Nitric oxide synthase inhibition causes acute increases in glomerular permeability in vivo, dependent upon reactive oxygen species

Arachidonic acid metabolism in health and disease

Arachidonic acid (AA), an n-6 essential fatty acid, is a major component of mammalian cells and can be released by phospholipase A2. Accumulating evidence indicates that AA plays essential biochemical roles, as it is the direct precursor of bioactive lipid metabolites of eicosanoids such as prostaglandins, leukotrienes, and epoxyeicosatrienoic acid obtained from three distinct enzymatic metabolic pathways: the cyclooxygenase pathway, lipoxygenase pathway, and cytochrome P450 pathway. AA metabolism is involved not only in cell differentiation, tissue development, and organ function but also in the progression of diseases, such as hepatic fibrosis, neurodegeneration, obesity, diabetes, and cancers. These eicosanoids are generally considered proinflammatory molecules, as they can trigger oxidative stress and stimulate the immune response. Therefore, interventions in AA metabolic pathways are effective ways to manage inflammatory-related diseases in the clinic. Currently, inhibitors targeting enzymes related to AA metabolic pathways are an important area of drug discovery. Moreover, many advances have also been made in clinical studies of AA metabolic inhibitors in combination with chemotherapy and immunotherapy. Herein, we review the discovery of AA and focus on AA metabolism in relation to health and diseases. Furthermore, inhibitors targeting AA metabolism are summarized, and potential clinical applications are discussed.

Nitric-Oxide-Mediated Signaling in Podocyte Pathophysiology

Nitric oxide (NO) is a potent signaling molecule involved in many physiological and pathophysiological processes in the kidney. NO plays a complex role in glomerular ultrafiltration, vasodilation, and inflammation. Changes in NO bioavailability in pathophysiological conditions such as hypertension or diabetes may lead to podocyte damage, proteinuria, and rapid development of chronic kidney disease (CKD). Despite the extensive data highlighting essential functions of NO in health and pathology, related signaling in glomerular cells, particularly podocytes, is understudied. Several reports indicate that NO bioavailability in glomerular cells is decreased during the development of renal pathology, while restoring NO level can be beneficial for glomerular function. At the same time, the compromised activity of nitric oxide synthase (NOS) may provoke the formation of peroxynitrite and has been linked to autoimmune diseases such as systemic lupus erythematosus. It is known that the changes in the distribution of NO sources due to shifts in NOS subunits expression or modifications of NADPH oxidases activity may be linked to or promote the development of pathology. However, there is a lack of information about the detailed mechanisms describing the production and release of NO in the glomerular cells. The interaction of NO and other reactive oxygen species in podocytes and how NO-calcium crosstalk regulates glomerular cells’ function is still largely unknown. Here, we discuss recent reports describing signaling, synthesis, and known pathophysiological mechanisms mediated by the changes in NO homeostasis in the podocyte. The understanding and further investigation of these essential mechanisms in glomerular cells will facilitate the design of novel strategies to prevent or manage health conditions that cause glomerular and kidney damage.

Brief Early Life Angiotensin Converting Enzyme Inhibition Offers Reno-Protection in Sheep with a Solitary Functioning Kidney at 8 Months of Age

Background: Children born with a solitary functioning kidney (SFK) are predisposed to develop hypertension and kidney injury. Glomerular hyperfiltration and hypertrophy contribute to the pathophysiology of kidney injury. Angiotensin converting enzyme inhibitors (ACEi) can mitigate hyperfiltration and may be therapeutically beneficial in reducing progression of kidney injury in SFK. Methods: SFK was induced in male sheep fetuses at 100 days gestation (term=150 day). Between 4-8 weeks of age, SFK lambs received enalapril (SFK+ACEi; 0.5mg/kg/day, once daily, orally) or vehicle (SFK). At 8 months we examined whether SFK+ACEi reduced elevation in blood pressure (BP) and improved basal kidney function, renal functional reserve (RFR; glomerular filtration rate (GFR) response to combined amino acid and dopamine infusion), GFR response to nitric oxide synthase (NOS) inhibition and basal nitric oxide (NO) bioavailability (basal urinary total nitrate+nitrite (NOx)). Results: SFK+ACEi prevented albuminuria, resulted in lower basal GFR (16%), higher renal blood flow (~22%), and lower filtration fraction ( 35%), but similar BP compared to ~ vehicle-treated SFK sheep. Together with greater recruitment of RFR (~14%) in SFK+ACEi animals than SFK, this indicates reduction in glomerular hyperfiltration-mediated kidney dysfunction. During NOS inhibition, the decrease in GFR ( 14%) was greater among SFK+ACEi than among SFK animals. Increased ( 85%) basal urinary total NOx in SFK+ACEi animals compared to SFK indicates elevated NO bioavailability likely contributing to improvements in kidney function and prevention of albuminuria. Conclusions: Brief and early ACEi in SFK is associated with reduced glomerular hyperfiltration-mediated kidney disease up to 8 months of age in a sheep model.

