Possible mechanisms of alteration in the capacities of carcinogen metabolizing enzymes during schistosomiasis and their role in bladder cancer induction

Praziquantel-encapsulated niosomes against Schistosoma mansoni with reduced sensitivity to praziquantel

Introduction:

Praziquantel (PZQ) is the only commercially available drug for schistosomiasis. The current shortage of alternative effective drugs and the lack of successful preventive measures enhance its value. The increase in the prevalence of PZQ resistance under sustained drug pressure is, therefore, an upcoming issue.

Objective:

To overcome the tolerance to PZQ using nanotechnology after laboratory induction of a Schistosoma mansoni isolate with reduced sensitivity to the drug during the intramolluscan phase.

Materials and methods:

Shedding snails were treated with PZQ doses of 200 mg/kg twice/ week followed by an interval of one week and then repeated twice in the same manner. The success of inducing reduced sensitivity was confirmed in vitro via the reduction of cercarial response to PZQ regarding their swimming activity and death percentage at different examination times.

Results:

Oral treatment with a single PZQ dose of 500 mg/kg in mice infected with cercariae with reduced sensitivity to PZQ revealed a non-significant reduction (35.1%) of total worm burden compared to non-treated control mice. Orally inoculated PZQ- encapsulated niosomes against S. mansoni with reduced sensitivity to PZQ successfully regained the pathogen’s sensitivity to PZQ as evidenced by measuring different parameters in comparison to the non-treated infected animals with parasites with reduced sensitivity to PZQ. The mean total worm load was 1.33 ± 0.52 with a statistically significant reduction of 94.09% and complete eradication of male worms. We obtained a remarkable increase in the percentage reduction of tissue egg counts in the liver and intestine (97.68% and 98.56%, respectively) associated with a massive increase in dead eggs and the complete absence of immature stages.

Conclusion:

PZQ-encapsulated niosomes restored the drug sensitivity against laboratory- induced S. mansoni adult worms with reduced sensitivity to PZQ.

A novel praziquantel solid lipid nanoparticle formulation shows enhanced bioavailability and antischistosomal efficacy against murine S. mansoni infection

Background

Schistosomiasis is responsible for a considerable global disease burden. This work aimed to improve the therapeutic outcome of the only available antischistosomal drug worldwide, praziquantel (PZQ), by incorporating it into a novel carrier, “solid lipid nanoparticles (SLNs)”, to enhance its solubility, bioavailability and efficacy. A simple, cost-effective method was used to prepare SLN-PZQ.

Results

Compared to market PZQ (M-PZQ), SLN-PZQ was more bioavailable, as denoted by higher serum concentrations in both normal and infected mice where elevated K_a, AUC_0–24, C_max, and t_1/2e with a decrease in k_el were demonstrated. The AUC_0–24 for SLN-PZQ in normal and Schistosoma mansoni-infected groups was almost nine- and eight-fold higher, respectively, than that for M-PZQ in corresponding groups. In normal and S. mansoni-infected mice, SLN-PZQ was detectable in serum at 24 h, while M-PZQ completely vanished 8 h post-treatment. Additionally, enhanced absorption with extended residence time was recorded for SLN-PZQ. Compared to M-PZQ, SLN-PZQ revealed superior antischistosomal activity coupled with enhanced bioavailability in all treated groups where higher percentages of worm reduction were recorded with all dosages tested. This effect was especially evident at the lower dose levels. The ED₉₅ of SLN-PZQ was 5.29-fold lower than that of M-PZQ, with a significantly higher reduction in both the hepatic and intestinal tissue egg loads of all treated groups and almost complete disappearance of immature deposited eggs (clearly evident at the low dose levels).

Conclusions

SLN-PZQ demonstrated enhanced PZQ bioavailability and antischistosomal efficacy with a safe profile despite the prolonged residence in the systemic circulation.

