Metabolism of aminonucleoside-8-14C in the rat and guinea pig

Glomerular Epithelial Cells-Targeted Heme Oxygenase-1 Over Expression in the Rat: Attenuation of Proteinuria in Secondary But Not Primary Injury

BACKGROUND/AIMS

Induction of heme oxygenase 1 (HO-1) in glomerular epithelial cells (GEC) in response to injury is poor and this may be a disadvantage. We, therefore, explored whether HO-1 overexpression in GEC can reduce proteinuria induced by puromycin aminonucleoside (PAN) or in anti-glomerular basement membrane (GBM) antibody (Ab)-mediated glomerulonephritis (GN).

METHODS

HO-1 overexpression in GEC (GECHO-1) of Sprague-Dawley rats was achieved by targeting a FLAG-human (h) HO-1 using transposon-mediated transgenesis. Direct GEC injury was induced by a single injection of PAN. GN was induced by administration of an anti-rat GBM Ab and macrophage infiltration in glomeruli was assessed by immunohistochemistry and western blot analysis, which was also used to assess glomerular nephrin expression.

RESULTS

In GECHO-1 rats, FLAG-hHO-1 transprotein was co-immunolocalized with nephrin. Baseline glomerular HO-1 protein levels were higher in GECHO-1 compared to wild type (WT) rats. Administration of either PAN or anti-GBM Ab to WT rats increased glomerular HO-1 levels. Nephrin expression markedly decreased in glomeruli of WT or GECHO-1 rats treated with PAN. In anti-GBM Ab-treated WT rats, nephrin expression also decreased. In contrast, it was preserved in anti-GBM Ab-treated GECHO-1 rats. In these, macrophage infiltration in glomeruli and the ratio of urine albumin to urine creatinine (Ualb/Ucreat) were markedly reduced. There was no difference in Ualb/Ucreat between WT and GECHO-1 rats treated with PAN.

CONCLUSION

Depending on the type of injury, HO-1 overexpression in GEC may or may not reduce proteinuria. Reduced macrophage infiltration and preservation of nephrin expression are putative mechanisms underlying the protective effect of HO-1 overexpression following immune injury.

Over-expression of adenosine deaminase in mouse podocytes does not reverse puromycin aminonucleoside resistance

Background

Edema in nephrotic syndrome results from renal retention of sodium and alteration of the permeability properties of capillaries. Nephrotic syndrome induced by puromycin aminonucleoside (PAN) in rats reproduces the biological and clinical signs of the human disease, and has been widely used to identify the cellular mechanisms of sodium retention. Unfortunately, mice do not develop nephrotic syndrome in response to PAN, and we still lack a good mouse model of the disease in which the genetic tools necessary for further characterizing the pathophysiological pathway could be used. Mouse resistance to PAN has been attributed to a defect in glomerular adenosine deaminase (ADA), which metabolizes PAN. We therefore attempted to develop a mouse line sensitive to PAN through induction of normal adenosine metabolism in their podocytes.

Methods

A mouse line expressing functional ADA under the control of the podocyte-specific podocin promoter was generated by transgenesis. The effect of PAN on urinary excretion of sodium and proteins was compared in rats and in mice over-expressing ADA and in littermates.

Results

We confirmed that expression of ADA mRNAs was much lower in wild type mouse than in rat glomerulus. Transgenic mice expressed ADA specifically in the glomerulus, and their ADA activity was of the same order of magnitude as in rats. Nonetheless, ADA transgenic mice remained insensitive to PAN treatment in terms of both proteinuria and sodium retention.

Conclusions

Along with previous results, this study shows that adenosine deaminase is necessary but not sufficient to confer PAN sensitivity to podocytes. ADA transgenic mice could be used as a background strain for further transgenesis.

