When sodium-glucose cotransporter-2 (SGLT2) inhibitors were first introduced a decade ago, no one expected them to have substantial effects beyond their known glucose-lowering effects, until the emergence of evidence of their robust renal and cardiovascular benefits showing that they could attenuate progression of kidney disease, irrespective of diabetes, as well as prevent the development of acute kidney injury. Still, the precise and elaborate mechanisms underlying the major organ protection of SGLT2 inhibitors remain unclear. SGLT2 inhibitors inhibit the reabsorption of sodium and glucose in the proximal tubule of the kidney and then recovers tubuloglomerular feedback, whereby SGLT2 inhibitors reduce glomerular hyperfiltration. This simple demonstration of their beneficial effects has perplexed experts in seeking more plausible and as yet undisclosed explanations for the whole effects of SGLT2 inhibitors, including metabolism reprogramming and the modulation of hypoxia, inflammation, and oxidative stress. Given that the renal benefits of SGLT2 inhibitors in patients with kidney disease but without diabetes were comparable to those seen in patients with diabetes, it may be reasonable to keep the emphasis on their hemodynamic actions. In this context, the aim of the present review is to provide a comprehensive overview of renal hemodynamics in individuals with diabetes who are treated with SGLT2 inhibitors, with a focus on natriuresis associated with the regulation of tubuloglomerular feedback and potential aquaresis. Throughout the discussion of alterations in renal sodium and water transports, particular attention will be given to the potential enhancement of adenosine and its receptors following SGLT2 inhibition.

Claudins are strategically located to exert their physiologic actions along with the nephron segments from the glomerulus. Claudin-1 is normally located in the Bowman’s capsule, but its overexpression can reach the podocytes and lead to albuminuria. In the proximal tubule (PT), claudin-2 forms paracellular channels selective for water, Na+, K+, and Ca2+. Claudin-2 gene mutations are associated with hypercalciuria and kidney stones. Claudin-10 has two splice variants, -10a and -10b; Claudin-10a acts as an anion-selective channel in the PT, and claudin-10b functions as a cation-selective pore in the thick ascending limb (TAL). Claudin-16 and claudin-19 mediate paracellular transport of Na+, Ca2+, and Mg2+ in the TAL, where the expression of claudin-3/16/19 and claudin-10b are mutually exclusive. The claudin-16 or -19 mutation causes familial hypomagnesemia with hypercalciuria and nephrocalcinosis. Claudin- 14 polymorphisms have been linked to increased risk of hypercalciuria. Claudin-10b mutations produce HELIX syndrome, which encompasses hypohidrosis, electrolyte imbalance, lacrimal gland dysfunction, ichthyosis, and xerostomia. Hypercalciuria and magnesuria in metabolic acidosis are related to downregulation of PT and TAL claudins. In the TAL, stimulation of calcium-sensing receptors upregulates claudin-14 and negatively acts on the claudin-16/19 complex. Claudin-3 acts as a general barrier to ions in the collecting duct. If this barrier is disturbed, urine acidification might be impaired. Claudin-7 forms a nonselective paracellular channel facilitating Cl– and Na+ reabsorption in the collecting ducts. Claudin-4 and -8 serve as anion channels and mediate paracellular Cl– transport; their upregulation may contribute to pseudohypoaldosteronism II and salt-sensitive hypertension.

Objective: Both hypouricemia and hyperuricemia are reportedly associated with reduced kidney function. This study investigated the association between uric acid levels and the risk of reduced renal function in men and women. Methods: We conducted a cross-sectional study using data from a government-funded health examinee cohort of a Korean genome and epidemiological study. A total of 172,970 participants (58,981 men, 113,989 women) aged 40∼79 years were included. A logistic regression test was performed, and the odds ratio (OR) and 95% confidence interval (CI) were calculated to examine the relationship between stratified uric acid levels and the frequency of chronic kidney disease. Results: As the uric acid level increased, the risk of reduced renal function increased. Moreover, for uric acid levels ≤2.0 mg/dL, the risk of reduced renal function was higher than that of the reference group. Among the total, man, and woman groups, a statistically significant association was observed in men (OR 1.71, 95% CI 0.945∼3.111, OR 5.003, 95% CI 1.405∼17.809, and OR 1.377, 95% CI 0.696∼2.724, respectively). Conclusion The OR of reduced renal function according to uric acid levels formed a J-shaped curve in both genders.

