Quantum yields for the cyclization and configurational isomerization of 4E,15Z-bilirubin.

Extraction of a solution of bilirubin configurational isomers in chloroform with an aqueous solution of human serum albumin was found to remove selectively the 4Z,15E-isomer. This phenomenon was used to develop a method for the purification of the 4E,15Z-isomer of bilirubin. The quantum yield for the cyclization and configurational isomerization of the 4E,15Z-isomer bound to a molar excess of human serum albumin was measured at 450 and 510 nm. The quantum yield for cyclization to form lumirubin was 0.12 and 0.19 at 450 and 510 nm, respectively. The quantum yield for configurational isomerization to form 4Z,15Z-bilirubin was 0.03 and 0.05 at 450 and 510 nm. An analysis of previously published data on the quantum yield for the formation of lumirubin from 4Z, 15Z-bilirubin bound to human serum albumin suggests that all of the formation of lumirubin may occur via consecutive photochemical processes with the 4E,15Z-isomer as an intermediate.

Blue light, green light, white light, more light: treatment of neonatal jaundice.

This article reviews the current understanding of how phototherapy, the most widely used treatment of neonatal jaundice, uses light energy to pump bilirubin out of a jaundiced infant. It provides a framework for understanding the often conflicting results of clinical comparisons of various phototherapeutic regimens, and stresses the importance of light intensity in the overall effectiveness of phototherapy.

Rapid clearance of a structural isomer of bilirubin during phototherapy.

During phototherapy for neonatal jaundice, bilirubin is converted into a variety of photoproducts. Determination of the relative importance of these photoproducts to the elimination of bilirubin requires knowledge of their rates of excretion. We have measured the rate at which the structural isomer of bilirubin, lumirubin, disappeared from the serum of nine jaundiced premature infants after the cessation of phototherapy. In all patients studied, the decline in serum lumirubin could be approximated by a first-order rate equation with a half-life of 80 to 158 min. This rate of disappearance is much faster than that previously determined for the other major bilirubin photoproducts. In samples of bile aspirated from the duodenum of infants undergoing phototherapy, lumirubin was the principal bilirubin photoproduct found. These results indicate that formation and excretion of lumirubin is an important route for bilirubin elimination during phototherapy.

Fatty acid enhancement of the quantum yield for the formation of lumirubin from bilirubin bound to human albumin.

During phototherapy for neonatal jaundice, bilirubin is converted into a number of different polar photoproducts. Because fatty acids are bound to human albumin in vivo and have been shown to affect the binding of bilirubin to albumin, we examined the effect of various fatty acids on the photochemistry of albumin-bound bilirubin. Fatty acids of carbon chain length of 10 or more were found to increase by as much as 3-fold the quantum yield for formation of lumirubin, an intramolecularly cyclized isomer of bilirubin. The binding of these same fatty acids was found to affect visible absorption and circular dichroic spectra of the bound bilirubin, a finding previously interpreted to be the result of a conformational change in the bilirubin. The increased quantum yield for the formation of lumirubin appears to be the result of an allosterically induced conformational change in bilirubin which is bound to albumin.

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.

Ionic effects on the structure of nucleoprotein cores from adenovirus.

Nucleoprotein cores, prepared from adenovirus type 5 with a deoxycholate/heat treatment, consist of the viral DNA and two major internal proteins. The core particles exhibit structural characteristics that are highly reproducible and dependent on their ionic environment. In low-ionic-strength buffer, the cores had a sedimentation coefficient of 180 S and appeared in the electron microscope as homogeneous particles with distinct centers from which numerous arms and loops radiated. Condensation of the cores was induced by Mg2+ or Ca2+ over the range 0 to 1 mM. The sedimentation coefficient increased monotonically with divalent cation concentration, reaching a maximum of 405 S in 1 mM Mg2+. A corresponding condensation in the core structure was observed by electron microscopy. Increasing concentrations of NaCl also produced a conformational change in the cores, with an almost linear increase in sedimentation velocity up to 274 S in 0.04 M NaCl. Between 0.05 and 1.0 M NaCl, the cores were insoluble. In 2.0 M NaCl, the cores were again soluble with an s20,w of 228 S. Under all ionic strength conditions in which the cores were soluble, both core proteins remained bound to the DNA.

Effect of spectral distribution on isomerization of bilirubin in vivo.

The purpose of our study was to compare the effects of narrow-spectrum blue light and broad-spectrum white light on the production of bilirubin photo-isomers in human infants with jaundice. Twelve preterm infants were studied under both white and blue light. Irradiance at 450 nm was controlled at 12 microW/cm2/nm for both light sources. Each light condition (white or blue) was administered for 12 hours. Bilirubin isomers (4Z,15E-bilirubin and lumirubin) were measured before therapy and after 12 hours of each sequential light condition. The percentage of 4Z,15E-bilirubin was greater under blue light than under white light (P less than 0.01) phototherapy. There was no significant difference in percentage lumirubin under white or blue light therapy. Our data indicate that blue light is more effective than white light in producing 4Z,15E-bilirubin in vivo. Our study demonstrates that when irradiance in the bilirubin absorbance spectrum is constant, the color of light (spectral distribution) will determine the relative concentrations of photo-isomers produced.

Bilirubin photoisomerization in premature neonates under low- and high-dose phototherapy.

