There is increasing evidence suggesting that chronic neuroinflammation is the most relevant pathological feature of Alzheimer’s disease (AD), regulating other pathological features, such as the accumulation of amyloid-β (Aβ) and hyperphosphorylation of Tau. Systemic inflammatory signals caused by systemic disorders are known to strongly influence neuroinflammation as a consequence of microglial activation, inflammatory mediator production, and the recruitment of peripheral immune cells to the brain, resulting in neuronal dysfunction.
Neurodegenerative diseases such as Alzheimer’s disease (AD), Parkinson’s disease (PD), and Multiple Sclerosis (MS) are characterized by neuronal degeneration and neuronal death in specific regions of the central nervous system. Neurodegeneration is mediated by inflammatory and neurotoxic mediators. Though inflammation is crucial in the onset and the progression of neurodegenerative diseases, anti-inflammatory drugs do not provide significant therapeutic effects.
It is well known that long-standing inflammation negatively influences the brain over the course of a lifetime due to the senescence of the immune system. In the case of AD, neuroinflammation can be considered part of a characteristic pathological triad involving Aβ plaques and NFTs, with plenty of evidence of an inflammatory response occurring in AD.
Neuroinflammation is defined as an inflammatory response within the brain or spinal cord. This inflammation is mediated by the production of cytokines, chemokines, reactive oxygen species, and secondary messengers.
Both brain and spinal cord injury involve an acute, beneficial initial inflammatory response which becomes damaging should it persist too long.
Repeated social defeat induces activation of microglia and increased pro-inflammatory cytokine and chemokine expression in the brain. Stress-induced neuropsychiatric disturbances may involve impaired neuroplasticity caused by microglial activation, monocyte recruitment, and enhanced neuroinflammatory signaling.
Both physical and emotional stress is associated with inflammatory cytokine release. Stress can also cause sleep disorders. Since individuals with irregular sleep schedules are more likely to have chronic inflammation than consistent sleepers, sleep disorders are also considered as one of the independent risk factors for chronic inflammation.
Systemic (chronic) inflammation, which leads to neuroinflammation, is likely a risk factor for the progression of neurodegenerative diseases. Chronic neuroinflammation is thought to be a key factor in the progression of neurodegenerative diseases. Age-related senescent inflammation is suspect. One key trigger during aging is changes in the gut, such as the increase in gut permeability and alterations in microbiota composition. Gut dysfunction may be a driver of systemic inflammation, and in turn neuroinflammation. This blog post on chronic inflammation is applicable.
People with irritable bowel syndrome (IBS) are more susceptible to gut hyperpermeability in later life than healthy individuals (26). Interestingly, those with IBS are also more at risk at developing AD, supporting the idea that gut hyperpermeability is a risk factor for AD. Microbiota dysbiosis proceeds AD development and, therefore, may be a driver in the disease progression.
Some short-chain fatty acids (SCFAs) are known to support intestinal barrier function, and these SCFAs, as well as the microbes that produce them, have been found to be in higher abundance in healthy older adults versus those who are frail or experiencing cognitive impairment. In addition, in older adults with cognitive performance from average to AD, anti-inflammatory SCFA concentrations were positively correlated with cognitive performance; whereas as pro-inflammatory microbial lipopolysaccharide concentrations were associated with poorer cognition. SCFAs downregulate the expression of pro-inflammatory cytokines, such as IL-1β which is associated with not only increased intestinal barrier permeability, but also blood brain barrier permeability and a glial cell inflammatory state.
Sodium butyrate is capable of decreasing microglial activation and pro-inflammatory cytokines secretion. Likewise, acetate treatment of microglia primary culture has been shown to reduce inflammatory signaling.
Cerebrospinal fluid provides immune protection to the brain. As people age, their CSF immune system becomes dysregulated. In cognitively impaired people, inflamed T-cells cloned themselves and flowed into the CSF. These inflamed T-cells can enter the brain and wreak havoc.
