UNDULY ENHANCED RESPONSE TO TOLVAPTAN IN A WOMAN SHOWING SYNDROME OF INAPPROPRIATE ANTIDIURETIC HORMONE SECRETION: AN INVESTIGATION OF POSSIBLE CAUSES

Objective: To investigate possible causes of an excessive response to tolvaptan in a woman with syndrome of inappropriate antidiuretic hormone secretion (SIADH). Methods: A 32-year-old woman was admitted to our cardiologic unit 3 months after delivery for hypertension and severe hyponatremia (120 mEq/L). Two hyponatremic episodes had already been documented in her medical history. SIADH was diagnosed and treatment with tolvaptan, an arginine vasopressin (AVP) antagonist, was instituted. After the first 15-mg dose, excessive polyuria (1 L/ hour) and a rapid increase in serum sodium (13 mEq/L in 8 hours) occurred, so that therapy was stopped and restarted 2 days later at a reduced dose (5 mg). This level was effective and well tolerated. To explore the possible pharmacokinetic and pharmacodynamic mechanisms underlying the patient\u2019s hyperresponsiveness, the following tests were carried out: (1) in vivo phenotyping of CYP3A4 activity, the cytochrome responsible for tolvaptan metabolism, with two probe drugs (omeprazole and dextromethorphan); and (2) search for mutations in genes involved in AVP signaling (AVP, V2R, AQP2, OXT)

Arginine 107 of yeast ATP synthase subunit g mediates sensitivity of the mitochondrial permeability transition to phenylglyoxal

Modification with arginine-specific glyoxals modulates the permeability transition (PT) of rat liver mitochondria, with inhibitory or inducing effects that depend on the net charge of the adduct(s). Here, we show that phenylglyoxal (PGO) affects the PT in a species-specific manner (inhibition in mouse and yeast, induction in human and Drosophila mitochondria). Following the hypotheses (i) that the effects are mediated by conserved arginine(s) and (ii) that the PT is mediated by the F-ATP synthase, we have narrowed the search to 60 arginines. Most of these residues are located in subunits alpha, beta, gamma, epsilon, a, and c and were excluded because PGO modification did not significantly affect enzyme catalysis. On the other hand, yeast mitochondria lacking subunit g or bearing a subunit g R107A mutation were totally resistant to PT inhibition by PGO. Thus, the effect of PGO on the PT is specifically mediated by Arg-107, the only subunit g arginine that has been conserved across species. These findings are evidence that the PT is mediated by F-ATP synthase.Peer reviewe

Channel formation by yeast F-ATP synthase and the role of dimerization in the mitochondrial permeability transition

Purified F-ATP synthase dimers of yeast mitochondria display Ca(2+)-dependent channel activity with properties resembling those of the permeability transition pore (PTP) of mammals. After treatment with the Ca(2+) ionophore ETH129, which allows electrophoretic Ca(2+) uptake, isolated yeast mitochondria undergo inner membrane permeabilization due to PTP opening. Yeast mutant strains \u394TIM11 and \u394ATP20 (lacking the e and g F-ATP synthase subunits, respectively, which are necessary for dimer formation) display a striking resistance to PTP opening. These results show that the yeast PTP originates from F-ATP synthase and indicate that dimerization is required for pore formation in situ

Haploinsufficiency of COQ4 causes coenzyme Q10 deficiency

PMCID: PMC3983946.-- et al.[Background]: COQ4 encodes a protein that organises the multienzyme complex for the synthesis of coenzyme Q10 (CoQ10). A 3.9 Mb deletion of chromosome 9q34.13 was identified in a 3-year-old boy with mental retardation, encephalomyopathy and dysmorphic features. Because the deletion encompassed COQ4, the patient was screened for CoQ10 deficiency. [Methods]: A complete molecular and biochemical characterisation of the patient's fibroblasts and of a yeast model were performed. [Results]: The study found reduced COQ4 expression (48% of controls), CoQ10 content and biosynthetic rate (44% and 43% of controls), and activities of respiratory chain complex II+III. Cells displayed a growth defect that was corrected by the addition of CoQ10 to the culture medium. Knockdown of COQ4 in HeLa cells also resulted in a reduction of CoQ10. Diploid yeast haploinsufficient for COQ4 displayed similar CoQ deficiency. Haploinsufficency of other genes involved in CoQ10 biosynthesis does not cause CoQ deficiency, underscoring the critical role of COQ4. Oral CoQ10 supplementation resulted in a significant improvement of neuromuscular symptoms, which reappeared after supplementation was temporarily discontinued. [Conclusion]: Mutations of COQ4 should be searched for in patients with CoQ10 deficiency and encephalomyopathy; patients with genomic rearrangements involving COQ4 should be screened for CoQ10 deficiency, as they could benefit from supplementation.This work was supported by Telethon Italy grant no GGP09207, CARIPARO foundation, the Spanish Ministerio de Sanidad (FIS) grant no PI 08/0500, University of Padova grant no 2010-CPDA102953, Italian Ministry of Health grant no GR-2009-1578914, National Institute of Health grant nos 1R01HD057543-01 and HD 32062, and Cariplo Foundation grant no 2007.5197.Peer reviewe

