A novel protamine variant reversal of heparin anticoagulation in human blood in vitro

PURPOSE

Protamine reversal of heparin anticoagulation during cardiovascular surgery may cause severe hypotension and pulmonary hypertension. A novel protamine variant, [+18RGD], has been developed that effectively reverses heparin anticoagulation without toxicity in canine experiments. Heretofore, human studies have not been undertaken. This investigation hypothesized that [+18RGD] would effectively reverse heparin anticoagulation of human blood in vitro.

METHODS

Fifty patients who underwent anticoagulation therapy during vascular surgery had blood sampled at baseline and 30 minutes after receiving heparin (150 IU/kg). Activated clotting times were used to define specific quantities of [+18RGD] or protamine necessary to completely reverse heparin anticoagulation in the blood sample of each patient. These defined amounts of [+18RGD] or protamine were then administered to the heparinized blood samples, and percent reversals of activated partial thromboplastin time, thrombin clotting time, and antifactor Xa/IIa levels were determined. In addition, platelet aggregation assays, as well as platelet and white blood cell counts were performed.

RESULTS

[+18RGD] and protamine were equivalent in reversing heparin as assessed by thrombin clotting time, antifactor Xa, antifactor IIa levels, and white blood cell changes. [+18RGD], when compared with protamine, was superior in this regard, as assessed by activated partial thromboplastin time (94.5 +/- 1.0 vs 86.5 +/- 1.3% delta, respectively; p < 0.001) and platelet declines (-3.9 +/- 2.9 vs -12.8 +/- 3.4 per mm3, respectively; p = 0.048). Platelet aggregation was also decreased for [+18RGD] compared with protamine (23.6 +/- 1.5 vs 28.5 +/- 1.9%, respectively; p = 0.048).

CONCLUSIONS

[+18RGD] was as effective as protamine for in vitro reversal of heparin anticoagulation by most coagulation assays, was statistically more effective at reversal than protamine by aPTT assay, and was associated with lesser platelet reductions than protamine. [+18RGD], if less toxic than protamine in human beings, would allow for effective clinical reversal of heparin anticoagulation.

Hemodynamically significant atherosclerotic renal artery stenosis: MR angiographic features

PURPOSE

To identify magnetic resonance (MR) angiographic features of hemodynamically significant renal artery stenosis.

MATERIALS AND METHODS

Forty-seven patients underwent MR angiography of the renal arteries, including T1-weighted spin-echo and three-dimensional gadolinium-enhanced spoiled gradient-echo and three-dimensional phase-contrast pulse sequences, followed by renal revascularization. Thirty-five patients (52 arteries) were identified who benefited from renal revascularization, which indicated that they had hemodynamically significant renal artery stenoses. Kidney length, cortical thickness, parenchymal enhancement, and poststenotic dilatation were measured. Arteries were also examined for signal drop-out (dephasing) on phase-contrast angiograms; dephasing was considered severe if the stenotic artery appeared occluded on phase-contrast angiograms.

RESULTS

Poststenotic dilatation of greater than 20% was present in 36 (59%) of 52 hemodynamically significant renal artery stenoses, and severe dephasing was present in 45 (87%) of 52. In patients with unilateral hemodynamically significant stenosis or occlusion, mean ischemic kidney length was reduced to 9.3 cm compared with 10.7 cm for the contralateral normal kidney (P = .009), mean parenchymal thickness was reduced (1.2 vs 1.7 cm; P < .001), and mean parenchymal enhancement was 15% less on the ischemic side (P = .05). Severe dephasing on phase-contrast angiograms was present in nine (75%) of 12 unilateral hemodynamically significant stenoses but in only one contralateral normal renal artery (P < .001).

CONCLUSION

MR angiography depicts features of renal artery stenosis that are markers of hemodynamic significance.

Differential clinical workloads among faculty at a major academic health center

OBJECTIVE

The authors analyzed patient care (1981-1995) and financial data (1991-1996) to determine if differential workloads existed at a major academic health center.

SUMMARY BACKGROUND DATA

Academic health centers differ markedly from community-based medical centers, but they are required to compete with others who have a more circumscribed mission and a responsibility for providing less complex care. Changes in health care systems may lessen incentives to generate clinical revenue and may adversely affect educational and research programs.

METHODS

Patient care data at the University of Michigan Health System were analyzed by discipline for level of activity from 1981 to 1995 and were compared to professional and institutional financial data from 1991 to 1995.

RESULTS

Surgeons represented 11% of the total full-time physicians throughout the period of the study (94 of the 836 Medical Center physicians, 1995). They accounted for 33% of hospital admissions (11,616 of 35,101) and 16% of outpatient visits (92,364 of 568,738). Since 1981, surgeons experienced a 249% increase in total operative workload (6799-16,909 procedures), representing a 30% increase in operations/surgeon (138-180 operations). Surgical efforts in 1995 accounted for 29% of the total professional fee revenue and $240 million of the $512-million University of Michigan Hospital revenue.

