Folic acid transport in organ-cultured mucosa of human intestine. Evidence for distinct carriers

Application of chimeric antigen receptor-engineered T cells in ovarian cancer therapy

Due to the critical role of T cells in the immune surveillance of ovarian cancer, adoptive T-cell therapies are receiving increased attention as an immunotherapeutic approach for ovarian cancer. Chimeric antigen receptors (CARs), constructed by incorporating the single-chain Fv fragment to a T-cell signaling domain such as CD3 ζ or Fc receptor γ chain, endow T cell with nonmajor histocompatibility complex-restricted specificity. Dual specificity, trans-signaling CARs and affinity-tuned single-chain Fv fragment have broadened the applicability of CAR-engineered T-cell therapy and may be considered preferential to T cell receptor T-cell therapy in clinical care. As new insights into the CAR-engineered T cells have emerged over the last decade, we review the development of CAR T-cell therapy and discuss the progress and safety concerns regarding its translation from basic research into clinical care of ovarian cancer.

Rigorous optimization and validation of potent RNA CAR T cell therapy for the treatment of common epithelial cancers expressing folate receptor

Using lentiviral technology, we recently demonstrated that incorporation of CD27 costimulation into CARs greatly improves antitumor activity and T cell persistence. Still, virus-mediated gene transfer is expensive, laborious and enables long-term persistence, creating therapies which cannot be easily discontinued if toxic. To address these concerns, we utilized a non-integrating RNA platform to engineer human T cells to express FRα-specific, CD27 CARs and tested their capacity to eliminate human FRα(+) cancer. Novel CARs comprised of human components were constructed, C4-27z and C4opt-27z, a codon-optimized variant created for efficient expression. Following RNA electroporation, C4-27z and C4opt-27z CAR expression is initially ubiquitous but progressively declines across T cell populations. In addition, C4-27z and C4opt-27z RNA CAR T cells secrete high levels of Th-1 cytokines and display strong cytolytic function against human FRα(+) cancers in a time- and antigen-dependent manner. Further, C4-27z and C4opt-27z CAR T cells exhibit significant proliferation in vivo, facilitate the complete regression of fully disseminated human ovarian cancer xenografts in mice and reduce the progression of solid ovarian cancer. These results advocate for rapid progression of C4opt-27z RNA CAR to the clinic and establish a new paradigm for preclinical optimization and validation of RNA CAR candidates destined for clinical translation.

Mechanism of drug-induced gingival overgrowth revisited: a unifying hypothesis

Drug-induced gingival overgrowth (DIGO) is a disfiguring side effect of anti-convulsants, calcineurin inhibitors, and calcium channel blocking agents. A unifying hypothesis has been constructed which begins with cation flux inhibition induced by all three of these drug categories. Decreased cation influx of folic acid active transport within gingival fibroblasts leads to decreased cellular folate uptake, which in turn leads to changes in matrix metalloproteinases metabolism and the failure to activate collagenase. Decreased availability of activated collagenase results in decreased degradation of accumulated connective tissue which presents as DIGO. Studies supporting this hypothesis are discussed.

Folate production by probiotic bacteria

Probiotic bacteria, mostly belonging to the genera Lactobacillus and Bifidobacterium, confer a number of health benefits to the host, including vitamin production. With the aim to produce folate-enriched fermented products and/or develop probiotic supplements that accomplish folate biosynthesis in vivo within the colon, bifidobacteria and lactobacilli have been extensively studied for their capability to produce this vitamin. On the basis of physiological studies and genome analysis, wild-type lactobacilli cannot synthesize folate, generally require it for growth, and provide a negative contribution to folate levels in fermented dairy products. Lactobacillus plantarum constitutes an exception among lactobacilli, since it is capable of folate production in presence of para-aminobenzoic acid (pABA) and deserves to be used in animal trials to validate its ability to produce the vitamin in vivo. On the other hand, several folate-producing strains have been selected within the genus Bifidobacterium, with a great variability in the extent of vitamin released in the medium. Most of them belong to the species B. adolescentis and B. pseudocatenulatum, but few folate producing strains are found in the other species as well. Rats fed a probiotic formulation of folate-producing bifidobacteria exhibited increased plasma folate level, confirming that the vitamin is produced in vivo and absorbed. In a human trial, the same supplement raised folate concentration in feces. The use of folate-producing probiotic strains can be regarded as a new perspective in the specific use of probiotics. They could more efficiently confer protection against inflammation and cancer, both exerting the beneficial effects of probiotics and preventing the folate deficiency that is associated with premalignant changes in the colonic epithelia.

Optimization of cell-based assays to quantify the anti-inflammatory/allergic potential of test substances in 96-well format

OBJECTIVE

There is an insistent need for robust, reliable, and optimized assays for screening novel drugs targeting the inflammatory/allergic markers. The present study describes about the optimization of eight cell-based assays utilizing mammalian cell lines in 96-well format for quantifying anti-inflammatory/allergic drug candidates.

MATERIALS AND METHODS

We estimated the inhibitory response of reference compounds: 1400 W dihydrochloride on LPS-induced NO release, celecoxib on LPS-induced PGE(2) production and dexamethasone on LPS-induced pro-inflammatory cytokines IL-1 beta, IL-6, and TNF-alpha production by J774A.1 murine macrophages. Response of acetylsalicylic acid and celecoxib was studied on A23187-induced TXB(2) production; captopril on A23187-stimulated LTB(4) production by HL-60 cells. Effect of ketotifen fumarate was evaluated on A23187-elicited histamine release by RBL-2H3 cells. Each experiment was repeated twice to assess the reproducibility and suitability of the assays by determining appropriate statistical tools viz. %CV, S/B and Z' factor.

RESULTS

1400 W dihydrochloride was capable of inhibiting LPS-induced NO levels (IC(50) = 10.7 μM). Dexamethasone attenuated LPS-induced IL-1 beta (IC(50) = 70 nM), IL-6 (IC(50) = 58 nM) and TNF-alpha (IC(50) = 44 nM) release, whereas celecoxib, a specific COX-2 inhibitor showed marked reduction in LPS-induced PGE(2) (IC(50) = 23 nM) production. Captopril (IC(50) = 48 μM) and ketotifen fumarate (IC(50) = 36.4 μM) demonstrated potent inhibitory effect against A23187-stimulated LTB(4) and histamine levels, respectively. Both acetylsalicylic acid (IC(50) = 5.5 μM) and celecoxib (IC(50) = 7.9 nM) exhibited concentration-dependent decrease in TXB(2) production. Results for all the cell assays from two experiments showed a Z' factor varying from 0.30 to 0.99; the S/B ratio ranged from 2.39 to 24.92; %CV ranged between 1.52 and 20.14.

CONCLUSION

The results proclaim that these cell-based assays can act as ideal tools for screening new anti-inflammatory/anti-allergic compounds.

