CYP46A1 converts cholesterol to 24-hydroxycholesterol, the principal mechanism for brain cholesterol removal and turnover. CYP46A1 can be allosterically activated with low-dose anti-HIV drug efavirenz and mitigate the manifestations of various neurologic diseases in mouse models and Niemann-Pick type C disease in humans. Yet the underlying reasons for such a broad range of efavirenz therapeutic effects are currently unknown. Here 5XFAD mice, a model of Alzheimer’s disease, were treated with low-dose efavirenz, and assessed for changes in their brain proteome, acetylproteome, and metabolome. Sex-independent increases in brain levels of phosphatidylcholines, sphingomyelins, and certain amino acids were documented, and various functional enrichments were identified. The most notable related to brain energy production, vascularization, and prevention of glutamatergic overactivation. Unexpectedly, these and many other enrichments were mediated by different proteins in female and male 5XFAD mice. Efavirenz treatment of 5XFAD mice was repeated, and energy-related compounds were quantified in the brain after in vivo isotopic labeling. Cerebral vasculature was assessed as well. We found increased glycolysis branching, carbon flux through the tricarboxylic acid cycle, and use of alternative energy sources (fatty acids, ketone bodies, and amino acids). Sex-independent improvements in brain vascularization and integrity of the blood-brain barrier were also documented. Collectively, our data suggested that CYP46A1 activation by efavirenz increases brain metabolic flexibility and thereby brain energetics. This enables the increase in production of the building blocks for cellular and tissue repair and rescue of brain pathology, thus explaining the therapeutic benefits for the broad spectrum of neurologic disorders.

Fentanyl is the leading contributor to opioid-involved overdose (OD) mortality in the United States. Despite the demonstrated efficacy, safety, and wide availability of naloxone (NAL), opioid-involved OD fatalities remain high. This suggests our understanding of the negative integrated physiological effects of fentanyl remains incomplete, and highlights the need to develop additional novel countermeasures. Here we tested whether the physiological and behavioral effects of intravenous fentanyl in adult female goats (n = 12) could be mitigated with NAL or the potential countermeasure d-cysteine ethyl ester (d-CYSee). As hypothesized, intravenous injections of high doses (HD) fentanyl caused immediate ventilatory suppression via reduced breathing frequency leading to hypoventilation and hypoxemia (≥10 min). HD fentanyl elicited immediate and sustained (≥90 min) increases in diaphragm, intercostal, abdominal, and laryngeal constrictor muscle activity along with an increased alveolar to arterial oxygen (A-a O2) gradient and hypertension. Intravenous NAL administered immediately following HD fentanyl mitigated most of these effects except the increased activation of respiratory pump and airway muscles. In contrast, d-CYSee administration immediately following HD fentanyl countered the initial hypoventilation but did not mitigate the increases in muscle activation and persistent hypoxemia. Neither treatment prevented acute withdrawal-like behaviors emerging >90 min after fentanyl administration. The data suggest that there are physiological effects of HD fentanyl that are NAL-insensitive, and d-CYSee can transiently normalize blood gases and counter opioid-induced respiratory depression (OIRD) in adult goats.NEW & NOTEWORTHY Here we determined whether any of the deleterious physiological effects of high-dose fentanyl could be countered by naloxone and/or d-cysteine ethyl ester (d-CYSee) in adult goats. Fentanyl induced hypoventilation and sustained increases in respiratory and airway muscle activity and hypoxemia. Naloxone reversed all fentanyl effects except tonic muscle activation, and d-CYSee reversed fentanyl-induced hypoventilation. These data suggest some effects of fentanyl are naloxone-insensitive and that d-CYSee may be a valuable countermeasure for OIRD.

Lipid homeostasis is subject to control by posttranslational modification machinery, such as sirtuin deacetylases that reverse coenzyme A (CoA)-dependent acetylation. Here, we showed that a mammalian denitrosylase (SCoR2), which counteracts CoA-dependent S-nitrosylation, promoted both fat storage and lipogenesis to impair metabolic health. In mice, SCoR2 protein abundance correlated with body mass, and deleting or pharmacologically inhibiting SCoR2 prevented both diet-induced obesity and metabolic dysfunction-associated steatotic liver disease (MASLD). Loss of SCoR2 in adipocytes promoted the S-nitrosylation of the actin cytoskeletal regulator myosin 9, which inhibited the activity of the lipogenesis-promoting transcription factors PPARγ, SREBP1, and CEBPα to prevent fat storage. In hepatocytes, inhibition of SCoR2-mediated denitrosylation of lipogenic enzymes reduced fat synthesis and induced fat oxidation. In humans, an obesity-linked polymorphism was associated with increased SCoR2 mRNA expression, and in patient adipose and liver tissues, SCoR2 protein or mRNA abundance directly correlated with adipocyte size or MASLD. These results indicate that SCoR2 regulates nutrient metabolism, similar to sirtuins, and is a potential drug target for obesity and MASLD.

