Ammonia Clearance Research Articles

Ammonium chloride reduces excitatory synaptic transmission onto CA1 pyramidal neurons of mouse organotypic slice cultures.

Acute liver dysfunction commonly leads to rapid increases in ammonia concentrations in both the serum and the cerebrospinal fluid. These elevations primarily affect brain astrocytes, causing modifications in their structure and function. However, its impact on neurons is not yet fully understood. In this study, we investigated the impact of elevated ammonium chloride levels (NH4Cl, 5 mM) on synaptic transmission onto CA1 pyramidal neurons in mouse organotypic entorhino-hippocampal tissue cultures. We found that acute exposure to NH4Cl reversibly reduced excitatory synaptic transmission and affected CA3-CA1 synapses. Notably, NH4Cl modified astrocytic, but not CA1 pyramidal neuron, passive intrinsic properties. To further explore the role of astrocytes in NH4Cl-induced attenuation of synaptic transmission, we used methionine sulfoximine to target glutamine synthetase, a key astrocytic enzyme for ammonia clearance in the central nervous system. Inhibition of glutamine synthetase effectively prevented the downregulation of excitatory synaptic activity, underscoring the significant role of astrocytes in adjusting excitatory synapses during acute ammonia elevation.

First Application of a Mixed Porcine-Human Repopulated Bioengineered Liver in a Preclinical Model of Post-Resection Liver Failure.

In this study, a mixed porcine-human bioengineered liver (MPH-BEL) was used in a preclinical setup of extracorporeal liver support devices as a treatment for a model of post-resection liver failure (PRLF). The potential for human clinical application is further illustrated by comparing the functional capacity of MPH-BEL grafts as assessed using this porcine PRLF model with fully human (FH-BEL) grafts which were perfused and assessed in vitro. BEL grafts were produced by reseeding liver scaffolds with HUVEC and primary porcine hepatocytes (MPH-BEL) or primary human hepatocytes (FH-BEL). PRLF was induced by performing an 85% liver resection in domestic white pigs and randomized into the following three groups 24 h after resection: standard medical therapy (SMT) alone, SMT + extracorporeal circuit (ECC), and SMT + MPH-BEL. The detoxification and metabolic functions of the MPH-BEL grafts were compared to FH-BEL grafts which were perfused in vitro. During the 24 h treatment interval, INR values normalized within 18 h in the MPH-BEL therapy group and urea synthesis increased as compared to the SMT and SMT + ECC control groups. The MPH-BEL treatment was associated with more rapid decline in hematocrit and platelet count compared to both control groups. Histological analysis demonstrated platelet sequestration in the MPH-BEL grafts, possibly related to immune activation. Significantly higher rates of ammonia clearance and metabolic function were observed in the FH-BEL grafts perfused in vitro than in the MPH-BEL grafts. The MPH-BEL treatment was associated with improved markers of liver function in PRLF. Further improvement in liver function in the BEL grafts was observed by seeding the biomatrix with human hepatocytes. Methods to reduce platelet sequestration within BEL grafts is an area of ongoing research.

A comprehensive review of advances in hepatocyte microencapsulation: selecting materials and preserving cell viability.

