Biomedical subjects

Meihua Li

Publications and source records attributed to Meihua Li.

18 recordsLinked to original sources

PubMed2006

View-independent reconstruction algorithms for cone beam CT with general saddle trajectory.

In Yang et al (2006 Phys. Med. Biol. 51 1157-72), an exact filtered backprojection (FBP) reconstruction algorithm was proposed for cone beam tomography with saddle trajectory based on the seminal works of Pack and Noo (2005a Inverse Problems 21 1105-20; 2005b 8th Int. Meeting on Fully 3D Reconstruction in Radiology and Nuclear Medicine (Salt Lake City) ed F Noo, H Kudo and L G Zeng pp 287-90). However, the artefacts due to discretization and/or sampling errors in the reconstructed images by this method were still visible, especially when the pitch is large. In this paper, two view-independent (VI) algorithms, which are similar to the FDK-type algorithms (Feldkamp et al 1984 J. Opt. Soc. Am. A 1 612-19), are proposed for planar detector geometry. The first VI algorithm involves two filtered projections and a small additional term (two-dimensional (2D) Radon transform term). One of the filtered projections is obtained by ramp filtering (as in the FDK algorithm for circular trajectory) and the other one is obtained by Hilbert transform. The 2D Radon transform term is just like the term which was first derived by Hu (1996 Scanning 18 572-81) for a circular trajectory. The second VI algorithm involves only one filtered projection term, which is obtained by differentiation followed by Hilbert transform and the 2D Radon transform term. Both algorithms involve only one backprojection step with a weighting factor as in the FDK algorithm. The simulation studies show that the pixel values of the reconstructed images by the VI algorithms are more accurate than those by the original view differencing (VD) algorithm, the streak artefacts are also reduced, and their computational times are comparable to that of the original VD algorithm. We also generalize the concept of saddle trajectory and the corresponding reconstruction algorithm. The generalized algorithm is also theoretically exact, has a shift-invariant FBP structure, and does not depend on the concept of pi-line.

Algorithms↗

PubMed2006

Reversible vagal blockade in conscious rats using a targeted delivery device.

Reversible methods of nerve blockade greatly aid neurophysiological and behavioral studies. We have developed an implantable device for the local delivery of anesthetics to the area surrounding the vagal nerve in rats. The device consists of a thick silicone tube for insulating the nerves from the surrounding tissue, and a thin silicone tube for the infusion of anesthetics into the insulating tube. The in vivo performance of the device was tested electrophysiologically, and cardiovascular responses to vagal stimulation were measured in conscious animals. Nerve conductivity was completely blocked by injection of a small amount (<20 microl) of 1% lidocaine, with conductivity subsequently recovering gradually after 10-40 min. Electrical stimulation of the right vagus nerve in conscious rats increased arterial pressure while decreasing heart rate. The local blockade of afferent fibers abolished the arterial pressure response but preserved the bradycardic response to vagal nerve stimulation. The targeted delivery device was useful for reversible vagal blockade in conscious rats.

Anesthetics, Local↗

PubMed2006

Exact cone beam reconstruction for a saddle trajectory.

We propose an exact shift-invariant filtered backprojection (FBP) algorithm for inversion of cone beam (CB) data in the case where the source trajectory is a saddle. The algorithm allows for axial truncation of the cone beam data. The algorithm involves only one family of filtering lines on the detector plane, and it does not depend on the existence of pi-lines. The algorithm is derived from a general formula in Pack and Noo (2005 Inverse Problems 21 1105-20). We also give the steps to implement the algorithm for planar detector geometry and discuss how to select the parameter of the saddle and the size of the detector when the trajectory is a standard saddle. The algorithm is tested by simulation studies.

Algorithms↗

PubMed2005

Vagal stimulation suppresses ischemia-induced myocardial interstitial norepinephrine release.

