Bilirubin/biliverdin-Cu(II) induced DNA breakage; reaction mechanism and biological significance

Biliverdin as a disease-modifying agent: An integrated viewpoint

Biliverdin is one of the three by-products of heme oxygenase (HO) activity, the others being ferrous iron and carbon monoxide. Under physiological conditions, once formed in the cell, BV is reduced to bilirubin (BR) by the biliverdin reductase (BVR). However, if BVR is inhibited by either genetic variants, as occurs in the Inuit ethnicity, or dioxin intoxication, BV accumulates in cells giving rise to a clinical syndrome known as green jaundice. Preclinical studies have demonstrated that BV not only has a direct antioxidant effect by scavenging free radicals, but also targets many signal transduction pathways, such as BVR, soluble guanylyl cyclase, and the aryl hydrocarbon receptor. Through these direct and indirect mechanisms, BV has shown beneficial roles in ischemia/reperfusion-related diseases, inflammatory diseases, graft-versus-host disease, viral infections and cancer. Unfortunately, no clinical data are available to confirm these potential therapeutic effects and the kinetics of exogenous BV in humans is unknown. These limitations have so far excluded the possibility of transforming BV from a mere by-product of heme degradation into a disease-modifying agent. A closer collaboration between basic and clinical researchers would be advantageous to overcome these issues and promote translational research on BV in free radical-induced diseases.

Biliverdin reductase as a target in drug research and development: Facts and hypotheses

Biliverdin reductase-A (BVR) catalyzes the reduction of heme-derived biliverdin into bilirubin, this latter being a powerful endogenous free radical scavenger. Furthermore, BVR is also endowed with both serine/threonine/tyrosine kinase and scaffold activities, through which it interacts with the insulin receptor kinase, conventional and atypical protein kinase C isoforms, mitogen-activated protein kinases as well as the phosphatidylinositol-3 kinase/Akt system. By regulating this complex array of signal transduction pathways, BVR is involved in the pathogenesis of neurodegenerative, metabolic, cardiovascular and immune-inflammatory diseases as well as in cancer. In addition, both BVR and BVR-B, this latter being an alternate isozyme predominant during fetal development but sometimes detectable through adulthood, have been studied as peripheral biomarkers for an early detection of Alzheimer's disease, atherosclerosis and some types of cancer. However, despite these interesting lines of evidence, to date BVR has not been considered as an appealing drug target. Only limited evidence supports the neuroprotective effects of atorvastatin and ferulic acid through BVR regulation in the aged canine brain and human neuroblastoma cells, whereas interesting results have been reported regarding the use of BVR-based peptides in preclinical models of cardiac diseases and cancer.

UGT1A1 dysfunction increases liver burden and aggravates hepatocyte damage caused by long-term bilirubin metabolism disorder

UGT1A1 is the only enzyme that can metabolize bilirubin, and its encoding gene is frequently mutated. UGT1A1*6 (G71R) is a common mutant in Asia which leads to the decrease of UGT1A1 activity and abnormal bilirubin metabolism. However, it is not clear whether low UGT1A1 activity-induced bilirubin metabolism disorder increases hepatocyte fragility. ugt1a^+/- mice were used to simulate the UGT1A1*6 (G71R) population. Under the same CCl₄ induction condition, ugt1a^+/- mice showed severer liver damage and fibrosis, indicating that ugt1a1 dysfunction increased liver burden and aggravated hepatocyte damage. In the animal experiment with a continuous intraperitoneal injection of bilirubin, the ugt1a^+/- mice livers had more serious unconjugated bilirubin accumulation. The accumulated bilirubin leads to hyperphosphorylation of IκB-α, Ikk-β, and p65 and a significant increase of inflammatory factor. The α-SMA and Collagen I proteins markedly up-regulated in the ugt1a^+/- mice livers. Immunofluorescence and confocal microscopy showed that hepatic stellate cells and Kupffer cells were activated in ugt1a^+/- mice. Comprehensive results show that there was a crosstalk relationship between low UGT1A1 activity-bilirubin-liver damage. Furthermore, cell experiments confirmed that unconjugated bilirubin activated the NF-κB pathway and induced DNA damage in hepatocytes, leading to the significant increase of inflammatory factors. UGT1A1 knockdown in hepatocytes aggravated the toxicity of unconjugated bilirubin. Conversely, overexpression of UGT1A1 had a protective effect on hepatocytes. Finally, Schisandrin B, an active ingredient with hepatoprotective effects, extracted from a traditional Chinese medicinal herb, which could protect the liver from bilirubin metabolism disorders caused by ugt1a1 deficiency by downregulating p65 phosphorylation, inhibiting Kupffer cells, reducing inflammation levels. Our data clarified the mechanism of liver vulnerability caused by cross-talk between low UGT1A1 activity bilirubin, and provided a reference for individualized prevention of liver fragility in Gilbert's syndrome.

