Parthenolide and DMAPT exert cytotoxic effects on breast cancer stem-like cells by inducing oxidative stress, mitochondrial dysfunction and necrosis.

Triple-negative breast cancers (TNBCs) are aggressive forms of breast carcinoma associated with a high rate of recidivism. In this paper, we report the production of mammospheres from three lines of TNBC cells and demonstrate that both parthenolide (PN) and its soluble analog dimethylaminoparthenolide (DMAPT) suppressed this production and induced cytotoxic effects in breast cancer stem-like cells, derived from dissociation of mammospheres. In particular, the drugs exerted a remarkable inhibitory effect on viability of stem-like cells. Such an effect was suppressed by N-acetylcysteine, suggesting a role of reactive oxygen species (ROS) generation in the cytotoxic effect. Instead z-VAD, a general inhibitor of caspase activity, was ineffective. Analysis of ROS generation, performed using fluorescent probes, showed that both the drugs stimulated in the first hours of treatment a very high production of hydrogen peroxide. This event was, at least in part, a consequence of activation of NADPH oxidases (NOXs), as it was reduced by apocynin and diphenylene iodinium, two inhibitors of NOXs. Moreover, both the drugs caused downregulation of Nrf2 (nuclear factor erythroid 2-related factor 2), which is a critical regulator of the intracellular antioxidant response. Prolonging the treatment with PN or DMAPT we observed between 12 and 24 h that the levels of both superoxide anion and hROS increased in concomitance with the downregulation of manganese superoxide dismutase and catalase. In addition, during this phase dissipation of mitochondrial membrane potential occurred together with necrosis of stem-like cells. Finally, our results suggested that the effect on ROS generation found in the first hours of treatment was, in part, responsible for the cytotoxic events observed in the successive phase. In conclusion, PN and DMAPT markedly inhibited viability of stem-like cells derived from three lines of TNBCs by inducing ROS generation, mitochondrial dysfunction and cell necrosis.

Torque Teno Virus--cause of viral liver disease following liver transplantation: a case report.

Torque Teno Virus (TTV), a nonenveloped human virus of the Circoviridae family, is hepatotropic, causing liver damage, cirrhosis, and, rarely, fulminant hepatitis. It prevails in 10% to 75% of blood donors due to environmental differences, independent of chronic hepatitis B virus (HBV)/HCV hepatitis, cryptogenic cirrhosis, alcoholic cirrhosis, and in fulminant hepatitis non-A-G. Reports about the efficacy of clinical alpha interferon are rare. In July 2007, a 65-year-old man who was serologically negative for A-E viruses presented with acute liver failure due to a ruptured hepatic artery aneurysm and underwent orthotopic liver transplantation (OLT). Immunosuppression was based on cyclosporine and steroids. At postoperative day 20, there was persistent hypertransaminasemia with otherwise normal liver function. A percutaneous hepatic biopsy documented pattern suggestive of a viral etiology. Multiple tests for hepatotropic viruses in the donor and the recipient from the pre- and post-OLT periods remained negative. Only the TTV qualitative test, assessed by polymerase chain reaction (PCR) on patient sera, was positive. Immunosuppressive therapy was not changed; no antiviral therapy was undertaken. At 6 months posttransplantation, transaminase levels spontaneously normalized and the clinical situation was unchanged. No complications were observed; the patient is in good clinical condition. No graft rejection was observed. In histologically proven non-A-E viral hepatitis, it is important to consider TTV as an incidental pathogenic agent. It may be useful to extend virological tests to TTV among transplant recipients and donors and to gain further knowledge about this virus.

Preliminary results of liver transplantation for hepatocellular carcinoma among allocation organ policy strategies, neoadjuvant treatments, and intention-to-treat analysis.

We retrospectively evaluated the impact of our strategy for patients with hepatocellular carcinoma (HCC) according to an intention-to-treat analysis and drop-out probability. We evaluated only patients within the Milan criteria. We analyzed the outcomes of neoadjuvant strategies for HCC, organ allocation policy, and systematic application of strategies to increase the deceased donor pool as the current tendency to expand transplantability criteria for those patients. Kaplan-Meier survival probability rates at 1, 3, and 5 years according to an intention-to-treat analysis were 87.02%, 74.53%, and 65.93% for transplanted patients (n=108), and 50%, 14.29%, and 14.29% for the excluded or waiting list group (n=13), respectively (P< .0001). Drop-out risk at 3, 6, and 12 months was 2.40%, 8.59%, and 16.54%, respectively. During the same period, the mortality probability rates at 3, 6, and 12 months among patients without HCC awaiting orthotopic liver transplantation (OLT) were 3.60%, 9.50%, and 18.34%, respectively. Drop-out rate was lower among patients treated before OLT (P< .0001). On the basis of the neoadjuvant treatment results to reduce drop-out risk, we suggest avoiding the high priority for the HCC cohort, particularly within the first 6 months from entrance on the waiting list, because this approach can reduce the chances of patients with end-stage liver disease (ESLD) alone.

