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Biomedical subjects

S Kannan

Publications and source records attributed to S Kannan.

At least 19 recordsLinked to original sources
PubMed2007

Characterization and in vivo evaluation of sol-gel derived hydroxyapatite coatings on Ti6Al4V substrates.

Hydroxyapatite (HAP) based coatings on titanium alloy Ti6Al4V were attempted by sol-gel process. Precursor sol was dip-coated onto the substrates and the formation of HAP as the main phase was ensured after the sintering of coatings at 900 degrees C, as confirmed by the characterization studies involving XRD, FT-IR, Raman, and SEM-EDXS analysis. The biocompatibility of HAP-based coated titanium implants was tested by implantation studies in rabbit's tibia for a period of 8 weeks. Bone remodelling and inflammatory responses of the implants were studied during the implantation period. The better tissue-implant interaction of the coated implants with respect to the uncoated implants was observed after a defect healing period of 8 weeks. A coated implant with no evidence of rejection is a further advantage of the sol-gel derived HAP coating.

Alloys↗
PubMed2006

Fluorine-substituted hydroxyapatite scaffolds hydrothermally grown from aragonitic cuttlefish bones.

Porous hydroxyapatite scaffolds with different levels of fluorine substitution (46% and 85%) on the OH sites were produced via hydrothermal transformation of aragonitic cuttlefish bones at 200 degrees C and calcination at temperatures up to 1200 degrees C. The increasing level of F substitution reduces the kinetics and probably the yield of the reaction. The incorporation of F in the lattice of hydroxypatite caused a lowering of the unit cell volume due to reduction of the length of the a-axis. The crystallites formed were close in size to bone-like apatite and were orientated along the a-axis rather than the c-axis. There was evidence of AB-type carbonated apatite.

Animals↗
PubMed2006

Thermally induced polytype transformations among the layered double hydroxides (LDHs) of Mg and Zn with Al.

The hydrotalcite-like layered double hydroxide (LDH) of Mg with Al shows dramatic changes in the peaks arising from the (h0l)/(0kl) family of reflections in its powder X-ray diffraction pattern during thermal treatment. DIFFaX simulations show that these changes arise due to the transformation of the disordered 3R1 polytype into the 1H polytype on dehydration. The 1H polytype is an essential precursor to the decomposition reaction, which results in the formation of an oxide residue with the rock salt structure. In contrast, the LDH of Zn with Al does not undergo any such transformation, retaining the structure of the 3R1 polytype until decomposition into the oxide residue. Given the poor octahedral site preference of the Zn2+ ion, the 1H polytype is neither structurally stable nor is it topochemically necessary for the thermal decomposition of the Zn-Al LDH, the end product of the decomposition reaction being an oxide with the wurtzite structure.

Journal Article↗
PubMed2006

Novel synthesis and structural characterization of fluorine and chlorine co-substituted hydroxyapatites.

Fluorine and chlorine co-substituted hydroxyapatites (HAP) were prepared through aqueous precipitation method. Characterization results from X-ray diffraction (XRD) revealed that co-substitution of these anions resulted in the formation of pure HAP phase except for the small observed difference in the lattice parameters of the resultant apatites. The elemental analysis and FT-IR results have also confirmed the incorporation of substituted anions in the apatite structure. The calculated crystallite size for all anionic substituted apatite fall well below the range of 50 nm size that tend to coincide with the value of bone mineral crystallite size.

Chemistry, Inorganic↗
PubMed2006

Carcinoma of tongue and the buccal mucosa represent different biological subentities of the oral carcinoma.

