Bidirectional relation between dipeptidyl peptidase 4 and angiotensin II type I receptor signaling

Cardiometabolic diseases are often associated with heightened levels of angiotensin II (Ang II), which accounts for the observed oxidative stress, inflammation, and fibrosis. Accumulating evidence indicates a parallel upregulation of dipeptidyl dipeptidase 4 (DPP4) activity in cardiometabolic diseases, with its inhibition shown to mitigate oxidative stress, inflammation, and fibrosis. These findings highlight an overlap between the pathophysiological mechanisms used by Ang II and DPP4. Recent evidence demonstrates that targeted inhibition of DPP4 prevents the rise in Ang II and its associated molecules in experimental models of cardiometabolic diseases. Similarly, inhibitors of the angiotensin I-converting enzyme (ACE) or Ang II type 1 receptor (AT1R) blockers downregulate DPP4 activity, establishing a bidirectional relationship between DPP4 and Ang II. Here, we discuss the current evidence supporting the cross talk between Ang II and DPP4, along with the potential mechanisms promoting this cross regulation. A comprehensive analysis of this bidirectional relationship across tissues will advance our understanding of how DPP4 and Ang II collectively promote the development and progression of cardiometabolic diseases.

Recent advances in wearable sensors and data analytics for continuous monitoring and analysis of biomarkers and symptoms related to COVID-19

The COVID-19 pandemic has changed the lives of many people around the world. Based on the available data and published reports, most people diagnosed with COVID-19 exhibit no or mild symptoms and could be discharged home for self-isolation. Considering that a substantial portion of them will progress to a severe disease requiring hospitalization and medical management, including respiratory and circulatory support in the form of supplemental oxygen therapy, mechanical ventilation, vasopressors, etc. The continuous monitoring of patient conditions at home for patients with COVID-19 will allow early determination of disease severity and medical intervention to reduce morbidity and mortality. In addition, this will allow early and safe hospital discharge and free hospital beds for patients who are in need of admission. In this review, we focus on the recent developments in next-generation wearable sensors capable of continuous monitoring of disease symptoms, particularly those associated with COVID-19. These include wearable non/minimally invasive biophysical (temperature, respiratory rate, oxygen saturation, heart rate, and heart rate variability) and biochemical (cytokines, cortisol, and electrolytes) sensors, sensor data analytics, and machine learning-enabled early detection and medical intervention techniques. Together, we aim to inspire the future development of wearable sensors integrated with data analytics, which serve as a foundation for disease diagnostics, health monitoring and predictions, and medical interventions.

Dipeptidylpeptidase 4 promotes survival and stemness of acute myeloid leukemia stem cells

Leukemic-stem-cell-specific targeting may improve the survival of patients with acute myeloid leukemia (AML) by avoiding the ablative effects of standard regimens on normal hematopoiesis. Herein, we perform an unbiased screening of compounds targeting cell surface proteins and identify clinically used DPP4 inhibitors as strong suppressors of AML development in both murine AML models and primary human AML cells xenograft model. We find in retrovirus-induced AML mouse models that DPP4-deficient AML cell-transplanted mice exhibit delay and reversal of AML development, whereas deletion of DPP4 has no significant effect on normal hematopoiesis. DPP4 activates and sustains survival of AML stem cells that are critical for AML development in both human and animal models via binding with Src kinase and activation of nuclear factor κB (NF-κB) signaling. Thus, inhibition of DPP4 is a potential therapeutic strategy against AML development through suppression of survival and stemness of AML cells.

Repair of Limb Ischemia Is Dependent on Hematopoietic Stem Cell Specific-SHP-1 Regulation of TGF-β1

BACKGROUND

Hematopoietic stem cell (HSC) therapy has shown promise for tissue regeneration after ischemia. Therefore, there is a need to understand mechanisms underlying endogenous HSCs activation in response to ischemic stress and coordination of angiogenesis and repair. SHP-1 plays important roles in HSC quiescence and differentiation by regulation of TGF-β1 signaling. TGF-β1 promotes angiogenesis by stimulating stem cells to secrete growth factors to initiate the formation of blood vessels and later aid in their maturation. We propose that SHP-1 responds to ischemia stress in HSC and progenitor cells (HSPC) via regulation of TGF-β1.

METHODS

A mouse hind limb ischemia model was used. Local blood perfusion in the limbs was determined using laser doppler perfusion imaging. The number of positive blood vessels per square millimeter, as well as blood vessel diameter (μm) and area (μm²), were calculated. Hematopoietic cells were analyzed using flow cytometry. The bone marrow transplantation assay was performed to measure HSC reconstitution.

RESULTS

After femoral artery ligation, TGF-β1 was initially decreased in the bone marrow by day 3 of ischemia, followed by an increase on day 7. This pattern was opposite to that in the peripheral blood, which is concordant with the response of HSC to ischemic stress. In contrast, SHP-1 deficiency in HSC is associated with irreversible activation of HSPCs in the bone marrow and increased circulating HSPCs in peripheral blood following limb ischemia. In addition, there was augmented auto-induction of TGF-β1 and sustained inactivation of SHP-1-Smad2 signaling, which impacted TGF-β1 expression in HSPCs in circulation. Importantly, restoration of normal T GF-β1 oscillations helped in the recovery of limb repair and function.

CONCLUSIONS

HSPC-SHP-1-mediated regulation of TGF-β1 in both bone marrow and peripheral blood is required for a normal response to ischemic stress.

Microneedle-Based Potentiometric Sensing System for Continuous Monitoring of Multiple Electrolytes in Skin Interstitial Fluids

Electrolytes play a pivotal role in regulating cardiovascular functions, hydration, and muscle activation. The current standards for monitoring electrolytes involve periodic sampling of blood and measurements using laboratory techniques, which are often uncomfortable/inconvenient to the subjects and add considerable expense to the management of their underlying disease conditions. The wide range of electrolytes in skin interstitial fluids (ISFs) and their correlations with those in plasma create exciting opportunities for applications such as electrolyte and circadian metabolism monitoring. However, it has been challenging to monitor these electrolytes in the skin ISFs. In this study, we report a minimally invasive microneedle-based potentiometric sensing system for multiplexed and continuous monitoring of Na⁺ and K⁺ in the skin ISFs. The potentiometric sensing system consists of a miniaturized stainless-steel hollow microneedle to prevent sensor delamination and a set of modified microneedle electrodes for multiplex monitoring. We demonstrate the measurement of Na⁺ and K⁺ in artificial ISFs with a fast response time, excellent reversibility and repeatability, adequate selectivity, and negligible potential interferences upon the addition of a physiologically relevant concentration of metabolites, dietary biomarkers, and nutrients. In addition, the sensor maintains the sensitivity after multiple insertions into the chicken skin model. Furthermore, the measurements in artificial ISFs using calibrated sensors confirm the accurate measurements of physiological electrolytes in artificial ISFs. Finally, the skin-mimicking phantom gel and chicken skin model experiments demonstrate the sensor's potential for minimally invasive monitoring of electrolytes in skin ISFs. The developed sensor platform can be adapted for a wide range of other applications, including real-time monitoring of nutrients, metabolites, and proteins.

Sphingosine kinase 2 restricts T cell immunopathology but permits viral persistence

Chronic viral infections are often established by the exploitation of immune-regulatory mechanisms that result in nonfunctional T cell responses. Viruses that establish persistent infections remain a serious threat to human health. Sphingosine kinase 2 (SphK2) generates sphingosine 1-phosphate, which is a molecule known to regulate multiple cellular processes. However, little is known about SphK2's role during the host immune responses to viral infection. Here, we demonstrate that SphK2 functions during lymphocytic choriomeningitis virus Cl 13 (LCMV Cl 13) infection to limit T cell immune pathology, which subsequently aids in the establishment of virus-induced immunosuppression and the resultant viral persistence. The infection of Sphk2-deficient (Sphk2-/-) mice with LCMV Cl 13 led to the development of nephropathy and mortality via T cell-mediated immunopathology. Following LCMV infection, Sphk2-/- CD4+ T cells displayed increased activity and proliferation, and these cells promoted overactive LCMV Cl 13-specific CD8+ T cell responses. Notably, oral instillation of an SphK2-selective inhibitor promoted protective T cell responses and accelerated the termination of LCMV Cl 13 persistence in mice. Thus, SphK2 is indicated as an immunotherapeutic target for the control of persistent viral infections.

