^99mTc标记的抗心肌肌钙蛋白Ⅰ单克隆抗体在心肌损伤大鼠体内的分布

目的研究^99mTc标记的抗心肌肌钙蛋白Ⅰ单克隆抗体（AcTnIMA）在实验性心肌损伤大鼠体内的分布，探讨^99mTc-AcTnIMA是否可以作为心脏放射免疫显像剂。方法第一批大鼠实验组：20只急性心肌损伤大鼠注射^99mTc-AcTnIMA0．2mci，分别于注射后2、4、6、8h处死（每次5只），取血液、肝、脾、肾、正常肌肉、肺、心脏，计算每克组织计数占总注入计数的百分比（ID％／g）及心-肺ID％／g比（HLR）；药物对照组：20只急性心肌损伤大鼠注射^99mTc标记的非特异性免疫球蛋白（N-IgG）0．2mci，处死方法同实验组。取肺及心脏，计算ID％／g及HLR；空白对照组：20只正常大鼠注射^99mTc-AcTnIMA0．2mci，处理方法同药物对照组。第二批50只心肌损伤大鼠分别于发生心肌损伤后2、4、6、8、12、24h，3、5、10、15d分10次静脉注射^99mTc-AcTnIMA0．2mci（每次5只），注射后4h处死，计算出ID％／g及HLR。结果损伤心肌摄取^99mTc-AcTnIMA为特异性摄取，摄取的高峰时间为4h；损伤心肌摄取^99mTc-AcTnIMA与损伤发生时间无关。结论^99mTc-AcTnIMA有望作为心脏放射免疫显像剂诊断心肌损伤。     

铼与抗结肠癌单克隆抗体的直接标记法及在荷瘤裸鼠体内的放射免疫显像

为探讨^180铼(^186Re)用于放射免疫显像的价值．用抗入结肠癌单克隆抗体(MAb)SC3A和以抗坏血酸为还原荆的直接标记法．对SnCl2还原的180RE标记物在荷结肠癌裸鼠体内的生物学分布及放射免疫显像进行研究。结果显示．本法的标记率均达96%～99%标记物较稳定．在体与250倍以上的二乙烯三胺五乙酸(DTPA)和人血清白蛋白在37℃共育24h．未见标记物786Re-SC3A解离。用过量肿瘤细胞抗原结合法测定．标记物抗体活性达90%～96％，48h活性下降相似文献   

胰岛素不同给药途径对糖尿病小鼠葡萄糖代谢的影响

目的：观察胰岛素治疗对糖尿病小鼠口服葡萄糖代谢的影响。方法：四氧嘧啶诱导小鼠糖尿病模型。糖尿病小鼠[^14C]-葡萄糖灌胃，同时腹腔或皮下注射胰岛素。每隔一定时间取尾静脉血测血糖和放射性，2h后处死小鼠，取心、肝、肾组织测放射性。结果：糖尿病小鼠口服[^14C]-葡萄糖后血糖迅速上升，但其血液放射性水平与正常小鼠和胰岛素给药小鼠无差异。糖尿病小鼠皮下注射胰岛素50％出现低血糖。口服[^14C]-葡萄糖后2h，糖尿病小鼠肝、肾放射性水平分别是正常小鼠的4倍和1．5倍，心脏放射性水平降低为正常小鼠的30％。腹腔注射胰岛素的糖尿病小鼠肝、肾和心脏的放射性水平与正常小鼠无统计学差异。皮下注射胰岛素使50％小鼠血糖降至正常，但其肝、肾的放射性水平仍显著高于正常小鼠。对于因皮下注射胰岛素而处于严重低血糖的糖尿病小鼠，肝、肾的放射性水平与正常小鼠无统计学差异，心脏的放射性水平仍显著低于正常小鼠。结论：皮下胰岛素给药可以纠正血糖．但不能纠正糖代谢异常。     

