Intestinal adaptation following spring insertion into a roux limb in mice

BACKGROUND/PURPOSE

Intraluminal springs have recently been shown to lengthen segments of intestine in a process known as distraction enterogenesis. We hypothesized that biocompatible springs could be used to lengthen defunctionalized murine small intestine and would lead to identifiable intestinal adaptations at the molecular level.

METHODS

Age and weight matched C57BL/6 mice underwent surgical insertion of nitinol spring-loaded capsules into a Roux limb of jejunum. Segment lengths were measured at initial spring placement and at euthanasia after 14 and 21 days. Histology and gene expression of the Roux limb were evaluated at scarification and compared to untreated control segments.

RESULTS

Intestinal segments loaded with compressed springs lengthened an average of 240%, which was significantly longer than control segments loaded with either empty capsules or uncompressed springs. Muscularis thickening was greater in spring-treated mice compared to controls without springs. Crypt depth and Lgr5+ expression was greater in mice that received compressed spring treatments when compared to control groups.

CONCLUSIONS

Insertion of a compressed nitinol spring into a Roux limb results in significant intestinal lengthening, smooth muscle thickening, and Lgr5+ expression in a mouse model. The ability to increase small bowel length in a defunctionalized murine model may be used to understand the mechanism of distraction enterogenesis.

The cellular regulators PTEN and BMI1 help mediate NEUROGENIN-3-induced cell cycle arrest

Neurogenin-3 (NEUROG3) is a helix-loop-helix (HLH) transcription factor involved in the production of endocrine cells in the intestine and pancreas of humans and mice. However, the human NEUROG3 loss-of-function phenotype differs subtly from that in mice, but the reason for this difference remains poorly understood. Because NEUROG3 expression precedes exit of the cell cycle and the expression of endocrine cell markers during differentiation, we investigated the effect of lentivirus-mediated overexpression of the human NEUROG3 gene on the cell cycle of BON4 cells and various human nonendocrine cell lines. NEUROG3 overexpression induced a reversible cell cycle exit, whereas expression of a neuronal lineage homolog, NEUROG1, had no such effect. In endocrine lineage cells, the cellular quiescence induced by short-term NEUROG3 expression required cyclin-dependent kinase inhibitor 1A (CDKN1A)/p21^CIP1 expression. Expression of endocrine differentiation markers required sustained NEUROG3 expression in the quiescent, but not in the senescent, state. Inhibition of the phosphatase and tensin homolog (PTEN) pathway reversed quiescence by inducing cyclin-dependent kinase 2 (CDK2) and reducing p21^CIP1 and NEUROG3 protein levels in BON4 cells and human enteroids. We discovered that NEUROG3 expression stimulates expression of CDKN2a/p16^INK4a and BMI1 proto-oncogene polycomb ring finger (BMI1), with the latter limiting expression of the former, delaying the onset of CDKN2a/p16^INK4a -driven cellular senescence. Furthermore, NEUROG3 bound to the promoters of both CDKN1a/p21^CIP1 and BMI1 genes, and BMI1 attenuated NEUROG3 binding to the CDKN1a/p21CIP1 promoter. Our findings reveal how human NEUROG3 integrates inputs from multiple signaling pathways and thereby mediates cell cycle exit at the onset of differentiation.

Concise Review: The Potential Use of Intestinal Stem Cells to Treat Patients with Intestinal Failure

Intestinal failure is a rare life‐threatening condition that results in the inability to maintain normal growth and hydration status by enteral nutrition alone. Although parenteral nutrition and whole organ allogeneic transplantation have improved the survival of these patients, current therapies are associated with a high risk for morbidity and mortality. Development of methods to propagate adult human intestinal stem cells (ISCs) and pluripotent stem cells raises the possibility of using stem cell‐based therapy for patients with monogenic and polygenic forms of intestinal failure. Organoids have demonstrated the capacity to proliferate indefinitely and differentiate into the various cellular lineages of the gut. Genome‐editing techniques, including the overexpression of the corrected form of the defective gene, or the use of CRISPR (clustered regularly interspaced short palindromic repeats)/Cas9 to selectively correct the monogenic disease‐causing variant within the stem cell, make autologous ISC transplantation a feasible approach. However, numerous techniques still need to be further optimized, including more robust ex vivo ISC expansion, native ISC ablation, and engraftment protocols. Large‐animal models can to be used to develop such techniques and protocols and to establish the safety of autologous ISC transplantation because outcomes in such models can be extrapolated more readily to humans. Stem Cells Translational Medicine2017;6:666–676

A dental myth bites the dust--no observable relation between the incidence of dental abscess and the weather and lunar phase: an ecological study

Background

Anecdotal reports assert a relationship between weather and lunar activity and the odontogenic abscess (OA) incidence, but this relationship has not been validated. Therefore, the present study investigated the relationship between oral pain caused by OA and a variety of meteorological parameters and cyclic lunar activity.

Methods

The records of all dental emergency patients treated at the AllDent Zahnzentrum Emergency Unit in Munich, Germany during 2012 were retrospectively reviewed. Patients with oral pain who were diagnosed with OA and treated surgically (n = 1211) were included in the analysis. The OA incidence was correlated to daily meteorological data, biosynoptic weather analysis, and cyclic lunar activity.

Results

There was no seasonal variation in the OA incidence. None of the meteorological parameters, lunar phase, or biosynoptic weather class were significantly correlated with the OA incidence, except the mean barometric pressure, which was weakly correlated (rho = -0.204). The OA incidence showed a decreasing trend as barometric pressure increased (p < 0.001). On multiple linear regression, the barometric pressure accounted for approximately 4% of the OA incidence.

Conclusion

There is no evidence supporting a correlation between the incidence of odontogenic abscess and the weather and lunar activities.

Type I collagen as an extracellular matrix for the in vitro growth of human small intestinal epithelium

Background

We previously reported in vitro maintenance and proliferation of human small intestinal epithelium using Matrigel, a proprietary basement membrane product. There are concerns over the applicability of Matrigel-based methods for future human therapies. We investigated type I collagen as an alternative for the culture of human intestinal epithelial cells.

Methods

Human small intestine was procured from fresh surgical pathology specimens. Small intestinal crypts were isolated using EDTA chelation. Intestinal subepithelial myofibroblasts were isolated from a pediatric sample and expanded in vitro. After suspension in Matrigel or type I collagen gel, crypts were co-cultured above a confluent layer of myofibroblasts. Crypts were also grown in monoculture with exposure to myofibroblast conditioned media; these were subsequently sub-cultured in vitro and expanded with a 1∶2 split ratio. Cultures were assessed with light microscopy, RT-PCR, histology, and immunohistochemistry.