A combination of pH-sensitive caplet coatings may be an effective noninvasive strategy to deliver bioactive substances, nutrients, or their precursors to the colon

We hypothesize that bacterially synthesized nutrients in the large intestine may significantly influence the nutritional status of humans and, specifically, that of the colonocytes. In vivo research with human subjects in this area has been extremely limited because of the absence of a noninvasive means to quantitatively deliver test doses of nutrients, or their precursors, to the colon. The purpose of this study was to design and test the effectiveness of a pH-dependent coating in delivering intact placebo caplets to the large intestine. Barium sulphate caplet cores (19.1 mm x 9.7 mm) were coated with 2 different pH-dependent acrylic copolymer products, Eudragit L100 and S100, in either a 1:0 ratio (100% Eudragit L100) or 3:1 ratio (75% Eudragit L100 and 25% S100). The disintegration profile of each formulation was determined through in vitro testing, then caplets were sequentially administered to 10 healthy volunteers, and monitored in vivo via serial abdominal fluoroscopic images. Test caplets with the 3:1 coating formulation had a 40% higher colon-targeting specificity compared with the 1:0-coated caplets, and tended to begin disintegrating at a later time after administration (p = 0.09). The total time from administration to complete disintegration was also significantly longer for the 3:1-coated caplets (p = 0.003). These results suggest that barium sulphate caplets with a 3:1 acrylic copolymer coating formulation ratio (Eudragit L100 and S100) may be a suitable delivery system for quantifying the biosynthesis of nutrients in the human large intestine and measuring their absorption across the colonic epithelium.

Folate is absorbed across the colon of adults: evidence from cecal infusion of (13)C-labeled [6S]-5-formyltetrahydrofolic acid

BACKGROUND

Folate deficiency increases the risk of several human diseases. Likewise, high intakes of folate, particularly synthetic folic acid intake, may be associated with adverse health outcomes in humans. A more comprehensive understanding of the "input side" of folate nutrition may help to set dietary recommendations that strike the right balance between health benefits and risks. It is well known that the microflora in the colon produce large quantities of folate that approach or exceed recommended dietary intakes; however, there is no direct evidence of the bioavailability of this pool in humans.

OBJECTIVE

The objective was to determine whether, and to what extent, the natural folate vitamer 5-formyltetrahydrofolic acid is absorbed across the intact colon of humans.

DESIGN

During screening colonoscopy, 684 nmol (320 microg) [(13)C]glutamyl-5-formyltetrahydrofolic acid was infused directly into the cecum of 6 healthy adults. Three or more weeks later, each subject received an intravenous injection of the same compound (172 nmol). Blood samples were collected before and after each treatment. The ratio of labeled to unlabeled folates was determined in plasma by tandem mass spectrometry.

RESULTS

The apparent rate of folate absorption across the colon of a bolus dose of [(13)C]5-formyltetrahydrofolic acid infused into the cecum was 0.6 +/- 0.2 nmol/h, as determined by the appearance of [(13)C(5)]5-methyltetrahydrofolic acid in plasma. In comparison, the rate of appearance of [(13)C(5)]5-methyltetrahydrofolic acid after an intravenous injection of [(13)C(5)]5-formyltetrahydrofolate was 7 +/- 1.2 nmol/h.

CONCLUSION

Physiologic doses of natural folate are absorbed across the intact colon in humans.

Tumor detection using folate receptor-targeted imaging agents

Folate receptors are up-regulated on a variety of human cancers, including cancers of the breast, ovaries, endometrium, lungs, kidneys, colon, brain, and myeloid cells of hematopoietic origin. This over-expression of folate receptors (FR) on cancer tissues can be exploited to target folate-linked imaging and therapeutic agents specifically to FR-expressing tumors, thereby avoiding uptake by most healthy tissues that express few if any FR. Four folate-targeted therapeutic drugs are currently undergoing clinical trials, and several folate-linked chemotherapeutic agents are in late stage preclinical development. However, because not all cancers express FR, and because only FR-expressing cancers respond to FR-targeted therapies, FR-targeted imaging agents have been required to select patients with FR-expressing tumors likely to respond to folate-targeted therapies. This review focuses on recent advances in the use of the vitamin folic acid to target PET agents, gamma-emitters, MRI contrast agents and fluorescent dyes to FR(+) cancers for the purpose of diagnosing and imaging malignant masses with improved specificity and sensitivity.

Quantification of folic acid in human feces after administration of Bifidobacterium probiotic strains

BACKGROUND

Folic acid, or vitamin B9, is involved in appropriate regulation of DNA replication, synthesis of purines and deoxythymidine (dTMP), conversion of homocysteine to methionine, histidine catabolism, and correct differentiation of the neural tube during fetal organogenesis. Folic acid from food sources is almost completely absorbed in the small intestine, mostly in the jejunum, and does not reach the large intestine. The administration of probiotic strains able to synthesize folates de novo and release them in the extracellular space may provide an additional, constant endogenous source of this important vitamin in the intestinal lumen of humans.

METHODS

A pilot study involving 23 healthy volunteers was conducted to evaluate the ability of 3 probiotic strains, Bifidobacterium adolescentis DSM 18350, B. adolescentis DSM 18352, and Bifidobacterium pseudocatenulatum DSM 18353, to produce folates in the human intestine. Volunteers were randomly assigned to 1 of 3 groups for treatment with a specific probiotic strain (5 x 10(9) colony forming units/d). Strain effectiveness was evaluated by determination of the folate concentration in feces evacuated within 48 hours before and after administration of the probiotics. Quantification of microorganisms belonging to the genus Bifidobacterium was performed in parallel to folate analysis.

RESULTS

Ingestion of these probiotic strains resulted in a significant increase of folic acid concentration in human feces in all treated groups. Analysis of the fecal Bifidobacteria confirmed the potential of all strains, especially B. adolescentis DSM 18352, to colonize the intestinal environment.

CONCLUSIONS

The demonstrated ability of the probiotic microorganisms B. adolescentis DSM 18350, B. adolescentis DSM 18352, and B. pseudocatenulatum DSM 18353 to synthesize and secrete folates in the human intestinal environment may provide a complementary endogenous source of such molecules, which is especially useful for the homeostasis of mucosal enterocytes of the colon and, unlike oral administration of the vitamin, ensures its constant bioavailability.

Administration of folate-producing bifidobacteria enhances folate status in Wistar rats

To develop a probiotic that provides the host with folate, we administered folate-overproducing bifidobacteria (Bifidobacteria adolescentis MB 227, B. adolescentis MB 239, and B. pseudocatenulatum MB 116) to Wistar rats with induced folate deficiency. Four groups of rats were fed a solid, low-folate diet with no supplements, folate-producing bifidobacteria [probiotic (PRO)], oligofructose [prebiotic (PRE)], or PRO plus PRE [symbiotic (SYM)] for 14 d. The SYM group also had a significantly higher (16.4 +/- 3.7 nmol/L) than in the PRO group (9.1 +/- 0.3 nmol/L), which was greater than in the control (4.8 +/- 0.5 nmol/L) and PRE groups (5.3 +/- 1.4 nmol/L). The SYM group also had a significantly higher hepatic folate concentration than in the other groups, whereas the kidney folate concentration did not differ among the groups. In the unsupplemented group, the pH of feces did not change during the trial, whereas diets containing bifidobacteria and/or oligofructose led to significant acidification due to enhanced saccharolytic metabolism. As a consequence of feeding rats PRE, PRO, and SYM diets, lactobacilli and bifidobacteria were significantly greater than in controls, whereas coliforms and enterococci were lower. This experiment showed that B. adolescentis MB 227, B. adolescentis MB 239, and B. pseudocatenulatum MB 116 exert both the beneficial effects of probiotics and produce folate in vivo, positively affecting the folate status of rats. The simultaneous administration of oligofructose and folate-producing bifidobacteria enhance their effectiveness on folate status. This study provides new perspectives on the specific use of probiotics to deliver important vitamins such as folate.

