Oxidative stress reduction by icodextrin-based glucose-free solutions in peritoneal dialysis: Support for new promising approaches.

BACKGROUND: Oxidative stress (OxSt) and inflammation are common in CKD and are known CV and mortality risk factors. In peritoneal dialysis (PD) OxSt and Inflammation even increase due to the use of glucose-based solutions. PATIENTS AND METHODS: This study analyzed in 15 PD patients the effect of 3 and 6 months of treatment with icodextrin-based glucose-free solutions on OxSt and inflammation, evaluating p22phox protein expression (Western blot), NADPH oxidase subunit, essential for OxSt activation, MYPT-1 phosphorylation state, marker of RhoA/Rho kinase pathway (ROCK) activity, involved in the induction of OxSt (Western blot) and Malondialdehyde (MDA) production (fluorimetric assay). Interleukin (IL)-6 blood level (chemiluminescence assay) has been measured and used as a marker of inflammation. RESULTS: p22phox protein expression, MYPT 1 phosphorylation, and MDA were reduced after 3 months from the start of icodextrin (1.28 ± 0.18 d.u. vs. 1.50 ± 0.19, p = 0.049; 0.89 ± 0.03 vs. 0.98 ± 0.03, p = 0.004; 4.20 ± 0.18 nmol/mL vs. 4.84 ± 0.32 nmol/mL, p = 0.045, respectively). In a subgroup of 9 patients who continued the treatment up to 6 months, MYPT-1 phosphorylation was further reduced at 6 months compared to baseline (0.84 ± 0.06 vs. 0.99 ± 0.04, p = 0.043), while p22phox protein expression was reduced only at 6 months versus baseline (1.03 ± 0.05 vs. 1.68 ± 0.22, p = 0.021). In this subgroup, MDA was reduced at 6 months versus baseline (4.03 ± 0.24 nmol/mL vs. 4.68 ± 0,32, p = 0.024) and also versus 3 months (4.03 ± 0.24 vs. 4.35 ± 0.21, p = 0.008). IL-6 level although reduced both at 3 and 6 months, did not reach statistical significance. CONCLUSIONS: The reduction of OxSt with icodextrin-based PD solutions, although obtained in a small patients cohort and in a limited time duration study, strongly supports the rationale of using osmo-metabolic agents-based fluids replacing glucose-based fluids. Ongoing studies with these agents will provide information regarding preservation of peritoneal membrane integrity, residual renal function, and reduction of CVD risk factors such as OxSt and inflammation.

Lymphatic vessels and the renin-angiotensin-system.

The lymphatic system is an integral part of the circulatory system and plays an important role in the fluid homeostasis of the human body. Accumulating evidence has recently suggested the involvement of lymphatic dysfunction in the pathogenesis of cardio-reno-vascular (CRV) disease. However, how the sophisticated contractile machinery of lymphatic vessels is modulated and, possibly impaired in CRV disease, remains largely unknown. In particular, little attention has been paid to the effect of the renin-angiotensin-system (RAS) on lymphatics, despite the high concentration of RAS mediators that these tissue-draining vessels are exposed to and the established role of the RAS in the development of classic microvascular dysfunction and overt CRV disease. We herein review recent studies linking RAS to lymphatic function and/or plasticity and further highlight RAS-specific signaling pathways, previously shown to drive adverse arterial remodeling and CRV organ damage that have potential for direct modulation of the lymphatic system.

Gitelman's and Bartter's Syndromes: From Genetics to the Molecular Basis of Hypertension and More.

BACKGROUND: Gitelman's and Bartter's syndromes (GS/BS) are rare genetic tubulopathies characterized by electrolyte imbalance and activation of the renin-angiotensin-aldosterone system (RAAS). These syndromes have intriguing biochemical and hormonal abnormalities that lead them to be protected from hypertension and cardiovascular and renal remodeling. SUMMARY: In this review, we explore the biochemical/molecular mechanisms induced by the activation of the RAAS and its counterregulatory arm which is particularly activated in GS/BS patients, in the context of blood pressure regulation. In addition, we report our findings in the context of the COVID-19 pandemic where we observed GS/BS subjects being protected from infection. KEY MESSAGES: The intracellular pathways induced by Ang II, starting from induction of oxidative stress and vasoconstriction, are crucial for the progression toward cardiovascular-renal remodeling and might be useful targets in order to reduce/halt the progression of Ang II/oxidative stress-induced cardiovascular-renal morbidity in several diseases.

