The influence of hemodynamics and wall biomechanics on the thrombogenicity of vein segments perfused in vitro

This study addresses the hypothesis that exposure to peripheral arterial (ART) or coronary (COR) hemodynamics and wall biomechanics affect platelet deposition on vein segments. Intact human saphenous vein (HSV) and porcine internal jugular vein (PIJV) segments were studied under venous (VEN), ART, and COR environments using in vitro perfusion systems. Wall shear stress (tau) and circumferential wall stress (sigma(theta)) were calculated for PIJV segments. Platelet deposition was measured using a radioactive assay. PIJV ART segments exhibited a 14% increase in inner diameter over time (P < 0.05). tau, acting on PIJV ART specimens, was less at 6 h compared with time 0 (P < 0.05). sigma(theta) was lower in the VEN specimens compared with ART and COR groups (P < 0.01). Platelet deposition decreased by 40% on PIJV ART segments (P < 0.05) but increased 3.2-fold on PIJV COR segments (P < 0.05) versus VEN control segments. Platelet deposition was increased 1.75-fold in COR HSV cases versus VEN segments. These data indicate that short-term exposure to COR conditions lead to enhanced platelet deposition, whereas ART conditions decrease platelet deposition.     

Plasma Vasopressin Levels and Urinary Sodium Excretion during Cardiopulmonary Bypass with and without Pulsatile Flow

The use of pulsatile perfusion during bypass should create a more physiological milieu and thus attenuate the vasopressin stress response. To determine this, 20 patients scheduled for elective coronary artery bypass operation were studied in two groups. Group 1 had standard nonpulsatile perfusion, and in Group 2 a pulsatile pump was used. Measurements were made before and after anesthesia, after surgical incision, and at 15 and 30 minutes during and after cardiopulmonary bypass.In both groups, vasopressin levels were significantly elevated after sternotomy (4.5 ± 1.5 to 37 ± 10 pg/ml in Group 1 and 3.1 ± 1.2 to 33 ± 9 pg/ml in Group 2, p < 0.05) and during bypass (198 ± 19 pg/ml in Group 1 and 113 ± 16 pg/ml in Group 2) but were higher in Group 1 (p < 0.05). With comparable perfusion pressures in both groups, Group 2 required higher flow (4.5 ± 0.2 versus 3.5 ± 0.3 L/min, p < 0.05) and had lower resistance (1,351 ± 182 versus 1,841 ± 229 dynes sec cm^-5, p < 0.05) and higher urine Na⁺ (123 ± 5 versus 101 ± 8 mEq/L, p < 0.05). These data demonstrate that pulsatile flow can significantly attenuate the vasopressin stress response to bypass. Since vasopressin, at these concentrations, is a potent vasoconstrictor and is capable of producing a Na⁺ diuresis, this may partially explain the higher flow requirements and the decrease in Na⁺ excretion.     

Vein adaptation to the hemodynamic environment of infrainguinal grafts

Purpose: Although arteries appear to remodel in response to changes in hemodynamic parameters such as shear stress, little is known about functioning human vein grafts. This study was designed to explore diameter changes in human saphenous vein grafts after infrainguinal bypass.Methods: We used duplex ultrasonography to measure hemodynamic variables that might affect the diameter of 48 in situ saphenous vein grafts during the first year after infrainguinal arterial bypass. Volumetric flow rate, average velocity, peak systolic velocity, and vein diameter in the proximal and distal thirds of these grafts were each measured at 1 week and at 3, 6, and 12 months after operation. Veins were divided into three groups based on initial size (1 week after bypass) in the below-knee segment: small, < 3.5 mm diameter; medium, 3.5 to 4 mm diameter; and large, > 4 mm diameter.Results: Distal vein diameters at 1 week for small, medium, and large grafts were 2.9 ± 0.1, 3.7 ± 0.1, and 4.3 ± 0.1 mm, respectively (p < 0.001), but by 12 months these diameters were 3.6 ± 0.2, 3.8 ± 0.2, and 3.9 ± 0.2 mm, respectively (p = 0.54). Large veins decreased in diameter, whereas small veins increased in diameter, as confirmed by linear regression of percent change in diameter versus initial vein graft diameter (r = -0.62, p < 0.001). Volumetric flow rate, peak systolic velocity, and shear stress also tended to approach uniform values over time. Of the hemodynamic variables studied, the best predictor of diameter change was shear stress (linear regression of percent change in diameter vs shear stress, r = 0.67, p < 0.001). Veins with a diameter increase greater than 10% over time had significantly higher initial shear stress than veins with a diameter decrease greater than 10% over time (28.6 ± 3.8 vs 13.1 ± 1.8 dynes/cm², p < 0.01), whereas initial volumetric flow rates in these two groups were similar (135 ± 23 vs 130 ± 15 ml/min).Conclusions: Infrainguinal in situ vein graft diameter, volume flow rate, peak systolic velocity, and shear stress all tend to stabilize at uniform values regardless of the initial vein graft diameter. Of the hemodynamic variables studied, shear stress is most strongly associated with the change in diameter over time. Thus human saphenous vein appears to be capable of adapting to its hemodynamic environment after arterial grafting by modulating diameter to normalize shear stress. (J VASC SURG 1994;19:970–9.)     

