A nanotechnology-based delivery system: Nanobots. Novel vehicles for molecular medicine

AIM

We previously demonstrated that adenovirus-mediated p53 gene transfer following balloon angioplasty, decreased neointimal hyperplasia. However, safety concerns arise because viral promoters can cause unrestricted transgene expression. The paucity of safe and efficient vehicles for gene transfer thus limits the potential for clinical utilization of gene therapy. Our objective was to design and clone a virus-free p53 construct, targeted to express specifically in vascular smooth muscle cells (SMCs), via a nanoparticle-based delivery system for therapeutic modulation in vascular wall.

METHODS

Biodegradable poly(lactide-co-glycolide) (PLGA), an FDA approved polymer, was used to formulate the nanoparticles. Cloned constructs consisting of SMC promoter, SM22, and p53 cDNA sequences along with enhanced green fluorescent protein (EGFP) gene, were loaded into PLGA nanoparticles. The affect of these nanobots on cell growth was examined.

RESULTS

The gene sequences carried by the nanobot are expressed in target cells. The p53/EGFP construct under the constitutive promoter was found to express in 293T human embryonic kidney cells, whereas the p53/EGFP with SMC promoter expressed only in human aortic SMCs. SMCs internalize these nanobots without compromising cell viability or growth kinetics.

CONCLUSION

A novel genetic sequence that targets a specific cell population has been successfully designed, cloned and encapsulated in a nanoparticle. This experiment is a significant step towards the development of a nanoparticle-based delivery system for therapeutic delivery of targeted gene-therapy towards attenuation of restenosis. Further work is necessary to expand the repertoire of this delivery system and determine whether it could become a versatile vehicle in molecular medicine.

Bayesian methods for meta-analysis of causal relationships estimated using genetic instrumental variables

Genetic markers can be used as instrumental variables, in an analogous way to randomization in a clinical trial, to estimate the causal relationship between a phenotype and an outcome variable. Our purpose is to extend the existing methods for such Mendelian randomization studies to the context of multiple genetic markers measured in multiple studies, based on the analysis of individual participant data. First, for a single genetic marker in one study, we show that the usual ratio of coefficients approach can be reformulated as a regression with heterogeneous error in the explanatory variable. This can be implemented using a Bayesian approach, which is next extended to include multiple genetic markers. We then propose a hierarchical model for undertaking a meta-analysis of multiple studies, in which it is not necessary that the same genetic markers are measured in each study. This provides an overall estimate of the causal relationship between the phenotype and the outcome, and an assessment of its heterogeneity across studies. As an example, we estimate the causal relationship of blood concentrations of C-reactive protein on fibrinogen levels using data from 11 studies. These methods provide a flexible framework for efficient estimation of causal relationships derived from multiple studies. Issues discussed include weak instrument bias, analysis of binary outcome data such as disease risk, missing genetic data, and the use of haplotypes.

The effectiveness and cost-effectiveness of biomarkers for the prioritisation of patients awaiting coronary revascularisation: a systematic review and decision model

OBJECTIVE

To determine the effectiveness and cost-effectiveness of a range of strategies based on conventional clinical information and novel circulating biomarkers for prioritising patients with stable angina awaiting coronary artery bypass grafting (CABG).

DATA SOURCES

MEDLINE and EMBASE were searched from 1966 until 30 November 2008.

REVIEW METHODS

We carried out systematic reviews and meta-analyses of literature-based estimates of the prognostic effects of circulating biomarkers in stable coronary disease. We assessed five routinely measured biomarkers and the eight emerging (i.e. not currently routinely measured) biomarkers recommended by the European Society of Cardiology Angina guidelines. The cost-effectiveness of prioritising patients on the waiting list for CABG using circulating biomarkers was compared against a range of alternative formal approaches to prioritisation as well as no formal prioritisation. A decision-analytic model was developed to synthesise data on a range of effectiveness, resource use and value parameters necessary to determine cost-effectiveness. A total of seven strategies was evaluated in the final model.

RESULTS

We included 390 reports of biomarker effects in our review. The quality of individual study reports was variable, with evidence of small study (publication) bias and incomplete adjustment for simple clinical information such as age, sex, smoking, diabetes and obesity. The risk of cardiovascular events while on the waiting list for CABG was 3 per 10,000 patients per day within the first 90 days (184 events in 9935 patients with a mean of 59 days at risk). Risk factors associated with an increased risk, and included in the basic risk equation, were age, diabetes, heart failure, previous myocardial infarction and involvement of the left main coronary artery or three-vessel disease. The optimal strategy in terms of cost-effectiveness considerations was a prioritisation strategy employing biomarker information. Evaluating shorter maximum waiting times did not alter the conclusion that a prioritisation strategy with a risk score using estimated glomerular filtration rate (eGFR) was cost-effective. These results were robust to most alternative scenarios investigating other sources of uncertainty. However, the cost-effectiveness of the strategy using a risk score with both eGFR and C-reactive protein (CRP) was potentially sensitive to the cost of the CRP test itself (assumed to be 6 pounds in the base-case scenario).