Liver failure represents a critical medical condition with a traditionally grim prognosis, where treatment options have been notably limited. Historically, liver transplantation has stood as the sole definitive cure, yet the stark disparity between the limited availability of liver donations and the high demand for such organs has significantly hampered its feasibility. This discrepancy has necessitated the exploration of hepatocyte transplantation as a temporary, supportive intervention. In light of this, our review delves into the burgeoning field of hepatocyte transplantation, with a focus on the latest advancements in maintaining hepatocyte function, co-microencapsulation techniques, xenogeneic hepatocyte transplantation, and the selection of materials for microencapsulation. Our examination of hepatocyte microencapsulation research highlights that, to date, most studies have been conducted in vitro or using liver failure mouse models, with a notable paucity of experiments on larger mammals. The functionality of microencapsulated hepatocytes is primarily inferred through indirect measures such as urea and albumin production and the rate of ammonia clearance. Furthermore, research on the mechanisms underlying hepatocyte co-microencapsulation remains limited, and the practicality of xenogeneic hepatocyte transplantation requires further validation. The potential of hepatocyte microencapsulation extends beyond the current scope of application, suggesting a promising horizon for liver failure treatment modalities. Innovations in encapsulation materials and techniques aim to enhance cell viability and function, indicating a need for comprehensive studies that bridge the gap between small-scale laboratory success and clinical applicability. Moreover, the integration of bioengineering and regenerative medicine offers novel pathways to refine hepatocyte transplantation, potentially overcoming the challenges of immune rejection and ensuring the long-term functionality of transplanted cells. In conclusion, while hepatocyte microencapsulation and transplantation herald a new era in liver failure therapy, significant strides must be made to translate these experimental approaches into viable clinical solutions. Future research should aim to expand the experimental models to include larger mammals, thereby providing a clearer understanding of the clinical potential of these therapies. Additionally, a deeper exploration into the mechanisms of cell survival and function within microcapsules, alongside the development of innovative encapsulation materials, will be critical in advancing the field and offering new hope to patients with liver failure.

Inflammatory liver diseases and susceptibility to sepsis.

Patients with inflammatory liver diseases, particularly alcohol-associated liver disease and metabolic dysfunction-associated fatty liver disease (MAFLD), have higher incidence of infections and mortality rate due to sepsis. The current focus in the development of drugs for MAFLD is the resolution of non-alcoholic steatohepatitis and prevention of progression to cirrhosis. In patients with cirrhosis or alcoholic hepatitis, sepsis is a major cause of death. As the metabolic center and a key immune tissue, liver is the guardian, modifier, and target of sepsis. Septic patients with liver dysfunction have the highest mortality rate compared with other organ dysfunctions. In addition to maintaining metabolic homeostasis, the liver produces and secretes hepatokines and acute phase proteins (APPs) essential in tissue protection, immunomodulation, and coagulation. Inflammatory liver diseases cause profound metabolic disorder and impairment of energy metabolism, liver regeneration, and production/secretion of APPs and hepatokines. Herein, the author reviews the roles of (1) disorders in the metabolism of glucose, fatty acids, ketone bodies, and amino acids as well as the clearance of ammonia and lactate in the pathogenesis of inflammatory liver diseases and sepsis; (2) cytokines/chemokines in inflammatory liver diseases and sepsis; (3) APPs and hepatokines in the protection against tissue injury and infections; and (4) major nuclear receptors/signaling pathways underlying the metabolic disorders and tissue injuries as well as the major drug targets for inflammatory liver diseases and sepsis. Approaches that focus on the liver dysfunction and regeneration will not only treat inflammatory liver diseases but also prevent the development of severe infections and sepsis.

Gasdermin-E-Dependent Non-Canonical Pyroptosis Promotes Drug-Induced Liver Failure by Promoting CPS1 deISGylation and Degradation.

Drug-induced liver injury (DILI) is a significant global health issue that poses high mortality and morbidity risks. One commonly observed cause of DILI is acetaminophen (APAP) overdose. GSDME is an effector protein that induces non-canonical pyroptosis. In this study, the activation of GSDME, but not GSDMD, in the liver tissue of mice and patients with APAP-DILI is reported. Knockout of GSDME, rather than GSDMD, in mice protected them from APAP-DILI. Mice with hepatocyte-specific rescue of GSDME reproduced APAP-induced liver injury. Furthermore, alterations in the immune cell pools observed in APAP-induced DILI, such as the replacement of TIM4+ resident Kupffer cells (KCs) by monocyte-derived KCs, Ly6C+ monocyte infiltration, MerTk+ macrophages depletion, and neutrophil increase, reappeared in mice with hepatocyte-specific rescue of GSDME. Mechanistically, APAP exposure led to a substantial loss of interferon-stimulated gene 15 (ISG15), resulting in deISGylation of carbamoyl phosphate synthetase-1 (CPS1), promoted its degradation via K48-linked ubiquitination, causing ammonia clearance dysfunction. GSDME deletion prevented these effects. Delayed administration of dimethyl-fumarate inhibited GSDME cleavage and alleviated ammonia accumulation, mitigating liver injury. This findings demonstrated a previously uncharacterized role of GSDME in APAP-DILI by promoting pyroptosis and CPS1 deISGylation, suggesting that inhibiting GSDME can be a promising therapeutic option for APAP-DILI.

