Computational Study of Ortho-Substituent Effects on Antioxidant Activities of Phenolic Dendritic Antioxidants.

Antioxidants are an important component of our ability to combat free radicals-an excess of which leads to oxidative stress, which is related to aging and numerous human diseases. Oxidative damage also shortens the shelf-life of foods and other commodities. Understanding the structure-activity relationship of antioxidants and their mechanisms of action is important for designing more potent antioxidants for potential use as therapeutic agents as well as preservatives. We report the first computational study on the electronic effects of ortho-substituents in dendritic tri-phenolic antioxidants, comprising a common phenol moiety and two other phenol units with electron-donating or electron-withdrawing substituents. Among the three proposed antioxidant mechanisms, sequential proton loss electron transfer (SPLET) was found to be the preferred mechanism in methanol for the dendritic antioxidants based on calculations using Gaussian 16. We then computed the total enthalpy values by cumulatively running SPLET for all three rings to estimate electronic effects of substituents on overall antioxidant activity of each dendritic antioxidant and establish their structure-activity relationships. Our results show that the electron-donating o-OCH3 group has a beneficial effect while the electron-withdrawing o-NO2 group has a negative effect on the antioxidant activity of the dendritic antioxidant. The o-Br and o-Cl groups did not show any appreciable effects. These results indicate that electron-donating groups such as o-methoxy are useful for designing potent dendritic antioxidants while the nitro and halogens do not add value to the radical scavenging antioxidant activity. We also found that the half-maximal inhibitory concentration (IC50) values of 2,2-diphenyl-1-picrylhydrazyl (DPPH) better correlate with the second step (electron transfer enthalpy, ETE) than the first step (proton affinity, PA) of the SPLET mechanism, implying that ETE is the better measure for estimating overall radical scavenging antioxidant activities.

Effect of electron donating groups on polyphenol-based antioxidant dendrimers.

Numerous studies have reported the beneficial effects of antioxidants in human diseases. Among their biological effects, a majority of antioxidants scavenge reactive radicals in the body, thereby reducing oxidative stress that is associated with the pathogenesis of many diseases. Antioxidant dendrimers are a new class of potent antioxidant compounds reported recently. In this study, six polyphenol-based antioxidant dendrimers with or without electron donating groups (methoxy group) were synthesized in order to elucidate the influence of electron donating groups (EDG) on their antioxidant activities. Syringaldehyde (2 ortho methoxy groups), vanillin (1 ortho methoxy group), and 4-hydroxybenzaldehyde (0 methoxy group) were derivatized with propargylamine to form building blocks for the dendrimers. All the six dendrimers contain polyether cores, which were synthesized by attaching pentaerythritol and methyl α-d-glucopyranoside to in-house prepared spacer units. To prepare generation 1 antioxidant dendrimers, microwave energy and granulated metallic copper catalyst were used to link the cores and building blocks together via alkyne-azide 1,3-cycloaddition click chemistry. These reaction conditions resulted in high yields of the target dendrimers that were free from copper contamination. Based on DPPH antioxidant assay, antioxidant dendrimers decorated with syringaldehyde and vanillin exhibited over 70- and 170-fold increase in antioxidant activity compared to syringaldehyde and vanillin, respectively. The antioxidant activity of dendrimers increased with increasing number of EDG groups. Similar results were obtained when the dendrimers were used to protect DNA and human LDL against organic carbon and nitrogen-based free radicals. In addition, the antioxidant dendrimers did not show any pro-oxidant activity on DNA in the presence of physiological amounts of copper. Although the dendrimers showed potent antioxidant activities against carbon and nitrogen free radicals, EPR and DNA protection studies revealed lack of effectiveness of these dendrimers against hydroxyl radicals. The dendrimers were not cytotoxic to CHO-K1 cells.

Copper-granule-catalyzed microwave-assisted click synthesis of polyphenol dendrimers.