CONCLUSIONS

Formally employing more information in the prioritisation of patients awaiting CABG appears to be a cost-effective approach and may result in improved health outcomes. The most robust results relate to a strategy employing a risk score using conventional clinical information together with a single biomarker (eGFR). The additional prognostic information conferred by collecting the more costly novel circulating biomarker CRP, singly or in combination with other biomarkers, in terms of waiting list prioritisation is unlikely to be cost-effective.

The effect of cotinine on telomerase activity in human vascular smooth muscle cells

AIM

Cotinine, the main stable metabolite of nicotine, has been shown to have a biological half-life approximately 10 times longer than nicotine. It has also been demonstrated to have a powerful effect on vascular smooth muscle cell (VSMC) proliferation. Telomerase activation is known to play an important role in cell viability and proliferation. The purpose of our experiment was to evaluate the effect of cotinine on proliferative potential of vascular smooth muscle cells via its effects on telomerase activity.

METHODS

Primary cultures of human VSMC obtained from greater saphenous veins were used in this experiment from 3(rd) to 5(th) passage. Cotinine was added in doses equivalent to plasma levels of cotinine in an active smoker by dissolving, 0.0, 2.88x10(-6), 5.76x10(-6), and 1.44x10(-5) mol/L of cotinine in the media. The number of viable cells was assessed by trypan blue exclusion. The Telomeric Repeat Amplification Protocol (TRAP) was used to detect telomerase activity. TRAP products were detected by ELISA.

RESULTS

The mitogenic effect of cotinine in VSMC was observed at 48 hours after treatment. The viable cell numbers were significantly increased (4.0x10(7)) at lower doses of cotinine exposure as compared to untreated cultures (2.5x10(5)). At the concentration of 1.44x10(-5) mol/L, cotinine was cytotoxic to VSMCs. Telomerase activity was detected in all sets of VSMC cultures treated with cotinine (P<0.01).

CONCLUSIONS

Cotinine causes abnormal cell proliferation as demonstrated by increased cell numbers and reactivation of telomerase in a dose dependent manner. This study demonstrated cotinine's stimulatory effect on human SMC proliferation in vitro at low doses while high doses of cotinine had a toxic effect. These data correlate with the results of other studies concerning the mitogenic effect of cotinine and telomerase activation during cellular proliferative response.

Carotid Artery Stump Pressure (CASP) in 1135 consecutive endarterectomies under general anesthesia: an old method that survived the test of times

AIM

Intraoperative electroencephalography, somato-sensory evoked potentials and transcranial Doppler have been proposed to replace carotid artery stump pressure measurement (CASP) as the test of choice in the evaluation of cerebral tolerance during temporary carotid occlusion. CASP is a simple, inexpensive test that does not require an additional specialist in the operating room. Herein, we attempt to demonstrate that CASP is a reliable test that does not need to be replaced by more sophisticated and expensive techniques.

METHODS

Over the last 6 years, 1 135 consecutive carotid endarterectomies (CEA) were performed under general anesthesia at our institution. There were 592 males and 429 female patients with an age range of 39 to 95 years (mean 72 +/- 9 years). Hypertension, diabetes, smoking, coronary artery disease and chronic renal insufficiency were present in 71%, 39%, 36%, 32% and 26%, respectively. Internal carotid artery (ICA) stenosis ? 70% was confirmed by duplex scanning in 92% of the cases. The remaining 8% of cases had 50% to 69% ICA stenosis in neurologically symptomatic patients. Asymptomatic patients accounted for 75% of the cases. Contralateral ICA occlusion was observed in 57 cases (5%). Indwelling shunts were used when CASP was < 45 mmHg. Carotid patches were used in 233 cases. Completion duplex scanning was performed in all cases. CASP was measured by inserting a 23-gauge needle into the common carotid artery (CCA) after clamping the ICA to avert possible embolization during needle insertion. Once the tip of the needle was confirmed intraluminally by pressure measurement and triphasic waveform tracing, the CCA and the external carotid artery were clamped. After a flat line tracing was depicted on the monitor, ICA clamp was released and CASP was recorded.

