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Biomedical subjects

A A Khan

Publications and source records attributed to A A Khan.

At least 19 recordsLinked to original sources
PubMed1992

IP3 receptor: localization to plasma membrane of T cells and cocapping with the T cell receptor.

Immune responses in lymphocytes require cellular accumulation of large amounts of calcium (Ca2+) from extracellular sources. In the T cell tumor line Jurkat, receptors for the Ca(2+)-releasing messenger inositol 1,4,5-trisphosphate (IP3) were localized to the plasma membrane (PM). Capping of the T cell receptor-CD3 complex, which is associated with signal transduction, was accompanied by capping of IP3 receptors. The IP3 receptor on T cells appears to be responsible for the entry of Ca2+ that initiates proliferative responses.

Antigens, CD↗
PubMed1992

Plasma membrane inositol 1,4,5-trisphosphate receptor of lymphocytes: selective enrichment in sialic acid and unique binding specificity.

The inositol 1,4,5-trisphosphate receptor (IP3R) associated with plasma membranes of lymphocytes differs in terminal sugar content and binding specificity from the cerebellar receptor, which is localized to endoplasmic reticulum. Lectin column chromatography reveals that 30% of IP3R in the thymus contains sialic acid, reflecting a plasma membrane association, in contrast to 5% of cerebellar IP3R. IP3R in thymus and plasma membrane fractions of Jurkat lymphocytes differs from IP3R of Jurkat microsomes and cerebellum in inositol phosphate specificity. The plasma membrane IP3R has lower affinity for IP3 but higher affinity for inositol 1,3,4,5-tetrakisphosphate, which may reflect a unique regulation of calcium at the plasma membrane by inositol phosphates.

Animals↗
PubMed1992

Use of a genetically engineered Escherichia coli strain to produce 1,2-dihydroxy-4'-chlorobiphenyl.

Genetically engineered kanamycin-resistant Escherichia coli HB101 containing the mutant chimeric plasmid pAW6194-T17 specifying biphenyl dioxygenase and dihydrodiol dehydrogenase and lacking the ability to produce active 3-phenylcatechol dioxygenase was used to produce 1,2-dihydroxy-4'-chlorobiphenyl (DHCB) from 4-chlorobiphenyl. Resting-cell suspensions of genetically engineered E. coli in mineral salts medium (pH 7.0) containing 880 microM 4-chlorobiphenyl produced 110 microM DHCB. The Km for 4-chlorobiphenyl was 3.3 mM. Biotransformation of DHCB from 4-chlorobiphenyl was maximum when cells (2.5 mg of protein per ml) were incubated with shaking (150 rpm) at pH 7.0 and 30 degrees C for 6 h. The enzymatically produced DHCB was a suitable substrate for assaying 3-phenylcatechol dioxygenase activity. Biologically produced DHCB showed UV and mass spectra similar to those of chemically synthesized DHCB. The bioconversion rate of ortho-substituted chlorobiphenyl was slower than that of the para- or meta-substituted chlorobiphenyl.

Biotransformation↗
PubMed1992

The effects of bradykinin and sequence-related analogs on the response properties of cutaneous nociceptors in monkeys.

