Statistics and replication experiments: Comparing interaction effects

A method is presented that allows the comparison and combination of interaction effects obtained in two or more experiments. Using an analysis of variance model, we first evaluated the interaction effects found in experiments conducted by Alloy and Abramson (1979, Experiment 2) and Bryson, Doan, and Pasquali (1984). Both experiments examined the same independent (level of depression and outcome frequency) and dependent (judgment of control) variables. Whereas Alloy and Abramson reported a significant depression ×outcome frequency interaction for female subjects, Bryson et al. failed to find any significant interaction effects. The latter authors challenged the replicability of the Alloy and Abramson results. Our reanalyses of the results from these two studies indicated that, for females, Bryson et al. produced an interaction effect not different from that of Alloy and Abramson. Our next task was to compare the conclusions reached from our analytical approach with those based on standard meta-analytic methods (Rosenthal, 1984). Finally, we evaluated the general utility of the two analytical approaches and made some general comments about replication experiments. We thank Margaret Murray for her contributions to early stages of this project. The comments and advice of Rebecca Warner, Paul Sweeney, William Stine, Carolyn Mebert, Ellen Cohn, Vernon Padgett, David Sugarman, and several anonymous reviewers are appreciated.     

Do current therapeutic anti-Aβ antibodies for Alzheimer’s disease engage the target?

Reducing amyloid-β peptide (Aβ) burden at the pre-symptomatic stages of Alzheimer’s disease (AD) is currently the advocated clinical strategy for treating this disease. The most developed method for targeting Aβ is the use of monoclonal antibodies including bapineuzumab, solanezumab and crenezumab. We have synthesized these antibodies and used surface plasmon resonance (SPR) and mass spectrometry to characterize and compare the ability of these antibodies to target Aβ in transgenic mouse tissue as well as human AD tissue. SPR analysis showed that the antibodies were able to bind Aβ with high affinity. All of the antibodies were able to bind Aβ in mouse tissue. However, significant differences were observed in human brain tissue. While bapineuzumab was able to capture a variety of N-terminally truncated Aβ species, the Aβ detected using solanezumab was barely above detection limits while crenezumab did not detect any Aβ. None of the antibodies were able to detect any Aβ species in human blood. Immunoprecipitation experiments using plasma from AD subjects showed that both solanezumab and crenezumab have extensive cross-reactivity with non-Aβ related proteins. Bapineuzumab demonstrated target engagement with brain Aβ, consistent with published clinical data. Solanezumab and crenezumab did not, most likely as a result of a lack of specificity due to cross-reactivity with other proteins containing epitope overlap. This lack of target engagement raises questions as to whether solanezumab and crenezumab are suitable drug candidates for the preventative clinical trials for AD.     

A Retrospective Quasi-Experimental Study of a Transitional Housing Program for Patients with Severe and Persistent Mental Illness

Transitional housing programs aim to improve living skills and housing stability for tenuously housed patients with mental illness. 113 consecutive Transitional Housing Team (THT) patients were matched to 139 controls on diagnosis, time of presentation, gender and prior psychiatric hospitalisation and compared using a difference-in-difference analysis for illness acuity and service use outcomes measured 1 year before and after THT entry/exit. There was a statistically significant difference-in-difference favouring THT participants for bed days (mean difference in difference ?20.76 days, SE 9.59, p = 0.031) and living conditions (HoNOS Q11 mean difference in difference ?0.93, SE 0.23, p < 0.001). THT cost less per participant (I$14,024) than the bed-days averted (I$17,348). The findings of reductions in bed days and improved living conditions suggest that transitional housing programs can have a significant positive impact for tenuously housed patients with high inpatient service usage, as well as saving costs for mental health services.     

Calcium Influx,But Not Intracellular Calcium Release,Supports PACAP-Mediated ERK Activation in HEK PAC1 Receptor Cells

In HEK cells expressing GFP-tagged PAC1Hop1 receptors, PACAP augments ERK phosphorylation through two parallel pathways: one through PACAP/PAC1 receptor internalization/endosome MEK/ERK signaling and the other through PLC/DAG/PKC activation. We examined whether elevation of intracellular calcium ([Ca²⁺]_i) was required for either of the PACAP/PAC1 receptor-mediated ERK activation mechanisms. The PACAP (25 nM)-induced elevation of [Ca²⁺]_i was greater with cells maintained in Ca²⁺-containing than in Ca²⁺-deficient solution, suggesting that both calcium release from internal stores and calcium influx contributed to the rise in [Ca²⁺]_i. A thapsigargin-induced increase in [Ca²⁺]_i also was greater with calcium in the external solution. OAG, the cell permeable analogue of DAG, increased [Ca²⁺]_i, but only in Ca²⁺-containing solution. Decreasing external calcium or depleting internal calcium stores did not block PACAP-induced PAC1 receptor internalization. Omission of calcium from the external solution, but not thapsigargin pretreatment, significantly blunted PACAP-stimulated ERK phosphorylation. The PKC inhibitor BimI decreased PACAP-mediated ERK activation in both Ca²⁺-containing or Ca²⁺-deficient solutions. In contrast, following Pitstop 2 pretreatment to block endocytic mechanisms, PACAP activated ERK only when calcium was present in the external solution. We conclude that the endosome signaling pathway is largely calcium-independent whereas calcium influx appears necessary for the PLC/DAG/PKC component of PACAP-induced ERK activation.     

Can There be a Place for Intraoperative Salvaged Blood in Spine Tumor Surgery?

Background

Intraoperative cell salvage (IOCS) has been used in musculoskeletal surgery extensively. However, it has never found its place in musculoskeletal oncologic surgery. We have conducted the first-ever study to evaluate the feasibility of IOCS in combination with a leucocyte-depletion filter (LDF) in metastatic spine tumor surgery. This was to pave the path for use of IOCS-LDF in musculoskeletal oncologic surgery.

Methods

Patients with a known primary epithelial tumor, who were offered surgery for metastatic spinal disease, were recruited. Blood samples were collected at three different stages during the surgery: from the operative field before IOCS processing, after IOCS processing, and after IOCS-LDF processing. Three separate samples (5 mL each) were taken at each stage. Samples were examined using immunohistochemical monoclonal antibodies to identify tumor cells of epithelial origin.

Results

Of 30 patients in the study, 6 were excluded for not fulfilling the inclusion criteria, leaving 24 patients. Malignant tumor cells were detected in the samples from the operative field before IOCS processing in eight patients and in the samples from the transfusion bag after IOCS processing in three patients. No viable malignant cell was detectable in any of the blood samples after passage through both IOCS and LDF.

Conclusions

The findings support the notion that the IOCS-LDF combination works effectively in eliminating tumor cells from salvaged blood, so this technique can be applied successfully in spine tumor surgery. This concept can then further be extended to whole musculoskeletal tumor surgery and other oncologic surgeries with further appropriate clinical studies.