Targeted disruption of the glucose transporter 4 selectively in muscle causes insulin resistance and glucose intolerance.

The prevalence of type 2 diabetes mellitus is growing worldwide. By the year 2020, 250 million people will be afflicted. Most forms of type 2 diabetes are polygenic with complex inheritance patterns, and penetrance is strongly influenced by environmental factors. The specific genes involved are not yet known, but impaired glucose uptake in skeletal muscle is an early, genetically determined defect that is present in non-diabetic relatives of diabetic subjects. The rate-limiting step in muscle glucose use is the transmembrane transport of glucose mediated by glucose transporter (GLUT) 4 (ref. 4), which is expressed mainly in skeletal muscle, heart and adipose tissue. GLUT4 mediates glucose transport stimulated by insulin and contraction/exercise. The importance of GLUT4 and glucose uptake in muscle, however, was challenged by two recent observations. Whereas heterozygous GLUT4 knockout mice show moderate glucose intolerance, homozygous whole-body GLUT4 knockout (GLUT4-null) mice have only mild perturbations in glucose homeostasis and have growth retardation, depletion of fat stores, cardiac hypertrophy and failure, and a shortened life span. Moreover, muscle-specific inactivation of the insulin receptor results in minimal, if any, change in glucose tolerance. To determine the importance of glucose uptake into muscle for glucose homeostasis, we disrupted GLUT4 selectively in mouse muscles. A profound reduction in basal glucose transport and near-absence of stimulation by insulin or contraction resulted. These mice showed severe insulin resistance and glucose intolerance from an early age. Thus, GLUT4-mediated glucose transport in muscle is essential to the maintenance of normal glucose homeostasis.

Redistribution of substrates to adipose tissue promotes obesity in mice with selective insulin resistance in muscle.

Obesity and insulin resistance in skeletal muscle are two major factors in the pathogenesis of type 2 diabetes. Mice with muscle-specific inactivation of the insulin receptor gene (MIRKO) are normoglycemic but have increased fat mass. To identify the potential mechanism for this important association, we examined insulin action in specific tissues of MIRKO and control mice under hyperinsulinemic-euglycemic conditions. We found that insulin-stimulated muscle glucose transport and glycogen synthesis were decreased by about 80% in MIRKO mice, whereas insulin-stimulated fat glucose transport was increased threefold in MIRKO mice. These data demonstrate that selective insulin resistance in muscle promotes redistribution of substrates to adipose tissue thereby contributing to increased adiposity and development of the prediabetic syndrome.

Exercise modulates postreceptor insulin signaling and glucose transport in muscle-specific insulin receptor knockout mice.

Physical exercise promotes glucose uptake into skeletal muscle and makes the working muscles more sensitive to insulin. To understand the role of insulin receptor (IR) signaling in these responses, we studied the effects of exercise and insulin on skeletal muscle glucose metabolism and insulin signaling in mice lacking insulin receptors specifically in muscle. Muscle-specific insulin receptor knockout (MIRKO) mice had normal resting 2-deoxy-glucose (2DG) uptake in soleus muscles but had no significant response to insulin. Despite this, MIRKO mice displayed normal exercise-stimulated 2DG uptake and a normal synergistic activation of muscle 2DG uptake with the combination of exercise plus insulin. Glycogen content and glycogen synthase activity in resting muscle were normal in MIRKO mice, and exercise, but not insulin, increased glycogen synthase activity. Insulin, exercise, and the combination of exercise plus insulin did not increase IR tyrosine phosphorylation or phosphatidylinositol 3-kinase activity in MIRKO muscle. In contrast, insulin alone produced a small activation of Akt and glycogen synthase kinase-3 in MIRKO mice, and prior exercise markedly enhanced this insulin effect. In conclusion, normal expression of muscle insulin receptors is not needed for the exercise-mediated increase in glucose uptake and glycogen synthase activity in vivo. The synergistic activation of glucose transport with exercise plus insulin is retained in MIRKO mice, suggesting a phenomenon mediated by nonmuscle cells or by downstream signaling events.

