Phosphorylcholine-coated metallic stents in rabbit iliac and porcine coronary arteries

The arterial wall reaction to phosphorylcholine-coated metal stents was examined in rabbits and pigs. Compared to non-coated stents, no significant difference was found by angiography and histology. We conclude that although phosphorylcholine-coating does not provoke arterial neointima formation or decrease luminal diameter compared to stainless steel stents, the coating does not seem to reduce restenosis.

Interaction of alpha-phenyl-N-tert-butyl nitrone and alternative electron acceptors with complex I indicates a substrate reduction site upstream from the rotenone binding site

Mitochondrial complexes I, II, and III were studied in isolated brain mitochondrial preparations with the goal of determining their relative abilities to reduce O2 to hydrogen peroxide (H2O2) or to reduce the alternative electron acceptors nitroblue tetrazolium (NBT) and diphenyliodonium (DPI). Complex I and II stimulation caused H2O2 formation and reduced NBT and DPI as indicated by dichlorodihydrofluorescein oxidation, nitroformazan precipitation, and DPI-mediated enzyme inactivation. The O2 consumption rate was more rapid under complex II (succinate) stimulation than under complex I (NADH) stimulation. In contrast, H2O2 generation and NBT and DPI reduction kinetics were favored by NADH addition but were virtually unobservable during succinate-linked respiration. NADH oxidation was strongly suppressed by rotenone, but NADH-coupled H2O2 flux was accelerated by rotenone. Alpha-phenyl-N-tert-butyl nitrone (PBN), a compound documented to inhibit oxidative stress in models of stroke, sepsis, and parkinsonism, partially inhibited complex I-stimulated H2O2 flux and NBT reduction and also protected complex I from DPI-mediated inactivation while trapping the phenyl radical product of DPI reduction. The results suggest that complex I may be the principal source of brain mitochondrial H2O2 synthesis, possessing an "electron leak" site upstream from the rotenone binding site (i.e., on the NADH side of the enzyme). The inhibition of H2O2 production by PBN suggests a novel explanation for the broad-spectrum antioxidant and antiinflammatory activity of this nitrone spin trap.

Human recombinant alpha 2-HS glycoprotein is produced in insect cells as a full length inhibitor of the insulin receptor tyrosine kinase

Human Alpha 2-HS glycoprotein (AHSG), a glycoprotein synthesized by hepatocytes, was expressed in insect cells using the recombinant baculovirus system. The protein was purified from the cell supernatant, and appeared as a single band at about 52 kDa. Western blot using a specific antibody to the B-chain of AHSG indicated that the connecting peptide was present in the protein. When incubated with solubilized insulin receptors, recombinant AHSG inhibited the tyrosine kinase activity of the receptors in a dose-dependent fashion at concentrations in the range of those of the circulating protein. AHSG did not interfere with the binding of insulin to its receptor. These results indicate that human AHSG represents a natural inhibitor of the insulin receptor tyrosine kinase, is active as a single-chain protein and possesses a biological role similar to that of its homologue in rats, pp63, described by Auberger et al. (1).

Ejection has both positive and negative effects on left ventricular isovolumic relaxation

In isovolumically beating hearts, the speed of left ventricular (LV) relaxation is uniquely determined by peak active stress (sigma max). In contrast, such a succinct description of relaxation is lacking for the ejection beats, although ejection is generally thought to hasten relaxation. We set out to determine how ejection modifies the relaxation-sigma max relationship obtained in the isovolumically beating hearts. Experiments were performed on five isolated rabbit hearts subjected to various loading conditions. Instantaneous LV pressure and volume were recorded and converted to active stress, from which isovolumic relaxation time (Tr) was defined as the time for stress to fall from 75 to 25% of sigma max (isovolumic beats) or its end-ejection value (ejection beats). Steady-state and transient isovolumic beat and steady-state ejection beat data were used to develop a multiple regression model. This model identified stress, current beat ejection, and previous beat ejection history as independent predictor variables of Tr and fit the data well in all hearts (r2 > 0.98). Furthermore, this model could predict relaxation in transient ejection beats (r2 = 0.30 for all hearts). Whereas the coefficient for the current beat ejection was negative (i.e., negative effect or hastening relaxation), the ejection history coefficient was positive (i.e., positive effect or slowing relaxation). The sum of these two coefficients was negative, corresponding to the commonly observed net negative effect of ejection on relaxation. The expected positive inotropic effect of ejection was also observed. The dissipations of both positive inotropic and relaxation effects were slow, suggesting a nonmechanical underlying mechanism(s). We postulate that these two effects are linked and caused by ejection-mediated changes in myofilament Ca2+ sensitivity.

Effects of overexpression of glutamine:fructose-6-phosphate amidotransferase (GFAT) and glucosamine treatment on translocation of GLUT4 in rat adipose cells

Insulin resistance is associated with diabetes. Hyperglycemia per se causes insulin resistance as well as increased flux of glucose through the hexosamine biosynthetic pathway. The rate-limiting enzyme for entry of glucose into this pathway is glutamine:fructose-6-phosphate amidotransferase (GFAT). To directly evaluate the role of GFAT in modulating insulin-stimulated glucose transport, we co-transfected primary cultures of rat adipose cells with expression vectors for human GFAT as well as an epitope-tagged GLUT4 and examined the effect of overexpressed GFAT on insulin-stimulated translocation of GLUT4. When we measured cell surface tagged GLUT4 in response to insulin, cells overexpressing GFAT and tagged GLUT4 had an insulin-dose response curve that was similar to that of control cells expressing only tagged GLUT4. As an alternative means of increasing flux through the hexosamine biosynthetic pathway, we incubated adipose cells with glucosamine (a substrate of the pathway downstream from GFAT) and insulin. Interestingly, for short incubation times (4 h) we observed a decrease in both basal and insulin-stimulated glucose transport without a detectable effect on insulin-stimulated translocation of GLUT4. However, for longer incubation times (16 h), we observed a significant decrease in the amount of GLUT4 in the plasma membrane. Our data suggest that products of the hexosamine biosynthetic pathway may cause insulin resistance, in part, by acutely decreasing intrinsic activity of GLUT4 as well as chronically altering the amount of GLUT4 at the cell surface.

Effect of intravascular irradiation on cell proliferation, apoptosis, and vascular remodeling after balloon overstretch injury of porcine coronary arteries

BACKGROUND

Ionizing radiation has been shown to reduce vascular lesion formation after balloon overstretch injury of pig coronary arteries. The present series of experiments examines the mechanism by which this occurs.

METHODS AND RESULTS

Balloon injury was performed on porcine coronary arteries, followed immediately by ionizing radiation using either a source train of 90Sr/Y or 192Ir seeds designed to deliver 14 or 28 Gy at a depth of 2 mm from the source. The animals were killed 3, 7, or 14 days after injury. Bromodeoxyuridine was administered 24 hours before euthanasia to label proliferating cells. Cell proliferation was significantly reduced on day 3 in the adventitia and media of the irradiated vessels compared with controls. Two weeks after injury, there were fewer alpha-actin-positive myofibroblasts in the adventitia of the irradiated vessels than in nonirradiated controls, and morphometric analysis indicated that the vessel perimeter of the irradiated vessels was significantly larger than in controls. Together, these results suggest a positive effect of intravascular irradiation on vascular remodeling. Apoptosis was estimated by terminal transferase dUTP-biotin nick-end labeling (TUNEL) 3 and 7 days after injury. TUNEL-labeled cells were found primarily in the adventitia at the medial tear, but no differences were detected between irradiated and control vessels.

CONCLUSIONS

These studies suggest that intracoronary radiation primarily inhibits the first wave of cell proliferation in the vessel wall and demonstrates a favorable effect on late remodeling by preventing adventitial fibrosis at the injury site.

Mechanism of glibenclamide inhibition of cystic fibrosis transmembrane conductance regulator Cl- channels expressed in a murine cell line

1. The sulphonylurea drug glibenclamide is a widely used inhibitor of the cystic fibrosis transmembrane conductance regulator (CFTR). To investigate how glibenclamide inhibits CFTR, we studied CFTR Cl- channels using excised inside-out membrane patches from cells expressing wild-type human CFTR. 2. Addition of glibenclamide (10-100 microM) to the intracellular solution caused a concentration-dependent decrease in the open time of CFTR Cl- channels, but closed times did not change. This suggests that glibenclamide is an open-channel blocker of CFTR. 3. Glibenclamide is a weak organic acid. Acidification of the intracellular solution relieved glibenclamide inhibition of CFTR, suggesting that the anionic form of glibenclamide inhibits CFTR. 4. To begin to identify the glibenclamide binding site in CFTR, we investigated whether glibenclamide competes with either MgATP or Cl- ions for a common binding site. Glibenclamide inhibition of CFTR was unaffected by nucleotide-dependent stimulation of CFTR, suggesting that glibenclamide and intracellular MgATP interact with CFTR at distinct sites. 5. Glibenclamide inhibition of CFTR was voltage dependent and enhanced when the external Cl- concentration was decreased. The data suggest that glibenclamide and Cl- ions may compete for a common binding site located within a large intracellular vestibule that is part of the CFTR pore.

