Effect of renal ischemia on cortical microsomal calcium accumulation

Biochemical mechanism underlying the pathogenesis of diabetic retinopathy and other diabetic complications in humans: the methanol-formaldehyde-formic acid hypothesis

Hyperglycemia in diabetic patients is associated with abnormally-elevated cellular glucose levels. It is hypothesized that increased cellular glucose will lead to increased formation of endogenous methanol and/or formaldehyde, both of which are then metabolically converted to formic acid. These one-carbon metabolites are known to be present naturally in humans, and their levels are increased under diabetic conditions. Mechanistically, while formaldehyde is a cross-linking agent capable of causing extensive cytotoxicity, formic acid is an inhibitor of mitochondrial cytochrome oxidase, capable of inducing histotoxic hypoxia, ATP deficiency and cytotoxicity. Chronic increase in the production and accumulation of these toxic one-carbon metabolites in diabetic patients can drive the pathogenesis of ocular as well as other diabetic complications. This hypothesis is supported by a large body of experimental and clinical observations scattered in the literature. For instance, methanol is known to have organ- and species-selective toxicities, including the characteristic ocular lesions commonly seen in humans and non-human primates, but not in rodents. Similarly, some of the diabetic complications (such as ocular lesions) also have a characteristic species-selective pattern, closely resembling methanol intoxication. Moreover, while alcohol consumption or combined use of folic acid plus vitamin B is beneficial for mitigating acute methanol toxicity in humans, their use also improves the outcomes of diabetic complications. In addition, there is also a large body of evidence from biochemical and cellular studies. Together, there is considerable experimental support for the proposed hypothesis that increased metabolic formation of toxic one-carbon metabolites in diabetic patients contributes importantly to the development of various clinical complications.

Intraoperative Verapamil Fails to Reduce Delayed Graft Function in Donation After Circulatory Death Renal Allografts

Background.

The shortage of transplantable organs has led to increased utilization of kidneys that may be particularly vulnerable to ischemia-reperfusion injury (IRI) and delayed graft function (DGF). Kidneys from donation after circulatory death (DCD) donors have additional IRI from donor procurement that results in increased risk of DGF. Verapamil may reduce IRI in kidney allografts when given at the time of organ reperfusion. This study sought to determine if intraoperative administration of verapamil (Ver) could reduce the risk of DGF in DCD kidney transplants.

Methods.

A single-center retrospective matched cohort study was performed of 93 Ver (–) kidney transplant recipients compared with 93 Ver (+) kidney transplant recipients, matched by donor age, Kidney Donor Profile Index, and DCD status. Covariates that could impact DGF risk were evaluated by univariate and multivariate logistic regression analyses.

Results.

The Ver (–) and Ver (+) matched cohorts did not have any significant differences in the demographic covariates. There was no difference in DGF rate between the Ver cohorts in either the overall study population or within the DCD subgroup. There was a trend toward reduced DGF in the Ver (+) cohort for cold ischemia time (CIT) ≤24 h, but this failed to achieve statistical significance. On multivariate analysis, only CIT was found to be independently associated with DGF.

Conclusions.

Intraoperative verapamil failed to reduce DGF risk in DCD kidney allografts. Limitations to this study include nonrandomization for the intraoperative administration of verapamil and the mean CIT >24 h in the study population. Only CIT was an independent prognosticator for DGF on multivariate analysis in a cohort matched for DCD status, consistent with prior studies.

