SLC25A51 is a mammalian mitochondrial NAD+ transporter.

Mitochondria require nicotinamide adenine dinucleotide (NAD+) to carry out the fundamental processes that fuel respiration and mediate cellular energy transduction. Mitochondrial NAD+ transporters have been identified in yeast and plants1,2, but their existence in mammals remains controversial3-5. Here we demonstrate that mammalian mitochondria can take up intact NAD+, and identify SLC25A51 (also known as MCART1)-an essential6,7 mitochondrial protein of previously unknown function-as a mammalian mitochondrial NAD+ transporter. Loss of SLC25A51 decreases mitochondrial-but not whole-cell-NAD+ content, impairs mitochondrial respiration, and blocks the uptake of NAD+ into isolated mitochondria. Conversely, overexpression of SLC25A51 or SLC25A52 (a nearly identical paralogue of SLC25A51) increases mitochondrial NAD+ levels and restores NAD+ uptake into yeast mitochondria lacking endogenous NAD+ transporters. Together, these findings identify SLC25A51 as a mammalian transporter capable of importing NAD+ into mitochondria.

RNA editing of SLC22A3 drives early tumor invasion and metastasis in familial esophageal cancer.

Like many complex human diseases, esophageal squamous cell carcinoma (ESCC) is known to cluster in families. Familial ESCC cases often show early onset and worse prognosis than the sporadic cases. However, the molecular genetic basis underlying the development of familial ESCC is mostly unknown. We reported that SLC22A3 is significantly down-regulated in nontumor esophageal tissues from patients with familial ESCC compared with tissues from patients with sporadic ESCCs. A-to-I RNA editing of the SLC22A3 gene results in its reduced expression in the nontumor esophageal tissues of familial ESCCs and is significantly correlated with lymph node metastasis. The RNA-editing enzyme ADAR2, a familial ESCC susceptibility gene identified by our post hoc genome-wide association study, is positively correlated with the editing level of SLC22A3 Moreover, functional studies showed that SLC22A3 is a metastasis suppressor in ESCC, and deregulation of SLC22A3 facilitates cell invasion and filopodia formation by reducing its direct association with α-actinin-4 (ACTN4), leading to the increased actin-binding activity of ACTN4 in normal esophageal cells. Collectively, we now show that A-to-I RNA editing of SLC22A3 contributes to the early development and progression of familial esophageal cancer in high-risk individuals.

The impact of Organic Anion-Transporting Polypeptides (OATPs) on disposition and toxicity of antitumor drugs: Insights from knockout and humanized mice.

It is now widely accepted that organic anion-transporting polypeptides (OATPs), especially members of the OATP1A/1B family, can have a major impact on the disposition and elimination of a variety of endogenous molecules and drugs. Owing to their prominent expression in the sinusoidal plasma membrane of hepatocytes, OATP1B1 and OATP1B3 play key roles in the hepatic uptake and plasma clearance of a multitude of structurally diverse anti-cancer and other drugs. Here, we present a thorough assessment of the currently available OATP1A and OATP1B knockout and transgenic mouse models as key tools to study OATP functions in vivo. We discuss recent studies using these models demonstrating the importance of OATPs, primarily in the plasma and hepatic clearance of anticancer drugs such as taxanes, irinotecan/SN-38, methotrexate, doxorubicin, and platinum compounds. We further discuss recent work on OATP-mediated drug-drug interactions in these mouse models, as well as on the role of OATP1A/1B proteins in the phenomenon of hepatocyte hopping, an efficient and flexible way of liver detoxification for both endogenous and exogenous substrates. Interestingly, glucuronide conjugates of both the heme breakdown product bilirubin and the protein tyrosine kinase-targeted anticancer drug sorafenib are strongly affected by this process. The clinical relevance of variation in OATP1A/1B activity in patients has been previously revealed by the effects of polymorphic variants and drug-drug interactions on drug toxicity. The development of in vivo tools to study OATP1A/1B functions has greatly advanced our mechanistic understanding of their functional role in drug pharmacokinetics, and their implications for therapeutic efficacy and toxic side effects of anticancer and other drug treatments.

Carnitine transport and fatty acid oxidation.