Syringaldehyde- and vanillin-based antioxidant dendrimers were synthesized via microwave-assisted alkyne-azide 1,3-dipolar cycloaddition using copper granules as a catalyst. The use of Cu(I) as a catalyst resulted in copper contaminated dendrimers. To produce copper-free antioxidant dendrimers for biological applications, Cu(I) was substituted with copper granules. Copper granules were ineffective at both room temperature and under reflux conditions (<5% yield). However, they were an excellent catalyst when dendrimer synthesis was performed under microwave irradiation, giving yields up to 94% within 8 h. ICP-mass analysis of the antioxidant dendrimers obtained with this method showed virtually no copper contamination (9 ppm), which was the same as the background level. The synthesized antioxidants, free from copper contamination, demonstrated potent radical scavenging with IC50 values of less than 3 µM in the 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay. In comparison, dendrimers synthesized from Cu(I)-catalyzed click chemistry showed a high level of copper contamination (4800 ppm) and no detectable antioxidant activity.

Clinical impact of the development of YMDD mutants in hepatitis B virus-associated glomerulonephritis.

BACKGROUND/AIMS: Elimination of chronic viral infection with lamivudine (LAM) has recently been proposed to induce remission of HBV-associated glomerulonephritis (GN). However, prolonged LAM therapy can lead to the development of LAM-resistant HBV, causing viral breakthrough in serum. The present study evaluated the effect of the development of YMDD mutations on renal disease in HBV-associated GN patients. METHODOLOGY: The database and clinical records of 4 patients, who were diagnosed with biopsyproven HBV-associated GN and had documented YMDD mutants following prolonged LAM therapy, were retrospectively reviewed. RESULTS: The mean LAM treatment duration before the development of YMDD mutants was 25±9 months. Before YMDD mutants developed, LAM therapy lowered HBV DNA titers in serum and reduced the amount of proteinuria. With the development of YMDD mutations, viral breakthrough in serum occurred, and three patients experienced aggravation of proteinuria and/or progressive renal deterioration. Among them, one patient had a considerable amount of proteinuria and progressive renal deterioration even after HBV DNA titer fell under detectable levels with the switch to adefovir dipivoxil. CONCLUSIONS: YMDD mutant-related viral breakthrough after prolonged LAM therapy might lead to the aggravation of renal disease in HBV-associated GN patients.

Potent antioxidant dendrimers lacking pro-oxidant activity.

It is well known that antioxidants have protective effects against oxidative stress. Unfortunately, in the presence of transition metals, antioxidants, including polyphenols with potent antioxidant activities, may also exhibit pro-oxidant effects, which may irreversibly damage DNA. Therefore, antioxidants with strong free radical-scavenging abilities and devoid of pro-oxidant effects would be of immense biological importance. We report two antioxidant dendrimers with a surface rich in multiple phenolic hydroxyl groups, benzylic hydrogens, and electron-donating ring substituents that contribute to their potent free radical-quenching properties. To minimize their pro-oxidant effects, the dendrimers were designed with a metal-chelating tris(2-aminoethyl)amine (TREN) core. The dendritic antioxidants were prepared by attachment of six syringaldehyde or vanillin molecules to TREN by reductive amination. They exhibited potent radical-scavenging properties: 5 times stronger than quercetin and 15 times more potent than Trolox according to the 1,1-diphenyl-2-picrylhydrazyl assay. The antioxidant dendrimers also protected low-density lipoprotein, lysozyme, and DNA against 2,2'-azobis(2-amidinopropane) dihydrochloride-induced free radical damage. More importantly, unlike quercetin and Trolox, the two TREN antioxidant dendrimers did not damage DNA via their pro-oxidant effects when incubated with physiological amounts of copper ions. The dendrimers also showed no cytotoxicity toward Chinese hamster ovary cells.

Synthesis and antioxidant properties of dendritic polyphenols.

Three dendritic polyphenols (generation 1) were synthesized: a syringaldehyde-based dendrimer (1), a vanillin-based dendrimer (2), and an iodinated vanillin-based dendrimer (3). They all showed strong antioxidant activity according to the 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical assay. The syringaldehyde dendrimer was twice and 10 times stronger than quercetin and Trolox, respectively. The vanillin-based dendrimer and its more hydrophobic iodinated derivative were also more potent antioxidants than quercetin and Trolox. The DPPH order of potency was 1>2, 3>quercetin>Trolox. All three dendrimers also protected human LDL from free radical attack in a dose-dependent manner. Their order of free radical scavenging was 1>3>2>quercetin>Trolox. The increased hydrophobic nature of the iodinated derivative may have contributed to its better LDL protection than 2. Protection of linoleic acid oxidation was studied by the beta-carotene-linoleate assay. Dendrimer 1 was clearly superior to the other antioxidants in protecting the fatty acid. In case of DNA protection against free radical damage, the order of activity was 1>quercetin>2>3, Trolox. Pro-oxidant effect on copper-induced DNA oxidation showed the following order: quercetin, Trolox>1>2>3. Results of the study show that dendritic antioxidants, even at the generation 1 level, provide promising antioxidant properties for their potential use as drug candidates for diseases associated with oxidative stress.

