Drug-eluting stents: a comprehensive appraisal

Intraprocedural endothelial cell seeding of arterial stents via biotin/avidin targeting mitigates in-stent restenosis

Impaired endothelialization of endovascular stents has been established as a major cause of in-stent restenosis and late stent thrombosis. Attempts to enhance endothelialization of inner stent surfaces by pre-seeding the stents with endothelial cells in vitro prior to implantation are compromised by cell destruction during high-pressure stent deployment. Herein, we report on the novel stent endothelialization strategy of post-deployment seeding of biotin-modified endothelial cells to avidin-functionalized stents. Acquisition of an avidin monolayer on the stent surface was achieved by consecutive treatments of bare metal stents (BMS) with polyallylamine bisphosphonate, an amine-reactive biotinylation reagent and avidin. Biotin-modified endothelial cells retain growth characteristics of normal endothelium and can express reporter transgenes. Under physiological shear conditions, a 50-fold higher number of recirculating biotinylated cells attached to the avidin-modified metal surfaces compared to bare metal counterparts. Delivery of biotinylated endothelial cells to the carotid arterial segment containing the implanted avidin-modified stent in rats results in immediate cell binding to the stent struts and is associated with a 30% reduction of in-stent restenosis in comparison with BMS.

Heparin-Tagged PLA-PEG Copolymer-Encapsulated Biochanin A-Loaded (Mg/Al) LDH Nanoparticles Recommended for Non-Thrombogenic and Anti-Proliferative Stent Coating

Drug-eluting stents have been widely implanted to prevent neointimal hyperplasia associated with bare metal stents. Conventional polymers and anti-proliferative drugs suffer from stent thrombosis due to the non-selective nature of the drugs and hypersensitivity to polymer degradation products. Alternatively, various herbal anti-proliferative agents are sought, of which biochanin A (an isoflavone phytoestrogen) was known to have anti-proliferative and vasculoprotective action. PLA-PEG diblock copolymer was tagged with heparin, whose degradation releases heparin locally and prevents thrombosis. To get a controlled drug release, biochanin A was loaded in layered double hydroxide nanoparticles (LDH), which are further encapsulated in a heparin-tagged PLA-PEG copolymer. LDH nanoparticles are synthesized by a co-precipitation process; in situ as well as ex situ loading of biochanin A were done. PLA-PEG-heparin copolymer was synthesized by esterification reaction, and the drug-loaded nanoparticles are coated. The formulation was characterized by FTIR, XRD, DSC, DLS, and TEM. In vitro drug release studies, protein adhesion, wettability, hemocompatibility, and degradation studies were performed. The drug release was modeled by mathematical models to further emphasize the mechanism of drug release. The developed drug-eluting stent coating is non-thrombogenic, and it offers close to zero-order release for 40 days, with complete polymer degradation in 14 weeks.

Evaluation of the use of tacrolimus ointment for the prevention of hypertrophic scars in experimental model

BACKGROUND

Tacrolimus, for its activity on modulation of collagen production and fibroblast activity, may have a role in the prevention of hypertrophic scars.

OBJECTIVES

Evaluate macroscopic, microscopic, metabolic, laboratory effects and side effects of the use of topical tacrolimus ointment, in different concentrations, in the prevention of hypertrophic scars.

METHODS

Twenty-two rabbits were submitted to the excision of 2 fragments of 1 cm of each ear, 4 cm apart, down to cartilage. The left ear of the animals was standardized as control and Vaseline applied twice a day. The right ear received tacrolimus ointment, at concentrations of 0.1% on the upper wound and 0.03% on the lower wound, also applied twice a day. Macroscopic, microscopic, laboratory criteria and the animals' weight were evaluated after 30 days of the experiment.

RESULTS

Wounds treated with tacrolimus, at concentrations of 0.1% and 0.03%, when compared to control, showed a lower average degree of thickening (p = 0.048 and p <0.001, respectively). The average of scar thickness and lymphocyte, neutrophil and eosinophil concentrations are lower in the treated wounds compared to the control (p <0.001, p=0.022, p=0.007, p=0.044, respectively). The mean concentration of lymphocytes is lower in wounds treated with a higher concentration of the drug (p=0.01).

STUDY LIMITATIONS

experiment lasted only 30 days.

CONCLUSIONS

Tacrolimus at the 2 concentrations evaluated reduced the severity of inflammatory changes and positively altered the macroscopic aspect of the scar in the short term. Its use was shown to be safe, with no evidence of systemic or local adverse effects.

