BackgroundSGLT2 inhibitors reduce the risk of heart failure (HF) mortality and morbidity, regardless of the presence or absence of diabetes, but the mechanisms underlying this benefit remain unclear. Experiments with nondiabetic HF rats tested the hypothesis that the SGLT2 inhibitor empagliflozin (EMPA) inhibits proximal tubule (PT) NHE3 activity and improves renal salt and water handling.MethodsMale Wistar rats were subjected to myocardial infarction or sham operation. After 4 weeks, rats that developed HF and sham rats were treated with EMPA or untreated for an additional 4 weeks. Immunoblotting and quantitative RT-PCR evaluated SGLT2 and NHE3 expression. Stationary in vivo microperfusion measured PT NHE3 activity.ResultsEMPA-treated HF rats displayed lower serum B-type natriuretic peptide levels and lower right ventricle and lung weight to tibia length than untreated HF rats. Upon saline challenge, the diuretic and natriuretic responses of EMPA-treated HF rats were similar to those of sham rats and were higher than those of untreated HF rats. Additionally, EMPA treatment prevented GFR decline and renal atrophy in HF rats. PT NHE3 activity was higher in HF rats than in sham rats, whereas treatment with EMPA markedly reduced NHE3 activity. Unexpectedly, SGLT2 protein and mRNA abundance were upregulated in the PT of HF rats.ConclusionsPrevention of HF progression by EMPA is associated with reduced PT NHE3 activity, restoration of euvolemia, and preservation of renal mass. Moreover, dysregulation of PT SGLT2 may be involved in the pathophysiology of nondiabetic HF.

Dipeptidyl peptidase IV (DPPIV) inhibitors are antidiabetic agents that exert renoprotective actions independently of glucose lowering. Cardiac dysfunction is one of the main outcomes of chronic kidney disease (CKD); however, the effects of DPPIV inhibition on cardiac impairment during CKD progression remain elusive. This study investigated whether DPPIV inhibition mitigates cardiac dysfunction and remodeling in rats with a 5/6 renal ablation and evaluated if these effects are associated with changes in the cardiac renin-angiotensin system (RAS). To this end, male Wistar rats underwent a 5/6 nephrectomy (Nx) or sham operation, followed by an 8-week treatment period with the DPPIV inhibitor sitagliptin (IDPPIV) or vehicle. Nx rats had lower glomerular filtration rate, overt albuminuria and higher blood pressure compared to sham rats, whereas CKD progression was attenuated in Nx + IDPPIV rats. Additionally, Nx rats exhibited cardiac hypertrophy and fibrosis, which were associated with higher cardiac DPPIV activity and expression. The sitagliptin treatment prevented cardiac fibrosis and mitigated cardiac hypertrophy. The isovolumic relaxation time (IRVT) was higher in Nx than in sham rats, which was suggestive of CKD-associated-diastolic dysfunction. Sitagliptin significantly attenuated the increase in IRVT. Levels of angiotensin II (Ang II) in the heart tissue from Nx rats were higher while those of angiotensin-(1-7) Ang-(1-7) were lower than that in sham rats. This cardiac hormonal imbalance was completely prevented by sitagliptin. Collectively, these results suggest that DPPIV inhibition may delay the onset of cardiovascular impairment in CKD. Furthermore, these findings strengthen the hypothesis that a crosstalk between DPPIV and the renin-angiotensin system plays a role in the pathophysiology of cardiorenal syndromes.

Sodium-glucose cotransporter 2 (SGLT2) inhibitors reduce the risk of heart failure (HF) mortality and morbidity, regardless of the presence or absence of diabetes, but the mechanisms underlying this benefit remain unclear. We tested the hypothesis that the SGLT2 inhibitor empagliflozin inhibits proximal tubule (PT) NHE3 activity and improves renal salt and water handling in nondiabetic rats with HF. Male Wistar rats were subjected to myocardial infarction or sham operation. After four weeks, rats that developed HF and sham rats were treated with empagliflozin (EMPA) or untreated for an additional four weeks. EMPA-treated HF rats displayed lower levels of serum BNP and lower right ventricle and lung weight to tibia length than untreated HF rats. Upon saline challenge, the diuretic and natriuretic responses of EMPA-treated HF rats were similar to those of sham rats and were higher than those of untreated HF rats. Additionally, EMPA treatment normalized the glomerular filtration rate and proteinuria in HF rats. PT NHE3 activity was higher in HF rats than in sham rats, whereas treatment with EMPA markedly reduced NHE3 activity. Unexpectedly, SGLT2 function and protein and mRNA abundance were upregulated in the PT of HF rats. Collectively, our data show that the prevention of HF progression by empagliflozin is associated with inhibition of PT NHE3 activity and restoration of euvolemia. Moreover, we propose that the dysregulation of PT SGLT2 may be involved in the pathophysiology of nondiabetic HF.

