Cognitive dysfunction in Duchenne muscular dystrophy: a possible role for neuromodulatory immune molecules

Duchenne muscular dystrophy (DMD) is an X chromosome-linked disease characterized by progressive physical disability, immobility, and premature death in affected boys. Underlying the devastating symptoms of DMD is the loss of dystrophin, a structural protein that connects the extracellular matrix to the cell cytoskeleton and provides protection against contraction-induced damage in muscle cells, leading to chronic peripheral inflammation. However, dystrophin is also expressed in neurons within specific brain regions, including the hippocampus, a structure associated with learning and memory formation. Linked to this, a subset of boys with DMD exhibit nonprogressing cognitive dysfunction, with deficits in verbal, short-term, and working memory. Furthermore, in the genetically comparable dystrophin-deficient mdx mouse model of DMD, some, but not all, types of learning and memory are deficient, and specific deficits in synaptogenesis and channel clustering at synapses has been noted. Little consideration has been devoted to the cognitive deficits associated with DMD compared with the research conducted into the peripheral effects of dystrophin deficiency. Therefore, this review focuses on what is known about the role of full-length dystrophin (Dp427) in hippocampal neurons. The importance of dystrophin in learning and memory is assessed, and the potential importance that inflammatory mediators, which are chronically elevated in dystrophinopathies, may have on hippocampal function is also evaluated.

Towards a cognitive neurobiology of brain-gut axis disorders

The past two decades have seen substantial gains in our understanding of the complex processes underlying disturbed brain-gut communication in disorders such as irritable bowel syndrome (IBS) and inflammatory bowel disease (IBD). Despite a growing understanding of the neurobiology of brain-gut axis dysfunction, there is a relative paucity of investigations into how the various factors involved in dysregulating the brain-gut axis, including stress, immune activation and pain, could impact on fundamental brain processes such as cognitive performance. To this end, we proposed a cognitive neurobiology of brain-gut axis dysfunction and took a novel approach to examine how disturbed brain-gut interactions may manifest as altered cognitive performance in IBS and IBD, both cross-sectionally and prospectively. We have demonstrated that, disorders of the brain-gut axis are characterised by stable deficits in specific cognitive domains. Specifically, patients with IBS exhibit a consistent hippocampal mediated visuospatial memory impairment. In addition we have found evidence to suggest a similar visuospatial impairment in IBD. However, our most consistent finding within this population was that patients with Crohn’s disease exhibit impaired selective attention/ response inhibition on the classic Stroop interference test. These cognitive deficits may serve to perpetuate and sustain brain-gut axis dysfunction. Furthermore, this research has shed light on some of the underlying neurobiological mechanisms that may be mediating cognitive dysfunction in IBS. Our findings may have significant implications for the individual who suffers from a brain-gut axis disorder and may also inform future treatment strategies. Taken together, these findings can be incorporated into existing neurobiological models of brain-gut axis dysfunction, to develop a more comprehensive model accounting for the cognitive-neurobiology of brain-gut axis disorders. This has furthered our understanding of disease pathophysiology and may ultimately aid in both the diagnosis and treatment of these highly prevalent, but poorly understood disorders.

Growing up in a bubble: using germ-free animals to assess the influence of the gut microbiota on brain and behavior

There is a growing recognition of the importance of the commensal intestinal microbiota in the development and later function of the central nervous system. Research using germ-free mice (mice raised without any exposure to microorganisms) has provided some of the most persuasive evidence for a role of these bacteria in gut-brain signalling. Key findings show that the microbiota is necessary for normal stress responsivity, anxiety-like behaviors, sociability, and cognition. Furthermore, the microbiota maintains central nervous system homeostasis by regulating immune function and blood brain barrier integrity. Studies have also found that the gut microbiota influences neurotransmitter, synaptic, and neurotrophic signalling systems and neurogenesis. The principle advantage of the germ-free mouse model is in proof-of-principle studies and that a complete microbiota or defined consortiums of bacteria can be introduced at various developmental time points. However, a germ-free upbringing can induce permanent neurodevelopmental deficits that may deem the model unsuitable for specific scientific queries that do not involve early-life microbial deficiency. As such, alternatives and complementary strategies to the germ-free model are warranted and include antibiotic treatment to create microbiota-deficient animals at distinct time points across the lifespan. Increasing our understanding of the impact of the gut microbiota on brain and behavior has the potential to inform novel management strategies for stress-related gastrointestinal and neuropsychiatric disorders.

