Influence of sex differences on the renal secretion of organic anions

Absorption, distribution, metabolism and excretion of linaprazan glurate in rats

Linaprazan (AZD0865, TX07) is one of potassium-competitive acid blockers. However, linaprazan is rapidly excreted from the body, shortening its acid inhibition property. Linaprazan glurate (X842) is a prodrug of linaprazan with a prolonged inhibitory effect on gastric acid secretion. Linaprazan glurate has entered clinical trials, but few studies have reported its metabolism in non-clinical and clinical settings. In this study, we studied the pharmacokinetics, tissue distribution, mass balance, and metabolism of linaprazan glurate in rats after a single oral dose of 2.4 mg/kg (100 µCi/kg) [14C]linaprazan glurate. The results demonstrated that linaprazan glurate was mainly excreted via feces in rats with 70.48% of the dose over 168 h. The plasma AUC0-∞ of linaprazan glurate in female rats was 2 times higher than that in male rats. Drug-related substances were mainly concentrated in the stomach, eyes, liver, small intestine, and large intestine after administration. In blood, drug-related substances were mostly distributed into plasma instead of hemocytes. In total, 13 metabolites were detected in rat plasma, urine, feces, and bile. M150 (2,6-dimethylbenzoic acid) was the predominant metabolite in plasma, accounting for 80.65% and 67.65% of AUC0-24h in male and female rats, respectively. Based on the structures, linaprazan glurate was mainly hydrolyzed into linaprazan, followed by a series of oxidation, dehydrogenation, and glucuronidation in rats. Besides, CES2 is the main metabolic enzyme involved in the hydrolysis of linaprazan glurate to linaprazan.

Finasteride-Induced Inhibition of 5α-Reductase Type 2 Could Lead to Kidney Damage-Animal, Experimental Study

In the pharmacological treatment of prostate cancer, benign prostatic hyperplasia and androgenetic alopecia finasteride is commonly used. This drug inhibits 5α-reductase type 2, which is why finasteride affects androgen homeostasis, since testosterone (T) cannot be reduced to dihydrotestosterone (DHT). As studies on sex-related renal injuries suggest a high probability of androgen-induced renal dysfunction, the aim of this study was to determine the potential harmful effects of finasteride on the kidneys of rats. The study was performed on sexually mature male Wistar rats given finasteride. Histological sections of the kidneys were used for immunohistochemical visualization of the androgen receptor (AR), junctional proteins (occluding (Occ); E-cad, N-cad, E-/N-cadherin; β-cat, β-catenin; connexin 43 (Cx43)), proliferating cell nuclear antigen (PCNA), IL-6, and lymphocyte markers (CD3 for T cell, CD19 for B cell). The TUNEL method was used for cell apoptosis identification, and picro sirius red staining was used to assess collagen fibers thickness. The levels of T, DHT and estradiol (E2) were determined in blood serum. It was shown that finasteride treatment affected steroid hormone homeostasis, altered the expression of AR and intracellular junction proteins, changed the ratio between cell apoptosis and proliferation, and caused lymphocyte infiltration and an increase of IL-6. The thickening of collagen fibers was observed as tubular fibrosis and glomerulosclerosis. Summarizing, finasteride-induced hormonal imbalance impaired the morphology (i.e., dysplastic glomeruli, swollen proximal convoluted tubules) and physiology (changed level of detected proteins/markers expression) of the kidneys. Therefore, it is suggested that patients with renal dysfunction or following renal transplantation, with androgen or antiandrogen supplementation, should be under special control and covered by extended diagnostics, because the adverse negative effect of DHT deficiency on the progression of kidney disease cannot be ignored.

Sub-acute administration of lower doses of nicotine caused sex-dependent improvement of renal function in Wistar rats

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Exposure to nicotine is associated with sex-dependent variation in electrolyte disturbances.

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Lower doses of sub-acute nicotine administration enhanced renal function.

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Nicotine-enhanced renal function is more pronounced in female than in male Wistar rats.

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Nicotine-enhanced renal function may be mediated through α7-nAchR.

The adverse and beneficial health effects of nicotine (NIC), the major alkaloid found in cigarettes and tobacco, are controversial. Most studies on NIC have focused on its effects on cardiovascular and nervous functions. This study aimed at determining dose- and sex-specific effects of sub-acute (28 days) NIC administration on some indices of kidney function in Wistar rats. Forty rats (20 males and 20 females), 8–9 weeks old (each housed in separate metabolic cage), were used for this study such that graded doses of NIC (1, 2 and 4 mg/kg i.p. for 28 days) were administered to both sexes while each control received distilled water at 0.2 mL/100 g i.p. Blood was collected under ketamine anesthesia (10 mg/kg i.m) for analyses and results obtained were compared at p < 0.05. The result showed beneficial alterations in plasma and urine level of creatinine, urea and uric acid (p < 0.05) as well as plasma and urine electrolyte level (Na⁺ and K⁺) in both sexes (p < 0.05). Also, there was significant improvement in creatinine clearance (p < 0.05) with no appreciable difference in their histological examination. Although these beneficial effects were more pronounced in the female than in the male (p < 0.05), administration at the highest dose showed potentially deleterious alterations from normal beneficial trend (p < 0.05) in both sexes. It was concluded that sub-acute administration of lower doses of NIC improves kidney function of Wistar rats; an effect that was more pronounced in the females than their male counterparts.

