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Biomedical subjects

J Deinum

Publications and source records attributed to J Deinum.

At least 37 records · Page 2Linked to original sources
PubMed2001

Evaluation and treatment of renal artery stenosis: impact on blood pressure and renal function.

The conventional non-invasive tests to diagnose renal artery stenosis in a general hypertensive population are not accurate enough for screening purposes. Magnetic resonance angiography might become the new gold standard, with the advantages of the absence of contrast toxicity, good accuracy, and information on flow characteristics. With regard to the treatment of hypertension in patients with renal artery stenosis, intervention is advised only when blood pressure cannot be controlled by at least three antihypertensive drugs. Patency after stenting is superior to angioplasty, although its clinical benefit has not been proved. As for renal function, evidence - although from uncontrolled studies - for the preservation of renal function by intervention is accumulating, especially in those patients with bilateral stenosis or stenosis in a single functioning kidney.

Blood Pressure↗
PubMed2000

Increased shedding of angiotensin-converting enzyme by a mutation identified in the stalk region.

Angiotensin-converting enzyme (ACE), an enzyme that plays a major role in vasoactive peptide metabolism, is a type 1 ectoprotein, which is released from the plasma membrane by a proteolytic cleavage occurring in the stalk sequence adjacent to the membrane anchor. In this study, we have discovered the molecular mechanism underlying the marked increase of plasma ACE levels observed in three unrelated individuals. We have identified a Pro(1199) --> Leu mutation in the juxtamembrane stalk region. In vitro analysis revealed that the shedding of [Leu(1199)]ACE was enhanced compared with wild-type ACE. The solubilization process of [Leu(1199)]ACE was stimulated by phorbol esters and inhibited by compound 3, an inhibitor of ACE-secretase. The results of Western blot analysis were consistent with a cleavage at the major described site (Arg(1203)/Ser(1204)). Two-dimensional structural analysis of ACE showed that the mutated residue was critical for the positioning of a specific loop containing the cleavage site. We therefore propose that a local conformational modification caused by the Pro(1199) --> Leu mutation leads to more accessibility at the stalk region for ACE secretase and is responsible for the enhancement of the cleavage-secretion process. Our results show that different molecular mechanisms are responsible for the common genetic variation of plasma ACE and for its more rare familial elevation.

Amino Acid Sequence↗
PubMed2000

The effect of balloon angioplasty on hypertension in atherosclerotic renal-artery stenosis. Dutch Renal Artery Stenosis Intervention Cooperative Study Group.

BACKGROUND: Patients with hypertension and renal-artery stenosis are often treated with percutaneous transluminal renal angioplasty. However, the long-term effects of this procedure on blood pressure are not well understood. METHODS: We randomly assigned 106 patients with hypertension who had atherosclerotic renal-artery stenosis (defined as a decrease in luminal diameter of 50 percent or more) and a serum creatinine concentration of 2.3 mg per deciliter (200 micromol per liter) or less to undergo percutaneous transluminal renal angioplasty or to receive drug therapy. To be included, patients also had to have a diastolic blood pressure of 95 mm Hg or higher despite treatment with two antihypertensive drugs or an increase of at least 0.2 mg per deciliter (20 micromol per liter) in the serum creatinine concentration during treatment with an angiotensin-converting-enzyme inhibitor. Blood pressure, doses of antihypertensive drugs, and renal function were assessed at 3 and 12 months, and patency of the renal artery was assessed at 12 months. RESULTS: At base line, the mean (+/-SD) systolic and diastolic blood pressures were 179+/-25 and 104+/-10 mm Hg, respectively, in the angioplasty group and 180+/-23 and 103+/-8 mm Hg, respectively, in the drug-therapy group. At three months, the blood pressures were similar in the two groups (169+/-28 and 99+/-12 mm Hg, respectively, in the 56 patients in the angioplasty group and 176+/-31 and 101+/-14 mm Hg, respectively, in the 50 patients in the drug-therapy group; P=0.25 for the comparison of systolic pressure and P=0.36 for the comparison of diastolic pressure between the two groups); at the time, patients in the angioplasty group were taking 2.1+/-1.3 defined daily doses of medication and those in the drug-therapy group were taking 3.2+/-1.5 daily doses (P<0.001). In the drug-therapy group, 22 patients underwent balloon angioplasty after three months because of persistent hypertension despite treatment with three or more drugs or because of a deterioration in renal function. According to intention-to-treat analysis, at 12 months, there were no significant differences between the angioplasty and drug-therapy groups in systolic and diastolic blood pressures, daily drug doses, or renal function. CONCLUSIONS: In the treatment of patients with hypertension and renal-artery stenosis, angioplasty has little advantage over antihypertensive-drug therapy.

