Expression Of Renal Transporters Research Articles

Balancing sodium and potassium: Implication of mTORC2-mediated ENaC activation in DCT2 and early CNT for potassium balance in high dietary potassium

Background: The activity of the epithelial sodium ion channel, ENaC, and ENaC-dependent potassium (K+) secretion through ROMK are influenced by both aldosterone-dependent and independent mechanisms in response to dietary potassium (K+). While ENaC activity in the late connecting tubule (CNT) and cortical collecting duct (CCD) depends on aldosterone, it is aldosterone-independent in the late distal convoluted tubule (DCT2) and early CNT (eCNT). Aldosterone-stimulated ENaC activity relies on SGK1, transcriptionally upregulated by aldosterone and subsequently phosphorylated and activated by mTOR complex-2 (mTORC2). Recent evidence suggests that high potassium can rapidly activate mTORC2/SGK1 signaling to stimulate ENaC. In this study, we explore mTORC2’s role in K+ secretion and aldosterone-independent ENaC regulation. Methods: Rictor, a core component of mTORC2, was selectively knocked out (KO'd) in DCT2, CNT and CD by utilizing Calbindin as Cre-driver (CRKO mice) or late CNT and CD, by employing AQP2 as the Cre-driver (ARKO mice). Both wild-type (WT) and KO mice were subjected to a high potassium (HK) diet for short-term (4 hours) or medium-term (48 hours) periods, enabling the monitoring of both the early response and prolonged adaptation to the HK diet. Parameters assessed include urinary and blood electrolyte levels, renal transporter expression, activity and localization, and mTORC2 target phosphorylation. Results: On a normal K+ diet, both KO mice maintained Na+ and K+ balance but CRKO mice had elevated aldosterone levels. After short-term (4-hour) HK intake, CRKO mice had disrupted Na+ and K+ balance, reduced K+ excretion and hyperkalemia. In contrast, ARKO mice maintained Na+ and K+ balance with elevated aldosterone. On a prolonged HK diet (48 hours), CRKO mice had severe hyperkalemia, reduced GFR and significantly elevated aldosterone level. Immunofluorescence studies indicated markedly reduced apical localization of active ENaC in DCT2/eCNT of CRKO mice. Conversely, ENaC apical localization in the late CNT and CCD was mostly unaffected. Phosphorylation of mTORC2 targets involved in ENaC regulation, such as SGK1, and SGK1’s target, Nedd4-2, was also reduced in CRKO mice. ARKO mice maintained ion balance with normal K+ levels but significantly increased aldosterone levels and maintained ENaC apical localization in the late CNT and CCD. Conclusions: The data suggest that high aldosterone can compensate mTORC2 deficiency and maintain ENaC activity in the late CNT and CCD. However, mTORC2 activity is crucial for maintaining ENaC activity in the late DCT and early CNT (aldosterone-independent) and preserving potassium balance during high dietary potassium intake. National Institutes of Health (R01- DK56695), James Hilton Manning and Emma Austin Manning Foundation. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

GHB toxicokinetics and renal monocarboxylate transporter expression are influenced by the estrus cycle in rats

BackgroundThe illicit use and abuse of gamma-hydroxybutyric acid (GHB) occurs due to its sedative/hypnotic and euphoric effects. Currently, there are no clinically available therapies to treat GHB overdose, and care focuses on symptom treatment until the drug is eliminated from the body. Proton- and sodium-dependent monocarboxylate transporters (MCTs (SLC16A) and SMCTs (SLC5A)) transport and mediate the renal clearance and distribution of GHB. Previously, it has been shown that MCT expression is regulated by sex hormones in the liver, skeletal muscle and Sertoli cells. The focus of the current study is to evaluate GHB toxicokinetics and renal monocarboxylate transporter expression over the estrus cycle in females, and in the absence of male and female sex hormones.MethodsGHB toxicokinetics and renal transporter expression of MCT1, SMCT1 and CD147 were evaluated in females over the estrus cycle, and in ovariectomized (OVX) female, male and castrated (CST) male rats. GHB was administered iv bolus (600 and 1000 mg/kg) and plasma and urine samples were collected for six hours post-dose. GHB concentrations were quantified using a validated LC/MS/MS assay. Transporter mRNA and protein expression was quantified by qPCR and Western Blot.ResultsGHB renal clearance and AUC varied between sexes and over the estrus cycle in females with higher renal clearance and a lower AUC in proestrus females as compared to males (intact and CST), and OVX females. We demonstrated that renal MCT1 membrane expression varies over the estrus cycle, with the lowest expression observed in proestrus females, which is consistent with the observed changes in GHB renal clearance.ConclusionsOur results suggest that females may be less susceptible to GHB-induced toxicity due to decreased exposure resulting from increased renal clearance, as a result of decreased renal MCT1 expression.

