Identification of OAT1/OAT3 as Contributors to Cisplatin Toxicity

Cisplatin is among the most widely used anticancer drugs and known to cause a dose‐limiting nephrotoxicity, which is partially dependent on the renal uptake carrier OCT2. We here report a previously unrecognized, OCT2‐independent pathway of cisplatin‐induced renal injury that is mediated by the organic anion transporters OAT1 and OAT3. Using transporter‐deficient mouse models, we found that this mechanism regulates renal uptake of a mercapturic acid metabolite of cisplatin that acts as a precursor of a potent nephrotoxin. The function of these two transport systems can be simultaneously inhibited by the tyrosine kinase inhibitor nilotinib through noncompetitive mechanisms, without compromising the anticancer properties of cisplatin. Collectively, our findings reveal a novel pathway that explains the fundamental basis of cisplatin‐induced nephrotoxicity, with potential implications for its therapeutic management.

Drug-induced ototoxicity: Mechanisms, Pharmacogenetics, and protective strategies

Drug ototoxicity limits the quality of life of patients after treatment, having serious consequences, especially for psychosocial development of children. Although the ototoxicity of many drugs resolves after treatment discontinuation, the use of platinum derivatives and aminoglycosides is associated with permanent hearing loss. In this review, we have listed ototoxic drugs and the mechanisms by which they damage the ears. Moreover, possible protective strategies and important methods for early detection of ototoxic effects are discussed.

Quantitative imaging of platinum based on laser ablation-inductively coupled plasma-mass spectrometry to investigate toxic side effects of cisplatin

This work presents a quantitative bioimaging method for platinum based on laser ablation-inductively coupled plasma-mass spectrometry and its application for a biomedical study concerning toxic side effects of cisplatin. To trace the histopathology back to cisplatin, platinum was localized and quantified in major functional units of testicle, cochlea, kidney, nerve and brain sections from cisplatin treated mice. The direct consideration of the histology enables precise interpretation of the Pt images and the novel quantitative evaluation approach allows significantly more precise investigations than the pure image. For the first time, platinum was detected and quantified in all major injured structures including organ of Corti of cochlea and seminiferous tubule of testicle. In this way, proximal tubule in kidney, Leydig cells in testicle, stria vascularis and organ of Corti in cochlea and nerve fibers in sciatic nerves are confirmed as targets of cisplatin in these organs. However, the accumulation of platinum in almost all investigated structures also raises questions about more complex pathogenesis including direct and indirect interruption of several biological processes.

Organic cation transporters

1. Organic cation transporters (OCTs) translocate endogenous (e.g. dopamine) and exogenous (e.g. drugs) substances of cationic nature and, therefore, play an important role in the detoxification of exogenous compounds. This review aims to furnish essential information on OCTs, with an emphasis on pharmacological aspects. 2. Analysis of the literature on OCTs makes clear that there is a species- and organ-specific distribution of the different isoforms, which can also be differentially regulated. OCTs are responsible for the excretion and/or distribution of many drugs and also for serious tissue-specific side-effects such as cisplatin-induced nephrotoxicity. The presence of single nucleotide polymorphisms in these transporters significantly influences the response of patients to medication, as demonstrated for the antidiabetic drug metformin. 3. A substantial amount of research has to be undertaken to clarify further the OCT structure-function relationships specifically to define the role of oligomerization on their activity and regulation, to identify intracellular interaction partners of OCTs, and to characterize their pharmacogenetic aspects.

