Role of inflammation and cellular stress in brain injury and central nervous system diseases

Role of astroglia in diet-induced central neuroplasticity

Obesity, characterized by increased adiposity that develops when energy intake outweighs expenditure, is rapidly becoming a serious health crisis that affects millions of people worldwide and is associated with severe comorbid disorders including hypertension, cardiovascular disease, and type II diabetes. Obesity is also associated with the dysregulation of central neurocircuits involved in the control of autonomic, metabolic, and cognitive functions. Systemic inflammation associated with diet-induced obesity (DIO) has been proposed to be responsible for the development of these comorbidities as well as the dysregulation of central neurocircuits. A growing body of evidence suggests, however, that exposure to a high-fat diet (HFD) may cause neuroinflammation and astroglial activation even before systemic inflammation develops, which may be sufficient to cause dysregulation of central neurocircuits involved in energy homeostasis before the development of obesity. The purpose of this review is to summarize the current literature exploring astroglial-dependent modulation of central circuits following exposure to HFD and DIO, including not only dysregulation of neurocircuits involved in energy homeostasis and feeding behavior, but also the dysregulation of learning, memory, mood, and reward pathways.

Endogenous repair signaling after brain injury and complementary bioengineering approaches to enhance neural regeneration

Traumatic brain injury (TBI) affects 5.3 million Americans annually. Despite the many long-term deficits associated with TBI, there currently are no clinically available therapies that directly address the underlying pathologies contributing to these deficits. Preclinical studies have investigated various therapeutic approaches for TBI: two such approaches are stem cell transplantation and delivery of bioactive factors to mitigate the biochemical insult affiliated with TBI. However, success with either of these approaches has been limited largely due to the complexity of the injury microenvironment. As such, this review outlines the many factors of the injury microenvironment that mediate endogenous neural regeneration after TBI and the corresponding bioengineering approaches that harness these inherent signaling mechanisms to further amplify regenerative efforts.

Transplantation of mesenchymal stem cells to the brain by topical application in an experimental traumatic brain injury model

Mesenchymal stem cells (MSCs) have been shown in various animal models to be capable of neurorepair and neuroprotection. To carry out a therapeutic function, MSCs must be delivered to the target organ. MSCs are administered to patients via systemic infusion, which has many drawbacks, including a low engraftment rate and the migration of MSCs to non-target organs. However, other approaches such as direct intracerebral injection of MSCs might cause cerebral bleeding. In this study, a traumatic brain injury (TBI) was induced over the right parietal cerebral cortex in Sprague Dawley rats, and green fluorescent protein (GFP)-expressing MSCs (GFP-MSCs), together with a thin layer of fibrin, were applied to the external surface of the contralateral side 2 days later. Within 5 days of topical application, the GFP-MSCs had migrated from the site of application on the cortical surface, through the white matter, and had emerged at the cortical surface of the TBI site on the contralateral cerebral hemisphere, apparently following axons along the corpus callosum. In sham-injured control animals, the topically applied GFP-MSCs proliferated superficially on the cortex at the site of application, and no GFP-MSCs were found at the contralateral cortical surface. In all instances, GFP-MSCs were not detected in other organs of either the test or the control animals. Our study demonstrated that MSCs topically applied to the brain surface can migrate to a TBI site.

Attenuated inflammatory response in aged mice brains following stroke

Background

Increased age is a major risk factor for stroke incidence, post-ischemic mortality, and severe and long-term disability. Stroke outcome is considerably influenced by post-ischemic mechanisms. We hypothesized that the inflammatory response following an ischemic injury is altered in aged organisms.

Methods and Results

To that end, we analyzed the expression pattern of pro-inflammatory cytokines (TNF, IL-1α, IL-1β, IL-6), anti-inflammatory cytokines (IL-10, TGFβ1), and chemokines (Mip-1α, MCP-1, RANTES) of adult (2 months) and aged (24 months) mice brains at different reperfusion times (6 h, 12 h, 24 h, 2 d, 7 d) following transient occlusion of the middle cerebral artery. The infarct size was assessed to monitor possible consequences of an altered inflammatory response in aged mice. Our data revealed an increased neuro-inflammation with age. Above all, we found profound age-related alterations in the reaction to stroke. The response of pro-inflammatory cytokines (TNF, and IL-1β) and the level of chemokines (Mip-1α, and MCP-1) were strongly diminished in the aged post-ischemic brain tissue. IL-6 showed the strongest age-dependent decrease in its post-ischemic expression profile. Anti-inflammatory cytokines (TGFβ1, and IL-10) revealed no significant age dependency after ischemia. Aged mice brains tend to develop smaller infarcts.

Conclusion

The attenuated inflammatory response to stroke in aged animals may contribute to their smaller infarcts. The results presented here highlight the importance of using aged animals to investigate age-associated diseases like stroke, and should be considered as a major prerequisite in the development of age-adjusted therapeutic interventions.