Application of physiologically-based pharmacokinetic modeling to explore the role of kidney transporters in renal reabsorption of perfluorooctanoic acid in the rat

Renal elimination and the resulting clearance of perfluorooctanoic acid (PFOA) from the serum exhibit pronounced sex differences in the adult rat. The literature suggests that this is largely due to hormonally regulated expression of organic anion transporters (OATs) on the apical and basolateral membranes of the proximal tubule cells that facilitate excretion and reabsorption of PFOA from the filtrate into the blood. Previously developed PBPK models of PFOA exposure in the rat have not been parameterized to specifically account for transporter-mediated renal elimination. We developed a PBPK model for PFOA in male and female rats to explore the role of Oat1, Oat3, and Oatp1a1 in sex-specific renal reabsorption and excretion of PFOA. Descriptions of the kinetic behavior of these transporters were extrapolated from in vitro studies and the model was used to simulate time-course serum, liver, and urine data for intravenous (IV) and oral exposures in both sexes. Model predicted concentrations of PFOA in the liver, serum, and urine showed good agreement with experimental data for both male and female rats indicating that in vitro derived physiological descriptions of transporter-mediated renal reabsorption can successfully predict sex-dependent excretion of PFOA in the rat. This study supports the hypothesis that sex-specific serum half-lives for PFOA are largely driven by expression of transporters in the kidney and contribute to the development of PBPK modeling as a tool for evaluating the role of transporters in renal clearance.

A novel, simple and inexpensive procedure for the simultaneous determination of iopamidol and p-aminohippuric acid for renal function assessment from plasma samples in awake rats

The purpose of the current study was to design, validate and implement a novel analytical method for the simultaneous plasma measurement of iopamidol and p-aminohippuric acid (PAH) to estimate renal function in awake rats. A reverse-phase high performance liquid chromatographic (RP-HPLC) method for the simultaneous measurement of iopamidol (for glomerular filtration rate estimation, GFR) and PAH (for tubular secretion determination, TS) was designed and validated using a C-18 column, 0.1M acetic acid-10% acetonitrile (90:10, v/v) as mobile phase, at a flow rate of 0.3 ml/min, and UV detection at 270 nm. Iopamidol (244.8 mg/kg) was administered intravenously followed immediately by sodium PAH (100 mg/kg) to healthy female Sprague-Dawley rats. Plasma samples obtained at 2.5, 5, 10, 15, 20, 30, 45, 60, 90, and 120 min after drug administration were deproteinized with 2.5% trichloroacetic acid containing p-aminobenzoic acid as internal standard, and separated by the validated RP-HPLC method described above. The iopamidol and PAH chromatographic data were analyzed using a non-compartmental model. The results demonstrated that the RP-HPLC method was linear in ranges between 15-120 μg/ml and 2.5-120 μg/ml for iopamidol and PAH, respectively. Precision and accuracy were within 15% for both drugs. Recovery of iopamidol and PAH was 92% and 100%, respectively. Plasma iopamidol and PAH clearances in awake rats, estimates for GFR and TS, respectively, were 1.49±0.20 ml/min and 3.73±0.38 ml/min. In conclusion, the method here described is a simple and reliable procedure, for the simultaneous and time-saving determination of GFR and TS from plasma samples in the conscious rat.

Life-stage-, sex-, and dose-dependent dietary toxicokinetics and relationship to toxicity of 2,4-dichlorophenoxyacetic acid (2,4-D) in rats: implications for toxicity test dose selection, design, and interpretation

Life-stage-dependent toxicity and dose-dependent toxicokinetics (TK) were evaluated in Sprague Dawley rats following dietary exposure to 2,4-dichlorophenoxyacetic acid (2,4-D). 2,4-D renal clearance is impacted by dose-dependent saturation of the renal organic anion transporter; thus, this study focused on identifying inflection points of onset of dietary nonlinear TK to inform dose selection decisions for toxicity studies. Male and female rats were fed 2,4-D-fortified diets at doses to 1600 ppm for 4-weeks premating, <2 weeks during mating, and to test day (TD) 71 to parental (P1) males and to P1 females through gestation/lactation to TD 96. F1 offspring were exposed via milk with continuing diet exposure until postnatal day (PND) 35. As assessed by plasma area under the curve for the time-course plasma concentration, nonlinear TK was observed ≥ 1200 ppm (63 mg/kg/day) for P1 males and between 200 and 400 ppm (14-27 mg/kg/day) for P1 females. Dam milk and pup plasma levels were higher on lactation day (LD) 14 than LD 4. Relative to P1 adults, 2,4-D levels were higher in dams during late gestation/lactation and postweaning pups (PND 21-35) and coincided with elevated intake of diet/kg body weight. Using conventional maximum tolerated dose (MTD) criteria based on body weight changes for dose selection would have resulted in excessive top doses approximately 2-fold higher than those identified incorporating critical TK data. These data indicate that demonstration of nonlinear TK, if present at dose levels substantially above real-world human exposures, is a key dose selection consideration for improving the human relevance of toxicity studies compared with studies employing conventional MTD dose selection strategies.

Changes in renal function during acute spinal cord injury: implications for pharmacotherapy

STUDY DESIGN

Laboratory investigation in rats submitted to experimental spinal cord injury (SCI).

OBJECTIVE

To characterize changes in renal function during acute SCI.

METHODS

Sprague Dawley rats were subjected to severe spinal cord contusion at T8 level or to laminectomy as control. Twenty-four hours after spine surgery, clearance assessments of a single dose of iohexol (120 mg kg(-1)) or of p-aminohippuric acid (PAH, 100 mg kg(-1)) were used to evaluate glomerular filtration rate (GFR) and tubular secretion (TS), respectively. Blood sampling was used to determine concentrations of both compounds by high-performance liquid chromatography for pharmacokinetic measurements.

RESULTS

Iohexol clearance decreased significantly after injury, which resulted in increased concentrations and half-life of iohexol in blood; PAH clearance remained unchanged.

CONCLUSION

GFR but not TS is altered during spinal shock. These observations should be of interest to professionals caring for early cord-injured patients, in order to prevent toxicity and therapeutic failure when administering drugs eliminated by the kidney.

