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Biomedical subjects

Lei Chen

Publications and source records attributed to Lei Chen.

At least 55 records · Page 3Linked to original sources
PubMed2006

Knockdown of hypoxia-inducible factor-1alpha in breast carcinoma MCF-7 cells results in reduced tumor growth and increased sensitivity to methotrexate.

The hypoxia-inducible factor (HIF) 1alpha is a key regulator of the cellular response to oxygen deprivation. Specific disruption of the HIF-1 pathway is important for exploring its role in tumor biology and developing more efficient weapons to treat cancer. In this study, we stably transfected human breast tumor MCF-7 cells with short hairpin RNA expression vectors targeting HIF-1alpha. After knockdown of HIF-1alpha, hypoxia-induced expression of its target genes such as vascular endothelial growth factor, Glut-1, phosphoglycerate kinase, and P-glycoprotein were markedly attenuated. Moreover, HIF-1alpha knockdown was found to suppress the shift from S-phase to G(1) induced by hypoxia and increase drug sensitivity to methotrexate. The growth rates of HIF1alpha-knockdown tumors were drastically retarded in both subcutaneous and orthotopic xenograft models, which were accompanied by decreased angiogenesis and reduced expression of glucose transporter in tissue sections. These data demonstrate that HIF-1alpha knockdown reduces tumorigenicity of MCF-7 cells and suggest a promising combination of both anti-HIF-1 strategy and traditional chemotherapy to improve cancer treatment.

Antineoplastic Agents↗
PubMed2006

Action of beta-amyloid peptide₁₋₄₀ on I(HVA) and its modulation by ginkgolide B.

Whole-cell patch clamp recording was used to investigate the action of beta-amyloid peptide(1-40) (Abeta(1-40)) on high voltage-activated calcium channel current (I(HVA)) in acutely isolated hippocampal CA1 pyramidal neurons in rats and observe its modulation by ginkgolide B (GB). Drug was applied by extracellular bath or adding in the pipette solution, and its effect was determined by comparing the amplitude of I(HVA) before and after the drug application. Bath application of aggregated Abeta(1-40) at concentrations of 0.01~30 mumol/L increased the amplitude of I(HVA) in a dose-dependent manner by (5.43+/-3.01)% (n=8, P>0.05), (10.49+/-4.13) % (n=11, P>0.05), (40.69+/-8.01) % (n=16, P<0.01), (58.32+/-4.85) % (n=12, P<0.01), and (75.45+/-5.81) % (n=6, P<0.01), respectively, but had no effect on the I-V curve of I(HVA); fresh Abeta(1-40) almost had no effect on I(HVA) (n=5, P>0.05). L-type calcium channel antagonist nifedipine abolished the increase of I(HVA)by Abeta(1-40). The increase of I(HVA) by Abeta(1-40) (1.0 mumol/L) was enhanced to (66.19+/-5.74) % (P<0.05) by 8-Br-cAMP (membrane permeable analogue of cAMP) and to (73.21+/-6.90) % (P<0.05) by forskolin, an adenylyl cyclase (AC) agonist, and reduced to (20.08+/-2.18) % (P<0.05) by H-89, cyclic adenosine monophosphate (cAMP)-dependent protein kinase A (PKA) antagonist. GB effectively inhibited the increase of I(HVA) by Abeta(1-40). The results indicate that Abeta(1-40) leads to an intracellular calcium overload by increasing I(HVA) via AC-cAMP-PKA. This may be one of the mechanisms for its neurotoxicity. GB can prevent neurons from neurotoxicity by inhibiting abnormal calcium influx caused by Abeta(1-40).

Amyloid beta-Peptides↗
PubMed2006

Increased mitochondrial reactive oxygen species production in newborn brain during hypoglycemia.

