Renoprotective Effects of SGLT2 Inhibitors

Fabry Disease: Insights into Pathophysiology and Novel Therapeutic Strategies

Fabry disease (FD) is an X-linked lysosomal storage disorder characterized by deficiency of α-galactosidase A (α-GalA), leading to the accumulation of glycosphingolipids and multi-organ dysfunction, particularly affecting the cardiovascular and renal systems. Disease-modifying treatments such as enzyme replacement therapy (ERT) and oral chaperone therapy (OCT) have limited efficacy, particularly in advanced disease, prompting a need for innovative therapeutic approaches targeting underlying molecular mechanisms beyond glycosphingolipid storage alone. Recent insights into the pathophysiology of FD highlights chronic inflammation and mitochondrial, lysosomal, and endothelial dysfunction as key mediators of disease progression. Adjunctive therapies such as sodium-glucose cotransporter-2 (SGLT2) inhibitors, glucagon-like peptide-1 (GLP-1) agonists, and mineralocorticoid receptor antagonists (MRAs) demonstrate significant cardiovascular and renal benefits in conditions including heart failure and chronic kidney disease. These drugs also modulate pathways involved in the pathophysiology of FD, such as autophagy, oxidative stress, and pro-inflammatory cytokine signaling. While theoretical foundations support their utility, dedicated trials are necessary to confirm efficacy in the FD-specific population. This narrative review highlights the importance of expanding therapeutic strategies in FD, advocating for a multi-faceted approach involving evidence-based adjunctive treatments to improve outcomes. Tailored research focusing on diverse FD phenotypes, including females and non-classical variants of disease, will be critical to advancing care and improving outcomes in this complex disorder.

Blood Pressure Management Strategies and Podocyte Health

Hypertension (HTN) is one of the key global cardiovascular risk factors, which is tightly linked to kidney health and disease development. Podocytes, glomerular epithelial cells that play a pivotal role in maintenance of the renal filtration barrier, are significantly affected by increased glomerular capillary pressure in HTN. Damage or loss of these cells causes proteinuria, which marks the initiation of the HTN-driven renal damage. It goes without saying that effective blood pressure (BP) management should not only mitigate cardiovascular risks but also preserve renal function by protecting podocyte integrity. This review offers a comprehensive examination of current BP management strategies and their implications for podocyte structure and function and emphasizes strategies for the reduction of proteinuria in HTN. We explore primary and secondary antihypertensive agents, including angiotensin-converting enzyme inhibitors, angiotensin receptor blockers, calcium channel blockers, and diuretics, as well as newer therapies (sodium-glucose cotransporter-2 blocking and endothelin receptor antagonism), emphasizing their mechanistic roles in safeguarding podocytes and curtailing proteinuria.

Randomized, Placebo-Controlled Trial on the Renal and Systemic Hemodynamic Effects of Empagliflozin

Introduction

Sodium-glucose cotransporter 2 inhibitors (SGLT2i) improve renal outcomes in type 2 diabetes mellitus (DM2) and chronic kidney disease (CKD). A decrease in renal blood flow (RBF) with attenuation of glomerular hyperfiltration may contribute. We examined renal and systemic hemodynamic effects of SGLT2i in relevant patient categories.

Methods

Using a double-blind placebo controlled cross-over design, we randomized patients with DM2 and estimated glomerular filtration rate (eGFR) > 60 ml/min per 1.73 m2 (n = 16), patients with DM2 and eGFR from 20 to 60 ml/min per 1.73 m2 (n = 17), and patients with nondiabetic CKD and eGFR from 20 to 60 ml/min per 1.73 m2 (n = 16) to empagliflozin 10 mg daily or placebo for 4 weeks and crossed over to the opposite treatment after 2-week washout. RBF was measured with 82Rubidium-positron emission-tomography/computed-tomography, glomerular filtration rate (GFR) with 99mTechnetium-diethylene-triamine-pentaacetate-clearance. A Mobil-O-graph was used to record 24-hour blood pressure (BP) and total vascular resistance (TVR).