[Natural history of gastric varices and risk factors for bleeding].

BACKGROUND/AIMS: Gastric varices (GV) are one of the most serious complications of portal hypertension, but there is limited information on the clinical course of GV in Korea. The aim of this study was to elucidate the natural history of GV bleeding in Korean patients. METHODS: Of 604 patients with GV diagnosed between May 1995 and May 2005 at the Samsung Medical Center, 237 patients without a history of variceal bleeding or previous intervention for varices were investigated. The cumulative incidence rates of GV bleeding, long-term survival rates, and risk factors for GV bleeding were evaluated. RESULTS: The cumulative incidence rates of GV bleeding were 4.8%, 19.9%, and 23.2% at 1, 3, and 5 years after diagnosis, respectively. The overall survival rates were 88.6%, 53.2%, and 37.2% at 1, 5, and 10 years. In the univariate analysis, fundal varices, large (F3) GV, red color sign, and poor liver function (Child-Pugh class B or C) were significant risk factors for GV bleeding. In the multivariate analysis, large GV (hazard ratio 2.49) and poor liver function (hazard ratio 3.95) were the independent risk factors. CONCLUSIONS: GV bleeding was more frequent in patients with fundal varices than in patients with type 1 gastroesophageal varices, and large GV and poor liver function were risk factors for GV bleeding. Close observation and prophylaxis for variceal bleeding might be warranted in high-risk patients.

Adaptive control for uncertain nonlinear systems based on multiple neural networks.

A new adaptive multiple neural network controller (AMNNC) with a supervisory controller for a class of uncertain nonlinear dynamic systems was developed in this paper. The AMNNC is a kind of adaptive feedback linearizing controller where nonlinearity terms are approximated with multiple neural networks. The weighted sum of the multiple neural networks was used to approximate system nonlinearity for the given task. Each neural network represents the system dynamics for each task. For a job where some tasks are repeated but information on the load is not defined and unknown or varying, the proposed controller is effective because of its capability to memorize control skill for each task with each neural network. For a new task, most similar existing control skills may be used as a starting point of adaptation. With the help of a supervisory controller, the resulting closed-loop system is globally stable in the sense that all signals involved are uniformly bounded. Simulation results on a cartpole system for the changing mass of the pole were illustrated to show the effectiveness of the proposed control scheme for the comparison with the conventional adaptive neural network controller (ANNC).

Synthesis and evaluation of 17alpha-20E-21-(4-substituted phenyl)-19-norpregna-1,3,5(10),20-tetraene-3,17beta-diols as probes for the estrogen receptor alpha hormone binding domain.

As part of our program to develop probes for the hormone binding domain of the estrogen receptor alpha (ERalpha), we prepared a series of 4-para-substituted phenylvinyl estradiol derivatives using a combination of solution and solid-phase Pd(0)-catalyzed methods. The compounds 5a-j were evaluated for their binding affinity using the ERalpha hormone binding domain (HDB) isolated from transfected BL21 cells. The results indicated that although the new compounds were somewhat lower in relative binding affinity (RBA at 25 degrees C is 1-60%) than estradiol (100%), most had higher affinity than the unsubstituted parent phenylvinyl estradiol (RBA = 9%). Because the substituents did not generate a structure-activity relationship directly based on physicochemical properties, the series was evaluated using molecular modeling and molecular dynamics to determine key interactions between the ligand, especially the para substituent, and the protein. The results suggest that the observed relative binding affinities are directly related to the calculated binding energies and that amino acids juxtaposed to the para position play a significant but not dominant role in binding. In conclusion, we have identified the 17alpha-E-(4-substituted phenyl)vinyl estradiols as a class of ligands that retain significant affinity for the ERalpha-HBD. In particular, 4-substitution tends to increase receptor affinity compared to the unsubstituted analogue, as exemplified by 5e (4-COCH(3)), which had the highest RBA value (60%) of the series. Palladium(0)-catalyzed coupling reactions on solid support or in solution using suitably substituted iodo arenes and 17alpha-E-tributylstannylvinyl estradiols offer a flexible approach to their preparation. Molecular modeling studies of the receptor suggest that there exists additional ligand accessible regions within the ERalpha-HBD to generate interactions that may enhance receptor affinity or modify efficacy in developing new therapeutic agents. Studies to undertake modification in the properties and/or position of the aryl substituents in subsequent series to further define that role are in progress.

