Rat enterocytes secrete SLPs containing alkaline phosphatase and cubilin in response to corn oil feeding

Transcriptome and computational approaches highlighting the molecular regulation of Zacco platypus induced by mesocosm exposure to common disinfectant chlorine

Chlorine (Cl₂) is a disinfectant often used in swimming pools and water treatment facilities. However, it is released into aquatic ecosystems, where it may harm non-targeted organisms. Here, we performed a mesocosm experiment exposing Zacco platypus (Z. platypus) to biocide Cl₂ for 30 days (30 d) at two days' time points 15 days (15 d) and 30 d samples were collected. Here, Z. platypus was exposed to a sublethal concentration (0.1 mg/L) of Cl₂, and comparative transcriptomics analyses were performed to determine their response mechanisms at the molecular level. According to RNA sequencing of the whole-body transcriptome, 860 and 1189 differentially expressed genes (DEGs) were identified from the 15 d and 30 d responses to Cl₂, respectively. After enrichment analysis of GO (Gene Ontology) functions and KEGG (Kyoto Encyclopedia of Genes and Genomes) pathways, identified DEGs were demonstrated to be associated with a variety of functions, including "ion binding and transmembrane transporters". Cl₂ also induced oxidative stress in Z. platypus by increasing the levels of reactive oxygen species (ROS) while decreasing the catalase (CAT) content and the levels of solute carrier family 22 member 11 (slc22a11), Caspase-8 (casp-8), inducible nitric oxide synthase (NOS2), cytosolic phospholipase A2 gamma (PLA2G4). However, Z. platypus still allows recovery during stress suspension by increasing the expression levels of solute carrier family proteins. The GO and KEGG annotation results revealed that the expression of DEGs were related to the detoxification process, immune response, and antioxidant mechanism. Additionally, protein-protein interaction networks (PPI) and cytoHubba analyses identified sixteen hub genes and their interaction. These findings elucidate the regulation of various DEGs and signaling pathways in response to Cl₂ exposure, which will improve our knowledge and laid foundation for further investigation of the toxicity of Cl₂ to Z. platypus.

Vitamin D restriction and/or a high-fat diet influence intestinal alkaline phosphatase activity and serum endotoxin concentration, increasing the risk of metabolic endotoxemia in rats

Vitamin D insufficiency induces calcification disorder of bone or a decrease in bone mineral density, increasing the risk of fracture. Alkaline phosphatase (ALP) activity, a differentiation marker for intestinal epithelial cells, is regulated by vitamin D. It has also been suggested that ALP may prevent metabolic endotoxemia by dephosphorylating lipopolysaccharide. We hypothesized that vitamin D restriction and/or a high-fat diet influences ALP activity in each tissue and serum lipopolysaccharide concentrations and increases the risk of metabolic endotoxemia. Eleven-week-old female rats were divided into 4 groups: basic control diet (Cont.), basic control diet with vitamin D restriction (DR), high-fat diet (HF), and high-fat diet with vitamin D restriction (DRHF) groups. They were acclimated for 28 days. The results of 2-way analysis of variance showed that intestinal ALP activity, which may contribute to an improvement in phosphate/lipid metabolism and longevity, in the high-fat diet groups (HF and DRHF) was higher than in the low-fat diet groups (Cont. and DR). ALP activity in the vitamin D-restricted groups (DR and DRHF) was lower than in the vitamin D-sufficient groups (Cont. and HF). Furthermore, serum endotoxin concentrations were significantly higher in the high-fat diet groups (HF and DRHF) than in the low-fat diet groups (Cont. and DR). In the vitamin D-restricted groups (DR and DRHF), serum endotoxin concentrations were also significantly higher than in the vitamin D-sufficient groups (Cont. and HF). These results suggest that vitamin D restriction and/or a high-fat diet increases the risk of metabolic endotoxemia.

Favorable Aspects of Silymarin in Linezolid Treatment Against Diabetic Methicillin-Resistant Staphylococcus aureus (MRSA) Infected Rats

Background:

Linezolid used for diabetic methicillin-resistant Staphylococcus aureus (MRSA) infections is limited due to hepatotoxicity, lactic acidosis, anemia, and oxidative stress induced by diabetes and linezolid therapy. Silymarin is a hepatoprotective, antioxidant, antibacterial, and antidiabetic.

Objective:

The research investigated the role of silymarin in linezolid treatment against MRSA-infected diabetic rats.

Methods:

Type 2 diabetes mellitus (T2DM) was induced by a high-fat diet (58% calories fat) for 2 weeks, followed by a single intraperitoneal injection of streptozotocin (STZ) 35 mg/kg into Wistar rats. The diabetic rats were rendered neutropenic and subcutaneously injected with 106 CFU/ml of MRSA. Linezolid and silymarin were administered orally at a dose of 50 mg/kg twice daily for 14 days. The bacterial load/abscess, hematological, biochemical, enzymatic parameters, antioxidants, and histopathological studies were performed on the 42nd day.

Results:

The MRSA was confirmed by PCR assay. The minimum inhibitory concentration of linezolid was found to be 0.5-2 μg/ml. The linezolid treated MRSA infected diabetic rats showed 9.69 x 103 CFU / abscess bacterial count, decreased intestinal alkaline phosphatase (IAP), RBC, antioxidants, elevated lactate, and liver markers than diabetic rats. The silymarin treatment showed a decrease in the bacterial count (2.98 x 103 CFU / abscess), serum lactate, liver markers, increased IAP levels, and antioxidants in linezolid treated diabetic infected rats.

Conclusion:

The research concluded that silymarin could be a better herbal therapeutic agent that attenuated diabetic and linezolid induced complications in MRSA-infected diabetic rats.

A new perspective on the function of Tissue Non-Specific Alkaline Phosphatase: from bone mineralization to intra-cellular lipid accumulation

Tissue-nonspecific alkaline phosphatase (TNAP) is one of four isozymes, which include germ cell, placental and intestinal alkaline phosphatases. The TNAP isozyme has 3 isoforms (liver, bone and kidney) which differ by tissue expression and glycosylation pattern. Despite a long history of investigation, the exact function of TNAP in many tissues is largely unknown. Only the bone isoform has been well characterised during mineralization where the enzyme hydrolyses pyrophosphate to inorganic phosphate, which combines with calcium to form hydroxyapatite crystals deposited as new bone. The inorganic phosphate also increases gene expression of proteins that support tissue mineralization. Recent studies have shown that TNAP is expressed in preadipocytes from several species, and that inhibition of TNAP activity causes attenuation of intracellular lipid accumulation in these and other lipid-storing cells. The mechanism by which TNAP stimulates lipid accumulation is not known; however, proteins that are important for controlling phosphate levels in bone are also expressed in adipocytes. This review examines the evidence that inorganic phosphate generated by TNAP promotes transcription that enhances the expression of the regulators of lipid storage and consequently, that TNAP has a major function of lipid metabolism.

