Monitoring volatile organic compounds (VOCs) for metabolic phenotyping

Transcription

1 Monitoring volatile organic compounds (VOCs) for metabolic phenotyping Martin Kistler German mouse clinic Institute of Experimental Genetics Neuherberg, 16/10/16

2 ~1 vol-% in human breath gas are volatile organic compounds Oxygen 16% Water 5% Carbon dioxide 5% Volatile organic compounds (VOCs) 1% Nitrogen 73% From W. Szymczak

3 Volatile organic compounds in human breath Volatile organic compounds (VOCs) any organic compound having an initial boiling point less than or equal to 250 C at kpa Up to 3500 VOCs Breath as a source of information No limitation in repetitive use, sample volume Study short/ long term effects Non-invasive < 1% VOCs Realtime detection Proton transfer-ms Ion mobility spectr. Selected ion flow tube-ms enoses Pre-concentration SPME GC-MS Needle Trap & GC-MS breath condensate: NMR/GC-MS Technologies

4 Breath gas analysis: from humans to mice Forced expiration Aprea et al Voluntary expiration - Single breath? - Low experimental stress - Avoid bag/pre-conc.? - environmental wash-in? ionicon.com

5 Mouse setup - Proton Transfer Reaction MS H 3 O + + VOC H 2 O + VOCH + Ion Source Drift Tube Transfer lenses TOF MS H 2 O VOCs from mice proton transfer from H 3 O + detection of molecules with proton affinity > H 2 0 soft ionization, low fragmentation fast, real-time measurement moderate specificity high sensitivity (ppb-ppt!) Synthetic VOC-free air supply

6 Mouse setup & calculation of source strength Example: Methanol concentration over time Fit with compartment model VOC source strength

7 HFD & MC4R - experimental setup 12 weeks 60 en% high fat diet (HFD, diet-induced) MC4R-ki (MC4R W16X, mono-genetic) nonsense mutation in melanocortin 4 receptor Low fat diet (LFD) High fat diet (HFD) ad libitum fed - afternoon fasted over night - morning MC4R-ki (MC4R-ki, chow) weeks

8 HFD & MC4R VOC importance for obesity classification permuted hits: HFD (0) / MC4R (1)

9 HFD & MC4R gaussian graphical model Gaussian graphical model Used for e.g. metabolomics data reconstructs underlying (bio-) chemical pathways/ reactions based on partial correlation

10 HFD & MC4R gaussian graphical model Acetone Ketone body Embedded in a fasting responsive subnetwork spontaneous decarboxylation of aceto-acetate Elevated in HFD fed mice & fasting HFD lipid oxidation Originally thought to have potential to monitor/ detect diabetes/ blood glucose but: high interpersonal variance!

11 HFD & MC4R gaussian graphical model Acrolein Elevated in HFD fed mice Endogenous & exogenous origin: lipid peroxidation, oxidative stress (Uchida et.al 1998, J. Biol. Chem. / PNAS) Acrolein-conjugated low-density lipoprotein induces macrophage foam cell formation (Watanabe et. al, 2013, Atherosclerosis) Acrolein Exposure Is Associated With Increased Cardiovascular Disease Risk (DeJarnett et. al, 2014, J Am Heart Assoc.)

12 HFD & MC4R gaussian graphical model (Methylthio)methanethiol? (Multiple candidates) Long-distance pheromone Originally found in male urine (not in castrated) & attracts female mice (Lin et al. 2005, Nature) Reception in main olfactory bulbus (Duan et al. 2012, PNAS) Elevated in HFD fed mice in ad libitum state Decreased in MC4R-ki mice Link MC4R - reproduction

13 HFD & MC4R gaussian graphical model Unassigned (C 3 H 8 O) Elevated in HFD fed mice? Methyl acetate

14 Diet matrix - Setup and supervised feature selection RF++ Variable importance (diet matrix) chow Semipurified high fat diet (HF) Semipurified low lard diet (LL) Semipurified high lard diet (HL) weeks

15 Diet matrix - Drop in several source strengths Methanol Methylacetate / Propionate DMSO 2 Hypothesis: methanol release by microbiota-driven pectine degradation in GI tract?

