Anti-Tumor Effects of Sodium Meta-Arsenite in Glioblastoma Cells with Higher Akt Activities.

Glioblastoma is a type of aggressive brain tumor that grows very fast and evades surrounding normal brain, lead to treatment failure. Glioblastomas are associated with Akt activation due to somatic alterations in PI3 kinase/Akt pathway and/or PTEN tumor suppressor. Sodium meta-arsenite, KML001 is an orally bioavailable, water-soluble, and trivalent arsenical and it shows antitumoral effects in several solid tumor cells via inhibiting oncogenic signaling, including Akt and MAPK. Here, we evaluated the effect of sodium meta-arsenite, KML001, on the growth of human glioblastoma cell lines with different PTEN expression status and Akt activation, including PTEN-deficient cells (U87-MG and U251) and PTEN-positive cells (LN229). The growth-inhibitory effect of KML001 was stronger in U87-MG and U251 cells, which exhibited higher Akt activity than LN229 cells. KML001 deactivated Akt and decreased its protein levels via proteasomal degradation in U87-MG cells. KML001 upregulated mutant PTEN levels via inhibition of its proteasomal degradation. KML001 inhibited cell growth more effectively in active Akt-overexpressing LN229 cells than in mock-expressing LN229 cells. Consistent with these results, KML001 sensitized PTEN-deficient cells more strongly to growth inhibition than it did PTEN-positive cells in prostate and breast cancer cell lines. Finally, we illustrated in vivo anti-tumor effects of KML001 using an intracranial xenograft mouse model. These results suggest that KML001 could be an effective chemotherapeutic drug for the treatment of glioblastoma cancer patients with higher Akt activity and PTEN loss.

Arsenic compounds activate the MAPK and caspase pathways to induce apoptosis in OEC­M1 gingival epidermal carcinoma.

Arsenic is a well­documented environmental toxicant that can induce neurotoxicity and peripheral vascular diseases. In fact, arsenic trioxide has been used to treat various cancer types. Oral cancer has been in the top ten common cancers for decades in Taiwan, and the incidence rate is continuously increasing. The majority of oral cancers are associated with excessive tobacco, alcohol consumption and betel chewing. To the best of our knowledge, no study has revealed the effect of arsenic compounds on oral cancers. Thus, the present study used OEC­M1 oral squamous carcinoma cells treated with sodium arsenite (NaAsO2) and dimethylarsenic acid (DMA) to determine whether both arsenic compounds could exert anticancer effects on oral cancer. The results demonstrated that NaAsO2 and DMA induced rounding up and membrane blebbing in OEC­M1 cells, which are morphological characteristics of apoptosis. Annexin V/PI double staining analysis further confirmed that both arsenic compounds induced apoptosis of OEC­M1 cells. In addition, NaAsO2 and DMA significantly decreased the survival rate and increased the percentage of OEC­M1 cells in the subG1 and G2/M phases (P<0.05). Furthermore, both arsenic compounds significantly activated the cleavage of caspase­8, ­9, ­3 and PARP, and the phosphorylation of JNK, ERK1/2 and p38 in OEC­M1 cells (P<0.05). Collectively, the findings of the present study indicated that NaAsO2 and DMA stimulate extrinsic and intrinsic apoptotic pathways through the activation of the MAPK pathways to induce apoptosis of OEC­M1 cells, suggesting that NaAsO2 and DMA may be used as novel anticancer drugs for oral cancers.

Sodium Arsenite Inhibits Lung Fibroblast Differentiation and Pulmonary Fibrosis.

Idiopathic pulmonary fibrosis (IPF) is a chronic interstitial lung disease with a high mortality and poor prognosis. Transforming growth factor (TGF)-ß plays crucial roles in the pathogenesis of IPF. To investigate the role of sodium arsenite (SA) on fibroblast differentiation and pulmonary fibrosis, we checked the effects of SA on TGF-ß-induced normal human lung fibroblasts (NHLFs) differentiation, and the anti-fibrotic effect of SA on bleomycin (BLM)-induced pulmonary fibrosis in mouse. SA treatment significantly inhibits α-smooth muscle actin and fibronectin (FN) expression in TGF-ß treated NHLFs; and SA also inhibits TGF-ß stimulated expression of NADPH oxidase 4 and accumulation of intracellular reactive oxygen species. TGF-ß-induced the phosphorylation of ERK and Smad3 were also blocked by SA. The administration of SA (IP) suppressed BLM-induced lung fibrosis characterized as the inhibition of collagen deposition, TGF-ß accumulation in bronchoalveolar lavage fluid, and the expression of FN and collagen 1a2 in lung tissue. This study revealed that SA inhibits TGF-ß-induced lung fibroblast differentiation and BLM-induced pulmonary fibrosis in mice, suggesting that SA could be a potential therapeutic approach to IPF.