Continuous renal replacement therapy and survival in acute liver failure: A systematic review and meta-analysis

ObjectiveAcute liver failure (ALF) is a rare syndrome leading to significant morbidity and mortality. An important cause of mortality is cerebral edema due to hyperammonemia. Different therapies for hyperammonemia have been assessed including continuous renal replacement therapy (CRRT). We conducted a systematic review and meta-analysis to determine the efficacy of CRRT in ALF patients. Materials and methodsWe searched MEDLINE, EMBASE, Cochrane Library, and Web of Science. Inclusion criteria included adult patients admitted to an ICU with ALF. Intervention was the use of CRRT for one or more indications with the comparator being standard care without the use of CRRT. Outcomes of interest were overall survival, transplant-free survival (TFS), mortality and changes in serum ammonia levels. ResultsIn total, 305 patients underwent CRRT while 1137 patients did not receive CRRT. CRRT was associated with improved overall survival [risk ratio (RR) 0.83, 95% confidence interval (CI) 0.70–0.99, p-value 0.04, I2 = 50%] and improved TFS (RR 0.65, 95% CI 0.49–0.85, p-value 0.002, I2 = 25%). There was a trend towards higher mortality with no CRRT (RR 1.24, 95% CI 0.84–1.81, p-value 0.28, I2 = 37%). Ammonia clearance data was unable to be pooled and was not analyzable. ConclusionUse of CRRT in ALF patients is associated with improved overall and transplant-free survival compared to no CRRT.

Ammonia scavenger and glutamine synthetase inhibitors cocktail in targeting mTOR/β-catenin and MMP-14 for nitrogen homeostasis and liver cancer.

The glutamine synthetase (GS) facilitates cancer cell growth by catalyzing de novo glutamine synthesis. This enzyme removes ammonia waste from the liver following the urea cycle. Since cancer development is associated with dysregulated urea cycles, there has been no investigation of GS's role in ammonia clearance. Here, we demonstrate that, although GS expression is increased in the setting of β-catenin oncogenic activation, it is insufficient to clear the ammonia waste burden due to the dysregulated urea cycle and may thus be unable to prevent cancer formation. In vivo study, a total of 165 male Swiss albino mice allocated in 11 groups were used, and liver cancer was induced by p-DAB. The activity of GS was evaluated along with the relative expression of mTOR, β-catenin, MMP-14, and GS genes in liver samples and HepG2 cells using qRT-PCR. Moreover, the cytotoxicity of the NH3 scavenger phenyl acetate (PA) and/or GS-inhibitor L-methionine sulfoximine (MSO) and the migratory potential of cells was assessed by MTT and wound healing assays, respectively. The Swiss target prediction algorithm was used to screen the mentioned compounds for probable targets. The treatment of the HepG2 cell line with PA plus MSO demonstrated strong cytotoxicity. The post-scratch remaining wound area (%) in the untreated HepG2 cells was 2.0%. In contrast, the remaining wound area (%) in the cells treated with PA, MSO, and PA + MSO for 48 h was 61.1, 55.8, and 78.5%, respectively. The combination of the two drugs had the greatest effect, resulting in the greatest decrease in the GS activity, β-catenin, and mTOR expression. MSO and PA are both capable of suppressing mTOR, a key player in the development of HCC, and MMP-14, a key player in the development of HCC. PA inhibited the MMP-14 enzyme more effectively than MSO, implying that PA might be a better way to target HCC as it inhibited MMP-14 more effectively than MSO. A large number of abnormal hepatocytes (5%) were found to be present in the HCC mice compared to mice in the control group as determined by the histopathological lesions scores. In contrast, PA, MSO, and PA + MSO showed a significant reduction in the hepatic lesions score either when protecting the liver or when treating the liver. The molecular docking study indicated that PA and MSO form a three-dimensional structure with NF-κB and COX-II, blocking their ability to promote cancer and cause gene mutations. PA and MSO could be used to manipulate GS activities to modulate ammonia levels, thus providing a potential treatment for ammonia homeostasis.