Carnitine is essential for the transfer of long-chain fatty acids across the inner mitochondrial membrane for subsequent ß-oxidation. It can be synthesized by the body or assumed with the diet from meat and dairy products. Defects in carnitine biosynthesis do not routinely result in low plasma carnitine levels. Carnitine is accumulated by the cells and retained by kidneys using OCTN2, a high affinity organic cation transporter specific for carnitine. Defects in the OCTN2 carnitine transporter results in autosomal recessive primary carnitine deficiency characterized by decreased intracellular carnitine accumulation, increased losses of carnitine in the urine, and low serum carnitine levels. Patients can present early in life with hypoketotic hypoglycemia and hepatic encephalopathy, or later in life with skeletal and cardiac myopathy or sudden death from cardiac arrhythmia, usually triggered by fasting or catabolic state. This disease responds to oral carnitine that, in pharmacological doses, enters cells using the amino acid transporter B(0,+). Primary carnitine deficiency can be suspected from the clinical presentation or identified by low levels of free carnitine (C0) in the newborn screening. Some adult patients have been diagnosed following the birth of an unaffected child with very low carnitine levels in the newborn screening. The diagnosis is confirmed by measuring low carnitine uptake in the patients' fibroblasts or by DNA sequencing of the SLC22A5 gene encoding the OCTN2 carnitine transporter. Some mutations are specific for certain ethnic backgrounds, but the majority are private and identified only in individual families. Although the genotype usually does not correlate with metabolic or cardiac involvement in primary carnitine deficiency, patients presenting as adults tend to have at least one missense mutation retaining residual activity. This article is part of a Special Issue entitled: Mitochondrial Channels edited by Pierre Sonveaux, Pierre Maechler and Jean-Claude Martinou.

Mitigation of acute kidney injury by cell-cycle inhibitors that suppress both CDK4/6 and OCT2 functions.

Acute kidney injury (AKI) is a potentially fatal syndrome characterized by a rapid decline in kidney function caused by ischemic or toxic injury to renal tubular cells. The widely used chemotherapy drug cisplatin accumulates preferentially in the renal tubular cells and is a frequent cause of drug-induced AKI. During the development of AKI the quiescent tubular cells reenter the cell cycle. Strategies that block cell-cycle progression ameliorate kidney injury, possibly by averting cell division in the presence of extensive DNA damage. However, the early signaling events that lead to cell-cycle activation during AKI are not known. In the current study, using mouse models of cisplatin nephrotoxicity, we show that the G1/S-regulating cyclin-dependent kinase 4/6 (CDK4/6) pathway is activated in parallel with renal cell-cycle entry but before the development of AKI. Targeted inhibition of CDK4/6 pathway by small-molecule inhibitors palbociclib (PD-0332991) and ribociclib (LEE011) resulted in inhibition of cell-cycle progression, amelioration of kidney injury, and improved overall survival. Of additional significance, these compounds were found to be potent inhibitors of organic cation transporter 2 (OCT2), which contributes to the cellular accumulation of cisplatin and subsequent kidney injury. The unique cell-cycle and OCT2-targeting activities of palbociclib and LEE011, combined with their potential for clinical translation, support their further exploration as therapeutic candidates for prevention of AKI.

Practical permeability-based hepatic clearance classification system (HepCCS) in drug discovery.

BACKGROUND: The use of liver microsomes and hepatocytes to predict total in vivo clearance is standard practice in the pharmaceutical industry; however, metabolic stability data alone cannot always predict in vivo clearance accurately. RESULTS: Apparent permeability generated from Mardin-Darby canine kidney cells and rat hepatocyte uptake for 33 discovery compounds were obtained. CONCLUSION: When there is underprediction of in vivo clearance, compounds with low apparent permeability (less than 3 × 10(-6) cm/s) all exhibited hepatic uptake. A systematic approach in the form of a classification system (hepatic clearance classification system) and decision tree that will help drug discovery scientists understand in vitro-in vivo clearance prediction disconnect early is proposed.

Exacerbation of mood symptoms associated to primary and secondary carnitine deficiency: a case report.

Rarely screened in psychiatric patients, primary and/or secondary Carnitine deficiency could be influencing and/or mimicking the mood symptoms of our patient population. The brain and specifically neurons are highly vulnerable to impairments in oxidative metabolism, which can lead to neuronal cell death and disorders of neurotransmitters causing changes in cognition and behavior. For this reason, identification of this disorder is important since its treatment could result in symptom improvement and better quality of life of our patients. We present a case where exacerbation of mood symptoms was associated to primary and secondary Carnitine deficiency.

