Using exomarkers to assess mitochondrial reactive species in vivo

BACKGROUND: The ability to measure the concentrations of small damaging and signalling molecules such as reactive oxygen species (ROS) in vivo is essential to understanding their biological roles. While a range of methods can be applied to in vitro systems, measuring the levels and relative changes in reactive species in vivo is challenging. SCOPE OF REVIEW: One approach towards achieving this goal is the use of exomarkers. In this, exogenous probe compounds are administered to the intact organism and are then transformed by the reactive molecules in vivo to produce a diagnostic exomarker. The exomarker and the precursor probe can be analysed ex vivo to infer the identity and amounts of the reactive species present in vivo. This is akin to the measurement of biomarkers produced by the interaction of reactive species with endogenous biomolecules. MAJOR CONCLUSIONS AND GENERAL SIGNIFICANCE: Our laboratories have developed mitochondria-targeted probes that generate exomarkers that can be analysed ex vivo by mass spectrometry to assess levels of reactive species within mitochondria in vivo. We have used one of these compounds, MitoB, to infer the levels of mitochondrial hydrogen peroxide within flies and mice. Here we describe the development of MitoB and expand on this example to discuss how better probes and exomarkers can be developed. This article is part of a Special Issue entitled Current methods to study reactive oxygen species - pros and cons and biophysics of membrane proteins. Guest Editor: Christine Winterbourn

In a 12-allele analysis HLA-DPB1 matching is associated with improved OS in leukaemic and myelodysplastic patients receiving myeloablative T-cell-depleted PBSCT from unrelated donors

The effect on survival of including HLA-DPB1 in a 12-allele matching strategy was retrospectively evaluated in 130 patients with acute leukaemia and myelodysplasia undergoing T-cell-depleted PBSC transplantation using unrelated donors. Patients received alemtuzumab in vivo T-cell depletion as part of a myeloablative (MA; n=61) or reduced-intensity conditioning regimen (n=69). No difference in OS was seen with single-locus mismatching (mm) when 10 conventional alleles (HLA-A, B, C, DRB1 and DQB1) were considered. However, the addition of HLA-DPB1 matching data proved highly discriminatory. Mismatches were identified in 87% of patients previously considered fully matched (1DPmm=49pts: 2DPmm=28pts), and in the 9/10 group 22 patients were reclassified as double and 16 as triple mismatches. In 10/10 transplants, there was a distinct trend to poorer OS with double DPB1 mm. If all 12 loci were considered, 98% of single mm were at HLA-DPB1. Furthermore, cumulative mm at two or more loci was associated with significantly poorer 3-year OS (34% vs 48%, P=0.013: hazard ratio 1.8 (95% confidence interval 1.14–3.06; P=0.017), although his detrimental effect was only apparent using MA conditioning, in which reduced OS was associated with increased chronic GVHD (61% vs 16%, P=0.018) and nonrelapse mortality (30% vs 9%, P=0.039)

Using the mitochondria-targeted ratiometric mass spectrometry probe MitoB to measure H₂O₂ in living <i>Drosophila</i>

The role of hydrogen peroxide (H&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;2&lt;/sub&gt;) in mitochondrial oxidative damage and redox signaling is poorly understood, because it is difficult to measure H&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;2&lt;/sub&gt; in vivo. Here we describe a method for assessing changes in H&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;2&lt;/sub&gt; within the mitochondrial matrix of living &lt;i&gt;Drosophila&lt;/i&gt;. We use a ratiometric mass spectrometry probe, MitoB ((3-hydroxybenzyl)triphenylphosphonium bromide), which contains a triphenylphosphonium cation component that drives its accumulation within mitochondria. The arylboronic moiety of MitoB reacts with H&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;2&lt;/sub&gt; to form a phenol product, MitoP. On injection into the fly, MitoB is rapidly taken up by mitochondria and the extent of its conversion to MitoP enables the quantification of H&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;2&lt;/sub&gt;. To assess MitoB conversion to MitoP, the compounds are extracted and the MitoP/MitoB ratio is quantified by liquid chromatography–tandem mass spectrometry relative to deuterated internal standards. This method facilitates the investigation of mitochondrial H&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;2&lt;/sub&gt; in fly models of pathology and metabolic alteration, and it can also be extended to assess mitochondrial H&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;2&lt;/sub&gt; production in mouse and cell culture studies

Targeting mitochondria with small molecules:The preparation of MitoB and MitoP as exomarkers of mitochondrial hydrogen peroxide

Small molecules can be physicochemically targeted to mitochondria using the lipophilic alkyltriphenylphosphonium (TPP) group. Once in the mitochondria the TPP-conjugate can detect or influence processes within the mitochondrial matrix directly. Alternatively, the conjugate can behave as a prodrug, which is activated by release from the TPP group either using an internal or external instruction. Small molecules can be designed that can be used in any cell line, tissue or whole organism, allow temporal control, and be applied in a reversible dose-dependent fashion. An example is the detection and quantification of hydrogen peroxide in mitochondria of whole living organisms by MitoB. Hydrogen peroxide produced within the mitochondrial matrix is involved in signalling and implicated in the oxidative damage associated with aging and a wide range of age-associated conditions including cardiovascular disease, neurodegeneration, and cancer. MitoB accumulates in mitochondria and is converted into the exomarker, MitoP, by hydrogen peroxide in the mitochondrial matrix. The hydrogen peroxide concentration is determined from the ratio of MitoP to MitoB after a period of incubation, and this ratio is determined by mass spectrometry using d15-MitoP and d15-MitoB as standard. Here we describe the synthesis of MitoB and MitoP and the deuterated standards necessary for this method of quantification