Potential Cellular and Biochemical Mechanisms of Exercise and Physical Activity on the Ageing Process

Inflammatory pathway communication with skeletal muscle-Does aging play a role? A topical review of the current evidence

Skeletal muscle plays an integral role in locomotion, but also as part of the integrative physiological system. Recent progress has identified crosstalk between skeletal muscle and various physiological systems, including the immune system. Both the musculoskeletal and immune systems are impacted by aging. Increased age is associated with decreased muscle mass and function, while the immune system undergoes "inflammaging" and immunosenescence. Exercise is identified as a preventative medicine that can mitigate loss of function for both systems. This review summarizes: (1) the inflammatory pathways active in skeletal muscle; and (2) the inflammatory and skeletal muscle response to unaccustomed exercise in younger and older adults. Compared to younger adults, it appears older individuals have a muted pro-inflammatory response and elevated anti-inflammatory response to exercise. This important difference could contribute to decreased regeneration and recovery following unaccustomed exercise in older adults, as well as in chronic disease. The current research provides specific information on the role inflammation plays in altering skeletal muscle form and function, and adaptation to exercise; however, the pursuit of more knowledge in this area will delineate specific interventions that may enhance skeletal muscle recovery and promote resiliency in this tissue particularly with aging.

The Effects of Acute and Chronic Exercise on Paraoxonase-1 (PON1): A Systematic Review With Meta-Analysis

Purpose: To determine the acute and chronic effects of exercise on Paraoxonase-1 (PON1) concentration and activity. Methods: A literature search was performed using 16 electronic databases. Effect sizes (ES) were computed and two-tailed α values < .05 and non-overlapping 95% confidence intervals (95%CI) were considered statistically significant. Heterogeneity, inconsistency (I²), and small-study effects using the LFK index were examined. Results: Eighteen studies (n = 377 participants) met the criteria for inclusion. The acute effects of exercise on PON1 concentration were trivial and non-significant (ES = -.03, 95%CI = -.39 to .34, p > .05), heterogeneous (p = .05), moderately inconsistent (I² = 48%), with minor asymmetry (LFK index = 1.34). The chronic effects of exercise on PON1 concentration were also trivial and non-significant (ES = -.04, 95%CI = -.53 to.45, p > .05), homogenous (p = .65), displayed low inconsistency (I² = 0%), and minor asymmetry (LFK index = -1.14). The acute effects of exercise on PON1 activity were trivial and non-significant (ES = .11, 95%CI = -.02 to.24, p > .05), homogenous (p = .85), showed low inconsistency (I² = 0%), and no asymmetry (LFK index = .82). The chronic effects of exercise on PON1 activity were trivial and non-significant (ES = .31, 95%CI = -.03 to.65, p > .05), homogenous (p = .17), moderately inconsistent (I² = 36%), with no asymmetry (LFK index = .60). Conclusion: Acute and chronic exercise training, overall, exerted a trivial effect on PON1 concentration and activity.

U-Shaped Association between Dietary Acid Load and Risk of Osteoporotic Fractures in 2 Populations at High Cardiovascular Risk

BACKGROUND

Bone contributes to maintaining the acid-base balance as a buffering system for blood pH. Diet composition also affects acid-base balance. Several studies have linked an imbalance in the acid-base system to changes in the density and structure of bone mass, although some prospective studies and meta-analyses suggest that acid load has no deleterious effect on bone.

OBJECTIVE

The aim of this study was to examine the associations between potential renal acid load (PRAL) and net endogenous acid production (NEAP) and the risk of osteoporotic fractures and bone mineral density (BMD) in 2 middle-aged and elderly Mediterranean populations.

METHODS

We conducted a longitudinal analysis including 870 participants from the PREvención con DIeta MEDiterranea (PREDIMED) Study and a cross-sectional analysis including 1134 participants from the PREDIMED-Plus study. Participants were adults, aged 55-80 y, either at high cardiovascular risk (PREDIMED) or overweight/obese with metabolic syndrome (PREDIMED-Plus), as defined by the International Diabetes Federation, the American Heart Association, and the National Heart Association. PRAL and NEAP were calculated from validated food-frequency questionnaires. BMD was measured using DXA scans. Fracture information was obtained from medical records. The association between mean PRAL and NEAP and fracture risk was assessed using multivariable-adjusted Cox models. BMD differences between tertiles of baseline PRAL and NEAP were evaluated by means of ANCOVA.

RESULTS

A total 114 new fracture events were documented in the PREDIMED study after a mean of 5.2 y of intervention and 8.9 y of total follow-up. Participants in the first and third PRAL and NEAP tertiles had a higher risk of osteoporotic fracture compared with the second tertile, showing a characteristically U-shaped association [HR (95% CI): 1.73 (1.03, 2.91) in tertile 1 and 1.91 (1.14, 3.19) in tertile 3 for PRAL, and 1.83 (1.08, 3.09) in tertile 1 and 1.87 (1.10, 3.17) in tertile 3 for NEAP]. Compared with the participants in tertile 1, the participants in the top PRAL and NEAP tertiles had lower BMD [PRAL: mean total femur BMD: 1.029 ± 0.007 and 1.007 ± 0.007 g/cm2; P = 0.006 (tertiles 1 and 3); NEAP: mean total femur BMD: 1.032 ± 0.007 and 1.009 ± 0.007 g/cm2; P = 0.017 (tertiles 1 and 3)].

