Experimental colitis: decreased Octn2 and Atb0+ expression in rat colonocytes induces carnitine depletion that is reversible by carnitine-loaded liposomes

Beyond nanoparticle-based oral drug delivery: transporter-mediated absorption and disease targeting

Various strategies at the microscale/nanoscale have been developed to improve oral absorption of therapeutics. Among them, gastrointestinal (GI)-transporter/receptor-mediated nanosized drug delivery systems (NDDSs) have drawn attention due to their many benefits, such as improved water solubility, improved chemical/physical stability, improved oral absorption, and improved targetability of their payloads. Their therapeutic potential in disease animal models (e.g., solid tumors, virus-infected lungs, metastasis, diabetes, and so on) has been investigated, and could be expanded to disease targeting after systemic/lymphatic circulation, although the detailed paths and mechanisms of endocytosis, endosomal escape, intracellular trafficking, and exocytosis through the epithelial cell lining in the GI tract are still unclear. Thus, this review summarizes and discusses potential GI transporters/receptors, their absorption and distribution, in vivo studies, and potential sequential targeting (e.g., oral absorption and disease targeting in organs/tissues).

Inflammation and Organic Cation Transporters Novel (OCTNs)

Inflammation is a physiological condition characterized by a complex interplay between different cells handled by metabolites and specific inflammatory-related molecules. In some pathological situations, inflammation persists underlying and worsening the pathological state. Over the years, two membrane transporters namely OCTN1 (SLC22A4) and OCTN2 (SLC22A5) have been shown to play specific roles in inflammation. These transporters form the OCTN subfamily within the larger SLC22 family. The link between these proteins and inflammation has been proposed based on their link to some chronic inflammatory diseases such as asthma, Crohn's disease (CD), and rheumatoid arthritis (RA). Moreover, the two transporters show the ability to mediate the transport of several compounds including carnitine, carnitine derivatives, acetylcholine, ergothioneine, and gut microbiota by-products, which have been specifically associated with inflammation for their anti- or proinflammatory action. Therefore, the absorption and distribution of these molecules rely on the presence of OCTN1 and OCTN2, whose expression is modulated by inflammatory cytokines and transcription factors typically activated by inflammation. In the present review, we wish to provide a state of the art on OCTN1 and OCTN2 transport function and regulation in relationships with inflammation and inflammatory diseases focusing on the metabolic signature collected in different body districts and gene polymorphisms related to inflammatory diseases.

Altered metabolome and microbiome features provide clues in predicting recurrence of ulcerative colitis

PURPOSE

Many studies have shown that the imbalance of the intestinal flora and metabolite can lead to the development of ulcerative colitis (UC), but their role in recurrent-UC is still unclear. We studied the intestinal flora and metabolites associated with recurrent-UC to elucidate the mechanism and biomarkers of recurrent-UC.

METHODS

Ulcerative colitis (UC) models in active, remission, and recurrence stages were established, and the abundance of intestinal flora was determined by 16 S rRNA sequencing. The changes in the metabolites present in feces and serum were analyzed by UPLC-MS/MS.

RESULTS

We identified 24 metabolites in feces and serum, which might be used as diagnostic and predictive biomarkers of recurrent-UC. The dominant flora of recurrent-UC included Romboutsia, UCG-005, etc. The results of a network analysis found that long-chain fatty acids and phenylalanine were strongly correlated with Firmicutes and Proteobacteria, which indicated that the recurrence of UC might be closely related to metabolites and microorganisms.

CONCLUSION

The changes in intestinal microbiota and metabolites are closely related to the development of UC. Microbiota is an important inducer of UC, which can regulate metabolites through the 'microorganism-gut-metabolite' axis. It may provide a new method for the prediction and treatment of UC.

Effects of enteral nutrition supplemented with octanoic acid on lipopolysaccharide-induced intestinal injury: role of peroxisome proliferator-activated receptor γ/STAT-1/myeloid differentiation factor 88 pathway

OBJECTIVE

Enteral nutrition is the key therapy in septic patients. Different formulas of enteral nutrition have various effects on gastrointestinal sepsis. Therefore, we investigated the effects of enteral nutrition supplemented with octanoic acid on lipopolysaccharide-induced intestinal injury and explored the potential mechanism.

METHODS

First, to investigate the effects of enteral nutrition supplemented with octanoic acid on lipopolysaccharide-induced intestinal injury, rats were randomly divided into four groups: sham, lipopolysaccharide, lipopolysaccharide + enteral nutrition, and lipopolysaccharide + enteral nutrition + octanoic acid. Then, to explore whether enteral nutrition supplemented with octanoic acid can prevent lipopolysaccharide-induced intestinal injury via the peroxisome proliferator-activated receptor γ/STAT-1/myeloid differentiation factor 88 pathway, rats were randomly divided into five groups: sham, lipopolysaccharide, lipopolysaccharide + enteral nutrition + octanoic acid, lipopolysaccharide + enteral nutrition + octanoic acid + SR202, and lipopolysaccharide + pioglitazone. All rats received nutritional support for 3 d. We examined the serum levels of inflammatory factors, pathologic changes, goblet cell density, intestinal tight junction protein expression, and the peroxisome proliferator-activated receptor γ/STAT-1/myeloid differentiation factor 88 pathway in the ileum and colon. The effect of octanoic acid on intestinal epithelium injury was also explored in vitro.

RESULTS

Enteral nutrition supplemented with octanoic acid significantly decreased the serum levels of inflammatory factors and prevented intestinal barrier dysfunction compared with enteral nutrition alone (P < 0.05). Inhibiting the peroxisome proliferator-activated receptor γ/STAT-1/myeloid differentiation factor 88 pathway exacerbated effects of enteral nutrition supplemented with octanoic acid on intestinal injury (P < 0.05). Activation of the peroxisome proliferator-activated receptor γ/STAT-1/myeloid differentiation factor 88 pathway prevented intestinal injury (P < 0.05). Octanoic acid also exerted a similar effect on intestinal epithelium injury in vitro.

CONCLUSIONS

Enteral nutrition supplemented with octanoic acid prevents lipopolysaccharide-induced intestinal injury via the peroxisome proliferator-activated receptor γ/STAT-1/myeloid differentiation factor 88 pathway.

Cross-generational effects of maternal exposure to imazalil on anaerobic components and carnitine absorption associated with OCTN2 expression in mice

Imazalil (IMZ) is a fungicide recommended by the Chinese ministry of agriculture. However, recent study was observed high level of IMZ by dietary exposure in pregnant women. To determine the cross-generational effects, C57BL/6 mice were exposed to IMZ at dietary levels of 0, 0.025‰, and 0.25‰ during the gestation and lactation periods. Then, we assessed the changes in growth phenotypes, carnitine levels, and gut microbiota in F₀, F₁ or F₂ generations. The growth phenotypes of dams didn't observe significant difference, but there were significant changes in the offspring. Plasma samples revealed low levels of free carnitine (C0), long-chain acyl-carnitines and total carnitine. In particular, C0 may be regarded as relatively potential, specific markers by maternal IMZ exposure. Caco2 cell culture and animal experiment confirmed IMZ affected carnitine absorption through the organic cation transporter type-2 (OCTN2) protein encoded by solute carrier family 22A member 5 (SLC22A5) gene in colon. Maternal IMZ exposure also had a greater effect on gut microbiota in offspring, especially anaerobic bacteria, which positively correlated with C0 and acyl-carnitines. These results suggested that maternal IMZ exposure affected carnitine absorption through OCTN2 protein, which led to the decline of anaerobic bacteria and unbalanced intestinal homeostasis.

