Monensin Improves the Effectiveness of meso-Dimercaptosuccinate when Used to Treat Lead Intoxication in Rats

Among divalent cations, the ionophore monensin shows high activity and selectivity for the transport of lead ions (Pb(2+)) across phospholipid membranes. When coadministered to rats that were receiving meso-dimercaptosuccinate for treatment of Pb intoxication, monensin significantly increased the amount of Pb removed from femur, brain, and heart. It showed a tendency to increase Pb removal from liver and kidney but had no effect of this type in skeletal muscle. Tissue levels of several physiologic (calcium, cobalt, copper, iron, magnesium, manganese, molybdenum, zinc) and nonphysiologic (arsenic, cadmium, chromium, nickel, strontium) elements were also determined after the application of these compounds. Among the physiologic elements, a number of significant changes were seen, including both rising and falling values. The size of these changes was typically around 20% compared with control values, with the largest examples seen in femur. These changes often tended to reverse those of similar size that had occurred during Pb administration. Among the nonphysiologic elements, which were present in trace amounts, the changes were smaller in number but larger in size. None of these changes appears likely to be significant in terms of toxicity, and there were no signs of overt toxicity under any of the conditions employed. Monensin may act by cotransporting Pb(2+) and OH(–) ions out of cells, in exchange for external sodium ions. The net effect would be to shuttle intracellular Pb(2+) to extracellular dimercaptosuccinic acid thereby enhancing its effectiveness. Thus, monensin may be useful for the treatment of Pb intoxication when applied in combination with hydrophilic Pb(2+) chelators

Ca2+ transport properties of ionophores A23187, ionomycin, and 4-BrA23187 in a well defined model system.

Models for the electroneutral transport of Ca2+ by ionophores A23187, ionomycin, and 4-BrA23187 have been tested in a defined system comprised of 1-palmitoyl-2-oleoyl-sn-glycerophosphatidylcholine vesicles prepared by freeze-thaw extrusion. Quin-2-loaded and CaCl2-loaded vesicles were employed to allow the investigation of transport in both directions. Simultaneous or parallel measurements of H+ transport and membrane potential, respectively, indicate that for any of these ionophores, electrogenic transport events do not exceed 1 in 10,000 when there is no preexisting transmembrane potential. When a potential of approximately 150 mV is imposed across the membrane, transport catalyzed by A23187 remains electroneutral; however, for ionomycin and 4-BrA23187, approximately 10% of transport events may be electrogenic. The defined vesicle system has also been utilized to determine how the rate of Ca2+ transport varies as a function of ionophore and Ca2+ concentration and with the direction of transport. Some aspects of the results are unexpected and should be considered by investigators using ionophores in biological systems. These include the apparent failure of these compounds to fully equilibrate Ca2+ with a high affinity Ca2+ indicator when these species are separated by a membrane, rates of transport that vary markedly with the direction of transport, and extents of transport that are a function of ionophore concentration. At least some of these unexpected behaviors can be explained by a strong influence of delta pH on forward and reverse transport kinetics. In the case of A23187, the data also give some initial insights into the relationship between formation of the transporting species and the entry of this species into the membrane hydrophobic region

Effects of pH conditions on Ca2+ transport catalyzed by ionophores A23187, 4-BrA23187, and ionomycin suggest problems with common applications of these compounds in biological systems.

Phospholipid vesicles loaded with Quin-2 and 2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein (BCECF) have been used to investigate the effects of pH conditions on Ca2+ transport catalyzed by ionophores A23187, 4-BrA23187, and ionomycin. At an external pH of 7.0, a delta pH (inside basic) of 0.4-0.6 U decreases the rate of Ca2+ transport into the vesicles by severalfold under some conditions. The apparent extent of transport is also decreased. In contrast, raising the pH by 0.4-0.6 U in the absence of a delta pH increases both of these parameters, although by smaller factors. The relatively large effects of a delta pH on the transport properties of Ca2+ ionophores seem to reflect a partial equilibration of the transmembrane ionophore distribution with the H+ concentration gradient across the vesicle membrane. This unequal distribution of ionophore can cause a very slow or incomplete ionophore-dependent equilibration of delta pCa with delta pH. A second factor of less certain origin retards full equilibration of delta pCa when delta pH = 0. These findings call into question several ionophore-based methods that are used to investigate the regulatory activities of Ca2+ and other divalent cations in biological systems. Notable among these are the null-point titration method for determining the concentration of free cations within cells and the use of ionophores plus external cation buffers to calibrate intracellular cation indicators. The present findings also indicate that the transport mode of Ca2+ ionophores is more strictly electroneutral than was thought, based upon previous studies

Transport properties of the calcium ionophore ETH-129.

