Physical resilience is a measure of healthy aging, but current assessment methods are underdeveloped, relying on a frailty panel of subjective tests. A quantitative, reliable test for resilience using endpoints aligning with healthy aging is needed to provide a standardized measurement of resistance to age-associated decline. The chemotherapeutic drug cyclophosphamide (CYP) is an immunosuppressant used in clinical medicine for certain types of cancer and autoimmune diseases. Precursor neutrophils are especially sensitive to this chemical stressor, such that a single low-level dose stops cell cycling with a decrease in mature neutrophils, but neutrophils rebound as the drug is eliminated from the body. This study sought to characterize the neutrophil rebound response in aging mice as a biological sensor for how an organism might respond to physical stress with increasing age. One intraperitoneal dose of CYP at 100 mg/kg was given to groups of mice at various ages. White blood cell differential and total counts were enumerated to monitor cellular response over a 25-day period. A robust and predictable drop in neutrophils occurred across age groups five days after injection of CYP, followed by a robust increase in neutrophils beyond baseline measurements at day seven in an age-dependent manner. Strength of the neutrophil rebound had a moderate correlation with strength and stamina as measured by rod hanging time, a test that corresponds to hand grip assessment in humans as an indication of frailty. This observation suggests that the neutrophil rebound response to the chemical stressor CYP in young adult mice can predict resilience to aging in older adult mice. The clinical implications are that an in vitro bench test could be developed using CYP-induced rebound response of human precursor neutrophils to predict resistance to frailty and produce a more accurate assessment of resilient healthy aging in older adults.

Sleep deprivation has serious health consequence with disturbances in cognitive function and metabolism, and increased risk for age-related diseases such as Alzheimer’s disease. Intervention strategies are therefore of interest, especially in individuals unable to routinely obtain healthful sleep time hours. This study was designed to investigate the effects of the repurpose drug phenylbutyrate (PBA) on learning impairment in a mouse model of short-term sleep deprivation. Histone deacetylase (HDAC) is activated by neuronal stress resulting in decreased gene expression and under-acetylation of histones linked to decreased cognitive function. As an HDAC inhibitor, PBA would be expected to alleviate cognitive dysfunction associated with sleep deprivation. Further rationale for testing PBA was provided by showing the drug enhanced expression of acetylated histones in mouse and human neuronal cell cultures. Nine CB6F1 male mice, 17 months of age, were started on treatment with PBA in the drinking water at a concentration of 6 g/L for twelve weeks. Nine control mice were provided drinking water with diluent only. During the last week of treatment, mice were maintained in an awake state 4 hours during the day for 4 days using a non-stressful protocol. All mice were then immediately tested in a box maze learning paradigm consisting of four successive trials to find an escape hole. Control mice had variable escape times over the four-trial test, while mice treated with PBA showed a consistent decrease in escape times with each successive trial. This observation suggests that pretreatment with PBA can prevent learning impairment induced by short term sleep deprivation in mice. Since PBA is already clinically approved to treat urea cycle disorders in children, there are intriguing implications for repurposing this drug for experimental trials in individuals with primary or secondary sleep disorders.

Wound healing in the elderly can be a serious health issue because of a delay in tissue repair and compromised immune response. In these circumstances successful treatment can be challenging. New drugs and preclinical animal models are needed to develop alternative treatment strategies. This study was designed to investigate the effectiveness of a novel mitochondrial specific peptide, designated as SS20, in enhancing wound healing in an aging mouse model using a novel and relatively noninvasive ear punch wound. Ten C57BL/6 female mice 26 months of age were ear punched through and through in the central area of both ears using a 2 mm dermal biopsy punch. C57BL/6 mice were chosen due to them being well defined aging models both genetically and physiologically, allowing us to compare aging parameters in the same background. Five mice were randomly selected for daily topical treatment directly on the wound with SS20 at 3mM concentration in a volume of 10 ul. Five mice were treated daily with topical saline in the same manner. Two individuals separately and independently measured diameter of the wounds in two directions (because the wounds were more elliptical than circular) on days 1, 7 and 14 when treatment was stopped. Wound surface areas were then calculated and average change over the 2 weeks was determined between mice with SS20 and saline. A significant decrease in surface area was seen in the left ears of mice treated with SS20 but not with saline as measured by both individuals. Interestingly there was no difference in change in surface area in the right ears of mice treated with SS20 or saline over the 14-day period, confirmed by both individual measurements. These observations suggest that SS20 can prevent a delay in wound healing in very old mice by targeting mitochondrial activity. Additional studies are needed, not only for SS20 effects, but also to investigate utility of the ear punch in aging mice as a model of age-related wound healing.