KML001 and doxercalciferol induce synergistic antileukemic effect in acute lymphoid leukemia cells.

KML001 (NaAsO2, sodium metaarsenite, KOMINOX), a kind of arsenic compound, that has shown promising efficacy in non-Hodgkin's lymphoma (NHL) both in vitro and in vivo. In our study, the antileukemic effect of KML001 on acute lymphoid leukemia (ALL) and its mechanism of action were investigated. The results showed that KML001 inhibited cell proliferation in two types of ALL cell lines, CCRF-CEM and Molt-4. Exposure of ALL cells to KML001 induced apoptosis in a time-dependent manner. KML001 caused cell cycle arrest at G2/M phase instead of G0/G1 phase shown in other leukemia cells. In addition, we also tested the possibility of synergy of KML001 with doxercalciferol, a vitamin D2 derivative. Also, we found that a combination of KML001 with doxercalciferol showed a synergistic effect on ALL cell lines and this could be due to its different mechanism of action. Overall, our findings demonstrated KML001 could be a promising antileukemic agent especially when it is combined with doxercalciferol in ALL treatment.

Calcifilaxis en una paciente sin insuficiencia renal avanzada / Calciphylaxis in a patient without advanced renal failure

La calcifilaxis es una enfermedad poco frecuente, aunque presenta una elevada tasa de mortalidad debido sobre todo a complicaciones como sepsis o gangrena. Generalmente se asocia a insuficiencia renal severa y en otras ocasiones a alteraciones del metabolismo calcio-fósforo o al uso de corticoides para enfermedades autoinmunes. Se presenta como lesiones cutáneas que se pueden ulcerar o infectar, debiendo diferenciarlas de las lesiones de causa vascular mediante el estudio histológico de la biopsia de la lesión. La biopsia cutánea muestra alteraciones histológicas características que facilitan el diagnóstico diferencial de esta patología. Para su tratamiento, se deben identificar y corregir los posibles factores implicados en su aparición. El tiosulfato de sodio es útil para el tratamiento. Presentamos el caso de una paciente con insuficiencia renal leve que padeció dicha entidad con buena evolución tras tratamiento (AU)

Calciphylaxis is a relatively rare disease associated with high mortality rates due to potential complications of sepsis or gangrene. It is observed mainly in patients with severe kidney disease, and in other cases it is associated with altered calcium-phosphorus metabolism or to the use of corticosteroids in the treatment of autoimmune diseases. It is characterized by painful skin lesions that may become ulcerated or infected. We must differentiate them from vascular lesions through a histological study of the lesion biopsy. The skin biopsy shows characteristic histological findings that facilitate differential diagnosis. As a treatment we must identify and correct risk factors involved in its development. Sodium thiosulphate has proved to be an effective treatment. We present the case of a patient with mild kidney disease who suffered calciphylaxis with good outcome after treatment (AU)

Underlying Mechanisms of Pituitary-Thyroid Axis Function Disruption by Chronic Iodine Excess in Rats.

BACKGROUND: Iodine is essential for thyroid hormone synthesis and is an important regulator of thyroid function. Chronic iodine deficiency leads to hypothyroidism, but iodine excess also impairs thyroid function causing hyperthyroidism, hypothyroidism, and/or thyroiditis. This study aimed to investigate the underlying mechanisms by which exposure to chronic iodine excess impairs pituitary-thyroid axis function. METHODS: Male Wistar rats were treated for two months with NaI (0.05% and 0.005%) or NaI+NaClO4 (0.05%) dissolved in drinking water. Hormone levels, gene expression, and thyroid morphology were analyzed later. RESULTS: NaI-treated rats presented high levels of iodine in urine, increased serum thyrotropin levels, slightly decreased serum thyroxine/triiodothyronine levels, and a decreased expression of the sodium-iodide symporter, thyrotropin receptor, and thyroperoxidase mRNA and protein, suggesting a primary thyroid dysfunction. In contrast, thyroglobulin and pendrin mRNA and protein content were increased. Kidney and liver deiodinase type 1 mRNA expression was decreased in iodine-treated rats. Morphological studies showed larger thyroid follicles with higher amounts of colloid and increased amounts of connective tissue in the thyroid of iodine-treated animals. All these effects were prevented when perchlorate treatment was combined with iodine excess. CONCLUSIONS: The present data reinforce and add novel findings about the disruption of thyroid gland function and the compensatory action of increased thyrotropin levels in iodine-exposed animals. Moreover, they draw attention to the fact that iodine intake should be carefully monitored, since both deficient and excessive ingestion of this trace element may induce pituitary-thyroid axis dysfunction.