Oxidative stress, inflammation, and peritoneal dialysis: A molecular biology approach.

The key role of oxidative stress (OxSt) and inflammation for the induction of cardiovascular disease, the leading cause of excess morbidity/mortality in chronic kidney disease and dialysis patients, is known and both the activations of NADPH oxidase and RhoA/Rho kinase (ROCK) pathway are pivotal for their effects. While specific hemodialysis procedures, such as hemodiafiltration with on-line reinfusion of ultrafiltrate and/or the use of vitamin E-coated dialyzers, are beneficial for OxSt and inflammation, studies in peritoneal dialysis (PD) are instead scarce and results seem not favorable. In nine patients under PD OxSt in terms of mononuclear cell protein level of p22phox (Western blot), subunit of NADPH oxidase, essential for the generation of OxSt, and MYPT-1 phosphorylation state (Western blot), a marker of ROCK activity, have been measured at the beginning and after 3 and 6 months of PD. Blood levels of interleukin 6 (IL-6), ferritin, and albumin have been considered for evaluating the inflammatory state. p22phox protein expression, MYPT-1-phosphorylation, and ferritin level were increased both at baseline vs healthy subjects (P = .02, P < .0001, P = .004, respectively) and vs baseline after 3 and 6 months of peritoneal dialysis (P = .007, P < .001, P = .004, respectively). Albumin was lower after 6 months of PD (P = .0014). IL-6 was increased at baseline vs reference values and remained unchanged at 3 and 6 months. OxSt and inflammation increase during PD confirming via molecular biology approach a report at biochemical level. To improve OxSt state in PD, a multitarget approach is necessary. It might include the use of more physiologic pH, low glucose degradation products, low lactate and iso-osmolar PD solutions, patients' strict glycemic control, optimal volume management, and antioxidant administration, such as N-acetylcysteine.

Sodium, Interstitium, Lymphatics and Hypertension-A Tale of Hydraulics.

Blood pressure is regulated by vascular resistance and intravascular volume. However, exchanges of electrolytes and water between intra and extracellular spaces and filtration of fluid and solutes in the capillary beds blur the separation between intravascular, interstitial and intracellular compartments. Contemporary paradigms of microvascular exchange posit filtration of fluids and solutes along the whole capillary bed and a prominent role of lymphatic vessels, rather than its venous end, for their reabsorption. In the last decade, these concepts have stimulated greater interest in and better understanding of the lymphatic system as one of the master regulators of interstitial volume homeostasis. Here, we describe the anatomy and function of the lymphatic system and focus on its plasticity in relation to the accumulation of interstitial sodium in hypertension. The pathophysiological relevance of the lymphatic system is exemplified in the kidneys, which are crucially involved in the control of blood pressure, but also hypertension-mediated cardiac damage. Preclinical modulation of the lymphatic reserve for tissue drainage has demonstrated promise, but has also generated conflicting results. A better understanding of the hydraulic element of hypertension and the role of lymphatics in maintaining fluid balance can open new approaches to prevent and treat hypertension and its consequences, such as heart failure.

Tmprss2 maintains epithelial barrier integrity and transepithelial sodium transport.

The mouse cortical collecting duct cell line presents a tight epithelium with regulated ion and water transport. The epithelial sodium channel (ENaC) is localized in the apical membrane and constitutes the rate-limiting step for sodium entry, thereby enabling transepithelial transport of sodium ions. The membrane-bound serine protease Tmprss2 is co-expressed with the alpha subunit of ENaC. αENaC gene expression followed the Tmprss2 expression, and the absence of Tmprss2 resulted not only in down-regulation of αENaC gene and protein expression but also in abolished transepithelial sodium transport. In addition, RNA-sequencing analyses unveiled drastic down-regulation of the membrane-bound protease CAP3/St14, the epithelial adhesion molecule EpCAM, and the tight junction proteins claudin-7 and claudin-3 as also confirmed by immunohistochemistry. In summary, our data clearly demonstrate a dual role of Tmprss2 in maintaining not only ENaC-mediated transepithelial but also EpCAM/claudin-7-mediated paracellular barrier; the tight epithelium of the mouse renal mCCD cells becomes leaky. Our working model proposes that Tmprss2 acts via CAP3/St14 on EpCAM/claudin-7 tight junction complexes and through regulating transcription of αENaC on ENaC-mediated sodium transport.