The organic cation transporters rOCT1 and hOCT2 are inhibited by cGMP

The electrogenic cation transporters OCT1 and OCT2 in the basolateral membrane of renal proximal tubules mediate the first step during secretion of organic cations. Previously we demonstrated stimulation and change of selectivity for rat OCT1 (rOCT1) by protein kinase C. Here we investigated the effect of cGMP on cation transport by rOCT1 or human OCT2 (hOCT2) after expression in human embryonic kidney cells (HEK293) or oocytes of Xenopus laevis. In HEK293 cells, uptake was measured by microfluorimetry using the fluorescent cation 4-(4-(dimethyl-amino)styryl)-N-methylpyridinium iodide (ASP + ) as substrate, whereas uptake into Xenopus laevis oocytes was measured with radioactively labelled cations. In addition, ASP +-induced depolarizations of membrane voltages (Vm) were measured in HEK293 cells using the slow whole-cell patch-clamp method. Incubation of rOCT1-expressing HEK293 cells for 10 min with 100 mM 8-Br-cGMP reduced initial ASP + uptake by maximally 78% with an IC50 value of 24 +/- 16 mM. This effect was not abolished by the specific PKG inhibitor KT5823, indicating that a cGMP-dependent kinase is not involved. An inhibition of ASP + uptake by rOCT1 in HEK293 cells was also obtained when the cells were incubated for 10 min with 100 mM cGMP, whereas no effect was obtained when cGMP was given together with ASP +. ASP + (100 mM)-induced depolarizations of Vm were reduced in the presence of 8-Br-cGMP (100 mM) by 44 +/- 11% (n = 6). Since it could be demonstrated that [3H]cGMP is taken up by an endogeneous cyanine863-inhibitable transporter, the effect of cGMP is probably mediated from inside the cell. Uptake measurements with [14C]tetraethylammonium and [3H]2-methyl-4-phenylpyridinium in Xenopus laevis oocytes expressing rOCT1 performed in the absence and presence of 8-Br-cGMP showed that cGMP does not interact directly with the transporter. The data suggest that the inhibition mediated by cGMP observed in HEK293 cells occurs most likely via a mammalian cGMP-binding protein that interacts with OCT1-2 transporters.

Cystatin C in a rat model of end-stage renal failure

BACKGROUND

Cystatin C (MW 13kDa) serum concentration reflects glomerular filtration rate better than creatinine. Like other low-molecular weight proteins it is not eliminated by dialysis. Still, cystatin C serum concentrations do not rise progressively in end-stage renal failure and rarely exceed 10 mg/L (i.e. 8 times the upper limit of normal).

OBJECTIVE

To study cystatin C kinetics in a rat model of end-stage renal failure.

METHODS

Sequential bilateral nephrectomy was performed seven days apart in 13 male Sprague-Dawley rats as described by Levine and Saltzman. Serum cystatin C (Cystatin C PET-kit, DAKO), creatinine and total protein were measured in daily intervals after the second nephrectomy. Linearity of the anti-human cystatin C assay for rat cystatin C was tested using dilutions of uremic rat serum. Rats were sacrificed for signs of severe uremia on days 10 (n=5), 11 (n=4) and 12 (n = 5).

RESULTS

At baseline, mean (+/- SE) cystatin C was 1.59+/-0.041 mg/L, creatinine 19.6+/-1.2 micromol/L. Following bilateral nephrectomy, cystatin C immediately rose to 3.82+/-0.15 mg/L, creatinine to 312+/-20 micromol/L. During the following days, cystatin C concentration stabilized to 4 mg/L approximately whereas creatinine continued to rise to 822+/-185 kmol/L on day 12. Correction for the decrease in serum total protein concentration from 48.9+/-2.3 g/L to 37.4+/-3.6 g/L did not alter these results.

CONCLUSION

The kinetics of cystatin C and creatinine in this rat model of end-stage renal failure are in accordance with human data suggesting a change in cystatin C production or extra-renal elimination in severe chronic uremia.

The "fixed" charge of glomerular capillary wall as determinant of permselectivity

The determinants of glomerular capillary wall (GCW) permeability to proteins have been subject of controversial discussion. To study this question we have developed a modified isolated perfused rat kidney model in which tubular transport processes are completely blocked by perfusion fixation with glutaraldehyde. This model allows to directly titrate the charge density of the GCW using albumin solutions buffered over a wide pH-range, a manipulation that cannot be performed in the intact kidney. Analyzing the results of these experiments helped to determine a fixed charge density of the GCW of 43 mEq/L. In the present work, we used the isolated perfused fixed rat kidney model to study the influence of this fixed charge on the transglomerular passage of proteins. To do this, the fixed kidney was perfused with albumin solutions containing different isoforms of horseradish peroxidase. The lowest sieving coefficient was obtained with the acidic isoform (0.035+/-0.008, n = 7), while the isoforms at pI 6.85 and 8.45 showed higher sieving coefficients (0.059+/-0.008, n = 7 and 0.090+/-0.008, n = 4, respectively). The highest sieving coefficient (0.59+/-0.031, n = 6) was observed in perfusion experiments of the fixed kidney with cationic HRP (pI > or = 9.30). However, when comparing the sieving coefficients, the highly cationic isoform was excluded because it has a lower molecular weight than the other isoforms. The sieving coefficients of the other isoforms were significantly different (p < 0.05. ANOVA, Scheffé test). In conclusion, the presence of a discrete (even if lower than previously thought) "fixed" charge on the GCW of 43 mEq/L restricts the transglomerular passage of isoforms of horseradish peroxidase by a factor 2-3. These results imply that the influence of charge selectivity has been overstated in the literature.

