Influence of Proteolytic Cleavage of ENaC's Gamma Subunit upon Na+ and K+ Handling

The ENaC γ subunit is essential for homeostasis of Na+, K+, and body fluid. Dual γ subunit cleavage before and after a short inhibitory tract allows dissociation of this tract, increasing channel open probability (PO), in vitro. Cleavage proximal to the tract occurs at a furin recognition sequence (143RKRR146, in the mouse γ subunit). Loss of furin-mediated cleavage prevents in vitro activation of the channel by proteolysis at distal sites. We hypothesized that 143RKRR146 mutation to 143QQQQ146 (γQ4) in 129/Sv mice would reduce ENaC PO, impair flow-stimulated flux of Na+ (JNa) and K+ (JK) in perfused collecting ducts, reduce colonic amiloride-sensitive short circuit current (ISC), and impair Na+, K+, and body fluid homeostasis. Immunoblot of γQ4/Q4 mouse kidney lysates confirmed loss of a band consistent in size with the furin-cleaved proteolytic fragment. However, γQ4/Q4 male mice on a low Na+ diet did not exhibit altered ENaC PO or flow-induced JNa, though flow-induced JK modestly decreased. Colonic amiloride-sensitive ISC in γQ4/Q4 mice was not altered. γQ4/Q4 males, but not females, exhibited mildly impaired fluid volume conservation when challenged with a low Na+ diet. Blood Na+ and K+ were unchanged on a regular, low Na+, or high K+ diet. These findings suggest that biochemical evidence of γ subunit cleavage should be used in isolation to evaluate ENaC activity. Further, factors independent of γ subunit cleavage modulate channel PO and the influence of ENaC on Na+, K+, and fluid volume homeostasis in 129/Sv mice, in vivo.

Magnesium in hypertension: mechanisms and clinical implications

Hypertension is associated with increased risk of cardiovascular disease and death. Evidence suggests that Mg2+ depletion contributes to hypertension. It is estimated that 25% or more of the United States population experiences chronic, latent Mg2+ depletion. This review explores mechanisms by which Mg2+ influences blood pressure, modifying risk of hypertension and complicating its treatment. Mechanisms addressed include effects upon i) sympathetic tone, via the modulation of N-methyl-D-aspartate (NMDA) receptor and N-type Ca2+ channel activity, influencing catecholamine release from sympathetic nerve endings; ii) vascular tone, via alteration of L-type Ca2+ and endothelial nitric oxide synthase (eNOS) activity and prostacyclin release; iii) renal K+ handling, influencing systemic K+ balance and potentially indirectly influencing blood pressure; iv) aldosterone secretion from the adrenal cortex; and v) modulation of pro-hypertensive inflammatory processes in dendritic cells and macrophages, including activation of the NLR family pyrin domain containing 3 (NLRP3) inflammasome and stimulation of isolevuglandin (IsoLG) production. Discovery of these mechanisms has furthered our understanding of the pathogenesis of hypertension, with implications for treatment and has highlighted the role of Mg2+ balance in hypertension and cardiovascular disease.

Proteolytic Cleavage of the ENaC γ Subunit - Impact Upon Na + and K + Handling

The ENaC gamma subunit is essential for homeostasis of Na + , K + , and body fluid. Dual subunit cleavage before and after a short inhibitory tract allows dissociation of this tract, increasing channel open probability (P O ), in vitro . Cleavage proximal to the tract occurs at a furin recognition sequence ( 143 RKRR 146 in mouse). Loss of furin-mediated cleavage prevents in vitro activation of the channel by proteolysis at distal sites. We hypothesized that 143 RKRR 146 mutation to 143 QQQQ 146 ( Q4 ) in 129/Sv mice would reduce ENaC P O , impair flow-stimulated flux of Na + (J Na ) and K + (J K ) in perfused collecting ducts, reduce colonic amiloride-sensitive short circuit current (I SC ), and impair Na + , K + , and body fluid homeostasis. Immunoblot of Q4/Q4 mouse kidney lysates confirmed loss of a band consistent in size with the furin-cleaved proteolytic fragment. However, Q4/Q4 male mice on a low Na + diet did not exhibit altered ENaC P O or flow-induced J Na , though flow-induced J K modestly decreased. Colonic amiloride-sensitive I SC in Q4/Q4 mice was not altered. Q4/Q4 males, but not females, exhibited mildly impaired fluid volume conservation when challenged with a low Na + diet. Blood Na + and K + were unchanged on a regular, low Na + , or high K + diet. These findings suggest that biochemical evidence of gamma subunit cleavage should not be used in isolation to evaluate ENaC activity. Further, factors independent of gamma subunit cleavage modulate channel P O and the influence of ENaC on Na + , K + , and fluid volume homeostasis in 129/Sv mice, in vivo .

Mice lacking γENaC palmitoylation sites maintain benzamil-sensitive Na+ transport despite reduced channel activity

Epithelial Na+ channels (ENaCs) control extracellular fluid volume by facilitating Na+ absorption across transporting epithelia. In vitro studies showed that Cys-palmitoylation of the γENaC subunit is a major regulator of channel activity. We tested whether γ subunit palmitoylation sites are necessary for channel function in vivo by generating mice lacking the palmitoylated cysteines (γC33A,C41A) using CRISPR/Cas9 technology. ENaCs in dissected kidney tubules from γC33A,C41A mice had reduced open probability compared with wild-type (WT) littermates maintained on either standard or Na+-deficient diets. Male mutant mice also had higher aldosterone levels than WT littermates following Na+ restriction. However, γC33A,C41A mice did not have reduced amiloride-sensitive Na+ currents in the distal colon or benzamil-induced natriuresis compared to WT mice. We identified a second, larger conductance cation channel in the distal nephron with biophysical properties distinct from ENaC. The activity of this channel was higher in Na+-restricted γC33A,C41A versus WT mice and was blocked by benzamil, providing a possible compensatory mechanism for reduced prototypic ENaC function. We conclude that γ subunit palmitoylation sites are required for prototypic ENaC activity in vivo but are not necessary for amiloride/benzamil-sensitive Na+ transport in the distal nephron or colon.

