A review of the experimental methods and results of testing the mechanical properties of Tunica Albuginea

The present work provides a comprehensive review of the literature on the mechanical properties and existing human tunica albuginea tissue testing methods. Assessments were completed on papers reporting experimental values of Young's modulus, tensile strength, puncture strength, stiffness, toughness, and strain at the ultimate tensile strength (UTS). A high degree of variability in the reported experimental values was found; Young's modulus ranged from 5 MPa to 118 MPa, and tensile strength went from 1.1 MPa to 6.1 MPa. A comparison of the variability of the reported experimental values for puncture strength, stiffness, toughness, and strain at the UTS could not be completed due to a lack of experimental results. This review discusses the pathophysiology and surgical treatment of erectile dysfunction and Peyronie's disease, variability in the existing reported mechanical properties, the impact of the variability of mechanical properties on in silico models and explores the absence of a standardised testing method as a possible reason for the variable in results. Finally, this work attempts to provide suggestions for standardising future mechanical testing of the tunica albuginea through minimising and reporting freeze/thaw cycling, noting the proximal/distal region of the cadaver tunica sample, reporting the orientation (o'clock position) of the cadaver tunica sample, and testing the cadaver tunica samples in bi-axial tension. Ultimately, standardising the testing methodologies of the tunica albuginea will provide higher confidence in reported mechanical property values.

Valve interstitial cells under impact load, a mechanobiology study

Understanding the relationship between mechanobiology and the biosynthetic activities of the valve interstitial cells (VICs) in health and disease under severe dynamic loading conditions is of particular interest. The purpose of this study is to further understand the mechanobiology of heart valve leaflet tissue and the VICs under impact forces. Two novel computational and experimental platforms were developed to study the effect of impact load on the VICs to monitor for apoptosis. The first objective was to design and develop an apparatus to experimentally study viability (apoptosis) of the porcine heart valve leaflet tissue VICs in the aortic position under controlled impact forces. Apoptosis was assessed based on terminal transferase dUTP nick end-labelling (TUNEL) assay. The second objective was to develop a computational platform to estimate the stress and strain fields in the vicinity of VICs when the tissue experiences impact forces. A nonlinear finite element (FE) model with an anisotropic, hyperelastic and heterogeneous material model for the matrix and cells was developed. Preliminary results confirm that interstitial cells are successfully resistant to impact loads up to 30 times more than normal physiological conditions. Additionally, the structure and composition of heart valve leaflet tissue provides a mechanical shield for VICs protecting them from excessive mechanical forces such as impact loads. Although, the entire tissue may experience excessive stresses, which may lead to structural damage, the stresses around and near VICs remain consistency low. Results of this study may be used for heart valve leaflet tissue-engineering, as well as further understanding the mechanobiology of the VICs in health and disease.

Computational study and validation of a novel passive hand tremor attenuator

Tremors are a prevalent movement disorder due to a nervous system condition that leads to involuntary muscle movements observed in patients. This paper converts the tremorous anatomical human arm model to a single degree of freedom (SDOF) forced vibration problem. The mathematical modelling with Euler-Lagrange's equation is performed for the SDOF human arm model with two different potential vibration absorbers. A computational study is conducted on MATLAB Simulink by MathWorks Inc. (Natick, MA) to compare two absorbers, and the results are verified on the multibody dynamics simulation solution software, MSC Adams by Hexagon AB. It is concluded that the T beam-shaped vibration absorber represented a higher amplitude reduction, up to 80%, compared to the inertial mass absorber, which had an amplitude reduction of 65% over the range of frequencies. Experiments conducted with the T beam absorber prototype also support the computational findings. Future research focuses on designing an ergonomic wearable device with a proposed T-beam absorber that can passively attenuate the tremor at various frequencies.

New synthetic mitral valve model for human prolapsed mitral valve reconstructive surgery for training

The training process of young surgeons is highly desirable in order for them to gain an understanding of the quality of care and patient safety required during cardiac surgeries, however, it may take a few years of practice in order for them to properly develop these skills. Artificial life-like platforms and models are extremely recommended for teaching hands-on and real-world practice in both junior and even experienced medical professionals and surgeons. Suitable and accessible training tools are of significant importance for simulating a particular surgery in order to provide practice opportunities for a specific surgical procedure. In this study, we focussed on the simulation of the human mitral valve prolapse reconstructive surgery. An innovative, artificial, biomimetic model was designed and fabricated made of Cryogel biomaterial developed in our lab that is suitable for the precise practice on the mitral valve prolapse model. The proposed model is mainly made up of polyvinyl alcohol (PVA) cryogel, which is designed to resemble the geometric and mechanical properties of a diseased (prolapse) mitral valve. We simulated the constructive prolapsed mitral valve surgery entirely on a synthetic platform. The platform was made available to four certified cardiac surgeon and there were unanimously very positive with no considerable differences in the procedural assessments between them. The proposed model has a similar appearance and texture to that of a diseased mitral valve and holds consistent mechanical properties to those of the real tissue. The offered technology may be used for other cardiothoracic reconstructive surgeries with high precision and consistency.

