Metabolic Communication by SGLT2 Inhibition

BACKGROUND

SGLT2 (sodium-glucose cotransporter 2) inhibitors (SGLT2i) can protect the kidneys and heart, but the underlying mechanism remains poorly understood.

METHODS

To gain insights on primary effects of SGLT2i that are not confounded by pathophysiologic processes or are secondary to improvement by SGLT2i, we performed an in-depth proteomics, phosphoproteomics, and metabolomics analysis by integrating signatures from multiple metabolic organs and body fluids after 1 week of SGLT2i treatment of nondiabetic as well as diabetic mice with early and uncomplicated hyperglycemia.

RESULTS

Kidneys of nondiabetic mice reacted most strongly to SGLT2i in terms of proteomic reconfiguration, including evidence for less early proximal tubule glucotoxicity and a broad downregulation of the apical uptake transport machinery (including sodium, glucose, urate, purine bases, and amino acids), supported by mouse and human SGLT2 interactome studies. SGLT2i affected heart and liver signaling, but more reactive organs included the white adipose tissue, showing more lipolysis, and, particularly, the gut microbiome, with a lower relative abundance of bacteria taxa capable of fermenting phenylalanine and tryptophan to cardiovascular uremic toxins, resulting in lower plasma levels of these compounds (including p-cresol sulfate). SGLT2i was detectable in murine stool samples and its addition to human stool microbiota fermentation recapitulated some murine microbiome findings, suggesting direct inhibition of fermentation of aromatic amino acids and tryptophan. In mice lacking SGLT2 and in patients with decompensated heart failure or diabetes, the SGLT2i likewise reduced circulating p-cresol sulfate, and p-cresol impaired contractility and rhythm in human induced pluripotent stem cell-derived engineered heart tissue.

CONCLUSIONS

SGLT2i reduced microbiome formation of uremic toxins such as p-cresol sulfate and thereby their body exposure and need for renal detoxification, which, combined with direct kidney effects of SGLT2i, including less proximal tubule glucotoxicity and a broad downregulation of apical transporters (including sodium, amino acid, and urate uptake), provides a metabolic foundation for kidney and cardiovascular protection.

SGLT2 inhibitor dapagliflozin protects the kidney in a murine model of Balkan nephropathy

Proximal tubular uptake of aristolochic acid (AA) forms aristolactam (AL)-DNA adducts, which cause a p53/p21-mediated DNA damage response and acute tubular injury. Recurrent AA exposure causes kidney function loss and fibrosis in humans (Balkan endemic nephropathy) and mice and is a model of (acute kidney injury) AKI to chronic kidney disease (CKD) transition. Inhibitors of the proximal tubule sodium-glucose transporter SGLT2 can protect against CKD progression, but their effect on AA-induced kidney injury remains unknown. C57BL/6J mice (15-wk-old) were administered vehicle or AA every 3 days for 3 wk (10 and 3 mg/kg ip in females and males, respectively). Dapagliflozin (dapa, 0.01 g/kg diet) or vehicle was initiated 7 days prior to AA injections. All dapa effects were sex independent, including a robust glycosuria. Dapa lowered urinary kidney-injury molecule 1 (KIM-1) and albumin (both normalized to creatinine) after the last AA injection and kidney mRNA expression of early DNA damage response markers (p53 and p21) 3 wk later at the study end. Dapa also attenuated AA-induced increases in plasma creatinine as well as AA-induced up-regulation of renal pro-senescence, pro-inflammatory and pro-fibrotic genes, and kidney collagen staining. When assessed 1 day after a single AA injection, dapa pretreatment attenuated AL-DNA adduct formation by 10 and 20% in kidney and liver, respectively, associated with reduced p21 expression. Initiating dapa application after the last AA injection also improved kidney outcome but in a less robust manner. In conclusion, the first evidence is presented that pretreatment with an SGLT2 inhibitor can attenuate the AA-induced DNA damage response and subsequent nephropathy.NEW & NOTEWORTHY Recurrent exposure to aristolochic acid (AA) causes kidney function loss and fibrosis in mice and in humans, e.g., in the form of the endemic Balkan nephropathy. Inhibitors of the proximal tubule sodium-glucose transporter SGLT2 can protect against CKD progression, but their effect on AA-induced kidney injury remains unknown. Here we provide the first evidence in a murine model that pretreatment with an SGLT2 inhibitor can attenuate the AA-induced DNA damage response and subsequent nephropathy.