Results

Compared to placebo, empagliflozin reduced RBF by 6% in the DM2-CKD group (P < 0.001) with nonsignificant decreases of 4% in the DM2 group and 1% in the CKD group (P = 0.29 and 0.72, respectively). Empagliflozin reduced GFR, BP, and TVR in all groups, whereas renal vascular resistance (RVR) remained unchanged.

Conclusion

Empagliflozin reduced RBF in patients with DM2 and CKD, whereas GFR, BP, and TVR were reduced in all groups. This pattern, together with a lack of reduction in RVR, suggests SGLT2i protect the glomerulus through combined preglomerular and post glomerular effects.

Favorable changes in the eGFR slope after dapagliflozin treatment and its association with the initial dip

BACKGROUND

Renoprotective effects of sodium glucose transporter 2 (SGLT2) inhibitors, including dapagliflozin, were observed in randomized controlled trials (RCTs). The suspected underlying mechanism is a correction of hyperfiltration, observed as an "initial dip". Whether SGLT2 inhibitors can attenuate the rate of decline in the estimated glomerular filtration rate (eGFR) in clinical settings, even when considering the pre-treatment decline rate, is unknown. Although several RCTs identified an association between the initial dip and long-term renal prognoses, a conclusion has not been reached.

METHODS

We collected the eGFR data of patients for whom dapagliflozin was initiated in our hospital and then calculated their eGFR slopes before and after the start of the treatment. We investigated the changes in the eGFR slopes (ΔeGFR slope) and the association between the ΔeGFR slope and the initial dip. Risks for rapid eGFR decliners (eGFR slope < - 3 mL/min/1.73 m2/year) were also examined.

RESULTS

The eGFR slope was significantly milder after dapagliflozin treatment (p < 0.01). A deeper initial dip was associated with a milder rate of eGFR decline (adjusted beta: - 0.29, p < 0.001). Dapagliflozin treatment reduced the proportion of rapid eGFR decliners from 52.9 to 14.7%, and a smaller initial dip was identified as a significant risk for post-treatment rapid eGFR decline (adjusted odds ratio: 1.73, p < 0.05).

CONCLUSIONS

Compared to before the administration of dapagliflozin, the rate of eGFR decline was significantly milder after its administration. The initial dip was significantly associated with long-term renoprotective effects and may be a useful predictor of treatment response.

Glomerular pressure and tubular oxygen supply: a critical dual target for renal protection

The primary treatment goal of chronic kidney disease (CKD) is preserving renal function and preventing its progression to end-stage renal disease. Glomerular hypertension and tubular hypoxia are critical risk factors in CKD progression. However, the renal hemodynamics make it difficult to avoid both factors due to the existence of peritubular capillaries that supply oxygen to the renal tubules downstream from the glomerulus through the efferent arteriole. In the treatment strategies for balancing glomerular pressure and tubular oxygen supply, afferent and efferent arterioles of the glomerulus determine glomerular filtration rate and blood flow to the peritubular capillaries. Therefore, sodium-glucose cotransporter 2 inhibitors and angiotensin receptor-neprilysin inhibitors as well as classical renin-angiotensin system inhibitors, which can change the diameter of afferent and/or efferent arterioles, are promising options for balancing this dual target and achieving renal protection. This review focuses on the clinical importance of glomerular pressure and tubular oxygen supply and proposes an effective treatment modality for this dual target.

Empagliflozin in Heart Failure: Regional Nephron Sodium Handling Effects

SIGNIFICANCE STATEMENT

The effect of sodium-glucose cotransporter-2 inhibitors (SGLT2i) on regional tubular sodium handling is poorly understood in humans. In this study, empagliflozin substantially decreased lithium reabsorption in the proximal tubule (PT) (a marker of proximal tubular sodium reabsorption), a magnitude out of proportion to that expected with only inhibition of sodium-glucose cotransporter-2. This finding was not driven by an "osmotic diuretic" effect; however, several parameters changed in a manner consistent with inhibition of the sodium-hydrogen exchanger 3. The large changes in proximal tubular handling were acutely buffered by increased reabsorption in both the loop of Henle and the distal nephron, resulting in the observed modest acute natriuresis with these agents. After 14 days of empagliflozin, natriuresis waned due to increased reabsorption in the PT and/or loop of Henle. These findings confirm in humans that SGLT2i have complex and important effects on renal tubular solute handling.