Results

Collagen supported viable human epithelium in vitro for at least one month in primary culture. Sub-cultured epithelium expanded through 12 passages over 60 days. Histologic sections revealed polarized columnar cells, with apical brush borders and basolaterally located nuclei. Collagen-based cultures gave rise to monolayer epithelial sheets at the gel-liquid interface, which were not observed with Matrigel. Immunohistochemical staining identified markers of differentiated intestinal epithelium and myofibroblasts. RT-PCR demonstrated expression of α-smooth muscle actin and vimentin in myofibroblasts and E-Cadherin, CDX2, villin 1, intestinal alkaline phosphatase, chromogranin A, lysozyme, and Lgr5 in epithelial cells. These markers were maintained through several passages.

Conclusion

Type I collagen gel supports long-term in vitro maintenance and expansion of fully elaborated human intestinal epithelium. Collagen-based methods yield familiar enteroid structures as well as a new pattern of sheet-like growth, and they eliminate the need for Matrigel for in vitro human intestinal epithelial growth. Future research is required to further develop this cell culture system for tissue engineering applications.

Brief report: CD24 and CD44 mark human intestinal epithelial cell populations with characteristics of active and facultative stem cells

Recent seminal studies have rapidly advanced the understanding of intestinal epithelial stem cell (IESC) biology in murine models. However, the lack of techniques suitable for isolation and subsequent downstream analysis of IESCs from human tissue has hindered the application of these findings toward the development of novel diagnostics and therapies with direct clinical relevance. This study demonstrates that the cluster of differentiation genes CD24 and CD44 are differentially expressed across LGR5 positive "active" stem cells as well as HOPX positive "facultative" stem cells. Fluorescence-activated cell sorting enables differential enrichment of LGR5 (CD24-/CD44+) and HOPX (CD24+/CD44+) cells for gene expression analysis and culture. These findings provide the fundamental methodology and basic cell surface signature necessary for isolating and studying intestinal stem cell populations in human physiology and disease.

Intestinal subepithelial myofibroblasts support the growth of intestinal epithelial stem cells

Intestinal epithelial stem cells (ISCs) are the focus of recent intense study. Current in vitro models rely on supplementation with the Wnt agonist R-spondin1 to support robust growth, ISC self-renewal, and differentiation. Intestinal subepithelial myofibroblasts (ISEMFs) are important supportive cells within the ISC niche. We hypothesized that co-culture with ISEMF enhances the growth of ISCs in vitro and allows for their successful in vivo implantation and engraftment. ISC-containing small intestinal crypts, FACS-sorted single ISCs, and ISEMFs were procured from C57BL/6 mice. Crypts and single ISCs were grown in vitro into enteroids, in the presence or absence of ISEMFs. ISEMFs enhanced the growth of intestinal epithelium in vitro in a proximity-dependent fashion, with co-cultures giving rise to larger enteroids than monocultures. Co-culture of ISCs with supportive ISEMFs relinquished the requirement of exogenous R-spondin1 to sustain long-term growth and differentiation of ISCs. Mono- and co-cultures were implanted subcutaneously in syngeneic mice. Co-culture with ISEMFs proved necessary for successful in vivo engraftment and proliferation of enteroids; implants without ISEMFs did not survive. ISEMF whole transcriptome sequencing and qPCR demonstrated high expression of specific R-spondins, well-described Wnt agonists that supports ISC growth. Specific non-supportive ISEMF populations had reduced expression of R-spondins. The addition of ISEMFs in intestinal epithelial culture therefore recapitulates a critical element of the intestinal stem cell niche and allows for its experimental interrogation and biodesign-driven manipulation.

A multicenter study to standardize reporting and analyses of fluorescence-activated cell-sorted murine intestinal epithelial cells

Fluorescence-activated cell sorting (FACS) is an essential tool for studies requiring isolation of distinct intestinal epithelial cell populations. Inconsistent or lack of reporting of the critical parameters associated with FACS methodologies has complicated interpretation, comparison, and reproduction of important findings. To address this problem a comprehensive multicenter study was designed to develop guidelines that limit experimental and data reporting variability and provide a foundation for accurate comparison of data between studies. Common methodologies and data reporting protocols for tissue dissociation, cell yield, cell viability, FACS, and postsort purity were established. Seven centers tested the standardized methods by FACS-isolating a specific crypt-based epithelial population (EpCAM+/CD44+) from murine small intestine. Genetic biomarkers for stem/progenitor (Lgr5 and Atoh 1) and differentiated cell lineages (lysozyme, mucin2, chromogranin A, and sucrase isomaltase) were interrogated in target and control populations to assess intra- and intercenter variability. Wilcoxon's rank sum test on gene expression levels showed limited intracenter variability between biological replicates. Principal component analysis demonstrated significant intercenter reproducibility among four centers. Analysis of data collected by standardized cell isolation methods and data reporting requirements readily identified methodological problems, indicating that standard reporting parameters facilitate post hoc error identification. These results indicate that the complexity of FACS isolation of target intestinal epithelial populations can be highly reproducible between biological replicates and different institutions by adherence to common cell isolation methods and FACS gating strategies. This study can be considered a foundation for continued method development and a starting point for investigators that are developing cell isolation expertise to study physiology and pathophysiology of the intestinal epithelium.

Isolation and characterization of intestinal stem cells based on surface marker combinations and colony-formation assay

BACKGROUND & AIMS

Identification of intestinal stem cells (ISCs) has relied heavily on the use of transgenic reporters in mice, but this approach is limited by mosaic expression patterns and difficult to directly apply to human tissues. We sought to identify reliable surface markers of ISCs and establish a robust functional assay to characterize ISCs from mouse and human tissues.

METHODS

We used immunohistochemistry, real-time reverse-transcription polymerase chain reaction, and fluorescence-activated cell sorting (FACS) to analyze intestinal epithelial cells isolated from mouse and human intestinal tissues. We compared different combinations of surface markers among ISCs isolated based on expression of Lgr5-green fluorescent protein. We developed a culture protocol to facilitate the identification of functional ISCs from mice and then tested the assay with human intestinal crypts and putative ISCs.

