Rat intestinal alkaline phosphatase secretion into lumen and serum is coordinately regulated

(Patho)Physiology of Glycosylphosphatidylinositol-Anchored Proteins I: Localization at Plasma Membranes and Extracellular Compartments

Glycosylphosphatidylinositol (GPI)-anchored proteins (APs) are anchored at the outer leaflet of plasma membranes (PMs) of all eukaryotic organisms studied so far by covalent linkage to a highly conserved glycolipid rather than a transmembrane domain. Since their first description, experimental data have been accumulating for the capability of GPI-APs to be released from PMs into the surrounding milieu. It became evident that this release results in distinct arrangements of GPI-APs which are compatible with the aqueous milieu upon loss of their GPI anchor by (proteolytic or lipolytic) cleavage or in the course of shielding of the full-length GPI anchor by incorporation into extracellular vesicles, lipoprotein-like particles and (lyso)phospholipid- and cholesterol-harboring micelle-like complexes or by association with GPI-binding proteins or/and other full-length GPI-APs. In mammalian organisms, the (patho)physiological roles of the released GPI-APs in the extracellular environment, such as blood and tissue cells, depend on the molecular mechanisms of their release as well as the cell types and tissues involved, and are controlled by their removal from circulation. This is accomplished by endocytic uptake by liver cells and/or degradation by GPI-specific phospholipase D in order to bypass potential unwanted effects of the released GPI-APs or their transfer from the releasing donor to acceptor cells (which will be reviewed in a forthcoming manuscript).

Inorganic Polymeric Materials for Injured Tissue Repair: Biocatalytic Formation and Exploitation

Two biocatalytically produced inorganic biomaterials show great potential for use in regenerative medicine but also other medical applications: bio-silica and bio-polyphosphate (bio-polyP or polyP). Biosilica is synthesized by a group of enzymes called silicateins, which mediate the formation of amorphous hydrated silica from monomeric precursors. The polymeric silicic acid formed by these enzymes, which have been cloned from various siliceous sponge species, then undergoes a maturation process to form a solid biosilica material. The second biomaterial, polyP, has the extraordinary property that it not only has morphogenetic activity similar to biosilica, i.e., can induce cell differentiation through specific gene expression, but also provides metabolic energy through enzymatic cleavage of its high-energy phosphoanhydride bonds. This reaction is catalyzed by alkaline phosphatase, a ubiquitous enzyme that, in combination with adenylate kinase, forms adenosine triphosphate (ATP) from polyP. This article attempts to highlight the biomedical importance of the inorganic polymeric materials biosilica and polyP as well as the enzymes silicatein and alkaline phosphatase, which are involved in their metabolism or mediate their biological activity.

The Role of Gut-Derived Lipopolysaccharides and the Intestinal Barrier in Fatty Liver Diseases

BACKGROUND

Hepatosteatosis is the earliest stage in the pathogenesis of nonalcoholic fatty (NAFLD) and alcoholic liver disease (ALD). As NAFLD is affecting 10-24% of the general population and approximately 70% of obese patients, it carries a large economic burden and is becoming a major reason for liver transplantation worldwide. ALD is a major cause of morbidity and mortality causing 50% of liver cirrhosis and 10% of liver cancer related death. Increasing evidence has accumulated that gut-derived factors play a crucial role in the development and progression of chronic liver diseases.

METHODS

A selective literature search was conducted in Medline and PubMed, using the terms "nonalcoholic fatty liver disease," "alcoholic liver disease," "lipopolysaccharide," "gut barrier," and "microbiome."

RESULTS

Gut dysbiosis and gut barrier dysfunction both contribute to chronic liver disease by abnormal regulation of the gut-liver axis. Thereby, gut-derived lipopolysaccharides (LPS) are a key factor in inducing the inflammatory response of liver tissue. The review further underlines that endotoxemia is observed in both NAFLD and ALD patients. LPS plays an important role in conducting liver damage through the LPS-TLR4 signaling pathway. Treatments targeting the gut microbiome and the gut barrier such as fecal microbiota transplantation (FMT), probiotics, prebiotics, synbiotics, and intestinal alkaline phosphatase (IAP) represent potential treatment modalities for NAFLD and ALD.

CONCLUSIONS

The gut-liver axis plays an important role in the development of liver disease. Treatments targeting the gut microbiome and the gut barrier have shown beneficial effects in attenuating liver inflammation and need to be further investigated.

The Effect of Bacterial Infections, Probiotics and Zonulin on Intestinal Barrier Integrity

The intestinal barrier plays an extremely important role in maintaining the immune homeostasis of the gut and the entire body. It is made up of an intricate system of cells, mucus and intestinal microbiota. A complex system of proteins allows the selective permeability of elements that are safe and necessary for the proper nutrition of the body. Disturbances in the tightness of this barrier result in the penetration of toxins and other harmful antigens into the system. Such events lead to various digestive tract dysfunctions, systemic infections, food intolerances and autoimmune diseases. Pathogenic and probiotic bacteria, and the compounds they secrete, undoubtedly affect the properties of the intestinal barrier. The discovery of zonulin, a protein with tight junction regulatory activity in the epithelia, sheds new light on the understanding of the role of the gut barrier in promoting health, as well as the formation of diseases. Coincidentally, there is an increasing number of reports on treatment methods that target gut microbiota, which suggests that the prevention of gut-barrier defects may be a viable approach for improving the condition of COVID-19 patients. Various bacteria-intestinal barrier interactions are the subject of this review, aiming to show the current state of knowledge on this topic and its potential therapeutic applications.

