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Biomedical subjects

B Oberg

Publications and source records attributed to B Oberg.

At least 55 records · Page 3Linked to original sources
PubMed1993

Human immunodeficiency virus type 1 (HIV-1) strains selected for resistance against the HIV-1-specific [2',5'-bis-O-(tert-butyldimethylsilyl)-3'-spiro- 5''-(4''-amino-1'',2''-oxathiole-2'',2''-dioxide)]-beta-D-pentofurano syl (TSAO) nucleoside analogues retain sensitivity to HIV-1-specific nonnucleoside inhibitors.

We recently reported that a newly discovered class of nucleoside analogues--[2',5'-bis-O-(tert-butyldimethylsilyl)- 3'-spiro-5''-(4''-amino-1'',2''-oxathiole-2'',2''-dioxide)]-beta-D - pentofuranosyl derivatives of pyrimidines and purines (designated TSAO)--are highly specific inhibitors of human immunodeficiency virus type 1 (HIV-1) and targeted at the nonsubstrate binding site of HIV-1 reverse transcriptase (RT). We now find that HIV-1 strains selected for resistance against three different TSAO nucleoside derivatives retain sensitivity to the other HIV-1-specific nonnucleoside derivatives (tetrahydroimidazo[4,5,1-jk][1,4]benzodiazepin-2(1H)-one and -thione (TIBO), 1-[(2-hydroxyethoxy)methyl]-6-phenylthiothymine, nevirapine, and pyridinone L697,661, as well as to the nucleoside analogues 3'-azido-3'-deoxythymidine, ddI, ddC, and 9-(2-phosphonylmethoxyethyl)adenine. Pol gene nucleotide sequence analysis of the TSAO-resistant and -sensitive HIV-1 strains revealed a single amino acid substitution at position 138 (Glu-->Lys) in the RT of all TSAO-resistant HIV-1 strains. HIV-1 RT in which the Glu-138-->Lys substitution was introduced by site-directed mutagenesis and expressed in Escherichia coli could not be purified because of rapid degradation. However, HIV-1 RT containing the Glu-138-->Arg substitution was stable. It lost its sensitivity to the TSAO nucleosides but not to the other HIV-1-specific RT inhibitors (i.e., TIBO and pyridinone). Our findings point to a specific interaction of the 4''-amino group on the 3'-spiro-substituted ribose moiety of the TSAO nucleosides with the carboxylic acid group of glutamic acid at position 138 of HIV-1 RT.

Antiviral Agents↗
PubMed1993

HIV-1-specific reverse transcriptase inhibitors show differential activity against HIV-1 mutant strains containing different amino acid substitutions in the reverse transcriptase.

Serial passage of HIV-1 in CEM or MT-4 cell cultures in the presence of different HIV-1-specific reverse transcriptase (RT) inhibitors yielded mutant viruses which were resistant (i.e., 200- to 1000-fold less sensitive) to the homologous compounds. The RT of these mutant HIV-1 strains showed different amino acid substitutions depending on the class of the HIV-1-specific RT inhibitors. The following amino acid substitutions were found: 138 Glu-->Lys (TSAO-T), 181 Tyr-->Cys (nevirapine), 181 Tyr-->Cys (pyridinone), and 100 Leu-->Ile (TIBO R82150). Four TIBO (R82913)-resistant HIV-1 strains contained different amino acid substitutions: 103 Lys-->Asn (strain 2), 100 Leu-->Ile and 138 Glu-->Lys (strain B02), 100 Leu-->Ile and 181 Tyr-->Cys (strain 1), 100 Leu-->Ile and 188 Tyr-->His (strain B22). The level of cross-resistance (or sensitivity) highly depends on the nature of the amino acid substitutions. As a rule, the TSAO-resistant HIV-1 strains (138 Glu-->Lys) and TIBO (R82150 or R82913)-resistant HIV-1 strains (Leu 100-->Ile or 103 Lys-->Asn) are sensitive to the other HIV-1-specific RT inhibitors, whereas the amino acid change 181 Tyr-->Cys results in a significant reduction of sensitivity to all classes of the HIV-1-specific RT inhibitors.

Amino Acid Sequence↗
PubMed1993

Disruption of a salt bridge between Asp 488 and Lys 465 in HIV-1 reverse transcriptase alters its proteolytic processing and polymerase activity.