Intracoronary radiation decreases the second phase of intimal hyperplasia in a repeat balloon angioplasty model of restenosis

PURPOSE

Repeat balloon angioplasty is likely to induce intimal proliferation, which is associated with a higher restenosis rate. This study examined the effect of intracoronary ionizing radiation on restenotic lesions using repeat balloon injury in a normolipemic swine.

METHODS AND MATERIALS

Eight domestic normolipemic pigs underwent overstretch balloon angioplasty with a 3.5 mm balloon in the LAD and LCX, followed by repeat balloon injury at the same sites 4 weeks after the initial injury. At that time a high activity 192Iridium source was introduced immediately after the angioplasty by random assignment to deliver 14 Gy at 2 mm in eight of the injured coronary arteries (LAD and LCX). One month later the animals were killed and the coronary arteries pressure perfusion fixed. Serial sections were stained with H&E and VVG, then evaluated by histopathologic and morphometric techniques. Maximal intimal thickness (MIT), intimal area (IA), and intimal area corrected for the extent of injury (IA/FL) were measured in the irradiated and control arteries and were compared to control arteries with single injuries from previous studies.

RESULTS

Repeat balloon injury induced significant additional medial damage, which was associated with marked intimal hyperplasia in a concentric pattern. Intracoronary irradiation significantly decreased the total of neointima area formation (IA 93 + 0.35 mm2 compared to control 1.38 + 0.33 mm2 p < 0.01) and the MIT was also significantly reduced in the irradiated vessels (0.57 + 0.18 mm vs. 0.71 + 0.08 mm, p = 0.05).

CONCLUSIONS

Intracoronary irradiation immediately after the second balloon dilatation inhibits the intimal hyperplasia due to that injury. However, there was no effect on the existing neointima from the initial injury.

Endoluminal local delivery of PCNA/cdc2 antisense oligonucleotides by porous balloon catheter does not affect neointima formation or vessel size in the pig coronary artery model of postangioplasty restenosis

Localized delivery of antisense oligonucleotides directed against cell cycle regulatory proteins has been proposed as a means to prevent restenosis after angioplasty. To test whether single endoluminal delivery of a combination of proliferating cell nuclear antigen (PCNA) and cell-division cycle 2 kinase (cdc2) antisense might affect restenosis, we delivered 2 ml of lipid-complexed PCNA/cdc2 antisense oligomers (1.35 mg) to the coronary arteries of pigs after balloon overstretch angioplasty (AS group) and performed planimetric histomorphometry on arterial sections of the tissue, harvested at 4 wk. Compared with controls receiving 3'-5' reversed sequence oligomers (REV group), there were no differences in absolute intimal area (AS 1.36 +/- 0.08 mm2, REV 1.23 +/- 0.10 mm2, P = NS), intimal area normalized to extent of injury (AS 0.67 +/- 0.03, REV 0.77 +/- 0.10, P = NS), or vessel perimeter (AS 7.72 +/- 0.19 mm, REV 7.36 +/- 0.22 mm, P = NS). We conclude that single endoluminal delivery of antisense against key cell cycle regulatory proteins does not affect neointima formation or vessel size in this model of restenosis.

Pharmacokinetics and tissue localization of antisense oligonucleotides in balloon-injured pig coronary arteries after local delivery with an iontophoretic balloon catheter

When delivered locally to the arterial wall by passive fluid transfer systems such as perforated balloons, water-soluble compounds in aqueous solution are not readily taken up by tissue, show low levels of cellular localization, and are quickly lost by wash-out. One approach to improve delivery is addition of an "active" component to the catheter system to change the nature of the drug-to-tissue interaction. Using an iontophoretic balloon catheter to deliver antisense oligonucleotide (ODN) to pig coronary arteries after balloon angioplasty, we determined the quantity and localization of ODN in the tissue. By radiolabeling, 7.3 +/- 2.4 micrograms ODN was present at 30 min, 1.5 +/- 0.6 at 2 h, 0.52 +/- 0.35 at 24 h, and 0.26 +/- 0.11 at 7 d. By fluorescent labeling, circumferential medial uptake and adventitial delivery at the site of medial injury was observed, with primarily cellular localization. The iontophoretic catheter thus appears to be a useful device for ODN delivery to arterial tissue.

Increased activity of the hexosamine synthesis pathway in muscles of insulin-resistant ob/ob mice

Enhanced glucose flux via the hexosamine biosynthetic pathway has been implicated in insulin resistance. We measured products of this pathway, UDP-N-acetyl hexosamines (UDP-HexNAc), and activity of the rate-limiting enzyme L-glutamine:D-fructose-6-phosphate amidotransferase (GFAT) in tissues of ob/ob mice and lean controls. Ob/ob mice were obese, hyperglycemic, and hyperinsulinemic. Resistance to the effect of insulin on glucose transport was demonstrated in isolated soleus muscles, although total GLUT-4 concentration was mildly increased in muscles from ob/ob mice. UDP-HexNAc concentrations in hindlimb muscles decreased between 8 and 17 wk but were always higher in ob/ob vs. controls (P < 0.001, mean increase 67%). Concentrations of UDP-hexoses and GDP-mannose were similar in ob/ob and control muscles. Muscle GFAT activity declined with age but was increased in ob/ob vs. controls at each age examined (P < 0.001, mean increase 108%). UDP-HexNAc concentrations and GFAT activity were similar in livers of ob/ob and controls. These data suggest that glucose flux via the hexosamine pathway is selectively increased in muscle but not liver of ob/ob mice and may contribute to muscle insulin resistance in this model of non-insulin-dependent diabetes mellitus.

Effects of exercise and feeding on the hexosamine biosynthetic pathway in rat skeletal muscle

Products of the hexosamine biosynthesis pathway (HSNP) have been implicated in glucose-induced insulin resistance. We measured the major products of HSNP, UDP-N-acetyl hexosamines (UDP-HexNAc), and the activity of L-glutamine: D-fructose-6-phosphate amidotransferase (GFAT, rate-limiting enzyme) in rat hindlimb muscles immediately after exercise and 1, 3, and 16 h postexercise (swimming) in fed and fasted rats and sedentary controls. Muscle glycogen decreased by 50-75% postexercise. In sedentary rats, muscle GFAT activity decreased by approximately 30% (P < 0.002) after an 18-h fast. GFAT activity was not affected by exercise under any condition. Muscle UDP-HexNAc increased approximately 30% postexercise (P < 0.01) in ad libitum-fed but not in fasted rats. UDP-HexNAc remained elevated (approximately 30%, P < 0.002) for 16 h if animals were fed postexercise. Concentrations of UDP-hexoses, GDP-mannose, and UDP were unchanged postexercise. Conclusions are that muscle GFAT activity is regulated by the nutritional state but not by acute exercise. Glucose flux via HNSP may be increased postexercise in muscles of ad libitum-fed rats. Increased HSNP products may serve as negative feedback regulators to limit excessive muscle glycogen deposition postexercise.

Selective degeneration fo Purkinje cells with Lewy body-like inclusions in aged NFHLACZ transgenic mice

Transgenic (NFHLacZ) mice expressing a fusion protein composed of a truncated high-molecular-weight mouse neurofilament (NF) protein (NFH) fused to beta-galactosidase (LacZ) develop inclusions in neurons throughout the CNS. These inclusions persist from birth to advanced age and contain massive filamentous aggregates including all three endogenous NF proteins and the NFHLacZ fusion protein. Further, the levels of endogenous NF proteins are selectively reduced in NFHLacZ mice. Because these inclusions resemble NF-rich Lewy bodies (LBs) in Parkinson's disease and LB dementia, we asked whether these lesions compromised the viability of affected neurons during aging. We studied hippocampal CA1 neurons, nearly all of which harbored inclusions (type I) devoid of cellular organelles, and cerebellar Purkinje cells, nearly all of which accumulated inclusions (type II) containing numerous entrapped organelles. Purkinje cells with type II inclusions began to degenerate in the NFHLacZ mice at approximately 1 year of age, and most were eliminated by 18 months of age. In contrast, there was no significant loss of type I inclusion-bearing CA1 neurons with age. These data suggest that the sequestration of cellular organelles in type II inclusions may isolate and impair the function of these organelles, thereby rendering Purkinje cells selectively vulnerable to degeneration with age as in neurodegenerative diseases of the elderly characterized by accumulation of LBs.