Representative Rodent Models for Renal Transporter Alterations in Human Nonalcoholic Steatohepatitis.

Alterations in renal elimination processes of glomerular filtration and active tubular secretion by renal transporters can result in adverse drug reactions. Nonalcoholic steatohepatitis (NASH) alters hepatic transporter expression and xenobiotic elimination, but until recently, renal transporter alterations in NASH were unknown. This study investigates renal transporter changes in rodent models of NASH to identify a model that recapitulates human alterations. Quantitative protein expression by surrogate peptide liquid chromatography-coupled mass spectrometry (LC-MS/MS) on renal biopsies from NASH patients was used for concordance analysis with rodent models, including methionine/choline deficient (MCD), atherogenic (Athero), or control rats and Leprdb/db MCD (db/db), C57BL/6J fast-food thioacetamide (FFDTH), American lifestyle-induced obesity syndrome (ALIOS), or control mice. Demonstrating clinical similarity to NASH patients, db/db, FFDTH, and ALIOS showed decreases in glomerular filtration rate (GFR) by 76%, 28%, and 24%. Organic anion transporter 3 (OAT3) showed an upward trend in all models except the FFDTH (from 3.20 to 2.39 pmol/mg protein), making the latter the only model to represent human OAT3 changes. OAT5, a functional ortholog of human OAT4, significantly decreased in db/db, FFDTH, and ALIOS (from 4.59 to 0.45, 1.59, and 2.83 pmol/mg protein, respectively) but significantly increased for MCD (1.67 to 4.17 pmol/mg protein), suggesting that the mouse models are comparable to human for these specific transport processes. These data suggest that variations in rodent renal transporter expression are elicited by NASH, and the concordance analysis enables appropriate model selection for future pharmacokinetic studies based on transporter specificity. These models provide a valuable resource to extrapolate the consequences of human variability in renal drug elimination. SIGNIFICANCE STATEMENT: Rodent models of nonalcoholic steatohepatitis that recapitulate human renal transporter alterations are identified for future transporter-specific pharmacokinetic studies to facilitate the prevention of adverse drug reactions due to human variability.

A Machine Learning Model to Estimate Toxicokinetic Half-Lives of Per- and Polyfluoro-Alkyl Substances (PFAS) in Multiple Species

Per- and polyfluoroalkyl substances (PFAS) are a diverse group of man-made chemicals that are commonly found in body tissues. The toxicokinetics of most PFAS are currently uncharacterized, but long half-lives (t½) have been observed in some cases. Knowledge of chemical-specific t½ is necessary for exposure reconstruction and extrapolation from toxicological studies. We used an ensemble machine learning method, random forest, to model the existing in vivo measured t½ across four species (human, monkey, rat, mouse) and eleven PFAS. Mechanistically motivated descriptors were examined, including two types of surrogates for renal transporters: (1) physiological descriptors, including kidney geometry, for renal transporter expression and (2) structural similarity of defluorinated PFAS to endogenous chemicals for transporter affinity. We developed a classification model for t½ (Bin 1: <12 h; Bin 2: <1 week; Bin 3: <2 months; Bin 4: >2 months). The model had an accuracy of 86.1% in contrast to 32.2% for a y-randomized null model. A total of 3890 compounds were within domain of the model, and t½ was predicted using the bin medians: 4.9 h, 2.2 days, 33 days, and 3.3 years. For human t½, 56% of PFAS were classified in Bin 4, 7% were classified in Bin 3, and 37% were classified in Bin 2. This model synthesizes the limited available data to allow tentative extrapolation and prioritization.

Elevated Maternal Testosterone Levels Alter PFOA Elimination and Tissue Distribution in Pregnant Rats.

Perfluorooctanoic acid (PFOA) is an enduring synthetic chemical that harms human health. Recent studies indicate heightened bioaccumulation of PFOA, particularly in pregnant women experiencing preeclampsia. Since plasma testosterone levels are elevated in pregnant women with preeclampsia, we hypothesized that hyperandrogenic conditions during pregnancy may hinder PFOA elimination and contribute to their higher body burden. Pregnant Sprague-Dawley rats were s/c injected with vehicle or testosterone propionate from gestational day (GD) 15 to 20 to increase plasma testosterone levels by 2-fold, similar to levels in preeclampsia. On GD 16, [14C]-PFOA (9.4 pmol/kg) was given intravenously, and subsequently, 14C radioactivity was measured in maternal blood, urine, feces, and tissues. PFOA was primarily eliminated through urine; however, less PFOA was excreted in urine of pregnant rats with elevated testosterone levels than controls. Fecal excretion of PFOA was minimal and did not significantly differ between groups. The total elimination of PFOA (urine plus feces) was significantly reduced by 12% in pregnant rats with elevated testosterone levels. In controls, PFOA distribution was highest in placenta, followed by the kidneys, liver, brain, heart, lungs, and spleen. Pregnant rats with elevated testosterone levels displayed 12% higher concentrations of PFOA in these tissues than controls. Furthermore, the renal expression of Oat2 and Oat3 was significantly decreased, while Oatp1 and Oat-k expression was significantly increased in pregnant rats with elevated testosterone levels than controls. In conclusion, elevated maternal testosterone levels decrease urinary elimination of PFOA, possibly through altered expression of renal transporters leading to increased tissue concentrations of PFOA in pregnant rats.

