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This chapter provides a broad overview of ion mobility-mass spectrometry (IM-MS) and its applications in separation science, with a focus on pharmaceutical applications. A general overview of fundamental ion mobility (IM) theory is provided with descriptions of several contemporary instrument platforms which are available commercially (i.e., drift tube and traveling wave IM). Recent applications of IM-MS toward the evaluation of structural isomers are highlighted and placed in the context of both a separation and characterization perspective. We conclude this chapter with a guided reference protocol for obtaining routine IM-MS spectra on a commercially available uniform-field IM-MS.
In this work, we established a collision cross section (CCS) library of primary metabolites based on analytical standards in the Mass Spectrometry Metabolite Library of Standards (MSMLS) using a commercially available ion mobility-mass spectrometer (IM-MS). From the 554 unique compounds in the MSMLS plate library, we obtained a total of 1246 CCS measurements over a wide range of biochemical classes and adduct types. Resulting data analysis demonstrated that the curated CCS library provides broad molecular coverage of metabolic pathways and highlights intrinsic mass-mobility relationships for specific metabolite superclasses. The separation and characterization of isomeric metabolites were assessed, and all molecular species contained within the plate library, including isomers, were critically evaluated to determine the analytical separation efficiency in both the mass ( m/ z) and mobility (CCS/ΔCCS) dimension required for untargeted metabolomic analyses. To further demonstrate the analytical utility of CCS as an additional molecular descriptor, a well-characterized biological sample of human plasma serum (NIST SRM 1950) was examined by LC-IM-MS and used to provide a detailed isomeric analysis of carbohydrate constituents by ion mobility.
BACKGROUND - Epidemiologic evidence on dietary carbohydrates and stroke risk remains controversial. Very few prospective cohort studies have been conducted in Asian populations, who usually consume a high-carbohydrate diet and have a high burden of stroke.
OBJECTIVE - We examined dietary glycemic index (GI), glycemic load (GL), and intakes of refined and total carbohydrates in relation to risks of total, ischemic, and hemorrhagic stroke and stroke mortality.
DESIGN - This study included 64,328 Chinese women, aged 40-70 y, with no history of cardiovascular disease, diabetes, or cancer. A validated, interviewer-administered food-frequency questionnaire was used to assess usual dietary intakes at baseline and during follow-up. Incident stroke cases and deaths were identified via follow-up interviews and death registries and were confirmed by review of medical records and death certificates.
RESULTS - During mean follow-ups of 10 y for stroke incidence and 12 y for stroke mortality, we ascertained 2991 stroke cases (2750 ischemic and 241 hemorrhagic) and 609 stroke deaths. After potential confounders were controlled for, we observed significant positive associations of dietary GI and GL with total stroke risk; multivariable-adjusted HRs (95% CIs) for high compared with low levels (90th compared with 10th percentile) were 1.19 (1.04, 1.36) for GI and 1.27 (1.04, 1.54) for GL (both P-linearity < 0.05 and P-overall significance < 0.05). Similar linear associations were found for ischemic stroke, but the associations with hemorrhagic stroke appeared to be J-shaped. Similar trends of positive associations with stroke risks were suggested for refined carbohydrates but not for total carbohydrates. No significant associations were found for stroke mortality after multivariable adjustment.
CONCLUSION - Our results suggest that high dietary GI and GL, primarily due to high intakes of refined grains, are associated with increased risks of total, ischemic, and hemorrhagic stroke in middle-aged and older urban Chinese women.
© 2016 American Society for Nutrition.
PURPOSE - High digestible carbohydrate intakes can induce hyperglycemia and hyperinsulinemia and collectively have been implicated in colorectal tumor development. Our aim was to explore the association between aspects of dietary carbohydrate intake and risk of colorectal adenomas and hyperplastic polyps in a large case-control study.
METHODS - Colorectal polyp cases (n = 1,315 adenomas only, n = 566 hyperplastic polyps only and n = 394 both) and controls (n = 3,184) undergoing colonoscopy were recruited between 2003 and 2010 in Nashville, Tennessee, USA. Dietary intakes were estimated by a 108-item food frequency questionnaire. Unconditional logistic regression analysis was applied to determine odds ratios (OR) and corresponding 95 % confidence intervals (CI) for colorectal polyps according to dietary carbohydrate intakes, after adjustment for potential confounders.
RESULTS - No significant associations were detected for risk of colorectal adenomas when comparing the highest versus lowest quartiles of intake for total sugars (OR 1.03; 95 % CI 0.84-1.26), starch (OR 1.01; 95 % CI 0.81-1.26), total or available carbohydrate intakes. Similar null associations were observed between dietary carbohydrate intakes and risk of hyperplastic polyps, or concurrent adenomas and hyperplastic polyps.
CONCLUSION - In this US population, digestible carbohydrate intakes were not associated with risk of colorectal polyps, suggesting that dietary carbohydrate does not have an etiological role in the early stages of colorectal carcinogenesis.