Local intracoronary heparin delivery with a microporous balloon catheter

Arterial thrombosis plays a major role in the pathogenesis of acute coronary syndromes such as unstable angina and acute myocardial infarction. Heparin is efficacious in treating both disorders; however, systemically administered heparin is associated with bleeding complications. Local intracoronary delivery of heparin may be a safer, more effective method of administration. This study was performed to determine the fate of heparin infused with a specially designed catheter for local intracoronary delivery. To quantitate heparin delivery, tritiated-labeled heparin was dissolved in a solution of unlabeled heparin (1,000 U/ml). A microporous balloon catheter was placed in the left anterior descending (LAD) and left circumflex arteries of anesthetized pigs (n = 15), and 1 ml of the heparin solution was infused. The animals were euthanized within 1 hour, and the treated arteries and controls were harvested, processed, and the tritiated activity was measured. To assess the distribution of the heparin in the arterial wall, 1 ml of fluorescein-isothiocyanate (FITC)-labeled heparin was locally delivered into the walls of the LAD and left circumflex arteries with the microporous balloon catheter. To visualize the dynamic fluid transfer of the device, a microporous balloon catheter was inflated in the LAD, and 1 ml of diluted contrast medium was infused under cinefluoroscopy. The arteries treated with tritiated-labeled heparin contained 0.6% +/- 0.2% of the infused heparin dose. Control arteries contained 0.01% of the administered heparin. Animals that were infused with FITC-labeled heparin displayed fluorescence throughout all layers of the artery, especially in the adventitia. In animals that were injected with 1 ml of diluted contrast medium through the microporous balloon, a relatively large amount of the infusate appeared in the arterial lumen proximal to the balloon. In conclusion, these results suggest that heparin can be delivered to coronary arteries with a microporous balloon catheter. However, <1% of the infused dose can be found in the artery 1 hour after delivery. Infused heparin is distributed throughout the arterial wall, but most of the infused solution appears in the arterial lumen proximal to the inflated balloon and is probably washed downstream after balloon deflation.

Differential effects of GLUT1 or GLUT4 overexpression on hexosamine biosynthesis by muscles of transgenic mice

Transgenic mice that overexpress GLUT1 or GLUT4 in skeletal muscle were studied; the former but not the latter develop insulin resistance. Because increased glucose flux via the hexosamine biosynthesis pathway has been implicated in glucose-induced insulin resistance, we measured the activity of glutamine:fructose-6-phosphate amidotransferase (GFAT; rate-limiting enzyme) and the concentrations of UDP-N-acetyl hexosamines (major products of the pathway) as well as UDP-hexoses and GDP-mannose in hind limb muscles and liver in both transgenic models and controls. GFAT activity was increased 60-70% in muscles of GLUT1 but not in GLUT4 transgenics. GFAT mRNA abundance was unchanged. The concentrations of all nucleotide-linked sugars were increased 2-3-fold in GLUT1 and were unchanged in GLUT4-overexpressing muscles. Similar results were obtained in fed and fasted mice. GFAT and nucleotide sugars were unchanged in liver, where the transgene is not expressed. We concluded that 1) glucose transport appears to be rate limiting for synthesis of nucleotide sugars; 2) chronically increased glucose flux increases muscle GFAT activity posttranscriptionally; 3) increased UDP-glucose likely accounts for the marked glycogen accumulation in muscles of GLUT1-overexpressing mice; and 4) glucose flux via the hexosamine biosynthetic pathway is increased in muscles of GLUT1-overexpressing but not GLUT4-overexpressing mice; products of the pathway may contribute to insulin resistance in GLUT1 transgenics.

Echocardiographic contrast agents and left ventricular contractility: evaluation using an isolated rabbit heart model

The effects of Albunex (Molecular Biosystems, Inc., San Diego, Calif.) and a second generation contrast agent, FS069, on left ventricular (LV) contractility were evaluated using an isolated rabbit heart model under constant loading conditions and heart rate. Contrast injections (2 ml total volume) were performed in two separate protocols (N1 = 6, N2 = 6). In protocol 1, various doses of Albunex (0.1 to 2.0 ml in saline solution) were used, and paired control injections of a matched dose of 5% solution of human albumin in saline solution were administered. In protocol 2, LV contractility was assessed during injections of the following solutions: (1) 1:250 suspension of FS069 in saline solution, which caused optimal myocardial contrast enhancement; (2) a 1:25 suspension of FS069; (3) a 1:25 suspension of FS069 prefiltered using an 8 microns pore filter; and (4) 2 ml saline solution as a control. Instantaneous LV pressure was analyzed for variations in peak systolic pressure (peak P) and maximum pressure derivative (peak P'), both indices of LV contractility under conditions of fixed heart rate and chamber volume. Albumin alone caused a transient, dose-dependent depression of LV contractility, reflected by decreases in both peak P and peak P' values. These decreases presumably were caused by the decreasing availability of ionized calcium as a result of calcium binding. No further decrease in contractility was noted when Albunex microspheres were present in the solution. Saline injections caused a transient minor increase in LV contractility, reflected by increases of 4.5% +/- 1.1% and 10.6% +/- 3.8% in peak P and peak P' values, respectively. These levels returned to baseline levels within 2 minutes. A similar response was observed when a 1:250 suspension of FS069 was used. The 1:25 suspension of FS069 caused a bimodal response, with initial rises in peak P and peak P' levels (5.2% +/- 3.6% and 12.8% +/- 6.5%, respectively), followed by minor reductions in contractility (2.0% +/- 2.4% and 1.7% +/- 2.1%, respectively). The latter decrease in contractility caused by the 1:25 suspension of FS069 was eliminated by filtering. The isolated rabbit heart model is a highly sensitive tool that allows accurate and direct assessment of possible adverse effects of intravascular contrast agents on LV contractility. Using this model, we showed that neither Albunex microspheres nor FS069 microspheres impaired myocardial contractility.

Long-term intracoronary stent placement: arteriographic and histologic results after 7 years in a dog model

Prosthetic intracoronary stenting has become an important adjunct to balloon angioplasty in the percutaneous treatment of coronary artery disease. However, there are few reports of the long-term histologic consequences of stenting in the world literature. We report the arteriographic, histologic, and ultrastructural examination of a flexible tantalum wire coil stent implanted in the coronary artery of a dog for 7 years. The vessel was arteriographically patent without evidence of either stenosis or ectasia. The stent had been incorporated into the arterial wall, and was covered with a neointima of approximately 100 microns maximum thickness. There was necrosis of the tunica media adjacent to the stent but the inflammatory response was restricted to occasional macrophages in the neointima of the immediate vicinity of the stent wire. The endothelial cell layer was normal in its morphologic appearance. In summary, the flexible tantalum wire coil stent was well tolerated by the host blood vessel and demonstrated acceptable biocompatibility for the 7-year duration of its implantation in the normal dog coronary artery.

Wave propagation in coupled left ventricle-arterial system. Implications for aortic pressure

The objective of this study was to examine the effects of wave propagation properties (global reflection coefficient gamma IG; pulse wave velocity, c(ph); and characteristic impedance zeta(o) on the mechanical performance of the coupled left ventricle-arterial system. Specifically, we sought to quantify effects on aortic pressure (P(ao)) and flow Q(ao) while keeping constant other determinants of P(ao) and Q(ao) (left ventricular end-diastolic volume, V(ed), and contractility, heart rate, and peripheral resistance, R(s)). Isolated rabbit hearts were subjected to real-time, computer-controlled physiological loading. The arterial circulation was modeled with a lossless tube terminating in a complex load. The loading system allowed for precise and independent control of all arterial properties as evidenced by accurate reproduction of desired input impedances and computed left ventricular volume changes. While propagation phenomena affected P(ao) and Q(ao) morphologies as expected, their effects on absolute P(ao) values were often contrary to the current understanding. Diastolic (Pd) and mean (Pm) P(ao) and stroke volume decrease monotonically with increases in gamma G, c(ph), or zeta(o) over wide ranges. In contrast, these increase had variable effects on peak systolic P(ao) (Ps): decreasing with gamma G, biphasic with c(ph), and increasing with zeta(o). There was an interaction between gamma G and c(ph) such that gamma G effects on P(m) and P(d) were augmented a higher C(ph) and vice versa. Despite large changes in system parameters, effects on Pm and Ps were modest ( < 10% and < 5%, respectively); effects on Pd were always two to four times greater. Similar results were obtained when the single-tube model of the arterial system was replaced by an asymmetrical T-tube configuration. Our data do not support the prevailing hypothesis that P(s) (and therefore ventricular load) can be selectively and significantly altered by manipulating gamma G, c(ph), and/or zeta o.

Transgenic mice carrying a human mutant superoxide dismutase transgene develop neuronal cytoskeletal pathology resembling human amyotrophic lateral sclerosis lesions

Mutations in the human Cu,Zn superoxide dismutase gene (SOD1) are found in 20% of kindreds with familial amyotrophic lateral sclerosis. Transgenic mice (line G1H) expressing a human SOD1 containing a mutation of Gly-93 --> Ala (G93A) develop a motor neuron disease similar to familial amyotrophic lateral sclerosis, but transgenic mice (line N1029) expressing a wild-type human SOD1 transgene do not. Because neurofilament (NF)-rich inclusions in spinal motor neurons are characteristic of amyotrophic lateral sclerosis, we asked whether mutant G1H and/or N1029 mice develop similar NF lesions. NF inclusions (i.e., spheroids, Lewy body-like inclusions) were first detected in spinal cord motor neurons of the G1H mice at 82 days of age about the time these mice first showed clinical evidence of disease. Other neuronal intermediate filament proteins (alpha-internexin, peripherin) also accumulated in these spheroids. The onset of accumulations of ubiquitin immunoreactivity in the G1H mice paralleled the emergence of vacuoles and NF-rich spheroids in neurons, but they did not colocalize exclusively with spheroids. In contrast, NF inclusions were not seen in the N1029 mice until they were 132 days old, and ubiquitin immunoreactivity was not increased in the N1029 mice even at 199 days of age. Astrocytosis in spinal cord was associated with a marked increase in glial fibrillary acidic protein immunoreactivity in the G1H mice, but not in the N1029 mice. Finally, comparative studies revealed a striking similarity between the cytoskeletal pathology in the G1H transgenic mice and in patients with amyotrophic lateral sclerosis. These findings link a specific SOD1 mutation with alterations in the neuronal cytoskeleton of patients with amyotrophic lateral sclerosis. Thus, neuronal cytoskeletal abnormalities may be implicated in the pathogenesis of human familial amyotrophic lateral sclerosis.