Causing DNA damage and stopping DNA repair - Vitamin D supplementation with Poly(ADP-ribose) polymerase 1 (PARP1) inhibitors may cause selective cell death of cancer cells: A novel therapeutic paradigm utilizing elevated copper levels within the tumour

Inhibitors of PARP1 are currently being used to treat malignancies and as maintenance drugs post chemotherapy. Vitamin D has been shown to have an anticancer effect (mediated by multiple mechanisms) and is usually deficient in cancer patients. We had previously proposed and experimentally validated the selective cell death of cancer cells caused due to interaction of vitamin D with elevated copper within malignant cells, leading to ROS mediated DNA damage. In this communication we propose a Vitamin D supplementation strategy with PARP1 inhibitor treatment which would have multifaceted benefits for therapy. Besides exerting its anticancer effects by other mechanisms and addressing the deficiency, Vitamin D in principle would cause selective ROS mediated DNA breakage in malignant cells, while sparing healthy non malignant cells. Since Vitamin D is also a known inhibitor of PARP1, this therapeutic strategy would push the malignant cells to apoptosis due to DNA breakage via the vitamin D-copper mechanism, in addition to inhibiting DNA repair. Since the available levels copper within normal cells are several fold less as compared to malignant cells, the normal cells would be spared of the Vitamin D induced, ROS mediated DNA damage and would be less likely to die due to PARP1 inhibition.

A novel gold nanocluster-based fluorometric biosensor for measuring prooxidant activity with a large Stokes shift

A chicken egg white protein-protected gold nanocluster (CEW-AuNC) based fluorogenic biosensor, where protein was used as both reducing and protecting agent, was developed to determine the Cu(II)-induced prooxidant activity of natural antioxidants abundant in food and biological samples. Gold nanoclusters, prepared using egg white proteins, exhibited strong fluorescence. The prooxidant activity of the tested antioxidants was indirectly measured by their reducing action on Cu(II) to Cu(I), and the reduced cuprous ion was bound to the thiol groups in the CEW-AuNC structure, causing a decrease in fluorescence intensity. Epicatechin, catechin, epigallocatechin gallate, morin, rutin, quercetin, gallic, chlorogenic, and rosmarinic acids, glutathione, cysteine, N-acetyl cysteine, bilirubin, resveratrol, and α-tocopherol were studied as natural antioxidants. A fluorometric method showing a large Stokes shift with excitation/emission maxima at 360∕640 nm was developed to sensitively measure the decrease in the fluorescence of CEW-AuNC associated with the binding of copper(I) to the protein structure. Total prooxidant activities of the binary, ternary, and quaternary synthetic mixtures and of some food and synthetic serum samples were determined. The biosensor response was statistically compared to that of its spectrophotometric counterpart. This method can be used for the control of the oxidative stability of foods with a prolonged shelf life.

Multiple origins of green blood in New Guinea lizards

Several species of lizards from the megadiverse island of New Guinea have evolved green blood. An unusually high concentration of the green bile pigment biliverdin in the circulatory system of these lizards makes the blood, muscles, bones, tongue, and mucosal tissues bright green in color, eclipsing the crimson color from their red blood cells. This is a remarkable physiological feature because bile pigments are toxic physiological waste products of red blood cell catabolism and, when chronically elevated, cause jaundice in humans and all other vertebrates. Although these lizards offer a promising system to examine the evolution of extraordinary physiological characteristics, little is known about the phylogenetic relationships of green-blooded lizards or the evolutionary origins of green blood. We present the first extensive phylogeny for green-blooded lizards and closely related Australasian lizards using thousands of genomic regions to examine the evolutionary history of this unusual trait. Maximum likelihood ancestral character state reconstruction supports four independent origins of green blood. Our results lay the phylogenetic foundation necessary to determine the role, if any, of natural selection in shaping this enigmatic physiological trait as well as understanding the genetic, proteomic, and biochemical basis for the lack of jaundice in those species that have independently evolved green blood.

