Mast Cells and Gastrointestinal Dysmotility in the Cystic Fibrosis Mouse

Background

Cystic fibrosis (CF) has many effects on the gastrointestinal tract and a common problem in this disease is poor nutrition. In the CF mouse there is an innate immune response with a large influx of mast cells into the muscularis externa of the small intestine and gastrointestinal dysmotility. The aim of this study was to evaluate the potential role of mast cells in gastrointestinal dysmotility using the CF mouse (Cftr^tm1UNC, Cftr knockout).

Methodology

Wild type (WT) and CF mice were treated for 3 weeks with mast cell stabilizing drugs (ketotifen, cromolyn, doxantrazole) or were treated acutely with a mast cell activator (compound 48/80). Gastrointestinal transit was measured using gavage of a fluorescent tracer.

Results

In CF mice gastric emptying at 20 min post-gavage did not differ from WT, but was significantly less than in WT at 90 min post-gavage. Gastric emptying was significantly increased in WT mice by doxantrazole, but none of the mast cell stabilizers had any significant effect on gastric emptying in CF mice. Mast cell activation significantly enhanced gastric emptying in WT mice but not in CF mice. Small intestinal transit was significantly less in CF mice as compared to WT. Of the mast cell stabilizers, only doxantrazole significantly affected small intestinal transit in WT mice and none had any effect in CF mice. Mast cell activation resulted in a small but significant increase in small intestinal transit in CF mice but not WT mice.

Conclusions

The results indicate that mast cells are not involved in gastrointestinal dysmotility but their activation can stimulate small intestinal transit in cystic fibrosis.     

Effects of laxative and N-acetylcysteine on mucus accumulation, bacterial load, transit, and inflammation in the cystic fibrosis mouse small intestine

The accumulation of mucus in affected organs is characteristic of cystic fibrosis (CF). The CF mouse small intestine has dramatic mucus accumulation and exhibits slower interdigestive intestinal transit. These factors are proposed to play cooperative roles that foster small intestinal bacterial overgrowth (SIBO) and contribute to the innate immune response of the CF intestine. It was hypothesized that decreasing the mucus accumulation would reduce SIBO and might improve other aspects of the CF intestinal phenotype. To test this, solid chow-fed CF mice were treated with an osmotic laxative to improve gut hydration or liquid-fed mice were treated orally with N-acetylcysteine (NAC) to break mucin disulfide bonds. Treatment with laxative or NAC reduced mucus accumulation by 43% and 50%, respectively, as measured histologically as dilation of the intestinal crypts. Laxative and NAC also reduced bacterial overgrowth in the CF intestine by 92% and 63%, respectively. Treatment with laxative normalized small intestinal transit in CF mice, whereas NAC did not. The expression of innate immune response-related genes was significantly reduced in laxative-treated CF mice, whereas there was no significant effect in NAC-treated CF mice. In summary, laxative and NAC treatments of CF mice reduced mucus accumulation to a similar extent, but laxative was more effective than NAC at reducing bacterial load. Eradication of bacterial overgrowth by laxative treatment was associated with normalized intestinal transit and a reduction in the innate immune response. These results suggest that both mucus accumulation and slowed interdigestive small intestinal transit contribute to SIBO in the CF intestine.     

LPS-induced neutrophilic inflammation and Bcl-2 expression in metaplastic mucous cells

Our previous studies show that Bcl-2, a regulator of apoptosis, may be involved in the reduction of mucous cell metaplasia (MCM) during recovery from inflammatory responses. The present study was to determine whether neutrophilic inflammation mediates Bcl-2 expression in mucous cells. Rats were intratracheally instilled with 50-1000 microg of LPS. The number of neutrophils recovered by bronchoalveolar lavage (BAL) increased with the dose of LPS, and the percentage of Bcl-2-expressing cells increased with the numbers of neutrophils in the BAL. Depletion of neutrophils did not reduce MCM, but the percentage of Bcl-2-positive cells increased 1.8-fold in neutrophil-depleted compared with controls. Injection of rats with bezafibrate, an inducer of cytochrome P-450, doubled the number of neutrophils in the BAL, decreased MCM twofold compared with vehicle-injected controls, and reduced Bcl-2 expression. Bcl-2 mRNA levels decreased in a tracheal epithelial cell line treated with bezafibrate. These data demonstrate that Bcl-2 expression is independent of the number of neutrophils in the BAL and that bezafibrate may directly reduce Bcl-2 expression in epithelial cells.     

