. Voluntary wheel running augments aortic L-arginine transport and endothelial function in rats with chronic kidney disease. Am J Physiol Renal Physiol 307: F418 -F426, 2014. First published June 25, 2014 doi:10.1152/ajprenal.00014.2014.-Reduced nitric oxide (NO) synthesis contributes to risk for cardiovascular disease in chronic kidney disease (CKD). Vascular uptake of the NO precursor L-arginine (ARG) is attenuated in rodents with CKD, resulting in reduced substrate availability for NO synthesis and impaired vascular function. We tested the effect of 4 wk of voluntary wheel running (RUN) and/or ARG supplementation on endotheliumdependent relaxation (EDR) in rats with CKD. Twelve-week-old male Sprague-Dawley rats underwent 5 ⁄6 ablation infarction surgery to induce CKD, or SHAM surgery as a control. Beginning 4 wk following surgery, CKD animals either remained sedentary (SED) or received one of the following interventions: supplemental ARG, RUN, or combined RUNϩARG. Animals were euthanized 8 wk after surgery, and EDR was assessed. EDR was significantly impaired in SED vs. SHAM animals after 8 wk, in response to ACh (10 Ϫ9 -10 Ϫ5 M) as indicated by a reduced area under the curve (AUC; 44.56 Ϯ 9.01 vs 100 Ϯ 4.58, P Ͻ 0.05) and reduced maximal response (Emax; 59.9 Ϯ 9.67 vs. 94.31 Ϯ 1.27%, P Ͻ 0.05). AUC was not improved by ARG treatment but was significantly improved above SED animals in both RUN and RUNϩARG-treated animals. Maximal relaxation was elevated above SED in RUNϩARG animals only. L-[ 3 H]arginine uptake was impaired in both SED and ARG animals and was improved in RUN and RUNϩARG animals. The results suggest that voluntary wheel running is an effective therapy to improve vascular function in CKD and may be more beneficial when combined with L-arginine. endothelial dysfunction; chronic kidney disease; L-arginine; exercise ENDOTHELIAL DYSFUNCTION CONTRIBUTES to the development of cardiovascular disease (CVD) in patients with chronic kidney disease (CKD) and is primarily associated with a decrease in nitric oxide (NO) production and impaired endothelium-dependent relaxation (EDR) (32). The decline in endothelial function precedes the development of atherosclerosis (17, 48) and has been extensively studied as a potential therapeutic target to treat CVD; however, the specific mechanisms of endothelial dysfunction in CKD have not been fully elucidated. Patients with CKD are more likely to die of CVD than progress to end-stage renal disease (26, 42); therefore, novel treatments to improve endothelial function in CKD are needed to reduce CVD-related mortality in CKD.Insufficient availability of the NO precursor L-arginine likely contributes to reduced NO synthesis in CKD (6). Interestingly, the use of L-arginine in studies of endothelial dysfunction in late-stage CKD has produced mixed results (7, 16) unlike other conditions where it has been largely effective (8,13,15,24). Evidence from cell culture studies suggests that urea and other uremic toxins inhibit L-arginine uptake into endothelial cells (52, 54) by...

Reduced nitric oxide bioavailability contributes to increased cardiovascular disease risk in patients with chronic kidney disease (CKD). Arginase has been implicated as a potential therapeutic target to treat vascular dysfunction by improving substrate availability for endothelial nitric oxide synthase. The purpose of this study was to determine if arginase contributes to endothelial dysfunction in the 5/6 ablation infarction (AI) rat model of CKD. Endothelium-dependent relaxation of aortic rings to acetylcholine was significantly impaired in AI animals versus sham after 8 weeks and was not improved by arginase inhibition (S-(2-Boronoethyl)-L-cysteine hydrochloride) alone or in combination with L-arginine. Additionally, scavenging of superoxide (Tempol, Tempol + L-arginine, Tempol + L-arginine + S-(2-Boronoethyl)-L-cysteine hydrochloride) was not effective, suggesting that a mechanism independent of oxidative stress contributes to endothelium-dependent relaxation in moderate to severe CKD. Aortic uptake of radiolabeled L-arginine was attenuated in AI animals and was associated with a reduced expression of the L-arginine transporter CAT-1. These data suggest that arginase does not contribute to endothelial dysfunction in CKD; however, impaired L-arginine transport may play an important role in diminishing substrate availability for nitric oxide production leading to endothelial dysfunction.