131I-Herceptin在胃癌裸鼠模型中的体内分布及抑瘤效应的研究

目的：研究131I-Herceptin在胃癌裸鼠模型体内的生物学分布及131I-Herceptin的抑瘤效果。方法：采用Iodogen法制备131I-Herceptin。以NCI-N87胃癌细胞皮下接种BALB/c-neu裸鼠建立动物模型，对荷瘤小鼠模型进行SPECT连续显像。测量小鼠用药后的4、12、24、48 h各脏器每克组织每分钟的放射性计数（epm/g），并计算T／NT以及每克组织的放射性计数占注射剂量放射性计数的百分比（％rD/s）。将荷瘤裸鼠随机分为3组：131I-Herceptin组、Herceptin组与生理盐水对照组。接种前后测量肿瘤长短径，并计算肿瘤生长的抑制率，流式细胞仪检测肿瘤细胞周期及细胞凋亡率。结果：实验组对比对照组，显像对比明显；实验组T/NT以及肿瘤组织％ID/g显著高于对照组（P<0．01）。3组间肿瘤抑制率及凋亡率均差别明显（F分别为84.59、304.38，P＜0.0001），其肿瘤抑制率及凋亡率由高到低分别为131I-Herceptin组、Herceptin组与生理盐水组。结论：131I-Herceptin在胃癌裸鼠肿瘤组织中有良好的靶向作用；131I-Herceptin具有良好的抑瘤作用。     

99mTc直接法标记抗心肌肌钙蛋白Ⅰ单克隆抗体

目的 探索99mTc直接法标记抗心肌肌钙蛋白Ⅰ单克隆抗体(AcTnIMA)的方法,并研究标记产物的体外稳定性.方法 用氯化亚锡(SnCl2)还原法进行AcTnIMA标记,并用正交实验设计筛选抗体量、SnCl2量、反应体系pH值及放射性活度四个因素的最佳组合;用纸层析法测定标记产物的标记率;用柱层析法测定标记物中99mTc-AcTnIMA的纯度;将标记物在室温(22℃)下放置0、2、4、6 h,观察其体外稳定性.结果 99mTc直接法标记AcTnIMA的最佳标记条件为抗体量30 μh,SnCl2量80 μg,反应体系pH值7.0,放射性活度50 mCi,标记率可达99%以上;标记物中99mTc-AcTnIMA的纯度较高;标记产物放置6 h后,标记率仍大于95%.结论 用99mTc直接法标记AcTnIMA简单高效,标记产物在体外有很好的稳定性.     

当归多糖锝标记物在癌细胞中摄取及荷瘤鼠体内显像研究

目的：研究HepG2和PC3荷瘤鼠是否影响当归多糖的肝靶向性。方法：当归多糖核素锝标记;^99mTc-DTPA-ASP体内SPECT/CT成像;检测HepG2和PC3对^99mTc-DTPA-ASP的摄取率;构建HepG2和PC3 2种裸鼠腋下移植瘤模型,通过SPECT显像来研究荷瘤鼠模型对当归多糖体内分布的影响。结果：细胞摄取实验结果显示,随着孵育时间的延长,肝癌细胞HepG2和非肝癌细胞PC3对当归多糖的摄取率逐渐增加,并在4 h后达到稳定,约为4.3%,说明2种癌细胞对当归多糖无明显特异性吸收。SPECT显像结果显示,荷瘤鼠注射^99mTc-DTPA-ASP后,2种模型肿瘤组织部分在SPECT图中出现显影,但亮度接近血液本底,且肝脏亮斑亮度几乎不受影响,说明移植瘤模型不影响当归多糖的体内分布。结论：癌细胞对当归多糖的低摄取率及荷瘤鼠显像肿瘤组织的弱亮斑,说明锝标记当归多糖探针探测体内肿瘤能力较弱,同时肿瘤组织不影响当归多糖的肝靶向性。     

致弱RH株弓形虫抗小鼠B16黑色素瘤的实验研究

目的观察紫外线辐照致弱RH株弓形虫对小鼠体内黑色素瘤生长的抑制作用。方法1×10^7紫外线致弱RH株弓形虫速殖子经腹腔注射免疫C57BL/6J小鼠,7d后再次接种相同数量弓形虫,并在接种当天给小鼠荷瘤,在荷瘤后21d处死小鼠,测定小鼠肿瘤体积与质量,并检测脾细胞T细胞亚群和淋巴细胞杀伤活性。结果致弱弓形虫能够显著抑制肿瘤生长,实验组小鼠肿瘤体积与质量显著小于对照组（P〈0．05）,抑瘤率为52．09％。实验组小鼠脾细胞CD3^＋、CD4^＋、CD8^＋、CD4^＋／CD8^＋、NK细胞杀伤活性显著高于对照组（P〈0．05）。结论致弱免疫弓形虫可以抑制小鼠体内黑色素瘤生长。     

