NF-κB blockade during short-term l-NAME and salt overload strongly attenuates the late development of chronic kidney disease.

Nitric oxide synthase inhibition by Nω-nitro-l-arginine methyl ester (l-NAME) plus a high-salt diet (HS) is a model of chronic kidney disease (CKD) characterized by marked hypertension and renal injury. With cessation of treatment, most of these changes subside, but progressive renal injury develops, associated with persistent low-grade renal inflammation. We investigated whether innate immunity, and in particular the NF-κB system, is involved in this process. Male Munich-Wistar rats received HS + l-NAME (32 mg·kg-1·day-1), whereas control rats received HS only. Treatment was ceased after week 4 when 30 rats were studied. Additional rats were studied at week 8 (n = 30) and week 28 (n = 30). As expected, HS + l-NAME promoted severe hypertension, albuminuria, and renal injury after 4 wk of treatment, whereas innate immunity activation was evident. After discontinuation of treatments, partial regression of renal injury and inflammation occurred, along with persistence of innate immunity activation at week 8. At week 28, glomerular injury worsened, while renal inflammation persisted and renal innate immunity remained activated. Temporary administration of the NF-κB inhibitor pyrrolidine dithiocarbamate, in concomitancy with the early 4-wk HS + l-NAME treatment, prevented the development of late renal injury and inflammation, an effect that lasted until the end of the study. Early activation of innate immunity may be crucial to the initiation of renal injury in the HS + l-NAME model and to the autonomous progression of chronic nephropathy even after cessation of the original insult. This behavior may be common to other conditions leading to CKD.

Pathogenic role of innate immunity in a model of chronic NO inhibition associated with salt overload.

Nitric oxide inhibition with Nω-nitro-l-arginine methyl ester (l-NAME), along with salt overload, leads to hypertension, albuminuria, glomerulosclerosis, glomerular ischemia, and interstitial fibrosis, characterizing a chronic kidney disease (CKD) model. Previous findings of this laboratory and elsewhere have suggested that activation of at least two pathways of innate immunity, Toll-like receptor 4 (TLR4)/NF-κB and nucleotide-binding oligomerization domain, leucine-rich repeat, and pyrin domain containing 3 (NLRP3) inflammasome/IL-1ß, occurs in several experimental models of CKD and that progression of renal injury can be slowed with inhibition of these pathways. In the present study, we investigated whether activation of innate immunity, through either the TLR4/NF-κB or NLRP3/IL-1ß pathway, is involved in the pathogenesis of renal injury in chronic nitric oxide inhibition with the salt-overload model. Adult male Munich-Wistar rats that received l-NAME in drinking water with salt overload (HS + N group) were treated with allopurinol (ALLO) as an NLRP3 inhibitor (HS + N + ALLO group) or pyrrolidine dithiocarbamate (PDTC) as an NF-κB inhibitor (HS + N + PDTC group). After 4 wk, HS + N rats developed hypertension, albuminuria, and renal injury along with renal inflammation, oxidative stress, and activation of both the NLRP3/IL-1ß and TLR4/NF-κB pathways. ALLO lowered renal uric acid and inhibited the NLRP3 pathway. These effects were associated with amelioration of hypertension, albuminuria, and interstitial inflammation/fibrosis but not glomerular injury. PDTC inhibited the renal NF-κB system and lowered the number of interstitial cells staining positively for NLRP3. PDTC also reduced renal xanthine oxidase activity and uric acid. Overall, PDTC promoted a more efficient anti-inflammatory and nephroprotective effect than ALLO. The NLRP3/IL-1ß and TLR4/NF-κB pathways act in parallel to promote renal injury/inflammation and must be simultaneously inhibited for best nephroprotection.

Unilateral Nephrectomy Stimulates ERK and Is Associated With Enhanced Na Transport.

