In vivo inhibition of mouse liver microsomal hydroxylating systems by methylenedioxyphenyl insecticidal synergists and related compounds

Pharmacokinetic analysis of acute and dietary exposure to piperonyl butoxide in the mouse

Piperonyl butoxide (PBO) is a popular insecticide synergist present in thousands of commercial, agricultural, and household products. PBO inhibits cytochrome P450 activity, impairing the ability of insects to detoxify insecticides. PBO was recently discovered to also inhibit Sonic hedgehog signaling, a pathway required for embryonic development, and rodent studies have demonstrated the potential for in utero PBO exposure to cause structural malformations of the brain, face, and limbs, or more subtle neurodevelopmental abnormalities. The current understanding of the pharmacokinetics of PBO in mice is limited, particularly with respect to dosing paradigms associated with developmental toxicity. To establish a pharmacokinetic (PK) model for oral exposure, PBO was administered to female C57BL/6J mice acutely by oral gavage (22-1800 mg/kg) or via diet (0.09 % PBO in chow). Serum and adipose samples were collected, and PBO concentrations were determined by HPLC-MS/MS. The serum concentrations of PBO were best fit by a linear one-compartment model. PBO concentrations in visceral adipose tissue greatly exceeded those in serum. PBO concentrations in both serum and adipose tissue decreased quickly after cessation of dietary exposure. The elimination half-life of PBO in the mouse after gavage dosing was 6.5 h (90 % CI 4.7-9.5 h), and systemic oral clearance was 83.3 ± 20.5 mL/h. The bioavailability of PBO in chow was 41 % that of PBO delivered in olive oil by gavage. Establishment of this PK model provides a foundation for relating PBO concentrations that cause developmental toxicity in the rodent models to Sonic hedgehog signaling pathway inhibition.

Mechanism-Based Inactivation of Cytochrome P450 Enzymes: Computational Insights

Mechanism-based inactivation (MBI) refers to the metabolic bioactivation of a xenobiotic by cytochrome P450s to a highly reactive intermediate which subsequently binds to the enzyme and leads to the quasi-irreversible or irreversible inhibition. Xenobiotics, mainly drugs with specific functional units, are the major sources of MBI. Two possible consequences of MBI by medicinal compounds are drug-drug interaction and severe toxicity that are observed and highlighted by clinical experiments. Today almost all of these latent functional groups (e.g., thiophene, furan, alkylamines, etc.) are known, and their features and mechanisms of action, owing to the vast experimental and theoretical studies, are determined. In the past decade, molecular modeling techniques, mostly density functional theory, have revealed the most feasible mechanism that a drug undergoes by P450 enzymes to generate a highly reactive intermediate. In this review, we provide a comprehensive and detailed picture of computational advances toward the elucidation of the activation mechanisms of various known groups with MBI activity. To this aim, we briefly describe the computational concepts to carry out and analyze the mechanistic investigations, and then, we summarize the studies on compounds with known inhibition activity including thiophene, furan, alkylamines, terminal acetylene, etc. This study can be reference literature for both theoretical and experimental (bio)chemists in several different fields including rational drug design, the process of toxicity prevention, and the discovery of novel inhibitors and catalysts.

In vitro and in vivo studies of the metabolic activation of chelidonine

Chelidonium majus L. is a herbal medicine widely employed in Europe and Western Asia. Chelidonine (CHE) is a major constituent of the herb and has been reported to be an inhibitor of the cytochrome P450 enzymes (CYP). The major objective of the present study was to study the metabolic pathways of CHE in order to identify potential reactive metabolites responsible for the enzyme inhibition. Three oxidative metabolites (M1-M3) were detected in human liver microsomal incubations after exposure to CHE. M1 and M2 were two isomers of catechol derivatives, and M3 was a dicatechol compound. The M1-M3 metabolites were also observed in bile of rats given CHE. A total of five glutathione (GSH) conjugates (M4-M8) were detected in microsomes containing CHE, GSH, and NADPH. Moreover, M4 and M6 originated from M1, M5 and M7 resulted from M2, and M8 was a M3-derived GSH conjugate. Three biliary CHE-derived GSH conjugates (M4, M5 and M8) were found in CHE-treated rats. This indicates that CHE was bioactivated to ortho-quinone derivatives both in vitro and in vivo. Recombinant P450 enzyme incubations demonstrated that the CYPs3A4, 1A2, 2C19 and 2D6 were mainly involved in metabolic activation of CHE. This study generated data that may be useful in understanding possible mechanisms of CHE-induced P450 inhibition.

