Metabolically efficient information processing

Energy-efficient information transmission may be relevant to biological sensory signal processing as well as to low-power electronic devices. We explore its consequences in two different regimes. In an "immediate" regime, we argue that the information rate should be maximized subject to a power constraint, and in an "exploratory" regime, the transmission rate per power cost should be maximized. In the absence of noise, discrete inputs are optimally encoded into Boltzmann distributed output symbols. In the exploratory regime, the partition function of this distribution is numerically equal to 1. The structure of the optimal code is strongly affected by noise in the transmission channel. The Arimoto-Blahut algorithm, generalized for cost constraints, can be used to derive and interpret the distribution of symbols for optimal energy-efficient coding in the presence of noise. We outline the possibilities and problems in extending our results to information coding and transmission in neurobiological systems.

Counting probability distributions: differential geometry and model selection

A central problem in science is deciding among competing explanations of data containing random errors. We argue that assessing the "complexity" of explanations is essential to a theoretically well-founded model selection procedure. We formulate model complexity in terms of the geometry of the space of probability distributions. Geometric complexity provides a clear intuitive understanding of several extant notions of model complexity. This approach allows us to reconceptualize the model selection problem as one of counting explanations that lie close to the "truth." We demonstrate the usefulness of the approach by applying it to the recovery of models in psychophysics.

Animal models for experimental tuberculosis

Animal models for tuberculosis vaccine assays have evolved through a series of sequential experiments aimed at optimizing the activity of a particular vaccine product. As a result, studies that use different animal models do not agree on the potency ranking of antituberculosis vaccines, and each major test-system variable contributes to the disagreement. Disagreements among laboratories about the efficacy of vaccines are in part due to differences in test systems. A survey of potency assays of tuberculosis vaccines suggests that, based on the choice of a specific combination of variables in the test model, an investigator can show that any given vaccine product has superior potency. In view of these problems with animal models for research on tuberculosis vaccines, we recommend that attention should be focused on those animal models that replicate the key aspects of the natural history of human tuberculosis. The development of vaccines by means of new technologies requires animal models to assay the protective potency of vaccines that, ideally, inhibit tubercle bacilli at the point of infection. The development of new tuberculosis vaccines may be handled most efficiently in a joint venture that includes both laboratories involved in vaccine production and laboratories concerned with animal models.

An analysis of some hypotheses related to the Chingelput bacille Calmette-Guérin trial

Investigation of several hypotheses related to the outcome of the Chingelput Bacille Calmette-Guérin (BCG) Trial suggests at least 2 factors that might explain the major scientific puzzle of a protective effect expected of 80% and a protective effect observed of 0% (i.e., equivalent protection for BCG and placebo). One factor that explains some of the low efficacy observed for BCG in this trial is the virtual saturation level of exposure to environmental mycobacteria (EM). Studies in animal models demonstrated that the protection afforded by infection with EM was equivalent to the protection that resulted from BCG vaccination. The second factor, pathogenetic pathway, explains why there was still a high case rate for tuberculosis, even though the population was fully vaccinated by EM. This hypothesis states that tuberculosis in India, as well as in most developing countries, results primarily from exogenous reinfection, a pathway against which BCG (or EM) exerts no protective effect beyond that induced by the first episode of infection with Mycobacterium tuberculosis.

Rapid Solubility Determination Using Vapor-Phase Osmometry

Because of the need for resource-sparing assays of the solubility of new drug candidates, we sought to develop and validate a rapid method for determining the solubility of nonvolatile pharmaceutical solids in water. Vapor-phase osmometry was used to determine the concentration of drugs in saturated solutions prepared by a rapid ultrasound-mediated dissolution protocol. The osmolality of saturated solutions as measured by the vapor-phase osmometer is an excellent predictor of the solubility of pharmaceutical solids in water. Each osmolality measurement requires less than 10 µl of saturated solution and takes less than 2 min to complete. For small-molecule drugs with solubilities greater than 10 g/kg, osmometry may prove to be a rapid and accurate method for determining the water solubilities of drugs.

