Free and albumin-bound bilirubin are efficient co-antioxidants for alpha-tocopherol, inhibiting plasma and low density lipoprotein lipid peroxidation

Improved resistance to serum oxidation in Gilbert's syndrome: a mechanism for cardiovascular protection

Bilirubin is a potent antioxidant, however, uncertainty surrounds its physiological importance. Individuals with Gilbert's syndrome (GS) have increased circulating bilirubin and a reduced prevalence of cardiovascular disease (CVD). The aim of this study was to investigate mechanisms that may link bilirubin to protection from CVD seen in GS by examining markers of antioxidant and oxidative stress status and the susceptibility of serum to oxidation. Nine individuals with GS and twelve controls, matched for age, height and weight, were assessed for plasma antioxidant status, red blood cell antioxidant enzyme activities, plasma malondialdehyde, the susceptibility of serum to copper (Cu(2+)) induced oxidation and blood lipid profile. Individuals with GS had significantly elevated unconjugated bilirubin (GS: 26.0+/-6.4; control: 9.7+/-3.0 micromol/L; P<0.001), increased trolox equivalent antioxidant capacity (GS: 1.59+/-0.07; control: 1.52+/-0.07 mmol/L trolox Equ; P=0.035) and ferric reducing ability of plasma (GS: 1.09+/-0.16; control: 0.92+/-0.14 mmol/L Fe(2+) Equ; P=0.024). The lag phase of serum oxidation was significantly longer in the GS group (GS: 121.4+/-10.5; control: 106.8+/-14.6 min; P=0.020) and was positively correlated with the bilirubin concentration (r=0.451, P=0.040). A trend toward elevated HDL:LDL ratio was observed in GS (GS 0.96+/-0.31; control: 0.73+/-0.21; P=0.072). In summary, individuals with GS have an increased circulating antioxidant status and an improved resistance to serum oxidation which may partially explain their reduced prevalence of CVD.

Initial photochemistry of bilirubin probed by femtosecond spectroscopy

Bilirubin is a breakdown product from heme catabolism, and reduced excretion of bilirubin can lead to jaundice. Phototherapy is the most common treatment for neonatal jaundice, a condition frequently encountered in newborn infants. Knowledge of the photochemistry of bilirubin, which is dominated by (ultra)fast components, is necessary for the profound understanding of the processes in phototherapy. Here, we report results from femtosecond fluorescence upconversion measurements on bilirubin and half-bilirubin model compounds, as well as pump-probe absorption measurements on bilirubin. A fast component of ca. 120 fs in the multiexponential fluorescence decay, being only visible in the bilirubin molecule, is interpreted as exciton localization within the molecular halves. The slower components of several hundreds of femtoseconds and a few picoseconds, occurring in bilirubin and the half-bilirubin model, are interpreted as relaxation to a (twisted) intermediate, which decays further with ca. 15 ps to the ground state.

Bilirubin as an antioxidant in micelles and lipid bilayers: its contribution to the total antioxidant capacity of human blood plasma

The antioxidant capacities, antioxidant activities, k(inh), and stoichiometric factors, n, of water-soluble derivatives of bilirubin (BR), BR-human serum albumin (BR-HSA), and BR-ditaurate disodium conjugate (BRC) were determined in aqueous/lipid dispersions of sodium dodecyl sulfate (SDS) micelles/methyl linoleate and in bilayers of dilinoleoylphosphatidylcholine (DLPC) during initiation by water-soluble azo-bis-amidinopropane dihydrochloride (ABAP). The inhibition rate constants for BRC and BR-HSA were similar in micelles (k(inh) approximately 1.3 x 10(4) M(-1) s(-1)), where n approximately 2, whereas the k(inh) for BR-HSA dropped by (1/2) in bilayers. The dimethyl ester of bilirubin (BRDE) gave a k(inh) only one-tenth that of the vitamin E analog, pentamethylhydroxychroman (PMHC) in SDS micelles/methyl linoleate when initiated by lipid-soluble azo-bis-2,4-dimethylvaleronitrile (DMVN). Biliverdin hydrochloride (BVHCl) was NOT an effective peroxyl radical-trapping agent in the micellar phase during initiation by ABAP or DMVN containing methyl linoleate but it inhibited oxygen uptake in the aqueous phase. Both BRC and BR-HSA extended the total radical antioxidant parameter (TRAP) of human blood plasma and their contribution to TRAP was in the range of 5-10% of the natural TRAP of blood plasma, depending on the BR content determined in the blood plasma.

Changes in the components of biliary and plasma lipids in selenium-deficient rats

We constructed a chronic oxidative stress model in which Se-deficient diet was fed to male Wister rats for 8 weeks. As expected, effects of oxidative damage, including Fe accumulation and increase in peroxidized lipids, were identified in the liver owing to the lack of glutathione peroxidase. Although the oxidative stress caused Fe accumulation in the liver, the Fe concentration in bile of the SeD rat was almost the same as that in the control rats. The constant excretion of Fe into bile supported the Fe accumulation in the liver. No differences were observed in the principal components of biliary lipids, i.e., bile acids, phospholipids, and cholesterol, between the two groups; moreover, these trends were also reflected in the plasma. Due to the trapping of reactive oxygen species, only bilirubin concentrations in the bile and plasma were decreased in the SeD group, when compared with those in the control group. Measurement of bilirubin concentration may be used as a supplemental oxidative stress marker.

Bilirubin and coronary heart disease risk in the Prospective Epidemiological Study of Myocardial Infarction (PRIME)

BACKGROUND

Classic coronary heart disease risk factors fail to explain the large coronary heart disease incidence gradient between Northern Ireland and France. The Prospective Epidemiological Study of Myocardial Infarction (PRIME), a multicentre prospective study of 10593 men, aims to investigate novel risk factors in these populations. We tested the hypothesis that higher bilirubin, a bile pigment possessing antioxidant properties, is associated with decreased coronary heart disease risk.

METHODS

Bilirubin was measured in 216 participants who had developed coronary heart disease at 5-year follow-up and in 434 matched controls.

RESULTS

Bilirubin was significantly lower in cases (geometric mean 7.95 micromol/l; interquartile range 5.32-12.33 micromol/l) compared with controls (9.07; 6.16-12.76; P=0.005). Conditional logistic regression, adjusted for classical and putative risk factors, showed a U-shaped pattern, with coronary heart disease risk significantly lower for bilirubin in the third and fourth fifths, compared with the first. Additionally, there was a significant quadratic relationship between coronary heart disease risk and fifths of bilirubin concentration (chi2=6.80, df=2; P=0.035).

CONCLUSIONS

These findings suggest that bilirubin is a novel coronary heart disease risk marker in middle-aged men, with a U-shaped relationship observed between bilirubin concentration and coronary heart disease risk.

The anti-mutagenic and antioxidant effects of bile pigments in the Ames Salmonella test

The aim of this study was to explore the potential pro- and anti-mutagenic effects of endogenous bile pigments unconjugated bilirubin (BR), biliverdin (BV) and a synthetic, water soluble conjugate, bilirubin ditaurate (BRT) in the Ames Salmonella test. The bile pigments were tested over a wide concentration range (0.01-2 micromol/plate) in the presence of three bacterial strains (TA98, TA100, TA102). A variety of mutagens including benzo[alpha]pyrene (B[alpha]P), 2,4,7 trinitrofluorenone (TNFone), 2-aminofluorene (2-AF), sodium azide (NaN(3)) and tertiary-butyl hydroperoxide (t-BuOOH), were used to promote the formation of mutant revertants. Tests were conducted with (B[alpha]P, 2-AF, t-BuOOH) and without (TNFone, NaN(3), t-BuOOH) metabolic activation incorporating the addition of the microsomal liver preparation, S9. The bile pigments alone did not induce mutagenicity in any of the strains tested (p>0.05). Anti-mutagenic effects of the bile pigments were observed in the presence of all mutagens except for NaN(3) and the anti-mutagenic effects appeared independent of the strain tested. For TNFone induced genotoxicity, the order of effectiveness was BR> or =BRT>BV. However, the order was BV> or =BRT> or =BR for 2-AF. Antioxidant testing in the TA102 strain revealed bile pigments could effectively inhibit the genotoxic effect of t-BuOOH induced oxidative stress. The apparent antioxidant and anti-mutagenic behaviour of bile pigments further suggests their presence in biological systems is of possible physiological importance.

