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Biomedical subjects

T Chen

Publications and source records attributed to T Chen.

At least 253 records · Page 14Linked to original sources
PubMed1996

Vagus nerve stimulation activates central nervous system structures in epileptic patients during PET H2(15)O blood flow imaging.

OBJECTIVE: To determine the central areas of activation by vagal nerve stimulation (VNS) in epilepsy. VNS is a promising neurosurgical method for treating patients with partial and secondary generalized epilepsy. The anti-epileptic mechanism of action from VNS is not well understood. METHODS: We performed H2(15)O PET blood flow functional imaging on three patients with epilepsy in a vagal nerve stimulation study (E04 Protocol with Cyberonics). The three patients included two that had previous epilepsy surgery but continued to have frequent seizures. Seizure onset was frontal in two patients and bitemporal in the third patient. Twelve PET scans per subject were acquired every 10 minutes with a Siemens 953/A scanner. In 6 stimulus scans, VNS was activated for 60 seconds (2 mA, 30 Hz) commensurate with isotope injection. In 6 control scans no VNS was administered. No clinical seizures were present during any scan. Three way ANOVA with linear contrasts subject, task, repetition) of coregistered images identified significant treatment effects. RESULTS: The difference between PET with VNS and without revealed that left VNS activated right thalamus (P < 0.0006), right posterior temporal cortex (P < 0.0003), left putamen (P < 0.0002), and left inferior cerebellum (P < 0.0009). CONCLUSIONS: VNS causes activation of several central areas including contralateral thalamus. Localization to the thalamus suggests a possible mechanism to explain the therapeutic benefit, consistent with the role of the thalamus as a generator and modulator of cerebral activity.

Adult↗
PubMed1996

A comparison of unipolar and bipolar electrodes during cardiac mapping studies.

Controversy exists as to whether the unipolar or bipolar electrode configuration is superior in detecting local activations during cardiac mapping studies. However, the strengths and weaknesses of each mode suggest that they may provide complementary information. To examine the relative merits of unipolar and bipolar electrode configurations, recordings by each were simultaneously acquired during episodes of ventricular tachycardia in eight consecutive patients undergoing map guided arrhythmia surgery. Unipolar electrograms were classified as either unambiguous or ambiguous according to whether or not they were polyphasic in nature. The activation times from the unambiguous electrograms were compared with activation times from the corresponding bipolar signals where local activation was measured both at the signal's peak amplitude (BI-PK), and at the point at which the waveform's first major, rapid transient crossed baseline (BI-TRN). Occurrences of discrete diastolic activations were also quantified from the unipolar and bipolar tracings. From a total of 415 unipolar electrograms, 301 unambiguous signals were identified as suitable for comparison with the bipolar signals. Both BI-PK and BI-TRN criteria for the determination of local activation were highly correlated with and not significantly different from the local activation from the unipolar electrogram. From 85 ambiguous unipolar electrograms, it was possible to determine local activation from the corresponding bipolar signal in 33% of the occurrences. From the eight patients, 64 diastolic potentials were recorded of which 42 were seen only in bipolar mode, 7 in only unipolar mode, and 15 were evident in both tracings. The prevalence of diastolic potentials was significantly greater in recordings made using bipolar mode. The results demonstrate that complementary information regarding local activations and diastolic potentials can be derived from unipolar and bipolar recordings and suggest that both electrode configurations should be used in multichannel cardiac mapping systems.

Electrocardiography↗
PubMed1996

Photochemical and photophysical studies of 3-amino-6-iodoacridine and the inactivation of lambda phage.

