Comparison between frail and non-frail older adults' gut microbiota: A systematic review and meta-analysis.

BACKGROUND: Emerging evidence suggests that the intestinal microbiota (IM) undergoes remodelling as we age, and this impacts the ageing trajectory and mortality in older adults. The aim was to investigate IM diversity differences between frail and non-frail older adults by meta-analysing previous studies. METHODS: The protocol of this systematic review with meta-analysis was registered on PROSPERO (CRD42021276733). We searched for studies comparing IM diversity of frail and non-frail older adults indexed on PubMed, Embase, Cochrane, and Web of Science in November 2021. RESULTS: We included 11 studies with 1239 participants, of which 340 were meta-analysed. Frailty was defined by a variety of criteria (i.e. Fried Scale, European Consensus on Sarcopenia). There were no differences in the meta-analyses between the frail and non-frail groups for species richness index (SMD = -0.147; 95% CI = -0.394, 0.100; p = 0.243) and species diversity index (SMD = -0.033; 95% CI = -0.315, 0.250; p = 0.820). However, we identified almost 50 differences between frail and non-frail within the relative abundance of bacteria phyla, families, genera, and species in the primary studies. CONCLUSIONS: The evidence to prove that there are differences between frail and non-frail IM diversity by meta-analysis is still lacking. The present results suggest that further investigation into the role of specific bacteria, their function, and their influence on the physiopathology of frailty is needed.

Innate and adaptive immune dysregulation in critically ill ICU patients.

This study aimed to evaluate whether ICU patients who developed persistent critical illness displayed an immune profile similar to an aged immune phenotype and any associations with patient outcomes. Twenty two critically ill ICU patients (27-76 years, 15 males), at day 5 of mechanical ventilation, and 22 healthy age-matched controls (27-77 years, 13 males) were recruited. Frequency and phenotype of innate and adaptive immune cells and telomere length in peripheral blood mononuclear cells (PBMCs) were measured. An elevated granulocyte count (p < 0.0001), increased numbers of immature granulocytes (p < 0.0001), increased CD16++ve monocytes (p = 0.003) and CD14+ve HLADRdim/low monocytes (p = 0.004) and lower NK cell numbers (p = 0.007) were observed in ICU patients compared to controls. Critically ill patients also had lower numbers of total T lymphocytes (p = 0.03), naïve CD4 T cells (p = 0.003) and PTK7+ve recent thymic emigrants (p = 0.002), and increased senescent CD28-ve CD57+ve CD4 T cells (p = 0.02), but there was no difference in PBMC telomere length. Regulatory immune cell frequency was affected with reduced circulating CD19+veCD24hiCD38hi regulatory B cells (p = 0.02). However, only a raised neutrophil:lymphocyte ratio and reduced frequency of CD14+ve HLADRdim/low monocytes were associated with poor outcomes. We conclude that persistent critical illness results in changes to immune cell phenotype only some of which are similar to that seen in physiological ageing of the immune system.

Major features of immunesenescence, including reduced thymic output, are ameliorated by high levels of physical activity in adulthood.

It is widely accepted that aging is accompanied by remodelling of the immune system including thymic atrophy and increased frequency of senescent T cells, leading to immune compromise. However, physical activity, which influences immunity but declines dramatically with age, is not considered in this literature. We assessed immune profiles in 125 adults (55-79 years) who had maintained a high level of physical activity (cycling) for much of their adult lives, 75 age-matched older adults and 55 young adults not involved in regular exercise. The frequency of naïve T cells and recent thymic emigrants (RTE) were both higher in cyclists compared with inactive elders, and RTE frequency in cyclists was no different to young adults. Compared with their less active counterparts, the cyclists had significantly higher serum levels of the thymoprotective cytokine IL-7 and lower IL-6, which promotes thymic atrophy. Cyclists also showed additional evidence of reduced immunesenescence, namely lower Th17 polarization and higher B regulatory cell frequency than inactive elders. Physical activity did not protect against all aspects of immunesenescence: CD28-ve CD57+ve senescent CD8 T-cell frequency did not differ between cyclists and inactive elders. We conclude that many features of immunesenescence may be driven by reduced physical activity with age.

Prehospital immune responses and development of multiple organ dysfunction syndrome following traumatic injury: A prospective cohort study.

