Antimicrobial characteristic of insoluble alkylpyridinium iodide.

Insoluble and soluble alkylpyridinium iodides (C8 to C18) were synthesized. The insoluble agents were quaternized 4-vinylpyridine-divinylbenzene copolymers. The insoluble agent [C12(50)] that contained 50% divinylbenzene and had a C12 alkyl chain was selected as the most suitable insoluble agent. C12(50) showed poor durability of the antibacterial activity, but C12(50), which had lost the activity, was refreshed by washing with ethanol. This washing became ineffective after a few cycles of antibacterial treatment and refreshment. Such C12(50) recovered the activity upon 1.0 N NaOH treatment. The antibacterial activity of C12(50) depended on its surface area. It showed high antimicrobial activity against gram-positive bacteria and also showed activity against gram-negative bacteria and yeasts. But the activities of C12(50) and laurylpyridinium iodide solution were different against some microbes. The antibacterial activities of the agents were investigated against Escherichia coli and Micrococcus luteus under various conditions. The activity of C12(50) was higher at a higher temperature or at a lower cell concentration. The activity of C12(50) decreased on addition of NaCl, glucose, or bovine albumin to the cell suspension or in 0.01 M sodium-potassium phosphate buffer. C12(50) showed less activity when cells were mixed with dead cells or the supernatant of dead cells killed in an autoclave. The mode of action of the laurylpyridinium iodide solution against E. coli and M. luteus was similar to that of C12(50) except for the influence of E. coli cell concentration.     

Uptake of iodide in the marine haptophyte Isochrysis sp. (T.ISO) driven by iodide oxidation

Uptake of iodide was studied in the marine microalga Isochrysis sp. (isol. Haines, T.ISO) during short‐term incubations with radioactive iodide (¹²⁵I^?). Typical inhibitors of the sodium/iodide symporter (NIS) did not inhibit iodide uptake, suggesting that iodide is not taken up through this transport protein, as is the case in most vertebrate animals. Oxidation of iodide was found to be an essential step for its uptake by T.ISO and it seemed likely that hypoiodous acid (HOI) was the form of iodine taken up. Uptake of iodide was inhibited by the addition of thiourea and of other reducing agents, like L‐ascorbic acid, L‐glutathione and L‐cysteine and increased after the addition of oxidized forms of the transition metals Fe and Mn. The simultaneous addition of both hydrogen peroxide (H₂O₂) and a known iodide‐oxidizing myeloperoxidase (MPO) significantly increased iodine uptake, but the addition of H₂O₂ or MPO separately, had no effect on uptake. This confirms the observation that iodide is oxidized prior to uptake, but it puts into doubt the involvement of H₂O₂ excretion and membrane‐bound or extracellular haloperoxidase activity of T.ISO. The increase of iodide uptake by T.ISO upon Fe(III) addition suggests the nonenzymatic oxidation of iodide by Fe(III) in a redox reaction and subsequent influx of HOI. This is the first report on the mechanism of iodide uptake in a marine microalga.     

Cryptosporidium parvum sporozoite staining by propidium iodide.

Modified Ziehl-Neelsen (ZN) acid-fast stain is the usual method for detection of Cryptosporidium oocysts in feces. Propidium iodide permitted us to stain free or intra-oocyst sporozoites. With the ZN method only 3-5% of the oocysts purified from three human and one experimentally infected lamb dichromate-preserved feces were stained by carbol fuchsin. These fuchsin-stained oocysts were free of intact sporozoites as identified by propidium iodide staining. Treatment with 10% formalin or 0.5% sodium hypochlorite increased the percentage of acid-fast stained oocysts and thus the sensitivity of acid-fast staining. Treatment with sodium hypochlorite induced intra-oocyst sporozoite alterations as demonstrated by flow cytometric analysis of the oocysts' DNA content. Propidium iodide staining of fixed oocysts is a simple and rapid method to visualize sporozoites and to assess oocyst preservation after different treatments.     

