Rituximab: a boot to protect the foot

Xenotransplantation: A New Era

Organ allotransplantation has now reached an impassable ceiling inherent to the limited supply of human donor organs. In the United States, there are currently over 100,000 individuals on the national transplant waiting list awaiting a kidney, heart, and/or liver transplant. This is in contrast with only a fraction of them receiving a living or deceased donor allograft. Given the morbidity, mortality, costs, or absence of supportive treatments, xenotransplant has the potential to address the critical shortage in organ grafts. Last decade research efforts focused on creation of donor organs from pigs with various genes edited out using CRISPR technologies and utilizing non-human primates for trial. Three groups in the United States have recently moved forward with trials in human subjects and obtained initial successful results with pig-to-human heart and kidney xenotransplantation. This review serves as a brief discussion of the recent progress in xenotransplantation research, particularly as it concerns utilization of porcine heart, renal, and liver xenografts in clinical practice.

Therapeutic apheresis in kidney transplantation: An updated review

Therapeutic apheresis is a cornerstone of therapy for several conditions in transplantation medicine and is available in different technical variants. In the setting of kidney transplantation, immunological barriers such as ABO blood group incompatibility and preformed donor-specific antibodies can complicate the outcome of deceased- or living- donor transplantation. Postoperatively, additional problems such as antibody-mediated rejection and a recurrence of primary focal segmental glomerulosclerosis can limit therapeutic success and decrease graft survival. Therapeutic apheresis techniques find application in these issues by separating and selectively removing exchanging or modifying pathogenic material from the patient by an extracorporeal aphaeresis system. The purpose of this review is to describe the available techniques of therapeutic aphaeresis with their specific advantages and disadvantages and examine the evidence supporting the application of therapeutic aphaeresis as an adjunctive therapeutic option to immunosuppressive agents in protocols before and after kidney transplantation.

Cloning, function, and localization of human, canine, and Drosophila ZIP10 (SLC39A10), a Zn2+ transporter

Zinc (Zn²⁺) is the second most abundant trace element, but is considered a micronutrient, as it is a cofactor for many enzymes and transcription factors. Whereas Zn²⁺ deficiency can cause cognitive immune or metabolic dysfunction and infertility, excess Zn²⁺ is nephrotoxic. As for other ions and solutes, Zn²⁺ is moved into and out of cells by specific membrane transporters: ZnT, Zip, and NRAMP/DMT proteins. ZIP10 is reported to be localized at the apical membrane of renal proximal tubules in rats, where it is believed to play a role in Zn²⁺ import. Renal regulation of Zn²⁺ is of particular interest in light of growing evidence that Zn²⁺ may play a role in kidney stone formation. The objective of this study was to show that ZIP10 homologs transport Zn²⁺, as well as ZIP10, kidney localization across species. We cloned ZIP10 from dog, human, and Drosophila ( CG10006), tested clones for Zn²⁺ uptake in Xenopus oocytes and localized the protein in renal structures. CG10006, rather than foi (fear-of-intimacy, CG6817) is the primary ZIP10 homolog found in Drosophila Malpighian tubules. The ZIP10 antibody recognizes recombinant dog, human, and Drosophila ZIP10 proteins. Immunohistochemistry reveals that ZIP10 in higher mammals is found not only in the proximal tubule, but also in the collecting duct system. These ZIP10 proteins show Zn²⁺ transport. Together, these studies reveal ZIP10 kidney localization, a role in renal Zn²⁺ transport, and indicates that CG10006 is a Drosophila homolog of ZIP10.

Plasma exchange in kidney transplantation: Still a valuable option for nephrotic syndrome recurrence

About 30% of the cases of steroid resistant nephrotic syndrome display a genetically determined disease and will not recur after kidney transplant; the other cases with fully or partially immunological pathogenesis display a high risk of post transplant recurrence. Although lots of studies were carried out in the last 50 years the pathogenetic mechanism is still obscure and the therapeutic approach mostly empirical. The cornerstones principles of the therapies are based on removal of a still undefined "permeability factor" through plasma-exchange or other apheresis techniques and inhibition of its synthesis by the immunological system through different drugs. The probability of successfully inducing persistant remission is nowadays around 30%through the different schemes experimented so far which mostly include plasmapheresis. Rituximab in the last years has significantly increased the efficacy of the treatments. Non responders are rapidly evolving to graft loss and will most probably recur also in subsequent transplant. Apart from genetics no other risk factors are predictive for recurrence.