DPP4 inhibition mitigates ANG II-mediated kidney immune activation and injury in male mice

Recent evidence suggests that dipeptidyl peptidase-4 (DPP4) inhibition with saxagliptin (Saxa) is renoprotective under comorbid conditions associated with activation of the renin-angiotensin-aldosterone system (RAAS), such as diabetes, obesity, and hypertension, which confer a high cardiovascular risk. Immune system activation is now recognized as a contributor to RAAS-mediated tissue injury, and, importantly, immunomodulatory effects of DPP4 have been reported. Accordingly, we examined the hypothesis that DPP4 inhibition with Saxa attenuates angiotensin II (ANG II)-induced kidney injury and albuminuria via attenuation of immune activation in the kidney. To this end, male mice were infused with either vehicle or ANG II (1,000 ng/kg/min, s.c.) for 3 wk and received either placebo or Saxa (10 mg/kg/day, p.o.) during the final 2 wk. ANG II infusion increased kidney, but not plasma, DPP4 activity in vivo as well as DPP4 activity in cultured proximal tubule cells. The latter was prevented by angiotensin receptor blockade with olmesartan. Further, ANG II induced hypertension and kidney injury characterized by mesangial expansion, mitochondrial damage, reduced brush border megalin expression, and albuminuria. Saxa inhibited DPP4 activity ∼50% in vivo and attenuated ANG II-mediated kidney injury, independent of blood pressure. Further mechanistic experiments revealed mitigation by Saxa of proinflammatory and profibrotic mediators activated by ANG II in the kidney, including CD8⁺ T cells, resident macrophages (CD11b^hiF4/80^loLy6C^-), and neutrophils. In addition, Saxa improved ANG II suppressed anti-inflammatory regulatory T cell and T helper 2 lymphocyte activity. Taken together, these results demonstrate, for the first time, blood pressure-independent involvement of renal DPP4 activation contributing to RAAS-dependent kidney injury and immune activation.NEW & NOTEWORTHY This work highlights the role of dipeptidyl peptidase-4 (DPP4) in promoting ANG II-mediated kidney inflammation and injury. Specifically, ANG II infusion in mice led to increases in blood pressure and kidney DPP4 activity, which then led to activation of CD8⁺ T cells, Ly6C^- macrophages, and neutrophils and suppression of anti-inflammatory T helper 2 lymphocytes and regulatory T cells. Collectively, this led to kidney injury, characterized by mesangial expansion, mitochondrial damage, and albuminuria, which were mitigated by DPP4 inhibition independent of blood pressure reduction.

Abstract P024: Proximal Tubule Specific Dpp4 Deletion Slows Kidney Disease Progression In Western Diet-fed Obese Mice

Background: Obesity is a major risk factor for Chronic Kidney Disease progression to End Stage Renal Disease and/or Dialysis. Increased absorption of fats and/or sugars from Western Diet (WD), likely leads to kidney tubular injury in obesity. We observed that global dipeptidyl peptidase 4 (DPP4) deletion as well as use of inhibitors in WD-fed mice results in decreased kidney injury which, in turn was associated with a decrease in proximal tubule DPP4. Therefore, we hypothesized that proximal tubule (PT) DPP4 activation leads to injury and progression of kidney disease.

Methods: PT DPP4-KO and WT littermates were fed a WD starting 4-6 wks of age and continued for 2 years. FITC-sinestrin-based GFR and albuminuria were monitored periodically. Tissue histology was performed at select intervals. GeLC-MS was used to separate kidney peptides and Scaffold 4/iPathwayguide used to analyze the Proteomics data.

Results: WD-fed WT mice gained 150-200% weight of chow-fed [CD] mice and had a greater decline in GFR than CD-fed animals over 2 years (50% vs. 20%, p<0.05). WD-fed PT-DPP4-KO mice had a lesser decline (~35%) when compared to WT mice. This was true for both male and female mice. Concomitantly, there was an increase in albuminuria in WD-fed WT mice that was mitigated in PT-DPP4-KO mice. PAS/PSR stained sections showed worsening fibrosis, tubular dilatation and glomerulomegaly, tubular vacuolization in WD-fed WT mice that was mitigated in PT-DPP4-KO mice. Oil Red O staining showed increased fat accumulation in glomeruli and tubules of WD-fed WT mice that was mitigated in KO mice. Proteomics analysis followed by immunoblots showed that WD-feeding led to an increase in cell adhesion proteins and ribosomal machinery that was significantly suppressed by KO. In addition, there was a shift towards reduction in gluconeogenesis and improved fatty acid oxidation in KO mice.

Conclusion: Obesity without diabetes can lead to chronic decline in GFR in both male and female mice. DPP4 inhibition may slow the decline if started early in the course of developing obesity and/or metabolic syndrome.

Diet-Induced Obesity Promotes Kidney Endothelial Stiffening and Fibrosis Dependent on the Endothelial Mineralocorticoid Receptor

Obesity is characterized by enhanced MR (mineralocorticoid receptor) activation, vascular stiffness, and associated cardiovascular and kidney disease. Consumption of a Western-style diet (WD), high in saturated fat and refined carbohydrates, by female mice, leads to obesity and vascular stiffening. Use of ECMR (endothelial cell-specific MR) knockout mice supports that ECMR activation is critical for development of vascular and cardiac fibrosis and stiffening. However, the role of ECMR activation in kidney inflammation and fibrosis remains unknown. We hypothesized that cell-specific deletion of ECMR would prevent WD-induced central aortic stiffness and protect the kidney from endothelial dysfunction and vascular stiffening. Four-week-old female ECMR KO and wild-type mice were fed either mouse chow or WD for 16 weeks. WD feeding increased body weight and fat mass, proteinuria, as well as vascular stiffness indices (pulse wave velocity and kidney artery stiffening) and impaired endothelial-dependent vasodilatation without blood pressure changes. The WD-induced kidney arterial stiffening was associated with attenuated eNOS (endothelial NO synthase) activation, increased oxidative stress, proinflammatory immune responses, alterations in extracellular matrix degradation pathways, and fibrosis. ECMR deletion prevented these abnormalities by improving eNOS activation and reducing macrophage proinflammatory M1 polarization, expression of TG2 (transglutaminase 2), and MMP (matrix metalloproteinase)-9. Our data support the concept that ECMR activation contributes to endothelial dysfunction, increased kidney artery fibrosis/stiffening, and impaired NOS (NO synthase) activation, processes associated with macrophage infiltration and polarization, inflammation, and oxidative stress, collectively resulting in tubulointerstitial fibrosis in females consuming a WD.

The combination of a neprilysin inhibitor (sacubitril) and angiotensin-II receptor blocker (valsartan) attenuates glomerular and tubular injury in the Zucker Obese rat

OBJECTIVE

Diabetic nephropathy (DN) is characterized by glomerular and tubulointerstitial injury, proteinuria and remodeling. Here we examined whether the combination of an inhibitor of neprilysin (sacubitril), a natriuretic peptide-degrading enzyme, and an angiotensin II type 1 receptor blocker (valsartan), suppresses renal injury in a pre-clinical model of early DN more effectively than valsartan monotherapy.

METHODS

Sixty-four male Zucker Obese rats (ZO) at 16 weeks of age were distributed into 4 different groups: Group 1: saline control (ZOC); Group 2: sacubitril/valsartan (sac/val) (68 mg kg^-1 day^-1; ZOSV); and Group 3: valsartan (val) (31 mg kg^-1 day^-1; ZOV). Group 4 received hydralazine, an anti-hypertensive drug (30 mg kg^-1 day^-1, ZOH). Six Zucker Lean (ZL) rats received saline (Group 5) and served as lean controls (ZLC). Drugs were administered daily for 10 weeks by oral gavage.

RESULTS

Mean arterial pressure (MAP) increased in ZOC (+ 28%), but not in ZOSV (- 4.2%), ZOV (- 3.9%) or ZOH (- 3.7%), during the 10 week-study period. ZOC were mildly hyperglycemic, hyperinsulinemic and hypercholesterolemic. ZOC exhibited proteinuria, hyperfiltration, elevated renal resistivity index (RRI), glomerular mesangial expansion and podocyte foot process flattening and effacement, reduced nephrin and podocin expression, tubulointerstitial and periarterial fibrosis, increased NOX2, NOX4 and AT₁R expression, glomerular and tubular nitroso-oxidative stress, with associated increases in urinary markers of tubular injury. None of the drugs reduced fasting glucose or HbA1c. Hypercholesterolemia was reduced in ZOSV (- 43%) and ZOV (- 34%) (p < 0.05), but not in ZOH (- 13%) (ZOSV > ZOV > ZOH). Proteinuria was ameliorated in ZOSV (- 47%; p < 0.05) and ZOV (- 30%; p > 0.05), but was exacerbated in ZOH (+ 28%; p > 0.05) (ZOSV > ZOV > ZOH). Compared to ZOC, hyperfiltration was improved in ZOSV (p < 0.05 vs ZOC), but not in ZOV or ZOH. None of the drugs improved RRI. Mesangial expansion was reduced by all 3 treatments (ZOV > ZOSV > ZOH). Importantly, sac/val was more effective in improving podocyte and tubular mitochondrial ultrastructure than val or hydralazine (ZOSV > ZOV > ZOH) and this was associated with increases in nephrin and podocin gene expression in ZOSV (p < 0.05), but not ZOV or ZOH. Periarterial and tubulointerstitial fibrosis and nitroso-oxidative stress were reduced in all 3 treatment groups to a similar extent. Of the eight urinary proximal tubule cell injury markers examined, five were elevated in ZOC (p < 0.05). Clusterin and KIM-1 were reduced in ZOSV (p < 0.05), clusterin alone was reduced in ZOV and no markers were reduced in ZOH (ZOSV > ZOV > ZOH).

CONCLUSIONS

Compared to val monotherapy, sac/val was more effective in reducing proteinuria, renal ultrastructure and tubular injury in a clinically relevant animal model of early DN. More importantly, these renoprotective effects were independent of improvements in blood pressure, glycemia and nitroso-oxidative stress. These novel findings warrant future clinical investigations designed to test whether sac/val may offer renoprotection in the setting of DN.

Glycemic control by the SGLT2 inhibitor empagliflozin decreases aortic stiffness, renal resistivity index and kidney injury

Background

Arterial stiffness is emerging as an independent risk factor for the development of chronic kidney disease. The sodium glucose co-transporter 2 (SGLT2) inhibitors, which lower serum glucose by inhibiting SGLT2-mediated glucose reabsorption in renal proximal tubules, have shown promise in reducing arterial stiffness and the risk of cardiovascular and kidney disease in individuals with type 2 diabetes mellitus. Since hyperglycemia contributes to arterial stiffness, we hypothesized that the SGLT2 inhibitor empagliflozin (EMPA) would improve endothelial function, reduce aortic stiffness, and attenuate kidney disease by lowering hyperglycemia in type 2 diabetic female mice (db/db).

