Trushin, Sergey A.

Abstract Background Despite recent approval of monoclonal antibodies that reduce amyloid (Ab) accumulation, the development of disease‐modifying strategies targeting the underlying mechanisms of Alzheimer’s Disease (AD) are urgently needed. We identified mitochondrial complex I (mtCI) as a small‐molecule druggable target for AD. Using cryo‐EM, we previously demonstrated that the neuroprotective tool compound CP2 directly binds to the Q‐site of mtCI and weakly inhibits its activity. Method Rational design and extensive structure‐activity relationship studies using CP2 as a tool compound allowed the development of novel classes of partial mtCI inhibitors with high selectivity, specificity, safety, and improved drug‐like properties. Target engagement, selectivity, efficacy, safety and the direct binding to mtCI were demonstrated using multiple in vitro assays. Efficacy in vivo was established using APP/PS1 mice. The best new leads, C458 and C273, were evaluated as preclinical candidates. Result Like CP2, C458 and C273 weakly inhibit mtCI, leading to AMPK activation, which triggers a neuroprotective stress response. This response enhances oxidative stress protection, promotes autophagy, and increases mitochondrial biogenesis and turnover, ultimately protecting against Aβ toxicity. Pretreatment with the irreversible mtCI inhibitor rotenone (at non‐toxic concentrations) blocked C458 and C273 from binding to mtCI and abrogated their protection against Aβ toxicity. Both C458 and C273 exhibited excellent bioavailability, blood–brain barrier penetrance, and a clean safety profile in the CEREP 44 safety panel. Chronic administration of C458 (25 mg/kg/day in drinking water ad lib ) to APP/PS1 mice for 7 months preserved cognition, improved long‐term potentiation, reduced oxidative stress and inflammation, and enhanced mitochondrial biogenesis. Similarly, C273 (20, 50, or 80 mg/kg/day) administered to C57BL/6 mice for one month showed no detectable side effects or toxicity in the heart or liver. Conclusion Mechanistic studies revealed that C458 and C273 activate a mitochondrial stress response, augmenting mitochondrial biogenesis, antioxidant signaling, and autophagy, which collectively provided protection against Aβ toxicity in multiple in vitro and in vivo models of AD. These findings demonstrate that weak mtCI inhibition by novel compounds C458 and C273, with improved drug‐like properties, is neuroprotective. This supports the feasibility of developing safe and efficacious mtCI inhibitors as a disease‐modifying strategy for AD.

Abstract Background Although novel treatments targeting amyloid‐beta (Aβ) have been recently approved by the FDA, there remains a critical need for alternative therapeutic strategies to delay the onset and progression of Alzheimer's disease (AD). Mitochondrial dysfunction and disrupted brain energy homeostasis are key hallmarks of early‐stage AD. Developing treatments that address these deficits could offer substantial benefits. We identified mitochondrial complex I (mtCI) as a druggable target and demonstrated that its mild inhibition using the small molecule CP2 improves brain energy homeostasis, restores synaptic and cognitive function, and activates neuroprotective signaling in AD mouse models. However, the mechanistic link between mtCI inhibition, glucose metabolism, and energy homeostasis remains unclear. Methods Cellular energy metabolism was assessed in neuroblastoma SH‐SY5Y cells expressing mutant human APP protein (APPswe) and in control cells. Glycolytic function, mitochondrial energetics, and fatty acid β‐oxidation (FAO) were measured using a Seahorse Analyzer. Glucose transporter (GLUT) translocation to the cell surface was evaluated using flow cytometry and immunofluorescence staining. Protein expression changes were analyzed via Western blot, and glucose uptake was quantified with the Glucose Uptake‐Glo™ assay. Additionally, metabolic flux analysis using 13C‐labeled glucose and targeted metabolomics by mass spectrometry were performed to measure specific metabolites. Results APPswe cells displayed significant reductions in glycolysis and spare respiratory capacity, indicative of impaired mitochondrial energy production under stress. These deficits were accompanied by reduced glucose uptake, which was partially compensated by an increase in FAO. At concentrations relevant to in vivo treatments, CP2 acutely enhanced GLUT translocation to the cell surface, increasing glucose uptake within one hour. Enhanced glucose utilization in OXPHOS machinery was confirmed by inhibition of PDH phosphorylation and increased conversion of pyruvate to acetyl‐CoA, fueling the TCA cycle and generating critical signaling metabolites essential for gene regulation. These mechanisms were mediated by AMPK. Conclusion Our findings suggest that mild inhibition of mtCI activates multiple neuroprotective mechanisms, including improved glucose metabolism and energy homeostasis. These consistent results in human cells and AD mouse models highlight the translational potential of this therapeutic approach for AD.

