TNF-alpha modulates hepatic Na+-K+ ATPase activity via PGE2 and EP2 receptors

Prostaglandin E2 activates melanin-concentrating hormone neurons to drive diet-induced obesity

Hypothalamic inflammation reduces appetite and body weight during inflammatory diseases, while promoting weight gain when induced by high-fat diet (HFD). How hypothalamic inflammation can induce opposite energy balance outcomes remains unclear. We found that prostaglandin E2 (PGE2), a key hypothalamic inflammatory mediator of sickness, also mediates diet-induced obesity (DIO) by activating appetite-promoting melanin-concentrating hormone (MCH) neurons in the hypothalamus in rats and mice. The effect of PGE2 on MCH neurons is excitatory at low concentrations while inhibitory at high concentrations, indicating that these neurons can bidirectionally respond to varying levels of inflammation. During prolonged HFD, endogenous PGE2 depolarizes MCH neurons through an EP2 receptor-mediated inhibition of the electrogenic Na+/K+-ATPase. Disrupting this mechanism by genetic deletion of EP2 receptors on MCH neurons is protective against DIO and liver steatosis in male and female mice. Thus, an inflammatory mediator can directly stimulate appetite-promoting neurons to exacerbate DIO and fatty liver.

Sanguinarine-Chelerythrine Fraction of Coptis chinensis Exerts Anti-inflammatory Activity in Carrageenan Paw Oedema Test in Rats and Reveals Reduced Gastrotoxicity

Inflammatory diseases are a common therapeutic problem and nonsteroidal anti-inflammatory drugs are not deprived of side effects, of which ulcerogenic activity is one of the most frequent. The aim of the study was to evaluate the anti-inflammatory activity of the sanguinarine-chelerythrine (SC) fraction of Coptis chinensis and its influence on the integrity of gastric mucosa. The study was conducted on sixty male rats randomly divided into six experimental groups: two control groups (a negative control group CON and a positive control group CAR); three groups receiving an investigational fraction of C. chinensis (1, 5, 10 mg/kg i.g.) named SC1, SC5, and SC10, respectively; and a group receiving indomethacin (IND) (10 mg/kg i.g.) as a reference drug. In all animals, the carrageenan-induced paw oedema was measured; PGE2 release, TNFα production, and MMP-9 concentration in inflamed tissue were determined. Additionally, the macroscopic and microscopic damage of gastric mucosa was evaluated. Administration of SC dose-dependently inhibited the second phase of carrageenan rat paw oedema and PGE2 release, decreased the production of TNFα, and reduced the concentration of MMP-9, and the efficacy of the highest dose was comparable to the effect of IND. Contrary to IND, no gastrotoxic activity of SC was detected. The investigated sanguinarine-chelerythrine fraction of C. chinensis seems to be a promising candidate for further research on new anti-inflammatory and analgesic drugs characterized with a safer gastric profile compared to existing NSAIDs.

The Expression and Regulation of Na+-K+-ATPase in Nasal Epithelial Cells of Chronic Rhinosinusitis with Nasal Polyps

OBJECTIVE

Na+-K+-ATPase (NKA) is essential in maintaining cell permeability, reserving potential energy, and preventing cellular edema. Nevertheless, how NKA expression is altered and regulated in chronic rhinosinusitis with nasal polyps (CRSwNPs) remain uncertain. Therefore, the present study aimed to explore the expression and regulation of NKA in CRSwNP.

METHODS

NKA immunolabeling was assessed by the immunohistochemistry method, NKA protein levels were detected with the Western blotting method, and mRNA levels of NKA and aquaporin-5 (AQP5) were assayed by real-time PCR in nasal tissues from CRSwNP and control subjects. The co-localization of NKA with inflammatory cells was evaluated by immunofluorescence staining. In addition, human nasal epithelial cells (HNECs) were cultured and stimulated using various stimulators to evaluate the regulation of NKA.

