Data splitting for artificial neural networks using SOM-based stratified sampling.

Data splitting is an important consideration during artificial neural network (ANN) development where hold-out cross-validation is commonly employed to ensure generalization. Even for a moderate sample size, the sampling methodology used for data splitting can have a significant effect on the quality of the subsets used for training, testing and validating an ANN. Poor data splitting can result in inaccurate and highly variable model performance; however, the choice of sampling methodology is rarely given due consideration by ANN modellers. Increased confidence in the sampling is of paramount importance, since the hold-out sampling is generally performed only once during ANN development. This paper considers the variability in the quality of subsets that are obtained using different data splitting approaches. A novel approach to stratified sampling, based on Neyman sampling of the self-organizing map (SOM), is developed, with several guidelines identified for setting the SOM size and sample allocation in order to minimize the bias and variance in the datasets. Using an example ANN function approximation task, the SOM-based approach is evaluated in comparison to random sampling, DUPLEX, systematic stratified sampling, and trial-and-error sampling to minimize the statistical differences between data sets. Of these approaches, DUPLEX is found to provide benchmark performance with good model performance, with no variability. The results show that the SOM-based approach also reliably generates high-quality samples and can therefore be used with greater confidence than other approaches, especially in the case of non-uniform datasets, with the benefit of scalability to perform data splitting on large datasets.

Improved human T-cell responses against synthetic HLA-0201 analog peptides derived from the WT1 oncoprotein.

Wilms tumor protein 1 (WT1) is a transcription factor overexpressed in several types of leukemia and solid tumors. For this reason, WT1 is an attractive target for immunotherapy. Four peptide nonamers from WT1 have been identified by others to generate a WT1-specific cytotoxic response in the context of human leukocyte antigen (HLA)-A0201 and A2402. However, as WT1 is a self-antigen, breaking tolerance is a potential obstacle to vaccination. Here, we use a strategy to circumvent tolerance by designing synthetic immunogenic analog peptides that could crossreact to the native peptides (a heteroclitic response). A number of synthetic peptides derived from nonamer sequences of the WT1 protein were designed in which single amino-acid substitutions were introduced at HLA-A0201 major histocompatibility complex (MHC)-binding positions. Several of new peptides could stabilize MHC class I A0201 molecules better than native sequences. Some analogs were also able to elicit WT1-specific T-cell recognition and cytotoxic T-cell lymphocytes more effectively than native sequences. Importantly, T cells stimulated with the new analogs crossreacted with the native WT1 peptide sequence and were able to kill HLA-matched chronic myeloid leukemia cell lines. In conclusion, analog heteroclitic WT1 peptides with increased immunogenicity can be synthesized and are potential cancer vaccine candidates.

Aerobic degradation of polychlorinated biphenyls by Alcaligenes sp. JB1: metabolites and enzymes.

In contrast to the degradation of penta- and hexachlorobiphenyls in chemostat cultures, the metabolism of PCBs by Alcaligenes sp. JB1 was shown to be restricted to PCBs with up to four chlorine substituents in resting-cell assays. Among these, the PCB congeners containing ortho chlorine substituents on both phenyl rings were found to be least degraded. Monochloro-benzoates and dichlorobenzoates were detected as metabolites. Resting cell assays with chlorobenzoates showed that JB1 could metabolize all three monochlorobenzoates and dichlorobenzoates containing only meta and para chlorine substituents, but not dichlorobenzoates possessing an ortho chlorine substituent. In enzyme activity assays, meta cleaving 2,3-dihydroxybiphenyl 1,2-dioxygenase and catechol 2,3-dioxygenase activities were constitutive, whereas benzoate dioxygenase and ortho cleaving catechol 1,2-dioxygenase activities were induced by their substrates. No activity was found for pyrocatechase II, the enzyme that is specific for chlorocatechols. The data suggest that complete mineralization of PCBs with three or more chlorine substituents by Alcaligenes sp. JB1 is unlikely.

In situ stimulation of aerobic PCB biodegradation in Hudson River sediments.

