[Changes in the synaptosomal membrane in the modelling of the phototherapeutic action used in bilirubin encephalopathy]

Continuous irradiation of bilirubin containing (3.10(-5) M) particles of the synaptosomal membrane (pH 7.2, at 10 degrees C) with blue light for 2 hours led to decrease of the total specific activity of ATPase, specific activity of Na, K-ATPase, and (less significantly and at a slower rate) specific activity of acetilcholinesterase. Pre-irradiation argon barbotage of the aqueous suspension of the synaptosomal membrane particles or addition of tocopherol acetate to the suspension counteracted the irradiation induced decrease of the enzyme activity. A counteraction was also produced by pre-irradiation alkalization of the suspension to pH 7.8 at 10 degrees C or addition of serum albumin to the suspension; the character of the effect of this protein on the activity of the membrane enzymes in irradiation was determined by certain peculiarities of its chemical composition. The strongest counteraction to the irradiation induced decrease of enzyme activity occurred in addition of monomeric albumin, freed of organophilic ligands, when pH of the suspension was 7.8 (10 degrees C). The activity of Na, K-ATPase and acetylcholinesterase was reduced most markedly when monomeric ligand containing albumin was added to a suspension of membrane particles which was acidified to pH 6.8 (10 degrees C) before the beginning of irradiation.

Metalloporphyrin-enhanced photodegradation of bilirubin in vitro

Solutions of bilirubin containing human serum albumin were exposed in vitro in the presence of 10 mumols/L of tin and zinc metalloporphyrins at 37 degrees C for 30 minutes to light sources used clinically for phototherapy of neonates. Bilirubin in the model solutions was photodegraded to approximately 60% of dark control in cool white light (17 microW/cm2 per nanometer). The presence of zinc protoporphyrin and zinc mesoporphyrin further reduced the bilirubin concentration slightly, but the tin analogues caused a significant enhancement of degradation to 35% and 25% of dark control, respectively. The results provide evidence that the zinc and tin metalloporphyrins are photosensitizers capable of enhancing the native photodegradation of bilirubin in biologic matrices, but that the tin compounds are more potent. The metalloporphyrin time course, dose-response curve, oxygen effects, and efficacy of phototherapy light sources were also studied.

Management of neonatal hyperbilirubinemia: rational use of phototherapy

Phototherapy has been used to treat neonatal hyperbilirubinemia for more than three decades; however, it is only during the last ten years that an understanding of the mechanism of action of phototherapy has emerged. While visible light is known to photooxidize and photoisomerize bilirubin, recent data suggest that the formation of bilirubin structural isomers (lumirubin) is responsible for the decrement in serum bilirubin. This paper discusses current clinical recommendations for light dosage and wavelength and develops new guidelines based upon recent information of how light effects a reduction in the serum bilirubin concentration.

Hypocrellin-A sensitized photooxidation of bilirubin

Hypocrellin A (HA) extracted from Hypocrellia bambusae (b.et Br.) sace, a derivative of 3,10-dihydroxy-4,9-perylenequinone, is a highly effective photosensitizer. Kinetic studies of the HA-sensitized photooxidation of bilirubin IX alpha (BR) in different solvents in the presence of various active oxygen quenchers indicate that in aprotic solvents the photooxidation goes via a Type II (1O2) mechanism, whereas in alkaline protic solvents Type I (electron transfer from an excited state of HA to the ground state of oxygen or the BR substrate). Type II and probably free radical reactions may occur simultaneously.

Quantum yields for laser photocyclization of bilirubin in the presence of human serum albumin. Dependence of quantum yield on excitation wavelength

The quantum yield for laser photocyclization of bilirubin to lumirubin in the presence of human serum albumin (phi LR) was measured at five monochromatic excitation wavelengths in the range 450-530 nm. Solutions used were optically thin throughout the wavelength range and precautions were taken to exclude contributions from photocyclization of bilirubin XIII alpha impurities. The values obtained (7.2-18 x 10(-4] were lower than those previously reported and showed the following wavelength dependence: 457.9 less than 488.0 less than 501.7 less than 514.5 approximately equal to 528.7. However, the rate of lumirubin formation, normalized to constant fluence, decreased with wavelength over the same wavelength range and no evidence was found that photoisomerization of bilirubin to lumirubin is faster with green (514.5 or 528.7 nm) than with blue (457.9 or 488.0 nm) light. The stereoselectivity of the configurational isomerization of bilirubin to 4Z,15E and 4E,15Z isomers also was studied. This reaction became less regioselective for the 4Z,15E isomer with increasing wavelength. The observed wavelength dependence of phi LR and of the [4E,15Z]: [4Z,15E] ratio at photoequilibrium are consistent with an exciton coupling model in which intramolecular energy transfer can occur between the two pyrromethenone chromophores of the bilirubin molecule in the excited state. Relative rates of lumirubin formation in vivo at different excitation wavelengths and constant fluence were estimated for different optical thicknesses and for different skin thicknesses. These estimates suggest that the recently reported clinical equivalence of blue and green phototherapy lights probably reflects the marked variation of skin transmittance with wavelength more than wavelength-dependent photochemistry. The calculations also indicated that the optimal wavelength for phototherapy is probably on the long wavelength side of the bilirubin absorption maximum.