Sex differences in cardiovascular drug-induced adverse reactions causing hospital admissions

AIMS

Cardiovascular disease in women is often underestimated. The effects of cardiovascular drugs differ between the sexes because of pharmacokinetic and pharmacodynamic differences. Adverse drug reactions (ADRs) within these drug classes may have serious consequences, leading to hospital admission. We aimed to study differences between men and women in hospital admissions for ADRs due to cardiovascular drugs.

METHODS

We conducted a nationwide study of all hospital admissions between 2000 and 2005 with data from the Dutch National Medical Register. Relative risks were calculated of hospital admissions due to ADRs to the different cardiovascular drug groups for women compared with men. By an ecological design, risks were adjusted for the total number of Dutch inhabitants and the total number of prescriptions.

RESULTS

In total, 14 207 of the hospital admissions (34% of all ADR-related admissions) were attributed to cardiovascular drugs [7690 in women (54%; 95% confidence interval 53-55%)]. 'Anticoagulants and salicylates' (n= 8988), 'high- and low-ceiling diuretics' (n= 2242) and 'cardiotonic glycosides' (n= 932) were responsible for the majority of the ADR-related hospital admissions. The most pronounced sex differences were seen in users of low-ceiling diuretics (relative risk 4.02; 95% confidence interval 3.12-5.19), cardiotonic glycosides (relative risk 2.38; 95% confidence interval 2.06-2.74), high-ceiling diuretics (relative risk 2.10; 95% confidence interval 1.91-2.32) and coronary vasodilators (relative risk 0.77; 95% confidence interval 0.65-0.91).

CONCLUSIONS

Clear sex differences exist in ADRs requiring hospital admission for different cardiovascular drug groups. Sex differences should be taken into account in the prescription and evaluation of drugs.

Endocrine and metabolic regulation of renal drug transporters

Renal xenobiotic transporters are important determinants of urinary secretion and reabsorption of chemicals. In addition to glomerular filtration, these processes are key to the overall renal clearance of a diverse array of drugs and toxins. Alterations in kidney transporter levels and function can influence the efficacy and toxicity of chemicals. Studies in experimental animals have revealed distinct patterns of renal transporter expression in response to sex hormones, pregnancy, and growth hormone. Likewise, a number of disease states including diabetes, obesity, and cholestasis alter the expression of kidney transporters. The goal of this review is to provide an overview of the major xenobiotic transporters expressed in the kidneys and an understanding of metabolic conditions and hormonal factors that regulate their expression and function.

Male-dominant activation of rat renal organic anion transporter 1 (Oat1) and 3 (Oat3) expression by transcription factor BCL6

Background

Organic anion transporters 1 (Oat1) and 3 (Oat3) mediate the transport of organic anions, including frequently prescribed drugs, across cell membranes in kidney proximal tubule cells. In rats, these transporters are known to be male-dominant and testosterone-dependently expressed. The molecular mechanisms that are involved in the sex-dependent expression are unknown. Our aim was to identify genes that show a sex-dependent expression and could be involved in male-dominant regulation of Oat1 and Oat3.

Methodology/Principal Findings

Promoter activities of Oat1 and Oat3 were analyzed using luciferase assays. Expression profiling was done using a SurePrint G3 rat GE 8×60K microarray. RNA was isolated from renal cortical slices of four adult rats per sex. To filter the achieved microarray data for genes expressed in proximal tubule cells, transcription database alignment was carried out. We demonstrate that predicted androgen response elements in the promoters of Oat1 and Oat3 are not functional when the promoters were expressed in OK cells. Using microarray analyses we analyzed 17,406 different genes. Out of these genes, 56 exhibit a sex-dependent expression in rat proximal tubule cells. As genes potentially involved in the regulation of Oat1 and Oat3 expression, we identified, amongst others, the male-dominant hydroxysteroid (17-beta) dehydrogenase 1 (Hsd17b1), B-cell CLL/lymphoma 6 (BCL6), and polymerase (RNA) III (DNA directed) polypeptide G (Polr3g). Moreover, our results revealed that the transcription factor BCL6 activates promoter constructs of Oat1 and Oat3.

Conclusion

The results indicate that the male-dominant expression of both transporters, Oat1 and Oat3, is possibly not directly regulated by the classical androgen receptor mediated transcriptional pathway but appears to be regulated by the transcription factor BCL6.

Low-dose indomethacin after ischemic acute kidney injury prevents downregulation of Oat1/3 and improves renal outcome

We have previously shown that expression of renal organic anion transporters Oat1 and Oat3 is diminished by prostaglandin E2 (PGE2) and that both transporters are downregulated after renal ischemia. Because PGE2 is increased after renal ischemia and is generated by cyclooxygenases (COX), we investigated the effect of the COX inhibitor indomethacin on expression of Oat1/3 after ischemic acute kidney injury (iAKI). iAKI was induced in rats by bilateral clamping of renal arteries for 45 min. Indomethacin (1 mg/kg) was given intraperitoneally as soon as reperfusion started. Sham-treated animals served as controls. Oat1/3 were determined by qPCR and Western blot. PGE2 in blood and urine was measured by enzyme-linked immunosorbent assay. Invasion of monocytes/macrophages was determined. Glomerular filtration rate and renal plasma flow were determined. All parameters were detected 24 h after ischemia. PAH net secretion, as well as clearance and secretion of PGE2 were calculated. In clamped animals, indomethacin restored expression of Oat1/3, as well as PAH net secretion, PGE2 clearance, or PGE2 secretion. Additionally, indomethacin substantially improved kidney function as measured by glomerular filtration and PAH clearance. Indomethacin did not affect ischemia-induced invasion of monocytes/macrophages. In conclusion, our study indicates that low-dose indomethacin applied after ischemia prevents ischemia-induced downregulation of Oat1/3 during reperfusion and has a substantial protective effect on kidney function after iAKI. The beneficial effect of low-dose indomethacin on renal outcome is likely due to an effect different from inhibition of inflammation. In accordance to the decreased PAH net secretion, renal excretion of an endogenous organic anion (PGE2) is also impaired after ischemia and reperfusion.

