Does aliskiren protect the kidney following ischemia reperfusion injury?

Delayed Graft Function and the Renin-angiotensin System

Delayed graft function (DGF) is a form of acute kidney injury (AKI) and a common complication following kidney transplantation. It adversely influences patient outcomes increases the financial burden of transplantation, and currently, no specific treatments are available. In developing this form of AKI, activation of the renin-angiotensin system (RAS) has been proposed to play an important role. In this review, we discuss the role of RAS activation and its contribution to the pathophysiology of DGF following the different stages of the transplantation process, from procurement and ischemia to transplantation into the recipient and including data from experimental animal models. Deceased kidney donors, whether during cardiac or brain death, may experience activation of the RAS. That may be continued or further potentiated during procurement and organ preservation. Additional evidence suggests that during implantation of the kidney graft and reperfusion in the recipient, the RAS is activated and may likely remain activated, extrapolating from other forms of AKI where RAS overactivity is well documented. Of particular interest in this setting is the status of angiotensin-converting enzyme 2, a key RAS enzyme essential for the metabolism of angiotensin II and abundantly present in the apical border of the proximal tubules, which is the site of predominant injury in AKI and DGF. Interventions aimed at safely downregulating the RAS using suitable shorter forms of angiotensin-converting enzyme 2 could be a way to offer protection against DGF.

The Effect of Nerolidol Renal Dysfunction following Ischemia-Reperfusion Injury in the Rat

Efforts to decrease the deleterious effects of renal ischemia-reperfusion injury (IRI) are ongoing. Recently, there has been increasing interest in using natural phytochemical compounds as alternative remedies in several diseases. Nerolidol is a natural product extracted from plants with floral odors and has been proven to be effective for the treatment of some conditions. We investigated the effect of nerolidol in a rat model of renal IRI. Nerolidol was dissolved in a vehicle and administered orally as single daily dose of 200 mg/kg for 5 days prior to IRI and continued for 3 days post IRI. G-Sham (n = 10) underwent sham surgery, whereas G-IRI (n = 10) and G-IRI/NR (n = 10) underwent bilateral warm renal ischemia for 30 min and received the vehicle/nerolidol, respectively. Renal functions and histological changes were assessed before starting the medication, just prior to IRI and 3 days after IRI. Nerolidol significantly attenuated the alterations in serum creatinine and urea, creatinine clearance, urinary albumin and the urinary albumin-creatinine ratio. Nerolidol also significantly attenuated the alterations in markers of kidney injury; proinflammatory, profibrotic and apoptotic cytokines; oxidative stress markers; and histological changes. We conclude that nerolidol has a renoprotective effect on IRI-induced renal dysfunction. These findings might have clinical implications.

View of the Renin-Angiotensin System in Acute Kidney Injury Induced by Renal Ischemia-Reperfusion Injury

Renal ischemia-reperfusion injury (RIRI) is a sequence of complicated events that is defined as a reduction of the blood supply followed by reperfusion. RIRI is the leading cause of acute kidney injury (AKI). Among the diverse mediators that take part in RIRI-induced AKI, the renin-angiotensin system (RAS) plays an important role via conventional (angiotensinogen, renin, angiotensin-converting enzyme (ACE), angiotensin (Ang) II, and Ang II type 1 receptor (AT1R)) and nonconventional (ACE2, Ang 1-7, Ang 1-9, AT2 receptor (AT2R), and Mas receptor (MasR)) axes. RIRI alters the balance of both axes so that RAS can affect RIRI-induced AKI. In overall, the alteration of Ang II/AT1R and AKI by RIRI is important to consider. This review has looked for the effects and interactions of RAS activities during RIRI conditions.

The effect of neprilysin and renin inhibition on the renal dysfunction following ischemia-reperfusion injury in the rat

The natriuretic peptide (NP) system counter-regulates the renin-angiotensin system (RAS), so enhancing the activity of natriuretic peptides (NPs) may be beneficial in conditions when RAS is activated such as ischemia-reperfusion injury (IRI). Neprilysin is the key enzyme responsible for the degradation of NPs. The effects of neprilysin inhibition or the combination of neprilysin inhibition and RAS inhibition on renal IRI-induced renal dysfunction have not been investigated yet. To investigate this, rats underwent sham surgery or bilateral IRI for 20 min. G-Als, G-Scb, and G-Als+Scb underwent similar protocol but received aliskiren (renin inhibitor), sacubitril (neprilysin inhibitor) or a combination of both pre- and post-IRI, respectively. IRI caused significant alterations in all renal functional parameters, markers of acute renal injury, pro-inflammatory and pro-fibrotic cytokines, and histological features. All these alterations were significantly attenuated in G-Als, G-Scb, and G-Als+Scb. The attenuations in the alterations in serum creatinine, creatinine clearance, and histological features were larger in G-Als+Scb compared to either G-Als or G-Scb. We conclude that RAS blockade by a renin inhibitor (aliskiren) or neprilysin inhibition by sacubitril separately led to significant attenuation in the renal IRI-induced renal dysfunction. The combination of aliskiren and sacubitril was more effective than either one alone.

