Biomedical subjects

Thomas Abraham

Publications and source records attributed to Thomas Abraham.

8 recordsLinked to original sources

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↗

PubMed2005

Isothermal titration calorimetry studies of the binding of the antimicrobial peptide gramicidin S to phospholipid bilayer membranes.

The binding of the amphiphilic, positively charged, cyclic beta-sheet antimicrobial decapeptide gramicidin S (GS) to various lipid bilayer model membrane systems was studied by isothermal titration calorimetry. Large unilamellar vesicles composed of the zwitterionic phospholipid 1-palmitoyl-2-oleoylphosphatidylcholine or the anionic phospholipid 1-palmitoyl-2-oleoylphosphatidylglycerol, or a binary mixture of the two, with or without cholesterol, were used to mimic the lipid compositions of the outer monolayers of the lipid bilayers of mammalian and bacterial membranes, respectively. Dynamic light scattering results suggest the absence of major alterations in vesicle size or appreciable vesicle fusion upon the binding of GS to the lipid vesicles under our experimental conditions. The binding isotherms can be reasonably well described by a one-site binding model. GS is found to bind with higher affinity to anionic phosphatidylglycerol than to zwitterionic phosphatidylcholine vesicles, indicating that electrostatic interactions in the former system facilitate peptide binding. However, the presence of cholesterol reduced binding only slightly, indicating that the binding of GS is not highly sensitive to the order of the phospholipid bilayer system. Similarly, the measured positive endothermic binding enthalpy (DeltaH) varies only modestly (2.6 to 4.4 kcal/mol), and the negative free energy of binding (DeltaG) also remains relatively constant (-10.9 to -12.1 kcal/mol). The relatively large but invariant positive binding entropy, reflected in relatively large TDeltaS values (13.4 to 16.4 kcal/mol), indicates that GS binding to phospholipid bilayers is primarily entropy driven. Finally, the relative binding affinities of GS for various phospholipid vesicles correlate relatively well with the relative lipid specificity for GS interactions with bacterial and erythrocyte membranes observed in vivo.

Animals↗

PubMed2005

Isothermal titration calorimetry studies of the binding of a rationally designed analogue of the antimicrobial peptide gramicidin s to phospholipid bilayer membranes.

The binding of the positively charged antimicrobial peptide cyclo[VKLdKVdYPLKVKLdYP] (GS14dK4) to various lipid bilayer model membranes was investigated using isothermal titration calorimetry. GS14dK4 is a diastereomeric lysine ring-size analogue of the naturally occurring antimicrobial peptide gramicidin S which exhibits enhanced antimicrobial and markedly reduced hemolytic activities compared with GS itself. Large unilamellar vesicles composed of various zwitterionic (1-palmitoyl-2-oleoyl-sn-glycero-3-phosphorylcholine [POPC]) and anionic phospholipids {1-palmitoyl-2-oleoyl-sn-glycero-3-[phospho-rac-(glycerol)] [POPG] and 1-palmitoyl-2-oleoyl-sn-glycero-3-[phosphoserine] [POPS]}, with or without cholesterol, were used as model membrane systems. Dynamic light scattering results indicate the absence of any peptide-induced major alteration in vesicle size or vesicle fusion under our experimental conditions. The binding of GS14dK4 is significantly influenced by the surface charge density of the phospholipid bilayer and by the presence of cholesterol. Specifically, a significant reduction in the degree of binding occurs when three-fourths of the anionic lipid molecules are replaced with zwitterionic POPC molecules. No measurable binding occurs to cholesterol-containing zwitterionic vesicles, and a dramatic drop in binding is observed in the cholesterol-containing anionic POPG and POPS membranes, indicating that the presence of cholesterol markedly reduces the affinity of this peptide for phospholipid bilayers. The binding isotherms can be described quantitatively by a one-site binding model. The measured endothermic binding enthalpy (DeltaH) varies dramatically (+6.3 to +26.5 kcal/mol) and appears to be inversely related to the order of the phospholipid bilayer system. However, the negative free energy (DeltaG) of binding remains relatively constant (-8.5 to -11.5 kcal/mol) for all lipid membranes examined. The relatively small variation of negative free energy of peptide binding together with a pronounced variation of positive enthalpy produces an equally strong variation of TDeltaS (+16.2 to +35.0 kcal/mol), indicating that GS14dK4 binding to phospholipids bilayers is primarily entropy driven.