Fructose overconsumption impairs hepatic manganese homeostasis and ammonia disposal

Arginase, a manganese (Mn)-dependent enzyme, is indispensable for urea generation and ammonia disposal in the liver. The potential role of fructose in Mn and ammonia metabolism is undefined. Here we demonstrate that fructose overconsumption impairs hepatic Mn homeostasis and ammonia disposal in male mice. Fructose overexposure reduces liver Mn content as well as its activity of arginase and Mn-SOD, and impairs the clearance of blood ammonia under liver dysfunction. Mechanistically, fructose activates the Mn exporter Slc30a10 gene transcription in the liver in a ChREBP-dependent manner. Hepatic overexpression of Slc30a10 can mimic the effect of fructose on liver Mn content and ammonia disposal. Hepatocyte-specific deletion of Slc30a10 or ChREBP increases liver Mn contents and arginase activity, and abolishes their responsiveness to fructose. Collectively, our data establish a role of fructose in hepatic Mn and ammonia metabolism through ChREBP/Slc30a10 pathway, and postulate fructose dietary restriction for the prevention and treatment of hyperammonemia.

A Case of Rising Serum Ammonia Associated with Early Detection of Antibiotic Resistant Pseudomonas Aeruginosa Pneumonia

Background: Hyperammonemia is frequently encountered in critical illness as a consequence of liver failure, but Nonhepatic Hyperammonemia (NHHA) can also occur in pathologies causing ammonia overproduction or inappropriate ammonia clearance. Sepsis-associated hyperammonemia is a subset of NHHA associated with urease producing infections causing ammonia overproduction. Case Description: We report an unusual case of sepsis-associated NHHA secondary to multi-drug resistant Pseudomonas aeruginosa pneumonia in a 50-year-old critically ill man who was admitted to the intensive care unit for cardiogenic shock, respiratory failure, and hepatic failure secondary to myocardial infarction with papillary muscle rupture. He subsequently developed P. aeruginosa pneumonia and was treated empirically with piperacillin/tazobactam and subsequently meropenem as guided by culture data. The patient’s serum ammonia concentration was incidentally trended to stratify risk for cerebral edema. Eight days into his pneumonia treatment course, the patient’s serum ammonia level abruptly doubled despite improving hepatic function, which prompted switching the P. aeruginosa treatment from meropenem to ciprofloxacin. Bronchial washings later revealed that the P. aeruginosa had acquired resistance to meropenem. The patient subsequently demonstrated clinical improvement and also had a downward trend in the serum ammonia concentration. Another trend of hyperammonemia without worsening hepatic function later in his hospital course correlated with P. aeruginosa infection with acquired resistance to ciprofloxacin, and which improved with the addition of inhaled tobramycin to the antibiotic regimen. Conclusions: In sepsis-associated NHHA, the serum ammonia trend may be a useful adjunct marker to indicate treatment response and provide an early indication of antibiotic treatment resistance.

P2 Whole-Body Clearance and Production of Ammonia Quantified by Constant Ammonia Infusion – The Effects of Cirrhosis and Ammonia Targeting Treatments

P2 Whole-Body Clearance and Production of Ammonia Quantified by Constant Ammonia Infusion – The Effects of Cirrhosis and Ammonia Targeting Treatments

Nutrition, frailty assessment, and interventions for the liver transplant candidate.

Nutrition, frailty assessment, and interventions for the liver transplant candidate.