FTO is the strongest known genetic susceptibility locus for obesity. Experimental studies in animals suggest the potential roles of FTO in regulating food intake. The interactive relation among FTO variants, dietary intake and body mass index (BMI) is complex and results from previous often small-scale studies in humans are highly inconsistent. We performed large-scale analyses based on data from 177,330 adults (154 439 Whites, 5776 African Americans and 17 115 Asians) from 40 studies to examine: (i) the association between the FTO-rs9939609 variant (or a proxy single-nucleotide polymorphism) and total energy and macronutrient intake and (ii) the interaction between the FTO variant and dietary intake on BMI. The minor allele (A-allele) of the FTO-rs9939609 variant was associated with higher BMI in Whites (effect per allele = 0.34 [0.31, 0.37] kg/m(2), P = 1.9 × 10(-105)), and all participants (0.30 [0.30, 0.35] kg/m(2), P = 3.6 × 10(-107)). The BMI-increasing allele of the FTO variant showed a significant association with higher dietary protein intake (effect per allele = 0.08 [0.06, 0.10] %, P = 2.4 × 10(-16)), and relative weak associations with lower total energy intake (-6.4 [-10.1, -2.6] kcal/day, P = 0.001) and lower dietary carbohydrate intake (-0.07 [-0.11, -0.02] %, P = 0.004). The associations with protein (P = 7.5 × 10(-9)) and total energy (P = 0.002) were attenuated but remained significant after adjustment for BMI. We did not find significant interactions between the FTO variant and dietary intake of total energy, protein, carbohydrate or fat on BMI. Our findings suggest a positive association between the BMI-increasing allele of FTO variant and higher dietary protein intake and offer insight into potential link between FTO, dietary protein intake and adiposity.
© The Author 2014. Published by Oxford University Press. All rights reserved. For Permissions, please email: firstname.lastname@example.org.
In dogs consuming a high-fat and -fructose diet (52 and 17% of total energy, respectively) for 4 wk, hepatic glucose uptake (HGU) in response to hyperinsulinemia, hyperglycemia, and portal glucose delivery is markedly blunted with reduction in glucokinase (GK) protein and glycogen synthase (GS) activity. The present study compared the impact of selective increases in dietary fat and fructose on liver glucose metabolism. Dogs consumed weight-maintaining chow (CTR) or hypercaloric high-fat (HFA) or high-fructose (HFR) diets diet for 4 wk before undergoing clamp studies with infusion of somatostatin and intraportal insulin (3-4 times basal) and glucagon (basal). The hepatic glucose load (HGL) was doubled during the clamp using peripheral vein (Pe) glucose infusion in the first 90 min (P1) and portal vein (4 mg·kg(-1)·min(-1)) plus Pe glucose infusion during the final 90 min (P2). During P2, HGU was 2.8 ± 0.2, 1.0 ± 0.2, and 0.8 ± 0.2 mg·kg(-1)·min(-1) in CTR, HFA, and HFR, respectively (P < 0.05 for HFA and HFR vs. CTR). Compared with CTR, hepatic GK protein and catalytic activity were reduced (P < 0.05) 35 and 56%, respectively, in HFA, and 53 and 74%, respectively, in HFR. Liver glycogen concentrations were 20 and 38% lower in HFA and HFR than CTR (P < 0.05). Hepatic Akt phosphorylation was decreased (P < 0.05) in HFA (21%) but not HFR. Thus, HFR impaired hepatic GK and glycogen more than HFA, whereas HFA reduced insulin signaling more than HFR. HFA and HFR effects were not additive, suggesting that they act via the same mechanism or their effects converge at a saturable step.
Copyright © 2014 the American Physiological Society.
Ion mobility-mass spectrometry measurements which describe the gas-phase scaling of molecular size and mass are of both fundamental and pragmatic utility. Fundamentally, such measurements expand our understanding of intrinsic intramolecular folding forces in the absence of solvent. Practically, reproducible transport properties, such as gas-phase collision cross-section (CCS), are analytically useful metrics for identification and characterization purposes. Here, we report 594 CCS values obtained in nitrogen drift gas on an electrostatic drift tube ion mobility-mass spectrometry (IM-MS) instrument. The instrument platform is a newly developed prototype incorporating a uniform-field drift tube bracketed by electrodynamic ion funnels and coupled to a high resolution quadrupole time-of-flight mass spectrometer. The CCS values reported here are of high experimental precision (±0.5% or better) and represent four chemically distinct classes of molecules (quaternary ammonium salts, lipids, peptides, and carbohydrates), which enables structural comparisons to be made between molecules of different chemical compositions for the rapid "omni-omic" characterization of complex biological samples. Comparisons made between helium and nitrogen-derived CCS measurements demonstrate that nitrogen CCS values are systematically larger than helium values; however, general separation trends between chemical classes are retained regardless of the drift gas. These results underscore that, for the highest CCS accuracy, care must be exercised when utilizing helium-derived CCS values to calibrate measurements obtained in nitrogen, as is the common practice in the field.