A 73-day field study of in situ aerobic biodegradation of polychlorinated biphenyls (PCBs) in the Hudson River shows that indigenous aerobic microorganisms can degrade the lightly chlorinated PCBs present in these sediments. Addition of inorganic nutrients, biphenyl, and oxygen enhanced PCB biodegradation, as indicated both by a 37 to 55 percent loss of PCBs and by the production of chlorobenzoates, intermediates in the PCB biodegradation pathway. Repeated inoculation with a purified PCB-degrading bacterium failed to improve biodegradative activity. Biodegradation was also observed under mixed but unamended conditions, which suggests that this process may occur commonly in river sediments, with implications for PCB fate models and risk assessments.

Evidence for novel mechanisms of polychlorinated biphenyl metabolism in Alcaligenes eutrophus H850.

Previous studies indicated that Alcaligenes eutrophus H850 attacks a different spectrum of polychlorinated biphenyl (PCB) congeners than do most PCB-degrading bacteria and that novel mechanisms of PCB degradation might be involved. To delineate this, we have investigated the differences in congener selectivity and metabolite production between H850 and Corynebacterium sp. strain MB1, an organism that apparently degrades PCBs via a 2,3-dioxygenase. H850 exhibited a superior ability to degrade congeners via attack on 2-, 2,4-, 2,5-, or 2,4,5-chlorophenyl rings in PCBs but an inferior ability to degrade congeners via attack on a 4-chlorophenyl ring. Reactivity preferences were also reflected in the products formed from unsymmetrical PCBs; thus MB1 attacked the 2,3-chlorophenyl ring of 2,3,2',5'-tetrachlorobiphenyl to yield 2,5-dichlorobenzoic acid, while H850 attacked the 2,5-chlorophenyl ring to yield 2,3-dichlorobenzoic acid and a novel metabolite, 2',3'-dichloroacetophenone. Furthermore, H850 oxidized 2,4,5,2',4',5'-hexachlorobiphenyl, a congener with no adjacent unsubstituted carbons, to 2',4',5'-trichloroacetophenone. The atypical congener selectivity pattern and novel metabolites produced suggest that A. eutrophus H850 may degrade certain PCB congeners by a new route beginning with attack by some enzyme other than the usual 2,3-dioxygenase.

5-Aminosalicylic acid enemas in refractory distal ulcerative colitis: a randomized, controlled trial.

5-Aminosalicylic acid (5-ASA), the presumed active moiety of sulfasalazine, has shown clinical efficacy when administered per rectum as initial therapy to patients with distal ulcerative colitis. We report the results of a randomized double-blind trial comparing nightly retention of a 4-g 5-ASA enema with continued administration of hydrocortisone enemas in 18 patients with persistent active distal ulcerative colitis after at least a 3-wk course of treatment with 100-mg hydrocortisone enemas with or without oral sulfasalazine. Continuation of hydrocortisone enemas rather than placebo was used in the control group to reflect the realistic alternative therapy likely to be employed in current practice. Response to therapy was assessed after 3 wk by comparing pretreatment and posttreatment point scores of clinical, sigmoidoscopic, and histological severity. Improvement in clinical score was achieved in seven of nine 5-ASA enema-treated patients versus one of nine hydrocortisone enema-treated patients (p less than 0.05). Sigmoidoscopic and histological improvement generally paralleled clinical improvement. We conclude that in patients with distal ulcerative colitis unresponsive to standard therapy, treatment with 5-ASA enemas results in significant short-term clinical and sigmoidoscopic improvement in a majority of cases. Moreover, a significantly greater number of refractory patients improve when switched to 5-ASA enemas than when continued on standard therapy.

A villous cell-derived inhibitor of intestinal cell proliferation.

To test the hypothesis that the intestinal villous cell synthesizes a mitotic inhibitor that is specific for crypt cells, we have partially purified an extract from rat intestinal villous cells (VCE) and have demonstrated that it strongly and reversibly inhibits cell division and DNA synthesis in an intestinal epithelial cell line (IEC-6 cells). VCE produced a 60--70% inhibition of [3H]thymidine incorporation into DNA and a similar magnitude of inhibition of labeling of nuclei in autoradiographic studies. This inhibition was not associated with cytotoxicity as assessed by the effect of VCE on 51Cr release, hexose or amino acid uptake, and protein synthesis. VCE appears specific for IEC-6 cells because it did not affect DNA synthesis in 10 other cell lines, and extracts derived from other cell lines and from colonic mucosa did not affect DNA synthesis in IEC-6 cells. VCE may represent a villous cell factor involved in the control of intestinal epithelial cell turnover in vivo.