Aged↗
PubMed2000

Biosensor analysis of drug-target interactions: direct and competitive binding assays for investigation of interactions between thrombin and thrombin inhibitors.

The sensitivity of BIACORE technology is sufficient for detection and characterization of binding events involving low-molecular-weight compounds and their immobilized protein targets. The technology requires no labeling and provides information on the stability of the compound/target complex with a single injection of the compound. This is useful for qualifying hits obtained in a primary screen and in lead optimization. Although immobilized targets can be reused, the surface may slowly deteriorate, solvent effects can distort binding levels during injection of compounds, and some compounds may exhibit broad protein selectivity rather than target specificity. A reliable direct binding assay for compounds binding to immobilized thrombin using a combination of two reference surfaces, a dextran surface for subtraction and calibration of solvent effects and a protein surface for identification of compounds that tend to bind proteins, has been developed. Eleven compounds with known binding specificity to thrombin and 159 additional compounds were investigated. All compounds with known binding specificity were identified at 1 and 10 microM concentration. One additional compound was scored as positive. The direct binding assay compared favorably with two competitive assay formats, a surface competitive assay and a inhibitor in solution assay, that were examined in parallel.

Antithrombins↗
PubMed2000

Stent placement for renal arterial stenosis: where do we stand? A meta-analysis.

PURPOSE: To perform a meta-analysis of renal arterial stent placement in comparison with renal percutaneous transluminal angioplasty (PTA) in patients with renal arterial stenosis. MATERIALS AND METHODS: Studies dealing with renal arterial stent placement (14 articles; 678 patients) and renal PTA (10 articles; 644 patients) published up to August 1998 were selected. A random-effects model was used to pool the data. RESULTS: Renal arterial stent placement proved highly successful, with an initial adequate performance in 98% and major complications in 11%. The overall cure rate for hypertension was 20%, whereas hypertension was improved in 49%. Renal function improved in 30% and stabilized in 38% of patients. The restenosis rate at follow-up of 6-29 months was 17%. Stent placement had a higher technical success rate and a lower restenosis rate than did renal PTA (98% vs 77% and 17% vs 26%, respectively; P <.001). The complication rate was not different between the two treatments. The cure rate for hypertension was higher and the improvement rate for renal function was lower after stent placement than after renal PTA (20% vs 10% and 30% vs 38%, respectively; P <.001). CONCLUSION: Renal arterial stent placement is technically superior and clinically comparable to renal PTA alone.

Aged↗
PubMed1999

Intravascular ultrasound evidence for coarctation causing symptomatic renal artery stenosis.

BACKGROUND: A recent study of human cadaveric renal arteries revealed that renal artery narrowing could be due not only to atherosclerotic plaque compensated for by adaptive remodeling, but also to hitherto undescribed focal narrowing of an otherwise normal renal arterial wall (ie, coarctation). The present study investigated whether vessel coarctation could be identified in patients with symptomatic renal artery stenosis (RAS). METHODS AND RESULTS: Consecutive symptomatic patients with angiographically proven atherosclerotic RAS who were referred for stent placement were studied by 30-MHz intravascular ultrasound before intervention (n=18) or after predilatation (n=18). Analysis included assessment of the media-bounded area and plaque area (PLA) at the most stenotic site and at a distal reference site (most distal cross-section in the main renal artery with normal appearance). Coarctation was considered present whenever the target/reference media-bounded area was </=85%. Before intervention, coarctation was observed in 9 of 18 patients and adaptive remodeling in 9 of 18 patients. Coarctation lesions had a significantly smaller PLA than adaptive remodeled lesions (P=0.001). Similarly, despite predilatation, coarctation was seen in 8 of 18 patients who had significantly smaller PLAs (P=0. 008) when compared with those patients who had adaptive remodeled lesions. No differences in severity of RAS or angiographic or clinical parameters were observed. CONCLUSIONS: Low-plaque coarctation may cause a considerable proportion of symptomatic RAS, which is angiographically and clinically indistinguishable from plaque-rich RAS.

Arteriosclerosis↗
PubMed1999

Protein movement during complex-formation between tissue plasminogen activator and plasminogen activator inhibitor-1.

