Immunoaffinity enrichment coupled to quantitative mass spectrometry reveals ubiquitin-mediated signaling events

Ubiquitination is one of the most prevalent posttranslational modifications in eukaryotic cells, with functional importance in protein degradation, subcellular localization and signal transduction pathways. Immunoaffinity enrichment coupled with quantitative mass spectrometry enables the in-depth characterization of protein ubiquitination events at the site-specific level. We have applied this strategy to investigate cellular response triggered by two distinct type agents: small molecule inhibitors of the tumor-associated kinases MEK and PI3K or the pro-inflammatory cytokine IL-17. Temporal profiling of protein ubiquitination events across a series of time points covering the biological response permits interrogation of signaling through thousands of quantified proteins, of which only a subset display significant and physiologically meaningful regulation. Distinctive clusters of residues within proteins can display distinct temporal patterns attributable to diverse molecular functions, although the majority of differential ubiquitination appears as a coordinated response across the modifiable residues present within an individual substrate. In cells treated with a combination of MEK and PI3K inhibitors, we found differential ubiquitination of MEK within the first hour after treatment and a series of mitochondria proteins at later time points. In the IL-17 signaling pathway, ubiquitination events on several signaling proteins including HOIL-1 and Tollip were observed. The functional relevance of these putative IL-17 mediators was subsequently validated by knockdown of HOIL-1, HOIP and TOLIP, each of which decreased IL-17-stimulated cytokine production. Together, these data validate proteomic profiling of protein ubiquitination as a viable approach for identifying dynamic signaling components in response to intracellular and extracellular perturbations.

Plasticity in sunflower leaf and cell growth under high salinity

A group of sunflower lines that exhibit a range of leaf Na(+) concentrations under high salinity was used to explore whether the responses to the osmotic and ionic components of salinity can be distinguished in leaf expansion kinetics analysis. It was expected that at the initial stages of the salt treatment, leaf expansion kinetics changes would be dominated by responses to the osmotic component of salinity, and that later on, ion inclusion would impose further kinetics changes. It was also expected that differential leaf Na(+) accumulation would be reflected in specific changes in cell division and expansion rates. Plants of four sunflower lines were gradually treated with a relatively high (130 mm NaCl) salt treatment. Leaf expansion kinetics curves were compared in leaves that were formed before, during and after the initiation of the salt treatment. Leaf areas were smaller in salt-treated plants, but the analysis of growth curves did not reveal differences that could be attributed to differential Na(+) accumulation, since similar changes in leaf expansion kinetics were observed in lines with different magnitudes of salt accumulation. Nevertheless, in a high leaf Na(+) -including line, cell divisions were affected earlier, resulting in leaves with proportionally fewer cells than in a Na(+) -excluding line. A distinct change in leaf epidermal pavement shape caused by salinity is reported for the first time. Mature pavement cells in leaves of control plants exhibited typical lobed, jigsaw-puzzle shape, whereas in treated plants, they tended to retain closer-to-circular shapes and a lower number of lobes.

Dual leucine zipper kinase is required for excitotoxicity-induced neuronal degeneration

Loss of dual leucine zipper kinase results in attenuated JNK/c-Jun stress response pathway activation and reduced neuronal degeneration after kainic acid–induced excitotoxic seizures.

Excessive glutamate signaling is thought to underlie neurodegeneration in multiple contexts, yet the pro-degenerative signaling pathways downstream of glutamate receptor activation are not well defined. We show that dual leucine zipper kinase (DLK) is essential for excitotoxicity-induced degeneration of neurons in vivo. In mature neurons, DLK is present in the synapse and interacts with multiple known postsynaptic density proteins including the scaffolding protein PSD-95. To examine DLK function in the adult, DLK-inducible knockout mice were generated through Tamoxifen-induced activation of Cre-ERT in mice containing a floxed DLK allele, which circumvents the neonatal lethality associated with germline deletion. DLK-inducible knockouts displayed a modest increase in basal synaptic transmission but had an attenuation of the JNK/c-Jun stress response pathway activation and significantly reduced neuronal degeneration after kainic acid–induced seizures. Together, these data demonstrate that DLK is a critical upstream regulator of JNK-mediated neurodegeneration downstream of glutamate receptor hyper-activation and represents an attractive target for the treatment of indications where excitotoxicity is a primary driver of neuronal loss.

