Biomedical subjects
S Nair
Publications and source records attributed to S Nair.
Is telemedicine justifiable?
A three-year experience in urban telemedicine is presented. The digital technology linking a community teaching hospital to a nearby clinic is described, as is the typical protocol for the consultations. The medical advantages and disadvantages, the security implications, and the cost-effectiveness of this project are analyzed.
Immunoproliferative small intestinal disease in South India: a clinical and immunomorphological study.
Immunoproliferative small intestinal disease (IPSID), a proliferative disorder affecting the intestinal immune system, has only been reported sporadically in India. Fifteen patients with malabsorption syndrome who were diagnosed to have IPSID were included in this study. Mucosal biopsies from all patients, full thickness surgical biopsies from 10 and autopsy material from four patients were examined by light microscopy and immunohistochemistry. The patients were predominantly young (aged 16-36 years) and male (13 of 15). Diarrhoea, weight loss, vomiting and abdominal pain were the major symptoms. The upper small bowel was involved in all cases. Involvement of large bowel was detected antemortem in three patients, but was found in all autopsied patients. Involvement of the stomach was noted in one patient at autopsy. Mesenteric lymph nodes were involved in all patients who underwent laparotomy. The plasmacytic infiltrate was uniformly positive for alpha-heavy chain, and either negative for light chain production or showed monotypic light chain production. Some of the blasts were also positive for alpha-heavy chain. Three patients died before therapy could be commenced. One patient with stage A disease is alive and clinically free of disease at 7 years. Of the remainder, there have been four long-term survivors with chemotherapy. Immunoproliferative small intestinal disease occurs in southern India and has characteristics similar to that in other parts of the world. Early diagnosis may improve outcome in this disease.
Bone marrow-generated dendritic cells pulsed with tumor extracts or tumor RNA induce antitumor immunity against central nervous system tumors.
Recent studies have shown that the brain is not a barrier to successful active immunotherapy that uses gene-modified autologous tumor cell vaccines. In this study, we compared the efficacy of two types of vaccines for the treatment of tumors within the central nervous system (CNS): dendritic cell (DC)-based vaccines pulsed with either tumor extract or tumor RNA, and cytokine gene-modified tumor vaccines. Using the B16/F10 murine melanoma (B16) as a model for CNS tumor, we show that vaccination with bone marrow-generated DCs, pulsed with either B16 cell extract or B16 total RNA, can induce specific cytotoxic T lymphocytes against B16 tumor cells. Both types of DC vaccines were able to protect animals from tumors located in the CNS. DC-based vaccines also led to prolonged survival in mice with tumors placed before the initiation of vaccine therapy. The DC-based vaccines were at least as effective, if not more so, as vaccines containing B16 tumor cells in which the granulocytic macrophage colony-stimulating factor gene had been modified. These data support the use of DC-based vaccines for the treatment of patients with CNS tumors.
Species-specific tRNA recognition in relation to tRNA synthetase contact residues.
In spite of variations in the sequences of tRNAs, the genetic code (anticodon trinucleotides) is conserved in evolution. However, non-anticodon nucleotides which are species specific are known to prevent a given tRNA from functioning in all organisms. Conversely, species-specific tRNA contact residues in synthetases should also prevent cross-species acylation in a predictable way. To address this question, we investigated the relatively small tyrosine tRNA synthetase where contacts of Escherichia coli tRNA(Tyr) with the alpha2 dimeric protein have been localized by others to four specific sequence clusters on the three-dimensional structure of the Bacillus stearothermophilus enzyme. We used specific functional tests with a previously not-sequenced and not-characterized Mycobacterium tuberculosis enzyme and showed that it demonstrates species-specific aminoacylation in vivo and in vitro. The specificity observed fits exactly with the presence of the clusters characteristic of those established as important for recognition of E. coli tRNA. Conversely, we noted that a recent analysis of the tyrosine enzyme from the eukaryote pathogen Pneumocystis carinii showed just the opposite species specificity of tRNA recognition. According to our alignments, the sequences of the clusters diverge substantially from those seen with the M. tuberculosis, B. stearothermophilus and other enzymes. Thus, the presence or absence of species-specific residues in tRNA synthetases correlates in both directions with cross-species aminoacylation phenotypes, without reference to the associated tRNA sequences. We suggest that this kind of analysis can identify those synthetase-tRNA covariations which are needed to preserve the genetic code. These co-variations might be exploited to develop novel antibiotics against pathogens such as M. tuberculosis and P. carinii.
