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Biomedical subjects

E Tan

Publications and source records attributed to E Tan.

At least 19 recordsLinked to original sources
PubMed2002

Mutations in GDAP1: autosomal recessive CMT with demyelination and axonopathy.

BACKGROUND: Mutations in the ganglioside-induced differentiation-associated protein 1 gene (GDAP1) were recently shown to be responsible for autosomal recessive (AR) demyelinating Charcot-Marie-Tooth disease (CMT) type 4A (CMT4A) as well as AR axonal CMT with vocal cord paralysis. METHODS: The coding region of GDAP1 was screened for the presence of mutations in seven families with AR CMT in which the patients were homozygous for markers of the CMT4A locus at chromosome 8q21.1. RESULTS: A nonsense mutation was detected in exon 5 (c.581C>G, S194X), a 1-bp deletion in exon 6 (c.786delG, G262fsX284), and a missense mutation in exon 6 (c.844C>T, R282C). CONCLUSIONS: Mutations in GDAP1 are a frequent cause of AR CMT. They result in an early-onset, severe clinical phenotype. The range of nerve conduction velocities (NCV) is variable. Some patients have normal or near normal NCV, suggesting an axonal neuropathy, whereas others have severely slowed NCV compatible with demyelination. The peripheral nerve biopsy findings are equally variable and show features of demyelination and axonal degeneration.

Age of Onset↗
PubMed2002

Gender and pramipexole effects on levodopa pharmacokinetics and pharmacodynamics.

The authors studied the pharmacokinetics of levodopa (LD) with and without pramipexole (PPX) in men and postmenopausal women with PD. Patients on stable dose of carbidopa/LD were randomized to receive escalating doses of placebo or PPX over 7 weeks. LD and PPX pharmacokinetics were performed after a single test dose 25/100 of carbidopa/LD, before initiation of PPX or placebo, at 1.5 mg/d and 4.5 mg/d of PPX or placebo. Compared to men, women had greater LD bioavailability. PPX did not alter LD bioavailability, and PPX pharmacokinetics were equivalent in men and women.

Aged↗
PubMed2002

Azathioprine in severe adult atopic dermatitis: a double-blind, placebo-controlled, crossover trial.

BACKGROUND: There is a limited range of treatments for severe atopic dermatitis (AD). Azathioprine has often been used but there has been no randomized controlled trial of this drug to confirm its efficacy in AD. OBJECTIVES: To establish or refute the efficacy of azathioprine in severe AD. To investigate the safety and tolerability of azathioprine in this patient population. METHODS: We performed a double-blind, randomized, placebo-controlled, crossover trial of azathioprine in adult patients with severe AD. Each treatment period was of 3 months' duration. Treatments were azathioprine 2.5 mg kg(-1) day(-1) and matched placebo. Disease activity was monitored using the SASSAD sign score. In addition, severity of pruritus, sleep disturbance and disruption of work/daytime activity were monitored using visual analogue scales. Adverse events were recorded and haematological and biochemical monitoring was performed. RESULTS: Thirty-seven subjects were enrolled, mean age 38 years (range 17-73). Sixteen were withdrawn, 12 during azathioprine treatment and four during placebo treatment. The SASSAD score fell by 26% during treatment with azathioprine vs. 3% on placebo (P < 0.01). Pruritus, sleep disturbance and disruption of work/daytime activity all improved significantly on active treatment but not on placebo. The difference in mean improvement between azathioprine and placebo was significant for disruption of work/daytime activity (P < 0.02) but not for pruritus or sleep disturbance. Gastrointestinal disturbances were reported by 14 patients during azathioprine treatment and four were withdrawn as a result of severe nausea and vomiting. Leukopenia was observed in two patients and deranged liver enzymes in eight during treatment with azathioprine. CONCLUSIONS: Azathioprine is an effective and useful drug in severe AD although it is not always well-tolerated. Monitoring of the full blood count and liver enzymes is advisable during treatment.

Adolescent↗
PubMed2001

Focal myopathy mimicking posterior interosseous nerve syndrome.

