Neuroprotective Effect of Nortriptyline in Overt Hepatic Encephalopathy Through Attenuation of Mitochondrial Dysfunction

Protocatechuic acid protects against thioacetamide-induced chronic liver injury and encephalopathy in mice via modulating mTOR, p53 and the IL-6/ IL-17/ IL-23 immunoinflammatory pathway

Protocatechuic acid (PCA), a natural phenolic acid, is known for antioxidant, anti-inflammatory, anti-apoptotic, and anti-fibrotic activities. However, the protective mechanisms of PCA on thioacetamide (TAA)-induced liver/brain injury are not well addressed. Chronic liver injury was induced in mice by intraperitoneal injection of TAA (200 mg/kg, 3 times/week) for 8 weeks. Simultaneously, PCA (100, 150 mg/kg/day, p.o.) was given daily from the 4th week. Protocatechuic acid ameliorated liver and brain damage indicated by the decrease in serum activities of aminotransferases, gamma-glutamyl transferase, alkaline phosphatase, lactate dehydrogenase, levels of bilirubin, and ammonia concomitant with restoration of normal albumin levels. Additionally, PCA treatment ameliorated oxidative stress in liver and brain, confirmed by the decrease in malondialdehyde and nitric oxide levels and the increase in antioxidant activities. Moreover, PCA showed anti-inflammatory actions through downregulation of TNF-α expression in the liver and IL-6/IL-17/IL-23 levels in the brain, which is confirmed by the decrease in CD4⁺ T brain cell numbers. Most importantly, PCA treatment showed a significant decrease in mTOR level and number of LC3 positive cells in both liver and brain tissues. Consequently, PCA could inhibit mTOR-induced apoptosis, as it showed anti-apoptotic actions through downregulation of caspase-3 expression in liver and p53 expression in liver and brain. Furthermore, liver and brain tissues of treated mice showed restoration of normal histology. It can be concluded that, several mechanisms, including: antioxidant, anti-inflammatory, anti-autophagic and anti-apoptotic activities can be implicated in the hepato- and neuroprotective potentials of PCA.

Syringic acid protects against thioacetamide-induced hepatic encephalopathy: Behavioral, biochemical, and molecular evidence

The objective of this study was to elucidate the effects of syringic acid on thioacetamide-induced hepatic encephalopathy which is a complex serious syndrome with neuropsychiatric abnormalities related to acute liver dysfunctions like cirrhosis. Rats were treated with syringic acid (50 and 100 mg/kg, p.o.) for 14 days in treatment groups. Hepatic encephalopathy was induced by three doses of (200 mg/kg i.p.) thioacetamide injection. Syringic acid effectively alleviated thioacetamide-induced hepatic injury via reduction in ammonia, AST, ALT, ALP, LDH and decrease in oxidative stress (decreased MDA, ROS and increased SOD and GSH). Syringic acid also attenuated inflammatory injury by suppressing TNF-α, IL-1β, and NF-κB and increasing IL-10. The caspase-3 expression was also down-regulated in both liver and brain tissues. Immunohistochemical results confirmed the recovery with syringic acid by downregulation of iNOS, 8-OHdG and GFAP expression. Syringic acid decreased the deteriorating effects of thioacetamide as seen by reduced ammonia concentration and also preserved astrocyte and hepatocyte structure. The behavioral test results from elevated plus maze test, similar to the open-field locomotor test results, confirmed that syringic acid can reverse behavioral impairments. In conclusion, syringic acid exerted hepatoprotective and neuroprotective effects against hepatic encephalopathy by mitigating hepatotoxicity biomarkers, exerting antioxidant, anti-inflammatory effects in addition to suppressing hyperammonemia.

Hepatic Encephalopathy: From Metabolic to Neurodegenerative

Hepatic encephalopathy (HE) is a neuropsychiatric syndrome of both acute and chronic liver disease. As a metabolic disorder, HE is considered to be reversible and therefore is expected to resolve following the replacement of the diseased liver with a healthy liver. However, persisting neurological complications are observed in up to 47% of transplanted patients. Several retrospective studies have shown that patients with a history of HE, particularly overt-HE, had persistent neurological complications even after liver transplantation (LT). These enduring neurological conditions significantly affect patient's quality of life and continue to add to the economic burden of chronic liver disease on health care systems. This review discusses the journey of the brain through the progression of liver disease, entering the invasive surgical procedure of LT and the conditions associated with the post-transplant period. In particular, it will discuss the vulnerability of the HE brain to peri-operative factors and post-LT conditions which may explain non-resolved neurological impairment following LT. In addition, the review will provide evidence; (i) supporting overt-HE impacts on neurological complications post-LT; (ii) that overt-HE leads to permanent neuronal injury and (iii) the pathophysiological role of ammonia toxicity on astrocyte and neuronal injury/damage. Together, these findings will provide new insights on the underlying mechanisms leading to neurological complications post-LT.

