Role of Dietary Antioxidant Agents in Chronic Kidney Disease

Chronic kidney disease (CKD) is defined as the atrophy of the kidney or progressive decline of renal function mainly caused by chronic diseases such as diabetes mellitus and hypertension. CKD affects more than 10% of the world\u27s population. Moreover, there is no single treatment to improve kidney function in CKD patients. Consequently, this condition is considered a worldwide public health problem. The development of novel CKD therapies is highly needed because current treatment methods are ineffective. Since oxidative stress plays a critical role in CKD, the study of the effect of antioxidants in this pathology is highly important. Dietary antioxidant agents have shown protective effects in CKD. Hence, they may be key for the development of feasible therapies. The aim of this chapter is to provide recent information about the therapeutic role of dietary antioxidants in experimental models of CKD and clinical trials, as well as to describe the mechanisms through which antioxidants exert nephroprotection. The dietary antioxidants revised in this chapter are curcumin, sulforaphane, resveratrol, quercetin, proanthocyanidins, flavan‐3‐ols, soy protein, red propolis, and Mediterranean diet

Impaired endocytosis in proximal tubule from subchronic exposure to cadmium involves angiotensin II type 1 and cubilin receptors

BACKGROUND: Chronic exposure to low cadmium (Cd) levels produces urinary excretion of low molecular weight proteins, which is considered the critical effect of Cd exposure. However, the mechanisms involved in Cd-induced proteinuria are not entirely clear. Therefore, the present study was designed to evaluate the possible role of megalin and cubilin (important endocytic receptors in proximal tubule cells) and angiotensin II type 1 (AT1) receptor on Cd-induced microalbuminuria. METHODS: Four groups of female Wistar rats were studied. Control (CT) group, vehicle-treated rats; LOS group, rats treated with losartan (an AT1 antagonist) from weeks 5 to 8 (10 mg/kg/day by gavage); Cd group, rats subchronically exposed to Cd (3 mg/kg/day by gavage) during 8 weeks, and Cd + LOS group, rats treated with Cd for 8 weeks and LOS from weeks 5–8. Kidney Cd content, glomerular function (evaluated by creatinine clearance and plasma creatinine), kidney injury and tubular function (evaluated by Kim-1 expression, urinary excretion of N-acetyl-β-D-glucosaminidase (NAG) and glucose, and microalbuminuria), oxidative stress (measured by lipid peroxidation and NAD(P)H oxidase activity), mRNA levels of megalin, expressions of megalin and cubilin (by confocal microscopy) and AT1 receptor (by Western blot), were measured in the different experimental groups. Data were analyzed by one-way ANOVA or Kruskal-Wallis test using GraphPad Prism 5 software (Version 5.00). P < 0.05 was considered statistically significant. RESULTS: Administration of Cd (Cd and Cd + LOS groups) increased renal Cd content. LOS-treatment decreased Cd-induced microalbuminuria without changes in: plasma creatinine, creatinine clearance, urinary NAG and glucose, oxidative stress, mRNA levels of megalin and cubilin, neither protein expression of megalin nor AT1 receptor, in the different experimental groups studied. However, Cd exposure did induce the expression of the tubular injury marker Kim-1 and decreased cubilin protein levels in proximal tubule cells whereas LOS-treatment restored cubilin levels and suppressed Kim-1 expression. CONCLUSION: LOS treatment decreased microalbuminuria induced by Cd apparently through a cubilin receptor-dependent mechanism but independent of megalin

Renoprotective effect of the antioxidant curcumin: Recent findings

For years, there have been studies based on the use of natural compounds plant-derived as potential therapeutic agents for various diseases in humans. Curcumin is a phenolic compound extracted from Curcuma longa rhizome commonly used in Asia as a spice, pigment and additive. In traditional medicine of India and China, curcumin is considered as a therapeutic agent used in several foods. Numerous studies have shown that curcumin has broad biological functions particularly antioxidant and antiinflammatory. In fact, it has been established that curcumin is a bifunctional antioxidant; it exerts antioxidant activity in a direct and an indirect way by scavenging reactive oxygen species and inducing an antioxidant response, respectively. The renoprotective effect of curcumin has been evaluated in several experimental models including diabetic nephropathy, chronic renal failure, ischemia and reperfusion and nephrotoxicity induced by compounds such as gentamicin, adriamycin, chloroquine, iron nitrilotriacetate, sodium fluoride, hexavalent chromium and cisplatin. It has been shown recently in a model of chronic renal failure that curcumin exerts a therapeutic effect; in fact it reverts not only systemic alterations but also glomerular hemodynamic changes. Another recent finding shows that the renoprotective effect of curcumin is associated to preservation of function and redox balance of mitochondria. Taking together, these studies attribute the protective effect of curcumin in the kidney to the induction of the master regulator of antioxidant response nuclear factor erythroid-derived 2 (Nrf2), inhibition of mitochondrial dysfunction, attenuation of inflammatory response, preservation of antioxidant enzymes and prevention of oxidative stress. The information presented in this paper identifies curcumin as a promising renoprotective molecule against renal injury