Oxidative stress and its role in Fabry disease.

Fabry disease is a rare X-linked disease characterized by deficient expression and activity of alpha-galactosidase A with consequent lysosomal accumulation of glycosphingolipids, particularly globotriaosylceramide in various organs. Currently, enzyme replacement therapy with recombinant human α-galactosidase is the cornerstone of the treatment of Fabry patients, although in the long term enzyme replacement therapy fails to halt disease progression, in particular in case of late diagnosis. This suggests that the adverse outcomes cannot be justified by the lysosomal accumulation of glycosphingolipids alone, and that additional therapies targeted at further pathophysiologic mechanisms might contribute to halting the progression of cardiac, cerebrovascular and kidney disease in Fabry patients. Recent evidence points toward the involvement of oxidative stress, oxidative stress signaling and inflammation in the pathophysiology of cardio cerebrovascular and kidney damage in Fabry patients. This review reports the current knowledge of the involvement of oxidative stress in Fabry disease, which clearly points toward the involvement of oxidative stress in the pathophysiology of the medium to long-term cardio-cerebrovascular-kidney damage of Fabry patients and summarizes the antioxidant therapeutic approaches currently available in the literature. This important role played by oxidative stress suggests potential novel additional therapeutic interventions by either pharmacologic or nutritional measures, on top of enzyme replacement therapy, aimed at improving/halting the progression of cardio-cerebrovascular disease and nephropathy that occur in Fabry patients.

The RAAS Goodfellas in Cardiovascular System.

In the last two decades, the study of the renin-angiotensin-aldosterone system (RAAS) has revealed a counterregulatory protective axis. This protective arm is characterized by ACE2/Ang 1-7/MasR and Ang 1-9 that largely counteracts the classic arm of the RAAS mediated by ACE/Ang II/AT1R/aldosterone and plays an important role in the prevention of inflammation, oxidative stress, hypertension, and cardiovascular remodeling. A growing body of evidence suggests that enhancement of this counterregulatory arm of RAAS represents an important therapeutic approach to facing cardiovascular comorbidities. In this review, we provide an overview of the beneficial effects of ACE2, Ang 1-7/MasR, and Ang 1-9 in the context of oxidative stress, vascular dysfunction, and organ damage.

Tracing angiotensin II's yin-yang effects on cardiovascular-renal pathophysiology.

Adverse changes in cardiovascular and renal systems are major contributors to overall morbidity and mortality. Human cardiovascular and renal systems exhibit a complex network of positive and negative feedback that is reflected in the control of vascular tone via angiotensin II (Ang II) based signaling. This review will examine in some depth, the multiple components and processes that control the status and reflect the health of these various cardiovascular and renal systems, such as pathways associated to monomeric G proteins, RhoA/Rho kinase system and ERK, oxidative stress and NO balance. It will specifically emphasize the "yin-yang" nature of Ang II signaling by comparing and contrasting the effects and activity of various systems, pathways and components found in hypertension to those found in Gitelman's and Bartter's syndromes (GS/BS), two rare autosomal recessive tubulopathies characterized by electrolytic imbalance, metabolic alkalosis, sodium wasting and prominent activation of the renin-angiotensin-aldosterone system. Notwithstanding the activation of the renin-angiotensin-aldosterone system, GS/BS are normo-hypotensive and protected from cardiovascular-renal remodeling and therefore can be considered the mirror image, the opposite of hypertension.

Calcineurin-Inhibitor-Induced Hypomagnesemia in Kidney Transplant Patients: A Monocentric Comparative Study between Sucrosomial Magnesium and Magnesium Pidolate Supplementation.