Toward a systems level understanding of organic anion and other multispecific drug transporters: a remote sensing and signaling hypothesis

Organic anion transporters (Oats) are located in the barrier epithelia of diverse organs, where they mediate the absorption and excretion of a wide range of metabolites, signaling molecules, and xenobiotics. Although their interactions with a broad group of substrates have been extensively studied and described, the primary physiological role of Oats remains elusive. The presence of overlapping substrate specificities among the different Oat isoforms, together with recent metabolomic data from the Oat1, Oat3, and renal-specific transporter (RST/URAT1) knockout mice, suggests a possible role in remote signaling wherein substrates excreted through one Oat isoform in one organ are taken up by another Oat isoform located in a different organ, thereby mediating communication between different organ systems, or even between different organisms. Here we further develop this "remote sensing and signaling hypothesis" and suggest how the regulation of SLC22 subfamily members (including those of the organic cation, organic carnitine, and unknown substrate transporter subfamilies) can be better understood by considering the organism's broader need to communicate between epithelial and other tissues by simultaneous regulation of transport of metabolites, signaling molecules, drugs, and toxins. This systems biology perspective of remote signaling (sensing) could help reconcile an enormous array of tissue-specific data for various SLC22 family genes and, possibly, other multispecific transporters, such as those of the organic anion transporting polypeptide (OATP, SLC21) and multidrug resistance-associated protein (MRP) families.

Sexually dimorphic effects of testosterone administration on brain allopregnanolone in gonadectomized rats

INTRODUCTION

Clinical and biological evidences have shown a wide range of neuroactive effects of testosterone administration.

AIM

Evaluation of the effects of 2-weeks treatment with testosterone (T), Dihydrotestosterone (DHT), and estradiol valerate (E2V) on brain and serum allopregnanolone (AP) in gonadectomized rats of both sexes.

MAIN OUTCOME MEASURES

AP levels were measured in frontal and parietal lobe, hippocampus, hypothalamus, anterior pituitary, and in serum.

METHODS

Eight groups of Wistar female and eight groups of Wistar male rats were included. For each sex, one group of fertile and one group of gonadectomized rats were employed as control receiving placebo. The others groups received subcutaneous T at the dose of 10 microg/kg/day and 100 microg/kg/day for female rats, and 1 mg/kg/day and 5 mg/kg/day for male rats, or DHT at the doses of 1 microg/kg/day, 10 microg/kg/day, and 100 microg/kg/day for females, and 0, 1 microg/kg/day, 1 mg/kg/day and 5 mg/kg/day for males, or E2V (0.05 mg/Kg/day).

RESULTS

Ovariectomy (OVX) and orchidectomy (OCX) induced a significant decrease in AP in all brain areas analyzed, as well as in serum. In OVX rats, T replacement, as well as E2V, significantly increased AP content in all brain areas and in plasma. In OCX, T and E2V did not actively result in influencing AP concentration in frontal and parietal lobe, while it produced a significant rise in AP levels in the hippocampus, hypothalamus, anterior pituitary, and serum. Conversely, DHT replacement had no affect on AP levels anywhere or at any administered dose, either in males or in female rats.

CONCLUSIONS

Gender difference and T therapy affect brain AP synthesis/release during the reproductive aging. This effect becomes particularly evident in the brain of ovariectomized animals, where the content of this specific neurosteroid is much more responsive than male animals to testosterone replacement.

Histological study of gender differences in accumulation of silver nanoparticles in kidneys of Fischer 344 rats

The tissue distribution of silver (Ag) nanoparticles showed a dose-dependent accumulation of Ag in all the tissues examined, including testes, kidneys, liver, brain, lungs, and blood. However, a gender-related difference in the accumulation of Ag was noted in the kidneys, with a twofold higher concentration in female kidneys compared males after subacute exposure to Ag nanoparticles via inhalation or oral ingestion. To investigate the gender-specific accumulation of Ag nanoparticles in kidneys of Fischer 344 rats, detailed histopathological studies were conducted by Ag enhancement staining. Female rats showed a higher accumulation of Ag nanoparticles in all kidney regions, including cortex, outer medulla, and inner medulla. In particular, the glomerulus in the cortex contained a higher accumulation in females than males. The Ag nanoparticles were also preferentially accumulated in the basement membranes of the renal tubules in the cortex, middle and terminal parts of the inner medulla, and outer medulla. In addition, Ag nanoparticles were detected in the cytoplasm and nuclei of interstitial cells in the inner medulla of the kidney.

Physiology, structure, and regulation of the cloned organic anion transporters

1. The transport of negatively charged drugs, xenobiotics, and metabolites by epithelial tissues, particularly the kidney, plays critical roles in controlling their distribution, concentration, and retention in the body. Thus, organic anion transporters (OATs) impact both their therapeutic efficacy and potential toxicity. 2. This review summarizes current knowledge of the properties and functional roles of the cloned OATs, the relationships between transporter structure and function, and those factors that determine the efficacy of transport. Such factors include plasma protein binding of substrates, genetic polymorphisms among the transporters, and regulation of transporter expression. 3. Clearly, much progress has been made in the decade since the first OAT was cloned. However, unresolved questions remain. Several of these issues--drug-drug interactions, functional characterization of newly cloned OATs, tissue differences in expression and function, and details of the nature and consequences of transporter regulation at genomic and intracellular sites--are discussed in the concluding Perspectives section.