UV excitable fluorescence of lumirubin

Solutions of bilirubin in different solvents show negligible fluorescence when they are excited with UV light. After irradiation, blue-violet fluorescence (400-450 nm) is observed, whose intensity and peak position depend on the irradiation time. The isolation of pure lumirubin led us to attribute this fluorescence specifically to this photoisomer, even if small contributions from other photoproducts cannot be ruled out. The emission peak of the pure lumirubin in aqueous solution (phosphate buffer) is at 415 nm while the main excitation peak is at 315 nm. Finally, an interpretation of the observed fluorescence is proposed on the basis of the similarity of the present results with previously reported experimental data.

Critical period of bilirubin-induced cerebellar hypoplasia in a new Sprague-Dawley strain of jaundiced Gunn rats

Homozygous (j/j) and heterozygous (j/+) newborn Gunn rats of the Sprague-Dawley strain were photoirradiated for 24 h at scheduled postnatal days and the effects of irradiation on the cerebellar development were examined at 30 days of life. Improvement of the survival rate was the most notable effect of photoirradiation. A single 24-h dose of photoirradiation during a period of postnatal days 4-11 effectively prevented hypoplasia in the j/j rat cerebellum. No prevention by light was observed at days 3 and 12. It was found that the most effective day of irradiation on the cerebellar development of j/j rats was centered on postnatal day 7. When plasma bilirubin was assessed during the period of postnatal days 7-10, a distinct diminution of the concentration was observed, restricted to only the period of the light treatment. Although there were some differences in the effective day as well as in the degree of efficacy of phototherapy among cerebellar lobules or sublobules, day 7 was the most critical for cerebellar hypoplasia due to bilirubin.

Bilirubin photoconversion induced by monochromatic laser radiation. Comparison between aerobic and anaerobic experiments in vitro

Structural and geometric photoisomerization of bilirubin bound to human serum albumin was investigated. Solutions were irradiated with monochromatic light emitted by an Ar ion laser, the 457.9, 488.0 and 514.5 nm wavelengths being selected. Photoproducts were separated and analysed by h.p.l.c. Visible-absorption spectra of pure ZZ-bilirubin, ZE-bilirubin and lumirubin in the eluent were registered in the 350-550 nm region by collecting single fractions by h.p.l.c. Wavelength-dependence of bilirubin photoconversion was studied within photoequilibrium and up to a large decrement of the total concentration. Experiments were performed in aerobic and anaerobic conditions in order to assess the contribution of the photo-oxidation to the overall process. The presence of O2 was found to increase the rate of bilirubin degradation and unexpectedly to favour lumirubin production. The ability of 514.5 nm irradiation to induce bilirubin cyclization was definitively confirmed.

Study of the mechanism of the photochemical oxidation of bilirubin by high-performance liquid chromatography

The photochemical degradation of bilirubin was studied in vitro using high-performance liquid chromatography and spectrophotometry. Attention was centered on the formation of biliverdin, which is produced as an intermediate in the photooxidation catalysed by riboflavin. approximate values of the overall and partial relative rate constants were calculated using the physiochemical criteria for a pseudo-monomolecular reaction. A more precise evaluation was made by non-linear regression programmes on a Hewlett-Packard 9835 A computer. In addition to the formation of biliverdin, attention was also paid to accompanying processes affecting the reaction mechanism, which were explained as aggregation and dimerization of bilirubin and biliverdin. It was also found that during phototherapy of newborn babies suffering from hyperbilirubinaemia the level of biliverdin in the plasma increased. The results are discussed from the point of view of phototherapy.

Renal handling of bilirubin photoderivatives

The renal handling of unconjugated bilirubin in the dark and during light exposure was analyzed using an isolated rat kidney preparation. The parameters tested were pigment disappearance from the perfusion medium, pigment uptake by tissue, and its renal clearance. The results indicated that despite the fact that pigment disappearance from the medium was similar for both forms of pigment, the extraction ratio was higher for irradiated pigment than for pigment in the dark. When renal clearance of pigment was plotted vs pigment uptake of tissue, the results indicated that irradiated pigment may be more efficiently removed by the kidney. In addition, data on the rate of secretion of p-aminohippurate suggested that both pigment forms shared a common site for secretion.

