Efficient regioselective enzymatic acylation of troxerutin: difference characterization of in vitro cellular uptake and cytotoxicity.

In this study, we developed a multi-site acylation strategy to improve the lipophilicity and cellular uptake of troxerutin, a natural flavonoid with many health-promoting bioactivities. By clarifying the acylation properties of troxerutin catalyzed by lipases from different sources, a series of troxerutin ester derivatives acylated at different sites was synthesized, including troxerutin dipropyl (TDP), tripropyl (TTP), tetrapropyl (TEP), dibutyl (TDB), monohexyl (TMH), monooctyl (TMO) and monodecyl (TMD) esters. Interestingly, the troxerutin esters acylated at multiple sites with shorter fatty chains (TDP, TTP and TEP) had similar lipophilicity to the mono-acylated esters bearing longer fatty chains (TMH, TMO and TMD, respectively) and meanwhile demonstrated surprisingly lower cytotoxicity than that of the long fatty-chain mono-esters. In particular, the multi-acylated esters with shorter fatty chains showed remarkably higher cellular uptake than the mono-esters with long fatty chains. In vitro gastrointestinal digestion suggested that the multi-acylated esters of troxerutin were more resistant to gastrointestinal degradation than the mono-esters. These results indicated that multi-site acylation with short fatty chains could be an effective alternative to introducing one-site mono-acylation for the modification of troxerutin and other flavonoid compounds.

Identification of the metabolites of the antioxidant flavonoid 7-mono-O-(ß-hydroxyethyl)-rutoside in mice.

The clinical use of the anticancer drug doxorubicin is limited by severe cardiotoxicity. In mice, the semisynthetic antioxidant flavonoid 7-mono-O-(ß-hydroxyethyl)-rutoside (monoHER) has been successfully used as a protector against doxorubicin-induced cardiotoxicity. However, most monoHER has already been cleared from the body at the time that doxorubicin concentrations are still high. This result suggests that not only the parent compound monoHER itself but also monoHER metabolites could be responsible for the observed cardioprotective effects in mice. Therefore, in the present study, we investigated the metabolism of monoHER in mice. Mice were administered 500 mg/kg monoHER intraperitoneally. At different time points after monoHER administration, bile was collected and analyzed for the presence of monoHER metabolites. The formed metabolites were identified by liquid chromatography-diode array detection-time of flight-mass spectrometry. Thirteen different metabolites were identified. The observed routes of monoHER metabolism are methylation, glucuronidation, oxidation of its hydroxyethyl group, GSH conjugation, and hydrolysis of its disaccharide. In line with other flavonoids, methylated monoHER and the monoHER glucosides are expected to have relatively high cellular uptake and low clearance from the body. Therefore, these metabolites might contribute to the observed protection of monoHER against doxorubicin-induced cardiotoxicity.

Troxerutin flavonoid has neuroprotective properties and increases neurite outgrowth and migration of neural stem cells from the subventricular zone.

Troxerutin (TRX) is a water-soluble flavonoid which occurs commonly in the edible plants. Recent studies state that TRX improves the functionality of the nervous system and neutralizes Amyloid-ß induced neuronal toxicity. In this study, an in vitro assay based upon Neural stem cell (NSCs) isolated from the subventricular zone of the postnatal balb/c mice was established to explore the impact of TRX on individual neurogenesis processes in general and neuroprotective effect against ß-amyloid 1-42 (Aß42) induced inhibition in differentiation in particular. NSCs were identified exploiting immunostaining of the NSCs markers. Neurosphere clonogenic assay and BrdU/Ki67 immunostaining were employed to unravel the impact of TRX on proliferation. Differentiation experiments were carried out for a time span lasting from 48 h to 7 days utilizing ß-tubulin III and GFAP as neuronal and astrocyte marker respectively. Protective effects of TRX on Aß42 induced depression of NSCs differentiation were determined after 48 h of application. A neurosphere migration assay was carried out for 24 h in the presence and absence of TRX. Interestingly, TRX enhanced neuronal differentiation of NSCs in a dose-dependent manner after 48 h and 7 days of incubation and significantly enhanced neurite growth. A higher concentration of TRX also neutralized the inhibitory effects of Aß42 on neurite outgrowth and length after 48 h of incubation. TRX significantly stimulated cell migration. Overall, TRX not only promoted NSCs differentiation and migration but also neutralized the inhibitory effects of Aß42 on NSCs. TRX, therefore, offers an interesting lead structure from the perspective of drug design especially to promote neurogenesis in neurological disorders i.e. Alzheimer's disease.

