Impairment of enzymatic antioxidant defenses is associated with bilirubin-induced neuronal cell death in the cerebellum of Ugt1 KO mice

Uridine diphosphate glucuronosyltransferase 1A1 prevents the progression of liver injury

BACKGROUND

Uridine diphosphate glucuronosyltransferase 1A1 (UGT1A1) plays a crucial role in metabolizing and detoxifying endogenous and exogenous substances. However, its contribution to the progression of liver damage remains unclear.

AIM

To determine the role and mechanism of UGT1A1 in liver damage progression.

METHODS

We investigated the relationship between UGT1A1 expression and liver injury through clinical research. Additionally, the impact and mechanism of UGT1A1 on the progression of liver injury was analyzed through a mouse model study.

RESULTS

Patients with UGT1A1 gene mutations showed varying degrees of liver damage, while patients with acute-on-chronic liver failure (ACLF) exhibited relatively reduced levels of UGT1A1 protein in the liver as compared to patients with chronic hepatitis. This suggests that low UGT1A1 levels may be associated with the progression of liver damage. In mouse models of liver injury induced by carbon tetrachloride (CCl4) and concanavalin A (ConA), the hepatic levels of UGT1A1 protein were found to be increased. In mice with lipopolysaccharide or liver steatosis-mediated liver-injury progression, the hepatic protein levels of UGT1A1 were decreased, which is consistent with the observations in patients with ACLF. UGT1A1 knockout exacerbated CCl4- and ConA-induced liver injury, hepatocyte apoptosis and necroptosis in mice, intensified hepatocyte endoplasmic reticulum (ER) stress and oxidative stress, and disrupted lipid metabolism.

CONCLUSION

UGT1A1 is upregulated as a compensatory response during liver injury, and interference with this upregulation process may worsen liver injury. UGT1A1 reduces ER stress, oxidative stress, and lipid metabolism disorder, thereby mitigating hepatocyte apoptosis and necroptosis.

Expression profiling of N6-methyladenosine-modified mRNA in PC12 cells in response to unconjugated bilirubin

BACKGROUND

Abnormal methylation of N6-methyladenosine (m6A) is reportedly associated with central nervous system disorders. However, the role of m6A mRNA methylation in unconjugated bilirubin (UCB) neurotoxicity requires further research.

METHODS

Rat pheochromocytoma PC12 cells treated with UCB were used as in vitro models. After the PC12 cells were treated with UCB (0, 12, 18, and 24 µM) for 24 h, the total RNA m6A levels were measured using an m6A RNA methylation quantification kit. The expression of m6A demethylases and methyltransferases was detected through western blotting. We determined the m6A mRNA methylation profile in PC12 cells exposed to UCB (0 and 18 µM) for 24 h using methylated RNA immunoprecipitation sequencing (MeRIP-seq).

RESULTS

Compared with the control group, UCB (18 and 24 µM) treatment decreased the expression of the m6A demethylase ALKBH5 and increased the expression of the methyltransferases METTL3 and METTL14, which resulted in an increase in the total m6A levels in PC12 cells. Furthermore, 1533 m6A peaks were significantly elevated and 1331 peaks were reduced in the UCB (18 µM)-treated groups compared with those in the control group. Genes with differential m6A peaks were mainly enriched in protein processing in the endoplasmic reticulum, ubiquitin-mediated proteolysis, cell cycle, and endocytosis. Through combined analysis of the MeRIP-seq and RNA sequencing data, 129 genes with differentially methylated m6A peaks and differentially expressed mRNA levels were identified.

CONCLUSION

Our study suggests that the modulation of m6A methylation modifications plays a significant role in UCB neurotoxicity.

Genetic alterations and molecular mechanisms underlying hereditary intrahepatic cholestasis

Hereditary cholestatic liver disease caused by a class of autosomal gene mutations results in jaundice, which involves the abnormality of the synthesis, secretion, and other disorders of bile acids metabolism. Due to the existence of a variety of gene mutations, the clinical manifestations of children are also diverse. There is no unified standard for diagnosis and single detection method, which seriously hinders the development of clinical treatment. Therefore, the mutated genes of hereditary intrahepatic cholestasis were systematically described in this review.