Nephron loss initiates compensatory hemodynamic and cellular effects on the remaining nephrons. Increases in single nephron glomerular filtration rate and tubular flow rate exert higher fluid shear stress (FSS) on tubules. In principal cell (PC) culture models FSS induces ERK, and ERK is implicated in the regulation of transepithelial sodium (Na) transport, as well as, proliferation. Thus, we hypothesize that high tubular flow and FSS mediate ERK activation in the cortical collecting duct (CCD) of solitary kidney which regulates amiloride sensitive Na transport and affects CCD cell number. Immunoblotting of whole kidney protein lysate was performed to determine phospho-ERK (pERK) expression. Next, sham and unilateral nephrectomized mice were stained with anti-pERK antibodies, and dolichos biflorus agglutinin (DBA) to identify PCs with pERK. Murine PCs (mpkCCD) were grown on semi-permeable supports under static, FSS, and FSS with U0126 (a MEK1/2 inhibitor) conditions to measure the effects of FSS and ERK inhibition on amiloride sensitive Na short circuit current (Isc). pERK abundance was greater in kidney lysate of unilateral vs. sham nephrectomies. The total number of cells in CCD and pERK positive PCs increased in nephrectomized mice (9.3 ± 0.4 vs. 6.1 ± 0.2 and 5.1 ± 0.5 vs. 3.6 ± 0.3 cell per CCD nephrectomy vs. sham, respectively, n > 6 per group, p < 0.05). However, Ki67, a marker of proliferation, did not differ by immunoblot or immunohistochemistry in nephrectomy samples at 1 month compared to sham. Next, amiloride sensitive Isc in static mpkCCD cells was 25.3 ± 1.7 µA/cm2 (n = 21), but after exposure to 24 h of FSS the Isc increased to 41.4 ± 2.8 µA/cm2 (n = 22; p < 0.01) and returned to 19.1 ± 2.1 µA/cm2 (n = 18, p < 0.01) upon treatment with U0126. Though FSS did not alter α- or γ-ENaC expression in mpkCCD cells, γ-ENaC was reduced in U0126 treated cells. In conclusion, pERK increases in whole kidney and, specifically, CCD cells after nephrectomy, but pERK was not associated with active proliferation at 1-month post-nephrectomy. In vitro studies suggest high tubular flow induces ERK dependent ENaC Na absorption and may play a critical role in Na balance post-nephrectomy.

Effect of parathyroidectomy on bone tissue biomarkers and body composition in patients with chronic kidney disease and secondary hyperparathyroidism.

BACKGROUND/OBJECTIVE: Loss of renal function may induce secondary hyperparathyroidism (s-HPT), which triggers several complications leading to an extreme decline in quality of life and increased mortality in affected patients. We evaluated whether parathyroidectomy (PTx), as surgical treatment for s-HPT, modifies body composition, and hormones involved in the protein-energy metabolism of affected patients. SUBJECTS/METHODS: Overall, 30 s-HPT patients were evaluated at two times, before PTx (pre PTx) and 6 months after PTx (post PTx). Patients were evaluated by biochemistry analysis, anthropometry, electrical bioimpedance (BIA), food intake diary, handgrip strength, and modified global subjective nutritional assessment (SGA). RESULTS: After PTx, patients showed decreased serum levels of total and ionic calcium, as well as decreased alkaline phosphatase and PTH, and increased 25 (OH) vitamin D. These results demonstrate that PTx was efficient to correct part of the mineral disorder. We also observed an increase in caloric intake, body weight, body mass index (BMI), phase angle, handgrip strength, SGA score, and a decreasing in the percentage of weight loss. The osteocalcin concentration of both carboxylated (cOC) and undercarboxylated form was diminished post PTx. The cOC correlated with bone metabolism markers and SGA score. CONCLUSIONS: PTx modified body composition improving nutritional status and preventing the progression of weight loss with increased of energy intake, BMI, handgrip strength, phase angle of BIA, and SGA score. The present study also suggests an association of cOC with bone markers and SGA score. Further studies are needed to better clarify these associations with larger sample size.

Renal Inflammation and Innate Immune Activation Underlie the Transition From Gentamicin-Induced Acute Kidney Injury to Renal Fibrosis.

Subjects recovering from acute kidney injury (AKI) are at risk of developing chronic kidney disease (CKD). The mechanisms underlying this transition are unclear and may involve sustained activation of renal innate immunity, with resulting renal inflammation and fibrosis. We investigated whether the NF-κB system and/or the NLRP3 inflammasome pathway remain activated after the resolution of AKI induced by gentamicin (GT) treatment, thus favoring the development of CKD. Male Munich-Wistar rats received daily subcutaneous injections of GT, 80 mg/kg, for 9 days. Control rats received vehicle only (NC). Rats were studied at 1, 30, and 180 days after GT treatment was ceased. On Day 1, glomerular ischemia (ISCH), tubular necrosis, albuminuria, creatinine retention, and tubular dysfunction were noted, in association with prominent renal infiltration by macrophages and myofibroblasts, along with increased renal abundance of TLR4, IL-6, and IL1ß. Regression of functional and structural changes occurred on Day 30. However, the renal content of IL-1ß was still elevated at this time, while the local renin-angiotensin system remained activated, and interstitial fibrosis became evident. On Day 180, recurring albuminuria and mild glomerulosclerosis were seen, along with ISCH and unabated interstitial fibrosis, whereas macrophage infiltration was still evident. GT-induced AKI activates innate immunity and promotes renal inflammation. Persistence of these abnormalities provides a plausible explanation for the transition of AKI to CKD observed in a growing number of patients.