Abnormally enhanced blood concentrations of vascular endothelial growth factor (VEGF) in metastatic cancer patients and their relation to circulating dendritic cells, IL-12 and endothelin-1.

Elevated VEGF blood concentrations have been proven to be associated with poor prognosis in human neoplasms. This finding is generally explained as a consequence of the potential angiogenic properties of VEGF itself. However, preliminary experimental studies suggest that VEGF, in addition to its angiogenic activity, may also play an immunosuppressant role by inhibiting dendritic cell (DC) maturation. The present study was performed to analyze blood levels of VEGF in cancer patients in relation to those of another potentially angiogenic tumor growth factor, endothelin-1 (ET-1), and to the absolute number of circulating immature and mature DC, and serum levels of the best known antitumor cytokine, IL-12. The study was performed in 100 healthy controls and in 80 solid tumor patients (colorectal cancer: 24; gastric cancer: 17; cancer of pancreas: 4; lung cancer: 13; breast cancer: 11; renal cell cancer: 6; gynecologic tumors: 5), 48 of whom showed distant organ metastases. In each patient, we have evaluated serum concentrations of VEGF-165, total VEGF, ET-1, IL-12 and the circulating number of immature (CD123+) and mature (CD11c+) DC. Mean serum levels of VEGF-165 were significantly higher in metastatic patients than in controls or in non-metastatic patients, whereas the total amounts of VEGF were not significantly higher. Moreover, it has been observed that patients with abnormally elevated blood concentrations of VEGF-165 showed significantly lower mean values of immature DC, mature DC and IL-12 and significantly higher mean levels of ET-1 than those with normal concentrations. This study, by confirming that advanced neoplastic disease may be associated with increased endogenous secretion of VEGF, seems to suggest that the association between high blood levels of VEGF and poor prognosis in cancer does not depend only on VEGF-induced stimulation of the neovascularization, but also on VEGF-related immunosuppression.

Surgery-induced decline in circulating dendritic cells in operable cancer patients: a possible explanation of postoperative immunosuppression.

BACKGROUND/AIMS: The recent advances in the immunobiology of tumor have demonstrated the essential role of dendritic cells in anticancer immunity. Dendritic cells activate anticancer immunity by secreting interleukin-12 and by activating T helper lymphocytes, with the following production of interleukin-2. Since surgery-induced immunosuppression has been proven to be associated with a decline in the blood levels of both interleukin-2 and interleukin-12, it could depend at least in part on a transient deficiency of dendritic cells system. Unfortunately, at present there are no data about changes in circulating dendritic cell number during the postoperative period. This preliminary study was performed to evaluate the influence of surgery on dendritic cell number in the peripheral blood. METHODOLOGY: The study included 14 consecutive operable gastrointestinal tract cancer patients, who were evaluated before and at day 7 of the postoperative period. The control group consisted of 50 healthy subjects. Immature (CD 123+) and mature (CD 11+) dendritic cell subsets were measured by FACS and monoclonal antibodies. RESULTS: Cancer patients showed a significantly lower mean number of immature dendritic cells with respect to that found in controls. The mean number of mature dendritic cells was also lower in patients than in controls, without, however, significant differences. Finally, surgery induced a statistically significant decline in the mean number of both immature and mature dendritic cells, and the decrease was particularly pronounced for immature dendritic cells. CONCLUSIONS: In addition to the well-demonstrated surgery-induced lymphocytopenia, this preliminary study shows that the surgical treatment may determine a significant decrease in circulating immature and mature dendritic cells. Because of the fundamental role of dendritic cells in regulating the immune responses, surgery-induced decline in circulating dendritic cells number could play a role in determining the immunosuppressive status, which characterizes the postoperative period.

