Sunlight-induced mutation of bilirubin in a long-distance runner

Effects of bilirubin configurational photoisomers on the measurement of direct bilirubin by the vanadate oxidation method

BACKGROUND

Direct-reacting bilirubin concentrations measured using vanadate chemical oxidation method do not exactly match the conjugated bilirubin concentration. One of the causes is the effect of bilirubin photoisomers. However, the quantitative evaluation of the effects of these photoisomers has not been sufficiently conducted. In particular, the influence of bilirubin configurational isomers on direct bilirubin is the most critical factor.

METHODS

Sixteen residual serum samples were used. For quantitative analysis based on the change in direct bilirubin and bilirubin configurational isomer, samples were irradiated via blue light-emitting diodes to suppress the production of bilirubin structural isomers. Total bilirubin and direct bilirubin concentrations were measured using the vanadate chemical oxidation method. Concentrations of 4Z,15Z-bilirubin IXα and its photoisomers were measured using high-performance liquid chromatography. The sum of 4Z,15E-bilirubin IXα and 4E,15Z-bilirubin IXα was notated as bilirubin configurational isomer, and the differences between the measured values of the irradiated and non-irradiated samples were calculated and notated as ΔDB and ΔBCI.

RESULTS

In non-irradiated and irradiated samples, total bilirubin and direct bilirubin concentrations were 10.73 mg/dL with significant a decrease to 10.60 mg/dL and 0.69 mg/dL with a significant increase to 0.78 mg/dL, while bilirubin configurational isomer values were 1.00 mg/dL and 1.52 mg/dL, respectively. The linear regression equation revealed a significant positive correlation of Y = 0.187X-0.006 between ΔDB (Y) and ΔBCI (X).

CONCLUSION

Applying the vanadate chemical oxidation method affected approximately 19% of the bilirubin configurational isomer concentration for direct bilirubin. Extreme caution is necessary when interpreting the measured values of samples indicative of unconjugated hyperbilirubinaemia.

Humoral Phototransduction: Blood Is a Messenger

Drawing upon the premise that there is a parsimony to nature, the author proposes that heme moieties and bile pigments in animals mediate some non-visual influences of light upon neuroactive gases and biological rhythms. Primary abnormalities in synthesis and regulation of blood and bile may, therefore, cause some neuropsychiatric illnesses. Light may play a critical role in neurotransmission. NEUROSCIENTIST 2:207-210, 1996

Early isomerization of bilirubin in phototherapy of neonatal jaundice

Neonatal jaundice is usually treated with phototherapy that converts bilirubin to more polar stereoisomers. These should theoretically be less able to cross the blood-brain barrier. The rates of photoisomer formation and concentrations accumulating in the circulation may have a bearing on the risk of kernicterus. The purpose of this study was to determine the rate of appearance of the major 4Z, 15E photoisomer of bilirubin during the early stages of phototherapy. Twenty jaundiced neonates were treated with phototherapy, and blood samples were drawn before and at approximately 15, 30, 60, and 120 min (10 infants) or at approximately 15, 60, 120, and 240 min (10 infants) after beginning phototherapy. Blood samples were analyzed for total serum bilirubin (TSB) and the 4Z, 15E photoisomer of bilirubin. Significant (p<0.0001) formation of the 4Z, 15E photoisomer was detectable within 15 min. The change in TSB from time 0 was insignificant at 120 min but reached significance at 240 min (p<0.001). The 4Z, 15E bilirubin constituted up to 20-25% of TSB at 2 h and may not have peaked by 4 h. Further studies are needed to determine whether this early shift in balance between bilirubin isomers with different polarities may impact the risk of bilirubin encephalopathy even before TSB starts to fall.

Crystallographic analysis of human serum albumin complexed with 4Z,15E-bilirubin-IXalpha

Bilirubin, an insoluble yellow-orange pigment derived from heme catabolism, accumulates to toxic levels in individuals with impaired or immature liver function. The resulting jaundice may be managed with phototherapy to isomerize the biosynthetic 4Z,15Z-bilirubin-IXalpha to more soluble and excretable isomers, such as 4Z,15E-bilirubin. Bilirubin and its configurational isomers are transported to the liver by human serum albumin (HSA) but their precise binding location(s) on the protein have yet to be determined. To investigate the molecular details of their interaction, we co-crystallised bilirubin with HSA. Strikingly, the crystal structure--determined to 2.42 A resolution--revealed the 4Z,15E-bilirubin-IXalpha isomer bound to an L-shaped pocket in sub-domain IB. We also determined the co-crystal structure of HSA complexed with fusidic acid, an antibiotic that competitively displaces bilirubin from the protein, and showed that it binds to the same pocket. These results provide the first crystal structure of a natural bilirubin pigment bound to serum albumin, challenge some of the present conceptions about HSA-bilirubin interactions, and provide a sound structural framework for finally resolving the long-standing question of where 4Z,15Z-bilirubin-IXalpha binds to the protein.