Bilirubin gates the TRPM2 channel as a direct agonist to exacerbate ischemic brain damage

Stroke prognosis is negatively associated with an elevation of serum bilirubin, but how bilirubin worsens outcomes remains mysterious. We report that post-, but not pre-, stroke bilirubin levels among inpatients scale with infarct volume. In mouse models, bilirubin increases neuronal excitability and ischemic infarct, whereas ischemic insults induce the release of endogenous bilirubin, all of which are attenuated by knockout of the TRPM2 channel or its antagonist A23. Independent of canonical TRPM2 intracellular agonists, bilirubin and its metabolic derivatives gate the channel opening, whereas A23 antagonizes it by binding to the same cavity. Knocking in a loss of binding point mutation for bilirubin, TRPM2-D1066A, effectively antagonizes ischemic neurotoxicity in mice. These findings suggest a vicious cycle of stroke injury in which initial ischemic insults trigger the release of endogenous bilirubin from injured cells, which potentially acts as a volume neurotransmitter to activate TRPM2 channels, aggravating Ca²⁺-dependent brain injury.

Models of bilirubin neurological damage: lessons learned and new challenges

OBJECTIVE

Jaundice (icterus) is the visible manifestation of the accumulation of bilirubin in the tissue and is indicative of potential toxicity to the brain. Since its very first description more than 2000 years ago, many efforts have been undertaken to understand the molecular determinants of bilirubin toxicity to neuronal cells to reduce the risk of neurological sequelae through the use of available chemicals and in vitro, ex vivo, in vivo, and clinical models. Although several studies have been performed, important questions remain unanswered, such as the reasons for regional sensitivity and the interplay with brain development. The number of new molecular effects identified has increased further, which has added even more complexity to the understanding of the condition. As new research challenges emerged, so does the need to establish solid models of prematurity.

METHODS

This review critically summarizes the key mechanisms of severe neonatal hyperbilirubinemia and the use of the available models and technologies for translational research.

IMPACT

We critically review the conceptual dogmas and models used for studying bilirubin-induced neurotoxicity. We point out the pitfalls and translational gaps, and suggest new clinical research challenges. We hope to inform researchers on the pro and cons of the models used, and to help direct their experimental focus in a most translational research.

Ameliorative effect of oregano (Origanum vulgare) versus silymarin in experimentally induced hepatic encephalopathy

Hepatic encephalopathy (HE) is a deterioration of brain function in patients suffering from chronic liver disease, cirrhosis as a result of elevated blood ammonia and the production of pseudo-neurotransmitters. Herein, we investigated the chemical composition of hexane extract from Origanum vulgare (O. vulgare) leaves as well as its possible protective effects against thioacetamide (TAA)-induced HE in rats. GC-MS analysis of the extract revealed tentative identification of twenty-five compounds (82.93%), predominated by cholesten-3-one (27.30%), followed by γ-tocopherol (13.52%), α-tocopherol (5.01%), β-amyrin (5.24%) and α-amyrin (4.89%). Albino rats were distributed into seven groups (n = 7). G₁ served as negative control; G₂ and G₃ served as controls treated with O. vulgare (100 and 200 mg/kg/p.o b.w, respectively); G₄ served as TAA-positive control group (100 mg/kg/day/i.p., three alternative days per week for six weeks); G5, G6, and G7 served as TAA -induced HE rat model that received O. vulgare 100, O. vulgare 200, and silymarin (100 mg/kg of SILY, as standard drug), respectively. TAA showed depressive and anxiety-like behaviors in forced swimming test (FST) and reduction of cognitive score in elevated plus-maze test (EPMT) as well as impairment of locomotor and exploratory activities in open-field test (OFT). TAA caused a significant decline in body weight gain; however, the relative liver weight and brain water content were statistically increased. TAA-intoxicated rats showed significant increase of serum biomarker enzymes, proinflammatory cytokines, blood ammonia levels, brain serotonin, acetyl cholinesterase and cellular lipid peroxidation with significant decrease of brain dopamine, norepinephrine, antioxidant status. The hepatoprotective/neuro-protective activities of O. vulgare was found to be comparable with that of SILY in HE rats model. Where, treatment of TAA-intoxicated rats with O. vulgare attenuated anxiety, depressive-related behaviors, and reduced the biochemical changes in HE-induced by TAA. Therefore, O. vulgare could be an excellent hepato-/neuroprotective against hepatic injury and HE via improving the oxidative/inflammatory status through its antioxidant and neuro-modulatory properties and its effect is equal to that of SILY.

Hyperbilirubinemia after surgical repair for acute type a aortic dissection: A propensity score-matched analysis

Background: Inflammation and oxidative stress are known to participate in the pathogenesis of hyperbilirubinemia. It has been known that acute type A aortic dissection (ATAAD) surgical repair often associates with complications which might affect the long-term prognosis. However, the clinical significance of postoperative hyperbilirubinemia (PH) has not been evaluated. Here in this study, we examined the incidence, risk factors, and prognosis of PH after ATAAD surgery.

