Short Term Exposure to Bilirubin Induces Encephalopathy Similar to Alzheimer’s Disease in Late Life

Iron Overload, Microbleeding and the Role of Bilirubin in Alzheimer's Disease Brain: Revisiting the Vascular Hypothesis

Alzheimer's disease (AD) and vascular dementia (VaD) are the two most prevalent forms of dementia, sharing overlapping clinical features yet distinct pathophysiological mechanisms. While AD is primarily driven by amyloid-beta (Aβ) plaques and tau neurofibrillary tangles, VaD results from cerebrovascular pathology, including ischemic lesions and chronic hypoperfusion. However, accumulating evidence suggests that vascular dysfunction is a crucial contributor to both conditions, bridging neurodegenerative and cerebrovascular pathologies. In this review, we explore the interplay between AD and VaD, focusing on shared pathways such as blood-brain barrier (BBB) breakdown, neuroinflammation, and microvascular damage. Notably, cerebral microbleeds have emerged as a common feature in both AD and VaD, further linking vascular pathology to neurodegeneration. Microbleeding contributes to BBB disruption, iron deposition, and exacerbated oxidative stress, creating a vicious cycle that accelerates cognitive decline. We highlight the role of iron dysregulation as a key driver in AD, exacerbating Aβ accumulation, tau hyperphosphorylation, and ferroptosis. Conversely, bilirubin emerges as a molecule with theranostic potential, acting as both a biomarker and a neuroprotective agent due to its antioxidant and anti-inflammatory properties. Despite its protective role, bilirubin's dysregulation under pathological conditions may contribute to oxidative damage and neurovascular dysfunction. In this context, the accumulation of iron from recurrent microbleeds may further disrupt bilirubin homeostasis, amplifying oxidative injury and inflammation. We propose a vascular hypothesis that integrates iron metabolism and bilirubin homeostasis, suggesting that their imbalance plays a central role in AD pathogenesis and worsening. Understanding the intricate molecular interplay between neurodegeneration and vascular dysfunction could provide novel insights into targeted interventions aimed at mitigating cognitive decline. Finally, we discuss the potential of bilirubin-based therapeutic strategies, including its role in counteracting oxidative stress and modulating neuroinflammatory pathways, offering promising avenues for future research and precision medicine in dementia.

Unraveling the dual role of bilirubin in neurological Diseases: A Comprehensive exploration of its neuroprotective and neurotoxic effects

Neurodegenerative disorders are characterized by a progressive loss of neurons, causing substantial deficits in motor and cognitive functioning. Bilirubin is a yellow by-product of heme, existing in two primary isoforms namely unconjugated and conjugated, while initially produced unconjugated isomer is lipophilic and cytotoxic in nature. At physiological levels, bilirubin has an important role in brain function by acting as a powerful antioxidant, preventing brain tissues from oxidative damage by eliminating reactive oxygen species (ROS). Additionally, it contributes to immune regulation through microglial activation, cytokine release, complement system interception, fragment crystallization (Fc) receptor modulation, and major histocompatibility complex (MHC II) expression modification, which lower the risk of inflammatory and autoimmune reactions in the central nervous system (CNS). As per the literature, serum bilirubin concentrations are associated with CNS diseases such as Alzheimer's disease (AD), Parkinson's disease (PD), ischemic stroke, hemorrhagic stroke, traumatic brain injury (TBI), multiple sclerosis (MS), epilepsy, schizophrenia and kernicterus spectrum disorder (KSD), which causes neuronal damage, especially in regions like the basal ganglia and cerebellum, which causes movement abnormalities and cognitive deficits. The aim of this article is to explore the dual role of bilirubin as neuroprotective and neurotoxic, essential for establishing effective therapeutic outcomes for neurodegenerative diseases by looking at its cellular mechanisms and discussing how bilirubin's antioxidant properties can shield neurons and, in some situations, may induce oxidative stress and apoptosis.