Deletion, but not heterozygosity, of eNOS raises blood pressure and aggravates nephropathy in BTBR ob/ob mice

INTRODUCTION

ob/ob mice are a leptin-deficient type 2 diabetes mellitus model, which, on a BTBR background, mimics glomerular pathophysiology of diabetic nephropathy (DN). Since leptin deficiency reduces blood pressure (BP), and endothelial nitric oxide synthase (eNOS) lowers BP and is kidney protective, we attempted to develop a more robust DN model by introducing eNOS deficiency in BTBR ob/ob mice.

METHODS

Six experimental groups included littermate male and female BTBR ob/ob or wild-type for ob (control) as well as wild-type (WT), heterozygote (HET) or knockout (KO) for eNOS. Systolic BP (by automated tail-cuff) and GFR (by FITC sinistrin plasma kinetics) were determined in awake mice at 27-30 weeks of age followed by molecular and histological kidney analyses.

RESULTS

Male and female ob/ob WT presented hyperglycemia and larger body and kidney weight, GFR, glomerular injury, and urine albumin to creatinine ratio (UACR) despite modestly lower BP vs control WT. These effects were associated with higher tubular injury score and renal mRNA expression of NGAL only in males, whereas female ob/ob WT unexpectedly had lower KIM-1 and COL1A1 expression vs control WT, indicating sex differences. HET for eNOS did not consistently alter BP or renal outcome in control or ob/ob. In comparison, eNOS KO increased BP (15-25 mmHg) and worsened renal markers of injury, inflammation and fibrosis, GFR, UACR, and survival rates, as observed in control and, more pronounced, in ob/ob mice and independent of sex.

CONCLUSIONS

Deletion, but not heterozygosity, of eNOS raises blood pressure and aggravates nephropathy in BTBR ob/ob mice.

Aristolochic acid-induced nephropathy is attenuated in mice lacking the neutral amino acid transporter B0AT1 (Slc6a19)

B0AT1 (Slc6a19) mediates absorption of neutral amino acids in the small intestine and in the kidneys, where it is primarily expressed in early proximal tubules (S1-S2). To determine the role of B0AT1 in nephropathy induced by aristolochic acid (AA), which targets the proximal tubule, littermate female B0AT1-deficient (Slc6a19-/-), heterozygous (Slc6a19+/-), and wild-type (WT) mice were administered AA (10 mg/kg ip) or vehicle every 3 days for 3 wk, and analyses were performed after the last injection or 3 wk later. Vehicle-treated mice lacking Slc6a19 showed normal body and kidney weight and plasma creatinine versus WT mice. The urinary glucose-to-creatinine ratio (UGCR) and urinary albumin-to-creatinine ratio (UACR) were two to four times higher in vehicle-treated Slc6a19-/- versus WT mice, associated with lesser expression of early proximal transporters Na+-glucose cotransporter 2 and megalin, respectively. AA caused tubular injury independently of B0AT1, including robust increases in cortical mRNA expression of p53, p21, and hepatitis A virus cellular receptor 1 (Havcr1), downregulation of related proximal tubule amino acid transporters B0AT2 (Slc6a15), B0AT3 (Slc6a18), and Slc7a9, and modest histological tubular damage and a rise in plasma creatinine. Absence of B0AT1, however, attenuated AA-induced cortical upregulation of mRNA markers of senescence (p16), inflammation [lipocalin 2 (Lcn2), C-C motif chemokine ligand 2 (Ccl2), and C-C motif chemokine receptor 2 (Ccr2)], and fibrosis [tissue inhibitor of metallopeptidase 1 (Timp1), transforming growth factor-β1 (Tgfb1), and collagen type I-α1 (Col1a1)], associated with lesser fibrosis staining, lesser suppression of proximal tubular organic anion transporter 1, restoration of Na+-glucose cotransporter 2 expression, and prevention of the AA-induced fivefold increase in the urinary albumin-to-creatinine ratio observed in WT mice. The data suggest that proximal tubular B0AT1 is important for the physiology of renal glucose and albumin retention but potentially deleterious for the kidney response following AA-induced kidney injury.NEW & NOTEWORTHY Based on insights from studies manipulating glucose transport, the hypothesis has been proposed that inhibiting intestinal uptake or renal reabsorption of energy substrates has unique therapeutic potential to improve metabolic disease and kidney outcome in response to injury. The present study takes this idea to B0AT1, the major transporter for neutral amino acids in the intestine and kidney, and shows that its absence attenuates aristolochic acid-induced nephropathy.