Using GPS Data to Study Neighborhood Walkability and Physical Activity.

INTRODUCTION: Urban form characteristics intended to support pedestrian activity, collectively referred to as neighborhood walkability, are thought to increase total physical activity. However, little is known about how neighborhood walkability influences utilization of neighborhood space by residents and their overall physical activity. METHODS: Sociodemographic information and data on mobility and physical activity over 1-week periods measured by GPS loggers and accelerometers were collected from 803 residents of New York City between November 2010 and November 2011. Potentially accessible neighborhood areas were defined as land area within a 1-kilometer distance of the subject's home (radial buffer) and within a 1-kilometer journey on the street network from the home (network buffer). To define actual areas utilized by subjects, a minimum convex polygon was plotted around GPS waypoints falling within 1 kilometer of the home. A neighborhood walkability scale was calculated for each neighborhood area. Data were analyzed in 2014. RESULTS: Total residential neighborhood space utilized by subjects was significantly associated with street intersection density and was significantly negatively associated with residential density and subway stop density within 1 kilometer of the home. Walkability scale scores were significantly higher within utilized as compared with non-utilized neighborhood areas. Neighborhood walkability in the utilized neighborhood area was positively associated with total weekly physical activity (32% [95% CI=17%, 49%] more minutes of moderate-equivalent physical activity across the interquartile range of walkability). CONCLUSION: Neighborhood walkability is associated with neighborhood spaces utilized by residents and total weekly physical activity.

A model to explore the interaction between muscle insulin resistance and beta-cell dysfunction in the development of type 2 diabetes.

Type 2 diabetes is a polygenic disease characterized by defects in both insulin secretion and insulin action. We have previously reported that isolated insulin resistance in muscle by a tissue-specific insulin receptor knockout (MIRKO mouse) is not sufficient to alter glucose homeostasis, whereas beta-cell-specific insulin receptor knockout (betaIRKO) mice manifest severe progressive glucose intolerance due to loss of glucose-stimulated acute-phase insulin release. To explore the interaction between insulin resistance in muscle and altered insulin secretion, we created a double tissue-specific insulin receptor knockout in these tissues. Surprisingly, betaIRKO-MIRKO mice show an improvement rather than a deterioration of glucose tolerance when compared to betaIRKO mice. This is due to improved glucose-stimulated acute insulin release and redistribution of substrates with increased glucose uptake in adipose tissue and liver in vivo, without a significant decrease in muscle glucose uptake. Thus, insulin resistance in muscle leads to improved glucose-stimulated first-phase insulin secretion from beta-cells and shunting of substrates to nonmuscle tissues, collectively leading to improved glucose tolerance. These data suggest that muscle, either via changes in substrate availability or by acting as an endocrine tissue, communicates with and regulates insulin sensitivity in other tissues.

Stimulation of aromatase P450 promoter (II) activity in endometriosis and its inhibition in endometrium are regulated by competitive binding of steroidogenic factor-1 and chicken ovalbumin upstream promoter transcription factor to the same cis-acting element.

