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Biomedical subjects

M A Khan

Publications and source records attributed to M A Khan.

At least 91 records · Page 5Linked to original sources
PubMed2001

Novel aluminum hydride derivatives from the reaction of H(3)Al.NMe(3) with the cyclosilazanes.

The amine hydrogen atoms of the cyclic trimeric silazane [Me(2)SiNH](3) are readily replaced by the H(2)Al. NMe(3) group in a simple aminolyis reaction of [Me(2)SiNH](3) with H(3)Al.NMe(3) to afford the aluminum amides (Me(2)SiNAlH(2).NMe(3))(n)(Me(2)SiNH)(3-n) (1, n = 3; 2, n = 1; 4, n = 2). The monosubstituted amide 2 could not be isolated, because it undergoes condensation to the tricyclic compound 1,1',2,2'-(HAlNMe(3))(2) (3). Contrary to these results the analogous reactions of the more flexible cyclic tetrameric silazane [Me(2)SiNH](4) with H(3)Al.NMe(3) did not give simple aluminum amides, but complicated mixtures were obtained from which the interesting polycyclic species Al(5)C(22)H(73)N(10)Si(8).C(6)H(6) (5) and Al(6)C(22)H(76)N(10)Si(8).1/4 C(6)H(14) (6) could be isolated in low yields. A key step in the formation of 5 and 6 is a low-temperature dehydrosilylation reaction which leads to cleavage of the silazane ring. Compounds 1, 3, and 4 were characterized spectroscopically ((1)H, (13)C, (27)Al NMR and FTIR) and by single crystal X-ray diffraction, whereas 5 and 6 were characterized by X-ray diffraction only. Thermolysis experiments involving 1 and 3 indicate that the onset of Al-N bond formation via dehydrosilylation is accompanied by loss of trimethylamine and formation of larger aggregates, which are stable to further silane elimination to at least 620 degrees C.

Journal Article↗
PubMed2001

Effectiveness of the direct observation component of DOTS for tuberculosis: a randomised controlled trial in Pakistan.

BACKGROUND: DOTS is the control strategy for tuberculosis promoted by WHO. Pakistan is currently developing its National Tuberculosis Programme, and requires guidance on types of direct observation of treatment appropriate for the local conditions. We did a randomised trial to assess the effectiveness of different packages for tuberculosis treatment under operational conditions in Pakistan. METHODS: We enrolled 497 adults with new sputum-positive tuberculosis. 170 were assigned DOTS with direct observation of treatment by health workers; 165 were assigned DOTS with direct observation of treatment by family members; and 162 were assigned self-administered treatment. The trial was done at three sites that provide tuberculosis services strengthened according to WHO guidelines for the purposes of the research, with a standard daily short-course drugs regimen (2 months of isoniazid, rifampicin, pyrazinamide, and ethambutol, followed by 6 months of isoniazid and ethambutol). The main outcome measures were cure, and cure or treatment completion. Analysis was by intention to treat. FINDINGS: Within the strengthened tuberculosis services, the health-worker DOTS, family-member DOTS, and self-administered treatment strategies gave very similar outcomes, with cure rates of 64%, 55%, and 62%, respectively, and cure or treatment-completed rates of 67%, 62%, and 65%, respectively. INTERPRETATION: None of the three strategies tested was shown to be superior to the others, and direct observation of treatment did not give any additional improvement in cure rates. The effectiveness of direct observation of treatment remains unclear, and further operational research is needed.

Adolescent↗
PubMed2001

Self-emulsifying drug delivery systems (SEDDS) of coenzyme Q10: formulation development and bioavailability assessment.