#3739 SHUNT PORTOSYSTEMIC COMPLICATED BY HYPERAMMONEMIA AND HEPATIC ENCEPHALOPATHY SUPPORTED BY DAILY DIALYSIS IN A CHRONIC HEMODIALYSIS PATIENT

Abstract Background and Aims Hepatic encephalopathy is a neuropsychiatric syndrome that may develop as a consequence of liver insufficiency. In acute liver failure, hepatic encephalopathy suggests the severity of the disease. In end-stage chronic liver diseases, episodes of hepatic encephalopathy are frequently fully and spontaneously reversible. Clinical manifestations vary from mild neuropsychiatric disorders to coma. The pathogenesis of hepatic encephalopathy is complex and not clearly understood. Ammonia plays a key role. In the healthy individual, ammonia is, during its first hepatic passage, directly degraded into urea, itself excreted by the kidney and the stools, and to a lesser degree in glutamine. Ammonia is also metabolized by the muscle striped. In case of liver failure and/or shunts portosystemic, there is a defect in hepatic clearance ammonia which is then found in excess in systemic circulation. Decreased muscle mass, linked to malnutrition, frequent in the patient cirrhotic and chronic hemodialysis, also helps to decrease metabolism ammonia. Due to the increase in permeability of the blood-brain barrier, the brain is exposed to excessive concentrations ammonia causing functional brain abnormalities and structural, which can partly explain the signs neurology of hepatic encephalopathy. In end stage chronic renal failure, clearance of ammonia via extracorporeal treatment has not been systematically evaluated. Several studies with small samples have demonstrated the effectiveness of hemodialysis, compared to peritoneal dialysis, in terms of ammonium purification in chronic renal failure, on dialysis or not on dialysis. The aim of this study was to evaluate the effectiveness of daily dialysis for the purification of ammoniumin a chronic hemodialysis patient with hepatic encephalopathy. Case Report A 40-year-old man undergoing chronic hemodialysis was referred to gastroenterology department of Mohammed VI University center of Marrakesh for inoperable shunt portosystemic complicated by hyperammonemia causing hepatic encephalopathy consisting of headaches and seizures. His medical history was significant for liver cirrhosis caused by infection with hepatitis B, end stage kidney disease due to membranoproliferative glomerulonephritis, for which the patient is on hemodialysis at the rate of 3 sessions per week. The patient went on to develop portal hypertension and ascites requiring frequent hospital admissions and treatment with diuretics. He was on a low-protein and low-sodium diet. While on oral furosemide 250 mg daily and spironolactone 100 mg daily, his diuresis was adequate. Before referral, this patient had already suffered 4 episodes of tonic clonic seizures. His 1st hemodialysis session in our training was on January 10, 2023, he was given daily hemodialysis sessions with daily blood tests, including immediate pre and post dialysis ammonia. Pre-dialytic ammonia levels varied between 103 and 161 µmol/l, as well as post-dialytic ammonia levels varied between 24 and 37 µmol/l, knowing that the normal value of laboratory ammonia varied between 10 and 51 µmol/l. The evolution was marked by a clear clinical improvement, with a disappearance of the seizures without a significant drop in ammonia after 14 daily hemodialysis sessions. Serum creatinine and urea declined, and sodium increased. Accumulation of ascites slowed and the patient could eat and sleep normally and was again independent with self care. The patient returned home on January 24. Conclusion This study shows the interest of daily hemodialysis sessions as a potential treatment for hyperammonemia in a patient on chronic intermittent hemodialysis, with a portosystemic shunt. The interest lies in the fact that the improvement is mainly clinical than biological (persistent hyperammonemia).

WED-354 - Whole body clearance and production of ammonia quantified by constant ammonia infusion-the effects of cirrhosis and ammonia targeting treatments

WED-354 - Whole body clearance and production of ammonia quantified by constant ammonia infusion-the effects of cirrhosis and ammonia targeting treatments

Clearance and production of ammonia quantified in humans by constant ammonia infusion – the effects of cirrhosis and ammonia-targeting treatments