In stromal cells of endometriosis, marked levels of aromatase P450 (P450arom) mRNA and activity are present and can be vigorously stimulated by (Bu)2cAMP or PGE2 to give rise to physiologically significant estrogen biosynthesis. Since eutopic endometrial tissue or stromal cells lack P450arom expression, we studied the molecular basis for differential P450arom expression in endometriosis and eutopic endometrium. First, we demonstrated by rapid amplification of cDNA 5'-ends that P450arom expression in pelvic endometriotic lesions is regulated almost exclusively via the alternative promoter II. Then, luciferase reporter plasmids containing deletion mutations of the 5'-flanking region of promoter II were transfected into endometriotic stromal cells. We identified two critical regulatory regions for cAMP induction of promoter II activity: 1) a-214/-100 bp proximal region responsible for a 3.7-fold induction, and 2) a -517/ -214 distal region responsible for potentiation of cAMP response up to 13-fold. In the -214/-100 region, we studied eutopic endometrial and endometriotic nuclear protein binding to a nuclear receptor half-site (NRHS, AGGTCA) and an imperfect cAMP response element (TGCACGTCA). Using electrophoretic mobility shift assay, cAMP response element-binding activity in nuclear proteins from both endometriotic and eutopic endometrial cells gave rise to formation of identical DNA-protein complexes. The NRHS probe, on the other hand, formed a distinct complex with nuclear proteins from endometriotic cells, which migrated at a much faster rate compared with the complex formed with nuclear proteins from eutopic endometrial cells. Employing recombinant proteins and antibodies against steroidogenic factor-1 (SF-1) and chicken ovalbumin upstream promoter transcription factor (COUP-TF), we demonstrated that COUP-TF but not SF-1 bound to NRHS in eutopic endometrial cells, whereas SF-1 was the primary NRHS-binding protein in endometriotic cells. In fact, COUP-TF transcripts were present in both eutopic endometrial (n = 12) and endometriotic tissues (n = 8), whereas SF-1 transcripts were detected in all endometriotic tissues (n = 12), but in only 3 of 15 eutopic endometrial tissues. Moreover, we demonstrated a dose-dependent direct competition between SF-1 and COUP-TF for occupancy of the NRHS, to which SF-1 bound with a higher affinity. Finally, overexpression of SF-1 in eutopic endometrial and endometriotic cells strikingly potentiated baseline and cAMP-induced activities of -517 promoter II construct, whereas overexpression of COUP-TF almost completely abolished these activities. In conclusion, COUP-TF might be one of the factors responsible for the inhibition of P450arom expression in eutopic endometrial stromal cells, which lack SF-1 expression in the majority (80%) of the samples; in contrast, aberrant SF-1 expression in endometriotic stromal cells can override this inhibition by competing for the same DNA-binding site, which is likely to account for high levels of baseline and cAMP-induced aromatase activity.

The 5'-flanking region of the ovarian promoter of the bovine CYP19 gene contains a deletion in a cyclic adenosine 3',5'-monophosphate-like responsive sequence.

Conversion of C19 steroids to estrogens is catalyzed by aromatase P450 (P450arom; the product of the CYP19 gene). In the ovary, P450arom is expressed in granulosa cells of both human (h) and bovine (b) follicles. After the ovulatory surge of gonadotropins, however, P450arom expression is maintained only in the luteinized granulosa cells of the human ovary and is absent from the bovine corpus luteum. We compared the regulation of expression of the ovary-specific human CYP19 (hCYP19ov) and the bovine CYP19 (bCYP19ov) gene by cAMP (forskolin) and sought to determine whether the divergence in the expression of P450arom with the onset of luteinization could be explained by specific cis-acting elements present uniquely in the 5'-flanking DNA of the hCYP19ov or bCYP19ov gene. We, therefore, subcloned DNA encompassing the promoters and 5'-flanking regions of the hCYP19ov or bCYP19ov gene into a promoterless luciferase vector. These constructs were transfected into luteinized bovine granulosa cells or bovine luteal cells in primary culture. Neither cell type exhibits endogenous expression of bovine P450arom. After transfection, cells were treated with either vehicle or 25 microM forskolin. There was little or no increase in luciferase activity after forskolin treatment in cells transfected with any of the bCYP19ov constructs, whereas all of the corresponding hCYP19ov constructs (-693/-16 to -214/-16 bp) expressed reporter activity in the presence of forskolin. This dramatic difference between the activities of the constructs of the two species occurred despite the fact that there is an 88% sequence identity between the bovine and human promoters in the region between -214 to -16 bp. One possible explanation for this variability may be that the bCYP19ov gene has a 1-bp deletion in a cAMP-response element-like sequence (CLS) present at -208 to -201 bp in the hCYP19ov gene that we have shown to be critical for cAMP-stimulated transcription of hCYP19ov in the ovary. When this region of the bCYP19ov promoter was mutated to the hCLS, a partial restoration in luciferase activity was observed after forskolin treatment. Therefore, these results suggest that another sequence in this -214 bp region of the bCYP19ov gene is also contributing to the lack of expression of P450arom after luteinization in the bovine ovary. This lack of expression of the bCYP19ov gene may be due to the presence of a repressive trans-acting factor expressed with the onset of luteinization of the bovine granulosa cell. These results further suggest that in the cow, elements upstream of those employed by the hCYP19ov gene may have been recruited to facilitate regulated expression of the bCYP19ov gene in the absence of a functional CLS.

