Pivotal role of xanthine oxidase in the initiation of tubulointerstitial renal injury in rats with hyperlipidemia

Global Oxidative Status Is Linked to Calcific Aortic Stenosis: The Differences Due to Diabetes Mellitus and the Effects of Metformin

Calcific aortic stenosis (CAS) and type 2 diabetes mellitus (T2DM) are related and often concomitant pathologies, accompanied by common comorbidities such as hypertension or dyslipidemia. Oxidative stress is one of the mechanisms that trigger CAS, and it can drive the vascular complications in T2DM. Metformin can inhibit oxidative stress, yet its effects have not been studied in the context of CAS. Here, we assessed the global oxidative status in plasma from patients with CAS, both alone and with T2DM (and under treatment with metformin), using multimarker scores of systemic oxidative damage (OxyScore) and antioxidant defense (AntioxyScore). The OxyScore was determined by measuring carbonyls, oxidized LDL (oxLDL), 8-hydroxy-20-deoxyguanosine (8-OHdG), and xanthine oxidase (XOD) activity. In contrast, the AntioxyScore was determined through the catalase (CAT) and superoxide dismutase (SOD) activity, as well as the total antioxidant capacity (TAC). Patients with CAS displayed enhanced oxidative stress compared to control subjects, probably exceeding their antioxidant capacity. Interestingly, patients with CAS and T2DM displayed less oxidative stress, possibly due to the benefits of their pharmacological therapy (metformin). Thus, reducing oxidative stress or enhancing antioxidant capacity through specific therapies could be a good strategy to manage CAS, focusing on personalized medicine.

Urate-lowering therapy for CKD patients with asymptomatic hyperuricemia without proteinuria elucidated by attribute-based research in the FEATHER Study

Attribute-based medicine is essential for patient-centered medicine. To date, the groups of patients with chronic kidney disease (CKD) requiring urate-lowering therapy are clinically unknown. Herein, we evaluated the efficacy of febuxostat using a cross-classification, attribute-based research approach. We performed post hoc analysis of multicenter, randomized, double-blind, placebo-controlled trial data for 395 patients with stage 3 CKD and asymptomatic hyperuricemia. Participants were divided into febuxostat or placebo groups and subcohorts stratified and cross-classified by proteinuria and serum creatinine concentrations. In patients stratified based on proteinuria, the mean eGFR slopes were significantly higher in the febuxostat group than in the placebo group (P = 0.007) in the subcohort without proteinuria. The interaction between febuxostat treatment and presence of proteinuria in terms of eGFR slope was significant (P for interaction = 0.019). When cross-classified by the presence of proteinuria and serum creatinine level, the mean eGFR slopes significantly differed between the febuxostat and placebo groups (P = 0.040) in cross-classified subcohorts without proteinuria and with serum creatinine level ≥ median, but not in the cross-classified subcohorts with proteinuria and serum creatinine level < median. Febuxostat mitigated the decline in kidney function among stage 3 CKD patients with asymptomatic hyperuricemia without proteinuria.

Hyperuricemia and chronic kidney disease: to treat or not to treat

Hyperuricemia is common in chronic kidney disease (CKD) and may be present in 50% of patients presenting for dialysis. Hyperuricemia can be secondary to impaired glomerular filtration rate (GFR) that occurs in CKD. However, hyperuricemia can also precede the development of kidney disease and predict incident CKD. Experimental studies of hyperuricemic models have found that both soluble and crystalline uric acid can cause significant kidney damage, characterized by ischemia, tubulointerstitial fibrosis, and inflammation. However, most Mendelian randomization studies failed to demonstrate a causal relationship between uric acid and CKD, and clinical trials have had variable results. Here we suggest potential explanations for the negative clinical and genetic findings, including the role of crystalline uric acid, intracellular uric acid, and xanthine oxidase activity in uric acid-mediated kidney injury. We propose future clinical trials as well as an algorithm for treatment of hyperuricemia in patients with CKD.

