Hyperbilirubinemia diminishes respiratory drive in a rat pup model

Association of serum total bilirubin and potential predictors with mortality in acute respiratory failure: A retrospective cohort study

BACKGROUND

Total serum bilirubin (TBIL) levels are a risk factor in critically ill patients. However, the relationship between the dynamics of TBIL and the prognosis of acute respiratory failure (ARF) patients is unclear.

OBJECTIVES

This study aimed to investigate the impact of different levels of TBIL during hospitalization on mortality in ARF patients.

METHODS

This study used a retrospective cohort study. We extracted information on ARF patients from the Medical Information Bank for Intensive Care (MIMIC)-III (version 1.4). We used propensity score matching (PSM) to adjust for the level of potential baseline-level differences between groups. Cox regression was used to analyze mortality risk factors in patients with ARF. Subgroup analysis was used to explore special populations.

RESULTS

2673 patients were included in the study, and 19.7% developed hyperbilirubinemia (TBIL ≥ 2 mg/dL) during their hospitalization. After PSM, multivariate Cox regression showed a 50% and 135% increased risk of death for a maximum value of TBIL ≥ 5 mg/dL and minimum value of TBIL ≥ 2 mg/dL during hospitalization, respectively, compared to the control population. In addition, age ≥ 65 years, previous comorbid malignancies, respiratory rate ≥ 22 beats/min, SpO2 ≥ 95, BUN ≥ 20 mg/dL, lactate ≥ 5 mmol/L, platelet < 100 * 10 ^ 9/L were independent risk factors for 1-year mortality in ARF patients. Subgroup analysis showed that high bilirubin had a greater effect on patients aged less than 65 years (P for interaction < 0.05).

CONCLUSIONS

Hyper TBIL (TBIL max ≥ 5 mg/dL or TBIL min ≥ 2 mg/dL) was an independent risk factor for 1-year mortality in patients with ARF. This study suggests that clinicians should be aware of TBIL levels and intervene early in these patients.

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.

Bilirubin enhances the activity of ASIC channels to exacerbate neurotoxicity in neonatal hyperbilirubinemia in mice

Neonatal hyperbilirubinemia is a common clinical condition that can lead to brain encephalopathy, particularly when concurrent with acidosis due to infection, ischemia, and hypoxia. The prevailing view is that acidosis increases the permeability of the blood-brain barrier to bilirubin and exacerbates its neurotoxicity. In this study, we found that the concentration of the cell death marker, lactate dehydrogenase (LDH) in cerebrospinal fluid (CSF), is elevated in infants with both hyperbilirubinemia and acidosis and showed stronger correlation with the severity of acidosis rather than increased bilirubin concentration. In mouse neonatal neurons, bilirubin exhibits limited toxicity but robustly potentiates the activity of acid-sensing ion channels (ASICs), resulting in increases in intracellular Ca2+ concentration, spike firings, and cell death. Furthermore, neonatal conditioning with concurrent hyperbilirubinemia and hypoxia-induced acidosis promoted long-term impairments in learning and memory and complex sensorimotor functions in vivo, which are largely attenuated in ASIC1a null mice. These findings suggest that targeting acidosis and ASICs may attenuate neonatal hyperbilirubinemia complications.

Influence of Moderate Hyperbilirubinemia on Cardiorespiratory Control in Preterm Lambs

Hyperbilirubinemia (HB) is responsible for neonatal jaundice in 60% of term newborns and 90% of preterm infants. Neonatal HB can induce neurological damage (acute HB encephalopathy) and has been associated with persistent apneas. The objective of the present study was to investigate the immediate and delayed effects of moderate, clinically-relevant HB on cardiorespiratory control in preterm lambs. Two groups of five preterm lambs, namely control and HB, were studied. At day five of life, moderate HB (150-250 μmol/L) was induced and maintained during 17 h in the HB group while control lambs received a placebo solution. Six hours after HB onset, 7-h polysomnographic recordings with electrocardiogram (ECG) and respiratory (RESP) signals were performed to assess the immediate effects of HB on heart rate variability (HRV), respiratory rate variability (RRV), and cardiorespiratory interrelations. Identical recordings were repeated 72 h after HB induction to examine the delayed effects of HB on HRV, RRV and cardiorespiratory interrelations. Our results demonstrate a higher HRV and vagal activity immediately after induction of moderate HB. Meanwhile, a decrease in respiratory rate with an increase in both long- and short-term RRV was also noted, as well as a higher amplitude of the respiratory sinus arrhythmia and cardiorespiratory coupling. Seventy-two hours later, the alterations in HRV, RRV, and cardiorespiratory interrelations were attenuated, although a number of them were still present, suggesting a lasting influence of HB on the basal control of the cardiorespiratory system. Our results pave the way for studies in human preterms to assess the relevance of monitoring HRV, RRV, and cardiorespiratory interrelations to detect the acute neurological effects of HB and consequently adapt the treatment of neonatal jaundice.