Plasminogen activator inhibitor-1 (PAI-1) rapidly inactivates tissue plasminogen activator (tPA). After initial binding and cleavage of the reactive-centre loop of PAI-1, this complex is believed to undergo a major rearrangement. Using surface plasmon resonance and SDS-PAGE, we have studied the influence of a panel of monoclonal antibodies on the reaction leading to the final covalent complex. On the basis of these data, we suggest the mechanisms for the action of different classes of inhibitory antibodies. We propose that the antibodies which convert PAI-1 into a substrate for tPA do this by means of preventing the conversion of the initial PAI-1/tPA complex into the final complex by sterical intervention. Moreover, the localisation of the binding epitopes on free PAI-1, as well as on the PAI-1/tPA complex, suggests that tPA in the final complex cannot be located near helices E and F, as has previously been proposed.

Antibodies, Monoclonal↗
PubMed1999

Increase in serum prorenin precedes onset of microalbuminuria in patients with insulin-dependent diabetes mellitus.

AIMS/HYPOTHESIS: The renin-angiotensin system is possibly involved in the pathogenesis of diabetic nephropathy. The most striking change in renin-angiotensin system components in blood of patients with diabetic nephropathy is an increased prorenin concentration. We investigated prospectively serum concentrations of renin-angiotensin system components and the time course of prorenin increase in normoalbuminuric diabetic patients developing microalbuminuria. METHODS: Patients (n = 199) with Type I (insulin-dependent) diabetes mellitus and normoalbuminuria at baseline were prospectively followed for 10 years. The prorenin concentrations and other variables possibly associated with the occurrence of microalbuminuria, were investigated by Cox-regression analysis. RESULTS: Of the patients 29 developed microalbuminuria. Glycated haemoglobin values were higher at baseline in these patients. Serum prorenin was similar at baseline but rose in the 29 patients before the development of microalbuminuria and was stable in patients with stable albumin excretion. Renin, angiotensinogen and angiotensin converting enzyme serum concentrations were stable in both groups. Prorenin and glycated haemoglobin were independent prognostic factors for the development of microalbuminuria. A prognostic index, based on these variables, was constructed to estimate the relative risk of developing microalbuminuria. CONCLUSIONS/INTERPRETATION: Increase in serum prorenin precedes onset of microalbuminuria in normotensive patients with insulin-dependent diabetes mellitus. High concentrations of prorenin in combination with high values of glycated haemoglobin can be used as a predictor of development of microalbuminuria.

Adult↗
PubMed1999

Sideroxylonal C, a new inhibitor of human plasminogen activator inhibitor type-1, from the flowers of Eucalyptus albens.

Sideroxylonal C (3), a new phloroglucinol dimer, was isolated from the flowers of Eucalyptus albens through bioassay-guided fractionation. The structure elucidation was based on 1D and 2D NMR experiments, MS analysis, and comparison with sideroxylonals A (1) and B (2). Sideroxylonal C inhibited human plasminogen activator inhibitor type-1 at 4.7 microM without any significant effect on human tissue plasminogen activator.

Benzofurans↗
PubMed1999

Plasma renin and prorenin and renin gene variation in patients with insulin-dependent diabetes mellitus and nephropathy.

BACKGROUND: The most striking abnormality in the renin angiotensin system in diabetic nephropathy (DN) is increased plasma prorenin. Renin is thought to be low or normal in DN. In spite of altered (pro)renin regulation the renin gene has not been studied for contribution to the development of DN. METHODS: We studied plasma renin, prorenin, and four polymorphic markers of the renin gene in 199 patients with IDDM and DN, and in 192 normoalbuminuric IDDM controls matched for age, sex, and duration of diabetes. Plasma renin and total renin were measured by immunoradiometric assays. Genotyping was PCR-based. RESULTS: Plasma renin was increased in patients with nephropathy (median (range), 26.3 (5.2-243.3) vs 18.3 (4.2-373.5) microU/ml in the normoalbuminuric group, P<0.0001). Prorenin levels were elevated out of proportion to renin levels in nephropathic patients (789 (88-5481) vs 302 (36-2226) microU/ml, P<0.0001). Proliferative retinopathy had an additive effect on plasma prorenin, but not on renin. DN was associated with a BglI RFLP in the first intron of the renin gene (bb-genotype: n=106 vs 82 in DN and normoalbuminuric patients respectively, P=0.037), but not with three other polymorphisms in the renin gene. A trend for association of higher prorenin levels with the DN-associated allele of this renin polymorphism was observed in a subgroup of patients with DN (bb vs Bb+BB, P=0.07). CONCLUSIONS: The results indicate that in DN there is an increase in both renin and prorenin levels. A renin gene polymorphism may contribute weakly to DN. Although speculative, one of the renin gene alleles could lead to increased renin gene expression, leading to higher renin and prorenin levels. These may play a role in the pathogenesis of DN.