Contrast echocardiographic quantification of regional myocardial perfusion: validation with an isolated rabbit heart model

Quantification of regional myocardial tissue blood flow (RMBF) based on contrast echocardiography has yet to be achieved. This study validated our recently proposed algorithm for quantification of RMBF with colored microspheres. Experiments were carried out in an isolated rabbit heart preparation (n = 11). Aortic root injections of perfluoropropane-filled albumin microsphere solution (FS069) and colored microspheres were performed at five levels of coronary flow achieved by altering perfusion pressure. During each injection of contrast material, consecutive end-diastolic images of the heart and an extracardiac reference chamber were acquired with a 7.5 MHz transducer and digitized. Time-intensity curves from the reference chamber and myocardial regions of interest, corresponding to the anatomic segments used for colored microsphere analysis, were analyzed for RMBF. Blood flow was calculated as the intravascular volume fraction (ratio of areas under myocardial and reference curves) divided by mean transit time (deconvolution of impulse response) and compared with those obtained with colored microspheres. Injections of FS069 resulted in highly reproducible enhancement of myocardial contrast. Analysis of time-intensity curves provided consistent measurements of RMBF (r = 0.91), which correlated highly with microsphere data (r = 0.84). The use of this new algorithm allows accurate quantification of RMBF in the isolated heart model. Further validation of this approach in an animal model with peripheral intravenous injections of contrast material will allow noninvasive clinical measurements of RMBF.

Characterization of a mutant GLUT4 lacking the N-glycosylation site: studies in transfected rat adipose cells

GLUT4, the insulin-responsive glucose transporter expressed primarily in muscle and adipose tissue, contains a single N-glycosylation site. We characterized a mutant GLUT4 lacking the N-glycosylation site (Asn57-->Gln) in primary cultures of rat adipose cells. We transiently transfected cells with expression vectors for epitope-tagged GLUT4 containing either wild-type (GLUT4-HA) or mutant (GLN57-HA) cDNA sequences. Expression of GLN57-HA in adipose cells was approximately 10-fold lower than for GLUT4-HA even though mRNA levels for both recombinant transporters were comparable. Biosynthetic labeling studies showed markedly decreased incorporation of [35S]-methionine/cysteine into GLN57-HA relative to GLUT4-HA consistent with either a decreased synthetic rate or accelerated degradation of GLN57-HA. Interestingly, transient transfection of GLUT4-HA and GLN57-HA in COS-7 cells (which do not express endogenous GLUT4) resulted in comparable levels of protein expression for both transporters. Thus, in the physiologically relevant adipose cell, glycosylation of GLUT4 appears to play an important functional role.

Effects of diabetes and hyperglycemia on the hexosamine synthesis pathway in rat muscle and liver

In vitro studies suggested that increased flux of glucose through the hexosamine biosynthesis pathway (HexNSP) contributes to glucose-induced insulin resistance. Glutamine:fructose-6- phosphate amidotransferase (GFAT) catalyzes glucose flux via HexSNP; its major products are uridine diphosphate (UDP)-N-acetyl hexosamines (UDP-HexNAc). We examined whether streptozotocin (STZ)-induced diabetes (4-10 days) or sustained hyperglycemia (1-2 h) in normal rats alters absolute or relative concentrations of nucleotide-linked sugars in skeletal muscle and liver in vivo. UDP-HexNAc and UDP-hexoses (UDP-Hex) were increased and decreased, respectively, in muscles of diabetic rats, resulting in an approximately 50% increase in the UDP-HexNAc:UDPHex ratio (P < 0.01). No significant changes in nucleotide sugars were observed in livers of diabetic rats. In muscles of normal rats, UDP-HexNAc concentrations increased (P < 0.01) and UDP-Hex decreased (P < 0.01) during hyperglycemia. The UDP-HexNAc:UDP-Hex ratio increased approximately 40% (P < 0.01) and correlated strongly with plasma glucose concentrations. Changes in liver were similar to muscle but were less marked. GFAT activity in muscle and liver was unaffected by 1-2 h of hyperglycemia. GFAT activity decreased 30-50% in muscle, liver, and epididymal fat of diabetic rats, and this was reversible with insulin therapy. No significant change in GFAT mRNA expression was detected, suggesting post-transcriptional regulation. The data suggest that glucose flux via HexNSP increases in muscle during hyperglycemic hyperinsulinemia and that the relative flux of glucose via HexNSP is increased in muscle in STZ-induced diabetes.(ABSTRACT TRUNCATED AT 250 WORDS)

Intracoronary low-dose beta-irradiation inhibits neointima formation after coronary artery balloon injury in the swine restenosis model

BACKGROUND

Neointima formation contributing to recurrent stenosis remains a major limitation of percutaneous transluminal angioplasty. Endovascular low-dose gamma-irradiation has been shown to reduce intimal thickening (hyperplasia) after balloon overstretch injury in pig coronary arteries, a model of restenosis. The objective of this study was to determine whether the use of a beta-emitting radioisotope for this application would have similar effects and to examine the dose-response relations with this approach.

METHODS AND RESULTS

Normal domestic pigs underwent balloon overstretch injury in the left anterior descending and left circumflex and coronary arteries. A flexible catheter was introduced by random assignment into one of these arteries and was afterloaded with a 2.5-cm ribbon of encapsulated 90Strontium/90Yttrium sources (90Sr/Y, a pure beta-emitter). It was left in place for a period of time sufficient to deliver one of four doses: 7, 14, 28, or 56 Gy, to a depth of 2 mm. Animals were killed 14 days after balloon injury, the coronary vasculature was pressure-perfusion fixed, and histomorphometric analysis of arterial cross sections was performed. All arteries treated with radiation demonstrated significantly decreased neointima formation compared with control arteries. The ratio of intimal area to medial fracture length was inversely correlated with increasing radiation dose: control (no radiation), 0.47; 7 Gy, 0.34; 14 Gy, 0.20; 28 Gy, 0.08; and 56 Gy, 0.02 (r = -.78, P < .000001). Scanning electron microscopy demonstrated a confluent layer of endothelium-like cells both in control and in 14 Gy-irradiated arteries. There was neither evidence of significant necrosis nor excess fibrosis in the media, adventitia, or perivascular space of the coronary arteries or adjacent myocardium in the irradiated groups. Furthermore, the exposure to the staff and the total body exposure to the pig with the beta source was a small fraction of the dose previously measured and calculated with 192Ir, a gamma-emitting radioisotope.

CONCLUSIONS

Administration of endovascular beta-radiation to the site of coronary arterial overstretch balloon injury in pigs with 90Sr/Y is technically feasible and safe. Radiation doses between 7 and 56 Gy showed evidence of inhibition of neointima formation. A dose-response relation was demonstrated, but no further inhibitory effect was seen beyond 28 Gy. These data suggest that intracoronary beta-irradiation is practical and feasible and may aid in preventing clinical restenosis.

Intracoronary radiation before stent implantation inhibits neointima formation in stented porcine coronary arteries

BACKGROUND

Stent implantation has been shown to reduce restenosis by establishing a larger lumen but not by reducing neointima formation. We have previously shown that ionizing radiation reduced neointima formation after balloon injury in a swine model of restenosis. The purpose of this study was to determine whether endovascular irradiation of the coronary artery before stent implantation would affect neointima formation.

METHODS AND RESULTS

Nine normolipemic pigs underwent coronary angiography, and segments of the left anterior descending and left circumflex arteries were chosen as targets for stenting. A high-activity 192Ir source was used to deliver 14 Gy by random assignment to one of the vessels. After this, 3.5-mm tantalum stents were implanted in both arteries. Three additional pigs were treated with a 90Sr/Y source (a pure beta-emitter) delivering 14 Gy to five segments of coronary vessels that were stented immediately after irradiation. Stent-to-artery ratio was similar in the radiated and the control arteries. Animals received aspirin 325 mg daily and were killed at 28 days. The intimal area was significantly reduced in the irradiated stented arteries compared with control arteries treated with stent only (1.98 mm2 with 192Ir and 2.53 mm2 with 90Sr/Y versus 3.82 mm2 in the control stented arteries, P < .005).

CONCLUSIONS

Endovascular radiation before coronary stenting reduces neointima formation and may further reduce the restenosis rate after stent implantation.

