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Biomedical subjects

M C Lee

Publications and source records attributed to M C Lee.

At least 217 records · Page 12Linked to original sources
PubMed1994

Cloning and expression of three abrin A-chains and their mutants derived by site-specific mutagenesis in Escherichia coli.

DNAs encoding of three abrin A-chains were obtained from the cDNA library of Abrus precatorius by polymerase chain reaction and ligated into the expression vector, pGEX-2T. The mature A-chains of abrins a, b and d have been expressed in the cytoplasm of Escherichia coli, and the yield of the soluble recombinant proteins was 7 mg/l induced culture. Three recombinant abrin A-chains were purified to be homogeneity and their N-glycosidase ability to inhibit protein biosynthesis in a cell-free system and to depurinate 28S rRNA in rat liver ribosomes was demonstrated in vitro. The recombinant abrin-a A-chain had the highest N-glycosidase activity among three recombinant abrin A-chains while the recombinant abrin-b A-chain, the least. Three mutants, glutamic-acid-to-alanine replacement (E164A), arginine to leucine (R167L) or double mutation (E164A and R167L) were constructed and expressed. The protein-biosynthesis-inhibitory activity of mutant (E164A), mutant (R167L) and the double mutant was found to be 25-fold, 625-fold and 1250-fold lower than that of wild type, respectively. The results indicated that Arg167 was essential for abrin toxin A-chain catalysis.

Abrin↗
PubMed1994

Stroke and restricted sensory syndromes.

There have been sporadic case reports of a restricted sensory syndrome caused by stroke, most often as a cheiro-oral syndrome. We describe 14 patients with stroke who showed various restricted sensory syndromes and correlated their symptoms with the radiological findings. Twelve had small infarcts and two had haemorrhages; six had lesions in the posterolateral thalamus, five in the pontine tegmentum, one in the lenticulocapsular area, one in the frontoparietal subcortex, and one in the frontal white matter. Sensory abnormalities were in the perioral area, hands, fingers, feet and toes, in various combinations. Two patients with pontine stroke had bilateral sensory abnormalities associated with paramedian lesions. Thus, strokes in the sensory pathways can cause various restricted sensory syndromes of which 'cheiro-oral syndrome' is only one variant. Magnetic resonance imaging is of interest in the clinicoradiological correlation, and helps elucidate the somatotopic pattern of the human sensory pathways.

Adult↗
PubMed1994

Finite element analysis of cerebral contusion.

Finite element analysis was carried out to study the mechanism of cerebral contusion. Clinical findings indicate that most cerebral contusions in the absence of skull fracture occur at the frontal and temporal lobes. To explain these observations, cavitation and shear strain theories have long been advocated. Plane strain finite element models of a parasagittal section of the human head were developed in the present study. The model was first validated against a set of experimental results from the literature. Frontal and occipital impacts were then simulated, and pressure and shear stress distributions in the brain were compared. While comparable negative pressures always developed in the contrecoup regions, shear stress distributions remained nearly identical regardless of the impact direction, consistent with the clinically observed pattern for contusion. Therefore, shear strain theory appears to account better for the clinical findings in cerebral contusion.

Acceleration↗
PubMed1994

Three-dimensional finite element analysis of the effects of posts on stress distribution in dentin.

A finite element analysis was conducted to study the influence of posts on dentinal stress in pulpless teeth. Three-dimensional models of an intact Chinese maxillary central incisor with and without post restoration were analyzed. When the tooth was subjected to masticatory and traumatic loads, stress distributions in dentin were similar whether or not the post was present. Maximal dentinal stresses were reduced by only 7% to 10% and 10% to 14.5%, respectively, with gold alloy and stainless steel posts. Thus the reinforcement effects from posts appeared limited in pulpless incisors.

Alveolar Process↗
PubMed1994

Role of neuropeptides in the regulation of feeding behavior: a review of cholecystokinin, bombesin, neuropeptide Y, and galanin.

The purpose of this report is to provide a review of four peptides (cholecystokinin, bombesin, neuropeptide Y, galanin) and their role in feeding behavior. Cholecystokinin (CCK) and bombesin (BBS) are considered satiety peptides, and neuropeptide Y (NPY) and galanin (GAL) have been proposed as appetite peptides. For the purposes of this review, satiety refers to the physiological cessation of feeding, and appetite refers to the drive to eat and exists in gradations.

Animals↗
PubMed1994

Isolated trigeminal sensory change due to pontine hemorrhage.

