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Biomedical subjects

C A Abbott

Publications and source records attributed to C A Abbott.

At least 19 recordsLinked to original sources
PubMed2003

Corneal confocal microscopy: a non-invasive surrogate of nerve fibre damage and repair in diabetic patients.

AIMS/HYPOTHESIS: The accurate detection, characterization and quantification of human diabetic neuropathy are important to define at risk patients, anticipate deterioration, and assess new therapies. Corneal confocal microscopy is a reiterative, rapid, non-invasive in vivo clinical examination technique capable of imaging corneal nerve fibres. The aim of this study was to define the ability of this technique to quantify the extent of degeneration and regeneration of corneal nerve fibres in diabetic patients with increasing neuropathic severity. METHODS: We scanned the cornea and collected images of Bowman's layer (containing a rich nerve plexus) from 18 diabetic patients and 18 age-matched control subjects. RESULTS: Corneal nerve fibre density (F(3)=9.6, p<0.0001), length (F(3)=23.8, p<0.0001), and branch density (F(3)=13.9, p<0.0001) were reduced in diabetic patients compared with control subjects, with a tendency for greater reduction in these measures with increasing severity of neuropathy. CONCLUSION/INTERPRETATION: Corneal confocal microscopy is a rapid, non-invasive in vivo clinical examination technique which accurately defines the extent of corneal nerve damage and repair and acts as a surrogate measure of somatic neuropathy in diabetic patients. It could represent an advance to define the severity of neuropathy and expedite assessment of therapeutic efficacy in clinical trials of human diabetic neuropathy.

Cornea↗
PubMed2002

Risk of diabetes-related amputation in South Asians vs. Europeans in the UK.

AIMS: To compare the risk of and risk factors for diabetes-related amputation in South Asians and Europeans. METHODS: This was a population-based case control study based in the health districts of Bolton, Oldham and Central Manchester in the UK. Cases with diabetes-related amputation performed between 1992 and 1997 (n = 172) and controls with diabetes and no amputation (n = 376) were selected from the primary care-based North-west Diabetes Foot Study database. Risk factor data were also collected. RESULTS: Age at diagnosis adjusted odds ratio (OR) of amputation in South Asians compared with Europeans was 0.26, 95% confidence interval (CI) 0.11-0.65, P = 0.004. In the control population, South Asians were less likely than Europeans to have peripheral vascular disease (PVD) (9% vs. 24%, P = 0.02), neuropathy (30% vs. 54%, P = 0.003), and less likely to have ever been smokers (31% vs. 57%, P = 0.03). When these factors were added to the model, the OR was attenuated to 0.84, 95% CI 0.23-3.08, P = 0.8. CONCLUSIONS: South Asians with diabetes have about a quarter of the risk of amputation of Europeans. This is mostly explained by low rates of PVD and neuropathy in South Asians, in part associated with low rates of smoking. The reasons for the South Asian protection from both PVD and neuropathy deserve further exploration.

Age of Onset↗
PubMed2002

The North-West Diabetes Foot Care Study: incidence of, and risk factors for, new diabetic foot ulceration in a community-based patient cohort.

AIMS: To determine the incidence of, and clinically relevant risk factors for, new foot ulceration in a large cohort of diabetic patients in the community healthcare setting. METHODS: Diabetic patients (n = 9710) underwent foot screening in six districts of North-west England in various healthcare settings. All were assessed at baseline for demographic information, medical and social history, neuropathy symptom score, neuropathy disability score, cutaneous pressure perception (insensitivity to the 10 g monofilament), foot deformities, and peripheral pulses. Two years later, patients were followed up via postal questionnaire to determine the incidence of new foot ulcers. Cox's proportional hazards regression analysis was used to determine the independent, relative risk of baseline variables for new foot ulceration. RESULTS: New foot ulcers occurred in 291/6613 patients who completed and returned their 2-year follow-up questionnaire (2.2% average annual incidence). The following factors were independently related to new foot ulcer risk: ulcer present at baseline (relative risk (95% confidence interval)) 5.32 (3.71-7.64), past history of ulcer 3.05 (2.16-4.31), abnormal neuropathy disability score (> or = 6/10) 2.32 (1.61-3.35), any previous podiatry attendance 2.19 (1.50-3.20), insensitivity to the 10 g monofilament 1.80 (1.36-2.39), reduced pulses 1.80 (1.40-2.32), foot deformities 1.57 (1.22-2.02), abnormal ankle reflexes 1.55 (1.01-2.36) and age 0.99 (0.98-1.00). CONCLUSIONS: More than 2% of community-based diabetic patients develop new foot ulcers each year. The neuropathy disability score, 10 g monofilament and palpation of foot pulses are recommended as screening tools in general practice.