The role of dietary magnesium deficiency in inflammatory hypertension

Nearly 30% of adults consume less than the estimated average daily requirement of magnesium (Mg2+), and commonly used medications, such as diuretics, promote Mg2+ deficiency. Higher serum Mg2+ levels, increased dietary Mg2+ in-take, and Mg2+ supplementation are each associated with lower blood pressure, suggesting that Mg2+-deficiency contributes to the pathogenesis of hypertension. Antigen-presenting cells, such as monocytes and dendritic cells, are well-known to be involved in the pathogenesis of hypertension. In these cells, processes implicated as necessary for increased blood pressure include activation of the NLRP3 inflammasome, IL-1β production, and oxidative modification of fatty acids such as arachidonic acid, forming isolevuglandins (IsoLGs). We hypothesized that increased blood pressure in response to dietary Mg2+-depletion leads to increased NLRP3, IL-1β, and IsoLG production in antigen presenting cells. We found that a Mg2+-depleted diet (0.01% Mg2+ diet) increased blood pressure in mice compared to mice fed a 0.08% Mg2+ diet. Mg2+-depleted mice did not exhibit an increase in total body fluid, as measured by quantitative magnetic resonance. Plasma IL-1β concentrations were increased (0.13 ± 0.02 pg/mL vs. 0.04 ± 0.02 pg/mL). Using flow cytometry, we observed increased NLRP3 and IL-1β expression in antigen-presenting cells from spleen, kidney, and aorta. We also observed increased IsoLG production in antigen-presenting cells from these organs. Primary culture of CD11c+ dendritic cells confirmed that low extracellular Mg2+ exerts a direct effect on these cells, stimulating IL-1β and IL-18 production. The present findings show that NLRP3 inflammasome activation and IsoLG-adduct formation are stimulated when dietary Mg2+ is depleted. Interventions and increased dietary Mg2+ consumption may prove beneficial in decreasing the prevalence of hypertension and cardiovascular disease.

Home Subcutaneous Magnesium Infusion in Refractory Hypomagnesemia: A Case Report

We describe a patient with renal magnesium wasting and prolonged, symptomatic hypomagnesemia that was refractory to oral therapies and intermittent intravenous infusion who achieved near-normal serum magnesium levels with subcutaneous magnesium infusions. A woman in her 40s was seen in nephrology clinic for evaluation and management of severe, chronic hypomagnesemia because of renal magnesium wasting in combination with frequent diarrhea. Clinical manifestations associated with hypomagnesemia included muscle weakness, cognitive impairment, and frequent seizures. Her hypomagnesemia had persisted for more than 20 years despite maximal oral magnesium supplementation and frequent intravenous magnesium infusions. To provide slower delivery of parenteral magnesium, she was prescribed 2 g/d of magnesium sulfate, delivered subcutaneously. This was well tolerated, rapidly normalized her serum magnesium levels, and improved her symptoms. We briefly discuss modalities used for treatment of hypomagnesemia, including shortcomings of intravenous therapy and limited literature discussing efficacy and tolerability of subcutaneous infusions. This case report demonstrates the efficacy and safety of subcutaneous magnesium infusions in a patient with refractory hypomagnesemia and suggests that subcutaneous infusion may be safe and effective for treatment of refractory hypomagnesemia in other patients with urinary magnesium wasting.

Influence of glycoprotein MUC1 on trafficking of the Ca2+-selective ion channels, TRPV5 and TRPV6, and on in vivo calcium homeostasis

Polymorphism of the gene encoding mucin 1 (MUC1) is associated with skeletal and dental phenotypes in human genomic studies. Animals lacking MUC1 exhibit mild reduction in bone density. These phenotypes could be a consequence of modulation of bodily Ca homeostasis by MUC1, as suggested by the previous observation that MUC1 enhances cell surface expression of the Ca2+-selective channel, TRPV5, in cultured unpolarized cells. Using biotinylation of cell surface proteins, we asked whether MUC1 influences endocytosis of TRPV5 and another Ca2+-selective TRP channel, TRPV6, in cultured polarized epithelial cells. Our results indicate that MUC1 reduces endocytosis of both channels, enhancing cell surface expression. Further, we found that mice lacking MUC1 lose apical localization of TRPV5 and TRPV6 in the renal tubular and duodenal epithelium. Females, but not males, lacking MUC1 exhibit reduced blood Ca2+. However, mice lacking MUC1 exhibited no differences in basal urinary Ca excretion or Ca retention in response to PTH receptor signaling, suggesting compensation by transport mechanisms independent of TRPV5 and TRPV6. Finally, humans with autosomal dominant tubulointerstitial kidney disease due to frame-shift mutation of MUC1 (ADTKD-MUC1) exhibit reduced plasma Ca concentrations compared to control individuals with mutations in the gene encoding uromodulin (ADTKD-UMOD), consistent with MUC1 haploinsufficiency causing reduced bodily Ca2+. In summary, our results provide further insight into the role of MUC1 in Ca2+-selective TRP channel endocytosis and the overall effects on Ca concentrations.

Abstract 078: Human Gain-of-function Mutation W521r In The Enac α-subunit Contributes To Salt-sensitive Hypertension In A Sex-specific Manner

The epithelial Na + channel (ENaC) plays a key role in regulating the extracellular fluid volume and blood pressure. Gain-of-function mutations in ENaC subunits are associated with hypertensive disorders including Liddle syndrome. We previously demonstrated that in male mice, dendritic cell ENaC mediates NADPH oxidase activation and increased accumulation of Isolevuglandins (IsoLGs), which act as neoantigens, promoting T cell activation and salt-induced hypertension. The mechanism by which dendritic cell ENaC is regulated, and the role of sex as a biological variable is still yet to be defined. One of the mechanisms by which ENaC is regulated is through sodium self-inhibition. We hypothesized that sodium self-inhibition plays a sex-specific role in regulating ENaC leading to salt-sensitive hypertension. To test this hypothesis, we generated mice with a gain-of-function mutation of a single nucleotide variant (W521R) in ENaC α-subunit using CRISPR/Cas9 in the wild-type (WT) salt-sensitive129/sv background. These mutant mice lack the sodium self-inhibition of ENaC. WT littermate male and female mice were used as controls. Using telemetry blood pressure monitoring, we found that WT males developed salt-induced hypertension, but WT females were protected (124.3 ± 5.15 vs. 95.37 ± 4.882 mmHg, p=0.0114). Moreover, W521R male mutants had elevated mean arterial pressure in response to 3 weeks of high salt-feeding (4% NaCl) compared to the salt-sensitive WT littermate males (169.3 ± 27.69 vs. 124.3 ± 5.15 mmHg, p= 0.0024). Similar to WT females, female W521R mice were protected from salt-induced blood pressure elevation (102.3± 5.23 mmHg). Using flow cytometry, we found that high Na + increased dendritic cell IsoLGs production in male W521R mice compared to littermate controls (3.97 ± 1.68% vs. 1.01 ± 0.08 % of dendritic cells, p=0.0386). Our findings suggest that W521R gain-of-function mutation contributes to inflammation and hypertension in male but not female mice.

Abstract 016: Magnesium Deficient Diet-induced Hypertension And Renal DC-specific NLRP3 Inflammasome Activation

Background: Analysis from a 2013-2016 dietary survey by the National Health and Nutrition Examination Survey Several found that less than 50% of Americans consume sufficient magnesium. Multiple studies have identified a link between dietary magnesium and inflammation associated with multiple pathologies including hypertension, chronic kidney disease, and cardiovascular disease. Additionally, magnesium sulfate inhibits NLRP3 inflammasome activation in human macrophages. We have previously shown that activation of the NLRP3 inflammasome is a key component of salt-sensitive hypertension. In this study, we hypothesize that a magnesium-deficient diet could promote NLRP3 inflammasome activation in myeloid cells and systemic hypertension.