Materials/methods

Ten-week-old female wild-type control (C57BLKS/J) and db/db (BKS.Cg-Dock7m+/+Leprdb/J) mice were divided into three groups: lean untreated controls (CkC, n = 17), untreated db/db (DbC, n = 19) and EMPA-treated db/db mice (DbE, n = 19). EMPA was mixed with normal mouse chow at a concentration to deliver 10 mg kg⁻¹ day⁻¹, and fed for 5 weeks, initiated at 11 weeks of age.

Results

Compared to CkC, DbC showed increased glucose levels, blood pressure, aortic and endothelial cell stiffness, and impaired endothelium-dependent vasorelaxation. Furthermore, DbC exhibited impaired activation of endothelial nitric oxide synthase, increased renal resistivity and pulsatility indexes, enhanced renal expression of advanced glycation end products, and periarterial and tubulointerstitial fibrosis. EMPA promoted glycosuria and blunted these vascular and renal impairments, without affecting increases in blood pressure. In addition, expression of “reversion inducing cysteine rich protein with Kazal motifs” (RECK), an anti-fibrotic mediator, was significantly suppressed in DbC kidneys and partially restored by EMPA. Confirming the in vivo data, EMPA reversed high glucose-induced RECK suppression in human proximal tubule cells.

Conclusions

Empagliflozin ameliorates kidney injury in type 2 diabetic female mice by promoting glycosuria, and possibly by reducing systemic and renal artery stiffness, and reversing RECK suppression.

Dipeptidyl Peptidase-4 Inhibition With Saxagliptin Ameliorates Angiotensin II-Induced Cardiac Diastolic Dysfunction in Male Mice

Activation of the renin-angiotensin-aldosterone system is common in hypertension and obesity and contributes to cardiac diastolic dysfunction, a condition for which no treatment currently exists. In light of recent reports that antihyperglycemia incretin enhancing dipeptidyl peptidase (DPP)-4 inhibitors exert cardioprotective effects, we examined the hypothesis that DPP-4 inhibition with saxagliptin (Saxa) attenuates angiotensin II (Ang II)-induced cardiac diastolic dysfunction. Male C57BL/6J mice were infused with either Ang II (500 ng/kg/min) or vehicle for 3 weeks receiving either Saxa (10 mg/kg/d) or placebo during the final 2 weeks. Echocardiography revealed Ang II-induced diastolic dysfunction, evidenced by impaired septal wall motion and prolonged isovolumic relaxation, coincident with aortic stiffening. Ang II induced cardiac hypertrophy, coronary periarterial fibrosis, TRAF3-interacting protein 2 (TRAF3IP2)-dependent proinflammatory signaling [p-p65, p-c-Jun, interleukin (IL)-17, IL-18] associated with increased cardiac macrophage, but not T cell, gene expression. Flow cytometry revealed Ang II-induced increases of cardiac CD45+F4/80+CD11b+ and CD45+F4/80+CD11c+ macrophages and CD45+CD4+ lymphocytes. Treatment with Saxa reduced plasma DPP-4 activity and abrogated Ang II-induced cardiac diastolic dysfunction independent of aortic stiffening or blood pressure. Furthermore, Saxa attenuated Ang II-induced periarterial fibrosis and cardiac inflammation, but not hypertrophy or cardiac macrophage infiltration. Analysis of Saxa-induced changes in cardiac leukocytes revealed Saxa-dependent reduction of the Ang II-mediated increase of cardiac CD11c messenger RNA and increased cardiac CD8 gene expression and memory CD45+CD8+CD44+ lymphocytes. In summary, these results demonstrate that DPP-4 inhibition with Saxa prevents Ang II-induced cardiac diastolic dysfunction, fibrosis, and inflammation associated with unique shifts in CD11c-expressing leukocytes and CD8+ lymphocytes.

Abstract P475: What’s in a Letter: N vs. J Determines Responses to Ang II/DOCA and DPP4 Gene Deletion

Activation of the renin-angiotensin-aldosterone system (RAAS) drives blood pressure (BP) responses and kidney injury in humans and rodent models. Previously, we reported activation of dipeptidyl peptidase 4 (DPP4) by RAAS which may play an important role in BP responses and kidney injury. Classically, either angiotensin II (Ang II) or deoxycorticosterone (DOCA)-salt administration to mice, raises their BP over a period of hours to days. Recently, the two have been combined to elicit more robust kidney injury and proteinuria. Although there are not many head to head comparison studies, it is known through historical association that different strains of mice have different baseline BPs and vary in their response to vasoconstrictor agents for BP peaks as well as associated kidney injury. In this regard, the C57Bl/6J and C57Bl/6N mice are genetically very similar although they differ with respect to their responses to circadian rhythm on salt sensitivity to BP. Therefore, we hypothesized that J versus N strain will have differential BP responses to Ang II/DOCA and kidney injury susceptibility. C57Bl/6 J and N mice ( DPP4 +/+ and DPP4 -/- ) were subjected to Ang II/DOCA salt infusion for 2 weeks (Ang II 1000ng/kg/min via miniosmotic pumps, DOCA 50mg pellet, 0.9% saline in drinking water) and compared to mice receiving saline only (osmotic pumps). BP was measured by Millar catheter. Kidney injury was quantified via albuminuria and histology. While the Ang II/DOCA treated J strain had mean BP (MBP) of 135mmHg, the Ang II/DOCA treated N strain had MBP of 125mmHg. There was no effect of DPP4 gene deletion on BP in either strain. The J strain treated with Ang II/DOCA salt had higher albuminuria when compared to the N strain (180ug/ml vs. 60ug/ml). DPP4 -/- mice on the J strain receiving Ang II/DOCA had a relative improvement in albuminuria (120ug/ml vs. 180ug/ml). Surprisingly, the DPP4 -/- mice on the N strain had higher albuminuria when compared to the DPP4 +/+ mice receiving Ang II/DOCA (143ug/ml vs. 60ug/ml). Taken together, our results suggest that mice strain plays an important role in BP and kidney injury responses to Ang II/DOCA and DPP4 gene deletion. These results highlight the importance of selecting patient populations carefully to maximize the benefit of DPP4 inhibitors.

Uric acid promotes vascular stiffness, maladaptive inflammatory responses and proteinuria in western diet fed mice

OBJECTIVE

Aortic vascular stiffness has been implicated in the development of cardiovascular disease (CVD) and chronic kidney disease (CKD) in obese individuals. However, the mechanism promoting these adverse effects are unclear. In this context, promotion of obesity through consumption of a western diet (WD) high in fat and fructose leads to excess circulating uric acid. There is accumulating data implicating elevated uric acid in the promotion of CVD and CKD. Accordingly, we hypothesized that xanthine oxidase(XO) inhibition with allopurinol would prevent a rise in vascular stiffness and proteinuria in a translationally relevant model of WD-induced obesity.

MATERIALS/METHODS

Four-week-old C57BL6/J male mice were fed a WD with excess fat (46%) and fructose (17.5%) with or without allopurinol (125mg/L in drinking water) for 16weeks. Aortic endothelial and extracellular matrix/vascular smooth muscle stiffness was evaluated by atomic force microscopy. Aortic XO activity, 3-nitrotyrosine (3-NT) and aortic endothelial sodium channel (EnNaC) expression were evaluated along with aortic expression of inflammatory markers. In the kidney, expression of toll like receptor 4 (TLR4) and fibronectin were assessed along with evaluation of proteinuria.

RESULTS

XO inhibition significantly attenuated WD-induced increases in plasma uric acid, vascular XO activity and oxidative stress, in concert with reductions in proteinuria. Further, XO inhibition prevented WD-induced increases in aortic EnNaC expression and associated endothelial and subendothelial stiffness. XO inhibition also reduced vascular pro-inflammatory and maladaptive immune responses induced by consumption of a WD. XO inhibition also decreased WD-induced increases in renal TLR4 and fibronectin that associated proteinuria.

CONCLUSIONS

Consumption of a WD leads to elevations in plasma uric acid, increased vascular XO activity, oxidative stress, vascular stiffness, and proteinuria all of which are attenuated with allopurinol administration.

Amiloride Improves Endothelial Function and Reduces Vascular Stiffness in Female Mice Fed a Western Diet

Obese premenopausal women lose their sex related cardiovascular disease protection and develop greater arterial stiffening than age matched men. In female mice, we have shown that consumption of a Western diet (WD), high in fat and refined sugars, is associated with endothelial dysfunction and vascular stiffening, which occur via activation of mineralocorticoid receptors and associated increases in epithelial Na⁺ channel (ENaC) activity on endothelial cells (EnNaC). Herein our aim was to determine the effect that reducing EnNaC activity with a very-low-dose of amiloride would have on decreasing endothelial and arterial stiffness in young female mice consuming a WD. To this end, we fed female mice either a WD or control diet and treated them with or without a very-low-dose of the ENaC-inhibitor amiloride (1 mg/kg/day) in the drinking water for 20 weeks beginning at 4 weeks of age. Mice consuming a WD were heavier and had greater percent body fat, proteinuria, and aortic stiffness as assessed by pulse-wave velocity than those fed control diet. Treatment with amiloride did not affect body weight, body composition, blood pressure, urinary sodium excretion, or insulin sensitivity, but significantly reduced the development of endothelial and aortic stiffness, aortic fibrosis, aortic oxidative stress, and mesenteric resistance artery EnNaC abundance and proteinuria in WD-fed mice. Amiloride also improved endothelial-dependent vasodilatory responses in the resistance arteries of WD-fed mice. These results indicate that a very-low-dose of amiloride, not affecting blood pressure, is sufficient to improve endothelial function and reduce aortic stiffness in female mice fed a WD, and suggest that EnNaC-inhibition may be sufficient to ameliorate the pathological vascular stiffening effects of WD-induced obesity in females.