Gender differences in kidney function

Sex hormones influence the development of female (F) and male (M) specific traits and primarily affect the structure and function of gender-specific organs. Recent studies also indicated their important roles in regulating structure and/or function of nearly every tissue and organ in the mammalian body, including the kidneys, causing gender differences in a variety of characteristics. Clinical observations in humans and studies in experimental animals in vivo and in models in vitro have shown that renal structure and functions under various physiological, pharmacological, and toxicological conditions are different in M and F, and that these differences may be related to the sex-hormone-regulated expression and action of transporters in the apical and basolateral membrane of nephron epithelial cells. In this review we have collected published data on gender differences in renal functions, transporters and other related parameters, and present our own microarray data on messenger RNA expression for various transporters in the kidney cortex of M and F rats. With these data we would like to emphasize the importance of sex hormones in regulation of a variety of renal transport functions and to initiate further studies of gender-related differences in kidney structure and functions, which would enable us to better understand occurrence and development of various renal diseases, pharmacotherapy, and drug-induced nephrotoxicity in humans and animals.

Downregulation of organic anion transporters OAT1 and OAT3 correlates with impaired secretion ofpara-aminohippurate after ischemic acute renal failure in rats

Ischemic acute renal failure (iARF) was described to reduce renal extraction of the organic anion para-aminohippurate (PAH) in humans. The rate-limiting step of renal organic anion secretion is its basolateral uptake into proximal tubular cells. This process is mediated by the organic anion transporters OAT1 and OAT3, which both have a broad spectrum of substrates including a variety of pharmaceutics and toxins. Using a rat model of iARF, we investigated whether impairing the secretion of the organic anion PAH might be associated with downregulation of OAT1 or OAT3. Inulin and PAH clearance was determined starting from 6 up to 336 h after ischemia-reperfusion (I/R) injury. Net secretion of PAH was calculated and OAT1 as well as OAT3 expression was analyzed by RT-PCR and Western blotting. Inulin and PAH clearance along with PAH net secretion were initially diminished after I/R injury with a gradual recovery during follow-up. This initial impairment after iARF was accompanied by decreased mRNA and protein levels of OAT1 and OAT3 in clamped animals compared with sham-operated controls. In correlation to the improvement of kidney function, both mRNA and protein levels of OAT1 and OAT3 were upregulated during the follow-up. Thus decreased expression of OAT1 and OAT3 is sufficient to explain the decline of PAH secretion after iARF. As a result, this may have substantial impact on excretion kinetics and half-life of organic anions. As a consequence, the biological effects of a variety of organic anions may be affected after iARF.

Application of the isolated perfused rat kidney model to assess gender effects on drug excretion

PURPOSE

To study the effect of gender on the renal disposition of two organic anions, p-aminohippuric acid (PAH) and furosemide (FSM) in the isolated perfused rat kidney (IPK).

METHODS

IPK experiments (3-4 per treatment group) were conducted using kidneys from male and female Sprague Dawley rats. PAH was administered as a continuous infusion (with loading dose, targeted steady-state concentration 10 ug/mL). FSM was added as a bolus dose (2.65 mg, targeted concentration 33 ug/mL). Urine was collected in 10-min. intervals and perfusate was sampled at the midpoint of each collection period. Control (drug naïve) perfusions were performed for both genders. PAH and FSM were measured by HPLC. Kidney viability (GFR [estimated using inulin clearance], sodium reabsorption, glucose reabsorption) was monitored continuously during each perfusion experiment (2-h duration).

RESULTS

Good kidney function was maintained across all study groups, and lower GFR estimates in female kidneys were due to differences in kidney weight. For PAH, kidney weight corrected renal clearance (0.88 +/- 0.37 mL/min/g vs. 0.59 +/- 0.19 mL/min/g) and excretion ratio (3.8 +/- 1.7 vs. 2.2 +/- 0.72) were significantly higher in male kidneys. For FSM, renal clearance was significantly lower in female (0.10 +/- 0.05 mL/min/g) compared to male kidneys (0.15 +/- 0.07 mL/min/g). Mass balance analysis showed that FSM cumulative urinary excretion was significantly higher and kidney accumulation was significantly lower in experiments with male kidneys.

CONCLUSIONS

The study demonstrates that the IPK is a useful model to assess gender effects on renal drug disposition. The renal excretion of organic anions is reduced in female rats, possibly due to gender differences in expression and/or activity of membrane transporters (both basolateral and luminal) in the kidney.

Indomethacin decreases furosemide-induced natriuresis and diuresis on the neonatal kidney

Indomethacin is used to pharmacologically occlude patent ductus arteriosus in preterm infants. It induces renal untoward effects and furosemide is administered simultaneously to counteract them. The effect of furosemide is blunted by indomethacin. We analyzed comparatively the interactions of furosemide and indomethacin at the organic anion transport system in adult and newborn individuals. Adult and 5-day-old Wistar rats were allocated into three groups: (1) indomethacin (10 mg/kg, ip); (2) furosemide (2 mg/kg, ip); and (3) indomethacin/furosemide, at the same doses. Urinary flow, glomerular filtration rate (GFR), sodium and potassium fractional excretions, and free-water and osmolal clearances were estimated. Para-aminohippuric acid (PAH) uptake was measured in renal cortical slices to study the organic anion's secretory pathway. In adult and newborn rats, furosemide-induced increments in urinary fluxes and excretions of sodium and potassium were blunted by indomethacin administered simultaneously. PAH uptake was decreased to a further extent by indomethacin than by furosemide, suggesting that inhibition of the diuretic effect might be related to competition in the secretion of furosemide. Inhibitory interaction between indomethacin and furosemide was achieved at approximately 10-fold lower concentrations in the newborn than in the adult rats, suggesting that tubular secretion in the neonate is more sensitive to the action of these drugs than in the adult individual.