CONCLUSIONS

The results of our study suggest that both high and low dietary acid are associated with a higher risk of osteoporotic fractures, although only high dietary acid was found to have a negative relation to BMD in senior adults with existing chronic health conditions. This trial was registered at http://www.isrctn.com/ as ISRCTN3573963 (PREDIMED) and ISRCTN89898870 (PREDIMED-Plus).

Exercise interventions preserve hippocampal volume: A meta-analysis

Hippocampal volume is a marker of brain health and is reduced with aging and neurological disease. Exercise may be effective at increasing and preserving hippocampal volume, potentially serving as a treatment for conditions associated with hippocampal atrophy (e.g., dementia). This meta-analysis aimed to identify whether exercise training has a positive effect on hippocampal volume and how population characteristics and exercise parameters moderate this effect. Studies met the following criteria: (a) controlled trials; (b) interventions of physical exercise; (c) included at least one time-point of hippocampal volume data before the intervention and one after; (d) assessed hippocampal volume using either manual or automated segmentation algorithms. Animal studies, voxel-based morphometry analyses, and multi-modal interventions (e.g., cognitive training or meditation) were excluded. The primary analysis in n = 23 interventions from 22 published studies revealed a significant positive effect of exercise on total hippocampal volume. The overall effect was significant in older samples (65 years of age or older) and in interventions that lasted over 24 weeks and had less than 150 min per week of exercise. These findings suggest that moderate amounts of exercise for interventions greater than 6 months have a positive effect on hippocampal volume including in older populations vulnerable to hippocampal atrophy.

Exercise Promotes the Osteoinduction of HA/β-TCP Biomaterials via the Wnt Signaling Pathway

To investigate the osteoinductive mechanism triggered by hydroxyapatite/β-tricalcium phosphate (HA/β-TCP) biomaterials in mice which keep exercising. Methods: The HA/β-TCP biomaterials were implanted in the muscle of bilateral thighs (non-osseous sites) of eighty Balb/C mice. All animals were then randomly divided into 4 groups (n = 20). In group 1 (negative control group), the mice were fed routinely. In group 2 (running group), all mice were put on a treadmill which was set to a 60-degree incline. The mice ran 20 min thrice each day. A 5-minute break was included in the routine from day three onwards. In group 3 (weight-bearing group), all mice underwent weight-bearing running. The mice in this group performed the same routine as group 2 while carrying 5 g rubber weights. In group 4 (positive control group), dexamethasone was injected in the implanted sites of the biomaterials from the day of the operation. All mice were injected once per week and received a total of 8 injections. One and eight weeks after surgery, the blood serum was collected to detect inflammatory and immunological factors by ELISA. In addition to this, biomaterial specimens were obtained to observe inflammatory and osteogenic levels via histological staining and to facilitate analysis of the osteogenic mechanism by Western Blot. Results: The inflammation indexes caused by surgery were alleviated through running or weight-bearing running: The tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6) levels were significantly reduced in groups 2 and 3 at week 8. Exercise also enhanced the secretion of interferon-γ (IFN-γ) in mice; this can strengthen their immunity. The new bone tissues were observed in all groups; however, the area percentage of new bone tissues and the number of osteoblasts were highest in the weight-bearing group. Furthermore, the key proteins of wingless/integrated (Wnt) signaling pathway, Wnt1, Wnt3a, and β-catenin, were up-regulated during osteoinduction. This up-regulation activated runt-related transcription factor-2 (Runx2), increased the expression of osteopontin (OPN) and osteocalcin (OCN). Conclusion: Weight-bearing exercise can promote the bone and bone marrow formation through the Wnt signaling pathway: Observations documented here suggest that the proper exercise is beneficial to the recovery of bone damage.

Inactivity and Skeletal Muscle Metabolism: A Vicious Cycle in Old Age

Aging is an inevitable and gradually progressive process affecting all organs and systems. The musculoskeletal system makes no exception, elderly exhibit an increased risk of sarcopenia (low muscle mass),dynapenia (declining muscle strength), and subsequent disability. Whereas in recent years the subject of skeletal muscle metabolic decline in the elderly has been gathering interest amongst researchers, as well as medical professionals, there are many challenges yet to be solved in order to counteract the effects of aging on muscle function efficiently. Noteworthy, it has been shown that aging individuals exhibit a decline in skeletal muscle metabolism, a phenomenon which may be linked to a number of predisposing (risk) factors such as telomere attrition, epigenetic changes, mitochondrial dysfunction, sedentary behavior (leading to body composition alterations), age-related low-grade systemic inflammation (inflammaging), hormonal imbalance, as well as a hypoproteic diet (unable to counterbalance the repercussions of the age-related increase in skeletal muscle catabolism). The present review aims to discuss the relationship between old age and muscle wasting in an effort to highlight the modifications in skeletal muscle metabolism associated with aging and physical activity.