Diabetes, hypertension, and chronic kidney disease progression: role of DPP4

The protein dipeptidyl peptidase 4 (DPP4) is a target in diabetes management and reduction of associated cardiovascular risk. Inhibition of the enzymatic function and genetic deletion of DPP4 is associated with tremendous benefits to the heart, vasculature, adipose tissue, and the kidney in rodent models of obesity, diabetes and hypertension, and associated complications. The recently concluded, "Saxagliptin Assessment of Vascular Outcomes Recorded in Patients with Diabetes Mellitus-Thrombolysis in Myocardial Infarction 53" trial revealed a reduction in proteinuria in chronic kidney disease patients (stages 1-3). These results have spurred immense interest in the nonenzymatic and enzymatic role of DPP4 in the kidney. DPP4 is expressed predominantly in the glomeruli and S1-S3 segments of the nephron and to a lesser extent in other segments. DPP4 is known to facilitate absorption of cleaved dipeptides and regulate the function of the sodium/hydrogen exchanger-3 in the proximal tubules. DPP4, also known as CD26, has an important role in costimulation of lymphocytes via caveolin-1 on antigen-presenting cells in peripheral blood. Herein, we present our perspectives for the ongoing interest in the role of DPP4 in the kidney.

mTORC1 inhibitors rapamycin and metformin affect cardiovascular markers differentially in ZDF rats

Mammalian target for rapamycin complex 1 (mTORC1) is a common target for the action of immunosuppressant macrolide rapamycin and glucose-lowering metformin. Inhibition of mTORC1 can exert both beneficial and detrimental effects in different pathologies. Here, we investigated the differential effects of rapamycin (1.2 mg/kg per day delivered subcutaneously for 6 weeks) and metformin (300 mg/kg per day delivered orally for 11 weeks) treatments on male Zucker diabetic fatty (ZDF) rats that mimic the cardiorenal pathology of type 2 diabetic patients and progress to insulin insufficiency. Rapamycin and metformin improved proteinuria, and rapamycin also reduced urinary gamma glutamyl transferase (GGT) indicating improvement of tubular health. Metformin reduced food and water intake, and urinary sodium and potassium, whereas rapamycin increased urinary sodium. Metformin reduced plasma alkaline phosphatase, but induced transaminitis as evidenced by significant increases in plasma AST and ALT. Metformin also induced hyperinsulinemia, but did not suppress fasting plasma glucose after ZDF rats reached 17 weeks of age, and worsened lipid profile. Rapamycin also induced mild transaminitis. Additionally, both rapamycin and metformin increased plasma uric acid and creatinine, biomarkers for cardiovascular and renal disease. These observations define how rapamycin and metformin differentially modulate metabolic profiles that regulate cardiorenal pathology in conditions of severe type 2 diabetes.

Abstract 059: Kidney Specific DPP4 Knockdown Prevents Ang II/DOCA Salt Injury and Proteinuria

Dipeptidyl peptidase 4 (DPP4) inhibition is widely used for glycemic control in type 2 diabetes mellitus (T2DM) subjects. The Saxagliptin Assessment of Vascular Outcomes Recorded in Patients with Diabetes Mellitus - Thrombolysis in Myocardial Infarction 53 (SAVOR-TIMI 53) trial showed that DPP4 inhibition improves proteinuria in type 2 DM (T2DM) subjects with chronic kidney disease (CKD). Our lab and others have observed that kidney DPP4 activation is associated with proteinuria in conditions of RAAS activation including obesity. However, it is not clear if kidney specific DPP4 directly plays a role in kidney injury. To test our hypothesis, right nephrectomy (UNx) mice were subjected to 1) sham surgery 2) left renal vein injection with lentivirus carrying DPP4 shRNA (UNx+DPP4) 3) scramble shRNA (UNx+SCRM) and the animals were allowed to recover for 2-3 wks. A 4 th group of non-UNx mice were added as additional controls. Next, angiotensin II (Ang II, 1000ng/kg/min) plus deoxycorticosterone (DOCA, 50mg) plus 0.9% NaCl (salt) or saline only was given for 2 wks. Ang II/DOCA salt caused heart hypertrophy in all groups when compared to saline infusion (p<0.05). DPP4 knockdown reduced albuminuria (UNx+Ang II/DOCA salt, 80.18±15.3 ug/mg Crt; UNx+DPP4+Ang II/DOCA salt, 25.76±19.3 ug/mg Crt; UNx+SCRM+Ang II/DOCA salt 100.1±17.6 ug/mg Crt, p<0.05). Flow cytometry analysis showed that DPP4 knockdown mitigated activation of CD4+ T cells by Ang II/DOCA salt as indicated by reduced surface expression of DPP4 on CD4+, CD44+CD127+ central memory and CD44+CD127- effector cells. In addition, DPP4 knockdown prevented Ang II/DOCA salt-mediated infiltration of Ly6ChiCD11bhiF4/80lo macrophages and decreased the Ly6C-CD11bloF4/80hi resident dendritic cells. DPP4 knockdown suppressed Ang II/DOCA salt mediated activation of pro-fibrotic markers, Col1A and CTGF. Lastly, DPP4 knockdown suppressed glomerulomegaly, mesangial expansion and interstitial inflammation on trichrome stain. In summary, RAAS activation is a prominent mechanism for kidney injury in T2DM and obese subjects. Kidney DPP4 is an important effector of RAAS mediated kidney inflammation, activation of pro-fibrotic markers and proteinuria, thereby implicating DPP4 in CKD initiation and progression.

Reliable and High Efficiency Extraction of Kidney Immune Cells

Immune system activation occurs in multiple kidney diseases and pathophysiological processes. The immune system consists of both adaptive and innate components and multiple cell types. Sometimes, the cell type of interest is present in very low numbers among the large numbers of total cells isolated from the kidney. Hence, reliable and efficient isolation of kidney mononuclear cell populations is important in order to study the immunological problems associated with kidney diseases. Traditionally, tissue isolation of kidney mononuclear cells have been performed via enzymatic digestions using different varieties and strengths of collagenases/DNAses yielding varying numbers of viable immune cells. Recently, with the development of the mechanical tissue disruptors for single cell isolation, the collagenase digestion step is avoided and replaced by a simple mechanical disruption of the kidneys after extraction from the mouse. Herein, we demonstrate a simple yet efficient method for the isolation of kidney mononuclear cells for every day immune cell extractions. We further demonstrate an example of subset analysis of immune cells in the kidney. Importantly, this technique can be adapted to other soft and non-fibrous tissues such as the liver and brain.

Abstract P233: Sodium Glucose Transporter Type-2 (SGLT-2) Inhibitor, Empagliflozin, Improves Cardiovascular Outcomes in Female Diabetic db/db Mice Independent of Blood Pressure Reduction

Dysglycemia, proteinuria, vascular stiffness, diastolic dysfunction (DD) and hypertension are abnormalities seen more frequently in the obese, diabetic population. SGLT-2 inhibitors (SGLT-2i), which increase urinary glucose/sodium excretion to lower HbA1c and blood pressure (BP), are emerging as unique diabetes therapies. We examined whether the SGLT-2i, empagliflozin (EMPA), ameliorates hypertension, dysglycemia, proteinuria, aortic stiffness and DD in obese/diabetic female db/db mice. Eleven week old mice were fed a diet with or without EMPA (10mg/kg/day) for 5 weeks. In vivo blood pressure (telemetry), diastolic function (echo), aortic stiffness (pulse wave velocity, PWV), proteinuria, renal resistivity (echo) and HbA1c were evaluated. Db/db had elevated BP that was not affected by SGLT2i. HbA1c, proteinuria and the renal resistivity index (RI) were elevated (P<0.001) in control (Db) mice vs treated mice (Db-EMPA) and lean control mice. Db exhibited DD that was ameliorated by SGLT2i as indicated by reduced LV filling pressure (<E/E’) and improved septal wall motion (E’/A’ ratio, not shown). Elevated PWV and aortic endothelial cell stiffness in Db-C were abrogated with SGLT2i. These results show that SGLT2i confers BP-independent cardiovascular and renal protective effects in obese diabetic female mice.

