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Biomedical subjects

S Narayanan

Publications and source records attributed to S Narayanan.

At least 127 records · Page 7Linked to original sources
PubMed1976

Immobilized glucose oxidase used in the continuous-flow determination of serum glucose.

We used a tubular glucose-oxidase wall reactor in the "AutoAnalyzer II" continuous-flow analytical system to determine glucose in blood serum. Sensitivity was high and wash characteristics were satisfactory with use of a 30-cm tube containing immobilized glucose oxidase. Results compared favorably with those of the conventional free-enzyme method. More than 25000 such assays can be performed with a single enzyme tube, which also shows long-term storage stability. Because of the steady-state chemistry 60 samples can be analyzed per hour. The linearity of the method is excellent and sample interaction from 5.0 to 1.0 g/liter is less than 5%. Results correlate well (greater than 0.993) with those obtained with both the neocuproine method used in the "SMA 12/60" multichannel analytical system and the free glucose oxidase method used in the AutoAnalyzer.

Autoanalysis↗
PubMedDate not supplied

Process development for the synthesis of 5'-O-(4,4'-dimethoxytrityl)-N2-isobutyryl-2'-O-(2-methoxyethyl)-guanosine--a potential precursor for the second generation antisense oligonucleotides: an improved process for the preparation of 2'-O-alkyl-2,6-diaminopurine riboside.

An efficient four step process for the preparation of 5'-O-(4,4'-dimethoxytrityl)-N2-isobutyryl-2'-O-(2-methoxyethyl)-guanosine 1 was developed. Direct 2'-O-alkylation of 2,6-diaminopurine riboside 2 was accomplished via inexpensive and commercially available reagents such as KOH, DMSO and alkyl halides at room temperature in 4-6 hrs. Pure 2'-O-(2-methoxyethyl)-DAPR 3 was isolated by crystallization from methanol. Enzymatic deamination of 3 followed by selective N2-isobutyrylation and 5'-O-dimethoxytritylation furnished desired 1 in high yield and purity. Fully optimized four step synthetic process has been scaled up to the pilot plant level.

Guanosine↗
PubMedDate not supplied

Multifunctional roles of thrombin.

Thrombin is an unique molecule that functions both as a procoagulant and anticoagulant. In its procoagulant role it activates platelets through its receptor on the platelets. It regulates its own generation by activating coagulation factors V, VIII and even XI resulting in a burst of thrombin formation. It activates factor XI, thus preventing fibrin clots from undergoing fibrinolysis. Thrombin not only cleaves fibrinogen to fibrin, but also through the activation of factor XIII effects the cross-linking of fibrin monomers to produce a firm fibrin clot. Thrombin's role as an anticoagulant is mediated through binding to thrombomodulin, a receptor protein on the endothelial membrane of the blood vessel, initiating a series of reactions that leads to fibrinolysis. Thrombin has chemotactic properties enabling it to exert its effects during inflammation and vascular injury. It has a mitogenic effect stimulating growth of mammalian cells, fibroblasts and macrophage-like tumor cell lines. It has also been implicated in brain development. A molecule with multifunctional roles such as thrombin has its activity in vivo modulated by only a few endogenous inhibitors.

Blood Coagulation↗
PubMedDate not supplied

Magnetization transfer ratio is unable to lateralize epileptic foci in patients with temporal lobe epilepsy.

BACKGROUND AND PURPOSE: A preliminary report suggested that magnetization transfer ratio (MTR) was useful to lateralize epileptic foci in patients with refractory temporal lobe epilepsy (TLE). We attempted to confirm this finding in a larger group by investigating the relationship between MTR of mesial temporal structures and seizure lateralization in patients with refractory TLE. METHODS: We compared the MTR of amygdalae and hippocampi of 10 patients with unilateral TLE to values obtained from 10 healthy control participants. RESULTS: Three of 10 patients with TLE had MTR values that were 2 SD below the normal mean; the MTR abnormality was concordant with electroclinical lateralization in only one of the three. CONCLUSION: We conclude that MTR measurements of amygdalae and hippocampi are not useful for lateralization of TLE.

Adult↗
PubMedDate not supplied

Overview of principles and current uses of DNA probes in clinical and laboratory medicine.