Background/Objectives: Ketone salt (KS) containing a racemic beta-hydroxybutyrate mixture is commonly used as an alternative fuel source as it may lead to improved health and/or performance. We postulate that KS will raise acetoacetate levels and represent the effectiveness of exogenous KS as an energy source. We conducted a pilot study to quantify changes in the circulating acetoacetate following KS and to determine if any changes in acetoacetate were associated with the changes in circulating beta-hydroxybutyrate. Methods: Thirteen adults (21.6 ± 4.3 years old; seven males/six females) completed this randomized, triple-blinded, placebo-controlled, cross-over design study. Participants consumed either KS or flavor-matched placebo with a one-week washout period between supplements. Blood samples were taken before and 30 min after consuming each supplement, and plasma acetoacetate and beta-hydroxybutyrate levels were measured by gas chromatography/mass spectrometry. Results: The consumption of KS resulted in a significant increase in acetoacetate from baseline. The increase in acetoacetate after the KS supplement was significantly greater than that following the consumption of a placebo (↑ 0.57 ± 0.44 mM vs. ↑ 0.07 ± 0.23 mM, p = 0.009, d = 0.86), and significantly and strongly related to the change in blood beta-hydroxybutyrate (r = 0.757, p < 0.001). Conclusions: Our findings indicate that KS markedly increases plasma ketone body interconversion, presumably to supply peripheral tissues for ATP generation.

An increased level of phosphorylation of eukaryotic translation initiation factor 2 subunit-α (eIF2α, encoded by EIF2S1; eIF2α-p) coupled with decreased guanine nucleotide exchange activity of eIF2B is a hallmark of the ‘canonical’ integrated stress response (c-ISR)1. It is unclear whether impaired eIF2B activity in human diseases including leukodystrophies2, which occurs in the absence of eIF2α-p induction, is synonymous with the c-ISR. Here we describe a mechanism triggered by decreased eIF2B activity, distinct from the c-ISR, which we term the split ISR (s-ISR). The s-ISR is characterized by translational and transcriptional programs that are different from those observed in the c-ISR. Opposite to the c-ISR, the s-ISR requires eIF4E-dependent translation of the upstream open reading frame 1 and subsequent stabilization of ATF4 mRNA. This is followed by altered expression of a subset of metabolic genes (for example, PCK2), resulting in metabolic rewiring required to maintain cellular bioenergetics when eIF2B activity is attenuated. Overall, these data demonstrate a plasticity of the mammalian ISR, whereby the loss of eIF2B activity in the absence of eIF2α-p induction activates the eIF4E–ATF4–PCK2 axis to maintain energy homeostasis. A study describes the split integrated stress response, a cellular stress response mechanism characterized by reduced eIF2B activity without eIF2α phosphorylation, which activates the eIF4E–ATF4–PCK2 axis, enabling metabolic reprogramming.

Crohn’s disease (CD) has been traditionally viewed as a chronic inflammatory disease that cause gut wall thickening and complications, including fistulas, by mechanisms not understood. By focusing on Parabacteroides distasonis (presumed modern succinate-producing commensal probiotic), recovered from intestinal microfistulous tracts (cavernous fistulous micropathologies CavFT proposed as intermediate between ‘mucosal fissures’ and ‘fistulas’) in two patients that required surgery to remove CD-damaged ilea, we demonstrate that such isolates exert pathogenic/pathobiont roles in mouse models of CD. Our isolates are clonally-related; potentially emerging as transmissible in the community and mice; proinflammatory and adapted to the ileum of germ-free mice prone to CD-like ileitis (SAMP1/YitFc) but not healthy mice (C57BL/6J), and cytotoxic/ATP-depleting to HoxB8-immortalized bone marrow derived myeloid cells from SAMP1/YitFc mice when concurrently exposed to succinate and extracts from CavFT-derived E. coli , but not to cells from healthy mice. With unique genomic features supporting recent genetic exchange with Bacteroides fragilis -BGF539, evidence of international presence in primarily human metagenome databases, these CavFT Pdis isolates could represent to a new opportunistic Parabacteroides species, or subspecies (‘ cavitamuralis’ ) adapted to microfistulous niches in CD.