Cancer related fatigue and self-care while undergoing chemotherapy: patients' perspectives

Background: Cancer related fatigue (CRF) is considered the most severe, debilitating and under-managed symptom of cancer. Patients receiving chemotherapy experience high levels of CRF which profoundly impacts on their lives. Aim: 1). To explore and measure CRF and determine the most effective self-care strategies used to combat CRF in a cohort of patients with a diagnosis of cancer (breast cancer, colorectal cancer, Hodgkin’s and Non-Hodgkin’s lymphoma) 2). To explore self-care agency and its relationship to CRF. Method: A mixed methods study which incorporated a descriptive, comparative, correlational design and qualitative descriptions of patients’ (n=362) experiences gleaned through open ended questions and use of a diary. The study utilised The Revised Pipers Fatigue Scale, the Appraisal of Self-Care Agency and a researcher developed Fatigue Visual Analogue Scale, Fatigue Self-Care Survey, and Diary. Findings: Having breast cancer, Hodgkin’s lymphoma, non-Hodgkin’s lymphoma; using the strategies of counselling, taking a 20–30 minute nap, resting and sleeping, self-monitoring and complementary therapies were all associated with increased odds of developing fatigue. Increased self-care agency; being in the divorced / separated cohort; being widowed; increased length of time since commencement of chemotherapy; engagement in exercise, and socializing were associated with a reduced risk of developing fatigue. Females had 20% higher fatigue levels than males (p=<.001). Receiving support was the strategy used most frequently and rated most effective. Fatigue was very problematic and distressing, four key qualitative categories emerged: the behavioural impact, affective impact, the sensory impact, and the cognitive impact. Keeping a diary was considered very beneficial and cathartic. Conclusions: Fatigue severely impacted on the daily lives of patients undergoing chemotherapy. There are a range of self-care strategies that patients should be encouraged to use e.g. exercise, socializing, and enhancement of psychological well-being. The enhancement of self-care agency and use of diaries should also be considered.

The gut microbiota as a contributing factor to antipsychotic-induced weight gain and metabolic dysfunction

Schizophrenia represents one of the world’s most devastating illnesses due to its often lifelong course and debilitating nature. The treatment of schizophrenia has vastly improved over recent decades with the discovery of several antipsychotic compounds; however these drugs are not without adverse effects that must be addressed to maximize their therapeutic value. Newer, atypical, antipsychotics are associated with a compilation of serious metabolic side effects including weight gain, insulin resistance, fat deposition, glucose dysregulation and ensuing co-morbidities such as type II diabetes mellitus. The mechanisms underlying these side effects remain to be fully elucidated and adequate interventions are lacking. Further understanding of the factors that contribute these side effects is therefore required in order to develop effective adjunctive therapies and to potentially design antipsychotic drugs in the future with reduced impact on the metabolic health of patients. We investigated if the gut microbiota represented a novel mechanism contributing to the metabolic dysfunction associated with atypical antipsychotics. The gut microbiota comprises the bacteria that exist symbiotically within the gastrointestinal tract, and has been shown in recent years to be involved in several aspects of energy balance and metabolism. We have demonstrated that administration of certain antipsychotics in the rat results in an altered microbiota profile and, moreover, that the microbiota is required for the full scale of metabolic dysfunction to occur. We have further shown that specific antibiotics can attenuate certain aspects of olanzapine and risperidone–induced metabolic dysfunction, in particular fat deposition and adipose tissue inflammation. Mechanisms underlying this novel link appear to involve energy utilization via expression of lipogenic genes as well as reduced inflammatory tone. Taken together, these data indicate that the gut microbiota is an important factor involved in the myriad of metabolic complications associated with antipsychotic therapy. Furthermore, these data support the future investigation of microbial-based therapeutics for not only antipsychotic-induced weight gain but also for tackling the global obesity epidemic.