Materials and Methods: In vivo studies were performed on mice with an SV/129 background given either a normal-magnesium (Norm-Mg 2+ ) diet (0.08%, as magnesium oxide) or low-magnesium (Low-Mg 2+ ) diet (0.01%) for 5 weeks. Systolic blood pressure (SBP) was monitored on a weekly basis by tail-cuff.

Results: Mice fed a Low-Mg 2+ diet had a significant increase in SBP compared to the Norm-Mg 2+ diet fed mice (105.8 ± 11.3 to 130.4 ± 7.4 mmHg vs 106.5 ± 9.4 to 121.8 ± 6.5 mmHg, [n=7, p=0.0071, 2 way ANOVA]). Using flow cytometry, we observed an increase in NLRP3 (34.1 ± 2.5 vs 7.4 ± 0.6 % of DCs, [n=5-7, p=0.0025, Mann-Whitney test]) and IL-1β (41.9 ± 6.6 vs 15.86 ± 6.6 % of DCs, [n=5-7, p=0.048, Mann-Whitney test]) expression in renal dendritic cells (DCs) of Low-Mg 2+ mice compared to Norm-Mg 2+ mice. There was a similar increase in IsoLG-adduct formation in renal DCs (8.5 ± 2.0 vs 0.6 ± 0.05 % of DCs, [n=5-7, p=0.0025, Mann-Whitney test). Interestingly, we found no difference in NLRP3 (24.92 ± 5.3 vs 31.54 ± 3.1 % of monocytes, [n=5-7, p=0.1376, Mann-Whitney test]), IL-1β (9.5 ± 4.3 vs 4.6 ± 0.4 % of monocytes, [n=5-7, p=0.7551, Mann-Whitney test]), or IsoLG-adduct formation (29.42 ± 3.6 vs 31.9 ± 3.6 % of monocytes, [n=5-7, p=<0.999, Mann-Whitney test]) in renal monocytes.

Conclusions: Our findings suggest a magnesium-deficient diet induces a hypertensive response and activates the NLRP3 inflammasome in renal DCs but not monocytes.

The molecular chaperone GRP170 protects against ER stress and acute kidney injury in mice

Molecular chaperones are responsible for maintaining cellular homeostasis, and one such chaperone, GRP170, is an endoplasmic reticulum (ER) resident that oversees both protein biogenesis and quality control. We previously discovered that GRP170 regulates the degradation and assembly of the epithelial sodium channel (ENaC), which reabsorbs sodium in the distal nephron and thereby regulates salt-water homeostasis and blood pressure. To define the role of GRP170 - and, more generally, molecular chaperones in kidney physiology - we developed an inducible, nephron-specific GRP170-KO mouse. Here, we show that GRP170 deficiency causes a dramatic phenotype: profound hypovolemia, hyperaldosteronemia, and dysregulation of ion homeostasis, all of which are associated with the loss of ENaC. Additionally, the GRP170-KO mouse exhibits hallmarks of acute kidney injury (AKI). We further demonstrate that the unfolded protein response (UPR) is activated in the GRP170-deficient mouse. Notably, the UPR is also activated in AKI when originating from various other etiologies, including ischemia, sepsis, glomerulonephritis, nephrotic syndrome, and transplant rejection. Our work establishes the central role of GRP170 in kidney homeostasis and directly links molecular chaperone function to kidney injury.

Salt sensitivity of volume and blood pressure in a mouse with globally reduced ENaC γ-subunit expression

The epithelial Na+ channel (ENaC) promotes the absorption of Na+ in the aldosterone-sensitive distal nephron, colon, and respiratory epithelia. Deletion of genes encoding subunits of ENaC results in early postnatal mortality. Here, we present the initial characterization of a mouse with dramatically suppressed expression of the ENaC γ-subunit. We used this hypomorphic (γmt) allele to explore the importance of this subunit in homeostasis of electrolytes and body fluid volume. At baseline, γ-subunit expression in γmt/mt mice was markedly suppressed in the kidney and lung, whereas electrolytes resembled those of littermate controls. Aldosterone levels in γmt/mt mice exceeded those seen in littermate controls. Quantitative magnetic resonance measurement of body composition revealed similar baseline body water, lean tissue mass, and fat tissue mass in γmt/mt mice and controls. γmt/mt mice exhibited a more rapid decline in body water and lean tissue mass in response to a low-Na+ diet than the controls. Replacement of drinking water with 2% saline selectively and transiently increased body water and lean tissue mass in γmt/mt mice relative to the controls. Lower blood pressures were variably observed in γmt/mt mice on a high-salt diet compared with the controls. γmt/mt also exhibited reduced diurnal blood pressure variation, a "nondipping" phenotype, on a high-Na+ diet. Although ENaC in the renal tubules and colon works to prevent extracellular fluid volume depletion, our observations suggest that ENaC in other tissues may participate in regulating extracellular fluid volume and blood pressure.NEW & NOTEWORTHY A mouse with globally suppressed expression of the epithelial Na+ channel γ-subunit showed enhanced sensitivity to dietary salt, including a transient increase in total body fluid, reduced blood pressure, and reduced diurnal blood pressure variation when given a dietary NaCl challenge. These results point to a role for the epithelial Na+ channel in regulating body fluid and blood pressure beyond classical transepithelial Na+ transport mechanisms.

L-WNK1 is required for BK channel activation in intercalated cells

Large-conductance K+ (BK) channels expressed in intercalated cells (ICs) in the aldosterone-sensitive distal nephron (ASDN) mediate flow-induced K+ secretion. In the ASDN of mice and rabbits, IC BK channel expression and activity increase with a high-K+ diet. In cell culture, the long isoform of with-no-lysine kinase 1 (L-WNK1) increases BK channel expression and activity. Apical L-WNK1 expression is selectively enhanced in ICs in the ASDN of rabbits on a high-K+ diet, suggesting that L-WNK1 contributes to BK channel regulation by dietary K+. We examined the role of IC L-WNK1 expression in enhancing BK channel activity in response to a high-K+ diet. Mice with IC-selective deletion of L-WNK1 (IC-L-WNK1-KO) and littermate control mice were placed on a high-K+ (5% K+, as KCl) diet for 10 or more days. IC-L-WNK1-KO mice exhibited reduced IC apical + subapical α-subunit expression and BK channel-dependent whole cell currents compared with controls. Six-hour urinary K+ excretion in response a saline load was similar in IC-L-WNK1-KO mice and controls. The observations that IC-L-WNK1-KO mice on a high-K+ diet have higher blood K+ concentration and reduced IC BK channel activity are consistent with impaired urinary K+ secretion, demonstrating that IC L-WNK1 has a role in the renal adaptation to a high-K+ diet.NEW & NOTEWORTHY When mice are placed on a high-K+ diet, genetic disruption of the long form of with no lysine kinase 1 (L-WNK1) in intercalated cells reduced relative apical + subapical localization of the large-conductance K+ channel, blunted large-conductance K+ channel currents in intercalated cells, and increased blood K+ concentration. These data confirm an in vivo role of L-WNK1 in intercalated cells in adaptation to a high-K+ diet.