Although electrical vagal stimulation exerts beneficial effects on the ischemic heart such as an antiarrhythmic effect, whether it modulates norepinephrine (NE) and acetylcholine (ACh) releases in the ischemic myocardium remains unknown. To clarify the neural modulation in the ischemic region during vagal stimulation, we examined ischemia-induced NE and ACh releases in anesthetized and vagotomized cats. In a control group (VX, n = 8), occlusion of the left anterior descending coronary artery increased myocardial interstitial NE level from 0.46+/-0.09 to 83.2+/-17.6 nM at 30-45 min of ischemia (mean+/-SE). Vagal stimulation at 5 Hz (VS, n = 8) decreased heart rate by approximately 80 beats/min during the ischemic period and suppressed the NE release to 24.4+/-10.6 nM (P < 0.05 from the VX group). Fixed-rate ventricular pacing (VSP, n=8) abolished this vagally mediated suppression of ischemia-induced NE release. The vagal stimulation augmented ischemia-induced ACh release at 0-15 min of ischemia (VX: 11.1+/-2.1 vs. VS: 20.7+/-3.9 nM, P < 0.05). In the VSP group, the ACh release was not augmented. In conclusion, vagal stimulation suppressed the ischemia-induced NE release and augmented the initial increase in the ACh level. These modulations of NE and ACh levels in the ischemic myocardium may contribute to the beneficial effects of vagal stimulation on the heart during acute myocardial ischemia.

Acetylcholine↗

PubMed2005

Genome-wide analysis of gene expression in human intrahepatic cholangiocarcinoma.

Intrahepatic cholangiocarcinoma is a neoplasm arising in the liver, and its incidence is increasing in Japan as well as in Western countries. Prognosis of patients with this type of tumor remains unsatisfactory because no effective chemotherapeutic drugs are available, we have no sensitive tumor markers to detect this tumor in its early stage, and it is difficult to identify a high-risk group for the disease. To clarify the molecular mechanism of tumorigenesis and identify molecular targets for diagnosis and treatment, we analyzed global gene-expression profiles of 25 intrahepatic cholangiocarcinomas using tumor cell populations purified by laser microbeam microdissection and a cDNA microarray containing 27,648 genes. We identified 52 genes that were commonly upregulated and 421 that were downregulated in intrahepatic cholangiocarcinomas compared with noncancerous biliary epithelial cells. From the 52 upregulated genes, we selected P-cadherin and survivin for further investigation and corroborated enhanced expression of their products in cancer tissues by immunohistochemical staining. Furthermore, comparison between tumors with lymph node metastasis and those without metastasis identified 30 genes that were associated with lymph node involvement. In conclusion, these data should be helpful for a better understanding of the tumorigenesis of intrahepatic cholangiocarcinoma and should contribute to the development of diagnostic and therapeutic strategies for this type of tumor. Supplementary material for this article can be found on the HEPATOLOGY website (http://www.interscience.wiley.com/jpages/0270-9139/suppmat/index.html).

Adult↗

PubMed2004

Comparison of gene-expression profiles between diffuse- and intestinal-type gastric cancers using a genome-wide cDNA microarray.

Gastric cancer is the fourth leading cause of cancer-related death in the world. Two histologically distinct types of gastric carcinoma, 'intestinal' and 'diffuse', have different epidemiological and pathophysiological features that suggest different mechanisms of carcinogenesis. A number of studies have investigated intestinal-type gastric cancers at the molecular level, but little is known about mechanisms involved in the diffuse type, which has a more invasive phenotype and poorer prognosis. To clarify the mechanisms that underlie its development and/or progression, we compared the expression profiles of 20 laser-microbeam-microdissected diffuse-type gastric-cancer tissues with corresponding noncancerous mucosae by means of a cDNA microarray containing 23,040 genes. We identified 153 genes that were commonly upregulated and more than 1500 that were commonly downregulated in the tumors. We also identified a number of genes related to tumor progression. Furthermore, comparison of the expression profiles of diffuse-type with those of intestinal-type gastric cancers identified 46 genes that may represent distinct molecular signatures of each histological type. The putative signature of diffuse-type cancer exhibited altered expression of genes related to cell-matrix interaction and extracellular-matrix (ECM) components, whereas that of intestinal-type cancer represented enhancement of cell growth. These data provide insight into different mechanisms underlying gastric carcinogenesis and may also serve as a starting point for identifying novel diagnostic markers and/or therapeutic targets for diffuse-type gastric cancers.