Extraocular phototransduction and circadian timing systems in vertebrates

It is widely accepted that, for organisms with eyes, the daily regulation of circadian rhythms is made possible by light transduction through those organs. Yet, it has been demonstrated repeatedly in recent years that ocular light receptors that mediate vision, at least in mammals, are not the same photoreceptors involved in circadian regulation. Moreover, it has been recognized for many years that circadian regulation can occur in organisms without eyes. In fact, extraocular circadian phototransduction (EOCP) appears to be a phylogenetic rule for the vast majority of species. EOCP has been reported in every nonmammalian species studied to date. In mammals, however, the story is very different. This paper presents findings from studies that have examined specifically the capacity for EOCP in vertebrate species. In addition, the literature addressing noncircadian aspects of extraocular phototransduction is briefly discussed. Finally, possible mechanisms underlying EOCP are discussed, as are some of the implications of the presence, or absence, of EOCP across phylogeny.

Bright light exposure of a large skin area does not affect melatonin or bilirubin levels in humans

BACKGROUND

Light treatment through the eyes is effective in alleviating the symptoms of some psychiatric disorders. A recent report suggested that skin light exposure can affect human circadian rhythms. Bilirubin can serve as a hypothetical blood-borne mediator of skin illumination into the brain. We studied whether bright light directed to a large body area could suppress the pineal melatonin secretion or decrease serum total bilirubin in conditions that could be used for therapeutic purposes.

METHODS

Seven healthy volunteers participated in two consecutive overnight sessions that were identical except for a light exposure on the chest and abdomen in the second night from 12:00 AM to 6:00 AM (10,000-lux, 32 W/m(2) cool white for six subjects and 3000-lux, 15 W/m(2) blue light for one subject). Hourly blood samples were collected from 7:00 PM to 7:00 AM for melatonin radioimmunoassays. Bilirubin was measured by a modified diazo method in blood samples taken at 12:00 AM and 6:00 AM and in urine samples collected from 7:00 PM to 11:00 PM and from 11:00 PM to 7:00 AM.

RESULTS

The skin light exposure did not cause any significant changes in serum melatonin or bilirubin levels. The excretion of bilirubin in urine was also the same in both sessions.

CONCLUSIONS

Significant melatonin suppression by extraocular light does not occur in humans. Robust concentration changes of serum total bilirubin do not have a role in mediating light information from the skin to the central nervous system.

Wavelength-dependent quantum yield for Z----E isomerization of bilirubin complexed with human serum albumin

The quantum yield, phi ZE, for configurational photoisomerization (4Z,15Z----4Z,15E) of bilirubin bound non-covalently to human serum albumin was determined (at 23 +/- 2 degrees C) by laser excitation and chromatographic analysis of products. Values obtained for photoexcitation at 465 nm were about one-half those previously reported. The quantum yield was dependent on excitation wavelength, decreasing from a value of 0.109 +/- 0.010 for excitation at 457.9 nm to a value of 0.054 +/- 0.005 for excitation at 514.5 nm. The wavelength dependence is consistent with rapid transfer of excitation energy between the two non-identical pyrromethenone chromophores of bilirubin in the singlet excited state. Since the quantum yields for photoisomerization and luminescence of bilirubin bound to serum albumin at room temperature are both low, internal conversion processes, rather than Z----E configurational isomerizations, are probably the major pathways for deactivation of photo-excited bilirubin.

Human serum bilirubin fractionation in various hepatobiliary diseases by the newly developed high performance liquid chromatography

Serum Bilirubin was fractionated by newly developed reversed phase high performance liquid chromatography (HPLC) into 5 fractions: delta (delta-Bilirubin, B delta), gamma (bilirubin diglucuronide, BDG), beta (Bilirubin monoglucuronide, BMG), beta' ((Z, E,)- and/or (E, Z)-bilirubin IX alpha) and alpha ((Z, Z)-bilirubin IX alpha). Sera of healthy subjects and of patients with unconjugated hyperbilirubinemia showed predominantly alpha fraction with a small amount of beta' fraction. Trace amounts of delta fraction were detected in a few cases. The results of fractionation of serum bilirubin in 159 patients with various hepatobiliary diseases suggested that the ratios B delta/(B delta + BDG + BMG) and BMG/B delta can be useful parameters to follow patients with jaundice, compared with the reported B delta/total bilirubin which did not always reflect the jaundice stage, especially in cases with low serum bilirubin levels.

Bilirubin is an antioxidant of possible physiological importance

Bilirubin, the end product of heme catabolism in mammals, is generally regarded as a potentially cytotoxic, lipid-soluble waste product that needs to be excreted. However, it is here that bilirubin, at micromolar concentrations in vitro, efficiently scavenges peroxyl radicals generated chemically in either homogeneous solution or multilamellar liposomes. The antioxidant activity of bilirubin increases as the experimental concentration of oxygen is decreased from 20% (that of normal air) to 2% (physiologically relevant concentration). Furthermore, under 2% oxygen, in liposomes, bilirubin suppresses the oxidation more than alpha-tocopherol, which is regarded as the best antioxidant of lipid peroxidation. The data support the idea of a "beneficial" role for bilirubin as a physiological, chain-breaking antioxidant.