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Biomedical subjects

M Ahmad

Publications and source records attributed to M Ahmad.

At least 19 recordsLinked to original sources
PubMed1992

Enzymatic semisynthesis of a superpotent analog of human growth hormone-releasing factor.

A superpotent analog of human growth hormone-releasing factor, [desNH2Tyr1,D-Ala2,Ala15]-GRF(1-29)-NH2 (4), was prepared from the precursor, [Ala15,29]-GRF(4-29)-OH (1), by a two-step enzymatic semisynthesis. The amidated C-terminus, essential for high biological potency, was obtained via a carboxypeptidase Y-catalyzed exchange of Ala29-OH for Arg29-NH2 to produce [Ala15]-GRF(4-29)-NH2 (2). The N-terminal desNH2Tyr-D-Ala moiety, which greatly increases in vivo duration of action, was then incorporated by V8 protease-catalyzed condensation of segment 2 with desNH2Tyr-D-Ala-Asp(OH)-OR [R = CH3CH2- (3a) or 4-NO2C6H4CH2-(3b)]. The main focus of this report was to develop conditions to use the V8 protease-catalyzed coupling while avoiding a competing cleavage of the proteolytically-sensitive Asp25-Ile26 bond in GRF. Conversion of 2 to 4 in couplings employing the alpha-ethyl ester of the acyl component 3a was limited to about 60% by competing proteolysis at Asp25-Ile26. This system was adequate for preparing, isolating, and fully characterizing the target analog 4 and identifying the side products. The 4-nitrobenzyl ester 3b proved to be a superior substrate, resulting in 90% conversion of 2 to 4 with no detectable loss to proteolysis and requiring significantly lesser amounts of catalyst. These results demonstrate that enzymatic semisynthesis of a biologically-active peptide amide which contains unnatural amino acids at the N-terminus can be achieved from a biosynthetic precursor in good yield and purity.

Amino Acid Sequence↗
PubMed1992

Kinetics of dipeptidyl peptidase IV proteolysis of growth hormone-releasing factor and analogs.

The kinetics and selectivity of proteolysis of synthetic human growth hormone-releasing factor and analogs by purified human placental dipeptidyl peptidase IV (DPP IV) were studied by HPLC. The initial rates of Ala2-Asp3 cleavage (pH 7.8, 37 degrees C, So = 0.15 mM) were all approx. 5 mumol min-1 mg-1 for the parent hormone, GRF(1-44)-NH2, and the fragments, GRF(1-29)-NH2 and GRF(1-20)-NH2. Lower activities observed for GRF(1-11)-OH, GRF(1-3)-OH, and cyclic lactam analogs indicate S1'-Sn' binding. Assays of [Trp6]-GRF(1-29)-NH2 versus [D-Trp6]-GFR(1-29)-NH2 indicate an S4' binding cavity. Peptides with D-configuration at P2, P1 or P1' and desNH2Tyr1 and N-MeTyr1 analogs of GRF were not cleaved. Catalytic parameters for the P1-substituted analogs [X2,Ala15]-GRF(1-29)-NH2 were found to vary with X as follows, Km: Abu less than Ala less than Pro less than Val less than Ser less than Gly much less than Leu; kcat: Pro greater than Ala greater than Abu greater than Ser greater than Gly much greater than Leu greater than Val; kcat/Km: Abu greater than Pro greater than Ala much greater than Ser greater than Gly = Val much greater than Leu. Km is at a minimum and kcat/Km at a maximum, for a hydrophobic P1 side-chain of about 0.25 nm in length, i.e., the ethyl side-chain of alpha-aminobutyric acid (Abu) is very close to optimal. These results further define the S1 selectivity of DPP IV and may be useful in the design of DPP IV resistant GRF analogs that can be produced by recombinant DNA methods and the design of DPP IV inhibitors.

Amino Acid Sequence↗
PubMed1992

Effect of dehydration on the disposition kinetics of erythromycin in rabbits.

The effect of water deprivation on the physiologic, biochemical, and disposition parameters of erythromycin was investigated in rabbits. The packed cell volume, plasma glucose, and total lipid concentration increased significantly in dehydration. The pharmacokinetic parameters of erythromycin after intravenous administration also changed, suggesting a need for monitoring toxicity of erythromycin in the water-deprived population.

Animals↗
PubMed1992

Cancer-related urinary proteinase inhibitor, EDC1: a new method for its isolation and evidence for multiple forms.

