In pulmonary artery hypertension (PAH), emerging evidence suggests that metabolic abnormalities may be contributing to cellular dysfunction in PAH. Metabolic abnormalities such as glycolytic shift have been observed intracellularly in several cell types in PAH, including microvacular endothelial cells (MVECs). Concurrently, metabolomics of human PAH samples has also revealed a variety of metabolic abnormalities; however the relationship between the intracellular metabolic abnormalities and the serum metabolome in PAH remains under investigation. In this study, we utilize the sugen/hypoxia (SuHx) rodent model of PAH to examine the RV, LV and MVEC intracellular metabolome (using targeted metabolomics) in normoxic and SuHx rats. We additionally validate key findings from our metabolomics experiments with data obtained from cell culture of normoxic and SuHx MVECs, as well as metabolomics of human serum samples from two different PAH patient cohorts. Taken together, our data, spanning rat serum, human serum and primary isolated rat MVECs reveal that: (1) key classes of amino acids (specifically, branched chain amino acids—BCAA) are lower in the pre‐capillary (i.e., RV) serum of SuHx rats (and humans); (2) intracellular amino acid levels (in particular BCAAs) are increased in SuHx‐MVECs; (3) there may be secretion rather than utilization of amino acids across the pulmonary microvasculature in PAH and (4) an oxidized glutathione gradient is present across the pulmonary vasculature, suggesting a novel fate for increased glutamine uptake (i.e., as a source of glutathione). in MVECs in PAH. In summary, these data reveal new insight into the shifts in amino acid metabolism occurring across the pulmonary circulation in PAH.

Background: Pulmonary arterial hypertension (PAH) is characterized by narrowing of the pulmonary arteries, endothelial cell dysfunction, and an increased vascular cell proliferation. Increased proliferation is also accompanied by glycolytic shift, where glucose is shunted towards anaerobic respiration and production of critical macromolecules. This decreases the available glucose that can be used as a fuel in the tricarboxylic acid (TCA) cycle. To compensate for the lack of TCA cycle metabolites, there is an increase in the use of non-glucose fuels - such as amino acids and fatty acids. However, the effect of this shift on other metabolic pathways is still unknown. In this study, we investigated the levels of metabolites across the pulmonary circulation to define the metabolic shift that cells undergo during PAH. Material & Methods: We carried out metabolomic analysis on serum samples taken from the right and left ventricles (RV and LV) of rats with PAH (SU5416/Hypoxia model: SuHx) and normoxic controls. We also isolated MVECs from each group and performed both targeted and untargeted metabolomics on the cell lysates. Results: Induction of PAH resulted in increased pulmonary artery pressures and RV hypertrophy. Metabolomics of the RV serum were different in PAH versus control rats. This was driven by lower metabolite levels of several amino acids, including glutamine, phenylalanine, and valine. Normoxia- and SuHx-MVEC lysates samples were also distinct, with increased levels of lactic acid contributing significantly to the differences between animals with PAH and controls. Importantly, and in contrast to the serum, where glutamine levels were decreased, we observed increased levels of intracellular glutamine in our analysis. Similarly, intracellular levels of amino acids like phenylalanine, tyrosine and leucine were increased in these lysates. This also contrasted with the serum, where levels of these amino acids were decreased. Interestingly, LV levels of amino acids like valine, glutamine and lysine were similar in normoxic and SuHx samples. However, we did observe increased citrulline levels in SuHx LV serum samples. Comparing the LV/RV ratio in our samples revealed that increased oxidized glutathione was a major determinant of the difference between the SuHx and control groups. Conclusion: Our data suggests that decreased RV serum levels of amino acids in SuHx rats may be driven by increased consumption in the pulmonary vasculature. Given that glutamine levels in the RV are decreased, while being increased intracellularly in MVECs, we hypothesize that glutamine consumption in the lung microvasculature may be driven in part, to produce reduced glutathione. This is also supported by the oxidized glutathione gradient across the pulmonary vasculature in our experiments. These results provide the basis for a mechanistic study aimed at understanding how interrupting glutathione and/or branched-chain amino acid metabolism in MVECs contributes to PAH. NHLBI grant K08HL145132 (J.S.), NHLBI grant R01HL148112 01 (L.S), NHLBI grant R01HL151530 (K.S) This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.