Are inflammatory markers associated with sarcopenia-related traits in older adults with sarcopenia? - A cross-sectional analysis of the ENHANce study

Mapping the causal associations of cytokines with sarcopenia and aging traits: Evidence from bidirectional Mendelian randomization

BACKGROUND

Cytokines and growth factors may serve as a bridge in studying the causal relationships between inflammaging and sarcopenia due to their roles in inflammaging. In this study, we aim to explore the causal association of cytokines with sarcopenia and aging traits and further identify the significant inflammation factors.

METHODS

Bidirectional Mendelian randomization (MR) analysis was used to identify the causality. Forty-one kinds of circulation cytokines and growth factors were set as exposures, and the data were from a summary genome-wide association study (GWAS) containing three cohorts with 8293 healthy participants of European ancestry from 1983 to 2011. Hand grip strength, adjusted appendicular lean mass (AALM), usual walking pace, moderate-to-vigorous physical activity (MVPA) levels, able to walk or cycle unaided for 10 min (AWCU10) and telomere length were selected as outcomes. Data for outcomes were obtained from meta-GWAS and the UK Biobank, and sample sizes ranged from 69 537 to 472 174. Low hand grip strength was defined by the European Working Group on Sarcopenia in Older People (EWGSOP) and Foundation for the National Institutes of Health (FNIH) cut-off points, respectively. Other outcome traits were defined and measured according to the UK Biobank and raw cohorts' criteria. We set two significance thresholds for single nucleotide polymorphisms (SNPs) associated with exposures to obtain adequate SNPs (5 × 10-6 and 5 × 10-8). Inverse-variance weighted, MR-Egger and weighted median were employed to estimate the causality.

RESULTS

Twenty-seven factors were identified to relate to sarcopenia and aging traits causally, and most were associated with only one outcome trait. IL16 (interleukin-16), CTACK (cutaneous T-cell attracting chemokine), MIP1b (macrophage inflammatory protein 1b) and PDGFbb (platelet-derived growth factor BB) were proven to relate causally to at least one sarcopenia and aging trait in both analyses with two significance thresholds. IL16 was causally associated with hand grip strength (0.977 [0.956-0.998] for EWGSOP and 0.933 [0.874-0.996] for FNIH), AALM (0.991 [0.984, 0.998]), MVPA (0.997 [0.995-1.000]) and AWCU10 (1.008 [1.003-1.013]). CTACK was proven to relate causally to hand grip strength (1.013 [1.007-1.019] for EWGSOP and 1.090 [1.041-1.142] for FNIH), AWCU10 (0.990 [0.986-0.994]) and telomere length (0.998 [0.983-0.994]). The results indicated that MIP1b has a causal effect on hand grip strength (1.032 [1.001-1.063] for EWGSOP), AWCU10 (0.994 [0.988-1.000] and 0.993 [0.988-0.998]) and telomere length (1.006 [1.000-1.012]). PDGFbb may causally relate to AALM (1.016 [1.001-1.030]) and telomere length (1.011 [1.007-1.015]). Reserve MR analyses also proved their unidirectional causal effects.

CONCLUSIONS

Twenty-seven factors were causally related to sarcopenia and aging traits, and the causal effects of IL16, CTACK, MIP1b and PDGFbb were proven in both analyses with two significance thresholds.

Inflammation Is a Histological Characteristic of Skeletal Muscle in Chronic Limb Threatening Ischemia

BACKGROUND

The loss of skeletal muscle is a prognostic factor in several diseases including in patients with chronic limb threatening ischemia (CLTI). Patients with CLTI also have a lower skeletal mass and area when compared to those with claudication. However, there are no currently available data regarding the histological characteristics of core muscles in patients with CLTI. This study aims to determine the differences in core skeletal muscles between patients with claudication and those with CLTI. The second aim is to evaluate the differences in myokines, which are molecules secreted by skeletal muscle, between patients with claudication and those with CLTI.

METHODS

An observational, prospective study was conducted from January 2018 to July 2022 involving consecutive patients with peripheral arterial disease (PAD). The clinical characteristics were registered. In PAD patients with surgical indication for common femoral artery approach, samples of sartorius skeletal muscle (and not from the limb muscles directly involved in the ischemic process) were collected. The samples were submitted to histological characterization on hematoxylin-eosin and to immunohistochemical analysis to detect CD45+ leukocytes and CD163+ macrophages. The extent of the inflammatory cells (leukocytes and macrophages) was semiquantitatively assessed using a 0-to-4 grade scale as follows: absent (0†), mild (†), moderate (††), severe (†††), and very severe (††††). Serum levels of myokines: irisin, myostatin, IL-8, and lL-6 were determined with multiplex bead-based immunoassay.

RESULTS

119 patients (mean age: 67.58 ± 9.60 years old, 79.80% males) 64 with claudication and 54 with CLTI were enrolled in the study. No differences were registered between patients with claudication and those with CLTI on age, gender, cardiovascular risk factors, and medication, except on smoking habits. There was a significantly higher prevalence of smokers and a higher smoking load in the claudication group. Samples of sartorius skeletal muscle from 40 patients (14 with claudication and 26 with CLTI) were submitted to histological analysis. No differences were found in skeletal muscle fibers preservation, trauma, or hemorrhage (on hematoxylin-eosin staining). However, in the immunohistochemistry study, we found more inflammatory cells CD45+ leukocytes in patients with CLTI when compared to those with claudication [CD45+ ≥ moderate (††): claudication (n = 14): 4; 28.57%; CLTI (n = 25): 16; 64.00%; P = 0.034]. Patients with CLTI also had higher tissue levels of CD163+ macrophages, but this difference was not significant [CD163+ ≥ moderate (††): claudication (n = 13): 7; 53.85%; CLTI (n = 27): 21; 77.78%; P = 0.122]. The serum levels of the myokines, irisin, and myostatin were below the lower limit of detection, in the majority of patients, so no valid results were obtained. However, patients with CLTI had a higher serum level of Interleukin (IL)-6 and IL-8.

