Adenosine A2 a receptor stimulation prevents proteinuria in diabetic rats by promoting an anti-inflammatory phenotype without affecting oxidative stress

Renoprotective strategies

Kidney disease remains a condition with an increasing incidence, high morbidity and mortality associated with cardiovascular events. The incidence of end-stage renal disease is expected to increase. Despite of the technical improvement, dialysis never achieved a full clearance of the blood dialysis. Therefore, the demand for new renoprotective measures has never been greater. Here, we report new strategies for preventing renal damage.

Adenosine reuptake inhibition reduces diabetes-induced glomerular hyperfiltration via the adenosine A2a receptor

Diabetes-induced glomerular hyperfiltration is an early alteration in kidney function in diabetes. Previous studies have shown that reduced adenosine A2a receptor signaling contributes to diabetes-induced glomerular hyperfiltration. The present study investigated the effects of enhanced interstitial adenosine concentration by inhibition of cellular adenosine reuptake, thereby promoting endogenous adenosine signaling. Insulinopenic diabetes was induced by streptozotocin in adult male Sprague-Dawley rats. Two weeks after diabetes induction, kidney function in terms of glomerular filtration rate, and total, cortical, and medullary renal blood flows were evaluated under thiobutabarbital anesthesia during baseline and after renal artery infusion of two doses of the adenosine reuptake inhibitor dilazep. Dilazep did not affect mean arterial pressure indicating that the effects of the interventions were intrarenal. Diabetics had increased glomerular filtration rate compared with controls and dilazep dose-dependently decreased glomerular filtration rate in diabetics, whereas it had no significant effect in controls. Dilazep increased cortical renal blood flows in controls, whereas medullary blood flow was not significantly changed. Dilazep did not affect total renal blood flow in any of the groups but decreased cortical blood flow in diabetics, resulting in decreased filtration fraction by dilazep in diabetics. Pretreatment with the adenosine A2a antagonist ZM241385 prevented intrarenal dilazep-mediated effects on glomerular filtration rate and filtration fraction in diabetics. In conclusion, enhancing intrarenal adenosine signaling by dilazep normalizes diabetes-induced glomerular hyperfiltration at least in part by activation of adenosine A2a receptors.

Nonselective and A2a-Selective Inhibition of Adenosine Receptors Modulates Renal Perfusion and Excretion Depending on the Duration of Streptozotocin-Induced Diabetes in Rats

Long-lasting hyperglycaemia may alter the role of adenosine-dependent receptors (P1R) in the control of kidney function. We investigated how P1R activity affects renal circulation and excretion in diabetic (DM) and normoglycaemic (NG) rats; the receptors' interactions with bioavailable NO and H₂O₂ were also explored. The effects of adenosine deaminase (ADA, nonselective P1R inhibitor) and P1A2a-R-selective antagonist (CSC) were examined in anaesthetised rats, both after short-lasting (2-weeks, DM-14) and established (8-weeks, DM-60) streptozotocin-induced hyperglycaemia, and in normoglycaemic age-matched animals (NG-14, NG-60, respectively). The arterial blood pressure, perfusion of the whole kidney and its regions (cortex, outer-, and inner medulla), and renal excretion were determined, along with the in situ renal tissue NO and H₂O₂ signals (selective electrodes). The ADA treatment helped to assess the P1R-dependent difference in intrarenal baseline vascular tone (vasodilation in DM and vasoconstriction in NG rats), with the difference being more pronounced between DM-60 and NG-60 animals. The CSC treatment showed that in DM-60 rats, A2aR-dependent vasodilator tone was modified differently in individual kidney zones. Renal excretion studies after the ADA and CSC treatments showed that the balance of the opposing effects of A2aRs and other P1Rs on tubular transport, seen in the initial phase, was lost in established hyperglycaemia. Regardless of the duration of the diabetes, we observed a tonic effect of A2aR activity on NO bioavailability. Dissimilarly, the involvement of P1R in tissue production of H₂O₂, observed in normoglycaemia, decreased. Our functional study provides new information on the changing interaction of adenosine in the kidney, as well as its receptors and NO and H₂O₂, in the course of streptozotocin diabetes.