Background/Aims: We investigated the distribution of serum uric acid (SUA) levels and estimated the prevalence of hyperuricemia and hypouricemia in the Korean population. Methods: This cross-sectional study used data from the Korean Genome and Epidemiology Study and included 172,970 participants (58,981 men and 113,989 women) aged 40 to 79 years. Hypouricemia and hyperuricemia were defined as SUA level ≤ 2.0 mg/dL and > 7 mg/dL, respectively. The prevalence of hyperuricemia and hypouricemia was evaluated by age and sex. Results: The mean SUA levels were significantly higher in men than in women (5.71 ± 1.27 mg/dL vs. 4.21 ± 0.96 mg/dL, p < 0.001). The mean SUA levels and prevalence of hyperuricemia increased with age in women but not in men. The overall prevalence of hyperuricemia and that in men and women was 50.82, 133.25, and 8.17 per 1,000 persons, respectively; the overall prevalence of hypouricemia and that in men and women was 4.16, 1.10, and 5.75 per 1,000 persons, respectively. The prevalence of hypouricemia in men was similar across all age groups; however, that in women was the highest in the age group of 40 to 49 years and the lowest in the age group of 50 to 59 years. Conclusions The distribution of SUA levels and prevalence of hyperuricemia and hypouricemia differed according to age and sex. Age and sex should be considered in studies on uric acid-related diseases.

Purpose: Oral adsorbents delay disease progression and improve uremic symptoms in patients with chronic kidney disease (CKD). DW-7202 is a newly developed oral adsorbent with high adsorptive selectivity for uremic toxins. We evaluated patient preference for and adherence to DW-7202 versus AST-120 therapy and compared treatment efficacy and safety in patients with pre-dialysis CKD. Materials and Methods: A seven-center, randomized, open-label, two-way crossover, active-controlled, phase IV clinical trial was conducted. Patients with stable CKD were randomly assigned to receive DW-7202 (capsule type) or AST-120 (granule type) for 12 weeks. The groups then switched to the other adsorbent and took it for the next 12 weeks. Patient preference was the primary outcome. Secondary outcomes included changes in estimated glomerular filtration rate (eGFR) and serum creatinine, cystatin C, and indoxyl sulfate (IS) levels. Results: Significantly more patients preferred DW-7202 than AST-120 (p<0.001). Patient adherence improved after switching from AST-120 to DW-7202; there was no apparent change in adherence after switching from DW-7202 to AST-120. Changes in eGFR and serum creatinine, cystatin C, and IS levels were not significantly different according to adsorbent type. There was also no significant difference in the incidences of adverse events during treatment with DW-7202 and AST-120. Conclusion DW-7202 can be considered as an alternative to AST-120 in patients who cannot tolerate or show poor adherence to granule type adsorbents. Further studies to evaluate factors affecting patient preferences and improved adherence are warranted (Clinical trial registration No. NCT02681952).

Objective: Both hypouricemia and hyperuricemia are reportedly associated with reduced kidney function. This study investigated the association between uric acid levels and the risk of reduced renal function in men and women. Methods: We conducted a cross-sectional study using data from a government-funded health examinee cohort of a Korean genome and epidemiological study. A total of 172,970 participants (58,981 men, 113,989 women) aged 40∼79 years were included. A logistic regression test was performed, and the odds ratio (OR) and 95% confidence interval (CI) were calculated to examine the relationship between stratified uric acid levels and the frequency of chronic kidney disease. Results: As the uric acid level increased, the risk of reduced renal function increased. Moreover, for uric acid levels ≤2.0 mg/dL, the risk of reduced renal function was higher than that of the reference group. Among the total, man, and woman groups, a statistically significant association was observed in men (OR 1.71, 95% CI 0.945∼3.111, OR 5.003, 95% CI 1.405∼17.809, and OR 1.377, 95% CI 0.696∼2.724, respectively). Conclusion The OR of reduced renal function according to uric acid levels formed a J-shaped curve in both genders.

