Effect of tacrolimus on the production of oxygen free radicals in hepatic mitochondria

OBJECTIVES

Cyclosporine (CsA) causes side effects that occur mainly in the kidney but also in the liver. Several reports have strongly suggested that the production of oxygen free radicals (OFRs) is a common mechanism of CsA toxicity. However, tacrolimus is believed to suppress the production of OFRs.

METHODS

We obtained the mitochondrial fraction with 96% purity from rat liver using a sucrose density gradient solution. Zero to 100 micromol/L tacrolimus was incubated with the mitochondrial fraction for 6 hours at 37 degrees C. OFRs were evaluated by measuring the fluorescent product from the oxidation of an oxidant-sensitive 2,7-dichlorefluorescein using a VICTOR3 multilabel counter.

RESULTS

The fluorescence units for OFR production were increased as the time of exposure to tacrolimus passed from 1 to 6 hours. The fluorescence units in 0.1 micromol/L tacrolimus were 6.0 x 10(5) at 1 hour, 7.8 x 10(5) at 2 hours, 9.0 x 10(5) at 3 hours, 10.0 x 10(5) at 4 hours, 11.1 x 10(5) at 5 hours, and 11.4 x 10(5) at 6 hours. However, the fluorescence units were similar although the tacrolimus concentration increases from 0.1 to 100 micromol/L.

CONCLUSIONS

The results in this experiment suggested that tacrolimus induced the production of OFRs depending on the exposure time.

Apoptosis by cyclosporine in mesangial cells

INTRODUCTION

The immunosuppressive agent cyclosporine (CsA) is widely used to treat allograft rejection and various autoimmune disorders. A major limiting factor in the use of CsA is chronic nephrotoxicity. The pathogenesis of CsA-induced nephrotoxicity is not fully understood. Several recent studies have suggested that CsA treatment directly induces apoptosis in several cell types. The present study was undertaken to investigate the effects of CsA on apoptosis of cultured rat mesangial cells (RMCs).

METHODS

RMCs were treated with CsA at concentrations of 0.1 to 40 mumol/L. Cell viability was determined by MTT assay. Apoptotic protein expression was determined by Western blot analysis.

RESULTS

Cell viability was decreased with increasing concentrations of CsA in dose-dependent manner. CsA produced dose-dependent induction of p53, caspase-6, and Bax protein expression. CsA treatment caused proteolytic cleavage of caspase-3 and induced the degradation of 116-kDa PARP into 89-kDa fragment. RMCs with CsA reduced Bcl-2 and cIAP expression.

CONCLUSIONS

In this study, CsA induced apoptosis by up-regulating proapoptotic factors, caspase-3 and -6, p53, Bax, cleaving PARP, and down-regulating antiapoptotic factor, Bcl-2, and cIAP. These results suggested that the increased cell apoptosis exerted by CsA may be one of the mechanisms promoting CsA-induced nephrotoxicity.

Total antioxidant status and oxygen free radicals during hepatic regeneration

OBJECTIVES

The damage induced by oxygen free radicals (OFRs) is caused by an imbalance of the production of versus the antioxidant defenses against OFRs.

METHODS

To understand hepatic damage induced by oxygen free radicals after hepatectomy in rats, total antioxidant status and total production of oxygen free radicals were serially measured in regeneration liver. At 1, 2, 3, 7, and 10 days after hepatectomy of Sprague-Dawley rats, blood was obtained into a capillary tube from a tail vein. Total antioxidant status and total production of oxygen free radicals were measured using the Randox kit, a colorimetric method, and the Free Radical Analytical System. We also measured the amount of malonyldialdehyde, which provides an indirect index of oxidative injury.

RESULTS

The level of malonyldialdehyde after hepatectomy was higher compared with that before hepatectomy. The level of total oxygen free radicals after hepatectomy was higher compared with that before hepatectomy. Total antioxidant status after hepatectomy was lower compared with that before hepatectomy.

CONCLUSIONS

The results suggested that the damage by OFRs to the regenerating liver was caused by increased production of OFRs and decreased antioxidant defense against OFRs.

