Metabolomics Signatures of serotonin reuptake inhibitor (Escitalopram), serotonin norepinephrine reuptake inhibitor (Duloxetine) and Cognitive Behavior Therapy on Key Neurotransmitter Pathways in Major Depressive Disorder

Metabolomics provides powerful tools that can inform about heterogeneity in disease and response to treatments. In this study, we employed an electrochemistry-based targeted metabolomics platform to assess the metabolic effects of three randomly-assigned treatments: escitalopram, duloxetine, and Cognitive Behavior Therapy (CBT) in 163 treatment-naïve outpatients with major depressive disorder. Serum samples from baseline and 12 weeks post-treatment were analyzed using targeted liquid chromatography-electrochemistry for metabolites related to tryptophan, tyrosine metabolism and related pathways. Changes in metabolite concentrations related to each treatment arm were identified and compared to define metabolic signatures of exposure. In addition, association between metabolites and depressive symptom severity (assessed with the 17-item Hamilton Rating Scale for Depression [HRSD17]) and anxiety symptom severity (assessed with the 14-item Hamilton Rating Scale for Anxiety [HRSA14]) were evaluated, both at baseline and after 12 weeks of treatment. Significant reductions in serum serotonin level and increases in tryptophan-derived indoles that are gut bacterially derived were observed with escitalopram and duloxetine arms but not in CBT arm. These include indole-3-propionic acid (I3PA), indole-3-lactic acid (I3LA) and Indoxyl sulfate (IS), a uremic toxin. Purine-related metabolites were decreased across all arms. Different metabolites correlated with improved symptoms in the different treatment arms revealing potentially different mechanisms between response to antidepressant medications and to CBT.

The DIRAC framework: Geometric structure underlies roles of diversity and accuracy in combining classifiers

Combining classification systems potentially improves predictive accuracy, but outcomes have proven impossible to predict. Similar to improving binary classification with fusion, fusing ranking systems most commonly increases Pearson or Spearman correlations with a target when the input classifiers are "sufficiently good" (generalized as "accuracy") and "sufficiently different" (generalized as "diversity"), but the individual and joint quantitative influence of these factors on the final outcome remains unknown. We resolve these issues. Building on our previous empirical work establishing the DIRAC (DIversity of Ranks and ACcuracy) framework, which accurately predicts the outcome of fusing binary classifiers, we demonstrate that the DIRAC framework similarly explains the outcome of fusing ranking systems. Specifically, precise geometric representation of diversity and accuracy as angle-based distances within rank-based combinatorial structures (permutahedra) fully captures their synergistic roles in rank approximation, uncouples them from the specific metrics of a given problem, and represents them as generally as possible.

Serum Bile Acids Improve Prediction of Alzheimer's Progression in a Sex-Dependent Manner

Sex disparities in serum bile acid (BA) levels and Alzheimer's disease (AD) prevalence have been established. However, the precise link between changes in serum BAs and AD development remains elusive. Here, authors quantitatively determined 33 serum BAs and 58 BA features in 4 219 samples collected from 1 180 participants from the Alzheimer's Disease Neuroimaging Initiative. The findings revealed that these BA features exhibited significant correlations with clinical stages, encompassing cognitively normal (CN), early and late mild cognitive impairment, and AD, as well as cognitive performance. Importantly, these associations are more pronounced in men than women. Among participants with progressive disease stages (n = 660), BAs underwent early changes in men, occurring before AD. By incorporating BA features into diagnostic and predictive models, positive enhancements are achieved for all models. The area under the receiver operating characteristic curve improved from 0.78 to 0.91 for men and from 0.76 to 0.83 for women for the differentiation of CN and AD. Additionally, the key findings are validated in a subset of participants (n = 578) with cerebrospinal fluid amyloid-beta and tau levels. These findings underscore the role of BAs in AD progression, offering potential improvements in the accuracy of AD prediction.

The MT1 receptor as the target of ramelteon neuroprotection in ischemic stroke

Stroke is the leading cause of death and disability worldwide. Novel and effective therapies for ischemic stroke are urgently needed. Here, we report that melatonin receptor 1A (MT1) agonist ramelteon is a neuroprotective drug candidate as demonstrated by comprehensive experimental models of ischemic stroke, including a middle cerebral artery occlusion (MCAO) mouse model of cerebral ischemia in vivo, organotypic hippocampal slice cultures ex vivo, and cultured neurons in vitro; the neuroprotective effects of ramelteon are diminished in MT1-knockout (KO) mice and MT1-KO cultured neurons. For the first time, we report that the MT1 receptor is significantly depleted in the brain of MCAO mice, and ramelteon treatment significantly recovers the brain MT1 losses in MCAO mice, which is further explained by the Connectivity Map L1000 bioinformatic analysis that shows gene-expression signatures of MCAO mice are negatively connected to melatonin receptor agonist like Ramelteon. We demonstrate that ramelteon improves the cerebral blood flow signals in ischemic stroke that is potentially mediated, at least, partly by mechanisms of activating endothelial nitric oxide synthase. Our results also show that the neuroprotection of ramelteon counteracts reactive oxygen species-induced oxidative stress and activates the nuclear factor erythroid 2-related factor 2/heme oxygenase-1 pathway. Ramelteon inhibits the mitochondrial and autophagic death pathways in MCAO mice and cultured neurons, consistent with gene set enrichment analysis from a bioinformatics perspective angle. Our data suggest that Ramelteon is a potential neuroprotective drug candidate, and MT1 is the neuroprotective target for ischemic stroke, which provides new insights into stroke therapy. MT1-KO mice and cultured neurons may provide animal and cellular models of accelerated ischemic damage and neuronal cell death.

Risk Factors for Type 2 Diabetes in the Multiethnic Cohort

OBJECTIVES

In this report, we investigated the association between established risk factors and type 2 diabetes (T2D) across 5 distinct ethnic groups and explored differences according to T2D definition within the Multiethnic Cohort (MEC) Study.

METHODS

Using the full MEC, with participants in Hawaii and Los Angeles (N=172,230), we applied Cox regression to estimate hazard ratios (HRs) and 95% confidence intervals (CIs). All participants completed questionnaires asking about demographics, anthropometrics, lifestyle factors, and regular diet. T2D status was determined from self-reported diagnosis/medication and Medicare claims. We assessed the associations between well-established risk factors and T2D in the full cohort, after stratification by ethnic group, according to the T2D definition, and in a biorepository subset. Effect modification by ethnicity was evaluated using Wald's tests.

RESULTS

Overall, 46,500 (27%) participants had an incident T2D diagnosis after a mean follow-up of 17.1±6.9 years. All predictors were significantly associated with T2D: overweight (HR=1.74), obesity (HR=2.90), red meat intake (HR=1.15), short (HR=1.04) and long (HR=1.08) sleep duration, and smoking (HR=1.26) predicted a significantly higher T2D incidence, whereas coffee (HR=0.90) and alcohol (HR=0.78) consumption, physical activity (HR=0.89), and diet quality (HR=0.96) were associated with lower T2D incidence. The strength of these associations was similar across ethnic groups with noteworthy disparities for overweight/obesity, physical activity, alcohol intake, coffee consumption, and diet quality.

CONCLUSIONS

These findings confirm the importance of known risk factors for T2D across ethnic groups, but small differences were detected that may contribute to disparate incidence rates in some ethnic groups, especially for obesity and physical activity.

Age-related changes in circadian regulation of the human plasma lipidome

Aging alters the amplitude and phase of centrally regulated circadian rhythms. Here we evaluate whether peripheral circadian rhythmicity in the plasma lipidome is altered by aging through retrospective lipidomics analysis on plasma samples collected in 24 healthy individuals (9 females; mean ± SD age: 40.9 ± 18.2 years) including 12 younger (4 females, 23.5 ± 3.9 years) and 12 middle-aged older, (5 females, 58.3 ± 4.2 years) individuals every 3 h throughout a 27-h constant routine (CR) protocol, which allows separating evoked changes from endogenously generated oscillations in physiology. Cosinor regression shows circadian rhythmicity in 25% of lipids in both groups. On average, the older group has a ~14% lower amplitude and a ~2.1 h earlier acrophase of the lipid circadian rhythms (both, p ≤ 0.001). Additionally, more rhythmic circadian lipids have a significant linear component in addition to the sinusoidal across the 27-h CR in the older group (44/56) compared to the younger group (18/58, p < 0.0001). Results from individual-level data are consistent with group-average results. Results indicate that prevalence of endogenous circadian rhythms of the human plasma lipidome is preserved with healthy aging into middle-age, but significant changes in rhythmicity include a reduction in amplitude, earlier acrophase, and an altered temporal relationship between central and lipid rhythms.

Circulating lipid profiles are associated with cross-sectional and longitudinal changes of central biomarkers for Alzheimer's disease

Investigating the association of lipidome profiles with central Alzheimer's disease (AD) biomarkers, including amyloid/tau/neurodegeneration (A/T/N), can provide a holistic view between the lipidome and AD. We performed cross-sectional and longitudinal association analysis of serum lipidome profiles with AD biomarkers in the Alzheimer's Disease Neuroimaging Initiative cohort (N=1,395). We identified lipid species, classes, and network modules that were significantly associated with cross-sectional and longitudinal changes of A/T/N biomarkers for AD. Notably, we identified the lysoalkylphosphatidylcholine (LPC(O)) as associated with "A/N" biomarkers at baseline at lipid species, class, and module levels. Also, GM3 ganglioside showed significant association with baseline levels and longitudinal changes of the "N" biomarkers at species and class levels. Our study of circulating lipids and central AD biomarkers enabled identification of lipids that play potential roles in the cascade of AD pathogenesis. Our results suggest dysregulation of lipid metabolic pathways as precursors to AD development and progression.