CONCLUSIONS

Surgeons had a greater collective and individual responsibility than did nonsurgeons for clinical activity and the financial viability of the academic health centers studied. Many proposals for financing health care delivery systems have the potential to exacerbate this differential. Restructuring of academic health centers must address this fact, lest their academic mission and scholarly activity be compromised.

David M. Hume memorial lecture. Surgical treatment of renovascular hypertension

BACKGROUND

Renal artery occlusive disease is the most common form of surgically correctable hypertension. Considerable scientific advances have improved our understanding of the pathophysiologic sequellae of a renal artery stenosis, the means of documenting the functional importance of such lesions, and the role of alternative surgical approaches in treating this disease. This work assesses the historical basis for the surgical treatment of renovascular hypertension.

DATA SOURCES

A review of the American literature on the subject of renovascular hypertension was undertaken, with particular attention to early work emanating from the University of California, San Francisco, the University of Michigan, and Vanderbilt University. These three institutions had considerable influence on the evolving techniques of operative intervention for renovascular hypertension.

CONCLUSIONS

The contemporary surgical management of renal artery stenotic disease causing secondary hypertension includes recognition of the heterogeneic character renal artery diseases, documentation of the functional significance of the stenoses, and performance of a properly chosen operation. Surgical therapy benefits 85% to 95% of properly selected patients having renovascular hypertension.

Vascular surgeons' resource use at a university hospital related to diagnostic-related group and source of admission

PURPOSE

To determine whether differences in the conduct of individual practices of attending vascular surgeons account for variations in resource use at a university hospital.

METHODS

The practice patterns of six attending vascular surgeons at the University of Michigan Hospital were assessed for patient length of stay (LOS), ancillary service use, and the number of nursing hours required. Included in the study were 1930 hospitalized patients who had one of the 10 most frequently encountered diagnostic related groups (DRGs). Statistical analyses of variables that were thought likely to affect resource use included multiple regression models.

RESULTS

Patient age, sex, insurance, source of admission (direct admission or transfer admission), surgeon, and DRG category together accounted for 22% of LOS variation, 27.7% of variation in ancillary service use, and 29.4% of variation in nursing hours. In no model did the individual surgeon's practice significantly effect the LOS, ancillary use, or nursing hours. Patients transferred from other hospitals had increased resource use in all models. The DRG category alone explained 20.9% of the variance in LOS, 25.2% of the variation in ancillary service use, and 21.2% of the variance in nursing hours.

CONCLUSION

Differences in the conduct of individual vascular surgeons' practices accounted for less than 1% variation in hospital resource use. The most important influences on resource use were the DRG category and the source of patient admission. Modification of the frequency and manner of accepting transfer patients to vascular surgery services of a university hospital may have a major impact on hospital resource use.

The changing vascular surgery workforce

An adequate workforce is requisite for efficient and quality surgical care of patients having vascular disease. Data from 1985 and 1992 United States workforce studies provide the basis for certain projections. Vascular surgeons performed 41% of vascular operations in 1985 and 51% in 1992. The basis for this change seems related to the fact that younger general surgeons are less likely to practice vascular surgery than retiring senior general surgeons, whom they are replacing, and vascular surgeons have assumed the care of patients usually treated by the latter group of surgeons. Our aging society compounds this change. Patients older than 65 years will exhibit a 73% increase from 2010 to 2030, with a subsequent greater need for more vascular operations, which are predicted to be 1,020,067 in 2020, compared with 583,000 in 1992. A larger workforce will be required to meet this need. Although innovative technology and changes in health care delivery may cause unpredictable changes in these anticipated workforce needs, the potential exists that there will be insufficient numbers of surgeons available to provide adequate surgical care early in the next century, unless changes occur in the training and practice of general and vascular surgeons.

Cell cycle effects of nitric oxide on vascular smooth muscle cells

We characterized the cell cycle block induced by nitric oxide (NO) on smooth muscle cells (SMC). We hypothesized that the inhibition of SMC proliferation by NO was due to a specific block in cell cycle progression. Treatment of cultured rat aortic SMC with the NO donors S-nitroso-N-acetylpenicillamine or S-nitrosoglutathione (0.1 mM for 48 h) resulted in a 50% decrease (P < 0.05) in the fraction of cells in the S and G2 + M phases and a corresponding increase in the G1 fraction, suggesting that NO inhibits entry into S phase, causing accumulation of cells in G1 phase. Application of both NO donors to cycling SMC resulted in a short-term, concentration-dependent (0.06-0.3 mM) inhibition of ongoing DNA synthesis as measured by radiothymidine incorporation, demonstrating that NO causes an S-phase arrest. The S-phase arrest by NO was not mimicked by exogenous guanosine 3',5'-cyclic monophosphate (cGMP, 10 mM) and was associated with, but not due to, a 20% inhibition of RNA synthesis. The S-phase block was completely reversed within 2 h of removal of the NO donors, similar to inhibition by the ribonucleotide reductase inhibitor hydroxyurea. Prolonged treatment of SMC with either NO donor (0.1 mM) did not synchronize cells at the G1-S boundary as expected after a prolonged S-phase arrest, but instead induced a quiescent G0-like state characterized by a 12- to 18-h lag before DNA synthesis returned to normal levels after NO removal. These findings demonstrate that NO inhibition of SMC proliferation is associated with two distinct and reversible cell cycle arrests, an immediate cGMP-independent S-phase block followed by a shift back in the cell cycle from the G1-S boundary to a quiescent G0-like state.