Protective Effect of Alkaline Phosphatase Supplementation on Infant Health

Alkaline phosphatase (ALP) is abundant in raw milk. Because of its high heat resistance, ALP negative is used as an indicator of successful sterilization. However, pasteurized milk loses its immune protection against allergy. Clinically, ALP is also used as an indicator of organ diseases. When the activity of ALP in blood increases, it is considered that diseases occur in viscera and organs. Oral administration or injecting ALP will not cause harm to the body and has a variety of probiotic effects. For infants with low immunity, ALP intake is a good prebiotic for protecting the infant’s intestine from potential pathogenic bacteria. In addition, ALP has a variety of probiotic effects for any age group, including prevention and treatment intestinal diseases, allergies, hepatitis, acute kidney injury (AKI), diabetes, and even the prevention of aging. The prebiotic effects of alkaline phosphatase on the health of infants and consumers and the content of ALP in different mammalian raw milk are summarized. The review calls on consumers and manufacturers to pay more attention to ALP, especially for infants with incomplete immune development. ALP supplementation is conducive to the healthy growth of infants.

Cubilin, the intrinsic factor-vitamin B12 receptor

Cubilin (CUBN), the intrinsic factor-vitamin B12 receptor is a large endocytic protein involved in various physiological functions: vitamin B12 uptake in the gut; reabsorption of albumin and maturation of vitamin D in the kidney; nutrient delivery during embryonic development. Cubilin is an atypical receptor, peripherally associated to the plasma membrane. The transmembrane proteins amnionless (AMN) and Lrp2/Megalin are the currently known molecular partners contributing to plasma membrane transport and internalization of Cubilin. The role of Cubilin/Amn complex in the handling of vitamin B12 in health and disease has extensively been studied and so is the role of the Cubilin-Lrp2 tandem in renal pathophysiology. Accumulating evidence strongly supports a role of Cubilin in some developmental defects including impaired closure of the neural tube. Are these defects primarily caused by the dysfunction of a specific Cubilin ligand or are they secondary to impaired vitamin B12 or protein uptake? We will present the established Cubilin functions, discuss the developmental data and provide an overview of the emerging implications of Cubilin in the field of cardiovascular disease and cancer pathogenesis.

Vitamin D pathway gene variation rs3740165 is associated with serological uric acid levels in healthy Chinese women

AIM

To investigate the relationship between gene polymorphisms involved in the vitamin D metabolic pathway and serum uric acid (UA) levels in Chinese women.

METHODS

Fifteen key genes within the vitamin D metabolic pathway were screened using 96 single nucleotide polymorphisms in a group of 1,206 (37.96 ± 13.08 years) unrelated healthy Chinese women (aged 20-85 years). Blood and urine tests were performed at the same time. The Wilcoxon Mann-Whitney test was used to compare groups aged ≤50 years and >50 years. The mean serum UA values were computed within each group of homozygous referent, heterozygous, and homozygous variant genotypes for each single nucleotide polymorphism.

RESULTS

The exclusion process left 1,169 participants (38.16 ± 13.13 years) for analysis. One single nucleotide polymorphism in the CUBN gene (rs3740165) was identified as being significantly associated with serum UA levels in the group aged over 50 years. The wild type (C/C) population had higher serum UA levels in this group (P<0.001). In women aged over 50 years, allele C was associated with a higher risk of hyperuricemia than allele T (odds ratio 2.752, 95% confidence interval 1.458-5.192; P = 0.002). There was also a higher risk of hyperuricemia in genotype TC + CC compared with genotype TT (odds ratio 3.326, 95% confidence interval 1.513-7.313; P = 0.003) in women over 50 years of age.

CONCLUSION

The results suggest that the CUBN gene contributes to variability in serum UA levels in healthy Chinese Han women over 50 years of age.

Cross-Talk Between Intestinal Microbiota and Host Gene Expression in Gilthead Sea Bream (Sparus aurata) Juveniles: Insights in Fish Feeds for Increased Circularity and Resource Utilization

New types of fish feed based on processed animal proteins (PAPs), insect meal, yeast, and microbial biomasses have been used with success in gilthead sea bream. However, some drawback effects on feed conversion and inflammatory systemic markers were reported in different degrees with PAP- and non-PAP-based feed formulations. Here, we focused on the effects of control and two experimental diets on gut mucosal-adherent microbiota, and how it correlated with host transcriptomics at the local (intestine) and systemic (liver and head kidney) levels. The use of tissue-specific PCR-arrays of 93 genes in total rendered 13, 12, and 9 differentially expressed (DE) genes in the intestine, liver, and head kidney, respectively. Illumina sequencing of gut microbiota yielded a mean of 125,350 reads per sample, assigned to 1,281 operational taxonomic unit (OTUs). Bacterial richness and alpha diversity were lower in fish fed with the PAP diet, and discriminant analysis displayed 135 OTUs driving the separation between groups with 43 taxa correlating with 27 DE genes. The highest expression of intestinal pcna and alpi was achieved in PAP fish with intermediate values in non-PAP, being the pro-inflammatory action of alpi associated with the presence of Psychrobacter piscatorii. The intestinal muc13 gene was down-regulated in non-PAP fish, with this gene being negatively correlated with anaerobic (Chloroflexi and Anoxybacillus) and metal-reducing (Pelosinus and Psychrosinus) bacteria. Other inflammatory markers (igm, il8, tnfα) were up-regulated in PAP fish, positively correlating the intestinal igm gene with the inflammasome activator Escherichia/Shigella, whereas the systemic expression of il8 and tnfα was negatively correlated with the Bacilli class in PAP fish and positively correlated with Paracoccus yeei in non-PAP fish. Overall changes in the expression pattern of il10, galectins (lgals1, lgals8), and toll-like receptors (tlr2, tlr5, tlr9) reinforced the anti-inflammatory profile of fish fed with the non-PAP diet, with these gene markers being associated with a wide range of OTUs. A gut microbiota-liver axis was also established, linking the microbial generation of short chain fatty acids with the fueling of scd1- and elovl6-mediated lipogenesis. In summary, by correlating the microbiome with host gene expression, we offer new insights in the evaluation of fish diets promoting gut and metabolism homeostasis, and ultimately, the health of farmed fish.

Effect of Food Endotoxin on Infant Health

Endotoxin is a complex molecule derived from the outer membrane of Gram-negative bacteria, and it has strong thermal stability. The processing of infant food can kill pathogenic bacteria but cannot remove endotoxin. Because the intestinal structure of infants is not fully developed, residual endotoxin poses a threat to their health by damaging the intestinal flora and inducing intestinal inflammation, obesity, and sepsis, among others. This paper discusses the sources and contents of endotoxin in infant food and methods for preventing endotoxin from harming infants. However, there is no clear evidence that endotoxin levels in infant food cause significant immune symptoms or even diseases in infants. However, in order to improve the safety level of infant food and reduce the endotoxin content, this issue should not be ignored. The purpose of this review is to provide a theoretical basis for manufacturers and consumers to understand the possible harm of endotoxin content in infant formula milk powder and to explore how to reduce its level in infant formula milk powder. Generally, producers should focus on cleaning the milk source, securing the cold chain, avoiding long-distance transportation, and shortening the storage time of raw milk to reduce the level of bacteria and endotoxin. After production and processing, the endotoxin content should be measured as an important index to test the quality of infant formula milk powder so as to provide high-quality infant products for the healthy growth of newborns.