Ser1292 autophosphorylation is an indicator of LRRK2 kinase activity and contributes to the cellular effects of PD mutations

Mutations in the leucine-rich repeat kinase 2 (LRRK2) gene are the most common cause of familial Parkinson's disease (PD). Although biochemical studies have shown that certain PD mutations confer elevated kinase activity in vitro on LRRK2, there are no methods available to directly monitor LRRK2 kinase activity in vivo. We demonstrate that LRRK2 autophosphorylation on Ser(1292) occurs in vivo and is enhanced by several familial PD mutations including N1437H, R1441G/C, G2019S, and I2020T. Combining two PD mutations together further increases Ser(1292) autophosphorylation. Mutation of Ser(1292) to alanine (S1292A) ameliorates the effects of LRRK2 PD mutations on neurite outgrowth in cultured rat embryonic primary neurons. Using cell-based and pharmacodynamic assays with phosphorylated Ser(1292) as the readout, we developed a brain-penetrating LRRK2 kinase inhibitor that blocks Ser(1292) autophosphorylation in vivo and attenuates the cellular consequences of LRRK2 PD mutations in vitro. These data suggest that Ser(1292) autophosphorylation may be a useful indicator of LRRK2 kinase activity in vivo and may contribute to the cellular effects of certain PD mutations.

JNK-mediated phosphorylation of DLK suppresses its ubiquitination to promote neuronal apoptosis

Neuronal injury induces JNK phosphorylation of DLK, which reduces DLK ubiquitination and creates a positive feedback loop to enhance JNK signaling and increase apoptosis.

Neurons are highly polarized cells that often project axons a considerable distance. To respond to axonal damage, neurons must transmit a retrograde signal to the nucleus to enable a transcriptional stress response. Here we describe a mechanism by which this signal is propagated through injury-induced stabilization of dual leucine zipper-bearing kinase (DLK/MAP3K12). After neuronal insult, specific sites throughout the length of DLK underwent phosphorylation by c-Jun N-terminal kinases (JNKs), which have been shown to be downstream targets of DLK pathway activity. These phosphorylation events resulted in increased DLK abundance via reduction of DLK ubiquitination, which was mediated by the E3 ubiquitin ligase PHR1 and the de-ubiquitinating enzyme USP9X. Abundance of DLK in turn controlled the levels of downstream JNK signaling and apoptosis. Through this feedback mechanism, the ubiquitin–proteasome system is able to provide an additional layer of regulation of retrograde stress signaling to generate a global cellular response to localized external insults.

Abstract 4462: Resistance to selective kinase inhibitors upon epithelial to mesenchymal transition

Epithelial to mesenchymal transition (EMT) is a pivotal mechanism contributing to cancer metastasis and has been associated with resistance to multiple cancer therapies including targeted kinase inhibitors (TKIs). EMT has been associated with an acquired resistance to the EGFR TKI erlotinib independent of known resistance mechanisms such as secondary mutations T790M or MET amplification. RTK-addicted cancer cell lines that are induced to undergo EMT with exogenous TGF-β become resistant to their appropriate TKI. In vitro-based assays determined that the resistance is not due to exogenous TGF-β, drug efflux, or autocrine/paracrine growth factor signaling. To identify potential therapeutic vulnerabilities specifically within the mesenchymal, TKI resistant cells, we performed a small molecule screen of approximately 200 agents using the EGFR mutant non-small cell lung cancer (NSCLC) HCC827 cell line and its corresponding TGF-β-induced mesenchymal derivative line. This screen revealed that the mesenchymal cells are cross-resistant to a variety of small molecules, including TKIs and chemotherapeutic agents. However, a small number of agents showed selective growth inhibitory activity against the mesenchymal cells, with the most potent being the dual Brc-Abl and Src inhibitor, dasatinib. Within the parental HCC827 cell line, we detected a non-proliferating vimentin positive sub-population of cells. Interestingly, when the parental cell line was co-treated with erlotinib and dasatinib the entire cell population was killed and drug-resistant clones failed to emerge after prolonged treatment. To determine the mechanism underlying the resistance observed within the mesenchymal cells a proteomic analysis was undertaken, which demonstrated that the focal adhesion kinase, FAK, is the most abundant differentially phosphorylated protein in the resistant mesenchymal cells that is specifically suppressed by dasatinib. However, specific gene knock-down of FAK was not sufficient to kill the mesenchymal cells or revert their sensitivity to Erlotinib suggesting that FAK alone is not required to maintain resistance upon EMT. These findings identify dasatinib as a potential therapeutic for treatment of erlotinib resistance associated with EMT.