Low serum bilirubin concentrations are associated with impaired aortic elastic properties, but not impaired left ventricular diastolic function

Elevated serum bilirubin concentrations protect from atherosclerotic diseases; however,it is not clear whether higher serum bilirubin concentrations in physiological ranges do the same. To investigate the association of high and low serum bilirubin concentrations with left ventricular diastolic function and aortic elastic properties.We evaluated left ventricular diastolic function and aortic elastic properties of 42 healthy subjects with hypobilirubinemia (total bilirubin 0.40 ± 0.08 mg ⁄ dl; mean age 37.0 ± 3.9) and 40 healthy subjects with hyperbilirubinemia (total bilirubin 1.56 ± 0.49 mg ⁄ dl; mean age 36.2 ± 6.0) using transthoracic second harmonic Doppler echocardiography. Age, gender, body mass index and coronary risk factors were similar between the groups, except high-sensitivity C-reactive protein (hsCRP).Left ventricular diastolic parameters were similar between the two groups. Aortic distensibility (AoD) was found to be significantly lower (11.1 ± 3.9 vs. 13.2 ± 4.9,p = 0.03) and aortic stiffness index (AoSI) (1.99 ± 0.30 vs. 1.85 ± 0.26,p = 0.02) and elastic modulus (AoEM) (2.06 ± 0.83 vs. 1.73 ± 0.68, p = 0.03;the low and high bilirubin groups, respectively) higher in the low bilirubin group.Serum total bilirubin concentration correlated with hsCRP levels, AoD, AoSI and AoEM. In conclusion, left ventricular systolic and diastolic functions were similar between hypo- and hyperbilirubinemic subjects, but aortic elastic properties were impaired in subjects with lower serum bilirubin concentrations.

Measuring circulating antioxidants in wild birds

Antioxidants protect against free radical damage, which is associated with various age-related pathologies. Antioxidants are also an important buffer against the respiratory burst of the immune system. This protection presumably has costs and therefore might underlie important life-history trade-offs. Studying such trade-offs in a comparative context requires field-applicable methods for assessing antioxidant capacity in wild animals. Here, we present modifications to a simple spectrophotometric assay (the TEAC or TAS assay) that can be applied to miniscule amounts of blood plasma to determine circulating antioxidant capacity. Additionally, uric acid, the most abundant circulating antioxidant, should be measured independently. Uric acid in birds is derived from amino acid catabolism, perhaps incidentally to its antioxidant function. The assay was validated in experimental studies on chickens showing effects of diet on antioxidant capacity, and in field measurements on 92 species of birds, which demonstrate substantial species differences in constitutive antioxidant capacity. Furthermore, most wild birds demonstrate a dramatic change in antioxidant capacity due to stress. These results show that this technique detects variation appropriate for both interspecific and intraspecific studies, and that antioxidants and uric acid change in response to conditions of interest to field ecologists, such as diet and stress.

The Heme Catabolic Pathway and its Protective Effects on Oxidative Stress‐Mediated Diseases

Bilirubin, the principal bile pigment, is the end product of heme catabolism. For many years, bilirubin was thought to have no physiological function other than that of a waste product of heme catabolism--useless at best and toxic at worst. Although hyperbilirubinemia in neonates has been shown to be neurotoxic, studies performed during the past decade have found that bilirubin has a number of new and interesting biochemical and biological properties. In addition, there is now a strong body of evidence suggesting that bilirubin may have a beneficial role in preventing oxidative changes in a number of diseases including atherosclerosis and cancer, as well as a number of inflammatory, autoimmune, and degenerative diseases. The results also suggest that activation of the heme oxygenase and heme catabolic pathway may have beneficiary effects on disease prevention either through the action of bilirubin or in conjunction with bilirubin. If so, it may be possible to therapeutically induce heme oxygenase, increase bilirubin concentrations, and lower the risk of oxidative stress-related diseases.

Association between the UGT1A1*28 allele, bilirubin levels, and coronary heart disease in the Framingham Heart Study

BACKGROUND

Bilirubin is an antioxidant that suppresses lipid oxidation and retards atherosclerosis formation. An inverse association between serum bilirubin and coronary heart disease has been reported. Linkage studies have identified a major locus at the chromosome 2q telomere that affects bilirubin concentrations. A candidate gene in the linkage region encodes hepatic bilirubin uridine diphosphate-glucuronosyltransferase (UGT1A1). The insertion of a TA in the TATAA box of the gene, an allele designated UGT1A1*28, decreases gene transcription. Individuals homozygous for UGT1A1*28 (genotype 7/7) have increased serum bilirubin levels compared with carriers of the 6 allele. To date, no significant association between UGT1A1*28 and cardiovascular disease (CVD) events has been reported. We performed an association study in the Framingham Heart Study population to investigate whether UGT1A1*28 is associated with the risk of CVD events.

METHODS AND RESULTS

The study population included 1780 unrelated individuals from the Offspring cohort (49% males, mean age 36 years at entry) who had been followed up for 24 years. Individuals with genotype 7/7 had significantly higher bilirubin levels (mean+/-SD 1.14+/-0.44 mg/dL) than those with genotypes 6/6 and 6/7 (mean+/-SD 0.69+/-0.27 mg/dL, P<0.01). Using the Cox proportional hazards model, we found significant associations between the UGT1A1*28 allele and decreased risk of CVD. Individuals with genotype 7/7 (population frequency of 11%) had approximately one third the risk for CVD and coronary heart disease as carriers of the 6 allele, which resulted in a hazard ratio (95% confidence interval) of 0.36 (0.18 to 0.74) and 0.30 (0.12 to 0.74), respectively.

CONCLUSIONS

Homozygote UGT1A1*28 allele carriers with higher serum bilirubin concentrations exhibit a strong association with lower risk of CVD.

Heme oxygenase-1/carbon monoxide: from basic science to therapeutic applications

The heme oxygenases, which consist of constitutive and inducible isozymes (HO-1, HO-2), catalyze the rate-limiting step in the metabolic conversion of heme to the bile pigments (i.e., biliverdin and bilirubin) and thus constitute a major intracellular source of iron and carbon monoxide (CO). In recent years, endogenously produced CO has been shown to possess intriguing signaling properties affecting numerous critical cellular functions including but not limited to inflammation, cellular proliferation, and apoptotic cell death. The era of gaseous molecules in biomedical research and human diseases initiated with the discovery that the endothelial cell-derived relaxing factor was identical to the gaseous molecule nitric oxide (NO). The discovery that endogenously produced gaseous molecules such as NO and now CO can impart potent physiological and biological effector functions truly represented a paradigm shift and unraveled new avenues of intense investigations. This review covers the molecular and biochemical characterization of HOs, with a discussion on the mechanisms of signal transduction and gene regulation that mediate the induction of HO-1 by environmental stress. Furthermore, the current understanding of the functional significance of HO shall be discussed from the perspective of each of the metabolic by-products, with a special emphasis on CO. Finally, this presentation aspires to lay a foundation for potential future clinical applications of these systems.

Carbon monoxide and bilirubin from heme oxygenase-1 suppresses reactive oxygen species generation and plasminogen activator inhibitor-1 induction

Heme oxygenase-1 (HO-1) responds to a variety of oxidative stresses. We examined whether HO-1 expression influences pro-thrombotic processes, in which the involvement of oxidative stress has been reported. Since HO-1 knockout mice with a C57/BL6J background were not viable, embryonic cells from HO-1 deficient mice (E11.5) were used. Cell viability, the level of plasminogen activator inhibitor-1 (PAI-1) expression and reactive oxygen species (ROS) generation of HO-1 deficient cells in response to the exposures to hydrogen peroxide and oxidized LDL were compared to those with wild-type cells. We also examined the effects of glutathione (GSH), desferrioxamine (DFO) and diphenyleneiodonium (DPI: an NADPH oxidase inhibitor) as well as of the HO reaction products, bilirubin (BR) and carbon monoxide (CO) on PAI-1 expression and ROS generation. PAI-1 expression and ROS generation were markedly elevated in HO-1 deficient cells compared to wild-type cells. Exposure to oxidized LDL significantly elevated PAI-1 expression and ROS production in HO-1 deficient cells. Interestingly, these increases in HO-1 deficient cells were significantly lowered by BR, CO, GSH and DPI while DFO had little effect. Furthermore, BR and CO were effective to improve viabilities of HO-1 deficient cells. These results suggest that HO-1 may be required to suppress ROS generation and the production of pro-thrombotic molecules such as PAI-1.