The endogenous peptide bradykinin is found in plasma and inflammatory exudates and has been implicated as a chemical mediator of inflammatory pain and hyperalgesia. Two subtypes of bradykinin receptors, B1 and B2, have been described, and antagonists for the receptor subtypes have been synthesized. The bradykinin analogs [desArg9,Leu8]BK and DArg[Hyp3,DPhe7]BK have been reported to have antagonist activity at the B1 and B2 bradykinin receptors in smooth muscle, respectively. Behavioral studies in rats indicate that the bradykinin analogs can block the algesic effects of bradykinin. We wished to determine the effects of bradykinin and the bradykinin analogs (B1 and B2 analogs, respectively) on cutaneous nociceptors in the monkey. In addition, we wished to determine the type of bradykinin receptor that mediates the sensitizing effects of bradykinin. Recordings were made from single C-fiber and A-fiber nociceptive afferents (CMHs and AMHs) that innervated hairy skin. Heat sensitivity before and after the injections was determined with a heat test sequence consisting of stimuli that ranged, in 1 degree C increments, from 41 degrees to 49 degrees C. Intradermal injections of vehicle (neutral normal saline) failed to alter the heat response of CMHs. Bradykinin (10 nmol in 10 microliters) evoked activity in 6 of 10 CMHs and sensitized all the fibers to heat stimuli. After the bradykinin injection, the mean heat threshold of the CMHs decreased from 44 +/- 0.5 degrees to 42.7 +/- 0.5 degrees C (mean +/- SEM, p less than 0.02), and the total response to the heat test sequence increased by 87% (p less than 0.002). In a related psychophysical study in human volunteers, the same dose of bradykinin resulted in a comparable (115%) increase in ratings of pain (Manning et al., 1991). Bradykinin also evoked activity in 10 of 17 AMHs and sensitized 8 AMHs to heat stimuli. Bradykinin failed to alter the threshold for activation of CMHs to mechanical stimuli as measured by application of von Frey hairs to the receptive field. In contrast to bradykinin, intradermal injection of the B1 and B2 analogs (10 nmol in 10 microliters) evoked activity in 2 of 6 and 0 of 5 CMHs, respectively. A noteworthy finding was that both analogs enhanced the response of CMHs to heat stimuli by 50% (B1 analog, 1.5 +/- 0.1; B2 analog, 1.5 +/- 0.2). The B1 (n = 10) and B2 (n = 5) analogs did not evoke activity in any of the 15 AMHs tested.(ABSTRACT TRUNCATED AT 400 WORDS)

Afferent Pathways↗
PubMed1991

Human immunodeficiency virus-associated Hodgkin's disease. Clinicopathologic studies of 24 cases and preponderance of mixed cellularity type characterized by the occurrence of fibrohistiocytoid stromal cells.

Hodgkin's disease (HD) was diagnosed in 24 patients who were either seropositive for human immunodeficiency virus (HIV) (21) or members of a high-risk group (three), but had not developed acquired immune deficiency syndrome (AIDS). Clinical presentation of the disease was characterized by constitutional symptoms in all, especially fever (23/24) and disseminated disease (22/24) at diagnosis. Mediastinal adenopathy was rare. Bone marrow involvement was particularly frequent (12/24), and a positive bone marrow biopsy preceded lymph node biopsy in 5 of the 12. Histopathologic features of these tumors included an increased number of nonlymphoid stromal cells, i.e., histiocytic and/or fibroblastoid. In some tumors these fibrohistiocytoid stromal cells were arranged in bundles, but distinct nodule with birefringent collagen band formation was not observed. Twenty-two patients were treated, most with combination chemotherapy; one was untreated; one, unknown. Sixteen, including the one untreated, died with disease at 3 to 25 months; one died of an unrelated cause; four were alive at 3 to 24 months; three were lost to follow-up. Frequent bone marrow involvement at presentation suggests the usefulness of the bone marrow biopsy for diagnosis in subjects at risk, especially when they present with spiking fever of unknown origin. Contrary to most previous series, virtually all of our cases were of mixed cellularity type, characterized by increased fibrohistiocytoid stromal cells in place of depleting lymphocytes. The classic nodular sclerosing feature with birefringent collagen band formation was not observed. In conclusion, HIV-associated HD was characterized by advanced stage with fever at presentation, preponderance of mixed cellularity histologic type with increased fibrohistiocytoid stromal cells, and poor outcome. Hodgkin's disease in AIDS patients presents an intriguing biological model to study the role of stromal histiocytes in immunodeficient patients.

Adult↗
PubMed1991

Sex steroids enhance endotoxin-stimulated phospholipase A2 activity in hum endometrial cells.

