Celastrol alleviates SGLT2 inhibitor-induced diabetic hyperketonemia by inhibiting hepatic ketogenesis

Abstract

SGLT2 inhibitor (SGLT2i)-induced diabetic hyperketonemia is a life-threatening acute complication of diabetes. While celastrol has been reported to have beneficial effects on obesity, its potential role in ketogenesis remains unclear. In this study, celastrol administration significantly attenuates the fasting-induced increase in blood β-hydroxybutyrate levels. Moreover, a 7-day course of celastrol (1 mg/kg/day) leads to reductions in body weight and fat mass. Mechanistically, celastrol specifically downregulates HMGCS2 expression and suppresses hepatic ketogenesis through the inhibition of PPARα expression in the short term (≤ 2 days). However, after prolonged treatment for 7 days, celastrol modulates both PPARα and serum free fatty acid (FFA) levels. Furthermore, the anti-ketogenic effect of celastrol is abolished in Pparα⁻/⁻ mice. Importantly, celastrol effectively ameliorates SGLT2i-induced hyperketonemia. In summary, celastrol curbs hepatic ketone overproduction in a PPARα-dependent manner, indicating its protective potential against SGLT2i-induced hyperketonemia.

1. Introduction

Ketogenesis primarily occurs in the hepatic mitochondrial matrix, and produces soluble ketone bodies such as acetone, acetoacetate (AcAc), and β-hydroxybutyrate (β-OHB) that serve as energy substrates in extrahepatic tissues through the breakdown of free fatty acids (FFAs) [1, 2]. Under the catalysis of acyl-CoA synthetase, FFAs are activated to acyl-CoA, which then traverses the mitochondrial membrane and undergoes β-oxidation. The rate-limiting enzyme of ketogenesis, 3-hydroxy-3-methylglutaryl-CoA synthase 2 (HMGCS2), catalyzes the condensation of acetoacetyl-CoA (AcAc-CoA) and acetyl-CoA to form hydroxymethylglutaryl (HMG)-CoA. This intermediate is subsequently cleaved by hydroxymethylglutaryl-coenzyme A lyase (HMGCL) to release acetyl-CoA and AcAc. AcAc can be further reduced to β-OHB or spontaneously decarboxylated to acetone. HMGCS2 expression is transcriptionally activated during fasting through the action of peroxisome proliferator-activated receptor α (PPARα), a central hepatic regulator that orchestrates the adaptive response to starvation by modulating both β-oxidation and ketogenic pathways [3].

Ketogenesis is physiologically enhanced under conditions of depleted carbohydrate reserves or elevated fatty acid availability. However, excessive production of ketone bodies may result in ketoacidosis, a potentially fatal metabolic state characterized by the accumulation of acidic ketones. Diabetic ketoacidosis (DKA) represents an acute and life-threatening complication of diabetes and is characterized by hyperglycemia, metabolic acidosis, and ketosis [4]. Euglycemic DKA (EDKA) is characterized by metabolic acidosis and ketosis but occurs in the absence of significant hyperglycemia (blood glucose < 200 mg/dL) [5]. Because of its atypical presentation, EDKA is often undiagnosed or diagnosed late, delaying treatment. Known triggers of EDKA include reduced caloric intake, excessive alcohol consumption, chronic liver disease, glycogen storage disorders, and the recent use of insulin or sodium-glucose cotransporter-2 inhibitor (SGLT2i) [5]. SGLT2i, a class of glucose-lowering agents used in type 2 diabetes (T2D), act by inhibiting renal glucose reabsorption. However, they are associated with an increased risk of DKA (including EDKA) mainly through promoting lipolysis, enhancing renal ketone reabsorption, and altering the glucagon/insulin ratio via stimulation of pancreatic α cells and suppression of β cells [5-7]. These risks highlight the clinical need for effective preventive and therapeutic strategies against SGLT2i-induced DKA.