Preoperative thromboxane A2/prostaglandin H2 receptor activity predicts early graft thrombosis

Purpose: This study was carried out to determine whether early failure of infrainguinal bypass grafts is associated with increased expression of platelet thromboxane A₂/prostaglandin H₂ (TXA₂/PGH₂) receptors. A prospective correlation of preoperative platelet TXA₂/PGH₂ receptor-mediated activity with lower extremity graft patency was sought. Methods: Twenty-five patients who underwent infrainguinal bypass surgery for limb salvage were studied at an inpatient academic tertiary referral center and Department of Veterans Affairs Medical Center. Outcome measures were primary graft patency rate at 3 months, platelet TXA₂/PGH₂ receptor activity by equilibrium binding with ₁₂₅I-BOP, and aggregation to the TXA₂-mimetic U46619. Results: Preoperative platelet TXA₂/PGH₂ receptor density was higher (B_max, 3100 ± 1300 vs 1500 ± 1100 sites/platelet [mean ± SD]; p = 0.004) in the five patients who had graft thrombosis within 3 months. The EC₅₀ for U46619 was lower (26 ± 6 nmol/L vs 57 ± 30 nmol/L; p < 0.05) in these patients as well, confirming the functional effect of the increased receptor density. Early graft thrombosis was more likely in patients with a platelet TXA₂/PGH₂ receptor density greater than 3000 sites/platelet (odds ratio, 76; 95% confidence interval, 3.9 to 1500) or an EC₅₀ for U46619 less than 30 nmol/L (odds ratio, 16; 95% confidence interval, 1.4 to 180). Conclusions: Elevated platelet TXA₂/PGH₂ receptor levels and enhanced sensitivity of platelet aggregation to TXA₂ predict early arterial graft thrombosis. Specific TXA₂/PGH₂ receptor antagonism may prevent one of the mechanisms that contributes to early graft occlusion. (J Vasc Surg 1998;27:317-28.)     

Reduction of vein graft intimal hyperplasia and preservation of endothelium-dependent relaxation by topical vascular endothelial growth factor

Purpose: Recent evidence suggests that vascular endothelial growth factor (VEGF), in addition to stimulating angiogenesis, also serves a repair/maintenance or survival function, modulating various aspects of endothelial cell function. This study was designed to examine the effect of VEGF pretreatment in a model of vein graft intimal hyperplasia. Methods: Reversed jugular vein–to–common carotid artery interposition grafts were constructed in New Zealand White rabbits. Vein conduits were immersed in solution containing 500 mg rhVEGF165 or saline solution for 20 minutes before implantation. Twenty-eight days later the vein grafts and contralateral control jugular veins were harvested for either histologic or isometric tension studies. Results: VEGF-treated vein grafts showed a 23% reduction in intimal area (0.76 ± 0.07 mm² vs 0.98 ± 0.06 mm²; p = 0.028) and a 30% reduction in intimal thickness (62 ± 6 μm vs 89 ± 5 μm; p = 0.001) when compared with control grafts. After precontraction with norepinephrine, the maximal relaxation to acetylcholine (endothelium-dependent, receptor-mediated agonist) for control vein grafts was 0%, whereas for VEGF-treated vein grafts it was 25% ± 9% (p < 0.05 vs control grafts). The maximal relaxation to the calcium ionophore A23187 (endothelium-dependent, receptor-independent agonist) was also greater in VEGF-treated grafts than in control grafts (172.3% ± 19.4% vs 122.5% ± 13.7%; p < 0.05). There was no difference in the response to sodium nitroprusside (endothelium-independent agonist) between the two groups. Conclusions: A single topical application of VEGF before implantation reduces intimal hyperplasia and improves endothelial function in a rabbit vein graft model. Further evaluation of this simple strategy to improve vein graft patency appears warranted. (J Vasc Surg 1998;27:167-73.)     

Treatment of vascular graft infection by in situ replacement with a rifampin-bonded gelatin-sealed Dacron graft

Purpose: The purpose of this study was to treat an established prosthetic vascular graft infection by in situ replacement with a rifampin-bonded gelatin-sealed Dacron graft in an animal model.Methods: The infrarenal aorta of 18 dogs was replaced with a gelatin-sealed graft contaminated in vitro by soaking it in a solution with Staphylococcus epidermidis. One week later, animals were randomized into three groups. In group I (control, (n = 6), the dogs did not undergo repeat operations. The dogs in groups II and III underwent repeat operation. In these animals the infected grafts were removed for bacteriologic analysis and replaced in situ with one of two types of grafts: group II (n = 6) received an untreated, gelatin-sealed graft; group III (n = 6) received a rifampin-bonded, gelatin-sealed graft. Antibiotic bonding was obtained by soaking grafts for 15 minutes in a 60 mg/ml saline solution of rifampin at 37° C. All 18 dogs received no systemic adjunct antibiotic therapy. Control grafts and replacement grafts were removed 4 weeks after the initial implantation for bacteriologic analysis. When harvested, all the grafts were cut into two fragments, and quantitative bacterial cultures were obtained from all the fragments. Results were expressed as colony-forming units (CFU)/cm² of graft material.Results: All 18 initially implanted grafts and all the untreated replacement grafts were grossly infected at the time of removal, whereas all the rifampin-bonded replacement grafts had normal incorporation. None of the rifampin-bonded grafts grew bacteria, whereas all the initially implanted and all the untreated replacement grafts were infected (p < 0.01). Bacterial counts from the infected fragments were similar in control grafts (2.6 ± 1.9 × 10⁶ CFU/cm²), in initially implanted grafts of groups II (9 ± 1.1 × 10⁵ CFU/cm²) and III (1.3 ± 1.5 × 10⁶ CFU/cm²), and in untreated replacement grafts of group II (1.7 ± 2.5 × 10⁶ CFU/cm²). Blood culture results and culture results of liver, spleen, kidney, and lung specimens at the time of sacrifice were negative.Conclusion: This study demonstrates that rifampin-bonded gelatin-sealed Dacron grafts are resistant to infection when used for in situ replacement of an infected graft in the dog. (J VASC SURG 1994;19:739-44.)     

