John F Ennever

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.

Phototherapy for Neonatal Jaundice

Visible light phototherapy treatment for neonatal hyperbilirubinemia is no doubt the most common therapeutic use of light. Introduced into routine use in the late 1960’s, phototherapy has been used on hundreds of thousands of infants in the United States, and perhaps millions of infants worldwide. Phototherapy has been proven effective in several large clinical trials (Brown et al . , 1985; Tan and Boey, 1986), and no significant toxicity has been identified. Bilirubin has been intensively studied over the years, partially because of its clinical importance. As a reward for this effort, we now know a great deal about the photochemistry of bilirubin in vitro and have a reasonable idea about which processes are important in the irradiated jaundiced infant. The photochemistry of bilirubin in vitro and in vivo has been reviewed recently (Lightner and McDonagh, 1984; McDonagh and Lightner, 1985a; Stoll, 1986; Bonnett and Ioannou, 1987). This review will focus on recent developments in the photochemistry of bilirubin and the metabolism of bilirubin photoproducts in human infants. Related topics, such as mechanisms of bilirubin toxicity (Odell and Schutta, 1985) and studies of bilirubin-albumin binding, are beyond the scope of this review. A linear representation of the structure of bilirubin I X a is shown in Fig. 1. It is not obvious from such a representation why a molecule with two propionic acid side chains and two lactam functional groups is nearly insoluble in water at neutral pH and therefore requires glucuronidation before it can

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

ABSTRACT: 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 < 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

Summary: 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.

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

Summary: 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.

WAVELENGTH DEPENDENCE OF THE QUANTUM YIELD FOR THE STRUCTURAL ISOMERIZATION OF BILIRUBIN

The quantum yield and the relative photochemical yield for lumirubin formation from bilirubin bound to human albumin were determined at eight wavelengths from 410 to 520 nm. The quantum yield averaged 0.0015 for irradiation between 450 and 490 nm. At 410 and 430 nm the quantum yield was slightly lower. At the long wavelength end of the absorption band, from 500 to 520 nm, the quantum yield averaged 0.003. The relative photochemical yield, normalized to constant fluence, was greatest at 500 nm.

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

Abstract: 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.

QUANTUM YIELDS FOR THE CYCLIZATION AND CONFIGURATIONAL ISOMERIZATION OF 4E, 15Z-BILIRUBIN

Abstract— 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.

Urinary excretion of an isomer of bilirubin during phototherapy.

ABSTRACT: 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.

Potential for Genetic Damage from Multivitamin Solutions Exposed to Phototherapy Illumination

Summary: 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.