Genetic loci of beta-aminoisobutyric acid are associated with aging-related mild cognitive impairment

We studied the genetic associations of a previously developed Metabolomic Risk Score (MRS) for Mild Cognitive Impairment (MCI) and beta-aminoisobutyric acid metabolite (BAIBA)-the metabolite highlighted by results from a genome-wide association study (GWAS) of the MCI-MRS, and assessed their association with MCI in datasets of diverse race/ethnicities. We first performed a GWAS for the MCI-MRS and BAIBA, in Hispanic/Latino adults (n = 3890) from the Hispanic Community Health Study/Study of Latinos (HCHS/SOL). We identified ten independent genome-wide significant (p value <5 × 10-8) variants associated with MCI-MRS or BAIBA. Variants associated with the MCI-MRS are located in the Alanine-Glyoxylate Aminotransferase 2 (AGXT2 gene), which is known to be associated with BAIBA metabolism. Variants associated with BAIBA are located in the AGXT2 gene and in the SLC6A13 gene. Next, we tested the variants' association with MCI in independent datasets of n = 3178 HCHS/SOL older individuals, n = 3775 European Americans, and n = 1032 African Americans from the Atherosclerosis Risk In Communities (ARIC) study. Variants were considered associated with MCI if their p value <0.05 in the meta-analysis of the three datasets and their direction of association was consistent with expectation. Rs16899972 and rs37369 from the AGXT2 region were associated with MCI. Mediation analysis supported the mediation effect of BAIBA between the two genetic variants and MCI (p value = 0.004 for causal mediated effect). In summary, genetic variants in the AGXT2 region are associated with MCI in Hispanic/Latino, African, and European American populations in the USA, and their effect is likely mediated by changes in BAIBA levels.

Plasma metabolites associated with cognitive function across race/ethnicities affirming the importance of healthy nutrition

INTRODUCTION

We studied the replication and generalization of previously identified metabolites potentially associated with global cognitive function in multiple race/ethnicities and assessed the contribution of diet to these associations.

METHODS

We tested metabolite-cognitive function associations in U.S.A. Hispanic/Latino adults (n = 2222) from the Community Health Study/ Study of Latinos (HCHS/SOL) and in European (n = 1365) and African (n = 478) Americans from the Atherosclerosis Risk In Communities (ARIC) Study. We applied Mendelian Randomization (MR) analyses to assess causal associations between the metabolites and cognitive function and between Mediterranean diet and cognitive function.

RESULTS

Six metabolites were consistently associated with lower global cognitive function across all studies. Of these, four were sugar-related (e.g., ribitol). MR analyses provided weak evidence for a potential causal effect of ribitol on cognitive function and bi-directional effects of cognitive performance on diet.

DISCUSSION

Several diet-related metabolites were associated with global cognitive function across studies with different race/ethnicities.

HIGHLIGHTS

Metabolites associated with cognitive function in Puerto Rican adults were recently identified. We demonstrate the generalizability of these associations across diverse race/ethnicities. Most identified metabolites are related to sugars. Mendelian Randomization (MR) provides weak evidence for a causal effect of ribitol on cognitive function. Beta-cryptoxanthin and other metabolites highlight the importance of a healthy diet.

Body Fat Distribution, Glucose Metabolism, and Diabetes Status Among Older Adults: The Multiethnic Cohort Adiposity Phenotype Study

BACKGROUND

As the proportion of visceral (VAT) to subcutaneous adipose tissue (SAT) may contribute to type 2 diabetes (T2D) development, we examined this relation in a cross-sectional design within the Multiethnic Cohort that includes Japanese Americans known to have high VAT. The aim was to understand how ectopic fat accumulation differs by glycemic status across ethnic groups with disparate rates of obesity, T2D, and propensity to accumulate VAT.

METHODS

In 2013-2016, 1,746 participants aged 69.2 (standard deviation, 2.7) years from five ethnic groups completed questionnaires, blood collections, and whole-body dual X-ray absorptiometry and abdominal magnetic resonance imaging scans. Participants with self-reported T2D and/or medication were classified as T2D, those with fasting glucose >125 and 100-125 mg/dL as undiagnosed cases (UT2D) and prediabetes (PT2D), respectively. Using linear regression, we estimated adjusted means of adiposity measures by T2D status.

RESULTS

Overall, 315 (18%) participants were classified as T2D, 158 (9%) as UT2D, 518 (30%) as PT2D, and 755 (43%) as normoglycemic (NG), with significant ethnic differences (P < 0.0001). In fully adjusted models, VAT, VAT/SAT, and percent liver fat increased significantly from NG, PT2D, UT2D, to T2D (P < 0.001). Across ethnic groups, the VAT/SAT ratio was lowest for NG participants and highest for T2D cases. Positive trends were observed in all groups except African Americans, with highest VAT/SAT in Japanese Americans.

CONCLUSION

These findings indicate that VAT plays an important role in T2D etiology, in particular among Japanese Americans with high levels of ectopic adipose tissue, which drives the development of T2D to a greater degree than in other ethnic groups.

Metabolomic and inflammatory signatures of symptom dimensions in major depression

BACKGROUND

Major depressive disorder (MDD) is a highly heterogenous disease, both in terms of clinical profiles and pathobiological alterations. Recently, immunometabolic dysregulations were shown to be correlated with atypical, energy-related symptoms but less so with the Melancholic or Anxious distress symptom dimensions of depression in The Netherlands Study of Depression and Anxiety (NESDA) study. In this study, we aimed to replicate these immunometabolic associations and to characterize the metabolomic correlates of each of the three MDD dimensions.

METHODS

Using three clinical rating scales, Melancholic, and Anxious distress, and Immunometabolic (IMD) dimensions were characterized in 158 patients who participated in the Predictors of Remission to Individual and Combined Treatments (PReDICT) study and from whom plasma and serum samples were available. The NESDA-defined inflammatory index, a composite measure of interleukin-6 and C-reactive protein, was measured from pre-treatment plasma samples and a metabolomic profile was defined using serum samples analyzed on three metabolomics platforms targeting fatty acids and complex lipids, amino acids, acylcarnitines, and gut microbiome-derived metabolites among other metabolites of central metabolism.

RESULTS

The IMD clinical dimension and the inflammatory index were positively correlated (r = 0.19, p = 0.019) after controlling for age, sex, and body mass index, whereas the Melancholic and Anxious distress dimensions were not, replicating the previous NESDA findings. The three symptom dimensions had distinct metabolomic signatures using both univariate and set enrichment statistics. IMD severity correlated mainly with gut-derived metabolites and a few acylcarnitines and long chain saturated free fatty acids. Melancholia severity was significantly correlated with several phosphatidylcholines, primarily the ether-linked variety, lysophosphatidylcholines, as well as several amino acids. Anxious distress severity correlated with several medium and long chain free fatty acids, both saturated and polyunsaturated ones, sphingomyelins, as well as several amino acids and bile acids.

CONCLUSION

The IMD dimension of depression appears reliably associated with markers of inflammation. Metabolomics provides powerful tools to inform about depression heterogeneity and molecular mechanisms related to clinical dimensions in MDD, which include a link to gut microbiome and lipids implicated in membrane structure and function.

Ranks underlie outcome of combining classifiers: Quantitative roles for diversity and accuracy

Combining classifier systems potentially improves predictive accuracy, but outcomes have proven impossible to predict. Classification most commonly improves when the classifiers are "sufficiently good" (generalized as " accuracy ") and "sufficiently different" (generalized as " diversity "), but the individual and joint quantitative influence of these factors on the final outcome remains unknown. We resolve these issues. Beginning with simulated data, we develop the DIRAC framework (DIversity of Ranks and ACcuracy), which accurately predicts outcome of both score-based fusions originating from exponentially modified Gaussian distributions and rank-based fusions, which are inherently distribution independent. DIRAC was validated using biological dual-energy X-ray absorption and magnetic resonance imaging data. The DIRAC framework is domain independent and has expected utility in far-ranging areas such as clinical biomarker development/personalized medicine, clinical trial enrollment, insurance pricing, portfolio management, and sensor optimization.

Type 2 Diabetes Among Filipino American Adults in the Multiethnic Cohort

INTRODUCTION

Several Asian racial and ethnic groups, including individuals of Filipino ancestry, are at higher risk of developing type 2 diabetes than White individuals, despite their lower body mass index (BMI). This study examined determinants of type 2 diabetes among Filipino American adults in the Multiethnic Cohort Study.

METHODS

Participants in Hawaii and Los Angeles completed questionnaires on demographics, diet, and anthropometrics. Generational status was determined according to birthplace of participants and their parents. Based on self-reported data and data on medications, type 2 diabetes status was classified as no, prevalent, or incident. We used polytomous logistic regression, while adjusting for confounders, to obtain odds ratios.

RESULTS

Among 10,681 Multiethnic Cohort Study participants reporting any Filipino ancestry, 57% were 1st-, 17% were 2nd-, and 25% were 3rd-generation Filipino Americans. Overall, 13% and 17% of participants had a prevalent or incident type 2 diabetes diagnosis. Overweight and obesity and the presence of other risk factors increased from the 1st to subsequent generations. First-generation immigrants were less likely to report type 2 diabetes at cohort entry than immigrants of subsequent generations who were born in the US or whose parents were born in the US; only the prevalence of type 2 diabetes was significantly elevated in the 2nd generation compared with the 1st generation.

