Metabolism of beta-ionone. Isolation, characterization and identification of the metabolitesin the urine of rabbits

Metabolic conversion of β-pinene to β-ionone in rats

Exposure to or ingestion of turpentine can alter the scent of urine, conferring it a flowery, violet-like scent. Turpentine's effect on urine was initially noticed after its use either as medicine or as a preservative in winemaking. Regardless of the source of exposure, the phenomenon requires metabolic conversion of turpentine component(s) to ionone, the molecule mainly responsible for the scent of violets.The purpose of this study was to identify the presence of ionone in the urine of rats that received β-pinene, and thus to demonstrate that the postulated conversion occurs.We treated rats intraperitoneally with normal saline (negative control), β-ionone (positive control), low-dose β-pinene (1/3 of LD50), and high-dose β-pinene (1/2 of LD50). Urine samples were collected up to 72 h after administration of the compounds, followed by gas chromatography/mass spectrometry identification of the presence of ionone.β-Ionone was found in the urine of rats exposed to both low and high doses of β-pinene. In contrast, α-ionone appears unlikely to have been formed in rats exposed to either low or high doses of β-pinene. β-pinene was converted to β-ionone, followed by partial excretion in the urine of rats. β-Ionone is a minor metabolite of β-pinene.

Vitamin A and its natural derivatives

Vitamin A and derivatives, the natural retinoids, underpin signaling pathways of cellular differentiation, and are key chromophores in vision. These functions depend on transfer across membranes, and carrier proteins to shuttle retinoids to specific cell compartments. Natural retinoids, ultimately derived from plant carotenoids by metabolism to all-trans retinol, are lipophilic and consist of a cyclohexenyl (β-ionone) moiety linked to a polyene chain. This structure constrains the orientation of retinoids within lipid membranes. Cis-trans isomerization at double bonds of the polyene chain and s-cis/s-trans rotational isomerization at single bonds define the functional dichotomy of retinoids (signaling/vision) and specificities of interactions with specific carrier proteins and receptors. Metabolism of all-trans retinol to 11-cis retinal, transfer to photoreceptors, and removal and recycling of all-trans retinal generated by photoreceptor irradiation, is the key process underlying vision. All-trans retinol transferred into cells is metabolized to all-trans retinoic acid and shuttled to the cell nucleus to regulate gene expression controlling organ, tissue and cell differentiation, and cellular homeostasis. Research methods need to address the potential of photoisomerization in vitro to confound research results, and data should be interpreted in the context of membrane-association properties of retinoids and physiological concentrations in vivo. Despite a century of research, there are many fundamental questions of retinoid cellular biochemistry and molecular biology still to be answered. Computational modeling techniques will have an important role for understanding the nuances of vitamin A signaling and function.

Study on the developmental toxicity of β-ionone in the rat

β-ionone (BIO) is used in fragrances, toiletries and non-cosmetic products, and as a flavor food additive. Notwithstanding the widespread human exposure, there are limited data on the reproductive toxicity of BIO. This study evaluated the developmental toxicity of BIO (0, 125, 250, 500 and 1000 mg/kg body weight/day) given orally to rats on days 6-15 of gestation (GD6-15). C-section was on GD21 and implantations, living and dead fetuses and resorptions were recorded. Fetuses were weighed, and examined for external abnormalities and skeleton and visceral anomalies. The embryotoxicity of a single oral dose of BIO (1000 mg/kg body wt) given on GD11 was evaluated as well. At the highest dose, BIO reduced weight gain and produced chromodacryorrhea and other signs of toxicity. BIO did not increase the frequency of malformations nor did it retard fetal growth. Nonetheless, BIO decreased the pregnancy rate in the group of females exposed on GD6-15, and increased the resorption rate in those treated on GD11 only. In conclusion, except for a higher embryolethality at a maternally toxic dose, BIO caused no embryotoxic effect over the dose range tested and the study NOAEL for maternal and developmental toxicity was 500 mg of BIO/ kg of body weight/day.

