The Sigma-1 Receptor Is a Novel Target for Improving Cold Preservation in Rodent Kidney Transplants

Kidney transplantation is the preferred treatment for patients with end-stage kidney disease. Maintaining organ viability between donation and transplantation, as well as minimizing ischemic injury, are critically important for long-term graft function and survival. Moreover, the increasing shortage of transplantable organs is a considerable problem; thus, optimizing the condition of grafts is a pivotal task. Here, rodent models of kidney transplantation and cold storage were used to demonstrate that supplementation of a preservation solution with Sigma-1 receptor (S1R) agonist fluvoxamine (FLU) reduces cold and warm ischemic injury. Post-transplant kidney function was improved, histological injury was mitigated, and mRNA expression of two tubular injury markers-kidney injury molecule-1 and neutrophil gelatinase-associated lipocalin-was robustly reduced. In addition, renal inflammation was diminished, as shown by reduced leukocyte infiltration and pro-inflammatory cytokine expression. In the cold ischemia model, FLU ameliorated structural injury profoundly after 2 h as well as 24 h. The reduced number of TUNEL-positive and Caspase 3-positive cells suggests the anti-apoptotic effect of FLU. None of these beneficial effects of FLU were observed in S1R^-/- mice. Of note, organ damage in FLU-treated kidneys after 24 h of cold storage was similar to just 2 h without FLU. These results indicate that S1R agonists can prolong storage time and have great potential in improving organ preservation and in alleviating the problem of organ shortages.

MO282: Sigma-1 Receptor Agonists are Protective in Renal Ischemia/Reperfusion Injury

BACKGROUND AND AIMS

Renal ischemia/reperfusion injury (IRI)-induced acute kidney injury is associated with high mortality and morbidity and effective therapies are lacking. We previously showed that Sigma-1 receptor (S1R) agonist fluvoxamine treatment is protective against renal IRI (Hosszu et al, 2017). Here in a rat model, we studied the renoprotective effect of specific, high affinity S1R agonists focusing on the S1R-Akt-eNOS signaling pathway and renal vasoregulation.

METHOD

8-week old male Wistar rats (n = 8/group) were subjected to 50 min unilateral ischemia with contralateral nephrectomy, kidney tissue was harvested 24 h after reperfusion. 30 min prior to the ischemic insult rats were treated i.p. as follows: (i) isotonic saline as vehicle; (ii) highly specific, high affinity S1R agonist SA-4503; or (iii) SA-4503 + S1R antagonist NE100. Sham-operated rats were used as controls. Renal functional parameters (BUN, serum creatinine, serum aspartate aminotransferase, kidney injury molecule 1 (Kim1), neutrophil gelatinase-associated lipocalin (Ngal) were evaluated. Structural damage was assessed on PAS-stained kidney sections. Renal S1R, phospho-Akt and phospho-eNOS, Hif-1α protein levels and serum nitric oxide (NO) concentration were measured. In vitro experiments were performed on HK2 human proximal tubular epithelial cells treated with a 10 µM dose of S1R agonist SA-4503 or PRE-084.

RESULTS

Impaired kidney function and structural damage after I/R were ameliorated by SA-4503. Expressions of early and sensitive tubular injury markers Kim1 and Ngal were markedly less elevated in SA-4503-treated rats. This recovery was blocked with the addition of the S1R antagonist NE100. S1R, phospho-Akt and phospho-eNOS protein levels were significantly elevated in the kidneys of SA-4503 treated rats. Vasodilator nitric oxide concentration was reduced in the kidney after IRI, but returned to control levels in SA-4503-treated rats. Treatment with S1R agonists SA-4503 and PRE-084 increased the NO production of HK-2 cells.

CONCLUSION

The specific and high affinity S1R agonist SA-4503 acts directly on proximal tubular cells by activating the S1R-NOS system. Thereby SA-4503 is renoprotective by increasing vasodilative NO production and thus improving post-ischemic renal perfusion. Based on our data activation of S1R and downstream signaling pathways could provide a novel therapeutic option in renal IRI.

Founding

OTKA PD-131 637; FK-124 491; 2020–4.1.1.-TKP2020-6 183 069 269; 2020–4.1.1.-TKP2020-6 183 169 273; KDP-2020/1 019 145

MO1019: Sigma-1 Receptor Agonists are Protective in a Rat Model of Kidney Transplantation

BACKGROUND AND AIMS

End-stage renal disease affects nearly 2 million people worldwide. The disease is associated with an irreversible deterioration in renal function and can only be treated by dialysis or kidney transplantation (KTx). KTx is associated with better long-term outcomes and quality of life compared with dialysis, but the shortage of donor organs is a serious and unsolved problem. Graft survival is highly dependent on the extent of cold and warm ischemic injury during Tx. We recently described the renoprotective effects of Sigma-1 receptor (S1R) agonist treatment in IRI. Thus, our aim was to develop a novel preservation solution that, with the addition of S1R agonist compounds, minimizes ischemic damage in order to improve the condition of grafts and so increase the number of organs suitable for Tx.