Proposed percutaneous aortic valve prosthesis made of cryogel

Transcatheter heart valves are promising for high-risk patients. Generally, their leaflets are made of pericardium stented in a Nitinol basket. Despite their relative success, they are associated with significant complications such as valve migration, implantation risks, stroke, coronary obstruction, myocardial infraction, acute kidney injury (which all are due to the release of detached solid calcific pieces in to the blood stream) and expected issues existing with tissue valves such as leaflet calcification. This study is an attempt to fabricate the first ever polymeric percutaneous valves made of cryogel following the geometry and mechanical properties of porcine aortic valve to address some of the above-mentioned shortcomings. A novel, one-piece, tricuspid percutaneous valve, consisting of leaflets made entirely from the hydrogel, polyvinyl alcohol cryogel reinforced by bacterial cellulose natural nanocomposite, attached to a Nitinol basket was developed and demonstrated. Following the natural geometry of the valve, a novel approach was applied based on the revolution about an axis of a hyperboloid shape. The geometry was modified based on avoiding sharp warpage of leaflets and removal of the central opening orifice area of the valve when valve is fully closed using the finite element analysis. The modified geometry was replaced by a cloud of (control) points and was essentially converted to Bezier surfaces for further adjustment. A cavity mold was then designed and fabricated to form the valve. The fabricated valve was sewn into the Nitinol basket which is covered by Dacron cloth. The models presented in this study merit further development and revisions for both aortic and mitral positions.

Abstract PD1-04: The contribution of rare variants, polygenic risk, and novel candidate genes to the hereditary risk of breast cancer in a large cohort of breast cancer families

Background: Identifying the missing hereditary factors underlying the familial risk of breast cancer could have a major and immediate impact on managing the breast cancer risk for these families.

Methods: We identified candidate breast cancer predisposition genes through whole exome sequencing of BRCAx families and subsequently sequenced up to 1325 genes, along with 76 common low penetrance variants associated with breast cancer, in index cases from 6,000 BRCAx families and 6,000 cancer free women (ethnically matched on principal component analysis).

Results: The role of recently described (PALB2) or suspected (MRE11A) moderately penetrant genes was confirmed. Conversely, the size of the cohort means that the absence of enrichment for loss of function (LoF mutations) provides strong evidence against other reported breast cancer genes (BRIP1, RINT1, RECQL). For further moderate risk variants (in CHEK2, ATM, BRCA2) we observed significant risk modification based on the polygenic risk score (PRS - calculated from the common variant data), with the risk restricted to the co-occurrence of the rare variant and high PRS. Novel candidate genes were identified based on LoF mutations, including NTHL1 (38 cases versus 15 controls, OR 2.5 p=0.002): a member of the base excision repair (BER) pathway. DNA sequencing of the breast carcinomas from 17 heterozygous NTHL1 mutation carriers revealed a strong bias towards a C:G>T:A (C>T) transitions, consistent with a BER defect, which confirmed the recent findings in colorectal carcinomas from bi-allelic NTHL1 mutation carriers. This data extends the cancer predisposition phenotype of NTHL1 to heterozygous carriers. In addition to NTHL1, there are a large number of candidate genes where the ratio of LoF mutations in cases versus controls indicates that they may convey an actionable level of risk; 46 genes (519 families) meet the basic criteria of multiple LoF variants and an OR >2 for cases versus controls – including previously proposed breast cancer genes MRE11A, BLM, MLH1, MYH, FANCD2 and functionally plausible candidates such as MLH3, PARP2 and ATR. Collectively the OR of breast cancer for LoF mutations in this group of genes is 3.3 (95% CI 2.7-3.9, P=3.5x10-41).

Conclusion: Our data shows that the effect of rare variation in established and novel breast cancer genes, along with consideration of the background polygenic risk, together explains a substantial component of the heritable risk of breast cancer in our cohort.