Bile-duct ligation renders the brain susceptible to hypotension-induced neuronal degeneration: Implications of ammonia

Hepatic encephalopathy (HE) is a debilitating neurological complication of cirrhosis. By definition, HE is considered a reversible disorder, and therefore HE should resolve following liver transplantation (LT). However, persisting neurological complications are observed in as many as 47% of LT recipients. LT is an invasive surgical procedure accompanied by various perioperative factors such as blood loss and hypotension which could influence outcomes post-LT. We hypothesize that minimal HE (MHE) renders the brain frail and susceptible to hypotension-induced neuronal cell death. Six-week bile duct-ligated (BDL) rats with MHE and respective SHAM-controls were used. Several degrees of hypotension (mean arterial pressure of 30, 60 and 90 mm Hg) were induced via blood withdrawal from the femoral artery and maintained for 120 min. Brains were collected for neuronal cell count and apoptotic analysis. In a separate group, BDL rats were treated for MHE with the ammonia-lowering strategy ornithine phenylacetate (OP; MNK-6105), administered orally (1 g/kg) for 3 weeks before induction of hypotension. Hypotension 30 and 60 mm Hg (not 90 mm Hg) significantly decreased neuronal marker expression (NeuN) and cresyl violet staining in the frontal cortex compared to respective hypotensive SHAM-operated controls as well as non-hypotensive BDL rats. Neuronal degeneration was associated with an increase in cleaved caspase-3, suggesting the mechanism of cell death was apoptotic. OP treatment attenuated hyperammonaemia, improved anxiety and activity, and protected the brain against hypotension-induced neuronal cell death. Our findings demonstrate that rats with chronic liver disease and MHE are more susceptible to hypotension-induced neuronal cell degeneration. This highlights MHE at the time of LT is a risk factor for poor neurological outcome post-transplant and that treating for MHE pre-LT might reduce this risk.

Cortistatin protects against intervertebral disc degeneration through targeting mitochondrial ROS-dependent NLRP3 inflammasome activation

Background: Intervertebral disc (IVD) degeneration is a common degenerative disease that can lead to collapse or herniation of the nucleus pulposus (NP) and result in radiculopathy in patients.

Methods: NP tissue and cells were isolated from patients and mice, and the expression profile of cortistatin (CST) was analysed. In addition, ageing of the NP was compared between 6-month-old WT and CST-knockout (CST^-/-) mice. Furthermore, NP tissues and cells were cultured to validate the role of CST in TNF-α-induced IVD degeneration. Moreover, in vitro and in vivo experiments were performed to identify the potential role of CST in mitochondrial dysfunction, mitochondrial ROS generation and activation of the NLRP3 inflammasome during IVD degeneration. In addition, NF-κB signalling pathway activity was tested in NP tissues and cells from CST^-/- mice.

Results: The expression of CST in NP cells was diminished in the ageing- and TNF-α-induced IVD degeneration process. In addition, compared with WT mice, aged CST^-/- mice displayed accelerated metabolic imbalance and enhanced apoptosis, and these mice showed a disorganized NP tissue structure. Moreover, TNF-α-mediated catabolism and apoptosis were alleviated by exogenous CST treatment. Furthermore, CST inhibited mitochondrial dysfunction in NP cells through IVD degeneration and suppressed activation of the NLRP3 inflammasome. In vitro and ex vivo experiments indicated that increased NF-κB pathway activity might have been associated with the IVD degeneration observed in CST^-/- mice.

Conclusion: This study suggests the role of CST in mitochondrial ROS and activation of the NLRP3 inflammasome in IVD degeneration, which might shed light on therapeutic targets for IVD degeneration.

Processing milk causes the formation of protein oxidation products which impair spatial learning and memory in rats

This study explored the effects of protein oxidation during milk processing on spatial learning and memory in rats. Increasing the heating time, fat content, and inlet air temperature during processing by boiling, microwave heating, spray-drying, or freeze-drying increases milk protein oxidation. Oxidative damage done to milk proteins by microwave heating is greater than that caused by boiling. Dityrosine (DT), as a kind of tyrosine oxidation product, is the most important marker of this process, especially during spray-drying. Rats received diets containing either SWM (spray-dried milk powder diet), FWM (freeze-dried milk powder diet), FWM + LDT (freeze-dried milk powder + low dityrosine diet, DT: 1.4 mg kg-1), or FWM + HDT (freeze-dried milk powder + high dityrosine diet, DT: 2.8 mg kg-1) for 6 weeks. We found that the SWM group, the FWM + LDT group, and the FWM + HDT group appeared to have various degrees of redox state imbalance and oxidative damage in plasma, liver, and brain tissues. Further, hippocampal inflammatory and apoptosis genes were significantly up-regulated in such groups, while learning and memory genes were significantly down-regulated. Eventually, varying degrees of spatial learning and memory impairment were demonstrated in those groups in the Morris water maze. This means that humans should control milk protein oxidation and improve the processing methods applied to food.