Hypoglycemia is associated with gray and white matter injury in immature brain, but the specific mechanisms responsible for hypoglycemic brain injury remain poorly defined. We postulated that mitochondrial electron transport chain function is altered during hypoglycemia due to the decreased availability of reducing equivalents, and that altered activity of the electron transport chain would increase mitochondrial production of free radicals and lead to mitochondrial oxidant injury. The present study tests the hypothesis that production of reactive oxygen species (ROS) by cerebral mitochondria is increased during acute hypoglycemia. Studies were performed in an awake, chronically catheterized newborn piglet model. Hypoglycemia (blood glucose 1 mmol/L for 2 h) was induced using a bolus of intravenous lispro insulin, 25 U/kg. Superoxide and hydrogen peroxide production by mitochondria isolated from cerebral cortex of normoglycemic and hypoglycemic newborn piglets was measured using lucigenin- and luminol-derived chemiluminescence. After 2 h of hypoglycemia, superoxide generation was 60% higher and hydrogen peroxide generation was two-fold higher in mitochondria from hypoglycemia animals than in controls (p < 0.005). These data confirm that the ability of the mitochondria to produce ROS is increased after hypoglycemia in immature brain, and are, to our knowledge, the first evidence that ROS may play a role in brain injury due to neonatal hypoglycemia. Increased mitochondrial ROS production could result in alterations in brain structure and function due to oxidant injury to mitochondrial proteins and DNA or changes in oxidant-sensitive signal transduction pathways in brain.

Animals↗
PubMed2006

A novel putative tyrosinase involved in periostracum formation from the pearl oyster (Pinctada fucata).

Tyrosinase (monophenol, L-DOPA: oxygen oxidoreductase, EC 1.14.18.1), a kind of copper-containing phenoloxidase, arouses great interests of scientists for its important role in periostracum formation. A cDNA clone encoding a putative tyrosinase, termed OT47 because of its estimated molecular mass of 47kDa, was isolated from the pearl oyster, Pinctada fucata. This novel tyrosinase shares similarity with the cephalopod tyrosinases and other type 3 copper proteins within two conserved copper-binding sites. RT-PCR analysis showed that OT47 mRNA was expressed only in the mantle edge. Further in situ hybridization analysis and tyrosinase activity staining revealed that OT47 was expressed at the outer epithelial cells of the middle fold, different from early histological results in Mercenaria mercenaria, suggesting a different model of periostracum secretion in P. fucata. Taken together, these results suggest that OT47 is most likely involved in periostracum formation. The identification and characterization of oyster tyrosinase also help to further understand the structural and functional properties of molluscan tyrosinase.

Amino Acid Sequence↗
PubMed2006

Solid-state NMR spectroscopy of anionic framework aluminophosphates: a new method to determine the al/p ratio.

A series of anionic framework aluminophosphates, with different Al/P ratios, have been investigated by various solid-state NMR techniques, including 27Al, 31P magic angle spinning (MAS), 27Al-->31P cross polarization (CP), 27Al{31P} rotational echo double resonance (REDOR), and 31P{27Al} transfer of population double resonance (TRAPDOR). Different Al coordinations (AlO4b, AlO5b, and AlO6b) and P coordinations (PO4b, PO3bOt, PO2bO2t, and PObO3t), where b represents bridging oxygens and t represents terminal oxygens, can be unambiguously determined based on the solid-state NMR spectroscopy. Furthermore, a new method to determine the Al/P ratio of open-framework aluminophosphates has been established, which is useful for the understanding of unknown aluminophosphate structures.

Journal Article↗
PubMed2006

Inhibition of cell growth and induction of G1-phase cell cycle arrest in hepatoma cells by steroid extract from Meretrix meretrix.

