ResearchPad - nuclear-physics Default RSS Feed en-us © 2020 Newgen KnowledgeWorks <![CDATA[Radioimmunotherapy of methicillin-resistant <i>Staphylococcus aureus</i> in planktonic state and biofilms]]> Implant associated infections such as periprosthetic joint infections are difficult to treat as the bacteria form a biofilm on the prosthetic material. This biofilm complicates surgical and antibiotic treatment. With rising antibiotic resistance, alternative treatment options are needed to treat these infections in the future. The aim of this article is to provide proof-of-principle data required for further development of radioimmunotherapy for non-invasive treatment of implant associated infections.MethodsPlanktonic cells and biofilms of Methicillin-resistant staphylococcus aureus are grown and treated with radioimmunotherapy. The monoclonal antibodies used, target wall teichoic acids that are cell and biofilm specific. Three different radionuclides in different doses were used. Viability and metabolic activity of the bacterial cells and biofilms were measured by CFU dilution and XTT reduction.ResultsAlpha-RIT with Bismuth-213 showed significant and dose dependent killing in both planktonic MRSA and biofilm. When planktonic bacteria were treated with 370 kBq of 213Bi-RIT 99% of the bacteria were killed. Complete killing of the bacteria in the biofilm was seen at 185 kBq. Beta-RIT with Lutetium-177 and Actinium-225 showed little to no significant killing.ConclusionOur results demonstrate the ability of specific antibodies loaded with an alpha-emitter Bismuth-213 to selectively kill staphylococcus aureus cells in vitro in both planktonic and biofilm state. RIT could therefore be a potentially alternative treatment modality against planktonic and biofilm-related microbial infections. ]]> <![CDATA[Molecular mechanisms of mesoporous silica formation from colloid solution: Ripening-reactions arrest hollow network structures]]>

The agglomeration of silica nanoparticles in aqueous solution is investigated from molecular simulations. Mimicking destabilization of colloidal solutions by full removal of protective moieties or surface charge, association of SiO2/Si(OH)4 core/shell particles leads to rapid proton transfer reactions that account for local silanole → silica ripening reactions. Yet, such virtually barrier-less binding is only observed within a limited contact zone. Agglomeration hence leads to the formation of oligomers of nanoparticles, whilst full merging into a compact precipitate is hampered by the need for extended structural reorganisation. Implementing sufficiently fast supply from colloidal solution, our simulations show the development of silica networks comprised of covalently bound, yet not fully merged nanoparticles. Within the oligomerized nanoparticle network, coordination numbers range from 2 to 5 –which is far below closest packing. Our simulations hence rationalize the formation of covalently bound network structures hosting extended pores. The resulting interfaces to the solvent show water immobilization only for the immediate contact layers, whilst the inner pores exhibit solvent mobility akin to bulk water.

<![CDATA[Issue framing in online voting advice applications: The effect of left-wing and right-wing headers on reported attitudes]]>

Voting Advice Applications (VAAs) provide voting recommendations to millions of people. As these voting recommendations are based on users’ answers to attitude questions, the framing of these questions can have far-reaching consequences. The current study reports on a field experiment in which the framing of the header above VAA statements (N = 17) was manipulated (condition 1: no header; condition 2: a right-wing header, e.g., finance; condition 3: a left-wing header, e.g., nature and environment). Visitors of a VAA developed for Utrecht, the fourth largest municipality in the Netherlands, were randomly guided to one of the versions of the tool in which the header type was varied. Results (based on Nrespondents = 27,404) show that providing a header (left-wing or right-wing) leads to more left-wing answers as compared a condition where there is no header above the attitude statement. This effect, however, is only observed for respondents with lower levels of political sophistication.

