Development and application of a method for identification of isothiocyanate-targeted molecules in colon cancer cells

Allyl Isothiocyanate Maintains DHA-Containing Glycerophospholipids and Ameliorates the Cognitive Function Decline in OVX Mice

Low-temperature-induced fatty acid desaturation is highly conserved in animals, plants, and bacteria. Allyl isothiocyanate (AITC) is an agonist of the transient receptor potential ankyrin 1 (TRPA1), which is activated by various chemophysiological stimuli, including low temperature. However, whether AITC induces fatty acid desaturation remains unknown. We showed here that AITC increased levels of glycerophospholipids (GP) esterified with unsaturated fatty acids, especially docosahexaenoic acid (DHA) in TRPA1-expressing HEK cells. Additionally, GP-DHA including phosphatidylcholine (18:0/22:6) and phosphatidylethanolamine (18:0/22:6) was increased in the brain and liver of AITC-administered mice. Moreover, intragastrical injection of AITC in ovariectomized (OVX) female C57BL/6J mice dose-dependently shortened the Δlatency time determined by the Morris water maze test, indicating AITC ameliorated the cognitive function decline in these mice. Thus, the oral administration of AITC maintains GP-DHA in the liver and brain, proving to be a potential strategy for preventing cognitive decline.

o-Anisidine Dimer, 2-Methoxy-N4-(2-methoxyphenyl) Benzene-1,4-diamine, in Rat Urine Associated with Urinary bladder Carcinogenesis

Monocyclic aromatic amines, o-toluidine (o-Tol) and its structural analog o-anisidine (o-Ans), are IARC Group 1 and Group 2A urinary bladder carcinogens, respectively, and are involved in metabolic activation and DNA damage. Our recent study revealed that 2-methyl-N⁴-(2-methylphenyl) benzene-1,4-diamine (MMBD), a p-semidine-type homodimer of o-Tol, was detected and identified in an in vitro reaction of o-Tol with S9 mix and in vivo urinary samples of o-Tol-exposed rats. Potent mutagenic, genotoxic, and cytotoxic activities were reported with MMBD, suggesting its involvement in urinary bladder carcinogenesis. However, it remains unknown whether o-Ans is converted to active metabolites to induce DNA damage in a similar manner as o-Tol. In this study, we report that a novel o-Ans metabolite, 2-methoxy-N⁴-(2-methoxyphenyl) benzene-1,4-diamine (MxMxBD), a dimer by head-to-tail binding (p-semidine form), was for the first time identified in o-Ans-exposed rat urine. MxMxBD induced a stronger mutagenicity in N-acetyltransferase overexpressed Salmonella typhimurium strains and potent genotoxicity and cytotoxicity in human bladder carcinoma T24 cells compared with o-Ans. These results suggest that MxMxBD may to some extent contribute toward urinary bladder carcinogenesis. In addition to homodimerization, such as MxMxBD, heterodimerizations were observed when o-Ans was coincubated with o-Tol or aniline (Ani) in in vitro reactions with S9 mix. This study highlights the important consideration of homodimerizations and heterodimerizations of monocyclic aromatic amines, including o-Ans, o-Tol, and Ani, in the evaluation of the combined exposure risk of bladder carcinogenesis.

Novel o-Toluidine Metabolite in Rat Urine Associated with Urinary Bladder Carcinogenesis

o-Toluidine (o-Tol), a monocyclic aromatic amine, causes bladder cancer in humans and experimental animals and is therefore classified as a Group 1 carcinogen (IARC) in which the carcinogenicity of o-Tol is involved in metabolic activation, DNA damage, and DNA adduct formation. In the DNA adduct formation mechanism, o-Tol is metabolized by N-hydroxylation, N-acetoxylation, and then deacetoxylation to produce an electrophilic nitrenium ion, which is able to bind to a DNA base, such as dG-C8. Therefore, dG-C8-o-Tol is thought to be a plausible DNA adduct of o-Tol exposure. However, direct detection of dG-C8-o-Tol in biological samples has not been reported yet. Here, we show that a novel o-Tol metabolite, 2-methyl-N¹-(2-methylphenyl)benzene-1,4-diamine (MMBD), a dimer by head-to-tail binding, was identified for the first time in o-Tol-exposed rat urine. MMBD was also detected in a reaction of o-Tol and S9 mix, indicating the formation was catalyzed by an enzymatic reaction. Moreover, MMBD showed a potent stronger mutagenicity in N-acetyltransferase overexpressed Salmonella typhimurium strains,and cytotoxicity in human bladder carcinoma T24 cells and human spleen lymphoblastoid TK6 cells compared with o-Tol. Furthermore, a DNA adduct (m/z 478.1) corresponding to dG-MMBD was detected in the reaction of calf thymus DNA with rat urine containing MMBD, and also in hepatic DNA of rats treated with o-Tol. These results therefore suggested that o-Tol-induced bladder carcinogenesis could be at least partly attributed to MMBD formation. The possible dimerization of monocyclic aromatic amines should be considered in the evaluation of the risk of bladder carcinogenesis after exposure.