METHOD

Kidneys of male Wistar rats were perfused and placed in ice cold (i) custodiol preservation solution; custodiol containing S1R agonists, (ii) fluvoxamine or (iii) SA-4503 for 2 h, then autotransplanted and sacrificed 24 h after reperfusion. Sham-operated rats served as controls. In a second experiment, kidneys of wild-type and S1R knockout mice were perfused and placed in an ice-cold preservation solution containing an original, selective S1R agonist compound (VCC) for 24 h of cold ischemia and tissue samples were collected. Renal function parameters were determined. Renal expression of tubular injury markers (Kim-1, Ngal) and inflammatory cytokines (Il-1α, Il-6, Tnf-α, Mcp-1) were measured. Periodic acid-Schiff staining was performed on kidney tissue sections to evaluate structural changes. CD45 immunostaining was performed on kidney sections to determine the extent of leukocyte infiltration. DNA fragmentation resulted by apoptotic events in the kidney was evaluated by TUNEL-assay.

RESULTS

S1R agonists mitigated renal functional impairment and tubular dilatation following Tx. Expression of early and sensitive tubular injury markers was markedly less elevated in S1R agonist-treated kidneys. S1R agonists alleviated renal apoptosis as shown on TUNEL-stained kidney sections. Decreased numbers of CD45 + leukocytes and decreased inflammatory cytokine expressions confirmed the anti-inflammatory effect of S1R agonists. The S1R agonist VCC compound mitigated cold ischemic structural kidney damage in wild-type but not in S1R KO mice, which confirms the protective role of the receptor.

CONCLUSION

The addition of S1R agonists to the preservation solution during Tx improves graft function and alleviates structural damage, thus improving long-term outcomes. S1R agonists reduce graft injury during cold storage, therefore the number of transplantable donor organs can be increased.

FUNDING

OTKA PD-131 637; FK-124 491; 2020–4.1.1.-TKP2020-6 183 069 269; 2020–4.1.1.-TKP2020-6 183 169 273; KDP-2020/1 019 145.

MO1016MULTIPLE-ORGAN DAMAGE FOLLOWING PERINATAL ASPHYXIA IN RAT MODEL

Background and Aims

Perinatal asphyxia (PA) is associated with more than half a million mature newborn deaths yearly. It may lead to severe complications including hypoxic encephalopathy, renal- hepatic- and cardiovascular injury, as well as respiratory distress, Basic research and clinical trials mainly focus on mitigating central nervous system damage by selective head or whole body cooling, which is currently the only routinely used treatment in clinical practice. However, the extent of PA-associated multi-organ damage is not clarified yet and effective therapies are lacking. Our aim was to investigate the acute renal, hepatic and cardiac impairment following PA and to identify pathways involved in the pathomechanism. In addition, we aimed to explore long-term effects of PA on permanent organ damage and susceptibility to ischemia/-reperfusion injury in adulthood.

Method

Postnatal 7 day-old male Wistar rat pups (n=5-10/group) were randomly grouped as follows: (i) Baseline; (ii) Control; (iii) PA. The PA group was separated from the dam and received asphyxic gas mixture (4% O2; 20% CO2 in N2) for 15 minutes, while Control animals received normal air following separation. Serum and tissue samples were collected after 4 (T4) or 24 (T24) hours. In a second experiment 35 min bilateral renal ischemic insult was performed on control and PA rats aged 6 months (n=6-7/group). Serum and tissue samples were collected 24 (T24 IR) hours after reperfusion (Figure 1). Serum levels of electrolytes, kidney and liver functional parameters, and myocardial ischemic protein Troponin I were determined. Highly selective and sensitive tubular injury markers (Kim1, Ngal) were measured. Expressions of hypoxic (Hif1a, Hif2a) inflammatory (Il1α, Il1β, Il6, Tnfα, Mcp1, Tlr2), apoptotic (Bax, Bcl-2) and angiogenic genes (Vegf, Epo) and heat shock proteins (Hsp27, Hsp72) were investigated. Periodic-Acid Schiff stained kidney sections and Hematoxylin & Eosin stained liver sections were evaluated for structural injury.

Results

Blood urea nitrogen (BUN) and serum GPT were elevated at T4 following PA. Kim1, Ngal and heat shock protein expressions were increased, inflammatory and angiogenic pathways were activated in the kidney after PA. In the liver hypoxic and apoptotic pathways were activated at T24 in controls and after asphyxia, but not in the Baseline group. Vacuolisation, cytoplasmic degradation, and the onset of necrosis were observed in the liver following PA. Serum Troponin I was elevated indicating myocardial damage, moreover inflammatory cytokines and heat shock proteins increased in the heart. In adult PA rats BUN levels were elevated, suggesting a long-term detrimental effect of PA on renal function. In addition, adult PA rats were more susceptible to renal ischemic insult, confirmed by higher serum creatinine and GPT levels, as well as increased expression of tubular injury, hypoxic and inflammatory markers compared to Control rats subjected to ischemia.