Role of albumin and glomerular capillary wall charge distribution on glomerular permselectivity: studies on the perfused-fixed rat kidney model

The charge-related determinants of albumin permeability are the subject of controversial discussion. To study this question we have developed an isolated perfused rat kidney model in which metabolic processes are eliminated by perfusion fixation with glutaraldehyde. The fixed kidneys were perfused with albumin solutions using the following approaches: 1. Modification of the charge of both the glomerular capillary wall (GCW) and albumin using different buffer systems in a pH range spanning the isoelectric points of albumin and the glomerular basement membrane (GBM), the extracellular matrix of the GCW. 2. Modification of the charge of the GCW by perfusing the isolated kidney with cations either before or after fixation. 3. Modification of the charge of albumin by cationization. In the model, the inulin "urine" to perfusate ratio was one. This shows that the tubules have no metabolic activity, that the glomerular filtration rate (GFR) is equal to "urine" flow rate and that the "urine" collected is identical to the ultrafiltrate. Therefore, sieving coefficients in this model can simply be calculated as the ratio between "urine" and perfusate protein concentrations. We could show that: 1. pH has a significant effect on the albumin sieving coefficient: it was maximally increased at pH 4.0 [(70.3 +/- 15.9) x 10(-3), n = 10 versus (8.7 +/- 3.7) x 10(-3), n = 11, at pH 7.4]. Only a pH as low as 4.0 should lead to a pronounced neutralization of the anionic charges of albumin and the GBM; the charge density of the GCW calculated with these data is 43 mEq/l at pH 7.4. 2. Modifying the ionic composition of the GCW with protamine before fixation with glutaraldehyde causes a bigger increase in the glomerular permeability for albumin [(51.2 +/- 22.5) x 10(-3), n = 10, glomerular charge density 21 mEq/l] than modifying the albumin charge by cationization. 3. Modifying the albumin charge by cationization increases the glomerular permeability for albumin [(20.0 +/- 6.7) x 10(-3), n = 8]. These findings support the hypothesis that at the onset of proteinuria changes in the charge and configuration of the GCW could be more important pathogenetic factors than changes in the charge of serum-derived proteins.

Mitochondria act as a reservoir for the basic amine HIPDM in the lung

The lungs are a site for the uptake, accumulation, and storage of exogenous basic amines. The compound N-N-N'-trimethyl-N'-(2-hydroxy-3-methyl-5-iodobenzyl)-1,3 propanediamine (HIPDM) is a basic amine that can be labelled with radioactive iodine and detected by external counting. Intravenously injected 123I-HIPDM is extracted by the human lung, where it is retained in a slowly effluxable pool. In the present study, we measured HIPDM lung kinetics and subcellular distribution in rabbits given i.v. 125I-HIPDM. Rabbits were killed from 2 min to 5 h after injection, and the radioactivity retained in their lungs was measured. Subcellular lung fractions (nuclear, mitochondrial, lysosomal, microsomal and postmicrosomal supernatant) were assayed for HIPDM radioactivity, protein content, and distribution of specific marker enzymes. HIPDM lung clearance in rabbits was nearly identical to that of humans. Virtually all the HIPDM radioactivity in lungs (98+/-1%) was associated with subcellular membranous structures. The highest HIPDM specific radioactivity was found in the mitochondrial fraction, and the subcellular distribution profile closely resembled that of the mitochondrial marker enzyme succinate cytochrome c reductase. No redistribution of HIPDM among subcellular compartments was observed over a 5 h period after injection. The data indicate that mitochondria act as reservoir for HIPDM in the lungs and contribute to the pulmonary persistence of this compound. HIPDM can be used to investigate the pulmonary uptake of basic amines in health and in lung disease.