Biliverdin protects against polymicrobial sepsis by modulating inflammatory mediators

Highly inducible heme oxygenase (HO)-1 is protective against acute and chronic inflammation. HO-1 generates carbon monoxide (CO), ferrous iron, and biliverdin. The aim of this study was to investigate the protective effects of biliverdin against sepsis-induced inflammation and intestinal dysmotility. Cecal ligation and puncture (CLP) was performed on Sprague-Dawley rats under isoflurane anesthesia with and without intraperitoneal biliverdin injections, which were done before, at the time of CLP, and after CLP. In vivo gastrointestinal transit was carried out with fluorescein-labeled dextran. Jejunal circular muscle contractility was quantified in vitro using organ bath-generated bethanechol dose-response curves. Neutrophilic infiltration into the muscularis externa was quantified. The jejunal muscularis was studied for cytokine mRNA expressions [interleukin (IL)-6, monocyte chemoattractant protein (MCP)-1, inducible nitric oxide synthase, cyclooxygenase-2, biliverdin, IL-10, and HO-1] using real-time RT-PCR. Biliverdin treatment prevented the sepsis-induced suppression of gastrointestinal muscle contractility in vivo and in vitro and significantly decreased neutrophilic infiltration into the jejunal muscularis. Inflammatory mRNA expressions for small bowel IL-6 and MCP-1 were significantly reduced after biliverdin treatment in CLP-induced septic animals compared with untreated septic animals. The anti-inflammatory mediator expression of small bowel IL-10 was significantly augmented after CLP at 3 h compared with untreated septic animals. These findings demonstrate that biliverdin attenuates sepsis-induced morbidity to the intestine by selectively modulating the inflammatory cascade and its subsequent sequelae on intestinal muscularis function.

Heme oxygenase-2 deficiency contributes to diabetes-mediated increase in superoxide anion and renal dysfunction

Heme oxygenase-1 (HO-1) and -2 play an important role in cytoprotection and are physiologic regulators of heme-dependent protein synthesis in renal tissues. The impact of HO-2 deletion comparing hyperglycemic HO-2 (+/+) mice and HO-2 knockout (-/-) mice was examined. Hyperglycemia was induced by streptozotocin (STZ) injection, and its effect on renal HO-1/HO-2 protein, HO activity, and creatinine levels were assessed. The effect of HO induction using systemic administration of the HO inducers heme or cobalt protoporphyrin and the effect of HO inhibition using systemic administration of the HO inhibitor tin mesoporphyrin also were assessed in STZ-treated mice. In STZ-treated HO-2 (-/-) mice, there was marked renal functional impairment as reflected by an increase in plasma creatinine, associated with acute tubular damage and microvascular pathology as compared with HO-2 (+/+). In these animals, HO activity was decreased with a concomitant increase in superoxide anion. Upregulation of HO-1 in HO-2 (-/-) mice by weekly administration of cobalt protoporphyrin prevented the increase in plasma creatinine levels and tubulointerstitial and microvascular pathology. Inhibition of HO activity by administration of tin mesoporphyrin accentuated superoxide production and increased creatinine levels in hyperglycemic HO-2 (-/-) mice. In conclusion, HO-2 deficiency enhanced STZ-induced renal dysfunction and morphologic injury and HO-1 upregulation in HO-2 (-/-) mouse rescue and prevented the morphologic damage. These observations indicate that HO activity is essential in preserving renal function and morphology in STZ-induced diabetic mice probably via mitigation of concomitant oxidative stress.

Low serum bilirubin levels are independently and inversely related to impaired flow-mediated vasodilation and increased carotid intima-media thickness in both men and women

BACKGROUND

Elevated levels of low-density lipoprotein (LDL) cholesterol and its oxidative modification have been described to be involved in the process of atherogenesis. Bilirubin, an antioxidant, prevents oxidative modification of LDL and therefore may protect from atherosclerosis and coronary heart disease (CHD). Impaired brachial artery flow-mediated dilatation (FMD), which means endothelial dysfunction (ED) and carotid intima-media thickness (IMT) are predictors for the development and progression of atherosclerosis. In the present study, FMD and IMT were studied in healthy subjects with lower and higher serum bilirubin concentrations in physiological ranges.

METHODS

Ninety-one healthy subjects between 25 and 45 years of age (47 with lower and 44 with higher serum bilirubin concentrations) were included in this study. Carotid IMT and brachial artery flow-mediated dilatation was measured by means of high-resolution vascular ultrasound. FMD was assessed by establishing reactive hyperemia and endothelium-independent dilatation (EID) was determined by using sublingual isosorbide dinitrate.

RESULTS

EDD in subjects with lower serum bilirubin concentrations was significantly worse than in those with higher serum bilirubin concentrations (11.6+/-4.4% versus 7.2+/-4.7%, respectively, p<0.0001). EID measurements were not significantly different between the groups (16+/-5.1% versus 16.8+/-7%, respectively). In addition, carotid IMT was significantly greater in subjects with lower serum bilirubin concentrations (0.5+/-0.13 mm versus 0.42+/-0.07 mm, p<0.0001). Furthermore, FMD in women with lower serum bilirubin concentrations was significantly lower than in women with higher serum bilirubin concentrations (11.5+/-4.9% and 17.5+/-4.7%, respectively, p<0.001). Accordingly, men with lower serum bilirubin concentrations had significantly lower FMD as compared to hyperbilirubinemic ones (11.7+/-3.6% versus 16.7+/-4.8%, respectively, p=0.009). Conversely, carotid IMT was significantly greater in both women and men with lower serum bilirubin concentrations compared to the subjects with elevated serum bilirubin concentrations (0.51+/-0.08 versus 0.41+/-0.08, p<0.001; 0.55+/-0.12 versus 0.40+/-0.07, p=0.002, in women and men, respectively).

CONCLUSION

The healthy subjects with lower serum bilirubin concentrations show significant ED and increased carotid IMT, which are predictors for atherosclerosis.

Influence of early postnatal nutritional management on oxidative stress and antioxidant defence in extreme prematurity

The increased survival of infants born at mid-gestation in the last decade is associated with significant oxygen free radical-mediated morbidities. Resuscitation with 100% oxygen, oxidant load from parenteral nutrition fluids, and oxidant stress inherent to the systemic inflammatory state subsequent to infection and tissue injury are all contributory.

CONCLUSION

Improving early postnatal protein nutrition and the formulation of parenteral nutrition fluids would potentially reduce the oxidative stress and enhance the antioxidant defence of extremely premature newborns.

Increase in heme oxygenase-1 levels ameliorates renovascular hypertension

BACKGROUND

The heme oxygenase system (HO-1 and HO-2) catalyzes the conversion of heme to free iron, carbon monoxide (CO), a vasodepressor, and biliverdin, which is further converted to bilirubin, an antioxidant. HO-1 induction has been shown to suppress arachidonic acid metabolism by cytochrome P450 (CYP450) monooxygenases and cyclooxygenases (COX), and to decrease blood pressure in spontaneously hypertensive rats (SHR). The Goldblatt 2K1C model is a model of renovascular hypertension in which there is increased expression of COX-2 in the macula densa and increased renin release from the juxtaglomerular apparatus of the clipped kidney. We examined whether HO-1 overexpression, as a prophylactic approach, would attenuate renovascular hypertension and evaluated potential mechanisms that may account for its effect.

