Hemolipodialysis attenuates oxidative stress and removes hydrophobic toxins

Application of Nanoparticles as Novel Adsorbents in Blood Purification Strategies

BACKGROUND

Blood purification therapy for patients overloaded with metabolic toxins or drugs still needs improvement. Blood purification therapies, such as in hemodialysis or peritoneal dialysis can profit from a combined application with nanoparticles.

SUMMARY

In this review, the published literature is analyzed with respect to nanomaterials that have been customized and functionalized as nano-adsorbents during blood purification therapy. Liposomes possess a distinct combined structure composed of a hydrophobic lipid bilayer and a hydrophilic core. The liposomes which have enzymes in their aqueous core or obtain specific surface modifications of the lipid bilayer can offer appreciated advantages. Preclinical and clinical experiments with such modified liposomes show that they are highly efficient and generally safe. They may serve as indirect and direct adsorption materials both in hemodialysis and peritoneal dialysis treatment for patients with renal or hepatic failure. Apart from dialysis, nanoparticles made of specially designed metal and activated carbon have also been utilized to enhance the removal of solutes during hemoadsorption. Results are a superior adsorption capacity and good hemocompatibility shown during the treatment of patients with toxication or end-stage renal disease. In summary, nanomaterials are promising tools for improving the treatment efficacy of organ failure or toxication.

KEY MESSAGES

(i) The pH-transmembrane liposomes and enzyme-loaded liposomes are two representatives of liposomes with modified aqueous inner core which have been put into practice in dialysis. (ii) Unmodified or physiochemically modified liposomal bilayers are ideal binders for lipophilic protein-bound uremic toxins or cholestatic solutes, thus liposome-supported dialysis could become the next-generation hemodialysis treatment of artificial liver support system. (iii) Novel nano-based sorbents featuring large surface area, high adsorption capacity and decent biocompatibility have shown promise in the treatment of uremia, hyperbilirubinemia, intoxication, and sepsis. (vi) A major challenge of production lies in avoiding changes in physical and chemical properties induced by manufacturing and sterilizing procedures.

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.

Hemodialysis raises oxidative stress through carbon-centered radicals despite improved biocompatibility

Leukocyte activation and the resulting oxidative stress induced by bioincompatible materials during hemodialysis impact the prognosis of patients. Despite multiple advances in hemodialysis dialyzers, the prognosis of hemodialysis patients with complications deeply related to oxidative stress, such as diabetes mellitus, remains poor. Thus, we re-evaluated the effects of hemodialysis on multiple reactive oxygen species using electron spin resonance-based methods for further improvement of biocompatibility in hemodialysis. We enrolled 31 patients in a stable condition undergoing hemodialysis using high-flux polysulfone dialyzers. The effects of hemodialysis on reactive oxygen species were evaluated by two methods: MULTIS, which evaluates serum scavenging activities against multiple hydrophilic reactive oxygen species, and i-STrap, which detects lipophilic carbon-center radicals. Similar to previous studies, we found that serum hydroxyl radical scavenging activity significantly improved after hemodialysis. Unlike previous studies, we discovered that scavenging activity against alkoxyl radical was significantly reduced after hemodialysis. Moreover, patients with diabetes mellitus showed a decrease in serum scavenging activity against alkyl peroxyl radicals and an increase in lipophilic carbon-center radicals after hemodialysis. These results suggest that despite extensive improvements in dialyzer membranes, the forms of reactive oxygen species that can be eliminated during dialysis are limited, and multiple reactive oxygen species still remain at increased levels during hemodialysis.