In this study, we report that the steroid extract 5alpha, 8alpha-epidioxycholest-6-ene-3beta-ol (MME) from Meretrix meretrix has the ability to inhibit growth of hepatoma cells and to induce G1-phase cell cycle arrest in two human hepatoma cell lines, HepG2 and Hep3B. HepG2 cells were more sensitive than Hep3B to MME. The extract markedly up-regulated the expression of p53 and p21WAF1/CIP1 in HepG2, suggesting that MME-induced G1 phase cell cycle arrest in HepG2 might be p53-dependent. Therefore, the up-regulation of p27KIP1and p16INK4A in both cell lines indicates that a p53-independent pathway might be involved in the mechanism of MME inducing cell cycle arrest. In conclusion, MME induces G1 phase cell cycle arrest via both p53-dependent and p53-independent pathways.

Bivalvia↗
PubMed2006

Low-frequency resonance Raman studies of the H(M202)G cavity mutant of bacterial photosynthetic reaction centers.

Low-frequency (90-435 cm(-1)) NIR-excitation (875-900 nm) resonance Raman (RR) studies are reported for the H(M202)G cavity mutant of bacterial photosynthetic reaction centers (RCs) from Rb. sphaeroides that was first described by Goldsmith et al. [(1996) Biochemistry 35: 2421-2428]. In this mutant, the His residue that axially ligates the Mg ion of the M-side bacteriochlorophyll (BChl) of the special pair primary donor (P) is replaced by a non-ligating Gly residue. Regardless, the Mg ion of P(M) in the H(M202)G RCs remains pentacoordinates and is presumably ligated by a water molecule, although this axial ligand has not been definitively identified. The low-frequency RR studies of the H(M202)G RCs are accompanied by studies of RCs exchanged with D(2)O and incubated with imidazole (Im). The RR studies of the cavity mutant RCs reveal the following: (1) The structure of P(M) in the H(M202)G RCs is different from that of the wild-type, consistent with an altered BChl core. (2) A water ligand for P(M) in the H(M202)G RCs is generally consistent with the low-frequency RR spectra. The Mg-OH(2) stretching vibration is tentatively assigned to a band at 318 cm(-1), a frequency higher than that of the Mg-His stretch of the native pigment ( approximately approximately 235 cm(-1)). (3) The BChl core structure of P(M) in the cavity mutant is rendered similar (but not identical) to that of the wild-type when the adventitious water axial ligand is replaced by Im. (4) Exchange with D(2)O results in more global structural changes, likely involving the protein, which in turn affect the structure of the BChls in P. (5) Assignment of the low-frequency vibrational spectrum of P is generally more complex than originally suggested.

Mutation↗
PubMed2006

High-resolution magic-angle spinning (13)C spectroscopy of brain tissue at natural abundance.

High-resolution magic-angle spinning (MAS) (1)H and (13)C magnetic resonance spectroscopy (MRS) has recently been applied to study the metabolism in intact biological tissue samples. Because of the low natural abundance and the low gyromagnetic ratio of the (13)C nuclei, signal enhancement techniques such as cross-polarization (CP) and distortionless enhancement by polarization transfer (DEPT) are often employed in MAS (13)C MRS to improve the detection sensitivity. In this study, several sensitivity enhancement techniques commonly used in liquid- and solid-state NMR, including CP, DEPT and nuclear Overhauser enhancement (NOE), were combined with MAS to acquire high-resolution (13)C spectra on intact rat brain tissue at natural abundance, and were compared for their performances. The results showed that different signal enhancement techniques are sensitive to different classes of molecules/metabolites, depending on their molecular weights and mobility. DEPT was found to enhance the signals of low-molecular weight metabolites exclusively, while the signals of lipids, which often are associated with membranes and have relatively lower mobility, were highly sensitive to CP enhancement.

Animals↗
PubMed2006

Large area, 38 nm half-pitch grating fabrication by using atomic spacer lithography from aluminum wire grids.

We wrapped 150 nm period aluminum wire grid polarizer (WGP) with AlSiOx by using atomic layer deposition at 250 degrees C. The nanometer precision coating defined the spacer to double the spatial frequency of the 100 mm diameter grating fabricated by using a legacy immersion holography setup at 351 nm wavelength. Half-pitch grating of approximately 38 nm was demonstrated with good pattern uniformity, excellent repeatability, and a wide processing window. We believe 10 nm half-pitch grating over even larger areas are viable, overcoming one major hurdle to commercialize nanoimprint.