Folate production by bifidobacteria as a potential probiotic property

The ability of 76 Bifidobacterium strains to produce folate was investigated. In order to evaluate folic acid productivity, bifidobacteria were cultivated in the folate-free semisynthetic medium SM7. Most of the tested strains needed folate for growth. The production and the extent of vitamin accumulation were not a function of species but were distinctive features of individual strains. Six strains among the 17 that grew without folate produced significantly higher concentrations of vitamin (between 41 and 82 ng ml(-1)). The effects of exogenous folate and p-aminobenzoic acid (PABA) concentrations on folate production were evaluated. In contrast to most of the other strains, the folate yield of B. adolescentis MB 239 was not negatively affected by either PABA or exogenous folic acid. Folate production by B. adolescentis MB 239 was studied in the pH range of the colonic environment, and a comparison of folate production on raffinose, lactose, and fructo-oligosaccharides, which belong to three important groups of fermentable intestinal carbon sources, was established. Differences in folate biosynthesis by B. adolescentis MB 239 were not observed as a function either of the pH or of the carbon source. Fecal culture experiments demonstrated that the addition of B. adolescentis MB 239 may increase the folate concentration in the colonic environment.

Topical Sulfamylon cream inhibits DNA and protein synthesis in the skin donor site wound

BACKGROUND

Whereas Sulfamylon is effective in treatment of burn wound infection, controversy exists regarding its effect on the healing process.

METHODS

A partial thickness skin donor site wound was created on the back and indwelling catheters were placed in the carotid artery and jugular vein in rabbits under general anesthesia. Sulfamylon cream (8.5%, BERTEK Pharmaceuticals Inc., Morgantown, W Va) was applied on the wound, with either open or occlusive dressing. The control wound was covered with dressings only. On day 7 after injury, stable isotope tracers were infused to determine the fractional synthetic rate (FSR) of DNA, and FSR and fractional breakdown rate (FBR) of protein in the wound.

RESULTS

In the Sulfamylon-open dressing group, the DNA FSR was 1.3 +/- 0.6%/day, the protein FSR was 8.0 +/- 3.5%/day, and the net protein deposition (FSR - FBR) was -0.3 +/- 3.7%/day. These values were lower (P < .01 to .05) than the corresponding values in the control group (DNA FSR: 2.9 +/- 0.9%/day; protein FSR: 20.5 +/- 8.4%/day; net protein deposition: 7.9 +/- 6.0%/day). Sulfamylon cream selectively inhibited DNA FSR from the de novo base synthesis pathway (2.3 +/- 1.2 vs 0.8 +/- 0.5%/day, P < .05 vs control). With the occlusive dressing Sulfamylon cream did not decrease wound DNA FSR due to a stimulation of the base salvage pathway, but still decreased protein FSR (11.5 +/- 5.1%/day, P < .05 vs control). Histologic slides indicated that Sulfamylon cream inhibited re-epithelialization, collagen formation, and angiogenesis in the wound.

CONCLUSIONS

Topical Sulfamylon cream application inhibited DNA and protein synthesis in the wound, which would be expected to retard the healing process.

Folate Receptor-Mediated Drug Targeting: From Therapeutics to Diagnostics

Folate targeted drug delivery has emerged as an alternative therapy for the treatment and imaging of many cancers and inflammatory diseases. Due to its small molecular size and high binding affinity for cell surface folate receptors (FR), folate conjugates have the ability to deliver a variety of molecular complexes to pathologic cells without causing harm to normal tissues. Complexes that have been successfully delivered to FR expressing cells, to date, include protein toxins, immune stimulants, chemotherapeutic agents, liposomes, nanoparticles, and imaging agents. This review will summarize the applications of folic acid as a targeting ligand and highlight the various methods being developed for delivery of therapeutic and imaging agents to FR-expressing cells.

Folate receptor expression in carcinomas and normal tissues determined by a quantitative radioligand binding assay

The folate receptor (FR) is a valuable therapeutic target that is highly expressed on a variety of cancers. The current development of folate-targeted cancer therapies has created the need for quantitating functional FRs in clinical specimens. In this article, we report on the creation of a highly sensitive radioactive binding method for quantitatively measuring FR expression in frozen tissue homogenates. Expression was positive in approximately 89% of human ovarian carcinomas but was negligible in both mucinous ovarian carcinomas and normal ovary. Expression was also significant in carcinomas of the kidney, endometrium, lung, breast, bladder, and pancreas. Normal tissues from humans and six different laboratory species were also analyzed; surprisingly, some interspecies variability in FR expression (especially in kidney, spleen, and lung tissue) was found. Interestingly, normal human lung tissue displayed high expression levels, whereas expression in normal lung of the other species was negligible. However, considering that folate-drug conjugates fail to accumulate in the lungs of patients, the consequence of this finding was not considered to be of clinical concern. Overall, this new methodology is reliable for determining functional FR expression levels in tissues, and it could possibly be a useful clinical test to determine patient candidacy for FR-targeted therapeutics.

A large pool of available folate exists in the large intestine of human infants and piglets

Many microorganisms in the large intestine are capable of synthesizing folate. Preliminary evidence suggests that this folate may be absorbed. The purpose of the 2 experiments reported herein was to estimate the pool of folate in the feces of human infants and piglets and to ascertain, if absorbed, whether the quantity and form of folate are sufficient to potentially affect the folate status of the host organism. The folate content of milk fed to and of fecal solids collected from exclusively human milk-fed (n = 12) and formula-fed (n = 10) term infants (1-6 mo old) was determined microbiologically before (short-chain folates) and after folate conjugase (total folate) treatment. The folate content of formula fed and of feces collected from 10-d-old piglets (n = 10) was also determined microbiologically. The proportion of 5-methyltetrahydrofolate (5-methylTHF) in feces of human infants and piglets that was monoglutamylated was determined by HPLC analysis. The folate content of fecal solids collected from infants was 93.2 +/- 92.8 nmol/d (mean +/- SD), representing on average 50% (8.0-170.1%) of their mean estimated dietary folate intake. Fecal folate was largely present as short-chain folate (66 +/- 21.3%) with the predominant form being 5-methylTHF, 52.5 +/- 30.1% of which was monoglutamylated. In piglets, the folate content of feces was 301.3 +/- 145.7 nmol/d, representing 36% of their dietary folate intake. Piglet fecal folate was largely present as short-chain folate (68.1 +/- 12.6%) with the predominant species being 5-methylTHF, 29.3 +/- 33.2% of which was monoglutamylated. Collectively, these data suggest that the quantity and form of folate (monoglutamylated) in the large intestine of human infants and piglets are sufficiently large to potentially affect folate status.