During the past several years, numerous laboratories have reported isolation and purification of proteinase inhibitors from human urine. Many of these molecules were incompletely characterized and some of them may have been artifacts in part because of harsh procedures used for their isolation. Consequently, there is disagreement and confusion regarding the biochemical characteristics of these inhibitors. We previously reported the isolation of a proteinase inhibitor, EDC1, from the urine of a leukemic patient. This molecule, M(r) 30 kDa, was antigenically related to plasma inter-alpha-trypsin inhibitor (IATI) and inhibited the growth of a virally transformed B cell line. Immunoreactive EDC1 was also the major component of low molecular weight proteinuria observed in cancer patients. We now report a new method for the isolation of EDC1 from urine of patients with adenocarcinomas of colon and lung and melanoma and compare its partial amino acid sequence with that of HI 30, a proteinase inhibitor previously isolated from pooled normal urine by Hochstrasser et al. [Hoppe-Seyler's Z Physiol Chem 357:153-162, 1976]. Our method involves i) a batchwise cation exchange, ii) gel filtration chromatography, iii) anion exchange chromatography on FPLC, and iv) reverse phase C18 chromatography on HPLC. This method is mild and results in an overall yield of 0.4 to 1.2 mg of EDC1/liter urine. On the basis of the partial N-terminal amino acid sequence of its N terminal (38 residues) and middle regions (29 residues), EDC1 appears to be identical with HI30. Surprisingly, during this isolation procedure, another proteinase inhibitor, M(r) 22 kDa, which cross-reacted with antisera to EDC1 and IATI, was also isolated. The 22 kDa molecule was a major component of the IATI related urinary molecules and was identical with the 30 kDa EDC1 in which first the 15 N terminal residues were clipped. The lower M(r) inhibitor was not an artifact formed during storage or isolation procedure because the Western blot analysis of fresh cancer and normal urine revealed the 30 and 22 kDa molecules. Thus, both the 30 kDa EDC1 (or HI30) and its clipped variant, the 22 kDa molecule, are physiologic components of IATI related urinary proteinase inhibitors and excretion of both forms may be increased in patients with advanced cancer.

Adenocarcinoma↗
PubMed1992

Mutagenic activity of oxathiolane steroids: structural requirement for the genotoxic activity in Salmonella and E. coli.

Oxathiolanes and disulfonyl derivatives of steroids were tested for mutagenic activity in the Ames tester strains. The test compounds exhibited mutagenic activity without metabolic activation although metabolic activation markedly enhanced their activity. A significant decrease in the survival of the radiation-sensitive mutants recA, lexA and rer of E. coli was observed as compared to their wild-type counterpart in the presence of the test steroid. Structural features which appear to be crucial for the mutagenic activity in these steroidal drugs are: (i) an electron-donating group at position 3, and (ii) a bulky group anchored at the 5th and 6th positions. The test steroids appear to damage DNA which in turn initiates the SOS repair with the concomitant induction of mutation.

Biotransformation↗
PubMed1992

Pilomatricoma: a retrospective study.

A study of 53 Pakistani patients with pilomatricoma diagnosed at AFIP during 1985-1989 is presented. It constituted 37.2% of all benign adnexal tumors, during the same period. 56.2% of patients were more than 30 years of age. Differences in site, sex, and age distribution from Western reports were observed. Unusual clinical presentations were also noted. This study outlines the clinicopathologic features of pilomatricoma in Pakistan.

Adolescent↗
PubMed1992

Observations of acoustic streaming fields around an oscillating ultrasonic file.

The steady acoustic streaming generated around straight and precurved oscillating ultrasonic files driven by the Piezon-Master 400 unit was examined in the free field and in small channels using a stereomicroscope. In addition, the effect of file-wall contact on streaming production was also investigated. The results indicated that the ultrasonic files can generate acoustic streaming both in the free field and in the small channel. Higher velocity streaming was observed when smaller size files were employed and when the file was precurved. Light file-wall contact did not totally inhibit streaming while severe file-wall contact inhibited movement of the file and, as a result, no streaming was observed. The positions and length scales of the streaming vortices appeared to be influenced by the presence of boundaries. In the free field, two rows of vortices were situated along the sides of the file while in the small channel, the vortices were positioned above the surface of the file. These results indicated that it is possible for acoustic streaming to occur in a confined space as in a root canal provided that severe file-wall contact is avoided. It is therefore recommended that light filing or allowing the file to freely vibrate during some stage of treatment should be carried out in order to generate streaming in the root canal.