Inducible rodent models of acquired podocyte diseases

Glomerular diseases remain the leading cause of chronic and end-stage kidney disease. Significant advances in our understanding of human glomerular diseases have been enabled by the development and better characterization of animal models. Diseases of the glomerular epithelial cells (podocytes) account for the majority of proteinuric diseases. Rodents have been extensively used experimentally to better define mechanisms of disease induction and progression, as well as to identify potential targets and therapies. The development of podocyte-specific genetically modified mice has energized the research field to better understand which animal models are appropriate to study acquired podocyte diseases. In this review we discuss inducible experimental models of acquired nondiabetic podocyte diseases in rodents, namely, passive Heymann nephritis, puromycin aminonucleoside nephrosis, adriamycin nephrosis, liopolysaccharide, crescentic glomerulonephritis, and protein overload nephropathy models. Details are given on the model backgrounds, how to induce each model, the interpretations of the data, and the benefits and shortcomings of each. Genetic rodent models of podocyte injury are excluded.

Does captopril change oxidative stress in puromycin aminonucleoside nephropathy?

Puromycin aminonucleoside (PAN) nephropathy in rats has been induced by the intraperitoneal injections of PAN. One group of animals which received PAN has been treated simultaneously with captopril (angiotensine converting enzyme-ACE-inhibitor) with the aim to test whether continuing treatment with captopril along with PAN injections would be able to modulate the toxic effects of PAN. The third group of rats was given only captopril. Morphological changes in the kidney were evaluated by scanning electron microscopy that showed the loss of podocyte foot processes in the kidney of PAN treated animals but also in the kidney of captopril treated ones as well as in the animals treated with both drugs simultaneously. Reduced glutathione content, catalase, superoxide dismutase (SOD), glutathione peroxidase (GSH-Px), xanthine oxidase activities as well as lipid peroxides were investigated in rat blood and kidney. Captopril given alone produced a significant decrease of plasma lipid peroxides, but it did not show any significant effect on investigated antioxidative factor levels neither in blood nor in the kidney. PAN given alone produced a significant depletion of plasma lipid peroxides, kidney catalase and erythrocyte GSH-Px activity as well as a significant increase of plasma catalase and erythrocyte SOD activity. Treatment of animals with both drugs simultaneously resulted in a significant increase of erythrocyte SOD activity and a significant decrease of plasma lipid peroxides, erythrocyte GSH-Px and kidney SOD activities. Kidney xanthine oxidase activity showed a significant increase in both PAN and PAN plus captopril treated animals in comparison with the values of captopril treated rats. These data suggest that PAN changes the antioxidative factor pattern in rat blood and kidney. Contrary to our expectations that captopril may protect the toxic effects of PAN it only to a certain extent modifies these effects showing protective effect only on tissue catalase activity.

NAD(P)H oxidase activity in cultured human podocytes: effects of adenosine triphosphate

Reactive oxygen species contribute to glomerular damage and proteinuria. In this study, we show that cultured human podocytes produce superoxide in response to extracellular adenosine triphosphate (ATP), and we identified the oxidases involved in this process. Adenosine triphosphate (10-4 M for 4 hr) raised superoxide production from 1.28 +/- 0.15 to 2.67 &/- 0.34 nmol/mg protein/min. Studies with podocyte homogenates revealed activation of both nicotinamide adenine dinucleotide (NADH; from 2.65 +/- 0.23 to 7.43 +/- 0.57) and nicotinamide adenine dinucleotide phosphate (NADPH) dependent oxidases [from 1.74 +/- 0.13 to 4.05 +/- 0.12 (nmol O2/mg protein/min)] by ATP. Activity of xanthine-oxidases was low and unchanged by ATP. Activation of the plasma-membrane bound NAD(P)H oxidases by ATP was time and dose dependent. Reverse transcribed-polymerase chain reaction (RT-PCR) studies with primers derived from monocyte sequences amplified mRNA for the NADPH oxidase subunits p22phox, p47phox, gp91phox, and p67phox, and the latter was transiently increased by ATP. Experiments with actinomycin D and cycloheximide suggested that ATP modulates enzyme activity at the transcriptional and translational levels. In conclusion, NAD(P)H dependent, membrane associated oxidases represent the major superoxide source in human podocytes. Activation of NAD(P)H oxidase by ATP might be secondary to increased mRNA expression of the NADPH oxidase subunit gp67phox.

