Mechanistic Approach to Preventing Atrophy and Restoring Function in Older Adults

Overview

As a function of the growing population of older adults, an estimated 3.48 million total knee arthroplasty (TKA) procedures will be performed annually in the U.S. by 2030. Despite the near-universal success of this surgery in mitigating chronic knee pain, TKA is not successful in restoring long-term physical function in older adults, primarily because of quadriceps muscle atrophy, which explains 77% of the strength deficits. Overall, strength and functional mobility in TKA patients is 30-50% below age-matched healthy controls. Functional tasks such as stair-climbing remain a clinical problem for 75% of patients following TKA. Muscle atrophy occurs in both operative and non-operative legs, and is essentially permanent for older patients because of their impaired ability to increase muscle mass. The purpose of this clinical research is to determine the effects of essential amino acid (EAA) supplementation on muscle mass, strength, and functional mobility following TKA in older adults. Based on strong preliminary data, the investigators hypothesize that twice-daily ingestion of 23 g of EAA for 1 wk before through 6 wk after TKA will increase basal rates of muscle protein synthesis via inactivation of catabolic signaling, and up-regulation of anabolic and cyto-protective proteins. The investigators further hypothesize that short-term atrophy prevention and accelerated return of functional mobility will lead to longer-term structural and functional adaptations, and improved quality of life in older TKA patients vs. Placebo. Identifying the mechanisms up-regulated by EAA treatment that preserve muscle volume and mobility will have a major impact on rehabilitation science. This study will accomplish two specific aims: (1) determine if EAA elevates basal rates of muscle protein synthesis by up-regulating anabolic pathways and cyto-protective proteins, and inactivating catabolic pathways in the short term vs. Placebo and (2) determine if short-term prevention of atrophy, weakness, and functional mobility leads to positive changes in muscle cell structure and function, and improved quality of life in the longer term vs. Placebo. This work is significant because it advances knowledge of the molecular and cellular changes occurring during muscle atrophy (Placebo) and atrophy prevention (EAA) in a clinical setting using a treatment that is broadly applicable, is well tolerated, and can be implemented immediately.

