Inhibition of sodium-glucose cotransporter 2 ameliorates renal injury in a novel medaka model of nonalcoholic steatohepatitis-related kidney disease

Effects of a novel selective PPARα modulator, statin, sodium-glucose cotransporter 2 inhibitor, and combinatorial therapy on the liver and vasculature of medaka nonalcoholic steatohepatitis model

OBJECTIVE

Nonalcoholic steatohepatitis (NASH) is a disease entity with an increasing incidence, with involvement of several metabolic pathways. Various organs, including the liver, kidneys, and the vasculature, are damaged in NASH, indicating the urgent need to develop a standard therapy. Therefore, this study was conducted to investigate the effects of drugs targeting various metabolic pathways and their combinations on a high-fat diet (HFD)-induced NASH medaka model.

METHODS

To investigate the effects of drugs on vascular structures, the NASH animal model was developed using the fli::GFP transgenic medaka fed with HFD at 20 mg/fish daily. The physiological changes, histological changes in the liver, vascular structures in the fin, and serum biochemical markers were evaluated in a time-dependent manner after treatment with selective peroxisome proliferator-activated receptor α modulator (pemafibrate), statin (pitavastatin), sodium-glucose cotransporter 2 inhibitor (tofogliflozin), and their combinations. Furthermore, to determine the mechanisms underlying the effects, whole transcriptome sequencing was conducted using medaka liver samples.

RESULTS

Histological analyses revealed significant suppression of fat accumulation and fibrotic changes in the liver after treatment with drugs and their combinations. The expression levels of steatosis- and fibrosis-related genes were modified by the treatments. Moreover, the HFD-induced vascular damages in the fin exhibited milder changes after treatment with the drugs.

CONCLUSION

The effects of treating various metabolic pathways on the medaka body, liver, and vascular structures of the NASH medaka model were evidenced. Moreover, to our knowledge, this study is the first to report whole genome sequence and gene expression evaluation of medaka livers, which could be helpful in clarifying the molecular mechanisms of drugs.

Antioxidant Roles of SGLT2 Inhibitors in the Kidney

The reduction-oxidation (redox) system consists of the coupling and coordination of various electron gradients that are generated thanks to serial reduction-oxidation enzymatic reactions. These reactions happen in every cell and produce radical oxidants that can be mainly classified into reactive oxygen species (ROS) and reactive nitrogen species (RNS). ROS and RNS modulate cell-signaling pathways and cellular processes fundamental to normal cell function. However, overproduction of oxidative species can lead to oxidative stress (OS) that is pathological. Oxidative stress is a main contributor to diabetic kidney disease (DKD) onset. In the kidney, the proximal tubular cells require a high energy supply to reabsorb proteins, metabolites, ions, and water. In a diabetic milieu, glucose-induced toxicity promotes oxidative stress and mitochondrial dysfunction, impairing tubular function. Increased glucose level in urine and ROS enhance the activity of sodium/glucose co-transporter type 2 (SGLT2), which in turn exacerbates OS. SGLT2 inhibitors have demonstrated clear cardiovascular benefits in DKD which may be in part ascribed to the generation of a beneficial equilibrium between oxidant and antioxidant mechanisms.