Journal Article↗
PubMed2006

Racial and ethnic differences in the rates of urinary tract infections in febrile infants in the emergency department.

OBJECTIVE: To characterize the racial and ethnic differences in rates of urinary tract infections among febrile infants who present to an urban pediatric emergency department. METHODS: A retrospective chart review was conducted using the medical records of an urban pediatric emergency department from the period between 5/2002 and 1/2003. Data were collected from infants aged 1 to 24 months from whom urine cultures were obtained as part of their fever workup. Demographic data were recorded as provided by the parents or caregivers of the patients. Urine culture results were also recorded. RESULTS: Four hundred and sixty five children had urine cultures performed during the study period and fulfilled the inclusion criteria. Parents characterized the children as white (45%), Hispanic (27%), African American (20%), Asian (3.9%), or others (4.3%). Clinical parameters including the height of fever, age of the patient, and proportion of men were similar between the subjects in each racial and ethnic group. Sixty-four children were diagnosed as having UTI. The overall prevalence of UTI was 14% (95% confidence interval [CI] 11%-17%). Rates of UTI (SD) were as follows: Asian 22% (10%), white 16% (2.4%), Hispanic 16% (3.1%), African American 4.0% (1.9%), and Others 11 % (6.2%). African American infants had a lower rate of UTI (p = 0.007) compared with the general population. The odds ratio (OR) of UTI in white versus African American children and Hispanic versus African American children were 4.4 (95% CI, 1.5 to 12.6) and 4.6 (95% CI, 1.5 to 13.9), respectively. These results were consistent after adjustment for sex. CONCLUSIONS: Urinary tract infections were common in our study population of racially and ethnically diverse children. Given similar clinical parameters, white and Hispanic children were much more likely to be diagnosed with UTI than African-American children.

Black or African American↗
PubMed2006

Universal approximation using incremental constructive feedforward networks with random hidden nodes.

According to conventional neural network theories, single-hidden-layer feedforward networks (SLFNs) with additive or radial basis function (RBF) hidden nodes are universal approximators when all the parameters of the networks are allowed adjustable. However, as observed in most neural network implementations, tuning all the parameters of the networks may cause learning complicated and inefficient, and it may be difficult to train networks with nondifferential activation functions such as threshold networks. Unlike conventional neural network theories, this paper proves in an incremental constructive method that in order to let SLFNs work as universal approximators, one may simply randomly choose hidden nodes and then only need to adjust the output weights linking the hidden layer and the output layer. In such SLFNs implementations, the activation functions for additive nodes can be any bounded nonconstant piecewise continuous functions g : R --> R and the activation functions for RBF nodes can be any integrable piecewise continuous functions g : R --> R and integral of R g(x)dx not equal to 0. The proposed incremental method is efficient not only for SFLNs with continuous (including nondifferentiable) activation functions but also for SLFNs with piecewise continuous (such as threshold) activation functions. Compared to other popular methods such a new network is fully automatic and users need not intervene the learning process by manually tuning control parameters.

Algorithms↗
PubMed2006

Amino acid 1-209 is essential for PDX-1-mediated repression of human CMV IE promoter activity.