Visualization of Unconjugated Bilirubin In Vivo with a Novel Approach Using Chemical Exchange Saturation Transfer Magnetic Resonance Imaging in a Rat Model

Unconjugated bilirubin (UCB) visualization is valuable for early bilirubin encephalopathy (BE) diagnosis and management. UCB neurotoxicity is a challenge, necessitating improved imaging modalities for precise localization and characterization. This study developed a noninvasive method for UCB imaging in the brain using chemical exchange saturation transfer (CEST) magnetic resonance imaging, which visualizes UCB distribution through amide-bulk water proton exchange, a process termed bilirubin CEST (Bil-CEST) imaging. Bil-CEST imaging parameters were initially optimized; the exchange rate of the amide protons of UCB was calculated. Bil-CEST imaging characteristics and specificity were assessed using in vitro images of UCB solutions under different conditions and images of other brain metabolites. Bil-CEST maps of the rat brain were collected at the baseline and dynamically, postinjection of the UCB solution or vehicle into lateral ventricles of Sprague-Dawley rats. The model was validated using a water maze and pathological staining. In vitro, the Bil-CEST effect was observed at approximately 5.5 ppm downfield from bulk water. This effect was proportional to the UCB concentration and B1 amplitude. In vivo, Bil-CEST imaging revealed a progressive enhancement following a lateral ventricular UCB injection. Conversely, no significant imaging changes were observed in the vehicle group. Compared with the vehicle group, the UCB group had more hippocampal neuronal apoptosis and worse cognitive function. These findings highlight the utility of Bil-CEST in direct UCB imaging, indicating its potential as a clinically valuable biomarker for BE diagnosis and management.

Neuropathological implication of high blood bilirubin in patients and model rats with depression

PURPOSE

Elevated bilirubin levels have been associated with major depressive disorder (MDD); however, the exact impact of bilirubin on MDD and the underlying molecular mechanisms remain unclear. Here, we explored the influence of bilirubin on MDD and sought to identify the mechanisms via which bilirubin induces depressive-like behavior.

PATIENTS AND METHODS

Forty patients who were diagnosed with MDD and received treatment with selective serotonin reuptake inhibitors (SSRIs) were included, with 43 healthy volunteers serving as controls. Clinical symptoms were evaluated using Hamilton depression rating scale-24 (HAMD-24) and the Hamilton anxiety rating scale. Serum concentrations of total bilirubin (TBIL) and indirect bilirubin (IBIL) were measured at baseline and after treatment using an automated biochemical analyzer. The connection between clinical symptoms and TBIL or IBIL was examined using Pearson correlation. Chronic restraint stress (CRS) was employed to generate a rat model of depression. TBIL, IBIL in rat serum were measured by ELISA. Reactive oxygen species (ROS) contents in rat hippocampal tissues were quantified by flow cytometry. The levels of microglial markers and the extent of neuronal damage in the rat hippocampus were assessed by immunofluorescence and transmission electron microscopy, respectively.

RESULTS

Serum TBIL and IBIL levels were higher in patients with MDD than in the healthy controls. After treatment with SSRIs, the serum levels of TBIL and IBIL in MDD patients were significantly reduced. The levels of TBIL and IBIL were associated with HAMD-24 in MDD patients. Compared with the controls, the serum levels of TBIL, IBIL and the hippocampal ROS contents were elevated in CRS-exposed rats. Fluoxetine lowered inflammatory factor levels, mitigated oxidative stress.

CONCLUSION

Our findings indicate a possible correlation between elevated serum bilirubin and depressive symptoms. Increases in ROS levels, along with neuronal damage, may represent pathological mechanisms underlying MDD.

