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Biomedical subjects

S Gopalakrishnan

Publications and source records attributed to S Gopalakrishnan.

At least 19 recordsLinked to original sources
PubMed2006

Toxicity of heavy metals on embryogenesis and larvae of the marine sedentary polychaete Hydroides elegans.

The toxicity of heavy metals to marine invertebrates has been widely investigated; however, the effects on marine sedentary polychaetes have largely been ignored. The toxicity of copper, aluminium, lead, nickel, and zinc on fertilization, embryogenesis, and larvae of Hydroides elegans was examined in laboratory acute-toxicity tests. Exposure to metal during fertilization or early developmental stages leads to fertilization block and arrested development, which resulted in morphologic abnormalities in embryo and larvae. Fertilization rate showed a drastic decrease at the highest metal concentration tested. Embryos of H. elegans showed a differential response to metals, and the responses were stage-specific. The different morphologic effects of heavy metals reflect differentiation of the early embryonic cells. For individual metals, the toxicity ranking for 24-hour trochophore larvae was Cu > Al > Pb > Ni > Zn, with EC(50) values of 0.122, 0.210, 0.231, 0.316, and 0.391 mg l(-1), respectively. Rate of larval development and embryogenesis were the most sensitive end points, although the latter is more advisable for routine assessment of seawater quality because of its greater simplicity. In addition to bivalves and sea urchins, polychaete embryos can provide biologic criteria for seawater quality taking into account the sensitivity of a polychaete and contributing to the detection of harmful chemicals with no marked effect on the species currently in use in seawater quality bioassays.

Animals↗
PubMed2006

Dietary ascorbic acid and alpha-tocopherol mitigates oxidative stress induced by copper in the thornfish Terapon jarbua.

The protective effects of vitamins C and E against oxidative stress were evaluated in various tissues of thornfish Terapon jarbua exposed to copper. Preliminary bioassay tests performed with copper and T. jarbua revealed that 4.0, 2.5 and 1.0 mg L(-1) of copper were lethal (LC(100)), medial lethal (LC(50)) and sublethal (LC(0)) respectively. Oxidative stress parameters viz. lipid peroxidation, superoxide dismutase, catalase, glutathione peroxidase, and glutathione were evaluated in control and experimental fishes. Lipid peroxidation activity increased in tissues of copper exposed fishes, while the antioxidant system exhibited a reduction in their activity. On the contrary copper stressed fishes fed with vitamins C and E enriched pellet feed showed significant reduction in lipid peroxidation activity and the antioxidant levels increased reaching near normal levels comparable to control values. Bioaccumulation of copper was studied in addition to oxidative stress. Substantial copper residue was detected in the tissues of T. jarbua exposed to copper and the level of copper in tissues reduced when the fishes were treated with vitamins ensuring copper depuration and thereby protecting them against stress. We concluded that vitamin supplementation offered significant reduction of the oxidative stress mediated by copper and we discuss the possible application of vitamins in costal aquaculture process.

Animals↗
PubMed2006

Immunomodulation the marine green mussel Perna viridis exposed to sub-lethal concentrations of Cu and Hg.

Environmental pollution is a growing concern and, more importantly, pollution of the aquatic ecosystem is alarming. Marine pollution may be one of the reasons for disease incidence in marine organisms, which is caused due to adverse effects of pollutants on the immune system. Bivalves are commonly used as bio-indicators of marine pollution, and immunomodulation due to toxicants is one of the important bio-markers used. Perna viridis too have been used as a bio-indicator, but this study is, to our knowledge, a first report on immunomodulation produced by metals, in P. viridis. Animals were exposed to copper and mercury at their sub-lethal concentrations of 20 microg L(-1) and 10 microg L(-1), respectively. Immune parameters including phenoloxidase, reactive oxygen species generation, and phagocytosis were monitored. The study period was for 25 days (chronic long-term exposure) and objectives established whether metals produced immunomodulation and to understand the effects of long-term exposure on immunomodulation. Results showed that both metals adversely affected immune parameters studied and, interestingly, there appears to be some level of recovery (depuration) from the toxic effects of metals.