Bilirubin acts as a multipotent guardian of cardiovascular integrity: more than just a radical idea

Bilirubin, a potentially toxic catabolite of heme and indicator of hepatobiliary insufficiency, exhibits potent cardiac and vascular protective properties. Individuals with Gilbert's syndrome (GS) may experience hyperbilirubinemia in response to stressors including reduced hepatic bilirubin excretion/increased red blood cell breakdown, with individuals usually informed by their clinician that their condition is of little consequence. However, GS appears to protect from all-cause mortality, with progressively elevated total bilirubin associated with protection from ischemic heart and chronic obstructive pulmonary diseases. Bilirubin may protect against these diseases and associated mortality by reducing circulating cholesterol, oxidative lipid/protein modifications, and blood pressure. In addition, bilirubin inhibits platelet activation and protects the heart from ischemia-reperfusion injury. These effects attenuate multiple stages of the atherosclerotic process in addition to protecting the heart during resultant ischemic stress, likely underpinning the profound reduction in cardiovascular mortality in hyperbilirubinemic GS. This review outlines our current knowledge of and uses for bilirubin in clinical medicine and summarizes recent progress in revealing the physiological importance of this poorly understood molecule. We believe that this review will be of significant interest to clinicians, medical researchers, and individuals who have GS.

Effect of unconjugated hyperbilirubinemia on neonatal autonomic functions: evaluation by heart rate variability

BACKGROUND

Serum bilirubin levels beyond the physiological limits, may lead to alterations in autonomic regulation in a newborn infant. Heart rate variability (HRV), is a noninvasive and quantitative marker of the activity of the autonomic nervous system (ANS). To date, few studies have demonstrated the undesirable effects of severe unconjugated hyperbilirubinemia (UHB) on autonomic functions, and only one study has used HRV as a marker of the autonomic activity. However, the relationship between altered cardiac autonomic functions and UHB by using the HRV derived from 24-hour Holter electrocardiography (ECG) recording has not been investigated previously.

OBJECTIVE

We aimed to assess whether a relationship exists between severe UHB and cardiac autonomic dysfunction by evaluating HRV via 24-hour Holter ECG recording.

METHODS

This single-center, prospective, case-control study was conducted on 50 full-term newborn infants with severe UHB requiring phototherapy and 50 healthy infants as controls. HRV assessment was performed by using 24-hour Holter ECG recording.

RESULTS

There was no significant difference in terms of mean average heart rate, mean maximum heart rate and mean RR duration between the groups. However, mean minimum heart rate was significantly lower in the study group. When 24-hour time and frequency domain parameters were compared, time and frequency domain parameters rMSDD as well as high frequency (HF), which represent parasymphathetic activity, were significantly higher in the study group. Furthermore, low frequency to high frequency (LF/HF) ratio, that serves as an indicator of sympathovagal balance, was significantly lower in the study group.

CONCLUSION

Severe UHB may cause cardiac autonomic dysfunction in favor of parasympathetic predominance in jaundiced neonates.

Moderate Hyperbilirubinemia Alters Neonatal Cardiorespiratory Control and Induces Inflammation in the Nucleus Tractus Solitarius