Abrogation of surgery-induced decline in circulating dendritic cells by subcutaneous preoperative administration of IL-2 in operable cancer patients.

Surgery-induced immunosuppression is characterized by a decline in lymphocyte count, particularly T lymphocyte number. In addition, preliminary studies have shown that the postoperative period is also characterized by a decline in the number of circulating dendritic cells (DC), whose fundamental anticancer role has been recently demonstrated. Previous studies had already shown that the preoperative injection of IL-2 may completely abrogate surgery-induced lymphocytopenia, whereas its eventual influence on DC system during the perioperative period is still unknown. The present study was performed to evaluate the influence of IL-2 preoperative immunotherapy on the perioperative changes in circulating DC number in patients affected by colorectal cancer. The study included 14 consecutive patients, who were randomized to be treated with or without IL-2 presurgical immunotherapy (12 million IU/day for 3 days subcutaneously). Circulating immature and mature cells were evaluated before surgery and at days 3 and 7 of the postoperative period. The detection was made by FACS using monoclonal antibodies against CD123 and CD11c to recognize immature and mature DC, respectively. Surgery induced a significant decline in the mean number of both immature and mature DC. The pre-surgical administration of IL-2 completely abrogated surgery-induced decline in immature DC cell amount. Moreover, mature DC mean number was diminished only at day 3 of the postoperative period, since the value observed at day 7 was not significantly lower than that found before surgery. This preliminary study shows that surgery-induced immunosuppression is characterized also by a significant decline in the mean number of both immature and mature DC. Moreover, this study would suggest that the preoperative immunotherapy with IL-2 may counteract surgery-induced failure of DC system. Because of the fundamental antitumor role of DC, this evidence could have a prognostic impact on the clinical course of the neoplastic disease.

Unilateral blindness as a complication of intraoperative positioning for cervical spinal surgery.

The authors report a case of unilateral blindness after surgical vertebral stabilization for C5-C6 subluxation. The blindness resulted from ischemia of the retina caused by prolonged compression of the eyeball on the surgical bed. This injury can be serious and irreversible, so it must be prevented by placing the patient in the proper position. The anesthetist must pay particular attention to avoid the consequences of possible intraoperative movement.

Circulating immature and mature dendritic cells in relation to lymphocyte subsets in patients with gastrointestinal tract cancer.

Cancer-related deficiency in circulating dendritic cells (DC), whose important anticancer role is well established, has been proven to be associated with lymphocytopenia. This study was performed to evaluate which lymphocyte subset is most markedly related to the failure of the DC system. The study included 30 patients with gastrointestinal tract cancer, 10 of whom had distant organ metastases. Immature and mature DCs were measured by FACS and monoclonal antibodies against CD123 and CD11c antigens, respectively. Low levels of immature and mature DCs were observed in 63% and 43% of patients, respectively. Patients with low levels of circulating mature DCs had significantly lower values of T lymphocytes, T helper lymphocytes and NK cells than those with normal mature DC levels. In contrast, no significant difference was seen between patients with normal or abnormally low values of immature DCs. Conversely, patients with a decreased number of T lymphocytes, T helper lymphocytes and NK cells showed significantly lower values of circulating mature DCs than those with lymphocyte subsets within the normal range, whereas no difference was seen in immature DC amounts. This study suggests that only mature DC deficiency may be associated with important lymphocyte subset alterations in cancer patients, whereas deficiency in immature DCs does not seem to be related to other immune cell disorders.

Mice deficient in cellular glutathione peroxidase show increased vulnerability to malonate, 3-nitropropionic acid, and 1-methyl-4-phenyl-1,2,5,6-tetrahydropyridine.