Murine postthymectomy autoimmune oophoritis develops in association with a persistent neonatal-like Th2 response.
Autoimmune oophoritis develops in some patients despite evidence of impaired cellular immunity. Here, using the murine postthymectomy model of autoimmune oophoritis, we investigate the hypothesis that neonatal thymectomy induces autoimmune oophoritis by disrupting the normal postnatal balance of T helper cell regulation. Stimulated CD4+ splenic lymphocytes from adult mice sham-operated as neonates produced the expected T helper type 1 (Th1) predominant response normally seen in adult mice (low levels of interleukin-4 and high levels of interferon gamma). In contrast, cells from adult mice thymectomized as neonates produced an inappropriate neonatal-like Th2-predominant response (high levels of interleukin-4 and low levels of interferon-gamma). Manipulations that restored the postnatal shift to an adult Th1-dominant pattern ameliorated the autoimmune oophoritis. Thus, neonatal thymectomy abrogates the postnatal shift to a Th1-dominant pattern, and the resulting persistent neonatal-like Th2-dominant response is tightly associated with the development of postthymectomy autoimmune oophoritis. These results (i) suggest that the postnatal shift to the normal adult Th1/Th2 balance is established by a thymus-dependent process and (ii) raise the possibility that specific genetic defects, as yet to be determined, might mimic the effect of neonatal thymectomy in this model, impair the development of normal Th1/Th2 balance, and be a cause autoimmunity. These results hold implications for the pathogenesis and possibly for the therapy of autoimmune polyglandular failure in humans.
Staphylococcus epidermidis produces a cell-associated proteinaceous fraction which causes bone resorption by a prostanoid-independent mechanism: relevance to the treatment of infected orthopaedic implants.
Staphylococcus epidermidis is the most commonly isolated coagulase-negative staphylococcus from the skin, gut and upper respiratory tract. Although it is less virulent than Staphylococcus aureus, it has emerged in recent years as an important causative agent of infections associated with metal implants, prosthetic devices and i.v. lines. We have previously demonstrated that a saline wash of S. aureus contained proteins which had potent bone-resorbing activity in vitro. The purpose of this study was to determine whether gently washing S. epidermidis in saline also released osteolytically active proteins. The so-called surface-associated material (SAM) eluted from S. epidermidis in saline was able to induce osteolysis, and activity was heat and trypsin sensitive, suggesting that the active component was proteinaceous. Fractionation studies have suggested that activity is due to a small number of cationic proteins. This SAM-induced bone resorption was not inhibited by the cyclo-oxygenase inhibitor, indomethacin, or the 5-lipoxygenase inhibitors BWA70C and MK886. However, it was partially inhibited by high concentrations of interleukin-1 receptor antagonist and was completely blocked by a neutralizing antibody to tumour necrosis factor-alpha. Thus, the SAM from this organism is a potent osteolytic agent which differs from that of S. aureus SAM in not being inhibited by cyclo-oxygenase inhibitors. As adjunctive therapy is becoming necessary in infectious diseases, either as a result of the side-effects of antibiotics or their lack of efficacy, consideration should be given to the future treatment of bone infections with staphylococci in the light of the different mechanisms of action of the surface proteins produced by these bacteria.
Interactions between periodontopathogenic bacteria and cytokines.
