Liposomes to Augment Dialysis in Preclinical Models: A Structured Review

Future of Uremic Toxin Management

During the progression of chronic kidney disease (CKD), the retention of uremic toxins plays a key role in the development of uremic syndrome. Knowledge about the nature and biological impact of uremic toxins has grown exponentially over the past decades. However, the science on reducing the concentration and effects of uremic toxins has not advanced in parallel. Additionally, the focus has remained for too long on dialysis strategies, which only benefit the small fraction of people with CKD who suffer from advanced kidney disease, whereas uremic toxicity effects are only partially prevented. This article reviews recent research on alternative methods to counteract uremic toxicity, emphasizing options that are also beneficial in the earlier stages of CKD, with a focus on both established methods and approaches which are still under investigation or at the experimental stage. We will consequently discuss the preservation of kidney function, the prevention of cardiovascular damage, gastro-intestinal interventions, including diet and biotics, and pharmacologic interventions. In the final part, we also review alternative options for extracorporeal uremic toxin removal. The future will reveal which of these options are valid for further development and evidence-based assessment, hopefully leading to a more sustainable treatment model for CKD than the current one.

Acute-On-Chronic Liver Failure: Current Interventional Treatment Options and Future Challenges

Acute-on-chronic liver failure (ACLF) is a frequent complication in patients with liver cirrhosis that has high short-term mortality. It is characterized by acute decompensation (AD) of liver cirrhosis, intra- and extrahepatic organ failure, and severe systemic inflammation (SI). In the recent past, several studies have investigated the management of this group of patients. Identification and treatment of precipitants of decompensation and ACLF play an important role, and management of the respective intra- and extrahepatic organ failures is essential. However, no specific treatment for ACLF has been established to date, and the only curative treatment option currently available for these patients is liver transplantation (LT). It has been shown that ACLF patients are at severe risk of waitlist mortality, and post-LT survival rates are high, making ACLF patients suitable candidates for LT. However, only a limited number of patients are eligible for LT due to related contraindications such as uncontrolled infections. In this case, bridging strategies (e.g., extracorporeal organ support systems) are required. Further therapeutic approaches have recently been developed and evaluated. Thus, this review focuses on current management and potential future treatment options.

Biomedical Nanosystems for In Vivo Detoxification: From Passive Delivery Systems to Functional Nanodevices and Nanorobots

The problem of low efficiency of nanotherapeutic drugs challenges the creation of new alternative biomedical nanosystems known as robotic nanodevices. In addition to encapsulating properties, nanodevices can perform different biomedical functions, such as precision surgery, in vivo detection and imaging, biosensing, targeted delivery, and, more recently, detoxification of endogenous and xenobiotic compounds. Nanodevices for detoxification are aimed at removing toxic molecules from biological tissues, using a chemical- and/or enzyme-containing nanocarrier for the toxicant to diffuse inside the nanobody. This strategy is opposite to drug delivery systems that focus on encapsulating drugs and releasing them under the influence of external factors. The review describes various kinds of nanodevices intended for detoxification that differ by the type of poisoning treatment they provide, as well as the type of materials and toxicants. The final part of the review is devoted to enzyme nanosystems, an emerging area of research that provides fast and effective neutralization of toxins in vivo.

Phosphate-Trapping Liposomes for Long-Term Management of Hyperphosphatemia

Hyperphosphatemia is a typical complication of end-stage renal disease, characterized by elevated and life-threatening serum phosphate levels. Hemodialysis does not enable sufficient clearance of phosphate, due to slow cell-to-plasma kinetics of phosphate ions; moreover, dietary restrictions and conventional treatment with oral phosphate binders have low success rates, together with adverse effects. Here, we developed a new concept of phosphate-trapping liposomes, to improve and prolong the control over serum phosphate levels. We designed liposomes modified with polyethylene glycol and encapsulated with the phosphate binder ferric citrate (FC liposomes). These liposomes were found to trap phosphate ions in their inner core, and thereby lower free phosphate ion concentrations in solution and in serum. The FC liposomes showed higher phosphate binding ability as phosphate concentrations increased. Moreover, these liposomes showed a time-dependent increase in uptake of phosphate, up to 25 h in serum. Thus, our findings demonstrate effective long-term phosphate trapping by FC liposomes, indicating their potential to reduce serum phosphate toxicity and improve current management of hyperphosphatemia.

pH Gradient Liposomes Extract Protein Bound Amitriptyline in Peritoneal Dialysis-Exploratory Work

