Impacts of global environmental change on future health and health care in tropical countries

The most common strategy in the development of HIV-1 protease inhibitors has been the design of high affinity transition state analogs that effectively compete with natural substrates for the active site. A second approach has been the development of compounds that inactivate the protease by destabilizing its quaternary or tertiary structure. A successful optimization of these strategies requires an accurate knowledge of the energetics of structural stabilization and binding, and the identification of those regions in the protease molecule that are critical to stability and function. Here the energetics of stabilization of the HIV-1 protease has been measured for the first time by high sensitivity differential scanning calorimetry. These studies have permitted the evaluation of the different components of the Gibbs energy of stabilization (the enthalpy, entropy and heat capacity changes). The stability of the protease is pH-dependent and due to its dimeric nature is also concentration-dependent. At pH 3.4 the Gibbs energy of stabilization is close to 10 kcal/mol at 25 degreesC, consistent with a dissociation constant of 5x10(-8) M. The stability of the protease increases at higher pH values. At pH 5, the Gibbs energy of stabilization is 14.5 kcal/mol at 25 degreesC, consistent with a dissociation constant of 2.3x10(-11) M. The pH dependence of the Gibbs energy of stabilization indicates that between pH 3.4 and pH 5 an average of 3-4 ionizable groups per dimer become protonated upon unfolding. A structure-based thermodynamic analysis of the protease molecule indicates that most of the Gibbs energy of stabilization is provided by the dimerization interface and that the isolated subunits are intrinsically unstable. The Gibbs energy, however, is not uniformly distributed along the dimerization interface. The dimer interface is characterized by the presence of clusters of residues (hot spots) that contribute significantly and other regions that contribute very little to subunit association. At the dimerization interface, residues located at the carboxy and amino termini contribute close to 75% of the total Gibbs energy (Cys95, Thr96, Leu97, Asn98 and Phe99 and Pro1, Ile3, Leu5). Residues Thr26, Gly27 and Asp29 located at the base of the active site are also important, and to a lesser extent Gly49, Ile50, Gly51 located at the tip of the flap region. The structure-based thermodynamic analysis also predicts the existence of regions of the protease with only marginal stability and a high propensity to undergo independent local unfolding. In particular, the flap region occupies a very shallow energy minimum and its conformation can easily be affected by relatively small perturbations. This property of the protease can be related to the ability of some mutations to elicit resistance towards certain inhibitors.     

Downregulation of the pro-apoptotic protein Bak is required for the ras-induced transformation of intestinal epithelial cells

Anoikis is a form of programmed cell death induced in normal epithelial cells by detachment from the extracellular matrix [1] [2] [3]. In epithelial cells of the intestine and other organs, activated rasinduces resistance to anoikis [3] [4], but the actual molecular effectors directly involved in the apoptotic machinery that execute or block anoikis have not yet been identified. Bak, a pro-apoptotic member of the Bcl-2 family, is downregulated in a high proportion of colorectal tumours [5]. In addition, Bak is an important regulator of apoptosis in normal intestinal epithelial cells [6] [7]. Here, we show that activated rasinduces the downregulation of Bak in rat and human intestinal epithelial cells. This ras-induced downregulation of Bak expression could be suppressed by an inhibitor of phosphatidylinositol (PI) 3-kinase, an enzyme already implicated in ras-induced resistance to anoikis [8]. Ectopic expression of Bak in ras-transformed rat intestinal epithelial IEC-18 cells inhibited ras-induced resistance to anoikis and significantly reduced their tumorigenicity. We conclude, therefore, that the ability of rasto downregulate Bak, and the consequent resistance to anoikis, are essential components of the transforming capacity of this oncogene in intestinal epithelial cells.     

Outcome of long-term enteral feeding

In the past two decades, many technical advances have made tube enteral feeding much more comfortable and acceptable to patients and their families. This has greatly expanded the use of this therapy, both in clinical conditions where it was traditionally prescribed and in many other diagnoses. This expanded use raises important questions about how much enteral nutrition is being used, the medical outcome in different clinical conditions, and the quality of life experienced by long-term therapy users. This article addresses these outcome issues for patients in the nonhospital setting.     

Magnetic resonance images of neuronal migration anomalies

Neuronal migration anomalies are a spectrum of brain malformations caused by insults to migrating neuroblasts during the sixth week to fifth month of gestation. To study the characteristics of MRI findings in migration anomalies, MR images of 36 patients (28 children and 8 adults) with migration anomalies were evaluated. Five patients had lissencephaly, eight had pachygyria, twelve had schizencephaly, six had heterotopias of gray matter, three had hemimegalencephaly, and two had polymicrogyria. The frequency of migration anomalies was 0.51% of all cranial MRI studies and 1.21% of pediatric cranial MRI studies at our hospital. The major clinical presentations of these patients were seizure (64%), development delay (42%), motor deficits (42%) and mental retardation (25%). Twenty-five patients (69%) associated with other brain anomalies, including: other migration anomalies in 12 cases (33%), absence of the septum pellucidum in 10 cases (28%), Dandy-Walker malformation/variant in 5 cases, arachnoid cyst in 4 cases, agenesis of the corpus callosum in 3 cases, holoprosencephaly in 2 cases, mega cisterna magna in 1 case and cephalocele in 1 case. Some of them presented with multiple complicated anomalies. As MR imaging provides superb gray-white matter distinction, details of cortical anatomy and multiplanar capability, it can clearly delineate the detail morphologic changes of the brain caused by neuronal migration disorders as well as the associated anomalies.     