Cytokines produced in response to plaque bacteria clearly play a key role in the periodontal diseases. However, we know very little about the interactions between cytokines and periodontopathogenic bacteria. The aims of this study were to determine whether the key pro-inflammatory cytokines interleukin-1 beta (IL-1 beta) and IL-6 could affect the growth of Actinobacillus actinomycetemcomitans or Porphyromonas gingivalis and to determine whether these organisms could hydrolyse IL-1 beta, IL-6 or the anti-inflammatory IL-1 receptor antagonist (IL-1ra). Culture medium containing up to 100 ng/ml of IL-1 beta or IL-6 was inoculated with A. actinomycetemcomitans (serotypes a, b and c) or P. gingivalis and growth was monitored by measuring changes in electrical conductivity every 3 min for up to 48 h. IL-1 beta, IL-6 or IL-1ra were added to culture supernatants and incubated for up to 24 h. Samples were taken at various times, analysed by SDS-PAGE and the separated proteins transferred by Western blotting to PVDF membranes and probed with anti-cytokine antibodies. None of the cytokines tested had any effect on the rate of growth or yield of A. actinomycetemcomitans or P. gingivalis. Supernatants from P. gingivalis cultures, but not those from A. actinomycetemcomitans, hydrolysed IL-1 beta, IL-6 and IL-1ra. The hydrolysate from the P. gingivalis supernatant-treated IL-1 beta was unable to stimulate the release of IL-6 from human gingival fibroblasts showing that it had lost biological activity. These results suggest that P. gingivalis can perturb the cytokine network, not only by stimulating the release of cytokines from host cells, but also by removing them from its local environment.
A single point mutation in the embB gene is responsible for resistance to ethambutol in Mycobacterium smegmatis.
Ethambutol [EMB; dextro-2,2'-(ethylenediimino)-di-1-butanol] is an effective drug when used in combination with isoniazid for the treatment of tuberculosis. It inhibits the polymerization of arabinan in the arabinogalactan and lipoarabinomannan of the mycobacterial cell wall. Recent studies have shown that arabinosyltransferases could be targets of EMB. These enzymes are encoded by the emb locus that was identified in Mycobacterium smegmatis, Mycobacterium leprae, Mycobacterium avium, and Mycobacterium tuberculosis. We demonstrate that a missense mutation in the M. smegmatis embB gene, one of the genes of the emb locus, confers resistance to EMB. The level of resistance is not dependent on the number of copies of the mutated embB gene, indicating that this is a true mechanism of resistance. The mutation is located in a region of the EmbB protein that is highly conserved among the different mycobacterial species. We also identified in this region two other independent mutations that confer EMB resistance. Furthermore, mutations have recently been described in the same region of the EmbB protein from clinical EMB-resistant M. tuberculosis isolates. Together, these data strongly suggest that one of the mechanisms of resistance to EMB consists of missense mutations in a particular region of the EmbB protein that could be directly involved in the interaction with the EMB molecule.
Non-Hodgkin's lymphoma presenting with prominent splenomegaly--clinicopathologic diversity in relationship to immunophenotype.
Splenomegaly is an uncommon presenting feature of non-Hodgkin's lymphoma. This is a study of 16 cases of non-Hodgkin's lymphoma presenting with prominent splenomegaly, which includes ten B-cell lymphomas and six T-cell lymphomas. There were distinct clinical and morphologic differences between these two immunologic types of splenic lymphomas, the B-cell types being predominantly low grade and occurring in older individuals whereas the T-cell lymphomas were predominantly high grade and occurred in adolescents and young adults.
Differential changes in genome structure and expression of the mdr gene family in multidrug-resistant murine erythroleukemia cell lines.
The genome structure and expression of mdr genes were examined in multidrug-resistant sublines of two different murine (DBA/2J) Friend erythroleukemia cell lines, PC4 and C7D, derived by stepwise exposure to increasing concentrations of adriamycin beginning with 5 ng/ml. The PC4 cell lines selected in higher drug concentrations (80-1280 ng/ml) demonstrated amplification of all three mdr genes with preferential amplification of mdr3. Overexpression of the mdr2 and mdr3 genes accompanied their genomic amplification; however, expression of mdr1 was not seen despite amplification. In the C7D cell lines selected with higher drug concentrations (40-160 ng/ ml), amplification and overexpression of mdr1 and mdr2 without mdr3 was observed. Increased expression of mdr1 occurred prior to gene amplification. The distribution of mdr-specific genes in micrococcal nuclease-generated chromatin fractions differing in transcriptionally active sequences and proteins was different between the parent and drug-resistant sublines. An enrichment (two- to threefold) of mdr3 genes in the H1-depleted mononucleosome fraction enriched for actively transcribed genes (e.g., globin) was detected by Southern analysis of chromatin fractions in PC4-80 cells (selected in 80 ng/ml of adriamycin and overexpressing mdr3), compared to the parental cells. mdr3 enrichment was also detected using a new PCR-based method, which examined mdr3 genes and repetitive sequences. Of note, the H1-depleted chromatin fraction from PC4-20 showed enrichment of the mdr3 gene, although mdr3 expression was not detected in the cell line. These studies showed a different pattern of gene amplification and overexpression in genetically related erythroleukemia cell lines selected for resistance to the same chemotherapeutic agent. A change in chromatin organization of mdr genes preceded overexpression and amplification of the mdr3 gene.
