Comparison of the incidence of vancomycin-associated nephrotoxicity following the change from trough-guided dosing to AUC-guided doing using trough-only data.

OBJECTIVES: Although use of AUC-guided vancomycin dosing was recommended in the revised 2020 consensus guideline, collection of multiple vancomycin serum samples to calculate AUC may cause clinical complications. AUC calculated from trough-only data (one-point AUC-guided dosing) has not been sufficiently validated. The aim of the present study was to compare the incidence of nephrotoxicity following the change from trough-guided to one-point AUC-guided dosing. METHODS: We conducted a single-centre, prospective cohort study to compare the incidence of nephrotoxicity between a trough-guided dosing group and one-point AUC-guided dosing group. RESULTS: One-point AUC-guided dosing significantly decreased the incidence of acute kidney injury (AKI) compared with trough-guided dosing (2.8% versus 17.4%, P = 0.002). Further, Kaplan-Meier plots for cumulative incidence of the AKI-free rate indicated that the onset of AKI was significantly longer in the one-point AUC-guided dosing group than in trough-guided dosing (HR, 6.5; 95% CI, 1.5-27.4; P = 0.011). Moreover, multivariate Cox proportional hazard analysis indicated that implementation of one-point AUC-guided dosing was a significant protective factor against the incidence of AKI (age-adjusted HR, 0.164; 95% CI, 0.04-0.69; P = 0.014). CONCLUSIONS: Compared with trough concentration-guided dosing, AUC-guided dosing using one-point sampling markedly reduced the incidence of AKI, without additional serum sampling.

Fluorescence properties of retinoid X receptor antagonist NEt-SB.

Ligands of retinoid X receptors (RXRs) are effective against various diseases, so there is a need for efficient screening methods to discover new ligands. Existing screening methods are complex and time-consuming, and a simple fluorescence assay would be highly desirable. Here, we focused on NEt-SB (4), which has a stilbene structure, as a candidate for this purpose, and examined its fluorescence properties in detail. The fluorescence intensity of 4 was remarkably increased in highly viscous solvents and upon binding to hRXRα-LBD, due to suppression of free rotation of the stilbene moiety. Although the relatively low fluorescence intensity and the short fluorescence wavelength of 4 make this compound itself unsuitable for use in RXR binding assay, our findings provide a basis for further structural evolution, which may lead to a derivative that would be suitable for fluorescence assay of RXR binders.

The Mitochondrial Respiratory Chain Maintains the Photosynthetic Electron Flow in Arabidopsis thaliana Leaves under High-Light Stress.

The plant respiratory chain includes the ATP-coupling cytochrome pathway (CP) and ATP-uncoupling alternative oxidase (AOX). Under high-light (HL) conditions, plants experience photoinhibition, leading to a damaged photosystem II (PSII). The respiratory chain is considered to affect PSII maintenance and photosynthetic electron transport under HL conditions. However, the underlying details remain unclear. In this study, we investigated the respiratory chain functions related to PSII maintenance and photosynthetic electron transport in plants exposed to HL stress. We measured the HL-induced decrease in the maximum quantum yield of PSII in the leaves of wild-type and AOX1a-knockout (aox1a) Arabidopsis thaliana plants in which CP was partially inhibited by a complex-III inhibitor. We also calculated PSII photodamage and repair rate constants. Both rate constants changed when CP was partially inhibited in aox1a plants, suggesting that the respiratory chain is related to both processes. Before HL stress, photosynthetic linear electron flow (LEF) decreased when CP was partially inhibited. After HL stress, aox1a in the presence of the CP inhibitor showed significantly decreased rates of LEF. The electron flow downstream from PSII and on the donor side of photosystem I may have been suppressed. The function of respiratory chain is required to maintain the optimal LEF as well as PSII maintenance especially under the HL stress.

Fluorine-18 (18F)-labeled retinoid x receptor (RXR) partial agonist whose tissue transferability is affected by other RXR ligands.