BACKGROUND: Almost all studies that have investigated the immune response to trauma have analysed blood samples acquired post-hospital admission. Thus, we know little of the immune status of patients in the immediate postinjury phase and how this might influence patient outcomes. The objective of this study was therefore to comprehensively assess the ultra-early, within 1-hour, immune response to trauma and perform an exploratory analysis of its relationship with the development of multiple organ dysfunction syndrome (MODS). METHODS AND FINDINGS: The immune and inflammatory response to trauma was analysed in 89 adult trauma patients (mean age 41 years, range 18-90 years, 75 males) with a mean injury severity score (ISS) of 24 (range 9-66), from whom blood samples were acquired within 1 hour of injury (mean time to sample 42 minutes, range 17-60 minutes). Within minutes of trauma, a comprehensive leukocytosis, elevated serum pro- and anti-inflammatory cytokines, and evidence of innate cell activation that included neutrophil extracellular trap generation and elevated surface expression of toll-like receptor 2 and CD11b on monocytes and neutrophils, respectively, were observed. Features consistent with immune compromise were also detected, notably elevated numbers of immune suppressive CD16BRIGHT CD62LDIM neutrophils (82.07 x 106/l ± 18.94 control versus 1,092 x 106/l ± 165 trauma, p < 0.0005) and CD14+HLA-DRlow/- monocytes (34.96 x 106/l ± 4.48 control versus 95.72 x 106/l ± 8.0 trauma, p < 0.05) and reduced leukocyte cytokine secretion in response to lipopolysaccharide stimulation. Exploratory analysis via binary logistic regression found a potential association between absolute natural killer T (NKT) cell numbers and the subsequent development of MODS. Study limitations include the relatively small sample size and the absence of data relating to adaptive immune cell function. CONCLUSIONS: Our study highlighted the dynamic and complex nature of the immune response to trauma, with immune alterations consistent with both activation and suppression evident within 1 hour of injury. The relationship of these changes, especially in NKT cell numbers, to patient outcomes such as MODS warrants further investigation.

Development of depressive symptoms post hip fracture is associated with altered immunosuppressive phenotype in regulatory T and B lymphocytes.

Hip fracture is a common physical trauma in older adults that is also associated with a high incidence of new onset depression. The immune system declines with age and is also compromised by physical and psychological stress. This study examined whether hip fracture and depressive symptoms had additive effects upon the aged immune system that might contribute to poor health outcomes after hip fracture. We assessed the frequency of regulatory T cells, Tregs (CD4(+) CD25(+) Foxp3(+)) and IL10 production by CD4 T cells, and the frequency and IL10 production by regulatory B cells, Bregs (CD19(+) CD24(hi) CD38(hi)) in 101 hip fracture patients (81 female) 6 weeks after injury and 43 healthy age-matched controls (28 female). 38 hip fracture patients (37%) developed depressive symptoms. Hip fracture did not have an effect on circulating Tregs frequency but a significant reduction in the frequency of Bregs was observed in patients who developed depression compared with non-depressed patients (p = 0.001) or healthy controls (p < 0.001). Bregs also showed a significant decline in IL10 production in depressed hip fracture patients compared with controls (p = 0.04) and non-depressed patients (p = 0.01). In contrast, there was an increase in IL10 production by CD4 T cells in hip fracture patients with new onset depression compared to hip fracture patients without depression (p = .04) and healthy controls (p = .02). We conclude that the reduced immunity associated with new onset depression post hip fracture could include a contribution by heightened Tregs function.

NK cell immunesenescence is increased by psychological but not physical stress in older adults associated with raised cortisol and reduced perforin expression.

NK cell cytotoxicity (NKCC) reduces with age and this has been associated previously with increased mortality. The immune response is also modulated by stress, and here, we assessed the effect of the physical stress of hip fracture and the psychological stress of depression on NKCC in an aged immune system. NKCC was assessed in 101 hip fracture patients (81 female) 6 weeks and 6 months after injury and in 50 healthy age-matched controls (28 female). Thirty-eight patients were depressed at 6 weeks post-injury, and NKCC was reduced in patients who developed depression compared with non-depressed hip fracture patients (p = 0.004) or controls (p < 0.02). NKCC remained lower in the depressed patients compared to those without depression 6 months post-fracture (p = 0.017). We found reduced expression of perforin in NK cells of depressed hip fracture patients compared with controls at 6 weeks (p = 0.001) post-fracture. Serum cortisol levels were also elevated in patients with depression compared to non-depressed patients at 6 weeks (p = 0.01) and 6 months (p = 0.05). NK cells treated with dexamethasone showed a concentration-dependent reduction in NKCC and perforin expression. We propose that depression is the major factor affecting NK cell immunity after hip fracture.

Depressive symptoms in hip fracture patients are associated with reduced monocyte superoxide production.

Ageing is accompanied by reduced functioning of the immune system, termed immunesenescence which is associated with increased risk of infection and mortality. However the immune system does not operate in isolation and can be modified by many environmental factors, including stress. In this study we determined whether physical stress (hip fracture) and psychological distress (depressive symptoms) had additive effects upon the aged immune system, specifically on monocyte numbers and function. We assessed immune function in 101 hip fracture patients (81 female) 6weeks and 6months after injury and 43 healthy age matched controls (28 females). Thirty-eight of the hip fracture group were found to be depressed at the 6week sampling. No differences in peripheral monocyte count, distribution of monocyte subsets or TNFα secretion were observed between hip fracture patients and healthy controls. However we observed significantly reduced superoxide production in response to Escherichia coli in the monocytes of hip fracture patients who developed depressive symptoms compared with non-depressed hip fracture patients (p=0.002) or healthy controls (p=0.008) 6weeks after the fracture which remained decreased 6months following injury. In previous studies we have shown an effect of depression on neutrophil superoxide generation in hip fracture patients, suggesting a particular susceptibility of this aspect of immune cell function to psychological stress.