In vivo evaluation of coumarin and nicotine as probe drugs to predict the metabolic capacity of CYP2A6 due to genetic polymorphism in Thais.

The association between the distribution characteristics of CYP2A6 catalytic activities toward nicotine and coumarin, and the frequency distribution of CYP2A6 variant alleles reported was estimated in 120 healthy Thais. The distributions of the subjects as classified by the amounts of 7-hydroxycoumarin (7-OHC) excreted in the urine and by cotinine/nicotine ratio in the plasma were clearly bimodal. However, the numbers of apparently poor metabolizers for coumarin and nicotine were different. The inter-individual variability in the in vivo dispositions of coumarin and nicotine closely related to the CYP2A6 genetic polymorphism. There was a close correlation between the rate of 7-OHC excretion in the urine and cotinine/nicotine ratio in the plasma among subjects (R=0.92, p<0.001). The frequency of CYP2A6 allele found in the present study was: CYP2A6*1A=32% (95% CI, 22.1-39.4%), CYP2A6*1B=27% (95% CI, 19.4-33.5%), CYP2A6*9=20% (95% CI, 17.6-23.3%), CYP2A6*4=14% (95% CI, 9.6-17.8%), CYP2A6*7=5% (95% CI, 3.7-9.4%), CYP2A6*10=2% (95% CI, 0.8-5.1%). Subjects having CYP2A6*1A/*1B were found to have a higher rate of 7-OHC excretion, as well as a higher cotinine/nicotine ratio in the plasma compared with those of the other genotypes. In contrast, subjects with CYP2A6*4/*7 and CYP2A6*7/*7 almost lacked any cotinine formation, whereas urinary 7-OHC was still detectable. CYP2A6*9 allele clearly resulted in reduced enzyme activities. Despite the absence of the homozygote for CYP2A6*10 allele, the presence of CYP2A6*10 allele significantly decreased the enzyme activities. The results of the present study demonstrate that in vivo phenotyping of CYP2A6 using nicotine and coumarin are not metabolically equivalent. Nicotine is a better probe according to its specificity, while coumarin is still valuable to be used for a routine CYP2A6 phenotyping since the test employs a non-invasive method.

Troxerutin, a natural flavonoid binds to DNA minor groove and enhances cancer cell killing in response to radiation.

Troxerutin, a flavonoid best known for its radioprotective and antioxidant properties is of considerable interest of study due to its broad pharmacological activities. The present study on troxerutin highlights its abilities to bind DNA and enhance cancer cell killing in response to radiation. Troxerutin showed strong binding with calf thymus DNA in vitro. Troxerutin-DNA interaction was confirmed by CD spectropolarimetry. The mode of binding of troxerutin to DNA was assessed by competing troxerutin with EtBr or DAPI, known DNA intercalator and a minor groove binder, respectively. DAPI fluorescence was drastically reduced with linear increase in troxerutin concentration suggesting possible binding of troxerutin to DNA minor groove. Further, computational studies of docking of troxerutin molecule on mammalian DNA also indicated possible troxerutin-DNA interaction at minor groove of DNA. Troxerutin was found to mainly localize in the nucleus of prostate cancer cells. It induced cytotoxicity in radioresistant (DU145) and sensitive (PC3) prostate cancer cells. When troxerutin pre-treated DU145 and PC3 cells were exposed to γ-radiation, cytotoxicity as estimated by MTT assay, was found to be further enhanced. In addition, the % subG1 population detected by propidium iodide staining also showed similar response when combined with radiation. A similar trend was observed in terms of ROS generation and DNA damage in DU145 cells when troxerutin and radiation were combined. DNA binding at minor groove by troxerutin may have contributed to strand breaks leading to increased radiation induced cell death.

Probing the interaction of troxerutin with transfer RNA by spectroscopic and molecular modeling.

