First described by Hayflick and Moorhead in 1961, senescence refers to a state of irreversible cell cycle arrest accompanied by phenotypic changes induced by stressors such as telomere shortening, DNA damage, oncogenic signaling, or oxidative stress [68]. SnCs remain metabolically active and influence the surrounding microenvironment through the secretion of pro-inflammatory cytokines, chemokines, and proteases collectively known as the SASP [69]. At the molecular level, senescence is orchestrated by multiple drivers, with p53/p21 and p16/retinoblastoma (RB) tumor suppressor pathways playing key roles [26, 70].

Senescence plays a critical role in maintaining tissue integrity, as acute senescence facilitates tissue repair and tumor suppression by halting the proliferation of damaged cells and engaging immune surveillance. However, with aging, chronic accumulation of SnCs promotes inflammation, fibrosis, and functional decline [45, 71–73]. Secreted SASP factors can induce paracrine senescence in neighboring cells and impair immune clearance, exacerbating tissue damage and reducing regenerative capacity [74, 75]. According to the threshold model of senescence, once a critical SnC burden is exceeded, SASP propagation together with inadequate immune clearance, drives accelerated biological aging [41, 64]. In transplantation, a young donor with comorbidities, such as advanced fibrosis, metabolic dysfunction (e.g., < high BMI), alcohol use or disorder, or drug-related injury, may already exceed this threshold and display a more pronounced aging-like phenotype than an older but biologically healthier donor. Assessing senescence could therefore help identify the “biological tipping point” between viable and marginal organs, supporting more precise donor selection.

Current efforts aim to define precise senescence-associated markers that capture the cellular and molecular alterations most relevant for ex situ reconditioning and graft viability [76].

Canonical senescence biomarkers include cell-cycle inhibitors p16^INK4a and p21^CIP1, DNA damage markers (e.g., γH2AX and 53BP1 foci), and components of SASP (e.g., IL-6, IL-8, and MCP-1, among many others). Additional markers include senescence associated-β-galactosidase (SA-β-Gal) activity, telomere attrition, lipofuscin accumulation, increased anti-apoptotic BCL-2 expression and presence of DCR2 in cholangiocytes [45, 77–79].

Beyond individual markers, transcriptomic signatures are increasingly applied in experimental and translational transplant settings to capture senescence gene profile across tissues. Single cell sequencing and spatial transcriptomics enable high-resolution mapping of senescent and immune cell heterogeneity in aged or injured liver tissue [26, 33, 70, 78, 80–82]. Moreover, machine-learning-based analysis of histological sections enables automated senescence detection and may have utility in liver graft assessment [83–85] (Figure 1).

Currently no universal senescence marker exists for use in liver grafts and tissue-processing methods affect biomarker reliability [86, 87]. Biomarkers accessible via minimally invasive sampling would be ideal but must account for genetic and phenotypic heterogeneity.

Integrating multi-OMICs profiling and tissue architecture assessment into liver transplant could facilitate the identification of SnC populations amenable to interventions [79].

The rationale for eliminating SnCs to restore tissue homeostasis emerged from observations that caloric restriction reduces SnC burden and extend health- and lifespan in mice [45]. Furthermore, selective clearance of SnCs delayed age-associated dysfunction in mice [46, 47]. Several approaches have emerged to eliminate SnCs and modulate their effects which can be grouped into the following categories, with Tables 1, 2 summarizing the relevant agents for liver applications.

Senolytics selectively eliminate SnCs.

SnCs persist within the tissue by activating senescent cell anti-apoptotic pathways (SCAPs), including BCL-2 (BCL-2, BCL-xL, BCL-w), PI3K-AKT signaling, SRC kinase–dependent survival pathways, and cell-cycle checkpoint-associated programs such as CDKN1A-linked signaling [107]. Multi-OMIC analysis has revealed that distinct SCAPs are upregulated across different SnC populations, highlighting the heterogeneity of their survival mechanisms. Senolytics exploit these SCAPs to tip the balance from senescence to apoptosis. Targeting key SCAP nodes using small interfering RNAs induced selective apoptosis in 30%–70% of SnCs while largely sparing non-SnCs [88]. Other senolytics target SnCs through alternative mechanisms, including ferroptosis and metabolic stress responses [90].

