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Evaluating the Beneficial and Detrimental Effects of Bile Pigments in Early and Later Life


Abstract and Figures

The heme degradation pathway has been conserved throughout phylogeny and allows for the removal of a pro-oxidant and the generation of unique molecules including bile pigments with important cellular functions. The impact of bile pigments on health and disease are reviewed, as is the special circumstance of neonatal hyperbilirubinemia. In addition, the importance of promoter polymorphisms in the UDP-glucuronosyl transferase gene (UGTA1), which is key to the elimination of excess bilirubin and to the prevention of its toxicity, are discussed. Overall, the duality of bile pigments as either cytoprotective or toxic molecules is highlighted.
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published: 22 June 2012
doi: 10.3389/fphar.2012.00115
Evaluating the beneficial and detrimental effects of bile
pigments in early and later life
Phyllis A. Dennery
Division of Neonatology, Childrens Hospital of Philadelphia, University of Pennsylvania School of Medicine, Philadelphia, PA, USA
Division of Neonatology, Department of Pediatrics, University of Pennsylvania, Philadelphia, PA, USA
Edited by:
Jaime Kapitulnik,The Hebrew
University of Jerusalem, Israel
Reviewed by:
David K. Stevenson, Stanford
University School of Medicine, USA
Michael Kaplan, Shaare Zedek
Medical Center, Israel
Phyllis A. Dennery , Division of
Neonatology, Department of
Pediatrics, University of Pennsylvania,
34th and Civic Center Boulevard,
Philadelphia, PA 19104-4318, USA.
The heme degradation pathway has been conserved throughout phylogeny and allows for
the removal of a pro-oxidant and the generation of unique molecules including bile pig-
ments with important cellular functions.The impact of bile pigments on health and disease
are reviewed, as is the special circumstance of neonatal hyperbilirubinemia. In addition,
the importance of promoter polymorphisms in the UDP-glucuronosyl transferase gene
(UGTA1), which is key to the elimination of excess bilirubin and to the prevention of its tox-
icity, are discussed. Overall, the duality of bile pigments as either cytoprotective or toxic
molecules is highlighted.
Keywords: neonatal jaundice, kernicterus, UDP-glucuronyltransferase, antioxidant, polymorphisms
The generation of bile pigments occurs through a unique pathway
for the degradation of heme, limited by the enzyme hemeoxy-
genase (HO). This enzymatic reaction requires molecular oxy-
gen (O
) and NADPH as a reducing equivalent and results in
the formation of biliverdin and the release of carbon monox-
ide (CO) in an equimolar ratio. In addition, reduction of heme
iron from Fe
occurs with the transfer of electrons from
oxygen with NADPH as a source of reducing equivalents. Also,
oxidative cleavage of the α-methene carbon bridge in the heme
molecule forms biliverdin, releases carbon monoxide and iron
(Figure 1). In most circumstances, heme does not accumulate
freely but rather, it is bound to hemo proteins that are essential
for cellular metabolism. An intricate enzymatic cascade regulates
the production of heme (Ryter and Tyrrell, 2000). In patholog-
ical conditions, free heme is released from hemoglobin and can
deposit in tissues because it is lipophilic and can lead to the for-
mation of oxygen radicals therefore, the enzymatic reaction of
HO is essential to preventing this since HO-1 is highly inducible
by the substrate heme or by oxidative stress (Chang et al., 2005).
The constitutive isoenzyme HO-2 can also catalyze the degrada-
tion of heme and is found in high abundance in the brain and
testes (Maines et al., 1986; Maines, 1988). In the last steps of
the reaction, biliverdin reductase (BVR), a microsomal enzyme,
converts biliverdin into bilirubin in a non-rate-limiting fashion
(Figure 1). Bilirubin, unlike biliverdin is not water soluble, but
rather lipophilic, and can penetrate cellular membranes. To be
made water soluble and therefore excretable in the gastrointestinal
tract, it must be conjugated. The latter is regulated by UDP-
glucuronosyl transferase 1A1 (UGT1A1), an enzyme that adds
two glucuronide residues to bilirubin to render it water soluble
(Figure 1).
The byproducts of HO-mediated heme degradation can have
both positive and negative effects on cellular function. These will
be outlined in this review.
Newborns have elevated numbers of red blood cells with a short-
ened life-span. When these cells lyse, heme is released from
hemoglobin. In addition, due to a reduced ability to conjugate
bilirubin formed during the degradation of heme, this pigment
can accumulate in the serum in the first days of life leading to
a transient hyperbilirubinemia, which typically resolves within
the first weeks of life. In fact, the average full-term newborn
infant has a peak serum bilirubin concentration of 5–6 mg/dL
(86–103 µmol/L). This level is referred to as physiologic jaundice.
However, in some circumstances, such as increased accumulation
of heme (i.e., birth trauma, bruising, hemolysis), serum bilirubin
levels can increase beyond the physiologic range. If serum biliru-
bin values are between 7 and 17 mg/dL (104–291 µmol/L), this is
then referred to as exaggerated physiologic jaundice. However, this
must be judged according to the infant’s age in hours on the biliru-
bin nomogram, as serum bilirubin levels change rapidly during
the first week of life. Serum bilirubin concentrations higher than
17 mg/dL in full-term infants are considered pathologic and can
be associated with adverse sequelae. Fortunately, most infants will
not be affected until their bilirubin levels are significantly higher
than 17 mg/dL because the toxicity of bilirubin is dictated by many
factors including age (the younger, the more vulnerable), matu-
rity (prematures are more vulnerable), and associated illnesses
(hemolysis, sepsis, acidosis worsen bilirubin toxicity) amongst
other factors. The most severe manifestation of bilirubin toxi-
city is kernicterus, a rare but devastating condition with acute June 2012 | Volume 3 | Article 115 | 1
Dennery Bilirubin good and bad
FIGURE 1 | Heme degradation pathway. Heme from hemoglobin and
cellular hemo proteins is metabolized in a rate-limiting step by HO. The
reaction utilizes molecular oxygen and NADPH as a reducing equivalent.
This leads to the release of iron, water, and CO as well as biliverdin. The
latter is converted in a non-rate-limiting fashion to bilirubin by BVR. Since
bilirubin is not water soluble, it is conjugated to monoglucuronide and
diglucuronide forms, which can then be excreted. These glucuronide
residues can be removed by intestinal bacteria and allow unconjugated
bilirubin to re-enter the circulation.
neurological abnormalities including seizures, opisthotonus, and
hypertonia and long lasting sequelae including sensorineural deaf-
ness, athetoid cerebral palsy, and delayed motor skills (Dennery
et al., 2001).
Prior to the late 1980s, physicians had a very aggressive
approach to the management of hyperbilirubinemia in neonates,
which included institution of phototherapy at low levels of biliru-
bin and exchange transfusion if the level exceeded 20 mg/dL in all
cases. This approach changed radically since kernicterus was such
a rare condition and, with the advent of Rhogam prophylaxis for
Rh-negative pregnant mothers, kernicterus was thought by some
to be nearly eradicated in developed nations (Watchko and Oski,
1983). In addition, reports of the beneficial, antioxidant effects
of bilirubin (Stocker et al., 1987, 1990; McDonagh, 1990) made
this aggressive approach seem even more unwarranted. Alas, with
this change in attitude, pediatricians saw a resurgence of biliru-
bin neurotoxicity, and were faced with litigation for the negligent
practice of not having taken simple measures to prevent the devas-
tating consequences of hyperbilirubinemia (Maisels and Newman,
2007; Bhutani et al., 1999). In the present day, we have adopted a
more thoughtful approach to this preventable problem by using
strict guidelines for universal screening and by instituting therapy
guided by age-based serum bilirubin thresholds (Bhutani et al.,
1999; Maisels and Newman, 2007).