Intestinal microbial metabolite stercobilin involvement in the chronic inflammation of ob/ob mice

It is crucial that the host and intestinal microflora interact and influence each other to maintain homeostasis and trigger pathological processes. Recent studies have shown that transplantation of the murine intestinal content to recipient germ-free mice enables transmission of the donor’s phenotypes, such as low level chronic inflammation associated with lifestyle-related diseases. These findings indicate that intestinal bacteria produce some molecules to trigger pathological signals. However, fecal microbial metabolites that induce obesity and the type II diabetic phenotype have not been fully clarified. Here, we showed that the intestinal bacterial metabolite stercobilin, a pigment of feces, induced proinflammatory activities including TNF-α and IL-1β induction in mouse macrophage RAW264 cells. Proinflammatory stercobilin levels were significantly higher in ob/ob mice feces than in the feces of control C57BL/6 J mice. Moreover, in this study, we detected stercobilin in mice plasma for the first time, and the levels were higher in ob/ob mice than that of C57BL/6 J mice. Therefore, stercobilin is potentially reabsorbed, circulated through the blood system, and contributes to low level chronic inflammation in ob/ob mice. Since, stercobilin is a bioactive metabolite, it could be a potentially promising biomarker for diagnosis. Further analyses to elucidate the metabolic rate and the reabsorption mechanism of stercobilin may provide possible therapeutic and preventive targets.

Phenethyl isothiocyanate activates leptin signaling and decreases food intake

Obesity, a principal risk factor for the development of diabetes mellitus, heart disease, and hypertension, is a growing and serious health problem all over the world. Leptin is a weight-reducing hormone produced by adipose tissue, which decreases food intake via hypothalamic leptin receptors (Ob-Rb) and the Janus kinase 2/signal transducer and activator of transcription 3 (JAK2/STAT3) signaling pathway. Protein tyrosine phosphatase 1B (PTP1B) negatively regulates leptin signaling by dephosphorylating JAK2, and the increased activity of PTP1B is implicated in the pathogenesis of obesity. Hence, inhibition of PTP1B may help prevent and reduce obesity. In this study, we revealed that phenethyl isothiocyanate (PEITC), a naturally occurring isothiocyanate in certain cruciferous vegetables, potently inhibits recombinant PTP1B by binding to the reactive cysteinyl thiol. Moreover, we found that PEITC causes the ligand-independent phosphorylation of Ob-Rb, JAK2, and STAT3 by inhibiting cellular PTP1B in differentiated human SH-SY5Y neuronal cells. PEITC treatment also induced nuclear accumulation of phosphorylated STAT3, resulting in enhanced anorexigenic POMC expression and suppressed orexigenic NPY/AGRP expression. We demonstrated that oral administration of PEITC to mice significantly reduces food intake, and stimulates hypothalamic leptin signaling. Our results suggest that PEITC might help prevent and improve obesity.

Physiological relevance of covalent protein modification by dietary isothiocyanates

Isothiocyanates (ITCs), naturally occurring in abundance in cruciferous vegetables, are the most well-studied organosulfur compounds having an electrophilic reactivity. ITCs have been accepted as major ingredients of these vegetables that afford their health promoting potentials. ITCs are able to modulate protein functions related to drug-metabolizing enzymes, transporters, kinases and phosphatases, etc. One of the most important questions about the molecular basis for the health promoting effects of ITCs is how they modulate cellular target proteins. Although the molecular targets of ITCs remains to be validated, dietary modulation of the target proteins via covalent modification by ITCs should be one of the promising strategies for the protection of cells against oxidative and inflammatory damage. This review discusses the plausible target proteins of dietary ITCs with an emphasis on possible involvement of protein modification in their health promoting effects. The fundamental knowledge of ITCs is also included with consideration of the chemistry, intracellular behavior, and metabolism.

Chemical alterations and regulations of biomolecules in lifestyle-related diseases

We know experientially that not only nutrient factors but also non-nutritive functional food factors are playing important roles in maintenance of homeostasis, health promotion, and disease prevention. Although some of these effective behaviors are supported by accumulating scientific evidences, it is in general difficult to determine properly in human. Therefore, the discovering of novel biomarker and developments of the analytical method are one of the prudent strategies to understand disease etiology and evaluate efficacies of functional food factors via monitoring the pathophysiological alteration in live body, tissue, and cells. This review describes recent our findings on (1) formation mechanism, bioactivities, quantitative determination of cholesterol ozonolysis product, secosterol as possible biomarker for lifestyle-related disease, and (2) chemical biology approach for the investigating molecular mechanisms of most promising cancer chemopreventive food factors, isothiocyanate-inducing bioactivities.

Allyl isothiocyanate induces replication-associated DNA damage response in NSCLC cells and sensitizes to ionizing radiation

Allyl isothiocyanate (AITC), a constituent of many cruciferous vegetables exhibits significant anticancer activities in many cancer models. Our studies provide novel insights into AITC-induced anticancer mechanisms in human A549 and H1299 non-small cell lung cancer (NSCLC) cells. AITC exposure induced replication stress in NSCLC cells as evidenced by γH2AX and FANCD2 foci, ATM/ATR-mediated checkpoint responses and S and G2/M cell cycle arrest. Furthermore, AITC-induced FANCD2 foci displayed co-localization with BrdU foci, indicating stalled or collapsed replication forks in these cells. Although PITC (phenyl isothiocyanate) exhibited concentration-dependent cytotoxic effects, treatment was less effective compared to AITC. Previously, agents that induce cell cycle arrest in S and G2/M phases were shown to sensitize tumor cells to radiation. Similar to these observations, combination therapy involving AITC followed by radiation treatment exhibited increased DDR and cell killing in NSCLC cells compared to single agent treatment. Combination index (CI) analysis revealed synergistic effects at multiple doses of AITC and radiation, resulting in CI values of less than 0.7 at Fa of 0.5 (50% reduction in survival). Collectively, these studies identify an important anticancer mechanism displayed by AITC, and suggest that the combination of AITC and radiation could be an effective therapy for NSCLC.