Regulation of prostaglandin synthesis by reduced glutathione in urinary bladder epithelium

GSH Induced Controlled Release of Levofloxacin from a Purpose-Built Prodrug: Luminescence Response for Probing the Drug Release in Escherichia coli and Staphylococcus aureus

Fluoroquinolones are third-generation broad spectrum bactericidal antibiotics and work against both Gram-positive and Gram-negative bacteria. Levofloxacin (L), a fluoroquinolone, is widely used in anti-infective chemotherapy and treatment of urinary tract infection and pneumonia. The main pathogen for urinary tract infections is Escherichia coli, and Streptococcus pneumoniae is responsible for pneumonia, predominantly a lower respiratory tract infection. Poor permeability of L leads to the use of higher dose of this drug and excess drug in the outer cellular fluid leads to central nervous system (CNS) abnormality. One way to counter this is to improve the lipophilicity of the drug molecule, and accordingly, we have synthesized two new Levofloxacin derivatives, which participated in the spatiotemporal release of drug via disulfide bond cleavage induced by glutathione (GSH). Recent studies with Streptococcus mutants suggest that it is localized in epithelial lining fluid (ELF) of the normal lower respiratory tract and the effective [GSH] in ELF is ∼430 μM. E. coli typically cause urinary tract infections and the concentration of GSH in porcine bladder epithelium is reported as 0.6 mM for a healthy human. Thus, for the present study we have chosen two important bacteria (Gram + ve and Gram - ve), which are operational in regions having high extracellular GSH concentration. Interestingly, this supports our design of new lipophilic Levofloxacin based prodrugs, which released effective drug on reaction with GSH. Higher lipophilicity favored improved uptake of the prodrugs. Site specific release of the drug (L) could be achieved following a glutathione mediated biochemical transformation process through cleavage of a disulfide bond of these purpose-built prodrugs. Further, appropriate design helped us to demonstrate that it is possible also to control the kinetics of the drug release from respective prodrugs. Associated luminescence enhancement helps in probing the release of the drug from the prodrug in bacteria and helps in elucidating the mechanistic pathway of the transformation. Such an example is scarce in the contemporary literature.

Effect of urothelium on bladder contractility in diabetic rats

AIM

It is known that physiopathological changes in diabetes affect the function of the bladder. In this study, we aimed to demonstrate the possible effects of diabetes on the urothelium during this physiopathological process.

METHODS

Diabetes was induced in rats by tail vein injection of 35 mg/kg streptozotocin. Eight weeks later, intact and denuded bladder strips were prepared from these rats. Electrical field stimulation (EFS; 0.5-32 Hz), carbachol (10(-8)-10(-3) mol/L; cumulative dosage-response curves) and KCl (120 mmol/L) were used for the evaluation of the contractile responses. All responses were expressed as mg tension developed per mg of bladder tissue. Weights of rats and of their bladders, blood glucose levels, and frequency- and concentration-response curves were compared using anova, the paired t-test and the independent t-test. Differences were considered significant at P<0.05.

RESULTS

Although no differences related to the weight of bladders of the control and diabetic groups were observed, there were differences in blood glucose levels and body weights between the two groups. Similarly, although there were no differences between the data obtained with EFS and KCl from tissues with intact and denuded strips in the control group, carbachol responses significantly differed between intact and denuded strips in the non-diabetic group. These differences were not observed in the diabetic group. In the control groups, in the presence of additional strips with intact urothelium placed in the medium containing denuded tissue, the differences in contractile responses between the intact control strip and the denuded strip disappeared.

CONCLUSIONS

Diabetes possibly changes the interaction between the relaxant factors that are released from urothelium and muscarinic stimulation, but these interactions are not completely understood yet. Consequently, the response of the bladder to contractile stimulants is also affected. Further studies are required to reveal the mechanism by which diabetes influences the urothelium.

Protease-activated receptor-2-mediated contraction in the rat urinary bladder: the role of urinary bladder mucosa

The role of protease-activated receptor-2 (PAR-2) in the regulation of the rat urinary bladder contractility was investigated. Both trypsin and PAR-2 activating peptide (SLIGRL-NH(2)) produced a concentration-dependent contractile response in the urinary bladder preparations. These contractions were abolished by removal of the urinary bladder mucosa and were significantly reduced by indomethacin (10 microM). These results suggest that activation of PAR-2 stimulates release of prostaglandins from mucosal layer and thereby contracts rat urinary bladder smooth muscles.