Humans↗
PubMed1992

Significance of perioperative blood transfusions in patients undergoing resection of stage I and II non-small-cell lung cancers.

Perioperative blood transfusions (BT) have been reported to reduce survival in patients undergoing curative resection of lung cancers. It is postulated that a state of BT-mediated immunosuppression favors the proliferation of tumor cells not resected during surgery. To evaluate this hypothesis and to determine factors influencing the administration of BT, we retrospectively studied the charts of 127 patients who underwent surgery for stage I and II non-small-cell carcinoma. Thirty (23.6 percent) patients received BT and 97 (76.4 percent) did not. Sex, age, race, smoking history, size and stage of the tumor, histology, extent of resection and preoperative hemoglobin values were analyzed. Only age (p = 0.01) and preoperative hemoglobin values (p less than 0.01) were related to transfusion status. Neither survival nor event-free survival differed significantly between the two groups (p = 0.29 and 0.26 respectively). Our results do not support the hypothesis that perioperative BTs have a significant detrimental effect on survival. A prospective study could clarify this controversial issue; however, such a study would be complex considering the multiple variables that affect survival in patients with non-small-cell lung cancers.

Age Factors↗
PubMed1992

Biopharmaceutical studies of spirobishexahydropyrimidine.

Oral administration of spirobishexahydropyrimidine showed an increase in the activity of serum transaminases, lactate dehydrogenase and alkaline phosphatase. Biological half life and other pharmacokinetic parameters showed rapid absorption and slow elimination of the drug.

Alanine Transaminase↗
PubMed1992

Anorectal melanoma in northern Pakistan.

Melanoma of the anorectum is a rare malignancy. At Armed Forces Institute of Pathology (AFIP), 11 cases were diagnosed over a 10 year period (1981-1990) constituting 14.2% of all primary malignant melanomas. The anorectum was the commonest site for noncutaneous melanomas (45.8%). The age group commonly affected was the fifth to seventh decade (72.7%). Most of the tumours were extensive involving both anal canal and rectum. The proportion of anorectal melanoma is much higher in our study as compared to western reports (0.4-1.6%). The distribution of noncutaneous melanomas in our population also differs, with a relatively lower proportion of ocular melanomas (33.3%) which are the commonest (80%) in western studies (JPMA 42: 155, 1992).

Adult↗
PubMed1992

Non-Hodgkin's lymphoma--clinicopathological pattern.

A study of histopathological and clinical features of non-Hodgkin's lymphoma in 495 consecutive cases, diagnosed at AFIP during 1984-1989 is presented. Children below the age of 15 years were not included in this study. The relative frequency of non-Hodgkin's lymphoma was 4.29% in our material. Non-Hodgkin's lymphoma was more frequent than Hodgkin's disease, ratio being 2.44:1. Lymphadenopathy (78.78%), fever (33.08%), weight loss (31.62%) and anemia (30.14%) were the main presenting features. New working formulation was used for morphological characterisation. Follicular lymphoma constituted 8.08% of all cases. Follicular lymphoma was seen only in older age whereas diffuse lymphoma occurred in all age groups. Intermediate and high grade lymphoma represented 73.54% of all NHL. Small lymphocytic lymphoma was common in low grade tumours (13.13%). Extra nodal lymphoma was encountered in a significant proportion (21.22%), gastrointestinal tract being the most frequent site. This study outlines certain interesting features of NHL in Pakistan.

Adolescent↗
PubMed1991

Vascular smooth muscle expresses a truncated Na+, K(+)-ATPase alpha-1 subunit isoform.

By regulating transmembrane Na+ and K+ concentrations and membrane potential, the Na+,K(+)-ATPase plays an important role in regulating cardiac, skeletal, and smooth muscle function. A high degree of amino acid sequence and structural identity characterizes the three Mr 100,000 Na+,K(+)-ATPase alpha subunit isoforms expressed in cardiac and skeletal muscle. Strikingly, vascular smooth muscle utilizes alternative RNA processing of the alpha-1 gene to express a structurally distinct Mr approximately 65,000 isoform, alpha 1-T (truncated). Analysis of both its mRNA and protein structure reveals that alpha-1-T represents a major, evolutionarily conserved, truncated Na+,K(+)-ATPase isoform expressed in vascular smooth muscle. This demonstrates an unexpected complexity in the regulation of vascular smooth muscle Na+,K(+)-ATPase gene expression and suggests that a structurally novel, truncated alpha subunit may play a role in vascular smooth muscle active ion transport.