RESULTS

CASP was < 45 mmHg in 233 cases (21%) (Group I) and > or = 45 mmHg in 902 cases (79%) (Group II). The mean CASP in presence of contralateral ICA occlusions was 40 +/- 15 mmHg while it was 65 +/- 27 mmHg for patent contralateral ICAs (P < 0.0001). The overall 30-day stroke rate was 1% (1 135 cases). It was 3% (7/233) for group I and 0.5% (4/902) for group II (P < 0.01). In patients with postoperative strokes CASP ranged from 23 to 44 mmHg (mean 33 +/- 8) in group I (shunted) and it varied from 59 to 116 mmHg (mean 99 +/- 28) in group II (non-shunted) with P < 0.001. The causes of stroke in group I were hyperperfusion (2), partial ICA thrombosis (2), embolization (2) and worsening of acute stroke (1). In group II there were 2 cases of embolization and 2 of ICA thrombosis. No patient had a stroke caused by decreased intraoperative global cerebral perfusion. The overall 30-day mortality rate was 0.5%. The overall combined stroke/death rate was 1.5%.

CONCLUSION

CASP > or = 45 mmHg was a reliable predictor of adequate cerebral perfusion during 1,135 consecutive CEAs performed under general anesthesia. The percentage of indwelling shunts utilized in this series was not significantly different from the ones using more expensive and sophisticated techniques.

Subintimal angioplasty

While the technique of subintimal dissection was described almost 2 decades ago, initial adoption of the technique was quite slow. Recently, a growing number of centers have embraced the technique as a valuable adjunct to standard endovascular and open revascularizations. During our experience with over 100 duplex guidance subintimal angioplasties (SIA) and over 100 flouroscopically guided SIA, we have encountered that persistence can be greatest ally. Fortunately, this is a trait that is common among vascular surgeons. Herein, we will describe the technique with focus on its limitations and advantages.

Activation of P38MAPK Signaling Cascade in a VSMC Injury Model: Role of P38MAPK Inhibitors in Limiting VSMC Proliferation

INTRODUCTION

P38 mitogen-activated protein kinase (MAPK) has a crucial role in regulating signaling pathways implicated in the cellular events leading to restenosis. We examine p38MAPK activation in response to vascular cell injury, its biological effects and determine whether selective p38MAPK inhibitors, SB220025/SB203580, decrease vascular smooth muscle cell (VSMC) proliferation.

METHODS

Human aortic VSMCs were cultured and wounds made on the monolayers to elicit mitogenic responses and induce p38MAPK activation. P38MAPK inhibitor pretreatment, at varying doses (1-100 microM) and treatment duration was used to block p38MAPK phosphorylation. Cytotoxicity, viability, proliferation and apoptosis were determined and expression of p38MAPK/phospho-p38MAPK was obtained by chemiluminiscent immunoblot analysis.

RESULTS

Phosphorylation of p38MAPK depended on injury severity and was inhibited by both p38MAPK inhibitors, but not by SB202474, a specific antagonist of p38MAPK inhibitors. VSMCs treated with p38MAPK inhibitors showed a dose-dependent decrease in viable cell number, apoptosis and proliferation, reversing the deleterious effects of p38MAPK activation comparable to controls (p < 0.05).

CONCLUSIONS

This wound injury model activates the p38MAPK-signaling cascade in VSMC and causes cell proliferation that can be abrogated by pre-incubation with p38MAPK selective synthetic inhibitors in a time and dose-dependent manner. SB220025 used here for the first time in VSMC reveals itself to be a stronger p38MAPK inhibitor than SB203580 and being a second generation inhibitor may be the preferred drug for novel therapeutic maneuvers.

Does repeat duplex ultrasound for lower extremity deep vein thrombosis influence patient management?

The clinical significance of lower extremity deep vein thrombus (DVT) propagation in the setting of anticoagulation therapy remains unclear. The purpose of this study is to compare results of thrombus outcome found with repeat duplex ultrasonography to the incidence of pulmonary embolism and mortality. During a recent 18-month period, 457 patients were diagnosed with lower extremity DVT with duplex ultrasonography and their data were retrospectively analyzed. Repeat examinations were available for review in 118 patients (51 men, 67 women). Results of repeat duplex exams were divided into 4 groups: resolved, improved, unchanged, or extended proximally. All patients received heparin and warfarin therapy. Ventilation-perfusion (V/ Q) scans were obtained only for signs and symptoms of pulmonary embolism (n=30). Mortality, the prevalence of high-probability V/ Q scans, frequency of intracaval filter insertion, gender, mean age, mean prothrombin time (PT), mean partial thromboplastin time (PTT), mean number of repeat ultrasounds per patient, and mean time over which the repeat ultrasounds took place were compared among the 4 groups. Patients who had proximal extension of DVT (19%) on repeat duplex ultrasound had an increased prevalence of pulmonary embolism (p<0.05). Also, patients whose DVT resolved were younger (p<0.05). There was no difference among the 4 groups in mortality, placement of Greenfield filters, mean PT, mean PTT, mean number of ultrasound exams per patient, or mean follow-up time over which the exams took place. Proximal extension of DVT documented by repeat duplex ultrasound is a significant risk factor for pulmonary embolism. Repeat duplex ultrasound can identify a group of patients who may benefit from insertion of an intracaval filter device.