Inhibition of fibroproliferation by pentoxifylline. Activity of metabolite-1 and lack of role of adenosine receptors

Pentoxifylline and Methylprednisolone Additively Alleviate Kidney Failure and Prolong Survival of Rats after Renal Warm Ischemia-Reperfusion

Renal ischemia-reperfusion injury (IRI) induces local inflammation leading to kidney damage. Since pentoxifylline (PTX) and steroids have distinct immunomodulatory properties, we aimed to evaluate for the first time their combined use in IRI-induced acute kidney injury (AKI) and chronic kidney disease (CKD) in rats. In two experiments, PTX (100 mg/kg body weight subcutaneously) was administered 90 min prior to renal IRI or/and methylprednisolone (MP; 100 mg/kg body weight intramuscularly) was infused 60 min after reperfusion of a solitary kidney (AKI model: 45 min ischemia, 48 male Sprague-Dawley rats) or one kidney with excision of contralateral kidney 2 weeks later (CKD model: 90 min ischemia, 38 rats). Saline was infused in place of PTX or/and MP depending on the group. Renal function (diuresis, serum creatinine, creatinine clearance, sodium and potassium excretion, and urine protein/creatinine) was assessed at 48 h and 120 h post-IRI (AKI model) or 4, 16 and 24 weeks after IRI, along with survival analysis (CKD model). More evidently at early stages of AKI or CKD, treated animals showed higher glomerular filtration and diminished tubular loss of electrolytes, more so with PTX + MP than PTX or MP (serum creatinine (μmol/L) at 48 h of AKI: 60.9 ± 19.1 vs. 131.1 ± 94.4 vs. 233.4 ± 137.0, respectively, vs. 451.5 ± 114.4 in controls, all p < 0.05; and at 4 weeks of CKD: 89.0 ± 31.9 vs. 118.1 ± 64.5 vs. 156.9 ± 72.6, respectively, vs. 222.9 ± 91.4 in controls, p < 0.05 for PTX or PTX + MP vs. controls and PTX + MP vs. MP). Survival was better by >2-fold with PTX + MP (89%) vs. controls (40%; p < 0.05). PTX + MP largely protect from IRI-induced AKI and CKD and subsequent mortality in rats. This calls for clinical investigations, especially in kidney transplantation.

Bioanalysis of pentoxifylline and related metabolites in plasma samples through LC-MS/MS

Analytical aspects related to the assay of pentoxifylline (PTX), lisofylline (M1) and carboxypropyl dimethylxanthine (M5) metabolites are discussed through comparison of two alternative analytical methods based on liquid chromatography separation and atmospheric pressure electrospray ionization tandem mass spectrometry detection. One method is based on a 'pure' reversed-phase liquid chromatography mechanism, while the second one uses the additional polar interactions with embedded amide spacers linking octadecyl moieties to the silicagel surface (C-18 Aqua stationary phase). In both cases, elution is isocratic. Both methods are equally selective and allows separation of unknowns (four species associated to PTX, two species associated to M1) detected through specific mass transitions of the parent compounds and owning respective structural confirmation. Plasma concentration-time patterns of these compounds follow typical metabolic profiles. It has been advanced that in-vivo formation of conjugates of PTX and M1 is possible, such compounds being cleaved back to the parent ones within the ion source. The first method was associated with a sample preparation procedure based on plasma protein precipitation by strong organic acid addition. The second method used protein precipitation by addition of a water miscible organic solvent. Both analytical methods were fully validated and used to assess bioequivalence between a prolonged release generic formulation and the reference product, under multidose and single dose approaches.