Chemical and immunological heterogeneity of fibrillar amyloid in plaques of Alzheimer's disease and Down's syndrome brains revealed by confocal microscopy

Amyloid beta peptides (A beta) are deposited in the brains of Alzheimer's disease (AD) and elderly Down's syndrome (DS) patients in a variety of amyloid plaques. Among these are classical plaques composed of a spherical core and corona. Analyzing AD tissue sections single and double stained with anti-A beta antibodies and thioflavin S (thioS) by bright field, fluorescence, and confocal microscopy revealed that spherical plaque cores consist of a thioS-positive center and an anti-A beta antibody immunoreactive rim. This indicates that there is a fibrillar form of amyloid that is thioS positive but not immunoreactive with anti-A beta antibodies. In contrast, classical plaques in DS patients have irregular cores that are thioS positive as well as anti-A beta immunoreactive. In addition, a subset of plaques in both DS and AD patients have a distinct "fibrous" appearance when stained with thioS, but are amorphous when immunostained. These findings suggest that anti-A beta antibodies and thioS stain similar; as well as different forms of fibrillar amyloid. A beta may become thioS positive by interacting with one or more of its known molecular chaperons, and this may be important for the pathogenesis of AD, given that thioS-positive A beta deposits are associated with neuritic and synaptic damage.

Transplanted human neurons derived from a teratocarcinoma cell line (NTera-2) mature, integrate, and survive for over 1 year in the nude mouse brain

Retinoic acid (RA) induces a human teratocarcinoma cell line (NTera-2 or NT2) to give rise exclusively to post-mitotic neuron-like (NT2N) cells, but NT2N cells never acquire a fully mature neuronal phenotype in vitro. To determine whether NT2N cells can mature into adult neuron-like cells in vivo, purified NT2N cells were grafted into different regions of the central nervous system (CNS) of adult and neonatal athymic mice, and the grafts were examined immunohistochemically by light, confocal, and electron microscopy using antibodies to a panel of developmentally regulated neuronal polypeptides. NT2N grafts were distinguished from endogenous mouse neurons with antibodies that recognize human or murine specific epitopes in selected neuronal polypeptides. Viable NT2N cells were identified in > 89% of graft recipients (N = 90), and some grafts survived 14 months. Within 3 weeks of implantation, grafted NT2N cells re-extended their processes, and the location of the grafts (e.g., septum versus neocortex) appeared to determine the extent to which processes were elaborated. Within the early post-transplantation period, grafted NT2N cells expressed the same neuronal polypeptides as their in vitro counterparts. However, between 6 weeks and 4-6 months post-implantation, the grafted NT2N cells progressively acquired the molecular phenotype of fully mature in vivo neurons as evidenced by dramatically increased expression of the most highly phosphorylated isoforms of the heavy neurofilament subunit, and the de novo expression of adult CNS tau. Notably, the time course for the extension of processes and the expression of neuronal polypeptides by NT2N grafts was similar in neonatal and adult mice. Although grafted NT2N cells formed synapse-like structures and elaborated dendrites and axons, these axons remained unmyelinated. Finally, none of the transplanted NT2N cells reverted to a neoplastic state. These studies demonstrate that pure populations of grafted human NT2N cells acquire a fully mature neuronal phenotype in vivo, and that these cells integrate and survive for > 1 year post-implantation in the mouse CNS. These human neuron-like cells are an attractive model system for studies of neuronal development, polarity and transplantation.

Seeding of intracoronary stents with immortalized human microvascular endothelial cells

Intracoronary stents are effective in decreasing the complications associated with acute closure during coronary angioplasty. A major complication associated with the use of coronary stents is acute thrombotic occlusion. It has been postulated that the stent loses its thrombogenic potential after it becomes covered with a layer of endothelial cells. Human dermal microvascular endothelial cells were transfected with a plasmid containing the simian virus 40 large T-antigen gene. Stents were placed in culture media with cells for 2 weeks. Seeding efficiency of the stent with the endothelial cells was assessed by scanning electron microscopy. Balloon-expandable coronary stents placed in cell culture with immortalized human microvascular endothelial cells showed near-complete coverage after 2 weeks. After balloon inflation, persistence of cells on the stent was noted only on the lateral aspect of the balloon-expanded stents. If these stents were placed in culture, complete recovery of the monolayer was noted after 3 days. Stents were then covered with endothelial cells and frozen for 4 days. After thawing, the cells adhered to the devices and divided to form a monolayer in tissue culture. Seeded balloon-expandable stents were frozen for 4 months, thawed, and then implanted in a pig coronary artery. Human endothelial cells were identified on the stent 4 hours after deployment. These studies demonstrate the feasibility of using a human microvascular endothelial cell line to seed an uncoated metal stent. The cells remain adherent to the stent, are functional after freezing, and remain on the stent at least 3 hours after intracoronary implantation.

Comparison of the thrombogenicity of stainless steel and tantalum coronary stents

This study was designed to compare the thrombogenicity of stainless steel and tantalum coronary stents of the same design. Stainless steel and tantalum coronary stents are being evaluated for their utility in treating acute closure and restenosis. A major disadvantage of stainless steel stents is radiolucency. To determine whether radioopaque tantalum stents may be safely substituted for stainless steel stents, we compared the relative thrombogenicity of these materials in stents of identical design. Total platelet and fibrin deposition on the stents were determined from measurements of indium 111-labeled platelet and iodine 125-labeled fibrinogen accumulation after deployment into exteriorized chronic arteriovenous shunts in seven untreated baboons. In another series of experiments, 111In-platelet deposition was compared 2 hours after stent implantation in coronary arteries of pigs. In baboons, platelet thrombus formation on stainless steel and tantalum stents was equivalent and plateaued at approximately 2.5 x 10(9) platelets after 1 hour (p > 0.05). Fibrin deposition averaged approximately 1 mg/stent and did not differ between the stainless steel and tantalum stents (p > 0.05). In the porcine coronary model there was no significant difference in 111In-labeled platelet deposition between the stainless steel and tantalum stents (p > 0.05). This result was confirmed by scanning electron microscopic analysis of the coronary stents. Based on these two models, we conclude that there is no significant difference in the thrombogenicity of stainless steel and tantalum wire coil stents.

Endovascular low-dose irradiation inhibits neointima formation after coronary artery balloon injury in swine. A possible role for radiation therapy in restenosis prevention

BACKGROUND

Restenosis after percutaneous transluminal coronary angioplasty remains a major limitation of the long-term success of this procedure. Restenosis is a form of wound healing. Low-dose ionizing radiation has been effective in inhibiting exuberant wound healing responses in a variety of clinical situations.

METHODS AND RESULTS

Vascular neointimal lesions resembling human restenosis were created in the coronary arteries of normal pigs by overstretch balloon angioplasty injury. To test the effect of low-dose endovascular gamma radiation on lesion formation, a high-activity 192Ir source was introduced into one of the injured arteries in each animal and left in place for a period sufficient to deliver one of three doses: 350, 700, or 1400 cGy. To test potential benefits of delayed irradiation, 700 cGy was given in another group 2 days after injury. Animals were killed 14 days after balloon injury and the coronary vasculature was pressure-perfusion fixed. To test the late effect and safety of endovascular low-dose irradiation, 700 or 1400 cGy was given in miniswine coronary arteries after injury as well as in noninjured carotid arteries; this group was followed up for 6 months. Tissue sections were measured by computer-assisted planimetry. All arteries treated with radiation demonstrated significantly decreased neointima formation compared with control arteries. The ratio of intimal area-to-medial fracture length (IA/FL) was inversely correlated with the different radiation doses: control, 0.59; 350 cGy, 0.38; 700 cGy, 0.42; and 1400 cGy, 0.17 (r = -0.75, P < .0001). Delay of 700-cGy irradiation for 2 days after injury significantly decreased neointima formation compared with the same dose given immediately after injury. Analysis of long-term specimens showed reduction of IA/FL in the arteries irradiated with 700 cGy (0.3, P = .009) and 1400 cGy (0.31, P = .001) compared with control arteries (0.50). There was no excess fibrosis in the media, adventitia, or perivascular space of the coronary arteries or adjacent myocardium in pigs that received radiation compared with control animals.

CONCLUSIONS

Low-dose intracoronary irradiation delivered to the site of coronary arterial overstretch balloon injury in pigs inhibited subsequent intimal thickening (hyperplasia). A dose-response relationship was demonstrated, and delay of treatment for 48 hours appeared to augment the inhibitory effect. Six months of follow-up without fibrosis or arteriosclerosis demonstrated the durability of the beneficial effect in the treated group. These data suggest that intracoronary irradiation therapy may aid in preventing clinical restenosis.

