Biomedical subjects

G R Upchurch

Publications and source records attributed to G R Upchurch.

At least 19 recordsLinked to original sources

PubMed2002

An atmospheric pCO2 reconstruction across the Cretaceous-Tertiary boundary from leaf megafossils.

The end-Cretaceous mass extinctions, 65 million years ago, profoundly influenced the course of biotic evolution. These extinctions coincided with a major extraterrestrial impact event and massive volcanism in India. Determining the relative importance of each event as a driver of environmental and biotic change across the Cretaceous-Tertiary boundary (KTB) crucially depends on constraining the mass of CO(2) injected into the atmospheric carbon reservoir. Using the inverse relationship between atmospheric CO(2) and the stomatal index of land plant leaves, we reconstruct Late Cretaceous-Early Tertiary atmospheric CO(2) concentration (pCO(2)) levels with special emphasis on providing a pCO(2) estimate directly above the KTB. Our record shows stable Late Cretaceous/Early Tertiary background pCO(2) levels of 350-500 ppm by volume, but with a marked increase to at least 2,300 ppm by volume within 10,000 years of the KTB. Numerical simulations with a global biogeochemical carbon cycle model indicate that CO(2) outgassing during the eruption of the Deccan Trap basalts fails to fully account for the inferred pCO(2) increase. Instead, we calculate that the postboundary pCO(2) rise is most consistent with the instantaneous transfer of approximately 4,600 Gt C from the lithic to the atmospheric reservoir by a large extraterrestrial bolide impact. A resultant climatic forcing of +12 W.m(-2) would have been sufficient to warm the Earth's surface by approximately 7.5 degrees C, in the absence of counter forcing by sulfate aerosols. This finding reinforces previous evidence for major climatic warming after the KTB impact and implies that severe and abrupt global warming during the earliest Paleocene was an important factor in biotic extinction at the KTB.

Carbon Dioxide↗

PubMed2001

Impact of chronic obstructive pulmonary disease on elective and emergency abdominal aortic aneurysm repair.

OBJECTIVE: Chronic obstructive pulmonary disease (COPD) is associated with abdominal aortic aneurysm (AAA) expansion and is considered by some to be a relative contraindication to conventional aortic surgery. This study was undertaken to determine if COPD increases operative death, morbidity, intensive care unit (ICU) length of stay (LOS), and hospital LOS, after AAA repair. METHODS: Data from national administrative records supplemented with laboratory data previously obtained for a system-wide study were analyzed in a retrospective review of 1053 consecutive patients (264 with and 789 without COPD) undergoing operation for intact or ruptured AAAs in Veterans Administration Hospitals from 1997 to 1998. Bivariate comparisons and multivariate regression were used to evaluate the impact of COPD on the number of days of ventilation, ICU LOS, total hospital LOS, and death, while controlling for other known risk factors, including acute myocardial infarction, renal failure, and age. RESULTS: The mortality rate in elective aneurysm patients did not differ (P =.99) between patients with (3.7%) or without COPD (3.7%). However, elective AAA repair was associated with longer hospital LOS (14.4 vs 12.3 days, P =.01), longer ICU LOS (6.5 vs 5.4 days, P =.01), and a higher incidence of requiring 96 hours or more ventilation (6.9% vs 3.6%, P =.02) in patients with COPD. Ruptured AAA affected 4.9% of patients and was strongly associated with COPD (P =.02); however, COPD did not result in a statistically significant increase in death (P =.25). CONCLUSIONS: Although COPD does not appear to increase operative death, it is associated with an increased risk of rupture. Elective repair of AAA should not be deferred in patients with COPD despite their higher LOSs and need for postoperative ventilation.

Aged↗

PubMed2001

Nitric oxide inhibition increases matrix metalloproteinase-9 expression by rat aortic smooth muscle cells in vitro.