Akt signal transduction dysfunction in the 3xTg-AD mouse model of Alzheimer's disease

Alzheimer’s disease (AD) is an incurable neurodegenerative disorder, accounting for over 60% of all cases of dementia. The primary risk factor for AD is age, however several genetic and environmental factors are also involved. The pathological characteristics of AD include extracellular deposition of the beta-amyloid peptide (Aβ) and intraneuronal accumulation of neurofibrillary tangles (NFTs) made of aggregated paired helical filaments (PHFs) of the hyperphosphorylated tau protein, along with synaptic loss and neuronal death. There are numerous biochemical mechanisms involved in AD pathogenesis, however the reigning hypothesis points to toxic oligomeric Aβ species as the primary causative factor in a cascade of events leading to neuronal stress and dyshomeostasis that initiate abnormal regulation of tau. The insulin and IGF-1 receptors (IR, IGF-1R) are the primary activators of PI3- K/Akt through which they regulate cell growth, development, glucose metabolism, and learning and memory. Work in our lab and others shows increased Akt activity and phosphorylation of its downstream targets in AD brain, along with insulin and insulin-like growth factor-1 signalling (IIS) dysfunction. This is supported by studies of AD models in vivo and in vitro. Our group and others hypothesise that Aβ activates Akt through IIS to initiate a negative feedback mechanism that desensitises neurons to insulin/IGF-1, and sustains activation of Akt. In this study the functions of endogenous Akt, IR, and the insulin receptor substrate (IRS-1) were examined in relationship to Aβ and tau pathology in the 3xTg-AD mouse model, which contains three mutant human transgenes associated with familial AD or dementia. The 3xTg-AD mouse develops Aβ and tau pathology in a spatiotemporal manner that best recapitulates the progression of AD in human brain. Western blotting and immunofluorescent microscopy techniques were utilised in vivo and in vitro, to examine the relationship between IIS, Akt, and AD pathology. I first characterised in detail AD pathology in 3xTg-AD mice, where an age-related accumulation of intraneuronal Aβ and tau was observed in the hippocampal formation, amygdala, and entorhinal cortex, and at late stages (18 months), extracellular amyloid plaques and NFTs, primarily in the subiculum and the CA1 layer of the hippocampal formation. Increased activity of Akt, detected with antibody to phosphoSer473-Akt, was increased in 3xTg-AD mice compared to age-matched non-transgenic mice (non-Tg), and in direct correlation to the accumulation of Aβ and tau in neuronal somatodendritic compartments. Akt phosphorylates tau at residue Ser214 within a highly specific consensus sequence for Akt phosphorylation, and phosphoSer214-tau strongly decreases microtubule (MT) stabilisation by preventing tau-MT binding. PhosphoSer214-tau increased concomitantly with this in the same age-related and region-specific fashion. Polarisation of tau phosphorylation was observed, where PHF-1 (tauSer396/404) and phosphoSer214-tau both appeared early in 3xTg-AD mice in distinct neuronal compartments: PHF-1 in axons, and phosphoSer214-tau in neuronal soma and dendrites. At 18 months, phosphoSer214-tau strongly colocalised with NFTs positive for the PHF- 1 and AT8 (tauSer202/Thr205) phosphoepitopes. IR was decreased with age in 3xTg-AD brain and in comparison to age-matched non-Tg, and this was specific for brain regions containing Aβ, tau, and hyperactive Akt. IRS-1 was similarly decreased, and both proteins showed altered subcellular distribution. Phosphorylation of IRS-1Ser312 is a strong indicator of IIS dysfunction and insulin resistance, and was increased in 3xTg-AD mice with age and in relation to pathology. Of particular note was our observation that abberant IIS and Akt signalling in 3xTg-AD brain related to Aβ and tau pathology on a gross anatomical level, and specifically localised to the brain regions and circuitry of the perforant path. Finally, I conducted a preliminary study of the effects of synthetic Aβ oligomers on embryonic rat hippocampus neuronal cultures to support these results and those in the literature. Taken together, these novel findings provide evidence for IIS and Akt signal transduction dysfunction as the missing link between Aβ and tau pathogenesis, and contribute to the overall understanding of the biochemical mechanisms of AD.