Effect of interferon-alpha, ribavirin, pentoxifylline, and interleukin-18 antibody on hepatitis C sera-stimulated hepatic stellate cell proliferation

Chronic hepatitis C virus (HCV) infection is a major cause of liver fibrosis ultimately leading to cirrhosis. Hepatic stellate cell (HSC) proliferation is crucial in fibrosis development. Current antiviral treatment for HCV involves interferon-alpha (IFN-alpha) and Ribavirin combination therapy. IL-18, a novel cytokine of the IL-1 family of cytokines, is involved in inflammation and may be important in HCV-related inflammation. We hypothesize that block of one of the crucial events will block fibrosis due to HCV. The effect of HCV patient sera with and without IFN-alpha, ribavirin, and IL-18 antibody on HSC proliferation was assessed by [(3)H]-thymidine incorporation assays. Western analysis was used to assess the effect of pentoxifylline (PTX) on c-Jun immediate early gene phosphorylation (p-c-Jun formation). We demonstrate that HCV patient sera-stimulated HSC proliferation. Ribavirin with or without IFN-alpha significantly decreased HCV sera-stimulated HSC proliferation by 50%. Western analysis revealed that HCV serum increased p-c-Jun levels, which were decreased with Ribavirin and PTX. ELISA results showed an elevation of IL-18 levels in HCV sera when compared to normal sera. IL-18 did not stimulate HSC proliferation. However, IL-18 antibody significantly decreased patient sera-stimulated HSC proliferation. In conclusion, Ribavirin decreased HSC proliferation and may act by decreasing p-c-Jun levels in HSCs. IL-18 alone did not stimulate HSC proliferation but IL-18 antibody decreased stimulation, suggesting that IL-18 may work in conjunction with some other factor to increase HSC proliferation.

A novel drug interaction between the quinolone antibiotic ciprofloxacin and a chiral metabolite of pentoxifylline

Pentoxifylline (PTX), a methylxanthine derivative, is metabolized to seven compounds in vivo, with metabolites 1 and 5 possessing biologic activity. Metabolite-1 is a chiral molecule and its S-enantiomer is selectively formed during PTX metabolism in vivo. We have developed a reproducible method of synthesizing a racemic mixture of the chiral metabolite-1 (M-1) of PTX. In this study, we examined the kinetics of racemic M-1 in mice compared to PTX. An interaction between PTX and the quinolone antibiotic ciprofloxacin has been demonstrated. A goal of this study was to determine if a similar interaction occurs between ciprofloxacin and M-1 in vivo. M-1 and PTX had similar absorption and elimination rates. M-1 was rapidly converted to PTX, while very little PTX was converted to M-1 in vivo. The peak concentration of biologically active drug (PTX+M-1) was 36% higher when M-1 was administered compared to PTX. Combination of ciprofloxacin and PTX significantly increased serum concentrations of both PTX and M-1 (2-fold) compared to controls. The combination of M-1 and ciprofloxacin significantly increased serum concentration of M-1 (3-fold) and PTX (2-fold). The ciprofloxacin/M-1 combination produced a significantly higher sera concentration of bioactive drug compared to all other groups suggesting that this combination may enhance the anti-fibrogenic effect.

Improving outcome in patients undergoing liver surgery

Liver surgery is associated with many factors, which may affect outcome. Preoperative assessment of patient's general condition, resectability, and liver reserve are paramount for success. The Child-Pugh score and other scoring systems only partially enables to assess the risk associated with liver surgery. The presence of portal hypertension per se is a major risk factor for hepatectomy. Intraoperatively, any attempts should be made to minimize blood loss. Low central venous pressure and inflow occlusion best prevent bleeding. Ischemic preconditioning and intermittent clamping are routinely applied in many centers to protect against long periods of ischemia, although the mechanisms of protection remain unclear. In this review we describe recent advances in activated pathways associated with protection against ischemia. Postoperatively, the best factor impacting on outcome probably resides in experienced medical care particularly in the intensive care setting. Currently, no drug or gene therapy approaches has reached the clinic. The future relies on new insight into mechanisms of ischemia-reperfusion injury.

Traitements complémentaires de l’hépatite chronique virale C

Pegylated interferon and ribavirin combination therapy represent the standard-of-care treatment for chronic hepatitis C, that allows to cure more than half of the patients. However, the success of this bitherapy is in balance with numerous side effects, especially hematologic and psychiatric. This review is focused on complementary treatments (erythropoietin, G-CSF, vitamin E, glutathion, ursodeoxycholic acid and antidepressants) likely to bring a benefit in maintaining adequate interferon and ribavirin dosages and in improving quality of life. This analysis has been performed by using the Medline(R) data base and with data from laboratories which commercialized these molecules. Erythropoietin, G-CSF and antidepressants are the best tools to optimize the bitherapy in its dose and its duration while privileging the quality of life of HCV-infected patients.