Citation Format: Campbell IG, Li N, Rowley S, Goode D, Devereux L, McInerny S, Grewal N, Lee A, Trainer A, Wong-Brown M, Scott R, Gorringe K, James P. The contribution of rare variants, polygenic risk, and novel candidate genes to the hereditary risk of breast cancer in a large cohort of breast cancer families [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr PD1-04.

Athletes' knowledge and views on OTC medication

A questionnaire was administered to elite athletes from Australia, Canada, the UK, and the USA representing 10 Olympic sports in order to explore knowledge and understanding of over-the-counter (OTC) medication since the removal of many of these substances from the World Anti-Doping Agency (WADA) Prohibited List, in 2004. Athletes demonstrated limited knowledge and understanding. Around half (50.5 %) knew the penalty incurred following a doping violation involving a banned OTC stimulant. The terms Monitoring Program and Specified Substance List were understood by 43.3 % and 67.5 % of respondents, respectively. Overall, the status of substances in relation to the Prohibited List was correctly identified in just 35.1 % of cases. As a whole, athletes were of the opinion that OTC stimulants posed a risk to health, were performance enhancing and that their use was against the spirit of sport. They were undecided as to whether these drugs should be returned to the Prohibited List. Elite athletes require targeted education programmes that will enable them to make informed decisions on the potential of OTC medications for therapeutic or performance enhancing purposes.

Reduction of experimental Salmonella and Campylobacter contamination of chicken skin by application of lytic bacteriophages

Lytic bacteriophages, applied to chicken skin that had been experimentally contaminated with Salmonella enterica serovar Enteritidis or Campylobacter jejuni at a multiplicity of infection (MOI) of 1, increased in titer and reduced the pathogen numbers by less than 1 log(10) unit. Phages applied at a MOI of 100 to 1,000 rapidly reduced the recoverable bacterial numbers by up to 2 log(10) units over 48 h. When the level of Salmonella contamination was low (< log(10) 2 per unit area of skin) and the MOI was 10(5), no organisms were recovered. By increasing the number of phage particles applied (i.e., MOI of 10(7)), it was also possible to eliminate other Salmonella strains that showed high levels of resistance because of restriction but to which the phages were able to attach.

Perceptions and experiences of primary nursing in an ICU: a combined methods approach

With the introduction of the Patient's Charter, greater emphasis has been placed on 'named nursing' (Department of Health 1991). While there is much literature extolling the benefits of this method of delivering care to patients (Reed 1988; Manley 1989; Macguire 1991); there is a dearth of empirical studies exploring primary nursing in an adult intensive care unit (ICU). In addition, little is known about how nurses feel about being a 'primary nurse'. The aim of this study was to determine qualified nurses' perceptions and experiences of the effect of primary nursing on patient care in an intensive care environment (ICU) and to explore nurses' experiences of being a primary nurse. This study was carried out in an ICU in Northern Ireland. Primary team nursing was the system of organizing care within this unit. This system consisted of teams of 'primary' and 'associate' nurses. A total of 65 qualified nurses were surveyed. Sixteen nurses took part in focus group interviews. A combined methods approach comprising a questionnaire and focus group interviews was employed for the study. Part one of the questionnaire provided data on professional and demographic details. Part two facilitated nurses to elaborate on their feelings and perceptions of the concept of primary nursing. The focus groups facilitated in-depth exploration of the respondents' personal feelings and experiences about their role as a primary nurse. The data obtained from the two-part questionnaire were analysed using descriptive statistic and content analysis. The data obtained from the focus groups were analysed using content analysis and the development of emerging themes. Analysis of the data revealed that the nurses' views were similar to those highlighted in the existing literature. Nurses perceived primary nursing to relate to the responsibility for the care of one patient, from admission to discharge with the primary nurse assessing, planning, implementing and evaluating care and the associate nurse assisting in the delivery of this care. Thus, continuity of care was seen as the major advantage of primary nursing. The findings, however, suggested that further teaching on the concept of primary nursing was required. In addition, many of the nurses admitted they experienced considerable stress, particularly in relation to their close proximity over a long period of time, with patients and their relatives. This is an important finding and highlights the need for primary nurses in ICU to have the opportunity (in some instances), to be relieved of their responsibility for a named patient, thereby reducing some of the potential for stress. It is acknowledged that the findings of this study may not be generalized beyond the identified sample. Further empirical studies exploring nurses' perceptions and experiences of primary nursing in an ICU are therefore needed.