OBJECTIVE: The hypothesis to be tested was that diminished bioavailable nitric oxide (NO) affects matrix metalloproteinase (MMP) expression and activation in vascular smooth muscle cells (SMCs). METHODS: Cultivated rat aortic SMCs (RA-SMCs) were exposed to increasing concentrations of L-N-monomethyl arginine (L-NMMA), a nonselective inhibitor of NO synthase, in the presence of proinflammatory cytokines (50 ng/mL interleukin [IL]-1beta, 50 ng/mL interferon-gamma, and 30 microg/mL lipopolysaccharide). Nitrite and nitrate, two of the final end products of NO metabolism, were measured in media collected at 48 hours with the use of the Saville assay (n = 4). MMP activity was measured with 1% gelatin zymography (n = 4). In separate experiments in which 2 ng/mL of IL-1beta and L-NMMA was used, MMP protein and messenger RNA (mRNA) levels were determined with Western blot analysis (n = 3) and semiquantitative reverse transcriptase-polymerase chain reaction (n = 3), respectively. Data were analyzed with nonparametric analysis of variance. RESULTS: Increasing concentrations of the NO synthase inhibitor L-NMMA caused a dose-dependent decrease (P <.05) in nitrite and nitrate production by RA-SMCs after cytokine exposure. Zymography documented an early dosedependent increase (P <.05 compared with cytokines alone) in 92-kd MMP activity, with no significant changes in 72-kd MMP activity after treatment with L-NMMA (P >.05 compared with cytokines alone). Reverse transcriptase-polymerase chain reaction and Western blot analysis revealed that the addition of L-NMMA to IL-1beta-stimulated RA-SMCs led to significant increases in MMP-9 mRNA (n = 3, P <.01 for 1.0 mmol/L L-NMMA) and MMP-9 protein levels (n = 3, P <.05), respectively. No differences in MMP-2 mRNA or protein levels were demonstrated. CONCLUSIONS: Inhibition of cytokine-induced NO expression in RA-SMCs is associated with a selective, dose-dependent increase in MMP-9 expression and synthesis. These findings suggest that alterations in local NO synthesis may influence MMP-9-dependent vessel wall damage.

Animals↗

PubMed2001

Efficacy and durability of autogenous saphenous vein conduits for lower extremity arterial reconstructions in preadolescent children.

OBJECTIVE: Limb length discrepancies (LLDs) in growing children may accompany extremity arterial occlusions. Revascularization with vein grafts has been questioned because of degenerative graft changes observed at other sites. This study was undertaken to define vein graft durability and efficacy in lower extremity revascularizations in preadolescent children. STUDY DESIGN: Fourteen children (10 boys, 4 girls) with a mean age of 7.3 years (range, 2-11 years) who underwent 16 lower extremity revascularizations with greater saphenous vein grafts were subjected to follow-up with graft ultrasonography, ankle/brachial indices (ABIs) with and without exercise, and limb length determinations. A mean of 5.7 years elapsed between the onset of ischemia and operation. Arterial occlusions resulted from cardiac catheterizations (11), arteritis (1), dialysis cannulation (1), and penetrating trauma (1). Indications for operation included LLD (6), claudication (4), both LLD and claudication (3), markedly diminished ABIs with a potential for LLD (2), and a traumatic transection with hemorrhage (1). The reconstructions with 15 reversed and one in situ vein grafts included iliofemoral (11), femorofemoral (1), aortofemoral (1), femoropopliteal (1), popliteal-popliteal (1), and popliteal-posterior tibial (1) arterial bypass grafts. RESULTS: Among patent grafts available for follow-up, 36% (5 of 14) remained unchanged, 50% (7 of 14) developed nonaneurysmal dilatation, and 14% (2 of 14) exhibited nonprogressive aneurysmal expansion. One graft became occluded, and one graft was lost to follow-up. Collectively, the grafts manifest an 11.2% expansion at an average of 10.7 years postoperatively. ABIs increased from 0.75 preoperatively to 0.97, at an average of 11.0 years postoperatively. LLDs were reduced from 1.66 to 1.24 cm, at an average of 11.4 years postoperatively. CONCLUSION: Vein graft reconstructions of lower extremity arteries in preadolescent children are durable. They provide an efficacious means of restoring normal blood flow, and in 70% of children their preexisting LLDs were reduced.