Citation Format: Catherine R. Wilson, Katrina Nicholes, Daisy Bustos, Eva Lin, Lily Shi, Donald Kirkpatrick, Jeffrey Settleman. Resistance to selective kinase inhibitors upon epithelial to mesenchymal transition. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 4462. doi:10.1158/1538-7445.AM2013-4462

HectD1 E3 ligase modifies adenomatous polyposis coli (APC) with polyubiquitin to promote the APC-axin interaction

The adenomatous polyposis coli (APC) protein functions as a negative regulator of the Wnt signaling pathway. In this capacity, APC forms a "destruction complex" with Axin, CK1α, and GSK3β to foster phosphorylation of the Wnt effector β-catenin earmarking it for Lys-48-linked polyubiquitylation and proteasomal degradation. APC is conjugated with Lys-63-linked ubiquitin chains when it is bound to Axin, but it is unclear whether this modification promotes the APC-Axin interaction or confers upon APC an alternative function in the destruction complex. Here we identify HectD1 as a candidate E3 ubiquitin ligase that modifies APC with Lys-63 polyubiquitin. Knockdown of HectD1 diminished APC ubiquitylation, disrupted the APC-Axin interaction, and augmented Wnt3a-induced β-catenin stabilization and signaling. These results indicate that HectD1 promotes the APC-Axin interaction to negatively regulate Wnt signaling.

Characterizing ubiquitination sites by peptide-based immunoaffinity enrichment

Advances in high resolution tandem mass spectrometry and peptide enrichment technologies have transformed the field of protein biochemistry by enabling analysis of end points that have traditionally been inaccessible to molecular and biochemical techniques. One field benefitting from this research has been the study of ubiquitin, a 76-amino acid protein that functions as a covalent modifier of other proteins. Seminal work performed decades ago revealed that trypsin digestion of a branched protein structure known as A24 yielded an enigmatic diglycine signature bound to a lysine residue in histone 2A. With the onset of mass spectrometry proteomics, identification of K-GG-modified peptides has emerged as an effective way to map the position of ubiquitin modifications on a protein of interest and to quantify the extent of substrate ubiquitination. The initial identification of K-GG peptides by mass spectrometry initiated a flurry of work aimed at enriching these post-translationally modified peptides for identification and quantification en masse. Recently, immunoaffinity reagents have been reported that are capable of capturing K-GG peptides from ubiquitin and its thousands of cellular substrates. Here we focus on the history of K-GG peptides, their identification by mass spectrometry, and the utility of immunoaffinity reagents for studying the mechanisms of cellular regulation by ubiquitin.

Complementary proteomic tools for the dissection of apoptotic proteolysis events

Proteolysis is a key regulatory event that controls intracellular and extracellular signaling through irreversible changes in a protein's structure that greatly alters its function. Here we describe a platform for profiling caspase substrates which encompasses two highly complementary proteomic techniques--the first is a differential gel based approach termed Global Analyzer of SILAC-derived Substrates of Proteolysis (GASSP) and the second involves affinity enrichment of peptides containing a C-terminal aspartic acid residue. In combination, these techniques have enabled the profiling of a large cellular pool of apoptotic-mediated proteolytic events across a wide dynamic range. By applying this integrated proteomic work flow to analyze proteolytic events resulting from the induction of intrinsic apoptosis in Jurkat cells via etoposide treatment, 3346 proteins were quantified, of which 360 proteins were identified as etoposide-induced proteolytic substrates, including 160 previously assigned caspase substrates. In addition to global profiling, a targeted approach using BAX HCT116 isogenic cell lines was utilized to dissect pre- and post-mitochondrial extrinsic apoptotic cleavage events. By employing apoptotic activation with a pro-apoptotic receptor agonist (PARA), a limited set of apoptotic substrates including known caspase substrates such as BH3 interacting-domain death agonist (BID) and Poly (ADP-ribose) polymerase (PARP)-1, and novel substrates such as Basic Transcription Factor 3, TRK-fused gene protein (TFG), and p62/Sequestosome were also identified.

