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Biomedical subjects

M B Rao

Publications and source records attributed to M B Rao.

At least 19 recordsLinked to original sources
PubMed2006

Melanin content and MC1R function independently affect UVR-induced DNA damage in cultured human melanocytes.

Malignant transformation of melanocytes leads to melanoma, the most fatal form of skin cancer. Ultraviolet radiation (UVR)-induced DNA photoproducts play an important role in melanomagenesis. Cutaneous melanin content represents a major photoprotective mechanism against UVR-induced DNA damage, and generally correlates inversely with the risk of skin cancer, including melanoma. Melanoma risk is also determined by susceptibility genes, one of which is the melanocortin 1 receptor (MC1R) gene. Certain MC1R alleles are strongly associated with melanoma. We hereby present experimental evidence for the role of two melanoma risk factors, constitutive pigmentation, as assessed by total melanin, eumelanin and pheomelanin contents, and MC1R genotype and function, in determining the induction and repair of DNA photoproducts in cultured human melanocytes after irradiation with increasing doses of UVR. We found that total melanin and eumelanin contents (MC and EC) correlated inversely with the extent of UVR-induced growth arrest, apoptosis and induction of cyclobutane pyrimidine dimers (CPD), but not with hydrogen peroxide release in melanocytes expressing functional MC1R. In comparison, melanocytes with loss-of-function MC1R, regardless of their MC or EC, sustained more UVR-induced apoptosis and CPD, and exhibited reduced CPD repair. Therefore, MC, mainly EC, and MC1R function are independent determinants of UVR-induced DNA damage in melanocytes.

Adult↗
PubMed2001

Involvement of a lysine residue in the active site of a thermostable xylanase from Thermomonospora sp.

A highly thermostable xylanase (Xyl I) produced by Thermomonospora sp. was purified to homogeneity and was classified as a family 10 xylanase based on its molecular weight (38,000 Da) and isoelectric point (4.1). K2d analysis showed that the secondary structure of Xyl I was made up of 38% alpha-helix and 10% beta-sheet. The optimal temperature for the activity of Xyl I was 80 degrees C. Xyl I was highly thermostable with half-lives of 86, 30, and 15 min at 80, 90, and 100 degrees C respectively. Xyl I was stable in an expansive pH range of 5 to 10 with more than 75% residual activity. Our present investigation using o-phthalaldehyde (OPTA) as the chemical initiator for fluorescent chemoaffinity labeling and trinitrobenzenesulphonic acid (TNBS) as chemical modifier have revealed the presence of a single lysine residue in the active site of Xyl I. The high pK value for the basic limb of the pH profile reflects the ionization of a lysine residue. The higher K(m) values and similar k(cat) values of the TNBS modified enzyme in comparison to native enzyme and the substrate protection against OPTA and TNBS, suggested the presence of the lysine residue in the substrate-binding site.

Actinomycetales↗
PubMed2001

Studies on carboxymethyl cellulase produced by an alkalothermophilic actinomycete.

A novel alkalothermophilic actinomycete having optimum growth at pH 9 and 50 degrees C was isolated from self-heating compost from the Barabanki district of Uttar Pradesh, India. Based on its morphology, susceptibility of spores to heat and novobiocin, guaninecytosine content of chromosomal DNA and cell wall composition, the organism was classified under Thermomonospora. The alkalothermophilic actinomycete produced 23 IU/ml carboxymethyl cellulase (CMCase). The CMCase was purified by fractional ammonium sulphate precipitation followed by cellulose affinity chromatography and Sephacryl S-200 gel filtration. The CMCase had a molecular weight of 38 KD and pI of 4.1. The enzyme exhibited optimum activity at pH 5 and temperature 50 degrees C. The CMCase showed pH stability in the range 7-10. The enzyme retained 100% activity at 50 degrees C for 72 h and had half-lives of 7 and 3 h at 60 degrees C and 70 degrees C, respectively. The CMCase was stable in the presence of commercial detergents such as Ariel, Henko and Surf Excel, indicating its potential as an additive to laundry detergents.

Actinomycetales↗
PubMed2001

A novel thermostable xylanase from Thermomonospora sp.: influence of additives on thermostability.