Abstract P213: Western Diet May Modulate Kidney Injury and Albuminuria Differentially in Female Mice Deficient in Mr in the Endothelium versus the Smooth Muscle

Activation of the mineralocorticoid receptor (MR) has been implicated in kidney injury and precipitation of proteinuria. In this regard, diet induced obesity (DIO), a condition of MR activation is characterized by increase in kidney injury and proteinuria. DIO and other conditions of MR activation also manifest vascular dysfunction that may play a role in kidney injury and proteinuria. Vascular dysfunction may be endothelial or smooth muscle mediated. Moreover, MR signaling in the endothelium versus smooth muscle may be important in vascular function. Data from the Jaffe lab and our preliminary data show that deficiency of smooth muscle and endothelial MR plays a protective role from vascular dysfunction such as increased pulse wave velocity and stiffness. However, the role of endothelial specific versus smooth muscle specific MR in kidney injury and proteinuria is not known. Hence, we hypothesized that deficiency of endothelial and smooth muscle specific MRs (ECMRKO and SMMRKO) will protect the mice from Western diet-fed (high fat/high sucrose, WD) kidney injury and proteinuria. We fed female ECMRKO/SMMRKO and their littermate controls WD for 16wks and collected urine and performed imaging, molecular and morphological analyses. We observed significantly less proteinuria in the ECMRKO mice fed WD when compared to their littermates (2.4mg/mg vs. 3.5mg/mg creatinine) (p<0.05), however there was no change in the SMMRKO mice fed a WD when compared to their littermates. Furthermore, we observed significantly less impairment in aortic/renal pulse wave velocity and stiffness in both the ECMRKO/SMMRKO models. Western blots showed that there was a tendency to suppression of MR protein in the ECMRKO on WD. This suppression of MR expression was contemporaneously observed with decreased phosphorylation of ribosomal protein S6 along with reduction in membrane localization suggesting endothelial MR may regulate S6 activation. In summary, our study suggests endothelial specific MR may mediate kidney injury in conditions of MR activation and a lesser role for smooth muscle specific MR.

Abstract P199: Uric Acid Promotes Vascular Stiffness, Immune Inflammatory Response and Proteinuria in Western Diet Fed Mice

Increased consumption of a diet high in fructose and fat (western diet, WD) is associated with an increase in cardiovascular disease (CVD) and kidney injury. In this regard, excess hepatic production of uric acid generated from excess fructose consumption is emerging as a risk factor for vascular stiffness, which underpins CVD and kidney injury. We hypothesized that a WD would increase uric acid levels and cardiovascular and renal xanthine oxidase (XO) activity and associated increased vascular stiffness and proteinuria. Furthermore, we proposed that inhibition of XO activity would prevent arterial stiffening and reduce proteinuria in a clinically relevant model of WD-induced CVD and renal injury. Four week-old C57BL6/J male mice were fed a WD containing high fat (46%), sucrose (17.5%), and high fructose corn syrup (17.5%) with or without allopurinol (125mg/L), a potent XO inhibitor for 16 weeks. XO inhibition significantly attenuated WD-induced increases in plasma and urine uric acid levels and aortic XO activity (WD, 0.225 + 0.031 mU/mL WD + allopurinol, 0.097+ 0.026mU/mL, P<0.05), as well as proteinuria (WD, 20.92 + 2.66 mg/ mg creatinine, WD + allopurinol, 13.48 + 1.56 mg/mg creatinine, P<0.05). XO inhibition had no effect on increases in body weight, fat mass, and HOMA-IR promoted by the WD. Blood pressure was not different between any of the groups. Stiffness of aortic endothelial cells, extracellular matrix and vascular smooth muscle cells, as determined by atomic force microscopy, was significantly increased in WD mice and this was prevented by XO inhibition. WD induced a significant macrophage pro-inflammatory response in aorta that was significantly suppressed by XO inhibition. Collectively, these findings support the notion that increased XO activity in the vasculature and kidney and increased hepatic production of uric acid secondary to consumption of a WD promotes vascular stiffness, vascular inflammation and a maladaptive immune response that lead to vascular stiffness and kidney injury.

Dipeptidyl peptidase-4 inhibition ameliorates Western diet-induced hepatic steatosis and insulin resistance through hepatic lipid remodeling and modulation of hepatic mitochondrial function

Novel therapies are needed for treating the increasing prevalence of hepatic steatosis in Western populations. In this regard, dipeptidyl peptidase-4 (DPP-4) inhibitors have recently been reported to attenuate the development of hepatic steatosis, but the potential mechanisms remain poorly defined. In the current study, 4-week-old C57Bl/6 mice were fed a high-fat/high-fructose Western diet (WD) or a WD containing the DPP-4 inhibitor, MK0626, for 16 weeks. The DPP-4 inhibitor prevented WD-induced hepatic steatosis and reduced hepatic insulin resistance by enhancing insulin suppression of hepatic glucose output. WD-induced accumulation of hepatic triacylglycerol (TAG) and diacylglycerol (DAG) content was significantly attenuated with DPP-4 inhibitor treatment. In addition, MK0626 significantly reduced mitochondrial incomplete palmitate oxidation and increased indices of pyruvate dehydrogenase activity, TCA cycle flux, and hepatic TAG secretion. Furthermore, DPP-4 inhibition rescued WD-induced decreases in hepatic PGC-1α and CPT-1 mRNA expression and hepatic Sirt1 protein content. Moreover, plasma uric acid levels in mice fed the WD were decreased after MK0626 treatment. These studies suggest that DPP-4 inhibition ameliorates hepatic steatosis and insulin resistance by suppressing hepatic TAG and DAG accumulation through enhanced mitochondrial carbohydrate utilization and hepatic TAG secretion/export with a concomitant reduction of uric acid production.

Mineralocorticoid receptor blockade prevents Western diet-induced diastolic dysfunction in female mice

Overnutrition/obesity predisposes individuals, particularly women, to diastolic dysfunction (DD), an independent predictor of future cardiovascular disease. We examined whether low-dose spironolactone (Sp) prevents DD associated with consumption of a Western Diet (WD) high in fat, fructose, and sucrose. Female C57BL6J mice were fed a WD with or without Sp (1 mg·kg(-1)·day(-1)). After 4 mo on the WD, mice exhibited increased body weight and visceral fat, but similar blood pressures, compared with control diet-fed mice. Sp prevented the development of WD-induced DD, as indicated by decreased isovolumic relaxation time and an improvement in myocardial performance (<Tei index) and septal annular velocity (<E'-to-A' ratio), as assessed by echocardiography, as well as decreased diastolic relaxation time/increased diastolic initial filling rate, as assessed by MRI. The relationship between passive sarcomere length of cardiac myocytes and ventricular pressure was monitored using di-8-ANEPPS staining of the t-tubule network in hearts ex vivo. Sp administration led to longer sarcomere lengths at each pressure indicative of improved ventricular compliance in WD-fed mice. Sp also prevented left ventricular hypertrophy, interstitial fibrosis, and oxidative stress. Sp prevented the WD-induced increased expression of myocardial proinflammatory M1 macrophage markers monocyte chemoattractant protein-1 and CD11c and increased the expression of the anti-inflammatory M2 macrophage marker CD206. These findings demonstrate that WD-induced DD is associated with increased oxidant stress, fibrosis, and immune dysregulation. Mineralocorticoid receptor antagonism enhanced M2 macrophage polarization and ameliorated oxidant stress and fibrosis. This work supports a novel blood pressure-independent effect of MR antagonism as a strategy to prevent diet-induced DD in women. Mineralocorticoid antagonism; low-dose spironolactone; aldosterone;high-fat diet; high-fructose diet; oxidative stress; inflammation; cardiac hypertrophy; myocardial compliance.

DPP4 inhibition attenuates filtration barrier injury and oxidant stress in the zucker obese rat

OBJECTIVE

Obesity-related glomerulopathy is characterized initially by glomerular hyperfiltration with hypertrophy and then development of proteinuria. Putative mechanisms include endothelial dysfunction and filtration barrier injury due to oxidant stress and immune activation. There has been recent interest in targeting dipeptidyl peptidase 4 (DPP4) enzyme due to increasing role in non-enzymatic cellular processes.

METHODS

The Zucker obese (ZO) rat (aged 8 weeks) fed a normal chow or diet containing the DPP4 inhibitor linagliptin for 8 weeks (83 mg/kg rat chow) was utilized.

RESULTS

Compared to lean controls, there were increases in plasma DPP4 activity along with proteinuria in ZO rats. ZO rats further displayed increases in glomerular size and podocyte foot process effacement. These findings occurred in parallel with decreased endothelial stromal-derived factor-1α (SDF-1α), increased oxidant markers, and tyrosine phosphorylation of nephrin and serine phosphorylation of the mammalian target of rapamycin (mTOR). DPP4 inhibition improved proteinuria along with filtration barrier remodeling, circulating and kidney tissue DPP4 activity, increased active glucagon like peptide-1 (GLP-1) as well as SDF-1α, and improved oxidant markers and the podocyte-specific protein nephrin.

CONCLUSIONS

These data support a role for DPP4 in glomerular filtration function and targeting DPP4 with inhibition improves oxidant stress-related glomerulopathy and associated proteinuria.

Abstract 200: Low Dose Spironolactone Treatment Prevents Cardiac Diastolic Dysfunction, Oxidant Stress and Fibrosis in a Female Model of Obesity in Concert with a Modulation of Inflammation

Obesity is a global epidemic with 1.5 billion overweight or obese people worldwide. The association of obesity and a high-fat/high-fructose Western diet (WD) markedly increases cardiovascular disease (CVD) particularly diastolic dysfunction in women. Few treatments exist for diastolic heart disease but, recent work implicates the mineralocorticoid receptor (MR) in inflammation, fibrosis and oxidant stress. We thus hypothesized that low-dose spironolactone (LDSp) could prevent diastolic dysfunction by reducing fibrosis, oxidant stress and inflammation. To test this hypothesis, we developed a female model of obesity induced diastolic dysfunction and examined preventative treatment with LDSp.