Deletion of Kir5.1 abolishes the effect of high Na+ intake on Kir4.1 and Na+-Cl- cotransporter

High sodium (HS) intake inhibited epithelial Na⁺ channel (ENaC) in the aldosterone-sensitive distal nephron and Na⁺-Cl^- cotransporter (NCC) by suppressing basolateral Kir4.1/Kir5.1 in the distal convoluted tubule (DCT), thereby increasing renal Na⁺ excretion but not affecting K⁺ excretion. The aim of the present study was to explore whether deletion of Kir5.1 compromises the inhibitory effect of HS on NCC expression/activity and renal K⁺ excretion. Patch-clamp experiments demonstrated that HS failed to inhibit DCT basolateral K⁺ channels and did not depolarize K⁺ current reversal potential of the DCT in Kir5.1 knockout (KO) mice. Moreover, deletion of Kir5.1 not only increased the expression of Kir4.1, phospho-NCC, and total NCC but also abolished the inhibitory effect of HS on the expression of Kir4.1, phospho-NCC, and total NCC and thiazide-induced natriuresis. Also, low sodium-induced stimulation of NCC expression/activity and basolateral K⁺ channels in the DCT were absent in Kir5.1 KO mice. Deletion of Kir5.1 decreased ENaC currents in the late DCT, and HS further inhibited ENaC activity in Kir5.1 KO mice. Finally, measurement of the basal renal K⁺ excretion rate with the modified renal clearance method demonstrated that long-term HS inhibited the renal K⁺ excretion rate and steadily increased plasma K⁺ levels in Kir5.1 KO mice but not in wild-type mice. We conclude that Kir5.1 plays an important role in mediating the effect of HS intake on basolateral K⁺ channels in the DCT and NCC activity/expression. Kir5.1 is involved in maintaining renal ability of K⁺ excretion during HS intake. NEW & NOTEWORTHY Kir5.1 plays an important role in mediating the effect of high sodium intake on basolateral K⁺ channels in the distal convoluted tubule and Na⁺-Cl^- cotransporter activity/expression.

Phylogeny and chemistry of biological mineral transport

Three physiologically mineralizing tissues - teeth, cartilage and bone - have critical common elements and important evolutionary relationships. Phylogenetically the most ancient densely mineralized tissue is teeth. In jawless fishes without skeletons, tooth formation included epithelial transport of phosphates, a process echoed later in bone physiology. Cartilage and mineralized cartilage are skeletal elements separate from bone, but with metabolic features common to bone. Cartilage mineralization is coordinated with high expression of tissue nonspecific alkaline phosphatase and PHOSPHO1 to harvest available phosphate esters and support mineralization of collagen secreted locally. Mineralization in true bone results from stochastic nucleation of hydroxyapatite crystals within the cross-linked collagen fibrils. Mineral accumulation in dense collagen is, at least in major part, mediated by amorphous aggregates - often called Posner clusters - of calcium and phosphate that are small enough to diffuse into collagen fibrils. Mineral accumulation in membrane vesicles is widely suggested, but does not correlate with a definitive stage of mineralization. Conversely mineral deposition at non-physiologic sites where calcium and phosphate are adequate has been shown to be regulated in large part by pyrophosphate. All of these elements are present in vertebrate bone metabolism. A key biological element of bone formation is an epithelial-like cellular organization which allows control of phosphate, calcium and pH during mineralization.

Abstract P131: Jak2 Expression In Cd11c+ Myeloid Cells Plays A Role In Salt-sensitive Hypertension Through An Enac-dependent Mechanism

Hypertension is a major risk factor for development of cardiovascular disease. Excess dietary salt contributes to inflammation and the genesis of hypertension. We recently found that gamma and alpha subunits of the epithelial sodium channel (ENaCαγ) on dendritic cells mediate NADPH oxidase-dependent formation of immunogenic isolevuglandin (IsoLG)-protein adducts leading to inflammation and salt-sensitive hypertension. We hypothesized that Jak2 expression, specifically in CD11c + myeloid cells, regulates expression of ENaCγ and promotes salt-sensitive hypertension. Our results indicate that deletion of Jak2 in CD11c + myeloid cells reduced the salt-induced expression of ENaCγ in CD11c+ cells. Moreover, mice lacking Jak2 in CD11c+ cells developed a blunted hypertensive response (123.8±4.7) during the high salt feeding phase of the N-Nitro-L-arginine methyl ester hydrochloride (L- NAME)/high salt model of salt-sensitive hypertension compared to their wildtype littermate controls (140.5±6.5). These mice also exhibited less infiltration of monocyte/macrophages in their kidneys and less volume retention (69.55±5.8) in response to high salt-feeding when compared to the wildtype litter mate controls (57.89±9.5). These results indicate that Jak2 expression in CD11c + myeloid cells plays a role in salt- sensitive hypertension through an ENaC-dependent mechanism.

Abstract MP38: High Salt Activates The NLRP3 Inflammasome In Antigen Presenting Cells Via ENaC To Promote Salt-Sensitive Hypertension

Salt-sensitivity is a major risk factor for hypertension and cardiovascular disease (CVD). Reducing dietary Na + decreases blood pressure and CVD risk. However, the precise mechanisms of how Na + leads to hypertension are still not well defined. Recently, we found that dendritic cells (DCs) in response to increases in extracellular [Na + ] exhibit an amiloride-sensitive epithelial Na + channel (ENaC)-dependent activation of NADPH-oxidase, superoxide production, reactive isolevuglandin (IsoLG)-protein adduct formation, and cytokine secretion which promote hypertension. We hypothesized that the NLRP3 inflammasome in antigen-presenting cells (APCs) mediates salt-sensitive hypertension through an ENaC-dependent mechanism. To test this hypothesis, we cultured mouse splenocytes in normal-salt or high-salt (HS) media with or without co-treatment with the ENaC inhibitor, amiloride (20 μM). Using flow cytometry, we found that HS increased monocyte and DC IL-1β production, which was confirmed through an ELISA assay detecting IL-1β release (2.131 ± 0.733 vs 12.75 ± 1.108 pg/mL, p<0.01) into the culture media, and amiloride treatment prevented IL-1β production (12.75 ± 1.108 vs 1.905 ± 0.3495 pg/mL, p<0.01) in these cells. To confirm our in vitro data, we treated salt-sensitive mice on a 129-SvJ background with a HS diet (4% NaCl) for 28 days with or without amiloride (1mg/kg/day in drinking water) or NLRP3 inflammasome inhibitor MCC950 (10mg/kg i.p.). Amiloride or MCC950 treated mice developed blunted hypertension in response to HS (120.4 ± 2.99; 101.0 ± 3.74) compared to vehicle controls (140.5 ± 3.98). Amiloride treated mice also exhibited less expression of NLRP3, pro-IL1β, and IsoLGs in DCs and monocytes compared to controls. Interestingly, MCC950 treated mice exhibited decreased pro-IL1β but not NLRP3 expression or IsoLG production. Using the DOCA-salt model, we found similar increases in NLRP3, pro-IL1β, and IsoLGs expression in DCs and monocytes, which was abolished after treatment with IsoLG scavenger 2-HOBA (1g/L). Our findings suggest a role for ENaC-dependent NLRP3 inflammasome activation in APCs in response to a HS diet, which may represent a promising treatment approach to salt-induced hypertension.