Targeted delivery of celastrol to glomerular endothelium and podocytes for chronic kidney disease treatment

The etiology of chronic kidney disease (CKD) is complex and diverse, which could be briefly categorized to glomerular- or tubular-originated. However, the final outcomes of CKD are mainly glomerular sclerosis, endothelial dysfunction and injury, and chronic inflammation. Thus, targeted delivery of drugs to the glomeruli in order to ameliorate glomerular endothelial damage may help alleviate CKD and help enrich our knowledge. The herb tripterygium wilfordii shows therapeutic effect on kidney disease, and celastrol (CLT) is one of its active ingredients but with strong toxicity. Therefore, based on the unique structure and pathological characteristics of the glomerulus, we designed a targeted delivery system named peptides coupled CLT-phospholipid lipid nanoparticles (PC-PLNs) to efficiently deliver CLT to damaged endothelial cells and podocytes in the glomerulus for CKD treatment and research. PC-PLNs could effectively inhibit inflammation, reduce endothelial damage, alleviate CKD severity, and reduce the toxicity of CLT. We also studied the mechanism of CLT in the treatment of nephropathy and found that CLT can increase the level of NO by increasing eNOS while inhibiting the expression of VCAM-1, thus provides an anti-inflammatory effect. Therefore, our study not only offered an efficient CKD drug formulation for further development, but also provided new medical knowledge about CKD.

ELECTRONIC SUPPLEMENTARY MATERIAL

Supplementary material (attached with all the supporting tables and figures mentioned in this work) is available in the online version of this article at 10.1007/s12274-021-3894-x.

Clemizole and La3+ salts ameliorate angiotensin II-induced glomerular hyperpermeability in vivo

Angiotensin II (Ang II) induces marked, dynamic increases in the permeability of the glomerular filtration barrier (GFB) in rats. After binding to its receptor, Ang II elicits Ca²⁺ influx into cells, mediated by TRPC5 and TRPC6 (transient receptor potential canonical type 5 and 6). Clemizole and La³⁺ salts have been shown to block TRPC channels in vitro, and we therefore tested their potential effect on Ang II‐induced glomerular hyperpermeability. Anesthetized male Sprague‐Dawley rats were infused with Ang II (80 ng kg^–1 min^–1) alone, or together with clemizole or low‐dose La³⁺ (activates TRPC5, blocks TRPC6) or high‐dose La³⁺ (blocks both TRPC5 and TRPC6). Plasma and urine samples were taken during baseline and at 5 min after the start of the infusions and analyzed by high‐performance size‐exclusion chromatography for determination of glomerular sieving coefficients for Ficoll 10–80 Å (1–8 nm). Ang II infusion evoked glomerular hyperpermeability to large Ficolls (50–80 Å), which was ameliorated by clemizole, having no significant effect on glomerular filtration rate (GFR) or Ang II‐mediated increase in mean arterial pressure (ΔMAP). In contrast, high‐ and low‐dose La³⁺ significantly lowered ΔMAP and reduced Ang II‐induced hyperpermeability. Combined, clemizole and low‐dose La³⁺ were less effective at ameliorating Ang II‐induced glomerular hyperpermeability than low‐dose La³⁺ alone. In conclusion, our data show that both clemizole and La3+ are effective against Ang II‐induced glomerular hyperpermeability, with differential effects on blood pressure. Further research using more specific blockers of TRPC5 and TRPC6 should be performed to reveal the underlying mechanisms.

