Critical Reanalysis of the Mechanisms Underlying the Cardiorenal Benefits of SGLT2 Inhibitors and Reaffirmation of the Nutrient Deprivation Signaling/Autophagy Hypothesis

Abstract

SGLT2 (sodium-glucose cotransporter 2) inhibitors produce a distinctive pattern of benefits on the evolution and progression of cardiomyopathy and nephropathy, which is characterized by a reduction in oxidative and endoplasmic reticulum stress, restoration of mitochondrial health and enhanced mitochondrial biogenesis, a decrease in proinflammatory and profibrotic pathways, and preservation of cellular and organ integrity and viability. A substantial body of evidence indicates that this characteristic pattern of responses can be explained by the action of SGLT2 inhibitors to promote cellular housekeeping by enhancing autophagic flux, an effect that may be related to the action of these drugs to produce simultaneous upregulation of nutrient deprivation signaling and downregulation of nutrient surplus signaling, as manifested by an increase in the expression and activity of AMPK (adenosine monophosphate-activated protein kinase), SIRT1 (sirtuin 1), SIRT3 (sirtuin 3), SIRT6 (sirtuin 6), and PGC1-α (peroxisome proliferator-activated receptor γ coactivator 1-α) and decreased activation of mTOR (mammalian target of rapamycin). The distinctive pattern of cardioprotective and renoprotective effects of SGLT2 inhibitors is abolished by specific inhibition or knockdown of autophagy, AMPK, and sirtuins. In the clinical setting, the pattern of differentially increased proteins identified in proteomics analyses of blood collected in randomized trials is consistent with these findings. Clinical studies have also shown that SGLT2 inhibitors promote gluconeogenesis, ketogenesis, and erythrocytosis and reduce uricemia, the hallmarks of nutrient deprivation signaling and the principal statistical mediators of the ability of SGLT2 inhibitors to reduce the risk of heart failure and serious renal events. The action of SGLT2 inhibitors to augment autophagic flux is seen in isolated cells and tissues that do not express SGLT2 and are not exposed to changes in environmental glucose or ketones and may be related to an ability of these drugs to bind directly to sirtuins or mTOR. Changes in renal or cardiovascular physiology or metabolism cannot explain the benefits of SGLT2 inhibitors either experimentally or clinically. The direct molecular effects of SGLT2 inhibitors in isolated cells are consistent with the concept that SGLT2 acts as a nutrient surplus sensor, and thus, its inhibition causes enhanced nutrient deprivation signaling and its attendant cytoprotective effects, which can be abolished by specific inhibition or knockdown of AMPK, sirtuins, and autophagic flux.

Keywords: TOR serine-threonine kinases; autophagy; heart failure; sirtuins; sodium-glucose transporter 2 inhibitors.

Figure 1.

Proposed framework by which SGLT2 (sodium-glucose cotransporter 2) inhibitors might exert cardioprotective and nephroprotective effects by acting to mute renal sympathetic nerve activity and promote natriuresis and osmotic diuresis. NHE3 indicates sodium-hydrogen exchanger isoform 3.

Figure 2.

Proposed framework by which SGLT2 (sodium-glucose cotransporter 2) inhibitors might act to increase delivery of substrates that could lead to enhanced synthesis of ATP (adenosine triphosphate).

Figure 3.

Effect of nutrient deprivation and nutrient surplus signaling on the evolution and progression of cardiomyopathy and nephropathy in experimental and clinical settings. Akt indicates protein kinase B; AMPK, adenosine monophosphate–activated protein kinase; mTOR, mammalian target of rapamycin; PGC-1α, peroxisome proliferator–activated receptor γ coactivator 1-α; SIRT1, sirtuin 1; SIRT3, sirtuin 3; and SIRT6, sirtuin 6.

Figure 4.

Proposed framework by which SGLT2 (sodium-glucose cotransporter 2) inhibitors can modulate nutrient deprivation signaling and thereby enhance autophagic flux and reduce cellular stress. AMPK indicates adenosine monophosphate–activated protein kinase; mTOR, mammalian target of rapamycin; and PGC-1α, peroxisome proliferator–activated receptor γ coactivator 1-α.