Adult↗
PubMed1999

Angiotensin I to angiotensin II conversion in the human forearm and leg. Effect of the angiotensin converting enzyme gene insertion/deletion polymorphism.

OBJECTIVE: The angiotensin-converting enzyme (ACE) gene I/D polymorphism accounts for part of the variation in ACE concentration; subjects with one or two D alleles have approximately 25 and 50% higher ACE levels, respectively, than subjects with two I alleles. Data from studies on the pressor effects of angiotensin (Ang) I in DD compared with II subjects are inconsistent, because enhanced conversion in DD subjects may have been masked by a decreased responsiveness to Ang II. Here we quantify ACE genotype-related Ang I to Ang II conversion in the human forearm and leg using non-pressor 125I-Ang I infusions. DESIGN AND METHODS: Infusions were given to 12 women and 17 men (age 24-67 years) who were undergoing renal vein sampling followed by renal angiography for diagnostic purposes. 125I-Ang I was infused for 20 min into the right antecubital vein, and blood samples for the measurement of 125I-labelled and endogenous Ang I and Ang II were taken from the aorta, the left antecubital vein and a femoral vein under steady-state conditions. Genotype frequencies were determined by polymerase chain reaction. RESULTS: Fractional conversion (i.e. the percentage of arterially delivered 125I-Ang I that is converted to 125I-Ang II) in the forearm (38+/-4, 30+/-3 and 31+/-6% in 8 II, 16 ID and 5 DD subjects, respectively; mean +/- SEM) and leg (52+/-4, 48+/-3 and 42+/-5%) was similar in all three groups. In addition, no genotype-related differences in plasma Ang II/I ratio (a measure of ACE activity) were observed at the three sampling sites. CONCLUSIONS: Regional Ang I to Ang II conversion does not parallel the previously described D allele-related differences in ACE concentration, suggesting that effects other than enhanced conversion may underlie the reported associations between the D allele and various cardiovascular diseases.

Adult↗
PubMed1999

Improved immunoradiometric assay for plasma renin.

BACKGROUND: Our renin IRMA overestimated renin in plasmas with high prorenin-to-renin ratios. We suspected that the overestimation of renin was caused less by cross-reactivity of the renin-specific antibody with prorenin than by a conformational change of prorenin into an enzymatically active form during the assay. METHODS: Because the inactive form of prorenin converts slowly into an active form at low temperature, we raised the assay temperature from 22 degrees C to 37 degrees C, simultaneously shortening the incubation time from 24 to 6 h. The former IRMA was performed in <1 working day with these modifications. RESULTS: The comeasurement of prorenin as renin was eliminated. Reagents were stable at 37 degrees C, and the new and old IRMAs were comparable in terms of precision and accuracy. The functional lower limit of the assay (4 mU/L) was below the lower reference limit (9 mU/L). The modified IRMA agreed closely with the activities measured with an enzyme-kinetic assay. Results were not influenced by the plasma concentration of angiotensinogen. At normal angiotensinogen concentrations, the IRMA closely correlated with the classical enzyme-kinetic assay of plasma renin activity. CONCLUSION: The modified IRMA, performed at 37 degrees C, avoids interference by prorenin while retaining the desirable analytical characteristics of the older IRMA and requiring less time.

Cross Reactions↗
PubMed1998

Probing epitopes on human prorenin during its proteolytic and non-proteolytic activation.

The conformational changes of prorenin (PR) that are associated with its reversible non-proteolytic activation and irreversible proteolytic activation were monitored with immunoradiometric assays, using antibodies against epitopes belonging to the propeptide or the renin part of PR. Binding of PR to the renin inhibitor remikiren or protonation of PR resulted in the slowly progressive and simultaneous expression (t1/2 congruent with3.5-5.0 h at 4 degreesC) of epitopes of the N-terminal and C-terminal halves of the propeptide and an epitope that is manifest on renin but not on native non-activated PR. During reversible PR activation-inactivation, expression and disappearance of these epitopes coincided with the appearance and disappearance of enzyme activity. Cleavage of the propeptide from the renin part of PR by plasmin, as demonstrated by the failure of remikiren to unmask the N-terminal and C-terminal propeptide epitopes, was, with some time lag, followed by the simultaneous expression (t1/2 congruent with60 min at 4 degreesC) of the renin-specific epitope and enzymatic activity. Based on these findings we propose a model for the non-proteolytic activation of PR that involves the formation of an intermediary form of activated PR with the following properties: (1) the covalently bound propeptide has moved out of the active-site cleft, so that binding sites are exposed to active site ligands, (2) the propeptide is still not in the 'relaxed' conformation that is characteristic for fully, non-proteolytically, activated PR, and (3) the N-terminal part of the renin polypeptide chain has not yet attained the proper location that is required for enzymatic activity.