The conserved aspartic acid residue 488 in the RNase H domain of HIV-1 reverse transcriptase (RT) was mutated to alanine. RT was expressed in Escherichia coli alone or with the entire pol-gene polyprotein consisting of proteinase, RT, and integrase and processed by the HIV-1 proteinase in the bacterial cell. Expression of mutant RT together with the proteinase resulted in an overproduction of RT p51 vs p66. The mutation also altered the conformation of the RT p66/p51 heterodimer as shown by the loss of binding of monoclonal antibodies to mutant RT in ELISA. Crystallographic data shows that a salt bridge exists between Asp 488 and Lys 465 of RNase H which stabilizes the uncleavable form of RT p66, and that substitution of Asp for Ala would prevent the formation of this salt bridge. Our results indicate that disruption of this salt bridge through mutation of Asp 488 interferes with the conformational changes that regulate the limited processing of p66 to 51 by the virus proteinase. Homology data suggest that such a bridge may be present in other lentiviruses. The mutation introduced caused a moderate decrease in both the RNase H activity and the polymerase activity of RT, indicating that the proper folding of the RNase H domain of RT is necessary to achieve full polymerase activity.

Amino Acid Sequence↗
PubMed1993

Efficacy of (-)-9-[4-hydroxy-2-(hydroxymethyl)butyl]guanine in African green monkeys infected with simian varicella virus.

(-)-9-[4-Hydroxy-2-(hydroxymethyl)butyl]guanine was evaluated for its efficacy in African green monkeys infected with simian varicella virus. Treatment by intramuscular injection was initiated 48 h after virus inoculation and was continued for 10 days; the treatment showed therapeutic effects on rash and viremia at dosages down to 1 mg/kg of body weight per day.

Acyclovir↗
PubMed1993

Dynamic strength in Parkinson's disease. Quantitative measurements following withdrawal of medication.

This study examined the influence of pharmacological treatment on muscle strength in Parkinson's disease (PD). Twelve patients, 7 men and 5 women, were tested with modified Cybex II equipment. Peak torques in isometric, concentric and eccentric contraction at 30, 120 and 180 degrees/s in ankle dorsiflexors were recorded before and after the withdrawal of medication. EMG were recorded during contraction. Clinical assessment was done according to Webster's and Hoehn and Yahr's rating scales. Clinical scores were significantly increased (p < 0.05). Peak torques in isometric, concentric and eccentric contraction (p < 0.05) decreased at almost all velocities after withdrawal of medication. Correlations were found between changes in clinical score and strength. Strength production in PD was influenced by medication, and the results correlated with changes in clinical ratings. Strength measurement may be used in the evaluation of pharmacological therapy.

Aged↗
PubMed1993

Antiviral therapy in human immunodeficiency virus infections. Current status (Part I).

Antiviral therapy has in the past met with limited success and only a few antiviral drugs have been available. The human immunodeficiency virus (HIV) epidemic has created an urgent need for the development of antiviral therapy against this infection. HIV replication offers several targets for inhibitory compounds, the foremost presently being the HIV reverse transcriptase and protease enzymes. Despite the short time since the beginning of the epidemic, 3 nucleoside analogue drugs (zidovudine, didanosine and zalcitabine) which act at the reverse transcriptase site are already licensed for use against HIV, and others (stavudine, alovudine and 3-TC) are still under clinical evaluation. Part II of this article discusses non-nucleoside reverse transcriptase inhibitors undergoing investigation, protease inhibitors, and compounds active against various other targets in HIV. Treatment guidelines are also provided in Part II.

Animals↗
PubMed1993

Antiviral therapy in human immunodeficiency virus infections. Current status (Part II).

Part I of this article reviewed the targets against which anti-HIV drugs can be directed, problems in assessing active compounds (e.g. resistance development and use of surrogate end-points). and nucleoside analogues effective against HIV reverse transcriptase. Intensive research is currently being undertaken in laboratories and hospitals to design and evaluate new inhibitors of HIV. In this work, combining different drugs is one important approach, both to decrease toxicity and to offset the rate of resistance development, which seems to be a major problem associated with therapy directed against the ever-changing HIV. Therapeutic vaccines and immunomodulators are other modalities being actively evaluated against HIV and AIDS, although this effort has not yet yielded any licensed treatment. It appears likely that new antiviral drugs and immunotherapies will be forthcoming during the next 5 years, that they will be used in a variety of combinations, and that the treatment options available for opportunistic infections will increase. These developments should improve the survival and the quality of life of patients with HIV infection.

Antiviral Agents↗
PubMed1992

The HIV replication inhibitor 3'-fluoro-3'-deoxythymidine blocks sialylation of N-linked oligosaccharides.

The ability of 3'-fluoro-3'-deoxythymidine (FLT) to interfere with glycosylation was investigated in an experimental system, where the effects on the herpes simplex virus type 1-specified glycoprotein gC were determined. By adding FLT to HSV-infected cells after the peak of DNA synthesis, it was possible to segregate possible effects on nucleic acid metabolism from the effects on glycosylation of gC. It was found that FLT treatment of HSV-infected cells at concentrations of 20-500 micrograms/ml resulted in a significant increase in the electrophoretic mobility of gC, indicating a reduction of the amount of carbohydrates incorporated into gC. Lectin-binding assays demonstrated that the FLT treatment blocked addition of sialic acid to complex type N-linked glycans. The effects on glycosylation were observed in cells infected with an HSV mutant, deficient in thymidine kinase (TK), but not in cells infected with wild type virus. The cells infected with the wild type virus contained five times more total FLT metabolites than the cells infected with the TK-deficient mutant, whereas the latter cell type contained significantly higher amounts of unmetabolized FLT. This result indicates that FLT itself, and not a metabolite, was responsible for the effects on glycosylation.