Glutathione peroxidase (GSHPx) is a critical intracellular enzyme involved in detoxification of hydrogen peroxide (H(2)O(2)) to water. In the present study we examined the susceptibility of mice with a disruption of the glutathione peroxidase gene to the neurotoxic effects of malonate, 3-nitropropionic acid (3-NP), and 1-methyl-4-phenyl-1,2,5,6-tetrahydropyridine (MPTP). Glutathione peroxidase knock-out mice showed no evidence of neuropathological or behavioral abnormalities at 2-3 months of age. Intrastriatal injections of malonate resulted in a significant twofold increase in lesion volume in homozygote GSHPx knock-out mice as compared to both heterozygote GSHPx knock-out and wild-type control mice. Malonate-induced increases in conversion of salicylate to 2,3- and 2, 5-dihydroxybenzoic acid, an index of hydroxyl radical generation, were greater in homozygote GSHPx knock-out mice as compared with both heterozygote GSHPx knock-out and wild-type control mice. Administration of MPTP resulted in significantly greater depletions of dopamine, 3,4-dihydroxybenzoic acid, and homovanillic acid in GSHPx knock-out mice than those seen in wild-type control mice. Striatal 3-nitrotyrosine (3-NT) concentrations after MPTP were significantly increased in GSHPx knock-out mice as compared with wild-type control mice. Systemic 3-NP administration resulted in significantly greater striatal damage and increases in 3-NT in GSHPx knock-out mice as compared to wild-type control mice. The present results indicate that a knock-out of GSHPx may be adequately compensated under nonstressed conditions, but that after administration of mitochondrial toxins GSHPx plays an important role in detoxifying increases in oxygen radicals.

Tissue transglutaminase is increased in Huntington's disease brain.

The polyglutamine-expanded N-terminal region of mutant huntingtin causes neurodegeneration in Huntington's disease (HD). Neuronal intranuclear and cytosolic inclusions composed of mutant huntingtin are found in brains of HD patients. Because tissue transglutaminase cross-links proteins into filamentous aggregates and polypeptide-bound glutamines are primary determining factors for tissue transglutaminase-catalyzed reactions, it has been hypothesized that tissue transglutaminase may contribute to the formation of these aggregates. In this report immunohistochemical and biochemical methods were used to demonstrate that tissue transglutaminase expression and transglutaminase activity are elevated in HD brains in a grade-dependent manner. In the striatum, tissue transglutaminase activity was significantly increased in the grade 3 HD cases compared with controls. When normalized to the neuronal marker calbindin D28k, immunoblot analysis revealed that in the striatum the levels of tissue transglutaminase were significantly increased in all HD cases compared with controls. Immunohistochemical staining of the HD striatum revealed that tissue transglutaminase immunoreactivity was markedly increased in all grades as compared with controls. In the superior frontal cortex, tissue transglutaminase activity was significantly higher in all HD cases as compared with controls. Quantitative analysis of immunoblots demonstrated that tissue transglutaminase levels were elevated in HD grades 2 and 3 cases. Tissue transglutaminase immunoreactivity within the superior frontal neocortex was also greater in all the HD cases compared with controls. These data clearly indicate that tissue transglutaminase is elevated in HD brain and may play a role in the disease process.

Oxidative stress is attenuated in mice overexpressing BCL-2.

The protooncogene Bcl-2 inhibits apoptosis in neural cells, which may involve mitochondrial stabilization and decreased generation of reactive oxygen species. Using in vivo microdialysis we found that following administration of the mitochondrial toxin 3-nitropropionic acid (3-NP) there was a significant increase in the conversion of 4-hydroxybenzoic acid (4-HBA) to 3,4-dihydroxybenzoic acid (3,4-DHBA) in control mice, but not in Bcl-2 overexpressing mice. Striatal lesions were observed in littermate control mice, whereas, lesions were minimal or absent in Bcl-2 overexpressing mice. This shows that Bcl-2 overexpression in vivo attenuates the generation of reactive oxygen species.

Neuroprotective effects of creatine and cyclocreatine in animal models of Huntington's disease.

The gene defect in Huntington's disease (HD) may result in an impairment of energy metabolism. Malonate and 3-nitropropionic acid (3-NP) are inhibitors of succinate dehydrogenase that produce energy depletion and lesions that closely resemble those of HD. Oral supplementation with creatine or cyclocreatine, which are substrates for the enzyme creatine kinase, may increase phosphocreatine (PCr) or phosphocyclocreatine (PCCr) levels and ATP generation and thereby may exert neuroprotective effects. We found that oral supplementation with either creatine or cyclocreatine produced significant protection against malonate lesions, and that creatine but not cyclocreatine supplementation significantly protected against 3-NP neurotoxicity. Creatine and cyclocreatine increased brain concentrations of PCr and PCCr, respectively, and creatine protected against depletions of PCr and ATP produced by 3-NP. Creatine supplementation protected against 3-NP induced increases in striatal lactate concentrations in vivo as assessed by 1H magnetic resonance spectroscopy. Creatine and cyclocreatine protected against malonate-induced increases in the conversion of salicylate to 2,3- and 2,5-dihydroxybenzoic acid, biochemical markers of hydroxyl radical generation. Creatine administration protected against 3-NP-induced increases in 3-nitrotyrosine concentrations, a marker of peroxynitrite-mediated oxidative injury. Oral supplementation with creatine or cyclocreatine results in neuroprotective effects in vivo, which may represent a novel therapeutic strategy for HD and other neurodegenerative diseases.