Increasing the removal of protein-bound uremic toxins by liposome-supported hemodialysis

Protein-bound uremic toxins (PBUTs) accumulate at high plasma levels and cause various deleterious effects in end-stage renal disease patients because their removal by conventional hemodialysis is severely limited by their low free-fraction levels in plasma. Here, we assessed the extent to which solute removal can be increased by adding liposomes to the dialysate. The uptake of liposomes by direct incubation in vitro showed an obvious dose-response relationship for p-cresyl sulfate (PCS) and indoxyl sulfate (IS) but not for hippuric acid (HA). The percent removal of both PCS and IS but not of HA was gradually increased with the increased concentration of liposomes in a rapid equilibrium dialysis setup. In vitro closed circulation showed that adding liposomes to the dialysate markedly increased the dialysances of PBUTs without greatly altering that of urea and creatinine. In vivo experiments in uremic rats demonstrated that adding liposomes to the dialysate resulted in higher reduction ratios (RRs) and more total solute removal (TSR) for several PBUTs compared to the conventional dialysate, which was approximately similar to the addition of bovine serum albumin to the dialysate. These findings highlight that as an adjunct to conventional hemodialysis, addition of liposomes to the dialysate could significantly improve the removal of protein-bound uremic solutes without greatly altering the removal of small, water-soluble solutes.

Hypoalbuminemia in hemodialyzed end stage renal disease patients: risk factors and relationships--a 2 year single center study

Background

Malnutrition affects 1/3 of hemodialysis patients and associates with a higher risk of morbidity and mortality. Serum albumin is a marker of nutrition and inflammation, and predicts mortality, particularly when <3.8 g/dL. This study was performed to identify risk factors for hypoalbuminemia (<3.8 g/dL) and the particular temporal relationship and strength of association between protein intake (nPCR) and serum albumin when confounding variables are taken into account.

Methods

Demographic, clinical, and dialysis-related data of 57 ESRD patients on hemodialysis over 24 months in 6 temporal segments were analyzed with serum albumin as a continuous, and categorical outcome (with 3.8 g/dl as cut-off) variable , against 13 potential independent variables [4 demographic factors, 3 nutrition-related, and 5 morbidity-related parameters, and % urea reduction ratio (URR)]. The temporal relationships between albumin and nPCR were analyzed for the concurrent & 3 subsequent months in each temporal segment.

Results

The impact of nPCR on serum albumin (p < 0.05) was significant but with no discernible temporal relationship. Advancing age, longer vintage, female gender, diabetes mellitus, nPCR, serum phosphate and ferritin had significant correlation with albumin <3.8 g/dl (p < 0.05). Serum phosphate levels correlated positively, and fever, bacteremia, hospital stay and weight loss negatively, with mean serum albumin but did not negate the effect of nPCR. Regression analysis showed that mean albumin associated with nPCR, fever, hospital stay, bacteremia, dialysis vintage, age, sex, and diabetes mellitus; and that an albumin level of <3.8 g/dl associated with age, female sex, diabetes, lower nPCR, and higher ferritin.

Conclusion

Suggested target albumin levels were not met in elderly, female, and diabetic patients. The association of nPCR with albumin was not nullified by confounding demographic or morbidity-related factors. nPCR had no demonstrable temporal relationship with albumin.

Human serum albumin: from bench to bedside

Human serum albumin (HSA), the most abundant protein in plasma, is a monomeric multi-domain macromolecule, representing the main determinant of plasma oncotic pressure and the main modulator of fluid distribution between body compartments. HSA displays an extraordinary ligand binding capacity, providing a depot and carrier for many endogenous and exogenous compounds. Indeed, HSA represents the main carrier for fatty acids, affects pharmacokinetics of many drugs, provides the metabolic modification of some ligands, renders potential toxins harmless, accounts for most of the anti-oxidant capacity of human plasma, and displays (pseudo-)enzymatic properties. HSA is a valuable biomarker of many diseases, including cancer, rheumatoid arthritis, ischemia, post-menopausal obesity, severe acute graft-versus-host disease, and diseases that need monitoring of the glycemic control. Moreover, HSA is widely used clinically to treat several diseases, including hypovolemia, shock, burns, surgical blood loss, trauma, hemorrhage, cardiopulmonary bypass, acute respiratory distress syndrome, hemodialysis, acute liver failure, chronic liver disease, nutrition support, resuscitation, and hypoalbuminemia. Recently, biotechnological applications of HSA, including implantable biomaterials, surgical adhesives and sealants, biochromatography, ligand trapping, and fusion proteins, have been reported. Here, genetic, biochemical, biomedical, and biotechnological aspects of HSA are reviewed.