Bexarotene (1), a retinoid X receptor (RXR) agonist approved for the treatment of cutaneous T cell lymphoma (CTCL), was reported to migrate into baboon brain based on findings obtained by positron emission tomography (PET) with a 11C-labeled tracer. However, co-administration of non-radioactive 1 had no effect on the distribution of [11C]1, probably due to non-specific binding of 1 as a result of its high lipophilicity. Here, we report a fluorine-18 (18F)-labeled PET tracer [18F]6 derived from RXR partial agonist CBt-PMN (2), which has lower lipophilicity and weaker RXR-binding ability than [11C]1. The concomitant administration of 1 or 2 with [18F]6 with resulted in decreased accumulation of [18F]6 in liver, together with increased brain uptake and increased accumulation in kidney and muscle, as visualized by PET. A plausible explanation of these findings is the inhibition of [18F]6 uptake into the liver by concomitantly administered 1 or 2, leading to an increase in blood concentration of [18F]6 followed by increased accumulation in other tissues.

Ligand Screening System for the RXRα Heterodimer Using the Fluorescence RXR Agonist CU-6PMN.

Retinoid X receptor (RXR), a nuclear receptor (NR) that regulates transcription of target genes in a ligand binding-dependent manner, is of interest as a drug target. RXR agonists have been developed as therapeutic agents for cutaneous invasive T-cell lymphoma (e.g., bexarotene (1)) and investigated as potential anti-inflammatory agents. Screening systems for the binding of RXR alone have been reported. However, although RXRs function as RXR heterodimers, information on systems to evaluate the differential binding of RXR agonists as RXR heterodimers has not been available until recently. Here we show that the fluorescent RXR agonist CU-6PMN (3), designed by our group, can be useful for assessing RXR binding to PPARγ/RXRα, and that the binding data differ from those of RXRα alone. This screening method opens a new avenue for binding assays for RXR heterodimers.

Effectiveness of countermeasure for polypharmacy by multidisciplinary team review in patients with diabetes mellitus.

AIMS/INTRODUCTION: Polypharmacy in diabetes patients is related to worse clinical outcomes. The aim of this study was to evaluate the usefulness of our countermeasure for polypharmacy, which combines a pharmacist check followed by a multidisciplinary team review in diabetic patients with polypharmacy. METHODS: A single-center, retrospective observational study was conducted at Gifu University Hospital. Study participants included diabetic patients taking six or more drugs on admission to the diabetes ward between July 2021 and June 2022. Drugs which were discontinued by the present countermeasure were examined, and the number of drugs being taken by each patient was compared between admission and discharge. RESULTS: 102 of 308 patients were taking six or more drugs on admission. The drugs being taken by these patients were evaluated by pharmacists using a checklist for polypharmacy. Eighty-four drugs which were evaluated as inappropriate or potentially inappropriate medications by pharmacists were discontinued following the multidisciplinary team review. The median and mean number of drugs taken by the 102 patients significantly decreased from 9.0 (IQR: 8-12) and 9.26 ± 2.64 on admission to 9.0 (IQR: 6-10) and 8.42 ± 2.95 on discharge (P = 0.0002). We followed up with these patients after discontinuation of the drugs and confirmed that their clinical status had not deteriorated. CONCLUSION: The present countermeasure for polypharmacy, which combines a pharmacist check based on a checklist for evaluating polypharmacy followed by a multidisciplinary team review, was useful for reducing the number of inappropriate or potentially inappropriate medications taken by diabetes patients with polypharmacy.

Feasibility of structural modification of retinoid X receptor agonists to separate blood glucose-lowering action from adverse effects: studies in KKA(y) type 2 diabetes model mice.

Retinoid X receptor (RXR) agonists are reported to exhibit blood glucose-lowering action owing to peroxisome proliferator-activated receptor (PPAR)/RXR or liver X receptor (LXR)/RXR activation, but may also cause adverse effects such as blood triglyceride elevation. In order to examine the feasibility of separating the glucose-lowering action from the adverse effects, we examined the effects of RXR agonists (NEt-TMN), NEt-3IB, and NEt-3IP, which have different heterodimer-activating patterns, in KKA(y) type 2 diabetes model mice. We found that NEt-3IB induced lower degrees of hepatomegaly and blood triglyceride (TG) elevation than the other RXR agonists, even though all of them showed similar blood glucose-lowering action on repeated administration. These findings indicate that structural modification of RXR agonists is a potentially effective strategy to reduce adverse effects while retaining desired activities.

