Biomarkers for clinical and incipient tuberculosis: performance in a TB-endemic country

Background

Simple biomarkers are required to identify TB in both HIV⁻TB⁺ and HIV⁺TB⁺ patients. Earlier studies have identified the M. tuberculosis Malate Synthase (MS) and MPT51 as immunodominant antigens in TB patients. One goal of these investigations was to evaluate the sensitivity and specificity of anti-MS and –MPT51 antibodies as biomarkers for TB in HIV⁻TB⁺ and HIV⁺TB⁺ patients from a TB-endemic setting. Earlier studies also demonstrated the presence of these biomarkers during incipient subclinical TB. If these biomarkers correlate with incipient TB, their prevalence should be higher in asymptomatic HIV⁺ subjects who are at a high-risk for TB. The second goal was to compare the prevalence of these biomarkers in asymptomatic, CD4⁺ T cell-matched HIV⁺TB⁻ subjects from India who are at high-risk for TB with similar subjects from US who are at low-risk for TB.

Methods and Results

Anti-MS and -MPT51 antibodies were assessed in sera from 480 subjects including PPD⁺ or PPD⁻ healthy subjects, healthy community members, and HIV⁻TB⁺ and HIV⁺TB⁺ patients from India. Results demonstrate high sensitivity (∼80%) of detection of smear-positive HIV⁻TB⁺ and HIV⁺TB⁺ patients, and high specificity (>97%) with PPD⁺ subjects and endemic controls. While ∼45% of the asymptomatic HIV⁺TB⁻ patients at high-risk for TB tested biomarker-positive, >97% of the HIV⁺TB⁻ subjects at low risk for TB tested negative. Although the current studies are hampered by lack of knowledge of the outcome, these results provide strong support for the potential of these biomarkers to detect incipient, subclinical TB in HIV⁺ subjects.

Conclusions

These biomarkers provide high sensitivity and specificity for TB diagnosis in a TB endemic setting. Their performance is not compromised by concurrent HIV infection, site of TB and absence of pulmonary manifestations in HIV⁺TB⁺ patients. Results also demonstrate the potential of these biomarkers for identifying incipient subclinical TB in HIV⁺TB⁻ subjects at high-risk for TB.     

Training-specific changes in cardiac structure and function: a prospective and longitudinal assessment of competitive athletes.

This prospective, longitudinal study examined the effects of participation in team-based exercise training on cardiac structure and function. Competitive endurance athletes (EA, n = 40) and strength athletes (SA, n = 24) were studied with echocardiography at baseline and after 90 days of team training. Left ventricular (LV) mass increased by 11% in EA (116 +/- 18 vs. 130 +/- 19 g/m(2); P < 0.001) and by 12% in SA (115 +/- 14 vs. 132 +/- 11 g/m(2); P < 0.001; P value for the compared Delta = NS). EA experienced LV dilation (end-diastolic volume: 66.6 +/- 10.0 vs. 74.7 +/- 9.8 ml/m(2), Delta = 8.0 +/- 4.2 ml/m(2); P < 0.001), enhanced diastolic function (lateral E': 10.9 +/- 0.8 vs. 12.4 +/- 0.9 cm/s, P < 0.001), and biatrial enlargement, while SA experience LV hypertrophy (posterior wall: 4.5 +/- 0.5 vs. 5.2 +/- 0.5 mm/m(2), P < 0.001) and diminished diastolic function (E' basal lateral LV: 11.6 +/- 1.3 vs. 10.2 +/- 1.4 cm/s, P < 0.001). Further, EA experienced right ventricular (RV) dilation (end-diastolic area: 1,460 +/- 220 vs. 1,650 +/- 200 mm/m(2), P < 0.001) coupled with enhanced systolic and diastolic function (E' basal RV: 10.3 +/- 1.5 vs. 11.4 +/- 1.7 cm/s, P < 0.001), while SA had no change in RV parameters. We conclude that participation in 90 days of competitive athletics produces significant training-specific changes in cardiac structure and function. EA develop biventricular dilation with enhanced diastolic function, while SA develop isolated, concentric left ventricular hypertrophy with diminished diastolic relaxation.     