Mechanisms of redox interactions of bilirubin with copper and the effects of penicillamine

Toxic effects of unconjugated bilirubin (BR) in neonatal hyperbilirubinemia have been related to redox and/or coordinate interactions with Cu²⁺. However, the development and mechanisms of such interactions at physiological pH have not been resolved. This study shows that BR reduces Cu²⁺ to Cu¹⁺ in 1:1 stoichiometry. Apparently, BR undergoes degradation, i.e. BR and Cu²⁺ do not form stable complexes. The binding of Cu²⁺ to inorganic phosphates, liposomal phosphate groups, or to chelating drug penicillamine, impedes redox interactions with BR. Cu¹⁺ undergoes spontaneous oxidation by O₂ resulting in hydrogen peroxide accumulation and hydroxyl radical production. In relation to this, copper and BR induced synergistic oxidative/damaging effects on erythrocytes membrane, which were alleviated by penicillamine. The production of reactive oxygen species by BR and copper represents a plausible cause of BR toxic effects and cell damage in hyperbilirubinemia. Further examination of therapeutic potentials of copper chelators in the treatment of severe neonatal hyperbilirubinemia is needed.

Study of DNA damage caused by dipyrone in presence of some transition metal ions

The DNA damage in the presence of dipyrone (used as its sodium salt, NaDip) and some transition metal ions in an air saturated ([O₂] ≈ 0.25 mM) non-buffered solution at T = (25.0 ± 0.5)°C was investigated by agarose gel electrophoresis. As metal ions Cu²⁺, Fe³⁺, Ni²⁺ and Mn³⁺ were selected and evaluated in the present study because of the important role they play in a biological system. pUC19 plasmid DNA damage-induced by NaDip (80-600 μM) was observed in the presence of 100 μM Cu²⁺. The damage was proportional to the NaDip concentration provided that the order of addition of reagents (pUC19 plasmid DNA + Cu²⁺ + NaDip) is obeyed. Addition in the reaction medium of ligands for Cu²⁺ and Cu⁺, respectively EDTA and neocuproine, promoted total inhibition or reduction of the pUC19 plasmid DNA damage suggesting the involvement of the Cu²⁺/Cu⁺ cycle. Besides, the decrease in the pUC19 plasmid DNA damage after addition of catalase (1.0 × 10^-4 mg μL^-1) in the same reaction medium indicates that H₂O₂ is also involved in the damage process. In NaDip concentration range (80-600 μM), and under same the experimental conditions, it was not possible to conclude whether there was pUC19 plasmid DNA damage caused by 10 μM Fe³⁺. No damage was observed in the presence of Mn³⁺ or Ni²⁺. Although the technique used in this study is sensitive to detect the pUC19 plasmid DNA damage it was not possible to identify in which DNA base this damage occurs. Further studies with other techniques should be made to unambiguously identify the oxidative intermediates that are responsible for the DNA damage. As far as we know, this is the first study dealing with the pUC19 plasmid DNA damage-induced by NaDip in presence of copper, iron, nickel and manganese ions.

Bilirubin and brain: A pharmacological approach

For many decades, the world scientific literature has accounted for a number of works on the biological effects of bilirubin-IXalpha (BR). The first studies focused on the neurotoxic effects of the excessive production of BR, in particular regarding both physiological neonatal jaundice and the more severe ones, typically as consequences of severe hemolysis or other underlying diseases. Only since 1987, has significant evidence, however, underlined the neuroprotective role of BR linked to the scavenging effect of free radicals as reactive oxygen species and nitric oxide and its congeners. Despite the presence in the literature of many excellent papers dealing with the multiple roles played by BR in health and disease, there were very few and somewhat dated reviews that summarize the key findings related to the neuroprotective and neurotoxic effects of the bile pigment and underlying mechanisms. In light of the previous statements, the aim of this review is to provide a summary of the main discoveries in the last years on the effects of BR on the central nervous system. An analytical description about the synthesis of BR, its distribution in the systemic circulation, liver metabolism and elimination through feces and urine will be provided, together with the main mechanisms claimed to describe the neurotoxicity and neuroprotection by the bile pigment. Finally, the possible translational aspects of pharmacological modulation in the production of BR in order to prevent or counteract toxic effects or enhance the protective actions, will be discussed.