Skeletal muscle is dynamically controlled by the balance of protein synthesis and degradation. Here we discover an unexpected function for the transcriptional repressor B cell lymphoma 6 (BCL6) in muscle proteostasis and strength in mice. Skeletal muscle-specific Bcl6 ablation in utero or in adult mice results in over 30% decreased muscle mass and force production due to reduced protein synthesis and increased autophagy, while it promotes a shift to a slower myosin heavy chain fibre profile. Ribosome profiling reveals reduced overall translation efficiency in Bcl6 -ablated muscles. Mechanistically, tandem chromatin immunoprecipitation, transcriptomic and translational analyses identify direct BCL6 repression of eukaryotic translation initiation factor 4E-binding protein 1 ( Eif4ebp1 ) and activation of insulin-like growth factor 1 ( Igf1 ) and androgen receptor ( Ar ). Together, these results uncover a bifunctional role for BCL6 in the transcriptional and translational control of muscle proteostasis.

Background: Recently, elevated levels of plasma erythritol have been associated with major adverse cardiovascular events (MACE). It is known that people with HIV (PWH) have a higher cardiovascular disease burden. Whether PWH have higher levels of plasma erythritol has not been evaluated. This study aimed to assess if blood erythritol levels are elevated in PWH and to examine relationships between erythritol and dietary, cardiometabolic, inflammatory, and gut health markers. Methods: Plasma erythritol levels were measured using frozen samples from 162 participants, including 109 PWH and 53 people without HIV (PWoH) in a parent study. General linear models were used to assess the linear relationship between characteristics, cardiovascular measures, markers of body composition, inflammation, and gut integrity with plasma erythritol. Logistic regression was used to assess risk factors associated with PWH, and cumulative logit models were used to investigate which factors were associated with having the highest plasma erythritol levels among PWH. Results: Compared to PWoH, PWH had higher plasma erythritol levels (p = 0.03). Every 10% increase in VLDL (p = 0.01), visceral adipose tissue (p < 0.0001), or TNFrI (p = 0.01) was associated with an approximately 1% increase in plasma erythritol. Among PWH, HgbA1c (p = 0.003), TNFrI (p = 0.002), and IFAB-P (p = 0.004) were associated with having the highest tertile of plasma erythritol (≥3.6 μM). Compared to PWoH, PWH were more than two times as likely (p = 0.03) to have plasma erythritol ≥ 3.6 μM. Conclusions: We identified positive associations between plasma erythritol levels and several factors, including HIV status, BMI, adipose tissue, TNFr1, HbA1c, and VLDL. These results underscore the importance of further investigating the role of elevated plasma erythritol levels in people with HIV, particularly in light of their increased vulnerability to cardiovascular and metabolic diseases.

Pancreatic Ductal Adenocarcinoma (PDAC) is highly resistant to chemotherapy. Effective alternative therapies have yet to emerge, as chemotherapy remains the best available systemic treatment. However, the discovery of safe and available adjuncts to enhance chemotherapeutic efficacy can still improve survival outcomes. We show that a hyperglycemic state substantially enhances the efficacy of conventional single- and multi-agent chemotherapy regimens against PDAC. Molecular analyses of tumors exposed to high glucose levels reveal that the expression of GCLC (glutamate-cysteine ligase catalytic subunit), a key component of glutathione biosynthesis, is diminished, which in turn augments oxidative anti-tumor damage by chemotherapy. Inhibition of GCLC phenocopies the suppressive effect of forced hyperglycemia in mouse models of PDAC, while rescuing this pathway mitigates anti-tumor effects observed with chemotherapy and high glucose.

Results: No CFTR was detected in crypts in the untreated and dexamethasone-treated groups, but apical CFTR was 17.7% and 54.5% greater in duodenal and jejunal crypts in dexamethasone+ETI-treated mice.CFTR was on the apical lateral membranes and basal cytoplasm of enterocytes in all groups, but was 18.9% and 31.5% greater on the apical domain of enterocytes than on the basal and lateral membranes in duodenum and jejunum of dexamethasone+ETI treated group.We observed cells resembling CFTR high expresser cells in all mice.In untreated mice, CFTR was on the apical lateral membranes and basal cytoplasm, whereas in the dexamethasone-and dexamethasone+ETI-treated mice, these cells displayed stronger apical CFTR.Immunoblots showed increased band C CFTR in dexamethasone and dexamethasone+ETI-treated mice.Ussing chamber electrophysiology from all groups showed lack of CFTR short circuit current response to forskolin.Conclusions: Activation of SGK1 and ETI improves morphologic and biochemical but not functional rescue of dF508 CFTR in humanized mice.