Absence seizure associated with coloprep consumption in colonoscopy / Convulsão de ausência com o uso de Coloprep em colonoscopia

Coloprep is a bowel preparatory solution given before endoscopic procedures to get a unobscured internal vision. It has among its constituent's sodium sulphate, potassium sulphate and magnesium sulphate which produce an osmotic effect in the bowel. However, the use of such agents in hyponatremic and patients predisposed to seizures can have adverse ramifications. The current case outlines manifestation of absence seizure in a 52-year-old male patient who was administered Coloprep for colonoscopy. There was absence of other predisposing factors and the symptoms were ameliorated using timely identification and rectification of the underlying derangements.

Coloprep é uma solução preparatória intestinal administrada antes de procedimentos endoscópicos, com o objetivo de se ter uma visão interna não obscurecida. Entre os constituintes de Coloprep, observa-se sulfato de sódio, sulfato de potássio e sulfato de magnésio, que provocam efeito osmótico no intestino. Mas o uso de tais agentes em pacientes hiponatrêmicos e com predisposição para convulsões pode ter ramificações adversas. O caso em tela delineia uma manifestação de convulsão de ausência em paciente do gênero masculino com 52 anos e que recebeu Coloprep para colonoscopia. Não havia outros fatores predisponentes e os sintomas melhoraram graças à oportuna identificação e correção dos transtornos subjacentes.

How sodium arsenite improve amyloid ß-induced memory deficit?

Evidence has shown that arsenic exposure, besides its toxic effects results in impairment of learning and memory, but its molecular mechanisms are not fully understood. In the present study, we examined sodium arsenite (1, 5, 10, 100nM) effects on contextual and tone memory of male rats in Pavlovian fear conditioning paradigm alone and in co-administration with ß-amyloid. We detected changes in the level of caspase-3, nuclear factor kappa-B (NF-κB), cAMP response element-binding (CREB), heme oxygenase-1 and NF-E2-related factor-2 (Nrf2) by Western blot. Sodium arsenite in high doses induced significant memory impairment 9 and 16days after infusion. By contrast, low doses of sodium arsenite attenuate memory deficit in Aß injected rats after 16days. Our data revealed that treatment with high concentration of sodium arsenite increased caspase-3 cleavage and NF-κB level, 9days after injection. Whereas, low doses of sodium arsenite cause Nrf2 and HO-1 activation and increased CREB phosphorylation in the hippocampus. These findings suggest the concentration dependent effects of sodium arsenite on contextual and tone memory. Moreover, it seems that the neuroprotective effects of ultra-low concentrations of sodium arsenite on Aß-induced memory impairment is mediated via an increase Nrf2, HO-1 and CREB phosphorylation levels and decrease caspase-3 and NF-κB amount.

Anti-leukemic effect of sodium metaarsenite (KML001) in acute myeloid leukemia with breaking-down the resistance of cytosine arabinoside.

Sodium metaarsenite (NaAs2O3: code name KML001) is an orally bioavailable arsenic compound with potential anti-cancer activity. However, the effect of KML001 has not been studied in acute myeloid leukemia (AML). We investigated the anti-leukemic effect of KML001 in AML, and determined the mode of action of KML001. KML001 inhibited the cellular proliferation in all AML cell lines and primary AML blasts as well as HL-60R (cytosine arabinoside-resistant HL-60) cells, while As2O3 was not effective in primary AML blasts and AML cell lines including HL-60R cells. KML001 induced G1 arrest and apoptosis in HL-60 and HL-60R cells. KML001 inhibited the activation of STAT (signal transducer and activator of transcription) 1, 3, 5, NF-κB, AKT and PI3K, while phosphorylated PTEN was upregulated. In addition, activation of ERK, p38 and JNK was observed in KML001-induced growth inhibition of HL-60 and HL-60R cells. Furthermore, KML001 induced telomeric terminal restriction fragment (TRF) length shortening in a time-dependent manner in HL-60 and HL-60R cells. Real­time PCR with RNA extracted from KML001-treated HL-60 and HL-60R cells showed a significant reduction of catalytic subunit of telomerase, hTERT, in a time-dependent manner. Additionally, γ-H2AX, a sensitive molecular marker of DNA damage, in HL-60 and HL-60R cells was induced by KML001. These results suggest that KML001 inhibits the proliferation of AML cells including cytosine arabinoside-resistant AML cells via various mechanisms such as cell cycle arrest, induction of apoptosis, inhibition of JAK/STAT and PI3K pathways, activation of MAPK pathway and telomere targeting.