Human placenta radioreceptor assay with digoxin and ouabain to detect endogenous digitalis-like factor(s) in human plasma and urine

We describe the optimization and validation of a clinically feasible radioreceptor assay to detect endogenous digitalis-like factor(s) (EDLF) in human plasma and urine. The assay is based on the competitive replacement of 125I-labeled digoxin on human placenta membranes by ligands present in sample extracts. Digoxin and ouabain were used as calibrators. We also describe simple and effective methods for extraction and enrichment of EDLF from human plasma and urine. Assay sensitivity and precision were enhanced by using a sequential saturation technique with appropriate concentrations of tracer and receptors. Filtration was used to separate bound from free ligand. A two-step solid-state extraction with acetonitrile allowed the separation of two EDLFs with different polarity (EDLF-1 and EDLF-2) from the same plasma sample. A one-step solid-state extraction with methanol was suitable for urine. EDLF-1 and EDLF-2 in healthy adults were respectively 204 +/- 155 and 207 +/- 423 pmol/L ouabain equivalents, or 312 +/- 241 and 302 +/- 581 pmol/L digoxin equivalents. Plasma concentrations of EDLFs in newborns and pregnant women were higher than in healthy adults, and the concentrations in urine were higher than in plasma. Several cross-reactivity experiments showed that physiological concentrations of endogenous steroids and lipids did not inhibit binding, and supported the hypothesis that EDLFs are endogenous compounds other than the steroids and lipids also investigated.

Human placenta radioreceptor assay with digoxin and ouabain to detect endogenous digitalis-like factor(s) in human plasma and urine

We describe the optimization and validation of a clinically feasible radioreceptor assay to detect endogenous digitalis-like factor(s) (EDLF) in human plasma and urine. The assay is based on the competitive replacement of 125I-labeled digoxin on human placenta membranes by ligands present in sample extracts. Digoxin and ouabain were used as calibrators. We also describe simple and effective methods for extraction and enrichment of EDLF from human plasma and urine. Assay sensitivity and precision were enhanced by using a sequential saturation technique with appropriate concentrations of tracer and receptors. Filtration was used to separate bound from free ligand. A two-step solid-state extraction with acetonitrile allowed the separation of two EDLFs with different polarity (EDLF-1 and EDLF-2) from the same plasma sample. A one-step solid-state extraction with methanol was suitable for urine. EDLF-1 and EDLF-2 in healthy adults were respectively 204 +/- 155 and 207 +/- 423 pmol/L ouabain equivalents, or 312 +/- 241 and 302 +/- 581 pmol/L digoxin equivalents. Plasma concentrations of EDLFs in newborns and pregnant women were higher than in healthy adults, and the concentrations in urine were higher than in plasma. Several cross-reactivity experiments showed that physiological concentrations of endogenous steroids and lipids did not inhibit binding, and supported the hypothesis that EDLFs are endogenous compounds other than the steroids and lipids also investigated.

[Growth factors and oncogenes in development and carcinogenesis. Role of the epidermal growth factor system]

The processes of cellular proliferation and progressive acquisition of a specialized phenotype show a remarkable degree of coordination that involves both intracellular programming and intercellular communication. One of the major incentives for studying factors that regulate the processes of cellular proliferation and differentiation is the recognition of their potential contribution to tumorigenesis. In normal cells, stimulatory and inhibitory events are believed to be under the control of growth factors and growth inhibitory factors, which are known to be protooncogene products. Growth regulatory mechanisms usually involve the binding of a growth factor to a specific receptor on the cell surface, which then through an intracellular biochemical cascade leads to cell division. The cell regulation pathways initiated by growth factors may be subverted at several distinct levels in cancer cells. Studies of oncogenes have shown that they may function as abnormal growth factors or abnormal receptors, induce expression of potential signal regulators or encode proteins which modulate gene transcription. The purpose of the present paper is to examine the role of growth factors, growth factor receptors and intracellular proteins involved in signal transduction (with particular regard to the epidermal growth factor receptor system) in the control of normal growth and differentiation, and their contribution to transformation and tumorigenesis. We also review the classical theories of neoplasia and various other models. Chemical carcinogenesis and Vogelstein-Lane model are presented.

