Immunological Characteristics of Hyperprogressive Disease in Patients with Non-small Cell Lung Cancer Treated with Anti-PD-1/PD-L1 Abs

Hyperprogressive disease (HPD) is a distinct pattern of progression characterized by acceleration of tumor growth after treatment with anti-PD-1/PD-L1 Abs. However, the immunological characteristics have not been fully elucidated in patients with HPD. We prospectively recruited patients with metastatic non-small cell lung cancer treated with anti-PD-1/PD-L1 Abs between April 2015 and April 2018, and collected peripheral blood before treatment and 7-days post-treatment. HPD was defined as ≥2-fold increase in both tumor growth kinetics and tumor growth rate between pre-treatment and post-treatment. Peripheral blood mononuclear cells were analyzed by multi-color flow cytometry to phenotype the immune cells. Of 115 patients, 19 (16.5%) developed HPD, 52 experienced durable clinical benefit (DCB; partial response or stable disease ≥6 months), and 44 experienced non-hyperprogressive progression (NHPD). Patients with HPD had significantly lower progression-free survival (p<0.001) and overall survival (p<0.001). When peripheral blood immune cells were examined, the pre-treatment frequency of CD39⁺ cells among CD8⁺ T cells was significantly higher in patients with HPD compared to those with NHPD, although it showed borderline significance to predict HPD. Other parameters regarding regulatory T cells or myeloid derived suppressor cells did not significantly differ among patient groups. Our findings suggest high pre-treatment frequency of CD39⁺CD8⁺ T cells might be a characteristic of HPD. Further investigations in a larger cohort are needed to confirm our results and better delineate the immune landscape of HPD.

Early reduction of regulatory T cells is associated with acute rejection in liver transplantation under tacrolimus-based immunosuppression with basiliximab induction

Regulatory T (Treg) cells are important in preventing acute rejection (AR) in solid organ transplantation, but the clinical relevance of the different kinetics early after liver transplantation (LT) in acute rejectors and non-rejectors is unclear. We analyzed peripheral blood samples of 128 LT recipients receiving basiliximab induction plus tacrolimus immunosuppression. Samples were obtained at pretransplant, D7, and D30 after LT. Frequency and phenotype of Tregs were analyzed by flow cytometry. The predictive value of Treg frequency at D7 was assessed for suspected acute rejection (SAR) and was validated for biopsy-proven AR (BPAR). We found that the frequencies of total and activated Tregs at D7 were significantly lower in recipients with SAR and BPAR. Treg was more reduced in BPARs by in vitro tacrolimus treatment in the presence of basiliximab. Moreover, an early reduction of Treg frequency in rejectors was associated with a greater increase in Treg apoptosis and further attenuated IL-2 signaling. D7 Treg frequency was an independent risk factor for SAR, which was also validated for BPAR. In conclusion, first-week peripheral blood Treg frequency correlates with AR after LT under tacrolimus-based immunosuppression, which needs to be proven in larger, geographically and clinically diverse populations.

IFNL3-adjuvanted HCV DNA vaccine reduces regulatory T cell frequency and increases virus-specific T cell responses

BACKGROUND & AIMS

Although direct-acting antiviral (DAA) treatment results in a sustained virologic response (SVR) in most patients with chronic HCV infection, they are at risk of re-infection. Moreover, the immune system is not completely normalized even after SVR (e.g. increased regulatory T [Treg] cell frequency). We developed a DNA vaccine, GLS-6150, to prevent re-infection of patients with DAA-induced SVR and evaluated its safety and immunogenicity in individuals with chronic HCV infection.

METHODS

GLS-6150 consists of plasmids encoding HCV non-structural proteins (NS3-NS5A) and adjuvant IFNL3. The vaccine was administered 4 times at 4-weekly intervals to 3 groups (1, 3, or 6 mg/vaccination; n = 6 per group), followed by a 6 mg boost at 24 weeks (n = 14). Peripheral blood T cell responses were evaluated by interferon (IFN)-γ enzyme-linked immunospot assays, intracellular cytokine staining, and major histocompatibility complex class-I (MHC-I) dextramer staining. Treg cell frequency was assessed by flow cytometry.

RESULTS

Severe adverse events or vaccine discontinuation were not reported. The IFN-γ spot-forming cells specific to NS3-NS5A were increased by GLS-6150. Both CD4+ and CD8+ T cells produced multiple cytokines. However, the frequency and phenotype of HCV-specific MHC-I dextramer+CD8+ T cells were not changed. Interestingly, the frequency of Treg cells, particularly activated Treg cells, was decreased by GLS-6150, as expected from previous reports that IFNL3 adjuvants decrease Treg cell frequency. Ex vivo IFN-λ3 treatment reduced Treg frequency in pre-vaccination peripheral blood mononuclear cells. Finally, Treg cell frequency inversely correlated with HCV-specific, IFN-γ-producing T cell responses in the study participants.

CONCLUSIONS

We demonstrate that GLS-6150 decreases Treg cell frequency and enhances HCV-specific T cell responses without significant side effects. A phase I clinical trial of GLS-6150 is currently underway in patients with DAA-induced SVR.

CLINICAL TRIAL NUMBER

NCT02027116.

LAY SUMMARY

Although direct-acting antivirals (DAAs) are successfully used for the treatment of chronic hepatitis C virus (HCV) infection, a prophylactic HCV vaccine needs to be developed, especially for patients who achieve a sustained virologic response. In the current study, we show that a DNA vaccine (GLS-6150) was safe and increased HCV-specific T cell responses. A clinical trial is underway to test this vaccine in patients with a sustained virologic response following DAA therapy.

Functions of human liver CD69+CD103-CD8+ T cells depend on HIF-2α activity in healthy and pathologic livers

BACKGROUND & AIMS

Human liver CD69⁺CD8⁺ T cells are ~95% CD103^- and ~5% CD103⁺. Although CD69⁺CD103⁺CD8⁺ T cells show tissue residency and robustly respond to antigens, CD69⁺CD103^-CD8⁺ T cells are not yet well understood.

METHODS

Liver perfusate and paired peripheral blood were collected from healthy living donors and recipients with cirrhosis during liver transplantation. Liver tissues were obtained from patients with acute hepatitis A. Phenotypic and functional analyses were performed by flow cytometry. Gene expression profiles were determined by microarray and quantitative reverse transcription PCR. PT-2385 was used to inhibit hypoxia-inducible factor (HIF)-2α.

RESULTS

Human liver CD69⁺CD103^-CD8⁺ T cells exhibited HIF-2α upregulation with a phenotype of tissue residency and terminal differentiation. CD103^- cells comprised non-hepatotropic virus-specific T cells as well as hepatotropic virus-specific T cells, but CD103⁺ cells exhibited only hepatotropic virus specificity. Although CD103^- cells were weaker effectors on a per cell basis than CD103⁺ cells, following T cell receptor or interleukin-15 stimulation, they remained the major CD69⁺CD8⁺ effector population in the liver, surviving with less cell death. An HIF-2α inhibitor suppressed the effector functions and survival of CD69⁺CD103^-CD8⁺ T cells. In addition, HIF-2α expression in liver CD69⁺CD103^-CD8⁺ T cells was significantly increased in patients with acute hepatitis A or cirrhosis.

CONCLUSIONS

Liver CD69⁺CD103^-CD8⁺ T cells are tissue resident and terminally differentiated, and their effector functions depend on HIF-2α. Furthermore, activation of liver CD69⁺CD103^-CD8⁺ T cells with HIF-2α upregulation is observed during liver pathology.

LAY SUMMARY

The immunologic characteristics and the role of CD69⁺CD103^-CD8⁺ T cells, which are a major population of human liver CD8⁺ T cells, remain unknown. Our study shows that these T cells have a terminally differentiated tissue-resident phenotype, and their effector functions depend on a transcription factor, HIF-2α. Furthermore, these T cells were activated and expressed higher levels of HIF-2α in liver pathologies, suggesting that they play an important role in immune responses in liver tissues and the pathogenesis of human liver disease.

Immune-related adverse events are clustered into distinct subtypes by T-cell profiling before and early after anti-PD-1 treatment

Although anti-programmed death-1 (PD-1) treatment has shown remarkable anti-tumor efficacy, immune-related adverse events (irAEs) develop with heterogeneous clinical manifestations. However, the immunological understanding of irAEs is currently limited. In the present study, we analyzed peripheral blood T cells obtained from cancer patients who received anti-PD-1 treatment to determine the immunological characteristics of irAEs. This study included 31 patients with refractory thymic epithelial tumor (TET) who were enrolled in a phase II trial of pembrolizumab (NCT02607631) and 60 patients with metastatic non-small cell lung cancer (NSCLC) who received pembrolizumab or nivolumab. T-cell profiling was performed by multicolor flow cytometry using peripheral blood obtained before treatment and 7 days after the first dose of anti-PD-1 antibodies. irAEs developed in 21 TET patients and 24 NSCLC patients. Severe (≥ grade 3) irAEs occurred in 7 TET patients (22.6%) and 6 NSCLC patients (10.0%). Patients with severe irAEs exhibited a significantly lower fold increase in the frequency of effector regulatory T (eTreg) cells after anti-PD-1 treatment, a higher ratio of T helper-17 (Th17) and T helper-1 cells at baseline, and a higher percentage of Ki-67⁺ cells among PD-1⁺CD8⁺ T cells posttreatment. In clustering analysis using the T-cell parameters, patients with irAEs were grouped into four distinct subtypes: Th17-related, TNF-related, CD8-related Treg-compensated, and CD8-related Treg-uncompensated. The T-cell parameters showed a predictive value for the development of each subtype of severe irAEs. In conclusion, severe irAEs after anti-PD-1 treatment were clustered into four immunological subtypes, and potential biomarkers for early prediction of severe irAEs were proposed.