Renal Transporter Alterations in Patients with Chronic Liver Diseases: Nonalcoholic Steatohepatitis, Alcohol-Associated, Viral Hepatitis, and Alcohol-Viral Combination.

Alterations in hepatic transporters have been identified in precirrhotic chronic liver diseases (CLDs) that result in pharmacokinetic variations causing adverse drug reactions (ADRs). However, the effect of CLD on the expression of renal transporters is unknown despite the overwhelming evidence of kidney injury in CLD patients. This study determines the transcriptomic and proteomic expression profiles of renal drug transporters in patients with defined CLD etiology. Renal biopsies were obtained from patients with a history of CLD etiologies, including nonalcoholic fatty liver disease (NAFLD), nonalcoholic steatohepatitis (NASH), alcohol-associated liver disease (ALD), viral hepatitis C (HCV), and combination ALD/HCV. A significant decrease in organic anion transporter (OAT)-3 was identified in NASH, ALD, HCV, and ALD/HCV (1.56 ± 1.10; 1.01 ± 0.46; 1.03 ± 0.43; 0.86 ± 0.57 pmol/mg protein) relative to control (2.77 ± 1.39 pmol/mg protein). Additionally, a decrease was shown for OAT4 in NASH (24.9 ± 5.69 pmol/mg protein) relative to control (43.8 ± 19.9 pmol/mg protein) and in urate transporter 1 (URAT1) for ALD and HCV (1.56 ± 0.15 and 1.65 ± 0.69 pmol/mg protein) relative to control (4.69 ± 4.59 pmol/mg protein). These decreases in organic anion transporter expression could result in increased and prolonged systemic exposure to drugs and possible toxicity. Renal transporter changes, in addition to hepatic transporter alterations, should be considered in dose adjustments for CLD patients for a more accurate disposition profile. It is important to consider a multiorgan approach to altered pharmacokinetics of drugs prescribed to CLD patients to prevent ADRs and improve patient outcomes. SIGNIFICANCE STATEMENT: Chronic liver diseases are known to elicit alterations in hepatic transporters that result in a disrupted pharmacokinetic profile for various drugs. However, it is unknown if there are alterations in renal transporters during chronic liver disease, despite strong indications of renal dysfunction associated with chronic liver disease. Identifying renal transporter expression changes in patients with chronic liver disease facilitates essential investigations on the multifaceted relationship between liver dysfunction and kidney physiology to offer dose adjustments and prevent adverse drug reactions.

Sodium Status Modulates the Effects of Aldosterone on Renal Transporter Expression and Tubular Remodeling

Aldosterone (aldo) is a steroid hormone that has a key role in extracellular volume and K+ homeostasis. While aldo levels are expected to be suppressed with high Na+intake, 5‐10% of hypertensives have chronic hyperaldosteronism regardless of Na+ intake. This combination of high sodium and high aldo can worsen end organ damage, especially in the kidney. We examined the effects of elevated aldo in the absence or presence of a high salt diet (HSD) on the expression of Na+ transporters in the distal nephron and on distal nephron remodeling to understand if these changes may play a role in the altered pathology. Male C57Bl/6 mice received either a control (0.4% NaCl) or HSD (4 weeks, 8% NaCl), +/‐ aldo via minipump for the final 2 weeks of treatment (240 μg/kg/day). Transporter expression levels and localization were analyzed by Western blot, qPCR and immunofluorescent staining. Expression of the α subunit of the epithelial sodium channel (ENaC) was increased with aldosterone regardless of Na+ intake, while subunits increased at both a transcript and protein level in mice receiving aldo and HSD. Both total levels of sodium chloride cotransporter (NCC) and active pNCC significantly increased with aldo alone, in association with a fall in blood [K+]. However, the addition of HSD markedly attenuated this increase in NCC and pNCC, despite more severe hypokalemia. This change was not associated with a difference in the expression of its upstream kinase SPAK. NKCC2 expression was not significantly altered in any of the conditions. We imaged whole tubules in thick kidney slices (300μm) to assess whether remodeling of the distal tubule could account for NCC expression differences. Sections were incubated with antibodies against pNCC and AQP2 and cleared with ethyl cinnamate to allow for imaging and analysis of whole distal tubules. Length of the distal tubule was analyzed as the pNCC positive portion. While aldo has previously been shown to promote hypertrophy of the distal tubule, we found a significant shortening of tubules in animals treated chronically with 2 weeks of aldo (Ctl 434m ± 63μm versus aldo 375m ± 88m, P&lt;0.05, n=38 and 30 respectively). However, the addition of HSD with aldo caused a significant increase in distal tubule length (486m ±68μm, P&lt;0.05, n=23). HSD by itself did not alter distal tubule length (428m ± 55m, n=17). Our results suggest that aldo‐mediated transcriptional regulation of ENaC subunits in the kidney changes according to dietary Na+ status. The attenuation of increased NCC and pNCC expression in kidneys of mice receiving HSD with aldo, despite profound hypokalemia and an increase in DCT length, suggest that factors other than blood [K+] have important roles in regulating NCC expression. Finally, aldo‐dependent DCT remodeling is dependent on dietary Na+.

