Effect of flaxseed on systemic inflammation and oxidative stress in diabetic rats with or without chronic kidney disease

Abstract

Background: Diabetes mellitus (DM) and chronic kidney disease (CKD) are common causes of morbidity and mortality. Flaxseed contains several bioactive compounds that have been shown to possess anti-inflammatory and antioxidative properties. The aim of the present study was to investigate the possible effect of flaxseed in diabetic rats with adenine-induced CKD.

Methods: Male Wister rats (n = 48) were randomly divided into seven equal groups and treated for 33 consecutive days as follows: G1: control. G2 adenine, G3: streptozotocin (STZ), G4: flaxseed, G5: adenine+flaxseed, G6: STZ+flaxseed, G7: adenine+STZ+flaxseed). DM or CKD were experimentally induced by a single intraperitoneal injection of streptozotocin (STZ) or by adenine via oral gavage, respectively.

Results: Rats fed adenine alone exhibited several changes including decreased body weight, increased food and water intake and urine output, increased urinary albumin/creatinine ratio. They also showed an increase in plasma urea and, creatinine, indoxyl sulfate, neutrophil gelatinase-associated lipocalin and cystatin C, and a decrease in renalase activity. These were associated with significant changes in inflammatory and oxidative biomarkers, e.g., increase in 8-isoprostane, 8 -hydroxy -2-deoxy guanosine and decrease in antioxidant enzymes, as well as increase in interleukins 1β and 6, and NF-κB, and a decrease in interlukin-10. Histopathologically, there was increased tubular necrosis and fibrosis. Concomitant administration of adenine and STZ further worsened the renal damage induced by adenine alone. Flaxseed significantly ameliorated the changes caused by adenine and STZ, given either singly or in combination.

Conclusion: These findings suggest that flaxseed is a potential therapeutic agent in attenuating the progression of CKD in diabetes.

Fig 1. Effect of flaxseed treatment (Fx, 15% w/w) on the renal concentrations of total antioxidant capacity (TAC), superoxide dismutase (SOD), catalase, 8-hydroxy-2’-deoxyguanosine (8-OHdG) and 8-isoprostane in control (Con) rats, and rats administered adenine (Ade, 150 mg/Kg/day), streptozotocin (Stz, 55 mg/Kg) or a combination of these.

Each vertical column with bar represents the mean ± SEM (n = 6). Differences between the groups were assessed by one-way analysis of variance (ANOVA) followed by Bonferroni’s multiple comparison test, where P < 0.05. ^adenotes significance of different groups vs. control group. ^bdenotes significance of different adenine treated groups vs. adenine alone group. ^cdenotes significance of different streptozotocin groups vs. streptozotocin alone group. ^ddenotes significance of the adenine + streptozotocin + flaxseed treated group vs. adenine + streptozotocin group.

Fig 2. Effect of flaxseed treatment (Fx, 15% w/w) on the renal concentrations of interleukin-1β (IL-1β), interleukin-6 (IL-6), interleukin-10 (IL-10) and nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) in control (Con) rats, and rats administered adenine (Ade, 150 mg/Kg/day), streptozotocin (Stz, 55 mg/Kg) or a combination of these.

Each vertical column with bar represents the mean ± SEM (n = 6). Differences between the groups were assessed by one-way analysis of variance (ANOVA) followed by Bonferroni’s multiple comparison test, where P < 0.05. ^adenotes significance of different groups vs. control group. ^bdenotes significance of different adenine treated groups vs. adenine alone group. ^cdenotes significance of different streptozotocin groups vs. streptozotocin alone group. ^ddenotes significance of the adenine + streptozotocin + flaxseed treated group vs. adenine + streptozotocin group.

Fig 3

Photomicrograph of renal tissues (Bar = 100μm, H&E stain): (A; control group) showing normal renal tissue with intact glomeruli and renal tubules (Score 0); (B; adenine group) showing marked renal tubular necrosis with pyknotic nuclei (arrowheads), cystic dilatation of multiple renal tubules (asterisks), marked basophilia, and dilatation of bowman’s capsule (arrow) (Score 4); (C; streptozotocin group) showing moderate basophilia with cystic dilation of few renal tubules (asterisk) and focal aggregates of mononuclear cells (arrowhead) (Score 2); (D; adenine + streptozotocin group) showing marked basophilia, renal tubular necrosis (arrowheads), cystic dilatation of multiple renal tubules (asterisks), and cellular casts in multiple tubules (arrow) (Score 4); (E; flaxseed group) showing histologically normal renal tubules with the exception of few dilated tubules (asterisk) (Score 1); (F; adenine + flaxseed group) showing tubular basophilia, tubular dilatations (asterisks) and cellular casts (arrow) (Score 3); (G; streptozotocin + flaxseed group) showing normal histological structures of the majority of the renal tubules with intact glomeruli (Score 1); (H; adenine + streptozotocin + flaxseed group) showing normal histological structures of the renal tubules with intact glomeruli (Score 0).

Fig 4

Photomicrograph of renal tissues (Bar = 100μm, A-G; Picro-Sirius red); renal tissues of groups A-H (A: control, B: adenine, C: streptozotocin, D: adenine + streptozotocin, E: flaxseed, F: adenine + flaxseed, G: streptozotocin + flaxseed, H: adenine + streptozotocin + flaxseed) showing the distribution of Sirius Red-stained fibrotic areas fibers (arrowheads) and yellow non-collagen structures.

Fig 5

Photomicrograph of renal tissues (Bar = 100μm, A-G; Periodic Acid Schiff (PAS)); renal tissues of groups A-H (A: control, B: adenine, C: streptozotocin, D: adenine + streptozotocin, E: flaxseed, F: adenine + flaxseed, G: streptozotocin + flaxseed, H: adenine + streptozotocin + flaxseed), showing tubular atrophy represented by a thickened tubular basement membrane (arrowheads) stained positive (magenta red) for PAS and loss of tubular brush borders (arrows).