Biomedical subjects

G Singh

Publications and source records attributed to G Singh.

At least 145 records · Page 8Linked to original sources

PubMed2000

General and efficient syntheses of C(18)-4,8-sphingadienines via S(N)2'-type homoallylic coupling reactions mediated by thioether-stabilized copper reagents.

The stereoselective syntheses of C(18)-4,8-sphingadienines 3 and 4 as analogues of sphingosine 1 are described. The key step in these syntheses involved a novel S(N)2'-type homoallylic coupling reaction between the corresponding thioether-stabilized allylic copper reagents and the allylic mesylate 7. The thioether-stabilized allylic copper reagents were easily prepared and retained the configuration of their double bond during the coupling reactions, thus overcoming the problem of isomerization which was normally associated with the use of allylic organometallic reagents in such applications.

Allyl Compounds↗

PubMed2000

A simple polar deacetylated caloporoside derivative is a positive modulator of the GABA(A) chloride channel complex in cortical mammalian neurones.

Synthesis of octyl-O-beta-D-mannopyranoside, a caloporoside analogue was achieved by the activation of 2,3,4,6-rerra-O-benzyl-1-O-1',3'2'-dioxaphosphacyclohexane-a lpha,beta-D-mannopyranosyl-2-oxide with TMSOTf (Trimethyl silyl triflate) and subsequent debenzylation. At 100 microM the molecule significantly and reversibly increased the magnitude of GABA(A) currents evoked in cultured rat pyramidal neurones whilst concomitantly reducing the incidence of spontaneous synaptic activity. These results contradict earlier proposals that such molecules bind to the TBPS (tert-Butylbicyclophosphorothionate) site to block the chloride channel.

Acetylation↗

PubMed2000

Liquid chromatography/electron capture atmospheric pressure chemical ionization/mass spectrometry: analysis of pentafluorobenzyl derivatives of biomolecules and drugs in the attomole range.

The corona discharge used to generate positive and negative ions under conventional atmospheric pressure chemical ionization conditions also provides a source of gas-phase electrons. This is thought to occur by displacement of electrons from the nitrogen sheath gas. Therefore, suitable analytes can undergo electron capture in the gas phase in a manner similar to that observed for gas chromatography/electron capture negative chemical ionization/mass spectrometry. This technique, which has been named electron capture atmospheric pressure chemical ionization/mass spectrometry, provided an increase in sensitivity of 2 orders of magnitude when compared with conventional atmospheric pressure chemical ionization methodology. It is a simple procedure to tag many biomolecules and drugs with an electron-capturing group such as the pentafluorobenzyl moiety before analysis. Pentafluorobenzyl derivatives have previously been used as electron capturing derivatives because they undergo dissociative electron capture in the gas phase to generate negative ions through the loss of a pentafluorobenzyl radical. A similar process was found to occur under electron capture atmospheric pressure chemical ionization conditions. By monitoring the negative ions that were formed, it was possible to obtain attomole sensitivity for pentafluorobenzyl derivatives of a representative steroid, steroid metabolite, prostaglandin, thromboxane, amino acid, and DNA-adduct.

Chromatography, Liquid↗

PubMed2000

Pathophysiologic interactions in skeletal metastasis.

BACKGROUND: This review summarizes evidence that the formation of bone metastases is the result of multiple synergistic cellular and molecular interactions between metastatic cells and the unique microenvironment in bone. METHODS: Molecular technologies have been used to detect cancer cells in bone and to define their genotypic and phenotypic properties. Bone organ cultures have been employed to analyze the ability of tumor cells to modulate bone resorption and to study the effects of resorption products on the phenotypic properties of cancer cells. Experimental models of bone metastasis provide the ability to examine the effects of modulating specific host or tumor properties in vivo by quantifying their effects on the formation of bone tumors. RESULTS: By means of the blood stream, cells from many common neoplasms seed bone marrow as an early clinical event. The subsequent growth of these cells into clinically significant metastatic lesions is associated with their ability to stimulate bone resorption through osteoclasts and macrophages or through a direct action on bone. In turn, the products of bone resorption, which include matrix-derived growth factors, act on the tumor cells to stimulate the expression of properties that promote their metastatic competence. These include the induction of integrin adhesion molecules, the stimulation of cell motility and chemotaxis, the enhanced expression of matrix metalloproteinases, and the stimulation of tumor cell growth. CONCLUSIONS: The interdependency of tumor cells and bone was recognized by Steven Paget over 100 years ago, and it provides a rational basis for the development of current therapeutic strategies against bone metastasis.