Effect of ketoconazole, a cytochrome P450 inhibitor, on the efficacy of quinine and halofantrine against Schistosoma mansoni in mice

The fear that schistosomes will become resistant to praziquantel (PZQ) motivates the search for alternatives to treat schistosomiasis. The antimalarials quinine (QN) and halofantrine (HF) possess moderate antischistosomal properties. The major metabolic pathway of QN and HF is through cytochrome P450 (CYP) 3A4. Accordingly, this study investigates the effects of CYP3A4 inhibitor, ketoconazole (KTZ), on the antischistosomal potential of these quinolines against Schistosoma mansoni infection by evaluating parasitological, histopathological, and biochemical parameters. Mice were classified into 7 groups: uninfected untreated (I), infected untreated (II), infected treated orally with PZQ (1,000 mg/kg) (III), QN (400 mg/kg) (IV), KTZ (10 mg/kg)+QN as group IV (V), HF (400 mg/kg) (VI), and KTZ (as group V)+HF (as group VI) (VII). KTZ plus QN or HF produced more inhibition (P<0.05) in hepatic CYP450 (85.7% and 83.8%) and CYT b5 (75.5% and 73.5%) activities, respectively, than in groups treated with QN or HF alone. This was accompanied with more reduction in female (89.0% and 79.3%), total worms (81.4% and 70.3%), and eggs burden (hepatic; 83.8%, 66.0% and intestinal; 68%, 64.5%), respectively, and encountering the granulomatous reaction to parasite eggs trapped in the liver. QN and HF significantly (P<0.05) elevated malondialdehyde levels when used alone or with KTZ. Meanwhile, KTZ plus QN or HF restored serum levels of ALT, albumin, and reduced hepatic glutathione (KTZ+HF) to their control values. KTZ enhanced the therapeutic antischistosomal potential of QN and HF over each drug alone. Moreover, the effect of KTZ+QN was more evident than KTZ+HF.

Comparative efficacy and bioavailability of different praziquantel brands

This study investigates the efficacy, bioavailability and drug metabolizing enzymes mainly involved in the metabolism of the commercial brands of praziquantel (PZQ) in Egypt in comparison with the original pure powder. Mice infected with PZQ-susceptible (CD) or PZQ-insusceptible (EE2) Schistosoma mansoni isolates were divided each into seven groups, six of them received PZQ brands (Distocide, Epiquantel, Biltricide, Bilharzid, Praziquantel, and pure PZQ), while the seventh one was left as infected untreated. Seven weeks post-infection, worms were quantified and hepatic CYP450 and CYT b5 were examined. For PZQ pharmacokinetics, groups of normal mice were given the different PZQ brands and divided into subgroups, killed at 2, 5, 15, 30, 60, 90, 120,150, 180, 240 and 360 min post-dosing. Physicochemical examination revealed better dissolution rates for Biltricide, Distocide and PZQ T3A rather than Epiquantel and Bilharzid. Significant decrease in worm burden was recorded in all groups of mice regardless of the brand of PZQ used, but with better results obtained with CD isolate rather than the EE2 isolate. Biltricide and Distocide showed higher C(max) and AUC(0-6h) in normal mice, in addition to higher worm reduction with least inhibition of CYP450 and CYT b5 in EE2-infected mice. PZQ T3A, Bilharzid and Epiquantel showed, in addition to lower efficacy, higher K(el), lower t(1/2e), C(max) and AUC(0-6h). The 32-46% reduction of their bioavailability reflected on their antischistosomal efficacy and recovery of drug metabolizing enzymes. Quality of generic PZQ should include, in addition to examining the physicochemical characteristics of the brands, biological testing including efficacy and bioavailability studies.

Diazinon toxicity affects histophysiological and biochemical parameters in rabbits

Diazinon is a widely used pesticide in agriculture. So, the current work aimed to investigate the effects of diazinon exposure on some physiological and biochemical parameters, as well as, histopathological changes and histochemical acetyl-cholinesterase activity (AChE). The red Baladi rabbits were dipped into water (Control Group), diazinon at low concentrations of 0.6 mg diazinon low concentration (DLC) or high concentration of 3mg diazinon high concentration (DHC) dissolved in 1l of water for 10s. Treatment was repeated after 10 days and animals were sacrificed between 0 and 21 days after the second treatment. Blood analysis revealed that Red blood cells (RBC's), hemoglobin (Hb) and plasma total protein (TP) were significantly decreased in both diazinon concentrations (P<0.01), (P<0.05), (P<0.01) respectively. Cholesterol and microsomal protein were increased (P<0.01), while, liver/ body weight and cytochrome P-450 were decreased in both concentrations (P<0.01). Also there was a highly significant effect of concentration X day interaction on all parameters (P<0.01). Histopathological changes of liver, kidney and brain were observed after DHC dipping. Glycogen content was decreased in liver and increased in kidney Bowman's capsule. Furthermore, AChE activity was inhibited in brain tissue, decreased in liver cells, but gradually increased in kidney glomerular cells. Therefore, kidney and brain were highly affected by diazinon exposure compared with the liver. Exposure of animals to diazinon caused extensive changes in physiological, biochemical, and histopathological parameters as well as histochemical AChE. So, contact exposure of diazinon leads to negative response on animal health.