The role of endoplasmic reticulum Ca2+-independent phospholipase a2γ in oxidant-induced lipid peroxidation, Ca2+ release, and renal cell death

Oxidant-induced lipid peroxidation and cell death are major components of ischemia/reperfusion and toxicant injury. Our previous studies showed that renal proximal tubular cells (RPTCs) express Ca(2+)-independent phospholipase A(2)γ (iPLA(2)γ) in endoplasmic reticulum (ER) and mitochondria and that iPLA(2)γ is cytoprotective. Our present studies reveal the role of ER-iPLA(2)γ in oxidant-induced ER lipid peroxidation, Ca(2+) release, and cell death. Oxidant tert-butyl hydroperoxide (TBHP) caused ER lipid peroxidation and Ca(2+) release in isolated rabbit kidney cortex microsomes. ER-iPLA(2)γ inhibition, using bromoenol lactone (BEL), potentiated both oxidant-induced ER lipid peroxidation and Ca(2+) release. Assessment of fatty acids using electrospray ionization-mass spectrometry revealed that ER-iPLA(2)γ mediates the TBHP-induced release of arachidonic acid (20:4), linoleic acid (18:2), and their oxidized forms (18:2-OH, 18:2-OOH, 20:4-OH, 20:4-OOH, 20:4-(OH)(3). iPLA(2)γ inhibition also accelerated oxidant-induced ER Ca(2+) release in RPTC. Depletion of ER Ca(2+) stores in RPTC with thapsigargin, an ER Ca(2+) pump inhibitor, prior to TBHP exposure reduced necrotic cell death and blocked the potentiation of TBHP-induced necrotic cell death by BEL. Together, these data provide strong evidence that ER-iPLA(2)γ protects renal cells from oxidant-induced necrotic cell death by releasing unsaturated and/or oxidized fatty acids from ER membranes, thereby preserving ER membrane integrity and preventing ER Ca(2+) release.

Salubrious Effect of Vitamin E Supplementation on Renal Stone Forming Risk Factors in Urogenital Tuberculosis Patients

The incidence of renal calculi has been evaluated to be 25% in urogenital tuberculosis patients. The stone could be caused due to the host, the pathogenic organism, or possibly by the treatment. Studies were carried out to find out the efficacy of vitamin E supplementation in reducing the risk of stone formation in renal tuberculosis patients. The study constituted four groups, Group I with 30 normal volunteers, the second group comprised of 36 renal tuberculosis patients (GuTb) a day before treatment. Third group comprised of 24 patients with regular anti tuberculosis drug regimen for sixty days. In the fourth group, 12 patients were treated with anti tuberculosis drug regimen along with supplementation of antioxidant vitamin E (200 mg/day) for sixty days. Hyperuricosuria and hypercalciuria were observed in group II and group III patients, along with increased excretion of oxalate and creatinine, accompanied by decreased excretion of inhibitors such as citrate and glycosaminoglycans (GAGs). Renal damage was evident with increased leakage of Lactate dehydrogenase (LDH), Alkaline phosphatase (ALP) and gamma-Glutamyl transferase (gamma-GT) in renal tuberculosis patients. From the results of the above study, it is obvious that increased urinary oxalate levels leads to cellular damage in GuTb patients, which is a prerequisite for crystal retention as revealed by the elevated urinary marker enzymes. Antioxidant therapy prevents membrane injury thereby reducing the risk of stone formation. Hence vitamin E supplementation has a salubrious effect in preventing stone forming tendency with routine anti tuberculosis drug regimen.

Altered expression of rat renal cortical OAT1 and OAT3 in response to bilateral ureteral obstruction

BACKGROUND

Bilateral ureteral obstruction (BUO) is characterized by the development of hemodynamic and tubular lesions. However, little is known about the expression of organic anion renal transporters. The objective of this work was to study the renal excretion of p-aminohippurate (PAH) and the cortical renal expression of the organic anion transporter 1 (OAT1) and organic anion transporter 3 (OAT3) in BUO rats.

METHODS

Male Wistar rats underwent bilateral obstruction of the proximal ureters for 24 hours (BUO) or sham operation. After 24 hours of ureteral releasing, the following studies were performed: PAH renal excretion employing conventional clearance techniques and OAT1 and OAT3 abundance (homogenates, intracellular and basolateral plasma membrane fractions from renal cortex) using immunoblotting and immunocytochemical techniques (light microscopic and confocal immunofluorescence microscopic analysis).