BACKGROUND

The effect of SGLT2i on regional tubular sodium handling is poorly understood in humans but may be important for the cardiorenal benefits.

METHODS

This study used a previously reported randomized, placebo-controlled crossover study of empagliflozin 10 mg daily in patients with diabetes and heart failure. Sodium handling in the PT, loop of Henle (loop), and distal nephron was assessed at baseline and day 14 using fractional excretion of lithium (FELi), capturing PT/loop sodium reabsorption. Assessments were made with and without antagonism of sodium reabsorption through the loop using bumetanide.

RESULTS

Empagliflozin resulted in a large decrease in sodium reabsorption in the PT (increase in FELi=7.5%±10.6%, P = 0.001), with several observations suggesting inhibition of PT sodium hydrogen exchanger 3. In the absence of renal compensation, this would be expected to result in approximately 40 g of sodium excretion/24 hours with normal kidney function. However, rapid tubular compensation occurred with increased sodium reabsorption both in the loop ( P < 0.001) and distal nephron ( P < 0.001). Inhibition of sodium-glucose cotransporter-2 did not attenuate over 14 days of empagliflozin ( P = 0.14). However, there were significant reductions in FELi ( P = 0.009), fractional excretion of sodium ( P = 0.004), and absolute fractional distal sodium reabsorption ( P = 0.036), indicating that chronic adaptation to SGLT2i results primarily from increased reabsorption in the loop and/or PT.

CONCLUSIONS

Empagliflozin caused substantial redistribution of intrarenal sodium delivery and reabsorption, providing mechanistic substrate to explain some of the benefits of this class. Importantly, the large increase in sodium exit from the PT was balanced by distal compensation, consistent with SGLT2i excellent safety profile.

CLINICAL TRIAL REGISTRY NAME AND REGISTRATION NUMBER

ClinicalTrials.gov ( NCT03027960 ).

2023 update and perspectives

Total 276 manuscripts were published in Hypertension Research in 2022. Here our editorial members picked up the excellent papers, summarized the current topics from the published papers and discussed future perspectives in the sixteen fields. We hope you enjoy our special feature, 2023 update and perspectives in Hypertension Research.

Profiling cellular heterogeneity and fructose transporter expression in the rat nephron by integrating single-cell and microdissected tubule segment transcriptomes

Single-cell RNA sequencing (scRNAseq) is a crucial tool in kidney research. These technologies cluster cells according to transcriptome similarity, irrespective of the anatomical location and ordering within the nephron. Thus, a cluster transcriptome may obscure heterogeneity of the cell population within a nephron segment. Elevated dietary fructose leads to salt-sensitive hypertension, in part by fructose reabsorption in the proximal tubule (PT). However, organization of the four known fructose transporters in apical PTs (SGLT4, SGLT5, GLUT5 and NaGLT1) remains poorly understood. We hypothesized that cells within each subsegment of the proximal tubule exhibit complex, heterogenous fructose transporter expression patterns. To test this hypothesis we analyzed rat and kidney transcriptomes and proteomes from publicly available scRNAseq and tubule microdissection databases. We found that microdissected PT-S1 segments consist of 81±12% cells with scRNAseq-derived transcriptional characteristics of S1, whereas PT-S2 express a mixture of 18±9% S1, 58±8% S2, and 19±5% S3 transcripts, and PT-S3 consists of 75±9% S3 transcripts. The expression of all four fructose transporters was detectable in all three PT segments, but key fructose transporters SGLT5 and GLUT5 progressively increased from S1 to S3, and both were significantly upregulated in S3 vs. S1/S2 (Slc5a10: 1.9 log 2 FC, p<1×10 -299 ; Scl2a5: 1.4 log 2 FC, p<4×10 -105 ). A similar distribution was found in human kidneys. These data suggest that S3 is the primary site of fructose reabsorption in both humans and rats. Finally, because of the multiple scRNAseq transcriptional phenotypes found in each segment our findings also imply that anatomic labels applied to scRNAseq clusters may be misleading.