Conclusion

Acute renal, hepatic and myocardial impairment was observed after PA. These results may justify the need for clinical follow-up and novel treatment strategies for possible multi-organ damage. The molecular pathways described here are potential targets for therapeutic intervention. In addition, birth asphyxia may increase sensitivity to renal injury in adulthood, which may be worth considering in clinical situations with potential renal impairment.

MO620ANTIFIBROTIC EFFECTS OF SGLT2 INHIBITION IN THE KIDNEY AND PROXIMAL TUBULAR CELLS*

Background and Aims

Diabetic kidney disease (DKD) is a major cause of chronic kidney disease and end stage renal disease, therefore identification of novel therapeutic strategies that reduce the risk of DKD is a research priority. Recent large clinical trials suggest that improved renal outcomes by sodium-glucose cotransporter 2 inhibitors (SGLT2i) are partly beyond their glucose lowering effects. Enhanced glucose reabsorption in diabetes leads to tubular hypoxia triggering fibrotic response. Hyperglycemia is in strong association with increased protein O-GlcNAcylation, a post-translational modification contributing to renal fibrosis. Considering the proximal tubular involvement in DKD pathogenesis and the key role of SGLT2 in glucose metabolism, here we investigated the effects of SGLT2i on tubular hypoxia and O-GlcNAcylation.

Method

Diabetes (D) was induced by streptozotocin (65 mg/bwkg, ip.) in adult, male Wistar rats. Following the onset of diabetes rats were treated for six weeks with dapagliflozin (D+DAPA, 1 mg/bwkg/day, po.). Metabolic parameters and renal function were evaluated. Novel urinary biomarkers of extracellular matrix remodeling (Pro-C3, uC3M, tumstatin) and profibrotic growth factors (TGF-β, CTGF, PDGF) were determined. Histological evaluation of glomerular damage (PAS), tubulointerstitial fibrosis (Masson’s trichrome, Picrosirius red) and fibronectin accumulation were performed. The effect of hyperglycemia was tested in human proximal tubular epithelial cells (HK-2) kept under normal glucose (5.5 mM), high glucose (35 mM) or high mannitol (osmotic control, 35 mM) conditions for 24 hours. HG cells were treated with 10 µM DAPA. O-GlcNAc, O-GlcNAc transferase (OGT) and O-GlcNAcase (OGA) were measured. To test the effect of hypoxia cells were treated with 10 µM DAPA and were placed in a hypoxic chamber (1% O2) for 2 hours. Hypoxic injury was investigated using three different methods (qRT-PCR, Western blot, immunofluorescence analysis). HIF-1α, EPO, VEGFA and profibrotic factors were measured.

Results

DAPA decreased blood glucose levels (D: 37±2.7 vs. D+DAPA: 18±5.6 mmol/L; p<0.05) and improved renal function (creatinine clearance: D: 3.8±0.4 vs. D+DAPA: 8.9±1.0 mL/min; p<0.01). In parallel, novel urinary biomarkers of extracellular matrix remodeling, profibrotic growth factor expressions and extensive fibrotic tissue accumulation were reduced in the kidney. DAPA minimized hyperglycemia-induced total protein O-GlcNAcylation in HK-2 cells. Hypoxia-induced HIF-1α elevation was suspended by DAPA treatment. Moreover, DAPA treatment prevented HIF-1α translocation to the nucleus, thereby confirming abolished HIF-1α activation. EPO, VEGFA and profibrotic factor levels were also increased in hypoxia and DAPA prevented EPO, TGFB and PDGF elevation.

Conclusion

These data highlight the role of ameliorated O-GlcNAcylation and diminished tubular hypoxia as important benefits of SGLT2i treatment. Our results support the link between glucose toxicity, tubular hypoxia and fibrosis, a vicious trio, which seem to be targeted by SGLT2i. All these mechanisms are important parts in the puzzle of the complex system behind the protective effect of SGLT2i.