Folate uptake in the human intestine: promoter activity and effect of folate deficiency

The intestinal folate absorption process occurs via a specialized mechanism that involves the reduced folate carrier (RFC). In humans, multiple variants of the hRFC (driven by multiple promoters) have been identified with variant I being the prominent form expressed in the intestine. While it is known that promoter B (pB) of hRFC drives the expression of this variant, little is known about the minimal region required for basal activity of this promoter in human intestinal epithelial cells. Also not known is whether folate absorption in the human intestine is up-regulated during folate deficiency (as occur in animal studies), and if so, whether transcriptional mechanisms via activation of hRFC pB are involved in such regulation. To address these issues, we have used deletion constructs of the hRFC pB and determined their activity in two human intestinal epithelial cell lines: the colon-derived Caco-2 cells, and the duodenum-derived HuTu-80 cells. Our results showed that activity of hRFC pB to be significantly higher in Caco-2 cells compared to HuTu-80 cells, a finding that corresponds with a higher level of folate uptake and endogenous hRFC mRNA levels in the former compared to the latter cell type. The minimal region required for basal activity of hRFC pB in Caco-2 cells was found to be encoded in a sequence between -1088 and -1043, while in HuTu-80 cells it was encoded in a sequence between -1431 and -1088. Growing Caco-2 cells in a folate deficient medium led to a significant and specific up-regulation in folate uptake. This up-regulation was associated with a parallel increase in hRFC protein and mRNA levels, and in the activity of hRFC pB. The most responsive sequence of pB to the effect of folate deficiency was found to be encoded in a sequence between -2016 and -1431, i.e., outside the minimal region of the pB. These results show that different minimal regions for hRFC pB are utilized by different intestinal epithelial cells. In addition, folate-deficiency was found to up-regulate folate uptake by human intestinal epithelial cells and that this regulation involves activation of hRFC pB.

Mechanism of folate transport across the human colonic basolateral membrane

Previous studies from our laboratory have demonstrated the existence of a folate transporter in the human colonic apical membranes. The current studies were undertaken to examine the possible presence and function of a folate carrier in the human colonic basolateral membrane vesicles (BLMV). BLMV were purified from mucosal scrapings of colons of organ donors by a Percoll-density gradient centrifugation technique, and uptake studies were performed using a rapid filtration technique. Our results on [(3)H]Pte-Glu uptake are summarized as follows: 1) uptake was sensitive to osmolarity of the incubation medium; 2) Na(+) removal from the incubation medium did not affect folate uptake into BLMV; 3) uptake was significantly increased with decreasing incubation buffer pH from 8 to 4; 4) uptake demonstrated saturation kinetics with an apparent Michaelis constant of 9.6 +/- 0.48 microM and a maximal velocity of 8.10 +/- 0.36 pmol x mg protein(-1) x 10 s(-1); 5) uptake was markedly inhibited by the structural analog methotrexate (inhibitory constant = 8.28 +/- 1.0 microM); 6) uptake into BLMV demonstrated a trans-stimulation phenomenon; 7) anion exchange inhibitors DIDS and SITS significantly inhibited folate uptake; and 8) uptake was potential-insensitive, as voltage clamping of vesicles or making them inside positive with K(+)/valinomycin failed to influence folate uptake. Western blot analysis using purified human colonic basolateral membrane preparations and specific polyclonal antibodies against the human reduced folate carrier (hRFC) has shown expression of the hRFC protein at this membrane domain. These data demonstrate the existence of a pH-dependent, DIDS-sensitive, electroneutral, carrier-mediated mechanism for folate transport across the human colonic basolateral membranes.

Folic acid

Folic acid is an essential nutrient from the B complex group of vitamins. Folate, as a cofactor, is involved in numerous intracellular reactions, and this is reflected in the various derivatives that have been isolated from biological sources. Folic acid is involved in single carbon transfer reactions and serves as a source of single carbon units in different oxidative states. The processes involved in the absorption, transport, and intracellular metabolism of this cofactor are complex. Much of folate is bound tightly to enzymes, indicating that there is not excess of this cofactor and that its cellular availability is protected as well as being strictly regulated. In animals, the liver controls the supply of folate through first pass metabolism, biliary secretion, enterohepatic recirculation, as well as through senescent erythrocyte recycling. Deficiencies of folate can occur for many reasons, including reduced intake, increased metabolism, and/or increased requirements as well as through genetic defects. The effects of folate deficiency include hyperhomocysteinemia, megaloblastic anemia, and mood disorders. Folate deficiency has also been implicated in disorders associated with neural tube defects. Supplementation of grain products such as cereals has been undertaken in several countries as a cost-effective means of reducing the prevelance of neural tube defects. Recently, common polymorphisms have been discovered in several genes associated with folate pathways that may play a role in diseases associated with folate deficiency, particularly mild folate deficiency.

Liposome targeting to tumors using vitamin and growth factor receptors

Liposome-encapsulated anticancer drugs reveal their potential for increased therapeutic efficacy and decreased nonspecific toxicities due to their ability to enhance the delivery of chemotherapeutic agents to solid tumors. Advances in liposome technology have resulted in the development of ligand-targeted liposomes capable of selectively increasing the efficacy of carried agents against receptor-bearing tumor cells. Receptors for vitamins and growth factors have become attractive targets for ligand-directed liposomal therapies due to their high expression levels on various forms of cancer and their ability to internalize after binding to the liposomes conjugated to receptors' natural ligands (vitamins) or synthetic agonists (receptor-specific antibodies and synthetic peptides). This chapter summarizes various strategies and advances in targeting liposomes to vitamin and growth factor receptors in vitro and in vivo with special emphasis on two extensively studied liposome-targeting systems utilizing folate receptor and HER2/neu growth factor receptor.

Adaptive regulation of intestinal folate uptake: effect of dietary folate deficiency

Folate is an essential micronutrient that, in mammals, must be obtained from exogenous sources via intestinal absorption. Previous studies have characterized different aspects of the mechanism of the intestinal folate uptake process. Much less, however, is known about regulation of this process. In this study, we examined the effect of dietary folate deficiency on intestinal folate uptake using the rat as an animal model. The results showed that dietary folate deficiency leads to a significant (P < 0.01) and specific upregulation in the transepithelial transport of folic acid. The upregulation in transepithelial folate transport 1) was found to be due to an induction in carrier-mediated folate uptake across the brush-border membrane (BBM) and was mediated via a significant (P < 0.01) increase in the maximal velocity but not the apparent Michaelis constant of the uptake process, 2) was associated with a marked increase in the steady-state mRNA level of reduced folate carrier-1 and in the level of the expressed protein at the intestinal BBM, and 3) was associated with a marked (>10-fold) increase in the activity of the intestinal BBM form of folate hydrolase. Results of this study demonstrate, for the first time, that dietary folate deficiency leads to a marked upregulation in intestinal folate uptake and in the activity of folate hydrolase. Furthermore, the upregulation in folate uptake is associated with an increase in mRNA and protein levels of folate carrier, suggesting possible involvement of a transcriptional regulatory mechanism(s) in the upregulation.

Isolated congenital malabsorption of folic acid in a male infant: insights into treatment and mechanism of defect

An instructive case of isolated congenital folate malabsorption provides insight into the understanding of this rare disease. Folate loading tests with both timed serum and cerebrospinal fluid folate determinations suggest that both of the two mechanisms involved in gastrointestinal folate absorption are defective in this condition.

