Interaction of hypoxanthine/xanthine oxidase with nitrergic relaxation in the porcine gastric fundus

Dose-dependent effects of allopurinol on human foreskin fibroblast cells and human umbilical vein endothelial cells under hypoxia

Allopurinol, an inhibitor of xanthine oxidase, has been used in clinical trials of patients with cardiovascular and chronic kidney disease. These are two pathologies with extensive links to hypoxia and activation of the transcription factor hypoxia inducible factor (HIF) family. Here we analysed the effects of allopurinol treatment in two different cellular models, and their response to hypoxia. We explored the dose-dependent effect of allopurinol on Human Foreskin Fibroblasts (HFF) and Human Umbilical Vein Endothelial Cells (HUVEC) under hypoxia and normoxia. Under normoxia and hypoxia, high dose allopurinol reduced the accumulation of HIF-1α protein in HFF and HUVEC cells. Allopurinol had only marginal effects on HIF-1α mRNA level in both cellular systems. Interestingly, allopurinol effects over the HIF system were independent of prolyl-hydroxylase activity. Finally, allopurinol treatment reduced angiogenesis traits in HUVEC cells in an in vitro model. Taken together these results indicate that high doses of allopurinol inhibits the HIF system and pro-angiogenic traits in cells.

Hydrogen sulfide chemical biology: pathophysiological roles and detection

Hydrogen sulfide (H2S) is the most recent endogenous gasotransmitter that has been reported to serve many physiological and pathological functions in different tissues. Studies over the past decade have revealed that H2S can be synthesized through numerous pathways and its bioavailability regulated through its conversion into different biochemical forms. H2S exerts its biological effects in various manners including redox regulation of protein and small molecular weight thiols, polysulfides, thiosulfate/sulfite, iron-sulfur cluster proteins, and anti-oxidant properties that affect multiple cellular and molecular responses. However, precise measurement of H2S bioavailability and its associated biochemical and pathophysiological roles remains less well understood. In this review, we discuss recent understanding of H2S chemical biology, its relationship to tissue pathophysiological responses and possible therapeutic uses.

Role of APE1 in differentiated neuroblastoma SH-SY5Y cells in response to oxidative stress: use of APE1 small molecule inhibitors to delineate APE1 functions

Oxidative DNA damage has been implicated in a number of central nervous system pathologies. The base excision repair (BER) pathway is one of the most important cellular protection mechanisms that respond to oxidative DNA damage. Human apurinic (apyrimidinic) endonuclease/redox effector factor (APE1/Ref-1 or APE1) is an essential enzyme in the BER pathway and is expressed in both mitotic and post-mitotic cells in humans. In neurons, a reduction of APE1 expression increases chemotherapy-induced cytotoxicity, while overexpression of APE1 protects cells against the cytotoxicity. However, given the multiple functions of APE1, knockdown of total APE1 is not completely informative of whether it is the redox or DNA repair activity, or interactions with other proteins. Therefore, the use of selective small molecules that can block each function independent of the other is of great benefit in ascertaining APE1 function in post-mitotic cells. In this study, we chose differentiated SH-SY5Y cells as our post-mitotic cell line model to investigate whether a drug-induced decrease in APE1 DNA repair or redox activity contributes to the growth and survival of post-mitotic cells under oxidative DNA damaging conditions. Here, we demonstrate that overexpression of WT-APE1 or C65-APE1 (repair competent) results in significant increase in cell viability after exposure to H(2)O(2). However, the 177/226-APE1 (repair deficient) did not show a protective effect. This phenomenon was further confirmed by the use of methoxyamine (MX), which blocks the repair activity of APE1 that results in enhanced cell killing and apoptosis in differentiated SH-SY5Y cells and in neuronal cultures after oxidative DNA damaging treatments. Blocking APE1 redox function by a small molecule inhibitor, BQP did not decrease viability of SH-SY5Y cells or neuronal cultures following oxidative DNA damaging treatments. Our results demonstrate that the DNA repair function of APE1 contributes to the survival of nondividing post-mitotic cells following oxidative DNA damage.