The goals of our investigations are to develop and characterize self-emulsifying drug delivery systems (SEDDS) of coenzyme Q10 (CoQ10), using polyglycolyzed glycerides (PGG) as emulsifiers and to evaluate their bioavailability in dogs. Solubility of CoQ10 was determined in various oils and surfactants. SEDDS consisted of oil, a surfactant and a cosurfactant. Four types of self-emulsifying formulations were prepared using two oils (Myvacet 9-45 and Captex-200), two emulsifiers (Labrafac CM-10 and Labrasol) and a cosurfactant (lauroglycol). In all the formulations, the level of CoQ10 was fixed at 5.66% w/w of the vehicle. The in vitro self-emulsification properties and droplet size analysis of these formulations upon their addition to water under mild agitation conditions were studied. Pseudo-ternary phase diagrams were constructed identifying the efficient self-emulsification region. From these studies, an optimized formulation was selected and its bioavailability was compared with a powder formulation in dogs. Medium chain oils and Myvacet 9-45 provided higher solubility than long chain oils. Efficient and better self-emulsification processes were observed for the systems containing Labrafac CM-10 than formulations containing Labrasol. Addition of a cosurfactant improved the spontaneity of self-emulsification. From these studies, an optimized formulation consisting of Myvacet 9-45 (40%), Labrasol (50%) and lauroglycol (10%) was selected for its bioavailability assessment. A two-fold increase in the bioavailability was observed for the self-emulsifying system compared to a powder formulation. SEDDS have improved the bioavailability of CoQ10 significantly. The data suggest the potential use of SEDDS to provide an efficient way of improving oral absorption of lipophilic drugs.

Animals↗
PubMed2001

Synthesis, characterization, solid-state molecular structures, and deprotonation reactions of cationic alcohol complexes of osmium nitrosyl porphyrins.

New alkoxide (OEP)Os(NO)(OR) (OEP = 2,3,7,8,12,13,17,18-octaethylporphyrinato dianion; R = ethyl, isopropyl, hexyl, cyclohexyl) compounds and alcohol [(OEP)Os(NO)(HOR)]+ complexes (R = methyl, ethyl, isopropyl, hexyl, cyclohexyl) have been prepared in high yields and have been fully characterized by IR, 1H NMR, and UV-vis spectroscopy, and by elemental analyses. The (OEP)Os(NO)(OEt) compound was characterized by single-crystal X-ray crystallography. The cationic aqua and alcohol [(OEP)Os(NO)(HOR)]+ complexes (R = ethyl, isopropyl, hexyl) complexes were also characterized by single-crystal X-ray crystallography, and the latter represent the first osmium alcohol structures to be reported. The electrophilic [(OEP)Os(NO)]+ cation in the [(OEP)Os(NO)(HOR)]+ complexes renders the coordinated alcohol ligands susceptible to deprotonation by pyridine to produce the corresponding alkoxide (OEP)Os(NO)(OR) derivatives. A one-pot reaction sequence for the preparation of new (OEP)Os(NO)(OR) complexes from (OEP)Os(NO)(OEt) was developed, which was based on (i) initial protonation of the ethoxide compound to give [(OEP)Os(NO)(HOEt)]+, (ii) alcohol substitution by ROH to give [(OEP)Os(NO)(HOR)]+, and (iii) deprotonation of the latter by pyridine to give (OEP)Os(NO)(OR).

Alcohols↗
PubMed2001

Effect of abciximab on cardiac enzyme elevation after transluminal extraction atherectomy (TEC) in high-risk saphenous vein graft lesions: comparison with a historical control group.