RESULTS

We found significantly decreased NKA positive cells, NKA protein levels, and mRNA levels of NKA and AQP5 in nasal tissues from CRSwNP patients compared to control subjects, especially in eosinophilic CRSwNP. Furthermore, NKA mRNA levels in HNECs were downregulated by staphylococcal enterotoxin B (SEB), lipopolysaccharides (LPSs), inflammatory cytokine (IFN)-γ, IL-4, IL-13, and IL-1β.

CONCLUSION

NKA and AQP5 expressions were decreased in CRSwNP. NKA in HNECs could be suppressed by SEB, LPS, IFN-γ, IL-4, IL-13, and IL-1β. Impairment of NKA may contribute to the genesis and development of CRSwNP via inducing AQP5 downregulation and edema.

Mechanism of Na-K-ATPase Inhibition by PGE2 in Intestinal Epithelial Cells

The primary means of intestinal absorption of nutrients by villus cells is via Na-dependent nutrient co-transporters located in the brush border membrane (BBM). These secondary active co-transport processes require a favorable transcellular Na gradient that is provided by Na-K-ATPase. In chronic enteritis, malabsorption of essential nutrients is partially due to inhibition of villus Na-K-ATPase activity mediated by specific immune inflammatory mediators that are known to be elevated in the inflamed mucosa. However, how Prostaglandin E2 (PGE2), a specific mediator of nutrient malabsorption in the villus BBM, may mediate the inhibition of Na-K-ATPase is not known. Therefore, this study aimed to determine the effect of PGE2 on Na-K-ATPase in villus cells and define its mechanism of action. In vitro, in IEC-18 cells, PGE2 treatment significantly reduced Na-K-ATPase activity, accompanied by a significant increase in the intracellular levels of cyclic Adenosine Monophosphate (cAMP). The treatment with cAMP analog 8-Bromo-cAMP mimicked the PGE2-mediated effect on Na-K-ATPase activity, while Rp-cAMP (PKA inhibitor) pretreatment reversed the same. The mechanism of inhibition of PGE2 was secondary to a transcriptional reduction in the Na-K-ATPase α1 and β1 subunit genes, which was reversed by the Rp-cAMP pretreatment. Thus, the PGE2-mediated activation of the PKA pathway mediates the transcriptional inhibition of Na-K-ATPase activity in vitro.

FTY720P inhibits the Na+/K+ ATPase in Caco-2 cells via S1PR2: PGE2 and NO are along the signaling pathway

AIMS

Sphingosine-1-phosphate (S1P) has been implicated lately in inflammatory bowel disease which has diarrhea as one of its symptoms. Diarrhea is due to altered water movements as a result of altered electrolyte transport, and in particular sodium. Sodium movements are geared by the sodium gradient established by the Na⁺/K⁺ ATPase. The aim of this work was to investigate if S1P can modulate the activity of the ATPase, using Caco-2 cells as a model and the S1P analogue, FTY720P.

MATERIALS AND METHODS

The activity of the ATPase was assayed by measuring the amount of inorganic phosphate liberated in presence and absence of ouabain. Protein expression of the various S1P receptors was studied by western blot analysis.

KEY FINDINGS

Caco-2 cells were found to express mainly S1PR2 and S1PR3. FTY720P (7.5 nM) reduced significantly the activity of the Na⁺/K⁺ ATPase when applied for 15 min. This inhibitory effect disappeared in presence of JTE-013, a specific blocker of S1PR2, and indomethacin, an inhibitor of cyclooxygenase enzymes, and was mimicked by CYM5520, a S1PR2 agonist and by exogenous PGE2. The inhibitory effect of PGE2 did not appear when EP3 receptors were blocked or when a nitric oxide scavenger was added. RpcAMP, a PKA inhibitor, reduced the activity of the Na⁺/K⁺ ATPase, while dbcAMP, a PKA activator was without any effect and when added, abrogated the effect of PGE2.