Replacement of the hydrophobic part of 9-cis-retinoic acid with cyclic terpenoid moiety results in RXR-selective agonistic activity.

Retinoid X receptor (RXR) agonists are interesting candidates for the treatment of metabolic syndrome. 9-Cis-retinoic acid (9cRA: 1) is a natural RXR agonist, that also works as a retinoic acid receptor (RAR) agonist. This fact prompted us to study the structure-activity relationship (SAR) of RXR agonists derived from 1. Though 3 and 4, in which the cyclohexene part of 1 is replaced with bulkier hydrophobic moieties, show RXR-selective agonistic activity, some analogs containing other ring structures show RAR agonistic activity. Thus, we were interested in establishing what kind of ring skeleton is required for RXR-selective agonistic activity. In this study, we systematically prepared 5 and 6, in which the cyclohexene ring of 1 is replaced with various cyclic terpenoid moieties, and evaluated their RXR and RAR agonistic activities. Our previously reported CsF-promoted Stille coupling reaction was employed as a key step for the comprehensive synthesis of 5 and 6. The results of transcriptional assay showed that compounds 5b-f, which possess a menthane skeleton, exhibit RXR-selective agonistic activity. These results should be helpful for the design of superior RXR-selective agonists based on the structure of 1.

Creation of Fluorescent RXR Antagonists Based on CBTF-EE and Application to a Fluorescence Polarization Binding Assay.

Retinoid X receptor (RXR) ligands often bind in modes in which the carboxy group forms a hydrogen bond inside the ligand-binding pocket (LBP). However, our previously reported RXR antagonist, CBTF-EE (4a), binds with its carboxy group directed outside the LBP and its alkoxy side chain located inside the LBP. Here, we examined the binding modes of 4b and 4c bearing a nitrobenzoxadiazole (NBD) or boron-dipyrromethene (BODIPY) fluorophore, respectively, at the end of the alkoxy chain of 4a. Both compounds function as RXR antagonists. 4c, but not 4b, was available for a fluorescence polarization binding assay, indicating that rotation of BODIPY, but not NBD, is restricted in the bound state. The fluorescence findings, supported by docking simulations, suggest the fluorophores are located outside the LBP, so that the binding mode of 4b and 4c is different from that of 4a. The assay results were highly correlated with those of a [3H]9-cis-retinoic acid assay.

Discovery of a "Gatekeeper" Antagonist that Blocks Entry Pathway to Retinoid X Receptors (RXRs) without Allosteric Ligand Inhibition in Permissive RXR Heterodimers.

Retinoid X receptor (RXR) heterodimers such as PPAR/RXR, LXR/RXR, and FXR/RXR can be activated by RXR agonists alone and are therefore designated as permissive. Similarly, existing RXR antagonists show allosteric antagonism toward partner receptor agonists in these permissive RXR heterodimers. Here, we show 1-(3-(2-ethoxyethoxy)-5,5,8,8-tetramethyl-5,6,7,8-tetrahydronaphthalen-2-yl)-2-(trifluoromethyl)-1H-benzo[d]imidazole-5-carboxylic acid (14, CBTF-EE) as the first RXR antagonist that does not show allosteric inhibition in permissive RXR heterodimers. This compound was designed based on the hypothesis that RXR antagonists that do not induce conformational changes of RXR would not exhibit such allosteric inhibition. CD spectra and X-ray co-crystallography of the complex of 14 and the RXR ligand binding domain (LBD) confirmed that 14 does not change the conformation of hRXR-LBD. The X-ray structure analysis revealed that 14 binds at the entrance of the ligand binding pocket (LBP), blocking access to the LBP and thus serving as a "gatekeeper".

Convenient Retinoid X Receptor Binding Assay Based on Fluorescence Change of the Antagonist NEt-C343.