Efflux of preloaded iodide from the thyroid induced by externally added iodide. A study using a biological model of the thyroid iodide transport system

Efflux of preloaded I- from the thyroid induced by externally added I- was studied using a biological model of the thyroid I- transport system. Phospholipid vesicles (P-vesicles) made from thyroid plasma membranes and soybean phospholipids were capable of accumulating I- in the presence of external Na+. P-vesicles incubated in 136 mM Na+ containing 0.9 microM I- with 125I- for 2 min accumulated I- so that the I- concentration in the vesicles became about 2 microM. Addition of 5-20 microM stable I- to the incubation mixture at 2 min incubation resulted in a dose-dependent decrease in previously loaded 125I- in the vesicles. In other words, a dose-dependent increase in efflux of preloaded 125I- was observed. While the efflux occurred, Na+-dependent I- influx into P-vesicles was preserved. When 2 mM ClO4-, a specific inhibitor of Na+-dependent I- influx, was added together with 10 microM I-, the external I- failed to diminish preloaded 125I- in P-vesicles. The 125I- efflux did not occur when a large amount of stable I- entered P-vesicles independently of Na+ in the presence of ClO4-. Similar 125I- efflux induced by externally added 5 microM SCN- was also blocked by simultaneously added ClO4-. These observations suggest that such I- efflux from the thyroid is a certain type of uphill I- transport which is closely related to Na+-dependent I- transport and that ClO4- and SCN- act on a common site of the I- transport system.     

Lithium iodide cardiac pacemakers: initial clinical experience.

A new long-life cardiac pacemaker pulse generator powered by a lithium iodide fuel cell was introduced in Canada in 1973. The compact, hermetically sealed unit is easily implanted and reliable, has excellent patient acceptance and has an anticipated battery life of almost 14 years. Among 105 patients who received a lithium iodide pacemaker, complications occurred in 18. The lithium iodide pacemaker represents a significant advance in pacemaker generator technology and is recommended for long-term cardiac pacing; the manufacturer guarantees the pulse generator for 6 years.     

A nonradioactive iodide uptake assay for sodium iodide symporter function

The standard assay for sodium iodide symporter (NIS) function is based on the measurement of radioiodide uptake (¹²⁵I) in NIS-expressing cells. However, cost and safety issues have limited the method from being used widely. Here we describe a simple spectrophotometric assay for the determination of iodide accumulation in rat thyroid-derived cells (FRTL5) based on the catalytic effect of iodide on the reduction of yellow cerium(IV) to colorless cerium(III) in the presence of arsenious acid (Sandell-Kolthoff reaction). The assay is fast and highly reproducible with a Z′ factor of 0.70. This procedure allows the screening of more than 800 samples per day and can easily be adapted to robotic systems for high-throughput screening of NIS function modulators. Using this method, the potency of several known inhibitors of NIS function was evaluated in a single day with high accuracy and reliability. Measured IC₅₀ values were essentially identical to those determined using Na¹²⁵I.     

1,25-Dihydroxycholecalciferol attenuates thyrotropin stimulated iodide accumulation in rat thyroid follicular FRTL-5 cells by reducing iodide porter number.

We have recently shown that rat thyroid follicular FRTL-5 cells have functional receptors for 1,25-dihydroxycholecalciferol (1,25- (OH)2D3) and that 1,25-(OH)2D3 attenuates the thyrotropin (TSH) induced iodide uptake. Here we show that the dibutyrylcyclic AMP induced iodide uptake was significantly reduced by 1,25-(OH)2D3, indicating that 1,25-(OH)2D3 affects the cAMP signal pathway beyond cAMP generation. The Vmax of the iodide porter was significantly reduced in 1,25-(OH)2D3 treated cells as compared to cells treated with TSH alone, indicating that 1,25-(OH)2D3 reduces the effective number of iodide porters in FRTL-5 cells.     

Propidium iodide as an indicator of Giardia cyst viability.

The use of propidium iodide, whose uptake indicates cell death or damage, was investigated to assess the viability of heat-inactivated and chemically inactivated Giardia muris cysts. This was done by comparing propidium iodide staining with excystation. We first determined that propidium iodide could be used with an immunofluorescence detection procedure by showing that the percentages of Giardia lamblia cysts stained with this dye before and after subjecting them to a fluorescence detection method were similar. G. muris cysts were then exposed to heat (56 degrees C), 0.5 to 4 mg of chlorine per liter (pH 7.0, 5 degrees C), 0.1 to 10 mg of a quaternary ammonium compound per liter, or 2 mg of preformed and forming monochloramine per liter (pH 7.2, 18 to 20 degrees C). A good positive correlation between percent propidium iodide-stained cysts and lack of excystation was demonstrated for G. muris cysts exposed either to heat or to the quaternary ammonium compound. However, no significant correlation between absence of excystation and propidium iodide staining was found for cysts exposed to chlorine or monochloramines. These results demonstrate that the propidium iodide staining procedure is not satisfactory for determining the viability of G. muris cysts exposed to these two commonly used drinking water disinfectants.     