Isolated trigeminal sensory change has been rarely described as a manifestation of pontine hemorrhage. We report a 31-year-old man who developed sudden and long-lasting trigeminal sensory disturbances. Brain magnetic resonance imaging showed a hemorrhage in the right lateral pontine tegmentum corresponding to the trigeminal sensory nucleus, and the venous phase angiogram demonstrated abnormal vascular structures. Pontine hemorrhage secondary to venous malformation can be one of the causes of isolated trigeminal sensory change.

Adult↗
PubMed1994

Writing tremor after discrete cortical infarction.

BACKGROUND: Hand tremor is a rare manifestation of stroke, and writing tremor has not been reported to be produced by stroke. We describe a patient who developed a unilateral hand tremor mimicking primary writing tremor after discrete cerebral cortical infarction. CASE DESCRIPTION: A 67-year-old man developed mild right hemiparesis. Brain magnetic resonance imaging showed a discrete cortical infarct in the left frontal area. After recovery of motor power, the patient showed significant right hand tremor exclusively during writing or similar motor activities including tooth brushing or shaving. The tremor was temporarily alleviated by clonazepam but persisted until 7 months of follow-up. Medical history suggested that the patient had mild essential tremor, but he did not experience tremor on writing before the onset of stroke. CONCLUSIONS: This observation suggests that unilateral hand tremor mimicking primary writing tremor may be produced by cortical infarction. It remains unclear whether the patient's previous essential tremor played an additional role in the development of this symptom.

Aged↗
PubMed1994

Spectrum of lateral medullary syndrome. Correlation between clinical findings and magnetic resonance imaging in 33 subjects.

BACKGROUND AND PURPOSE: Computed tomography is insufficient in evaluation of medullary lesions. Although lateral medullary infarction is a relatively common type of cerebrovascular disease, detailed correlation between clinical findings and magnetic resonance imaging (MRI) has not yet been reported. METHODS: We studied 33 consecutive patients with lateral medullary infarction who showed appropriate MRI lesions and correlated their clinical findings with the MRI results. RESULTS: Gait ataxia (88%), vertigo/dizziness (91%), nausea/vomiting (73%), dysphagia (61%), hoarseness (55%), Horner sign (73%), and facial (85%) and hemibody (94%) sensory changes were frequent clinical findings. MRI results showed that the lesions located in the rostral part of the medulla were usually diagonal band-shaped and were associated with more severe dysphagia, hoarseness, and the presence of facial paresis, whereas the caudal lesions, situated usually in the lateral surface of the medulla, appeared to correlate with more marked vertigo, nystagmus, and gait ataxia. Nausea/vomiting and Horner sign were common regardless of the lesion location, and lesions extending ventromedially correlated with facial sensory change on the contralateral side of the lesion. CONCLUSIONS: Analysis of MRI findings in rostrocaudal and dorsoventral aspects allows us, although not unequivocally, to make anatomicoclinical correlations in the evaluation of patients with lateral medullary stroke syndrome.

Adult↗
PubMed1994

Small primary intracerebral hemorrhage. Clinical presentation of 28 cases.

BACKGROUND: Although there have been sporadic reports of patients with small intracerebral hemorrhages presenting with discrete clinical features, the clinical and distributional characteristics of these hemorrhages have not been adequately investigated. CASE DESCRIPTIONS: We studied 28 patients who had primary intracerebral hemorrhage of a longest diameter < or = 1.5 cm as seen in computed tomographic scan and/or magnetic resonance imaging. Small primary intracerebral hemorrhages were found in the basal ganglia in 8 patients (2 with intraventricular hemorrhage), the posterior limb of the internal capsule in 8, the area of the fourth ventricle of the cerebellum in 7 (5 with intraventricular hemorrhage), the pontine tegmentum in 4, and the thalamomesencephalic area in 1. All patients except 3 were hypertensive, suggesting that most of the hemorrhages may have occurred because of rupture of small end arteries secondary to long-standing hypertension. Depending on their location, the hemorrhages clinically manifested as pure motor stroke in 7, pure sensory stroke in 6, vertigo/ataxia in 7, sensorimotor stroke in 4, and ataxic hemiparesis in 2 patients. One patient with thalamomesencephalic hemorrhage showed vertical gaze disturbance, and 1 with basal ganglionic hemorrhage presented with symptoms of acute hydrocephalus secondary to a relatively large amount of intraventricular hemorrhage. The prognosis of small intracerebral hemorrhage was generally excellent except for when patients were very old or when there was a significant amount of intraventricular bleeding. CONCLUSIONS: Small primary intracerebral hemorrhage has its predilection sites: basal ganglia, posterior limb of the internal capsule, area of the fourth ventricle of the cerebellum, and pontine tegmentum. Most of the hemorrhages are probably caused by rupturing of the small end arteries in the setting of chronic hypertension. They produce discrete clinical syndromes often mimicking classic lacunar syndrome, of which pure sensory stroke is relatively common.