Improved quantitative mass spectrometry methods for characterizing complex ubiquitin signals

Ubiquitinated substrates can be recruited to macromolecular complexes through interactions between their covalently bound ubiquitin (Ub) signals and Ub receptor proteins. To develop a functional understanding of the Ub system in vivo, methods are needed to determine the composition of Ub signals on individual substrates and in protein mixtures. Mass spectrometry has emerged as an important tool for characterizing the various forms of Ub. In the Ubiquitin-AQUA approach, synthetic isotopically labeled internal standard peptides are used to quantify unbranched peptides and the branched -GG signature peptides generated by trypsin digestion of Ub signals. Here we have built upon existing methods and established a comprehensive platform for the characterization of Ub signals. Digested peptides and isotopically labeled standards are analyzed either by selected reaction monitoring on a QTRAP mass spectrometer or by narrow window extracted ion chromatograms on a high resolution LTQ-Orbitrap. Additional peptides are now monitored to account for the N terminus of ubiquitin, linear polyUb chains, the peptides surrounding K33 and K48, and incomplete digestion products. Using this expanded battery of peptides, the total amount of Ub in a sample can be determined from multiple loci within the protein, minimizing possible confounding effects of complex Ub signals, digestion abnormalities, or use of mutant Ub in experiments. These methods have been useful for the characterization of in vitro, multistage ubiquitination and have now been extended to reactions catalyzed by multiple E2 enzymes. One question arising from in vitro studies is whether individual protein substrates in cells may be modified by multiple forms of polyUb. Here we have taken advantage of recently developed polyubiquitin linkage-specific antibodies recognizing K48- and K63-linked polyUb chains, coupled with these mass spectrometry methods, to further evaluate the abundance of mixed linkage Ub substrates in cultured mammalian cells. By combining these two powerful tools, we show that polyubiquitinated substrates purified from cells can be modified by mixtures of K48, K63, and K11 linkages.

K11-linked polyubiquitination in cell cycle control revealed by a K11 linkage-specific antibody

Polyubiquitination is a posttranslational modification where ubiquitin chains containing isopeptide bonds linking one of seven ubiquitin lysines with the C terminus of an adjoining ubiquitin are covalently attached to proteins. While functions of K48- and K63-linked polyubiquitin are understood, the role(s) of noncanonical K11-linked chains is less clear. A crystal structure of K11-linked diubiquitin demonstrates a distinct conformation from K48- or K63-linked diubiquitin. We engineered a K11 linkage-specific antibody and use it to demonstrate that K11 chains are highly upregulated in mitotic human cells precisely when substrates of the ubiquitin ligase anaphase-promoting complex (APC/C) are degraded. These chains increased with proteasomal inhibition, suggesting they act as degradation signals in vivo. Inhibition of the APC/C strongly impeded the formation of K11-linked chains, suggesting that a single ubiquitin ligase is the major source of mitotic K11-linked chains. Our results underscore the importance of K11-linked ubiquitin chains as critical regulators of mitotic protein degradation.

Loss of maternally derived human herpesvirus-6 immunity and natural infection in Argentinian infants

BACKGROUND

Human herpesvirus-6 (HHV-6) infection is widespread throughout the world. No data are available in Argentina about the loss of maternally derived HHV-6 immunity and natural infection in infants.

METHODS

A population of 100 pregnant women and 407 children between 1 and 15 months of age were assayed by indirect immunofluorescence to detect and quantify specific IgG anti-human herpesvirus-6 (anti-HHV-6) antibodies in Córdoba City, Argentina.

RESULTS

There was no significant difference in the positive rate between infants aged 1 to 9 months (range, 43.6 35.5%) and pregnant women (37%). Seropositive ratio dropped in the 10-month group (23.33% seropositive) and rose sharply in the 11-month group (38.89%), 12-month (60.61%), and 13- to 15-month group (63.46%). The geometric mean titer (GMT) for infants in the 12 to 15 months age group (23.4 41.64) was significantly higher than the GMT for infants 10 months of age (11.04) (P < 0.05 with the Tukey-HSD test).

