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Biomedical subjects

J Hultén

Publications and source records attributed to J Hultén.

18 recordsLinked to original sources
PubMed2002

Resistance profiles of cyclic and linear inhibitors of HIV-1 protease.

Resistance to anti-HIV protease drugs is a major problem in the design of AIDS drugs with long-term efficacy. To identify structural features associated with a certain resistance profile, the inhibitory properties of a series of symmetric and asymmetric cyclic sulfamide, cyclic urea and linear transition-state analogue inhibitors of HIV-1 protease were investigated using wild-type and mutant enzyme. To allow a detailed structure-inhibition analysis, enzyme with single, double, triple and quadruple combinations of G48V, V82A, 184V and L90M substitutions was used. Kinetic analysis of the mutants revealed that catalytic efficiency was 1-30% of that for the wild-type enzyme, a consequence of reduced kcat in all cases and an increased KM for all mutants except for the G48V enzyme. The overall structure-inhibitory profiles of the cyclic compounds were similar, and the inhibition of the V82A, 184V and G48V/L90M mutants were less efficient than of the wild-type enzyme. The greatest increase in Ki was generally observed for the 184V mutant and least for the G48V/L90M mutant, and additional combinations of mutations did not result in improved inhibition profiles for the cyclic compounds. An extended analysis of additional mutants, and including a set of linear compounds, showed that the profile was unique for each compound, and did not reveal any general structural features associated with a certain inhibition profile. The effects of structural modifications in the inhibitors, or of mutations, were not additive and they differed depending on their context. The results demonstrate the difficulties in predicting resistance, even for closely related compounds, and designing compounds with improved resistance profiles.

Drug Resistance, Viral↗
PubMed2001

Synthesis and comparative molecular field analysis (CoMFA) of symmetric and nonsymmetric cyclic sulfamide HIV-1 protease inhibitors.

We have previously reported on the unexpected flipped conformation in the cyclic sulfamide class of inhibitors. An attempt to induce a symmetric binding conformation by introducing P2/P2' substituents foreseen to bind preferentially in the S2/S2' subsite was unsuccessful. On the basis of the flipped conformation we anticipated that nonsymmetric sulfamide inhibitors, with P2/P2' side chains modified individually for the S1' and S2 subsites, should be more potent than the corresponding symmetric analogues. To test this hypothesis, a set of 18 cyclic sulfamide inhibitors (11 nonsymmetric and 7 symmetric) with different P2/P2' substituents was prepared and evaluated in an enzyme assay. To rationalize the structure-activity relationship (SAR) and enable the alignment of the nonsymmetric inhibitors, i.e., which of the P2/P2' substituents of the nonsymmetric inhibitors interact with which subsite, a CoMFA study was performed. The CoMFA model, constructed from the 18 inhibitors in this study along with seven inhibitors from previous work by our group, has successfully been used to rationalize the SAR of the cyclic sulfamide inhibitors. Furthermore, from the information presented herein, the SAR of the cyclic sulfamide class of inhibitors seems to differ from the SAR of the related cyclic urea inhibitors reported by DuPont and DuPont-Merck.

Crystallography, X-Ray↗
PubMed2001

P1/P1' modified HIV protease inhibitors as tools in two new sensitive surface plasmon resonance biosensor screening assays.

The commonly used HIV-1 protease assays rely on measurements of the effect of inhibitions on the hydrolysis rate of synthetic peptides. Recently an assay based on surface plasmon resonance (SPR) was introduced. We have taken advantage of the fact that the SPR signal is proportional to the mass of the analyte interacting with the immobilised molecule and developed two new improved efficient competition assay methods. Thus, high molecular weight binders were used as amplifiers of the surface plasmon resonance signal. Linkers were attached by a Heck reaction to the para-positions of the P1/P1' benzyloxy groups of a linear C2-symmetric C-terminal duplicated inhibitor to enable (a) biotin labelling or (b) direct immobilisation of the inhibitor to the biosensor surface matrix. The interaction properties of a series of 17 structurally diverse inhibitors was assessed and compared to previously reported data. The most sensitive assay was obtained by immobilising the enzyme and amplifying the signal with an antibody, giving a detection range between 0.1 nM and 10 microM. Immobilisation of the inhibitor resulted in a stable and durable surface but a narrower detection range (1-100 nM). The two competition assays are anticipated to be very suitable for fast screening of potential HIV inhibitors.

Biosensing Techniques↗
PubMed1999

Inhibitors of the C(2)-symmetric HIV-1 protease: nonsymmetric binding of a symmetric cyclic sulfamide with ketoxime groups in the P2/P2' side chains.