Bone Neoplasms↗

PubMed2000

Risk of seizures and neurocysticercosis in household family contacts of children with single enhancing lesions.

A small, single enhancing lesion (SEL) is often noted upon computed tomography (CT) in children and young adults with recent focal or generalized seizures. A high frequency of seizures has been reported in family members of persons with SEL. We studied the prevalence of seizures and cysticercus electro-immuno-transfer blot (EITB) based seropositivity among family members, specifically household family contacts of pediatric subjects with a SEL. An attempt was also made to determine the etiology of seizures in household family contacts using magnetic resonance imaging (MRI). Information regarding seizure semiology, personal and food habits and detailed family pedigrees was obtained from 20 consecutive pediatric subjects with a SEL and 51 of their household family contacts. EITB sero-assays and stool examinations were performed on all participating subjects. MRIs were done on all EITB positive household family contacts. A family history of seizures was obtained in six index children (30%) (five household first-degree relatives and two distant relatives). Seventeen index children (85%) and 14 family contacts (27%) were EITB positive. A tendency towards clustering of EITB positive cases within individual families was observed. Stool examinations did not reveal Taenia species ova in any of EITB positive subjects. Neuroimaging studies revealed abnormalities consistent with active or inactive neurocysticercosis in all five household family contacts with history of seizures. Four of these five subjects were EITB positive and one was EITB negative. We concluded that children with SEL and seizures may have a family history of seizures. There is a high seropositivity rate in household family contacts of pediatric subjects with solitary cysticercus granulomas (SCGs). EITB based seropositivity in household family contacts with seizures, strongly predicts a cysticercal etiology for seizures. It may be worthwhile to screen household family contacts of children with SEL for taeniasis-cysticercosis.

Cerebral Cortex↗

PubMed2000

Immunomodulatory activity of hexapeptides related to proline rich peptide from colostrum.

Twelve analogues of an immunomodulatory hexapeptide YVPGFP (I) derived from Proline rich peptide (from colostrum) have been synthesized with modifications at positions 2, 4 and 6. In MLR assay one of the analogues exhibited approx 50% inhibition at 0.1 microg/mL concentration in contrast to prednisolone and I which caused around 70 and 20% suppression respectively, at the same concentration.

Adjuvants, Immunologic↗

PubMed2000

Cloning and expression studies during vegetative and sexual development of Pbs1, a septin gene homologue from Pyrenopeziza brassicae.

A septin gene homologue designated Pyrenopeziza brassicae septin 1 (Pbs1) has been identified and cloned from the plant pathogenic fungus Pyrenopeziza brassicae and its expression analysed. Pbs1 is present in both mating types and in a single copy within each genome and is transcribed in proportionate levels during both vegetative and sexual growth.

Amino Acid Sequence↗

PubMed2000

Abundance of cyclin B1 regulates gamma-radiation-induced apoptosis.

gamma-Radiation is a potent inducer of apoptosis. There are multiple pathways regulating DNA damage-induced apoptosis, and we set out to identify novel mechanisms regulating gamma-radiation-induced apoptosis in hematopoietic cells. In this report, we present data implicating the cyclin B1 protein as a regulator of apoptotic fate following DNA damage. Cyclin B1 is the regulatory subunit of the cdc2 serine/threonine kinase, and accumulation of cyclin B1 in late G2 phase of the cell cycle is a prerequisite for mitotic initiation in mammalian cells. We find that abundance of the cyclin B1 protein rapidly increases in several mouse and human hematopoietic cells (Ramos, DP16, HL60, thymocytes) undergoing gamma-radiation-induced apoptosis. Cyclin B1 accumulation occurs in all phases of the cell cycle. Antisense inhibition of cyclin B1 accumulation decreases apoptosis, and ectopic cyclin B1 expression is sufficient to induce apoptosis. These observations are consistent with the idea that cyclin B1 is both necessary and sufficient for gamma-radiation-induced apoptosis. (Blood. 2000;95:2645-2650)

Animals↗

PubMed2000

Influence of the proto-oncogene c-fos on cisplatin sensitivity.