Involvement of the BLT2 receptor in the itch-associated scratching induced by 12-(S)-lipoxygenase products in ICR mice

BACKGROUND AND PURPOSE

Recently, we reported that 12(S)-HPETE (12(S)-hydroperoxyeicosa-5Z,8Z,10E,14Z-tetraenoic acid) induces scratching in ICR mice. We hypothesized that 12(S)-HPETE might act as an agonist of the low-affinity leukotriene B4 receptor BLT2. To confirm the involvement of the BLT2 receptor in 12(S)-HPETE-induced scratching, we studied the scratch response using the BLT2 receptor agonists compound A (4'-[[pentanoyl (phenyl) amino]methyl]-1,1'-biphenyl-2-carboxylic acid) and 12(S)-HETE (12(S)-hydroxyeicosa-5Z,8Z,10E,14Z-tetraenoic acid).

EXPERIMENTAL APPROACH

A video recording was used to determine whether the BLT2 receptor agonists caused itch-associated scratching in ICR mice. Selective antagonists and several chemicals were used.

KEY RESULTS

Both 12(S)-HETE and compound A dose dependently induced scratching in the ICR mice. The dose-response curve for compound A showed peaks at around 0.005-0.015 nmol per site. Compound A- and 12(S)-HETE-induced scratching was suppressed by capsaicin and naltrexon. We examined the suppressive effects of U75302 (6-[6-(3-hydroxy-1E,5Z-undecadienyl)-2-pyridinyl]-1,5-hexanediol, the BLT1 receptor antagonist) and LY255283 (1-[5-ethyl-2-hydroxy-4-[[6-methyl-6-(1H-tetrazol-5-yl)heptyl]oxy]phenyl]-ethanone, the BLT2 receptor antagonist) on the BLT2 agonist-induced scratching. LY255283 suppressed compound A- and 12(S)-HETE-induced scratching, but U75302 did not. LY255283 required a higher dose to suppress the compound A-induced scratching than it did to suppress the 12(S)-HETE-induced scratching. One of the BLT(2) receptor agonists, 12(R)-HETE (12(R)-hydroxyeicosa-5Z,8Z,10E,14Z-tetraenoic acid), also induced scratching in the ICR mice.

CONCLUSIONS AND IMPLICATIONS

Our present results corroborate the hypothesis that the BLT2 receptor is involved in 12(S)-lipoxygenase-product-induced scratching in ICR mice. We also confirmed that this animal model could be a valuable means of evaluating the effects of BLT2 receptor antagonists.

A Novel Phospholipid Derivative of Indomethacin, DP-155 [Mixture of 1-Steroyl and 1-Palmitoyl-2-{6-[1-(p-chlorobenzoyl)-5-methoxy-2-methyl-3-indolyl acetamido]hexanoyl}-sn-glycero-3-phosophatidyl Choline], Shows Superior Safety and Similar Efficacy in Reducing Brain Amyloid β in an Alzheimer's Disease Model

Indomethacin has been suggested for the treatment of Alzheimer's disease (AD), but its use is limited by gastrointestinal and renal toxicity. To overcome this limitation, D-Pharm Ltd. (Rehovot, Israel) developed DP-155 (mixture of 1-steroyl and 1-palmitoyl-2-{6-[1-(p-chlorobenzoyl)-5-methoxy-2-methyl-3-indolyl acetamido] hexanoyl}-Sn-glycero-3-phosophatidyl [corrected] choline), a lecithin derivative of indomethacin. Safety was tested by daily oral administration of DP-155 or indomethacin to rats in a dose range of 0.007 to 0.28 mmol/kg. The prevalence of gastrointestinal ulceration was significantly lower (10-fold) for DP-155 than for indomethacin, and the ulcerations were delayed. Signs of renal toxicity, namely reduced urine output and increased urine N-acetyl glycosaminidase to creatinine ratio, were 5-fold lower for DP-155. Indomethacin, but not an equimolar dose of DP-155, reduced urine bicyclo-prostaglandin E(2). An equimolar oral dose of DP-155 or indomethacin, administered every 4 h for 3 days, was equally efficacious in reducing the levels of Abeta42 in the brains of Tg2576 mice. Indomethacin was the principal metabolite of DP-155 in the serum. After DP-155 oral administration, indomethacin's half-life in the serum and the brain was 22 and 93 h, respectively, compared with 10 and 24 h following indomethacin oral administration. The brain to serum ratio was 3.5 times higher for DP-155 than indomethacin. This finding explains the efficacy of DP-155 in reducing Abeta42 brain levels, despite the low systemic blood concentrations of indomethacin derived from DP-155. In conclusion, compared with indomethacin, DP-155 has significantly lower toxicity in the gut and kidney while maintaining similar efficacy to indomethacin in lowering Abeta42 in the brains of Tg2576 mice. This superior safety profile highlights DP-155's potential as an improved indomethacin-based therapy for AD.

Characterization of the TSU-PR1 cell line by chromosome painting and flow cytometry

TSU-PR1 was originally reported as a prostatic carcinoma cell line derived from a lymph node metastasis. Recently, however, this cell line was reported to be derived from T24 bladder carcinoma cells, and thus further definition of its origin is needed. Conventional cytogenetic study of TSU-PR1 showed aneuploidy, ranging from 65 to 86 chromosome with a modal number of 80, and with 10 marker chromosomes, thus conventional cytogenetics cannot be used to determine which chromosomes or regions of chromosomes are critical in cancer development and progression of this cell line. The present study was conducted to characterize genetic changes of the cell line using comparative genomic hybridization (CGH), fluorescence in situ hybridization (FISH), and flow cytometry. CGH results showed that green-to-red fluorescence ratios were within the range of 0.85-1.15, except for a few chromosomes, which reflected near tetraploidy in TSU-PR1. Flow cytometric analysis of TSU-PR1 revealed a DNA index of 3.46n, which is close to the 3.48n calculated from a modal number of 80. The copy numbers of chromosomes 4, 6, 7, 17, and 20 determined by the DNA index and the CGH analyses were 2.85 +/- 0.09, 3.22 +/- 0.77, 3.01 +/- 0.26, 4.05 +/- 0.44, and 4.99 +/- 0.48, respectively. These numbers are also in accordance with the chromosome copy numbers determined with FISH: 2.98 +/- 0.23, 2.91 +/- 0.44, 2.74 +/- 0.44, 3.93 +/- 0.38, and 5.05 +/- 0.78 for chromosomes 4, 6, 7, 17, and 20, respectively (P > 0.05).

A stomatin and a degenerin interact in lipid rafts of the nervous system of Caenorhabditis elegans

In Caenorhabditis elegans, the gene unc-1 controls anesthetic sensitivity and normal locomotion. The protein UNC-1 is a close homolog of the mammalian protein stomatin and is expressed primarily in the nervous system. Genetic studies in C. elegans have shown that the UNC-1 protein interacts with a sodium channel subunit, UNC-8. In humans, absence of stomatin is associated with abnormal sodium and potassium levels in red blood cells. Stomatin also has been postulated to participate in the formation of lipid rafts, which are membrane microdomains associated with protein complexes, cholesterol, and sphingolipids. In this study, we isolated a low-density, detergent-resistant fraction from cell membranes of C. elegans. This fraction contains cholesterol, sphingolipids, and protein consistent with their identification as lipid rafts. We then probed Western blots of protein from the rafts and found that the UNC-1 protein is almost totally restricted to this fraction. The UNC-8 protein is also found in rafts and coimmunoprecipitates UNC-1. A second stomatin-like protein, UNC-24, also affects anesthetic sensitivity, is found in lipid rafts, and regulates UNC-1 distribution. Mutations in the unc-24 gene alter the distribution of UNC-1 in lipid rafts. Each of these mutations alters anesthetic sensitivity in C. elegans. Because lipid rafts contain many of the putative targets of volatile anesthetics, they may represent a novel class of targets for volatile anesthetics.

Overproduction of PDR3 suppresses mitochondrial import defects associated with a TOM70 null mutation by increasing the expression of TOM72 in Saccharomyces cerevisiae

Most mitochondrial proteins are synthesized with cleavable amino-terminal targeting signals that interact with the mitochondrial import machinery to facilitate their import from the cytosol. We previously reported that the presequence of the F(1)-ATPase beta subunit precursor (pre-F(1)beta) acts as an intramolecular chaperone that maintains the precursor in an import-competent conformation prior to import (P. Hajek, J. Y. Koh, L. Jones, and D. M. Bedwell, Mol. Cell. Biol. 17:7169-7177, 1997). We also found that a mutant form of pre-F(1)beta with a minimal targeting signal (Delta 1,2 pre-F(1)beta) is inefficiently imported into mitochondria because it rapidly folds into an import-incompetent conformation. We have now analyzed the consequences of reducing the pre-F(1)beta targeting signal to a minimal unit in more detail. We found that Delta 1,2 pre-F(1)beta is more dependent upon the Tom70p receptor for import than WT pre-F(1)beta is, resulting in a growth defect on a nonfermentable carbon source at 15 degrees C. Experiments using an in vitro mitochondrial protein import system suggest that Tom70p functions to maintain a precursor containing the Delta 1,2 pre-F(1)beta import signal in an import-competent conformation. We also identified PDR3, a transcriptional regulator of the pleiotropic drug resistance network, as a multicopy suppressor of the mitochondrial import defects associated with Delta 1,2 pre-F(1)beta in a tom70 Delta strain. The overproduction of PDR3 mediated this effect by increasing the import of Delta 1,2 pre-F(1)beta into mitochondria. This increased the mitochondrial ATP synthase activity to the extent that growth of the mutant strain was restored under the selective conditions. Analysis of the transcription patterns of components of the mitochondrial outer membrane import machinery demonstrated that PDR3 overproduction increased the expression of TOM72, a little studied TOM70 homologue. These results suggest that Tom72p possesses overlapping functions with Tom70p and that the pleiotropic drug resistance network plays a previously unappreciated role in mitochondrial biogenesis.