Facing the nuclear threat: thyroid blocking revisited.

CONTEXT: People being exposed to potentially harmful amounts of radioactive iodine need prophylaxis to prevent high radiation-absorbed doses to the thyroid. OBJECTIVE: Parameters determining the individual protective effect of a pharmacological intervention were investigated. DESIGN AND PARTICIPANTS: Biokinetics of (123)I was evaluated in 27 healthy volunteers (aged 22-46 yr, median 25 yr, in total 48 assessments) twice in a baseline measurement of the undisturbed kinetics and in an intervention assessment 48 h later. INTERVENTIONS: Seven regimens using single doses of potassium iodide (KI) or sodium perchlorate (SP) at different times relative to exposure were compared: 100 mg KI (-24, 2, 8, 24 h), 100 mg SP (2 h), or 1 g SP (2, 8 h). MAIN OUTCOME MEASURES: Different drugs and dosages and the influence of individual parameters of iodine kinetics should be tested. RESULTS: Mean dose reductions for interventions at -24, 2, 8, and 24 h relative to the activity incorporation were 88.7, 59.7, 25.4, and 2.8%, respectively. One gram SP was equally effective as 100 mg KI; residual uptake was observed after 100 mg SP. The individual dose reduction decreased exponentially with the effective half-life of the activity in the blood. Kinetics in subjects older than 40 yr was as assumed in official guidelines for the prophylaxis after nuclear accidents but was faster in younger participants. CONCLUSIONS: Data on the efficacy of thyroid blocking used in the guidelines are adequate for older people but not for young individuals with their typically faster kinetics. SP may be used for thyroid blocking as alternative for individuals with iodine hypersensitivity.

The efficacy of bromides, stiripentol and levetiracetam in two patients with malignant migrating partial seizures in infancy.

The syndrome of malignant migrating partial seizures in infancy is a devastating, age-specific, epileptic encephalopathy, which still presents an aetiological, pathophysiological and therapeutic problem. In this study, we present two patients who were diagnosed with the disease, based on electroclinical symptoms. The patients were treated with a combination of sodium bromide, stiripentol and levetiracetam. The first patient unequivocally responded, following a course of ineffective conventional drugs, and the second, who was diagnosed and treated immediately, showed a more significant therapeutic response. Antiepileptic drugs, previously reported to be beneficial in case reports, when given concomitantly, may substantially reduce the number and severity of seizures, without influence on psychomotor development. [Published with video sequences].

Morphological changes of the neural cells after blast injury of spinal cord and neuroprotective effects of sodium beta-aescinate in rabbits.

OBJECTIVE: Explosive blast neurotrauma is becoming more and more common not only in the military population but also in civilian life due to the ever-present threat of terrorism and accidents. However, little attention has been offered to the studies associated with blast wave-induced spinal cord injury in the literatures. The purpose of this study is to report a rabbit model of explosive blast injury to the spinal cord, to investigate the histological changes, focusing especially on apoptosis, and to reveal whether beta-aescinate (SA) has the neuroprotective effects against the blast injury. METHODS: Adult male New Zealand white rabbits were randomly divided into sham group, experimental group and SA group. All rabbits except the sham group were exposed to the detonation, produced by the blast tube containing 0.7 g cyclotrimethylene trinitramine, with the mean peak overpressure of 50.4 MP focused on the dorsal surface of T9-T10 level. After evaluation of the neurologic function, spinal cord of the rabbits was removed at 8 h, 1, 3, 7, 14 or 30 days and the H&E staining, EM examination, DNA gel electrophoresis and TUNEL were progressively performed. RESULTS: The study demonstrated the occurrence of both necrosis and apoptosis at the lesion site. Moreover, the SA therapy could not only improve the neurologic outcomes (P<0.05) but also reduce the loss of motoneuron and TUNEL-positive rate (P<0.05). CONCLUSIONS: In the rabbit model of explosive blast injury to the spinal cord, the coexistent apoptotic and necrotic changes in cells was confirmed and the SA had neuroprotective effects to the blast injury of the spinal cord in rabbits. This is the first report in which the histological characteristics and drug treatment of the blast injury to the spinal cord is demonstrated.