Adolescent↗
PubMed2002

A comparison of the Neuropen against standard quantitative sensory-threshold measures for assessing peripheral nerve function.

AIMS: To investigate the efficacy of the Neuropen, a new clinical device that assesses both pain and pressure perception, to evaluate peripheral nerve function in diabetic patients compared with standard clinical testing methods. METHODS: Peripheral nerve function was assessed in 124 diabetic patients attending a multidisciplinary diabetes clinic, using (i) the modified Neuropathy Disability Score (NDS), derived from assessment of vibration, pinprick (pain), temperature sensation plus ankle reflexes, and (ii) vibration perception threshold (VPT) measured at the hallux. Patients were stratified into various neuropathic groups according to their NDS score. In addition, nerve function was assessed using the Neuropen, a device combining a 10-g monofilament and a weighted Neurotip. Inability to feel sensation on either or both feet for each test of the Neuropen (i.e. the monofilament or the Neurotip) was defined as an abnormal response. RESULTS: The sensitivity of the Neuropen to detect neuropathy compared with the NDS (score > or = 6/10) was high using either an abnormal monofilament response (87.8%), an abnormal Neurotip response (91.8%) or a combination of the two (82.0%). Neuropen specificity improved, however, when the combination of abnormal monofilament and abnormal Neurotip responses was used (68%), rather than the individual tests (57% and 41%, respectively). CONCLUSIONS: The Neuropen is a sensitive device for assessing nerve function and may provide an inexpensive alternative screening method to identify patients with moderate to severe neuropathy.

Age of Onset↗
PubMed2001

Identification of novel molecules and pathogenic pathways in primary biliary cirrhosis: cDNA array analysis of intrahepatic differential gene expression.

BACKGROUND: Primary biliary cirrhosis (PBC) is an autoimmune disease in which the pathogenesis of progressive liver injury is poorly understood. AIM: To provide novel insights into the pathogenesis of PBC related liver injury using cDNA array analysis, which simultaneously examines expression of many genes. METHODS: Utilising cDNA arrays of 874 genes, PBC was compared with primary sclerosing cholangitis (PSC) associated cirrhosis and non-diseased liver. Differential expression of 10 genes was confirmed by real time quantitative reverse transcriptase-polymerase chain reaction (RT-PCR). RESULTS: Array analysis identified many differentially expressed genes that are important in inflammation, fibrosis, proliferation, signalling, apoptosis, and oxidative stress. PBC was associated with increased expression of both Th1 and Th2 type molecules of the immune response. Fibrosis related gene expression featured upregulation of connective tissue growth factor and transforming growth factor beta3. Many more apoptosis associated molecules exhibited increased expression, consistent with apoptosis being a more active and regulated process, in PSC associated cirrhosis than in PBC. Increased expression of many genes of the Wnt and notch pathways implicated these highly conserved and linked pathways in PBC pathogenesis. The observed increases in expression of c-jun, c-myc, and c-fos related antigen 1 are consistent with increased Wnt pathway activity in PBC. Differential expression of four components of the Wnt pathway, Wnt-5a, Wnt-13, FRITZ, and beta-catenin, was confirmed by quantitative RT-PCR. CONCLUSION: Many genes implicated in intrahepatic inflammation, fibrosis, and regeneration were upregulated in PBC cirrhosis. In particular, increased expression of a number of Drosophila homologues was seen in PBC.

Apoptosis↗
PubMed2001

A foot care program for diabetic unilateral lower-limb amputees.

