Rhodamine 123 as a probe of mitochondrial membrane potential: evaluation of proton flux through F0 during ATP synthesis

AbstractRhodamine 123 (RH-123) was used to monitor the membrane potential of mitochondria isolated from rat liver. Mitochondrial energization induces quenching of RH-123 fluorescence and the rate of fluorescence decay is proportional to the mitochondrial membrane potential. Exploiting the kinetics of RH-123 fluorescence quenching in the presence of succinate and ADP, when protons are both pumped out of the matrix driven by the respiratory chain complexes and allowed to diffuse back into the matrix through ATP synthase during ATP synthesis, we could obtain an overall quenching rate proportional to the steady-state membrane potential under state 3 condition. We measured the kinetics of fluorescence quenching by adding succinate and ADP in the absence and presence of oligomycin, which abolishes the ADP-driven potential decrease due to the back-flow of protons through the ATP synthase channel, F0. As expected, the initial rate of quenching was significantly increased in the presence of oligomycin, and conversely preincubation with subsaturating concentrations of the uncoupler carbonyl cyanide p-trifluoro-metoxyphenilhydrazone (FCCP) induced a decreased rate of quenching. N,N′-dicyclohexylcarbodiimide (DCCD) behaved similarly to oligomycin in increasing the rate of quenching. These findings indicate that RH-123 fluorescence quenching kinetics give reliable and sensitive evaluation of mitochondrial membrane potential, complementing steady-state fluorescence measurements, and provide a mean to study proton flow from the mitochondrial intermembrane space to the matrix through the F0 channel

Conformational changes of the mitochondrial F1-ATPase epsilon-subunit induced by nucleotide binding as observed by phosphorescence spectroscopy.

Changes in conformation of the epsilon-subunit of the bovine heart mitochondrial F1-ATPase complex as a result of nucleotide binding have been demonstrated from the phosphorescence emission of tryptophan. The triplet state lifetime shows that whereas nucleoside triphosphate binding to the enzyme in the presence of Mg2+ increases the flexibility of the protein structure surrounding the chromophore, nucleoside diphosphate acts in an opposite manner, enhancing the rigidity of this region of the macromolecule. Such changes in dynamic structure of the epsilon-subunit are evident at high ligand concentration added to both the nucleotide-depleted F1 (Nd-F1) and the F1 preparation containing the three tightly bound nucleotides (F1(2,1)). Since the effects observed are similar in both the F1 forms, the binding to the low affinity sites must be responsible for the conformational changes induced in the epsilon-subunit. This is partially supported by the observation that the Trp lifetime is not significantly affected by adding an equimolar concentration of adenine nucleotide to Nd-F1. The effects on protein structure of nucleotide binding to either catalytic or noncatalytic sites have been distinguished by studying the phosphorescence emission of the F1 complex prepared with the three noncatalytic sites filled and the three catalytic sites vacant (F1(3,0)). Phosphorescence lifetime measurements on this F1 form demonstrate that the binding of Mg-NTP to catalytic sites induces a slight enhancement of the rigidity of the epsilon-subunit. This implies that the binding to the vacant noncatalytic site of F1(2,1) must exert the opposite and larger effect of enhancing the flexibility of the protein structure observed in both Nd-F1 and F1(2,1). The observation that enhanced flexibility of the protein occurs upon addition of adenine nucleotides to F1(2,1) in the absence of Mg2+ provides direct support for this suggestion. The connection between changes in structure and the possible functional role of the epsilon-subunit is discussed

Stability of Oscillating Gaseous Masses in Massive Brans-Dicke Gravity

This paper explores the instability of gaseous masses for the radial oscillations in post-Newtonian correction of massive Brans-Dicke gravity. For this purpose, we derive linearized perturbed equation of motion through Lagrangian radial perturbation which leads to the condition of marginal stability. We discuss radius of instability of different polytropic structures in terms of the Schwarzschild radius. It is concluded that our results provide a wide range of difference with those in general relativity and Brans-Dicke gravity.Comment: 31 pages, 11 figures, to appear in IJMP