β-Ionone and its analogs as promising anticancer agents

β-Ionone is an end-ring analog of β-carotenoids which widely distributed in fruit and vegetables. Recent studies have demonstrated anti-proliferative, anti-metastatic and apoptosis induction properties of β-ionone in vitro and in vivo. Also, the studies have focused on investigating the β-ionone action on different types of malignant cells and the possible mechanisms of action. Moreover, the quest of new synthetic β-ionone-based compounds possessing anti-proliferative, anti-metastatic and apoptosis induction activities may enable the discovery of compounds which can be used in combination regimes thus overcoming tumor resistance to conventional anticancer agents. These new agents will also be useful for targeting distinct signaling pathways, to activate selectively mechanisms for apoptosis in cancer cells but devoid of undesirable side effects. In this paper, we reviewed the potentialities of β-ionone and related compounds in cancer prevention and chemotherapy.

β-ionone induces cell cycle arrest and apoptosis in human prostate tumor cells

3-Hydroxy-3-methylglutaryl coenzyme A (HMG CoA) reductase is the rate-limiting activity in the mevalonate pathway that provides essential intermediates for posttranslational modification of growth-associated proteins. Assorted dietary isoprenoids found in plant foods suppress HMG CoA reductase and have cancer chemopreventive activity. β-Ionone, a cyclic sesquiterpene and an end-ring analog of β-carotene, induced concentration-dependent inhibition of the proliferation of human DU145 (IC50 = 210 μmol/L) and LNCaP (IC50 = 130 μmol/L) prostate carcinoma cells and PC-3 prostate adenocarcinoma cells (IC50 = 130 μmol/L). Concomitantly, β-ionone-induced apoptosis and cell cycle arrest at the G1 phase in DU145 and PC-3 cells were shown by fluorescence microscopy, flow cytometry, and TUNEL reaction, and downregulation of cyclin-dependent kinase 4 (Cdk4) and cyclin D1 proteins. Growth suppression was accompanied by β-ionone-induced downregulation of reductase protein. A blend of β-ionone (150 μmol/L) and trans, trans-farnesol (25 μmol/L), an acyclic sesquiterpene that putatively initiates the degradation of reductase, suppressed the net growth of DU145 cells by 73%, an impact exceeding the sum of those of β-ionone (36%) and farnesol (22%), suggesting a synergistic effect. β-ionone, individually or in combination with other HMG CoA reductase suppressors, may have potential in prostate cancer chemoprevention and/or therapy.

Biotransformation of β-ionone by engineered cytochrome P450 BM-3

Wild-type cytochrome P450 monooxygenase from Bacillus megaterium (P450 BM-3) has a low hydroxylation activity for beta-ionone (<1 min(-1)). Substitution of phenylalanine by valine at position 87 led to a more than 100-fold increase in beta-ionone hydroxylation activity (115 min(-1)). Enzyme activity could be further increased by both site-directed and random mutagenesis. The mutant R47L Y51F F87V, designed by site-directed mutagenesis, and the mutant A74E F87V P386S, obtained after two rounds of error-prone polymerase chain reaction, exhibited an increase in activity of up to 300-fold compared to the wild-type enzyme. The triple mutant R47 LY51F F87V exhibited moderate enantioselectivity, forming (R)-4-hydroxy-beta-ionone with an optical purity of 39%. All mutants regioselectively converted beta-ionone into 4-hydroxy-beta-ionone. The regioselectivity is determined amongst others by the absolute configuration of the substrate.

Biotransformation of alpha-isomethylionone to 1-(2,6,6-trimethyl-2-cyclohexen-1-yl)propan-2-one

The main biodegradation product of (+/-)-alpha-isomethylionone (2) with standard activated sludge was characterized as (+/-)-1-(2,6,6-trimethyl-2-cyclohexen-1-yl)propan-2-one (1) by its analysis and synthesis. Both enantiomers (1a and 1b) of 1 were synthesized by starting from (R)- and (S)-2,4,4-trimethyl-2-cyclohexen-1-ol (3a and 3b), respectively.

