PEDOT doped with algal, mammalian and synthetic dopants: polymer properties, protein and cell interactions, and influence of electrical stimulation on neuronal cell differentiation.

Poly(3,4-ethylenedioxythiophene) (PEDOT) films were electrochemically polymerised with several synthetic (dodecylbenzosulfonic acid (DBSA)) and biological (dextran sulphate (DS), chondroitin sulphate (CS), alginic acid (ALG) and ulvan (ULV)) dopant anions, and their physical, mechanical and electrochemical properties characterised. PEDOT films incorporating the biological dopants ALG and ULV produced films of the greatest surface roughness (46 ± 5.1 and 31 ± 1.9 nm, respectively), and demonstrated significantly lower shear modulus values relative to all other PEDOT films (2.1 ± 0.1 and 1.2 ± 0.2 MPa, respectively). Quartz crystal microgravimetry was used to study the adsorption of the important extracellular matrix protein fibronectin, revealing protein adsorption to be greatest on PEDOT doped with DS, followed by DBSA, ULV, CS and ALG. Electrical stimulation experiments applying a pulsed current using a biphasic waveform (250 Hz) were undertaken using PEDOT doped with either DBSA or ULV. Electrical stimulation had a significant influence on cell morphology and cell differentiation for PEDOT films with either dopant incorporated, with the degree of branching per cell increased by 10.5× on PEDOT-DBSA and 6.5× on PEDOT-ULV relative to unstimulated cells, and mean neurite length per cell increasing 2.6× and 2.2× on stimulated vs. unstimulated PEDOT-DBSA and PEDOT-ULV, respectively. We demonstrate the cytocompatibility of synthetic and biologically doped PEDOT biomaterials, including the new algal derived polysaccharide dopant ulvan, which, along with DBSA doped PEDOT, is shown to significantly enhance the differentiation of PC12 neuronal cells under electrical stimulation.

Thin-film micro-electrode stimulation of the cochlea in rats exposed to aminoglycoside induced hearing loss.

The multi-channel cochlear implant (CI) provides sound and speech perception to thousands of individuals who would otherwise be deaf. Broad activation of auditory nerve fibres when using a CI results in poor frequency discrimination. The CI also provides users with poor amplitude perception due to elicitation of a narrow dynamic range. Provision of more discrete frequency perception and a greater control over amplitude may allow users to better distinguish speech in noise and to segregate sound sources. In this research, thin-film (TF) high density micro-electrode arrays and conventional platinum ring electrode arrays were used to stimulate the cochlea of rats administered sensorineural hearing loss (SNHL) via ototoxic insult, with neural responses taken at 434 multiunit clusters in the central nucleus of the inferior colliculus (CIC). Threshold, dynamic range and broadness of response were used to compare electrode arrays. A stronger current was required to elicit CIC threshold when using the TF array compared to the platinum ring electrode array. TF stimulation also elicited a narrower dynamic range than the PR counterpart. However, monopolar stimulation using the TF array produced more localised CIC responses than other stimulation strategies. These results suggest that individuals with SNHL could benefit from micro stimulation of the cochlea using a monopolar configuration which may provide discrete frequency perception when using TF electrode arrays.

Conductive and protein resistant polypyrrole films for dexamethasone delivery.

The development of inherently conducting polymers as controllable/programmable drug delivery systems has attracted significant interest in medical bionics, and the interfacial properties of the polymers, in particular, protein adsorption characteristics, is integral to the stability of the overall performance. Herein we report a hybrid conducting system based on polypyrrole doped with an anti-inflammatory prodrug, dexamethasone phosphate (DexP), upon which post-surface modification was conducted to render the polymer more biostable. We firstly investigated the influence of the current density and DexP concentration on the physiochemical properties and surface characteristics of the resulting polymer films. Films were then surface modified with thiolated poly(ethylene glycol). The influence of surface modification on inhibition of nonspecific protein adsorption to the polymer surfaces was evaluated using electrochemistry and quartz crystal microbalance. Furthermore, studies were undertaken to examine the effect of surface coatings on the drug release behaviour triggered by electrical stimulation. Our results demonstrated that both the physiochemical and interfacial properties of conducting polymers can be modulated to enhance the performance of the materials as biocompatible drug delivery systems. This provides important insight into molecular engineering of conducting polymers to facilitate their applications in medical bionics.

TRPM8 on mucosal sensory nerves regulates colitogenic responses by innate immune cells via CGRP.

