Multivitamin solutions for enteral supplementation: a source of peroxides

Vitamin C in sepsis

Bacterial bloodstream infection causes septic syndromes that range from systemic inflammatory response syndrome (SIRS) and encephalopathy to severe sepsis and septic shock. Microvascular dysfunction, comprising impaired capillary blood flow and arteriolar responsiveness, precedes multiple organ failure. Vitamin C (ascorbate) levels are low in critically ill patients. The impact of ascorbate administered orally is moderate because of its limited bioavailability. However, intravenous injection of ascorbate raises plasma and tissue concentrations of the vitamin and may decrease morbidity. In animal models of polymicrobial sepsis, intravenous ascorbate injection restores microvascular function and increases survival. The protection of capillary blood flow and arteriolar responsiveness by ascorbate may be mediated by inhibition of oxidative stress, modulation of intracellular signaling pathways, and maintenance of homeostatic levels of nitric oxide. Ascorbate scavenges reactive oxygen species (ROS) and also inhibits the NADPH oxidase that synthesizes superoxide in microvascular endothelial cells. The resulting changes in redox-sensitive signaling pathways may diminish endothelial expression of inducible nitric oxide synthase (iNOS), tissue factor and adhesion molecules. Ascorbate also regulates nitric oxide concentration by releasing nitric oxide from adducts and by acting through tetrahydrobiopterin (BH4) to stimulate endothelial nitric oxide synthase (eNOS). Therefore, it may be possible to improve microvascular function in sepsis by using intravenous vitamin C as an adjunct therapy.

Urinary Metabolites of Oxidative Stress and Nitric Oxide in Preterm and Term Infants

BACKGROUND

Many neonatal diseases have been associated with oxidative stress and altered nitric oxide status.

OBJECTIVE

To determine the effects of clinical interventions on the levels of urinary peroxides, a marker of oxidative stress, and urinary nitrate/nitrites, indices of nitric oxide production and metabolism, in the first 72 h of life in premature infants.

METHODS

A single, spot urine sample was collected from 82 premature and 20 healthy term infants within the first 72 h of life. The peroxide levels were quantified using a fluorometric method, and nitrate/nitrite levels were quantified by chemiluminescence.

RESULTS

Premature infants had a median peroxide level of 10.0 micromol/mmol creatinine (Cr) (interquartile range 4.8-20.0 micromol/mmol Cr). These values were significantly higher than term infants (median 5.0 micromol/mmol Cr, interquartile range 2.7-10.0 micromol/mmol Cr). Urinary nitrate/nitrite levels were not significantly different between preterm (220.5 micromol/mmol Cr, interquartile range 161-287 micromol/mmol Cr) and healthy term infants (244 micromol/mmol Cr, interquartile range 194-316 micromol/mmol Cr). For urinary peroxides, infants on TPN had significantly higher urinary peroxide levels than infants who were not on TPN at the time of urine collection (p = 0.006). Administration of indomethacin was associated with lower levels of urinary nitrate/nitrites (p = 0.0003). Both effects remained significant after controlling for gestational age, degree of respiratory distress and day of urine collection.

CONCLUSION

Monitoring the level of both peroxides and nitrate/nitrite may offer added information about the degree of oxidative stress experienced by a newborn but needs to account for clinical and therapeutic interventions.