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Biomedical subjects

A W Thomas

Publications and source records attributed to A W Thomas.

At least 55 records · Page 3Linked to original sources
PubMed2000

The Frontal Behavioral Inventory in the differential diagnosis of frontotemporal dementia.

A personality and behavioral disorder is an important and defining feature of frontal lobe dementia (FLD) or frontotemporal degeneration (FTD). The diagnosis usually depends on the progressive development of various behavioral symptoms rather than a set of neuropsychological measures. Quantification of the personality-behavior disorder is important for standardizing the diagnosis. An inventory was constructed to capture the major positive and negative behaviors and personality change, and it was administered prospectively to caregivers of 108 patients in a cognitive neurology clinic, at the time of first diagnostic assessment. The prevalence and extent of behavioral abnormality was quantitated in the clinic population of FLD, vascular dementia (VaD), Alzheimer's disease (AD), primary progressive aphasia (PPA), and depressive disorder (DD) patients. The mean scores of FLD patients were significantly above all other groups. Scores in VaD were also higher than in AD, PPA, and DD. Interrater reliability (Cohen's kappa of .90) and item consistency (a Cronbach alpha of .89) were both high. Perseveration, indifference, inattention, inappropriateness, and loss of insight rated highest in FLD, significantly different from all other groups. Apathy, aspontaneity, inflexibility, disorganization, impulsivity, personal neglect, and poor judgment were also significantly higher in FLD. Discriminant function correctly classified 92.7% versus all other patients (NON-FLD) in the study. A total of 18.8% of VaD patients were misclassified as FLD. Indifference, alien hand, and inappropriateness were the highest discriminant functions. Perseveration and verbal apraxia were important discriminatory items for FLD and PPA, respectively. The FBI is a standardized behavioral inventory useful to diagnose FLD, to differentiate it from other dementias, and to quantify the behavior disorder.

Aged↗
PubMed2000

Expression of beta-defensin-1 in chimpanzee (Pan troglodytes) airways.

In human airways, beta-defensins function in the elimination of various pathogens. They have been identified in a wide range of species. Here we report the identification and expression of chimpanzee beta-defensin-1 (cBD1), which is a homolog of human beta-defensin-1, in chimpanzee airways and skin. The cBD1 cDNA sequence differs by only one synonymous nucleotide substitution compared to the human cDNA sequence. In situ hybridization revealed that in lung tissue beside alveolar macrophages also airway epithelial cells, endothelial cells and type II pneumocytes express cBD1 mRNA. In skin, cBD1 mRNA was expressed in keratinocytes and endothelial cells. Together, these results show similarity in structure and expression pattern and perhaps in function.

Animals↗
PubMed2000

Protection against Plasmodium falciparum malaria in chimpanzees by immunization with the conserved pre-erythrocytic liver-stage antigen 3.

In humans, sterile immunity against malaria can be consistently induced through exposure to the bites of thousands of irradiated infected mosquitoes. The same level of protection has yet to be achieved using subunit vaccines. Recent studies have indicated an essential function for intrahepatic parasites, the stage after the mosquito bite, and thus for antigens expressed during this stage. We report here the identification of liver-stage antigen 3, which is expressed both in the mosquito and liver-stage parasites. This Plasmodium falciparum 200-kilodalton protein is highly conserved, and showed promising antigenic and immunogenic properties. In chimpanzees (Pan troglodytes), the primates most closely related to humans and that share a similar susceptibility to P. falciparum liver-stage infection, immunization with LSA-3 induced protection against successive heterologous challenges with large numbers of P. falciparum sporozoites.

Animals↗
PubMed2000

Lower urinary tract symptoms, benign prostatic obstruction and the overactive bladder.

Lower urinary tract symptoms (LUTS), benign prostatic obstruction (BPO), and the overactive bladder have increasing prevalence with age in both men and women (with the obvious exception). The question is, are they interrelated or independently related to age? The specific issue is whether BPO causes the overactive bladder. There are two pieces of evidence that might appear to suggest such a cause and effect. First, the overactive bladder is more common in men than in women of the same age, although physiologically, men are 5-10 years older at the same biological age. Second, the overactive bladder resolves in two-thirds of individuals after surgical interventions such as transurethral prostatectomy. The symptoms suggestive of an overactive bladder are the most troublesome, even though they may not be the most prevalent. Long-term follow-up studies with repeated urodynamic investigations have shown that the incidence of the overactive bladder and its attendant symptoms increases despite there being no deterioration in outlet obstruction over follow-up periods of 10 and 20 years. These data, and others, indicate that the situation is not as straightforward as some believe. The statement that 'the overactive bladder is secondary to BPO' cannot be made, as there are too many unanswered questions and pieces of the puzzle that do not fit. The overactive bladder is undoubtedly associated with BPO, and it leads to the most troublesome LUTS in older men. Epidemiological research, coupled with urodynamic evaluation, may provide further evidence. We also need better and more relevant models (e.g. ageing animals), together with further histological and other biological data before the waters become crystal clear.