The photochemistry and photophysics of 3-amino-6-iodoacridine (Acr-I) was studied. Photolysis (350 nm) of Acr-I (free base) generates products consistent with a free radical intermediate in methanol, benzene and carbon tetrachloride. The Acr-I hydrochloride is shown to bind to calf thymus DNA and to the self-complementary dinucleotide cytidylyl-(3'-5')-guanosine (CpG) miniduplex in a manner similar to that of proflavine (Acr-NH2), a known DNA intercalator. The Acr-I is shown to more efficiently nick supercoiled plasmid DNA pBR322 upon 350 nm or 420 nm photolysis than Acr-NH2. The efficiency of Acr-I-sensitized DNA nicking is not oxygen dependent. Photolysis of the Acr-I/(CpG)2 complex leads to cleavage of the dinucleotide and to cytidine base release by selective damage to a specific ribose moiety. Dinucleotide cleavage occurs equally well in the presence or absence of oxygen, thereby eliminating a singlet oxygen- or peroxyl radical-mediated process. Photolysis of Acr-I in the presence of a mononucleotide (GMP) or a non-self-complementary dinucleotide (uridylyl-[3'-5']-cytidine-UpC) does not lead to fragmentation and base release. Similarly, photolysis of the Acr-NH2/(CpG)2 complex does not lead to fragmentation and base release. The data indicate that photolysis of an iodinated intercalator bound to CpG or plasmid DNA generates an intercalated aryl radical and that the reactive intermediate initiates a sequence of reactions that efficiently nick nucleic acids. The inactivation of lambda phage sensitized by Acr-I with UV (350 nm) light is oxygen independent but with visible (420 nm) light is strongly oxygen dependent. The Acr-I fluoresces more intensely when excited at 446 than at 376 nm. Thus, UV photolysis may lead to C-I bond homolysis and free radical formation, a process that is not energetically feasible with visible light. The results demonstrate the difficulty of extrapolating model studies involving simple molecules and DNA to understanding the mechanism of viral inactivation with a particular sensitizer.

Aminoacridines↗
PubMed1996

Modulation of microsomal cytochrome P450 by Scutellariae Radix and Gentianae scabrae Radix in rat liver.

The present study has determined the effects of Scutellariae Radix (Huangqin) and Gentianae scabrae Radix (Longdan) on liver microsomal cytochrome P450 (P450)-dependent mono-oxygenases using rats pretreated with crude extracts of medicinal herbs. Scutellariae Radix resulted in a 53% decrease of pentoxyresorufin O-dealkylase activity in liver microsomes. In contrast, Gentianae scabrae Radix caused a 50% increase of benzo(a)pyrene hydroxylase activity. Immunoblotting analysis of liver microsomes revealed that Scutellariae Radix induced and suppressed the levels of P450 1A and 2B proteins, respectively. Scutellariae and Gentianae scabrae Radixes had no effects on microsomal aniline hydroxylase activity and P450 2E1 protein.

Animals↗
PubMed1996

The effect of season and latitude on in vitro vitamin D formation by sunlight in South Africa.

AIMS: To assess the effect of season and latitude on the in vitro formation of previtamin D3 and vitamin D3 from 7-dehydrocholesterol (7-DHC) by sunlight in two cities in South Africa, Cape Town and Johannesburg. METHODS: An in vitro study utilising vials containing 7-DHC, which were exposed to sunlight for a period of 1 hour between 8:00 and 17:00 on 1 day a month for a year. Previtamin D3 and vitamin D3 were separated from 7-DHC by high-performance liquid chromatography, and the amounts formed were calculated with the use of external standards. RESULTS: A marked seasonal variation in vitamin D3 production was noted in Cape Town, with very little being formed during the winter months of April through September. In Johannesburg, in vitro formation changed little throughout the year, and was similar to that found in Cape Town during the summer. During sunlit hours, vitamin D3 production was maximal at midday and small quantities were still being formed between 8:00 and 9:00, and between 16:00 and 17:00 during the summer. During winter in Cape Town, peak formation at midday was less than one-third of that in Johannesburg, and negligible amounts were formed before 10:00 and after 15:00. CONCLUSIONS: The previously documented seasonal variation in serum 25-hydroxyvitamin D recorded in patients in Johannesburg is probably a consequence of the increased clothing worn and the decreased time spent out of doors during winter, rather than decreased ultraviolet radiation reaching the earth. The limited in vitro formation of vitamin D3 during winter in Cape Town may have clinical implications insofar as the management of metabolic bone diseases like rickets and osteoporosis is concerned. Breast-fed infants resident in the area are likely to suffer from vitamin D deficiency rickets unless vitamin D supplements are provided, or the mothers are encouraged to take their children out of doors.