Intestinal phenotype of variable-weight cystic fibrosis knockout mice

Cystic fibrosis (CF) transmembrane conductance regulator (Cftr) knockout mice present the clinical features of low body weight and intestinal disease permitting an assessment of the interrelatedness of these phenotypes in a controlled environment. To identify intestinal alterations that are affected by body weight in CF mice, the histological phenotypes of crypt-villus axis height, goblet cell hyperplasia, mast cell infiltrate, crypt cell proliferation, and apoptosis were measured in a population of 12-wk-old (C57BL/6 x BALB/cJ) F2 Cftr(tm1UNC) and non-CF mice presenting a range of body weight. In addition, cardiac blood samples were assessed, and gene expression profiling of the ileum was completed. Crypt-villus axis height decreased with increasing body weight in CF but not control mice. Intestinal crypts from CF mice had fewer apoptotic cells, per unit length, than did non-CF mice, and normalized cell proliferation was similar to control levels. Goblet cell hyperplasia and mast cell infiltration were increased in the CF intestine and identified to be independent of body weight. Blood triglyceride levels were found to be significantly lower in CF mice than in control mice but were not dependent on CF mouse weight. By expression profiling, genes of DNA replication and lipid metabolism were among those altered in CF mice relative to non-CF controls, and no differences in gene expression were measured between samples from CF mice in the 25th and 75th percentile for weight. In this CF mouse model, crypt elongation, due to an expanded proliferative zone and decreased apoptosis, was identified to be dependent on body weight.     

The expression of cytochrome P-450 and cytochrome P-450 reductase genes in the simultaneous transformation of corticosteroids and phenanthrene by Cunninghamella elegans

The expression of cytochrome P-450 and cytochrome P-450 reductase (CPR) genes in the conterminous biotransformation of corticosteroids and PAHs was studied in Cunninghamella elegans 1785/21Gp. We had previously used this strain as a microbial eucaryotic model for studying the relationship between mammalian steroid hydroxylation and the metabolization of PAHs. We reported that cytochrome P-450 reductase is involved in the biotransformaton of cortexolone and phenanthrene. RT-PCR and Northern blotting analyses indicated that the cytochrome P-450 and CPR genes appear to be inducible by both steroids and PAHs. The expression of the cytochrome P-450 gene was increased ninefold and the expression of the CPR gene increased 6.4-fold in cultures with cortexolone and/or phenanthrene in comparison with controls. We conclude that the increase in cytochrome P-450 gene expression was accompanied by an increase in cytochrome P-450 enzymatic activity levels.     

Differential induction and tissue-specific expression of closely related members of the phenobarbital-inducible rabbit cytochrome P-450 gene family

We have examined the tissue-specific expression of three rabbit genes that are closely related members of a subfamily of the phenobarbital-inducible cytochrome P-450 gene family. Analysis of the levels of mRNA in liver revealed that (a) cytochrome P-450PBc1 mRNA was not detectable in livers from control animals but was present in livers from animals treated with phenobarbital, (b) cytochrome P-450PBc2 was present in control tissue and was increased by about 3-fold 24 h after phenobarbital treatment, and (c) the levels of cytochrome P-450PBc3 mRNA was the same in livers from control and treated animals. In the kidney, only P-450PBc2 mRNA was detected at a level 15% of that in the liver, and the levels increased about 3-fold after phenobarbital treatment. None of the mRNAs was detected in lung tissue. Multiple species of RNA were observed that hybridized to probes for cytochrome P-450PBc1 and P-450PBc2 cDNAs by Northern blot analysis ranging in size from 2300 to 4000 nucleotides. Differential sites for polyadenylation probably cause the heterogeneity in size. A single species of RNA of 2200 nucleotides that hybridized to cytochrome P-450PBc3 cDNA probes was observed. These data demonstrate that three closely related cytochrome P-450 genes are differentially responsive to phenobarbital treatment and that they exhibit different tissue-specific patterns of expression.     