The Crucial Role of Xanthine Oxidase in CKD Progression Associated with Hypercholesterolemia

In the present study, we investigated the effects of xanthine oxidase (XO) inhibition on cholesterol-induced renal dysfunction in chronic kidney disease (CKD) mice, and in low-density lipoprotein (LDL)-treated human kidney proximal tubule epithelial (HK-2) cells. ApoE knockout (KO) mice underwent uninephrectomy to induce CKD, and were fed a normal diet or high-cholesterol (HC) diet along with the XO inhibitor topiroxostat (1 mg/kg/day). HK-2 cells were treated with LDL (200 µg/mL) and topiroxostat (5 µM) or small interfering RNA against xanthine dehydrogenase (siXDH; 20 nM). In uninephrectomized ApoE KO mice, the HC diet increased cholesterol accumulation, oxidative stress, XO activity, and kidney damage, while topiroxostat attenuated the hypercholesterolemia-associated renal dysfunction. The HC diet induced cholesterol accumulation by regulating the expressions of genes involved in cholesterol efflux (Nr1h3 and Abca1) and synthesis (Srebf2 and Hmgcr), which was reversed by topiroxostat. Topiroxostat suppressed the expressions of genes related to hypercholesterolemia-associated inflammation and fibrosis in the unilateral kidney. LDL stimulation evoked changes in the cholesterol metabolism, nicotinamide adenine dinucleotide phosphate (NADPH) oxidase, and NF-κB pathways in HK-2 cells, which were mitigated by XO inhibition with topiroxostat or siXDH. These findings suggest that XO inhibition exerts renoprotective effects against hypercholesterolemia-associated kidney injury. XO could be a novel therapeutic target for hypercholesterolemia-associated kidney injury in uninephrectomized patients.

The emerging role of xanthine oxidase inhibition for suppression of breast cancer cell migration and metastasis associated with hypercholesterolemia

Hypercholesterolemia is reported to increase reactive oxygen species (ROS) and to promote breast cancer progression. ROS play an important role in tumor biology, and xanthine oxidase (XO) is an enzyme that generates ROS. The effects of febuxostat (FBX), an XO inhibitor, on breast cancer cell migration under LDL stimulation in vitro and metastasis of breast cancer associated with hypercholesterolemia in vivo were studied. In vitro, FBX significantly inhibited LDL-induced ROS production and cell migration. Treatment of small interfering RNA against XO was consistent with the findings of FBX treatment. In vivo, a significant increase of tumor growth and pulmonary metastasis was observed in a xenograft mouse model with 4T1 cells on a high cholesterol diet (HCD), both of which were markedly inhibited by FBX or allopurinol treatment. Moreover, ERK represented the main target-signaling pathway that was affected by FBX treatment in a xenograft mouse model on an HCD evaluated by NanoString nCounter analysis. Consistently, MEK/ERK inhibitors directly decreased the LDL-induced cell migration in vitro. In conclusion, FBX mitigates breast cancer cell migration and pulmonary metastasis in the hyperlipidemic condition, associated with decreased ROS generation and MAPK phosphorylation. The inhibition of ERK pathways is likely to underlie the XO inhibitor-mediated suppression of breast cancer cell migration.-Oh, S.-H., Choi, S.-Y., Choi, H.-J., Ryu, H.-M., Kim, Y.-J., Jung, H.-Y., Cho, J.-H., Kim, C.-D., Park, S.-H., Kwon, T.-H., Kim, Y.-L. The emerging role of xanthine oxidase inhibition for suppression of breast cancer cell migration and metastasis associated with hypercholesterolemia.

Tumor necrosis factor-α-dependent infiltration of macrophages into the dorsal root ganglion in a rat disc herniation model

STUDY DESIGN

A prospective molecular mechanism of macrophages infiltration in experimental disc herniation.

OBJECTIVE

To investigate the mechanisms of macrophages infiltration into the dorsal root ganglion (DRG) in a rat model of disc herniation.

SUMMARY OF BACKGROUND DATA

Macrophages infiltrate the DRG after application of nucleus pulposus (NP) on the DRG, and may play an important role in radiculopathy. However, the mechanisms of macrophages infiltration after NP application remain poorly understood.

METHODS

After experimental disc herniation in this study, we investigated changes in the expression of ED1 (a marker of macrophages) and vascular cell adhesion molecule-1 (VCAM-1) in DRG using immunofluorescence. We also investigated the expression of ED1 and VCAM-1 in DRG by treatment with tumor necrosis factor-α (TNF-α) inhibitor at the time of surgery.

RESULTS

We found a massive ED1-positive macrophages infiltrated the DRG, and VCAM-1-like immunoreactivity vessels became evident after NP application. Furthermore, both macrophage infiltration and VCAM-1 expression were prevented by treatment with TNF-α inhibitor at the time of surgery.