Breast Feeding↗
PubMed1996

[The hepatitis A virus isolated and adapted in human diploid fibroblast cells (KMB17)].

Three hepatitis A virus (HAV) strains (L8, H32 and H52) were isolated from stool specimens of hepatitis A patients during an epidemic in 1988 in Shanghai and were adapted to grow in human diploid fibroblast cell strain (KMB17). The strains were serially carried through 10 passages in KMB17. The infectious titrations of these virus strains cultured for 28 days at the 10th passage were high up to 7.0-7.75 log TCID50/ml. The maximum virus yields occured in the 28th day after infection. Immune electronic microscopic studies revealed that the viral particles were 27-30 nm in diameter. The strains were neutralized by specific anti-HAV serum. Special fluorescent stained particles were observed clearly in the infected cellular plasma by direct IF. The above data suggest that the three strains are HAV and may be useful for further study.

Cell Line↗
PubMed1996

[Analysis of 822 infants with limb reduction defect in China].

This work is aimed at the basic condition of infants with limb reduction defect (LRD) in China. 822 cases of LRD occurring among 1,243,284 live and stillbirths of 28 or more gestation weeks in China from Oct. 1986 to Sept. 1987 were analysed. The overall prevalence of LRD was 6.6 per 10,000 ranging from 14.4 per 10,000 to 3.6 per 10,000. No sex difference was observed. The prevalence of LRD in infants with low birthweight was significantly higher than that in infants with normal birthweight (P < 0.001). Also the prevalence of LRD in rural area was higher than that in urban area (P < 0.001). Four-limb involvement was most common. The cases with only upper limb involvement (278/451, 61.6%) were significantly more prevalent than those with only lower limb involvement (173/451, 38.4%, P < 0.001), but no difference was found between the left LRD and right LRD (P > 0.05), nor was a significant difference noted between single LRD and multiple LRD. 75.8% of the infants with LRD had defects in other systems.

Abnormalities, Multiple↗
PubMed1996

[Cataract surgery in very long axial myopia].

OBJECTIVE: The incidence, refractive characters, operative results and the situations of intraocular lens (IOL) implantation in a series of eyes with very long axial length (> or = 27.00 mm) were analyzed. METHODS: According to the measurements of preoperative axial length and the degree of implanted IOL, the eyes with lengths of 27.00 mm or more selected from 1,000 eyes of consecutive senile cataract surgery were included in this group. The eyes requiring + 3.00D or more IOL were implanted with IOL. Simple extracapsular cataract extraction was performed on eyes requiring <+3.00D or negative lens. The postoperative follow-up was 20.0 +/- 8.5 months. RESULTS: There were 81 eyes in this group with a range of axial length of 27.00-34.71 mm and an average corneal curvature of 43.91 +/- 1.81D. The range of IOL power for these eyes was +11.30-11.57D (mean, +2.10 +/- 5.41D). The average axial length of 39 eyes with IOL implantation was 28.04 +/- 0.68 mm and their postoperative corrected visual acuities (PCVA) in 82.1% of eyes were 10/20 or more. The average length of 42 eyes without IOL implantation was 31.68 +/- 1.47 mm and the PCVAs in 42.9% of the eyes were 10/20 or more. CONCLUSIONS: The myopia with very long axial length is quite common in China. Its operative complications are not frequently seen. The cause of its poor PCVA is due to its pathologic changes in the fundus and the PCVA becomes worse as its axial length is increasing. An IOL with negative power is sometimes necessary for a myopic eye with very long axis.

Aged↗
PubMed1996

[An analysis of posterior capsular rupture in cataract surgery].