Effects of cyclosporine and tacrolimus on the oxidative stress in cultured mesangial cells

OBJECTIVES

Cyclosporine (CsA) and tacrolimus (Tac) are two primary immunosuppressive agents used for the prevention of graft rejection. However, their use is associated with significant side effects, most notably nephrotoxicity. The mechanisms of this toxicity are not fully understood, but they seem to be associated with increases in the production of oxygen free radicals (OFRs). This present work examined the effect of CsA and Tac on the production of OFRs in cultured rat renal mesangial cells (RMCs).

METHODS

Varying concentrations of CsA and Tac (0 to 40 micromol/L) were added to RMCs and incubated for 60 minutes at 37 degrees C. The production of OFRs was evaluated by measuring the fluorescent product from the oxidation of an oxidant-sensitive 2', 7'-dichlorofluorescin.

RESULTS

At 60 minutes, the relative fluorescence units (RFU) for OFRs production in RMCs exposure to CsA were increased by 2.5%, 11.5%, 22.5%, 57.2%, and 174% at 2.5, 5, 10, 20, and 40 micromol/L, respectively. Tac increased the RFU by 15.9%, 13.6%, 14.8%, 13.2%, 21.4%, 13.2%, and 28.1% at 0.1, 1, 2.5, 5, 10, 20, and 40 micromol/L, respectively. In RMCs, the RFU produced by CsA was higher than that by Tac.

CONCLUSIONS

The results of this experiment suggest that CsA and Tac induced renal injury by OFRs.

Selective left-lobe atrophy by nodularin treatment accompanied by reduced protein phosphatase 1/2A and increased peroxisome proliferation in rat liver

The effect of nodularin on selective atrophy of left lobes in the liver was investigated in F344 rats. Nodularin was injected for 10 weeks from the third week of initiation with saline or N-nitrosodiethylamine (DEN), grouped as S/N and D/N, respectively. Nodularin significantly decreased weights of left (LL) and caudate (CL) lobes but increased right (RL) and middle (ML) lobes in S/N rats. Activity of protein phosphatases [types 1 (PPI) and 2A (PP2A)] was more severely reduced in S/N than D/N rats; moreover, in LL compared with RL of S/N rats, activity was significantly inhibited by nodularin treatment from week 4, which corresponded to 2 weeks after nodularin injection. However, nodularin significantly induced peroxisomal palmitoyl-CoA oxidase and cytochrome P-450 4A1 expression in S/N compared with D/N rats. An effect of nodularin on apoptosis was evident since expression of Bcl-Xs was clearly induced in LL of S/N rats as opposed to various inductions of Bcl-XL. However, Bcl-XL in RL was persistently induced, with undetectable Bcl-Xs expression. These results demonstrate biochemical evidence of selective atrophy of LL by inhibition of PP1 and PP2A activity, increase of peroxisomal enzymes and induction of Bcl-Xs expression, in contrast to proliferation of RL in rats treated with nodularin alone. However, nodularin endowed DEN-altered hepatocytes with regenerating power and concomitant restoration of phosphatase activity as well as persistent expression of Bcl-XL in D/N rats.

Chronic peritoneal inflammation by cyanate in rats

OBJECTIVE

During peritoneal dialysis, the peritoneum is exposed to waste products, including urea. Urea forms cyanate spontaneously at body temperature and pH, and cyanate carbamylates amino acids, peptides, and proteins. Cyanate may contribute to peritoneal injury with morphological changes in the peritoneum. To test this hypothesis, we injected cyanate into rats.

METHODS

Experiments were performed in two groups of 7 rats each. In the cyanate group, each rat received 1 mL of 1.5 micromol/L potassium cyanate dissolved in 40 mmol/L sodium bicarbonate solution intraperitoneally each experiment day. In the control group, each rat received 1 mL of 1.5 micromol/L potassium bicarbonate instead of potassium cyanate. The rats in both groups were anesthetized and killed at the 85th day after the first injection. After formalin fixation, tissue samples from abdominal walls and livers were sliced, embedded in a standard manner, and stained with hematoxylin and eosin.