Ketone salt (KS) supplementation induces temporary nutritional ketosis to achieve potential exercise performance and health benefits. Racemic KS includes both D/L isomers of β-hydroxybutyrate, yet commercially available measurement devices (i.e., blood meters) only measure the D variant. The aim of this study was to investigate the efficacy of a blood meter to measure serum β-hydroxybutyrate in comparison with gas chromatography–mass spectrometry (GC-MS) before and 30 min after consuming a placebo or racemic KS. In this triple-blinded cross-over study, 16 healthy adults were administered either a placebo or KS drink, and the circulating β-hydroxybutyrate concentration was measured at baseline (PRE) and 30 min following consumption (POST) using a blood ketone meter and by GC-MS. Compared to the placebo, both GC-MS and the blood meter obtained significantly greater β-hydroxybutyrate levels from PRE to POST time-points after consuming KS. Additionally, GC-MS results showed significantly higher levels of β-hydroxybutyrate with both the placebo and KS at PRE and POST time-points, as compared to the blood meter. These results indicate that (1) even in the absence of KS, the blood meter yields significantly lower β-hydroxybutyrate values than GC-MS, and (2) the inability of the blood meter to measure L-β-hydroxybutyrate values POST KS warrants the further development of publicly available ketone measurement apparatuses.

EDITORIAL article Front. Oncol., 12 September 2023Sec. Cancer Metabolism Volume 13 - 2023 | https://doi.org/10.3389/fonc.2023.1286086

Pancreatic β-cells are prone to endoplasmic reticulum (ER) stress due to their role in insulin secretion. They require sustainable and efficient adaptive stress responses to cope with this stress. Whether episodes of chronic stress directly compromise β-cell identity is unknown. We show here under reversible, chronic stress conditions β-cells undergo transcriptional and translational reprogramming associated with impaired expression of regulators of β-cell function and identity. Upon recovery from stress, β-cells regain their identity and function, indicating a high degree of adaptive plasticity. Remarkably, while β-cells show resilience to episodic ER stress, when episodes exceed a threshold, β-cell identity is gradually lost. Single cell RNA-sequencing analysis of islets from type 1 diabetes patients indicates severe deregulation of the chronic stress-adaptation program and reveals novel biomarkers of diabetes progression. Our results suggest β-cell adaptive exhaustion contributes to diabetes pathogenesis.

Previous work has shown that active targeting of nanobubble (NB) ultrasound contrast agents to the prostate-specific membrane antigen (PSMA) significantly prolongs ultrasound signal enhancement in PSMA-expressing prostate cancer. However, the specific mechanism behind this effect is not well understood. Furthermore, prior studies were carried out using clinical ultrasound scanners in a single imaging plane. Because tumor heterogeneity can have a drastic effect on bubble kinetics and resulting contrast enhancement, a single region of interest in one imaging plane over time may not fully represent the contrast dynamics of the entire tumor. Accordingly, in the current work, we used high-frequency dynamic parametric contrast-enhanced ultrasound (DCE-US) imaging to gain a detailed understanding of NB kinetics in prostate tumors in mice. Specifically, we examined the differences in enhancement between the tumor periphery and tumor core in the same imaging plane. We also quantified intact nanobubble retention in the entire tumor volume. To better understand the mechanism behind prolonged tumor enhancement, intracellular retention and the acoustic activity of PSMA-NB were evaluated in cell culture. DCE-US US data suggest that both tumor wash-in and retention of PSMA-NB are delayed due to biomarker interaction and binding. The longer retention of PSMA-NB signal in tumor core supported target-driven bubble extravasation. In vitro studies demonstrated a higher level of internalization and prolonged-acoustic activity of internalized PSMA-NB. GC/MS analysis confirmed gas persistence in the cells after PSMA-NB internalization. The active-targeting of NB results in cellular internalization via receptor-mediated endocytosis, and the location with intracellular vesicles (late-stage endosomes/lysosomes) significantly prolongs gas retention within the cells. These features can enable background-free diagnostic imaging of the target cells/tissues, as well as highly focused ultrasound-modulated therapeutic interventions.

