N-acetylcysteine prevents spatial memory impairment induced by chronic early postnatal glutaric acid and lipopolysaccharide in rat pups.

BACKGROUND AND AIMS:Glutaric aciduria type I (GA-I) is characterized by accumulation of glutaric acid (GA) and neurological symptoms, such as cognitive impairment. Although this disease is related to oxidative stress and inflammation, it is not known whether these processes facilitate the memory impairment. Our objective was to investigate the performance of rat pups chronically injected with GA and lipopolysaccharide (LPS) in spatial memory test, antioxidant defenses, cytokines levels, Na+, K+-ATPase activity, and hippocampal volume. We also evaluated the effect of N-acetylcysteine (NAC) on theses markers. METHODS:Rat pups were injected with GA (5 umol g of body weight-1, subcutaneously; twice per day; from 5th to 28th day of life), and were supplemented with NAC (150 mg/kg/day; intragastric gavage; for the same period). LPS (2 mg/kg; E.coli 055 B5) or vehicle (saline 0.9%) was injected intraperitoneally, once per day, from 25th to 28th day of life. Oxidative stress and inflammatory biomarkers as well as hippocampal volume were assessed. RESULTS:GA caused spatial learning deficit in the Barnes maze and LPS potentiated this effect. GA and LPS increased TNF-α and IL-1β levels. The co-administration of these compounds potentiated the increase of IL-1β levels but not TNF-α levels in the hippocampus. GA and LPS increased TBARS (thiobarbituric acid-reactive substance) content, reduced antioxidant defenses and inhibited Na+, K+-ATPase activity. GA and LPS co-administration did not have additive effect on oxidative stress markers and Na+, K+ pump. The hippocampal volume did not change after GA or LPS administration. NAC protected against impairment of spatial learning and increase of cytokines levels. NAC Also protected against inhibition of Na+,K+-ATPase activity and oxidative markers. CONCLUSIONS:These results suggest that inflammatory and oxidative markers may underlie at least in part of the neuropathology of GA-I in this model. Thus, NAC could represent a possible adjuvant therapy in treatment of children with GA-I

Effect of early postnatal chronic GA, NAC and LPS administration on hippocampal volume.

<p>Data represent means ± S.E.M. for n = 5-6 in each group. No significant differences between groups were detected.</p

Effect of early postnatal chronic GA, NAC and LPS administration on NPSH content, GSH level, CAT and SOD activities.

<p>NAC prevented the decrease of antioxidant defenses induced by GA and LPS.*P < 0.001 compared with saline treated group and ^#P< 0.001 compared with respective control group (Duncan’s multiple comparisons test). Data are presented as means ± S.E.M. for n = 7 in each group.</p

Effect of early postnatal chronic GA, NAC and LPS administration on TBARS content.

<p>NAC prevented the increase of TBARS content induced by GA and LPS. *P < 0.01 compared with saline treated group and ^#P< 0.05 compared with respective control group (Duncan’s multiple comparisons test). Data are presented as means ± S.E.M. for n = 7 in each group.</p

Effect of early postnatal chronic GA, NAC and LPS administration on cytokine levels on the second day of Barnes maze.

<p>NAC prevented the increase in TNF-α (A) and IL-1β (B) levels. *P < 0.001 compared with saline treated group, ^#P< 0.001 compared with the respective control group and ^δP < 0.05 compared with GA-treated group (Duncan’s multiple comparisons test). Data are presented as means ± S.E.M. for n = 6-7 in each group.</p

Effect of early postnatal chronic GA, NAC and LPS administration on physical development of animals.

<p>Data are presented as means ± S.E.M. for n = 8–9 in each group. No significant differences between groups were detected.</p

NAC prevents the memory deficit induced by GA and LPS measured as escape latency of rat pups in the Barnes maze.

<p>*P < 0.05 compared with saline treated group, ^#P< 0.05 compared with respective control group and ^δP < 0.001 compared with GA-treated group (Duncan’s multiple comparisons test). Data are presented as means ± S.E.M. for n = 7-9 in each group. <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0078332#pone-0078332-g003" target="_blank">Figures 3B and 3C</a> show an amplification of the second day of test.</p

NAC prevented the decrease of α1 subunit activity of Na⁺,K⁺-ATPase enzyme.

<p>Effect of early postnatal chronic GA, NAC and LPS administration on Na⁺,K⁺-ATPase total activity (A); on α1 subunit activity of Na⁺,K⁺-ATPase enzyme (B); and on α2/3 subunit activity of Na⁺,K⁺-ATPase enzyme (C), on the second day of Barnes maze.*P < 0.001 compared with saline traded group and ^#P< 0.001 compared with respective control group (Student–Newman–Keuls test). Data are presented as means ± S.E.M. for n = 7-9 in each group.</p

Digitized images of dorsal hippocampus showing similarities in the volume of this region between the different experimental groups.

<p>Schematic drawing obtained from Paxinos and Watson's Atlas. </p