Intravitreal and subconjunctival melphalan for retinoblastoma in transgenic mice.

Purpose. To measure the chemotherapeutic effects of focal melphalan (intravitreal and subconjunctival) on tumor burden, hypoxia, and vasculature in LHBETATAG murine retinoblastoma model. Methods. LHBETATAG transgenic mice were treated with a single 1 mcg intravitreal injection of melphalan, 100 mcg subconjunctival injection, or semiweekly 10 mcg subconjunctival injections for 3 weeks. At 1 or 3 weeks, eyes were enucleated, serially sectioned, and processed with haematoxylin and eosin (H&E) for tumor burden measurements and probed with immunofluorescence to analyze tumor hypoxia and vasculature. Results. Focal melphalan significantly reduced retinal tumor size (P < 0.02) when given intravitreally or subconjunctivally. Eyes treated with a one-time intravitreal injection of 1 mcg melphalan had significantly smaller tumors at both 1 week (P = 0.017) and at 3 weeks after injection (P = 0.005). Intratumoral hypoxia showed a significant decline in hypoxia at 1 week following intravitreal injection and after maximum dosage of subconjunctival melphalan. Total vasculature was not significantly affected following intravitreal administration. Conclusion. Focal delivery of melphalan via intravitreal or subconjunctival injection has a significant effect on reducing tumor burden, hypoxia, and vasculature, in the treatment of murine retinoblastoma tumors.

Use of lambda phage DNA as a hybrid internal control in a PCR-enzyme immunoassay to detect Chlamydia pneumoniae.

An inherent problem in the diagnostic PCR assay is the presence of ill-defined inhibitors of amplification which may cause false-negative results. Addition of an amplifiable fragment of foreign DNA in the PCR to serve as a hybrid internal control (HIC) would allow for a simple way to identify specimens containing inhibitors. Two oligonucleotide hybrid primers were synthesized to contain nucleic acid sequences of the Chlamydia pneumoniae 16S rRNA primers in a position flanking two primers that target the sequences of a 650-bp lambda phage DNA segment. By using the hybrid primers, hybrid DNA comprising a large sequence of lambda phage DNA flanked by short pieces of chlamydia DNA was subsequently generated by PCR, cloned into a plasmid vector, and purified. Plasmids containing the hybrid DNA were diluted and used as a HIC by adding them to each C. pneumoniae PCR test. Consequently, C. pneumoniae primers were able to amplify both chlamydia DNA and the HIC DNA. The production of a 689-bp HIC DNA band on an acrylamide gel indicated that the specimen contained no inhibitors and that internal conditions were compatible with PCR. Subsequently, a biotinylated RNA probe for the HIC was transcribed from a nested sequence of the HIC and was used for its hybridization. Detection of the HIC DNA-RNA hybrid was achieved by enzyme immunoassay (EIA). This PCR-EIA system with a HIC was initially tested with 12 previously PCR-positive and 14 previously PCR-negative specimens. Of the 12 PCR-positive specimens, 11 were reconfirmed as positive; 1 had a negative HIC value, indicating inhibition. Of the 14 previously PCR-negative specimens, 13 were confirmed as true negative; 1 had a negative HIC value, indicating inhibition. The assay was then used with 237 nasopharyngeal specimens from patients with pneumonia. Twenty-one of 237 (8.9%) were positive for C. pneumoniae, and 42 (17.7%) were found to inhibit the PCR. Specimens showing inhibitory activity were diluted 1:10 and were retested. Ten specimens were still inhibitory to the PCR and required further DNA purification. No additional positive samples were detected and 3 nasopharyngeal specimens remained inhibitory to PCR. Coamplification of a HIC DNA can help confirm true-negative PCR results by ruling out the presence of inhibitors of DNA amplification.

Alzheimer's presenilin mutation sensitizes neural cells to apoptosis induced by trophic factor withdrawal and amyloid beta-peptide: involvement of calcium and oxyradicals.

Most autosomal dominant inherited forms of early onset Alzheimer's disease (AD) are caused by mutations in the presenilin-1 (PS-1) gene on chromosome 14. PS-1 is an integral membrane protein with six to nine membrane-spanning domains and is expressed in neurons throughout the brain wherein it is localized mainly in endoplasmic reticulum (ER). The mechanism or mechanisms whereby PS-1 mutations promote neuron degeneration in AD are unknown. Recent findings suggest links among deposition of amyloid beta-peptide (Abeta), oxidative stress, disruption of ion homeostasis, and an apoptotic form of neuron death in AD. We now report that expression of the human PS-1 L286V mutation in PC12 cells increases their susceptibility to apoptosis induced by trophic factor withdrawal and Abeta. Increases in oxidative stress and intracellular calcium levels induced by the apoptotic stimuli were exacerbated greatly in cells expressing the PS-1 mutation, as compared with control cell lines and lines overexpressing wild-type PS-1. The antiapoptotic gene product Bcl-2 prevented apoptosis after NGF withdrawal from differentiated PC12 cells expressing mutant PS-1. Elevations of [Ca2+]i in response to thapsigargin, an inhibitor of the ER Ca2+-ATPase, were increased in cells expressing mutant PS-1, and this adverse effect was abolished in cells expressing Bcl-2. Antioxidants and blockers of calcium influx and release from ER protected cells against the adverse consequences of the PS-1 mutation. By perturbing cellular calcium regulation and promoting oxidative stress, PS-1 mutations may sensitize neurons to apoptotic death in AD.