Magnesium (Mg) contributes to DNA stability, protein synthesis and cardiac excitability, while Mg deficiency leads to increased cardiovascular mortality, diabetes, hyperparathyroidism and risk of fractures. In kidney transplant patients, calcineurin inhibitors (CNIs) downregulating Mg channel TRPM6 in the distal collecting tubule induce early hypomagnesemia (HypoMg), which is associated with a faster decline in allograft function. A new formulation, sucrosomial Mg (SucrMg), for oral supplements encapsulates Mg oxide in a phospholipid membrane covered by a sucrester matrix, enhancing gastric and intestinal Mg absorption. This study has evaluated Mg bioavailability, effectiveness and tolerance of SucrMg compared to the conventional preparation of Mg pidolate (PidMg). The association of blood Mg with risk of post-transplant dysglycemia and hyperparathyroidism has also been investigated. Forty hypomagnesemic adult single, double or combined kidney-pancreas or kidney-liver transplant recipients within 2 years from transplantation were recruited. In total, 16 patients received PidMg and 27 received SucrMg. Blood Mg was measured at baseline (T0), after 15 days (T1) and after 6 months (T2) of treatment. PTH, fasting glucose and calcium were measured at baseline and after 6 months of treatment. The tolerance was evaluated at the ambulatory visits. SucrMg compared to PidMg was more efficient at increasing Mg bioavailability at T1: p < 0.0001 vs. p = 0.72 ns, respectively, with a ∆% increase of 12.4% vs. 5.4%, p = 0.04. Both preparations increased blood Mg at T2, p < 0.0001 and p = 0.002, respectively. SucrMg was better tolerated. No difference was observed for fasting plasma glucose, PTH and calcium. On one hand, our study is the first among transplant patients to evaluate the efficacy of SucrMg in the correction of HypoMg, which might justify the limited number of patients enrolled and the short observation time; on the other hand, our results could serve as a useful working hypothesis for further studies with a larger number of transplant patients and an extended study duration to confirm the benefits observed with SucrMg.

Biochemical Mechanisms beyond Glycosphingolipid Accumulation in Fabry Disease: Might They Provide Additional Therapeutic Treatments?

Fabry disease is a rare X-linked disease characterized by deficient expression and activity of alpha-galactosidase A (α-GalA) with consequent lysosomal accumulation of glycosphingolipid in various organs. Currently, enzyme replacement therapy is the cornerstone of the treatment of all Fabry patients, although in the long-term it fails to completely halt the disease's progression. This suggests on one hand that the adverse outcomes cannot be justified only by the lysosomal accumulation of glycosphingolipids and on the other that additional therapies targeted at specific secondary mechanisms might contribute to halt the progression of cardiac, cerebrovascular, and renal disease that occur in Fabry patients. Several studies reported how secondary biochemical processes beyond Gb3 and lyso-Gb3 accumulation-such as oxidative stress, compromised energy metabolism, altered membrane lipid, disturbed cellular trafficking, and impaired autophagy-might exacerbate Fabry disease adverse outcomes. This review aims to summarize the current knowledge of these pathogenetic intracellular mechanisms in Fabry disease, which might suggest novel additional strategies for its treatment.

Pathomechanism of oxidative stress in cardiovascularrenal remodeling and therapeutic strategies.

The high prevalence of cardiovascular disease in patients with chronic kidney disease indicates significant interactions between pathogenic pathways operating in the kidney and heart. These interactions involve all cell types (endothelial cells, smooth muscle cells, macrophages, and others), components of the vasculature, glomeruli, and heart that are susceptible to oxidative damage and structural alterations. A vicious cycle occurs whereby harmful factors such as reactive oxygen species and inflammation damage of vascular structures that themselves become sources of additional dangerous/toxic components released into the local environment. The evidence of this vicious cycle in chronic kidney disease should therefore lead to add other factors to both traditional and nontraditional risk factors. This review will examine the processes occurring during progressive kidney dysfunction with regard to vascular injury, renal remodeling, cardiac hypertrophy, and the transversal role of oxidative stress in the development of these complications.

[Reduced oxidative stress in ADPKD patients treated with tolvaptan].

Autosomal dominant polycystic kidney disease (ADPKD) is the most frequent monogenic kidney disease. It causes hypertension and progressive renal failure, both strictly linked to oxidative stress (OxSt). Treatment with tolvaptan is a consolidate option which slows renal deterioration rate, although the molecular mechanisms involved are not fully clarified. We evaluated the OxSt state in tolvaptan-treated ADPKD patients, untreated patients and healthy subjects. OxSt was assessed in 9 patients for each group as mononuclear cell protein expression, MYPT-1 phosphorylation state (Western blot) and heme oxygenase (HO-1) (ELISA). p22 phox protein expression was lower in tolvaptan treated ADPKD and controls compared to untreated patients: 0.86 ±0.15 d.u. p=0.015; 0.53 ±0.11, p<0.001; 1.42 ±0.11 respectively. The same was observed for phosphorylated MYPT-1: 0.68 ±0.09, p=0.013 and vs 0.47 ±0.13, p<0.001, 0.96 ±0.28, while HO-1 of untreated patients was significantly lower compared to treated and controls: 5.33 ±3.34 ng/mL, 2.08 ±0.79, p=0.012, 1.97 ±1.22, p=0.012. Tolvaptan-treated ADPKD patients have reduced OxSt, which might contribute to slowing down the loss of renal function.