Amino Acid Sequence↗

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

Glycolipid based cubic nanoparticles: preparation and structural aspects.

Kinetically stable cubic colloidal particle dispersion was produced from a glycolipid using a novel preparation strategy based on the dialysis principle. The use of synchrotron small-angle X-ray diffraction (SSAXD) permitted the identification of exact structure of these dispersed particles in the colloidal state. Dynamic light scattering methods were used to obtain size and size distributions. A glycoside, 1-O-phytanyl-beta-D-xyloside (beta-XP), that exhibits Pn3m cubic phase in an excess aqueous medium, was used as the lipid material. The dialysis technique includes controlled stirring action both inside and outside of the dialysis membrane tube. Initially, a mixed micellar system composed of beta-XP, n-octyl-beta-D-glucopyranoside (beta-OG) and a triblock copolymer, Pluronic F127 (PL) was prepared in the aqueous medium. About 10 wt.% of PL to lipid weight was found to be sufficient to produce stable colloidal dispersions. The mean volume diameter of these colloidal particles was found to be in the range of 0.85 +/-0.05 microm. The cubic phase structure of these colloidal particles is greatly depended on the final beta-OG concentration level in the system. Coexistence of Im3m and Pn3m cubic structures has been identified in these colloidal particles. This coexistence has the characteristics of Bonnet relation, which forms a compelling case for the infinite periodic minimal surface (IPMS) descriptions. These colloidal particles could restore pure Pn3m phase structure, but a longer dialysis time was needed. This work, in general, will open up new possibilities for membrane protein reconstitution and other relevant biological applications using colloidal cubic lipid particles.

Dialysis↗

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↗

PubMedDate not supplied

Polymer-dispersed bicontinuous cubic glycolipid nanoparticles.

We found that certain amphiphilic polymers such as PEO-PPO-PEO triblock copolymer (PL) can directly disperse a cubic glycolipid, 1-O-phytanyl-beta-D-xyloside (beta-XP), into bicontinuous cubic nanoparticles in water medium. The use of synchrotron small-angle X-ray diffraction (SSAXD) permitted the identification of the exact structure of these dispersed particles in the colloidal state. Dynamic light scattering method was used to obtain particle size distributions. The dispersion quality and the dispersion time can be improved by co-dissolving the lipid and the polymer in a common solvent. The mean volume diameter of these dispersed colloidal particles depends on the mixing time and polymer concentration. About 5 wt % (0.18 mol %) of polymer to lipid weight was found to be sufficient to produce stable colloidal dispersions. At this polymer content and at 3 h of stirring time, the mean volume diameter of cubic colloidal particles was found to be 1.0 microm. Increase of dispersion time to 6 h reduced the colloidal particle size from 1.0 microm to 660 nm. At 3 h of mixing time, the increase of polymer content, from approximately 5 to approximately 10 wt %, reduced the particle mean diameter from 1.0 microm to 675 nm. Irrespective of these dispersion times and polymer contents, the dispersed colloidal particles exhibit predominately the Pn3m cubic phase structure, the same as that of a beta-XP-water binary mixture, although a weak coexistence of Im3m cubic phase is identified in these colloidal particles. This coexistence is found to have the characteristics of a Bonnet relation, which forms convincing evidence for the infinite periodic minimal surface descriptions (IPMS). Considering the biotechnological significance, the preparation of these colloidal dispersions was carried out in a phosphate-buffered saline (PBS) system. These cubic colloidal dispersions exhibited good stability and the cubic phase structure remained intact in the PBS system.

Biotechnology↗