16 Is it possible to follow a volatile introduced by diet through the body? Mice C57BL6 3 week LFD versus chow diet Breath Source strength measured in ad lib fed state 7:00 AM 1:00 PM Blood Ketamine injection retrorbital blood sampling Organ sampling Liquid nitrogen shock freezing Storage at -80 C Tissue homogenates Organ VOCs Headspace of ~250 mg sample After ctrgenpath.net Gas Internal organ Gut Content

17 Methanol: diet-driven separation possible (PCA) Methanol Acetone

18 Methanol difference recovered in fluids Methanol Acetone Gas Internal organ Gut Content

19 Methanol difference recovered in internal organs Methanol Acetone Gas Internal organ Gut Content

20 Methanol is quantitatively released in cecum log Methanol Acetone Gas Internal organ Gut Content

21 Summary & Outlook Obesity is changing the VOC signature is there a potential for predictive volatile biomarkers for disease (diabetes, liver disease, etc.)? specific obesogenic mechanisms might be distinguishable Proof of principle: methanol (VOC) recovery in organ headspace Outlook: Phenotyping Biomarker combination with indirect calorimetry Challenge experiments Organ contributions? Dietary versus microbial influx gut barrier for VOCs?

22 Acknowledgement Jan Rozman Martin Hrabě de Angelis Valerie Gailus-Durner Helmut Fuchs Ann-Elisabeth Schwarz Ralf Kühn Wolfgang Wurst Martin Klingenspor Nadine Rink Florian Bolze Thank you for your attention Wilfried Szymczak Christoph Hoeschen Andreea Muntean Stefan Keller

23 End+1 - Start of supplementary slides This is the end.

24 Quality control is key in unrestrained mouse measurement Humidity Methanethiol pk127b PTR-MS Feces Removal or box exchange Acetone Urine Mouse cleaning box exchange

25 HFD & MC4R heatmaps DIET FAST BODY MASS HFD GEN FAST BODY MASS MC4R

26 Graphical summary Lipid peroxidation / Oxidative stress Pheromones Ketone bodies GGM for data visualization/ molecule identification

27 Data analysis Webapp

28 Mouse setup - Proton Transfer Reaction MS H 3 O + + VOC H 2 O + VOCH + Ion Source Drift Tube Transfer lenses TOF MS H 2 O VOCs from mice proton transfer from H 3 O + detection of molecules with proton affinity > H 2 0 soft ionization, low fragmentation fast, real-time measurement moderate specificity high sensitivity (ppb-ppt!) Synthetic air supply

29 HFD & MC4R AUC- random forest model validity Feature selection protocol: - ROC curve optimization - 5 fold cross-validation (20 iterations) - Cut-off: 70% selection probability - Label permutation ROC curves of a single 5-fold CV

30 HFD & MC4R obesity characteristics

31 The laboratory mouse as a model organism for VOC analysis Defined diets reduced variance Homogenous / defined/ no microbiome Defined pharmacologic situation Homogenous genetic background Precise genetic manipulation Environmental standardization reduced and constant wash-in of external VOCs Obligate nose breathing Sampling compliance / mode of sampling?

32 Proof of principle - change to high fat diet Source strength (a.u) * C57 BL/6N mice (n = 14) Control chow 60en% High fat diet (4 weeks) * p < * * * * Diet fat content? Diet matrix? Weight gain? Aging? Candidates: M31 M33 M43 M45 M47 M61 M73 M75 M93 Methanol Propanol Ethanol Acetaldehyde Acetic acid Propionic acid From W. Szymczak, AMSD

33 Diet matrix random forest for supervised feature selection DATA Subset2 Several hundred Subset1peaks chow / purified effects? Methanol Chow (n=9) Methyl acetate >Y [ppb] Ammonia >Y [ppb] Chow (n=7) Purified (n=2) >X [ppb] MTMT Purified (n=1) >X [ppb] Chow (n=1) Acetone > Z [ppb] Acetone > Z [ppb] Chow (n=3) Purified (n=8) Purified (n=9) Compare to the rest of DATA (OOB-error) Majority vote Importance for classification

34 Feature selection AUC - Random Forest True positive rate Area under ROC curve Remove less important variables True positive ratearea under ROC curve Remove less important variables True positive ratearea under ROC curv False positive rate False positive rate False positive rate ROC-AUC VOCs selected 20 times repeated 5 fold cross-validation Selection frequency

35 Feature selection Random Forest Subset2 DATA Subset1 Acrolein>X Acrolein>X Acetic acid > Y Acetic acid > Y 5 HFD / 1 LFD 5 HFD / 1 LFD Ammonia > Z Ammonia > Z 0 HFD / 8 LFD Acetone > Q 0 HFD / 8 LFD Acetone > Q 0 HFD / 1 LFD 5 HFD / 0 LFD 0 HFD / 1 LFD 5 HFD / 0 LFD Compare to the rest of DATA (OOB-error) Majority vote