Identification of glutathione conjugates of troglitazone in human hepatocytes

Troglitazone (TGZ) is an orally active antihyperglycemic agent used in the treatment of noninsulin-dependent diabetes mellitus. Several cases of liver failure following TGZ administration led to its withdrawal from the market. The mechanism of toxicity is still not understood. The formation of toxic metabolites is believed to play an important role. Herein, we report the biotransformation of TGZ in human hepatocytes. TGZ at 50 microM concentration was incubated with cryopreserved human hepatocytes. Four metabolites were found-glucuronide, sulfate, and two glutathione (GSH) conjugates of TGZ. The two GSH metabolites could be conjugation at the 6-hydroxychromane nucleus and the thiazolidinedione ring. Alternatively, the conjugation could be one of the two rings, with the two GSH metabolites are diastereomers. The sulfate conjugate was the major metabolite found. The cytochrome P450 (CYP) inhibitors furafylline (CYP1A1/2), omeprazole (CYP2C19), ketoconazole (CYP3A4), and sulfaphenazole (CYP2C9) had no inhibitory effect on the TGZ metabolism suggesting that several P450s may play a role in the TGZ metabolic pathway. Previous studies in our laboratory have shown a large interindividual variation between different donors in cytotoxicity after dosing with TGZ. Based on EC(50) values, donors were classified as sensitive or resistant. The sensitive human donors were found to form significantly less troglitazone GSH conjugates and glucuronides than the resistant donors.     

Comparative Studies on Chitosan and Polylactic-co-glycolic Acid Incorporated Nanoparticles of Low Molecular Weight Heparin

This study was performed to test the feasibility of chitosan and polylactic-co-glycolic acid (PLGA) incorporated nanoparticles as sustained-release carriers for the delivery of negatively charged low molecular weight heparin (LMWH). Fourier transform infrared (FTIR) spectrometry was used to evaluate the interactions between chitosan and LMWH. The shifts, intensity, and broadening of the characteristic peaks for the functional groups in the FTIR spectra indicated that strong interactions occur between the positively charged chitosans and the negatively charged LMWHs. Three types of LMWH nanoparticles (NP-1, NP-2, and NP-3) were prepared using chitosan with or without PLGA: NP-1 nanoparticles were formed by polyelectrolyte complexation after single mixing, NP-2 nanoparticles were prepared by polyelectrolyte complexation after single emulsion–diffusion–evaporation, and NP-3 nanoparticles were optimized by double emulsion–diffusion–evaporation. NP-3 nanoparticles of LMWH prepared by the emulsion–diffusion–evaporation method showed significant differences in particle morphology, size, zeta potential, and drug release profile compared to NP-1 nanoparticles formed by polyelectrolyte complexation. Another ionic complex of LMWH with chitosan-incorporated PLGA nanoparticles (NP-2) showed lower drug entrapment efficiency than that of NP-1 and NP-3. The drug release rate of NP-3 was slower than the release rates of NP-1 and NP-2, although particle morphology of NP-3 was similar to that of NP-2. Cell viability was not adversely affected when cells were treated with all three types of nanoparticles. The data presented in this study demonstrate that nanoparticles formulated with chitosan–PLGA could be a safe sustained-release carrier for the delivery of LMWH.Key words: chitosan, low molecular weight heparin, nanoparticles, PLGA     

Optimal matching with minimal deviation from fine balance in a study of obesity and surgical outcomes

In multivariate matching, fine balance constrains the marginal distributions of a nominal variable in treated and matched control groups to be identical without constraining who is matched to whom. In this way, a fine balance constraint can balance a nominal variable with many levels while focusing efforts on other more important variables when pairing individuals to minimize the total covariate distance within pairs. Fine balance is not always possible; that is, it is a constraint on an optimization problem, but the constraint is not always feasible. We propose a new algorithm that returns a minimum distance finely balanced match when one is feasible, and otherwise minimizes the total distance among all matched samples that minimize the deviation from fine balance. Perhaps we can come very close to fine balance when fine balance is not attainable; moreover, in any event, because our algorithm is guaranteed to come as close as possible to fine balance, the investigator may perform one match, and on that basis judge whether the best attainable balance is adequate or not. We also show how to incorporate an additional constraint. The algorithm is implemented in two similar ways, first as an optimal assignment problem with an augmented distance matrix, second as a minimum cost flow problem in a network. The case of knee surgery in the Obesity and Surgical Outcomes Study motivated the development of this algorithm and is used as an illustration. In that example, 2 of 47 hospitals had too few nonobese patients to permit fine balance for the nominal variable with 47 levels representing the hospital, but our new algorithm came very close to fine balance. Moreover, in that example, there was a shortage of nonobese diabetic patients, and incorporation of an additional constraint forced the match to include all of these nonobese diabetic patients, thereby coming as close as possible to balance for this important but recalcitrant covariate.     