Symmetric cyclic sulfamides, substituted in the P2/P2' position with functional groups foreseen to bind preferentially to the S2/S2' subsites of HIV-1 protease, have been prepared. Despite efforts to promote a symmetric binding, the sulfamides seemed prone to bind nonsymmetrically, as deduced from X-ray crystal structure analysis of one of the most potent inhibitors, possessing ketoxime groups in the P2/P2' side chains. Ab initio calculations suggested that the nonsymmetric conformation of the cyclic sulfamide scaffold had lower energy than the corresponding symmetric, cyclic urea-like conformation.

Crystallography, X-Ray↗
PubMed1997

Unexpected binding mode of a cyclic sulfamide HIV-1 protease inhibitor.

Two cyclic, C2-symmetric HIV-1 protease inhibitors, one sulfamide and one urea derivative, both comprising phenyl ether groups in the P1/P1' positions, were cocrystallized with HIV-1 protease, and the crystal structures were determined to 2.0 A resolution. The structure of the urea 2 showed a conformation similar to that reported for the related urea 3 by Lam et al., while the sulfamide 1 adopted an unanticipated conformation in which the P1' and P2' side chains were transposed.

Azepines↗
PubMed1997

Cyclic HIV-1 protease inhibitors derived from mannitol: synthesis, inhibitory potencies, and computational predictions of binding affinities.

Ten C2-symmetric cyclic urea and sulfamide derivatives have been synthesized from L-mannonic gamma-lactone and D-mannitol. The results of experimental measurement of their inhibitory potencies against HIV-1 protease were compared to calculated free energies of binding derived from molecular dynamics (MD) simulations. The compounds were selected, firstly, to enable elucidation of the role of stereochemistry for binding affinity (1a-d) and, secondly, to allow evaluation of the effects of variation in the link to the P1 and P1' phenyl groups on affinity (1a and 2-5). Thirdly, compounds with hydrogen bond-accepting or-donating groups attached to the phenyl groups in the P2 and P2' side chains (6 and 7) were selected. Binding free energies were estimated by a linear response method, whose predictive power for estimating binding affinities from MD simulations was demonstrated.

Anti-HIV Agents↗
PubMed1997

Human immunodeficiency virus type 1 proteinase resistance to symmetric cyclic urea inhibitor analogs.

Resistant virus was isolated from virus propagated in cell culture in the presence of the human immunodeficiency virus type 1 (HIV-1) proteinase inhibitor DMP 323, Ro 31-8959, or A-75925. The proteinase gene of resistant virus was sequenced, and key mutations (G48V, V82A, I84V, L90M, and G48V/L90M) were introduced into clones used for the expression, purification, and further characterization of the enzyme. The mutant enzymes were all less active than the wild-type enzyme, as judged by k(cat) and k(cat)/Km values. L90M had a lower Km than the wild type, whereas the G48V/L90M double mutant had an increased Km compared with that of the wild type, contributing to a 10-fold reduction in the k(cat)/Km. Vitality values were used to show that the enzyme of the I84V mutant is the enzyme most resistant to the two cyclic urea inhibitors DMP 323 and AHA 008. Virus with the same mutation is also resistant, although the double mutation L10F/I84V confers even greater resistance. All of these mutants are more resistant to DMP 323 than to AHA 008. The resistance of the I84V mutant may be attributed to a loss of van der Waals interactions with the inhibitor, since the larger amino acid side chain involved in the interaction is replaced by a smaller side chain. This is supported by the lower level of resistance to AHA 008 that was observed. The phenyl groups of AHA 008 should protrude deeper into the S1 and S1' subsites than those of the smaller compound DMP 323, reducing the loss of interaction energy. These results reveal that small structural modifications of inhibitors that do not affect the inhibitory effect on wild-type virus can influence the inhibition of resistant strains. This is of importance for optimizing drugs with respect to their potency and resistance.

Cells, Cultured↗
PubMed1993

On clinical loading of osseointegrated implants. A methodological and clinical study.

Strain gauges were used to record in vivo and in vitro functional deformations in a fixed prosthetic appliance supported and retained by osseointegrated titanium implants. Four linear gauges were attached to each of totally 5 implant abutment cylinders and gauge signals were transferred into a computer via a digital converter. A computer program (ASYST) was used for collection, calibration and analysis of data obtained. Based on the results of a series of explorative in vitro tests, in vivo experiments were performed at maximum biting as well as during chewing on certain normally available food items. The results show fundamental differences between in vitro and in vivo testing conditions. Unexpectedly high bending of the implants was recorded in many of the in vivo loading situations.

Aged↗
PubMed1993

Long term clinical evaluation of conical crown retained dentures.