Comparison of the hemodynamic and hematologic toxicity of a protamine variant after reversal of low-molecular-weight heparin anticoagulation in a canine model

Using the dog as an animal model, we developed an experimental preparation to compare hemodynamic and hematologic toxicity of anticoagulation reversal. Currently, protamine sulfate reversal of standard unfractionated heparin and low-molecular-weight heparin (LMWH) anticoagulation causes adverse side effects, including decreased systemic mean arterial pressure (MAP), decreased cardiac output (CO), decreased oxygen consumption (VO2), and thrombocytopenia. In addition, standard protamine is only marginally effective at reversing the factor Xa inhibition induced by LMWHs. We have produced protamine-like variant peptides to decrease the adverse responses attributed to standard protamine. The hemodynamic, hematologic, and coagulation effects of standard protamine and the protamine variant (+18RGD) were assessed after reversal of LMWH anticoagulation in anesthetized dogs. Flow probes and vascular catheters were surgically implanted for measurement of hemodynamic parameters including MAP, CO, VO2, and heart rate (HR). Hematologic studies (platelet and white blood cell counts) and coagulation studies (activated clotting time [ACT], activated partial thromboplastin time [aPTT], thrombin clotting time [TCT], antifactor Xa and antifactor IIa values) also were performed. The protamine variant +18RGD was less toxic, induced less thrombocytopenia, and was more effective in anticoagulation reversal than was standard protamine sulfate. Results of this study indicate that the dog may be a useful model for investigating important hemodynamic, hematologic, and coagulation parameters during reversal of LMWH anticoagulation by use of synthetic protamine variants.

Dual cell cycle-specific mechanisms mediate the antimitogenic effects of nitric oxide in vascular smooth muscle cells

OBJECTIVE

To determine the cell cycle specificity and intracellular mechanisms involved in inhibition by nitric oxide (NO) of vascular smooth muscle cell mitogenesis.

METHODS

Cultured rat aortic smooth muscle cells were synchronized by serum withdrawal, treated with the NO donor S-nitroso-N-acetylpenicillamine and the cyclic GMP analog 8-Br-cGMP at various times during cell cycle progression, and DNA synthesis measured during the S phase. Two additional NO donors, 5-nitroso-glutathione and diethylamine NONOate, were used to confirm the inhibition of DNA synthesis by S-nitroso-N-acetylpenicillamine, and the ability of two antagonists of free NO to reverse the effects of NO donors was also evaluated. Bypass of ribonucleotide reductase by use of exogenous deoxynucleosides was attempted to determine whether inhibition of this S-phase enzyme was the mechanism by which NO inhibited DNA synthesis during the S phase.

RESULTS

Vascular smooth muscle cell mitogenesis was inhibited by cyclic GMP (cGMP) up to late G1 phase of the cell cycle, which corresponded to the point of greatest sensitivity to exogenous NO. In contrast to cGMP, three different NO donors inhibited DNA synthesis when added to cells synchronized in S phase, beyond the restriction point of cell cycle control in late G1 phase. This S-phase inhibition was reversible by removal of the NO donor or addition of two NO antagonists and was not observed with non-NO analogs of the donors. Inhibition by NO donors in S phase was neither reversed by the guanylate cyclase inhibitor methylene blue nor mimicked by exogenous cGMP. The S-phase inhibition by all three NO donors was reversed partially by bypass of ribonucleotide reductase, establishing this enzyme as an S-phase target of NO.

CONCLUSIONS

These findings demonstrate that NO inhibits smooth muscle mitogenesis by cGMP-dependent and -independent mechanisms acting at distinct points in the cell cycle. NO is the first endogenous substance to have been shown to inhibit mitogenesis beyond the restriction point in late G1 phase, suggesting that it plays a role in regulation of cells that have lost normal mechanisms of G1 growth control, such as the hyperproliferative smooth muscle cells noted in hypertension and restenosis.

Gender differences in abdominal aortic aneurysm prevalence, treatment, and outcome

PURPOSE

The purpose of this study was to investigate gender differences in the management of and outcome of surgery for abdominal aortic aneurysms (AAA).

METHODS

Hospital discharge data from all acute care hospitals in Michigan, as compiled in the Michigan Inpatient Data Base, were retrospectively analyzed to assess sex differences in regard to AAA prevalence, treatment, and surgical outcome from 1980 to 1990. This population database included 11,512 women and 29,846 men 50 years of age and older with diagnoses of intact or ruptured AAA.

