The contribution of antibiotics, pneumonia and the immune response to stroke outcome

Top-Down and Bottom-Up Mechanisms of Motor Recovery Poststroke

Stroke remains a leading cause of disability. Motor recovery requires the interaction of top-down and bottom-up mechanisms, which reinforce each other. Injury to the brain initiates a biphasic neuroimmune process, which opens a window for spontaneous recovery during which the brain is particularly sensitive to activity. Physical activity during this sensitive period can lead to rapid recovery by potentiating anti-inflammatory and neuroplastic processes. On the other hand, lack of physical activity can lead to early closure of the sensitive period and downstream changes in muscles, such as sarcopenia, muscle stiffness, and reduced cardiovascular capacity, and blood flow that impede recovery.

New horizons in understanding oral health and swallowing function within the context of frailty

Frailty is a complex and multidimensional condition wherein declines in physiologic reserve and function place individuals in a state of heightened vulnerability and decreased resiliency. There has been growing interest in both research and clinical settings to understand how to best define, assess and characterise frailty in older adults. To this end, various models and clinical assessment tools have been used to define and measure frailty. While differences exist among these models and tools, a common unifying theme is a focus on physical function and activity. Notably absent across many available conceptual models and clinical tools are items directly related to oral and swallowing function. This is an important oversight as widespread changes to both oral and swallowing function are evident in older adults. Indeed, emerging evidence suggests many of the functional domains affected in frail older adults, such as nutrition and sarcopenia, have cyclical relationships with impairments in oral (oral hypofunction) and swallowing function (dysphagia) as well. The increasing appreciation for the interrelationships among oral hypofunction, dysphagia and frailty provides an opportunity for refinement of frailty assessment and characterisation in older adults to incorporate metrics specific to oral and swallowing function.

Cephalosporins-induced intestinal dysbiosis exacerbated pulmonary endothelial barrier disruption in streptococcus pneumoniae-infected mice

Antibiotic abuse is growing more severe in clinic, and even short-term antibiotic treatment can cause long-term gut dysbiosis, which may promote the development and aggravation of diseases. Cephalosporins as the broad-spectrum antibiotics are widely used for prevention and treatment of community-acquired respiratory tract infection in children. However, their potential consequences in health and disease have not been fully elaborated. In this study, the effects of cefaclor, cefdinir and cefixime on intestinal microbiota and lung injury were investigated in Streptococcus pneumoniae (Spn)-infected mice. The results showed that the proportion of coccus and bacillus in intestinal microbiota were changed after oral administration with cefaclor, cefdinir and cefixime twice for 10 days, respectively. Compared with the Spn-infected group, the proportion of Bifidobacterium and Lactobacillus in intestine were significantly reduced, while Enterococcus and Candida was increased after cephalosporin treatment. Furthermore, 3 cephalosporins could obviously increase the number of total cells, neutrophils and lymphocytes in BALF as well as the serum levels of endotoxin, IL-2, IL-1β, IL-6 and TNF-α. Mechanically, cephalosporins accelerated Spn-induced pulmonary barrier dysfunction via mediating the mRNA expressions of endothelial barrier-related proteins (Claudin 5, Occludin, and ZO-1) and inflammation-related proteins (TLR4, p38 and NF-κB). However, all of those consequences could be partly reversed by Bifidobacterium bifidum treatment, which was closely related to the elevated acetate production, indicating the protective effects of probiotic against antibiotic-induced intestinal dysbiosis. Therefore, the present study demonstrated that oral administration with cephalosporins not only disrupted intestinal microecological homeostasis, but also increased the risk of Spn infection, resulting in severer respiratory inflammation and higher bacterial loads in mice.

CD4+ T cells promote delayed B cell responses in the ischemic brain after experimental stroke