Methods: This retrospective study enrolled a total of 970 patients who received ATAAD surgical repair from January 2014 to December 2019. PH was defined as serum total bilirubin >3.0 mg/dl within the first week after the surgery. Propensity score matching was used to reduce selection bias and eliminate potential confounding factors. Kaplan–Meier survival and Cox proportional hazards regression analyses were conducted to explore the association between PH and postoperative long-term survival.

Results: Development of PH (183 patients) was associated with a higher 30-Day mortality (20.8% vs. 9.0%, p < 0.001). Advanced age [odds ratio (OR) 1.538, p = 0.006], higher baseline total bilirubin level (OR 1.735, p = 0.026), preoperative pericardial tamponade (OR 3.192, p = 0.024), prolonged cardiopulmonary bypass (CPB) duration (OR 2.008, p = 0.005), and elevated postoperative central venous pressure (CVP) level (OR 2.183, p < 0.001) were associated with PH. The Kaplan-Meier analysis showed patients who developed PH were associated with poor long-term survival (p = 0.044). Cox analysis showed that the presence of PH (hazard ratio 2.006, p = 0.003) was an independent risk factor for increased mortality.

Conclusion: PH is a common complication in patients undergoing ATAAD surgical repair that associates with worse short- and long-term prognosis. Our data indicated that age, preoperative total bilirubin level, pericardial tamponade, CPB duration, and postoperative CVP level were risk factors for the development of PH.

Bilirubin-Induced Neurological Damage: Current and Emerging iPSC-Derived Brain Organoid Models

Bilirubin-induced neurological damage (BIND) has been a subject of studies for decades, yet the molecular mechanisms at the core of this damage remain largely unknown. Throughout the years, many in vivo chronic bilirubin encephalopathy models, such as the Gunn rat and transgenic mice, have further elucidated the molecular basis of bilirubin neurotoxicity as well as the correlations between high levels of unconjugated bilirubin (UCB) and brain damage. Regardless of being invaluable, these models cannot accurately recapitulate the human brain and liver system; therefore, establishing a physiologically recapitulating in vitro model has become a prerequisite to unveil the breadth of complexities that accompany the detrimental effects of UCB on the liver and developing human brain. Stem-cell-derived 3D brain organoid models offer a promising platform as they bear more resemblance to the human brain system compared to existing models. This review provides an explicit picture of the current state of the art, advancements, and challenges faced by the various models as well as the possibilities of using stem-cell-derived 3D organoids as an efficient tool to be included in research, drug screening, and therapeutic strategies for future clinical applications.

Calycosin alleviates hyperbilirubin nerve injury in Ugt1-/- mice by inhibiting oxidative stress, apoptosis, and mitochondrial function

BACKGROUND AND PURPOSE

Hyperbilirubinemia is a common condition in neonates that is associated with poor neurodevelopmental outcomes. Although studies have proposed that calycosin has a neuroprotective effect, the exact molecular mechanism underlying calycosin treatment of hyperbilirubinemia remains elusive. To fill this gap, we analyzed the mechanism of calycosin treatment in hyperbilirubinemia model mice.

METHOD

Thirty neonatal mice were randomly divided into wide type (WT), Ugt1^-/- and calycosin treatment group. Neuronal damage was observed with Nissl staining. Immunofluorescence staining were carried out to determine DNA damage repair and neurodegeneration. Oxidative stress was investigated by immunostaining with 4-hydroxynonenal (4-HNE). Western blot (WB) and Qpcr were used to detect relative protein and mRNA expression levels. Mitochondrial CI/CII activity of mitochondria was analyzed with a spectrophotometer.

RESULT

The total bilirubin concentration was significantly higher in Ugt1-/- group compared with WT, but calycosin treatment reduced concentration of bilirubin. The total bilirubin and bilirubin/albumin ratio were significantly higher at postnatal day 4 compared with day 2. Calycosin treatment reduced serum bilirubin concentration and bilirubin/albumin ratio. After calycosin treatment, Nissl body count increased, apoptosis-related protein was downregulated and 4-HNE level decreased. Compared with Ugt-/- group, calycosin treatment increased neurons (NeuN+) and calbindin positive cells and decreased fluorojade C(FJC)positive neurons in WT group. In mitochondria, calycosin alleviated mitochondrial electron transport chain dysfunction in Ugt1-/- mice.

CONCLUSION

We demonstrated that the mechanism of calycosin treatment on hyperbilirubinemia-induced Ugt1^-/- was associated mainly with antioxidant effects, antiapoptosis and inhibition of normal mitochondrial function.

Pathological Significance and Prognostic Roles of Indirect Bilirubin/Albumin Ratio in Hepatic Encephalopathy

Background and Aim: Hepatic encephalopathy (HE) is a neurological disease caused by severe liver disease. Early identification of the risk factor is beneficial to the prevention and treatment of HE. Free bilirubin has always been considered to be the culprit of neonatal kernicterus, but there is no research to explore its role in HE. In this study, we aim to study the clinical significance of the indirect bilirubin-albumin ratio in HE.