Radioreceptor assay for the measurement of endogenous digitalis-like factors using membrane particulate fraction of human placenta and 125I-digoxin: comparison with RIA method

We measured purified extracts of serum (plasma) or urine samples of newborns, pregnant women, normal adults, and uremic patients by a radioreceptor assay (RRA), which uses particulate membrane fractions from human placenta as a binding system, and 125I-digoxin as a tracer. We also measured the digoxin-like immunoreactivity by a sensitive RIA, and results were compared with those found by the RRA. Specific 125I-digoxin binding to placental receptors was competitively inhibited by purified plasma and/or urine extracts of newborns, adult subjects, pregnant women and uremic patients. A linear relationship was found between inhibition of binding and volume of plasma and urine assayed. Moreover, a significant correlation was found between the values obtained by RRA and those found by RIA (n = 17, r = 0.699, p = 0.0012). Our data confirm that increased circulating and/or urinary levels of substances with biological and immunological activity similar to cardiac glycoside drugs are present in newborns, pregnant women and uremic patients compared to healthy adult subjects. In addition, our preliminary study indicates that these endogenous factors are able to bind to the specific receptor of digitalis drugs on the placental membranes.

Specific binding of cardiac glycoside drugs and endogenous digitalis-like substances to particulate membrane fractions from human placenta

We studied the characteristics of binding of cardiac glycosides to particulate membrane fractions from human placenta, to demonstrate that placental tissue is a suitable source of receptors for digitalis drugs. Moreover, we performed preliminary experiments with 125I-labeled digoxin and placental particulates to develop a radioreceptor assay for measurement of endogenous substances with activity similar to cardiac glycoside drugs (EDLS). Placental membrane fractions were incubated with [3H]ouabain (10 nmol/L) or 125I-labeled digoxin (50 pmol/L). With both ligands, binding followed a pseudo-first-order reaction kinetics and was saturable. Scatchard analysis revealed a single class of sites [for ouabain, KD = 20.2 +/- 5.8 nmol/L (mean +/- SEM), Bmax = 3.1 +/- 0.9 nmol per gram of protein; for digoxin, KD = 29.7 +/- 1.9 nmol/L, Bmax = 24.3 +/- 1.1 nmol per gram of protein]. As expected, digoxin was less potent than ouabain in displacing both tracers from digitalis drugs receptors; progesterone, cortisone, digitoxose, furosemide, bumetanide, and propranolol had no or little effect. Specific 125I-labeled digoxin binding was competitively inhibited by plasma and (or) urine extracts from newborns, adults, pregnant women, and patients with renal insufficiency. Inhibition of binding and volume of plasma and urine assayed were linearly related. These findings support the hypothesis that cardiac glycosides and EDLS can interact with the human placenta and suggest placental tissue to be a suitable source of receptors for cardiac glycosides.

Specific binding of cardiac glycoside drugs and endogenous digitalis-like substances to particulate membrane fractions from human placenta

We studied the characteristics of binding of cardiac glycosides to particulate membrane fractions from human placenta, to demonstrate that placental tissue is a suitable source of receptors for digitalis drugs. Moreover, we performed preliminary experiments with 125I-labeled digoxin and placental particulates to develop a radioreceptor assay for measurement of endogenous substances with activity similar to cardiac glycoside drugs (EDLS). Placental membrane fractions were incubated with [3H]ouabain (10 nmol/L) or 125I-labeled digoxin (50 pmol/L). With both ligands, binding followed a pseudo-first-order reaction kinetics and was saturable. Scatchard analysis revealed a single class of sites [for ouabain, KD = 20.2 +/- 5.8 nmol/L (mean +/- SEM), Bmax = 3.1 +/- 0.9 nmol per gram of protein; for digoxin, KD = 29.7 +/- 1.9 nmol/L, Bmax = 24.3 +/- 1.1 nmol per gram of protein]. As expected, digoxin was less potent than ouabain in displacing both tracers from digitalis drugs receptors; progesterone, cortisone, digitoxose, furosemide, bumetanide, and propranolol had no or little effect. Specific 125I-labeled digoxin binding was competitively inhibited by plasma and (or) urine extracts from newborns, adults, pregnant women, and patients with renal insufficiency. Inhibition of binding and volume of plasma and urine assayed were linearly related. These findings support the hypothesis that cardiac glycosides and EDLS can interact with the human placenta and suggest placental tissue to be a suitable source of receptors for cardiac glycosides.