OBJECTIVE: To analyze the incidence, features and related factors of posterior capsular rupture (PCR) in extracapsular cataract extraction, the main intraoperative complication impairing the procedure of intraocular lens (IOL) implantation. METHODS: The PCR including zonular break and vitreous loss was recorded according to the stage of operative procedure in 757 eyes with senile cataract (the average age was 67.3 +/- 8.3 years). RESULTS: There were 51 eyes (6.7%) with PCR and 42 eyes (5.5%) of them accompanied with vitreous loss. The PCR in 17 eyes (33.3%) occurred during manual expression of the nucleus, 25 eyes (49.0%) in the course of aspiration of the cortex, and 9 eyes in the subsequent manipulations. Except the unexpected damage to the posterior capsule, the main factors were: smaller incision for the nucleus expression, lens dislocation during capsulotomy, small pupil in the course of cortex aspiration, high pressure from the posterior chamber and traction on capsular bag when removing anterior part of the cortex. CONCLUSION: Intraoperatively, the prevention of PCR and improvement of management ability are very important for the IOL I-stage implantation.

Aged↗
PubMed1996

[Quantitative analysis of organochlorine pesticide residues in Chinese drugs].

This paper reports the GC determination of 20 organochlorine pesticides in Chinese drugs Flos Ionicerae and Moluodan etc by the present method of Japan for determinaing pesticide residues. The results suggest that except Folium Isatidis, Radix Codonopsis and Sanqi Pian all accord with the for provisions pesticide residues in Japanese foodstuffs.

Chromatography, Gas↗
PubMed1995

Comparative allelotype of in situ and invasive human breast cancer: high frequency of microsatellite instability in lobular breast carcinomas.

To better understand the timing for presentation of allelic losses in human breast carcinogenesis, we compared the allelotypic profile of 23 in situ ductal carcinomas with that of 29 invasive ductal carcinomas. We also compared the allelotype of the invasive ductal breast carcinomas with that of 23 invasive lobular breast carcinomas. These studies were performed by means of microsatellite length polymorphisms from microdissected paraffin sections. We observed that involvement of chromosome arms 1p, 3p, 3q, 6p, 16p, 18p, 18q, 22q, and possibly 6q and 11p appear to be late events in breast cancer progression because allelic losses or imbalances affecting these areas were observed with very low frequency at the in situ stage. On the other hand, allelic imbalances and losses affecting chromosome arms 7p, 16q, 17p, and 17q appear to be early abnormalities because they were observed in approximately 25-30% of ductal carcinoma in situ lesions. Allelic losses and imbalances affecting the 8p arm were frequently observed in invasive lobular breast carcinomas. It was also interesting that microsatellite instability, also known as replication error (RER) phenotype, was found to occur at a high frequency in invasive lobular breast carcinomas because 9 of 23 (39%) were RER+, compared with 7 of 52 (13.5%) RER+ of breast cancers with ductal differentiation (P = 0.012, chi 2 test). Our findings provide for the first time molecular evidence suggesting that invasive lobular breast carcinomas may arise by a different mechanism of carcinogenesis than ductal carcinomas.

Adult↗
PubMed1995

Adherence of pilus- Opa+ gonococci to epithelial cells in vitro involves heparan sulfate.

Neisseria gonorrhoeae attaches to host epithelial cells via pili and opacity-associated (Opa) outer membrane proteins. Pilus- gonococci (Gc) of strain MS11 adhere to both human and nonhuman cells, but only when particular Opa proteins are expressed; OpaA+ variants adhere best, OpaC+ variants are next best, and the seven other Opa+ variants adhere poorly or not at all. The adherence of OpaA+ Gc to Chinese hamster ovary (CHO) cells is inhibited by heparin or heparan sulfate (HS), but not by chondroitin sulfate. OpaA+ Gc do not adhere to CHO cells devoid of HS proteoglycans; low concentrations of heparin restore OpaA+ Gc adherence to these HS-deficient CHO cells and high concentrations inhibit it. 3H-heparin binding to whole Gc parallels their adherence abilities (OpaA+ > OpaC+ > OpaH+ >> Opas B, D, E, F, G, I = Opa- = 0). Opa proteins separated by SDS-PAGE also bind 3H-heparin. These data suggest that adherence of pilus-, Opa+ Gc involves HS-proteoglycan of eukaryotic cells.