Cubilin, the Intrinsic Factor-Vitamin B12 Receptor in Development and Disease

Gp280/Intrinsic factor-vitamin B12 receptor/Cubilin (CUBN) is a large endocytic receptor serving multiple functions in vitamin B12 homeostasis, renal reabsorption of protein or toxic substances including albumin, vitamin D-binding protein or cadmium. Cubilin is a peripheral membrane protein consisting of 8 Epidermal Growth Factor (EGF)-like repeats and 27 CUB (defined as Complement C1r/C1s, Uegf, BMP1) domains. This structurally unique protein interacts with at least two molecular partners, Amnionless (AMN) and Lrp2/Megalin. AMN is involved in appropriate plasma membrane transport of Cubilin whereas Lrp2 is essential for efficient internalization of Cubilin and its ligands. Observations gleaned from animal models with Cubn deficiency or human diseases demonstrate the importance of this protein. In this review addressed to basic research and medical scientists, we summarize currently available data on Cubilin and its implication in renal and intestinal biology. We also discuss the role of Cubilin as a modulator of Fgf8 signaling during embryonic development and propose that the Cubilin-Fgf8 interaction may be relevant in human pathology, including in cancer progression, heart or neural tube defects. We finally provide experimental elements suggesting that some aspects of Cubilin physiology might be relevant in drug design.

Inhibition of the gut enzyme intestinal alkaline phosphatase may explain how aspartame promotes glucose intolerance and obesity in mice

Diet soda consumption has not been associated with tangible weight loss. Aspartame (ASP) commonly substitutes sugar and one of its breakdown products is phenylalanine (PHE), a known inhibitor of intestinal alkaline phosphatase (IAP), a gut enzyme shown to prevent metabolic syndrome in mice. We hypothesized that ASP consumption might contribute to the development of metabolic syndrome based on PHE's inhibition of endogenous IAP. The design of the study was such that for the in vitro model, IAP was added to diet and regular soda, and IAP activity was measured. For the acute model, a closed bowel loop was created in mice. ASP or water was instilled into it and IAP activity was measured. For the chronic model, mice were fed chow or high-fat diet (HFD) with/without ASP in the drinking water for 18 weeks. The results were that for the in vitro study, IAP activity was lower (p < 0.05) in solutions containing ASP compared with controls. For the acute model, endogenous IAP activity was reduced by 50% in the ASP group compared with controls (0.2 ± 0.03 vs 0.4 ± 0.24) (p = 0.02). For the chronic model, mice in the HFD + ASP group gained more weight compared with the HFD + water group (48.1 ± 1.6 vs 42.4 ± 3.1, p = 0.0001). Significant difference in glucose intolerance between the HFD ± ASP groups (53 913 ± 4000.58 (mg·min)/dL vs 42 003.75 ± 5331.61 (mg·min)/dL, respectively, p = 0.02). Fasting glucose and serum tumor necrosis factor-alpha levels were significantly higher in the HFD + ASP group (1.23- and 0.87-fold increases, respectively, p = 0.006 and p = 0.01). In conclusion, endogenous IAP's protective effects in regard to the metabolic syndrome may be inhibited by PHE, a metabolite of ASP, perhaps explaining the lack of expected weight loss and metabolic improvements associated with diet drinks.

Recent discoveries on absorption of dietary fat: Presence, synthesis, and metabolism of cytoplasmic lipid droplets within enterocytes

Dietary fat provides essential nutrients, contributes to energy balance, and regulates blood lipid concentrations. These functions are important to health, but can also become dysregulated and contribute to diseases such as obesity, diabetes, cardiovascular disease, and cancer. Within enterocytes, the digestive products of dietary fat are re-synthesized into triacylglycerol, which is either secreted on chylomicrons or stored within cytoplasmic lipid droplets (CLDs). CLDs were originally thought to be inert stores of neutral lipids, but are now recognized as dynamic organelles that function in multiple cellular processes in addition to lipid metabolism. This review will highlight recent discoveries related to dietary fat absorption with an emphasis on the presence, synthesis, and metabolism of CLDs within this process.

A High Level of Intestinal Alkaline Phosphatase Is Protective Against Type 2 Diabetes Mellitus Irrespective of Obesity

Mice deficient in intestinal alkaline phosphatase (IAP) develop type 2 diabetes mellitus (T2DM). We hypothesized that a high level of IAP might be protective against T2DM in humans. We determined IAP levels in the stools of 202 diabetic patients and 445 healthy non-diabetic control people. We found that compared to controls, T2DM patients have approx. 50% less IAP (mean +/- SEM: 67.4 +/- 3.2 vs 35.3 +/- 2.5 U/g stool, respectively; p < 0.000001) indicating a protective role of IAP against T2DM. Multiple logistic regression analyses showed an independent association between the IAP level and diabetes status. With each 25 U/g decrease in stool IAP, there is a 35% increased risk of diabetes. The study revealed that obese people with high IAP (approx. 65 U/g stool) do not develop T2DM. Approx. 65% of the healthy population have < 65.0 U/g stool IAP, and predictably, these people might have 'the incipient metabolic syndrome', including 'incipient diabetes', and might develop T2DM and other metabolic disorders in the near future. In conclusion, high IAP levels appear to be protective against diabetes irrespective of obesity, and a 'temporal IAP profile' might be a valuable tool for predicting 'the incipient metabolic syndrome', including 'incipient diabetes'.

Absorption and blood/cellular transport of folate and cobalamin: Pharmacokinetic and physiological considerations

The systems involving folate and cobalamin have several features in common: 1) their dietary forms require luminal digestion for absorption; 2) intestinal bacteria in the upper intestine synthesize and utilize both vitamins, creating possible competition for the nutrients; 3) there is one major intestinal brush border protein essential for absorption; 4) both are subject to extensive entero-hepatic circulation. Finally, human mutations have confirmed the role of specific transporters and receptors in these processes. There are other features, however, that distinguish the metabolism of these vitamins: 1) upper intestinal bacteria tend to produce folate, while cobalamin (cbl) utilization is more common; 2) cbl absorption requires a luminal binding protein, but folate does not; 3) folate absorption can occur throughout the small bowel, but the cbl receptor, cubilin, is restricted to the distal half of the small bowel; 4) movement into cells uses transporters, exchangers, and symporters, whereas cbl is transferred by receptor-mediated endocytosis; 5) folate is carried in the blood mostly in red blood cells, whereas cbl is carried on specific binding-proteins; 6) folate can enter cells via multiple systems, but cbl uptake into all tissues use the transcobalamin receptor (TC-R), with the asialoglycoprotein receptor (ASGP-R) present in hepatocytes for uptake of haptocorrin-cbl (HC-cbl) complexes. In summary, the systems for absorption and distribution of folate and cobalamin are complex. These complexities help to explain the variable clinical responses after oral administration of the vitamins, especially when provided as supplements.