Photoisomerization of native bilirubin to more polar configurational isomers (Z,E-bilirubin) and structural isomers (lumirubin) was studied in 20 premature infants with physiologic jaundice to determine the effect of low-dose (6 microW/cm2/nm) v high-dose (12 microW/cm2/nm) phototherapy. Patients were assigned prospectively to receive either low- or high-dose treatment. Study groups were comparable with regard to birth weight, gestational age, and total bilirubin prior to the initiation of phototherapy. Treatment was administered with white light produced by a commercially available halogen-tungsten lamp. Dose was measured periodically during the study to ensure a uniform distribution of irradiance and constant exposure. Sera for photoisomers were obtained before initiation of treatment and at two, four, and eight hours. Photoisomers expressed as a percent of total bilirubin were determined using high-pressure liquid chromatography. Serum proportion of both configurational and structural isomers increased with the duration of phototherapy in both treatment groups. There was no significant difference between the percent of configurational isomers in low- and high-dose phototherapy groups. However, high-dose treatment produced a significantly higher proportion of the structural isomer lumirubin after four hours (0.7% low dose v 1.3% high dose, P less than .05). These data confirm that phototherapy results in both configurational and structural isomerization of bilirubin in vivo. Furthermore, the previously described "dose" effect of phototherapy may be attributed to the production of the structural isomer, lumirubin.

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.

Phototherapy for neonatal jaundice: in vivo clearance of bilirubin photoproducts.

Phototherapy results in the conversion of native bilirubin to more water-soluble configurational and structural isomers. The serum half-life for the configurational isomer, the principal photoproduct in vivo, was determined by high pressure liquid chromatography in six premature infants following cessation of phototherapy. The mean half-life for this isomer was 15 h. The excretion of this isomer, calculated from the measured half-life, is less than half of daily bilirubin production, and therefore cannot account for the total bilirubin elimination observed during phototherapy. The serum concentration of the structural isomer, lumirubin, is lower than that of the configurational isomer; however, excretion is more rapid (serum half-life less than 2 h). Because of its rapid excretion, lumirubin may be an important pathway for bilirubin elimination during phototherapy.

Phototherapy for neonatal jaundice: in vitro comparison of light sources.

Phototherapy results in the conversion of bilirubin to more water-soluble isomers. Six clinically used phototherapy lamps which differ in their emission spectra have been compared in their ability to produce configurational and structural isomers of bilirubin in vitro. For all of the lamps, the initial rate of configurational isomerization was highly correlated (r = 0.969) with the intensity of irradiation falling within the bilirubin absorption band. The percentage of the total bilirubin converted to the configurational isomer at equilibrium was dependent upon the spectral distribution of the lamp, and was greatest (26.2 +/- 1.3%) with the special blue lamp, which has a narrow spectral output centered at 445 nm. The rate of formation of the structural isomer, lumirubin, was generally dependent upon the intensity of irradiation within the bilirubin absorption band.

Phototherapy for neonatal jaundice: optimal wavelengths of light.

Phototherapy results in transformation of bilirubin to more water-soluble isomers. The efficacy of monochromatic visible light from 350 to 550 nm in the fastest photoisomerization reaction was quantitated by high-pressure liquid chromatography. The most effective wavelengths in vitro (i.e., leading to greater than 25% photoisomer) were in the blue spectrum from approximately 390 to 470 nm. Green light (530 nm) was not only ineffective for production of photoisomer, but capable of reversing the reaction. The results indicate that any clinically useful phototherapy unit must include the blue portion of the visible spectrum, and suggest that the effectiveness of phototherapy may be increased by elimination of green light.

Short communication. Photochemical reactions of riboflavin: covalent binding to DNA and to poly (dA) . poly (dT).

Standard phototherapy illumination of human cells in the presence of riboflavin is known to produce single-strand breaks in intracellular DNA. A new photochemical reaction is described between riboflavin and purified DNA in which an adduct is formed. Unlike the previously described oxygen-dependent reaction between light-activated riboflavin and deoxyguanosine, this new photochemical reaction is oxygen-independent and involves deoxyadenosine or thymidine.

Potential for genetic damage from multivitamin solutions exposed to phototherapy illumination.

The ability of standard phototherapy illumination to produce damage in intracellular DNA is well established. In this study, the addition of a dilute solution (1:6400) of a clinically-used multivitamin concentrate to human KB cells was found to enhance the generation of single-strand DNA breaks produced by broad-spectrum fluorescent light. The effect of the exogenous photosensitizing agent (multivitamins) was blocked by the enzyme catalase; thus, the photoproduct responsible for the DNA modification was hydrogen peroxide, an extremely reactive molecule capable of damaging a variety of biologic macromolecules.

Photodynamic reaction of riboflavin and deoxyguanosine.

Previous studies have demonstrated that phototherapy depresses serum riboflavin in jaundiced infants. The potential long-term hazards of this in vivo reaction may be significant in view of the in vitro reaction of riboflavin which modifies intracellular DNA in eukaryotic and prokaryotic cells. Previous investigations have suggested that the DNA-modifying activity of riboflavin results from the generation of singlet oxygen and photooxidation of the guanine moieties of the DNA. In the present study, we demonstrate that singlet oxygen is not involved in the photodynamic reaction of riboflavin and deoxyguanosine.