Role of CYP1A2 and CYP2E1 in the pentoxifylline ciprofloxacin drug interaction

In this study the drug interaction between ciprofloxacin (CIPRO) and pentoxifylline (PTX) was investigated and the role of CYP1A2 in the drug interaction was determined with the aid of a selective CYP1A2 inhibitor, furafylline (FURA), and the Cyp1A2 knockout mouse. Serum concentrations of PTX (83.4+/-1 micromol/l) and metabolite-1 (M-1) (13.7+/-2.8 micromol/l) following a single injection of PTX (100 mg/kg i.p.) were significantly higher (P<0.05) in mice treated with CIPRO (25 mg/kg i.p. 9 days) compared to serum concentrations of PTX (46.3+/-0.5 micromol/l) and M-1 (6.4+/-1.1 micromol/l) in mice administered saline. Murine hepatic microsomes were incubated with PTX alone or the combination of PTX and CIPRO. The metabolism of PTX in the murine hepatic microsomes containing both CIPRO and PTX was significantly decreased compared to microsomes incubated with PTX alone, suggesting that CIPRO may inhibit the metabolism of PTX. To further clarify the role of CYP1A2 in the metabolism of PTX in mice, the effect of a selective CYP1A2 mechanism based inhibitor, FURA, on the metabolism of PTX was investigated and our results indicate that FURA inhibited metabolism of PTX. We then investigated PTX elimination in the Cyp1A2 knockout mouse. Blood levels of PTX were assessed at 2 and 20 min following a single injection of PTX (32 mg/kg i.v). Serum concentration of PTX was determined in Cyp1A2 knockout mice compared to Cyp1A2 wild type control mice. The serum concentration of PTX in Cyp1A2 wild type mice (n=9) was 22.2+/-3.2 micromol/l at 20 min following injection of PTX. The serum concentration of PTX in Cyp1A2 knockout mice (n=11) was significantly elevated at 20 min following injection of PTX compared to Cyp1A2 wild type mice. These results clearly indicate that inhibition of CYP1A2 catalytic activity that occurs in the Cyp1A2 knockout mice is sufficient to alter metabolism of PTX and result in markedly elevated levels in serum of Cyp1A2 knockout mice. The results of Western analysis in murine microsomes suggest that CYP1A2 protein levels were not altered by CIPRO indicating that CIPRO did not downregulate Cyp1A2. The results of Western analysis also indicated that CIPRO treatment increased CYP2E1 in mouse microsomes and the implications of these will be discussed.

Effects of pentoxifylline administration on urinary N-acetyl-beta-glucosaminidase excretion in type 2 diabetic patients: a short-term, prospective, randomized study

BACKGROUND

Tubulointerstitial injury is a major feature of diabetic nephropathy and an important predictor of renal dysfunction. In 45 patients with type 2 diabetes mellitus (DM), we prospectively analyzed urinary excretion of N-acetyl-beta-glucosaminidase (NAG), a marker of tubular renal damage; the potential relationship with urinary protein excretion; and effects of pentoxifylline (PTF) administration.

METHODS

Forty-five patients with type 2 DM initially were compared with 15 healthy controls matched for age and sex. After randomization, PTF (1,200 mg/d) was administered for 4 months to 30 patients and results were compared with data from a control group (n = 15).

RESULTS

Proteinuria and urinary NAG excretion were significantly greater in patients with DM with respect to healthy controls. Before PTF administration, baseline parameters were similar in both groups of patients with DM. At the end of the study, urinary protein excretion and NAG-creatinine ratios decreased in the active group from 920 +/- 522 mg/d and 14.3 +/- 16.9 U/g to 803 +/- 523 mg/d (P < 0.001) and 10.5 +/- 9.3 U/g (P < 0.05), respectively. Conversely, proteinuria and urinary NAG excretion did not change in the control group. Regression analysis showed that urinary NAG excretion was significantly associated with duration of DM (r = 0.61; P < 0.001) and proteinuria (r = 0.51; P < 0.001).

