Adenosine A2 receptor-mediated regulation of renal hemodynamics and glomerular filtration rate is abolished in diabetes

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.

Update on Pathogenesis of Glomerular Hyperfiltration in Early Diabetic Kidney Disease

In the existing stages of diabetic kidney disease (DKD), the first stage of DKD is called the preclinical stage, characterized by glomerular hyperfiltration, an abnormally elevated glomerular filtration rate. Glomerular hyperfiltration is an independent risk factor for accelerated deterioration of renal function and progression of nephropathy, which is associated with a high risk for metabolic and cardiovascular disease. It is imperative to understand hyperfiltration and identify potential treatments to delay DKD progress. This paper summarizes the current mechanisms of hyperfiltration in early DKD. We pay close attention to the effect of glucose reabsorption mediated by sodium-glucose cotransporters and renal growth on hyperfiltration in DKD patients, as well as the mechanisms of nitric oxide and adenosine actions on renal afferent arterioles via tubuloglomerular feedback. Furthermore, we also focus on the contribution of the atrial natriuretic peptide, cyclooxygenase, renin-angiotensin-aldosterone system, and endothelin on hyperfiltration. Proposing potential treatments based on these mechanisms may offer new therapeutic opportunities to reduce the renal burden in this population.

The Adenosinergic System as a Therapeutic Target in the Vasculature: New Ligands and Challenges

Adenosine is an adenine base purine with actions as a modulator of neurotransmission, smooth muscle contraction, and immune response in several systems of the human body, including the cardiovascular system. In the vasculature, four P1-receptors or adenosine receptors—A₁, A_2A, A_2B and A₃—have been identified. Adenosine receptors are membrane G-protein receptors that trigger their actions through several signaling pathways and present differential affinity requirements. Adenosine is an endogenous ligand whose extracellular levels can reach concentrations high enough to activate the adenosine receptors. This nucleoside is a product of enzymatic breakdown of extra and intracellular adenine nucleotides and also of S-adenosylhomocysteine. Adenosine availability is also dependent on the activity of nucleoside transporters (NTs). The interplay between NTs and adenosine receptors’ activities are debated and a particular attention is given to the paramount importance of the disruption of this interplay in vascular pathophysiology, namely in hypertension., The integration of important functional aspects of individual adenosine receptor pharmacology (such as in vasoconstriction/vasodilation) and morphological features (within the three vascular layers) in vessels will be discussed, hopefully clarifying the importance of adenosine receptors/NTs for modulating peripheral mesenteric vascular resistance. In recent years, an increase interest in purine physiology/pharmacology has led to the development of new ligands for adenosine receptors. Some of them have been patented as having promising therapeutic activities and some have been chosen to undergo on clinical trials. Increased levels of endogenous adenosine near a specific subtype can lead to its activation, constituting an indirect receptor targeting approach either by inhibition of NT or, alternatively, by increasing the activity of enzymes responsible for ATP breakdown. These findings highlight the putative role of adenosinergic players as attractive therapeutic targets for cardiovascular pathologies, namely hypertension, heart failure or stroke. Nevertheless, several aspects are still to be explored, creating new challenges to be addressed in future studies, particularly the development of strategies able to circumvent the predicted side effects of these therapies.

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.

Impact of Iodinated Contrast on Renal Function and Hemodynamics in Rats with Chronic Hyperglycemia and Chronic Kidney Disease