Lung tissue binding of iodobenzyl-propanediamine: involvement of beta-adrenergic receptors

The basic compound N-N-N'-trimethyl-N'-(2-hydroxy-3-methyl-5-iodobenzyl)-1,3- propanediamine (HIPDM) accumulates in human and rabbit lungs, where it forms a slowly effluxable pool. In isolated perfused rat lung, HIPDM is taken up by a saturable, energy-independent mechanism, which is competitively inhibited by imipramine, chlorpromazine and propranolol. To ascertain whether beta-adrenergic receptors are involved in the binding process of HIPDM to lung tissue, the ability of unlabelled HIPDM to displace the beta-adrenergic receptor ligand [125I]iodocyanopindolol (ICYP) from rabbit lung beta-receptors was examined. Lung microsomal membrane fractions (75 micrograms ml-1) were incubated at 37 degrees C for 3 h with 68 pM ICYP (with or without 1 microM of (+/-)-propranolol) in the presence of HIPDM (10(-10)-10(-3) M). Bound and free radioactivity were separated through glass-fibre filters and the retained radioactivity was counted in a gamma-spectrometer. HIPDM competed with ICYP for beta-adrenoceptors (13% displacement at 10(-5) M. 50% at 5 x 10(-5) M, and 90% at 2 x 10(-4) M). The inhibition curve of ICYP binding by HIPDM was similar to that observed for (-)-noradrenaline. Although the results of the in vitro studies cannot be extrapolated to in vivo conditions, they suggest that beta-adrenergic receptors may be involved in the observed lung uptake of the basic amine HIPDM.

Binding of 14C-furosemide to isolated human erythrocytes

The incubation of 14C-furosemide at high specific activity with intact red blood cells at 37 degrees C, pH 7.4, has enabled the furosemide binding sites to be characterized with respect to time course, affinity and specificity. The binding reaction was rapid, reversible and close to thermodynamic equilibrium. Binding was dependent on cell and furosemide concentration and was saturable. At equilibrium, pharmacological doses of furosemide competitively inhibited 14C-furosemide binding with 50% inhibition at 3 x 10(-5) M. The Na+/K+ pump inhibitor ouabain had no effect on the 14C-furosemide binding. Bumetanide, which is more potent than furosemide as inhibitor of Na+/K+ co-transport system and equally effective in inhibiting anion transport, was less effective than furosemide in displacing 14C-furosemide from its binding sites, suggesting a different mechanism of action for the two drugs in the red blood cell. The preincubation of erythrocytes with 4,4'-diisothiocyano-stilbene-2,2'-disulphonic acid (DIDS), the potent and specific inhibitor of anion permeability, reduced specific furosemide binding by more than 80% at a furosemide concentration of 0.1 microM, while it had little effect on the non-specific furosemide binding. Taken together, these data suggest that furosemide interacts with specific binding sites in the human red blood cell, whose nature has not been clarified, but whose location is probably on (or near) the protein in band 3, i.e. the membrane macromolecule-mediating anion transport.

Demonstration of beta 1-adrenergic receptors in human placenta by (-)[125I]iodocyanopindolol binding

The highly specific beta-adrenergic radioligand (-)[125I]iodocyanopindolol (ICYP) was used to characterize the beta-adrenergic receptor subtype present in human placenta. Binding of ICYP to membranes from human placenta was saturable with time and ligand concentration, of high affinity, and demonstrated appropriate stereoselectivity and agonist rank order of potency for binding to a beta-adrenergic receptor. From saturation binding curves, the KD and Bmax values for ICYP binding were 233 +/- 51 pM and 690 +/- 139 fmol/mg of proteins, respectively. Analysis of inhibition of ICYP binding by beta 1- and beta 2-selective adrenergic antagonists via Hofstee analysis resulted in linear plots, indicating the existence of a homogeneous population of beta-adrenergic receptors. From the resulting KI-values for the beta 1-selective drugs practolol (4.0 +/- 0.9 microM) and metoprolol (0.19 +/- 0.07 microM) and for the beta 2-selective drug ICI 118,551 (0.30 +/- 0.06 microM) it is concluded that the beta-adrenergic receptor in human placenta is of the beta 1-subtype. This is further supported by the fact that (-)-noradrenaline and (-)-adrenaline were equipotent in inhibiting ICYP binding.