Talat Makhmoor

Antioxidant and antimicrobial activities of Tamarix ramosissima

The ethylacetate and water-acetone extracts of Tamarix ramosissima were screened for their antioxidant, antibacterial, antifungal and DNA damaging activities through in vitro experiments. All fractions as well as precipitates showed significant antioxidant activity. A known compound tamarixetin (1) was isolated which showed significant DNA damaging activity in mutant yeast bioassay. Results revealed that antioxidant and antibacterial activities were associated with the presence of polyphenolic substances.

Characterization of Structural Features Controlling the Receptiveness of Empty Class II MHC Molecules

MHC class II molecules (MHC II) play a pivotal role in the cell-surface presentation of antigens for surveillance by T cells. Antigen loading takes place inside the cell in endosomal compartments and loss of the peptide ligand rapidly leads to the formation of a non-receptive state of the MHC molecule. Non-receptiveness hinders the efficient loading of new antigens onto the empty MHC II. However, the mechanisms driving the formation of the peptide inaccessible state are not well understood. Here, a combined approach of experimental site-directed mutagenesis and computational modeling is used to reveal structural features underlying “non-receptiveness.” Molecular dynamics simulations of the human MHC II HLA-DR1 suggest a straightening of the α-helix of the β1 domain during the transition from the open to the non-receptive state. The movement is mostly confined to a hinge region conserved in all known MHC molecules. This shift causes a narrowing of the two helices flanking the binding site and results in a closure, which is further stabilized by the formation of a critical hydrogen bond between residues αQ9 and βN82. Mutagenesis experiments confirmed that replacement of either one of the two residues by alanine renders the protein highly susceptible. Notably, loading enhancement was also observed when the mutated MHC II molecules were expressed on the surface of fibroblast cells. Altogether, structural features underlying the non-receptive state of empty HLA-DR1 identified by theoretical means and experiments revealed highly conserved residues critically involved in the receptiveness of MHC II. The atomic details of rearrangements of the peptide-binding groove upon peptide loss provide insight into structure and dynamics of empty MHC II molecules and may foster rational approaches to interfere with non-receptiveness. Manipulation of peptide loading efficiency for improved peptide vaccination strategies could be one of the applications profiting from the structural knowledge provided by this study.

Free radical scavenging phenylethanoid glycosides from Leucas indica Linn.

A new phenylethanoid glycoside, 2-(3,4-dihydroxyphenyl)-ethyl-O-α-L-rhamnopyranosyl-(1 → 3)-O-α-L-rhamnopyranosyl-(1 → 6)-4-O-E-feruloyl-β-D-glucopyranoside (3-O-methyl poliu-moside, 1) along with five known phenylethanoid glycosides (2–6) were isolated from the aerial parts of Leucas indica Linn. The structure of compound 1 has been elucidated on the basis of spectral data. Compounds 1–6 exhibited significant antioxidant activity in 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical assay method. These compounds were also found to be moderate inhibitors of xanthine oxidase (XO) enzyme.

Synthesis, characterization and Cu(2+) triggered selective fluorescence quenching of Bis-calix[4]arene tetra-triazole macrocycle.

A novel fluorescent bis-calix[4]arene macrocycle 9 incorporating metal-binding pockets was successfully prepared. The structure of macrocycle 9 and its precursors were characterized via EI-MS, MALDI-TOF-MS, ESI-MS, (1)H NMR, (13)CNMR, 2D NMR, and X-ray crystallography. The macrocycle 9 displayed selective fluorescence quenching after interacting with Cu(2+) in the presence competing metal cations including Mg(2+), Ca(2+), Ba(2+), Ag(+), Zn(2+), Ti(4+),Cd(2+), Hg(2+), Pb(2+), In(3+), La(3+), Cr(3+), Ni(2+), Sb(3+), V(5+), Fe(3+), Co(2+), Sn(2+), Sn(2+), and Tl(+). The Cu(2+) limit of detection was found to be 40 nM much lower than its threshold level (∼ 20 μM) in drinking water permitted by the U.S Environmental Protection Agency (EPA). Furthermore, drinking water samples from Karachi University (Pakistan) spiked with Cu(2+) were analysed with the sensing system and the results showed an excellent agreement with the fluorescence quenching phenomenon of macrocycle 9 examined in deionized water. Importantly, the chemosensor 9 could be used to detect Cu(2+) in living cells.

Highly Oxygenated Triterpenes from the Roots of Atropa Acuminata

Two new oleanane triterpenes; 2 f ,3 f ,24-trihydroxyolean-12-ene-28,30-dioic acid ( 1 ) and 2 f ,3 f ,24,28-tetrahydroxyolean-12-ene ( 2 ) have been isolated from the roots of Atropa acuminata . Anti-oxidant p -hydroxyphenethyl trans -ferulate ( 3 ), g -sitosterol-3- O - g - d -glucopyranoside ( 4 ) and oleanolic acid ( 5 ) have also been reported for the first time from this species. The structures were determined by spectroscopic studies including 2D-NMR.