OBJECTIVE: To assess the efficacy of a specialist foot care program designed to prevent a second amputation and to assess peripheral vascular disease (PVD) and peripheral neuropathy in diabetic unilateral lower-limb amputees. RESEARCH DESIGN AND METHODS: Investigations were carried out in 143 diabetic lower-limb unilateral amputees referred to a subregional rehabilitation center for prosthetic care from a catchment area of approximately 3 million people. Peripheral vascular and nerve assessment, education, and podiatry were provided for each patient. RESULTS: For the patients referred to the foot care program, there were no baseline differences between the patients who proceeded to a bilateral amputation (n = 22) and those who remained as unilateral amputees (n = 121) in their level of foot care knowledge and mean neuropathy scores. Mean ankle-brachial pressure index was significantly lower for the bilateral amputees (0.75 +/- 0.04) compared with the unilateral amputees (0.90 +/- 0.03, mean +/- SEM, P < 0.05), but there was no difference in the level of oxygen in the skin. However, the level of carbon dioxide was significantly lower in patients with bilateral amputation (24.21 +/- 2.16 vs. 31.20 +/- 0.85 mmHg, P < 0.03). Overall, the establishment of a specialist foot care program made no impact on contralateral limb amputation (22 of 143, 15.4%) compared with matched patients without the program (21 of 148, 14%) over a 2-year outcome period for each patient. CONCLUSIONS: PVD is more closely associated with diabetic bilateral amputation than neuropathy or level of foot care knowledge. Preventative foot care programs for diabetic unilateral amputees should therefore place greater emphasis on peripheral vascular assessment to identify patients at risk and on the development of timely intervention strategies.

Aged↗
PubMed2001

Peripheral vascular and nerve function associated with lower limb amputation in people with and without diabetes.

Multiple factors, including peripheral vascular disease and neuropathy, contribute to the development and perpetuation of complications of the lower extremities in diabetes. The main aim of the present study was to assess the peripheral vascular and nerve status of diabetic and non-diabetic subjects that had undergone lower limb amputation. Various non-invasive tests of peripheral vascular and nerve function were carried out on subjects who had undergone unilateral lower limb amputation and were now attending a Rehabilitation Centre. The control group (n=23), the diabetic amputee group (n=64) and the non-diabetic amputee group (n=32) were age-matched. Only the diabetic amputee group had evidence of medial arterial calcification. Transcutaneous oxygen levels were significantly lower in the diabetic amputee group (median 43 mmHg; interquartile range 33-49 mmHg) than in the control (59; 56-74 mmHg) and non-diabetic amputee (57; 43-65 mmHg) groups (control compared with diabetic amputee group, P<0.001; diabetic amputee compared with non-diabetic amputee group, P<0.01). The same trend was found for carbon dioxide levels in the skin [mmHg: diabetic amputees, 25 (21-37); controls, 38 (32-42); non-diabetic amputee, 34 (31-39)] (control compared with diabetic amputee, P<0.01; diabetic amputee compared with non-diabetic amputee, P<0.05). Vibration and pressure perception measurements (which assess Abeta nerve fibre function) showed that both the diabetic amputee and non-diabetic amputee subjects had significantly greater impairment than the controls. However, measures of Aalpha and C nerve fibre function were abnormal only in the diabetic amputee group. Thus the peripheral vascular and nerve functions of age-matched diabetic and non-diabetic subjects having undergone lower limb amputation show specific differences, with non-diabetic amputees exhibiting signs of neuropathy. This indicates that factors characteristic of diabetes (such as hyperglycaemia and non-enzymic glycation) are associated with calcification, lower oxygen and carbon dioxide levels in the skin, and abnormal Aalpha and C nerve fibre function.

Aged↗
PubMed2000

Post-proline-cleaving peptidases having DP IV like enzyme activity. Post-proline peptidases.

DP IV has been studied extensively in disease and in the immune system by the use of enzyme assays which detect hydrolysis of Gly-Pro or Ala-Pro substrate. In addition many studies have used inhibitors of DP IV enzyme activity. The characterisation of a novel DP IV like protein, DPP4R, and of other proteases which have a substrate specificity similar to DP IV or that bind DP IV inhibitors suggests that these studies require further evaluation.