Preparation, Characterization and In Vitro Evaluation of Eudragit S100-Coated Bile Salt-Containing Liposomes for Oral Colonic Delivery of Budesonide

The aim of this study was to prepare a liposomal formulation of a model drug (budesonide) for colonic delivery by incorporating a bile salt (sodium glycocholate, SGC) into liposomes followed by coating with a pH-responsive polymer (Eudragit S100, ES100). The role of the SGC is to protect the liposome from the emulsifying effect of physiological bile salts, while that of ES100 is to protect the liposomes from regions of high acidity and enzymatic activity in the stomach and small intestine. Vesicles containing SGC were prepared by two preparation methods (sonication and extrusion), and then coated by ES100 (ES100-SGC-Lip). ES100-SGC-Lip showed a high entrapment efficiency (>90%) and a narrow size distribution (particle size = 275 nm, polydispersity index < 0.130). The characteristics of liposomes were highly influenced by the concentration of incorporated SGC. The lipid/polymer weight ratio, liposome charge, liposome addition, and mixing rate were critical factors for efficient and uniform coating. In vitro drug release studies in various simulated fluids indicate a pH-dependent dissolution of the coating layer, and the disintegration process of ES100-SGC-Lip was evaluated. In conclusion, the bile salt-containing ES100-coated liposomal formulation has potential for effective oral colonic drug delivery.

Polyphenol Rich Forsythia suspensa Extract Alleviates DSS-Induced Ulcerative Colitis in Mice through the Nrf2-NLRP3 Pathway

This study systematically evaluated the effect of Forsythia suspensa extract on dextran sodium sulfate (DSS)-induced ulcerative colitis (UC) and determined its mechanism of action. The results showed that Forsythia suspensa extract significantly inhibited DSS-induced UC in mice. In vivo mechanistic studies revealed that Forsythia suspensa extract relieved the symptoms of colitis by enhancing antioxidant activity and inhibiting pyroptosis. Further in vitro experiments on the mechanism of Forsythia suspensa showed that it reduced the level of reactive oxygen species (ROS) in J774A.1 cells. We found that Forsythia suspensa extract enhanced cellular antioxidation activity and inhibited pyroptosis. After silencing NLRP3, it was found to play an important role in pyroptosis. In addition, after Nrf2 was silenced, the inhibitory effect of Forsythia suspensa extract on cell pyroptosis was eliminated, indicating an interaction between Nrf2 and NLRP3. Metabonomics revealed that Forsythia suspensa extract significantly improved metabolic function in colitis mice by reversing the abnormal changes in the levels of 9 metabolites. The main metabolic pathways involved were glutathione metabolism, aminoacyl-tRNA biosynthesis and linoleic acid metabolism. In conclusion, we found that Forsythia suspensa extract significantly alleviated DSS-induced UC injury through the Nrf2-NLRP3 pathway and relieved metabolic dysfunction.

PPARγ: The Central Mucus Barrier Coordinator in Ulcerative Colitis

Ulcerative colitis (UC) is an idiopathic, long-term inflammatory disorder of the colon, characterized by a continuous remitting and relapsing course. The intestinal mucus barrier is the first line at the interface between the host and microbiota and acts to protect intestinal epithelial cells from invasion. Data from patients and animal studies have shown that an impaired mucus barrier is closely related to the severity of UC. Depletion of the mucus barrier is not just the strongest but is also the only independent risk factor predicting relapse in patients with UC. Peroxisome proliferator-activated receptor gamma (PPARγ), a nuclear transcription regulator, is involved in the regulation of inflammatory cytokine expression. It is also known to promote mucus secretion under pathological conditions to expel pathogenic bacteria or toxins. More important, PPARγ has been shown to affect host-microbiota interactions by modulating the energy metabolism of colonocytes and the oxygen availability of the intestinal microbiome. It is well known that gut microbiota homeostasis is essential for butyrate generation by the commensal bacteria to supply energy resources for colonocytes. Therefore, it can be speculated that PPARγ, as a central coordinator of the mucus barrier, may be a promising target for the development of effective agents to combat UC.

Extra virgin olive oil and related by-products (Olea europaea L.) as natural sources of phenolic compounds for abdominal pain relief in gastrointestinal disorders in rats

Management of abdominal pain, a common symptom of IBDs and IBS, is still a clinical problem. Extra virgin olive oil (EVOO), a main component of the Mediterranean diet, shows positive effects on chronic inflammation in IBDs. In this study, the effect of the oral administration of EVOO (3 mL) and two olive milling by-products, DPA (300 mg kg^-1) and DRF (300 mg kg^-1), on preventing the development of abdominal pain in a DNBS-induced colitis model in rats was evaluated. The doses were chosen with the aim of simulating a plausible daily intake in humans. DPA and EVOO treatments significantly reduced the abdominal viscero-motor response to colon-rectal distension at 2 and 3 mL of balloon distension volume, both 7 and 14 days after the DNBS-injection. DRF showed efficacy in the reduction of visceral hypersensitivity only with 3 mL balloon inflation. In awake animals, DPA and DRF reduced pain perception (evaluated as abdominal withdrawal reflex) with all balloon distension volumes, while EVOO was effective only with higher distension volumes. Fourteen days after the DNBS-injection, all samples reduced the macroscopic intestinal damage (quantified as the macroscopic damage score) also showing, at the microscopic level, a reduction of the inflammatory infiltrate (quantified by hematoxylin and eosin analysis), fibrosis (highlighted by picrosirius red staining), the increase in mast cells and their degranulation (analyzed by triptase immunohistochemistry). This is the first report on the promotion of abdominal pain relief in a rat model obtained administering EVOO and two derived by-products. Our results suggest a protective role of phenol-rich EVOO and milling by-products, which may be proposed as food ingredients for novel functional foods.

Update on SLC6A14 in lung and gastrointestinal physiology and physiopathology: focus on cystic fibrosis

The solute carrier family 6 member 14 (SLC6A14) protein imports and concentrates all neutral amino acids as well as the two cationic acids lysine and arginine into the cytoplasm of different cell types. Primarily described as involved in several cancer and colonic diseases physiopathological mechanisms, the SLC6A14 gene has been more recently identified as a genetic modifier of cystic fibrosis (CF) disease severity. It was indeed shown to have a pleiotropic effect, modulating meconium ileus occurrence, lung disease severity, and precocity of P. aeruginosa airway infection. The biological mechanisms explaining the impact of SLC6A14 on intestinal and lung phenotypes of CF patients are starting to be elucidated. This review focuses on SLC6A14 in lung and gastrointestinal physiology and physiopathology, especially its involvement in the pathophysiology of CF disease.

Downregulation of OCTN2 by cytokines plays an important role in the progression of inflammatory bowel disease

Inflammatory bowel diseases (IBD) are characterized by chronic relapsing disorders of the gastrointestinal tract. OCTN2 (SLC22A5) and its substrate l-carnitine (l-Car) play crucial roles in maintaining normal intestinal function. An aim of this study was to delineate the expression alteration of OCTN2 in IBD and its underlying mechanism. We also investigated the impact of OCTN2 on IBD progression and the possibility of improving IBD through OCTN2 regulation. Our results showed decreased OCTN2 expression levels and l-Car content in inflamed colon tissues of IBD patients and mice, which negatively correlated with the degree of colonic inflammation in IBD mice. Mixed proinflammatory cytokines TNF-α, IL-1β and IFNγ downregulated the expression of OCTN2 and subsequently reduced the l-Car content through PPARγ/RXRα pathways in FHC cells. OCTN2 silencing reduced the proliferation rate of the colon cells, whereas OCTN2 overexpression increased the proliferation rate. Furthermore, the ability of PPARγ agonist, luteolin, to increase OCTN2 expression resulted in the alleviation of colonic inflammatory responses. In conclusion, OCTN2 was downregulated in IBD by proinflammatory cytokines via the PPARγ/RXRα pathways, which reduced l-Car concentration and subsequently induced IBD deterioration. Upregulation of OCTN2 by the PPARγ agonist alleviated colonic inflammation. Our findings suggest that, OCTN2 may serve as a therapeutic target for IBD therapy.