Modulation of skin cell functions by transforming growth factor-beta1 and ACTH after ultraviolet irradiation

A new method was developed for binding poly-(ethylene oxide) (PEO) to polymer surfaces that involves the use of electron beam irradiation in two steps. In the first, methacrylic acid was grafted and polymerized to a polymer surface, changing it from hydrophobic to hydrophilic. Exposure of this surface to aqueous PEO solutions resulted in strong hydrogen bonding of the PEO, which was covalently grafted in a second radiation step. The PEO grafts were stable; they could not be removed with extensive washing with water, soaking in basic solution, or gentle mechanical scraping. Both monolayers and multilayers of PEO were formed. The density of the monolayers were found to have little dependence on the molecular weight or concentration of the PEO solution; multilayers could be controlled by varying the viscosity of the PEO solution and the method of application. The PEO-grafted monolayers were tested for their ability to prevent protein adsorption of cytochrome-c, albumin, and fibronectin. Monolayers of star PEO were the most effective, at best showing a 60% decrease in adsorption from untreated controls. One million molecular wight linear PEO monolayers were almost as effective as star monolayers, and 35,000 g/mol linear PEO was bound too closely to the surface, owing to its small size, to have much impact in preventing protein adsorption. The reason for the continued protein adsorption was believed to be due to a close grafting of the PEO to the surface, as well as the grafted methacrylic acid chains being long enough to extend through the PEO monolayer, thus being accessible on the surface.     

Classical/nonclassical hybrid cannabinoids: southern aliphatic chain-functionalized C-6beta methyl, ethyl, and propyl analogues

The stereoelectronic requirements for interaction of the southern aliphatic hydroxyl of cannabimimetic pharmacophores with the CB1 and CB2 receptors are explored. The stereoselective syntheses of three series of classical/nonclassical hybrid cannabinoids are described. These compounds were designed to investigate the importance of the southern aliphatic hydroxyl (SAH) pharmacophore for cannabimimetic activity. Variation in the chain length of the SAH moiety in these 6beta-(hydroxyalkyl)dihydrobenzopyran analogues, from 6beta-hydroxymethyl to 6beta-(omega-hydroxyethyl) and 6beta-(omega-hydroxypropyl), and the effects of replacing the hydroxyl functionality by hydride and iodide are reported. Our results indicate that the SAH pharmacophore has less pronounced effects than the C-3 aliphatic chain on cannabinoid activity. Furthermore, it appears that this southern molecular component is capable of interacting with two different subsites on the receptor and that the nature of this interaction is determined by the terminal substituent on the C-6beta alkyl group. One of the subsites can accommodate the relatively polar SAH pharmacophore, while the second subsite interacts with more hydrophobic C-6beta substituents and can accommodate large spherical pharmacophores separated by three methylene carbons from the tricyclic cannabinoid template.     

Effects of methyltestosterone on insulin secretion and sensitivity in women

The frequent coexistence of hyperandrogenism and insulin resistance is well established; however, whether a cause and effect relationship exists remains to be established. In this study we tested the hypothesis that short-term androgen administered to women would induce insulin resistance. To test this hypothesis, regularly menstruating, nonobese women were studied before and during methyltestosterone administration (5 mg tid for 10-12 days) by the hyperglycemic (n=8) and euglycemic, hyperinsulinemic (n=7) clamp techniques. Short-term methyltestosterone administration had no significant effects on the fasting levels of glucose, insulin, c-peptide, glucagon, or glucose turnover. During the hyperglycemic clamp studies, the mean glucose level during the final hour was 203+/-2 and 201+/-1 mg/dL in the methyltestosterone and control studies, respectively. The insulin response to this hyperglycemic challenge was slightly but not significantly greater during methyltestosterone treatment (first phase 59+/-8 vs. 50+/-8 microU/mL in controls; second phase 74+/-9 vs. 67+/-9 microU/mL in controls; total insulin response 133+/-16 vs. 117+/-15 microU/mL in controls). In spite of this, glucose uptake was reduced from the control study value of 10.96+/-1.11 to 7.3+/-0.70 mg/kg/min by methyltestosterone (P < 0.05). The ratio of glucose uptake per unit of insulin was also significantly reduced from a control study value of 14.3+/-1.4 to 9.4+/-1.3 mg/kg/min per microU/mL x 100 during methyltestosterone administration. In the euglycemic hyperinsulinemic clamp studies, insulin was infused at rates of 0.25 and 1.0 mU/kg/min to achieve insulin levels of approximately 25 and 68 microU/mL, respectively. During low-dose insulin infusion, rates of endogenous hepatic glucose production were equivalently suppressed from basal values of 2.37+/-0.29 and 2.40+/-0.27 mg/kg/min to 0.88+/-0.25 and 0.77+/-0.26 mg/kg/min in the methyltestesterone and control studies respectively. Whole body glucose uptake during low-dose insulin infusion was minimally affected. During the high-dose insulin infusion, endogenous hepatic glucose production was nearly totally suppressed in both groups. However, whole body glucose uptake was reduced from the control value of 6.11+/-0.49 mg/kg/min to 4.93+/-0.44 mg/kg/min during methyltestosterone administration (P < 0.05). Our data demonstrate that androgen excess leads to the development of insulin resistance during both hyperglycemic and euglycemic hyperinsulinemia. These findings provide direct evidence for a relationship between hyperandrogenemia and insulin resistance, and its associated risk factors for cardiovascular disease.