Seeding of vascular grafts with an immortalized human dermal microvascular endothelial cell line

Small-caliber vascular grafts (< 6 mm) for arterial bypass frequently fail owing either to acute thrombosis or long-term fibrosis. One strategy to enhance patency is the coverage ("seeding") of luminal polymeric graft surfaces with endothelial cells (EC), which may in themselves be thromboresistant and antiproliferative, or which could be transfected with genes whose products are thrombolytic or growth-inhibitory. Advances in understanding of EC-biomaterial interaction have led to improvements in cell coverage and retention, but the sources of EC for such procedures have been limited to large vessels (autologous veins) and microvascular endothelium isolated from autologous adipose tissue. Before the practice of graft seeding can gain widespread clinical acceptance, the practical constraints of EC harvest, EC culture, and quick access to the seeded prosthesis for the surgical procedure must be overcome. Ideally, an EC line with a high proliferative capacity could be preestablished on the grafts, which could then be cryopreserved and made available as needed. The authors have seeded Dacron graft material with an immortalized human dermal microvascular EC line, HMEC-1. These cells were initially transfected with simian virus 40A large T antigen and have been passaged more than 100 times without signs of senescence. They also express von Willebrand factor, take yp acetylated low density lipoproteins, and rapidly form tubes when cultured on matrigel. Confluent coverage of Dacron graft segments, either untreated or coated with gelatin, was achieved in two weeks. The cells formed a monolayer over topographically elevated regions or appeared to be > one layer thick in other areas. Cells were also shown to remain viable after freezing.2+These results suggest a potential practical method for

Expression and structural analysis of 14-3-3 proteins

The 14-3-3 family of proteins plays a role in a wide variety of cellular functions including regulation of protein kinase C and exocytosis. Using antisera specific for the N termini of 14-3-3 isoforms described previously and an additional antiserum specific for the C terminus of epsilon isoform, protease digestion of intact 14-3-3 showed that the N-terminal half of 14-3-3 (a 16 kDa fragment) was an intact, dimeric domain of the protein. Two isoforms of 14-3-3, tau and epsilon, were expressed in E. coli and their secondary structure was shown by circular dichroism to be identical to wild-type protein, and expression of N-terminally-deleted epsilon 14-3-3 protein showed that the N-terminal 26 amino acids are important for dimerization. Intact 14-3-3 is a potent inhibitor of protein kinase C, but the N-terminal domain does not inhibit PKC activity. Site-specific mutagenesis of several regions in the tau isoform of 14-3-3, including the mutation of a putative pseudosubstrate site to a potential substrate sequence, did not alter its inhibitory activity. Intact 14-3-3 proteins are phosphorylated by protein kinase C with a low stoichiometry, but truncated isoforms are phosphorylated much more efficiently by this kinase. This may imply that the proteins may adopt a different structural conformation, possibly upon binding to the membrane, which could modulate their activity. 14-3-3 proteins are found at high concentration on synaptic plasma membranes and this binding is mediated through the N-terminal 12 kDa of 14-3-3.

A gene from the hyperthermophile Pyrococcus furiosus whose deduced product is homologous to members of the prolyl oligopeptidase family of proteases

The mlr-2 gene from the hyperthermophilic archaeum Pyrococcus furiosus was identified from a family of clones whose expression was influenced by the presence of maltose in the medium. The sequence of 2100 bp of DNA containing mlr-2 and its flanking regions revealed a 616-amino-acid (71 kDa) open reading frame (ORF). The ORF's initiation codon appeared 10 nt into the mlr-2 message and was not preceded by any apparent ribosome-binding site. The deduced product shared homology with prolyl endopeptidases from both eukaryotic and eubacterial sources (52-57% similarity, 30-37% identity) and signature domains containing the Ser-Asp-His triad, which is characteristic of this family of proteases, were present. Northern blot experiments revealed the presence of an approx. 2.0-kb transcript in P. furiosus extracts, corresponding in length to that expected from mlr-2 expression. Initiation of transcription occurred 23 bp downstream from a putative BoxA promoter element.

Isolation, sequence and characterization of the maltose-regulated mlrA gene from the hyperthermophilic archaeum Pyrococcus furiosus

The mlrA (maltose regulated) gene from the hyperthermophilic archaeum Pyrococcus furiosus was identified from a family of clones whose expression was influenced by the presence of maltose in the medium. Sequencing of the 2276 bp of DNA containing mlrA and flanking regions revealed a 753-amino-acid (aa) (88 kDa) open reading frame (ORF). The ORF is preceded by a bacterial-like ribosome-binding site. The deduced product shared extensive homology with pyruvate dikinases (PDK) from both eukaryal and eubacterial sources (35-61% similarity) and the signature domains characteristic of this class of proteins were present. Northern blot experiments demonstrated the presence of an approx. 2.4-kb transcript in P. furiosus extracts, corresponding in length to that expected from expression of mlrA. P. furiosus cultures grown in the presence of maltose were found to contain approx. 5-10-fold greater mlrA mRNA than those grown without maltose. Initiation of transcription under both cultural conditions occurred at the same transcription start point (tsp), 23 bp downstream from a putative BoxA promoter element.

Effects of left ventricular pressure on sonicated albumin microbubbles: evaluation using an isolated rabbit heart model

OBJECTIVES

We used an isolated, crystalloid-perfused rabbit heart model to test the hypothesis that the phasic changes in left ventricular contrast are due to bubble compression and decompression during systole and diastole, respectively.

BACKGROUND

Contrast enhancement of the left ventricular cavity has been shown to decrease during ventricular systole. This phenomenon has been attributed to pressure-induced microbubble destruction. Such destruction, if confirmed, would severely confound the quantitative interpretation of contrast echocardiographic data.

METHODS

A fixed volume of contrast solution (5% human albumin and Albunex, approximately 400:1 ratio) was introduced into a latex balloon placed within the left ventricular cavity of an isolated paced rabbit heart preparation (n = 12). Instantaneous left ventricular pressure was measured using a high fidelity microtip catheter and digitized on-line. The beating heart was placed in a water tank, and ultrasound images were obtained using a 7.5-MHz transducer and were recorded and digitized off-line at 12 frames/s. Simultaneously, the pacing signal was used for gated on-line acquisition of end-diastolic frames. A simple theoretic model based on surface tension physical principles was used to predict changes in bubble size and, consequently, the reflection intensity in response to the measured changes in left ventricular pressure.

RESULTS

We found that under peak left ventricular systolic pressures ranging from 89 to 155 mm Hg, 1) end-diastolic videointensity decreased by 8 +/- 6% (mean +/- SD) over 25 consecutive heart beats; and 2) intracyclic variations in measured videointensity were in close agreement with the theoretic calculations: 80.1 +/- 2.9% versus 80.2 +/- 4.6% of diastolic videointensity at systole.

CONCLUSIONS

The major cause of systolic decrease in contrast enhancement is periodic bubble compression (as opposed to bubble destruction) induced by high systolic pressures. The minor progressive decrease in end-diastolic videointensity reflects the degree of instability of Albunex microbubbles under left ventricular pressures. However, the clinical impact of these destructive effects is likely to be only minor because of the rapid transit of microbubbles through the left heart chambers and myocardial microcirculation.

Effect of immobilization on glucose transporter expression in rat hindlimb muscles

Three days after denervation, the expression of GLUT4 mRNA and protein decreases by approximately 50% in rat hindlimb muscles, while GLUT1 mRNA increases transiently by approximately 500%. Although postreceptor insulin resistance of glucose transport develops before GLUT4 declines, the latter likely contributes to the time-dependent increased severity of the resistance. To determine whether muscle inactivity contributes to changes in glucose transporter expression, one rat hindlimb was immobilized in a plaster cast for 3 days; the unencumbered hindlimb served as control. Muscle GLUT4 mRNA decreased by 32% (P < .02) and GLUT4 protein by 40% (P < .05) after 3 days' immobilization. There was no significant change in GLUT1 mRNA or skeletal muscle alpha-actin mRNA expression or in the total RNA concentration. The data suggest that electromyogenic and/or contractile activity regulates GLUT4 expression in skeletal muscle at a pretranslational step.

Delayed processing of the insulin proreceptor by hepatocytes from diabetic rats

The effect of diabetes on insulin receptor processing was assessed in rat hepatocytes, 2-4 weeks after the induction of diabetes with streptozotocin. Isolated hepatocytes from control and diabetic rats were labelled for 30 min with [35S]methionine in methionine-free medium and chased with complete medium for 1-3 hrs. Solubilized cell extracts were immunoprecipitated with a site-specific anti-insulin receptor antibody, proteins were separated by electrophoresis and labelling quantified following autoradiography. After 1 hr chase, only the insulin proreceptor was labelled in both groups. After 3 hrs, the ratio of labelled proreceptors to labelled insulin receptors was 0.57 +/- 0.063 in controls and 1.33 +/- 0.24 in hepatocytes from diabetic rats. Insulin added in vitro did not affect transit time. Delayed processing of the insulin proreceptor may reflect altered N-glycosylation and may also involve other glycoproteins.

Isolation of maltose-regulated genes from the hyperthermophilic archaeum, Pyrococcus furiosus, by subtractive hybridization

The hyperthermophilic archaeum, Pyrococcus furiosus, utilizes maltose as a preferred carbon source for growth. 32P-labeled complementary DNA (cDNA) probes representing maltose-regulated genes were obtained by a subtractive hybridization procedure that minimized retrieval of ribosomal RNA (rRNA) sequences during screening. Genomic DNA clones were isolated by positive hybridization to these probes. Genes whose expression varied both in the level of transcription, relative to rRNA, as well as in the degree of regulation were obtained; the extent of regulation varied over a wide range, from as little as fivefold to as high as 50-100-fold. DNA sequence analysis of several of these regulated genes indicated that the subtraction library included gene products required for maltose utilization (e.g., pyruvate dikinase), as well as growth-rate-related genes such as those encoding ribosomal proteins and RNA polymerase subunits. Our approach is applicable to studying gene regulation in organisms that are not amenable to classical genetic techniques.