Animals↗
PubMed1995

Systematic screening for RNA with skipped exons--splicing mutations of the ferrochelatase gene.

A systematic method was designed to screen a large population of patients with erythropoietic protoporphyria (EPP) for aberrant ferrochelatase RNA with skipped exons. The method utilizes the new junction sequence created by exon skipping as the probe to detect such RNA species. In 7 of 17 EPP families, an aberrant ferrochelatase RNA with one exon missing was observed. Two previously unreported splicing mutations were also identified in 2 EPP families. One was a G >> T transversion at the +1 position of the acceptor site of intron 8, causing exon 9 to be skipped during RNA splicing. Both the patient and her father were found to be heterozygous for this mutation. In another family, an A >> G transition at the +3 position of the donor site of intron 10 was identified, associated with exon 10 skipping during RNA splicing. Both the patient and her father were heterozygous for this mutation.

Adult↗
PubMed1995

Ecdysteroid regulation and DNA binding properties of Drosophila nuclear hormone receptor superfamily members.

Pulses of the steroid hormone 20-hydroxyecdysone (20E) trigger the larval-to-adult metamorphosis of Drosophila by reprogramming gene expression throughout the organism. 20E directly induces a small set of early regulatory genes that repress their own expression and induce a large set of late secondary-response genes. We show here that two members of the Drosophila nuclear hormone receptor superfamily, DHR3 and DHR39, are rapidly induced by 20E, in parallel with the early regulatory genes. Both genes also require protein synthesis at high 20E concentrations for their maximal induction by the hormone. Developmental Northern blot analysis reveals that DHR39 is induced in mid third instar larvae and expressed throughout most of third instar larval and prepupal development, while DHR3 is briefly expressed in late third instar larvae and early prepupae. The 20E-induction and temporal patterns of DHR3 and DHR39 transcription strongly suggest that these genes function together with the early regulatory genes to coordinate the complex gene networks that direct the early stages of Drosophila metamorphosis. In an initial effort to understand how these two orphan receptors might function during development, we examined their DNA binding properties and compared them with the known Drosophila nuclear receptor superfamily members that are involved in the ecdysteroid response: EcR, Usp, E75A, E78A, and beta FTZ-F1. Upon testing all pairwise combinations of these seven proteins on a panel of seven oligonucleotides, only EcR and Usp bound DNA as a heterodimer, indicating that this interaction is highly specific. With the exception of E78A, which did not bind any sequence tested, each of the remaining proteins is able to bind to a single consensus AGGTCA half-site; however, each displayed different specificities depending on the flanking nucleotide sequence. These observations suggest that the 20E-regulated orphan receptors function as monomers to control the expression of their target genes.

Animals↗
PubMed1995

Induction of peroxisome proliferation and increase of catalase activity in yeast, Candida albicans, by cadmium.

The effects of cadmium on the growth rate, catalase activity, and peroxisome proliferation in yeast, Candida albicans, were evaluated. The yeast growth was markedly inhibited by 1 mM cadmium at the initial hours. The toxic effect of cadmium on the cell growth persisted. The catalase activity of the cells treated with 1 mM Cd2+ first decreased, and then rose at 24 h to about 2.6 times that of the controls. The average number of peroxisomes per cell in the yeast treated with 1 mM Cd2+ was about sixfold higher than the control groups. The proliferation of peroxisomes and the increase of catalase activity following cadmium toxicity gives credence to the hypothesis that cadmium toxicity is related to its potential to induce oxidative stress in cells.

Cadmium↗