Final Report on the Safety Assessment of Sesame Oil

Sesame Oil is primarily composed of oleic, linoleic, palmitic, and stearic acids and is used in a variety of cosmetics that come into contact with skin, eyes, hair, and mucous membranes. The oral LD50 of a lipstick containing Sesame Oil (10–11 %) was greater than 5 g/kg. This ingredient is neither a primary skin nor ocular irritant. A formulation containing Sesame Oil was neither a sensitizer nor a photosensitizer. Although not teratogenic, Sesame Oil increased resorptions and deciduomas in mice. Extracts of sesame seeds were not mutagenic with metabolic activation. On the basis of the information presented in the report, it is concluded that Sesame Oil is safe for use as a cosmetic ingredient.

Metabolism of [14C]-5-chloro-1,3-benzodioxol-4-amine in male Wistar-derived rats following intraperitoneal administration

[14C]-5-chloro-1,3-benzodioxol-4-amine was administered intraperitoneally (i.p.) to bile duct-cannulated rats (Alpk:ApfSD, Wistar derived) at 25 mg kg-1 to determine the rates and routes of excretion of the compound and to investigate its metabolic fate. A total of 89.1% of the dose was excreted in the 48 h following administration, the majority being recovered in the urine during the first 12 h. The main metabolite in both urine and bile, detected by high-performance liquid chromatography (HPLC) with radioprofiling and mass spectrometry, was identified as a demethylenated monosulfate conjugate. Unchanged parent compound formed a major component of the radiolabel excreted in urine and, in addition to unchanged parent and demethylenated sulphate conjugate, a large number of minor metabolites were detected in urine and bile. The overall metabolic fate of 5-chloro-1,3-benzodioxol-4-amine in the rat was complex, with some similarities to previously studied methylenedioxyphenyl compounds.

Risks associated with consumption of herbal teas

Plants have been used for medicinal purposes for centuries. Health-oriented individuals are turning to herbal teas as alternatives to caffeinated beverages such as coffee, tea, and cocoa and for low-caloric supplements. The popularity of herbal tea consumption has increased significantly during the past two decades in the U.S. Hundreds of different teas made up of varied mixtures of roots, leaves, seeds, barks, or other parts of shrubs, vines, or trees are sold in health food stores. Although chemists have been characterizing toxic plant constituents for over 100 years, toxicological studies of herbal teas have been limited and, therefore, the safety of many of these products is unknown. Plants synthesize secondary metabolites that are not essential in the production of energy and whose role may be in the defense mechanisms as plant toxins to their interactions with other plants, herbivores, and parasites. Pyrrolizidine alkaloids (PAs) were among the first naturally occurring carcinogens identified in plant products, and their presence in herbal teas is a matter of public health significance. Some herbal tea mixtures and single-ingredient herbal teas have been analyzed for toxic/mutagenic potential by bioassay and chromatographic techniques. Numerous human and animal intoxications have been associated with naturally occurring components, including pyrrolizidine alkaloids, tannins, and safrole. Thus, the prevention of human exposure to carcinogens or mutagens present in herbal tea mixture extracts is crucial. Preparation of infusion drinks prepared from plants appears to concentrate biologically active compounds and is a major source of PA poisoning. The quantity and consumption over a long period of time is of major concern. It is recommended that widespread consumption of herbal infusions should be minimized until data on the levels and varieties of carcinogens, mutagens, and toxicants are made available.