Enhanced biocompatibility of CD47-functionalized vascular stents

The effectiveness of endovascular stents is hindered by in-stent restenosis (ISR), a secondary re-obstruction of treated arteries due to unresolved inflammation and activation of smooth muscle cells in the arterial wall. We previously demonstrated that immobilized CD47, a ubiquitously expressed transmembrane protein with an established role in immune evasion, can confer biocompatibility when appended to polymeric surfaces. In present studies, we test the hypothesis that CD47 immobilized onto metallic surfaces of stents can effectively inhibit the inflammatory response thus mitigating ISR. Recombinant CD47 (recCD47) or a peptide sequence corresponding to the Ig domain of CD47 (pepCD47), were attached to the surfaces of both 316L-grade stainless steel foils and stents using bisphosphonate coordination chemistry and thiol-based conjugation reactions to assess the anti-inflammatory properties of CD47-functionalized surfaces. Initial in vitro and ex vivo analysis demonstrated that both recCD47 and pepCD47 significantly reduced inflammatory cell attachment to steel surfaces without impeding on endothelial cell retention and expansion. Using a rat carotid stent model, we showed that pepCD47-functionalized stents prevented fibrin and platelet thrombus deposition, inhibited inflammatory cell attachment, and reduced restenosis by 30%. It is concluded that CD47-modified stent surfaces mitigate platelet and inflammatory cell attachment, thereby disrupting ISR pathophysiology.

Plasma torch toothbrush a new insight in fear free dentisry

Dental treatment is considered painful either because of fear or anxiety. Even though fear and anxiety could be managed; the needle pricks and the heat generated with drills are both painful and destructive to the tissues of the tooth. A new technology which can reduce the pain and destruction of the dental tissues will be of huge value. Plasma torch toothbrush fits into such criteria and when developed fully, will be able to apply for many of the dental procedures for increasing the efficiency.

Risk evaluation and mitigation strategies: a focus on the mammalian target of rapamycin inhibitors

OBJECTIVE

To review the history of risk evaluation and mitigation strategies (REMS) with the mammalian target of rapamycin (mToR) inhibitors, evaluate their required REMS elements, and delineate the reasons for them being released from their REMS requirements.

DATA SOURCES AND EXTRACTION

Articles were identified through a literature search of MEDLINE and EMBASE (January 2007-July 2012) using the search terms: risk evaluation and mitigation strategies, REMS, everolimus, sirolimus and organ transplant (individual organs also were searched). Information from the Federal Register, the Food and Drug Administration, and the manufacturers of the mToR inhibitors was also evaluated.

DATA SYNTHESIS

REMS are strategies implemented to manage known or potential risks associated with medications and to ensure ongoing pharmacovigilance throughout the life of a pharmaceutical product. The mToR inhibitors have been associated with several potential risks, including proteinuria, graft thrombosis, and wound-healing complications. The Food and Drug Administration approved REMS programs for both sirolimus and everolimus. The manufacturers of both medications complied with the components of their approved REMS, but after less than 2 years, both medications have been relieved of their REMS obligations.

CONCLUSION

The only element of the sirolimus REMS was a medication guide, whereas the everolimus REMS consisted of a medication guide and a communication plan. The sirolimus REMS was implemented more than 10 years after its initial approval by the Food and Drug Administration, but was released from its REMS requirement within 7 months of its implementation. The everolimus REMS was instituted upon initial approval and was removed approximately 2 years later. Both medications' REMS were always intended to educate health care providers and patients about the potential risks associated with this transplant immunosuppressant. Transplant practitioners should be familiar with the mToR inhibitors' associated risks and properly educate patients regarding the inhibitors' risk-benefit profiles.

A patient with repeated catastrophic multi-vessel coronary spasm after zotarolimus-eluting stent implantation

Drug-eluting stents (DES) have gained great popularity because of extraordinarily low rates of restenosis. Despite these superior clinical outcomes, several cases regarding the severe multi-vessel coronary spasm, although rare, after the placement of first generation DES have been reported. We report a case of severe, multi-vessel coronary spasm that occurred two occasions after placement of a zotarolimus-eluting stent, one of the second generation DES, in a 42-year-old man with unstable angina. The first incidence was relieved by intracoronary nitroglycerin alone, and second incident, which had combined fixed stenosis was treated with intracoronary nitroglycerin and everolimus-eluting stent.