Saphenous vein graft (SVG) intervention has been associated with an increased incidence of distal embolization. Long lesions and lesions associated with thrombus are particularly at increased risk. This study was performed to determine whether abciximab may decrease this risk in high risk SVG angioplasty. From June 1994 to June 1998, 84 patients with at least one high risk factor, i.e., lesion length >20 mm or angiographic evidence of thrombus, underwent Transluminal extraction atherectomy (TEC) procedure followed by balloon dilatation or stenting. Of these 84 patients, 37 who had procedure after September 1995 underwent TEC with abciximab (Abciximab Group) and 47 who had their procedure before that date had TEC without abciximab thereby serving as historic control (Non-Abciximab Group). All patients had normal pre-procedure CK and CK-MB. Total creatine kinase (CK) and CK-MB were measured every 8 hr post-procedure for 24 hr. Baseline demographics, angiographic characteristics, incidence of LV dysfunction and triple vessel disease were similar between the two groups. Graft age was similar between two groups (122 +/- 70 vs. 117 +/- 54 months). Graft diameter, pre and post-procedure percent stenoses were not different between the two groups. Stents were used in 65% in the Abciximab group and 45% in Non-Abciximab group (P = 0. 14). There was no in-hospital repeat PTCA, urgent bypass surgery, or cardiac death. There was no difference between the two groups in regards to the incidence of any elevation of total CK (27% vs. 21. 3%) or CK-MB (54% vs. 51%). When used in conjunction with TEC in treating high risk vein graft lesions, abciximab did not reduce post procedure CK-MB elevation in this patient population.

Abciximab↗
PubMed2001

Substituent-dependent, positive and negative modulation of Bombyx mori adenylate cyclase by synthetic octopamine/tyramine analogues.

Octopamine (OCT)/tyramine (TYR) analogues, mainly including p- and beta-substituted phenylethylamines, were prepared as probes for the ligand-binding site(s) of adenylate cyclase-coupled OCT or TYR receptors, and were examined for their effects on cAMP production in the head membranes of Bombyx mori larvae. Small structural changes in OCT and TYR proved to lead to three types of OCT/TYR analogues: (1) compounds that increase the cAMP level by themselves and also depress OCT-stimulated cAMP production, (2) compounds that do not stimulate cAMP production by themselves but inhibit OCT-stimulated cAMP production, and (3) compounds that are not active in either the stimulation of cAMP production or the inhibition of OCT-stimulated cAMP production. Tyramine, which belongs to the second group, also inhibited the basal level of cAMP production at high concentrations. The data indicate that two biogenic amine systems that positively and negatively regulate the level of the second messenger cAMP are present in the head part of B. mori larvae. This finding points to the necessity of separately evaluating the positive and negative regulatory effects in order to quantitatively understand the structure-activity relationships of OCT receptor ligands. Arch.

Adenylyl Cyclases↗
PubMed2001

Design, in vitro stability, and ocular hypotensive activity of t-butalone chemical delivery systems.

The objective of this work was to synthesize two bioreversible diacyl derivatives of t-butalone (chemical delivery systems), determine their chemical and in vitro stability, and investigate their potential use as topical antiglaucoma agents. The stability of these compounds was determined in isotonic phosphate buffers (pH range 5-8) and in selected biological media, including human whole blood, rabbit and rat blood, and the anterior segment tissues of rabbit. The ocular hypotensive activity of these compounds in unrestrained, normotensive albino rabbits was determined with a pneumatonometer. The two compounds were stable at lower pH. The stability decreased as the pH increased, suggesting their lability to base-catalyzed hydrolysis. These compounds exhibited significant differences in the hydrolytic rates in the whole blood among species examined (rat > rabbit > human). The observed rates of disappearance in different ocular tissues were indicative of relative enzyme activity in these media (iris-ciliary body > cornea > aqueous humor). The two compounds exhibited a significant ocular hypotensive activity (P < 0.01) at 2% dose level. The peak activity was found between 2 and 4 h, and the activity was maintained for 4.5 to 7 h. The dipivalyl derivative of t-butalone exhibited more pronounced decrease in intraocular pressure than that of diisovaleryl derivative. The present study suggests the possible use of diacyl derivatives of t-butalone as ocular hypotensive agents.

Animals↗
PubMed2001

The effect of nitric oxide and peroxynitrite on rabbit cavernosal smooth muscle relaxation.

