Claudins in kidney health and disease

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

Anti-Inflammatory Action of Sitagliptin and Linagliptin in Doxorubicin Nephropathy

Background/Aims: Dipeptidyl peptidase-4 (DPP4) inhibitors are known to have a protective effect on diabetic kidney disease, possibly via reduction of oxidative stress and inflammation in the kidney. However, whether these potential mechanisms play a role in non-diabetic proteinuric kidney diseases is not clear. Methods: Two different animal experiments were carried out using sitagliptin and linagliptin for DPP4 inhibition. In each experiment, male Sprague-Dawley rats were uninephrectomized and randomly divided into vehicle-treated and doxorubicin-treated rats, with or without DPP4 inhibition. Administration of a DPP4 inhibitor was performed daily by oral gavage over six weeks. Results: A single intravenous injection of doxorubicin resulted in hypertension and remarkable proteinuria. Linagliptin, but not sitagliptin, lowered systolic blood pressure in rats with doxorubicin nephropathy. By contrast, sitagliptin ameliorated tubulointerstitial injury, inflammatory cell infiltration, and interstitial fibrosis in rat kidneys with doxorubicin nephropathy. Quantitative polymerase chain reaction analysis revealed that mRNA expression of NLRP3, caspase-1, ASC, and IL-1β was remarkably increased in rat kidneys with doxorubicin nephropathy, and that this upregulation of the major components of the NLRP3 inflammasome was effectively suppressed by treatment with either sitagliptin or linagliptin. Additionally, upregulation of IL-6 was reversed by linagliptin, but not by sitagliptin. On the other hand, sitagliptin, but not linagliptin, reversed the increase in mRNA expression of gp91phox, p47phox, and p67phox in rat kidneys with doxorubicin nephropathy. Conclusion: NLRP3 inflammasome activation was shown in our rat model of doxorubicin nephropathy. DPP4 inhibitors can suppress the activity of NLRP3, with or without relieving NADPH oxidase 2-related oxidative stress

Conversational Agents for Body Weight Management: Systematic Review

BackgroundObesity is a public health issue worldwide. Conversational agents (CAs), also frequently called chatbots, are computer programs that simulate dialogue between people. Owing to better accessibility, cost-effectiveness, personalization, and compassionate patient-centered treatments, CAs are expected to have the potential to provide sustainable lifestyle counseling for weight management. ObjectiveThis systematic review aimed to critically summarize and evaluate clinical studies on the effectiveness and feasibility of CAs with unconstrained natural language input for weight management. MethodsPubMed, Embase, the Cochrane Library (CENTRAL), PsycINFO, and ACM Digital Library were searched up to December 2022. Studies were included if CAs were used for weight management and had a capability for unconstrained natural language input. No restrictions were imposed on study design, language, or publication type. The quality of the included studies was assessed using the Cochrane risk-of-bias assessment tool or the Critical Appraisal Skills Programme checklist. The extracted data from the included studies were tabulated and narratively summarized as substantial heterogeneity was expected. ResultsIn total, 8 studies met the eligibility criteria: 3 (38%) randomized controlled trials and 5 (62%) uncontrolled before-and-after studies. The CAs in the included studies were aimed at behavior changes through education, advice on food choices, or counseling via psychological approaches. Of the included studies, only 38% (3/8) reported a substantial weight loss outcome (1.3-2.4 kg decrease at 12-15 weeks of CA use). The overall quality of the included studies was judged as low. ConclusionsThe findings of this systematic review suggest that CAs with unconstrained natural language input can be used as a feasible interpersonal weight management intervention by promoting engagement in psychiatric intervention-based conversations simulating treatments by health care professionals, but currently there is a paucity of evidence. Well-designed rigorous randomized controlled trials with larger sample sizes, longer treatment duration, and follow-up focusing on CAs’ acceptability, efficacy, and safety are warranted

