Biomedical subjects

Mahmood Akhtar

Publications and source records attributed to Mahmood Akhtar.

6 recordsLinked to original sources

PubMed2004

Protective role of arginase in a mouse model of colitis.

Arginase is the endogenous inhibitor of inducible NO synthase (iNOS), because both enzymes use the same substrate, l-arginine (Arg). Importantly, arginase synthesizes ornithine, which is metabolized by the enzyme ornithine decarboxylase (ODC) to produce polyamines. We investigated the role of these enzymes in the Citrobacter rodentium model of colitis. Arginase I, iNOS, and ODC were induced in the colon during the infection, while arginase II was not up-regulated. l-Arg supplementation of wild-type mice or iNOS deletion significantly improved colitis, and l-Arg treatment of iNOS(-/-) mice led to an additive improvement. There was a significant induction of IFN-gamma, IL-1, and TNF-alpha mRNA expression in colitis tissues that was markedly attenuated with l-Arg treatment or iNOS deletion. Treatment with the arginase inhibitor S-(2-boronoethyl)-l-cysteine worsened colitis in both wild-type and iNOS(-/-) mice. Polyamine levels were increased in colitis tissues, and were further increased by l-Arg. In addition, in vivo inhibition of ODC with alpha-difluoromethylornithine also exacerbated the colitis. Taken together, these data indicate that arginase is protective in C. rodentium colitis by enhancing the generation of polyamines in addition to competitive inhibition of iNOS. Modulation of the balance of iNOS and arginase, and of the arginase-ODC metabolic pathway may represent a new strategy for regulating intestinal inflammation.

Animals↗

PubMed2004

Green tea polyphenol (-)-epigallocatechin gallate blocks epithelial barrier dysfunction provoked by IFN-gamma but not by IL-4.

A characteristic of many enteropathies is increased epithelial permeability, a potentially pathophysiological event that can be evoked by T helper (Th)-1 (i.e., IFN-gamma) and Th2 (i.e., IL-4) cytokines and bacterial infection [e.g., enteropathogenic Escherichia coli (EPEC)]. The green tea polyphenol (-)-epigallocatechin gallate (EGCG) has immunosuppressive properties, and we hypothesized that it would ameliorate the increased epithelial permeability induced by IFN-gamma, IL-4, and/or EPEC. EGCG, but not the related epigallocatechin, completely prevented the increase in epithelial (i.e., T84 cell monolayer) permeability caused by IFN-gamma exposure as gauged by transepithelial resistance and horseradish peroxidase flux; EGCG did not alleviate the barrier disruption induced by IL-4 or EPEC. IFN-gamma-treated T84 and THP-1 (monocytic cell line) cells displayed STAT1 activation (tyrosine phosphorylation on Western blot analysis, DNA binding on EMSA) and upregulation of interferon response factor-1 mRNA, a STAT1-dependent gene. All three events were inhibited by EGCG pretreatment. Aurintricarboxylic acid also blocked IFN-gamma-induced STAT1 activation, but it did not prevent the increase in epithelial permeability. Additionally, pharmacological blockade of MAPK signaling did not affect IFN-gamma-induced epithelial barrier dysfunction. Thus, as a potential adjunct anti-inflammatory agent, EGCG can block STAT1-dependent events in gut epithelia and monocytes and prevent IFN-gamma-induced increased epithelial permeability. The latter event is both a STAT1- and MAPK-independent event.

Adjuvants, Immunologic↗

PubMed2003

Brain death and related issues.

Concerns about the erroneous diagnosis of death and premature burial have been expressed from times immemorial. Patients with brain stem death have absolutely no chance of recovery. brain death is considered at par with death in most of the countries. General public in most parts of the world shows reluctance to accept this concept due to different social, cultural and religious backgrounds and state of literacy and awareness. The criteria for the diagnosis of brain death have been established which include certain pre-conditions, exclusions and tests of the brain stem function. These criteria are universally accepted. The criteria in children are somewhat different from the adults. The subject is intimately related with organ transplantation. If the patient is registered as organ donor or the family consents, organs can be harvested from brain dead patients for transplantation. Pakistan is amongst the few countries where no legislation exists to accept brain death as being at par with death of an individual, and to facilitate and regulate, cadaveric organ donation and transplantation.

Brain Death↗

PubMed2003

Adenoviral transfer of the murine oncostatin M gene suppresses dextran-sodium sulfate-induced colitis.