同位素标记示踪法测定G蛋白竞争性抑制肽-27在动物体内的分布与排泄

目的：利用同位素标记示踪法研究G蛋白竞争性抑制肽（GCIP）-27在动物体内的分布和排泄。方法：^125I-GCIP采用Iodogen法标记，按组织器官直接测定法和TCA沉淀法进行体内分布实验，以每毫克组织器官的^125I-GCIP放射性计数表示GCIP在小鼠体内的分布；以不同时间段大鼠胆汁、尿、粪及小鼠的尿、粪放射性总排泄量占给药量放射性的百分比表示其在体内的排泄。结果：GCIP-27在小鼠体内分布广泛，其中肾、血管、胃、肺、心、小肠等组织分布较高，肌肉、脂肪等组织相对较低，脑最低。大鼠72h粪、尿、胆汁原形药物排泄量分别为给药量的26．13％，0．95％和4．12％。小鼠72h粪、尿原形药物排泄量分别为给药量的27，92％，0．84％。结论：GCIP-27在小鼠体内广泛分布，主要经尿液排泄，肾为主要排泄器官。     

~(99m)Tc标记磁性纳米Fe_3O_4颗粒双模态探针的制备及其成像实验研究

目的制备99mTc标记磁性纳米Fe_3O_4颗粒双模态探针(SPECT/MRI),考察该探针应用于裸鼠模型的SPECT/MRI成像及其在体内、体外的靶向行为。方法选用多聚醇法制备经过PEG表面修饰的Fe_3O_4纳米颗粒为核心,在EDC/NHS的催化作用下,将多肽RGD和DTPA偶联在PEG上,在此基础上标记核素99mTc,制备了SPECT/MRI双模态探针。结果经DLS表征,该探针能在生理环境下能稳定分散,且放化活度测定核素标记率在90%以上。SPECT/MRI成像证明了细胞对探针的吞噬是由受体介导的。在SPECT/MRI成像结果中,核素计数(ID/g%:靶向组0.27%0.24%竞争组)有较明显差异。在MRI成像实验中进行了T1加权成像和T2加权成像,发现T1和T2加权成像增强较为明显,达到预期效果。结论制备的99mTc标记Fe3O4@PEG-DTPA-RGD双模态探针既具备T2造影能力,又具有T1造影潜能。     

NC100668, a new tracer tested for imaging of venous thromboembolism: pharmacokinetics and metabolism in humans.

The (99m)Tc-complex of NC100668 [Acetyl-Asn-Gln-Glu-Gln-Val-Ser-Pro-Tyr(3-iodo)-Thr-Leu-Leu-Lys-Gly-NC100194] is a new tracer tested for nuclear medical imaging of venous thromboembolism. NC100668 is a 13-amino acid peptide with a Tc-binding chelator [NC100194; -NH-CH2-CH2-N(CH2-CH2-NH-C(CH3)2-C(CH3)=N-OH)2] linked to the C-terminal end. The present study was performed following injection of (99m)Tc-NC100668 in healthy human volunteers with five dose levels of NC100668 (20-2000 microg) and a constant radioactivity dose. The rate at which the radioactivity was cleared from blood was independent of gender and dose of NC100668; more than half of the 82% urinary clearance of radioactivity was obtained 2 h postinjection. The radioactivity in blood was reduced to 50% of initial values within 12 min; this was followed by a more gradual decrease with a half-life of 1.2 h and a terminal elimination half-life of 10.5 h. The plasma concentration of NC100668 decreased rapidly with an initial half-life of 5 to 10 min. The half-life after this initial phase could be estimated for only two of the subjects in the highest-dose group because the NC100668 concentration in the other samples at these time points was below the limit of detection of the liquid chromatography/mass spectrometry (LC/MS) method. LC/MS analyses of urine samples revealed the identity of two metabolites generated from the C-terminal end of the molecule; Gly-NC100194 was identified as the major metabolite and NC100194 as a minor metabolite. The estimated sum of these two metabolites is in the same magnitude as the recoveries of (99m)Tc in these samples, indicating that most of the (99m)Tc excreted in urine is bound to one of these metabolites.     

