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Biomedical subjects

I Ahmad

Publications and source records attributed to I Ahmad.

At least 19 recordsLinked to original sources
PubMed1995

Liposomal entrapment of the neutrophil-derived peptide indolicidin endows it with in vivo antifungal activity.

Indolicidin, a cationic tridecapeptide amide isolated from the granules of bovine neutrophils, has been found to possess potent antimicrobial activity in vitro but its nonselective toxicity could restrict its therapeutic utility. We found that the concentration at which indolicidin disrupts washed human red blood cell membranes coincided with the concentration at which indolicidin self associates. Because of a preponderance of hydrophobic residues, we believed that indolicidin would partition into liposomes which would restrict its exchange with biological tissues and consequently reduce its toxicity. Fluorescence spectroscopy of indolicidin added to 100 nm liposomes comprised of POPC, POPC/cholesterol (60:40 mol%), DPPC, or DPPC/cholesterol (60:40) revealed a large blue-shift and an increase in intensity of the emission profile indicating insertion into the bilayer. Of the lipids tested, POPC exhibited the highest degree of indolicidin binding as determined by fluorescence and encapsulation efficiency. By sequestering indolicidin within the lipid bilayer of 100 nm POPC liposomes we significantly reduced its toxicity to CHO/K1 cells. Likewise, the systemic toxicity of liposomal indolicidin in Balb/c mice was decreased dramatically relative to aqueous solutions; the maximum dose at which no deaths occurred was 0.4 mg/kg for free indolicidin versus 40 mg/kg for indolicidin-POPC. Because of this decrease in toxicity, we were able to administer liposomally encapsulated material at significantly higher concentrations than unencapsulated aqueous material and achieve efficacy in treating animals systemically infected with Aspergillus fumigatus. Liposomal but not free indolicidin was found to be effective in obtaining cures. This report is the first description of the in vivo therapeutic activity of a neutrophil-derived antimicrobial peptide and suggests that liposomal treatment modalities will provide effective strategies for endowing this class of compounds with pharmacological utility.

Amino Acid Sequence↗
PubMed1995

DNA recognition by the EcoP15I and EcoPI modification methyltransferases.

The DNA-binding properties of the EcoP15I DNA methyltransferase (M.EcoP15I; MTase) were studied using electrophoretic mobility shift assays. We show by molecular size-exclusion chromatography and dimethyl suberimidate cross-linking that M.EcoP15I is a dimer in solution. While M.EcoP15I binds approx. threefold more tightly to its recognition sequence, 5'-CAGCAG-3', than to non-specific sequences in the presence of AdoMet or its analogs, the discrimination between specific and non-specific sequences significantly increases in presence of ATP. These results suggest for the first time a role for ATP in DNA recognition by type-III restriction-modification enzymes. Furthermore, we show that although c2 EcoPI mutant MTases are defective in AdoMet binding, they are still able to bind DNA in a sequence-specific manner.

Adenosine Triphosphate↗
PubMed1995

Mammalian phosphoribosyl-pyrophosphate synthetase.

PRPP synthetase from rat liver exists as large molecular weight aggregates composed of at least three different components. Cloning of cDNA for the catalytic subunit revealed the presence of two highly homologous isoforms of 34 kDa, designated as PRS I and PRS II. Northern blot analysis showed tissue-differential expression of the two isoform genes. cDNA was expressed in E. coli and studies on the recombinant isoforms showed differences in sensitivity to inhibition by ADP and GDP and to heat inactivation. The rat gene for PRS I has 22 kb and is split into 7 exons. cDNAs for human enzymes were also cloned. Human genes for PRS I and PRS II are localized at different regions on the X-chromosome and their promoter regions were examined. Another component, PRPP synthetase-associated protein of 39 kDa (PAP39), was cloned from cDNA library of the rat liver. The deduced amino acid sequence of PAP39 is remarkably similar to those of PRS I and PRS II. Evidence indicated molecular interaction between PAP39 and the catalytic subunits and an inhibitory effect of PAP39 on the catalytic activity. Expression of the PAP39 gene is tissue-differential like the PRS genes, indicating that the composition of PRPP synthetase may differ with the tissue, hence properties of the enzyme would differ. Further studies on these components and their interaction are expected to reveal various mechanisms governing mammalian PRPP synthetase.

