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K Chen

Publications and source records attributed to K Chen.

At least 37 records · Page 2Linked to original sources
PubMed2004

Termite feeding deterrent from Japanese larch wood.

Extraction of flavonoids from Japanese larch (Larix leptolepis) wood with water was carried out to prepare a termite feeding deterrent. A two-stage procedure for the extraction was adopted. The first extraction step was performed at ambient temperature (22 degrees C) and the second at elevated temperatures ranging 50-100 degrees C. The first step mainly gave a mixture of polysaccharides together with small amount of flavonoids. At the second step, the yield of extract and its chemical composition were greatly affected by the temperature. The yield of solubilised carbohydrates steadily increased with a rise in the temperature, while the overall yield of flavonoids reached its optimum at 70 degrees C. An additional increase in the temperature resulted in a decrease in the yield. Model experiments using dihydroflavonols confirmed the occurrence of oxidative dehydrogenation and/or intramolecular rearrangement during the hydrothermal treatment at higher temperatures. The crude water extracts showed strong feeding deterrent activities against the subterranean termite, Coptotermes formosanus, in a choice paper disc assay. The extracts containing flavonoids in large quantities exhibited potent termite feeding deterrent activities.

Animals↗
PubMed2004

Persistence of abnormal neural responses to a meal in postobese individuals.

OBJECTIVE: To determine whether abnormal obese-like neural responses to a meal persist in postobese individuals, who achieved and maintained a normal body weight despite a past history of severe obesity. DESIGN AND SUBJECTS: Cross-sectional study of the brain's response to tasting and consuming a satiating meal in 11 postobese (age: 40+/-6 y, body mass index (BMI): 23.6+/-1.9 kg/m(2)), 23 obese (age: 29+/-6 y, BMI: 39.6+/-3.8 kg/m(2)) and 21 lean (age: 33+/-9 y, BMI: 22.8+/-2.1 kg/m(2)) subjects. MEASUREMENTS: Regional cerebral blood flow (rCBF, a marker of neural activity) at baseline (after a 36-h fast), after tasting and after consuming a satiating liquid meal was assessed using positron emission tomography and state-dependent changes (taste-baseline; satiation-baseline), and compared across groups. Subjective ratings of hunger and fullness were measured by a visual analogue scale and body fatness by dual-energy X-ray absorptiometry. RESULTS: In response to tasting the liquid meal, changes in rCBF were different in the obese as compared to the lean individuals (P<0.05, corrected for multiple comparisons) in the middle insula (peak voxel, x=-41, y=1, z=8; Montreal Neurological Institute coordinates) and posterior cingulate cortex (peak voxel, x=17, y=-47, z=40). The middle insular cortex exhibited a similar increase of neural activity in the obese and postobese subjects, whereas in the lean subjects the regional activity did not change. In the posterior cingulate cortex, the changes in rCBF in the postobese subjects were not different from those in the other groups. In response to a satiating amount of the same liquid meal, changes in rCBF were different in the obese as compared to the lean individuals (P<0.05, corrected for multiple comparisons) in the posterior hippocampus (peak voxel, x=21, y=-45, x=4), posterior cingulate cortex (peak voxel, x=17, y=-47, z=40), and amygdala (peak voxel, x=27, y=1, z=-24). The posterior hippocampus exhibited a similar decrease of neural activity in the obese and postobese subjects, whereas in the lean subjects the regional activity increased. In the posterior cingulate cortex and amygdala, the changes in rCBF were not different between the postobese and lean individuals. None of the changes in neural activity were correlated with the age of the individuals, the subjective ratings of hunger and fullness, or the meal induced-changes in plasma glucose, insulin, or serum free fatty acids. CONCLUSION: Persistence of abnormal neural responses to a meal in the postobese individuals, a group at high risk for relapse, indicates that a predisposition to obesity may involve areas of the brain that control complex aspects of eating behavior including anticipation and reward, chemosensory perception, and autonomic control of digestion (insular cortex), as well as enteroception and learning/memory (hippocampus).