Transformation of human granulosa cells with the E6 and E7 regions of human papillomavirus.

Ovarian granulosa cells are the primary site of estrogen and progesterone synthesis and play an essential role in the maturation of the developing ovum. Freshly isolated granulosa cells are often used to study the regulation of steroid and protein biosynthesis, but the small number of cells available for these cultures has proven inadequate for many detailed gene regulatory studies. The goal of this study was to develop human granulosa (HG) cell lines that maintain differentiated function. The E6 and E7 open reading frames of high risk strains of human papillomavirus have been used to produce immortalized cell lines. Primary cultures of human luteinized granulosa cells were infected with defective retroviruses containing the E6 and E7 regions of human papillomavirus 16 and with the neomycin phosphotransferase gene to confer G418 resistance. Three of eight clones that were isolated after selection in medium containing G418 were found to produce progesterone following treatment with forskolin or dibutyryl cAMP for 48 h. Forskolin caused these cells to retract in the characteristic rounding response, as described in primary HG cultures. One clone, HGL5, was used for a detailed characterization of differentiated function. HGL5 cells retained the ability to increase progesterone production and convert exogenously added androstenedione to estradiol in response to agonists of the protein kinase-A pathway (forskolin and dibutyryl cAMP), but were not responsive to FSH or LH treatment. A key enzyme in the production of estradiol, cytochrome P450 aromatase, has proven difficult to maintain in long term cultures of granulosa cells. For that reason, we examined the expression of aromatase in the transformed HGL5 clone by monitoring mRNA levels. Aromatase mRNA increased by 4- to 5-fold after forskolin treatment, as determined by Northern analysis. This human granulosa cell culture line maintains many of the functions of normal cells and should provide an important model to study the molecular events controlling granulosa cell differentiation and function.

A CRE-like sequence that binds CREB and contributes to cAMP-dependent regulation of the proximal promoter of the human aromatase P450 (CYP19) gene.

The major physiological regulator of human aromatase P450 gene expression in the ovary is follicle stimulating hormone (FSH), which acts by increasing intracellular cAMP levels. This study describes the identification of an element in the aromatase proximal promoter that is critical for the full transcriptional response of this promoter to cAMP. The cAMP-responsive element (CRE)-like sequence (CLS) was originally identified by its sequence similarity to a palindromic CRE, from which it differs by the insertion of a single cytosine. Mutation of the CLS in the context of 278 bp of 5'-flanking DNA resulted in the loss of cAMP-induced reporter gene expression in transfected ovarian luteal cells. A cell line survey EMSA revealed that CLS binding factors are ubiquitously distributed, although the migration pattern of CLS-nuclear protein complexes varied among different nuclear extracts. An extended half-site for binding members of the basic-leucine zipper class of transcription factors was found to be responsible for ovarian luteal cell nuclear protein binding and cAMP-dependent transcriptional transactivation. Competition and supershift EMSAs revealed that the CLS-nuclear protein complexes that regulate cAMP-induced transcription were indistinguishable from homodimeric CREB bound to the CRE oligonucleotide, yet the interaction with the CLS was of lower affinity.

17alpha-Hydroxylase gene expression in the bovine ovary: mechanisms regulating expression differ from those in adrenal cells.

