Biphasic regulation by bile acids of dermal fibroblast proliferation through regulation of cAMP production and COX-2 expression level

Bile Acid Administration Elicits an Intestinal Antimicrobial Program and Reduces the Bacterial Burden in Two Mouse Models of Enteric Infection

In addition to their chemical antimicrobial nature, bile acids are thought to have other functions in the homeostatic control of gastrointestinal immunity. However, those functions have remained largely undefined. In this work, we used ileal explants and mouse models of bile acid administration to investigate the role of bile acids in the regulation of the intestinal antimicrobial response. Mice fed on a diet supplemented with 0.1% chenodeoxycholic acid (CDCA) showed an upregulated expression of Paneth cell α-defensins as well as an increased synthesis of the type-C lectins Reg3b and Reg3g by the ileal epithelium. CDCA acted on several epithelial cell types, by a mechanism independent from farnesoid X receptor (FXR) and not involving STAT3 or β-catenin activation. CDCA feeding did not change the relative abundance of major commensal bacterial groups of the ileum, as shown by 16S analyses. However, administration of CDCA increased the expression of ileal Muc2 and induced a change in the composition of the mucosal immune cell repertoire, decreasing the proportion of Ly6G⁺ and CD68⁺ cells, while increasing the relative amount of IgGκ⁺ B cells. Oral administration of CDCA to mice attenuated infections with the bile-resistant pathogens Salmonella enterica serovar Typhimurium and Citrobacter rodentium, promoting lower systemic colonization and faster bacteria clearance, respectively. Our results demonstrate that bile acid signaling in the ileum triggers an antimicrobial program that can be potentially used as a therapeutic option against intestinal bacterial infections.

Effects of high doses of dexamethasone on hemodynamic and immunohistochemical characteristics of acute paraquat intoxication in rat kidneys

Paraquat (1,1'-dimethyl-4,4'-bipyridinium) (PQ), is a nonselective contact herbicide that is highly toxic to humans. The kidney is affected during PQ intoxication. Dexamethasone (Dexa) has anti-inflammatory effects and is used to treat cases of PQ poisoning. We investigated in rat kidney hemodynamic effects and immunohistochemical characteristics of Dexa treatment in acute PQ poisoning. Adult male rats were divided into four groups: 1, untreated control; 2, treated with 100 mg/kg Dexa; 3, treated with 25 mg/kg PQ; 4, treated with PQ + Dexa. Mean arterial pressure (MAP) and heart rate (HR) were recorded during the experimental period (2 h). Tissues were removed after 2 h and immunohistochemistry was performed after 24 h. Paraffin sections of kidney were prepared and anti-cyclo-oxygenase-1 (COX-1), anti-cyclo-oxygenase-2 (COX-2), anti-angiotensin converting enzyme (ACE), anti-aquaporin-1 (AQU-1), anti-vascular cell adhesion molecule (VCAM) primary antibodies were used for immunohistochemical examination. Immunoreactivities were scored as: (1) minimal, (2) weak, (3) mild, (4) moderate, (5) strong and (6) very strong. MAP and HR were measured at 10 min, 20 min, 1 h and 2 h. MAP at 10 and 20 min and 1 h was increased in the Dexa group. HR also was increased in all groups compared to controls at 2 h. Compared to groups 2 and 4, MAP values decreased significantly in group 3 at 1 h. The intensity of all of immunoreactivities was decreased in group 2. In group 3, immunoreactivities of COX-1, COX-2 and ACE were decreased compared to the control and the other groups, whereas AQU-1 and VCAM immunoreactivities were the same as the control group. ACE and VCAM immunoreactivities were decreased in group 4 compared to the control group, while COX-1, COX-2 and AQU-1 immunoreactivities were close to those of the control group. Dexa appears to be useful for treating PQ intoxication.

Differential effects of prostaglandin E(2) and enamel matrix derivative on the proliferation of human gingival and dermal fibroblasts and gingival keratinocytes

BACKGROUND AND OBJECTIVE

Elevated levels of prostaglandins contribute to periodontal destruction but can impair gingival healing by affecting local fibroblasts. Enamel matrix derivative (EMD) has beneficial effects on supporting and gingival tissues. We showed that prostaglandin E(2) (PGE(2) ) inhibits the proliferation of human gingival fibroblasts (hGFs) and that EMD stimulates it. Prostaglandins and EMD may also affect skin healing by targeting dermal fibroblasts (DFs). Thus, we compared the effects of these two agents on the proliferation of hGFs, human gingival keratinocytes (hGKs) and hDFs.