Age-related cognitive decline is accelerated in alcohol use disorder

This study aimed to examine potential cognitive impairments in patients with alcohol use disorder (AUD), and explore the factors affecting them. We recruited 97 inpatients with AUD, showing superficially normal cognitive function (mini-mental state examination score ≥24) for this study. We assessed cognitive function after a 4-week post-abstinence period using the Brief Assessment of Cognition in Schizophrenia-Japanese version (BACS-J). Relationships between BACS-J subcategory/composite raw scores and Z-scores (deviation from standard data in healthy Japanese) and background factors such as age, sex, education, smoking status, mini-mental state examination score, body mass index, systolic blood pressure, severity of depression, alcohol consumption, and laboratory findings were analyzed. Multiple regression analysis showed that the age (p < 0.001) and total bilirubin level (p = 0.014) were worsening factors for the BACS-J composite raw score, whereas education (p < 0.001) was a protective factor. An inverse correlation was apparent between the age and the composite Z-score of the BACS-J (r = -0.431, p < 0.001). Receiver operating characteristic (ROC) analysis identified 53 years as the cutoff age for predicting more than -2SD cognitive decline from the normal standard, with a high negative predictive value (95%). Patients with AUD aged ≥53 years showed more pronounced impairments in verbal memory, working memory, verbal fluency, and attention than those younger than 53 years (p < 0.05). These findings clearly demonstrate accelerated age-related cognitive decline in patients with AUD, especially those aged ≥53 years, suggesting the necessity of early intervention in patients with AUD to prevent progressive cognitive impairment and preserve their quality of life.

Preservation of Biomarkers Associated with Alzheimer's Disease (Amyloid Peptides 1-38, 1-40, 1-42, Tau Protein, Beclin 1) in the Blood of Neonates after Perinatal Asphyxia

Perinatal asphyxia is a complex disease involving massive death of brain cells in full-term newborns. The most impressive consequence of perinatal asphyxia is a neurodegenerative brain injury called hypoxic-ischemic encephalopathy. Management of newborns after perinatal asphyxia is very difficult due to the lack of measurable biomarkers that would be able to assess the severity of the brain injury in the future, help in the selection of therapy, assess the results of treatment and determine the prognosis for the future. Thus, these limitations make long-term neurodevelopmental outcomes unpredictable during life. Quantifying biomarkers that can detect subclinical changes at a stage where routine brain monitoring or imaging is still mute would be a major advance in the care of neonates with brain neurodegeneration after asphyxia. Understanding the effect of perinatal asphyxia on changes in blood neurodegenerative biomarkers over time, which would be commonly used to assess the severity of postpartum encephalopathy, would be an important step in developing precision in predicting the consequences of brain injuries. We urgently need more accurate early predictive markers to guide clinicians when to use neuroprotective therapy. The needed neurodegenerative biomarkers may represent neuronal pathological changes that can be recognized by new technologies such as genomic and proteomic. Nevertheless, the simultaneous blood tau protein and various amyloid changes with the addition of an autophagy marker beclin 1 after perinatal asphyxia have not been studied. We decided to evaluate serum biomarkers of neuronal injury characteristic for Alzheimer's disease such as amyloid peptides (1-38, 1-40 and 1-42), tau protein and beclin 1, which can predict the progression of brain neurodegeneration in future. In this paper, we report for the first time the significant changes in the above molecules in the blood after asphyxia compared to healthy controls during the 1-7, 8-14 and 15+ days ELISA test.

Regulation of mild cognitive impairment associated with liver disease by humoral factors derived from the gastrointestinal tract and MRI research progress: a literature review

Patients with liver disease are prone to various cognitive impairments. It is undeniable that cognitive impairment is often regulated by both the nervous system and the immune system. In this review our research focused on the regulation of mild cognitive impairment associated with liver disease by humoral factors derived from the gastrointestinal tract, and revealed that its mechanisms may be involved with hyperammonemia, neuroinflammation, brain energy and neurotransmitter metabolic disorders, and liver-derived factors. In addition, we share the emerging research progress in magnetic resonance imaging techniques of the brain during mild cognitive impairment associated with liver disease, in order to provide ideas for the prevention and treatment of mild cognitive impairment in liver disease.

The relationship between UGT1A1 gene & various diseases and prevention strategies

UDP-glucuronyltransferase 1A1 (UGT1A1) is a member of the Phase II metabolic enzyme family and the only enzyme that can metabolize detoxified bilirubin. Inactivation and very low activity of UGT1A1 in the liver can be fatal or lead to lifelong Gilbert's syndrome (GS) and Crigler-Najjar syndrome (CN). To date, more than one hundred UGT1A1 polymorphisms have been discovered. Although most UGT1A1 polymorphisms are not fatal, which diseases might be associated with low activity UGT1A1 or UGT1A1 polymorphisms? This scientific topic has been studied for more than a hundred years, there are still many uncertainties. Herein, this article will summarize all the possibilities of UGT1A1 gene-related diseases, including GS and CN, neurological disease, hepatobiliary disease, metabolic difficulties, gallstone, cardiovascular disease, Crohn's disease (CD) obesity, diabetes, myelosuppression, leukemia, tumorigenesis, etc., and provide guidance for researchers to conduct in-depth study on UGT1A1 gene-related diseases. In addition, this article not only summarizes the prevention strategies of UGT1A1 gene-related diseases, but also puts forward some insights for sharing.

