The coupling of metabolic to secretory events in pancreatic islets. The possible role of glutathione reductase

The participation of glutathione reductase in the process of nutrient-stimulated insulin release was investigated in rat pancreatic islets exposed to 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU). BCNU caused a time-and dose-related, irreversible inhibition of glutathione reductase activity. This coincided with a fall in both GSH/GSSG ratio and the thiol content of the islets. Pretreatment of the islets with BCNU inhibited the oxidation of glucose and its stimulant action upon both 45Ca net uptake and insulin release. Although BCNU (up to 0.5 mM) failed to affect the oxidation of L-leucine and L-glutamine, it also caused a dose-related inhibition of insulin release evoked by the combination of these two amino acids. The latter inhibition was apparently not fully accounted for by the modest to negligible effects of BCNU upon 45Ca uptake, 45Ca efflux, 86Rb efflux and cyclic AMP production. Since BCNU failed to inhibit insulin release evoked by the association of Ba2+ and theophylline, these results support the view that glutathione reductase participates in the coupling of metabolic to secretory events in the process of nutrient-stimulated insulin release. However, the precise modality of such a participation, for example the control of intracellular Ca2+ distribution, remains to be elucidated.     

Mycobacterium tuberculosis lipolytic enzymes as potential biomarkers for the diagnosis of active tuberculosis

Background

New diagnosis tests are urgently needed to address the global tuberculosis (TB) burden and to improve control programs especially in resource-limited settings. An effective in vitro diagnostic of TB based on serological methods would be regarded as an attractive progress because immunoassays are simple, rapid, inexpensive, and may offer the possibility to detect cases missed by standard sputum smear microscopy. However, currently available serology tests for TB are highly variable in sensitivity and specificity. Lipolytic enzymes have recently emerged as key factors in lipid metabolization during dormancy and/or exit of the non-replicating growth phase, a prerequisite step of TB reactivation. The focus of this study was to analyze and compare the potential of four Mycobacterium tuberculosis lipolytic enzymes (LipY, Rv0183, Rv1984c and Rv3452) as new markers in the serodiagnosis of active TB.

Methods

Recombinant proteins were produced and used in optimized ELISA aimed to detect IgG and IgM serum antibodies against the four lipolytic enzymes. The capacity of the assays to identify infection was evaluated in patients with either active TB or latent TB and compared with two distinct control groups consisting of BCG-vaccinated blood donors and hospitalized non-TB individuals.

Results

A robust humoral response was detected in patients with active TB whereas antibodies against lipolytic enzymes were infrequently detected in either uninfected groups or in subjects with latent infection. High specifity levels, ranging from 93.9% to 97.5%, were obtained for all four antigens with sensitivity values ranging from 73.4% to 90.5%, with Rv3452 displaying the highest performances. Patients with active TB usually exhibited strong IgG responses but poor IgM responses.

Conclusion

These results clearly indicate that the lipolytic enzymes tested are strongly immunogenic allowing to distinguish active from latent TB infections. They appear as potent biomarkers providing high sensitivity and specificity levels for the immunodiagnosis of active TB.     

Real-Time PCR for the Detection and Quantification of Geodermatophilaceae from Stone Samples and Identification of New Members of the Genus Blastococcus

Real-time PCR (RT-PCR) technology was used for the specific detection and quantification of members of the family Geodermatophilaceae in stone samples. Differences in the nucleotide sequences of the 16S rRNA gene region were used to design a pair of family-specific primers that were used to detect and quantify by RT-PCR DNA from members of this family in stone samples from different geographical origins in Spain. These primers were applied later to identify by PCR-specific amplification new members of the family Geodermatophilaceae isolated from the same stone samples. The diversity and taxonomic position of the wild-type strains identified from ribosomal sequence analysis suggest the presence of a new lineage within the genus Blastococcus.     

Characteristic of GLP-1 effects on glucose metabolism in human skeletal muscle from obese patients

Direct effects of GLP-1, kinase-mediated, on glucose and lipid metabolism in rat and human extrapancreatic tissues, are amply documented and also changes in type-2 diabetic (T2D) patients. Here, we explored the characteristics of the GLP-1 action and those of its analogs Ex-4 and Ex-9, on muscle glucose transport (GT) and metabolism in human morbid obesity (OB), as compared with normal and T2D subjects. In primary cultured myocytes from OB, GT and glycogen synthase a (GSa) activity values were lower than normal, and comparable to those reported in T2D patients; GT was increased by either GLP-1 or Ex-9 in a more efficient manner than in normal or T2D, up to normal levels; the Ex-4 increasing effect on GSa activity was two times that in normal cells, while Ex-9 failed to modify the enzyme activity. In OB, the control value of all kinases analyzed - PI3K, PKB, MAPKs, and p70s6K - although lower than that in normal or T2D subjects, the cells maintained their response capability to GLP-1, Ex-4, Ex-9 and insulin, with some exceptions. GLP-1 and exendins showed a direct normalizing action in the altered glucose uptake and metabolism in the muscle of obese subjects, which in the case of GLP-1 could account, at least in part, for the reported restoration of the metabolic conditions of these patients after restrictive surgery.     

Geographic association and temporal variation of chemical and physical defense and leaf damage in Datura stramonium

The evolution of plant defense traits has traditionally been explained trough the “coevolutionary arms race” between plants and herbivores. According to this, specialist herbivores have evolved to cope effectively with the defensive traits of their host plants and may even use them as a cue for host location. We analyzed the geographic association between leaf trichomes, two tropane alkaloids (putative resistance traits), and leaf damage by herbivores in 28 populations of Datura stramonium in central Mexico. Since the specialist leaf beetles Epitrix parvula and Lema trilineata are the main herbivores of D. stramonium in central Mexico, we predicted a positive association between plant defense and leaf damage across populations. Also, if physical environmental conditions (temperature or precipitation) constrain the expression of plant defense, then the geographic variation in leaf damage should be explained partially by the interaction between defensive traits and environmental factors. Furthermore, we studied the temporal and spatial variation in leaf trichome density and leaf damage in five selected populations of D. stramonium sampled in two periods (1997 vs. 2007). We found a positive association between leaf trichomes density and atropine concentration with leaf damage across populations. The interaction between defensive traits and water availability in each locality had a significant effect on the geographic variation in leaf damage. Differences among populations in leaf trichome density are maintained over time. Our results indicate that local plant–herbivore interaction plays an important role in shaping the geographic and temporal variation in plant defense in D. stramonium.