Dietary antioxidant inhibits lipoprotein oxidation and renal injury in experimental focal segmental glomerulosclerosis

Lipid peroxidation may be involved in the pathogenesis of focal segmental glomerulosclerosis (FSGS). In the present study we examined whether lipid-soluble antioxidants, probucol and vitamin E, could inhibit renal injury in rats with chronic puromycin aminonucleoside (PA) nephrosis and dietary hypercholesterolemia by protecting lipoproteins from oxidation. Male Sprague-Dawley rats received six intraperitoneal injections of PA over a 10 week period and were fed a high cholesterol (HC) diet (PA-HC) or the same diet supplemented with either 1% probucol or vitamin E (100 IU/kg) for 32 weeks. For comparison, a group of rats received PA injections and a normal diet (PA-normal) with or without probucol or vitamin E. Another group rats received saline injections instead of PA and were fed a HC diet (Sal-HC) with or without probucol or vitamin E. At the end of the experiment, proteinuria, FSGS and tubulointerstitial lesions were present in the untreated rats with PA-HC or PA-normal. The magnitude of these lesions was significantly greater in the PA-HC rats than the PA-normal. In contrast to the PA-HC group with hypercholesterolemia, the PA-normal group did not show hypercholesterolemia from week 16 onwards. The rats with PA-HC alone showed significantly higher renal cortical malondialdehyde (MDA) levels and greater susceptibility of plasma very low density lipoprotein (VLDL) + low density lipoprotein (LDL) to the copper-mediated oxidation than the rats with PA-normal or Sal-HC alone. The administration of probucol or vitamin E in the rats with PA-HC significantly reduced the susceptibility of plasma VLDL + LDL to in vitro oxidation, renal cortical MDA level, proteinuria, mesangial volume density and magnitude of FSGS and interstitial lesions. Immunohistochemical staining of renal tissue showed focal segmental distribution of oxidized LDL (Ox-LDL) in the glomeruli of rats with PA-HC. Administration of probucol or vitamin E reduced the intensity of Ox-LDL staining. The staining with ED1 demonstrated that infiltrating glomerular macrophages were significantly more prevalent in the untreated rats with PA-HC than PA-normal or Sal-HC. Treatment with probucol or vitamin E significantly reduced the number of glomerular macrophages in the rats with PA-HC. These results suggest that alimentary hypercholesterolemia aggravates the renal damage in association with increased renal lipid peroxides in chronic PA nephrosis, and that dietary probucol or vitamin E attenuates renal injury in rats with PA-HC possibly by making lipoproteins resistant to oxidation and by inhibiting intraglomerular macrophage infiltration.

Time course analysis of serum and urinary proteins by SDS-PAGE in experimental nephrotic syndrome

Serum and urinary proteins from rats with nephrotic syndrome (NS) induced by puromycin aminonucleoside (PAN) were analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). Analysis was made on days 2, 4, 6, 8, 10, 12, 16, 20, and 30 after PAN injection. Data were compared with control rats (C). Rats developed proteinuria on days 4-30 and hypoproteinemia on days 4-16. Total protein concentration in serum and urine was similar on day 6. SDS-PAGE revealed that urinary albumin augmented on days 4-30 and serum albumin decreased markedly on days 4-20. Albumin concentration in serum and urine was similar on days 4-16. In addition, the study examined serum changes of 7 other proteins (designed as A, B, C, D, E, F, and G) which appeared or increased in urine, and whose molecular weights were higher (A, B, and C) or lower (D, E, F, and G) than that of albumin. In serum, protein A remained unchanged; protein B and G increased; proteins C, D, E, and F decreased. The qualitative pattern of urinary proteins remained essentially unchanged on days 4-30. During the intense proteinuria, the serum concentrations of protein B and albumin were similar and the urine concentrations of proteins C and D became comparable to that found in serum. These 7 serum proteins did not show the same behavior although all of them were excreted in urine. These data indicate that in PAN-nephrotic rats: (a) urinary proteins can be of low and high molecular weight, (b) serum proteins can be regulated independently of their urinary excretion and molecular weight, (c) the urine concentration of total protein and some specific proteins can reach values similar to that found in serum during the intense hypoproteinemia, and (d) the qualitative pattern of urinary proteins was unrelated to the magnitude of proteinuria.