A rapid spectrofluorimetric technique for determining drug-serum protein binding suitable for high-throughput screening

PURPOSE

To develop and validate a rapid method for determining the dissociation constants with which pharmaceutical candidates and drugs bind to serum albumin and to alpha1-acid glycoprotein with the goal of deducing the extent of binding.

METHODS

The quenching of the intrinsic tryptophan fluorescence of serum albumin and alpha1-acid glycoprotein was monitored by spectrofluorimetry and the data were used to calculate the apparent dissociation constant. Sodium warfarin was used to probe the warfarin-binding site of serum albumin and diazepam was used to probe the benzodiazepine binding site. Additionally, the binding of sodium salicylate, phenylbutazone, sulfinpyrazone, iophenoxic acid, theophylline, chloramphenicol, acetaminophen, lithium chloride and ampicillin were also investigated. Chlorpromazine hydrochloride and imipramine hydrochloride were used as probes for alpha1-acid glycoprotein. The assays were also extended to the multiwell format. The quenching curves were fitted to the quadratic binding equation to determine the dissociation constants.

RESULTS

Intrinsic fluorescence measurements are an excellent predictor of the drug binding to human serum albumin and to alpha1-acid glycoprotein. These measurements detect binding to the warfarin and benzodiazepine binding sites of human serum albumin. The dissociation constants estimated using the method compare favorably to the dissociation constants previously reported by Epps et al. using extrinsic fluorescence methodology, and the results correlate well with equilibrium dialysis using drug displacement endpoints.

CONCLUSIONS

These measurements can be carried out with small samples and do not require separation of the bound and unbound species. Additionally, the proposed methods eliminate membrane separations, are not compound specific and do not require analytical chromatography or mass spectrometry for quantitation. Spectrofluorimetry may prove to be a useful method for rapidly determining the protein binding of combinatorial libraries.

Glycosaminoglycans alter the conformation of interferon-gamma

Interferon-gamma (IFN-gamma) is a potent immunomodulatory cytokine whose physiological roles are modulated by the extracellular matrix. Here, circular dichroism and fluorescence spectroscopic techniques are used to demonstrate that low molecular weight heparin and chondroitin sulfate cause significant changes in secondary and tertiary structure of IFN-gamma. The results suggest that heparin and chondroitin sulfate modulate IFN-gamma activity by causing structural changes in the IFN-gamma dimer.

Comparison of polyethylene glycol versus combination of magnesium sulphate and bisacodyl for colon preparation

Colon preparation using polyethylene glycol (PEGLEC) and combination of bisacodyl and magnesium sulphate was compared in 74 patients. Type of preparation did not influence patient discomfort. The quality of preparation was excellent with PEGLEC in 63.6% as compared to 41.6% with combination preparation. The completion rates were similar in both groups. Good preparation was linked with shorter procedure duration (p = 0.001) and greater depth of examination. No major side effects were noted with both preparations. To conclude, polyethylene glycol is recommended for screening of right colon while combination of bisacodyl and magnesium sulphate is a good and cheap preparation modality to screen the left colon.

Residence-time dependent changes in fibrinogen adsorbed to polymeric biomaterials

It has generally been accepted that biomaterials adsorbing the least amount of the plasma protein fibrinogen following exposure to blood will support less platelet adhesion and therefore exhibit less thrombogenicity. Several studies suggest, however, that the conformation or orientation of immobilized fibrinogen rather than the total amount adsorbed plays an important role in determining the blood compatibility of biomaterials. The purpose of this study was to investigate time-dependent functional changes in fibrinogen adsorbed to polytetrafluoroethylene (PTFE), polyethylene (PE), and silicone rubber (SR). Fibrinogen was adsorbed to these materials for 1 min and then allowed to 'reside" on the surfaces for up to 2 h prior to assessing its biological activity. Changes in fibrinogen reactivity were determined by measuring the adhesion of 51Cr-labeled platelets, the binding of a monoclonal antibody (mAb) directed against an important functional region of the fibrinogen molecule (the gamma-chain dodecapeptide sequence 400-411), and the ability of blood plasma to displace previously adsorbed fibrinogen. Platelet adhesion differed among the polymeric materials studied, and PTFE and PE samples exhibited a small decrease in adhesion with increasing fibrinogen residence time. Platelet adhesion to SR was the least among all materials studied and showed no variation with residence time. When using PTFE and SR as substrates, mAb recognition of adsorbed fibrinogen did not change with residence time whereas that on PE decreased slightly. The mAb binding was least to fibrinogen adsorbed to SR, which is in agreement with the platelet adhesion results. Finally, the ability of plasma to displace previously adsorbed fibrinogen decreased dramatically with increasing residence time on all materials. These in vitro studies support the hypothesis that fibrinogen undergoes biologically significant conformational changes upon adsorption to polymeric biomaterials, a phenomenon that may contribute to the hemocompatibility of the materials following implantation in the body.