METHODS

2K1C rats were treated with cobalt protoporphyrin (CoPP) or tin mesoporphyrin (SnMP) one day before surgery and weekly for three weeks thereafter. We measured systolic blood pressure, HO activity, HO-1, HO-2, COX-1 and COX-2 protein expression, heme content, and nitrotyrosine levels as indices of oxidative stress. Urinary prostaglandin excretion (PGE2), plasma renin activity (PRA), and plasma aldosterone levels were also measured.

RESULTS

CoPP administration induced renal HO-1 expression by 20-fold and HO activity by 6-fold. This was associated with a reduction in heme content, nitrotyrosine levels, COX-2 expression and urinary PGE2 excretion, and attenuation of the development of hypertension in the 2K1C rats. There was no decrease in plasma renin activity; however, plasma aldosterone levels were significantly lower. In the 2K1C SnMP-treated rats, blood pressure was significantly higher than that of untreated 2K1C rats throughout the study, and the difference in the size of the smaller left clipped kidney compared to the nonclipped right kidney was significantly increased.

CONCLUSION

These findings define an action of prolonged HO-1 induction to interrupt and counteract the influence of the renin-angiotensin-aldosterone system (RAAS) to increase in blood pressure in the 2K1C model of renovascular hypertension. Multiple mechanisms include a decrease in oxidative stress as indicated by the decrease in cellular heme and nitrotyrosine levels, an anti-inflammatory action as evidenced by a decrease in COX-2 and PGE2, interference with the action of angiontensin II (Ang II) as evidenced by an increase in PRA in the face of a decrease in PGE2 and aldosterone, as well as the inhibition of aldosterone synthesis.

High Serum Bilirubin Concentrations Preserve Coronary Flow Reserve and Coronary Microvascular Functions

BACKGROUND

Elevated serum bilirubin concentrations protect against atherosclerotic diseases; however, it is not clear whether higher serum bilirubin concentrations in physiological ranges work in favor of the cardiovascular system in younger persons with no cardiovascular risk factors. Accordingly, we investigated the effects of high, intermediate, and low serum bilirubin concentrations on coronary flow reserve (CFR).

METHODS AND RESULTS

Fifty-two healthy subjects with hyperbilirubinemia (total bilirubin 1.43+/-0.33 mg/dL; mean age 35.9+/-7.3), 55 subjects with intermediate bilirubin level (total bilirubin: 0.69+/-0.11 mg/dL; mean age: 36.4+/-6.8), and 53 healthy subjects with hypobilirubinemia (total bilirubin 0.37+/-0.08 mg/dL; mean age, 37.6+/-6.6) were studied. Transthoracic second harmonic Doppler echocardiography examination was performed using an Acuson Sequoia C256 Echocardiography System. Coronary diastolic peak flow velocities were measured at baseline and after dipyridamole infusion (0.84 mg/kg over 6 minutes). CFR was calculated as the ratio of hyperemic to baseline diastolic peak velocities. Demographic features, coronary risk factors, echocardiographic measurements, and biochemical measurements were similar among the 3 groups, except high-sensitivity C-reactive protein (hsCRP). CFR values were significantly higher in subjects with high bilirubin concentrations than those were in the intermediate and the low bilirubin groups (3.19+/-0.73; 2.75+/-0.42; 2.56+/-0.52, respectively; P<0.0001), and hsCRP levels were significantly lower in subjects with high bilirubin concentrations than those in both intermediate and low bilirubin groups (1.4+/-1.0, 2.0+/-1.7, 3.0+/-1.9 mg/L, respectively; P<0.001). hsCRP levels correlated with total bilirubin concentration and with CFR.

CONCLUSIONS

Elevated serum bilirubin concentrations protect from CFR impairment, coronary microvascular dysfunction, and possibly coronary atherosclerosis.

Heme Oxygenase and Atherosclerosis

Overproduction of reactive oxygen species under pathophysiological conditions, including dyslipidemia, hypertension, diabetes, and smoking, is integral in the development of cardiovascular diseases (CVD). The reactive oxygen species released from all types of vascular cells regulate various signaling pathways that mediate not only vascular inflammation in atherogenesis but also antioxidative and antiinflammatory responses. One such protective and stress-induced protein is heme oxygenase (HO). HO is the first rate-limiting enzyme in heme breakdown to generate equimolar quantities of carbon monoxide, biliverdin, and free ferrous iron. Accumulating evidence has shown that inducible HO (HO-1) and its products function as adaptive molecules against oxidative insults. The proposed mechanisms by which HO-1 exerts its cytoprotective effects include its abilities to degrade the pro-oxidative heme, to release biliverdin and subsequently convert it bilirubin, both of which have antioxidant properties, and to generate carbon monoxide, which has antiproliferative and antiinflammatory as well as vasodilatory properties. Herein, I highlight the relationship of HO and cardiovascular disease, especially atherosclerosis, gene-targeting approaches in animal models, and the potential for and concern about HO-1 as a novel therapeutic target for cardiovascular diseases.

Alpha-lipoic acid-induced heme oxygenase-1 expression is mediated by nuclear factor erythroid 2-related factor 2 and p38 mitogen-activated protein kinase in human monocytic cells

OBJECTIVE

Heme oxygenase-1 (HO-1), the rate-limiting enzyme in heme catabolism, plays a protective role in the vascular system. HO-1 induction inhibits cytokine production in macrophages. Antioxidants induce HO-1 expression in various cell types. Alpha-lipoic acid (ALA), a thiol-containing dietary antioxidant, exhibits protective effects in vascular disease and induces anti-inflammatory effects in monocytes. This study examined the effects of ALA on HO-1 expression in human monocytic cells.

METHODS AND RESULTS

ALA time and dose-dependently induced HO-1 mRNA expression in THP-1 cells, with peak expression at 4 hours and returning to baseline by 24 hours. This correlated with an increase in HO-1 protein expression. ALA stimulated translocation of the transcription factor nuclear factor-erythroid 2-related factor 2 (Nrf2) into the nucleus and binding to a human HO-1 antioxidant response element (ARE) by 30 minutes. A dominant-negative Nrf2 inhibitor reduced ALA-induced HO-1 mRNA expression by 66%. Pretreatment with SB203580, a p38 mitogen-activated protein kinase inhibitor, reduced ALA-induced HO-1 mRNA expression by 75% and inhibited ALA-induced Nrf2 binding to the HO-1 ARE.

CONCLUSIONS

These results demonstrate that ALA induces HO-1 expression in THP-1 monocytic cells via Nrf2 and p38. Further studies are required to investigate whether the protective effects of ALA in monocytes are mediated by HO-1.

Induction of heme oxygenase 1 by moderately oxidized low-density lipoproteins in human vascular smooth muscle cells: role of mitogen-activated protein kinases and Nrf2

Oxidized low-density lipoproteins (LDL) play a central role in atherogenesis and induce expression of the antioxidant stress protein heme oxygenase 1 (HO-1). In the present study we investigated induction of HO-1 and adaptive increases in reduced glutathione (GSH) in human aortic smooth muscle cells (SMC) in response to moderately oxidized LDL (moxLDL, 100 microg protein/ml, 24 h), a species containing high levels of lipid hydroperoxides. Expression and activity of HO-1 and GSH levels were elevated to a greater extent by moxLDL than highly oxidized LDL but unaffected by native or acetylated LDL. Inhibitors of protein kinase C (PKC) or mitogen-activated protein kinases (MAPK) p38(MAPK) and MEK or c-jun-NH2-terminal kinase (JNK) significantly attenuated induction of HO-1. Phosphorylation of p38(MAPK), extracellular signal-regulated kinase (ERK1/2), or JNK and nuclear translocation of the transcription factor Nrf2 were enhanced following acute exposure of SMC to moxLDL (100 microg protein/ml, 1-2 h). Pretreatment of SMC with the antioxidant vitamin C (100 microM, 24 h) attenuated the induction of HO-1 by moxLDL. Native and oxidized LDL did not alter basal levels of intracellular ATP, mitochondrial dehydrogenase activity, or expression of the lectin-like oxidized LDL receptor (LOX-1) in SMC. These findings demonstrate for the first time that activation of PKC, p38(MAPK), JNK, ERK1/2, and Nrf2 by oxidized LDL in human SMC leads to HO-1 induction, constituting an adaptive response against oxidative injury that can be ameliorated by vitamin C.