Effect of Two‐Year Caloric Restriction on Bone Metabolism and Bone Mineral Density in Non‐Obese Younger Adults: A Randomized Clinical Trial

Although caloric restriction (CR) could delay biologic aging in humans, it is unclear if this would occur at the cost of significant bone loss. We evaluated the effect of prolonged CR on bone metabolism and bone mineral density (BMD) in healthy younger adults. Two‐hundred eighteen non‐obese (body mass index [BMI] 25.1 ± 1.7 kg/m²), younger (age 37.9 ± 7.2 years) adults were randomly assigned to 25% CR (CR group, n = 143) or ad libitum (AL group, n = 75) for 2 years. Main outcomes were BMD and markers of bone turnover. Other outcomes included body composition, bone‐active hormones, nutrient intake, and physical activity. Body weight (–7.5 ± 0.4 versus 0.1 ± 0.5 kg), fat mass (–5.3 ± 0.3 versus 0.4 ± 0.4 kg), and fat‐free mass (–2.2 ± 0.2 versus –0.2 ± 0.2 kg) decreased in the CR group compared with AL (all between group p < 0.001). Compared with AL, the CR group had greater changes in BMD at 24 months: lumbar spine (–0.013 ± 0.003 versus 0.007 ± 0.004 g/cm²; p < 0.001), total hip (–0.017 ± 0.002 versus 0.001 ± 0.003 g/cm²; p < 0.001), and femoral neck (–0.015 ± 0.003 versus –0.005 ± 0.004 g/cm²; p = 0.03). Changes in bone markers were greater at 12 months for C‐telopeptide (0.098 ± 0.012 versus 0.025 ± 0.015 μg/L; p < 0.001), tartrate‐resistant acid phosphatase (0.4 ± 0.1 versus 0.2 ± 0.1 U/L; p = 0.004), and bone‐specific alkaline phosphatase (BSAP) (–1.4 ± 0.4 versus –0.3 ± 0.5 U/L; p = 0.047) but not procollagen type 1 N‐propeptide; at 24 months, only BSAP differed between groups (–1.5 ± 0.4 versus 0.9 ± 0.6 U/L; p = 0.001). The CR group had larger increases in 25‐hydroxyvitamin D, cortisol, and adiponectin and decreases in leptin and insulin compared with AL. However, parathyroid hormone and IGF‐1 levels did not differ between groups. The CR group also had lower levels of physical activity. Multiple regression analyses revealed that body composition, hormones, nutrients, and physical activity changes explained ～31% of the variance in BMD and bone marker changes in the CR group. Therefore, bone loss at clinically important sites of osteoporotic fractures represents a potential limitation of prolonged CR for extending life span. Further long‐term studies are needed to determine if CR‐induced bone loss in healthy adults contributes to fracture risk and if bone loss can be prevented with exercise. © 2015 American Society for Bone and Mineral Research.     

Long-term performance of an external stent for saphenous vein grafts: the VEST IV trial

Background

Externally stenting saphenous vein grafts reduces intimal hyperplasia, improves lumen uniformity and reduces oscillatory shear stress 1 year following surgery. The present study is the first to present the longer-term (4.5 years) performance and biomechanical effects of externally stented saphenous vein grafts.

Methods

Thirty patients previously implanted with the VEST external stent in the randomized, within-patient-controlled VEST I study were followed up for adverse events; 21 of these were available to undergo coronary angiography and intravascular ultrasound.

Results

Twenty-one stented and 29 nonstented saphenous vein grafts were evaluated by angiography and ultrasound at 4.5?±?0.3 years. Vein graft failure rates were comparable between stented and nonstented grafts (30 and 23% respectively; p?=?0.42). All failures were apparent at 1 year except for one additional nonstented failure at 4.5 years. In patent vein grafts, Fitzgibbon perfect patency remained significantly higher in the stented versus nonstented vein grafts (81 and 48% respectively, p?=?0.002), while intimal hyperplasia area (4.27 mm²?±?1.27 mm² and 5.23 mm²?±?1.83 mm² respectively, p?<?0.001) and thickness (0.36 mm?±?0.09 mm and 0.42 mm?±?0.11 mm respectively, p?<?0.001) were significantly reduced. Intimal hyperplasia proliferation correlated with lumen uniformity and with the distance between the stent and the lumen (p?=?0.04 and p?<?0.001 respectively).

Conclusions

External stenting mitigates saphenous vein graft remodeling and significantly reduces diffuse intimal hyperplasia and the development of lumen irregularities 4.5 years after coronary artery bypass surgery. Close conformity of the stent to the vessel wall appears to be an important factor.

Trial registration

NCT01415245. Registered 11 August 2011.

