A Comparison of Two Mouse Frailty Assessment Tools

The intersection of frailty and metabolism

On average, aging is associated with unfavorable changes in cellular metabolism, which are the processes involved in the storage and expenditure of energy. However, metabolic dysregulation may not occur to the same extent in all older individuals as people age at different rates. Those who are aging rapidly are at increased risk of adverse health outcomes and are said to be "frail." Here, we explore the links between frailty and metabolism, including metabolic contributors and consequences of frailty. We examine how metabolic diseases may modify the degree of frailty in old age and suggest that frailty may predispose toward metabolic disease. Metabolic interventions that can mitigate the degree of frailty in people are reviewed. New treatment strategies developed in animal models that are poised for translation to humans are also considered. We suggest that maintaining a youthful metabolism into older age may be protective against frailty.

Preclinical Studies on the Effects of Frailty in the Aging Heart

Age is a major risk factor for the development of cardiovascular diseases in men and in women. However, not all people age at the same rate and those who are aging rapidly are considered frail, compared with their fit counterparts. Frailty is an important clinical challenge because those who are frail are more likely to develop and die from illnesses, including cardiovascular diseases, than fit people of the same age. This increase in susceptibility to cardiovascular diseases in older individuals might occur as the cellular and molecular mechanisms involved in the aging process facilitate structural and functional damage in the heart. Consistent with this, recent studies in murine frailty models have provided strong evidence that maladaptive cardiac remodelling in older mice is the most pronounced in mice with a high level of frailty. For example, there is evidence that ventricular hypertrophy and contractile dysfunction increase as frailty increases in aging mice. Additionally, fibrosis and slowing of conduction in the sinoatrial node and atria are proportional to the level of frailty. These modifications could predispose frail older adults to diseases like heart failure and atrial fibrillation. This preclinical work also raises the possibility that emerging interventions designed to "treat frailty" might also treat or prevent cardiovascular diseases. These findings might help to explain why frail older people are most likely to develop these disorders as they age.

Cellular senescence and frailty: a comprehensive insight into the causal links

Senescent cells may have a prominent role in driving inflammation and frailty. The impact of cellular senescence on frailty varies depending on the assessment tool used, as it is influenced by the criteria or items predominantly affected by senescent cells and the varying weights assigned to these items across different health domains. To address this challenge, we undertook a thorough review of all available studies involving gain- or loss-of-function experiments as well as interventions targeting senescent cells, focusing our attention on those studies that examined outcomes based on the individual frailty phenotype criteria or specific items used to calculate two humans (35 and 70 items) and one mouse (31 items) frailty indexes. Based on the calculation of a simple "evidence score," we found that the burden of senescent cells related to musculoskeletal and cerebral health has the strongest causal link to frailty. We deem that insight into these mechanisms may not only contribute to clarifying the role of cellular senescence in frailty but could additionally provide multiple therapeutic opportunities to help the future development of a desirable personalized therapy in these extremely heterogeneous patients.

Comprehensive longitudinal non-invasive quantification of healthspan and frailty in a large cohort (n = 546) of geriatric C57BL/6 J mice

Frailty is an age-related condition characterized by a multisystem functional decline, increased vulnerability to stressors, and adverse health outcomes. Quantifying the degree of frailty in humans and animals is a health measure useful for translational geroscience research. Two frailty measurements, namely the frailty phenotype (FP) and the clinical frailty index (CFI), have been validated in mice and are frequently applied in preclinical research. However, these two tools are based on different concepts and do not necessarily identify the same mice as frail. In particular, the FP is based on a dichotomous classification that suffers from high sample size requirements and misclassification problems. Based on the monthly longitudinal non-invasive assessment of frailty in a large cohort of mice, here we develop an alternative scoring method, which we called physical function score (PFS), proposed as a continuous variable that resumes into a unique function, the five criteria included in the FP. This score would not only reduce misclassification of frailty but it also makes the two tools, PFS and CFI, integrable to provide an overall measurement of health, named vitality score (VS) in aging mice. VS displays a higher association with mortality than PFS or CFI and correlates with biomarkers related to the accumulation of senescent cells and the epigenetic clock. This longitudinal non-invasive assessment strategy and the VS may help to overcome the different sensitivity in frailty identification, reduce the sample size in longitudinal experiments, and establish the effectiveness of therapeutic/preventive interventions for frailty or other age-related diseases in geriatric animals.