Adult↗
PubMed1994

Poor renal uptake of technetium-99m-DMSA and technetium-99m-MDP in a patient with Fanconi syndrome and near normal glomerular filtration rate.

We present a patient with Fanconi syndrome who demonstrated poor renal uptake of 99mTc-DMSA and high urinary concentration of the tracer. A 99mTc-DTPA scan was normal and the creatinine clearance only minimally decreased. These findings suggest that 99mTc-DMSA may be accumulated in the kidney by glomerular filtration and subsequent tubular reabsorption, with the nonabsorbed fraction appearing in the urine. In Fanconi Syndrome the tubular reabsorption of DMSA may also be reduced, thus explaining the poor renal uptake in this patient. A 99mTc-MDP bone scan showed faint renal uptake and diffuse high uptake mainly in the spine, demonstrating that the metabolic bone disease associated with Fanconi Syndrome can be another mechanism for poor renal visualization on bone scan.

Fanconi Syndrome↗
PubMed1994

The biologic role of ganglioside in neuronal differentiation--effects of GM1 ganglioside on human neuroblastoma SH-SY5Y cells.

Human neuroblastoma SH-SY5Y cell is a cloned cell line which has many attractive features for the study of neuronal proliferation and neurite outgrowth, because it has receptors for insulin, IGF-I and PDGF. Gangliosides are sialic acid containing glycosphingolipids which form an integral part of the plasma membrane of many mammalian cells. They inhibit cell growth mediated by tyrosine kinase receptors and ligand-stimulated tyrosine kinase activity, and autophosphorylation of EGF(epidermal growth factor) and PDGF receptors. The experiment was designed to study the effects of GM1 ganglioside on growth of human neuroblastoma SH-SY5Y cells stimulated with trophic factor in vitro. The cells were plated in Eagle's minimum essential medium without serum. The number and morphologic change of SH-SY5Y cells were evaluated in the serum free medium added GM1 ganglioside with insulin or PDGF. SH-SY5Y cells were maintained for six days in serum-free medium, and then cultured for over two weeks in serum-free medium containing either insulin or PDGF. The effect of insulin on cell proliferation developed earlier and was more potent than that of PDGF. These proliferative effects were inhibited by GM1 ganglioside, and the cells showed prominent neurites outgrowth. These findings suggest that GM1 ganglioside inhibits the cell proliferation mediated by tyrosine kinase receptors and directly induces neuritogenesis as one of the neurotrophic factors.

Cell Differentiation↗
PubMed1994

Modulation of transglutaminase expression in rat skeletal muscle by induction of atrophy and endurance training.

The persistence of muscle fiber number regardless of size reduction in muscle atrophy has not yet been fully explained. For the mechanism inherent in skeletal muscle tissues for preventing cellular death, the protective function of muscle tissue through transglutaminases has been tested, since the enzyme is responsible for structural stabilization and participates in signal transduction. In the present experiment, hindlimb suspension for two weeks caused a marked muscle atrophy in Wistar female rats. Comparison of muscle weight and histological analysis showed that suspension-induced atrophy in the hindlimb was more prominent in the soleus muscle, comprised mainly of type I fiber than that in the plantaris muscle of type II fibers. The immunohistochemical analysis with antitransglutaminase C antibody (anti TGase C Ab) showed that some atrophic bundles of soleus muscle were positively reacted with the antibody. The anti-TGase C Ab-reactive substances were observed to disappear significantly after endurance exercise, indicating their characteristic atrophy-dependency. The enzymatic analysis of transglutaminase showed the increase in activity in the atrophic soleus muscle tissue, compared with that in the normal or exercise-trained muscle tissues. From these results, the expression of TGase in the atrophic muscle is suggested to be the possible marker for muscle atrophy and its expression is probably related with the protective mechanism of the muscle tissue to prevent further cellular damage in the atrophic process.

Animals↗
PubMed1994

Tumor concentration and distribution of carcinoembryonic antigen measured by in vitro quantitative autoradiography.