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.

Intestinal Alkaline Phosphatase Combined with Voluntary Physical Activity Alleviates Experimental Colitis in Obese Mice. Involvement of Oxidative Stress, Myokines, Adipokines and Proinflammatory Biomarkers

Intestinal alkaline phosphatase (IAP) is an essential mucosal defense factor involved in the process of maintenance of gut homeostasis. We determined the effect of moderate exercise (voluntary wheel running) with or without treatment with IAP on the course of experimental murine 2,4,6-trinitrobenzenesulfonic acid (TNBS) colitis by assessing disease activity index (DAI), colonic blood flow (CBF), plasma myokine irisin levels and the colonic and adipose tissue expression of proinflammatory cytokines, markers of oxidative stress (SOD2, GPx) and adipokines in mice fed a standard diet (SD) or high-fat diet (HFD). Macroscopic and microscopic colitis in sedentary SD mice was accompanied by a significant decrease in CBF, and a significant increase in the colonic expression of tumor necrosis factor-alpha (TNF-α), IL-6, IL-1β and leptin mRNAs and decrease in the mRNA expression of adiponectin. These effects were aggravated in sedentary HFD mice but reduced in exercising animals, potentiated by concomitant treatment with IAP, especially in obese mice. Exercising HFD mice demonstrated a substantial increase in the mRNA for adiponectin and a decrease in mRNA leptin expression in intestinal mucosa and mesenteric fat as compared to sedentary animals. The expression of SOD2 and GPx mRNAs was significantly decreased in adipose tissue in HFD mice, but these effects were reversed in exercising mice with IAP administration. Our study shows for the first time that the combination of voluntary exercise and oral IAP treatment synergistically favored healing of intestinal inflammation, strengthened the antioxidant defense and ameliorated the course of experimental colitis; thus, IAP may represent a novel adjuvant therapy to alleviate inflammatory bowel disease (IBD) in humans.

If Hoofbeats are not From Horses, It Could be Zebras!! Isolated Hyper-alkaline Phosphatasemia

Alkaline phosphatase (AP) is a membrane bound enzyme and when it is elevated in blood, it is mostly due to either hepatobiliary or bone diseases. We report isolated intestinal hyperphosphatasemia (IAP) in two sisters. Both sisters presented with identical trends of isolated AP elevation. Both underwent extensive workup for liver diseases including cholangiograms, and none was identified. Subsequent isoenzyme electrophoresis showed that 45%-56% of the elevated AP was due to IAP. This elevation of the intestinal AP is consistent with a rare hereditary biochemical abnormality, benign familial intestinal hyperphosphatemia. This condition should be considered in the differential diagnosis of otherwise isolated serum AP levels to avoid unnecessary investigations.

Intestinal Alkaline Phosphatase Deficiency Is Associated with Ischemic Heart Disease

Background

We have previously shown that the deficiency of the gut enzyme intestinal alkaline phosphatase (IAP) is associated with type 2 diabetes mellitus (T2DM) in humans, and mice deficient in IAP develop the metabolic syndrome, a precipitant of T2DM and ischemic heart disease (IHD). We hypothesized that IAP deficiency might also be associated with IHD in humans. We aimed to determine the correlation between the IAP level and IHD in humans.

Methods and Results

The IHD patients were recruited from the National Institute of Cardiovascular Diseases (NICVD), Dhaka, Bangladesh, and the control healthy participants were recruited from a suburban community of Dhaka. We determined the IAP level in the stools of 292 IHD patients (187 males, 105 females) and 331 healthy control people (84 males, 247 females). We found that compared to controls, IHD patients have approx. 30% less IAP (mean ± SEM: 63.7 ± 3.5 vs. 44.9 ± 2.1 U/g stool, respectively; p < 0.000001), which indicates that IAP deficiency is associated with IHD, and a high level of IAP is probably protective against IHD in humans. The adjusted generalized linear model (GLM) of regression analysis predicted a strong association of IAP with IHD (p = 0.0035). Multiple logistic regression analysis showed an independent inverse relationship between the IAP level and the IHD status (odds ratio, OR = 0.993 with 95% CI 0.987-0.998; p < 0.01).

Conclusions

IAP deficiency is associated with IHD, and a high level of IAP might be protective against IHD.

The effect of the branched-chain amino acids on the in-vitro activity of bovine intestinal alkaline phosphatase

Branched-chain amino acids (BCAA) are used as nutritional support for patients with a range of conditions including liver cirrhosis and in-born errors of amino acid metabolism, and they are commonly used “sports” or exercise supplements. The effects of the BCAA on the in-vitro activity of calf intestinal alkaline phosphatase (EC. 3.1.3.1) were studied. All three BCAA were found to be uncompetitive inhibitors of the enzyme with L-leucine being the most potent ([Formula: see text] = 24.9 mmol/L) and L-valine, the least potent ([Formula: see text] = 37 mmol/L). Mixed BCAA are able to act in combination to inhibit the enzyme. Given the important role of intestinal alkaline phosphatase in gut homeostasis, these findings have potential implications for those taking high levels of BCAA as supplements.

Intestinal Alkaline Phosphatase Attenuates Alcohol-Induced Hepatosteatosis in Mice

BACKGROUND AND AIMS

Bacterially derived factors from the gut play a major role in the activation of inflammatory pathways in the liver and in the pathogenesis of alcoholic liver disease. The intestinal brush-border enzyme intestinal alkaline phosphatase (IAP) detoxifies a variety of bacterial pro-inflammatory factors and also functions to preserve gut barrier function. The aim of this study was to investigate whether oral IAP supplementation could protect against alcohol-induced liver disease.

