Background: Cysteine (CYS) is accepted as an indispensable amino
acid for infants receiving parenteral nutrition (PN), and CYS is unstable in
solution. Thus, developing a method to supply CYS in PN for neonates is
needed. N-acetyl-l-cysteine (NAC) is stable in solution
and safe for use in humans; therefore, NAC may be a means of supplying
parenteral CYS. Methods: We determined the bioavailability of NAC in
intravenously (IV)-fed piglets randomized to 1 of 4 diet treatments, each
supplying 0.3 g/kg/d methionine and either 0.2 g/kg/d CYS (CON), 0 NAC
(zeroNAC), 0.13 NAC (lowNAC), or 0.27 g/kg/d NAC (highNAC). Piglets (2 days
old; 1.8 kg, n = 20) were surgically implanted with femoral and jugular
catheters. On day 3 postsurgery, test diets were initiated and continued until
day 8. Piglets were weighed daily. Blood was sampled 6 hours before test diet
initiation and at 0, 6, 12, 18, 24, 36, 48, 60, 72, 84, 96, 108, and 120
hours. Urine was collected on ice in 24-hour sample periods. Results:
Total mean weight gain was not different between groups; however, average
daily gain in the zeroNAC and lowNAC groups declined significantly (p< .05) over the 5-day treatment period. Nitrogen retention was similar
between the CON and highNAC groups, both were higher than the lowNAC group,
and the zeroNAC treatment produced the lowest nitrogen retention. NAC percent
retention was not different between lowNAC and highNAC and was 85.4% and
82.6%, respectively. Plasma NAC was higher in highNAC than lowNAC (p< .05). Conclusions: These data demonstrate that NAC is available
as a precursor for CYS to support growth and protein (nitrogen) accretion in
piglets administered a parenteral solution.
Stepwise addition of N-acetyl-l-cysteine to a limiting sulfur amino acid parenteral solution significantly increased nitrogen retention and growth in neonatal piglets. Compared with a solution containing l-cysteine, equal growth rates and nitrogen retention were achieved with an equimolar amount of N-acetyl-l-cysteine.