DRUG-METABOLIZING ENZYMES AND PRAZIQUANTEL BIOAVAILABILITY IN MICE HARBORING SCHISTOSOMA MANSONI ISOLATES OF DIFFERENT DRUG SUSCEPTIBILITIES

The level of drug-metabolizing enzymes (cytochrome P450 [CYP450] and cytochrome b5 [cyt b5]) and the bioavailability of praziquantel (PZQ) were investigated in batches of mice infected with Schistosoma mansoni displaying either a decreased susceptibility to PZQ ("EE2" and "BANL"-isolates), or a normal susceptibility to the drug ("CD" isolate). Each batch was divided into 2 groups. The first group was further subdivided into 5 subgroups. Subgroups 1 to 4 were treated 7 wk postinfection (PI) with oral PZQ at 25, 50, 100, and 200 mg/kg for 5 consecutive days, whereas the fifth subgroup was administered the vehicle only as control. Animals were perfused 9 wk PI, and worms were counted to estimate PZQ ED50. CYP450 and cyt b5 were examined in hepatic microsomes of infected untreated mice and of infected mice treated with 25 and 200 mg/ kg PZQ. The second group was given PZQ 7 wk PI and was further subdivided into 11 subgroups, killed at 2, 5, 15, 30, 60, 90, 120, 150, 180, 240, and 360 min postdosing to study pharmacokinetic parameters of PZQ. Mice harboring S. mansoni isolates having higher PZQ ED50 (170.3 mg/kg for EE2 and 249.9 mg/kg for BANL vs. 82.96 mg/kg for CD) had higher levels of CYP450 and cyt b5, a PZQ Cmax decreased by 19-30% and area under the serum concentration-time curve0-6 hr decreased by 57-74%. Data suggest that S. mansoni isolates that are less sensitive to PZQ induce a lower inhibition of hepatic drug-metabolizing enzymes, with a consequently higher metabolic transformation of PZQ.

Increased CYP1A1 expression in human exfoliated urothelial cells of cigarette smokers compared to non-smokers

Polycyclic aromatic hydrocarbons, arylamines and nitrosamines, constituents of cigarette smoke, are known inducers of bladder cancer. The biochemical response of the target tissue, the bladder urothelium, following inhalation of cigarette smoke has not been studied so far. We used exfoliated transitional urothelial cells from human urine samples to analyze effects of smoking on induction of the cytochrome P450 enzyme CYP1A1. Samples of 40 subjects, including male and female smokers and non-smokers, were examined. A prerequisite for the immunofluorescence microscopic analysis of the cells was the enrichment of the urothelial cell population. This was achieved by a new method which is based on magnetic cell sorting exploiting specific binding of immobilized Griffonia simplicifolia lectin to the surface of urothelial cells. Immunostaining of the final cell preparation with a monoclonal antibody to CYP1A1 showed that about 6% of the urothelial cells of non-smokers stained positive for CYP1A1. However, this fraction of positive cells was more than 44% of the urothelial cells in samples from cigarette smokers. In spite of the individual variation, the difference was statistically significant. There were no gender-related differences in the portion of CYP1A1 expressing urothelial cells of smokers and non-smokers. In essence, we show for the first time that human urothelial cells respond to cigarette smoking by induction of CYP1A1. The approach opens new fields of mechanistic and biomarker research with respect to the pathogenetic processes of cancer development in the human bladder.