CONCLUSION

The results support the hypothesis that Filipino migrants adopt lifestyle factors of the host country and subsequent generations experience higher type 2 diabetes rates due to changes in risk factor patterns.

The gut microbiome and type 2 diabetes status in the Multiethnic Cohort

BACKGROUND

The gut microbiome may play a role in inflammation associated with type 2 diabetes (T2D) development. This cross-sectional study examined its relation with glycemic status within a subset of the Multiethnic Cohort (MEC) and estimated the association of circulating bacterial endotoxin (measured as plasma lipopolysaccharide-binding protein (LBP)) with T2D, which may be mediated by C-reactive protein (CRP).

METHODS

In 2013-16, cohort members from five ethnic groups completed clinic visits, questionnaires, and stool and blood collections. Participants with self-reported T2D and/or taking medication were considered T2D cases. Those with fasting glucose >125 and 100-125 mg/dL were classified as undiagnosed (UT2D) and pre-diabetes (PT2D) cases, respectively. We characterized the gut microbiome through 16S rRNA gene sequencing and measured plasma LBP and CRP by standard assays. Linear regression was applied to estimate associations of the gut microbiome community structure and LBP with T2D status adjusting for relevant confounders.

RESULTS

Among 1,702 participants (59.9-77.4 years), 735 (43%) were normoglycemic (NG), 506 (30%) PT2D, 154 (9%) UT2D, and 307 (18%) T2D. The Shannon diversity index decreased (ptrend = 0.05), while endotoxin, measured as LBP, increased (ptrend = 0.0003) from NG to T2D. Of 10 phyla, Actinobacteria (ptrend = 0.007), Firmicutes (ptrend = 0.003), and Synergistetes (ptrend = 0.02) were inversely associated and Lentisphaerae (ptrend = 0.01) was positively associated with T2D status. Clostridium sensu stricto 1, Lachnospira, and Peptostreptococcaceae were less, while Escherichia-Shigella and Lachnospiraceae were more abundant among T2D patients, but the associations with Actinobacteria, Clostridium sensu stricto 1, and Escherichia-Shigella may be due metformin use. PT2D/UT2D values were closer to NG than T2D. No indication was detected that CRP mediated the association of LBP with T2D.

CONCLUSIONS

T2D but not PT2D/UT2D status was associated with lower abundance of SCFA-producing genera and a higher abundance of gram-negative endotoxin-producing bacteria suggesting that the gut microbiome may contribute to chronic systemic inflammation and T2D through bacterial translocation.

Associations of the gut microbiome with hepatic adiposity in the Multiethnic Cohort Adiposity Phenotype Study

Nonalcoholic fatty liver disease (NAFLD) is a risk factor for liver cancer and prevalence varies by ethnicity. Along with genetic and lifestyle factors, the gut microbiome (GM) may contribute to NAFLD and its progression to advanced liver disease. Our cross-sectional analysis assessed the association of the GM with hepatic adiposity among African American, Japanese American, White, Latino, and Native Hawaiian participants in the Multiethnic Cohort. We used MRI to measure liver fat and determine nonalcoholic fatty liver disease (NAFLD) status (n = 511 cases) in 1,544 participants, aged 60-77 years, with 12-53% overall adiposity (BMI of 17.8-46.2 kg/m2). The GM was measured by 16S rRNA gene sequencing and, on a subset, by metagenomic sequencing. Alpha diversity was lower overall with NAFLD and in certain ethnicities (African Americans, Whites, and Latinos). In models regressing genus on NAFLD status, 62 of 149 genera (40%) exhibited a significant interaction between NAFLD and ethnicity stratified analysis found 69 genera significantly associated with NAFLD in at least one ethnic group. No single genus was significantly associated with NAFLD across all ethnicities. In contrast, the same bacterial metabolic pathways were over-represented in participants with NAFLD regardless of ethnicity. Imputed secondary bile acid and carbohydrate pathways were associated with NAFLD, the latter of which was corroborated by metagenomics, although different genera in different ethnicities were associated with these pathways. Overall, we found that NAFLD was associated with altered bacterial composition and metabolism, and that bacterial endotoxin, assessed by plasma lipopolysaccharide binding protein (LBP), may mediate liver fat-associated systemic inflammation in a manner that seems to vary by ethnicity.

Posterior Cervical Keyhole Laminoforaminotomy: A Cadaveric Comparative Study to Evaluate Limits of Bony Resection

BACKGROUND

The posterior cervical keyhole (KH) laminoforaminotomy has been described to involve the lateral portion of cervical laminae of the upper vertebra alone (small KH) or of both upper and lower vertebrae (large KH).

OBJECTIVE

To microscopically compare the two keyhole techniques in terms of their ability to expose the corresponding cervical roots.

METHODS

Ten cadaveric specimens were operated bilaterally from C3-4 to C6-7 level to expose a total of 80 nerve roots. The large KH was applied to the left side, the small KH to the right side. The maximal length of exposed nerve roots was measured under microscope. The virtual optimal KH surface area was determined using digital software. Each root was inspected for exposure of its root and axilla.

RESULTS

The maximal exposed nerve root length on the large KH side was significantly larger than on the small KH side at C3-4, C5-6, and C6-7 levels (P = .031, P = .002, P = .003). No significance was reported for C4-5 (P = .06). We could expose right axillae in (3/40) and left axillae in (33/40; P < .001). Optimal keyhole surface areas were 37.9, 38.2, 38.7, and 46.2 mm2 in craniocaudal order.

CONCLUSION

Large KH defects involving both upper and lower laminae and facets can expose the roots to greater extent than small KH defects at C3-4, C5-6, and C6-7 levels. Large KH defects may allow better exposure of nerve roots axillae than small KH defects.

Genome-Wide Association Study of Liver Fat: The Multiethnic Cohort Adiposity Phenotype Study

The global rise in fatty liver is a major public health problem. Thus, it is critical to identify both global and population-specific genetic variants associated with liver fat. We conducted a genome-wide association study (GWAS) of percent liver fat and nonalcoholic fatty liver disease (NAFLD) assessed by magnetic resonance imaging in 1,709 participants from the population-based Multiethnic Cohort Adiposity Phenotype Study. Our participants comprised older adults of five U.S. racial/ethnic groups: African Americans (n = 277), Japanese Americans (n = 424), Latinos (n = 348), Native Hawaiians (n = 274), and European Americans (n = 386). The established missense risk variant rs738409 located in patatin-like phospholipase domain containing 3 (PNPLA3) at 22q13 was confirmed to be associated with percent liver fat (P = 3.52 × 10-15) but more strongly in women than men (P heterogeneity = 0.002). Its frequency correlated with the prevalence of NAFLD across the five ethnic/racial groups. Rs738409 was also associated with homeostasis model assessment of insulin resistance (HOMA-IR) (beta = 0.028; P = 0.009) and circulating levels of insulin (beta = 0.022; P = 0.020) and alanine aminotransferase (beta = 0.016; P = 0.030). A novel association of percent liver fat with rs77249491 (located at 6q13 between limb region 1 domain containing 1 [LMBRD1] and collagen type XIX alpha 1 chain [COL19A1] (P = 1.42 × 10-8) was also observed. Rs7724941 was associated with HOMA-IR (beta = 0.12; P = 0.0005), insulin (beta = 0.11; P = 0.0003), triglycerides (beta = 0.059; P = 0.01), high-density lipoprotein (beta = -0.046; P = 0.04), and sex hormone binding globulin (beta = -0.084; P = 0.0012). This variant was present in Japanese Americans (minor allele frequency [MAF], 8%) and Native Hawaiians (MAF, 2%). Conclusion: We replicated the PNPLA3 rs738409 association in a multiethnic population and identified a novel liver fat risk variant in Japanese Americans and Native Hawaiians. GWASes of percent liver fat in East Asian and Oceanic populations are needed to replicate the rs77249491 association.

Characterizing the human APOE epsilon 4 knock-in transgene in female and male rats with multimodal magnetic resonance imaging

The APOE Ɛ4 genotype is the most prevalent genetic risk for Alzheimer's disease (AD). Women carriers of Ɛ4 have higher risk for an early onset of AD than men. Human imaging studies suggest apolipoprotein Ɛ4 may affect brain structures associated with cognitive decline in AD many years before disease onset. It was hypothesized that female APOE Ɛ4 carriers would present with decreased cognitive function and neuroradiological evidence of early changes in brain structure and function as compared to male carriers. Six-month old wild-type (WT) and human APOE Ɛ4 knock-in (TGRA8960), male and female Sprague Dawley rats were studied for changes in brain structure using voxel-based morphometry, alteration in white and gray matter microarchitecture using diffusion weighted imaging with indices of anisotropy, and functional coupling using resting state BOLD functional connectivity. Images from each modality were registered to, and analyzed, using a 3D MRI rat atlas providing site-specific data on over 168 different brain areas. Quantitative volumetric analysis revealed areas involved in memory and arousal were significantly different between Ɛ4 and wild-type (WT) females, with few differences between male genotypes. Diffusion weighted imaging showed few differences between WT and Ɛ4 females, while male genotypes showed significant different measures in fractional anisotropy and apparent diffusion coefficient. Resting state functional connectivity showed Ɛ4 females had greater connectivity between areas involved in cognition, emotion, and arousal compared to WT females, with male Ɛ4 showing few differences from controls. Interestingly, male Ɛ4 showed increased anxiety and decreased performance in spatial and episodic memory tasks compared to WT males, with female genotypes showing little difference across behavioral tests. The sex differences in behavior and diffusion weighted imaging suggest male carriers of the Ɛ4 allele may be more vulnerable to cognitive and emotional complications compared to female carriers early in life. Conversely, the data may also suggest that female carriers are more resilient to cognitive/emotional problems at this stage of life perhaps due to altered brain volumes and enhanced connectivity.