Aleurone flour is a rich source of bioavailable folate in humans

With the use of novel milling technology, it has become commercially viable to isolate the aleurone layer of cells from wheat grain and to prepare a novel flour from this fraction that has a natural folate concentration of approximately 500 microgram/100 g. The aim of this study was to determine the relative bioavailability of natural folate from aleurone flour when ingested as a cereal. Using a series of randomized, short-term intervention trials with a cross-over involving eight men and eight women aged between 29 and 50 y, we compared the increment of plasma folate following ingestion of 1) 100 g wheat bran cereal (low folate control), 2) 100 g aleurone cereal, and 3) a tablet containing 500 microgram folic acid taken together with 100 g wheat bran cereal (high folate control). Folate absorption was measured by estimating the area under the plasma folate concentration versus time curve. The extent of increase in plasma folate over the 7-hour period following ingestion of aleurone cereal was more than fourfold greater than that observed following the wheat bran cereal (P < 0.0001) and not different from that observed following the 500 microgram folic acid tablet taken with wheat bran cereal. Differences were significant when data for males and females were analyzed separately (P < 0.001). This study has shown that cereal made from wheat aleurone flour is a good source of bioavailable, natural folate.

Passive deformability of mature, immature, and active neutrophils in healthy and septicemic neonates

Obstruction of narrow vessels by rigid neutrophils may contribute to ischemic organ injury. In septicemia, a substantial portion of the neutrophils may become activated and the number of circulating immature neutrophils may rise sharply. Volume and deformability of mature (PMN) and immature neutrophils in healthy preterm and full-term infants and in septicemic neonates were studied by means of a micropipette system. Membrane cytoplasm tongues were aspirated into 2.5-microm (diameter) pipettes over a period of 60 s. Volume and tongue growth of mature resting PMN were similar in healthy preterm and full-term neonates and adults. Compared with mature PMN (about 360 fl), the volumes of band cells (415 fl), metamyelocytes (470 fl), and less mature cells (myeloblasts, promyelocytes, and myelocytes; 490 fl) were significantly increased (p < 0.005). Final tongue lengths of band cells, metamyelocytes, and less mature cells were decreased by about 50, 60, and 70%, respectively, when compared with passive mature cells. In septic neonates, the percentage of immature neutrophils was increased, but the deformability and volume of the cell subpopulations were not affected by septicemia. Active PMN were characterized by pseudopod formation. More active PMN were found in group B streptococcal (14% of total PMN), gram-negative (12%), and Staphylococcus epidermidis septicemia (8%) than in healthy neonates and adults (4%). The main bodies of active PMN were less deformable than passive PMN, and the pseudopods showed very little membrane deformation. The increased number of rigid active and immature neutrophils may contribute to impaired microcirculation and the high risk for organ injury in septic patients.

Ischaemia-reperfusion injury to the intestine

Ischaemia-reperfusion injury (IRI) is of obvious relevance in situations where there is an interruption of blood supply to the gut, as in vascular surgery, or in the construction of free intestinal grafts. It is now appreciated that IRI also underlies the guy dysfunction that occurs in early shock, sepsis, and trauma. The events that occur during IRI are complex. However, recent advances in cellular biology have started to unravel these underlying processes. The aim of this review is to provide an outline of current knowledge on the mechanisms and consequences of IRI. Initially, IRI appears to be mediated by reactive oxygen metabolites and, at a later stage, by the priming and activation of polymorphonuclear neutrophils (PMN). Ischaemia-reperfusion injury can diminish the barrier function of the gut, and can promote an increase in the leakage of molecules (intestinal permeability) or the passage of microbes across the wall of the bowel (bacterial translocation). Ischaemia-reperfusion injury to the gut can result in the generation of molecules that may also harm distant tissues.

Characterization of folate transport mediated by a low pH route in mouse L1210 leukemia cells with defective reduced folate carrier function

Folate influx at low pH was characterized in MTXrA cells, an L1210 mouse leukemia cell line with a functional defect in the reduced folate carrier. Folic acid influx in MTXrA cells was negligible at pH 7.5, increased 13-fold as the pH was decreased to 6.0, and was indistinguishable from that in L1210 cells. In contrast, while methotrexate (MTX) influx in MTXrA cells at pH 6.0 was 15-fold higher than at pH 7.5, in L1210 cells it was decreased by half. Influx of MTX, folic acid, 5-methyltetrahydrofolate and 5-formyltetrahydrofolate in MTXrA cells was increased at pH < 7.0, but their pH optima and profile differed substantially. Influx of MTX and 5-methyltetrahydrofolate at pH 6.0 showed saturability, with a Kt of 2.65 and 0.56 microM, and a Vmax of 0.45 and 0.083 nmol/g dry wt/min, respectively. MTX influx mediated by the low pH transporter was insensitive to the anionic composition of the transport buffer and affected minimally (approximately 20%) by Na+ substitution. The anion transport inhibitors sulfobromophthalein, diisothiocyanatostilbene disulfonic acid, and acetamidoisothiocyanatostilbene disulfonic acid were not effective inhibitors of the low pH route. MTX transport at low pH did not increase in MTXrA-R16 cells, an MTXrA derivative with 10-fold overexpression of the reduced folate carrier (RFC) due to transfection with RFC1 cDNA. Inhibition of reduced folate carrier activity with acetamidoisothiocyanatostilbene disulfonic acid resulted in identical MTX influx in L1210, MTXrA, and MTXrA-R16 cells at pH 5.5. Finally, low pH-mediated MTX influx was reduced by energy inhibitors and partially inhibited by ionophores (nigericin > monensin >> valinomycin). The data indicate that L1210 and MTXrA cells express similar activities of a low pH folate transporter that has properties distinct from, and independent of, the reduced folate carrier.

Increased activity of a novel low pH folate transporter associated with lipophilic antifolate resistance in chinese hamster ovary cells

Previous studies described a Chinese hamster ovary cell line, PyrR100, resistant to lipid-soluble antifolates due to the loss of an energy-coupled folate exporter resulting in a marked increase in intracellular folate cofactor accumulation. There was, in addition, an unexplained increase in folic acid influx in PyrR100 cells which is shown in this paper to be mediated by a transporter with a low pH optimum. The pH profile for folic acid influx in parental Chinese hamster ovary AA8 cells indicated peak activity at pH 6; this was increased >3-fold in PyrR100 cells. In contrast, methotrexate (MTX) influx in AA8 cells showed two peaks of comparable activities at pH 6 and 7.5; in PyrR100 cells, the component at pH 6 was increased 2-fold. Folic acid was a potent inhibitor of [3H]MTX or [3H]folic acid influx (1 microM) via the low pH route with IC50 values of approximately 1 microM. Prostaglandin A1 was a potent inhibitor of [3H]MTX influx via the reduced folate carrier 1 at pH 7.5 with only a small inhibitory effect on the low pH route. The addition of 10 microM folic acid to PyrR100 cells resulted in a MTX influx pH profile identical to that of AA8 cells, consistent with suppression of the low pH route. In contrast, addition of 25 microM prostaglandin A1 to PyrR100 cells resulted in a MTX influx pH profile comparable to that of folic acid, consistent with the loss of the reduced folate carrier-mediated component. Inhibition ( approximately 70%) of [3H]folic acid influx by approximately 10 microM unlabeled folic acid at pH 7.5 indicated that the low pH transporter accounts for the majority of folic acid transport at physiological pH. This study demonstrates the functional importance of a low pH folate transporter that is increased when enhanced folic acid entry into cells is required as an adaptive response to antifolate selective pressure. This may represent a mechanism of resistance to new antifolate inhibitors of folate cofactor-dependent enzymes in which cytotoxic activity is limited by expanded cellular folate pools.