     

The merit of polytetrafluoroethylene extensions and interposition grafts to salvage failing infrainguinal vein bypasses

Purpose: The purpose of this study was to evaluate the merit of polytetrafluoroethylene (PTFE) extensions and interpositions for the management of failing infrainguinal vein bypass grafts.Methods: The treatment of 133 failing vein grafts in 125 patients over a 10-year period was retrospectively reviewed. Twenty-two graft-threatening lesions were detected in patients who did not have a usable autogenous vein conduit as determined by preoperative and intraoperative evaluations. A PTFE extension or interposition graft was used for the necessary reconstruction in all cases.Results: Ten lesions were within the vein graft, 11 were proximal to the graft in the femoral or popliteal artery segments, and one was distal to the graft in the popliteal artery. The treatment of these lesions included 19 extensions and three mid graft interpositions. The vein graft lesions developed significantly sooner (mean 10.6 ± 2.5 months) after the bypass ( p < 0.05) than the arterial lesions (mean 28.0 ± 6.1 months). The 3-year cumulative secondary patency rate for these vein grafts treated with PTFE extensions or interpositions was 84% ± 8%. This was not significantly different from the 3-year cumulative secondary patency rate for vein grafts treated with vein extensions or interpositions at our institution over the same time period (82% ± 10%). The 3-year limb salvage rates were 95% and 89%, respectively.Conclusions: These results indicate that PTFE extensions and interpositions can be used successfully to maintain the patency of failing vein grafts and may serve to prolong limb salvage in patients without any usable autogenous vein. Early reintervention with a PTFE conduit in this difficult group of patients is appropriate to salvage a failing vein graft. (J VASC SURG 1996;23:329-35.)     

Mesenteric shunting decreases visceral ischemia during thoracoabdominal aneurysm repair

Purpose: A technique to decrease visceral ischemic time during thoracoabdominal aneurysm (TAA) repair is reported. Methods: A 10 mm Dacron side-arm graft is attached to the aortic prosthesis and positioned immediately distal to the planned proximal thoracic aortic anastomosis. On completion of the anastomosis, a 16 to 22 Fr perfusion catheter is attached to the side-arm graft and inserted into the orifice of the celiac axis or superior mesenteric artery. The cross-clamp is then placed on the aortic graft distal to the mesenteric side-arm graft. Pulsatile arterial perfusion is thus established to the visceral circulation while intercostal anastomoses or reconstruction of celiac, superior mesenteric, and right renal arteries is performed. Visceral ischemic time and the rise in end-tidal Pco₂ after reconstruction of the visceral vessels in patients with mesenteric shunting was compared with a control group matched for aneurysm extent and treated immediately before use of the mesenteric shunt technique. Results: Between July and Oct, 1996, the technique was applied in 15 patients undergoing type I, II, or III TAA repair with a clamp and sew technique. The mean decrease in systolic arterial pressure was 12.5 ± 8.5 mm Hg, with a concomitant rise in end-tidal Pco₂ (mean, 6.9 ± 5.8 mm Hg), after perfusion was established through the mesenteric shunt. Mean time to establishment of visceral perfusion through the shunt was 25.5 ± 4.4 minutes; the resultant decrement in visceral ischemic time averaged 31.3 minutes (i.e., until celiac, superior mesenteric, and right renal arteries were reconstructed). Compared with controls, patients with shunts had a significantly decreased (6.9 ± 5.8 versus 21.6 ± 8.4 mm Hg; p = 0.0003) rise in end-tidal CO₂ on completion of visceral vessel reconstruction. Conclusions: In-line mesenteric shunting is a simple method to decrease visceral ischemia during TAA repair, and it is adaptable to clamp and sew or partial bypass and distal perfusion operative techniques.(J Vasc Surg 1998;27:745-9.)     

Selective adenosine-A2A activation reduces lung reperfusion injury following transplantation

Background: The adenosine-A_2A receptor on the neutrophil is responsible for several anti-inflammatory actions. We hypothesized that DWH-146e, a selective adenosine-A_2A agonist, would reduce lung reperfusion injury following transplantation.MethodsWe used an isolated, whole blood–perfused, ventilated rabbit lung model. Donor rabbits underwent lung harvest after pulmonary arterial PGE₁ injection and Euro-Collins preservation solution flush, and lungs were preserved for 18 hours at 4°C. Group I lungs (n = 9) served as control subjects. Group II lungs (n = 9) were reperfused with whole blood that was first passed through a leukocyte-depleting filter. In group III (n = 9), DWH-146e was added to the blood reperfusate (25 μg/kg) immediately before reperfusion and was administered throughout the reperfusion period (1 μg/kg/min). All lungs were reperfused for 30 minutes.ResultsArterial oxygenation in group II and group III was significantly higher than that of group I after 30 minutes of reperfusion (514.27 ± 35.80 and 461.12 ± 43.77 vs 91.41 ± 20.58 mm Hg, p < .001). Pulmonary vascular resistance was significantly reduced in group III (22,783 ± 357 dynes · s · cm⁻⁵) compared to both group II and group I (31,057 ± 1743 and 36,911 ± 2173 dynes · s · cm⁻⁵, p < .001). Airway compliance was improved in groups II and III when compared to group I (1.68 ± 0.08 and 1.68 ± 0.05 vs 1.36 ± 0.13, p = .03). Microvascular permeability in group III was reduced to 106.82 ± 17.09 compared with 165.70 ± 21.83 ng Evans blue dye per gram of tissue in group I (p = .05). Group III myeloperoxidase activity was 39.88 ± 4.87 compared with 88.70 ± 18.69 ΔOD/g/min in group I (p = .03); group II myeloperoxidase activity was 56.06 ± 7.46.ConclusionsDWH-146e reduced lung neutrophil sequestration and dramatically improved pulmonary graft function. Neutrophils are important components of the inflammatory cascade of reperfusion injury and their source may include both the circulating blood and the lung graft itself. Selective adensosine-A_2A activation interrupts the neutrophil-mediated inflammatory response and reduces lung reperfusion injury following transplantation.     