Depression of Pyroptosis by Inhibiting Caspase-1 Activation Improves Neurological Outcomes of Kernicterus Model Rats

Kernicterus is a severe complication of extreme neonatal hyperbilirubinemia. Prolonged exposure to high-level unconjugated bilirubin (UCB) directly damages brain tissue. Neuroinflammation is believed to contribute to UCB-induced neurotoxicity. Pyroptosis has been as a highly inflammatory form of programmed cell death. Therefore, this study aimed to explore whether pyroptosis was involved in the pathogenesis of UCB neurotoxicity in kernicterus model rats. VX-765, a specific inhibitor of caspase-1, was intraperitoneally administered to the model rats to observe its effects on the short-term and long-term outcomes of the model animals at the molecular, cellular, morphological, and behavioral levels. The results indicated that UCB significantly induced the activation of caspase-1 and gasdermin D(GSDMD), and VX-765 inhibited caspase-1-GSDMD pathway. Compared with those of the UCB group and the vehicle+UCB group, VX-765-treated rats released lower levels of IL-1β and IL-18. Furthermore, H&E and TUNEL staining showed that nerve cells in the VX-765-treated group were better preserved and had less DNA fragmentation. Most importantly, VX-765 improved both the short-term and long-term neurological functions of kernicterus model rats. This study demonstrated that pyroptosis was involved in the pathogenesis of kernicterus through caspase-1 activation, which could be inhibited by VX-765, exerting a neuroprotective effect in kernicterus model rats.

Bilirubin Restrains the Anticancer Effect of Vemurafenib on BRAF-Mutant Melanoma Cells Through ERK-MNK1 Signaling

Melanoma, the most threatening cancer in the skin, has been considered to be driven by the carcinogenic RAF-MEK1/2-ERK1/2 signaling pathway. This signaling pathway is usually mainly dysregulated by mutations in BRAF or RAS in skin melanomas. Although inhibitors targeting mutant BRAF, such as vemurafenib, have improved the clinical outcome of melanoma patients with BRAF mutations, the efficiency of vemurafenib is limited in many patients. Here, we show that blood bilirubin in patients with BRAF-mutant melanoma treated with vemurafenib is negatively correlated with clinical outcomes. In vitro and animal experiments show that bilirubin can abrogate vemurafenib-induced growth suppression of BRAF-mutant melanoma cells. Moreover, bilirubin can remarkably rescue vemurafenib-induced apoptosis. Mechanically, the activation of ERK-MNK1 axis is required for bilirubin-induced reversal effects post vemurafenib treatment. Our findings not only demonstrate that bilirubin is an unfavorable for patients with BRAF-mutant melanoma who received vemurafenib treatment, but also uncover the underlying mechanism by which bilirubin restrains the anticancer effect of vemurafenib on BRAF-mutant melanoma cells.

Abnormal Serum Bilirubin/Albumin Concentrations in Dementia Patients With Aβ Deposition and the Benefit of Intravenous Albumin Infusion for Alzheimer's Disease Treatment

Background

Our previous study in animal models revealed that bilirubin could induce Aβ formation and deposition. Bilirubin may be important in neurodegenerative dementia with Aβ deposition. Hence, lowering the concentration of the free bilirubin capable of crossing the blood brain-barrier may benefit the treatment of Alzheimer's disease (AD).

Objectives

The objectives of this study were to examine the change in the serum bilirubin and albumin concentrations of dementia patients with Aβ deposition, and to determine the effects of intravenous administration of albumin in the treatment of AD.