Absorptive transport of amino acids by the rat colon

The capacity of the colon to absorb microbially produced amino acids (AAs) and the underlying mechanisms of AA transport are incompletely defined. We measured the profile of 16 fecal AAs along the rat ceco-colonic axis and compared unidirectional absorptive AA fluxes across mucosal tissues isolated from the rat jejunum, cecum, and proximal colon using an Ussing chamber approach, in conjunction with ¹H-NMR and ultra-performance liquid chromatography-mass spectrometry chemical analyses. Passage of stool from cecum to midcolon was associated with segment-specific changes in fecal AA composition and a decrease in total AA content. Simultaneous measurement of up to 16 AA fluxes under native luminal conditions, with correction for endogenous AA release, demonstrated absorptive transfer of AAs across the cecum and proximal colon at rates comparable (30-80%) to those across the jejunum, with significant Na⁺-dependent and H⁺-stimulated components. Expression profiling of 30 major AA transporter genes by quantitative PCR revealed comparatively high levels of transcripts for 20 AA transporters in the cecum and/or colon, with the levels of 12 exceeding those in the small intestine. Our results suggest a more detailed model of major apical and basolateral AA transporters in rat colonocytes and provide evidence for a previously unappreciated transfer of AAs across the colonic epithelium that could link the prodigious metabolic capacities of the luminal microbiota, the colonocytes, and the body tissues.NEW & NOTEWORTHY This study provides evidence for a previously unappreciated transfer of microbially generated amino acids across the colonic epithelium under physiological conditions that could link the prodigious metabolic capacities of the luminal microbiota, the colonocytes, and the body tissues. The segment-specific expression of at least 20 amino acid transporter genes along the colon provides a detailed mechanistic basis for uniport, heteroexchange, Na⁺-cotransport, and H⁺-cotransport components of colonic amino acid absorption.

LC-MS-based metabolomics analysis of Berberine treatment in ulcerative colitis rats

Inflammatory bowel disease (IBD) is often accompanied by metabolic imbalance and Berberine can relieve the symptoms of IBD, but the mechanism is still unclear. To explore the relationship between IBD, metabolism and Berberine, dextran sulfate sodium-induced ulcerative colitis (UC) model was built and urine and feces samples were analyzed with ultra-performance liquid chromatography combined with quadrupole-time-of-flight mass spectrometry, followed by multivariate statistical analyses. Targeted metabolomics was applied to verify and supplement the result of amino acids tested by non-targeted metabolomics. The study found that Berberine could ameliorate UC and improve metabolic disorders. The level of 4 metabolites increased and 35 decreased in urine and these metabolites mainly belong to amino acid, glucide, organic acid and purine. Besides, Berberine could reduce the level of 5 metabolites and raise the level of 7 metabolites in feces, which mainly belong to amino acid and lipid. Additionally, these altered metabolites were mainly related to amino acids metabolism, purine metabolism, vitamin metabolism, lipid metabolism and citrate cycle pathways. Furthermore, microbiome metabolism may be regulated by Berberine in UC. In general, this study provides a useful approach for exploring the mechanism of Berberine in the treatment of UC from the perspective of metabolomics.

Recent advances in drug delivery via the organic cation/carnitine transporter 2 (OCTN2/SLC22A5)

INTRODUCTION

Transporters in the plasma membrane have been exploited successfully for the delivery of drugs in the form of prodrugs and nanoparticles. Organic cation/carnitine transporter 2 (OCTN2, SLC22A5) has emerged as a viable target for drug delivery. OCTN2 is a Na⁺-dependent high-affinity transporter for L-carnitine and a Na⁺-independent transporter for organic cations. OCTN2 is expressed in the blood-brain barrier, heart, liver, kidney, intestinal tract and placenta and plays an essential role in L-carnitine homeostasis in the body. Areas covered: In recent years, several studies have been reported in the literature describing the utility of OCTN2 to enhance the delivery of drugs, prodrugs and nanoparticles. Here we summarize the salient features of OCTN2 in terms of its role in the cellular uptake of its physiological substrate L-carnitine in physiological and pathological context; the structural requirements for recognition and the recent advances in OCTN2-targeted drug delivery systems, including prodrugs and nanoparticles, are discussed. Expert opinion: This transporter has great potential to be utilized as a target for drug delivery to improve oral absorption of drugs in the intestinal tract. It also has potential to facilitate the transfer of drugs across the biological barriers such as the blood-brain barrier, blood-retinal barrier, and maternal-fetal barrier.

The Impact of Carnitine on Dietary Fiber and Gut Bacteria Metabolism and Their Mutual Interaction in Monogastrics

Carnitine has vital roles in the endogenous metabolism of short chain fatty acids. It can protect and support gut microbial species, and some dietary fibers can reduce the available iron involved in the bioactivity of carnitine. There is also an antagonistic relationship between high microbial populations and carnitine bioavailability. This review shows the interactions between carnitine and gut microbial composition. It also elucidates the role of carnitine bacterial metabolism, mitochondrial function, fiber fermentability, and short chain fatty acids (SCFAs).

PPARα-dependent exacerbation of experimental colitis by the hypolipidemic drug fenofibrate

Fibrates, such as fenofibrate, are peroxisome proliferator-activated receptor-α (PPARα) agonists and have been used for several decades as hypolipidemic agents in the clinic. However, contradictory observations exist on the role of fibrates in host response to acute inflammation, with unclear mechanisms. The role of PPARα in colitis was assessed using fenofibrate and Ppara-null mice. Wild-type or Ppara-null mice were subjected to acute colitis under three distinct protocols, dextran sulfate sodium, trinitrobenzenesulfonic acid, and Salmonella Typhi. Serum and colon lipidomics were analyzed to characterize the metabolic profiles by ultra-performance liquid chromatography-coupled with electrospray ionization quadrupole time-of-flight mass spectrometry. Messenger RNAs of PPARα target genes and genes involved in inflammation were determined by qunatitative PCR analysis. Fenofibrate treatment exacerbated inflammation and tissue injury in acute colitis, and this was dependent on PPARα activation. Lipidomics analysis revealed that bioactive sphingolipids, including sphingomyelins (SM) and ceramides, were significantly increased in the colitis group compared with the control group; this was further potentiated following fenofibrate treatment. In the colon, fenofibrate did not reduce the markedly increased expression of mRNA encoding TNFα found in the acute colitis model, while it decreased hydrolysis and increased synthesis of SM, upregulated RIPK3-dependent necrosis, and elevated mitochondrial fatty acid β-oxidation, which were possibly related to the exacerbated colitis.

