Changes in reduced glutathione, oxidized glutathione, and glutathione peroxidase in cats with naturally occurring chronic kidney disease

Supplementation of vitamin E as an addition to a commercial renal diet does not prolong survival of cats with chronic kidney disease

BACKGROUND

The aim of this double-blind, placebo-controlled study was to investigate the effect of vitamin E supplementation as an addition to a commercial renal diet on survival time of cats with different stages of chronic kidney disease (CKD). In addition, we were interested whether vitamin E supplementation affects selected oxidative stress and clinical parameters. Thirty-four cats with CKD and 38 healthy cats were included in the study. Cats with CKD were classified according to the IRIS Guidelines; seven in IRIS stage 1, 15 in IRIS stage 2, five in IRIS stage 3 and seven in IRIS stage 4. Cats with CKD were treated according to IRIS Guidelines. Cats with CKD were randomly assigned to receive vitamin E (100 IU/cat/day) or placebo (mineral oil) for 24 weeks in addition to standard therapy. Plasma malondialdehyde (MDA) and protein carbonyl (PC) concentrations, DNA damage of peripheral lymphocytes and plasma vitamin E concentrations were measured at baseline and four, eight, 16 and 24 weeks thereafter. Routine laboratory analyses and assessment of clinical signs were performed at each visit.

RESULTS

Vitamin E supplementation had no effect on the survival time and did not reduce the severity of clinical signs. Before vitamin E supplementation, no significant differences in vitamin E, MDA and PC concentrations were found between healthy and CKD cats. However, plasma MDA concentration was statistically significantly higher (p = 0.043) in cats with early CKD (IRIS stages 1 and 2) than in cats with advanced CKD (IRIS stages 3 and 4). Additionally, DNA damage was statistically significantly higher in healthy cats (p ≤ 0.001) than in CKD cats. Plasma vitamin E concentrations increased statistically significantly in the vitamin E group compared to the placebo group four (p = 0.013) and eight (p = 0.017) weeks after the start of vitamin E supplementation. During the study and after 24 weeks of vitamin E supplementation, plasma MDA and PC concentrations and DNA damage remained similar to pre-supplementation levels in both the placebo and vitamin E groups.

CONCLUSIONS

Vitamin E supplementation as an addition to standard therapy does not prolong survival in feline CKD.

Glycine supplementation can partially restore oxidative stress-associated glutathione deficiency in ageing cats

Intracellular levels of glutathione, the major mammalian antioxidant, are reported to decline with age in several species. To understand whether ageing affects circulating glutathione levels in cats, blood was sampled from two age groups, < 3 years and > 9 years. Further, to determine whether dietary supplementation with glutathione precursor glycine (GLY) affects glutathione concentrations in senior cats (> 8 years), a series of free GLY inclusion level dry diets were fed. Subsequently, a 16-week GLY feeding study was conducted in senior cats (> 7 years), measuring glutathione, and markers of oxidative stress. Whole blood and erythrocyte total, oxidised and reduced glutathione levels were significantly decreased in senior cats, compared with their younger counterparts (P ≤ 0·02). The inclusion level study identified 1·5 % free GLY for the subsequent dry diet feeding study. Significant increases in erythrocyte total and reduced glutathione were observed between senior cats fed supplemented and control diets at 4 weeks (P ≤ 0·03; maximum difference of 1·23 µM). Oxidative stress markers were also significantly different between groups at 8 (P = 0·004; difference of 0·68 nG/ml in 8-hydroxy-2'-deoxyguanosine) and 12 weeks (P ≤ 0·049; maximum difference of 0·62 nG/mG Cr in F2-isoprostane PGF2α). Senior cats have lower circulating glutathione levels compared with younger cats. Feeding senior cats a complete and balanced dry diet supplemented with 1·5 % free GLY for 12 weeks elevated initial erythrocyte glutathione and altered markers of oxidative stress. Dietary supplementation with free GLY provides a potential opportunity to restore age-associated reduction in glutathione in cats.