Podocyte-actin dynamics in health and disease

Genetic studies of hereditary forms of nephrotic syndrome have identified several proteins that are involved in regulating the permselective properties of the glomerular filtration system. Further extensive research has elucidated the complex molecular basis of the glomerular filtration barrier and clearly established the pivotal role of podocytes in the pathophysiology of glomerular diseases. Podocyte architecture is centred on focal adhesions and slit diaphragms - multiprotein signalling hubs that regulate cell morphology and function. A highly interconnected actin cytoskeleton enables podocytes to adapt in order to accommodate environmental changes and maintain an intact glomerular filtration barrier. Actin-based endocytosis has now emerged as a regulator of podocyte integrity, providing an impetus for understanding the precise mechanisms that underlie the steady-state control of focal adhesion and slit diaphragm components. This Review outlines the role of actin dynamics and endocytosis in podocyte biology, and discusses how molecular heterogeneity in glomerular disorders could be exploited to deliver more rational therapeutic interventions, paving the way for targeted medicine in nephrology.

Membranous nephropathy: Pilot study of a novel regimen combining cyclosporine and Rituximab

INTRODUCTION

There is broad consensus that high grade basal proteinuria and failure to achieve remission of proteinuria are key determinants of adverse renal prognosis in patients with primary membranous nephropathy. Based on the fact that current regimens are not ideal due to short and long-term toxicity and propensity to relapse after treatment withdrawal, we developed a treatment protocol based on a novel combination of rituximab and cyclosporine which targets both the B and T cell limbs of the immune system. Herein, we report pilot study data on proteinuria, changes in autoantibody levels and renal function that offer a potentially effective new approach to treatment of severe membranous nephropathy.

METHODS

Thirteen high-risk patients defined by sustained high-grade proteinuria (mean 10.8 g/d) received combination induction therapy with rituximab plus cyclosporine for 6 months, followed by a second cycle of rituximab and tapering of cyclosporine during an 18 month maintenance phase.

RESULTS

Mean proteinuria decreased by 65% at 3 months and by 80% at 6 months. Combined complete or partial remission was achieved in 92% of patients by 9 months; 54% achieved complete remission at 12 months. Two patients relapsed during the trial. All patients with autoantibodies to PLA₂R achieved antibody depletion. Renal function stabilized. The regimen was well tolerated.

DISCUSSION

We report these encouraging preliminary results for their potential value to other investigators needing prospectively collected data to inform the design and power calculations of future randomized clinical trials. Such trials will be needed to formally compare this novel regimen to current therapies for membranous nephropathy.

Sulfate and thiosulfate inhibit oxalate transport via a dPrestin (Slc26a6)-dependent mechanism in an insect model of calcium oxalate nephrolithiasis

Nephrolithiasis is one of the most common urinary tract disorders, with the majority of kidney stones composed of calcium oxalate (CaOx). Given its prevalence (US occurrence 10%), it is still poorly understood, lacking progress in identifying new therapies because of its complex etiology. Drosophila melanogaster (fruitfly) is a recently developed model of CaOx nephrolithiasis. Effects of sulfate and thiosulfate on crystal formation were investigated using the Drosophila model, as well as electrophysiological effects on both Drosophila (Slc26a5/6; dPrestin) and mouse (mSlc26a6) oxalate transporters utilizing the Xenopus laevis oocyte heterologous expression system. Results indicate that both transport thiosulfate with a much higher affinity than sulfate Additionally, both compounds were effective at decreasing CaOx crystallization when added to the diet. However, these results were not observed when compounds were applied to Malpighian tubules ex vivo. Neither compound affected CaOx crystallization in dPrestin knockdown animals, indicating a role for principal cell-specific dPrestin in luminal oxalate transport. Furthermore, thiosulfate has a higher affinity for dPrestin and mSlc26a6 compared with oxalate These data indicate that thiosulfate's ability to act as a competitive inhibitor of oxalate via dPrestin, can explain the decrease in CaOx crystallization seen in the presence of thiosulfate, but not sulfate. Overall, our findings predict that thiosulfate or oxalate-mimics may be effective as therapeutic competitive inhibitors of CaOx crystallization.