Mass Balance Study of the Engineered Cationic Antimicrobial Peptide, WLBU2, Following a Single Intravenous Dose of 14C-WLBU2 in Mice

BACKGROUND

To address multidrug resistance, we developed engineered Cationic Antimicrobial Peptides (eCAPs). Lead eCAP WLBU2 displays potent activity against drug-resistant bacteria and effectively treats lethal bacterial infections in mice, reducing bacterial loads to undetectable levels in diverse organs.

OBJECTIVE

To support the development of WLBU2, we conducted a mass balance study.

METHODS

CD1 mice were administered 10, 15, 20 and 30 mg/kg of QDx5 WLBU2 or a single dose of [14C]-WLBU2 at 15 mg/kg IV. Tolerability, tissue distribution and excretion were evaluated with liquid scintillation and HPLC-radiochromatography.

RESULTS

The maximum tolerated dose of WLBU2 is 20 mg/kg IV. We could account for greater than >96% of the radioactivity distributed within mouse tissues at 5 and 15 min. By 24h, only ~40-50% of radioactivity remained in the mice. The greatest % of the dose was present in liver, accounting for ~35% of radioactivity at 5 and 15 min, and ~ 8% of radioactivity remained at 24h. High radioactivity was also present in kidneys, plasma, red blood cells and lungs, while less than 0.2% of radioactivity was present in brain, fat, or skeletal muscle. Urinary and fecal excretion accounted for 12.5 and 2.2% of radioactivity at 24h.

CONCLUSION

WLBU2 distributes widely to mouse tissues and is rapidly cleared with a terminal radioactivity half-life of 22 h, a clearance of 27.4 mL/h/kg, and a distribution volume of 0.94 L/kg. At 2-100 μg-eq/g, the concentrations of 14C-WLBU2 appear high enough in the tissues to account for the inhibition of microbial growth.

Evolving understanding of cardiovascular protection by SGLT2 inhibitors: focus on renal protection, myocardial effects, uric acid, and magnesium balance

Robust clinical data indicate that inhibitors of the sodium/glucose cotransporter 2 (SGLT2) dramatically improve clinical outcomes in diabetes, especially heart failure and progression of kidney disease. Factors that may contribute to these findings include: 1) improved glycemic control, 2) diuresis and reduced extracellular fluid volume, 3) reduced serum uric acid levels, 3) direct myocardial effects, 4) reduction in proteinuria and preservation of kidney function, and 5) correction of diabetic magnesium deficiency. Understanding the mechanisms by which SGLT2 inhibitors improve cardiovascular outcomes has the potential to improve clinical management not only of diabetes, but also of other cardiovascular disorders such as heart failure and chronic kidney disease.

Effects of extreme potassium stress on blood pressure and renal tubular sodium transport

We characterized mouse blood pressure and ion transport in the setting of commonly used rodent diets that drive K⁺ intake to the extremes of deficiency and excess. Male 129S2/Sv mice were fed either K⁺-deficient, control, high-K⁺ basic, or high-KCl diets for 10 days. Mice maintained on a K⁺-deficient diet exhibited no change in blood pressure, whereas K⁺-loaded mice developed an ~10-mmHg blood pressure increase. Following challenge with NaCl, K⁺-deficient mice developed a salt-sensitive 8 mmHg increase in blood pressure, whereas blood pressure was unchanged in mice fed high-K⁺ diets. Notably, 10 days of K⁺ depletion induced diabetes insipidus and upregulation of phosphorylated NaCl cotransporter, proximal Na⁺ transporters, and pendrin, likely contributing to the K⁺-deficient NaCl sensitivity. While the anionic content with high-K⁺ diets had distinct effects on transporter expression along the nephron, both K⁺ basic and KCl diets had a similar increase in blood pressure. The blood pressure elevation on high-K⁺ diets correlated with increased Na⁺-K⁺-2Cl^- cotransporter and γ-epithelial Na⁺ channel expression and increased urinary response to furosemide and amiloride. We conclude that the dietary K⁺ maneuvers used here did not recapitulate the inverse effects of K⁺ on blood pressure observed in human epidemiological studies. This may be due to the extreme degree of K⁺ stress, the low-Na⁺-to-K⁺ ratio, the duration of treatment, and the development of other coinciding events, such as diabetes insipidus. These factors must be taken into consideration when studying the physiological effects of dietary K⁺ loading and depletion.

Intercalated cell BKα subunit is required for flow-induced K+ secretion

BK channels are expressed in intercalated cells (ICs) and principal cells (PCs) in the cortical collecting duct (CCD) of the mammalian kidney and have been proposed to be responsible for flow-induced K+ secretion (FIKS) and K+ adaptation. To examine the IC-specific role of BK channels, we generated a mouse with targeted disruption of the pore-forming BK α subunit (BKα) in ICs (IC-BKα-KO). Whole cell charybdotoxin-sensitive (ChTX-sensitive) K+ currents were readily detected in control ICs but largely absent in ICs of IC-BKα-KO mice. When placed on a high K+ (HK) diet for 13 days, blood [K+] was significantly greater in IC-BKα-KO mice versus controls in males only, although urinary K+ excretion rates following isotonic volume expansion were similar in males and females. FIKS was present in microperfused CCDs isolated from controls but was absent in IC-BKα-KO CCDs of both sexes. Also, flow-stimulated epithelial Na+ channel-mediated (ENaC-mediated) Na+ absorption was greater in CCDs from female IC-BKα-KO mice than in CCDs from males. Our results confirm a critical role of IC BK channels in FIKS. Sex contributes to the capacity for adaptation to a HK diet in IC-BKα-KO mice.