Inhibition of white blood cell adhesion at reperfusion decreases tissue damage in postischemic striated muscle.

PURPOSE: To determine the impact of white blood cell (WBC)-endothelium adhesion on tissue damage in the setting of ischemia-reperfusion injury in striated muscle. METHODS: The cremaster muscle of four groups of anesthetized Sprague-Dawley rats was subjected to 4 hours of global, warm (37 degrees C) ischemia and 2 hours of reperfusion. At reperfusion two groups of animals received intravenous injections of monoclonal antibodies directed against either CD11b/CD18 (1B6) or ICAM-1 (1A29). The remaining two groups of animals received saline injections (NoRx) or nonreactive IgG1. In vivo light microscopic techniques were used to determine WBC adherence (number of WBCs per 100 microns postcapillary venules) at different intervals of reperfusion. Muscle viability was assessed with computer-assisted image analysis by measuring the optical intensity of transilluminated muscles after incubation with nitroblue tetrazolium. RESULTS: Our results (mean +/- SEM) demonstrate a significant increase in the number of adherent WBCs relative to baseline (8.0 +/- 0.5) after 4 hours of global ischemia in animals receiving NoRx or IgG1. The significant increase occurred at 30 minutes of reperfusion (17.6 +/- 0.6 and 17.4 +/- 0.4 for NoRx or IgG1, respectively) and was sustained for the duration of the experiment. This increase in adherence was attenuated by 1B6 and 1A29 (12.2 +/- 2.2 and 12.4 +/- 0.8, respectively; p < 0.05 compared with NoRx and IgG1). The decrease in WBC adhesion was associated with a decrease in reperfusion injury to the muscle, as indicated by lower optical intensity values for the 1B6 and 1A29 groups (123 +/- 3 and 129 +/- 2) compared with the NoRx and IgG1 groups (151 +/- 2 and 158 +/- 4). CONCLUSIONS: Our data support an important role for WBCs in the pathogenesis of ischemia-reperfusion injury. Interfering with the WBC-endothelium interactions by using monoclonal antibodies directed against WBCs and endothelial cell adhesion molecules may help to limit ischemia-reperfusion injury.

Motor neurons in Cu/Zn superoxide dismutase-deficient mice develop normally but exhibit enhanced cell death after axonal injury.

The discovery that some cases of familial amyotrophic lateral sclerosis (FALS) are associated with mutations in the gene encoding Cu/Zn superoxide dismutase (SOD1) has focused much attention on the function of SOD1 as related to motor neuron survival. Here we describe the creation and characterization of mice completely deficient for this enzyme. These animals develop normally and show no overt motor deficits by 6 months in age. Histological examination of the spinal cord reveals no signs of pathology in animals 4 months in age. However Cu/Zn SOD-deficient mice exhibit marked vulnerability to motor neuron loss after axonal injury. These results indicate that Cu/Zn SOD is not necessary for normal motor neuron development and function but is required under physiologically stressful conditions following injury.

Blockade of neuronal nitric oxide synthase protects against excitotoxicity in vivo.

Nitric oxide may be a key mediator of excitotoxic neuronal injury in the central nervous system. We examined the effects of the neuronal nitric oxide synthase inhibitor 7-nitroindazole (7-NI) on excitotoxic striatal lesions. 7-NI significantly attenuated lesions produced by intrastriatal injections of NMDA, but not kainic acid or alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) 7-NI attenuated secondary striatal excitotoxic lesions produced by the succinate dehydrogenase inhibitor malonate, and the protection was reversed by L-arginine but not by D-arginine, 7-NI produced nearly complete protection against striatal lesions produced by systemic administration of 3-nitropropionic acid (3-NP), another succinate dehydrogenase inhibitor, 7-NI protected against malonate induced decreases in ATP, and increases in lactate, as assessed by 1H magnetic resonance spectroscopy. 7-NI had no effects on spontaneous electrophysiologic activity in the striatum in vivo, suggesting that its effects were not mediated by an interaction with excitatory amino acid receptors. 7-NI attenuated increases in hydroxyl radical, 8-hydroxy-2-deoxyguanosine and 3-nitrotyrosine generation in vivo, which may be a consequence of peroxynitrite formation. The present results implicate neuronal nitric oxide generation in the pathogenesis of both direct and secondary excitotoxic neuronal injury in vivo. As such they suggest that neuronal nitric oxide synthase inhibitors may be useful in the treatment of neurologic diseases in which excitotoxic mechanisms play a role.