Abstract IA38: Racial/ethnic differences in liver fat, an obesity-associated risk factor for liver cancer

Background: Nonalcoholic fatty liver disease (NAFLD) is thought to be the main driver for the recent rise of chronic liver disease and liver cancer. NAFLD is also associated with other obesity-related metabolic diseases. Relative fat deposition in the liver varies by race/ethnicity and may partially account for liver cancer disparities. Thus, we aimed to compare liver fat content across five racial/ethnic groups, assess their contribution to the metabolic syndrome (MetSx), and predict NAFLD using common blood biomarkers.

Methods: We conducted a cross-sectional study within the Multiethnic Cohort. A total of 1,861 healthy men and women aged 60-77 years were recruited, after stratification on sex, ethnicity (African, Japanese, Latino, Native Hawaiian, or white ancestry), and six BMI categories (range, 17.1-49.8 kg/m2). We estimated total fat mass using DXA and liver fat content using abdominal MR imaging. Fasting blood was analyzed for ~50 markers including adipocytokines, insulin and IGFs, lipids and lipid-soluble micronutrients, liver enzymes, and steroid hormones, using multiple assay platforms. Liver fat amounts were compared across sex and ethnic groups after adjustment for age, total fat mass, and height. The contribution of liver fat to MetSx was estimated in multivariable-adjusted mediation analysis. A prediction model for NAFLD was developed using regularized logistic regression.

Results: The correlation between liver fat and total fat was only moderate (rSp = 0.34) and varied across ethnic groups (0.20-0.55). Liver fat content was similar between the sexes but differed by ethnicity (p&lt;.0001), with a four-fold range in NAFLD prevalence between Japanese Americans (57% in men, 72% in women) and African Americans (12%, 19%) after adjustment for total fat mass. Total fat-adjusted prevalence of MetSx also differed by ethnicity: compared to whites, it was higher among Japanese Americans and Native Hawaiian women and lower among African Americans and Latinos. This ethnic difference was significantly mediated by liver fat among African Americans (proportion mediated =19-24%), Japanese Americans (22-34%), and Native Hawaiian women (20%). The final prediction model for NAFLD included age, sex, BMI, waist circumference, waist/hip, and top five biomarker predictors (IGFBP2, HOMA-IR, TG, adiponectin, SHBG). Discrimination of NAFLD cases in a validation dataset had high accuracy (AUC=0.90), across ethnic groups (AUCs of 0.80-0.96), and was significantly improved by the biomarkers (p's for contrast&lt;.0001, except in African Americans).

Conclusions: Relative fat storage in the liver varies substantially by race/ethnicity. In particular, Japanese Americans and Native Hawaiian women appear to experience a greater metabolic burden from their propensity to store excess fat in ectopic areas, which is consistent with a stronger association of BMI with liver cancer in these groups. Key metabolism markers may be used to successfully detect and monitor NAFLD patients of in various ethnic groups.

Citation Format: Unhee Lim, Lynne R. Wilkens, Kristine R. Monroe, Iona Cheng, Bruce S. Kristal, Johanna W. Lampe, Meredith A. Hullar, John Shepherd, Thomas Ernst, Loic Le Marchand. Racial/ethnic differences in liver fat, an obesity-associated risk factor for liver cancer [abstract]. In: Proceedings of the Eleventh AACR Conference on the Science of Cancer Health Disparities in Racial/Ethnic Minorities and the Medically Underserved; 2018 Nov 2-5; New Orleans, LA. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2020;29(6 Suppl):Abstract nr IA38.

Abstract A31: Genome-wide association study (GWAS) of host DNA sequence variation and the gut microbiome in the Multiethnic Cohort

Patterns of microbiome diversity vary across human populations, and although variation is largely driven by diet and lifestyle, genetically encoded differences between hosts may be important in shaping the microbiome and health outcomes, including cancer. We report preliminary results from a GWAS of the gut microbiome in 6,217 individuals from the Multiethnic Cohort Study, including African Americans, Japanese Americans, Native Hawaiians, Latinos, and Whites. Genome-wide SNP data was based on existing data from a variety of Illumina Infinium arrays (500,000 to 2.5 million single nucleotide polymorphisms (SNPs); n=4,363) as well as genotyping 1,853 individuals using the Illumina MEGA EX array. SNP imputation was conducted using a cosmopolitan reference panel of all 1000 Genomes samples. The stool microbiome was assessed by paired-end sequencing (Illumina MiSeq) of the16S rRNA gene (V1-3). SNP-genera association tests were conducted using linear regression of covariate-adjusted bacterial genera abundance quintiles on SNP genotype. The chi-square statistics were adjusted by the genomic inflation factor. A threshold of p=5 × 10−8 was used to determine genome-wide statistical significance. The covariate-adjusted genera values were computed as the residuals of a logistic ordinal regression of genera abundance quintiles on variables expected to affect the microbiome (i.e., age, sex, genetic ancestry proportions, sample month, and sequencing batch). Initial results yielded 22 genome-wide significant associations across SNPs in 15 different human chromosomes and 11 bacterial genera. Notably, Fusobacteria was significantly associated with star-related lipid transfer domain (STARD3, chromosome 13q13; p=2.8 × 10−8), voltage-dependent calcium channel gamma 3 subunit (CACNG3, chromosome 16p12; p=3.1 × 10−8), organic anion transporter polypeptide (OATP, SCLO2B1, chromosome 11q13; p=2.8 × 10−8), and E-cadherin (CDHR3, chromosome 7q22, p=1.6 × 10−8). Some Fusobacterial species have been associated with increased risk of colon tumors. Coprobacillus was significantly associated with ubiquitin modifier activating enzyme 2 (UBA2, chromosome 19q13, p=4.1 × 10−9). The pathogen Slackia was significantly associated with variants in the zinc finger 850 gene (ZNF850, chromosome 19p13; p=4.3 × 10−8). These results suggest that host gene variants may be important in shaping the microbiome and may influence bacterial pathogen-associated cancer outcomes.

Citation Format: Meredith A. Hullar, Johanna W. Lampe, Timothy Randolph, Keith R. Curtis, Unhee Lim, Lynne R. Wilkens, Loic Le Marchand, Bruce S. Kristal, Kris R. Monroe, Kechen Zhao, Daniel Stram, Iona Cheng. Genome-wide association study (GWAS) of host DNA sequence variation and the gut microbiome in the Multiethnic Cohort [abstract]. In: Proceedings of the AACR Special Conference on the Microbiome, Viruses, and Cancer; 2020 Feb 21-24; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2020;80(8 Suppl):Abstract nr A31.

Circulating Biomarker Score for Visceral Fat and Risks of Incident Colorectal and Postmenopausal Breast Cancer: The Multiethnic Cohort Adiposity Phenotype Study

BACKGROUND

Visceral adipose tissue (VAT) may play a greater role than subcutaneous fat in increasing cancer risk but is poorly estimated in epidemiologic studies.

METHODS

We developed a VAT prediction score by regression equations averaged across 100 least absolute shrinkage and selection operator models in a cross-sectional study of 1,801 older adults in the Multiethnic Cohort (MEC). The score was then used as proxy for VAT in case-control studies of postmenopausal breast (950 case-control pairs) and colorectal (831 case-control pairs) cancer in an independent sample in MEC. Abdominal MRI-derived VAT; circulating biomarkers of metabolic, hormonal, and inflammation dysfunctions; and ORs for incident cancer adjusted for BMI and other risk factors were assessed.

RESULTS

The final score, composed of nine biomarkers, BMI, and height, explained 11% and 15% more of the variance in VAT than BMI alone in men and women, respectively. The area under the receiver operator curve for VAT >150 cm² was 0.90 in men and 0.86 in women. The VAT score was associated with risk of breast cancer [OR (95% confidence interval [CI]) by increasing tertiles: 1.00, 1.09 (0.86-1.39), 1.48 (1.16-1.89); P _trend = 0.002] but not with colorectal cancer (P = 0.84), although an association [1.00, 0.98 (0.68-1.39), 1.24 (0.88-1.76); P _trend = 0.08] was suggested for this cancer after excluding cases that occurred within 7 years of blood draw (P _{heterogeneity} = 0.06).

CONCLUSIONS

The VAT score predicted risks of postmenopausal breast cancer and can be used for risk assessment in diverse populations.

IMPACT

These findings provide specific evidence for a role of VAT in breast cancer.

The integration of LC-MS and NMR for the analysis of low molecular weight trace analytes in complex matrices

This review discusses the integration of liquid chromatography (LC), mass spectrometry (MS), and nuclear magnetic resonance (NMR) in the comprehensive analysis of small molecules from complex matrices. We first discuss the steps taken toward making the three technologies compatible, so as to create an efficient analytical platform. The development of online LC-MS-NMR, highlighted by successful applications in the profiling of highly concentrated analytes (LODs 10 μg) is discussed next. This is followed by a detailed overview of the alternative approaches that have been developed to overcome the challenges associated with online LC-MS-NMR that primarily stem from the inherently low sensitivity of NMR. These alternative approaches include the use of stop-flow LC-MS-NMR, loop collection of LC peaks, LC-MS-SPE-NMR, and offline NMR. The potential and limitations of all these approaches is discussed in the context of applications in various fields, including metabolomics and natural product discovery.