Clinical signs, risk factors, and outcomes associated with bromide toxicosis (bromism) in dogs with idiopathic epilepsy.

OBJECTIVE: To evaluate clinical signs, risk factors, and outcomes associated with bromide toxicosis (bromism) in dogs with idiopathic epilepsy treated with potassium or sodium bromide. DESIGN: Retrospective case-control study. ANIMALS: 83 clinically ill epileptic dogs with (cases; n = 31) and without (controls; 52) bromism. PROCEDURES: Medical records were reviewed for information regarding signalment, epilepsy history, treatment, diet, clinicopathologic test results, concurrent diseases, clinical signs, and outcome. Case and control dogs were matched by the veterinary hospitals from which they were referred and by month of admission. A presumptive diagnosis of bromism was made in case dogs when treatment for primary clinical signs was limited to induction of diuresis or reduction in the dose of bromide administered, and this diagnosis was supported by serum bromide concentrations. Potential risk factors for bromism were identified via univariate and subsequent multivariate logistic regression analyses. RESULTS: Common clinical signs of bromism included alterations in consciousness, ataxia, and upper and lower motor neuron tetraparesis and paraparesis. The multivariate analysis identified bromide dose at admission to the hospital as the only factor significantly associated with bromism. In all dogs with bromism, treatment via dose reduction or facilitated renal excretion of bromide resulted in rapid clinical improvement, although breakthrough seizures happened during treatment in 8 of 31 (26%) dogs. CONCLUSIONS AND CLINICAL RELEVANCE: Bromism is a clinically heterogeneous, dose-dependent neurotoxicosis that is largely reversible with treatment. Regular serial monitoring of serum bromide concentrations is recommended to optimize anticonvulsant treatment in dogs with idiopathic epilepsy.

Sodium phosphates and colonoscopy: renal failure.

Sodium phosphate solutions used for bowel cleansing before colonoscopy increase the risk of renal failure, especially in the elderly or in patients treated with angiotensin-converting enzyme inhibitors or other drugs that can affect renal function.

Role of heat shock protein 70 in hepatic ischemia-reperfusion injury in mice.

It is well established that liver ischemia-reperfusion induces the expression of heat shock protein (HSP) 70. However, the biological function of HSP70 in this injury is unclear. In this study, we sought to determine the role of HSP70 in hepatic ischemia-reperfusion injury in mice. Male mice were subjected to 90 min of partial hepatic ischemia followed by up to 8 h of reperfusion. HSP70 was rapidly upregulated after reperfusion. To explore the function of HSP70, sodium arsenite (8 mg/kg iv) was injected before surgery. We found that this dose induced HSP70 expression within 6 h of treatment. Induction of HSP70 with arsenite resulted in a >50% reduction in liver injury as determined by serum transaminases and histology. In addition, arsenite similarly reduced liver neutrophil recruitment and liver nuclear factor-kappaB activation, and attenuated serum levels of tumor necrosis factor-alpha and macrophage inflammatory protein-2, but increased levels of interleukin (IL)-6. In HSP70 knockout mice, arsenite did not protect against liver injury but did reduce liver neutrophil accumulation. Arsenite-induced reductions in neutrophil accumulation in HSP70 knockout mice were found to be mediated by IL-6. To determine whether extracellular HSP70 contributed to the injury, recombinant HSP70 was injected before surgery. Intravenous injection of 10 microg of recombinant HSP70 had no effect on liver injury after ischemia-reperfusion. The data suggest that intracellular HSP70 is directly hepatoprotective during ischemia-reperfusion injury and that extracellular HSP70 is not a significant contributor to the injury response in this model. Targeted induction of HSP70 may represent a potential therapeutic option for postischemic liver injury.

Down-regulation of wt1 expression in leukemia cell lines as part of apoptotic effect in arsenic treatment using two compounds.