Expression and function of three cytochrome P-450 isozymes in rat extrahepatic tissues

Western blots using a polyclonal and a monoclonal antibody raised against rat liver cytochrome P-450b indicate tissue-specific expression of low levels of cytochrome P-450's b and e. P-450b and P-450e were expressed very selectively in, respectively, lung and adrenal microsomes of untreated rats but neither isozyme was detected in the corresponding kidney or small intestine microsomes. The regioselectivity of microsomal metabolism of 7,12-dimethylbenz[a]anthracene (DMBA) as well as the sensitivity to inhibition by anti P-450b/e IgG established that low levels of "b-like" P-450's are functional in lung and adrenal microsomes from uninduced rats, but not in microsomes from the kidney or small intestine. Functional P-450c was also detected at low levels in liver, lung, kidney, and adrenals of untreated rats. Among the extrahepatic tissues examined, DMBA metabolism was the highest in rat adrenal microsomes. However, only 30% of this activity was due to P-450's b, e, or c. Phenobarbital (PB) treatment of rats increased microsomal DMBA metabolism in all extrahepatic tissues examined. The selectivity of this increase for 12-methyl hydroxylation of DMBA and the near complete inhibition by anti-P-450b/e are consistent with induction of P-450e even though P-450b was preferentially induced in each of the extrahepatic tissues examined. The levels of expression of P-450b were increased by PB in all sets of adrenal, lung, and intestinal microsomes and in three out of six sets of kidney microsomes. The levels of P-450e were also increased by PB in all sets of adrenal microsomes. Following PB treatment, P-450e became immunoquantifiable (greater than 2 pmol/mg protein) in three of six sets of lung and kidney microsomes but remained below detection in all sets of intestinal microsomes. Based on the activity of purified P-450e, undetectable levels (less than 1 pmol/mg protein) could account for increased DMBA metabolism in this tissue. The high constitutive level of P-450b in the lung (approximately 40 pmol/mg), was remarkably inactive in DMBA metabolism and was only slightly increased by PB treatment (50%). In contrast, PB treatment caused a 2.5- to 10-fold increase in 12-methyl hydroxylation of DMBA that was highly sensitive to anti-P-450b/e. A protein comigrating with P-450e was well above detection (6-7 pmol/mg) in two of six preparations of lung microsomes that showed highest induction of this activity.(ABSTRACT TRUNCATED AT 400 WORDS)     

Induction and repression of the major phenobarbital-induced cytochrome P-450 measured by radioimmunoassay.

Two independent radioimmunoassay techniques for the major phenobarbital-inducible cytochrome P-450 (PB P-450) of rat liver microsomal membranes are described. The first technique employs as the source of radiolabelled antigen the products of translation in vitro labelled with [35S]methionine. The second technique employs purified antigen labelled with 125I and is quicker, less expensive and more precise. Both assays are highly specific for PB P-450 and can detect quantities of this variant as small as 1 ng. This is several orders of magnitude more sensitive than any method described previously for the quantification of cytochromes P-450, and consequently the technique is particularly well suited for the quantification of so-called constitutive cytochrome P-450 variants that are present in very low amounts. The results of the radioimmunoassays demonstrate that the apparent 2.6-fold induction of total cytochromes P-450 after phenobarbital treatment is due to a 43-fold increase in Pb P-450. Although beta-naphthoflavone increases the total content of cytochrome P-450 of microsomal membranes 1.4-fold, it actually causes a 55% decrease in the amount of PB P-450. Thus different xenobiotics can have differential effects on the expression of the genes for specific cytochrome P-450 variants.     

Role of gastrin/pentagastrin in regulation of intestinal cytochrome P-450

1. In the absence of intraluminal inducers, low "basal" levels of cytochrome P-450 and its dependent MFO activities are detected in the rat intestinal mucosa, and may be regulated by endogenous hormones. 2. Rats were nutritionally maintained by either short term (48 hr) intravenous glucose infusion or chronic (8 days) intravenous hyperalimentation, and were treated with various doses of pentagastrin in the infusate. 3. Regardless of the dose (6-90 micrograms/kg/hr) or duration of infusion (2-8 days), pentagastrin had no effect on small intestinal cytochrome P-450, its dependent MFO activity, or the activity of delta-aminolevulinic acid synthetase. 4. The intestinal trophic peptide hormone, gastrin, apparently does not regulate the cytochrome P-450-dependent MFO system of the small intestine.     