Angiography, Digital Subtraction↗

PubMed2001

Computed tomographic venography is specific but not sensitive for diagnosis of acute lower-extremity deep venous thrombosis in patients with suspected pulmonary embolus.

PURPOSE: Duplex ultrasound scanning (US) is the accepted standard means of diagnosis for lower-extremity suprageniculate deep venous thrombosis (LE-DVT). Computed tomographic venography (CTV) has been proposed as an alternative modality for diagnosis of LE-DVT in patients with suspected pulmonary embolism (PE). This study compared CTV with US as a means of diagnosing acute LE-DVT. METHODS: A retrospective review of US and CTV scans from 136 patients with suspected PE who underwent both studies to exclude acute LE-DVT at a single institution was performed. Studies were reviewed and coded in a blinded manner. US was considered to be the reference test. Direct costs of each study were determined by using commercial software. RESULTS: The sensitivity and specificity rates of CTV were 71% and 93%, respectively. The positive predictive value, negative predictive value, and accuracy rates of CTV were 53%, 97%, and 90%, respectively. DVT localization was the same in eight of 10 cases in which the results of both US and CTV were positive. CTV costs and charges per study were greater than those of US by $46.88 and $602.00, respectively. CONCLUSION: CTV is specific, but has a lower sensitivity rate and positive predictive value for the diagnosis of acute LE-DVT compared with US. Additionally, CTV is more costly than US scanning. Because of the lower sensitivity rate and positive predictive value and the increased cost of CTV, US remains the screening study of choice in cases of suspected acute LE-DVT.

Costs and Cost Analysis↗

PubMed2001

Impact of increasing comorbidity on infrainguinal reconstruction: a 20-year perspective.

OBJECTIVE: To examine trends in patient and procedural variables and outcomes associated with autogenous lower extremity arterial reconstruction (LER) in a single center during a period of two decades. SUMMARY BACKGROUND DATA: Surgical arterial reconstruction is of proven value in the therapy of patients with critical ischemia of the lower extremities. Changing demographics and increasing comorbidity are resulting in an increasing prevalence and associated complexity of peripheral vascular disease. The effect of these variables on the types and outcomes of surgical reconstructions is not known. METHODS: The authors performed a retrospective analysis of all autogenous LER procedures performed at their institution from 1978 to 1997. Procedures were divided into 5-year intervals: group 1, 1978 to 1982; group 2, 1983 to 1987; group 3, 1988 to 1992; group 4, 1993 to 1997. Categorical parameters were compared using chi-square analysis; rates were computed by the life-table method and compared using Mantel-Cox log-rank analysis. RESULTS: A total of 1,642 autogenous LER procedures were performed in 1,274 patients. A significant increase in age, female gender, diabetes mellitus, renal failure, and prior coronary artery bypass grafting was noted in group 4. Increased technical complexity in this group was reflected by a greater incidence of tissue necrosis as the indication for LER, the use of ectopic or composite vein, and more distal levels of outflow. The surgical death rate remained unchanged (2%) throughout. Patient survival, primary and secondary graft patency, and limb salvage at 5 years for the entire cohort were 70 +/- 2%, 63 +/- 2%, 73 +/- 1%, and 85 +/- 1%, respectively. Hospital length of stay was reduced 25% from a mean of 15.7 +/- 0.8 days in group 3 to 11.7 +/- 0.4 days in group 4. CONCLUSION: In a tertiary practice setting, patients requiring LER present an increasingly complex medical and surgical challenge compared with the previous decade. Excellent outcomes may still be achieved by an aggressive approach relying on autogenous vein conduit.

Aged↗

PubMed2001

Renal artery aneurysms: a 35-year clinical experience with 252 aneurysms in 168 patients.