Cancer associated malnutrition: prevalence of cachexia, sarcopenia and impact on treatment outcomes, survival and health related quality of life

Malnutrition, sarcopenia and cancer cachexia (CC) are prevalent among cancer patients and can have detrimental effects on clinical outcomes such as quality of life (QoL) and overall survival. Cachexia is associated with lower tolerance for chemotherapy, which limits the total dose that can be delivered, the number of symptomatic responses and any survival advantage that might be accrued. Moreover, for the majority who do not respond, cachexia may be exacerbated by systemic chemotherapy, thus increasing the net symptom burden experienced by patients. The multitude of interactions between cancer location, treatments, nutritional status and QoL has never been thoroughly explored in an Irish cancer cohort. The objectives of this thesis were to further understand nutritional status, especially body composition in ambulatory cancer patients and determine the relationship between nutritional status using different assessment criteria and QoL, chemotherapy toxicity and survival among cancer patients undergoing chemotherapy. Results aimed to identify baseline factors that may be predictive of poor outcome, toxicities to chemotherapy and disease-free and overall survival. This thesis broadly divides into two sections. The first section (Chapters 3 & 4) focuses on improving our knowledge of the nutritional status of Irish cancer outpatients using a cross sectional study design. A study of 517 patients referred for chemotherapy was conducted using computed tomography (CT) imaging (body composition) and a survey that documented oncologic data, weight loss (WL) data and QoL data. We revealed that a significant proportion of Irish cancer patients undergoing chemotherapy experience unintentional WL over the previous 6 months (62%), sarcopenia (45%) and CC (43%), and the distribution of WL and nutritional risk were associated with site of primary tumour and treatment intent. Patients that had sarcopenia, nutritional risk, or CC had significantly reduced functional abilities, more symptoms and adverse global QoL. In the second section of this thesis (Chapters 5 & 6) the potential link between developing toxicity to antineoplastic regimens in patients with sarcopenia was conducted by way of retrospective studies. A retrospective serial CT analysis defined the prevalence of sarcopenia in patients with metastatic renal cell carcinoma (mRCC) and metastatic castrate resistant prostate cancer (mCRPC), which was then correlated with dose limiting toxicities of sunitinib and docetaxel respectively. Sarcopenia was prevalent in patients with mRCC and mCRPC, was an occult condition in patients with normal/high BMI, was associated with less treatment days, was a significant predictor of DLT in patients receiving sunitinib and a significant predictor of neutropenia and neurosensory toxicities in patients receiving docetaxel. This thesis attempted to address the underlying research deficiencies in Irish oncology nutritional data at national level. The findings from this thesis have implications for the planning of cancer care interventions and indicate that further research is required to improve nutritional screening, in particular for CC and sarcopenia, in the hope that timely intervention can improve both patient-centered and oncologic outcomes.

Lost in translation? The potential psychobiotic Lactobacillus rhamnosus (JB-1) fails to modulate stress or cognitive performance in healthy male subjects

Background: Preclinical studies have identified certain probiotics as psychobiotics a live microorganisms with a potential mental health benefit. Lactobacillus rhamnosus (JB-1) has been shown to reduce stress-related behaviour, corticosterone release and alter central expression of GABA receptors in an anxious mouse strain. However, it is unclear if this single putative psychobiotic strain has psychotropic activity in humans. Consequently, we aimed to examine if these promising preclinical findings could be translated to healthy human volunteers. Objectives: To determine the impact of L. rhamnosus on stress-related behaviours, physiology, inflammatory response, cognitive performance and brain activity patterns in healthy male participants. An 8 week, randomized, placebo-controlled, cross-over design was employed. Twenty-nine healthy male volunteers participated. Participants completed self-report stress measures, cognitive assessments and resting electroencephalography (EEG). Plasma IL10, IL1β, IL6, IL8 and TNFα levels and whole blood Toll-like 4 (TLR-4) agonist-induced cytokine release were determined by multiplex ELISA. Salivary cortisol was determined by ELISA and subjective stress measures were assessed before, during and after a socially evaluated cold pressor test (SECPT). Results: There was no overall effect of probiotic treatment on measures of mood, anxiety, stress or sleep quality and no significant effect of probiotic over placebo on subjective stress measures, or the HPA response to the SECPT. Visuospatial memory performance, attention switching, rapid visual information processing, emotion recognition and associated EEG measures did not show improvement over placebo. No significant anti-inflammatory effects were seen as assessed by basal and stimulated cytokine levels. Conclusions: L. rhamnosus was not superior to placebo in modifying stress-related measures, HPA response, inflammation or cognitive performance in healthy male participants. These findings highlight the challenges associated with moving promising preclinical studies, conducted in an anxious mouse strain, to healthy human participants. Future interventional studies investigating the effect of this psychobiotic in populations with stress-related disorders are required.