FC022: IPI3K/AKT/MTOR Pathway Regulates Renal Expression of Klotho

BACKGROUND AND AIMS

Chronic kidney disease (CKD) represents an important and growing burden on health worldwide, mainly driven by the increase in the incidence of associated risk factors like diabetes. As kidney function declines, changes in mineral metabolism occur, which contribute to the increased risk of cardiovascular disease in CKD patients. In this respect, Klotho was described as an anti-ageing protein, mainly expressed in the kidney, where it acts as an obligatory co-receptor of the Fibroblast Growth Factor (FGF23), which is involved in urinary phosphate excretion. The earliest mineral metabolism change in CKD is the fall in renal and plasma Klotho levels, followed by an increase in FGF23. Klotho loss is related to inflammatory and fibrotic processes contributing not only to the progression of CKD but also to the increase in cardiovascular risk. Clinically, there is a growing interest in maintaining renal Klotho expression in patients, but the mechanisms in Klotho decline remain unknown.

PTEN is the main negative regulator of PI3K-AKT-mTOR pathway. PTEN degrades PIP3 to PIP2 decreasing the activation of the canonical insulin pathway. The involvement of PTEN in cancer has been broadly investigated. Furthermore, the PI3K/PTEN signalling pathways are involved in a wide variety of diseases including cardiac hypertrophy, heart failure, hypertension and acute kidney injury. However, its potential role in CKD has not been properly assessed.

The objective of this study was to investigate the role of PTEN and the PI3K/AKT/mTOR pathways in kidney Klotho levels and the modulation of phosphorus metabolism.

METHOD

We generated a proximal tubule conditional PTEN knockout mouse model (PT-PTEN-cKO), in which a high phosphorus diet (HPD) and rapamycin treatment were administered in order to analyse how PI3K/AKT/mTOR pathway participates in phosphorus metabolism and kidney Klotho levels. We used human proximal tubular cell (PTC) line HK-2 to knock down PTEN by means of transfection with shPTEN lentiviral vector, to study the direct effect of PTEN elimination in Klotho levels in vitro.

RESULTS

PT-PTEN-cKO mice present a specific activation of the PI3K/AKT/mTOR pathway in the proximal tubule. PTEN mRNA decrease correlates with a drop in kidney Klotho levels, accompanied by an increment of inflammatory and fibrotic markers. In addition, our model showed an increase in both, plasma phosphate and FGF23, with a decrease in the fractional excretion of phosphate (% FEPi). This fact can be explained by the inability of kidney cells to respond to FGF23, because of Klotho loss. Moreover, parathyroid hormone (PTH) and bone resorption were increased. We observe that PT-PTEN-KO mice in an HPD needed higher FGF23 levels in order to excrete phosphate than control mice. Rapamycin administration restored Klotho levels.

In vitro, PTEN silencing in PTC, leads to an increase in PI3K/AKT/mTOR activity and also to a reduction in Klotho expression. Finally, the inhibition of mTOR phosphorylation by rapamycin reestablished Klotho expression in vitro.

CONCLUSION

The overactivation of PI3K/AKT/mTOR pathway, in PTC, decreases Klotho kidney levels. Our findings constitute an important breakthrough in the research of new therapeutic targets in order to maintain renal Klotho levels and it may be useful in the treatment of kidney disease patients.

PTEN Deletion in Adult Mice Induces Hypoinsulinemia With Concomitant Low Glucose Levels

The PI3K/AKT pathway, negatively regulated by PTEN, plays a paramount role in glucose metabolism regulation due to its activation by the insulin receptor signaling pathway. We generated a PTEN-KO mouse to evaluate the systemic effect of the overactivation of the PI3K/AKT pathway in insulin signaling and glucose homeostasis. Our results demonstrate that PTEN-KO mice show very low glucose levels in the fasted state, which poorly respond to glucose and pyruvate administration. Insulinemia decreased without alterations in pancreatic islets. Among the possible reasons, we uncover the deregulation of the expression of proximal tubule glucose transporter and consequent glycosuria. Moreover, we evidence an altered activation of hepatic gluconeogenesis-related genes. In addition, the expression of several genes related to β-oxidation showed a delayed or even absent response to fasting, suggesting that the lack of PTEN not only impairs glucose metabolism but also slows down the use of lipids as a metabolic fuel. We conclude that the inducible full PTEN-KO mice could be a good model to study the metabolic interactions between glycidic and lipidic metabolism in hypoinsulinemic hypoglycemia and that PTEN could be an important mediator in the disease and/or a potential drug target.