OBJECTIVE: To define the relevance of treating renal artery aneurysms (RAAs) surgically. SUMMARY BACKGROUND DATA: Most prior definitions of the clinical, pathologic, and management features of RAAs have evolved from anecdotal reports. Controversy surrounding this clinical entity continues. METHODS: A retrospective review was undertaken of 168 patients (107 women, 61 men) with 252 RAAs encountered over 35 years at the University of Michigan Hospital. Aneurysms were solitary in 115 patients and multiple in 53 patients. Bilateral RAAs occurred in 32 patients. Associated diseases included hypertension (73%), renal artery fibrodysplasia (34%), systemic atherosclerosis (25%), and extrarenal aneurysms (6.5%). Most RAAs were saccular (79%) and noncalcified (63%). The main renal artery bifurcation was the most common site of aneurysms (60%). RAAs were often asymptomatic (55%), with a diagnosis made most often during arteriographic study for suspected renovascular hypertension (42%). RESULTS: Surgery was performed in 121 patients (average RAA size 1.5 cm), including 14 patients undergoing unilateral repair with contralateral RAA observation. The remaining 47 patients (average RAA size 1.3 cm) were not treated surgically. Operations included aneurysmectomy and angioplastic renal artery closure or segmental renal artery reimplantation, aneurysmectomy and renal artery bypass, and planned nephrectomy for unreconstructable renal arteries or advanced parenchymal disease. Eight patients underwent unplanned nephrectomy, being considered a technical failure of surgical therapy. Dialysis-dependent renal failure occurred in one patient. There were no perioperative deaths. Late follow-up (average 91 months) was available in 145 patients (86%). All but two arterial reconstructions remained clinically patent. Secondary renal artery procedures included percutaneous angioplasty, branch embolization, graft thrombectomy, and repeat bypass for late aneurysmal change of a vein conduit. Among 40 patients with clearly documented preoperative and postoperative blood pressure measurements, 60% had a significant decline in blood pressure after surgery while taking fewer antihypertensive medications. Late RAA rupture did not occur in the nonoperative patients, but no lessening of this group's hypertension was noted. CONCLUSION: Surgical therapy of RAAs in properly selected patients provides excellent long-term clinical outcomes and is often associated with decreased blood pressure.

Adolescent↗

PubMed2001

Experimental abdominal aortic aneurysms in mice lacking expression of inducible nitric oxide synthase.

To determine if nitric oxide synthase (NOS) contributes to the pathophysiology of abdominal aortic aneurysms (AAAs), C57BL/6J mice underwent transient aortic injury to induce a chronic inflammatory response. Wild-type mice developed a significant increase in aortic diameter within 14 days of elastase perfusion (115+/-16%, 40% incidence of AAAs), along with intense and widespread staining for nitrotyrosine, mononuclear inflammation, and delayed destruction of the elastic lamellae. Expression of both endothelial and neuronal forms of NOS was substantially decreased within AAAs, whereas inducible NOS (iNOS) mRNA was increased 360%, and the enzyme was localized to infiltrating inflammatory cells. By using mice with targeted deletion of iNOS to evaluate the functional importance of this enzyme, male iNOS(-/-) mice developed the same extent of aneurysmal dilatation as congenic controls (121+/-22%, 40% incidence of AAAs) and exhibited similar structural features except for diminished nitrotyrosine staining. Aneurysmal dilatation was actually enhanced in female iNOS(-/-) mice (141+/-16%, 80% incidence of AAAs; P<0.05), but this effect was reversed by previous oophorectomy. Although extensive protein nitration and increased expression of iNOS accompany the development of elastase-induced experimental AAAs, iNOS is not required in this process and its absence may be deleterious.

Animals↗

PubMed2001

Heparin reacts with and inactivates nitric oxide.