OTKA-FK124491-K135398, 2017-1.3.1-VKE-2017-00006, 2020-4.1.1.-TKP2020-6183169273, 2020-4.1.1.-TKP2020-6183069269

Animal Models of Renal Pathophysiology and Disease

Renal diseases remain devastating illnesses with unacceptably high rates of mortality and morbidity worldwide. Animal models are essential tools to better understand the pathomechanisms of kidney-related illnesses and to develop new, successful therapeutic strategies. Magnetic resonance imaging (MRI) has been actively explored in the last decades for assessing renal function, perfusion, tissue oxygenation as well as the degree of fibrosis and inflammation. This chapter aims to provide a comprehensive overview of animal models of acute and chronic kidney diseases, highlighting MRI-specific considerations, advantages, and pitfalls, and thus assisting the researcher in experiment planning.This publication is based upon work from the COST Action PARENCHIMA, a community-driven network funded by the European Cooperation in Science and Technology (COST) program of the European Union, which aims to improve the reproducibility and standardization of renal MRI biomarkers.

Reversible (Patho)Physiologically Relevant Test Interventions: Rationale and Examples

Renal tissue hypoperfusion and hypoxia are early key elements in the pathophysiology of acute kidney injury of various origins, and may also promote progression from acute injury to chronic kidney disease. Here we describe test interventions that are used to study the control of renal hemodynamics and oxygenation in experimental animals in the context of kidney-specific control of hemodynamics and oxygenation. The rationale behind the use of the individual tests, the physiological responses of renal hemodynamics and oxygenation, the use in preclinical studies, and the possible application in humans are discussed.This chapter is based upon work from the COST Action PARENCHIMA, a community-driven network funded by the European Cooperation in Science and Technology (COST) program of the European Union, which aims to improve the reproducibility and standardization of renal MRI biomarkers.

Antidepressant effect in diabetes-associated depression: A novel potential of RAAS inhibition

The incidence of depression doubles in diabetic patients and is associated with poor outcomes. Studies indicate that renin-angiotensin-aldosterone system inhibitors (RAASi) might relieve depression, however the mechanism of action is not well understood. We recently showed that angiotensin receptor blockers have antidepressant effects in experimental diabetes comorbid depression. Here we investigated whether all types of RAASi exhibit antidepressant and neuroprotective properties. Diabetes was induced by streptozotocin in adult male Wistar rats. After 5 weeks of diabetes, rats were treated per os with non-pressor doses of enalapril, ramipril, spironolactone or eplerenone for 2 weeks. Behavior was evaluated using forced swim test and open field test. Inflammatory response and brain-derived neurotrophic factor (BDNF) signaling were investigated in the hippocampus. Both ACEi and MR antagonists reversed diabetes-induced behavioral despair confirming their antidepressant-like effect. This may occur via alterations in hippocampal cytokine-mediated inflammatory response. Repressed BDNF production was restored by RAASi. Both ACEi and MR antagonists facilitated the BDNF-tropomyosin receptor kinase B-cAMP response element-binding protein signaling pathway as part of their neuroprotective effect. These data highlight the important benefits of ACEi and MR antagonists in the treatment of diabetes-associated depressive symptoms. Our novel findings support the link between diabetes comorbid depression, inflammation and repressed BDNF signaling. RAASi could provide new therapeutic options to improve the outcomes of both disorders.

Sex differences in renal ischemia-reperfusion injury

Ischemia-reperfusion injury of the kidney is caused by the sudden and temporary obstruction of blood flow to the organ. Renal ischemia-reperfusion injury is associated with high morbidity and mortality, but effective therapies are lacking. Sexual dimorphism in renal injury has been acknowledged since the 1940s, and the possible role of sex hormones has been intensively investigated in the past decades. Clinical and experimental data demonstrate sexual differences in renal anatomy, physiology, and susceptibility to renal diseases including but not limited to ischemia-reperfusion injury. Some data suggest the protective role of female sex hormones, whereas others highlight the detrimental effect of male hormones in renal ischemia-reperfusion injury. Although the important role of sex hormones is evident, the exact underlying mechanisms remain to be elucidated. This review focuses on collecting the current knowledge about sexual dimorphism of renal ischemia-reperfusion injury, with emphasis on molecular mechanisms and potential novel therapeutic strategies.

P0556MULTI-ORGAN DAMAGE FOLLOWING PERINATAL ASPHYXIA IN RAT MODEL

Background and Aims

Perinatal asphyxia (PA) leads to the death of more than half a million mature newborns yearly. PA is associated with several serious complications, including hypoxic encephalopathy, renal- hepatic- and cardiovascular injury, as well as respiratory distress. Basic research and clinical trials mainly focus on mitigating central nervous system damage by selective head or whole body cooling, which is currently the only routinely used treatment in clinical practice. However, the extent of PA-associated multi-organ damage is not clarified yet and effective therapies are lacking. The aim of the present study was to determine the acute renal, hepatic and cardiac impairment following PA and to identify pathways involved in the pathomechanism. In addition, we aimed to investigate long-term effects of PA on permanent organ damage and susceptibility to ischemia/-reperfusion injury in adulthood.