Four week-old C57BL6/J female mice were fed a WD with/without 1.0mg/kg/day of Sp (n=7 for each group). This dose of LDSp exerts no effect on blood pressure. After 16 weeks, we conducted detailed phenotypic analysis and assessed diastolic function by cardiac MRI. Immunohistochemistry was also done for cardiac oxidant stress, fibrosis, collagen content and insulin receptor (IRS-1) expression. Flow cytometry of heart tissue was utilized to examine inflammatory mechanisms.

We found WD feeding caused diastolic dysfunction that was prevented by LDSp (LV diastolic relaxation time 33.4 ± 1.2ms for WD, 20.6 ± 1.5ms for control and 24.3 ± 0.9ms for WD+LDSp, p <0.01). 3-nitrotyrosine staining showed significant cardiac oxidant stress with WD feeding that was ameliorated by LDSp. Cardiac fibrosis and the collagen 1:3 ratio were markedly increased with WD but prevented by LDSp. IRS-1 expression and phosphorylation were markedly reduced by WD feeding but not improved by LDSp. Flow cytometry showed evidence towards reduced M2 macrophage polarization with lower CD11b/CD301 double positive cells in WD fed hearts with trend toward improvement with LDSp.

These findings suggest WD induces cardiac diastolic dysfunction in females by increasing oxidant stress and fibrosis potentially mediated by deficiency in anti-inflammatory M2 macrophages. MR antagonism with spironolactone may prevent the decrease in M2 macrophage polarization reducing oxidant stress and fibrosis. This work supports a novel mechanism for spironolactone in treatment of WD induced heart disease.

Abstract 030: Dpp4 Inhibition Substantially Reverses Ang II-mediated Inflammation And Kidney Injury Independent Of BP Reduction

Objectives: DPP4 is thought to play an important role in co-stimulation of T-lymphocytes and activation of DPP4 is thought to play a role in hypertension both via degradation of glucagon like peptide-1 (GLP-1) and via direct mechanisms. However, the triggers for DPP4 activation in hypertension are largely unknown except for one study showing insulin-mediated release of DPP4 from adipocytes. Recently, our lab demonstrated increased DPP4 activity in the plasma and kidney tissue of a Western diet-fed C57Bl/6 mouse that had elevated BP, proteinuria and inflammation with M2 to M1 macrophage polarization. In the same model, we observed activation of kidney renin-angiotensin system (unpublished data). Additionally, we observed that Ang II (angiotensin II) is able to increase DPP4 activity in proximal tubule cells in vitro (PTCs, (unpublished data). Therefore, we hypothesized that Ang II activation of DPP4 in mice will lead to inflammation in the kidney and albuminuria.

Methods: Pressor dose Ang II (1000ng/kg/min) was infused into C57Bl/6 mice for 3 wks and BP was measured in conscious mice by radiotelemetry. Kidney tissue was analyzed via DPP4 activity assay, FACS, Western Blot, light and electron microscopy.

Results: Ang II infused mice were characterized by elevated BP and albuminuria (4.5 fold) concomitant with mesangial widening and PTC injury. We also observed an increase in CD4+CD44 high CD62L low (1.5 fold), decrease in CD4+FoxP3 (1.5 fold) concomitant with increased expression of DPP4 on CD3+CD4+ T-cells. Saxagliptin (10mg/kg/day) administered in peanut butter starting at 1 wk after Ang II, decreased DPP4 activity (~50%) in the plasma and kidney tissue. Saxagliptin had no effect on BP and albuminuria although there was amelioration of mesangial widening and PTC injury. Saxagliptin also mitigated DPP4 expression on CD3+CD4+ T-cells and reversed the changes in memory T-cells and Tregs.

Conclusions: Ang II mediates BP increase and albuminuria via modulation of adaptive immunity which in turn may be regulated by DPP4. Saxagliptin reverses DPP4-mediated modulation of adaptive immunity and ameliorates kidney injury partially although it is unable to reverse established increases in BP and albuminuria.

Prevention of obesity-induced renal injury in male mice by DPP4 inhibition

Therapies to prevent renal injury in obese hypertensive individuals are being actively sought due to the obesity epidemic arising from the Western diet (WD), which is high in fructose and fat. Recently, activation of the immune system and hyperuricemia, observed with high fructose intake, have been linked to the pathophysiology of hypertension and renal injury. Because dipeptidyl peptidase 4 (DPP4) is a driver of maladaptive T-cell/macrophage responses, renal-protective benefits of DPP4 inhibition in the WD-fed mice were examined. Mice fed a WD for 16 weeks were given the DPP4 inhibitor MK0626 in their diet beginning at 4 weeks of age. WD-fed mice were obese, hypertensive, and insulin-resistant and manifested proteinuria and increased plasma DPP4 activity and uric acid levels. WD-fed mice also had elevated kidney DPP4 activity and monocyte chemoattractant protein-1 and IL-12 levels and suppressed IL-10 levels in the kidney, suggesting macrophage-driven inflammation, glomerular and tubulointerstitial injury. WD-induced increases in DPP4 activation in the plasma and kidney and proteinuria in WD mice were abrogated by MK0626, although blood pressure and systemic insulin sensitivity were not improved. Contemporaneously, MK0626 reduced serum uric acid levels, renal oxidative stress, and IL-12 levels and increased IL-10 levels, suggesting that suppression of DPP4 activity leads to suppression of renal immune/inflammatory injury responses to a WD. Taken together, these results demonstrate that DPP4 inhibition prevents high-fructose/high-fat diet-induced glomerular and tubular injury independent of blood pressure/insulin sensitivity and offers a potentially novel therapy for diabetic and obesity-related kidney disease.

Is there a role for the incretin system in blood pressure regulation?

Incretin-based therapies are now well established for diabetes management and are among the frontline agents for control of hyperglycemia. In addition to their antihyperglycemic effects, evidence is emerging on the role of these agents on blood pressure regulation, cardioprotective and renoprotective properties. Because of the pleiotropic nature of these affects, these agents could offer significant benefits with regards to the cardiorenal metabolic complications that are part of the diabetes and obesity epidemic in the United States and worldwide. We review the various known mechanisms or pathways by which incretin based therapy exerts its regulation of blood pressure with emphasis on novel mechanisms such as inflammation/immunomodulation and oxidative stress.

The role of tissue Renin-Angiotensin-aldosterone system in the development of endothelial dysfunction and arterial stiffness

Epidemiological studies support the notion that arterial stiffness is an independent predictor of adverse cardiovascular events contributing significantly to systolic hypertension, impaired ventricular-arterial coupling and diastolic dysfunction, impairment in myocardial oxygen supply and demand, and progression of kidney disease. Although arterial stiffness is associated with aging, it is accelerated in the presence of obesity and diabetes. The prevalence of arterial stiffness parallels the increase of obesity that is occurring in epidemic proportions and is partly driven by a sedentary life style and consumption of a high fructose, high salt, and high fat western diet. Although the underlying mechanisms and mediators of arterial stiffness are not well understood, accumulating evidence supports the role of insulin resistance and endothelial dysfunction. The local tissue renin-angiotensin-aldosterone system (RAAS) in the vascular tissue and immune cells and perivascular adipose tissue is recognized as an important element involved in endothelial dysfunction which contributes significantly to arterial stiffness. Activation of vascular RAAS is seen in humans and animal models of obesity and diabetes, and associated with enhanced oxidative stress and inflammation in the vascular tissue. The cross talk between angiotensin and aldosterone underscores the importance of mineralocorticoid receptors in modulation of insulin resistance, decreased bioavailability of nitric oxide, endothelial dysfunction, and arterial stiffness. In addition, both innate and adaptive immunity are involved in this local tissue activation of RAAS. In this review we will attempt to present a unifying mechanism of how environmental and immunological factors are involved in this local tissue RAAS activation, and the role of this process in the development of endothelial dysfunction and arterial stiffness and targeting tissue RAAS activation.

Resistance to insulin and kidney disease in the cardiorenal metabolic syndrome; role for angiotensin II

The presence of insulin resistance is increasingly recognized as an important contributor to early stage kidney disease independent of the contribution of diabetes. Important in this relationship is the strong correlation between hyperinsulinemia and low levels of albuminuria (e.g. microalbuminuria). Recent work highlight mechanisms for glomerular/tubulointerstitial injury with excess insulin and emerging evidence identifies a unique role for insulin metabolic signaling and altered handling of salt reabsorption at the level of the proximal tubule. Evidence is also emerging for the role of insulin signaling in the glomerulus both epithelial and endothelial. Central to the mechanism of injury is inappropriate activation of the RAAS.

Abstract 391: Enhanced Coronary Vasoconstriction in Western Diet-Induced Obesity is Associated with Alterations in NHE1, SERCA2a and 3

Cardiovascular disease (CVD) remains a major risk factor and cause of mortality in type 2 diabetes but, the effect of western diet (WD) on coronary artery vasoconstriction has not been well characterized. Therefore, the purpose of this study was to identify potential calcium (Ca 2+ ) molecular mechanism(s) underlying alterations in coronary constriction in WD-induced obesity. C57Bl/6J mice were fed a WD or control diet for 16wks. Coronary vascular function was assessed with wire myography and human coronary vascular smooth muscle cells (VSMC) were cultured. WD enhanced coronary constriction to the thromboxane analog U46619. This was associated with increased coronary VSMC expression of sodium-hydrogen exchanger 1 (NHE1) and SERCA3 with decreased expression of SERCA2a. Oxidation of SERCA2a cysteine-674, a signal for SERCA2a degradation, was increased in WD coronary VSMC. Exposure of cultured human coronary VSMC to hyperinsulinemic conditions elicited similar changes in SERCA2a, 3 and NHE1. This study suggests that enhanced thromboxane-mediated coronary constriction in WD and insulin resistance/hyperinsulinemia may result from NHE1-dependent changes in intracellular pH and/or impaired Ca 2+ handling at the level of the sarcoplasmic reticulum.