Growing evidence suggests an association between intra-amniotic infection and preterm labor. We recently demonstrated that some factor(s) including endotoxin produced by the organism stimulated endogenous phospholipase A2 resulting in liberation of arachidonic acid and prostaglandin formation (Takahashi et al. 1988). The studies presented in this report were designed to evaluate whether ovarian steroids alter activity of the phospholipase A2 responsive to endotoxin. Exposure of human endometrial proliferative- or secretory-phases epithelium to endotoxin from Escherichia coli increased the level of lysophosphatidylcholine (lyso-PC) by 15- and 25-fold, respectively. When the endometrial cells were preincubated with progesterone alone or progesterone and estradiol-17 beta for 16 h, the increase of lyso-PC by endotoxin was enhanced by approximately 1.5-fold. Progesterone showed a stimulatory effect on the response of phospholipase A2 to bacterial endotoxin in endometrial cells. These observations may explain the mechanism(s) by which preterm or term labor associated with intra-amniotic infection is initiated.

Amniotic Fluid↗
PubMed1991

Cytotoxic effects of hydrogen sulfide on pulmonary alveolar macrophages in rats.

Respiratory rates (basal and zymosan-stimulated) and cell viability were monitored in pulmonary alveolar macrophages (PAM) from rats exposed to 0, 70, 280, and 560 mg/m3 (0, 50, 200, and 400 ppm) hydrogen sulfide (H2S) gas for 4 h. Zymosan-stimulated respiratory rates were markedly reduced in PAM collected from rats exposed to 280 and 560 mg/m3 H2S; however, their basal respiratory rates were not affected. Significant decrease in cell viability was also observed in samples from 560 mg/m3 H2S-treated rats, but it remained high and unchanged in other treatments. In vitro incubation of PAM from control rats with sulfide (a precursor of H2S) and its two oxidation products, sulfite and sulfate, showed that sulfide was markedly more inhibitory to both respiratory rates than sulfite or sulfate. These treatments did not affect cell viability.

Administration, Inhalation↗
PubMed1991

Risk analysis of a gas-processing complex in India.

ONGC's Hazira Gas-Processing Complex (HGPC) consists of facilities for receiving natural gas along with associated condensate from an off-shore field at a rate of 20 MMN M3 per day. After separating the condensate, which is processed in condensate fractionation units, the gas is processed through various steps to recover LPG and to reduce its dew point to less than 5 degrees C in order to make it suitable for transportation over long distances. The acid gas recovered during the gas-sweetening step is processed to obtain sulphur. The major products manufactured at HGPC therefore are lean sweet gas, LPG, NGL, and sulphur. The Oil and Natural Gas Commission awarded the assignment on Hazard Study and Risk Analysis of their Hazira Gas-Processing Complex (HGPC) to the Council of Scientific and Industrial Research (CSIR) in association with the Netherlands Organisation for Applied Scientific Research (TNO). The scope of this assignment covered a number of closely related and fully defined activities normally encountered in this type of work. Identification of hazards through the most appropriate methods, assigning frequency of occurrence of major unwanted incidents, quantification and assessment of probable damage to plant equipment, environment, human and animal life due to an unexpected event, and evaluation of various methods for reducing risk, together constituted the methodology for this assignment. Detailed recommendations aimed at reducing risk and enhancing reliability of plant and machinery were made. This article gives an overview of the assignment.

Accidents, Occupational↗
PubMed1991

Expression, localization, and functional analysis of polychlorinated biphenyl degradation genes cbpABCD of Pseudomonas putida.

Genes of Pseudomonas putida strains that are capable of degrading polychlorinated biphenyls were cloned in the plasmid vector pUC19. The resultant hybrid plasmid, pAW6194, contained cbpABCD genes on a 9.0-kb DNA fragment that was necessary for the catabolism of polychlorinated biphenyls. These genes were further subcloned on an 8.0-kb HindIII fragment of pAW540. Degradation of 3-chlorobiphenyl, 2,4-dichlorobiphenyl, and 2,4,5-trichlorobiphenyl into a chloro derivative of benzoic acid was found in Escherichia coli harboring chimeric plasmid pAW540. Expression of cbpA (biphenyl dioxygenase, 6.2 U/mg of protein) and cbpC (3-phenylcatechol dioxygenase, 611.00 U/mg of protein) genes was also found in E. coli containing the hybrid plasmid pAW540. These enzyme activities were up to 10-fold higher than those found in P. putida OU83. These results led us to conclude that cbpABCD genes of P. putida OU83 were encoded on cloned DNA and expressed in E. coli. Whether the expression of cbpABCD genes of P. putida OU83 was driven by its own promoters located on the cloned DNA or by the lacZ promoter of pUC19 was examined by subcloning a 8.0-kb DNA fragment encoding the cbpABCD genes, in both orientations, in the HindIII site of the promoter probe vector pKK232-8. The resulting recombinant plasmids, pAW560 and pAW561, expressed cbpABCD genes and conferred chloramphenicol resistance only in E. coli harboring pAW560, indicating that the expression of chloramphenicol acetyltransferase is independent of cbpABCD gene expression.(ABSTRACT TRUNCATED AT 250 WORDS)