Technetium-99m labeled pyridyl benzofuran derivatives as single photon emission computed tomography imaging probes for β-amyloid plaques in Alzheimer's brains

Three novel (99m)Tc-labeled pyridyl benzofuran derivatives were tested as potential probes for imaging β-amyloid plaques using single photon emission computed tomography (SPECT). The (99m)Tc and corresponding rhenium complexes were synthesized with bis(aminoethanethiol) (BAT) as a chelating ligand. All Re complexes showed affinity for Aβ(1-42) aggregates (K(i) = 13.6-149.6 nM). Biodistribution experiments in normal mice revealed that the (99m)Tc-labeled derivatives displayed sufficient uptake in the brain (1.41-1.80% ID/g at 2 min postinjection). Notably, [(99m)Tc]BAT-Bp-2 showed a good initial uptake (1.80% ID/g at 2 min) and a reasonable washout from the brain (0.79% ID/g at 60 min). Ex vivo autoradiography with [(99m)Tc]BAT-Bp-2 revealed substantial labeling of β-amyloid plaques in sections of brain tissue from Tg2576 transgenic mice but not in the age-matched controls. [(99m)Tc]BAT-Bp-2 may be a potential SPECT probe for imaging β-amyloid plaques in Alzheimer's brains.     

Synthesis and in vivo evaluation of 99m Tc-Transferrin conjugate for detection of inflamed site

Transferrin is one of acute phase reactants in inflamed lesion. Expression of transferrin receptor is increased in activated macrophage during inflammation process. Conjugates of target ligand with novel water-soluble chitosan for fast excretion of background radioactivity have been shown to be selectively taken up via the target molecules. In this study, radiolabeled 99m Tc-Transferrin conjugate was synthesized and evaluated its efficacy in vivo as a targeted agent for the rapid detection of inflamed lesion that expresses relatively high level of transferrin receptors. Transferrin was conjugated with HYNIC-chitosan and radiolabeled with 99m Tc. The biodistribution and scintigraphic images with the 99m Tc-HYNIC-chitosan-Transferrin conjugate (99m Tc-Tfc) were studied in a murine infection model in which the infection was induced with Escherichia coli (2 x 10(6) colonies). The %ID/g was as follows: 1.612 +/- 0.098, 2.473 +/- 0.202 and 2.617 +/- 0.646% at 30, 120 min and 6 h after injection, respectively. Gamma camera imaging rapidly visualized the infection/inflammation lesion, with the lesion-to-background ratio improving with time up to 5.68 +/- 0.48. 99m Tc-Tfc scintigraphy allows rapid and good imaging of an inflamed lesion.     

Preparation,quality control and stability of 99mTc‐sparafloxacin complex,a novel agent for detecting sites of infection

Labeling of sparafloxacin with technetium‐99m using stannous chloride as a reducing agent was investigated. Dependence of the yield of ^99mTc‐sparafloxacin complex on the concentration of sparafloxacin, reducing agent, pH and reaction time was studied. Under optimum conditions, the labeling yield of ^99mTc‐sparafloxacin complex (95%) was achieved by using 2.5 mg of sparafloxacin, 50 µg of Sn(II), pH 10 and 30‐min reaction time. ^99mTc‐sparafloxacin complex was stable for 3 h after labeling, then the yield decreased gradually to 81.9% at 6 h. Biodistribution studies in rats were carried out in experimentally induced infection in the left thigh using Staphylococcus aureus. The ratios of bacterial infected thigh/contralateral thigh were then evaluated. The time for the maximum accumulation of ^99mTc‐sparafloxacin at the site of the infection was 30 min after the administration followed by gradual decline. The abscess‐to‐muscle ratio for ^99mTc‐sparafloxacin was 5.9±0.7, while that for the commercially available ^99mTc‐ciprofloxacin was 3.8±0.5 under the same experimental paradigm, indicating that ^99mTc‐sparafloxacin could be used for infection imaging. Copyright © 2009 John Wiley & Sons, Ltd.     