Data on nephroprotective effect of all-trans retinoic acid in early diabetic nephropathy

Data showed in this report are related to the research article entitled “All-trans retinoic acid ameliorates inflammatory response mediated by TLR4/NF-кB during the initiation of diabetic nephropathy” by Sierra-Mondragon et al. (2018) [1]. Diabetic nephropathy (DN) has become the main cause of renal failure. Inflammatory molecules such as cytokines, chemokines and growth factors play a key role in DN-induced renal injury Pichler et al. (2016) [2]. Results illustrate the effect of all-trans retinoic acid (ATRA), an active metabolite of vitamin A, on the renal alterations related to diabetes, among them glomerular and tubular dysfunction, and its effect on renal inflammation in different nephron segments: glomeruli, proximal and distal tubules in an initial stage of DN. Data were obtained by physical-biochemical measurements and Western blot assays performed on isolated glomeruli, proximal and distal tubules from rat kidneys. Keywords: Diabetic nephropathy, Inflammation, All-trans retinoic acid, Cytokine

Aldosterone signaling regulates the over-expression of claudin-4 and -8 at the distal nephron from type 1 diabetic rats

<div><p>Hyperglycemia in diabetes alters tight junction (TJ) proteins in the kidney. We evaluated the participation of aldosterone (ALD), and the effect of spironolactone (SPL), a mineralocorticoid receptor antagonist, on the expressions of claudin-2, -4, -5 and -8, and occludin in glomeruli, proximal and distal tubules isolated from diabetic rats. Type 1 diabetes was induced in female Wistar rats by a single tail vein injection of streptozotocin (STZ), and SPL was administrated daily by gavage, from days 3–21. Twenty-one days after STZ injection the rats were sacrificed. In diabetic rats, the serum ALD levels were increased, and SPL-treatment did not have effect on these levels or in hyperglycemia, however, proteinuria decreased in SPL-treated diabetic rats. Glomerular damage, evaluated by nephrin and Wilm’s tumor 1 (WT1) protein expressions, and proximal tubular damage, evaluated by kidney injury molecule 1 (Kim-1) and heat shock protein 72 kDa (Hsp72) expressions, were ameliorated by SPL. Also, SPL prevented decrement in claudin-5 in glomeruli, and claudin-2 and occludin in proximal tubules by decreasing oxidative stress, evaluated by superoxide anion (O₂^●―) production, and oxidative stress markers. In distal tubules, SPL ameliorated increase in mRNA, protein expression, and phosphorylation in threonine residues of claudin-4 and -8, through a serum and glucocorticoid-induced kinase 1 (SGK1), and with-no-lysine kinase 4 (WNK4) signaling pathway. In conclusion, this is the first study that demonstrates that ALD modulates the expression of renal TJ proteins in diabetes, and that the blockade of its actions with SPL, may be a promising therapeutic strategy to prevent alterations of TJ proteins in diabetic nephropathy.</p></div

SPL treatment ameliorated diabetes-induced increased expression of SGK1, WNK4 and co-IP of WNK4 with SGK1.

<p>SGK1 expression was evaluated by IB analysis of isolated DT. As shown in panel A, DBT induced SGK1 expression. Densitometric analysis is shown in panel B (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0177362#pone.0177362.s007" target="_blank">S7 Fig</a>). Diabetic condition also induced co-IP of WNK4 with SGK1, and serine, but not threonine phosphorylation of WNK4 (C). SPL treatment prevented these changes. GAPDH was used as loading control in isolated DT and input extracts. As shown in panel C, no signal was found under nonspecific conditions of IP performed with an unrelated antibody. Data are mean±SEM from 3 rats per group. **p<0.01.</p

Diabetic condition induces co-localization of WNK4 with cldn-4 and -8 in the TJ of DT.