Aging↗
PubMed2000

Reactivity of human T-lymphocyte-specific antibodies with peripheral blood mononuclear cells and spleen of Aotus azarae ssp. boliviensis (owl monkey).

Aotus monkeys offer one of the few models that can be used for the evaluation of the immunogenicity and efficacy of new vaccine candidates against the human malarias, Plasmodium falciparum and Plasmodium vivax. However, the tools available for evaluation of the immune responses in these New World primates are still limited. In the present study, a previously selected set of monoclonal antibodies that were raised against human T cell determinants and were reactive with at least one other primate species was investigated for its reactivity with Aotus lymphocytes using FACS analysis, indirect immunofluorescence (IFA) and immunohistochemistry. From a panel of 19 mAb, six were found to react consistently with Aotus lymphocytes using FACS analysis. Further evaluation of the mAb using IFA confirmed these findings. Analysis of the selected mAb on spleen sections of Aotus monkeys identified one anti-CD4 and one anti-CD8 mAb that can be used for immunohistochemical studies. The set of mAb identified in this study can be used for the detection of various T lymphocyte markers in peripheral blood and in tissues of Aotus monkeys. Together with data published by others, mAb are now identified for detection of six different markers of Aotus T lymphocytes. These mAb are very valuable for the characterisation of immune responses after vaccination and infection in the Aotus malaria models.

Animals↗
PubMed2000

Immunization with parasite-derived apical membrane antigen 1 or passive immunization with a specific monoclonal antibody protects BALB/c mice against lethal Plasmodium yoelii yoelii YM blood-stage infection.

We have purified apical merozoite antigen 1 (AMA-1) from extracts of red blood cells infected with the rodent malaria parasite Plasmodium yoelii yoelii YM. When used to immunize mice, the protein induced a strong protective response against a challenge with the parasite. Monoclonal antibodies specific for P. yoelii yoelii AMA-1 were prepared, and one was very effective against the parasite on passive immunization. A second protein that appears to be located in the apical rhoptry organelles and associated with AMA-1 was identified.

Animals↗
PubMed1999

Three new mutations in the uroporphyrinogen decarboxylase gene in familial porphyria cutanea tarda. Mutation in brief no. 237. Online.

We have characterised three new mutations in the uroporphyrinogen decarboxylase gene in familial porphyria cutanea tarda. The first of these was a G to A substitution in the 5' splice junction of exon 4 which generated an mRNA that lacked exon 4. The second was a nonsense mutation in exon 5 which changed the arginine residue at position 142 to a stop codon, and the third mutation, also in exon 5, was a triple base substitution from nucleotide position 417 to 419. This mutation encompassed two codons but only changed the amino acid predicted from the second codon, resulting in the replacement of valine with glutamine at position 134. This missense mutation has been described previously by Meguro et al. 1994, on one allele in a compound heterozygote with hepatoerythropoietic porphyria. This is the third case of an hepatoerythropoietic porphyria mutation in an individual diagnosed with familial porphyria cutanea tarda.

Humans↗
PubMed1999

High-level expression of Plasmodium vivax apical membrane antigen 1 (AMA-1) in Pichia pastoris: strong immunogenicity in Macaca mulatta immunized with P. vivax AMA-1 and adjuvant SBAS2.

The apical membrane antigen 1 (AMA-1) family is a promising family of malaria blood-stage vaccine candidates that have induced protection in rodent and nonhuman primate models of malaria. Correct conformation of the protein appears to be essential for the induction of parasite-inhibitory responses, and these responses appear to be primarily antibody mediated. Here we describe for the first time high-level secreted expression (over 50 mg/liter) of the Plasmodium vivax AMA-1 (PV66/AMA-1) ectodomain by using the methylotrophic yeast Pichia pastoris. To prevent nonnative glycosylation, a conservatively mutagenized PV66/AMA-1 gene (PV66Deltaglyc) lacking N-glycosylation sites was also developed. Expression of the PV66Deltaglyc ectodomain yielded similar levels of a homogeneous product that was nonglycosylated and was readily purified by ion-exchange and gel filtration chromatographies. Recombinant PV66Deltaglyc43-487 was reactive with conformation-dependent monoclonal antibodies. With the SBAS2 adjuvant, Pichia-expressed PV66Deltaglyc43-487 was highly immunogenic in five rhesus monkeys, inducing immunoglobulin G enzyme-linked immunosorbent assay titers in excess of 1:200,000. This group of monkeys had a weak trend showing lower cumulative parasite loads following a Plasmodium cynomolgi infection than in the control group.