Diabetic ketoacidosis, hyperlipidemia, and acute pancreatitis: the enigmatic triangle.
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Spine surgery in geriatric patients.
AIM: Many elderly patients are crippled by degenerative spine conditions. Operative treatment is often not offered due to fear of complications and consideration of life span. The objective of this study was to look at the diagnosis, surgical results and post-operative complications of elderly patients who underwent spinal surgery. METHODS: A cohort of 44 patients, 65 years and older, who had surgery in Tan Tock Seng Hospital from January 1990-August 1995 were reviewed. Twenty-five of them had spinal stenosis, II had tumour and 9 had traumatic fracture/dislocation/subluxation. There were 3 patients each with disc herniation, infection and spondylolisthesis. Nine patients had more than one diagnosis. All patients were investigated post-operatively. The data was entered into a computer-coded protocol. The diagnosis was determined intraoperatively. Type of surgery, co-morbid conditions and results were looked into. Patient's opinion on relief symptoms was graded on a 5-point scale. Functional improvement was tabulated as the patient's ambulatory status. RESULTS: The analysis of results was divided into two groups, patients with tumour and those without tumour. Twenty-seven of the 33 patients without tumour were alive at follow-up. Twenty-six of these patients had improvement of symptoms and 18 of 27 had improved functional status post-operatively. In the group with tumours, 2 had worsening symptoms and 3 had decreased function. CONCLUSION: Surgical intervention should be a treatment option in elderly patients with spinal disease.
Chalcone synthase in rice (Oryza sativa L.): detection of the CHS protein in seedlings and molecular mapping of the chs locus.
The chalcone synthase is a key enzyme that catalyses the first dedicated reaction of the flavonoid pathway in higher plants. The chs gene and its protein product in rice has been investigated. The presence of a chalcone synthase (CHS) protein in rice seedlings and its developmental stage-specific expression has been demonstrated by western analysis. The chalcone synthase of rice was found to be immunologically similar to that of maize. A rice cDNA clone, Os-chs cDNA, encoding chalcone synthase, isolated from a leaf cDNA library of an indica rice variety Purpleputtu has been mapped to the centromeric region of chromosome 11 of rice. It was mapped between RFLP markers RG2 and RG103. RG2 is the nearest RFLP marker located at a genetic distance of 3.3 cM. Some segments of chromosome 11 of rice including chs locus are conserved on chromosome 4 of maize. The markers, including chs locus on chromosome 11 of rice are located, though not in the same order, on chromosome 4 of maize. Genetic analysis of purple pigmentation in two rice lines, Abhaya and Shyamala, used in the present mapping studies, indicated the involvement of three genes, one of which has been identified as a dominant inhibitor of leaf pigmentation. The Os-chs cDNA shows extensive sequence homology, both for DNA and protein (deduced), to that of maize, barley and also to different monocots and dicots.
Simple, cost-efficient valve suture organizer.
A simple, efficient, disposable valve suture organizer is described. It is easy to construct and helps in the smooth conduct of a valve replacement procedure.
Physical mapping of Mycobacterium bovis BCG pasteur reveals differences from the genome map of Mycobacterium tuberculosis H37Rv and from M. bovis.