Amino Acid Sequence↗
PubMed1991

Amino acid sequence analysis of proteins in the human corneal stromal cell membrane.

Plasma membrane proteins from human corneal stromal fibroblasts were isolated and separated by two-dimensional polyacrylamide gel electrophoresis. Separated polypeptides were electroeluted onto polyvinylidene difluoride (PVDF) membranes and individual polypeptides were subjected to NH2-terminal amino acid sequence analysis. Of a total of 33 polypeptides sequenced, 26 were found to be blocked at their NH2-terminus. Seven major membrane polypeptides were sequenced and further analyzed. One polypeptide, designated #18, was determined to be homologous to the beta subunit of prolyl hydroxylase/protein disulfide isomerase/thyroid hormone-binding protein. The other six polypeptides were found to have no significant sequence homology with any known polypeptides, as revealed by a protein data base homology search. Polypeptide Bands #90, #102, and #103 were found to have the same NH2-terminal amino acid sequence and the same overall molecular weight, yet separated from one another according to pI. These three polypeptides probably arose from differential posttranslational modification of the same original protein. Synthetic peptides were prepared from the #18 and #19 sequence and antibodies were produced. Immunostaining of cultured human corneal stromal cells and frozen sections of corneas demonstrated that these membrane polypeptides were present in corneal keratocytes, both in vitro and in vivo. Antibody against #18 stained fixed cultured corneal fibroblasts in a very fibrous pattern, with more intense staining in the perinuclear region of the cell, while antibody against #19 stained the cell surface in a much more uniform pattern. In sections of human cornea, both antibodies stained only the keratocytes in the stroma, but they also appeared to stain epithelial cells.

Amino Acid Sequence↗
PubMed1991

Localization of technetium-99m-glucarate in zones of acute cerebral injury.

The potential structural similarity of technetium-99m-labeled glucaric acid (99mTc-glucarate) to that of fructose suggests that this agent may enter cells by a sugar transport system. Studies with LLC-PK1 cells demonstrated inhibition of 99mTc-glucarate uptake by fructose, confirming this potential relationship. Since anaerobic metabolism can use either glucose or fructose, we hypothesized that 99mTc-glucarate may concentrate in areas of acute ischemic injury. To test this hypothesis, 63 adult rats with middle cerebral artery (MCA) occlusion followed by reperfusion were injected with 99mTc-glucarate and in vivo and ex vivo images were acquired. Seven animals were also studied with 18FDG and high resolution PET imaging. The radionuclide images were compared to the results of triphenyl tetrazolium chloride (TTC) staining and conventional histopathology. Thirty-five rats had significant accumulation of 99mTc-glucarate and no TTC staining (indicating infarction) in the involved hemisphere. Of the remaining 28 rats with TTC staining (suggesting viability) of the involved hemisphere, 16 (57%) had 99mTc-glucarate accumulation. In the seven rats that were studied with both 99mTc-glucarate and 18FDG, 99mTc-glucarate accumulated at the center of the occluded MCA territory while 18FDG activity was decreased in this region. These results suggest that 99mTc-glucarate is a sensitive marker of acute severe cerebral injury, but its mechanism of localization is probably different from that of 18FDG.

Animals↗
PubMed1979

An ultrafiltration technique for labeling red blood cells with Tc-99m.

This method automates the preparation of autologous Tc-99m labeled red blood cells utilizing the Amicon on-line column eluate concentrator to separate the plasma from the red blood cells. The red blood cells were pre-tinned with stannous diphosphonate and continuously recirculated over a 0.6 mu filter until all of the plasma was removed and the red blood cells remained suspended in a solution of 0.9% sodium chloride. Once the plasma has been removed the red blood cells are incubated with Tc-99m pertechnetate. The above Tc-99m red blood cells were compared to Tc-99m red blood cells produced in a similar manner except that centrifugation was used to separate the red blood cells from the plasma. Both preparations had a tagging efficiency of 98% or greater and rat distribution studies demonstrate that both preparations are equally stable as an in vivo intravascular agent.

Animals↗