RESULTS

BUO rats showed a lower renal excretion of PAH. In obstructed kidneys, immunoblotting revealed a significant decrease in the abundance of both OAT1 and OAT3 in basolateral plasma membranes from renal cortex. An increase of OAT1 expression was observed in homogenates and in intracellular membrane fractions in kidneys from BUO rats compared with sham-operated ones, indicating an internalization of this carrier. Immunocytochemical techniques confirmed these results. On the contrary, OAT3 expression was reduced both in homogenates and in intracellular membrane fractions in obstructed kidneys.

CONCLUSION

BUO was associated with down-regulation of OAT1 and OAT3 in basolateral plasma membranes from proximal tubule cells, thus these carriers may play important roles in the impaired organic anion excretion displayed in the obstructed kidney.

Methanol and formic acid toxicity: biochemical mechanisms

Metabolism of methanol, methyl ethers, esters and amides give rise to formic acid. This acid is an inhibitor of the mitochondrial cytochrome oxidase causing histotoxic hypoxia. Formic acid is a weaker inhibitor than cyanide and hydrosulphide anions. The body burden of formate in methanol poisoning is high enough to cause acidosis, and other clinical symptoms. Part of the protons can be attributed to formic acid whereas the most significant acid load results from the hypoxic metabolism. The acidosis causes e.g. dilatation of cerebral vessels, facilitation of the entry of calcium ions into cells, loss of lysosomal latency and deranged production of ATP. The latter effect seems to impede parathormone-dependent calcium reabsorption in the kidney tubules. Besides, urinary acidification is affected by formic acid. Its excretion causes continuous recycling of the acid by the tubular cell Cl-/formate exchanger. This sequence of events may partially explain an accumulation of formate in urine. Occupational exposure to vapours of methanol and formic acid can be quantitatively monitored by urinary formic acid determinations. Formic acid toxicity may prove a suitable model for agents causing histotoxic hypoxia.

Cellular mechanism of ischemic acute renal failure: role of Ca2+ and calcium entry blockers

This presentation briefly reviews the cellular mechanism of ischemic acute renal failure (ARF) with particular emphasis on the role of Ca2+ and calcium entry blockers (CEB). Vascular consequences of an ischemic renal insult including vasoconstriction, diminished glomerular permeability, loss of autoregulation, and hypersensitivity to renal nerve stimulation may relate to increased cellular Ca2+ concentration in the renal afferent arteriole and glomerular mesangial cells. Evidence is also presented that the ischemic injury to tubular plasma membranes is associated with increased Ca2+ uptake. With an ischemic insult of a short duration, the renal mitochondria are able to buffer the increased cellular Ca2+. However, after an ischemic insult of long duration, the Ca2+ over-loaded mitochondria deteriorate, adenosine triphosphate (ATP) synthesis decreases, and cell death follows. If a sufficient number of renal tubular cells undergo this cell death, tubular obstruction, i.e. the maintenance phase of ARF, occurs.

Lipid peroxidation in the cortex and medulla of rabbit kidneys subjected to cold ischaemia and the value of protective agents

The storage of rabbit kidneys for 24 hr at 0 degrees C in isotonic saline resulted in significantly increased rates of lipid peroxidation, as measured by the formation of thiobarbituric acid-reactive material and Schiff bases during in vitro incubation of homogenates prepared from the cortex and medulla. In addition, the content of thiobarbituric acid-reactive material in the medulla was also significantly elevated as a result of cold storage for 24 hr. The effects of antioxidants (vitamin E), iron-chelation (desferrioxamine) and inhibitors of arachidonic acid oxidation (indomethacin and dazmegrel) on the rate of lipid peroxidation in homogenates prepared from ischaemic kidneys were studied. This demonstrated that lipid peroxidation in the cortex was predominantly non-specific and iron-catalysed whereas in the medulla approximately 50% of the TBA-reactive material was formed enzymically from arachidonic acid by cyclooxygenase.