Robert Chott

Commitment to glycolysis sustains survival of NO-producing inflammatory dendritic cells

TLR agonists initiate a rapid activation program in dendritic cells (DCs) that requires support from metabolic and bioenergetic resources. We found previously that TLR signaling promotes aerobic glycolysis and a decline in oxidative phosphorylation (OXHPOS) and that glucose restriction prevents activation and leads to premature cell death. However, it remained unclear why the decrease in OXPHOS occurs under these circumstances. Using real-time metabolic flux analysis, in the present study, we show that mitochondrial activity is lost progressively after activation by TLR agonists in inflammatory blood monocyte-derived DCs that express inducible NO synthase. We found that this is because of inhibition of OXPHOS by NO and that the switch to glycolysis is a survival response that serves to maintain ATP levels when OXPHOS is inhibited. Our data identify NO as a profound metabolic regulator in inflammatory monocyte-derived DCs.

Increased in Vivo Amyloid-β42 Production, Exchange, and Loss in Presenilin Mutation Carriers

Aβ42 kinetics are altered in the central nervous system of patients with autosomal dominant Alzheimer’s disease. Aβ42: A Cycle of Gain and Loss The amyloid hypothesis of Alzheimer’s disease (AD) proposes that increased production or impaired clearance of Aβ42 peptide causes deposition of amyloid in plaques, nerve destruction, and ultimately AD dementia. Animal model studies based on human autosomal dominant mutations have shown that increasing the production of Aβ peptides, especially Aβ42, can recapitulate amyloidosis. Potter et al. have now used a stable isotope labeling kinetics (SILK) approach to measure Aβ isoform kinetics to test specific hypotheses regarding the production rates of the Aβ38, Aβ40, and Aβ42 peptides in individuals carrying autosomal dominant AD mutations and related noncarriers. The authors found an increased Aβ42 production rate in AD mutation carriers that was ~25% higher than that in noncarriers. In addition to increased production rates, the authors unexpectedly found altered Aβ42 kinetics in mutation carriers that indicated both a reversible exchange pool and increased irreversible loss. Future studies could quantify the effects of proposed disease-modifying drugs to normalize altered Aβ kinetics and provide a metric to gauge target engagement for therapeutic trials. Alzheimer’s disease (AD) is hypothesized to be caused by an overproduction or reduced clearance of amyloid-β (Aβ) peptide. Autosomal dominant AD (ADAD) caused by mutations in the presenilin (PSEN) gene have been postulated to result from increased production of Aβ42 compared to Aβ40 in the central nervous system (CNS). This has been demonstrated in rodent models of ADAD but not in human mutation carriers. We used compartmental modeling of stable isotope labeling kinetic (SILK) studies in human carriers of PSEN mutations and related noncarriers to evaluate the pathophysiological effects of PSEN1 and PSEN2 mutations on the production and turnover of Aβ isoforms. We compared these findings by mutation status and amount of fibrillar amyloid deposition as measured by positron emission tomography (PET) using the amyloid tracer Pittsburgh compound B (PIB). CNS Aβ42 to Aβ40 production rates were 24% higher in mutation carriers compared to noncarriers, and this was independent of fibrillar amyloid deposits quantified by PET PIB imaging. The fractional turnover rate of soluble Aβ42 relative to Aβ40 was 65% faster in mutation carriers and correlated with amyloid deposition, consistent with increased deposition of Aβ42 into plaques, leading to reduced recovery of Aβ42 in cerebrospinal fluid (CSF). Reversible exchange of Aβ42 peptides with preexisting unlabeled peptide was observed in the presence of plaques. These findings support the hypothesis that Aβ42 is overproduced in the CNS of humans with PSEN mutations that cause AD, and demonstrate that soluble Aβ42 turnover and exchange processes are altered in the presence of amyloid plaques, causing a reduction in Aβ42 concentrations in the CSF.

An Antidepressant Decreases CSF Aβ Production in Healthy Individuals and in Transgenic AD Mice