Adjuvants, Immunologic↗
PubMed1999

Transformed Toxoplasma gondii tachyzoites expressing the circumsporozoite protein of Plasmodium knowlesi elicit a specific immune response in rhesus monkeys.

Toxoplasma gondii tachyzoites were transformed with the coding sequence of the circumsporozoite (CS) protein of the primate malaria parasite Plasmodium knowlesi. A single inoculation of live transformed tachyzoites elicited an antibody response directed against the immunodominant repeat epitope (EQPAAGAGG)2 of the P. knowlesi CS protein in rhesus monkeys. Notably, these animals failed to show a positive serum conversion against T. gondii. Antibodies against Toxoplasma antigens were detected only after a second inoculation with a higher number of transformed tachyzoites. This boost induced an increased antibody response against the P. knowlesi CS protein associated with immunoglobulin class switching, thus demonstrating the establishment of immunological memory. These results indicate that the Toxoplasma-derived CS protein is efficiently recognized by the monkey immune system and represents an immunodominant antigen in transformed parasites.

Amino Acid Sequence↗
PubMed1999

Phylogenetic analysis of mitochondrial DNA in type 2 diabetes: maternal history and ancient population expansion.

Several studies have suggested a maternal excess in the transmission of type 2 (non-insulin-dependent) diabetes. However, the majority of these reports rely on patients recalling parental disease status and hence are open to criticism. An alternative approach is to study mitochondrial DNA (mtDNA) lineages. The hypervariable region 1 of the rapidly evolving noncoding section of mtDNA is suitable for investigating maternal ancestry and has been used extensively to study the origins of human racial groups. We have sequenced this 347-bp section of mtDNA from leukocytes of subjects with type 2 diabetes (n = 63) and age- and race-matched nondiabetic control subjects (n = 57). Consensus sequences for the two study groups were identical. Pairwise sequence analysis showed unimodal distribution of pairwise differences for both groups, suggesting that both populations had undergone expansion in ancient times. The distributions were significantly different (chi2 = 180, df = 11, P < 0.001); mean pairwise differences were 4.7 and 3.8 for the diabetic and control subjects, respectively. These data suggest that the diabetic subjects belong to an ancient maternal lineage that expanded before the major expansion observed in the nondiabetic population. Phylogenetic trees constructed using maximum parsimony, neighbor-joining, Fitch-Margolish, or maximum likelihood methods failed to show the clustering of all (or a subset) of the diabetic subjects into one or more distinct lineages.

DNA, Mitochondrial↗
PubMed1999

Differential expression of mRNA in human thyroid cells depleted of mitochondrial DNA by ethidium bromide treatment.

A wide variety of human diseases have been associated with defects in mitochondrial DNA (mtDNA). The exact mechanism by which specific mtDNA mutations cause disease is unknown and, although the disparate phenotypes might be explained on the basis of impaired mitochondrial gene function alone, the role of altered nuclear gene expression must also be considered. In recent years, the experimental technique of depleting cells of mtDNA by culturing them with ethidium bromide has become a popular method of studying mitochondrial disorders. However, apart from depleting mtDNA, ethidium bromide may have many other intracellular and nuclear effects. The aim of the present study was to investigate the effects of ethidium bromide treatment on nuclear gene expression. A simian-virus-40-transformed human thyroid cell line was depleted of mtDNA by culture in ethidium bromide, and differential display reverse transcriptase-PCR (DDRT-PCR) was then employed to compare mRNA expression between wild-type, mtDNA-replete (rho(+)) and ethidium bromide-treated, mtDNA-depleted (rho(0)) cells. Expression of the majority of nuclear-encoded genes, including those for subunits involved in oxidative phosphorylation, remained unaffected by the treatment. Seven clones were found to be underexpressed; three of the clones showed significant similarity with sequences of the human genes encoding RNase L inhibitor, human tissue factor and ARCN1 (archain vesicle transport protein 1), a highly conserved species which is related to vesicle structure and trafficking proteins. We conclude that the effects of ethidium bromide treatment on nuclear gene expression are not simply limited to changes in pathways directly associated with known mitochondrial function. Further studies will be required to elucidate which of these changes are due to mtDNA depletion, ATP deficiency or other disparate effects of ethidium bromide exposure. Given that most genes appear unaffected, the results suggest that depleting cells of mtDNA by ethidium bromide treatment is a valuable approach for the study of mitochondrial mutations by cybrid techniques.