Effects of Human LAV-BPIFB4 Gene Therapy on the Epigenetic Clock and Health of Aged Mice

The homozygous genotype of the Longevity-Associated Variant (LAV) in Bactericidal/Permeability-Increasing Fold-Containing Family B member 4 (BPIFB4) is enriched in long-living individuals of three independent populations and its genetic transfer in C57BL/6J mice showed a delay in frailty progression and improvement of several biomarkers of aging and multiple aspects of health. The C57BL/6J strain is a suitable model for studying therapies aimed at extending healthy aging and longevity due to its relatively short lifespan and the availability of aging biomarkers. Epigenetic clocks based on DNA methylation profiles are reliable molecular biomarkers of aging, while frailty measurement tools are used to evaluate overall health during aging. In this study, we show that the systemic gene transfer of LAV-BPIFB4 in aged C57BL/6J mice was associated with a significant reduction in the epigenetic clock-based biological age, as measured by a three CpG clock method. Furthermore, LAV-BPIFB4 gene transfer resulted in an improvement of the Vitality Score with a reduction in the Frailty Index. These findings further support the use of LAV-BPIFB4 gene therapy to induce beneficial effects on epigenetic mechanisms associated with aging and frailty in aged mice, with potential implications for future therapies to prevent frailty in humans.

MyMD-1 Improves Health Span and Prolongs Life Span in Old Mice: A Noninferiority Study to Rapamycin

Aging and age-related diseases represent a compelling therapeutic goal for senolytics and drugs targeting inflammatory or metabolic pathways. We compared MyMD-1, a synthetic derivative of the alkaloid myosmine capable of suppressing TNF-α production, to rapamycin, the best characterized drug endowed with antiaging properties. In vivo, a longitudinal cohort of 54 C57BL/6 mice, 19-month-old at the start, was randomized to receive MyMD-1, high-dose (126 ppm) rapamycin, or low-dose (14 ppm) rapamycin plus metformin. Each treatment arm included 18 mice (10 females and 8 males) and was followed for 16 months or until death. Life span was significantly longer in MyMD-1 than rapamycin (p = .019 vs high-dose and .01 vs low-dose) in a Cox survival model that accounted for sex and serum levels of IL-6, TNF-α, and IL-17A. MyMD-1 also improved several health span characteristics, resulting in milder body weight loss, greater muscle strength, and slower progression to frailty. In vitro, MyMD-1 and rapamycin were compared using a panel of 12 human primary cell systems (BioMAP Diversity PLUS), where a total of 148 biomarkers were measured. MyMD-1 possessed antiproliferative, anti-inflammatory, and antifibrotic properties. Many were shared with rapamycin, but MyMD-1 was more active in the inhibition of proinflammatory and profibrotic biomarkers. Overall, MyMD-1 emerges as a new compound that, even when begun at an advanced age, induces beneficial effects on health and life span by modulating inflammation and tissue remodeling.

The Use of Dietary Supplements and Amino Acid Restriction Interventions to Reduce Frailty in Pre-Clinical Models

Frailty is a state of accelerated aging that increases susceptibility to adverse health outcomes. Due to its high societal and personal costs, there is growing interest in discovering beneficial interventions to attenuate frailty. Many of these interventions involve the use of lifestyle modifications such as dietary supplements. Testing these interventions in pre-clinical models can facilitate our understanding of their impact on underlying mechanisms of frailty. We conducted a narrative review of studies that investigated the impact of dietary modifications on measures of frailty or overall health in rodent models. These interventions include vitamin supplements, dietary supplements, or amino acid restriction diets. We found that vitamins, amino acid restriction diets, and dietary supplements can have beneficial effects on frailty and other measures of overall health in rodent models. Mechanistic studies show that these effects are mediated by modifying one or more mechanisms underlying frailty, in particular effects on chronic inflammation. However, many interventions do not measure frailty directly and most do not investigate effects in both sexes, which limits their applicability. Examining dietary interventions in animal models allows for detailed investigation of underlying mechanisms involved in their beneficial effects. This may lead to more successful, translatable interventions to attenuate frailty.