SIGNIFICANCE

It was concluded that FTY720P inhibits the Na+/K+ ATPase via activation of S1PR2 and generation of PGE2 nitric oxide.

Epinephrine modulates Na+/K+ ATPase activity in Caco-2 cells via Src, p38MAPK, ERK and PGE2

Epinephrine, a key stress hormone, is known to affect ion transport in the colon. Stress has been associated with alterations in colonic functions leading to changes in water movements manifested as diarrhea or constipation. Colonic water movement is driven by the Na⁺-gradient created by the Na⁺/K⁺-ATPase. Whether epinephrine acts via an effect on the Na⁺/K⁺-ATPase hasn’t been studied before. The aim of this work was to investigate the effect of epinephrine on the Na⁺/K⁺-ATPase and to elucidate the signaling pathway involved using CaCo-2 cells as a model. The activity of the Na⁺/K⁺-ATPase was assayed by measuring the amount of inorganic phosphate released in presence and absence of ouabain, a specific inhibitor of the enzyme. Epinephrine, added for 20 minutes, decreased the activity of the Na⁺/K⁺-ATPase by around 50%. This effect was found to be mediated by α2 adrenergic receptors as it was fully abolished in the presence of yohimbine an α2-blocker, but persisted in presence of other adrenergic antagonists. Furthermore, treatment with Rp-cAMP, a PKA inhibitor, mimicked epinephrine’s negative effect and didn’t result in any additional inhibition when both were added simultaneously. Treatment with indomethacin, PP2, SB202190, and PD98059, respective inhibitors of COX enzymes, Src, p38MAPK, and ERK completely abrogated the effect of epinephrine. The effect of epinephrine did not appear also in presence of inhibitors of all four different types of PGE2 receptors. Western blot analysis revealed an epinephrine-induced increase in the phosphorylation of p38 MAPK and ERK that disappeared in presence of respectively PP2 and SB2020190. In addition, an inhibitory effect, similar to that of epinephrine’s, was observed upon incubation with PGE2. It was concluded that epinephrine inhibits the Na⁺/K⁺-ATPase by the sequential activation of α2 adrenergic receptors, Src, p38MAPK, and ERK leading to PGE2 release.

Signaling pathway involved in the inhibitory effect of FTY720P on the Na+/K+ ATPase in HepG2 cells

The Na+/K+ ATPase modulates the activity of many transporters in the liver, and maintains the ionic constancy of the intracellular milieu, preserving thus normal functioning of hepatocytes. Previous work showed that FTY720P, a sphingosine one phosphate receptor agonist used in the treatment of multiple sclerosis, exerts in HepG2 cells, an inhibitory effect on the activity of the ATPase, mediated via PGE2. This study is an attempt to identify the signaling molecules involved downstream of the prostaglandin. The activity of the ATPase was assayed by measuring the amount of inorganic phosphate liberated in presence and absence of ouabain, a specific inhibitor of the enzyme. The effect of FTY720P and PGE2 disappeared completely in presence of PF-04418948, a blocker of EP2 receptors, RpcAMP, an inhibitor of PKA, PD98059, an inhibitor of ERK, as well as in presence of PTIO, a nitric oxide synthase inhibitor, but was mimicked by butaprost, an EP2 agonist, dbcAMP, a cell permeable cAMP analogue, and SNAP1,a nitric oxide generator. PGE2 and dbcAMP increased the expression of phosphorylated ERK but not total ERK. This increase did not appear however in presence of PTIO, indicating that PKA is upstream of NO. It was concluded that FTY 720P induces PGE2 release which activates NOS leading to NO production and ERK activation. ERK then inhibits directly or indirectly the Na+/K+ ATPase.