<![CDATA[Highly efficient and sensitive patient-specific quality assurance for spot-scanned proton therapy]]>

The purpose of this work was to develop an end-to-end patient-specific quality assurance (QA) technique for spot-scanned proton therapy that is more sensitive and efficient than traditional approaches. The patient-specific methodology relies on independently verifying the accuracy of the delivered proton fluence and the dose calculation in the heterogeneous patient volume. A Monte Carlo dose calculation engine, which was developed in-house, recalculates a planned dose distribution on the patient CT data set to verify the dose distribution represented by the treatment planning system. The plan is then delivered in a pre-treatment setting and logs of spot position and dose monitors, which are integrated into the treatment nozzle, are recorded. A computational routine compares the delivery log to the DICOM spot map used by the Monte Carlo calculation to ensure that the delivered parameters at the machine match the calculated plan. Measurements of dose planes using independent detector arrays, which historically are the standard approach to patient-specific QA, are not performed for every patient. The nozzle-integrated detectors are rigorously validated using independent detectors in regular QA intervals. The measured data are compared to the expected delivery patterns. The dose monitor reading deviations are reported in a histogram, while the spot position discrepancies are plotted vs. spot number to facilitate independent analysis of both random and systematic deviations. Action thresholds are linked to accuracy of the commissioned delivery system. Even when plan delivery is acceptable, the Monte Carlo second check system has identified dose calculation issues which would not have been illuminated using traditional, phantom-based measurement techniques. The efficiency and sensitivity of our patient-specific QA program has been improved by implementing a procedure which independently verifies patient dose calculation accuracy and plan delivery fidelity. Such an approach to QA requires holistic integration and maintenance of patient-specific and patient-independent QA.

<![CDATA[Gamma radiation induces locus specific changes to histone modification enrichment in zebrafish and Atlantic salmon]]>

Ionizing radiation is a recognized genotoxic agent, however, little is known about the role of the functional form of DNA in these processes. Post translational modifications on histone proteins control the organization of chromatin and hence control transcriptional responses that ultimately affect the phenotype. The purpose of this study was to investigate effects on chromatin caused by ionizing radiation in fish. Direct exposure of zebrafish (Danio rerio) embryos to gamma radiation (10.9 mGy/h for 3h) induced hyper-enrichment of H3K4me3 at the genes hnf4a, gmnn and vegfab. A similar relative hyper-enrichment was seen at the hnf4a loci of irradiated Atlantic salmon (Salmo salar) embryos (30 mGy/h for 10 days). At the selected genes in ovaries of adult zebrafish irradiated during gametogenesis (8.7 and 53 mGy/h for 27 days), a reduced enrichment of H3K4me3 was observed, which was correlated with reduced levels of histone H3 was observed. F1 embryos of the exposed parents showed hyper-methylation of H3K4me3, H3K9me3 and H3K27me3 on the same three loci, while these differences were almost negligible in F2 embryos. Our results from three selected loci suggest that ionizing radiation can affect chromatin structure and organization, and that these changes can be detected in F1 offspring, but not in subsequent generations.

<![CDATA[Synthesis and characterizations of o-nitrochitosan based biopolymer electrolyte for electrochemical devices]]>

For the past decade, much attention was focused on polysaccharide natural resources for various purposes. Throughout the works, several efforts were reported to prepare new function of chitosan by chemical modifications for renewable energy, such as fuel cell application. This paper focuses on synthesis of the chitosan derivative, namely, O-nitrochitosan which was synthesized at various compositions of sodium hydroxide and reacted with nitric acid fume. Its potential as biopolymer electrolytes was studied. The substitution of nitro group was analyzed by using Attenuated Total Reflectance Fourier Transform Infra-Red (ATR-FTIR) analysis, Nuclear Magnetic Resonance (NMR) and Elemental Analysis (CHNS). The structure was characterized by X-ray Diffraction (XRD) and its thermal properties were examined by using differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA). Whereas, the ionic conductivity of the samples was analyzed by electrochemical impedance spectroscopy (EIS). From the IR spectrum results, the nitro group peaks of O-nitrochitosan, positioned at 1646 and 1355 cm-1, were clearly seen for all pH media. At pH 6, O-nitrochitosan exhibited the highest degree of substitution at 0.74 when analyzed by CHNS analysis and NMR further proved that C-6 of glucosamine ring was shifted to the higher field. However, the thermal stability and glass transition temperatures were decreased with acidic condition. The highest ionic conductivity of O-nitrochitosan was obtained at ~10−6 cm-1. Overall, the electrochemical property of new O-nitrochitosan showed a good improvement as compared to chitosan and other chitosan derivatives. Hence, O-nitrochitosan is a promising biopolymer electrolyte and has the potential to be applied in electrochemical devices.