RESULTS

Parietal peritoneum from rats in the cyanate group showed a mild increase in the number of fibroblasts, with collagen deposits, infiltration by mononuclear cells, vascular congestion, round-shaped transformation of mesothelial cells, widening of submesothelial spaces, and abundant denudation of mesothelial cells. The visceral peritoneum from rats in the cyanate group showed collagen deposits with fibroblastic proliferation.

CONCLUSIONS

Cyanate can induce chronic inflammation in the peritoneum, and exposure of the peritoneum to cyanate may contribute to peritoneal injury in patients being treated with peritoneal dialysis.

Cyanate as a hemolytic factor

During advanced renal failure, and particularly in patients with end-stage renal disease, proteins are carbamylated as a result of a reaction with cyanate. If the carbamylation of proteins adversely alters their biologic activities and structures, then urea must be viewed as an uremic toxin, rather than a surrogate. Therefore, we studied in this paper the role of cyanate as a hemolytic factor of erythrocytes to explain anemia observed in patients with high blood urea levels due to inadequate dialysis. Cyanate was added to make the final concentration 150, 300 and 600 nmol to each test tube containing the final concentration of 140 x 10(6) with human erythrocytes per mL of phosphate buffered saline solution. And they were incubated at 37 degrees C for 24, 48 and 72 hours. The extent of hemolysis and carbamylation was monitored. The levels of hemolysis and carbamylated erythrocytes increased as the time of exposure to cyanate increased from 24 hours to 72 hours. Furthermore, those increased as cyanate concentration in the incubation media rose from 150 nmol to 600 nmol. Cyanate can induce hemolysis by carbamylation of erythrocytes. Urea, through cyanate, may contribute to hemolysis. If one extrapolates these results to patients with end-stage renal disease, it may help explain one of the reasons for the anemia in patients with high levels of BUN due to inadequate dialysis.

Dehydroepiandrosterone-dependent induction of peroxisomal proliferation can be reduced by aspartyl esterification without attenuation of inhibitory bone loss in ovariectomy animal model

The purpose of this study was to determine whether esterification of dehydroepiandrosterone with aspartate (DHEA-aspartate) could reduce peroxisomal proliferation induced by DHEA itself, without loss of antiosteoporotic activity. Female Sprague-Dawley rats were ovariectomized, then DHEA or DHEA-aspartate was administered intraperitoneally at 0.34 mmol/kg BW 3 times a week for 8 weeks. DHEA-aspartate treatment in ovariectomized rats significantly increased trabeculae area in tibia as much as DHEA treatment. Urinary Ca excretion was not significantly increased by DHEA or DHEA-aspartate treatment in ovariectomized rats, while it was significantly increased by ovariectomy. Osteocalcin concentration and alkaline phosphatase activity in serum and cross linked N-telopeptide type I collagen level in urine were not significantly different between DHEA-aspartate and DHEA treated groups. DHEA-aspartate treatment significantly reduced liver weight and hepatic palmitoyl-coA oxidase activity compared to DHEA treatment. DHEA-aspartate treatment maintained a nearly normal morphology of peroxisomes, while DHEA treatment increased the number and size of peroxisomes in the liver. According to these results, it is concluded that DHEA-aspartate ester has an inhibitory effect on bone loss in ovariectomized rats with a marked reduction of hepatomegaly and peroxisomal proliferation compared to DHEA.

Target site search and effective inhibition of leukaemic cell growth by a covalently closed multiple anti-sense oligonucleotide to c-myb

Systematic secondary structure simulation of a target mRNA sequence is shown to be effective for locating a good anti-sense target site. Multiple selected anti-sense sequences were placed in a single molecule. The anti-sense oligonucleotide (oligo) was covalently closed to avoid exonuclease activities and was designated CMAS (covalently closed multiple anti-sense)-oligo. CMAS-oligo was found to be stable, largely preserving its structural integrity after 24 h of incubation in the presence of either exonuclease III or serum. When human c-myb mRNA was targeted by the c-myb CMAS-oligo, expression of the gene was completely abolished. Further, tumour cell growth was inhibited by 82+/-3% as determined by an MTT [3-(4, 5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide] assay and by 90+/-1% by [(3)H]thymidine incorporation. When a leukaemic cell line K562 was treated with CMAS-oligo, colony formation on soft agarose was also decreased by 93%. In contrast, treatment with a scrambled control oligo did not significantly inhibit leukaemic cell growth. These results suggest that a rational target site search is possible for an anti-sense oligo and that CMAS-oligo can be employed as an effective anti-sense agent with enhanced stability.