Metabolites of (+)-dehydroabietic acid in rabbits

The seven metabolites of (+)-dehydroabietic acid (DHA) were newly isolated from rabbit urine by liquid chromatography. On the basis of chemical and spectral data their structures were established to be (15S)-8,11.13-abietatrien-16,18-dioic acid, 2 alpha-hydroxy-8,11,13,15-abietatetraen-18-oic acid, (15R)-15,16-dihydroxy-8,11,13-abietatrien-18-oic acid, 2 beta,15-dihydroxy-8,11,13-abietatrien-18-oic acid, (15S)-2 beta,16-dihydroxy-8,11,13-abietatrien-18-oic acid, 2 alpha,15-dihydroxy-8,11,13-abietatrien-18-oic acid, and (15S)-2 alpha,16-dihydroxy-8,11,13-abietatrien-18-oic acid. The possible hydroxylation routes of DHA in rabbits and the difference between the metabolism of DHA in microorganisms and that in rabbits are discussed.

Further studies of trans-sobrerol metabolism: rat, dog and human urine

The urinary metabolites of d, l-trans-sobrerol were investigated after oral administration to rats, dogs and humans. Structural analysis of the urinary metabolites indicates that allylic hydroxylation, oxidation and glucuronylation are the common interspecies modes of trans-sobrerol biotransformation. Comparison of the findings of trans-sobrerol with previous investigations of cyclic monoterpenes shows similarities in their metabolism in vivo, including the resistance to oxidation of the cyclic trisubstituted double bond.

Studies on the metabolism of d-limonene (p-mentha-1,8-diene). IV. Isolation and characterization of new metabolites and species differences in metabolism

1. The main route of elimination of d-limonene administered orally was via the urine in animals and man, 75-95% of the administered radioactivity being excreted in the urine during 2-3 days. Faecal excretion accounted for less than 10% of the dose in animals during 2-3 days. 2. In addition to six metabolites, namely p-mentha-1,8-dien-10-ol (M-I), p-menth-1-ene-8,9-diol (M-II), perillic acid (M-III), perillic acid-8,9-diol (M-IV), p-mentha-1,8-dien-10-yl-beta-D-glucopyranosiduronic acid (M-V) and 8-hydroxy-p-meth-1-en-9-yl-beta-D-glucopyranosiduronic acid (M-VI) isolated from rabbit urine previously (Kodama et al., 1974), five new metabolites have been isolated from dog and rat urine, and which were characterized as 2-hydroxy-p-menth-8-en-7-oic acid (M-VII), perillylglycine (M-VIII), perillyl-beta-D-glucopyranosiduronic acid (M-IX), p-mentha-1,8-dien-6-ol (M-X) and probably p-menth-1-ene-6,8,9-triol (M-XI). 3. The major metabolite of d-limonene in the urine was M-IV in rat and rabbit, M-IX in hamster, M-II in dog and M-VI in guinea pig and man.

A multienzyme complex for CO2 fixation

Acetyl-coenzyme A carboxylase from Euglena gracilis strain Z was isolated as a component of a multienzyme complex which includes phosphoenolpyruvate carboxylase and malate dehydrogenase. The multienzyme complex was shown to exist in crude extracts and was purified to a homogeneous protein with a molecular weight of 360,000 by gel filtration. The ratio of the activities of the constituent enzymes was acetyl-CoA carboxylase:phosphoenolpyruvate carboxylase:malate dehydrogenase, 1:25:500. The complex is proposed to operate in conjunction with malic enzyme, which is present in Euglena, to facilitate the formation of substrates, malonyl-CoA, and NADPH, for fatty acid biosynthesis. The interaction of the enzymes may represent a means of control of acetyl-CoA carboxylase activity in organisms which do not possess an enzyme subject to allosteric regulation. The acetyl-CoA carboxylase activity from Euglena is unaffected by citrate and isocitrate.