Frailty in rodents: Models, underlying mechanisms, and management

Frailty is a clinical geriatric syndrome characterized by decreased multisystem function and increased vulnerability to adverse outcomes. Although numerous studies have been conducted on frailty, the underlying mechanisms and management strategies remain unclear. As rodents share homology with humans, they are used extensively as animal models to study human diseases. Rodent frailty models can be classified broadly into the genetic modification and non-genetic modification models, the latter of which include frailty assessment models (based on the Fried frailty phenotype and frailty index methods) and induced frailty models. Such models were developed for use in investigating frailty-related physiological changes at the gene, cellular, molecular, and system levels, including the organ system level. Furthermore, exercise, diet, and medication interventions, in addition to their combinations, could improve frailty status in rodents. Rodent frailty models provide novel and effective tools for frailty research. In the present paper, we review research progress in rodent frailty models, mechanisms, and management, which could facilitate and guide further clinical research on frailty in older adults.

Physiological Systems in Promoting Frailty

Frailty is a complex syndrome affecting a growing sector of the global population as medical developments have advanced human mortality rates across the world. Our current understanding of frailty is derived from studies conducted in the laboratory as well as the clinic, which have generated largely phenotypic information. Far fewer studies have uncovered biological underpinnings driving the onset and progression of frailty, but the stage is set to advance the field with preclinical and clinical assessment tools, multiomics approaches together with physiological and biochemical methodologies. In this article, we provide comprehensive coverage of topics regarding frailty assessment, preclinical models, interventions, and challenges as well as clinical frameworks and prevalence. We also identify central biological mechanisms that may be at play including mitochondrial dysfunction, epigenetic alterations, and oxidative stress that in turn, affect metabolism, stress responses, and endocrine and neuromuscular systems. We review the role of metabolic syndrome, insulin resistance and visceral obesity, focusing on glucose homeostasis, adenosine monophosphate-activated protein kinase (AMPK), mammalian target of rapamycin (mTOR), and nicotinamide adenine dinucleotide (NAD⁺ ) as critical players influencing the age-related loss of health. We further focus on how immunometabolic dysfunction associates with oxidative stress in promoting sarcopenia, a key contributor to slowness, weakness, and fatigue. We explore the biological mechanisms involved in stem cell exhaustion that affect regeneration and may contribute to the frailty-associated decline in resilience and adaptation to stress. Together, an overview of the interplay of aging biology with genetic, lifestyle, and environmental factors that contribute to frailty, as well as potential therapeutic targets to lower risk and slow the progression of ongoing disease is covered. © 2022 American Physiological Society. Compr Physiol 12:1-46, 2022.

Preclinical frailty assessments: Phenotype and frailty index identify frailty in different mice and are variably affected by chronic medications

Use of different objective frailty assessment tools may improve understanding of the biology of frailty and allow evaluation of effects of interventions on frailty. Polypharmacy is associated with increased risk of frailty in epidemiologic studies, regardless of frailty definition, but the pathophysiology of the association is not well understood. This study aims to (1) assess and compare the prevalence of frailty from middle to old age following control, chronic polypharmacy or monotherapy treatment, when measured using the clinical frailty index assessment and the mouse frailty phenotype tools; and (2) to evaluate and compare the effects of chronic polypharmacy regimens with zero, low and high Drug Burden Index (DBI) and monotherapies from middle to old age on the rate of deficit accumulation on the frailty index, mean number of phenotype criteria, odds of being frail assessed by the frailty index or phenotype, and the time to onset of frailty assessed by the frailty index or phenotype. In a longitudinal study, middle-aged (12 months) male C57BL/6J(B6) mice were administered non medicated control feed and water, or therapeutic doses of different polypharmacy combinations or monotherapies in feed and/or water. Frailty assessments were performed at 12, 15, 18, 21 and 24 months. There was limited overlap between animals identified as frail using different frailty assessments. Polypharmacy has measurable and different effects on each frailty assessment. Long-term chronic administration of some polypharmacy and monotherapy therapeutic drug regimens increased the number of frailty deficits (clinical frailty index: low DBI polypharmacy (15 and 21 months), high DBI polypharmacy (15-21 months), oxycodone (15-18 months), oxybutynin (15-18 months), citalopram (15-21 months) and metoprolol monotherapy (15 months) and modified frailty phenotype assessment (over the whole duration of treatment, low DBI polypharmacy (adjusted Risk Ratio(aRR) = 1.97, 95% confidence interval (CI) 1.43-2.72), high DBI polypharmacy (aRR = 1.88; 95% CI 1.36-2.60), oxybutynin (aRR = 1.48; 95% CI 1.01-2.16) and citalopram monotherapy (aRR = 1.96; 95% CI 1.41-2.74), p < 0.05) . The odds of developing frailty measured with the clinical frailty index increased with high DBI polypharmacy (adjusted odds ratio (aOR) = 3.13; 95% CI 1.01-9.66) and when measured with the frailty phenotype assessment increased with low DBI polypharmacy (aOR = 4.38, 95% CI 1.40-13.74), high DBI polypharmacy (aOR = 3.43; 95% CI 1.12-10.50) and citalopram monotherapy (aOR = 4.63; 95% CI 1.39-15.54)). No treatment affected time to frailty using either frailty assessment. Analysis of the number of deficits on the frailty index or number of positive criteria on the frailty phenotype allows analysis of rate of change and provides greater sensitivity, while the odds of being frail analysis provided a clinically relevant indicator of whether mice had greater chance of reaching a cut-off for becoming frail with medication exposure than without. Our results are consistent with clinical studies, demonstrating that certain polypharmacy regimens induce frailty, with different relationships observed when using different frailty assessments and analyses.

