Thiazolidinediones: effects on insulin resistance and the cardiovascular system.

Abstract
Thiazolidinediones (TZDs) have been used for the treatment of hyperglycaemia in type 2 diabetes for the past 10 years. They may delay the development of type 2 diabetes in individuals at high risk of developing the condition, and have been shown to have potentially beneficial effects on cardiovascular risk factors. TZDs act as agonists of peroxisome proliferator-activated receptor-gamma (PPAR-gamma) primarily in adipose tissue. PPAR-gamma receptor activation by TZDs improves insulin sensitivity by promoting fatty acid uptake into adipose tissue, increasing production of adiponectin and reducing levels of inflammatory mediators such as tumour necrosis factor-alpha (TNF-alpha), plasminogen activator inhibitor-1(PAI-1) and interleukin-6 (IL-6). Clinically, TZDs have been shown to reduce measures of atherosclerosis such as carotid intima-media thickness (CIMT). However, in spite of beneficial effects on markers of cardiovascular risk, TZDs have not been definitively shown to reduce cardiovascular events in patients, and the safety of rosiglitazone in this respect has recently been called into question. Dual PPAR-alpha/gamma agonists may offer superior treatment of insulin resistance and cardioprotection, but their safety has not yet been assured

A new monoclonal antibody, P2A8(6), that specifically recognizes a novel epitope on the multidrug resistance-associated protein 1 (MRP1), but not on MRP2 nor MRP3

Multidrug resistance (NIDR) is a major problem in the chemotherapeutic treatment of cancer. Overexpression of the multidrug resistance-associated protein 1 (MRP1), is associated with NIDR in certain tumors. A number of MRP1-specific MAbs, which facilitate both clinical and experimental investigations of this protein, are available. To add to this panel of existing antibodies, we have now generated an additional MRP1-specific monoclonal antibody (MAb), P2A8(6), which detects a unique heat stable epitope on the MRP1 molecule. Female Wistar rats were immunized via footpad injections with a combination of two short synthetic peptides corresponding to amino acids 235-246 (peptide A) and 246-260 (peptide B) of the MRP1 protein. Immune reactive B cells were then isolated from the popliteal lymph nodes for fusion with SP2/O-Ag14 myeloma cells. Resultant hybridoma supernatants were screened for MRP1-specific antibody production. Antibody P2A8(6) was characterized by Western blotting and immunocytochemistry on paired multidrug resistant (MRP1 overexpressing) and sensitive parental cell lines. The antibody detects a protein of 190 kDa in MRP1-expressing cell lines but not in MRP2- or MRP3-transfected cell lines. P2A8(6) stains drug-selected and MRP1-transfected cell lines homogeneously by immunocytochemistry and recognizes MRP1 by immunohistochemistry on formalin-fixed paraffin wax-embedded tissue sections. Peptide inhibition studies confirm that P2AS(6) reacts with peptide B (amino acids 246-260), therefore recognizing a different epitope from that of all currently available MRP1 MAbs. This new MAb, chosen for its specificity to the MRP1 protein, may be a useful addition to the currently available range of MRP1-specific MAbs.

Selection with melphalan or paclitaxel (Taxol) yields variants with different patterns of multidrug resistance, integrin expression and in vitro invasiveness

A melphalan-resistant variant (Roswell Park Memorial Institute (RPMI)-2650M1) and a paclitaxel-resistant variant (RPMI-1650Tx) of the drug-sensitive human nasal carcinoma cell line, RPMI-2650. were established. The multidrug resistance (MDR) phenotype in the RPMI-2650Tx appeared to be P-glycoprotein (PgP)-mediated. Overexpression of multidrug resistant protein (MRP) family members was observed in the RPMI-2650M1 cells, which were also much more invasive in vitro than the parental cell line or the paclitaxel-resistant variant. Increased expression of alpha (2), alpha (5), alpha (6), beta (1) and beta (4) integrin subunits, decreased expression of alpha (4) integrin subunit, stronger adhesion to collagen type IV, laminin, fibronectin and matrigel, increased expression of MMP-2 and MMP-9 and significant motility compared with the parental cells were observed, along with a high invasiveness in the RPMI-7650M1 cells. Decreased expression of the alpha (2) integrin subunit, decreased attachment to collagen type IV, absence of cytokeratin 18 expression, no detectable expression of gelatin-degrading proteases and poor motility may be associated with the non-invasiveness of the RPMI-2650Tx variant. These results suggest that melphalan exposure can result in not only a MDR phenotype. but could also make cancer cells more invasive, whereas paclitaxel exposure resulted in MDR without increasing the in vitro invasiveness in the RPMI-2650 cells. (C) 2001 Elsevier Science Ltd. All rights reserved.