Poisoning is a significant cause of injury-related death worldwide. Dialysis is usually ineffective in removing the toxin once it has been absorbed because of drug protein binding and high volumes of distribution. In this work, we explore whether the addition of liposomes to peritoneal dialysate could extract protein bound amitriptyline. Liposomes were prepared using the thin film hydration method. In the in vitro experiment, 3 mL of 20% albumin with a concentration of 6000 nmol/L amitriptyline in a proprietary dialysis cartridge was dialysed against 125 mL of phosphate-buffered saline with and without 80 mg 1,2-dioleoyl-sn-glycero-3-phosphoglycerol (DOPG) liposomes. In the in vivo arm, peritoneal dialysis was undertaken in 6 rats with pH gradient liposome augmented dialysate after intravenous amitriptyline injection. Peritoneal blood flow was estimated by CO₂ extraction. Total amitriptyline extracted was compared to freely dissolved (non-protein bound) and total amitriptyline perfusing the membrane during the peritoneal dwell. Mean liposome size for DOPG and acidic centre pH gradient liposomes was 119 nm and 430 nm, respectively. In the in vitro experiment, more amitriptyline was extracted into the liposome containing dialysate than the control dialysate (40 +/- 2 nmol/L vs. 27 +/- 1 nmol/L). In the in vivo experiment, the total amitriptyline in dialysate was 5240 +/- 2750 nmol. Mean total free amitriptyline perfusing the peritoneal membrane was 93 +/- 46 nmol. Mean total blood amitriptyline perfusing the peritoneal membrane was 23,920 +/- 6920 nmol. Two of the six animals were excluded due to overestimation of peritoneal blood flow. This exploratory work suggests the addition of liposome nanoparticles to peritoneal dialysate extracted protein bound amitriptyline from blood.

Removal of Uremic Solutes from Dialysate by Activated Carbon

BACKGROUND AND OBJECTIVES

Adsorption of uremic solutes to activated carbon provides a potential means to limit dialysate volumes required for new dialysis systems. The ability of activated carbon to take up uremic solutes has, however, not been adequately assessed.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Graded volumes of waste dialysate collected from clinical hemodialysis treatments were passed through activated carbon blocks. Metabolomic analysis assessed the adsorption by activated carbon of a wide range of uremic solutes. Additional experiments tested the ability of the activated carbon to increase the clearance of selected solutes at low dialysate flow rates.

RESULTS

Activated carbon initially adsorbed the majority, but not all, of 264 uremic solutes examined. Solute adsorption fell, however, as increasing volumes of dialysate were processed. Moreover, activated carbon added some uremic solutes to the dialysate, including methylguanidine. Activated carbon was particularly effective in adsorbing uremic solutes that bind to plasma proteins. In vitro dialysis experiments showed that introduction of activated carbon into the dialysate stream increased the clearance of the protein-bound solutes indoxyl sulfate and p-cresol sulfate by 77%±12% (mean±SD) and 73%±12%, respectively, at a dialysate flow rate of 200 ml/min, but had a much lesser effect on the clearance of the unbound solute phenylacetylglutamine.

CONCLUSIONS

Activated carbon adsorbs many but not all uremic solutes. Introduction of activated carbon into the dialysate stream increased the clearance of those solutes that it does adsorb.

Liposome Formulation and In Vitro Testing in Non-Physiological Conditions Addressed to Ex Vivo Kidney Perfusion

This work focuses on formulating liposomes to be used in isolated kidney dynamic machine perfusion in hypothermic conditions as drug delivery systems to improve preservation of transplantable organs. The need mainly arises from use of kidneys from marginal donors for transplantation that are more exposed to ischemic/reperfusion injury compared to those from standard donors. Two liposome preparation techniques, thin film hydration and microfluidic techniques, are explored for formulating liposomes loaded with two model proteins, myoglobin and bovine serum albumin. The protein-loaded liposomes are characterized for their size by DLS and morphology by TEM. Protein releases from the liposomes are tested in PERF-GEN perfusion fluid, 4 °C, and compared to the in vitro protein release in PBS, 37 °C. Fluorescent liposome uptake is analyzed by fluorescent microscope in vitro on epithelial tubular renal cell cultures and ex vivo on isolated pig kidney in hypothermic perfusion conditions. The results show that microfluidics are a superior technique for obtaining reproducible spherical liposomes with suitable size below 200 nm. Protein encapsulation efficiency is affected by its molecular weight and isoelectric point. Lowering incubation temperature slows down the proteins release; the perfusion fluid significantly affects the release of proteins sensitive to ionic media (such as BSA). Liposomes are taken up by epithelial tubular renal cells in two hours’ incubation time.