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Biomedical subjects

M C Thomas

Publications and source records attributed to M C Thomas.

At least 37 records · Page 2Linked to original sources
PubMed2004

Identification of angiotensin converting enzyme 2 in the rodent retina.

PURPOSE: An active renin-angiotensin system has been found in the retina of rats and humans. Angiotensin-converting enzyme 2 (ACE2) is a recently discovered enzymatic homologue of Angiotensin-converting enzyme (ACE) that may be an important new component of the renin-angiotensin system (RAS). This study assesses the involvement of ACE2 in the normal and diabetic rodent retina and its modulation by ACE inhibition. METHODS: Sprague-Dawley rats were randomised into three groups, control, diabetes, and diabetes plus ramipril, with diabetes induced with the cell toxin streptozocin and the study run for 24 weeks. ACE2 and ACE gene levels were measured using quantitative real-time polymerase chain reaction (QRT-PCR), ACE2 protein expression was confirmed by Western blotting, and ACE and ACE2 catalytic activity were measured using specific activity assays in the rat retina. Localisation of ACE2 mRNA and protein were determined by in situ hybridisation and immunohistochemistry, respectively. RESULTS: ACE mRNA levels were decreased to approximately 50% in the diabetic retina, but ACE2 mRNA levels were not significantly changed. ACE but not ACE2 gene expression was influenced by ramipril treatment. Following immunostaining, both ACE2 and ACE protein were localised predominantly to the inner nuclear layer (INL) but also to photoreceptors. In the diabetic retina, ACE enzyme activity was decreased, whereas ACE2 enzyme activity was increased. CONCLUSIONS: This study has identified ACE2 gene and catalytically active protein in the rodent retina. In diabetes, the major changes were a decrease in ACE but an increase in ACE2 enzymatic activity. The ACE inhibitor ramipril did not reduce ACE2 enzymatic activity.

Angiotensin-Converting Enzyme 2↗
PubMed2004

Elevated iron indices in patients with diabetes.

AIMS: Excess iron has been implicated in the pathogenesis of diabetes and its complications. This study documents the assessment of plasma iron indices and the correlation between transferrin saturation with biochemical and clinical parameters in a cross-sectional survey of 820 patients with diabetes in long-term follow-up in a single clinic. METHODS: Plasma iron indices, together with the biochemical and clinical profile of all patients, were recorded over a 2-year period. Predictors of the transferrin saturation were identified using multiple and logistic regression analysis. RESULTS: Eighty per cent of patients had Type 2 diabetes. The prevalence of elevated transferrin saturation (> 35%) was 3-4-fold higher in patients with diabetes, compared with historical prevalence described in the general population. Independent associations with elevated transferrin saturation were male gender, low C-reactive protein, and increased fasting plasma glucose (all P < 0.0001). Patients with Type 1 diabetes were also more likely to have an elevated transferrin saturation [odds ratio 3.9 (95% CI 1.9-8.0), P < 0.001]. Patients with an elevated transferrin saturation were younger, but had a similar duration of diabetes, possibly suggesting an earlier age of onset. There was no correlation between the presence of diabetic complications and the presence of elevated iron indices. CONCLUSIONS: Elevated iron indices are more common in patients with diabetes. Excess iron may have a role in the development of diabetes and subsequently in glycaemic control. This should be balanced by the strong association between iron indices and anaemia in patients with diabetes.

Adolescent↗
PubMed2004

Molecular characterization of the Leishmania braziliensis L6 ribosomal protein.

By screening a Leishmania braziliensis complementary DNA library with a pool of sera from leishmaniasis patients, the gene coding for L6 ribosomal protein was isolated. The sequence, genomic organization, and transcription of this gene are described in this article. The sequence analysis of the L. braziliensis L6 gene shows a single open reading frame, which codes for a protein of 192 amino acids (aa) with a hypothetical molecular mass of 20.9 kDa. The protein exhibits significant sequence similarity to L6 ribosomal proteins from higher eukaryotes and yeast. Thus, the L. braziliensis L6 protein contains 4 functional motifs, which are located at equivalent positions in other L6 ribosomal proteins described previously. Interestingly, the L6 ribosomal protein from L. braziliensis contains a specific region of 14 aa and a tyrosine kinase motif, which is absent in human and C. elegans L6 protein. The locus coding the L. braziliensis L6 ribosomal protein is formed by 2 gene copies arranged in tandem and located in a chromosome of approximately 0.9. Mb. The genes are actively transcribed as 2 polyadenylated transcripts of approximately 1.15 and 0.85 kb, which differ in their steady-state level and stability.