TRPM8 is the molecular sensor for cold; however, the physiological role of TRPM8+ neurons at mucosal surfaces is unclear. Here we evaluated the distribution and peptidergic properties of TRPM8+ fibers in naive and inflamed colons, as well as their role in mucosal inflammation. We found that Trpm8(-/-) mice were hypersusceptible to dextran sodium sulfate (DSS)-induced colitis, and that Trpm8(-/-) CD11c+ DCs (dendritic cells) showed hyperinflammatory responses to toll-like receptor (TLR) stimulation. This was phenocopied in calcitonin gene-related peptide (CGRP) receptor-deficient mice, but not in substance P receptor-deficient mice, suggesting a functional link between TRPM8 and CGRP. The DSS phenotype of CGRP receptor-deficient mice could be adoptively transferred to wild-type (WT) mice, suggesting that CGRP suppresses the colitogenic activity of bone marrow-derived cells. TRPM8+ mucosal fibers expressed CGRP in human and mouse colon. Furthermore, neuronal CGRP contents were increased in colons from naive and DSS-treated Trpm8(-/-) mice, suggesting deficient CGRP release in the absence of TRPM8 triggering. Finally, treatment of Trpm8(-/-) mice with CGRP reversed their hyperinflammatory phenotype. These results suggest that TRPM8 signaling in mucosal sensory neurons is indispensable for the regulation of innate inflammatory responses via the neuropeptide CGRP.

In sickness and in health: Corneal epithelial stem cell biology, pathology and therapy.

Our window to the world is provided by the cornea on the front surface of the eye. The integrity and functionality of the outermost corneal epithelium is essential for vision. A population of limbal epithelial stem cells (LESCs) are responsible for maintaining the epithelium throughout life by providing a constant supply of daughter cells that replenish those constantly lost from the ocular surface during normal wear and tear and following injury. LESC deficiency leads to corneal opacification, inflammation, vascularization and discomfort (Daniels et al., 2001, 2007). Cultured LESC delivery is one of several examples of successful adult stem cell therapy in patients. The clinical precedence for use of stem cell therapy and the accessibility of the transparent stem cell niche make the cornea a unique model for the study of adult stem cells in physiological conditions as well as in disease.

Socioeconomic deprivation adversely affects survival of patients with rectal cancer.

BACKGROUND: The aim was to examine the influence of socioeconomic deprivation on stage at presentation, perioperative mortality, permanent stoma rates and overall survival in patients with rectal cancer. METHODS: Data on patient demographics, mode and stage of presentation, and short- and longer-term outcomes were extracted from a database of patients with rectal cancer. Comparisons were made after stratification into quintiles of socioeconomic deprivation. RESULTS: In total 486 patients were identified. Fewer patients from the most deprived group than from the least deprived group underwent resectional surgery (79.2 versus 93 per cent; P = 0.005). Permanent stoma rates among patients who had surgery were 40.8 and 30 per cent respectively (P = 0.110). The overall 5-year survival rate was 32.8 per cent for the most deprived compared with 64.0 per cent for the least deprived patients (P < 0.001). Respective rates for those who underwent resectional surgery were 49.9 and 72 per cent (P = 0.030). CONCLUSION: In rectal cancer, socioeconomic deprivation appears to be associated with poorer outcomes and survival. This has important implications for healthcare planning.

Heliox for asthma in the emergency department: a review of the literature.

January 2002 saw the relaunch by BOC of Heliox, a gaseous mixture of helium and oxygen, for the use in a wide range of respiratory conditions. Despite a lapse of over 65 years since it was first used, and a large number of studies and case reports advocating its use, it remains an enigma, its use sporadic, and its role undefined. This paper reviews the discovery of helium and early medical use of helium oxygen mixtures and outlines areas where Heliox already has confirmed benefit as well as one or two areas that are currently under investigation. It will also look specifically at the use of Heliox in acute exacerbations of asthma and perform a thorough review of the current literature.

Effects of chewing gum on responses to routine painful procedures in children.

In infants, sweet taste and sucking on a pacifier both have analgesic effects. Animal studies suggest that sweet taste may involve opioids, while rhythmic oral movements, as with a pacifier, increase the release of serotonin, which is involved in the gating of nociceptive afferents. The present study was designed to see if these effects produce an analgesic effect in children. Two studies were performed, during blood draws in a pediatric test center in 7- to 12-year-old children, and during vaccination at school in 9- to 11-year-old children. Using unsweetened or sweetened chewing gum, there were four groups: control, sweet, chew, and sweet plus chew. Overall, there was no effect of either sweet taste or chewing on pain responses. However, in boys sweet taste tended to increase pain ratings, but only in conjunction with chewing, while in girls sweet taste tended to decrease pain ratings in conjunction with chewing and increased them in the absence of chewing. Ratings of pain intensity and affective state were correlated. Affective state before the painful stimulus was related to pain response in the girls and in the boys in the test center, but not in the schools. In the schools, the presence of peers may have influenced the ratings.