Attenuated Ochratoxin A Transporter Expression in a Mouse Model of Nonalcoholic Steatohepatitis Protects against Proximal Convoluted Tubule Toxicity.

Ochratoxin A (OTA) is an abundant mycotoxin, yet the toxicological impact of its disposition is not well studied. OTA is an organic anion transporter (OAT) substrate primarily excreted in urine despite a long half-life and extensive protein binding. Altered renal transporter expression during disease, including nonalcoholic steatohepatitis (NASH), may influence response to OTA exposure, but the impact of NASH on OTA toxicokinetics, tissue distribution, and associated nephrotoxicity is unknown. By inducing NASH in fast food-dieted/thioacetamide-exposed mice, we evaluated the effect of NASH on a bolus OTA exposure (12.5 mg/kg by mouth) after 3 days. NASH mice presented with less gross toxicity (44% less body weight loss), and kidney and liver weights of NASH mice were 11% and 24% higher, respectively, than healthy mice. Organ and body weight changes coincided with reduced renal proximal tubule cells vacuolation, degeneration, and necrosis, though no OTA-induced hepatic lesions were found. OTA systemic exposure in NASH mice increased modestly from 5.65 ± 1.10 to 7.95 ± 0.61 mg*h/ml per kg BW, and renal excretion increased robustly from 5.55% ± 0.37% to 13.11% ± 3.10%, relative to healthy mice. Total urinary excretion of OTA increased from 24.41 ± 1.74 to 40.07 ± 9.19 µg in NASH mice, and kidney-bound OTA decreased by ∼30%. Renal OAT isoform expression (OAT1-5) in NASH mice decreased by ∼50% with reduced OTA uptake by proximal convoluted cells. These data suggest that NASH-induced OAT transporter reductions attenuate renal secretion and reabsorption of OTA, increasing OTA urinary excretion and reducing renal exposure, thereby reducing nephrotoxicity in NASH. SIGNIFICANCE STATEMENT: These data suggest a disease-mediated transporter mechanism of altered tissue-specific toxicity after mycotoxin exposure, despite minimal systemic changes to ochratoxin A (OTA) concentrations. Further studies are warranted to evaluate the clinical relevance of this functional model and the potential effect of human nonalcoholic steatohepatitis on OTA and other organic anion substrate toxicity.

Antioxidant effect of ascorbic acid against cisplatin-induced nephrotoxicity and P-glycoprotein expression in rats

Cisplatin (CDDP) is a highly potent anticancer drug that is widely used in the treatment of several cancers. CDDP-induced nephrotoxicity (CIN) is one of the most significant adverse effects, and oxidative stress is thought to be one of the mechanisms underlying CIN. Although there are some studies available on the variability in transporter expression in the kidney after a single CDDP dose, none have reported the change in renal transporter expression after multiple CDDP dose administrations. P-glycoprotein (P-gp), a transporter, is reported to be induced by oxidative stress. Ascorbic acid is a vitamin with antioxidant potential and therefore, may regulate the expression of P-gp transporter and affect CIN. In the present study, our aim was to assess the variability in expression of several renal transporters after multiple CDDP dose administrations and the antioxidant effect of ascorbic acid against transporter expression and CIN. Multiple doses of CDDP affected markers of kidney injury and antioxidants in the kidneys. Also, the expression of P-gp, breast cancer resistance protein, and multidrug resistance-associated protein 4 was upregulated by CDDP. Using a normal kidney cell line, we demonstrated that ascorbic acid attenuated CDDP-induced cytotoxicity due to its high superoxide scavenging ability. CDDP and ascorbic acid were injected into rats once a week for three weeks, and it was observed that co-administration of ascorbic acid attenuated CIN and regulated antioxidant marker. In addition, ascorbic acid reduced P-gp expression, which was upregulated by CDDP. In conclusion, ascorbic acid may attenuate CIN and reverse P-gp-mediated changes in drug pharmacokinetics.