Method

Postnatal 7 day-old male Wistar rat pups (n=5-10/group) were randomly grouped as follows: (i) Baseline; or separated from the dam and placed in a treatment chamber for 15 minutes

(ii) Control

normal air;

(iii) PA

4% O2; 20% CO2 in N2 gas mixture. Serum and tissue samples were collected after 4 (T4) and 24 (T24) hours respectively. In a second experiment 35 min bilateral renal ischemic insult was performed on control and PA rats aged 6 months (n=6-7/group). Serum and tissue samples were collected 24 (T24 IR) hours after reperfusion (Figure 1).

Serum levels of electrolytes, kidney and liver functional parameters, and myocardial ischemic protein Troponin I were determined. Highly selective tubular injury markers (Kim1, Ngal) were measured. Expressions of hypoxic (Hif1a, Hif2a) inflammatory (Il1α, Il1β, Il6, Tnfα, Mcp1, Tlr2), apoptotic (Bax, Bcl-2) and angiogenic genes (Vegf, Epo) and heat shock proteins (Hsp27, Hsp72) were investigated. Periodic-Acid Schiff staining and CD45 immunostaining on kidney tissue sections, and Hematoxylin & Eosin staining on liver tissue sections were performed.

Results

Blood urea nitrogen (BUN) and serum GPT were elevated at T4 following PA. Kim1, Ngal and heat shock protein expressions were increased, inflammatory and angiogenic pathways were activated in the kidney after PA. CD45 staining showed increased leukocyte infiltration. In the liver hypoxic and apoptotic pathways were activated at T24 in controls and after asphyxia, but not in the Baseline group. Vacuolisation, cytoplasmic degradation, and the onset of necrosis were observed in the liver following PA. Serum Troponin I was elevated indicating myocardial damage, moreover inflammatory cytokines and heat shock proteins increased in the heart. In adult PA rats BUN levels were elevated, suggesting a long-term detrimental effect of PA on renal function. In addition, adult PA rats were more susceptible to renal ischemic insult, confirmed by higher serum creatinine and GPT levels, as well as increased expression of tubular injury, hypoxic and inflammatory markers compared to Control rats subjected to ischemia.

Conclusion

Acute renal, hepatic and myocardial impairment was observed after PA. These results may justify the need for clinical follow-up and novel treatment strategies for possible multi-organ damage. The molecular pathways described here are potential targets for therapeutic intervention. In addition, birth asphyxia may increase sensitivity to renal injury even in adulthood, which may be worth considering in clinical situations with potential renal impairment such as major surgeries.

P1669PROGNOSTIC IMPORTANCE OF BRAIN-DERIVED NEUROTROPHIC FACTOR (BDNF) IN RENAL TRANSPLANTATION

Background and Aims

The prevalence of end-stage renal disease (ESRD) has increased ten times higher in the past twenty years, where renal replacement therapy (dialysis or kidney transplantation (KTx)) is the sole life-saving treatment. KTx is the preferred option as it is associated with improved survival and quality of life as well. Delayed graft function (DGF) is one of the main problems affecting long-term kidney survival. Brain-derived neurotrophic factor (BDNF) signalling pathways play pivotal role in mitigating cerebral ischemia/reperfusion injury (IRI), however the relation of BDNF and IRI in KTx is unknown. The aim of our human clinical study was to explore the relationship between serum BDNF concentration, BDNF gene polymorphism and renal graft function after KTx.

Method

Study characteristics: We enrolled 59 ESRD patients with average age of 54.8±12 years who received KTx. Proportion of male patients was 57%. Average cold ischemic time was 927±310 min, warm ischemic time was 54.5±39 min. DGF occurred in 5 cases. Baseline triple immunosuppression therapy consisted of tacrolimus, mycophenolate or everolimus, and prednisolone. Until now, 44 patients completed the 2 years follow-up. For a comparable control group, we collected blood samples from 79 healthy volunteers with average age of 53.9±16 years and with male gender proportion of 52%. Serum BDNF, creatinine, blood urea nitrogen, haemoglobin, blood glucose level and thrombocyte numbers were measured before KTx and 1 week, 1-, 3-, 6 months, and 1-, 2 years after transplantation, as well as in controls. GFR was estimated based on the CKD-EPI formula. BDNF Val66Met polymorphism was determined by PCR-RFLP.

Results

There was no difference in genotype or allele distribution between any of the groups, and no correlation could be observed between serum BDNF and different genotypes either. Serum BDNF level was lower in ESRD patients than healthy controls (p=0.03). There was a weak correlation and marginal significance (p=0.056) between eGFR and serum BDNF level in controls, while in KTx recipients this correlation reached higher significance (p=0.01). Above median BDNF values at 1 month after KTx were predictive for better graft function during the 2 observed years.

Conclusion

Our preliminary human study proposes that BDNF could be a novel biomarker of posttransplant graft function, however further clinical studies with significantly larger population are definitely needed to confirm these results.