The ability to respond to physical stress can be useful in gauging resilience to aging. Vaccine inoculation is an immune stress that triggers an easily quantifiable antibody response. This study was designed to identify antibody response patterns to a clinically relevant pneumococcal vaccine in mice, in order to show an association with resistance to age-related decline. Twenty C57BL/6 and twenty CB6F1 male mice in age groups of 8, 16, 24, and 32 months were inoculated with one subcutaneous dose of pneumococcal capsular antigen in adjuvant. Serum was collected 16 days later, diluted 1 to 625, and immunoglobulin G antibody levels were measured by an enzyme-linked immunosorbent assay (ELISA) using 410/490 optical density. All data points were standardized against serum from non-vaccinated mice. There was a clear differentiation between high and low antibody responders in both mouse strains, within the range of antibody levels following inoculation. Interestingly, the high antibody response pattern seen in mice at 8 months of age was also seen in a robust manner in mice at ages 16, 24, and 32 months, as opposed to their low-responding counterparts which actually showed decreasing antibody response patterns in an age-dependent manner. In general, C57BL/6 mice had a more vigorous antibody response than CB6F1 mice. These observations suggest that age impacts the effectiveness of a pneumococcal vaccine in conferring an adaptive immune response, and that certain individual mice can robustly respond regardless of age. This high response pattern can thus be very valuable in determining if a robust antibody response is a resilience factor capable of predicting resistance to age-related decline. The concept is clinically relevant since pneumococcal vaccine, for example Prevnar-13, is routinely used to protect elderly populations, and sera can be readily available to test robustness of antibody responses in relation to aging related parameters.     

Dementia and learning impairment are associated with increasing age, and age-related diseases such as Alzheimer’s disease. There is evidence to suggest age-related cognitive decline is also associated with increased metabolic stress and disturbances in insulin signaling. Diets high in animal fat and table sugar are metabolically stressful, especially with increasing age, and place greater demands on mitochondrial bioenergetic machinery. This study was designed to show that a metabolically stressful diet would increase the severity of cognitive dysfunction in aging mice. Ten C57BL/6 male mice were fed a high fat and sugar (HFS) diet starting at 21 months of age. The diet consisted of 15% protein (casein), 58% fat (lard), and 27% carbohydrates (sucrose), as well as a vitamin and mineral mix. Nine mice were fed regular rodent chow (RC) diet, consisting of 24.5% protein (balanced amino acid mix), 13.1% fat (soy bean oil), 62.4% carbohydrates (28.2% starch and 3.25% sucrose), and a vitamin and mineral mix, for the same time period. Mice were weighed weekly and assessed for body fat using quantitative magnetic resonance imaging. After 7 weeks, mice were tested for learning impairment using a box maze paradigm. Mice on the HFS diet gained an average of 9.62 grams of body weight, with an average 18.7% increase in fat mass compared to mice on the RC diet. Mice on the RC diet showed moderate levels of learning impairment. Surprisingly, mice on the HFS diet showed very little learning impairment, suggesting that some component in the HFS diet had a sparing effect on cognitive decline. This observation may be unique to mice, and certainly requires additional studies, but still raises an intriguing implication for how clinicians and dieticians might consider alternative intervention strategies for cognitively impaired individuals.