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Background: Sodium glucose cotransporter 2 inhibitors may reduce kidney hyperfiltration, thereby preventing diabetic kidney disease progression, which may in turn reduce cardiovascular risk, including heart failure. However, the mechanisms that regulate renal function responses to sodium glucose cotransporter 2 inhibition are not yet fully understood. We explored the renal protective effects of sodium glucose cotransporter 2 inhibition with empagliflozin, with a focus on glomerular hemodynamic effects and tubuloglomerular feedback using in vivo multiphoton microscopy imaging techniques. Methods: C57BL/6 mice and spontaneously diabetic Ins2 +/Akita mice were studied. The mice were treated with empagliflozin (20 mg·kg –1 ·d –1 ) and insulin for 4 weeks, and the single-nephron glomerular filtration rate was measured using multiphoton microscope. A neuronal nitric oxide synthase inhibitor (7-nitroindazole, 20 mg·kg –1 ·d –1 ) or a cyclooxygenase-2 inhibitor (SC58236, 6 mg/L), or an A1 adenosine receptor antagonist (8-cyclopentyl-1,3-dipropylxanthine, 1 mg·kg –1 ·d –1 ) was administered to elucidate the mechanisms of tubuloglomerular feedback signaling and single-nephron glomerular filtration rate regulation. Results: The urinary excretion of adenosine, nitric oxide metabolites, and the prostanoid prostaglandin E2 was also quantified. The single-nephron glomerular filtration rate in the Ins2 +/Akita group was higher than in controls (C57BL/6; 4.9±1.3 nL/min versus Ins2 +/Akita ; 15.8±6.8 nL/min) and lower in Ins2 +/Akita /empagliflozin to 8.0±3.3 nL/min ( P <0.01). In vivo imaging also revealed concomitant afferent arteriolar dilation ( P <0.01) and increased glomerular permeability of albumin in the Ins2 +/Akita group. Empagliflozin ameliorated these changes ( P <0.01). Urinary adenosine excretion in the Ins2 +/Akita /empagliflozin group was higher than in Ins2 +/Akita ( Ins2 +/Akita ; 3.4±1.4 nmol/d, Ins2 +/Akita /empagliflozin; 11.2±3.0 nmol/d, P <0.05), whereas nitric oxide metabolites and prostaglandin E2 did not differ. A1 adenosine receptor antagonism, but not neuronal nitric oxide synthase or cyclooxygenase-2 inhibition, blocked the effect of empagliflozin on renal function. Empagliflozin increased urinary adenosine excretion and reduced hyperfiltration via afferent arteriolar constriction, effects that were abolished by A1 adenosine receptor blockade. Conclusions: Adenosine/A1 adenosine receptor pathways play a pivotal role in the regulation of the single-nephron glomerular filtration rate via tubuloglomerular feedback mechanisms in response to sodium glucose cotransporter 2 inhibition, which may contribute to renal and cardiovascular protective effects reported in clinical trials.

BackgroundMultiple preclinical studies have highlighted AMP-activated protein kinase (AMPK) as a potential therapeutic target for autosomal dominant polycystic kidney disease (ADPKD). Both metformin and canagliflozin indirectly activate AMPK by inhibiting mitochondrial function, while salsalate is a direct AMPK activator. Metformin, canagliflozin and salsalate (a prodrug dimer of salicylate) are approved for clinical use with excellent safety profile. Although metformin treatment had been shown to attenuate experimental cystic kidney disease, there are concerns that therapeutic AMPK activation in human kidney might require a higher oral metformin dose than can be achieved clinically.MethodsIn this study, we tested metformin-based combination therapies for their additive (metformin plus canagliflozin) and synergistic (metformin plus salsalate) effects and each drug individually in an adult-onset conditional Pkd1 knock-out mouse model (n = 20 male/group) using dosages expected to yield clinically relevant drug levels.FindingsCompared to untreated mutant mice, treatment with salsalate or metformin plus salsalate improved kidney survival (i.e. blood urea nitrogen <20 mmol/L at the time of sacrifice) and reduced cystic kidney disease severity. However, the effects of metformin plus salsalate did not differ from salsalate alone; and neither metformin nor canagliflozin was effective. Protein expression and phosphorylation analyses indicated that salsalate treatment was associated with reduction in mTOR (mammalian target of rapamycin) activity and cellular proliferation in Pkd1 mutant mouse kidneys. Global gene expression analyses suggested that these effects were linked to restoration of mitochondrial function and suppression of inflammation and fibrosis.InterpretationSalsalate is a highly promising candidate for drug repurposing and clinical testing in ADPKD.