It is not clear why bilirubin accumulates in the first days of
life and what is its value. Physiologic hyperbilirubinemia is a
phenomenon only seen in mammals. Many have speculated a tele-
ological benefit to this reaction (McDonagh, 1990) and laboratory
investigations do confirm that bilirubin has significant antioxidant
properties both in vitro (Stocker et al., 1987; Mireles et al., 1999;
Granato et al., 2003) and in vivo (Dennery et al., 1995; Mayer,
2000). Perhaps this may be useful in the transition from the rela-
tively hypoxic environment of the wound to ambient air. This is
not yet clear. Also, the exact dose at which bilirubin is toxic to cells
vs. beneficial is also not yet known.
In infants with Rh hemolytic disease, peak serum bilirubin con-
centrations above 20 mg/dL predict poor outcome however, many
infants without an obvious hemolytic etiology for their jaun-
dice are normal at serum bilirubin concentrations of 25 mg/dL
or higher. Looking at this more closely, 8% of infants with Rh-
associated hemolysis and serum bilirubin concentrations of 19–
24 mg/dL had kernicterus whereas this condition was observed
in 73% of infants with concentrations of 30–40 mg/dL demon-
strating the dose effect of bilirubin, at least in hemolytic children.
Bilirubin enters the brain and targets the basal ganglia (Johnston
and Hoon, 2000) and the auditory nerve preferentially (Shapiro
and Nakamura, 2001). This occurs if bilirubin is not bound to
albumin or is unconjugated or if there has been damage to the
blood–brain barrier. As an example,a newborn infant with a serum
albumin concentration of 3 g/dL can bind 25 mg/dL of bilirubin.
In current clinical practice, the bilirubin albumin ratio is taken into
consideration to determine levels at which physicians should pro-
ceed to more aggressive management of hyperbilirubinemia (i.e.,
exchange transfusion). If the serum albumin concentration is low,
the risk of kernicterus increases because free bilirubin enters tissues
and causes its toxic effects (Ahlfors et al., 2009). Conditions that
alter the blood–brain barrier, such as infection, acidosis, hyper-
oxia, sepsis, prematurity, and hyperosmolarity, may also affect the
entry of bilirubin into the brain (Dennery et al., 2001).
Bilirubin has high affinity for membrane phospholipids thereby
entering cells and inhibiting mitochondrial enzymes (Chuniaud
et al., 1996; Rodrigues et al., 2002a), interfering with DNA syn-
thesis, inducing DNA-strand breaks (Rosenstein et al., 1983), and
inhibiting protein synthesis and phosphorylation. In the brain,
bilirubin inhibits the uptake of tyrosine, reduces synaptic trans-
mission, and inhibits N -methyl-d-aspartate-receptor ion chan-
nels. Overall, bilirubin can interfere with neuro excitatory signals
and impair nerve conduction particularly in the auditory nerve
(Bratlid, 1990). Unconjugated bilirubin directly interacts with
mitochondria influencing membrane lipid and protein proper-
ties, redox status, and cytochrome c content (Rodrigues et al.,
2002b). It can work in concert with amyloid β peptide to activate
apoptosis in neural cells (Rodrigues et al., 2000). Interestingly,
younger animals are less susceptible to bilirubin-related mito-
chondrial injury (Rodrigues et al., 2002c) and the toxicity of
bilirubin is not restricted to neonates. In patients with Crigler–
Najjar I syndrome and absent activity of the UGTA1, therefore
a complete lack of ability to conjugate bilirubin, the risk of ker-
nicterus is quite high especially in the face of intercurrent illnesses
and these patients require life-long phototherapy and/or liver
transplantation (Strauss et al., 2006).
In the nervous system, the susceptibility of bilirubin varies with
cell type (Ngai et al., 2000). In brain endothelial cells, bilirubin
resulted in apoptosis in a time-dependent manner (Akin et al.,
Frontiers in Pharmacology | Drug Metabolism and Transport June 2012 | Volume 3 | Article 115 | 2
Dennery Bilirubin good and bad
2002). Unconjugated bilirubin induced protein oxidation and
lipid peroxidation and reduced antioxidant defenses in neuronal
cells in culture (Brito et al., 2008). Although toxic to cultured
neuroblastoma cells, exposure to unconjugated bilirubin induced
genes involved in the endoplasmic reticulum stress response in
surviving cells thereby enhancing cellular homeostasis (Calligaris
et al., 2009). In astrocytes, unconjugated bilirubin up-regulated
the multidrug resistance-associated protein-1 and increased its
trafficking to the plasma membrane, thus reducing its cytotoxi-
city by preventing its intracellular accumulation (Gennuso et al.,
The toxic effects of bilirubin are not limited to the brain.
Unconjugated bilirubin can mediate apoptosis in cultured hepa-
tocytes by increasing oxidative stress and enhancing caspase-9
activity (Oakes and Bend, 2005). In erythrocytes, high biliru-
bin concentrations can induce hemolysis and lead to membrane
disruption, which could theoretically worsen hemolytic anemia
(Brites et al., 1997). We observed that in erythrocytes derived
from cord blood, concentrations of bilirubin equal to or exceed-
ing 30 mg/dL were associated with increased protein oxidation,
decreased erythrocyte glucose-6 phosphate dehydrogenase and
adenosine triphosphatase activity as well as altered cell mem-
brane integrity (Mireles et al., 1999). There was a correlation
between the release of unconjugated bilirubin and hepatotoxic-
ity after TNF-a administration, in mice and this was resolved with
HO inhibitors (Van Molle and Libert, 2003). Another important
cytotoxicity of bilirubin involves its effects on complement acti-
vation, a key element of immune defense. Unconjugated bilirubin
interferes with the interaction between C1q and immunoglob-
ulins, which results in decreased complement activation via the
classical pathway (Basiglio et al., 2010).
Despite the fact that bilirubin may be toxic at higher concentra-
tions, there is still significant evidence that it is a potent antioxidant
at micromolar concentrations in vitro and in vivo. In fact, biliru-
bin is the most abundant cellular antioxidant. In vitro, bilirubin is
a chain-breaking molecule that can scavenge the hydroxyl radical
better than a-tocopherol, a well-known antioxidant against lipid
peroxidation (Stocker et al., 1987; Mireles et al., 1999). Although
incubation with bilirubin and albumin at concentrations greater
than 30 mg/dL was associated with dose-dependent injury in ery-
throcytes derived from cord blood, protection against lipid per-
oxidation was seen at lower concentrations (Mireles et al., 1999),
indicating the duality of bilirubin as a cytotoxic and cytoprotec-
tive molecule. Similarly, hemeoxygenase is both detrimental and
beneficial based on levels of activity. Nevertheless, in that study, no
change in bilirubin levels could be detected to explain the toxicity
of hemeoxygenase (Suttner and Dennery, 1999).