Fundamental considerations of deoxyribonucleic acid (DNA) probe hybridization reaction including concept of stringency is reviewed. Restriction fragment length polymorphism (RFLP) and its detection using DNA probes are discussed together with the importance of RFLP in genetic linkage analysis. Methodological considerations, such as limitations in sample preparation and improvements effected in techniques, cloning DNA, and labelling of DNA probes, are addressed. Principles of hybridization technology and blotting techniques are reviewed. Amplification of DNA by the polymerase chain reaction (PCR), labelling with PCR, detection of PCR products and separation procedures prior to use of PCR are discussed. Other amplification methods and in-situ hybridization (ISH) procedures are reviewed. Selected current applications of DNA probes in the area of infectious diseases, genetic diseases, HLA typing, paternity and forensic testing are briefly discussed. Emphasis is placed on the use of DNA probes in the area of oncology. Background on activation of proto oncogene, loss of tumor suppressor genes, chromosomal translocation, and chromosome analysis are provided for understanding DNA probe assays for ph1 positive leukemias and applications of Interphase cytogenetic technique in oncology. Finally, analytical strategies for detection of tumor suppressor genes are addressed.

DNA Probes↗
PubMedDate not supplied

Applications of restriction fragment length polymorphism.

The availability of a variety of restriction endonuclease enzymes that cleave deoxyribonucleic acid (DNA) at specific sites has made it possible to identify the presence of polymorphic regions in the isolated fragments. Such restriction fragment length polymorphism (RFLP) results owing to a variation in the number of tandem repeats (VNTR) of a short DNA segment. These VNTR sequences can uniquely specify an individual and, as such, are used in DNA fingerprinting and in paternity testing. Restriction fragment length polymorphism may be found close to a disease gene, and, as such, can be used as a genetic disease marker. Certain criteria need to be fulfilled, however, for RFLP to be useful as a genetic disease marker, such as its closeness to the disease gene. Materials and methodology for detecting RFLP are reviewed with the current emphasis on amplification procedures utilizing the polymerase chain reaction (PCR).

Genetic Diseases, Inborn↗
PubMedDate not supplied

Laboratory monitoring of gestational diabetes.

The consequences of uncontrolled gestational diabetes is severe to both maternal and fetal well-being. An ideal laboratory test to monitor gestational diabetes should accurately reflect short-term glucose changes. Glycated albumin, by virtue of its short half-life of 14 to 19 days, lends itself as a test to monitor and control gestational diabetes. Analytical approaches for the measurement of glycated albumin are reviewed, and the non-specificity of the simple colorimetric fructosamine assay is stressed. The performance characteristics of fructosamine assay, and the merits of the one hour oral glucose screening test and three-hour oral glucose tolerance test are discussed. An objective strategy for laboratory monitoring of gestational diabetes would include other assays such as fasting plasma glucose to correlate with glycated albumin (fructosamine) and even to complement the less sensitive glycated hemoglobin assay.

Diabetes, Gestational↗
PubMedDate not supplied

Incidence of ocular myiasis due to infection with the larva of oestrus ovis (Oestridae Diptera).

The present paper is the result of the study of frequent occurrences of ocular myiasis due to the infection by the insect larva in 14 patients. The collected larvae were identified as first stage larva of oestrus ovis. The results of the examinations of the infected eyes show swollen conjunctiva, redness and watering of the eyes. These symptoms may be mistaken for mucopurulent conjunctivitis. The above results are discussed with earlier literature.

Acute Disease↗
PubMedDate not supplied

Serum alkaline phosphatase isoenzymes as markers of liver disease.

A perspective on serum alkaline phosphatase isoenzymes in liver disease is provided with a brief discussion of the location of the enzyme in liver and its presumed function. Mechanisms of entry of alkaline phosphatase into serum in liver disease are discussed. Characterization of high molecular weight alkaline phosphatase in obstructive jaundice is reviewed. The relationship between blood group O and the appearance of the intestinal enzyme in sera of such subjects with cirrhosis of liver is discussed. Properties of hepatoma alkaline phosphatase and the genesis of liver alkaline phosphatase in diseases not related to the liver are explored. Methods for detection of serum alkaline phosphatase isoenzymes in liver disease are discussed from the standpoint of the limitations of electrophoretic procedures, and the promise of procedures such as isoelectric focusing and high performance liquid chromatography that are currently non-routine.

Alkaline Phosphatase↗
PubMedDate not supplied

Inhibition of in vitro platelet aggregation and release and fibrinolysis.

Inhibition of in vitro platelet aggregation and release of contents of platelet granules is necessary in order to assess accurately platelet activation in vivo. This can be accomplished by using a variety of inhibitors added to blood collection containers. An additive mixture of citrate, theophylline, adenosine, and dipyridamole (CTAD) provides a practical alternative to a mixture of acid citrate dextrose (ACD), acetylsalicylic acid (aspirin), and prostaglandin E1 (PGE1) because of the stability problems associated with PGE1. Inhibition of in vitro fibrinolysis is essential for the accurate measurement of fibrin degradation products (FDP). This can be accomplished by using a mixture of thrombin, soybean trypsin, or aprotinin into which blood is collected. However, in patients receiving heparin, the fibrinolysis inhibitor mixture is ineffective unless it is supplemented with reptilase. With increasing use of recombinant tissue-type plasminogen activator therapy (rt-PA), an inhibitor such as D-phenylalanine-proline-arginine-chloromethylketone (PPACK) used as a blood collection additive is superior to a conventional protease inhibitor, such as aprotinin.