Base Sequence↗

PubMed2004

SMYD3 encodes a histone methyltransferase involved in the proliferation of cancer cells.

Colorectal and hepatocellular carcinomas are some of the leading causes of cancer deaths worldwide, but the mechanisms that underly these malignancies are not fully understood. Here we report the identification of SMYD3, a gene that is over-expressed in the majority of colorectal carcinomas and hepatocellular carcinomas. Introduction of SMYD3 into NIH3T3 cells enhanced cell growth, whereas genetic knockdown with small-interfering RNAs (siRNAs) in cancer cells resulted in significant growth suppression. SMYD3 formed a complex with RNA polymerase II through an interaction with the RNA helicase HELZ and transactivated a set of genes that included oncogenes, homeobox genes and genes associated with cell-cycle regulation. SMYD3 bound to a motif, 5'-CCCTCC-3', present in the promoter region of downstream genes such as Nkx2.8. The SET domain of SMYD3 showed histone H3-lysine 4 (H3-K4)-specific methyltransferase activity, which was enhanced in the presence of the heat-shock protein HSP90A. Our findings suggest that SMYD3 has histone methyltransferase activity and plays an important role in transcriptional regulation as a member of an RNA polymerase complex. Furthermore, activation of SMYD3 may be a key factor in human carcinogenesis.

Amino Acid Sequence↗

PubMed2004

Bezold-Jarisch reflex blunts arterial baroreflex via the shift of neural arc toward lower sympathetic nerve activity.

Although the Bezold-Jarisch (BJ) reflex is potentially evoked during acute myocardial ischemia or infarction, its effects on the static characteristics of the arterial baroreflex remain to be analyzed in terms of an equilibrium diagram between the neural and peripheral arcs. The neural arc represents the static input-output relationship between baroreceptor pressure input and efferent sympathetic nerve activity (SNA), whereas the peripheral arc represents that between SNA and arterial pressure (AP). In 8 anesthetized rabbits, we increased carotid sinus pressure stepwise from 40 to 160 mmHg in increments of 20 mmHg at one-minute intervals while measuring renal SNA and AP under control conditions and during the activation of the BJ reflex by intravenous administration of phenylbiguanide (PBG, 100 microg.kg(-1).min(-1)). The neural arc approximated a sigmoid curve whereas the peripheral arc approximated a straight line. PBG decreased AP at the operating point from -91.3 +/- 2.4 to -71.7 +/- 3.1 mmHg (P < 0.01), and attenuated the total loop gain at the operating point from -1.31 +/- 0.44 to -0.51 +/- 0.14 (P < 0.05). The equilibrium diagram indicated that PBG caused a parallel shift of the neural arc toward lower SNA such that the maximum SNA was reduced to approximately 60% of control. PBG decreased neural and peripheral arc gains at the operating point to approximately 43% and 77%, respectively. In conclusion, the BJ reflex blunts arterial baroreflex via the shift of the neural arc toward lower SNA.

Animals↗

PubMed2004

Genes associated with liver metastasis of colon cancer, identified by genome-wide cDNA microarray.

To uncover mechanisms underlying progression of colorectal carcinogenesis and to identify genes associated with liver metastasis, we analyzed expression profiles of 14 primary colorectal cancers (CRCs) with liver metastases, and compared them with profiles of 11 non-metastatic carcinomas and those of 9 adenomas of the colon. A hierarchical cluster analysis using data from a cDNA microarray containing 23,040 genes indicated that the cancers with metastasis had different expression profiles from those without metastasis, although a number of genes were commonly up-regulated in primary cancers of both categories. We documented 54 genes that were frequently up-regulated and 375 that were frequently down-regulated in primary tumors with metastases to liver, but not in tumors without metastasis. Subsequent quantitative PCR experiments confirmed that PRDX4, CKS2, MAGED2, and an EST (GenBank accession number BF696304) were expressed at significantly higher levels in tumors with metastasis. These data should contribute to a better understanding of the progression of colorectal tumors, and facilitate prediction of their metastatic potential.