SGLT2 inhibitors improve kidney function and morphology by regulating renal metabolic reprogramming in mice with diabetic kidney disease

Diabetic kidney disease (DKD) is the leading cause of end-stage renal disease (ESRD) worldwide. SGLT2 inhibitors are clinically effective in halting DKD progression. However, the underlying mechanisms remain unclear. The serum and kidneys of mice with DKD were analyzed using liquid chromatography with tandem mass spectrometry (LC–MS/MS)-based metabolomic and proteomic analyses. Three groups were established: placebo-treated littermate db/m mice, placebo-treated db/db mice and EMPA-treated db/db mice. Empagliflozin (EMPA) and placebo (10 mg/kg/d) were administered for 12 weeks. EMPA treatment decreased Cys-C and urinary albumin excretion compared with placebo by 78.60% and 57.12%, respectively (p < 0.001 in all cases). Renal glomerular area, interstitial fibrosis and glomerulosclerosis were decreased by 16.47%, 68.50% and 62.82%, respectively (p < 0.05 in all cases). Multi-omic analysis revealed that EMPA treatment altered the protein and metabolic profiles in the db/db group, including 32 renal proteins, 51 serum proteins, 94 renal metabolites and 37 serum metabolites. Five EMPA-related metabolic pathways were identified by integrating proteomic and metabolomic analyses, which are involved in renal purine metabolism; pyrimidine metabolism; tryptophan metabolism; nicotinate and nicotinamide metabolism, and glycine, serine and threonine metabolism in serum. In conclusion, this study demonstrated metabolic reprogramming in mice with DKD. EMPA treatment improved kidney function and morphology by regulating metabolic reprogramming, including regulation of renal reductive stress, alleviation of mitochondrial dysfunction and reduction in renal oxidative stress reaction.

Adenosine receptors as emerging therapeutic targets for diabetic kidney disease

Diabetic kidney disease (DKD) is now a pandemic worldwide, and novel therapeutic options are urgently required. Adenosine, an adenosine triphosphate metabolite, plays a role in kidney homeostasis through interacting with four types of adenosine receptors (ARs): A1AR, A2AAR, A2BAR, and A3AR. Increasing evidence highlights the role of adenosine and ARs in the development and progression of DKD: 1) increased adenosine in the plasma and urine of diabetics with kidney injury, 2) increased expression of each of the ARs in diabetic kidneys, 3) the protective effect of coffee, a commonly ingested nonselective AR antagonist, on DKD, and 4) the protective effect of AR modulators in experimental DKD models. We propose AR modulators as a new therapeutic option to treat DKD. Detailed mechanistic studies on the pharmacology of AR modulators will help us to develop effective first-in-class AR modulators against DKD.

Pharmacological Tuning of Adenosine Signal Nuances Underlying Heart Failure With Preserved Ejection Fraction

Heart failure with preserved ejection fraction (HFpEF) roughly represents half of the cardiac failure events in developed countries. The proposed 'systemic microvascular paradigm' has been used to explain HFpHF presentation heterogeneity. The lack of effective treatments with few evidence-based therapeutic recommendations makes HFpEF one of the greatest unmet clinical necessities worldwide. The endogenous levels of the purine nucleoside, adenosine, increase significantly following cardiovascular events. Adenosine exerts cardioprotective, neuromodulatory, and immunosuppressive effects by activating plasma membrane-bound P1 receptors that are widely expressed in the cardiovascular system. Its proven benefits have been demonstrated in preclinical animal tests. Here, we provide a comprehensive and up-to-date critical review about the main therapeutic advantages of tuning adenosine signalling pathways in HFpEF, without discounting their side effects and how these can be seized.