Cellular and extracellular matrix of bone, with principles of synthesis and dependency of mineral deposition on cell membrane transport

Bone differs from other connective tissues; it is isolated by a layer of osteoblasts that are connected by tight and gap junctions. This allows bone to create dense lamellar type I collagen, control pH, mineral deposition, and regulate water content forming a compact and strong structure. New woven bone formed after degradation of mineralized cartilage is rapidly degraded and resynthesized to impart structural order for local bone strength. Ossification is regulated by thickness of bone units and by patterning via bone morphogenetic receptors including activin, other bone morphogenetic protein receptors, transforming growth factor-β receptors, all part of a receptor superfamily. This superfamily interacts with receptors for additional signals in bone differentiation. Important features of the osteoblast environment were established using recent tools including osteoblast differentiation in vitro. Osteoblasts deposit matrix protein, over 90% type I collagen, in lamellae with orientation alternating parallel or orthogonal to the main stress axis of the bone. Into this organic matrix, mineral is deposited as hydroxyapatite. Mineral matrix matures from amorphous to crystalline hydroxyapatite. This process includes at least two-phase changes of the calcium-phosphate mineral as well as intermediates involving tropocollagen fibrils to form the bone composite. Beginning with initiation of mineral deposition, there is uncertainty regarding cardinal processes, but the driving force is not merely exceeding the calcium-phosphate solubility product. It occurs behind a epithelial-like layer of osteoblasts, which generate phosphate and remove protons liberated during calcium-phosphate salt deposition. The forming bone matrix is discontinuous from the general extracellular fluid. Required adjustment of ionic concentrations and water removal from bone matrix are important details remaining to be addressed.

Case report: extreme coronary calcifications and hypomagnesemia in a patient with a 17q12 deletion involving HNF1B

Background

17q12 deletion syndrome encompasses a broad constellation of clinical phenotypes, including renal magnesium wasting, maturity-onset diabetes of the young (MODY), renal cysts, genitourinary malformations, and neuropsychiatric illness. Manifestations outside of the renal, endocrine, and nervous systems have not been well described.

Case presentation

We report a 62-year-old male referred to the Undiagnosed Diseases Program (UDP) at the National Institutes of Health (NIH) who presented with persistent hypermagnesiuric hypomagnesemia and was found to have a 17q12 deletion. The patient exhibited several known manifestations of the syndrome, including severe hypomagnesemia, renal cysts, diabetes and cognitive deficits. Coronary CT revealed extensive coronary calcifications, with a coronary artery calcification score of 12,427. Vascular calcifications have not been previously reported in this condition. We describe several physiologic mechanisms and a review of literature to support the expansion of the 17q12 deletion syndrome to include vascular calcification.

Conclusion

Extensive coronary and vascular calcifications may be an extension of the 17q12 deletion phenotype, particularly if hypomagnesemia and hyperparathyroidism are prevalent. In patients with 17q12 deletions involving HNF1B, hyperparathyroidism and hypomagnesemia may contribute to significant cardiovascular risk.

Murine epithelial sodium (Na+) channel regulation by biliary factors

The epithelial sodium channel (ENaC) mediates Na+ transport in several epithelia, including the aldosterone-sensitive distal nephron, distal colon, and biliary epithelium. Numerous factors regulate ENaC activity, including extracellular ligands, post-translational modifications, and membrane-resident lipids. However, ENaC regulation by bile acids and conjugated bilirubin, metabolites that are abundant in the biliary tree and intestinal tract and are sometimes elevated in the urine of individuals with advanced liver disease, remains poorly understood. Here, using a Xenopus oocyte-based system to express and functionally study ENaC, we found that, depending on the bile acid used, bile acids both activate and inhibit mouse ENaC. Whether bile acids were activating or inhibiting was contingent on the position and orientation of specific bile acid moieties. For example, a hydroxyl group at the 12-position and facing the hydrophilic side (12α-OH) was activating. Taurine-conjugated bile acids, which have reduced membrane permeability, affected ENaC activity more strongly than did their more membrane-permeant unconjugated counterparts, suggesting that bile acids regulate ENaC extracellularly. Bile acid-dependent activation was enhanced by amino acid substitutions in ENaC that depress open probability and was precluded by proteolytic cleavage that increases open probability, consistent with an effect of bile acids on ENaC open probability. Bile acids also regulated ENaC in a cortical collecting duct cell line, mirroring the results in Xenopus oocytes. We also show that bilirubin conjugates activate ENaC. These results indicate that ENaC responds to compounds abundant in bile and that their ability to regulate this channel depends on the presence of specific functional groups.

Urea for the Treatment of Hyponatremia

BACKGROUND AND OBJECTIVES

Current therapies for hyponatremia have variable effectiveness and tolerability, and in certain instances, they are very expensive. We examined the effectiveness, safety, and tolerability of urea for the treatment of inpatient hyponatremia.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

We identified all patients hospitalized at the University of Pittsburgh Medical Center between July 2016 and August 2017 with hyponatremia (plasma sodium <135 mEq/L) who received urea, including a subgroup of patients who received urea as the sole drug therapy for hyponatremia (urea-only treated). We matched urea only-treated patients to a group of patients with hyponatremia who did not receive urea (urea untreated) and compared changes in plasma sodium at 24 hours and the end of therapy as well as the proportion of patients who achieved plasma sodium ≥135 mEq/L. We abstracted data on adverse events and reported side effects of urea.

RESULTS

Fifty-eight patients received urea (7.5-90 g/d) over a median of 4.5 (interquartile range, 3-8) days and showed an increase in plasma sodium from 124 mEq/L (interquartile range, 122-126) to 131 mEq/L (interquartile range, 127-134; P<0.001). Among 12 urea only-treated patients, plasma sodium increased from 125 mEq/L (interquartile range, 122-127) to 131 mEq/L (interquartile range, 129-136; P=0.001) by the end of urea therapy. There was a larger increase in plasma sodium at 24 hours in urea only-treated patients compared with urea-untreated patients (2.5 mEq/L; interquartile range, 0-4.5 versus -0.5 mEq/L; interquartile range, -2.5 to 1.5; P=0.04), with no difference in change in plasma sodium by the end of therapy (6 mEq/L; interquartile range, 3.5-10 versus 5.5 mEq/L; interquartile range, 3-7.5; P=0.51). A greater proportion of urea only-treated patients achieved normonatremia, but this difference was not statistically significant (33% versus 8%; P=0.08). No patients experienced overly rapid correction of plasma sodium, and no serious adverse events were reported.

CONCLUSIONS

Urea seems effective and safe for the treatment of inpatient hyponatremia, and it is well tolerated.

Urinary Plasmin(ogen) as a Prognostic Factor for Hypertension

Introduction

Plasmin and its precursor, plasminogen, are detectable in urine from patients with glomerular disease. Urinary plasmin(ogen) levels correlate with blood pressure (BP) and may contribute to renal Na⁺ retention by activating the epithelial Na⁺ channel (ENaC). In a longitudinal nested-cohort study, we asked whether urinary plasmin(ogen) levels predict subsequent increase in BP, incident hypertension, or mortality in subjects with type I diabetes, who often develop proteinuria.

Methods

The Pittsburgh Epidemiology of Diabetes Complications (EDC) study followed up type I diabetic subjects for 25 years. Urine specimens from 70 subjects with a spectrum of baseline urinary albumin levels were examined. Outcomes included increased BP after 2 years (≥1 SD over baseline systolic or diastolic BP, examined via logistic regression), 25-year incident hypertension (≥140/90 mm Hg or initiating BP-lowering medications), and all-cause or cardiovascular mortality, examined using Cox regression.