Tissue alkaline phosphatase is involved in lipid metabolism and gene expression and secretion of adipokines in adipocytes

BACKGROUND

Alkaline phosphatases are dimeric hydrolytic enzymes that dephosphorylate nucleotides and proteins. AP-TNAP is found primarily in skeletal tissues were it plays a major role in the mineralization of the extracellular matrix and bone formation.

METHODS

In this study we found through conventional and real time PCR assays that Alpl, the gene encoding for AP-TNAP is expressed in adipose tissue and in 3 T3-F442A adipocytes. We evaluated, using RNAi its role in adipocyte metabolism, and its cytoplasmic location by immunohistochemistry.

RESULTS

Alpl is highly expressed late in adipogenesis during adipose terminal differentiation. Knocking down Alpl increased the expression of the genes encoding for glycerophosphate dehydrogenase, and for the adipokines adiponectin, and FABP4 (aP2) but decreased that of leptin, and it also increased secretion of FABP4; these 3 proteins are important in adipocyte systemic signaling and insulin sensitivity. Inhibition of alkaline phosphatase activity in adipocytes by levamisole reduced lipolysis and the expression of various lipogenic genes. We found the enzyme intracytoplasmically, forming aggregates in close surroundings of the lipid droplets during lipolysis.

CONCLUSIONS

We suggest that AP-TNAP activity is involved in lipid and energy metabolism of fat cells, and it might regulate glucose metabolism and insulin sensitivity via adipokine synthesis and secretion.

GENERAL SIGNIFICANCE

The activity of AP-TNAP might have a critical role in the energy balance of the adipocyte, probably participating in obesity and metabolic syndrome.

Effect of particle agglomeration in nanotoxicology

The emission of engineered nanoparticles (ENPs) into the environment in increasing quantity and variety raises a general concern regarding potential effects on human health. Compared with soluble substances, ENPs exhibit additional dimensions of complexity, that is, they exist not only in various sizes, shapes and chemical compositions but also in different degrees of agglomeration. The effect of the latter is the topic of this review in which we explore and discuss the role of agglomeration on toxicity, including the fate of nanomaterials after their release and the biological effects they may induce. In-depth investigations of the effect of ENP agglomeration on human health are still rare, but it may be stated that outside the body ENP agglomeration greatly reduces human exposure. After uptake, agglomeration of ENPs reduces translocation across primary barriers such as lungs, skin or the gastrointestinal tract, preventing exposure of "secondary" organs. In analogy, also cellular ENP uptake and intracellular distribution are affected by agglomeration. However, agglomeration may represent a risk factor if it occurs after translocation across the primary barriers, and ENPs are able to accumulate within the tissue and thus reduce clearance efficiency.

The intestinal epithelial cell differentiation marker intestinal alkaline phosphatase (ALPi) is selectively induced by histone deacetylase inhibitors (HDACi) in colon cancer cells in a Kruppel-like factor 5 (KLF5)-dependent manner

The histone deacetylase inhibitor (HDACi) sodium butyrate promotes differentiation of colon cancer cells as evidenced by induced expression and enzyme activity of the differentiation marker intestinal alkaline phosphatase (ALPi). Screening of a panel of 33 colon cancer cell lines identified cell lines sensitive (42%) and resistant (58%) to butyrate induction of ALP activity. This differential sensitivity was similarly evident following treatment with the structurally distinct HDACi, MS-275. Resistant cell lines were significantly enriched for those harboring the CpG island methylator phenotype (p = 0.036, Chi square test), and resistant cell lines harbored methylation of the ALPi promoter, particularly of a CpG site within a critical KLF/Sp regulatory element required for butyrate induction of ALPi promoter activity. However, butyrate induction of an exogenous ALPi promoter-reporter paralleled up-regulation of endogenous ALPi expression across the cell lines, suggesting the presence or absence of a key transcriptional regulator is the major determinant of ALPi induction. Through microarray profiling of sensitive and resistant cell lines, we identified KLF5 to be both basally more highly expressed as well as preferentially induced by butyrate in sensitive cell lines. KLF5 overexpression induced ALPi promoter-reporter activity in resistant cell lines, KLF5 knockdown attenuated butyrate induction of ALPi expression in sensitive lines, and butyrate selectively enhanced KLF5 binding to the ALPi promoter in sensitive cells. These findings demonstrate that butyrate induction of the cell differentiation marker ALPi is mediated through KLF5 and identifies subsets of colon cancer cell lines responsive and refractory to this effect.

Cubilin expression is monoallelic and epigenetically augmented via PPARs

Background

Cubilin is an endocytic receptor that is necessary for renal and intestinal absorption of a range of ligands. Endocytosis mediated by cubilin and its co-receptor megalin is the principal mechanism for proximal tubule reabsorption of proteins from the glomerular filtrate. Cubilin is also required for intestinal endocytosis of intrinsic factor-vitamin B₁₂ complex. Despite its importance, little is known about the regulation of cubilin expression.

Results

Here we show that cubilin expression is under epigenetic regulation by at least two processes. The first process involves inactivation of expression of one of the cubilin alleles. This monoallelic expression state could not be transformed to biallelic by inhibiting DNA methylation or histone deacetylation. The second process involves transcriptional regulation of cubilin by peroxisome proliferator-activated receptor (PPAR) transcription factors that are themselves regulated by DNA methylation and histone deacetylation. This is supported by findings that inhibitors of DNA methylation and histone deacetylation, 5Aza and TSA, increase cubilin mRNA and protein in renal and intestinal cell lines. Not only was the expression of PPARα and γ inducible by 5Aza and TSA, but the positive effects of TSA and 5Aza on cubilin expression were also dependent on both increased PPAR transcription and activation. Additionally, 5Aza and TSA had similar effects on the expression of the cubilin co-receptor, megalin.

Conclusions

Together, these findings reveal that cubilin and megalin mRNA expression is under epigenetic control and thus point to new avenues for overcoming pathological suppression of these genes through targeting of epigenetic regulatory processes.

Intestinal alkaline phosphatase prevents metabolic syndrome in mice

Metabolic syndrome comprises a cluster of related disorders that includes obesity, glucose intolerance, insulin resistance, dyslipidemia, and fatty liver. Recently, gut-derived chronic endotoxemia has been identified as a primary mediator for triggering the low-grade inflammation responsible for the development of metabolic syndrome. In the present study we examined the role of the small intestinal brush-border enzyme, intestinal alkaline phosphatase (IAP), in preventing a high-fat-diet-induced metabolic syndrome in mice. We found that both endogenous and orally supplemented IAP inhibits absorption of endotoxin (lipopolysaccharides) that occurs with dietary fat, and oral IAP supplementation prevents as well as reverses metabolic syndrome. Furthermore, IAP supplementation improves the lipid profile in mice fed a standard, low-fat chow diet. These results point to a potentially unique therapy against metabolic syndrome in at-risk humans.