Reactive oxygen species in puromycin aminonucleoside nephrosis: in vitro studies

We examined the role of reactive oxygen species (ROS) in puromycin aminonucleoside (PAN)-induced changes to glomerular epithelial cells (GECs) in vitro. Levels of superoxide anion (O2.-), hydrogen peroxide (H2O2) and hydroxyl radical (HO.) were measured in rat kidney-slice cultures containing PAN with or without antioxidants (allopurinol, probucol and alpha-tocopherol/ascorbic acid). GEC morphology was assessed after three days of culture using transmission (TEM) and scanning (SEM) electron microscopy. The effects of hypoxanthine on GEC ultrastructure was also assessed. O2.-, H2O2 and HO. were generated when PAN was added to kidney-slice cultures in Medium 199. TEM morphometry revealed that incubation with PAN (100 micrograms/ml) significantly (P < 0.05 at least) retarded the loss of GEC foot processes normally seen in vitro. When the hydrophobic antioxidants probucol or alpha-tocopherol/ascorbic acid, which scavenged/inhibited generation of O2.-, H2O2 and HO., were added to cultures containing PAN, the effect of PAN on foot processes was abolished. The TEM appearance of GECs now resembled that seen in control cultures. On the other hand, SEM revealed that probucol and alpha-tocopherol/ascorbic acid provided no protection against the changes induced by PAN in GEC cell bodies or major processes. Allopurinol provided no protection against the changes induced by PAN in GEC cell bodies, major processes or foot processes. The addition of hypoxanthine to kidney-slice cultures did not result in the generation of O2.-, H2O2 or HO., or alter GEC ultrastructure. These findings indicate that ROS play a role in PAN-induced alterations to GEC foot process architecture in vitro. However, the xanthine oxidase pathway does not appear to play a major role in generating ROS from PAN in vitro.

The role of reactive oxygen species in animal models of glomerular disease

Reactive oxygen metabolites have been demonstrated to play a pathobiologic role in a number of experimental models of both immune and nonimmune glomerular injury. Using scavenging substances, enzyme inhibitors, and transition metal chelators, all of the major reactive oxygen metabolites have been implicated in glomerular injury. In addition, in neutrophil-dependent models, interaction between neutrophil-derived myeloperoxidase and halide anions has been shown to be involved in glomerular damage, as well as halogenation of the glomerular basement membrane (GBM). Finally, recent attention has focused on the role of cytokines (perhaps elaborated by infiltrating monocytes/macrophages) in stimulating mesangial cells (MC) to produce reactive oxygen species. Theoretically, this pathobiologic sequence could further enhance an inflammatory state within the glomerular tuft and enable the propagation of initial glomerular injury, which may be associated with an increase in monocyte infiltration into the mesangium, to glomerulosclerosis in experimental models that manifest this transition.

Metabolism and pharmacokinetics of the anti-varicella-zoster virus agent 6-dimethylaminopurine arabinoside

