Rapamycin and 8‑Oxoguanine: Effects on Oxidative DNA Damage
Background: 8‑OxoG as an Aging Biomarker
8‑Oxoguanine (8‑oxoG) – often measured as 8‑hydroxy‑2′‑deoxyguanosine (8‑OH-dG) – is a DNA lesion caused by reactive oxygen species (ROS). It is a well-established marker of oxidative DNA damage that accumulates with aging and in chronic stress conditions . Elevated 8‑oxoG can lead to GC→TA mutations if not repaired, linking oxidative stress to aging, cancer, and degenerative diseases . The body mitigates 8‑oxoG via base-excision repair, primarily through the 8‑oxoG DNA glycosylase enzyme OGG1 . Rapamycin (sirolimus) is an mTORC1 inhibitor with anti-aging properties – it extends lifespan in mice and modulates many age-related pathways (protein synthesis, autophagy, inflammation). A key question is whether rapamycin reduces oxidative guanine damage, thereby lowering 8‑oxoG levels, in the context of aging and oxidative stress.
Evidence from Animal Studies
Multiple animal studies have examined rapamycin’s effect on 8‑oxoG or related oxidative damage markers:
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Normal Aging Models: In a landmark lifespan study (JCI 2013), late-life rapamycin treatment extended mouse longevity but had limited effects on some aging phenotypes. Notably, rapamycin did not significantly reduce 8‑OH-dG levels in the DNA of old mouse livers, despite older mice showing higher 8‑OH-dG than young controls . Similarly, in diabetic rodent kidneys, mTOR inhibition failed to lower already-elevated urinary 8‑OH-dG (though it prevented further increases) . However, other studies report clearer benefits. For example, Martínez-Cisuelo et al. (2016) found that rapamycin reversed age-related oxidative damage in middle-aged mouse liver: it lowered mitochondrial ROS production and markers of oxidative stress (like lipofuscin accumulation and mtDNA damage) to more youthful levels . In aged rats, a short course of rapamycin (0.5 mg/kg for 28 days) significantly blunted “aging” oxidative stress in the brain, accompanying improved mitochondrial function . These findings suggest that while rapamycin’s impact on 8‑oxoG in normal aging can be modest or context-dependent, it tends to reduce the overall oxidative damage burden in tissues.
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Disease/Stress Models: Rapamycin’s protective effects on 8‑oxoG are more pronounced under high oxidative stress conditions. For instance, in a diabetic mouse model (streptozotocin-induced), chronic hyperglycemia caused aberrant increases in hippocampal 8‑OH-dG and lipid peroxidation (4-HNE), along with cognitive deficits . Rapamycin treatment prevented these increases, normalizing 8‑OH-dG levels and improving memory . Likewise, in a neurotoxic zinc exposure model (which induces Alzheimer-like tau pathology and oxidative damage), rapamycin dramatically attenuated the oxidative DNA damage. Zinc-injected rats showed significantly elevated 8‑OH-dG in hippocampal neurons, whereas those given rapamycin had far lower 8‑OH-dG signals (p=0.013) . Figure 1 illustrates this effect: zinc causes intense 8‑OH-dG staining in neurons, which is markedly reduced by rapamycin co-treatment. In this model, rapamycin lowered 8‑OH-dG (and 4-HNE) levels almost back to control levels .
Immunofluorescence of 8‑OH-dG (green) in a cell culture model and rat hippocampal slices . Zinc exposure (“Zn”) increases 8‑OH-dG levels (strong green nuclear/cytosolic staining) compared to controls, indicating DNA oxidation. Rapamycin co-treatment (“Zn+Rapa”) markedly reduces 8‑OH-dG signal intensity in both cultured neurons (A) and hippocampal CA1 neurons of rats (B). Bar graphs (right) show quantified 8‑OH-dG intensity fold-change: rapamycin lowers the zinc-induced 8‑OH-dG accumulation by ~60–75% in cells and ~30% in vivo .
Another striking example comes from an acute kidney injury model. Gentamicin antibiotic causes severe renal oxidative DNA damage, with 8‑OH-dG and γ-H2AX (DNA break marker) rising over 10 days . Rapamycin (0.3 mg/kg/day) strongly protected the kidneys: it activated autophagy and significantly reduced gentamicin-induced 8‑OH-dG accumulation in renal cells, concomitant with less tubular injury . Thus, under intense oxidative stress (diabetes, toxins), rapamycin reliably lowers 8‑oxoG and related damage, often translating to functional protection (improved cognition or organ function).
