Bidirectional modulation of TCA cycle metabolites and anaplerosis by metformin and its combination with SGLT2i
Authors: Adam Jonathan , Harada Makoto , Covic Marcela , Brandmaier Stefan , Muschet Caroline , Huang Jialing , Han Siyu , Ge Jianhong , Rommel Martina , Rotter Markus , Heier Margit , Mohney Robert P. , Krumsiek Jan , Kastenmüller Gabi , Rathmann Wolfgang , Zou Zhongmei , Zukunft Sven , Scheerer Markus F. , Neschen Susanne , Adamski Jerzy , Gieger Christian , Peters Annette , Ankerst Donna P. , Meitinger Thomas , Alderete Tanya L. , Angelis Martin Hrabe , Suhre Karsten , Wang-Sattler Rui 
Published: February 2024

Background
Metformin and sodium-glucose-cotransporter-2 inhibitor (SGLT2i) are cornerstone therapies for managing hyperglycemia in diabetes, yet their nuanced impacts on metabolic processes, particularly in the citric acid (TCA) cycle and its anaplerotic pathways, are not fully delineated. This study aims to investigate the tissue-specific metabolic effects of metformin, both as a monotherapy and in combination with SGLT2i, on the TCA cycle and associated anaplerotic reactions.
Methods
Our study employed a three-pronged approach: first, comparing metformin-treated diabetic mice (MET) with vehicle-treated controls (VG) and non-diabetic wild types (WT) to identify metformin-specific metabolic changes; second, assessing these changes in human cohorts (KORA and QBB) and a longitudinal KORA study of metformin-naïve patients; third, contrasting MET with those on combination therapy (SGLT2i + MET). Metabolic profiling was conducted on 716 metabolites from plasma, liver, and kidney tissues post-treatment. Linear regression analysis and Bonferroni correction were used for rigorous statistical evaluation across all comparisons, complemented by pathway analyses to elucidate the pathophysiological implications of the metabolites involved.
Results
Metformin monotherapy was significantly associated with upregulation of TCA cycle intermediates, such as malate, fumarate, and α-ketoglutarate (α-KG), in plasma, along with anaplerotic substrates including hepatic glutamate and renal 2-hydroxyglutarate (2-HG) in diabetic mice. Conversely, downregulated hepatic taurine was observed. However, the addition of SGLT2i reversed these metabolic effects, indicating a complex interplay between these antidiabetic drugs in regulating the central energy metabolism. Human T2D subjects on metformin therapy exhibited significant systemic alterations in metabolites, including increased malate but decreased citrulline. The drugs' bidirectional modulation of TCA cycle intermediates appeared to influence four key anaplerotic pathways linked to glutaminolysis, tumorigenesis, immune regulation, and antioxidative responses.
Conclusion
This study elucidates the specific metabolic consequences of metformin and SGLT2i on the TCA cycle and beyond, reflecting potential impacts on the immune system. Metformin shows promise for its anti-inflammatory properties, while the addition of SGLT2i may provide liver protection in conditions like non-alcoholic fatty liver disease (NAFLD). These observations highlight the potential for repurposing these drugs for broader therapeutic applications and underscore the importance of personalized treatment strategies.