The studies on the interaction between tRNA (transfer RNA) and small molecules are an area of remarkable recent attention. For this notion a fundamental knowledge of the molecular features involving the interaction of small molecules with tRNA is crucial. Hence, in the present study we have investigated the interaction of TXER (troxerutin), natural bioflavonoid rutin derivative with yeast tRNA by using various spectroscopic techniques and molecular docking studies. The UV absorption and fluorescence emission studies demonstrated external binding of TXER on tRNA with low binding constant values as compared to strong binders. Circular dichroism (CD) spectroscopy study revealed that TXER did not show any significant modification on native conformation of tRNA. Furthermore in electrochemical study, the complex of TXER-tRNA did not expose any noticeable positive potential peak shift which indicated an interaction of TXER with tRNA by electrostatic or external binding mode. The docking study showed that the hydrogen and hydrophobic interactions were involved in binding of TXER-tRNA with docking score -7.0 kcal/mol. These findings led us to confirm the interaction of TXER on tRNA through external binding with low binding affinity, indicating its potential bioapplication in the future.

Spectroscopic and molecular docking studies on the interaction of troxerutin with DNA.

Troxerutin (TXER) is a derivative of naturally occurring bioflavonoid rutin. It possesses different biological activities in rising clinical world. The biological activity possessed by most of the drugs mainly targets on macromolecules. Hence, in the current study we have examined the interaction mechanism of TXER with calf thymus DNA (CT-DNA) by using various spectroscopic methods, isothermal titration calorimetry (ITC) and molecular docking studies. Further, DNA cleavage study was carried out to find the DNA protection activity of TXER. UV-absorption and emission spectroscopy showed low binding constant values via groove binding. Circular dichroism study indicates that TXER does not modify native B-form of DNA, and it retains the native B-conformation. Furthermore, no effective positive potential peak shift was observed in TXER-DNA complex during electrochemical analysis by which it represents an interaction of TXER with DNA through groove binding. Molecular docking study showed thymine guanine based interaction with docking score -7.09 kcal/mol. This result was compared to experimental ITC value. The DNA cleavage study illustrates that TXER does not cause any DNA damage as well as TXER showed DNA protection against hydroxyl radical induced DNA damage. From this study, we conclude that TXER interacts with DNA by fashion of groove binding.

The contribution of the major metabolite 4'-O-methylmonoHER to the antioxidant activity of the flavonoid monoHER.

The antioxidant flavonoid 7-mono-O-(ß-hydroxyethyl)-rutoside (monoHER) effectively protects against doxorubicin-induced cardiotoxicity in mice. Doxorubicin is a very effective anticancer drug. The clinical use of doxorubicin is limited by severe cardiotoxicity. Free radicals, i.e., hydroxyl and superoxide radicals play a crucial role in this toxicity. In this study the involvement of the major metabolite of monoHER, 4'-O-methylmonoHER (methylmonoHER) in the protective effect of monoHER is studied. MethylmonoHER displayed antioxidant activity i.e., TEAC, hydroxyl and superoxide radical scavenging activity; nevertheless monoHER appeared to be superior compared to methylmonoHER. As a result of scavenging, flavonoids are oxidized and display reactivity towards thiols. Oxidized methylmonoHER, is far less thiol reactive towards creatine kinase than monoHER, which indicates that methylmonoHER is less toxic towards thiol containing enzymes. The thiol-reactivity of oxidized methylmonoHER was also negligible towards KEAP1 compared to monoHER. These results indicate that methylmonoHER hardly protects against radical damage via scavenging or via activating the NRF2 defense system. Also in HUVECs, methylmonoHER provided far less protection against oxidative stress (EC50>100µM) than monoHER which was a very potent protector (EC50=80nM). The results indicate that the contribution of methylmonoHER to the protection against doxorubicin-induced cardiotoxicity by monoHER is relatively low.

The affinity of troxerutin for the venous wall measured by laser scanning microscopy.

The uptake and localization of troxerutin, a trihydroxy-ethyl-rutoside, in the venous wall have been studied in patients undergoing long saphenous vein surgery. Troxerutin, an autofluorescent drug, is currently used to relieve oedema and subjective symptoms in patients with chronic venous insufficiency. In order to determine the localization of the troxerutin, a confocal scanning laser microscope has been used to record the fluorescence from vein cross sections. The quantified fluorescence was used as a measure of the local concentration of troxerutin. In order to reduce the effects of local variation, several images have been scanned from each specimen. Then the recorded data have been analysed to see how the fluorescence varies in the radial direction within the venous wall. Results showed that troxerutin was significantly accumulated in both inner and outer parts of the venous wall. Whereas inner wall troxerutin uptake resulted from direct diffusion through the lumen, the outer wall uptake proceeded likely from the vasa vasorum circulation.