Changes of renal transporters in the kinetic process of VCM-induced nephrotoxicity in mice.

Renal transporters involved in tubular excretion pathway are considered to be the key concern in drug evaluations in nephrotoxicity. However, the relationship between the alternation of renal transporters and the kinetic process of vancomycin (VCM)-induced nephrotoxicity has not been fully elucidated. The present study investigated the alteration of renal transporters expression in the kinetic process of VCM-induced nephrotoxicity in mice. C57BL/6 mice were administrated with normal saline or VCM for 7days. Biochemical and pathological analyses were conducted to investigate the nephrotoxicity induced by VCM administration. Renal oxidative status, plasma, and kidney content of VCM were monitored. Quantitative real-time polymerase chain reaction and immunohistochemistry analyses were performed to analyze the expression of renal transporters. Finally, our data showed that the exposure of VCM (400mg/kg) caused a slight nephrotoxicity in mice, whereas exposure of VCM (600mg/kg) resulted in the severe nephrotoxicity in mice as evidenced by biochemical parameters and renal morphological changes. In addition, the accumulation of VCM in kidney is higher than plasma. Interestingly, VCM (600mg/kg, body weight) resulted in the induction of Oct2-Mate1 and Oat1/3-Mrp2/Mrp4/Bcrp pathways. However, VCM (400mg/kg, body weight) caused the induction of Oct2-Mate1/Mate2 and Oat1/3-Mrp4/Bcrp pathways. The changes of renal transporters in association with the kinetic process of VCM-induced nephrotoxicity may exert important practical implications for its optimal use in clinic.

Altered cisplatin pharmacokinetics during nonalcoholic steatohepatitis contributes to reduced nephrotoxicity

Disease-mediated alterations to drug disposition constitute a significant source of adverse drug reactions. Cisplatin (CDDP) elicits nephrotoxicity due to exposure in proximal tubule cells during renal secretion. Alterations to renal drug transporter expression have been discovered during nonalcoholic steatohepatitis (NASH), however, associated changes to substrate toxicity is unknown. To test this, a methionine- and choline-deficient diet-induced rat model was used to evaluate NASH-associated changes to CDDP pharmacokinetics, transporter expression, and toxicity. NASH rats administered CDDP (6 mg/kg, i.p.) displayed 20% less nephrotoxicity than healthy rats. Likewise, CDDP renal clearance decreased in NASH rats from 7.39 to 3.83 mL/min, renal secretion decreased from 6.23 to 2.80 mL/min, and renal CDDP accumulation decreased by 15%, relative to healthy rats. Renal copper transporter-1 expression decreased, and organic cation transporter-2 and ATPase copper transporting protein-7b increased slightly, reducing CDDP secretion. Hepatic CDDP accumulation increased 250% in NASH rats relative to healthy rats. Hepatic organic cation transporter-1 induction and multidrug and toxin extrusion protein-1 and multidrug resistance-associated protein-4 reduction may contribute to hepatic CDDP sequestration in NASH rats, although no drug-related toxicity was observed. These data provide a link between NASH-induced hepatic and renal transporter expression changes and CDDP renal clearance, which may alter nephrotoxicity.

An Improved Vascularized, Dual-Channel Microphysiological System Facilitates Modeling of Proximal Tubular Solute Secretion.

A vascularized human proximal tubule model in a dual-channel microphysiological system (VPT-MPS) was developed, representing an advance over previous, single-cell-type kidney microphysiological systems. Human proximal tubule epithelial cells (PTECs) and human umbilical vein endothelial cells (HUVECs) were cocultured in side-by-side channels. Over 24 h of coculturing, PTECs maintained polarized expression of Na+/K+ ATPase, tight junctions (ZO-1), and OAT1. HUVECs showed the absence of ZO-1 but expressed endothelial cell marker (CD-31). In time-lapse imaging studies, fluorescein isothiocyanate (FITC)-dextran passed freely from the HUVEC vessel into the supporting extracellular matrix, confirming the leakiness of the endothelium (at 80 min, matrix/intravessel fluorescence ratio = 0.2). Dextran-associated fluorescence accumulated in the matrix adjacent to the basolateral aspect of the PTEC tubule with minimal passage of the compound into the tubule lumen observed (at 80 min, tubule lumen/matrix fluorescence ratio = 0.01). This demonstrates that the proximal tubule compartment is the rate-limiting step in the secretion of compounds in VPT-MPS. In kinetic studies with radiolabeled markers, p-aminohippuric acid (PAH) exhibited greater output into the tubule lumen than did paracellular markers mannitol and FITC-dextran (tubule outflow/vessel outflow concentration ratio of 7.7% vs 0.5 and 0.4%, respectively). A trend toward reduced PAH secretion by 45% was observed upon coadministration of probenecid. This signifies functional expression of renal transporters in PTECs that normally mediate the renal secretion of PAH. The VPT-MPS holds the promise of providing an in vitro platform for evaluating the renal secretion of new drug candidates and investigating the dysregulation of tubular drug secretion in chronic kidney disease.