Sex Differences in the Relation Between Frailty and Endothelial Dysfunction in Old Mice

Vascular endothelial function declines with age on average, but there is high variability in the magnitude of this decline within populations. Measurements of frailty, known as frailty index (FI), can be used as surrogates for biological age, but it is unknown if frailty relates to the age-related decline in vascular function. To examine this relation, we studied young (4-9 months) and old (23-32 months) C57BL6 mice of both sexes. We found that FI was greater in old compared with young mice, but did not differ between old male and female mice. Middle cerebral artery (MCA) and mesenteric artery endothelium-dependent dilation (EDD) also did not differ between old male and female mice; however, there were sex differences in the relations between FI and EDD. For the MCA, FI was inversely related to EDD among old female mice, but not old male mice. In contrast, for the mesenteric artery, FI was inversely related to EDD among old male mice, but not old female mice. A higher FI was related to a greater improvement in EDD with the superoxide scavenger TEMPOL in the MCAs for old female mice and in the mesenteric arteries for old male mice. FI related to mesenteric artery gene expression negatively for extracellular superoxide dismutase (Sod3) and positively for interleukin-1β (Il1b). In summary, we found that the relation between frailty and endothelial function is dependent on sex and the artery examined. Arterial oxidative stress and pro-inflammatory signaling are potential mediators of the relations of frailty and endothelial function.

Identifying Biomarkers for Biological Age: Geroscience and the ICFSR Task Force

The International Conference on Frailty and Sarcopenia Research Task Force met in March 2020, in the shadow of the COVID-19 pandemic, to discuss strategies for advancing the interdisciplinary field of geroscience. Geroscience explores biological mechanisms of aging as targets for intervention that may delay the physiological consequences of aging, maintain function, and prevent frailty and disability. Priorities for clinical practice and research include identifying and validating a range of biomarkers of the hallmarks of aging. Potential biomarkers discussed included markers of mitochondrial dysfunction, proteostasis, stem cell dysfunction, nutrient sensing, genomic instability, telomere dysfunction, cellular senescence, and epigenetic changes. The FRAILOMICS initiative is exploring many of these through various omics studies. Translating this knowledge into new therapies is being addressed by the U.S. National Institute on Aging Translational Gerontology Branch. Research gaps identified by the Task Force include the need for improved cellular and animal models as well as more reliable and sensitive measures.

Allicin Reversed the Process of Frailty in Aging Male Fischer 344 Rats With Osteoporosis

The research and development of pharmaceutical intervention is insufficient for the frail older adults, especially in preclinical stage for the frail individuals with osteoporosis. Garlic exerts an antiosteoporotic effect and its vital component allicin could protect organisms against aging. The present study aimed to investigate the effect of long-term intragastric administration of allicin (low dose of 4 mg·kg⁻¹·d⁻¹; middle dose of 8 mg·kg⁻¹·d⁻¹; high dose of 16 mg·kg⁻¹·d⁻¹) on frailty with osteoporosis in aging male Fischer 344 rats. Frailty was assessed with a 27-item frailty index based on quantifying health-related deficits in adult male rats varied from 13 to 21 months and in control rats from 6 to 9 months. Osteoporosis was appraised by bone mineral density detected by dual-energy X-ray absorptiometry, biomechanical properties measured by a three-point bending test, and bone metabolic analysis using ELISA. Allicin could attenuate frailty index scores by reducing the accumulation of health deficits in aging male Fischer 344 rats. Meanwhile, allicin could protect against senile osteoporosis, and the underlying mechanism may involve in increasing low bone turnover through elevation of both bone formation and bone resorption, and subsequently lead to increase of bone mineral density, contributing to reversing deleterious bone biomechanical features associated with aging. The present study reveals firstly that long-term oral administration with allicin attenuated frailty with osteoporosis during the process of aging, which provides a preclinical evidence for intervention of frailty.