An alkalothermophilic Thermomonospora sp. producing high levels of xylanase was isolated from self-heating compost. The culture produced 125 IU/ml of xylanase when grown in shake flasks at pH 9 and 50 degrees C for 96 h. The culture filtrate also contained cellulase (23 IU/ml), mannanase (1 IU/ml) and beta-xylosidase (0.1 IU/ml) activities. The xylanase was active at a broad range of pH (5-9) and temperature (40-90 degrees C). The optimum pH and temperature were 7 and 70 degrees C, respectively. The enzyme was stable in the pH range 5-8 and was thermostable with half-lives of 8 and 4 h at 60 degrees C and 70 degrees C, respectively, but only 9 min at 80 degrees C. The effects of a variety of compounds to enhance the stability of xylanase at 80 degrees C was studied. Addition of sorbitol, mannitol and glycerol increased the thermostability of xylanase in proportion to the number of hydroxyl groups per polyol molecule. Glycine also offered protection against thermoinactivation. Xylan, trehalose, gelatin and trehalose-gelatin mixture had marginal effect on the thermostability of xylanase at 80 degrees C.

Actinomycetales↗
PubMed2001

Conformation and polarity of the active site of xylanase I from Thermomonospora sp. as deduced by fluorescent chemoaffinity labeling. Site and significance of a histidine residue.

A fluorescent chemoaffinity label o-phthalaldehyde (OPTA) was used to ascertain the conformational flexibility and polarity at the active site of xylanase I (Xyl I). The kinetics of inactivation of Xyl I with OPTA revealed that complete inactivation occurred due to the binding of one molecule of OPTA to the active site of Xyl I. The formation of a single fluorescent isoindole derivative corroborated these findings. OPTA has been known to form a fluorescent isoindole derivative by crosslinking the proximal thiol and amino groups of cysteine and lysine. The involvement of cysteine in the formation of a Xyl I-isoindole derivative has been negated by fluorometric and chemical modification studies on Xyl I with group-specific reagents and by amino-acid analysis. The kinetic analysis of diethylpyrocarbonate-modified Xyl I established the presence of an essential histidine at or near the catalytic site of Xyl I. Modification of histidine and lysine residues by diethylpyrocarbonate and 2,4,6-trinitrobenzenesulfonic acid, respectively, abolished the ability of the enzyme to form an isoindole derivative with OPTA, indicating that histidine and lysine participate in the formation of the isoindole complex. A mechanism for the reaction of OPTA with histidine and lysine residues present in the protein structure has been proposed. Experimental evidence presented here suggests for the first time that the active site of Xyl I is conformationally more flexible and more easily perturbed in the presence of denaturants than the molecule as a whole. The changes in the fluorescence emission maxima of a model compound (isoindole adduct) in solvents of different polarity were compared with the fluorescence behaviour of the Xyl I-isoindole derivative, leading to the conclusion that the active site is located in a microenvironment of low polarity.

Actinomycetales↗
PubMed2000

Clinical and echocardiographic predictors of left atrial clot and spontaneous echo contrast in patients with severe rheumatic mitral stenosis: a prospective study in 200 patients by transesophageal echocardiography.

The objective of this study was to prospectively investigate various clinical and echocardiographic variables to predict the left atrial and left atrial appendage clot and spontaneous echo contrast in patients with severe rheumatic mitral stenosis. We studied 200 consecutive patients (112 males and 88 females; mean age 29.6+/-9.6 years). Left atrial clot and spontaneous echo contrast were present in 26 and 53.5% of cases, respectively. There were no significant differences in the mitral valve area, mean transmitral diastolic gradient and left ventricular ejection fraction between patients with and without clot. Patients with clot were older (34.4+/-11.4 vs. 28.2+/-8.5 years, P<0.001), had longer duration of symptoms (41. 4+/-36.0 vs. 28.8+/-22.9 months, P<0.001), more frequent atrial fibrillation and spontaneous echo contrast (69.2 vs. 16.9%, P<0. 00001 and 76.9 vs. 45.3%, P<0.00001, respectively) and larger left atrial area and diameter (41.0+/-12.7 vs. 29.9+/-7.4 cm(2), P<0.00001 and 53.9+/-8.3 vs. 47.6+/-7.4 mm, P<0.0001, respectively) as compared to patients without clot. Similarly patients with spontaneous echo contrast were older (31+/-10.4 vs. 27.8+/-8.3 years, P<0.01), had more frequent atrial fibrillation (48.6 vs. 9.7%, P<0.0001), left atrial clot (37.4 vs. 12.9%, P<0.0001), larger left atrial area and diameter (37.6+/-11.2 vs. 28.1+/-6.7 cm(2), P<0.00001 and 52.2+/-8.3 vs. 45.9+/-6.5 mm, P<0.00001, respectively) and smaller mitral valve area (0.77+/-0.14 vs. 0.84+/-0.13 cm(2), P<0.01) as compared to patients without spontaneous echo contrast. There were no significant differences in the mean transmitral diastolic gradient and left ventricular ejection fraction. On multiple regression and discriminant function analysis, atrial fibrillation and left atrial area were independent predictors of left atrial clot formation. In a subgroup of patients with sinus rhythm, larger left atrial area and presence of spontaneous echo contrast were significantly associated with the presence of clot in left atrium and appendage. We conclude that in patients with severe mitral stenosis, the presence of atrial fibrillation and in the subgroup of the patients with sinus rhythm the presence of large left atrium (> or =40 cm(2)) and spontaneous echo contrast were associated with higher risk of clot formation in the left atrium and might be benefited by prophylactic anticoagulation.

