An Investigation of PS-b-PEO Polymersomes for the Oral Treatment and Diagnosis of Hyperammonemia.

Ammonia-scavenging transmembrane pH-gradient poly(styrene)-b-poly(ethylene oxide) polymersomes are investigated for the oral treatment and diagnosis of hyperammonemia, a condition associated with serious neurologic complications in patients with liver disease as well as in infants with urea cycle disorders. While these polymersomes are highly stable in simulated intestinal fluids at extreme bile salt and osmolality conditions, they unexpectedly do not reduce plasmatic ammonia levels in cirrhotic rats after oral dosing. Incubation in dietary fiber hydrogels mimicking the colonic environment suggests that the vesicles are probably destabilized during the dehydration of the intestinal chyme. The findings question the relevance of commonly used simulated intestinal fluids for studying vesicular stability. With the encapsulation of a pH-sensitive dye in the polymersome core, the local pH increase upon ammonia influx could be exploited to assess the ammonia concentration in the plasma of healthy and cirrhotic rats as well as in other fluids. Due to its high sensitivity and selectivity, this polymersome-based assay could prove useful in the monitoring of hyperammonemic patients and in other applications such as drug screening tests.

Vesicular Diagnostics: A Spotlight on Lactate- and Ammonia-Sensing Systems.

Liposomes are a highly successful drug delivery system with over 15 FDA-approved formulations. Beyond delivering drugs, lipid and polymer vesicles have successfully been used for diagnostic applications. These applications range from more traditional uses, such as releasing diagnostic agents in a controlled manner, to leveraging the unique membrane properties to separate analytes and provide isolated reaction compartments in complex biological matrices. In this Spotlight on Applications, I highlight the complexities in the development and translation of diagnostic vesicles with two case studies, a liposomal reaction compartment for lactate sensing and a transmembrane pH-gradient polymersome for ammonia sensing.

Breakthrough treatments for accelerated wound healing.

Skin injuries across the body continue to disrupt everyday life for millions of patients and result in prolonged hospital stays, infection, and death. Advances in wound healing devices have improved clinical practice but have mainly focused on treating macroscale healing versus underlying microscale pathophysiology. Consensus is lacking on optimal treatment strategies using a spectrum of wound healing products, which has motivated the design of new therapies. We summarize advances in the development of novel drug, biologic products, and biomaterial therapies for wound healing for marketed therapies and those in clinical trials. We also share perspectives for successful and accelerated translation of novel integrated therapies for wound healing.

Development of a liposomal near-infrared fluorescence lactate assay for human blood.

In emergency medicine, blood lactate is a commonly used biomarker of hypoxia (e.g., sepsis, trauma, cardiac arrest) but the median time to obtain the results from a clinical lactate test is 3 h. We recently developed a near-infrared fluorescent blood lactate assay based on a two-step enzymatic cascade in a vesicular reaction compartment. Previously, we reported a response of this assay to lactate-spiked bovine blood after 10 min. To develop a point-of-care test, we optimized this assay in commercial human blood, validated it in fresh capillary blood of healthy volunteers in an institutional review board-approved study, and improved the stability of the formulation. External pH and luminal enzyme concentrations were identified as key parameters of sensor response and kinetics, as they impact transmembrane lactate diffusion and turnover rate. The preparation process was also simplified and the stability was improved to allow storage at 4 °C for at least 5 days. The final formulation exhibited a strong and linear response to lactate-spiked human blood in a clinically relevant range, and accurately quantified a lactate standard at a clinically used cut-off in fresh capillary blood after 2 min. These findings motivate a clinical evaluation of this rapid and easy-to-use lactate assay.

Preclinical evaluation of liposome-supported peritoneal dialysis for the treatment of hyperammonemic crises.

Liposome-supported peritoneal dialysis (LSPD) with transmembrane pH-gradient liposomes was previously shown to enhance ammonia removal in cirrhotic rats and holds promise for the treatment of hyperammonemic crises-associated disorders. The main objective of this work was to conduct the preclinical evaluation of LSPD in terms of pharmacokinetics, ammonia uptake, and toxicology to seek regulatory approval for a first-in-human study. The formulation containing citric acid-loaded liposomes was administered intraperitoneally at two different doses once daily for ten days to healthy minipigs. It was also tested in a domestic pig model of hyperammonemia. The pharmacokinetics of citric acid and 1,2-dipalmitoyl-sn-glycero-3-phosphocholine was linear following intraperitoneal administration of medium and high dose. There was no systemic accumulation following daily doses over ten days. The systemic exposure to phospholipids remained low. Furthermore, the liposome-containing peritoneal fluid contained significantly higher ammonia levels than the liposome-free control, demonstrating efficient ammonia sequestration in the peritoneal space. This was indeed confirmed by the ability of LSPD to decrease plasmatic ammonia levels in artificially induced hyperammonemic pigs. LSPD was well tolerated, and no complement activation-related pseudoallergy reactions were observed. The safety profile, the linear pharmacokinetics of citric acid following repeated administrations of LSPD as well as the linear dose-dependent ammonia sequestration in the peritoneal space provide a strong basis for the clinical investigation of LSPD.

Liposome-supported peritoneal dialysis in the treatment of severe hyperammonemia: An investigation on potential interactions.

Peritoneal dialysis (PD) performed with transmembrane pH-gradient liposomes was reported to efficiently remove ammonia from the body, representing a promising alternative to current standard-of-care for patients with severe hepatic encephalopathy. In this study, we further characterized the properties of liposome-supported peritoneal dialysis (LSPD) by 1) assessing its in-use stability in the presence of ascitic fluids from liver-disease patients; 2) investigating its interactions with drugs that are commonly administered to acute-on-chronic liver failure patients; and 3) analyzing the in vivo extraction profile of LSPD. We found that LSPD fluid maintained its in vitro ammonia uptake capability when combined with ascitic fluids. The co-incubation of selected drugs (e.g., beta-blockers, antibiotics, diuretics) with LSPD fluids and ammonia resulted in limited interaction effects for most compounds except for two fluoroquinolones and propranolol. However, considering the experimental set-up, these results should be interpreted with caution and confirmatory drug-drug interaction studies in a clinical setting will be required. Finally, metabolite-mapping analysis on dialysates of LSPD-treated rats revealed that the liposomes did not remove important metabolites more than a conventional PD fluid. Overall, these findings confirm that LSPD is a potentially safe and effective approach for treating hyperammonemic crises in the context of acute-on-chronic liver failure.

Sustained gastrointestinal activity of dendronized polymer-enzyme conjugates.

Methods to stabilize and retain enzyme activity in the gastrointestinal tract are investigated rarely because of the difficulty of protecting proteins from an environment that has evolved to promote their digestion. Preventing the degradation of enzymes under these conditions, however, is critical for the development of new protein-based oral therapies. Here we show that covalent conjugation to polymers can stabilize orally administered therapeutic enzymes at different locations in the gastrointestinal tract. Architecturally and functionally diverse polymers are used to protect enzymes sterically from inactivation and to promote interactions with mucin on the stomach wall. Using this approach the in vivo activity of enzymes can be sustained for several hours in the stomach and/or in the small intestine. These findings provide new insight and a firm basis for the development of new therapeutic and imaging strategies based on orally administered proteins using a simple and accessible technology.