Gastric intrinsic factor: the gastric and small intestinal stages of cobalamin absorption. a personal journey

Intrinsic factor (IF) was first identified as a component of the gastric mucosa that reacted with an extrinsic factor, later discovered to be vitamin B12 (VB12). IF has been extensively characterized, and its cloned cDNA used to produce sufficient IF to produce high quality antibodies, and to elucidate its 3-dimensional structure bound to cobalamin (Cbl, VB12). The absorption of the IF-Cbl complex involves internalization by endocytosis, incorporation into multivesicular/lysosomal bodies, release of Cbl by lysosomal proteolysis and pH effects, with subsequent binding to transcobalamin (TC). Hereditary IF deficiency is rare, consistent with the need for IF to absorb Cbl, a vitamin essential for cell replication. When mutations occur, they are most often associated with loss of function, but some mutations occur outside the coding region. The IF-mediated intestinal uptake of Cbl has been harnessed for use as a transporter for peptides, proteins and even nanoparticles. Nanoparticle (NP) technology has produced Cbl-coated NPs that can incorporate peptides (insulin, IgG) that can be absorbed orally to function as hormones and antibodies in rodent models, but these systems are not yet ready for clinical use.

Of microbes and meals: the health consequences of dietary endotoxemia

The human intestinal tract comprises a rich and complex microbial ecosystem. This intestinal microbota provides a large reservoir of potentially toxic molecules, including bacterial endotoxin (ie, lipopolysaccharide [LPS]). This potent inflammatory molecule is detectable in the circulation of healthy individuals, and levels transiently increase following ingestion of energy-rich meals. Chronic exposure to circulating endotoxin has been associated with obesity, diabetes, and cardiovascular disease. Western-style meals augment LPS translocation and by this mechanism may contribute to the pathogenesis of these diseases. By contrast, the gut and other organs have evolved mechanisms to detoxify endotoxin and neutralize the potentially inflammatory qualities of circulating endotoxin. Of specific interest to clinicians is evidence that acute postprandial elevation of circulating endotoxin is dependent on meal composition. In this review, the authors present an overview of the biochemical and cellular mechanisms that lead to endotoxemia, with emphasis on the interplay between microbial and nutrition determinants of this condition. The link between endotoxemia, diet, and changes in the intestinal microbiota raise the possibility that dietary interventions can, at least in part, ameliorate the detrimental outcomes of endotoxemia.

Expression profiling identifies novel gene targets and functions for Pdx1 in the duodenum of mature mice

Transcription factor pancreatic and duodenal homeobox 1 (Pdx1) plays an essential role in the pancreas to regulate its development and maintain proper islet function. However, the functions of Pdx1 in mature small intestine are less known. We aimed to investigate the intestinal role of Pdx1 by profiling the expression of genes differentially regulated in response to inactivation of Pdx1 specifically in the intestinal epithelium. Pdx1 was conditionally inactivated in the intestinal epithelium of Pdx1(flox/flox);VilCre mice. Total RNA was isolated from the first 5 cm of the small intestine from mature Pdx1(flox/flox);VilCre and littermate control mice. Microarray analysis identified 86 probe sets representing 68 genes significantly upregulated or downregulated 1.5-fold or greater in Pdx(flox/flox);VilCre mice maintained under standard conditions. Ingenuity Pathway Analysis revealed that functions of the differentially expressed genes are significantly associated with metabolism of nutrients including lipids and iron. Network analysis examining the interactions among the differentially expressed genes further supports the notion that Pdx1 may modulate metabolism of lipids and iron from mature intestinal epithelium. Following forced oil feeding, Pdx1(flox/flox);VilCre mice showed diminished lipid staining in the duodenal epithelium and decreased serum triglyceride levels, indicating reduced lipid absorption compared with control duodenal epithelium. Blood samples from Pdx1(flox/flox);VilCre mice have significantly lower mean values for mean corpuscular volume and mean corpuscular hemoglobin, consistent with iron deficiency. The absence of nonheme iron in the villous epithelium and lamina propria of Pdx1(flox/flox);VilCre duodenum indicates that the duodenal epithelium lacking Pdx1 may have defects in importing iron through enterocytes, resulting in iron deficiency in Pdx1(flox/flox);VilCre mice.

Production of ectopic gastric intrinsic factor in gastric mucosa of humans with chronic gastritis

BACKGROUND

Ectopic expression of gastric intrinsic factor (IF) has been described in rodent models of chronic gastritis.

AIMS

The current study undertook to determine if ectopic IF was also present in chronic gastritis in humans and might identify the process of ectopic protein expression as part of the response to chronic injury.

METHODS

Archived biopsies from mid-body, angularis and prepylorus of 9 patients with and without chronic gastritis and food-cobalamin malabsorption were examined in a blinded fashion by immunocytochemistry as were biopsies from 5 normal subjects. Cells with ectopic IF were further examined with antibodies against pepsin or with Griffonia simplicifolia II (GSII) to identity cells in the mucous neck cell compartment.

RESULTS

Ectopic IF production in non-parietal cells was identified in cells that were H(+),K(+)-ATPase-negative but IF-positive in 7 of the 9 patients (6/9 in the angularis and/or prepylorus biopsies and 1/9 only in the mid-body). These included 5 of the 6 H. pylori-infected patients and all 5 patients with severe food-cobalamin malabsorption. No normal control subjects demonstrated ectopic IF. The cells with ectopic IF were pepsinogen-positive peptic cells and were not GSII-positive. Expression was most extensive in patients and gastric regions with inflammation. In all but one sample, ectopic IF was observed near anatomical mucosal junctions, such as antral/body and prepylorus/duodenum junctions.

CONCLUSIONS

These data in humans with and without gastritis are consistent with the hypothesis that local factors influence ectopic gastric IF expression, arising from either the anatomical location, the focal inflammation, or both.

Tissue-nonspecific alkaline phosphatase is activated in enterocytes by oxidative stress via changes in glycosylation

BACKGROUND

Intestinal inflammation produces an induction of alkaline phosphatase (AP) activity that is attributable in part to augmented expression, accompanied by a change in isoform, in epithelial cells.

METHODS

This study focuses on induction of AP in intestinal epithelial cells in vitro.

RESULTS

Treatment with the oxidants H2O2, monochloramine, or tButOOH increases AP activity in vitro in Caco-2, HT29, and IEC18 cells. We selected IEC18 cells for further testing. Basal AP activity in IEC18 cells is of the tissue-nonspecific (bone-liver-kidney) type, as indicated by Northern and Western blot analysis. Oxidative stress augments AP activity and the sensitivity of the enzyme to levamisole, homoarginine, and heat in IEC18 cells. Increased immunoreactivity to tissue-nonspecific AP antibodies suggests an isoform shift from liver to either kidney or bone type. This effect occurs without changes at the mRNA level and is sensitive to tunicamycin, an inhibitor of N-glycosylation, and neuraminidase digestion. Saponin and deoxycholate produce similar effects to oxidants. Butyrate but not proinflammatory cytokines or LPS can induce a similar effect but without toxicity. The AP increase is not prevented by modulators of the MAPK, NF-κB, calcium, and cyclic adenosine monophosphate (cAMP) pathways, and is actually enhanced by actinomycin D via higher cell stress.