Investigations into the lymphatic vessels and their valves in the fore-limb of the pig.

Measurements were carried out on the lymphatics of the fore-limb of the pig, the values recorded in tabular form and further classified. In this way lymph transport was considered, particularly through the lymphokinetic action of a drug, and by using patent blue violet.

The metabolism and excretion of 7-mono-0-(beta-hydroxyethyl) rutoside in the dog.

Following i.v. administration of mono-HR to the beagle, plasma levels of both mono-HR and its glucuronide conjugates fell rapidly, neither being detectable 8 h after injection. Following oral administration of 14C-mono-HR, mono-HR-glucuronide was detected in plasma, confirming the absorption of mono-HR, and low levels of 14C were detectable up to 72 h after dosage. Following either oral or i.v. administration of mono-HR, the major route of excretion was fecal elimination of the compound as its aglycone form. Urinary excretion was slight being less than 15% following i.v. dosage and 4% following oral administration. Metabolism of mono-HR was confined to glucuronidation and hydrolytic cleavage of the glycoside side chain. Ring fission products of mono-HR were not detected.

Differences in pharmacological activities of the antioxidant flavonoid monoHER in humans and mice are caused by variations in its metabolic profile.

Despite its well-known cardiotoxicity, the anthracycline doxorubicin continues to be a widely used chemotherapeutic agent. The flavonoid 7-mono-O-(ß-hydroxyethyl)-rutoside (monoHER) has shown protection against doxorubicin-induced cardiotoxicity in mice. However, this protection has not been observed in humans. This prompted us to investigate monoHER metabolism in humans and compare it with that in mice. Five healthy volunteers received monoHER by intravenous infusion. After infusion, bile fluid was collected, and the monoHER metabolites were identified by liquid chromatography-diode-array detection (LC-DAD), time-of-flight mass spectrometry (TOF-MS), and (1)H-nuclear magnetic resonance (NMR). Thirteen different metabolites were identified. MonoHER was predominantly converted into inactive glucuronidated metabolites. In mice, the major metabolic route is methylation, which forms bioactive metabolites that are implicated in the cardioprotective effect of monoHER. This indicates that the different pharmacological effects of monoHER in mice and humans might be explained by a difference in monoHER metabolism. This study adds to the growing appreciation of flavonoid metabolites as bioactive compounds.

An essential difference between the flavonoids monoHER and quercetin in their interplay with the endogenous antioxidant network.

Antioxidants can scavenge highly reactive radicals. As a result the antioxidants are converted into oxidation products that might cause damage to vital cellular components. To prevent this damage, the human body possesses an intricate network of antioxidants that pass over the reactivity from one antioxidant to another in a controlled way. The aim of the present study was to investigate how the semi-synthetic flavonoid 7-mono-O-(ß-hydroxyethyl)-rutoside (monoHER), a potential protective agent against doxorubicin-induced cardiotoxicity, fits into this antioxidant network. This position was compared with that of the well-known flavonoid quercetin. The present study shows that the oxidation products of both monoHER and quercetin are reactive towards thiol groups of both GSH and proteins. However, in human blood plasma, oxidized quercetin easily reacts with protein thiols, whereas oxidized monoHER does not react with plasma protein thiols. Our results indicate that this can be explained by the presence of ascorbate in plasma; ascorbate is able to reduce oxidized monoHER to the parent compound monoHER before oxidized monoHER can react with thiols. This is a major difference with oxidized quercetin that preferentially reacts with thiols rather than ascorbate. The difference in selectivity between monoHER and quercetin originates from an intrinsic difference in the chemical nature of their oxidation products, which was corroborated by molecular quantum chemical calculations. These findings point towards an essential difference between structurally closely related flavonoids in their interplay with the endogenous antioxidant network. The advantage of monoHER is that it can safely channel the reactivity of radicals into the antioxidant network where the reactivity is completely neutralized.

Metabolism of hydroxyethylrutosides (HR): metabolism of [14C]-HR in man.

