Adenosine A1 receptors contribute to mitochondria vulnerability to pro-oxidant stressors

Caffeine attenuates seizure and brain mitochondrial disruption induced by Tramadol: the role of adenosinergic pathway

Tramadol (TR) is an analgesic drug used to treat moderate-to-severe pain but it induces seizure even at therapeutic doses. The exact mechanism of TR-inducing seizure is not clear but inhibition of the serotonin, GABA, and nitrous oxide (NOS) pathways are the commonly proposed mechanisms. Adenosinergic system has a crucial function in the modulation of seizure. Also, oxidative damage is an unavoidable effect of the seizure. This study was conducted to evaluate the role of the adenosinergic system on the seizure and oxidative stress biomarkers induced by TR using antagonist of the adenosinergic receptors in the Albino mice. For that purpose, generated clonic seizure, as seizure threshold, was evaluated by TR. Caffeine (CAF; 8 mg/kg, i.p.), a nonselective antagonist of adenosine receptors, was administered 1 hour before the seizure induction. The seizure threshold significantly increased by CAF-treated group when compared to TR group (p < 0.001). Oxidative stress biomarkers such as reactive oxygen species, protein carbonyl content, and lipid peroxidation significantly decreased and glutathione content significantly increased by CAF in brain mitochondria compared to the TR group, whereas oxidative biomarkers significantly increased in the TR group compared to the control group. The results of the present study suggested that the adenosinergic system is involved in seizure induced by TR and meanwhile, inhibition of adenosine receptors can decrease the TR seizure threshold and also decrease the induced oxidative damage in the brain mitochondria.

Adenosine receptors: regulatory players in the preservation of mitochondrial function induced by ischemic preconditioning of rat liver

Although adenosine A₁ receptors (A1R) have been associated to ischemic preconditioning (IPC), direct evidence for their ability to preserve mitochondrial function upon hepatic preconditioning is still missing and could represent a novel strategy to boost the quality of liver transplants. We tested if the A1R antagonist 8-cyclopentyl-1,3-dipropylxanthine (DPCPX) prevented IPC in the liver and if the A1R agonist 2-chloro-N⁶-cyclopentyladenosine (CCPA) might afford a pharmacological preconditioning. Livers underwent a 120 min of 70% warm ischemia and 16 h of reperfusion (I/R), and the IPC group underwent a 5-min ischemic episode followed by a 10-min period of reperfusion before I/R. DPCPX or CCPA was administered intraperitoneally 2 h before IPC or I/R. The control of mitochondrial function emerged as the central element affected by IPC and controlled by endogenous A1R activation. Thus, livers from IPC- or CCPA-treated rats displayed an improved oxidative phosphorylation with higher state 3 respiratory rate, higher respiratory control ratio, increased ATP content, and decreased lag phase. IPC and CCPA also prevented the I/R-induced susceptibility to calcium-induced mitochondrial permeability transition, the rate of reactive oxygen species (ROS) generation, and the decreased mitochondrial content of phospho-Ser⁹ GSK-3β. DPCPX abrogated these effects of IPC. These implicate the control of GSK-3β activity by Akt-mediated Ser⁹-GSK-3β phosphorylation preserving the efficiency of oxidative phosphorylation and ROS-mediated cell death in the ability of A1R activation to mimic IPC in the liver. In conclusion, the parallel between IPC and A1R-mediated preconditioning also paves the way to consider a putative therapeutic use of the later in liver transplants.

The Tm7sf2 Gene Deficiency Protects Mice against Endotoxin-Induced Acute Kidney Injury

Cholesterol is essential for diverse cellular functions and cellular and whole-body cholesterol homeostasis is highly controlled. Cholesterol can also influence cellular susceptibility to injury. The connection between cholesterol metabolism and inflammation is exemplified by the Tm7sf2 gene, the absence of which reveals an essential role in cholesterol biosynthesis under stress conditions but also results in an inflammatory phenotype, i.e. NF-κB activation and TNFα up-regulation. Here, by using Tm7sf2^+/+and Tm7sf2^−/− mice, we investigated whether the Tm7sf2 gene, through its role in cholesterol biosynthesis under stress conditions, is involved in the renal failure induced by the administration of LPS. We found that the loss of Tm7sf2 gene results in significantly reduced blood urea nitrogen levels accompanied by decreased renal inflammatory response and neutral lipid accumulation. The increased expression of fatty acids catabolic enzymes reduces the need of the renal autophagy, a known crucial nutrient-sensing pathway in lipid metabolism. Moreover, we observed that the Tm7sf2 insufficiency is responsible for the inhibition of the NF-κB signalling thus dampening the inflammatory response and leading to a reduced renal damage. These results suggest a pivotal role for Tm7sf2 in renal inflammatory and lipotoxic response under endotoxemic conditions.