CONCLUSION

These findings indicated that macrophages infiltration into the DRG was TNF-α-dependent, and might be partly mediated by VCAM-1 in the early stage of experimental lumbar disc herination. Taken together, this study provides important preliminary data suggesting that TNF-α plays an important role in the macrophage infiltration.

LEVEL OF EVIDENCE

N/A.

The role of xanthine oxidase in hemodialysis-induced oxidative injury: relationship with nutritional status

The role of xanthine oxidase (XOD) in patients undergoing chronic hemodialysis treatment (HD) is poorly understood. Geriatric nutritional risk index (GNRI) ≤ 90 could be linked with malnutrition-inflammation complex syndrome. This study measured XOD, myeloperoxidase (MPO), superoxide dismutase (SOD), lipid hydroperoxides, total free thiol groups, and advanced oxidation protein products (AOPP) in 50 HD patients before commencing (pre-HD) and immediately after completion of HD session (post-HD) and in 22 healthy controls. Pre-HD serum hydroperoxides, AOPP, XOD, and SOD were higher and total thiol groups were lower in patients than in controls (P < 0.05, resp.). Compared to baseline values, serum MPO activity was increased irrespective of GNRI status. Serum XOD activity was increasing during HD treatment in the group with GNRI ≤ 90 (P = 0.030) whilst decreasing in the group with GNRI > 90 (P = 0.002). In a multiple regression analysis, post-HD serum XOD activity was independently associated with GNRI ≤ 90 (β  ± SE: 0.398 ± 0.151; P = 0.012) and HD vintage (β  ± SE: −0.349 ± 0.139; P = 0.016). These results indicate that an upregulated XOD may be implicated in HD-induced oxidative injury contributing to accelerated protein damage in patients with GNRI ≤ 90.

Lipid droplet accumulation is associated with an increase in hyperglycemia-induced renal damage: prevention by liver X receptors

Dyslipidemia is a frequent component of the metabolic disorder of diabetic patients contributing to organ damage. Herein, in low-density lipoprotein receptor-deficient hyperlipidemic and streptozotozin-induced diabetic mice, hyperglycemia and hyperlipidemia acted reciprocally, accentuating renal injury and altering renal function. In hyperglycemic-hyperlipidemic kidneys, the accumulation of Tip47-positive lipid droplets in glomeruli, tubular epithelia, and macrophages was accompanied by the concomitant presence of the oxidative stress markers xanthine oxidoreductase and nitrotyrosine, findings that could also be evidenced in renal biopsy samples of diabetic patients. As liver X receptors (LXRα,β) regulate genes linked to lipid and carbohydrate homeostasis and inhibit inflammatory gene expression in macrophages, the effects of systemic and macrophage-specific LXR activation were analyzed on renal damage in hyperlipidemic-hyperglycemic mice. LXR stimulation by GW3965 up-regulated genes involved in cholesterol efflux and down-regulated proinflammatory/profibrotic cytokines, inhibiting the pathomorphology of diabetic nephropathy, renal lipid accumulation, and improving renal function. Xanthine oxidoreductase and nitrotyrosine levels were reduced. In macrophages, GW3965 or LXRα overexpression significantly suppressed glycated or acetylated low-density lipoprotein-induced cytokines and reactive oxygen species. Specifically, in mice, transgenic expression of LXRα in macrophages significantly ameliorated hyperlipidemic-hyperglycemic nephropathy. The results demonstrate the presence of lipid droplet-induced oxidative mechanisms and the pathophysiologic role of macrophages in diabetic kidneys and indicate the potent regulatory role of LXRs in preventing renal damage in diabetes.

Uric acid as a target of therapy in CKD

The prevalence of chronic kidney disease (CKD) has increased and will continue to increase in the United States and worldwide. This is alarming considering that CKD is an irreversible condition and patients who progress to chronic kidney failure have reduced quality of life and high mortality rates. As such, it is imperative to identify modifiable risk factors to develop strategies to slow CKD progression. One such factor is hyperuricemia. Recent observational studies have associated hyperuricemia with kidney disease. In addition, hyperuricemia is largely prevalent in patients with CKD. Data from experimental studies have shown several potential mechanisms by which hyperuricemia may contribute to the development and progression of CKD. In this article, we offer a critical review of the experimental evidence linking hyperuricemia to CKD, highlight gaps in our knowledge on the topic as it stands today, and review the observational and interventional studies that have examined the potential nephroprotective effect of decreasing uric acid levels in patients with CKD. Although uric acid also may be linked to cardiovascular disease and mortality in patients with CKD, this review focuses only on uric acid as a potential therapeutic target to prevent kidney disease onset and progression.

