Vasodilator effects of sulforaphane in cerebral circulation: A critical role of endogenously produced hydrogen sulfide and arteriolar smooth muscle KATP and BK channels in the brain.

We investigated the effects of sulforaphane (SFN), an isothiocyanate from cruciferous vegetables, in the regulation of cerebral blood flow using cranial windows in newborn pigs. SFN administered topically (10 µM-1 mM) or systemically (0.4 mg/kg ip) caused immediate and sustained dilation of pial arterioles concomitantly with elevated H2S in periarachnoid cortical cerebrospinal fluid. H2S is a potent vasodilator of cerebral arterioles. SFN is not a H2S donor but it acts via stimulating H2S generation in the brain catalyzed by cystathionine γ-lyase (CSE) and cystathionine ß-synthase (CBS). CSE/CBS inhibitors propargylglycine, ß-cyano-L-alanine, and aminooxyacetic acid blocked brain H2S generation and cerebral vasodilation caused by SFN. The SFN-elicited vasodilation requires activation of potassium channels in cerebral arterioles. The inhibitors of KATP and BK channels glibenclamide, paxilline, and iberiotoxin blocked the vasodilator effects of topical and systemic SFN, supporting the concept that H2S is the mediator of the vasodilator properties of SFN in cerebral circulation. Overall, we provide first evidence that SFN is a brain permeable compound that increases cerebral blood flow via a non-genomic mechanism that is mediated via activation of CSE/CBS-catalyzed H2S formation in neurovascular cells followed by H2S-induced activation of KATP and BK channels in arteriolar smooth muscle.

Development of novel azabenzofuran TRPA1 antagonists as in vivo tools.

The transient receptor potential ankyrin 1 (TRPA1) channel is activated by noxious stimuli including chemical irritants and endogenous inflammatory mediators. Antagonists of this channel are currently being investigated for use as therapeutic agents for treating pain, airway disorders, and itch. A novel azabenzofuran series was developed that demonstrated in vitro inhibition of allyl isothiocyanate (AITC)-induced (45)Ca(2+) uptake with nanomolar potencies against both human and rat TRPA1. From this series, compound 10 demonstrated in vivo target coverage in an AITC-induced flinching model in rats while providing unbound plasma concentrations up to 16-fold higher than the TRPA1 rat IC50.

Cytotoxicity of benzyl isothiocyanate in normal renal proximal tubular cells and its modulation by glutathione.

In the present study, we examined the toxicity of benzyl ITC (BITC) and its urinary mercapturic acid metabolite (BITC-NAC), using a normal renal proximal tubular cell line, pig LLC-PK1. BITC increased cell death with an IC(50) value of about 7 µM, whereas the cytotoxic effect of BITC-NAC was five times weaker than that of BITC. We observed a significant necrosis of the compounds on LLC-PK1 cells with oxidative stress. In the presence of 5 mM glutathione (GSH), comparable to physiological levels, the cytotoxicity of BITC-NAC as well as BITC was significantly reduced. Furthermore, the increase in intracellular GSH levels by pretreatment with NAC before the BITC treatment resulted in inhibition of the BITC-induced necrotic events as well as intracellular oxidative stress. These results suggest that GSH is a determinant of cellular resistance against the BITC-mediated and oxidative stress-dependent cytotoxicity in renal proximal tubular cells.

Metabolism as a key to histone deacetylase inhibition.

There is growing interest in the epigenetic mechanisms that are dysregulated in cancer and other human pathologies. Under this broad umbrella, modulators of histone deacetylase (HDAC) activity have gained interest as both cancer chemopreventive and therapeutic agents. Of the first generation, FDA-approved HDAC inhibitors to have progressed to clinical trials, vorinostat represents a "direct acting" compound with structural features suitable for docking into the HDAC pocket, whereas romidepsin can be considered a prodrug that undergoes reductive metabolism to generate the active intermediate (a zinc-binding thiol). It is now evident that other agents, including those in the human diet, can be converted by metabolism to intermediates that affect HDAC activity. Examples are cited of short-chain fatty acids, seleno-α-keto acids, small molecule thiols, mercapturic acid metabolites, indoles, and polyphenols. The findings are discussed in the context of putative endogenous HDAC inhibitors generated by intermediary metabolism (e.g. pyruvate), the yin-yang of HDAC inhibition versus HDAC activation, and the screening assays that might be most appropriate for discovery of novel HDAC inhibitors in the future.

A cautionary note on using N-acetylcysteine as an antagonist to assess isothiocyanate-induced reactive oxygen species-mediated apoptosis.

N-Acetylcysteine (NAC) has been widely used in cell culture-based studies for the role of reactive oxygen species (ROS) generation in apoptosis induction by isothiocyanates (ITCs). Here we have demonstrated, using [(14)C]phenethyl ITC and [(14)C]sulforaphane, that NAC pretreatment significantly reduces ITC cellular uptake by conjugating with ITCs in the medium, suggesting that reduced uptake of ITCs, rather than the antioxidant activity of NAC itself, is responsible for the diminished downstream apoptotic effects. The study provides a cautionary note on the assay in studying mechanisms of apoptosis by ITCs and other electrophilic and thiol-reactive compounds.

Effect of free-SH containing compounds on allyl isothiocyanate antimicrobial activity against Escherichia coli O157:H7.