Amino Acid Sequence↗
PubMed2003

Superior renoprotective effects of combination therapy with ACE and AGE inhibition in the diabetic spontaneously hypertensive rat.

AIMS/HYPOTHESIS: Diabetic renal disease has been postulated to progress as a result of an interaction between metabolic and haemodynamic pathways. Our aim was to assess the functional, structural, molecular and cellular aspects of renal disease in an experimental model of diabetes with associated hypertension. METHOD: Streptozotocin-induced diabetic spontaneously hypertensive rats were randomised to no treatment, the ACE inhibitor, perindopril (2 mg/l), the AGE formation inhibitor, aminoguanidine (1 g/l) and a combination of both agents and were followed for 32 weeks. RESULTS: Diabetes was associated with a considerable increase in albumin excretion rate. Both aminoguanidine and perindopril retarded the increase in albuminuria, which was completely abrogated by combination therapy. Glomerulosclerosis and tubulointerstitial damage was reduced by both monotherapies with further renoprotection afforded by combination therapy in both cases. Combination therapy was also associated with a superior restoration in diabetes-induced nephrin protein depletion compared to either monotherapy. TGFbeta1 expression as assessed by in situ hybridisation was increased in the diabetic rats and reduced by perindopril and aminoguanidine. CONCLUSION/INTERPRETATION: These findings indicate that in the context of diabetes-related renal injury, blocking both the renin-angiotensin and advanced glycation pathways offers superior renoprotection and could be considered as a therapeutic strategy in the prevention and retardation of progressive-diabetic renal injury.

Albuminuria↗
PubMed2003

The endonuclease NL1Tc encoded by the LINE L1Tc from Trypanosoma cruzi protects parasites from daunorubicin DNA damage.

In the present paper we show that the overexpression of the NL1Tc protein, encoded by the L1Tc non-LTR retrotransposon from Trypanosoma cruzi, led to a reduction of about 60% of DNA damage caused by daunorubicin treatment. This repair effect is not observed in transfected parasites overexpressing the NL1Tc mutated in the aspartic acid located in the active site of the enzyme. In addition, NL1Tc overexpression protects the parasite from the negative effect that daunorubicin has on parasite's growth rate. Thus, parasites overexpressing NL1Tc show, after treatment with 4 microM of daunorubicin, growth rate two to three times higher than the growth rate observed in treated control parasites transformed with the empty vector or overexpressing the mutated NL1Tc. Likewise, parasites overexpressing the NL1Tc protein and irradiated with a single dose of gamma-radiation (6 or 9 Gy) show higher growth rates than the parasites overexpressing the mutated NL1Tc or the control transfected parasites.

Animals↗
PubMed2003

Characterization of reverse transcriptase activity of the L1Tc retroelement from Trypanosoma cruzi.

The recombinant protein RTL1Tc, encoded by the non-LTR (long terminal repeat) retrotransposon L1Tc from Trypanosoma cruzi, has been shown to have reverse transcriptase (RT) activity using poly(rA)/oligo(dT) and poly(rC)/oligo(dG) homopolymers as template/primers. The optimal RT activity was detected at a concentration of 5 mM Mg2+, pH 8 and between 28 and 37% degrees C. Site-directed mutagenesis in the RT catalytic site proved that substitution of aspartic acid 313 for isoleucine (RT D313IL1Tc) practically abolishes the RT activity of the RTL1Tc protein. RT-polymerase chain reaction assays revealed that the RTL1Tc protein has the ability to use both homologous and heterologous RNA templates. Also, it is shown that the RTL1Tc protein is capable of synthesizing complementary DNA molecules by consecutive switching of the oligo molecule, which the protein uses as a template. This template switching may be involved in the retroelement integration process.