Similarly, in vivo, there are several examples of the beneficial
effects of hyperbilirubinemia. In 50 patients older than 40 years
with Gilbert syndrome, a relatively benign condition leading to
mild to moderate unconjugated hyperbilirubinemia because of
impaired glucuronidation, occurrence of ischemic heart disease
was compared to that of a large cohort of patients without the dis-
ease. Ischemic heart disease occurred in only 2% of the Gilbert
patients compared to 12.1% of the controls and, interestingly,
hyperbilirubinemia rather than elevation of HDL cholesterol lev-
els seemed to be more important in protection from ischemic
heart disease (Vitek et al., 2002). In a case report, resolution of
corticosteroid- and cyclophosphamide-resistant pulmonary fibro-
sis occurred with onset of hyperbilirubinemia due to biliary
obstruction in a patient who developed elevated conjugated biliru-
bin levels (Ohrui et al., 2001), suggesting that higher serum biliru-
bin levels could reverse pulmonary fibrosis. The mechanisms by
which this could occur are not yet explored. In organ transplan-
tation, bilirubin can be protective against graft rejection (Ollinger
et al., 2007). Injection of bilirubin in mouse organ recipients pro-
longed islet allograft survival and induced tolerance induction
and graft acceptance via a regulatory T cell-dependent mech-
anism involving CD4(+) and CD25(+) cells. In fact, bilirubin
enhanced de novo generation of regulatory T cells in the recipients
thereby preventing rejection (Rocuts et al., 2010). Another novel
mechanisms by which bilirubin may be protective is by the regu-
lation of rapid eye movement sleep and by mediating some of the
antidepressant effects of ambient light (Oren, 1997). Whether the
antioxidant effects mediate these benefits is not yet clear.
Overall, the beneficial effects of bilirubin have been demon-
strated in various models but beyond a certain threshold, bilirubin
is clearly toxic.
To further understand whether bilirubin is cytoprotective in
humans, epidemiologic studies can provide a clue. Regulation
of bilirubin conjugation is key in the accumulation of bilirubin
and its potential benefits or toxicity, therefore, studies compar-
ing patients with differences in the ability to conjugate biliru-
bin may provide clues. The promoter of the UGT1A1 gene has
regions of TA repeats, which regulate its transcriptional effi-
ciency. In Caucasian populations, an additional TA repeat (TA
vs. TA
) is necessary but not sufficient to cause Gilbert syndrome
(Bartlett and Gourley, 2011). Strong associations between poly-
morphisms in the UGT1A1 gene and human disease have been
shown. In particular, there have been associations with altered
bilirubin conjugation and the occurrence of various cancers. The
common UGT1A1
28 allele results in elevated plasma bilirubin
levels and is strongly associated with Gilbert syndrome in Cau-
casians. Low serum bilirubin levels observed in a Caucasian cohort
with predicted high activity of UGT1A1 were associated with an
increased risk of esophageal cancer. Interestingly, the UGT1A8
and UGT2B4 genotypes, associated with decreased UGT enzyme
activity and increased unconjugated bilirubin levels, were also
significantly associated with increased risk of esophageal cancer
(Dura et al., 2012). In another study, the UGT1A gene cluster
on chromosome 2q37.1 was identified in a cohort of patients
with bladder cancer suggesting that enhanced UGT1A may pro-
tect from bladder cancer by increasing the removal of carcinogens
from bladder epithelium (Tang et al., 2012). In a meta-analysis of
21 case-control studies cancer risk was associated with intermedi-
ate, and low activity of UGT1A7 genotypes, found predominantly
in Asians (Lu et al., 2011). In contrast to the other studies, the
TA repeat polymorphism of UGT1A1 gene did not alter prostate
cancer risk susceptibility in Caucasian men (Karatzas et al., 2010). June 2012 | Volume 3 | Article 115 | 3
Dennery Bilirubin good and bad
Overall, these studies suggest that the concentration of bilirubin
in the serum determines whether it is beneficial or detrimental.
Not only does the UGT1 gene play a role in cancer, it appears to
have important effects in other diseases. For example, the homozy-
gous state associated with higher serum bilirubin levels appeared
to be protective against Crohns disease (de Vries et al., 2012).
Serum bilirubin, independent of variation in UGT promoter
activity, is also associated with diseases in large populations, in
particular in cardiovascular disease. In a Swedish cohort, plasma
bilirubin was lower in 231 cases of ischemic stroke than in 462
matched controls but the difference reached significance only in
women (Ekblom et al., 2010). In males with coronary artery dis-
ease, there was inverse association between serum total bilirubin
and coronary artery calcification score. Additionally, bilirubin was
associated with reduced c-reactive protein levels, which could
explain the lower calcification scores (Zhang et al., 2012). In
another study, bilirubin levels were also inversely associated with
the presence of coronary heart disease. Interestingly, bilirubin lev-
els were significantly raised after treatment with 80 mg simvastatin
independent of changes in liver enzymes (Nolting et al., 2011).
Despite the beneficial effects of bilirubin, the biggest challenge
remains determining a specific threshold at which bilirubin is
toxic vs. beneficial. It seems paradoxical that early events in biliru-
bin toxicity may involve increased oxidative stress and changes in
redox status (Tell and Gustincich, 2009) yet conversely, bilirubin
alleviates oxidative stress.
Although biliverdin does not accumulate in mammals, since
it is rapidly converted to bilirubin through the action of
biliverdin reductase (BVR), it may have important signaling
effects. In macrophages, biliverdin activates endothelial nitric
oxide, resulting in NO-dependent S-nitrosylation of BVR. The
mechanisms by which biliverdin mediates this effect was via
the repression of Toll-like receptor-4 (Wegiel et al., 2011). In
another study, rats injected intraperitoneally with biliverdin before
undergoing lung transplantation had less evidence of inflamma-
tion, oxidative injury, and apoptosis suggesting that biliverdin has
anti-inflammatory and anti-apoptotic effects (Wang et al., 2010).
Despite these data, the most plausible effect of biliverdin is to serve
as a signaling molecule that may regulate BVR (Lerner-Marmarosh
et al., 2008). The properties of this enzyme have been reviewed at
length in a previous issue of this journal (Gibbs et al., 2012).
Although the byproducts of the HO-1 reaction are important
cytoprotective molecules, a likely factor that influences the ben-
eficial effects of the HO reaction is the degradation of a potent
oxidant, heme. In one example, induction of HO-1 prevented pho-
todynamic therapy-induced tumor necrosis, but neither bilirubin,
biliverdin nor CO was responsible for this cytoprotection. In fact,
the iron chelator desferrioxamine enhanced the cytotoxic effects
of photodynamic therapy suggesting that heme was key important
to enhancing the tumor killing effects of this therapy (Nowis et al.,
Overall, the byproducts of the HO reaction are important cytopro-
tective molecules that have clinically significant effects in various
diseases. Nevertheless, in most cases, these molecules can also be
cytotoxic under specific circumstances and/or at high concentra-
tions. Potential therapeutic interventions will need to balance the
potential benefits with the risk of toxicity to be most effective.
Ahlfors, C. E., Amin, S. B., and Parker,
A. E. (2009). Unbound bilirubin pre-
dicts abnormal automated auditory
brainstem response in a diverse new-
born population. J. Perinatol. 29,
Akin, E., Clower, B., Tibbs, R., Tang, J.,
and Zhang, J. (2002). Bilirubin pro-
duces apoptosis in cultured bovine
brain endothelial cells. Brain Res.
931, 168–175.
Bartlett, M. G., and Gourley, G. R.
(2011). Assessment of UGT poly-
morphisms and neonatal jaundice.
Semin. Perinatol. 35, 127–133.