Blotting, Northern↗
PubMed1998

Characterisation of the Cdc2-related kinase 2 gene from Plasmodium knowlesi and P. berghei.

The complete sequence of the cdc2-related kinase 2 (CRK2) gene from Plasmodium knowlesi and from P. berghei was determined. In both species, the CRK2 gene is closely linked to an elongation factor 1 alpha gene. The two CRK2 proteins are highly homologous to the P. falciparum PfPK5 protein. The CRK2 gene of both species is expressed at a low level during the asexual cell-cycle within the host erythrocytes. The P. berghei CRK2 mRNA is also present in gametocytes and in stages during development in the mosquito, suggesting a role of this protein in different parts of the life cycle. A conserved sequence located in the 5' untranslated region immediately upstream of the initiator ATG has the potential to form a stem-loop structure. Although the CRK2 protein possesses most of the domains that are conserved among cdc2-proteins, neither a recombinant P. knowlesi CRK2 protein nor a recombinant P. berghei protein was able to complement a yeast cdc28ts mutant. Furthermore and in contrast to the P. falciparum PfPK5 protein, a recombinant monomeric P. knowlesi CRK2 protein showed no kinase activity.

Amino Acid Sequence↗
PubMed1998

Malaria parasites contain two identical copies of an elongation factor 1 alpha gene.

Elongation factor 1alpha (EF-1alpha) is an abundant protein in eukaryotic cells, involved chiefly in translation of mRNA on the ribosomes, and is frequently encoded by more than one gene. Here we show the presence of two identical copies of the EF-1alpha gene in the genome of three malaria parasites, Plasmodium knowlesi, P. berghei and P. falciparum. They are organized in a head-to-head orientation and both genes are expressed in a stage specific manner at a high level, indicating that the small intergenic region contains either two strong promoters or a single bidirectional one. Both genes are expressed at the same time during erythrocytic development of the parasite. This expression pattern and the 100% similarity of the two genes excludes the possibility that the duplicated genes developed in accordance to the different types of ribosomes in Plasmodium. It is more likely that the duplication reflects a gene dosage effect. Comparison of codon usage in the Cdc2-related kinase genes (CRK2) of Plasmodium, which are expressed at a very low level, with the EF-1alpha genes indicates the existence of a codon bias for highly expressed genes, as has been shown in other organisms.

Amino Acid Sequence↗
PubMed1998

Precise timing of expression of a Plasmodium falciparum-derived transgene in Plasmodium berghei is a critical determinant of subsequent subcellular localization.

The development of transfection technology for malaria parasites holds significant promise for a more detailed characterization of molecules targeted by vaccines or drugs. One asexual blood stage vaccine candidate, apical membrane antigen-1 (AMA-1) of merozoite rhoptries has been shown to be the target of inhibitory, protective antibodies in both in vitro and in vivo studies. We have investigated heterologous (trans-species) expression of the human malaria Plasmodium falciparum AMA-1 (PF83/AMA-1) in the rodent parasite Plasmodium berghei. Transfected P. berghei expressed correctly folded and processed PF83/AMA-1 under control of both pb66/ama-1 and dhfr-ts promoters. Timing of expression was highly promoter-dependent and was critical for subsequent subcellular localization. Under control of pb66/ama-1, PF83/AMA-1 expression and localization in P. berghei was limited to the rhoptries of mature schizonts, similar to that observed for PF83/AMA-1 in P. falciparum. In contrast the dhfr-ts promoter permitted PF83/AMA-1 expression throughout schizogony as well as in gametocytes and gametes. Localization was aberrant and included direct expression at the merozoite and gamete surface. Processing from the full-length 83-kDa protein to a 66-kDa protein was observed not only in schizonts but also in gametocytes, indicating that processing could be mediated outside of rhoptries by a common protease. Trans-species expressed PF83/AMA-1 was highly immunogenic in mice, resulting in a response against a functionally critical domain of the molecule.

Animals↗
PubMed1998

Transfection systems for animal models of malaria.

Transfection of malaria parasites is a rapidly emerging technology that offers great promise for the investigation of many aspects of infection. Animal models of malaria have always played an important role in the investigation of the disease. In this article, two of the Dutch groups that have been involved in combining transfection with animal models describe the relevant techniques and recent vector developments for the expression of transgenes, giving examples of their application.

Journal Article↗