Hyperammonaemia is a key pathological feature of liver disease and the primary driver of hepatic encephalopathy (HE). However, the relative roles of increased ammonia production and reduced clearance are poorly understood as is the action of ammonia-targeting drugs for HE. We aimed to quantify whole-body ammonia metabolism in healthy persons and patients with cirrhosis and to validate our method by examining the effects of glycerol phenylbutyrate and lactulose+ rifaximin treatment. Ten healthy men and ten male patients with cirrhosis were investigated by 90-minute constant ammonia infusion to achieve steady-state plasma ammonia. Whole-body ammonia clearance was calculated as infusion rate divided by steady-state concentration increase and ammonia production was calculated as clearance multiplied by baseline ammonia concentration. Participants were re-investigated after the ammonia-targeting interventions. In healthy persons, ammonia clearance was 3.5 (3.1-3.9) L/min and ammonia production was 49 (35-63) μmol/min. Phenylbutyrate increased clearance by 11% (4-19%, p= 0.009). In patients with cirrhosis, ammonia clearance was 20% lower at 2.7 (2.1-3.3) L/min (p= 0.02) and production was nearly threefold higher at 131 (102-159) μmol/min (p <0.0001). Lactulose+ rifaximin reduced production by 20% (2-37%, p= 0.03). The infusion was generally well-tolerated apart from in one hyperammonaemic patient, with cirrhosis and possible bleeding unrelated to the infusion, who developed clinical HE that reverted when infusion was discontinued. Whole-body ammonia clearance and production may be measured separately using the described technique. This technique identified a lower clearance and a higher production of ammonia in patients with cirrhosis, and showed that phenylbutyrate increases clearance, whereas lactulose+ rifaximin reduces production. High blood ammonia plays a key role in cirrhosis-related brain dysfunction. However, the relative roles of reduced ammonia clearance and increased ammonia production are poorly understood as is the action of ammonia-targeting treatments. This study presents a relatively simple test to measure ammonia metabolism. By using this test, it was possible to show that patients with cirrhosis exhibit decreased ammonia clearance and increased ammonia production compared to healthy persons, and to quantify the unique effects of different ammonia-targeting treatments. The test described herein may be used to examine a range of questions related to normal physiology, pathophysiology and the mechanisms of action of ammonia-targeting treatments. ClinicalTrials.gov (1-16-02-297-20).

Microenvironmental ammonia enhances T cell exhaustion in colorectal cancer

Effective therapies are lacking for patients with advanced colorectal cancer (CRC). The CRC tumor microenvironment has elevated metabolic waste products due to altered metabolism and proximity to the microbiota. The role of metabolite waste in tumor development, progression, and treatment resistance is unclear. We generated an autochthonous metastatic mouse model of CRC and used unbiased multi-omic analyses to reveal a robust accumulation of tumoral ammonia. The high ammonia levels induce Tcell metabolic reprogramming, increase exhaustion, and decrease proliferation. CRC patients have increased serum ammonia, and the ammonia-related gene signature correlates with altered Tcell response, adverse patient outcomes, and lack of response to immune checkpoint blockade. We demonstrate that enhancing ammonia clearance reactivates Tcells, decreases tumor growth, and extends survival. Moreover, decreasing tumor-associated ammonia enhances anti-PD-L1 efficacy. These findings indicate that enhancing ammonia detoxification can reactivate Tcells, highlighting a new approach to enhance the efficacy of immunotherapies.

Glutamine synthetase limits β-catenin-mutated liver cancer growth by maintaining nitrogen homeostasis and suppressing mTORC1.

Glutamine synthetase (GS) catalyzes de novo synthesis of glutamine that facilitates cancer cell growth. In the liver, GS functions next to the urea cycle to remove ammonia waste. As a dysregulated urea cycle is implicated in cancer development, the impact of GS's ammonia clearance function has not been explored in cancer. Here, we show that oncogenic activation of β-catenin (encoded by CTNNB1) led to a decreased urea cycle and elevated ammonia waste burden. While β-catenin induced the expression of GS, which is thought to be cancer promoting, surprisingly, genetic ablation of hepatic GS accelerated the onset of liver tumors in several mouse models that involved β-catenin activation. Mechanistically, GS ablation exacerbated hyperammonemia and facilitated the production of glutamate-derived nonessential amino acids, which subsequently stimulated mechanistic target of rapamycin complex 1 (mTORC1). Pharmacological and genetic inhibition of mTORC1 and glutamic transaminases suppressed tumorigenesis facilitated by GS ablation. While patients with hepatocellular carcinoma, especially those with CTNNB1 mutations, have an overall defective urea cycle and increased expression of GS, there exists a subset of patients with low GS expression that is associated with mTORC1 hyperactivation. Therefore, GS-mediated ammonia clearance serves as a tumor-suppressing mechanism in livers that harbor β-catenin activation mutations and a compromised urea cycle.