AIM: To explore the different roles of pancreatic duodenal homeobox factors-1 (PDX-1) domains in PDX-1 mediated repression of human cytomegalovirus immediately early (CMV IE) promoter. METHODS: A series of truncated PDX-1 mutants were constructed. The binding of PDX-1 and CMV IE promoter was identified by electrophoretic mobility shift assay (EMSA). The dual-reporter assay was applied to examine the repression activities of PDX-1 mutants on CMV IE promoter. In addition, RNAi technology was used to specifically knock down the endogenous PDX-1 expression. RESULTS: The reporter assay indicated that compared to the mock controls (pEGFP-N2), overexpression of PDX-1 resulted in a 41% decrease of CMV IE promoter activity in the 293 cells (P< 0.05) and 43% decrease in HeLa cells (P< 0.05), and the repression levels of various truncated mutants played on CMV IE promoter were different. Specific knock down of the endogenous PDX-1 expression significantly restored the activity of CMV IE promoter. EMSA demonstrated that domain 3 is necessary for nuclear localization and DNA binding activity of PDX-1. However, binding of PDX-1 alone to CMV IE promoter was not sufficient to inhibit its transcriptional activity, and other domains of PDX-1 presented were also required. CONCLUSION: Our data suggested that the DNA binding activity of PDX-1 domain 3 and the cooperative binding of PDX-1 domain 1/2 with other proteins were required for PDX-1 mediated repression of CMV IE promoter.

Base Sequence↗
PubMed2006

Expression of B cell-specific activator protein/PAX5 in acute myeloid leukemia with t(8;21)(q22;q22).

The blasts of acute myeloid leukemia (AML) with t(8;21)(q22;q22) frequently express the B-cell antigen CD19, which is regulated by B cell-specific activator protein (BSAP) encoded by the PAX5 gene, a protein important for B-cell lineage commitment and development. We assessed for BSAP expression in 28 AML cases with t(8;21) and 46 AML cases of other types. CD19 was expressed by 26 (93%) cases of AML with t(8;21) and 1 AML case (2%) without t(8;21). We also tested a subset of cases for the B-cell transcription factors Oct2 and OCA-B (BOB.1) and the B-cell antigens CD20, CD22, and CD79a. Immunostaining performed on bone marrow biopsy specimens demonstrated BSAP expression in all 28 AML cases with t(8;21): weak, 21; strong, 7. By contrast, BSAP was expressed weakly in only 1 AML case without t(8;21). Oct2 was expressed strongly in 12 of 16 AML cases with t(8;21) and 19 of 46 without t(8;21). OCA-B, CD20, CD22, or CD79a were negative in all cases assessed. These results indicate that silencing of PAX5 is not required for commitment to myeloid differentiation and that BSAP expression in AML is found mainly in cases with t(8;21).

Acute Disease↗
PubMed2006

Incidence and predictors of serious bacterial infections among 57- to 180-day-old infants.

BACKGROUND: Numerous researchers have investigated fever in infants <2 months of age. However, the etiology of fever and usefulness of screening tests in older (2-6 months) infants is not well studied. METHODS: This was a prospective study of febrile infants 57-180 days old. Evaluation included blood and urine tests and direct fluorescent antibody (DFA) of nasal swabs for respiratory viruses. Additional studies were performed at the discretion of managing clinicians. RESULTS: Serious bacterial illness (SBI) was diagnosed in 44 (10.3%) of 429 infants: 41 with bacteruria and 4 with bacteremia (1 infant had concurrent Escherichia coli bacteruria and bacteremia). Lumbar puncture, performed in 58 (13.5%) infants, revealed no cases of bacterial meningitis. DFAs were positive in 163 (38.0%) infants: the majority were respiratory syncytial virus or influenza A. SBI was noted in 4.9% of infants with positive DFA. Age and height of fever were not significant predictors of SBI. White blood cell count (17.1 K/mm3 vs 12.4 K/mm3) and CRP (2.6 mg/dL vs 0.9 mg/dL) were elevated in infants with SBI, as was the Yale Observation Score (9.4 vs 8.0). CONCLUSIONS: A substantial proportion (10.3%) of older febrile infants has SBI. In the postpneumococcal vaccine era, only 1 infant had pneumococcal disease; bacteremia was noted in 0.9%. Bacteruria is commonly associated with fever in this age range. Infants older than 8 weeks remain at risk for bacteremia and bacteruria, regardless of positive DFA or other apparent source of fever. CRP is a better indicator than white blood cell count, but no single ideal indicator of SBI was identified for this age group.