Dual Actions of A2A and A3 Adenosine Receptor Ligand Prevents Obstruction-Induced Kidney Fibrosis in Mice

Kidney fibrosis is the final outcome of chronic kidney disease (CKD). Adenosine plays a significant role in protection against cellular damage by activating four subtypes of adenosine receptors (ARs), A₁AR, A_2AAR, A_2BAR, and A₃AR. A_2AAR agonists protect against inflammation, and A₃AR antagonists effectively inhibit the formation of fibrosis. Here, we showed for the first time that LJ-4459, a newly synthesized dual-acting ligand that is an A_2AAR agonist and an A₃AR antagonist, prevents the progression of tubulointerstitial fibrosis. Unilateral ureteral obstruction (UUO) surgery was performed on 6-week-old male C57BL/6 mice. LJ-4459 (1 and 10 mg/kg) was orally administered for 7 days, started at 1 day before UUO surgery. Pretreatment with LJ-4459 improved kidney morphology and prevented the progression of tubular injury as shown by decreases in urinary kidney injury molecular-1 (KIM-1) and neutrophil gelatinase-associated lipocalin (NGAL) excretion. Obstruction-induced tubulointerstitial fibrosis was attenuated by LJ-4459, as shown by a decrease in fibrotic protein expression in the kidney. LJ-4459 also inhibited inflammation and oxidative stress in the obstructed kidney, with reduced macrophage infiltration, reduced levels of pro-inflammatory cytokines, as well as reduced levels of reactive oxygen species (ROS). These data demonstrate that LJ-4459 has potential as a therapeutic agent against the progression of tubulointerstitial fibrosis.

Hyperhomocysteinemia and Cardiovascular Disease: Is the Adenosinergic System the Missing Link?

The influence of hyperhomocysteinemia (HHCy) on cardiovascular disease (CVD) remains unclear. HHCy is associated with inflammation and atherosclerosis, and it is an independent risk factor for CVD, stroke and myocardial infarction. However, homocysteine (HCy)-lowering therapy does not affect the inflammatory state of CVD patients, and it has little influence on cardiovascular risk. The HCy degradation product hydrogen sulfide (H2S) is a cardioprotector. Previous research proposed a positive role of H2S in the cardiovascular system, and we discuss some recent data suggesting that HHCy worsens CVD by increasing the production of H2S, which decreases the expression of adenosine A2A receptors on the surface of immune and cardiovascular cells to cause inflammation and ischemia, respectively.

Role of Cardiac A2A Receptors Under Normal and Pathophysiological Conditions

This review presents an overview of cardiac A2A-adenosine receptors The localization of A2A-AR in the various cell types that encompass the heart and the role they play in force regulation in various mammalian species are depicted. The putative signal transduction systems of A2A-AR in cells in the living heart, as well as the known interactions of A2A-AR with membrane-bound receptors, will be addressed. The possible role that the receptors play in some relevant cardiac pathologies, such as persistent or transient ischemia, hypoxia, sepsis, hypertension, cardiac hypertrophy, and arrhythmias, will be reviewed. Moreover, the cardiac utility of A2A-AR as therapeutic targets for agonistic and antagonistic drugs will be discussed. Gaps in our knowledge about the cardiac function of A2A-AR and future research needs will be identified and formulated.

Purinergic signalling in the kidney: In physiology and disease

Historically, the control of renal vascular and tubular function has, for the most part, concentrated on neural and endocrine regulation. However, in addition to these extrinsic factors, it is now appreciated that several complex humoral control systems exist within the kidney that can act in an autocrine and/or paracrine fashion. These paracrine systems complement neuroendocrine regulation by dynamically fine-tuning renal vascular and tubular function to buffer rapid changes in nephron perfusion and flow rate of tubular fluid. One of the most pervasive is the extracellular nucleotide/P2 receptor system, which is central to many of the intrinsic regulatory feedback loops within the kidney such as renal haemodynamic autoregulation and tubuloglomerular feedback (TGF). Although physiological actions of extracellular adenine nucleotides were reported almost 100 years ago, the conceptual framework for purinergic regulation of renal function owes much to the work of Geoffrey Burnstock. In this review, we reflect on our >20-year collaboration with Professor Burnstock and highlight the research that is still unlocking the potential of the renal purinergic system to understand and treat kidney disease.