Effects of dietary salt restriction on puromycin aminonucleoside nephrosis

Dietary salt restriction may reduce proteinuria although the mechanism is not clear. We investigated the effects of dietary salt restriction on rat kidneys in an animal model of glomerular proteinuria. Male Sprague-Dawley rats were divided into 3 groups: vehicle-treated normal-salt controls, puromycin aminonucleoside (PA)-treated normal-salt rats, and PA-treated low-salt rats. PA was given at a dose of 150 mg/kg BW at time 0, followed by 50 mg/kg BW on days 28, 35, and 42. Sodium-deficient rodent diet with and without additional NaCl (0.5%) were provided for normal-salt rats and low-salt rats, respectively. On day 63, kidneys were harvested for histopathologic examination. PA treatment produced overt proteinuria and renal damage. Dietary salt restriction insignificantly reduced proteinuria in PA-treated rats, and PA-treated low-salt rats had lower urine output and smaller creatinine clearance than vehicle-treated normal-salt controls. The tubulointerstitial injury score positively correlated with proteinuria. It was significantly increased by PA treatment and relieved by low-salt diet. ED1-positive infiltrating cells and immunostaining for interstitial collagen III were significantly increased by PA treatment. These changes appeared less in PA-treated low-salt rats although the differences in PA-treated normal-salt versus low-salt rats did not reach the statistical significance. Our results suggest that renal histopathology in PA nephrosis may potentially be improved by dietary salt restriction. The decreasing tendency in glomerular filtration rate induced by low-sodium diet might be beneficial in retarding renal progression

Alteration of Tight Junction Protein Expression in Dahl Salt-Sensitive Rat Kidney

Background/Aims: Altered pressure natriuresis is an important mechanism of hypertension, but it remains elusive at the molecular level. We hypothesized that in the kidney, tight junctions (TJs) may have a role in pressure natriuresis because paracellular NaCl transport affects interstitial hydrostatic pressure. Methods: To assess the association of salt-sensitive hypertension with altered renal TJ protein expression, Dahl salt-sensitive (SS) and salt-resistant (SR) rats were put on an 8% NaCl-containing rodent diet for 4 weeks. Systolic blood pressure (SBP) and urine NaCl excretion were measured weekly, and kidneys were harvested for immunoblotting and quantitative PCR analysis at the end of the animal experiments. Results: SBP was significantly higher in SS rats than in SR rats during the first to fourth weeks of the animal experiments. During the first and second week, urinary NaCl excretion was significantly lower in SS rats as compared with SR rats. However, the difference between the two groups vanished at the third and fourth weeks. In the kidney, claudin-4 protein and mRNA were significantly increased in SS rats as compared with SR rats. On the other hand, occludin protein and mRNA were significantly decreased in SS rats as compared with SR rats. The expression of claudin-2, claudin-7, and claudin-8 did not vary significantly between the two groups. Conclusions: In SS rats, SS hypertension was associated with differential changes in renal TJ protein expression. Both upregulation of claudin-4 and downregulation of occludin might increase paracellular NaCl transport in the kidney, resulting in impaired pressure natriuresis in SS rats

Effects of Dietary Salt Restriction on Renal Progression and Interstitial Fibrosis in Adriamycin Nephrosis

Background/Aims: Although high salt intake is thought to accelerate renal progression in proteinuric kidney disease, it is not known whether strict dietary salt restriction could delay renal inflammation and interstitial fibrosis. Here, we sought to answer this question in a rat model of adriamycin-induced nephrotic syndrome. Methods: Adriamycin was administered via the femoral vein in a single bolus (7.5 mg/kg), and the rats were put on a sodium-deficient rodent diet. Rats with intact kidneys were studied for 5 weeks (experiment 1), and uninephrectomized rats were studied for 6 weeks (experiment 2). Results: In experiment 1, restricting salt intake improved renal tubulointerstitial histopathology in adriamycin-treated rats. Immunohistochemical and immunoblot results additionally showed that restricting dietary salt lowered adriamycin-induced expression of osteopontin, collagen III, and fibronectin. In experiment 2, salt restriction improved adriamycin-induced azotemia, although it did not affect proteinuria or blood pressure. Dietary salt restriction also reduced adriamycin-induced infiltration of ED1-positive cells and the upregulated expression of osteopontin and a-SMA. Masson's trichrome and Sirius red staining revealed that salt restriction slowed Adriamycin-induced progression of renal interstitial fibrosis. Finally, qPCR revealed that adriamycin-induced expression of TNF-a, IκB-a, gp91phox, p47phox, and p67phox mRNA was blocked by salt restriction. Conclusion: Our findings demonstrate that strict dietary salt restriction delays the progress of renal inflammation and fibrosis in proteinuric kidney disease, most likely via relieving the reactive oxygen species-mediated NF-κB activation