Drug delivery strategies in the therapy of inflammatory bowel disease

Inflammatory bowel disease (IBD) is a frequently occurring disease in young people, which is characterized by a chronic inflammation of the gastrointestinal tract. The therapy of IBD is dominated by the administration of anti-inflammatory and immunosuppressive drugs, which suppress the intestinal inflammatory burden and improve the disease-related symptoms. Established treatment strategies are characterized by a limited therapeutical efficacy and the occurrence of adverse drug reactions. Thus, the development of novel disease-targeted drug delivery strategies is intended for a more effective therapy and demonstrates the potential to address unmet medical needs. This review gives an overview about the established as well as future-oriented drug targeting strategies, including intestine targeting by conventional drug delivery systems (DDS), disease targeted drug delivery by synthetic DDS and disease targeted drug delivery by biological DDS. Furthermore, this review analyses the targeting mechanisms of the respective DDS and discusses the possible field of utilization in IBD.

Where does N(ε)-trimethyllysine for the carnitine biosynthesis in mammals come from?

N^ε-trimethyllysine (TML) is a non-protein amino acid which takes part in the biosynthesis of carnitine. In mammals, the breakdown of endogenous proteins containing TML residues is recognized as starting point for the carnitine biosynthesis. Here, we document that one of the main sources of TML could be the vegetables which represent an important part of daily alimentation for most mammals. A HPLC-ESI-MS/MS method, which we previously developed for the analysis of N^G-methylarginines, was utilized to quantitate TML in numerous vegetables. We report that TML, believed to be rather rare in plants as free amino acid, is, instead, ubiquitous in them and at not negligible levels. The occurrence of TML has been also confirmed in some vegetables by a HPLC method with fluorescence detection. Our results establish that TML can be introduced as free amino acid in conspicuous amounts from vegetables. The current opinion is that mammals utilize the breakdown of their endogenous proteins containing TML residues as starting point for carnitine biosynthesis. However, our finding raises the question of whether a tortuous and energy expensive route as the one of TML formation from the breakdown of endogenous proteins is really preferred when the substance is so easily available in vegetable foods. On the basis of this result, it must be taken into account that in mammals TML might be mainly introduced by diet. However, when the alimentary intake becomes insufficient, as during starvation, it might be supplied by endogenous protein breakdown.

Enzymes involved in L-carnitine biosynthesis are expressed by small intestinal enterocytes in mice: implications for gut health

BACKGROUND

Carnitine is essential for mitochondrial β-oxidation of long-chain fatty acids. Deficiency of carnitine leads to severe gut atrophy, ulceration and inflammation in animal models of carnitine deficiency. Genetic studies in large populations have linked mutations in the carnitine transporters OCTN1 and OCTN2 with Crohn's disease (CD), while other studies at the same time have failed to show a similar association and report normal serum carnitine levels in CD patients.

METHODS

In this report, we have studied the expression of carnitine-synthesizing enzymes in intestinal epithelial cells to determine the capability of these cells to synthesize carnitine de novo. We studied expression of five enzymes involved in carnitine biosynthesis, namely 6-N-trimethyllysine dioxygenase (TMLD), 4-trimethylaminobutyraldehyde dehydrogenase (TMABADH), serine hydroxymethyltransferase 1 and 2 (SHMT1 and 2) and γ-butyrobetaine hydroxylase (BBH) by real-time PCR in mice (C3H strain). We also measured activity of γ-BBH in the intestine using an ex vivo assay and localized its expression by in situ hybridization.

RESULTS

Our investigations show that mouse intestinal epithelium expresses all five enzymes required for de novo carnitine biosynthesis; the expression is localized mainly in villous surface epithelial cells throughout the intestine. The final rate-limiting enzyme γ-BBH is highly active in the small intestine; its activity was 9.7 ± 3.5 pmol/mg/min, compared to 22.7 ± 7.3 pmol/mg/min in the liver.

CONCLUSIONS

We conclude that mouse gut epithelium is able to synthesize carnitine de novo. This capacity to synthesize carnitine in the intestine may play an important role in gut health and can help explain lack of clinical carnitine deficiency signs in subjects with mutations with OCTN transporters.

Studies on the chemopreventive effect of carnitine on tumorigenesis in vivo, using two experimental murine models of colon cancer

Carnitine is known for its essential role in intermediary metabolism. In vitro studies suggest that its antioxidant and anti-inflammatory properties are potentially beneficial toward cancer prevention. This study tested effects of carnitine on the development of colon cancer in vivo using 2 murine models: azoxymethane (AOM) treatment as a model of carcinogen-induced colon cancer and a genetically induced model using Apc (Min/+) mice. AOM and Apc (Min/+) mice divided into dietary groups varying in lipid content, with or without carnitine supplementation (0.08%). AOM-exposed mice on a high butterfat diet had significantly increased aberrant crypts (ACF) (9.3 ± 0.88 vs. 6.3 ± 0.65), and macroscopic tumors (3.8 ± 0.95 vs. 2.0 ± 0.25) compared to mice on a control diet. In AOM mice fed the high butterfat diet, carnitine supplementation inhibited ACF (4.9 ± 0.7 vs. 9.3 ± 0.88, P < 0.001), crypt multiciplicity (1.6 ± 0.08 vs. 1.92 ± 0.1, P < 0.01) and tumors (1.5 ± 0.38 vs. 3.8 ± 0.95, P < 0.001). Carnitine supplementation resulted in significantly increased tissue carnitine and acylcarnitine levels. Carnitine inhibited the development of precancerous lesions and macroscopic colonic tumors in AOM-treated mice. However, carnitine did not exert protective effects on intestinal tumors in Apc (Min/+) mice.

Application of liposomes in drug development--focus on gastroenterological targets

Over the past decade, liposomes became a focal point in developing drug delivery systems. New liposomes, with novel lipid molecules or conjugates, and new formulations opened possibilities for safely and efficiently treating many diseases including cancers. New types of liposomes can prolong circulation time or specifically deliver drugs to therapeutic targets. This article concentrates on current developments in liposome based drug delivery systems for treating diseases of the gastrointestinal tract. We will review different types and uses of liposomes in the development of therapeutics for gastrointestinal diseases including inflammatory bowel diseases and colorectal cancer.

Relationship between serum fibronectin levels and carnitine administration: an experimental study in rats

We aimed to investigate the relationship between dorsal flap viability and serum fibronectin levels in carnitine-administered rats. A total of 24 rats were equally divided into three groups and operated on. Group 1 (sham group n = 8): following surgery, no agent was given. Group 2 (control group, n = 8): following surgery, sterile saline solution at 0·9% with a dose of 100 mg/kg per day for 7 days was administered intraperitoneally. Group 3 (study group, n = 8): following surgery, carnitine with a dose of 100 mg/kg per day for 7 days was administered intraperitoneally. The flap model used was a 10 × 3 cm dorsal flap extending from the tip of the scapula to the hip joint. This was elevated, and then sutured back to its original site. At the end of postoperative day 8, the animals were anaesthetised and blood samples were collected from intracardiac space. Then, the animals were euthanised. Flap viability was then evaluated measuring the surviving area, using a transparent graph paper. Finally, excised tissue was examined histopathologically. The percentages of viable areas in groups 1, 2 and 3 were 64·68 ± 3·37%, 67·35 ± 5·82% and 75·15 ± 3·56%, respectively. The mean value of fibronectin levels in groups 1, 2 and 3 were 22·3 ± 3·5, 23·1 ± 3·5 and 31 ± 6·8 mg/dl, respectively. The results of this study demonstrated that 100 mg/kg carnitine administration led to an increase in flap viability, and increased serum fibronectin levels might have a role in this process.

Encapsulation of Liposomes within pH Responsive Microspheres for Oral Colonic Drug Delivery

A novel liposome-in-microsphere (LIM) formulation has been created comprising drug-loaded liposomes within pH responsive Eudragit S100 microspheres. The liposomes contained the model drug 5-ASA and were coated with chitosan in order to protect them during encapsulation within the microspheres and to improve site-specific release characteristics. In vitro drug release studies showed that LIMs prevented drug release within simulated stomach and small intestine conditions with subsequent drug release occurring in large intestine conditions. The formulation therefore has potential for oral colonic drug delivery.