Cyclooxygenase-2 protein and prostaglandin E(2) production are up-regulated in a rat bladder inflammation model

Cyclooxygenase-1 and cyclooxygenase-2 mRNAs and proteins and prostaglandin E(2) production are evaluated in a rat model of inflammation in which Escherichia coli lipopolysaccharide is intraperitoneally injected or intravesically instilled into the bladder. While cyclooxygenase-1 mRNA and protein and cyclooxygenase-2 mRNA do not change in bladders treated with lipopolysaccharide, cyclooxygenase-2 protein is elevated in bladders from rats intravesically instilled with lipopolysaccharide or phosphate buffered saline (PBS) or intraperitoneally injected with lipopolysaccharide. Urinary prostaglandin E(2) levels and prostaglandin E(2) synthesis in bladder particulates are elevated by intravesical instillation and intraperitoneal injection of lipopolysaccharide. The nitric oxide donor, S-nitroso-N-acetyl-D,L-penicillamine, increases prostaglandin E(2) synthesis in bladders from lipopolysaccharide intravesically instilled and intraperitoneally injected rats. Lipopolysaccharide increases prostaglandin E(2) synthesis by increasing cyclooxygenase-2 protein levels in rat bladder and prostaglandin E(2) synthesis may be further elevated by increases in nitric oxide caused by an up-regulation of inducible nitric oxide synthase (iNOS).

Role of prostaglandins in the urinary bladder: an update

Our knowledge of prostanoids is rapidly increasing. In this review we survey the factors governing the synthesis of prostanoids by the urinary bladder, their role in the maintenance of normal bladder function, the pattern of their secretion in bladder disease and the possible use of prostanoids in the treatment of bladder pathology.

Prostaglandin E2 synthesis after oxidant stress is dependent on cell glutathione content

The role of glutathione in protecting prostaglandin (PG) generation after exposure of fibroblasts to oxidant stress was investigated. Exposure of 3T3 fibroblasts to H2O2, followed by washing and then 20 microM arachidonic acid, caused a dose-dependent decrease in PG synthesis as assessed by radioimmunoassay. PGE2 production decreased from 3.7 +/- 1.1 to 0.15 +/- 0.04 pmol/microgram protein, and prostacyclin (PGI2) formation decreased from 0.56 +/- 0.03 to 0.06 +/- 0.03 pmol/microgram protein after exposure to 200 microM H2O2. Decreasing intracellular glutathione with 50 micrograms/ml 1,3-bis(chloroethyl)-1-nitrosourea (BCNU) enhanced the H2O2-induced decrease in PGE2 synthesis. Another glutathione-depleting agent, 1-chloro-2,4-dinitrobenzene (CDNB), also potentiated the H2O2-induced decrease in PGE2 formation. However, although PGI2 production was decreased by H2O2, neither BCNU nor CDNB potentiated this decrease. Without oxidant stress, extreme glutathione depletion decreased PGE2 synthesis and caused PGI2 synthesis to exceed PGE2. In summary, oxidant stress decreases both PGE2 and PGI2 formation. However, the primary effect of decreasing cell glutathione during oxidant stress is a reduction in PGE2 formation, not PGI2. This implies that the predominant effect of glutathione depletion during oxidant stress is on the PGE2 isomerase(s) and not PGH synthase or PGI2 synthase.

Concentration-activity profile of the modulation of cyclooxygenase product formation by reduced glutathione in microsomal fractions from the goat lung