Animals↗
PubMed2003

RAPD method useful for distinguishing Leishmania species: design of specific primers for L. braziliensis.

The technique of Random Amplification Polymorphic DNA allows fragments of the genome to be amplified by means of polymerase chain reaction (PCR) without previous knowledge of their sequences. The protozoa of the genus Leishmania present great genetic variability, making it difficult to characterize the different species. A method is developed with a single 10-mers long primer, which allows the species L. braziliensis, L. mexicana, L. infantum, L. tropica, L. chagasi, L. amazonensis and L. major to be differentiated. These products amplified by RAPD have also facilitated the design of some primers that amplify L. braziliensis DNA exclusively.

Animals↗
PubMed2003

Differential CD86 and CD40 co-stimulatory molecules and cytokine expression pattern induced by Trypanosoma cruzi in APCs from resistant or susceptible mice.

Differential aspects of the host immune response generated by Trypanosoma cruzi infection were examined in two different mouse strains, BALB/c (haplotype H2-Kd) which does not overcome the acute phase of the infection and C57BL/6 (haplotype H2-Kb) which survives to the acute phase. After infection an increase in CD3+ T cells was observed in both mouse strains in the peritoneal cavity. However, while the CD3+ T cells from the BALB/c mice showed an increase in the IL-4 cytokine expression level, the same type of cells from the C57BL/6 mice showed an increase in IFN-gamma expression. In addition, only the macrophages from the C57BL/6 mice were activated secreting IL-12 and TNF-alpha and producing, moreover, high levels of nitrites. It was observed that also after parasite infection the expression of macrophage and dendritic cells CD40 and CD86 co-stimulation molecules from the spleen were diminished in BALB/c but not in C57BL/6 mice. In correlation with this observation the macrophages from the spleen of infected BALB/c mice secreted lower concentrations of nitrites than the C57BL/6 mouse cells. Also, the spleen dendritic cells from infected BALB/c mice had a small potential to present alloantigens in contrast to that observed in the infected C57BL/6 mouse cells.

Animals↗
PubMed2002

Non-attendance at re-examination 20 years after screening in the British Regional Heart Study.

BACKGROUND: Maintenance of high participation rates in longitudinal studies is critical to their validity because of the possibility of bias associated with non-participation, which may differ between studies. This paper examines factors associated with participation status over time, by comparing the characteristics of non-attenders and attenders at a 20 year follow-up examination in a cardiovascular cohort study with an initial participation rate of 78 percent. METHODS: A baseline examination was carried out between 1978 and 1980 and subjects have been followed up through regular reviews of general practice records, postal questionnaires, and a clinical re-examination of survivors in 1998-2000. Data obtained by questionnaire in 1996 (Q96) and at baseline examination have been used to compare the characteristics of these recent non-attenders and attenders who remain in the cohort for further follow-up. RESULTS: The non-attendance rate of available survivors at re-examination was 23 per cent (n = 1313). Rates of non-attendance were highest in Scotland and lowest in Southern England. Non-attenders were older than attenders, more likely to smoke, and reported more disabling conditions and greater use of multiple medications at Q96, but recalled similar rates of diagnosed coronary heart disease. Marked differences in social factors were identified. Total mortality rates within 1 year of re-examination were over three times higher amongst non-attenders than attenders. CONCLUSIONS: Non-attendance is related to health status, risk factor status and social circumstances and may affect some estimates of disease prevalence, but does not appearto have a major impact on the estimated prevalence of coronary heart disease. Information collected on non-attenders in longitudinal studies helps to estimate, adjust and minimize these effects.

Adult↗
PubMed2002

Cloning and molecular characterization of the cDNA encoding histone H1 from Leishmania braziliensis.

The isolation and molecular characterization of the histone H1-encoding gene from Leishmania braziliensis was carried out. The gene is present in the genome as a single copy and transcribed as a polyadenylated transcript of 830 nucleotides. The deduced amino acid sequence has in its central region the DNA binding K-[K/R]-A-A-[A/P] motif, which is repeated in tandem 9 times.