Circulating cell-free DNA, telomere length and bilirubin in the Vienna Active Ageing Study: exploratory analysis of a randomized, controlled trial

Telomere length (TL) in blood cells is widely used in human studies as a molecular marker of ageing. Circulating cell-free DNA (cfDNA) as well as unconjugated bilirubin (UCB) are dynamic blood constituents whose involvement in age-associated diseases is largely unexplored. To our knowledge, there are no published studies integrating all three parameters, especially in individuals of advanced age. Here we present a secondary analysis from the Vienna Active Aging Study (VAAS), a randomized controlled intervention trial in institutionalized elderly individuals (n = 101). Using an exploratory approach we combine three blood-based molecular markers (TL, UCB and cfDNA) with a range of primary and secondary outcomes from the intervention. We further look at the changes occurring in these parameters after 6-month resistance exercise training with or without supplementation. A correlation between UCB and TL was evident at baseline (p < 0.05), and both were associated with increased chromosomal anomalies such as nucleoplasmatic bridges and nuclear buds (p < 0.05). Of the three main markers explored in this paper, only cfDNA decreased significantly (p < 0.05) after 6-month training and dietary intervention. No clear relationship could be established between cfDNA and either UCB or TL. The trial was registered at ClinicalTrials.gov (NCT01775111).

Chitosan-DNA nanoparticles delivered by intrabiliary infusion enhance liver-targeted gene delivery

The goal of this study was to examine the efficacy of liver-targeted gene delivery by chitosan-DNA nanoparticles through retrograde intrabiliary infusion (RII). The transfection efficiency of chitosan-DNA nanoparticles, as compared with PEI-DNA nanoparticles or naked DNA, was evaluated in Wistar rats by infusion into the common bile duct, portal vein, or tail vein. Chitosan-DNA nanoparticles administrated through the portal vein or tail vein did not produce detectable luciferase expression. In contrast, rats that received chitosan-DNA nanoparticles showed more than 500 times higher luciferase expression in the liver 3 days after RII; and transgene expression levels decreased gradually over 14 days. Luciferase expression in the kidney, lung, spleen, and heart was negligible compared with that in the liver. RII of chitosan-DNA nanoparticles did not yield significant toxicity and damage to the liver and biliary tree as evidenced by liver function analysis and histopathological examination. Luciferase expression by RII of PEI-DNA nanoparticles was 17-fold lower than that of chitosan-DNA nanoparticles on day 3, but it increased slightly over time. These results suggest that RII is a promising routine to achieve liver-targeted gene delivery by non-viral nanoparticles; and both gene carrier characteristics and mode of administration significantly influence gene delivery efficiency.

Synthesis, crystal structure and DNA binding studies of a binuclear copper(II) complex with phenanthroline

A new binuclear copper(II) complex, [Cu2Phen2Cl4] (Phen=1,10-phenanthroline), has been synthesized and characterized. Single crystal X-ray diffraction results suggest that this complex structure belongs to monoclinic crystal system, Cc (no. 9) with the cell dimensions: a=9.849(2)A, b=17.833(4)A, c=13.374(3)A, beta=106.61(3) degrees , V=2251.0(8)A(3), Dc=1.8569 Mgm(-3), F(000)=1256.0, Z=4. One Cu(II) central atom situated in a distorted square planar geometry is four-coordinated. The other situated in a distorted square pyramidal geometry is five-coordinated. Only one bridging Cl atom exists in the complex. Spectroscopic studies, including electronic absorption and fluorescence spectra, conductivity measurements and parallel factor analysis (PARAFAC) of fluorescence excitation-emission three-way data array, were carried out on the DNA binding behavior of the complex. All the results suggested that the breakage of DNA secondary structure took place at low molar ratio of complex to DNA (0.3 at most) and intercalation into the base pair of DNA took place at high molar ratio. Additionally, the equilibrium concentration of EB-DNA and EB (EB: ethidium bromide) could be directly obtained by PARAFAC algorithm, proved to be a convincing method for studying the interaction of complexes with DNA.