<![CDATA[Haralick texture feature analysis for quantifying radiation response heterogeneity in murine models observed using Raman spectroscopic mapping]]>

Tumour heterogeneity plays a large role in the response of tumour tissues to radiation therapy. Inherent biological, physical, and even dose deposition heterogeneity all play a role in the resultant observed response. We here implement the use of Haralick textural analysis to quantify the observed glycogen production response, as observed via Raman spectroscopic mapping, of tumours irradiated within a murine model. While an array of over 20 Haralick features have been proposed, we here concentrate on five of the most prominent features: homogeneity, local homogeneity, contrast, entropy, and correlation. We show that these Haralick features can be used to quantify the inherent heterogeneity of the Raman spectroscopic maps of tumour response to radiation. Furthermore, our results indicate that Haralick-calculated textural features show a statistically significant dose dependent variation in response heterogeneity, specifically, in glycogen production in tumours irradiated with clinically relevant doses of ionizing radiation. These results indicate that Haralick textural analysis provides a quantitative methodology for understanding the response of murine tumours to radiation therapy. Future work in this area can, for example, utilize the Haralick textural features for understanding the heterogeneity of radiation response as measured by biopsied patient tumour samples, which remains the standard of patient tumour investigation.

<![CDATA[Mutation in DDM1 inhibits the homology directed repair of double strand breaks]]>

In all organisms, DNA damage must be repaired quickly and properly, as it can be lethal for cells. Because eukaryotic DNA is packaged into nucleosomes, the structural units of chromatin, chromatin modification is necessary during DNA damage repair and is achieved by histone modification and chromatin remodeling. Chromatin remodeling proteins therefore play important roles in the DNA damage response (DDR) by modifying the accessibility of DNA damage sites. Here, we show that mutation in a SWI2/SNF2 chromatin remodeling protein (DDM1) causes hypersensitivity in the DNA damage response via defects in single-strand annealing (SSA) repair of double-strand breaks (DSBs) as well as in the initial steps of homologous recombination (HR) repair. ddm1 mutants such as ddm1-1 and ddm1-2 exhibited increased root cell death and higher DSB frequency compared to the wild type after gamma irradiation. Although the DDM1 mutation did not affect the expression of most DDR genes, it did cause substantial decrease in the frequency of SSA as well as partial inhibition in the γ-H2AX and Rad51 induction, the initial steps of HR. Furthermore, global chromatin structure seemed to be affected by DDM1 mutations. These results suggest that DDM1 is involved in the homology directed repair such as SSA and HR, probably by modifying chromatin structure.

<![CDATA[Social dominance orientation as an obstacle to intergroup apology]]>

Social Dominance Orientation (SDO) has engaged the interest of social and personality psychologists as it has deep implications for the psychology of intergroup conflict, particularly regarding factors such as prejudice and discrimination, as well as international conflict resolution. Nevertheless, few studies have directly assessed how SDO relates to intergroup reconciliation. This study (effective N = 819) measured participants’ SDO along with their attitudes toward various governmental apologies to test the hypothesis that SDO is associated with unwillingness to issue intergroup apologies. The results showed that SDO was negatively correlated with supportive attitudes toward government-issued international apologies. This negative correlation remained intact after controlling for the effects of political conservatism and militarism.