The antidepressant drug citalopram decreased CSF amyloid-β in healthy humans, and in an aged transgenic mouse model of Alzheimer’s disease, it decreased ISF amyloid-β in a dose-dependent manner. Reducing Amyloid-β with SSRIs Higher rates of cognitive decline have been shown in cognitively normal individuals with increased brain amyloid burden, suggesting that increased amyloid burden represents a preclinical phase of Alzheimer’s disease (AD). Increased amyloid burden can occur decades before the onset of cognitive symptoms. Working in an AD mouse model and in healthy young humans, Sheline et al. tested whether an antidepressant drug could help to lower brain amyloid burden. The drug used in this study, citalopram, belongs to the selective serotonin reuptake inhibitor (SSRI) class of antidepressant drugs. The authors selected this drug because serotonin signaling is known to suppress generation of amyloid-β (Aβ) in animal models of AD. They show that in an aged transgenic AD mouse model, citalopram decreased brain Aβ concentrations in a dose-dependent manner. Further, citalopram halted the growth of preexisting brain amyloid plaques and reduced the appearance of new plaques by 78%. In healthy human volunteers, citalopram’s effects on Aβ production and Aβ concentrations in cerebrospinal fluid (CSF) were measured prospectively. Aβ production in CSF was slowed by 37% in the citalopram group compared to placebo, and there was a 38% decrease in total CSF Aβ concentrations. The ability to safely decrease Aβ concentrations is potentially important as a preventive strategy for AD. Serotonin signaling suppresses generation of amyloid-β (Aβ) in vitro and in animal models of Alzheimer’s disease (AD). We show that in an aged transgenic AD mouse model (APP/PS1 plaque-bearing mice), the antidepressant citalopram, a selective serotonin reuptake inhibitor, decreased Aβ in brain interstitial fluid in a dose-dependent manner. Growth of individual amyloid plaques was assessed in plaque-bearing mice that were chronically administered citalopram. Citalopram arrested the growth of preexisting plaques and reduced the appearance of new plaques by 78%. In healthy human volunteers, citalopram’s effects on Aβ production and Aβ concentrations in cerebrospinal fluid (CSF) were measured prospectively using stable isotope labeling kinetics, with CSF sampling during acute dosing of citalopram. Aβ production in CSF was slowed by 37% in the citalopram group compared to placebo. This change was associated with a 38% decrease in total CSF Aβ concentrations in the drug-treated group. The ability to safely decrease Aβ concentrations is potentially important as a preventive strategy for AD. This study demonstrates key target engagement for future AD prevention trials.

Age and amyloid effects on human central nervous system amyloid-beta kinetics.

Age is the single greatest risk factor for Alzheimers disease (AD), with the incidence doubling every 5 years after age 65. However, our understanding of the mechanistic relationship between increasing age and the risk for AD is currently limited. We therefore sought to determine the relationship between age, amyloidosis, and amyloid‐beta (Aβ) kinetics in the central nervous system (CNS) of humans.

In vivo kinetic approach reveals slow SOD1 turnover in the CNS

Therapeutic strategies that target disease-associated transcripts are being developed for a variety of neurodegenerative syndromes. Protein levels change as a function of their half-life, a property that critically influences the timing and application of therapeutics. In addition, both protein kinetics and concentration may play important roles in neurodegeneration; therefore, it is essential to understand in vivo protein kinetics, including half-life. Here, we applied a stable isotope-labeling technique in combination with mass spectrometric detection and determined the in vivo kinetics of superoxide dismutase 1 (SOD1), mutation of which causes amyotrophic lateral sclerosis. Application of this method to human SOD1-expressing rats demonstrated that SOD1 is a long-lived protein, with a similar half-life in both the cerebral spinal fluid (CSF) and the CNS. Additionally, in these animals, the half-life of SOD1 was longest in the CNS when compared with other tissues. Evaluation of this method in human subjects demonstrated successful incorporation of the isotope label in the CSF and confirmed that SOD1 is a long-lived protein in the CSF of healthy individuals. Together, the results of this study provide important insight into SOD1 kinetics and support application of this technique to the design and implementation of clinical trials that target long-lived CNS proteins.

CNS Amyloid-β, Soluble APP-α and -β Kinetics during BACE Inhibition

BACE, a β-secretase, is an attractive potential disease-modifying therapeutic strategy for Alzheimers disease (AD) as it results directly in the decrease of amyloid precursor protein (APP) processing through the β-secretase pathway and a lowering of CNS amyloid-β (Aβ) levels. The interaction of the β-secretase and α-secretase pathway-mediated processing of APP in the rhesus monkey (nonhuman primate; NHP) CNS is not understood. We hypothesized that CNS inhibition of BACE would result in decreased newly generated Aβ and soluble APPβ (sAPPβ), with increased newly generated sAPPα. A stable isotope labeling kinetics experiment in NHPs was performed with a 13C6-leucine infusion protocol to evaluate effects of BACE inhibition on CNS APP processing by measuring the kinetics of sAPPα, sAPPβ, and Aβ in CSF. Each NHP received a low, medium, or high dose of MBI-5 (BACE inhibitor) or vehicle in a four-way crossover design. CSF sAPPα, sAPPβ, and Aβ were measured by ELISA and newly incorporated label following immunoprecipitation and liquid chromatography-mass spectrometry. Concentrations, kinetics, and amount of newly generated APP fragments were calculated. sAPPβ and sAPPα kinetics were similar, but both significantly slower than Aβ. BACE inhibition resulted in decreased labeled sAPPβ and Aβ in CSF, without observable changes in labeled CSF sAPPα. ELISA concentrations of sAPPβ and Aβ both decreased and sAPPα increased. sAPPα increased by ELISA, with no difference by labeled sAPPα kinetics indicating increases in product may be due to APP shunting from the β-secretase to the α-secretase pathway. These results provide a quantitative understanding of pharmacodynamic effects of BACE inhibition on NHP CNS, which can inform about target development.