Animals↗
PubMed2006

Assessment of biochemical components and enzyme activities in the estuarine crab Scylla tranquebarica from naphthalene contaminated habitants.

To document the impact of naphthalene, a comparative toxicological research was performed in the estuarine crab Scylla tranquebarica habitant of Ennore creek (polluted site) and Kovalam creek (pristine site) for a period of 6 months. The biochemical constituents, such as protein, carbohydrate, lipid and enzyme activities like acid and alkaline phosphatase, aspartate and alanine transaminase were analysed in hepatopancreas, heamolymph and ovary of the female crabs collected from the two creeks. The results revealed that there was a significant measurable difference in these parameters in the tissues of crabs sampled from the polyaromatic hydrocarbon (PAH) polluted site (Ennore creek) when compared with the reference site (Kovalam creek). In addition naphthalene was detected in gill, hepatopancrease, heamolymph and ovary of the crabs sampled from the polluted creek. The results indicate that the indicators selected for toxic impact in S. tranquebarica may be related to the uptake of naphthalene in the tissues examined and support the feasibility of employing these types of analyses as biochemical biomarkers for PAH contaminant-exposed organisms.

Animals↗
PubMed2005

Lamb wave characteristics of thickness-graded piezoelectric IDT.

An equivalent single layer model of Lamb wave generation by thickness-graded piezoelectric IDT on host structure is developed. Various additional complexities, such as the coupling between the Lamb wave modes, complicated nature of the electro-mechanical excitation are considered. The model of infinite IDT is extended to deal with the finite IDT with edge discontinuities. The effects of electromechanical coupling and thickness gradation on the wavelength shifts are investigated. The problem of electrically driven instability within the IDT is analyzed. Numerical results are reported by considering Al2O3/PZT IDT as integral part of the host structure, which show that there are significant changes and improvements in the Lamb wave characteristics due to the graded configuration. Most important among these is the reduced dispersiveness of the Lamb wave modes, which is useful in launching a SAW that propagates with narrower pulse width and less attenuation.

Electrodes↗
PubMed2004

Anti-inflammatory and antinociceptive activities of Trewia polycarpa roots.

The alcoholic extract of Trewia polycarpa roots, when administered orally to rats at doses of 50-400 mg/kg, exhibited a dose-dependent anti-inflammatory activity in both acute and chronic models. It also showed a significant antinociceptive action mice in the dose range of 25-200 mg/kg. The extract did not reveal any toxicity in rats up to a dose of 3.2 g/kg (p.o.). It showed the presence of terpenoids, alkaloids, flavonoids, quinones and glycosides on phytochemical screening.

Acetic Acid↗
PubMed2003

Free radical scavenging activity of the alcoholic extract of Trewia polycarpa roots in arthritic rats.

The alcoholic extract of Trewia polycarpa roots (TPE), which exhibited significant anti-inflammatory activity, was evaluated for the possible mode of action by studying its antioxidant potential in adjuvant-induced arthritic rats. The biological defence system constituting the superoxide dismutase, glutathione peroxidase, ascorbic acid showed a significant increase while the lipid peroxide content was found to decrease to a large extent on TPE treatment thereby indicating the extracts free radical scavenging property. Histopathological studies too supported anti-arthritic potential of the roots of Trewia polycarpa.

Animals↗
PubMed2002

A lignan from the root of Ecbolium linneanum Kurz.

From the chloroform extract of the root of Ecbolium linneanum Kurz., a furofuran type of unsymmetrical lignan named as Ecbolin A was isolated. The structure was established by spectroscopic methods and confirmed by single crystal X-ray diffraction studies.

Acanthaceae↗
PubMed2001

Jugular phlebectasia: theory of pathogenesis and review of literature.