Bilirubin and the risk of common non-hepatic diseases

Bilirubin is a potent antioxidant but can be toxic at high concentrations. This article critically reviews the reported relationships of plasma bilirubin levels to the severity and/or incidence of various common non-hepatic diseases. Plasma bilirubin levels are reportedly negatively related to the risk of atherosclerotic diseases, cancers, demyelinating neuropathies and seasonal affective disorder. By contrast, the incidence and severity of schizophrenia are increased by elevated bilirubin levels. The data strongly suggest that the level of plasma bilirubin should be considered as a risk factor for several common non-hepatic diseases. Additional studies are needed to clarify the mechanisms of this influence, which are thought to be related to unconjugated bilirubin counteracting the oxidative stress underlying these disorders.

Heme oxygenase-1 levels and oxidative stress-related parameters in non-alcoholic fatty liver disease patients

BACKGROUND/AIMS

Non-alcoholic steatohepatitis (NASH) is a disorder that is histologically characterized by macrovesicular steatosis and lobular hepatitis with necrosis or ballooning degeneration and fibrosis. NASH can range from a benign condition to end-stage liver disease. The mechanisms promoting transition from steatosis to NASH appear to involve multiple cellular adaptations to the oxidative stress occurring when fatty acid metabolism is altered. We evaluated the relationship between lipid peroxidation and other oxidative stress biomarkers with changes in expression of heme oxygenase-1 (HO-1) in human hepatic steatosis ranging from simple steatosis to NASH.

METHODS

HO-1 expression, lipid peroxidation, ferritin and GSH levels were assayed from liver biopsies obtained from 60 subjects: 35 with NASH, 15 with simple steatosis and 10 controls.

RESULTS

The HO-1 expression was significantly increased in NASH patients and the increase reflected the severity of the disease. A significant correlation was observed between the increased levels of HO-1 and ferritin, and between the increased levels of HO-1 and lipid peroxidation. Moreover, NASH patients with lower levels of GSH exhibited higher expression of HO-1.

CONCLUSIONS

The induction of HO-1 is an adaptive response against oxidative damage elicited by lipid peroxidation and it may be critical in the progression of the disease.

Chemistry and biology of vitamin E

Our understanding of the role of vitamin E in human nutrition, health, and disease has broadened and changed over the past two decades. Viewed initially as nature's most potent lipid-soluble antioxidant (and discovered for its crucial role in mammalian reproduction) we have now come to realize that vitamin E action has many more facets, depending on the physiological context. Although mainly acting as an antioxidant, vitamin E can also be a pro-oxidant; it can even have nonantioxidant functions: as a signaling molecule, as a regulator of gene expression, and, possibly, in the prevention of cancer and atherosclerosis. Since the term vitamin E encompasses a group of eight structurally related tocopherols and tocotrienols, individual isomers have different propensities with respect to these novel, nontraditional roles. The particular beneficial effects of the individual isomers have to be considered when dissecting the physiological impact of dietary vitamin E or supplements (mainly containing only the alpha-tocopherol isomer) in clinical trials. These considerations are also relevant for the design of transgenic crop plants with the goal of enhancing vitamin E content because an engineered biosynthetic pathway may be biased toward formation of one isomer. In contrast to the tremendous recent advances in knowledge of vitamin E chemistry and biology, there is little hard evidence from clinical and epidemiologic studies on the beneficial effects of supplementation with vitamin E beyond the essential requirement.

Characterization of the oxidation products of BO-653 formed during peroxyl radical-mediated oxidation of human plasma

4,6-Di-tert-butyl-2,3-dihydro-2,2-dipentyl-5-benzofuranol (BO-653) is a novel antioxidant synthesized by theoretical findings and considerations. Here we report on the aqueous peroxyl radical-induced oxidation of human plasma in the presence of BO-653. When BO-653 was given to healthy human subjects at 400 mg twice daily for 28 days, lipids in the resulting plasma were protected from oxidation compared with lipids present in plasma from subjects receiving placebo. Similarly, BO-653 added in vitro at 50 muM inhibited the peroxyl radical-induced accumulation of cholesteryl ester hydroperoxides that occurred in the presence of alpha-tocopherol, although BO-653 did not decrease the rate of consumption of ascorbate, albumin-bound bilirubin, and uric acid. The antioxidant action of in vivo and in vitro added BO-653 was associated with the formation of two major reaction products of BO-653, the structures of which were elucidated by mass spectrometry and nuclear magnetic resonance analyses. The products were identified as stereoisomers of dioxybis(4,6-di-tert.-butyl-2,3,5,7a-tetrahydro-2,2-dipentylbenzofuran-5-one). These dialkylperoxides of BO-653 might be useful markers to assess the antioxidant function of BO-653 in biological systems in vivo.

Role of oxidative modifications in atherosclerosis

This review focuses on the role of oxidative processes in atherosclerosis and its resultant cardiovascular events. There is now a consensus that atherosclerosis represents a state of heightened oxidative stress characterized by lipid and protein oxidation in the vascular wall. The oxidative modification hypothesis of atherosclerosis predicts that low-density lipoprotein (LDL) oxidation is an early event in atherosclerosis and that oxidized LDL contributes to atherogenesis. In support of this hypothesis, oxidized LDL can support foam cell formation in vitro, the lipid in human lesions is substantially oxidized, there is evidence for the presence of oxidized LDL in vivo, oxidized LDL has a number of potentially proatherogenic activities, and several structurally unrelated antioxidants inhibit atherosclerosis in animals. An emerging consensus also underscores the importance in vascular disease of oxidative events in addition to LDL oxidation. These include the production of reactive oxygen and nitrogen species by vascular cells, as well as oxidative modifications contributing to important clinical manifestations of coronary artery disease such as endothelial dysfunction and plaque disruption. Despite these abundant data however, fundamental problems remain with implicating oxidative modification as a (requisite) pathophysiologically important cause for atherosclerosis. These include the poor performance of antioxidant strategies in limiting either atherosclerosis or cardiovascular events from atherosclerosis, and observations in animals that suggest dissociation between atherosclerosis and lipoprotein oxidation. Indeed, it remains to be established that oxidative events are a cause rather than an injurious response to atherogenesis. In this context, inflammation needs to be considered as a primary process of atherosclerosis, and oxidative stress as a secondary event. To address this issue, we have proposed an "oxidative response to inflammation" model as a means of reconciling the response-to-injury and oxidative modification hypotheses of atherosclerosis.

Antioxidant activities of bile pigments

Biliverdin and bilirubin are reducing species and hence potential antioxidants formed by the action of heme oxygenase and biliverdin reductase. Indeed, there is increasing evidence for the suggestion that a beneficial role of the potentially toxic bilirubin may be to act as a powerful chain-breaking antioxidant in biological systems, and that bilirubin may contribute to the cellular and tissue protection seen with increased heme oxygenase. This article reviews the in vitro antioxidant activities of the two bile pigments with emphasis on the different physiological forms of bilirubin and types of oxidants, and discusses these properties in light of the presence and reactivity other nonproteinaceous antioxidants.

Lipoprotein-X reduces LDL atherogenicity in primary biliary cirrhosis by preventing LDL oxidation

Hypercholesterolemic human LDL contains oxidized subfractions that have atherogenic properties. Paradoxically, atherosclerosis incidence is low in patients with primary biliary cirrhosis (PBC), a disease characterized by marked increases in plasma LDL, including the LDL subfraction lipoprotein-X (Lp-X). To investigate the mechanisms underlying this paradox, we first examined the propensity to oxidation of unfractionated LDL isolated from PBC patients. After prolonged incubation with copper, PBC-LDL failed to increase the oxidation index or electrophoretic mobility noted in control LDL. An admixture of PBC-LDL or Lp-X with control LDL prevented oxidation of the latter in a dose-dependent manner. PBC-LDL was also noncompetitive against copper-oxidized LDL (oxLDL) for binding with a murine monoclonal anti-oxLDL antibody in a competitive ELISA. OxLDL exerts its proapoptotic and antiangiogenic effects in part by inhibiting fibroblast growth factor 2 (FGF2) expression. Preincubation of oxLDL with PBC-LDL, but not control LDL, attenuated the inhibitory effects of oxLDL on FGF2 expression in cultured bovine aortic endothelial cells (ECs). The antioxidant and prosurvival properties of PBC-LDL diminished after the patients underwent orthotopic liver transplantation. These results suggest that Lp-X reduces LDL atherogenicity by preventing LDL oxidation to protect EC integrity in the presence of hypercholesterolemia. They also suggest that altering LDL composition may be as important as reducing LDL concentration in preventing or treating atherosclerosis.

