Adaptive Optimal Designs for Dose-Finding Studies with Time-to-Event Outcomes

We consider optimal design problems for dose-finding studies with censored Weibull time-to-event outcomes. Locally D-optimal designs are investigated for a quadratic dose–response model for log-transformed data subject to right censoring. Two-stage adaptive D-optimal designs using maximum likelihood estimation (MLE) model updating are explored through simulation for a range of different dose–response scenarios and different amounts of censoring in the model. The adaptive optimal designs are found to be nearly as efficient as the locally D-optimal designs. A popular equal allocation design can be highly inefficient when the amount of censored data is high and when the Weibull model hazard is increasing. The issues of sample size planning/early stopping for an adaptive trial are investigated as well. The adaptive D-optimal design with early stopping can potentially reduce study size while achieving similar estimation precision as the fixed allocation design.     

RFa-related peptides are algogenic: evidence in vitro and in vivo

RFamide (RFa)-related peptides modulate pain processing in the mammalian CNS. The effects of these peptides are generally considered as 'anti-opioid'. They also decrease the rate of desensitization of acid-sensing ionic channels (ASICs), putative nociceptors in dorsal root ganglia neurons [C. Askwith et al. (2000) Neuron, 26, 133-141]. We have tested the role of mollusc-derived peptide, FMRFa (Phe-Met-Arg-Phe-amide) and its synthetic analogues in peripheral nociception. Here we demonstrate that RFa-related peptides powerfully excite the majority of C-fibres in the skin-nerve preparation of rat: 76% of 55 tested fibres with the conduction velocity below 2 m/s responded with long-lasting discharges to the application of peptides (20 microm). When injected subcutaneously in vivo (mice), they initiate nociceptive behaviour. We confirm the data on humans [S. Ugawa et al. (2002) J. Clin. Invest., 110, 1185-1190]: the activation of C-fibres by acid is inhibited by channel blocker of ASICs, amiloride. However, there is no correlation in the sensitivity of C-fibres to RFa peptides, protons and amiloride: 74% of tested RFa-sensitive C-fibres were insensitive to protons and in 67% of cases the response to peptides was insensitive to amiloride. Thus, powerful excitatory/algogenic action of RFa-related peptides cannot be interpreted solely in terms of their interaction with ASICs. The peptides do not activate any conductance in the somatic membrane of dorsal root ganglion neurons of rats and probably affect still unidentified molecular target(s) responsible for nociceptive signalling.     

Interaction of coagulation factor VIII with members of the low-density lipoprotein receptor family follows common mechanism and involves consensus residues within the A2 binding site 484-509

Coagulation factor VIII interacts with several members of the low-density lipoprotein receptor family including low-density lipoprotein receptor-related protein, low-density lipoprotein receptor, and very low-density lipoprotein receptor. The present study was aimed to compare the mechanisms of factor VIII interaction with low-density lipoprotein receptor-related protein, megalin, low-density lipoprotein receptor, and very low-density lipoprotein receptor in order to reveal a general mode of these interactions. Binding of plasma-derived factor VIII and its fragments to recombinant soluble ligand-binding domain of low-density lipoprotein receptor (sLDLR1-7) and purified megalin was studied in solid phase and surface plasmon resonance assays. Full-length factor VIII and its light chain bound to the receptors with similar affinities (KD = 260 +/- 9 and 156 +/- 4 nmol/l, respectively, for megalin and KD = 210 +/- 3 and 174 +/- 13 nmol/l, respectively, for sLDLR1-7). Von Willebrand factor inhibited factor VIII binding to both receptors. In contrast to the light chain, exposure of the high-affinity receptor-binding site within the heavy chain (KD = 22 +/- 4 nmol/l for megalin and 17 +/- 3 nmol/l for sLDLR1-7) required proteolytic cleavage by thrombin. This site was mapped to the A2 domain residues 484-509, based on the inhibitory effects of anti-A2 monoclonal antibody 413, and is shared by all four receptors. Using a panel of A2 mutants, we identified key amino acid residues- positively charged K466, R471, R489 and R490, and hydrophilic residues Y487 and S488- which form the frame of this 'consensus' binding site. We conclude that interaction of factor VIII with the members of the low-density lipoprotein receptor family follows the general mode, requires dissociation of factor VIII from von Willebrand factor, and is activation sensitive.     

Pulmonary effects of inhaled diesel exhaust in aged mice

Pulmonary morbidity and mortality resulting from exposure to fine particulate matter (PM) increases with age. The present studies analyzed potential mechanisms underlying increased susceptibility of the elderly to PM using diesel exhaust (DE) as a model. Mice (2 m and 18 m) were exposed to DE (0, 300, and 1000 μg/m³) for 3 h once (single) or 3 h/day for 3 days (repeated). Bronchoalveolar lavage fluid (BAL), serum and lung tissue were collected 0 and 24 h later. Exposure to DE resulted in structural alterations in the lungs of older but not younger mice, including patchy thickening of the alveolar septa and inflammatory cell localization in alveolar spaces. These effects were most pronounced 24 h after a single exposure to the higher dose of DE. Significant increases in BAL nitrogen oxides were also noted in older mice, as well as expression of lipocalin 24p3, an oxidative stress marker in the lung with no effects in younger mice. Following DE inhalation, expression of Tumor Necrosis Factor alpha (TNFα) was upregulated in lungs of both younger and older mice; however, this was attenuated in older animals. Whereas exposure to DE resulted in increases in lung Interleukin-6 (IL-6) expression in both older and younger mice, IL-8 increased only in older animals. In younger mice, constitutive expression of manganese superoxide dismutase (MnSOD) decreased after DE exposure, while in older mice, constitutive MnSOD was not detectable and DE had no effect on expression of this antioxidant. Taken together, these results suggest that altered generation of inflammatory mediators and MnSOD may contribute to increased susceptibility of older mice to inhaled DE.     

A 3D Model of Human Cerebrovasculature Derived from 3T Magnetic Resonance Angiography

The human cerebrovasculature is extremely complicated and its three dimensional (3D) highly parcellated models, though necessary, are unavailable. We constructed a digital cerebrovascular model from a high resolution, 3T 3D time-of-flight magnetic resonance angiography scan. This model contains the arterial and venous systems and is 3D, geometric, highly parcellated, fully segmented, and completely labeled with name, diameter, and variants. Our approach replaces the tedious and time consuming process of checking and correcting automatic segmentation results done at 2D image level with an aggregate and faster process at 3D model level. The creation of the vascular model required vessel pre-segmentation, centerline extraction, vascular segments connection, centerline smoothing, vessel surface construction, vessel grouping, tracking, editing, labeling, setting diameter, and checking correctness and completeness. For comparison, the same scan was segmented automatically with 59.8% sensitivity and only 16.5% of vessels smaller than 1 pixel size were extracted. To check and correct this automatic segmentation requires 8 weeks. Conversely, the speedup of our approach (the number of 2D segmented areas/the number of 3D vascular segments) is 34. This cerebrovascular model can serve as a reference framework in clinical, research, and educational applications. The wealth of information aggregated with its quantification capabilities can augment or replace numerous textbook chapters. Five applications of the vascular model were described. The model is easily extendable in content, parcellation, and labeling, and the proposed approach is applicable for building a whole body vascular system.