A novel mechanism of G protein-coupled receptor functional selectivity. Muscarinic partial agonist McN-A-343 as a bitopic orthosteric/allosteric ligand

Many G protein-coupled receptors (GPCRs) possess allosteric binding sites distinct from the orthosteric site utilized by their cognate ligands, but most GPCR allosteric modulators reported to date lack signaling efficacy in their own right. McN-A-343 (4-(N-(3-chlorophenyl)carbamoyloxy)-2-butynyltrimethylammonium chloride) is a functionally selective muscarinic acetylcholine receptor (mAChR) partial agonist that can also interact allosterically at the M(2) mAChR. We hypothesized that this molecule simultaneously utilizes both an allosteric and the orthosteric site on the M(2) mAChR to mediate these effects. By synthesizing progressively truncated McN-A-343 derivatives, we identified two, which minimally contain 3-chlorophenylcarbamate, as pure allosteric modulators. These compounds were positive modulators of the orthosteric antagonist N-[(3)H]methylscopolamine, but in functional assays of M(2) mAChR-mediated ERK1/2 phosphorylation and guanosine 5'-3-O-([(35)S]thio)triphosphate binding, they were negative modulators of agonist efficacy. This negative allosteric effect was diminished upon mutation of Y177A in the second extracellular (E2) loop of the M(2) mAChR that is known to reduce prototypical allosteric modulator potency. Our results are consistent with McN-A-343 being a bitopic orthosteric/allosteric ligand with the allosteric moiety engendering partial agonism and functional selectivity. This finding suggests a novel and largely unappreciated mechanism of "directed efficacy" whereby functional selectivity may be engendered in a GPCR by utilizing an allosteric ligand to direct the signaling of an orthosteric ligand encoded within the same molecule.     

Selective targeting of leukemic cell growth in vivo and in vitro using a gene silencing approach to diminish S-adenosylmethionine synthesis

We exploited the fact that leukemic cells utilize significantly higher levels of S-adenosylmethionine (SAMe) than normal lymphocytes and developed tools that selectively diminished their survival under physiologic conditions. Using RNA interference gene silencing technology, we modulated the kinetics of methionine adenosyltransferase-II (MAT-II), which catalyzes SAMe synthesis from ATP and l-Met. Specifically, we silenced the expression of the regulatory MAT-IIbeta subunit in Jurkat cells and accordingly shifted the K(m L-Met) of the enzyme 10-15-fold above the physiologic levels of l-Met, thereby reducing enzyme activity and SAMe pools, inducing excessive apoptosis and diminishing leukemic cell growth in vitro and in vivo. These effects were reversed at unphysiologically high l-Met (>50 microm), indicating that diminished leukemic cell growth at physiologic l-Met levels was a direct result of the increase in MAT-II K(m L-Met) due to MAT-IIbeta ablation and the consequent reduction in SAMe synthesis. In our NOD/Scid IL-2Rgamma(null) humanized mouse model of leukemia, control shRNA-transduced Jurkat cells exhibited heightened engraftment, whereas cells lacking MAT-IIbeta failed to engraft for up to 5 weeks post-transplant. These stark differences in malignant cell survival, effected by MAT-IIbeta ablation, suggest that it may be possible to use this approach to disadvantage leukemic cell survival in vivo with little to no harm to normal cells.     

Role of N-acetylglucosaminidase and N-acetylmuramidase activities in Enterococcus faecalis peptidoglycan metabolism