Expression and functional analysis of intestinal organic cation/L-carnitine transporter (OCTN) in Crohn's disease

BACKGROUND

The IBD5 locus is a genetic risk factor for IBD, particularly Crohn's Disease, coding for the organic cation/carnitine transporters (OCTN1 and 2). Two variants of OCTN are associated with susceptibility to Crohn's Disease. Modified transport of carnitine in vitro has been reported for a polymorphism of OCTN1. The aim was to investigate the function of intestinal OCTNs in IBD in relation to genetic polymorphisms.

METHODS

Intestinal tissue was obtained from endoscopic biopsies and surgical resections from IBD patients (n=33 and 14, resp.) and controls (n=22 and 14, resp.). OCTN protein levels were measured in intestinal biopsies and carnitine transport was quantified in intestinal resections.

RESULTS

OCTN1 protein levels were significantly higher in ileal versus colonic tissue (2.95% ± 0.4 vs 0.66% ± 0.2, resp.; p<0.0002). OCTN1 expression was higher in Crohn's disease patients with mutant homozygous or heterozygous genotypes (0.6% ± 0.1 vs 3% ± 0.8, resp., p<0.02). Carnitine transport was very rapid and Na+ dependent (10s). It was not different comparing Crohn's Disease and control groups (0.45 ± 0.12 vs 0.51 ± 0.12 nM carnitine/mg prot/min, resp.). Carnitine transport tended to be higher in subjects with mutant homozygous and heterozygous OCTN1 and OCTN2 genotypes (0.19 vs 0.59 and 0.25 vs 0.6, respectively).

CONCLUSIONS

The present data reveal that OCTN protein levels appear to be similar in intestinal tissue from Crohn's Disease patients and controls. Overall, ileal carnitine transport appears to as well equal in Crohn's Disease and control groups. However, there was a trend towards higher carnitine transport in subjects with OCTN1 and OCTN2 mutations.

Mitochondrial dysfunction in autism spectrum disorders: a systematic review and meta-analysis

A comprehensive literature search was performed to collate evidence of mitochondrial dysfunction in autism spectrum disorders (ASDs) with two primary objectives. First, features of mitochondrial dysfunction in the general population of children with ASD were identified. Second, characteristics of mitochondrial dysfunction in children with ASD and concomitant mitochondrial disease (MD) were compared with published literature of two general populations: ASD children without MD, and non-ASD children with MD. The prevalence of MD in the general population of ASD was 5.0% (95% confidence interval 3.2, 6.9%), much higher than found in the general population (≈ 0.01%). The prevalence of abnormal biomarker values of mitochondrial dysfunction was high in ASD, much higher than the prevalence of MD. Variances and mean values of many mitochondrial biomarkers (lactate, pyruvate, carnitine and ubiquinone) were significantly different between ASD and controls. Some markers correlated with ASD severity. Neuroimaging, in vitro and post-mortem brain studies were consistent with an elevated prevalence of mitochondrial dysfunction in ASD. Taken together, these findings suggest children with ASD have a spectrum of mitochondrial dysfunction of differing severity. Eighteen publications representing a total of 112 children with ASD and MD (ASD/MD) were identified. The prevalence of developmental regression (52%), seizures (41%), motor delay (51%), gastrointestinal abnormalities (74%), female gender (39%), and elevated lactate (78%) and pyruvate (45%) was significantly higher in ASD/MD compared with the general ASD population. The prevalence of many of these abnormalities was similar to the general population of children with MD, suggesting that ASD/MD represents a distinct subgroup of children with MD. Most ASD/MD cases (79%) were not associated with genetic abnormalities, raising the possibility of secondary mitochondrial dysfunction. Treatment studies for ASD/MD were limited, although improvements were noted in some studies with carnitine, co-enzyme Q10 and B-vitamins. Many studies suffered from limitations, including small sample sizes, referral or publication biases, and variability in protocols for selecting children for MD workup, collecting mitochondrial biomarkers and defining MD. Overall, this evidence supports the notion that mitochondrial dysfunction is associated with ASD. Additional studies are needed to further define the role of mitochondrial dysfunction in ASD.

Human OCTN2 (SLC22A5) is down-regulated in virus- and nonvirus-mediated cancer

The expression of carnitine plasma membrane transporter OCTN2 was evaluated in virus and nonvirus-mediated cancer. Both OCTN2 mRNA and protein levels were reduced in keratinocytes retrotransduced with HPV16 E6 and E7 compared with the control. The OCTN2 expression was reduced also in keratinocytes retrotransduced with the sole HPV16 E6. A similar down-regulation of OCTN2 mRNA level was observed in a naturally HPV16-infected cancer cell line, CaSki, harbouring several copies of HPV16 whole genome. The mechanism of down-regulation is not related to p53 transcriptional activity because in SAOS (p53-null) cell line, the restoration of p53 expression did not rescue OCTN2 expression. The treatment of keratinocytes retrotransduced with HPV16 E6 and E7 with 5-aza-cytidine rescued the OCTN2 expression, indicating that the mechanism of down-regulation is linked to DNA methylation. Low levels of mRNA expression of OCTN2 were found also in several nonvirus-related epithelial cancer cell lines. The treatment of those cell lines with 5-aza-cytidine again rescued the expression of OCTN2 as well. These data demonstrate for the first time that the OCTN2 transporter is generally down-regulated in virus and nonvirus-mediated epithelial cancers, probably via methylation of its promoter region.

Kinetics of butyrate metabolism in the normal colon and in ulcerative colitis: the effects of substrate concentration and carnitine on the β-oxidation pathway

BACKGROUND

Butyrate, a colonic metabolite of carbohydrates, is considered as the major energy source for the colonic mucosa. An impaired butyrate metabolism has been reported in ulcerative colitis (UC), however, the cause still remains unknown.

AIM

In the present study, we investigated whether higher butyrate concentrations could normalise the oxidation rate in UC. Furthermore, it was investigated whether carnitine could enhance the butyrate oxidation.

METHODS

Mucosal biopsies from a total of 26 UC patients and 25 controls were incubated with (14)C-labelled Na-butyrate and the produced (14)CO(2) was measured. First, the rate of oxidative metabolism was compared at three different concentrations of Na-butyrate (0.05 mm, 1 mm and 10 mm). Then, incubations of biopsies were performed with carnitine alone or combined with ATP.

RESULTS

Overall, butyrate oxidation in UC was significantly lower than that in controls. The maximum rate of butyrate oxidation was achieved in UC and control subjects from 1 mm onwards. Increasing the butyrate concentration to a level to be present in the colonic lumen, i.e. 10 mm, did not increase the rate of butyrate oxidation in UC to the rate observed in controls. Addition of carnitine alone or combined with ATP caused no effects.

CONCLUSIONS

Saturation of butyrate kinetics was achieved from 1 mm in UC and control subjects. The rate of butyrate metabolism was significantly impaired in active ulcerative colitis. The addition of compounds interfering with the β-oxidation pathway had no effect on the butyrate metabolism in UC.

Cytokine regulation of OCTN2 expression and activity in small and large intestine

BACKGROUND

The organic cation transporter OCTN2 is located on the IBD5 risk allele and has been implicated in the pathogenesis of inflammatory bowel diseases (IBD). OCTN2 is expressed in the apical membrane and transports many solutes including bacteria-derived mediators that may be involved in host-microbial interactions. To explore its role further, we examined potential regulatory factors in human IBD and in experimental models of OCTN2 expression.