METHODS

Mice underwent acute binge or chronic ethanol exposure to induce alcoholic liver injury and steatosis ± IAP supplementation. Liver tissue was assessed for biochemical, inflammatory, and histopathological changes. An ex vivo co-culture system was used to examine the effects of alcohol and IAP treatment in regard to the activation of hepatic stellate cells and their role in the development of alcoholic liver disease.

RESULTS

Pretreatment with IAP resulted in significantly lower serum alanine aminotransferase compared to the ethanol alone group in the acute binge model. IAP treatment attenuated the development of alcohol-induced fatty liver, lowered hepatic pro-inflammatory cytokine and serum LPS levels, and prevented alcohol-induced gut barrier dysfunction. Finally, IAP ameliorated the activation of hepatic stellate cells and prevented their lipogenic effect on hepatocytes.

CONCLUSIONS

IAP treatment protected mice from alcohol-induced hepatotoxicity and steatosis. Oral IAP supplementation could represent a novel therapy to prevent alcoholic-related liver disease in humans.

Leaky Gut As a Danger Signal for Autoimmune Diseases

The intestinal epithelial lining, together with factors secreted from it, forms a barrier that separates the host from the environment. In pathologic conditions, the permeability of the epithelial lining may be compromised allowing the passage of toxins, antigens, and bacteria in the lumen to enter the blood stream creating a “leaky gut.” In individuals with a genetic predisposition, a leaky gut may allow environmental factors to enter the body and trigger the initiation and development of autoimmune disease. Growing evidence shows that the gut microbiota is important in supporting the epithelial barrier and therefore plays a key role in the regulation of environmental factors that enter the body. Several recent reports have shown that probiotics can reverse the leaky gut by enhancing the production of tight junction proteins; however, additional and longer term studies are still required. Conversely, pathogenic bacteria that can facilitate a leaky gut and induce autoimmune symptoms can be ameliorated with the use of antibiotic treatment. Therefore, it is hypothesized that modulating the gut microbiota can serve as a potential method for regulating intestinal permeability and may help to alter the course of autoimmune diseases in susceptible individuals.

Subchronic and Chronic Toxicity/Carcinogenicity Feeding Studies with Lactitol in Rats

The toxicity and possible carcinogenicity of lactitol, a lactose-derived reduced calorie sugar substitute, were examined in Wistar Cpb:WU rats. In a first 13-week study, groups of 10 weanling rats of each sex were fed diets containing 0, 5, 10, or 20% lactitol, or 25% lactose. In a second 13-week study, groups of 20 rats of each sex received diets with 0, 10, or 20% lactitol, or 25% lactose starting from an age of 3 months. In a lifetime toxicity/cancerogenicity study with in utero exposure, groups of 50 rats of each sex consumed diets with 0, 2, 5, or 10% lactitol, or 20% lactose for 130 weeks. Satellite groups of 10 rats/group received the same diet but were sacrificed after 53 weeks. Subchronic and chronic ingestion of lactitol and lactose was generally well tolerated and an effect on mortality rate was not seen. Body weight gains were slightly decreased in a dose-related manner in all experiments. Dose-related cecal enlargement was observed consistently with lactitol and lactose. Examinations for hematological parameters and urine composition did not reveal any treatment-related abnormalities. The clinical chemistry examinations revealed increased plasma alkaline phosphatase (AP) levels in rats fed 5 or 10% lactitol, or 20% lactose. Slight (microscopic) cytoplasmic alterations in the staining pattern of hepatocytes were observed in the first but not the second 13-week study in a number of male rats of the 10 and 20% lactitol groups. In the chronic study, a statistically significant increase in bile duct hyperplasia was noted in female rats fed 5 or 10% lactitol, or 20% lactose. Measurement of femur calcium content in terminated female rats revealed a dose-related, yet statistically nonsignificant decrease in the lactitol groups and lowest levels in the 20% lactose group. The histopathological examination of rats treated with lactitol and lactose for their lifetime showed an increased incidence of (1) pelvic nephrocalcinosis (5% lactitol females, and 10% lactitol and 20% lactose males and females), (2) adrenomedullary proliferative changes (10% lactitol and 20% lactose males), and (3) hyperplastic and neoplastic changes of Leydig cells (10% lactitol and 20% lactose males). Results from other studies suggest that nephrocalcinosis and adrenal medullary proliferative disease represent sequelae of a chronic, treatment-related hyperabsorption of calcium which does not occur in man. The mechanism of the testicular effect is not yet identified. However, lactitol gave completely negative results in standard tests for mutagenicity and clastogenicity, and no testicular effects or other neoplastic response was observed in lactitol-fed mice. Since Leydig cell tumors occur in humans at an extremely low rate despite the ingestion of substantial amounts of lactose with ordinary meals, the observation made in rats lacks apparent relevance for man.