Nutrient-deprived conditions in the tumor microenvironment (TME) restrain cancer cell viability due to increased free radicals and reduced energy production. In pancreatic cancer cells a cytosolic metabolic enzyme, wild-type isocitrate dehydrogenase 1 (wtIDH1), enables adaptation to these conditions. Under nutrient starvation, wtIDH1 oxidizes isocitrate to generate α-ketoglutarate (αKG) for anaplerosis and NADPH to support antioxidant defense. In this study, we show that allosteric inhibitors of mutant IDH1 (mIDH1) are potent wtIDH1 inhibitors under conditions present in the TME. We demonstrate that low magnesium levels facilitate allosteric inhibition of wtIDH1, which is lethal to cancer cells when nutrients are limited. Furthermore, the Food & Drug Administration (FDA)-approved mIDH1 inhibitor ivosidenib (AG-120) dramatically inhibited tumor growth in preclinical models of pancreatic cancer, highlighting this approach as a potential therapeutic strategy against wild-type IDH1 cancers.

Regeneration of myelin in the central nervous system is being pursued as a potential therapeutic approach for multiple sclerosis. Several labs have reported small molecules that promote oligodendrocyte formation and remyelination in vivo. Recently, we reported that many such molecules function by inhibiting a narrow window of enzymes in the cholesterol biosynthesis pathway. Here we describe a new high-throughput screen of 1,836 bioactive molecules and a thorough re-analysis of more than 60 molecules previously identified as promoting oligodendrocyte formation from human, rat, or mouse oligodendrocyte progenitor cells. These studies highlight that an overwhelming fraction of validated screening hits, including several molecules being evaluated clinically for remyelination, inhibit cholesterol pathway enzymes like emopamil-binding protein (EBP). To rationalize these findings, we suggest a model that relies on the high druggability of sterol-metabolizing enzymes and the ability of cationic amphiphiles to mimic the transition state of EBP. These studies further establish cholesterol pathway inhibition as a dominant mechanism among screening hits that enhance human, rat, or mouse oligodendrocyte formation.

Rats trained to hold a lever down for at least 1.0 s but less than 1.3 s could differentiate the reinforced response duration on about 50% of the trials. The response duration frequency distribution was a normal distribution with a peak near the minimum reinforced response duration. Dose-effect curves were determined for the effects of phencyclidine (PCP) and methamphetamine. Subsequently, rats continued to be trained for 3 days a week with responses between 1.0 and 1.3 s reinforced, but on days when injections were given either the maximum reinforced duration was increased to 2.3 s, or the minimum reinforced duration was lowered to 0.5. When the maximum duration was increased to 2.3 s, the percentage of reinforced responses increased to 60% and when the minimum reinforced duration was decreased to 0.5 s, the percentage of reinforced responses increased to 89%. Despite the increased percentage of reinforced responses when the time window was widened, the effects of PCP and methamphetamine were not changed. These data suggest that the effects of drugs on response duration differentiation are not greatly influenced by transient changes in reinforcement frequency.

Background: Cystic fibrosis liver disease (CFLD) affects 27% to 35% of patients [1] and is the third-leading cause of death in people with CF after lung disease and transplantation complications [2].Although cirrhosis is the classic phenotype of CFLD, hepatic steatosis is most prevalent, occurring in up to 60% of patients.Steatosis on its own is not indicative of CFLD but is associated with fibrosis and cirrhosis in people with CF and may be present independent of classic CFLD, with similarities to nonalcoholic fatty liver disease [3].Steatosis occurs in the CF mouse, and CF mice exposed to high-fat, ketogenic diets fail to thrive and have higher morbidity and worse hepatic steatosis than wild-type mice that thrive under the same conditions with no detectable steatosis.A study in rats demonstrated that infusions of angiotensin II, a component of the reninangiotensin signaling pathway, increased triglyceride production, resulting in accumulation of free fatty acids in the liver, which is a hallmark of steatosis.Pharmacological inhibition of the angiotensin II type-2 receptor (AGTR2) suppresses this phenomenon, normalizing plasma triglyceride and free fatty acid levels [4].A large CF genome-wide association study identified a genetic region containing AGTR2 as being associated with CF lung disease severity, and our studies concluded that absence or antagonism of AGTR2 improves pulmonary function indices in CF mice carrying various CFTR mutations [5].The goal of this study was to determine whether loss of AGTR2 in CF mice would not only improve pulmonary function, but also correct the CF-specific steatosis phenotypes evident during ketogenic challenge.Methods: F508del CF mice, C57BL/6 WT, and Agtr2/F508del double knockout mice were weighed and fasted on aspen bedding for 24 hours, given free access to a high-fat ketogenic diet, and monitored for 3 days.On the fourth day, livers were visually assessed for a white, punctiform appearance, indicative of steatosis.Liver samples and blood were obtained for mass spectrometry analyses, and liver was fixed for Oil red staining.Results: All mice lost 5% to 10% of their bodyweight during the 24-hour fast.After access to high-fat food, CF mice failed to thrive over the course of the ketogenic challenge, progressively losing weight, whereas WT and Agtr2/CF mice stabilized and gained weight by day 4. Macroscopically, CF mice developed severe steatosis, whereas WT and Agtr2/CF mice displayed normal, healthy liver color and texture.Oil red staining in the CF liver revealed larger, more-numerous oil droplets, indicating lipid invasion than WT and Agtr2/CF mice.Pending mass spectrometry analysis of blood and liver will reveal any differences in lipid composition between the groups.Conclusions: Not only does loss of AGTR2 act as an effective modifier of CF pulmonary disease, but also seems to confer some protection against lipid invasion, steatosis, and failure to thrive in CF mice during metabolic challenge.CF mice that lack AGTR2 are nearly indistinguishable from their WT counterparts, suggesting that CFTR-associated steatosis can be reduced or potentially eliminated by loss or blocking of AGTR2.This protection against steatosis could have a marked impact on the occurrence of fibrosis, cirrhosis, and other liver diseases in adults with CF.Taken together, these data suggest that AGTR2 is a valuable CFTR-independent target for pharmacological therapy in CF.