Early senolytic discovery followed a hypothesis-driven approach, focusing on natural compounds and repurposed drugs with established safety profiles [41, 88]. More recently, high-throughput screening has expanded the senolytic landscape, enabling the identification of second-generation senolytics with improved selectivity and potency [41, 51, 108].

Senoblockers inhibit upstream senescent drivers, and, unlike senolytics, prevent the formation of new SnCs.

Senoblockers act by interfering with key signaling pathways that induce senescence. These include p53/p21 and p16/Rb axes via selective targeting Hsp72, Bruton’s tyrosine kinase, and the histone demethylase LSD1 among others [109].

Senomorphics (senostatics) do not eliminate SnCs but rather modulate their functional phenotype.

Senomorphics act primarily by suppressing the SASP pro-inflammatory signaling, targeting pathways such as NF-κB, JAK/STAT, mTORC1, p38, and MAPK signaling. Additional senomorphic strategies target mitochondrial complex-I or -IV, modulate NAD⁺/NADH metabolism, or inhibit HSP90 [107, 110]. By exploiting these pathways, senomorphics attenuate the secretion of deleterious cytokines, chemokines, and proteases. By preserving SnCs while limiting inflammatory signaling, senomorphics help to maintain tissue integrity, prevent tumors, reduce senescence footprint and induce regeneration [41].

Immune-mediated clearance of SnCs seeks to enhance the physiological removal of SnCs.

This group includes multiple approaches including immune checkpoint inhibitors, senescence-targeted chimeric antigen receptor (CAR) T cells, vaccines or antibody-drug conjugates, which aim to increase SnC immunosurveillance [111–113].

Certain compounds may exert senomorphic or senolytic effects depending on dose, treatment duration or cellular context. For example, the flavonoid procyanidin C1 is senomorphic at low concentrations and senolytic at higher doses [100]. The translation of these concepts into clinical practice remains in its early stages. To date, human senolytic trial data are limited and predominantly based on Phase I/II studies, demonstrating that intermittent regimens are feasible and well-tolerated. The most studied regimen is oral dasatinib + quercetin (D + Q) for 3 consecutive days repeated in 3-week cycles (D 100 mg/day; Q 1,000–1,250 mg/day), with non-serious adverse events [114, 115]. A landmark Phase II randomized controlled trial demonstrated that response to D + Q is influenced by baseline SnC burden, with significant benefits in individuals with high p16^INK4 expression [116]. In addition, fisetin has been evaluated at 20 mg/kg/day for 3 consecutive days on an intermittent schedule (NCT04313634).

In liver disease, only one Phase I/II trial of D + Q in metabolic-associated steatotic liver disease (MASLD) has been initiated (NCT05506488) with outstanding results. Looking ahead, the senotherapeutic landscape is expected to expand rapidly.

Senotherapeutics offer potential benefits yet entail risks, varying across the different categories:

Senolytics reduce inflammation, tissue dysfunction, and propagation of secondary senescence [41]. This mechanism offers a conceptual advantage over senomorphics, allowing for intermittent, “hit-and-run” administration rather than continuous exposure. However, SnCs can exert beneficial physiological roles (e.g., tumor suppression, promoting wound healing, tissue remodeling and fibrosis resolution) [117, 118]. During wound healing, SNCs can promote closure through PDGF-AA secretion, and senolytic treatment during this period could compromise surgical site healing and anastomotic integrity [119]. Similarly, senescence functions as a tumor suppressor mechanism and prolonged SnC ablation may impair immune surveillance [113, 117, 118]. In the liver, senescence in endothelial cells (LSECs) is protective and compensatory and helps to maintain clearance of toxins during aging [120]. SnC ablation can therefore disrupt tissue homeostasis [32, 121–123]. Many senolytics work within a narrow therapeutic window and are cytotoxic at higher doses [124]. Therapeutic responses may vary according to biological context, sex [121] and senescence heterogeneity [122].

