The exposure of red cells to phototherapy light in the presence of a sensitizer (bilirubin) resulted in oxidative injury to the red cell membrane as manifested by a significant increase in the concentration of the products of lipid peroxidation (TBA reactants and diene conjugation) in the membrane and hemolysis. To induce a photo-oxidized membrane injury, the sensitizer (bilirubin) has to be membrane bound. Thus, by altering the availability of free bilirubin in the red cell suspension through changes in the molar concentration ratio of bilirubin to albumin, one is able to regulate the occurrence and extent of the oxidative red cell membrane injury. The clinical implications of these findings are discussed.

Laminin, a glycoprotein component of basal laminae, is synthesized and secreted in culture by a human malignant cell line (JAR) derived from gestational choriocarcinoma. Biosynthetically labeled human laminin subunits A (Mr approximately 400,000) and B (Mr = 200,000 doublet) are glycoslyated with asparagine-linked high mannose oligosaccharides that are processed to complex oligosaccharides before the laminin molecule is externalized by the cell. The rate-limiting step in the processing of the asparagine-linked glycans of laminin is at the point of action of alpha-mannosidase I since the principal laminin forms that accumulate in JAR cells contain Man9GlcNAc2 and Man8GlcNAc2 oligosaccharide units. The combination of subunits to form the disulfide-linked laminin molecule (Mr approximately 950,000) occurs rapidly within the cell at a time when the subunits contain these high mannose oligosaccharides. The production of laminin is limited by the availability of the A subunit such that excess B subunit forms accumulate intracellularly as uncombined B and a disulfide-linked B dimer. Pulse-chase kinetic studies establish these B forms as intermediates in the assembly of the laminin molecule. The fully assembled laminin undergoes further oligosaccharide processing and translocation to the cell surface, but uncombined B and B dimer are neither processed nor secreted to any significant extent. Therefore, laminin subunit combination appears to be a prerequisite for intracellular translocation, processing, and secretion. The mature laminin that contains complex oligosaccharides does not accumulate intracellularly but is rapidly externalized upon completion, either secreted into the culture medium (25%) or associated with the cell surface (75%) as determined by susceptibility to degradation by trypsin. About one-third of the laminin molecules secreted or shed by JAR cells into the chase medium contain a smaller A subunit form that appears to have been modified by limited proteolytic cleavage. The putative proteolytic event is closely timed to the release of the laminin into the culture medium.

Vitamin E and beta-carotene are two important natural antioxidants. However, the mean (+/- SD) serum concentrations of beta-carotene in the cord blood of term (17.9 +/- 4.4 micrograms/dl) and preterm (14.04 +/- 4.7 micrograms/dl) infants are one eighth the concentration in the maternal serum (131 +/- 43 micrograms/dl). Likewise the serum concentrations of vitamin E in the term (0.31 +/- 0.09 mg/dl) and preterm (0.29 +/- 0.08 mg/dl) infants are one-third the concentration in the maternal serum (0.97 +/- 0.16 mg/dl). Human breast milk, particularly colostrum, contains very high concentrations of both vitamin E (3.28 +/- 2.93 mg/dl) and beta-carotene (213 +/- 166 micrograms/dl). Thus the breast-fed, term infant attains serum levels of both vitamin E and beta-carotene comparable to those in the adult within 4 to 6 days of breast-feeding. This study shows that the seeming barrier in the fetus to access to the antioxidants vitamin E and beta-carotene, in rapidly corrected and the substances are replenished postnatally through breast-feeding. This study therefore alludes to the possible role of breast-feeding in providing for the infant's defense against oxygen toxicity.