17alpha-Hydroxylase cytochrome P450 (P450(17alpha)) is the enzyme which synthesizes C19 steroids in a two-step reaction in which 17alpha-OH pregnenolone is an intermediate. In the bovine and human adult female, 17alpha-hydroxylase is expressed in adrenocortical cells where 17alpha-OH pregnenolone and 17alpha-OH progesterone are precursors of cortisol, and in theca cells of the ovary where these intermediates are precursors of C19 steroids. In both adrenal cortex and theca, 17alpha-hydroxylase gene expression is stimulated by cyclic AMP (cAMP). The aim of this study was to determine the mechanism regulating 17alpha-hydroxylase gene expression in the bovine ovary. Our results indicate that the bovine 17alpha-hydroxylase gene is regulated in a tissue-specific fashion. Primer extension and S1 nuclease protection assays reveal that the start site of transcription in the theca is identical to that in the adrenal. Transfection studies employing beta-globin reporter gene constructs fused to successive deletions of the 5' regulatory region of the bovine 17alpha-hydroxylase gene indicate that sequences between -80 and -37 basepairs (bp) (CRS2) confer cAMP-regulated transcription in bovine theca cells in culture. These results are in contrast to similar studies conducted in bovine adrenocortical cells, which indicate that the major cAMP response element (referred to as CRS1) is located at -243 to -225 bp. The Ad4 element (AGGTCA, -42 to -37 bp) within CRS2, which has been shown to be involved in cAMP responsiveness in other steroidogenic P450 genes, cannot by itself confer cAMP-regulated reporter gene expression in bovine cells. These results indicate that in the cow, 17alpha-hydroxylase gene expression is regulated in a tissue-specific fashion, and that this regulation may be conferred, at least in part, by the use of tissue-specific cis-acting elements in the bovine 17alpha-hydroxylase gene.

Endocrine disorders associated with inappropriately high aromatase expression.

Aromatase P450 (P450arom) is responsible for conversion of C19 steroids to estrogens in a number of human tissues, such as the placenta, gonads, adipose tissue, skin and the brain. Aromatase expression in human tissues is regulated by use of alternative promoters in the placenta (promoter I.1), adipose tissue (promoters I.4, I.3 and II) and gonads (promoter II). Aromatase expression is absent in the disease-free adult liver, adrenal and uterine tissues. Excessive or inappropriate aromatase expression in adipose fibroblasts and endometriosis-derived stromal cells, as well as in testicular, hepatic, adrenal and uterine tumors, is associated with abnormally high circulating estrogen levels and/or with increased local estrogen concentrations in these tissues. Whether systemically delivered or locally produced, elevated estrogen levels will in turn promote the growth of hormone-responsive tissues. We recently studied aromatase expression in testicular tumor and adipose tissue samples from prepubertal boys with gynecomastia, in hepatocellular cancer and adrenocortical tumor samples from adult men with gynecomastia, in breast adipose tissue samples proximal to breast tumors, and in endometrial cancer, leiomyoma and endometriosis tissues. Excessive aromatase activity and P450arom transcript levels were found in these tissue samples or in cultured cells derived from these tissues. In these neoplastic or non-neoplastic tissues or cells, the regulation of aromatase expression was studied in terms of alternative promoter use, both in vivo and in response to various hormonal stimuli. Our results were suggestive of a common metabolic abnormality associated with activation of a cyclic AMP-dependent signalling pathway that gives rise to transcriptional transactivation of aromatase expression via promoters I.3 and II in all of the above tissues. This article describes the common pathophysiological and molecular features of excessive aromatase expression in these disease states.

Knockout mice challenge our concepts of glucose homeostasis and the pathogenesis of diabetes mellitus.

The failure of insulin to stimulate muscle glucose uptake and suppress hepatic glucose production represents two of the fundamental pathophysiologic lesions in type 2 diabetes mellitus (DM). Defining insulin action at the molecular level, therefore, provides the critical background against which to elucidate the mechanisms of insulin resistance that underlie type 2 DM, obesity and many other disorders. Over the past two decades substantial progress has been made in identifying many of the molecular mechanisms involved in insulin signaling. Much of this progress has been due to the use of homologous recombinant gene targeting. The present review examines the various insights that have been provided by studies of knockout mice strains. Taken together, the results present the possibility of a unifying hypothesis for type 2 DM, in which insulin resistance in the beta-cell synergizes with insulin resistance in the periphery to produce the two classic defects of this disease: relative hypoinsulinemia and peripheral insulin resistance.