Animals↗
PubMed2000

Relating structure to function in the beta-propeller domain of dipeptidyl peptidase IV. Point mutations that influence adenosine deaminase binding, antibody binding and enzyme activity.

Point mutations in human CD26/DP IV were analysed for adenosine deaminase (ADA) binding, monoclonal antibody (mAb) binding and DP IV enzyme activity. Point mutations at either Leu294 or Val341 ablated ADA binding. Binding by mAbs that inhibit ADA binding was found to involve both Leu340 to Arg343 and Thr440/Lys441. Glu205 and Glu206 were found to be essential for enzyme activity. All residues of interest were mapped onto a model of the beta-propeller domain of DP IV. These data led us to suggest that in DP IV and related peptidases ligand and antibody binding sites are non-linear and that enzyme activity depends on charged sidechains that surround the entrance to the central tunnel of the beta-propeller.

Amino Acid Substitution↗
PubMed2000

Molecular pathogenesis of liver disease: an approach to hepatic inflammation, cirrhosis and liver transplant tolerance.

The hallmarks of chronic liver diseases are chronic inflammation, cellular damage, regeneration and fibrosis. An appreciation of intrahepatic molecular expression patterns in normal and diseased liver provides clues for understanding pathogenic pathways whilst studies of the structure and function of molecules implicated in liver disease provide insights into their potential as therapeutic targets. We have examined the expression, function, molecular structure and structure-function relationships of type IV dipeptidyl aminopeptidases. In particular, the roles of CD26/DPPIV in T-cell proliferation and chemotaxis and of fibroblast activation protein in human cirrhosis are discussed. We have investigated the pathogenesis of liver disease by characterising patterns of cytokine and growth factor expression in experimental and human cirrhosis. We have quite recently expanded this approach to use differential gene expression analyses to elucidate overall pathways of gene activation and suppression in human cirrhosis. In addition, our detailed molecular and cellular studies of the mechanisms of spontaneous liver transplant tolerance have generated novel insights into this process. This review touches on these diverse aspects of liver function and disease.

Adenosine Deaminase↗
PubMed2000

Cloning, expression and chromosomal localization of a novel human dipeptidyl peptidase (DPP) IV homolog, DPP8.

Dipeptidyl peptidase (DPP) IV has roles in T-cell costimulation, chemokine biology, type-II diabetes and tumor biology. Fibroblast activation protein (FAP) has been implicated in tumor growth and cirrhosis. Here we describe DPP8, a novel human postproline dipeptidyl aminopeptidase that is homologous to DPPIV and FAP. Northern-blot hybridization showed that the tissue expression of DPP8 mRNA is ubiquitous, similar to that of DPPIV. The DPP8 gene was localized to chromosome 15q22, distinct from a closely related gene at 19p13.3 which we named DPP9. The full-length DPP8 cDNA codes for an 882-amino-acid protein that has about 27% identity and 51% similarity to DPPIV and FAP, but no transmembrane domain and no N-linked or O-linked glycosylation. Western blots and confocal microscopy of transfected COS-7 cells showed DPP8 to be a 100-kDa monomeric protein expressed in the cytoplasm. Purified recombinant DPP8 hydrolyzed the DPPIV substrates Ala-Pro, Arg-Pro and Gly-Pro. Thus recombinant DPP8 shares a postproline dipeptidyl aminopeptidase activity with DPPIV and FAP. DPP8 enzyme activity had a neutral pH optimum consistent with it being nonlysosomal. The similarities between DPP8 and DPPIV in tissue expression pattern and substrates suggests a potential role for DPP8 in T-cell activation and immune function.

Amino Acid Sequence↗
PubMed1999

Two highly conserved glutamic acid residues in the predicted beta propeller domain of dipeptidyl peptidase IV are required for its enzyme activity.

Dipeptidyl peptidase IV (DPP IV) is a member of the prolyl oligopeptidase family and modifies the biological activities of certain chemokines and neuropeptides by cleaving their N-terminal dipeptides. This paper reports the identification and possible significance of a novel conserved sequence motif Asp-Trp-(Val/Ile/Leu)-Tyr-Glu-Glu-Glu (DW(V/I/L)YEEE) in the predicted beta propeller domain of the DPP IV-like gene family. Single amino acid point mutations in this motif identified two glutamates, at positions 205 and 206, as essential for the enzyme activity of human DPP IV. This observation suggests a novel role in proteolysis for residues of DPP IV distant from the Ser-Asp-His catalytic triad.