Amino Acid Sequence↗
PubMed1995

Augmentation of chrysotile-induced oxidative stress by BHA in mice lungs.

Asbestos is known to induce oxidative stress in the lung. The consumption of butylated hydroxyanisole (BHA) in preserved food and soft drinks is increasing in the general population, which includes workers in asbestos factories. Because there is no information on the effect of co-exposure to chrysotile and BHA, the time-dependent effects of a single intratracheal dose of chrysotile (1 mg per mouse) and a single ip dose of BHA (350 mg/kg body weight) on various indices of oxidative stress such as lipid peroxidation, hydrogen peroxide generation, glutathione peroxidase (GPX), glutathione reductase (GR), catalase, glucose-6-phosphate dehydrogenase (G6PDH) and glutathione (GSH) were followed for up to 14 days. Microsomal lipid peroxidation (as well as that induced by NADPH) was significantly enhanced by BHA in the chrysotile-exposed group. GPX and GR activities in the same group were gradually decreased by BHA. Non-significant modulation of catalase activity by BHA was also noted. BHA induces GSH to a significant extent in lungs exposed with chrysotile. An increase in the G6PDH activity was maximal (19%; P < 0.05) at day 3. The results clearly demonstrate that BHA enhances chrysotile-induced oxidative stress in the lung.

Animals↗
PubMed1995

Rhinocerebral invasive mycosis: occurrence in immunocompetent individuals.

We report the computed tomographic appearance of invasive fungal disease of the paranasal sinuses in 13 patients. Coronal and axial computed tomographic images were obtained in each patient and data were analysed. Eight patients had Aspergillus flavus infection, four had Mucormycosis, and one had mixed Candida and Mucor. Our experience was different from that of other workers in many respects. All of our patients were immunocompetent. On radiological imaging by computed tomography, ethmoid sinuses were involved in 85% of our patients. In previously reported series maxillary sinuses were most frequently affected. Calcification in the inflammatory mass was not encountered in any of our patients, whereas this feature was present in many reported cases. Features in our patients that were similar to other studies were contrast enhancement, extension of the disease into the orbit and cranial cavity and a high mortality. The clinical course and radiological features of invasive mycosis simulate malignancy. Certain features that may help to differentiate invasive fungal infection from malignancy are discussed. We conclude that invasive fungal infection can affect immunocompetent individuals and should be considered in the differential diagnosis in appropriate clinical settings.

Adolescent↗
PubMed1995

Interactions between opioid drugs and propofol in laboratory models of seizures.

Propofol (i.v. and i.p.) exhibited anticonvulsant activity in three models of seizure in the mouse, induced by bicuculline, kainic acid and N-methyl-DL-aspartic acid (NMDLA). Morphine, pethidine and fentanyl, which showed a biphasic dose-response relationship with respect to seizure modulation, abolished the anticonvulsant activity of propofol to exhibit their own intrinsic activity in proconvulsant doses. This occurred with very low doses of fentanyl and pethidine (15 micrograms kg-1 and 0.5 mg kg-1, respectively) in the NMDLA model. Thus it appears that propofol has anticonvulsant activity only when a convulsion is elicited directly; it does not prevent the actions of compounds that lower seizure threshold to convulsant stimuli. The anticonvulsant doses of morphine and fentanyl did not summate with the anticonvulsant activity of propofol. However, there was some evidence of summation of anticonvulsant activity between pethidine and propofol in the NMDLA model.

Analgesics, Opioid↗
PubMed1995

In vivo effects of acetaminophen on rat RBC and role of vitamin E.