O(6)-Methylguanine-DNA methyltransferase in glioma therapy: Promise and problems

Gliomas are the most frequent adult primary brain tumor, and are invariably fatal. The most common diagnosis glioblastoma multiforme (GBM) afflicts 12,500 new patients in the U.S. annually, and has a median survival of approximately one year when treated with the current standard of care. Alkylating agents have long been central in the chemotherapy of GBM and other gliomas. The DNA repair protein O(6)-methylguanine-DNA methyltransferase (MGMT), the principal human activity that removes cytotoxic O(6)-alkylguanine adducts from DNA, promotes resistance to anti-glioma alkylators, including temozolomide and BCNU, in GBM cell lines and xenografts. Moreover, MGMT expression assessed by immunohistochemistry, biochemical activity or promoter CpG methylation status is associated with the response of GBM to alkylator-based therapies, providing evidence that MGMT promotes clinical resistance to alkylating agents. These observations suggest a role for MGMT in directing adjuvant therapy of GBM and other gliomas. Promoter methylation status is the most clinically tractable measure of MGMT, and there is considerable enthusiasm for exploring its utility as a marker to assign therapy to individual patients. Here, we provide an overview of the biochemical, genetic and biological characteristics of MGMT as they relate to glioma therapy. We consider current methods to assess MGMT expression and discuss their utility as predictors of treatment response. Particular emphasis is given to promoter methylation status and the methodological and conceptual impediments that limit its use to direct treatment. We conclude by considering approaches that may improve the utility of MGMT methylation status in planning optimal therapies tailored to individual patients.     

Molecular evolution of rodent insulins

Several trees of amino acid sequences of rodent insulins were derived with the maximum-parsimony procedure. Possible orthologous and paralogous relationships were investigated. Except for a recent gene duplication in the ancestor of rat and mouse, there are no strong arguments for other paralogous relationships. Therefore, a tree in agreement with other biological data is the most reasonable one. According to this tree, the capacity to form zinc-binding hexamers was lost once in the ancestor of the hystricomorph rodents, followed by moderately increased evolutionary rates in the lineages to African porcupine and chinchilla but highly increased rates in at least three independent lines to other taxa of this suborder: guinea pig, cuis, and Octodontoidea (coypu and casiragua).      

Effect of 3,4-ethylenedioxy-extension of thiophene core on the DNA/RNA binding properties and biological activity of bisbenzimidazole amidines

Novel bisbenzimidazoles (4–6), characterized by 3,4-ethylenedioxy-extension of thiophene core, revealed pronounced affinity and strong thermal stabilization effect toward ds-DNA. They interact within ds-DNA grooves as dimmers or even oligomers and agglomerate along ds-RNA. Compounds 4–6 have shown moderate to strong antiproliferative effect toward panel of eight carcinoma cell lines. Compound 5 displayed the best inhibitory potential and in equitoxic concentration (IC₅₀ = 1 × 10^?6 M) induced accumulation of cells in G2/M phase after 48 h of incubation. Fluorescence microscopy showed that 5 entered into live HeLa cells within 30 min, but did not accumulate in nuclei even after 2.5 h. Compound 5 inhibited the growth of Trypanosome cruzi epimastigotes (IC₅₀ = 4.3 × 10^?6 M).     

Effects of nutrient addition on growth and rhizosphere pH of Leucadendron ‘Safari Sunset’

A greenhouse experiment was conducted to establish the optimal fertilization management for Leucadendron Safari Sunset (Leucadendron salignum × L. laureolum). Addition of NPK and micronutrient fertilizer or raising phosphorus concentration by itself increased total fresh weight and improved plant growth. Elevating the total nutrients or P concentration increased N and P concentrations. Clusters of proteoid roots were present along the root system of plants irrigated with tap-water, whereas few proteoid roots developed on plants irrigated with complete nutrient solution when only P was omitted, and none developed in any of the other treatments with P present.The pH in leachate of plants irrigated with tap water or with high nutrient levels (100, 20 and 100 mg L^-1 of N, P and K, respectively) was consistently lower compared with leachate without plants. Increasing concentration resulted in a significant change in the pH values (pH in leachate with plant – pH in leachate without plant) from negative to positive. This phenomenon is probably related to rhizosphere effects due to plant and microbial activity.     

Dynamic redistribution of paxillin in bovine osteoblasts stimulated with adenosine 5′-triphosphate

Exposure to extracellular 5′-adenosine triphosphate (ATP) is known to induce membrane blebbing. In this study, we investigated the subcellular distribution of the cytoskeletal adaptor protein paxillin in primary bovine osteoblasts upon stimulation with ATP. Cells expressing a fusion protein of green fluorescent protein (GFP) and paxillin were followed by time-lapse video-microscopy after stimulation with 100?μM ATP. Within 100?s, GFP-paxillin became incorporated in numerous de novo formed focal aggregates localized at the cell periphery. The assembly of individual paxillin-containing aggregates occurred with a mean half-life time of <60?s, whereas their disassembly lasted twice as long. Despite the ongoing presence of ATP, the formation of paxillin aggregates was self-limiting within 25?min. Paxillin clustering was preceded by a transient rise in cytoplasmic calcium transients, which peaked already 20?s after adding ATP. The high mobility of paxillin was confirmed by measuring the dissociation rate of GFP-paxillin at mature focal adhesions, demonstrating the presence of a highly mobile fraction with a mean recovery half-life of 8.2?±?1.2?s, followed by a slower phase (53?±?20?s). Thus, both the exchange of paxillin at mature focal adhesions and the increase in intracellular calcium concentrations upon ATP stimulation are very rapid processes, which override the time course of ATP-induced paxillin membrane clustering by one to two orders of magnitude. Our data demonstrate that the transient recruitment of paxillin in membrane protuberances is based on the high intracytoplasmic mobility of unbound paxillin molecules and their rapid focal accumulation.