<p>Localization of WNK4 and cldn-4 and -8 was evaluated by IF in the four experimental groups. As shown, diabetes induced co-localization of WNK4 (green label) with cldn-4 (panel A, red label) and, with cldn-8 (panel B, red label) in cell borders of DT. Nuclei were marked DAPI blue label). An approach of WNK4 with cldn-4 and -8 is shown under diabetic condition, showing that WNK4 localizes in cell borders and cytoplasm. SPL treatment decreased co-localization of WNK4 with cldn-4 and -8 induced by diabetes. Similar results were found between CTL and SPL groups. Images are representative of three different experiments performed in the four experimental groups. Bar = 20 μm.</p

SPL decreases diabetes-induced oxidative stress in GL and PT.

<p>To evaluate oxidative stress, superoxide anion (O₂^●―) production, lipid peroxidation, protein carbonylation and reduced glutathione (GSH) content were measured in isolated GL and PT. SPL treatment prevents diabetes-induced increment in O₂^●― production (A) by using nicotinamide adenine dinucleotide phosphate (NADPH) as substrate and, diphenyleneiodonium (DPI) as inhibitor, lipid peroxidation (B) and protein carbonylation (C) and decreased GSH content (D) in GL (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0177362#pone.0177362.s003" target="_blank">S3 Fig</a>). Also, SPL diminished diabetes-induced increment of O₂^●― production (E), lipid peroxidation (F) and protein carbonylation (G) and decreased GSH content (H) in PT (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0177362#pone.0177362.s003" target="_blank">S3 Fig</a>). Similar results were found between CTL and SPL groups. Data are mean±SEM from 5–6 rats per group. *p<0.05; **p<0.01 and ***p<0.001.</p

SPL treatment decreases diabetes-induced co-immunoprecipitation (co-IP) of cldn-4 and -8.

<p>To evaluate direct interaction of cldn-4 and -8, co-IP analyzes from isolated DT from the four experimental groups were performed. As shown in panel A, cldn-4 co-immunoprecipitated with cldn-8; densitometric analysis (B) shows that diabetic condition increased their interaction and SPL treatment prevents this change (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0177362#pone.0177362.s005" target="_blank">S5 Fig</a>). Also, increased co-IP of cldn-8 with cldn-4 was found under diabetic condition and SPL decreased this interaction (C), densitometric analysis show that these changes were significant (D) (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0177362#pone.0177362.s005" target="_blank">S5 Fig</a>). As shown in panels A and C, no signal was found under nonspecific conditions of IP performed with an unrelated antibody. GAPDH was used in input extract as loading control. Data are mean±SEM from 3 rats per group. *p<0.05.</p

SPL treatment prevents diabetes-induced glomerular and tubular damage.

<p>(A) Schematic representation of the experimental strategy used in this study. Four groups of rats were studied: Control (CTL), Diabetic (DBT), DBT+SPL and SPL, respectively (for detail see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0177362#sec002" target="_blank">Material and methods</a>). (B) Purity of isolated glomerular and proximal tubular segments was evaluated by IB analysis of Wilm´s tumor 1 (WT1) and dipeptidylpeptidase (DppD) expressions, respectively. (C) IB analysis of nephrin and WT1 shows that SPL treatment prevents diabetes-induced glomerular damage; densitometric analysis of nephrin (D) and WT1 (E) are shown (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0177362#pone.0177362.s001" target="_blank">S1 Fig</a>). (F) IB analysis of kidney injury molecule 1 (Kim)-1 and heat shock protein of 72 KDa (Hsp72) show that SPL treatment decreases diabetes-induced proximal tubular damage, densitometric analysis of Kim-1 (G) and Hsp72 (H) are shown (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0177362#pone.0177362.s001" target="_blank">S1 Fig</a>). No changes were found in SPL group compared to CTL group. (I) IF analysis confirms that SPL treatment decreases diabetes-induced Kim-1 expression (green label) in PT labeled with DppD (red label). Nuclei were marked with 4', 6-diamidino- 2-phenylindole (DAPI, blue label). No significant changes were found between SPL and CTL groups. Glyceraldehyde 3-phosphate dehydrogenase (GAPDH) was used as loading control for IB. Data are mean±SEM from 3 rats per group. *p<0.05; **p<0.01 and ***p<0.001. Images are representative of three different experiments performed in the four experimental groups. Bar = 50 μm.</p