RESULTS

Hospitalizations for intact or ruptured AAA were approximately five times more common among men compared with women. After controlling for age and year of surgery, men were 1.8 times as likely as women to have an intact AAA treated surgically and 1.4 times as likely to have a ruptured AAA treated surgically (95% confidence intervals, 1.7 to 1.9 and 1.2 to 1.7, respectively). Women who had operations for intact AAA had a 1.4 times greater risk of dying compared with men, and women who had operations for ruptured AAA had a 1.45 times greater risk of dying, after controlling for other predictors of death (95% confidence intervals, 1.14 to 1.73 and 1.10 to 1.90, respectively).

CONCLUSIONS

In a population-based statewide experience, women who had intact or ruptured AAA were less likely than men to undergo aortic reconstruction and, when they did, were less likely than men to survive to discharge.

Differential effects of novel protamine variants on myocyte contractile function with left ventricular failure

BACKGROUND

Protamine administration can cause left ventricular (LV) dysfunction, which may have clinical significance in the setting of congestive heart failure (CHF). Protamine variants have recently been constructed with heparin reversal capacity similar to protamine. The purpose of this study was to examine the potential differential effects of these protamine variants on isolated myocyte contractile function in normal myocytes and in myocytes after the development of CHF.

METHODS

Contractile function was measured by means of computer-aided videomicroscopy in myocytes from five normal pigs and five pigs with CHF induced by rapid pacing (240 beats/min for 3 weeks). Myocyte contractility was examined in the presence of 40 micrograms/ml native protamine or one of three protamine variants: (1) reduced charge (+18) and lysine substituted for arginine; (2) lysine-substituted variant with glutamic acid substituted for the initial proline; or (3) arginine-rich peptide with a terminal arginine-glycine-aspartic acid (RGD) amino acid sequence.

RESULTS

In the presence of native protamine, myocyte percent shortening fell from baseline in both the normal (2.86 +/- 0.15 versus 4.58 +/- 0.08, p < 0.05) and the CHF groups (1.01 +/- 0.06 versus 2.07 +/- 0.05, p < 0.05). With both of the lysine-substituted protamine variants, percent shortening fell from baseline in the normal group (3.42 +/- 0.20 for arginine and 3.74 +/- 0.20 for glutamic acid versus 4.58 +/- 0.08, p < 0.05), and was unchanged in the CHF group (1.94 +/- 0.13 versus 2.07 +/- 0.05, p = 0.34 for arginine; and 1.96 +/- 0.10 versus 2.07 +/- 0.05, p = 0.31, for glutamic acid). However, with the arginine/RGD variant, percent shortening fell from baseline in both the normal (2.86 +/- 0.23 versus 4.58 +/- 0.08, p < 0.05) and the CHF groups (1.32 +/- 0.10 versus 2.07 +/- 0.05, p < 0.05).

CONCLUSIONS

Specific changes in the primary and secondary structures of protamine had different effects on myocyte contractile function. Furthermore, the negative effects of lysine-substituted protamine variants on myocyte contractility were less pronounced in both CHF and normal myocytes. Thus protamine variants may be of clinical use, particularly in the setting of preexisting LV dysfunction.

Transforming growth factor-beta 1 increases lysyl oxidase enzyme activity and mRNA in rat aortic smooth muscle cells

PURPOSE

This investigation was designed to test the hypothesis that transforming growth factor-beta 1 (TGF-beta 1) regulates lysyl oxidase secretion from vascular smooth muscle cells. Lysyl oxidase is an enzyme that catalyzes an essential step in collagen and elastin cross-linking in the extracellular matrix, and TGF-beta 1 has been implicated in the pathogenesis of restenosis after vascular injury. The effect of TGF-beta 1 on lysyl oxidase in vascular smooth muscle cells has not been previously defined.

METHODS

Rat aortic smooth muscle cells were grown in culture to confluence. Cells in passage 2 to 6 were incubated for 24 hours in media containing 0.1, 0.5, 1.0, or 10.0 ng/ml of TGF-beta 1. Lysyl oxidase activity in the media was quantitated with a tritium-release bioassay against an insoluble 3H-labeled aortic clastin substrate. Northern blot analyses were performed to determine steady-state levels of lysyl oxidase mRNA in the smooth muscle cells.

RESULTS

Lysyl oxidase activity in the media increased 1.5-fold above control levels after exposure to 10 ng/ml of TGF-beta 1 (p < 0.01). This increase in lysyl oxidase activity was associated with a concentration-dependent increase in steady-state levels of lysyl oxidase mRNA, being 4.3- and 6.2-fold above control levels after exposure to 1 and 10 ng/ml TGF-beta 1, respectively (p < 0.01). The observed increase in steady-state lysyl oxidase mRNA after exposure to TGF-beta 1 was also time-dependent over the 24-hour experimental period.