Senomorphics, preserve tissue homeostasis by retaining SnCs while mitigating their harmful effects. However, targeting specific pathways is challenging in a dynamic context where SnCs adaptively alter their SASP in response to the environment. For example, broad suppression of inflammatory mediators may result in off-target effects, including unintended inhibition of cytokine production by non-SnCs, potentially impairing necessary responses [107, 110, 113].

Senoblockers do not eliminate SnCs but prevent new SnC forming, potentially blocking senescent dependent tumor-suppressive functions. Therefore, their efficacy and safety remain to be established [109].

Immune-mediated strategies aim to enhance physiological SnC clearance but face several limitations: immunosenescence and age-related immune dysfunction can reduce the efficiency of SnC recognition and elimination, while the SASP may suppress immune surveillance. CAR-T cell mediated approaches risk off-target immune activation and tissue toxicity [90, 111, 112].

Combination strategies offer promising means to enhance efficacy while limiting toxicity. Combined D + Q treatment targets multiple SCAPs and demonstrates superior efficacy compared with treatment using dasatinib or quercetin alone [88]. Galacto-conjugation and β-galactosidase–activated prodrug strategies have been developed to further improve selectivity [123, 124]. Current evidence relies heavily on rodent data and fails to capture human heterogeneity. Natural compounds such as quercetin and fisetin have variable bioavailability and systemic endpoints are difficult to establish given the wide nature of senescence. The ex vivo MP scenario allows a uniquely controlled environment where the graft is isolated and senescence can be measured from biopsies, perfusate, or bile. Drugs delivered directly into the perfusion circuit bypass systemic limitations, allow higher local dosing, and provide a controlled, time-limited treatment window.

Strategic considerations for assessing and targeting senescence in the donor pool are summarized in Information Box 1 (Figure 3).

High SnC burden in donors can increase organ immunogenicity, exacerbate alloimmune responses, and ultimately compromise graft function and survival. Importantly, the increased SnCs burden is not limited to the donor organ itself. Emerging data suggest that SnCs can exert systemic, non-cell autonomous effects, propagating the senescent blueprint from graft to recipient, thereby contributing to post-transplant dysfunction. This is exemplified by the transfer of SnCs into young mice, which induces secondary senescence and pathological traits in distant tissues [126–129]. Consistently, cardiac transplantation from aged C57BL/6 donors into young recipients increases SnC burden and SASP across multiple recipient tissues, accompanied by impaired physical performance, and reduced cognitive function within 30 days post-transplantation [31]. Aging also activates profibrotic pathways in the liver, inducing senescence LSECs and increasing SASP, which promotes leukocyte adhesion and chronic inflammation [130]. This highlights the context-dependent role of LSEC senescence: protective for toxin clearance but potentially harmful when excessive or chronic. In addition, hepatocellular senescence induces secondary senescence in other organs, exacerbating systemic inflammation and driving multi-organ dysfunction [131].

Potential approaches for senescence assessment and targeting during organ recovery are outlined in Information Box 2 (Figure 4).

Importantly, the senescence landscape at this stage is also shaped by the type of donation. Compared with donations after brain death (DBD), DCD are subjected to warm ischemia prior to cold ischemia, which experimental evidence suggests may increase senescence [29, 30].

Conceptually, several strategies could be integrated into organ recovery, including single or repeated in situ graft flushing, delivery of senotherapeutics via regional perfusion circuits, or targeted bench flushing prior to preservation. Pilot studies incorporating quercetin and sucrose [102] or ABT-737 [29] to preservation solutions during SCS and perfusion models showed decrease SnC burden and enhanced regenerative capacity. However, because organs are routinely flushed with preservation solutions and exposed to various medications during standard procurement, concerns remain regarding drug interactions and reduced efficacy under hypothermic, metabolically suppressed conditions.

