Biliverdin as a disease-modifying agent: An integrated viewpoint

Metabolomic analysis of rat arterial serum under hypobaric hypoxia: Adaptive regulation of physiological systems by metabolic reprogramming

Objective

To investigate the associations between metabolic changes and functions, including energy metabolism, immune response, and redox balance, under short-term hypobaric hypoxia exposure. Non-targeted metabolomics and bioinformatics analysis were applied to explore the adaptive mechanisms of organisms in hypobaric hypoxia.

Methods

Healthy adult male Sprague-Dawley rats were placed in environments simulating altitudes of 6500 m (HC group) and 1588 m (Control group). After 14 days, arterial serum samples were analyzed using Liquid Chromatography-Tandem Mass Spectrometry (LC-MS/MS). Significant metabolites (P < 0.05, VIP >1) were identified, and KEGG enrichment analysis was conducted. Differential metabolites were globally analyzed with MetaboAnalyst 5.0.

Results

A total of 117 significantly altered metabolites were identified. In the HC group, 84 metabolites significantly increased, while 33 metabolites significantly decreased compared to the Control group. KEGG enrichment analysis revealed significant metabolic pathways, including the PPAR signaling pathway, bile secretion, arginine biosynthesis, alcoholism, and cholesterol metabolism (P < 0.05). Global analysis indicated that these differential metabolites were involved in various pathways, such as energy metabolism, amino acid metabolism, nucleotide metabolism, lipid metabolism, vitamin and cofactor metabolism, steroid metabolism, neurotransmitter metabolism, and heme metabolism, all of which play crucial roles in multiple biological processes.

Conclusion

Short-term hypobaric hypoxia exposure significantly altered the metabolite profiles in the arterial serum samples of rats, revealing adaptive metabolic reprogramming in energy metabolism, redox balance, immune function, endocrine regulation, and neurological systems.

Quantitative LC-MS/MS Analysis of Endogenous Pseudomonas aeruginosa Isomeric Metabolites Biliverdin IX Alpha, Beta, and Delta in Cell Culture Supernatant, Cell Pellet, and Lung Tissue

Pseudomonas aeruginosa (Pa) utilizes heme as an iron source from the host during infection. Biliverdin beta and delta (BVIXβ and BVIXδ) are generated by HemO, specific to Pa, while biliverdin alpha is generated from the bacterial BphO system and by mammalian heme oxygenases. Here, we have developed and characterized a quantitative LC-MS/MS assay for the separation of three endogenous isomers, BVIXα, BVIXβ, and BVIXδ. The assay was validated for accuracy, precision, linearity, extraction recovery, solution stability, freeze-thaw stability, benchtop stability, postextraction stability, and nonspecific oxidation of BVIX. The addition of an antioxidant, butylated hydroxytoluene, during sample preparation is needed in order to prevent coupled oxidation from inflating quantitative values of BVIX. The assay development included optimization of a liquid-liquid extraction for bacterial culture supernatants and sample preparation procedures for cell pellets and tissue homogenate to reduce sample demand and automate the extraction procedure in a 96-well format, to enhance extraction throughput. This method was applied to analyze isomer distribution in Pa supernatant, bacterial pellet, and infected lung tissue from Pa-challenged mice. This method can be used in the future for low-volume culture samples, as well as tissue samples, to understand the mechanisms of virulence and inform future drug development.

The Heme Oxygenase/Biliverdin Reductase System and Its Genetic Variants in Physiology and Diseases

Heme oxygenase (HO) metabolizes heme into ferrous iron, carbon monoxide (CO), and biliverdin-IXα (BV), the latter being reduced into bilirubin-IXα (BR) by the biliverdin reductase-A (BVR). Heme oxygenase exists as two isoforms, HO-1, inducible and involved in the cell stress response, and HO-2, constitutive and committed to the physiologic turnover of heme and in the intracellular oxygen sensing. Many studies have identified genetic variants of the HO/BVR system and suggested their connection in free radical-induced diseases. The most common genetic variants include (GT)n dinucleotide length polymorphisms and single nucleotide polymorphisms. Gain-of-function mutations in the HO-1 and HO-2 genes foster the ventilator response to hypoxia and reduce the risk of coronary heart disease and age-related macular degeneration but increase the risk of neonatal jaundice, sickle cell disease, and Parkinson's disease. Conversely, loss-of-function mutations in the HO-1 gene increase the risk of type 2 diabetes mellitus, chronic obstructive pulmonary disease, and some types of cancers. Regarding BVR, the reported loss-of-function mutations increase the risk of green jaundice. Unfortunately, the physiological role of the HO/BVR system does not allow for the hypothesis gene silencing/induction strategies, but knowledge of these mutations can certainly facilitate a medical approach that enables early diagnoses and tailored treatments.

Intracellular biliverdin dynamics during ferroptosis

Ferroptosis is a cell death mechanism mediated by iron-dependent lipid peroxidation. Although ferroptosis has garnered attention as a cancer-suppressing mechanism, there are still limited markers available for identifying ferroptotic cells or assessing their sensitivity to ferroptosis. The study focused on biliverdin, an endogenous reducing substance in cells, and examined the dynamics of intracellular biliverdin during ferroptosis using a biliverdin-binding cyanobacteriochrome. It was found that intracellular biliverdin decreases during ferroptosis and that this decrease is specific to ferroptosis amongst different forms of cell death. Furthermore, the feasibility of predicting sensitivity to ferroptosis by measuring intracellular biliverdin was demonstrated using a ferroptosis model induced by the re-expression of the transcription factor BACH1. These findings provide further insight into ferroptosis research and are expected to contribute to the development of cancer therapies that exploit ferroptosis.

Peroxynitrite-Free Nitric Oxide-Embedded Nanoparticles Maintain Nitric Oxide Homeostasis for Effective Revascularization of Myocardial Infarcts

Revascularization is crucial for treating myocardial infarction (MI). Nitric oxide (NO), at an appropriate concentration, is recognized as an ideal and potent pro-angiogenic factor. However, the application of NO in the treatment of MI is limited. Improper NO supplementation is harmful to revascularization because NO is converted into harmful peroxynitrite (ONOO-) in MI tissues with high reactive oxygen species (ROS) levels. We overcome these obstacles by embedding biliverdin and NO into Prussian blue (PB) nanolattices to obtain an ONOO--free NO-embedded nanomedicine (OFEN). Unlike previous NO donors, OFEN provides NO stably and spontaneously for a longer time (>7 days), which makes it possible to maintain a stable concentration of NO, suitable for angiogenesis, through dose optimization. More importantly, based on the synergy between PB and biliverdin, OFEN converts ROS into beneficial O2 and inhibits the production of ONOO- from the source. OFEN specifically targets MI tissues and achieves sustained and stable NO delivery at the MI site. OFEN effectively promotes revascularization in the MI tissue, significantly reduces myocardial death and fibrosis, and ultimately promotes the complete recovery of cardiac function. Our strategy provides a promising approach for the treatment of myocardial and other ischemic diseases.

Neuroprotective Roles of the Biliverdin Reductase-A/Bilirubin Axis in the Brain

Biliverdin reductase-A (BVRA) is a multi-functional enzyme with a multitude of important roles in physiologic redox homeostasis. Classically, BVRA is well known for converting the heme metabolite biliverdin to bilirubin, which is a potent antioxidant in both the periphery and the brain. However, BVRA additionally participates in many neuroprotective signaling cascades in the brain that preserve cognition. Here, we review the neuroprotective roles of BVRA and bilirubin in the brain, which together constitute a BVRA/bilirubin axis that influences healthy aging and cognitive function.