Methods: A retrospective case-control study of 204 patients with liver failure was conducted. Human serum albumin (HSA) or heme oxygenase-1 (HO-1) inhibitor SnPP (Tin protoporphyrin IX dichloride) was injected intraperitoneally into Ugt1^−/− mice to establish a treatment model for endogenous hyperbilirubinemia.

Results: IBil/albumin ratio (OR = 1.626, 95% CI1.323–2.000, P < 0.001), white blood cell (WBC) (OR = 1.128, 95% CI 1.009–1.262, P = 0.035), ammonia (OR = 1.010, 95% CI 1.001–1.019, P = 0.027), platelet (OR=1.008, 95% CI 1.001–1.016, P = 0.022), Hb (OR = 0.977, 95% CI 0.961–0.994, P = 0.007), and PTA (OR = 0.960, 95% CI 0.933–0.987, P = 0.005) were independent factors of HE. Patients with a history of liver cirrhosis and severe HE (OR = 12.323, 95% CI 3.278–47.076, P < 0.001) were more likely to die during hospitalization. HSA or SnPP treatment improved cerebellum development and reduced apoptosis of cerebellum cells.

Conclusion: The IBil/albumin ratio constitutes the most powerful risk factor in the occurrence of HE, and reducing free bilirubin may be a new strategy for HE treatment.

Quantitative proteomic characterization of microvesicles/exosomes from the cerebrospinal fluid of patients with acute bilirubin encephalopathy

Severe hyperbilirubinemia causes neurotoxicity and may lead to acute bilirubin encephalopathy (ABE) during the critical period of central nervous system development. The aim of the present study was to identify differentially expressed proteins (DEPs) in microvesicles/exosomes (MV/E) isolated from the cerebrospinal fluid (CSF) of patients with ABE. Co-precipitation was used to isolate the MV/E from the CSF of patients with ABE and age-matched controls. Isobaric tagging for relative and absolute quantification-based proteomic technology combined with liquid chromatography/tandem mass spectrometry was used to identify DEPs in the MV/E. Bioinformatics analysis was subsequently performed to investigate Gene Ontology functional annotation and Kyoto Encyclopedia of Genes and Genomes enriched signaling pathways of these DEPs. A total of four proteins were selected for further validation via western blotting. A total of 291 dysregulated proteins were identified by comparing the patients with ABE with the controls. Bioinformatics analysis indicated the involvement of immune-inflammation-associated cellular processes and signaling pathways in the pathophysiology of ABE. In conclusion, the present study identified the proteomic profile of MV/E isolated from the CSF of patients with ABE. These results may provide an improved understanding of the pathogenesis of ABE and may help to identify early diagnostic biomarkers and therapeutic targets.

Experimental models assessing bilirubin neurotoxicity

The molecular and cellular events leading to bilirubin-induced neurotoxicity, the mechanisms regulating liver and intestine expression in neonates, and alternative pathways of bilirubin catabolism remain incompletely defined. To answer these questions, researchers have developed a number of model systems to closely recapitulate the main characteristics of the disease, ranging from tissue cultures to engineered mouse models. In the present review we describe in vitro, ex vivo, and in vivo models developed to study bilirubin metabolism and neurotoxicity, with a special focus on the use of engineered animal models. In addition, we discussed the most recent studies related to potential therapeutic approaches to treat neonatal hyperbilirubinemia, ranging from anti-inflammatory drugs, activation of nuclear receptor pathways, blockade of bilirubin catabolism, and stimulation of alternative bilirubin-disposal pathways.

Minocycline protects neurons against glial cells-mediated bilirubin neurotoxicity

Unconjugated bilirubin, the end product of heme catabolism and antioxidant, induced brain damage in human neonates is a well-recognized clinical syndrome. However, the cellular and molecular mechanisms underlying bilirubin neurotoxicity remain unclear. To characterize the sequence of events leading to bilirubin-induced neurotoxicity, we investigated whether bilirubin-induced glial activation was involved in bilirubin neurotoxicity by exposing co-cultured rat glial cells and cerebellar granule neurons (CGN) to bilirubin. We found that bilirubin could markedly induce the expression of TNF-α and iNOS in glial cells, and even at low concentrations, the co-culture of glial cells with neurons significantly enhances neurotoxicity of bilirubin. Pretreatment of the co-cultured cells with minocycline protected CGN from glia-mediated bilirubin neurotoxicity and inhibited overexpression of TNF-α and iNOS in glia. Furthermore, we found that high doses of bilirubin were able to induce glial injury, and minocycline attenuated bilirubin-induced glial cell death. Our data suggest that glial cells play an important role in brain damage caused by bilirubin, and minocycline blocks bilirubin-induced encephalopathy possibly by directly and indirectly inhibiting neuronal death pathways.