CONCLUSIONS

This study shows a significant association between loss of passive HHV-6 antibody and age among infants. The results support evidence that HHV-6 enters the susceptible population at 11 months, leading to a high prevalence of antibodies in children between 13 and 15 months of age.

Quantification of fecal neutrophils by MPO determination (myeloperoxidase) in patients with invasive diarrhea. Cuantificación de neutrofilos fecales mediante la determinación de MPO (Mieloperoxidasa) en pacientes con diarrea invasiva

Myeloperoxidase (MPO), a specific polymorphonuclear leukocyte enzyme, has been used previously to quantify the number of neutrophils in tissue. MPO activity was found to be linearly related to the number of neutrophil cells. In an attempt to use this method in leukocytes measuring in stool, fecal MPO was solubilized with hexadecyltrimethylammonium bromide and the MPO activity was measured by a dianisidine-H2O2 assay. Stools from 10 normal subjects and 39 patients with diarrhea produced by enteropathogenic bacteria were examined for leukocytes by MPO activity as well as microscopically using methylene blue stain, MPO activity was positive in 36 patients (92%) and leukocytes were present by microscopic observation in 30 (77%). Fecal leukocytes were not found in healthy controls and the MPO activity was undectable. Stool MPO activity had a range of from 1.6 to 2,830.0 x 10(3) UMPO per gram of feces (median 460.0). The number of neutrophils obtained through MPO activity had a range of 6.0 to 13,216.0/ mm3 (median 1,261.0). Fecal MPO activity is a simple biochemical assay for the detection and quantification of fecal leukocytes.

Conversion from azathioprine [correction of azathioprina] to mycophenolate mofetil in pediatric renal transplant recipients with chronic rejection

BACKGROUND

Chronic rejection is the leading cause of graft failure. Both nonimmunological and immunological mechanisms contribute to this pathology.

METHODS

We studied changes in kidney function, mixed lymphocyte culture, cell-mediated lympholysis, serum HLA class I antigens, cytotoxic antibodies, and lymphocyte population before and after 6 months of follow-up in 22 pediatric renal transplanted patients. The immunosuppressive protocol used was: cyclosporine, azathioprine, and corticosteroids. Eight patients demonstrated chronic graft rejection (by biopsy), group I; and eight patients had no clinical evidence of chronic and/or acute rejection, group II. Substitution of mycophenolate mofetil (MMF) (600 mg/m2 bid for azathioprine was done in patients of groups I and II. Another six patients with chronic rejection, did not receive MMF, group III.

RESULTS

Creatinine clearance increased in group I (44+/-5 vs. 51.1+/- ml/min/1.73 m2, P<0.03) but it decreased in group III (30+/-3 vs. 25+/-2, P<0.01). Urinary protein excretion decreased only in group I (0.3+/-0.03 to 0.06+/-0.03 g/24 hr, P<0.03). During MMF therapy antidonor mixed lymphocyte culture decreased 62 and 70% (P<0.05) in group I and II. Cell-mediated lympholysis against lymphocyte of the donor decreased 65% (P<0.05) in group I. Cell-mediated lympholysis toward control cells decreased 54% (P<0.01) in group II. Serum HLA class I antigens, only decreased from 0.7+/-0.1 to 0.5+/-0.1 microl/ml, P<0.05, in group I. CD19+ decreased from 7.9+/-1.1 to 5.6+/-0.8%, P<0.05, and 7.8+/-1.2 to 5.5+/-0.9%, P<0.05, in groups I and II, respectively. CD16+ increased from 5.7+/-1.1 to 8.6+/-1.3 (P<0.05) only in group I.

CONCLUSIONS

Our data suggest that substituting MMF for azathioprine therapy leads to an improvement in the immunosuppression and renal function in children with on-going chronic rejection.