CONCLUSIONS

TGF-beta 1 appears to regulate lysyl oxidase in cultured rat aortic smooth muscle cells. Increases in lysyl oxidase activity may be one of the mechanisms by which TGF-beta 1 contributes to arterial restenosis after vascular injury.

Gadolinium-enhanced MR angiography of visceral arteries in patients with suspected chronic mesenteric ischemia

The purpose of this study was to evaluate accuracy of dynamic gadolinium-enhanced MR angiography (MRA) of the celiac, superior, and inferior mesenteric arteries in patients with suspected mesenteric ischemia compared with catheter angiography or surgery. Sixty-five patients with suspected mesenteric ischemia underwent three-dimensional spoiled gradient-recalled acquisition in the steady state (GRASS) gadolinium-enhanced MRA. Correlative studies were performed on 14 patients, catheter angiography alone was performed on 12 patients, and surgery alone was performed on two patients. Six patients had mesenteric ischemia. In all patients, the celiac artery (CA) and superior mesenteric artery (SMA) were seen well enough to evaluate; however, the inferior mesenteric artery (IMA) could be evaluated in only 9 of the 14 patients. MRA showed severe stenosis (> 75%) or occlusion of the celiac axis in seven patients, of the SMA in six patients, and of the IMA in four patients. The overall sensitivity and specificity were 100% and 95%, respectively, compared with catheter angiography and surgery. The two errors were caused by overgrading the severity of IMA disease. Three-dimensional gadolinium-enhanced MRA can accurately demonstrate the origins of the CA and SMA and is useful in evaluation of patients with suspected mesenteric ischemia.

Tissue plasminogen activator increases canine endothelial cell proliferation rate through a plasmin-independent, receptor-mediated mechanism

BACKGROUND

Tissue plasminogen activator (tPA) is elevated in cancer patients and is thought to promote tumor angiogenesis by facilitating endothelial cell migration through plasmin-mediated degradation of extracellular matrix. Due to the presence of an epidermal growth factor (EGF)-finger domain in the tPA A-chain and the existence of an endothelial cell (EC) receptor that binds this domain, it was hypothesized that tPA has a direct receptor-mediated effect on EC proliferation, independent of plasmin.

METHODS AND RESULTS

Using cultured canine ECs, tPA (7.25 microg/ml, approximately 107 nM) increased proliferation as much as 50 and 170% in the absence and presence of growth factors, respectively. tPA-induced increases in EC proliferation occurred independent of plasmin generation, as the plasmin inhibitor, aprotinin (10 microg/ml) did not inhibit tPA-induced proliferation. However, tPA-induced proliferation was inhibited dose-dependently to a maximum of 78% using a monoclonal antibody against the tPA EGF-finger domain. This antibody, known to inhibit tPA binding to its receptor, did not inhibit tPA-induced plasmin generation. To investigate the role of potential signal transduction pathways, ECs were exposed to lavendustin A, a tyrosine kinase inhibitor, at 33.5 microM (IC50 for basic fibroblast growth factor). Lavendustin A did not inhibit tPA-induced EC proliferation. However, Rp-cAMP, an inhibitor of cAMP-dependent kinases, specifically inhibited tPA-induced EC proliferation in a dose-dependent manner (IC50 = 50.5 microM). Pertussis toxin at maximal concentrations for this system (0.5 ng/ml) did not inhibit tPA-induced EC proliferation.

CONCLUSION

These results lend support to the hypothesis that tPA may have a direct receptor-mediated effect on EC proliferation and that this effect occurs independent of plasmin and may be dependent upon protein kinase A activity.

Retroviral-mediated transduction of endothelial cells with the lac Z gene impairs cellular proliferation in vitro and graft endothelialization in vivo

PURPOSE

An endothelialized lumen within a synthetic graft that expresses recombinant proteins with anticoagulant or antiproliferative activity has the potential to improve graft function. However, preliminary data suggest that genetic modification of endothelial cells (ECs) impairs their proliferation. The purpose of this investigation was to test the hypothesis that retroviral transduction of cultured ECs with the lac Z gene encoding for beta-galactosidase would decrease EC proliferation in vitro and graft endothelialization in vivo.

METHODS

In vitro studies compared canine EC proliferation over a 14-day period among early-passage ECs (two and three) and late-passage ECs (six and nine) transduced with the BAG vector (containing the lac Z gene and the neomycin resistance gene), ECs transduced with the neomycin resistance gene only, the nontransduced ECs. In vivo canine studies assessed endothelialization of expanded polytetrafluoroethylene thoracoabdominal grafts seeded with autologous lac Z-transduced ECs (n = 7) or nontransduced ECs (n = 3) compared with that of nonseeded grafts (n = 3). Histochemical staining and DNA polymerase chain reaction was used 6 weeks after implantation to detect the presence of the lac Z gene in the grafts' cellular linings and perigraft tissues. Endothelialization was assessed by light microscopy and electron microscopy.