Reduced O-GlcNAcylation and tubular hypoxia contribute to the antifibrotic effect of SGLT2 inhibitor dapagliflozin in the diabetic kidney

Diabetic kidney disease is a worldwide epidemic, and therapies are incomplete. Clinical data suggest that improved renal outcomes by Na⁺-glucose cotransporter 2 inhibitor (SGLT2i) are partly beyond their antihyperglycemic effects; however, the mechanisms are still elusive. Here, we investigated the effect of the SGLT2i dapagliflozin (DAPA) in the prevention of elevated O-GlcNAcylation and tubular hypoxia as contributors of renal fibrosis. Type 1 diabetes was induced by streptozotocin in adult male Wistar rats. After the onset of diabetes, rats were treated for 6 wk with DAPA or DAPA combined with losartan (LOS). The effect of hyperglycemia was tested in HK-2 cells kept under normal or high glucose conditions. To test the effect of hypoxia, cells were kept in 1% O₂ for 2 h. Cells were treated with DAPA or DAPA combined with LOS. DAPA slowed the loss of renal function, mitigated renal tubular injury markers (kidney injury molecule-1 and neutrophil gelatinase-associated lipocalin), and reduced tubulointerstitial fibrosis. DAPA diminished high glucose-induced protein O-GlcNAcylation and moderated the tubular response to hypoxia through the hypoxia-inducible factor pathway. DAPA alone was as effective as combined treatment with LOS in all outcome parameters. These data highlight the role of ameliorated O-GlcNAcylation and diminished tubular hypoxia as important benefits of SGLT2i treatment. Our results support the link between glucose toxicity, tubular hypoxia, and fibrosis, a vicious trio that could be targeted by SGLT2i in kidney diseases of other origins as well.

Novel therapeutic potential of angiotensin receptor 1 blockade in a rat model of diabetes-associated depression parallels altered BDNF signalling

AIMS/HYPOTHESIS

Diabetes is a worldwide epidemic linked with diverse diseases of the nervous system, including depression. A few studies suggested a connection between renin-angiotensin-aldosterone system blockers and reduced depressive symptoms, although underlying mechanisms are unclear. Here we investigated the antidepressant effect and the mechanisms of action of the angiotensin receptor 1 blocker (ARB) losartan in an experiential model of diabetes-associated depression.

METHODS

Experimental diabetes was induced by streptozotocin in adult male Wistar rats. After 5 weeks of diabetes, rats were treated for 2 weeks with a non-pressor oral dose of losartan (20 mg/kg). In protocol 1, cerebrovascular perfusion and glial activation were evaluated by single-photon emission computed tomography-MRI and immunohistochemistry. In protocol 2, behaviour studies were performed (forced swim test and open field test). Hippocampal proinflammatory response and brain-derived neurotrophic factor (BDNF) signalling were also assessed.

RESULTS

Here, we show that diabetic rats exhibit depression-like behaviour, which can be therapeutically reversed by losartan. This action of losartan occurs via changes in diabetes-induced neuroinflammatory responses rather than altered cerebral perfusion. We also show that as a part of its protective effect losartan restores BDNF production in astrocytes and facilitates BDNF-tropomyosin receptor kinase B-cAMP response element-binding protein signalling in the diabetic brain.

CONCLUSIONS/INTERPRETATION

We identified a novel effect of losartan in the nervous system that may be implemented to alleviate symptoms of diabetes-associated depression. These findings explore a new therapeutic horizon for ARBs as possible antidepressants and suggest that BDNF could be a target of future drug development in diabetes-induced complications.

RAAS inhibitors directly reduce diabetes-induced renal fibrosis via growth factor inhibition

KEY POINTS

Increased activation of the renin-angiotensin-aldosterone system (RAAS) and elevated growth factor production are of crucial importance in the development of renal fibrosis leading to diabetic kidney disease. The aim of this study was to provide evidence for the antifibrotic potential of RAAS inhibitor (RAASi) treatment and to explore the exact mechanism of this protective effect. We found that RAASi ameliorate diabetes-induced renal interstitial fibrosis and decrease profibrotic growth factor production. RAASi prevents fibrosis by acting directly on proximal tubular cells, and inhibits hyperglycaemia-induced growth factor production and thereby fibroblast activation. These results suggest a novel therapeutic indication and potential of RAASi in the treatment of renal fibrosis.