BAPTA/AM, an intracellular calcium chelator, induces delayed necrosis by lipoxygenase-mediated free radicals in mouse cortical cultures

1. Disruption of calcium homeostasis during neurodegenerative diseases is known to trigger apoptotic or necrotic death in neuronal cells. Recently, the authors reported that intracellular calcium restriction by NMDA receptor antagonists induces apoptosis in cortical cultures. To evaluate whether further restriction of intracellular free calcium can induce apoptosis or necrosis, we examined the neurotoxic characterization of BAPTA/AM, a permeable free calcium chelator, in mouse cortical cultures. 2. Exposure of mixed (glia and neuron) cortical cultures (DIV 13-16) to 3-10 microM BAPTA/AM (non-toxic concentration for glial cells) for 24-48 hr resulted in delayed and necrotic neuronal death. The necrotic findings included swelling and loss of mitochondria and endoplasmic reticulum (ER) with neuronal membrane rupture 24 hr after treatment with BAPTA/AM. Simultaneously, we observed a few TUNEL-positive cells in the neuronal subpopulation of the same cultures. 3. The neurotoxicity evoked by BAPTA/AM (10 microM) was significantly attenuated by the addition of 0.5 microM cycloheximide (a protein synthesis inhibitor), 10 microM actinomycin D (an RNA transcription inhibitor), a high extracellular potassium concentration (total 15 mM KCl), 100 microM t-ACPD (a metabotrophic agonist), 100 microM alpha-tocopherol (a free radical scavenger), 100 microM deferoxamine (a ferric ion chelator), 100 microM L-NAME (a nitric oxide synthase (NOS) inhibitor), 50 microM DNQX (a non-NMDA receptor blocker), and 3-30 microM esculetin (a lipoxygenase inhibitor). However, 0.3-3 mM ASA (a cyclooxygenase inhibitor), 100 ng/ml nerve growth factor (NGF), 10 microM MK-801 (a NMDA receptor antagonist), 20 microM zVAD-fmk (caspase inhibitor) and 50 U/ml catalase failed to inhibit the injury. 4. However, NGF and catalase blocked the neurotoxicity induced by BAPTA/AM in young neuronal cells (DIV 6). BAPTA/AM (10 microM) did not alter the expression of inducible nitric oxide synthase (iNOS) on glial cells. 5. These results suggest that the feature of neuronal death induced by BAPTA/AM exhibits predominantly delayed necrosis mediated by lipoxygenase-dependent free radicals.

Protection by pyruvate against transient forebrain ischemia in rats

Pyruvate has a remarkable protective effect against zinc neurotoxicity. Because zinc neurotoxicity is likely one of the key mechanisms of ischemic brain injury, the neuroprotective effect of pyruvate was tested in a rat model of transient forebrain ischemia. Control experiments in mouse cortical culture showed that pyruvate almost completely blocked zinc toxicity but did not attenuate calcium-overload neuronal death. Adult rats subjected to 12 min forebrain ischemia exhibited widespread zinc accumulation and neuronal death throughout hippocampus and cortex 72 hr after reperfusion. However, rats injected intraperitoneally with sodium pyruvate (500-1000 mg/kg) within 1 hr after 12 min forebrain ischemia showed almost no neuronal death. In addition, the mortality was markedly decreased in the pyruvate-protected groups (3.8%) compared with the NaCl-injected control group (58.1%). The neuroprotective effect persisted even at 30 d after the insult. The spectacular protection without noticeable side effects makes pyruvate a promising neuroprotectant in human ischemic stroke.

Zinc and disease of the brain

Zinc is one of the most abundant transition metals in the brain. A substantial fraction (10-15%) of brain zinc is located inside presynaptic vesicles of certain glutamatergic terminals in a free or loosely bound state. This vesicle zinc is released with neuronal activity or depolarization, probably serving physiologic functions. However, with excess release, as may occur in a variety of pathologic conditions, zinc may translocate to and accumulate in postsynaptic neurons, events which may contribute to selective neuronal cell death. Intracellular mechanisms of zinc neurotoxicity may include disturbances in energy metabolism, increases in oxidative stress, and activation of apoptosis cascades. Zinc inhibits glyceraldehyde-3-phosphate dehydrogenase (GAPDH), and depletes nicotinamide adenine dinucleotide (NAD(+)) and adenosine triphosphate (ATP). On the other hand, zinc activates protein kinase C (PKC) and extracellular signal-regulated kinase (Erk-1/2), and induces NADPH oxidase; these events result in oxidative neuronal injury. Zinc can also trigger caspase activation and apoptosis via the p75(NTR) pathway. Interestingly, the converse-depletion of intracellular zinc-also induces neuronal death, but in this case, exclusively via classical apoptosis. In addition to the neurotoxic effect, zinc may contribute to the pathogenesis of chronic neurodegenerative disease. For example, in Alzheimer's disease (AD), mature amyloid plaques, but not preamyloid deposits, are found to contain high levels of zinc, suggesting the role of zinc in the process of plaque maturation. Further insights into roles of zinc in brain diseases may help set a new direction toward the development of effective treatments.

Depletion of intracellular zinc and copper with TPEN results in apoptosis of cultured human retinal pigment epithelial cells

PURPOSE

Although zinc deficiency may contribute to the pathogenesis of age-related macular degeneration, how it leads to retinal pigment epithelium (RPE) degeneration is unknown. To investigate this, cultured human RPE cells were rendered zinc depleted with a membrane-permeant metal chelator, N,N,N',N-tetrakis(2-pyridylmethyl) ethylenediamine (TPEN), and the resultant cytopathic changes were examined.

METHODS

RPE cell degeneration was examined with light microscopy, TdT-mediated dUTP nick end labeling (TUNEL) staining, Hoechst dye staining, and electron microscopy and quantified with cell counting or lactate dehydrogenase release assay. The effect of sublethal zinc depletion on the vulnerability of RPE cells to UV irradiation or hydrogen peroxide (H(2)O(2)) exposure, was studied in cultures without or with pretreatment with low-concentration TPEN.

RESULTS

Exposure to 1 to 4 microM TPEN for 48 hours induced RPE cell death in a concentration-dependent manner. Features of apoptosis such as membrane blebbing, chromatin condensation, nuclear fragmentation, and caspase-3 activation, accompanied the TPEN-induced cell death. Addition of equimolar zinc or copper completely reversed TPEN-induced apoptosis, whereas addition of iron had no effect. As in apoptosis of several other cell types including neurons, a protein synthesis inhibitor as well as caspase inhibitors blocked TPEN-induced apoptosis. On the contrary, at sublethal concentrations, TPEN increased the vulnerability of RPE cells to subsequent UV irradiation but not to H(2)O(2) exposure.

CONCLUSIONS

The present results suggest that depletion of intracellular zinc and copper, but not copper alone, may be harmful to RPE cells, directly inducing apoptosis or indirectly increasing vulnerability of RPE cells to UV injury. The present culture model may be useful for gaining insights into the mechanisms of zinc depletion-associated RPE cell degeneration.

Co-induction of p75NTR and p75NTR-associated death executor in neurons after zinc exposure in cortical culture or transient ischemia in the rat

Recently, a 22 kDa protein termed p75(NTR)-associated death executor (NADE) was discovered to be a necessary factor for p75(NTR)-mediated apoptosis in certain cells. However, the possible role for p75(NTR)/NADE in pathological neuronal death has yet been undetermined. In the present study, we have examined this possibility in vivo and in vitro. Exposure of cortical cultures to zinc induced both p75(NTR) and NADE in neurons, whereas exposure to NMDA, ionomycin, iron, or H(2)O(2) induced neither. In addition, zinc exposure increased neuronal NGF expression and its release into the medium. A function-blocking antibody of p75(NTR) (REX) inhibited association between p75(NTR) and NADE as well as neuronal death induced by zinc. Conversely, NGF augmented zinc-induced neuronal death. Caspase inhibitors reduced zinc-induced neuronal death, indicating that caspases were involved. Because reduction of NADE expression with cycloheximide or NADE antisense oligonucleotides attenuated zinc-induced neuronal death, NADE appears to contribute to p75(NTR)-induced cortical neuronal death as shown in other cells. Because zinc neurotoxicity may be a key mechanism of neuronal death after transient forebrain ischemia, we next examined this model. After ischemia, p75(NTR) and NADE were induced in degenerating rat hippocampal CA1 neurons. There was a close correlation between zinc accumulation and p75(NTR)/NADE induction. Suggesting the role of zinc here, injection of a metal chelator, CaEDTA, into the lateral ventricle completely blocked the induction of p75(NTR) and NADE. Our results suggest that co-induction of p75(NTR) and NADE plays a role in zinc-triggered neuronal death in vitro and in vivo.

