Losses of functional reserve across multiple physiological systems have been identified in frail patients, yet the exact aetiology of frailty remains unclear. Although strongly associated with chronological age, frailty often develops at a younger age in patients with organ failure. Frailty is prevalent in patients with kidney failure; however, individuals experience improvements in physical frailty measures following kidney transplantation. This makes younger patients with kidney failure a unique population for studying both the accelerated onset of frailty and its reversal. This research project aims to test the hypothesis that frailty secondary to organ failure and age-related frailty are associated with similar molecular and physiological measures.

This longitudinal study will recruit 150 patients in three groups. Group A (kidney transplant recipients aged ≥40 years; n=50) and Group B (patients aged ≥40 years active on the kidney transplant waitlist; n=50) will comprise younger adults with frailty from organ failure. Group C (adults aged ≥65 years (or ≥55 years for Aboriginal and Torres Strait Islander patients); n=50) will comprise older community dwellers. The primary outcome is the Frailty Index (FI). Secondary outcomes include the change in FI over time, and at baseline when considering various clinical metadata, immune parameters, kidney function and nutrition intake which will be measured at baseline and 12-month time points. Longitudinal changes in frailty will be analysed using linear mixed models with multiple testing corrections for false discovery rates.

Endocrine profiles and metabolomics, measures of immune function and microcirculatory dysfunction, will be measured by liquid chromatography-mass spectrometry and/or gas chromatography-mass spectrometry. The gut microbiome will be sequenced via shotgun metagenomics (Illumina NextSeq500, 150 bp paired-end, ³Gbp/sample). Circulating cell-free DNA/mitochondrial DNA will be quantified through droplet digital PCR. Microcirculation will be assessed via sublingual dark field videomicroscopy with glycocalyx markers measured by ELISA.

This study will be conducted with all stipulations of this protocol, and the conditions of the ethics committee approval. Ethical principles have their origin in the Declaration of Helsinki, all Australian and local regulations and in the spirit of the standard of Good Clinical Practice (as defined by the International Conference on Harmonisation). Organs/tissues will be sourced ethically and will not be sourced from executed prisoners or prisoners of conscience or other vulnerable groups.

Ethics approval was received by the Metro South Health Research Ethics Committee (HREC/2023/QMS/95392) and ratified by the University of Queensland.

Results will be disseminated through peer-reviewed publications, academic conferences, participant newsletters and health organisation collaboration.