Use of the porous balloon in porcine coronary arteries: rationale for low pressure and volume delivery

Using agents administered systemically, attempts to control the restenotic myoproliferative response associated with angioplasty have been unsuccessful. The porous balloon has the advantage of achieving high local concentrations by directly infusing agents into the arterial wall. The purpose of this study is to identify any acute and chronic morphological changes in swine coronary arteries infused with normal saline through the porous balloon at different driving pressures. In order to establish the safety of local arterial wall infusion through the porous balloon, swine underwent porous balloon infusion of 3, 6, or 10 ml of saline at 5 atmospheres, or infusion of 3 ml of normal saline delivered at either 2, 5, or 10 atmospheres of pressure into the normal left anterior descending and left circumflex arteries. To assess the histopathologic alterations induced by the porous balloon, sized 1.1 to 1 with respect to the artery, animals were sacrificed either immediately after porous balloon infusion or 14 ays later. Acute vessels were evaluated for the presence of medial injury, disruption and/or dissection, whereas chronic vessels underwent morphometric analysis measuring the residual luminal area (Lumen area/Intimal area+Lumen area) and the maximal intimal thickness. Adequate adventitial penetration was confirmed by infusing as little as 2-3 ml of methylene blue at 2 atmospheres of pressure. Infusion of 3 ml of normal saline at 2 atmospheres resulted in minor focal medial edema and disorganization, detected both acutely and 14 days after porous balloon infusion. At delivery pressures of 5 or 10 atmospheres, proportionally more acute injury was noted and measurable neointimal lesions were observed 2 weeks after infusion.(ABSTRACT TRUNCATED AT 250 WORDS)

Pre-exposure to glucosamine induces insulin resistance of glucose transport and glycogen synthesis in isolated rat skeletal muscles. Study of mechanisms in muscle and in rat-1 fibroblasts overexpressing the human insulin receptor

Increased routing of glucose through the hexosamine-biosynthetic pathway has been implicated in the development of glucose-induced insulin resistance of glucose transport in cultured adipocytes. Because both glucosamine and glucose enter this pathway as glucosamine-6-phosphate, we examined the effects of preincubation with glucosamine in isolated rat diaphragms and in fibroblasts overexpressing the human insulin receptor (HIR-cells). In muscles, pre-exposure to glucosamine inhibited subsequent basal and, to a greater extent, insulin-stimulated glucose transport in a time- and dose-dependent manner and abolished the stimulation by insulin of glycogen synthesis. Insulin receptor number, activation of the insulin receptor tyrosine kinase in situ and after solubilization, and the total pool of glucose transporters (GLUT4) were unaffected, and glycogen synthase was activated by glucosamine pretreatment. In HIR-cells, which express GLUT1 and not GLUT4, basal and insulin-stimulated glucose transport were unaffected by glucosamine, but glycogen synthesis was markedly inhibited. Insulin-stimulated activation of protein kinases (MAP and S6) was unaffected, and the fractional velocity and apparent total activity of glycogen synthase was increased in glucosamine-treated HIR-cells. In pulse-labeling studies, addition of glucosamine during the chase prolonged processing of insulin proreceptors to receptors and altered the electrophoretic mobility of proreceptors and processed alpha-subunits, consistent with altered glycosylation. Glucosamine-induced insulin resistance of glucose transport appears to be restricted to GLUT4-expressing cells, i.e., skeletal muscle and adipocytes; it may reflect impaired translocation of GLUT4 to the plasmalemma. The glucosamine-induced imbalance in UDP sugars, i.e., increased UDP-N-acetylhexosamines and decreased UDP-glucose, may alter glycosylation of critical proteins and limit the flux of glucose into glycogen.

Okadaic acid, insulin, and denervation effects on glucose and amino acid transport and glycogen synthesis in muscle

Effects of okadaic acid (OKA) and calyculin A, cell-permeating specific inhibitors of phosphoprotein phosphatases-1 and -2A, were studied in isolated rat hemidiaphragms. OKA stimulated glucose transport (half-maximum = approximately 0.1 microM; maximum = approximately 1 microM) but was less effective than 6 nM insulin. Insulin and OKA effects were not additive. OKA diminished or abolished glucose transport-stimulation by insulin. System A amino acid transport was also stimulated by OKA, insulin was more effective, and preexposure to OKA inhibited insulin stimulation. Calyculin A affected both transport systems similarly to OKA. OKA did not affect basal glycogen synthesis but abolished its stimulation by insulin. Denervated muscles develop post-receptor insulin resistance. Glucose transport and glycogen synthesis were essentially unresponsive to insulin 3 days postdenervation; however, glucose transport was stimulated by OKA similarly to controls. OKA did not affect glycogen synthesis in denervated muscle except for abolishing a small insulin effect. The data suggest similar acute regulation of glucose and system A amino acid transport in muscle. Enhanced Ser/Thr phosphorylation of unidentified protein(s) stimulates both processes but inhibits their full stimulation by insulin. Postdenervation insulin resistance likely reflects impaired signal transduction.

Discordant results for determinations of triglycerides in pig sera

We recently determined triglyceride concentrations in pig sera by three fully enzymatic methods (Kodak Ektachem 700, Hitachi 707, and Abbott EPx) and obtained significantly lower values than those obtained with chemical or enzymatic methods based on chemical hydrolysis. All methods used involve microbial lipases for liberating glycerol from glycerides and glycerol phosphate dehydrogenases or oxidases for subsequent oxidation. The methods were validated against reference methods by using fresh human sera and survey materials. The discordant results were not from matrix sample-method interaction but from incomplete hydrolysis of pig serum triglycerides by the lipolytic enzymes. When serum triglycerides from 10 pigs showing the highest biases were hydrolyzed by microbial lipases and the reaction mixture was subjected to thin-layer and gas-liquid chromatography, the predominant end products were palmitoyl monoglyceride and a mixture of free fatty acids with the following composition (fatty acid as percent of total +/- SD): 16:0, 7.8 +/- 2; 18:0, 5.4 +/- 2.2; 18:1, 53 +/- 12; 18:2, 31 +/- 4.6; and 18:3, 2.5 +/- 1. Assuming that the lipases exhibit the usual specificity toward the 1 and 3 positions of the triglyceride, the data suggest that, in pig, triglycerides 18:1 and 18:2 occupy the 1 and 3 positions and 16:0 (palmitic acid) predominantly occupies the 2 position. Triglycerides of this structure may not be well hydrolyzed by the typical lipolytic enzymes in clinical assays.

Discordant results for determinations of triglycerides in pig sera

We recently determined triglyceride concentrations in pig sera by three fully enzymatic methods (Kodak Ektachem 700, Hitachi 707, and Abbott EPx) and obtained significantly lower values than those obtained with chemical or enzymatic methods based on chemical hydrolysis. All methods used involve microbial lipases for liberating glycerol from glycerides and glycerol phosphate dehydrogenases or oxidases for subsequent oxidation. The methods were validated against reference methods by using fresh human sera and survey materials. The discordant results were not from matrix sample-method interaction but from incomplete hydrolysis of pig serum triglycerides by the lipolytic enzymes. When serum triglycerides from 10 pigs showing the highest biases were hydrolyzed by microbial lipases and the reaction mixture was subjected to thin-layer and gas-liquid chromatography, the predominant end products were palmitoyl monoglyceride and a mixture of free fatty acids with the following composition (fatty acid as percent of total +/- SD): 16:0, 7.8 +/- 2; 18:0, 5.4 +/- 2.2; 18:1, 53 +/- 12; 18:2, 31 +/- 4.6; and 18:3, 2.5 +/- 1. Assuming that the lipases exhibit the usual specificity toward the 1 and 3 positions of the triglyceride, the data suggest that, in pig, triglycerides 18:1 and 18:2 occupy the 1 and 3 positions and 16:0 (palmitic acid) predominantly occupies the 2 position. Triglycerides of this structure may not be well hydrolyzed by the typical lipolytic enzymes in clinical assays.

Increasing resistance of enterococci to ciprofloxacin

We determined that resistance to ciprofloxacin has emerged in enterococci over the last 5 years in our hospital, mainly in strains demonstrating the phenotype of high-level gentamicin resistance. All high-level-gentamicin-resistant isolates from 1985 and 1986 were susceptible, whereas 24% of isolates from 1989 and 1990 were resistant to ciprofloxacin. Plasmid and genomic DNA typing showed at least six unique strains exhibiting resistance, but one type accounted for 80% of recent resistant isolates, suggesting a role for cross infection in the emergence of resistance.