Evaluation of 17alpha-E-(trifluoromethylphenyl)vinyl estradiols as novel estrogen receptor ligands.

As part of our program to develop novel ligands for the estrogen receptor, we synthesized the series of isomeric 17alpha-(trifluoromethyl)phenylvinyl estradiols using our solid-phase organic synthesis methodology. The compounds were evaluated for their relative binding affinity (RBA) using the ERalpha-LBD and in vivo potency using the immature rat uterotrophic growth assay. The ortho-isomer had the highest RBA values, 48-223, and the highest estrogenicity in vivo. The other isomers had significantly lower affinities and were weaker agonists in the uterotrophic assay. The results suggest that introduction of substituents at the 17alpha-position of estradiol is tolerated by the ER-LBD and permit agonist responses in the intact animal, however, the effect is sensitive to the position of groups on the phenyl ring. This study demonstrates that the 17alpha-position of estradiol is a reasonable site for modification but the position and physicochemical properties of such modifications may significantly affect the affinity and efficacy of the ligand.

[Prospective randomized trial of intravenous ciprofloxacin for prevention of bacterial infection in cirrhotic patients with esophageal variceal bleeding].

BACKGROUND/AIMS: In cirrhotic patients with esophageal variceal bleeding, bacterial infections are a frequent complication. Oral antibiotic prophylaxis decreases the incidence of bacterial infections. The administration of oral antibiotics, however, may be difficult in some cirrhotic patients with active bleeding. The purpose of this study was to assess the efficacy of prophylactic intravenous antibiotics for the prevention of bacterial infections in cirrhotic patients with esophageal variceal bleeding. METHODS: From December 1998 to September 2001, a total of 40 consecutive cirrhotic patients with Child-Pugh class B or C were enrolled after emergent endoscopic esophageal variceal ligation (EVL) was taken because of esophageal variceal bleeding. Enrolled patients were randomized into a treatment group and a control group. The treatment group (n=20) received the intravenous ciprofloxacin 200mg IV q 12 hours for 3 days while the control group(n=20) didn,t. RESULTS: Bacterial infection developed in nine patients (45%) of the control group and only two patients (10%) in the treatment group. The incidence of bacterial infections was significantly lower in the treatment group than the control group (p < 0.005). The hospital cost and length of hospital stay decreased in the treatment group compared with the control group (p < 0.001). There were no differences in the hospital course and mortality within 30 days between the two groups. CONCLUSIONS: In cirrhotic patients with variceal bleeding and with Child-Pugh class B or C, the use of intravenous ciprofloxacin for 3 days after EVL was not only effective in the prevention of bacterial infections but also cost-effective.

Stress-induced cardiomyopathy presenting as acute myocardial infarction.

Stress-induced cardiomyopathy is described as an acute cardiomyopathy that occurs under the influence of an excessive level of catecholamine related to intense emotional stress. A 64-year-old woman presented with symptoms of acute myocardial infarction after emotional upset, but her coronary angiographic findings were revealed to be normal. Diffuse T wave inversions were observed in her electrocardiograms with akinetic wall motions sparing the basal segments in her left ventriculography. After four months, her electrocardiogram and echocardiogram findings had completely returned to normal. The precise diagnosis of this acute cardiomyopathy must be emphasized because it can initially be misdiagnosed as acute coronary syndromes. However in complete contrast to acute myocardial infarction, it has a rapid and favorable recovery with hardly any sequelae after a few months.