Adult↗
PubMed2004

Iodine nutritional status of adults during a period of salt iodization.

BACKGROUND: To measure the iodine nutritional status of island adults in Zhoushan, China. METHODS: A comparison study was carried out in eight villages. These were selected from iodized salt and non-iodized salt districts of Zhoushan island by random sampling. The Mann-Whitney test was used to compare the urinary iodine concentration and dietary iodine intake between the two districts. RESULTS: The median of urinary iodine concentration in the non-iodized salt group was 90 micrograms/l, which was lower than 194 micrograms/l in the iodized salt group (u = 14.673; p < 0.000), whereas the median of daily dietary iodine intake in the two groups was 128 and 147 micrograms, respectively (u = 1.847; p = 0.065). There was no significant correlation between dietary iodine intake and urinary iodine concentration (p = 0.095). CONCLUSIONS: Salt iodization is necessary. Special characteristics of the island diet should also be considered.

Adult↗
PubMed2004

MAO-B knockout mice exhibit deficient habituation of locomotor activity but normal nicotine intake.

Low levels of monoamine oxidase-B (MAO-B) activity, such as those observed in smokers, are also associated with behavioral traits such as a heightened responsiveness to novelty. However, the exact mechanism by which low MAO-B activity influences smoking and heightened responsiveness to novelty is still poorly understood. We used MAO-B knockout (KO) mice to test the hypothesis that MAO-B concomitantly affects locomotor responses in a novel inescapable open field and nicotine intake. Male wild-type (WT) and MAO-B KO mice were placed in an inescapable open field and their horizontal locomotor activity was measured for 30 min per day for 5 days. MAO-B KO mice exhibited impaired within-session habituation of locomotor activity, as compared to WT mice. Separate groups of male WT and MAO-B KO mice were individually housed in their home cages with two water bottles. One of the bottles contained tap water and the other contained nicotine (0, 3.125, 6.25, 12.5, 25, 50 or 100 micro g/ml). The total amount of water and nicotine solution consumed was measured every three days for 16 days. MAO-B KO mice and WT mice consumed equal amounts of nicotine and exhibited comparable concentration-dependent nicotine preference and aversion over a period of 16 days. The data suggest that the absence of MAO-B impairs the ability of mice to habituate in the inescapable environment, but does not alter their nicotine intake.

Administration, Oral↗
PubMed2004

Cloning and characterization of the mouse Arht2 gene which encodes a putative atypical GTPase.

ARHT is a new subgroup of the Rho family identified recently, which consists of two Rho-like genes, Arht1 and Arht2. ARHT may be involved in mitochondrial homeostasis and apoptosis. Constitutively active mutants of ARHT1 induced an aggregation of the mitochondrial network and resulted in an increased apoptotic rate of the cells. Here we report the molecular cloning and characterization of a novel mouse cDNA encoding a putative atypical GTPase protein, Arht2. Mouse Arht2 consists of 19 exons and has been mapped to mouse chromosome 17A3.3. Both human and mouse Arht2 genes are ubiquitously expressed in adult tissues. The results of RT-PCR experiments indicated that the Arht2 gene is expressed in all stages of mouse testis and reached the adult level of transcription at postnatal day 30. In situ hybridization revealed strong hybridization signals of Arht2 in residual bodies. In the mouse testis, Arht2 may be involved in the differentiation of testis and spermiogenesis. The molecular characterization of the mouse Arht2 gene may provide a clue for functional studies of the human ARHT genes.

Amino Acid Sequence↗
PubMed2004

Regulation of MAO-A and MAO-B gene expression.