MATERIAL AND METHODS

Cells from healthy human gingiva or skin were treated with PGE(2) and/or EMD, and proliferation was assessed by measuring cell number and DNA synthesis.

RESULTS

In hGFs, PGE(2) (1 μm) inhibited proliferation while EMD stimulated it. When present together, EMD abolished the PGE(2) -induced inhibition. Serum increased (by a factor of 10) the amount of phosphorylated extracellular signal-regulated kinase (p-ERK), PGE(2) reduced it (by 70-80%) and EMD restored it when present with PGE(2). Prostaglandin E(2) stimulated cAMP production in hGFs while serum or EMD did not. Enamel matrix derivative stimulated hDF proliferation, but the inhibitory effect of PGE(2) was milder than with hGFs. When present together, EMD abolished the PGE(2) -induced inhibition. Enamel matrix derivative inhibited the proliferation of primary hGKs, but PGE(2) had no effect. Finally, we found that hDFs contained about five times less prostaglandin EP(2) receptor mRNA than hGFs, while hGKs contained none.

CONCLUSION

Prostaglandin E(2) inhibits and EMD stimulates hGF proliferation via distinct pathways. The different sensitivities of hDFs and hGKs to PGE(2) can be explained by the levels of EP(2) expression.

Bile acid stimulates hepatocyte polarization through a cAMP-Epac-MEK-LKB1-AMPK pathway

This study describes a unique function of taurocholate in bile canalicular formation involving signaling through a cAMP-Epac-MEK-Rap1-LKB1-AMPK pathway. In rat hepatocyte sandwich cultures, polarization was manifested by sequential progression of bile canaliculi from small structures to a fully branched network. Taurocholate accelerated canalicular network formation and concomitantly increased cAMP, which were prevented by adenyl cyclase inhibitor. The cAMP-dependent PKA inhibitor did not prevent the taurocholate effect. In contrast, activation of Epac, another cAMP downstream kinase, accelerated canalicular network formation similar to the effect of taurocholate. Inhibition of Epac downstream targets, Rap1 and MEK, blocked the taurocholate effect. Taurocholate rapidly activated MEK, LKB1, and AMPK, which were prevented by inhibition of adenyl cyclase or MEK. Our previous study showed that activated-LKB1 and AMPK participate in canalicular network formation. Linkage between bile acid synthesis, hepatocyte polarization, and regulation of energy metabolism is likely important in normal hepatocyte development and disease.

Bile acids and signal transduction: role in glucose homeostasis

Bile acids are mainly recognized for their role in dietary lipid absorption and cholesterol homeostasis. However, recent progress in bile acid research suggests that bile acids are important signaling molecules that play a role in glucose homeostasis. Among the various supporting evidence, several reports have demonstrated an improvement of the glycemic index of type 2 diabetic patients treated with diverse bile acid binding resins. Herein, we review the diverse interactions of bile acids with various signaling/response pathways, including calcium mobilization and protein kinase activation, membrane receptor-mediated responses, and nuclear receptor responses. Some of the effects of the bile acids are direct through the activation of specific receptors, i.e., TGR5, CAR, VDR, and FXR, while others imply modulation of the hormonal, growth factor and/or neuromediator responses, i.e., glucagon, EGF, and acetylcholine. We also discuss recent evidence implicating the interaction of bile acids with glucose homeostasis mechanisms, with the integration of our understanding of how the signaling mechanisms modulated by bile acid could regulate glucose metabolism.