Biologically active alkaloids and a free radical scavenger from Prosopis species

The biological activity of extracts from the aerial parts of five Argentinian Prosopis species and the exudate of P. flexuosa were assessed for DNA binding, beta-glucosidase inhibition and free radical scavenging effect using the DPPH decoloration assay. DNA binding effect was found mainly in the basic fraction. The alkaloids tryptamine as well as piperidine and phenethylamine derivatives were isolated from the basic extracts. At 0.50 mg/ml, DNA binding activities ranged from 28% for tryptamine to 0-27% for the phenethylamine and 47-54% for the piperidine derivatives. Tryptamine and 2-beta-methyl-3-beta-hydroxy-6-beta-piperidinedodecanol showed a moderate inhibition (27-32%) of the enzyme beta-glucosidase at 100 microg/ml. The exudate of P. flexuosa displayed a strong free radical scavenger effect in the DPPH decoloration assay. The main active constituent was identified as catechin.

Colonic proteinases: increased activity in patients with ulcerative colitis

In order to study the colonic intraluminal proteinase-antiproteinase imbalance under inflammatory conditions, we determined proteolytic activity (PA), alpha-1-antitrypsin and the activities of trypsin, chymotrypsin and neutrophil elastase in feces from patients with ulcerative colitis (UC) comparing the results with a control group. A fecal sample was obtained from each 25 patients with ulcerative colitis and 10 control subjects were studied. The severity of the disease was assessed by the Truelove index. Proteolytic activity was measured using azocasein as proteolytic substrate. The fecal concentration of alpha-1-antitrypsin was measured by radial immunodiffusion and the activities of the enzymes were measured using specific substrates. We found an increase in fecal PA, alpha-1-antitrypsin and neutrophil elastase in patients with UC and the correlation between the severity of the disease and the PA was statistically significant (r = 0.62, P < 0.05). We conclude that elevated colonic proteinase activity could contribute to the pathophysiology of ulcerative colitis.

Primary mycotic aneurysm of the ascending aorta diagnosed by transesophageal echocardiography

Primary mycotic aneurysms are rare, and they can be difficult to diagnose before rupture. Early diagnosis is the cornerstone to effective management. Preoperative diagnosis has traditionally involved angiography and computed tomography. We report a case of Staphylococcus aureus aortitis with an aortic wall abscess and posterior pseudoaneurysm formation involving the ascending aorta in which transesophageal echocardiography was fundamental in diagnosis and patient management.

In vitro response of Plasmodium falciparum to atovaquone and correlation with other antimalarials: comparison between African and Asian strains

Atovaquone (dihydroxynaphthoquinone 566C80) is a broad-spectrum antiprotozoal compound demonstrating potent antimalarial activity against multidrug-resistant malaria. We present the results of in vitro drug sensitivity tests of 142 Plasmodium falciparum isolates, 108 from 14 countries of West and Central Africa, 32 from the Philippines, and one each from Laos and Myanmar. These were tested in vitro against nine drugs: the classic antimalarials chloroquine, quinine, mefloquine and halofantrine, the four qinghaosu derivatives, artemisinin, artemether, artesunate, and arteether, and the new compound atovaquone. Results showed the Asian strains have a higher median 50% inhibitory concentration (IC50) to almost all drugs compared with those from Africa. This was significantly different for chloroquine, halofantrine, and artemisinin. We used three different approaches to estimate the threshold for resistance of atovaquone to be approximately 5-7 nmol/L. The global median of 96 pooled strains is 1.4 nmol/L and the 90th percentile is 5.5 nmol/L for atovaquone. There were no correlations of atovaquone with the eight other antimalarials among African strains, but significant correlations, except for halofantrine, were observed among Asian strains. The absence of a correlation between atovaquone and the other available drugs indicates the potential of atovaquone as an alternative antimalarial in Africa. The correlation observed among Asian strains, however, suggests that atovaquone has to be used cautiously in Asia. Nevertheless, the association with proguanil in recently concluded clinical trials in Europe, South America, Asia, and Africa has demonstrated its antimalarial efficacy.