FTY720P inhibits hepatic Na(+)-K(+) ATPase via S1PR2 and PGE2

Sphingosine-1-phosphate (S1P) was found previously to inhibit Na(+)-K(+) ATPase in HepG2 cells. Whether fingolimod (FTY720), a S1P receptor (S1PR) agonist, similarly inhibits the ATPase is a question that needs to be addressed. The aim of this work was to study the effect of FTY720P, the active form of the drug, on the activity of Na(+)-K(+) ATPase in HepG2 cells and determine its mechanism of action. The activity of the ATPase was assayed by measuring the amount of inorganic phosphate liberated in the presence and the absence of ouabain. FTY720-P (7.5 nmol/L, 15 min) significantly reduced the activity of the ATPase. This effect disappeared completely in the presence of JTE-013, which is a specific blocker of sphingosine-1-phosphate receptor 2 (S1PR2), as well as in the presence of calphostin and indomethacin, which are inhibitors of protein kinase C (PKC) and COX-2, respectively. The effect of FTY720P was mimicked by prostaglandin E2 (PGE2) and PMA, but abrogated by NF-κB inhibition. When NF-κB was inhibited, the effect of exogenous PGE2 still appeared, but that of PMA did not manifest, suggesting that NF-κB is upstream of PGE2 and downstream of PKC. It was concluded that FTY720P activates via S1PR2, PKC, and NF-κB. The latter induces PGE2 generation and inhibits Na(+)-K(+) ATPase.

Boswellic acids extract attenuates pulmonary fibrosis induced by bleomycin and oxidative stress from gamma irradiation in rats

BACKGROUND

Interstitial pulmonary fibrosis is characterized by an altered cellular composition of the alveolar region with excessive deposition of collagen. Lung inflammation is also common in pulmonary fibrosis. This study aims to test the inhibition of 5-lipooxygenase (5-LOX) by boswellic acid (BA) extract in an experimental model of pulmonary fibrosis using bleomycin (BL).

METHODS

Boswellic acid extract (1 g/kg) was force-fed to rats seven days prior to administration of BL or gamma irradiation or both. BL (0.15 U/rat) in 25 μl of 0.9% normal saline (NS) or 0.9% NS alone was administered intratracheally. Rats were exposed to two fractionated doses of gamma irradiation (0.5 Gy/dose/week) with a gamma cell-40 (Cesium-137 irradiation units, Canada) during the last two weeks of the experiment. BA was administered during BL or irradiation treatment or both. After the animals were sacrificed, bronchoalveolar lavage was performed; lungs were weighed and processed separately for biochemical and histological studies.

RESULTS

In rats treated with BL, levels of transforming growth factor-β1 (TGF-β1) and tumor necrosis factor-α (TNF-α) were significantly elevated (P = 0.05 and P = 0.005). Hydroxyproline was highly and extensively expressed. Immunoreactive compounds were abundantly expressed, represented in the levels of macrophages infiltrate, accumulation of eosinophils and neutrophils in the lung as well as the aggregation of fibroblasts in the fibrotic area. The levels of lipoxygenase enzyme activity were significantly increased (P = 0.005). Antioxidant activities measured in BL-treated rats deteriorated, coupled with the elevation of both levels of plasma lipid peroxide (LP) content and bronchoalveolar lavage lactate dehydrogenase activity. BA-treated rats had reduced number of macrophages, (P = 0.01), neutrophils in bronchoalveolar lavage (P = 0.01) and protein (P = 0.0001). Moreover, the hydroxyproline content was significantly lowered in BA-treated rats (P = 0.005). BA extract inhibited the TGF-ß induced fibrosis (P = 0.01) and 5-LOX activity levels (P = 0.005).Histologically, BA reduced the number of infiltrating cells, ameliorated the destruction of lung architecture and attenuated lung fibrosis.

CONCLUSION

BA attenuates the BL-induced injury response in rats, such as collagen accumulation, airway dysfunction and injury. This study suggests that the blocking of 5-LOX may prevent the progression of fibrosis.

Prostaglandin receptors mediate effects of substances released from ischaemic rat hearts on non-ischaemic cardiomyocytes

BACKGROUND

After ischaemia and during reperfusion, rat hearts release cardiodepressive substances that are putatively cyclooxygenase-2-dependent. The present study analyses the mechanisms by which these substances mediate their effect downstream of cyclooxygenase-2.