Endotoxin mediates recruitment of RNA polymerase II to target genes in acute renal failure

Acute renal failure (ARF) sensitizes the kidney to endotoxin (LPS)-driven production of cytokines and chemokines. This study assessed whether this LPS hyperresponsiveness exists at the genomic level. Three heterogeneous mouse models of ARF were studied: Maleate nephrotoxicity, unilateral ureteral obstruction, and LPS preconditioning. In all cases, LPS was injected approximately 18 h after injury was induced, and over the next 0 to 90 min, RNA polymerase II recruitment to the genome at three LPS-responsive genes (TNF-alpha, monocyte chemoattractant-1 [MCP-1], and heme oxygenase-1 [HO-1]) was assessed by chromatin immunoprecipitation. LPS hyperresponsiveness was noted in each model, measured by exaggerated increases in TNF-alpha and MCP-1 mRNA (approximately two to 10 times higher than LPS-injected controls). Corresponding increases in the recruitment of RNA polymerase II to the TNF-alpha and MCP-1 genes were observed, and increased trimethylation of histone 3 lysine 4 (H3K4m3) at these sites may have played a role in this recruitment. Conversely, recruitment of RNA polymerase II to the HO-1 gene was suppressed ("tolerance"), and no increase in H3K4m3 was observed at HO-1 exons. The ARF-induced changes in mRNA did not correlate with mRNA stability, suggesting the mechanistic importance of RNA polymerase II-mediated transcriptional events. In conclusion, LPS hyperresponsiveness after ARF is likely mediated at the genomic level, possibly by H3K4m3.

Gentamicin suppresses endotoxin-driven TNF-alpha production in human and mouse proximal tubule cells

Gentamicin is a mainstay in treating gram-negative sepsis. However, it also may potentiate endotoxin (LPS)-driven plasma TNF-alpha increases. Because gentamicin accumulates in renal tubules, this study addressed whether gentamicin directly alters LPS-driven tubular cell TNF-alpha production. HK-2 proximal tubular cells were incubated for 18 h with gentamicin (10-2,000 microg/ml). Subsequent LPS-mediated TNF-alpha increases (at 3 or 24 h; protein/mRNA) were determined. Gentamicin effects on overall protein synthesis ([(35)S]methionine incorporation), monocyte chemoattractant protein-1 (MCP-1) levels, and LPS-stimulated TNF-alpha generation by isolated mouse proximal tubules also were assessed. Finally, because gentamicin undergoes partial biliary excretion, its potential influence on gut TNF-alpha/MCP-1 mRNAs was probed. Gentamicin caused striking, dose-dependent inhibition of LPS-driven TNF-alpha production (up to 80% in HK-2 cells/isolated tubules). Surprisingly, this occurred despite increased TNF-alpha mRNA accumulation. Comparable changes in MCP-1 were observed. These changes were observed at clinically relevant gentamicin concentrations and despite essentially normal overall protein synthetic rates. Streptomycin also suppressed LPS-driven TNF-alpha increases, suggesting an aminoglycoside drug class effect. Gentamicin doubled basal TNF-alpha mRNA in cecum and in small intestine after LPS. Gentamicin can suppress LPS-driven TNF-alpha production in proximal tubule cells, likely by inhibiting its translation. Overall preservation of protein synthesis and comparable MCP-1 suppression suggest a semiselective blockade within the LPS inflammatory mediator cascade. These results, coupled with increases in gut TNF-alpha/MCP-1 mRNAs, imply that gentamicin may exert protean, countervailing actions on systemic cytokine/chemokine production during gram-negative sepsis.

“Subclinical” gentamicin nephrotoxicity: a potential risk factor for exaggerated endotoxin-driven TNF-α production

This study sought to determine whether gentamicin, a mainstay in treating Gram-negative sepsis, alters endotoxin (lipopolysaccharide; LPS)-driven TNF-α increases. CD-1 mice received 1 day of gentamicin treatment. Either 0, 24, or 72 h later, gentamicin-treated and control mice were injected with LPS. Renal cortical and plasma TNF-α, as well as MCP-1, protein levels were measured 2 or 24 h post-LPS injection. Renal cortical mRNAs for TNF-α, MCP-1, IL-10, and inducible nitric oxide synthase (iNOS) were also determined. Finally, gentamicin's potential impact(s) on TNF-α/MCP-1 mRNA levels in nontraditional “target” organs (liver, spleen) was assessed. Gentamicin, when administered alone, slightly increased renal cortical TNF-α and MCP-1 mRNAs, but without changing plasma or renal TNF-α/MCP-1 protein levels. The gentamicin protocol induced no overt renal damage (assessed by blood urea nitrogen, creatinine, and histology). Nevertheless, gentamicin augmented LPS responsiveness, as manifested, in part, by a doubling of LPS-induced plasma TNF-α increases (vs. LPS injection alone). Plasma and renal cortical MCP-1 protein levels were also selectively enhanced. Gentamicin augmented LPS-driven renal mRNA increases (TNF-α, MCP-1, IL-10, iNOS). However, this was not an entirely renal-specific response, since gentamicin also enhanced basal and LPS-stimulated hepatic TNF-α mRNA levels. Subclinical gentamicin toxicity can potentiate LPS-driven TNF-α increases. Alterations in multiple proinflammatory (TNF-α; MCP-1; iNOS) and anti-inflammatory (IL-10) genes in the kidney, and possibly in extrarenal organs, may be involved. Thus gentamicin's activity in Gram-negative sepsis may extend beyond its traditional antimicrobial effect.