Mouse models and strain-dependency of Chédiak-Higashi syndrome-associated neurologic dysfunction

Chédiak-Higashi syndrome (CHS) is a lethal disorder caused by mutations in the LYST gene that involves progressive neurologic dysfunction. Lyst-mutant mice exhibit neurologic phenotypes that are sensitive to genetic background. On the DBA/2J-, but not on the C57BL/6J-background, Lyst-mutant mice exhibit overt tremor phenotypes associated with loss of cerebellar Purkinje cells. Here, we tested whether assays for ataxia could measure this observed strain-dependency, and if so, establish parameters for empowering phenotype- and candidate-driven approaches to identify genetic modifier(s). A composite phenotypic scoring system distinguished phenotypes in Lyst-mutants and uncovered a previously unrecognized background difference between wild-type C57BL/6J and DBA/2J mice. Accelerating rotarod performance also distinguished phenotypes in Lyst-mutants, but at more advanced ages. These results establish that genetic background, Lyst genotype, and age significantly influence the severity of CHS-associated neurologic deficits. Purkinje cell quantifications likewise distinguished phenotypes of Lyst-mutant mice, as well as background differences between wild-type C57BL/6J and DBA/2J mice. To aid identification of potential genetic modifier genes causing these effects, we searched public datasets for cerebellar-expressed genes that are differentially expressed and/or contain potentially detrimental genetic variants. From these approaches, Nos1, Prdx2, Cbln3, Gnb1, Pttg1 were confirmed to be differentially expressed and leading candidates.

High unbound bilirubin for age: a neurotoxin with major effects on the developing brain

Neonatal hyperbilirubinemia is one of the most frequent diagnoses made in neonates. A high level of unconjugated bilirubin that is unbound to albumin is neurotoxic when the level exceeds age-specific thresholds or at lower levels in neonates with neurotoxic risk factors. Lower range of unbound bilirubin results in apoptosis, while moderate-to-high levels result in neuronal necrosis. Basal ganglia and various brain stem nuclei are more susceptible to bilirubin toxicity. Proposed mechanisms of bilirubin-induced neurotoxicity include excessive release of glutamate, mitochondrial energy failure, release of proinflammatory cytokines, and increased intracellular calcium concentration. These mechanisms are similar to the events that occur following hypoxic-ischemic insult in neonates. Severe hyperbilirubinemia in term neonates has been shown to be associated with increased risk for autism spectrum disorders. The neuropathological finding of bilirubin-induced neurotoxicity also includes cerebellar injury with a decreased number of Purkinje cells, and disruption of multisensory feedback loop between cerebellum and cortical neurons which may explain the clinical characteristics of autism spectrum disorders. Severe hyperbilirubinemia occurs more frequently in infants from low- and middle-income countries (LMIC). Simple devices to measure bilirubin, and timely treatment are essential to reduce neurotoxicity, and improve outcomes for thousands of neonates around the world.

Bilirubin-Induced Oxidative Stress Leads to DNA Damage in the Cerebellum of Hyperbilirubinemic Neonatal Mice and Activates DNA Double-Strand Break Repair Pathways in Human Cells

Unconjugated bilirubin is considered a potent antioxidant when present at moderate levels. However, at high concentrations, it produces severe neurological damage and death associated with kernicterus due to oxidative stress and other mechanisms. While it is widely recognized that oxidative stress by different toxic insults results in severe damage to cellular macromolecules, especially to DNA, no data are available either on DNA damage in the brain triggered by hyperbilirubinemia during the neonatal period or on the activation of DNA repair mechanisms. Here, using a mouse model of neonatal hyperbilirubinemia, we demonstrated that DNA damage occurs in vivo in the cerebellum, the brain region most affected by bilirubin toxicity. We studied the mechanisms associated with potential toxic action of bilirubin on DNA in in vitro models, which showed significant increases in DNA damage when neuronal and nonneuronal cells were treated with 140 nM of free bilirubin (Bf), as determined by γH2AX Western blot and immunofluorescence analyses. Cotreatment of cells with N-acetyl-cysteine, a potent oxidative-stress inhibitor, prevented DNA damage by bilirubin, supporting the concept that DNA damage was caused by bilirubin-induced oxidative stress. Bilirubin treatment also activated the main DNA repair pathways through homologous recombination (HR) and nonhomologous end joining (NHEJ), which may be adaptive responses to repair bilirubin-induced DNA damage. Since DNA damage may be another important factor contributing to neuronal death and bilirubin encephalopathy, these results contribute to the understanding of the mechanisms associated with bilirubin toxicity and may be of relevance in neonates affected with severe hyperbilirubinemia.