Effect of mutations of murine lens alphaB crystallin on transfected neural cell viability and cellular translocation in response to stress

We examined the influence of over-expressed native and mutant murine lens alphaB crystallin on the response of a murine neural cell line to heat and ionic strength shock. Native and mutant (F27R and KK174/175LL) murine alphaB crystallin amplicons were subcloned into a Lac-Switch IPTG-inducible RSV promoter eukaryotic vector, and transfected into N1E-115 cells using lipofectin. Expression was induced maximally 8 h after addition of IPTG (optimal final concentration 1 mM) to the medium. Cells grew normally after transfection with native and mutant murine alphaB crystallin. We demonstrated expression of the protein using specific anti-alpha crystallin antibodies. Viability under severe heat and ionic strength stress increased when cells had been transfected with native alphaB crystallin, but not with mutants F27R or KK174/175LL. Heat shock caused translocation of both native and mutant alphaB crystallins into the central region of the cells. These results show that mutations in alphaB crystallin that effect its chaperone-like activity may also influence viability of N1E-115 neural cells under stress, while not influencing the distribution of the protein within the cell.

Aldose reductase: a window to the treatment of diabetic complications?

Kinetic studies on the aldose reductase protein (AR2) have shown that it does not behave as a classical enzyme in relation to ring aldose sugars. These results have been confirmed by X-ray crystallography studies, which have pinpointed binding sites for pharmacological "aklose reductase inhibitors" (ARIs). As with non-enzymic glycation reactions, there is probably a free-radical element involved derived from monosaccharide autoxidation. In the case of AR2, there is free radical oxidation of NADPH by autoxidising monosaccharides, enhanced in the presence of the NADPH-binding protein. Whatever the behaviour of AR2, many studies have showed that sorbitol production is not an initiating aetiological factor in the development of diabetic complications in humans. Vitamin E (alpha-tocopherol), other antioxidants and high fat diets can delay or prevent cataract in diabetic animals even though sorbitol and fructose levels are not modified; vitamin C acts as an AR1 in humans. Protein post-translational modification by glyc-oxidation or other events is probably the key factor in the aetiology of diabetic complications. There is now no need to invoke AR2 in xylitol biosynthesis. Xylitol can be produced in the lens from glucose, via a pathway involving the enzymes myo-inositol-oxygen oxidoreductase, D-glucuronate reductase. L-gulonate NAD(+)-3-oxidoreductase and L-iditol-NAD(+)-5-oxidoreductase, all of which have recently been found in bovine and rat lens. This chapter investigates the molecular events underlying AR2 and its binding and kinetics. Induction of the protein by osmotic response elements is discussed, with detailed analysis of recent in vitro and in vivo experiments on numerous ARIs. These have a number of actions in the cell which are not specific, and which do not involve them binding to AR2. These include peroxy-radical scavenging and recently discovered effects of metal ion chelation. In controlled experiments, it has been found that incubation of rat lens homogenate with glucose and the copper chelator o-phenanthroline abolishes production of sorbitol. Taken together, these results suggest AR2 is a vestigial NADPH-binding protein, perhaps similar in function to a number of non-mammalian crystallins which have been recruited into the lens. There is mounting evidence for the binding of reactive aldehyde moieties to the protein, and the involvement of AR2 either as a 'housekeeping' protein, or in a free-radial-mediated 'catalytic' role. Interfering with the NADPH binding and flux levels--possibly involving free radicals and metal ions--has a deleterious effect. We have yet to determine whether aldose reductase is the black sheep of the aldehyde reductase family, or whether it is a skeleton in the cupboard, waiting to be clothed in the flesh of new revelations in the interactions between proteins, metal ions and redox metabolites.

Effects of controlled mutations on the N- and C-terminal extensions of chick lens beta B1 crystallin

BACKGROUND

While gamma-crystallin exists as a monomer, beta-crystallin, which unlike gamma-crystallin contains N- and C-terminal arms, associates to form homodimers.

METHODS

In order to answer the question of whether the extensions are involved in dimerisation of chick lens beta B1 crystallin, we have developed a heterologous expression system for chicken beta B1 crystallin in Escherichia coli, and produced three mutations by site-directed mutagenesis. We have substituted residues in the PAPA segment of the N-terminal extension, curtailed the N-terminal extension by five residues, and deleted 16 residues from the C-terminal extension.