Abnormal fecal flora in a patient with short bowel syndrome. An in vitro study on effect of pH on D-lactic acid production

D-Lactic acidosis associated with encephalopathy is a clinical condition that occurs in patients with short bowel syndrome. We studied the fecal flora and the composition of fecal water of a child who developed this unusual disorder. Bacteriological studies showed that the patient's stool contained a marked predominance of gram-positive anaerobes. Two strains were identified, Lactobacillus plantarum and Lactobacillus salivarius, as the main bacteria isolated. Fecal water showed pH 4.8 and total lactic acid (sum of L- and D-lactic acids) was the principal organic anion found in the feces. We also incubated the patient's stool in a continuous culture with a view to determining the effect of the pH on the production of volatile fatty acids (VFA) and L- and D-lactic acids. The culture was maintained at pH 5.0, 5.5, 6.0, and 6.5 for four consecutive periods of four days each. We then studied the culture for a further four days at pH 5.0 once again. This study showed that with the progressive rise of the pH from 5.0 to 6.5 L- and D-lactic acids decreased and VFA production increased. D-Lactic acid formation was inhibited at pH 6.5, but when the culture was returned to pH 5.0, it increased to a high level again. These results suggest that the pH plays an important role in the ecological changes in the colonic bacteria that result in D-lactic acid production.

Prevention of asthma with ketotifen in preasthmatic children: a three-year follow-up study

Growing morbidity and mortality rates call for research towards more effective methods of preventing asthma. During the last decade several groups have reported the results of natural history and asthma prevention studies. However, the attempt to prevent development of asthma in genetically predisposed children, has not resulted in a generally accepted management scheme. The aim of this study was to evaluate the effectiveness of ketotifen in preventing the onset of asthma in infants considered to be at high risk of developing the disease, but who had no history of respiratory obstruction. These children have been described as preasthmatic. In this double-blind, placebo-controlled, parallel study, 100 infants with a family history of major allergy and elevated serum IgE levels, but with no history of bronchial obstruction, were treated with either ketotifen (n = 50) or placebo (n = 50) over a 3-year period. There were no statistically significant differences between the two groups with regard to age, sex, degree of hereditary allergy, levels of serum IgE upon joining the study, and family smoking habits. At the end of 3 years, only four of the 45 infants who had received ketotifen had developed asthma (9%). Of the 40 children given placebo, 14 had developed asthma (35%) (P = 0.003). These results suggest that ketotifen is effective in preventing the onset of asthma in preasthmatic children.

Fecal lactate and short bowel syndrome

In patients with short bowel syndrome (SBS), the carbohydrate overload to the colon may disturb the normal pattern of colonic fermentation with production of D-lactic acid and subsequent development of a metabolic D-lactic acidosis. We measured D-lactic acid in blood, urine, and feces, as well as the composition of fecal water and fecal reducing substances from 11 patients with SBS, comparing the results with those from normal subjects. The fecal water from patients with SBS was characterized by low pH, potassium, and volatile fatty acids, high osmotic gap, and high concentration of L- and D-lactic acid. Five of 11 had abnormal amounts of fecal reducing substances. Fecal D-lactic acid was increased in nine of 11 patients. However, none of these patients showed D-lactic acid in urine, and only one had a very low concentration in plasma. These results show that D-lactic acid was overproduced in the colon of most of the patients with SBS. However, other factors such as absorption or impaired D-lactic acid metabolism may be necessary for a plasmatic increase of D-lactic acid.

Colonic proteolysis following pancreatic duct ligation in the rat

Luminal proteolytic activity (PA) of different colonic segments was ascertained in animals subjected to pancreatic duct ligation (PDL) and in control rats. The PDL rats revealed a significant PA reduction in the cecum, proximal colon (P < 0.01), and distal colon (P < 0.005). Proteolytic activity, trypsin, and chymotrypsin activity in control rats diminished progressively from the cecum to the distal colon. Conversely in PDL rats, we found maximal PA in distal colon. The conclusion is drawn that a significant proportion of colonic proteolytic activity can be attributed to pancreatic proteases with a maximal contribution at cecum level.

Polymorphism in Plasmodium vivax MSA1 gene--the result of intragenic recombinations?

The diversity in a 925 bp portion of the Plasmodium vivax MSA1 gene in isolates from the Philippines, China, the Solomon Islands and Papua New Guinea was investigated. A total of 74 base pair changes was found in the amplified fragment from 18 isolates. Most of these changes were single or double base pair substitutions. In several regions, these point changes were tightly linked with one set always present or always absent in the different isolates. Seven such blocks were identified. These blocks were present in different combinations in the different isolates indicating that extensive intragenic recombination has occurred.