Alteration of drug biotransformation and elimination during infection and inflammation

During infection or inflammation, the expression of cytochrome P450 and its dependent biotransformation pathways are modified. This results in a change in the capacity of the liver to handle drugs and in alterations in the production and elimination of endogenous substances throughout the body. The majority of the CYP isoforms are modified at pre-translational steps in protein synthesis, and, in most cases, cytokines are involved as mediators of the response. Recent information suggests that inflammatory responses that are localized to the CNS cause a loss of CYP within the brain. This is accompanied by a parallel down-regulation of CYP in peripheral organs that is mediated by a signaling pathway between the brain and periphery. This review covers the loss that occurs in the major mammalian CYP families in response to infection/inflammation and the mediator pathways that are key to this response.

Infections as a major preventable cause of human cancer

Infections may be responsible for over 15% of all malignancies worldwide. Important mechanisms by which infectious agents may induce carcinogenesis include the production of chronic inflammation, the transformation of cells by insertion of oncogenes and inhibition of tumour suppressors, and the induction of immunosuppression. Common characteristics shared by infectious agents linked to malignancies are that they are persistent in the host, often highly prevalent in the host population and induce cancer after a long latency. The associations between a selection of infectious agents and malignancies are covered in detail.

Relationship between schistosomiasis and bladder cancer

Carcinoma of the urinary bladder is the most common malignancy in the Middle East and parts of Africa where schistosomiasis is a widespread problem. Much evidence supports the association between schistosomiasis and bladder cancer: this includes the geographical correlation between the two conditions, the distinctive patterns of gender and age at diagnosis, the clinicopathological identity of schistosome-associated bladder cancer, and extensive evidence in experimentally infected animals. Multiple factors have been suggested as causative agents in schistosome-associated bladder carcinogenesis. Of these, N-nitroso compounds appear to be of particular importance since they were found at high levels in the urine of patients with schistosomiasis-associated bladder cancer. Various strains of bacteria that can mediate nitrosation reactions leading to the formation of N-nitrosamines have been identified in the urine of subjects with schistosomiasis at higher intensities of infection than in normal subjects. In experimental schistosomiasis, the activities of carcinogen-metabolizing enzymes are increased soon after infection but are reduced again during the later chronic stages of the disease. Not only could this prolong the period of exposure to activated N-nitrosamines, but also inflammatory cells, stimulated as a result of the infection, may induce the endogenous synthesis of N-nitrosamines as well as generating oxygen radicals. Higher than normal levels of host cell DNA damage are therefore anticipated, and they have indeed been observed in the case of alkylation damage, together with an inefficiency in the capacity of relevant enzymes to repair this damaged DNA. In experimental schistosomiasis, it was also found that endogenous levels of host cell DNA damage were related to the intensity of infection. All of these factors could contribute to an increased risk of bladder cancer in patients with schistosomiasis, and in particular, the gene changes observed may have potential for use as biomarkers in the early detection of bladder cancer that may assist in alleviating the problem.

O6-methylguanine and O6-methylguanine-DNA [corrected] methyltransferase activity in tissues of BDF-1 mice treated with antiparasitic drugs

Levels of the DNA promutagenic methylation damage, O6-methylguanine (O6-MeG) and the activity of the O6-methylguanine-DNA methyltransferase (MGMT), the enzyme responsible for repairing O6-MeG, were measured at various time intervals in tissues of BDF-I mice administered a single therapeutic dose of the antischistosomal agents hycanthone, oxaminiquine and metrifonate. Hycanthone increased O6-MeG in the liver-DNA after 6 h, then decreased by 3-fold after 48 h. Lower levels of the adduct and a slower rate of formation were found in the intestine and bladder. MGMT activities were significantly lower in the liver (74%) and bladder (25%) compared to control animals after 6 h, then restored by 48 h. Oxaminiquine increased O6-MeG in all tissues, but spleen, after 6 h and persisted only in the bladder after 48 h. Liver and bladder tissues of these animals exhibited a pattern of alteration in the MGMT activity similar to that observed for hycanthone. Metrifonate induced a profile of O6-MeG comparable to that of oxaminiquine but the levels of the adduct were about 2-fold lower. Hepatic MGMT in these animals was significantly lower (approximately 38%) than the control values after 6 h, then restored by 48 h. A significant negative correlation was obtained between O6-MeG and MGMT activity in the liver (r=- 0.85), intestine (r=- 0.62) and bladder (r=- 0.59). These results demonstrate that treatment with antischistosomal agents may lead to the formation of promutagenic alkylation damage in the tissue DNA and alterations in the DNA repair capacity.