Nitric oxide (NO) mediates penile erection by inducing cavernosal smooth muscle relaxation. Superoxide anion (O2-) can influence the activity of NO by reacting with it to produce peroxynitrite (PN). This is a highly reactive species that is known to attack a variety of biological targets. It is far more reactive and damaging than its precursors. We therefore, investigated the effect of PN on rabbit cavernosal smooth muscle relaxation and compared it to NO. Cavernosal strips from nine adult New Zealand White rabbits were excised (n = 12 strips for each arm of the study) and mounted in organ baths. After pre-contraction with phenylephrine (PE) (100 microM) the strips were exposed to either NO or PN (1-100 microM) and subsequent smooth muscle relaxations monitored. Some tissues were incubated with oxadiazoloquinoxalin-1-one (ODQ; 10 microM), an inhibitor of guanylyl cyclase, before the addition of NO or PN. NO and PN induced concentration-dependent relaxations in all strips. However, PN (IC50: 26 +/- 3.6 microM) was significantly less potent than NO (IC50: 11 +/- 0.7 microM) [P < 0.01]. Relaxation induced by NO was immediate and short-lived, with the tension returning to its original level. In contrast, PN-initiated relaxations were of a slower onset and more prolonged, with the tissues unable to recover tension. However, after several washouts the tissues were fully responsive to PE. Both NO- and PN-mediated relaxations were inhibited by ODQ, suggesting the involvement of cGMP in this process. Although PN mediates cavernosal smooth muscle relaxation, it is much less potent than NO. As PN is thought to play a role in a variety of pathologies where erectile dysfunction is prominent, it may also contribute to the pathogenesis of erectile dysfunction.

Animals↗
PubMed2001

Side effects and oral contraceptive discontinuation in rural Bangladesh.

Using data from a survey on oral contraceptive (OC) compliance in rural Bangladesh, this study examines the role of side effects on OC discontinuation along with other potential predictors. A total of 1403 currently married women aged 15-49 years were interviewed; of these 43% discontinued OCs. Of the women who discontinued, 53% did so because of side effects, which was the main self-reported reason for OC discontinuation. Multivariate analysis revealed that after adjusting for duration of OC use, women who experienced side effects were 1.4 times more likely to discontinue OC use than their counterparts without such experience. Discontinued OC use was also associated with being Muslim, not being visited by field-workers, OC use as first method of contraception, lack of husband's support, and was inversely associated with duration of OC use. Adequate counseling about OC use, emphasizing the possibility of side effects, and better management of them, coupled with improved client-provider interaction and husband's supportive role could help in reducing OC discontinuation in rural Bangladesh.

Adolescent↗
PubMed2001

Synthesis, structure and biological activity of nickel(II) complexes of 5-methyl 2-furfural thiosemicarbazone.

5-Methyl 2-furfuraldehyde thiosemicarbazone (M5HFTSC) with nickel(II) leads to three types of complexes: [Ni(M5HFTSC)(2)X(2)], [Ni(M5FTSC)(2)] and [Ni(M5FTSC)(2)] x 2DMF. In the first type the ligand remains in thione form, while in the two other, the anionic thiolato form is involved. The species [Ni(M5HFTSC)(2)X(2)] has been characterized spectroscopically. The structures of [Ni(M5FTSC)(2)] x 2DMF and [Ni(M5FTSC)(2)] have been solved using X-ray diffraction. Biological studies of [Ni(M5HFTSC)(2)Cl(2)] have been carried out in vitro for antifungal activity on human pathogenic fungi, Aspergillus fumigatus and Candida albicans, and in vivo for toxicity on mice. The results are compared to those of the ligand, the metal salt and a similar copper complex [Cu(M5HFTSC)Cl(2)].

Animals↗
PubMed2001

Immunoneutralisation of GnRH-I, without cross-reactivity to GnRH-II, in the development of a highly specific anti-fertility vaccine for clinical and veterinary use.