RESULTS

CD44(+)CD24(lo)CD166(+) cells, isolated by FACS from mouse small intestine and colon, expressed high levels of stem cell-associated genes. Transit-amplifying cells and progenitor cells were then excluded based on expression of GRP78 or c-Kit. CD44(+)CD24(lo)CD166(+) GRP78(lo/-) putative stem cells from mouse small intestine included Lgr5-GFP(hi) and Lgr5-GFP(med/lo) cells. Incubation of these cells with the GSK inhibitor CHIR99021 and the E-cadherin stabilizer Thiazovivin resulted in colony formation by 25% to 30% of single-sorted ISCs.

CONCLUSIONS

We developed a culture protocol to identify putative ISCs from mouse and human tissues based on cell surface markers. CD44(+)CD24(lo)CD166(+), GRP78(lo/-), and c-Kit(-) facilitated identification of putative stem cells from the mouse small intestine and colon, respectively. CD44(+)CD24(-/lo)CD166(+) also identified putative human ISCs. These findings will facilitate functional studies of mouse and human ISCs.

Use of collagen gel as an alternative extracellular matrix for the in vitro and in vivo growth of murine small intestinal epithelium

Methods for the in vitro culture of primary small intestinal epithelium have improved greatly in recent years. A critical barrier for the translation of this methodology to the patient's bedside is the ability to grow intestinal stem cells using a well-defined extracellular matrix. Current methods rely on the use of Matrigel(™), a proprietary basement membrane-enriched extracellular matrix gel produced in mice that is not approved for clinical use. We demonstrate for the first time the capacity to support the long-term in vitro growth of murine intestinal epithelium in monoculture, using type I collagen. We further demonstrate successful in vivo engraftment of enteroids co-cultured with intestinal subepithelial myofibroblasts in collagen gel. Small intestinal crypts were isolated from 6 to 10 week old transgenic enhanced green fluorescent protein (eGFP+) mice and suspended within either Matrigel or collagen gel; cultures were supported using previously reported media and growth factors. After 1 week, cultures were either lysed for DNA or RNA extraction or were implanted subcutaneously in syngeneic host mice. Quantitative real-time polymerase chain reaction (qPCR) was performed to determine expansion of the transgenic eGFP-DNA and to determine the mRNA gene expression profile. Immunohistochemistry was performed on in vitro cultures and recovered in vivo explants. Small intestinal crypts reliably expanded to form enteroids in either Matrigel or collagen in both mono- and co-cultures as confirmed by microscopy and eGFP-DNA qPCR quantification. Collagen-based cultures yielded a distinct morphology with smooth enteroids and epithelial monolayer growth at the gel surface; both enteroid and monolayer cells demonstrated reactivity to Cdx2, E-cadherin, CD10, Periodic Acid-Schiff, and lysozyme. Collagen-based enteroids were successfully subcultured in vitro, whereas pure monolayer epithelial sheets did not survive passaging. Reverse transcriptase-polymerase chain reaction demonstrated evidence of Cdx2, villin 1, mucin 2, chromogranin A, lysozyme 1, and Lgr5 expression, suggesting a fully elaborated intestinal epithelium. Additionally, collagen-based enteroids co-cultured with myofibroblasts were successfully recovered after 5 weeks of in vivo implantation, with a preserved immunophenotype. These results indicate that collagen-based techniques have the capacity to eliminate the need for Matrigel in intestinal stem cell culture. This is a critical step towards producing neo-mucosa using good manufacturing practices for clinical applications in the future.

Perioperative processes and outcomes after implementation of a hospitalist-run preoperative clinic

BACKGROUND

A structured, medical preoperative evaluation may positively impact the perioperative course of medically complex patients. Hospitalists are in a unique position to assist in preoperative evaluations, given their expertise with inpatient medicine and postoperative surgical consultation.

OBJECTIVE

To evaluate specific outcomes after addition of a Hospitalist-run, medical Preoperative clinic to the standard Anesthesia preoperative evaluation.

DESIGN, SETTING, PATIENTS

A pre/post retrospective, comparative review of outcomes of 5223 noncardiac surgical patients at a tertiary care Veterans Administration (VA) medical center.

RESULTS

Length of stay was reduced for inpatients with an American Society of Anesthesia (ASA) score of 3 or higher (P < 0.0001). There was a trend towards a reduction in same-day, medically avoidable surgical cancellations (8.5% vs 4.9%, P = 0.065). More perioperative beta blockers were used (P < 0.0001) and more stress tests were ordered (P = 0.012). Inpatient mortality rates were reduced (1.27% vs 0.36%, P = 0.0158).

CONCLUSION

A structured medical preoperative evaluation may benefit medically complex patients and improve perioperative processes and outcomes.

A nomenclature for intestinal in vitro cultures

Many advances have been reported in the long-term culture of intestinal mucosal cells in recent years. A significant number of publications have described new culture media, cell formations, and growth patterns. Furthermore, it is now possible to study, e.g., the capabilities of isolated stem cells or the interactions between stem cells and mesenchyme. However, at the moment there is significant variation in the way these structures are described and named. A standardized nomenclature would benefit the ability to communicate and compare findings from different laboratories using the different culture systems. To address this issue, members of the NIH Intestinal Stem Cell Consortium herein propose a systematic nomenclature for in vitro cultures of the small and large intestine. We begin by describing the structures that are generated by preparative steps. We then define and describe structures produced in vitro, specifically: enterosphere, enteroid, reconstituted intestinal organoid, induced intestinal organoid, colonosphere, colonoid, and colonic organoid.

Intestinal subepithelial myofibroblasts support in vitro and in vivo growth of human small intestinal epithelium

The intestinal crypt-niche interaction is thought to be essential to the function, maintenance, and proliferation of progenitor stem cells found at the bases of intestinal crypts. These stem cells are constantly renewing the intestinal epithelium by sending differentiated cells from the base of the crypts of Lieberkühn to the villus tips where they slough off into the intestinal lumen. The intestinal niche consists of various cell types, extracellular matrix, and growth factors and surrounds the intestinal progenitor cells. There have recently been advances in the understanding of the interactions that regulate the behavior of the intestinal epithelium and there is great interest in methods for isolating and expanding viable intestinal epithelium. However, there is no method to maintain primary human small intestinal epithelium in culture over a prolonged period of time. Similarly no method has been published that describes isolation and support of human intestinal epithelium in an in vivo model. We describe a technique to isolate and maintain human small intestinal epithelium in vitro from surgical specimens. We also describe a novel method to maintain human intestinal epithelium subcutaneously in a mouse model for a prolonged period of time. Our methods require various growth factors and the intimate interaction between intestinal sub-epithelial myofibroblasts (ISEMFs) and the intestinal epithelial cells to support the epithelial in vitro and in vivo growth. Absence of these myofibroblasts precluded successful maintenance of epithelial cell formation and proliferation beyond just a few days, even in the presence of supportive growth factors. We believe that the methods described here can be used to explore the molecular basis of human intestinal stem cell support, maintenance, and growth.