MAO A and B genes are made of 15 exons with identical exon-intron organization. They are located on X-chromosome organized in opposite direction, tail to tail with 24 kb apart. Both promoters are GC-rich and regulated by transcription factor Sp1. However, they have distinctly different features. MAO B gene, but not MAO A gene, has TATA box. MAO B promoter contains two clusters of overlapping Sp1 sites, the CACCC repressor element. Transcription factors Sp1 and Sp4 can activate MAO B promoter activity through the proximal cluster of Sp1 sites and its activation can be repressed by the over-expression of Sp3 and a related family member, BTEB2. Decreased methylation and transcription repressor Sp3 upregulate human MAO B, but not MAO A, gene expression during Caco-2 differentiation. MAO B, but not MAO A gene, could be activated by PMA (phorbol 12-myristate 13-acetate) by protein kinase C, MAPkinase signal transduction pathway involves cJun and Egr-1. The differences in MAO A and B gene regulation may explain the different tissue-specific expression and functions of these two important isoenzymes.

Animals↗
PubMed2003

All-optical neural-net-like image processing with photosensitive nonlinear nematic film.

Received June 30, 2003 We demonstrate that some neural-net image-processing operations can be realized in an all-optical manner by use of the natural diffraction property of light in conjunction with the photosensitivity and optical nonlinearities of a transparent thin film. An example of image edge enhancement is illustrated with photosensitive supranonlinear nematic liquid-crystal films.

Journal Article↗
PubMed2003

Nitric oxide alleviates oxidative damage in the green alga Chlorella pyrenoidosa caused by UV-B radiation.

The effect of ultraviolet-B radiation (UV-B; 280-320 nm) on induction of nitric oxide was estimated in the suspensions of green alga Chlorella pyrenoidosa with or without the NO scavenger N-acetyl-L-cysteine, and reductants such as 1,4-dithiothreitol, glutathione (reduced form), and ascorbic acid. Exogenously added sodium nitroprusside (NO donor), glutathione, 1,4-dithiothreitol, and ascorbic acid were able to prevent chlorophyll loss mediated by UV-B. Addition of NO to algal suspensions irradiated by UV-B increased the activity of catalase and superoxide dismutase but lowered the activity of phenylalanine ammonia-lyase. UV-B thus appears to be a strong inducer of NO production, exogenously added NO and reductants protecting the green alga against UV-B-induced oxidative damage.

Acetylcysteine↗
PubMed2003

Malonyl-CoA and AMP-activated protein kinase (AMPK): possible links between insulin resistance in muscle and early endothelial cell damage in diabetes.

Based on available evidence, we would propose the following. (i) Excesses of glucose and free fatty acids cause insulin resistance in skeletal muscle and damage to the endothelial cell by a similar mechanism. (ii) Key pathogenetic events in this mechanism very likely include increased fatty acid esterification, protein kinase C activation, an increase in oxidative stress (demonstrated to date in endothelium) and alterations in the inhibitor kappa B kinase/nuclear factor kappa B system. (iii) Activation of AMP-activated protein kinase (AMPK) inhibits all of these events and enhances insulin signalling in the endothelial cell. It also enhances insulin action in muscle; however, the mechanism by which it does so has not been well studied. (iv) The reported beneficial effects of exercise and metformin on cardiovascular disease and insulin resistance in humans could be related to the fact that they activate AMPK. (v) The comparative roles of AMPK in regulating metabolism, signalling and gene expression in muscle and endothelial cells warrant further study.

AMP-Activated Protein Kinases↗
PubMed2003

Epidemiology and aetiology of basal cell carcinoma.

Basal cell carcinoma is the most common malignancy among caucasians worldwide. Accurate epidemiological data can be difficult to obtain, but does suggest that the overall incidence is increasing. Risk factors include skin type, prior skin cancers and immunosuppression. Research in free radical-mediated cellular injury and innate defence mechanisms, and ultraviolet radiation-induced genetic mutations have improved our understanding of the development of this disorder.

Basal Cell Carcinoma↗
PubMed2003

Summary of actinic keratosis studies with imiquimod 5% cream.

