LC-MS-based metabolomics analysis to identify meprin-β-associated changes in kidney tissue from mice with STZ-induced type 1 diabetes and diabetic kidney injury

Traditional Chinese medicine improved diabetic kidney disease through targeting gut microbiota

CONTEXT

Diabetic kidney disease (DKD) affects nearly 40% of diabetic patients, often leading to end-stage renal disease that requires renal replacement therapies, such as dialysis and transplantation. The gut microbiota, an integral aspect of human evolution, plays a crucial role in this condition. Traditional Chinese medicine (TCM) has shown promising outcomes in ameliorating DKD by addressing the gut microbiota.

OBJECTIVE

This review elucidates the modifications in gut microbiota observed in DKD and explores the impact of TCM interventions on correcting microbial dysregulation.

METHODS

We searched relevant articles from databases including Web of Science, PubMed, ScienceDirect, Wiley, and Springer Nature. The following keywords were used: diabetic kidney disease, diabetic nephropathy, gut microbiota, natural product, TCM, Chinese herbal medicine, and Chinese medicinal herbs. Rigorous criteria were applied to identify high-quality studies on TCM interventions against DKD.

RESULTS

Dysregulation of the gut microbiota, including Lactobacillus, Streptococcus, and Clostridium, has been observed in individuals with DKD. Key indicators of microbial dysregulation include increased uremic solutes and decreased short-chain fatty acids. Various TCM therapies, such as formulas, tablets, granules, capsules, and decoctions, exhibit unique advantages in regulating the disordered microbiota to treat DKD.

CONCLUSION

This review highlights the importance of targeting the gut-kidney axis to regulate microbial disorders, their metabolites, and associated signaling pathways in DKD. The Qing-Re-Xiao-Zheng formula, the Shenyan Kangfu tablet, the Huangkui capsule, and the Bekhogainsam decoction are potential candidates to address the gut-kidney axis. TCM interventions offer a significant therapeutic approach by targeting microbial dysregulation in patients with DKD.

A metabonomics-based renoprotective mechanism analysis of empagliflozin in obese mice

With an increasing prevalence of obesity related kidney disease, exploring the mechanisms of therapeutic method is of critical importance. Empagliflozin is a new antidiabetic agent with broad clinical application prospect in cardiovascular and renal diseases. However, a metabonomics-based renoprotective mechanism of empagliflozin in obesity remains unclear. Our results showed that empagliflozin significantly alleviated the deposition of lipid droplet, glomerular and tubular injury. The innovation lied in detection of empagliflozin-targeted differential metabolites in kidneys. Compared with normal control mice, obese mice showed higher levels of All-trans-heptaprenyl diphosphate, Biliverdin, Galabiose, Galabiosylceramide (d18:1/16:0), Inosine, Methylisocitric acid, Uric acid, Xanthosine, O-glutarylcarnitine, PG(20:3(8Z,11Z,14Z)/0:0), PG(20:4(5Z,8Z,11Z,14Z)/0:0), PE(O-16:0/0:0), PG(22:6(4Z,7Z,10Z,13Z,16Z,19Z)/0:0), and lower level of Adenosine. Empagliflozin regulated these metabolites in the opposite direction. Associated metabolic pathways were Phospholipids metabolism, Purine metabolism, and Biliverdin metabolism. Most of metabolites were associated with inflammatory response and oxidative stress. Empagliflozin improved the oxidative stress and inflammation imbalance. Our study revealed the metabonomics-based renoprotective mechanism of empagliflozin in obese mice for the first time. Empagliflozin may be a promising tool to delay the progression of obesity-related kidney disease.

The Biochemical Pathways of Nicotinamide-Derived Pyridones

As catabolites of nicotinamide possess physiological relevance, pyridones are often included in metabolomics measurements and associated with pathological outcomes in acute kidney injury (AKI). Pyridones are oxidation products of nicotinamide, its methylated form, and its ribosylated form. While they are viewed as markers of over-oxidation, they are often wrongly reported or mislabeled. To address this, we provide a comprehensive characterization of these catabolites of vitamin B3, justify their nomenclature, and differentiate between the biochemical pathways that lead to their generation. Furthermore, we identify an enzymatic and a chemical process that accounts for the formation of the ribosylated form of these pyridones, known to be cytotoxic. Finally, we demonstrate that the ribosylated form of one of the pyridones, the 4-pyridone-3-carboxamide riboside (4PYR), causes HepG3 cells to die by autophagy; a process that occurs at concentrations that are comparable to physiological concentrations of this species in the plasma in AKI patients.

Meprin-β activity modulates the β-catalytic subunit of protein kinase A in ischemia-reperfusion-induced acute kidney injury

Meprin metalloproteases have been implicated in the progression of kidney injury. Previous work from our group has shown that meprins proteolytically process the catalytic subunit of protein kinase A (PKA-C), resulting in decreased PKA-C kinase activity. The goal of the present study was to determine the PKA-C isoforms impacted by meprin-β and whether meprin-β expression affects downstream mediators of the PKA signaling pathway in ischemia-reperfusion (IR)-induced kidney injury. IR was induced in 12-wk-old male wild-type (WT) and meprin-β knockout (βKO) mice. Madin-Darby canine kidney cells transfected with meprin-β cDNA were also subjected to 2 h of hypoxia. Western blot analysis was used to evaluate levels of total PKA-C, PKA-Cα, PKA-Cβ, phosphorylated (p-)PKA-C, and p-ERK1/2. Meprin-β expression enhanced kidney injury as indicated by levels of neutrophil gelatinase-associated lipocalin and cystatin C. IR-associated decreases were observed in levels of p-PKA-C in kidney tissue from WT mice but not βKO mice, suggesting that meprin-β expression/activity is responsible for the in vivo reduction in kinase activity. Significant increases in levels of PKA-Cβ were observed in kidney lysates for WT mice but not βKO mice at 6 h post-IR. Proximal tubule PKA-Cβ increases in WT but not βKO kidneys were demonstrated by fluorescent microscopy. Furthermore, IR-induced injury was associated with significant increases in p-ERK levels for both genotypes. The present data demonstrate that meprin-β enhances IR-induced kidney injury in part by modulating mediators of the PKA-Cβ signaling pathway.