A prospective study of the determinants of vein graft flow velocity: Implications for graft surveillance

Purpose: Serial monitoring of vein graft peak systolic flow velocity (PSFV) has been endorsed as a technique for vein graft surveillance with low values (<45 cm/sec) considered a marker for impending graft failure. Optimal application of this method requires an understanding of the factors affecting PSFV in normal grafts. A prospective evaluation of 46 consecutive elective infrainguinal vein grafts (6 popliteal/29 tibial/11 pedal) was undertaken to assess the major determinants of PSFV.Methods: Factors recorded for each patient included vein graft diameter (VGD), measured outflow resistance (MOR), conduit length, outflow level (popliteal/tibial/pedal), inflow level (femoral/popliteal), systolic blood pressure, cardiac ejection fraction, the presence of a patent plantar arch, and Society for Vascular Surgery/International Society for Cardiovascular Surgery resistance scoring. MOR was measured by occluding graft inflow and infusing saline solution through a proximal graft cannula at 60 cc/min while simultaneously recording the pressure at the distal anastomosis via a separate cannula. MOR was calculated by dividing the resultant pressure by the infusion rate. MORs were expressed in resistance units and were measured before and after the infusion of papaverine (MOR_(PAP)). PSFVs and VGDs were measured 4 to 6 cm from the distal anastomosis 3 weeks after surgery with duplex scanning (60 degree angle with midstream sample volume).Results: PSFVs ranged from 22 to 148 cm/sec and averaged 83.4 ± 4.8 cm/sec. Pedal bypass grafts had significantly lower PSFVs (64 ± 10 vs 89.5 ± 5 cm/sec, p = 0.02) and significantly higher MOR_(PAP)s (0.86 ± 0.15 vs 0.51 ± 0.05 resistance units, p = 0.05) than bypasses to the popliteal/tibial level. When subjected to univariate analysis the factors correlating with PSFV were MOR (r = -0.59, p = 0.0001), MOR_(PAP) (r = -0.69, p = 0.0001) VGD (r = -0.31, p = 0.06), the Society for Vascular Surgery/International Society for Cardiovascular Surgery score (r = -0.35, p = 0.04), inflow level (r = -0.47, p = 0.002), and outflow level (r = -0.35, p = 0.03). When subjected to multiple regression analysis, only MOR_(PAP) (r ² = 0.51, p = 0.001) and VGD (r ² = 0.14, p =0.001) contributed significantly to the overall model (r ² = 0.65, p = 0.0001) withMOR_(PAP)) eliminating the effect of the other variables. The multiple regression model predicts PSFV as follows: PSFV = 176 + VGD_(mm)( -11.7) + MOR_(PAP))( -63.4).Conclusions: Clinically successful and hemodynamically normal vein grafts have widely variable, yet predictable flow characteristics that are influenced primarily by outflow resistance and VGD. This wide variability suggests that no single lower threshold value for PSFV is universally applicable in identifying all grafts at risk for failure. Detection of focal areas of flow acceleration within the graft may be more accurate in identifying grafts at risk for failure. (J VASC SURG 1994;19:259-67.)     

Haplotypes of Promoter and Intron 1 Polymorphisms in the <Emphasis Type="Italic">COLIA1</Emphasis> Gene Are Associated with Increased Risk of Osteoporosis

Osteoporosis is a common age-related disease with a strong genetic influence. COLIA1 is one of the most extensively studied candidate genes and has consistently been associated with BMD and fracture. We examined the effects of the polymorphisms –1997G>T, –1663indelT, and +1245G>T and their haplotypes on vertebral fractures and bone mineral density (BMD) in a case-control study comprising 462 osteoporotic patients and 336 controls. The ?1663indelT polymorphism was associated with a decreased lumbar spine (ls) BMD, 0.75 ± 0.14 g/cm², in individuals with the del/del genotype versus 0.83 ± 0.18 and 0.85 ± 0.18 g/cm² in individuals with the ins/del and ins/ins genotypes, respectively (p = 0.02). The T-allele of the +1245G>T polymorphism, which was in strong linkage disequilibrium (LD) with –1663indelT, was also associated with a decreased lsBMD (p = 0.02). –1997G>T was not significantly associated with lsBMD. The three most common haplotypes accounted for 98.5% of the alleles. Individuals with one or two copies of haplotype 1 (–1997G/–1663ins/+1245G) had a significantly higher lsBMD, 0.84 ± 0.18 and 0.85 ± 0.15 g/cm², respectively, versus 0.78 ± 0.15 g/cm² in noncarriers (p = 0.01). Individuals with two copies of haplotype 2 (–1997G/–1663del/+1245T) had a significantly lower lsBMD, 0.76 ± 0.14 g/cm², versus 0.85 ± 0.18 and 0.82 ± 0.18 g/cm², respectively, in individuals with zero or one copy (p = 0.03). The odds ratio for vertebral fracture in individuals carrying the variant T-allele of the –1997G>T polymorphism was 1.49 (CI, 1.03–2.16; p = 0.03). Logistic regression revealed that this effect was partly independent of BMD. In conclusion, the ?1663del and +1245T alleles influence BMD negatively, whereas the –1997T-allele has a minor effect on BMD but increases the risk of vertebral fractures. These findings are in agreement with functional studies showing that these polymorphisms influence gene expression.     