PURPOSE: Clinico-epidemiological studies show that the behaviour of the tongue cancer is different from the cancer originating at other sites of the oral cavity. However, studies identifying the reason for such difference are lacking in the literature. METHODS: In the present study, we have attempted to see whether any difference existed in the cell cycle regulatory mechanism of these tumours by comparing immunohistochemically the expression of major cell cycle regulatory proteins in 147 buccal and 94 tongue carcinoma (anterior two-third of tongue) prospectively. RESULTS: On comparison of buccal and tongue carcinoma, expression of p16 and p21 showed significant difference. In combined analysis, simultaneous down regulation of p16 and p21 was seen in 47% of tongue cancer cases as against 28% in buccal carcinoma (P=0.004). In univariate analysis, none of the clinico-biological variables studied showed significant association with survival in tongue carcinoma, whereas, some of the clinico-biological variables associated with survival in buccal carcinoma. Among the biological markers, the overexpression of cyclin D1 (P=0.007) and p53, detected using both the clones of antibodies-DO7 (P=0.008) and PAb240 (P=0.014) and the down regulation of p16 (0.033), showed significant association with shorter disease free survival (DFS) in these cases. Whereas in the case of overall survival (OS), overexpression of p53 [DO7 (P=0.031) and PAb240 (P=0.017)] and cyclin D1 (P=0.001) associated with poor survival. In multivariate analysis, the expression pattern of p53 and p16 protein influences the DFS whereas cyclin D1 expression showed independent association with the OS in buccal carcinoma. CONCLUSIONS: Thus, tongue and buccal cancers represent different biological subentities, and such differences should be considered in oral cancer management.

Adult↗
PubMed2006

Influence of single nucleotide polymorphisms in H-Ras and cyclin D1 genes on oral cancer susceptibility.

Although tobacco usage and alcohol consumption are the major risk factors for oral cancer, there are individual variations in genetic susceptibility to oral cancer. The Ras pathway plays an important role in oral carcinogenesis. High percentage of Ras mutation in oral carcinoma was reported from India. Cyclin D1, a downstream member of the Ras pathway, was also shown to be overexpressed in the majority of oral cancers and the overexpression was shown to be associated with poor prognosis. In the present study, we have evaluated the association of the single nucleotide polymorphisms in the H-Ras (C81T) and cyclin D1 (A870G and C1722G) genes and oral cancer risk in 176 oral cancer cases and 142 hospital based controls matched by age and sex. All the polymorphisms studied conformed to Hardy-Weinberg equilibrium. The comparison of the CCND1 A870G and C1722G genotype frequencies in cases and controls did not show any significant association with oral cancer risk. In H-Ras C81T polymorphism, TC+CC genotype showed a one and half fold increased risk (OR=1.59) for oral cancer. On stratified analysis, the observed increased risk was more evident among men (OR=2), while such an increased risk was not seen among women. Thus, our data suggests that the variant 'C' allele of the H-Ras (C81T) is associated with a higher risk for oral carcinoma, particularly in male population and thus, this polymorphism could be a low penetrance gene predisposition factor for oral carcinoma.

Adult↗
PubMed2006

Hydrothermal growth of hydroxyapatite scaffolds from aragonitic cuttlefish bones.

Scaffolds of AB-type carbonated hydroxyapatite (HA) were successfully produced via hydrothermal transformation (HT) of aragonitic cuttlefish bones at 200 degrees C. The transformation was seemingly complete after 9 h of HT and no intermediate products were registered. Beyond low production cost, worldwide availability, and natural-biological origin of raw materials, the produced scaffolds preserved the initial structure of cuttlefish bone, featuring good biocompatibility in osteoblasts tests and ideal pore size ( approximately 80 microm in width and approximately 100 microm in height) and interconnectivity for supporting biological activities, such as bone tissue growth and vascularization. The highly channeled structure and the use of fresh cuttlefish bones favored the diffusion of the reaction solution towards the aragonite resulting in fast kinetics (after 1 h, hydroxyapatite was the dominant crystalline phase).

Animals↗
PubMed2006

Human 8-oxoguanine DNA glycosylase increases resistance to hyperoxic cytotoxicity in lung epithelial cells and involvement with altered MAPK activity.

It is unknown whether base excision DNA repair (BER) proteins interact with mitogen-activated protein kinases (MAPK) under oxidation. Here, we explored roles of BER proteins in signaling transduction involving MAPK during hyperoxia. We demonstrated that ERK1/2 phosphorylation in A549 cells was increased in 95% O(2). p38 activity in A549 cells was also increased by exposure to 95% O(2). To evaluate regulatory roles of MAPK, we have transduced A549 cells and primary alveolar epithelial type II cells (AECII) to overexpress 8-oxoguanine DNA glycosylase (hOgg1). Overexpression of hOgg1 reduced hyperoxic toxicity in A549 and AECII cells. Furthermore, protection by BER against hyperoxia appeared to involve an upregulation of ERK1/2 and downregulation of p38. These observations demonstrate, for the first time, that reduction of hyperoxic toxicity by BER proteins may be involved with MAPK activity, thereby impacting cell survival. Furthermore, our studies suggest that modulation of MAPK may be used in combination with BER proteins to counteract hyperoxic toxicity.