Endotoxin and cisplatin synergistically induce renal dysfunction and cytokine production in mice

A major toxicity of the cancer chemotherapeutic agent cisplatin is acute renal failure. Sepsis is a common cause of acute renal failure in humans and patients who receive cisplatin are at increased risk for sepsis. Accordingly, this study examined the interactions between cisplatin and endotoxin in vivo with respect to renal function and cytokine production. Mice were treated with either a single dose of cisplatin or two doses of LPS administered 24 h apart, or both agents in combination. Administration of 10 mg/kg cisplatin had no effect on blood urea nitrogen or creatinine levels throughout the course of the study. LPS resulted in a modest rise in blood urea nitrogen at 24 and 48 h, which returned to normal by 72 h. In contrast, mice treated with both cisplatin and LPS developed severe renal failure and an increase in mortality. Urine, but not serum, TNF-alpha levels showed a synergistic increase by cisplatin and LPS. Urinary IL-6, MCP-1, KC, and GM-CSF also showed a synergistic increase with cisplatin+LPS treatment. The renal dysfunction induced by cisplatin+LPS was completely dependent on TLR4 signaling and partially dependent on TNF-alpha production. Increased cytokine production was associated with a moderate increase in infiltrating leukocytes which was not different between cisplatin+LPS and LPS alone. These results indicate that cisplatin and LPS act synergistically to produce nephrotoxicity which may involve proinflammatory cytokine production.

Toll-like receptor (TLR4) shedding and depletion: acute proximal tubular cell responses to hypoxic and toxic injury

Acute renal failure (ARF) induces tubular hyperresponsiveness to TLR4 ligands, culminating in exaggerated renal cytokine/chemokine production. However, the fate of TLR4 protein during acute tubular injury remains unknown. The study sought new insights into this issue. Male CD-1 mice were subjected to 1) unilateral ischemia-reperfusion (I/R), 2) cisplatin (CP) nephrotoxicity, or 3) glycerol-induced myohemoglobinuric ARF. Renal cortical TLR4 protein (Western blotting, immunohistochemistry) and TLR4 mRNA levels (RT-PCR) were determined thereafter (90 min-4 days). Urinary TLR4 excretion post-I/R or CP injection was also assessed. To gain proximal tubule-specific results, TLR4 protein and mRNA were quantified in posthypoxic or oxidant (Fe)-challenged isolated mouse tubules. Finally, TLR4 mRNA was determined in antimycin A-injured cultured proximal tubular (HK-2) cells. Acute in vivo renal injury reduced proximal tubule TLR4 content. These changes corresponded with the appearance of TLR4 fragment(s) in urine and a persistent increase in renal cortical TLR4 mRNA. Isolated proximal tubules responded to injury with rapid TLR4 reductions, dramatic extracellular TLR4 release, and increases in TLR4 mRNA. Glycine blocked these processes, implying membrane pore formation was involved. HK-2 cell injury increased TLR4 mRNA, but not protein levels, suggesting intact transcriptional, but not translational, pathways. Diverse forms of acute tubular injury rapidly reduce proximal tubular TLR4 content. Plasma membrane TLR4 release through glycine-suppressible pores, possibly coupled with a translation block, appears to be involved. Rapid postinjury urinary TLR4 excretion suggests its potential utility as a "biomarker" of impending ARF.