Retinoid X receptor (RXR) modulators (rexinoids) are considered to have therapeutic potential for multiple diseases, such as Alzheimer's disease and Parkinson's disease. To overcome various disadvantages of prior screening methods, we previously developed an RXR binding assay using a fluorescent RXR ligand, CU-6PMN (4). However, this ligand binds not only at the ligand-binding domain (LBD) but also at the dimer-dimer interface of hRXRα. Here, we present a new fluorescent RXR antagonist 6-[N-ethyl-N-(5-isobutoxy-4-isopropyl-2-(11-oxo-2,3,6,7-tetrahydro-1H,5H,11H-pyrano[2,3-f]pyrido[3,2,1-ij]quinoline-10-carboxamido)phenyl)amino]nicotinic acid (NEt-C343, 7), which emits strong fluorescence only when bound to the RXR-LBD. It allows us to perform a rapid, simple, and nonhazardous binding assay that does not require bound/free separation and uses a standard plate reader. The obtained Ki values of known compounds were correlated with the Ki values obtained using the standard [3H]9cis-retinoic acid assay. This assay should be useful for drug discovery as well as for research on endocrine disruptors, functional foods, and natural products.

Fluorescent retinoid X receptor ligands for fluorescence polarization assay.

Retinoid X receptor (RXR) agonists are candidate agents for the treatment of metabolic syndrome and type 2 diabetes via activation of peroxisome proliferator-activated receptor (PPAR)/RXR or liver X receptor (LXR)/RXR-heterodimers, which control lipid and glucose metabolism. Reporter gene assays or binding assays with radiolabeled compounds are available for RXR ligand screening, but are unsuitable for high-throughput screening. Therefore, as a first step towards stabilizing a fluorescence polarization (FP) assay system for high-throughput RXR ligand screening, we synthesized fluorescent RXR ligands by modification of the lipophilic domain of RXR ligands with a carbostyril fluorophore, and selected the fluorescent RXR agonist 6-[ethyl(1-isobutyl-2-oxo-4-trifluoromethyl-1,2-dihydroquinolin-7-yl)amino]nicotinic acid 8d for further characterization. Compound 8d showed FP in the presence of RXR and the FP was decreased in the presence of the RXR agonist LGD1069 (2). This compound should be a lead compound for use in high-throughput assay systems for screening RXR ligands.

Modification at the acidic domain of RXR agonists has little effect on permissive RXR-heterodimer activation.

Retinoid X receptors (RXRs) function as homo- or heterodimers with other nuclear receptors, such as peroxisome proliferator-activated receptors (PPARs), which are targets for treatment of hyperlipidemia and type 2 diabetes, or liver X receptors (LXRs), which are involved in glucose/lipid metabolism. PPAR/RXR or LXR/RXR are known as permissive RXR-heterodimers because they are activated by RXR agonists alone. Interestingly, the pattern of RXR-heterodimer activation is different depending on the RXR agonist structure, but the structure-activity relationship has not been reported. Here we show that modification or replacement of the carboxyl group in the acidic domain of RXR agonists has little or no effect on permissive RXR-heterodimer activation. Phosphonic acid (9), tetrazole (10), and hydroxamic acid (12) analogues were synthesized from the common bromo intermediate 7. Except for 9, these compounds showed RXR full-agonistic activities in the concentration range of 1-10 microM. The order of agonistic activity toward both PPARgamma/RXRalpha and LXRalpha/RXRalpha was the same as it was for RXR, that is, 11>10>12. These results should be useful for the development of RXR agonists with improved bioavailability.

Competitive Binding Assay with an Umbelliferone-Based Fluorescent Rexinoid for Retinoid X Receptor Ligand Screening.