Jugular phlebectasia is an entity that is being increasingly recognised in recent years. The term phlebectasia indicates dilatation of the vein without tortuosity. It has been described in almost all cervical veins. Internal jugular phlebectasia is seen more often on the right side. This paper reports two new cases, reviews all cases of internal jugular phlebectasia in children published in English literature upto 1996 and recommends diagnostic methods and treatment policy. This article also discusses a theory of pathogenesis for this condition based on the regional anatomical features, principles of vascular physics and pathologic findings.

Child↗
PubMed2001

Role of mastoid obliteration in patients with persistent cavity problems following modified radical mastoidectomy.

A randomized clinical trial was conducted to determine the efficacy of mastoid obliteration in controlling persistent ear discharge, wax accumulation, fungal infection and granulation tissue formation in patients with cavity problems following modified radical mastoidectomy (MRM). Thirty patients underwent revision mastoidectomy with mastoid obliteration using a temporoparietal fascial flap. They were then followed up over a one-year period and the stated parameters observed. They were compared with 30 patients with similar complaints who were treated conservatively and kept under observation for 12 months. On follow-up, the number of patients in both the groups suffering from various cavity problems was compared. The chi-squared test was applied to the results and it was determined that there was a significantly lower incidence of discharging ear and formation of granulations in the operative group. However, audiological status, development of otomycosis and wax accumulation did not reveal any significant variation between the two groups.

Adult↗
PubMed2000

Inhibiting cadherin function by dominant mutant E-cadherin expression increases the extent of tight junction assembly.

Previous studies have shown that induction of cadherin-mediated cell-cell adhesion leads to tight junction formation, and that blocking cadherin-mediated cell-cell adhesion inhibits tight junction assembly. Here we report analysis of tight junction assembly in MDCK cells overexpressing a mutant E-cadherin protein that lacks an adhesive extracellular domain (T151 cells). Mutant E-cadherin overexpression caused a dramatic reduction in endogenous cadherin levels. Despite this, tight junction assembly was extensive. The number of tight junction strands observed by freeze-fracture electron microscopy significantly increased in T151 cells compared to that in control cells. Our data indicate that the hierarchical regulation of junctional complex assembly is not absolute, and that inhibition of cadherin function has both positive and negative effects on tight junction assembly.

Animals↗
PubMed1999

Reactivity of guanine at m5CpG steps in DNA: evidence for electronic effects transmitted through the base pairs.

BACKGROUND: Mitomycin C (MC), a DNA cross-linking and alkylating agent, targets guanines in the m5CpG sequence with 2-3-fold preference over guanines in unmethylated CpG. Benzo[a]pyrenediolepoxide (BPDE) and several other aromatic carcinogens form guanine adducts with an identical selectivity for m5CpG, and in certain cancers G to T transversion mutation 'hotspots' in the p53 tumor suppressor gene are more frequent at this sequence than at guanines in other sequences. MC appears suitable to probe the general mechanism of this selectivity. RESULTS: A 162-bp DNA fragment containing C, m5C or f5C (5-fluoro cytosine) at all cytosine positions was cross-linked by MC at guanines in CpG steps. The extent of cross-linking increased in the order f5C < C < m5C. Monoalkylation or cross-linking of duplex 12-mer oligonucleotides containing a single CpG, f5CpG or m5CpG step gave yields of adducts that increased in the same order. The rates showed a correlation with the Hammett sigma constant of the methyl and fluoro substituents of the cytosine. Only the base-pair cytosine substituent influenced reactivity of guanine. CONCLUSIONS: The 2-amino group of guanine in the m5CpG sequence of DNA has a greater nucleophilic reactivity with mitomycin than CpG. Evidence is presented for a novel mechanism: transmission of the electron-donating effect of the 5-methyl substituent of the cytosine to guanine through H-bonding of the m5C.G base pair. The results explain the enhanced reaction of BPDE at m5CpG in DNA and the origin of G-T mutational hotspots in the p53 gene in cancer.