Cell Line, Tumor↗

PubMed2004

[The regulation of PKCalpha in eosinophil infiltration and proliferation in nasal polyps].

OBJECTIVE: To explore the regulation of protein kinase C (PKC) isoform--PKCalpha in eosinophil (EOS) proliferation and infiltration in nasal polyp tissues. METHOD: With the methods of in situ hybridization staining and immunohistochemistry MGG staining, to check out the relationship between PKC and bcl-2/BaxmRNA and associated protein, especially PKC isoform--PKCalpha, PKCbeta1 , PKCbeta2, and PKCgamma did not express at all. RESULT: There were PKC expression in the eosinophils of 26 cases from nasal polyps, and the expression of PKC and Bcl-2 mRNA/their protein in EOS of nasal polyps showed remarkably positive relation (r1 = 0.0875, r2 = 0.0823, P < 0.01), but in PKC isoforms, PKCalpha expression was the strongest, but PKCbeta1 and PKCbeta2 expressed thinner and PKCgamma did not express at all. CONCLUSION: The reason of eosinophil proliferation and infiltration in nasal polyps is that PKC signal transduction pathway was activated, and leaded to inhibition of eosinophil apoptosis, and eosinophil survival was delayed, and eosinophil proliferated and infiltrated, and in PKC family, PKCalpha is main.

Adult↗

PubMed2003

Vagal nerve stimulation markedly improves long-term survival after chronic heart failure in rats.

BACKGROUND: Diminished cardiac vagal activity and higher heart rate predict a high mortality rate of chronic heart failure (CHF) after myocardial infarction. We investigated the effects of chronic electrical stimulation of the vagus nerve on cardiac remodeling and long-term survival in an animal model of CHF after large myocardial infarction. METHODS AND RESULTS: Two weeks after the ligation of the left coronary artery, surviving rats were randomized to vagal- and sham-stimulated groups. Using an implantable miniature radio-controlled electrical stimulator, we stimulated the right vagal nerve of CHF rats for 6 weeks. The intensity of electrical stimulation was adjusted for each rat, so that the heart rate was lowered by 20 to 30 beats per minute. The treated rats had significantly lower left ventricular end-diastolic pressure (17.1+/-5.9 versus 23.5+/-4.2 mm Hg, P<0.05) and higher maximum dp/dt of left ventricular pressure (4152+/-237 versus 2987+/-192 mm Hg/s, P<0.05) than the untreated rats. Improvement of cardiac pumping function was accompanied by a decrease in normalized biventricular weight (2.75+/-0.25 versus 3.14+/-0.22 g/kg, P<0.01). Although the 140-day survival of the untreated group was only half, vagal stimulation markedly improved the survival rate (86% versus 50%, P=0.008). Vagal stimulation therapy achieved a 73% reduction in a relative risk ratio of death. CONCLUSIONS: Vagal nerve stimulation markedly improved the long-term survival of CHF rats through the prevention of pumping failure and cardiac remodeling.

Animals↗

PubMed2003

Involvement of the FGF18 gene in colorectal carcinogenesis, as a novel downstream target of the beta-catenin/T-cell factor complex.

To search for potential molecular targets for development of novel anticancer drugs, we have been analyzing expression profiles of clinical samples from cancer patients, using a genome-wide cDNA microarray. In experiments with colon cancer cells, the gene encoding fibroblast growth factor 18 (FGF18) was among those that showed elevated expression. The promoter region of this gene was found to contain putative Tcf4-binding motifs; moreover a reporter-gene assay using luciferase activity as a marker and an electromobility shift assay indicated that FGF18 is a downstream transcription target in the beta-catenin/Tcf4 pathway. We showed that exogenous FGF18 promoted growth of NIH3T3 cells in an autocrine manner and that transfection of FGF18 short interfering RNAs suppressed growth of colon cancer cells in culture. Our results indicate that FGF18 is activated in colon cancers as a direct downstream target of the Wnt signaling pathway and that it might represent a marker for early diagnosis and a molecular target for treatment of this life-threatening tumor.