CONCLUSIONS

Oxidative stress causes a distinct increase in enterocyte AP activity together with cell toxicity via changes in the glycosylation of the enzyme that correspond to a shift in isotype within the tissue-nonspecific paradigm. We speculate that this may have physiological implication for gut defense.

Identification of specific targets for the gut mucosal defense factor intestinal alkaline phosphatase

Intestinal alkaline phosphatase (IAP) is a small intestinal brush border enzyme that has been shown to function as a gut mucosal defense factor, but its precise mechanism of action remains unclear. We investigated the effects of IAP on specific bacteria and bacterial components to determine its molecular targets. Purulent fluid from a cecal ligation and puncture model, specific live and heat-killed bacteria (Escherichia coli, Salmonella typhimurium, and Listeria monocytogenes), and a variety of proinflammatory ligands (LPS, CpG DNA, Pam-3-Cys, flagellin, and TNF) were incubated with or without calf IAP (cIAP). Phosphate release was determined by using a malachite green assay. The various fluids were applied to target cells (THP-1, parent HT-29, and IAP-expressing HT-29 cells) and IL-8 secretion measured by ELISA. cIAP inhibited IL-8 induction by purulent fluid in THP-1 cells by >35% (P < 0.005). HT29-IAP cells had a reduced IL-8 response specifically to gram-negative bacteria; >90% reduction compared with parent cells (P < 0.005). cIAP had no effect on live bacteria but attenuated IL-8 induction by heat-killed bacteria by >40% (P < 0.005). cIAP exposure to LPS and CpG DNA caused phosphate release and reduced IL-8 in cell culture by >50% (P < 0.005). Flagellin exposure to cIAP also resulted in reduced IL-8 secretion by >40% (P < 0.005). In contrast, cIAP had no effect on TNF or Pam-3-Cys. The mechanism of IAP action appears to be through dephosphorylation of specific bacterial components, including LPS, CpG DNA, and flagellin, and not on live bacteria themselves. IAP likely targets these bacterially derived molecules in its role as a gut mucosal defense factor.

Assay format as a critical success factor for identification of novel inhibitor chemotypes of tissue-nonspecific alkaline phosphatase from high-throughput screening

The tissue-nonspecific alkaline phosphatase (TNAP) isozyme is centrally involved in the control of normal skeletal mineralization and pathophysiological abnormalities that lead to disease states such as hypophosphatasia, osteoarthritis, ankylosis and vascular calcification. TNAP acts in concert with the nucleoside triphosphate pyrophosphohydrolase-1 (NPP1) and the Ankylosis protein to regulate the extracellular concentrations of inorganic pyrophosphate (PP(i)), a potent inhibitor of mineralization. In this review we describe the serial development of two miniaturized high-throughput screens (HTS) for TNAP inhibitors that differ in both signal generation and detection formats, but more critically in the concentrations of a terminal alcohol acceptor used. These assay improvements allowed the rescue of the initially unsuccessful screening campaign against a large small molecule chemical library, but moreover enabled the discovery of several unique classes of molecules with distinct mechanisms of action and selectivity against the related placental (PLAP) and intestinal (IAP) alkaline phosphatase isozymes. This illustrates the underappreciated impact of the underlying fundamental assay configuration on screening success, beyond mere signal generation and detection formats.

Pdx1 inactivation restricted to the intestinal epithelium in mice alters duodenal gene expression in enterocytes and enteroendocrine cells

Null mutant mice lacking the transcription factor pancreatic and duodenal homeobox 1 (Pdx1) are apancreatic and survive only a few days after birth. The role of Pdx1 in regulating intestinal gene expression has therefore yet to be determined in viable mice with normal pancreatic development. We hypothesized that conditional inactivation of Pdx1 restricted to the intestinal epithelium would alter intestinal gene expression and cell differentiation. Pdx1(flox/flox);VilCre mice with intestine-specific Pdx1 inactivation were generated by crossing a transgenic mouse strain expressing Cre recombinase, driven by a mouse villin 1 gene promoter fragment, with a mutant mouse strain homozygous for loxP site-flanked Pdx1. Pdx1 protein is undetectable in all epithelial cells in the intestinal epithelium of Pdx1(flox/flox);VilCre mice. Goblet cell number and mRNA abundance for mucin 3 and mucin 13 genes in the proximal small intestine are comparable between Pdx1(flox/flox);VilCre and control mice. Similarly, Paneth cell number and expression of Paneth cell-related genes Defa1, Defcr-rs1, and Mmp7 in the proximal small intestine remain statistically unchanged by Pdx1 inactivation. Although the number of enteroendocrine cells expressing chromogranin A/B, gastric inhibitory polypeptide (Gip), or somatostatin (Sst) is unaffected in the Pdx1(flox/flox);VilCre mice, mRNA abundance for Gip and Sst is significantly reduced in the proximal small intestine. Conditional Pdx1 inactivation attenuates intestinal alkaline phosphatase (IAP) activity in the duodenal epithelium, consistent with an average 91% decrease in expression of the mouse enterocyte IAP gene, alkaline phosphatase 3 (a novel Pdx1 target candidate), in the proximal small intestine following Pdx1 inactivation. We conclude that Pdx1 is necessary for patterning appropriate gene expression in enterocytes and enteroendocrine cells of the proximal small intestine.

Isolation and biochemical characterisation of lipid rafts from Atlantic cod (Gadus morhua) intestinal enterocytes

Lipid rafts are glycosphingolipid/cholesterol-enriched membrane microdomains that have been extensively studied during the past two decades. Our aim was to isolate and perform biochemical characterization of lipid rafts from the intestinal brush border membrane (BBM) of Atlantic cod (Gadus morhua) to confirm their existence in a cold-water species and compare their characteristics with lipid rafts from other species in terms of lipid and protein content. To validate the isolation process, we assayed marker enzymes for subcellular organelles, including alkaline phosphatase (AP) and leucine aminopeptidase (LAP), both well-known marker enzymes for BBM and lipid rafts. All biochemical methods showed enrichment of AP in both the BBM and lipid raft fractions. Proteomic studies were performed by MALDI-TOF mass spectrometry using trypsin digested SDS-PAGE samples. Various proteins were associated with the cod intestinal lipid raft preparation such as aminopeptidase-N, prohibitin, and beta-actin. Lipid analysis with (31)P NMR and thin layer chromatography on BBMs and lipid rafts samples gave higher content of sphingomyelin than previously reported in the BBM and lower content of phosphatidylcholine. Furthermore, sphingomyelin was highly dominant in the lipid rafts together with cholesterol. The existence of lipid rafts containing previously reported lipid raft characteristics from the cod intestine has, therefore, been confirmed in a ray-finned fish for the first time to the best of our knowledge.