Oxaliplatin-induced neurotoxicity is dependent on the organic cation transporter OCT2.

Oxaliplatin is an integral component of colorectal cancer therapy, but its clinical use is associated with a dose-limiting peripheral neurotoxicity. We found that the organic cation transporter 2 (OCT2) is expressed on dorsal root ganglia cells within the nervous system where oxaliplatin is known to accumulate. Cellular uptake of oxaliplatin was increased by 16- to 35-fold in cells overexpressing mouse Oct2 or human OCT2, and this process was associated with increased DNA platination and oxaliplatin-induced cytotoxicity. Furthermore, genetic or pharmacologic knockout of Oct2 protected mice from hypersensitivity to cold or mechanical-induced allodynia, which are established tests to assess acute oxaliplatin-induced neurotoxicity. These findings provide a rationale for the development of targeted approaches to mitigate this debilitating toxicity.

Coexistence of passive and proton antiporter-mediated processes in nicotine transport at the mouse blood-brain barrier.

Nicotine, the main tobacco alkaloid leading to smoking dependence, rapidly crosses the blood-brain barrier (BBB) to become concentrated in the brain. Recently, it has been shown that nicotine interacts with some organic cation transporters (OCT), but their influence at the BBB has not yet been assessed in vivo. In this study, we characterized the transport of nicotine at the mouse luminal BBB by in situ brain perfusion. Its influx was saturable and followed the Michaelis-Menten kinetics (K(m)=2.60 mM, V(max)=37.60 nmol/s/g at pH 7.40). At its usual micromolar concentrations in the plasma, most (79%) of the net transport of nicotine at the BBB was carrier-mediated, while passive diffusion accounted for 21%. Studies on knockout mice showed that the OCT Oct1-3, P-gp, and Bcrp did not alter [(3)H]-nicotine transport at the BBB. Neither did inhibiting the transporters Mate1, Octn, or Pmat. The in vivo manipulation of intracellular and/or extracellular pH, the chemical inhibition profile, and the trans-stimulation experiments demonstrated that the nicotine transporter at the BBB shared the properties of the clonidine/proton antiporter. The molecular features of this proton-coupled antiporter have not yet been identified, but it also transports diphenhydramine and tramadol and helps nicotine cross the BBB at a faster rate and to a greater extent. The pharmacological inhibition of this nicotine/proton antiporter could represent a new strategy to reduce nicotine uptake by the brain and thus help curb addiction to smoking.

[Primary carnitine deficiency in 17 patients: diagnosis, treatment and follow up].

OBJECTIVE: Many children were found to have low free carnitine level in blood by tandem mass spectrometry technology. In some of the cases the problems occurred secondary to malnutrition, organic acidemia and other fatty acid oxidation metabolic diseases, and some of cases had primary carnitine deficiency (PCD). In the present article, we discuss the diagnosis of PCD and evaluate the efficacy of carnitine in the treatment of PCD. METHOD: We measured the free carnitine (C0) and acylcarnitine levels in the blood of 270 000 neonates from newborns screening program and 12 000 children with suspected clinical inherited metabolic diseases by tandem mass spectrometry. The mutations of carnitine transporter protein were tested to the children with low C0 level and the diagnosis was made. The children with PCD were treated with 100 - 300 mg/kg of carnitine. RESULT: Seventeen children were diagnosed with PCD, 6 from newborn screening program and 11 from clinical patients. Mutations were found in all of them. The average C0 level [(2.9 ± 2.0) µmol/L] in patients was lower than the reference value (10 µmol/L), along with decreased level of different acylcarnitines. The clinical manifestations were diverse. For the 6 patients from newborn screening, 4 were asymptomatic, 1 showed hypoglycaemia and 1 showed movement intolerance from 2 years of age. For the 11 clinical patients, 8 showed hepatomegaly, 7 showed myasthenia, 6 showed cardiomyopathy, 1 showed chronic abdominal pain, and 1 showed restlessness and learning difficulty. Among these patients, 14 cases were treated with carnitine. Their clinical symptoms disappeared 1 to 3 months later. The C0 level in the blood rose to normal, with the average from (4.0 ± 2.7) µmol/L to (20.6 ± 8.3) µmol/L (P < 0.01). However, the level was still lower than the average level of healthy children [(27.1 ± 4.5) µmol/L, P < 0.01]. CONCLUSION: Seventeen patients were diagnosed with PCD by the test levels of free carnitine and acylcarnitines in blood with tandem mass spectrometry, and gene mutation test. Large dose of carnitine had a good effect in treatment of the PCD patients.