RESULTS

High-resolution gel filtration chromatography and non-denaturing gel electrophoresis show that the mutations did not influence dimerisation of the beta B1 crystallin, while circular dichroism and tryptophan fluorescence indicated that the mutations did not have a major influence on beta B1 crystallin structure or its heat stability.

CONCLUSIONS

Our experiments show that as with rat lens beta B2 crystallin, dimerisation of beta B1 crystallin is not affected by alterations to the conserved PAPA region and that the peptide linker region rather than the N- and C-terminal extensions must be important in dimerisation.

Studies on the binding of alpha-crystallin to recombinant prochymosins and chymosin

PURPOSE

To further investigate the binding of alpha-crystallin to other proteins as part of its chaperone-like activity, we studied interactions of alpha-crystallin with recombinant calf prochymosins and chymosin.

METHODS

Recombinant calf prochymosin B and one C-terminal mutant (PC+2, with two additional residues, Histidine-Glycine) were expressed as inclusion bodies in E. coli. Native and mutant proteins were denatured in 8 M urea before being refolded by dilution slowly in phosphate buffer, pH 10.7, in the presence and absence of alpha-crystallin at different concentration ratios. After dialysis, the folded proteins were converted to the active chymosin by acidification. The resulting enzyme activities at standard protein concentrations were determined by a microtitre milk-clotting assay.

RESULTS

Refolding of 1.0 mg/ml of protein inclusion bodies diluted in phosphate buffer at 0.32 M urea in the presence of alpha-crystallin resulted in enhanced chymosin activity relative to the control without alpha-crystallin. When lower inclusion body concentrations were used, enzyme activity was not enhanced relative to the control. The mutant enzyme (PC+2) showed no conversion to the active form in the presence of alpha-crystallin. alpha-Crystallin formed a complex with refolded prochymosin, as well as with prochymosin during refolding, but not with active chymosin. Removal of the 43-residue propeptide resulted in loss of alpha-crystallin binding. The addition of two residues (Histidine-Glycine) to the prochymosin C-terminus resulted in precipitation of the mutant prochymosin-alpha-crystallin complex and loss of enzyme activity.

CONCLUSIONS

Our experiments show that even under stringent refolding conditions, alpha-crystallin, which retains its gross oligomeric integrity, can bind to unfolded proteins in inclusion bodies and enhance the apparent yield of chymosin activity from high concentrations of inclusion bodies. alpha-Crystallin shows some specificity for binding to its target protein; this specificity may be based on steric considerations as well as residue-specific interactions.

Ibuprofen protects alpha-crystallin against posttranslational modification by preventing protein cross-linking

Posttranslational modification of bovine alpha-crystallin by D-erythrose-4-phosphate, fructose-6-phosphate, D-ribose-5-phosphate and carbamylation using potassium cyanate induced the loss of chaperone-like activity, as assessed by gamma-crystallin aggregation. The presence of high-molecular-weight aggregates indicated that erythrosylated, fructosylated and carbamylated alpha-crystallins were modified by non-reducible cross-linking. In contrast, ribosylation of alpha-crystallin induced the formation of reducible cross-links. Analysis of ribosylated, erythrosylated and carbamylated alpha-crystallin using non-denaturing acrylamide gels showed that the cross-linking did not sterically inhibit the normal aggregate formation or alter the oligomerisation of the aggregate. Co-incubation of ibuprofen in the presence of alpha-crystallin and the modifying agents protected the chaperone-like activity of alpha-crystallin, enabling the inhibition of gamma-crystallin aggregation. In addition, ibuprofen inhibited the formation of both reducible and non-reducible cross-linked high-molecular-weight alpha-crystallin aggregates. We show in this paper that ibuprofen can inhibit in vitro cross-linking events responsible for the loss of chaperone-like activity of alpha-crystallin and suggest that the protective effect of ibuprofen may be exerted by the binding of ibuprofen breakdown products to alpha-crystallin lysine groups, preventing posttranslational modification responsible for the loss of chaperone-like activity.