Equilibrative nucleoside transporter 3 depletion in β-cells impairs mitochondrial function and promotes apoptosis: Relationship to pigmented hypertrichotic dermatosis with insulin-dependent diabetes

Loss of function recessive mutations in the SLC29A3 gene that encodes human equilibrative nucleoside transporter 3 (ENT3) have been identified in patients with pigmented hypertrichotic dermatosis with insulin-dependent diabetes (PHID). ENT3 is a member of the equilibrative nucleoside transporter (ENT) family whose primary function is mediating transport of nucleosides and nucleobases. The aims of this study were to characterise ENT3 expression in islet β-cells and identify the effects of its depletion on β-cell mitochondrial activity and apoptosis. RT-PCR amplification identified ENT3 expression in human and mouse islets and exocrine pancreas, and in MIN6 β-cells. Immunohistochemistry using human and mouse pancreas sections exhibited extensive ENT3 immunostaining of β-cells, which was confirmed by co-staining with an anti-insulin antibody. In addition, exposure of dispersed human islet cells and MIN6 β-cells to MitoTracker and an ENT3 antibody showed co-localisation of ENT3 to β-cell mitochondria. Consistent with this, Western blot analysis confirmed enhanced ENT3 immunoreactivity in β-cell mitochondria-enriched fractions. Furthermore, ENT3 depletion in β-cells increased mitochondrial DNA content and promoted an energy crisis characterised by enhanced ATP-linked respiration and proton leak. Finally, inhibition of ENT3 activity by dypridamole and depletion of ENT3 by siRNA-induced knockdown resulted in increased caspase 3/7 activities in β-cells. These observations demonstrate that ENT3 is predominantly expressed by islet β-cells where it co-localises with mitochondria. Depletion of ENT3 causes mitochondrial dysfunction which is associated with enhanced β-cell apoptosis. Thus, apoptotic loss of islet β-cells may contribute to the occurrence of autoantibody-negative insulin-dependent diabetes in individuals with non-functional ENT3 mutations.

Adenosine A1-receptor deficiency diminishes afferent arteriolar and blood pressure responses during nitric oxide inhibition and angiotensin II treatment

Adenosine mediates tubuloglomerular feedback responses via activation of A1-receptors on the renal afferent arteriole. Increased preglomerular reactivity, due to reduced nitric oxide (NO) production or increased levels of ANG II and reactive oxygen species (ROS), has been linked to hypertension. Using A1-receptor knockout (A1−/−) and wild-type (A1+/+) mice we investigated the hypothesis that A1-receptors modulate arteriolar and blood pressure responses during NO synthase (NOS) inhibition or ANG II treatment. Blood pressure and renal afferent arteriolar responses were measured in nontreated mice and in mice with prolonged Nω-nitro-l-arginine methyl ester hydrochloride (l-NAME) or ANG II treatment. The hypertensive responses to l-NAME and ANG II were clearly attenuated in A1−/− mice. Arteriolar contractions to l-NAME (10−4 mol/l; 15 min) and cumulative ANG II application (10−12 to 10−6 mol/l) were lower in A1−/− mice. Simultaneous treatment with tempol (10−4 mol/l; 15 min) attenuated arteriolar responses in A1+/+ but not in A1−/− mice, suggesting differences in ROS formation. Chronic treatment with l-NAME or ANG II did not alter arteriolar responses in A1−/− mice, but enhanced maximal contractions in A1+/+ mice. In addition, chronic treatments were associated with higher plasma levels of dimethylarginines (asymmetrical and symmetrical) and oxidative stress marker malondialdehyde in A1+/+ mice, and gene expression analysis showed reduced upregulation of NOS-isoforms and greater upregulation of NADPH oxidases. In conclusion, adenosine A1-receptors enhance preglomerular responses during NO inhibition and ANG II treatment. Interruption of A1-receptor signaling blunts l-NAME and ANG II-induced hypertension and oxidative stress and is linked to reduced responsiveness of afferent arterioles.