Age-related changes in pulmonary formation of arachidonic acid (AA) metabolites are thought to play an important role in regulating cardiopulmonary function. This study addresses the potential role of reduced glutathione (GSH) in modulating cyclooxygenase product formation in the developing lung. Prostaglandin H2 (PGH2) metabolism was studied in microsomal fractions isolated from the lungs of unventilated fetal, neonatal and adult goats. GSH-dependent PGH2 to PGE2 isomerase activity in microsomal fractions from the perinatal (fetal and neonatal) goat lung was not saturable with respect to GSH and can respond to changes in GSH concentration over the range of 0.01 to 30 mM, which encompasses the full range the intracellular GSH levels reported in the literature. However, in fractions from the adult, a lower rate of PGE2 formation is observed at higher GSH concentrations. In addition, the tissue levels of GSH exhibited developmental stage-related differences with fetal being higher than neonatal or adult. The present observations may have physiologic relevance, in that decreases in pulmonary GSH levels after birth may contribute to decreases in plasma PGE2 levels by decreasing pulmonary PGE2 synthesis, thereby contributing to closure of the ductus arteriosus; conversely, increased GSH levels associated with hyperoxia may contribute to persistence of ductal patency. Formation of 6-keto-PGF1 alpha and of TXB2 (the stable metabolites of prostacyclin and TXA2) was decreased when PGE2 formation was increased by GSH activation of PGE2 isomerase in fractions isolated from all three developmental stages. A similar pattern of product formation was observed when AA was employed as substrate. These data suggest the possibility that changes in GSH concentration may modulate eicosanoid formation in cells that contain GSH-dependent PGE2 isomerase, as well as either or both prostacyclin or thromboxane synthase(s).

Hemorrhagic cystitis: a review

Acute, fulminant bladder hemorrhage usually is seen at tertiary care centers in which cancer patients are treated with oxazaphosphorine alkylating agents, particularly cyclophosphamide and isophosphamide. These agents also are used to treat benign conditions, such as lupus erythematosis and Wegener's granulomatosis. Radiation effects from treatment of prostatic or cervical carcinoma can appear for the first time as late as 15 to 20 years after initial treatment. Other iatrogenic causes of bleeding include treatment with penicillins and, rarely, danazol. Occasionally, bladder hemorrhage may be the presenting sign of metabolic disease, such as secondary amyloidosis in rheumatic arthritis. Cases of mild to moderate hemorrhagic cystitis arising in the otherwise healthy patients should lead one to pursue the possibility of environmental toxins, accidental poisoning, recreational drug use or viruses. In all cases the diagnosis should be reserved until more common causes of hematuria, such as bacterial or fungal infection, stones, cysts or tumors, have been ruled out. Prevention of chemotherapeutically induced cystitis ideally will follow careful attention to adequate hydration and the prophylactic use of antitoxins, such as mesna. Treatment, as outlined previously, consists of a series of measures beginning with the most conservative. Intervention thereby is tailored to the gravity of the clinical situation.

L-buthionine sulfoximine-induced loss of glutathione does not elicit PGH synthase inactivation in cultured bovine lens epithelial cells

Previous studies from this laboratory have indicated that exposure of cultured bovine lens epithelial cells (BLECs) to minimal essential medium (MEM) containing 40 mM galactose (Gal) for as short a duration as 20 h results in a reduction of microsomal prostaglandin biosynthesis as demonstrated by a decrease in PGH synthase activity (Invest. Ophthalmol. Vis. Sci. 29:1452-1460, 1988). The present study shows that upon brief exposure of BLECs to Gal, the cellular content of glutathione (GSH) decreases as galactitol increases. Studies were therefore undertaken to establish whether a positive correlation existed between polyol accumulation, GSH content and the activity of PGH synthase (an enzyme known to auto-oxidize) utilizing BLECs exposed to hypergalactosemic conditions. The inhibitor of glutathione biosynthesis, L-buthionine sulfoximine (L-BSO) was used in order to lower the intracellular pool of GSH in MEM-incubated cells to a level below that routinely observed in Gal-incubated cells, under conditions whereby no galactitol accumulation had occurred. The galactitol content was 92 nmol/micrograms PO4 in Gal-incubated cells after a 20 h exposure period; no detectable level of galactitol was observed in BLECs maintained in galactose-free MEM. L-(BSO) (1 mM) was co-administered to BLECs maintained in either MEM or Gal for 20 h. The cellular content of GSH was 1.70 +/- .02 micrograms GSH/micrograms PO4 in MEM alone and 0.540 +/- .02 micrograms GSH/micrograms PO4 in MEM + BSO. Furthermore, the GSH content in BLECs after 20 h of exposure to Gal was 0.960 +/- .01 microgram GSH/microgram PO4 but decreased to 0.110 +/- .01 microgram GSH/microgram PO4 in Gal + BSO.(ABSTRACT TRUNCATED AT 250 WORDS)