New mechanistic explanation for the localization of ulcers in the rat duodenum: role of iron and selective uptake of cysteamine.

Cysteamine, a coenzyme A metabolite, induces duodenal ulcers in rodents. Our recent studies showed that ulcer formation was aggravated by iron overload and diminished in iron deficiency. We hypothesized that cysteamine is selectively taken up in the duodenal mucosa, where iron absorption primarily occurs, and is transported by a carrier-mediated process. Here we report that cysteamine administration in rats leads to cysteamine accumulation in the proximal duodenum, where the highest concentration of iron in the gastrointestinal tract is found. In vitro, iron loading of intestinal epithelial cells (IEC-6) accelerated reactive oxygen species (ROS) production and increased [(14)C]cysteamine uptake. [(14)C]Cysteamine uptake by isolated gastrointestinal mucosal cells and by IEC-6 was pH-dependent and inhibited by unlabeled cysteamine. The uptake of [(14)C]cysteamine by IEC-6 was Na(+)-independent, saturable, inhibited by structural analogs, H(2)-histamine receptor antagonists, and organic cation transporter (OCT) inhibitors. OCT1 mRNA was markedly expressed in the rat duodenum and in IEC-6, and transfection of IEC-6 with OCT1 siRNA decreased OCT1 mRNA expression and inhibited [(14)C]cysteamine uptake. Cysteamine-induced duodenal ulcers were decreased in OCT1/2 knockout mice. These studies provide new insights into the mechanism of cysteamine absorption and demonstrate that intracellular iron plays a critical role in cysteamine uptake and in experimental duodenal ulcerogenesis.

Renal tubular secretion of varenicline by multidrug and toxin extrusion (MATE) transporters.

Multidrug and toxin extrusion (MATE) 1 and MATE2-K, H(+)/organic cation antiporters, are located at the brush-border membrane of renal proximal tubules. The present study aimed to clarify the role of MATE transporters in tubular secretion of varenicline. Varenicline at a dose of 5 mg/kg was administered to wild-type and Mate1-knockout mice via the jugular vein, and its uptake was measured by high-performance liquid chromatography. The renal secretory clearance of and systemic exposure to varenicline were significantly decreased (54.6%, p < 0.05) and increased (116%, p < 0.05) respectively, by the genetic disruption of Mate1 in mice. Uptake of varenicline and [(14)C]tetraethylammonium (TEA) was examined in HEK293 cells transiently expressing the human (h) MATE1, hMATE2-K, mouse (m) MATE1, and hOCT2 basolateral organic cation transporter. [(14)C]TEA uptake in HEK293 cells expressing MATE transporters and hOCT2 was decreased in the presence of varenicline. The calculated IC(50) values for hMATE1, hMATE2-K, mMATE1, and hOCT2 were 62.2 ± 6.5, 122.3 ± 67.6, 255.0 ± 37.9, and 1,003.9 ± 135.8 (µM; mean ± S.E. for three separate experiments), respectively. Varenicline uptake was significantly increased in HEK293 cells expressing mMATE1, hMATE1, or hMATE2-K cDNA as well as hOCT2 compared to empty vector-transfected cells. In conclusion, renal MATE transporters were found to be responsible for renal tubular secretion of varenicline.

Ablation of both organic cation transporter (OCT)1 and OCT2 alters metformin pharmacokinetics but has no effect on tissue drug exposure and pharmacodynamics.