<![CDATA[The molecular structure of β-alanine is resistant to sterilising doses of gamma radiation]]>

β-alanine is the rate-limiting point for the endogenous synthesis of carnosine in skeletal muscle. Carnosine has a wide range of implications for health, normal function and exercise performance. Whilst the physiological relevance of carnosine to different tissues remains enigmatic, β-alanine administration is a useful strategy to investigate the physiological roles of carnosine in humans. Intravenous administration of β-alanine is an interesting approach to study carnosine metabolism. However, sterilisation is mandatory due to the nature of the administration route. We evaluated whether sterilising doses of gamma radiation damages the molecular structure and leads to the loss of functional characteristics of β-alanine. Pure β-alanine was sterilised by gamma radiation in sealed glass vials using a 60Co multipurpose irradiator at a dose rate of 8.5 kGy.hour-1 totalising 10, 20, 25 30 and 40 kGy. The molecular integrity was assessed by X-ray Diffraction and changes in content were determined by High Performance Liquid Chromatography (UV-HPLC) and Triple Quadrupole Mass Spectrometer (HPLC/MS-MS). Sterility assurance was evaluated by inoculation assay. To examine whether functional properties were preserved, β-alanine was infused in one participant, who rated the level of paraesthesia on the skin using a 0–3 scale. Urinary β-alanine was quantified before and 24-h following β-alanine infusion using HPLC-ESI+-MS/MS. Irradiation resulted in no change in the crystal structure of β-alanine, no degradation, and no new peaks were identified in the dose range assayed. The inoculation assay showed the absence of viable microorganisms in all β-alanine samples, including those that did not undergo irradiation. Intravenous infusion of β-alanine resulted in paraesthesia and it detected in the urine as per normal. We conclude that gamma radiation is a suitable technique for the sterilisation of β-alanine. It does not lead to degradation, damage to the β-alanine structure, content or loss of function within the evaluated irradiation conditions.

<![CDATA[Calcium phosphate precipitation inhibits mitochondrial energy metabolism]]>

Early studies have shown that moderate levels of calcium overload can cause lower oxidative phosphorylation rates. However, the mechanistic interpretations of these findings were inadequate. And while the effect of excessive calcium overload on mitochondrial function is well appreciated, there has been little to no reports on the consequences of low to moderate calcium overload. To resolve this inadequacy, mitochondrial function from guinea pig hearts was quantified using several well-established methods including high-resolution respirometry and spectrofluorimetry and analyzed using mathematical modeling. We measured key mitochondrial variables such as respiration, mitochondrial membrane potential, buffer calcium, and substrate effects for a range of mitochondrial calcium loads from near zero to levels approaching mitochondrial permeability transition. In addition, we developed a computer model closely mimicking the experimental conditions and used this model to design experiments capable of eliminating many hypotheses generated from the data analysis. We subsequently performed those experiments and determined why mitochondrial ADP-stimulated respiration is significantly lowered during calcium overload. We found that when calcium phosphate levels, not matrix free calcium, reached sufficient levels, complex I activity is inhibited, and the rate of ATP synthesis is reduced. Our findings suggest that calcium phosphate granules form physical barriers that isolate complex I from NADH, disrupt complex I activity, or destabilize cristae and inhibit NADH-dependent respiration.

<![CDATA[<i>PLoS Genetics</i> Issue Image | Vol. 15(1) January 2019]]>

DNA repair during meiosis and chromosomal bridges.

Meiotic cells respond to DNA damage triggering diverse repair mechanisms in a cell cycle-dependent manner. Sequential activation of these mechanisms contribute to accurately maintain genome integrity. However, when spermatocytes are exposed to exogenous DNA damaging agents, like gamma radiation, repair homeostasis may be stressed and chromosomes sometimes engage in aberrant connections with non-homologous chromosomes. Super-resolution fluorescence image (STED) of two meiotic bivalents labelled with an antibody against the SYCP3 protein of the synaptonemal complex. Parallel lines represent the trajectory of homologous chromosomes within each bivalent. A protein filament bridges from one bivalent to the other, connecting two non-homologous chromosomes. See Enguita-Marruedo et al.

