Jean-Claude Lavoie

Influence of Bilirubin on the Antioxidant Capacity of Plasma in Newborn Infants

In vitro, bilirubin is a strong antioxidant, but in vivo its capacity to act as a scavenger of toxic oxygen radicals remains poorly documented. The aim of this study was to evaluate of bilirubin had antioxidant properties in jaundiced infants. The antioxidant capacity of neonatal plasma was measured in Trolox equivalents (TEAC, mmol/l) and correlated in vitro with plasma bilirubin concentrations (r2 = 0.99). Plasma TEAC was compared before and after exchange transfusions for neonatal hyperbilirubinemia (250-435 mumol/l). The antioxidant properties of the paired blood samples before and after exchange transfusions (TEAC: 1.67 +/- 0.12 vs. 1.37 +/- 0.09 mmol/l, n = 11) varied in proportion to the serum bilirubin levels. The changes in other antioxidants were not large enough to account for the magnitude of change in antioxidant capacity. Therefore, in vivo, the plasma antioxidant capacity of jaundiced newborn infants is related to the level of bilirubin.

Gender and Maturation Affect Glutathione Status in Human Neonatal Tissues

Gender and maturation affect glutathione status in human neonatal tissues. The objective was to verify if human tissues derived from baby girls had a greater ability then tissues derived from males to stimulate the glutathione-reductase, when faced with an oxidative challenge. In vitro, the effect of a calibrated oxidative challenge was studied in endothelial cells. In vivo, the effect of a clinically relevant oxidative challenge was studied in cells from tracheal aspirates derived from oxygen-dependent newborn infants. In endothelial cells, the oxidant tert-butylhydroperoxide had a stimulating effect on GSSG-R activity in cells derived from females. The peroxide produced a time, concentration and gender-dependent cytotoxicity, with female-derived cells exhibiting a better viability. In vivo, the intracellular total glutathione content was higher in female-derived cells and in cells from more mature babies; postnatal age and gestational age had a positive effect on the activity of GSSG-R. Oxygen (FiO2 > or = 0.3) was associated with a lower activity of GSSG-R in boys, early in life. Considering that glutathione is a central element in the antioxidant defense, these results suggest that specific tissues derived from the baby girl are potentially better protected against an oxidative stress than those derived from the boy.

Neonatal Oxygen Exposure in Rats Leads to Cardiovascular and Renal Alterations in Adulthood

Long-term vascular and renal consequences of neonatal oxidative injury are unknown. Using a rat model, we sought to investigate whether vascular function and blood pressure are altered in adult rats exposed to hyperoxic conditions as neonates. We also questioned whether neonatal O2 injury causes long-term renal damage, important in the pathogenesis of hypertension. Sprague-Dawley pups were kept with their mother in 80% O2 or room air from days 3 to 10 postnatal, and blood pressure was measured (tail cuff) from weeks 7 to 15. Rats were euthanized, and vascular reactivity (ex vivo carotid rings), oxidative stress (lucigenin chemiluminescence and dihydroethidium fluorescence), microvascular density (tibialis anterior muscle), and nephron count were studied. In male and female rats exposed to O2 as newborns, systolic and diastolic blood pressures were increased (by an average of 15 mm Hg); ex vivo, maximal vasoconstriction (both genders) and sensitivity (males only) specific to angiotensin II were increased; endothelium-dependant vasodilatation to carbachol but not to NO-donor sodium nitroprussiate was impaired; superoxide dismutase analogue prevented vascular dysfunction to angiotensin II and carbachol; vascular superoxide production was higher; and capillary density (by 30%) and number of nephrons per kidney (by 25%) were decreased. These data suggest that neonatal hyperoxia leads in the adult rat to increased blood pressure, vascular dysfunction, microvascular rarefaction, and reduced nephron number in both genders. Our findings support the hypothesis of developmental programming of adult cardiovascular and renal diseases and provide new insights into the potential role of oxidative stress in this process.