A cyclic peptide accelerates the loading of peptide antigens in major histocompatibility complex class II molecules

Major histocompatibility complex (MHC)-loading enhancers (MLE) have recently attracted attention because of their ability to enhance the efficacy of peptide immunotherapeutics. As small molecular weight compounds, they influence the loading of peptides in MHC molecules by converting them from a non-receptive to a receptive state. Herein, we report a 14-mer cyclic peptide 1 (CP-1) as a new class of MLE-peptide. This peptide was used to investigate its loading on human leukocyte antigen (HLA)-DR molecules. It was found that CP-1 strongly accelerates peptide-loading on both soluble and cell surface HLA-DR molecules in a dose-dependent manner. The effect was evident for all subsets of HLA-DR tested, including HLA-DRB1*1501, indicating that it acts independently of P1-pocket size, which is the canonical MLE-binding site. Importantly, increased peptide-loading by CP-1 was correlated with improved CD4(+) T cell responses in vitro, while propidium iodide staining indicated low peptide-induced cytotoxicity. Thus, this study revealed a new class of peptide-based enhancers that catalyze peptide-loading by allosteric interactions with MHC molecules. Because of its low cellular cytotoxicity and high MLE activity, it may be useful in stimulating antigen-specific T cell responses for therapeutic purposes.

Hepatoprotection by chemical constituents of the marine brown alga Spatoglossum variabile: A relation to free radical scavenging potential

Context: In the course of searching hepatoprotective agents from natural sources, the protective effect of chemical constituents of the marine brown alga Spatoglossum variabile Figaro et DE Notar (Dictyoaceae) against CCl4-induced liver damage in Wistar rats was investigated. The compounds were first investigated for in vitro radical scavenging potential and were also tested for β-glucuronidase inhibition to further explore the relationship between hepatoprotection and antiradical potential. Methods: The compounds cinnamic acid esters 1 and 2 and aurone derivatives 3 and 4 were first investigated for in vitro radical scavenging potential against 1,1-diphenyl-2-picrylhydrazyl radicals (DPPH), and superoxide anion radicals. In vivo hepatoprotective studies were performed in seven groups (n = 6) of Wistar rats. The test groups were pretreated with compounds (10 mg/kg body weight, po) orally for 30 min before the intraperitoneal administration of a dose of 20% CCl4 diluted with dietary cooking oil. Moreover, compounds were also tested for β-glucuronidase inhibition to explore the relationship between hepatoprotection and radical scavenging potential. Results: The test compounds 1–4 were found to exhibit antiradical activity against 1,1-diphenyl-2-picrylhydrazyl radicals with IC50 values ranging between 54 and 138 µM, whereas aurone derivatives 3 and 4 additionally exhibited superoxide anion scavenging effects with IC50 values of 95 and 87 µM, respectively. In addition, these compounds were found to be weak inhibitors of xanthine oxidase (IC50 ≥1000 µM). In animal model, pretreatment with compounds 2–4 significantly blocked the CCl4-induced increase in the levels of the serum biochemical markers. Conclusion: It appears that the hepatoprotection afforded by these compounds was mainly due to their radical scavenging activity that protected the cells from the free radicals generated by CCl4-induced hepatotoxicity.

Brine shrimp lethality assay 'an effective prescreen': microwave-assisted synthesis, BSL toxicity and 3DQSAR studies-based designing, docking and antitumor evaluation of potent chalcones.

Abstract Context: In the course of searching potential antitumor agents from a library of chalcones synthesized under microwave irradiations, the brine shrimp lethality (BSL) assay and a 3D structure–activity relationship (3DQSAR) studies were followed by the antitumor evaluation of most potent analogues. Objective: The objective of the current study was to effectively use the BSL assay for the identification of potential cytotoxic analogues from a set of compounds. Methods: We applied the comparative molecular field analysis (CoMFA) and devised 3DQSAR on 33 synthesized chalcones leading to prediction of five related compounds with improved activity. The scope of BSL assay for the prediction of antitumor potency was tested through the in vitro antitumor studies against six human tumor cell-lines, docking studies and the tubulin-polymerization assay. Results: The newly designed compounds 34–38 displayed very promising cytotoxic potency. From our results, the BSL toxicity, antitumor efficacy and docking outcomes could be easily co-related. Conclusion: The study draws a very good relationship between a simple, inexpensive, and bench-top BSL assay and the antitumor potential of the cytotoxic compounds. Devising the CoMFA analysis helped in designing chalcones with improved cytotoxic potential as displayed through their BSL and cytotoxic activity against human tumor cell lines. The studies are noteworthy as such comprehensive studies were never performed before on the BSL assay. The present studies widen the scope of the BSL model that may prove quite helpful as a preliminary screen in the antitumor drug designing and synthesis expeditions.