Toxicological significance of dog liver cytochrome P-450: examination with the enzyme expressed in Saccharomyces cerevisiae using recombinant expression plasmid.

A complementary DNA (cDNA) coding for a form of beagle dog cytochrome P-450 (Dah1), which is the orthologue to the CYP1A1 cDNA of rat, mouse and human, was inserted between the alcohol dehydrogenase (ADH) promoter and terminator regions of the yeast expression vector pAAH5. On introduction of the resulting recombinant plasmid pDC-1, Saccharomyces cerevisiae strain AH22 cells synthesized up to 1.5 x 10(5) molecules per cell of cytochrome P-450 protein (P-450(Dah1)). The carbon monoxide-bound reduced form of P-450(Dah1) showed an absorption peak at 447 nm and specific content of P-450(Dah1) was about 0.1 nmole P-450 per mg of microsomal protein. P-450(Dah1) cross-reacted with antibodies to rat P-448-H (CYP1A2) and dog P-450-D2 (CYP1A2). P-450(Dah1) activated 2-amino-3-methyl-imidazo[4,5-f]quinoline (IQ) and 2-amino-3,4-dimethylimidazo[4,5-f]quinoline (MeIQ) most efficiently in the umu test and exhibited a high activity of aryl hydrocarbon hydroxylase toward benzo[a]pyrene.     

Regulation of steroidogenesis in rat Leydig cells in culture: effect of human chorionic gonadotropin and dibutyryl cyclic AMP on the synthesis of cholesterol side chain cleavage cytochrome P-450 and adrenodoxin

Rat Leydig cells in primary culture were used as a model system to investigate the effects of human chorionic gonadotropin (hCG) and dibutyryl cyclic AMP (Bt2cAMP) on the synthesis of cholesterol side chain cleavage cytochrome P-450 (cytochrome P-450scc) and the iron-sulfur protein, adrenodoxin. Leydig cells isolated from the testes of mature rats were placed in monolayer culture in the absence of stimulatory factors for 8 days. HCG (10 mIU/ml) or Bt2cAMP (1 mM) were then added to some of the cultures and the incubations were continued for up to 48 h. Testosterone production was increased markedly in cells incubated with hCG or Bt2cAMP. A significant accumulation of pregnenolone in the medium of cells treated with Bt2cAMP was also observed. Both hCG and Bt2cAMP increased the rates of synthesis of cytochrome P-450scc and adrenodoxin. In hCG-treated cells the apparent rate of synthesis of cytochrome P-450scc was increased 13-fold over that of controls after 48 h of incubation; the rate of adrenodoxin synthesis was increased 4-fold by hCG treatment. In Bt2cAMP-treated cells the rate of synthesis of cytochrome P-450scc was 37-fold greater than that of control cells after 48 h of incubation; adrenodoxin synthesis was increased 36-fold over controls. In hCG- and Bt2cAMP-treated cells, the concentration of immunoreactive cytochrome P-450scc and adrenodoxin increased with increasing time of incubation, and were correlated with the stimulatory effects of these agents on cytochrome P-450scc activity and on total steroid production. The results of this study are indicative that the maintenance by LH/hCG of elevated levels of testosterone synthesis by the Leydig cell is mediated, in part, by induction of the synthesis of cytochrome P-450scc and its associated protein, adrenodoxin. Since Bt2cAMP had effects similar to those observed with hCG, it is suggested that the stimulatory effects of hCG on the synthesis of cytochrome P-450scc and adrenodoxin are mediated by increased cyclic AMP formation.     

Cytochrome P-450- and Peroxidase-Dependent Activation of Procarbazine and Iproniazid in Mammalian Cells

Metabolism of hydrazine derivatives, procarbazine and iproniazid, to reactive free radical intermediates has been studied using spin-trapping techniques in intact human promyelocytic leukemia (HL60) and mouse hepatic cell lines. While HL60 cells have been shown to contain both myeloperoxidase and cytochrome P-450 enzymes, the hepatic cell line shows only cytochrome P-450 activity. Both peroxidases and cytochrome P-450 have been reported to catalyze biotransformation of hydrazines. Procarbazine and iproniazid were rapidly metabolized in these cell lines to methyl and isopropyl radicals, respectively. However, in HL60 cells, procarbazine was metabolized by myeloperoxidase while iproniazid was metab olized mostly by the cytochrome P-450 system. In the hepatic cells, both of these compounds were metabolized by the P-450 system.     