Intestinal smooth muscle cell maintenance by basic fibroblast growth factor

Intestinal tissue engineering is a potential therapy for patients with short bowel syndrome. Tissue engineering scaffolds that promote smooth muscle cell proliferation and angiogenesis are essential toward the regeneration of functional smooth muscles for peristalsis and motility. Since basic fibroblast growth factor (bFGF) can stimulate smooth muscle proliferation and angiogenesis, the delivery of bFGF was employed to stimulate proliferation and survival of primary intestinal smooth muscle cells. Two methods of local bFGF delivery were examined: the incorporation of bFGF into the collagen coating and the encapsulation of bFGF into poly(D,L-lactic-co-glycolic acid) microspheres. Cell-seeded scaffolds were implanted into the omentum and were retrieved after 4, 14, and 28 days. The seeded cells proliferated from day 4 to day 14 in all implants; however, at 28 days, significantly higher density of implanted cells and blood vessels was observed, when 10 microg of bFGF was incorporated into the collagen coating of scaffolds as compared to scaffolds with either no bFGF or 1 microg of bFGF in collagen. Microsphere encapsulation of 1 microg of bFGF produced similar effects as 10 microg of bFGF mixed in collagen and was more effective than the delivery of 1 microg of bFGF by collagen incorporation. The majority of the implanted cells also expressed alpha-smooth muscle actin. Scaffolds coated with microsphere-encapsulated bFGF and seeded with smooth muscle cells may be a useful platform for the regeneration of the intestinal smooth muscle.

Comparison of polyester scaffolds for bioengineered intestinal mucosa

INTRODUCTION

Biodegradable polyester scaffolds have proven useful for growing neointestinal tissue equivalents both in vitro and in vivo. These scaffolds allow cells to attach and grow in a 3-dimensional space while nutrient flow is maintained throughout the matrix. The purpose of this study was to evaluate different biopolymer constructs and to determine mucosal engraftment rates and mucosal morphology.

HYPOTHESIS

We hypothesized that different biopolymer constructs may vary in their ability to provide a good scaffolding onto which intestinal stem cell organoids may be engrafted.

STUDY DESIGN

Eight different microporous biodegradable polymer tubes composed of polyglycolic acid (PGA), polylactic acid, or a combination of both, using different fabrication techniques were seeded with intestinal stem cell clusters obtained from neonatal rats. Three different seeded polymer constructs were subsequently placed into the omentum of syngeneic adult recipient rats (n = 8). Neointestinal grafts were harvested 4 weeks after implantation. Polymers were microscopically evaluated for the presence of mucosal growth, morphology, scar formation and residual polymer.

RESULTS

Mucosal engraftment was observed in 7 out of 8 of the polymer constructs. A maximal surface area engraftment of 36% (range 5-36%) was seen on nonwoven, randomly entangled, small fiber PGA mesh coated with aerosolized 5% poly-L-lactic acid. Villous and crypt development, morphology and created surface area were best on PGA nonwoven mesh constructs treated with poly-L-lactic acid. Electrospun microfiber PGA had poor overall engraftment with little or no crypt or villous formation.

CONCLUSION

Intestinal organoids can be engrafted onto biodegradable polyester scaffoldings with restitution of an intestinal mucosal layer. Variability in polymer composition, processing techniques and material properties (fiber size, luminal dimensions and pore size) affect engraftment success. Future material refinements should lead to improvements in the development of a tissue-engineered intestine.

Orthotopic transplantation of intestinal mucosal organoids in rodents

BACKGROUND

Orthotopic transplantation of intestinal mucosal organoids that contain putative mucosal stem cells serves as an important step toward implementing intestinal gene therapy and treatment for malabsorption syndromes in animals and humans. We hypothesized that intestinal mucosal organoids can be transplanted along the axis of the small bowel giving rise to a neomucosa expressing proteins of its donor origin.

METHODS

Epithelial organoids were harvested from neonatal mice or rat small intestine with the use of a combination of enzymatic digestion with dispase and collagenase, and gravity sedimentation. In adult syngeneic recipients, a 7-cm segment of midjejunum was isolated, leaving its vascular pedicle intact. The remaining proximal and distal segments were anastomosed to restore intestinal continuity. The isolated segments were randomly subjected to surgical or chemical mucosectomy with a chelator solution for 30, 45, or 60 minutes and then compared. Histologic examination was used to confirm the presence of enterocytes, goblet cells, enteroendocrine cells, and Paneth cells in the neomucosal segments. To confirm the presence of ileal bile acid transporter (IBAT) gene message and function, we measured sodium-dependent bile acid uptake and IBAT-messenger RNA. Immunohistochemical examination using anti-IBAT antibodies was performed to demonstrate the expression of IBAT in the neomucosal segments. Experiments were repeated in a murine model transgenic for the green fluorescent protein to verify donor origin of the engrafted mucosa expressing IBAT.

RESULTS

The area of peak IBAT function was found to be located in the terminal ileum. Organoid units harvested from this region were capable of generating a small-bowel neoileal mucosa after being seeded into the jejunum. This mucosa was histologically confirmed to differentiate into all 4 intestinal lineages and to express IBAT signal, confirming its donor-derived origin. Optimal engraftment of mucosa expressing the IBAT protein was found in isolated jejunal segments debrided for 45 minutes. Sodium-dependent bile acid uptake was 5-fold higher in the neoileum, compared with the jejunum. IBAT-mRNA levels in the neoileum were 18-100-fold higher than those in the jejunum. Areas of green fluorescent protein-positive mucosa stained positively with anti-IBAT antibody in adjacent sections, suggesting that the regenerated mucosa is from transplanted ileal stem cells.

CONCLUSIONS

Orthotopic transplantation of epithelial organoids containing ileal stem cells was used to generate a neoileal mucosa that expressed all 4 intestinal lineages along with a new zone of active bile acid uptake and IBAT expression in a recipient jejunal segment.

Optical tissue window: a novel model for optimizing engraftment of intestinal stem cell organoids

BACKGROUND

Intestinal malabsorption disorders and short bowel syndrome lead to significant morbidity. We recently demonstrated that grafting of intestinal organoids can grow a bioengineered intestinal neomucosa and cure bile acid malabsorption in rats. Now we have developed a novel system that permits direct observation of intestinal organoids in vivo to optimize conditions for engraftment.