"Adenosine an old player with new possibilities in kidney diseases": Preclinical evidences and clinical perspectives

Renal injury might originate from multiple factors like ischemia reperfusion (I/R), drug toxicity, cystic fibrosis, radio contrast agent etc. The four adenosine receptor subtypes have been identified and found to show diverse physiological and pathological roles in kidney diseases. The activation of A₁ adenosine receptor (A₁) protects against acute kidney injury by improving renal hemodynamic alterations, decreasing tubular necrosis and its inhibition might facilitate removal of toxin or drug metabolite in chronic kidney disease models. Furthermore, recent findings revealed that A_2A receptor subtype activation regulates macrophage phenotype in experimental models of nephritis. Interestingly the emerging role of adenosine kinase inhibitors in kidney diseases has been discussed which act by increasing adenosine availability at target sites and thereby promote A_2A receptor stimulation. In addition, the least explored adenosine receptor subtype A₃ inhibition was observed to exert anti- oxidant, immunosuppressive and anti-fibrotic effects, but more studies are required to confirm its benefits in other renal injury models. The clinical studies targeting A₁ receptor in patients with pre-existing kidney disease have yielded disappointing results, perhaps owing to the origin of unexpected neurological complications during the course of trial. Importantly, conducting well designed clinical trials and testing adenosine modulators with lesser brain penetrability could clear the way for clinical approval of these agents for patients with renal functional impairments.

Alteration of purinergic signaling in diabetes: Focus on vascular function

Diabetes is an important risk factor for the development of cardiovascular disease including atherosclerosis and ischemic heart disease. Vascular complications including macro- and micro-vascular dysfunction are the leading causes of morbidity and mortality in diabetes. Disease mechanisms at present are unclear and no ideal therapies are available, which urgently calls for the identification of novel therapeutic targets/agents. An altered nucleotide- and nucleoside-mediated purinergic signaling has been implicated to cause diabetes-associated vascular dysfunction in major organs. Alteration of both purinergic P1 and P2 receptor sensitivity rather than the changes in receptor expression accounts for vascular dysfunction in diabetes. Activation of P2X₇ receptors plays a crucial role in diabetes-induced retinal microvascular dysfunction. Recent findings have revealed that both ecto-nucleotidase CD39, a key enzyme hydrolyzing ATP, and CD73, an enzyme regulating adenosine turnover, are involved in the renal vascular injury in diabetes. Interestingly, erythrocyte dysfunction in diabetes by decreasing ATP release in response to physiological stimuli may serve as an important trigger to induce vascular dysfunction. Nucleot(s)ide-mediated purinergic activation also exerts long-term actions including inflammatory and atherogenic effects in hyperglycemic and diabetic conditions. This review highlights the current knowledge regarding the altered nucleot(s)ide-mediated purinergic signaling as an important disease mechanism for the diabetes-associated vascular complications. Better understanding the role of key receptor-mediated signaling in diabetes will provide more insights into their potential as targets for the treatment.

Orally active, species-independent novel A3 adenosine receptor antagonist protects against kidney injury in db/db mice

Diabetic kidney disease (DKD) is the leading cause of end-stage kidney disease, and the current pharmacological treatment for DKD is limited to renin-angiotensin system (RAS) inhibitors. Adenosine is detectable in the kidney and is significantly elevated in response to cellular damage. While all 4 known subtypes of adenosine receptors, namely, A₁AR, A_2aAR, A_2bAR, and A₃AR, are expressed in the kidney, our previous study has demonstrated that a novel, orally active, species-independent, and selective A₃AR antagonist, LJ-1888, ameliorates unilateral ureteral obstruction-induced tubulointerstitial fibrosis. The present study examined the protective effects of LJ-2698, which has higher affinity and selectivity for A₃AR than LJ-1888, on DKD. In experiment I, dose-dependent effects of LJ-2698 were examined by orally administering 1.5, 5, or 10 mg/kg for 12 weeks to 8-week-old db/db mice. In experiment II, the effects of LJ-2698 (10 mg/kg) were compared to those of losartan (1.5 mg/kg), which is a standard treatment for patients with DKD. LJ-2698 effectively prevented kidney injuries such as albuminuria, glomerular hypertrophy, tubular injury, podocyte injury, fibrosis, inflammation, and oxidative stress in diabetic mice as much as losartan. In addition, inhibition of lipid accumulation along with increases in PGC1α, a master regulator of mitochondrial biogenesis, were demonstrated in diabetic mice treated with either LJ-2698 or losartan. These results suggest that LJ-2698, a selective A₃AR antagonist, may become a novel therapeutic agent against DKD.