CONCLUSION

Urinary NAG excretion is elevated in patients with type 2 DM compared with healthy individuals and increases as nephropathy progresses. PTF administration is effective in reducing proteinuria and urinary NAG excretion in these patients. These findings suggest that PTF may have beneficial effects on tubulointerstitial damage in diabetic kidney disease.

Selective down-regulation of c-jun gene expression by pentoxifylline and c-jun antisense interrupts platelet-derived growth factor signaling: pentoxifylline inhibits phosphorylation of c-Jun on serine 73

Platelet-derived growth factor (PDGF) signals through several pathways, including mitogen-activated protein (MAP) kinase, Jun kinase, and C kinase, and stimulates proliferation of fibroblasts. Pentoxifylline inhibits PDGF-driven proliferation of fibroblasts. We have reported that pentoxifylline did not inhibit binding of PDGF to its specific cell-surface receptors or PDGF receptor phosphorylation. In this study, we investigated the effect of PDGF on the expression of c-fos and c-jun, because c-fos and c-jun form activator protein-1 complexes that stimulate genes involved in proliferation. We determined whether pentoxifylline would alter the expression of c-fos and c-jun. Our results indicate that PDGF induced the expression of both c-fos and c-jun. Pentoxifylline effectively reduced c-jun gene expression, which had been up-regulated by PDGF, but did not alter c-fos gene expression. The lack of effect on c-fos supports other studies from this laboratory, which indicate that pentoxifylline did not inhibit PDGF activation of MAP kinase. Treatment of fibroblasts with a phosphothioate c-jun antisense oligodeoxynucleotide reduced the levels of c-Jun protein and blocked PDGF-stimulated proliferation, suggesting a critical role for c-jun in PDGF-mediated proliferation. Combination of pentoxifylline and c-jun antisense suggested that they were likely inhibiting PDGF-stimulated proliferation at a single site in the PDGF signaling pathway. These results suggest that pentoxifylline inhibits PDGF-stimulated proliferation by selectively decreasing c-jun expression. To further define the mechanism of action of pentoxifylline, we assessed the effect of pentoxifylline on c-Jun and phosphorylated c-Jun immunoreactivity in cells treated with PDGF and cells that were transfected with wild-type c-jun plasmid using immunocytochemistry and Western blot analyses, and our results indicate that pentoxifylline inhibited phosphorylation of c-Jun on serine 73.

Inhibition of human CYP1A2 activity in vitro by methylxanthines: potent competitive inhibition by 8-phenyltheophylline

1. Humans are exposed in vivo to methylxanthines by dietary ingestion, as well as from their use as therapeutic agents. The inhibitory effect of a series of these compounds on high-affinity phenacetin O-deethylase activity in the human liver microsomal fraction, a measure of CYP1A2 activity, has been evaluated. 2. Paracetamol, the product of phenacetin O-deethylase activity, was analysed by gas chromatography/negative-ion mass spectrometry using a novel bistrifluoromethylbenzoyl/ trimethylsilyl derivative, and incubation conditions for assessing high-affinity phenacetin O-deethylase activity were examined and optimized. 3. 1-Methylxanthine, caffeine, theophylline, 8-methylxanthine, pentoxyfylline and 3isobutyl-1-methylxanthine caused moderate inhibition with IC50 = 260, 140, 120, 100, 62 and 36 microM respectively. 4. 8-Phenyltheophylline was a potent competitive inhibitor of high-affinity phenacetin O-deethylase activity with an IC50 = 0.7 microM and Ki = 0.11 microM. 5. The specificity of inhibition by 8-phenyltheophylline was assessed by measuring its effect on debrisoquine 4-hydroxylase (CYP2D6), terfenadine hydroxylase (CYP3A4), chlorzoxazone 6-hydroxylase (CYP2E1) and tolbutamide 4-hydroxylase (CYP2C9) activities in human liver microsomal fraction. No inhibition of any of these activities was observed. 6. The potency and specificity of 8-phenyltheophylline as an inhibitor of human hepatic CYP1A2 indicate that the compound may be useful as a chemical inhibitor of this enzyme for further in vitro studies.