Preparation and biological evaluation of 99mTc–ropinirole as a novel radiopharmaceutical for brain imaging

Noninvasive brain imaging is a process that allows scientists and physicians to view and monitor the areas of the brain. The aim of this study was to formulate a novel radiopharmaceutical for the detection of brain disorders at early stages in susceptible patients. ^99mTc–ropinirole was prepared by the direct complexation of ropinirole with technetium‐99m. The results showed that the radiochemical yield ^99mTc–ropinirole was 92 ± 2.87% and the radiochemical yield was evaluated by paper chromatography and HPLC. In vitro studies showed that the formed complex was stable for up to 6 h. In vivo uptake of ^99mTc–ropinirole in the brain was 4.87 ± 0.15% injected dose/g organ at 30 min post‐injection, which cleared from the brain with time till it reaches 2.3% at 2 h post‐injection indicating that the brain uptake of ^99mTc–ropinirole is higher than that of the commercially available ^99mTc‐HMPAO, which is 2.25% at 30 min. Pre‐dosing mice with cold ropinirole reduced the brain uptake to 0.26 ± 0.01% injected dose/g organ, so this confirms the high specificity and selectivity of this radiotracer for the assessment of the dopamine receptors.     

Tumor targeting with a 99mTc-labeled AS1411 aptamer in prostate tumor cells

AS1411, a 26-base guanine-rich oligonucleotide aptamer, has high affinity to nucleolin, mainly on tumor cell surfaces. In this study, a modified AS1411 was labeled with ^99mTc and evaluated as a potential tumor-targeting agent for imaging. The AS1411 aptamer was conjugated with HYNIC and labeled with ^99mTc in the presence a co-ligand. Radiochemical purity and stability testing of the ^99mTc–HYNIC–AS1411 aptamer were carried out with thin layer chromatography and a size-exclusion column in normal saline and human serum. Cellular nucleolin-specific binding, cellular internalization in DU-145 cells, as high levels of nucleolin expression, were performed. Additionally, biodistribution in normal mice and DU-145 tumour-bearing mice was assessed. Radiolabeling of the aptamer resulted in a reasonable yield and radiochemical purity after purification. The aptamer was stable in normal saline and human serum, and cellular experiments demonstrated specific binding of the AS1411 aptamer to the nucleolin protein. Based on biodistribution assessment of ^99mTc–HYNIC–AS1411, rapid blood clearance was seen after injection and it appears that the excretion route was via the urinary system at 1?h post-injection. Tumours also showed a higher accumulation of radioactivity with this labeled aptamer. ^99mTc–AS1411 can be a potential tool for the molecular imaging of nucleolin-overexpressing cancers.     

Potent bombesin-like peptides for GRP-receptor targeting of tumors with 99mTc: a preclinical study

Four open chain tetraamine-functionalized bombesin (BB) analogues were synthesized [parent tetradecapeptide-based Demobesin 3 and 4 and BB(7-14)-based Demobesin 5 and 6]. Labeling with (99m)Tc afforded high-purity and high specific activity radiotracers. Peptides showed high affinity for the human GRP-R (GRP-R = gastrin releasing peptide receptor) expressed in PC-3 cells. In human tumors preferentially expressing single bombesin receptor subtypes, they showed high affinity for the GRP-R, less affinity for the NMB-R (NMB-R = neuromedin B receptor) and no affinity for the orphan BB(3)-R (bombesin subtype 3 receptor). [(99m)Tc]Demobesin 3-6 efficiently internalized in a time- and dose-dependent manner in PC-3 cells and showed a high and specific uptake in human PC-3 xenografts and the pancreas of nude mice. [(99m)Tc]Demobesin 3 and 4 were rapidly excreted via the kidneys while the truncated analogues were predominantly processed by the hepatobiliary system. Patient studies are scheduled for validating the suitability of [(99m)Tc]Demobesin 3 and 4 in the GRP-R-targeted imaging of tumors.     

Accumulation of PEG-liposomes in the Inflamed Colon of Rats: Potential for Therapeutic and Diagnostic Targeting of Inflammatory Bowel Diseases

