The in vivo effect of lipopolysaccharide on Na+,K(+)-ATPase catalytic (alpha) subunit isoforms in rat sciatic nerve

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 (5umol g of body weight-1, subcutaneously; twice per day; from 5th to 28th day of life), and were supplemented with NAC (150mg/kg/day; intragastric gavage; for the same period). LPS (2mg/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.

Lipopolysaccharide hyperpolarizes guinea pig airway epithelium by increasing the activities of the epithelial Na(+) channel and the Na(+)-K(+) pump

Earlier, we found that systemic administration of lipopolysaccharide (LPS; 4 mg/kg) hyperpolarized the transepithelial potential difference (V(t)) of tracheal epithelium in the isolated, perfused trachea (IPT) of the guinea pig 18 h after injection. As well, LPS increased the hyperpolarization component of the response to basolateral methacholine, and potentiated the epithelium-derived relaxing factor-mediated relaxation responses to hyperosmolar solutions applied to the apical membrane. We hypothesized that LPS stimulates the transepithelial movement of Na(+) via the epithelial sodium channel (ENaC)/Na(+)-K(+) pump axis, leading to hyperpolarization of V(t). LPS increased the V(t)-depolarizing response to amiloride (10 μM), i.e., offset the effect of LPS, indicating that Na(+) transport activity was increased. The functional activity of ENaC was measured in the IPT after short-circuiting the Na(+)-K(+) pump with basolateral amphotericin B (7.5 μM). LPS had no effect on the hyperpolarization response to apical trypsin (100 U/ml) in the Ussing chamber, indicating that channel-activating proteases are not involved in the LPS-induced activation of ENaC. To assess Na(+)-K(+) pump activity in the IPT, ENaC was short-circuited with apical amphotericin B. The greater V(t) in the presence of amphotericin B in tracheas from LPS-treated animals compared with controls revealed that LPS increased Na(+)-K(+) pump activity. This finding was confirmed in the Ussing chamber by inhibiting the Na(+)-K(+) pump via extracellular K(+) removal, loading the epithelium with Na(+), and observing a greater hyperpolarization response to K(+) restoration. Together, the findings of this study reveal that LPS hyperpolarizes the airway epithelium by increasing the activities of ENaC and the Na(+)-K(+) pump.

Lipopolysaccharide induces biochemical alterations in chicks trained on the passive avoidance learning task

We have recently shown that activation of the immune system with lipopolysaccharide (LPS) results in memory-processing deficits for the passive avoidance learning task in the day-old chick. The current study examined two important issues in understanding the mechanisms underlying these memory deficits associated with immune system activation, namely, whether LPS (1) impairs Na(+)/K(+)-ATPase functioning and (2) increases corticosterone (CORT) concentrations in chicks trained on the task. As the effects of LPS on sickness behavior have only previously been characterized in older chickens, this study also tested whether LPS is able to produce similar alterations in day-old chicks. LPS decreased brain Na(+)/K(+)-ATPase activity and increased plasma concentrations of CORT in chicks trained on the passive avoidance learning task. These findings give an insight into some of the mechanisms that may be responsible for the LPS-induced memory-processing deficits. Consistent with previous research in older chickens, LPS increased body temperature in a dose-dependent manner, however, only the lowest dose of LPS tested significantly decreased food intake in the day-old chicks.

Alterations in the properties and isoforms of sciatic nerve Na(+), K(+)-ATPase in methylcyclopentadienyl manganese tricarbonyl-treated mice

The in vivo effect of methylcyclopentadienyl manganese tricarbonyl (MMT), an organic manganese-containing compound, on the mouse motor nerve was studied. The motor nerve conduction velocity was markedly decreased in MMT-treated mice. The Na(+),K(+)-ATPase activity of sciatic nerve isolated from MMT-treated mice was decreased; however, the sciatic nerve Na(+),K(+)-ATPase activity was not affected by the in vitro treatment of MMT. Moreover, [(3)H]ouabain binding of sciatic nerve isolated from MMT-treated mice was decreased. Using Western blot analysis, the amount of Na(+),K(+)-ATPase catalytic alpha1 subunit polypeptide in sciatic nerve of MMT-treated mice was also decreased. These results indicate that a causal relationship may exist between reduced nerve Na(+),K(+)-ATPase activity and motor nerve conduction velocity in MMT-treated mice and that a measurable decrease in alpha1 catalytic subunit isoform of Na(+),K(+)-ATPase may be necessary for the development of peripheral neuropathy by MMT.

Nitric oxide inhibits transcription of the Na+-K+-ATPase alpha1-subunit gene in an MTAL cell line

Nitric oxide (NO) has been implicated as an autocrine modulator of active sodium transport. To determine whether tonic exposure to NO influences active sodium transport in epithelial cells, we established transfected medullary thick ascending limb of Henle (MTAL) cell lines that overexpressed NO synthase-2 (NOS2) and analyzed the effects of deficient or continuous NO production [with or without NG-nitro-L-arginine methyl ester (L-NAME) in the culture medium, respectively] on Na+-K+-ATPase function and expression. The NOS2-transfected cells exhibited high-level NOS2 expression and NO generation, which did not affect cell viability or cloning efficiency. NOS2-transfected cells were grown in the presence of vehicle, NG-nitro-D-arginine methyl ester (D-NAME), or L-NAME for 16 h, after which 86Rb+ uptake assays, Northern analysis, or nuclear run-on transcription assays were performed. The NOS2-transfected cells allowed to produce NO continuously (vehicle or D-NAME) exhibited lower rates of ouabain-sensitive 86Rb+ uptake ( approximately 65%), lower levels of Na+-K+-ATPase alpha1-subunit mRNA ( approximately 60%), and reduced rates of de novo Na+-K+-ATPase alpha1-subunit transcription compared with L-NAME-treated cells. These results have uncovered a novel effect of NO to inhibit transcription of the Na+-K+-ATPase alpha1-subunit gene.

Lipopolysaccharide treatment modifies pH- and cation-dependent ecto-ATPase activity of endothelial cells

The aim of this study was to investigate the distribution pattern of Ca2+- and Mg2+-dependent ecto-ATPases on the surface of rat brain capillary endothelial cells (ECs) in control and lipopolysaccharide (LPS)-treated animals. Ecto-ATPases in the membrane of vascular endothelial cells are suggested to play a crucial role in thromboregulation. Loss of this enzyme activity after oxidative stress and upregulation of the enzyme chain hydrolyzing extracellular ATP after transient forebrain ischemia have also been reported. We used histochemistry to localize the activities of this enzyme on ECs and found pH- and cation-dependent changes in the localization of enzyme activity both in control and in LPS-treated animals. These findings suggest the presence of more than one ecto-ATPase enzyme on the surface of rat capillary ECs. The different behavior of ECs after LPS treatment is the target of further investigations. The increased ecto-nucleotidase activity might play a role in nucleotide-mediated cellular responses after bacterial infections.