METHODS

Human colonic epithelial cells (Caco2BBE) were used to investigate the effects of inflammatory mediators on OCTN2 activity and expression. Apical membrane expression of OCTN2 was assessed by surface biotinylation. Rag-1(-/-) -deficient mice were used to determine the potential role of adaptive immune cells in the regulation of OCTN2 expression. C57Bl/6 mice were treated with the cytokines interferon-gamma (IFN-γ) and tumor necrosis factor-alpha (TNF-α) to determine the effects on OCTN2 expression and activity. OCTN2 expression in human IBD specimens was assessed by Western blotting and immunohistochemistry.

RESULTS

OCTN2 activity and expression are regulated by the state of intestinal inflammation. OCTN2 expression in colonic tissues of Rag-1(-/-) -deficient mice was reduced. Treatment with IFN-γ and TNF-α increased intestinal OCTN2 expression, particularly in the colon. IFN-γ increased both total and apical membrane expression of Caco2BBE OCTN2, whereas TNF-α stimulated apical expression. Colonic epithelial OCTN2 expression was increased in actively inflamed areas of both Crohn's disease and ulcerative colitis.

CONCLUSIONS

Intestinal epithelial OCTN2 expression is increased by intestinal inflammation, most likely through increased levels of proinflammatory cytokines. These findings suggest that OCTN2 may participate to restoration of intestinal homeostasis under conditions of inflammation-associated stress.

L-Carnitine and intestinal inflammation

The intestinal barrier is one of the most dynamic surfaces of the body. It is here where a single layer of epithelial cells mediates the intricate encounters that occur between the host's immune system and a multitude of potential threats present in the intestinal lumen. Several key factors play an important role in the final outcome of this interaction, including the state of oxidative stress, the level of activation of the immune cells, and the integrity of the epithelial barrier. This chapter describes the main evidence demonstrating the impact that l-carnitine has on each of these factors. These findings, combined with the demonstrated safety profile of l-carnitine, underscore the potential therapeutic value of l-carnitine supplementation in humans suffering from intestinal inflammation and highlight the functional data supporting an association between Crohn's disease and mutations in the l-carnitine transporter genes.

Colon OCTN2 gene expression is up-regulated by peroxisome proliferator-activated receptor gamma in humans and mice and contributes to local and systemic carnitine homeostasis

In the large intestine organic cation transporter type-2 (OCTN2) is recognized as a transporter of compounds such as carnitine and colony sporulation factor, promoting health of the colon intestinal epithelium. Recent reports suggest that OCTN2 expression in small intestine is under control of peroxisome proliferator-activated receptor-alpha (PPARalpha). However, PPARalpha contribution to colonic OCTN2 expression remains controversial. Here we examined the transcriptional regulation of colon OCTN2 gene by PPARgamma. To exclude any additional modulation of other PPAR to OCTN2 expression, we used both in vivo and in vitro PPAR-null models and specific PPAR inhibitors. The PPARgamma agonists thiazolidinediones increased both OCTN2 mRNA and protein expression in colonic epithelial cell lines independently by PPARalpha expression. The induction was blocked only by PPARgamma antagonists or by gammaORF4, a PPARgamma isoform with dominant negative activity, suggesting a PPARgamma-dependent mechanism. A conserved noncanonical PPAR-responsive element was found by computational analysis in the first intron of human OCTN2 gene and validated by EMSA assay. Promoter-reporter assays further confirmed transcriptional functionality of the putative PPAR response element, whereas selective mutation caused complete loss of responsiveness to PPARgamma activation. Finally, adenovirus-mediated overexpression of constitutively active PPARgamma mutant increased colon OCTN2 expression in PPARalpha(-/-) mice. Interestingly, animals overexpressing colon PPARgamma showed a significant increase in plasma carnitine, thus demonstrating the functional contribution of large intestine to systemic carnitine homeostasis. This study reveals a PPARgamma-dependent absorption machinery in colon that is likely involved in the health of colon epithelium, in the microbiota-host interactions and in the absorption of nutraceuticals and drugs.

Identification by nuclear magnetic resonance spectroscopy of an active-site hydrogen-bond network in human monoacylglycerol lipase (hMGL): implications for hMGL dynamics, pharmacological inhibition, and catalytic mechanism

Intramolecular hydrogen bonding is an important determinant of enzyme structure, catalysis, and inhibitor action. Monoacylglycerol lipase (MGL) modulates cannabinergic signaling as the main enzyme responsible for deactivating 2-arachidonoylglycerol (2-AG), a primary endocannabinoid lipid messenger. By enhancing tissue-protective 2-AG tone, targeted MGL inhibitors hold therapeutic promise for managing pain and treating inflammatory and neurodegenerative diseases. We report study of purified, solubilized human MGL (hMGL) to explore the details of hMGL catalysis by using two known covalent hMGL inhibitors, the carbamoyl tetrazole AM6701 and N-arachidonoylmaleimide (NAM), that act through distinct mechanisms. Using proton nuclear magnetic resonance spectroscopy (NMR) with purified wild-type and mutant hMGLs, we have directly observed a strong hydrogen-bond network involving Asp239 and His269 of the catalytic triad and neighboring Leu241 and Cys242 residues. hMGL inhibition by AM6701 alters this hydrogen-bonding pattern through subtle active-site structural rearrangements without influencing hydrogen-bond occupancies. Rapid carbamoylation of hMGL Ser122 by AM6701 and elimination of the leaving group is followed by a slow hydrolysis of the carbamate group, ultimately regenerating catalytically competent hMGL. In contrast, hMGL titration with NAM, which leads to cysteine alkylation, stoichiometrically decreases the population of the active-site hydrogen bonds. NAM prevents reformation of this network, and in this manner inhibits hMGL irreversibly. These data provide detailed molecular insight into the distinctive mechanisms of two covalent hMGL inhibitors and implicate a hydrogen-bond network as a structural feature of hMGL catalytic function.

Plasma carnitine ester profiles in Crohn's disease and ulcerative colitis patients with different IGR2230a_1 genotypes

An association has been repeatedly demonstrated between inflammatory bowel disease (IBD) and the IBD5 locus in the 5q31 chromosomal region. The aim of the present study was to examine the prevalence of the IGR2230a_1 intronic nucleotide polymorphism of the slc22a5 gene (coding for the OCTN2 carnitine transporter protein) lying within this region, and its possible relationship with the carnitine metabolism in Hungarian IBD patients and controls. We genotyped by restriction fragment length polymorphism 200 Crohn's disease (CD) and 246 ulcerative colitis (UC) patients, as well as 187 healthy controls. From plasma samples we determined detailed carnitine ester profiles of 76 CD, 43 UC patients and 45 control persons using electrospray ionization triple quadruple tandem mass spectrometry. The distribution of the genotypes was not significantly different in the CD or the UC group compared with the controls. We found no significant alterations of the carnitine profile in the carrier/non-carrier or the homozygote/non-homozygote comparisons in both the CD and the UC groups, stratified by IGR2230a_1 genotype. Our data suggest that this polymorphism alone is not associated with CD and UC in the Hungarian population, and has no effect on the carnitine metabolism.