Vascular cell attachment and procoagulant activity on metal alloys

The attachment and growth of vascular smooth muscle cells on biomaterials used as components of devices implanted in the vascular space may influence the biocompatibility of such materials. The nature of the materials may affect the attachment and/or the activation of these cells' procoagulant responses. Therefore, the main objective of this study was to measure the strength of adhesion of these vascular cells to potential biomaterials (titanium, zirconium alloys, and stainless steel) by exposing them to a range of shear stresses (50-300 dyn cm(-2)) in a parallel plate flow chamber. The procoagulant responses of the cells were evaluated by measuring the tissue factor (TF) activity promoted by the different materials under flow conditions. The materials supported distinctly different levels of initial cell adhesion in static culture. However, the fraction of adherent cells did not decline significantly with incrementally increasing shear stress within the range tested. TF expression, as measured by factor Xa (FXa) production. was material-dependent. For example, cells cultured on Ti1313 exhibited more FXa production (13.2 nM 10(-5) cells) than Ti1313(DH) (8.5 nM 10(-5) cells) or stainless steel (2 nM 10(-5) cells). Thus, our studies indicate that the level of adhesion, strength of attachment and the expression of procoagulant activity of adherent vascular cells depend strongly on the nature of the underlying biomaterial.

Cancer chemopreventive activity of synthetic colorants used in foods, pharmaceuticals and cosmetic preparations

In continuation with our studies to uncover cancer chemopreventive effects of non-toxic natural colorants and other products of biologic and synthetic origin, we tested several Food and Drug Administration-approved synthetic colorants for antitumor promoting potential by the in vitro Epstein-Barr virus early antigen activation in Raji cells in response to the tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA). Among 29 such colorants used in foods, pharmaceuticals and cosmetics and evaluated in vitro, six of the 10 most effective had an azo group. Three structurally unrelated colorants tested in this assay were also studied in vivo for chemoprevention of 7,12-dimethylbenz[a]anthracene (DMBA)-induced TPA-promoted mouse skin carcinogenesis. The results indicate that tartrazine, indigo carmine and erythrosine are potent inhibitors of skin tumor promotion in mice treated with DMBA and TPA.

Interferon-gamma-inhibitory oligodeoxynucleotides alter the conformation of interferon-gamma

The aptamer mechanism of action involves the direct interaction of oligonucleotide with protein and is responsible for the biological effects of many pharmacologically active oligodeoxynucleotides. In the work reported here, we have determined the effects of aptamers on the secondary, tertiary, and quaternary structures of the proteins with which they interact using interferon-gamma and the interferon-gamma-inhibitory aptamer oligonucleotide, 5'-GGG GTT GGT TGT GTT GGG TGT TGT GT, as a model system. CD, fluorescence spectroscopy studies, and antibody binding studies in this system demonstrate that the interferon-gamma-inhibitory aptamer oligonucleotide causes significant changes in secondary and tertiary structures of interferon-gamma. These structural changes do not result in, or resemble, protein denaturation or aggregation, and the results suggest that aptamer oligodeoxynucleotides can significantly alter the structure of the proteins they interact with.