The investigative team has completed recent studies showing that essential amino acid (EAA) supplementation attenuates quadriceps atrophy and accelerates the return of functional mobility following TKA. For patients on EAA, quadriceps atrophy was only -6% and -3% in the operative and non-operative quadriceps, respectively, 6 wks after TKA, but -18% and -10%, respectively, in patients on Placebo, a threefold difference. Of clinical relevance, the patients on EAA were able to maintain strength and demonstrated an accelerated return of functional mobility vs. Placebo 6 wks post-TKA. Positive changes at the cellular level are likely responsible for the reduction in muscle loss and preservation of strength, and to explain the acceleration of the return of functional mobility. As such, we hypothesize that twice-daily ingestion of 23 g of EAA from 1 wk before to 6 wks after TKA will increase basal rates of muscle protein synthesis via inactivation of catabolic signaling (FoxO3a), and up-regulation of anabolic and cyto-protective proteins. We also propose that short-term atrophy prevention and accelerated return of functional mobility will translate into long-term (6 mo and 1 yr post-TKA) structural and functional adaptations, leading to improved quality of life in TKA patients with EAA supplementation vs. Placebo. The study will use a two-arm parallel design to determine the effect of EAA supplementation on post-TKA muscle cell structure and function, and quality of life in the shorter term (6 months post-TKA) and long term (1 yr post-TKA) vs. Placebo. Subjects will be 80 older male and female adults having primary TKA at the Slocum Center for Orthopedics and Sports Medicine, Eugene, Oregon. Slocum study staff will pre-screen/identify potential subjects for recruitment based on inclusion/exclusion criteria. Eligible patients will be invited to join the study. After the completion of informed consent procedures, participants will be assigned a unique patient identification number, and randomly assigned to either EAA or Placebo on a 1:1 allocation ratio, with blinding of treatment condition to subject and research staff/statisticians collecting data. Twice-daily ingestion of 23 g of supplement will begin 7 days prior to TKA and end at 6 wks post. EAA subjects will receive EAA and Placebo subjects will receive the non-essential amino acid Alinine. Subjects will document compliance with the supplement protocol in a log book and will return empty vials. Subjects will be followed for 1 yr. Key research questions are: (a) Does EAA prevent shorter-term (6 wks post-TKA) bilateral muscle atrophy, preserve quadriceps strength, and accelerate the return of functional mobility vs. Placebo? (b) Are there shorter-term sex differences on outcome measures? (c) Will EAA increase longer-term (6 mo post-TKA) quadriceps strength and functional mobility vs. Placebo? (d) Does EAA improve long-term (1 yr post-TKA) functional mobility and measures of quality of life vs. Placebo? (e) Are there long-term sex differences in functional mobility or measures of quality of life? Assessment points will be at 6 wks, 4 wks, and 1 wk prior to surgery, and 1 wk, 2 wks, 6 wks, 6 mos, and 1 yr post-TKA. At different assessment points, we will collect demographic, medical (e.g., length of hospital stay, tourniquet use), physiological (e.g., muscle biopsy, MRI, DEXA, strength; blood tests), pharmacologic, functional mobility, physical activity (accelerometer), psychometric (e.g., quality of life; Veterans RAND 12-item Health Survey \[VR-12\]), food intake (3-day diary), physical therapy, and perceived pain data. The following schedule of assessments will be followed: no more than 6 mo pre-TKA (enrollment and screening), 6 wks pre-TKA (screening, surveys, DEXA scan, MRI test, physical activity and food recording), 4 weeks pre-TKA (blood draw, strength and functional mobility testing, muscle and fat biopsy); 1 wk pre-TKA and in hospital (physical activity and food recording); 1 wk post-TKA (physical activity and food recording); 2 wks post-TKA (blood draw, physical activity and food recording); 6 wks post-TKA (blood draw, MRI test, strength and functional mobility testing, physical activity and food recording, muscle and fat biopsy); 3 mos post-TKA (surveys, strength and functional mobility testing, physical activity and food recording); 6 mos post-TKA (surveys, DEXA scan, MRI test, strength and functional mobility testing, physical activity and food recording, muscle and fat biopsy), and 1 yr (surveys, DEXA scan, MRI test, strength and functional mobility testing, physical activity and food recording, muscle and fat biopsy). Data will be collected from a variety of sources, including surveys, electronic medical records, medical and functional tests, and staff reports. Data will be entered and double-verified in password-protected spreadsheets sand databases stored behind a firewall. Any electronic medical records data captured will use secure data transfer and HIPAA-compliant protocols approved by the University of Oregon IRB. Staff reports will be forwarded directly to project data managers. All personal data will be identified by numbers rather than names. Interim reports of project results will be made to the Data and Safety Monitoring Board. Power analyses indicated that a sample size of 80 subjects would be sufficient to detect anticipated effects on primary outcomes: operative leg quadriceps volume (MRI), non-operative leg quadriceps volume (MRI), isometric strength, Get Up And Go test, stair climb up test, stair climb down test, and six-minute walk test. The mean effect size across these outcomes, based on baseline- to 6-week percent change in pilot data) was d = 1.01, reflecting large effects. For a sample size of 30/group, this study can detect ESs of d \> .79 with 85% power, and the minimally detectable ES drops to 0.68 or 0.52 with pretest covariates of r = .50 or .75. Every effort will be made to reduce attrition and obtain data on all participants at all assessment points. However, attrition is expected. Because this study will have power to detect anticipated physiological and functional effects with 30 subjects per condition, we will enroll 80 total subjects (40/condition) to account for possible attrition. The EAA intervention is designed to attenuate muscle loss, improve functional outcomes, and enhance quality of life. Data analyses will focus on shorter-term, longer-term results, and change over time. Preliminary analyses will employ descriptive statistics to understand the nature of the data and ensure that data distributions are appropriate for the statistical tests employed. Chi-square tests and analyses of variance, as appropriate, will be conducted to evaluate the equivalence of continuing participants vs. dropouts on demographic, medical history, and recent levels of dependent variables. We will conduct random coefficients analysis (RCA) to model muscle and functional mobility across time, as well as covariates that could affect outcomes, such as age, sex, physical activity, and dietary intake. RCA models trajectories from assessments nested within subjects; test of condition are represented by the interaction between a time factor and treatment condition. The RCA avoids the many pitfalls associated with traditional repeated measures ANOVA: It adjusts for within-individual dependence or autocorrelation in the data, can model nonlinear growth, does not require fixed spacing among assessments, and accommodates missing values over time. By using any available data across time, the RCA will limit the effects of missing data, reducing bias and increasing power. Based on our preliminary data, we estimate that we will be able to collect \>92% of all data points. Expected study outcomes are as follows: 1. With successful completion of this research, we expect to demonstrate that EAA prevents muscle atrophy bilaterally, as our preliminary data suggest. To date, it is not known if EAA can prevent atrophy. 2. We expect to show that atrophy prevention will lead to strength gains and accelerated return of functional mobility. We further expect to show that EAA may have positive effects on central activation deficits, as our preliminary data suggest that strength is increased by 6 wks with EAA. To date, it is not known if preserving muscle following TKA will increase strength and augment the return of functional mobility. 3. We expect to document that EAA will increase muscle cell size (CSA) bilaterally, in the vastus lateralis of the operative and non-operative quadriceps. It is not known if atrophy prevention and early return of functional mobility will stimulate positive gains in muscle cell structure. 4. We expect to demonstrate that EAA increases mitochondrial mass bilaterally and increases mitochondrial respiration at rest. By sampling from the non-operative (control leg) and operative leg, we expect to show that EAA normalizes mitochondrial function over time (6 mo and/or 1 yr post-TKA). It is not known if early gains in functional mobility will positively impact muscle cell function. 5. We expect to show that quality of life (as measured by instruments such as VR-12) will be significantly increased with EAA. It is not known to what extent the above positive gains will have on longer-term (6 mo and 1 yr) quality of life. We expect each of the above to stimulate and be transformative. EAA supplements are inexpensive ($800/patient or $16/day), are well tolerated, and can be implemented immediately.