Search PubMed⌕ Search

Biomedical subjects

I Husain

Publications and source records attributed to I Husain.

At least 37 records · Page 2Linked to original sources
PubMed1990

Effect of the diaminocyclohexane carrier ligand on platinum adduct formation, repair, and lethality.

Platinum compounds with the diaminocyclohexane (dach) carrier ligand are of particular interest because cell lines that have developed resistance to platinum compounds in general often retain sensitivity to dach-platinum compounds, suggesting that the dach carrier ligand affects the formation, repair, or lethality of platinum-DNA adducts. The effect of the dach ligand on platinum adduct formation was assessed by using the (HaeIII-HindIII)146 fragment of pBR322 treated to give equal amounts of dach- or ethylene-diamine-platinum adducts. The sites of adduct formation were mapped by digestion with Escherichia coli ABC excinuclease. There were no significant effects of the dach carrier ligand on the types or sites of platinum adduct formation. The effect of the dach ligand on platinum adduct repair was determined by using synthetic oligomers designed to have single, specific platinum adducts (G monoadduct; GG, AG, or GNG diadduct) with either the dach or ethylenediamine (en) carrier ligand. These adducts differed significantly in their ability to serve as substrates for ABC excinuclease with GNG greater than or equal to G greater than AG greater than GG. The dach carrier ligand had little effect on the recognition of AG and GG adducts by ABC excinuclease, but significantly improved the ability of ABC excinuclease to excise G monoadducts and GNG diadducts. These data suggest that if the carrier ligand has any effect on the repair of platinum adducts, it is more likely to exert that effect on the repair of platinum monoadducts or GNG diadducts rather than on the more abundant AG or GG diadducts. [14C]Thiourea incorporation was used to quantitate the rate of monoadduct to diadduct conversion.(ABSTRACT TRUNCATED AT 250 WORDS)

Base Sequence↗
PubMed1990

Critique of the Dornier HM3 lithotripter as a clinical algesimeter.

The power and nociceptive intensity of shock waves generated by the Dornier HM3 extracorporeal shock wave lithotripter (ESWL) are voltage dependent and suited to algesimetry in a controllable voltage range of 8-30 kV. Fidelity of the HM3 as an algesimeter was tested by: (1) In vitro measurements of shock pressure at voltages between 14 and 30 kV were recorded by a force transducer at the point of clinical focus. (2) Unanaesthetized volunteer (n = 5) assessment and VAS pain scores of shocks in the range of 10-24 kV, yielding highly significant correlations between blinded randomized shock voltage (r = 0.88), and VAS scores (r = 0.84). (3) Voltage-tolerance curves generated from 33 ASA class 1 or 2 patients undergoing ESWL treatment under epidural analgesia with 0.125% bupivacaine, fortified with a bolus epidural dose of 100 micrograms fentanyl if pain arose during treatment. Voltage tolerance was increased by 50% after an epidural bolus of 100 micrograms fentanyl (P less than 0.001). The respiratory consequences of epidural fentanyl were assessed by changes of respiratory rate and rhythm recorded from capnographic tracings of expired carbon dioxide. This study indicates that the Dornier HM3 system provides a valuable opportunity to conduct precise, quantitative measurements of induced deep truncal pain, as well as the effectiveness and respiratory cost of analgesic interventions directly applicable to the safe management of acute pain.

Analgesia, Epidural↗
PubMed1990

Synapse formation on quail trochlear neurons transplanted in duck embryos before naturally occurring motor neuron death.

About half of the trochlear motor neurons in duck and quail embryos die during normal development. In a previous study the role of target muscle in controlling the number of surviving motor neurons was investigated by reducing the number of neurons innervating the muscle. This was accomplished by removing the midbrain of the duck embryo and grafting in its place the midbrain of the quail embryo before motor neuron death begins. It was observed that the number of surviving trochlear motor neurons in the quail-duck chimera embryos was not significantly different from that of the normal quail. The present investigation was undertaken to determine whether trochlear motor neurons in the chimera embryos received afferent synapses. Brains of duck, quail and chimera embryos on days 16 and 20 were processed for electron microscopical observations. Synapses formed on motor neurons of the chimera embryos. Surprisingly, synapses on motor neurons of quail differed from those of duck, both qualitatively and quantitatively. Synapses on the motor neurons of the chimera embryos developed in a fashion similar to that for the duck motor neurons. Our failure to rescue trochlear motor neurons in the chimera embryos suggests that the developing motor neurons may respond to a larger target muscle only if they received a normal complement of afferent synaptic input.

Animals↗
PubMed1990

On the industrialization of small towns in Pakistan.