Comparison of intestinal folate carrier clone expressed in IEC-6 cells and in Xenopus oocytes

We recently identified a cDNA clone from mouse small intestine, which appears to be involved in folate transport when expressed in Xenopus oocytes. The open reading frame of this clone is identical to that of the reduced folate carrier (RFC) (K. H. Dixon, B. C. Lanpher, J. Chiu, K. Kelley, and K. H. Cowan. J. Biol. Chem. 269: 17-20, 1994). The characteristics of this cDNA clone [previously referred to as intestinal folate carrier 1 (IFC-1)] expressed in Xenopus oocytes, however, were found to be different from the characteristics of folate transport in native small intestinal epithelial cells. To further study these differences, we determined the characteristics of RFC when expressed in an intestinal epithelial cell line, IEC-6, and compared the findings to its characteristics when expressed in Xenopus oocytes. RFC was stably transfected into IEC-6 cells by electroporation; its cRNA was microinjected into Xenopus oocytes. Northern blot analysis of poly(A)+ RNA from IEC-6 cells stably transfected with RFC cDNA (IEC-6/RFC) showed a twofold increase in RFC mRNA levels over controls. Similarly, uptake of folic acid and 5-methyltetrahydrofolate (5-MTHF) by IEC-6/RFC was found to be fourfold higher than uptake in control sublines. This increase in folic acid and 5-MTHF uptake was inhibited by treating IEC-6/RFC cells with cholesterol-modified antisense DNA oligonucleotides. The increase in uptake was found to be mainly mediated through an increase in the maximal velocity (Vmax) of the uptake process [the apparent Michaelis-Menten constant (K(m)) also changed (range was 0.31 to 1.56 microM), but no specific trend was seen]. In both IEC-6/RFC and control sublines, the uptake of both folic acid and 5-MTHF displayed 1) pH dependency, with a higher uptake at acidic pH 5.5 compared with pH 7.5, and 2) inhibition to the same extent by both reduced and oxidized folate derivatives. These characteristics are very similar to those seen in native intestinal epithelial cells. In contrast, RFC expressed in Xenopus oocytes showed 1) higher uptake at neutral and alkaline pH 7.5 compared with acidic pH 5.5 and 2) higher sensitivity to reduced compared with oxidized folate derivatives. Results of these studies demonstrate that the characteristics of RFC vary depending on the cell system in which it is expressed. Furthermore, the results may suggest the involvement of cell-or tissue-specific posttranslational modification(s) and/or the existence of an auxiliary protein that may account for the differences in the characteristics of the intestinal RFC when expressed in Xenopus oocytes compared with when expressed in intestinal epithelial cells.

A protein-tyrosine kinase-regulated, pH-dependent, carrier-mediated uptake system for folate in human normal colonic epithelial cell line NCM460

A significant proportion of the bacterially synthesized folate in the large intestine exists in the form of folate monoglutamate. Recent studies in our laboratory using human colonic apical membrane vesicles have shown the existence of an efficient carrier-mediated system for folate uptake. Nothing, however, is known about the cellular regulation of the colonic uptake process. In this study, we used a recently established human normal colonic epithelial cell line NCM460 to address this issue. Uptake of folic acid by NCM460 cells was: 1) linear with time for 4 min of incubation and occurred with minimal metabolic alterations, 2) temperature- and pH- (but not Na+) dependent, 3) saturable as a function of concentration (apparent Km of 1.4 microM), 4) inhibited by structural analogs and anion transport inhibitors, and 5) energy-dependent. These characteristics of folic acid uptake by NCM460 cells are similar to those seen with apical membrane vesicles derived from human native colonic tissue. Using these cells, we found that protein kinase C- and Ca2+/calmodulin-mediated pathways have no role in regulating folic acid uptake. On the other hand, cAMP (through a mechanism independent of protein kinase A) and protein-tyrosine kinase-mediated pathways were found to play a role in the regulation of folic acid uptake by these cells. These results establish the suitability of NCM460 cells as an in vitro model system for investigating the details of the mechanism of colonic folate uptake and its regulation. Folic acid uptake by these cells appears to involve a carrier-mediated system, which is temperature-, pH-, and energy-dependent and appears to be under the regulation of cAMP and protein tyrosine kinase.

Intestinal absorption of water-soluble vitamins in rainbow trout (Onchorhynchus mykiss)

The intestinal uptake of water-soluble vitamins, nicotinamide, riboflavin, biotin and folic acid, was studied in isolated everted intestinal sleeves of the cold-water teleost rainbow trout (Onchorhynchus mykiss). The presence of a carrier-mediated transport mechanism was determined by competitive inhibition and by Michaelis-Menten kinetics. The uptake of riboflavin, biotin or folic acid was not only subject to competitive inhibition but also a saturable function of increasing vitamin concentration in the incubation medium. The kinetic constants of the saturable mechanism were for riboflavin: K(m), 2.32 +/- 0.76 microM; Vmax, 0.26 +/- 0.04 pmol/mg min; for biotin: K(m), 9.70 +/- 3.76 microM; Vmax, 0.31 +/- 0.07 pmol/mg min; and for folic acid: K(m), 32.9 +/- 21.2 microM; Vmax, 3.63 +/- 0.99 pmol/mg min. In contrast, the uptake of nicotinamide was not subject to competitive inhibition and was a linear function of concentration (Kd, 0.140 +/- 0.012 pmol/mg min microM). Folic acid was absorbed more rapidly than and was not inhibited by its derivative, 5-methyl-tetrahydrofolate. Thus, the intestinal uptake of riboflavin, biotin and folic acid is carrier-mediated while that of nicotinamide occurs by simple diffusion. These mechanisms are similar to those found in the channel catfish for the same vitamins, except for folic acid, which is absorbed by diffusion in this warm-water omnivorous species.

Intestinal folate transport: identification of a cDNA involved in folate transport and the functional expression and distribution of its mRNA

Although the mechanism of folate intestinal transport has been the subject of intensive studies, very little is known about the molecular identity of the transport system(s) involved. In this investigation, we screened a mouse intestinal cDNA library using as probe the cDNA clone of a reduced folate carrier (RFC1) of mouse leukemia L1210 cells, and identified a positive clone, IFC1(RFC1). The cloned cDNA consisted of 2274 base pairs with an open reading frame that encodes a putative polypeptide of 512 amino acids with a predicted molecular mass of 58,112 daltons and 12 putative transmembrane domains. The polypeptide appears to carry a net positive charge (pI = 8.6) which may be important for its interaction with the negatively charged substrate. Functional identity of the IFC1(RFC1) clone was established by expression in Xenopus oocytes. An 11-fold increase in 5-methyltetrahydrofolate (5-MTHF) uptake was observed in oocytes injected with 10 ng IFC1(RFC1) cRNA compared to water-injected controls. The expressed folate uptake in the cRNA injected oocyte was (1) 4,4'-diisothiocyanatosilbene-2,2'-disulfonic acid (DIDS)-sensitive; and (2) saturable with an apparent Km of 1.99 +/- 0.32 micrometers and a V(max) of 3782 +/- 188 fmol/oocyte per h. The distribution of mRNA species complementary to IFC1(RFC1) in different mouse tissues was examined by Northern blot analysis. In addition to the small intestine, expression of such mRNA species were also found in the kidney, large intestine, brain, heart and liver. Furthermore, mRNA species complementary to IFC1(RFC1) were also detected by Northern blot analysis in the small intestine of human and other animal species (rat and rabbit). Expression of mRNA complementary to IFC1(RFC1) was markedly higher in rat intestinal villus cells than in crypt cells. These results represent the first identification of a folate transporter in mammalian intestine.