Ligands for retinoid X receptors (RXRs), "rexinoids", are attracting interest as candidates for therapy of type 2 diabetes and Alzheimer's and Parkinson's diseases. However, current screening methods for rexinoids are slow and require special apparatus or facilities. Here, we created 7-hydroxy-2-oxo-6-(3,5,5,8,8-pentamethyl-5,6,7,8-tetrahydronaphthalen-2-yl)-2H-chromene-3-carboxylic acid (10, CU-6PMN) as a new fluorescent RXR agonist and developed a screening system of rexinoids using 10. Compound 10 was designed based on the fact that umbelliferone emits strong fluorescence in a hydrophilic environment, but the fluorescence intensity decreases in hydrophobic environments such as the interior of proteins. The developed assay using 10 enabled screening of rexinoids to be performed easily within a few hours by monitoring changes of fluorescence intensity with widely available fluorescence microplate readers, without the need for processes such as filtration.

Synthesis of 11C-Labeled RXR Partial Agonist 1-[(3,5,5,8,8-Pentamethyl-5,6,7,8-tetrahydronaphthalen-2-yl)amino]benzotriazole-5-carboxylic Acid (CBt-PMN) by Direct [11C]Carbon Dioxide Fixation via Organolithiation of Trialkyltin Precursor and PET Imaging Thereof.

The retinoid X receptor (RXR) partial agonist 1-[(3,5,5,8,8-pentamethyl-5,6,7,8-tetrahydronaphthalen-2-yl)amino]benzotriazole-5-carboxylic acid (1; CBt-PMN, Emax = 75%, EC50 = 143 nM) is a candidate for treatment of central nervous system (CNS) diseases such as Alzheimer's and Parkinson's diseases based on reports that RXR-full agonist 4-[1-(3,5,5,8,8-pentamethyl-5,6,7,8-tetrahydro-2-naphthyl)ethynyl]benzoic acid (bexarotene) shows therapeutic effects on these disease in rodent models. Here, we synthesized carbon-11-labeled ([11C]1) as a tracer for positron emission tomography (PET) and used it in a PET imaging study to examine the brain uptake and biodistribution of 1. We found that 11CO2 fixation after tin-lithium exchange at -20 °C afforded [11C]1. This methodology may also be useful for synthesizing 11CO2H-PET tracer derivatives of other compounds bearing π-rich heterocyclic rings. A PET/CT imaging study of [11C]1 in mice indicated 1 is distributed to the brain and is thus a candidate for treatment of CNS diseases.

Positron emission tomography to elucidate pharmacokinetic differences of regioisomeric retinoid x receptor agonists.

RXR partial agonist NEt-4IB (2a, 6-[ethyl-(4-isobutoxy-3-isopropylphenyl)amino]pyridine-3-carboxylic acid: EC50 = 169 nM, E max = 55%) showed a blood concentration higher than its E max after single oral administration at 30 mg/kg to mice, and repeated oral administration at 10 mg/kg/day to KK-A(y) mice afforded antitype 2 diabetes activity without the side effects caused by RXR full agonists. However, RXR full agonist NEt-3IB (1a), in which the isobutoxy and isopropyl groups of 2a are interchanged, gave a much lower blood concentration than 2a. Here we used positron emission tomography (PET) with tracers [(11)C]1a, [(11)C]2a and fluorinated derivatives [(18)F]1b, [(18)F]2b, which have longer half-lives, to examine the reason why 1a and 2a exhibited significantly different blood concentrations. As a result, the reason for the high blood concentration of 2a after oral administration was found to be linked to higher intestinal absorbability together with lower biliary excretion, compared with 1a.

RXR partial agonist produced by side chain repositioning of alkoxy RXR full agonist retains antitype 2 diabetes activity without the adverse effects.

We previously reported RXR partial agonist CBt-PMN (1-(3,5,5,8,8-pentamethyl-5,6,7,8-tetrahydro-2-naphthyl)-1H-benzotriazole-5-carboxylic acid: 5, EC50 = 143 nM, Emax = 75%), which showed a potent glucose-lowering effect without causing serious adverse effects. However, it remains important to elucidate the structural requirements for RXR efficacy and the glucose-lowering effect because RXR-permissive heterodimers such as PPAR/RXR or LXR/RXR are reported to be activated differently depending upon the chemical structure of RXR agonists. In this work, we show that an RXR partial agonist, NEt-4IB (6-[ethyl-(4-isobutoxy-3-isopropylphenyl)amino]pyridine-3-carboxylic acid: 8b, EC50 = 169 nM, Emax = 55%), can be obtained simply by repositioning the side chains (interchanging the isobutoxy and isopropoxy groups) at the hydrophobic moiety of the RXR full agonist NEt-3IB (6-[ethyl-(3-isobutoxy-4-isopropylphenyl)amino]pyridine-3-carboxylic acid: 7b, EC50 = 19 nM). NEt-4IB (8b) showed antitype 2 diabetes activity without the above side effects upon repeated oral administration to mice at 10 mg/kg/day, similarly to 5.