Escherichia coli O157:H7 contamination is a significant meat safety issue in many countries. Allyl isothiocyanate (AIT) is a natural compound found to limit the survival of E. coli O157:H7 and other pathogens in meat and meat products. In the present study, it was found that glutathione and cysteine naturally present in meat can interfere with AIT antimicrobial activity. Spectroscopy, HPLC, and LC-MS were used to confirm that glutathione was able to react with AIT and formed a conjugate with no or low bactericidal activity against the tested organisms. The same reaction also occurred at pH values of 4.9 and 5.8 at 25 and 4 degrees C, respectively, which broadly represent storage conditions in raw beef (pH 5.8) and during fermented sausage (pH 4.9) manufacture. Reactions observed help to explain reduction in antimicrobial potency of AIT in food (meat) systems.

Proteasome-mediated degradation of cell division cycle 25C and cyclin-dependent kinase 1 in phenethyl isothiocyanate-induced G2-M-phase cell cycle arrest in PC-3 human prostate cancer cells.

Phenethyl isothiocyanate (PEITC), a constituent of many cruciferous vegetables, offers significant protection against cancer in animals induced by a variety of carcinogens. The present study demonstrates that PEITC suppresses proliferation of PC-3 cells in a dose-dependent manner by causing G(2)-M-phase cell cycle arrest and apoptosis. Interestingly, phenyl isothiocyanate (PITC), which is a structural analogue of PEITC but lacks the -CH(2) spacers that link the aromatic ring to the -N=C=S group, neither inhibited PC-3 cell viability nor caused cell cycle arrest or apoptosis. These results indicated that even a subtle change in isothiocyanate (ITC) structure could have a significant impact on its biological activity. The PEITC-induced cell cycle arrest was associated with a >80% reduction in the protein levels of cyclin-dependent kinase 1 (Cdk1) and cell division cycle 25C (Cdc25C; 24 h after treatment with 10 micro M PEITC), which led to an accumulation of Tyr(15) phosphorylated (inactive) Cdk1. On the other hand, PITC treatment neither reduced protein levels of Cdk1 or Cdc25C nor affected Cdk1 phosphorylation. The PEITC-induced decline in Cdk1 and Cdc25C protein levels and cell cycle arrest were significantly blocked on pretreatment of PC-3 cells with proteasome inhibitor lactacystin. A 24 h exposure of PC-3 cells to 10 micro M PEITC, but not PITC, resulted in about 56% and 44% decrease in the levels of antiapoptotic proteins Bcl-2 and Bcl-X(L), respectively. However, ectopic expression of Bcl-2 failed to alter sensitivity of PC-3 cells to growth inhibition or apoptosis induction by PEITC. Treatment of cells with PEITC, but not PITC, also resulted in cleavage of procaspase-3, procaspase-9, and procaspase-8. Moreover, the PEITC-induced apoptosis was significantly attenuated in the presence of general caspase inhibitor and specific inhibitors of caspase-8 and caspase-9. In conclusion, our data indicate that PEITC-induced cell cycle arrest in PC-3 cells is likely due to proteasome-mediated degradation of Cdc25C and Cdk1, and ectopic expression of Bcl-2 fails to confer resistance to PEITC-induced apoptosis. Furthermore, the results of the present study point toward involvement of both caspase-8- and caspase-9-mediated pathways in apoptosis induction by PEITC.

Effect of benzyl isothiocyanate on spontaneous and induced force of rat uterine contraction.

The present study examines the effect of benzyl isothiocyanate (BITC) on uterine contraction in vitro. BITC (10-320 microM) caused irreversible, concentration-dependent inhibition of the spontaneous, prostaglandin F(2alpha) (PGF(2alpha)) and oxytocin-induced force of gravid and non-gravid rat uterine contractions in contrast to equivalent concentrations of DMSO (solvent control). At 160 microM of BITC, spontaneous, PGF(2alpha) and oxytocin-induced force of gravid rat myometrial contractions were reduced to 16 +/- 6%, 15 +/- 7 % and 17 +/- 4% (of the control contractions), respectively. Moreover, at 320 microM of BITC, spontaneous, PGF(2alpha) and oxytocin-induced force of non-gravid rat uterine contractions were reduced to 10+/-5 %, 4+/-1 % and 7+/-2 % (of the control contractions), respectively. Incubation of isolated non-gravid rat uterine strips in Ringer Locke solution containing 100 microM of BITC for 1h prior to recording their activity also caused significant and irreversible depression of KCl (60mM)-induced tension development in the uterus relative to the solvent control (P < 0.01). In 56% of BITC-pretreated uterine tissues, spontaneous contractions were totally abolished. Cryosections of BITC-treated uterus (hematoxyline and eosin stained) examined under light microscope revealed structural disintegrity with marked vacuolar degeneration of the endometrium and myometrium. It thus appears that like the vascular smooth muscle (reported by previous workers), BITC is also capable of causing functional aberration of isolated uterus by provoking degeneration of the myometrium.

Augmented gene expression of quinone reductase by 6-(methylsulfinyl)hexyl isothiocyanate through avoiding its cytotoxicity.

We examined both the induction of quinone reductase (QR) by 6-(methylsulfinyl)hexyl isothiocyanate and its cytotoxicity in Hepa1c1c7 cells, and compared the sensitivity of these two responses to NAC. QR activity was increased by 6-(methylsulfinyl)hexyl isothiocyanate in a dose-dependent manner. At 80 microM, the compound was significantly toxic to cells, but the resulting QR inhibition was dose-dependently overcome by NAC. Augmentation of QR activity by 6-(methylsulfinyl)hexyl isothiocyanate seemed to be due to augmented expression of QR mRNA, which was significantly increased by the compound. Inhibition of QR gene expression was seen at 80 microM and could be overcome by NAC. Optimal induction of QR gene expression by the compound (at 40 microM) was slightly but significantly inhibited by 10 mM NAC but not by 1 mM. The present study suggests that induction of Phase 2 detoxification enzymes by isothiocyanate compounds may be further enhanced by suppression of their inherent cytotoxic activity.