RESULTS

Proliferation of late-passage lac Z-transduced ECs in vitro was significantly decreased compared with neomycin resistance-transduced ECs or nontransduced ECs. Among early-passage ECs smaller but significant decreases in proliferation were noted among lac Z-transduced cells compared with nontransduced cells. Six of seven expanded polytetrafluoroethylene grafts seeded with transduced ECs showed lac Z gene expression. Lac Z gene expression was not found on grafts seeded with nontransduced ECs or nonseeded grafts. The endothelialized luminal surface area was significantly less in grafts seeded with lac Z-transduced ECs compared with grafts seeded with nontransduced ECs.

CONCLUSIONS

Retroviral-mediated transduction of canine ECs with the lac Z gene encoding for beta-galactosidase impairs EC proliferation in vitro and the ability of transduced ECs to form a confluent EC monolayer on the luminal surface of synthetic grafts in vivo.

Systemic delivery of the interleukin-1 receptor antagonist protein using a new strategy of direct adenoviral-mediated gene transfer to skeletal muscle capillary endothelium in the isolated rat hindlimb

Current gene therapy strategies using adenoviral vectors to target the lung or liver have been complicated by an acute inflammatory response that can result in loss of transgene expression as well as tissue injury and necrosis. Skeletal muscle comprises 40% of total body weight; it possesses a high density, accessible capillary network that is resistant to injury and thus may be a logical target for adenoviral vectors. We hypothesized that adenoviral transduction of the rat skeletal muscle capillary bed during vascular isolation would achieve efficient gene transfer sufficient to achieve systemic serum levels of a recombinant protein without significant tissue injury. During vascular isolation of the hindleg, a replication-incompetent adenovirus (Ad) encoding for either the marker gene, human placental alkaline phosphatase (hpAP), or interleukin-1 receptor antagonist (IL-1ra) was infused and subsequently flushed from the circulation after a 30-min dwell period. Gene transfer over a 10(9)-10(12) particle/ml range to the gastrocnemius capillary endothelium and muscle fibers was highly efficient and titer-dependent, reaching maximum transduction rates of 71 +/- 7% and 25 +/- 5%, respectively, 5 days after gene transfer (n = 3-8 rats/group, p < 0.05). hpAP transgene expression was barely detectable at 14 days. No significant tissue injury or necrosis of the skeletal muscle was observed at 5 and 14 days, and distant organ gene transfer was minimal or absent. Gastrocnemius muscle from rats (n = 4) given Ad-IL-1ra had 241 +/- 66 pg IL-1ra/mg protein at 5 days, while those given Ad-hpAP, negative control (n = 3) had 35 +/- 14 pg IL-1ra/mg protein (p < 0.05). Ad-IL-1ra rats (n = 4) had serum levels of 185 +/- 20 pg/ml IL-1ra at 5 days whereas Ad-hpAP control rats (n = 5) had no IL-1ra detectable (p < 0.0001). Athymic rats given Ad-IL-1ra (n = 6) had serum levels of 493 +/- 62 pg/ml IL-1ra 14 days after transduction, and IL-1ra was detected for up to 98 days. Sera from Ad-IL-1ra athymic rats significantly inhibited IL-1 beta-induced (1 ng/ml) prostaglandin E2 (PGE2) production from cultured endothelial cells by 82 +/- 2% (p < 0.001). Thus, this gene transfer strategy is the first to result in substantial transduction of both skeletal muscle capillary endothelium and fibers, sufficient to achieve pharmacologic levels of IL-1ra. Although no acute tissue injury or necrosis was observed, persistence of transgene expression in athymic rats suggests that loss of expression in normal rats was by an immune-mediated mechanism.

A [+18RGD] protamine variant for nontoxic and effective reversal of conventional heparin and low-molecular-weight heparin anticoagulation

Protamine sulfate reversal of heparin anticoagulation causes adverse side effects. Additionally, protamine sulfate is relatively ineffective at reversing factor Xa inhibition caused by low-molecular weight heparin (LMWH, Enoxaparin). Previously, a +18 compound partially reversed heparin and LMWH with minimal toxicity. In the present study, a new +18 protamine-like variant, [+18RGD], with an added RGD sequence [acetyl-EA(R2A2R2A)4R2GRGDSPA-amide], was compared to a previously developed compound, [+18BE,Acetyl-EAA-(K2A2K2A)4K2-Amide] and standard protamine [Prot +21] regarding the reversal of conventional unfractionated heparin (Hep) and LMWH. These three agents were given at 1 mg per 100 IU activity of Hep or LMWH rapidly over 10 sec. Hemodynamic toxicity was based on maximum declines in blood pressure, heart rate, cardiac output, and oxygen consumption over the first 5 min after reversal (calculated as a total toxicity score, TTS). The more negative the TTS, the more toxic the agent. Degrees of toxicity (TTS) of [+18RGD], [+18BE],and[Prot +21] for reversal of Hep were -1.19, -2.00, and -7.32, respectively; and for reversal of LMWH they were -2.85, -3.98,and -6.17, respectively. These differences were significant for Hep (P < 0.01) and approached significance for LMWH (P = 0.07). Maximum hemodynamic perturbations paralleled the TTS pattern. [+18RGD] provided equal reversal efficacy to [Prot +21] for Hep, with a statistically significant (P < 0.05) lessening of platelet count declines (Plt 27, -46, and -55%, respectively). [+18RGD] improved reversal efficacy for LMWH, at 3, 10, and 30 min following its administration. At 3 min, antifactor Xa reversal was 72, 40, and 30%, respectively, for [+18RGD], [+18BE], and [Prot +21]; [+18RGD] effects were significantly better (P < 0.01). [+18RGD] reversed both Hep and LMWH anticoagulation with minimal toxicity. Such a compound should decrease clinical complications attending the use of standard protamine for reversal of conventional heparin or LMWH anticoagulation.

