Biomedical subjects

H B Pyo

Publications and source records attributed to H B Pyo.

5 recordsLinked to original sources

PubMed1999

Multistability analysis of phase locking patterns in an excitatory coupled neural system.

We quantitatively analyze the multistability of dynamic patterns of a bursting neural system with diffusive coupling. Through effective coupling analysis, we show that the system is not in-phase locking but exhibits various phase locking patterns, each of which corresponds to the stable fixed points of the effective coupling. The simulation proves the validity of the effective coupling method in analyzing the multistability of neural systems which presents complicated dynamic patterns such as bursting.

Computer Simulation↗

PubMed1999

Effects of time-delayed interactions on dynamic patterns in a coupled phase oscillator system.

We investigate the effects of time delayed interactions in the network of neural oscillators. We perform the stability analysis in the vicinity of a synchronized state at vanishing time delay and present a related phase diagram. In the simulations it is shown that time delay induces various phenomena such as clustering where the system is spontaneously split into two phase locked groups, synchronization, and multistability. Time delay effects should be considered both in the natural and artificial neural systems whose information processing is based on the spatiotemporal dynamic patterns.

Journal Article↗

PubMed1999

Body fat measurement in computed tomography image.

In this paper, we suggest an automatic fat region setting method in computed tomography to measure body fat. Quantitative measurement of body fat is important for the diagnosis and treatment of diseases related to obesity. The evaluation methods of obesity such as weight and height ratio, waiste and hip circumference ratio, and subcutaneous fat thickness by clipper, have a weak point that they do not measure body fat quantitatively. To overcome the weak point a body fat measurement method by computed tomography has been tried recently. The body fat measurement by computed tomography presents volume of body fat quantitatively at a specific region such as subcutaneous and abdominal fats. Computed tomography provides an image consisting of voxels with Hounsfield unit which is proportional to the density at the voxels. In general, the Hounsfield units of the body fat is known as it has the values from -150 to -50. However, the Hounsfield unit range of the fat is different for every person and every region of a person. In this paper, we show the difference of the body fat range in the Hounsfield units for 20 persons and various regions of a person, and we suggest an automatic setting method of the body fat region in the Hounsfield units due to the Gaussian function fitting of the histogram in the computed tomography image.

Adipose Tissue↗

PubMedDate not supplied

New cosmetic agents for skin whitening from Angelica dahurica.

To develop a new whitening agent for cosmetics from natural products, Angelica dahurica was selected for its inhibitory effect on melanogenesis in B16 melanoma cells. From the mechanism study, it was clarified that the ethanolic extracts of this plant showed the suppression of tyrosinase synthesis but no inhibition of tyrosinase activity. In order to find the active constituents from this plant, the ethanol extracts were chromatographed repeatedly with silica gel. Two coumarin compounds were isolated from A. dahurica. Their structures were identified by physicochemical and spectral data such as UV, IR, NMR, and MS. It was shown that the active substance was isoimperatorin (10-[(3-methyl-2-butenyl)oxy]-7H-furo[3,2-g][1] benzopyran-7-one) and imperatorin (9-[(3-methyl-2-butenyl)oxy]-7H-furo[3,2-g][1] benzopyran-7-one). They significantly inhibited tyrosinase synthesis in B16 melanoma cells. To elucidate the action mechanism of the active compounds of A. dahurica, we investigated the changes in the mRNA level of tyrosinase using the RT-PCR technique. As a result, the mRNA level of tyrosinase was markedly reduced by active compounds of A. dahurica. From these results, we suggest that these extracts might be useful as a new whitening agent in cosmetics, but the in vitro findings must be verified in in vivo skin-lightening studies.

Angelica↗

PubMedDate not supplied

Inhibitory effects of antioxidant constituents from Melothria heterophylla on matrix metalloproteinase-1 expression in UVA-irradiated human dermal fibroblasts.

Matrix metalloproteinases (MMPs) are known to play an important role in photoaging by mediating the degradation of extracellular matrix proteins. To develop a new anti-aging agent for cosmetics from natural products, Melothria heterophylla (Lour.) Cogn. was selected for its antioxidant activity and inhibitory effect on expression of MMP-1 in UVA-irradiated human skin fibroblasts. Two compounds (compounds 1 and 2 ) were isolated from an ethyl acetate soluble fraction of the ethanolic extracts; they were identified as 1,2,4,6-tetra-O-galloyl-beta-(D)-glucopyranose (1) and 3,4,5-trihydroxybenzoic acid (2). These compounds were found to scavenge radicals and reactive oxygen species (ROS) and were measured to have SC50 values of 3.9 microM and 13.3 microM against 1,1-diphenyl-2-picrylhydrazyl (DPPH) radicals and values of 4.3 microM and 4.0 microM against superoxide radicals in the xanthine/xanthine oxidase system, respectively. Compounds 1 and 2 showed a dose-dependent inhibitory effect on the expression and activity of MMP-1 in UVA-induced human skin fibroblasts, but no inhibition of MMP-1 mRNA expression. Therefore, we concluded that compounds 1 and 2 significantly inhibited MMP-1 expression at the protein level. Also, these compounds were determined to have a potent antioxidant activity. From these results, we suggest that these compounds might be useful as a new anti-aging agent for photodamaged skin, but the in vitro findings must be verified in in vivo studies.

Antioxidants↗