Gastrointestinal and hepatic mechanisms limiting entry and dissemination of lipopolysaccharide into the systemic circulation

The human microbiota consists of 100 trillion microorganisms that provide important metabolic and biological functions benefiting the host. However, the presence in host plasma of a gut-derived bacteria component, the lipopolysaccharide (LPS), has been identified as a causal or complicating factor in multiple serious diseases such as sepsis and septic shock and, more recently, obesity-associated metabolic disorders. Understanding the precise mechanisms by which gut-derived LPS is transported from the gut lumen to the systemic circulation is crucial to advance our knowledge of LPS-associated diseases and elaborate targeted strategies for their prevention. The aim of this review is to synthetize current knowledge on the host mechanisms limiting the entry and dissemination of LPS into the systemic circulation. To prevent bacterial colonization and penetration, the intestinal epithelium harbors multiple defense mechanisms including the secretion of antimicrobial peptides and mucins as well as detoxification enzymes. Despite this first line of defense, LPS can reach the apical site of intestinal epithelial cells (IECs) and, because of its large size, likely crosses IECs via transcellular transport, either lipid raft- or clathrin-mediated endocytosis or goblet cell-associated passage. However, the precise pathway remains poorly described. Finally, if LPS crosses the gut mucosa, it is directed via the portal vein to the liver, where major detoxification processes occur by deacetylation and excretion through the bile. If this disposal process is not sufficient, LPS enters the systemic circulation, where it is handled by numerous transport proteins that clear it back to the liver for further excretion.

Intestinal alkaline phosphatase: a summary of its role in clinical disease

Over the past few years, there is increasing evidence implicating a novel role for Intestinal Alkaline Phosphatase (IAP) in mitigating inflammatory mediated disorders. IAP is an endogenous protein expressed by the intestinal epithelium that is believed to play a vital role in maintaining gut homeostasis. Loss of IAP expression or function is associated with increased intestinal inflammation, dysbiosis, bacterial translocation and subsequently systemic inflammation. As these events are a cornerstone of the pathophysiology of many diseases relevant to surgeons, we sought to review recent research in both animal and humans on IAP's physiologic function, mechanisms of action and current research in specific surgical diseases.

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'.

Intestinal alkaline phosphatase deficiency leads to lipopolysaccharide desensitization and faster weight gain

Animals develop in the presence of complex microbial communities, and early host responses to these microbes can influence key aspects of development, such as maturation of the immune system, in ways that impact adult physiology. We previously showed that the zebrafish intestinal alkaline phosphatase (ALPI) gene alpi.1 was induced by Gram-negative bacterium-derived lipopolysaccharide (LPS), a process dependent on myeloid differentiation primary response gene 88 (MYD88), and functioned to detoxify LPS and prevent excessive host inflammatory responses to commensal microbiota in the newly colonized intestine. In the present study, we examined whether the regulation and function of ALPI were conserved in mammals. We found that among the mouse ALPI genes, Akp3 was specifically upregulated by the microbiota, but through a mechanism independent of LPS or MYD88. We showed that disruption of Akp3 did not significantly affect intestinal inflammatory responses to commensal microbiota or animal susceptibility to Yersinia pseudotuberculosis infection. However, we found that Akp3(-/-) mice acquired LPS tolerance during postweaning development, suggesting that Akp3 plays an important role in immune education. Finally, we demonstrated that inhibiting LPS sensing with a mutation in CD14 abrogated the accelerated weight gain in Akp3(-/-) mice receiving a high-fat diet, suggesting that the weight gain is caused by excessive LPS in Akp3(-/-) mice.

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.

Modulation of symbiont lipid A signaling by host alkaline phosphatases in the squid-vibrio symbiosis

The synergistic activity of Vibrio fischeri lipid A and the peptidoglycan monomer (tracheal cytotoxin [TCT]) induces apoptosis in the superficial cells of the juvenile Euprymna scolopes light organ during the onset of the squid-vibrio symbiosis. Once the association is established in the epithelium-lined crypts of the light organ, the host degrades the symbiont's constitutively produced TCT by the amidase activity of a peptidoglycan recognition protein (E. scolopes peptidoglycan recognition protein 2 [EsPGRP2]). In the present study, we explored the role of alkaline phosphatases in transforming the lipid A of the symbiont into a form that changes its signaling properties to host tissues. We obtained full-length open reading frames for two E. scolopes alkaline phosphatase (EsAP) mRNAs (esap1 and esap2); transcript levels suggested that the dominant light organ isoform is EsAP1. Levels of total EsAP activity increased with symbiosis, but only after the lipid A-dependent morphogenetic induction at 12 h, and were regulated over the day-night cycle. Inhibition of total EsAP activity impaired normal colonization and persistence by the symbiont. EsAP activity localized to the internal regions of the symbiotic juvenile light organ, including the lumina of the crypt spaces where the symbiont resides. These data provide evidence that EsAPs work in concert with EsPGRPs to change the signaling properties of bacterial products and thereby promote persistent colonization by the mutualistic symbiont.

IMPORTANCE

The potential for microbe-associated molecular patterns (MAMPs) to compromise host-tissue health is reflected in the often-used nomenclature for these molecules: lipopolysaccharide (LPS) is also called "endotoxin" and the peptidoglycan monomer is also called "tracheal cytotoxin" (TCT). With constant presentation of MAMPs by the normal microbiota, mechanisms to tolerate their effects have developed. The results of this contribution provide evidence that host alkaline phosphatases (APs) dephosphorylate and inactivate the symbiont MAMP lipid A. As such, APs work in synergy with a peptidoglycan recognition protein, which inactivates symbiont-exported TCT, to alter the symbiont MAMPs and promote persistence of the partnership. Not only may these activities serve to "tame" the MAMPs, but also the resulting products may themselves be important signals in persistent mutualisms. The finding of lipid A modification by APs in an invertebrate mutualism provides evidence that this specific strategy for dealing with symbiotic partners is conserved across the animal kingdom.