Organic cation transporter (OCT)1 and OCT2 mediate hepatic uptake and secretory renal clearance of metformin, respectively. Pharmacokinetic/pharmacodynamic (PK/PD) implications of simultaneous impairment of both transporters, such as by systemic pan-OCT inhibition, have not been studied directly. At present metformin PK/PD, distribution, and excretion were studied in Oct1/Oct2-knockout mice. Metformin clearance was reduced 4.5-fold from renal blood flow to unbound glomerular filtration rate, and volume of distribution was reduced 3.5-fold in Oct1/Oct2-knockout mice. Oral bioavailability was not affected (F = 64 ± 4 versus 59 ± 11; knockout versus wild type). Liver- and kidney-to-plasma concentration ratios were decreased in Oct1/Oct2-knockout mice 4.2- and 2.5-fold, respectively. The 2.9-fold increase in oral metformin exposure and reduced tissue partitioning yielded little to no net change in tissue drug concentrations. Absolute kidney exposure was unchanged (knockout/wild type = 1.1 ± 0.2), and liver exposure was only modestly decreased (knockout/wild type = 0.6 ± 0.1). Oral glucose area under the curve (AUC) lowering by metformin was not impaired in Oct1/Oct2-knockout mice at the five dose levels tested (ED50 = 151 versus 110 mg/kg; glucose lowering at highest dose = 42 ± 1 versus 39 ± 4%; knockout versus wild type); however, higher systemic metformin exposures were necessary in knockout mice to elicit the same effect (half-maximal efficacious AUC = 70 versus 26 µg x h/ml). Despite major changes in metformin clearance and volume of distribution in Oct1/Oct2-knockout mice, tissue drug exposure and PD were not affected. These findings challenge the presumption that systemic OCT inhibition will affect metformin pharmacology.

Organic anion transporting polypeptide 1a1 null mice are sensitive to cholestatic liver injury.

Organic anion transporting polypeptide 1a1 (Oatp1a1) is predominantly expressed in livers of mice and is thought to transport bile acids (BAs) from blood into liver. Because Oatp1a1 expression is markedly decreased in mice after bile duct ligation (BDL). We hypothesized that Oatp1a1-null mice would be protected against liver injury during BDL-induced cholestasis due largely to reduced hepatic uptake of BAs. To evaluate this hypothesis, BDL surgeries were performed in both male wild-type (WT) and Oatp1a1-null mice. At 24 h after BDL, Oatp1a1-null mice showed higher serum alanine aminotransferase levels and more severe liver injury than WT mice, and all Oatp1a1-null mice died within 4 days after BDL, whereas all WT mice survived. At 24 h after BDL, surprisingly Oatp1a1-null mice had higher total BA concentrations in livers than WT mice, suggesting that loss of Oatp1a1 did not prevent BA accumulation in the liver. In addition, secondary BAs dramatically increased in serum of Oatp1a1-null BDL mice but not in WT BDL mice. Oatp1a1-null BDL mice had similar basolateral BA uptake (Na(+)-taurocholate cotransporting polypeptide and Oatp1b2) and BA-efflux (multidrug resistance-associated protein [Mrp]-3, Mrp4, and organic solute transporter α/ß) transporters, as well as BA-synthetic enzyme (Cyp7a1) in livers as WT BDL mice. Hepatic expression of small heterodimer partner Cyp3a11, Cyp4a14, and Nqo1, which are target genes of farnesoid X receptor, pregnane X receptor, peroxisome proliferator-activated receptor alpha, and NF-E2-related factor 2, respectively, were increased in WT BDL mice but not in Oatp1a1-null BDL mice. These results demonstrate that loss of Oatp1a1 function exacerbates cholestatic liver injury in mice and suggest that Oatp1a1 plays a unique role in liver adaptive responses to obstructive cholestasis.

Impact of Oatp1c1 deficiency on thyroid hormone metabolism and action in the mouse brain.

Organic anion-transporting polypeptide 1c1 (Oatp1c1) (also known as Slco1c1 and Oatp14) belongs to the family of Oatp and has been shown to facilitate the transport of T(4). In the rodent brain, Oatp1c1 is highly enriched in capillary endothelial cells and choroid plexus structures where it may mediate the entry of T(4) into the central nervous system. Here, we describe the generation and first analysis of Oatp1c1-deficient mice. Oatp1c1 knockout (KO) mice were born with the expected frequency, were not growth retarded, and developed without any overt neurological abnormalities. Serum T(3) and T(4) concentrations as well as renal and hepatic deiodinase type 1 expression levels were indistinguishable between Oatp1c1 KO mice and control animals. Hypothalamic TRH and pituitary TSH mRNA levels were not affected, but brain T(4) and T(3) content was decreased in Oatp1c1-deficient animals. Moreover, increased type 2 and decreased type 3 deiodinase activities indicate a mild hypothyroid situation in the brain of Oatp1c1 KO mice. Consequently, mRNA expression levels of gene products positively regulated by T(3) in the brain were down-regulated. This central nervous system-specific hypothyroidism is presumably caused by an impaired passage of T(4) across the blood-brain barrier and indicates a unique function of Oatp1c1 in facilitating T(4) transport despite the presence of other thyroid hormone transporters such as Mct8.

