A hydrodynamic hypothesis for the pathogenesis of glymphatic system impairment in hepatic encephalopathy

Connecting the Dots: The Cerebral Lymphatic System as a Bridge Between the Central Nervous System and Peripheral System in Health and Disease

As a recently discovered waste removal system in the brain, cerebral lymphatic system is thought to play an important role in regulating the homeostasis of the central nervous system. Currently, more and more attention is being focused on the cerebral lymphatic system. Further understanding of the structural and functional characteristics of cerebral lymphatic system is essential to better understand the pathogenesis of diseases and to explore therapeutic approaches. In this review, we summarize the structural components and functional characteristics of cerebral lymphatic system. More importantly, it is closely associated with peripheral system diseases in the gastrointestinal tract, liver, and kidney. However, there is still a gap in the study of the cerebral lymphatic system. However, we believe that it is a critical mediator of the interactions between the central nervous system and the peripheral system.

Inhibition of autotaxin alleviates pathological features of hepatic encephalopathy at the level of gut-liver-brain axis: an experimental and bioinformatic study

There is accumulating evidence that the circulatory levels of autotaxin (ATX) and lysophosphatidic acid (LPA) are increased in patients with severe liver disease. However, the potential role of the ATX-LPA axis in hepatic encephalopathy (HE) remains unclear. Our study aimed to investigate the role of the ATX-LPA signaling pathway in mice with thioacetamide (TAA) induced acute HE. To show the role of the ATX-LPA axis in the context of HE, we first measured the involvement of ATX-LPA in the pathogenesis of TAA-induced acute HE. Then, we compared the potential effects of ATX inhibitor (HA130) on astrocyte responses at in vitro and gut-liver-brain axis at in vivo levels. The inflammatory chemokine (C-C motif) ligand 3 was significantly increased in the hyperammonemic condition and could be prevented by ATX inhibition in astrocytes at in vitro level. Further statistical tests revealed that plasma and tissue pro-inflammatory cytokines were inhibited by HA130 in mice. Furthermore, the stage of HE was significantly improved by HA130. The most surprising result was that HA130 alleviated immune infiltrating cells in the liver and intestine and decreased mucus-secreting cells in the intestine. Further analysis showed that the levels of liver enzymes in serum were significantly decreased in response to ATX inhibition. Surprisingly, our data indicated that HA130 could recover permeabilization of the blood-brain barrier, neuroinflammation, and recognition memory. Besides that, we found that the changes of Interleukin-1 (IL-1) and aquaporin-4 (AQP4) in HE might have a connection with the glymphatic system based on bioinformatics analyses. Taken together, our data showed that the ATX-LPA axis contributes to the pathogenesis of HE and that inhibition of ATX improves HE.

The Glymphatic System May Play a Vital Role in the Pathogenesis of Hepatic Encephalopathy: A Narrative Review

Hepatic encephalopathy (HE) is a neurological complication of liver disease resulting in cognitive, psychiatric, and motor symptoms. Although hyperammonemia is a key factor in the pathogenesis of HE, several other factors have recently been discovered. Among these, the impairment of a highly organized perivascular network known as the glymphatic pathway seems to be involved in the progression of some neurological complications due to the accumulation of misfolded proteins and waste substances in the brain interstitial fluids (ISF). The glymphatic system plays an important role in the clearance of brain metabolic derivatives and prevents aggregation of neurotoxic agents in the brain ISF. Impairment of it will result in aggravated accumulation of neurotoxic agents in the brain ISF. This could also be the case in patients with liver failure complicated by HE. Indeed, accumulation of some metabolic by-products and agents such as ammonia, glutamine, glutamate, and aromatic amino acids has been reported in the human brain ISF using microdialysis technique is attributed to worsening of HE and correlates with brain edema. Furthermore, it has been reported that the glymphatic system is impaired in the olfactory bulb, prefrontal cortex, and hippocampus in an experimental model of HE. In this review, we discuss different factors that may affect the function of the glymphatic pathways and how these changes may be involved in HE.

The lymphatic system: a therapeutic target for central nervous system disorders

The lymphatic vasculature forms an organized network that covers the whole body and is involved in fluid homeostasis, metabolite clearance, and immune surveillance. The recent identification of functional lymphatic vessels in the meninges of the brain and the spinal cord has provided novel insights into neurophysiology. They emerge as major pathways for fluid exchange. The abundance of immune cells in lymphatic vessels and meninges also suggests that lymphatic vessels are actively involved in neuroimmunity. The lymphatic system, through its role in the clearance of neurotoxic proteins, autoimmune cell infiltration, and the transmission of pro-inflammatory signals, participates in the pathogenesis of a variety of neurological disorders, including neurodegenerative and neuroinflammatory diseases and traumatic injury. Vascular endothelial growth factor C is the master regulator of lymphangiogenesis, a process that is critical for the maintenance of central nervous system homeostasis. In this review, we summarize current knowledge and recent advances relating to the anatomical features and immunological functions of the lymphatic system of the central nervous system and highlight its potential as a therapeutic target for neurological disorders and central nervous system repair.