Decreased circulating transforming growth factor-beta (TGF-β) and kidney TGF-β immunoreactivity predict renal disease in cats with naturally occurring chronic kidney disease

OBJECTIVES

The aim of the present study was to compare the circulating transforming growth factor-beta (TGF-β) of clinically normal age-matched and naturally occurring chronic kidney disease (CKD) cats and to determine the correlation between the TGF-β expression and histopathological changes in cats with CKD.

METHODS

A total of 11 clinically normal age-matched and 27 cats with naturally occurring CKD were included in this study. Circulating TGF-β was quantified by immunoassays. Kaplan-Meier analysis was used to calculate the association between survival time and the concentration of circulating TGF-β. A general linear model was used to compare the circulating TGF-β between groups. Immunohistochemical analyses revealed TGF-β expression in renal tissues from cats with CKD that died during the study (n = 7) and in available archived renal tissue specimens taken at necropsy from cats that had previous CKD with renal lesions (n = 10). Correlations of the TGF-β expression and clinical parameters (n = 7) and histopathological changes (n = 17) were analysed using Spearman's rank correlation.

RESULTS

The median survival time of cats with a lower concentration of circulating TGF-β was shorter than that of cats with a higher concentration. The area under the curve of circulating TGF-β for predicting CKD was 0.781, indicating good differentiation. The study indicated a significant difference in circulating TGF-β concentrations between clinically normal cats and those with CKD and demonstrated that TGF-β expression is correlated with tubular atrophy.

CONCLUSIONS AND RELEVANCE

The study findings suggest that decreased serum TGF-β and tubular atrophy with TGF-β immunoreactivity may be significant in cats with CKD.

Immunohistochemical analysis of renal oxidative damage in senior and geriatric cats with chronic kidney disease

Oxidative stress is a well-known cause of chronic kidney disease (CKD). In this study, renal oxidative damage in azotaemic and non-azotaemic aged cats with naturally occurring CKD was investigated using immunohistochemistry for 8-hydroxy-2'-deoxyguanosine (8-OHdG) and 4-hydroxynonenal (4-HNE) as markers of oxidative tissue damage. Kidneys were obtained from aged (>10 years old) azotaemic (n = 13) and non-azotaemic (n = 7) cats. Immunoreactivity for 8-OHdG was found in the nuclei of glomeruli, proximal and distal tubules, loops of Henle and collecting ducts, whereas 4-HNE-positive signals were detected in the cytoplasm of distal nephrons in azotaemic and non-azotaemic cats. Quantitative analysis did not identify any significant differences between the azotaemic and non-azotaemic groups for any of the parameters examined. These results indicate that renal oxidative damage occurs in the kidneys of aged cats with CKD, regardless of whether they are azotaemic or non-azotaemic, emphasizing the importance of oxidative stress during early-stage CKD in senior and geriatric cats.

Indoxyl-Sulfate-Induced Redox Imbalance in Chronic Kidney Disease

The accumulation of the uremic toxin indoxyl sulfate (IS) induces target organ damage in chronic kidney disease (CKD) patients, and causes complications including cardiovascular diseases, renal osteodystrophy, muscle wasting, and anemia. IS stimulates reactive oxygen species (ROS) production in CKD, which impairs glomerular filtration by a direct cytotoxic effect on the mesangial cells. IS further reduces antioxidant capacity in renal proximal tubular cells and contributes to tubulointerstitial injury. IS-induced ROS formation triggers the switching of vascular smooth muscular cells to the osteoblastic phenotype, which induces cardiovascular risk. Low-turnover bone disease seen in early CKD relies on the inhibitory effects of IS on osteoblast viability and differentiation, and osteoblastic signaling via the parathyroid hormone. Excessive ROS and inflammatory cytokine releases caused by IS directly inhibit myocyte growth in muscle wasting via myokines’ effects. Moreover, IS triggers eryptosis via ROS-mediated oxidative stress, and elevates hepcidin levels in order to prevent iron flux in circulation in renal anemia. Thus, IS-induced oxidative stress underlies the mechanisms in CKD-related complications. This review summarizes the underlying mechanisms of how IS mediates oxidative stress in the pathogenesis of CKD’s complications. Furthermore, we also discuss the potential role of oral AST-120 in attenuating IS-mediated oxidative stress after gastrointestinal adsorption of the IS precursor indole.