Cisplatin resistance has been associated with overexpression of the c-fos gene in a human ovarian carcinoma cell line. To determine whether the correlation between c-fos overexpression and cisplatin resistance was limited to this cell line or was a more generalized phenomenon, we investigated cisplatin sensitivity in rat fibroblast cells that overexpressed the c-fos gene. The cisplatin Ic50 values for two different c-fos transfectants, CMVc-fos and L1-3c-fos, were 7.6 +/- 0.8 and 5.6 +/- 1.0 microM, respectively, whereas the cisplatin Ic50 value for the parental line, 208F, was 2.4 +/- 0.1 microM. This represented a 3.2- and 2.3-fold resistance to cisplatin for CMVc-fos and L1-3c-fos cells, respectively. The correlation between c-fos expression and cisplatin resistance also was examined in a human ovarian carcinoma cell line, 2008, and its cisplatin-resistant variant, C13*. Expression of c-fos was elevated slightly at both the mRNA and protein levels in the C13* cells compared with 2008 cells, and c-Fos protein levels were induced in C13* cells following cisplatin treatment. In addition, it was observed that C13* cells were significantly more sensitive than 2008 cells to a c-fos antisense oligonucleotide. The Ic50 values for the c-fos antisense oligonucleotide were 19.9 +/- 5.0 pmol for C13* cells and 58.1 +/- 6.0 pmol for 2008 cells (P = 0.0012). Furthermore, combinations of c-fos antisense and cisplatin reduced the amount of cisplatin required to kill 50% of the C13* cells, although the interaction was not synergistic. These results suggest that expression of the c-fos gene can influence cisplatin sensitivity, and that c-fos antisense oligonucleotide based therapy may be effective at killing parental and cisplatin-resistant ovarian carcinoma cells, either alone or in combination with cisplatin.

Animals↗

PubMed2000

Phrenic nerve conduction studies in acute organophosphate poisoning.

Phrenic nerve conduction studies were performed within 48 h of admission and subsequently in 29 patients (14 of whom required mechanical ventilation) with acute organophosphate (OP) poisoning. The mean (+/-SD) amplitude of the diaphragmatic compound muscle action potential (CMAP) in patients requiring mechanical ventilation (119.09 +/- 173.85 microV) was significantly lower than in those not requiring mechanical ventilation (461.63 +/- 138.69 microV) (P < 0.0001). Diaphragmatic CMAP amplitudes in ventilated patients increased with time during the course of hospitalization and were normal in 5 (36%) patients and only mildly reduced in another 6 (43%) patients prior to discontinuation of mechanical ventilation, which was undertaken 4-18 days (mean 7 +/- 3 days) after poisoning. Eleven patients (79%) were successfully weaned from mechanical ventilation at the first attempt. In the 3 (21%) remaining patients, mechanical ventilation had to be reestablished because of weaning failure. The mean (+/-SD) diaphragmatic CMAP amplitude, prior to discontinuation of ventilatory assistance, was 242.6 +/- 94.1 microV in these 3 patients. After ventilatory discontinuation, it fell to 95.5 +/- 105.8 microV. Thus, reduced diaphragmatic CMAP amplitudes correlate with the need for mechanical ventilation in acute OP poisoning.

Action Potentials↗

PubMed2000

Effect of growth factors on proliferation of normal, borderline, and malignant breast epithelial cells.

Growth factors play an important role in the development and growth regulation of normal breast. They are also known to be autocrine or paracrine stimulators of breast cancer cells. However, their role on cells of proliferative breast disease has not been studied so far. This study was undertaken to quantitate the proliferative effect of various growth factors on "normal," borderline, and malignant breast epithelial cells. For this purpose, epithelial cell lines of histologically normal human breast and histologically proven proliferative breast diseases were established. Cell lines MCF-7 and T47D were used as malignant cells. The growth factors under study include epidermal growth factor, fibroblast growth factors acidic and basic, platelet-derived growth factor, and insulin-like growth factors 1 (IGF-1) and 2 (IGF-2). Their proliferative effect was determined by incubating the cells with growth factors for 24 h after achieving basal conditions in serum-free medium for 72 h, followed by quantitating the S-phase fraction by flow cytometry. All of the growth factors were found to be capable of inducing cellular proliferation on the entire range of mammary epithelia. Epidermal growth factor was consistently found to be a potent mitogen. Fibroblast growth factor acidic had a higher effect compared to fibroblast growth factor basic in inducing the cells to move from G(0)/G(1) to S-phase. Platelet-derived growth factor had a moderate proliferative response. In the family of insulin-like growth factors, IGF-1 was the dominant mitogen for normal cells and IGF-2 was the dominant proliferative stimulus for the cell line MCF-7. In the cell lines of proliferative breast disease and T47D, both were at par as mitogenic agents. These results suggest that the cells of proliferative breast disease develop some of the biological characteristics of malignancy.