CD4⁺ T lymphocytes are key mediators of tissue damage after ischemic stroke. However, their infiltration kinetics and interactions with other immune cells in the delayed phase of ischemia remain elusive. We hypothesized that CD4⁺ T cells facilitate delayed autoreactive B cell responses in the brain, which have been previously linked to post-stroke cognitive impairment (PSCI). Therefore, we treated myelin oligodendrocyte glycoprotein T cell receptor transgenic 2D2 mice of both sexes with anti-CD4 antibody following 60-minute middle cerebral artery occlusion and assessed lymphocyte infiltration for up to 72 days. Anti-CD4-treatment eliminated CD4⁺ T cells from the circulation and ischemic brain for 28 days and inhibited B cell infiltration into the brain, particularly in animals with large infarcts. Absence of CD4⁺ T cells did not influence infarct maturation or survival. Once the CD4⁺ population recovered in the periphery, both CD4⁺ T and B lymphocytes entered the infarct site forming follicle-like structures. Additionally, we provide further evidence for PSCI that could be attenuated by CD4 depletion. Our findings demonstrate that CD4⁺ T cells are essential in delayed B cell infiltration into the ischemic brain after stroke. Importantly, lymphocyte infiltration after stroke is a long-lasting process. As CD4 depletion improved cognitive functions in an experimental set-up, these findings set the stage to elaborate more specific immune modulating therapies in treating PSCI.

Interaction of microglia with infiltrating immune cells in the different phases of stroke

Stroke, in association with its complications, is one of the leading causes of mortality and morbidity worldwide. Cerebral ischemia triggers an inflammatory response in the brain that is controlled by the activation of resident microglia as well as the infiltration of peripheral myeloid and lymphoid cells into the brain parenchyma. This inflammation has been shown to have both beneficial and detrimental effects on stroke outcome. The focus of this review lies on the functions of myeloid cells and their interaction with infiltrating lymphocytes in different phases of stroke. A detailed and time-specific understanding of the contribution of different immune cell subsets during the course of cerebral ischemia is crucial to specifically promote beneficial and inhibit detrimental effects of inflammation on stroke outcome.

Infection as a Stroke Risk Factor and Determinant of Outcome After Stroke

Understanding the relationship between infection and stroke has taken on new urgency in the era of the coronavirus disease 2019 (COVID-19) pandemic. This association is not a new concept, as several infections have long been recognized to contribute to stroke risk. The association of infection and stroke is also bidirectional. Although infection can lead to stroke, stroke also induces immune suppression which increases risk of infection. Apart from their short-term effects, emerging evidence suggests that poststroke immune changes may also adversely affect long-term cognitive outcomes in patients with stroke, increasing the risk of poststroke neurodegeneration and dementia. Infections at the time of stroke may also increase immune dysregulation after the stroke, further exacerbating the risk of cognitive decline. This review will cover the role of acute infections, including respiratory infections such as COVID-19, as a trigger for stroke; the role of infectious burden, or the cumulative number of infections throughout life, as a contributor to long-term risk of atherosclerotic disease and stroke; immune dysregulation after stroke and its effect on the risk of stroke-associated infection; and the impact of infection at the time of a stroke on the immune reaction to brain injury and subsequent long-term cognitive and functional outcomes. Finally, we will present a model to conceptualize the many relationships among chronic and acute infections and their short- and long-term neurological consequences. This model will suggest several directions for future research.

Antibiotic treatment for pneumonia complicating stroke: Recommendations from the pneumonia in stroke consensus (PISCES) group

Purpose

The microbiological aetiology of pneumonia complicating stroke is poorly characterised. In this second Pneumonia in Stroke ConsEnsuS statement, we propose a standardised approach to empirical antibiotic therapy in pneumonia complicating stroke, based on likely microbiological aetiology, to improve antibiotic stewardship.

Methods

Systematic literature searches of multiple databases were undertaken. An evidence review and a round of consensus consultation were completed prior to a final multi-disciplinary consensus meeting in September 2017, held in Barcelona, Spain. Consensus was approached using a modified Delphi technique and defined a priori as 75% agreement between the consensus group members.Findings: No randomised trials to guide antibiotic treatment of pneumonia complicating stroke were identified. Consensus was reached for the following: (1) Stroke-associated pneumonia may be caused by organisms associated with either community-acquired or hospital-acquired pneumonia; (2) Treatment for early stroke-associated pneumonia (<72 h of stroke onset) should cover community-acquired pneumonia organisms; (3) Treatment for late stroke-associated pneumonia (≥72 h and within seven days of stroke onset) should cover community-acquired pneumonia organisms plus coliforms +/- Pseudomonas spp. if risk factors; (4) No additional antimicrobial cover is required for patients with dysphagia or aspiration; (5) Pneumonia occurring after seven days from stroke onset should be treated as for hospital-acquired pneumonia; (6) Treatment should continue for at least seven days for each of these scenarios.