Folate status of gastrointestinal epithelial cells is not predicted by serum and red cell folate values in replete subjects

Localised folate deficiency has been implicated in colonic carcinogenesis and supplementation has been proposed for certain populations at risk. However, identifying those groups that may benefit is difficult as the relation between blood folate and gut epithelial cell values is unknown. The aim of this study was to define this relation. Epithelial cells mean (SEM) (sigmoid: 5.35 (0.56) x 10(6) cells, caecum: 6.6 (0.71) x 10(6) cells, duodenum: 4.0 (0.62) x 10(6) cells) were isolated from four endoscopic mucosal biopsy specimens (n = 25) by incubation with dithiothreitol (three hours) and EDTA (one hour). Lamina propria contamination was < 1%, with < 6% intraepithelial lymphocytes. Folate assay of isolates showed sigmoid colon folate content to be 20.1 (1.8) pg/micrograms DNA (10.2-46.6). In the same subject, caecal folate concentrations were lower (p < 0.01, n = 11) than sigmoid values, whereas duodenal isolates mirrored those of the sigmoid (19.4 (2.9) v 20.5 (3.2), n = 5). Sigmoid folate values were consistent over one to three weeks (n = 3). In a single case with blood folate deficiency, colonic values were normal. Serum folate and red cell folate correlated poorly with sigmoid epithelial cell folate content (r = 0.41, p = 0.063 and r = 0.17, p > 0.05 respectively). This study reports a modified ion-chelation isolation method for colonic biopsy specimens that yields large numbers of viable epithelial cells. Cell folate values remain constant with time though vary with intestinal region. The inability of serum or red cell folate values to predict those of the sigmoid epithelium suggests that they cannot identify those patients that might benefit from folate supplements.

Methotrexate for inflammatory bowel disease: pharmacology and preliminary results

OBJECTIVE

To review the limited published experience with methotrexate treatment for inflammatory bowel disease, to examine the proposed anti-inflammatory and immune-modifying mechanism of action and pharmacologic properties of methotrexate, and to detail its limiting toxicities.

DESIGN

A comprehensive synopsis of methotrexate is presented to aid physicians who treat patients with inflammatory bowel disease.

RESULTS

Methotrexate and its polyglutamate metabolites are folic acid analogues with inhibitory activity against many enzymes in the metabolic pathway of folic acid. Long-term low-dose methotrexate therapy (25 mg or less once a week) inhibits production of thymidylate, purines, and methionine and leads to accumulation of adenosine, a potent anti-inflammatory substance. These actions inhibit cellular proliferation, decrease formation of antibodies, and decrease production of mediators of inflammation such as interleukins and eicosanoids. Three uncontrolled trials and two controlled trials have demonstrated efficacy of low-dose methotrexate therapy for induction of remission in Crohn's disease and have also suggested possible benefit for ulcerative colitis and for remission maintenance indications in both diseases. Although methotrexate is generally well tolerated for long-term use at a low dose, several serious toxicities potentially limit its use.

CONCLUSION

Methotrexate is a promising new agent for the treatment of inflammatory bowel disease.

Spatial heterogeneity of mucosal blood flow during ischemia-reperfusion injury of rat stomach investigated by laser Doppler perfusion imaging

Spatial alterations in blood flow during the development of mucosal injury induced by ischemia-reperfusion in rats were determined with a two-dimensional laser Doppler tissue perfusion imager. The rats were anesthetized with pentobarbital, and the stomach was exteriorized on a stage; the mucosa was then sequentially scanned. The mucosa was constantly superfused with 0.1 N HCl in physiological saline. Systemic arterial pressure was continuously monitored and blood was stepwisely withdrawn from the femoral artery by 20-mmHg stage and then maintained at 20 mmHg for 20 min. The shed blood was reinfused and the stomach was removed 30 min later. Under control conditions, the average perfusion of the forestomach was usually greater than that in the glandular stomach. When systemic blood pressure was stepwisely decreased, the extent of decrease in the mucosal blood perfusion unit was always greater than that in systemic blood pressure, but mucosal perfusion appeared to be uniformly decreased throughout the stomach. Ten min after reperfusion, a hypoperfused area began to appear in the corpus near the greater curvature, and this area subsequently increased. The area of ulcer formation corresponded with the hypoperfused area in the gastric mucosa 30 min after reperfusion. Pretreatment with CV-6209, a platelet-activating factor antagonist, significantly attenuated the hypoperfusion induced by reperfusion and also prevented gastric mucosal damage. Our results suggest that hypoperfusion in the mucosal microcirculation is indeed an important factor contributing to the localized occurrence of gastric mucosal lesions and that the laser Doppler perfusion imager is useful for the detection of local hypoperfused areas in the gastric mucosa.

Antiinflammatory effects of second-generation leukotriene B4 receptor antagonist, SC-53228: impact upon leukotriene B4- and 12(R)-HETE-mediated events

Leukotriene B4 (LTB4) and 12(R)-hydroxyeicosatetraenoic acid [12(R)-HETE] are proinflammatory products of arachidonic acid metabolism that have been implicated as mediators in a number of inflammatory diseases. When injected intradermally into the guinea pig. LTB4 and 12(R)-HETE elicit a dose-dependent migration (chemotaxis) of neutrophils (PMNs) into the injection sites as assessed by the presence of a neutrophil marker enzyme myeloperoxidase. SC-41930 (7-[3-(4-acetyl-3-methoxy-2-propylphenoxy)propoxyl]-3,4-dihy dro-8-propyl-2H - 1-benzopyran-2-carboxylic acid), a first-generation LTB4 receptor antagonist, inhibited the chemotactic actions of LTB4 when given orally with an ED50 value of 1.7 mg/kg. The second-generation LTB4 receptor antagonist, SC-53228 [(+)-(S)-7-(3-(2-(cyclopropylmethyl)-3-methoxy-4- [(methylamino)carbonyl]phenoxy)propoxy)-3,4-dihydro-8-propyl-2H-1- benzopyran-2-propanoic acid], inhibited LTB4-induced chemotaxis when given intragastrically with an ED50 value of 0.07 mg/kg. Furthermore, SC-53228 inhibited 12(R)-HETE-induced granulocyte chemotaxis with an oral ED50 value of 5.8 mg/kg. When dosed orally over a range of 0.03-100 mg/kg, SC-53228 gave Cmax plasma concentrations of 0.015-41.1 micrograms/ml. SC-53228 inhibited LTB4-primed membrane depolarization of human neutrophils with an IC50 value of 34 nM. As a potent LTB4 receptor antagonist, SC-53228 may well have application in the medical management of disease states such as asthma, rheumatoid arthritis, inflammatory bowel disease, contact dermatitis, and psoriasis, in which LTB4 and/or 12(R)-HETE are implicated as inflammatory mediators.