PKH26 and 125I-PKH95: characterization and efficacy as labels for in vitro and in vivo endothelial cell localization and tracking

PKH26, a fluorescent cell label, and PKH95, a 125 I-radioactive cell label, are both potentially valuable endothelial cell labels because they bind irreversibly within cell membranes. These labels would be particularly well suited to tract transplanted endothelial cells in vivo. However, no previous studies documenting lack of transfer of the label to unlabeled endothelial cells, as well as the effect of the label on endothelial cell function, have been undertaken. The purpose of this study was to determine the optimal method of endothelial cell (EC) labeling with PKH26 and PKH95, whether significant to EC-to-EC transfer of the label occurs, the effects of these labels on EC proliferation and membrane function, and the feasibility of using these labels for long-term quantitative EC tracking in vivo. Canine ECs in confluent monolayers or in cell suspension were labeled by exposure to 1.0 or 5.0 microM PKH26 for 1, 3, or 5 min. Cell viability was determined by trypan blue exclusion. The percentage of cells labeled and their fluorescence intensity were determined in a fluorescent-activated cell sorter (FACS). Effect of the label on cell function was assessed by measuring EC proliferation rates as well as intercellular adhesion molecule (ICAM) expression before and after induction with tumor necrosis factor (TNF). To determine if transfer of the label occurs, both labeled and nonlabeled ECs were grown in coculture and subjected to FACS analysis. For in vivo cell tracking, doubly labeled ECs were injected into the femoral artery of rat hind-limbs, and whole-body tissue analysis was undertaken to determine labeled-EC distribution at 60 days. Endothelial cells were labeled with equal efficacy as monolayers or in suspension. Labeling had no effect on EC proliferation rates nor on TNF-induced upregulation of ICAM expression. Coculture experiments revealed no significant label transfer to nonlabeled ECs. In vivo cell tracking studies documented that 8% of label remained within the skeletal muscle capillaries at 60 days after injection. PKH26 and PKH95 labels incorporate stably into EC membranes, do not alter endothelial cell function, and provide a precise means for quantitative EC tracking and histologic localization both in vitro and in vivo. These labels should prove to be very useful for studies of endothelial cell biology and transplantation.

Effects of differing rates of protamine reversal of heparin anticoagulation

BACKGROUND

Protamine sulfate reversal of heparin anticoagulation may be associated with adverse cardiovascular side effects. The purpose of this study was to determine whether diminished systemic oxygen consumption and hemodynamic changes were more likely to accompany rapid versus slow protamine administration.

METHODS

Fifteen patients undergoing abdominal aortic aneurysm resection in a prospective randomized double-blinded study received intravenous protamine (1.5 mg/kg) rapidly during a 3-minute period (group I, n = 7) or slowly during a 15-minute period (group II, n = 8). Systemic oxygen consumption (VO2) and hemodynamic parameters were assessed for up to 20 minutes after protamine administration began.

RESULTS

Blood pressure declines (millimeters of mercury) were greatest in group I with rapid protamine administration (-19 systolic and -9 diastolic) compared with group II with slow protamine administration (-12 systolic and -1 diastolic). Heart rate fell markedly in both groups I and II. Cardiac output (CO) declined in group I at virtually all time periods. Similar CO declines in group II occurred 10 minutes after protamine infusion had begun and persisted for 3 minutes after protamine administration was complete. Maximum VO2 decreases were -16% (60 seconds into protamine infusion) and -13% (1.5 minutes after protamine infusion) in groups I and II, respectively, with statistically significant declines (p < 0.05) occurring only in group I compared with baseline values. Statistically significant differences (p < 0.01), however, were found when mean declines during and after protamine infusion were compared with controls for both CO and VO2 in both groups.

CONCLUSIONS

Significant declines in systemic VO2 and hemodynamic perturbations accompany protamine reversal of heparin anticoagulation during aortic surgery. Rapid protamine administration increases the magnitude of these adverse responses.