Basiglio, C. L., Arriaga, S. M., Pelusa,
F., Almara, A. M., Kapitulnik, J.,
and Mottino, A. D. (2010). Comple-
ment activation and disease: protec-
tive effects of hyperbilirubinaemia.
Clin. Sci. 118, 99–113.
Bhutani, V. K., Johnson, L. H., and
Sivieri, E. M. (1999). Predictive
ability of a predischarge hour-
specific serum bilirubin for sub-
sequent significant hyperbilirubine-
mia in healthy term and near-term
newborns. Pediatrics 103, 6–14.
Bratlid, D. (1990). How bilirubin gets
into the brain. Clin. Perinatol. 17,
Brites, D., Silva, R., and Brito, A. (1997).
Effect of bilirubin on erythro-
cyte shape and haemolysis, under
hypotonic, aggregating or non-
aggregating conditions, and correla-
tion with cell age. Scand. J. Clin. Lab.
Invest. 57, 337–349.
Brito, M. A., Lima, S., Fernandes, A.,
Falcao, A. S., Silva, R. F., Butter-
field, D. A., and Brites, D. (2008).
Bilirubin injury to neurons: contri-
bution of oxidative stress and res-
cue by glycoursodeoxycholic acid.
Neurotoxicology 29, 259–269.
Calligaris, R., Bellarosa, C., Foti, R.,
Roncaglia, P., Giraudi, P., Krmac,
H., Tiribelli, C., and Gustincich,
S. (2009). A transcriptome analy-
sis identifies molecular effectors of
unconjugated bilirubin in human
neuroblastoma SH-SY5Y cells. BMC
Genomics 10,543. doi:10.1186/1471-
Chang, E. F., Claus, C. P., Vreman, H. J.,
Wong, R. J., and Noble-Haeusslein,
L. J. (2005). Heme regulation in
traumatic brain injury: relevance
to the adult and developing brain.
J. Cereb. Blood Flow Metab. 25,
Chuniaud, L., Dessante, M., Chantoux,
F., Blondeau, J. P., Francon, J., and
Trivin, F. (1996). Cytotoxicity of
bilirubin for human fibroblasts and
rat astrocytes in culture. Effect of the
ratio of bilirubin to serum albumin.
Clin. Chim. Acta 256, 103–114.
de Vries, H. S., Te Morsche, R. H.,
Jenniskens, K., Peters, W. H., and
De Jong, D. J. (2012). A functional
polymorphism in UGT1A1 related
to hyperbilirubinemia is associated
with a decreased risk for Crohns
disease. J. Crohns Colitis. 6, 597–602.
Dennery, P. A., McDonagh, A. F., Spitz,
D. R., Rodgers, P. A., and Stevenson,
D. K. (1995). Hyperbilirubinemia
results in reduced oxidative injury
in neonatal Gunn rats exposed to
hyperoxia. Free Radic. Biol. Med. 19,
Dennery, P. A., Seidman, D. S., and
Stevenson, D. K. (2001). Neonatal
hyperbilirubinemia. N. Engl. J. Med.
344, 581–590.
Dura, P., Salomon, J., Te Morsche,
R. H., Roelofs, H. M., Kristins-
son, J. O., Wobbes, T., Witteman,
B. J., Tan, A. C., Drenth, J. P., and
Peters, W. H. (2012). High enzyme
activity UGT1A1 or low activity
UGT1A8 and UGT2B4 genotypes
increase esophageal cancer risk.
Int. J. Oncol. 40, 1789–1796.
Ekblom, K., Marklund, S. L., Johans-
son, L., Osterman, P., Hallmans,
G., Weinehall, L., Wiklund, P. G.,
and Hultdin, J. (2010). Bilirubin
and UGT1A128 are not associ-
ated with lower risk for ischemic
stroke in a prospective nested case-
referent setting. Cerebrovasc. Dis. 30,
Gennuso, F., Fernetti, C., Tirolo, C.,
Testa, N., L’Episcopo, F., Caniglia, S.,
Morale, M. C., Ostrow, J. D., Pascolo,
L., Tiribelli, C., and Marchetti, B.
(2004). Bilirubin protects astrocytes
from its own toxicity by inducing
up-regulation and translocation
of multidrug resistance-
associated protein 1 (Mrp1).
Proc. Natl. Acad. Sci. U.S.A. 101,
Frontiers in Pharmacology | Drug Metabolism and Transport June 2012 | Volume 3 | Article 115 | 4
Dennery Bilirubin good and bad
Gibbs, P. E., Tudor, C., and Maines,
M. D. (2012). Biliverdin reduc-
tase: more than a namesake
the reductase, its Peptide frag-
ments, and biliverdin regulate activ-
ity of the three classes of protein
kinase C. Front. Pharmacol. 3:31.
Granato, A., Gores, G., Vilei, M.
T., Tolando, R., Ferraresso, C.,
and Muraca, M. (2003). Bilirubin
inhibits bile acid induced apop-
tosis in rat hepatocytes. Gut 52,
Johnston, M. V., and Hoon, A. H.
Jr. (2000). Possible mechanisms in
infants for selective basal ganglia
damage from asphyxia, kernicterus,
or mitochondrial encephalopathies.
J. Child Neurol. 15, 588–591.
Karatzas, A., Giannatou, E., Tzortzis, V.,
Gravas, S., Aravantinos, E., Mout-
zouris, G., Melekos, M., and Tsezou,
A. (2010). Genetic polymorphisms
in the UDP-glucuronosyltransferase
1A1 (UGT1A1) gene and prostate
cancer risk in Caucasian men. Can-
cer Epidemiol. 34, 345–349.
Lerner-Marmarosh, N., Miralem, T.,
Gibbs, P. E., and Maines, M. D.
(2008). Human biliverdin reductase
is an ERK activator; hBVR is an ERK
nuclear transporter and is required
for MAPK signaling. Proc. Natl.
Acad. Sci. U.S.A. 105, 6870–6875.
Lu, P. H., Chen, M. B., Wu, X. Y., Gu,
J. H., Liu, Y., and Gu, R. M. (2011).
Genetic polymorphisms of UGT1A7
and cancer risk: evidence from 21
case-control studies. Cancer Invest.
29, 645–654.
Maines, M. D. (1988). Heme oxyge-
nase: function, multiplicity, regula-
tory mechanisms, and clinical appli-
cations. FASEB J. 2, 2557–2568.
Maines, M. D., Trakshel, G. M., and
Kutty, R. K. (1986). Characteriza-
tion of two constitutive forms of rat
liver microsomal heme oxygenase.
Only one molecular species of the
enzyme is inducible. J. Biol. Chem.
261, 411–419.
Maisels, M. J., and Newman, T. B.
(2007). Kernicterus, the Daubert
decision, and evidence-based med-
icine. Pediatrics 119, 1038; author
reply 1038–1039.
Mayer, M. (2000). Association of serum
bilirubin concentration with risk of
coronary artery disease. Clin. Chem.
46, 1723–1727.
McDonagh, A. F. (1990). Is bilirubin
good for you? Clin. Perinatol. 17,
Mireles, L. C., Lum, M. A., and Dennery,
P. A. (1999). Antioxidant and cyto-
toxic effects of bilirubin on neona-
tal erythrocytes. Pediatr. Res. 45,
Ngai, K. C., Yeung, C. Y., and Leung, C.
S. (2000). Difference in susceptibili-
ties of different cell lines to bilirubin
damage. J. Paediatr. Child Health 36,
Nolting, P. R., Kusters, D. M., Hutten, B.