Phenotypic Frailty Assessment in Mice: Development, Discoveries, and Experimental Considerations

The underlying mechanisms contributing to the onset of frailty, its progression, and its mortality risk remain unknown. Recently, the two most common human frailty assessments were reverse-translated to mice. Here, we highlight the development of the mouse frailty phenotype, unique discoveries, experimental considerations, and future perspectives.

Relevance of oxidative stress and inflammation in frailty based on human studies and mouse models

Frailty represents a state of vulnerability and increases the risk of negative health outcomes, which is becoming an important public health problem. Over recent years, multiple independent studies have attempted to identify biomarkers that can predict, diagnose, and monitor frailty at the biological level. Among them, several promising candidates have been associated with frailty status including antioxidants and free radicals, and also inflammatory response biomarkers. In this review, we will summarize the more recent advances in this field. Moreover, the identification of scales and measurements to detect and quantify frailty in aged mice, as well as the generation of mouse models, have started to unravel the underlying biological and molecular mechanisms of frailty. We will discuss them here with an emphasis on murine models with overexpression of glucose-6-phosphate dehydrogenase and loss of function of superoxide dismutase and interleukin 10, which reveal that altered oxidative stress and inflammation pathways are involved in the physiopathology of frailty. In summary, we provide the current available evidence, from both human cohorts and experimental animal models, that highlights oxidative damage and inflammation as relevant biomarkers and drivers of frailty.

A toolbox for the longitudinal assessment of healthspan in aging mice

The number of people aged over 65 is expected to double in the next 30 years. For many, living longer will mean spending more years with the burdens of chronic diseases such as Alzheimer's disease, cardiovascular disease, and diabetes. Although researchers have made rapid progress in developing geroprotective interventions that target mechanisms of aging and delay or prevent the onset of multiple concurrent age-related diseases, a lack of standardized techniques to assess healthspan in preclinical murine studies has resulted in reduced reproducibility and slow progress. To overcome this, major centers in Europe and the United States skilled in healthspan analysis came together to agree on a toolbox of techniques that can be used to consistently assess the healthspan of mice. Here, we describe the agreed toolbox, which contains protocols for echocardiography, novel object recognition, grip strength, rotarod, glucose tolerance test (GTT) and insulin tolerance test (ITT), body composition, and energy expenditure. The protocols can be performed longitudinally in the same mouse over a period of 4-6 weeks to test how candidate geroprotectors affect cardiac, cognitive, neuromuscular, and metabolic health.

LAV-BPIFB4 associates with reduced frailty in humans and its transfer prevents frailty progression in old mice

Background: There is an increasing concern about age-related frailty because of the growing number of elderly people in the general population. The Longevity-Associated Variant (LAV) of the human BPIFB4 gene was found to correct endothelial dysfunction, one of the mechanisms underlying frailty, in aging mice whereas the RV-BPIFB4 variant induced opposite effects. Thus, we newly hypothesize that, besides being associated with life expectancy, BPIFB4 polymorphisms can predict frailty.

Aim and Results: Here we investigated if the BPIFB4 haplotypes, LAV, wild-type (WT) and RV, differentially associate with frailty in a cohort of 237 elderly subjects from Calabria region in Southern Italy. Moreover, we studied the effect of systemic adeno-associated viral vector-mediated LAV-BPIFB4 gene transfer on the progression of frailty in aging mice. We found an inverse correlation of the homozygous LAV-BPIFB4 haplotype with frailty in elderly subjects. Conversely, carriers of the RV-BPIFB4 haplotype showed an increase in the frailty status and risk of death. Moreover, in old mice, LAV-BPIFB4 gene transfer delayed frailty progression.

Conclusions: These data indicate that specific BPIFB4 haplotypes could represent useful genetic markers of frailty. In addition, horizontal transfer of a healthy gene variant can attenuate frailty in aging organisms.