A therapeutic treatment targeting a protein involved in the progression of diabetic kidney disease (DKD) shows promise in mouse trials. Between 30 and 40 per cent of diabetic patients suffer from DKD, a common cause to fatal end-stage kidney disease. Protein receptors, commonly expressed on cell surfaces throughout the body, play both positive and negative roles in diseases. The A₃ adenosine receptor (A₃AR) is highly expressed in diabetic kidney tissue, and is linked to disease progression. Hunjoo Ha at Ewha Womans University in Seoul, Republic of Korea, and co-workers demonstrated the positive effect of a novel drug in targeting A₃AR in mice with DKD. A 12-week treatment of the drug prevented kidney injury, lowered oxidative stress and inflammation, and improved kidney function. It may prove an invaluable drug, particularly in combination with an existing DKD drug.

Esculin ameliorates cognitive impairment in experimental diabetic nephropathy and induces anti-oxidative stress and anti-inflammatory effects via the MAPK pathway

Esculin is a derivative of coumarin, which is also an active ingredient of ash bark, and has antibacterial, anti-inflammatory, anti‑allergy and skin protective effects. The underlying mechanism and protective effects of esculin on cognitive impairment in experimental diabetic nephropathy (DN) was investigated in the present study. Male C57BL/6J 6‑week‑old mice were injected intravenously with a single dose of streptozotocin (STZ; 30 mg/kg). At 2 weeks after the STZ injection, mice received intravenous injection with 5, 10 or 20 mg/kg esculin for 2 weeks. In the present study, the results of the Morris water maze test demonstrated that esculin significantly improved behavior and recognition memory in STZ‑induced diabetic rats. Furthermore, treatment of STZ‑induced diabetic rats with esculin significantly inhibited tumor necrosis factor‑α, interleukin‑6, malondialdehyde, monocyte chemoattractant protein‑1 and intracellular adhesion molecule‑1 activity levels, and increased the activity of superoxide dismutase, in the kidney, which was determined by ELISA. In addition, esculin treatment significantly suppressed the renal protein expression of activator protein 1, phosphorylated (p)‑p38 mitogen activated protein kinase (MAPK) and p‑c‑Jun N‑terminal kinase, and increased p‑extracellular signal regulated kinase 1/2 protein expression, in STZ‑induced diabetic rats, as determined by western blotting. These results indicate that esculin may ameliorate cognitive impairment in experimental DN, and exert anti‑oxidative stress and anti‑inflammatory effects, via the MAPK signaling pathway. Thus, it may serve as a potential target for cognitive impairment of DN in the future.

Purinergic Signalling: Therapeutic Developments

Purinergic signalling, i.e., the role of nucleotides as extracellular signalling molecules, was proposed in 1972. However, this concept was not well accepted until the early 1990's when receptor subtypes for purines and pyrimidines were cloned and characterised, which includes four subtypes of the P1 (adenosine) receptor, seven subtypes of P2X ion channel receptors and 8 subtypes of the P2Y G protein-coupled receptor. Early studies were largely concerned with the physiology, pharmacology and biochemistry of purinergic signalling. More recently, the focus has been on the pathophysiology and therapeutic potential. There was early recognition of the use of P1 receptor agonists for the treatment of supraventricular tachycardia and A2A receptor antagonists are promising for the treatment of Parkinson's disease. Clopidogrel, a P2Y12 antagonist, is widely used for the treatment of thrombosis and stroke, blocking P2Y12 receptor-mediated platelet aggregation. Diquafosol, a long acting P2Y2 receptor agonist, is being used for the treatment of dry eye. P2X3 receptor antagonists have been developed that are orally bioavailable and stable in vivo and are currently in clinical trials for the treatment of chronic cough, bladder incontinence, visceral pain and hypertension. Antagonists to P2X7 receptors are being investigated for the treatment of inflammatory disorders, including neurodegenerative diseases. Other investigations are in progress for the use of purinergic agents for the treatment of osteoporosis, myocardial infarction, irritable bowel syndrome, epilepsy, atherosclerosis, depression, autism, diabetes, and cancer.

