[Tubular transporters OAT1 and MRP2 and clearance of adefovir]

Efficient proximal tubule-on-chip model from hiPSC-derived kidney organoids for functional analysis of renal transporters

Renal transporters play critical roles in predicting potential drug-drug interactions. However, current in vitro models often fail to adequately express these transporters, particularly solute carrier proteins, including organic anion transporters (OAT1/3), and organic cation transporter 2 (OCT2). Here, we developed a hiPSC-derived kidney organoids-based proximal tubule-on-chip (OPTC) model that emulates in vivo renal physiology to assess transporter function. Compared to chips based on immortalized cells, OPTC derived from the two most commonly used differentiation protocols exhibited significant improvement in expression level and polarity of OAT1/3 and OCT2. Hence, the OPTC demonstrates enhanced functionality in efflux and uptake assessments, and nephrotoxicity. Furthermore, these functionalities are diminished upon adding inhibitors during substrate-inhibitor interactions, which were closer to in vivo observations. Overall, these results support that OPTC can reliably assess the role of renal transporters in drug transport and nephrotoxicity, paving the way for personalized models to assess renal transport and disease modeling.

Osteomalacia and renal failure due to Fanconi syndrome caused by long-term low-dose Adefovir Dipivoxil: a case report

Background

Progressive bone pain and fracture and abnormal positron emission tomography combined with a computed tomography are main reasons for the oncologists suspecting bone tumor. During the patient’s medical treatment, the oncologists’ unfamiliarity with adverse reactions to anti-HBV drugs were main reason for the long-term exposure to the drug and the adverse reaction (ADR) experienced by the patient.

Case presentation

A 63-year-old Chinese man had a 27-month history of progressive generalized bone pain combined with spontaneous fractures. Positron emission tomography combined with a computed tomography, revealed an abnormal increase in ribose metabolism and low positron serum inorganic phosphorus concentration (0.7; 0.78–1.65 mmol/L). Serum creatinine level was 252 μmol/L (53–97) μmol/L, and glomerular filtration rate was 22.79 mL/min/1.73 m². The patient was referred to a multidisciplinary clinic to clarify the diagnosis of myeloma or bone tumor for further treatment in 2017. His medical history revealed that he had a 30-year history of chronic hepatitis B infection. He had received lamivudine at a daily dose of 100 mg for 19 years (1990 to 2009), which had been changed to adefovir (10 mg/day) owing to lamivudine resistance in 2009. Based on the changes in the patient’s laboratory markers and the results of emission computed tomography and other radiographic findings, adefovir-induced hypophosphatemic osteomalacia due to acquired renal Fanconi syndrome was suspected by the clinical pharmacist. Considerable clinical improvement was observed after adefovir discontinuation and the administration of entecavir (1.0 mg, every other day).

Conclusion

Fanconi syndrome with osteomalacia can develop in patients with chronic hepatitis B infection being treated with adefovir at a conventional low dosage of 10 mg/day. This case highlights the importance of ADR as a differential diagnosis and the need of pharmacists with drug safety expertise expert in the patient management.

Osteomalacia induced by long-term low-dose adefovir dipivoxil: Clinical characteristics and genetic predictors

CONTEXT

Adefovir dipivoxil (ADV) was an important cause of adult-onset hypophosphatemic osteomalacia. However, its clinical characteristics and mechanisms have not been well defined.

OBJECTIVE

The objective of the study was to summarize the clinical characteristics of ADV-induced osteomalacia and to explore the association between ADV-associated tubulopathy and polymorphisms in genes encoding drug transporters.

DESIGN, SETTING, PATIENTS, AND MAIN OUTCOME MEASURE

Seventy-six affected patients were clinically studied. The SLC22A6 and ABCC2 genes were screened and compared with healthy people from the HapMap.

