ATP/ADP Turnover and Import of Glycolytic ATP into Mitochondria in Cancer Cells Is Independent of the Adenine Nucleotide Translocator.

Non-proliferating cells oxidize respiratory substrates in mitochondria to generate a protonmotive force (Δp) that drives ATP synthesis. The mitochondrial membrane potential (ΔΨ), a component of Δp, drives release of mitochondrial ATP(4-) in exchange for cytosolic ADP(3-) via the electrogenic adenine nucleotide translocator (ANT) located in the mitochondrial inner membrane, which leads to a high cytosolic ATP/ADP ratio up to >100-fold greater than matrix ATP/ADP. In rat hepatocytes, ANT inhibitors, bongkrekic acid (BA), and carboxyatractyloside (CAT), and the F1FO-ATP synthase inhibitor, oligomycin (OLIG), inhibited ureagenesis-induced respiration. However, in several cancer cell lines, OLIG but not BA and CAT inhibited respiration. In hepatocytes, respiratory inhibition did not collapse ΔΨ until OLIG, BA, or CAT was added. Similarly, in cancer cells OLIG and 2-deoxyglucose, a glycolytic inhibitor, depolarized mitochondria after respiratory inhibition, which showed that mitochondrial hydrolysis of glycolytic ATP maintained ΔΨ in the absence of respiration in all cell types studied. However in cancer cells, BA, CAT, and knockdown of the major ANT isoforms, ANT2 and ANT3, did not collapse ΔΨ after respiratory inhibition. These findings indicated that ANT was not mediating mitochondrial ATP/ADP exchange in cancer cells [corrected]. We propose that suppression of ANT contributes to low cytosolic ATP/ADP, activation of glycolysis, and a Warburg metabolic phenotype in proliferating cells.

Voltage-dependent anion channels modulate mitochondrial metabolism in cancer cells: regulation by free tubulin and erastin.

Respiratory substrates and adenine nucleotides cross the mitochondrial outer membrane through the voltage-dependent anion channel (VDAC), comprising three isoforms--VDAC1, 2, and 3. We characterized the role of individual isoforms in mitochondrial metabolism by HepG2 human hepatoma cells using siRNA. With VDAC3 to the greatest extent, all VDAC isoforms contributed to the maintenance of mitochondrial membrane potential, but only VDAC3 knockdown decreased ATP, ADP, NAD(P)H, and mitochondrial redox state. Cells expressing predominantly VDAC3 were least sensitive to depolarization induced by increased free tubulin. In planar lipid bilayers, free tubulin inhibited VDAC1 and VDAC2 but not VDAC3. Erastin, a compound that interacts with VDAC, blocked and reversed mitochondrial depolarization after microtubule destabilizers in intact cells and antagonized tubulin-induced VDAC blockage in planar bilayers. In conclusion, free tubulin inhibits VDAC1/2 and limits mitochondrial metabolism in HepG2 cells, contributing to the Warburg phenomenon. Reversal of tubulin-VDAC interaction by erastin antagonizes Warburg metabolism and restores oxidative mitochondrial metabolism.

Diagnosis and treatment of pulmonary tuberculosis in one day: Way forward for END TB Strategy 2015.

BACKGROUND: According to Revised National Tuberculosis Control Program (RNTCP), diagnosis of pulmonary tuberculosis (TB) in India requires examination of two sputum samples collected over 2 days, that is, "spot" and next day "morning" samples. OBJECTIVE: To assess the feasibility of diagnosing pulmonary TB by examining two spot sputum samples in 1 day and to compare this approach with the current RNTCP protocol. MATERIALS AND METHOD: A total of 375 subjects having cough >2 weeks were enrolled into the study. Three sputum samples were collected from each of the study participant; first spot (S1), second extra-spot (S2) sample 1 h after collection of the first sample, and third morning (M) sample collected next day morning. These specimens were subjected to standard sputum smear microscopy for acid-fast bacilli as per RNTCP guidelines. For 1-day protocol, results of "S1 and S2" samples and for 2-day protocol results of "S1 and M" samples were considered. RESULTS: The number of sputum-positive pulmonary TB cases diagnosed with standard 2-day protocol was 119, whereas the experimental 1-day protocol diagnosed 120 cases (P = 0.7). Comparing with standard 2-day protocol, this new 1-day protocol had sensitivity 98.32%, specificity 100%, positive predictive value 100%, and negative predictive value 99.17%. CONCLUSION: Single-day method can be adopted as the standard diagnostic approach for pulmonary TB after large-scale multicenter randomized controlled trials.

An unusual case of spontaneous esophagopleural fistula.

Esophago-pleural fistula (EPF) is an uncommon condition, despite of an anatomical proximity of these structures. Causes of EPF include pneumonectomy for suppurative or tubercular disease of lung and carcinoma lung, malignancy of esophagus. Benign EPF is rare and may be due to trauma or infection. The most common infectious cause is tuberculosis. Spontaneous development of fistula between esophagus and pleura is rarely described in literature. We, hereby present a spontaneous case of such a rare entity in a middle-aged male.

A comparative study of status of RNTCP in tribal and non-tribal districts of Odisha.

To compare the RNTCP outreach in the tribal districts with that of non-tribal districts. The annual status reports on RNTCP was analysed to evaluate the performance in tribal districts and non-tribal districts. The case detection parameters were far better in the tribal districts than in the non-tribal districts. Treatment success was almost equal in the tribal districts to that of non-tribal districts.

Free tubulin modulates mitochondrial membrane potential in cancer cells.

Formation of the mitochondrial membrane potential (ΔΨ) depends on flux of respiratory substrates, ATP, ADP, and Pi through voltage-dependent anion channels (VDAC). As tubulin promotes single-channel closure of VDAC, we hypothesized that tubulin is a dynamic regulator of ΔΨ, which in cultured cancer cells was assessed by confocal microscopy of the potential-indicating fluorophore tetramethylrhodamine methylester (TMRM). Microtubule destabilizers, rotenone, colchicine, and nocodazole, and the microtubule stabilizer paclitaxel increased and decreased cellular free tubulin, respectively, and in parallel decreased and increased ΔΨ. Protein kinase A (PKA) activation by cAMP analogues and glycogen synthase kinase 3ß (GSK-3ß) inhibition decreased ΔΨ, whereas PKA inhibition hyperpolarized, consistent with reports that PKA and GSK-3ß decrease and increase VDAC conductance, respectively. Plasma membrane potential assessed by DiBAC(4)(3) was not altered by any of the treatments. We propose that inhibition of VDAC by free tubulin limits mitochondrial metabolism in cancer cells.