Everolimus: a proliferation signal inhibitor with clinical applications in organ transplantation, oncology, and cardiology

Everolimus, a proliferation signal inhibitor in the mammalian target of rapamycin (mTOR) drug class, has many clinical applications, including in organ transplantation, oncology, and cardiology. It currently has United States Food and Drug Administration (FDA) approval for prophylaxis against rejection in de novo renal transplant recipients, treatment of renal cell carcinoma, and use as a drug-eluting stent. To review the pharmacology, pharmacokinetics, efficacy, and safety of everolimus, we performed a search of the MEDLINE database (January 1997-April 2010) for all English-language articles of in vitro and in vivo studies that evaluated everolimus, as well as abstracts from recent scientific meetings and the manufacturer. In transplantation, everolimus demonstrates immunosuppressive properties and has been used to prevent acute rejection in cardiac, liver, lung, and renal transplant recipients. It appears that this agent may be potent enough to allow for the minimization or removal of calcineurin inhibitors in the long-term management of renal transplant recipients. In oncology, everolimus has been proven effective for the management of treatment-resistant renal cell carcinoma. In cardiology, everolimus is available as a drug-coated stent and is used in percutaneous coronary interventions for prevention of restenosis. In transplant recipients and patients with renal cell carcinoma, everolimus appears to have an extensive adverse-event profile. The pharmacologic properties of everolimus differentiate this agent from other drugs used in these clinical areas, and its pharmacokinetic properties differentiate it from sirolimus.

Reduced mortality and moderate alcohol consumption: the phospholipase D-mTOR connection

Many studies have suggested that moderate alcohol consumption reduces mortality. There is also substantial evidence that lifespan is extended with suppression of TOR (target of rapamycin). It was reported recently that rapamycin is able to extend the lifespan of a mammal--implicating the mammalian TOR (mTOR). mTOR has a requirement for the lipid second messenger phosphatidic acid (PA), which is generated by phospholipase D (PLD). Therefore, in principle, suppression of PLD would be similar to treatment with rapamycin. Significantly, PLD utilizes ethanol preferentially over water in the hydrolysis reaction that ordinarily generates PA. In the presence of ethanol, phosphatidyl-ethanol is generated at the expense of PA leading to the suppression of mTOR. This reaction, known as the transphosphatidylation reaction, provides a mechanistic basis for the reduced mortality observed with moderate consumption of alcohol--that being the suppression of mTOR.

Effects of azithromycin in combination with vancomycin, daptomycin, fosfomycin, tigecycline, and ceftriaxone on Staphylococcus epidermidis biofilms

Staphylococcal biofilms on surgical implants are the underlying cause of a lack of response to antimicrobial treatment. We investigated the effects of vancomycin (VAN), daptomycin (DAP), fosfomycin (FOS), tigecycline (TGC), and ceftriaxone (CRX), alone and in combination with azithromycin (AZI), on established biofilms of Staphylococcus epidermidis. Biofilms were studied using the static microtiter plate model with established S. epidermidis biofilms, with an initial inoculum of 10(6)/ml in 96-well polystyrene flat-bottom microtiter plates. Biofilms were inoculated with VAN, DAP, FOS, TGC, or CRX at two concentrations, alone or in combination with AZI (2, 512, or 1,024 mg/liter). To assess the reduction in biomass, the optical density ratio (ODr), calculated as (optical density [OD] of the treated biofilm)/(OD of the untreated biofilm, taken as 1), was used. For antibacterial efficacy, the viable bacterial count was used. Reductions in the biofilm ODr were observed for VAN (15 and 40 mg/liter) and FOS (200 mg/liter) only (ODr [mean +/- standard deviation] for VAN at 15 and 40 mg/liter, 0.77 +/- 0.32 and 0.8 +/- 0.35, respectively; ODr for FOS at 200 mg/liter, 0.78 +/- 0.26; P < 0.05), but not for DAP (2 and 5 mg/liter), TGC (0.2 and 2 mg/liter), or CRX (600 and 2,400 mg/liter). The addition of AZI had no further effect on the ODr, but a significant reduction of bacterial growth was achieved with high doses of AZI plus TGC or AZI plus CRX (a 3-log count reduction for AZI at 1,024 mg/liter plus CRX at 600 mg/liter and for AZI at 512 or 1,024 mg/liter plus CRX at 2,400 mg/liter; a 2-log count reduction for AZI at 512 or 1,024 mg/liter plus TGC at 2 mg/liter [P < 0.05]). No significant reduction in bacterial growth was observed for FOS (50 and 200 mg/liter), DAP (2 and 5 mg/liter), or TGC (0.2 mg/liter) in combination with AZI. None of the antibiotics at either concentration reduced the bacterial count of the biofilms when used alone. Thus, the use of a combination of AZI plus TGC, FOS, or CRX at high concentrations has little effect on biofilm density but significantly reduces bacterial growth.