The use of biologics has promising potential in the treatment of inflammation. Studies with cultured cells and mouse models of disease have ascribed proinflammatory and anti-inflammatory functions to oncostatin M (OSM) and the related cytokine, interleukin-6 (IL-6). Here, we examined the effect of systemic administration of adenoviral (Ad) vectors encoding either murine OSM (AdMuOSM) or murine IL-6 (AdMuIL-6) in a mouse model of colitis. BALB/c mice were treated with a 5-day course of 4% dextran-sodium sulfate (DSS) water with or without administration of adenoviral vectors (i.p. or i.m. at 10(7) plaque-forming units [pfu]) given as a cotreatment or therapy. The deletion variant of the adenovirus served as a control for adenoviral infection. Colitis was assessed by (1) morphology (damage score, macrophage infiltration, apoptosis) and (2) function (myeloperoxidase activity and Ussing chamber analysis of epithelial ion transport). Infection with adenovirus alone did not affect colonic form or function. AdMuOSM (either i.p. or i.m.) significantly reduced the severity of the DSS-induced colitis. There was less damage, reduced macrophage infiltration, fewer apoptotic bodies, and a significant improvement in stimulated ion transport in colonic tissues from the treated mice. No benefit of AdMuIL-6 treatment was observed in this model system. Thus, systemic administration of AdMuOSM given as a cotreatment and to a lesser extent as a therapy was found to be of benefit in DSS-induced colitis, a murine model of inflammatory bowel disease (IBD).

Acute-Phase Proteins↗

PubMed2003

Bacterial DNA evokes epithelial IL-8 production by a MAPK-dependent, NF-kappaB-independent pathway.

Recognition of bacterial products by the innate immune system is dependent on pattern-recognition receptors: toll-like receptor 9 (TLR-9) in the case of bacterial DNA. We hypothesized that bacterial DNA can directly affect enteric epithelial cells. RT-PCR revealed constitutive TLR-9 mRNA expression in three human colonic epithelial cell lines (T84, HT-29, Caco-2) and THP-1 monocytes. Epithelial cells, in six-well culture plates or on filter supports, were exposed to E. coli DNA (1-50 microg/ml), synthetic CpG-rich oligonucleotides, or calf thymus DNA for 6-48 h. Exposure to E. coli DNA resulted in an increase in IL-8 mRNA, and a time- and dose-dependent increase in IL-8 secretion. Also, CpG oligonucleotides induced epithelial IL-8 production, whereas calf thymus DNA did not. Exposure to E. coli DNA resulted in phosphorylation of ERK 1/2 MAPK and inhibitors of ERK activity (PD98059, UO126) significantly reduced the evoked IL-8 production. In contrast, inhibitors of NFkappaB activity (PDTC, SN50) did not block E. coli DNA-induced IL-8 production. Electrophoretic mobility shift assays revealed that E. coli DNA stimulated epithelial AP-1 but not NFkappaB activation. The barrier (i.e., transepithelial resistance) and ion transport parameters of epithelial monolayers (assessed in Ussing chambers) were unaltered following E. coli DNA exposure. Thus model gut epithelia express TLR-9 mRNA and, while maintaining their barrier function, can respond to E. coli DNA by increased IL-8 production.

Caco-2 Cells↗

PubMed2002

Dextran sodium sulphate-induced colitis perturbs muscarinic cholinergic control of colonic epithelial ion transport.

1. Neuronal cholinergic input is an important regulator of epithelial electrolyte transport and hence water movement in the gut. 2. In this study, colitis was induced by treating mice with 4% (w v(-1)) dextran sodium-sulphate (DSS)-water for 5 days followed by 3 days of normal water. Mid-colonic segments were mounted in Ussing chambers and short-circuit current (Isc, indicates net ion movement) responses to the cholinergic agonist, carbachol (CCh; 10(-4) M)+/-tetrodotoxin, atropine (ATR), hexamethonium (HEX), naloxone or phenoxybenzamine were assessed. 3. Tissues from mice with DSS-induced colitis displayed a drop in Isc in response to CCh (-11.3+/-3.3 microA/cm(2)), while those from control mice showed a transient increase in Isc (76.3+/-13.0 microA/cm(2)). The DeltaIsc in colon from DSS-treated mice was tetrodotoxin-sensitive, atropine-insensitive and was reversed by hexamethonium (HEX+CCh=16.7+/-7.8 microA/cm(2)), indicating involvement of a nicotinic receptor. 4. CCh induced a drop in Isc in tissues from controls only when they were pretreated with the cholinergic muscarinic receptor blocker, atropine: ATR+CCh=-21.3+/-7.0 microA/cm(2). Nicotine elicited a drop in Isc in Ussing-chambered colon from both control and DSS-treated mice that was TTX-sensitive. 5. The drop in Isc evoked by CCh challenge of colonic tissue from DSS-treated mice or ATR+CCh challenge of control tissue was not significantly affected by blockade of opiate or alpha-adrenergic receptors by naloxone or phenoxybenzamine, respectively. 6. The data indicate that DSS-colitis reveals a nicotinic receptor that becomes important in cholinergic regulation of ion transport.

Animals↗