Effects of site-directed mutations on the chaperone-like activity of alphaB-crystallin

Recombinant alphaB-crystallin has been shown to exhibit chaperone-like activity, suppressing the thermal aggregation of gamma-crystallin and aggregation of the reduced insulin B chain conferring thermotolerance to Escherichia coli BL21(DE3) cells. Mutations were made in three specific areas of the alphaB-crystallin, the N terminus D2G, the conserved phenylalanine-rich region, F24R, F27R, F27A, and the two C-terminal lysines K174L/K175L, K174G/K175G. Biophysical characterization of the mutant alphaB-crystallins using far-UV CD revealed no change in secondary structural elements. Tryptophan fluorescence demonstrated global structural changes. Heat stability of the mutant alphaB-crystallins was not significantly affected as indicated by tryptophan fluorescence of heat-treated proteins. Mutations within the phenylalanine-rich region abolish the chaperone-like activity as measured by both in vivo and in vitro assays. Proteins with mutations at the C terminus demonstrated no significant chaperone-like activity, failing to confer thermotolerance on E. coli and demonstrating no significant inhibition of protein aggregation in either gamma-crystallin or reduced insulin B chain assays. The N-terminal mutation D2G demonstrated a significant reduction in efficiency of the chaperone-like activity although some thermotolerance was conferred in the E. coli assay. In vitro assays showed that complete inhibition of aggregation was only achieved at 10-fold higher concentrations of D2G than that required by the native alphaB-crystallin. Consistent changes in the chaperone-like activity of the site-directed mutants were demonstrated by the three assays. The results suggested that both charge-charge and hydrophobic interactions are important in protein binding by alphaB-crystallin and that the conserved RLFDQFF region is vital for chaperone-like activity.

Accumulation of xylitol in the mammalian lens is related to glucuronate metabolism

Cataract remains the major cause of blindness worldwide and a common complication of diabetes. Polyol accumulation in the lens is associated with cataract formation. Here we present evidence for a novel pathway for xylitol production in the lens involving glucuronate metabolism. Xylitol can be produced in rat and bovine lens from glucose, via the enzymes myo-inositol-oxygen oxidoreductase, D-glucuronate reductase, L-gulonate NAD(+)-3-oxidoreductase and L-iditol-NAD(+)-5-oxidoreductase, which have been found in the mammalian lens for the first time. Glucuronate reductase has been purified and was inhibited by thiol quenching reagents. UDP-glucuronyl transferase is also present in mammalian lenses; this enzyme may be an anti-toxic defense mechanism in the lens.

Protein folds and functional similarity; the Greek key/immunoglobulin fold

Investigations on a number of proteins in the Greek key/immunoglobulin superfold group using computer methods suggested that proteins containing modified Greek keys might exhibit some protein-protein interactions similar to those seen with immunoglobulins. The two domain beta-sheet modified Greek key structure of the beta/gamma-crystallins is shared by other proteins, for example the chaperone protein PapD. Based on computer analysis, we tested for protein-protein interactions using protein A from Staphylococcus aureus, and showed that gamma-crystallin, unlike alpha- or gamma s-crystallin, exhibits weak protein A binding. beta-Crystallin exhibits much weaker binding than gamma-crystallin. Protein A interaction may involve hydrophobic interactions around the interconnecting peptide region. We discuss the implications for the molecular evolution of the crystallins, the superfold, and for the molecular interactions in the mammalian lens that could be important in maintaining transparency.

Modelling molecular stability in gamma B crystallin

Molecular modelling and dynamics simulations of gamma B crystallin and a number of its adducts were used to simulate effects of post-translational modifications. N-terminal modifications which disrupted the surface charge network of gamma-crystallin did not produce significant unfolding in any part of the gamma-crystallin molecule (P > 0.05) consistent with the results of in vitro aggregation studies. There were no significant changes to the molecular volume of the protein, suggesting that adduct formation did not result in molten globule formation. Adduct formation did however increase the vulnerability of particular gamma-crystallin cysteine residues to sulphydryl bond formation and so increased the possibility of mixed disulphide formation with glutathione. Modelling of such secondary modification products (containing both N-terminal modifications and glutathione adducts) demonstrated significant (P < 0.05) structural changes. This suggests that a post-translational modification pathway leading to crystallin cross-linking and cataractogenesis proceeds via a number of co-operative steps involving both modification at the N-terminus and mixed glutathione formation.

Heterologous expression of gamma E-crystallin produces protein with an aberrant tertiary structure

Expression of complete rat gamma E-crystallin cDNA in Saccheromyces cerevisiae and in Escherichia coli at 25 degrees C produced soluble proteins similar to rat gamma E-crystallin but with an altered tertiary structure as judged by tryptophan fluorescence. Expression of rat gamma E-crystallin cDNA in E. coli at 37 degrees C produced insoluble inclusion bodies. Refolding of denatured rat gamma E-crystallin from these inclusion bodies produced a protein similar to rat gamma E-crystallin but with altered secondary and tertiary structure, judged by tryptophan fluorescence and circular dichroism. The secondary structure of the refolded gamma-crystallin was similar in beta-sheet content to the native gamma-crystallin structure but was somewhat shifted from the native spectrum, suggesting some alteration in the relative position of the beta-sheets in the refolded structure. These results have implications for crystallin folding, in particular the importance of lens-specific factors (alpha-crystallin, low water content, redox potential) and crystallin hydration.