Dysregulation of renal transporters in a rodent model of viral Infection

Inflammation elicited by viral mimetic poly I:C has been shown to impose changes in the expression of drug transporters in the placenta and maternal liver in rats at term pregnancy. This was associated with altered drug disposition in the mother and fetus. Renal transporters play an important role in the elimination of several drugs taken by pregnant women. We examined the impact of poly I:C on the expression of renal transporters in pregnant rats at term. Pregnant Sprague-Dawley rats received single intraperitoneal dose of either poly I:C (5 mg/kg) or saline at gestation day 18 (n = 8/group). Animals were euthanized 24 h after the injection. The mRNA and protein expression of pro-inflammatory cytokines and transporters were measured by qRT-PCR and western blot. Poly I:C caused a fourfold increase in the mRNA of IL-6 in the kidney. As compared to saline controls, the mRNA expression of Mrp2, Bcrp, Octn1, Oat1, Oat2, Oat3, Urat1, Oatp4c1, and Pept2 was downregulated, whereas the Ent1 mRNA was increased. Protein expression of Bcrp, Urat1 and Pept2 were significantly decreased. While there was a trend towards reduced Mrp2, Oat2 and Oat3 protein expression, this did not reach significance. Poly I:C did not impact mRNA levels of Mdr1a, Mdr1b, Mrp4, Oct1, Oct2, Oct3, Octn2, Mate1, Ent2 or Pept1. Viral-induced inflammation mediates significant changes in the expression of several key drug transporters in the kidney of pregnant rats. Many clinically important drugs are substrates for these transporters. Therefore, inflammation-mediated alterations in transporter expression could affect their maternal and fetal disposition.

Impact of Viral Inflammation on the Expression of Renal Drug Transporters in Pregnant Rats.

Inflammation impacts the expression and function of drug transporters at term-gestation; however, the impact of inflammation on the expression of drug transporters at mid-gestation is largely unknown. Since renal drug transporters play a key role in the clearance of many drugs prescribed during pregnancy, our objective was to study the impact of the viral mimetic poly I:C on the expression of renal transporters in pregnant rats at mid-gestation. Poly I:C (10 mg/kg) or saline was administered intraperitoneally to pregnant Sprague–Dawley rats on gestational day 14. Expression of renal transporters was measured at 6, 24, and 48 h by qRT-PCR and Western blot. The mRNA levels of Mdr1a, Mrp4, Oct2, Octn1, Octn2, Mate1, Oat1-3, Urat1, Oatp4c1, Ent1, and Pept2 were significantly lower in the poly I:C group at 6 h. At 24 h, only the mRNA levels of Oct2, Oatp4c1, and Ent1 were decreased compared to saline. Poly I:C significantly decreased protein expression of Urat1 at 24 h, and P-gp, Oct2, Mate1, Oat1, Oat3 at 48 h,. Poly I:C imposed significant reductions in the expression of several key renal transporters at mid-gestation in pregnant rats. Thus, viral infection may impact renal excretion of drug transporter substrates, potentially leading to drug–disease interactions.

Magnesium co-administration decreases cisplatin-induced nephrotoxicity in the multiple cisplatin administration

PurposePretreatment with magnesium (Mg) has been reported to attenuate cisplatin (CDDP)-induced nephrotoxicity (CIN). This attenuation involves modulation of the expression of renal transporters, resulting in reduced renal platinum accumulation after a single round of CDDP treatment. In this study, we investigated whether Mg co-administration ameliorates CIN after multiple doses of CDDP as effectively as after a single dose. MethodsRats were divided into control, Mg alone, CDDP alone, and CDDP with Mg groups. Rats received CDDP (2.5mg/kg), MgSO4 (40mg/kg), or saline once per week for three weeks. Seven days after the third round of treatment, the kidneys were excised, and the expression of renal transporters and renal platinum accumulation were analyzed. ResultsCDDP significantly elevated serum creatinine levels, which were significantly reduced by Mg co-administration. Renal platinum accumulation was significantly lower in the CDDP-Mg group than in the CDDP group. Expression of renal organic cation transporter 2 (rOct2) and multidrug and toxin extrusion protein 1 (rMate1), which are involved in CDDP transport, did not differ between the groups. However, the expression of copper transporter 1 (rCtr1) was significantly downregulated after Mg co-administration. ConclusionMg co-administration significantly attenuated CIN by reducing renal platinum accumulation even after multiple rounds of treatment with CDDP as effectively as in a model of a single CDDP administration. However, the specific underlying mechanism was different between single and multiple administrations, further studies will be needed to identify what contributes to this difference and to elucidate how Mg regulates the expression of renal transporters.