A., and Kastelein, J. J. (2011). Serum
bilirubin levels in familial hypercho-
lesterolemia: a new risk marker for
cardiovascular disease? J. Lipid Res.
52, 1755–1759.
Nowis, D., Legat, M., Grzela, T.,
Niderla, J., Wilczek, E., Wilczynski,
G. M., Glodkowska, E., Mrowka, P.,
Issat, T., Dulak, J., Jozkowicz, A.,
Was, H., Adamek, M., Wrzosek, A.,
Nazarewski, S., Makowski, M., Stok-
losa, T., Jakobisiak, M., and Golab,
J. (2006). Heme oxygenase-1 pro-
tects tumor cells against photody-
namic therapy-mediated cytotoxic-
ity. Oncogene 25, 3365–3374.
Oakes, G. H., and Bend, J. R. (2005).
Early steps in bilirubin-mediated
apoptosis in murine hepatoma
(Hepa 1c1c7) cells are character-
ized by aryl hydrocarbon receptor-
independent oxidative stress and
activation of the mitochondrial
pathway. J. Biochem. Mol. Toxicol. 19,
Ohrui, T., Higuchi, M., Kanda, A., Mat-
sui,T., Sato,E.,and Sasaki, H. (2001).
A patient with exacerbation of idio-
pathic pulmonary fibrosis which was
resolved probably due to the coex-
isting hyperbilirubinemia? Tohoku J.
Exp. Med. 193, 245–249.
Ollinger, R., Wang, H., Yamashita, K.,
Wegiel, B., Thomas, M., Margre-
iter, R., and Bach, F. H. (2007).
Therapeutic applications of biliru-
bin and biliverdin in transplan-
tation. Antioxid. Redox Signal. 9,
Oren, D. A. (1997). Bilirubin, REM
sleep, and phototransduction of
environmental time cues. A hypoth-
esis. Chronobiol. Int. 14, 319–329.
Rocuts, F., Zhang, X., Yan, J., Yue, Y.,
Thomas, M., Bach, F. H., Czismadia,
E., and Wang, H. (2010). Bilirubin
promotes de novo generation of T
regulatory cells. Cell Transplant. 19,
Rodrigues, C. M., Sola, S., and Brites,
D. (2002a). Bilirubin induces apop-
tosis via the mitochondrial path-
way in developing rat brain neurons.
Hepatology 35, 1186–1195.
Rodrigues, C. M., Sola, S., Brito, M.
A., Brites, D., and Moura, J. J.
(2002b). Bilirubin directly disrupts
membrane lipid polarity and fluid-
ity, protein order, and redox status
in rat mitochondria. J. Hepatol. 36,
Rodrigues, C. M., Sola, S., Silva, R. F.,
and Brites, D. (2002c). Aging confers
different sensitivity to the neurotoxic
properties of unconjugated biliru-
bin. Pediatr. Res. 51, 112–118.
Rodrigues, C. M., Sola, S., Silva, R.,
and Brites, D. (2000). Bilirubin
and amyloid-beta peptide induce
cytochrome c release through mito-
chondrial membrane permeabiliza-
tion. Mol. Med. 6, 936–946.
Rosenstein, B. S., Ducore, J. M., and
Cummings, S. W. (1983). The mech-
anism of bilirubin-photosensitized
DNA strand breakage in human
cells exposed to phototherapy light.
Mutat. Res. 112, 397–406.
Ryter, S. W., and Tyrrell, R. M. (2000).
The heme synthesis and degradation
pathways: role in oxidant sensitivity.
Heme oxygenase has both pro- and
antioxidant properties. Free Radic.
Biol. Med. 28, 289–309.
Shapiro, S. M., and Nakamura, H.
(2001). Bilirubin and the auditory
system. J. Perinatol. 21(Suppl. 1),
S52–S55; discussion S59–S62.
Stocker, R., McDonagh, A. F., Glazer, A.
N., and Ames, B. N. (1990). Antiox-
idant activities of bile pigments:
biliverdin and bilirubin. Meth. Enzy-
mol. 186, 301–309.
Stocker, R., Yamamoto, Y., McDonagh,
A. F., Glazer, A. N., and Ames, B. N.
(1987). Bilirubin is an antioxidant of
possible physiological importance.
Science 235, 1043–1046.
Strauss, K. A., Robinson, D. L., Vre-
man, H. J., Puffenberger, E. G.,
Hart, G., and Morton, D. H. (2006).
Management of hyperbilirubinemia
and prevention of kernicterus in 20
patients with Crigler-Najjar disease.
Eur. J. Pediatr. 165, 306–319.
Suttner, D. M., and Dennery, P. A.
(1999). Reversal of HO-1 related
cytoprotection with increased
expression is due to reactive iron.
FASEB J. 13, 1800–1809.
Tang, W., Fu, Y. P., Figueroa, J. D.,
Malats, N., Garcia-Closas, M., Chat-
terjee, N., Kogevinas, M., Baris, D.,
Thun, M., Hall, J. L., De Vivo, I.,
Albanes, D., Porter-Gill, P., Purdue,
M. P., Burdett, L., Liu, L., Hutchin-
son, A., Myers, T., Tardon, A., Serra,
C., Carrato, A., Garcia-Closas, R.,
Lloreta, J., Johnson,A., Schwenn, M.,
Karagas, M. R., Schned, A., Black,
A., Jacobs, E. J., Diver, W. R., Gap-
stur, S. M., Virtamo, J., Hunter, D.
J., Fraumeni, J. F. Jr., Chanock, S. J.,
Silverman, D. T., Rothman, N., and
Prokunina-Olsson, L. (2012). Map-
ping of the UGT1A locus identifies
an uncommon coding variant that
affects mRNA expression and pro-
tects from bladder cancer. Hum.Mol.
Genet. 21, 1918–1930.
Tell, G., and Gustincich, S. (2009).
Redox state, oxidative stress, and
molecular mechanisms of protective
and toxic effects of bilirubin on cells.
Curr. Pharm. Des. 15, 2908–2914.
Van Molle, W., and Libert, C. (2003).
Bilirubin release induced by tumor
necrosis factor in combination with
galactosamine is toxic to mice.
Cytokine 23, 94–100.
Vitek, L., Jirsa, M., Brodanova, M.,
Kalab, M., Marecek, Z., Danzig, V.,
Novotny, L., and Kotal, P. (2002).
Gilbert syndrome and ischemic
heart disease: a protective effect of
elevated bilirubin levels. Atheroscle-
rosis 160, 449–456.
Wang, J., Zhou, H. C., Pan, P., Zhang,
N., and Li, W. Z. (2010). Exoge-
nous biliverdin improves the func-
tion of lung grafts from brain dead
donors in rats. Transplant. Proc. 42,
Watchko, J. F., and Oski, F. A. (1983).
Bilirubin 20 mg/dL = vigintiphobia.
Pediatrics 71, 660–663.
Wegiel, B., Gallo, D., Csizmadia, E.,
Roger, T., Kaczmarek, E., Harris,
C., Zuckerbraun, B. S., and Otter-
bein, L. E. (2011). Biliverdin inhibits
Toll-like receptor-4 (TLR4) expres-
sion through nitric oxide-dependent
nuclear translocation of biliverdin
reductase. Proc. Natl. Acad. Sci.
U.S.A. 108, 18849–18854.
Zhang, Z. Y., Bian, L. Q., Kim,S. J.,Zhou,
C. C., and Choi, Y. H. (2012). Inverse
relation of total serum bilirubin to
coronary artery calcification score
detected by multidetector computed
tomography in males. Clin. Cardiol.