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Image Credit: Marta Martín-Ruiz

<![CDATA[Monte-Carlo simulation of the Siemens Artiste linear accelerator flat 6 MV and flattening-filter-free 7 MV beam line]]>

The aim of our work is to provide the up-to-now missing information on the Siemens Artiste FFF 7 MV beam line using a Monte-Carlo model fit to the realistic dosimetric measurements at the linear accelerator in clinical use at our department. The main Siemens Artiste 6MV and FFF 7MV beams were simulated using the Geant4 toolkit. The simulations were compared with the measurements with an ionization chamber in a water phantom to verify the validation of simulation and tuning the primary electron parameters. Hereafter, other parameters such as surface dose, spectrum, electron contamination, symmetry, flatness/unflatness, slope, and characteristic off-axis changes were discussed for both Flat and FFF mode. The mean electron energy for the FFF beam was 8.8 MeV and 7.5 MeV for Flat 6 MV, the spread energy and spot size of the selected Gaussian distribution source were 0.4 MeV and 1mm, respectively. The dose rate of the FFF beam was 2.8 (2.96) times higher than for the flattened beam for a field size of 10×10 (20×20) cm2. The electron contamination has significant contribution to the surface dose especially for the flattened beam. The penumbra, surface dose and the mean energy of photons decrease by removing the flattening filter. Finally, the results show that off-axis changes have no strong effect on the mean energy of FFF beams, while this effect was more considerable for the flattened beam.

<![CDATA[Implementation and assessment of the black body bias correction in quantitative neutron imaging]]>

We describe in this paper the experimental procedure, the data treatment and the quantification of the black body correction: an experimental approach to compensate for scattering and systematic biases in quantitative neutron imaging based on experimental data. The correction algorithm is based on two steps; estimation of the scattering component and correction using an enhanced normalization formula. The method incorporates correction terms into the image normalization procedure, which usually only includes open beam and dark current images (open beam correction). Our aim is to show its efficiency and reproducibility: we detail the data treatment procedures and quantitatively investigate the effect of the correction. Its implementation is included within the open source CT reconstruction software MuhRec. The performance of the proposed algorithm is demonstrated using simulated and experimental CT datasets acquired at the ICON and NEUTRA beamlines at the Paul Scherrer Institut.

<![CDATA[Raman spectroscopy of a near infrared absorbing proteorhodopsin: Similarities to the bacteriorhodopsin O photointermediate]]>

Microbial rhodopsins have become an important tool in the field of optogenetics. However, effective in vivo optogenetics is in many cases severely limited due to the strong absorption and scattering of visible light by biological tissues. Recently, a combination of opsin site-directed mutagenesis and analog retinal substitution has produced variants of proteorhodopsin which absorb maximally in the near-infrared (NIR). In this study, UV-Visible-NIR absorption and resonance Raman spectroscopy were used to study the double mutant, D212N/F234S, of green absorbing proteorhodopsin (GPR) regenerated with MMAR, a retinal analog containing a methylamino modified β-ionone ring. Four distinct subcomponent absorption bands with peak maxima near 560, 620, 710 and 780 nm are detected with the NIR bands dominant at pH <7.3, and the visible bands dominant at pH 9.5. FT-Raman using 1064-nm excitation reveal two strong ethylenic bands at 1482 and 1498 cm-1 corresponding to the NIR subcomponent absorption bands based on an extended linear correlation between λmax and γC = C. This spectrum exhibits two intense bands in the fingerprint and HOOP mode regions that are highly characteristic of the O640 photointermediate from the light-adapted bacteriorhodopsin photocycle. In contrast, 532-nm excitation enhances the 560-nm component, which exhibits bands very similar to light-adapted bacteriorhodopsin and/or the acid-purple form of bacteriorhodopsin. Native GPR and its mutant D97N when regenerated with MMAR also exhibit similar absorption and Raman bands but with weaker contributions from the NIR absorbing components. Based on these results it is proposed that the NIR absorption in GPR-D212N/F234S with MMAR arises from an O-like chromophore, where the Schiff base counterion D97 is protonated and the MMAR adopts an all-trans configuration with a non-planar geometry due to twists in the conjugated polyene segment. This configuration is characterized by extensive charge delocalization, most likely involving nitrogens atoms in the MMAR chromophore.