Effects of the Soluble Guanylate Cyclase Stimulator Praliciguat in Diabetic Kidney Disease: A Randomized Placebo-Controlled Clinical Trial

BACKGROUND AND OBJECTIVES

Impaired nitric oxide signaling through soluble guanylate cyclase has been implicated in the pathophysiology of diabetic kidney disease. Praliciguat, a soluble guanylate cyclase stimulator that amplifies nitric oxide signaling, inhibited kidney inflammation and fibrosis in animal models.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

In a phase 2 trial, 156 adults with type 2 diabetes, eGFR 30-75 ml/min per 1.73 m², and urine albumin-creatinine ratio 200-5000 mg/g treated with renin-angiotensin system inhibitors were randomly allocated 1:1:1 to placebo, 20 mg praliciguat, or 40 mg praliciguat daily for 12 weeks. The primary efficacy and safety outcomes were change from baseline to weeks 8 and 12 in urine albumin-creatinine ratio and treatment-emergent adverse events, respectively. Other outcomes assessed were 24-hour ambulatory BP and metabolic parameters.

RESULTS

Of 156 participants randomized, 140 (90%) completed the study. The primary efficacy analysis demonstrated a mean change from baseline in urine albumin-creatinine ratio of -28% (90% confidence interval, -36 to -18) in the pooled praliciguat group and -15% (-28 to 0.4) in the placebo group (difference -15%; -31 to 4; P=0.17). Between-group decreases from baseline to week 12 for praliciguat versus placebo were seen in mean 24-hour systolic BP (-4 mm Hg; -8 to -1), hemoglobin A1c (-0.3%; -0.5 to -0.03), and serum cholesterol (-10 mg/dl; -19 to -1). The incidence of treatment-emergent adverse events was similar in the pooled praliciguat and placebo groups (42% and 44%, respectively). Serious adverse events, events leading to study drug discontinuation, and events potentially related to BP lowering were reported at higher frequency in the 40-mg group but were similar in 20-mg and placebo groups.

CONCLUSIONS

Praliciguat treatment for 12 weeks did not significantly reduce albuminuria compared with placebo in the primary efficacy analysis. Nonetheless, the observed changes in urine albumin-creatinine ratio, BP, and metabolic variables may support further investigation of praliciguat in diabetic kidney disease.

CLINICAL TRIAL REGISTRY NAME AND REGISTRATION NUMBER

A Study to Evaluate the Soluble Guanylate Cyclase (sGC) Stimulator IW-1973 in Diabetic Nephropathy/Diabetic Kidney Disease as Measured by Albuminuria, NCT03217591.

Riociguat ameliorates kidney injury and fibrosis in an animal model

Chronic kidney disease (CKD) is one of the greatest health burdens with an increasing global prevalence. Renal fibrosis (RF) is the hallmark of all forms of CKD which shows a strong positive correlation with severity of the disease. However, there are no therapeutic options available for treatment of RF. In the present study, we used an animal model based on unilateral ureteral obstruction (UUO), for renal injury and fibrosis. The UUO animals were treated with soluble guanylyl cyclase (sGC) stimulator, riociguat (RIO) (1, 3 and 10 mg/kg) to investigate its possible renoprotective effects. Kidneys of animals treated with RIO were found to show less abnormalities as compared to UUO control. Further, the levels of proinflammatory cytokines were reduced in RIO treated group. Furthermore, administration of RIO reduced expression of collagen-1, TGF-β, CTGF, α-SMA, vimentin along with transcription factors including Snail and Slug. The results of the present study provided strong evidence to support the antifibrotic activity of RIO.