Mitochondrial involvement in genetically determined transition metal toxicity II. Copper toxicity

Copper, like iron, is an essential transition metal ion in which its redox reactivity, whilst essential for the activity of mitochondrial enzymes, can also be a source of harmful reactive oxygen species if not chelated to biomolecules. Therefore, both metals are sequestered by protein chaperones and moved across membranes by protein transporters with the excess held in storage proteins for future use. In the case of copper, the storage proteins in the mitochondria are a distinct ceruloplasmin and metallothionein (MT). If the cell accumulates too much copper or copper is needed by other cells, then copper can be chaperoned to the trans-Golgi secretory compartment where it is transported into the Golgi by ATP-dependent pumps ATP7A/B. In liver, the copper is then incorporated into ceruloplasmin in vesicles that travel to the plasma membrane and release ceruloplasmin into the plasma. This paper reviews the genetic basis for diseases associated with copper deficit or excess, particularly those attributed to defective ATP7A/B transporters, with special emphasis on pathologies related to a loss of mitochondrial function.

Bilirubin exhibits a novel anti-cancer effect on human adenocarcinoma

Anti-oxidants are essential for intracellular free radical scavenging, as free radicals are one of the causes for tumorigenesis. Our objective was to use bilirubin and investigate its action on human carcinoma cell lines. Bilirubin manifested as a prooxidant showing its cytopathic effect on TMK-1, showing growth inhibition close to 50%. Cell cycle analysis showed an arrest at G0/G1. Flow cytometry investigations with Red CC-1 showed an increase by more than 2 times suggesting a prooxidative role of bilirubin. To check the effect of radicals on DNA, a Comet Assay displayed a typical comet's tail with bilirubin treated slides, only. Further, staining with DAPI showed apoptotic action of bilirubin. Decreased mitochondrial function by bilirubin was observed with Mitotracker Green FM staining. These unexpected data have led us to conclude that bilirubin has anti-cancer activity as a prooxidant and may have a more vital role in the human body than realized.

Chitosan-g-PEG/DNA complexes deliver gene to the rat liver via intrabiliary and intraportal infusions

BACKGROUND

Chitosan has been shown to be a non-toxic and efficient vector for in vitro gene transfection and in vivo gene delivery through pulmonary and oral administrations. Recently, we have shown that chitosan/DNA nanoparticles could mediate high levels of gene expression following intrabiliary infusion 1. In this study, we have examined the possibility of using polyethylene glycol (PEG)-grafted chitosan/DNA complexes to deliver genes to the liver through bile duct and portal vein infusions.

METHODS

PEG (Mw: 5 kDa) was grafted onto chitosan (Mw: 47 kDa, deacetylation degree: 94%) with grafting degrees of 3.6% and 9.6% (molar percentage of chitosan monosaccharide units grafted with PEG). The stability of chitosan-g-PEG/DNA complexes was studied by measuring the change in particle size and by agarose gel electrophoresis against bile or serum challenge. The influence of PEG grafting on gene transfection efficiency was evaluated in HepG2 cells using luciferase reporter gene. Chitosan and chitosan-g-PEG/DNA complexes were delivered to the liver through bile duct and portal vein infusions with a syringe pump. Gene expression in the liver and the distribution of gene expression in other organs were evaluated. The acute liver toxicity of chitosan and chitosan-g-PEG/DNA complexes was examined by measuring serum alanine aminotranferase (ALT) and aspartate aminotransferase (AST) activities as a function of time.

RESULTS

Both chitosan and chitosan-g-PEG displayed comparable gene transfection efficiency in HepG2 cells. After challenge with serum and bile, chitosan-g-PEG/DNA complexes, especially those prepared with chitosan-g-PEG (GD = 9.6%), did not form large aggregates like chitosan/DNA complexes but remained stable for up to 30 min. In addition, chitosan-g-PEG prevented the degradation of DNA in the presence of serum and bile. On day 3 after bile duct infusion, chitosan-g-PEG (GD = 9.6%)/DNA complexes mediated three times higher gene expression in the liver than chitosan/DNA complexes and yielded background levels of gene expression in other organs. On day 1 following portal vein infusion, gene expression level induced by chitosan/DNA complexes was hardly detectable but chitosan-g-PEG (GD = 9.6%) mediated significant transgene expression. Interestingly, transgene expression by chitosan-g-PEG/DNA complexes in other organs after portal vein infusion increased with increasing grafting degree of PEG. The ALT and AST assays indicated that grafting of PEG to chitosan reduced the acute liver toxicity towards the complexes.

CONCLUSION

This study demonstrated the potential of chitosan-g-PEG as a safe and more stable gene carrier to the liver.