Using a Single Daytime Performance Test to Identify Most Individuals at High-Risk for Performance Impairment during Extended Wake

We explored the predictive value of a neurobehavioral performance assessment under rested baseline conditions (evaluated at 8 hours awake following 8 hours of sleep) on neurobehavioral response to moderate sleep loss (evaluated at 20 hours awake two days later) in 151 healthy young participants (18-30 years). We defined each participant's response-to-sleep-loss phenotype based on the number of attentional failures on a 10-min visual psychomotor vigilance task taken at 20 hours awake (resilient: less than 6 attentional failures, n = 26 participants; non-resilient: 6 or more attentional failures, n = 125 participants). We observed that 97% of rested participants with 2 or more attentional failures (n = 73 of 151) and 100% of rested participants with 3 or more attentional failures (n = 57 of 151) were non-resilient after moderate sleep loss. Our approach can accurately identify a significant proportion of individuals who are at high risk for neurobehavioral performance impairment from staying up late with a single neurobehavioral performance assessment conducted during rested conditions. Additional methods are needed to predict the future performance of individuals who are not identified as high risk during baseline.

The Consortium of Metabolomics Studies (COMETS): Metabolomics in 47 Prospective Cohort Studies

The Consortium of Metabolomics Studies (COMETS) was established in 2014 to facilitate large-scale collaborative research on the human metabolome and its relationship with disease etiology, diagnosis, and prognosis. COMETS comprises 47 cohorts from Asia, Europe, North America, and South America that together include more than 136,000 participants with blood metabolomics data on samples collected from 1985 to 2017. Metabolomics data were provided by 17 different platforms, with the most frequently used labs being Metabolon, Inc. (14 cohorts), the Broad Institute (15 cohorts), and Nightingale Health (11 cohorts). Participants have been followed for a median of 23 years for health outcomes including death, cancer, cardiovascular disease, diabetes, and others; many of the studies are ongoing. Available exposure-related data include common clinical measurements and behavioral factors, as well as genome-wide genotype data. Two feasibility studies were conducted to evaluate the comparability of metabolomics platforms used by COMETS cohorts. The first study showed that the overlap between any 2 different laboratories ranged from 6 to 121 metabolites at 5 leading laboratories. The second study showed that the median Spearman correlation comparing 111 overlapping metabolites captured by Metabolon and the Broad Institute was 0.79 (interquartile range, 0.56-0.89).

Propensity for Intra-abdominal and Hepatic Adiposity Varies Among Ethnic Groups

BACKGROUND & AIMS

We compared fat storage in the abdominal region among individuals from 5 different ethnic-racial groups to determine whether fat storage is associated with disparities observed in metabolic syndrome and other obesity-associated diseases.

METHODS

We collected data from 1794 participants in the Multiethnic Cohort Study (60-77 years old; of African, European [white], Japanese, Latino, or Native Hawaiian ancestry) with body mass index values of 17.1-46.2 kg/m². From May 2013 through April 2016, participants visited the study clinic to undergo body measurements, an interview, and a blood collection. Participants were evaluated by dual-energy x-ray absorptiometry and abdominal magnetic resonance imaging. Among ethnic groups, we compared adiposity of the trunk, intra-abdominal visceral cavity, and liver, adjusting for total fat mass; we evaluated the association of adult weight change with abdominal adiposity; and we examined the prevalence of metabolic syndrome mediated by abdominal adiposity.

RESULTS

Relative amounts of trunk, visceral, and liver fat varied significantly with ethnicity-they were highest in Japanese Americans, lowest in African Americans, and intermediate in the other groups. Compared with African Americans, the mean visceral fat area was 45% and 73% greater in Japanese American men and women, respectively, and the mean measurements of liver fat were 61% and 122% greater in Japanese American men and women. The visceral and hepatic adiposity associated with weight gain since participants were 21 years old varied in a similar pattern among ethnic-racial groups. In the mediation analysis, visceral and liver fat jointly accounted for a statistically significant fraction of the difference in metabolic syndrome prevalence, compared with white persons, for African Americans, Japanese Americans, and Native Hawaiian women, independently of total fat mass.

CONCLUSIONS

In an analysis of data from the participants in the Multiethnic Cohort Study, we found extensive differences among ethnic-racial groups in the propensity to store fat intra-abdominally. This observation should be considered by clinicians in the prevention and early detection of metabolic disorders.

Optimization of Electrospray Ionization Source Parameters for Lipidomics To Reduce Misannotation of In-Source Fragments as Precursor Ions

Lipidomics requires the accurate annotation of lipids in complex samples to enable determination of their biological relevance. We demonstrate that unintentional in-source fragmentation (ISF, common in lipidomics) generates ions that have identical masses to other lipids. Lysophosphatidylcholines (LPC), for example, generate in-source fragments with the same mass as free fatty acids and lysophosphatidylethanolamines (LPE). The misannotation of in-source fragments as true lipids is particularly insidious in complex matrixes since most masses are initially unannotated and comprehensive lipid standards are unavailable. Indeed, we show such LPE/LPC misannotations are incorporated in the data submitted to the National Institute of Standards and Technology (NIST) interlaboratory comparison exercise. Computer simulations exhaustively identified potential misannotations. The selection of in-source fragments of highly abundant lipids as features, instead of the correct recognition of trace lipids, can potentially lead to (i) missing the biologically relevant lipids (i.e., a false negative) and/or (ii) incorrect assignation of a phenotype to an incorrect lipid (i.e., false positive). When ISF is not eliminated in the negative ion mode, ∼40% of the 100 most abundant masses corresponding to unique phospholipids measured in plasma were artifacts from ISF. We show that chromatographic separation and ion intensity considerations assist in distinguishing precursor ions from in-source fragments, suggesting ISF may be especially problematic when complex samples are analyzed via shotgun lipidomics. We also conduct a systematic evaluation of electrospray ionization (ESI) source parameters on an Exactive equipped with a heated electrospray ionization (HESI-II) source with the objective of obtaining uniformly appropriate source conditions for a wide range of lipids, while, at the same time, reducing in-source fragmentation.

Dietary protein restriction reduces circulating VLDL triglyceride levels via CREBH-APOA5-dependent and -independent mechanisms

Hypertriglyceridemia is an independent risk factor for cardiovascular disease. Dietary interventions based on protein restriction (PR) reduce circulating triglycerides (TGs), but underlying mechanisms and clinical relevance remain unclear. Here, we show that 1 week of a protein-free diet without enforced calorie restriction significantly lowered circulating TGs in both lean and diet-induced obese mice. Mechanistically, the TG-lowering effect of PR was due, in part, to changes in very low-density lipoprotein (VLDL) metabolism both in liver and peripheral tissues. In the periphery, PR stimulated VLDL-TG consumption by increasing VLDL-bound APOA5 expression and promoting VLDL-TG hydrolysis and clearance from circulation. The PR-mediated increase in Apoa5 expression was controlled by the transcription factor CREBH, which coordinately regulated hepatic expression of fatty acid oxidation-related genes, including Fgf21 and Ppara. The CREBH-APOA5 axis activation upon PR was intact in mice lacking the GCN2-dependent amino acid-sensing arm of the integrated stress response. However, constitutive hepatic activation of the amino acid-responsive kinase mTORC1 compromised CREBH activation, leading to blunted APOA5 expression and PR-recalcitrant hypertriglyceridemia. PR also contributed to hypotriglyceridemia by reducing the rate of VLDL-TG secretion, independently of activation of the CREBH-APOA5 axis. Finally, a randomized controlled clinical trial revealed that 4-6 weeks of reduced protein intake (7%-9% of calories) decreased VLDL particle number, increased VLDL-bound APOA5 expression, and lowered plasma TGs, consistent with mechanistic conservation of PR-mediated hypotriglyceridemia in humans with translational potential as a nutraceutical intervention for dyslipidemia.

Diffusion imaging of mild traumatic brain injury in the impact accelerated rodent model: A pilot study

PRIMARY OBJECTIVE

There is a need to understand pathologic processes of the brain following mild traumatic brain injury (mTBI). Previous studies report axonal injury and oedema in the first week after injury in a rodent model. This study aims to investigate the processes occurring 1 week after injury at the time of regeneration and degeneration using diffusion tensor imaging (DTI) in the impact acceleration rat mTBI model.

RESEARCH DESIGN

Eighteen rats were subjected to impact acceleration injury, and three rats served as sham controls. Seven days post injury, DTI was acquired from fixed rat brains using a 7T scanner. Group comparison of Fractional Anisotropy (FA) values between traumatized and sham animals was performed using Tract-Based Spatial Statistics (TBSS), a method that we adapted for rats.

MAIN OUTCOMES AND RESULTS

TBSS revealed white matter regions of the brain with increased FA values in the traumatized versus sham rats, localized mainly to the contrecoup region. Regions of increased FA included the pyramidal tract, the cerebral peduncle, the superior cerebellar peduncle and to a lesser extent the fibre tracts of the corpus callosum, the anterior commissure, the fimbria of the hippocampus, the fornix, the medial forebrain bundle and the optic chiasm.

CONCLUSION

Seven days post injury, during the period of tissue reparation in the impact acceleration rat model of mTBI, microstructural changes to white matter can be detected using DTI.