"Migration to large metropolitan cities in Pakistan from rural areas and small towns has put enormous pressure on those cities and created many socio-economic and demographic problems. This article suggests that, in conjunction with other steps, many smaller towns should be developed and industrialized to ease the pressure on the larger cities, as has been done in other areas of the world."

Asia↗
PubMed1989

Purification and properties of Methanobacterium thermoautotrophicum DNA photolyase.

We have purified DNA photolyase from the autotrophic anaerobic archaebacterium Methanobacterium thermoautotrophicum to near homogeneity by a two-column affinity chromatography. The purified enzyme has an Mr = 60,000 and shows near UV absorption peak at 440 nm and a fluorescence emission maximum at 462 nm indicating that it contains 8-hydroxy-5-deazaflavin (coenzyme F420) as an intrinsic chromophore. The photolyase binds with high specificity to thymine dimer in DNA with an equilibrium binding constant, KA = 1.4 x 10(9) M-1, and a dissociation rate constant, koff = 1.4 x 10(-4) s-1 (t1/2 = 43 min). Despite 6-fold higher affinity compared to the folate-containing Escherichia coli photolyase the two enzymes apparently contact the same phosphates around the thymine dimer: the phosphate immediately 5' and the three phosphates immediately 3' to the dimer on the damaged strand and the phosphate across from the dimer in the minor groove on the complementary strand. The absolute action spectrum of the Methanobacterium photolyase in the 400-500-nm region closely matches the absorption of the enzyme-bound F420. The quantum yield (phi) over this region is constant and is approximately 0.2. The value is measurably smaller than the quantum yields reported for other DNA photolyases.

Amino Acid Sequence↗
PubMed1989

Human nucleotide excision repair in vitro: repair of pyrimidine dimers, psoralen and cisplatin adducts by HeLa cell-free extract.

We searched for nucleotide excision repair in human cell-free extracts using two assays: damage-specific incision of DNA (the nicking assay) and damage-stimulated DNA synthesis (the repair synthesis assay). HeLa cell-free extract prepared by the method of Manley et al. (1980) has a weak nicking activity on UV irradiated DNA and the nicking is only slightly reduced when pyrimidine dimers are eliminated from the substrate by DNA photolyase. In contrast to the nicking assay, the extract gives a strong signal with UV irradiated substrate in the repair synthesis assay. The repair synthesis activity is ATP dependent and is reduced by about 50% by prior treatment of the substrate with DNA photolyase indicating that this fraction of repair synthesis is due to removal of pyrimidine dimers by nucleotide excision. Psoralen and cisplatin adducts which are known to be removed by nucleotide excision repair also elicited repair synthesis activity 5-10 fold above the background synthesis. When M13RF DNA containing a uniquely placed psoralen adduct was used in the reaction, complete repair was achieved in a fraction of molecules as evidenced by the restoration of psoralen inactivated KpnI restriction site. This activity is absent in xeroderma pigmentosum group A cells. We conclude that our cell-free extract contains the human nucleotide excision repair enzyme activity.

Cell-Free System↗
PubMed1989

Influence of Dornier HM3 system on respiration during extracorporeal shock-wave lithotripsy.

Patients undergoing extracorporeal shock-wave lithotripsy (ESWL) for renal stones in the Dornier HM3 apparatus are immersed to the clavicles in water and anchored by abdominal and leg restraining straps. The respiratory effects of this system and sedation with midazolam were studied in 70 awake patients anesthetized with epidural blockade. On immersion, surface abdominal pressure and respiratory frequency (f) increased. Tidal volume (VT) and arterial saturation (SaO2) decreased. After intravenous midazolam 0.045 mg/kg body weight, VT decreased further to 35% below pre-immersion values and stone excursions measured by fluoroscopy diminished by more than 50%; reduction of VT and stone excursions were linearly correlated (R = 0.45). SaO2 declined sharply to 6.1% (range -1.5-13.8%) below pre-immersion values, whereas end-tidal CO2 (PETCO2) increased more slowly and f remained above the pre-immersion rate. In three patients, SaO2 decreased to below 85% but was rapidly restored to 98-100% by oxygen administration. The respiratory effects of sedative drugs are exaggerated by the Dornier HM3 system, and continuous monitoring of gas exchange and appropriate oxygen administration are recommended in patients receiving regional anesthesia and sedation.

Adolescent↗
PubMed1988

Thymine dimers bend DNA.

A 32-base-pair DNA fragment containing a thymine photodimer was constructed and ligated head-to-tail to obtain multimers of this sequence in which thymine dimers were in phase with the helix screw axis (approximately equal to 3 turns apart). The ligation products were analyzed by one- and two-dimensional gel electrophoresis and quantitative electron microscopy. These analyses show that the thymine photodimer introduces a bend of approximately equal to 30 degrees in DNA, which causes anomalously slow migration of DNA fragments in polyacrylamide gels and facilitates the formation of small covalent circles. Repair of thymine dimers by DNA photolyase abolishes the anomalous migration.