Adenocarcinoma↗

PubMed2003

Uniformity in dynamic baroreflex regulation of left and right cardiac sympathetic nerve activities.

Functional laterality of cardiac sympathetic nerve stimulation in chronotropic and inotropic effects is well known. Whether left (LSNA) and right (RSNA) cardiac sympathetic nerve activities show laterality during dynamic baroreflex activation remains to be determined. In nine anesthetized, vagotomized, and aortic-denervated rabbits, we randomly perturbed intracarotid sinus pressure (CSP) in both carotid sinus regions while simultaneously recording LSNA and RSNA. The baroreflex neural arc transfer function from CSP to LSNA and from CSP to RSNA revealed derivative characteristics, i.e., the magnitude of LSNA and RSNA responses became greater as the input frequency of CSP perturbation increased. The average slope of increasing gain in the frequencies between 0.03 and 0.3 Hz showed no difference between LSNA and RSNA responses (9.7 +/- 2.9 vs. 9.7 +/- 3.1 dB/decade, means +/- SD). The amplitude ratio and phase difference between LSNA and RSNA approximated unity and zero radians, respectively, in the frequencies from 0.01 to 1 Hz. In addition, the LSNA-RSNA relationship during stepwise CSP perturbation from 40 to 160 mmHg showed a straight line (r(2) ranged from 0.969 to 0.999). These findings indicate no laterality in the dynamic as well as static baroreflex regulation of LSNA and RSNA as far as grouped axonal activity is concerned.

Adrenergic Fibers↗

PubMed2003

Intravenous angiotensin II does not affect dynamic baroreflex characteristics of the neural or peripheral arc.

Although the elevation of angiotensin II (Ang II) associated with cardiovascular diseases has been considered to suppress the arterial baroreflex function, how Ang II affects dynamic arterial pressure (AP) regulation remains unknown. The aim of the present study was to elucidate the acute effects of Ang II on dynamic AP regulation by the arterial baroreflex. In seven anesthetized Japanese white rabbits, we randomly perturbed intra-carotid sinus pressure (CSP) according to a binary white noise sequence while recording renal sympathetic nerve activity (RSNA) and AP. We estimated the neural arc transfer function from CSP to RSNA and the peripheral arc transfer function from RSNA to AP before and after 30-min intravenous administration of Ang II (100 ng/kg/min). Ang II increased mean AP from 75.7 +/- 3.1 to 95.5 +/- 5.1 mmHg (p < 0.01), while it did not affect mean RSNA (from 5.9 +/- 1.3 to 5.7 +/- 1.2 a.u.). The neural arc transfer functions did not differ before or after Ang II administration (dynamic gain: -0.94 +/- 0.04 vs. -0.94 +/- 0.13, corner frequency: 0.06 +/- 0.01 vs.0.06 +/- 0.01 Hz, pure delay: 0.16 +/- 0.01 vs. 0.17 +/- 0.02 s). The peripheral arc transfer function did not differ before or after Ang II administration (dynamic gain: 1.18 +/- 0.05 vs. 1.06 +/- 0.11, natural frequency: 0.07 +/- 0.01 vs. 0.08 +/- 0.01 Hz, damping ratio: 1.19 +/- 0.06 vs. 1.24 +/- 0.19, pure delay: 0.83 +/- 0.06 vs. 0.78 +/- 0.05 s). Intravenous Ang II hardly affects the dynamic characteristics of neural and peripheral arc around the physiological operating pressure.

Algorithms↗

PubMed2003

Protein kinase C in proliferation and infiltration of eosinophils in nasal polyp.