Increased oxidative phosphorylation in response to acute and chronic DNA damage

Accumulation of DNA damage is intricately linked to aging, aging-related diseases and progeroid syndromes such as Cockayne syndrome (CS). Free radicals from endogenous oxidative energy metabolism can damage DNA, however the potential of acute or chronic DNA damage to modulate cellular and/or organismal energy metabolism remains largely unexplored. We modeled chronic endogenous genotoxic stress using a DNA repair-deficient Csa^-/-|Xpa^-/- mouse model of CS. Exogenous genotoxic stress was modeled in mice in vivo and primary cells in vitro treated with different genotoxins giving rise to diverse spectrums of lesions, including ultraviolet radiation, intrastrand crosslinking agents and ionizing radiation. Both chronic endogenous and acute exogenous genotoxic stress increased mitochondrial fatty acid oxidation (FAO) on the organismal level, manifested by increased oxygen consumption, reduced respiratory exchange ratio, progressive adipose loss and increased FAO in tissues ex vivo. In multiple primary cell types, the metabolic response to different genotoxins manifested as a cell-autonomous increase in oxidative phosphorylation (OXPHOS) subsequent to a transient decline in steady-state NAD+ and ATP levels, and required the DNA damage sensor PARP-1 and energy-sensing kinase AMPK. We conclude that increased FAO/OXPHOS is a general, beneficial, adaptive response to DNA damage on cellular and organismal levels, illustrating a fundamental link between genotoxic stress and energy metabolism driven by the energetic cost of DNA damage. Our study points to therapeutic opportunities to mitigate detrimental effects of DNA damage on primary cells in the context of radio/chemotherapy or progeroid syndromes.

Simple LC-MS Method for Differentiation of Isobaric Phosphatidylserines and Phosphatidylcholines with Deuterated Mobile Phase Additives

Lipids from different classes sometimes can exhibit the same exact mass upon electrospray ionization; this presents an analytical challenge in lipidomics. In the negative ionization mode, for example, this can occur with phosphatidylcholines (PCs) and phosphatidylserines (PSs), making them indistinguishable in the absence of fragmentation data. PSs are found at low concentrations in biological samples, making MS/MS spectra difficult to obtain. Moreover, while PCs and PSs are distinguishable in the positive mode, PSs do not ionize as well as PCs, and their ionization is suppressed by the PCs. Here, we show that, in the negative ionization mode, substituting protiated LC-MS additives with their deuterated forms provides a way to distinguish PCs and PSs without chemical derivatization. The method described leverages the differential ionization mechanism of PCs and PSs. PCs are ionized via adduction with salts, whereas PSs ionize via hydrogen abstraction. Substituting the salts used for LC-MS with their deuterated form shifts the mass of PCs by the number of deuterium atoms in the salt, while the mass of PSs remains the same. This comparative shift enables their direct differentiation. We demonstrate that the use of deuterated formate shifts the mass of PCs and provides a direct method to distinguish PCs and PSs, even at biologically relevant low concentrations. The utility of the method was established and validated in the simultaneous analysis of PCs and PSs in lipid extracts from isolated liver mitochondria in two different rat strains. Thirteen low concentration PSs were identified that would otherwise not have been distinguishable from low concentration PCs.

Surgical injury induces local and distant adipose tissue browning

The adipose organ, which comprises brown, white and beige adipocytes, possesses remarkable plasticity in response to feeding and cold exposure. The development of beige adipocytes in white adipose tissue (WAT), a process called browning, represents a promising route to treat metabolic disorders. While surgical procedures constantly traumatize adipose tissue, its impact on adipocyte phenotype remains to be established. Herein, we studied the effect of trauma on adipocyte phenotype one day after sham, incision control, or surgical injury to the left inguinal adipose compartment. Caloric restriction was used to control for surgery-associated body temperature changes and weight loss. We characterized the trauma-induced cellular and molecular changes in subcutaneous, visceral, interscapular, and perivascular adipose tissue using histology, immunohistochemistry, gene expression, and flow cytometry analysis. After one day, surgical trauma stimulated adipose tissue browning at the site of injury and, importantly, in the contralateral inguinal depot. Browning was not present after incision only, and was largely independent of surgery-associated body temperature and weight loss. Adipose trauma rapidly recruited monocytes to the injured site and promoted alternatively activated macrophages. Conversely, PDGF receptor-positive beige progenitors were reduced. In this study, we identify adipose trauma as an unexpected driver of selected local and remote adipose tissue browning, holding important implications for the biologic response to surgical injury.

Protein and Calorie Restriction Contribute Additively to Protection from Renal Ischemia Reperfusion Injury Partly via Leptin Reduction in Male Mice

BACKGROUND

Short-term dietary restriction (DR) without malnutrition preconditions against surgical stress in rodents; however, the nutritional basis and underlying nutrient/energy-sensing pathways remain poorly understood.

OBJECTIVES

We investigated the relative contribution of protein restriction (PR) vs. calorie restriction (CR) to protection from renal ischemia reperfusion injury (IRI) and changes in organ-autonomous nutrient/energy-sensing pathways and hormones underlying beneficial effects.

METHODS

Mice were preconditioned on experimental diets lacking total calories (0-50% CR) or protein/essential amino acids (EAAs) vs. complete diets consumed ad libitum (AL) for 1 wk before IRI. Renal outcome was assessed by serum markers and histology and integrated over a 2-dimensional protein/energy landscape by geometric framework analysis. Changes in renal nutrient/energy-sensing signal transduction and systemic hormones leptin and adiponectin were also measured. The genetic requirement for amino acid sensing via general control non-derepressible 2 (GCN2) was tested with knockout vs. control mice. The involvement of the hormone leptin was tested by injection of recombinant protein vs. vehicle during the preconditioning period.

RESULTS

CR-mediated protection was dose dependent up to 50% with maximal 2-fold effect sizes. PR benefits were abrogated by EAA re-addition and additive with CR, with maximal benefits at any given amount of CR occurring with a protein-free diet. GCN2 was not required for functional benefits of PR. Activation and repression of nutrient/energy-sensing kinases, AMP-activated protein kinase (AMPK) and mechanistic target of rapamycin complex 1 (mTORC1), respectively, on PR reflected a state of negative energy balance, paralleled by 13% weight loss and an 87% decrease in leptin, independent of calorie intake. Recombinant leptin administration partially abrogated benefits of dietary preconditioning against renal IRI.

CONCLUSIONS

In male mice, PR and CR both contributed to the benefits of short-term DR against renal IRI independent of GCN2 but partially dependent on reduced circulating leptin and coincident with AMPK activation and mTORC1 repression.

Genome-wide meta-analysis identifies six novel loci associated with habitual coffee consumption

Coffee, a major dietary source of caffeine, is among the most widely consumed beverages in the world and has received considerable attention regarding health risks and benefits. We conducted a genome-wide (GW) meta-analysis of predominately regular-type coffee consumption (cups per day) among up to 91,462 coffee consumers of European ancestry with top single-nucleotide polymorphisms (SNPs) followed-up in ~30 062 and 7964 coffee consumers of European and African-American ancestry, respectively. Studies from both stages were combined in a trans-ethnic meta-analysis. Confirmed loci were examined for putative functional and biological relevance. Eight loci, including six novel loci, met GW significance (log10Bayes factor (BF)>5.64) with per-allele effect sizes of 0.03-0.14 cups per day. Six are located in or near genes potentially involved in pharmacokinetics (ABCG2, AHR, POR and CYP1A2) and pharmacodynamics (BDNF and SLC6A4) of caffeine. Two map to GCKR and MLXIPL genes related to metabolic traits but lacking known roles in coffee consumption. Enhancer and promoter histone marks populate the regions of many confirmed loci and several potential regulatory SNPs are highly correlated with the lead SNP of each. SNP alleles near GCKR, MLXIPL, BDNF and CYP1A2 that were associated with higher coffee consumption have previously been associated with smoking initiation, higher adiposity and fasting insulin and glucose but lower blood pressure and favorable lipid, inflammatory and liver enzyme profiles (P<5 × 10(-8)).Our genetic findings among European and African-American adults reinforce the role of caffeine in mediating habitual coffee consumption and may point to molecular mechanisms underlying inter-individual variability in pharmacological and health effects of coffee.

Qualitative characterization of the rat liver mitochondrial lipidome using all ion fragmentation on an Exactive benchtop Orbitrap MS

Untargeted lipidomics profiling by liquid chromatography-mass spectrometry (LC-MS) allows researchers to observe the occurrences of lipids in a biological sample without showing intentional bias to any specific class of lipids and allows retrospective reanalysis of data collected. Typically, and in the specific method described, a general extraction method followed by LC separation is used to achieve nonspecific class coverage of the lipidome prior to high-resolution accurate mass (HRAM) MS detection. Here we describe a workflow including the isolation of mitochondria from liver tissue, followed by mitochondrial lipid extraction and the LC-MS conditions used for data acquisition. We also highlight how, in this method, all-ion fragmentation can be used to identify species of lower abundances, often missed by data-dependent fragmentation techniques. Here we describe the isolation of mitochondria from liver tissue, followed by mitochondrial lipid extraction and the LC-MS conditions used for data acquisition.

Preoperative dietary restriction reduces intimal hyperplasia and protects from ischemia-reperfusion injury

OBJECTIVE

Whereas chronic overnutrition is a risk factor for surgical complications, long-term dietary restriction (reduced food intake without malnutrition) protects in preclinical models of surgical stress. Building on the emerging concept that acute preoperative dietary perturbations can affect the body's response to surgical stress, we hypothesized that short-term high-fat diet (HFD) feeding before surgery is detrimental, whereas short-term nutrient/energy restriction before surgery can reverse negative outcomes. We tested this hypothesis in two distinct murine models of vascular surgical injury, ischemia-reperfusion (IR) and intimal hyperplasia (IH).

