The Ketone Body β-Hydroxybutyrate Mitigates Diabetic Kidney Disease through Metabolic Reprogramming

Background: Diabetic kidney disease (DKD) is the most common cause of end-statge renal disease and need for renal replacement therapies. Metabolic dysregulation plays a pivotal role in the pathogenesis of DKD. Recent research has highlighted the link between ketone body, beta-hydroxybutyrate (BHB), and kidney function in humans; and the reno-protective effect in animal models via reduction of inflammation and fibrosis and a potential pathway through which SGLT2 inhibitors are effective. However, how BHB exerts its renoprotective effects is unknown and the focus of this work. Methods: We collected the plasma, urine, and kidney from 24 weeks old diabetic db/db mice and control db/+ mice. BHB was measured by LC-MS based targeted metabolomics. In order to determine whether further increase in BHB would impact DKD, db/db mice were fed with 20% 1,3-Butanediol (v/v in drinking water; 1,3-BD), which is a precursor of BHB and DKD metrics including albuminuria were measured. We quantified post-translational beta-hydroxybutyrylation (BHBylation) of proteins in db/db vs. db/+ mice. In HK-2 cell, mitochondrial function and BHB’s effect on TCA cycle metabolism were tested by LC/MS based metabolic flux analysis. Results: We found that BHB level is significantly higher in plasma (db/+ 26.2±5.8 uM vs db/db 456.95±143.21 uM), urine (db/+ 0.234±0.04 M BHB per M creatinine vs db/db 119.87±33.43 M BHB per M creatinine), and kidney cortex (db/+ 4.48±0.97 pmole BHB per mg protein vs db/db 53.33±17.87 pmole BHB per mg protein) in diabetic mice. 1,3-BD feeding further reduced urinary albumin level (albumin/creatinine: db/db 6.58±2.12 vs db/db+1,3-BD 1.89±0.205) in diabetic mice. We found that diabetic mice have significantly higher BHBylated lysine levels compared to non-diabetic controls. BHB increased the flux of TCA cycle metabolites, implying improved mitochondrial function in HK-2 cells. Conclusion: To summarize, BHB and BHBylated protein levels were higher in diabetic conditions, and supplementation with the BHB precursor, 1,3-Butanediol, led to lower urinary albumin excretion consistent with improved DKD. Increased in BHBylation associated with this protection suggests key role of this posttranslational modification in mediating improved mitochondrial function (enhanced TCA flux), metabolic rewiring in DKD and associated renoprotection. Funding: NIDDK Support, Private Foundation Support