Functional and molecular evaluation of using aliskiren during acute and chronic partial ureteral obstruction in rat solitary kidney

AIMS

To study the effect of direct renin inhibitor (aliskiren) on the renal function during acute and chronic partial ureteral obstruction (PUO) in rat solitary kidney.

MAIN METHODS

Sixty male Sprague-Dawley rats were randomly allocated into three groups (20 rats each); sham, PUO and aliskiren groups. Right nephrectomy was performed in all groups. Rats in PUO and aliskiren groups were subjected to left PUO and received no treatment and aliskiren (10 mg/kg, orally, once per day till sacrification), respectively. Blood samples were then collected for biochemical measurements. Ten rats from each group were sacrificed after two weeks, while the remaining rats were sacrificed after four weeks. Left kidneys were harvested for histopathological examination, BCL-2, interleukin (IL)-6, transforming growth factor (TGF)-β1, collagen I and fibronectin relative gene expression and assessment of glutathione (GSH), superoxide dismutase (SOD), malondialdehyde (MDA) and nitric oxide (NO) activity.

KEY FINDINGS

After two and four weeks of PUO, aliskiren significantly recompensed the rise of serum creatinine (Scr) and blood urea nitrogen (BUN). Aliskiren also revealed significantly better histopathological results regarding cortical and medullary necrosis, regeneration and inflammatory cell infiltration. Aliskiren group showed statistically significant up-regulation of BCL-2 and down-regulation of IL-6, TGF-β1, collagen I and fibronectin relative gene expression. Aliskiren significantly increased GSH and SOD activity and reduced MDA and NO activity. Moreover, aliskiren administration for four weeks after PUO significantly yielded more renoprotective effect compared to its administration for two weeks.

SIGNIFICANCE

Aliskiren ameliorates the deterioration of the renal function during acute and chronic PUO in a solitary kidney.

Aliskiren, Fosinopril, and Their Outcome on Renin-Angiotensin-Aldosterone System (RAAS) in Rats with Thyroid Dysfunction

BACKGROUND AND OBJECTIVES

Thyroid hormones have an important role in the growth and development of various tissues including the kidney, which is the major site of renin release and the consequent angiotensin and aldosterone formation. Therefore any derangement in thyroid function can result in abnormal functioning in the renin-angiotensin-aldosterone system. The current study was undertaken to find the impact of using a direct renin inhibitor (Aliskiren) and an angiotensin-converting enzyme inhibitor (Fosinopril) on the components of the renin-angiotensin-aldosterone system (RAAS) in rats with thyroid dysfunctions.

METHOD

Forty-two male albino rats were divided into three subgroups. First group (6 rats) served as control. Second group (18 rats) served as hyperthyroid group (6 rats positive control, 6 rats given Aliskiren, and 6 rats given Fosinopril). Third group (18 rats) served as hypothyroid group (6 rats positive control, 6 rats given Aliskiren, and 6 rats given Fosinopril). Induction of hyperthyroidism and hypothyroidism was done through daily oral administration of L-Thyroxine and Propylthiouracil, respectively. On day 40 of the study, the rats were sacrificed and blood was collected for estimation of renin, angiotensin I, angiotensin II, aldosterone, TSH, T₃, and T₄. The collected blood samples were also used for estimation of levels blood urea, serum creatinine, liver enzymes, and serum electrolytes. Blood pressure and urine collection were done on days 1 and 40. The collected urine was used for estimation of urine flow, sodium excretion, and potassium excretion rates.