RESULTS

Hypophosphatemia, high serum alkaline phosphatase (ALP) levels, hypouricemia, nondiabetic glycosuria, proteinuria, metabolic acidosis and high bone turnover markers were the main metabolic characteristics. Fractures and pseudofractures occurred in 39 patients. Stopping ADV administration, supplementing calcitriol and calcium was effective during the follow-up period. Single SNP analysis revealed a higher percentage of the G/A genotype at c.2934 in exon 22 of the ABCC2 gene (rs3740070) in patients than in healthy people (12% [7 of 58 patients] vs. 0% [0 of 45 patients]; P=0.017), while there was no subject with homozygosity for the A allele at c.2934.

CONCLUSIONS

ADV can be nephrotoxic at a conventional dosage. The G/A genotype at c.2934 of the ABCC2 gene may be a predictor of patients at greater risk for developing ADV-associated tubulopathy. Larger case-control studies are needed to further verify this finding.

Multiple Drug Transporters Are Involved in Renal Secretion of Entecavir

Entecavir (ETV) is a first-line antiviral agent for the treatment of chronic hepatitis B virus infection. Renal excretion is the major elimination path of ETV, in which tubular secretion plays the key role. However, the secretion mechanism has not been clarified. We speculated that renal transporters mediated the secretion of ETV. Therefore, the aim of our study was to elucidate which transporters contribute to the renal disposition of ETV. Our results revealed that ETV (50 μM) remarkably reduced the accumulation of probe substrates in MDCK cells stably expressing human multidrug and toxin efflux extrusion proteins (hMATE1/2-K), organic cation transporter 2 (hOCT2), and carnitine/organic cation transporters (hOCTNs) and increased the substrate accumulation in cells transfected with multidrug resistance-associated protein 2 (hMRP2) or multidrug resistance protein 1 (hMDR1). Moreover, ETV was proved to be a substrate of the above-described transporters. In transwell studies, the transport of ETV in MDCK-hOCT2-hMATE1 showed a distinct directionality from BL (hOCT2) to AP (hMATE1), and the cellular accumulation of ETV in cells expressing hMATE1 was dramatically lower than that of the mock-treated cells. The accumulation of ETV in mouse primary renal tubular cells was obviously affected by inhibitors of organic anion transporter 1/3 (Oat1/3), Oct2, Octn1/2, and Mrp2. Therefore, the renal uptake of ETV is likely mediated by OAT1/3 and OCT2 while the efflux is mediated by MATEs, MDR1, and MRP2, and OCTN1/2 may participate in both renal secretion and reabsorption.

Severe recurrent rhabdomyolysis-induced acute kidney injury in a HIV-infected patient on antiretroviral therapy

Antiretroviral medications, specifically tenofovir, have been linked to acute tubular necrosis in humans with a suggested mechanism of direct tubular injury. Rhabdomyolysis has rarely been described in patients on highly active antiretroviral therapy (HAART). To the best of our knowledge, severe recurrent rhabdomyolysis-induced acute kidney injury (AKI) in a HIV-infected patient on two different triple antiretroviral regimens has not been reported. We present a HIV-positive patient who first developed heme pigment-induced oliguric AKI due to non-traumatic rhabdomyolysis, 5 days after initiation of triple antiretroviral therapy. Renal function normalized 2 months after discontinuation of antiretroviral therapy. Two weeks after reinitiating a different HAART regimen, our patient developed a recurrent episode of severe rhabdomyolysis-induced AKI. Both rhabdomyolysis and AKI resolved after discontinuation of the second antiretroviral regimen. First tenofovir and subsequently abacavir seem to be the likely culprits in our case. We also briefly discuss tenofovir nephrotoxicity followed by a literature review on rhabdomyolysis in HIV-infected patients.