Paradoxical Role of Ascorbic Acid and Riboflavin in Solutions of Total Parenteral Nutrition: Implication in Photoinduced Peroxide Generation

In the presence of light, a multivitamin preparation is the main source of peroxides in solutions of total parenteral nutrition (TPN). This preparation contains two photosensitive products, 5′-phosphate flavin mononucleotide(FMN) and polysorbates (PS), as well as electron donors such as ascorbate(AH). We hypothesized that the admixture of FMN or PS with electron donors generates peroxides in TPN and alters the quality of nutrients. Using xylenol orange, peroxide concentrations were measured in solutions containing AH, FMN, and/or PS in water, a dextrose solution, an amino acid preparation, and a lipid emulsion. Thiol functions were evaluated by reduction of 5,5-dithiobis(2-nitrobenzoic acid) in the amino acid preparation. After 24-h light exposure, dextrose solutions with admixtures of AH + FMN or AH + FMN + PS generated peroxides at concentrations similar to those observed in a 1% multivitamin solution, and over three times higher than those observed with FMN, PS, or AH alone. However, in the presence of amino acids, FMN alone induced a generation of peroxides comparable to that observed with FMN + AH. In the lipid emulsion, peroxides increased over 3-fold in the presence of FMN or FMN + AH. The addition of catalase suggested that lipid peroxides and H2O2 were produced, and the loss of thiol function suggested that an oxidation of amino acids occurred. When exposed to light, FMN induces reactions with amino acids, polyunsaturated fatty acids, and even AH, altering the quality of nutrients. Paradoxically, AH without FMN has a protective effect on peroxide generation in TPN.

Protecting solutions of parenteral nutrition from peroxidation

BACKGROUND Light exposure induces the generation of peroxides in solutions of total parenteral nutrition (TPN). Peroxide toxicity has been documented in cell, in tissue, and in isolated organs. To decrease the infused peroxide load and to protect the quality of the parenteral nutrients, we tested the photoprotective properties of different infusion sets. METHODS Solutions of fat-free TPN and all-in-one total nutrient admixture (TNA) were run through sets of bags (clear and covered) and tubings (clear and colored: black, orange, and yellow) offering different levels of protection against light. Peroxide levels were determined by ferrous oxidation of xylenol orange, thiol functions by the 5,5,-dithiobis(2-nitrobenzoic acid) technique, and absorbance of tubings by spectroscopy. RESULTS Protection of only the bag had little effect on peroxide generation. In fat-free TPN solutions kept in covered bags, peroxide concentrations were 1.5 to 2 times higher when run through clear compared with colored tubings. When exposed to phototherapy or in the presence of lipids, peroxides were two to three times higher with the clear compared with the black tubing; meanwhile, orange and yellow tubings offered varying levels of protection related to their light-absorbing properties. Colored tubings offered a greater protection against the disappearance of thiol functions. CONCLUSIONS Covering bags and using orange and yellow tubings may be a practical solution to reduce infused peroxide loads from about 400 to 100 microM. This is especially relevant in patients with an immature or a compromised antioxidant capacity or when phototherapy or preparations of TNA are used.

Photooxidation of Parenteral Multivitamins Induces Hepatic Steatosis in a Neonatal Guinea Pig Model of Intravenous Nutrition

Photooxidation of multivitamin solutions results in the generation of peroxides. Because peroxides are associated with hepatic steatosis and fibrosis as well as cholestasis, we questioned whether multivitamins are implicated in hepatic complications of parenteral nutrition. Guinea pig pups were assigned to groups receiving intravenously either total parenteral nutrition, photo-protected or not, or a control solution (5% dextrose + 0.45% NaCl) supplemented with either a) multivitamins; b) photo-protected multivitamins; c) multivitamins without riboflavin; or d) peroxides (H2O2, tert-butylhydroperoxide). After 4 d, liver was sampled for histology and isoprostane-F2α levels, a marker of radical attack. Multivitamins as well as total parenteral nutrition were associated with steatosis (scored 0–4), the severity of which was reduced (p < 0.05) by photo protection. Although H2O2 is the major peroxide contaminating multivitamins, it did not induce steatosis scores different than the controls. Compared with controls, hepatic isoprostane-F2α content increased in animals infused with H2O2 (p < 0.05), but not in those infused with Multi-12 pediatric multivitamins or total parenteral nutrition. Results suggest that peroxides and/or free radicals are not mediators of the induction of steatosis observed with infusion of photo-exposed multivitamins, as there was no correspondence between histologic findings and hepatic levels of isoprostanes. It is suspected that a component of the multivitamin solution becomes hepato-toxic after photo-exposure, as indicated by the protective effect observed when withdrawing riboflavin. Photo-oxidation of multivitamins might be the common link between reports involving amino acids, lipids, and light exposure in the ethiology of hepatic complications of parenteral nutrition.