Blood Platelets↗
PubMedDate not supplied

Laboratory evaluation of the adrenogenital syndrome.

The adrenogenital syndrome is a result of the deficiency of one of the enzymes involved in the pathway leading to the synthesis of cortisol by the adrenal cortex. Laboratory evaluation of the adrenogenital syndrome involves measurement of hormones and metabolites accumulated prior to the enzymic block as well as hormones whose synthesis is affected by deficiency of a specific enzyme. Laboratory measurements of hormone metabolites in urine, because of their nonspecificity, lack of sensitivity, and multiple assay steps resulting in poor yield, have been supplanted by specific and sensitive radioimmunoassays of steroid hormones in plasma. In the laboratory evaluation of the adrenogenital syndrome, problems involved in some of the immunoassays of selected hormones should be addressed. Variables owing to specimen collection, storage and handling, and the assay itself should be minimized and controlled.

3-Hydroxysteroid Dehydrogenases↗
PubMedDate not supplied

Biochemistry and clinical relevance of lipoprotein X.

Lipoprotein X (LP-X) is an abnormal lipoprotein that appears in the sera of patients with obstructive jaundice and is thus a marker for cholestasis. The presence of LP-X in serum does not allow discrimination between intra- and extra-hepatic cholestasis. In addition LP-X is present in the plasma of patients with familial plasma lecithin: cholesterol acyl transferase (LCAT) deficiency. It is a spherical particle that aggregates strongly. Phospholipids and unesterified cholesterol make up the bulk of LP-X, which is a low density lipoprotein. Protein, cholesterol esters, and triglycerides together make up 12 percent of the composition of LP-X. Lithocholic acid is the major bile acid in LP-X. Three species of LP-X have been isolated (LP-X1, LP-X2 and LP-X3). Because of its aggregating properties, LP-X complexes with enzymes, such as alkaline phosphatase. Electrophoretic and immunochemical methods are available for assay of LP-X. The fact that bile lipoprotein can be converted to LP-X by addition of albumin, and LP-X can be converted to bile lipoprotein by the addition of bile salts may suggest that the integrity of the LPX molecule depends on a certain critical bile salts to albumin ratio. Phospholipase in plasma is implicated in the catabolism of LP-X. The role of LP-X in cholestasis is apparently related to the removal of free cholesterol from the circulation as a consequence of its aggregating properties.

Bile↗
PubMedDate not supplied

Alkaline phosphatase as tumor marker.

Applications and limitations of alkaline phosphatase as a tumor marker are discussed. This review focuses on three characteristic isoenzymes that have been found in the serum of cancer patients: (1) the Regan isoenzyme in bronchogenic carcinoma; (2) the Nagao isoenzyme in pleuritis carcinomatosa; and (3) the hepatoma alkaline phosphatase. Tumor variants of alkaline phosphatase are classified based on their heat stability properties resembling or differing from the placental isoenzyme. They can also be differentiated in their behavior to specific inhibitors. The presence of electrophoretic variants and enzyme-immunoglobulin complexes in other cancers are also described.

Alkaline Phosphatase↗
PubMedDate not supplied

Sialic acid as a tumor marker.

The term sialic acid is used to describe derivatives of neuraminic acid, where the amino group of neuraminic acid is substituted by either an acetyl or glycolyl group. The unique structural features of the molecule, which includes a negative charge owing to a carboxyl group, enables it to play a role in cellular functions, such as transport of positively charged compounds, cell-to-cell repulsion, influencing conformation of glycoproteins on cell membranes, and even masking antigenic determinants on receptor molecules. Focus on sialic acid as a tumor marker should be examined from the perspective of aberrant glycosylation in cancer cell membranes owing to activation of new glycosyl transferases that are characteristic of tumor cells, and the role played by sialic acid in tumor cell metastasis including increased capacity to adhere to vascular endothelium, and decreased capacity of cancer cells to be destroyed by host defence mechanisms. The high sensitivity of sialic acid as a tumor marker has been reported in a variety of cancerous conditions. Its specificity, however, is relatively low since there is also an increase in sialic acid-rich glycoproteins in inflammatory diseases. Sialic acid measurements, however, have value in monitoring cancer patients during treatment. A variety of methods are available for the measurement of both total and lipid associated sialic acids in serum or plasma. The newer high performance liquid chromatographic procedures can detect picogram levels of sialic acid and are relatively free of interferences seen with classical procedures.

Biomarkers, Tumor↗