Ammonia detoxification promotes CD8+ T cell memory development by urea and citrulline cycles.

Amino acid metabolism is essential for cell survival, while the byproduct ammonia is toxic and can injure cellular longevity. Here we show that CD8+ memory T (TM) cells mobilize the carbamoyl phosphate (CP) metabolic pathway to clear ammonia, thus promoting memory development. CD8+ TM cells use β-hydroxybutyrylation to upregulate CP synthetase 1 and trigger the CP metabolic cascade to form arginine in the cytosol. This cytosolic arginine is then translocated into the mitochondria where it is split by arginase 2 to urea and ornithine. Cytosolic arginine is also converted to nitric oxide and citrulline by nitric oxide synthases. Thus, both the urea and citrulline cycles are employed by CD8+ T cells to clear ammonia and enable memory development. This ammonia clearance machinery might be targeted to improve T cell-based cancer immunotherapies.

Sex is associated with differences in oxidative stress and susceptibility to severe hepatic encephalopathy in bile-duct ligated rats.

Hepatic encephalopathy (HE) is a debilitating neurological complication of chronic liver disease (CLD). Hyperammonemia plays an important role in HE's pathogenesis, acting synergistically with systemic oxidative stress. During CLD, muscle plays a compensatory role in detoxifying ammonia, and therefore muscle loss leads to an increase in the risk of developing HE. With most animal studies involving males, sex's impact on the development of CLD and associated complications such as HE and muscle loss remains unknown. Therefore, we aimed to identify the impact of sex on CLD, HE, and muscle mass loss in a rodent model of CLD. Liver injury markers, hyperammonemia, oxidative stress, muscle mass, and ammonia clearance were measured in female and male bile-duct ligated (BDL) rats. In addition, covert HE was assessed in females while ammonia-precipitated severe HE was assessed in female and male BDL rats, and male BDL rats treated with allopurinol (100 mg/kg), an antioxidant (xanthine oxidase inhibitor). Female BDL developed CLD and HE (impaired motor coordination and night activity) compared to respective SHAM. Hyperammonemia and muscle ammonia clearance were similar between female and male BDL. However, only female BDL rats did not develop muscle loss, brain edema, and short-term memory impairment (vs. female SHAM) and systemic oxidative stress and decreased albumin levels (vs. male BDL). Furthermore, both female BDL and allopurinol-treated male BDL rats were protected against ammonia-induced overt HE. In conclusion, female and male BDL rats develop distinct features of CLD and HE, with systemic oxidative stress playing a pivotal role in the susceptibility to ammonia-precipitated overt HE.

Dysregulation of Astrocytic Glutamine Transport in Acute Hyperammonemic Brain Edema.

Acute liver failure (ALF) impairs ammonia clearance from blood, which gives rise to acute hyperammonemia and increased ammonia accumulation in the brain. Since in brain glutamine synthesis is the only route of ammonia detoxification, hyperammonemia is as a rule associated with increased brain glutamine content (glutaminosis) which correlates with and contributes along with ammonia itself to hyperammonemic brain edema-associated with ALF. This review focuses on the effects of hyperammonemia on the two glutamine carriers located in the astrocytic membrane: Slc38a3 (SN1, SNAT3) and Slc7a6 (y + LAT2). We emphasize the contribution of the dysfunction of either of the two carriers to glutaminosis- related aspects of brain edema: retention of osmotically obligated water (Slc38a3) and induction of oxidative/nitrosative stress (Slc7a6). The changes in glutamine transport link glutaminosis- evoked mitochondrial dysfunction to oxidative-nitrosative stress as formulated in the “Trojan Horse” hypothesis.

