Erythropoietin alters the pharmacokinetics of organic anions mainly eliminated by the kidney in rats

Erythropoietin (EPO) is a cytokine originally used for its effects on the hematopoietic system, and is widely prescribed around the world. In the present study, the effects of EPO administration on p-aminohippurate (PAH, a prototype organic anion) pharmacokinetics and on the renal expression of PAH transporters were evaluated. Male Wistar rats were treated with EPO or saline (control group). After 42 h, PAH was administered, and plasma samples were obtained at different time points to determine PAH levels. PAH levels in renal tissue and urine were also assessed. The renal expression of PAH transporters was evaluated by Western blotting. EPO-treated rats showed an increase in PAH systemic clearance, in its elimination rate constant, and in urinary PAH levels, while PAH in renal tissue was decreased. Moreover, EPO administration increased the expression of the transporters of the organic anions evaluated. The EPO-induced increase in PAH clearance is accounted for by the increase in its renal secretion mediated by the organic anion transporters. The goal of this study is to add important information to the wide knowledge gap that exists regarding drug–drug interactions. Owing to the global use of EPO, these results are useful in terms of translation into clinical practice.

Attenuated renal vascular responses to acute angiotensin II infusion in smooth muscle-specific Na+/Ca2+ exchanger knockout mice

Recent studies in smooth muscle-specific Na+/Ca2+ exchanger-1 knockout (NCX1sm−/−) mice reveal reduced arterial pressure and impaired myogenic responses compared with heterozygous littermates. In this study, we determined renal function in male anesthetized NCX1sm−/− mice and NCX1 heterozygous (NCX1+/−) littermates before and during acute ANG II infusions. Systolic blood pressure in awake mice was lower in NCX1sm−/− mice compared with NCX1+/− mice (119 ± 4 vs. 131 ± 3 mmHg, P < 0.05). Acute ANG II infusions (5 ng·min−1·g−1 body wt) increased mean arterial pressure in anesthetized NCX1+/− (109 ± 2 to 134 ± 3 mmHg, P < 0.001, n = 8) and NCX1sm−/− (101 ± 8 to 129 ± 8 mmHg, P < 0.01, n = 6) mice to a similar extent (Δ25 ± 1 vs. Δ28 ± 4 mmHg, P > 0.05). In response to ANG II infusions, PAH clearance (CPAH) decreased from 1.39 ± 0.27 to 0.98 ± 0.22 ml·min−1·g−1 ( P < 0.05) and glomerular filtration rate (GFR) was reduced from 0.50 ± 0.09 to 0.32 ± 0.06 ml·min−1·g−1 ( P < 0.05) in NCX1+/− mice. In contrast, the NCX1sm−/− did not exhibit significant reductions in either CPAH (1.16 ± 0.30 to 1.22 ± 0.34 ml·min−1·g−1, P > 0.05) or GFR (0.48 ± 0.08 to 0.41 ± 0.05 ml·min−1·g−1, P > 0.05) during acute ANG II infusions. Using flometry to measure renal blood flow continuously, NCX1sm−/− mice had significantly attenuated responses to ANG II infusions (−34.2 ± 3.9%, P < 0.05) compared with those in NCX1+/− mice (−48 ± 2%) or in wild-type mice (−69 ± 7%). These data indicate that renal vascular responses to ANG II are attenuated in NCX1sm−/− mice compared with NCX1+/− mice and that NCX1 contributes to the renal vasoconstriction response to acute ANG II infusions.

Downregulation of organic anion transporters OAT1 and OAT3 correlates with impaired secretion of para-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.

Increased renal expression of bilirubin glucuronide transporters in a rat model of obstructive jaundice

Regulation of bilirubin glucuronide transporters during hyperbilirubinemia in hepatic and extrahepatic tissues is not completely clear. In the present study, we evaluated the regulation of the bilirubin glucuronide transporters, multidrug resistance-associated proteins (MRP)2 and 3, in rats with obstructive jaundice. Bile duct ligation (BDL) or sham operation was performed in Wistar rats. Liver and kidneys were removed 1, 3, and 5 days after BDL ( n = 4, in each group). Serum and urine were collected to measure bilirubin levels just before animal killing. MRP2 And MRP3 mRNA expressions were determined by real-time RT-PCR. Protein expression of MRP2 and MRP3 was determined by Western blotting. Renal MRP2 function was evaluated by para-aminohippurate (PAH) clearance. The effect of conjugated bilirubin, unconjugated bilirubin, human bile, and sulfate-conjugated bile acid on MRP2 gene expression was also evaluated in renal and hepatocyte cell lines. Serum bilirubin and urinary bilirubin excretion increased significantly after BDL. In the liver, the mRNA expression of MRP2 decreased 59, 86, and 82%, and its protein expression decreased 25, 74, and 93% compared with sham-operated animals after 24, 72, and 120 h of BDL, respectively. In contrast, the liver expression of MRP3 mRNA increased 138, 2,137, and 3,295%, and its protein expression increased 560, 634, and 612% compared with sham-operated animals after 24, 72, and 120 h of BDL, respectively. On the other hand, in the kidneys, the mRNA expression of MRP2 increased 162, 73, and 21%, and its protein expression increased 387, 558, and 472% compared with sham-operated animals after 24, 72, and 120 h of BDL, respectively. PAH clearance was significantly increased after BDL. The mRNA expression of MRP2 increased in renal proximal tubular epithelial cells after treatment with conjugated bilirubin, sulfate-conjugated bile acid or human bile. Upregulation of MRP2 in the kidneys and MRP3 in the liver may be a compensatory mechanism to improve bilirubin clearance during obstructive jaundice.

PAH extraction and estimation of plasma flow in human postischemic acute renal failure

We determined the effect of postischemic injury to the human renal allograft on p-aminohippurate (PAH) extraction (EPAH) and renal blood flow. We evaluated renal function in 44 allograft recipients on two occasions: 1–3 h after reperfusion ( day 0) and again on postoperative day 7. On day 0 subsets underwent intraoperative determination of renal blood flow ( n = 35) by Doppler flow meter and EPAH( n = 25) by renal venous assay. Blood flow was also determined in another subset of 16 recipients on postoperative day 7 by phase contrast-cine-magnetic resonance imaging, and EPAH was computed from the simultaneous PAH clearance. Glomerular filtration rate (GFR) on day 7 was used to divide subjects into recovering ( n = 23) and sustained ( n = 21) acute renal failure (ARF) groups, respectively. Despite profound depression of GFR in the sustained ARF group, renal plasma flow was only slightly depressed, averaging 296 ± 162 ml ⋅ min−1 ⋅ 1.73 m−2 on day 0 and 202 ± 72 ml ⋅ min−1 ⋅ 1.73 m−2 on day 7, respectively. These values did not differ from corresponding values in the recovering ARF group: 252 ± 133 and 280 ± 109 ml ⋅ min−1 ⋅ 1.73 m−2, respectively. EPAH was profoundly depressed on day 0, averaging 18 ± 14 and 10 ± 7% in recovering and sustained ARF groups, respectively, vs. 86 ± 6% in normal controls ( P < 0.001). Corresponding values on day 7remained significantly depressed at 65 ± 20 and 11 ± 22%, respectively. We conclude that postischemic injury to the renal allograft results in profound impairment of EPAH that persists for at least 7 days, even after the onset of recovery. An ensuing reduction in urinary PAH clearance results in a gross underestimate of renal plasma flow, which is close to the normal range in the initiation, maintenance, and recovery stages of this injury.