Table 1 summarizes key studies of rapamycin on 8‑oxoG/8‑OH-dG:
| Study (Year) |
Model (Species)
|
Rapamycin Regimen |
8‑OxoG Marker (Tissue) |
Outcome on 8‑OxoG/8‑OH-dG |
| Ehninger et al. 2013 |
Aged mice (26 mo) – normal aging |
Diet (≈14 ppm) in late life (8 wks) |
8‑OH-dG in liver DNA |
No significant change vs. age-matched controls (old mice had higher 8‑OH-dG than young; rapamycin did not lower it) . |
| Martínez-Cisuelo 2016 |
Middle-aged mice (16–20 mo) – aging |
Rapamycin (dose not given; short-term) |
“Oxidative stress” markers in liver (ROS, mtDNA damage, lipofuscin) |
Reversed age-related increases in mitochondrial ROS and oxidative damage; 8‑oxoG not explicitly stated, but oxidative DNA/RNA lesions in liver were reduced to youthful levels . |
| Singh et al. 2019 |
Old rats (24 mo) – aging brain |
0.5 mg/kg d i.p. for 28 days |
Oxidative stress markers in brain (MDA, etc.) |
Reduced aging-induced oxidative stress (~20–30% lower MDA, 4-HNE, etc.) and neuronal death; although 8‑OH-dG not directly measured, overall DNA/lipid oxidation was lowered . |
| Ding et al. 2021 |
Diabetic mice (STZ-induced) – AD model |
1 mg/kg d i.p. for 8 wks (est.) |
8‑OH-dG in hippocampus (IHC) |
Diabetes raised 8‑OH-dG and 4-HNE levels in brain; rapamycin normalized 8‑OH-dG (levels comparable to non-diabetic controls) and improved memory . |
| Lai et al. 2022 |
Zinc-induced tauopathy (rats) – neurotoxicity |
20 ng/ml in vitro; 1 mg/kg d (i.c.v.) for 1 wk in vivo
|
8‑OH-dG in neurons (cells & brain slices) |
Zn caused ~2–8× increase in 8‑OH-dG intensity; rapamycin cut 8‑OH-dG levels by ~50–75% in cells, ~30% in rat hippocampus (p<0.05) . |
| Cui et al. 2015 |
Gentamicin toxicity (mini-pigs) – acute kidney injury |
0.3 mg/kg d p.o. for 10 days |
8‑OH-dG in kidney (IHC) |
Gentamicin increased renal 8‑OH-dG (and γ-H2AX) dramatically; rapamycin prevented 8‑OH-dG accumulation, correlating with preserved kidney function . |
(Abbreviations: STZ = streptozotocin; IHC = immunohistochemistry; i.p. = intraperitoneal; i.c.v. = intracerebroventricular; MDA = malondialdehyde.)
Mechanisms: How Rapamycin Lowers Oxidative Guanine Damage
Rapamycin likely reduces 8‑oxoG through multiple, complementary mechanisms:
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mTORC1 Inhibition and Mitochondrial ROS: By inhibiting mTORC1, rapamycin reprograms metabolism in ways that diminish ROS production. Treated mice show lower mitochondrial ROS generation (especially at electron transport chain complex I) . For example, rapamycin reversed the age-related rise in mitochondrial H_2O_2 output in mouse livers . Less ROS means fewer 8‑oxoG lesions formed in DNA. Rapamycin also improves mitochondrial quality control via mitophagy activation . Dysfunctional, ROS-leaking mitochondria are cleared more efficiently, as seen in models of heteroplasmic mutant mtDNA where rapamycin-driven mitophagy selectively removed damaged mitochondria . This mitochondrial renewal lowers the chronic oxidative stress that causes 8‑oxoG accumulation.
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Enhanced DNA Repair (OGG1): There is evidence that rapamycin boosts the capacity to repair oxidized guanine. Rapamycin can activate the energy-sensing kinase AMPK, which in turn upregulates OGG1 expression . In cancer cell studies, mTOR inhibition by rapamycin increased OGG1 levels and other base-excision repair activities, presumably via AMPK and downstream factors . An Oncotarget editorial noted this “upregulation of the DNA repair enzyme OGG1 by rapamycin” as a novel mechanism to reduce tumorigenesis . In diabetic kidney cells, activating AMPK (with AICAR) similarly raised OGG1 and lowered 8‑oxoG burden , supporting the idea that rapamycin (which shares some AMPK activation effects) can bolster the repair of 8‑oxoG lesions.
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Induction of Autophagy: Rapamycin is a potent autophagy inducer. Macroautophagy can degrade oxidatively damaged macromolecules and organelles, indirectly reducing DNA oxidation. Notably, stimulation of autophagy in aged cells has been shown to “rescue older cells from 8‑OHdG mtDNA accumulation” . By clearing damaged mitochondria (mitophagy) and protein aggregates, rapamycin curtails sources of intracellular ROS and may even remove cytosolic oxidized DNA fragments . In the gentamicin AKI model, rapamycin’s renal protection was autophagy-dependent – blockade of autophagy negated its reduction of oxidative damage . Thus autophagic “cleanup” is a key mechanism for rapamycin’s reduction of oxidative stress.