Iodinated contrast (IC) is clinically used in diagnostic and interventional procedures, but its use can result in contrast-induced acute kidney injury (CI-AKI). Chronic kidney disease (CKD) and chronic hyperglycemia (CH) are important predisposing factors to CI-AKI. The aim of this study was to investigate the impact of iodinated contrast on the renal function and hemodynamics in rats with chronic hyperglycemia and chronic kidney disease. A total of 30 rats were divided into six groups; Sham: control of chronic renal disease; Citrate: control of chronic hyperglycemia (CH); Nx5/6: rats with 5/6 nephrectomy; Chronic Hyperglycemia: rats receiving Streptozotocin 65 mg/kg; Nx5/6 + IC: rats Nx5/6 received 6 mL/kg of IC; CH + IC: Chronic hyperglycemia rats receiving 6 mL/kg of IC. Renal function (inulin clearance; urinary neutrophil gelatinase-associated lipocalin, NGAL) and hemodynamics (arterial blood pressure; renal blood flow; renal vascular resistance) were evaluated. Iodinated contrast significantly increased urinary NGAL and reduced inulin clearance, while the hemodynamics parameters showed changes in arterial blood pressure, renal blood flow, and renal vascular resistance in both CKD and CH groups. The results suggest that the iodinated contrast in risk factors models has important impact on renal function and hemodynamics. NGAL was confirmed to play a role of highlight in diagnosis of CI-AKI.

Differences in susceptibility to develop parameters of diabetic nephropathy in four mouse strains with type 1 diabetes

One-third of diabetes mellitus patients develop diabetic nephropathy, and with underlying mechanisms unknown it is imperative that diabetic animal models resemble human disease. The present study investigated the susceptibility to develop diabetic nephropathy in four commonly used and commercially available mouse strains with type 1 diabetes to determine the suitability of each strain. Type 1 diabetes was induced in C57Bl/6, NMRI, BALB/c, and 129Sv mice by alloxan, and conscious glomerular filtration rate, proteinuria, and oxidative stress levels were measured in control and diabetic animals at baseline and after 5 and 10 wk. Histological alterations were analyzed using periodic acid-Schiff staining. Diabetic C57Bl/6 displayed increased glomerular filtration rate, i.e., hyperfiltration, whereas all other parameters remained unchanged. Diabetic NMRI developed the most pronounced hyperfiltration as well as increased oxidative stress and proteinuria but without glomerular damage. Diabetic BALB/c did not develop hyperfiltration but presented with pronounced proteinuria, increased oxidative stress, and glomerular damage. Diabetic 129Sv displayed proteinuria and increased oxidative stress without glomerular hyperfiltration or damage. However, all strains displayed intrastrain correlation between oxidative stress and proteinuria. In conclusion, diabetic C57Bl/6 and NMRI both developed glomerular hyperfiltration but neither presented with histological damage, although NMRI developed low-degree proteinuria. Thus these strains may be suitable when investigating the mechanism causing hyperfiltration. Neither BALB/c nor 129Sv developed hyperfiltration although both developed pronounced proteinuria. However, only BALB/c developed detectable histological damage. Thus BALB/c may be suitable when studying the roles of proteinuria and histological alterations for the progression of diabetic nephropathy.

Why is diabetes mellitus a risk factor for contrast-induced nephropathy?

Contrast-induced nephropathy (CIN) remains a leading cause of iatrogenic acute kidney injury, as the usage of contrast media for imaging and intravascular intervention keeps expanding. Diabetes is an important predisposing factor for CIN, particularly in patients with renal functional impairment. Renal hypoxia, combined with the generation of reactive oxygen species, plays a central role in the pathogenesis of CIN, and the diabetic kidney is particularly susceptible to intensified hypoxic and oxidative stress following the administration of contrast media. The pathophysiology of this vulnerability is complex and involves various mechanisms, including a priori enhanced tubular transport activity, oxygen consumption, and the generation of reactive oxygen species. The regulation of vascular tone and peritubular blood flow may also be altered, particularly due to defective nitrovasodilation, enhanced endothelin production, and a particular hyperresponsiveness to adenosine-related vasoconstriction. In addition, micro- and macrovascular diseases and chronic tubulointerstitial changes further compromise regional oxygen delivery, and renal antioxidant capacity might be hampered. A better understanding of these mechanisms and their control in the diabetic patient may initiate novel strategies in the prevention of contrast nephropathy in these susceptible patients.