ABSTRACT

In diabetic kidney disease (DKD) increased activation of renin-angiotensin-aldosterone system (RAAS) contributes to renal fibrosis. Although RAAS inhibitors (RAASi) are the gold standard therapy in DKD, the mechanism of their antifibrotic effect is not yet clarified. Here we tested the antifibrotic and renoprotective action of RAASi in a rat model of streptozotocin-induced DKD. In vitro studies on proximal tubular cells and renal fibroblasts were also performed to further clarify the signal transduction pathways that are directly altered by hyperglycaemia. After 5 weeks of diabetes, male Wistar rats were treated for two more weeks per os with the RAASi ramipril, losartan, spironolactone or eplerenone. Proximal tubular cells were cultured in normal or high glucose (HG) medium and treated with RAASi. Platelet-derived growth factor (PDGF) or connective tissue growth factor (CTGF/CCN2)-induced renal fibroblasts were also treated with various RAASi. In diabetic rats, reduced renal function and interstitial fibrosis were ameliorated and elevated renal profibrotic factors (TGFβ1, PDGF, CTGF/CCN2, MMP2, TIMP1) and alpha-smooth muscle actin (αSMA) levels were decreased by RAASi. HG increased growth factor production of HK-2 cells, which in turn induced activation and αSMA production of fibroblasts. RAASi decreased tubular PDGF and CTGF expression and reduced production of extracellular matrix (ECM) components in fibroblasts. In proximal tubular cells, hyperglycaemia-induced growth factor production increased renal fibroblast transformation, contributing to the development of fibrosis. RAASi, even in non-antihypertensive doses, decreased the production of profibrotic factors and directly prevented fibroblast activation. All these findings suggest a novel therapeutic role for RAASi in the treatment of renal fibrosis.

The role of Sigma-1 receptor in sex-specific heat shock response in an experimental rat model of renal ischaemia/reperfusion injury

We previously showed that female rats are more protected against renal ischaemia/reperfusion (I/R) injury than males, which is partly attributed to their more pronounced heat shock response. We recently described that Sigma-1 receptor (S1R) activation improves postischaemic survival and renal function. 17β-estradiol activates S1R, thus here we investigated the role of sex-specific S1R activation and heat shock response in severe renal I/R injury. Proximal tubular cells were treated with 17β-estradiol, which caused direct S1R activation and subsequent induction of heat shock response. Uninephrectomized female, male and ovariectomized female (Ovx) Wistar rats were subjected to 50-min renal ischaemia followed by 2 (T2) and 24 (T24) hours of reperfusion. At T24 renal functional, impairment was less severe and structural damage was less prominent in females versus males or Ovx. Postischaemic increase in S1R, pAkt, HSF-1, HSP72 levels were detected as early as at T2, while pHSP27 was elevated later at T24. Abundance of heat shock proteins was higher in healthy female rats and remained higher at T2 and T24 (female versus male or Ovx; resp.). We propose a S1R-dependent mechanism, which contributes to the relative renoprotection of females after I/R injury by enhancing the heat shock response.

σ1-Receptor Agonism Protects against Renal Ischemia-Reperfusion Injury

Mechanisms of renal ischemia-reperfusion injury remain unresolved, and effective therapies are lacking. We previously showed that dehydroepiandrosterone protects against renal ischemia-reperfusion injury in male rats. Here, we investigated the potential role of σ1-receptor activation in mediating this protection. In rats, pretreatment with either dehydroepiandrosterone or fluvoxamine, a high-affinity σ1-receptor agonist, improved survival, renal function and structure, and the inflammatory response after sublethal renal ischemia-reperfusion injury. In human proximal tubular epithelial cells, stimulation by fluvoxamine or oxidative stress caused the σ1-receptor to translocate from the endoplasmic reticulum to the cytosol and nucleus. Fluvoxamine stimulation in these cells also activated nitric oxide production that was blocked by σ1-receptor knockdown or Akt inhibition. Similarly, in the postischemic rat kidney, σ1-receptor activation by fluvoxamine triggered the Akt-nitric oxide synthase signaling pathway, resulting in time- and isoform-specific endothelial and neuronal nitric oxide synthase activation and nitric oxide production. Concurrently, intravital two-photon imaging revealed prompt peritubular vasodilation after fluvoxamine treatment, which was blocked by the σ1-receptor antagonist or various nitric oxide synthase blockers. In conclusion, in this rat model of ischemia-reperfusion injury, σ1-receptor agonists improved postischemic survival and renal function via activation of Akt-mediated nitric oxide signaling in the kidney. Thus, σ1-receptor activation might provide a therapeutic option for renoprotective therapy.

Abstract P266: Thromboxane-prostanoid Receptors (tp-rs) Mediate Hypertension, H2o2 Generation and Impaired Renal Afferent Arteriolar Myogenic Responses Leading to Nephropathy in Doca/salt Mice

Background: DOCA/uninephrectomy/high salt (DOCA) is a model of hypertensive nephropathy. Afferent arteriolar myogenic responses prevent hypertensive renal barotrauma but myogenic tone is blocked by vascular generation of H 2 O 2 . Since thromboxane-prostanoid receptors (TP-Rs) generate H 2 O 2 , we tested the hypothesis that they mediate hypertensive nephropathy.