Intestinal alkaline phosphatase: multiple biological roles in maintenance of intestinal homeostasis and modulation by diet

The diverse nature of intestinal alkaline phosphatase (IAP) functions has remained elusive, and it is only recently that four additional major functions of IAP have been revealed. The present review analyzes the earlier literature on the dietary factors modulating IAP activity in light of these new findings. IAP regulates lipid absorption across the apical membrane of enterocytes, participates in the regulation of bicarbonate secretion and of duodenal surface pH, limits bacterial transepithelial passage, and finally controls bacterial endotoxin-induced inflammation by dephosphorylation, thus detoxifying intestinal lipopolysaccharide. Many dietary components, including fat, protein, and carbohydrate, modulate IAP expression or activity and may be combined to sustain a high level of IAP activity. In conclusion, IAP has a pivotal role in intestinal homeostasis and its activity could be increased through the diet. This is especially true in pathological situations (e.g., inflammatory bowel diseases) in which the involvement of commensal bacteria is suspected and when intestinal AP is too low to detoxify a sufficient amount of bacterial lipopolysaccharide.

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.

Duodenal brush border intestinal alkaline phosphatase activity affects bicarbonate secretion in rats

We hypothesized that duodenal HCO(3)(-) secretion alkalinizes the microclimate surrounding intestinal alkaline phosphatase (IAP), increasing its activity. We measured AP activity in rat duodenum in situ in frozen sections with the fluorogenic substrate ELF-97 phosphate and measured duodenal HCO(3)(-) secretion with a pH-stat in perfused duodenal loops. We examined the effects of the IAP inhibitors L-cysteine or L-phenylalanine (0.1-10 mM) or the tissue nonspecific AP inhibitor levamisole (0.1-10 mM) on AP activity in vitro and on acid-induced duodenal HCO(3)(-) secretion in vivo. AP activity was the highest in the duodenal brush border, decreasing longitudinally to the large intestine with no activity in stomach. Villous surface AP activity measured in vivo was enhanced by PGE(2) intravenously and inhibited by luminal L-cysteine. Furthermore, incubation with a pH 2.2 solution reduced AP activity in vivo, whereas pretreatment with the cystic fibrosis transmembrane regulator (CFTR) inhibitor CFTR(inh)-172 abolished AP activity at pH 2.2. L-Cysteine and L-phenylalanine enhanced acid-augmented duodenal HCO(3)(-) secretion. The nonselective P2 receptor antagonist suramin (1 mM) reduced acid-induced HCO(3)(-) secretion. Moreover, L-cysteine or the competitive AP inhibitor glycerol phosphate (10 mM) increased HCO(3)(-) secretion, inhibited by suramin. In conclusion, enhancement of the duodenal HCO(3)(-) secretory rate increased AP activity, whereas inhibition of AP activity increased the HCO(3)(-) secretory rate. These data support our hypothesis that HCO(3)(-) secretion increases AP activity by increasing local pH at its catalytic site and that AP hydrolyzes endogenous luminal phosphates, presumably ATP, which increases HCO(3)(-) secretion via activation of P2 receptors.

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.

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 secretion in oil-fed rats

Oil feeding is known to increase the secretion of intestinal alkaline phosphatase (IAP) into serum and this phenomenon is shown to be mediated by surfactant-like particles. These lipoprotein particles are secreted by enterocytes and are rich in phosphatidyl choline and IAP. The exact mechanisms underlying this phenomenon are not known. We studied the effect of feeding different oils varying in fatty acid composition, i.e., coconut oil, corn oil, and cod liver oil, on the secretion of IAP into serum. Also, the effect of actinomycin D treatment on this phenomenon was evaluated. Male albino rats were fed 2 ml of various oils. Alkaline phosphatase activity was measured in serum, luminal washings, and other intestinal fractions. Cod liver oil was found to maximally enhance the soluble and membrane-bound IAP as well as secretion of IAP into lumen and serum. Administration of actinomycin D significantly reduced the enzyme activity in serum and various intestinal fractions in both control and cod liver oil-fed rats. These results were further substantiated by 5-bromo-4-chloroindolyl phosphate staining of IAP in acrylamide gels and by western blotting. The effect of cod liver oil feeding was specific for IAP, as there was no change in the activity of another brush border enzyme, sucrase, under these conditions. These findings suggest that fatty acid composition of the oil determines the amount of IAP secretion and there is coordination between IAP synthesis and its secretion for transport into serum in response to oil feeding.

Distension enterogenesis: increasing the size and function of small intestine

INTRODUCTION

The purpose of this study is to evaluate the feasibility of using saline infusion to lengthen small bowel while preserving intestinal enzymatic function.

METHODS

Male Sprague-Dawley rats had a 3-cm jejunal segment taken out of continuity. A catheter was inserted in the proximal end, and the distal end was oversewn. Continuous infusion of saline into the isolated jejunal segment was started 2 weeks postoperatively. Segments were harvested 1 week later. Segment weights and lengths were measured preoperatively and at the time of harvest. Histology of harvested segments was performed. Alkaline phosphatase (ALP) and lactase assays were performed. Comparisons were made with normal jejunum from control animals.

RESULTS

A 32% increase in length was achieved with saline distension of small intestine. The segment weight to length ratio was significantly increased by saline distension; however, the total protein-to-weight ratio was unchanged. Specific activities of ALP and lactase were not affected by saline distension. Because of the increased length and weight of the distended jejunal segments, total segment activities for both enzymes were significantly increased.