Adolescent↗
PubMed2000

Is epilepsy surgery possible in countries with limited resources?

This study illustrates the outcome and cost-effectiveness of anterior temporal lobectomy (ATL) among patients with medically refractory temporal lobe epilepsy (TLE) treated in an epilepsy center in Kerala, South India. Patients for ATL were selected on the basis of a noninvasive protocol comprising clinical, interictal scalp electroencephalogram (EEG), magnetic resonance imaging, and ictal video-EEG data. The authors compared the outcome and direct cost of 119 patients (mean age, 25.6 years; mean duration of epilepsy before ATL, 16.1 years) who have completed at least 1 year follow-up after ATL with 71 refractory TLE patients (mean age, 27.1 years; mean duration of epilepsy, 15.4 years) who did not undergo ATL. Patients in the study who underwent ATL had a 70% likelihood of becoming seizure-free after ATL and a 30% chance of being completely off of antiepileptic drug treatment within 3 years after ATL. The out-of-pocket one-time payment for ATL (including presurgical evaluation) in this setup is Indian Rupees (INR) 47,000 (US$ 1,200). The total direct medical cost of caring for TLE patients aged 26 to 60 years would be INR 200,000 (US$ 5,000). Patients freed from seizures often can be better employed and achieve an improved quality of life. It is concluded that ATL for refractory TLE is a more cost-effective option than continued medical treatment. Epilepsy surgery is not only possible in a developing country but can also be undertaken in a cost-effective way.

Adolescent↗
PubMed2000

Atypical meningioma: a clinicopathological analysis.

In this retrospective study, 382 operated cases of meningiomas were reviewed. 32 cases (8.3%) were histopathologically classified as atypical meningioma. The anatomical locations and histological features in all the thirty-two cases were correlated with their recurrence rates and biological behaviour. The overall recurrence rate for atypical meningioma within two years was 28% as compared to 9.3% in benign meningiomas. It is being emphasized that an accurate histopathological interpretation of atypical meningioma is essential for predicting the recurrence, biological behavior as well as post-operative management modalities.

Adult↗
PubMed1999

Juvenile tricuspid stenosis and rheumatic tricuspid valve disease: an echocardiographic study.

Tricuspid valve involvement is not uncommon in patients with rheumatic heart disease and is frequently missed on routine clinical examination. We prospectively studied the echocardiographic profile of tricuspid valve disease in 788 consecutive patients with rheumatic heart disease. Out of these patients 9% (70) had tricuspid valve disease and 55.7% (39) of these were of < or = 20 years of age. Of these 60% were females and 40% were males. Their ages ranged from 9 to 64 years (mean 24.2+/-13.6 years). Of these patients, 50% had tricuspid stenosis with or without tricuspid regurgitation whereas 50% had isolated tricuspid regurgitation. Isolated tricuspid stenosis was present in 7.4% of these cases. All patients had associated mitral stenosis. Severe mitral stenosis was present more commonly in patients with juvenile tricuspid stenosis compared to older patients (94.1% vs. 55.6%, P<0.005). Mitral regurgitation was present more commonly in juvenile age group patients compared to older patients (53.8% vs. 25.8%, P<0.01). A combination of mitral, aortic and tricuspid stenosis was present in five cases and four of these were in the juvenile age group. Left ventricular enlargement and dysfunction were present in 28.6 and 14.3% patients, respectively, and the majority of these patients were in the juvenile age group (P<0.05). We conclude that rheumatic tricuspid valve disease occurs early in the course of the disease and progresses faster in India and is always associated with mitral stenosis. Juvenile tricuspid stenosis is more commonly associated with severe mitral stenosis, mitral regurgitation, left ventricular enlargement and dysfunction as compared with older patients.