Results

Subjects experiencing a 2-year increase in BP had higher baseline urinary plasmin(ogen)/creatinine levels (uPl/Cr) than other subjects (P = 0.04); the difference in baseline urinary albumin/creatinine levels (uAlb/Cr) was similar (P = 0.07). Baseline uPl/Cr was associated with increased 25-year hypertension incidence (hazard ratio = 2.05, P = 0.001), all-cause mortality (HR = 2.05, P = 0.01) and cardiovascular mortality (HR = 3.30, P = 0.005), although not independent of uAlb/Cr.

Conclusion

This is the first long-term prospective study addressing clinical outcomes associated with increased urinary plasmin(ogen). Findings are consistent with a role for plasmin(ogen) in promoting increased BP, but also demonstrate the difficulty in distinguishing effects due to plasmin(ogen) from those of albuminuria.

Trial of Amiloride in Type 2 Diabetes with Proteinuria

Introduction

Renal sodium (Na⁺) retention and extracellular fluid volume expansion are hallmarks of nephrotic syndrome, which occurs even in the absence of activation of hormones that stimulate renal Na⁺ transporters. Plasmin-dependent activation of the epithelial Na⁺ channel has been proposed to have a role in renal Na⁺ retention in the setting of nephrotic syndrome. We hypothesized that the epithelial Na⁺ channel inhibitor amiloride would be an effective therapeutic agent in inducing a natriuresis and lowering blood pressure in individuals with macroscopic proteinuria.

Methods

We conducted a pilot double-blind randomized cross-over study comparing the effects of daily administration of either oral amiloride or hydrochlorothiazide to patients with type 2 diabetes and macroscopic proteinuria. Safety and efficacy were assessed by monitoring systolic blood pressure, kidney function, adherence, weight, urinary Na⁺ excretion, and serum electrolytes. Nine subjects were enrolled in the trial.

Results

No significant difference in systolic blood pressure or weight was seen between subjects receiving hydrochlorothiazide and those receiving amiloride (P ≥ 0.15). Amiloride induced differences in serum potassium (P < 0.001), with a 0.88 ± 0.30 mmol/l greater acute increase observed. Two subjects developed acute kidney injury and hyperkalemia when treated with amiloride. Four subjects had readily detectable levels of urinary plasminogen plus plasmin, and 5 did not. Changes in systolic blood pressure in response to amiloride did not differ between individuals with versus those without detectable urinary plasminogen plus plasmin.

Discussion

In summary, among patients with type 2 diabetes, normal renal function, and proteinuria, there were reductions in systolic blood pressure in groups treated with hydrochlorothiazide or amiloride. Acute kidney injury and severe hyperkalemia were safety concerns with amiloride.

Human epithelial Na+ channel missense variants identified in the GenSalt study alter channel activity

Mutations in genes encoding subunits of the epithelial Na⁺ channel (ENaC) can cause early onset familial hypertension, demonstrating the importance of this channel in modulating blood pressure. It remains unclear whether other genetic variants resulting in subtler alterations of channel function result in hypertension or altered sensitivity of blood pressure to dietary salt. This study sought to identify functional human ENaC variants to examine how these variants alter channel activity and to explore whether these variants are associated with altered sensitivity of blood pressure to dietary salt. Six-hundred participants of the Genetic Epidemiology Network of Salt Sensitivity (GenSalt) study with salt-sensitive or salt-resistant blood pressure underwent sequencing of the genes encoding ENaC subunits. Functional effects of identified variants were examined in a Xenopus oocyte expression system. Variants that increased channel activity included three in the gene encoding the α-subunit (αS115N, αR476W, and αV481M), one in the β-subunit (βS635N), and one in the γ-subunit (γL438Q). One α-subunit variant (αA334T) and one γ-subunit variant (βD31N) decreased channel activity. Several α-subunit extracellular domain variants altered channel inhibition by extracellular Na⁺ (Na⁺ self-inhibition). One variant (αA334T) decreased and one (αV481M) increased cell surface expression. Association between these variants and salt sensitivity did not reach statistical significance. This study identifies novel functional human ENaC variants and demonstrates that some variants alter channel cell surface expression and/or Na⁺ self-inhibition.

Case report: proximal tubule impairment following volatile anesthetic exposure

The safety of contemporary volatile anesthetic agents with respect to kidney function is well established, and growing evidence suggests that volatile anesthetics even protect against ischemic nephropathy. However, studies examining effects of volatile anesthetics on kidney function frequently demonstrate transient proteinuria and glycosuria following exposure to these agents, although the cause of these findings has not been thoroughly examined. We describe the case of a patient who underwent a neurosurgical procedure, then experienced glycosuria without hyperglycemia that resolved within days. Following a second neurosurgical procedure, the patient again developed glycosuria, now associated with ketonuria. Further examination demonstrated nonalbuminuric proteinuria in conjunction with urinary wasting of phosphate and potassium, indicative of proximal tubule impairment. We suggest that transient proximal tubule impairment may play a role in the proteinuria and glycosuria described following volatile anesthetic exposure and discuss the relationship between these observations and the ability of these agents to protect against ischemic nephropathy.

Functional Roles of Clusters of Hydrophobic and Polar Residues in the Epithelial Na+ Channel Knuckle Domain

The extracellular regions of epithelial Na(+) channel subunits are highly ordered structures composed of domains formed by α helices and β strands. Deletion of the peripheral knuckle domain of the α subunit in the αβγ trimer results in channel activation, reflecting an increase in channel open probability due to a loss of the inhibitory effect of external Na(+) (Na(+) self-inhibition). In contrast, deletion of either the β or γ subunit knuckle domain within the αβγ trimer dramatically reduces epithelial Na(+) channel function and surface expression, and impairs subunit maturation. We systematically mutated individual α subunit knuckle domain residues and assessed functional properties of these mutants. Cysteine substitutions at 14 of 28 residues significantly suppressed Na(+) self-inhibition. The side chains of a cluster of these residues are non-polar and are predicted to be directed toward the palm domain, whereas a group of polar residues are predicted to orient their side chains toward the space between the knuckle and finger domains. Among the mutants causing the greatest suppression of Na(+) self-inhibition were αP521C, αI529C, and αS534C. The introduction of Cys residues at homologous sites within either the β or γ subunit knuckle domain resulted in little or no change in Na(+) self-inhibition. Our results suggest that multiple residues in the α subunit knuckle domain contribute to the mechanism of Na(+) self-inhibition by interacting with palm and finger domain residues via two separate and chemically distinct motifs.

Sodium retention and volume expansion in nephrotic syndrome: implications for hypertension

Sodium retention is a major clinical feature of nephrotic syndrome. The mechanisms responsible for sodium retention in this setting have been a subject of debate for years. Excessive sodium retention occurs in some individuals with nephrotic syndrome in the absence of activation of the renin-angiotensin-aldosterone system, suggesting an intrinsic defect in sodium excretion by the kidney. Recent studies have provided new insights regarding mechanisms by which sodium transporters are activated by factors present in nephrotic urine. These mechanisms likely have a role in the development of hypertension in nephrotic syndrome, where hypertension may be difficult to control, and provide new therapeutic options for the management of blood pressure and edema in the setting of nephrotic syndrome.