Imiquimod is being investigated as a therapeutic option for the management of actinic keratosis. Three recent clinical trials have demonstrated a reasonable efficacy rate and high safety profile. 'Cycle' therapy may improve the safety profile while maintaining efficacy. 'Field' treatment with imiquimod may uncover and treat 'subclinical' actinic keratoses, which in turn may potentially result in fewer recurrences. Longer follow-up studies are required to investigate this possibility.

Adjuvants, Immunologic↗
PubMed2003

Treatment of Bowen's disease using a cycle regimen of imiquimod 5% cream.

Bowen's disease (BD; intraepithelial squamous cell carcinoma) is a challenging condition to treat because lesions, which can be multiple, are often located at sites that heal poorly, such as the shin. The disease is usually persistent and progressive and appears as an enlarging, demarcated erythematous plaque. Two elderly female patients with Bowen's disease of the lower leg are presented. Imiquimod 5% cream was applied in a cycle of three times weekly for 3 weeks followed by a 4-week rest period. The treatment was successful after a second cycle of therapy, with both cases clinically clear at 2- and 3-month follow-up visits.

Adjuvants, Immunologic↗
PubMed2003

A randomised, double masked, multicentre clinical trial comparing bimatoprost and timolol for the treatment of glaucoma and ocular hypertension.

AIM: To evaluate the safety and efficacy of bimatoprost 0.03% once daily or twice daily compared with timolol 0.5% twice daily in patients with glaucoma or ocular hypertension. METHODS: Multicentre, double masked, randomised, parallel group, 3 month trial comparing bimatoprost once daily (n=240), bimatoprost twice daily (n=240), and timolol twice daily (n=122). The primary efficacy end point was diurnal intraocular pressure (IOP) (8 am, 10 am, 4 pm). Safety measures included adverse events, ocular parameters, and systemic variables. RESULTS: Bimatoprost once daily provided significantly lower mean IOP than timolol twice daily at all times and follow up visits (p<0.001). At month 3, mean IOP reductions from baseline at 10 am (peak timolol effect) were bimatoprost once daily, 8.0 mm Hg (32.4%); bimatoprost twice daily, 6.3 mm Hg (25.2%); timolol, 5.5 mm Hg (22.7%). Bimatoprost twice daily was also more effective than timolol, but was not as effective as bimatoprost once daily. A higher percentage of patients achieved low target pressures with bimatoprost once daily than with timolol. The most frequent side effects with bimatoprost were eyelash growth and mild conjunctival hyperaemia. Systemic safety parameters were not affected by bimatoprost. CONCLUSIONS: Bimatoprost 0.03% once daily demonstrated superior efficacy compared with timolol 0.5% twice daily in patients with elevated IOP. Bimatoprost once daily was more effective than twice daily dosing.

Adult↗
PubMed2002

Effects of image resolution on autoradiographic measurements of posterior cingulate activity in PDAPP mice: implications for functional brain imaging studies of transgenic mouse models of Alzheimer's Disease.

Fluorodeoxyglucosepositron emission tomography (PET) studies find that persons with Alzheimer's disease have preferential reductions in posterior cingulate activity. Using fluorodeoxyglucose autoradiography, we found that transgenic mice overexpressing a mutant form of the human amyloid precursor protein have preferentially reduced activity in the same region, providing a potential brain imaging indicator of Alzheimer's disease in these animals. In this study, we considered the feasibility of using in vivo imaging techniques, such as PET, to detect this reduction despite their limitations in spatial resolution. Autoradiographic measurements of posterior cingulate activity were remeasured in the previously studied PDAPP transgenic and littermate control mice after the images were filtered to lower spatial resolutions. We continued to detect significantly lower cingulate activity in the transgenic mice when the images were blurred to 0.50 mm, failed to detect significantly abnormal activity when the images were blurred to 0.75 mm, and, indeed, found significantly higher activity when the images were blurred to 1.0 mm. Reversal in direction of the abnormality appears attributable to a previously observed truncation in the corpus callosum in PDAPP mice. With the possible exception of future in vivo imaging techniques that have a spatial resolution greater than or equal to 0.50 mm and high sensitivity, noninvasive functional brain imaging techniques like PET may not be suitable for detecting declines in regional activity in PDAPP mice. It remains possible that these imaging techniques will prove useful in transgenic mouse lines that do not exhibit the same morphological abnormalities in neighboring white matter regions.