METHODS

Optical Windows were created in C57BL/6J mice by externalizing an omental pedicle into a dorsal skin flap chamber. Following creation of windows, 5000 intestinal organoids from green-fluorescent protein transgene (GFP)+ donor mice were seeded directly either on omentum or on polyglycolic acid (PGA) disks that had been placed on omentum at 1 or 5 days. Engraftment of green fluorescent cells was evaluated on postseeding days 1, 3, 5, 7, 10, 12, and 21 using fluorescence microscopy.

RESULTS

An initial group had seeding onto omentum (n = 5) or biopolymer disks (n = 5) on postoperative day 1. After 7 days, there was mucosal cell engraftment onto omental tissue and biopolymers. GFP+ organoids engrafted significantly better when seeded onto biopolymers compared to omentum (P < 0.05). In a second study with increased sample size (n = 24) up to day 12, all four groups demonstrated adherence and growth. However, GFP+ organoids seeded onto delayed PGA biopolymer demonstrated significantly better engraftment (P < 0.05).

CONCLUSIONS

This novel system allows continuous in vivo observation of engrafted cells that are seeded on externalized omentum. The use of PGA mesh biopolymer may improve engraftment of intestinal organoids.

To Make a New Intestinal Mucosa

A number of clinical conditions are caused by disorders affecting the mucosal lining of the gastrointestinal tract. Some patients suffer from a loss of mucosal surface area due to congenital defects or due to surgical resections ("short bowel syndrome"). Other patients have inborn or acquired defects of certain mucosal functions (e.g., glucose-galactose malabsorption, bile acid malabsorption). Many patients with these mucosal disorders could be more effectively treated if healthy mucosa were available in larger quantities as a replacement or functional supplement. We therefore developed methods to transplant mucosal stem cells from one part of the intestine to another and to make bioengineered intestinal mucosa. We generated an animal model of bile acid malabsorption using rats that underwent resection of the distal 25% of their small intestine (ileum). This resulted in significant losses of bile acids with the fecal excretions in these animals. We subsequently harvested ileal stem cell clusters from neonatal donors, removed the mucosa from a segment of proximal intestine (jejunum), and implanted the stem cell clusters into the debrided segment of jejunum. After four weeks, the animals had developed a functional "neomucosa." We inserted the "neo-ileal" segment into continuity as a substitute ileum. Postoperative measurements of fecal bile acid excretion showed that we were able to reverse the malabsorption syndrome in this model. This was the first reported neo-mucosa-based treatment of a malabsorption syndrome in vivo. We subsequently studied different biodegradable PGA and PLLA scaffoldings to generate bioengineered intestinal mucosa. We implanted these materials into omentum of rats and were able to identify a PGA/PLLA hybrid material on which engraftment rates of 36% of the available surface area could be achieved. Most recently, we developed a novel technique that permits direct observation of cell-biomaterial interactions after implantation into omentum or intestine in vivo. This method will help to optimize engraftment conditions for stem cell clusters on biomaterials.

Engraftment of mucosal stem cells into murine jejunum is dependent on optimal dose of cells

BACKGROUND

Transplantation of intestinal mucosal stem cells is an important step in the development of intestinal gene therapy and treatment of intestinal mucosal diseases. We hypothesized that engraftment rates increase proportionally with increasing doses of seeded stem cells and increasing jejunal débridment.

MATERIALS AND METHODS

Intestinal mucosal organoids were harvested from neonatal mice carrying a green-fluorescent protein (GFP) transgene and transplanted into adult GFP(-) mice (n = 66). In recipients, two jejunal segments (1.5 cm) were isolated with their blood circulation left intact with anastomosis of the distal and proximal segments to restore continuity. Debridement of native enterocytes was performed by perfusing luminally with ethylene diamine tetraacetc acid solutions for 20 min. A total of 5,000, 10,000, or 25,000 organoids were then seeded. Three weeks later, cross sections (n = 398) of the segments were evaluated for the presence of GFP(+) neomucosa using fluorescence microscopy. Additional segments were débrided for 30 and 40 min (n = 83). Other conditions were not tested because of the rate of high mortality in these experiments.

RESULTS

The group seeded with 10,000 organoid units at 20 min showed the highest engraftment of GFP(+) epithelium. Engraftment was improved by increasing débridment times at this seeding density. Overall mortality was 70%.

CONCLUSIONS

These findings suggest that there is an optimal seeding density of stem cell clusters for enhanced engraftment in this model. Mortality prohibited complete testing of all combinations of seeding density and debridement times.

Treatment of bile acid malabsorption using ileal stem cell transplantation

BACKGROUND

We hypothesized that ileal stem cell clusters transplanted into a segment of jejunum can be used to treat bile acid malabsorption.

STUDY DESIGN

In adult Lewis rats, a 15-cm segment of jejunum was isolated with its blood circulation left intact and partially stripped of enterocytes using luminal high-velocity perfusions with 3mmol/L ethylenediamine tetra-acetic acid solutions. Continuity was restored by anastomosing the proximal and distal gut. Ileal stem cell clusters were harvested from neonatal Lewis rats and transplanted into the stripped segments to generate a "neoileum." After 4weeks, recipients underwent resection of the native ileum, and the isolated neoileum was anastomosed in its place. After an additional 4weeks, a 48-hour stool collection was performed. The engrafted segment was harvested for taurocholate uptake studies, ileal bile acid transporter (IBAT) protein by immunohistomorphometry, and IBAT mRNA quantitation by reverse transcription polymerease chain reaction. Data were analyzed by ANOVA/t-test. Rats undergoing ileectomy, jejunectomy, or sham operations served as controls.

RESULTS

Total bile acid loss in the stool was markedly lower in rats with a neoileum compared with rats with an ileectomy (p < 0.001). Total taurocholate uptake was notably increased in the neoileum compared with the jejunum (p < 0.001). IBAT protein signal intensity was considerably higher in the neoileum compared with jejunum (p < 0.001). IBAT mRNA amounts in the neoileal group were comparable with those in normal rat ileum and were considerably higher (p = 0.003) than in the jejunum.

CONCLUSIONS

Ileal stem cell clusters were used to establish a new zone of bile acid uptake and IBAT expression in a jejunal segment. This neoileum eliminated loss of bile acids in the stool after ileectomy. This is the first time that transplantation of intestinal stem cell clusters has been shown to correct a clinical malabsorption syndrome.

