Tcherkez, G. G. B. | bioRxiv Science

bioRxiv2026

Breast cancer metabolism and responsiveness to dichloroacetate: relationships with 15N and 13C natural abundance

BackgroundMetabolic reprogramming is a hallmark of breast cancer (BrCa), with alterations in glycolysis, glutamine metabolism, and the urea cycle contributing to tumour progression. Dichloroacetate (DCA), a pyruvate dehydrogenase kinase (PDK) inhibitor, shifts metabolism toward oxidative phosphorylation and has been proposed as a therapeutic agent. While isotope tracing is well-established, natural isotope abundance ({delta}{superscript 1}3C, {delta}{superscript 1}N) is emerging as a biomarker of metabolic alterations in cancer. MethodsWe investigated the relationship between isotope composition and metabolism in BrCa using two BALB/c mouse mammary tumour models (V14 and 4T1) and assessed the effects of DCA treatment using metabolomics, lipidomics and isotopomics. ResultsV14 and 4T1 tumours exhibited isotopic patterns similar to human tumours, with {delta}{superscript 1}3C enrichment and {delta}{superscript 1}N depletion relative to non-cancerous mammary tissue. V14 tumours were more {delta}{superscript 1}N-depleted than 4T1, reflecting differences in nitrogen metabolism. Multivariate analysis integrating isotopic, metabolomic, and lipidomic data revealed isotopic features as key discriminators between tumours and normal tissues. Compared to V14, 4T1 tumours were enriched in TCA intermediates, sphingolipids, and amino acids, whereas V14 tumours showed elevated glutaminolytic and nitrogenous metabolites. DCA treatment differentially affected tumour growth, with V14 tumours more sensitive than 4T1. DCA altered nitrogen metabolism, increasing the arginine-to-ornithine ratio, and modulating {delta}{superscript 1}N values in a tumour-specific manner increasing V14 and decreasing 4T1 {delta}{superscript 1}N values. DCA had little effect on {delta}{superscript 1}3C. {delta}{superscript 1}3C values were primarily determined by the balance between lipid and TCA cycle metabolites, rather than glycolytic flux. {delta}{superscript 1}N variation was linked to nitrogen metabolism, including urea cycle intermediates and sphingolipid composition, with a potential role for choline-related fractionation in {delta}{superscript 1}N depletion. Altered gene expression of Hacd2 and Acot12 in V14 tumours after DCA treatment was reflected in shorter fatty acid tails in phosphatidyl cholines, supporting the lipidomics data. ConclusionsThese findings support the hypothesis that cancer-associated metabolic reprogramming influences natural isotope abundance. Correlations between isotope shifts and metabolic signatures highlight the potential of lipid-derived {delta}{superscript 1}N as a biomarker of tumour metabolic state, with implications for noninvasive metabolic profiling in BrCa. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=141 SRC="FIGDIR/small/710495v1_ufig1.gif" ALT="Figure 1"> View larger version (32K): org.highwire.dtl.DTLVardef@1589d0eorg.highwire.dtl.DTLVardef@af2ad4org.highwire.dtl.DTLVardef@24e67forg.highwire.dtl.DTLVardef@98da7f_HPS_FORMAT_FIGEXP M_FIG C_FIG

biochemistry↗

bioRxiv2023

Concurrent measurement of O2 and isoprene production during photosynthesis: pros, cons, and metabolic implications

During oxygenic photosynthesis, oxygen (O2) is generated from water photolysis, which provides reducing power to sustain CO2 assimilation. To date, traditional leaf gas-exchange experiments have been focused on net CO2 exchange (Anet), with limited observations of net oxygen production (NOP). Here, we present the first gas-exchange/fluorescence system, coupling CO2/H2O analysis (photosynthesis and transpiration) with NOP and isoprene emission measurements. This configuration allowed us to calculate the assimilatory quotient (AQ = Anet/NOP) and thus obtain a more complete picture of the photosynthetic redox budget via photosynthetic production of O2, electron transport rate (ETR), and isoprene biosynthesis. We used cottonwood leaves (Populus trichocarpa) and carried out response curves to light, CO2 and temperature along with 18O-labelling with 18O-enriched water. We found that Anet and NOP were linearly correlated across environmental variables with AQ of 1.27 +/- 0.12 regardless of light, CO2, and temperature. Anet and NOP had optimal temperatures (Topt) of 31{degrees}C, while ETR (35{degrees}C) and isoprene emissions (39{degrees}C) had distinctly higher Topt. Leaves labelled with H218O produced labeled (18O16O) oxygen with the same Topt as ETR (35{degrees}C). The results confirm a tight connection between water oxidation and ETR and are consistent with a suppression of Anet and NOP at high temperature driven by an acceleration of (photo)respiration. The findings support the view of isoprene biosynthesis primarily driven by excess photosynthetic ATP/NADPH not consumed by the Calvin cycle during photorespiratory conditions as an important thermotolerance mechanism linked with high rates of CO2 and O2 recycling. KeywordsPhotosynthesis, net oxygen production, gross oxygen production, H218O labeling One sentence summaryA leaf gas-exchange system is presented enabling a more complete picture of the photosynthetic redox budget and calculation of the assimilatory quotient.

plant biology↗