<![CDATA[Prediction of perturbed proton transfer networks]]>

The transfer of protons through proton translocating channels is a complex process, for which direct samplings of different protonation states and side chain conformations in a transition network calculation provide an efficient, bias-free description. In principle, a new transition network calculation is required for every unsampled change in the system of interest, e.g. an unsampled protonation state change, which is associated with significant computational costs. Transition networks void of or including an unsampled change are termed unperturbed or perturbed, respectively. Here, we present a prediction method, which is based on an extensive coarse-graining of the underlying transition networks to speed up the calculations. It uses the minimum spanning tree and a corresponding sensitivity analysis of an unperturbed transition network as initial guess and refinement parameter for the determination of an unknown, perturbed transition network. Thereby, the minimum spanning tree defines a sub-network connecting all nodes without cycles and minimal edge weight sum, while the sensitivity analysis analyzes the stability of the minimum spanning tree towards individual edge weight reductions. Using the prediction method, we are able to reduce the calculation costs in a model system by up to 80%, while important network properties are maintained in most predictions.

<![CDATA[Surgery and protontherapy in Grade I and II skull base chondrosarcoma: A comparative retrospective study]]>


Skull base chondrosarcoma is a rare tumour usually treated by surgery and proton therapy. However, as mortality rate is very low and treatment complications are frequent, a less aggressive therapeutic strategy could be considered. The objective of this study was to compare the results of surgery only vs surgery and adjuvant proton therapy, in terms of survival and treatment adverse effects, based on a retrospective series.


Monocentric retrospective study at a tertiary care centre. All patients treated for a skull base grade I and II chondrosarcoma were included. We collected data concerning surgical and proton therapy treatment and up-to-date follow-up, including Common Terminology Criteria for Adverse Events (CTCAE) scores.


47 patients (23M/24F) were operated on between 2002 and 2015; mean age at diagnosis was 47 years-old (10–85). Petroclival and anterior skull base locations were found in 34 and 13 patients, respectively. Gross total resection was achieved in 17 cases (36%) and partial in 30 (64%). Adjuvant proton therapy (mean total dose 70 GyRBE,1.8 GyRBE/day) was administered in 23 cases. Overall mean follow-up was 91 months (7–182). Of the patients treated by surgery only, 8 (34%) experienced residual tumour progression (mean delay 51 months) and 5 received second-line proton therapy. Adjuvant proton therapy was associated with a significantly lower rate of relapse (11%; p = 0.01). There was no significant difference in 10-year disease specific survival between patients initially treated with or without adjuvant proton therapy (100% vs 89.8%, p = 0.14). Difference in high-grade toxicity was not statistically significant between patients in both groups (25% (7) vs 11% (5), p = 0.10). The most frequent adverse effect of proton therapy was sensorineural hearing loss (39%).


Long-term disease specific survival was not significantly lower in patients without adjuvant proton therapy, but they experienced less adverse effects. We believe a surgery only strategy could be discussed, delaying as much as possible proton therapy in cases of relapse. Further prospective studies are needed to validate this more conservative strategy in skull base chondrosarcoma.