These findings indicate that the modulation of Ca2+ handling may be one of the molecular mechanisms underlying the effect of salt intake on myocardial function in hypertension.

This study investigated the molecular mechanisms underlying the antiproteinuric effect of DPP4 inhibition in 5/6 renal ablation rats and tested the hypothesis that the urinary activity of DPP4 correlates with chronic kidney disease (CKD) progression. Experiments were conducted in male Wistar rats who underwent 5/6 nephrectomy (Nx) or sham operation, followed by 8 weeks of treatment with the DPP4 inhibitor (DPP4i) sitagliptin or vehicle. Proteinuria increased progressively in Nx rats throughout the observation period. This increase was remarkably mitigated by sitagliptin. Higher levels of proteinuria in Nx rats compared to control rats were accompanied by higher urinary excretion of retinol-binding protein 4 (RBP4), a marker of tubular proteinuria, as well as higher urinary levels of podocin, a marker of glomerular proteinuria. RBP4 and podocin were not detected in the urine of Nx+DPP4i rats. Tubular and glomerular proteinuria was associated with the reduced expression of megalin and podocin in the renal cortex of Nx rats. Sitagliptin treatment partially prevented this decrease. Besides, the angiotensin II renal content was significantly reduced in the Nx rats that received sitagliptin compared to vehicle-treated Nx rats. Interestingly, both urinary DPP4 activity and abundance increased progressively in Nx rats. Additionally, urinary DPP4 activity correlated positively with serum creatinine levels, proteinuria, and blood pressure. Collectively, these results suggest that DPP4 inhibition ameliorated both tubular and glomerular proteinuria and prevented the reduction of megalin and podocin expression in CKD rats. Furthermore, these findings suggest that urinary DPP4 activity may serve as a biomarker of renal disease and progression.

The ACE/Ang II and ACE2/Ang-(1-7) pathways are coexpressed in most tissues. The balance between these pathways determines, at least in part, whether tissue damage will occur in response to pathological stimuli. This study tested the hypothesis that male sex and high blood pressure are associated with ACE/ACE2 imbalance in the lungs. Experiments were conducted in male and female Wistar rats and spontaneously hypertensive rats (SHRs). Lung ACE and ACE2 gene expression was also evaluated in normotensive and hypertensive humans using the Genotype-Tissue Expression (GTEx) project. Compared to Wistar rats and female SHRs, male SHRs displayed reduced lung ACE2 mRNA, ACE2 protein abundance and ACE2 activity, and increased Ang II concentration. Lung ACE mRNA levels were higher in male SHRs than in Wistar rats, whereas lung ACE protein abundance and activity were similar among the four groups of rats. Lung Ang-(1-7) concentration was higher in female than in male SHRs (89 ± 17 vs. 43 ± 2 pg/g, P < 0.05). Lung ACE to ACE2 mRNA expression in hypertensive patients was significantly higher than that in normotensive subjects. Taken together, these results demonstrate that male hypertensive rats display imbalance between the ACE/Ang II and ACE2/Ang-(1-7) pathways in the lungs mainly attributable to ACE2 downregulation. Further studies should be conducted to investigate whether this imbalance between ACE/ACE2 may promote and accelerate lung injury in respiratory infections, including COVID-19.