Crystal structure of human heme oxygenase-1 in a complex with biliverdin

Heme oxygenase oxidatively cleaves heme to biliverdin, leading to the release of iron and CO through a process in which the heme participates both as a cofactor and as a substrate. Here we report the crystal structure of the product, iron-free biliverdin, in a complex with human HO-1 at 2.19 A. Structural comparisons of the human biliverdin-HO-1 structure with its heme complex and the recently published rat HO-1 structure in a complex with the biliverdin-iron chelate [Sugishima, M., Sakamoto, H., Higashimoto, Y., Noguchi, M., and Fukuyama, K. (2003) J. Biol. Chem. 278, 32352-32358] show two major differences. First, in the absence of an Fe-His bond and solvent structure in the active site, the distal and proximal helices relax and adopt an "open" conformation which most likely encourages biliverdin release. Second, iron-free biliverdin occupies a different position and orientation relative to heme and the biliverdin-iron complex. Biliverdin adopts a more linear conformation and moves from the heme site to an internal cavity. These structural results provide insight into the rate-limiting step in HO-1 catalysis, which is product, biliverdin, release.

Overexpression of human heme oxygenase-1 attenuates endothelial cell sloughing in experimental diabetes

Heme oxygenase (HO)-1 represents a key defense mechanism against oxidative injury. Hyperglycemia produces oxidative stress and various perturbations of cell physiology. The effect of streptozotocin (STZ)-induced diabetes on aortic HO activity, heme content, the number of circulating endothelial cells, and urinary 8-epi-isoprostane PGF2alpha (8-Epi) levels in control rats and rats overexpressing or underexpressing HO-1 was measured. HO activity was decreased in hyperglycemic rats. Hyperglycemia increased urinary 8-Epi, and this increase was augmented in rats underexpressing HO-1 and diminished in rats overexpressing HO-1. The number of detached endothelial cells and O2- formation increased in diabetic rats and in hyperglycemic animals underexpressing HO-1 and decreased in diabetic animals overexpressing HO-1 compared with controls. These data demonstrate that HO-1 gene transfer in hyperglycemic rats brings about a reduction in O2- production and a decrease in endothelial cell sloughing. Upregulation of HO-1 decreases oxidant production and endothelial cell damage and shedding and may attenuate vascular complications in diabetes.

Thiocyanate catalyzes myeloperoxidase-initiated lipid oxidation in LDL

There is evidence that LDL oxidation may render the lipoprotein atherogenic. The myeloperoxidase-hydrogen peroxide (MPO/H2O2) system of activated phagocytes may be involved in this process. Chloride is supposed to be the major substrate for MPO, generating reactive hypochlorous acid (HOCl), modifying LDL. The pseudo-halide thiocyanate (SCN-) has been shown to be a suitable substrate for MPO, forming reactive HOSCN/SCN*. As relatively abundant levels of SCN- are found in plasma of smokers--a well-known risk group for cardiovascular disease--the ability of SCN- to act as a catalyst of LDL atherogenic modification by MPO/H2O2 was tested. Measurement of conjugated diene and lipid hydroperoxide formation in LDL preparations exposed to MPO/H2O2 revealed that SCN- catalyzed lipid oxidation in LDL. Chloride did not diminish the effect of SCN- on lipid oxidation. Surprisingly, SCN inhibited the HOCl-mediated apoprotein modification in LDL. Nitrite--recently found to be a substrate for MPO--showed some competing properties. MPO-mediated lipid oxidation was inhibited by heme poisons (azide, cyanide) and catalase. Ascorbic acid was the most effective compound in inhibiting the SCN- -catalyzed reaction. Bilirubin showed some action, whereas tocopherol was ineffective. When LDL oxidation was performed with activated human neutrophils, which employ the MPO pathway, SCN- catalyzed the cell-mediated LDL oxidation. The MPO/H2O2/SCN- system may have the potential to play a significant role in the oxidative modification of LDL--an observation further pointing to the link between the long-recognized risk factors of atherosclerosis: elevated levels of LDL and smoking.

Urinary biopyrrins levels are elevated in relation to severity of heart failure

OBJECTIVES

We investigated the relationship between the urinary levels of biopyrrins and the severity of heart failure (HF).

BACKGROUND

Oxidative stress is evident in heart disease and contributes to the development of ventricular dysfunction in patients with HF. Biopyrrins, oxidative metabolites of bilirubin, have been discovered as potential markers of oxidative stress.

METHODS

We measured the levels of urinary biopyrrins and plasma B-type natriuretic peptide (BNP) in 94 patients with HF (59 men; mean age 65 years) and 47 control subjects (30 men; mean age 65 years). Urine and blood samples were taken after admission in all subjects. Further urine samples were obtained from 40 patients after treatment of HF.

RESULTS

The urinary biopyrrins/creatinine levels (micromol/g creatinine) were the highest in patients in New York Heart Association (NYHA) class III/IV (n = 26; 17.05 [range 7.85 to 42.91]). The urinary biopyrrins/creatinine levels in patients in NYHA class I (n = 35; 3.46 [range 2.60 to 5.42]) or II (n = 33; 5.39 [range 3.37 to 9.36]) were significantly higher than those in controls (2.38 [range 1.57 to 3.15]). There were significant differences in urinary biopyrrins/creatinine levels among each group. The treatment of HF significantly decreased both urinary biopyrrins/creatinine levels (from 7.43 [range 3.84 to 17.05] to 3.07 [range 2.21 to 5.71]) and NYHA class (from 2.5 +/- 0.1 to 1.7 +/- 0.1). Log biopyrrins/creatinine levels were positively correlated with log BNP levels (r = 0.650, p < 0.001).

CONCLUSIONS

These results indicate that urinary biopyrrins levels are increased in patients with HF and are elevated in proportion to its severity.

Protective role of heme oxygenase in the blood vessel wall during atherogenesis

Several lines of evidence suggest that antioxidant processes and (or) endogenous antioxidants inhibit proatherogenic events in the blood vessel wall. Heme oxygenase (HO), which catabolizes heme to biliverdin, carbon monoxide, and catalytic iron, has been shown to have such antioxidative properties. The HO-1 isoform of heme oxygenase is ubiquitous and can be increased several fold by stimuli that induce cellular oxidative stress. Products of the HO reaction have important effects: carbon monoxide is a potent vasodilator, which is thought to play a role in modulation of vascular tone; biliverdin and its by-product bilirubin are potent antioxidants. Although HO induction results in an increase in catalytic free iron release, the enhancement of intracellular ferritin protein through HO-1 has been reported to decrease the cytotoxic effects of iron. Oxidized LDL has been shown to increase HO-1 expression in endothelial and smooth muscle cell cultures, and during atherogenesis. Further evidence of HO-1 expression associated with atherogenesis has been demonstrated in human, murine and rabbit atherosclerotic lesions. Moreover, genetic models of HO deficiency suggest that the actions of HO-1 are important in modulating the severity of atherosclerosis. Recent experiments in gene therapy using the HO gene suggest that interventions aimed at HO in the vessel wall could provide a novel therapeutic approach for the treatment or prevention of atherosclerotic disease.Key words: heme oxygenase, atherosclerosis, antioxidant enzymes, oxidized LDL, gene therapy.

Bilirubin as an Antioxidant: Kinetic Studies of the Reaction of Bilirubin with Peroxyl Radicals in Solution, Micelles, and Lipid Bilayers

Bilirubin (BR) showed very weak antioxidant activity in a nonpolar medium of styrene or cumene in chlorobenzene. In contrast, BR exhibited strong antioxidant activity in polar media such as aqueous lipid bilayers or SDS micelles/methyl linoleate (pH 7.4), where the rate with peroxyl radicals, k(inh) = 5.0 x 10(4) M(-)(1) s(-)(1), was comparable to that with vitamin E analogues, Trolox, or PMHC. An electron-transfer mechanism accounts for the effect of the medium on the antioxidant properties of BR.