Retinoid X receptor ligands: a patent review (2007 - 2013).

INTRODUCTION: Retinoid X receptors (RXRs) are nuclear receptors that act as ligand-dependent transcription factors. RXRs function as homodimers or as heterodimers with other nuclear receptors, such as retinoic acid receptors, PPARs, liver X receptors, farnesoid X receptor, vitamin D receptor or thyroid hormone receptors. RXR ligands (agonists or antagonists) show various physiological effects, depending on their partner receptors. RXR agonist bexarotene (Targretin®) is used for the treatment of cutaneous T-cell lymphoma in clinical practice. RXR agonists were also reported to be useful for treatment of type 2 diabetes, autoimmune disease and Alzheimer's disease. RXR antagonists were also reported to be effective in type 2 diabetes treatment. AREAS COVERED: Here patent applications (2007 - 2013) concerning RXR ligands are summarized, and the usefulness of RXR ligands as pharmaceutical agents is discussed. EXPERT OPINION: RXR agonists show a wide variety of biological effects. However, they cause serious side effects, such as blood triglyceride elevation, hypothyroidism and others. Thus, for clinical application of RXR agonists, abrogation of these side effects is required. RXR heterodimer-selective agonists and RXR partial agonists exhibiting desired effects without side effects are expected to find clinical application.

Mechanism of retinoid X receptor partial agonistic action of 1-(3,5,5,8,8-pentamethyl-5,6,7,8-tetrahydro-2-naphthyl)-1H-benzotriazole-5-carboxylic acid and structural development to increase potency.

We have reported that retinoid X receptor (RXR) partial agonist 1-(3,5,5,8,8-pentamethyl-5,6,7,8-tetrahydro-2-naphthyl)-1H-benzotriazole-5-carboxylic acid (CBt-PMN, 4a) shows a significant antidiabetes effect in the KK-A(y) type 2 diabetes model mice, with reduced side effects compared to RXR full agonists. To elucidate the mechanism of the RXR partial agonist activity of 4a, we synthesized derivatives of 4a, evaluated their RXR agonist activity, and performed structure-activity relationship analysis. Reporter gene assay revealed that though 6b, which possesses an amino group at the 2-position of 5-carboxybenzimidazole, showed RXR full-agonist activity, compounds 6d and 6e, which possess an oxygen atom and a sulfur atom at the corresponding position, respectively, showed weak RXR agonist activity. On the other hand, 6c, which has a trifluoromethyl group at the corresponding position, acts as an RXR partial agonist, having similar Emax (67 ± 2%) and lower EC50 (15 ± 0 nM) compared to those of 4a (Emax = 75 ± 4%, EC50 = 143 ± 2 nM). A fluorescence polarization assay of cofactor recruitment confirmed that fluorescein-labeled D22 coactivator peptide was less efficiently recruited to RXR by 4a and 6c than by LGD1069 (1), a known RXR full agonist. Electrostatic potential field calculations and computational docking studies suggested that full agonists show an electrostatic attraction, which stabilizes the holo structure and favors coactivator recruitment, between the side chain at the benzimidazole 2-position and the α-carbonyl oxygen of asparagine-306 in helix 4 (H4) of the RXR receptor. However, RXR partial agonists 4a and 6c lack this interaction. Like 4a, 6c showed a significant antidiabetes effect in KK-A(y) type 2 diabetes model mice with reduced levels of the side effects associated with RXR full agonists. These findings should aid the design of new RXR partial agonists as antitype 2 diabetes drug candidates.