Febuxostat suppressed renal ischemia-reperfusion injury via reduced oxidative stress

Febuxostat is a novel selective inhibitor of xanthine oxidase (XO), approved for treating hyperuricemia. XO inhibits the generation of uric acid (UA) as well as the resulting generation of superoxide. During renal ischemia-reperfusion (I/R) injury, the burst of reactive oxygen species (ROS) can trigger the inflammation and the tubular cell injury. As XO is a critical source of ROS, inhibition of XO could be a therapeutic target for I/R injury. Therefore, we performed this study to test the therapeutic effect of febuxostat on renal I/R injury. Sprague-Dawley rats, received vehicle or febuxostat, were subjected to right nephrectomy and left renal I/R injury. Febuxostat significantly suppressed XO activity, and thereby reduced oxidative stress, assessed by nitrotyrosine, thiobarbituric acid-reactive substances (TBARS) and urine 8-isoprostane. Furthermore, febuxostat reduced the induction of endoplasmic reticulum (ER) stress, assessed by GRP-78, ATF4, and CHOP. Vehicle-treated I/R injured rats exhibited elevated serum creatinine and UN, which were significantly suppressed in febuxostat-treated I/R-injured rats. Histological analysis revealed that fubuxostat-treated rats showed less tubular injury and interstitial fibrosis with reduction in ED1-positive macrophage infiltration, TUNEL positive apoptotic tubular cells, and interstitial smooth muscle α actin (SMαA) expression, compared to vehicle-treated rats. In conclusion; novel XO inhibitor, febuxostat, can protect kidney from renal I/R injury, and may contribute to preserve kidney function.

Xanthine oxidoreductase depletion induces renal interstitial fibrosis through aberrant lipid and purine accumulation in renal tubules

Xanthine oxidoreductase (XOR) is an enzyme responsible for purine degradation, reactive oxygen species production, and adipogenesis. XOR gene-disrupted (XOR(-/-)) mice demonstrate renal failure and early death within several months. The aim of this study was to elucidate the mechanism of renal damage in XOR(-/-) mice and to determine the physiological role of XOR in the kidney. Histological analysis revealed that renal tubular damage in XOR(-/-) mice was accompanied by deposition of crystals and lipid-rich substances. Triglyceride content in renal homogenates was significantly increased in XOR(-/-) mice. The level of lipogenesis-related gene expression was comparable in XOR(+/+) and XOR(-/-) mice, whereas the expression of adipogenesis-related gene expression was significantly elevated in XOR(-/-) mice. Urinary excretions of xanthine and hypoxanthine were markedly elevated in XOR(-/-) mice. Immunohistochemical analysis, Western blotting, and real time RT-PCR revealed that various markers of fibrosis, inflammation, ischemia, and oxidative stress were increased in XOR(-/-) mice. Finally, we demonstrate that primary renal epithelial cells from XOR(-/-) mice are more readily transformed to myofibroblasts, which is a marker of increased epithelial mesenchymal transition. These results suggest that XOR gene disruption induced the depletion of uric acid and the accumulation of triglyceride-rich substances, xanthine, and hypoxanthine in the renal tubules. We believe that these changes contribute to a complex cellular milieu characterized by inflammation, tissue hypoxia, and reactive oxygen species production, ultimately resulting in renal failure through increased renal interstitial fibrosis.

Oxidants in chronic kidney disease

Chronic kidney disease is a worldwide public health problem that affects approximately 10% of the US adult population and is associated with a high prevalence of cardiovascular disease and high economic cost. Chronic renal insufficiency, once established, tends to progress to end-stage kidney disease, suggesting some common mechanisms for ultimately causing scarring and further nephron loss. This review defines the term reactive oxygen metabolites (ROM), or oxidants, and presents the available experimental evidence in support of the role of oxidants in diabetic and nondiabetic glomerular disease and their role in tubulointerstitial damage that accompanies progression. It concludes by reviewing the limited human data that provide some proof of concept that the observations in experimental models may be relevant to human disease.