A 25-year-old man developed weakness of extension of the right index, middle, and fourth fingers at the metacarpophalangeal joints, over 2 years. No sensory deficit was present. Nerve conduction studies, including the right radial nerve, were within normal limits. Needle electromyographic (EMG) examination showed myopathic changes that were limited to the right extensor digitorum communis and extensor indicis proprius muscles. An intravenous edrophonium chloride test had no effect on weakness and repetitive stimulation showed no significant decremental response. An EMG-guided open biopsy of the extensor digitorum communis muscle revealed severe myopathic changes. Evaluation for the cause of myopathic involvement was negative. After 13 months, clinical examination and electrophysiological studies showed no significant progression. This case exemplifies the fact that a focal myopathy may mimic an entrapment neuropathy.

Adult↗
PubMed2001

Transgenic Bcl-2 expressed in photoreceptor cells confers both death-sparing and death-inducing effects.

To examine its potential role within the retina as a modulator of cell death and photoreceptor degeneration, bcl-2 expression was targeted to the photoreceptors of transgenic mice by the human IRBP promoter. Three transgenic families were established, with levels of transgene expression between 0.2 and two-fold relative to that of endogenous bcl-2. The effect of bcl-2 expression on genetically programmed photoreceptor degeneration was evaluated by crossing these transgenic mice with mice that develop a rapid degeneration of rod photoreceptors due to expression of a distinct transgene, SV40 T antigen (Tag). Transgenic Bcl-2 was localized to photoreceptor inner segments and was capable of abrogating the activation of caspase activity and the resulting cell death associated with ectopic expression of Tag. However, Bcl-2 itself ultimately caused photoreceptor cell death and retinal degeneration. Several proteins not expressed normally in Tag or other transgenic retinas undergoing photoreceptor degeneration were induced in the Bcl-2 transgenic retinas. Analysis by mass spectroscopy identified one of these proteins as alphaA-crystallin, a member of a protein family that associates with cellular stress. Since Bcl-2 can promote as well as spare cell death in the same photoreceptor population, its potential utility in ameliorating photoreceptor death in human hereditary blinding disorders is compromised.

Animals↗
PubMed2001

Free radical changes in rat muscle tissue after exercise.

Intense exercise accompanied by a manifold increase in oxygen utilization over resting conditions has been shown to elevate the probability of the appearance of free radicals. One of the effects of free radicals appears to be the peroxidation of cell membrane lipids resulting in malondialdehyde formation, which is detrimental to cell function. A common method for the measurement of malondialdehyde involves a reaction with thiobarbituric acid. The aim of this study was to evaluate the influence of exercise on concentrations of thiobarbituric acid-reactive substances (TBARS) in the gastrocnemius and soleus muscles of rats. Thirty male rats were used in this study. Soleus and gastrocnemius muscle biopsies were performed and TBARS levels were studied in these two muscles. The rats were randomly assigned to three groups of ten each. Group A was the control group and did not perform exercise. In group B, gastrocnemius and soleus muscle biopsies were performed immediately after exercise, and in group C muscle biopsies were performed on the 2nd postexercise day. The exercise resulted in a significant increase in TBARS in the gastrocnemius muscle. In the soleus, TBARS also increased, but this was not statistically significant. In conclusion, exercise-induced free radical changes may depend on the muscle type studied.

Animals↗
PubMed2001

Acute bilateral cerebellar infarction in the territory of the medial branches of posterior inferior cerebellar arteries.

The most frequent type of cerebellar infarcts involved the posterior inferior cerebellar artery (PICA) and superior cerebellar artery territories but bilateral involvement of lateral or medial branches of PICA is extremely rare. In this report, we present a 55-year-old male who admitted to hospital with vomiting, nausea and dizziness. On examination left-sided hemiparesia and ataxic gait were detected. Infarct on bilateral medial branch of PICA artery territories was found out with cranial magnetic resonance imaging (MRI) technique and 99% stenosis of the left vertebral artery was found out with digital subtraction arteriography. The patient was put on heparin treatment. After 3 weeks, his complaints and symptoms had disappeared except for mild gait ataxia.