Identification of the full complement of peptidoglycan hydrolases detected by zymogram in Enterococcus faecalis extracts led to the characterization of two novel hydrolases that we named AtlB and AtlC. Both enzymes have a similar modular organization comprising a central catalytic domain fused to two LysM peptidoglycan-binding modules. AtlB and AtlC displayed N-acetylmuramidase activity, as demonstrated by tandem mass spectrometry analyses of peptidoglycan fragments generated by the purified enzymes. The genes encoding AtlB and AtlC were deleted either alone or in combination with the gene encoding AtlA, a previously described N-acetylglucosaminidase. No autolytic activity was detected in the triple mutant indicating that AtlA, AtlB, and AtlC account for the major hydrolytic activities in E. faecalis. Analysis of cell size distribution by flow cytometry showed that deletion of atlA resulted in the formation of long chains. Thus, AtlA digests the septum and is required for cell separation after cell division. We found that AtlB could act as a surrogate for AtlA, although the enzyme was less efficient at septum digestion. Deletion of atlC had no impact on cell morphology. Labeling of the peptidoglycan with N-[14C]acetylglucosamine revealed an unusually slow turnover as compared with model organisms, almost completely dependent upon the combined activities of AtlA and AtlB. In contrast to atlA, the atlB and atlC genes are located in putative prophages. Because AtlB and AtlC were produced in the absence of cell lysis or production of phage progeny, these enzymes may have been hijacked by E. faecalis to contribute to peptidoglycan metabolism.     

Ziram causes dopaminergic cell damage by inhibiting E1 ligase of the proteasome

The etiology of Parkinson disease (PD) is unclear but may involve environmental toxins such as pesticides leading to dysfunction of the ubiquitin proteasome system (UPS). Here, we measured the relative toxicity of ziram (a UPS inhibitor) and analogs to dopaminergic neurons and examined the mechanism of cell death. UPS (26 S) activity was measured in cell lines after exposure to ziram and related compounds. Dimethyl- and diethyldithiocarbamates including ziram were potent UPS inhibitors. Primary ventral mesencephalic cultures were exposed to ziram, and cell toxicity was assessed by staining for tyrosine hydroxylase (TH) and NeuN antigen. Ziram caused a preferential damage to TH+ neurons and elevated alpha-synuclein levels but did not increase aggregate formation. Mechanistically, ziram altered UPS function through interfering with the targeting of substrates by inhibiting ubiquitin E1 ligase. Sodium dimethyldithiocarbamate administered to mice for 2 weeks resulted in persistent motor deficits and a mild reduction in striatal TH staining but no nigral cell loss. These results demonstrate that ziram causes selective dopaminergic cell damage in vitro by inhibiting an important degradative pathway implicated in the etiology of PD. Chronic exposure to widely used dithiocarbamate fungicides may contribute to the development of PD, and elucidation of its mechanism would identify a new potential therapeutic target.     

The amyloid-beta rise and gamma-secretase inhibitor potency depend on the level of substrate expression

The amyloid-beta (Abeta) peptide, which likely plays a key role in Alzheimer disease, is derived from the amyloid-beta precursor protein (APP) through consecutive proteolytic cleavages by beta-site APP-cleaving enzyme and gamma-secretase. Unexpectedly gamma-secretase inhibitors can increase the secretion of Abeta peptides under some circumstances. This "Abeta rise" phenomenon, the same inhibitor causing an increase in Abeta at low concentrations but inhibition at higher concentrations, has been widely observed. Here we show that the Abeta rise depends on the beta-secretase-derived C-terminal fragment of APP (betaCTF) or C99 levels with low levels causing rises. In contrast, the N-terminally truncated form of Abeta, known as "p3," formed by alpha-secretase cleavage, did not exhibit a rise. In addition to the Abeta rise, low betaCTF or C99 expression decreased gamma-secretase inhibitor potency. This "potency shift" may be explained by the relatively high enzyme to substrate ratio under conditions of low substrate because increased concentrations of inhibitor would be necessary to affect substrate turnover. Consistent with this hypothesis, gamma-secretase inhibitor radioligand occupancy studies showed that a high level of occupancy was correlated with inhibition of Abeta under conditions of low substrate expression. The Abeta rise was also observed in rat brain after dosing with the gamma-secretase inhibitor BMS-299897. The Abeta rise and potency shift are therefore relevant factors in the development of gamma-secretase inhibitors and can be evaluated using appropriate choices of animal and cell culture models. Hypothetical mechanisms for the Abeta rise, including the "incomplete processing" and endocytic models, are discussed.