OBJECTIVE: To explore the significance of protein kinase C (PKC) in proliferation and infiltration of eosinophils in nasal polyps. METHODS: With in situ hybridization and immunohistochemistry staining methods, PKC, pro-apoptotic, and anti-apoptotic gene (Bax, bcl-2) expressions were measured in nasal polyp tissues from 26 patients and inferior turbinate mucosa tissues (ITMTs) from 20 healthy persons. The May-Grünwald-Giemsa (MGG) staining method was used to identify eosinophils. RESULTS: In eosinophils, the positive cell expressive rates of Bcl-2 mRNA and its protein were significantly higher in the group with nasal polyps than in the ITMT group (P < 0.01). Although the positive cell expressive rate of Bax mRNA and associated protein were a little higher in the group with nasal polyp tissues than in the ITMT group, the difference was not significant (P > 0.05). There was PKC expression in the eosinophils of 26 cases of nasal polyps, but occasional PKC expression in 7 of 20 ITMT cases. In the two groups, PKC positive cell expression was significantly different, and the expression of PKC and bcl-2 mRNA as well as associated protein in eosinophils of nasal polyps showed a remarkably positive relationship (r1 = 0.0875, r2 = 0.0823, P < 0.01). CONCLUSIONS: Increased PKC expression in eosinophils of nasal polyp tissues is closely associated with apoptosis inhibition, and it is presumed that eosinophil apoptosis inhibition in nasal polyp tissues is obtained by activation of the PKC signal transduction pathway.

Adult↗

PubMed2002

Genome-wide analysis of gene expression in intestinal-type gastric cancers using a complementary DNA microarray representing 23,040 genes.

To shed light on mechanisms that underlie development and/or progression of intestinal-type gastric cancer, we compared expression profiles of cancer cells obtained by laser-capture microdissection of 20 intestinal-type gastric tumors with expression of genes in corresponding noncancerous mucosae, by a cDNA microarray consisting of 23,040 genes. We identified 61 genes that were commonly up-regulated and 63 that were commonly down-regulated in the cancer tissues. Altered expression of 12 of those genes was associated with lymph node metastasis. A "predictive score," based on expression profiles of five of the genes that were able to distinguish tumors with metastasis from node-negative tumors in our panel, correctly diagnosed the lymph node status of nine additional gastric cancers. This genome-wide information contributes to an improved understanding of molecular changes during the development of intestinal-type gastric cancers. It may help clinicians predict metastasis to lymph nodes and assist researchers in identifying novel therapeutic targets for this type of cancer.

Adenocarcinoma↗

PubMed2002

Input-size dependence of the baroreflex neural arc transfer characteristics.

Static characteristics of the baroreflex neural arc from pressure input to sympathetic nerve activity (SNA) show sigmoidal nonlinearity, whereas its dynamic characteristics approximate a derivative filter where the magnitude of SNA response becomes greater as the input frequency increases. To reconcile the static nonlinear and dynamic linear components, we examined the effects of input amplitude on the apparent linear transfer function of the neural arc. In nine anesthetized rabbits, we perturbed isolated carotid sinus pressure by using binary white noise while varying the input amplitude among 5, 10, 20, and 40 mmHg. With increasing input amplitude, the transfer gain at 0.01 Hz decreased from 1.21 +/- 0.27 to 0.49 +/- 0.28 arbitrary units/mmHg (P < 0.01). Moreover, the slope of the transfer gain between 0.03 and 0.3 Hz decreased from 14.3 +/- 3.7 to 6.5 +/- 2.5 dB/decade (P < 0.01). We conclude that the model consisting of a sigmoidal component following rather than preceding a derivative component explains the observed results and thus can be used as a first approximation of the overall neural arc transfer characteristics.

Acoustic Stimulation↗

PubMed2002

An accurate iterative reconstruction algorithm for sparse objects: application to 3D blood vessel reconstruction from a limited number of projections.

Based on the duality of nonlinear programming, this paper proposes an accurate row-action type iterative algorithm which is appropriate to reconstruct sparse objects from a limited number of projections. The cost function we use is the Lp norm with p approximately 1.1. This norm allows us to pick up a sparse solution from a set of feasible solutions to the measurement equation. Furthermore, since it is both strictly convex and differentiable, we can use the duality of nonlinear programming to construct a row-action type iterative algorithm to find a solution. We also impose the bound constraint on pixel values to pick up a better solution. We demonstrate that this method works well in three-dimensional blood vessel reconstruction from a limited number of cone beam projections.

Algorithms↗