Clinical features and treatment outcome of intussusception in premature neonates

BACKGROUND/PURPOSE

Less than 1.3% of all cases of intussusception occur in term neonates. Intussusception in premature neonates (IPN) is exceedingly rare. Its rarity and difficulty to differentiate IPN from common neonatal diseases like necrotizing enterocolitis (NEC) often delays its diagnosis. The authors set out to characterize diagnosis, treatment, and outcome of this rare condition.

METHODS

The authors analyzed 2 new cases of IPN and 33 previously reported cases from the literature.

RESULTS

The 35 patients with IPN had an average gestational age, postconceptual age at diagnosis, and birth weight of 28.4 +/- 0.6 weeks (all data, mean +/- SEM), 31.1 +/- 0.5 weeks, and 1,165 +/- 21 g, respectively. Gastrointestinal symptoms first presented at age 8 +/- 1 days. A preoperative diagnosis of NEC was assumed in 24 patients, delaying diagnosis by 10 +/- 2 days. Intussusception was diagnosed radiographically in 2 patients (1 contrast enema and 1 ultrasound scan) and during surgery or autopsy in the remainder. Resection was reported in 28 patients for bowel that was irreducible, necrotic, or perforated. The overall mortality rate was 20%, mainly owing to sepsis.

CONCLUSIONS

Intussusception in the premature neonate often is misdiagnosed as NEC, delaying operative intervention. Contrast enema has limited diagnostic capability. Early diagnosis may be achieved with use of ultrasound scan. Intussusception can be treated successfully with resection and primary anastomosis, achieving good results.

Identification of optimal harvest sites of ileal stem cells for treatment of bile acid malabsorption in a dog model

Ileal mucosal stem cells expressing the sodium-dependent ileal bile acid transporter (IBAT) have been successfully transplanted into the jejunum of rodents in projects aimed at creating a "neoileum" to treat bile acid malabsorption. To find optimal harvest sites for a dog model of stem cell transplantation, the exact location of peak IBAT expression in the donor ileum needs to be known. We therefore mapped IBAT function, IBAT mRNA, and IBAT protein in the ileum of Beagle dogs (N=3). Mucosal samples were taken every 5 cm in the ileum and every 20 cm in the jejunum of each dog. Sodium-dependent (active) and sodium-independent (passive) taurocholate uptake rates were measured using a standardized everted sleeve technique. IBAT mRNA concentrations were determined by semiquantitative reverse transcriptase-polymerase chain reaction and IBAT protein concentrations by fluorometric immunohistochemical analysis. The small bowel measured 208+/-17 cm (mean+/-standard error of the mean). Active and passive uptake rates were found to follow distinct distribution curves. Significant active uptake was seen only at the terminal 50 cm and peaked at 479+/-176 pM/mm(2). Depending on location, active uptake accounted for approximately half of the total uptake. IBAT mRNA and protein distributions corroborated uptake curves. The terminal 10 to 50 cm of ileum has the highest bile acid uptake capacity. This short segment appears to be the most promising donor site for ileal stem cell transplants to create a "neoileum" in dogs.

The utility of routine preoperative computed tomography scanning in the management of veterans with colon cancer

BACKGROUND

The aim of this study is to assess the clinical utility of routine preoperative computed tomography (CT) scanning in patients with cancer of the intraperitoneal colon.

METHODS

From November 1997 to June 2001, all patients at VA Puget Sound Healthcare System with a diagnosis of colon cancer were referred for a preoperative CT scan. Medical records and operative notes were reviewed to determine the influence of preoperative CT on clinical management.

RESULTS

Seventy patients received a CT per protocol. Preoperative CT provided information that was used in treatment planning and management in 26 (37%) cases. However, if preoperative scans had not been performed, the clinical management would have been definitively altered in only 13 (19%) patients.

CONCLUSIONS

Although these data suggest potential benefit for routine preoperative CT scanning, we believe additional study, including cost analysis, should precede the adoption of CT scanning as a routine preoperative study in patients with colon cancer.

Pitfalls in preparation of (3)H-unconjugated bilirubin by biosynthetic labeling from precursor (3)H-5-aminolevulinic acid in the dog

We report problems encountered during preparation of tritium-labeled unconjugated bilirubin ((3)H-UCB) from precursor (3)H-5-aminolevulinic acid ((3)H-ALA) in 2 dogs with external biliary drainage installed into the animals under general anesthesia. Under prolonged sedation, 12.9 or 14.0 mCi of (3)H-ALA was administered intravenously in two divided doses, and bile was collected for 9 hours. In one animal, taurocholate (TC) infusion was needed to maintain bile flow. (3)H-UCB was isolated from the bile and recrystallized with the improved method of Webster et al (Webster CC, Tiribelli C, Ostrow JD. J Lab Clin Med 2001;137:370-3). Based on radioactivity and pigment content, hourly bile collections were pooled to optimize specific activities. Surprisingly, in the first dog, only 2.9% of injected radioactivity was recovered in bile and only 14.1% in urine, and the specific activities of the crystalline (3)H-UCB from the two pools were only 39.5 and 30.0 x 10(3) dpm/microg. High-performance liquid chromatography analysis revealed that only 4% of ALA degraded during 5 minutes in injection solution at pH 6.8. The low incorporation of (3)H-ALA and low specific activity of (3)H-UCB was apparently caused mainly by prior degradation and exchange of labile tritium of the (3)H-ALA and probably by enhanced endogenous ALA synthesis caused by the anesthetic/sedative agents. Revised procedures in the second dog improved the incorporation of (3)H-ALA to 11.9% excreted in bile and the specific activity of the crystalline (3)H-UCB to 122.0 and 50.8 x 10(3) dpm/microg, while urinary excretion of tritium increased to 28.5%. These experiences emphasize possible pitfalls in preparing (3)H-UCB by biosynthetic labeling from (3)H-ALA administered to dogs.

Ileal mucosal bile acid absorption is increased in Cftr knockout mice

BACKGROUND

Excessive loss of bile acids in stool has been reported in patients with cystic fibrosis. Some data suggest that a defect in mucosal bile acid transport may be the mechanism of bile acid malabsorption in these individuals. However, the molecular basis of this defect is unknown. This study examines the expression of the ileal bile acid transporter protein (IBAT) and rates of diffusional (sodium independent) and active (sodium dependent) uptake of the radiolabeled bile acid taurocholate in mice with targeted disruption of the cftr gene.

METHODS

Wild-type, heterozygous cftr (+/-) and homozygous cftr (-/-) mice were studied. Five one-cm segments of terminal ileum were excised, everted and mounted onto thin stainless steel rods and incubated in buffer containing tracer 3H-taurocholate. Simultaneously, adjacent segments of terminal ileum were taken and processed for immunohistochemistry and Western blots using an antibody against the IBAT protein.