Although heparin is a well-known anticoagulant, in some cases it promotes a prothrombotic state and does so through both antibody-dependent and antibody-independent platelet activation. In this study, heparin was found to reverse the antiplatelet effect of an NO donor. S-nitroso-glutathione (SNO-Glu), with an EC(50) of 1.8 U/mL. Ultraviolet/visible spectral analysis and the Griess assay showed that increasing heparin concentrations on a dose-dependent basis eliminated acidified NO(x) species. Since heparin is a heterogeneous mixture of glycosaminoglycans, the effects of six different heparin disaccharides were compared with various substitutions on the hexose rings to determine which functional group(s) of the polysaccharide interact with acidified NO(x). Among the six disaccharides tested, only types I-S and II-S had the effect, suggesting that the sulfamino-group at the C2 position of the glucosamine moiety was critical for the elimination of acidified NO(x) species. Mass spectrometry experiments gave results consistent with these observations, indicating that only the I-S and II-S heparin disaccharides were modified upon treatment with NaNO(2)/HCl. Negative-ion electro-spray ionization MS and tandem MS analyses of the native compounds and their deuterium-labeled analogs confirmed that the reaction products from nitrosation of these N-sulfated disaccharides had eliminated the C2-sulfamino-moiety and replaced it with methoxide derived from the solvent. Participation of the 6-sulfato-substituent appears to facilitate the elimination reaction. These data show that heparin can impair the antiplatelet properties of nitric oxide by interacting with the nitrosating species, and suggest that heparin-like glycosamino-glycans may interact with endothelium-derived nitric oxide in vivo to regulate the bioactivity of this important antiplatelet and vasorelaxant substance.

Anticoagulants↗

PubMed2000

Infrainguinal arterial reconstructions with vein grafts in patients with prior aortic procedures: the influence of aneurysm and occlusive disease.

PURPOSE: This study assessed whether infrainguinal reconstructions with autogenous vein (IR) performed in patients with prior abdominal aortic aneurysm (AAA) repairs have altered graft patency, compared with those in patients who have undergone prior aortobifemoral bypass grafting procedures (ABF) for aortoiliac occlusive disease. METHODS: From 1979 to 1998, 54 patients with prior aortic reconstructions underwent 64 autogenous single-segment saphenous IRs solely for infrainguinal occlusive disease. Included in this cohort were 30 IRs with an earlier AAA repair and 34 IRs with an earlier ABF repair. During the same period, 1274 patients underwent 1642 autogenous vein lower-extremity bypass grafting procedures (LEB). Lower-extremity native arterial (AAA, n = 6; ABF, n = 11) and vein graft diameters (AAA, n = 6; ABF, n = 6) were determined by means of angiography and duplex ultrasonography, respectively. The three reconstruction groups (AAA, ABF, LEB) were compared. RESULTS: The patients in the three groups were similar in sex, indication for operation, proximal and distal anastomotic site, and number of distal runoff vessels. The cumulative 5-year primary graft patency rate in the AAA group (92% +/- 5%) was significantly higher (P <. 001) than that in the LEB group (63% +/- 2%) and the ABF group (44% +/- 11%). Furthermore, cumulative 5-year primary patency was decreased in the ABF group compared with the LEB group (P =.05). A significant increase in both native arterial (P =.001) and vein graft diameter (P <.05) was demonstrated by using linear regression and a Student t test, respectively, in the AAA group compared with the ABF group. CONCLUSION: These data demonstrate that, compared with those in patients without a previous aortic procedure, IRs in patients with prior AAA repairs have significantly improved graft patency, and IRs in patients with prior ABF reconstructions for aortoiliac occlusive disease have significantly decreased graft patency. Larger arterial diameter and altered vein graft adaptation may contribute to the superior long-term outcomes of IRs in patients with prior AAA repairs.

Adaptation, Physiological↗

PubMed1999

Improved graft patency and altered remodeling in infrainguinal vein graft reconstruction for aneurysmal versus occlusive disease.

PURPOSE: This study attempted to determine whether autogenous vein used for infrainguinal reconstruction in patients with aneurysmal disease might demonstrate an altered adaptive response compared with those patients who underwent reconstructive surgery for occlusive disease, potentially altering graft patency. METHODS: From 1974 to 1997, 43 patients underwent vein grafting for 60 popliteal artery aneurysms (PAA). RESULTS: In an attempt to monitor early vein graft adaptation, serial graft surveillance by Duplex ultrasound scan was performed in a statistically valid subset of age-, sex-, and distal anastomotic site-matched patients with PAA and patients with occlusive disease (OD; n = 8 PAA; n = 8 OD). Compared with an age-matched and sex-matched cohort of patients (n = 60 grafts in each group) with occlusive disease and who had femoral below-knee bypass grafts (FBP) only, patients undergoing infrainguinal reconstruction for PAA had a higher 5-year primary graft patency (92% +/- 4% for PAA vs 66% +/- 7% for FBP; P <.01). Duplex surveillance demonstrated a progressive increase in arterialized vein graft diameter in the PAA group versus the OD group. In univariant analysis, aneurysmal disease was a significant predictor of final follow-up diameter (P =.002). In a linear regression model, controlling for diameter at first follow-up after bypass grafting, first follow-up diameter was also predictive of final follow-up diameter. CONCLUSION: These data suggested altered remodeling of vein grafts in patients with popliteal artery aneurysm, which may have a beneficial effect on patency.