Effects of the microtubule depolymerizing and stabilizing agents Nocodazole and taxol on glucose-induced insulin secretion from hamster islet tumor (HIT) cells

Hamster islet tumor (HIT) cells retain much of the capacity of normal beta cells to act as glucose sensors. When stimulated with glucose or glucose plus forskolin, HIT cells release much more insulin than unstimulated cells. Ultrastructural analysis reveals that the secretory product of these cells is stored in membrane-bound granules that associate with microtubules under certain circumstances. Immunofluorescence studies using insulin antibody confirm the presence of insulin in granular structures in these cells. The microtubule inhibitor Nocodazole reduces the number of polymerized microtubules and inhibits the sustained phase of insulin secretion in HIT cells. Thus, the structural integrity of microtubules is important for the sustained phase of the insulin secretion to occur. The microtubule stabilizing drug taxol does not decrease insulin secretion. Since taxol blocks microtubule depolymerization, microtubule polymerization-depolymerization alone does not appear to be responsible for insulin granule transport. The increased use of these drugs in cancer research and therapy makes it important to understand their effects on insulin secretion.

Survival in patients with recurrent glioma as a measure of treatment efficacy: prognostic factors following nitrosourea chemotherapy

The assessment of efficacy of treatment in patients with recurrent glioma is notoriously difficult, and survival is the most objective endpoint. Between 1970 and 1992, a cohort of 211 patients with recurrent glioma received nitrosourea-based chemotherapy at the time of disease progression. The median survival from the start of chemotherapy was 7 months, with 30% 1-year and 10% 2-year survival probabilities. One-year survival was 22% in 147 patients with recurrent high-grade astrocytoma, 41% in 37 patients with low-grade astrocytoma and 45% in 24 patients with oligodendroglioma. Age, histological grade and Karnofsky performance status (KPS) at recurrence were independent prognostic factors for survival on multivariate analysis. Based on patients' age, tumour grade and KPS, it was possible to define three distinct prognostic groups with 1-year survival probabilities of 60, 21 and 17% (P < 0.005). Response to chemotherapy was difficult to assess but correlated with prognostic subgroup, with highest response rate (46%) in the most favourable group and lowest (13%) in the poor prognostic group. In patients with recurrent glioma, patient and tumour parameters are the major determinants of outcome which are identical to prognostic factors at the time of primary diagnosis. They can be used to provide prognostic information for the individual patient, and to stratify patients particularly in trials assessing the efficacy of novel treatments.

Nonlinear steady-state kinetics of chloramphenicol acetyltransferase

Steady-state kinetic analysis of chloramphenicol acetyltransferase showed that medium effects (higher temperatures or pH, higher ionic strengths, or lower values for dielectric constant) altered the kinetic behaviour of the enzyme with acetyl-CoA as substrate, but did not significantly affect behaviour with chloramphenicol. This was manifest as an increase in the degree of the rate equation to a 2:2 function. This is interpreted in terms of perturbations to the enzyme at or near the acetyl-CoA binding region of the enzyme.

Lysine vasopressin in the treatment of refractory hemodialysis-induced hypotension

The etiology of hemodialysis-induced hypotension is multifactorial. We assessed the efficacy of intranasal lysine vasopressin (LV) in 6 patients with refractory hemodialysis-induced hypotension. Autonomic testing was abnormal in all. Intranasal LV and placebo were assessed in a double-blind crossover fashion. With LV, the mean number of hypotensive episodes was less (0.9 +/- 0.8 vs. 1.5 +/- 1; t = 3.95, p less than 0.05), as was the total volume of intravenous fluid administered because of hypotension (155 +/- 57 vs. 280 +/- 123 cm3; t = 2.98, p less than 0.05). Systolic, diastolic, and mean arterial blood pressures were significantly greater at 90 min of the dialysis session. Measured baseline epinephrine, norepinephrine, and antidiuretic hormone levels were elevated above normal levels and fell with hypotension despite the use of LV. The results from this study demonstrate the utility of LV in the treatment of refractory hemodialysis-induced hypotension.

