Conjugate Screening

Introduction

Glutathion (GSH) conjugates of xenobiotics usually result in characteristic MS/MS fragments and neutral losses (Brink et al., 2014). This vignette shows you two approaches, one relying on MS/MS fragments and one relying on neutral losses, to screen a metabolomics data set with associated MS/MS spectra for GSH conjugates. If you want to learn more about drug metabolism you can visit the Wikipedia page (https://en.wikipedia.org/wiki/Drug_metabolism). The data set was obtained by treating HepG2 cells with the redox cycler menadione and measuring the samples in ESI positive mode.

Prepare the data set

This vignette uses data from a separate GitHub repository. More information about the data can be found there.

First, the featuretable, the sample metadata, and the MS/MS spectra have to be imported and joined together. The metamorphr package provides several convenience functions to help with these tasks. To read the sample metadata in the form of a .csv file, readr::read_csv can be used.

menadione_ft <- read_featuretable(
  "https://github.com/yasche/metamorphr-data/raw/refs/heads/main/RP18/pos/MetaboScape/menadione/menadione.csv", 
  label_col = 3, 
  metadata_cols = 1:15)

menadione_metadata <- readr::read_csv(
  "https://github.com/yasche/metamorphr-data/raw/refs/heads/main/RP18/pos/MetaboScape/menadione/menadione_metadata.csv", 
  show_col_types = FALSE)

menadione_msn <- read_mgf("https://github.com/yasche/metamorphr-data/raw/refs/heads/main/RP18/pos/MetaboScape/menadione/menadione.gnps.mgf",
                          show_progress = F)

After the files have been imported successfully, they can be joined together. First the sample metadata is joined using the convenience function join_metadata. The MS/MS spectra can simply be added via dplyr::left_join.

menadione_ft <- menadione_ft %>%
  join_metadata(menadione_metadata) %>%
  dplyr::left_join(menadione_msn, by = "FEATURE_ID")

head(menadione_ft)
#> # A tibble: 6 × 30
#>     UID Feature    Sample           Intensity FEATURE_ID    RT   CCS SIGMA_SCORE
#>   <int> <chr>      <chr>                <dbl>      <dbl> <dbl> <dbl>       <dbl>
#> 1     1 186.015    QC_1_07-Aug-24_…      745.          1  13.6  133.        NA  
#> 2     2 837.83232  QC_1_07-Aug-24_…     1256.          2  24.2  152.        NA  
#> 3     3 769.84306  QC_1_07-Aug-24_…     3594.          3  24.6  223.        NA  
#> 4     4 1403.71268 QC_1_07-Aug-24_…       NA           4  24.7  341.        NA  
#> 5     5 1539.68908 QC_1_07-Aug-24_…       NA           5  25    354.        NA  
#> 6     6 244.22612  QC_1_07-Aug-24_…    25572.          6  25.9  157.        12.9
#> # ℹ 22 more variables: NAME_METABOSCAPE <chr>, MOLECULAR_FORMULA <chr>,
#> #   ADDUCT <chr>, KEGG <chr>, CAS <chr>, MaxIntensity <dbl>,
#> #   Condition_QC_MeanIntensity <dbl>, Condition_BLANK_MeanIntensity <dbl>,
#> #   Condition_Control_MeanIntensity <dbl>,
#> #   Condition_Treatment_MeanIntensity <dbl>, Group <chr>, Replicate <dbl>,
#> #   Batch <dbl>, Factor <dbl>, SCANS <dbl>, PEPMASS <dbl>, MSLEVEL <dbl>,
#> #   CHARGE <chr>, POLARITY <chr>, RTINMINUTES <dbl>, ION <chr>, MSn <list>

Find potential glutathion conjugates

To find potential GSH conjugates, two approaches can be used: (i) search for specific MS/MS spectra and (ii) search for specific neutral losses. Functions for both approaches are implemented in the metamorphr package and are shown below. Results can be easily visualized using the ‘ggplot2’ package. Characteristic fragments and neutral losses are described in Brink et al., 2014.

menadione_ft <- menadione_ft %>%
  dplyr::filter(Group != "QC") %>%
  filter_grouped_mv(min_found = 0.75)  %>%
  filter_blank(blank_samples = c("blank", "control"),
               blank_as_group = T,
               group_column = Group,
               min_frac = 3) %>%
  dplyr::filter(Group != "blank")

fragments <- c(308.0911,
               179.0485,
               177.0328,
               162.0219,
               130.0499)

menadione_ft %>%
  filter_msn(fragments = fragments, 
             min_found = 2, 
             tolerance = 5, 
             tolerance_type = "ppm", 
             show_progress = F) %>%
  ggplot2::ggplot(ggplot2::aes(Group, Intensity)) +
    ggplot2::geom_point(position = "jitter") +
    ggplot2::facet_wrap(~ Feature) +
    ggplot2::ylim(c(0, NA))
#> Warning: Removed 12 rows containing missing values or values outside the scale range
#> (`geom_point()`).

losses <- c(75.0320,
            129.0426,
            232.0696,
            146.0692,
            249.0961,
            273.0961,
            275.1117,
            305.0682,
            307.0838)

menadione_ft %>%
  calc_neutral_loss(m_z_col = PEPMASS) %>%
  filter_neutral_loss(losses = losses, 
                      min_found = 4, 
                      tolerance = 10, 
                      tolerance_type = "ppm",
                      show_progress = F) %>%
  ggplot2::ggplot(ggplot2::aes(Group, Intensity)) +
    ggplot2::geom_point(position = "jitter") +
    ggplot2::facet_wrap(~ Feature) +
    ggplot2::ylim(c(0, NA))
#> Warning: Removed 24 rows containing missing values or values outside the scale range
#> (`geom_point()`).

References

Brink, A., Fontaine, F., Marschmann, M., Steinhuber, B., Cece, E. N., Zamora, I., & Pähler, A. (2014). Post-acquisition analysis of untargeted accurate mass quadrupole time-of-flight MS E data for multiple collision-induced neutral losses and fragment ions of glutathione conjugates: Neutral losses and fragment ion analysis of glutathione conjugates. Rapid Communications in Mass Spectrometry, 28(24), 2695–2703. DOI 10.1002/rcm.7062

Mauzeroll, J., Bard, A. J., Owhadian, O., & Monks, T. J. (2004). Menadione metabolism to thiodione in hepatoblastoma by scanning electrochemical microscopy. Proceedings of the National Academy of Sciences, 101(51), 17582–17587. DOI 10.1073/pnas.0407613101