In recent years, several forms of gonadotrophin releasing hormone (GnRH) molecules have been isolated from primate brain. These molecules are very similar in sequence and this raises the question of whether previously developed neutralisation vaccines based on GnRH (now termed GnRH-I) would remove other forms of GnRH (namely GnRH-II) as well. As the function of these other molecules has not yet been clearly defined, potential health risks could exist by their ablation. In view of the high sequence homology between the molecules, this paper describes the production of highly specific polyclonal antibodies against GnRH-I and GnRH-II, with negligible cross-reactivity. The ultimate aim of this is to develop an anti-fertility vaccine which does not present any inappropriate side-effects, caused by neutralisation of a GnRH molecule which may or may not be directly involved in reproduction. Several formulations were investigated, based on analogues of the following molecules, conjugated to tetanus toxoid: 1. GnRH-I pGlu-His-Trp-Ser-Try-Gly-Leu-Arg-Pro-Gly-NH2 and 2. GnRH-II pGlu-His-Trp-Ser-His-Gly-Trp-Tyr-Pro-Gly-NH2. The specificity of the antibodies produced was examined, together with effects on fertility and any inappropriate side-effects. Immunostaining of hypothalamic sections was carried out, using the generated antisera, to determine the regional distribution of GnRH-I and GnRH-II neurones, as well as to further evaluate the specificity of the antibodies.

Animals↗
PubMed2001

HLA-B27 polymorphism.

HLA-B27 is a serologic specificity that encompasses 25 different alleles that encode 23 different products (proteins): HLA-B*2701 to B*2723. These alleles are also called subtypes of HLA-B27, and they may have evolved from the most widespread subtype, B*2705. These subtypes are distinguished from changes mostly in exons 2 and 3, which encode the alpha 1 and alpha 2 domains of the B27 molecule, respectively. Occurrence of ankylosing spondylitis (AS) or related spondyloarthropathy (SpA) has thus far been documented in subjects possessing any one of the first ten (B*2701 to B*2710) subtypes studied. However, B*2706 in Southeast Asian and B*2709 in the Italian island population of Sardinia seem not to be associated with AS. The 13 most recent subtypes have not yet been studied for disease association. It is important to investigate which of them are and are not associated with AS and related SpA, and whether certain subtypes show any preferential association with some of the clinical features or forms of these diseases among the various ethnic/racial populations and geographic regions of the world. This is expected to provide clues as to the mechanism of disease association, and one of the strongest reasons to study the B27 subtypes is to learn the effects of the sequence variations on the peptide-binding specificity of the molecule. Among these peptides may be the putative arthritogenic peptide(s).

Alleles↗
PubMed2001

Quantitative analysis of surface-located triacylglycerol in intact emulsion particles.

The amount of triacylglycerol (TG) in the surface monolayer of intact phospholipid-stabilized emulsions was determined using (13)C nuclear magnetic resonance ((13)C NMR). (13)C NMR spectra of emulsions composed of bulk long-chain or medium-chain TG were prepared with [(13)C(3)]-carbonyl-enriched triolein, tripalmitin, or trioctanoin, and were analyzed and compared with NMR spectra of phosphatidylcholine vesicles with and without added TG. Identification of carbonyl peaks intermediate between those of phosphatidylcholine carbonyls and bulk TG confirmed the presence of surface TG in each emulsion. The surface of emulsions contained 2.2 mol % tripalmitin and 1.4 mol % triolein, but significantly more medium-chain TG, 9.1 mol % trioctanoin, as predicted by measurements of TG in phospholipid vesicles. Thus, medium-chain TGs are more accessible than long-chain TGs to enzymes or pro-oxidants in the continuous phase of phospholipid-stabilized emulsion systems. The quantitative determination of surface-located TG in intact particles will advance the understanding of emulsion colloidal properties, physicochemical stability, and metabolic behavior.

Carbon Isotopes↗
PubMed2001

The effect of superoxide dismutase on nitric oxide-mediated and electrical field-stimulated diabetic rabbit cavernosal smooth muscle relaxation.

