Key enzyme in charge of ketone reabsorption of renal tubular SMCT1 may be a new target in diabetic kidney disease.

OBJECTIVE: A ketogenic diet or mildly increased ketone body levels are beneficial for diabetic kidney disease (DKD) patients. Our previous study has found that sodium-coupled monocarboxylate transporter 1 (SMCT1), a key enzyme in charge of ketone reabsorption, possesses beneficial effects on the function of renal tubular epithelial cells (TECs) in energy crisis. Our present study is to investigate whether SMCT1 is important in maintaining the physiological function of renal tubular and plays a role in DKD. METHODS: We tested the expression of SMCT1 in kidney tissues from DKD patients receiving kidney biopsy as well as diabetes mice. We compared the difference of ß-hydroxybutyrate (ß-HB) levels in serum, urine and kidney tissues between diabetic mice and control. Using recombinant adeno-associated viral vector containing SMCT1 (encoded by Slc5a8 gene), we tested the effect of SMCT1 upregulation on microalbuminuria as well as its effects on mitochondrial energy metabolism in diabetic mice. Then we investigated the role of SMCT1 and its ß-HB reabsorption function in maintaining the physiological function of renal tubular using renal tubule-specific Slc5a8 gene knockout mice. Transcriptomes and proteomics analysis were used to explore the underlying mechanism. RESULTS: SMCT1 downregulation was found in DKD patients as well as in diabetic mice. Moreover, diabetic mice had a decreased renal ß-HB level compared with control, and SMCT1 upregulation could improve microalbuminuria and mitochondrial energy metabolism. In renal tubule-specific Slc5a8 gene knockout mice, microalbuminuria occurred early at 24 weeks of age, accompanied by ATP shortage and metabolic reprogramming in the kidney; however, supplementation with ß-HB precursor substance 1,3-butanediol in food alleviated kidney damage as well as energy metabolic reprogramming. CONCLUSIONS: Decreased SMCT1 expression and its ketone reabsorption function play an important role in the occurrence of DKD. SMCT1 may be a new promising target in treating DKD.

[Determination of eight steroidal saponins in 15 kinds of genus Paris].

The study was established an HPLC method for simultaneous determination of 8 steroidal saponins (polyphyllins Ⅶ, H, Ⅵ, Ⅱ, Ⅰ, and Ⅴ, dioscin, and gracillin) in Paridis Rhizoma, and made an evaluation by determining steroidal saponins in 15 kinds of genus Paris. The analysis was performed on a Waters Acquity H-ClassTM UPLC ultrafine liquid chromatography system coupled with a PDA detector. The chromatographic separation was achieved through a CAPCELL PAK ADME (4.6 mm× 250 mm, 5 µm) column and the optimal mobile phase consisted of acetonitrile and water. The column was maintained at 21 ℃, and the flow rate was 0.8 mL•min ⁻¹. The UV detection wavelength was 203 nm. The results showed that ① the detected components can be well separated and all with good correlation coefficients. The standard calibration curves were linearly good (R2>0.999 9). The linearity was obtained over 0.041 70-3.812 00 µg. The average recoveries ranged from 95.91% to 103.8%. ② there are significant differences in the content of steroidal saponins from different species. The steroidal saponins are low content or almost none in P. mairei, P. polyphylla var. stenophylla, and P. delavayi have low content or almost did not contain, so these species are not suitable for medicinal use. The contents of steroidal saponins in P. polyphylla var. chinensis are varied from different places. There were high content of steroidal saponins in P. polyphylla var. yunnanensis, P. forrestii, P. daliensis, and P. axialis, even up to 5.0%, which indicated that they had the potential pharmic value of development.