RESULTS

In hypothyroid induced rats, serum renin level dropped as expected, while the use of Aliskiren and Fosinopril on these hypothyroid rats raised renin level due to the feedback mechanism. Both angiotensin I and II were significantly (P <0.05) lower than normal levels in the hypothyroid rats, unlike the level of aldosterone, which was higher than normal level. There was nonsignificant lowering in BP (systolic, diastolic, and mean BP) in the hypothyroid rats. Treatment of these rats with Aliskiren and Fosinopril did not lower the blood pressure more than normal when compared to the hypothyroid group. The hypothyroid rats also showed a decrease in level of serum creatinine. In hyperthyroid rats, there was a rise in levels of serum renin, angiotensin II, and aldosterone; nevertheless, the increase in angiotensin I level was significant. The use of Aliskiren and Fosinopril increased the level of renin nonsignificantly (decreased angiotensin I significantly). Hyperthyroid rats showed a significant increase in systolic, diastolic, and mean blood pressure. Both Aliskiren and Fosinopril increased urine flow, Na⁺ excretion, and K⁺ excretion rates. Aliskiren was better at reducing the high blood pressure.

CONCLUSION

Aliskiren and Fosinopril in hyperthyroid rats decreased serum angiotensin I, angiotensin II, and aldosterone. Blockade of renin and inhibition of angiotensin-converting enzyme both resulted in a rebound increase in level of renin in hypothyroid rats. Aliskiren is better at controlling blood pressure in hyperthyroid rats. Urine flow, sodium excretion, and potassium excretion rates were improved by the use of Aliskiren and Fosinopril in hyperthyroid rats.

Alda-1, an aldehyde dehydrogenase-2 agonist, causes deterioration in renal functions following ischemia-reperfusion injury due to crystalline nephropathy

Renal ischemia-reperfusion injury (IRI) induces the production of aldehydes which are detoxified by aldehyde dehydrogenases (ALDHs). Alda-1 is a selective ALDH2 agonist and its protective effect was demonstrated in several conditions. The effect of Alda-1 on the kidney or on renal IRI was not investigated. We investigated the effect of Alda-1 on the renal dysfunction following IRI. Wistar rats underwent left IRI for 40 min. Group-Alda (n = 11) received Alda-1 starting 24 h before IRI and continued for 7 days thereafter when renal functions were measured. Group-Vx (n = 11) underwent similar protocol but received the dissolvent. Alda-1 did not affect renal blood flow or glomerular filtration rate in the left ischemic kidney in Group-Alda compared to Group-Vx (3.05 ± 0.50 vs. 3.53 ± 0.70, and 0.40 ± 0.06 vs. 0.51 ± 0.08, respectively, p > .05 for both). However, left renal fractional sodium excretion was higher in Group-Alda (2.80 ± 0.43 vs. 1.37 ± 0.36, p = .02). Alda-1 also adversely affected the gene expressions of kidney injury molecule-1 and neutrophil gelatinase-associated lipocalin (217 ± 38 vs. 99 ± 13 and 49 ± 13 vs. 20 ± 5, respectively, p < .05 for both) and the alterations in tumor necrosis factor-α, transforming growth factor-β1, plasminogen activator inhibitor-1, fibronectin 1 and p53 (4.4 ± 0.9 vs. 2.1 ± 0.3, 1.5 ± 0.1 vs. 1.1 ± 0.1, 30.0 ± 2.7 vs. 11.7 ± 2.3, 3.6 ± 0.4 vs. 2.1 ± 0.2 and 1.3 ± 0.1 vs. 0.9 ± 0.07, respectively, p ≤ .05 for all). This was associated with intratubular crystal deposition suggestive of crystalline nephropathy. Alda-1 exacerbated the IRI-induced renal tubular dysfunction and alterations in markers of acute kidney injury, biomarkers of inflammation, fibrosis and apoptosis and this was associated with intratubular crystal deposition suggestive of crystalline nephropathy.

The renin inhibitor aliskiren protects rat lungs from the histopathologic effects of fat embolism

BACKGROUND

Fat embolism (FE) and the consequent FE syndrome occurring after trauma or surgery can lead to serious pulmonary injury, including ARDS and death. Current treatment of FE syndrome is limited to supportive therapy. We have shown in a rat model that the renin angiotensin system plays a significant role in the pathophysiology of FE because drugs interfering with the renin angiotensin system, captopril and losartan reduce the histopathologic pulmonary damage. The purpose of the current study was to determine if inhibition of renin by aliskiren, an FDA-approved drug for treating hypertension, would produce effective protection in the same model.

METHODS

The FE model used intravenous injection of the neutral fat triolein in unanesthetized rats. Intraperitoneal injections of saline or aliskiren at either 50 or 100 mg/kg were performed 1 hour after FE induction via triolein. Rats were euthanized at 48 hours, and various histologic stains were used to examine the lungs.