Histone acetylation as a new mechanism for bilirubin-induced encephalopathy in the Gunn rat

Bilirubin neurotoxicity has been studied for decades and has been shown to affect various mechanisms via significant modulation of gene expression. This suggests that vital regulatory mechanisms of gene expression, such as epigenetic mechanisms, could play a role in bilirubin neurotoxicity. Histone acetylation has recently received attention in the CNS due to its role in gene modulation for numerous biological processes, such as synaptic plasticity, learning, memory, development and differentiation. Aberrant epigenetic regulation of gene expression in psychiatric and neurodegenerative disorders has also been described. In this work, we followed the levels of histone 3 lysine 14 acetylation (H3K14Ac) in the cerebellum (Cll) of the developing (2, 9, 17 days after the birth) and adult Gunn rat, the natural model for neonatal hyperbilirubinemia and kernicterus. We observed an age-specific alteration of the H3K14Ac in the hyperbilirubinemic animals. The GeneOntology analysis of the H3K14Ac linked chromatin revealed that almost 45% of H3K14Ac ChiP-Seq TSS-promoter genes were involved in CNS development including maturation and differentiation, morphogenesis, dendritogenesis, and migration. These data suggest that the hallmark Cll hypoplasia in the Gunn rat occurs also via epigenetically controlled mechanisms during the maturation of this brain structure, unraveling a novel aspect of the bilirubin-induced neurotoxicity.

Iron-mediated oxidative cell death is a potential contributor to neuronal dysfunction induced by neonatal hemolytic hyperbilirubinemia

The review article discusses current knowledge of iron-mediated oxidative cell death (ferroptosis) and its potential role in the pathogenesis of neuronal dysfunction induced by neonatal hemolytic hyperbilirubinemia. The connection between metabolic conditions related to hemolysis (iron and bilirubin overload) and iron-induced lipid peroxidation is highlighted. Neurotoxicity of iron and bilirubin is associated with their release from destructed erythrocytes in response to hemolytic disease. Iron overload initiates lipid peroxidation through the reactive oxygen species production resulting to oxidative damage to cells. Excessive loading of immature brain cells by iron-induced formation of reactive oxygen species contributes to the development of various neurodevelopmental disorders. The causal relationship between iron overload and susceptibility of brain cells to oxidative damage by ferroptosis appears to be associated not only with the amount of redox-active iron involved in oxidative cell damage but also with the degree of maturity of the neonatal brain. Neuronal dysfunction induced by neonatal hemolytic disease can represent a specific model of ferroptosis. The mechanism by which iron overload triggers ferroptosis is not completely explained. However, hemolysis of neonatal red blood cells appears to be a determining factor. Potential therapeutic strategy with iron-chelating agents to inhibit ferroptosis has a promising future in postnatal care.

The p53 Family in Brain Disease

SIGNIFICANCE

The p53 family of transcription factors, including p53, p63, and p73, plays key roles in both biological and pathological processes, including cancer and neural development. Recent Advances: In recent years, a growing body of evidence has indicated that the entire p53 family is involved in the regulation of the central nervous system (CNS) functions as well as in the pathogenesis of several neurological disorders. Mechanistically, the p53 proteins control neuronal cell fate, terminal differentiation, and survival, via a complex interplay among the family members.

CRITICAL ISSUES

In this article, we discuss the involvement of the p53 family in neurobiology and in pathological conditions affecting the CNS, including neuroinflammation.

FUTURE DIRECTIONS

Understanding the molecular mechanism(s) underlying the function of the p53 family could improve our general knowledge of the pathogenesis of brain disorders and potentially pave the road for new therapeutic intervention. Antioxid. Redox Signal. 29, 1-14.

Reverse chemical ecology: Olfactory proteins from the giant panda and their interactions with putative pheromones and bamboo volatiles

The giant panda Ailuropoda melanoleuca belongs to the family of Ursidae; however, it is not carnivorous, feeding almost exclusively on bamboo. Being equipped with a typical carnivorous digestive apparatus, the giant panda cannot get enough energy for an active life and spends most of its time digesting food or sleeping. Feeding and mating are both regulated by odors and pheromones; therefore, a better knowledge of olfaction at the molecular level can help in designing strategies for the conservation of this species. In this context, we have identified the odorant-binding protein (OBP) repertoire of the giant panda and mapped the protein expression in nasal mucus and saliva through proteomics. Four OBPs have been identified in nasal mucus, while the other two were not detected in the samples examined. In particular, AimelOBP3 is similar to a subset of OBPs reported as pheromone carriers in the urine of rodents, saliva of the boar, and seminal fluid of the rabbit. We expressed this protein, mapped its binding specificity, and determined its crystal structure. Structural data guided the design and preparation of three protein mutants bearing single-amino acid replacements in the ligand-binding pocket, for which the corresponding binding affinity spectra were measured. We also expressed AimelOBP5, which is markedly different from AimelOBP3 and complementary in its binding spectrum. By comparing our binding data with the structures of bamboo volatiles and those of typical mammalian pheromones, we formulate hypotheses on which may be the most relevant semiochemicals for the giant panda.