7,8-Dihydro-7,8-dihydroxybenzo(a)pyrene 9,10-oxide↗
PubMed1998

Rho GTPase signaling regulates tight junction assembly and protects tight junctions during ATP depletion.

Tight junctions control paracellular permeability and cell polarity. Rho GTPase regulates tight junction assembly, and ATP depletion of Madin-Darby canine kidney (MDCK) cells (an in vitro model of renal ischemia) disrupts tight junctions. The relationship between Rho GTPase signaling and ATP depletion was examined. Rho inhibition resulted in decreased localization of zonula occludens-1 (ZO-1) and occludin at cell junctions; conversely, constitutive Rho signaling caused an accumulation of ZO-1 and occludin at cell junctions. Inhibiting Rho before ATP depletion resulted in more extensive loss of junctional components between transfected cells than control junctions, whereas cells expressing activated Rho better maintained junctions during ATP depletion than control cells. ATP depletion and Rho signaling altered phosphorylation signaling mechanisms. ZO-1 and occludin exhibited rapid decreases in phosphoamino acid content following ATP depletion, which was restored on recovery. Expression of Rho mutant proteins in MDCK cells also altered levels of occludin serine/threonine phosphorylation, indicating that occludin is a target for Rho signaling. We conclude that Rho GTPase signaling induces posttranslational effects on tight junction components. Our data also demonstrate that activating Rho signaling protects tight junctions from damage during ATP depletion.

Adenosine Triphosphate↗
PubMed1997

Anti-inflammatory activity of Salacia oblonga Wall. and Azima tetracantha Lam.

The anti-inflammatory activity of Salacia oblonga rootbark powder and Azima tetracantha leaf powder was assayed in male albino rats using carrageenan-induced rat paw oedema (acute inflammation) and cotton pellet granuloma (chronic inflammation) methods. Both the crude drugs were maximally active at a dose of 1000 mg/kg. In the cotton pellet granuloma assay, these drugs were able to suppress the transudative, exudative and proliferative components of chronic inflammation. Furthermore, these drugs were able to lower the lipid peroxide content of exudate and liver, gamma-glutamyl transpeptidase activity in the exudate of cotton pellet granuloma. The increased acid and alkaline phosphatase activity and decreased serum albumin in cotton pellet granulomatous rats were normalised after treatment with these drugs. It is likely that these drugs may exert their activity by antiproliferative, antioxidative and lysosomal membrane stabilization.

Acid Phosphatase↗
PubMed1997

Immortalization of primary epithelial cells by E1A 12S requires late, second exon-encoded functions in addition to complex formation with pRB and p300.

Immortalization of primary cells is an early and important event in multistep tumorigenesis and is itself a multistep process. Adenovirus E1A 12S encodes an oncoprotein that can rescue cells from senescence and overcome apoptosis, leading to their immortalization. Five regions of 12S, located in both exons, are required for immortalization. Two regions in the first exon are necessary to activate the cell cycle, increase the number of population doublings, and overcome the M1 stage of mortality. However, extension of life span requires overcoming crisis or M2, which can be accomplished by the expression of the second exon. Several cellular proteins associate with the peptide encoded by the first exon of 12S including pRB, p107, p130, and p300. The importance of pRB-E1A and p300-E1A complexes in transformation is well established; however, their roles in 12S-mediated immortalization remain undefined. Results obtained from the present study using a panel of second exon immortalization-defective mutants demonstrate that formation of pRB-E1A and p300-E1A complexes is insufficient for immortalization of primary cells. We further demonstrate that the expression levels of another tumor suppressor protein, p53, also do not correlate with the inability of the mutants to immortalize. Thus, mutations in the second exon of 12S do not affect the early steps in the immortalization pathway. The second exon mutants are defective in performing a late function in immortalization, involving the reactivation of the cell cycle, indicating that it is a crucial event in immortalization.

Adenovirus E1A Proteins↗