RESULTS

(1) Fibrosis: rats treated with triolein showed significant fibrotic changes with increased collagen and myofibroblast activation (p < 0.0001 for both trichrome and α-smooth muscle actin staining). Aliskiren blocked this inflammatory and profibrotic process to a level indistinguishable from the controls (p < 0.0001 for both trichrome and α-smooth muscle actin staining). (2) Fat: rats treated with triolein showed a statistically significant increase in fat (p = 0.0006). Subsequent aliskiren administration at both doses reduced the size, distribution, and amount of fat droplets (low dose, p = 0.0095; high dose, p = 0.0028). (3) Vessel patency: the low dose of aliskiren blocked the reduction of lumen patency observed after triolein administration (p = 0.0058).

CONCLUSIONS

Aliskiren protected the lungs of rats from gross and histopathologic FE-induced pulmonary damage at 48 hours. Clinical implications include the use of aliskiren both prophylactically (before certain orthopedic procedures) and therapeutically (after severe trauma) to prevent the consequent severe pulmonary pathologic sequelae.

Inhibition of Angiotensin-II Production Increases Susceptibility to Acute Ischemia/Reperfusion Arrhythmia

BACKGROUND Myocardial ischemia and reperfusion lead to impairment of electrolyte balance and, eventually, lethal arrhythmias. The aim of this study was to investigate the effects of pharmacological inhibition of angiotensin-II (Ang-II) production on heart tissue with ischemia-reperfusion damage, arrhythmia, and oxidative stress. MATERIAL AND METHODS Rats were divided into 4 groups: only ischemia/reperfusion (MI/R), captopril (CAP), aliskiren (AL), and CAP+AL. The drugs were given by gavage 30 min before anesthesia. Blood pressure and electrocardiography (ECG) were recorded during MI/R procedures. The heart tissue and plasma was kept so as to evaluate the total oxidant (TOS), antioxidant status (TAS), and creatine kinase-MB (CK-MB). RESULTS Creatine kinase-MB was not different among the groups. Although TAS was not affected by inhibition of Ang-II production, TOS was significantly lower in the CAP and/or AL groups than in the MI/R group. Furthermore, oxidative stress index was significantly attenuated in the CAP and/or AL groups. Captopril significantly increased the duration of VT during ischemia; however, it did not have any effect on the incidence of arrhythmias. During reperfusion periods, aliskiren and its combinations with captopril significantly reduced the incidence of other types of arrhythmias. Captopril alone had no effect on the incidence of arrhythmias, but significantly increased arrhythmias score and durations of arrhythmias during reperfusion. MAP and heart rate did not show changes in any groups during ischemic and reperfusion periods. CONCLUSIONS Angiotensin-II production appears to be associated with elevated levels of reactive oxygen species, but Ang-II inhibitions increases arrhythmia, mainly by initiating ventricular ectopic beats.

Sex differences in renin response and changes of capillary diameters after renal ischemia/reperfusion injury

Activation of the RAS has a crucial role in the progression of ischemia/reperfusion-associated CAD. The regulation of RAS differs in the two genders. However, the extent of gender differences and locations of renin production have not been revealed yet. We investigated in vivo the local renin production in the two genders during ischemia/reperfusion injury. In male and female Wistar rats, renal ischemia was induced followed by a reperfusion period of two, eight, 16, 24, or 48 h. We applied flow cytometry to measure renin content and multiphoton imaging to visualize renin granules and changes of peritubular diameters in vivo during ischemia/reperfusion. Renin content decreased in CD in the first eight h of reperfusion; however, after 16 h, its amount increased. In males, the production of renin was more pronounced, and the duration of vasoconstriction was longer with a subsequent phase of vessel hyperdilation compared to females. Renal ischemia/reperfusion injury induces renin response not only in the JGA, but also in the CD segment. Renin production is more explicit in males than in females which, via increased angiotensin II production, might explain the different dynamism of renal vessel regulation between the two genders.