Repeated AAV-mediated gene transfer by serotype switching enables long-lasting therapeutic levels of hUgt1a1 enzyme in a mouse model of Crigler-Najjar Syndrome Type I

Adeno-associated virus (AAV) -mediated gene therapy is a promising strategy to treat liver-based monogenic diseases. However, two major obstacles limit its success: first, vector dilution in actively dividing cells, such as hepatocytes in neonates/children, due to the non-integrating nature of the vector; second, development of an immune response against the transgene and/or viral vector. Crigler-Najjar Syndrome Type I is a rare monogenic disease with neonatal onset, caused by mutations in the liver-specific UGT1 gene, with toxic accumulation of unconjugated bilirubin in plasma, tissues and brain. To establish an effective and long lasting cure, we applied AAV-mediated liver gene therapy to a relevant mouse model of the disease. Repeated gene transfer to adults by AAV-serotype switching, upon neonatal administration, resulted in lifelong correction of total bilirubin (TB) levels in both genders. In contrast, vector loss over time was observed after a single neonatal administration. Adult administration resulted in lifelong TB levels correction in male, but not female Ugt1^-/- mice. Our findings demonstrate that neonatal AAV-mediated gene transfer to the liver supports a second transfer of the therapeutic vector, by preventing the induction of an immune response and supporting the possibility to improve AAV-therapeutic efficacy by repeated administration.

Developmental, Genetic, Dietary, and Xenobiotic Influences on Neonatal Hyperbilirubinemia

Hyperbilirubinemia, caused by the accumulation of unconjugated bilirubin, is one of the most common clinical diagnoses in both premature and term newborns. Owing to the fact that bilirubin is metabolized solely through glucuronidation by UDP-glucuronosyltransferase (UGT) 1A1, it is now known that immaturity of UGT1A1, in combination with the overproduction of bilirubin during the developmental stage, acts as a bottleneck to bilirubin elimination and predisposes the infant to high total serum bilirubin levels. Although neonatal jaundice is mostly benign, excessively high levels of serum bilirubin in a small percentage of newborns can cause bilirubin-induced neurologic dysfunction, potentially leading to permanent brain damage, a condition known as kernicterus Although a large portion of hyperbilirubinemia cases in newborns are associated with hemolytic diseases, we emphasize here the impaired ability of UGT1A1 to eliminate bilirubin that contributes to hyperbilirubinemia-induced neurotoxicity in the developmental stage. As a series of hereditary UGT1A1 mutations have been identified that are associated with UGT1A1 deficiency, new evidence has verified that delayed expression of UGT1A1 during the early stages of neonatal development is a tightly controlled event involving coordinated intrahepatic and extrahepatic regulation. This review recapitulates the progress that has been made in recent years in understanding the causes and physiopathology of severe hyperbilirubinemia, investigating molecular mechanisms underlying bilirubin-induced encephalopathy, and searching for potential therapies for treating pathologic hyperbilirubinemia. Several animal models have been developed to make it possible to examine bilirubin-induced neurotoxicity from multiple directions. Moreover, environmental factors that may alleviate or worsen the condition of hyperbilirubinemia are discussed.

Inflammatory signature of cerebellar neurodegeneration during neonatal hyperbilirubinemia in Ugt1 -/- mouse model

Background

Severe hyperbilirubinemia is toxic during central nervous system development. Prolonged and uncontrolled high levels of unconjugated bilirubin lead to bilirubin-induced neurological damage and eventually death by kernicterus. Bilirubin neurotoxicity is characterized by a wide array of neurological deficits, including irreversible abnormalities in motor, sensitive and cognitive functions, due to bilirubin accumulation in the brain. Despite the abundant literature documenting the in vitro and in vivo toxic effects of bilirubin, it is unclear which molecular and cellular events actually characterize bilirubin-induced neurodegeneration in vivo.

Methods

We used a mouse model of neonatal hyperbilirubinemia to temporally and spatially define the response of the developing cerebellum to the bilirubin insult.

Results

We showed that the exposure of developing cerebellum to sustained bilirubin levels induces the activation of oxidative stress, ER stress and inflammatory markers at the early stages of the disease onset. In particular, we identified TNFα and NFKβ as key mediators of bilirubin-induced inflammatory response. Moreover, we reported that M1 type microglia is increasingly activated during disease progression.