99mTc-labeling of a hydrazinonicotinamide-conjugated vitronectin receptor antagonist useful for imaging tumors.

This report describes the (99m)Tc labeling of a HYNIC-conjugated vitronectin receptor antagonist (SQ168 = [2-[[[5-[carboonyl]-2-pyridinyl]hydrazono]methyl]benzenesulfonic acid]-Glu(cyclo[Lys-Arg-Gly-Asp-D-Phe])-cyclo[Lys-Arg-Gly-Asp-D-Phe]). The ternary ligand complex [(99m)Tc(SQ168)(tricine)(TPPTS)] (RP593) was prepared using a non-SnCl(2)-containing formulation. The corresponding (99)Tc analogue, [(99)Tc]RP593, was also prepared and characterized by HPLC and LC-MS. A HPLC concordance experiment using RP593 and [(99)Tc]RP593 showed that the same technetium complex was prepared at both the tracer and macroscopic levels. The LC-MS data is completely consistent with the 1:1:1:1 composition for Tc:SQ168:tricine:TPPTS and provides direct evidence that the two radiometric peaks in the radio-HPLC chromatogram of RP593 are indeed due to the resolution of diastereomers. In an in vitro receptor binding assay, [(99)Tc]RP593 was shown to have comparable binding affinity for the vitronectin receptor to that of SQ168 itself.

Towards developing a non-SnCl2 formulation for RP444, a new radiopharmaceutical for thrombus imaging.

There are many factors influencing the yield and radiochemical purity (RCP) of the radiopharmaceutical RP444. These include heating temperature, heating time, pH, the use of a buffering agent and a bulking agent, as well as the component (XV066, tricine, TPPTS, and Na99mTcO4) concentration. Through a series of radiolabeling experiments, we found that a formulation comprised of 20 microg of XV066, 6.5 mg of tricine, 40 mg of mannitol, 5 mg of TPPTS, and 0.1 mg of Pluronic acid dissolved in 1.0 mL of 250 mM succinate buffer (pH 5.0) gives the best RCP for RP444. The formulation can be lyophilized to form a stable crystal "cake". The radiolabeling is achieved by adding 1.5 mL generator eluant (33-133 mCi of Na99mTcO4) to a lyophilized vial and heating the reaction mixture at 100 degrees C for 10 min. Using this formulation, RP444 is prepared consistently in high yield with RCP > or = 90%. Formation of [99mTc]colloid is minimal (< 0.5%).

Phase change in tetraphenylphosphonium perchlorate.

The title compound, C(24)H(20)P(+).ClO(4)(-), undergoes a sudden reversible phase change in the region of 173-180 K which involves ordering of three quarters of the perchlorate anions.

Solid formulations of binucleate Rhizoctonia isolates suppress Rhizoctonia solani and Pythium ultimum in potting medium.

Two isolates of binucleate Rhizoctonia spp., previously selected for efficacy in suppression of Rhizoctonia solani and Pythium spp., as well as plant growth promotion, were incorporated into various solid substrate formulations. These formulated products were assayed at three doses in three glass-house experiments for biocontrol of damping-off diseases in Capsicum annuum. R. solani anastomosis group 4 or Pythium ultimum var. sporangiiferum were incorporated into pasteurized potting medium with each formulated binucleate Rhizoctonia product. All formulations were effective against both pathogens in at least two experiments, but some formulations of one isolate of binucleate Rhizoctonia did not give consistent control of R. solani in one experiment. The most consistent formulation, which provided control of both pathogens at all doses of binucleate Rhizoctonia, was the simple substrate of rice hulls. The implications for commercialization of a biocontrol product are discussed.

Biocontrol of Rhizoctonia solani and Pythium ultimum on Capsicum by Trichoderma koningii in potting medium.

Two isolates of Trichoderma koningii were evaluated for efficacy in control of damping-off diseases in seedlings of Capsicum annuum grown in pasteurized potting medium in a glasshouse. A selected isolate of binucleate Rhizoctonia and two fungicides were also included as standards for control of Rhizoctonia solani and Pythium ultimum var. sporangiiferum. Both isolates of T. koningii reduced seedling death caused by R. solani in one of two experiments, and by P. u. sporangii-ferum in two of three experiments. Neither isolate of T. koningii suppressed damping-off caused by either pathogen as consistently as the binucleate Rhizoctonia or fungicides. The implications of these results for commercial disease management are discussed.