Contraction of muscle evokes the exercise pressor reflex (EPR), which is expressed partly by increases in heart rate and arterial pressure. Patients with peripheral artery disease (PAD) show an exaggerated EPR, sometimes report pain when walking and are at risk for cardiac arrthymias. Previous research suggested that reactive oxygen species (ROS) mediate the exaggerated EPR associated with PAD. To examine the effects of ROS on the EPR, we infused a superoxide scavenger, tiron, into the superficial epigastric artery of decerebrated rats. In some, we simulated PAD by ligating a femoral artery for 72 h before the experiment. The peak EPR in 'ligated' rats during saline infusion averaged 31 ± 4 mmHg, whereas the peak EPR in these rats during tiron infusion averaged 13 ± 2 mmHg (n = 12; P < 0.001); the attenuating effect of tiron on the EPR was partly reversed when saline was reinfused into the superficial epigastric artery (21 ± 2 mmHg; P < 0.01 vs. tiron). The peak EPR in 'ligated' rats was also attenuated (n = 7; P < 0.01) by infusion of gp91ds-tat, a peptide that blocks the activity of NAD(P)H oxidase. Tiron infusion had no effect on the EPR in rats with patent femoral arteries (n = 9). Western blots showed that the triceps surae muscles of 'ligated' rats expressed more Nox2 and p67phox, which are components of NADPH oxidase, compared to triceps surae muscles of 'freely perfused' rats. Tiron added to muscle homogenates reduced ROS production in vitro. The results of the present study provide further evidence indicating that ROS mediates the exaggeration of EPR in rats with simulated PAD.

A reduction in progenitor cell populations that help preserve vascular continuity and induce vascularization may accentuate endothelial cell apoptosis and dysfunction, ultimately contributing to organ failure and increased cardiovascular disease in chronic kidney disease (CKD). We hypothesized that CD45+ myeloid and CD34+ hematopoietic circulating progenitor cell (CPC) subpopulations would be reduced, peripheral blood mononuclear cell (PBMNC) colony-forming units (CFU) would be impaired, and flow-mediated dilation (FMD) would be impaired in patients with moderate-to-severe CKD as compared with healthy controls. Eleven moderate-to-severe CKD patients (mean estimated glomerular filtration rate [eGFR]: 36 ± 5) and 14 healthy controls were studied; blood was drawn and FMD was assessed by brachial artery FMD. CPCs were quantified via flow cytometry, and isolated PBMNCs were cultured for the colony-forming assay. CKD patients had significantly impaired FMD; lower CD34+, CD34+/KDR+, CD34+/CD45- and CD34+/KDR+/CD45- hematopoietic CPCs; lower CD45+, CD45+/KDR+, CD34+/CD45+ and CD34+/KDR+/CD45+ myeloid CPCs; and impaired CFUs as compared with healthy controls. Regression analysis revealed that CD34+, CD34+/KDR+ and CD34+/CD45- hematopoietic CPCs were associated positively with eGFR and negatively with blood urea nitrogen and serum creatinine. The CD45+/KDR+ myeloid CPCs also were associated positively with eGFR and negatively with serum creatinine. CD34+ hematopoietic CPCs and CD45+/KDR+ as well as CD34+/CD45+ myeloid CPCs were associated positively with FMD. In conclusion, myeloid and hematopoietic CPCs are reduced and associated with renal function as well as FMD in CKD. Therefore, reductions in CPCs may be a potential mechanism by which vascular integrity is compromised, increasing cardiovascular disease risk and contributing to renal disease progression in CKD.

Mechanical unloading stimulates rapid changes in skeletal muscle morphology, characterized by atrophy of muscle fibre cross-sectional area and a partial fibre-type shift from slow to fast twitch. Recent studies revealed that oxidative stress contributes to activation of forkhead box O3a (FoxO3a), proteolytic signalling and unloading-induced muscle atrophy via translocation of the μ-splice variant of neuronal nitric oxide synthase (nNOSμ) and activation of FoxO3a. There is limited understanding of the role of reactive oxygen species in the Akt-mammalian target of rapamycin (mTOR) pathway signalling during unloading. We hypothesized that Eukarion-134 (EUK-134), a mimetic of the antioxidant enzymes superoxide dismutase and catalase, would protect Akt-mTOR signalling in the unloaded rat soleus. Male Fischer 344 rats were separated into the following three study groups: ambulatory control (n = 11); 7 days of hindlimb unloading + saline injections (HU, n = 11); or 7 days of HU + EUK-134; (HU + EUK-134, n = 9). EUK-134 mitigated unloading-induced dephosphorylation of Akt, as well as FoxO3a, in the soleus. Phosphorylation of mTOR in the EUK-treated HU rats was not different from that in control animals. However, EUK-134 did not significantly rescue p70S6K phosphorylation. EUK-134 attenuated translocation of nNOSμ from the membrane to the cytosol, reduced nitration of tyrosine residues and suppressed upregulation of caveolin-3 and dysferlin. EUK-134 ameliorated HU-induced remodelling, atrophy of muscle fibres and the 12% increase in type II myosin heavy chain-positive fibres. Attenuation of the unloaded muscle phenotype was associated with decreased reactive oxygen species, as assessed by ethidium-positive nuclei. We conclude that oxidative stress affects Akt-mTOR signalling in unloaded skeletal muscle. Direct linkage of abrogation of nNOSμ translocation with Akt-mTOR signalling during unloading is the subject of future investigation.