Sodium‐glucose cotransporter 2 (SGLT2) inhibitors improve glycemic control by suppressing glucose reuptake in the renal proximal tubule (PT). Primarily designed as antidiabetic agents, these drugs also reduce cardiovascular death and hospitalization for heart failure (HF), regardless of the presence or absence of type 2 diabetes. However, the mechanisms underlying the cardioprotective effects of SGLT2 inhibitors remain unknown. Given the importance of the cardiorenal axis in HF care, this study aimed to test the hypothesis that the SGLT2 inhibitor empagliflozin (EMPA) is capable of exerting renoprotective effects in the setting of nondiabetic HF. To this end, male Wistar rats were subjected to ligation of the anterior descending coronary artery or sham operation. Four weeks after surgery, rats were fed normal chow, with or without EMPA, for an additional 4 weeks. Compared with sham‐groups, HF rats treated with EMPA had similar serum BNP levels, whereas cardiac dysfunction deteriorated it further in HF rats (Sham: 0.5 ± 0.1; Sham+EMPA: 0.5 ± 0.1; HF: 2.1 ± 0.3; HF+EMPA: 0.9 ± 0.1 ng/mL). Additionally, HF rats exhibited an increase in lung (Sham: 3.2 ± 1.5; Sham+EMPA: 31.8 ± 1.1; HF: 44.7 ± 3.3; HF+EMPA: 32.7 ± 1.7 mg/mm) and right ventricle (Sham: 6.3 ± 0.2; Sham+EMPA: 5.2 ± 0.2; HF: 8.9 ± 1.0; HF+EMPA: 6.4 ± 0.3 mg/mm) mass. Renal function was impaired in HF rats as evidenced by low glomerular filtration rate (GFR) and high levels of plasma urea and urinary protein excretion. However, EMPA treatment restored these parameters to sham rats levels [(GFR, Sham: 6.5 ± 0.2; Sham+EMPA: 7.7 ± 0.6; HF: 4.5 ± 0.4; HF+EMPA: 7.7 ± 0.4 mL/min/kg) (Plasma urea, Sham: 37 ± 1; Sham+EMPA: 38 ± 2; HF: 48 ± 2; HF+EMPA: 39 ± 1 mg/dL) (Urine protein to creatinine ratio, Sham: 1.2 ± 0.1; Sham+EMPA: 1.0 ± 0.1; HF: 1.8 ± 0.1; HF+EMPA: 1.3 ± 0.1)]. Furthermore, EMPA prevented reduction of hematocrit in HF rats (Sham: 48.7 ± 0.3; Sham+EMPA: 49.5 ± 0.7; HF: 45.8 ± 0.5; HF+EMPA: 49.7 ± 0.4 %). In vivo stationary microperfusion showed that EMPA reduced Na+/H+ exchanger isoform 3 (NHE3) activity in HF rats, similar to sham‐groups (Sham: 2.05 ± 0.04; Sham+EMPA: 1.40 ± 0.05; HF: 4.36 ± 0.08; HF+EMPA: 1.54 ± 0.05 nmol/cm2). Collectively, these findings demonstrate that SGLT2 inhibition ameliorates renal dysfunction and improves the volemic status of nondiabetic HF rats. Support or Funding Information Supported by FAPESP and CAPES.

Objective: The transverse aortic constriction (TAC) model mimics cardiac hypertrophy (CH) caused by hypertension. The model of kidney injury by consumption of soluble sodium oxalate (SO) in the feed also mimics lesions similar to hypertension. Our objective is to test the hypothesis that mice submitted to TAC and gavage with SO will represent an effective model of cardiorenal dysfunction. Design and method: Forty male C57BL mice were randomized into 4 groups: sham-operated animals that received gavage for 15 days with water or sodium oxalate (SO) and animals that received TAC and gavage also for 15 days with water or SO. In the fourth and eighth weeks, an echocardiogram was evaluated. Metabolic cage, direct hemodynamic recording, and histological analysis were performed in the eighth week. Data were analyzed using 1-2 way ANOVA followed by Bonferroni's posthoc, considering significant differences for p<0.05. Results: The TAC+SO group showed increased serum urea (SHAM:37.85±3 vs. TAC+SO:49.9±2.6mg/dL, p = 0.02) and, compared to the SHAM+SO group, a decrease in water consumption and water balance. The TAC+SO group had the highest systolic (SHAM:122.4±5.2 vs. TAC+SO:160±5.2mmHg, p<0.01), diastolic (SHAM:78.9±5.4 vs. TAC+SO:105±5mmHg, p<0.01) and mean pressure (SHAM:100.6±5 vs. TAC+SO:132±4.8mmHg, p<0.01) values. Compared to the SHAM+SO and the SHAM, TAC+SO showed increased double product (DP) (SHAM:64.6 ± 4.7 vs. SHAM+SO:62.7±3.3 vs. TAC+SO:96.6±5.2, p<0.01). The TAC group had the highest weight of corrected ventricles (SHAM:6.73 ± 0.1 vs.TAC:10±0.6mg/mm, p<0.01), and the TAC+SO group had the highest pulmonary congestion index. The SHAM+SO group showed increased autonomic modulation and HR variability, while the TAC+SO group showed an important reduction. TAC animals had the highest mean BP variability. The reflex tachycardia of the TAC, SHAM+SO and TAC+SO groups was very reduced, and only the TAC+SO group had a reduction in the alpha index. Conclusions: TAC surgery caused CH, reduction in reflex tachycardia, and changes in autonomic modulation. Gavage with SO for 15 days promoted primary renal injury, and separately it was able to increase autonomic modulation. TAC surgery associated with SO gavage caused greater cardiac and renal dysfunction.