Background Down syndrome is a chromosomal disorder with considerable neurodevelopmental impact and neurodegenerative morbidity. In a pilot trial in young adults with Down syndrome, memantine (a drug approved for Alzheimer's disease) showed a significant effect on a secondary measure of episodic memory. We aimed to test whether memantine would improve episodic memory in adolescents and young adults with Down syndrome. Methods We did a randomised, double-blind, placebo-controlled phase 2 trial with a parallel design, stratified by age and sex. Participants (aged 15-32 years) with either trisomy 21 or complete unbalanced translocation of chromosome 21 and in general good health were recruited from the community at one site in Brazil and another in the USA. Participants were randomly assigned (1:1) to receive either memantine (20 mg/day orally) or placebo for 16 weeks. Computer-generated randomisation tables for both sites (allocating a placebo or drug label to each member of a unique pair of participants) were centrally produced by an independent statistician and were shared only with investigational pharmacists at participating sites until unblinding of the study. Participants and investigators were masked to treatment assignments. Neuropsychological assessments were done at baseline (T1) and week 16 (T2). The primary outcome measure was change from baseline to week 16 in the California Verbal Learning Test-second edition short-form (CVLT-II-sf) total free recall score, assessed in the per-protocol population (ie, participants who completed 16 weeks of treatment and had neuropsychological assessments at T1 and T2). Linear mixed effect models were fit to data from the per-protocol population. Safety and tolerability were monitored and analysed in all participants who started treatment. Steady-state concentrations in plasma of memantine were measured at the end of the trial. This study is registered at ClinicalTrials.gov, number NCT02304302. Findings From May 13, 2015, to July 22, 2020, 185 participants with Down syndrome were assessed for eligibility and 160 (86%) were randomly assigned either memantine (n=81) or placebo (n=79). All participants received their allocated treatment. Linear mixed effect models were fit to data from 149 (81%) participants, 73 in the memantine group and 76 in the placebo group, after 11 people (eight in the memantine group and three in the placebo group) discontinued due to COVID-19 restrictions, illness of their caregiver, adverse events, or low compliance. The primary outcome measure did not differ between groups (CVLT-II-sf total free recall score, change from baseline 0.34 points [95% CI -0.98 to 1.67], p=0.61). Memantine was well tolerated, with infrequent mild-to-moderate adverse events, the most common being viral upper respiratory infection (nine [11%] participants in the memantine group and 12 [15%] in the placebo group) and transient dizziness (eight [10%] in the memantine group and six [8%] in the placebo group). No serious adverse events were observed. Amounts of memantine in plasma were substantially lower than those considered therapeutic for Alzheimer's disease. Interpretation Memantine was well tolerated, but cognition-enhancing effects were not recorded with a 20 mg/day dose in adolescents and young adults with Down syndrome. Exploratory analyses point to a need for future work. Funding Alana Foundation. Copyright (C) 2021 Elsevier Ltd. All rights reserved.