Adenosine contribution to normal renal physiology and chronic kidney disease

Adenosine is a nucleoside that is particularly interesting to many scientific and clinical communities as it has important physiological and pathophysiological roles in the kidney. The distribution of adenosine receptors has only recently been elucidated; therefore it is likely that more biological roles of this nucleoside will be unveiled in the near future. Since the discovery of the involvement of adenosine in renal vasoconstriction and regulation of local renin production, further evidence has shown that adenosine signaling is also involved in the tubuloglomerular feedback mechanism, sodium reabsorption and the adaptive response to acute insults, such as ischemia. However, the most interesting finding was the increased adenosine levels in chronic kidney diseases such as diabetic nephropathy and also in non-diabetic animal models of renal fibrosis. When adenosine is chronically increased its signaling via the adenosine receptors may change, switching to a state that induces renal damage and produces phenotypic changes in resident cells. This review discusses the physiological and pathophysiological roles of adenosine and pays special attention to the mechanisms associated with switching homeostatic nucleoside levels to increased adenosine production in kidneys affected by CKD.

Exogenously administered adenosine attenuates renal damage in streptozotocin-induced diabetic rats

BACKGROUND

Diabetic nephropathy (DNP) is one of the most serious complications of diabetes mellitus (DM). In the present study, we investigated the potential of adenosine as a therapeutic candidate for preventing DNP.

METHODS

Twenty-one adult male rats were included in the study. Fourteen rats were administered a single dose of 60 mg/kg streptozotocin (STZ) to induce diabetes. Seven rats served as normal control group. Diabetic rats were randomly divided into two groups: one group was treated with 1 mL/kg saline/day (DM + saline) and the other group was treated with 5 mg/kg/day adenosine (DM + adenosine) for 6 weeks. After 6 weeks, biochemical parameters including urea, creatinine, blood urea nitrogen (BUN), kidney injury molecule-1 (KIM-1) and tumor necrosis factor-α (TNF-α) were measured in plasma samples. Also, kidneys were removed for histopathological assessment.

RESULTS

Both of plasma KIM-1 and TNF-α levels were significantly higher in DM + saline group compared to controls. However, treatment of diabetic rats with adenosine significantly decreased the plasma KIM-1 and TNF-α levels compared to DM + saline group. Significant histopathological changes were observed in diabetic rats whereas adenosine treatment effectively prevented these changes.

CONCLUSIONS

The findings of the present study suggest that adenosine may be a useful therapeutic agent for preventing DNP.

Specific Activation of A3, A2A and A1 Adenosine Receptors in CD73-Knockout Mice Affects B16F10 Melanoma Growth, Neovascularization, Angiogenesis and Macrophage Infiltration