AbstractBackgroundWe identified small molecule tricyclic pyrone compound CP2 as a mild mitochondrial complex I (MCI) inhibitor that induces neuroprotection in multiple mouse models of AD. One of the major concerns while targeting mitochondria is the production of reactive oxygen species (ROS). CP2 consists of two diastereoisomers, D1 and D2, with distinct activity and toxicity profiles. This study was designed to understand how structure of D1 and D2 affects their binding to MCI and the consequential impact on ROS production.MethodThe X‐ray crystallography and cryo‐electron microscopy (cryo‐EM) at global resolution of 3.25‐3.27Å were employed to identify the molecular structure of D1 and D2 and the D1 binding to the isolated ovine MCI. The assessment of the MCI inhibition and the extent of ROS generation were done in isolated MCI and human neuroblastoma MC65 cells using flow cytometry, a Seahorse extracellular flux analyzer, and the kinetic studies.ResultIn the closed conformation of MCI, D1 selectively binds to the deep Quinone‐site (Qd) but not to the shallow Q‐site (Qs), sharing the same binding pocket as rotenone. In the open MCI state, D1 exclusively binds to the Qs in contrast to rotenone, which binds Qd and Qs in both closed and open states. At the same concentrations, D1 inhibits respiration to a greater extent compared to D2 (5:1 ratio) and produces higher level of ROS.ConclusionCryo‐EM unambiguously identified binding of D1 to both the Qd and Qs sites, contingent upon the conformational state of MCI. In contrast to rotenone, D1 binds Qd only in the closed conformation during catalytic cycle, leading to mild inhibition. Superimposing X‐ray crystallography data of D1 and D2 onto cryo‐EM data suggests that the orientation of the methyl group in D2 induces a flatter conformation, resulting in lower binding affinity to MCI, which correlates with lower inhibition and toxicity compared to D1. At physiologically relevant concentrations, CP2 (D1:D2 = 1:1) demonstrates low MCI inhibition yielding negligible ROS levels. This observation provides new insight into the absence of toxicity associated with CP2 treatment in vivo, further highlighting feasibility for the development of safe and efficacious MCI inhibitors.

AbstractBackgroundWhile disease‐modifying treatments that reduce Aβ have been recently approved by the FDA, the identification of novel therapeutic targets and strategies that target underlying mechanisms to delay the AD development are still needed. Abnormal brain energy homeostasis and mitochondria dysfunction are observed early in AD. Therefore, the development of treatments to restore these defects could be beneficial. We identified small molecule (code name CP2) as a mild and specific mitochondrial complex I (MCI) inhibitor. Application of CP2 improved brain energy homeostasis, restored synaptic and cognitive function in APP/PS1 and 3xTgAD mice. However, mechanistic relationship between MCI inhibition, glucose uptake/utilization and mitochondrial function remains to be determined.MethodCellular energy metabolism was assessed in the neuroblastoma SH‐SY5Y cells that express either mutant human APP protein (APPswe) or empty vector (control) treated with vehicle or CP2. A Seahorse Extracellular Flux Analyzer was used to measure glycolysis, oxygen consumption rate, and fatty acids β‐oxidation (FAO). Flow cytometry allowed determining the translocation of glucose transporters to the cell surface. Changes in protein expression in response to treatment were assessed using Western Blot analysis. Changes in mitochondrial morphology were monitored using electron microscopy. The non‐radioactive Glucose Uptake‐Glo™ assay was utilized for measuring glucose uptake in cells. Metabolic flux analysis was done using 13C D‐Glucose stable isotope‐labeling.ResultsAPPswe cells have a significant decrease in glycolysis and spare respiratory capacity, an indicator of the mitochondrial ability to produce energy under stress conditions. These observations were consistent with decreased glucose uptake, which was compensated by an increased FAO to provide axillary fuel for ATP production. Mechanistically, at the concentrations relevant to in vivo treatment in APP/PS1 and 3xTgAD mice, acute CP2 treatment increased glucose uptake and utilization through the translocation of glucose transporters to the plasma membrane while prolong CP2 treatment activated metabolic sensors and mitochondrial morphofunctional pathways (e.g., fission, fusion, biogenesis, and turnover) consistent with the improved cellular bioenergetics in the AMPK‐dependent pathway.ConclusionData suggested that mild MCI inhibition activates multiple neuroprotective mechanisms improving cellular energy homeostasis and mitochondrial function in vivo and in vitro, representing promising strategy that target early AD mechanisms.