Amino Acid Sequence↗
PubMed2001

Early peri-operative glycaemic control and allograft rejection in patients with diabetes mellitus: a pilot study.

BACKGROUND: Hyperglycemia alters the inflammatory response to infection and ischemia. We hypothesize that perioperative glycemic control could also influence the risk for allograft rejection. METHODS: Consecutive patients with established diabetes undergoing their first cadaveric renal transplantation and receiving steroid-sparing immunosuppression were identified (n=50). Records of capillary glucose observations over the first 100 hr following surgery and transplantation variables pertaining to graft function, acute rejection, and postoperative infection were identified and entered into multivariate analysis. RESULTS: Perioperative glycemic control was associated with an increased incidence of infection and acute rejection. Only 3 of 27 patients (11%) with optimal glycemic control during the 100 hr following surgery (mean<11.2 mmol/L) had rejection episodes compared with 58% of patients with poor control (>11.2 mmol/L). All patients with poor glycemic control experienced postoperative infection. CONCLUSIONS: This pilot study suggests that hyperglycemia may be associated with an increased risk of both allograft rejection and postoperative infection in patients with diabetes.

Adult↗
PubMed2001

Morphogenesis of prechordal plate and notochord requires intact Eph/ephrin B signaling.

Eph receptors and their ligands, the ephrins, mediate cell-to-cell signals implicated in the regulation of cell migration processes during development. We report the molecular cloning and tissue distribution of zebrafish transmembrane ephrins that represent all known members of the mammalian class B ephrin family. The degree of homology among predicted ephrin B sequences suggests that, similar to their mammalian counterparts, zebrafish B-ephrins can also bind promiscuously to several Eph receptors. The dynamic expression patterns for each zebrafish B-ephrin support the idea that these ligands are confined to interact with their receptors at the borders of their complementary expression domains. Zebrafish B-ephrins are expressed as early as 30% epiboly and during gastrula stages: in the germ ring, shield, prechordal plate, and notochord. Ectopic overexpression of dominant-negative soluble ephrin B constructs yields reproducible defects in the morphology of the notochord and prechordal plate by the end of gastrulation. Notably disruption of Eph/ephrin B signaling does not completely destroy structures examined, suggesting that cell fate specification is not altered. Thus abnormal morphogenesis of the prechordal plate and the notochord is likely a consequence of a cell movement defect. Our observations suggest Eph/ephrin B signaling plays an essential role in regulating cell movements during gastrulation.

Amino Acid Sequence↗
PubMed2001

The immunization of A2/K(b) transgenic mice with the KMP11-HSP70 fusion protein induces CTL response against human cells expressing the T. cruzi KMP11 antigen: identification of A2-restricted epitopes.

Cytotoxic T lymphocyte response against Jurkat-A2/K(b) cells expressing the T. cruzi KMP11 protein has been evaluated after immunization of C57BL/6-A2/K(b) transgenic mice with the KMP11 and KMP11-HSP70 recombinant proteins. The results show that mice immunized with KMP11 covalently fused to the T. cruzi HSP70 protein, but not mice immunized with KMP11 alone, elicit a CTL response against the Jurkat-A2/K(b) cells expressing the KMP11 protein. The data also show that spleen cells from mice immunized with the fusion protein and stimulated with the K1 peptide induce lysis of both the Jurkat-A2/K(b) cells transfected with the KMP11 coding gene and the Jurkat-A2-K(b) cells pulsed with the K1 peptide. Splenocytes stimulated with the K3 peptide induce lysis of the Jurkat-A2/K(b) cells loaded with the K3 peptide but they do not recognize the target cells expressing the KMP11 protein. Similar results were obtained using lymph node from mice immunized with the peptides. Thus, we believe there are two cytotoxic T cell epitopes restricted to the A2 molecule (K1(KMP11) (4-12) and K3(KMP11) (41-50)) in the KMP11 protein, and suggest that the K1 peptide could be considered an immunodominant antigen whilst the K3 peptide may be regarded as a cryptic epitope. The fact that the CTL lines induced in B6-A2/K(b) mice recognize human cells expressing KMP11 protein, indicates that the KMP11 antigen fused to HSP70 could be a good candidate for the induction of immunoprotective cytotoxic responses against T. cruzi natural infection.

