Acute exposure to cobalt induces transient methemoglobinuria in rats

Detecting metabolites of different transition metal-lithospermate B complexes after intravenous injection in rats

AIM

Lithospermate B (LSB) isolated from the traditional Chinese medicine danshen (Salvia miltiorrhiza) is an effective Na(+)/K(+)-ATPase inhibitor and used to treat congestive heart failure. The inhibition of LSB on Na(+)/K(+)-ATPase is potentiated by forming complexes with transition metal ions. Here we investigated the safety and metabolites of different transition metal-LSB complexes in rats.

METHODS

LSB complexed with six different transition metal ions (Mg(2+), Zn(2+), Cr(3+), Co(2+), Ni(2+) and Mn(2+)) were prepared. Adult male SD rats were injected with the different metal-LSB complexes (50 mg/kg, iv), and their bile and blood samples were collected. The metabolites of the metal-LSB complexes in the samples were analyzed using mass spectroscopy.

RESULTS

In rats injected with LSB complexed with Mg(2+), Zn(2+), Cr(3+), Ni(2+) or Mn(2+), LSB and its four putative metabolites were equivalently detected in their bile samples. Mn(2+)-LSB exhibited distinct metabolite profiles compared with the other four metal-LSB complexes. The four putative metabolites were identified as 3-monomethyl-LSB, 3,3''-dimethyl-LSB, 3,3'''-dimethyl-LSB and 3,3'',3'''-trimethyl-LSB. The tracking of successive bile samples of rats injected with Mg(2+)-LSB, Zn(2+)-LSB and Mn(2+)-LSB concurrently demonstrated that LSB was firstly methylated at position 3, then at position 3'', and, finally, the 3''' hydroxyl group. All rats injected with Co(2+)-LSB died.

CONCLUSION

Zn(2+)-LSB, Cr(3+)-LSB, Ni(2+)-LSB or Mn(2+)-LSB produces identical four methylated metabolites of LSB in rats, and seemed to be as safe as LSB or Mg(2+)-LSB.

Suppression of erythropoietin induction by diethylstilbestrol in rats

Diethylstilbestrol is an estrogenic endocrine disrupter that has diverse health effects in humans. Bisphenol A is another estrogen-like chemical with possible similar effects to diethylstilbestrol, which has been increasingly used for industry to lead to globally widespread human exposure to it. Hematopoiesis is another of their possible targets, since estrogen suppresses erythropoietin induction to induce anemia. The aim of this study was to clarify the effects of diethylstilbestrol and bisphenol A on erythropoietin induction in rats. We observed the effects of one-shot subcutaneous injection of diethylstilbestrol or bisphenol A on hypoxia-, bleeding-, and cobalt-stimulated erythropoietin induction within 24 h and the hematological outcomes after repeated subcutaneous injection of diethylstilbestrol three times a week for 1 month in rats. Diethylstilbestrol at 10-1,000 μg/kg suppressed stimulus-elevated levels of plasma erythropoietin and its renal mRNA induction. In contrast, bisphenol A at 1,000 μg/kg did not suppress plasma erythropoietin elevated by any stimuli. Repeated injection of diethylstilbestrol at 1,000 μg/kg to rats for 1 month induced an anemic trend due to decelerated erythropoiesis through the insufficient production of erythropoietin, mimicking the effects of estradiol. In conclusion, diethylstilbestrol has a suppressive effect on erythropoietin induction, leading to deceleration of erythropoiesis and the development of anemia.

Hypoxic preconditioning with cobalt of bone marrow mesenchymal stem cells improves cell migration and enhances therapy for treatment of ischemic acute kidney injury

Mesenchymal stem cell (MSC) administration is known to enhance the recovery of the kidney following injury. Here we tested the potential of hypoxic-preconditioned-MSC transplantation to enhance the efficacy of cell therapy on acute kidney injury (AKI) by improving MSC migration to the injured kidney. Cobalt was used as hypoxia mimetic preconditioning (HMP). MSC were subjected to HMP through 24 h culture in 200 µmol/L cobalt. Compared to normoxia cultured MSC (NP-MSC), HMP significantly increased the expression of HIF-1α and CXCR4 in MSC and enhanced the migration of MSC in vitro. This effect was lost when MSC were treated with siRNA targeting HIF-1α or CXCR4 antagonist. SPIO labeled MSC were administered to rats with I/R injury followed immediately by magnetic resonance imaging. Imaging clearly showed that HMP-MSC exhibited greater migration and a longer retention time in the ischemic kidney than NP-MSC. Histological evaluation showed more HMP-MSC in the glomerular capillaries of ischemic kidneys than in the kidneys receiving NP-MSC. Occasional tubules showed iron labeling in the HMP group, while no tubules had iron labeling in NP group, indicating the possibility of tubular transdifferentiation after HMP. These results were also confirmed by fluorescence microscopy study using CM-DiI labeling. The increased recruitment of HMP-MSC was associated with reduced kidney injury and enhanced functional recovery. This effect was also related to the increased paracrine action by HMP-MSC. Thus we suggest that by enhancing MSC migration and prolonging kidney retention, hypoxic preconditioning of MSC may be a useful approach for developing AKI cell therapy.

Methemoglobin--it's not just blue: a concise review

Hemoglobin has functions besides carrying oxygen to the tissues, and regulates vascular tone and inflammation via a redox couple with methemoglobin. Hemoglobin has iron in the reduced valance Fe(II) and methemoglobin has iron in the oxidized valance Fe (III), with a free energy capable of producing water from oxygen. In generating methemoglobin the couple functions as a nitrite reductase. The degree of oxidation of hemoglobin senses the oxygen level in the blood and uses its ability to produce nitric oxide from nitrite to control vascular tone, increasing blood flood when the proportion of oxygenated hemoglobin falls. Additional cardiovascular damage is produced by methemoglobin mediated oxidation of light density lipoproteins, accelerating arteriosclerosis. In addition, the release of heme from methemoglobin is an important factor in inflammation. These physiologic functions are paralleled by the well-described role in the oxidation of various drugs resulting in methemoglobinemia.

The effects of iron deficiency on estradiol-induced suppression of erythropoietin induction in rats: implications of pregnancy-related anemia

Pregnant women often develop anemia concomitant with the increase in serum erythropoietin levels, which are actually lower than those of nonpregnant anemic women due to the possible suppressive effect of endogenous estradiol on erythropoietin induction. The anemia, derived from hemodilution, does not act as a drive for erythropoietin induction, but iron deficiency, often observed during pregnancy, might. In order to demonstrate this, we investigated the effects of iron deficiency on estradiol-induced suppression of erythropoietin induction in rats. Single doses of estradiol suppressed hypoxia-, cobalt-, and bleeding-stimulated elevation of plasma erythropoietin levels and renal erythropoietin mRNA expression. Repeated administration of estradiol at 0.1 and 1 mg/kg for 2 months induced a slight anemic trend without elevation of plasma erythropoietin. Feeding an iron-deficient diet for 2 months induced plasma erythropoietin elevation without obvious anemia, but the simultaneous repeated administration of estradiol suppressed it and reversed the iron deficiency. Plasma erythropoietin levels had distinct negative correlations with plasma iron, plasma ferritin, and iron concentrations in the organs, but not with plasma hemoglobin level. These results suggest that iron deficiency would significantly stimulate erythropoietin induction during pregnancy, although estradiol might suppress it through iron restoration.