The Emerging Role of Exosomes in the Treatment of Human Disorders With a Special Focus on Mesenchymal Stem Cells-Derived Exosomes

Extracellular vesicles (EVs) are produced by diverse eukaryotic and prokaryotic cells. They have prominent roles in the modulation of cell-cell communication, inflammation versus immunomodulation, carcinogenic processes, cell proliferation and differentiation, and tissue regeneration. These acellular vesicles are more promising than cellular methods because of the lower risk of tumor formation, autoimmune responses and toxic effects compared with cell therapy. Moreover, the small size and lower complexity of these vesicles compared with cells have made their production and storage easier than cellular methods. Exosomes originated from mesenchymal stem cells has also been introduced as therapeutic option for a number of human diseases. The current review aims at summarization of the role of EVs in the regenerative medicine with a focus on their therapeutic impacts in liver fibrosis, lung disorders, osteoarthritis, colitis, myocardial injury, spinal cord injury and retinal injury.

Glymphatic System as a Gateway to Connect Neurodegeneration From Periphery to CNS

The classic concept of the absence of lymphatic vessels in the central nervous system (CNS), suggesting the immune privilege of the brain in spite of its high metabolic rate, was predominant until recent times. On the other hand, this idea left questioned how cerebral interstitial fluid is cleared of waste products. It was generally thought that clearance depends on cerebrospinal fluid (CSF). Not long ago, an anatomically and functionally discrete paravascular space was revised to provide a pathway for the clearance of molecules drained within the interstitial space. According to this model, CSF enters the brain parenchyma along arterial paravascular spaces. Once mixed with interstitial fluid and solutes in a process mediated by aquaporin-4, CSF exits through the extracellular space along venous paravascular spaces, thus being removed from the brain. This process includes the participation of perivascular glial cells due to a sieving effect of their end-feet. Such draining space resembles the peripheral lymphatic system, therefore, the term "glymphatic" (glial-lymphatic) pathway has been coined. Specific studies focused on the potential role of the glymphatic pathway in healthy and pathological conditions, including neurodegenerative diseases. This mainly concerns Alzheimer's disease (AD), as well as hemorrhagic and ischemic neurovascular disorders; other acute degenerative processes, such as normal pressure hydrocephalus or traumatic brain injury are involved as well. Novel morphological and functional investigations also suggested alternative models to drain molecules through perivascular pathways, which enriched our insight of homeostatic processes within neural microenvironment. Under the light of these considerations, the present article aims to discuss recent findings and concepts on nervous lymphatic drainage and blood-brain barrier (BBB) in an attempt to understand how peripheral pathological conditions may be detrimental to the CNS, paving the way to neurodegeneration.

Retention enema with traditional Chinese medicine for hepatic encephalopathy: A protocol for a systematic review and meta-analysis

BACKGROUND

Hepatic encephalopathy (HE) is one of the common complications of many serious liver diseases. Western medicine treatment is mainly symptomatic treatment such as neutralizing blood ammonia and protecting liver, which has poor curative effect, easy repetition and high mortality. Retention enema with traditional Chinese medicine (TCM) has been used on treatment of HE in China for many years. And it has been clinically proved that retention enema with TCM is effective and safe. But there is absent convincing evidence-based medicine to confirm the efficacy of retention enema with TCM for HE. Thus, we aimed to conduct this meta-analysis to summarize the efficacy of retention enema with TCM in patients with HE.

METHODS

The study only selects clinical randomized controlled trials of retention enema with TCM for HE. We will search each database from the built-in until December 31, 2020. The English literature mainly searches Cochrane Library, Pubmed, EMBASE, and Web of Science. While the Chinese literature comes from CNKI, CBM, VIP, and Wanfang database. Meanwhile, we will retrieve clinical trial registries and gray literature. Two researchers worked independently on literature selection, data extraction and quality assessment. The dichotomous data is represented by relative risk (RR), and the continuous is expressed by mean difference (MD) or standard mean difference (SMD), eventually the data is synthesized using a fixed effect model (FEM) or a random effect model (REM) depending on the heterogeneity. The total effective rate, blood ammonia and the total bilirubin were evaluated as the main outcomes. While several secondary outcomes were also evaluated in this study. The statistical analysis of this Meta-analysis was conducted by RevMan software version 5.3.

RESULTS

This study will synthesize and provide high-quality evidence based on the data of the currently published retention enema with TCM for the treatment of HE.

CONCLUSION

This meta-analysis aims to evaluate the benefits of retention enema with TCM for the treatment of HE reported in randomized controlled trials, and provide more options for clinicians and patients with HE.

REGISTRATION NUMBER

INPLASY202080107.