Non-therapeutic toxic dose (250 mg/kg) of acetaminophen (paracetamol), in vivo to albino rats significantly decreased red cell reduced glutathione (GSH) content and activity of (Na+, K+)-ATPase enzyme, whereas osmotic fragility (O.F.) was increased. However, no change was observed in the activity of glutathione reductase (GR) after acetaminophen treatment, while acetaminophen plus vitamin E treated rats showed significant increase in GR activity. Supplementation of vitamin E to the drug treated rats effectively brought the GSH content, (Na+, K+)-ATPase activity and O.F. back to almost normal. The results suggest that acetaminophen toxic dose treatment induces metabolic and membranal alterations making red cells prone to hemolysis, while vitamin E which is an antioxidant shows its ameliorating role to these changes.

Acetaminophen↗
PubMed1994

Interaction of EcoP15I DNA methyltransferase with oligonucleotides containing the asymmetric sequence 5'-CAGCAG-3'.

EcoP15I DNA methyltransferase (Mtase) recognizes the asymmeteric sequence CAGCAG and catalyzes the transfer of a methyl group from S-adenosyl-L-methionine to the second adenine residue. We have investigated the DNA binding properties of EcoP15I DNA Mtase using gel mobility shift assays. EcoP15I DNA Mtase binds approximately threefold more tightly to DNA containing its recognition sequence, CAGCAG, than to non-specific sequences in the absence or presence of cofactors. Interestingly, in the presence of ATP the discrimination between specific and non-specific sequences increases significantly. These results suggest for the first time a role for ATP in DNA recognition by type III restriction-modification enzymes. In addition, we have shown that bromodeoxyuridine-containing oligonucleotides form complexes with EcoP15I DNA Mtase that are crosslinked upon irradiation. More importantly, we have shown that the crosslink site is at the site of DNA binding, since it can be suppressed by an excess of unmodified oligonucleotide. EcoP15I DNA Mtase exhibited Michaelis-Menten kinetics with both unmodified and bromodeoxyuridine-substituted DNA, with a higher specificity constant for the latter. Furthermore, gel mobility shift assays showed that proteolyzed EcoP15I DNA Mtase formed a specific complex with DNA, which had similar mobility as the native protein-DNA complex. Taken together these results form the basis for a detailed structure-function analysis of EcoP15I DNA Mtase.

Base Sequence↗
PubMed1994

Identification of amino-acid residues linked to different properties of phosphoribosylpyrophosphate synthetase isoforms I and II.

The catalytic subunit of rat liver phosphoribosylpyrophosphate synthetase is composed of two isoforms, PRS I and PRS II. The amino-acid sequences differ only by 13 residues, out of which two Lys residues of PRS I at positions 4 and 152 give net additional positive charges to PRS I. Previous work has shown that PRS I is more sensitive to inhibition by ADP and GDP and more stable to heat treatment than is PRS II. To identify amino-acid residues responsible for the different properties, five chimeric enzymes between rat PRS I and PRS II and two mutated enzymes with a single point mutation at position 152 were constructed; these enzymes were produced in Escherichia coli. Changing Lys-4 of PRS I to Val, together with Ile-5 to Leu, completely abolished sensitivity to GDP inhibition of PRS I, indicating that Lys-4 in PRS I is critical for GDP inhibition. The substitutions at position 152 had little effect on GDP inhibition. Characterization of the chimeric enzymes revealed that residues between residues 54-110 and 229-317, namely, Val-55 and/or Ala-81, and Arg-242 and/or Cys-264 of PRS I also contribute to the strong GDP inhibition. Lys-4 was also important for the strong ADP inhibition of PRS I. Regarding the physical properties, chimeric enzymes bearing residues 12-53 of PRS I were stable at 49 degrees C and with digestion with papain and proteinase K. Our observations suggest that Lys-17, Ile-18, and/or Cys-40 of PRS I contribute to stability of the enzyme.

Amino Acids↗
PubMed1994

Photolabeling of the EcoP15 DNA methyltransferase with S-adenosyl-L-methionine.