Cannabidiol, a safe and non-psychotropic ingredient of the marijuana plant Cannabis sativa, is protective in a murine model of colitis

Inflammatory bowel disease affects millions of individuals; nevertheless, pharmacological treatment is disappointingly unsatisfactory. Cannabidiol, a safe and non-psychotropic ingredient of marijuana, exerts pharmacological effects (e.g., antioxidant) and mechanisms (e.g., inhibition of endocannabinoids enzymatic degradation) potentially beneficial for the inflamed gut. Thus, we investigated the effect of cannabidiol in a murine model of colitis. Colitis was induced in mice by intracolonic administration of dinitrobenzene sulfonic acid. Inflammation was assessed both macroscopically and histologically. In the inflamed colon, cyclooxygenase-2 and inducible nitric oxide synthase (iNOS) were evaluated by Western blot, interleukin-1beta and interleukin-10 by ELISA, and endocannabinoids by isotope dilution liquid chromatography-mass spectrometry. Human colon adenocarcinoma (Caco-2) cells were used to evaluate the effect of cannabidiol on oxidative stress. Cannabidiol reduced colon injury, inducible iNOS (but not cyclooxygenase-2) expression, and interleukin-1beta, interleukin-10, and endocannabinoid changes associated with 2,4,6-dinitrobenzene sulfonic acid administration. In Caco-2 cells, cannabidiol reduced reactive oxygen species production and lipid peroxidation. In conclusion, cannabidiol, a likely safe compound, prevents experimental colitis in mice.

Changes in mRNA expression levels of solute carrier transporters in inflammatory bowel disease patients

Inflammatory bowel disease (IBD) is an inflammatory condition that affects the gastrointestinal tract. The solute carrier (SLC) superfamily of transporters comprise proteins involved in the uptake of drugs, hormones, and other biologically active compounds. The purpose of this study was to determine the mRNA expression levels of 15 solute carrier transporters in two regions of the intestine in IBD patients. Endoscopic biopsy specimens were taken from two locations (terminal ileum and colon) for histological examination and RNA extraction. We quantitatively measured the mRNA expression of 15 SLC transporters in 107 IBD patients (53 with Crohn's disease and 54 with ulcerative colitis) and 23 control subjects. mRNA expression was evaluated using the quantitative reverse transcription-polymerase chain reaction technique. We observed that in the ileum of IBD patients, mRNA levels for serotonin transporter, equilibrative nucleoside transporter (ENT) 1, ENT2, and organic anion-transporting polypeptide (OATP) 2B1 were significantly elevated, whereas levels for apical sodium-dependent bile acid transporter (ASBT) and organic zwitterion/cation transporter (OCTN) 2 were significantly lower. In colon, mRNA levels for ENT1, ENT2, concentrative nucleoside transporter (CNT) 2, OATP2B1, and OATP4A1 were significantly higher, whereas mRNA levels for OCTN2 were significantly decreased. In inflamed colon of IBD patients the mRNA expression levels of ENT1, ENT2, CNT2, OATP2B1, OATP4A1, and peptide transporter 1 were significantly higher. We conclude that intestinal SLC mRNA levels are dysregulated in IBD patients, which may be linked to the inflammation of the tissue and provides an indication about the role of inflammatory signaling in regulation of SLC expression.

CB1 receptors mediate the analgesic effects of cannabinoids on colorectal distension-induced visceral pain in rodents

Activation of cannabinoid receptors (CB(1), CB(2) and GPR(55)) produces analgesic effects in several experimental pain models, including visceral pain arising from the gastrointestinal tract. We assessed the role of CB(1), CB(2), and GPR(55) receptors and the endogenous cannabinoid system on basal pain responses and acute mechanical hyperalgesia during colorectal distension (CRD) in rodents. The effects of cannabinoid receptor agonists and antagonists on pain-related responses to CRD were assessed in rats and in wild-type and CB(1) receptor knock-out mice. The dual CB(1/2) agonist, WIN55,212-2, and the peripherally acting CB(1)-selective agonist, SAB-378, inhibited pain-related responses to repetitive noxious CRD (80 mmHg) in a dose-related manner in rats. The analgesic effects of WIN55,212-2 and SAB-378 were blocked by the selective CB(1) antagonist SR141716, but were not affected by the selective CB(2) antagonist SR144528. SR141716, per se, increased the responses to repetitive noxious CRD, indicative of hyperalgesia, and induced pain-related responses during non-noxious CRD (20 mmHg), indicative of allodynia. The cannabinoid receptor agonists anandamide, virodhamine and O-1602 had no effect. At analgesic doses, WIN55,212-2 did not affect colonic compliance. In accordance to the rat data, WIN55,212-2 produced analgesia, whereas SR141716 induced hyperalgesia, during noxious CRD (55 mmHg) in wild-type but not in CB(1)-knock-out mice. These data indicate that peripheral CB(1) receptors mediate the analgesic effects of cannabinoids on visceral pain from the gastrointestinal tract. The allodynic and hyperalgesic responses induced by SR141716 suggest the existence of an endogenous cannabinoid tone and the activation of CB(1) receptors during noxious CRD.

L-carnitine, a diet component and organic cation transporter OCTN ligand, displays immunosuppressive properties and abrogates intestinal inflammation

Allele variants in the L-carnitine (LCAR) transporters OCTN1 (SLC22A4, 1672 C --> T) and OCTN2 (SLC22A5, -207 G --> C) have been implicated in susceptibility to Crohn's disease (CD). LCAR is consumed in the diet and transported actively from the intestinal lumen via the organic cation transporter OCTN2. While recognized mainly for its role in fatty acid metabolism, several lines of evidence suggest that LCAR may also display immunosuppressive properties. This study sought to investigate the immunomodulatory capacity of LCAR on antigen-presenting cell (APC) and CD4+ T cell function by examining cytokine production and the expression of activation markers in LCAR-supplemented and deficient cell culture systems. The therapeutic efficacy of its systemic administration was then evaluated during the establishment of colonic inflammation in vivo. LCAR treatment significantly inhibited both APC and CD4+ T cell function, as assessed by the expression of classical activation markers, proliferation and cytokine production. Carnitine deficiency resulted in the hyperactivation of CD4+ T cells and enhanced cytokine production. In vivo, protection from trinitrobenzene sulphonic acid colitis was observed in LCAR-treated mice and was attributed to the abrogation of both innate [interleukin (IL)-1beta and IL-6 production] and adaptive (T cell proliferation in draining lymph nodes) immune responses. LCAR therapy may therefore represent a novel alternative therapeutic strategy and highlights the role of diet in CD.

Alternative drug delivery approaches for the therapy of inflammatory bowel disease

This article shall give an overview on drug delivery systems for new therapeutic strategies in the treatment of inflammatory bowel disease. The various features of the different approaches allowing locally restricted drug delivery to the inflamed colon are discussed including the main physiological and pathophysiological limitations for the different systems. Conventional drug delivery systems are tightly adapted from developments for colonic delivery by oral administration triggered by release mechanisms owing to the physiological environment that these systems encounter in the colonic region. The newer developments in this context aim for an increased selectivity of drug delivery by targeting mechanisms which have a closer relation to pathophysiological particularities of the disease. Therefore, we were focused especially on new strategies for such treatment including liposomal formulations, cyclodextrins, micro- or nanoparticles, viral gene therapy approaches, and others. Effective and selective delivery even of an otherwise nonspecifically acting drug could provide new therapeutic pathways in the treatment of inflammatory bowel disease.

PPARalpha-mediated effects of dietary lipids on intestinal barrier gene expression

Background

The selective absorption of nutrients and other food constituents in the small intestine is mediated by a group of transport proteins and metabolic enzymes, often collectively called 'intestinal barrier proteins'. An important receptor that mediates the effects of dietary lipids on gene expression is the peroxisome proliferator-activated receptor alpha (PPARα), which is abundantly expressed in enterocytes. In this study we examined the effects of acute nutritional activation of PPARα on expression of genes encoding intestinal barrier proteins. To this end we used triacylglycerols composed of identical fatty acids in combination with gene expression profiling in wild-type and PPARα-null mice. Treatment with the synthetic PPARα agonist WY14643 served as reference.