The metabolism of 6-dimethylaminopurine arabinoside (ara-DMAP), a potent inhibitor of varicella-zoster virus replication in vitro, was studied in rats and cynomolgus monkeys. Rats dosed intraperitoneally or orally with ara-DMAP excreted unchanged ara-DMAP and one major metabolite, 6-methylaminopurine arabinoside (ara-MAP), in the urine. They also excreted allantoin and small amounts (less than 4% of the dose each) of hypoxanthine arabinoside (ara-H) and adenine arabinoside (ara-A). The relative amount of each urinary metabolite excreted remained fairly constant for intraperitoneal ara-DMAP doses of 0.3 to 50 mg/kg of body weight. Rats pretreated with an inhibitor of microsomal N-demethylation, SKF-525-A, excreted more unchanged ara-DMAP and much less ara-MAP than did rats given ara-DMAP alone. Rats pretreated with the adenosine deaminase inhibitor deoxycoformycin excreted more ara-MAP and much less ara-H and allantoin. ara-MAP was shown to be a competitive alternative substrate inhibitor of adenosine deaminase (Ki = 16 microM). Rats given ara-DMAP intravenously rapidly converted it to ara-MAP and purine metabolism end products; however, ara-A generated from ara-DMAP had a half-life that was four times longer than that of ara-A given intravenously. In contrast to rats, cynomolgus monkeys dosed intravenously with ara-DMAP formed ara-H as the major plasma and urinary end metabolite. Rat liver microsomes demethylated ara-DMAP much more rapidly than human liver microsomes did. ara-DMAP is initially N-demethylated by microsomal enzymes to form ara-MAP. This metabolite is further metabolized by either adenosine deaminase, which removes methylamine to form ara-H, or by microsomal enzymes, which remove the second methyl group to form ara-A.

Activity of serum enzymes in puromycin aminonucleoside-induced nephrotic syndrome

Total serum protein, serum albumin, total urine protein excretion, and the serum activity of several enzymes--aldolase (ALS), cholinesterase (CHS), leucine aminopeptidase (LAP), isocitrate dehydrogenase (ICD), aspartate aminotransferase (AST), alanine aminotransferase (ALT), lactate dehydrogenase (LDH), alpha-hydroxybutyrate dehydrogenase (HBD), creatine kinase (CK), alkaline phosphatase (ALP), and gamma-glutamyl transferase (GGT)--were estimated in rats with nephrotic syndrome (NS) at 2, 4, 6, 8, 10, 12, 16, 20, and 30 days after a single injection of puromycin aminonucleoside (PAN). It was found that: (a) total serum protein and serum albumin diminished on day 4 and returned to control values on days 20 and 30, respectively; (b) total urine protein excretion rose on day 4, reached a peak value on day 8, and then fell substantially but still remained higher than control values on day 30; (c) ALS and CHS activities increased; (d) LAP, ICD, and AST activities showed a biphasic pattern, first increasing and then decreasing; (e) ALT, LDH, HBD, CK, and ALP activities decreased; and (f) GGT activity remained unchanged. The differences in the profiles of the enzyme activities suggest their independent regulation in experimental NS induced by PAN.

A role for oxygen free radicals in aminonucleoside nephrosis

The cellular processes responsible for the proteinuria induced by the aminonucleoside of puromycin (PA) remain inadequately defined. Hypoxanthine is both a metabolic breakdown product of PA as well as a substrate for xanthine oxidase, which catalyzes its enzymatic conversion to xanthine and uric acid, yielding the superoxide anion in the process. We examined whether oxygen free radical production contributes to the development of proteinuria in this model. Seven groups of male Sprague-Dawley rats were studied. Proteinuria was quantitated and histology examined 7 days after rats were treated with PA intravenously over 5 min. PA-treated animals received either saline, dimethyl sulfoxide, superoxide dismutase, or catalase over 30 min prior to and 30 min following PA administration. Another group received allopurinol over 4 hr prior to PA. The superoxide dismutase and allopurinol treatment groups had a significant suppression of urinary protein excretion compared to the PA control group. There were also less severe glomerular morphologic changes in the superoxide dismutase group vs. the PA controls, which demonstrated a pathologic pattern that included epithelial cell blebbing, segmental mesangial cell proliferation and matrix expansion, loss of glomerular capillary lumina, and occasional adhesions between the glomerular tuft and Bowman's capsule. The allopurinol group exhibited normal glomerular morphology on light microscopy, with the exception of occasional epithelial cell blebs. All groups showed spreading of the epithelial cell cytoplasm along the glomerular basement membrane with loss of foot processes, focal areas of lifting of the epithelial cell from the glomerular basement membrane, cytoplasmic vacuolization, and protein reabsorption droplets; however, allopurinol-treated animals demonstrated these changes to a lesser extent.(ABSTRACT TRUNCATED AT 250 WORDS)