Acute renal toxicity of thiabendazole (TBZ) in ICR mice

The acute toxic effects of thiabendazole [2-(4'-thiazolyl)benzimidazole; TBZ] on the kidneys of ICR mice were investigated. The mice were given 0, 250, 500 or 1000 mg TBZ/kg body weight by gavage (using olive oil as a vehicle), and the kidneys were subjected to pathological examination at 1, 3, 5 or 24 hr after dosing. Gross findings were slight enlargement and the presence of whitish areas (white maculae) in kidneys of treated mice at 3, 5 or 24 hr after dosing. Histological findings were desquamation of degenerated cells in proximal tubules of treated mice at 1 hr. Dilation of proximal, distal and collecting tubules was apparent in treated mice at 3, 5 and 24 hr. TBZ-induced renal injury was reduced by pretreatment with inducers of the microsomal monooxygenase system (sodium phenobarbital, beta-naphthoflavone and 3-methylcholanthrene) and were enhanced by pretreatment with inhibitors of that system (2-diethylaminoethyl-2,2-diphenylvalerate hydrochloride and piperonyl butoxide). The concentration of TBZ in blood at 1 or 5 hr after dosing was lower in mice pretreated with microsomal monooxygenase system inducers and was higher in those pretreated with the inhibitors, than in those given TBZ alone. These results suggest that TBZ-induced renal injury may be attributable to the parent compound rather than its metabolites. Measurement of organic ion uptake into renal slices revealed significant depression of [1-14C]tetraethylammonium bromide (TEA) uptake in treated mice at 1 or 5 hr, whereas uptake of p-[glycyl-2-3H]aminohippurate (PAH) was not depressed at 1 or 5 hr after dosing. The reduction in uptake of TEA is interpreted as the result of competitive suppression of the tubular transport of TEA by TBZ. TBZ-induced renal injury was reduced by organic cation transport inhibitors [N'-methylnicotinamide (NMN) or thiamine] but not by organic anion transport inhibitor [p-(dipropylsulphamyl)benzoic acid probenecid], suggesting that the reduction of TBZ-induced renal injury is the result of competitive suppression of the tubular transport of TBZ by NMN or thiamine.

Structural requirements for the inhibition of phthalate ester hydrolysis in rainbow trout by methylenedioxyphenyl compounds

1. The ability of a number of methylenedioxyphenyl compounds and paraoxon to inhibit the hydrolysis and oxidation of di-2-ethylhexyl phthalate by rainbow trout tissue preparations was examined. 2. In addition to paraoxon, only the methylenedioxyphenyl compounds with long side-chains (piperonyl butoxide and tropital) inhibited the hydrolysis of di-2-ethylhexyl phthalate by trout liver subcellular fractions and trout serum. 3. Paraoxon decreased the production of the major metabolite of di-2-ethylhexyl phthalate by trout liver microsomes (+ NADPH) suggesting that this metabolite arises via further metabolism of mono-2-ethylhexyl phthalate.

The analysis of essential oils and extracts (oleoresins) from seasonings--a critical review

A critical review of the analytical methods employed for the determination of the relevant components of seasonings is presented. Where the available methods were inadequate, new ones have been devised. Particular emphasis has been placed on those methods of analysis that provide a rapid and sufficiently accurate appraisal of seasoning extracts and essential oils from seasonings under routine control laboratory conditions. At the same time, the margin of error of these methods has been determined. The individual seasoning extracts were assessed according to the following criteria: (1) essential oil--cardamom, laurel leaves, cloves, origanum (marjoram), sage, and thyme; (2) essential oil and nonvolatile lipids--dillseed, coriander, caraway, mace, nutmeg, pimento (allspice), and celery seed; (3) essential oil and/or pungent ingredients--capsicum, ginger, and pepper; (4) essential oil and/or coloring matter--turmeric (curcuma) and paprika; (5) essential oil and other components--garlic, onion, and cinnamon.

Effects of piperonyl butoxide on dimethylnitrosamine metabolism and toxicity in Swiss mice

The effects of piperonyl butoxide (PB) on the metabolism and toxicity of dimethylnitrosamine (DMN) in Swiss mice were determined. PB, at doses of 10 and 20 mg/kg, inhibited DMN demethylase 45 min after treatment by 18 and 37%. These inhibitory effects were marked 0.5 hr after PB (640 mg/kg) treatment and reached maximal effects at 2 hr when there was 55% inhibition of enzyme activity. The inhibition by PB continued for 24 hr where enzyme activity was suppressed by 35%. At 48 hr after treatment there was stimulation of enzyme activity. Enzyme kinetic determinations showed no change in Km but Vmax decreased from 129 to 49 mumol CH2O/min-g liver. PB (640 mg/kg) inhibited DMN (500 mg/kg; im) mutagenicity in the host-mediated assay, decreasing the mutant frequency by 42%. Paradoxically, PB (640 mg/kg) had no effect on the alkylation of nucleic acids or proteins in mouse liver, kidney, lung, or spleen. In addition, pretreatment with PB (640 mg/kg) had no effect on the LD50 of DMN.