Correlation of low SLC22A18 expression with poor prognosis in patients with glioma.

We investigated the expression of the putative tumor suppressor SLC22A18 to evaluate it as a prognostic marker in glioma patients. Immunohistochemical and Western blot analyses of clinical tissue samples obtained from 120 patients with glioma were performed. Low expression of SLC22A18 was observed in 71.7% of patients. Loss of SLC22A18 expression in glioma was significantly related to pathological grade (p = 0.003). High pathological grade (World Health Organization III-IV) was correlated with negative (low or absent) expression of SLC22A18, which was correlated with a significantly shorter overall patient survival than in those with positive (high) expression (p = 0.007). Multivariate Cox regression analysis indicated that SLC22A18 expression level is an independent survival prognostic factor for patients with glioma (p = 0.011). Western blotting analysis confirmed decreased expression of SLC22A18 in glioma tissues compared with adjacent brain tissues. This study suggests that SLC22A18 functions as a tumor suppressor in glioma and represents a candidate biomarker for long-term survival in this disease.

Deficiency of multidrug and toxin extrusion 1 enhances renal accumulation of paraquat and deteriorates kidney injury in mice.

Multidrug and toxin extrusion 1 (MATE1/solute carrier 47A1) mediates cellular transport of a variety of structurally diverse compounds. Paraquat (PQ), which has been characterized in vitro as a MATE1 substrate, is a widely used herbicide and can cause severe toxicity to humans after exposure. However, the contribution of MATE1 to PQ disposition in vivo has not been determined. In the present study, we generated Mate1-deficient (Mate1-/-) mice and performed toxicokinetic analyses of PQ in Mate1-/- and wild-type (Mate1+/+) mice. After a single intravenous administration of PQ (50 mg/kg), Mate1-/- mice exhibited significantly higher plasma PQ concentrations than Mate1+/+ mice. The renal PQ concentration was markedly increased in Mate1-/- mice compared with Mate1+/+ mice. The subsequent nephrotoxicity of PQ were examined in these mice. Three days after intraperitoneal administration of PQ (20 mg/kg), the transcript levels of N-acetyl-ß-D-glucosaminidase (Lcn2) and kidney injury molecule-1 (Kim-1) in the kidney were remarkably enhanced in the Mate1-/- mice. This was accompanied by apparent difference in renal histology between Mate1-/- and Mate1+/+ mice. In conclusion, we demonstrated that Mate1 is responsible for renal elimination of PQ in vivo and the deficiency of Mate1 function confers deteriorated kidney injury caused by PQ in mice.

Disruption of multidrug and toxin extrusion MATE1 potentiates cisplatin-induced nephrotoxicity.

Multidrug and toxin extrusion 1 (MATE1/SLC47A1) is expressed in the brush-border membrane of renal proximal tubules and mediates the efflux of cationic drugs. In the present study, the role of MATE1 in the nephrotoxicity of cisplatin was investigated in vivo and in vitro. Cisplatin (15mg/kg) was administered intraperitoneally to wild-type (Mate1(+/+)) and Mate1 knockout (Mate1(-/-)) mice. Lifespan was significantly shorter in Mate1(-/-) mice than Mate1(+/+) mice. Three days after the administration of cisplatin, plasma creatinine and blood urea nitrogen (BUN) levels were increased in both Mate1(+/+) and Mate1(-/-) mice compared with vehicle-treated controls, and creatinine clearance was decreased. Moreover, a significant rise in creatinine and BUN levels was observed in cisplatin-treated Mate1(-/-) mice in comparison to Mate1(+/+) mice. A pharmacokinetic analysis revealed the plasma concentration and renal accumulation of cisplatin to be higher in Mate1(-/-) mice than Mate1(+/+) mice 1h after a single intravenous administration of cisplatin (0.5mg/kg). Furthermore, the combination of a selective MATE inhibitor, pyrimethamine, with cisplatin also elevated creatinine and BUN levels compared to cisplatin alone. In experiments in vitro, the cellular uptake of cisplatin was stimulated by the expression of mouse MATE1 as well as organic cation transporters OCT1 and OCT2. In conclusion, MATE1 mediates the efflux of cisplatin and is involved in cisplatin-induced nephrotoxicity.