Lymphocyte adherence in the reperfused rat liver: mechanisms and effects

Leukocyte adhesion may play a central role in the pathogenesis of preservation-reperfusion injury to liver grafts. We previously showed that lymphocyte adhesion to sinusoids is dependent on the length of cold ischemia. In the present study we examined the mechanisms of lymphocyte adherence after harvesting combined with a short and a long preservation time. The effects of lymphocyte adherence on liver function were also examined. Rat livers were stored at 1 degrees C in University of Wisconsin solution for 45 min or 30 hr and then reperfused at 37 degrees C in the isolated perfused rat liver with isogeneic lymphocytes in an asanguineous perfusate. The role of reactive oxygen intermediates was investigated with allopurinol, a vitamin E analog and ascorbate or superoxide dismutase and catalase. For us to determine the role of Kupffer cells, Kupffer cell blockade was produced by gadolinium chloride. Leukotriene B4 effects were examined with the lipooxygenase inhibitor, nordihydroguaiaretic acid. We evaluated the possible presence of mechanical obstruction by studying flow rates and the circulation of red blood cells. We examined the role of adhesion molecules by pretreating lymphocytes with trypsin or neuraminidase and by exposing livers to arabinogalactan. We investigated the effects of lymphocyte adhesion on liver function by comparing perfusate liver enzymes in livers reperfused with and without lymphocytes, with trypsinized lymphocytes and with an increased number of lymphocytes. Allopurinol significantly reduced hypoxanthine degradation, and nordihydroguaiaretic acid inhibited leukotriene B4 release into the perfusate. The ability of gadolinium chloride to inhibit Kupffer cells was shown by colloid carbon uptake. In livers harvested and preserved for 45 min, lymphocytes decreased about 40% during reperfusion. In livers preserved for 30 hr, the reduction was significantly greater (about 80%). Lymphocyte adherence was lessened in livers preserved for 45 min by all three of the reactive oxygen intermediate protectants and by gadolinium chloride. In contrast, neither reactive oxygen intermediate protectants nor gadolinium chloride reduced adherence in livers preserved for 30 hr. Nordihydroguaiaretic acid had no effect in livers preserved for either 45 min or 30 hr. Portal flow in livers preserved for 45 min and 30 hr was similar, suggesting an absence of mechanical obstruction, and this finding was supported by a complete absence of red cell trapping. Trypsinization of lymphocytes and exposure of livers to arabinogalactan significantly lessened lymphocyte adherence in livers preserved for 30 hr but not in those preserved for 45 min.(ABSTRACT TRUNCATED AT 400 WORDS)

Drug interactions in intestinal transport of folic acid and methotrexate

The effect of sulfasalazine and olsalazine on the transport of [3H]folic acid and of [3H]methotrexate (MTX) was investigated in organ-cultured endoscopic biopsy specimens of small intestinal mucosa from normal subjects. Biopsy specimens obtained from patients undergoing routine diagnostic upper gastrointestinal endoscopy were organ-cultured at pH 5.5 and the effect of these two drugs on the initial rate of uptake of the two folates was determined. Both drugs inhibited the transport of [3H]folic acid with similar Ki values (1.38 and 1.32 mM for sulfasalazine and olsalazine, respectively). However, the uptake of [3H]MTX was only partially inhibited by sulfasalazine and was unaffected by olsalazine. Sulfasalazine inhibited 26.2% of the total flux of MTX, in close agreement with the fraction of MTX flux that has been shown previously to be inhibited by folic acid. These data corroborate previous findings of heterogeneity of transport of MTX in the mucosa of the human small intestine.

Effects of SC-41930 on leukocyte adherence and emigration in rat mesenteric venules

This study demonstrates that SC-41930, 7-[3-(4-acetyl-3-methoxy-2-propylphenoxy)-propoxy]-3,4-dihydro-8-p ropyl-2H-1-benzopyran-2-carboxylic acid, an orally active LTB4 receptor antagonist, reduces LTB4-induced leukocyte adhesion and emigration in rat mesenteric venules. The mesentery of Sprague-Dawley rats was prepared for intravital microscopic examination and venules of 25-35 microns were chosen for evaluation. In control animals, LTB4 (20 nM) was superfused over the mesentery for 30 min. In the treatment group SC-41930 (5 microM) was superfused for 30 min, followed by a 30 min superfusion with SC-41930 and LTB4. The LTB4-induced increase in leukocyte adherence and emigration in postcapillary venules was significantly attenuated by pretreatment with SC-41930. Other experiments demonstrated that platelet-activating-factor-induced leukocyte adherence was not affected by SC-41930. These results indicate that SC-41930 is a potent inhibitor of LTB4-induced leukocyte-endothelial cell adhesive interactions in postcapillary venules.

Methotrexate transport in the human intestine. Evidence for heterogeneity

The transport of methotrexate (MTX) was investigated in organ-cultured endoscopic biopsy specimens of intestinal mucosa from normal subjects. In biopsy specimens from the proximal small intestine incubated with [3H]MTX (0.1 microM) for 2 hr at pH 5.5, [3H]MTX accumulated in the intracellular fluid to a concentration 3.5-fold higher than that of the medium, but at pH 6.5 and 7.5, the concentration was the same as that of the medium. In biopsy specimens from the cecum incubated under similar conditions, no accumulation against a concentration gradient was found. However, the accumulation of MTX was significantly higher at pH 5.5 than at 7.5. At [MTX] = 0.1 microM, the initial rate of MTX transport in the small intestine was significantly affected by medium pH and was optimal at pH 5.5. The relationship between the initial rate of uptake and medium [H+] was hyperbolic, suggestive of saturability with respect to [H+] with a Km of 132.2 nm [H+], corresponding to a medium pH of 6.88. At medium [MTX] = 10 microM, this effect was abolished. At pH 5.5, the relationship between the initial rate of uptake and medium [MTX] was sigmoidal, suggestive of a positive cooperativity, with napp of 1.8. [MTX] at 0.5 Vmax was 20.37 microM. Folic acid inhibited 37% of MTX flux. At pH 7.5, the relationship between the initial rate of uptake of MTX and medium [MTX] was linear. These data indicate the presence of a proton-dependent active transport of MTX in the human proximal small intestine, which is partially shared with folic acid.

Induction of colitis in rats by 2-2'-azobis(2-amidinopropane) dihydrochloride

Reactive oxygen metabolites (ROM) may play a role in the pathophysiology of inflammatory bowel disease (IBD) and ischemia-reperfusion-induced intestinal injury. Although there are many reports of intestinal mucosal injury associated with neutrophil-derived ROM, free radicals themselves have not been reported to induce intestinal mucosal injury. We administered intrarectally 2,2'-azobis(2-amidinopropane) dihydrochloride (AAPH) to rats, an azo compound that generates free radicals in vitro. Acute mucosal injury was assessed histologically by light microscopy and biochemically by myeloperoxidase (MPO) activity. Intrarectal administration of AAPH (60, 90, 150 mg/kg) caused erythema, edema, and histologically verifiable mucosal inflammation. MPO activity was increased 9- to 18-fold above the control level. The levels of thiobarbituric acid (TBA) reactants and sulfhydryls (SH) were significantly (P less than 0.01) increased and decreased, respectively, by 90 mg/kg AAPH. Sulfasalazine, 5-aminosalicylic acid, the LTB4 receptor antagonist SC-41930, and the antioxidant glutathione prevented the inflammation. This model of mucosal inflammation may be useful in evaluating new therapeutic agents for the treatment of IBD.