Urinary excretion of an isomer of bilirubin during phototherapy

Lumirubin, a water-soluble photoproduct of bilirubin formed in vivo during phototherapy, is excreted in the urine. In premature infants with little or no bilirubin conjugating activity, lumirubin is the principal yellow pigment found in the urine during phototherapy. The clearance rate of lumirubin in nine premature infants varied from 0.05 to 0.65 ml/min and increased with postconceptional age in parallel with increased creatinine clearance rate. The amount of lumirubin excreted per 24 h was estimated to be from 0.2 to 9.4 mg with a mean of 3.2 mg. The urinary excretion of lumirubin is a significant pathway for pigment elimination during phototherapy.

Laser investigation of bilirubin-photobilirubin photoconversion

The reversibility of the configurational photoisomerization process of bilirubin (BR) with laser lines in the blue-green spectral region is investigated. Photoisomerization efficiency of BR is found to depend strongly on wavelength, and to decrease when the excitation wavelength is increased from blue to green. Reversion of BR photoisomers (identical to photobilirubin, PBR) back to native BR is demonstrated for several laser lines by irradiating PBR/BR mixtures with wavelengths greater than the excitation wavelengths. Green lines turn out to be very efficient for PBR----BR reversion. The PBR concentrations at photoequilibrium, obtained from the spectrophotometric data, are in close agreement with the corresponding values measured with the high performance liquid chromatography technique in the case of 10 nm bandwidth filtered light reported in the literature. The 457 nm blue laser line produces 32% PBR concentration at photoequilibrium; only 14, 7, and 3% PBR concentrations are produced by the blue-green lines at 488, 501, 514 nm, respectively. The effect on the photostationary PBR/BR mixture of successive irradiations with different wavelengths, and the influence of the wavelength sequence are reported. In the case of blue lines our results support the assumption of the first-order kinetics for the BR in equilibrium PBR photoreaction. Departures are observed with green-lines (501, 514 nm). The present results, together with the i) good clinical efficiency reported for fluorescent green lamps; and ii) slow elimination of configurational photoisomers in infants, tend to confirm the lumirubin-pathway as the main mechanism for phototherapy, and call for clinical investigation of narrow-spectrum lamps with peak emission wavelength in the (biologically safer) 480 divided by 530 nm range.

Photodynamic damage induced by bilirubin on human platelets: possible relevance to newborn pathology

Several reports have appeared showing the possibility of bilirubin-sensitized photodamage. We have extended these observations to platelets. In the presence of 300 microM bilirubin the in vitro irradiation of isolated platelets or platelet-rich plasmas with visible light induced significant lysis as determined by the release of lactate dehydrogenase (LDH). The extent of LDH release was a function of irradiation time, being about 20% after 2 h of irradiation. A loss membrane-bound ATPase activity was also observed at earlier times, indicating that membrane damage was preliminary to the lytic effect. The release of beta-thromboglobulin, induced by close cell-to-cell contact, was lower in bilirubin- and light-treated platelets with respect to controls. Our results suggest that bilirubin may act as a photodynamic agent producing some damage on human blood platelets.

The elevation of blood levels of zinc protoporphyrin in mice following whole body irradiation

Elevation of zinc protoporphyrin (ZPP) levels in the blood has served as an indicator of lead poisoning and iron deficiency anemia for many years. We have discovered that sublethal doses of whole body irradiation with x-rays also elevates ZPP 2-3-fold over normal levels. The ZPP level does not begin to increase until days 12-14 postirradiation and peaks between days 18 and 20 before returning to normal levels between days 28 and 35. Increasing the radiation dose delays the onset of the rise in ZPP, but does not affect the magnitude of the elevation. At lethal doses, ZPP elevation is not observed. Neither of the two previously described mechanisms that cause elevations of ZPP, namely iron deficiency and inhibition of ferrochelatase, are responsible for the radiation-induced elevation of ZPP. The elevation of ZPP appears to be correlated with the recovery of the hematopoietic system from radiation injury.

[Spatial distribution of light intensity under a phototherapy unit]

The distribution of energy under a phototherapy unit containing 8 tubes is uneven; a significant maximum in energy is observed at the centre of the unit. It is therefore desirable to situate the baby at this point of maximum energy. The presence of lateral reflectors however (either metal foil or white sheets), result in not only an increase in energy, but also a more even energy distribution. Therefore the necessity of placing the baby at a special position is no longer required.

The radical ions and photoionization of bile pigments

The semireduced, semioxidized, and OH(.)-adduct radicals of bilirubin (BR) and biliverdin (BV) have been characterized using pulse radiolysis techniques. Laser flash photolysis (265-nm) of these pigments led to monophotonic photoionization with quantum yields of 0.08 for BR and 0.03 for BV. No evidence for triplet formation or for photoisomerization was found after 265-nm laser excitation. However, 347-nm excitation of BR in chloroform led to simultaneous photoisomerization and radical formation, but the radicals are thought to have originated from a pathway other than photoionization. The relevance of these observations to BR photoreactivity is discussed. BR radical ions in alkaline solution did not react with tryptophan (TrpH), but the semioxidized TrpH radical oxidized BR with k = 4.3 X 10(8) dm3 mole-1 sec-1. When human serum albumin (HSA) was oxidized using radiolytically generated azide radicals, a radical transformation involving TrpH and TyrOH residues occurred with k = 3.8 X 10(3) sec-1. When BR was complexed with the protein the transformation rate was reduced to 1.6 X 10(3) sec-1. This was interpreted in terms of a conformational change in the protein. Identification of the probable residues involved provided information about the primary BR binding site which was consistent with an earlier report.