Pharmaceutically important pre- and posttranslational modifications on human serum albumin

Recombinant technology allows engineering and production of proteins with desirable properties. Human serum albumin has been developed with recombinant technology, and thus plays an increasing role as a drug carrier in the clinical setting. Genetic variations usually occur on the surface of the protein, and do not impose significant effects on the conformation of albumin. However, binding of fatty acids by genetic variants is affected according to the location of the mutation. Albumin undergoes three major posttranslational modifications, namely, oxidation, glycation, and S-nitrosylation. This review gives an account of the different posttranslational modifications that should be taken into consideration when designing albumin mutant analogues with desirable pharmaceutical properties.

A bench to bedside view of uremic toxins

Reviewing the current picture of uremic toxicity reveals its complexity. Focusing on cardiovascular damage as a model of uremic effects resulting in substantial morbidity and mortality, most molecules with potential to affect the function of a variety of cell types within the vascular system are difficult to remove by dialysis. Examples are the larger middle molecular weight molecules and protein-bound molecules. Recent clinical studies suggest that enhancing the removal of these compounds is beneficial for survival. Future therapeutic options are discussed, including improved removal of toxins and the search for pharmacologic strategies blocking responsible pathophysiologic pathways.

Overproduction of reactive oxygen species in end-stage renal disease patients: a potential component of hemodialysis-associated inflammation

During the past decade, hemodialysis (HD)-induced inflammation has been linked to the development of long-term morbidity in end-stage renal disease (ESRD) patients on regular renal replacement therapy. Because interleukins and anaphylatoxins produced during HD sessions are potent activators for nicotinamide adenine dinucleotide phosphate (NADPH) oxidase, an example of an enzyme that is responsible for overproduction of reactive oxygen species (ROS), this may constitute a link between leukocyte activation and cell or organ toxicity. Oxidative stress, which results from an imbalance between oxidant production and antioxidant defense mechanisms, has been documented in ESRD patients using lipid and/or protein oxidative markers. Characterization of HD-induced oxidative stress has included identification of potential activators for NADPH oxidase. Uremia per se could prime phagocyte oxidative burst. HD, far from improving the oxidative status, results in an enhancement of ROS owing to hemoincompatibility of the dialysis system, hemoreactivity of the membrane, and trace amounts of endotoxins in the dialysate. In addition, the HD process is associated with an impairment in antioxidant mechanisms. The resulting oxidative stress has been implicated in long-term complications including anemia, amyloidosis, accelerated atherosclerosis, and malnutrition. Prevention of oxidative stress in HD might focus on improving the hemocompatibility of the dialysis system, supplementation of deficient patients with antioxidants, and modulation of NADPH oxidase by pharmacologic approaches.

Uremic toxins: a new focus on an old subject

The uremic syndrome is characterized by an accumulation of uremic toxins due to inadequate kidney function. The European Uremic Toxin (EUTox) Work Group has listed 90 compounds considered to be uremic toxins. Sixty-eight have a molecular weight less than 500 Da, 12 exceed 12,000 Da, and 10 have a molecular weight between 500 and 12,000 Da. Twenty-five solutes (28%) are protein bound. The kinetics of urea removal is not representative of other molecules such as protein-bound solutes or the middle molecules, making Kt/V misleading. Clearances of urea, even in well-dialyzed patients, amount to only one-sixth of physiological clearance. In contrast to native kidney function, the removal of uremic toxins in dialysis is achieved by a one-step membrane-based process and is intermittent. The resulting sawtooth plasma concentrations of uremic toxins contrast with the continuous function of native kidneys, which provides constant solute clearances and mass removal rates. Our increasing knowledge of uremic toxins will help guide future treatment strategies to remove them.

Oxidative stress and uremia

Oxidative stress is a pathogenic element of great importance in uremic patients, with a great impact on their survival. The cause of oxidative stress in patients on hemodialysis is traditionally attributed to the recurrent activation of polymorphonucleate neutrophils and monocytes. The effects of oxidative stress are evident on all biochemical components of biological tissues: lipids, proteins, carbohydrates, and nucleic acids. This study briefly reviews the effects of different dialytic techniques and of kidney transplant on several parameters of oxidative stress. Many different modalities of pharmaceutical intervention are then analyzed, and the clinical evidences reported.