Discussion

Consensus recommendations for antibiotic treatment of the spectrum of pneumonia complicating stroke are proposed. However, there was limited evidence available to formulate consensus on choice of specific antibiotic class for pneumonia complicating stroke.

Conclusion

Further studies are required to inform evidence-based treatment of stroke-associated pneumonia including randomised trials of antibiotics and validation of candidate biomarkers.

Antibiotic Class and Outcome in Post-stroke Infections: An Individual Participant Data Pooled Analysis of VISTA-Acute

Introduction: Antibiotics used to treat post-stroke infections have differing antimicrobial and anti-inflammatory effects. Our aim was to investigate whether antibiotic class was associated with outcome after post-stroke infection. Methods: We analyzed pooled individual participant data from the Virtual International Stroke Trials Archive (VISTA)-Acute. Patients with ischemic stroke and with an infection treated with systemic antibiotic therapy during the first 2 weeks after stroke onset were eligible. Antibiotics were grouped into eight classes, according to antimicrobial mechanism and prevalence. The primary analysis investigated whether antibiotic class for any infection, or for pneumonia, was independently associated with a shift in 90 day modified Rankin Scale (mRS) using ordinal logistic regression. Results: 2,708 patients were eligible (median age [IQR] = 74 [65 to 80] y; 51% female; median [IQR] NIHSS score = 15 [11 to 19]). Pneumonia occurred in 35%. Treatment with macrolides (5% of any infections; 9% of pneumonias) was independently associated with more favorable mRS distribution for any infection [OR (95% CI) = 0.59 (0.42 to 0.83), p = 0.004] and for pneumonia [OR (95% CI) = 0.46 (0.29 to 0.73), p = 0.001]. Unfavorable mRS distribution was independently associated with treatment of any infection either with carbapenems, cephalosporins or monobactams [OR (95% CI) = 1.62 (1.33 to 1.97), p < 0.001], penicillin plus β-lactamase inhibitors [OR (95% CI) = 1.26 (1.03 to 1.54), p = 0.025] or with aminoglycosides [OR (95% CI) = 1.73 (1.22 to 2.46), p = 0.002]. Conclusion: This retrospective study has several limitations including effect modification and confounding by indication. Macrolides may have favorable immune-modulatory effects in stroke-associated infections. Prospective evaluation of the impact of antibiotic class on treatment of post-stroke infections is warranted.

Chemical Sympathectomy, but not Adrenergic Blockade, Improves Stroke Outcome

BACKGROUND

A robust adrenergic response following stroke impairs lymphocyte function, which may prevent the development of autoimmune responses to brain antigens. We tested whether inhibition of the sympathetic response after stroke would increase the propensity for developing autoimmune responses to brain antigens.

METHODS

Male Lewis rats were treated with 6-hydroxydopamine (OHDA) prior to middle cerebral artery occlusion (MCAO), labetalol after MCAO, or appropriate controls. Behavior was assessed weekly and animals survived to 1 month at which time ELISPOT assays were done on lymphocytes from spleen and brain to determine the Th1 and Th17 responses to myelin basic protein (MBP), ovalbumin (OVA), and concanavalin A. A subset of animals was sacrificed 72 hours after MCAO for evaluation of infarct volume and lymphocyte responsiveness. Plasma C-reactive protein (CRP) was measured as a biomarker of systemic inflammation.

RESULTS

Despite similar initial stroke severity and infarct volumes, 6-OHDA-treated animals lost less weight and experienced less hyperthermia after stroke. 6-OHDA-treated animals also had decreased CRP in circulation early after stroke and experienced better neurological outcomes at 1 month. The Th1 and Th17 responses to MBP did not differ among treatment groups at 1 month, but the Th1 response to OVA in spleen was more robust in labetalol and less robust in 6-OHDA-treated animals.

CONCLUSIONS

Chemical sympathectomy with 6-OHDA, but not treatment with labetalol, decreased systemic markers of inflammation early after stroke and improved long-term outcome. An increase in Th1 and Th17 responses to MBP was not seen with inhibition of the sympathetic response.

Preventive Antibiotics for Poststroke Infection in Patients With Acute Stroke: A Systematic Review and Meta-analysis

AIMS

To determine if preventive antibiotics is effective in poststroke infection in patients with acute stroke in comparison with no prophylaxis.