A Dral restriction map of the approximately 4.35 Mb circular chromosome of the vaccine strain Mycobacterium bovis BCG Pasteur was constructed by linking all 21 Dral fragments, ranging in size from 6 to 820 kb, using specific clones that spanned the Dral recognition sites as hybridization probes. The positions of 20 known genes were also established. Comparison of the resultant genome map with that of the virulent tubercle bacillus Mycobacterium tuberculosis H37Rv revealed extensive global conservation of the genomes of these two members of the M. tuberculosis complex. Possible sites of evolutionary rearrangements were localized on the chromosome of M. bovis BCG Pasteur by comparing the Asnl restriction profile with that of M. tuberculosis H37Rv. When selected cosmids from the corresponding areas of the genome of M. tuberculosis H37Rv were used as hybridization probes to examine different BCG strains, wild-type M. bovis and M. tuberculosis H37Rv, a number of deletions up to 10 kb in size, insertions and other polymorphisms were detected. In addition to the known deletions covering the genes for the protein antigens ESAT-6 and mpt64, other genetic loci exhibiting polymorphisms or rearrangements were detected in M. bovis BCG Pasteur.
Comparison of the pro-inflammatory cytokine-stimulating activity of the surface-associated proteins of periodontopathic bacteria.
Saline extraction of the periodontopathic bacterium, Actinobacillus actinomycetemcomitans, releases surface-associated material (SAM), a complex mixture of proteins and carbohydrates with potent biological actions on isolated bone and on various mammalian cell populations. In this study, the relative ability of the SAM from 5 organisms, implicated in the pathology of periodontal disease, to stimulate human mesenchymal and myelomonocytic cells to synthesize the proinflammatory cytokines - interleukin (IL)-1 beta, IL-6 and tumour necrosis factor (TNF)alpha has been investigated. The bacteria investigated were Actinobacillus actinomycetemcomitans, Eikenella corrodens, Porphyromonas gingivalis, Prevotella intermedia and Campylobacter rectus. Human cells were exposed to a four log order range of concentrations of the SAM, or of Escherichia coli lipopolysaccharide, to provide full agonist dose responses in order to allow comparison of the potency and efficacy of each SAM. All SAMs demonstrated the capacity to stimulate human gingival fibroblasts (HGFs), human peripheral blood mononuclear cells (PBMCs) or the myelomonocytic cell line - Mono-Mac-6 to release one or all of the cytokines assayed. Activity was heat- and trypsin-sensitive suggesting that the active components were proteinaceous. However, there were substantial differences in the potency and efficacy of each SAM when compared on a concentration basis (w/v). The most active SAM was from A. actinomycetemcomitans with those from E. corrodens and P. gingivalis being slightly less active. The least active cytokine-stimulating SAMs were from C. rectus and Pr. intermedia. One major difference between the SAMs and E. coli LPS was the inability of the former to stimulate HGFs to release IL-1 beta or TNF alpha although they could stimulate PBMCs to release these cytokines. This may have relevance to the pathology of the periodontal diseases.
Susceptibility to murine experimental autoimmune oophoritis is associated with genes outside the major histocompatibility complex (MHC).
PROBLEM: Neonatal thymectomy induces experimental autoimmune oophoritis in certain strains of mice, and this serves as a model for human autoimmune oophoritis. Because strong MHC associations have been noted in human autoimmune conditions, we investigated the role of MHC in determining susceptibility to murine experimental autoimmune oophoritis. Strain A mice are highly susceptible to post-thymectomy autoimmunity, whereas strain B10 mice are relatively resistant. The availability of congenic strains of mice makes it possible to separate the effects of genetic background and specific H-2 haplotype METHODS: We neonatally thymectomized A and B10 background female mice, and their H-2 congenic counterparts, and then evaluated the resulting ovarian disease at age 6 weeks. RESULTS: A. By mice, which have the A background and the H-2b haplotype, developed severe disease equivalent to strain A mice. Similarly, B10.A mice, which have the B background and the H-2a haplotype, failed to develop disease. Thus, H-2a haplotype did not convey disease susceptibility. CONCLUSIONS: Our findings suggest that immune-regulatory regions outside the H-2 locus play an important role in determining susceptibility to murine post-thymectomy autoimmune oophoritis. This is in accord with our previous findings in women that showed no association between MHC and premature ovarian failure. Thus, in this respect this model is similar to human autoimmune ovarian failure. This suggests that the non-MHC genes conveying susceptibility to autoimmune oophoritis in mice might represent similar predisposing genes for premature ovarian failure in women.