High-Conductance Channel Formation in Yeast Mitochondria is Mediated by F-ATP Synthase e and g Subunits

Background/Aims: The permeability transition pore (PTP) is an unselective, Ca2+-dependent high conductance channel of the inner mitochondrial membrane whose molecular identity has long remained a mystery. The most recent hypothesis is that pore formation involves the F-ATP synthase, which consistently generates Ca2+-activated channels. Available structures do not display obvious features that can accommodate a channel; thus, how the pore can form and whether its activity can be entirely assigned to F-ATP synthase is the matter of debate. In this study, we investigated the role of F-ATP synthase subunits e, g and b in PTP formation. Methods: Yeast null mutants for e, g and the first transmembrane (TM) α-helix of subunit b were generated and evaluated for mitochondrial morphology (electron microscopy), membrane potential (Rhodamine123 fluorescence) and respiration (Clark electrode). Homoplasmic C23S mutant of subunit a was generated by in vitro mutagenesis followed by biolistic transformation. F-ATP synthase assembly was evaluated by BN-PAGE analysis. Cu2+ treatment was used to induce the formation of F-ATP synthase dimers in the absence of e and g subunits. The electrophysiological properties of F-ATP synthase were assessed in planar lipid bilayers. Results: Null mutants for the subunits e and g display dimer formation upon Cu2+ treatment and show PTP-dependent mitochondrial Ca2+ release but not swelling. Cu2+ treatment causes formation of disulfide bridges between Cys23 of subunits a that stabilize dimers in absence of e and g subunits and favors the open state of wild-type F-ATP synthase channels. Absence of e and g subunits decreases conductance of the F-ATP synthase channel about tenfold. Ablation of the first TM of subunit b, which creates a distinct lateral domain with e and g, further affected channel activity. Conclusion: F-ATP synthase e, g and b subunits create a domain within the membrane that is critical for the generation of the high-conductance channel, thus is a prime candidate for PTP formation. Subunits e and g are only present in eukaryotes and may have evolved to confer this novel function to F-ATP synthase

Studio di una putativa proteasi nucleare essenziale per la cellula di lievito e conservata dagli archebatteri all'uomo

In questo lavoro analizziamo alcune caratteristiche della proteina Kae1 di Saccharomyces cerevisiae. Essa \ue8 codificata da un gene essenziale ed \ue8 classificata come metallo-proteasi in base all\u2019omologia di sequenza con una O-Sialo-Glico-Endo-Peptidasi di Pasteurella haemolytica. Kae1, che \ue8 localizzata prevalentemente nel nucleo, fa parte di un complesso multi proteico al quale appartiene anche la proteina piD261/Bud32. Quest\u2019ultima \ue8 una Ser-Thr protein chinasi appartenente ad una sub famiglia, molto conservata, originatasi prima della divergenza tra Archebatteri ed Eucarioti. Il suo ruolo nel lievito \ue8 essenziale per la normale crescita cellulare e anche l\u2019omologo umano, PRPK, \ue8 probabilmente coinvolto nel controllo della crescita cellulare, dal momento che \ue8 in grado di fosforilare p53 in corrispondenza di Ser-15, evento che porta al blocco del ciclo cellulare in seguito a danni al DNA. Anche la sequenza di Kae1 \ue8 molto conservata ed il suo omolog umano \ue8 chiamato OSGEP. Qui mostreremo come PRPK e OSGEP siano omologhi funzionali delle corrispondenti proteine di lievito, grazie a saggi di complementazione fenotipica e anche che le due proteine PRPK e OSGEP sono in grado di interagire tra loro a supporto di un rilevante significato fisiologico di tale interazione. Dimostreremo inoltre che il mantenimento del motivo di legame al metallo HCIGH in Kae1 e OSGEP \ue8 correlato all\u2019attivit\ue0 di tali proteine, dato che la sostituzione delle due istidine causa un fenotipo letale indistinguibile dalla delezione genica. Il nostro interesse \ue8 rivolto anche alla caratterizzazione del legame del metallo, data la particolarit\ue0 della presenza inusuale di una cisteina nel motivo. L\u2019aspettativa \ue8 quella di dimostrare l\u2019attivit\ue0 catalitica in vitro della putativa proteasi Kae1 isolata da lievito e di confermare il legame dello ione metallico, definendo i residui coinvolti in tale legame, attraverso saggi di assorbimento atomico sulle proteine, di tipo selvatico e mutanti, espresse in E. coli