Abstract 371: DPPIV Inhibitor MK0626 Prevents Western Diet Induced Renal Injury via Suppression of Kidney Tissue Ras

Objectives: Obesity is an independent risk factor for development and progression of renal injury. High fructose corn syrup consumption has coincided with the obesity epidemic in the United States. High fructose (60%) diets have been demonstrated to be associated with elevation in BP and worsening insulin resistance along with renal injury via increased hepatic production of uric acid. Recently, DPPIV inhibitors have been shown to improve diabetic changes and sodium excretion, effects that are beyond glycemic control. Therefore, the renal protective benefits of DPPIV inhibition in a clinically relevant Western diet fed mouse model were examined.

Methods: Mice fed a high fat/high fructose (WD) diet for 16 weeks and given a DPPIV inhibitor MK0626 in their diet were examined for metabolic parameters, inflammation, kidney renin-angiotensin system (RAS) and oxidative stress. Renal injury was assessed by biochemical, immunohistological and electron microscopy techniques. In vitro , angiotensin II (Ang II) effects on OKP-PTCs were assessed for mechanism.

Results: MK0626 ameliorated WD-induced increases in serum uric acid, oxidative stress and RAS. WD induced suppression of IL-10 was reversed by MK0626. There was a tendency to improve HOMA-IR by MK0626 but no effect on BP and body weights. Diet induced DPPIV activation in the plasma and kidney of WD mice was abrogated by MK0626 (~80%). WD mice were characterized by increased proteinuria (~3-fold), mesangial expansion and podocyte effacement and these changes were prevented by MK0626. In addition, the PTC endocytosis protein megalin and basilar canalicular network and mitochondrial ultrastructure abnormalities were reversed by MK0626. WD mice had decreased sodium excretion which was improved by MK0626. Ang II directly increased DPPIV activity and sodium hydrogen exchanger activity in PTCs and decreased megalin protein, which was effectively prevented by MK0626.

Conclusion: Thus, WD induced increases in DPPIV activity is associated with elevations in uric acid, renal RAS, inflammation and oxidative stress which may result in renal injury. These results suggest that DPPIV inhibitors prevent WD induced renal injury and offer a novel therapy for diabetic and obesity associated renal disease.

Dipeptidylpeptidase inhibition is associated with improvement in blood pressure and diastolic function in insulin-resistant male Zucker obese rats

Diastolic dysfunction is a prognosticator for future cardiovascular events that demonstrates a strong correlation with obesity. Pharmacological inhibition of dipeptidylpeptidase-4 (DPP-4) to increase the bioavailability of glucagon-like peptide-1 is an emerging therapy for control of glycemia in type 2 diabetes patients. Accumulating evidence suggests that glucagon-like peptide-1 has insulin-independent actions in cardiovascular tissue. However, it is not known whether DPP-4 inhibition improves obesity-related diastolic dysfunction. Eight-week-old Zucker obese (ZO) and Zucker lean rats were fed normal chow diet or diet containing the DPP-4 inhibitor, linagliptin (LGT), for 8 weeks. Plasma DPP-4 activity was 3.3-fold higher in ZO compared with Zucker lean rats and was reduced by 95% with LGT treatment. LGT improved echocardiographic and pressure volume-derived indices of diastolic function that were impaired in ZO control rats, without altering food intake or body weight gain during the study period. LGT also blunted elevated blood pressure progression in ZO rats involving improved skeletal muscle arteriolar function, without reducing left ventricular hypertrophy, fibrosis, or oxidative stress in ZO hearts. Expression of phosphorylated- endothelial nitric oxide synthase (eNOS)(Ser1177), total eNOS, and sarcoplasmic reticulum calcium ATPase 2a protein was elevated in the LGT-treated ZO heart, suggesting improved Ca(2+) handling. The ZO myocardium had an abnormal mitochondrial sarcomeric arrangement and cristae structure that were normalized by LGT. These studies suggest that LGT reduces blood pressure and improves intracellular Cai(2+) mishandling and cardiomyocyte ultrastructure, which collectively result in improvements in diastolic function in the absence of reductions in left ventricular hypertrophy, fibrosis, or oxidative stress in insulin-resistant ZO rats.

DPP-4 Inhibitors as Therapeutic Modulators of Immune Cell Function and Associated Cardiovascular and Renal Insulin Resistance in Obesity and Diabetes

The prevalence of obesity and diabetes continues to rise in the United States and worldwide. These findings parallel the expansion of childhood obesity and diabetes. Obesity is a central component of the cardiorenal metabolic syndrome (CRS) which increases the risk for cardiovascular disease (CVD) and chronic kidney disease (CKD). The hallmark of obesity, CRS, and early type 2 diabetes is insulin resistance, a result of decreased insulin metabolic signaling due, in part, to enhanced serine phosphorylation and/or proteasome-mediated degradation of the insulin receptor substrate. Cardiovascular and renal insulin resistance significantly contributes to endothelial dysfunction, impaired cardiac diastolic and vascular relaxation, glomerular injury, and tubular dysfunction. In this context, multiple factors including oxidative stress, increased inflammation, and inappropriate activation of the renin-angiotensin-aldosterone and the sympathetic nervous system contribute to overweight- and obesity-induced systemic and tissue insulin resistance. One common link between obesity and the development of insulin resistance appears to be a low-grade inflammatory response resulting from dysfunctional innate and adaptive immunity. In this regard, there has been recent work on the role of dipeptidyl peptidase-4 (DPP-4) in modulating innate and adaptive immunity. The direct effects of DPP-4 on immune cells and the indirect effects through GLP-1-dependent and -independent pathways suggest effects of DPP-4 inhibition may have beneficial effects beyond glycemic control in improving CVD and renal outcomes. Accordingly, this review addresses new insights into the role of DPP-4 in immune modulation and the potential beneficial effects of DPP-4 inhibitors in insulin resistance and associated CVD and CKD prevention.

Angiotensin type 1 receptor resistance to blockade in the opossum proximal tubule cell due to variations in the binding pocket

Blockade of the angiotensin (ANG) II receptor type 1 (AT(1)R) with angiotensin receptor blockers (ARBs) is widely used in the treatment of hypertension. However, ARBs are variably effective in reducing blood pressure, likely due, in part, to polymorphisms in the ARB binding pocket of the AT(1)R. Therefore, we need a better understanding of variations/polymorphisms that alter binding of ARBs in heterogeneous patient populations. The opossum proximal tubule cell (OKP) line is commonly used in research to evaluate renal sodium handling and therefore blood pressure. Investigating this issue, we found natural sequence variations in the opossum AT(1)R paralleling those observed in the human AT(1)R. Therefore, we posited that these sequence variations may explain ARB resistance. We demonstrate that OKP cells express AT(1)R mRNA, bind (125)I-labeled ANG II, and exhibit ANG II-induced phosphorylation of Jak2. However, Jak2 phosphorylation is not inhibited by five different ARBs commonly used to treat hypertension. Additionally, nonradioactive ANG II competes (125)I-ANG II efficiently, whereas a 10-fold molar excess of olmesartan and the ANG II receptor type 2 blocker PD-123319 is unable to block (125)I-ANG II binding. In contrast, ANG II binding to OKP cells stably expressing rat AT(1A)Rs, which have a conserved AT(1)R-binding pocket with human AT(1)R, is efficiently inhibited by olmesartan. A novel observation was that resistance to ARB binding to opossum AT(1)Rs correlates with variations from the human receptor at positions 108, 163, 192, and 198 within the ARB-binding pocket. These observations highlight the potential utility of evaluating AT(1)R polymorphisms within the ARB-binding pocket in various hypertensive populations.

Abstract 606: DPP-4 Inhibition Improves Diastolic dysfunction in obese mice fed a Western Diet

Background and rationale: Obesity and diabetes are associated with insulin resistance, salt sensitive hypertension and cardiovascular dysfunction. Pharmacological inhibition of dipeptidylpeptidase-4 (DPP-4) to increase the bioavailability of glucagon like peptide-1 (GLP-1) is a contemporary therapy for control of glycemia in Type2 diabetes patients. Whether DPP-4 inhibition lowers blood pressures and improves pre-diabetic cardiomyopathy in a diet induced obesity (DIO) mouse model has not been examined in detail.

Methods: C57Bl/6 mice were fed high fat/high sucrose (Western diet, WD) for 16wks starting at ∼4 wks of age and treated with MK-0626 (10mg/kg/day, Merck).

Results: When compared to normal chow-fed mice, Western diet-fed (DIO) mice manifested increased MAP (15-20mmHg), heart (50%) and body weight (33%), increased blood sugars (FBS) and sodium retention (urine sodium 6.9μmol/day/gBW vs. 2.3μmol/day/gBW, respectively). In addition to correcting FBS, MK-0626 lowered MAP and increased sodium excretion and corrected cardiac diastolic dysfunction ( Table ). Indeed, echocardiographic indices of diastolic function, including tissue doppler E’/A’ ratio, estimates of LV filling pressure (E/E’), isovolemic relaxation time and the Tei index, all abnormal in mice fed a WD, were improved by MK-0626. Contemporaneous with these cardiac functional abnormalities, the mTOR/S6K and ERK1/2 growth signaling pathways were activated in DIO mice and improved by 16 wks of MK-0626 treatment.