Cytochrome P-450- and Peroxidase-Dependent Activation of Procarbazine and Iproniazid in Mammalian Cells

Metabolism of hydrazine derivatives, procarbazine and iproniazid, to reactive free radical intermediates has been studied using spin-trapping techniques in intact human promyelocytic leukemia (HL60) and mouse hepatic cell lines. While HL60 cells have been shown to contain both myeloperoxidase and cytochrome P-450 enzymes, the hepatic cell line shows only cytochrome P-450 activity. Both peroxidases and cytochrome P-450 have been reported to catalyze biotransformation of hydrazines. Procarbazine and iproniazid were rapidly metabolized in these cell lines to methyl and isopropyl radicals, respectively. However, in HL60 cells, procarbazine was metabolized by myeloperoxidase while iproniazid was metab olized mostly by the cytochrome P-450 system. In the hepatic cells, both of these compounds were metabolized by the P-450 system.     

Monooxygenase activity of Saccharomyces cerevisiae cells transformed with expression plasmids carrying rat cytochrome P-450MC cDNA

The recombinant plasmids pAMC1 and pJMC1 were constructed; the former contained the cytochrome P-450MC (P-450MC) cDNA expression unit consisting of yeast alcohol dehydrogenase I (ADH) promoter, rat P-450MC cDNA and ADH terminator, and the Leu 2 marker gene, and the latter contained the same expression unit and the leu 2-d gene. Saccharomyces cerevisiae AH22 cells transformed with each of the recombinant plasmids were examined for plasmid copy number, P-450MC mRNA level, P-450MC content, and monooxygenase activity. The S. cerevisiae AH22/pJMC1 cells contained about 2-fold higher levels of the plasmid, P-450MC mRNA, and P-450MC than the AH22/pAMC1 cells. Monooxygenase activity towards 7-ethoxycoumarin and acetanilide of the AH22/pJMC1 cells was 1.7-fold and 1.5-fold higher than that of the AH22/pAMC1 cells, respectively, whereas the activity of the AH22/pAMC1 cells towards 7-ethoxycoumarin and acetanilide was more than 1,000-fold 10-fold higher than that of the control AH22/pAAH5 cells which contain no P-450MC cDNA, respectively. Therefore, it is likely that monooxygenase activity of the AH22 cells carrying rat P-450MC cDNA was approximately proportional to the expression level of P-450MC cDNA.     

Fatty acid omega and (omega-1)-Hydroxylation in rabbit intestinal mucosa microsomes.

The microsomes from rabbit intestinal mucosa which had been washed quickly and thoroughly with phenylmethylsulfonyl fluoride were found to catalyze the hydroxylation of fatty acids in the presence of NADPH and molecular oxygen. Myristic and palmitic acids were converted to the corresponding omega-and (omega-1)-hydroxy fatty acids, whereas lauric acid was converted only to 12-hydroxylauric acid, and capric acid, to 9-and 10-hydroxycapric acids together with an unknown polar acid.Among these fatty acids, both myristic and lauric acids appeared to be the most efficient substrates. The inhibition of the hydroxylation by SKF 525-A and carbon monoxide suggested that the activity depended upon cytochrome P-450. The specific activity of the fatty acid hydroxylation was almost constant along the small intestine, while the aminopyrine N-demethylation activity and the cytochrome P-450 content were highest at the proximal end of the intestine and progressively declined toward the caudal end. The cytochrome P-450 was solubilized from the intestinal microsomes and purified by 6-amino-n-hexyl Sepharose 4B chromatography. The partially purified cytochrome P-450 was active in fatty acid hydroxylation in combination with intestinal NADPH-cytochrome c reductase and phosphatidylcholine.     

