Lipoprotein-associated phospholipase A2 and risk of venous thrombosis in older adults

Advanced liposome and polymersome-based drug delivery systems: Considerations for physicochemical properties, targeting strategies and stimuli-sensitive approaches

Liposomes and polymersomes are colloidal vesicles that are self-assembled from lipids and amphiphilic polymers, respectively. Because of their ability to encapsulate both hydrophilic and hydrophobic therapeutics, they are of great interest in drug delivery research. Today, the applications of liposomes and polymersomes have expanded to a wide variety of complex therapeutic molecules, including nucleic acids, proteins and enzymes. Thanks to their chemical versatility, they can be tailored to different drug delivery applications to achieve maximum therapeutic index. This review article evaluates liposomes and polymersomes from a perspective that takes into account the physical and biological barriers that reduce the efficiency of the drug delivery process. In this context, the design approaches of liposomes and polymersomes are discussed with representative examples in terms of their physicochemical properties (size, shape, charge, mechanical), targeting strategies (passive and active) and response to different stimuli (pH, redox, enzyme, temperature, light, magnetic field, ultrasound). Finally, the challenges limiting the transition from laboratory to practice, recent clinical developments, and future perspectives are addressed.

Stimulus-responsive liposomes for biomedical applications

Liposomes are amphipathic lipidic supramolecular aggregates that are able to encapsulate and carry molecules of both hydrophilic and hydrophobic nature. They have been widely used as in vivo drug delivery systems for some time because they offer features such as synthetic flexibility, biodegradability, biocompatibility, low immunogenicity, and negligible toxicity. In recent years, the chemical modification of liposomes has paved the way to the development of smart liposome-based drug delivery systems, which are characterized by even more tunable and disease-directed features. In this review, we highlight the different types of chemical modification introduced to date, with a particular focus on internal stimuli-responsive liposomes and prodrug activation.

Lipoprotein-associated phospholipase A2 and venous thromboembolism: a prospective study

INTRODUCTION

Plasma lipoprotein-associated phospholipase A2 (Lp-PLA2) is an inflammatory marker associated positively with atherothrombotic risk. Whether Lp-PLA2 is related to risk of venous thromboembolism (VTE) is incompletely studied.

METHODS

We assessed Lp-PLA2 activity in 10,687 Atherosclerosis Risk in Communities (ARIC) Study participants and followed them a median of 8.3 years (from 1996-98 through 2005) for VTE occurrence (n=226).

RESULTS

There was no significant association between baseline Lp-PLA2 quartiles and risk of VTE, neither overall nor stratified as provoked or unprovoked. Adjusted for other risk factors, the hazard ratios (95% confidence interval) of total VTE across quartiles of Lp-PLA2 were 1.0 (reference), 0.95 (0.64, 1.42), 1.03 (0.69, 1.56), and 1.26 (0.83, 1.91). In the subset of participants with LDL-cholesterol ≥130 mg/dL, hazard ratios of total VTE were 1.00, 1.39 (0.44, 4.44), 2.45 (0.84, 7.11), and 2.84 (0.99, 8.14).

CONCLUSION

Our study does not support the overall hypothesis that elevated Lp-PLA2 contributes to VTE occurrence in the general population. However, in the presence of high LDL-cholesterol there was some evidence that Lp-PLA2 may increase VTE risk.

Variation of lipoprotein associated phospholipase A2 across demographic characteristics and cardiovascular risk factors: a systematic review of the literature

BACKGROUND

Lipoprotein association phospholipase A2 (Lp-PLA(2)), an enzyme which has been found in atherosclerotic plaque is currently under investigation in large Phase III clinical trials of vascular disease prevention. We assessed in a variety of different population settings variation of Lp-PLA(2) mass and activity across gender, ethnicity, diabetes, kidney disease and metabolic syndrome. We also assessed correlations with measures of circulating lipids, systemic inflammation and adiposity.

METHODS

Systematic review of studies measuring Lp-PLA(2) and at least one of the relevant characteristics in >50 participants.

RESULTS

We identified a total of 77 studies involving 102,499 participants meeting the inclusion criteria. Lp-PLA(2) mass and activity were consistently approximately 10% higher in males than females and 15% higher in Caucasians than African Americans or Hispanics. There were no clear associations of Lp-PLA(2) mass or activity with type II diabetes, markers of systemic inflammation (C-reactive protein, fibrinogen) or with body mass index. Correlations of Lp-PLA(2) mass or activity with low density lipoprotein cholesterol and apolipoprotein B were moderate and positive, whilst correlations with high density lipoprotein cholesterol were negative and moderate to weak. There was no clear differences in associations with any of the above characteristics in groups defined based upon prevalent cardiovascular disease or its risk factors.

CONCLUSIONS

Despite considerable variability in absolute levels of Lp-PLA(2) across studies, the variability of Lp-PLA(2) across gender, ethnicity, and levels of circulating lipids and markers of systemic inflammation are more consistent and appear not to vary importantly across categories defined by CVD or its risk factors.