Role of pinaverium bromide in south Indian patients with irritable bowel syndrome

The effect of pinaverium bromide in controlling gastrointestinal symptoms in 61 patients with irritable bowel syndrome was studied, as an open trial. Individually, there was significant relief in abdominal discomfort/pain as well as in bowel symptoms in most of the patients. Abdominal pain was reduced in 49%, stool consistency improved in 74%, straining and urgency decreased in 71% and mucus decreased in 64%. Tolerance to the drug administered was good and side-effects reported were few.

Inhibition of 12-O-tetradecanoylphorbol-13-acetate induced Epstein-Barr virus early antigen activation by natural colorants

Natural colorants such as anthocyanins, betalains, carotenoids, curcuminoids and chlorophylls have been widely used in the food processing industry and in beverages. Most of these colorants constitute part of human dietary components and are considered to be harmless and non-toxic. As a part of the study of natural products to identify non-toxic cancer chemopreventive agents, we have investigated several natural colorant extracts from vegetables and fruits of daily human consumption for their cancer chemopreventive action using the short-term in vitro assay which involves inhibition of Epstein-Barr virus early antigen activation (EBV-EA) induced by phorbol esters. Our study has identified several plant extracts that show profound activity in the EBA assay.

Tenderness variation among loin steaks from A and C maturity carcasses of heifers similar in chronological age

Fifty-two Angus x Gelbvieh rotationally crossed virgin, ovariectomized, or single-calf heifers were slaughtered after 100 d on a high-concentrate diet. Heifers from each treatment were approximately 31, 33, or 35 mo of age, and they produced 31 A, 5 B, and 16 C maturity carcasses. Because of the small number, B maturity carcasses were not included in this study. Number of A maturity carcasses decreased as age increased. No differences (P > .05) in slaughter weight, total weight gain, dressing percentage, longissimus muscle area, or kidney fat percentage existed between carcass maturity groups, but C maturity heifers had 3.56 mm more fat (P < .01) over the longissimus muscle than A maturity heifers. Marbling scores of slight79 and small0 for A and C maturity carcasses, respectively, did not differ (P > .05). The A and C maturity heifers had similar amounts of collagen and hydroxylysyl-pyridinium crosslinks in metacarpal bone cortex and in longissimus muscle. Neither means for panel tenderness nor Warner-Bratzler shear values differed (P > .05) between maturity groups. Coefficients of variation for tenderness were slightly higher in steaks from C maturity carcasses, but CV for shear values between A and C maturity groups were similar. Because inconsistent meat tenderness is a recognized problem in the beef industry, more research on tenderness variability within maturity and marbling groups is needed. This information, in addition to pooled SEM and differences between means, should aid in finding ways to reduce beef tenderness variability.

Anti-tumor promoting effects of naphthoquinone derivatives on short term Epstein-Barr early antigen activation assay and in mouse skin carcinogenesis

In continuation of our studies of natural and synthetic products as cancer chemopreventive agents, we have examined a number of naphthoquinone derivatives including monomeric, dimeric and tetrameric naphthaquinones occurring in the Diospyros and other selected plant genera. Several synthetic naphthoquinones were also evaluated. Initially these compounds were tested for in vitro anti-tumor promoting effect on Epstein-Barr virus early antigen activation produced by the tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA) and thereafter in in vivo on two-stage mouse skin carcinogenesis. Our studies show some of these compounds have potent anti-tumor promoting activity.

Growth, carcass, and tenderness characteristics of virgin, spayed, and single-calf heifers