35, 301–306.
Conflict of Interest Statement: The
author declares that the research was
conducted in the absence of any com-
mercial or financial relationships that
could be construed as a potential con-
flict of interest.
Received: 10 April 2012; paper pend-
ing published: 23 April 2012; accepted:
29 May 2012; published online: 22 June
Citation: Dennery PA (2012) Evalu-
ating the beneficial and detrimental
effects of bile pigments in early and
later life. Front. Pharmacol. 3:115. doi:
This article was submitted to Frontiers
in Drug Metabolism and Transport, a
specialty of Frontiers in Pharmacology.
Copyright © 2012 Dennery. This is an
open-access article distributed under the
terms of the Creative Commons Attribu-
tion Non Commercial License, which per-
mits non-commercial use, distribution,
and reproduction in other forums, pro-
vided the original authors and source are
credited. June 2012 | Volume 3 | Article 115 | 5
... HO-2 is constitutively produced under physiologic conditions, where it facilitates the majority of heme catabolism [1]. Upon its production, bilirubin has been found to confer both neuroprotective antioxidant characteristics as well as neurotoxic properties [3]. A thorough understanding of the intricate interactions between bilirubin and the central nervous system is necessary since it may have profound implications on the treatment modalities used in the care of critically ill patients. ...
... Upon degradation of heme by HO, the product biliverdin is rapidly converted to unconjugated bilirubin by biliverdin reductase (BVR) [3]. Unconjugated bilirubin is prevented from crossing an intact blood brain barrier, and thus from accumulating in the central nervous system, because it is mostly bound to albumin in the plasma [4]. ...
... Furthermore, experimental evidence in a mouse model of cerebral ischemia demonstrated greater neuronal damage in HO2 −/− knockout mice compared to their wild type counterparts, providing additional support for bilirubin's neuroprotective role in the brain [8]. Due to bilirubin's antioxidant capabilities, many have proposed that physiologic neonatal unconjugated hyperbilirubinemia evolutionarily developed as a protective mechanism [3]. ...
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Bilirubin is a primary product of heme catabolism and exhibits both neuroprotective and neurotoxic effects. When present at physiologic concentrations, bilirubin is a potent antioxidant and serves to protect brain tissue from oxidative stress insults. The use of the anesthetic propofol attenuates ischemic injury in rats by exploiting these neuroprotective properties. At pathologic levels, bilirubin has been implicated as a neurotoxic agent, demonstrating the ability to aggregate and adhere to cellular membranes, thereby disrupting normal cellular function. Bilirubin-associated toxicities are amplified by administering drugs such as anesthetics that compete with bilirubin for albumin binding sites, resulting in increased plasma bilirubin concentrations. As such, it is crucial that bilirubin is considered in the critical care management of patients with hemorrhagic stroke, cerebral ischemic damage, and critically ill newborns.
... Bilirubin is considered toxic in high concentrations because it exerts harmful effects on the central nervous system.[6] The anti-oxidant activity of bilirubin was shown in for the first time in the 1980s.[7] ...
... We believe that BV is more suitable for clinical use than bilirubin because BV is water soluble, readily excreted, and nontoxic. BV is converted to bilirubin by BVR in mammalian tissue, and hyperbilirubinemia is associated with a risk of neurological deficit.[6] The 35-mg/kg dose of BV elevated serum bilirubin levels 1 h after treatment, although the elevated level was not outside the high normal range of <1 mg/dl in this study. ...
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Hemorrhagic shock and resuscitation induces pulmonary inflammation that leads to acute lung injury. Biliverdin, a metabolite of heme catabolism, has been shown to have potent cytoprotective, anti-inflammatory, and anti-oxidant effects. This study aimed to examine the effects of intravenous biliverdin administration on lung injury induced by hemorrhagic shock and resuscitation in rats. Biliverdin or vehicle was administered to the rats 1 h before sham or hemorrhagic shock-inducing surgery. The sham-operated rats underwent all surgical procedures except bleeding. To induce hemorrhagic shock, rats were bled to achieve a mean arterial pressure of 30 mmHg that was maintained for 60 min, followed by resuscitation with shed blood. Histopathological changes in the lungs were evaluated by histopathological scoring analysis. Inflammatory gene expression was determined by Northern blot analysis, and oxidative DNA damage was assessed by measuring 8-hydroxy-2' deoxyguanosine levels in the lungs. Hemorrhagic shock and resuscitation resulted in prominent histopathological damage, including congestion, edema, cellular infiltration, and hemorrhage. Biliverdin administration prior to hemorrhagic shock and resuscitation significantly ameliorated these lung injuries as judged by histopathological improvement. After hemorrhagic shock and resuscitation, inflammatory gene expression of tumor necrosis factor-α and inducible nitric oxide synthase were increased by 18- and 8-fold, respectively. Inflammatory gene expression significantly decreased when biliverdin was administered prior to hemorrhagic shock and resuscitation. Moreover, after hemorrhagic shock and resuscitation, lung 8-hydroxy-2' deoxyguanosine levels in mitochondrial DNA expressed in the pulmonary interstitium increased by 1.5-fold. Biliverdin administration prior to hemorrhagic shock and resuscitation decreased mitochondrial 8-hydroxy-2' deoxyguanosine levels to almost the same level as that in the control animals. We also confirmed that biliverdin administration after hemorrhagic shock and resuscitation had protective effects on lung injury. Our findings suggest that biliverdin has a protective role, at least in part, against hemorrhagic shock and resuscitation-induced lung injury through anti-inflammatory and anti-oxidant mechanisms.
... 104 ), and numerous similarities between the activities of CO and the antidiabetes drug metformin have been observed in immunometabolism and metabolic disease 105 . Meanwhile, Gilbert syndrome (adult hyperbilirubinaemia) is believed to be protective against metabolic syndrome, diabetes and obesity 106,107 , and an iron-rich diet has been reported to improve glucose tolerance in mice via activation of AMPK 108 . ...
Haem oxygenase 1 (HO-1), an inducible enzyme responsible for the breakdown of haem, is primarily considered an antioxidant, and has long been overlooked by immunologists. However, research over the past two decades in particular has demonstrated that HO-1 also exhibits numerous anti-inflammatory properties. These emerging immunomodulatory functions have made HO-1 an appealing target for treatment of diseases characterized by high levels of chronic inflammation. In this Review, we present an introduction to HO-1 for immunologists, including an overview of its roles in iron metabolism and antioxidant defence, and the factors which regulate its expression. We discuss the impact of HO-1 induction in specific immune cell populations and provide new insights into the immunomodulation that accompanies haem catabolism, including its relationship to immunometabolism. Furthermore, we highlight the therapeutic potential of HO-1 induction to treat chronic inflammatory and autoimmune diseases, and the issues faced when trying to translate such therapies to the clinic. Finally, we examine a number of alternative, safer strategies that are under investigation to harness the therapeutic potential of HO-1, including the use of phytochemicals, novel HO-1 inducers and carbon monoxide-based therapies.
... The role of glial cells and inflammation in bilirubin neurotoxicity (Brites, 2012) and the transport and metabolism of bilirubin at blood-brain interfaces and neural cells (Gazzin et al., 2012) illustrate the complex nature of bilirubin-induced brain damage. The effects of bilirubin vary with age (Dennery, 2012), and metalloporphyrins have been suggested to reduce excessive hyperbilirubinemia and brain damage in newborns (Schulz et al., 2012). ...