A role for tubular Na+/H+ exchanger NHE3 in the natriuretic effect of the SGLT2 inhibitor empagliflozin

Inhibitors of proximal tubular Na⁺-glucose cotransporter 2 (SGLT2) are natriuretic, and they lower blood pressure. There are reports that the activities of SGLT2 and Na⁺-H⁺ exchanger 3 (NHE3) are coordinated. If so, then part of the natriuretic response to an SGLT2 inhibitor is mediated by suppressing NHE3. To examine this further, we compared the effects of an SGLT2 inhibitor, empagliflozin, on urine composition and systolic blood pressure (SBP) in nondiabetic mice with tubule-specific NHE3 knockdown (NHE3-ko) and wild-type (WT) littermates. A single dose of empagliflozin, titrated to cause minimal glucosuria, increased urinary excretion of Na⁺ and bicarbonate and raised urine pH in WT mice but not in NHE3-ko mice. Chronic empagliflozin treatment tended to lower SBP despite higher renal renin mRNA expression and lowered the ratio of SBP to renin mRNA, indicating volume loss. This effect of empagliflozin depended on tubular NHE3. In diabetic Akita mice, chronic empagliflozin enhanced phosphorylation of NHE3 (S552/S605), changes previously linked to lesser NHE3-mediated reabsorption. Chronic empagliflozin also increased expression of genes involved with renal gluconeogenesis, bicarbonate regeneration, and ammonium formation. While this could reflect compensatory responses to acidification of proximal tubular cells resulting from reduced NHE3 activity, these effects were at least in part independent of tubular NHE3 and potentially indicated metabolic adaptations to urinary glucose loss. Moreover, empagliflozin increased luminal α-ketoglutarate, which may serve to stimulate compensatory distal NaCl reabsorption, while cogenerated and excreted ammonium balances urine losses of this "potential bicarbonate." The data implicate NHE3 as a determinant of the natriuretic effect of empagliflozin.

P0717EPIGENETIC REGULATION OF CHRONIC KIDNEY DISEASE ACCELERATED-ATHEROSCLEROSIS

Background and Aims

Atherosclerosis and its related clinical complications are the leading causes of death in western countries. Multiple processes are involved in atherosclerosis like endothelial dysfunction, inflammation, vascular proliferation, neovascularization, oxidative stress, apoptosis, extracellular matrix degradation and thrombosis. Moreover atherosclerosis could be accelerated in some diseases like chronic kidney disease (CKD). In this regard, miRNAs have been elucidated as important factors in the regulation of different cellular and molecular processes involved in atherosclerosis development. Our aim is to identify specific miRNAs that could be involved in chronic kidney disease (CKD) accelerated-atherosclerosis.

Method

A CKD accelerated-atherosclerosis mouse model was developed by subtotal nephrectomy (5/6 nephrectomy) in APOE-/- mice fed on a high fat diet (HFD) during 10 weeks and compared to mice with normal renal function. Urine and blood samples were collected every week. Western-blot, RT-PCR, immunohistochemistry and confocal microscopy analysis were performed. In previous studies mir23a-3p and miR652-3p have been suggested as possible regulators of the atherosclerotic process. Therefore the expression levels of these miRNAs and its possible target genes (FER and BTLA) were analyzed in mice total blood.

Results

APOE-/-+ERC+HFD mouse showed a progressive decrease in renal function and an increase of renal damage markers such as KIM-1. These animals showed structural glomerular damage characterized by de-cellularization, mesangial cell expansion and podocyte (WT1+,podocalixin+), endothelial (CD31+) and mesangial (GATA3+) loss. Lipid profile modifications were also observed in APOE-/-+ERC+HFD mice with an increase in plasma total cholesterol levels. Moreover atherosclerotic plaque size was also increased in APOE-/-+ERC+HFD animals in comparison with atherosclerotic plaque size of APOE-/-+HFD mice. CKD mice showed lower fibrosis (sirius red staining) and higher inflammatory markers in its atherosclerotic plaques. The presence of macrophages (CD68+) and T lymphocytes (CD3+) was increased in APOE-/-+ERC+HFD group in contrast with APOE-/-+HFD animals. Moreover, in samples from the aortic arch of APOE-/-+ERC+HFD mice, ICAM1 protein levels were increased. Finally we found decreased levels of mir23a-3p and mir652-3p gene in total blood samples of APOE-/-+ ERC+ HFD mice. On the other hand, in aortic arc and descendent aorta tissues, mir23a-3p and mir652-3p expression levels were similar between groups. The expression levels of mRNAs of potential targets of this miRNAs (FER and BTLA) were increased in total blood and aortic arch samples. In addition, we observed that BTLA and FER expression were localized in vascular smooth muscle cells and endothelial cells respectively.