Antibodies, Monoclonal↗
PubMed1992

Early appearance of simian immunodeficiency virus (SIV) antigen and antibodies as variables in evaluating antiviral drugs in macaques.

SIV infection in macaques has become an important animal model for HIV-1 infection in humans. An antibody assay was therefore developed and compared to a commercially available antigen assay with respect to their usefulness to monitor the course of simian immunodeficiency virus (SIV) infection in cynomolgus monkeys. A peptide, JB6T, consisting of 21 amino acids with the sequence NSWGCAFRQVCHTTVPWVNDS corresponding to a segment in the env protein of human immunodeficiency virus (HIV) type 2 was used as antigen in an enzyme-linked immunosorbent assay (ELISA). JB6T was found to detect IgG and IgM antibodies to viral antigens with high specificity. The earliest anti-SIV IgM antibodies were detected at days 13-16, with a maximum at day 20 and subsequently the levels fell. Specific IgG antibody levels increased at day 16-20 after SIV infection and reached a plateau at day 60. The commercially available HIV-1 p24/26 antigen test could, due to cross-reactivity, be employed to detect SIV antigen delay, peak and duration.

Amino Acid Sequence↗
PubMed1992

Prevention of HIV-2 and SIV infections in cynomolgus macaques by prophylactic treatment with 3'-fluorothymidine.

The aim of this study was to determine the usefulness of human immunodeficiency virus type 2 (HIV-2) for in vivo evaluation of antiviral drugs in monkeys and to study if prophylactic treatment with 3'-fluorothymidine (FLT) could prevent infection against a low challenge dose of HIV-2 or simian immunodeficiency virus (SIV). Protection against infection was assessed by virus isolation and polymerase chain reaction (PCR) on monkey peripheral blood mononuclear cells (PBMC) as well as by antibody and viral antigen assays. Prophylactic treatment with FLT 3 x 5 mg/kg/day, starting 8 h prior to virus inoculation, prevented HIV-2 infection in 3 of 8 monkeys. In another experiment 2 of 4 monkeys resisted 2-10 monkey infectious doses (MID50) of SIV with the same prophylactic treatment. All control animals (HIV-2 n = 8, SIV n = 4) became infected. Thus, FLT treatment prevented HIV-2 and SIV infection in 5 of 12 animals.

Animals↗
PubMed1992

Penetration of zidovudine and 3'-fluoro-3'-deoxythymidine into the brain, muscle tissue, and veins in cynomolgus monkeys: relation to antiviral action.

Cynomolgus monkeys had microdialysis probes implanted under ketamine anesthesia into peripheral veins, thigh muscles, and the brain in order to sample the extracellular fluid for the concentrations of unbound nucleoside analogs. A dose of 25 mg of zidovudine or 3'-fluoro-3'-deoxythymidine (FLT) per kg was administered subcutaneously to each of three animals. Relatively high antiviral concentrations of FLT and zidovudine were present in peripheral tissues and in the brain. It was found that the concentration of zidovudine in the brain was approximately one-third of that in muscle and veins; the same relation was observed for FLT. The in vivo unbound concentrations of both drugs in the brain, muscle, and venous blood exceeded those reported to inhibit human immunodeficiency virus replication in vitro. In addition, in a correlative study we found that the appearance of p24 antigen in sera of monkeys infected with simian immunodeficiency virus was significantly delayed by both compounds (15 mg/kg three times daily for 9 days after infection). Thus, we have shown that the extracellular concentrations of unbound FLT and zidovudine in the brain and peripheral tissues attained with in vivo antiviral doses exceed in vitro antiviral concentrations.

Animals↗
PubMed1992

Pharmacokinetics and distribution over the blood brain barrier of two acyclic guanosine analogs in rats, studied by microdialysis.

The free extracellular concentrations of acyclovir and (R)-9-[4-hydroxy-2-(hydroxymethyl)butyl]guanine (H2G) in the blood and in brain tissue of rats were measured in microdialysis samples by high-pressure liquid chromatography with UV detection. The half-life of acyclovir in blood was 2 h, while that of H2G was 28 min. The concentration attained in the brain compared with the concentration in blood was slightly lower for H2G than for acyclovir. The results show that the pharmacokinetic profiles of acyclic nucleosides may vary as a consequence of the structure of the acyclic chain corresponding to the sugar moiety.