Application of water-soluble radical initiator, 2,2'-azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride, to a study of oxidative stress

It is essential to generate free radicals at a controled and constant rate for specific duration and at specific site to study the dynamics of oxidation and also antioxidation. Both hydrophilic and lipophilic azo compounds have been used for such purpose. In the present work, the action of 2,2'-azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride (AIPH) was examined and compared with those of 2,2'-azobis(2-amidinopropane) dihydrochloride (AAPH) and 2,2'-azobis[2-methyl-N-(2-hydroxyethyl)-propionamide] (AMHP). The rate constant of free radical formation (ek(d)) for AIPH was 2.6 x 10(-6)/s at 37 degrees C in PBS (pH 7.4) solution, indicating that AIPH gives 3.8 times more free radicals than AAPH under the same conditions. It was found that the dynamics of oxidation and antioxidation induced by AIPH can be studied satisfactorily in the oxidation in micelles, LDL and erythrocyte suspensions, plasma, and cultured cells. The extent of cell death induced by AIPH and AAPH was directly proportional to the total free radicals formed. Interestingly, it was found that rats would not drink water containing AAPH, but they drank water containing AIPH. The levels of 8-iso-prostaglandin F2alpha (8-isoPs), 7-hydroxycholesterol (FCOH), lysophosphatidylcholine in the plasma of rats given water containing 50 mM AIPH for 1 month increased compared with those of control rats which drank water without AIPH. It may be concluded that AIPH is useful for kinetic and mechanistic studies on oxidative stress to membranes, lipoproteins, cells, and even animal models.

Studies of LDL particle size and susceptibility to oxidation and association with glucose metabolism in children after heart transplantation

BACKGROUND

Increased concentrations of serum triglyceride and low-density lipoprotein (LDL) cholesterol are common after heart transplantation (HTx). These abnormalities may promote transplant vascular disease and atherosclerosis, especially if LDL is small, dense, and oxidized. There have been no previous studies of LDL particle size and LDL susceptibility to oxidation in children after HTx.

METHODS

Twenty-three HTx recipients (aged 3-19 years) who received triple-drug immunosuppression therapy after HTx and 181 controls within the same age range participated in the study. Total, high-density lipoprotein, and LDL-cholesterol concentrations; triglyceride concentration, and glucose and insulin concentrations during oral glucose tolerance tests were determined an average of 3 years after HTx (range, 1-7 years). Moreover, we determined serum lipoprotein (a) concentration, apolipoprotein E phenotype, LDL particle size, and indices of LDL susceptibility to copper-induced oxidation in 12 HTx recipients.

RESULTS

We found hypertriglyceridemia in 56.5% and hyperinsulinemia in 30.4% of patients. Triglyceride concentration and body mass index were associated significantly with insulin concentration (p < 0.008 for both). Low-density lipoprotein particle size, LDL susceptibility to in vitro oxidation, and lipoprotein (a) concentrations did not differ significantly between HTx patients and controls. Low-density lipoprotein particle size was associated inversely with cyclosporine through level (Neoral, r = -0.59, p = 0.045), whereas weight-adjusted dosage of cyclosporine correlated positively with longer lag time of LDL oxidation (r = 0.69, p = 0.013).

CONCLUSIONS

Hypertriglyceridemia and hyperinsulinemia were common in children receiving triple-drug immunosuppression therapy after HTx. Increased cyclosporine through concentration was associated with small LDL particle size but did not increase LDL susceptibility to oxidation.

The effect of a promoter polymorphism in the heme oxygenase-1 gene on the risk of ischaemic cerebrovascular events

Heme oxygenase-1 (HO-1) has been demonstrated to exert potent anti-oxidant and anti-inflammatory effects in the context of atherosclerotic vascular disease, and therefore was referred to as a potential vascular protective factor. A (GT)n dinucleotide repeat polymorphism in the HO-1 promoter has been shown to modulate HO-1 gene expression. Short (<25) GT repeats were associated with HO-1 up-regulation, and therefore may influence susceptibility to ischaemic vascular events. We investigated the association of HO-1 repeat length with the risk of cerebrovascular events in a case control study and assessed possible interrelations with vascular risk factors. We determined the number of GT repeats in the HO-1 promoter in 399 patients with ischaemic cerebrovascular events and 398 healthy controls and compared the frequencies of short (<25) repeat (class S) and long (> or =25) repeat (class L) alleles after adjustment for potentially confounding factors. Genotype distributions of S/S, S/L and L/L in patients were 9.8% (n=39), 45.1% (n=180) and 45.1% (n=180), which was similar to the distribution in controls with 11.5% (n=46), 44.5% (n=177) and 44.0% (n=175). In the presence of vascular risk factors, the HO-1 genotype became functionally relevant: in patients without hyperlipidemia the S/S genotype exerted a protective effect on the development of ischaemic cerebrovascular events (OR 0.2; 95% CI 0.1-0.6), while this effect was no longer present in hyperlipidemic patients. Short (<25 GT) repeats in the HO-1 gene promoter confer a reduced risk for cerebrovascular events in individuals with normal plasma lipid levels. This may explain controversial findings in different populations.

Susceptibility of plasma lipids to peroxidation

Lipid peroxidation is an old and yet novel subject. It induces membrane disturbance and damage and its products are known to induce the generation of various cytokines and cell signaling. In the present work, the susceptibility and specificity of human plasma lipids to oxidation were studied, aiming specifically at elucidating the effects of oxidation milieu and oxidants. Cholesteryl esters (CEs) and phosphatidylcholines (PCs) were more readily oxidized in plasma than in organic solution under similar conditions. The susceptibilities of PC and free cholesterol (FC) relative to CE to free radical-mediated lipid peroxidation induced by peroxyl radicals and peroxynitrite were smaller in plasma than in organic solution. The higher rate of CE oxidation by free radicals than PC may be accounted for by the physical effects as well as higher content of polyunsaturated lipids in CE than PC. On the contrary, PC was more readily oxidized than CE by lipoxygenases. The lipid hydroperoxides were stable in organic solution but reduced to the corresponding hydroxides in plasma, the rate being much faster for PC hydroperoxides than for CE and FC hydroperoxides. It was confirmed that free radical-mediated oxidation gave both cis,trans and trans,trans, racemic, random hydroperoxides, while that by lipoxygenase gave only regio- and stereo-specific cis,trans-hydroperoxide.

Neonatal blood plasma is less susceptible to oxidation than adult plasma owing to its higher content of bilirubin and lower content of oxidizable Fatty acids

Newborn infants are susceptible to a range of problems attributed to excessive production of free radicals. Because of a higher content of antioxidants, above all bilirubin, and a lower content of oxidizable lipids, newborn plasma should be better protected against oxidation than adult plasma. To test this hypothesis, we measured the susceptibility of plasma to in vitro oxidation in microsamples (7 microL) from 57 healthy newborns and 18 adults. Heparin plasma was diluted 150-fold and oxidized by 50 microM Cu2+. Oxidation was monitored as an increase in sample absorbance at 234 nm. Plasma oxidizability was found to be significantly lower in newborns than in adults. Accordingly, the level of bilirubin, an important antioxidant, was significantly higher, and the level of polyunsaturated fatty acids, a major substrate of lipid peroxidation, was significantly lower in newborn plasma. In addition, plasma oxidizability correlated positively with the level of polyunsaturated fatty acids and negatively with that of bilirubin. These data indicate that plasma is better protected against oxidative stress in newborns than in adults, owing to its higher content of antioxidants like bilirubin and its lower content of oxidizable lipids.