The Effect of Green Tea as an Adjuvant to Enzyme Replacement Therapy on Oxidative Stress in Fabry Disease: A Pilot Study.

Enzymatic replacement therapy (ERT) is not very effective in halting the progression of Fabry disease (FD) toward cardiovascular (CV)-renal remodeling, particularly in case of late diagnosis. FD patients have increased oxidative stress (OS), critical for the induction of CV-renal remodeling. We investigated the effects of an adjuvant antioxidant treatment to ERT on OS and the possible advantages for related complications. OS was evaluated in 10 patients with FD before ERT, after 12 months of ERT, and after 6 months of adjuvant green tea (GT) to ERT by the following experiments: expression of p22phox; phosphorylation state of MYPT-1 and ERK 1/2 (by western blotting); and quantification of malondialdehyde (MDA) and heme oxygenase (HO)-1 levels (by ELISA). p22 phox and MYPT-1 phosphorylation decreased after ERT and significantly further decreased after GT. ERK 1/2 phosphorylation and MDA levels remained unchanged after ERT, but significantly decreased after GT. HO-1 significantly increased after ERT and further increased after GT. This study provides preliminary data highlighting the antioxidant effect exerted by ERT itself, further amplified by the adjuvant antioxidant treatment with GT. The results of this study provide evidence of the positive effect of early additive antioxidant treatment to reduce OS and prevent/alleviate cardio and cerebrovascular-renal complications related to OS.

Effects of Tolvaptan on Oxidative Stress in ADPKD: A Molecular Biological Approach.

Autosomal dominant polycystic disease (ADPKD) is the most frequent monogenic kidney disease. It causes progressive renal failure, endothelial dysfunction, and hypertension, all of which are strictly linked to oxidative stress (OxSt). Treatment with tolvaptan is known to slow the renal deterioration rate, but not all the molecular mechanisms involved in this effect are well-established. We evaluated the OxSt state in untreated ADPKD patients compared to that in tolvaptan-treated ADPKD patients and healthy subjects. OxSt was assessed in nine patients for each group in terms of mononuclear cell p22phox protein expression, NADPH oxidase key subunit, MYPT-1 phosphorylation state, marker of Rho kinase activity (Western blot) and heme oxygenase (HO)-1, induced and protective against OxSt (ELISA). p22phox protein expression was higher in untreated ADPKD patients compared to treated patients and controls: 1.42 ± 0.11 vs. 0.86 ± 0.15 d.u., p = 0.015, vs. 0.53 ± 0.11 d.u., p < 0.001, respectively. The same was observed for phosphorylated MYPT-1: 0.96 ± 0.28 vs. 0.68 ± 0.09 d.u., p = 0.013 and vs. 0.47 ± 0.13 d.u., p < 0.001, respectively, while the HO-1 expression of untreated patients was significantly lower compared to that of treated patients and controls: 5.33 ± 3.34 vs. 2.08 ± 0.79 ng/mL, p = 0.012, vs. 1.97 ± 1.22 ng/mL, p = 0.012, respectively. Tolvaptan-treated ADPKD patients have reduced OxSt levels compared to untreated patients. This effect may contribute to the slowing of renal function loss observed with tolvaptan treatment.

The Pivotal Role of Oxidative Stress in the Pathophysiology of Cardiovascular-Renal Remodeling in Kidney Disease.

The excessive activation of the renin-angiotensin system in kidney disease leads to alteration of intracellular pathways which concur altogether to the induction of cardiovascular and renal remodeling, exposing these patients since the very beginning of the renal injury to chronic kidney disease and progression to end stage renal disease, a very harmful and life threatening clinical condition. Oxidative stress plays a pivotal role in the pathophysiology of renal injury and cardiovascular-renal remodeling, the long-term consequence of its effect. This review will examine the role of oxidative stress in the most significant pathways involved in cardiovascular and renal remodeling with a focus on the detrimental effects of oxidative stress-mediated renal abnormalities on the progression of the disease and of its complications. Food for thoughts on possible therapeutic target are proposed on the basis of experimental evidences.