Induction and activation by zinc of NADPH oxidase in cultured cortical neurons and astrocytes

Zinc overload may be a key mechanism of neuronal death in acute brain injury. We have demonstrated previously that zinc overload neurotoxicity involves protein kinase C (PKC)-dependent rises in intracellular levels of reactive oxygen species (ROS). However, the cascade linking PKC activation to ROS generation in cultured cortical neurons has been unknown. A recent study has demonstrated that ROS-generating NADPH oxidase is present in sympathetic neurons and contributes to NGF deprivation-induced cell death. Because NADPH oxidase is activated by PKC, in the present study, we examined the possibility that NADPH oxidase is the effector for oxidative stress in zinc-overloaded cortical cells. Reverse transcription-PCR and Western blot analyses revealed that naive cultured cortical cells express subunits of NADPH oxidase at low levels. Exposure to zinc substantially increased levels of NADPH oxidase subunits in both neurons and astrocytes. In addition, zinc exposure induced translocation of the p47(PHOX) and p67(PHOX) subunits to the membrane, a signature event for NADPH oxidase activation. Addition of a selective PKC inhibitor, GF109203X, blocked both the induction and the membrane translocation of NADPH oxidase by zinc. Supporting the role for NADPH oxidase in zinc-triggered oxidative injury, NADPH oxidase inhibitors attenuated ROS production and cortical neuronal death induced by zinc. In addition, Cu/Zn-superoxide dismutase and catalase attenuated zinc-induced cortical neuronal death. Our results have demonstrated that zinc overload induces and activates NADPH oxidase in cortical neurons and astrocytes in a PKC-dependent manner. Thus, NADPH oxidase may be an enzyme contributing to ROS generation in zinc-overloaded cortical neurons and astrocytes.

Medial medullary infarction with restricted sensory symptom

Sensory abnormalities in patients with medial medullary infarction (MMI) usually involve half of the patient's body and extremities. We report 3 patients with restricted sensory symptoms due to MMI. Patient 1 had sensory symptoms restricted to the contralateral foot secondary to an infarct selectively involving the ventral portion of the medial lemniscus that probably corresponds to leg-representing area. Patient 2 had restricted sensory changes over the contralateral perioral area caused by lesions predominantly involving the posterior part of the medulla that may have affected a part of the ascending trigeminal tract. Patient 3 had sensory symptoms limited to the upper part of his body and the arms (pseudosyringomyelia pattern) due to bilateral MMI that may have resulted from the ventral-dorsal difference in the severity of the lesion. These patients illustrate that restricted sensory abnormalities can occur in patients with MMI. Our MRI-clinical correlation study is consistent with the previously reported sensory topography of the medial lemniscus and the ascending trigeminal tract: the leg-representing area is located ventrally in the medial lemniscus whereas the perioral-representing area is situated most medially in the ascending trigeminal tract.

Zn(2+): a novel ionic mediator of neural injury in brain disease

Zn(2+) is the second most prevalent trace element in the body and is present in particularly large concentrations in the mammalian brain. Although Zn(2+) is a cofactor for many enzymes in all tissues, a unique feature of brain Zn(2+) is its vesicular localization in presynaptic terminals, where its release is dependent on neural activity. Although the physiological significance of synaptic Zn(2+) release is little understood, it probably plays a modulatory role in synaptic transmission. Furthermore, several lines of evidence support the idea that, upon excessive synaptic Zn(2+) release, its accumulation in postsynaptic neurons contributes to the selective neuronal loss that is associated with certain acute conditions, including epilepsy and transient global ischaemia. More speculatively, Zn(2+) dis-homeostasis might also contribute to some degenerative conditions, including Alzheimer's disease. Further elucidation of the pathological actions of Zn(2+) in the brain should result in new therapeutic approaches to these conditions.

Protein synthesis-dependent but Bcl-2-independent cytochrome C release in zinc depletion-induced neuronal apoptosis

Previously, we reported that chelation of intracellular zinc with N, N,N',N'-tetrakis(2-pyridylmethyl)ethylenediamine (TPEN)-induced macromolecule synthesis-dependent apoptosis of cultured cortical neurons. According to the current theory of apoptosis, release of mitochondrial cytochrome C into the cytosol is required for caspase activation. In the present study, we examined whether cytochrome C release is dependent on macromolecule synthesis. Exposure of cortical cultures to 2 microM TPEN for 24 hr induced apoptosis as previously described. Fluorescence immunocytochemical staining as well as immunoblots of cell extracts revealed the release of cytochrome C into the cytosol 18-20 hr after the exposure onset. The cytochrome C release was completely blocked by the addition of cycloheximide or actinomycin D. Addition of the caspase inhibitor zVAD-fmk did not attenuate the cytochrome C release, whereas it blocked TPEN-induced apoptosis. Because Bcl-2 has been shown to block cytochrome C release potently, we exposed human neuroblastoma cells (SH-SY5Y) to TPEN. Whereas Bcl-2 overexpression completely blocked both cytochrome C release and apoptosis induced by staurosporine, it attenuated neither induced by TPEN. The present results suggest that, in neurons, macromolecule synthesis inhibitors act upstream of cytochrome C release to block apoptosis and that, in addition to the classical Bcl-2 sensitive pathway, there may exist a Bcl-2-insensitive pathway for cytochrome C release.

A novel neuroprotective mechanism of riluzole: direct inhibition of protein kinase C

In addition to its antiexcitotoxic action, the anti-amyotrophic lateral sclerosis (ALS) neuroprotectant riluzole protects against nonexcitotoxic oxidative neuronal injury. In light of evidence that protein kinase C (PKC) mediates oxidative stress in cortical culture, we examined the possibility that riluzole's antioxidative neuroprotection involves PKC inhibition. Riluzole (30 microM) blocked phorbol 12-myristate 13-acetate (PMA)-induced increases in membrane PKC activity in cultured cortical cells. Suggesting a direct action, riluzole also inhibited the activity of purified PKC. Consistently, both PKC depletion and oxidative neuronal death induced by PMA were markedly attenuated by riluzole. The site of action of riluzole on PKC was not likely the diacylglycerol binding site but the catalytic domain, since riluzole did not alter radiolabeled phorbol-12,13-dibutyrate binding, but inhibited PKM, the catalytic domain of PKC. However, increasing ATP concentrations did not alter the inhibition of PKC by riluzole, making it unlikely that riluzole is a competitive inhibitor of ATP binding at PKM. Present results have demonstrated that riluzole directly inhibits PKC, which action may contribute to its antioxidative neuroprotective effects. In addition, it appears possible that PKC inhibition may be able to explain some of its well-known channel inhibitory and neuroprotective effects. Combined with findings that PKC activity is increased in ALS, the present results suggest that PKC may be a potential therapeutic target in ALS.

Epidermal growth factor induces oxidative neuronal injury in cortical culture

Recently, we have demonstrated that certain neurotrophic factors can induce oxidative neuronal necrosis by acting at the cognate tyrosine kinase-linked receptors. Epidermal growth factor (EGF) has neurotrophic effects via the tyrosine kinase-linked EGF receptor (EGFR), but its neurotoxic potential has not been studied. Here, we examined this possibility in mouse cortical culture. Exposure of cortical cultures to 1-100 ng/ml EGF induced gradually developing neuronal death, which was complete in 48-72 h; no injury to astrocytes was noted. Electron microscopic findings of EGF-induced neuronal death were consistent with necrosis; severe mitochondrial swelling and disruption of cytoplasmic membrane occurred, whereas nuclei appeared relatively intact. The EGF-induced neuronal death was accompanied by increased free radical generation and blocked by the anti-oxidant Trolox. Suggesting mediation by the EGFR, an EGFR tyrosine kinase-specific inhibitor, C56, attenuated EGF-induced neuronal death. In addition, inhibitors of extracellular signal-regulated protein kinase 1/2 (Erk-1/2) (PD98056), protein kinase A (H89), and protein kinase C (GF109203X) blocked EGF-induced neuronal death. A p38 mitogen-activated protein kinase inhibitor (SB203580) or glutamate antagonists (MK-801 and 6-cyano-7-nitroquinoxaline-2,3-dione) showed no protective effect. The present results suggest that prolonged activation of the EGFR may trigger oxidative neuronal injury in central neurons.

Depletion of intracellular zinc induces macromolecule synthesis- and caspase-dependent apoptosis of cultured retinal cells

Although zinc deficiency may contribute to age-related macular degeneration (ARMD), the pathogenic mechanism is as yet uncertain. In light of evidence that cellular zinc depletion induces apoptosis in cortical neurons and thymocytes, in the present study, we examined the possibility that the same phenomenon occurs also in retinal cells. Exposure of primary retinal cell cultures to 1-3 microM of a cell membrane-permeant zinc chelator TPEN for 24 h induced concentration-dependent death of neurons, photoreceptor cells, and astrocytes. Addition of zinc or copper reversed TPEN toxicity to all cell components, indicating the particular involvement of zinc chelation in cell death. Consistent with apoptosis, oligonucleosomal DNA fragmentation and chromatin condensation accompanied, and the protein synthesis inhibitor cycloheximide blocked the TPEN-induced retinal cell death. During TPEN-induced retinal cell apoptosis, cleavage/activation of procaspase-1, but little of procaspase-3, was observed. Consistent with this finding, a broad-spectrum caspase inhibitor (zVAD-fmk) was significantly more protective than a caspase-3-selective inhibitor (DEVD-fmk). The present study has demonstrated that depletion of intracellular zinc is sufficient to induce macromolecule synthesis- and caspase-dependent apoptosis of cultured retinal cells. In light of the possibility that zinc depletion may contribute to the pathogenesis of ARMD, the current culture model may be a useful tool for the investigation of the mechanism of zinc depletion-induced retinal cell death.

