Dialysis at a Crossroads: Reverse Engineering Renal Replacement Therapy

Health Policy for Dialysis Care in Canada and the United States

Contemporary dialysis treatment for chronic kidney failure is complex, is associated with poor clinical outcomes, and leads to high health costs, all of which pose substantial policy challenges. Despite similar policy goals and universal access for their kidney failure programs, the United States and Canada have taken very different approaches to dealing with these challenges. While US dialysis care is primarily government funded and delivered predominantly by private for-profit providers, Canadian dialysis care is also government funded but delivered almost exclusively in public facilities. Differences also exist for regulatory mechanisms and the policy incentives that may influence the behavior of providers and facilities. These differences in health policy are associated with significant variation in clinical outcomes: mortality among patients on dialysis is consistently lower in Canada than in the United States, although the gap has narrowed in recent years. The observed heterogeneity in policy and outcomes offers important potential opportunities for each health system to learn from the other. This article compares and contrasts transnational dialysis-related health policies, focusing on key levers including payment, finance, regulation, and organization. We also describe how policy levers can incentivize favorable practice patterns to support high-quality/high-value, person-centered care and to catalyze the emergence of transformative technologies for alternative kidney replacement strategies.

Functional genomic analysis identifies indoxyl sulfate as a major, poorly dialyzable uremic toxin in end-stage renal disease

Background

Chronic renal failure is characterized by progressive renal scarring and accelerated arteriosclerotic cardiovascular disease despite what is considered to be adequate hemodialysis or peritoneal dialysis. In rodents with reduced renal mass, renal scarring has been attributed to poorly filtered, small protein-bound molecules. The best studied of these is indoxyl sulfate (IS).

Methods

We have attempted to establish whether there are uremic toxins that are not effectively removed by hemodialysis. We examined plasma from patients undergoing hemodialysis, employing global gene expression in normal human renal cortical cells incubated in pre- and post- dialysis plasma as a reporter system. Responses in cells incubated with pre- and post-dialysis uremic plasma (n = 10) were compared with responses elicited by plasma from control subjects (n = 5). The effects of adding IS to control plasma and of adding probenecid to uremic plasma were examined. Plasma concentrations of IS were measured by HPLC (high pressure liquid chromatography).

Results

Gene expression in our reporter system revealed dysregulation of 1912 genes in cells incubated with pre-dialysis uremic plasma. In cells incubated in post-dialysis plasma, the expression of 537 of those genes returned to baseline but the majority of them (1375) remained dysregulated. IS concentration was markedly elevated in pre- and post-dialysis plasma. Addition of IS to control plasma simulated more than 80% of the effects of uremic plasma on gene expression; the addition of probenecid, an organic anion transport (OAT) inhibitor, to uremic plasma reversed the changes in gene expression.

Conclusion

These findings provide evidence that hemodialysis fails to effectively clear one or more solutes that effect gene expression, in our reporter system, from the plasma of patients with uremia. The finding that gene dysregulation was simulated by the addition of IS to control plasma and inhibited by addition of an OAT inhibitor to uremic plasma identifies IS as a major, poorly dialyzable, uremic toxin. The signaling pathways initiated by IS and possibly other solutes not effectively removed by dialysis may participate in the pathogenesis of renal scarring and uremic vasculopathy.

Uremic toxicity, oxidative stress, and hemodialysis as renal replacement therapy

Patients with uremia are subject to greatly increased cardiovascular risk that cannot be completely explained by traditional cardiovascular risk factors. An increase in oxidative stress and inflammation has been proposed as contributory nontraditional uremic cardiovascular risk factors. Oxidative stress reflects the balance between oxidant generation and antioxidant defense mechanisms. Reduction/oxidation (redox) reactions may result in a stochastic process leading to oxidation of neighboring macromolecules. However, in many instances the reactive oxygen species target particular amino acid residues or lipid moieties. This provides a mechanism by which increased oxidative stress and/or alteration of antioxidant mechanisms can alter cell signaling. In individuals with advanced chronic kidney disease, the redox balance is not in equilibrium and is tipped toward oxidation resulting in the dysregulation of cellular process with subsequent vascular and tissue injury. In this review, the major oxidant and antioxidant pathways and the biomarkers to assess redox status in uremia are discussed, as well as the data linking the pathogenesis of oxidative stress, inflammation, cardiovascular events, and the progressive loss of kidney function in chronic kidney disease.

Creating research infrastructure and functionality to address chronic kidney disease: the Kidney Research Institute

An expanding proportion of people in the United States and worldwide are affected by kidney disease, leading to a growing concern over the public health implications. Despite the high prevalence and the considerable associated health risks of kidney disease, major gaps in our knowledge base hinder the delivery of optimal medical care to affected individuals. Moreover, research progress that translates into clinical benefit has been slow. For example, over the past 20 years, there has been no successful implementation of a new therapeutic agent specifically designed for the treatment of glomerular diseases, which in part explains why glomerular diseases remain the leading cause of kidney disease in the United States and worldwide. Similarly, the limitations of current approaches to dialysis as treatment of end-stage kidney disease are becoming more apparent, with marginal improvements in risks for hospitalization or mortality over time. Along with recognition of changes in the public health burden of kidney disease, and perception of limited progress in the clinical treatment of kidney disease, a change in kidney disease research is now underway. We are entering a new era in biomedicine emphasizing interdisciplinary and translational research. We here delineate the purpose, mission, and goals, and describe the evolving vision, infrastructure, and research platform of a new Kidney Research Institute, designed to overcome barriers to researching improvements in effective clinical care.

Combining dialysate and blood recirculation to boost uremic toxin removal: theory and simulation study

Emerging concepts in renal replacement therapies such as daily hemodialysis (HD) and wearable artificial kidney (WAK) meet the challenges derived from the aging of renal disease population. The successful results of blood recirculation to improve the dialysis clearance of medium-high uremic toxins suggest that this technique could be used both in daily HD and WAK. However, blood recirculation induces a reduction of small solutes clearance. This work analyzes the ability of a nonregenerated recirculating dialysate technique to avoid that reduction. The study uses in silico simulations with in vitro data from several commercial dialyzers and very compact dialyzer models derived from them. The resulting combined optimization system (recirculating blood-dialysate system [RBDS]) reached low solute dialysance improvements above 100% in different scenarios. Our outcomes show the RBDS performs best with very compact dialyzers, in agreement with the requirements of daily HD and WAK.