Alzheimer's PS-1 mutation perturbs calcium homeostasis and sensitizes PC12 cells to death induced by amyloid beta-peptide.

Mutations in the presenilin-1 (PS-1) gene on chromosome 14 are linked to autosomal dominant early-onset Alzheimer's disease. The amino acid sequence of PS-1 predicts an integral membrane protein and immunocytochemical studies indicate that PS-1 is localized to endoplasmic reticulum (ER). We report that expression of PS-1 mutation L286V in cultured PC12 cells exaggerates Ca2+ responses to agonists (carbachol and bradykinin) that induce Ca2+ release from ER. Cells expressing L286V exhibit enhanced elevations of [Ca2+]i following exposure to amyloid beta-peptide (A beta) and increased vulnerability to A beta toxicity. An antagonist of voltage-dependent calcium channels (nifedipine), and a blocker of Ca2+ release from ER (dantrolene), counteract the adverse consequences of the PS-1 mutation. By perturbing Ca2+ homeostasis, PS-1 mutations may sensitize neurons to A beta-induced apoptosis.

Increased activity-regulating and neuroprotective efficacy of alpha-secretase-derived secreted amyloid precursor protein conferred by a C-terminal heparin-binding domain.

Proteolytic cleavage of beta-amyloid precursor protein (beta APP) by alpha-secretase results in release of one secreted form (sAPP) of APP (sAPP alpha), whereas cleavage by beta-secretase releases a C-terminally truncated sAPP (sAPP beta) plus amyloid beta-peptide (A beta). beta APP mutations linked to some inherited forms of Alzheimer's disease may alter its processing such that levels of sAPP alpha are reduced and levels of sAPP beta increased. sAPP alpha s may play important roles in neuronal plasticity and survival, whereas A beta can be neurotoxic. sAPP alpha was approximately 100-fold more potent than sAPP beta in protecting hippocampal neurons against excitotoxicity, A beta toxicity, and glucose deprivation. Whole-cell patch clamp and calcium imaging analyses showed that sAPP beta was less effective than sAPP alpha in suppressing synaptic activity, activating K+ channels, and attenuating calcium responses to glutamate. Using various truncated sAPP alpha and sAPP beta APP695 products generated by eukaryotic and prokaryotic expression systems, and synthetic sAPP peptides, the activity of sAPP alpha was localized to amino acids 591-612 at the C-terminus. Heparinases greatly reduced the actions of sAPP alpha s, indicating a role for a heparin-binding domain at the C-terminus of sAPP alpha in receptor activation. These findings indicate that alternative processing of beta APP has profound effects on the bioactivity of the resultant sAPP products and suggest that reduced levels of sAPP alpha could contribute to neuronal degeneration in Alzheimer's disease.

cDNA cloning and chromosome mapping of the human Fe65 gene: interaction of the conserved cytoplasmic domains of the human beta-amyloid precursor protein and its homologues with the mouse Fe65 protein.

Using the yeast two hybrid system, a mouse embryo cDNA library was screened for proteins that interact with the C-terminus of the human beta-amyloid precursor protein (beta PP). A fusion protein was identified that interacts specifically with the cytoplasmic domain of beta PP and does not interact with the beta-amyloid region. The protein encoded by this partial mouse cDNA is identical to the C-terminus of the rat Fe65 protein. This mouse protein also interacts with the homologous C-terminal domains of the mouse amyloid precursor-like proteins, APLP1 and APLP2. These conserved cytoplasmic regions contain a common amino acid motif, Asn-Pro-Thr-Tyr, which has previously been shown to influence both the secretion and internalization of beta PP. Fe65 has been implicated in regulatory and cell signaling mechanisms because it contains two different motifs involved in protein binding, a WW domain (a variant of Src homology 3 domains) and a phosphotyrosine interaction domain (PID). Interestingly, the PID domain binds to the same motif present in the conserved cytoplasmic domains of the beta PP and beta PP-like proteins. RNA analyses reveal that Fe65 is predominantly expressed in brain and in the regions most affected by Alzheimer's disease (AD)-associated neuropathology. The human Fe65 mRNA was cloned from a fetal brain cDNA library. The message encodes a protein of 735 amino acids that is 95% identical to the rat Fe65 protein. The human Fe65 gene was mapped on human metaphase chromosomes to band 11p15 using fluorescence in situ hybridization.