Acute Disease↗
PubMed2001

Cremaster muscle is not sexually dimorphic, but that from boys with undescended testis reflects alterations related to autonomic innervation.

BACKGROUND/PURPOSE: The genitofemoral nerve and its motor neuron are known to be sexually dimorphic. An association has been suggested to exist between antiandrogen-induced undescended testis and the genitofemoral nerve. Therefore, the cremaster muscles (CM) from boys and girls with inguinal hernia and boys with undescended testis were compared to evaluate the failed descent through sexual dimorphism. METHODS: Samples of CM were obtained from 10 boys and 10 girls with inguinal hernia and 10 boys with undescended testis. Sections were stained for ATPase reactions after acid and alkaline preincubations, and for the expression of myosine heavy chains. The percentages of type 1 and type 2 fibers, and mean diameters of fibers according to the types were determined for each group. Values were compared through Mann-Whitney U test, and P values less than .05 were considered to be significant. RESULTS: CM have mainly been composed of type 1 fibers. Distributions of type 1 and 2 fibers have not shown a difference among groups. Mean diameters of both type 1 and type 2 fibers from girls (P < .05), and mean diameter of type 2 fibers from boys with undescended testis have been significantly smaller than those encountered in boys with inguinal hernia (P < .05). CONCLUSIONS: Although the mean diameter of type 1 fibers from boys with undescended testis has been as large as those encountered in boys with inguinal hernia, mean diameter of type 2 fibers has been as small as those encountered in girls. Among various reasons to selectively diminish the size of type 2 fibers, lack of beta adrenergic effect appears to be the most satisfactory explanation. J Pediatr Surg 36:877-880.

Autonomic Nervous System↗
PubMed2001

Myasthenia gravis and lymphoblastic lymphoma involving the thymus: a rare association.

Myasthenia gravis (MG) is an autoimmune neuromuscular junction disease. An association between thymic epithelial neoplasms and MG is well known. However, it is rarely associated with hematologic malignancies. In particular, very few cases of lymphoblastic lymphoma involving the thymus and MG have been reported. Here we report a case T-cell lymphoblastic lymphoma involving the thymus who developed MG after the initial diagnosis. The patient initially presented with a mediastinal mass which was diagnosed as lymphoblastic lymphoma. MG was diagnosed during leukemic relapse in this patient and was based on clinical presentation and neurophysiologic studies including single fiber electromyography (EMG) and repetitive nerve stimulation tests. In contrast to the other cases with such an association, the myasthenic symptoms presented nine months after the diagnosis of lymphoma by thymectomy. The patient had a highly aggressive clinical course and was resistant to various chemotherapy regimens.

Adult↗
PubMed2001

Sulfation is rate limiting in the futile cycling between estrone and estrone sulfate in enriched periportal and perivenous rat hepatocytes.

The metabolic activities and tissue binding of estrone (E1) and estrone sulfate (E1S) on futile cycling were examined. Desulfation of E1S in the 9000g supernatant fraction (S9) of periportal (PP) and perivenous (PV) rat hepatocytes were of similar V (2.9 +/- 1.0 and 2.4 +/- 0.9 nmol/min/mg of S9 protein), K (30.4 +/- 8.3 and 34.8 +/- 6.6 microM), and desulfation intrinsic clearances (V/K of 77 and 55 microl/min/10(6) cells). The intrinsic clearance towards E1 sulfation (1 microM) in cytosolic preparations of PV hepatocytes was 4 times that of PP hepatocytes (V/K of 26.4 +/- 9.5 versus 6.1 +/- 2.2 microl/min/mg of cytosolic protein or 13 +/- 5 versus 3.1 +/- 1.1 microl/min/10(6) cells). The observation was consistent with the immunolocalization of estrogen sulfotransferase (PV/PP ratio of 3.4 +/- 1.1) but not hydroxysteroid sulfotransferase (PV/PP ratio of 0.29 +/- 0.21) nor phenol sulfotransferase (PV/PP ratio of 1.13 +/- 0.23). Upon incubation of E1S (1-125 microM) with hepatocytes (30 min), higher concentrations of E1S and E1 were observed within PP than in PV cells, and saturation was evident at the higher concentrations. Based on the in vitro metabolic and tissue binding parameters for E1S and E1 and the published zonal uptake clearances of E1S (116 microl/min/10(6) cells), fitting revealed that uptake of E1 (1484 and 1463 microl/min/10(6) cells) by PP and PV cells was rapid and similar, and E1 sulfation was the slowest step in futile cycling. The greater metabolism of E1 in PV region led to higher levels of E1 and E1S in PP hepatocytes, and the nonlinear uptake, binding, and vesicular accumulation of E1S resulted in different t(1/2) values for E1S and E1.