A laparoscopic endovascular aortobifemoral conduit that can be retained as a long-term bypass: a solution for patients with inadequate iliac access.

PURPOSE: To present a laparoscopic technique for placing a partially stented aortobifemoral (ABF) conduit that can be used for more proximal endovascular manipulations and then be retained as a permanent bypass of occlusive iliac disease. TECHNIQUE: Ethical approval was obtained to use a fresh frozen cadaver. The left common iliac artery, distal aorta, and proximal right common iliac artery were dissected laparoscopically. A curved hollow needle was inserted into the distal aorta, and wire access was obtained. A partially stented bifurcated Dacron bypass graft was deployed under fluoroscopic guidance into the distal aorta. The limbs of the bypass were then used as conduits for endovascular access before being tunneled behind the ureters and anastomosed to the femoral arteries in the usual way, retaining the stented graft as an ABF bypass. CONCLUSION: This novel technique combines laparoscopic access with endovascular manipulation to place an ABF conduit, which can be retained as a permanent bypass without the need for an abdominal incision. This technique could provide a minimally invasive solution for pelvic occlusive disease that hinders endovascular repairs, as well as a minimally invasive means of securing endoluminal access in patients with iliac arteries of inadequate caliber.

Computed tomography virtual intravascular endoscopy in the evaluation of fenestrated stent graft repair of abdominal aortic aneurysms.

BACKGROUND: This study aimed to investigate the diagnostic value of computed tomography virtual intravascular endoscopy (VIE) in the follow-up of patients with abdominal aortic aneurysm (AAA) treated with fenestrated stent grafts. METHODS: A total of 19 patients (17 males and 2 females; mean age: 75 years) with AAA undergoing fenestrated stent grafts were retrospectively studied. Pre- and post-fenestration computed tomography data were reconstructed for the generation of VIE images of aortic ostia and fenestrated stents and compared with two-dimensional axial and multiplanar reformation (MPR) images. Serum creatinine was measured pre and post fenestration to evaluate the renal function. RESULTS: The mean intra-aortic length measured by VIE, two-dimensional axial and MPR were 4.7, 4.4 and 4.6 mm, respectively, for the right renal stent; 5.0, 4.9 and 5.0 mm, respectively, for the left renal stent; and 5.9, 6.0 and 6.0 mm, respectively, for the superior mesenteric artery stent. Comparisons of these measurements did not show significant difference (P > 0.05). The mean diameters of renal artery ostia measured on VIE visualization pre and post fenestration were 9.2 x 8.3 and 10 x 8.9 mm for the right renal ostium; 8.3 x 7.1 and 9.9 x 8.9 mm for the left renal ostium, with significant changes observed (P < 0.01). No renal dysfunction was observed in this group. CONCLUSION: VIE is a valuable visualization tool in the follow-up of fenestrated stent graft repair of AAA by providing intraluminal appearance of fenestrated stents and measuring the length of stent protrusion.

Experimental measurement and mathematical modeling of pulsatile forces on a symmetric, bifurcated endoluminal stent graft model.

The objective of this study was to measure the pulsatile forces acting on a symmetric, bifurcated endoluminal stent graft to validate a computational fluid dynamics (CFD) and analytic model so that they can be used for various graft dimensions. We used a load cell to measure the force owing to the movement of an acrylic model of a bifurcated stent graft under pulsatile flow. This was then simulated with a CFD and analytic model. The main features of the experimental pulsatile force data and the CFD results were consistent. The results showed that the total force was proportional to the inlet pressure cycle. The force rose from 3.32 N at 130 mm Hg systolic to 17.5 N at 250 mm Hg systolic pressure. For the more variable regions of the flow, the experimentally measured forces lagged the computational and analytic results. The CFD and analytic models provide approximate descriptions for the forces acting on a bifurcated stent graft subjected to pulsatile flow. Such models should be of assistance to designers of endoluminal stent grafts.