Contribution of Multivitamins, Air, and Light in the Generation of Peroxides in Adult and Neonatal Parenteral Nutrition Solutions

OBJECTIVE: To compare the concentrations of peroxides between adult and neonatal total parenteral nutrition (TPN) solutions in response to protection against inducers of peroxidation such as multivitamins and exposure to light or air. METHODS: Peroxide concentrations were measured in freshly prepared adult and neonatal solutions of fat-free TPN in four settings: with or without an air inlet, and protected or unprotected from ambient light. An oxygen washout was performed by exposing a fat-free neonatal TPN solution to a continuous flow of nitrogen. RESULTS: Globally, light was the main inducer of peroxides in adult and neonatal solutions. However, in adult solutions the concentration of peroxides remained <15 μmol/L, while in neonatal solutions the peroxide concentration was as high as 300 μmol/L in ambient light. Although the oxygen washout did prevent the generation of peroxides, avoiding air inlet was not as effective as was photoprotection in decreasing the important peroxide load in the neonatal TPN solution. CONCLUSIONS: The higher concentration of peroxides found in neonatal solutions compared with adult solutions is explained by the differences in nutrient composition between the two solutions. Contamination of parenteral solutions by air during compounding accounts for the photoinduced generation of peroxides in TPN solutions. It is more convenient to protect TPN solutions from light exposure after the admixture of the multivitamin solution than to avoid contact with oxygen.

Antiperoxide activity of sodium metabisulfite: A double-edged sword

Sulfites are chemical substances that are used widely in the pharmaceutical industry to reduce or prevent oxidation. Sodium metabisulfite (Na2S2O5) is still present in several parenteral amino acid solutions. Since intravenous lipid emulsions are contaminated by hydroperoxides, we evaluated whether metabisulfite had an antioxidant activity against hydroperoxides. In vitro, Na2S2O5 inhibited the oxidant activity of H2O2, tert-butyl-, and cumene hydroperoxides. The antioxidant capacity of metabisulfite was supported in vivo by the lower (P < 0.01) excretion of malondialdehyde, a stable end product of lipid peroxidation, in babies receiving metabisulfite in their parenteral nutrition. However, for concentrations outside the range found in solutions for parenteral nutrition, the reduction of hydroperoxides by Na2S2O5 could transform this compound into an oxidant, like a sulfite radical. It is suggested that metabisulfite has antiperoxide properties that, under specific conditions, contribute to the generation of toxic oxidants.

Determinants of oxidant stress in extremely low birth weight premature infants

Early in life, premature neonates are at risk of oxidant stress. They often require total parenteral nutrition (TPN), which is, however, contaminated with oxidation products. Coadministration of parenteral multivitamins (MVP) with a lipid emulsion (LIP) prevents lipid peroxidation. We hypothesized that LIP+MVP induces a lower oxidant load compared to preparations in which MVP is administered with an amino acid solution (AA+MVP). The aim of this study was to compare markers of oxidant stress in premature neonates receiving LIP+MVP, either exposed to or protected from light, or AA+MVP. Antioxidant vitamins, the redox potential of glutathione, isoprostane, and dityrosine were measured in urine or blood sampled on days 7 and 10 from babies requiring low (<0.25) vs high (≥0.25) fractional inspired O(2). Oxygen supplementation induced a more oxidized redox potential and increased dityrosine with AA+MVP only. Adding MVP in the lipid rather than the amino acid moiety of TPN protects against the oxidant stress associated with O(2) supplementation. Photoprotection added no benefit. Blood transfusions were found to produce a pronounced oxidant load masking the beneficial effect of LIP+MVP. The impact of these findings relates to a strong association between a more oxidized redox potential and later bronchopulmonary dysplasia, a clinical marker of oxidant stress.

3β-Hydroxysteroid dehydrogenase activity in human fetal membranes

Abstract A 36-hydroxysteroid dehydrogenase (3βHSD) was demonstrated in term human fetal membranes (chorion and amnion) with both dehydroepiandrosterone (3β-hydroxy-5-androsten-17-one) and pregnenolone (3β-hydroxy-5-pregnen-20-one as substrates, and the subcellular distribution substrate and nucleotide specificity of the enzyme was studied. In both membranes the microsomal fraction (particles which sedimented at 105,000 g after 90 min) had the highest specific activity. The chorion was more active than the amnion but the enzyme in both tissues had similar substrate and nucleotide specificity. NAD was the preferred cofactor, and pregnenolone was a better substrate than dehydroepiandrosterone in the presence of NAD. However, with NADP as cofactor both steroids were equally good substrates. When the 3β-hydroxysteroid dehydrogenase activity of chorion microsomes was compared with that of placental microsomes, the specific activities were found to be of the same order of magnitude, and the substrate, nucleotide specificity and steroid binding properties were almost identical.