Trace metal and essential fatty acid deficiency during total parenteral nutrition.

While deficiences of trace metals and essential fatty acids are rare in humans fed orally, the widespread use of total parenteral nutrition (TPN) has increased the likelihood of encountering these deficiences. A 14-year-old boy, with total villous atrophy of the small intestine, suffered from severe malnutrition and was placed on a conventional TPN regimen. Although not immediately recognized, he rapidly developed deficiencies of zinc, copper and essential fatty acids. Careful monitoring of the course of the illness and the responses to sequential treatments with zinc, lipid, and copper given intravenously allowed examination of the effects of the deficiencies on skin, intestine, liver, and hemopoietic systems and helped to establish normal requirements for the metals. The progress of the illness suggested that patients with intestinal malabsorption may be especially at risk of developing some of these lesser known complications of TPN.

Actions of peptides isolated from amphibian skin on pancreatic acinar cells.

In dispersed acinar cells prepared from guinea pig pancreas, peptides isolated from amphibian skin (caerulein, bombesin, litorin, and physalaemin) as well as eledoisin, a peptide isolated from the posterior salivary gland of a Mediterranean octopod, increased outflux of 45Ca, release of bound 45Ca, accumulation of cyclic GMP, and release of amylase. In addition, bombesin, litorin, physalaemin, and eledoisin each increased the initial uptake of 45Ca by dispersed acinar cells, whereas C-terminal octapeptide of porcine cholecystokinin (CCK-OP) and carbamylcholine did not increase the initial uptake of 45Ca but, rather, abolished the increase caused by the other agents. None of the actions of these amphibian peptides was altered by concentrations of atropine sufficient to abolish the effects of muscarinic cholinergic agents. None of the amphibian peptides altered cellular cyclic AMP or the increase caused by secretin or porcine vasoactive intestinal peptide (VIP). Acinar cells preincubated with 45Ca plus bombesin showed the same rate of release of 45Ca as did control cells and this rate was not altered by adding bombesin but was increased fivefold by adding CCK-OP. In terms of their chemical structures as well as the potency and efficacy with which they alter acinar cell function, the amphibian peptides plus CCK-OP can be grouped into three pairs: caerulein with CCK-OP, bombesin with litorin, and physalaemin with eledoisin.

H2-Histamine receptor blocking agents in the Zollinger-Ellison syndrome. Experience in seven cases and implications for long-term therapy.

H2-Histamine receptor blocking agents metiamide and cimetidine were assessed in seven patients with Zollinger-Ellison syndrome (serum gastrin greater than 300 microgram/ml, basal acid output greater than 15 meq/h, ratio of basal acid output to maximal acid output greater than 0.5). Intravenous or oral administration of the drugs lowered acid secretion by at least 70% in all cases. Subsequent treatment of six patients for 3 to 15 months (oral therapy) and one patient for 1 month (intravenous therapy) showed that the drugs abolished symptoms in all seven, abolished diarrhea in five, allowed ulcer healing in six, and were well tolerated without adverse effects in seven. No patient failed to respond to the drug, although one died from tumor progression and two required total gastrectomy for complex reasons. The results indicate that patients with Zollinger-Ellison syndrome can be managed medically and, in light of current mortality trends, gain little from the extra risks attending total gastrectomy.

Particulate' hexokinase activity in rat intestine. The comparative contributions of mitochondria and brush-border membranes.

The activity of hexokinase was examined in brush-border membranes purified from rat intestine. Compared with homogenates, purified membranes exhibited a 20-fold increase in sucrase specific activity and a 15-fold decrease in hexokinase specific activity, which argues against the structural localization of hexokinase within the brush-border membrane.