Aliskiren - a promising strategy for ovarian ischemia/reperfusion injury protection in rats via RAAS

The aim of this study was to evaluate the effects of aliskiren, direct renin inhibitor, as an antioxidant and tissue protective agent and evaluate the molecular, biochemical, and histopathological changes in experimental ischemia and ischemia/reperfusion injury in rat ovaries. Forty-eight female rats were randomly divided into eight groups: in Group 1, only sham operation was performed. Group 2 received 100 mg/kg aliskiren and sham operated. In Group 3, 3 h-period of bilateral ovarian ischemia was applied. Group 4 received a 3-h period of ischemia followed by 3 h of reperfusion. Groups 5 and 6 received 50 and 100 mg/kg, respectively, of aliskiren and bilateral ovarian ischemia was applied (after a 3-h period of ischemia, both ovaries were surgically removed). To Groups 7 and 8, 50 and 100 mg/kg of aliskiren were administered, respectively, and the induction of ischemia was performed. At the end of a 3-h period of ischemia, bilateral vascular clips were removed, and 3 h of reperfusion continued. After the experiments, IL-1β, IL-6, TNF-α, and iNOS mRNA expressions and SOD, GSH, MDA, renin, and angiotensin-II levels were determined and histopathological changes were examined in rat ovaries. Aliskiren treatment normalized excessive changes in cytokine and oxidative stress markers in both ischemia and ischemia/reperfusion injury. Histopathologically, treatment with aliskiren ameliorated the development of ischemia and/or ischemia/reperfusion tissue injury. This study concluded that aliskiren treatment is effective in reversing ischemia and/or ischemia/reperfusion induced ovary damage via the improvement of oxidative stress, reduction of inflammation, and suppression of the renin-angiotensin aldosterone system.

Renoprotective effects of aliskiren on adenine-induced tubulointerstitial nephropathy: possible underlying mechanisms

The present study investigated the possible renoprotective effect of direct renin inhibitor (aliskiren) on renal dysfunctions, as well as its underlying mechanisms in rat model of adenine-induced tubulointerstitial nephropathy. Forty male Sprague-Dawley rats were randomized into 4 groups; normal group, aliskiren group (normal rats received 10 mg/kg aliskiren), adenine group (animals received high-adenine diet for 4 weeks and saline for 12 weeks), and adenine + aliskiren group (animals received adenine for 4 weeks and aliskiren 10 mg/kg for 12 weeks). It was found that adenine caused significant decrease in body mass, Hb, HR, serum Ca(2+), eNOS and nrf2 expression, GSH, and catalase in kidney tissues with significant increase in arterial blood pressure (ABP), serum creatinine, BUN, plasma renin activity (PRA), K(+) and P, urinary albumin excretion (UAE), caspase-3, and MDA (lipid peroxidation marker) in kidney tissues compared to normal group (p < 0.05). Administration of aliskiren caused significant improvement in all studied parameters compared to adenine group (p < 0.05). We concluded that aliskiren has renoprotective effect against adenine-induced nephropathy. This might be due to inhibition of PRA, attenuation of oxidative stress, activation of Nrf2 and eNOS genes, and suppression of caspase-3.

Aliskiren restores renal AQP2 expression during unilateral ureteral obstruction by inhibiting the inflammasome

Ureteral obstruction is associated with reduced expression of renal aquaporins (AQPs), urinary concentrating defects, and an enhanced inflammatory response, in which the renin-angiotensin system (RAS) may play an important role. We evaluated whether RAS blockade by a direct renin inhibitor, aliskiren, would prevent the decreased renal protein expression of AQPs in a unilateral ureteral obstruction (UUO) model and what potential mechanisms may be involved. UUO was performed for 3 days (3UUO) and 7 days (7UUO) in C57BL/6 mice with or without aliskiren injection. In 3UUO and 7UUO mice, aliskiren abolished the reduction of AQP2 protein expression but not AQP1, AQP3, and AQP4. mRNA levels of renal AQP2 and vasopressin type 2 receptor were decreased in obstructed kidneys of 7UUO mice, which were prevented by aliskiren treatment. Aliskiren treatment was also associated with a reduced inflammatory response in obstructed kidneys of UUO mice. Aliskiren significantly decreased mRNA levels of several proinflammatory factors, such as transforming growth factor-β and tumor necrosis factor-α, seen in obstructed kidneys of UUO mice. Interestingly, mRNA and protein levels of the NOD-like receptor family, pyrin domain-containing 3 (NLRP3) inflammasome components apoptosis-associated speck-like protein containing a caspase recruitment domain, caspase-1, and IL-1β were dramatically increased in obstructed kidneys of 7UUO mice, which were significantly suppressed by aliskiren. In primary cultured inner medullary collecting duct cells, IL-1β significantly decreased AQP2 expression. In conclusions, RAS blockade with the direct renin inhibitor aliskiren increased water channel AQP2 expression in obstructed kidneys of UUO mice, at least partially by preventing NLRP3 inflammasome activation in association with ureteral obstruction.