3-Acetylpyridine produces age-dependent excitotoxic lesions in rat striatum.

The effects of 3-acetylpyridine (3-AP) were studied in rat striatum. Striatal injections of 3-AP produced dose-dependent lesions. The lesion size was significantly increased in 4- and 12-month-old rats compared to 1-month-old rats. Coinjection of the competitive N-methyl-D-aspartate (NMDA) antagonist 2-amino-5-phosphonovaleric acid (APV) or systemic administration of the noncompetitive NMDA antagonist MK-801, the competitive NMDA antagonist LY274614, or the glutamate release inhibitor lamotrigine partially but significantly attenuated striatal lesion volume. Consistent with an NMDA receptor-mediated excitotoxic effect, histologic studies showed that 3-AP lesions result in relative sparing of NADPH-diaphorase neurons. Using freeze clamp, 3-AP resulted in a marked depletion of ATP. Two-dimensional water-suppressed proton chemical shift magnetic resonance imaging showed a striatal depletion of the neuronal marker N-acetylaspartate but no focal increase in lactate during the first 3 h after intrastriatal 3-AP injections. Pretreatment with fructose-1,6-biphosphate attenuated the lesion volume significantly, which may be due to its ability to serve as a substrate for glycolytic metabolism, with resulting ATP production. The results of the present studies support the hypothesis that 3-AP produces an impairment of energy metabolism due to its substitution for niacinamide in the formation of NAD(P). Furthermore, 3-AP toxicity may involve a secondary excitotoxic mechanism mediated by NMDA receptors.

In healthy primates, circulating autoreactive T cells mediate autoimmune disease.

A T cell response against myelin basic protein (MBP) is thought to contribute to the central nervous system (CNS) inflammation that occurs in the human demyelinating disease multiple sclerosis. To test whether MBP-reactive T cells that are normally retrieved from the circulation are capable of inducing CNS disease, MBP-reactive T cell clones were isolated from the peripheral blood of healthy, unimmunized Callithrix jacchus (C. jacchus) marmosets. This primate species is characterized by a natural chimerism of bone marrow elements between siblings that should make possible adoptive transfer of MBP-reactive T cells. We report that MBP-reactive T cell clones efficiently and reproducibly transfer CNS inflammatory disease between members of C. jacchus chimeric sets. The demyelination that is characteristic of experimental allergic encephalomyelitis induced in C. jacchus by immunization against human white matter did not occur after adoptive transfer of the MBP-reactive clones. It was noteworthy that encephalitogenic T cell clones were diverse in terms of their recognition of different epitopes of MBP, distinguishing the response in C. jacchus from that in some inbred rodents in which restricted recognition of MBP occurs. These findings are the first direct evidence that natural populations of circulating T cells directed against a CNS antigen can mediate an inflammatory autoimmune disease.

Histologic assessment of dose-related diffusion and muscle fiber response after therapeutic botulinum A toxin injections.

Fiber diameter variability, acetylcholinesterase staining properties, and average fiber diameter were determined 5 weeks after varying doses of botulinum A toxin were administered into albino rabbit longissimus dorsi muscle. The average fiber diameter within the muscle appeared to be a function of the dose of botulinum toxin injected. Fiber diameter variability correlated with the dose of botulinum toxin administered. Both fiber diameter variability and acetylcholinesterase spread characteristics showed a distinct diffusion gradient over a defined field within a muscle. At lower doses (1 IU), collapse of the diffusion gradient occurred over a 15-30-mm segment of muscle. At higher doses (5-10 IU), diffusion of botulinum A toxin effect occurred throughout the entire muscle with no apparent end point. This study demonstrated that botulinum A toxin produces a gradient of denervation in a given muscle and that both the magnitude of denervation and the extent of the gradient are dose dependent. Furthermore, both muscle fiber diameter variability and acetylcholinesterase staining were useful as measures of chemodenervation.