Stress resistance and disease resistance in seaweeds: The role of reactive oxygen metabolism

It has become clear over the last 15-20 years that the immediate effect of a wide range of environmental stresses, and of infection, on vascular plants is to increase the formation of reactive oxygen species (ROS) and to impose oxidative stress on the cells. Since 1994, sufficient examples of similar responses in a broad range of marine macroalgae have been described to show that reactive oxygen metabolism also underlies the mechanisms by which seaweeds respond (and become resistant) to stress and infection. Desiccation, freezing, low temperatures, high light, ultraviolet radiation, and heavy metals all tend to result in a gradual and continued buildup of ROS because photosynthesis is inhibited and excess energy results in the formation of singlet oxygen. The response to other stresses (infection or oligosaccharides which signal that infection is occurring, mechanical stress, hyperosmotic shock) is quite different-a more rapid and intense, but short-lived production of ROS, described as an

Lys(9) for Glu(9) substitution in glucagon-like peptide-1(7-36)amide confers dipeptidylpeptidase IV resistance with cellular and metabolic actions similar to those of established antagonists glucagon-like peptide-1(9-36)amide and exendin (9-39)

The incretin hormone glucagon-like peptide-1(7-36)amide (GLP-1) has been deemed of considerable importance in the regulation of blood glucose. Its effects, mediated through the regulation of insulin, glucagon, and somatostatin, are glucose-dependent and contribute to the tight control of glucose levels. Much enthusiasm has been assigned to a possible role of GLP-1 in the treatment of type 2 diabetes. GLIP-l's action unfortunately is limited through enzymatic inactivation caused by dipeptidylpeptidase IV (DPP IV). It is now well established that modifying GLP-1 at the N-terminal amino acids, His(7) and Ala(8), can greatly improve resistance to this enzyme. Little research has assessed what effect Glu(9)-substitution has on GLP-1 activity and its degradation by DPP IV. Here, we report that the replacement of Glu(9) of GLP-1 with Lys dramatically increased resistance to DPP IV. This analogue, (Lys(9))GLP-1, exhibited a preserved GLP-1 receptor affinity, but the usual stimulatory effects of GLP-1 were completely eliminated, a trait duplicated by the other established GLP-1-antagonists, exendin (9-39) and GLP-1 (9-36)amide. We investigated the in vivo antagonistic actions of (Lys(9))GLP-1 in comparison with GLP-1(9-36)amide and exendin (9-39) and revealed that this novel analogue may serve as a functional antagonist of the GLP-1 receptor. (C) 2004 Elsevier Inc. All rights reserved.

DPP IV resistance and insulin releasing activity of a novel di-substituted analogue of glucose-dependent insulinotropic polypeptide, (Ser(2)-Asp(13))GIP

Structure-function studies suggest that preservation of the N-terminus and secondary structure of glucose-dependent insulinotropic polypeptide (GIP) is important for biological activity. Therefore, a novel di-substituted analogue of GIP, (Ser(2)-Asp(13))GIP, containing a negatively charged Asp residue in place of an Ala in position 13, seas synthesised and evaluated for in vitro biological activity. Incubation with dipeptidyl peptidase IV (DPP IV) showed the half-lives of GIP and (Ser(2)-Asp(13))GIP to be 2.3 and >4 h, respectively. Insulin releasing studies in clonal pancreatic BRIN-BD11 cells demonstrated that (Ser(2)-Asp(13))GIP (10(-12) to 10(-7) mol/l) was significantly less potent (60-90%; P

Transfer of resistance training to enhance rapid coordinated force production by older adults

The purpose of this study was to examine the capacity of resistance training to enhance the rapid and coordinated production of force by older people. Thirty adults (greater than or equal to 60 years) completed a visually guided aiming task that required the generation of isometric torque in 2 df about the elbow prior to and following a 4-week training period. Groups of six participants were allocated to two progressive ( 40 - 100% maximal voluntary contraction (MVC)) resistance-training (PRT) groups, to two constant low-load (10% MVC) training groups (CLO) and to one no-training control group. Training movements required the generation of either combined flexion and supination (FLESUP), or combined extension and supination (EXTSUP). In response to training, target acquisition times in the aiming task decreased for all groups; however, both the nature of the training load and the training movement influenced the pattern and magnitude of improvements (EXTSUP_ CLO: 36%, FLESUP_ PRT 26%, EXTSUP_ PRT 22%, FLESUP_ CLO 20%, CONTROL 15%). For one group that trained with progressively increasing loads, there arose a subsequent decrease in performance in one condition of the transfer task. For each group, these adaptations were accompanied by systematic changes in the coordination of muscles about the elbow joint, particularly the biceps brachii.

The consequences of resistance training for movement control in older adults

Older adults who undertake resistance training are typically seeking to maintain or increase their muscular strength with the goal of preserving or improving their functional capabilities. The extent to which resistance training adaptations lead to improved performance on tasks of everyday living is not particularly well understood. Indeed, studies examining changes in functional task performance experienced by older adults following periods of resistance training have produced equivocal findings. A clear understanding of the principles governing the transfer of resistance training adaptations is therefore critical in seeking to optimize the prescription of training regimes that have as their aim the maintenance and improvement of functional movement capacities in older adults. The degenerative processes that occur in the aging motor system are likely to influence heavily any adaptations to resistance training and the subsequent transfer to functional task performance. The resulting characteristics of motor behavior, such as the substantial decline in the rate of force development and the decreased steadiness of force production, may entail that specialized resistance training strategies are necessary to maximize the benefits for older adults. In this review, we summarize the alterations in the neuromuscular system that are responsible for the declines in strength, power, and force control, and the subsequent deterioration in the everyday movement capabilities of older adults. We examine the literature concerning the neural adaptations that older adults experience in response to resistance training, and consider the readiness with which these adaptations will improve the functional movement capabilities of older adults.