[Postmortem diagnosis of cardiac amyloidosis in the aged. Anatomoclinical correlation]

The absence of specific clinical signs makes the diagnosis of cardiac amyloidosis difficult. Moreover, it is established that this condition, the prevalence of which increases with age, aggravates the prognosis of cardiac failure. The present study was undertaken to identify the clinical or paraclinical signs enabling more accurate diagnosis of this disease. Analysis of 2589 autopsy reports from the University Institutes of Geriatrics of Geneva between January 1972 and January 1990 recensed 58 cases of microscopic cardiac amyloidosis, but this diagnosis was not made in any of these patients before death. Of the potential indicators, the good specificity but poor sensitivity of atrial fibrillation and low voltage electrocardiogram was confirmed. On the other hand, the author's research found the association of radiological cardiomegaly and a raised erythrocyte sedimentation rate in nearly 70% of cases of cardiac amyloidosis with a false positive rate of only 10% in a control group.

Effects of right hemicolectomy on fecal nitrogen excretion in rats

The influence of right hemicolectomy (RH) on fecal nitrogen excretion was determined with selected protein levels up to 25%. The endogenous fecal N was determined by extrapolating protein intake to zero. Fecal N was higher in RH than in control rats at all protein levels used. However, the slope of regression curves describing fecal nitrogen excretion was greater for RH compared with the control group. The endogenous fecal nitrogen was not significantly different between the two groups of rats. The feces from rats fed with 25% of protein were partitioned into individual fractions by physical separation and a study was made of the distribution of nitrogen in the bacterial, soluble and fiber fractions of the stool. RH decreased the N excreted in the bacterial fraction by 33% (from 1.71 +/- 0.32 to 1.15 +/- 0.18 mmol/day) and increased the N excreted in the soluble fraction by 280% (from 1.60 +/- 0.30 to 6.08 +/- 1.16 mmol/day). These results show that the RH increased the fecal N excretion and that this N is mainly in the soluble fraction.

Effects of right hemicolectomy on nitrogen balance in the rat

Rats with right hemicolectomy were divided into two groups. One group was free-fed (RHFF), the other group pair-fed (RHPF) and both were compared with a group of control animals. The nitrogen balance (NB) was studied for 5 days at 2 and 14 weeks after surgery. The two groups of rats with right hemicolectomy excreted significantly more fecal nitrogen than the control group (p less than 0.01) during the two periods of study. At 2 weeks the RHFF group increased N intake so that their NB was similar to that of the control group. In the same period the nitrogen lost in urine and the NB were reduced in the RHPF rats (p less than 0.01). At 14 weeks the results were similar to those for 2 weeks although the increase in food intake for RHFF and the decrease in NB for RHPF were not statistically significant. The rats with right hemicolectomy showed a decreased gain in body weight. This decrease was more pronounced in the RHPF group. The nitrogen content of the carcass and liver was significantly reduced in the RHPF group 4 months after surgery. It is concluded that the rats with right hemicolectomy were characterized by an increment in the nitrogen lost in feces, and when they were only allowed the same intake of food as the control group, the animals showed marked abnormalities in growth and in the nitrogen content of the organism.

Cloning of a fresh isolate of Plasmodium falciparum and drug sensitivity of the clones

A freshly isolated strain of Plasmodium falciparum was cloned by limited dilution using a co-culture of infected erythrocytes on monolayers of functionally active rodent hepatocytes. 15 clones were isolated, and the anti-malarial activity of chloroquine, quinine, mefloquine and halofantrine against the clones, the original isolate, and a culture-adapted isolate was determined using a 48 h radioisotope microdilution method. The multiplication rates of all clones and the culture-adapted isolate were estimated by counting the number of parasitized cells on Giemsa-stained thin smears. Variations found in drug sensitivity and multiplication rate of different clones provided strong evidence of heterogeneity of a single strain parasite population. No morphological variation was detected by light microscopy. The use of a hepatocyte feeder layer improved the adaptation of cloned parasites to continuous culture conditions and thus enabled us to clone directly a fresh isolate, without losing clones during the culture-adaptation process.