Involvement of kynurenines in Huntington's disease and stroke-induced brain damage

Several components of the kynurenine pathway of tryptophan metabolism are now recognised to have actions of profound biological importance. These include the ability to modulate the activation of glutamate and nicotinic receptors, to modify the responsiveness of the immune system to inflammation and infection, and to modify the generation and removal of reactive oxygen species. As each of these factors is being recognised increasingly as contributing to major disorders of the central nervous system (CNS), so the potentially fundamental role of the kynurenine pathway in those disorders is presenting a valuable target both for understanding the progress of those disorders and for developing potential drug treatments. This review will summarise some of the evidence for an important contribution of the kynurenines to Huntington's disease and to stroke damage in the CNS. Together with preliminary evidence from a study of kynurenine metabolites after major surgery, an important conclusion is that kynurenine pathway activation closely reflects cognitive function, and may play a significant role in cognitive ability.

Biochemical and immunopathological changes in experimental neurotoxocariasis

Toxocariasis is a widespread soil-transmitted parasitic disease. Toxocara canis larvae migrate through the tissues with a special predilection for the central nervous system. Recently, neurotoxocariasis is being diagnosed in humans with increasing frequency due to improved diagnostic tools. The present study aimed at exploring the biochemical and immunopathological alterations in the brain in experimental T. canis infection. For this purpose, 75 Toxocara-infected mice were sacrificed at 2, 5, and 16 weeks post-infection. The brains were removed and assayed for total larval count, pro-inflammatory cytokines (TNF-alpha, IL-6), and central neurotransmitters (gamma-aminobutyric acid, glutamate, dopamine, norepinephrine, and serotonin). Brain sections were also stained for histopathological study, and for assessment of the expression of inducible nitric oxide synthase (iNOS), and glial fibrillary acidic protein (GFAP) by immunohistochemical methods. We found that larval recovery showed progressive increase over the course of infection. Furthermore, the infected mice displayed increased expression of pro-inflammatory cytokines and iNOS, as well as significant disturbances in neurotransmitter profile. Astrocytic activation, evidenced by enhanced expression of GFAP, was also manifest in infected animals. These changes were maximal in the chronic stage of infection or intensified over time. In conclusion, experimental neurotoxocariasis is associated with significant biochemical, immunological, and pathological changes.

Differences of peripheral inflammatory markers between mild cognitive impairment and Alzheimer's disease

Multiple pathogenic factors may contribute to the pathophysiology of Alzheimer's disease (AD). Peripheral markers have been used to assess biochemical alterations associated with AD and mild cognitive impairment (MCI) involved in its pathophysiology. The present study was conducted to evaluate inflammatory peripheral markers in elderly patients with MCI, patients with AD and normal elderly subjects. We measured plasma levels of different cytokines (IL-6, TNF-alpha and IFN-alpha) and platelet levels of cyclooxigenase-2 (COX-2) from 34 patients with MCI, 45 patients with AD and 28 age-matched control subjects. MCI and AD patients showed similarities in TNF-alpha and COX-2 levels, and differences in IL-6 and INF-alpha. Whereas augmented IL-6 levels have been found in AD patients, a significant increase in INF-alpha has been detected only in patients with MCI possibly associated with the depression stage frequently found in cognitive impairment. In conclusion, inflammatory response may be an early factor in AD development and these changes in circulating markers are possibly related to the progression of MCI to AD.

Altered kynurenine metabolism correlates with infarct volume in stroke

Inflammation and oxidative stress are involved in brain damage following stroke, and tryptophan oxidation along the kynurenine pathway contributes to the modulation of oxidative stress partly via the glutamate receptor agonist quinolinic acid and antagonist kynurenic acid, and via redox-active compounds such as 3-hydroxyanthranilic acid. We have confirmed that following a stroke, patients show early elevations of plasma neopterin, S100B and peroxidation markers, the latter two correlating with infarct volume assessed from computed tomography (CT) scans, and being consistent with a rapid inflammatory response. We now report that the kynurenine pathway of tryptophan metabolism was also activated, with an increased kynurenine : tryptophan ratio, but with a highly significant decrease in the ratio of 3-hydroxyanthranilic acid : anthranilic acid, which was strongly correlated with infarct volume. Levels of kynurenic acid were significantly raised in patients who died within 21 days compared with those who survived. The results suggest that increased tryptophan catabolism is initiated before or immediately after a stroke, and is related to the inflammatory response and oxidative stress, with a major change in 3-hydroxyanthranilic acid levels. Together with previous evidence that inhibiting the kynurenine pathway reduces brain damage in animal models of stroke and cerebral inflammation, and that increased kynurenine metabolism directly promotes oxidative stress, it is proposed that oxidative tryptophan metabolism may contribute to the oxidative stress and brain damage following stroke. Some form of anti-inflammatory intervention between the rise of S100B and the activation of microglia, including inhibition of the kynurenine pathway, may be valuable in modifying patient morbidity and mortality.