99mTc-labeling of hydrazones of a hydrazinonicotinamide conjugated cyclic peptide.

Eight HYNICtide hydrazones (three with aliphatic substituents and five with aromatic groups) were studied for their potential use as the final intermediate for preparation of RP444, a new radiopharmaceutical under development for imaging thrombosis. The goal of this study is to screen various hydrazones through stability testing and radiolabeling and find those which are able to remain stable without significant degradation in the manufacturing process and at the same time are reactive to produce enough free hydrazine in situ for successful (99m)Tc-labeling. In an initial screening study, only hydrazones 6 and 8, which contain aliphatic substituents, gave satisfactory (>/=90%) yields of RP444 using 50 degrees C and 30 min of heating. However, their solution instability excludes them from being used as commercial reagents. Hydrazones 1 and 4 gave >/=90% yields when the reaction mixtures were heated at 80 degrees C for 30 min. Both hydrazone 1 and hydrazone 4 can be used as the final intermediate for preparation of RP444. The combination of 40 mg of tricine, 1-10 mg of TPPTS, 20-40 microg of hydrazone 1 or 4 for 50 mCi of [(99m)Tc]pertechnetate, 20-50 microg of stannous chloride, pH 4.5 +/- 0.5, and heating at 80 degrees C for 30 min gives the best yield for RP444. It is surprising that hydrazones 1 and 4 have both the solution stability with respect to decomposition and to reaction with aldehydes and ketones and yet are able to hydrolyze in situ to produce enough free HYNICtide for the (99m)Tc-labeling.

RP463: a stabilized technetium-99m complex of a hydrazino nicotinamide derivatized chemotactic peptide for infection imaging.

A HYNIC-conjugated chemotactic peptide (fMLFK-HYNIC) was labeled with (99m)Tc using tricine and TPPTS as coligands. The combination of fMLFK-HYNIC, tricine, and TPPTS with (99m)Tc produced a ternary ligand complex [(99m)Tc(fMLFK-HYNIC)(tricine)(TPPTS)] (RP463). RP463 was synthesized either in two steps, in which the binary ligand complex [(99m)Tc(fMLFK-HYNIC)(tricine)(2)] (RP469) was formed first and then reacted with TPPTS, or in one step by direct reduction of [(99m)Tc]pertechnetate with stannous chloride in the presence of fMLFK-HYNIC, tricine, and TPPTS. The radiolabeling yield for RP463 was usually >/=90% using 10 microg of fMLFK-HYNIC and 100 mCi of [(99m)Tc]pertechnetate. Unlike RP469, which decomposed rapidly in the absence of excess tricine coligand, RP463 was stable in solution for at least 6 h. [(99)Tc]RP463 was prepared and characterized by HPLC and electrospray mass spectrometry. In an in vitro assay, [(99)Tc]RP463 showed an IC(50) of 2 nM against binding of [(3)H]fMLF to receptors on PMNs. [(99)Tc]RP463 also induces effectively the superoxide release of polymorphonuclear leukocytes (PMNs) with an EC(50) value of 0.2 +/- 0.2 nM. The localization of RP463 in the infection foci was assessed in a rabbit infection model. RP463 was cleared from the blood faster than RP469 and was excreted mainly through the renal system. As a result of rapid blood clearance and increased uptake, the target-to-background ratios continuously increased from 1.5 +/- 0.2 at 15 min postinjection to 7.5 +/- 0.4 at 4 h postinjection. Visualization of the infected area could be as early as 2 h. A transient decrease in white blood cell count of 35% was observed during the first 30 min after injection of the HPLC-purified RP463 in the infected rabbit. This suggests that future research in this area should focus on developing highly potent antagonists for chemotactic peptide receptor or other receptors on PMNs and monocytes.

Oral contraceptives and oral antibiotics: interactions and advice in an accident and emergency setting.