Alternatively, in situ normothermic regional perfusion (NRP), which partially restores circulation and metabolism, could create an additional window for senescence assessment and targeted intervention [132].

Following procurement, the graft is fully isolated from both donor and recipient, allowing prolonged organ interventions under highly controlled conditions, offering a unique window for senescence evaluation, organ stratification and targeted therapies. Key opportunities for senescence evaluation and targeted intervention during organ preservation are presented in Information Box 3 (Figure 5).

SCS elicits distinct, cell-type specific responses within the liver: hepatocytes predominantly undergo apoptosis, while cholangiocytes enter senescence with prolonged cold ischemic times [29]. This has been shown to directly alter/disrupt biliary architecture and impair liver regeneration, potentially affecting post-transplant outcomes. Mechanistically, DCR2 has been shown to play a pivotal role in the development of cholangiocyte senescence [29]. Moreover, prolonged ischemia shortens primary cilia in cholangiocytes (organelles essential for bile flow sensing) and triggers senescence [30]. These findings position organ preservation not merely as a passive holding period, but as an active biological phase during which senescence is induced, amplified, and potentially therapeutically reversible.

At graft implantation, the preserved organ is revascularized and connected to the recipient’s circulation. Although the graft remains physically accessible, opportunities for interventions are limited: prior to implantation and reperfusion, the organ is ischemic and unlikely to metabolize drugs, and after reperfusion, there is a risk of systemic exposure to any agents administered at this stage. However, IRI is an inherent component of implantation and it has been associated with SnC accumulation and impaired tissue repair, effects that may be reversible with senotherapeutic treatment [28, 137, 138]. Consistently, treatment of rats with rapamycin immediately after kidney transplantation led to reduced senescence and SASP response [139]. Evolving perspectives on senescence assessment and therapeutic targeting at the time of transplantation are detailed in Information Box 4 (Figure 6).

This stage is crucial for monitoring rejection, optimizing immunosuppression and detecting complications [140]. It represents a phase in which graft-intrinsic biology intersects with recipient systemic factors and determines long-term outcomes. Practical considerations for evaluating and addressing senescence after transplantation are provided in Information Box 5 (Figure 7). SnCs contribute to sustained inflammatory and fibrogenic signaling in graft and recipient. Supporting evidence links senescent cholangiocytes to both acute cellular rejection and chronic rejection in liver transplant recipients and also implicates cholangiocyte senescence as a driver of EAD, long-term graft dysfunction and biliary complications [29, 59, 141–144].

Once maintenance immunosuppression is established, senolytic approaches may be less suitable, and senomorphic strategies may offer a safer alternative. Notably, commonly used immunosuppressive agents, including mTOR inhibitors, exhibit senomorphic properties, suggesting that partial senescence modulation may occur within existing regimes.

Drug-drug interactions remain a key concern [42]. For instance, dasatinib may enhance glucocorticoid-mediated T-cell suppression [145], potentially reducing the need for conventional immunosuppressant but also increasing the risk of over-immunosuppression. Panobinostat may potentiate calcineurin inhibitors (e.g., tacrolimus, cyclosporine) [146], and flavonoids such as quercetin and fisetin may synergize with mTOR-inhibitors (e.g., rapamycin) [147, 148]. While these interactions could theoretically reduce overall drug exposure, they also increase the risk of excessive immunosuppression, opportunistic infection, and malignancy. Conversely, some interactions may be advantageous. For instance, mTOR inhibitors, already used for immunosuppression, possess senomorphic properties, suggesting that partial senescence modulation may be achievable within existing therapeutic regimens without additional agents. Careful dose optimization, immune monitoring, and phase-specific application will be essential.