Animals↗
PubMed2001

Four cases of CMV ureteritis: emergence of a new pattern of disease?

Although cytomegalovirus (CMV) infection is common in renal transplant recipients, urinary tract involvement has been rare. Only six cases of symptomatic ureteritis have been reported in renal transplant recipients and all within the last five years. We describe an additional four cases of CMV ureteritis. The presentation of CMV ureteritis is obstructive nephropathy often in the absence of systemic illness. Presentation may also mimic allograft rejection with minimal obstructive symptoms. We hypothesize that CMV ureteritis is an emerging complication of CMV disease, possibly due to changes in transplant practice.

Adult↗
PubMed2001

Mapping of the antigenic determinants of the T. cruzi kinetoplastid membrane protein-11. Identification of a linear epitope specifically recognized by human Chagasic sera.

The high variability among strains and isolates of Trypanosoma cruzi and the existence of shared antigenic determinants with other pathogens, particularly with members of the Leishmania genus make difficult the specific diagnosis of Chagas' disease. The data reported in this paper show that the T. cruzi KMP11 protein is an immunodominant antigen highly recognized by the sera from chagasic and leishmaniasis patients. By the use of amino- and carboxyl-terminal truncated KMP11 recombinant proteins and synthetic peptides, evidence is provided that while the sera from chagasic patients recognize linear peptides the sera from patients with visceral leishmaniasis must be predominantly directed against conformational epitopes. We found that a particular linear determinant, located in the carboxyl-terminal region of the protein, is recognized with high specificity and sensitivity only by sera from Chagas' disease patients, suggesting it could be a good candidate for differential serodiagnosis of Chagas' disease.

Adult↗
PubMed2001

Small intestinal mucosal immunity and morphometry in luminal overgrowth of indigenous gut flora.

OBJECTIVE: The aim of this study was to investigate the separate effects of indigenous oropharyngeal- and colonic-type flora on small intestinal mucosal immunity and morphometry in small intestinal bacterial overgrowth (SIBO). METHODS: A duodenal aspirate and random biopsies of underlying mucosa were obtained from 52 adult subjects (age range, 18-90 yr; median, 60 yr) without disorders that may otherwise disturb small intestinal histology or mucosal immunity. Villus height, crypt depth, villus/crypt ratios, counts of intraepithelial lymphocytes (IELs) and lamina propria total mononuclear cells, IgA, IgM, and IgG plasma cells, mast cells, and B and T lymphocytes were determined in relation to the presence or absence of SIBO and the nature of the overgrowth flora in all subjects. CD4+ve and CD8+ve T-cell counts were determined in 24 subjects. RESULTS: SIBO was present in 26 of 52 (50%) subjects. Overgrowth flora included colonic-type bacteria in 20 subjects and oropharyngeal-type flora alone in 6 subjects. Lamina propria IgA plasma cell counts were significantly increased in subjects with SIBO, irrespective of whether the overgrowth flora comprised oropharyngeal-type flora alone or included colonic-type bacteria. Neither villus height, crypt depth, villus/crypt ratios, nor total or other mononuclear cell counts in lamina propria differed significantly between subjects with and without SIBO, irrespective of the nature of the overgrowth flora. IEL counts were significantly higher than in culture-negative subjects only when the overgrowth flora included colonic-type bacteria. Even then, IEL counts were within a range currently considered normal. A significant, inverse correlation between advancing age and IEL counts became apparent after adjusting for the effect of SIBO of colonic-type flora. CONCLUSIONS: SIBO of oropharyngeal- and colonic-type flora are associated with differing disturbances of local duodenal mucosa. Nonetheless, these would not be readily apparent during routine histological assessment. Old age independently influences duodenal IEL counts.

Bacterial Infections↗