Aged mice show an increased mortality after anesthesia with a standard dose of ketamine/xylazine

Geriatric animal models are crucial for a better understanding and an improved therapy of age-related diseases. We observed a high mortality of aged mice after anesthesia with a standard dose of ketamine/xylazine, an anesthetic regimen frequently used in laboratory veterinary medicine.

C57BL/6-N mice at the age of 2.14 ± 0.23 months (young mice) and 26.31 ± 2.15 months (aged mice) were anesthetized by intraperitoneal injection of 2 mg ketamine and 0.2 mg xylazine. 4 of 26 aged mice (15.4%) but none of 26 young mice died within 15 min after injection of the anesthetics. The weight of aged mice was significantly higher than that of young mice (32.8 ± 5.4 g versus 23.2 ± 3.4 g, p < 0.0001). Thus, aged mice received lower doses of anesthetics in relation to their body weight which are within the lower range of doses recommended in the literature or even beneath. There were no differences between deceased and surviving aged mice concerning their sex, weight and their motor performance prior to anesthesia.

Our data clearly show an age-related increase of mortality upon anesthesia with low standard doses of ketamine/xylazine. Assessment of weight and motor performance did not help to predict vulnerability of aged mice to the anesthetics. Caution is necessary when this common anesthetic regimen is applied in aged mice: lower doses or the use of alternative anesthetics should be considered to avoid unexpected mortality.

The present data from our geriatric mouse model strongly corroborate an age-adjusted reduction of anesthetic doses to reduce anesthesia-related mortality in aged individuals.

Frailty biomarkers in humans and rodents: Current approaches and future advances

Even though they would have great benefit across research and clinical fields, currently there are no accepted biomarkers of frailty. Cross-sectional studies in humans have identified promising candidates including inflammatory markers such as IL-6, immune markers such as WBC count, clinical markers such as albumin, endocrine markers such as vitamin D, oxidative stress markers such as isoprostanes, proteins such as BDNF and epigenetic markers such as DNA methylation, but there are limitations to the current state of the research. Future approaches to the identification of frailty biomarkers should include longitudinal studies, studies using animal models of frailty, studies incorporating novel biomarkers combined into composite panels, and studies investigating sex differences and potential overlap between markers of biological age and frailty.

High intensity interval training improves physical performance in aged female mice: A comparison of mouse frailty assessment tools

Frailty syndrome increases the risk for disability and mortality, and is a major health concern amidst the geriatric shift in the population. High intensity interval training (HIIT), which couples bursts of vigorous activity interspersed with active recovery intervals, shows promise for the treatment of frailty. Here we compare and contrast five Fried physical phenotype and one deficit accumulation based mouse frailty assessment tools for identifying the impacts of HIIT on frailty and predicting functional capacity, underlying pathology, and survival in aged female mice. Our data reveal a 10-minute HIIT regimen administered 3-days-a-week for 8-weeks increased treadmill endurance, gait speed and maintained grip strength. One frailty tool identified a benefit of HIIT for frailty, but many were trending suggesting HIIT was beneficial for physical performance in these mice, but the 8-week timeframe may have been insufficient to induce frailty benefits. Finally, most frailty tools distinguished between surviving or non-surviving mice, whereas half correlated with functional capacity measured by nest building ability, and none correlated with underlying pathology. In summary, this study supports the ongoing development of mouse assessment tools as useful instruments for frailty research.

The biology of frailty in humans and animals: Understanding frailty and promoting translation

Frailty is a state of high vulnerability to adverse health outcomes. This concept is used to explain the heterogeneity in rates of aging in people of the same age. Frailty has important clinical implications, because even minor stressors can lead to adverse outcomes, including death, in frail individuals. Although frailty mechanisms are not well understood, advances in our ability to qualify frailty have encouraged efforts in this area. Quantification of frailty with both "frailty phenotype" and "frailty index" approaches has begun to highlight putative frailty mechanisms and new animal models of frailty are inspiring preclinical research. These models either adapt frailty phenotype and frailty index tools for use in animals or they use genetically manipulated mice that mimic conditions seen in frailty (eg, inflammation, sarcopenia, weakness). This review: describes commonly used tools to quantify frailty clinically, discusses potential frailty mechanisms, and describes animal models of frailty. It also highlights how these models have been used to explore frailty mechanisms and potential frailty interventions, including pharmacological treatments, diet, and exercise. These exciting new developments in the field have the potential to facilitate translational research, improve our understanding of mechanisms of frailty, and help develop new interventions to mitigate frailty in our aging population.

