Reactive oxygen species impair Na+ transport and renal components of the renin-angiotensin-aldosterone system after paraquat poisoning.

Paraquat (1,1'-dimethyl-4,4'-bipyridyl dichloride) is an herbicide widely used worldwide and officially banned in Brazil in 2020. Kidney lesions frequently occur, leading to acute kidney injury (AKI) due to exacerbated reactive O2 species (ROS) production. However, the consequences of ROS exposure on ionic transport and the regulator local renin-angiotensin-aldosterone system (RAAS) still need to be elucidated at a molecular level. This study evaluated how ROS acutely influences Na+-transporting ATPases and the renal RAAS. Adult male Wistar rats received paraquat (20 mg/kg; ip). After 24 h, we observed body weight loss and elevation of urinary flow and serum creatinine. In the renal cortex, paraquat increased ROS levels, NADPH oxidase and (Na++K+)ATPase activities, angiotensin II-type 1 receptors, tumor necrosis factor-α (TNF-α), and interleukin-6. In the medulla, paraquat increased ROS levels and NADPH oxidase activity but inhibited (Na++K+)ATPase. Paraquat induced opposite effects on the ouabain-resistant Na+-ATPase in the cortex (decrease) and medulla (increase). These alterations, except for increased serum creatinine and renal levels of TNF-α and interleukin-6, were prevented by 4-hydroxy-2,2,6,6-tetramethylpiperidin-1-oxyl (tempol; 1 mmol/L in drinking water), a stable antioxidant. In summary, after paraquat poisoning, ROS production culminated with impaired medullary function, urinary fluid loss, and disruption of Na+-transporting ATPases and angiotensin II signaling.

Renal ischemia-reperfusion leads to hypertension and changes in proximal tubule Na+ transport and renin-angiotensin-aldosterone system: Role of NADPH oxidase.

Acute renal injury (AKI) is a risk factor for the development of hypertension, which involves oxidative stress, changes in Na+ handling, and the intrarenal renin-angiotensin-aldosterone system (RAAS) as underlying mechanisms. We investigated in rats whether renal ischemia-reperfusion (IR) leads to changes in the proximal tubule ATP-dependent Na+ transport and the intrarenal content of RAAS components, as well as the role of NADPH oxidase. Rats weighing 300-350 g were submitted to AKI by bilateral IR (n = 25). After IR injury, the animals were followed up for 4 weeks. One part (n = 7) received daily treatment with the NADPH oxidase inhibitor apocynin (100 mg/kg, drinking water), while another part (n = 9) received apocynin 24 h before and after IR. One group was submitted to sham surgery (n = 8). Four weeks after IR, the rats presented elevated systolic blood pressure, as well as increased lipid peroxidation, NADPH oxidase activity, (Na++K+)ATPase activity, and upregulation of type 1 angiotensin II receptor in the renal cortex. On the other hand, there was a decrease in Na+-ATPase activity and downregulation of the isoforms 1 and 2 of the angiotensin-converting enzyme, type 2 angiotensin II receptor, and of the α and ε isoforms of protein kinase C. Most of these alterations was prevented by both apocynin treatment protocols. Thus, we conclude that AKI-induced by IR may induce changes in proximal tubule ATPases and RAAS components compatible with renal Na+ retention and hypertension. These data also indicate that the NADPH oxidase represents a key factor in the origin of these alterations.

Maternal endotoxemia induces renal collagen deposition in adult offspring: Role of NADPH oxidase/TGF-ß1/MMP-2 signaling pathway.

Maternal endotoxemia has been shown to increase renal collagen deposition in the offspring. Renal fibrosis is a hallmark of progressive chronic kidney disease. It was investigated whether maternal reactive oxygen species (ROS) leads to renal fibrosis or exacerbates unilateral ureteral obstruction (UUO)-induced renal fibrosis in the offspring of dams treated with lipopolysaccharide (LPS). Furthermore, it was studied the role of matrix metalloproteinases (MMPs) in these changes. Adults Wistar rats were obtained from dams submitted to LPS administration through the third part of gestation. To evaluate the role of maternal ROS, part of the dams received α-tocopherol simultaneously with LPS. Part of the offspring in each group was submitted to UUO at adulthood when sub-groups were treated with NADPH oxidase inhibitor, apocynin. Maternal LPS administration increased proteinuria, systolic arterial pressure and renal collagen deposition in adult offspring. LPS offspring rats also presented higher MMP-2 activity in parallel to a decreased renal cortical TIMP-2 content. These changes were correlated to increased amounts of TGF-ß1 and NOX2. Maternal α-tocopherol treatment prevented collagen deposition and reduced arterial pressure in adult offspring. α-Tocopherol also inhibited maternal endotoxemia-induced changes in TGF-ß1/NOX2/MMP-2 signaling. UUO led to increased collagen deposition in the contralateral kidneys of LPS offspring, which was correlated to increased NADPH oxidase activity and prevented by NADPH oxidase inhibition. In summary, maternal endotoxemia led to alterations in the TGF-ß1/NOX2/MMP-2 signaling pathway in renal tissue concomitant with collagen deposition, therefore contributing to hypertension in adult offspring.

NO mediates the effect of the synthetic natriuretic peptide NPCdc on kidney and aorta in nephrectomised rats.

NPCdc is a synthetic natriuretic peptide that was originally derived from another peptide, the NP2_Casca, isolated from Crotalus durissus cascavella venom. These molecules share 70% structural homology with natriuretic peptides obtained from different species, including humans. NP2_Casca induces vasorelaxation and increases nitric oxide levels independently of natriuretic peptide receptors A and B. This study aimed to investigate whether NPCdc-induced hypotension in control rats and rats with a reduced kidney mass is associated with effects on the glomerular filtration rate, NADPH oxidase activity and components downstream of natriuretic peptide receptor C (NPR-C). Anaesthetized Wistar rats that were subjected to a sham operation and 5/6 nephrectomy (5/6Nx) were infused with saline (vehicle) or NPCdc (7.5 µg/kg/min) for 70 min. The NPCdc treatment decreased the mean arterial pressure and NADPH oxidase activity while simultaneously increasing the glomerular filtration rate, fractional Na+ excretion and nitric oxide level. After 70 min, the levels of p-AKT Ser-473, p-eNOS Ser-1177, p-nNOS Ser-1417 and p-iNOSTyr-151 were not affected. However, p-ERK1/2 Thr-202/Tyr-204 levels were altered. Thus, nitric oxide and components of NPR-C signalling mediate the effects of NPCdc. The results suggest a potential therapeutic application of this peptide for cardiorenal syndrome.