Multislice CT angiography in the follow-up of fenestrated endovascular grafts: effect of slice thickness on 2D and 3D visualization of the fenestration stents.

PURPOSE: To investigate the effect of multislice computed tomography (CT) protocols on the visualization of target vessel stents in patients with abdominal aortic aneurysm (AAA) treated with fenestrated endovascular grafts. METHODS: Twenty-one patients (19 men; mean age 75 years, range 63-86) undergoing fenestrated endovascular repair of AAA were retrospectively studied. Multislice CT angiography was performed with several protocols, and the section thicknesses used in each were compared to identify any relationship between slice thickness and target vessel stents visualized on 2-dimensional (2D) axial, multiplanar reformatted (MPR), and 3-dimensional (3D) virtual intravascular endoscopy (VIE) images. Image quality was assessed based on the degree of artifacts and their effect on the ability to visualize the configuration, intra-aortic location, and intraluminal appearance of the target vessel stents and measure their protrusion into the aortic lumen. RESULTS: There were 7 different multislice CT scanning protocols employed in the 21 patients (25 datasets, with 2 sets of follow-up images in 4 patients). The slice thicknesses and numbers (n) of studies included were 0.5 (n=3), 0.625 (n=6), 1.0 (n=1), 1.25 (n=9), 2.5 (n=3), 3.0 (n=1), and 5.0 mm (n=2). Of these CT protocols, images (especially 2D/3D reconstructions) acquired at 2.5, 3.0, and 5.0 mm were significantly compromised by interference from artifacts. Images acquired with a slice thickness of 1.0 or 1.25 mm were scored equal to or lower than those acquired with a submillimeter section thickness (0.5 or 0.625 mm), with minor degrees of artifacts resulting in acceptable image quality. CONCLUSION: Visualization of the target vessel stents depends on the appropriate selection of multislice CT scanning protocols. Our results showed that studies performed with a slice thickness of 1.0 or 1.25 mm produced similar image quality to those with a thickness of 0.5 or 0.625 mm. Submillimeter slices are not recommended in imaging patients treated with fenestrated stent-grafts, as they did not add additional information to the visualization.

Modeling of antegrade and retrograde flow into a branch artery of the aorta: implications for endovascular stent-grafting and extra-anatomical visceral bypass.

PURPOSE: To compare antegrade and retrograde flow characteristics in a branch of a conduit under typical pulsatile pressure and flows, seeking an answer to the question: "Does it matter whether inflow to a branch vessel is antegrade or retrograde?" METHODS: A model was built to simulate an abdominal aorta with a branch designed to approximate a typical renal artery. Experiments were conducted to measure the flow rates from 40- and 200-mm-long inflow conduit tubes simulating a branch with antegrade and retrograde inflow configurations. For the base case with a flush origin of the branch, the pressure difference between the main conduit and branch vessel was adjusted so that the average branch flow rate was 1.22 L/min, representing average renal artery flow. A pump produced a pulsatile 5-L/min flow of a glycerol/water solution through a tube to mimic blood flow through the aorta at a mean inlet pressure of 97 mmHg, with systolic and diastolic pressures of 121 and 78 mmHg, respectively. Computational fluid dynamics (CFD) simulations were performed for the flush, antegrade inflow, and retrograde inflow cases. The CFD-predicted flow rates at the branch vessel outlet for all 3 geometries were compared with the experiments. RESULTS: From the experiments, the mean time-average branch vessel outflow rate through a 40-mm conduit for the antegrade case was 1.22+/-0.01 L/min, which was the same as the retrograde case (1.21+/-0.01 L/min; within the experimental error). However, the branch vessel outflow flow rate through a 200-mm conduit for the retrograde case was 0.07 L/min lower than the antegrade. The results from the CFD model were in good agreement with the experiments. CONCLUSION: The experiments and CFD results suggest that there is negligible difference in the outflow rates to a branch vessel in antegrade and retrograde directions for 40-mm-long conduits. However, for a 200-mm conduit, the flow to a branch vessel through the retrograde path is lower than for the antegrade direction, which has implications for the insertion of branches to stent-grafts and extra-anatomical surgical bypass for visceral revascularization.