Renal expression of organic anion transporter OAT2 in rats and mice is regulated by sex hormones

The renal reabsorption and/or excretion of various organic anions is mediated by specific organic anion transporters (OATs). OAT2 (Slc22a7) has been identified in rat kidney, where its mRNA expression exhibits gender differences [females (F) > males (M)]. The exact localization of OAT2 protein in the mammalian kidney has not been reported. Here we studied the expression of OAT2 mRNA by RT-PCR and its protein by Western blotting (WB) and immunocytochemistry (IC) in kidneys of adult intact and gonadectomized M and F, sex hormone-treated castrated M, and prepubertal M and F rats, and the protein in adult M and F mice. In adult rats, the expression of OAT2 mRNA was predominant in the outer stripe (OS) tissue, exhibiting 1) gender dependency (F > M), 2) upregulation by castration and downregulation by ovariectomy, and 3) strong downregulation by testosterone and weak upregulation by estradiol and progesterone treatment. A polyclonal antibody against rat OAT2 on WB of isolated renal membranes labeled a approximately 66-kDa protein band that was stronger in F. By IC, the antibody exclusively stained brush border (BB) of the proximal tubule S3 segment (S3) in the OS and medullary rays (F > M). In variously treated rats, the pattern of 66-kDa band density in the OS membranes and the staining intensity of BB in S3 matched the mRNA expression. The expression of OAT2 protein in prepubertal rats was low and gender independent. In mice, the expression pattern largely resembled that in rats. Therefore, OAT2 in rat (and mouse) kidney is localized to the BB of S3, exhibiting gender differences (F > M) that appear in puberty and are caused by strong androgen inhibition and weak estrogen and progesterone stimulation.

Gender differences in renal tubular taurocholate transport

The bile acids filtered through the glomeruli nearly completely escape urinary excretion due to an efficient tubular reabsorption process. Reabsorption is mediated by the sodium-dependent bile acid transporter ASBT, which is localized in the brush border membranes of proximal tubular cells. The purpose of the present study was to assess whether tubular taurocholate transport is regulated by sex hormones. Clearance studies and studies on proximal tubular cells freshly isolated from rat kidneys were performed. The studies with the isolated proximal tubular cells revealed a cell to bath 3H-taurocholate accumulation ratio of 5.63+/-0.28 in male and of 3.67+/-0.43 in female rats (p<0.01). This difference in cellular taurocholate uptake was corroborated by the clearance studies, which showed a 3H-taurocholate clearance of 133.9+/-28.1 in male rats and of 262.0+/-45.4 microl/min x 100 g b.w. in female rats (p<0.05). Testosterone treatment of female rats did not significantly alter the cell to bath 3H-taurocholate accumulation ratio. However, the cellular taurocholate accumulation significantly decreased, by 61.6+/-10.1%, following ethinylestradiol treatment of male rats. Ovariectomy, chemical castration of female rats with buserelin or treatment of female rats with the estrogen receptor antagonist ICI 182780 did not affect taurocholate uptake, but treatment of ovariectomized rats with ethinylestradiol decreased the taurocholate accumulation ratio by 53.7+/-15.8%. By determination of serum bile acids the possibility was excluded that this change was an indirect effect of cholestasis induced by ethinylestradiol. This study demonstrates gender differences in the renal handling of taurocholate in rats that may be related to an inhibitory effect of estrogens on taurocholate transport in proximal tubular cells. Since the ASBT protein content of the proximal tubular cells was found not to be different between male and female rats, a nongenomic mechanism may underly this estrogen effect.

Immunocytochemical characterization of the incubated rat renal cortical slices

The use of renal cortical slices in vitro and the data obtained in these studies have been subjects of controversy, largely due to uncertain viability, e.g., structural and functional integrity of the proximal and other tubules. However, detailed studies of tubule integrity have not been reported. To correlate functional and structural viability of the hand-cut rat renal cortical slices, incubated in optimally conditioned media for up to 25 h, we studied the time course of p-aminohippurate (PAH) uptake, the immunocytochemical distribution of several proteins that reside in the proximal tubule basolateral [Na/K-ATPase, organic anion transporters (OAT)1 and OAT3], or brush border [megalin, sodium-proton exchanger (NHE)3] membrane, as well as the general integrity of the tubule epithelium and its cytoskeleton (actin filaments, microtubules). PAH uptake in slices was proportional to time within 1 h of incubation and gradually declined thereafter. The immunostaining experiments indicated a fast, time-dependent loss of basolateral transporters, at a rate of OAT1 > Na/K-ATPase > OAT3. In the brush border membrane, the loss of megalin was faster than that of NHE3, and a partial redistribution of NHE3 into the basolateral domain indicated the loss of cell polarity. The loss of intracellular actin and tubulin cytoskeleton in the proximal tubule was already visible after 15 min of incubation and gradually increased with time, whereas a partial redistribution of actin to the basolateral domain indicated a compromised polarity of the cells. The data also revealed very early (after 15 min) necrotic events in the proximal tubule epithelium, with sloughing of brush border and cell debris into the tubule lumen, detachment of cells from the basal membrane, and opening and widening of the tubule lumen. We conclude that the loss of cellular structure, cytoskeleton, and cell membrane transporters in the nephron epithelium is a very early event in the incubated rat renal cortical slices.

Rat renal cortical OAT1 and OAT3 exhibit gender differences determined by both androgen stimulation and estrogen inhibition

In rats, the secretion of p-aminohippurate (PAH) by the kidney is higher in males (M) than in females (F). The role of the major renal PAH transporters, OAT1 and OAT3, in the generation of these gender differences, as well as the responsible hormones and mechanisms, has not been clarified. Here we used various immunocytochemical methods to study effects of gender, gonadectomy, and treatment with sex hormones on localization and abundance of OAT1 and OAT3 along the rat nephron. Both transporters were localized to the basolateral membrane: OAT1 was strong in proximal tubule S2 and weak in the S3 segments, whereas OAT3 was stained in proximal tubule S1 and S2 segments, thick ascending limb, distal tubule, and in principal cells along the collecting duct. Gender differences in the expression of both transporters in adult rats (M > F) were observed only in the cortical tubules. OAT1 in the cortex was strongly reduced by castration in adult M, whereas the treatment of castrated M with testosterone, estradiol, or progesterone resulted in its complete restitution, further depression, or partial restitution, respectively. In adult F, ovariectomy weakly increased, whereas estradiol treatment of ovariectomized F strongly decreased, the expression of OAT1. The expression of OAT3 in the M and F cortex largely followed a similar pattern, except that ovariectomy and progesterone treatment showed no effect, whereas in other tissue zones gender differences were not observed. In prepubertal rats, the expression of OAT1 and OAT3 in the kidney cortex was low and showed no gender differences. Our data indicate that gender differences in the rat renal cortical OAT1 and OAT3 (M > F) appear after puberty and are determined by both a stimulatory effect of androgens (and progesterone in the case of OAT1) and an inhibitory effect of estrogens.