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Degradation of heme involves its conversion to biliverdin by heme oxygenase followed by reduction of biliverdin to bilirubin by biliverdin reductase. There is ample evidence for the role of heme oxygenase in protecting cells from the toxic effects of heme, as well as for the pleiotropic functions of biliverdin reductase in cell signaling and regulation of gene expression. This enzyme plays a major role in glucose uptake and the stress response. Bilirubin has been shown to behave as a “double-edged sword.” It can exert either cytotoxic or cytoprotective effects, depending on the blood and/or tissue concentration of its free fraction, the nature of the target cell or tissue, and the cellular redox state. The central nervous system is particularly sensitive to the neurotoxic effects of bilirubin. Its antioxidant effect is the basis for the proposed cardioprotective effect of bilirubin in humans with moderate hyperbilirubinemia, as is the case in subjects with the Gilbert syndrome. This Research Topic forum is intended to serve as a platform for updating information and presenting advances in basic and clinical research in the above and related subjects. The topic is discussed by leading experts in the field of bile pigments, and presented in 15 Reviews, 3 Original Research articles and 1 Opinion article. It covers important aspects related to the enzymes involved in the heme catabolic pathway: the role of heme oxygenase in inflammation and fibrosis (Lundvig et al., 2012) as well as in atherosclerosis (Araujo et al., 2012) and immune-mediated inflammatory diseases (Larsen et al., 2012), the regulation of cell signaling by biliverdin reductase and its peptide fragments (Gibbs et al., 2012), and the regulation of bilirubin clearance (Bock, 2011). The role of glial cells and inflammation in bilirubin neurotoxicity (Brites, 2012) and the transport and metabolism of bilirubin at blood-brain interfaces and neural cells (Gazzin et al., 2012) illustrate the complex nature of bilirubin-induced brain damage. The effects of bilirubin vary with age (Dennery, 2012), and metalloporphyrins have been suggested to reduce excessive hyperbilirubinemia and brain damage in newborns (Schulz et al., 2012). The regulatory properties of bile pigments and the role of biliverdin reductase in mediating their antioxidative (Jansen and Daiber, 2012) and anti-inflammatory effects (Wegiel and Otterbein, 2012), and their role in aging and age-related diseases (Kim and Park, 2012), are only part of the known protective functions of bile pigments. Bilirubin displays antiviral activity (Santangelo et al., 2012; Schmidt et al., 2012), ameliorates renal hemodynamics and blood pressure in an animal model of hypertension (Stec et al., 2012), and has beneficial effects in pulmonary and vascular diseases (Ryter, 2012). The protective effects of bilirubin in the vasculature include inhibition of neointima formation and reduction of vascular smooth muscle cell proliferation and migration (Peyton et al., 2012). In microvascular endothelial cells, low (“physiological”) bilirubin concentrations induce apoptosis, which is exacerbated under hyperglycemic conditions. Endothelial cells of the blood-brain barrier are particularly sensitive to these effects of bilirubin (Kapitulnik et al., 2012).
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Intracranial bleeding is one of the most prominent aspects in the clinical diagnosis and prognosis of traumatic brain injury (TBI). Substantial amounts of blood products, such as heme, are released because of traumatic subarachnoid hemorrhages, intraparenchymal contusions, and hematomas. Despite this, surprisingly few studies have directly addressed the role of blood products, in particular heme, in the setting of TBI. Heme is degraded by heme oxygenase (HO) into three highly bioactive products: iron, bilirubin, and carbon monoxide. The HO isozymes, in particular HO-1 and HO-2, exhibit significantly different expression patterns and appear to have specific roles after injury. Developmentally, differences between the adult and immature brain have implications for endogenous protection from oxidative stress. The aim of this paper is to review recent advances in the understanding of heme regulation and metabolism after brain injury and its specific relevance to the developing brain. These findings suggest novel clinical therapeutic options for further translational study.
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Esophageal cancer (EC) has a globally increasing incidence with poor curative treatment options and survival rates. Environmental and dietary factors have crucial roles in esophageal carcinogenesis. Polymorphisms in the UGT genes, a superfamily of enzymes essential for the detoxification of carcinogens, may alter enzyme activity and subsequently may play a role in EC etiology. Rather than solely establishing differences in genotype distribution, we investigated whether functional polymorphisms in UGT genes that can predict enzyme activity in vivo, may influence EC risk. A case-control study including 351 Caucasian EC patients and 592 Caucasian controls was conducted and polymorphisms in seven UGT genes were determined, using the polymerase chain reaction. On the basis of allelic in vitro enzyme activity measurements, genotypes were categorized according to their predicted in vivo enzyme activity into high, medium and low categories. Predicted enzyme activity groups were combined and compared between patients and controls. The UGT1A1 and UGT1A8 predicted high enzyme activity genotypes were significantly more (OR=1.62; 95% CI, 1.02-2.56) and less frequent (OR=0.36; 95% CI, 0.15-0.84) among patients with esophageal squamous cell carcinoma (ESCC), respectively. High (OR=0.42; 95% CI, 0.22-0.84) and medium (OR=0.25; 95% CI, 0.12-0.52) activity UGT2B4 genotypes were significantly less often present in ESCC patients. No association was detected between UGT genotypes and esophageal adenocarcinoma (EAC) risk. Polymorphisms in UGT genes, resulting in altered enzyme activity genotypes, do not seem modifiers of EAC risk. However, the predicted high activity UGT1A1 genotype, associated with low serum levels of the antioxidant bilirubin, was associated with an increased ESCC risk. The UGT1A8 and UGT2B4 genotypes associated with decreased predicted enzyme activities, were significantly associated with an increased risk of ESCC, probably by a decreased detoxification of carcinogens.
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A recent genome-wide association study of bladder cancer identified the UGT1A gene cluster on chromosome 2q37.1 as a novel susceptibility locus. The UGT1A cluster encodes a family of UDP-glucuronosyltransferases (UGTs), which facilitate cellular detoxification and removal of aromatic amines. Bioactivated forms of aromatic amines found in tobacco smoke and industrial chemicals are the main risk factors for bladder cancer. The association within the UGT1A locus was detected by a single nucleotide polymorphism (SNP) rs11892031. Now, we performed detailed resequencing, imputation and genotyping in this region. We clarified the original genetic association detected by rs11892031 and identified an uncommon SNP rs17863783 that explained and strengthened the association in this region (allele frequency 0.014 in 4035 cases and 0.025 in 5284 controls, OR = 0.55, 95%CI = 0.44-0.69, P = 3.3 × 10(-7)). Rs17863783 is a synonymous coding variant Val209Val within the functional UGT1A6.1 splicing form, strongly expressed in the liver, kidney and bladder. We found the protective T allele of rs17863783 to be associated with increased mRNA expression of UGT1A6.1 in in-vitro exontrap assays and in human liver tissue samples. We suggest that rs17863783 may protect from bladder cancer by increasing the removal of carcinogens from bladder epithelium by the UGT1A6.1 protein. Our study shows an example of genetic and functional role of an uncommon protective genetic variant in a complex human disease, such as bladder cancer.