Hyperammonemia Post Lung Transplant: A Rare and Fatal Complication

Introduction Among the extra pulmonary complications associated with lung transplantation, severe hyperammonemia has been reported as a rare and fatal complication with an incidence of up to 4% and a fatality rate of 67% in some case series. We present a case report of a patient who underwent bilateral lung transplantation and developed severe hyperammonemia in his immediate post-operative course. Case Report A 66 year old male with past medical history of idiopathic pulmonary fibrosis was referred to our center for evaluation for bilateral lung transplantation. He underwent a technically uncomplicated successful procedure and his immediate post-operative course was complicated by metabolic acidosis and acute renal failure. On post op day 4 he developed mental status changes and was noted to have elevated plasma ammonia of 154 mcmol/L. Laboratory and imaging studies were negative for acute hepatic dysfunction. A head CT was negative for cerebral edema or acute findings. He was started on rifaximin, lactulose enemas and via nasogastric tube, in addition to empiric macrolide therapy. Despite these interventions his mental examination and ammonia level did not improve in the following 24 hours. He was initiated on L-arginine, sodium benzoate and levocarnitine for possible undiagnosed glutathione synthase deficiency. Continuous renal replacement therapy (CRRT) for more rapid ammonia clearance was also started. He required CRRT for 5 days with gradual improvement in mental status. CRRT was discontinued once plasma levels normalized. He was slowly weaned off the above pharmacological interventions in the ensuing 3 weeks. He was discharged to inpatient rehabilitation without the need of any medical therapies for hyperammoenmia on post op day 30. He remained well for a period of 4 years post-transplant and eventually succumbed to chronic lung allograft dysfunction. Summary The primary underlying mechanism for post transplant hyperammonemia remains unknown, but several risk factors have been linked to this condition. The most commonly reported are disseminated opportunistic infection with ureaplasma or mycoplasma, high nitrogen loads, pulmonary hypertension and hepatic glutamine synthetase deficiency. Treatment regimens are multimodal but overall aimed at reducing ammonia levels and providing neuroprotection. Early initiation of treatment is paramount for improving survival and outcomes. Among the extra pulmonary complications associated with lung transplantation, severe hyperammonemia has been reported as a rare and fatal complication with an incidence of up to 4% and a fatality rate of 67% in some case series. We present a case report of a patient who underwent bilateral lung transplantation and developed severe hyperammonemia in his immediate post-operative course. A 66 year old male with past medical history of idiopathic pulmonary fibrosis was referred to our center for evaluation for bilateral lung transplantation. He underwent a technically uncomplicated successful procedure and his immediate post-operative course was complicated by metabolic acidosis and acute renal failure. On post op day 4 he developed mental status changes and was noted to have elevated plasma ammonia of 154 mcmol/L. Laboratory and imaging studies were negative for acute hepatic dysfunction. A head CT was negative for cerebral edema or acute findings. He was started on rifaximin, lactulose enemas and via nasogastric tube, in addition to empiric macrolide therapy. Despite these interventions his mental examination and ammonia level did not improve in the following 24 hours. He was initiated on L-arginine, sodium benzoate and levocarnitine for possible undiagnosed glutathione synthase deficiency. Continuous renal replacement therapy (CRRT) for more rapid ammonia clearance was also started. He required CRRT for 5 days with gradual improvement in mental status. CRRT was discontinued once plasma levels normalized. He was slowly weaned off the above pharmacological interventions in the ensuing 3 weeks. He was discharged to inpatient rehabilitation without the need of any medical therapies for hyperammoenmia on post op day 30. He remained well for a period of 4 years post-transplant and eventually succumbed to chronic lung allograft dysfunction. The primary underlying mechanism for post transplant hyperammonemia remains unknown, but several risk factors have been linked to this condition. The most commonly reported are disseminated opportunistic infection with ureaplasma or mycoplasma, high nitrogen loads, pulmonary hypertension and hepatic glutamine synthetase deficiency. Treatment regimens are multimodal but overall aimed at reducing ammonia levels and providing neuroprotection. Early initiation of treatment is paramount for improving survival and outcomes.