Amino Acid Sequence↗
PubMed1999

Fibroblast activation protein: a cell surface dipeptidyl peptidase and gelatinase expressed by stellate cells at the tissue remodelling interface in human cirrhosis.

Fibroblast activation protein (FAP) is a cell surface-bound protease of the prolyl oligopeptidase gene family expressed at sites of tissue remodelling. This study aimed to delineate the expression of FAP in cirrhotic human liver and examine its biochemical activities. Seventeen cirrhotic and 8 normal liver samples were examined by immunohistochemistry and reverse-transcriptase polymerase chain reaction (RT-PCR). Hepatic stellate cells (HSC) were isolated and immunostained. Recombinant FAP and immunopurified, natural FAP were analyzed for protease activities and similarities to dipeptidyl peptidase IV (DPPIV), a structurally related enzyme. FAP-specific messenger RNA and immunoreactivity were detected in cirrhotic, but not normal, livers. FAP immunoreactivity was most intense on perisinusoidal cells of the periseptal regions within regenerative nodules (15 of 15 cases); this pattern coincides with the tissue remodelling interface. In addition, human FAP was expressed by cells within the fibrous septa (10 of 15 cases). Cell morphology, location, and colocalization with glial fibrillary acidic protein (GFAP) indicated that FAP is present on HSC in vivo. Similarly, isolated HSC expressed FAP in vitro. Both natural FAP from cirrhotic liver and recombinant FAP were shown to have gelatinase and dipeptidyl peptidase activities. FAP is a cell-bound, dual-specificity dipeptidyl peptidase and gelatinase expressed by activated HSC at the tissue remodelling interface in human cirrhosis. FAP may contribute to the HSC-induced extracellular matrix (ECM) changes of cirrhosis.

Actins↗
PubMed1999

Binding to human dipeptidyl peptidase IV by adenosine deaminase and antibodies that inhibit ligand binding involves overlapping, discontinuous sites on a predicted beta propeller domain.

Dipeptidyl peptidase IV (DPPIV) is an atypical serine protease that modifies the biological activities of certain chemokines and neuropeptides. In addition, human DPPIV, also known as the T-cell activation antigen CD26, binds adenosine deaminase (ADA) to the T-cell surface, thus protecting the T-cell from adenosine-mediated inhibition of proliferation. Mutations were engineered into DPPIV (five point, 16 single point and six deletion mutations) to examine the binding of ADA and 19 monoclonal antibodies. Deletions of C-terminal residues from the 738-residue extracellular portion of DPPIV showed that the 214 residues C-terminal to Ser552 were not required for ADA binding and that peptidase activity could be ablated by deletion of 20 residues from the C-terminus. Point mutations at either of two locations, Leu294 and Val341, ablated ADA binding. Binding by six anti-DPPIV antibodies that inhibited ADA binding was found to require Leu340 to Arg343 and Thr440/Lys441 but not the 214 residues C-terminal to Ser552. The 13 other antibodies studied bound to a truncated DPPIV consisting of amino acids 1-356. Therefore, the binding sites on DPPIV of ADA and antibodies that inhibit ADA binding are discontinuous and overlapping. Moreover, the 47 and 97 residue spacing of amino acids in these binding sites concords with their location on a beta propeller fold consisting of repeated beta sheets of about 50 amino acids.

Adenosine Deaminase↗
PubMed1999

A comparative study of the Podotrack, a simple semiquantitative plantar pressure measuring device, and the optical pedobarograph in the assessment of pressures under the diabetic foot.