Conclusion: These studies suggest that MK-0626 increases cardiac and renal bioavailability of GLP-1 and improves myocardial GLP-1R signaling, myocardial remodeling resulting in increased renal sodium excretion and improvements in cardiac diastolic function in pre-diabetic insulin resistant DIO mice.

Table: Summary of 2D M-Mode, pulse wave and tissue doppler Echo measurements on 20 wk old mice on control diet (CD), Western diet (WD), or Western Diet with MK-0626 (WD-MK). Values are mean ± SE. Numbers in parentheses are sample sizes. Paired t-tests: *p<0.05 CD vs WDC; † P<0.05 WDC vs WD-MKE, velocity of early mitral flow; E’, peak velocity of septal annulus; E/E’ index of LA filling pressure; Vp, flow propogation velocity; E/Vp, index of LV filling pressure; IVRT, isovolumic relaxation time; MPI, myocardial performance index.

Abstract 478: Is Ang II-mediated mTOR/S6K1 Activation in Proximal Tubule Cells mTORC2-dependent?

Introduction: Activation of the mTOR nutrient sensing pathway in early diabetes has been implicated in glomerulomegaly, hyperfiltration and hypertrophy of the nephrons. Recent studies show that excess/deletion of mTOR/raptor (mTORC1) in the podocytes results in diabetic changes. Interestingly, mTOR exists in another complex called mTORC2 (mTOR/rictor), which has been shown to phosphorylate Akt at S473 and is proposed to regulate cell motility and actin cytoskeleton. Recently, growth factors such as angiotensin II (Ang II) have been identified as activators of mTORC1 in cardiomyocytes, intestinal epithelial cells and embryonic cell. However, the precise mechanism of mTORC1 activation in the proximal tubule cells (PTC) is largely unknown. We hypothesized that Ang II activation of mTORC1 is dependent on mTORC2 activation.

Methods: Mice were subjected to Ang II (200ng/kg/min) via osmotic minipump and whole kidney lysates analyzed for mTORC1 activation. In parallel, acute Ang II (10 -7 M, 10min) treatment of opossum PTCs stably expressing rat AT1 B R was carried out on 24 hour starved cultures preceded by 1 hour pretreatment with various inhibitors.

Results: Ang II activated mTORC1/S6 kinase in kidney lysates (1.5-fold) and cultured PTCs (3-5 fold) as evidenced by increased phosphorylation of T389-S6K1, S240/244-RPS6 and T36/45-4EBP1. Ang II also activated mTORC2 (2-fold) as evidenced by p-S473-Akt. Upstream, Ang II caused phosphorylation of EGF receptor and inhibition of EGFR activation resulted in 30% inhibition of Akt activation and partial inhibition of mTOR/S6 kinase. Inhibition of PKC also resulted in partial inhibition of mTOR/S6 activation but the magnitude (50%) was higher than inhibition of EGFR signaling. Rapamycin (10nM) inhibited mTORC1 activation and not mTORC2 but PP242 (ATP site inhibitor, 8nM) completely abolished both mTORC1 and mTORC2 activation.

Conclusion: Ang II activation of mTOR/S6K follows a distinct pattern in PTC when compared to other cell types. Ang II induced activation of mTOR/S6 kinase is mediated by both PKC and EGFR activation. mTORC2 appears to play a central role in regulating Ang II induced activation of mTOR/S6 kinase.

Anemia and chronic kidney disease: making sense of the recent trials

Anemia is a very common complication of chronic kidney disease (CKD). Anemia confers significant risk of cardiovascular disease and contributes to decreased quality of life. Anemia in CKD patients can be multi-factorial, including but not invariably due to the underlying renal insufficiency. Identifying the type of anemia is important in this group of patients and can often be challenging. Diagnosing anemia of renal disease due to erythropoietin (EPO) deficiency is a diagnosis of exclusion. Erythropoiesis stimulating agents (ESA) are the mainstay for the treatment of anemia secondary to CKD. However, over the last four years the use of ESA in the treatment of anemia in CKD patients has undergone a severe interrogation as several trials have reported adverse outcomes with targeting higher hemoglobin (Hb) levels with these agents. Thereby, this review describes the pathophysiology of anemia in CKD patients, diagnosis and the current role of ESA's as it relates to anemia of CKD as well as safety and efficacy of ESA's.

Gestational Diabetes and the Offspring: Implications in the Development of the Cardiorenal Metabolic Syndrome in Offspring

The risk of developing type 2 diabetes and cardiovascular disease in women who had previously been diagnosed with gestational diabetes (GDM) is well established. There is increasing evidence that the offspring of women with GDM are at increased risk for the development of all components of the cardiorenal metabolic syndrome. Overall, it appears that these offspring have an increased risk for overweight/obesity, insulin resistance, higher blood pressure, renal disease, and type 2 diabetes. However, distinct differences in regional populations, lack of routine screening and treatment of GDM worldwide, and long follow-up periods for offspring represent a challenge in assessing the risk for development of these abnormalities in the offspring of women who have had GDM.

Combination of direct renin inhibition with angiotensin type 1 receptor blockade improves aldosterone but does not improve kidney injury in the transgenic Ren2 rat

Enhanced renin-angiotensin-aldosterone system (RAAS) activation contributes to proteinuria and chronic kidney disease by increasing glomerular and tubulointerstitial oxidative stress, promotion of fibrosis. Renin activation is the rate limiting step in angiotensin (Ang II) and aldosterone generation, and recent work suggests direct renin inhibition improves proteinuria comparable to that seen with Ang type 1 receptor (AT(1)R) blockade. This is important as, even with contemporary use of AT(1)R blockade, the burden of kidney disease remains high. Thereby, we sought to determine if combination of direct renin inhibition with AT(1)R blockade in vivo, via greater attenuation of kidney oxidative stress, would attenuate glomerular and proximal tubule injury to a greater extent than either intervention alone. We utilized the transgenic Ren2 rat with increased tissue RAS activity and higher serum levels of aldosterone, which manifests hypertension and proteinuria. Ren2 rats were treated with renin inhibition (aliskiren), AT(1)R blockade (valsartan), the combination (aliskiren+valsartan), or vehicle for 21days. Compared to Sprague-Dawley controls, Ren2 rats displayed increased systolic pressure (SBP), circulating aldosterone, proteinuria and greater urine levels of the proximal tubule protein excretory marker beta-N-acetylglucosaminidase (β-NAG). These functional and biochemical alterations were accompanied by increases in kidney tissue NADPH oxidase subunit Rac1 and 3-nitrotyrosine (3-NT) content as well as fibronectin and collagen type III. These findings occurred in conjunction with reductions in the podocyte-specific protein podocin as well as the proximal tubule-specific megalin. Further, in transgenic animals there was increased tubulointerstitial fibrosis on light microscopy as well as ultrastructural findings of glomerular podocyte foot-process effacement and reduced tubular apical endosomal/lysosomal activity. Combination therapy led to greater reductions in SBP and serum aldosterone, but did not result in greater improvement in markers of glomerular and tubular injury (i.e. β-NAG) compared to either intervention alone. Further, combination therapy did not improve markers of oxidative stress and podocyte and proximal tubule integrity in this transgenic model of RAAS-mediated kidney damage despite greater reductions in serum aldosterone and BP levels.

Mineralocorticoid receptor-dependent proximal tubule injury is mediated by a redox-sensitive mTOR/S6K1 pathway

BACKGROUND/AIMS

The mammalian target of rapamycin (mTOR) is a serine kinase that regulates phosphorylation (p) of its target ribosomal S6 kinase (S6K1), whose activation can lead to glomerular and proximal tubular cell (PTC) injury and associated proteinuria. Increased mTOR/S6K1 signaling regulates signaling pathways that target fibrosis through adherens junctions. Recent data indicate aldosterone signaling through the mineralocorticoid receptor (MR) can activate the mTOR pathway. Further, antagonism of the MR has beneficial effects on proteinuria that occur independent of hemodynamics.

METHODS

Accordingly, hypertensive transgenic TG(mRen2)27 (Ren2) rats, with elevated serum aldosterone and proteinuria, and age-matched Sprague-Dawley rats were treated with either a low dose (1 mg/kg/day) or a conventional dose (30 mg/kg/day) of spironolactone (MR antagonist) or placebo for 3 weeks.

RESULTS

Ren2 rats displayed increases in urine levels of the PTC brush border lysosomal enzyme N-acetyl-β-aminoglycosidase (β-NAG) in conjunction with reductions in PTC megalin, the apical membrane adherens protein T-cadherin and basolateral α-(E)-catenin, and fibrosis. In concert with these abnormalities, Ren2 renal cortical tissue also displayed increased Ser2448 (p)/activation of mTOR and Thr389 (p)-S6K1 and increased 3-nitrotyrosine (3-NT) content, a marker for peroxynitrite. Low-dose spironolactone had no effect on blood pressure but decreased proteinuria and β-NAG comparable to a conventional dose of this MR antagonist. Both doses of spironolactone attenuated ultrastructural maladaptive alterations and led to comparable reductions in (p)-mTOR/(p)-S6K1, 3-NT, fibrosis, and increased expression of α-(E)-catenin, T- and N-cadherin.

CONCLUSIONS

Thereby, MR antagonism improves proximal tubule integrity by targeting mTOR/S6K1 signaling and redox status independent of changes in blood pressure.