Failure to counteract this overwhelming stress condition resulted in the induction of the apoptotic pathway and the generation of the glial scar. Finally, bilirubin induced the autophagy pathway in the stages preceding death of the animals.

Conclusions

This study demonstrates that inflammation is a key contributor to bilirubin damage that cooperates with ER stress in the onset of neurotoxicity. Pharmacological modulation of the inflammatory pathway may be a potential intervention target to ameliorate neonatal lethality in Ugt1^-/- mice.

Electronic supplementary material

The online version of this article (doi:10.1186/s12974-017-0838-1) contains supplementary material, which is available to authorized users.

Impact of Exposure to Fenitrothion on Vital Organs in Rats

This study was designed to investigate the impact of oral administration of fenitrothion (10 mg/kg) on liver, kidney, brain, and lung function in rats. The effect was studied on days 7, 14, 21, 28, and 42. Our results have shown deterioration in liver function as evidenced by the elevation in serum ALT, AST, ALP, and bilirubin and reduction in albumin and hepatic glycogen. This was associated with a state of hyperglycemia and hyperlipidemia and increased prothrombin time, while hemoglobin content was reduced. In addition, the kidney function was reduced as indicated by the elevation in serum creatinine, uric acid, and BUN, while the serum levels of magnesium, potassium, and sodium were reduced. This study also showed an impairment in brain neurotransmitter (elevated 5-HT, glutamate, GABA, and reduced dopamine and norepinephrine level). This was associated with a reduction in the barrier capacity in brain and lung. Fenitrothion also caused a decrease in cholinesterase activity in serum, lung, and brain activity associated with a state of oxidative stress in all tested organs and hyperammonemia. These results support the hazards of pesticide use and shows the importance of minimizing pesticide use or discovering new safe pesticides.

Flavonoid Interaction with a Chitinase from Grape Berry Skin: Protein Identification and Modulation of the Enzymatic Activity

In the present study, an antibody raised against a peptide sequence of rat bilitranslocase (anti-peptide Ab) was tested on microsomal proteins obtained from red grape berry skin. Previously, this antibody had demonstrated to recognize plant membrane proteins associated with flavonoid binding and transport. Immuno-proteomic assays identified a number of proteins reacting with this particular antibody, suggesting that the flavonoid binding and interaction may be extended not only to carriers of these molecules, but also to enzymes with very different functions. One of these proteins is a pathogenesis-related (PR) class IV chitinase, whose in vitro chitinolytic activity was modulated by two of the most representative flavonoids of grape, quercetin and catechin, as assessed by both spectrophotometric and fluorimetric assays in grape microsomes and commercial enzyme preparations. The effect of these flavonoids on the catalysis and its kinetic parameters was also evaluated, evidencing that they determine a hormetic dose-dependent response. These results highlight the importance of flavonoids not only as antioxidants or antimicrobial effectors, but also as modulators of plant growth and stress response. Implications of the present suggestion are here discussed in the light of environment and pesticide-reduction concerns.

Reduced Myelination and Increased Glia Reactivity Resulting from Severe Neonatal Hyperbilirubinemia

Bilirubin-induced neurologic dysfunction (BIND) and kernicterus has been used to describe moderate to severe neurologic dysfunction observed in children exposed to excessive levels of total serum bilirubin (TSB) during the neonatal period. Here we use a new mouse model that targets deletion of the Ugt1 locus and the Ugt1a1 gene in liver to promote hyperbilirubinemia-induced seizures and central nervous system toxicity. The accumulation of TSB in these mice leads to diffuse yellow coloration of brain tissue and a marked cerebellar hypoplasia that we characterize as kernicterus. Histologic studies of brain tissue demonstrate that the onset of severe neonatal hyperbilirubinemia, characterized by seizures, leads to alterations in myelination and glia reactivity. Kernicterus presents as axonopathy with myelination deficits at different brain regions, including pons, medulla oblongata, and cerebellum. The excessive accumulation of TSB in the early neonatal period (5 days after birth) promotes activation of the myelin basic protein (Mbp) gene with an accelerated loss of MBP that correlates with a lack of myelin sheath formation. These changes were accompanied by increased astroglial and microglial reactivity, possibly as a response to myelination injury. Interestingly, cerebellum was the area most affected, with greater myelination impairment and glia burden, and showing a marked loss of Purkinje cells and reduced arborization of the remaining ones. Thus, kernicterus in this model displays not only axonal damage but also myelination deficits and glial activation in different brain regions that are usually related to the neurologic sequelae observed after severe hyperbilirubinemia.