Urate is produced in the liver by the degradation of purines from the diet and nucleotide turnover and excreted by the kidney and gut. The kidney is the major route of urate removal and has a pivotal role in the regulation of urate homeostasis. Approximately 10% of the glomerular filtered urate is excreted in the urine, and the remainder is reabsorbed by the proximal tubule. However, the transport of urate in the proximal tubule is bidirectional: reabsorption and secretion. Thus, an increase in reabsorption or a decrease in secretion may induce hyperuricemia.In contrast, a decrease in reabsorption or an increase in secretion may result in hyperuricosuria. In the proximal tubule, urate reabsorption is mainly mediated by apical URAT1 (SLC22A12) and basolateral GLUT9 (SLC2A9) transporter. OAT4 (SLC22A11) also acts in urate reabsorption in the apical membrane, and its polymorphism is associated with the risk of hyperuricemia. Renal hypouricemia is caused by SLC22A12 or SLC2A9 loss-of-function mutations, and it may be complicated by exercise-induced acute kidney injury. URAT1 and GLUT9 are also drug targets for uricosuric agents. Sodium-glucose cotransporter inhibitors may induce hyperuricosuria by inhibiting GLUT9b located in the apical plasma membrane. Urate secretion is mediated by basolateral OAT1 (SLC22A6) and OAT3 (SLC22A8) and apical ATP-binding cassette super-family G member 2 (>ABCG2), NPT1 (SLC17A1), and NPT4 (SLC17A3) transporter in the proximal tubule. NPT1 and NPT4 may be key players in renal urate secretion in humans, and deletion of SLC22A6 and SLC22A8 in mice leads to decreased urate excretion. Dysfunctional variants of >ABCG2 inhibit urate secretion from the gut and kidney and may cause gout. In summary, the net result of urate transport in the proximal tubule is determined by the dominance of transporters between reabsorption (URAT1, OAT4, and GLUT9) and secretion (ABCG2, NPT1, NPT4, OAT1, and OAT3).

Chronic kidney disease (CKD) can be progressive, and its prognosis is worse because of increased mortality when it is associated with diabetes and cardiac disease. The outcomes of diabetic kidney disease (DKD) need to be improved, despite multifactorial interventions including glucose and blood pressure (BP) control, and the use of renin-angiotensin system (RAS) inhibitors, statins, and aspirin. Recent clinical trials suggest that sodium-glucose cotransporter-2 (SGLT2) inhibitors offer additional cardiorenal protection in DKD and non-diabetic CKD on top of RAS inhibition. The action of SGLT2 inhibitors is derived from the proximal tubule of the kidney, but their systemic effects beyond glucose-lowering involve hemodynamic and non-hemodynamic mechanisms. First, SGLT2 inhibitors restore tubuloglomerular feedback and relieve glomerular hypertension and albuminuria. Second, natriuresis and renal glycosuria lead to fluid and weight loss, resulting in BP lowering and prevention of heart failure. Third, SGLT2 inhibitors have anti-inflammatory and anti-oxidative actions that can reduce renal and cardiac inflammation and fibrosis, probably via adenosine monophosphate-activated protein kinase and sirtuin-1 activation. Finally, the proximal tubular workload is relieved, accompanied by increased erythropoiesis. Hypoxia-inducible factor 1 may be stimulated by renal outer medullary hypoxia when tubular sodium transport shifts from the proximal convoluted tubule to the proximal straight tubule and thick ascending limb, due to SGLT2 inhibition. These effects may also be beneficial in non-diabetic CKD, and we anticipate that SGLT2 inhibitors will prove effective for albuminuria reduction and preservation of kidney function in primary kidney diseases, including glomerulonephritis.

No abstract available.
Cardio-Renal Syndrome ; Hepcidins