Methods

Bilirubin and albumin concentrations in dementia patients with Aβ deposition were examined. Cell viability and apoptosis were determined in dopaminergic neuron-like cells MN9D treated with bilirubin in the presence of diverse concentrations of serum. Human albumin at a dose of 10 g every 2 weeks for 24 weeks was administered intravenously to AD patients to examine the effect of albumin on AD symptoms.

Results

Significantly higher indirect bilirubin (IBIL) concentrations, lower albumin concentrations, and higher ratio of IBIL to albumin (IBIL/ALB) were observed in dementia patients with Aβ deposition, including AD, dementia with Lewy bodies, and general paresis of insane. In vitro assays showed that bilirubin-induced injury in cultured dopaminergic neuron-like cells negatively depends on the concentration of serum in the culture medium. General linear model with repeated measures analysis indicated a main effect of group on the change in albumin concentrations and Alzheimer's Disease Cooperative Study Activities of Daily Living Inventory scale (ADCS-ADL) scores, and the main effect of time and group, and group-by-time interaction on the change of Clinical Dementia Rating Scale-Sum of Boxes (CDR-SB) scores. Analysis of the combined data of the entire 28 weeks of assessment period using the area under curve convincingly showed significantly improvements in the change of albumin concentrations, ADCS-ADL scores, and CDR-SB scores.

Conclusion

IBIL and the IBIL/ALB ratio are significantly higher in dementia patients with Aβ deposition, and intravenous administration of albumin is beneficial to AD treatment.

Trial Registration

The intervention study was registered at http://www.chictr.org.cn (ChiCTR-IOR-17011539). Date of registration: June 1, 2017.

Microglia Susceptibility to Free Bilirubin Is Age-Dependent

Increased concentrations of unconjugated bilirubin (UCB), namely its free fraction (Bf), in neonatal life may cause transient or definitive injury to neurons and glial cells. We demonstrated that UCB damages neurons and glial cells by compromising oligodendrocyte maturation and myelination, and by activating astrocytes and microglia. Immature neurons and astrocytes showed to be especially vulnerable. However, whether microglia susceptibility to UCB is also age-related was never investigated. We developed a microglia culture model in which cells at 2 days in vitro (2DIV) revealed to behave as the neonatal microglia (amoeboid/reactive cells), in contrast with those at 16DIV microglia that performed as aged cells (irresponsive/dormant cells). Here, we aimed to unveil whether UCB-induced toxicity diverged from the young to the long-cultured microglia. Cells were isolated from the cortical brain of 1- to 2-day-old CD1 mice and incubated for 24 h with 50/100 nM Bf levels, which were associated to moderate and severe neonatal hyperbilirubinemia, respectively. These concentrations of Bf induced early apoptosis and amoeboid shape in 2DIV microglia, while caused late apoptosis in 16DIV cells, without altering their morphology. CD11b staining increased in both, but more markedly in 2DIV cells. Likewise, the gene expression of HMGB1, a well-known alarmin, as well as HMGB1 and GLT-1–positive cells, were enhanced as compared to long-maturated microglia. The CX3CR1 reduction in 2DIV microglia was opposed to the 16DIV cells and suggests a preferential Bf-induced sickness response in younger cells. In conformity, increased mitochondrial mass and NO were enhanced in 2DIV cells, but unchanged or reduced, respectively, in the 16DIV microglia. However, 100 nM Bf caused iNOS gene overexpression in 2DIV and 16DIV cells. While only arginase 1/IL-1β gene expression levels increased upon 50/100 nM Bf treatment in long-maturated microglia, MHCII/arginase 1/TNF-α/IL-1β/IL-6 (>10-fold) were upregulated in the 2DIV microglia. Remarkably, enhanced inflammatory-associated microRNAs (miR-155/miR-125b/miR-21/miR-146a) and reduced anti-inflammatory miR-124 were found in young microglia by both Bf concentrations, while remained unchanged (miR/21/miR-125b) or decreased (miR-155/miR-146a/miR-124) in aged cells. Altogether, these findings support the neurodevelopmental susceptibilities to UCB-induced neurotoxicity, the most severe disabilities in premature babies, and the involvement of immune-inflammation neonatal microglia processes in poorer outcomes.