Breast↗

PubMed2000

The cost-effectiveness of different management strategies for type I diabetes: a Swiss perspective.

AIMS/HYPOTHESIS: A computer model was developed to determine the health outcomes and economic consequences of different combinations of diabetes interventions in newly diagnosed patients with Type I (insulin-dependent) diabetes in Switzerland. METHODS: We modelled seven complications of diabetes: hypoglycaemia, ketoacidosis, acute myocardial infarction, stroke, lower extremity amputation, nephropathy, and retinopathy. Transition probabilities and costs were taken from published literature. The Swiss health insurance payer perspective was taken. Various combinations of diabetes management strategies, including intensive or conventional insulin therapy and screening and treatment strategies for renal and eye disease were defined. Life expectancy, cumulative incidences of complications, and mean expected total lifetime costs per patient were calculated under six different management strategies. Incremental cost-effectiveness ratios were calculated in terms of costs per life-year gained compared with conventional insulin therapy alone. RESULTS: The addition of screening for microalbuminuria and retinopathy followed by appropriate treatment, if detected, were cost saving, with reduction in cumulative incidence of end stage renal disease and blindness respectively, and, in the case of microalbulminuria screening and treatment, an improvement in life expectancy. Intensive therapy improved life expectancy but increased total lifetime costs. CONCLUSION/INTERPRETATION: Optimal management of Type I diabetic patients, including secondary and tertiary prevention, leads to reduced complications and improved life expectancy, with the increased costs of prevention offset to varying degrees by cost savings due to complications avoided.

Albuminuria↗

PubMed2000

Urinary diversion for incontinence in women.

Urinary incontinence is a common condition affecting up to 50% of the female population, but only a third seek medical help. Although the majority of these are satisfactorily managed with conservative or conventional surgical treatment, 10%-15% continue to remain incontinent despite intervention. Urinary diversion is a management option for this group. The different techniques of urinary diversion, their results, complications and long-term sequelae are discussed, with a review of the literature.

Female↗

PubMed2000

A complication of scleral expansion surgery for treatment of presbyopia.

PURPOSE: To report a patient who developed complications from an experimental technique using scleral expansion to treat presbyopia. METHODS: Case report of a 46-year-old woman who underwent scleral expansion surgery on her right eye. Postoperatively, the patient developed chronic pain and swelling that necessitated removal of the scleral expanders. RESULTS: After removal of the scleral expanders, the patient demonstrated a -1.4 diopter myopic shift in the right eye relative to her preoperative refraction. Axial length of the right eye was 1.15 mm longer than of the left, whereas preoperative axial lengths were equal. CONCLUSION: This patient developed scleral thinning with resultant axial lengthening and myopic shift, akin to the phenomenon observed with scleral buckles used to treat retinal detachments. We believe this was responsible for improved near vision in her right eye, rather than any increased accommodative potential purported to result from this operation.

Female↗

PubMed2000

Template-constrained cyclic peptide analogues of somatostatin: subtype-selective binding to somatostatin receptors and antiangiogenic activity.

Beta-turns are a common secondary structure motif found in proteins that play a role in protein folding and stability and participate in molecular recognition interactions. Somatostatin, a peptide hormone possessing a variety of therapeutically-interesting biological activities, contains a beta-turn in its bioactive conformation. The beta-turn and biological activities of somatostatin have been succesfully mimicked in cyclic hexapeptide analogues. Two novel, structured, non-peptidic molecules were developed that are capable of holding the bioactive tetrapeptide sequence of somatostatin analogues in a beta-turn conformation, as measured by somatostatin receptor (SSTR) binding. Template-constrained cyclic peptides in which the ends of the -Tyr-D-Trp-Lys-Val-tetrapeptide were linked by scaffolds based on either an N,N'-dimethyl-N,N'-diphenylurea or a substituted biphenyl system (DJS631 and DJS811, respectively), bound selectively to mouse SSTR2B and rat and human SSTR5 with affinities as high as 1 nM. DJS811, at a dose of 3 mg/kg/day, was shown in a mouse Matrigel model to inhibit angiogenesis to a level of 79%. The development of structured turn scaffolds allows beta-turn sequences to be contained in the context of a compact structure, with less peptidic nature and potentially greater bioavailability than cyclic hexapeptides. These systems can be used to study the determinants of beta-turn formation, as well as to probe the importance of turn sequences occurring in molecular recognition interactions. The antiangiogenic activity of DJS811 suggests that it may have antitumor activity as well. In addition, because SSTR2 is overexpressed on many types of tumors, DJS631 and DJS811 may be useful in the development of agents for tumor imaging or the radiotherapy of cancer.