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Activation of Antioxidant Responses: Rapamycin can activate stress-response pathways like Nrf2 (Nuclear factor erythroid 2–related factor 2). Nrf2 is a transcription factor that upregulates antioxidant and Phase II detoxifying enzymes (including HO-1, glutathione synthesis enzymes, etc.). In aging and Alzheimer’s models, Nrf2 activity is often blunted . Rapamycin has been shown to restore Nrf2–HO-1 pathway activity, thereby increasing cellular antioxidant capacity . In the zinc-induced neurotoxic model, rapamycin reversed the zinc-mediated suppression of Nrf2/HO-1, aligning with reduced ROS and 8‑OH-dG levels . This suggests rapamycin helps cells neutralize ROS more effectively, preventing the formation of 8‑oxoG. Additionally, rapamycin’s inhibition of mTORC1 may reduce the pro-oxidant “anabolic drive” – e.g. lowering translation of inflammation-related proteins. Studies indicate rapamycin suppresses the pro-inflammatory SASP (senescence-associated secretory phenotype) of senescent cells , which could otherwise sustain chronic oxidative stress via cytokines and NOX (NADPH oxidase) activation. By tamping down inflammation, rapamycin creates a cellular environment less conducive to oxidative DNA damage.
Relevance to Healthy Aging vs. Disease States
The significance of rapamycin’s 8‑oxoG-lowering effect may differ between healthy aging and overt disease conditions:
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In Healthy Aging: Aging is associated with a gradual increase in oxidative DNA lesions (8‑oxoG accumulates in tissues over time ). Rapamycin’s modest reduction of oxidative damage could contribute to its geroprotective effects, but this might not manifest as large immediate drops in 8‑oxoG in a healthy organism. For example, in lifespan studies of otherwise-healthy mice, rapamycin did not dramatically alter steady-state 8‑OH-dG in DNA . This could be because baseline oxidative stress in lab rodents is relatively low, or because rapamycin’s benefits accrue via long-term prevention of damage (which short-term measurements might miss). Importantly, rapamycin did reduce cancer incidence in old mice , and since 8‑oxoG is mutagenic, even subtle reductions in DNA oxidation over time might lower mutation rates and cancer risk. For healthy aging, rapamycin’s influence on 8‑oxoG might thus be preventive – slowing the accumulation of oxidative DNA damage rather than reversing it overnight. This aligns with rapamycin’s known ability to extend lifespan and healthspan, presumably by curbing age-related molecular damage.
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In Disease and High-Stress Conditions: In contrast, when oxidative stress is highly elevated (as in diabetes, neurodegeneration, or toxic exposures), rapamycin’s impact on 8‑oxoG is robust and therapeutically relevant. The diabetic brain and AKI examples show that rapamycin can sharply reduce pathological 8‑oxoG elevations, translating to functional improvements (preserved cognition, nephroprotection) . This makes rapamycin an attractive candidate not just for anti-aging, but for diseases where oxidative DNA damage is part of the pathology (e.g. Alzheimer’s, Parkinson’s, diabetic complications). By lowering 8‑oxoG and related damage, rapamycin may help break cycles of oxidative injury and inflammation in tissues. However, it’s worth noting that in certain contexts rapamycin might not lower oxidative markers – for instance, one study found no drop in urinary 8‑OH-dG with mTOR inhibition in diabetic rats . The outcome may depend on dosing, timing, and whether rapamycin’s benefits (autophagy, Nrf2, etc.) fully engage in that model. Overall, rapamycin appears to tilt the balance toward damage control in stress conditions: it activates repair/cleanup pathways faster than damage is produced, thereby net reducing oxidative lesions like 8‑oxoG.
Conclusion
In summary, rapamycin shows a clear ability to reduce 8‑oxoguanine levels and oxidative DNA damage in many experimental settings, especially those involving elevated oxidative stress. Animal studies demonstrate that rapamycin can lower 8‑OH-dG in tissues (brain, liver, kidney) by anywhere from ~20% up to 70+% depending on the model, with notable improvements in functional health . Mechanistically, rapamycin’s inhibition of mTORC1 engages multiple protective pathways – fewer ROS from mitochondria, more antioxidant and repair activity (OGG1, Nrf2), and increased autophagy – all of which contribute to less oxidative guanine damage. For healthy organisms, this could mean a slower accumulation of DNA lesions over time, contributing to healthier aging and reduced disease incidence. In disease states, rapamycin’s oxidative stress reduction can mitigate tissue damage and improve outcomes (as seen in neurodegeneration and nephrotoxicity models). While human data are still limited (no clinical trial yet has reported 8‑oxoG levels with rapamycin), the converging evidence from recent decades strongly suggests that rapamycin alleviates oxidative DNA damage. This positions rapamycin as not only a geroprotective drug but also a potential therapeutic adjunct in conditions where 8‑oxoG-driven damage is a concern. Future studies – including in humans – will clarify the extent to which rapamycin can clean up the “rust” of aging (oxidative lesions) and how that translates to long-term health benefits.
Sources: Recent peer-reviewed studies and reviews (2013–2022) were prioritized, including animal experiments and mechanistic analyses . The table and discussion integrate data on rapamycin doses, duration, and outcomes on 8‑oxoG/8‑OH-dG from key publications as cited above. These sources collectively underpin the conclusion that rapamycin can indeed help reduce 8‑oxoguanine levels through multi-faceted actions on oxidative stress and cellular repair mechanisms, with relevance for both aging and disease contexts.
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there’s some preliminary evidence PQQ can reduce it [one study]