CONCLUSIONS

CLTI patients exhibit increased quantities of leukocytes in their sartorius muscle, as well as elevated serum levels of myokines IL-8 and IL-6. Inflamed skeletal muscle can contribute to the loss of muscle mass and account for the lower density of skeletal muscle observed in CLTI. Additionally, inflamed skeletal muscle may contribute to the development of systemic inflammation through the secretion of pro-inflammatory cytokines into the systemic circulation. Halting the inflammatory process could eventually improve the prognosis of CLTI patients.

Inflammatory Biomarkers and Gait Impairment in Older Adults: A Systematic Review

Peripheral inflammation and gait speed alterations are common in several neurological disorders and in the aging process, but the association between the two is not well established. The aim of this systematic literary review is to determine whether proinflammatory markers are a positive predictor for gait impairments and their complications, such as falls in older adults, and may represent a risk factor for slow gait speed and its complications. The systematic review was performed in line with the Preferred Report Items for Systematic Review and Meta-Analyses (PRISMA). A protocol for literature searches was structured a priori and designed according to the International Perspective Register of Systemic Review (PROSPERO: CRD42023451108). Peer-reviewed original articles were identified by searching seven electronic databases: Excerpta Medica Database (EMBASE), SciVerse (ScienceDirect), Scopus, PubMed, Medline, Web of Science, and the Cochrane Library. The search strategy was formulated based on a combination of controlled descriptors and/or keywords related to the topic and a manual search was conducted of the reference lists from the initially selected studies to identify other eligible studies. The studies were thoroughly screened using the following inclusion criteria: older adults, spatiotemporal gait characteristics, and proinflammatory markers. A meta-analysis was not performed due to the heterogeneity of the studies, and the results were narratively synthesized. Due to the clinical and methodological heterogeneity, the studies were combined in a narrative synthesis, grouped by the type of biomarkers evaluated. A standardized data extraction form was used to collect the following methodological outcome variables from each of the included studies: author, year, population, age, sample size, spatiotemporal gait parameters such as gait velocity, and proinflammatory markers such as TNF-α, high sensitivity C-reactive (CRP) proteins, and IL-6. We included 21 out of 51 studies in our review, which examined the association between inflammatory biomarkers and gait impairment. This review highlights the role of TNF-α, CRP, and IL-6 in gait impairment. Biomarkers play an important role in the decision-making process, and IL-6 can be an effective biomarker in establishing the diagnosis of slow gait speed. Further longitudinal research is needed to establish the use of molecular biomarkers in monitoring gait impairment.

Inflammatory markers and physical frailty: towards clinical application

Global population aging poses a tremendous burden on the health care system worldwide. Frailty is associated with decreased physical reserve and is considered an important indicator of adverse events in the older population. Therefore, there is growing interest in the early diagnosis and intervention of frailty, but the cellular mechanisms responsible for frailty are still not completely understood. Chronic inflammation is related to decreased physical function and increased disease risk. Additionally, multiple human and animal studies suggest that inflammation probably plays the largest role in contributing to frailty. Some inflammatory markers have been proposed to predict physical frailty. However, there are still large gaps in knowledge related to the clinical application of these markers in frail patients. Therefore, understanding the biological processes and identifying recognized and reliable markers are urgent and pivotal tasks for geriatricians. In the present review, we broadly summarize the inflammatory markers that may have potential diagnostic and therapeutic use, thereby translating them into health care for older people with frailty in the near future.

Enhanced serum levels of tumor necrosis factor-α, interleukin-1β, and -6 in sarcopenia: alleviation through exercise and nutrition intervention

BACKGROUND

Limited research has been conducted on the post-intervention inflammatory status in sarcopenic patients, despite previous studies revealing elevated pro-inflammatory markers. This study aimed to investigate the potential elevation of specific pro-inflammatory cytokines in sarcopenic patients and evaluate the effects of exercise and nutritional support interventions on these cytokine levels.

METHODS

In this post-hoc analysis of a randomized controlled trial (RCT), 57 individuals with sarcopenia from the RCT and 57 non-sarcopenic participants from the same geriatric community cohort that did not participate in the RCT were enrolled. Grip strength and body composition measurements were recorded. Tumor necrotizing factor (TNF)-α, interleukin (IL)-1β, IL-6, and IL-15 levels were assessed at baseline for both groups and after a 12-week intervention consisting of resistive exercise and supplementation with branched-chain amino acids, calcium, and vitamin D3 in the patients with sarcopenia.

RESULTS

The sarcopenic group demonstrated significantly lower body weight, body mass index, grip strength, and skeletal muscle mass index. Moreover, sarcopenic patients exhibited higher levels of TNF-α (p=0.007), IL-1β (p<0.001), and IL-6 (p<0.001), while no significant difference was observed in IL-15 (p=0.345) between participants with and those without sarcopenia. Following the intervention, the sarcopenic group experienced significant improvements in grip strength and skeletal muscle mass index with a notable reduction in TNF-α (p=0.003), IL-1β (p=0.012) and IL-6 (p=0.001) levels.

CONCLUSIONS

Sarcopenic patients exhibit elevated levels of TNF-α, IL-1β, and IL-6, which declined after nutrition support and exercise interventions. However, further research is necessary to evaluate the long-term impact of these interventions on cytokine levels.