Methods: DOCA and Sham TP-R +/+ and -/- mice (n=6/group) were studied at 2 weeks and myogenic responses recorded from the diameter of perfused single afferent arterioles studied in a bath preparation during increased perfusion pressure (40 to 80 mmHg).

Results: DOCA treatment in TP-R +/+ mice increased (p<0.001) 24-hour excretion of H 2 O 2 (45 ± 3 vs 220 + 15 nmol) , TxB 2 (4 ± 2 vs 29 ± 4 pmol) and albumin (20 ± 5 vs 270 ± 20 mg) and increased MAP by 35 ± 5 mmHg. However, all effects of DOCA were prevented in TP-R -/- mice. Sham treatment had no effect in TPR +/+ or -/- mice. Myogenic responses were severely impaired in DOCA vs sham WT mice (Δ diameter: -4 ± 1 vs -8 ± 1%; p< 0.005). Myogenic responses also were reduced by incubation of arterioles with 10 -10 mol·l -1 of the TP-R mimetic, U-46,619 vs vehicle added to the bath for 10 minutes (Δ diameter: -7 ± 1 vs -10 ± 1%; p<0.01) and in WT mice infused for 3 days with U-46,619 (500 ng·kg -1 ·d -1 x 3) vs vehicle (Δ diameter: -3 ± 1 vs -10 ± 1%; p<0.005).

Conclusion: Hypertensive nephropathy is dependent on TP-Rs that mediate the increase in H 2 O 2 and blood pressure and likely the impaired myogenic responses that expose the kidney to barotrauma

The role of sigma-1 receptor and brain-derived neurotrophic factor in the development of diabetes and comorbid depression in streptozotocin-induced diabetic rats

RATIONALE

Depression is highly prevalent in diabetes (DM). Brain-derived neurotrophic factor (BDNF) which is mainly regulated by the endoplasmic reticulum chaperon sigma-1 receptor (S1R) plays a relevant role in the development of depression.

OBJECTIVES

We studied the dose-dependent efficacy of S1R agonist fluvoxamine (FLU) in the prevention of DM-induced depression and investigated the significance of the S1R-BDNF pathway.

METHODS

We used streptozotocin to induce DM in adult male rats that were treated for 2 weeks p.o. with either different doses of FLU (2 or 20 mg/bwkg) or FLU + S1R antagonist NE100 (1 mg/bwkg) or vehicle. Healthy controls were also enrolled. Metabolic, behaviour, and neuroendocrine changes were determined, and S1R and BDNF levels were measured in the different brain regions.

RESULTS

In DM rats, immobility time was increased, adrenal glands were enlarged, and thymuses were involuted. FLU in 20 mg/bwkg, but not in 2 mg/bwkg dosage, ameliorated depression-like behaviour. S1R and BDNF protein levels were decreased in DM, while FLU induced SIR-BDNF production. NE100 suspended all effects of FLU.

CONCLUSIONS

We suggest that disturbed S1R-BDNF signaling in the brain plays a relevant role in DM-induced depression. The activation of this cascade serves as an additional target in the prevention of DM-associated depression.

Role of O-linked N-acetylglucosamine modification in diabetic nephropathy

Increased O-linked β-N-acetylglucosamine glycosylation (O-GlcNAcylation) is a known contributor to diabetes; however, its relevance in diabetic nephropathy (DN) is poorly elucidated. Here, we studied the process and enzymes of O-GlcNAcylation with a special emphasis on Akt-endothelial nitric oxide synthase (eNOS) and heat shock protein (HSP)72 signaling. Since tubular injury is the prominent site of DN, the effect of hyperglycemia was first measured in proximal tubular (HK2) cells cultured in high glucose. In vivo O-GlcNAcylation and protein levels of O-GlcNAc transferase (OGT), O-GlcNAcase (OGA), phosphorylated (p)Akt/Akt, peNOS/eNOS, and HSP72 were assessed in the kidney cortex of streptozotocin-induced diabetic rats. The effects of various renin-angiotensin-aldosterone system (RAAS) inhibitors were also evaluated. In proximal tubular cells, hyperglycemia-induced OGT expression led to increased O-GlcNAcylation, which was followed by a compensatory increase of OGA. In parallel, peNOS and pAkt levels decreased, whereas HSP72 increased. In diabetic rats, elevated O-GlcNAcylation was accompanied by decreased OGT and OGA. RAAS inhibitors ameliorated diabetes-induced kidney damage and prevented the elevation of O-GlcNAcylation and the decrement of pAkt, peNOS, and HSP72. In conclusion, hyperglycemia-induced elevation of O-GlcNAcylation contributes to the progression of DN via inhibition of Akt/eNOS phosphorylation and HSP72 induction. RAAS blockers successfully inhibit this process, suggesting a novel pathomechanism of their renoprotective action in the treatment of DN.