Abstract Alveolar macrophages play a crucial role in initiating the inflammatory response in allergic asthma through the cross-linking of the low affinity IgE receptors (FcεRIIb or CD23) by IgE-allergen immunocomplexes. We have previously shown that CD23 cross-linking in monocytes and U937 cells targets IκBα, leading to the activation of the transcription factor NF-κB. We demonstrate in this paper that CD23-initiated signaling in U937 cells leads to hyperphosphorylation of IκBα at Ser32/Ser36 residues. Overexpression of a dominant-negative IκBα transgene containing mutations at Ser32/Ser36 completely inhibits degradation of IκBα, NF-κB activation, and gene transcription that follows CD23 cross-linking. Investigation of the second messengers mediating the CD23-dependent activation of NFκB demonstrates that IκB kinases (IKKs) but not p90rsk are selectively activated following CD23 cross-linking and mediates the phosphorylation of IκBα. Cotransfection experiments with an IKKβ negative dominant completely inhibit CD23 induced NFκB activation. Furthermore, the activation of tyrosine kinase(s) by CD23 is required for the induction of IKK activity, IκBα degradation, and NF-κB nuclear translocation. Taken together, our results show that CD23 cross-linking in the monocytic lineage induces tyrosine kinase activation followed by activation of IKK, which phosphorylates IκBα at the N-terminal domain (Ser32/Ser36), inducing its degradation, NF-κB activation and gene transcription.

Context.— Prostate-specific antigen (PSA) is a 34-kDa glycoprotein with chymotrypsin-like enzyme activity that circulates both in free forms and complexed to various enzyme inhibitors including antichymotrypsin and α 2 -macroglobulin. Prostate-specific antigen bound to α 2 -macroglobulin is not detected by commercial PSA immunoassays. Objective.— To develop a mass spectrometry assay that detects the same forms of PSA as the immunoassays, which could serve as a reference for harmonizing PSA immunoassays. Design.— Prostate-specific antigen was immune extracted from serum, trypsin was digested, and the LSEPAELTDAVK peptide was quantitated on an API 5000 spectrometer. Calibrators were made by adding 10% free and 90% antichymotrypsin-bound PSA to female sera. The assay was standardized to the World Health Organization 96/670 reference standard. Validation of clinical utility and comparisons with 2 immunoassays (Roche cobas and Beckman Access) were performed using frozen sera aliquots from 100 men undergoing prostate biopsy (50 negative, 50 with cancer) and 5 serial samples collected over time from 5 men with advanced prostate cancer. Results.— The antibody extraction efficiency was greater than 99%. The assay has an analytic range from 1.2 to 76 ng/mL, with precision ranging from 8.6% at 1.5 ng/mL to 5.4% at 27 ng/mL. The mass spectrometry assay correlated well with 2 immunoassays. All 3 assays showed statistically equivalent separation of prostate cancer from benign disease using receiver operating characteristic curve analysis. Conclusions.— This mass spectrometry assay can reliably measure PSA concentrations in human serum and could serve as a reference standard for harmonizing PSA immunoassays.

Abstract HIV-1 infection causes the depletion of host CD4 T cells through direct and indirect (bystander) mechanisms. Although HIV Env has been implicated in apoptosis of uninfected CD4 T cells via gp120 binding to either CD4 and/or the chemokine receptor 4 (CXCR4), conflicting data exist concerning the molecular mechanisms involved. Using primary human CD4 T cells, we demonstrate that gp120 binding to CD4 T cells activates proapoptotic p38, but does not activate antiapoptotic Akt. Because ligation of the CD4 receptor alone or the CXCR4 receptor alone causes p38 activation and apoptosis, we used the soluble inhibitors, soluble CD4 (sCD4) or AMD3100, to delineate the role of CD4 and CXCR4 receptors, respectively, in gp120-induced p38 activation and death. sCD4 alone augments gp120-induced death, suggesting that CXCR4 signaling is principally responsible. Supporting that model, AMD3100 reduces death caused by gp120 or by gp120/sCD4. Finally, prevention of gp120-CXCR4 interaction with 12G5 Abs blocks p38 activation and apoptosis, whereas inhibition of CD4-gp120 interaction with Leu-3a has no effect. Consequently, we conclude that gp120 interaction with CXCR4 is required for gp120 apoptotic effects in primary human T cells.