METHODS

Short-term overnutrition was achieved by feeding mice a HFD consisting of 60% calories from fat for 2 weeks. Short-term dietary restriction consisted of either 1 week of restricted access to a protein-free diet (protein/energy restriction) or 3 days of water-only fasting immediately before surgery; after surgery, all mice were given ad libitum access to a complete diet. To assess the impact of preoperative nutrition on surgical outcome, mice were challenged in one of two fundamentally distinct surgical injury models: IR injury to either kidney or liver, or a carotid focal stenosis model of IH.

RESULTS

Three days of fasting or 1 week of preoperative protein/energy restriction attenuated IH development measured 28 days after focal carotid stenosis. One week of preoperative protein/energy restriction also reduced plasma urea, creatinine, and damage to the corticomedullary junction after renal IR and decreased aspartate transaminase, alanine transaminase, and hemorrhagic necrosis after hepatic IR. However, exposure to a HFD for 2 weeks before surgery had no significant impact on kidney or hepatic function after IR or IH after focal carotid stenosis.

CONCLUSIONS

Short-term dietary restriction immediately before surgery significantly attenuated the vascular wall hyperplastic response and improved IR outcome. The findings suggest plasticity in the body's response to these vascular surgical injuries that can be manipulated by novel yet practical preoperative dietary interventions.

Soluble, prefibrillar α-synuclein oligomers promote complex I-dependent, Ca2+-induced mitochondrial dysfunction

α-Synuclein (αSyn) aggregation and mitochondrial dysfunction both contribute to the pathogenesis of Parkinson disease (PD). Although recent studies have suggested that mitochondrial association of αSyn may disrupt mitochondrial function, it is unclear what aggregation state of αSyn is most damaging to mitochondria and what conditions promote or inhibit the effect of toxic αSyn species. Because the neuronal populations most vulnerable in PD are characterized by large cytosolic Ca(2+) oscillations that burden mitochondria, we examined mitochondrial Ca(2+) stress in an in vitro system comprising isolated mitochondria and purified recombinant human αSyn in various aggregation states. Using fluorimetry to simultaneously measure four mitochondrial parameters, we observed that soluble, prefibrillar αSyn oligomers, but not monomeric or fibrillar αSyn, decreased the retention time of exogenously added Ca(2+), promoted Ca(2+)-induced mitochondrial swelling and depolarization, and accelerated cytochrome c release. Inhibition of the permeability transition pore rescued these αSyn-induced changes in mitochondrial parameters. Interestingly, the mitotoxic effects of αSyn were specifically dependent upon both electron flow through complex I and mitochondrial uptake of exogenous Ca(2+). Our results suggest that soluble prefibrillar αSyn oligomers recapitulate several mitochondrial phenotypes previously observed in animal and cell models of PD: complex I dysfunction, altered membrane potential, disrupted Ca(2+) homeostasis, and enhanced cytochrome c release. These data reveal how the association of oligomeric αSyn with mitochondria can be detrimental to the function of cells with high Ca(2+)-handling requirements.

Identification of metabolites from liquid chromatography-coulometric array detection profiling: gas chromatography-mass spectrometry and refractionation provide essential information orthogonal to LC-MS/microNMR

Liquid chromatography-coulometric array detection (LC-EC) is a sensitive, quantitative, and robust metabolomics profiling tool that complements the commonly used mass spectrometry (MS) and nuclear magnetic resonance (NMR)-based approaches. However, LC-EC provides little structural information. We recently demonstrated a workflow for the structural characterization of metabolites detected by LC-EC profiling combined with LC-electrospray ionization (ESI)-MS and microNMR. This methodology is now extended to include (i) gas chromatography (GC)-electron ionization (EI)-MS analysis to fill structural gaps left by LC-ESI-MS and NMR and (ii) secondary fractionation of LC-collected fractions containing multiple coeluting analytes. GC-EI-MS spectra have more informative fragment ions that are reproducible for database searches. Secondary fractionation provides enhanced metabolite characterization by reducing spectral overlap in NMR and ion suppression in LC-ESI-MS. The need for these additional methods in the analysis of the broad chemical classes and concentration ranges found in plasma is illustrated with discussion of four specific examples: (i) characterization of compounds for which one or more of the detectors is insensitive (e.g., positional isomers in LC-MS, the direct detection of carboxylic groups and sulfonic groups in (1)H NMR, or nonvolatile species in GC-MS), (ii) detection of labile compounds, (iii) resolution of closely eluting and/or coeluting compounds, and (iv) the capability to harness structural similarities common in many biologically related, LC-EC-detectable compounds.

Dietary macronutrients modulate the fatty acyl composition of rat liver mitochondrial cardiolipins

The interaction of dietary fats and carbohydrates on liver mitochondria were examined in male FBNF1 rats fed 20 different low-fat isocaloric diets. Animal growth rates and mitochondrial respiratory parameters were essentially unaffected, but mass spectrometry-based mitochondrial lipidomics profiling revealed increased levels of cardiolipins (CLs), a family of phospholipids essential for mitochondrial structure and function, in rats fed saturated or trans fat-based diets with a high glycemic index. These mitochondria showed elevated monolysocardiolipins (a CL precursor/product of CL degradation), elevated ratio of trans-phosphocholine (PC) (18:1/18:1) to cis-PC (18:1/18:1) (a marker of thiyl radical stress), and decreased ubiquinone Q9; the latter two of which imply a low-grade mitochondrial redox abnormality. Extended analysis demonstrated: i) dietary fats and, to a lesser extent, carbohydrates induce changes in the relative abundance of specific CL species; ii) fatty acid (FA) incorporation into mature CLs undergoes both positive (>400-fold) and negative (2.5-fold) regulation; and iii) dietary lipid abundance and incorporation of FAs into both the CL pool and specific mature tetra-acyl CLs are inversely related, suggesting previously unobserved compensatory regulation. This study reveals previously unobserved complexity/regulation of the central lipid in mitochondrial metabolism.

Abstract 214: Protein Restriction Attenuates Intimal Hyperplasia and Alters Blood Lipid Profiles

Introduction

Dietary restriction (DR: reduced enteral intake without malnutrition) diminishes the acute phase response to surgical stress in preclinical models. We hypothesized that short-term preoperative protein-free DR would attenuate the vascular response to injury (intimal hyperplasia: IH) while perturbing systemic circulating lipids.

Methods

After 2 weeks of 60% fat kcal diet, 8 week old B6D2F1/J mice had ad lib access to a complete 10% fat kcal diet (n=10) or a reduced calorie, protein-free diet (DR group, n=10) 1 week before induction of IH, then an ad lib complete diet. IH was induced via a validated model placing a nylon suture tie around the distal carotid artery and external 35g needle mandrel (outer diameter=0.14mm). Subsequent removal of the mandrel created a focal area of stenosis (~78% lumen diameter/~85% flow reduction). 4 weeks later, tissues were harvested for morphology and immunohistochemistry for CD45. Separately, serum was collected from mice fed a complete or DR diet for 1 week absent any surgical stress (n=20/group) for mass spectrometry-based lipidomics.

Results

DR mice showed less intimal area (p = 0.032) vs controls with statistically equivalent intimal leukocyte infiltration. DR mice also had significantly larger internal elastic lamina length (p = 0.003), a remodeling measure. DR serum exhibited significant decreases in certain classes of circulating lipids, including a collapse of multiple triglyceride types.

Conclusions

One week of protein-free DR dramatically decreased circulating lipids and attenuated arterial IH. Preoperative dietary manipulations may offer a practical means of extending durability of vascular interventions.

Qualitative Characterization of the Rat Liver Mitochondrial Lipidome using LC-MS Profiling and High Energy Collisional Dissociation (HCD) All Ion Fragmentation

Lipids play multiple roles essential for proper mitochondrial function, from their involvement in membrane structure and fluidity, cellular energy storage, and signaling. Lipids are also major targets for reactive species, and their peroxidation byproducts themselves mediate further damage. Thousands of lipid species, from multiple classes and categories, are involved in these processes, suggesting lipid quantitative and structural analysis can help provide a better understanding of mitochondrial physiological status. Due to the diversity of lipids that contribute to and reflect mitochondrial function, analytical methods should ideally cover a wide range of lipid classes, and yield both quantitative and structural information. We developed a high resolution LC-MS method that is able to monitor the major lipid classes found in biospecimens (ie. biofluids, cells and tissues) with relative quantitation in an efficient, sensitive, and robust manner while also characterizing individual lipid side-chains, by all ion HCD fragmentation and chromatographic alignment. This method was used to profile the liver mitochondrial lipids from 192 rats undergoing a dietary macronutrient study in which changes in mitochondria function are related to changes in the major fat and glycemic index component of each diet. A total of 381 unique lipids, spanning 5 of the major LIPID MAPS defined categories, including fatty acyls, glycerophospholipids, glycerolipids, sphingolipids and prenols, were identified in mitochondria using the non-targeted LC-MS analysis in both positive and negative mode. The intention of this report is to show the breadth of this non-targeted LC-MS profiling method with regards to its ability to profile, identify and characterize the mitochondrial lipidome and the details of this will be discussed.