Expression of glutathione S-transferase activity and glutathione content in squamous cell carcinoma of bladder associated with schistosomiasis in a population in Egypt

The present study was designed to describe the expression of the glutathione S-transferase/glutathione system in squamous cell carcinoma of the bladder in a population in Egypt. The glutathione-S transferase activity was significantly higher in bladder cancer specimens (n = 40) in comparison with schistosomiasis cystitis tissue (n = 42) (4-fold, p = 1 x 10(-12)) and with healthy control samples (n = 9) (10-fold, p = 1 x 10(-6)). The glutathione content was also significantly higher in bladder cancer than in cystitis tissue (2-fold, p = 8 x 10(-6)) and in control samples (6-fold, 8 x 10(-6)). When control mucosa and cystitis samples were compared, 2-fold increased values were obtained for glutathione-S transferase (p = 4 x 10(-3)) and glutathione (p = 1 x 10(-3)) in schistosomiasis bladder tissue. Results describe an over-expression of glutathione-S transferase and glutathione levels in squamous cell carcinoma of the bladder, and indicate a possible role in chemoresistance to pharmacological therapy.

N-nitroso compounds induce changes in carcinogen-metabolizing enzymes

The bioactivation of N-nitrosoamines and polycyclic aromatic hydrocarbons (PAH) is mediated by the mixed function oxidase system, which includes dimethylnitrosamine N-demethylase I (DMN-dI), arylhydrocarbon hydroxylase (AHH), cytochrome P-450, cytochrome b5 and NADPH-cytochrome c reductase of liver microsomes. The present study shows the influence of N-nitroso compounds on the activities of the above-mentioned enzymes. Single-dose treatment (20 mg/kg body weight) of male mice with ethylbutylnitrosamine, propylbutylnitrosamine, or dibutylnitrosamine: increased (1) the activity of DMN-dI by 108%, 104%, 51%, respectively; (2) the cytochrome P-450 content by 106%, 72%, 51%, respectively; (3) the activity of AHH by 95%, 106%, 80% respectively; (4) the cytochrome b5 content by 164%, 97%, 94% respectively; and (5) decreased the activity of NADPH-cytochrome c reductase by 55%, 50% and 45%, respectively. Methylpropylnitrosamine decreased the activity of DMN-dI by 44% and the P-450 content by 50%. Diphenylnitrosamine also decreased cytochrome P-450 by 54%, AHH activity by 64% but increased the activity of DMN-dI by 42%, the cytochrome b5 content by 159% and NADPH-cytochrome c reductase activity by 57%. It seems from this study that the activity of AHH is dependent on P-450 content but DMN-dI is not since the compounds that increased or decreased the activity of AHH had parallel effects on P-450 content. Also, the extent to which the altered activities of DMN-dI, P-450, AHH, cytochrome b5 and NADPH-cytochrome c reductase depends on the type of alkyl groups linked to the nitroso group.

Molecular and genetic events in schistosomiasis-associated human bladder cancer: role of oncogenes and tumor suppressor genes

Carcinoma of the urinary bladder is the most common malignancy in many tropical and subtropical countries and is mainly due to endemic schistosomal infection. Schistosomiasis-associated bladder cancer defines a characteristic pathology and cellular and molecular biology that differs from urothelial carcinoma of non-schistosomal origin. N-Nitroso compounds are suspected etiologic agents in the process of bladder cancer induction during schistosomiasis. Elevated levels of DNA alkylation damage have been detected in schistosome-infected bladders and are accompanied by an inefficient capacity of DNA repair mechanisms. Consequently, high frequency of G --> A transition mutations were observed in the H-ras gene and at the CpG sequences of the p53 tumor suppressor gene. Genetic changes have also been detected in the c-erbB-1 and c-erbB-2 oncogenes and in the cdkn2 and Rb tumor suppressor genes. The potential application of these mutational patterns in providing a biological marker suitable for the biomonitoring and early detection of this neoplasm could indicate new avenues of approach that might alleviate the problem in the future. It can also assist in elucidating the mechanisms by which schistosomiasis augments human bladder cancers.