OBJECTIVE: To investigate the effect of superoxide dismutase (SOD, the enzyme that accelerates the breakdown of the superoxide anion, O2- to H2O) on nitric oxide (NO)-mediated and electrical field stimulated (EFS) relaxation in diabetic rabbit cavernosal smooth muscle. Materials and methods Diabetes was induced with alloxan (65 mg/kg) in six adult New Zealand White rabbits. After 6 months, cavernosal smooth muscle strips from age-matched controls and diabetic animals were mounted in organ baths. After precontraction with phenylephrine (10 micromol/L) in the presence of atropine (1 micromol/L), guanethidine (5 micromol/L) and indomethacin (10 micromol/L), relaxation responses to EFS (1-20 Hz), carbachol (10(-8)-10(-4) mol/L) and sodium nitroprusside (SNP, 10(-9)-10(-4) mol/L) were assessed in the presence and absence of SOD (100 IU/mL). RESULTS: SNP- and carbachol-mediated (endothelium-independent and -dependent, respectively) relaxations were impaired in the diabetic cavernosal smooth muscle strips compared with controls (concentration required for 50% inhibition, 1.4 micromol/L for diabetic and 0.75 micromol/L for control with SNP, and 44 micromol/L for diabetic and 0.4 micromol/L for control with carbachol). SOD significantly enhanced both SNP- and carbachol-mediated diabetic cavernosal smooth muscle relaxations (both P < 0.05). EFS-mediated relaxations were also significantly (P < 0.05) impaired in the diabetic cavernosal smooth muscle strips; these relaxations were also significantly (P < 0.05) enhanced by SOD. CONCLUSION: NO- and EFS-mediated cavernosal smooth muscle relaxation is impaired in a rabbit model of diabetes but SOD significantly reversed the impaired relaxation. Therefore, in diabetes, the generation of reactive oxygen species may play an important role in the development of erectile dysfunction.

Alloxan↗
PubMed2001

Prevalence and clinical characteristics of headache in medical students in oman.

OBJECTIVES: To perform a descriptive epidemiological study of headache in medical students at Sultan Qaboos University, analyzing prevalence, symptom profile, and pattern of health care utilization. BACKGROUND: Headache is one of the most common complaints in medical practice. To our knowledge, headache has not been the subject of investigation in medical students in the Arabian Gulf. METHODS: Lifetime and last-year prevalence of headache was based on a detailed structured headache assessment questionnaire. Besides demographic data, headache characteristics and pattern of health care utilization were evaluated. In addition, questions were included referring to the use of traditional remedies. Interviewers included three previously trained final-year medical students. The evaluation was done per cohort, and the students were guided through the assessment questionnaire by the interviewers. Migraine and tension-type headache were diagnosed according to the criteria of the International Headache Society. RESULTS: Four hundred three students (95.3%) completed the questionnaire: 151 men (37.5%) and 252 women (62.5%). The lifetime and last-year prevalence of headache was 98.3% and 96.8%, respectively. A positive family history of headache was found in 57.6% of students. The prevalence rate of migraine and tension-type headache was found to be the same (12.2%), with a difference in distribution across sexes: 6.6% of the men and 15.5% of the women had migraine, while 13.9% of the men and 11.1% of the women suffered from tension-type headache. Only 23.3% of students sought medical assistance during headache episodes, and 80.3% took medication: 24.6% took prescribed medication, 72.9% took nonprescription medication, and only 2.5% took traditional remedies. Acetaminophen (83.1%) followed by mefenamic acid (24.6%) were the most commonly used drugs. CONCLUSIONS: The results of this prospective epidemiological study show that headache is highly prevalent among medical students at this university. The high prevalence rate of migraine sufferers in this student population might be due to the high female-to-male ratio (1.7:1). It is likely that analgesic use/overuse also coexists with headache in medical students at Sultan Qaboos University, since a large majority of them rely on nonprescription medications.

Adult↗