Radioactivity from S-adenosyl-L-[methyl-3H]methionine ([methyl-3H]AdoMet) was bound to the EcoP15 DNA methyltransferase (M.EcoP15) following short-wave ultraviolet (UV) irradiation. The labeled protein was subjected to polyacrylamide-gel electrophoresis in the presence of sodium dodecyl sulfate (SDS-PAGE), and detected by fluorography and autoradiography. Labeling was found to be dependent on the concentration of AdoMet and time of UV irradiation. The photolabeling by [methyl-3H]AdoMet was specific and blocked by S-adenosyl-L-homocysteine (AdoHcy) and sinefungin which are known to function as competitive inhibitors. Limited digestion of the M.EcoP15-AdoMet adduct by Staphylococcus aureus protease V8 generated three peptides of approx. 50, 32 and 30 kDa. Interestingly, only the 30-kDa peptide fragment contained radioactivity, as detected by SDS-PAGE, followed by fluorography and autoradiography. Further, sequencing of a few amino acids at the N-terminus of these peptides showed that the 30-kDa fragment was the N-terminal portion of M.EcoP15. These results suggest that photolabeling is at the AdoMet-binding site and that the N-terminal half of M.EcoP15 may be involved in substrate binding.

Affinity Labels↗
PubMed1994

Peritoneal Kaposi's sarcoma: a cause of ascites in acquired immunodeficiency syndrome.

The investigation of ascites in a homosexual man with acquired immunodeficiency syndrome and mucocutaneous Kaposi's sarcoma (KS) revealed only numerous purplish nodules of KS in the parietal and serosal peritoneum, observed at laparoscopy. KS lesions of the peritoneum, a finding not reported in the literature previously, was the only and likely cause of ascites in our patient. Increased red cells and high serum-ascites albumin gradient in a patient with acquired immunodeficiency syndrome should suggest the possibility of peritoneal KS as a cause of ascites.

Acquired Immunodeficiency Syndrome↗
PubMed1994

The activity of opioid analgesics in seizure models utilizing N-methyl-DL-aspartic acid, kainic acid, bicuculline and pentylenetetrazole.

Morphine, fentanyl and pethidine exhibited a biphasic dose response relationship with respect to their effects on seizure thresholds to bicuculline, pentylenetetrazole, N-methyl-DL-aspartate (NMDLA) and kainic acid in mice. The usual pattern was for low doses to be anticonvulsant and higher doses to be proconvulsant. However this pattern was reversed for fentanyl and pethidine when NMDLA was used to induce seizures. The low dose effects of all three opioid drugs was sensitive to 1 mg kg-1 naloxone in all seizure models. The responses to high doses of pethidine were unaffected or enhanced by this dose of naloxone. Naloxone reversed the effects of the higher doses of morphine and fentanyl in all models except bicuculline induced seizures.

Analgesics, Opioid↗
PubMed1994

Primitive trigeminal artery associated with cavernous aneurysm: case report.

A case of unruptured aneurysm at the junction of the cavernous segment of the right internal carotid artery and the primitive trigeminal artery (PTA) is presented. The posterior circulation was not dependent on PTA, thus the PTA was of an adult type in this case. This patient was successfully treated by external carotid artery-anterior temporal artery long vein graft bypass, internal carotid artery ligation at neck, and PTA clipping through the right subtemporal approach. A follow-up angiography showed thrombotic occlusion of the aneurysm. In review of the literature, there are 27 cases reported of PTA aneurysm; among them only 11 cases, including ours, treated surgically. The surgical treatment plan for PTA aneurysm, according to the review of literature is discussed.

Carotid Artery Diseases↗
PubMed1994

Retinal ganglion cells express a cGMP-gated cation conductance activatable by nitric oxide donors.