Adult↗

PubMed1999

Endothelial cell nitric oxide production in acute chest syndrome.

Acute chest syndrome (ACS) is the most common form of acute pulmonary disease associated with sickle cell disease. To investigate the possibility that alterations in endothelial cell (EC) production and metabolism of nitric oxide (NO) products might be contributory, we measured NO products from cultured pulmonary EC exposed to red blood cells and/or plasma from sickle cell patients during crisis. Exposure to plasma from patients with ACS caused a 5- to 10-fold increase in S-nitrosothiol (RSNO) and a 7- to 14-fold increase in total nitrogen oxide (NO(x)) production by both pulmonary arterial and microvascular EC. Increases occurred within 2 h of exposure to plasma in a concentration-dependent manner and were associated with increases in endothelial nitric oxide synthase (eNOS) protein and eNOS enzymatic activity, but not with changes in nitric oxide synthase (NOS) III or NOS II transcripts, inducible NOS (iNOS) protein nor iNOS enzymatic activity. RSNO and NO(x) increased whether plasma was obtained from patients with ACS or other forms of vasoocclusive crisis. Furthermore, an oxidative state occurred and oxidative metabolites of NO, particularly peroxynitrite, were produced. These findings suggest that altered NO production and metabolism to damaging oxidative molecules contribute to the pathogenesis of ACS.

Animals↗

PubMed1997

Stimulation of endothelial nitric oxide production by homocyst(e)ine.

Hyperhomocyst(e)inemia, characterized by accelerated atherosclerosis, is believed to induce endothelial cell injury and promote atherothrombosis by supporting the generation of hydrogen peroxide. Earlier observations in our laboratory demonstrated that in vitro nitrosation of homocyst(e)ine (HCY) prevents the generation of hydrogen peroxide. We, therefore, hypothesized that stimulating the production of nitric oxide (NO) by endothelial cells would detoxify HCY by forming the corresponding S-nitrosothiol, S-nitroso-homocysteine. In an attempt to prove this hypothesis, media containing 1 mM L-arginine, 1 microM bradykinin, a known NO agonist, and one of the biologically relevant thiols (HCY, cysteine, or glutathione) at concentrations of 0, 0.05, 0.5 and 5.0 mM were incubated with bovine aortic endothelial cells (BAEC) for 0.5, 1 and 4 h. S-nitrosothiol (RSNO) concentrations were measured by photolysis-chemiluminescence. Nitric oxide synthase (eNOS or isoform 3) activity and Nos 3 steady-state mRNA levels were determined by the conversion of [3H]L-arginine to [3H]L-citrulline and Northern analysis, respectively. Results demonstrate that increasing concentrations of HCY, and not cysteine or glutathione, in the presence of bradykinin at 0.5, 1, and 4 h led to significant (P < 0.05 by ANOVA) time- and dose-dependent increases in RSNO produced by BAEC. Cells exposed to 1 microM calcium ionophore A23187 in the presence of 5.0 mM HCY also produced a time-dependent increase in RSNO compared to control (P < 0.05 by ANOVA). In an attempt to determine if de novo synthesis was occurring, BAEC were treated with bradykinin following a 4 h pretreatment with HCY. Pretreatment with HCY followed by stimulation also led to a time- and dose-dependent increase in RSNO production (P < 0.05 by ANOVA). Using high performance liquid chromatography with electrochemical detection, S-nitroso-homocysteine was identified following treatment of BAEC with HCY and bradykinin. The increase in RSNO production in the presence of bradykinin and HCY at 4 h occurred concomitantly with a 78% increase in eNOS activity and a 58% increase in steady-state Nos 3 mRNA, with no change in Nos 3 mRNA half-life, compared to control. A partial explanation for HCY's unique ability to support an increase in NO production was demonstrated by showing that the t1/2 of HCY in media was greater than that of cysteine or glutathione. These data show that, in the presence of an NO agonist, HCY increases RSNO production in a time- and dose-dependent fashion that is reflected by an increase in eNOS activity and Nos 3 transcription. These results suggest that stimulation of endogenous NO, or provision of an exogenous NO donor, may ameliorate endothelial cell injury and thereby decrease the atherothrombotic risk of hyperhomocyst(e)inemic states.