Cisplatin-induced downregulation of OCTN2 affects carnitine wasting.

PURPOSE: Carnitine is an essential cofactor for mitochondrial fatty acid oxidation that is actively reabsorbed by the luminal transporter Octn2 (Slc22a5). Because the nephrotoxic agent cisplatin causes urinary loss of carnitine in humans, we hypothesized that cisplatin may affect Octn2 function. EXPERIMENTAL DESIGN: Excretion of carnitine and acetylcarnitine was measured in urine collected from mice with or without cisplatin administration. The transport of carnitine was assessed in cells that were transfected with OCT1 or OCT2. The effect of cisplatin treatment on gene expression was analyzed using a mouse GeneChip array and validated using quantitative reverse transcriptase-PCR. RESULTS: In wild-type mice, urinary carnitine excretion at baseline was ∼3-fold higher than in mice lacking the basolateral cisplatin transporters Oct1 and Oct2 [Oct1/2(-/-) mice], indicating that carnitine itself undergoes basolateral uptake into the kidney. Transport of carnitine by OCT2, but not OCT1, was confirmed in transfected cells. We also found that cisplatin caused an increase in the urinary excretion of carnitine and acetylcarnitine in wild-type mice but not in Oct1/2(-/-) mice, suggesting that tubular transport of cisplatin is a prerequisite for this phenomenon. Cisplatin did not directly inhibit the transport of carnitine by Octn2 but downregulated multiple target genes of the transcription factor peroxisome proliferator activated receptor α, including Slc22a5, in the kidney of wild-type mice that were absent in Oct1/2(-/-) mice. CONCLUSION: Our study shows a pivotal role of Oct1 and Oct2 in cisplatin-related disturbances in carnitine homeostasis. We postulate that this phenomenon is triggered by deactivation of peroxisome proliferator activated receptor α and leads to deregulation of carnitine-shuttle genes.

Influence of Oct1/Oct2-deficiency on cisplatin-induced changes in urinary N-acetyl-beta-D-glucosaminidase.

PURPOSE: This study aimed to test the influence of functional renal organic cation transporters (OCT2 in humans, Oct1 and Oct2 in mice) on biomarkers of cisplatin nephrotoxicity, such as urinary activity of N-acetyl-beta-D-glucosaminidase (NAG). EXPERIMENTAL DESIGN: Temporal cisplatin-induced nephrotoxicity was assessed by histopathology and biomarkers. Cisplatin-mediated NAG changes and survival were determined in wild-type and Oct1/2(-/-) mice. Identification of OCT2 inhibitors was done in transfected 293Flp-In cells, and the NCI(60) cell line panel was used to assess contribution of OCT2 to cisplatin uptake in cancer cells. RESULTS: Classical biomarkers such as blood urea nitrogen and serum creatinine were not elevated until 72 hours after cisplatin administration and substantial kidney damage had occurred. Oct1/2(-/-) mice had 2.9-fold lower NAG by 4 hours (P < 0.0001) and 2.3-fold increased survival (P = 0.0097). Among 16 agents, cimetidine strongly inhibited uptake of tetraethylammonium bromide (P = 0.0006) and cisplatin (P < 0.0001), but did not have an influence on cisplatin uptake in SK-OV-3 cells, the cancer line with the highest OCT2 mRNA levels. In wild-type mice, cimetidine inhibited cisplatin-induced NAG changes (P = 0.016 versus cisplatin alone) to a degree similar to that seen in Oct1/2(-/-) mice receiving cisplatin (P = 0.91). Cumulative NAG activity of >0.4 absorbance units (AU) was associated with 21-fold increased odds for severe nephrotoxicity (P = 0.0017), which was linked with overall survival (hazard ratio, 8.1; 95% confidence interval, 2.1-31; P = 0.0078). CONCLUSIONS: Cimetidine is able to inhibit OCT2-mediated uptake of cisplatin in the kidney, and subsequently ameliorate nephrotoxicity likely with minimal effect on uptake in tumor cells.