The conical crown was introduced by K.H. Körber more than twenty years ago, as a development of the well known telescopic crown. In combination with a removable denture, the conical crown has become widely used in Germany and Sweden, since the system enable modifications with maintained function if abutments are lost. All 78 patients treated with conical crown retained dentures, at the School of Dentistry, Dept. Prosthetic Dentistry, Lund University, 1983-1988, were included in a 40 month follow up study using the CDA quality evaluation system. More than 80% of the removable dentures and abutments were in function at the time of examination. Forty-four percent of the conical crown retained dentures were considered having acceptable quality while 56% were not acceptable, mainly due to caries at the abutments margins.

Aged↗
PubMed1992

Influence of low-viscosity liners on the retention of three luting materials.

A number of materials are available to protect the pulp from postoperative sensitivity. The effect of a calcium hydroxide liner and a dentinal desensitizing agent (potassium oxalate) on crown retention was investigated. Gold crowns were cemented on standardized crown preparations with zinc phosphate cement, glass-ionomer cement, or one of two resin cements. A tensile force was applied until separation occurred. The mean applied force at rupture varied greatly among the groups, indicating that the pulpal protection agent may have a distinct effect on the retention of cast restorations. In addition, other clinical factors, such as angle of convergence, crown height, and total surface area of the tooth should be considered.

Analysis of Variance↗
PubMed1991

Absorption of irrigating fluid during transurethral prostatic resection as measured by ethanol, radioisotopes, and regular-interval monitoring.

Ethanol monitoring is a novel noninvasive method for immediate detection of absorption of irrigating fluid during transurethral prostatic resection. Its accuracy was evaluated during thirteen resections using 5% mannitol +2% ethanol as the irrigating fluid. The ethanol concentration in the expired breath correlated strongly with the degree of absorption of intravascular irrigating fluid as determined by a radioisotope technique, and fluid volume measurements, and with the changes in the serum sodium concentration. Extravascular absorption of the irrigating fluid resulted in prolonged elevation of the ethanol concentration and gave smaller changes in the serum sodium concentration.

Absorption↗
PubMed1991

Monitoring of irrigating fluid absorption during transurethral prostatectomy. A study in anaesthetised patients using a 1% ethanol tag solution.

A simple, reliable method to detect absorption of irrigating fluid during transurethral prostatectomy is to tag irrigating fluids with 1% ethanol and monitor expired breath ethanol concentrations. This method correlated well (n = 0.79) with other existing methods of absorption monitoring in 20 anaesthetised patients. Ethanol (1%) tagging does not alter the optical quality of the irrigating fluid and is harmless to the patient. The technique is non-invasive, repeatable, cheap and gives instant results. It can be used in anaesthetised or awake patients and can detect absorption of as little as 100-150 ml in any 10-minute period.

Absorption↗
PubMed1984

Prevention of irrigating fluid absorption during transurethral resection of the prostate.

This thesis contains studies on the prerequisites for fluid absorption during transurethral resection of the prostate (TURP) and suggestions on its prevention. The pressure gradient bladder-prostatic fossa to pelvic veins and its relation to fluid absorption were studied in patients using a sensitive detection technique with a radionuclide. It is concluded that to prevent fluid entering the vascular system, the bladder pressure should be kept below the pressure in the pelvic veins. The physical properties of the irrigating jet of resectoscopes were investigated in model experiments including an artificial, "bleeding" prostatic fossa. The dynamic pressure of the jet amounts to only 1-3% of the driving head and thus is of marginal importance in fluid absorption. The effect of various flow rates on the optical field was also demonstrated. In patients with prostatism epidural and spinal analgesia increased the bladder capacity but always with a corresponding increase in bladder pressure. In a preliminary study a correlation was found between the minimum urethral resistance and the compliance of the detrusor during epidural analgesia. This may suggest a relation between prostatic obstruction and changes of the viscoelastic properties of the bladder wall. The effects of various irrigating flow rates on the pressure-volume response of the bladder and its relation to the pressure in the pelvic veins was also investigated. From this study it was concluded that the detrusor response was unaffected by flow rates used during TURP. The critical bladder pressure above which fluid is absorbed changed with the position of the patient. In the Trendelenburg (20 degrees) position it was 0.25 kPa (approximately equal to 2.5 cmH2O), increasing to 1.25 kPa in the horizontal and 1.75 kPa in the half-sitting (20 degrees) position. To prevent absorption bladder pressure must be monitored. A simple pressure warning device with an adjustable warning level and which can be combined with any irrigating technique is presented. Irrigation with a large driving head may thus be combined with a low pressure resection.

Absorption↗
PubMed1983

Treatment of fingertip amputations with bone exposure. A comparative study between surgical and conservative treatment methods.

The long-term results following 36 surgically and 34 conservatively treated fingertip amputations with bone exposure are presented in a retrospective study. Surgery did not produce better results even though it was performed by skilled hand surgeons. The advantages of the conservative (mainly adhesive zinc tape) treatment method are pointed out. The regenerative capacity of the amputated fingertip is shown and discussed.

Adolescent↗