MATERIALS AND METHODS

MEDLINE (1950 to January 2017), the Cochrane Central Register of Controlled Trials (CENTRAL, The Cochrane Library, Issue 1, 2017) and EMBASE (1974 to January 2017) databases were used to search for randomized controlled trials with intervening measures related to the preventive antibiotics in patients with acute stroke. Besides, the reference lists of the retrieved publications were manually searched to explore other relevant studies.

RESULTS

We included 6 randomized controlled trials involving 4110 stroke patients. The study population, study design, intervening measures, and definition of infection were different. Preventive antibiotics significantly reduced the incidence of algorithm-defined infection in patients with acute stroke from 11.14% (220/1975) to 7.43% (149/2006); odds ratio (OR)=0.41; 95% confidence interval (CI), 0.20-0.87; P=0.02. There was no difference in mortality between 2 groups, the mortality in preventive antibiotics group was 17.03% (347/2037) and control group was 16.10% (328/2037); OR=1.07; 95% CI, 0.90-1.27; P=0.44. And preventive antibiotics did not improve the proportion of good outcome, the proportion of good outcome in preventive antibiotics group was 45.47% (909/1999) and control group was 45.76% (913/1995); OR=0.89; 95% CI, 0.62-1.28; P=0.53. None of the studies reported severe adverse relevant to the study antibiotics.

CONCLUSIONS

Preventive antibiotics significantly reduced the incidence of algorithm-defined infection in patients with acute stroke, but did not decrease the mortality or improve the proportion of good outcome. Future research should aim to identify the group of stroke patients who will benefit most from antibiotic prophylaxis.

No effects without causes: the Iron Dysregulation and Dormant Microbes hypothesis for chronic, inflammatory diseases

Since the successful conquest of many acute, communicable (infectious) diseases through the use of vaccines and antibiotics, the currently most prevalent diseases are chronic and progressive in nature, and are all accompanied by inflammation. These diseases include neurodegenerative (e.g. Alzheimer's, Parkinson's), vascular (e.g. atherosclerosis, pre-eclampsia, type 2 diabetes) and autoimmune (e.g. rheumatoid arthritis and multiple sclerosis) diseases that may appear to have little in common. In fact they all share significant features, in particular chronic inflammation and its attendant inflammatory cytokines. Such effects do not happen without underlying and initially 'external' causes, and it is of interest to seek these causes. Taking a systems approach, we argue that these causes include (i) stress-induced iron dysregulation, and (ii) its ability to awaken dormant, non-replicating microbes with which the host has become infected. Other external causes may be dietary. Such microbes are capable of shedding small, but functionally significant amounts of highly inflammagenic molecules such as lipopolysaccharide and lipoteichoic acid. Sequelae include significant coagulopathies, not least the recently discovered amyloidogenic clotting of blood, leading to cell death and the release of further inflammagens. The extensive evidence discussed here implies, as was found with ulcers, that almost all chronic, infectious diseases do in fact harbour a microbial component. What differs is simply the microbes and the anatomical location from and at which they exert damage. This analysis offers novel avenues for diagnosis and treatment.

Emerging Role of Immunity in Cerebral Small Vessel Disease

Cerebral small vessel disease (CSVD) is one of the main causes of vascular dementia in older individuals. Apart from risk containment, efforts to prevent or treat CSVD are ineffective due to the unknown pathogenesis of the disease. CSVD, a subtype of stroke, is characterized by recurrent strokes and neurodegeneration. Blood-brain barrier (BBB) impairment, chronic inflammatory responses, and leukocyte infiltration are classical pathological features of CSVD. Understanding how BBB disruption instigates inflammatory and degenerative processes may be informative for CSVD therapy. Antigens derived from the brain are found in the peripheral blood of lacunar stroke patients, and antibodies and sensitized T cells against brain antigens are also detected in patients with leukoaraiosis. These findings suggest that antigen-specific immune responses could occur in CSVD. This review describes the neurovascular unit features of CSVD, the immune responses to specific neuronal and glial processes that may be involved in a distinct mechanism of CSVD, and the current evidence of the association between mechanisms of inflammation and interventions in CSVD. We suggest that autoimmune activity should be assessed in future studies; this knowledge would benefit the development of effective therapeutic interventions in CSVD.