The Impact of the Nitric Oxide (NO)/Soluble Guanylyl Cyclase (sGC) Signaling Cascade on Kidney Health and Disease: A Preclinical Perspective

Chronic Kidney Disease (CKD) is a highly prevalent disease with a substantial medical need for new and more efficacious treatments. The Nitric Oxide (NO), soluble guanylyl cyclase (sGC), cyclic guanosine monophosphate (cGMP) signaling cascade regulates various kidney functions. cGMP directly influences renal blood flow, renin secretion, glomerular function, and tubular exchange processes. Downregulation of NO/sGC/cGMP signaling results in severe kidney pathologies such as CKD. Therefore, treatment strategies aiming to maintain or increase cGMP might have beneficial effects for the treatment of progressive kidney diseases. Within this article, we review the NO/sGC/cGMP signaling cascade and its major pharmacological intervention sites. We specifically focus on the currently known effects of cGMP on kidney function parameters. Finally, we summarize the preclinical evidence for kidney protective effects of NO-donors, PDE inhibitors, sGC stimulators, and sGC activators.

Glomerular hyperpermeability after acute unilateral ureteral obstruction: effects of Tempol, NOS, RhoA, and Rac-1 inhibition

It is well known that proteinuria following urinary tract obstruction is mainly of a tubular nature. However, it is unknown whether there are also changes in glomerular permeability. In this study, we compared glomerular sieving coefficients (θ) of polydisperse fluorescein isothiocyanate (FITC)-Ficoll 70/400 following a 120- or 180-min unilateral ureteral obstruction (UUO) in anesthetized Sprague-Dawley rats. Samples were collected from the obstructed kidney at 5, 15, and 30 min postrelease and analyzed by means of high-pressure size-exclusion chromatography. After 120-min UUO, mean θ for Ficoll_70Å was increased ( P < 0.01) from 2.2 ± 0.5 × 10^-5 (baseline) to 10.6 ± 10 × 10^-5 15 min postrelease (highest value). After 180-min UUO, mean θ for Ficoll_70Å was further increased ( P < 0.001) from 1.4 ± 0.5 × 10^-5 (baseline) to 40 ± 10 × 10^-5 at 5 min postrelease (highest value). Administration of a reactive oxygen species (ROS) scavenger (Tempol; 1 mg·kg^-1·min^-1) partly abrogated the permeability effects following 120-min UUO but not after 180 min. Moreover, administration of the RhoA kinase inhibitor Y-27632, the nitric oxide synthase inhibitor N^G-nitro-l-arginine methyl ester, or Rac-1 inhibition did not ameliorate glomerular hyperpermeability following 180-min UUO. We show, for the first time, that acute UUO results in marked elevations in glomerular permeability. In addition, our data suggest a time-dependent pathophysiology of UUO-induced hyperpermeability, where reactive oxygen species generation may play an important role in the early stages.

Nitric oxide production by glomerular podocytes

Nitric Oxide (NO), a potent vasodilator and vital signaling molecule, has been shown to contribute to the regulation of glomerular ultrafiltration. However, whether changes in NO occur in podocytes during the pathogenesis of salt-sensitive hypertension has not yet been thoroughly examined. We showed here that podocytes produce NO, and further hypothesized that hypertensive animals would exhibit reduced NO production in these cells in response to various paracrine factors, which might contribute to the damage of glomeruli filtration barrier and development of proteinuria. To test this, we isolated glomeruli from the kidneys of Dahl salt-sensitive (SS) rats fed a low salt (LS; 0.4% NaCl) or high salt (HS; 4% NaCl, 3 weeks) diets and loaded podocytes with either a combination of NO and Ca²⁺ fluorophores (DAF-FM and Fura Red, respectively) or DAF-FM alone. Changes in fluorescence were observed with confocal microscopy in response to adenosine triphosphate (ATP), angiotensin II (Ang II), and hydrogen peroxide (H₂O₂). Application of Ang II resulted in activation of both NO and intracellular calcium ([Ca²⁺]_i) transients. In contrast, ATP promoted [Ca²⁺]_i transients, but did not have any effects on NO production. SS rats fed a HS diet for 3 weeks demonstrated impaired NO production: the response to Ang II or H₂O₂ in podocytes of glomeruli isolated from SS rats fed a HS diet was significantly reduced compared to rats fed a LS diet. Therefore, glomerular podocytes from hypertensive rats showed a diminished NO release in response to Ang II or oxidative stress, suggesting that podocytic NO signaling is dysfunctional in this condition and likely contributes to the development of kidney injury.