Application of High‐Resolution Skeletal Imaging to Measurements of Volumetric BMD and Skeletal Microarchitecture in Chinese‐American and White Women: Explanation of a Paradox

Asian women have lower rates of hip and forearm fractures despite lower areal BMD (aBMD) by DXA compared with white women and other racial groups. We hypothesized that the lower fracture rates may be explained by more favorable measurements of volumetric BMD (vBMD) and microarchitectural properties, despite lower areal BMD. To address this hypothesis, we used high‐resolution pQCT (HRpQCT), a new method that can provide this information noninvasively. We studied 63 premenopausal Chinese‐American (n = 31) and white (n = 32) women with DXA and HRpQCT. aBMD by DXA did not differ between groups for the lumbar spine (1.017 ± 0.108 versus 1.028 ± 0.152 g/cm²; p = 0.7), total hip (0.910 ± 0.093 versus 0.932 ± 0.134 g/cm²; p = 0.5), femoral neck (0.788 ± 0.083 versus 0.809 ± 0.129 g/cm²; p = 0.4), or one‐third radius (0.691 ± 0.052 versus 0.708 ± 0.047 g/cm²; p = 0.2). HRpQCT at the radius indicated greater trabecular (168 ± 41 versus 137 ± 33 mg HA/cm³; p = <0.01) and cortical (963 ± 46 versus 915 ± 42 mg HA/cm³; p < 0.0001) density; trabecular bone to tissue volume (0.140 ± 0.034 versus 0.114 ± 0.028; p = <0.01); trabecular (0.075 ± 0.013 versus 0.062 ± 0.009 mm; p < 0.0001) and cortical thickness (0.98 ± 0.16 versus 0.80 ± 0.14 mm; p < 0.0001); and lower total bone area (197 ± 34 versus 232 ± 33 mm²; p = <0.001) in the Chinese versus white women and no difference in trabecular number, spacing, or inhomogeneity before adjustment for covariates. Similar results were observed at the weight‐bearing tibia. At the radius, adjustment for covariates did not change the direction or significance of differences except for bone, which became similar between the groups. However, at the tibia, adjustment for covariates attenuated differences in cortical BMD and bone area and accentuated differences in trabecular microarchitecture such that Chinese women additionally had higher trabecular number and lower trabecular spacing, as well as inhomogeneity after adjustment. Using the high‐resolution technology, the results provide a mechanistic explanation for why Chinese women have fewer hip and forearm fractures than white women.     

Does graft mass impact on pediatric kidney transplant outcomes?

Background

The aim of this study is to assess the evolution of renal size and function in pediatric transplant patients according to the graft mass/recipient size ratio.

Methods

Fifty pediatric renal transplant recipients were followed over 2 years. Grafts were weighed, and three different graft mass/m² ratios were determined: (1) low graft mass (58 g/m², range?31–57 g/m²), (2) median (142 g/m², range?59–141 g/m²) and high (267 g/m², range?143–353 g/m²). Patients underwent repeated ultrasound Doppler scans and repeated measurements of estimated glomerular filtration rate (eGFR; 1 week and 1, 6, 12 and 24 months), urinary retinol-binding protein (RBP) and proteinuria (1 week and 6, 12 and 24 months).

Results

The volume of renal tissue increased by 12?±?5.6 cm³ at 24 months (p?=?0.035) in the low graft mass and decreased by ?14?±?7 cm³ (p?=?0.046) in the high graft mass. The eGFR increased when either low (30?±?5 ml/min/1.73 m², p?<?0.001) or median (19?±?4 ml/min/1.73 m², p?<?0.001) graft mass was transplanted but remained stable when high graft mass was transplanted. The resistive index (RI) presented a significant decrease throughout early follow-up in the transplants involving low and median graft mass, whereas a slight rise was observed in those involving high graft mass. A significant difference was apparent 6 months post-transplant. Transplants of low and median graft mass were associated with an initial higher urinary RBP. No significant differences in proteinuria were detected.

Conclusions

Small kidneys undergo increases in volume and function without escalation of either proteinuria or urinary RBP, characterizing an adequate adaptation to the recipient. Children receiving larger kidneys present a reduction in volume, stable GFR and higher RI at 6 months.     