Serum sodium level variability as a prognosticator in older adults

Our aim was to explore biological variation of serum sodium levels as a method of quantifying health risk in older adults. We investigated whether dynamic changes in serum sodium levels could provide additional prognostic information to standard predictors of mortality in older people. Analysis of routinely collected clinical datasets containing information on demographics, hospitalisation, biochemistry, haematology and physical function for Dundee in-patient rehabilitation services, between 1999 and 2011. Older people admitted to inpatient rehabilitation following an acute medical or surgical hospitalisation. Five dynamic measures of sodium levels homeostasis - minimum, maximum, standard deviation, and minimum and maximum deviation from mean - were derived for each individual, using biochemistry data from the year preceding their rehabilitation discharge. Cox regression models tested for associations with time to death. Covariates included age, sex, discharge Barthel score, co-morbid diagnoses, haemoglobin, albumin and eGFR. 3021 patients were included (mean age 84 years, 1776 (58.8%) females). 1651 (54.7%) patients experienced hyponatraemia and 446 (14.8%) became hypernatraemic. Mean sodium was correlated with all mean, minimum and SD of sodium. Kaplan-Meier survival curves showed that those without sodium perturbations had the best mortality outcomes, whilst those with both hyponatremia and hypernatremia had the worst. Multivariate Cox regression showed that standard deviation and hypernatraemia were significant predictors of death in non-adjusted models, but not fully adjusted models. All dynamic measures of dysnatraemia were associated with increased mortality risk, but failed to add predictive value to established static measures after adjusting for covariates.

Rodent models of frailty and their application in preclinical research

In clinical medicine, the concept of frailty is viewed as a state of high vulnerability to adverse health outcomes in people of the same age. Frailty is an important challenge because the loss of physiological reserve means that even minor stressors can lead to disability and death in those who are frail. Even so, the biology of frailty is not well understood. Rodent models of frailty are stimulating research into the biology of frailty. These pre-clinical models are based on "reverse-translation". Investigators have adapted either the "frailty phenotype" approach or the "frailty index" approach, originally developed in humans, for use in animals. This review briefly describes rodent models of frailty, discusses how these models have been used to explore mechanisms of frailty and how they have been employed to assess the impact of frailty on various experimental outcomes. The review also highlights studies that have used rodent models to investigate interventions to attenuate frailty, including drug treatment, dietary modifications and exercise. The ability to model frailty in animals is an exciting development that promises to accelerate the translation of laboratory discoveries into new clinical interventions, and situates frailty research in the larger context of geroscience.

Nrf2 deficiency exacerbates frailty and sarcopenia by impairing skeletal muscle mitochondrial biogenesis and dynamics in an age-dependent manner

AIM

Mitochondrial dysfunction during aging is a key factor that contributes to sarcopenia. Nuclear factor erythroid 2-related factor 2 (Nrf2) has been increasingly recognized to regulate mitochondrial function. The present study aimed to investigate the role of Nrf2 in the development of frailty and sarcopenia during aging, and to demonstrate whether Nrf2 contributes to the maintenance of muscle mass and function by regulation of mitochondrial biogenesis and dynamics during the aging process.

METHODS

Young (5-6 months), middle-aged (11-13 months), old (20-24 months) Nrf2-/- (knockout, KO) mice and age-matched wild-type (WT) C57/BL6 mice were used in this study. Physical function of the mice in the 6 groups was assessed by grip strength test, four paw inverted hanging test, rotarod analysis, open field analysis, and treadmill endurance test. Muscle mass was measured by cross-sectional area (CSA) of tibialis anterior muscles and gastrocnemius muscle weight. The frailty status of the 25 old WT mice and 23 old KO mice were assessed based on the mouse frailty phenotype assessment. Expression levels of genes involved in mitochondrial biogenesis (nuclear respiratory factor 1 (Nrf1), peroxisome proliferative activated receptor, gamma, coactivator 1 alpha (PGC-1α), mitochondrial transcription factor A (TFAM)) and mitochondrial dynamics (optic atrophy protein 1 (Opa1), mitofusin 1 (Mfn1), mitofusin 2 (Mfn2), and dynamin-related protein 1 (Drp1)) were measured in the skeletal muscle. SDH staining was performed and mitochondrial DNA (mtDNA) copy number was measured. Transmission electron microscopy was used to measure the mitochondria number and morphology.