The mechanism of bilirubin-photosensitized DNA strand breakage in human cells exposed to phototherapy light

Exposure of normal human fibroblasts to visible light (420-490 nm) in the presence of exogenously added 1-100 micrograms/ml bilirubin enhanced the level of DNA strand breakage compared with cells irradiated in the absence of added bilirubin. Treatment of cells in the dark with an irradiated bilirubin solution also induced DNA strand breaks. However, strand breakage was not detected in cells treated with an irradiated bilirubin solution that had been incubated with catalase (H2O2: H2O2 oxidoreductase EC 1.11.1.6). Examination of irradiated bilirubin solutions demonstrated the presence of hydrogen peroxide although, apparently, not at concentrations sufficient to account for the level of DNA strand breakage detected. Hence, irradiation of bilirubin results in the generation of hydrogen peroxide and possibly other peroxides that can cause DNA damage.

[Study on radiosterilization of crude drug pill involving bezoar bovis--radiolysis of bilirubin and cholic acids in hydrous starch pellet (author's transl)]

Radiolysis of bilirubin and cholic acids (cholic acid, desoxycholic acid and lithocholic acid) in hydrous pellet have been investigated with following parameters, which were hydrous content, radiation dose and the dose rate, to discuss the application of gamma-irradiation for sterilization of crude drug pill involving bezoar bovis. At 774 C/kg (3.0 MR) irradiation for 5% and 10% hydrous contents pellets, the radiolysis percent of those components were less than 5%. However, the higher hydrous pellet, the radiolysis percents of those are more increase. At the same irradiated condition for 20% hydrous contents pellets, the radiolysis percents of those were 15-22%. The hydrous percent of commercial crude drug pill involving bezoar bovis are about 9%, so that the radiolysis of those components will be less than 5% on the sterilization. The radiolysis percent of bilirubin are constant to variation of radiation dose rate between 51.6-722.5 C/kg.hr (0.2-2.8 MR/hr). But, the values of cholic acids don't definite such as that of bilirubin, because of larger analytical error.

Bilirubin, reserve albumin for binding of bilirubin and pH in plasma during phototherapy (ordinary and double light) of term newborn infants

Forty-five term newborn infants with uncomplicated hyperbilirubinaemia were treated continuously with phototherapy for 24 hours. Twenty-eight infants received double light treatment and 17 infants ordinary phototherapy. During both treatments a significant decrease in the serum unconjugated bilirubin concentration, a significant increase in the serum reserve albumin concentration for binding of bilirubin determined by the [14C] MADDS method, and a significant decrease in the index of serum bilirubin toxicity occurred. The changes in these parameters were significantly greater during the double light treatment than during the ordinary phototherapy. During the treatment the fall in index was constant. No significant change in plasma pH was seen. Thus, the study gives further evidence that the risk of bilirubin encephalopathy is reduced by phototherapy and that double light treatment is in the respect superior to ordinary phototherapy. Prior to phototherapy the molar ratio in serum of unconjugated bilirubin plus reserved albumin for binding of bilirubin to albumin was only 0.60, on average, and during the treatment the increase in the serum reserve albumin concentration was less than the decrease in the serum bilirubin concentration. This can be explained either by the presence in infant serum of an unknown ligand interfering competitively or allosterically in the binding of MADDS and bilirubin to albumin, or by the existence of a foetal albumin with a lower affinity for MADDS than adult albumin.

The photoinduced isomerization of bilirubin in cationic detergent solutions

When bilirubin IX alpha in solution in a buffered aqueous cationic detergent near neutral pH is irradiated with visible light, a rapid equilibrium with bilirubin III alpha and XIII alpha is set up. Little isomerization can be detected under comparable conditions in anionic or neutral detergents. The rapid disproportionation of bilirubin monoglucuronide into unconjugated bilirubin and bilirubin diglucuronide also takes place on irradiation in a solution of a cationic detergent.

High-pressure liquid chromatographic analysis of anaerobic photoproducts of bilirubin-IX alpha in vitro and its comparison with photoproducts in vivo

To carry out photochemical experiments under conditions similar to those prevailing for neonatal bilirubin metabolism in jaundice phototherapy, we have studied photoproducts produced by the action of light on a bilirubin--albumin solution and further clarified the relationship between the photoproducts obtained from experiments in vitro and in vivo. (1) An accurate and sensitive separation method by high-pressure liquid chromatography for photoproducts of bilirubin under anaerobic irradiation of visible light is described. (2) There were two main photoproducts obtained from experiments both in vivo and in vitro. (3) Exact correspondence of retention time on high-pressure liquid chromatography, diazo-reactivity, thermal reversion and absorption-spectrum maxima was observed between unknown pigment and photobilirubin-IX alpha from biological fluids, and the comparable peaks 2 and 3 from experiments in vitro. (4) The behaviour of photoproducts in various solutions in the absence of light and O2 is described. (5) A lower affinity of photoproducts, especially unknown pigment, for human serum albumin than with bilirubin-IX alpha for the albumin was demonstrated by the gel-filtration method.

Comparison of efficiency of commercially available phototherapy units

The efficiency of two phototherapy units was compared by exposing solutions of bilirubin in vitro. Both units are commercially available.

New concepts in phototherapy: photoisomerization of bilirubin IX alpha and potential toxic effects of light

New information is summarized, indicating that configurational photoisomerization of bilirubin at the 5 and 15 carbon bridges is the major mechanism of bilirubin photocatabolism in vivo, and that singlet oxygen photooxidation plays only a minor role. The literature is reviewed concerning potentially damaging photodynamic reactions that are observed in vitro with vitamins, proteins, lipids, and nucleic acids, and their possible relationships to the limited number of toxic side-effects that have been detected with clinical phototherapy of neonatal jaundice. Secondary toxic effects, mediated by bilirubin photoderivatives or by retina-neuroendocrine pathways are also considered. Areas requiring further investigations are delineated.