The F1Fo-ATPase inhibitor protein IF1 in pathophysiology

The endogenous inhibitor of ATP synthase is a protein of about 10 kDa, known as IF1 which binds to the catalytic domain of the enzyme during ATP hydrolysis. The main role of IF1 consists of limiting ATP dissipation under condition of severe oxygen deprivation or in the presence of dysfunctions of mitochondrial respiratory complexes, causing a collapse in mitochondrial membrane potential and therefore ATP hydrolysis. New roles of IF1 are emerging in the fields of cancer and neurodegeneration. Its high expression levels in tumor tissues have been associated with different roles favouring tumor formation, progression and evasion. Since discordant mechanisms of action have been proposed for IF1 in tumors, it is of the utmost importance to clarify them in the prospective of defining novel approaches for cancer therapy. Other IF1 functions, including its involvement in mitophagy, may be protective for neurodegenerative and aging-related diseases. In the present review we aim to clarify and discuss the emerging mechanisms in which IF1 is involved, providing a critical view of the discordant findings in the literature

Catalytic activities of mitochondrial ATP synthase in patients with mitochondrial DNA T8993G mutation in the ATPase 6 gene encoding subunit a.

We investigated the biochemical phenotype of the mtDNA T8993G point mutation in the ATPase 6 gene, associated with neurogenic muscle weakness, ataxia, and retinitis pigmentosa (NARP), in three patients from two unrelated families. All three carried >80% mutant genome in platelets and were manifesting clinically various degrees of the NARP phenotype. Coupled submitochondrial particles prepared from platelets capable of succinate-sustained ATP synthesis were studied using very sensitive and rapid luminometric and fluorescence methods. A sharp decrease (>95%) in the succinate-sustained ATP synthesis rate of the particles was found, but both the ATP hydrolysis rate and ATP-driven proton translocation (when the protons flow from the matrix to the cytosol) were minimally affected. The T8993G mutation changes the highly conserved residue Leu(156) to Arg in the ATPase 6 subunit (subunit a). This subunit, together with subunit c, is thought to cooperatively catalyze proton translocation and rotate, one with respect to the other, during the catalytic cycle of the F(1)F(0) complex. Our results suggest that the T8993G mutation induces a structural defect in human F(1)F(0)-ATPase that causes a severe impairment of ATP synthesis. This is possibly due to a defect in either the vectorial proton transport from the cytosol to the mitochondrial matrix or the coupling of proton flow through F(0) to ATP synthesis in F(1). Whatever mechanism is involved, this leads to impaired ATP synthesis. On the other hand, ATP hydrolysis that involves proton flow from the matrix to the cytosol is essentially unaffected

Robotic versus laparoscopic left colectomy: a systematic review and meta-analysis

Background: This study aimed to review the new evidence to understand whether the robotic approach could find some clear indication also in left colectomy. Methods: A systematic review of studies published from 2004 to 2022 in the Web of Science, PubMed, and Scopus databases and comparing laparoscopic (LLC) and robotic left colectomy (RLC) was performed. All comparative studies evaluating robotic left colectomy (RLC) versus laparoscopic (LLC) left colectomy with at least 20 patients in the robotic arm were included. Abstract, editorials, and reviews were excluded. The Newcastle–Ottawa Scale for cohort studies was used to assess the methodological quality. The random-effect model was used to calculate pooled effect estimates. Results: Among the 139 articles identified, 11 were eligible, with a total of 52,589 patients (RLC, n = 13,506 versus LLC, n = 39,083). The rate of conversion to open surgery was lower for robotic procedures (RR 0.5, 0.5–0.6; p < 0.001). Operative time was longer for the robotic procedures in the pooled analysis (WMD 39.1, 17.3–60.9, p = 0.002). Overall complications (RR 0.9, 0.8–0.9, p < 0.001), anastomotic leaks (RR 0.7, 0.7–0.8; p < 0.001), and superficial wound infection (RR 3.1, 2.8–3.4; p < 0.001) were less common after RLC. There were no significant differences in mortality (RR 1.1; 0.8–1.6, p = 0.124). There were no differences between RLC and LLC with regards to postoperative variables in the subgroup analysis on malignancies. Conclusions: Robotic left colectomy requires less conversion to open surgery than the standard laparoscopic approach. Postoperative morbidity rates seemed to be lower during RLC, but this was not confirmed in the procedures performed for malignancies