RESULTS

Physical function and muscle mass decreased during aging. The mRNA expression levels of Nrf2 decreased with increasing frailty phenotype scores in the old WT mice. There were minimal differences in the physical function and muscle mass between the WT and KO mice in the young groups, whereas Nrf2 deficiency caused a declined physical function and muscle mass in the middle-aged and old mice, and exacerbated frailty in the old mice. The decreases of the physical function and muscle mass were accompanied by the reduced expression levels of genes involved in mitochondrial biogenesis and dynamics, as well as a reduction of mitochondrial number, mitochondrial content, mtDNA copy number, and an impaired mitochondria morphology in the skeletal muscle.

CONCLUSION

Nrf2 deficiency exacerbated frailty and sarcopenia during aging, at least partially by impairing skeletal muscle mitochondrial biogenesis and dynamics in an age-dependent manner.

Frailty and Caenorhabditis elegans as a Benchtop Animal Model for Screening Drugs Including Natural Herbs

Caenorhabditis elegans has been used in research for years to clarify the genetic cascades and molecular mechanisms of aging, longevity, and health span. Health span is closely related to frailty; however, frailty has a different concept and is evaluated using various parameters in humans, such as Fried's Frailty Criteria. The C. elegans model has several advantages when performing a chemical screen to identify drug candidates. Several mouse models of frailty were recently developed, including a homozygous IL-10 knockout. These mouse models are useful for understanding human frailty; however, they are not appropriate for primary drug screening because they require large spaces, expensive cost, and time consuming assessments. Therefore, a combination of these models may be a promising tool for discovering drugs and understanding the mechanisms of frailty. In addition, natural products, and herbs are attractive sources of novel drugs with pharmacological activity and low toxicity, in fact, over 60% of currently-available drugs are estimated to be related to natural compounds. In this review, the possibility of identifying natural agents (i.e., herb extracts and compounds) that could improve frailty are proposed, and the advantages and limitations of these models are also discussed.

High Intensity Interval Training Improves Physical Performance and Frailty in Aged Mice

Sarcopenia and frailty are highly prevalent in older individuals, increasing the risk of disability and loss of independence. High intensity interval training (HIIT) may provide a robust intervention for both sarcopenia and frailty by achieving both strength and endurance benefits with lower time commitments than other exercise regimens. To better understand the impacts of HIIT during aging, we compared 24-month-old C57BL/6J sedentary mice with those that were administered 10-minute uphill treadmill HIIT sessions three times per week over 16 weeks. Baseline and end point assessments included body composition, physical performance, and frailty based on criteria from the Fried physical frailty scale. HIIT-trained mice demonstrated dramatic improvement in grip strength (HIIT 10.9% vs -3.9% in sedentary mice), treadmill endurance (32.6% vs -2.0%), and gait speed (107.0% vs 39.0%). Muscles from HIIT mice also exhibited greater mass, larger fiber size, and an increase in mitochondrial biomass. Furthermore, HIIT exercise led to a dramatic reduction in frailty scores in five of six mice that were frail or prefrail at baseline, with four ultimately becoming nonfrail. The uphill treadmill HIIT exercise sessions were well tolerated by aged mice and led to performance gains, improvement in underlying muscle physiology, and reduction in frailty.

Is Delirium the Cognitive Harbinger of Frailty in Older Adults? A Review about the Existing Evidence

Frailty is a clinical syndrome defined by the age-related depletion of the individual’s homeostatic reserves, determining an increased susceptibility to stressors and disproportionate exposure to negative health changes. The physiological systems that are involved in the determination of frailty are mutually interrelated, so that when decline starts in a given system, implications may also regard the other systems. Indeed, it has been shown that the number of abnormal systems is more predictive of frailty than those of the abnormalities in any particular system. Delirium is a transient neurocognitive disorder, characterized by an acute onset and fluctuating course, inattention, cognitive dysfunction, and behavioral abnormalities, that complicates one out of five hospital admissions. Delirium is independently associated with the same negative outcomes of frailty and, like frailty, its pathogenesis is usually multifactorial, depending on complex inter-relationships between predisposing and precipitating factors. By definition, a somatic cause should be identified, or at least suspected, to diagnose delirium. Delirium and frailty potentially share multiple pathophysiologic mechanisms and pathways, meaning that they could be thought of as the two sides to the same coin. This review aims at summarizing the existing evidence, referring both to human and animal models, to postulate that delirium may represent the cognitive harbinger of a state of frailty in older persons experiencing an acute clinical event.