The Ω-3 fatty acids have shown anti-amyloid, anti-tau and anti-inflammatory actions in the brains of animals. Ω-3 fatty acids are involved in both the reduction in and resolution of inflammation. Docosahexaenoic acid (DHA), the main Ω-3 PUFA in the brain, modulates oxidative reactions and inflammatory cytokine production in microglial and neuronal cells. Docosahexaenoic acid prevents neuroinflammation by inhibiting transcription factor NFkappaB, preventing cytokine secretion, blocking the synthesis of prostaglandins, leukotrienes, and thromboxanes, and modulating leukocyte trafficking.
Apigenin protects neurons against neuroinflammation. Curcumin and apigenin have proven antioxidant, anti-inflammatory, anti-amyloidogenic, neuroprotective, and cognition-enhancing effects. The best dietary sources of apigenin are parsley and chamomile.
Numerous evidence has indicated that green tea catechins have protective effects against neuroinflammation.
Curcumin may prevent neuroinflammation via AMPK activation. Neuroinflammation is associated with the induction and progression of chronic pain. Curcumin improves chronic pain by diminishing the release of inflammatory mediators from the spinal glia. Curcumin protects the brain from toxicity by inhibiting the production of nitric oxide, prostaglandin E2, ROS, and proinflammatory cytokines. Curcumin is fat-soluble, and too much will cause anemia.
Neuroinflammation has been associated with either the cause or consequence of chronic oxidative stress, a key feature of all the neurodegenerative diseases that causes genetic structural alteration, resulting in neurodegeneration. This blog post on oxidative stress may be applicable.
As demonstrated in mice, high intensity interval training protects the central nervous system against autoimmune neuroinflammation by reducing microglial-derived reactive oxygen species formation, neurotoxicity, and pro-inflammatory responses involved in the propagation of autoimmune neuroinflammation.
Preoperative resistance exercise in mice improved surgery-induced adverse effects including cognitive impairment, synaptic deficit and neuroinflammation, possibly by facilitate mitochondrial health.
A running exercise in rats lowered microglial neuroinflammation. Short duration (less than two weeks) of 30 min of daily low-intensity treadmill exercise can favourably shift the ratio of pro- to anti-inflammatory cytokines in the hippocampus of aged rats.
Resistance training improved cognitive performance and reduced neuropathological and neuroinflammatory changes in the frontal cortex and hippocampus of mice.
Avoid a high-fat (fast food) diet, as well as arachidonic acid (from meat). Consumption of a high-fat diet — specifically diets that include high amounts of fats and carbohydrates — stimulates hypothalamic inflammation as early as three days after consumption of a high-fat diet, even before the body begins to display signs of obesity.
Avoid head injury – wear a helmet.
Dietary luteolin enhanced spatial working memory in mice by mitigating microglial-associated inflammation in the hippocampus. Luteolin is found in rosemary, celery, thyme, green peppers, cabbage, chamomile, and especially: radichio.
Sesamin markedly improved depression and memory loss via inhibiting neuroinflammation in mice.
Sulforaphane is a powerful antioxidant and anti-inflammatory phytochemical with great promise in its ability to protect the nervous system from many diseases and toxins and reduce the symptomatic burden of multiple pervasive diseases. The neuroprotective role of sulforaphane is correlated with the Nrf2 pathway. The reduction of neuroinflammation by sulforaphane plays a prominent role plays a prominent role in protecting against many toxins, as well as neuronal damage associated with Alzheimer’s disease, Parkinson’s disease, epileptic seizures, cerebral infarction, hepatic encephalopathy, Huntington’s disease, and spinal cord injury. The richest source of sulforaphane is broccoli sprouts.
Consumption of added sugars, particularly high-fructose corn syrup, negatively impacts hippocampal function, metabolic outcomes, and neuroinflammation when consumed in excess during the adolescent period of development.