RESULTS

In all ileal segments, taurocholate uptake rates were fourfold higher in cftr (-/-) and two-fold higher in cftr (+/-) mice compared to wild-type mice. Passive uptake was not significantly higher in cftr (-/-) mice than in controls. IBAT protein was comparably increased. Immuno-staining revealed that the greatest increases occurred in the crypts of cftr (-/-) animals.

CONCLUSIONS

In the ileum, IBAT protein densities and taurocholate uptake rates are elevated in cftr (-/-) mice > cftr (+/-) > wild-type mice. These findings indicate that bile acid malabsorption in cystic fibrosis is not caused by a decrease in IBAT activity at the brush border. Alternative mechanisms are proposed, such as impaired bile acid uptake caused by the thick mucus barrier in the distal small bowel, coupled with a direct negative regulatory role for cftr in IBAT function.

Systemic effects of acute terminal ileitis on uninflamed gut aggravate bile acid malabsorption

BACKGROUND

Some patients with terminal ileitis suffer from significant bile acid malabsorption even if the inflammation is locally limited. We hypothesized that inflammation in the terminal ileum may lead to changes in mucosal absorption in more proximal intestinal segments and aggravate bile acid malabsorption.

METHODS

Five hamsters underwent laparotomy and localized instillation of 2,4,6-trinitrobenzenesulfonic acid (TNBS) in 10% ethanol into the last 4 cm of ileum to create terminal ileitis. A control group (n = 5) underwent instillation of saline. Animals were sacrificed after 24 h. Active and passive transport of radiolabeled bile acids was measured in the proximal and terminal ileum and glucose absorption in the jejunum using an everted sleeve technique. Myeloperoxidase (MPO) activity and histomorphology were examined by standard methods.

RESULTS

In animals with ileitis, active bile acid uptake decreased by 84% in the terminal ileum (t test, P <0.001) and by 58% in the proximal ileum (P < 0.05) compared with saline-treated controls. Jejunal glucose absorption decreased by 59% (P < 0.01). Passive bile acid and glucose absorption rates were not significantly changed in any segments of treated animals versus controls. Histological examination of the treated group revealed signs of acute terminal ileitis without changes in the proximal ileum and jejunum. All control tissues were uninflamed. MPO activity was 13-fold increased in the inflamed ileal samples compared with controls (P <0.001). No significant changes were seen in the proximal ileum and jejunum. There was no evidence of reflux of TNBS into proximal ileum. Nominal mucosal surface area values showed no significant changes between groups. Pretreatment of an additional group of hamsters (n = 5) with acetylsalicylic acid before TNBS instillation ameliorated the inflammatory response in the terminal ileum and largely abrogated the negative effects on ileal bile acid absorption.

CONCLUSION

These data suggest that limited acute ileitis impairs active bile acid uptake in the terminal ileum. It also diminishes active bile acid and glucose absorption in more proximal segments of the small intestine, likely by a systemic effect. This systemic effect may aggravate bile acid malabsorption in patients with limited ileitis.

A simple method for measuring of intestinal solute transport in mucosal biopsy specimens

Accurate in vitro measurements of intestinal mucosal solute uptake in humans are often difficult because only small amounts of tissue material are available. We describe a miniaturized everted sleeve method of measuring intestinal solute uptake in endoscopy biopsy samples that combines simplicity, good tissue viability and reproducibility. Biopsies were mounted on a dressmaker needle head stationed immediately over a stirring bar rotating at 1200 rpm. This approach was used to measure taurocholate uptake in sheep and human endoscopy biopsies. Comparison was made to conventional standardized everted sleeve preparations. Na+-dependent uptake rates correlated well among individual sheep (R2 = 0.88, P < 0.05). There was excellent correlation between conventional and biopsy preparations in humans (R2 = 0.98; P < 0.05). The biopsy method overestimated diffusional uptake rates in sheep and humans by two to three fold when compared to conventional everted sleeve preparations. We conclude that this method is valuable to measure Na+-dependent solute uptake rates in biopsy samples from human intestine.

Percutaneous cholecystostomy for acute cholecystitis in veteran patients

BACKGROUND

Surgical cholecystostomy has been shown to carry a significantly higher mortality rate at Veterans Administration (VA) hospitals than at non-federal hospitals in the past.

METHODS

A retrospective outcomes study was undertaken at a large VA medical center with a policy favoring radiologic over surgical cholecystostomy over the past 9 years. Records of 24 consecutive patients with acute cholecystitis were reviewed to evaluate the effectiveness of the procedure.

RESULTS

Cholecystostomy was performed radiologically in 22 patients and surgically in 2 patients. Most (78%) of patients improved within 48 hours. The periprocedural mortality was 25%. The majority of these patients died from unrelated illnesses. Four patients developed complications, none of which required operative intervention.

CONCLUSIONS

Comorbidities are the most important mortality factor for cholecystostomies in VA patients. Radiologic tube placement is effective and uncomplicated in most cases.

Atypical gastrointestinal symptoms are not associated with gallstones in patients with spinal cord injury

OBJECTIVE

To determine if nonspecific gastrointestinal (GI) symptoms justify cholecystectomy in patients with spinal cord injury (SCI).

DESIGN

The frequency of GI symptoms was determined in a sample of patients with SCI in whom the presence or absence of gallstones had been previously determined by screening ultrasonography or a known history of cholecystectomy. The prevalence of various symptoms in patients with and without gallstones was compared.

SETTING

The Spinal Cord Injury Unit of the Veterans Affairs Puget Sound Health Care System, which provides rehabilitation and longitudinal primary care for SCI veterans.

PATIENTS

Two hundred ninety-four patients who had undergone either right upper quadrant ultrasonography or cholecystectomy in the past, and who completed a questionnaire concerning GI symptoms.

MAIN OUTCOME MEASURE

Bivariate logistic regression was used to calculate odds ratios (ORs) to determine the strength of associations between the presence of each symptom and the presence of gallstones.

RESULTS

Pain in the right upper quadrant or epigastrium that occurred after meals or at night was significantly associated with gallstones (OR: 3.5; 95% confidence interval [CI] 1.02-11.73). Abdominal pain in other locations and nonspecific symptoms such as bloating and nausea, were not predictive of the presence of gallstones.

CONCLUSIONS

Nonspecific symptoms in patients with SCI are not associated with gallstones and do not justify cholecystectomy in patients with otherwise asymptomatic gallstones.