Strain- and sex-related differences of carbonyl reductase activities in kidney microsomes and cytosol of rats

This study was designed to elucidate strain- and sex-related differences of carbonyl reductase activity in rat kidney by using the oral antidiabetic drug acetohexamide as substrate. The frequency distribution of carbonyl reductase activities in kidney microsomes of male Fischer 344 (Fischer), Sprague-Dawley, Wistar and Wistar-Imamichi (Wistar-IM) rats exhibited a marked strain-related difference. Furthermore, the enzyme activities in kidney microsomes of Fischer, Sprague-Dawley and Wistar rats were male-specific, resulting insignificant sex-related differences in these strains. There was no sex-related difference of carbonyl reductase activity in kidney microsomes of the Wistar-IM strain, which lacked its activity in both sexes. On the other hand, although carbonyl reductase activities were fully detectable in kidney cytosols from all the strains of male and female rats, no strain- or sex-related difference was observed among the cytosolic enzyme activities. These results provide new information for understanding the influence of internal factors on the renal metabolism of ketone-containing xenobiotics.

Modulatory effects of hormones, drugs, and toxic events on renal organic anion transport

The human body is exposed continuously to a wide variety of exogenous compounds, many of which are anionic compounds. In addition, products of phase II biotransformation reactions are negatively charged, viz. glucuronides, sulfate esters, or glutathiones. Renal transport of organic anions is an important defense mechanism of the organism against foreign substances. The combination of the rate of uptake and efflux and the intracellular disposition of organic anions in the proximal tubule determines the intracellular concentration and the nephrotoxic potential of a compound. Modulation of organic anion secretion is observed after exposure of proximal tubules to various hormones, and the subsequent receptor-mediated response is signaled by protein kinases. Transport of anionic compounds across the basolateral as well as the luminal membrane is modified by activation or inhibition of protein kinases. Protein kinase C activation reduces the uptake of organic anions mediated by the organic anion transporter 1 (OAT1/Oat1) and Oat3 and reduces Mrp2-mediated efflux. In addition, activation of protein kinase C has been shown to inhibit transport by the organic anion transporting polypeptide 1 (Oatp1) across the luminal membrane. Additional protein kinases have been implicated in the regulation of organic anion transport, and the role of nuclear factors in xenobiotic excretion is an emerging field. The physiological regulation of organic anion transporters may also be influenced by exogenous factors, such as exposure to xenobiotics and cellular stress. This commentary discusses the current knowledge of endogenous and exogenous influences on renal anionic xenobiotic excretion.

Principles and Clinical Application of Assessing Alterations in Renal Elimination Pathways

Drugs and metabolites are eliminated from the body by metabolism and excretion. The kidney makes the major contribution to excretion of unchanged drug and also to excretion of metabolites. Net renal excretion is a combination of three processes - glomerular filtration, tubular secretion and tubular reabsorption. Renal function has traditionally been determined by measuring plasma creatinine and estimating creatinine clearance. However, estimated creatinine clearance measures only glomerular filtration with a small contribution from active secretion. There is accumulating evidence of poor correlation between estimated creatinine clearance and renal drug clearance in different clinical settings, challenging the 'intact nephron hypothesis' and suggesting that renal drug handling pathways may not decline in parallel. Furthermore, it is evident that renal drug handling is altered to a clinically significant extent in a number of disease states, necessitating dosage adjustment not just based on filtration. These observations suggest that a re-evaluation of markers of renal function is required. Methods that measure all renal handling pathways would allow informed dosage individualisation using an understanding of renal excretion pathways and patient characteristics. Methodologies have been described to determine individually each of the renal elimination pathways. However, their simultaneous assessment has only recently been investigated. A cocktail of markers to measure simultaneously the individual renal handling pathways have now been developed, and evaluated in healthy volunteers. This review outlines the different renal elimination pathways and the possible markers that can be used for their measurement. Diseases and other physiological conditions causing altered renal drug elimination are presented, and the potential application of a cocktail of markers for the simultaneous measurement of drug handling is evaluated. Further investigation of the effects of disease processes on renal drug handling should include people with HIV infection, transplant recipients (renal and liver) and people with rheumatoid arthritis. Furthermore, changes in renal function in the elderly, the effect of sex on renal function, assessment of living kidney donors prior to transplantation and the investigation of renal drug interactions would also be potential applications. Once renal drug handling pathways are characterised in a patient population, the implications for accurate dosage individualisation can be assessed. The simultaneous measurement of renal function elimination pathways of drugs and metabolites has the potential to assist in understanding how renal function changes with different disease states or physiological conditions. In addition, it will further our understanding of fundamental aspects of the renal elimination of drugs.

Sex differences in p-aminohippuric acid transport in rat kidney: role of membrane fluidity and expression of OAT1

Sex differences in the kinetic parameters of p-aminohippuric acid (PAH) transport in brush border (BBMV) and basolateral (BLMV) membrane vesicles from kidney cortex have been observed. Membrane fluidity of BBMV was higher in females as compared with male rats as indicated by anisotropy values (0.1897 +/- 0.0010 vs. 0.2003 +/- 0.0014, p < 0.05, for females and males respectively). Membrane fluidity of BLMV were similar in both sexes. Western blot studies revealed that OAT1 protein in female BLMV was present at only 40% of level found in BLMV from male rats. The lower expression of OAT1 in BLMV in association with the higher BBMV fluidity (which may affect the affinity of PAH transporter in this membrane domain) observed in females may be responsible, at least in part, for the gender difference described in renal PAH secretion.