Gastric cancer in Zambian adults: a prospective case-control study that assessed dietary intake and antioxidant status by using urinary isoprostane excretion

BACKGROUND Gastric cancer is increasingly recognized in Zambia. Although nutritional factors contribute to gastric cancer risk, their effect in Zambia is unknown. OBJECTIVE The objective was to investigate the association between intake of dietary antioxidants, urinary 8-iso prostaglandin F2α (8-iso PGF2α) as a marker of oxidative stress, and gastric cancer. DESIGN This was a case-control study at the University Teaching Hospital in Zambia. Gastric cancer cases were compared with age- and sex-matched controls. Urine 8-iso PGF2α was measured primarily by ELISA, and by gas chromatography-mass spectrometry in a subset, expressed as a ratio to creatinine. Blood was collected for Helicobacter pylori, HIV serology, gastrin-17, and pepsinogen 1 and 2 concentrations. Clinical and dietary data were collected by using questionnaires. Food items were broadly classified into 7 major categories (fruit, vegetables, fish, meat, insects, cereals, and starches). RESULTS Fifty cases with gastric cancer (mean age: 61 y; n = 31 males) and 90 controls (mean age: 54 y; n = 41 males) were enrolled. Median urinary 8-iso PGF2α excretion was higher in cases (0.014; IQR: 0.008-0.021) than in controls (0.011; IQR: 0.006-0.018; P = 0.039). On univariate analysis, habitual fruit intake was lower in cases than in controls during the dry season (P = 0.02). On multivariate analysis, smoking (OR: 7.22; IQR: 1.38-37.9) and gastric atrophy (OR: 2.43; IQR: 1.12-5.13) were independently associated with cancer, and higher fruit intake was protective (OR: 0.44; IQR: 0.20-0.95). Isoprostane excretion was inversely correlated with total fruit intake (ρ = -0.23; n = 140; P = 0.006). CONCLUSION Urinary 8-iso PGF2α excretion was associated with the risk of gastric cancer, as were smoking and gastric atrophy, but increased fruit intake conferred protection. This trial was registered at www.pactr.org as ISRCTN52971746.

Age and Amyloid Effects on Human CNS Amyloid-Beta Kinetics

Age is the single greatest risk factor for Alzheimers disease (AD), with the incidence doubling every 5 years after age 65. However, our understanding of the mechanistic relationship between increasing age and the risk for AD is currently limited. We therefore sought to determine the relationship between age, amyloidosis, and amyloid‐beta (Aβ) kinetics in the central nervous system (CNS) of humans.

Age and amyloid effects on human central nervous system amyloid-beta kinetics: Age and Amyloid affects Aβ kinetics

Age is the single greatest risk factor for Alzheimers disease (AD), with the incidence doubling every 5 years after age 65. However, our understanding of the mechanistic relationship between increasing age and the risk for AD is currently limited. We therefore sought to determine the relationship between age, amyloidosis, and amyloid‐beta (Aβ) kinetics in the central nervous system (CNS) of humans.

Tau kinetics in the human cns

new datasets), increasing our discovery sample to 21,433 cases and 44,340 controls. Methods: All datasets were imputed to a 1000 Genomes reference panel (Phase 1 v3, March 2012) of over 37 million variants, many of which are low-frequency single nucleotide variants (SNV) and indels. Single-variant-based association analysis was conducted adjusting for age, sex and population substructure. Individual datasets were analyzed with the score test for case-control datasets and general estimating equations (with generalized linear mixed model for rare variants) for family-based analyses. Within-study results were meta-analyzed in METAL. Gene-based testing was conducted on summary statistics using VEGAS. Results: Imputation produced approximately nine million high-quality low-frequency variants for analyses. Twenty-five loci were genomewide significant at P 5310-8, including five novel loci. Three of these novel loci are driven by significant low-frequency variants, while two are associations of common intergenic variants between the genes USP6NL and ECHDC3 at Chr10: 10:11720308 (P1⁄42.91x10) and the genes CYYR1 and ADAMTS1 at Chr21: 28,156,856 (P1⁄41.44x10). Previously reported rare and low-frequency variants in TREM2 and SORL1 were also significantly associated, while low-frequency SNVs in the common loci BIN1 (MAF1⁄40.026) and CLU (MAF1⁄40.029) show suggestive significance (P 5310-7). Twelve additional loci produced signals with suggestive significance, seven driven by low-frequency or rare variants and five driven by common variants. Genotyping to confirm imputation quality, and replication genotyping using the Sequenom MassArray are underway. Gene-based analyses identified 13 significantly associated genes (Bonferroni P 2.83x10-6), four of which are novel loci driven by nominally significant low-frequency variants. Conclusions: Using an imputation set with a large number of rare variants we identified several novel candidate loci for LOAD, giving support to the hypothesis that rare and low-frequency variant imputation can identify novel associations with disease.