Phosphorylation of the rodent negative acute-phase protein alpha 1-inhibitor-III by the insulin receptor tyrosine kinase

alpha 1-Inhibitor-III (alpha 1I3), a broad range proteinase inhibitor, member of the alpha-macroglobulin family, is abundant in normal rat plasma. Insulin-dependent tyrosine phosphorylation of a monomeric 195K glycoprotein (pp195) was observed in wheatgerm agglutinin (WGA)-Sepharose-purified insulin receptor preparations from rat liver and muscle. Phosphorylation of pp195 in vitro required a basic poly-amino acid, i.e. poly-L-lysine. We present evidence identifying pp195 as alpha 1I3. In situ perfusion with saline essentially removed pp195 from rat livers. Addition of normal rat plasma to liver homogenates or to WGA eluates restored insulin-stimulated phosphorylation of pp195; plasma from streptozotocin-diabetic rats was much less effective. Liver-derived pp195 copurified with an abundant plasma protein, with the characteristics of alpha 1I3, on size exclusion and ion-exchange chromatography. An approximately 195K protein, comigrating with alpha 1I3, was markedly diminished in plasma from diabetic rats, and alpha 1I3 concentration was decreased by approximately 70% upon immunoblot analysis. Highly purified alpha 1I3 was phosphorylated by muscle- or liver-derived insulin receptors in the presence of 1 microM poly-L-lysine and comigrated with pp195 on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. alpha 1I3 phosphorylation was half-maximal at approximately 70 nM and was stimulated by insulin 7-fold. Hindlimb perfusion removed more than 90% plasma albumin but only approximately 20% pp195 from muscles. alpha 1I3 messenger RNA was identified in liver but not in muscle. A specific antibody against alpha 1I3 immunoprecipitated phosphorylated pp195 in WGA-purified insulin receptor preparations from nonperfused liver and from saline perfused and nonperfused muscle. alpha 1I3 is bound and internalized by alpha-macroglobulin receptors; whether it is phosphorylated in vivo is unknown. Hepatic alpha 1I3 synthesis may diminish in diabetic rats.

Coronary intimal proliferation after balloon injury and stenting in swine: an animal model of restenosis

OBJECTIVES

This study was designed to compare the proliferative response in coronary arteries after tantalum stent placement or balloon injury in a normolipemic swine model of restenosis.

BACKGROUND

Restenosis remains a significant complication of percutaneous transluminal coronary angioplasty. Efforts to study restenosis have been hampered by the lack of a suitable animal model.

METHODS

In an attempt to create lesions resembling those of human restenosis, normolipemic swine underwent injury of either the left anterior descending or the left circumflex coronary artery with either balloon inflation or deployment of a tantalum stent. At 4 weeks, they were killed and the injured vessels processed for histopathologic analysis. Intimal area, lumen area and maximal intimal thickness were measured. The degree of stenosis was expressed as residual lumen area (lumen area/intimal area ratio).

RESULTS

Vessels injured by either method demonstrated significant intimal smooth muscle proliferation leading to reduction in lumen area. In the 18 stented vessels residual lumen area measured 0.64 +/- 0.18 and maximal intimal thickness measured 0.6 +/- 0.3 mm; in the 15 balloon-injured vessels these values were 0.75 +/- 0.18 and 0.4 +/- 0.3 mm, respectively (p less than 0.05). In addition, most stented vessels had reactive inflammatory infiltrates surrounding the stent wires composed of lymphocytes, histiocytes and many eosinophils.

CONCLUSIONS

These data indicate that coronary artery injury in swine with either balloon inflation or stenting leads to intimal smooth muscle cell proliferation similar to that seen in human restenosis. The degree of intimal proliferation appears to be greater after stenting than after balloon injury. Intracoronary stenting in swine is associated with a marked inflammatory reaction around the stent wires. These models may be helpful in planning systemic and local antirestenosis strategies.

Skeletal muscle insulin-receptor kinase. Effects of substrate inhibition and diabetes

Insulin receptor tyrosine kinase activity solubilized from hind limb muscle of control and streptozocin-induced diabetic (STZ-D) rats (2-3 wk) was studied with the substrates histone H2B and poly glutamic acid-tyrosine (glu-tyr) (4:1). Basal and insulin-stimulated kinase activities were inhibited when high concentrations of either substrate were added before initiation of phosphorylation with ATP. Under these conditions, insulin-stimulated activities of diabetic- and control-derived receptor kinase toward H2B were similar at 0.008 mg/ml H2B. However, higher concentrations of H2B (0.04-1 mg/ml) progressively reduced the ratios of diabetic-derived to control-derived receptor kinase activities to approximately 0.5. When inhibition of receptor kinase activities was prevented by allowing maximal autophosphorylation of insulin receptors before addition of H2B, kinase activity of diabetic- and control-derived receptors was similar at all H2B concentrations. Diabetic-derived insulin-receptor tyrosine kinase activity toward poly glu-tyr (4:1) was not significantly different from that of control rats. Under conditions of substrate inhibition (0.4 mg/ml H2B), insulin receptor H2B kinase activity from muscles of rats with severe diabetes (85 mg/kg STZ, 7 days) was significantly decreased, whereas the same activity from rats with moderate diabetes (50 mg/kg STZ, 7 days) was not significantly different from control rats. Insulin receptor alpha,beta dimers were not detectable in muscle preparations from control or diabetic rats. The data suggest that the impairment of muscle-derived insulin-receptor tyrosine kinase activity associated with insulinopenic diabetes reflects, in part, enhanced inhibition by some substrates. If solubilized insulin receptors and the exogenous substrates studied model in vivo events, impaired signaling of the muscle insulin receptor in insulinopenic diabetes may depend on the type and concentration of intracellular tyrosine kinase substrates and the severity of the metabolic derangements.

Effect of denervation on the expression of two glucose transporter isoforms in rat hindlimb muscle

Denervation rapidly (within 24 h) induces insulin resistance of several insulin-responsive pathways in skeletal muscle, including glucose transport; resistance is usually maximal by 3 d. We examined the effect of denervation on the expression of two glucose transporter isoforms (GLUT-1 and GLUT-4) in rat hindlimb muscle; GLUT-4 is the predominant species in muscle. 1 d postdenervation, GLUT-1 and GLUT-4 mRNA and protein concentrations were unchanged. 3 and 7 d postdenervation, GLUT-4 mRNA and protein (per microgram DNA) were decreased by 50%. The minor isoform, GLUT-1 mRNA increased by approximately 500 and approximately 100%, respectively, on days 3 and 7 while GLUT-1 protein increased by approximately 60 and approximately 100%. The data suggest that the insulin resistance of glucose transport early after denervation does not reflect a decrease in total glucose transporter number; however, decreased GLUT-4 expression may contribute to its increased severity after 3 d. Parallel decreases in GLUT-4 mRNA and GLUT-4 protein postdenervation are consistent with pretranslational regulation; GLUT-1 expression may be regulated pre- and posttranslationally. The cell type(s) which overexpress GLUT-1 postdenervation need to be identified. Nervous stimuli and/or contractile activity may modulate the expression of GLUT-1 and GLUT-4 in skeletal muscle tissue.

Ultrastructure of coronary arterial endothelium in atherosclerotic swine suggests lipid retro-endocytosis

During experimental atherosclerosis, arterial endothelial cells show characteristic ultrastructural changes including the appearance of increased numbers of plasmalemmal and cytoplasmic vesicles. These structures have been shown by tracer studies to participate in the transcellular transport of low-density lipoprotein cholesterol and beta-very-low-density lipoprotein cholesterol from the arterial lumen into the abluminal extracellular matrix. Although this probably represents the major lipid transport pathway, other forms of transport may exist. We document the presence of apparent lipid structures averaging approximately 300 nm in diameter at or near the luminal surface of coronary arterial endothelium of atherosclerotic miniature swine. The structures exhibited a particulate nature with subunits of a heterogenous size distribution. The appearance of the endothelial plasmalemma adjacent and subjacent to these structures suggests exocytosis. We hypothesize that this previously unreported morphology may represent an in vivo structural correlate for the lipoprotein retro-endocytosis pathway which has been recently identified using biochemical methods in smooth muscle cells and fibroblasts in vitro.

Effects of insulin and phospholipase C in control and denervated rat skeletal muscle

Phospholipase C (PLC), an enzyme that increases endogenous 1,2-diacylglycerol (DAG), caused dose-dependent stimulation of 2-deoxy-D-glucose (2-DG) uptake in rat soleus muscles; the maximal effect was less than that of insulin. In denervated muscles the effect of insulin on 2-DG uptake was markedly reduced, whereas the response to PLC was identical to that of control muscles. Both PLC and insulin stimulated glucose incorporation into glycogen in control but not in denervated solei. Amino acid transport was unaffected by PLC; however, the enzyme completely inhibited the stimulation of amino acid transport by insulin. PLC did not activate the insulin receptor tyrosine kinase but decreased activation of the receptor by insulin in vivo. Basal muscle DAG content increased after denervation. Incubation with PLC markedly increased DAG in control and in denervated muscle. Insulin increased total DAG mass less than PLC in control muscles and did not affect DAG in denervated muscles. In media without added Ca2+, PLC stimulation of DAG production was impaired, and 2-DG uptake was unresponsive to PLC. The data are consistent with, but do not prove, that a subpopulation of DAGs may participate in insulin-mediated stimulation of glucose transport. They also suggest that the denervation-induced insulin resistance of glucose transport may reflect impaired generation of certain DAGs involved in the signaling cascade.