Are advanced oxidation protein products potential uremic toxins?

Oxidative stress, defined as a disruption of the equilibrium between the generation of oxidants and the activity of anti-oxidant systems, plays a significant role in the development of the inflammatory syndrome associated with chronic renal failure and hemodialysis. In our recent work, the aim of which was to better characterize oxidative stress in dialysis patients, we described the presence of oxidized protein products, which we have termed advanced oxidation protein products (AOPP), in the plasma of dialysis patients and we proposed AOPP as new markers of oxidative stress and potential inflammatory mediators. AOPP represent an exquisite marker of phagocyte-derived oxidative stress, and their role in the pathophysiology of chronic renal failure and dialysis-related complications might be of great importance. Regarding the mechanisms of generation of AOPP, we pointed out the importance of myeloperoxidase and the subsequent generation of chlorinated oxidants, previously considered solely as microbicidal agents, in the formation of AOPP. Indeed, AOPP appear to act as true inflammatory mediators since they are able to trigger the oxidative burst and the synthesis of inflammatory cytokines in neutrophils, as well as in monocytes. Thus, it could be hypothesized that the AOPP, which arise from the reaction between chlorinated oxidants and plasma proteins, constitute new uremic toxins with pro-inflammatory effects.

Evolution of oxidative stress and inflammation during hemodialysis and their contribution to cardiovascular disease

End-stage renal disease patients have increased cardiovascular morbidity and mortality. These patients have many unique risk factors, such as an accumulation of uremic toxins, electrolyte imbalances, metabolic disturbances, anemia, chronic inflammation, and thrombogenic disturbances. Oxidative stress has been implicated in many of these disturbances. This review will focus on some of the factors that may accelerate cardiovascular disease in uremic patients, with an emphasis on mechanisms and interactions of various components of oxidative stress and inflammation. Understanding the mechanisms of these pathways may be useful in developing effective prevention and treatment strategies.

Oxidative stress during ex vivo hemodialysis of blood is decreased by a novel hemolipodialysis procedure utilizing antioxidants

The high cardiovascular mortality in patients receiving hemodialysis (HD) has been attributed, in part, to oxidative stress. Here we examined the effectiveness of antioxidants introduced by means of a novel hemolipodialysis (HLD) procedure in terms of reducing oxidative stress during ex vivo blood circulation. Oxidative stress was studied in a model HD system resembling the extracorporeal circulation of blood during clinical HD. Blood circulation produced an increase of up to 280% in free hemoglobin levels and an increase of 320% in electronegative LDL (LDL(-)) subfraction. A significant correlation between LDL(-) and free hemoglobin levels confirmed previous findings that LDL(-) formation during ex vivo circulation of blood can be mediated by the oxidative activity of free hemoglobin. These effects were significantly attenuated during HLD using a dialysis circuit containing vitamin E with or without vitamin C. By contrast, HLD with vitamin C alone had a marked pro-oxidant effect. TBARS, lipid hydroperoxides, vitamin E and beta-carotene content in LDL were not significantly altered by the HD procedure. These findings demonstrate the occurrence of oxidative stress in human plasma where lipoproteins are a target and indicate antioxidant-HLD treatment as a specific new approach to decreasing the adverse oxidative stress frequently associated with cardiovascular complications in high-risk populations of uremic patients.

Oxidant stress in hemodialysis: prevention and treatment strategies

Oxidant stress has been implicated in a number of pathologies associated with uremia and hemodialysis. These patients have an increased incidence of cardiovascular disease, amyloidosis associated with protein modification, and notable changes in both function and structure of many cellular components. Oxidative reactions most frequently involving free radical intermediates play an important role in these processes and participate both directly and indirectly by further amplification of the inflammatory responses or in activation of signaling cascades mediating proliferation, differentiation, and cell death. Proteins and lipids are susceptible to oxidative degradation. These changes can ultimately alter important structural and functional characteristics and lead to pathological changes. This article addresses some of the diverse mechanisms and pathways involved in these changes, and suggests new therapeutic strategies in preventing oxidative damage.