Accumulation of zinc in degenerating hippocampal neurons of ZnT3-null mice after seizures: evidence against synaptic vesicle origin

In several brain injury models, zinc accumulates in degenerating neuronal somata. Suggesting that such zinc accumulation may play a causal role in neurodegeneration, zinc chelation attenuates neuronal death. Because histochemically reactive zinc is present in and released from synaptic vesicles of glutamatergic neurons in the forebrain, it was proposed that zinc translocation from presynaptic terminals to postsynaptic neurons may be the mechanism of toxic zinc accumulation. To test this hypothesis, kainate seizure-induced neuronal death was examined in zinc transporter 3 gene (ZnT3)-null mice, a strain that completely lacks histochemically reactive zinc in synaptic vesicles. Intraperitoneal injection of kainate induced seizures to a similar degree in wild type and ZnT3-null mice. Staining of hippocampal sections with a zinc-specific fluorescent dye, N-(6-methoxy-8-quinolyl)-p-carboxybenzoylsulfonamide, revealed that zinc accumulated in degenerating CA1 and CA3 neurons in both groups, indicating that zinc originated from sources other than synaptic vesicles. Injection of CaEDTA into the cerebral ventricle almost completely blocked zinc accumulation in ZnT3-null mice, suggesting that increases in extracellular zinc concentrations may be a critical event for zinc accumulation. Arguing against the possibility that zinc accumulation results from nonspecific breakdown of zinc-containing proteins, injection of kainate into the cerebellum did not induce zinc accumulation in degenerating granule neurons. Taken together, these results support the existing idea that zinc is released into extracellular space and then enters neurons to exert a cytotoxic effect. However, the origin of zinc is not likely to be synaptic vesicles, because zinc accumulation robustly occurs in ZnT3-null mice lacking synaptic vesicle zinc.

Anti-oxidative neuroprotection by estrogens in mouse cortical cultures

Estrogen replacement therapy in postmenopausal women may reduce the risk of Alzheimer's disease, possibly by ameliorating neuronal degeneration. In the present study, we examined the neuroprotective spectrum of estrogen against excitotoxicity, oxidative stress, and serum-deprivation-induced apoptosis of neurons in mouse cortical cultures. 17beta-estradiol as well as 17alpha-estradiol and estrone attenuated oxidative neuronal death induced by 24 hr exposure to 100 microM FeCl2, excitotoxic neuronal death induced by 24 hr of exposure to 30 microM N-methyl-D-aspartate (NMDA) and serum-deprivation induced neuronal apoptosis. Furthermore, estradiol attenuated neuronal death induced by Abeta25-35. However, all these neuroprotective effects were mediated by the anti-oxidative action of estrogens. When oxidative stress was blocked by an antioxidant trolox, estrogens did not show any additional protection. Addition of a specific estrogen receptor antagonist ICI182,780 did not reverse the protection offered by estrogens. These findings suggest that high concentrations of estrogen protect against various neuronal injuries mainly by its anti-oxidative effects as previously shown by Behl et al. Our results do not support the view that classical estrogen receptors mediate neuroprotection.

Zinc as a paracrine effector in pancreatic islet cell death

Because of a huge amount of Zn2+ in secretory granules of pancreatic islet beta-cells, Zn2+ released in certain conditions might affect the function or survival of islet cells. We studied potential paracrine effects of endogenous Zn2+ on beta-cell death. Zn2+ induced insulinoma/islet cell death in a dose-dependent manner. Chelation of released endogenous Zn2+ by CaEDTA significantly decreased streptozotocin (STZ)-induced islet cell death in an in vitro culture system simulating in vivo circumstances but not in the conventional culture system. Zn2+ chelation in vivo by continuous CaEDTA infusion significantly decreased the incidence of diabetes after STZ administration. N-(6-methoxy-quinolyl)-para-toluene-sulfonamide staining revealed that Zn2+ was densely deposited in degenerating islet cells 24 h after STZ treatment, which was decreased by CaEDTA infusion. We show here that Zn2+ is not a passive element for insulin storage but an active participant in islet cell death in certain conditions, which in time might contribute to the development of diabetes in aged people.

Induction by synaptic zinc of heat shock protein-70 in hippocampus after kainate seizures

Following seizures, heat shock protein (HSP)-70 is induced in various brain regions. Since zinc that can induce HSP-70 in various cell systems is enriched in certain glutamatergic terminals and translocates to postsynaptic neurons with seizures, we examined the possibility that HSP-70 induction in the epileptic brain is mediated by synaptic zinc. Adult rats were injected intraperitoneally with kainate to induce seizures. Seizures were halted 3 h after the kainate administration by the injection of phenytoin. Staining of brain sections with zinc-specific fluorescent dye TFL at 24 h after the kainate injection revealed a one-to-one correlation between dense TFL fluorescence and acidophilic neuronal degeneration in the hippocampus. Subsequent staining with anti-HSP-70 antibody, however, revealed that more numerous neurons than degenerating neurons exhibited HSP-70 immunoreactivity. Most of the HSP-70(+) neurons were not stained with acid fuchsin but exhibited mild zinc fluorescence in the cytoplasm. Intraventricular injection of CaEDTA attenuated neuronal death as well as the HSP-70 induction in a dose-dependent manner. Supporting the specificity of zinc rather than calcium as the inducer of HSP-70 in neurons, exposure to zinc but not to a calcium ionophore or excitotoxins increased expression of HSP-70 mRNA and protein in cultured cortical neurons. The present results suggest that not only selective neuronal death, but also HSP-70 induction in neurons after seizures, is mediated by the translocation of endogenous synaptic zinc.

Ethambutol-induced vacuolar changes and neuronal loss in rat retinal cell culture: mediation by endogenous zinc

Ethambutol is an efficacious antituberculosis agent. However, its use has been limited by the occurrence of ocular toxicity. To investigate characteristics and possible mechanisms of ethambutol ocular toxicity, we used primary rat retinal cultures as a model. Primary rat retinal cultures were obtained from newborn Sprague-Dawley rats and used for experiments after maturation (DIV > or = 10). Cytopathologic changes were examined under light and electron microscopes. Thy-1 (a membrane glycoprotein expressed by retinal ganglion neurons)-containing neurons and gamma-aminobutyric acid (GABA)-ergic neurons were identified immunocytochemically. Exposure of retinal cultures for 24-48 h to ethambutol induced cytoplasmic vacuolar changes and neuronal loss. Vacuolar changes were partially reversible with the termination of ethambutol exposure. Of neurons, Thy-1(+) ganglion neurons were more vulnerable than GABA(+) neurons. Glutamate antagonists, an antioxidant (trolox), or cycloheximide, did not attenuate either vacuolar changes or neuronal loss. A cell-permeant zinc chelator N,N,N',N'-tetrakis (2-pyridylmethyl) ethylenediamine (TPEN) markedly attenuated vacuolar degeneration and neuronal loss, while the addition of zinc augmented both. In rat retinal cultures, ethambutol induces reversible vacuolar degeneration as well as irreversible neuronal loss, more preferentially of Thy-1(+) ganglion neurons. Contrary to the current theories, ethambutol-induced retinal cytotoxicity in the present study is mediated not by excitotoxicity or zinc deficiency but by a mechanism requiring intracellular zinc. In addition, features of the ethambutol-induced cell death were not consistent with those of apoptosis.

Prevention of neuronal apoptosis by phorbol ester-induced activation of protein kinase C: blockade of p38 mitogen-activated protein kinase

Consistent with previous studies on cell lines and non-neuronal cells, specific inhibitors of protein kinase C induced mouse primary cultured neocortical neurons to undergo apoptosis. To examine the complementary hypothesis that activating protein kinase C would attenuate neuronal apoptosis, the cultures were exposed for 1 h to phorbol-12-myristate-13-acetate, which activated protein kinase C as evidenced by downstream enhancement of the mitogen-activated protein kinase pathway. Exposure to phorbol-12-myristate-13-acetate, or another active phorbol ester, phorbol-12,13-didecanoate, but not to the inactive ester, 4alpha-phorbol-12,13-didecanoate, markedly attenuated neuronal apoptosis induced by serum deprivation. Phorbol-12-myristate-13-acetate also attenuated neuronal apoptosis induced by exposure to beta-amyloid peptide 1-42, or oxygen-glucose deprivation in the presence of glutamate receptor antagonists. The neuroprotective effects of phorbol-12-myristate-13-acetate were blocked by brief (non-toxic) concurrent exposure to the specific protein kinase C inhibitors, but not by a specific mitogen-activated protein kinase 1 inhibitor. Phorbol-12-myristate-13-acetate blocked the induction of p38 mitogen-activated protein kinase activity and specific inhibition of this kinase by SB 203580 attenuated serum deprivation-induced apoptosis. c-Jun N-terminal kinase 1 activity was high at rest and not modified by phorbol-12-myristate-13-acetate treatment. These data strengthen the idea that protein kinase C is a key modulator of several forms of central neuronal apoptosis, in part acting through inhibition of p38 mitogen-activated protein kinase regulated pathways.