Fifty-three Angus/Gelbvieh rotationally crossed heifers were slaughtered after 100 d on a high-concentrate diet. The average slaughter age for each of three different groups was 31, 33, or 35 mo, which falls within the USDA's 30- to 42-mo age range for animals producing "B" maturity carcasses. Each age group consisted of five or six heifers that had never been bred (virgin), six heifers ovariectomized at 1 yr of age (spayed), and six heifers that had weaned calves approximately 120 d postpartum (single-calf). Slaughter weight was higher (P < .05) for the virgin heifers but total weight gain in the feedlot was similar among the three groups. Single-calf heifers fed 100 d after weaning calves tended to be fatter than virgin or spayed heifers. Carcass maturity scores for the single-calf, virgin, and spayed heifers were different (P < .05); single-calf heifers produced carcasses that appeared older and spayed heifers produced carcasses that appeared younger. Maturity scores coupled with lighter and shorter metacarpal bone weights indicated single-calf heifers matured earlier (P < .05) than the other groups. Panel tenderness and Warner-Bratzler (WB) shear values of rib roasts from virgin, spayed, and single-calf heifers were determined. No differences among groups of heifers existed but scores within each group varied greatly. Marbling score was correlated (P < .05) with panel tenderness and shear force and the hydroxylysylpyridinium (HP) crosslink of muscle collagen was correlated (P < .05) with shear values. Because no significant (P < .05) correlation existed between HP in bone collagen or HP or WB shear values in muscle, we concluded that collagen maturation processes in muscle and bone occur independently. With the exception of differences in bone maturity scores, few meaningful differences in characteristics of virgin, spayed, and single-calf heifers existed, but these maturity differences could change carcass grade and influence value.

An integrated map of the genome of the tubercle bacillus, Mycobacterium tuberculosis H37Rv, and comparison with Mycobacterium leprae

An integrated map of the genome of the tubercle bacillus, Mycobacterium tuberculosis, was constructed by using a twin-pronged approach. Pulsed-field gel electrophoretic analysis enabled cleavage sites for Asn I and Dra I to be positioned on the 4.4-Mb circular chromosome, while, in parallel, clones from two cosmid libraries were ordered into contigs by means of fingerprinting and hybridization mapping. The resultant contig map was readily correlated with the physical map of the genome via the landmarked restriction sites. Over 165 genes and markers were localized on the integrated map, thus enabling comparisons with the leprosy bacillus, Mycobacterium leprae, to be undertaken. Mycobacterial genomes appear to have evolved as mosaic structures since extended segments with conserved gene order and organization are interspersed with different flanking regions. Repetitive sequences and insertion elements are highly abundant in M. tuberculosis, but the distribution of IS6110 is apparently nonrandom.

Allelic exchange in Mycobacterium tuberculosis with long linear recombination substrates

Genetic studies of Mycobacterium tuberculosis have been greatly hampered by the inability to introduce specific chromosomal mutations. Whereas the ability to perform allelic exchanges has provided a useful method of gene disruption in other organisms, in the clinically important species of mycobacteria, such as M. tuberculosis and Mycobacterium bovis, similar approaches have thus far been unsuccessful. In this communication, we report the development of a shuttle mutagenesis strategy that involves the use of long linear recombination substrates to reproducibly obtain recombinants by allelic exchange in M. tuberculosis. Long linear recombination substrates, approximately 40 to 50 kb in length, were generated by constructing libraries in the excisable cosmid vector pYUB328. The cosmid vector could be readily excised from the recombinant cosmids by digestion with PacI, a restriction endonuclease for which there exist few, if any, sites in mycobacterial genomes. A cosmid containing the mycobacterial leuD gene was isolated, and a selectable marker conferring resistance to kanamycin was inserted into the leuD gene in the recombinant cosmid by interplasmid recombination in Escherichia coli. A long linear recombination substrate containing the insertionally mutated leuD gene was generated by PacI digestion. Electroporation of this recombination substrate containing the insertionally mutated leuD allele resulted in the generation of leucine auxotrophic mutants by homologous recombination in 6% of the kanamycin-resistant transformants for both the Erdman and H37Rv strains of M. tuberculosis. The ability to perform allelic exchanges provides an important approach for investigating the biology of this pathogen as well as developing new live-cell M. tuberculosis-based vaccines.