UNLABELLED: One of the most critical factors in successful immunoscintigraphy and radioimmunotherapy is the local concentration and distribution of the target antigen. The purpose of this study was to evaluate the concentration and distribution of carcinoembryonic antigen (CEA) in various carcinomas. METHODS: In vitro quantitative autoradiography was performed in carcinomas of the stomach (32 cases), colon (20 cases), breast (29 cases) and lung (26 cases). Frozen tumor sections were incubated with varying concentrations of 125I-labeled monoclonal antibody (Mab) CEA-79.1 (IgG2a), which is specific for CEA. Digitized autoradiographic images from these sections were compared to adjacent H & E and immunoperoxidase-stained sections. Computer analysis of specific antibody binding quantitated the maximal value (Bmax), which is equal to the concentrations of CEA. RESULTS: Stomach cancer expressed CEA in 31 cases (97%). All colon cancer specimens exhibited CEA and breast cancer expressed CEA in 24 cases (83%). In adenocarcinoma of the lung, CEA was measured in all specimens. The concentration of CEA did not vary significantly among the pathologic types or among the various degrees of differentiation in each carcinoma. CEA was expressed homogeneously in adenocarcinomas of the colon and lung. However, CEA exhibited a heterogeneous distribution in a significant number of breast cancer (42%) and bronchogenic squamous-cell carcinoma (78%) specimens. CONCLUSIONS: CEA was expressed in most cases of stomach, colon, breast and lung carcinomas. These carcinomas, however, exhibited wide variation in the concentration and distribution of CEA expression. The concentration and distribution of CEA in a particular tumor type should be considered before undertaking tumor targeting methods.

Adenocarcinoma↗
PubMed1993

Cloning and expression of the gene encoding Acacia confusa trypsin inhibitor that is active without post-translational proteolysis.

A recombinant plasmid containing the coding regions for Acacia confusa trypsin inhibitor (ACTI) has been constructed and expressed in Escherichia coli cells, as a fusion protein between ACTI and glutathione S-transferase (GST). The GST-fusion was produced as a soluble protein which did not require denaturing agents such as urea to solubilize it. The recombinant ACTI (reACTI) was obtained by treating the GST-fusion protein with thrombin. Both the reACTI and fusion protein have a strong inhibitory effect on trypsin activity without post-translational proteolysis.

Acacia↗
PubMed1993

Primary structure of three distinct isoabrins determined by cDNA sequencing. Conservation and significance.

A family of toxic proteins, the isoabrins, which possess N-glycosylase activity toward eukaryotic 28 S r-RNA, may have potential use in cancer chemotherapy. By polymerase chain reaction techniques, cDNA clones of three isoabrins, carrying A and B-chain sequences, were isolated and their nucleotide sequences were determined. The isoabrins consist of an A-chain comprised of 250 of 251 amino acids, followed by a 10 amino acid linker and a B-chain of 267 amino acids. There is substantial conservation in the B-chain of the three isoabrins, with less than six amino acid substitutions, whereas as many as 46 amino acid substitutions occur in the A-chains. Based on the relationships between the biological activities and the putative amino acid sequences of the isoabrins, three isoabrins, abrin-a, -b and -d, could be identified and the potential epitope of immunological response of these isoabrins could be assigned.

Abrin↗
PubMed1993

Independent control of reflex and volitional EMG modulation during sinusoidal pursuit tracking in humans.

It is well known that during volitional sinusoidal tracking the long-latency reflex modulates in parallel with the volitional EMG activity. In this study, a series of experiments are reported demonstrating several conditions in which an uncoupling of reflex from volitional activity occurs. The paradigm consists of a visually guided task in which the subject tracked a sinusoid with the wrist. The movement was perturbed by constant torque or controlled velocity perturbations at 45 degrees intervals of the tracking phase. Volitional and reflex-evoked EMG and wrist displacement as functions of the tracking phase were recorded. The relationship of both short-latency (30-60 ms) and longer-latency (60-100 ms) reflex components to the volitional EMG was evaluated. In reflex tracking, the peak reflex amplitude occurs at phases of tracking which correspond to a maximum of wrist joint angular velocity in the direction of homonymous muscle shortening and a minimum of wrist compliance. Uncoupling of the reflex and volitional EMG was observed in three situations. First, during passive movement of the wrist through the sinusoidal tracking cycle perturbation-evoked long-latency stretch reflex peak is modulated as for normal, volitional tracking. However, with passive joint movement the volitional EMG modulation is undetectable. Second, a subset of subjects demonstrate a normally modulated and positioned long-latency reflex with a single peak. However, these subjects have distinct bimodal peaks of volitional EMG. Third, the imposition of an anti-elastic load (positive position feedback) shifts the volitional EMG envelope by as much as 180 degrees along the tracking phase when compared with conventional elastic loading. Yet the long-latency reflex peak remains at its usual phase in the tracking cycle, corresponding to the maximal velocity in the direction of muscle shortening. Furthermore, comparison of the results from elastic and anti-elastic loads reveals a dissociation of short- and long-latency reflex activity, with the short-latency reflex shifting with the volitional EMG envelope. Comparable results were also obtained for controlled velocity perturbations used to control for changes in joint compliance. The uncoupling of the reflex and volitional EMG activity in the present series of experiments points to a flexible relationship between reflex and volitional control systems, altered by peripheral input and external load.

Adult↗