Protective effects of asiaticoside derivatives against beta-amyloid neurotoxicity

Asiaticoside (AS) derivatives were tested for potential protective effects against Abeta-induced cell death. Of the 28 AS derivatives tested, asiatic acid (AA), asiaticoside 6 (AS6), and SM2 showed strong inhibition of Abeta-induced death of B103 cells at 1 microM. The three AS derivatives were further tested for their effects on free radical injury and apoptosis. All three AS derivatives reduced H(2)O(2)-induced cell death and lowered intracellular free radical concentration, but AA showed the strongest protection. In contrast, SM2 was the most effective blocker of staurosporine-induced apoptosis. These results suggest that the three AS derivatives block Abeta toxicity by acting through different cellular mechanisms. When applied to hippocampal slices, AA, SM2, and AS6 did not alter n-methyl-D-aspartic acid (NMDA) or non-NMDA receptor-mediated synaptic transmission, paired-pulse facilitation or induction of long-term potentiation in the field CA1. These results indicate that the three AS derivatives do not alter physiological properties of the hippocampus at the concentration that blocks Abeta-induced cell death. Therefore AS6, AA, and SM2 can be regarded as reasonable candidates for a therapeutic Alzheimer's disease drug that protects neurons from Abeta toxicity.

N-Methyl-D-aspartate receptor blockade induces neuronal apoptosis in cortical culture

Whereas excessive activation of the NMDA receptor may contribute to ischemic neuronal injury, physiologic activation may promote neuronal survival under certain conditions. Consistently, it has recently been shown that NMDA antagonists induce apoptosis of central neurons in immature rats. In the present study, we have examined whether NMDA antagonists induce neuronal apoptosis also in a culture condition. Exposure of cortical cultures (DIV 10-13) to MK-801 (1-10 microM) for 48 h resulted in death of about 30-40% of neurons. Similar neuronal death was induced by exposure to other NMDA antagonists, D-AP5 and dextromethorphan. The neuronal death was dependent on the culture age; MK-801 induced much less neuronal death in younger (DIV 7) and older (DIV 16-19) cultures. The NMDA antagonist-induced neuronal death was accompanied by cell body shrinkage, nuclear fragmentation, and cleavage/activation of caspase-3. Furthermore, it was attenuated by cycloheximide and zVAD-fmk, indicating that the death occurred mainly by the apoptosis mechanism. As in several other apoptosis models, high-potassium medium blocked the NMDA antagonist-induced apoptosis, which was reversed by voltage-gated calcium channel blockers. The present results demonstrate that NMDA antagonists induce neuronal apoptosis in cortical culture, consistent with the findings obtained in immature rats. Since the activation of the voltage-gated calcium channels attenuated the NMDA antagonist-induced apoptosis, it may be another example of the "calcium set point hypothesis."

Insulin-induced oxidative neuronal injury in cortical culture: mediation by induced N-methyl-D-aspartate receptors

While effectively attenuating neuronal apoptosis in mouse cortical culture, insulin paradoxically induced neuronal necrosis with 48 h of exposure. The insulin neurotoxicity was blocked by an antioxidant but not by caspase inhibitors. Exposure to insulin led to tyrosine phosphorylation of the insulin receptor and the insulin-like growth factor-1 (IGF-1) receptor and activation of protein kinase C (PKC) and phosphoinositide 3-kinase (PI3-kinase). Inhibitors of tyrosine kinase and PKC, but not PI3-kinase, attenuated the insulin neurotoxicity. Conversely, the inhibitor of PI3-kinase but not PKC reversed the antiapoptotic effect of insulin. Suggesting that the gene activity-dependent emergence of excitotoxicity contributed to insulin neurotoxicity, macromolecule synthesis inhibitors and N-methyl-D-aspartate (NMDA) antagonists blocked it. Consistently, exposure to insulin increased the level of the NR2A subunit of the NMDA receptor without much altering NR1 or NR2B levels. The present study suggests that insulin can be both neuroprotective and neurotoxic in the same cell system but by way of different signaling cascades.

Induction of an immediate early gene egr-1 by zinc through extracellular signal-regulated kinase activation in cortical culture: its role in zinc-induced neuronal death

Egr-1 is one of the immediate early transcription factors that are induced after brain insults. However, the mechanism and the role of Egr-1 induction are not yet determined. In the present study, using mouse cortical cultures, we examined the ionic mechanism of Egr-1 induction and its role in neuronal death. Although zinc, NMDA, or ionomycin induced comparable neuronal death in cortical culture, only zinc increased Egr-1 expression, which was attenuated by blocking zinc influx. It is intriguing that brief exposure to zinc induced sustained extracellular signal-regulated kinase (Erk) activation. PD098059, an inhibitor of the Erk 1/2 upstream kinase mitogen-activated protein kinase kinase 1 (MEK1), blocked Erk 1/2 activation, Egr-1 induction, and neuronal death by zinc. The present study has demonstrated that zinc, rather than calcium, induces lasting Egr-1 expression in cortical culture by activating Erk 1/2, which is part of a cascade that may play an active role in zinc neurotoxicity. We propose that translocation of endogenous zinc may be the key mechanism of Egr-1 induction and neuronal death in brain ischemia.

Presenilin 1 mediates protein kinase C dependent alpha-secretase derived amyloid precursor protein secretion and mitogen-activated protein kinase activation in presenilin 1 transfected human embryonic kidney 293 cell

We investigated the role of presenilin 1 (PS1) in the secretion of alpha-secretase derived amyloid precursor protein (sAPP alpha) and associated intracellular signaling pathways. Human embryonic kidney (HEK) 293 cells were transfected with exon 9 deletion (deltaE9) mutant PS1 cDNA in an ecdyson-inducible system. sAPPalpha secretion was lower in the mutant PS1 expressing cells compared with non-expressing cells. When activated by PDBu, secretion of sAPPalpha and the level of phosphorylated mitogen activated protein kinase (MAPK) were greatly enhanced in deltaE9 PS1 uninduced cells, but not in the mutant PS1 induced cells. PD98059, a MAPK inhibitor, blocked PDBu induced sAPPalpha secretion from deltaE9 PS1 uninduced cells but had no effect on the mutant PS1 induced cells. These data indicate that PS1 mediates PDBu-induced sAPPalpha secretion and MAPK activation.

Histochemically reactive zinc in plaques of the Swedish mutant beta-amyloid precursor protein transgenic mice

Endogenous metals such as zinc may contribute to beta-amyloid (Abeta) aggregation and hence the plaque formation. In the present study, we examined brains of four Swedish mutant amyloid precursor protein (APP) transgenic mice at 12 months of age for histochemically reactive zinc in the plaques. Here, we report that all the Congo red (+) mature plaques contained chelatable zinc, as demonstrated by staining with the zinc-specific fluorescent dye 6-methoxy-8-quinolyl-para-toluenesulfonamide (TSQ). On the other hand, Congo red (-) preamyloid Abeta deposits were not stained with TSQ. Interestingly, although cerebellum contained similar degree of preamyloid Abeta deposits as cerebral cortex, it was completely devoid of Congo red- or TSQ-stained mature plaques. Although zinc from plaques was only slowly and partially removed by a specific zinc remover, dithizone, treatment of brain sections with heparinase-III, which degrades heparan sulfate proteoglycan (HSPG), another major constituent of plaques, greatly fastened the zinc removal with dithizone. The present study has demonstrated the presence of histochemically reactive zinc in plaques, but not preamyloid Abeta deposits, of the Swedish mutant APP transgenic mice. Because preamyloid Abeta deposits fail to develop into congophilic plaques in cerebellum where synaptic vesicle zinc is deficient, the synaptic zinc may be a necessary element in the plaque formation. In holding zinc inside plaques, HSPG may contribute in addition to Abeta.

Calcium ionophores can induce either apoptosis or necrosis in cultured cortical neurons

Cultured cortical neurons exposed for 24 h to low concentrations of the Ca2+ ionophores, ionomycin (250 nM) or A-23187 (100 nM), underwent apoptosis, accompanied by early degeneration of neurites, cell body shrinkage, chromatin condensation and internucleosomal DNA fragmentation. This death could be blocked by protein synthesis inhibitors, as well as by the growth factors brain-derived neurotrophic factor or insulin-like growth factor I. If the ionomycin concentration was increased to 1-3 microM, then neurons underwent necrosis, accompanied by early cell body swelling without DNA laddering, or sensitivity to cycloheximide or growth factors. Calcium imaging with Fura-2 suggested a possible basis for the differential effects of low and high concentrations of ionomycin. At low concentrations, ionomycin induced greater increases in intracellular Ca2+ concentration in neurites than in neuronal cell bodies, whereas at high concentrations, ionomycin produced large increases in intracellular Ca2+ concentration in both neurites and cell bodies. We hypothesize that the ability of low concentrations of Ca2+ ionophores to raise intracellular Ca2+ concentration preferentially in neurites caused early neurite degeneration, leading to loss of growth factor availability to the cell body and consequent apoptosis, whereas high concentrations of ionophores produced global cellular Ca2+ overload and consequent necrosis.

Nonproteolytic neuroprotection by human recombinant tissue plasminogen activator

Human recombinant tissue plasminogen activator (tPA) may benefit ischemic stroke patients by dissolving clots. However, independent of thrombolysis, tPA may also have deleterious effects on neurons by promoting excitotoxicity. Zinc neurotoxicity has been shown to be an additional key mechanism in brain injuries. Hence, if tPA affects zinc neurotoxicity, this may provide additional insights into its effect on neuronal death. Independent of its proteolytic action, tPA markedly attenuated zinc-induced cell death in cortical culture, and, when injected into cerebrospinal fluid, also reduced kainate seizure-induced hippocampal neuronal death in adult rats.