Animals↗
PubMed2001

The relationship between opsin overexpression and photoreceptor degeneration.

PURPOSE: To characterize the process by which overexpression of normal opsin leads to photoreceptor degeneration. METHODS: Three transgenic mouse lines were generated that express different levels of an opsin with three amino acid modifications at the C terminus. These modifications created an epitopic site that can be readily distinguished from the endogenous protein using a bovine opsin-specific antibody. Evidence of degeneration associated with opsin overexpression was provided by anatomic studies and electroretinogram (ERG) recordings. Western blot analysis was used to confirm the production of the transgenic opsin, and an enzyme-linked immunosorbent assay (ELISA) was used to determine the amounts of opsin overexpressed in each line. Immunocytochemistry was used to determine the cellular localization of transgenic opsin. Amounts of 11-cis retinal were determined by extraction and high-performance liquid chromatography (HPLC). RESULTS: Opsin expression levels in the three lines were found to be 123%, 169%, and 222% of the level measured in nontransgenic animals, providing direct correlation between the level of transgene expression and the severity of the degenerative phenotype. In the lower expressing lines, ERG a-wave amplitudes were reduced to less than approximately 30% and 15% of normal values, whereas responses of the highest expressing line were indistinguishable from noise. In the lowest expressor, a 26% elevation in 11-cis retinal was observed, whereas in the medium and the high expressors, 11-cis retinal levels were increased by only 30% to 33%, well below the 69% and 122% increases in opsin levels. CONCLUSIONS: The overexpression of normal opsin induces photoreceptor degeneration that is similar to that seen in many mouse models of retinitis pigmentosa. This degeneration can be induced by opsin levels that exceed by only approximately 23% that of the normal mouse retina. Opsin overexpression has potential implications in retinitis pigmentosa.

Amino Acid Sequence↗
PubMed2001

Futile cycling of estrone sulfate and estrone in the recirculating perfused rat liver preparation.

The futile cycling of estrone sulfate (E(1)S) and estrone (E1) was investigated in the recirculating, perfused, rat liver preparation. Although E(1)S was not distributed into bovine erythrocytes, the compound was highly bound to albumin [4% bovine serum albumin (BSA), unbound fraction of 0.03 +/- 0.01]. By contrast, E1 was bound and metabolized to estradiol (E2) by bovine erythrocytes, with metabolic clearances of 0.061 to 0.069 ml/min when normalized to the hematocrit. Due to strong binding of E1 to albumin, BSA (4%) greatly reduced the red cell clearance to a minimum (0.0024 to 0.0031 ml/min/unit of hematocrit). Despite the low unbound fractions of E(1)S (0.027 +/- 0.004) and E1 (0.036 +/- 0.006), clearances of the simultaneously delivered tracers [(3)H]E(1)S and [(14)C]E1 in perfusate (4% BSA and 20% erythrocytes) by the recirculating, perfused rat liver (flow rate of 0.91 +/- 0.1 ml/min/g of liver) were high (0.53 +/- 0.08 and 0.85 +/- 0.2 ml/min/g of liver, respectively). Although low levels of [(3)H]E1 were observed following the tracer [(3)H]E(1)S, both parent and metabolite species displayed similar decay half-lives that were characteristic of compounds undergoing futile cycling. The same decay profile was observed for [(14)C]E(1)S but the half-life of administered [(14)C]E1 was shorter in comparison. A series-compartment liver model that incorporated previously noted heterogeneity in estrone sulfation and glucuronidation activities among periportal and perivenous hepatocytes, and homogeneity in sinusoidal transport and desulfation was used to explain the discrepant half-lives. The model described a high partitioning of E1 in the endoplasmic reticulum and the segregation of estrone sulfation activities in the cytosolic space from the desulfation and glucuronidation activities in the endoplasmic reticulum space.