OBJECTIVE: (1) To determine what advice, if any, would be given by accident and emergency (A&E) doctors to women who were taking the combined oral contraceptive pill (OCP) if they had been issued with broad spectrum antibiotics and (2) after an audit programme had been instigated, whether appropriate advice was given to such women. METHODS: A questionnaire was circulated to 12 doctors working in the Exeter A&E department to assess their level of knowledge in prescribing antibiotics to women taking the OCP. Notes of women aged 15-50 who had been prescribed broad spectrum antibiotics were examined to see if a contraceptive history had been taken. If the patient was found to be taking the combined OCP it was noted whether documented advice had been given about using an additional form of contraception. Six months later after two education sessions had been held, prescriptions and notes were examined. A patient education leaflet was produced to be given to these women, indicating what additional precautions should be taken after having been prescribed antibiotics. SETTING: The A&E department of a busy district general hospital. SUBJECTS: Women aged 15-50 who had been issued with broad spectrum antibiotics. RESULTS: The level of knowledge in regard to contraceptive advice given to women taking the OCP among doctors working in an A&E department was poor. However, after educational sessions and the production of a patient information leaflet, there was an improvement in women receiving correct advice. CONCLUSIONS: The clinical significance of drug interactions between oral contraceptives and antibiotics indicates the importance of asking a full contraceptive drug history of any woman of childbearing age and documenting this in the notes. Regular audit of this topic is needed to keep it at the front of doctors' minds.

A novel ternary ligand system for 99mTc-labeling of hydrazino nicotinamide-modified biologically active molecules using imine-N-containing heterocycles as coligands.

A hydrazinonicotinamide-functionalized cyclic platelet glycoprotein IIb/IIIa (GPIIb/IIIa) receptor antagonist [HYNICtide, cyclo(D-Val-NMeArg-Gly-Asp-Mamb(5-(6-(6-hydrazinonicotina mido)hexanamide)))] was labeled with 99mTc using tricine and a series of imine-N-containing heterocycles as coligands. The imine-N-containing heterocycles include N-omega-Acetylhistamine (HIS-AC), N-(2-hydroxyethyl)isonicotinamide (ISONIC-HE), isonicotinic acid (ISONIC), isonicotinoyl-L-aspartic acid dimethyl ester (ISONIC-L-Asp-OMe2), 4-methyl-5-thiazoleethanol (MTE), nicotinic acid (NIC), 3-nitro-1,2,4-triazole (NTZ), 4-pyridylacetic acid (PA), 4-pyridineethanesulfonic acid (PES), and 3-pyridinesulfonic acid (PSA). The synthesis of these new ternary ligand [99mTc]HYNICtide complexes can be performed in one or two steps in high yield and high specific activity (>/=10 000 Ci/mmol HYNICtide). For example, the reaction of HYNICtide, [99mTc]pertechnetate, nicotinic acid, stannous chloride, and tricine at pH approximately 5 and 100 degreesC for 20 min results in the complex [99mTc(HYNICtide)(tricine)(NIC)] in >/=90% yield as determined by radio-HPLC. It was found that ternary ligand technetium complexes, [99mTc(HYNICtide)(tricine)(L)] (L = ISONIC, ISONIC-L-Asp-OMe2, ISONIC-HE, MTE, PA, PES, and PSA) are formed as equal mixtures of two isomeric forms. Complex [99mTc(HYNICtide)(tricine)(L)] (L = HIS-AC and NTZ) showed more than two well-resolved radiometric peaks at the retention times of interest, suggesting that they may have more than two forms in solution due to different bonding modalities of HIS-AC and NTZ. By a chirality experiment, it was found that the presence of two radiometric peaks is a result of the resolution of the two diastereomers which are formed by the combination of the chiral HYNICtide and the chiral technetium chelate. The formation of two diastereomers was also observed when a chiral imine-N-containing coligand was used for the radiolabeling of HYNIC-BA. The new ternary ligand [99mTc]HYNICtide complexes were found to be stable for up to 6 h in the reaction mixture. The high solution stability is attributed to their kinetic inertness. The composition of these complexes was determined to be 1:1:1:1 for Tc:HYNICtide:L:tricine (L = imine-N-containing heterocycles) through a series of mixed ligand experiments on the tracer (99mTc) level. The lipophilicity of the ternary ligand [99mTc]HYNICtide complexes can be systematically varied by the choice of polyaminocarboxylate and imine-N-containing coligands. Using the combination of tricine and an imine-N-containing coligand, HYNIC-derivatized peptides or other small molecules can be labeled with 99mTc in high specific activity and high stability for potential use as radiopharmaceuticals.

New and versatile ternary ligand system for technetium radiopharmaceuticals: water soluble phosphines and tricine as coligands in labeling a hydrazinonicotinamide-modified cyclic glycoprotein IIb/IIIa receptor antagonist with 99mTc.