Circulating adhesion molecules and purine nucleotides during kidney allograft reperfusion

The impairment of organ function due to ischemia-reperfusion injury is still an important problem in solid organ transplantation. Numerous experimental and clinical studies of native organs have shown that ischemia-reperfusion constitutes an acute inflammatory process involving cell surface adhesion molecule expression. These markers are crucial for the recruitment and infiltration of effector cells into the postischemic tissue. Purines released by the postischemic tissue as the products of the degradation of high-energy nucleotides can be regarded as markers of disturbed energy metabolism. The aim of this study was to examine the correlation between circulating adhesion molecules and purine metabolites in graft renal vein plasma during 49 cases of kidney reperfusion. E-selectin, ICAM-1, and VCAM-1 concentrations correlated positively with hypoxanthine concentrations during reperfusion, whereas the concentrations of ICAM-1 correlated negatively with xanthine concentrations. The results of the present study suggested that the concentrations of adhesion molecules in the renal vein during reperfusion correlated with purine metabolites, reflecting metabolic changes in renal tissue.

Effect of trimetazidine on xanthine oxidoreductase expression in rat kidney with ischemia--reperfusion injury

Ischemia/reperfusion (I/R) injury is often responsible for delayed graft function after transplantation. Trimetazidine (TMZ) is an anti-ischemic and antioxidant agent used to protect grafts from I/R injury. With the supply of molecular oxygen upon reperfusion of ischemic tissues, xanthine oxidoreductase (XOR) metabolizes xanthine and hypoxanthine to uric acid and free radicals are generated. The aim of the study was to examine the effect of TMZ on XOR expression in rat kidney with I/R injury. The study was carried out on Wistar rats divided into two groups: animals treated with TMZ and control group receiving placebo. TMZ (10 mg/kg/day) was administered for 30 days. There were no significant differences in XOR expression in kidneys without ischemia between rats treated with TMZ and control group, whereas the XOR expression in kidneys with ischemia was significantly decreased in rats treated with TMZ as compared with control animals. The XOR expression in ischemic kidney was significantly lower in comparison with kidney without ischemia in the group treated with TMZ. We suggest that the decrease in xanthine oxidoreductase expression is one of the beneficial mechanisms of TMZ on I/R injury, preventing the degradation of purine nucleotides during the oxidation of hypoxanthine to xanthine and uric acid and formation of free radicals.

Oxypurine and purine nucleoside concentrations in renal vein of allograft are potential markers of energy status of renal tissue

BACKGROUND

Impairment of organ function derived from ischemia-reperfusion injury is an important problem in solid organ transplantation. Cell alterations induced by ischemia prime the tissue for subsequent damage that occurs during the reperfusion phase. Purine nucleosides and oxypurines are products of adenine nucleotides degradation. Reperfusion and reoxygenation are accompanied by production of reactive oxygen species and free radicals, which lead to damage of graft tissue. The aim of this study was to measure concentrations of adenine nucleotides and their metabolites in renal allograft vein as well as in recipient's peripheral veins during the reperfusion period and to evaluate their usefulness as markers of tissue metabolism in kidney allografts.

METHODS

The study enrolled 20 renal transplant recipients. The first blood sample was taken from the recipient's ulnar vein before anastomosing of the kidney graft's vessels with recipient's iliac vessels. Samples were then taken from the renal allograft and ulnar veins 5 min after total graft reperfusion measured with an infrared camera. High-performance liquid chromatography (HPLC) was performed to measure whole blood and plasma concentrations of adenosine triphosphate (ATP), adenosine monophosphate (AMP), guanosine (Guo), inosine (Ino), hypoxanthine (Hyp), xanthine (Xan), uric acid (UA), and uridine (Urd).

RESULTS

Hyp and Xan concentrations were significantly increased in renal allograft vein after reperfusion as compared with peripheral vein during the pre- and post-reperfusion periods.

CONCLUSIONS

The results of the present study suggest that differences in Hyp and Xan concentrations between renal and peripheral veins reflect metabolic alterations in renal tissue during reperfusion and may be useful for graft function monitoring during reperfusion.

Oxypurine and nucleoside concentrations in renal veins during reperfusion are predictors of early graft function

OBJECTIVE

To examine whether purine and pyrimidine nucleoside concentrations as well as oxypurine concentrations in renal and peripheral veins during reperfusion correlate with graft function parameters.

MATERIAL AND METHODS

The study population comprised 25 recipients of cadaver kidney transplant. A first blood sample was taken from the recipient's peripheral vein before anastomosing the kidney allograft vessels with the recipient's iliac vessels. Subsequent samples were taken from the allograft renal vein and the recipient's peripheral vein 5 min after beginning reperfusion. High-performance liquid chromatography was done to measure plasma concentrations of the oxypurines hypoxanthine (Hyp), xanthine (Xan) and uric acid and the nucleosides guanosine, inosine (Ino) and uridine (Urd).