CONCLUSIONS

Saline infusion appears to be a viable method for increasing small intestinal length without compromising enzymatic function. This phenomenon may provide a new method for the treatment of patients with short bowel syndrome in the future, and further study is warranted.

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.

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

Surfactant-like particles (SLP) are unilamellar secreted membranes associated with the process of lipid absorption and isolated previously only from the apical surface of enterocytes. In this paper, the intracellular membrane has been isolated from corn oil-fed animals, identified by its content of the marker protein intestinal alkaline phosphatase (IAP). Another brush-border protein, cubilin, and its anchoring protein megalin have been identified as components of extracellular SLP, but only cubilin is present to any extent in intracellular SLP. During fat absorption, IAP is modestly enriched in intracellular SLP, but full-length cubilin (migrating at 210 kDa in fat-fed mucosal fractions) falls by one-half, although fragments of cubilin are abundant in the intracellular SLP. Both IAP and cubilin colocalize to the same cells during corn oil absorption and colocalize around lipid droplets. This localization is more intense during feeding of corn oil with Pluronic L-81, a detergent that allows uptake of fatty acids and monoglycerides from the lumen, but blocks chylomicron secretion. Confocal microscopy confirms the colocalization of IAP and the ligand for cubilin, intrinsic factor. Possible roles for cubilin in intracellular SLP include facilitating movement of the lipid droplet through the cell and binding to the basolateral membrane before reverse endocytosis.

Intestinal alkaline phosphatase release is not associated with chylomicron formation

Intestinal alkaline phosphatase (IAP) is one of the major sources of alkaline phosphatase in circulation. It is secreted into the intestinal lumen, serum, and lymph. After the ingestion of lipid, lymphatic alkaline phosphatase secretion increases significantly. We have found that the nonabsorbable fat olestra is unable to stimulate lymphatic alkaline phosphatase secretion. We also found that the hydrophobic surfactant Pluronic L-81, which blocks chylomicron formation, fails to inhibit this increase in lymphatic alkaline phosphatase secretion. These results suggest that it is the lipid uptake into the mucosa and/or reesterification to form triacylglycerols, but not the formation of chylomicrons, that is necessary for the stimulation of the secretion of alkaline phosphatase into the lymph.

Semiautomated analysis of alkaline phosphatase isoenzymes in serum of normal cynomolgus monkeys (Macaca fascicularis)

Alkaline phosphatase (ALP) isoenzyme analysis, using a combination of wheat germ lectin (WGL) precipitation, levamisole inhibition and an automated p-nitrophenylphosphate assay was validated for use with serum from monkeys (Macaca fascicularis) and used to determine the activities of liver ALP (LALP), bone ALP (BALP) and intestinal ALP (IALP). Based on serial dilution studies and within-run and between-run coefficients of variation, each assay had excellent linearity and acceptable precision. In addition, liver and intestinal mucosa extracts for tissue specific alkaline phosphatases were used to confirm assay validations. Gender-specific differences for total ALP, LALP, and BALP activities were present in sera from normal monkeys between 2 and 4 years of age. Males had 1.3-fold higher total ALP and LALP activities, and 1.5-fold higher BALP activity compared with females. The majority of ALP activity in normal monkey serum was LALP isoenzyme activity, which ranged from 56.7% to 94.7% of total activity. Serum BALP activity ranged from 5.3% to 42.8%. There was negligible IALP activity in all serum samples.

Surfactant-like particles mediate tissue-specific functions in epithelial cells

Lipid-rich, unilamellar membranes appear to be relatively common structures lining the apical or 'exposed' surface of epithelial cells. They have now been described in the intestinal tract from the esophagus to the rectum and have been isolated from tissues, such as the stomach, the small bowel, the colon, and the bladder. The presence of a lining layer in the lungs has been known for some time, and its functions, structure, and metabolism have been extensively studied, as can be gleaned from the multitude of reports presented at this symposium. The 'other' surfactants, however, have attracted far less attention and have been investigated in detail in only a few reports. This paucity of information, when compared to the pulmonary system, is most likely due to the fact that a generalized function (sufficiency state) or disease (deficiency state) has not yet been recognized for either the intestinal or urinary forms of surfactant. It seems reasonable to assume that the role of the SLP will vary, at least in part, with the organ or tissue with which it is associated, although the widespread nature of the membrane assumes that some functions (e.g. protective) will be shared. Thus, pulmonary surfactant's primary function in the lung may be to reduce surface tension and prevent lung collapse; but it also plays a significant part in the lung's defenses against bacterial and/or chemical invasion. It is hoped that future studies will shed some light on the function of the various SLPs and lead to a better appreciation for their role in both maintaining a healthy environment and contributing to the proper functioning of their host tissues.