Magnesium attenuates cisplatin-induced nephrotoxicity by regulating the expression of renal transporters

Cisplatin (CDDP)-induced nephrotoxicity (CIN) is one of the most serious toxicities caused by this potent antitumor agent. It has been reported that Mg premedication attenuates CIN in clinical trials; however, the mechanism underlying its nephroprotection is not fully understood. Therefore, the aim of this study was to determine whether Mg administration affects CDDP accumulation by regulating the expression level of renal transporters. Rats were divided into control, Mg (40mg/kg) alone, 2.5mg/kg CDDP with (20 and 40mg/kg) and without Mg, 5mg/kg CDDP groups. These substances were administered on the same day and 7 days later their kidneys were removed. The expression levels of renal transporters and platinum (Pt) accumulation were analyzed. The serum creatinine level was significantly increased by CDDP administration and treatment with Mg significantly ameliorated such elevation. The expressions of the renal organic cation transporter 2 (rOct2) and renal multidrug and toxin extrusion protein 1 (rMate1) were downregulated and upregulated, respectively following co-administration with Mg, which significantly reduced the renal Pt accumulation in the 2.5mg/kg CDDP-treated group. Moreover, Mg dose-dependently downregulated rOct2, not affecting rMate expression, resulting in the attenuation of CIN. Mg co-administration protected the downregulation of the transient receptor potential subfamily Melastatin 6 (rTrpm6), but not the epidermal growth factor (rEgf), as a result, Mg co-injection attenuated CDDP-induced hypomagnesemia. In conclusion, Mg co-administration reduced Pt accumulation by regulating the expression of the renal transporters, rOct2 and rMate1 and, thereby, attenuated CIN.

Renal‐selective Snx5 gene silencing increases blood pressure and renal sodium transporters in mice

We have reported that sorting nexin 5 (SNX5) plays an important role in the positive regulation of the renal dopamine receptor subtype 1 (D1R). siRNA‐mediated gene silencing of renal Snx5 results in anti‐natriuresis and increases further the elevated blood pressure (BP) of spontaneously hypertensive rats. We tested the hypothesis that the increased renal sodium transport and increased BP following Snx5 gene silencing is accompanied by changes in the expression of renal transporters in C57BL6/J mice. We infused subcapsularly the Snx5‐specific siRNA (3 μg/kg/day), or non‐silencing “mock” siRNA as control, for 7 days in 8 1‐year old, previously uninephrectomized male C57BL6 mice. A 24‐hour urine was collected from the mice housed in metabolic cages a day prior to the end of the siRNA infusion. Renal SNX5 protein expression was decreased by 60% with Snx5‐siRNA relative to control group. Renal SNX5‐depleted mice had elevated systolic (119±5.2 mm Hg, measured under anesthesia) and diastolic BPs (91.8±7.3 mm Hg) relative to control mice (systolic BP=101.5±0.5 mm Hg, diastolic BP=72±2.3 mm Hg). Urine sodium excretion tended to decrease in SNX5‐depleted mice (0.68±0.22 mmol/Cr mg) relative to controls (1.08±0.30 mmol/ Cr mg). Moreover, renal SNX5 depletion shifted the pressure natriuresis curve to the right. Food and water intake, body weight, urine volume, and heart rate were similar in the two groups. SNX5 is mainly located at the apical membrane of proximal tubules (PT), thick ascending limbs of loop of Henle (TAL) and distal convoluted tubules (DCT). SNX5 was observed via confocal microscopy to colocalize with NHE3, NKCC2 and NCC in C57Bl/6J mice under basal conditions. However, the co‐staining is strongest with NHE3 in the PT, relative to NKCC 2 and NCC which are expressed in TAL and DCT, respectively. The expression of renal NHE3 (172±29 % of control), NaPi2 (223±12%), NKCC2 (440±12%) and NCC (177±23%) were greater in SNX5‐depleted mice than in control mice. Renal protein expressions of α,β,γ‐ENaCs, Na+K+ATPase and actin were similar in the 2 groups. These findings suggest that inhibition of SNX5 expression with siRNA increases sodium transporters in proximal and distal nephron segments. This may lead to the inability of renal D1R to inhibit renal sodium transport and may be responsible for the increased BP in Snx5‐siRNA‐ treated mice.Support or Funding InformationThis work was supported in part by grants from the National Institutes of Health, R37HL023081, R01DK039308, P01HL068686, P01HL074940, and R01HL092196. Dr. Xiaoyan Wang was supported, in part, by National Kidney Foundation of Maryland (Professional Development Award, 2014).