Wavelength dependence of the geometric and structural photoisomerization of bilirubin bound to human serum albumin

The two quantitatively important photoisomers in bilirubin metabolism during phototherapy are (ZE)-bilirubin and (EZ)-cyclobilirubin. We describe in vitro studies on the wavelength dependence for the geometric (delta 4Z, delta 15Z----delta 4Z, delta 15E) and structural (endovinyl cyclization) photoisomerization of bilirubin bound to human serum albumin by a high performance liquid chromatography method. For the geometric photoisomerization from (ZZ)-bilirubin to (ZE)-bilirubin, the most effective wavelength in vitro was 410 nm. For the structural photoisomerization, green light at 510 nm is the most efficient for causing cyclization of (ZZ)-bilirubin to (EZ)-cyclobilirubin via (EZ)-bilirubin and this may depend on a larger cross-section of (EZ)-bilirubin than (ZZ)-bilirubin in this spectral region and/or on a larger quantum yield for cyclization than geometric photoisomerization.

The effect of bilirubin photoisomers on unbound-bilirubin concentrations estimated by the peroxidase method

Unbound bilirubin is oxidized to nearly colourless substances in the presence of H2O2 or ethyl hydroperoxide and horseradish peroxidase. To predict the risk of kernicterus (degenerated yellow pigmentation of nerve cells), this principle has been widely utilized for estimating the concentration of unbound bilirubin in hyperbilirubinaemic serum. However, the serum contains polar geometric photoisomers of bilirubin. Therefore, to clarify the effect of bilirubin photoisomer concentrations on unbound-bilirubin concentration, the concentration of bilirubin and its photoisomer and of unbound bilirubin in samples obtained from experiments in vivo and in vitro were simultaneously and individually estimated by h.p.l.c. and the peroxidase method. During photoirradiation, both in vivo and in vitro, the serum polar (ZE)-bilirubin IX alpha concentration increased remarkably, but unbound-bilirubin values were not affected at all. However, during experiments in vitro, unbound bilirubin concentrations increased only when concentrations of the rather polar (EZ)- and (EE)-cyclobilirubin IX alpha increased considerably in a human serum albumin-bilirubin solution irradiated with blue light. Thus it is concluded that unbound-bilirubin concentrations, and consequently the initial rate of the peroxidase reaction, is not accelerated by the increase in either (ZE)-bilirubin or (EZ)-cyclobilirubin concentration within the clinically observed range.

Transcutaneous bilirubinometry. III. Dermal bilirubin kinetics under green and blue light phototherapy

Using the transcutaneous bilirubinometer, we studied the response of cutaneous bilirubin to different colors of light during phototherapy. Three groups of ten infants were exposed to blue, green, and blue-green lights at a mean postnatal age ranging from 50 to 77 hours. Patched areas served as controls. Every 15 minutes during four hours of phototherapy, we obtained simultaneous measurements from exposed and covered areas. After the onset of phototherapy, transcutaneous bilirubinometer values from the covered areas in all groups remained stable. The overall rate of bleaching was lowest in the green light group and highest in the blue-green combination group. In this group of infants, green light appeared to enhance the effectiveness of blue light in reducing dermal bilirubin concentrations as measured by the transcutaneous bilirubinometer.

Phototherapy in a new light

Visible light phototherapy has been used in the treatment of neonatal jaundice for more than 25 years. This article reviews the current state of knowledge of how phototherapy works and provides a framework for understanding why green may soon become the color of choice for phototherapy lamps.

Effect of combined treatment with 2,3,7,8-tetrachlorodibenzo-p-dioxin and phototherapy on bilirubin metabolism in the jaundiced Gunn rat

2,3,7,8-Tetrachlorodibenzo-p-dioxin, a potent inducer of microsomal cytochrome P448-dependent monoxygenases, and phototherapy both accelerate bilirubin metabolism and decrease jaundice in Gunn rats. The effects of combined treatment with 2,3,7,8-tetrachlorodibenzo-p-dioxin and light were studied in these rats by applying phototherapy for 65 hr, beginning 5 days after induction with 2,3,7,8-tetrachlorodibenzo-p-dioxin. 2,3,7,8-Tetrachlorodibenzo-p-dioxin pretreatment caused a 75% decline in plasma bilirubin in 5 days, with no change thereafter, whether or not the rats were exposed subsequently to phototherapy. In the uninduced rats, plasma bilirubin levels declined by 55% after 40 hr of phototherapy. As determined by [14C]bilirubin kinetics, both 2,3,7,8-tetrachlorodibenzo-p-dioxin and phototherapy increased fractional bilirubin turnover and decreased the total bilirubin pool. In the 2,3,7,8-tetrachlorodibenzo-p-dioxin-induced rats, the contracted bilirubin pool shifted from skin to liver, but these tissue pools did not change further during phototherapy. By contrast, in uninduced rats, phototherapy decreased the cutaneous bilirubin pool, which is the main target of phototherapy. 2,3,7,8-Tetrachlorodibenzo-p-dioxin was more effective than phototherapy in diminishing plasma bilirubin levels and the total bilirubin pool, but the combined treatment (2,3,7,8-tetrachlorodibenzo-p-dioxin followed by phototherapy) was no more effective than 2,3,7,8-tetrachlorodibenzo-p-dioxin alone.