Conclusion

Levels of mir23a-3p, mir652-3p and its related mRNA (FER and BTLA) are altered in CKD and may be a potential therapeutic target for CKD-accelerated atherosclerosis treatment.

Effect of renal tubule-specific knockdown of the Na+/H+ exchanger NHE3 in Akita diabetic mice

Na+/H+ exchanger isoform 3 (NHE3) contributes to Na+/bicarbonate reabsorption and ammonium secretion in early proximal tubules. To determine its role in the diabetic kidney, type 1 diabetic Akita mice with tubular NHE3 knockdown [Pax8-Cre; NHE3-knockout (KO) mice] were generated. NHE3-KO mice had higher urine pH, more bicarbonaturia, and compensating increases in renal mRNA expression for genes associated with generation of ammonium, bicarbonate, and glucose (phosphoenolpyruvate carboxykinase) in proximal tubules and H+ and ammonia secretion and glycolysis in distal tubules. This left blood pH and bicarbonate unaffected in nondiabetic and diabetic NHE3-KO versus wild-type mice but was associated with renal upregulation of proinflammatory markers. Higher renal phosphoenolpyruvate carboxykinase expression in NHE3-KO mice was associated with lower Na+-glucose cotransporter (SGLT)2 and higher SGLT1 expression, indicating a downward tubular shift in Na+ and glucose reabsorption. NHE3-KO was associated with lesser kidney weight and glomerular filtration rate (GFR) independent of diabetes and prevented diabetes-associated albuminuria. NHE3-KO, however, did not attenuate hyperglycemia or prevent diabetes from increasing kidney weight and GFR. Higher renal gluconeogenesis may explain similar hyperglycemia despite lower SGLT2 expression and higher glucosuria in diabetic NHE3-KO versus wild-type mice; stronger SGLT1 engagement could have affected kidney weight and GFR responses. Chronic kidney disease in humans is associated with reduced urinary excretion of metabolites of branched-chain amino acids and the tricarboxylic acid cycle, a pattern mimicked in diabetic wild-type mice. This pattern was reversed in nondiabetic NHE3-KO mice, possibly reflecting branched-chain amino acids use for ammoniagenesis and tricarboxylic acid cycle upregulation to support formation of ammonia, bicarbonate, and glucose in proximal tubule. NHE3-KO, however, did not prevent the diabetes-induced urinary downregulation in these metabolites.

Peritoneal Dialysis Is an Independent Factor Associated to Lower Intima Media Thickness in Dialysis Patients Free From Previous Cardiovascular Disease

Carotid intima media thickness (cIMT) displays prognostic value as a marker of cardiovascular risk in dialysis patients. However, few data are available regarding the impact of dialysis modality on cIMT. The aim of this study is to determine whether the modality of dialysis influences cIMT values. We compared 237 peritoneal dialysis (PD) and 451 hemodialysis (HD) patients without previous cardiovascular disease included in NEFRONA, a prospective, observational and multicenter study. This cross sectional study included the determination of cIMT in 6 carotid territories by arterial ultrasound. cIMT was determined in territories without atheroma plaque and averaged. A second analysis was performed using all territories, giving a truncated cIMT value of 1,5 mm to territories presenting with atheroma plaque. Age and plaque presence at baseline were the clinical variables more closely associated to cIMT in dialysis patients. The evaluation of the impact of the modality of dialysis on cIMT showed that PD patients had lower cIMT than HD patients, both in territories with no plaques and when using truncated cIMT values. No differences were found between right and left sides, neither in cIMT or truncated cIMT values. Lineal multivariate analysis adjusted by several clinical variables showed a statistically significant association of PD with a lower cIMT (slope -0.036; SD 0.010). These results were also confirmed when truncated cIMT values were used. We conclude that the modality of dialysis has an impact on cITM. HD patients have greater global cIMT than PD patients, and PD is and independent factor associated with a lower cIMT.