CT virtual intravascular endoscopy in the visualization of fenestrated stent-grafts.

PURPOSE: To report the diagnostic value of computed tomographic (CT) virtual intravascular endoscopy (VIE) in the assessment of patients with abdominal aortic aneurysm (AAA) treated with fenestrated endovascular grafts. METHODS: Eight patients (7 men; mean age 76 years, range 70-82) with AAAs unsuitable for open surgery or conventional endovascular repair had fenestrated endovascular grafts implanted. Both pre- and post-fenestration multislice CT data were used to generate VIE images of the visceral artery ostia and the side branch fenestrated stents. CT VIE images were compared with conventional 2-dimensional (2D) axial CT and multiplanar reformatted (MPR) images for the ability to visualize the intraluminal appearance of stents, as well as to measure the length of stents that protruded into the aortic lumen. RESULTS: Various fenestrations were deployed in 27 aortic branches. Scalloped and large fenestrations were implanted in 6 side branch ostia, respectively, and small fenestrations in 15 renal artery ostia. Fewer than half of the stents (37%) were found to be circular on VIE images, while the remaining stents were flared to varying extents at the inferior portion. The majority (96%) of stents protruded into the lumen up to 7.0 mm. Although the configuration of the side branch ostia changed to a variable extent, no significant difference was apparent between the diameters of branch ostia before and after fenestration (p>0.05). CONCLUSION: Our preliminary study shows that VIE proved superior to conventional 2D or MPR images in visualizing the final configuration of the fenestrated vessels and was comparable to the other techniques in measuring stent protrusion into the aortic lumen. VIE could be a valuable technique to identify any suspected abnormalities associated with fenestrated endovascular grafts by demonstrating the final intraluminal configuration of the stents in the fenestrated vessels.

Treatment of infrarenal abdominal aortic aneurysms with oversized (36-mm) Zenith endografts.

PURPOSE: To evaluate the outcome of treating infrarenal abdominal aortic aneurysms with unfavorable necks using the 36-mm Zenith endograft. METHODS: The indication for use of the 36-mm endograft for infrarenal aortic aneurysm was a minimum 20-mm-long sealing zone and a diameter >28 mm at any point but <34 mm, varying more than 3 mm in contour. A series of 67 patients (64 men; mean age 76.2 years, range 59.5 to 88.3) who had been treated with the 36-mm endografts between June 1999 and February 2004 were assessed for medium-term outcomes. The patients were identified from the device planning records. Follow-up was carried out using chart review and direct patient contact. The indication for use of the endograft was checked with the aneurysm neck profile from the original planning diagrams. Cause of death was ascertained from the treating clinician, the medical record, or the State Death Registry. Outcome endpoints were proximal type I and type III endoleaks, migration, sac size change, and death. RESULTS: The mean diameter of the sealing zone was 31.9+/-1.6 mm within the 20-mm segment from the lowest renal artery. Stent-graft delivery was achieved in all 67 patients. Two (3%) patients died within 30 days from non-graft-related cardiorespiratory causes. Proximal type I endoleaks were identified in 3 (4.5%) patients: 2 during deployment and another at 9 days. The mean follow-up period for the 65 patients who survived 30 days was 26.9+/-12.6 months (range 2-66). Migration occurred in 1 patient with development of a type III endoleak and sac reperfusion due to separation of the graft body from the bare anchor stent owing to suture breakage. Forty-seven patients were alive at the last review. The aneurysm sac had contracted or was unchanged in 45 (96%) cases. Minor enlargements of the sac were observed in 2 patients. The re-intervention rate was 16.4% (11 patients). There was 1 conversion to open repair to treat perigraft sepsis. The aneurysm- and procedure-related mortality was 4.5%; no patient experienced rupture. All-cause mortality was 29.9% (20/67). CONCLUSION: Large caliber endografts such as the Zenith 36-mm are an alternative option to open surgery or fenestrated endografting for some infrarenal aneurysms.