Mycobacterial infection in guinea pigs

We described published reports of the chaos which exists in research concerning laboratory animal models for assay of tuberculosis (TB) vaccines and proposed a "rational animal model" as a solution to the problem. This animal model, an aerosol challenge model in guinea pigs, was recently applied to the problem of differences in growth characteristics of sputum isolates of low and high virulence. The same model was used to investigate the protective effect of high dose BCG given aerogenically. Based on studies in the guinea pig model of experimental airborne TB, and a review of the literature on pathogenesis of human TB, we described an "integrated model" for the pathogenesis of TB, a model which includes a role for both the endogenous reactivation and the exogenous reinfection pathways. Our hypothesis is that tubercle bacilli must be able to gain access to the "vulnerable region" in the lung apex in order to survive the effects of the CMI response. In endogenous reactivation TB (virulent tubercle bacilli), this access occurs via the bloodstream. Whereas in exogenous reinfection TB, access to the vulnerable region occurs via multiple exposures via the respiratory tract. Central to our perspective is the acceptance of the evidence that during first infection with virulent organisms, tubercle bacilli enter the bloodstream via the efferent lymphatics. We believe the hypotheses we have proposed have the potential to lead to a further increase in our knowledge of these mechanisms and are a prerequisite to studies aimed at the development of new vaccines.

Pathogenesis of tuberculosis: pathway to apical localization

We have examined the published work of investigators which dealt with the pathogenesis of tuberculosis, especially the following: the infective dose, the yield of bacilli from the primary lesion and primary complex, the predominant location of the minimal lesion, the hypotheses of a vulnerable region in the lung and the specific pathways (endogenous or exogenous) by which tubercle bacilli cause disease. More knowledge of the pathogenic pathway to tuberculosis would provide clues to the development of new vaccines and drug regimens that can intervene at a specific stage in the pathogenesis. Based on the examination of the literature on pathogenesis of human tuberculosis and our findings in a guinea-pig model of experimental airborne tuberculosis, we have proposed an hypothesis which integrates the endogenous and exogenous pathways to tuberculosis. This hypothesis is based on the following observations: 1. The infectious dose is very low, usually 1-5 tubercle bacilli. 2. The first implant can occur anywhere in the lungs. 3. The cavitary lesion, characteristic of tuberculous disease, is often located in the apical regions in the lungs. 4. Whereas the primary implant can occur anywhere in the lungs, for the progression from infection to disease, the tubercle bacilli must gain access to the 'vulnerable' regions in the apex of the lungs. Our hypothesis states that in areas of the world where there is a low risk of infection with tubercle bacilli low incidence of vaccination or sensitization to environmental mycobacteria, or high incidence of high virulent isolates, the virulent tubercle bacilli reach the vulnerable region via a bacillemia during the first infection. In areas of the world where there is a high risk of infection with tubercle bacilli, high incidence of vaccination or sensitization to environmental mycobacteria or a high incidence of low virulent isolates, the tubercle bacilli reach the vulnerable region via the airway, which requires repeated episodes of infection as the probability of a first implant occurring in the vulnerable regions is low.

inhA, a gene encoding a target for isoniazid and ethionamide in Mycobacterium tuberculosis

Isoniazid (isonicotinic acid hydrazide, INH) is one of the most widely used antituberculosis drugs, yet its precise target of action on Mycobacterium tuberculosis is unknown. A missense mutation within the mycobacterial inhA gene was shown to confer resistance to both INH and ethionamide (ETH) in M. smegmatis and in M. bovis. The wild-type inhA gene also conferred INH and ETH resistance when transferred on a multicopy plasmid vector to M. smegmatis and M. bovis BCG. The InhA protein shows significant sequence conservation with the Escherichia coli enzyme EnvM, and cell-free assays indicate that it may be involved in mycolic acid biosynthesis. These results suggest that InhA is likely a primary target of action for INH and ETH.

BCG-induced protection in guinea pigs vaccinated and challenged via the respiratory route

Since studies on cellular immune responses have demonstrated the role of the mucosal lymphoid system of the respiratory tract, we have studied responses obtained from the local respiratory route, compared to the systemic intradermal route, of BCG immunization. Guinea pigs vaccinated with different doses of BCG via both routes served to follow lymphoid cell proliferation, hilar lymph node and lung BCG clearance, lung granuloma formation and protection induced after virulent challenge. Results demonstrate that the aerogenic route of vaccination with BCG has no harmful side-effects for the host. In comparison with the intradermal route of vaccination, aerogenic vaccination with 10(5) BCG cfu induced higher local cellular immune responses and a substantially improved protective effect.