Increased Plasma Exposures of Conjugated Metabolites of Morinidazole in Renal Failure Patients: A Critical Role of Uremic Toxins.

Morinidazole is a 5-nitroimidazole drug. Its sulfate conjugate M7 was a sensitive substrate of organic anion transporter 1 (OAT1) and OAT3, whereas N+-glucuronides M8-1 and M8-2 were only OAT3 substrates. In chronic renal failure (CRF) patients, plasma exposures of the three conjugates increased by 15-fold, which were also found in 5/6 nephrectomized (5/6 Nx) rats in this study. Although the transcriptions of Oat1 and Oat3 in 5/6 Nx rat kidneys decreased by 50%, no difference was observed on the three conjugate uptakes between control and 5/6 Nx rat kidney slices. Thus, the highly elevated endogenous uremic toxins in 5/6 Nx rats and humans, namely, 3-carboxy-4-methyl-5-propyl-2-furanpropionate (CMPF), hippuric acid (HA), and indoxyl sulfate (IS), were considered as influential factors. In rat kidney slices, the uptake of M7, M8-1, and M8-2 was dose dependently reduced by HA and IS, whose plasma concentrations were elevated 5 times in 5/6 Nx rats. In OAT3-overexpressed cells, the three conjugate uptakes were inhibited by CMPF, HA, and IS with IC50 values of 19.2, 87.4, and 222 μM (M7); 8.53, 39.4, and 161 μM (M8-1); and 6.75, 24.1, and 78.3 μM (M8-2), respectively. In OAT1-overexpressed cells, CMPF, HA, and IS showed weak inhibition on M7 uptake with IC50 values of 187, 162, and 200 μM, correspondingly. Results suggest that the reduced mRNA expression of renal transporters in CRF patients may not influence the activities of these transporters. However, accumulated uremic toxins may inhibit the transporters, particularly OAT3, leading to plasma exposure changes of relevant substrates.

M-RNA Expression of Renal Transporters and Drug Metabolizing Enzymes Changes With Time Following Living and Deceased Donor Renal Transplantation.

Introduction:A renal allograft undergoes cold ischemia(CI), warm-reperfusion injury, and calcineurin-inhibitor nephrotoxicity during its functional life-time. These abuses may alter the expression and activity of renal drug transporters(RDTs) and drug metabolizing enzymes(DMEs) which may inturn alter Transplant(Tx) medication disposition. Rodent data from our group suggests changes in mRNA expression of RDTs post-Tx. The objective of this study was to evaluate the effect of prolonged CI on longitudinal changes in RDTs and DMEs post-Tx in living donor(LD) and deceased donor(DD) renal-Tx recipients. Methods:GSE11166 microarray dataset (GPL570 Affymetrix-GeneChip) with baseline biopsies from 14DD and 14LD and 67 protocol renal biopsies obtained at 3, 6, 12 and 24months post-Tx was accessed through the NIH-Gene Expression Omnibus(GEO). Partek Genomic Suite® was used to analyze significant changes in mRNA expression of RDTs and DMEs deemed important for drug disposition by the FDA and EMA. Results:DD kidneys exhibited 1.5-5 fold decline in ABCB1, SLC22A1, CYP2B6, CYP3A4, and CYP3A7 and a 1.6-2.7 fold increase in SLCO4C1, SLC15A1, SLC22A1, CYP2C9 and UGT1A1 mRNA expression compared to LD.Table: No Caption available.ABCB4, SLC22A3, and CYP3A4 mRNA expression significantly and non-uniformly increased by 2 fold in DD kidney-Tx recipients, whereas ABCC4, SLC15A1, SLC22A5, SLCO4C1, CYP2C9 and UGT1A6 mRNA expression is significantly and non-uniformly decreased(ratio:0.32-0.54) in DD kidney-Tx recipients. Conclusion:Prolonged CI, Warm reperfusion injury, surgical stress associated with kidney-Tx and calcineurin-inhibitor nephrotoxicity significantly alters the mRNA expression of important RDTs and DMEs in DD transplant recipients compared to LD. GEO database combined with Partek Genomic Suite® is an invaluable tool to understand the changes in gene expression of target genes in publicly available NIH funded biosets.

Cold Ischemia, Renal Transplantation and Tacrolimus Significantly Alter the Gene Expression of Renal Transporters in Rats.

Cold Ischemia, Renal Transplantation and Tacrolimus Significantly Alter the Gene Expression of Renal Transporters in Rats.