A trapped intracellular cation modulates K+ channel recovery from slow inactivation

Upon depolarization, many voltage-gated potassium channels undergo a time-dependent decrease in conductance known as inactivation. Both entry of channels into an inactivated state and recovery from this state govern cellular excitability. In this study, we show that recovery from slow inactivation is regulated by intracellular permeant cations. When inactivated channels are hyperpolarized, closure of the activation gate traps a cation between the activation and inactivation gates. The identity of the trapped cation determines the rate of recovery, and the ability of cations to promote recovery follows the rank order K+ > NH4+ > Rb+ > Cs+ >> Na+, TMA. The striking similarity between this rank order and that for single channel conductance suggests that these two processes share a common feature. We propose that the rate of recovery from slow inactivation is determined by the ability of entrapped cations to move into a binding site in the channel's selectivity filter, and refilling of this site is required for recovery.

Effects of dietary L-arginine on structure and function of flow-restricted vein grafts

PURPOSE

Experiments were designed to determine effects of dietary supplementation with L -arginine on structure and function of flow-restricted vein grafts.

METHODS

Saphenous veins were placed as bilateral interposition grafts in femoral arteries of two groups of adult male mongrel dogs; one group was maintained on a normal diet (control), the other group supplemented with L -arginine (200 mg/kg per day) beginning 1 week before surgery. In each dog, flow was reduced by 50% in one graft by placing an adjustable clamp on the artery distal to the distal anastomosis. Plasma amino acids and oxidized products of nitric oxide (NO(x )) were measured before and after L -arginine feeding. At postoperative week 4, grafts were removed and prepared for organ chamber studies to determine functions of the endothelium or smooth muscle and for histology.

RESULTS

Plasma L -arginine increased within 3 hours after feeding and increased from 141 +/- 8 nmol/mL to 169 +/- 11 nmol/mL (n = 6) after 5 weeks of supplementation. Plasma ornithine and citrulline paralleled arginine, whereas circulating NO(x ) was unchanged. Maximal contractions to 60 mmol/L KCl were reduced in grafts from L -arginine-fed dogs. Endothelium-dependent relaxations to the calcium ionophore A23187 and relaxations of the smooth muscle NO were reduced in grafts from L -arginine-fed dogs. Neointimal hyperplasia was increased in grafts with reduced flow and not affected by arginine feeding.

CONCLUSIONS

Dietary supplementation with L -arginine did not increase plasma NO in dogs with peripheral vein grafts or increase endothelium-dependent relaxations in control or flow-restricted grafts. Therefore, dietary supplementation with L -arginine may not improve long-term functions of flow-restricted peripheral bypass grafts.

Inhibition of extracellular signal-regulated kinase 1/2 phosphorylation and induction of apoptosis by sulindac metabolites

Regular use of nonsteroidal anti-inflammatory drugs (NSAIDs) such as aspirin and sulindac is associated with a decreased mortality from colorectal cancer. Sulindac causes regression of precancerous adenomatous polyps and inhibits the growth of cultured colon cell lines. Whereas induction of apoptotic cell death is thought to account for the growth inhibitory effect of sulindac, less is known about its biochemical mechanism(s) of action. Sulindac is metabolized in vivo to sulfide and sulfone derivatives. Both the sulfide and sulfone metabolites of sulindac as well as more potent cyclic GMP-dependent phosphodiesterase inhibitors were shown to cause inhibition of extracellular signal-regulated kinase (ERK)1/2 phosphorylation at doses (40-600 microM) and times (1-5 days) consistent with the induction of apoptosis by the drugs. Treatment of HCT116 human colon cancer cells with the specific mitogen-activated protein kinase kinase, U0126 (5-50 microM) resulted in a time- and dose-dependent inhibition of ERK1/2 phosphorylation, and induction of apoptosis. U0126 treatment (20 microM) increased basal apoptosis, and potentiated the apoptotic effect of sulindac sulfide and sulindac sulfone. These results suggest that the inhibition of ERK1/2 phosphorylation is responsible for at least part of the induction of programmed cell death by sulindac metabolites. Inhibition of ERK1/2 activity may, therefore, be a useful biochemical target for the development of chemopreventive and chemotherapeutic drugs for human colon cancer.

Effects of dietary L-arginine on the reactivity of canine coronary arteries

Experiments were designed to determine the effects of supplemental dietary L-arginine on the endothelial and smooth muscle function of canine coronary arteries. One group of dogs was fed the standard laboratory chow while another group was supplemented with 250 mg/kg per day L-arginine. All dogs had undergone bilateral reversed interposition saphenous vein grafting and received 325 mg/day oral aspirin. After 5 weeks of arginine feeding, left circumflex coronary arteries were removed, cut into rings, and suspended for the measurement of isometric force in organ chambers. Concentration-response curves were obtained to L-arginine, UK-14,304 (alpha2-adrenergic agonist) and A23187 (calcium ionophore) in the absence and presence of N(G)-monomethyl-L-arginine (L-NMMA) and tetraethylammonium (TEA) alone or in combination. Serum concentrations of L-arginine increased by about 20% following 2 weeks of arginine feeding and remained elevated throughout the study. In rings with and without endothelium contracted with prostaglandin F2alpha, L-arginine caused concentration-dependent contractions in rings from control animals but no significant change in tension in rings from arginine-fed animals. Contractions to L-arginine in control animals were reduced by either L-NMMA or TEA. Endothelium-dependent relaxations to the alpha2-adrenergic agonist were decreased with arginine feeding while relaxations to the calcium ionophore and the endothelium-derived factor nitric oxide were similar among groups. Relaxations to UK-14,304 were reduced by L-NMMA in both groups but by TEA only in rings from control animals. These results suggest that dietary supplementation with L-arginine modifies reactivity of endothelium and smooth muscle by at least two mechanisms: one associated with activation of potassium channels and the other with receptor-coupled release of nitric oxide.

Ability of the Cognitive Behavioral Driver's Inventory to distinguish malingerers from brain-damaged subjects

The Cognitive Behavioral Driver's Inventory (CBDI) was analyzed for its ability to discriminate brain-damaged patients from intact subjects who feigned brain-damage. In a sample of 251 neurologically impaired patients and 48 malingering volunteers, the computer-administered distinguished most malingerers from genuine patients. A jackknifed count revealed that the CBDI had 90% sensitivity for detecting malingerers, and 98% specificity for detecting non-malingering brain damaged patients. Success was due to the inability of malingerers to avoid quantitative errors: excessive response latencies, unusual error rates, inflated variability in response latencies, and excessive within-subject, between-item variability. The computer-administered battery may be an effective clinical tool for identifying patients who malinger brain-damage in neuropsychological testing.