Mediation by membrane protein kinase C of zinc-induced oxidative neuronal injury in mouse cortical cultures

Transsynaptic movement of endogenous zinc may play a key role in selective neuronal death after brain ischemia and prolonged seizures. As to the mechanism, we have reported recently that zinc-induced neuronal death occurs mainly by oxidative stress in cortical cultures. Here we present evidence supporting the idea that activation of membrane protein kinase C (PKC) in neurons is likely to play a key role in zinc-induced oxidative neuronal injury. Exposure of cortical cultures to 300 microM zinc for 15 min induced increases in the activity, without changing the amount, of membrane PKC to two- to threefold of control values, followed by neuronal death over the next day. Addition of a zinc chelator, Ca-EDTA, or PKC inhibitors with zinc completely abolished the zinc-induced increase in the membrane PKC activity. Indicating the participation of PKC in zinc-induced oxidative stress and neuronal death, the selective PKC inhibitor GF109203X attenuated both. Furthermore, as in zinc-induced neuronal death, activation of PKC with phorbol esters induced free radical generation and neuronal death, which were blocked by GF109203X or an antioxidant, Trolox. The present results support the idea that zinc influx activates PKC in the membrane, which contributes to free radical generation and neuronal death. As an increasing body of evidence suggests that zinc neurotoxicity is an important mechanism of pathological neuronal death, timely prevention of PKC activation after acute brain insult may prove useful in ameliorating this type of neuronal death.

High vulnerability of GABA-immunoreactive neurons to kainate in rat retinal cultures: correlation with the kainate-stimulated cobalt uptake

Like other areas of the central nervous system, the retina is highly vulnerable to ischemia. In particular, neurons in the inner nuclear layer, including gamma-amino butyric acid (GABA)-ergic amacrine neurons, are highly vulnerable. Since excitotoxicity is likely a major mechanism of ischemic retinal injury, using rat retinal cell culture, we examined whether GABAergic retinal neurons are differentially vulnerable to particular excitotoxins. The neuronal population as a whole, identified by anti-microtubule associated protein-2 (MAP-2) immunocytochemistry, was equally vulnerable to kainate, but more resistant to N-methyl-d-aspartate (NMDA) than cultured cortical neurons. Compared to Thy-1 immunoreactive neurons, GABA immunoreactive neurons were more vulnerable to kainate, but more resistant to NMDA neurotoxicity. Double staining of cultures with anti-GABA immunocytochemistry and the kainate-stimulated cobalt uptake method, revealed a close correlation between the two. However, unlike in other neuronal cells, there was no clear correlation between GluR2 immunoreactivity and the cobalt staining. The heightened vulnerability of GABAergic neurons to kainate, as compared to the general neuronal population, may be due to the calcium-permeable AMPA/kainate receptors they have, as identified functionally by the kainate-stimulated cobalt uptake staining. Since these neurons are preferentially injured in ischemia, AMPA/kainate receptor-mediated neurotoxicity may contribute significantly to ischemic retinal injury.

Zinc-induced cortical neuronal death with features of apoptosis and necrosis: mediation by free radicals

Some studies have provided evidence that delayed death of hippocampal CA1 neurons in transient global ischemia occurs by classical apoptosis. Recently, translocation of synaptic zinc has been shown to play a key role in ischemic CA1 neuronal death. With these two lines of evidence, we examined in mouse cortical cultures the possibility that zinc neurotoxicity, slowly triggered over a day, may occur by classical apoptosis. Exposure of cortical cultures to 30-35 microM zinc for 24 h resulted in slowly evolving death of neurons only, while exposure to zinc at higher concentrations ( > or = 40 microM) produced near-complete death of both neurons and glia. DNA agarose gel electrophoresis revealed internucleosomal DNA fragmentation, and the terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling method revealed DNA breaks in degenerating neurons after 24 h exposure to 30-35 microM zinc, suggesting that the death may occur by apoptosis. However, electron-microscopic examinations revealed ultrastructural changes clearly indicative of necrosis, such as marked swelling of intracellular organelles and disruption of cell membranes amid relatively intact nuclear membranes. Furthermore, the slowly triggered zinc neurotoxicity was not attenuated by cycloheximide, neurotrophins (brain-derived neurotrophic factor, neurotrophin-3, neurotrophin-4/5) or high potassium, all of which effectively reduced several forms of apoptosis in our cortical cultures. Interestingly, a vitamin E analogue trolox almost completely blocked slowly triggered zinc neurotoxicity, indicating that free radical injury is the main mechanism of zinc neurotoxicity. Consistently, exposure to zinc increased membrane lipid peroxidation assessed by the thiobarbituric acid reactive substance assay. Although zinc-induced neuronal death, slowly triggered over a day, is associated with DNA fragmentation, overall it exhibited features more typical of necrosis. This neuronal death is probably mediated by free radical injury. Further studies appear warranted to investigate the mechanistic link between toxic zinc influx and free radical generation and the possibility that selective neuronal death in transient global ischemia also occurs by zinc-triggered neuronal death exhibiting features of both apoptosis and necrosis.

Vertebrobasilar artery territory infarction as an initial manifestation of systemic lupus erythematosus

Cerebral infarction is a well-documented complication of systemic lupus erythematosus (SLE), that usually occurs several years after the diagnosis of SLE. To our knowledge, however, strokes associated with vertebrobasilar artery involvement were not reported to present as an initial manifestation of SLE. We report two patients, who presented with vertebrobasilar territory infarction as an initial manifestation of SLE. Patient 1 was a 16-year-old girl, who developed dysarthria and ataxia. MRI showed multiple infarcts in the pons, cerebellum and thalamus. Four-vessel cerebral angiography showed multifocal stenoses in the vertebral and basilar arteries with beaded appearance. Patient 2 was a 26-year-old woman, who developed headache associated with dysarthria, dizziness and ataxia. MRI showed multiple infarcts in the cerebellum, medulla, pons, midbrain and thalamus. Cerebral angiography revealed occlusion of both vertebral arteries at the first cervical vertebral level with non-visualization of the basilar artery. Both patients were diagnosed as having SLE supported by laboratory results. Although rare, posterior circulation stroke can present as an initial manifestation of SLE, which may be attributed to vasculitis or dissection in the vertebral/basilar artery.

Antioxidative and proapoptotic effects of riluzole on cultured cortical neurons

Riluzole is used clinically in patients with amyotrophic lateral sclerosis. As oxidative stress, in addition to excitotoxicity, may be a major mechanism of motoneuron degeneration in patients with amyotrophic lateral sclerosis, we examined whether riluzole protects against nonexcitotoxic oxidative injury. Probably reflecting its weak antiexcitotoxic effects, riluzole (1-30 microM) attenuated submaximal neuronal death induced by 24-h exposure to 30 microM kainate or NMDA, but not that by 100 microM NMDA, in cortical cultures. Riluzole also attenuated nonexcitotoxic oxidative injury induced by exposure to FeCl3 in the presence of MK-801 and CNQX. Consistent with its antioxidative effects, riluzole reduced Fe3+-induced lipid peroxidation, and inhibited cytosolic phospholipase A2. By contrast, riluzole did not attenuate neuronal apoptosis induced by staurosporine. Rather unexpectedly, 24-48-h exposure to 100-300 microM riluzole induced neuronal death accompanied by nuclear and DNA fragmentations, which was attenuated by caspase inhibitor carbobenzyloxy-Val-Ala-Asp-fluoromethyl ketone but not by protein synthesis inhibitor cycloheximide. The present study demonstrates that riluzole has direct antioxidative actions, perhaps in part by inhibiting phospholipase A2. However, in the same neurons, riluzole paradoxically induces neuronal apoptosis in a caspase-sensitive manner. Considering current clinical use of riluzole, further studies are warranted to investigate its potential cytolethal effects.

Zn2+ entry produces oxidative neuronal necrosis in cortical cell cultures

Evidence has accumulated that Zn2+ plays a central role in neurodegenerative processes following brain injuries including ischaemia or epilepsy. In the present study, we examined patterns and possible mechanisms of Zn2+ neurotoxicity. Inclusion of 30-300 microM Zn2+ for 30 min caused neuronal necrosis apparent by cell body and mitochondrial swelling in cortical cell cultures. This Zn2+ neurotoxicity was not attenuated by antiapoptosis agents, inhibitors of protein synthesis or caspase. Blockade of glutamate receptors or nitric oxide synthase showed no beneficial effect against Zn2+ neurotoxicity. Interestingly, antioxidants, trolox or SKF38393, attenuated Zn(2+)-induced neuronal necrosis. Pretreatment with insulin or brain-derived neurotrophic factor increased the Zn(2+)-induced free radical injury. Kainate or AMPA facilitated Zn2+ entry and potentiated Zn2+ neurotoxicity in a way sensitive to trolox. Reactive oxygen species and lipid peroxidation were generated in the early phase of Zn2+ neurotoxicity. These findings indicate that entry and accumulation of Zn2+ result in generation of toxic free radicals and then cause necrotic neuronal degeneration under certain pathological conditions in the brain.