Biodegradation, Environmental↗
PubMed1991

Oral health manpower projection methods and their implications for developing countries: the case of Zimbabwe.

Manpower projections for oral health are generally held to be more accurate than those for other health sectors since the diseases involved and their treatment times can be predicted more precisely. Nevertheless most oral health manpower projections are either overestimates or are not in line with the resources of individual countries, especially in developing countries. Zimbabwe was taken as the study case, and oral health manpower projections were made using two of the most commonly employed methods and one new approach. The projections obtained using the three methods were all different, and even the lowest projection is beyond the resources of the country. It is recommended that in making oral health manpower projections, the facilities available to accommodate these personnel should also be taken into account.

Dental Hygienists↗
PubMed1990

Effects of hydrogen sulfide exposure on lung mitochondrial respiratory chain enzymes in rats.

Fischer-344 rats were exposed for 4 hr to various concentrations of hydrogen sulfide (H2S) gas and killed either immediately or at 1, 24, or 48 hr after exposure. Mitochondrial fractions from lung tissues were assayed for the activities of respiratory chain enzymes. Exposure of rats to a low concentration (10 ppm) of H2S caused no significant changes in the activities of lung mitochondrial enzymes. However, exposure to sublethal concentrations of H2S (50-400 ppm) produced marked and highly significant depressions in the activities of cytochrome c oxidase and succinate oxidase complexes of the respiratory chain. The inhibition of cytochrome c oxidase activity in lungs was most severe (greater than 90%) in rats that died from acute exposure to greater than 500 ppm H2S. In rats exposed to 200 and 400 ppm H2S, a marked recovery in cytochrome c oxidase activity of lungs was observed at 24 and 48 hr postexposure. Studies in vitro with rat lung mitochondria showed that low concentrations of sulfide also caused a similar and selective inhibition of cytochrome c oxidase activity. This effect was reversed upon removal of sulfide either by washing or by oxidation with methemoglobin. The nature of sulfide inhibition of cytochrome c oxidase was noncompetitive with respect to ferrocytochrome c. Because the activities of NADH-cytochrome c reductase and succinate-cytochrome c reductase were not significantly altered by H2S exposure and in vitro treatments with low concentrations of sulfide, it is concluded that under physiological conditions H2S would block the respiratory chain primarily by inhibiting cytochrome c oxidase. Such a biochemical impairment would lead to functional (histotoxic) hypoxia in the lung tissues.

Administration, Inhalation↗
PubMed1990

Apical hypertrophic cardiomyopathy in a non-Oriental man.

Japanese investigators first described apical HCM in 2.9% of patients who had diagnostic left ventricular catheterization for suspected ischemic heart disease or cardiomyopathy. This entity was initially thought to be limited to individuals of Asian origin and has been uncommonly described in patients of Western origin. Patients of Western origin differ in several ways from those in the original description of Yamaguchi et al, but they both share the same classic criterion of hypertrophy of the left ventricular apex. The major differences probably relate to the anatomic variation in the distribution of the left ventricular hypertrophy as described by Maron et al. It is not known whether racial, genetic, or environmental factors account for the variation of disease expression in Asian and Western patients. Our case illustrates that this diagnosis should be considered in patients who have chest pain (anginal or atypical) and markedly abnormal findings on electrocardiograms in the absence of hypertension or significant coronary artery disease.

Aged↗