Salt-sensitive (SS) hypertension is accompanied with severe cardiorenal complications. In this condition, elevated blood pressure (BP) resulting from salt retention is associated with counterintuitively lower levels of atrial natriuretic peptide (ANP). In plasma, ANP is degraded by the neprilysin; therefore, pharmacological inhibition of this metalloprotease (i.e., with sacubitril) can be employed to increase ANP level. We have shown earlier that sacubitril in combination with valsartan (75 lg/day each) had beneficial effects on renal function in Dahl SS rats. The goal of this study was to evaluate the effects of a higher dose of sacubitril on renal damage in this model. To induce hypertension, male Dahl SS rats were fed a 4% NaCl diet (HS) for 21 days, and were administered sacubitril (125 lg/day) or vehicle via s.c. osmotic pumps. At the end of the HS challenge, both groups exhibited similar outcomes for GFR, heart weight, plasma electrolytes, BUN, and creatinine. Sacubitril exacerbated kidney hypertrophy, but did not affect levels of renal fibrosis. We also observed aggravated glomerular lesions and increased formation of protein casts in the sacubitril-treated animals compared to controls. Thus, in Dahl SS rats, administration of sacubitril without renin-angiotensin-system blockage had adverse effects on renal disease progression, particularly in regards to glomerular damage and protein cast formation. We can speculate that while ANP levels are increased because of neprilysin inhibition, there are off-target effects of sacubitril, which are detrimental to renal function in the SS hypertensive state.
Introduction Sex differences are implicated in many cardiovascular and renal pathologies; for instance, premenopausal females are typically less prone to renovascular damage than males. However, although mitochondrial bioenergetics per se is a well‐known factor that can mediate the progression of the renal diseases, it is not known if there are sex‐related dissimilarities in the performance of renal mitochondria prior to the development of any disease. The goal of this study was to test the differences in renal cortical and medullary mitochondrial function in healthy male versus female rats. Methods . Mitochondria were isolated from the kidneys collected from male and female Sprague Dawley (SD) rats procured from Charles River labs at 11 weeks of age. Mitochondrial membrane potential, superoxide and H2O2 levels were measured with luminescent or fluorescent dyes (TMRM, MCLA and Amplex Red) in mitochondria isolated from renal cortex and medulla. To measure the oxygen consumption rate (OCR) and mitochondrial calcium uptake, seahorse assay and spectrofluorimetry with CaGreen dye, respectively, were performed on isolated mitochondria. Lipid peroxide radical formation was detected using electron spin resonance spectroscopy (ESR) with in vivo spin trapping. The SOD activity and total antioxidant capacity were measured using commercially available kits. In order to analyze the expression levels of various mitochondria‐related proteins, Western blot analysis was performed on snap‐frozen isolated renal mitochondria. Results . Kidneys from SD male (SDM) and female rats (SDF) were divided into cortex (SDMC, FC) and medulla (SDMM, FM). We report higher membrane potential in SDFM compared to SDMM (p<0.001). H2O2 levels were elevated in both the SDFC and SDFM mitochondria compared to SDM (p<0.01), and GPX4 level was significantly increased the SDFM samples. Interestingly, superoxide production was increased in the medulla compared to the cortex for both SDM and SDF, while SOD2 expression was similar. Total SOD activity was increased in SDFC compared to all other groups (p<0.01). ESR showed similar lipid peroxide radical levels in all groups. Antioxidant capacity was reduced in SDFM tissues compared to other groups (p<0.05). Female mitochondria exhibited decreased OCR compared to males, and all OCR parameters were lower in medullary vs cortical mitochondria, independent of sex. Interestingly, calcium uptake was more active in the medulla vs cortex for both males and females, whereas the mitochondrial permeability transition pore (mPTP) opening was recorded earlier in females than males. Conclusions . We report differences in mitochondrial function in the cortex and medulla of young healthy male and female rats, primarily, in their ability to handle reactive oxygen species. The observed sex‐related dissimilarities open new avenues of research aimed at establishing the mechanisms that may affect the predisposition of males and females to kidney disease development later in life.