DNA↗
PubMed1988

Primary choice of intervention for distal ureteric stone: ureteroscopy or ESWL?

Either transurethral ureteroscopy (URS) or extracorporeal shock wave lithotripsy (ESWL) was the primary method of intervention in two series of patients presenting consecutively with stones located in the ureter distal to the radiological marking of the sacroiliac joint. Of 65 patients treated by URS, successful evacuation of the major part of the stone was achieved in 97% in one or two sessions. Of those subsequently attending for review, 93% proved stone-free but 3% required surgery for serious complications. In the ESWL series of 53 patients, successful stone fragmentation was recorded in 94%, with 2 patients requiring a supplementary endourological or surgical procedure. No significant complications were related to ESWL and 90% of those followed up after successful ESWL proved stone-free at 6 weeks. In uncomplicated cases, the mean procedure time for ESWL was one-third of that required for URS and the hospital stay one-half. It is suggested that ESWL should be the primary method of intervention in patients with distal ureteric stone, with URS reserved for the small number that prove refractory to such treatment.

Endoscopy↗
PubMed1987

Mechanism of damage recognition by Escherichia coli DNA photolyase.

Escherichia coli DNA photolyase binds to DNA containing pyrimidine dimers with high affinity and then breaks the cyclobutane ring joining the two pyrimidines of the dimer in a light- (300-500 nm) dependent reaction. In order to determine the structural features important for this level of specificity, we have constructed a 43 base pair (bp) long DNA substrate that contains a thymine dimer at a unique location and studied its interaction with photolyase. We find that the enzyme protects a 12-16-bp region around the dimer from DNase I digestion and only a 6-bp region from methidium propyl-EDTA-Fe (II) digestion. Chemical footprinting experiments reveal that photolyase contacts the phosphodiester bond immediately 5' and the 3 phosphodiester bonds immediately 3' to the dimer but not the phosphodiester bond between the two thymines that make up the dimer. Methylation protection and interference experiments indicate that the enzyme makes major groove contacts with the first base 5' and the second base 3' to the dimer. These data are consistent with photolyase binding in the major groove over a 4-6-bp region. However, major groove contacts cannot be of major significance in substrate recognition as the enzyme binds equally well to a thymine dimer in a 44-base long single strand DNA and protects a 10-nucleotide long region around the dimer from DNase I digestion. It is therefore concluded that the unique configuration of the phosphodiester backbone in the strand containing the pyrimidine dimer, as well as the cyclobutane ring of the dimer itself are the important structural determinants of the substrate for recognition by photolyase.

Base Sequence↗
PubMed1987

Binding of E. coli DNA photolyase to a defined substrate containing a single T mean value of T dimer.

The E. coli DNA photolyase is a flavoprotein that catalyzes the photoreversal of pyrimidine dimers. The enzyme binds to DNA containing pyrimidine dimers in a light-independent step and repairs the dimer upon absorbing a photon in the 300-600 nm range. The rate and equilibrium constants for the light-independent reaction were determined before, using randomly modified substrates that contained T mean value of T, T mean value of C and C mean value of C dimers in random sequence surrounding. In this paper we have determined these constants for a defined substrate (a 43 bp oligomer containing a T mean value of T dimer) using the gel retardation assay. We find that: the equilibrium constant and the off rate obtained with this substrate by this technique are similar to those obtained with randomly modified DNA using filter binding and flash photolysis techniques. the off rate with the defined substrate is heterogeneous indicating heterogeneity in the enzyme population or in the enzyme-substrate complexes, and the enzyme has 7.5 X 10(4)-fold higher affinity for pyrimidine dimer compared to non-dimer DNA nucleotides.

Base Sequence↗
PubMed1987

Transurethral ureteroscopy. Safety guide wire as an aid to a more aggressive approach.

In an unselected, consecutive series of patients, ureteroscopy was carried out for removal or manipulation of stones in 48 patients and for evaluation of suspected ureteric tumours in two. A success rate of 92% was achieved. The use of an intra-ureteric safety guide wire, indwelling throughout the procedure, facilitated ureteroscopic manipulation, minimised complications, reduced the need for subsequent open surgery and has been a prerequisite for our comparatively aggressive approach to ureteric disorders. The procedure may be time-consuming but prolonged manipulation within the ureter seems to carry little morbidity.

Adult↗
PubMed1987

Photoreactivation in phr mutants of Escherichia coli K-12.