Evidence for the presence of cholesterol side chain cleavage cytochrome P-450 and adrenodoxin in fresh granulosa cells. Effects of follicle-stimulating hormone and cyclic AMP on cholesterol side chain cleavage cytochrome P-450 synthesis and activity

The synthesis of cholesterol side chain cleavage cytochrome P-450 (cytochrome P-450scc) and adrenodoxin was studied both in freshly harvested bovine granulosa cells and in granulosa cells maintained in primary monolayer culture. In addition, the action of follicle-stimulating hormone (FSH) and cyclic AMP analogs to stimulate the synthesis of cytochrome P-450scc was investigated in cultured cells. Precursor forms of cytochrome P-450scc and adrenodoxin were immunoisolated from a cell-free translation system directed by RNA prepared from freshly obtained granulosa cells that were not luteinized. Furthermore, the presence of cytochrome P-450scc in lysates of granulosa cells freshly obtained from very small follicles (containing less than 0.1 ml of follicular fluid) and in mitochondria of freshly obtained granulosa cells was demonstrated by using an immunoblotting technique. Continuous treatment of cultured granulosa cells with FSH or with cyclic AMP analogs (dibutyryl cyclic AMP or 8-bromo cyclic AMP) for 72 h increased incorporation of [35S]methionine into immunoprecipitable cytochrome P-450scc. Moreover, FSH, dibutyryl cyclic AMP, and 8-bromo cyclic AMP stimulated pregnenolone production by cultured granulosa cells (2.3-, 4.0-, and 7.5-fold increase over control, respectively), indicative of an increase in cholesterol side chain cleavage activity. The results of this study demonstrate for the first time the presence of two components of the cholesterol side chain cleavage system in freshly obtained granulosa cells, and provide direct evidence for the trophic effect of FSH and its presumed mediator, cyclic AMP, on the synthesis of cytochrome P-450scc in granulosa cells.     

Ferredoxin and cytochrome P-450scc concentrations in granulosa cells of porcine ovaries during follicular cell growth and luteinization

The concentrations of cytochrome P-450scc and ferredoxin, two of the three proteins which comprise the mitochondrial steroidogenic electron transport chain, were measured in granulosa and luteal cells from porcine ovaries by an immunoblot procedure. During the follicular phase of the ovarian cycle the concentration of cytochrome P-450scc increased 5-fold and ferredoxin increased 3-fold. When the large follicles developed into corpora lutea the cytochrome P-450scc concentration increased a further 7-fold while ferredoxin increased only 3-fold. These changes were coincident with an overall 4-fold increase in the concentration of ferredoxin reductase during follicular cell development and luteinization. Analysis of the data revealed that the concentration of ferredoxin, which shuttles electrons from ferredoxin reductase to cytochrome P-450scc, was always adequate to saturate both the reductase and cytochrome P-450scc. This came about from a co-ordinate increase in the concentration of cytochrome P-450scc and the concentration of ferredoxin minus ferredoxin reductase.     

cDNA cloning of cytochrome P-450 related to P-450p-2 from the cDNA library of human placenta. Gene structure and expression

We have isolated and analyzed cDNA (designated P-450HP cDNA) clones from a human placenta cDNA library, using the cDNA for rabbit pulmonary cytochrome P-450p-2, a prostaglandin omega-hydroxylase, as a hybridization probe. The cDNA obtained encoded a polypeptide comprising 511 amino acids with a calculated molecular mass of 58987 Da, and the amino acid sequence similarity with P-450p-2 and rat liver laurate omega-hydroxylase (P-450LA omega) was only about 50%. RNA blot analysis showed that the mRNA hybridizable with the human P-450HP cDNA was inducibly expressed 3-5-fold in rabbit small intestine and lung by gestation, but the expression remained constant in rabbit liver and kidney. This mode of expression was quite different from that of P-450p-2 and P-450LA omega. Interestingly, the mRNA hybridized with the cDNA of P-450HP was found to be expressed in all the human tumor tissues so far examined, in sharp contrast with the facts that almost all the other species of P-450s are known to disappear in the tumor tissues. Taken together, the deduced hemoprotein termed P-450HP dose not seem to be the human counterpart of rabbit P-450p-2 or rat P-450LA omega, and is presumably a new member of the P-450 family including P-450p-2 and P-450LA omega. Furthermore, the corresponding genomic DNA was also cloned and analyzed. The gene of P-450HP spanned 18.8 kb and was separated into 11 exons by 10 introns whose locations were completely different from those of P-450 genes so far determined.