The protective effect of allopurinol on cholestatic liver injury induced by bile duct ligation

To determine whether oxygen free radicals are responsible for the pathogenesis of the cholestasis induced by ligation of common bile duct (CBD) variables which reflect the hepatic function in the serum, the amount of superoxide radical production, and xanthine oxidase(XO) activity were studied. The activity of serum alanine aminotransferase, bilirubin level in the serum and the amount of superoxide radical production were lower in a CBD ligation with allopurinol treated group than in a CBD ligation without allopurinol treated group. Abnormalities of the microscopic structures were reduced in a CBD ligation with allopurinol treated group than in a CBD ligation without allopurinol treated group. Allopurinol, an inhibitor of XO, prevented the hepatic damage induced by CBD ligation through the inhibition of XO. These experiments demonstrate that oxygen free radicals are responsible for the pathogenesis of the cholestatic liver.

Effect of hypocapnia on extracellular glutamate and glycine concentrations during the periischemic period in rabbit hippocampus

Glutamate (GLU) is a neurotransmitter. Massive release of GLU and glycine (GLY) into the brain's extracellular space may be triggered by ischemia, and may result in acute neuronal lysis or delayed neuronal death. The aim of this study was to evaluate the possible relationship between hyperventilation and the level of GLU and GLY during brain ischemia. Rabbits were anesthetized with halothane and oxygen. Group 1 was allowed to hyperventilate (PaCO2 25-35 mmHg). PaCO2 was maintained throughout the study. Group 2 was a normal control group that maintained normocapnia. Two global cerebral ischemic episodes were produced. Microdialysate was collected during the periischemic and reperfusion periods from the dorsal hippocampus. GLU and GLY concentrations were determined using high-performance liquid chromatography. In the control group, GLU and GLY were significantly elevated during each episode of ischemia; these levels returned to baseline within 10 minutes after reperfusion. In contrast, in the hyperventilation group GLU and GLY concentrations increased during ischemia, but they were not statistically significant. Two way ANOVA for the periischemic periods (t = 15,80; p = 0.06) revealed lower GLU values for the hyperventilated animals. A similar analysis for periischemic GLY concentrations revealed significantly lower values in the hyperventilated group (t = 10,15,75,80: p = 0.03) as compared to normal controls. We were able to demonstrate that hypocapnia during periischemic period lowered extracellular GLU and GLY concentrations. These results can explain a part of the protective action of hypocapnia during cerebral ischemia.

Effect of hypocapnia on extracellular glutamate and glycine concentrations during peri-ischemic period in the rabbit hippocampus

Glutamate (GLU) is a neurotransmitter. Massive release of GLU and glycine (GLY) into the brain's extracellular space may be triggered by ischemia, and may result in acute neuronal lysis or delayed neuronal death. The aim of this study was to evaluate the possible relationship between hyperventilation and the level of GLU and GLY during brain ischemia. Rabbits were anesthetized with halothane and oxygen. Group 1 was allowed to hyperventilate (PaCO2 25-35 mmHg). PaCO2 was maintained throughout the study. Group 2 was a normal control group that maintained normocapnia. Two global cerebral ischemic episodes were produced. Microdialysate was collected during the peri-ischemic and reperfusion periods from the dorsal hippocampus. GLU and GLY concentrations were determined using high-performance liquid chromatography. In the control group, GLU and GLY were significantly elevated during each episode of ischemia; these levels returned to baseline within 10 minutes after reperfusion. In contrast, in the hyperventilation group GLU and GLY concentrations increased during ischemia, but they were not statistically significant. We were able to demonstrate that hypocapnia during periischemic period lowered extracellular GLU and GLY concentrations. These results can explain a part of the protective action of hypocapnia during cerebral ischemia.