Photooxidations Initiated or Sensitized by Biological Molecules: Singlet Oxygen Versus Radical Peroxidation in Micelles and Human Blood Plasma¶

Biomolecules common in blood plasma, including 2-methyl-1,4-naphthoquinone (vitamin K-0, 2), 2,3-dimethoxy-5-methyl-1,4-benzoquinone (ubiquinone-0, 3), bilirubin, 4, and urocanic acid, 5, were used as photoactivators for the photooxidation of methyl linoleate (ML) in 0.50 M sodium dodecyl sulfate micelles to mimic a bioenvironment. UV irradiation of 2 in this system initiated H-atom abstraction from ML (Type-I mechanism). The evidence includes kinetics of oxygen uptake, inhibition of oxidation by an antioxidant ((R)-(+)-6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid [Trolox], 7) and the analysis of four geometric hydroperoxides formed (cis, trans to trans, trans ratio of 0.5). In contrast, irradiation with a singlet-oxygen sensitizer, 3,5-di-t-butyl-1,2-benzoquinone, 1, formed six isomers by a Type-II mechanism, yielding a cis, trans to trans, trans isomer ratio of 6. Peroxidation activated by 3 or 4 with visible light occurred by a singlet-oxygen pathway (Type-II mechanism), as shown by kinetics of oxygen uptake and the effect of quenchers. In contrast, peroxidation in the presence of 5 in this system initiated H-atom abstraction from ML as shown by oxygen uptake and inhibition by Trolox. A comparison of thermal free-radical peroxidation with direct photooxidation of human blood plasma samples showed important differences. Blood plasma resisted thermal peroxidation because of natural antioxidants or on the addition of Trolox. In contrast, direct photooxidation involved singlet oxygen, according to the effect of quenchers and the lack of inhibition by antioxidants.

Biliverdin reductase: a major physiologic cytoprotectant

Bilirubin, an abundant pigment that causes jaundice, has long lacked any clear physiologic role. It arises from enzymatic reduction by biliverdin reductase of biliverdin, a product of heme oxygenase activity. Bilirubin is a potent antioxidant that we show can protect cells from a 10,000-fold excess of H2O2. We report that bilirubin is a major physiologic antioxidant cytoprotectant. Thus, cellular depletion of bilirubin by RNA interference markedly augments tissue levels of reactive oxygen species and causes apoptotic cell death. Depletion of glutathione, generally regarded as a physiologic antioxidant cytoprotectant, elicits lesser increases in reactive oxygen species and cell death. The potent physiologic antioxidant actions of bilirubin reflect an amplification cycle whereby bilirubin, acting as an antioxidant, is itself oxidized to biliverdin and then recycled by biliverdin reductase back to bilirubin. This redox cycle may constitute the principal physiologic function of bilirubin.

Protective effect of HO-1 against oxidative stress in human hepatoma cell line (HepG2) is independent of telomerase enzyme activity

Heme oxygenase-1 (HO-1) is a stress response protein and its induction is associated with protection against oxidative stress. Cell survival during exposure to environmental stresses is associated with elevation of HO-1. Telomerase plays an important role in cell proliferation and immortalization. Our objective was to determine whether the adaptive cellular response to survive exposure to environmental stresses is dependent on expression of HO-1 and telomerase activity in hepatoma cell line (HepG2). Exposure of HepG2 to oxidants, H(2)O(2) (100 microM), as well as HO-1 inducers, heme (10 microM) and stannic chloride (SnCl(2)) (10 microM), resulted in an increased HO-1 mRNA, protein and total HO activity. On the other hand, HO activity was inhibited by addition of stannic mesoporphyrin (SnMP) (10 microM). These effects were brought about without altering endogenous HO-2 protein levels. Telomerase activity was not affected by oxidants, inducers of HO-1 or inhibitors of HO activity. Similarly, the catalytic subunit of telomerase enzyme human telomerase reverse transcriptase (hTERT), which is considered as the major regulator of telomerase activity, was not affected by oxidants, heme and H(2)O(2), or downregulation of HO gene activity by SnMP. This study demonstrates, for the first time, that induction of HO-1 gene mediates protection against oxidants and increases cell survival by a mechanism independent of telomerase enzyme activity. Suppression of HO activity by SnMP decreased cell resistance to oxidant stressors without altering telomerase activity.

Heme oxygenase-1 gene promoter polymorphism is associated with coronary artery disease in Japanese patients with coronary risk factors

OBJECTIVE

Heme oxygenase (HO) is important in the defense against oxidative stress and as a factor in an antiatherogenic mechanism. Compared with long (GT)(n) repeats, short (GT)(n) repeats in the human HO-1 gene promoter were shown to have higher transcriptional activity in response to oxidative stress. There is a strong link between oxidative stress and the pathogenesis of coronary artery disease (CAD).

METHODS AND RESULTS

We screened the allelic frequencies of (GT)(n) repeats in the HO-1 gene promoter in 577 patients who underwent coronary angiography. Because the distribution of numbers of (GT)(n) repeats was bimodal, we divided the alleles into 2 subclasses: class S included shorter (<27) repeats, and class L included longer (> or =27) repeats. Multivariate logistic regression models including standard coronary risk factors revealed that the genotypes were significantly related to CAD status in hypercholesterolemic, diabetic patients or in smokers. In this study, the patients with shorter GT repeats were less likely to have CAD.

CONCLUSIONS

Length polymorphism in the HO-1 gene promoter is related to CAD susceptibility in Japanese people who also have coronary risk factors such as hypercholesterolemia, diabetes, and smoking. HO-1 may play an antiatherogenic role in Japanese patients with these coronary risk factors.

A genome scan for loci influencing anti-atherogenic serum bilirubin levels

Epidemiological studies have shown an association of decreased serum bilirubin levels with coronary artery disease. Two segregation analyses in large pedigrees have suggested a major gene responsible for high bilirubin levels occurring in about 12% of the population. Based on a recessive model from a previous segregation analysis, we performed a genome scan using 587 markers genotyped in 862 individuals from 48 Utah pedigrees to detect loci linked to high bilirubin levels. As a complementary approach, non-parametric linkage (NPL) analysis was performed. These two methods identified four regions showing evidence for linkage. The first region is on chromosome 2q34-37 with multipoint LOD and NPL scores of 3.01 and 3.22, respectively, for marker D2S1363. This region contains a previously described gene, uridine diphosphate glycosyltransferase 1, which has been associated with high bilirubin levels. A polymorphism in the promoter of this gene was recently shown to be responsible for Gilbert syndrome which is associated with mild hyperbilirubinemia. The other regions were found on chromosomes 9q21, 10q25-26, and 18q12 with maximum NPL scores of 2.39, 1.55, and 2.79, respectively. Furthermore, we investigated in these pedigrees the association between bilirubin levels and coronary artery disease. One-hundred and sixty-one male and 41 female subjects had already suffered a coronary artery disease event. Male patients showed significantly lower bilirubin concentrations than age-matched controls. This association, however, was not observed in females. These results provide evidence that loci influencing bilirubin variation exist on chromosomes 2q34-37, 9q21, 10q25-26, and 18q12 and confirms the association of low bilirubin levels with coronary artery disease in males.

Heme oxygenase as an intrinsic defense system in vascular wall: implication against atherogenesis

Recent developments in our understanding of the atherosclerotic process and factors that trigger ischemic cardiovascular disease have led to the consideration of antioxidative responses or exogenous antioxidants, which are proposed to inhibit multiple proatherogenic and prothrombotic events in arterial wall. Heme oxygenases (HO), an enzyme essential for heme degradation, have been shown to have such antioxidative properties via the production of bile pigments, carbon monoxide and ferritin induction. We have demonstrated that mildly oxidized LDL markedly induces HO-1, an inducible form of HO, in human aortic endothelial and smooth muscle cell cocultures and that its induction results in the attenuation of monocyte chemotaxis induced by mildly oxidized LDL. We also confirmed abundant expression of HO-1 in human, murine and rabbit atherosclerotic lesions. By modulating HO activities in LDL-receptor knockout mice and Watanabe heritable hyperlipidemic rabbits during their atherosclerotic lesion developments, anti-atherogenic properties of HO have demonstrated as judged by the quantitative analyses of atherosclerotic lesion formation. HO expression was inversely correlated with the levels of plasma and tissue lipid peroxides. HO also influenced on nitric oxide pathway. These observations may suggest that HO, induced during atherosclerotic process, functions as an intrinsic protective pathway in vascular wall.