MATERIALS AND METHODS

After 10 min of global stop-flow ischaemia, isolated rat hearts were reperfused and post-ischaemic coronary effluent was collected over a period of 30 s. Non-ischaemic effluent collected before ischaemia was used as a control. We investigated the effect of the effluents on cell shortening and Ca(++)-metabolism, by application of fluorescence microscopy of field-stimulated adult rat cardiomyocytes incubated with fura-2. Cells were pre-incubated with inhibitors of protein kinase A and C and with antagonists of protein kinase A-dependent prostaglandin receptors. We examined the expression of prostaglandin receptors in cardiomyocytes by Western blotting.

RESULTS

In contrast to non-ischaemic effluent, post-ischaemic effluent induced reduction of Ca(++) transient and cell shortening in the cardiomyocytes. In contrast to protein kinase C inhibitor Myr-PKC [19-27], the protein kinase A inhibitor Rp-cAMPS completely blocked the effect of post-ischaemic effluent. Furthermore, we determined a cyclic adenosine monophosphate increase in cardiomyocytes that were pre-incubated with post-ischaemic effluent. The antagonist of prostaglandin E-receptor EP2 AH6809 and the antagonist of receptor subtype EP4 AH23848 attenuated the effect of post-ischaemic effluent in contrast to other antagonists of prostaglandin D and I receptors, which did not influence the effect. In lysates of adherend cardiomyocytes, expression of prostaglandin D, E and I receptors was detected by Western blotting.

CONCLUSIONS

The effect of post-ischaemic effluent is mediated by the protein kinase A-dependent prostaglandin-receptor subtypes EP2 and EP4 downstream of cyclooxygenase-2.

The Role of Tumor Necrosis Factor Alpha in Lipopolysaccharide/Ranitidine-Induced Inflammatory Liver Injury

Exposure to a nontoxic dose of bacterial lipopolysaccharide (LPS) increases the hepatotoxicity of the histamine-2 (H2) receptor antagonist, ranitidine (RAN). Because some of the pathophysiologic effects associated with LPS are mediated through the expression and release of inflammatory mediators such as tumor necrosis factor alpha (TNF), this study was designed to gain insights into the role of TNF in LPS/RAN hepatotoxicity. To determine whether RAN affects LPS-induced TNF release at a time near the onset of liver injury, male Sprague-Dawley rats were treated with 2.5 x 10(6) endotoxin units (EU)/kg LPS or its saline vehicle (iv) and 2 h later with either 30 mg/kg RAN or sterile phosphate-buffered saline vehicle (iv). LPS administration caused an increase in circulating TNF concentration. RAN cotreatment enhanced the LPS-induced TNF increase before the onset of hepatocellular injury, an effect that was not produced by famotidine, a H2-receptor antagonist without idiosyncrasy liability. Similar effects were observed for serum interleukin (IL)-1beta, IL-6, and IL-10. To determine if TNF plays a causal role in LPS/RAN-induced hepatotoxicity, rats were given either pentoxifylline (PTX; 100 mg/kg, iv) to inhibit the synthesis of TNF or etanercept (Etan; 8 mg/kg, sc) to impede the ability of TNF to reach cellular receptors, and then they were treated with LPS and RAN. Hepatocellular injury, the release of inflammatory mediators, hepatic neutrophil (PMN) accumulation, and biomarkers of coagulation and fibrinolysis were assessed. Pretreatment with either PTX or Etan resulted in the attenuation of liver injury and diminished circulating concentrations of TNF, IL-1beta, IL-6, macrophage inflammatory protein-2, and coagulation/fibrinolysis biomarkers in LPS/RAN-cotreated animals. Neither PTX nor Etan pretreatments altered hepatic PMN accumulation. These results suggest that TNF contributes to LPS/RAN-induced liver injury by enhancing inflammatory cytokine production and hemostasis.