Effect of tissue non-specific alkaline phosphatase in maintenance of structure of murine colon and stomach

The gastrointestinal tract of mammals secretes a phospholipid-rich membrane that is enriched in alkaline phosphatase (AP) and surfactant proteins (surfactant-like particle, SLP). The production of this particle is stimulated in the small intestine by fat feeding and in cultured cells in vitro by transfection with intestinal alkaline phosphatase (IAP). To test whether tissue non-specific alkaline phosphatase (TNAP) was a factor in stimulating surfactant-like particle production in stomach and colon (tissues expressing TNAP), mice lacking this enzyme were studied. Mice were harvested at 8 days of life, when body weight of homozygous animals (TNAP -/-) was about half that of congenic controls (TNAP +/+) or heterozygotes (TNAP +/-), but before seizures had begun. No difference in content of the major SLP protein (65 kDa) by Western blotting or immunocytochemistry was seen in stomach or colon of TNAP -/- vs. TNAP +/+ animals, but the content was only about half in the IAP-expressing small bowel. Transmission electron microscopy of the TNAP -/- small bowel showed large dilated lysosomes and residual bodies. Colonocytes and gastric surface epithelial cells from the same animals showed mitochondria containing homogeneous dense inclusions, consistent with neutral lipid. In the underweight homozygous animals, there was a decrease in the neuronal content of submucosal ganglia in the jejunum and ileum and of myenteric ganglia in the jejunum of TNAP -/- animals. These findings suggest that (1) TNAP is not important in maintaining surfactant-like particle content of tissues that express TNAP, (2) normal fat absorption is important in maintaining SLP content in the small intestine, and (3) TNAP is important in the maintenance of some intestinal structures, and perhaps their function.

Differences between duodenal and jejunal rat alkaline phosphatase

OBJECTIVES

The aim of this study was to kinetically characterize rat tissue-nonspecific-alkaline phosphatase (TNS-ALP) and intestinal (duodenal- and jejunal-IALP), and to determine the effect of substances known to affect phosphorylation/dephosphorylation on TNS- and IALP activity.

DESIGN AND RESULTS

The ranking order of ALP activity (K(enzyme)) was duodenal mucosa (IALP) > jejunal mucosa (IALP) > kidney (TNS-ALP) > brain (TNS-ALP). Levamisole was found to produce a concentration-dependent decrease of ALP activity in kidney and brain. However, levamisole had no effect on duodenal ALP activity and produced a concentration-dependent increase on jejunum ALP activity. In brain and jejunum homogenates, octreotide, a stable somatostatin analogue, produced a concentration-dependent increase in ALP activity. In relation to duodenum ALP activity, octreotide produced a biphasic effect.Reverse transcription-polymerase chain reaction showed the presence of IALP-I mRNA both in duodenal and jejunal mucosa, but IALP-II only in duodenal mucosa.

CONCLUSIONS

The results show that duodenal- and jejunal-IALP differ in kinetic parameters and in drug sensitivity. Thus, we can speculate on a different physiologic role for duodenal- and jejunal-IALP, particularly in relation to their dephosphorylation targets.

Rat intestinal alpha1-antitrypsin secretion is regulated by triacylglycerol feeding

alpha1-Antitrypsin (AAT) is secreted by the enterocyte, but its regulation of expression, intramucosal distribution, and functional status are unclear. After corn oil gavage (plus Pluronic L-81 to block chylomicron release), rat intestine was examined for mRNA encoding AAT, immunoreactivity by light and electron microscopy, and protein content by Western blot. Species-specific antisera used were raised against both AAT and surfactant-like particle (SLP), a membrane secreted by the enterocyte in response to fat feeding. Purified luminal SLP was fractionated by Bio-Gel P-200 chromatography to assess its interaction with AAT. Triacylglycerol feeding maximally increased mucosal mRNA-encoding AAT and AAT intracellular protein content by 3 and 5 h, respectively. Immunocytochemistry revealed predominance of AAT in basolateral spaces around enterocytes and Pluronic-blocked extracellular accumulation of AAT, patterns nearly identical to those of secreted SLP. About 10% of AAT was reversibly associated with SLP. Luminal AAT was smaller (51 kDa) than mature AAT (55 kDa) and did not form a complex with pancreatic elastase. When the common bile duct was tied, excluding pancreatic proteases from the lumen, mature AAT that was cleaved by pancreatic elastase was secreted. The luminal secretion of AAT and its reversible association with SLP suggest an intracellular association and a possible role for AAT during lipid digestion and absorption.

Development and hormonal modulation of postnatal expression of intestinal alkaline phosphatase mRNA species and their encoded isoenzymes

In the rat, intestinal alkaline phosphatase (IAP) activity in the duodenum, but not jejunum, increases on day 22-24 after birth and exhibits higher activity hydrolysing phenyl phosphate (PhP) than beta-glycerophosphate (beta GP) [Moog and Yeh (1973) Comp. Biochem. Physiol. 44B, 657-666]. The mechanism underlying these developmental changes remains unknown. To define possible mechanisms, we have measured IAP activity and mRNA levels, and analysed IAP mRNA species and isoenzymes on postnatal days 12, 18, 24 and 32. Duodenal IAP activity and mRNA content were identical on postnatal days 12 and 18, but were 7-fold and 3-fold higher on day 24, respectively than on day 18. The increased IAP activity exhibited a high PhP/beta GP ratio and was accompanied by initial appearance of the 3.0 kb mRNA and 90 kDa isoenzyme. On day 32, duodenal IAP activity did not increase over the levels on day 24, whereas mRNA levels doubled. The lack of enzyme increase might be related in part to increased apical release, as luminal IAP activity increased from 2% of total mucosal IAP on days 12 and 18 to 7% and 14% on days 24 and 32 respectively. In the jejunum, IAP activity decreased postnatally, but mRNA content was unaltered; only the 2.7 kb mRNA and 65 kDa IAP isoenzyme were present. Administration of cortisone or cortisone+thyroxine induced simultaneous appearance of the duodenal 3.0 kb mRNA and 90 kDa isoenzyme with an increased PhP/beta GP ratio. Thus postnatal increase in duodenal IAP activity is related to the expression of a 90 kDa PhP-preferring isoenzyme encoded by the 3.0 kb mRNA. The low-PhP/beta GP-ratio 65 kDa isoenzyme is expressed in the duodenum and in the jejunum and is encoded by the 2.7 kb mRNA.