Propidium iodide as an indicator of Giardia cyst viability.

The use of propidium iodide, whose uptake indicates cell death or damage, was investigated to assess the viability of heat-inactivated and chemically inactivated Giardia muris cysts. This was done by comparing propidium iodide staining with excystation. We first determined that propidium iodide could be used with an immunofluorescence detection procedure by showing that the percentages of Giardia lamblia cysts stained with this dye before and after subjecting them to a fluorescence detection method were similar. G. muris cysts were then exposed to heat (56 degrees C), 0.5 to 4 mg of chlorine per liter (pH 7.0, 5 degrees C), 0.1 to 10 mg of a quaternary ammonium compound per liter, or 2 mg of preformed and forming monochloramine per liter (pH 7.2, 18 to 20 degrees C). A good positive correlation between percent propidium iodide-stained cysts and lack of excystation was demonstrated for G. muris cysts exposed either to heat or to the quaternary ammonium compound. However, no significant correlation between absence of excystation and propidium iodide staining was found for cysts exposed to chlorine or monochloramines. These results demonstrate that the propidium iodide staining procedure is not satisfactory for determining the viability of G. muris cysts exposed to these two commonly used drinking water disinfectants.     

EDTA inhibits peroxidase-catalyzed iodide oxidation through interaction at the iodide binding site

EDTA inhibits the formation of I3- from iodide catalysed by various pure peroxidases. The inhibition is concentration-dependent and chloroperoxidase (CPO) is more sensitive than horseradish peroxidase (HRP) and lactoperoxidase (LPO). EDTA is more active than EGTA or other biological chelators tested. Zn2+, Mn2+ and Co2+ are equally active in reversing the effect of EDTA on both CPO and HRP almost completely, but ineffective in the case of LPO. The effect of EDTA on HRP can be reversed by a higher concentration of iodide but not by H2O2. EDTA causes a hypsochromic change in the absorption of the Soret band of HRP at 402 nm, and iodide can reverse this effect. EDTA can effectively displace radioiodide specifically bound to HRP. It is suggested that EDTA inhibits iodide oxidation by interacting at the iodide binding site of the HRP.     

Dynamic iodide trapping by tumor cells expressing the thyroidal sodium iodide symporter

The thyroidal sodium iodide symporter (NIS) in combination with various radioactive isotopes has shown promise as a therapeutic gene in various tumor models. Therapy depends on adequate retention of the isotope in the tumor. We hypothesized that in the absence of iodide organification, isotope trapping is a dynamic process either due to slow efflux or re-uptake of the isotope by cells expressing NIS. Iodide efflux is slower in ARH-77 and K-562 cells expressing NIS compared to a thyroid cell line. Isotope retention half times varied linearly with the number of cells expressing NIS. With sufficient NIS expression, iodide efflux is a zero-order process. Efflux kinetics in the presence or absence of perchlorate also supports the hypothesis that iodide re-uptake occurs and contributes to the retention of the isotope in tumor cells. Iodide organification was insignificant. In vivo studies in tumors composed of mixed cell populations confirmed these observations.     

Mutations in the sodium/iodide symporter (NIS) gene as a cause for iodide transport defects and congenital hypothyroidism.