Effect of preoperative interventions on outcome following liver resection in a rat model of cirrhosis

BACKGROUND/AIMS

High morbidity and mortality rates in cirrhotic patients undergoing resections for hepatocellular malignancies underscore the need for identifying a therapy that will decrease fibrosis or enhance hepatic regenerative activity in the perioperative period. Thus, in the present study, 104 carbon tetrachloride-induced cirrhotic rats received either saline (untreated cirrhotic controls) or one of the following agents that have been reported to decrease hepatic fibrosis or increase hepatic regeneration; pentoxifylline, ciprofloxacin or a traditional Chinese herbal remedy (TCHR). Twelve additional rats served as healthy, non-cirrhotic controls.

METHODS

Treatments were administered daily by gavage for 4 weeks followed by a 70% partial hepatectomy. Hepatic fibrosis was documented at the time of surgery by computer-assisted quantitation of collagen content. Liver function and hepatic regenerative activity were documented 24 h post partial hepatectomy by serum bilirubin determinations and a combination of 3[H]-Thymidine incorporation into hepatic DNA and proliferating cell nuclear antigen (PCNA) quantitation, respectively.

RESULTS

Compared to untreated cirrhotic controls (8.1 +/- 0.7%), fibrosis was significantly reduced in the pentoxifylline- and ciprofloxacin-treated groups (4.6 +/- 0.2%, p<0.005 and 5.5 +/- 0.6%, p<0.05) but unchanged in the TCHR-treated group (6.6 +/- 11.0%). Post-operatively, total serum bilirubin levels were lower in the pentoxifylline (1.40 +/- 0.15 mg/dl,p<0.01) and ciprofloxacin (1.87 +/- 0.25 mg/dl, p<0.05)-treated groups, but unchanged in the TCHR group (2.20 +/- 0.45 mg/dl), when compared to untreated cirrhotic controls (3.00 +/- 0.37 mg/dl). Hepatic regenerative activity was also significantly improved in the pentoxifylline-treated group (17.8 +/- 2.2 versus 9.9 +/- 1.9 DPM/microg DNA in untreated cirrhotic controls, p<0.05), but unchanged in the ciprofloxacin (16.1 +/- 1.8 DPM/microg DNA) and TCHR (10.9 +/- 1.2 DPM/microg DNA)-treated groups. PCNA protein determinations were in keeping with the 3[H]-Thymidine results

CONCLUSIONS

Pre-operative pentoxifylline holds promise as a useful therapeutic intervention for patients with cirrhosis requiring hepatic resection.

The inhibitory effect of ursodeoxycholic acid and pentoxifylline on platelet derived growth factor-stimulated proliferation is distinct from an effect by cyclic AMP

This study assessed the ability of ursodeoxycholic acid (UDCA) and one of its metabolites, tauroursodeoxycholic acid (TUDCA), to inhibit platelet derived growth factor (PDGF) stimulated fibroproliferation and compared these results to the effect of pentoxifylline and its metabolite-1 [1-(5-hydroxyhexyl)-3,7-dimethylxanthine] and assessed the potential role of cyclic AMP in this process. Fibroproliferative activity was measured by the tritiated thymidine uptake assay in human fibroblast cultures. All four compounds: pentoxifylline, metabolite-1, UDCA and TUDCA inhibited the fibroproliferative activity stimulated by PDGF (8 ng/ml). Incubation of fibroblasts with dibutyryl cyclic AMP reduced proliferation stimulated by PDGF suggesting that the PDGF stimulated proliferation was sensitive to inhibition by a membrane permeable analogue of cyclic AMP. Incubation of myofibroblasts with dibutyryl cyclic AMP significantly inhibited PDGF stimulated proliferation suggesting that cyclic AMP can regulate PDGF stimulated proliferation in the myofibroblast. To determine if the effect of pentoxifylline on fibroproliferation was mediated by cyclic AMP, we used dideoxyadenosine, a potent inhibitor of adenylyl cyclase. The effect of pentoxifylline on fibroproliferation was not prevented by dideoxyadenosine, which inhibits formation of cyclic AMP, thus suggesting that the inhibitory effect of pentoxifylline on PDGF-stimulated proliferation of fibroblasts was not mediated by cyclic AMP, arguing against a role for cyclic AMP in this process. Combinations of UDCA (250 microM) plus pentoxifylline (120 microM) or UDCA (250 microM) plus TUDCA (250 microM) inhibited fibroproliferative activity stimulated by PDGF to a greater extent than either drug alone. As UDCA has been reported to decrease cyclic AMP these results argue against a role for cyclic AMP in this process. Finally the results suggest that UDCA may inhibit PDGF-stimulated proliferation via an inhibition of C-kinase.