Antibodies, Monoclonal↗
PubMed1998

Interfering with the inhibitory mechanism of serpins: crystal structure of a complex formed between cleaved plasminogen activator inhibitor type 1 and a reactive-centre loop peptide.

BACKGROUND: Plasminogen activator inhibitor type 1 (PAI-1) is an important endogenous regulator of the fibrinolytic system. Reduction of PAI-1 activity has been shown to enhance dissolution of blood clots. Like other serpins, PAI-1 binds covalently to a target serine protease, thereby irreversibly inactivating the enzyme. During this process the exposed reactive-centre loop of PAI-1 is believed to undergo a conformational change becoming inserted into beta sheet A of the serpin. Incubation with peptides from the reactive-centre loop transform serpins into a substrate for their target protease. It has been hypothesised that these peptides bind to beta sheet A, thereby hindering the conformational rearrangement leading to loop insertion and formation of the stable serpin-protease complex. RESULTS: We report here the 1.95 A X-ray crystal structure of a complex of a glycosylated mutant of PAI-1, PAI-1-ala335Glu, with two molecules of the inhibitory reactive-centre loop peptide N-Ac-TVASS-NH2. Both bound peptide molecules are located between beta strands 3A and 5A of the serpin. The binding kinetics of the peptide inhibitor to immobilised PAI-1-Ala335Glu, as monitored by surface plasmon resonance, is consistent with there being two different binding sites. CONCLUSIONS: This is the first reported crystal structure of a complex formed between a serpin and a serpin inhibitor. The localisation of the inhibitory peptide in the complex strongly supports the theory that molecules binding in the space between beta strands 3A and 5A of a serpin are able to prevent insertion of the reactive-centre loop into beta sheet A, thereby abolishing the ability of the serpin to irreversibly inactivate its target enzyme. The characterisation of the two binding sites for the peptide inhibitor provides a solid foundation for computer-aided design of novel, low molecular weight PAI-1 inhibitors.

Binding Sites↗
PubMed1998

Identification of the binding site for a low-molecular-weight inhibitor of plasminogen activator inhibitor type 1 by site-directed mutagenesis.

A novel low-molecular-weight inhibitor, AR-H029953XX, was developed from a known fibrinolytic compound, flufenamic acid, which prevented complex formation of human plasminogen activator inhibitor type 1 (PAI-1) with tissue plasminogen activator (tPA) by inhibition of PAI-1. To explore the binding site for AR-H029953XX, mutants of human PAI-1 were constructed by site-directed mutagenesis and were then expressed in CHO cells, purified, activated, and characterized. (1) PAI-1 with mutations in the reactive center loop: L1-PAI-1 (P10, Ser337Glu) had stability and activity similar to those of wild-type PAI-1 (wt-PAI-1), and L2-PAI-1 (P12, Ala335Glu) was highly stable but was a substrate for tPA. (2) PAI-1 with mutations near the binding epitope for the strongly inhibiting monoclonal antibody CLB-2C8: C1-PAI-1 (Phe114Glu), C2-PAI-1 (Val121Phe), C3-PAI-1 (Arg76Glu/Arg115Glu/Arg118Glu), and C4-PAI-1 (Arg115Glu) were all comparable in activity and stability to wt-PAI-1. AR-H029953XX (Ki = 25 microM) prevented complex formation between tPA and active wt-PAI-1 as well as that with mutants L1-, L2-, C1-, C2-, and C4-PAI-1. AR-H029953XX also inhibited binding of these PAI-1 variants to the antibody CLB-2C8, as measured by surface plasmon resonance. In contrast, AR-H029953XX had almost no inhibitory effect on the complex formation of tPA with C3-PAI-1. Moreover, AR-H029953XX had no effect on the binding rate of CLB-2C8 to C3-PAI-1, or on the binding to latent PAI-1 or to cleaved L2-PAI-1. The binding site of AR-H029953XX thus appears to be located in the neighborhood of the postulated epitope for CLB-2C8, near residues Arg76 and/or Arg118. This specific domain of the PAI-1 molecule might thus also be important for the mechanism of inhibitory activity toward tPA. Moreover, the structure of this region in active PAI-1 has to be different from the corresponding regions in latent and cleaved PAI-1.

Animals↗