Blotting, Western↗
PubMed2005

Formation of hydroxyapatite onto glasses of the CaO-MgO-SiO2 system with B2O3, Na2O, CaF2 and P2O5 additives.

New bioactive glasses with compositions based on the CaO-MgO-SiO(2) system and additives of B(2)O(3), P(2)O(5), Na(2)O, and CaF(2) were prepared. The in vitro mineralization behaviour was tested by immersion of powders or bulk glasses in simulated body fluid (SBF). Monitoring of ionic concentrations in SBF and scanning electron microscopy (SEM) observations at the surface of the glasses were conducted over immersion time. Raman and infrared (IR) spectroscopy shed light on the structural evolution occurring at the surface of the glasses that leads to formation of hydroxyapatite.

Biocompatible Materials↗
PubMed2005

Scaffolds for bone restoration from cuttlefish.

Scaffolds of pure hydroxyapatite suitable for either direct clinical use or tissue-engineering applications were successfully produced via hydrothermal transformation of aragonite, obtained from fresh cuttlefish bones, at 200 degrees C followed by sintering. Beyond low production cost, worldwide availability and natural-biological origin of raw materials, the produced scaffolds have ideal pore size and interconnectivity features suitable for supporting biological activities, such as bone tissue growth and vascularization. Bioactivity in vitro tests were excellent: (a) rapid and pronounced formation of hydroxyapatite occurred when the scaffolds were immersed in simulated body fluid (SBF), and (b) outstanding proliferation of osteoblasts was registered. The produced scaffolds can be machined and shaped very easily at any stage of processing. Therefore, these ceramic scaffolds can satisfy both bioactivity demands and the requirements for shaping of tailor-made individualized implants, especially for randomly damaged bones.

Animals↗
PubMed2005

Phenotypic alterations in Rb pathway have more prognostic influence than p53 pathway proteins in oral carcinoma.

The two well-defined pathways that are shown to be prominently altered in a variety of cancers are the cell cycle regulatory pathways led by either p53 or Rb genes. The present study is undertaken to find the pathway that is more altered in oral carcinoma at protein level, with special emphasis on its prognostic significance. The expression pattern of key molecules of the Rb and p53 pathways, such as Rb, cyclin D1, CDK4, p16, p53, p21 and Bcl-2 and the proliferative marker PCNA were analysed in 348 oral carcinoma specimens by immunohistochemical technique. The expression index of these molecules and various clinicopathological factors were statistically correlated with treatment end points to assess its prognostic efficacy after following up these patients up to a maximum of 48 months with a median of 23 months. Rb pathway proteins, Rb (P=0.016), cyclin D1 (P=0.0001) and p16 (P=0.012) showed significant association with disease-free survival, and p16 (P=0.041) and cyclin D1 (P=<0.0001) with the overall survival. Among p53 pathway proteins studied, only p53 expression index showed association with both disease-free survival and overall survival. Multivariate analyses confirmed that the biological variables, cyclin D1 and p16 and the clinical variable, 'stage of disease' were independent predictors of disease-free survival and overall survival. Subgrouping of the patients on the basis of p16 and cyclin D1 expression revealed that the subgroup having downregulation of p16 and overexpression of cyclin D1 exhibited the worst disease-free survival and overall survival compared to the other subgroups. The present data showed that disabling of the Rb and p53 pathways were frequent events in oral carcinoma. The study also demonstrated that the Rb pathway proteins are comparatively more important than p53 pathway proteins for the prognostication of oral carcinoma patients. The combined evaluation of p16 and cyclin D1 in oral carcinoma could identify a group of patients with the worst survival who might therefore need alternate or more intense treatment strategies.

Aged↗
PubMed2004

p53, p16 and cyclin D1: molecular determinants of radiotherapy treatment response in oral carcinoma.

