Guylaine Bouchard

Gangliogenesis in the enteric nervous system: Roles of the polysialylation of the neural cell adhesion molecule and its regulation by bone morphogenetic protein‐4

The neural crest–derived cells that colonize the fetal bowel become patterned into two ganglionated plexuses. The hypothesis that bone morphogenetic proteins (BMPs) promote ganglionation by regulating neural cell adhesion molecule (NCAM) polysialylation was tested. Transcripts encoding the sialyltransferases, ST8Sia IV (PST) and ST8Sia II (STX), which polysialylate NCAM, were detectable in fetal rat gut by E12 but were downregulated postnatally. PSA‐NCAM‐immunoreactive neuron numbers, but not those of NCAM, were developmentally regulated similarly. Circular smooth muscle was transiently (E16–20) PSA‐NCAM‐immunoreactive when it is traversed by migrating precursors of submucosal neurons. Neurons developing in vitro from crest‐derived cells immunoselected at E12 with antibodies to p75NTR expressed NCAM and PSA‐NCAM. BMP‐4 promoted neuronal NCAM polysialylation and clustering. N‐butanoylmannosamine, which blocks NCAM polysialylation, but not N‐propanoylmannosamine, which does not, interfered with BMP‐4‐induced neuronal clustering. Observations suggest that BMP signaling enhances NCAM polysialylation, which allows precursors to migrate and form ganglionic aggregates during the remodeling of the developing ENS. Developmental Dynamics 236:44–59, 2007.

Decreased biliary glutathione content is responsible for the decline in bile salt-independent flow induced by ethinyl estradiol in rats

Glutathione appears to be a major osmotic factor in the generation of bile salt-independent flow (BSIF). This study was designed to investigate its importance in the pathology of 17-alpha-ethinyl estradiol (EE)-induced cholestasis. Five-day EE treatment at the dose level of 5 mg/kg/day significantly decreased bile flow (57% of controls) and biliary glutathione secretion. Evaluation of the contribution of bile salt dependent flow (BSDF), glutathione dependent flow (GSDF) and the bile flow generated independently of both bile salts and glutathione (BS-GSIF) revealed that EE decreased all portions of the flow (63, 44 and 52% of control values, respectively). At 4 and 20 h after a single administration of the same EE dose, a significant diminution of bile flow was noted (decreases of 17 and 29%, respectively) in association with a significant fall in biliary glutathione content. Under these conditions, BSDF and BS-GSIF were not modified (98 and 112% of control BSDF values, respectively; 96 and 99% of control BS-GSIF values, respectively) while GSDF was decreased markedly, representing 65 and 50% of control values. Biliary glutathione secretion was diminished without modification of liver and blood glutathione concentration or redox status following single EE dose whereas, after 5 days of EE treatment, a significant increase in liver glutathione was observed, suggesting that EE may interfere with the glutathione secretory process. This study demonstrates that EE rapidly alters biliary glutathione content, leading to a marked decline in GSDF. This reduction may explain the decrease in BSIF produced by EE at the outset of cholestasis.

Role of glutathione and oxidative stress in phalloidin-induced cholestasis.