Animals↗

PubMed1997

Homocyst(e)ine decreases bioavailable nitric oxide by a mechanism involving glutathione peroxidase.

Hyperhomocyst(e)inemia is believed to injure endothelial cells in vivo through a number of mechanisms, including the generation of hydrogen peroxide (H2O2). Earlier in vitro studies demonstrated that homocyst(e)ine (Hcy) decreases the biological activity of endothelium-derived relaxing factor and that this decrease can be reversed by preventing the generation of hydrogen peroxide. Here we show that Hcy treatment of bovine aortic endothelial cells leads to a dose-dependent decrease in NOx (p = 0.001 by one-way analysis of variance) independent of endothelial nitric-oxide synthase activity or protein levels and nos3 transcription, suggesting that Hcy affects the bioavailability of NO, not its production. We hypothesized that, in addition to increasing the generation of H2O2, Hcy decreases the cell's ability to detoxify H2O2 by impairing intracellular antioxidant enzymes, specifically the intracellular isoform of glutathione peroxidase (GPx). To test this hypothesis, confluent bovine aortic endothelial cells were treated with a range of concentrations of Hcy, and intracellular GPx activity was determined. Compared with control cells, cells treated with Hcy showed a significant reduction in GPx activity (up to 81% at 250 microM Hcy). In parallel with the decrease in GPx activity, steady-state GPx mRNA levels were also significantly decreased compared with control levels after exposure to Hcy, which appeared not to be a consequence of message destabilization. These data suggest a novel mechanism by which Hcy, in addition to increasing the generation of hydrogen peroxide, may selectively impair the endothelial cell's ability to detoxify H2O2, thus rendering NO more susceptible to oxidative inactivation.

Animals↗

PubMed1997

Homocysteine, oxidative stress, and vascular disease.

First recognized in patients with rare inborn errors of metabolism, the association of elevated plasma homocysteine concentrations with atherosclerosis and thrombosis now seems relevant to the general population as well. The mechanism of injury appears to involve oxidative damage to endothelial cells. Vitamin supplementation can normalize homocysteine levels and may lower the incidence of atherothrombotic vascular disease.

Age Factors↗

PubMed1997

High-dose heparin decreases nitric oxide production by cultured bovine endothelial cells.

BACKGROUND: Abrupt cessation of heparin therapy can lead to a recrudescence of thrombosis and acute ischemia. Endothelial NO is an important endogenous inhibitor of platelet-mediated thrombosis, yet biochemical studies examining the effect of heparin on NO production by the endothelium have heretofore been lacking. METHODS AND RESULTS: In an attempt to address the effect of heparin on endothelial cell production of NO, confluent bovine aortic endothelial cells (BAECs) on microcarrier beads were incubated in the presence or absence of heparin. Results indicate that BAECs incubated with heparin were less able to inhibit platelet aggregation than control cells (P<.005 by ANOVA) and that this effect correlated with a decrease in NO production (36% decrease for heparin compared with control, P<.05). Dextran sulfate evoked the same response (67% decrease, P<.0001 compared with control), suggesting that the decrease in NO after heparin treatment is secondary to its negative charge rather than to a specific polysaccharide sequence. The decrease in NO production by heparin was accompanied by a 72% decrease in steady-state Nos 3 mRNA as well as a 49% decrease in immunodetectable endothelial NO synthase (eNOS) protein. CONCLUSIONS: These data show that high-dose heparin at concentrations achieved in some acute cardiovascular settings increases in vitro platelet aggregation in media conditioned by endothelial cells by decreasing endothelial NO production through a mechanism that involves a decrease in steady-state Nos 3 mRNA and eNOS protein. These observations suggest a possible mechanism by which to explain in part the prothrombotic effects of heparin.