Polyurethane vascular prostheses decreases neointimal formation compared with expanded polytetrafluoroethylene

Purpose: Synthetic grafts have been increasingly used for complex vascular reconstructions in patients with limited autologous vein availability. Materials currently in use induce increased stenosis and graft thrombosis compared with autologous vein, especially in smaller vessels. We examined whether grafts constructed of a porous biodegradation-resistant polycarbonate polyurethane (PU) exert better biocompatibility in terms of faster endothelialization and decreased chronic proliferation of intimal cells compared with expanded polytetrafluoroethylene (ePTFE). Methods: PU or ePTFE interposition grafts were implanted into the abdominal aortas of male Sprague-Dawley rats (PU, n = 37; ePTFE, n = 32). Grafts were removed at days 1, 7, 14, 28, and 56 and 6 months and were evaluated by immunohistochemical, electron microscopic, and morphometric techniques. Bromodeoxyuridine (BrdU) was injected at 1 and 24 hours before death to determine cellular proliferation. Endothelial cells and smooth muscle cells were identified with antibodies to von Willebrand factor and α-actin, respectively. Results:The luminal surface of PU grafts took 4 weeks to completely endothelialize, whereas ePTFE grafts took 24 weeks (P < .05). Neointimal cell proliferation was lower in PU grafts compared with ePTFE at 56 days (1.4 ± 0.1 versus 8.6 ± 1.5, P < .001) and at 6 months (0.15 ± 0.002 versus 3.4 ± 0.5, p < .001). Neointimal thickness at 6 months after implantation was 3.2 ± 0.8 μm for PU compared with 10.3 ± 3.1 μm for ePTFE (P < .05). Conclusion: Polycarbonate polyurethane small vascular prostheses promoted faster luminal endothelialization, induced less chronic intimal proliferation, and produced a significantly thinner neointima than ePTFE grafts. These findings suggest that aliphatic-polycarbonate urethanes may offer advantages over standard materials such as ePTFE for vascular graft construction. (J Vasc Surg 1999;29:168-76)     

Smoking is associated with impaired bone mass development in young adult men: A 5-year longitudinal study

It has previously been shown that smoking is associated with reduced bone mass and increased fracture risk, but no longitudinal studies have been published investigating altered smoking behavior at the time of bone mass acquisition. The aim of this study was to investigate the development of bone density and geometry according to alterations in smoking behavior in a 5‐year, longitudinal, population‐based study of 833 young men, age 18 to 20 years (baseline). Furthermore, we aimed to examine the cross‐sectional, associations between current smoking and parameters of trabecular microarchitecture of the radius and tibia, using high‐resolution peripheral quantitative computed tomography (HR‐pQCT), in young men aged 23 to 25 years (5‐year follow‐up). Men who had started to smoke since baseline had considerably smaller increases in areal bone mineral density (aBMD) at the total body (mean ± SD, 0.020 ± 0.047 mg/cm² versus 0.043 ± 0.040 mg/cm², p < 0.01) and lumbar spine (0.027 ± 0.062 mg/cm² versus 0.052 ± 0.065 mg/cm², p = 0.04), and substantially greater decreases in aBMD at the total hip (?0.055 ± 0.058 mg/cm² versus ?0.021 ± 0.062 mg/cm², p < 0.01) and femoral neck (?0.077 ± 0.059 mg/cm² versus ?0.042 ± 0.070 mg/cm², p < 0.01) than men who were nonsmokers at both the baseline and follow‐up visits. At the tibia, subjects who had started to smoke had a smaller increment of the cortical cross‐sectional area (CSA) than nonsmokers (8.1 ± 4.3 mm² versus 11.5 ± 8.9 mm², p = 0.03), and a larger decrement of trabecular volumetric BMD (vBMD) than nonsmokers (?13.9 ± 20.5 mg/mm³ versus ?4.1 ± 13.9 mg/mm³, p < 0.001). In the cross‐sectional analysis at follow‐up (23–25 years of age), smokers had significantly lower trabecular vBMD at the tibia (7.0%, p < 0.01) due to reduced trabecular thickness (8.9%, p < 0.001), as assessed using HR‐pQCT, than nonsmokers. In conclusion, this study is the first to report that men who start to smoke in young adulthood have poorer development of their aBMD at clinically important sites such as the spine and hip than nonsmokers, possibly due to augmented loss of trabecular density and impaired growth of cortical cross‐sectional area. © 2012 American Society for Bone and Mineral Research.     

NF-κB-dependent increase in tissue factor expression is responsible for hypoxic podocyte injury

Background

Fibrin deposition within glomeruli is commonly seen in kidney biopsy specimens, suggesting enhanced coagulant activity. Tissue factor (TF) is a coagulation factor which is also related to various biological effects, and TF is upregulated by hypoxia in cancer cells. Recently, hypoxic podocyte injury has been proposed, therefore, we investigated TF expression in hypoxia.

Methods

Conditionally immortalized human podocytes were differentiated and treated under hypoxic or normoxic conditions. mRNA expressions of TF and tissue factor pathway inhibitor (TFPI) were analyzed by quantitative RT-PCR. Protein levels of TF and TFPI were tested by enzyme-linked immunosorbent assay. We employed small interfering RNA (siRNA) to temporary knockdown early growth response protein 1 (Egr-1), hypoxia-inducible factor-1α (HIF-1α) and TF. The expression of CD2-associated protein (CD2AP) mRNA and phalloidin staining was examined to assess podocyte injury.

Results

Hypoxia increased mRNA expression of TF (6 h: 2.3 ± 0.05 fold, p < 0.001, 24 h: 5.6 ± 2.4 fold, p < 0.05) and suppressed TFPI (6 h: 0.54 ± 0.04 fold, p < 0.05, 24 h: 0.24 ± 0.06 fold, p < 0.001) compared with normoxia. Similarly, protein levels of TF were increased and TFPI were decreased. Egr-1 siRNA did not change TF mRNA expression. Pyrrolidine dithiocarbamate (PDTC), a nuclear factor kappa B (NF-κB) inhibitor, significantly reduced hypoxia induced TF expression, and HIF-1α knockdown further increased TF. Hypoxia resulted in decreased CD2AP and actin reorganization in podocytes, and these changes were attenuated by TF siRNA.

