Influence of predialysis oxidative stress on peroxidation processes after renal transplantation

Cannabinoid-2 receptor activation ameliorates hepatorenal syndrome

STUDY RATIONALE

Hepatorenal syndrome (HRS) is a life-threatening complication of end-stage liver disease characterized by the rapid decline of kidney function. Herein, we explored the therapeutic potential of targeting the cannabinoid-2 receptor (CB₂-R) utilizing a commonly used mouse model of liver fibrosis and hepatorenal syndrome (HRS), induced by bile duct ligation (BDL).

METHODS

Gene expression analysis, histological evaluation, determination of serum levels of renal injury-biomarkers were used to characterize the BDL-induced organ injury; laser speckle analysis to measure microcirculation in the kidneys.

KEY RESULTS

We found that liver injury triggered marked inflammation and oxidative stress in the kidneys of BDL-operated mice. We detected pronounced histopathological alterations with tubular injury paralleled with increased inflammation, oxidative/nitrative stress and fibrotic remodeling both in hepatic and renal tissues as well as endothelial activation and markedly impaired renal microcirculation. This was accompanied by increased CB₂-R expression in both the liver and the kidney tissues of diseased animals. A selective CB₂-R agonist, HU-910, markedly decreased numerous markers of inflammation, oxidative stress and fibrosis both in the liver and in the kidneys. HU-910 also attenuated markers of kidney injury and improved the impaired renal microcirculation in BDL-operated mice.

CONCLUSIONS

Our results suggest that oxidative stress, inflammation and microvascular dysfunction are key events in the pathogenesis of BDL-associated renal failure. Furthermore, we demonstrate that targeting the CB₂-R by selective agonists may represent a promising new avenue to treat HRS by attenuating tissue and vascular inflammation, oxidative stress, fibrosis and consequent microcirculatory dysfunction in the kidneys.

Influence of temperature in thermal and oxidative stress responses in estuarine fish

The influence of increasing temperatures in thermal and oxidative stress responses were studied in the muscle of several estuarine fish species (Diplodus vulgaris, Diplodus sargus, Dicentrarchus labrax, Gobius niger and Liza ramada). Selected fish were collected in July at the Tagus estuary (24±0.9°C; salinity of 30±4‰; pH=8). Fish were subjected to a temperature increase of 1°C.h(-1) until they reached their Critical Thermal Maximum (CTMax), starting at 24°C (control temperature). Muscle samples were collected during the trial and results showed that oxidative stress biomarkers are highly sensitive to temperature. Results from stress oxidative enzymes show alterations with increasing temperature in all tested species. Catalase (CAT; EC 1.11.1.6) activity significantly increased in L. ramada, D. labrax and decreased in D. vulgaris. Glutathione S-transferase (GST; EC 2.5.1.18) activity increased in L. ramada, D. sargus, D. vulgaris, and D. labrax. In G. niger it showed a cycle of increase-decrease. Lipid peroxidation (LPO) increased in L. ramada, D. sargus and D. labrax. With respect to correlation analysis (Pearson; Spearman r), the results showed that oxidation products and antioxidant defenses were correlated in L. ramada (LPO-CAT and LPO-GST, D. sargus (LPO-CAT), and D. labrax (LPO-CAT). Oxidative biomarkers were correlated with thermal stress biomarker (Hsp70) in L. ramada (CAT-Hsp70), D. vulgaris (LPO-Hsp70), D. labrax (GST-Hsp70) and G. niger (LPO-Hsp70). In conclusion, oxidative stress does occur with increasing temperatures and there seems to be a relation between thermal stress response and oxidative stress response. The results suggest that oxidative stress biomarkers should be applied with caution, particularly in field multi-species/multi-environment studies.

Oxidative stress and 'monocyte reprogramming' after kidney transplant: a longitudinal study