The transport mechanism and specificities of ionophore ETH-29 have been investigated in a highly defined phospholipid vesicle system, with the goal of facilitating the application of this compound to biological problems. ETH-129 transports Ca(2+) via an electrogenic mechanism, in contrast to A23187 and ionomycin, which function in a charge neutral manner. The rate of transport is a function of membrane potential, increasing by 3.9-fold per 59 mV over a broad range of that parameter. Rate is independent of the transmembrane pH gradient and strongly stimulated by the uncoupler carbonyl cyanide m-chlorophenylhydrazone when no external potential has been applied. The effect of uncoupler reflects the collapse of an opposing potential arising during Ca(2+) transport, but also reflects the formation of a mixed complex between the uncoupler, ETH-129, and Ca(2+) that readily permeates the vesicle membrane. Oleate does not substitute for the uncoupler in either regard. ETH-129 transports polyvalent cations according to the selectivity sequence La(3+) > Ca(2+) > Zn(2+) approximately equal to Sr(2+) > Co(2+) approximately equal to Ni(2+) approximately equal to Mn(2+), with the magnitude of the selectivity coefficients reflecting the cation concentration range considered. There is little or no activity for the transport of Na(+), K(+), and Mg(2+). These properties suggest that ETH-129 will be useful for investigating the consequences of a mitochondrial Ca(2+) overload in mammalian cells, which is difficult to pursue through the application of electroneutral ionophores

Monensin Improves the Effectiveness of -Dimercaptosuccinate when Used to Treat Lead Intoxication in Rats-11

<p><b>Copyright information:</b></p><p>Taken from "Monensin Improves the Effectiveness of -Dimercaptosuccinate when Used to Treat Lead Intoxication in Rats"</p><p>Environmental Health Perspectives 2005;114(4):484-493.</p><p>Published online 29 Sep 2005</p><p>PMCID:PMC1440769.</p><p>This is an Open Access article: verbatim copying and redistribution of this article are permitted in all media for any purpose, provided this notice is preserved along with the article's original DOI.</p

Monensin Improves the Effectiveness of -Dimercaptosuccinate when Used to Treat Lead Intoxication in Rats-7

<p><b>Copyright information:</b></p><p>Taken from "Monensin Improves the Effectiveness of -Dimercaptosuccinate when Used to Treat Lead Intoxication in Rats"</p><p>Environmental Health Perspectives 2005;114(4):484-493.</p><p>Published online 29 Sep 2005</p><p>PMCID:PMC1440769.</p><p>This is an Open Access article: verbatim copying and redistribution of this article are permitted in all media for any purpose, provided this notice is preserved along with the article's original DOI.</p

Monensin Improves the Effectiveness of -Dimercaptosuccinate when Used to Treat Lead Intoxication in Rats-6

<p><b>Copyright information:</b></p><p>Taken from "Monensin Improves the Effectiveness of -Dimercaptosuccinate when Used to Treat Lead Intoxication in Rats"</p><p>Environmental Health Perspectives 2005;114(4):484-493.</p><p>Published online 29 Sep 2005</p><p>PMCID:PMC1440769.</p><p>This is an Open Access article: verbatim copying and redistribution of this article are permitted in all media for any purpose, provided this notice is preserved along with the article's original DOI.</p

Artificial Intelligence for Kidney Stone Spectra Analysis: Using Artificial Intelligence Algorithms for Quality Assurance in the Clinical Laboratory

Objective: To determine if a set of artificial intelligence (AI) algorithms could be leveraged to interpret Fourier transform infrared spectroscopy (FTIR) spectra and detect potentially erroneous stone composition results reported in the laboratory information system by the clinical laboratory. Background: Nephrolithiasis (kidney stones) is highly prevalent, causes significant pain, and costs billions of dollars annually to treat and prevent. Currently, FTIR is considered the reference method for clinical kidney stone constituent analysis. This process, however, involves human interpretation of spectra by a qualified technologist and is susceptible to human error. Methods: This prospective validation study was conducted from October 29, 2020, to October 28, 2021, to test if the addition of AI algorithm overreads to FTIR spectra could improve the detection rate of technologist-misclassified FTIR spectra. The preceding year was used as a control period. Disagreement between the AI overread and technician interpretation was resolved by an independent human interpretation. The rate of verified human misclassifications that resulted in revised reported results was the primary end point. Results: Spectra of 81,517 kidney stones were reviewed over the course of 1 year. The overall clinical concordance between the technologist and algorithm was 90.0% (73,388/81,517). The report revision rate during the AI implementation period was nearly 8 times higher than that during the control period (relative risk, 7.9; 95% CI, 4.1–15.2). Conclusion: This study demonstrated that an AI quality assurance check of human spectra interpretation resulted in the identification of a significant increase in erroneously classified spectra by clinical laboratory technologists