Animals↗

PubMed1997

An acute phase reaction in diabetic patients with foot ulcers.

The acute phase reaction is a molecular response to noxious stimuli. Over 50 glycoproteins have been identified as reactants. While this is likely a protective response, some of the changes could be detrimental to body homeostasis. The objective of this study was to examine whether an acute phase reaction occurs in diabetic patients with foot ulcers. In age- and sex-matched populations, measurements of C-reactive protein, fibrinogen, albumin, hematocrit, whole blood viscosity and protein C were performed on: (i) 24 diabetic patients with a foot ulcer (group A); (ii) eight diabetic patients without foot ulcer (group B); and (iii) seven patients without diabetes (group C). Analysis of variance was used to compare means of each respective group (mean (s.d.)). Group A demonstrated an increase in C-reactive protein (5.6 (5.4) mg/dl) compared with group B (0.78 (0.46) mg/dl; P = 0.013) and group C (0.71 (0.26) mg/dl; P = 0.026). Fibrinogen was also increased in group A (619 (205) mg/dl) compared with group B (310 (58) mg/dl; P = 0.005) and group C (370 (88) mg/dl; P = 0.04). Hematocrit (37 (6)%) and albumin (3.5 (0.5) g/dl) were decreased in group A compared with group B (hematocrit 46 (4)%; P < 0.0001; albumin 4.3 (0.3) g/dl; P = 0.0005) and group C (hematocrit 45 (3)%; P = 0.005; albumin 4.6 (0.3) g/dl; P < 0.0001). No difference was found in whole blood viscosity and levels of protein C. There also was no significant difference demonstrated between any of the parameters studied when comparing groups B and C. In conclusion, these results indicate that diabetic patients with a foot ulcer undergo an acute phase reaction as evidenced by a rise in C-reactive protein and fibrinogen compared with diabetic patients without a foot ulcer and normal control patients. As more is learned about the acute phase reaction, this information may prove valuable in the management of the diabetic patient.

Acute-Phase Reaction↗

PubMed1997

Changes in the amplitude of cyclic load biphasically modulate endothelial cell DNA synthesis and division.

Several physical factors, including shear stress and cyclic load, modulate the ability of endothelial cells to respond to injury. The objective of these experiments was to test the hypothesis that cyclic mechanical load stimulates endothelial cell DNA synthesis and division in vitro. Rabbit aortic endothelial cells were cultured on Flex I flexible-bottomed culture plates, and subjected to load amplitudes of increasing magnitude (0, 0.18, 0.24 and 0.27 load at 1 Hz) using a Flexercell strain unit. Cells were harvested enzymatically and cell numbers determined on days 1, 3 and 5 after initiating the load regimen. DNA synthesis was quantified after trichloroacetic acid precipitation of [3H]thymidine-labeled cells from: (1) whole culture wells and (2) areas of minimum and maximum strain in culture cells. Data were analyzed using analysis of variance and a Tukey's test (n = 6 observations/strain regimen per day in triplicate). Results from analysis of endothelial cells in whole, subconfluent cultures showed that cells subjected to strains of 0.18 had a decreased rate of cell division (76% of control) and DNA synthesis (63% of control), while cells subjected to strains of 0.24 and 0.27 had an increased rate of cell division (108 and 83% increase, respectively, compared with control; p < 0.001) and DNA synthesis (39 and 172% increase, respectively, compared with control; p < 0.001 for 0.27) on day 3 when compared with control cells. The results indicate that endothelial cells respond to various physiologic levels of cyclic load in a biphasic manner to initiate DNA synthesis and cell division. These data suggest that endothelial cell mitogenesis may be modulated by specific levels of cyclic load.

Animals↗