Background: Atrial natriuretic peptide ( ANP) is a hormone produced primarily in the heart, which induces vasodilation and natriuresis. We showed previously that a knockout of ANP in Dahl SS rat results in hypertension and HFpEF phenotype. There is a gap in knowledge regarding the role of inflammation and mitochondrial function in HFpEF that accompanies SSH. We hypothesize that the ANP deficiency in SSH leads to pressure overload, which affects cardiac inflammation and mitochondrial function. Methods: At 8 weeks of age, male wild type (SS WT ) and Nppa knockout (ANP knockout, SS Nppa-/- ) Dahl SS rats were placed on normal salt ( NS , 0.4% NaCl) or a high salt ( HS , 4% NaCl) for 21 days. Tissues were harvested for histological and Western analysis. TEM was used to obtain electron micrographs. EPR spectroscopy was performed in snap-frozen tissues post injection of POBN. 2-way ANOVA was employed for statistical comparison. Results: Heart-to-body-weight ratio was higher in SS Nppa-/- rats (p<0.001), on NS and HS diet ( p <0.001). SS Nppa-/- rats displayed increases in cardiac fibrosis following HS diet ( p <0.01). EPR demonstrated that SS Nppa-/- hearts exhibit a trend for increased lipid peroxidation compared to SS WT . Cardiac cytokine profile demonstrated an increase in IL-1α, IL-1β, L-6, IL-17, TNF-α, sICAM-1, MIP-1α, MIP-3α, in the SS WT rats fed a HS diet vs NS diet, and lower levels of these in the HS-diet fed SS Nppa-/- rats vs SS WT . HS diet was sufficient to induce increases in mitochondrial area ( p <0.001), and decreases in density ( p 0.001), and overall health score ( p <0.001) in both SS WT and SS Nppa-/- rats, but no genotype-specific differences were reported. We observed changes in fission/fusion proteins: Opa1 expression was elevated in SS Nppa-/- vs SS WT ( p <0.01), and Parkin expression was lower in all rats on a HS diet ( p <0.05). Conclusions: Although SS Nppa-/- rats develop a HFpEF phenotype, exacerbated cardiac fibrosis and higher lipid peroxidation vs SS WT rats, inflammation and overall mitochondrial damage are diminished in the hearts of these animals at day 21 of the HS diet. Further studies are needed to elucidate the mechanisms by which inflammation may affect the development of HFpEF during SS hypertension in a cell-specific and time-dependent manner.
Introduction . Histamine is a regulatory agent involved in the immune response, neurotransmission, and gastric acid secretion, and is produced and released from the mast cells and basophils. Elevated histamine levels and increased expression of histamine metabolizing enzymes have been reported in kidney diseases. The goal of this study is to provide insight into the physiological importance of the histamine‐related pathways in salt‐sensitive hypertension (SSH), a disease accompanied with inflammation‐driven kidney damage. Methods . SSH was induced in Dahl Salt‐Sensitive (DSS) rats by a 3‐week long high salt diet challenge (HS, 4% NaCl); age‐matched normal salt diet (NS, 0.4% NaCl) fed rats were used as a control group. To characterize the expression of histamine receptors, mast cells markers, and histamine metabolism‐related enzymes, Western blot or IHC were performed on renal tissues collected from DSS rats maintained on HS or NS diets for 3 weeks. In order to test the effects of histamine receptor 2 (HR2) inhibition, he DSS rats were injected with a single daily i.p. dose of an HR2 blocker, ranitidine (RAN, 25mg/kg in saline) or saline (VEH), for 3 consecutive days before the switch to a HS diet, and at the end of the 21‐day long HS challenge. Urine and water consumption were assessed in metabolic cages during hours 0‐8 (acute), and 8‐24 post‐injections. At the end of the protocol, GFR was measured, and tissues were harvested. Results . Western blots revealed similar expression of the mast cell markers’ (FCER1A and tryptase) in NS and HS diet fed rats, however, we observed significantly lower histamine decarboxylase (HDC, p=0.002), and higher histamine N‐methyltransferase (HNMT, p=0.035) levels in HS diet fed rats. Renal IHC revealed that expression of HR2 was downregulated, while HR3 and HR4 were upregulated in the collecting ducts of HS diet fed rats. In vivo experiments showed that RAN‐administered rats on NS diet exhibited an acute (8‐24 hr period) decrease in urine output and 24 h water intake on day 1 of injections (p=0.01). We observed trends for an increase in urinary electrolytes, and an overall increase in the excretion of osmolesin RAN vs VEH animals 24 hours post day 1 injection on the NS diet. Post HS challenge, electrolyte excretion, urine flow and water intake were similar between RAN and VEH animals. At the endpoint on HS, GFR between the groups was similar on day 3 post‐injection. Conclusions . Differential expression of HRs, as well as changes in the enzymes responsible for histamine synthesis and metabolism between HS and NS fed rats, indicate a shift in the renal histaminergic tone during SSH development. Similar mast cell levels suggest an alternate, perhaps intrarenal, source of histamine. Our in vivo data show that inhibition of HR2 has effects on urine output and water consumption in SSH. Further research is required to discern the molecular pathways downstream of specific HRs, as well as the consequences of chronic administration of HR‐specific pharmacology, in renal pathophysiology.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.