The pro-oncogenic protein IF1 does not contribute to the Warburg effect and is not regulated by PKA in cancer cells

: The endogenous inhibitor of mitochondrial F1Fo-ATPase (ATP synthase), IF1, has been shown to exert pro-oncogenic actions, including reprogramming of cellular energy metabolism (Warburg effect). The latter action of IF1 has been reported to be hampered by its PKA-dependent phosphorylation, but both reprogramming of metabolism and PKA-dependent phosphorylation are intensely debated. To clarify these critical issues, we prepared stably IF1-silenced clones and compared their bioenergetics with that of the three parental IF1-expressing cancer cell lines. All functional parameters: respiration rate, ATP synthesis rate (OXPHOS), and mitochondrial membrane potential were similar in IF1-silenced and control cells, clearly indicating that IF1 cannot inhibit the ATP synthase in cancer cells when the enzyme works physiologically. Furthermore, all cell types exposed to PKA modulators and energized with NAD+-dependent substrates or succinate showed similar OXPHOS rate regardless of the presence or absence of IF1. Therefore, our results rule out that IF1 action is modulated by its PKA-dependent phosphorylated/dephosphorylated state. Notably, cells exposed to a negative PKA modulator and energized with NAD+-dependent substrates showed a significant decrease of the OXPHOS rate matching previously reported inactivation of complex I. Overall, this study definitively demonstrates that IF1 inhibits neither mitochondrial ATP synthase nor OXPHOS in normoxic cancer cells and does not contribute to the Warburg effect. Thus, currently the protection of cancer cells from severe hypoxia/anoxia and apoptosis remain the only unquestionable actions of IF1 as pro-oncogenic factor that may be exploited to develop therapeutic approaches

Implementation of a patient blood management in an Italian City Hospital: is it effective in reducing the use of red blood cells?

To evaluate the effect of patient blood management (PBM) since its introduction, we analyzed the need for transfusion and the outcomes in patients undergoing abdominal surgery for different types of tumor pre- and post-PBM. Patients undergoing elective gastric, liver, pancreatic, and colorectal surgery between 2017 and 2020 were included. The implementation of the PBM program was completed on May 1, 2018. The patients were grouped as follows: those who underwent surgery before the implementation of the program (pre-PBM) versus after the implementation (post-PBM). A total of 1302 patients were included in the analysis (445 pre-PBM vs. 857 post-PBM). The number of transfused patients per year decreased significantly after the introduction of PBM. A strong tendency for a decreased incidence of transfusion was evident in gastric and pancreatic surgery and a similar decrease was statistically significant in liver surgery. With regard to gastric surgery, a single-unit transfusion scheme was used more frequently in the post-PBM group (7.7% vs. 55% after PBM; p = 0.049); this was similar in liver surgery (17.6% vs. 58.3% after PBM; p = 0.04). Within the subgroup of patients undergoing liver surgery, a significant reduction in the use of blood transfusion (20.5% vs. 6.7%; p = 0.002) and a decrease in the Hb trigger for transfusion (8.5, 8.2-9.5 vs. 8.2, 7.7-8.4 g/dl; p = 0.039) was reported after the PBM introduction. After the implementation of a PBM protocol, a significant reduction in the number of patients receiving blood transfusion was demonstrated, with a strong tendency to minimize the use of blood products for most types of oncologic surgery