Effects of gender on the pharmacokinetics of drugs secreted by the renal organic anions transport systems in the rat

The importance of considering sex differences in drug handling studies was admitted recently. The present work evaluates the sex influences on the pharmacokinetics of para-aminohippuric acid (PAH), the reference substance for the renal organic anion transports systems, and furosemide (FS), a standard loop diuretic which is also a substrate for this transport system. Female rats displayed a lower PAH and FS systemic clearance, and a lower value of the elimination rate microconstant from the central compartment for both drugs. These results may be explained by the diminution of the renal clearance of both PAH and FS observed in females. In summary, sex modifies the pharmacokinetics of organic anions. Although additional experimental work must be done to bridge the gap between studies using animals and humans, the reported experimental observations may have potentially important pharmacological implications. So, caution must be exercised in administering drugs like organic anions to females.

Characterization of the mechanisms involved in the gender differences in p-aminohippurate renal elimination in rats

Gender differences in the renal handling on drugs and toxins have received too little attention. In the present study, a variety of preparations were used to examine the basis for the greater effectiveness of the male kidneys in the elimination of p-aminohippurate (PAH) in rats. Renal clearance of PAH was significantly lower in female rats as consequence of its smaller filtered and secreted load. The gender difference in the filtered load may be accounted for the lower value of glomerular filtration rate (GFR) displayed by female rats as compared with males. The lower value of the renal blood flow observed in females might explain, at least in part, the decrease in the GFR and in the secreted load of PAH. In females, maximal uptake for PAH transport into renal basolateral membrane vesicles decreased to 52 ± 9 % (P < 0.05) and Michaelis-Menten constant for PAH uptake into renal brush border membrane vesicles was increased to 163 ± 8 % (P < 0.05). These changes might also explain the lower secreted load of PAH. The sex difference in the renal clearance of PAH was also evidenced by the reduced systemic clearance observed in female rats.Key words: organic anions, transport in renal membrane vesicles, renal clearance, systemic clearance, sex.

Regulation of renal tubular secretion of organic compounds

BACKGROUND

Information on the molecular basis underlying organic anion and cation transport in renal tubules has expanded in recent years with the identification and characterization of numerous transporters. However, little is known about the regulation of this transport.

METHODS

Both English and Russian language studies dealing with the regulation of organic ion transport by the kidney have been reviewed.

RESULTS

This review summarizes the literature on the physiological and pharmacological aspects of the regulation of organic ion transport, linking this information where possible to underlying transport mechanisms. Current models of the tubular secretion of organic anions and cations are reviewed. Factors that inhibit or enhance tubular secretion of xenobiotics are described, and their influence on proximal tubule cell transport and function is discussed. Important roles for substrate stimulation, the adrenergic nervous system, numerous hormones, P-glycoprotein, and protein kinase C activity have been identified.

CONCLUSIONS

Despite considerable advances in the understanding of basic transport pathways and mechanisms involved in the tubular secretion of organic compounds, there is still relatively little information on the regulation of this transport. Studies combining the techniques of integrative and cell physiology and molecular biology will provide significant new insights into the pathways regulating the tubular transport of these compounds.

Genomic structure and in vivo expression of the human organic anion transporter 1 (hOAT1) gene

The human organic anion transporter 1 (hOAT1) plays a key role in the secretion of an array of potentially toxic organic anions including many clinically important drugs. Here we report on the genomic cloning of hOAT1. A human genomic library was used for screening of a PAC (P1 artificial chromosome) clone applying PCR techniques. Sequencing of several restriction subclones and of a PCR-generated clone revealed that the hOAT1 gene spans 8.2 kb and is composed of 10 exons divided by 9 introns. RT-PCR studies in a human kidney specimen led to the detection of two new splice variants, hOAT1-3 and hOAT1-4, showing a 132-bp in-frame deletion. Using fluorescence in situ hybridization (FISH) we mapped the hOAT1 gene as a single signal to chromosome 11q13.1-q13.2. Additionally, 600 bp of the 5' flanking region was analyzed, illustrating the probable transcription start site at nt -280, a NF-kappaB-site at nt -397 and several putative transcription factor binding sites.

Gender differences in expression of organic cation transporter OCT2 in rat kidney

The organic cation transporter (OCT) mediates translocation of various cationic molecules including drugs, toxins and endogenous substances. We examined gender differences in the expression of rat (r) OCT2 in the kidney. Slices and basolateral membrane vesicles of male rat kidney showed a higher transport activity for tetraethylammonium than those of female rat kidney. The expression levels of rOCT2 mRNA and protein in the kidney of males were much higher than those in females. There was no gender difference in mRNA expression of rOCT1 and rOCT3. These findings suggest that rOCT2 is responsible for the gender differences in renal basolateral membrane organic cation transport activity.

Renal transport of organic anions

This review deals with the different transport mechanisms mediating the apical and basolateral transport of organic anions, all of which are restricted to the proximal tubule. Several transport mechanisms, such as the para-aminohippurate basolateral transporter and the apical proton coupled di- and tripeptide transporter have been cloned, and their role in renal transport has been well characterized. Other transport proteins have been cloned from the kidney, liver, or intestine, but their role in the renal transport of organic anions needs to be elucidated. This is the case with Mdr2, oatp1 and OAT-K1, which were identified in the apical membrane of the proximal tubule, and with MDR1, the precise localization of which is still uncertain. Other apical transport mechanisms, sodium coupled transports and anion exchangers are involved in organic anion reabsorption.