Hyperbilirubinemia (HB) occurs in 90% of preterm newborns. Moderate HB can induce acute neurological disorders while severe HB has been linked to a higher incidence of apneas of prematurity. The present study aimed to test the hypothesis that even moderate HB disrupts cardiorespiratory control in preterm lambs. Two groups of preterm lambs (born 14 days prior to term), namely control (n = 6) and HB (n = 5), were studied. At day 5 of life, moderate HB (150–250 μmol/L) was induced during 17 h in the HB group after which cardiorespiratory control as well as laryngeal and pulmonary chemoreflexes were assessed during baseline recordings and during hypoxia. Recordings were repeated 72 h after HB induction, just before euthanasia. In addition, neuropathological studies were performed to investigate for cerebral bilirubin deposition as well as for signs of glial reactivity in brainstem structures involved in cardiorespiratory control. Results revealed that sustained and moderate HB: (i) decreased baseline respiratory rate and increased the time spent in apnea; (ii) blunted the cardiorespiratory inhibition normally observed during both laryngeal and pulmonary chemoreflexes; and (iii) increased heart rate in response to acute hypoxia. These acute physiological changes were concurrent with an activation of Alzheimer type II astrocytes throughout the brain, including the brainstem. Concomitantly, bilirubin deposits were observed in the leptomeninges, but not in brain parenchyma. While most cardiorespiratory alterations returned to normal 72 h after HB normalization, the expression of glial fibrillary acid protein (GFAP) and ionized calcium binding adaptor molecule 1 (Iba1) was still increased within the nucleus tractus solitarius. In conclusion, moderate and sustained HB in preterm lambs induced cardiorespiratory alterations, the latter of which were associated with neurohistopathological changes. These changes are indicative of an inflammatory response in the brainstem neuroanatomical substrates involved in cardiorespiratory control.

Plasma BNP level combined with surgical Apgar score to predict operative major cardiac adverse events in malignant obstructive jaundice patients

Objective:

To investigate the predictive effect of major adverse cardiac events (MACE) in malignant obstructive jaundice (OJ) patients using plasma brain natriuretic peptide (BNP) level and surgical Apgar scoring (SAS) system.

Methods:

Forty one malignant OJ patients undergoing surgical treatments were studied at a single center. Pre-and postoperative plasma BNP level, total bilirubin (TBil) and data of cardiac function (HR, CVP, CI, LVEF%) were detected, the SAS was calculated during the surgery, the relationship of both plasma BNP level and SAS with MACE after surgery was analyzed.

Results:

Thirteen patients out of 41 (31.71%) experienced MACE without cardiac death. OJ patients had a higher plasma BNP level than baseline before operation (191.61±105.76 pg/ml VS 175 pg/ml, P<0.05), the cardiac function data was improved (CVP: t=4.761, p=0.000; CI: t=3.539, p=0.001; LVEF%: t=3.632, p=0.001) after the operation. Patients with lower SAS had increasing incidence of MACE after surgery.

Conclusion:

Malignant OJ patients with higher preoperative BNP level and lower surgical Apgar score were identified at high risk of MACE after surgery.

Auditory evoked potentials in a newborn Wistar rat model of hyperbilirubinemia

Introduction

Hyperbilirubinemia is a common health problem in newborns. Its effects can be different according to the level and duration of the hyperbilirubinemia. The toxic effect of bilirubin on the auditory system can be seen as a sensory neural hearing loss or auditory neuropathy spectrum disorder (ANSD).

Objective

The purpose of our study was to determine the effects of toxic bilirubin level on the auditory system by using Auditory Brainstem Response audiometry.

Methods

Rats are used as animal models due to their low cost and easy attainability. Auditory Brainstem Response was used for auditory assessment. In this study, three groups were established: experimental, control and placebo groups.

Results

In the experimental group, which consists of rats with hyperbilirubinemia, sensory neural hearing loss was found bilaterally in 4 rats (66.67%) and unilaterally in 2 rats (16.67%) and auditory neuropathy spectrum disorder was found unilaterally in 1 rat (8.33%). Auditory Brainstem Response thresholds were significantly elevated compared to control and placebo groups (p < 0.05).

Conclusion

Hyperbilirubinemia of newborn rats may result both in sensory neural hearing loss and auditory neuropathy spectrum disorder.

High glucose regulates LN expression in human liver sinusoidal endothelial cells through ROS/integrin αvβ3 pathway

Diabetes mellitus can cause a wide variety of vascular complications and is one of the major risk factors for Non Alcoholic Fatty Liver Disease (NAFLD). The present study was designed investigate the expression of laminin (LN) in human liver sinusoidal endothelial cells (HLSECs) induced by high glucose and the role of reactive oxygen species (ROS) and integrin αvβ3 in the regulation of LN expression. HLSECs were cultured and treated with media containing 25 mM glucose in the presence or absence of N-acetylcysteine (NAC) or clone LM609. The level of intracellular ROS of HLSECs was measured with 2',7' dichloro-fluorescein diacetate (DCFH-DA) probe. Expression of integrin αvβ3 was measured using RT-PCR and Western blot. Expression of LN was testified by immunofluorescence assay. Compared with that in control group, ROS level and the expression of integrin αvβ3 and LN increased in high glucose group. Compared with that in high glucose group, antioxidant NAC inhibited the expression of integrin αvβ3, NAC and the anti-body for blocking integrin αvβ3 (clone LM609) down-regulated the expression of LN. However, the above parameters did not differ between control and mannitol groups. High glucose up-regulates expression of LN in HLSECs through ROS/integrin αvβ3 pathway.