The ability to concentrate iodide actively is a characteristic feature of the thyroid gland and several other tissues. This function is mediated through the sodium iodide symporter (NIS), a protein that is located in the basolateral membrane of the thyrocyte. A defect in the NIS (iodide trapping defect) can result in hypothyroidism, the severity of which is variable and influenced, in part, by the amount of iodine supply. The molecular cloning of NIS and characterization of its genomic organization allowed the identification of NIS gene mutations in patients expressing the phenotype of iodide trapping defect. Six mutations (G93R, Q267E, C272X, T354P, Y531X and G543E) have been so far identified and their properties have been partially characterized. G93R, Q267E and Y531X were found in a compound heterozygous individual with NIS defect, C272X and G543E were detected in a homozygous state and T354P has been identified in both homozygotes and heterozygotes in combination with G93R. Heterozygous family members, expressing one normal allele, are clinically not affected. This was confirmed by in vitro analysis where all six mutants produced NISs with virtually no biological activity that did not interfere with the wild-type NIS function when cotransfected in mammalian cells. While the precise mechanisms by which mutant NISs cause iodide trapping defect are still unknown, preliminary data suggest that 354P interferes with the iodide transport function rather than targeting to the cell membrane.     

Reaction of liver alcohol dehydrogenase with halogenoacids. Fate of the iodide anion released by carboxymethylation and enzymic catalysis of iodide solvolysis

The fate of the iodide liberated during carboxymethylation of Cys-46 in horse liver alcohol dehydrogenase has been determined with 125I-labeled iodoacetate. The [125I]iodoacetic acid was prepared from mesyloxyacetic acid and sodium [125I]iodide. When carboxymethylation of the enzyme is carried out in solution or in the crystalline state, no iodide is bound to the protein. The rate of iodide during the reaction of iodoacetate, determined with an iodide-specific electrode, has been found to be biphasic: the fast phase corresponds to the carboxymethylation and the slow phase to iodide liberation due to the presence of protein. With 3-iodopropionate (2.5 mM), no inactivation was detected, but in the presence of the enzyme, 10 equivalents of iodide were liberated per subunit in 1 hr. NADH does not inhibit this reaction. The electron density attributed to an iodide bound to the zinc atom of the crystalline enzyme is reinterpreted in view of these results as due to an imidazole bound to the active-site zinc. In the carboxymethylation, the reactivity of bromoacetate is higher than that of iodoacetate.     

Quenching of tryptophanyl fluorescence of human growth hormone by iodide.

Quenching of tryptophanyl fluorescence of human growth hormone by I- followed saturation kinetics and was abolished by KSCN. In the presence of 6 M guanidine hydrochloride quenching was linear between 0 to 0.2 M KI. These results suggest that I- quenched the fluorescence of the native hormone by binding at or near the single tryptophanyl residue. Quenching by 0.1 M KI decreased exponentially with increasing concentrations of human and bovine growth hormones. Acidification did not have a significant effect on quenching of the human hormone, but it markedly decreased quenching of the bovine hormone. Conformational differences at the vicinity of the lone tryptophanyl residue that could be inferred by these and other experiments may be contributing to the biological specificity of native human and bovine growth hormones.     

Effect of internally loaded iodide, thiocyanate, and perchlorate on sodium-dependent iodide uptake by phospholipid vesicles reconstituted with thyroid plasma membranes: iodide counterflow mediated by the iodide transport carrier

Na+-dependent I- transport and I- counterflow were studied using phospholipid vesicles (P-vesicles) made of porcine thyroid plasma membranes and soybean phospholipid by sonication. 1) I- uptake by P-vesicles incubated in the presence of external Na+ was higher than that by P-vesicles incubated in choline+ instead of Na+. The vesicles exhibited Na+-dependent I- uptake. When P-vesicles were internally loaded with I- prior to incubation in Na+, a further increase in Na+-dependent I- uptake was observed, although the concentration of internal I- was very much higher than that outside. In the absence of external Na+, I- uptake by P-vesicles preloaded with I- was comparable to baseline uptake. 2) Na+-dependent I- uptake by P-vesicles not loaded with I- and enhanced Na+-dependent I- uptake by P-vesicles preloaded with I- were both inhibited by either of SCN- and ClO4- added outside the vesicles. 3) When P-vesicles were loaded with SCN- instead of I- and incubated in Na+, I- uptake by these vesicles was also higher than baseline Na+-dependent I- uptake. However, a ClO4- load did not result in an increase in I- uptake. These results indicate that Na+-dependent I- transport including Na+-dependent I- counterflow is specifically mediated by the thyroid I- carrier. SCN- - I- counterflow in addition to I- - I- counterflow occurs dependently on Na+, but ClO4- - I- counterflow does not.