AIMS: To test the Podotrack, a simple inexpensive semiquantitative footprint mat, for potential use as a screening tool for high plantar pressures, against the optical pedobarograph (a computerized device). METHODS: The Podotrack was superimposed on the pedobarograph for simultaneous measurement of pressures from both systems. Three independent observers quantified the pressures of Podotrack footprints from healthy controls and diabetic patients, both before (n=164) and after (n=183) training. The sensitivity of the Podotrack to identify high pressure areas measured by the pedobarograph (> 12.3 kg/cm2) was 78.7%, 45.8% and 44.3% (observer A, B and C) before training, but improved to 96.2%, 92.4% and 91.1% after training (P<0.01). Specificity for all three observers was more than 90% before and after training. Inter-observer agreement improved significantly after training (P<0.001). CONCLUSION: After a simple training of the observers, the Podotrack identified approximately all high pressure areas, suggesting that the Podotrack could be a useful screening tool to identify areas at risk of ulceration in diabetic patients. We recommend a standard training package for new Podotrack users, to optimize identification of diabetic patients at risk of foot ulceration.

Case-Control Studies↗
PubMed1998

The potential role of cell adhesion molecules in the pathogenesis of diabetic neuropathy.

Cross-sectional studies have shown plasma cell adhesion molecules (CAMs) to be increased in patients with diabetes-related complications. In the first prospective study of CAMs, we have shown that plasma CAMs may be a predictor of the development of diabetic neuropathy. We followed up 28 diabetic patients (13 neuropathic) over a 5 year period, starting from 1991. All patients had peroneal nerve conduction velocity (PNCV), vibration perception threshold and plasma CAMs measured at baseline and follow-up. We found P-selectin and intercellular adhesion molecule-1 (ICAM-1) to be increased at baseline in patients with neuropathy compared to non-neuropathic patients. P-selectin and E-selectin were also found to be significantly higher at baseline in patients who at follow-up showed deterioration in PNCV of more than 3 m/s (p<0.05; p=0.01; respectively). P-selectin and ICAM-1 strongly correlated with PNCV. Univariate and multivariate regression analyses showed a significant inverse association between increasing log P-selectin, log E-selectin and log ICAM-1 with decreasing PNCV, and remained significant even after adjustment for glycaemic control. P-selectin and E-selectin, odds ratios of 8.8 (95% CI: 1.1-68.8; p=0.038) and 12.5 (95% CI: 1.2-132.1; p=0.036), respectively, were significantly associated with the risk of deterioration of PNCV after 5 years. This study suggests that plasma cell adhesion molecules may play an important role in the development and progression of peripheral neuropathy in diabetes mellitus.

Adult↗
PubMed1998

An analysis of dynamic forces transmitted through the foot in diabetic neuropathy.

OBJECTIVE: Biomechanical studies in diabetic neuropathy have clearly demonstrated abnormal foot pressures, but information on other aspects of gait is limited. This study aimed to investigate and describe the forces transmitted through the foot during walking in diabetic subjects with varying degrees of peripheral neuropathy and to determine if abnormalities in these forces might contribute to the risk of plantar ulceration. RESEARCH DESIGN AND METHODS: Subjects from the following groups were included: healthy control subjects (C); diabetic control subjects (D); subjects with diabetic neuropathy (DN); subjects with previous neuropathic ulceration (DNU); and subjects with Charcot neuro-arthropathy (CH). Gait analysis was performed as subjects walked over a Kistler force plate. Peak forces were measured (as percent body weight) in the vertical and horizontal planes. Comparisons were made between all of the groups and between each diabetic group and a healthy control group matched for walking speed. RESULTS: There were 181 subjects studied. In comparison with that of the speed-matched controls, the mean peak vertical force was higher in each of the diabetic groups, especially in the most neuropathic subjects (DNU, 113 vs. 110%, P < 0.01). This increase was entirely due to higher forces during heel contact (DNU, 111 vs. 106%, P < 0.001). The single peak force occurred during heel strike (rather than during foot push-off) in 23-38% of footsteps of healthy and diabetic control subjects but in 53-73% of footsteps of neuropathic subjects. There was also a trend for higher peak medial forces (CH, 6.2 vs. 5.5%, P < 0.05). CONCLUSIONS: Diabetic neuropathy is associated with a change in the time pattern of the forces transmitted through the foot and an increase in the vertical forces through the heel. The magnitude of the changes is small in absolute terms, but these changes may contribute to the risk of plantar foot ulceration.

Adult↗