Acyclovir↗
PubMed1992

Long-term tolerance and efficacy of 3'-azidothymidine and 3'-fluorothymidine treatment of asymptomatic monkeys infected with simian immunodeficiency virus.

Macaques chronically infected with simian immunodeficiency virus were treated with zidovudine (20 mg/kg of body weight per day for 9 weeks) or 3'-fluorothymidine (5 mg/kg of body weight per day for 9 weeks or three doses of 2 mg/kg per day for 24 days). Hematological changes in the treated animals included macrocytic anemia and leukopenia. Determination of antiviral effects in this model requires improved assay methods.

Anemia↗
PubMed1991

Comparison of the substrate specificities of human thymidine kinase 1 and 2 and deoxycytidine kinase toward antiviral and cytostatic nucleoside analogs.

Deoxynucleoside kinases are required for the 5'-phosphorylation of deoxynucleoside analogs used in chemotherapy. Cytoplasmic thymidine kinase (TK1), deoxycytidine kinase (dCK) and mitochondrial thymidine kinase (TK2) were completely purified from human leukemic spleen and their capacities to phosphorylate 43 nucleoside analogs were compared. TK1 showed the most restricted substrate specificity but tolerated 3'-modifications of the sugar ring and some 5-substitutions of the pyrimidine ring. TK2 showed a much broader specificity and phosphorylated pyrimidine bases with bulky 5-substitutions, including cytosine analogs, while sugar analogs with substituents other than OH in the 2' and 3' positions were very poor substrates. dCK showed a very broad specificity phosphorylating several cytosine analogs with 2' and 3' modifications as well as acyclic sugar analogs. Purine deoxyribonucleosides were also efficiently phosphorylated by dCK but in this case sugar modifications led to drastically decreased activity.

Antiviral Agents↗
PubMed1991

High-yield purification of HIV-1 proteinase expressed by a synthetic gene in Escherichia coli.

A rapid and simple purification procedure for human immunodeficiency virus type 1 (HIV-1) proteinase from a synthetic gene expressed in Escherichia coli has been developed. The synthetic gene was constructed from oligonucleotides containing several restriction enzyme sites in order to allow simple construction of homologous genes. The protein was translated as a precursor which was autocatalytically processed into the mature protein as shown by N-terminal sequence analysis of the purified protein. Immunoblot analysis was used to verify the nature of the expression product and it was found that 2 of 10 anti-peptide antibodies, covering the whole proteinase sequence, were able to react with the enzyme in crude bacterial lysates. These two anti-peptide antibodies represent a continuous sequence partially overlapping the active site. The purification involves two initial precipitation steps followed by cation-exchange and size-exclusion chromatography. A high yield and a high specific activity were achieved.

Amino Acid Sequence↗
PubMed1991

Simian immunodeficiency virus (SIVsm) isolation from blood and brain of experimentally infected macaques.

The possibility of using simian immunodeficiency virus (SIV)-infected macaques to study pathogenic events linked to HIV infection of the brain prompted us to investigate some of the virological features in SIV-infected macaques. Nine cynomolgus macaques were inoculated with SIVsm and killed at different times. We successfully isolated virus from the blood of all the animals and from the brains of eight. These results point to the early and regular spread of this lentivirus to the brain. Neutralizing activity was studied in the serum and cerebrospinal fluid specimens obtained from these macaques against a selected group of isolates. Cerebrospinal fluid did not show any neutralizing activity. Our findings integrate the observations from HIV-1 infection in man and indicate that SIV infection of macaques is a useful model for studying pathogenic events of brain infection.

Animals↗
PubMed1991

Hypoalgesia following epidural morphine: a controlled quantitative experimental study.

The efficacy, duration, and spread of epidural morphine hypoalgesia were assessed by an experimentally induced pricking pain evoked by laser stimulation. Four mg of plain morphine was injected epidurally in 7 volunteers at the L2-L3 interspace. Thresholds to warmth and pain perception, and pain-evoked potentials were measured. In the first experiment, hypoalgesia was monitored each hour for 7 h at various dermatomes. Hypoalgesia was detected at S1 dermatome after 2 h, but 3 h elapsed before hypoalgesia could be detected at the L1, T12, T10, T8, and T6 dermatomes. No effect was found at C7. No conduction delay was found along the pain pathway during hypoalgesia. Hypoalgesia lasted more than 7 h at S1, whereas hypoalgesia could not be detected after 5 h at other dermatomes. In the second experiment, naloxone (0.8 mg i.v.) was injected 230 min after injection of epidural morphine, and the subsequent recording 10 min later showed that hypoalgesia had been partly reversed. The onset and duration of hypoalgesia are different for experimentally induced pain and clinical pain. Experimentally laser-induced pain has the advantage of being quantitative, and is, as such, useful to assess hypoalgesia, and to test the potency of narcotics.

Analgesia↗