RESULTS

Concentrations of Hyp, Xan and Ino were significantly higher in the renal than the peripheral vein. The differences between the Xan, Hyp, Ino and Urd plasma concentrations in the renal and peripheral veins before and 5 min after reperfusion correlated positively and significantly with serum creatinine concentrations 24 and 72 h after graft transplantation. Moreover, the concentrations of Hyp were significantly increased in renal transplant recipients with delayed graft function.

CONCLUSION

The results of this study suggest that the concentration of Hyp in the kidney allograft vein can be a useful predictor of early graft function.

Hypoxanthine as a graft ischemia marker stimulates catalase activity in the renal vein during reperfusion in humans

BACKGROUND

The impairment of organ function derived from ischemia-reperfusion injury is still an important problem in solid organ transplantation. Cell alterations induced by ischemia prime the tissue for subsequent damage occurring during the reperfusion phase. Purine nucleotides and oxypurines are products of adenine nucleotide degradation. Reperfusion and reoxygenation are characterized by great production of reactive oxygen species and free radicals. On the contrary, superoxide dismutase, catalase, glutathione, and glutathione peroxidase are involved in protecting against free radicals. The aim of the study was to examine the correlation between concentrations of ischemia markers (hypoxanthine or inosine) and the activity of erythrocyte superoxide dismutase, catalase, or glutathione peroxidase.

PATIENTS AND METHODS

The study included 40 renal transplant recipients. Before anastomosis of the kidney vessels with the recipient's iliac vessels, a "0" blood sample was taken from the iliac vein. Then, after anastomosis, the renal vein of the graft was cannulated and blood samples I, II, and III were obtained. The reperfusion of the transplanted kidney was measured with a thermovision camera ThermaCAM SC500.

RESULTS

The plasma concentrations of hypoxanthine and inosine increased in statistically significant fashion immediately after total tissue reperfusion (P < .0001). Catalase activity at 4 minutes after total tissue reperfusion correlated positively with hypoxanthine concentrations immediately after total tissue reperfusion (Rs = +0.49), 2 minutes after total tissue reperfusion (Rs = +0.47), and 4 minutes after total tissue reperfusion (Rs = +0.46). There were no statistically significant correlations between hypoxanthine or inosine concentrations or superoxide dismutase or glutathione peroxidase activities.

CONCLUSIONS

The results of the present study suggest that catalase activity may correlate with the concentration of hypoxanthine in the graft renal vein and other mediators of oxidative stress.

Effect of trimetazidine on the nucleotide profile in rat kidney with ischemia-reperfusion injury

Ischemia-reperfusion injury is often responsible for delayed graft function after transplantation. Trimetazidine (TMZ) is an antioxidant agent used to protect grafts from ischemia-reperfusion injury. The aim of the study was to examine the effect of TMZ on nucleotide profile in rat kidney with ischemia-reperfusion injury. The study was carried out on Wistar rats divided into two groups: animals treated with TMZ and control group receiving placebo. TMZ 10mg/kg/day was administrated for 30 days. Concentrations of adenosine triphosphate (ATP), adenosine diphosphate (ADP), adenosine monophosphate (AMP), adenosine (Ado), guanosine triphosphate (GTP), guanosine diphosphate (GDP), guanosine monophosphate (GMP), guanosine (Guo), inosine monophosphate (IMP), inosine (Ino), hypoxanthine (Hyp), xanthine (Xan), uric acid (UA), uridine (Urd), nicotinamide adenine dinucleotide (NAD) and nicotinamide adenine dinucleotide phosphate (NADP) were determined in kidney tissues after ischemia-reperfusion using HPLC. The total adenine nucleotide concentration (TAN) and adenylate energy charge (AEC) were also determined. Moreover the kidneys were evaluated histologically. Tissue concentrations of ATP, ADP, AMP, TAN and AEC were significantly increased in kidneys from rats treated with TMZ in comparison with rats receiving placebo. Concentrations of products of nucleotide degradation: inosine (Ino), guanosine (Guo) and uridine (Urd), as well as oxypurines: Hyp and Xan, were significantly decreased in rats treated with trimetazidine. Moreover, significantly less pronounced acute tubular necrosis was observed in kidneys of rats treated with TMZ. These results suggest that trimetazidine protects against dephosphorylation of nucleotides and ischemic damage.