Plant compounds may protect aging muscle by fixing mitochondrial cleanup and curbing protein breakdown

Sarcopenia affects roughly 10-16% of older adults worldwide and independently raises frailty and all-cause mortality risk. This narrative review by Zeng and Wang argues that muscle loss is not one problem but a tangled network. Failing mitochondrial cleanup, runaway protein breakdown, and cell death feed one another. The authors ask whether plant compounds such as urolithins, resveratrol, quercetin, and curcumin can act on several nodes of that network at once, and whether nanotechnology can overcome their poor absorption.

The authors searched PubMed, Web of Science, Embase, and Scopus from January 2000 through February 2026, with emphasis on 2020-2025. They included mechanistic muscle studies, rodent sarcopenia models with quantitative data, nanoformulations reporting physical characteristics such as particle size and encapsulation efficiency, and human randomized trials. They excluded preprints, conference abstracts, crude botanical extracts without quantified constituents, and non-English papers. No formal quality scoring or meta-analysis is described, so this is a narrative synthesis rather than a pooled estimate.

The central idea is that ubiquitination is a double-edged process. In healthy muscle, PINK1 accumulates on depolarized mitochondria and phosphorylates ubiquitin and Parkin. Parkin then tags outer-membrane proteins such as VDAC1 and MFN1/2 with K63/K48 chains, recruiting receptors (OPTN, NDP52) and TBK1 to clear the damaged organelle. In sarcopenia this flux is suppressed. Meanwhile the E3 ligases MuRF-1 and Atrogin-1, driven by FoxO1/FoxO3a when PI3K/Akt/mTOR signaling falls, tag myosin heavy chain and troponin for destruction. A good therapy must boost the first process while restraining the second.

These pathways connect to cell death and inflammation. When mitophagy fails, mitochondrial outer-membrane permeabilization releases cytochrome c and triggers apoptosis. Sub-lethal caspase-3 activity can also cleave actin into fragments that the proteasome degrades faster. Inflammaging cytokines (TNF-α, IL-6, IL-1β) sustain NF-κB signaling, reinforcing both oxidative stress and proteolysis. The authors also describe pyroptosis (NLRP3), ferroptosis (GPX4), and ER-mitochondria contact defects. Organ crosstalk adds more drivers, including liver-derived FGF21 and hyperammonemia in cirrhosis, DKK3 in COPD, and copper-exacerbated oxidative damage in SOD1(G93A) mice.

The phytochemical evidence is largely preclinical. Urolithin A restored PINK1, Parkin, and LAMP1 expression in SOD1(G93A) mice and improved gastrocnemius atrophy and motor function. Urolithin B activated mTORC1 through the androgen receptor and suppressed proteasomal activity in C2C12 myotubes. Resveratrol enhanced PINK1/Parkin flux and eased mitochondrial fusion-fission abnormalities in diabetic mice. Quercetin blocks FoxO3a nuclear translocation, lowering MuRF-1 and Atrogin-1, and curcumin antagonizes NF-κB. The authors also cite a human study suggesting urolithin A improves muscle mitochondrial metabolism, and cohort data linking higher flavonoid intake to less frailty.

The main hurdles are translational. Oral bioavailability is often below 1%, many benefits depend on individual gut microbiota converting precursors into active metabolites, and no phase III trials exist. The authors propose nanodelivery systems and gut-muscle axis strategies as solutions. The supplied text cuts off before the detailed nanodelivery section, and most mechanistic claims rest on cell and rodent models, so the human benefit of these compounds remains unproven.