Management of oral cancer by radiotherapy has witnessed promising advances in the past few years, with patient-tailored radio fractionation regimens. Different fractionation schedules, conventional and altered regimes, have been used in curative radiotherapy. Although contribution of biological markers on radio response has been evaluated, its unique influence on various radio fractionation schemes has not been accounted so far. Our study analyses a set of proteins that previously demonstrated radio response influence for their possible prognostic value in decision-making process between the respective fractionation schemes. Expression patterns of regulatory proteins such as p53, cyclin D1, p16, Cdk4, p21, Rb, bcl-2 and PCNA were determined by immunohistochemistry utilizing monoclonal antibodies in 125 patients who received curative radiotherapy dose. Among these 125 patients, 90 (72%) received altered fractionation, whereas 35 (28%) received conventional fractionation. p53 over-expression correlated with local treatment failure among the patients treated with conventional fractionation whereas cyclin D1 over-expression and p16 underexpression were associated with local treatment failure as well as overall survival in altered fractionation treated cases. Our findings suggest that wild-type p53 status may be an important parameter for achieving high local control in those patients undergoing conventional fractionation, where as intact p16 and cyclin D1 status may be beneficial for effective local control in patients who are treated with altered fractionation. Furthermore, it can be assumed that conventional fractionation employs p53-mediated apoptosis, whereas altered fractionation activates the functional G1 cell-cycle checkpoint for tumor growth suppression.

Adult↗
PubMed2004

Fourier transform infrared study of low-temperature CO adsorption on CuMgAl-hydrotalcite.

Single-phase CuMgAl ternary hydrotalcite with (Cu+Mg)/Al atomic ratio of 3.0 and Cu/Mg atomic ratio of 1.0 was synthesized by coprecipitation. Thermoanalytical studies of this sample showed transformations in three stages in the temperature range up to ca. 900 K yielding mainly CuO phase. In situ diffuse reflectance infrared Fourier transform (DRIFT) spectroscopic measurements showed the presence of carbonates even after calcination of the sample at 973 K. The genesis of Cu+ sites during thermal treatment in vacuo at different temperatures for this sample was followed by IR spectroscopy of CO adsorbed at low temperature. Essentially no Cu+ sites are present on a sample calcined at 723 K, consistent with X-ray photoelectron spectroscopic (XPS) data. However, sample subjected to activation (1 h of O2 treatment at 723 K followed by 1 h of evacuation at the same temperature) upon CO adsorption at 85 K unambiguously showed the presence of Cu+ sites. 12CO-13CO coadsorption studies confirmed the presence of dicarbonyls, which are converted to linear Cu+-CO species during evacuation at 85 K. Concentration of the accessible Cu+ sites increased with the increase in activation temperature up to 873 K and decreased with a further temperature rise. The copper sites on the sample are heterogeneously distributed and their distribution depends on the activation temperature. Two routes of reduction of Cu2+ to Cu+ are proposed: (i) autoreduction during evacuation and (ii) reduction by CO.

Journal Article↗
PubMed2004

Utility of serodiagnostic tests for leprosy: a study in an endemic population in South India.

In order to evaluate the usefulness of natural disaccharide (PGL1) and 35 kDa antigens based serology in diagnosis of leprosy and in detecting high risk groups for leprosy, this study was conducted in an endemic population in South India. Out of 3346 cases and their households and neighbouring household contacts, serum samples from 2994 and 2875 individuals were screened for antibodies against PGL1 and 35kDa antigens respectively. While the overall positivity for contacts and leprosy cases was 3.3% for PGL1 antibody, the positivity for 35 kDa antibody was 6.3%. The positivity for contact population was 2.7% and 5.4% for PGL1 and 35 kDa antibodies, respectively. Lepromatous and borderline lepromatous patients showed positivity of 35.1% for PGL1 antibody and 45.7% for 35 kDa antibody. Follow-up of contacts showed that the majority (>90%) remained seronegative for both the antibodies and most of the new cases emerged from the seronegative group. The study clearly indicates that specific serological assays are not sensitive enough for application, both for diagnosis and for identifying any individual at risk for leprosy in the south Indian endemic population.

Adult↗
PubMed2003

meso-Bis(phenylsulfinyl)methane.

The title compound, meso-C(13)H(12)O(2)S(2), is in an anti conformation, with R and S configurations around the S atoms. The two O atoms are trans to each other, and the same applies for the two benzene rings. The phenylsulfinyl groups are nearly orthogonal to the central dithiomethane group, and the orientation of the two phenyl rings are determined by the interactions in which they are involved. The packing is built from molecular columns stabilized by weak C-H...O interactions.

Journal Article↗