Uremia has been implicated in increased oxidative stress (OS) and decreased monocyte HLA-DR expression in chronic kidney disease (CKD) patients. Thus, one would expect normalization of these parameters after successful kidney transplant (KTx). Our aim was to describe patterns of OS and HLA-DR expression after KTx and to explore the effect of renal function and different immunosuppression regimens. 30 KTx patients (20 male; 48 +/- 11 years) were enrolled and compared with 20 healthy controls. We measured advanced oxidation protein products (AOPP) and the percentage of monocytes expressing HLA-DR (%DR+) before (preKTx) and after KTx (on days 2, 30, 90, 180 and after 1 year). Compared to controls, patients had a higher preKTx AOPP (152.6 vs. 69.3 micromol/l; p < 0.001). AOPP decreased at 48 h after KTx, achieving values similar to controls. Thereafter, it increased again and remained significantly higher compared to controls, returning to preKTx levels at 90 days. Prior to KTx there was a trend for lower %DR+ in KTx patients compared to controls (96 vs. 98%; NS). Following KTx, patients had a lower %DR+ in the 1st month; then it gradually returned to preKTx levels during the 1st year; at no time did it reach a value similar to controls. Cyclosporine (CyA)-treated patients had a significantly higher AOPP (161.5 vs. 99.5 micromol/l; p = 0.03) and a lower %DR+ (91.7 vs. 96.4; p < 0.05) at 30 days than patients on tacrolimus (FK). Patients on mycophenolate mofetil (MMF) showed a low AOPP (106.9 vs. 168.1 micromol/l; p = 0.05) and a high %DR+ (96.7 vs. 88.2%; p = 0.001) than those on everolimus. After 3 months, CyA-treated patients had a non-significant increase in AOPP levels, whereas those on FK showed a decrease (p < 0.05) as did those treated with MMF (p < 0.05). Successful KTx reduced but did not normalize AOPP, suggesting ongoing OS, perhaps due to persistent mild renal dysfunction and the effects of immunosuppression. HLA-DR expression remained low after KTx, which may be a possible contributing factor to infectious complications after transplantation. Immunosuppressive agents appear to have diverse effects on OS and HLA-DR expression.

Interrelationship between uremic toxicity and oxidative stress

Uremic syndrome is associated with several metabolic disturbances. Oxidative stress is an important factor involved in the pathologic mechanism of these changes. The goal of this study was to understand the relationship between oxidative stress markers and two compounds included among uremic toxins. Two independent studies were performed, one with 29 peritoneal dialysis patients and the other with 43 predialysis subjects. In both groups of patients, known oxidative stress markers, malonyldialdehyde (MDA) and carbonyl groups (CG) formation were measured. Additionally, in the predialysis group, glutathione in erythrocytes (GSH) was estimated. In peritoneal dialysis patients, the concentration of advanced glycation end products (AGEs) was found to be significantly increased and correlated with both markers of oxidative stress. In predialysis patients, the increment of newly described uremic toxin purine nucleotide end products (Me2PY and Me4PY) were found and significant correlation was observed between both compounds versus MDA (positive) and GSH (negative). This relationship was visible especially in patients with more advanced renal failure. CG concentration was within the normal values and did not show any correlation with estimated toxin concentrations. In summary, results of both studies suggest that the interrelationship between uremic toxicity and oxidative stress is an important component of uremic syndrome. Nevertheless, further complex studies are needed to elucidate closer pathogenic links.

Expression of scavenger receptor CD36 in chronic renal failure patients

BACKGROUND

Patients with chronic renal failure (CRF) are at increased risk of atherosclerosis development. One of the major steps in pathogenesis of atherosclerosis is formation of foam cells. Scavenger receptor CD36 is among the major receptors for oxidized low density lipoproteins (oxLDL) and therefore it plays a crucial role in foam cell formation. The aim of the present study was to investigate the expression of CD36 on blood monocytes of CRF patients.

METHODS

Expression of CD36 on blood monocytes of CRF patients treated with hemodialysis (HD), peritoneal dialysis (PD), those not yet on dialysis (predialysis), and controls was assessed with the use of flow cytometry. Additionally, the major lipid peroxidation markers, malondialdehyde (MDA) and 4-hydroxyalkenals (HAE), were measured. Further, impact of treatment with HMG-CoA reductase inhibitors (statins) on CD36 expression in CRF patients was evaluated.

RESULTS

Expression of monocyte CD36, measured as mean fluorescence intensity (MFI) was significantly higher in HD and PD patients, when compared to controls without renal insufficiency (respectively: 1011 +/- 288 and 1000 +/- 309 vs. 710 +/- 313; P < 0.01 for both groups). This was not the case in predialysis group (828 +/- 363 vs. 710 +/- 313). Higher concentrations of lipid peroxidation indicators, MDA and HAE were observed in all three subgroups of CRF patients (2.1 +/- 0.51, 2.02 +/- 0.27, and 1.81 +/- 0.53 microm in HD, PD, and predialysis group, respectively, vs. 1.13 +/- 0.59 microm in controls; P < 0.01). Patients treated with statins showed significantly lower CD36 expression than patients without statin therapy.

CONCLUSIONS

The present study, for the first time, demonstrates increased expression of CD36 scavenger receptor in CRF patients. This may be a possible risk factor for accelerated atherogenesis observed in this group of patients.