Adolescent↗
PubMed1999

Pathology of temporal lobe epilepsy: An analysis of 100 consecutive surgical specimens from patients with medically refractory epilepsy.

The neuropathological features of temporal lobe epilepsy were studied utilising 100 consecutive surgical specimens from patients with medically refractory complex partial seizures. A wide spectrum of neuropathological changes was recorded in 98 specimens. Fifty-eight specimens showed features of Ammon's horn sclerosis. Diffuse accumulation of corpora amylacea were demonstrated in the resected temporal lobes from 54 patients. Six patients had neoplastic lesions of temporal lobe. One unique case of dysembryoplastic neuroepithelial tumour showed a melanotic component within the tumour. The neuropathological features were regarded as nonspecific in 31% of cases. Our results indicate that a majority of patients with medically intractable epilepsy of temporal lobe origin reveal significant neuropathological features. Careful documentation of the neuropathological features and its correlation with radiological, electrophysiological and pre- and post-surgical clinical features will help in predicting the seizure outcome after temporal lobectomy for medically refractory epilepsy.

Brain Neoplasms↗
PubMed1998

Long-term outcome of intracoronary microstent implantation: lesion matched comparison with Palmaz-Schatz stent.

We performed a lesion matched comparison of AVE Microstent and Palmaz-Schatz stent implants with 6 month follow-up angiography to compare the occurrence of restenosis. Thirty-three pairs of lesions were matched for lesion location, ACC/AHA lesion type, reference diameter, lesion length, and angiographic descriptors. Age, sex, clinical profile, and indication for stenting were comparable. Quantitative coronary analysis before and after the procedure was comparable in the two groups but minimum lumen diameter (MLD) at follow-up was less with Microstent--2.01 +/- 1.01 mm than Palmaz-Schatz stent--2.43 +/- 0.96 mm (P = 0.05). Binary restenosis was present in 33% and 21% and was diffuse in 55% and 29% of the two groups, respectively. Typical angina at follow-up was more frequent with Microstent (36%) than Palmaz-Schatz stent (15%; P = 0.038). When implanted in lesions of similar complexity, Microstent yields similar post procedure angiographic results but smaller MLD at follow-up and more frequent angina than Palmaz-Schatz stent.

Adult↗
PubMed1998

Molecular and biotechnological aspects of microbial proteases.

Proteases represent the class of enzymes which occupy a pivotal position with respect to their physiological roles as well as their commercial applications. They perform both degradative and synthetic functions. Since they are physiologically necessary for living organisms, proteases occur ubiquitously in a wide diversity of sources such as plants, animals, and microorganisms. Microbes are an attractive source of proteases owing to the limited space required for their cultivation and their ready susceptibility to genetic manipulation. Proteases are divided into exo- and endopeptidases based on their action at or away from the termini, respectively. They are also classified as serine proteases, aspartic proteases, cysteine proteases, and metalloproteases depending on the nature of the functional group at the active site. Proteases play a critical role in many physiological and pathophysiological processes. Based on their classification, four different types of catalytic mechanisms are operative. Proteases find extensive applications in the food and dairy industries. Alkaline proteases hold a great potential for application in the detergent and leather industries due to the increasing trend to develop environmentally friendly technologies. There is a renaissance of interest in using proteolytic enzymes as targets for developing therapeutic agents. Protease genes from several bacteria, fungi, and viruses have been cloned and sequenced with the prime aims of (i) overproduction of the enzyme by gene amplification, (ii) delineation of the role of the enzyme in pathogenecity, and (iii) alteration in enzyme properties to suit its commercial application. Protein engineering techniques have been exploited to obtain proteases which show unique specificity and/or enhanced stability at high temperature or pH or in the presence of detergents and to understand the structure-function relationships of the enzyme. Protein sequences of acidic, alkaline, and neutral proteases from diverse origins have been analyzed with the aim of studying their evolutionary relationships. Despite the extensive research on several aspects of proteases, there is a paucity of knowledge about the roles that govern the diverse specificity of these enzymes. Deciphering these secrets would enable us to exploit proteases for their applications in biotechnology.

Amino Acid Sequence↗
PubMed1997

Conformation and microenvironment of the active site of xylose reductase inferred by fluorescent chemoaffinity labeling.