PURPOSE - Magnetic resonance images of biological media based on chemical exchange saturation transfer (CEST) show contrast that depends on chemical exchange between water and other protons. In addition, spin-lattice relaxation rates in the rotating frame (R1ρ) are also affected by exchange, especially at high fields, and can be exploited to provide novel, exchange-dependent contrast. Here, we evaluate and compare the factors that modulate the exchange contrast for these methods using simulations and experiments on simple, biologically relevant samples.
METHODS - Simulations and experimental measurements at 9.4 T of rotating frame relaxation rate dispersion and CEST contrast were performed on solutions of macromolecules containing amide and hydroxyl exchanging protons.
RESULTS - The simulations and experimental measurements confirm that both CEST and R1ρ measurements depend on similar exchange parameters, but they manifest themselves differently in their effects on contrast. CEST contrast may be larger in the slow and intermediate exchange regimes for protons with large resonant frequency offsets (e.g. >2 ppm). Spin-locking techniques can produce larger contrast enhancement when resonant frequency offsets are small (<2 ppm) and exchange is in the intermediate-to-fast regime. The image contrasts scale differently with field strength, exchange rate and concentration.
CONCLUSION - CEST and R1ρ measurements provide different and somewhat complementary information about exchange in tissues. Whereas CEST can depict exchange of protons with specific chemical shifts, appropriate R1ρ-dependent acquisitions can be employed to selectively portray protons of specific exchange rates.
The potential long-term association between carbohydrate intake and the risk of coronary heart disease (CHD) remains unclear, especially among populations who habitually have high-carbohydrate diets. We prospectively examined intakes of carbohydrates and staple grains as well as glycemic index and glycemic load in relation to CHD among 117,366 Chinese women and men (40-74 years of age) without history of diabetes, CHD, stroke, or cancer at baseline in Shanghai, China. Diet was assessed using validated food frequency questionnaires. Incident CHD cases were ascertained during follow-ups (in women, the mean was 9.8 years and in men, the mean was 5.4 years) and confirmed by medical records. Carbohydrate intake accounted for 67.5% of the total energy intake in women and 68.5% in men. Seventy percent of total carbohydrates came from white rice and 17% were from refined wheat products. Positive associations between carbohydrate intakess and CHD were found in both sexes (all P for heterogeneity > 0.35). The combined multivariate-adjusted hazard ratios for the lowest to highest quartiles of carbohydrate intake, respectively, were 1.00, 1.38, 2.03, and 2.88 (95% confidence interval: 1.44, 5.78; P for trend = 0.001). The combined hazard ratios comparing the highest quartile with the lowest were 1.80 (95% confidence interval: 1.01, 3.17) for refined grains and 1.87 (95% confidence interval: 1.00, 3.53) for glycemic load (both P for trend = 0.03). High carbohydrate intake, mainly from refined grains, is associated with increased CHD risk in Chinese adults.
UNLABELLED - Maternal nutritional deficiency in-utero is known to predict risk of complex disorders like cardiovascular disease, diabetes and many neurological disorders in the offspring and vitamin B12 is one such critical micronutrient. Here we performed 2D-DIGE followed by MALDI TOF/TOF analysis to identify proteins that are differentially expressed in liver of pups born to mothers fed vitamin B12 deficient diet vis-à-vis control diet. To further establish causality, we analyzed the effect of B12 rehabilitation at parturition on the protein levels and the phenotype in pups. We identified 38 differentially expressed proteins that were enriched in pathways involved in the regulation of amino acid, lipid and carbohydrate metabolism. Further, three enzymes in the β-oxidation pathway (hydroxyacyl-coenzyme A dehydrogenase, medium-chain specific acyl-CoA dehydrogenase, 3-ketoacyl-CoA thiolase) were down-regulated in pups born to mothers fed vitamin B12 deficient diet. We observed age-dependent differential expression of peroxisome proliferator activated-receptor (PPAR) α and γ in the deficient pups. Interestingly, expression of 27 proteins that were differentially expressed was restored to the control levels after rehabilitation of female rats with vitamin B12 from parturition. Our study thus provides the first evidence that maternal vitamin B12 deficiency influences lipid and other micronutrient metabolism in pups through regulation of PPAR signaling pathway.
BIOLOGICAL SIGNIFICANCE - Maternal vitamin B12 deficiency has been shown to predict the onset of complex disorders like atherosclerosis, type II diabetes etc. in the next generation during their adulthood. We have shown earlier that pups born to female rats fed with vitamin B12 deficient diet were obese and developed high levels of other intermediate traits such as triglycerides, cholesterol etc. that are related to the risk of diabetes and cardiovascular disorders. In this piece of work using differential proteomic approach we have identified the altered metabolic processes in the liver of vitamin B12 deficient pups. We have also documented that the proteins involved in β-oxidation pathway are down-regulated. Further, differential expression of PPARα and PPARγ was evidently documented as the master regulator for the alteration of lipid, amino acid and carbohydrate metabolism during maternal vitamin B12 deficiency.
© 2013. Published by Elsevier B.V. All rights reserved.