Results

We identified 74 barrier genes that were PPARα-dependently regulated 6 hours after activation with WY14643. For eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA) and oleic acid (OA) these numbers were 46, 41, and 19, respectively. The overlap between EPA-, DHA-, and WY14643-regulated genes was considerable, whereas OA treatment showed limited overlap. Functional implications inferred form our data suggested that nutrient-activated PPARα regulated transporters and phase I/II metabolic enzymes were involved in a) fatty acid oxidation, b) cholesterol, glucose, and amino acid transport and metabolism, c) intestinal motility, and d) oxidative stress defense.

Conclusion

We identified intestinal barrier genes that were PPARα-dependently regulated after acute activation by fatty acids. This knowledge provides a better understanding of the impact dietary fat has on the barrier function of the gut, identifies PPARα as an important factor controlling this key function, and underscores the importance of PPARα for nutrient-mediated gene regulation in intestine.

Transport of butyryl-L-carnitine, a potential prodrug, via the carnitine transporter OCTN2 and the amino acid transporter ATB(0,+)

L-carnitine is absorbed in the intestinal tract via the carnitine transporter OCTN2 and the amino acid transporter ATB(0,+). Loss-of-function mutations in OCTN2 may be associated with inflammatory bowel disease (IBD), suggesting a role for carnitine in intestinal/colonic health. In contrast, ATB(0,+) is upregulated in bowel inflammation. Butyrate, a bacterial fermentation product, is beneficial for prevention/treatment of ulcerative colitis. Butyryl-L-carnitine (BC), a butyrate ester of carnitine, may have potential for treatment of gut inflammation, since BC would supply both butyrate and carnitine. We examined the transport of BC via ATB(0,+) to determine if this transporter could serve as a delivery system for BC. We also examined the transport of BC via OCTN2. Studies were done with cloned ATB(0,+) and OCTN2 in heterologous expression systems. BC inhibited ATB(0,+)-mediated glycine transport in mammalian cells (IC(50), 4.6 +/- 0.7 mM). In Xenopus laevis oocytes expressing human ATB(0,+), BC induced Na(+) -dependent inward currents under voltage-clamp conditions. The currents were saturable with a K(0.5) of 1.4 +/- 0.1 mM. Na(+) activation kinetics of BC-induced currents suggested involvement of two Na(+) per transport cycle. BC also inhibited OCTN2-mediated carnitine uptake (IC(50), 1.5 +/- 0.3 microM). Transport of BC via OCTN2 is electrogenic, as evidenced from BC-induced inward currents. These currents were Na(+) dependent and saturable (K(0.5), 0.40 +/- 0.02 microM). We conclude that ATB(0,+) is a low-affinity/high-capacity transporter for BC, whereas OCTN2 is a high-affinity/low-capacity transporter. ATB(0,+) may mediate intestinal absorption of BC when OCTN2 is defective.

Therapeutic Potential of Endocannabinoid-Hydrolysing Enzyme Inhibitors

The specific protein target of delta9-tetrahydrocannabinol (delta9-THC), the main active ingredient of Cannabis sativa L., was characterized from rat brain nearly 20 years ago, and several endogenous compounds and proteins comprising the endocannabinoid (eCB) system have since been discovered. It has become evident that the eCB system consists of at least two cannabinoid receptors (i.e. the CB1 and CB2 receptors), in addition to their endogenous ligands (the eCBs) and several enzymes involved in the biosynthesis and catabolism of the eCBs. The two well-established eCBs, N-arachidonoylethanolamide (AEA) and 2-arachidonoylglycerol (2-AG), are produced by neurons on demand, act near their sites of synthesis and are effectively metabolized by fatty acid amide hydrolase (FAAH) and monoglyceride lipase (MGL), respectively. Inhibitors specifically targeting these enzymes could offer novel therapeutic approaches (e.g. for the treatment of pain and movement disorders). This MiniReview summarizes the literature concerning the potential therapeutic potential of FAAH and MGL inhibitors.

Increased endocannabinoid levels reduce the development of precancerous lesions in the mouse colon

Colorectal cancer is an increasingly important cause of death in Western countries. Endocannabinoids inhibit colorectal carcinoma cell proliferation in vitro. In this paper, we investigated the involvement of endocannabinoids on the formation of aberrant crypt foci (ACF, earliest preneoplastic lesions) in the colon mouse in vivo. ACF were induced by azoxymethane (AOM); fatty acid amide hydrolase (FAAH) and cannabinoid receptor messenger ribonucleic acid (mRNA) levels were analyzed by the quantitative reverse transcription polymerase chain reaction (RT-PCR); endocannabinoid levels were measured by liquid chromatography-mass spectrometry; caspase-3 and caspase-9 expressions were measured by Western blot analysis. Colonic ACF formation after AOM administration was associated with increased levels of 2-arachidonoylglycerol (with no changes in FAAH and cannabinoid receptor mRNA levels) and reduction in cleaved caspase-3 and caspase-9 expression. The FAAH inhibitor N-arachidonoylserotonin increased colon endocannabinoid levels, reduced ACF formation, and partially normalized cleaved caspase-3 (but not caspase-9) expression. Notably, N-arachidonoylserotonin completely prevented the formation of ACF with four or more crypts, which have been show to be best correlated with final tumor incidence. The effect of N-arachidonoylserotonin on ACF formation was mimicked by the cannabinoid receptor agonist HU-210. No differences in ACF formation were observed between CB(1) receptor-deficient and wild-type mice. It is concluded that pharmacological enhancement of endocannabinoid levels (through inhibition of endocannabinoid hydrolysis) reduces the development of precancerous lesions in the mouse colon. The protective effect appears to involve caspase-3 (but not caspase-9) activation.

Overactivity of the intestinal endocannabinoid system in celiac disease and in methotrexate-treated rats

The endocannabinoid system is upregulated in both human inflammatory bowel diseases and experimental models of colitis. In this study, we investigated whether this upregulation is a marker also of celiac disease-induced atrophy. The levels of the cannabinoid CB(1) receptor, of the endocannabinoids, anandamide, and 2-arachidonoyl-glycerol (2-AG), and of the anti-inflammatory mediator palmitoylethanolamide (PEA) were analyzed in bioptic samples from the duodenal mucosa of celiac patients at first diagnosis assessed by the determination of antiendomysial antibodies and histological examination. Samples were analyzed during the active phase of atrophy and after remission and compared to control samples from non-celiac patients. The levels of anandamide and PEA were significantly elevated (approx. 2- and 1.8-fold, respectively) in active celiac patients and so were those of CB(1) receptors. Anandamide levels returned to normal after remission with a gluten-free diet. We also analyzed endocannabinoid and PEA levels in the jejunum of rats 2, 3, and 7 days after treatment with methotrexate, which causes inflammatory features (assessed by histopathological analyses and myeloperoxidase activity) similar to those of celiac patients. In both muscle/serosa and mucosa layers, the levels of anandamide, 2-AG, and PEA peaked 3 days after treatment and returned to basal levels at remission, 7 days after treatment. Thus, intestinal endocannabinoid levels peak with atrophy and regress with remission in both celiac patients and methotrexate-treated rats. The latter might be used as a model to study the role of the endocannabinoid system in celiac disease.