Method development for fecal lipidomics profiling

Robust methodologies for the analysis of fecal material will facilitate the understanding of gut (patho)physiology and its role in health and disease and will help improve care for individual patients, especially high-risk populations, such as premature infants. Because lipidomics offers a biologically and analytically attractive approach, we developed a simple, sensitive, and quantitatively precise method for profiling intact lipids in fecal material. The method utilizes two separate, complementary extraction chemistries, dichloromethane (DCM) and a methyl tert-butyl ether/hexafluoroisopropanol (MTBE) mixture, alone or with high pressure cycling. Extracts were assessed by liquid chromatography-high-resolution mass spectrometry-based profiling with all ion higher energy collisional dissociation fragmentation in both positive and negative ionization modes. This approach provides both class-specific and lipid-specific fragments, enhancing lipid characterization. Solvents preferentially extracted lipids based on hydrophobicity. More polar species preferred MTBE; more hydrophobic compounds preferred DCM. Pressure cycling differentially increased the yield of some lipids. The platform enabled analysis of >500 intact lipophilic species with over 300 lipids spanning 6 LIPID MAPS categories identified in the fecal matter from premature infants. No previous report exists that provides these data; thus, this study represents a new paradigm for assessing nutritional health, inflammation, and infectious disease in vulnerable populations.

Structural characterization of plasma metabolites detected via LC-electrochemical coulometric array using LC-UV fractionation, MS, and NMR

Liquid chromatography (LC) separation combined with electrochemical coulometric array detection (EC) is a sensitive, reproducible, and robust technique that can detect hundreds of redox-active metabolites down to the level of femtograms on column, making it ideal for metabolomics profiling. EC detection cannot, however, structurally characterize unknown metabolites that comprise these profiles. Several aspects of LC-EC methods prevent a direct transfer to other structurally informative analytical methods, such as LC-MS and NMR. These include system limits of detection, buffer requirements, and detection mechanisms. To address these limitations, we developed a workflow based on the concentration of plasma, metabolite extraction, and offline LC-UV fractionation. Pooled human plasma was used to provide sufficient material necessary for multiple sample concentrations and platform analyses. Offline parallel LC-EC and LC-MS methods were established that correlated standard metabolites between the LC-EC profiling method and the mass spectrometer. Peak retention times (RT) from the LC-MS and LC-EC system were linearly related (r(2) = 0.99); thus, LC-MS RTs could be directly predicted from the LC-EC signals. Subsequent offline microcoil-NMR analysis of these collected fractions was used to confirm LC-MS characterizations by providing complementary, structural data. This work provides a validated workflow that is transferrable across multiple platforms and provides the unambiguous structural identifications necessary to move primary mathematically driven LC-EC biomarker discovery into biological and clinical utility.

Abstract IA24: Biomarkers of diet predict disease risk

Over-nutrition and suboptimal dietary macronutrient choices are arguably the major environmental stressor in individuals living in Western societies. Obesity and poor diet are estimated to cause or contribute to as many as 25% of all cancer. One of the most clear examples of this, dietary or caloric restriction (CR), is the most potent and reproducible known means of increasing longevity and reducing morbidity in mammals. CR is also accepted to reduce cancer risk in animals. As one example, risk of breast cancer is generally decreased by more than 90% in CR rodents, and the CR-mediated effects are usually dominant to those induced by genetic risk factors, carcinogens, or co-carcinogens. The robust observations of reduced morbidity in CR animals is directly analogous to studies in humans that link obesity with poor health outcomes, including increased risk of neoplastic disease. We therefore proposed to test the general concept that biomarkers of diet in rats will predict risk of future disease in humans.

Methods: Metabolomics measurements in sera/plasma were conducted HPLC coupled with coulometric detector arrays (N∼600 rats, ∼1700 humans). Classification and predictive power were tested, optimized, and subsequently validated using a series of megavariate data analysis approaches in sequential blinded cohorts.

Results: Exploratory studies identified 93 redox-active small molecules from sera (measured by) with potential to distinguish dietary groups in both male and female rats (60 6 month old FBFN1 rats/group, AL/CR/male females in primary set). Partial Least Squares Projection to Latent Structures Discriminant Analysis, a projection method optimized for class separation built models with &gt;95% accuracy in distinguishing groups. Data processing choices of transformation, scaling, and winsorizing (outlier removal) each affected strength of the models, and, in some cases, revealed distinct metabolites to be of importance in building these models, often in gender-specific ways. Diets varying in extent and duration of CR were used to develop models for intermediate caloric intakes, which are more relevant for human studies (total N=∼180 males, 180 females). Markers were adapted for human study, analytically validated at both the instrumentation (N=30; 100% accuracy in blinded splits) and at the sample collection levels (N=34; majority stable under worst case shipping conditions), then biologically validated (N∼200, metabolites and profiles had intra-class correlation coefficients from ∼0.65-0.85). We will present these modeling approaches, the models and their ability to distinguish sera based on caloric intake, as well as data from the initial application of these markers to address risk of breast cancer in case-control studies nested within the Nurses' Health Study. We will address some of the checks and cross-checks used to evaluate these data.

Conclusion: Metabolomics profiles offer a potential biochemical approach to validate nutritive status and contribute to epidemiological investigations.

Citation Format: Bruce S. Kristal. Biomarkers of diet predict disease risk. [abstract]. In: Proceedings of the AACR Special Conference on Post-GWAS Horizons in Molecular Epidemiology: Digging Deeper into the Environment; 2012 Nov 11-14; Hollywood, FL. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2012;21(11 Suppl):Abstract nr IA24.

Dietary Omega-3 Fatty Acids Do Not Change Resistance of Rat Brain or Liver Mitochondria to Ca(2+) and/or Prooxidants

Omega-3 polyunsaturated fatty acids (n-3 PUFAs) block apoptotic neuronal cell death and are strongly neuroprotective in acute and chronic neurodegeneration. Theoretical considerations, indirect data, and consideration of parsimony lead to the hypothesis that modulation of mitochondrial pathway(s) underlies at least some of the neuroprotective effects of n-3 PUFAs. We therefore systematically tested this hypothesis on healthy male FBFN1 rats fed for four weeks with isocaloric, 10% fat-containing diets supplemented with 1, 3, or 10% fish oil (FO). High resolution mass spectrometric analysis confirmed expected diet-driven increases in docosahexaenoic acid (DHA, 22:6, n-3) and eicosapentaenoic acid (EPA, 20:5, n-3) in sera, liver and nonsynaptosomal brain mitochondria. We further evaluated the resistance of brain and liver mitochondria to Ca(2+) overload and prooxidants. Under these conditions, neither mitochondrial resistance to Ca(2+) overload and prooxidants nor mitochondrial physiology is altered by diet, despite the expected incorporation of DHA and EPA in mitochondrial membranes and plasma. Collectively, the data eliminate one of the previously proposed mechanism(s) that n-3 PUFA induced augmentation of mitochondrial resistance to the oxidant/calcium-driven dysfunction. These data furthermore allow us to define a specific series of follow-up experiments to test related hypotheses about the effect of n-3 PUFAs on brain mitochondria.

Separation of cis-trans phospholipid isomers using reversed phase LC with high resolution MS detection

The increased presence of synthetic trans fatty acids into western diets has been shown to have deleterious effects on physiology and raising an individual's risk of developing metabolic disease, cardiovascular disease, and stroke. The importance of these fatty acids for health and the diversity of their (patho) physiological effects suggest that not only should the free trans fatty acids be studied but also monitoring the presence of these fats into the side chains of biological lipids, such as glycerophospholipids, is also essential. We developed a high resolution LC-MS method that quantitatively monitors the major lipid classes found in biospecimens in an efficient, sensitive, and robust manner while also characterizing individual lipid side chains through the use of high energy collisional dissociation (HCD) fragmentation and chromatographic alignment. We herein show how this previously described reversed phase method can baseline separate the cis-trans isomers of phosphatidylglycerol and phosphatidylcholine (PC) with two 18:1 side chains, in both positive and negative mode, as neat solutions and when spiked into a biological matrix. Endogenous PC (18:1/18:1)-cis and PC (18:1/18:1)-trans isomers were examined in mitochondrial and serum profiling studies, where rats were fed diets enriched in either trans 18:1 fatty acids or cis 18:1 fatty acids. In this study, we determined the cis:trans isomer ratios of PC (18:1/18:1) and related this ratio to dietary composition. This generalized LC-MS method enables the monitoring of trans fats in biological lipids in the context of a nontargeted method, allowing for relative quantitation and enhanced identification of unknown lipids in complex matrixes.

The use of underloaded C(18) solid-phase extraction plates increases reproducibility of analysis of tryptic peptides from unfractionated human plasma

Bottom-up proteomics requires the digestion of proteins into peptides by processes that use salts for denaturing and buffering purposes. These salts need to be removed prior to mass spectrometry analysis to reduce ion suppression; solid-phase extraction (SPE) is a commonly used strategy. There are many commercially available SPE sorbent types and sizes, which are generally provided with manufacturer recommendations for use, including protein loading capacity. We found that these general suggestions were often not ideal, and our data suggest that context-specific evaluation of sorbent type and amount can improve reproducibility. Specifically, the universal Oasis HLB sorbent provided better retention of the more hydrophilic peptides than the traditional C(18) reversed-phase SPE, but it did so at the expense of an increased loss of the more hydrophobic peptides. We found that increasing the amount of the C(18) sorbent beyond the manufacturer's guidelines decreased breakthrough (i.e., increased retention) of 12 hydrophilic, identifiable peptides without loss of hydrophobic peptides. This procedure was robust in a 96-well plate format.