Therapeutic intervention in inflammatory bowel diseases (IBDs) is often associated with severe toxicity related to the nonspecific and ubiquitous interaction of drugs with the organs and tissues. In order to prevent side effects from aggressive and prolonged treatment with glucocorticoids and immunosuppressive agents, preferential accumulation of these potent drugs in diseased tissue is desired. In this work, we report that liposomes show a remarkable tendency to accumulate in inflamed colon of rats with experimental colitis. The disposition of liposomes was monitored by labeling them with Tc-99m followed by gamma camera imaging, and determining biodistribution of radioactivity in various organs. The images showed distinct accumulation of radioactivity in the colon of rats with colitis, while the abdomen of normal rats was conspicuously free of any visible radioactivity. Although images acquired 4 h after Tc-99m-liposome injection were clear enough for diagnostic indication, the real potential of liposomes for drug delivery was evident in 24 h images where the major organs of liposome accumulation were dwarfed by intense colon activity in animals with colitis. On necropsy, 13.5% ± 5.48 of the activity accumulated in the inflamed colon as compared to only 0.1% in the normal colon, giving a target-to-nontarget ratio of 135. The blood borne radioactivity was 9% ± 2.12 (colitis) and 25.7% ± 4.27 (normal), indicating that the decrease in circulating liposomes is associated with an increase in liposome accumulation in the inflammatory site. The other two major organs that accumulated liposomes were spleen (10.7% normal vs. 11% colitis) and liver (8% normal vs. 10.1% colitis). In conclusion, this study demonstrates the innate propensity of liposomes to accumulate in the sites of inflammation and potential of liposomes loaded with therapeutic drugs or diagnostic agents for targeting colitis.     

Accumulation of PEG-liposomes in the inflamed colon of rats: potential for therapeutic and diagnostic targeting of inflammatory bowel diseases

Therapeutic intervention in inflammatory bowel diseases (IBDs) is often associated with severe toxicity related to the nonspecific and ubiquitous interaction of drugs with the organs and tissues. In order to prevent side effects from aggressive and prolonged treatment with glucocorticoids and immunosuppressive agents, preferential accumulation of these potent drugs in diseased tissue is desired. In this work, we report that liposomes show a remarkable tendency to accumulate in inflamed colon of rats with experimental colitis. The disposition of liposomes was monitored by labeling them with Tc-99m followed by gamma camera imaging, and determining biodistribution of radioactivity in various organs. The images showed distinct accumulation of radioactivity in the colon of rats with colitis, while the abdomen of normal rats was conspicuously free of any visible radioactivity. Although images acquired 4 h after Tc-99m-liposome injection were clear enough for diagnostic indication, the real potential of liposomes for drug delivery was evident in 24 h images where the major organs of liposome accumulation were dwarfed by intense colon activity in animals with colitis. On necropsy, 13.5% +/- 5.48 of the activity accumulated in the inflamed colon as compared to only 0.1% in the normal colon, giving a target-to-nontarget ratio of 135. The blood borne radioactivity was 9% +/- 2.12 (colitis) and 25.7% +/- 4.27 (normal), indicating that the decrease in circulating liposomes is associated with an increase in liposome accumulation in the inflammatory site. The other two major organs that accumulated liposomes were spleen (10.7% normal vs. 11% colitis) and liver (8% normal vs. 10.1% colitis). In conclusion, this study demonstrates the innate propensity of liposomes to accumulate in the sites of inflammation and potential of liposomes loaded with therapeutic drugs or diagnostic agents for targeting colitis.     

Synthesis and in vivo evaluation of 99mTc–Transferrin conjugate for detection of inflamed site

Transferrin is one of acute phase reactants in inflamed lesion. Expression of transferrin receptor is increased in activated macrophage during inflammation process. Conjugates of target ligand with novel water-soluble chitosan for fast excretion of background radioactivity have been shown to be selectively taken up via the target molecules. In this study, radiolabeled ^99mTc–Transferrin conjugate was synthesized and evaluated its efficacy in vivo as a targeted agent for the rapid detection of inflamed lesion that expresses relatively high level of transferrin receptors. Transferrin was conjugated with HYNIC-chitosan and radiolabeled with ^99mTc. The biodistribution and scintigraphic images with the ^99mTc–HYNIC–chitosan–Transferrin conjugate (^99mTc–Tfc) were studied in a murine infection model in which the infection was induced with Escherichia coli (2 × 10⁶ colonies). The %ID/g was as follows: 1.612 ± 0.098, 2.473 ± 0.202 and 2.617 ± 0.646% at 30, 120 min and 6 h after injection, respectively. Gamma camera imaging rapidly visualized the infection/inflammation lesion, with the lesion-to-background ratio improving with time up to 5.68 ± 0.48. ^99mTc–Tfc scintigraphy allows rapid and good imaging of an inflamed lesion.