Arsenic trioxide (As2O3) induces remission in patients with acute promyelocytic leukemia (APL). To better understand molecular mechanisms of arsenic actions, this study investigated the effect of two different arsenic compounds on gene expression of apoptosis and cellular proliferation related genes. The Wilms' tumor gene (wt1) is up-regulated in acute myeloid leukemia (AML) and a variety of leukemia cell lines. The expression of wt1 in these cells is proposed to have an anti-apoptotic effect. HL-60 and K562 were treated with arsenic trioxide (As2O3) and sodium arsenite (NaAsO2) at concentrations between 0 - 10 microM for up to 48 h. The induction of apoptosis was accompanied by down-regulation of hTERT and wt1 mRNA and protein expression but up-regulation of par-4. Low concentrations of 0.1 microM arsenic induced expression of the anti-apoptotic bcl-2 gene in both cell lines HL-60 and K562. There were no major differences encountered between compounds. After arsenic treatment of the leukemia cell lines HL-60 and K562 the up-regulation of par-4 may contribute to the induction of apoptosis rather than down-regulation of bcl-2. The therapeutic effect of arsenic is the induction of apoptosis by modulating the gene expression profile of pro- and anti-apoptotic genes including the wt1 gene.

Epilepsy in Wolf-Hirschhorn syndrome (4p-).

PURPOSE: We investigated the evolution of epilepsy, seizure types, and effective drugs in Wolf-Hirschhorn syndrome, which is a malformation syndrome often with refractory seizures and status epilepticus. METHODS: We reviewed 11 cases of Wolf-Hirschhorn syndrome (age range, 2-25 years; SD, 7.2 years) and who were treated in Osaka University or Osaka Medical Center of Research Institute for Maternal and Child Health. RESULTS: In all patients, febrile or afebrile convulsions had developed. Epileptic seizures included alternative hemiconvulsions, generalized tonic-clonic seizures, focal clonic seizures, tonic seizures, and epileptic spasms. Seizures were often induced by a high fever or a hot bath. Status epilepticus occurred in all patients, including one patient who died at the first status epilepticus. In some cases, intratracheal intubation was needed because of respiratory insufficiency. The effective antiepileptic drugs for long-term use were sodium bromide (four of four), followed by clorazepate (CLP; one of two), and nitrazepam (NZP; two of four). Sodium bromide was particularly effective for preventing status epilepticus. The mean age of last status epilepticus in patients receiving sodium bromide (1 year 8 months) was significantly younger than that in those not treated with sodium bromide (3 year 4 months). CONCLUSIONS: We identified that, in most patients of Wolf-Hirschhorn syndrome, the frequency of both seizures and status epilepticus decreased gradually after age 5 years. However, during infancy, status epilepticus sometimes resulted in permanent disability or even death. We propose that sodium bromide should be used as the initial treatment for the prevention of the development of status epilepticus associated with Wolf-Hirschhorn syndrome.

Arsenic-induced alterations in the contact hypersensitivity response in Balb/c mice.

Previous studies in our laboratory indicate that arsenic alters secretion of growth promoting and inflammatory cytokines in the skin that can regulate the migration and maturation of Langerhans cells (LC) during allergic contact dermatitis. Therefore, we hypothesized that arsenic may modulate hypersensitivity responses to cutaneous sensitizing agents by altering cytokine production, LC migration, and T-cell proliferation. To investigate this hypothesis, we examined the induction and elicitation phases of dermal sensitization. Mice exposed to 50 mg/l arsenic in the drinking water for 4 weeks demonstrated a reduction in lymph node cell (LNC) proliferation and ear swelling following sensitization with 2,4-dinitrofluorobenzene (DNFB), compared to control mice. LC and T-cell populations in the draining lymph nodes of DNFB-sensitized mice were evaluated by fluorescence-activated cell sorting; activated LC were reduced in cervical lymph nodes, suggesting that LC migration may be altered following arsenic exposure. Lymphocytes from arsenic-treated animals sensitized with fluorescein isothiocyanate (FITC) exhibited reduced proliferative responses following T-cell mitogen stimulation in vitro; however, lymphocyte proliferation from nonsensitized, arsenic-treated mice was comparable to controls. Arsenic exposure also reduced the number of thioglycollate-induced peritoneal macrophages and circulating neutrophils. These studies demonstrate that repeated, prolonged exposure to nontoxic concentrations of sodium arsenite alters immune cell populations and results in functional changes in immune responses, specifically attenuation of contact hypersensitivity.