Angiogenesis Inhibitors↗

PubMed2000

Immunolocalization of matrix metalloproteinases and their inhibitors in clinical specimens of bone metastasis from breast carcinoma.

Matrix metalloproteinases (MMPs) are essential in several stages of the metastatic process, and in normal bone development and remodeling. We explored whether the interaction between tumor cells and bone leads to changes in MMP and tissue inhibitor of MMP (TIMP) expression thus affecting osteolysis in metastatic bone disease. Using immunohistochemistry we have investigated the MMP/TIMP expression in tumor cells, fibroblasts, osteoblasts and osteoclasts. Thirty one specimens of bone metastasis from breast carcinoma were stained for MMP-1, -2, -9, MT1-MMP and TIMP-1, and -2 and compared with staining in normal breast tissue, primary breast carcinoma and normal bone. Specimens came from patients in three clinical scenarios: from open biopsies without or with pathological fracture, or bone marrow biopsies containing tumor from patients with pancytopenia but without clinical evidence of osteolysis. By bone histomorphometry the latter group showed a heavy tumor load not different from the open biopsy groups but displayed little active bone resorption and low numbers of osteoclasts. Cell type-specific MMP/TIMP expression was observed and the staining patterns were comparable between the three groups of patients. Though no major differences in the MMP/TIMP staining of tumor cells and fibroblasts were observed between bone metastasis and primary tumor, we showed that tumor cells do express MMPs capable of degrading bone matrix collagen. The number and activity of osteoclasts and osteoblasts was increased dramatically in bone metastases, their MMP/TIMP profiles, however, were not different from normal bone, suggesting that the mechanism of bone degradation by osteoclasts is not different from normal bone remodelling.

Bone Neoplasms↗

PubMed2000

Dosage of once-daily gentamicin in spinal cord injury patients.

INTRODUCTION: In patients with spinal cord injury (SCI), serum creatinine does not accurately reflect the level of renal function. Therefore, in SCI patients, the dose of potentially nephrotoxic drugs should be adjusted on an individual basis from the estimated creatinine clearance. CASE REPORT: A 41-year-old male with tetraplegia due to cervical spinal cord injury underwent extended pyelolithotomy for staghorn calculus in the right kidney. The blood urea level was 9.9 mmol/l; creatinine was 112 umol/l (reference range: 0-135). We were conscious of this patient's renal disease, and therefore, administered only 3 mg/kg of gentamicin (240 mg) instead of the standard dose of 5 mg/kg body weight. Despite taking this precaution, the gentamicin level measured 22.5 h after the initial dose, was in the potentially toxic range 3.3 mg/l. CONCLUSION: We recommend that even the first dose of gentamicin in the once-daily regimen, which is 5 mg/kg, should be individualised in SCI patients based on age, sex, weight, height, level of spinal cord injury, and renal function.

Adult↗

PubMed2000

Milk of calcium in the inferior calyx of a hydronephrotic kidney in a tetraplegic patient - a diagnosis to be made before scheduling for extracorporeal shock wave lithotripsy.

STUDY DESIGN: A Case Report of renal milk of calcium in a tetraplegic subject. OBJECTIVES: To increase the awareness of renal milk of calcium in spinal cord injury (SCI) physicians. Renal milk of calcium contains a colloidal suspension of calcium crystals. Since upright views of the kidneys are not performed in tetraplegic subjects, the renal milk of calcium may be misinterpreted as renal lithiasis by routine radiography taken in supine position. SETTING: Regional Spinal Injuries Centre, Southport, England. METHOD: In a 41-year-old male with traumatic tetraplegia, X-ray of abdomen in supine position showed multiple opacities in the region of the left kidney. These radio opaque shadows were interpreted as renal calculi. Subsequently, computed tomography (CT) of the kidneys was performed. RESULTS: CT confirmed the presence of calculi in the mid-polar calyx. However, the density situated in the inferior calyx of the hydronephrotic left kidney exhibited a horizontal upper edge. This specific radiological finding as observed in the CT of kidneys, provided the clue to the presence of milk of calcium in the inferior calyx of the hydronephrotic left kidney. CONCLUSION: As plain film of the abdomen in standing position is not performed in SCI patients, physicians caring for SCI patients should have a high index of suspicion for renal milk of calcium. Prompt diagnosis of renal milk of calcium will help to avoid unnecessary surgery, or extracorporeal shock wave lithotripsy.

Adult↗