1. following oral administration of a [14C]-hydroxyethylrutoside (Paroven, Venoruton) preparation (HR) to three subjects, 3.05--5.97% of the administered [14C] was excreted in urine. Unchanged urinary [14C]-hydroxyethylrutosides represented 1.57--1.96% of the total dose. 2. Significant levels of [14C] were detected in plasma within 1 h of oral administration of HR. Peak levels were observed from 2--9 h. 3. The presence in urine of [14C]-3',4',5,7-tetra-O-(beta-hydroxyethyl)rutoside, [14C]-3',4',7-tri-O-(beta-hydroxyethyl)rutoside and [14C]-4',7-di-O-(beta-hydroxyethyl)rutoside was shown by radioscanning and/or spectal methods. 4. Administration of a second oral dose of [14C]-HR to each of the three subjects following extended dosage of nonlabelled HR did not result in any increase in urinary [14C] excretion over that observed after administration of a single oral dose. 5. Observations on urinary excretion in man are compatible with the finding in experimental animals that the major route of hydroxyethylrutoside excretion is via the biliary-enteric route.

[Studies in animal experiments on determination of blood and organ levels of o-(beta-hydroxyethyl)-rutosides (HR) after i.p. administration (author's transl)]. / Tierexperimentelle Untersuchungen zur Bestimmung von Wirkstoffkonzentrationen in Blut und Organen nach intraperitonealer Verabreichung von O-(beta-Hydroxyethyl)-rutosiden.

The concentration of O-(beta-hydroxyethyl)-rutosides (HR, Venoruton) in different organs and serum was investigated after i.p. injections in C3H-mice. There was found a distinct but brief maximum level in serum within 10 to 25 min after i.p. injection. This result explains some of the positive and negative papers about the problem of radiation protection by HR. Therefore it seems important to expand knowledge on time factors and excretion mode of HR in different organs and serum to judge on the radioprotective ability of this substance.

The disposition and metabolism of 3',4',7-tri-O-(beta-hydroxyethyl)rutoside and 7-mono-O-(beta-hydroxyethyl)rutoside in the mouse.

1. Following intravenous administration of 3',4',7-tri-O-(beta-hydroxy[14C2]ethyl)rutoside or 7-mono-O-(beta-hydroxy[14C2]ethyl)rutoside to male mice, 68% of the dose of each is excreted in faeces as the corresponding hydroxyethyl-quercetin within 72 h of dosage. Mean urinary excretions of mono- and tri-hydroxyethylrutosides in 72 h were 27 and 21% respectively. Unchanged rutosides and their glucuronides were detected in urine. 2. In biliary-cannulated animals, the mean biliary excretion of both tri- and mono-hydroxyethylrutosides was 71%, in 24 h of dosage. In both cases most 14C was excreted in 3 h, as unchanged rutosides and glucuronide conjugates. 3. Fall of blood 14C concn, was rapid for both compounds. Neither compound was detected in brain but there was short-term accumulation in liver and kidney, and 2--3 h after dosage, most 14C for both compounds was associated with the gastro-intestinal contents. 4. Animals killed 72 h after dosage of either compound contained less than 7% of dose, mostly in the colon and caecal contents. 5. Foetuses removed 3 h after dosage of either compound to the dams did not contain 14C; foetuses removed 5 min after dosage contained low levels of 14C, substantially below the maternal blood level and equiv. to less than 0-1% of dose in each case. No 14C was detected in amniotic fluid.

Hepatic clearance and disposition of hydroxyethylrutosides.

Although salts of rutin on i-v admin. undergo insolubilization giving rise to concretions and suppurative inflammation in the liver this was not observed in respect of the vaso-active hydroxyethylrutosides (Pfeifer et al., 1970). I-v admin. of 3',4',7-tri0-(beta-hydroxy[14C]ethyl)-rutoside (tri-HR) and 7-mono0-(beta-hydroxy[14C]ethyl)rutoside (mono-HR) to mice showed rapid biliary excretion (approx. 71% within 24 h). Approx. 2/3 of the dose was subsequently excreted in faeces and ca. 25% in urine over 72 h. Autoradiography and scintilation counting showed short term concentration in the liver over the initial 4 h period but at 72 h less than 0.22% of tri-HR and 0.59% of mono-HR was detectable in hepatic tissue. Carcasses of mice killed at 72 h contained less than 7% of the initial dose which was mainly present in intestinal contents.