Depletion of intracellular zinc induces protein synthesis-dependent neuronal apoptosis in mouse cortical culture

The central nervous system (CNS) contains a large amount of zinc; a substantial fraction of it is located inside synaptic vesicles of glutamatergic terminals in chelatable forms and released in a calcium-dependent manner with intense neuronal activity. Recently, it has been shown that excessive zinc influx can kill neurons in rats subjected to transient forebrain ischemia. On the other hand, severe depletion of zinc has been also reported to induced cell death in certain nonneuronal cells. Since decreases in tissue zinc have been associated with Alzheimer's disease (AD) and senile macular degeneration, we examined whether depletion of intracellular zinc with a zinc chelator can directly induce neuronal death in mouse cortical cultures. Exposure of cortical cultures to a cell-permeant zinc-chelator, N,N,N',N'-tetrakis (2-pyridylmethyl) ethylenediamine (TPEN, 0.5-3.0 microM) induced gradually developing neuronal degeneration accompanied by various features of apoptosis: cell body shrinkage, nuclear condensation and fragmentation, and internucleosomal DNA breakage. At higher concentrations, TPEN induced additional glial cell death. TPEN-induced cell death was completely blocked by coaddition of zinc. Addition of a protein synthesis inhibitor cycloheximide as well as a caspase inhibitor carbobenzoxy-valyl-alanyl-aspartyl-fluoromethyl ketone (zVAD-fmk) markedly attenuated TPEN-induced neuronal death. On the other hand, brain-derived neurotrophic factor (BDNF), insulin-like growth factor-1 (IGF-1), phorbol 12-myristate 13-acetate (PMA), high K+, or an antioxidant, trolox, did not show any protective effect. The present results demonstrated that depletion of intracellular zinc induces protein synthesis-dependent neuronal apoptosis in cortical culture. Combined with the findings that extracellular zinc may promote extracellular beta-amyloid (A beta) aggregation and that total tissue zinc is reduced in AD, present results suggest a possibility that redistribution of zinc from intracellular to extracellular space may synergistically contribute to neuronal apoptosis in AD.

p53 mutations and human papillomavirus DNA in oral squamous cell carcinoma: correlation with apoptosis

Forty-two oral squamous cell carcinomas (SCCs) were analysed for p53 mutations and human papillomavirus (HPV) infection to examine the prevalency of these factors and correlation with apoptotic index (AI; number of apoptotic cells per 100 tumour cells) of the tumour tissue. In polymerase chain reaction (PCR)-Southern blot analysis, HPV DNAs were detected from 22 out of 42 SCCs (52%) with predominance of HPV-16 (68%). p53 mutations in exons 5-8, screened by nested PCR-single-strand conformation polymorphism (PCR-SSCP) analysis, were observed in 16 of 42 tumours (38%). The state of the p53 gene did not show any correlation with HPV infection. The terminal deoxynucleotidyl transferase (TdT)-mediated dUTP-biotin nick end labelling (TUNEL) method was used for detection of apoptotic cells. The mean AI was 2.35, ranging from 0.31 to 6.63. SCCs associated with p53 mutation had significantly lower AI than those without p53 mutation (P < 0.01), whereas no difference in AI was found between SCCs with and without HPV infection. The results of this study confirmed that HPV infection and/or p53 mutations are implicated, but are not mutually exclusive events, in carcinogenesis of oral SCC and also showed that decrease in apoptosis is more closely related to p53 mutation than HPV infection.

Zinc and brain injury

Zinc is an essential catalytic or structural element of many proteins, and a signaling messenger that is released by neural activity at many central excitatory synapses. Growing evidence suggests that zinc may also be a key mediator and modulator of the neuronal death associated with transient global ischemia and sustained seizures, as well as perhaps other neurological disease states. Manipulations aimed at reducing extracellular zinc accumulation, or cellular vulnerability to toxic zinc exposure, may provide a novel therapeutic approach toward ameliorating pathological neuronal death in these settings.

Measurement of intracellular free zinc in living cortical neurons: routes of entry

We used the ratioable fluorescent dye mag-fura-5 to measure intracellular free Zn2+ ([Zn2+]i) in cultured neocortical neurons exposed to neurotoxic concentrations of Zn2+ in concert with depolarization or glutamate receptor activation and identified four routes of Zn2+ entry. Neurons exposed to extracellular Zn2+ plus high K+ responded with a peak cell body signal corresponding to a [Zn2+]i of 35-45 nM. This increase in [Zn2+]i was attenuated by concurrent addition of Gd3+, verapamil, omega-conotoxin GVIA, or nimodipine, consistent with Zn2+ entry through voltage-gated Ca2+channels. Furthermore, under conditions favoring reverse operation of the Na+-Ca2+ exchanger, Zn2+ application induced a slow increase in [Zn2+]i and outward whole-cell current sensitive to benzamil-amiloride. Thus, a second route of Zn2+ entry into neurons may be via transporter-mediated exchange with intracellular Na+. Both NMDA and kainate also induced rapid increases in neuronal [Zn2+]i. The NMDA-induced increase was only partly sensitive to Gd3+ or to removal of extracellular Na+, consistent with a third route of entry directly through NMDA receptor-gated channels. The kainate-induced increase was highly sensitive to Gd3+ or Na+ removal in most neurons but insensitive in a minority subpopulation ("cobalt-positive cells"), suggesting that a fourth route of neuronal Zn2+ entry is through the Ca2+-permeable channels gated by certain subtypes of AMPA or kainate receptors.

The amino terminus of the F1-ATPase beta-subunit precursor functions as an intramolecular chaperone to facilitate mitochondrial protein import

Mitochondrial import signals have been shown to function in many steps of mitochondrial protein import. Previous studies have shown that the F1-ATPase beta-subunit precursor (pre-F1beta) of the yeast Saccharomyces cerevisiae contains an extended, functionally redundant mitochondrial import signal at its amino terminus. However, the full significance of this functionally redundant targeting sequence has not been determined. We now report that the extended pre-F1beta signal acts to maintain the precursor in an import-competent conformation prior to import, in addition to its previously characterized roles in mitochondrial targeting and translocation. We found that this extended signal is required for the efficient posttranslational mitochondrial import of pre-F1beta both in vivo and in vitro. To determine whether the pre-F1beta signal directly influences precursor conformation, fusion proteins that contain wild-type and mutant forms of the pre-F1beta import signal attached to the model passenger protein dihydrofolate reductase (DHFR) were constructed. Deletions that reduced the import signal to a minimal functional unit decreased both the half-time of precursor folding and the efficiency of mitochondrial import. To confirm that the reduced mitochondrial import associated with this truncated signal was due to a defect in its ability to maintain DHFR in a loosely folded conformation, we introduced structurally destabilizing missense mutations into the DHFR passenger to block precursor folding independently of the import signal. We found that the truncated signal imported this destabilized form of DHFR as efficiently as the intact targeting signal, indicating that the primary defect associated with the minimal signal is an inability to maintain the precursor in a loosely folded conformation. Our results suggest that the loss of this intramolecular chaperone function leads to defects in the early stages of the import process.

Slowly triggered excitotoxicity occurs by necrosis in cortical cultures

This study examined the possibility that the excitotoxin-induced death of cultured cortical neurons might occur by apoptosis, specifically focusing on the slowly triggered death induced by low concentrations of excitotoxin. Cultured murine cortical neurons (days in vitro 10-12) were exposed continuously to N-methyl-D-aspartate (10-15 microM), alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (3-100 microM) or kainate (30-60 microM) over 24 h. Within 2 h of exposure onset, neuronal cell body swelling was visible under phase-contrast optics. At this point, transmission electron microscopy revealed disruption of cell membranes and organelles, mitochondrial swelling and scattered chromatin condensation at the periphery of nuclei. By 8 h after exposure onset, many neurons were devoid of cytoplasmic structures, but nuclear membranes remained relatively intact. This excitotoxic degeneration was not blocked by the protein synthesis inhibitor, cycloheximide, or the growth factors, brain-derived neurotrophic factor or insulin-like growth factor-1, agents that did block serum deprivation-induced apoptosis death in other cultures. DNA agarose gel electrophoresis, however, revealed the transient occurrence of internucleosomal DNA fragmentation, appearing 4-8 h after exposure onset, but absent 24 h after exposure onset. The present results suggest that even slowly triggered excitotoxicity occurs by necrosis, and raise a cautionary note in interpreting internucleosomal DNA fragmentation in isolation as evidence for apoptosis.

The role of zinc in selective neuronal death after transient global cerebral ischemia

Zinc is present in presynaptic nerve terminals throughout the mammalian central nervous system and likely serves as an endogenous signaling substance. However, excessive exposure to extracellular zinc can damage central neurons. After transient forebrain ischemia in rats, chelatable zinc accumulated specifically in degenerating neurons in the hippocampal hilus and CA1, as well as in the cerebral cortex, thalamus, striatum, and amygdala. This accumulation preceded neurodegeneration, which could be prevented by the intraventricular injection of a zinc chelating agent. The toxic influx of zinc may be a key mechanism underlying selective neuronal death after transient global ischemic insults.

NADPH diaphorase-containing striatal or cortical neurons are resistant to apoptosis

The small subpopulation of striatal neurons containing nicotinamide adenine dinucleotide phosphate diaphorase (NADPH-d, recently identified as nitric oxide synthase, NOS) is selectively spared in Huntington's disease. Previous search for pathogenic mechanisms capable of destroying striatal neurons but sparing NADPH-d(+) cells has identified only NMDA receptor-mediated excitotoxicity. In view of suggestions that neuronal death in Huntington's disease may occur by apoptosis, we examined the vulnerability of NADPH-d(+) neurons to apoptosis. Murine striatal or cortical cultures exposed to serum deprivation developed extensive neuronal apoptosis, but NADPH-d(+) neurons were relatively spared. This sparing was seen when cultures were exposed to several other apoptosis-inducing insults. It was not seen after toxic exposure to H2O2, and it was not blocked by NOS inhibition. The selective resistance of NADPH-d(+) neurons to several forms of apoptosis provides key support for the possibility that apoptosis may contribute to the pathogenesis of Huntington's disease.