Animals↗
PubMed2001

Malignant melanoma seen in a tertiary dermatological centre, Singapore.

INTRODUCTION: Primary malignant melanoma is an uncommon skin tumour in Singapore compared with the Western countries. The clinical characteristics of melanoma have been rarely reported in Asians. OBJECTIVES: Our purpose was to study the incidence, clinical characteristics and risk factors of biopsy proven malignant melanoma seen in a tertiary referral skin hospital. METHODS: Case records of patients with histology proven malignant melanoma from January 1989 to December 1998 were retrieved. Patients were interviewed and a complete skin and systemic examination was performed. Data on demographics, histological types, clinical characteristics and risk factors were collated. RESULTS: Between 1989 and 1998, 27 patients were diagnosed with histology proven malignant melanoma. There was a predominance of Chinese with a female to male ratio of 1.3:1. There was a mean lag period of 1.6 years to diagnosing melanoma and there is a general lack of knowledge among the local patients. Most of the lesions (89%) occurred on the extremities. Acral lentiginous melanoma (41%) and nodular melanoma (41%) were the two commonest histologic types. Of the nodular melanomas, 64% were observed in patients below 50 years (64%) while majority of the acral lentiginous melanomas occurred in those above 50 years (91%). In terms of risk factors, we reported a high prevalence of diabetes mellitus with acral lentiginous melanoma. CONCLUSIONS: This study highlighted interesting aspects in terms of clinical characteristics and risk factors in our local patients. It also served as a remainder of the need to raise awareness among the public and medical community of skin cancers or melanomas as they are potentially treatable if detected early.

Adolescent↗
PubMed2001

[Toxicity of different pesticides to Haemadipsa hainana and its control].

Laboratory determination on the toxicity of sumicidin, isoprocarb, dicofol, thiocyclam, dimethoate and glyphosate to Haemadipsa hainana showed that LD50 for the six pesticides followed the order of sumicidin > isoprocarb > dicofol > thiocyclam > dimethoate, but glyphosate was not virulent. "Glyphosate + sumicidin" had much more toxicity. The susceptibility of H. hainana to sumicidin differed in the order of adult > juvenile > subadult. Field tests showed that the control effect of 1.5% sumicidin to H. hainana was 95.08% of total number of its population. Applied tests showed that the control effect of "Glyphosate + 0.5% sumicidin" was 94.7%, and "glyphosate + 1% isoprocarb" was 90.5%. "Glyphosate + pesticides" was more effective both in controlling H. hainana and in destroying its habitat weed.

Animals↗
PubMed2000

Distribution and morphometry of fiber types in cremaster muscles of boys with inguinal hernia or undescended testis.

In the present study, we determined and compared the distribution and mean diameters of fiber in the cremaster muscles (CM) of boys with either inguinal hernia (IH) or undescended testis (UT). Samples of CM were obtained from 20 patients (10 boys with IH, and 10 boys with UT) of similar age. The CM muscles of two boys each, without inguinal pathology, were sampled during autopsy. Sections were stained for oxidative and glycolytic enzymes, as well as for ATP-ase reactions after acid (pH: 4.6) and alkaline (pH: 10.6) preincubations. Specimens were also analyzed morphometrically using a KONTRON 400 computerized image analysis system. The Mann- Whitney U test was applied to compare the percentages of fiber types and mean diameters of fibers according to the types of the CM of boys with IH or UT. In boys, the CM is mainly composed of type 1 fibers. The CMs of patients with UT reveal alterations of neurogenic origin. Although both type 1 and type 2 fibers reveal alterations, type 2 fibers appear to be affected more profoundly and characterized by significantly decreased mean diameters. Significantly decreased mean diameters of type 2 fibers in CM may support disuse, lack of sensitivity to the hormonal influences, or an alteration in the corticospinal tracts of boys with UT.

Child↗