Conformation and microenvironment at the active site of xylose reductase (XR) from Neurospora crassa was probed with fluorescent chemoaffinity labeling (FCAL) using o-phthalaldehyde as a chemical initiator. Formation of a single isoindole derivative resulted in complete inactivation of the enzyme as judged by spectroscopic and fluorescence studies. Kinetic analysis of the 2,4,6-trinitrobenzenesulfonic-acid-modified XR implicated the presence of an essential lysine residue at the active site of XR. Modification of lysine in XR abolished the ability of the enzyme to form isoindole derivative, indicating that the lysine residue involved in the reaction with 2,4,6-trinitrobenzenesulfonic acid and o-phthalaldehyde is the same and that the probe o-phthalaldehyde is directed to the active site. Fluorescence studies revealed that inactivation of XR by Gdn/HCl precedes gross conformational change and the possibility of secondary-conformational change was eliminated by acrylamide quenching studies. The enzyme inactivated by low concentrations of Gdn/HCl retained its ability to form the fluorescent XR-isoindole derivative indicating that inactivation is not due to conformational changes at or near the active site of XR. Gdn/HCl also had no effect on the high-affinity and low-affinity NADPH-binding sites of XR. Energy-transfer experiments further revealed structural integrity at the active site of the Gdn/HCl-inactivated XR. Changes in the fluorescence emission maximum of 1-(beta-hydroxyethylthio)-2-beta hydroxyethyl isoindole (EA adduct) in solvents of varying polarity was studied, the data obtained were utilized to interpret the fluorescence behaviour of XR-isoindole derivative and assess the polarity at the active site. Experimental evidence presented here serves to suggest that the inactivation of XR by Gdn/HCl precedes conformational changes at the active site located in a microenvironment of low polarity.

Affinity Labels↗
PubMed1997

A result on a 2 x 2 survival experiment.

Lifetime data classified according to categorical variables under the proportionality of the hazard functions of response variables for various treatment combinations is assumed. The proposed model is a combination of Cox's proportional hazards model and ANOVA model. The existence of a solution to the marginal likelihood function is examined for the case of 2 x 2 two-way classification. We provide an easily verifiable condition for the existence of a unique estimate.

Humans↗
PubMed1997

Suprasellar meningioma subsequent to treatment for a pituitary adenoma: case report.

The authors report a case of suprasellar meningioma that developed 16 years after surgery and radiation therapy for a pituitary adenoma. The patient had significant recovery of visual loss following excision of the meningioma. We believe that this tumor was induced by radiation received by the patient previously and we stress that tissue diagnosis should be obtained in patients who develop a recurrent tumor after a long period following initial radiotherapy. Radiation induced meningioma has to be considered in the differential diagnosis of any patient who has a recurrence after therapeutic radiation. This is especially essential in the absence of biochemical and clinical signs of a previously functioning pituitary adenoma and before the initiation of medical therapy for recurrent pituitary adenomas.

Adenoma↗
PubMed1996

Purification, kinetic characterization and involvement of tryptophan residue at the NADPH binding site of xylose reductase from Neurospora crassa.

Xylose reductase (XR) from Neurospora crassa was purified to homogeneity and was found to be specific to NADPH (nicotinamide adenine dinucleotide phosphate). The purified enzyme showed M(r) of 60 and 29 kDa by gel filtration and SDS-PAGE indicating the presence of two subunits. The kinetic mechanism of xylose reductase is 'iso-ordered bi bi'. Inactivation of XR by N-bromosuccinimide (NBS) was found to be biphasic with second-order rate constants of 2.5 x 10(2) and 80 M-1S-1 for the fast (kf) and slow phase (ks), respectively. NADPH protected 90% of XR activity against inhibition by NBS. The fluorescence and circular dichroism (CD) studies revealed that inactivation was not due to gross conformational change in the enzyme. Analysis of the modified Stern-Volmer plot indicated that 49% of the tryptophanyl fluorescence was available for quenching which was completely abolished in the presence of NADPH confirming the involvement of tryptophan at the coenzyme binding site. Experimental evidence presented here serves to implicate the involvement of a tryptophan residue at the low-affinity NADPH binding site and the nature of this site has been assessed by using the hydrophobic probe ANS.

Aldehyde Reductase↗
PubMed1996

Craniospinal and spinal enterogenous cysts--report of three cases.

We report three cases of enterogenous cyst, one craniospinal and two spinal manifesting with features of spinal cord compression. In one the cyst was intramedullary in location and in the other two it was intradural, extramedullary. The unusual clinical presentation, location and magnetic resonance imaging (MRI) characteristics are discussed. None of the three patients had any vertebral anomaly or other congenital malformation. All patients had excellent outcome following surgery.

Brain↗