A possible role for rat intestinal surfactant-like particles in transepithelial triacylglycerol transport

To further examine whether surfactant-like particles (DeSchryver-Kecskemeti, K., R. Eliakim, S. Carroll, W. F. Stenson, M. A. Moxley, and D. H. Alpers. 1989. J. Clin. Invest. 84:1355-1361) were involved in the transepithelial transport of lipid, alkaline phosphatase activity and surfactant-like particle content were measured in apical mucosal scrapings, enterocytes, lamina propria, and serum after inhibition of chylomicron transport. Serum triacylglycerol levels were decreased 60-76% by Pluronic L-81, fenfluramine, and choline deficiency compared with fat-fed controls. 5 h after triacylglycerol feed, alkaline phosphatase activity in all three experimental groups was decreased compared with controls by 52-69% in mucosal scrapings and by 33-72% in serum. A parallel decline (60%) in alkaline phosphatase activity occurred in the lamina propria of Pluronic-treated animals. Total particle content (measured by an ELISA using antiserum against purified particle) after Pluronic treatment was decreased in mucosal scrapings, lamina propria, and serum by 16, 22, and 29% at 3 h and by 33, 40, and 8%, respectively, at 5 h after fat feeding. In contrast, particle content was increased in enterocytes by 29% 3 h and by 8% 5 h after fat feeding. By electron microscopy, enterocytes from Pluronic- and fenfluramine-treated animals exhibited a two- to threefold increase in large intracellular cytoplasmic lipid globules and the appearance of lamellae in apposition, with a marked decrease in the number of surfactant-like particles overlying the brush border. These changes, produced by inhibition of chylomicron transport, in the distribution of surfactant-like particles and particle-bound alkaline phosphatase are consistent with a role for these particles in transepithelial triacylglycerol transport across and out of the enterocyte.

A 91-day feeding study in rats with caprenin

Caprenin, a randomized triglyceride primarily comprising caprylic (C8:0), capric (C10:0), and behenic (C22:0) acids, was administered in a semi-purified diet to weanling Sprague-Dawley rats (25/sex/group) at dose levels of 5.23, 10.23 or 15.00% (w/w) for 91 days. Corn oil was added at 8.96, 5.91 and 3.00%, respectively, to provide essential fatty acids and digestible fat calories. Corn oil alone (12.14%) and a blend of medium-chain triglyceride (MCT) oil plus corn oil (11.21 and 3.13%, respectively) served as controls. All diets were formulated to provide about 4000 kcal/kg of diet and 26.8% of digestible calories from fat by assuming that corn oil, MCT oil, and caprenin provided 9, 7 and 5 kcal/g, respectively. Survival, clinical signs, body weight, feed consumption, feed efficiency, organ weights, organ-to-body-weight ratios, organ-to-brain-weight ratios, haematological values and clinical chemistry parameters were evaluated in all groups. Histopathology of a full complement of tissues was evaluated in the corn oil and MCT oil control groups as well as the high-dose caprenin group. Additional rats (n = 5/sex/group) were included in the study to determine whether there was marked storage of C22:0 in heart, liver or perirenal fat at the end of the 91-day feeding period. No significant differences in body weight gain were measured with the balanced caloric diets, although feed conversion efficiency was reduced in the high-dose caprenin group. No adverse effects from the ingestion of caprenin were detected, nor were significant amounts of C22:0 present in the fat extracted from the selected fat depot sites. These results establish a no-observable-adverse-effect level (NOAEL) of more than 15% (w/w) caprenin in the diet (or more than 83% of total dietary fat), which is equal to a mean exposure level of more than 13.2 g/kg/day for male rats and more than 14.6 g/kg/day for female rats.

Human intestinal alkaline phosphatase--release to the blood is linked to lipid absorption, but removal from the blood is not linked to lipoprotein clearance

To evaluate a possible quantitative relationship between the rise in intestinal alkaline phosphatase (IAP) activity and triglyceride-rich lipoproteins in the blood after an oral fat intake, a specific and sensitive immunocatalytic assay was used. First, day to day variation of the basal IAP activity in the blood of eight volunteers was evaluated. One group of subjects with high basal IAP activity and great variations from one day to the other was distinguished from a group with low basal IAP activity and small day to day variations. The subjects with high basal IAP activities were all secretors of red blood cell antigens, while those with low basal IAP activities were non-secretors. The IAP activity in the blood rose after fat rich meals but not after fat free meals. To further investigate this, IAP activities were measured in the blood of 28 men before 3, 6, 9 and 12 h after a standardized oral fat load of a mixed meal type. The activity rose in all individuals and showed a similar time course as the rise in plasma TG concentration. The elevations of the IAP activity were, however, not quantitatively correlated with the elevations in TG concentration, nor were there any relations in time to peak levels. Subjects with high basal IAP increased their IAP activity more than those with low basal IAP, but within neither group there was any correlation between the basal IAP activity and the rise in IAP activity. IAP did not float with lipoproteins on ultracentrifugation of plasma, nor did IAP bind to lipid droplets from a fat emulsion added to plasma.(ABSTRACT TRUNCATED AT 250 WORDS)