<![CDATA[A statistical framework for radiation dose estimation with uncertainty quantification from the γ-H2AX assay]]>

Over the last decade, the γ–H2AX focus assay, which exploits the phosphorylation of the H2AX histone following DNA double–strand–breaks, has made considerable progress towards acceptance as a reliable biomarker for exposure to ionizing radiation. While the existing literature has convincingly demonstrated a dose–response effect, and also presented approaches to dose estimation based on appropriately defined calibration curves, a more widespread practical use is still hampered by a certain lack of discussion and agreement on the specific dose–response modelling and uncertainty quantification strategies, as well as by the unavailability of implementations. This manuscript intends to fill these gaps, by stating explicitly the statistical models and techniques required for calibration curve estimation and subsequent dose estimation. Accompanying this article, a web applet has been produced which implements the discussed methods.

<![CDATA[Cranial anatomy of the gorgonopsian Cynariops robustus based on CT-reconstruction]]>

Gorgonopsia is one of the major clades of non-mammalian synapsids, and includes an array of large-bodied carnivores that were the top terrestrial predators of the late Permian. Most research on the clade has focused on these largest members; small-bodied gorgonopsians are relatively little-studied. Here, we redescribe a small gorgonopsian skull (MB.R.999) from the late Permian (Tropidostoma Assemblage Zone) of South Africa on the basis of neutron and synchrotron CT reconstructions, which yield new data on internal cranial morphology in Gorgonopsia. Because of the largely undistorted nature of MB.R.999, we were also able to reconstruct unossified areas such as the brain endocast and the otic labyrinth. MB.R.999 can be referred to the taxon Cynariops robustus based on its general skull proportions, postcanine tooth count, preparietal morphology, and vomerine morphology. We refer additional small gorgonopsian specimens from the Victoria West area to Cynariops robustus, and consider Cynarioides grimbeeki and Cynarioides laticeps to be synonymous with C. robustus. Inclusion of Cynariops in a phylogenetic analysis of Gorgonopsia recovers it within a large clade of African taxa, more closely related to Lycaenops and rubidgeines than Eriphostoma or Gorgonops.

<![CDATA[Apilimod, a candidate anticancer therapeutic, arrests not only PtdIns(3,5)P2 but also PtdIns5P synthesis by PIKfyve and induces bafilomycin A1-reversible aberrant endomembrane dilation]]>

PIKfyve, an evolutionarily conserved kinase synthesizing PtdIns5P and PtdIns(3,5)P2, is crucial for mammalian cell proliferation and viability. Accordingly, PIKfyve inhibitors are now in clinical trials as anti-cancer drugs. Among those, apilimod is the most promising, yet its potency to inhibit PIKfyve and affect endomembrane homeostasis is only partially characterized. We demonstrate here for the first time that apilimod powerfully inhibited in vitro synthesis of PtdIns5P along with that of PtdIns(3,5)P2. HPLC-based resolution of intracellular phosphoinositides (PIs) revealed that apilimod triggered a marked reduction of both lipids in the context of intact cells. Notably, there was also a profound rise in PtdIns3P resulting from arrested PtdIns3P consumption for PtdIns(3,5)P2 synthesis. As typical for PIKfyve inhibition and the concomitant PtdIns(3,5)P2 reduction, apilimod induced the appearance of dilated endomembrane structures in the form of large translucent cytoplasmic vacuoles. Remarkably, bafilomycin A1 (BafA1) fully reversed the aberrant cell phenotype back to normal and completely precluded the appearance of cytoplasmic vacuoles when added prior to apilimod. Inspection of the PI profiles ruled out restoration of the reduced PtdIns(3,5)P2 pool as a molecular mechanism underlying BafA1 rescue. Rather, we found that BafA1 markedly attenuated the PtdIns3P elevation under PIKfyve inhibition. This was accompanied by profoundly decreased endosomal recruitment of fusogenic EEA1. Together, our data demonstrate that apilimod inhibits not only PtdIns(3,5)P2 but also PtdIns5P synthesis and that the cytoplasmic vacuolization triggered by the inhibitor is precluded or reversed by BafA1 through a mechanism associated, in part, with reduction in both PtdIns3P levels and EEA1 membrane recruitment.