Can pentoxifylline prevent renal disease?

The characteristics of pentoxifylline(Trental) suggest that it is an ideal agent to be used as adjunct in the therapy of chronic proliferative glomerulonephritides. Theoretical considerations suggest that pentoxifylline should also protect against and even ameliorate tubulo-interstitial fibrosis of affected kidneys.

Platelet-derived growth factor and pentoxifylline modulation of collagen synthesis in myofibroblasts

Fibroblast proliferation and extracellular matrix accumulation are two major events occurring in fibrosis. Hepatic stellate cells are the major collagen-producing cells of the liver and are transformed into proliferative myofibroblasts following activation. Whether proliferation and extracellular matrix production are regulated by the same cytokines is not known. Monocyte-conditioned medium obtained from pigs with yellow phosphorus-induced hepatic fibrosis increased the collagen production by cultured procine myofibroblasts. Liver biopsies from these same fibrotic animals had increased levels of collagen alpha 1(I) and alpha 1(III) mRNA compared to control animals. Preincubation with platelet-derived growth factor (PDGF) B/B antibody significantly reduced the collagen-stimulating ability of the monocyte-conditioned medium. Recombinant PDGF stimulated proliferation in nonconfluent myofibroblasts and stimulated collagen production in confluent cultures of myofibroblasts without increasing cell number, suggesting that these events can occur independent of each other. Pentoxifylline and one of its active metabolites (metabolite-1) inhibited PDGF-stimulated collagen production in cultured porcine myofibroblasts. These results demonstrate the importance of PDGF in the pathogenesis of liver fibrosis and provide evidence that pentoxifylline interferes with PDGF-mediated events during experimental liver fibrosis.

Drug-metabolizing enzymes in rat liver myofibroblasts

The myofibroblast is considered to be a key component in the pathogenesis of hepatic fibrosis. There is a need for therapeutic intervention in hepatic fibrosis, and, to date, the number of efficacious anti-fibrotic drugs is negligible. At best, the current therapeutic modalities reduce liver enzymes, an indicator of liver damage, but cannot reduce or prevent fibrosis. We have described the anti-fibrotic effect of pentoxifylline in an experimental model of hepatic fibrosis. Evidence suggests that, in addition to pentoxifylline itself, at least two of the metabolites of pentoxifylline are of therapeutic interest. We have reported that one of these metabolites (M-1) has a biological activity similar to that of its parent drug. The second metabolite (M-1R) has been reported to be more potent than the parent drug. Recent evidence suggests that inhibition of cytochrome P450 1A2 (CYP1A2) results in higher levels of pentoxifylline and M-1 and may be responsible for the production of the novel, potent metabolite (M-1R). We therefore investigated whether the myofibroblast, the cell with a crucial role in fibrosis, contains drug-metabolizing enzymes and thus may play a critical role in the anti-fibrotic actions of pentoxifylline. Our results showed that myofibroblasts contain aryl hydrocarbon hydroxylase activity, ethoxyresorufin O-deethylase activity, and methoxyresorufin O-demethylase activity. The results presented here also indicate that aryl hydrocarbon hydroxylase and methoxyresorufin O-demethylase activities can be increased by treatment of cells with dibenzanthracene, an inducer of CYP1A activities.