Bacteremia↗
PubMed2006

The mitochondrial K-ATP channel opener, diazoxide, prevents ischemia-reperfusion injury in the rabbit spinal cord.

Paraplegia resulting from ischemia is a catastrophic complication of thoracoabdominal aortic surgery. The current study was designed to investigate the effects of diazoxide (DZ) on mitochondrial structure, neurological function, DNA damage-repair, and apoptosis in spinal cord ischemia-reperfusion injury. Rabbits were subjected to 30 minutes of spinal cord ischemia and reperfusion (1 hour) with or without diazoxide (n = 6 in each group) by clamping and releasing the infrarenal aorta. The neurological functional score was significantly improved in the DZ-treated ischemia-reperfusion injury group. Electron microscopic studies demonstrated that mitochondrial damage in the spinal cord after injury was significantly reduced by DZ. Mitochondrial superoxide and hydrogen peroxide levels were also markedly decreased in the DZ-treated injury group compared with the untreated group. DZ decreased levels of the oxidative DNA damage product 8-oxoG and increased levels of the DNA repair enzyme OGG-1. Furthermore, DZ inhibited apoptosis via caspase-dependent and -independent pathways. These studies indicate for the first time that the mitochondrial K-ATP channel opener diazoxide improves neurological function after spinal cord ischemia and reperfusion by diminishing levels of reactive oxygen species, decreasing DNA oxidative damage, and inhibiting caspase-dependent and -independent apoptotic pathways while preserving mitochondrial structure.

Animals↗
PubMed2006

Fatal hemorrhage secondary to ulcerated epiphrenic pseudodiverticulum.

A 47-year-old man was found unconscious after experiencing severe hematemesis. He had a history of alcohol abuse, hepatic cirrhosis, and previous episodes of gastrointestinal bleeding. Imaging studies indicated that the left gastric artery was the probable source of bleeding. A severe coagulopathy was also noted clinically. Angiographic embolization of the left gastric artery failed to staunch bleeding, and the patient died shortly after admission. Autopsy demonstrated a large, ulcerated epiphrenic esophageal pseudodiverticulum, the base of which was in close proximity to an esophageal branch of the left gastric artery. Cystic dilatation of adjacent esophageal submucosal glands was also seen. Gelatin embolic material, without associated thrombus formation, was found within the left gastric artery. Esophageal pseudodiverticulosis is an uncommon disorder that may be associated with dysphagia, stricture, and odynophagia. Bleeding and perforation are very rare complications. This case may be the first fatality proven by autopsy to be secondary to esophageal pseudodiverticulosis.

Diverticulum, Esophageal↗
PubMed2006

Cell death-inducing DFF45-like effector may take part in neuronal apoptosis of the lumbar spinal cord after sciatic nerve injury caused by a firearm.

OBJECTIVE: To investigate neuronal apoptosis and gene regulation after peripheral nerve injury caused by a firearm. METHODS: A rabbit model of sciatic nerve injury caused by a firearm was used. Neuronal apoptosis was determined by using terminal transferase-mediated dUTP nick end-labeling and flow cytometry. Differentially expressed genes were screened with mouse_8192S GeneChips. Cell death-inducing DFF45-like effector (CIDE-B) gene expression in spinal cord after sciatic nerve injury was detected with reverse transcription-polymerase chain reaction. RESULTS: The size of the injury caused by the firearm was widely extended. Neuronal apoptosis was found in days 1, 3, and 7 groups. The expression of apoptosis-related gene CIDE-B was high according to analysis of the GeneChips and reverse transcription-polymerase chain reaction detection. The trend of CIDE-B expression was consistent with neuronal apoptosis after nerve injury. CONCLUSIONS: Neuronal apoptosis is an important pathological change after peripheral nerve injury caused by firearms, and CIDE-B may be an important regulator.

Animals↗