Conclusion

Hypoxia increased the expression of TF in human podocytes NF-κB dependently. TF may have a critical role in the hypoxic podocyte injury.

     

Chronic in vitro shear stress stimulates endothelial cell retention on prosthetic vascular grafts and reduces subsequent in vivo neointimal thickness

Objective: The absence of endothelial cells at the luminal surface of a prosthetic vascular graft potentiates thrombosis and neointimal hyperplasia, which are common causes of graft failure in humans. This study tested the hypothesis that pretreatment with chronic in vitro shear stress enhances subsequent endothelial cell retention on vascular grafts implanted in vivo. Methods: Cultured endothelial cells derived from Fischer 344 rat aorta were seeded onto the luminal surface of 1.5-mm internal diameter polyurethane vascular grafts. The seeded grafts were treated for 3 days with 1 dyne/cm² shear stress and then for an additional 3 days with 1 or 25 dyne/cm² shear stress in vitro. The grafts then were implanted as aortic interposition grafts into syngeneic rats in vivo. Grafts that were similarly seeded with endothelial cells but not treated with shear stress and grafts that were not seeded with endothelial cells served as controls. The surgical hemostasis time was monitored. Endothelial cell identity, density, and graft patency rate were evaluated 24 hours after implantation. Endothelial cell identity in vivo was confirmed with cells transduced in vitro with β-galactosidase complementary DNA in a replication-deficient adenoviral vector. Histologic, scanning electron microscopic, and immunohistochemical analyses were performed 1 week and 3 months after implantation to establish cell identity and to measure neointimal thickness. Results: The pretreatment with 25 dyne/cm²—but not with 0 or 1 dyne/cm²—shear stress resulted in the retention of fully confluent endothelial cell monolayers on the grafts 24 hours after implantation in vivo. Retention of seeded endothelial cells was confirmed by the observation that β-galactosidase transduced cells were retained as a monolayer 24 hours after implantation in vivo. In the grafts with adherent endothelial cells that were pretreated with shear stress, immediate graft thrombosis was inhibited and surgical hemostasis time was significantly prolonged. Confluent intimal endothelial cell monolayers also were present 1 week and 3 months after implantation. However, 1 week after implantation, macrophage infiltration was observed beneath the luminal cell monolayer. Three months after the implantation in vivo, subendothelial neointimal cells that contained α–smooth muscle actin were present. The thickness of this neointima averaged 41 ± 12 μm and 60 ± 23 μm in endothelial cell–seeded grafts that were pretreated with 25 dyne/cm² shear stress and 1 dyne/cm² shear stress, respectively, and 158 ± 46 μm in grafts that were not seeded with endothelial cells. Conclusion: The effect of chronic shear stress on the enhancement of endothelial cell retention in vitro can be exploited to fully endothelialize synthetic vascular grafts, which reduces immediate in vivo graft thrombosis and subsequent neointimal thickness. (J Vasc Surg 1999;29:157-67.)     

Prevention of Vascular Graft Infections with Antibiotic Graft Impregnation Prior to Implantation: In Vitro Comparison between Daptomycin,Rifampin and Nebacetin

ObjectiveTo compare the in vitro efficacy of graft impregnation with nebacetin versus rifampin versus daptomycin against vascular graft infections caused by Staphylococcus epidermidis and Staphylococcus aureus and nebacetin versus rifampin against Pseudomonas aeruginosa and Escherichia coli.MaterialsTwenty-three Dacron-grafts (1 cm²) for each micro-organism were microbiologically tested and eight grafts per antibiotic underwent viability tests against human umbilical vein endothelial cells (ECs). Fifteen grafts (5/antibiotic agent) underwent 15 min impregnation and contamination with 4 ml bacterial solution (optical density (OD_600 nm): 0.20 ± 0.02). After 24-h-incubation, all grafts were washed with phosphate-buffered saline and underwent sonification to release viable adherent bacteria. OD_600 nm of the solution was measured. Afterwards, six 1:10 dilution steps took place and colony-forming units (CFUs) were counted.ResultsNebacetin showed comparable efficacy to daptomycin against Gram-positive bacteria. Both eradicated more efficiently S. epidermidis than rifampin (daptomycin:0, rifampin:5 ± 7.3, nebacetin:0 CFU ml^?1, P = 0.0003). All antibiotics showed comparable antibacterial activity against S. aureus. Nebacetin was more efficient than rifampin to eradicate Gram-negative organisms (P. aeruginosa: rifampin:1308 ± 252, nebacetin:8 ± 8 CFU ml^?1, P = 0.01, E. coli: rifampin:294 ± 159, nebacetin:0.2 ± 0.5 CFU ml^?1, P = 0.001), while only rifampin was toxic against ECs (daptomycin:30.88 ± 5.44, rifampin:5.13 ± 5.08, nebacetin:28.50 ± 3.82 ECs/field, P = 0.0003).ConclusionsNebacetin showed excellent in vitro antibacterial activity against both Gram-positive and -negative pathogens representing an effective candidate for vascular graft impregnation.