BACKGROUND/AIMS Biliary glutathione is an important generator of the bile-salt independent flow, and is known to be regulated by the hepatic glutathione availability. We investigated, in an acute model of phalloidin-induced cholestasis, biliary glutathione secretion and the role of hepatic glutathione, oxidative stress, and protein kinase c activation, which have been implicated in many hepatotoxin-induced hepatic dysfunctions. METHODS Rats were given a single dose of 80 microg/100 g body weight of phalloidin and the hepatic thiols and glutathione content, redox state and vesicular activity were evaluated during both development of and recovery from cholestasis. The prophylactic effect of N-acetylcysteine (a precursor of glutathione synthesis and an antioxidant) was also examined. In addition, in the isolated perfused rat liver, we studied the prophylactic effect of the PKc inhibitor H7 on phalloidin-induced cholestasis. RESULTS In the early stages of cholestasis, phalloidin induced a decline in bile flow, mainly related to a disruption of biliary glutathione secretion. The decline in biliary glutathione content was not associated with increased glutathione degradation, indicated by a parallel decline in biliary non-protein thiols and by the lack of an increase in biliary gamma-glutamyltranspeptidase. There was also no evidence of hepatic depletion of glutathione or of oxidative stress, as measured by the oxidized-to-reduced glutathione ratio. Moreover, phalloidin resulted in inhibition of vascular transcytosis as assessed by horseradish peroxidase labeling. Pre-treatment with N-acetylcysteine did not counteract the decline in biliary glutathione secretion and bile flow produced by phalloidin, supporting the view that the hepatic availability of glutathione and oxidative stress injury are not implicated in the early stages of cholestatic injury. Moreover, treatment with H-7 did not alter the biliary glutathione output, or the decline in bile flow induced by the toxin. CONCLUSIONS This study suggests that the phalloidin-induced inhibition of bile formation may be attributed to rapid disruption of the hepatocanalicular transport of glutathione.

Moderate Long-Term Physical Activity Improves the Age-Related Decline in Bile Formation and Bile Salt Secretion in Rats

Abstract This study examined the effect of moderate long-term exercise, begun soon after weaning, on the age-related decline in bile formation and the secretory rate maximum (SRm) of taurocholate (TC), the major bile salt (BS) in rats. Eight-month-old sedentary (S) female Sprague-Dawley rats showed a significant decrease in basal and TC-stimulated bile formation when compared with 2.5-month-old S controls. As in younger rats, decreased biliary phospholipid (PL) output was associated with the TC SRm, but this change appeared much more rapidly in S animals, which also exhibited significant increased plasma lipids and higher TC concentrations in plasma and liver at the end of TC infusion. Exercise significantly improved bile flow (BF), including the bile salt-dependent and -independent fractions under basal and TC-stimulated conditions in 8 month-old rats. Although all the biliary parameters evaluated were improved, maximal BF and PL secretion values were affected the most and were virtually not different from those obtained in younger S animals. Exercise also significantly lowered the age-related elevation of plasma PL. Thus, moderate long-term exercise exerts a beneficial effect on hepatobiliary function and the BS SRm, an effect that may be attributed in part to increased availability of a biliary PL pool previously implicated in regulation of the BS SRm.

Combined effects of EFA deficiency and tumor necrosis factor-α on circulating lipoproteins in rats

Both tumor necrosis factor-α (TNF-α) and EFA deficiency (EFAD) have been established as causes of marked perturbations in lipid and lipoprotein metabolism. Excessive levels of circulating TNF-α can coexist with EFAD in various clinical disorders such as cystic fibrosis and type I diabetes. The present study therefore aimed to investigate their combined effects on lipid profile and lipoprotein composition by administering TNF-α to EFAD rats. Lipoprotein lipase (LPL), the ratelimiting enzyme in TG catabolism, was also measured in epididymal adipose tissue. EFAD, after a 4-wk period, induced significant increases in plasma TG (80%, P<0.001), total cholesterol (TC, 27%, P<0.025), and HDL-cholesterol (HDL-C, 62%). Two hours after the administration of TNF-α, a further rise in TG (43%, P<0.05) was noted in controls, but not EFAD animals. TC and HDL-C were unaffected by TNF-α treatment. In addition, TNF-α modified lipoprotein-lipid composition. VLDL and HDL2 derived from EFAD rats were depleted in apolipoprotein (apo) E and apo A-II, and enriched in apo A-12 h after TNF-α administration. Finally, TNF-α decreased adipose tissue LPL activity in both control and EFAD animals. The TNF-α-induced inhibition was more marked in EFAD rats. The present results demonstrated that TNF-α can amplify or antagonize the effects of EFAD on lipid profile, lipoprotein composition, and LPL activity. These data also suggest that the hosts nutritional status is a determining factor for the modulating effect of TNF-α on lipid metabolism.