A hydrazinonicotinamide-functionalized cyclic platelet glycoprotein IIb/IIIa (GPIIb/IIIa) receptor antagonist [cyclo(D-Val-NMeArg-Gly-Asp-Mamb(5-(6-(6-hydrazinonicotin amido) hexanamide))) (HYNIC-tide)] was labeled with 99mTc using tricine and a water soluble phosphine (TPPTS, trisodium triphenylphosphine-3,3',3"-trisulfonate; TPPDS, disodium triphenylphosphine-3,3'-disulfonate; or TPPMS, sodium triphenylphosphine-3-monosulfonate] as coligands. The synthesis of technetium complexes, [99mTc(HYNICtide)(L)(tricine)] (1, L = TPPTS; 2, L = TPPDS; 3, L = TPPMS), can be performed in one or two steps in high yield and with high specific activity (> or = 20,000 Ci/mmol). For example, the reaction of the HYNICtide, [99mTc]pertechnetate, stannous chloride, and tricine at pH 4-5 and room temperature results in the complex [99mTc(HYNICtide)(tricine)2], which reacts with TPPTS (50 degrees C for 30 min) to give complex 1 in > or = 90% yield as determined by radio-HPLC. Complexes 1-3 are formed as equal mixtures of two isomeric forms and are stable for > or = 6 h in the reaction mixture and in dilute solution. Both isomeric forms of complex 1 were found by a platelet-binding assay to contain the 99mTc-labeled HYNICtide and possess biological activity. The composition of these complexes was determined to be 1:1:1:1 for Tc:HYNICtide:L:tricine through a series of mixed ligand experiments on the tracer (99mTc) level. Surprisingly, this composition is maintained over a wide range of relative ligand ratios. The relative bonding capability of the three phosphine coligands to the Tc was determined by spiking various amounts of TPPDS or TPPMS into TPPTS and falls in the order TPPMS > TPPDS > TPPTS. The lipophilicity of the [99m Tc]HYNICtide complexes can be systematically varied by the choice of the phosphine and aminocarboxylate coligands. Using the combination of tricine and a phosphine ligand, HYNIC-derivatized peptides or other small molecules can be labeled with 99mTc in high specific activity and with high stability for potential use as radiopharmaceuticals.

Labeling a hydrazino nicotinamide-modified cyclic IIb/IIIa receptor antagonist with 99mTc using aminocarboxylates as coligands.

A series of 99mTc complexes containing a hydrazinonicotinamide-conjugated cyclic IIb/IIIa receptor antagonist, cyclo(D-Val-NMeArg-Gly-Asp-Mamb-(hydrazinonicotinyl-5- (6-aminocaproic acid))), were synthesized in high yield using tricine or other aminocarboxylates as coligands. These 99mTc complexes have the potential to be used as thrombus imaging agents. The radiolabeling of the HYNIC-conjugated cyclic IIb/IIIa peptide (HYNICtide) was carried out by reaction with pertechnetate in the presence of excess tricine and stannous chloride at pH 4-5. The reaction time and temperature depend on the amount of the HYNICtide and pertechnetate used for the radiolabeling. Very high specific activity (> or = 20,000 mCi/mumol) can be achieved for the complex [99mTc(HYNICtide)(tricine)2] without postlabeling purification. The complex [99mTc(HYNICtide)(tricine)2] was found by two reversed phase HPLC methods to exist as multiple species, some of which interconvert, depending on the temperature, reaction time, and pH of the reaction mixture. The presence of these multiple species is most likely due to different bonding modalities of either the hydrazine moiety of the HYNICtide or the two tricine coligands. The complex [99mTc(HYNICtide)(EDDA)] (EDDA = ethylenediamine-N,N'-diacetic acid) was prepared either by reacting the cyclic IIb/IIIa HYNICtide with pertechnetate, excess EDDA, and stannous chloride at pH 4-5 and 75 degrees C for 30 min or by reacting excess EDDA with [99mTc(HYNICtide)(tricine)2]. The complex [99mTc(HYNICtide)(EDDA)] was found to be stable for at least 12 h in the reaction mixture. Three major species were detected in the radio-HPLC chromatograms, presumably due to the more limited number of possible coordination isomers. Similar results were obtained using other polydentate aminocarboxylates (such as HEDTA, N-(2-hydroxyethyl)ethylenediaminetriacetic acid) as coligands. It is clear that the replacement of tricine by other polydentate aminocarboxylates produces 99mTc-HYNICtide complexes with higher stability and fewer coordination isomers.