Distribution of bile acid absorption and bile acid transporter gene message in the hamster ileum

The apical, Na-dependent, ileal bile acid transporter (IBAT) is critical for the reabsorption of bile acids in the ileum. Bile acid transport capacities as well as the distribution of bile acid transporter messenger ribonucleic acid (mRNA) and transporter protein were studied along the axis of the ileum. Na-dependent and Na-independent taurocholate uptake was measured in the hamster ileum using an everted-sleeve technique. The distribution of IBAT mRNA and protein were mapped by in-situ hybridization, immunohistochemistry, and Western blotting. Na-dependent and Na-independent bile acid uptake rates were highest 1-4 cm before the ileocecal valve (maxima 780 and 120 pmol/mm2 per min, respectively) and decreased proximally and distally. Na-independent absorption was increased in the last 6 cm of the ileum. IBAT mRNA and protein expression were linked closely to the distribution of uptake capacity. IBAT mRNA was more abundant near the crypt-villus junction whereas the protein was expressed evenly along the villus axis. We conclude that Na-dependent and Na-independent bile acid absorption capacities both have distinct distribution curves in the hamster ileum. All ileocytes on villi in the high-uptake area of the ileum express IBAT mRNA and protein.

[Surgery education in the USA]

Surgical education in the United States historically was influenced by the German educational system. Currently residents spend five years to become general surgeons. Education focuses on the teaching of surgical basic sciences and practical instruction in the operating room and at the bedside. Students interested in General Surgery are selected largely based on their performance in medical school. Admission into first-rate programs is highly competitive. In many university-based programs residents are expected to spend an additional two years in research as part of their training. While on their clinical rotations residents usually spend 80 to 100 hours per week in the hospital. Resident salaries are moderate.

The presentation of gallstones and results of biliary surgery in a spinal cord injured population

BACKGROUND

Since spinal cord injured patients lack visceral sensation, their clinical manifestations of gallstones could be relatively occult. A higher proportion of these individuals may present with advanced biliary disease compared with the general population. Prophylactic cholecystectomy for asymptomatic stones may therefore be justified.

METHODS

All spinal cord injured patients seen at the Seattle Veterans Hospital over a 5-year period were retrospectively surveyed to define a set of patients who had undergone a cholecystectomy. The operative indications and results were compared with those from a series of cholecystectomies in neurologically intact patients.

RESULTS

The presentation of biliary disease in spinal cord injured patients was not more advanced than that of neurologically intact patients. Patients with high cord injuries presented in a similar fashion to those with low injuries.

CONCLUSIONS

Since most spinal cord injured patients with biliary disease present with typical findings, prophylactic removal of gallstones in these patients is not warranted.

[Telesurgery--experiences from the USA]

Recent advances in telecommunications formed the basis for studies on the use of video and high resolution television for surgical teleconsulting. Experience from hospitals of the American Veterans Administration suggests the technology to be a valuable asset. Telesurgical techniques improve health care in remote areas, save costs by reducing the need for transfers, and ease the professional isolation of health care personnel. Clear recommendations for both primary care and referral centers about how to conduct telesurgical consulting are given in the text.

Colonic perforations after renal transplantation

BACKGROUND

Perforation of the colon is a rare but serious complication in renal transplantation; allograft recipients constitute a patient population uniquely at risk with end-stage renal failure, maintenance therapy with dialysis before transplantation, and then chronic immunosuppression thereafter.

STUDY DESIGN

In 1,401 consecutive transplants performed between 1951 and 1995 at the Brigham and Women's Hospital, 30 recipients (2.1 percent) experienced 34 episodes of colonic perforations, 13 of which (38 percent) were fatal. The medical records and clinic charts of each person were analyzed for variables between those who survived and those who died of the colon perforation.

RESULTS

Significant differences in patient demography and clinical and laboratory findings including age, mean corticosteroid dose, and nutritional status were noted between the two groups. Early diagnosis and intervention improved the prognosis; 22 percent of those operated on within 24 hours died; 47 percent died after delayed intervention. Excision of the lesion with end-to-end anastomosis was effective in most right colon perforations, and removal of the lesion and formation of an end-colostomy and Hartmann pouch was preferred in rectosigmoid perforations. The incidence and outcome of posttransplant colonic perforations were associated with the intensity of immunosuppression, with 28 percent of perforations occurring within the first month after engraftment and 47 percent within the first 3 months; the mean daily dose of corticosteroids was three times higher in those who died compared with those who survived. The levels of serum albumin were significantly lower among nonsurvivors.

CONCLUSIONS

Colon perforation is a catastrophic event in immunosuppressed renal transplant recipients. Prompt diagnosis and treatment are critical; because of the masking effects of corticosteroids on symptoms and signs, a high index of suspicion and urgent investigation are indicated. Prompt surgical intervention and attention to the nutritional status are essential for survival.

The neuronal and epithelial human high affinity glutamate transporter. Insights into structure and mechanism of transport

High affinity transport of glutamate across plasma membranes of brain neurons and epithelial is mediated by a Na(+)- and K(+)-coupled electrogenic transporter. Here we report the primary structure and functional characterization of the human high affinity glutamate transporter (HEAAC1). A unique characteristic of HEAAC1-mediated transport is that the affinity for glutamate and the maximal transport rate are strongly dependent on membrane potential. Our data provide new insights into individual steps of high affinity glutamate transport and show that the transport mechanism is distinct from that of the gamma-aminobutyric acid transporter GAT-1 and the Na+/glucose transporter SGLT1. Under voltage clamp condition, HEAAC1 mediated large substrate-evoked inward currents (up to 1 microA). The substrate specificity, stereospecificity, the Km value (30 +/- 3 microM at -60 mV) of the L-glutamate-evoked current, and Northern analysis all agree with previously reported characteristics of high affinity glutamate transport in brain. In contrast to SGLT1 and GAT-1, voltage jump studies of HEAAC1 yielded only minor relaxation currents. Classic inhibitors of brain glutamate uptake such as DL-threo-beta-hydroxyaspartate, L-trans-pyrrolidine 2,4,-dicarboxylic acid (PDC), and dihydrokainate were found to be either transport substrates or to have no significant effect on glutamate transport. We also found that the maximal transport rate for PDC was markedly reduced compared to that for L-glutamate. We propose that PDC most likely reduces the turnover rate of the transporter. A search of the sequence data bases revealed weak homology of HEAAC1 to the H(+)-coupled vesicular monoamine transporter, suggesting an evolutionary link between plasma membrane and vesicular transporters.