Unbound unconjugated hyperbilirubinemia is associated with central apnea in premature infants

OBJECTIVE

To evaluate whether jaundice, indexed by unbound bilirubin (UB), is associated with central apnea in premature infants.

STUDY DESIGN

A prospective observational study was performed with 27-33 weeks' gestational age infants who were not requiring either mechanical ventilation or noninvasive ventilation with continuous positive airway pressure beyond 24 hours after birth. Infants with congenital infections, chromosomal disorders, craniofacial anomalies, and/or family history of hearing loss were excluded. Total serum bilirubin and UB were measured twice daily during the first postnatal week and then when clinically indicated. Central apnea was evaluated by visual inspection of continuous, electronic cardiorespiratory recordings until 2 weeks of age.

RESULTS

One hundred infants were subdivided into 2 groups via median peak UB level: the high UB group (greater than median) and low UB group (less than median). The high UB group had an increased frequency of apnea events during the first 2 weeks compared with infants in the low UB group. After we controlled for confounders, the high UB group had more events of apnea during the first 2 postnatal weeks compared with the low UB group (incidence rate ratio: 1.9, 95% CI 1.2-3.2).

CONCLUSIONS

Our findings suggest that jaundice, as indexed by UB, is associated with central apnea in premature infants.

The clinical syndrome of bilirubin-induced neurologic dysfunction

Clinicians have hypothesized a spectrum of minor neurologic manifestations, consistent with neuroanatomical reports and collectively termed as a "syndrome of bilirubin-induced neurologic dysfunction (BIND)," which can occur in the absence of classical kernicterus. The current review builds on these initial reports with a focus on clinical signs and symptoms that are assessed by standardized tools and manifest from neonatal age to childhood. These clinical manifestations are characterized by the following domains: (i) neuromotor signs; (ii) muscle tone abnormalities; (iii) hyperexcitable neonatal reflexes; (iv) variety of neurobehavior manifestations; (v) speech and language abnormalities; and (vi) evolving array of central processing abnormalities, such as sensorineural audiology and visuomotor dysfunctions. Concerns remain that the most vulnerable infants are likely to acquire BIND, either because their exposure to bilirubin is not identified as severe enough to need treatment or is prolonged but slightly below current threshold levels for intervention. Knowing that a total serum/plasma bilirubin (TB) level is not the most precise indicator of neurotoxicity, the role of expanded biomarkers or a "bilirubin panel" has yet to be validated in prospective studies. Future studies that correlate early "toxic" bilirubin exposure to long-term academic potential of children are needed to explore new insights into bilirubin's effect on the structural and functional maturation of an infant's neural network topology.

Effects of Moderate Hyperbilirubinemia on Nutritive Swallowing and Swallowing-Breathing Coordination in Preterm Lambs

BACKGROUND

Hyperbilirubinemia (HB) occurs in 90% of preterm newborns. HB induces acute neurological disorders (somnolence, abnormal tone, feeding difficulties, auditory dysfunction) and alterations in respiratory control. These findings suggest brainstem neurotoxicity that could also affect swallowing centers.

OBJECTIVE

To test the hypothesis that HB impairs nutritive swallowing (NS) and swallowing-breathing coordination.

METHODS

Two groups of preterm lambs (born 14 days prior to term), namely control (n = 6) and HB (n = 5), were studied. On day 5 of life (D0), moderate HB (150-250 µmol/l) was induced during 17 h in the HB group. Swallowing was assessed via recording of pharyngeal pressure and respiration by respiratory inductance plethysmography and pulse oximetry. The effect of HB on NS was assessed during standardized bottle-feeding. A second recording was performed 48 h after recovery from HB (D3).

