators focused on a concentration of 100 micromolar chlorogenic acid, which produced the most favorable outcomes in the reported experiments. Eight weeks after transplantation, they assessed whether the donor SSCs had populated the recipient testes and whether they showed evidence of proliferation and differentiation. Flow-cytometry and morphological analyses examined markers including SALL4 and PAX7, proteins associated with spermatogonial populations and stem or progenitor-cell identity. The presence of these markers was used to evaluate the cells’ ability to colonize the seminiferous epithelium, the multilayered tissue lining the testicular tubules where sperm development normally occurs. The study’s design allowed the team to compare freshly transplanted cells with cells that had endured cryopreservation, while testing whether chlorogenic acid could reduce the performance gap.

According to the researchers, chlorogenic-acid supplementation enhanced SSC proliferation and differentiation compared with the basal freezing medium. The treated group also showed larger seminiferous tubule diameters and thicker germinal epithelium, structural features consistent with improved restoration of the tissue that supports sperm production. These measurements do not by themselves prove that fertile sperm were generated, but they indicate that the transplanted cells had a more substantial influence on the damaged testicular environment. In a fertility-restoration strategy, that distinction matters: successful transplantation requires more than short-term cell viability. SSCs must remain sufficiently healthy to divide, maintain a stem-cell pool and produce differentiating descendants over time.

The molecular results point to two possible mechanisms. Chlorogenic acid was associated with increased expression of genes in the PI3K/Akt/Nrf2 pathway, a signaling network involved in cell survival and antioxidant defense. PI3K and Akt can transmit signals that promote growth and resistance to stress, while Nrf2 acts as a central regulator of genes that help neutralize reactive molecules and repair oxidative damage. Activation of this pathway could give thawed SSCs a better chance of coping with the metabolic shock of transplantation. The study also found changes in the apoptosis-associated genes Bax and Bcl-2. Bax generally promotes mitochondrial pathways leading to apoptosis, whereas Bcl-2 helps preserve mitochondrial integrity and suppress cell death. A shift toward lower Bax activity and greater Bcl-2 protection would be consistent with reduced apoptosis, although gene-expression changes are indirect evidence and do not fully capture the complex biology of cell survival.

The results fit a growing body of research exploring antioxidants as additives for reproductive-cell cryopreservation. Previous studies have examined compounds such as melatonin, pentoxifylline, selenium, caffeic acid and resveratrol in germ cells, sperm or testicular tissue. Chlorogenic acid has also shown protective effects in other models of oxidative injury, including damage to sperm and reproductive tissues. Its appeal lies partly in its broad biological activity: rather than acting as a simple chemical scavenger of free radicals, it may influence cellular signaling, inflammatory responses and endogenous antioxidant systems. But antioxidant biology is not straightforward. Reactive oxygen species are damaging at excessive levels, yet they also serve as signaling molecules required for normal cell function. A compound that suppresses them too aggressively, or at the wrong dose, could disrupt rather than improve development. The favorable concentration in this mouse experiment should therefore not be interpreted as a dosage for people.

Important questions remain before the technique could move toward clinical use. The study measured SSC markers, tissue architecture and molecular indicators eight weeks after transplantation, but the abstract does not establish whether the animals produced functional sperm capable of fertilization or whether their offspring were healthy. Long-term surveillance would also be needed to determine whether preserved SSCs maintain genomic stability, retain appropriate developmental control and avoid forming abnormal growths after transplantation. Human testicular tissue is more complex than mouse tissue, and the processes used to isolate, enrich, freeze and transplant SSCs may behave differently across species. Researchers would also need to resolve practical and ethical issues surrounding the collection and storage of tissue from children, as well as the timing and safety of returning manipulated cells to the body.

For now, the study presents chlorogenic acid as a promising component of a future fertility-preservation protocol rather than a treatment for infertility. Its significance is that it targets a critical bottleneck: the loss of stem-cell quality during freezing and thawing, before transplantation even begins. If subsequent experiments confirm that the compound improves long-term sperm production, genetic integrity and reproductive function, it could help transform stored prepubertal testicular tissue from a biological archive into a more dependable source of future fertility. The researchers’ work underscores a broader lesson in regenerative medicine: protecting stem cells during the journey through extreme temperatures may be just as important as placing them in the right tissue once the journey is over.