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The expanse of human biliverdin reductase (hBVR) functions in the cells is arguably unmatched by any single protein. hBVR is a Ser/Thr/Tyr-kinase, a scaffold protein, a transcription factor, and an intracellular transporter of gene regulators. hBVR is an upstream activator of the insulin/IGF-1 signaling pathway and of protein kinase C (PKC) kinases in the two major arms of the pathway. In addition, it is the sole means for generating the antioxidant bilirubin-IXα. hBVR is essential for activation of ERK1/2 kinases by upstream MAPKK-MEK and by PKCδ, as well as the nuclear import and export of ERK1/2. Small fragments of hBVR are potent activators and inhibitors of the ERK kinases and PKCs: as such, they suggest the potential application of BVR-based technology in therapeutic settings. Presently, we have reviewed the function of hBVR in cell signaling with an emphasis on regulation of PKCδ activity.
This report presents the case of a patient with corticosteroid and cyclophosphamide resistant exacerbation of idiopathic pulmonary fibrosis (IPF), which was definitely resolved in accordance with increased levels of serum conjugated bilirubin due to biliary tract obstruction. Histological examination of the lung showed an accumulation of bile pigments in the alveolar mural tissues, especially in the cytoplasm of the alveolar macrophages, which play crucial roles in the development of IPF. This case suggests that bile pigments have some important roles in tissue protection against inflammatory damage in IPF, and may illustrate an important key for treatment of this fatal disorder.
Blood components such as oxyhemoglobin are believed to cause cerebral vasospasm by inducing contraction and cell death in cerebral arteries. We have observed previously that oxyhemoglobin produces apoptotic changes in cultured endothelial cells. This study was undertaken to explore if bilirubin, a bi-product of hemoglobin degradation, will produce similar cytotoxicity in endothelial cells. Cultured bovine brain microvascular endothelial cells were incubated in four concentrations of bilirubin (10, 25, 50, and 100 μM) for varying times (6, 12, and 24 h). Control cells were incubated in saline or vehicle (NaOH solution, <0.01% of 0.01 N) for similar time periods. The cultured cells were then observed microscopically for evidence of cellular alterations. Bilirubin (10–100 μM) produced apoptosis that appeared time-dependent but not clearly concentration-dependent. Biochemical markers for apoptosis such as DNA fragmentation and PARP cleavage were induced by bilirubin. We conclude that endothelial cells may undergo apoptosis after exposure to bilirubin.
Bilirubin is a potent antioxidant in vitro. To determine whether bilirubin also is an antioxidant in vivo, we studied markers of oxidative injury in the Gunn rat model exposed to hyperoxia. Homozygous jaundiced males were mated with heterozygous nonjaundiced females to obtain both jaundiced and nonjaundiced pups within a litter. Once delivered, the pups and their mother were placed in air (21% O2) or hyperoxia (> 95% O2) for 3 d. Both jaundiced and nonjaundiced pups were removed from the chambers daily. Animals were sacrificed and blood was drawn for determination of serum bilirubin, blood thiobarbituric acid-reactive substances (TBARS) by fluorescence assay, serum hydroperoxides, and serum protein oxidation. Tissues (liver, lung, and brain) were assayed for lipid peroxides (TBARS, conjugated dienes [CD], loss of polyunsaturated fatty acid content [PUFA]). We also measured a wide range of serum antioxidants including superoxide dismutase, catalase, glutathione, vitamins A, C, and E, and uric acid. Blood TBARS were significantly decreased in the jaundiced pups compared to the nonjaundiced pups on day 3 of hyperoxia, and blood TBARS were inversely correlated to serum bilirubin on day 3 of hyperoxia (R2 = .89). Similar decreases in serum lipid hydroperoxides and serum protein carbonyl content were detected in the jaundiced pups as compared to their nonjaundiced littermates. Other serum antioxidants were not increased in jaundiced animals compared to nonjaundiced animals. Relative lung weight was lower in jaundiced pups exposed to hyperoxia compared to similarly exposed nonjaundiced pups, suggesting a reduction in hyperoxia-induced lung edema. We detected no significant effects of bilirubin on parameters of lipid peroxidation in solid tissues. We conclude that serum bilirubin protects against serum oxidative damage in the first days of life in neonatal Gunn rats exposed to hyperoxia. We speculate that bilirubin is a functionally important transitional antioxidant in the circulation of human neonates and that it may be involved in modulation of injury due to hyperoxia.
Serum total bilirubin has been suggested to have potential anti-inflammatory and antioxidant effects on the vasculature, acting against plaque formation and subsequent atherosclerosis. This study was designed to assess the association of serum total bilirubin with coronary artery calcification (CAC). Individuals with higher bilirubin level would be less likely to develop CAC. Male subjects (N = 3408) underwent evaluation of CAC by cardiac computed tomography. Correlation and logistic regression analysis were performed to assess the relationships between CAC score and other variables. Subjects with a higher CAC score had significantly lower total bilirubin level (P = 0.001). Total bilirubin level was negatively correlated with CAC score (r = -0.052, P = 0.002). A 0.1-mg/dL increase in bilirubin was associated with a reduced odds ratio (OR) of the risk by 29.2% for a CAC score above 100 (OR: 0.708, 95% confidence interval: 0.542-0.927, P = 0.012) after adjustment for several variables. Bilirubin was inversely correlated with high-sensitivity C-reactive protein (hsCRP) (r = -0.117, P < 0.001). This study demonstrated an independent inverse association between serum total bilirubin and CAC score in males. Low serum bilirubin concentration would be useful as a potential risk factor for CAC in males. Additionally, reduced hsCRP may be 1 of the mechanisms for how bilirubin reduces CAC.
An imbalance between the production of reactive oxygen species (ROS) and their capturing by antioxidants results in oxidative stress, this may play an important role in the pathogenesis of inflammatory bowel disease (IBD). Since bilirubin is an important endogenous antioxidant, increased levels of bilirubin may protect against IBD. UDP-glucuronosyltransferase 1A1 (UGT1A1) is the only enzyme involved in the conjugation of bilirubin and the common UGT1A1*28 allele in the UGT1A1 gene, which is strongly associated with Gilbert's syndrome in Caucasians, results in elevated plasma bilirubin levels. To test the hypothesis that the UGT1A1*28 allele is associated with lower disease susceptibility to, and disease behavior within, IBD. In addition, a possible altered risk for developing IBD-drug related side-effects was explored. Genomic DNA of 751 patients with IBD (209 patients with ulcerative colitis and 542 patients with Crohn's disease) and 930 healthy controls was genotyped for the UGT1A1*28 promoter polymorphism, and genotype distribution was compared between patients and controls. Genotype phenotype interactions were also investigated. Patients with Crohn's disease significantly less often bear the UGT1A1*28 homozygous genotype compared to the control group, with an odds ratio of 0.64, 95% CI: 0.42-0.98. The ulcerative colitis group showed no significant differences compared to controls. The homozygous state of the UGT1A1*28 polymorphism, associated with higher serum bilirubin levels, may be protective for the development of Crohn's disease, suggesting that the anti-oxidant capacity of bilirubin may play a part.
The aim of our meta-analysis was to assess the association between UGT1A7 polymorphisms and cancer risk. Case?control studies containing available polymorphic alleles (UGT1A7*1,*2,*3, and*4) and genotypes categorized according to enzymatic activity (High, Intermediate, and Low) were chosen to assess this association. Twenty-one case?control studies were identified. Meta-analysis indicated that UGT1A7 had a significant effect on cancer risk. In subgroup analysis, a significantly increased risk was associated with East Asians, hepatocellular cancer, and colorectal cancer. This meta-analysis suggested that there is a cancer risk associated with UGT1A7*3, Intermediate, and Low activity UGT1A7 genotypes, which is most evident in Asian individuals.