Nitric oxide reversibly inhibits the migration of cultured vascular smooth muscle cells

Augmentation of nitric oxide (NO) production in vivo decreases lesions in a variety of models of arterial injury, and inhibition of NO synthase exacerbates experimental intimal lesions. Both vascular smooth muscle cell (VSMC) proliferation and migration contribute to lesion formation. Although NO inhibits VSMC proliferation, its effects on VSMC migration are unknown. To test the hypothesis that NO inhibits VSMC migration independent of inhibition of proliferation, we examined migration of rat aortic VSMCs after wounding of a confluent culture in the presence of chemical donors of NO. Hydroxyurea was used to eliminate any confounding effect of NO on proliferation. Three NO donors, diethylamine NONOate, spermine NONOate, and S-nitrosoglutathione, exhibited concentration-dependent inhibition of both number of migrating VSMCs and maximal distance migrated. Inhibition of migration was also seen with 8-Br-cGMP, suggesting that activation of guanylate cyclase may play a role in mediating the antimigratory effects of NO. Migration resumed after removal of NO donors, as evidenced by an increase in distance migrated. Measurement of VSMC protein synthesis and mitochondrial respiration indicated that inhibition of migration by NO donors was not due to metabolic cytostasis. These findings indicate that NO reversibly inhibits VSMC migration independent of proliferation or cytotoxicity, a novel mechanism by which both endogenous and pharmacological NO may alter vascular pathology.

Vascular surgery in the United States: workforce issues. Report of the Society for Vascular Surgery and the International Society for Cardiovascular Surgery, North American Chapter, Committee on Workforce Issues

The Committee on Workforce Issues of the Society for Vascular Surgery (SVS) and the North American Chapter, International Society for Cardiovascular Surgery (NA-ISCVS) generated data on the numbers and trends of operations performed and workforce requirements to provide surgical care of patients with vascular disease. Data for analysis were obtained from The National Center for Health Statistics-National Hospital Discharge Survey and questionnaires sent to 2732 vascular surgeons. The data showed that SVS/NA-ISCVS and regional vascular society (RVS) surgeons performed 51% of 583,000 vascular procedures undertaken in the United States in 1992. This represents a 24% increase over the 41% reported in 1985 by similarly defined surgeons. Analysis of 1992 index cases documented that SVS/NA-ISCVS and RVS surgeons accounted for 80% of 31,000 aortoiliofemoral bypasses, 68% of 46,000 aortic aneurysmectomies, 64% of 91,000 carotid endarterectomies, and 72% of 98,000 angioaccess procedures. The mean numbers of vascular operations performed in 1992 by SVS/NA-ISCVS and RVS surgeons were 144 and 100, respectively. These procedures represented 64% and 39% of the total surgical caseload of SVS/NA-ISCVS and RVS surgeons, respectively. American Board of Surgery (ABS)-certified vascular surgeons performed a mean of 171 vascular operations in 1992. Other surgeons, including ABS-certified general surgeons, appear to be performing fewer vascular operations. The latter fact and the increasing incidence of vascular disease in an expanding elderly population supports a continued need for vascular surgery specialists. Evolving technology and new health care delivery systems, however, may lessen the need for surgical care of these patients. Continued assessments of workforce activity will allow better definition of changing vascular surgery needs.

Cerebral oximetry in patients undergoing carotid endarterectomy under regional anesthesia

BACKGROUND AND PURPOSE

Near-infrared spectroscopy is a technique that can potentially monitor changes in cerebral oxygenation. There are at present limited clinical data regarding the value of this technology in relating neurological outcome to cerebrovascular hemoglobin oxygen saturation (ScO2). This investigation reports changes in ScO2 due to carotid cross-clamping during carotid endarterectomy in awake patients.

METHODS

ScO2 was monitored in 38 adult patients undergoing 41 carotid endarterectomies under regional anesthesia. Ipsilateral and contralateral hemispheres were monitored simultaneously during 36 operations, with ipsilateral monitoring alone in the remaining 5 operations.

RESULTS

No significant difference was detected between ipsilateral and contralateral ScO2 during preclamp or postclamp periods. Carotid cross-clamping caused a statistically significant (P < .01) decrease in the ipsilateral ScO2, which decreased from 71.8 +/- 6.91% to 65.8 +/- 8.2%, while the contralateral ScO2 remained stable at 70.5 +/- 7.5% and 70.3 +/- 7.9%. The change in ipsilateral ScO2 ranged from +2.6% to -28.6% of the preclamp value. The difference between ipsilateral and contralateral ScO2 during cross-clamping was statistically significant (P < .001). The duration of cross-clamping was 39 +/- 11 minutes (range, 18 to 89 minutes). The decrease in ipsilateral ScO2 was highly variable from patient to patient and did not correlate with the duration of cross-clamping.

CONCLUSIONS

These results suggest that carotid artery occlusion causes a statistically significant but variable decrease in ScO2 in the majority of patients. Data in this investigation provide a range of ScO2 values that was not associated with a clinically detectable neurological dysfunction.