We have identified a putative cGMP-gated cation conductance in rat retinal ganglion cells. Both in situ hybridization and polymerase chain reaction amplification detected transcripts in ganglion cells that were highly homologous to the cGMP-gated cation channel expressed in rod photoreceptors. Whole-cell patch-clamp recordings detected a current stimulated by cGMP due to activation of nonselective cation channels. This current had a reversal potential near 0 mV, showed some outward rectification, and could be blocked by Cd2+. The current could also be activated by a phosphodiesterase inhibitor and the nitric oxide donors sodium nitroprusside and S-nitrosocysteine. We propose that nitric oxide released from an identified subpopulation of amacrine cells may activate this channel to modulate ganglion cell activity.

1-Methyl-3-isobutylxanthine↗
PubMed1994

A cis-acting element, T alpha-1, in the upstream region of rod alpha-transducin gene that binds a developmentally regulated retina-specific nuclear factor.

The G protein transducin (T) is an integral component of the signal transduction pathway in photoreceptors. We have identified a cis-acting element, T alpha-1, in the upstream region of the mouse rod alpha-T (Tr alpha) gene that may be important for tissue-specific expression. T alpha-1 binds a retina-specific nuclear factor of apparent molecular mass of 90 kDa. Binding to the T alpha-1 site is developmentally regulated and peaks between postnatal days 6 and 9. This corresponds to the time of rod photoreceptor maturation and the rise in Tr alpha gene expression. The sequence of T alpha-1 shows homology with RET-1, a cis-acting element in the proximal promoter of opsin gene that binds a distinct retina-specific factor. T alpha-1 and RET-1 sequences may have been derived from a prototype T alpha-1/RET-1 sequence, evolved to confer photoreceptor specificity on retina-specific genes.

Animals↗
PubMed1994

Effect of elimination of phagocytic cells by liposomal dichloromethylene diphosphonate on aspergillosis virulence and toxicity of liposomal amphotericin B in mice.

The role of macrophages in the toxicity and efficacy of liposomal amphotericin B (L-Amp B) was studied in a murine aspergillosis model infection. Macrophages and polymorphonuclear phagocytes (PMN cells) were depleted in the liver and spleen of mice by the administration of liposome encapsulated dichloromethylene diphosphonate. Macrophage depletion had no effect on the lethality of Fungizone, a commercial deoxycholate preparation of Amp B, but significantly increased the lethality of L-Amp B (P < 0.01). Macrophage depletion led to an increase in the fungal loads in the lung, liver and kidney (P < 0.05) and to an increase in the virulence of aspergillosis (P < 0.05). Tissue distribution analysis of L-Amp B revealed that in macrophage/PMN-depleted mice there was a decrease in the concentration of Amp B in the liver, with concomitant increases in the circulation, spleen and lung, both in the uninfected and in the infected conditions. The results clearly demonstrate that depletion of macrophage/PMN cells increases the virulence of aspergillosis, as well as the toxicity of L-Amp B. Moreover, L-Amp B treatment does not improve the survival rate of macrophage/PMN-depleted mice subjected to aspergillosis challenge.

Amphotericin B↗
PubMed1994

Isolation and characterization of saponins from Castanospermum australe Cunn. et Fraser.

Three new triterpenoid saponins, their methyl esters designated as castaralesides F (1), G (2) and H (3), were isolated from the fresh leaves of Castanospermum australe. The structures of these three saponins were elucidated on the basis of chemical and spectral data as 3 beta-O-[beta-galactopyranosyl-(1-->4)-beta-glucuronopyranosyl]-2 beta,23-dihydroxyolean-12-en-28-oic acid; 3 beta-O-[alpha-rhamnopyranosyl-(1-->4)-beta-galactopyranosyl-(1-->2)-beta - glucurono-pyranosyl]-2 beta,28-dihydroxyolean-12-ene; and 3 beta-O-[alpha-rhamnopyranosyl-(1-->4)-beta-xylopyranosyl-(1-->2)-beta- glucuronopyranosyl]-2 beta,28-dihydroxyolean-12-ene.

Carbohydrate Sequence↗