CD73 (ecto-5'-nucleotidase), a cell surface enzyme hydrolyzing AMP to adenosine, was lately demonstrated to play a direct role in tumor progression including regulation of tumor vascularization. It was also shown to stimulate tumor macrophage infiltration. Interstitial adenosine, accumulating in solid tumors due to CD73 enzymatic activity, is recognized as a main mediator regulating the production of pro- and anti-angiogenic factors, but the engagement of specific adenosine receptors in tumor progression in vivo is still poorly researched. We have analyzed the role of high affinity adenosine receptors A₁, A_2A, and A₃ in B16F10 melanoma progression using specific agonists (CCPA, CGS-21680 and IB-MECA, respectively). We limited endogenous extracellular adenosine background using CD73 knockout mice treated with CD73 chemical inhibitor, AOPCP (adenosine α,β-methylene 5’-diphosphate). Activation of any adenosine receptor significantly inhibited B16F10 melanoma growth but only at its early stage. At 14th day of growth, the decrease in tumor neovascularization and MAPK pathway activation induced by CD73 depletion was reversed by all agonists. Activation of A₁AR primarily increased angiogenic activation measured by expression of VEGF-R2 on tumor blood vessels. However, mainly A₃AR activation increased both the microvessel density and expression of pro-angiogenic factors. All agonists induced significant increase in macrophage tumor infiltration, with IB-MECA being most effective. This effect was accompanied by substantial changes in cytokines regulating macrophage polarization between pro-inflammatory and pro-angiogenic phenotype. Our results demonstrate an evidence that each of the analyzed receptors has a specific role in the stimulation of tumor angiogenesis and confirm significantly more multifaceted role of adenosine in its regulation than was already observed. They also reveal previously unexplored consequences to extracellular adenosine signaling depletion in recently proposed anti-CD73 cancer therapy.

Endothelin type A receptor inhibition normalises intrarenal hypoxia in rats used as a model of type 1 diabetes by improving oxygen delivery

AIMS/HYPOTHESIS

Intrarenal tissue hypoxia, secondary to increased oxygen consumption, has been suggested as a unifying mechanism for the development of diabetic nephropathy. Increased endothelin-1 signalling via the endothelin type A receptor (ETA-R) has been shown to contribute to the development of chronic kidney disease, but its role in kidney oxygen homeostasis is presently unknown.

METHODS

The effects of acute ETA-R inhibition (8 nmol/l BQ-123 for 30-40 min directly into the left renal artery) on kidney function and oxygen metabolism were investigated in normoglycaemic control and insulinopenic male Sprague Dawley rats (55 mg/kg streptozotocin intravenously 2 weeks before the main experiment) used as a model of type 1 diabetes.

RESULTS

Local inhibition of ETA-R in the left kidney did not affect BP in either the control or the diabetic rats. As previously reported, diabetic rats displayed increased kidney oxygen consumption resulting in tissue hypoxia in both the kidney cortex and medulla. The inhibition of ETA-Rs restored normal kidney tissue oxygen availability in the diabetic kidney by increasing renal blood flow, but did not affect oxygen consumption. Furthermore, ETA-R inhibition reduced the diabetes-induced glomerular hyperfiltration and increased the urinary sodium excretion. Kidney function in normoglycaemic control rats was largely unaffected by BQ-123 treatment, although it also increased renal blood flow and urinary sodium excretion in these animals.

CONCLUSIONS/INTERPRETATION

Acutely reduced intrarenal ETA-R signalling results in significantly improved oxygen availability in the diabetic kidney secondary to elevated renal perfusion. Thus, the beneficial effects of ETA-R inhibition on kidney function in diabetes may be due to improved intrarenal oxygen homeostasis.

Twenty years after ACEIs and ARBs: emerging treatment strategies for diabetic nephropathy

Diabetic nephropathy (DN) is a serious complication of both type 1 and type 2 diabetes mellitus. The disease is now the most common cause of end-stage kidney disease (ESKD) in developed countries, and both the incidence and prevalence of diabetes mellitus is increasing worldwide. Current treatments are directed at controlling hyperglycemia and hypertension, as well as blockade of the renin angiotensin system with angiotensin-converting enzyme inhibitors (ACEIs), and angiotensin receptor blockers. Despite these therapies, DN progresses to ESKD in many patients. As a result, much interest is focused on developing new therapies. It has been over two decades since ACEIs were shown to have beneficial effects in DN independent of their blood pressure-lowering actions. Since that time, our understanding of disease mechanisms in DN has evolved. In this review, we summarize major cell signaling pathways implicated in the pathogenesis of diabetic kidney disease, as well as emerging treatment strategies. The goal is to identify promising targets that might be translated into therapies for the treatment of patients with diabetic kidney disease.