RESULTS

Swallows were less frequent (p = 0.003) and of smaller volume (p = 0.01) in HB lambs while swallowing frequency was decreased (p = 0.004). These differences disappeared after HB normalization. Swallowing-breathing coordination was impaired in HB lambs, with a decrease in percent time with NS burst-related apneas/hypopneas at D0 and D3. Simultaneously, HB lambs tended to experience more severe desaturations (<80%) during bottle-feeding. Finally, following bottle-feeding, the respiratory rate was significantly lower, along with an increased apnea duration in HB lambs.

CONCLUSIONS

Swallowing and swallowing-breathing coordination are altered by acute moderate HB in preterm lambs. Decreased efficiency at bottle-feeding is accompanied by continuation of breathing during swallow bursts, which may promote lung aspiration.

Apnea in acute bilirubin encephalopathy

Central apnea, defined as cessation of breathing for ≥20s, is frequent in premature infants born at <34 weeks׳ gestation but uncommon among healthy late preterm (34(0/7)-36(6/7) weeks׳ gestation) and term (≥37 weeks׳ gestation) infants, where it is usually a clinical manifestation of a neurological or metabolic problem. There is growing evidence that marked unconjugated hyperbilirubinemia is associated with central apnea in neonates. This article explores the reported association between acute bilirubin encephalopathy and symptomatic apneic events in newborns and the possible mechanisms involved in the pathogenesis of this phenomenon. The prevalence of symptomatic apneic events in reports of acute bilirubin encephalopathy suggests this clinical finding should be considered a sign of bilirubin neurotoxicity.

Apnea of prematurity

Apnea of prematurity is a significant problem due to immaturity of the central neural control circuitry responsible for integrating afferent input and central rhythm. In this review, we provide an overview of the pathogenesis of apnea of prematurity--including our current understanding of the role that afferent input to the brain stem plays in synergy with the central pattern generation circuitry in the emergence of apnea of prematurity. We then discuss the interplay of apnea, bradycardia, desaturation, as well as the genesis of central, mixed, and obstructive apnea. Finally, we provide a summary of the physiological basis for current therapeutic approaches to treating apnea of prematurity, and conclude with an overview of proposed long-term consequences of the resultant intermittent hypoxic episodes.

Apnea of prematurity: from cause to treatment

Apnea of prematurity (AOP) is a common problem affecting premature infants, likely secondary to a "physiologic" immaturity of respiratory control that may be exacerbated by neonatal disease. These include altered ventilatory responses to hypoxia, hypercapnia, and altered sleep states, while the roles of gastroesophageal reflux and anemia remain controversial. Standard clinical management of the obstructive subtype of AOP includes prone positioning and continuous positive or nasal intermittent positive pressure ventilation to prevent pharyngeal collapse and alveolar atelectasis, while methylxanthine therapy is a mainstay of treatment of central apnea by stimulating the central nervous system and respiratory muscle function. Other therapies, including kangaroo care, red blood cell transfusions, and CO(2) inhalation, require further study. The physiology and pathophysiology behind AOP are discussed, including the laryngeal chemoreflex and sensitivity to inhibitory neurotransmitters, as are the mechanisms by which different therapies may work and the potential long-term neurodevelopmental consequences of AOP and its treatment.

Operable malignant jaundice: To stent or not to stent before the operation?

Traditionally, pre-operative biliary drainage (PBD) was believed to improve multi-organ dysfunction, and for this reason, was practiced worldwide. Over the last decade, this concept was challenged by many reports, including meta-analyses that showed no difference in morbidity and mortality between surgery with, and surgery without PBD, in operable malignant jaundice. The main disadvantages of PBD are seen to be the additional cost of the procedure itself, and the need for longer hospitalization. In addition, many studies showed the significance of specific complications resulting from PBD, such as recurrent jaundice, cholangitis, pancreatitis, cutaneous fistula, and bleeding. However, the results of these studies remain inconclusive as to date there has been no perfect study that equally randomized comparable patients according to the level of obstruction and technique used for PBD. Generally, endoscopic stent insertion (ES) is preferred for common duct obstruction, whereas endoscopic nasobiliary drainage and percutaneous biliary drainage is reserved for hilar obstruction, since ES in hilar block confers a high rate of cholangitis. Although, there is no guideline which either supports or refutes this approach, certain subgroups of patients, including those with symptomatic jaundice, cholangitis, impending renal failure, hilar block requiring preoperative portal vein embolization, and those who need pre-operative neoadjuvant therapy, are suitable candidates for PBD.