Role of lysophosphatidylcholine in brush-border intestinal alkaline phosphatase release and restoration

Intestinal alkaline phosphatase (IAP) is a brush-border membrane ectoenzyme (BBM-IAP) that is released into the lumen (L-IAP) after a high-fat diet. We examined the effects of oil feeding and the addition of mixed-lipid micelles on the formation of L-IAP in oil-fed rat intestine, Caco-2 cell monolayers, and mouse intestinal loops. We localized IAP in the duodenum of rats fed corn oil using fluorescence microscopy with enzyme-labeled fluorescence-97 as substrate. Four hours after oil feeding, L-IAP increased approximately 10-fold accompanied by the loss of BBM-IAP, consistent with BBM-IAP release. Rat IAP isozyme mRNAs progressively increased 4-6 h after oil feeding, followed by the increase of IAP activity in the subapical location at 6 h, consistent with the restoration of IAP protein. Postprandial lipid-micelle components, sodium taurocholate with or without oleic acid, mono-oleylglycerol, cholesterol, or lysophosphatidylcholine (lysoPC) were applied singly or as mixed-lipid micelles to the apical surface of polarized Caco-2 cell monolayers. LysoPC increased L-IAP >10-fold over basal release. LysoPC released IAP into the apical medium more than other intestinal brush-border enzymes, 5'-nucleotidase, sucrase, aminopeptidase N, and lactase, without comparable lactate dehydrogenase release or cell injury. LysoPC increased human IAP mRNA levels by 1.5-fold in Caco-2 cells. Luminally applied lysoPC also increased release of IAP preferentially in mouse intestinal loops. These data show that lysoPC accelerates the formation of L-IAP from BBM-IAP, followed by enhanced IAP synthesis, suggesting the role that lysoPC might play in the turnover of brush-border proteins.

Effect of fat feeding on pro-oxidant and anti-oxidant enzyme systems in rat intestine: possible role in the turnover of enterocytes

Immature epithelial cells generated in the crypt base undergo differentiation while progressing to the villus tip, where the cells upon apoptosis are detached from the underlying muscular tissue. We previously reported that lipid peroxidation might be involved in the turnover of enterocytes across the crypt-villus axis in rat intestine (Dig Dis Sci 52:1840-1844, 2007). To examine whether long-term feeding of fat with different fatty-acid composition influences this process, in the present study we investigated the effect of feeding fish oil (n - 3) and corn oil (n - 6) polyunsaturated fatty acids on lipid per-oxidation and anti-oxidant systems in different epithelial cell fractions isolated in rat intestine. Feeding fish oil or corn oil markedly enhanced lipid per-oxidation levels of enterocytes throughout villus height compared with control, but there was no difference in the distribution profile of pro- and anti-oxidant enzyme systems and lipid per-oxidation across the crypt-villus axis under these conditions. Analysis of lipid peroxidation levels in different cell fractions revealed that the thiobarbituric acid reactive substance were 9- to 11-fold higher at the villus tip compared with at the crypt base. The activities of glutathione reductase and glutathione-S-transferase were 2- to 5-fold higher in villus tip compared to the crypt region. However, the activities of superoxide dismutase and catalase were 6- to 8-fold high at the crypt base compared with at villus tip cells. Immunocytolocalization of superoxide dismutase showed high staining in crypt base compared with that in villus, tip cells. These findings further suggest that generation of reactive oxygen species in enterocytes across the crypt-villus axis may be involved in turnover of enterocytes across the crypt-villus unit in rat intestine.

Intestinal alkaline phosphatase is a gut mucosal defense factor maintained by enteral nutrition

Under conditions of starvation and disease, the gut barrier becomes impaired, and trophic feeding to prevent gut mucosal atrophy has become a standard treatment of critically ill patients. However, the mechanisms responsible for the beneficial effects of enteral nutrition have remained a mystery. Using in vitro and in vivo models, we demonstrate that the brush-border enzyme, intestinal alkaline phosphatase (IAP), has the ability to detoxify lipopolysaccharide and prevent bacterial invasion across the gut mucosal barrier. IAP expression and function are lost with starvation and maintained by enteral feeding. It is likely that the IAP silencing that occurs during starvation is a key component of the gut mucosal barrier dysfunction seen in critically ill patients.

Intestinal alkaline phosphatase: selective endocytosis from the enterocyte brush border during fat absorption

Absorption of dietary fat in the small intestine is accompanied by a rise of intestinal alkaline phosphatase (IAP) in the serum and of secretion of IAP-containing surfactant-like particles from the enterocytes. In the present work, fat absorption was studied in organ cultured mouse intestinal explants. By immunofluorescence microscopy, fat absorption caused a translocation of IAP from the enterocyte brush border to the interior of the cell, whereas other brush-border enzymes were unaffected. By electron microscopy, the translocation occurred by a rapid (5 min) induction of endocytosis via clathrin-coated pits. By 60 min, IAP was seen in subapical endosomes and along membranes surrounding fat droplets. IAP is a well-known lipid raft-associated protein, and fat absorption was accompanied by a marked change in the density and morphology of the detergent-resistant membranes harboring IAP. A lipid analysis revealed that fat absorption caused a marked increase in the microvillar membrane contents of free fatty acids. In conclusion, fat absorption rapidly induces a transient clathrin-dependent endocytosis via coated pits from the enterocyte brush border. The process selectively internalizes IAP and may contribute to the appearance of the enzyme in serum and surfactant-like particles.

Immunoregulatory role of intestinal surfactant-like particles during Salmonella typhimurium infection

Surfactants like particles (SLP) are secreted by Intestinal epithelium. These particles have the ability to lower surface tension of intestinal epithelial cells and contain small amounts of surfactant specific proteins A, B, and D. In the intestinal lumen they are known to function as lubricants and/or as a vehicle to deliver digestive enzymes to the luminal fluid. These particles have been found to have the ability in binding of uropathogenic E.coli. But their immunological function is not known. The present study was designed to assess the role of the SLP in the regulation of immune response during Salmonella (S) typhimurium infection using a rat an enteric model. The animals were divided in four different groups including control (PBS), rats fed fat diet (corn oil), rats fed fat diet followed with S. typhimurium infection and rats with S. typhimurium infection alone. The Peyer's patches (PP), intraepithelial (IE) and lamina propria (LP) mononuclear cells were isolated from the above-mentioned groups. These mononuclear cells were then incubated in presence of S. typhimurium lysate alone, SLP alone and S. typhimurium lysate and SLP together. T cell markers CD4 and CD8, cytokines mainly pro-inflammatory ones including IFN-γ, TNF-α, IL-12 etc were studied under such conditions. In addition histological studies were also carried out under these conditions. We report in this study that SLP plays an important role in modulating the cytokine level during infection. The pro-inflammatory cytokines were found significantly reduced in SLP induced diet along with the infection group compared to the infection group alone. Histopathological studies revealed the breakdown of duodenal villi after infection while only broadening of villi was observed in rats given corn oil induced SLP along with infection. These results suggested an important immuno-modulatory role for SLP during Salmonella infection.