Translocation of nucleoside analogs across the plasma membrane in hematologic malignancies

Nucleoside analogs are currently used in the treatment of various hematologic malignancies due to their ability to induce apoptosis of lymphoid cells. For nucleoside-derived drugs to exert their action, they must enter cells via nucleoside transporters from two gene families, SLC28 and SLC29 (CNT and ENT, respectively). Once inside the cell, these drugs must be phosphorylated to their active forms. In contrast, some members of the ATP-binding cassette (ABC) protein family have been identified as responsible for the efflux of the phosphorylated forms of these nucleoside-derived drugs. Here, we review the main nucleoside analogs used in hematologic malignancies and focus especially on those that are currently used in chronic lymphocytic leukemia (CLL). Moreover, we discuss the pharmacological profile of the nucleoside transporters, which determines the bioavailability of and cell sensitivity to these nucleoside-derived drugs. We also discuss the expression of nucleoside transporters and their activities in CLL as well as the possibility of modulating these transporter activities as a means of modulating intracellular drug availability and, consequently, responsiveness to therapy.

Analysis of three-dimensional systems for developing and mature kidneys clarifies the role of OAT1 and OAT3 in antiviral handling

The organic anion transporters OAT1 (SLC22A6, originally identified by us as NKT) and OAT3 (SLC22A8) are critical for handling many toxins, metabolites, and drugs, including antivirals (Truong, D. M., Kaler, G., Khandelwal, A., Swaan, P. W., and Nigam, S. K. (2008) J. Biol. Chem. 283, 8654-8663). Although microinjected Xenopus oocytes and/or transfected cells indicate overlapping specificities, the individual contributions of these transporters in the three-dimensional context of the tissues in which they normally function remain unclear. Here, handling of HIV antivirals (stavudine, tenofovir, lamivudine, acyclovir, and zidovudine) was analyzed with three-dimensional ex vivo functional assays using knock-out tissue. To investigate the contribution of OAT1 and OAT3 in various nephron segments, the OAT-selective fluorescent tracer substrates 5-carboxyfluorescein and 6-carboxyfluorescein were used. Although OAT1 function (uptake in oat3(-/-) tissue) was confined to portions of the cortex, consistent with a proximal tubular localization, OAT3 function (uptake in oat1(-/-) tissue) was apparent throughout the cortex, indicating localization in the distal as well as proximal nephron. This functional localization indicates a complex three-dimensional context, which needs to be considered for metabolites, toxins, and drugs (e.g. antivirals) handled by both transporters. These results also raise the possibility of functional differences in the relative importance of OAT1 and OAT3 in antiviral handling in developing and mature tissue. Because the HIV antivirals are used in pregnant women, the results may also help in understanding how these drugs are handled by developing organs.

Drug transporter pharmacogenetics in nucleoside-based therapies

This article focuses on the different types of transporter proteins that have been implicated in the influx and efflux of nucleoside-derived drugs currently used in the treatment of cancer, viral infections (i.e., AIDS) and other conditions, including autoimmune and inflammatory diseases. Genetic variations in nucleoside-derived drug transporter proteins encoded by the gene families SLC15, SLC22, SLC28, SLC29, ABCB, ABCC and ABCG will be specifically considered. Variants known to affect biological function are summarized, with a particular emphasis on those for which clinical correlations have already been established. Given that relatively little is known regarding the genetic variability of the players involved in determining nucleoside-derived drug bioavailability, it is anticipated that major challenges will be faced in this area of research.

Tenofovir-induced kidney injury

Tenofovir disoproxil fumarate is a nucleotide reverse transcriptase inhibitor with activity against both HIV and the hepatitis B virus. It has had minimal nephrotoxic effects in early clinical trials, but as clinical use has widened, case reports describing tenofovir-induced renal tubular damage, Fanconi's syndrome and diabetes insipidus have been described. The authors review the pharmacokinetics, mechanism of action and clinical uses of tenofovir disoproxil fumarate. The large clinical trials, as well as the case reports of tenofovir-induced kidney injury, are also reviewed. The potential mechanism of renal damage is discussed and recommendations for evaluation and treatment of tenofovir-induced kidney injury are given.