Alzheimer Disease↗
PubMed2002

Increased baroreceptor response in mice deficient in monoamine oxidase A and B.

The recent development of mice doubly deficient for monoamine oxidase A and B (MAO-A/B, respectively) has raised questions about the impact of these mutations on cardiovascular function, in so far as these animals demonstrate increased tissue levels of the vasoactive amines serotonin, norepinephrine, dopamine, and phenylethylamine. We recorded femoral arterial pressures and electrocardiograms in adult MAO-A/B-deficient mice during halothane-nitrous oxide anesthesia as well as 30 min postoperatively. During both anesthesia and recovery, systolic, diastolic, and mean arterial pressures were 10-15 mmHg lower in MAO-A/B-deficient mice compared with normal controls (P < 0.01). Mutants also showed a greater baroreceptor-mediated reduction in heart rate in response to hypertension after intravenous pulses of phenylephrine or angiotensin II. Tachycardia elicited in response to hypotension after nitroprusside was greater in mutants than in controls. Heart rate responsiveness to changes in arterial pressure was abolished after administration of glycopyrrolate, with no differences in this phenomenon noted between genotypes. These data suggest that prevention of hypertension may occur in chronic states of catecholaminergic/indoleaminergic excess by increased gain of the baroreflex.

Adrenergic beta-Antagonists↗
PubMed2002

Heart rate dynamics in monoamine oxidase-A- and -B-deficient mice.

Heart rate (HR) dynamics were investigated in mice deficient in monoamine oxidase A and B, whose phenotype includes elevated tissue levels of norepinephrine, serotonin, dopamine, and phenylethylamine. In their home cages, spectral analysis of R-R intervals revealed more pronounced fluctuations at all frequencies in the mutants compared with wild-type controls, with a particular enhancement at 1-4 Hz. No significant genotypic differences in HR variability (HRV) or entropies calculated from Poincaré plots of the R-R intervals were noted. During exposure to the stress of a novel environment, HR increased and HRV decreased in both genotypes. However, mutants, unlike controls, demonstrated a rapid return to baseline HR during the 10-min exposure. Such modulation may result from an enhanced vagal tone, as suggested by the observation that mutants responded to cholinergic blockade with a decrease in HRV and a prolonged tachycardia greater than controls. Monoamine oxidase-deficient mice may represent a useful experimental model for studying compensatory mechanisms responsible for changes in HR dynamics in chronic states of high sympathetic tone.

Animals↗
PubMed2002

Changes of biophysical behavior of k562 cells for p16 gene transfer.

p16 gene was transferred into human erythroleukemia cell line K562 that had been subjected to p16 deletion. The changes of biophysical behavior of K562 cells after gene transfer were studied with the micropipette technique. The micropipette data were analyzed with a standard solid viscoelastic model. In comparison to untransfected control K562 cells and the cells transfected with an empty vector, the p16-transfected K562 cells showed an increase in the elastic element K(1), which is inversely proportional to the maximum deformation over a long period of time, whereas the viscous element mu and the other elastic element K(2) showed no significant difference. The results indicate that K562 cells became more rigid after p16 transfer. The p16-transfected K562 cells also had a higher surface charge density. This study contributes to our knowledge about the suppression effect of p16 gene on tumor cell migration and about its use in gene therapy.

Biophysical Phenomena↗