Disruption of the murine intestinal alkaline phosphatase gene Akp3 impairs lipid transcytosis and induces visceral fat accumulation and hepatic steatosis

Intestinal alkaline phosphatase (IAP) is involved in the process of fat absorption, a conclusion confirmed by an altered lipid transport and a faster body weight gain from 10 to 30 wk in both male and female mice with a homozygous null mutation of the IAP coding gene (Akp3(-/-) mice). This study was aimed to delineate morphologically and quantitatively the accelerated lipid absorption in male Akp3(-/-) mice. Feeding a corn oil bolus produced an earlier peak of triacylglycerol in serum (2 vs. 4 h for Akp3(-/-) and wild-type mice, respectively) and an approximately twofold increase in serum triacylglycerol concentration in Akp3(-/-) mice injected with a lipolysis inhibitor, Triton WR-1339. A corn oil load induced the threefold enlargement of the Golgi vacuoles in male wild-type mice but not in Akp3(-/-) mice, indicating that absorbed lipids rarely reached the Golgi complex and that the transcytosis of lipid droplets does not follow the normal pathway in male Akp3(-/-) mice. Force feeding an exaggerated fat intake by a 30% fat chow for 10 wk induced obesity in both male Akp3(-/-) and wild-type mice, and therefore no phenotypic difference was observed between the two. On the other hand, the forced high-fat chow induced an 18% greater body weight gain, hepatic steatosis, and visceral fat accumulation in female Akp3(-/-) mice but not in female wild-type controls. These results provide further evidence that IAP is involved in the regulation of the lipid absorption process and that its absence leads to progressive metabolic abnormalities in certain fat-forced conditions.

Intestinal alkaline phosphatase gene expression is activated by ZBP-89

Intestinal alkaline phosphatase (IAP) is an enterocyte differentiation marker that functions to limit fat absorption. Zinc finger binding protein-89 (ZBP-89) is a Kruppel-type transcription factor that appears to promote a differentiated phenotype in the intestinal epithelium. The purpose of this study was to investigate the regulation of IAP gene expression by ZBP-89. RT-PCR, quantitative real-time RT-PCR, Western blot analyses, and reporter assays were used to determine the regulation of IAP by ZBP-89 in HT-29 and Caco-2 colon cancer cells. ZBP-89 knockdown was achieved by specific short interfering (si)RNA. EMSA and chromatin immunoprecipitation (ChIP) were performed to examine the binding of ZBP-89 to the IAP promoter. The results of RT-PCR, quantitative real-time PCR, and Western blot analyses showed that ZBP-89 was expressed at low levels in Caco-2 and HT-29 cells, whereas IAP was minimally expressed and absent in these cells, respectively. Transfection with ZBP-89 expression plamid increased IAP mRNA and protein levels in both cell lines, whereas knockdown of endogenous ZBP-89 by siRNA reduced basal levels of IAP gene expression in Caco-2 cells. IAP-luciferase reporter assays, EMSA, and ChIP established that ZBP-89 activated the IAP gene through a response element (ZBP-89 response element: 5'-CCTCCTCCC-3') located between -1018 and -1010 bp upstream of the AUG start codon. We conclude that ZBP-89 is a direct transcriptional activator of the enterocyte differentiation marker IAP. These findings are consistent with the role that this transcription factor is thought to play as a tumor suppressor and suggests its possible function in the physiology of fat absorption.

Involvement of intestinal alkaline phosphatase in serum apolipoprotein B-48 level and its association with ABO and secretor blood group types

Serum levels of intestinal alkaline phosphatase (IAP), a protein implicated in transcellular transport of chylomicrons, vary among ABO blood groups. In rat enterocytes, IAP is associated with chylomicron secretion, but the rat expresses only blood group A. It is not known whether chylomicron secretion may be affected in humans who express multiple blood group types. Serum samples from 40 healthy subjects were obtained after overnight fast and 3h after a high-fat meal, and assayed for IAP and apolipoprotein B-48 (apoB-48), both proteins exclusive to intestine, although only apoB-48 is found in chylomicrons. The two proteins were greater in subjects without blood antigen A (B and O) than in those with this antigen (A and AB); 2.4- and 4.7-fold for IAP and 1.5- and 2.0-fold for apoB-48 before and after the meal, respectively. Moreover, IAP and apoB-48 levels were strongly correlated in the subjects with the secretor phenotype (r > 0.81). These results indicate that IAP is strongly involved in chylomicron formation and fatty acid metabolism might change among ABO blood type. In addition, ABO blood type classification in apoB-48 measurement would improve the diagnostic value in the evaluation of metabolic syndrome.

Differential regulation of intestinal alkaline phosphatase gene expression by Cdx1 and Cdx2

We have examined the role that the caudal-related homeobox transcription factors Cdx1 and Cdx2 play in activating the enterocyte differentiation marker gene intestinal alkaline phosphatase (IAP). Human colon cancer Caco-2 cells were transiently transfected with Cdx1 and/or Cdx2, and semiquantitative RT-PCR was used to study the effects on IAP mRNA expression. Transfections with a variety of IAP-luciferase reporter constructs were used to identify a Cdx response element located within the human IAP gene promoter. Protein-DNA interactions were examined by EMSA. Results showed that Cdx1 markedly induced IAP mRNA expression, whereas Cdx2 did not, and, in fact, inhibited the Cdx1 effects. Functional analysis revealed that Cdx1 transactivates (fourfold, P < 0.05) the IAP promoter through a novel Cdx response element (GTTTAGA) located between -2369 and -2375 upstream of the translational start site. EMSA showed that both Cdx1 and Cdx2 could bind to the cis element, but in cotransfection experiments, Cdx2 inhibited the Cdx1 effects by approximately 50%. Thus we have identified a previously unrecognized interaction between two important gut transcription factors, Cdx1 and Cdx2, in the context of IAP gene regulation. Cdx1 activates the IAP gene via a novel cis element, whereas Cdx2 inhibits the Cdx1 effects.

Accelerated fat absorption in intestinal alkaline phosphatase knockout mice

Intestinal alkaline phosphatase (IAP) is the most ancestral of the tissue-specific members of the AP gene family. Several studies have suggested an absorptive function for IAP, but in vivo data to this effect have been lacking. We inactivated the mouse IAP gene in embryo-derived stem cells and generated mice homozygous for the null mutation. The mice were macroscopically and histologically normal and fertile and showed no difference from the wild-type controls under normal laboratory conditions. However, when maintained long-term on a high-fat diet, the IAP-deficient mice showed faster body weight gain than did control animals. Histological examination revealed an accelerated transport of fat droplets through the intestinal epithelium and elevation of serum triglyceride levels in the IAP-deficient mice compared to wild-type mice. Our study suggests that IAP participates in a rate-limiting step regulating fat absorption.