Depressive symptoms post hip fracture in older adults are associated with phenotypic and functional alterations in T cells.

BACKGROUND: Ageing is accompanied by reduced immunity, termed immunesenescence. The immune system does not act in isolation and is sensitive to both psychological and physical stress. Hip fracture is a common physical stressor in older adults with a high incidence of new onset depression, which relates to poorer prognosis. We therefore set out to examine the possible synergistic effects of physical stress (hip fracture) and psychological stress (depressive symptoms) on the aged immune system. RESULTS: T cell phenotype and function was assessed in 101 hip fracture patients (81 female) 6 weeks after hip fracture and 43 healthy age-matched controls (26 female). 38 fracture patients had depressive symptoms at 6 weeks. T cell frequency (p = .01) and numbers (p = .003) were both lower in depressed hip fracture patients compared to healthy controls. The frequency of senescent CD28(-ve) (p = .001), CD57(+ve) (p = .001), KLRG1(+ve) (p = .03) CD8 T cells, as well as senescent CD28(-ve) CD4(+ve) (p = .01) and CD57(+ve) CD4(+ve) (p = .003) T cells were higher in depressed hip fracture patients compared with healthy controls and the frequency of CD28(-ve) CD8 T cells was also higher when compared to patients with hip fracture alone (p = .01). Additionally, activated CD69(+ve) (p = .005) and HLADR(+ve) (p < .001) CD8 T cells, were also higher in depressed hip fracture patients compared to healthy controls. On examining cytokine production by activated T cells, a significant increase in TNFα (p = .03) and IL6 (p = .04) production was observed in CD4 T cells from hip fracture patients with depressive symptoms compared to healthy controls. CONCLUSIONS: As none of the patients in the study had a prior history of depression, our data suggest that the development of depressive symptoms in hip fracture patients is associated with altered T cell phenotype and increased pro-inflammatory function which is not seen in patients who do not develop depression after hip fracture. Treating depressive symptoms promptly in hip fracture patients may therefore improve immunity and outcomes in these patients.

Depressive symptoms are associated with reduced neutrophil function in hip fracture patients.

Hip fracture is a common trauma in older adults with a high incidence of depression, which relates to poorer prognosis including increased risk of infection. Ageing is accompanied by reduced immunity, termed immunesenescence, resulting in increased susceptibility to infection. We examined whether physical trauma (hip fracture) and psychological distress (depressive symptoms) had additive effects upon the aged immune system that might contribute to poor outcomes after injury. Neutrophil function was assessed in 101 hip fracture patients (81 female) 6 weeks and 6 months after injury and 43 healthy age-matched controls (28 female). Thirty eight fracture patients had depressive symptoms at 6 weeks. No difference in neutrophil phagocytosis of Escherichia coli was observed between controls and hip fracture patients, but superoxide production was significantly reduced in hip fracture patients with depressive symptoms compared with patients without symptoms (p=.001) or controls (p=.004) at 6 weeks. Superoxide production improved 6 months following fracture to the level seen in controls. We detected elevated serum cortisol, reduced dehydroepiandrosterone sulphate (DHEAS) and an increased cortisol:DHEAS ratio in fracture patients with depressive symptoms compared with patients without depressive symptoms or controls at 6 weeks and 6 months after injury. Serum IL6, TNFα and IL10 were higher among patients with depressive symptoms at 6 weeks. The cortisol:DHEAS ratio and IL6 levels related to depressive symptom scores but not to neutrophil function. In conclusion, depressive symptoms related to poorer neutrophil function after hip fracture, but this was not driven by changes in stress hormone or cytokine levels.

Depression following hip fracture is associated with increased physical frailty in older adults: the role of the cortisol: dehydroepiandrosterone sulphate ratio.

BACKGROUND: Hip fracture in older adults is associated with depression and frailty. This study examined the synergistic effects of depression and hip fracture on physical frailty, and the mediating role of the cortisol:dehydroepiandrosterone sulphate (DHEAS) ratio. METHODS: This was an observational longitudinal study of patients with a hip fracture carried out in a hospital setting and with follow up in the community. Participants were 101 patients aged 60+ years (81 female) with a fractured neck of femur. Measurements of the ability to carry out activities of daily living (ADL), cognitive function, physical frailty and assays for serum cortisol and DHEAS were performed six weeks and six months post-hip fracture. Depressed and non-depressed groups were compared by ANOVA at each time point. RESULTS: Hip fracture patients who developed depression by week six (n = 38) had significantly poorer scores on ADL and walking indices of frailty at both week six and month six, and poorer balance at week six. The association with slower walking speed was mediated by a higher cortisol:DHEAS ratio in the depressed group. CONCLUSION: Depression following hip fracture is associated with greater physical frailty and poorer long term recovery post-injury. Our data indicate that the underlying mechanisms may include an increased cortisol:DHEAS ratio and suggest that correcting this ratio for example with DHEA supplementation could benefit this patient population.