We have investigated the genetics of photoreactivation in Escherichia coli K-12. We found that strains with point mutations or deletions in the phr gene showed a significant residual level of photoreactivation after exposure to large fluences of photoreactivating light. It had been previously proposed that a gene in the gal-att lambda interval is also involved in photoreactivation and that the residual photoreactivating activity might be due to this so-called phrA gene located at this interval. We found that deletions of the gal-att lambda region had no effect on either the rate or the final extent of photoreactivation observed in phr+ cells or phr mutants; however strains carrying the delta (gal-att lambda) deletions displayed increased sensitivity to near-UV radiation.

Bacterial Proteins↗
PubMed1986

Interaction between the soluble F1 ATPase and its naturally occurring inhibitor protein. Studies using hydrophilic high-performance liquid chromatography and immunoelectron microscopy.

Binding of the isolated ATPase (F1) to its naturally occurring inhibitor protein was studied by two novel, independent techniques. High-pressure gel permeation chromatography revealed one tight binding site (Kd = 0.46 microM) for the inhibitor on F1, and a number of weak, non-specific sites. Use of an antibody directed against a non-binding region of the inhibitor protein demonstrated the formation of inhibitor/F1/immunoglobulin G complexes of 1:1:1 and 2:2:1 stoichiometry, but not of the putatively more stable cyclic 4:2:2 complexes. It was concluded that, despite the presence of three beta-subunits, only one site per F1 molecule is available for binding its inhibitor protein.

Animals↗
PubMed1986

Sequences of Escherichia coli uvrA gene and protein reveal two potential ATP binding sites.

We have determined the nucleotide sequence of the uvrA gene of Escherichia coli. The coding region of the gene is 2820 base pairs which specifies a protein of 940 amino acids and Mr = 103,874. The polypeptide sequence predicted from the DNA sequence was confirmed by analyzing the UvrA protein: the sequence of the first 7 NH2-terminal amino acids as well as the amino acid composition of the pure protein agreed with those predicted from the nucleotide sequence. By comparing the sequence of UvrA protein to the amino acid sequences of other ATPases, we found that two regions in the UvrA protein, separated from one another by about 600 amino acids, have the highly conserved G-X4-GKT(S)-X6-I(V) sequence found at the active sites of many, but not all, ATPases. Our findings suggest that UvrA protein may have two ATP binding sites.

Adenosine Triphosphatases↗
PubMed1986

Effects of the bidentate malonate ligand on the utilization and cytotoxicity of platinum compounds in the L1210 cell line.

Previous studies have investigated the cytotoxicity of platinum(II) compounds with bidentate leaving ligands, but little is known about their uptake or mechanism of action inside the cell. We have compared the uptake and intracellular effects of cis-1,2-diaminocyclohexanemalonatoplatinum(II) [Pt(mal)(cis-DACH)] and cis-1,2-diaminocyclohexanedichloroplatinum(II) [PtCl2(cis-DACH)] in the L1210 cell line. In the 3-h colony formation assay, PtCl2(cis-DACH) is almost 10 times more cytotoxic than Pt(mal)(cis-DACH). However, when the time of incubation with platinum drug is increased from 3 to 24 h the cytotoxicity of PtCl2(cis-DACH) changes relatively little while the cytotoxicity of Pt(mal)(cis-DACH) increases over 10-fold. As a consequence, Pt(mal)(cis-DACH) is only slightly less cytotoxic than the dichloro compound by 24 h. These data can readily be explained by differences in the time course of uptake. Pt(mal)(cis-DACH) is initially taken by the cell at a much slower rate than PtCl2(cis-DACH), but the uptake continues linearly for at least 24 h with the malonate compound, while uptake for the dichloro compound begins to plateau between 5 and 8 h. The earlier plateauing of PtCl2(cis-DACH) uptake is most likely to be due to a quicker approach to equilibrium between intracellular and extracellular concentrations of unchanged drug which is caused by a more rapid inactivation of PtCl2(cis-DACH) in the media coupled with the more rapid uptake of PtCl2(cis-DACH) by the cells. When compared at equal cytotoxicity, the uptake of platinum into the intracellular pool of low molecular weight platinum compounds is significantly greater for Pt(mal)(cis-DACH) even though the rate of platinum incorporation into DNA is essentially the same for both compounds at early times. These data suggest that a smaller percentage of the low molecular weight platinum is in a reactive form inside the cell for Pt(mal)(cis-DACH). While the inhibition of cell survival exactly parallels incorporation of platinum into DNA for both compounds, there is a significant lag before the onset of inhibition of DNA synthesis for Pt(mal)(cis-DACH). This observation suggests that the conversion of monoadducts to diadducts may be slower for platinum compounds with bidentate leaving ligands.

Animals↗