Nutrient intake and influence on markers of oxidative stress in zoo-managed male snow leopards (Uncia uncia)

Oxidative stress (OS) results from the overproduction of reactive species. Nutrient intake can contribute positively or negatively to OS, and the lack of established nutrient requirements for most of the exotic species managed in zoos exacerbates the possibilities for nutrient imbalances that potentially could lead to reactive species production. The objective of this study was to evaluate the influence of nutrient intake and nutritional husbandry on markers of OS in male snow leopards (n = 14) maintained in U.S. facilities (n = 12). Diet samples and husbandry information were obtained and snow leopards were immobilized once for collection of blood. Samples were analyzed for chemical composition (diet and blood), antioxidant capacity (blood), and markers of OS (blood). Correlations between weekly nutrient intakes and markers of OS were analyzed by linear regression. Analyzed markers of OS included antioxidant enzymes (superoxide dismutase [SOD] and glutathione peroxidase [GPx]) and ferric reducing antioxidant potential that are protective against OS, and protein carbonyls, thiobarbituric acid reactive substances, and DNA/RNA damage that are indicative of oxidative damage. Weekly copper intake (10.1 to 80.2 mg) was negatively correlated with DNA/RNA damage (R² = 0.44; P = 0.01). Weekly sodium intake (4.4 to 12.7 g) was positively correlated with GPx activity (R² = 0.43; P = 0.04). More frequent feeding of whole prey (0.3 to 3 times/wk) was correlated with increased blood SOD activity (R² = 0.55; P < 0.01). In conclusion, greater dietary copper intake and more frequent feeding of whole prey may reduce OS in snow leopards. Dietary sodium intake and relationship with GPx activity should be further evaluated to determine benefit or detriment. No cause and effect can be inferred from our results, but our data suggest altering dietary form and nutrient concentrations may influence OS in snow leopards.

N-Acetylcysteine Attenuates the Development of Renal Fibrosis in Transgenic Mice with Dilated Cardiomyopathy

Mechanisms underlying the renal pathology in cardiorenal syndrome (CRS) type 2 remain elusive. We hypothesised that renal glutathione deficiency is central to the development of CRS type 2. Glutathione precursor, N-acetylcysteine (NAC;40 mg/kg/day; 8 weeks) or saline were administered to transgenic mice with dilated cardiomyopathy (DCM) and wild-type (WT) controls. Cardiac structure, function and glutathione levels were assessed at the end of this protocol. Renal fibrosis, glutathione content, expression of inflammatory and fibrotic markers, and function were also evaluated. In both genotypes, NAC had minimal effect on cardiac glutathione, structure and function (P ≥ 0.20). In NAC treated DCM mice, loss of glomerular filtration rate (GFR), tubulointerstitial and glomerular fibrosis and renal oxidised glutathione levels were attenuated by 38%, 99%, 70% and 52% respectively, compared to saline treated DCM mice (P ≤ 0.01). Renal expression of PAI-1 was greater in saline treated DCM mice than in WT mice (P < 0.05). Renal PAI-1 expression was less in NAC treated DCM mice than in vehicle treated DCM mice (P = 0.03). Renal IL-10 expression was greater in the former cohort compared to the latter (P < 0.01). These data indicate that normalisation of renal oxidized glutathione levels attenuates PAI-1 expression and renal inflammation preventing loss of GFR in experimental DCM.