Incorporation and turnover of labeled exogenous tubulin in the mitotic spindles of Chaetopterus oocytes and HeLa cells

The incorporation of tubulin into mitotic spindles in situ was studied by incubating permeabilized mitotic cells in solutions containing [3H]GTP-labeled or dichlorotriazinylamino fluorescein (DTAF)-labeled tubulin. Metaphase HeLa cells or spindle-containing "minicells" from Chaetopterus oocytes were lysed in a microtubule-assembly buffer plus 0.5% Nonidet P-40, 1 mg/ml 120,000g supernatant mammalian brain tubulin, and [3H]GTP. After different periods of incubation, mitotic spindles were isolated in 2 M-glycerol-containing assembly buffer and separated from unbound counts by centrifugation through a 4 M-glycerol cushion; 3H counts per mg protein increase linearly for 8-12 min and then reach a plateau or steady state in both Chaetopterus oocytes and HeLa cells. Addition of 4 mM CaCl2 blocks or reverses incorporation. Little or no [3H]GTP is incorporated if exogenous tubulin or lysed cells are omitted from the assembly mixture. To measure the loss rate of [3H]GTP-tubulin from mitotic spindles, cells were incubated in tubulin plus [3H]GTP for 30 min, and a 20-fold excess of cold GTP (2 mM) was added. Samples were removed after incubation for different periods, and spindles were isolated as described above and counted for 3H content. [3H]GTP is lost from spindles at a rate of about 16%/min until a new steady state is reached in about 8 min. These results are consistent with an incorporation and turnover of [3H]GTP-tubulin in spindle microtubules of these lysed-cell models. The location of this newly incorporated tubulin in the spindle was investigated by incorporating fluorescent DTAF-tubulin into mitotic spindles of these lysed cell types.(ABSTRACT TRUNCATED AT 250 WORDS)

Bacteriophage typing of strains of Mycobacterium tuberculosis from Nepal

One hundred strains of Mycobacterium tuberculosis isolated from cases of pulmonary tuberculosis in Nepalese villagers were typed with the World Health Organization set of bacteriophages. The number of strains in the 3 major phage types A, I, and B were 19, 53, and 28 respectively. This distribution is significantly different from those described in other geographical regions. In particular there was a relatively low incidence of type A strains and, in common with South India, there was a high proportion of type I strains. All the strains in this study were resistant to 5-Furan-2 carbonic acid hydrazine and 34 were highly resistant to isoniazid. Representative strains of the 3 phage types, including 4 isoniazid-resistant type I strains, did not differ in their virulence in the guinea pig; thus the type I strains found in Nepal may not be of the same origin as those of this phage type from India which are usually attenuated in the guinea pig. This study provides further evidence for the existence of geographical differences in the types of tubercle bacilli.

Microtubule turnover as a mechanism of mitosis and its possible evolution

Movement of chromosomes during mitosis appears to be coupled to the unidirectional turnover of spindle microtubules. This paper outlines a directional turnover model of mitosis which hypothesizes that: (1) Unidirectional turnover of tubulin subunits and microtubule-associated proteins occurs from an assembly site at one end to a disassembly site at the other end of mitotic apparatus microtubules. (2) The components of interpolar microtubules are continuously moving toward each pole due to their assembly in the opposite half spindle and disassembly in the near half spindle. (3) Mitotic chromosome movements are coupled to this directional turnover by selective formation of semi-stable lateral interactions or bridges between kinetochore microtubules and parallel interpolar microtubules. (4) The anaphase velocity of kinetochores relative to the poles is determined by the rate that kinetochore microtubules disassemble on their poleward ends minus the rate they assemble at their kinetochore ends. (5) Spindle elongation occurs when assembly of interpolar microtubules is more rapid than their disassembly or when interpolar microtubules slide in an anti-parallel arrangement. (6) The velocity of chromosome separation is the sum of spindle elongation and the poleward movements of sister chromosomes. Evidence for and against these hypotheses and some possible steps in the evolution of this type of mechanism are discussed.

Stimulation of human chorionic gonadotropin by JAr line choriocarcinoma after inhibition of DNA synthesis

Treatment of choriocarcinoma cells (JAr line) for 24 hr with methotrexate, fluorodeoxyuridine, 1-beta-D-arabinofuranosylcytosine, or hydroxyurea, in doses that inhibit DNA synthesis, results in a 2.5- to 12-fold increase in human chorionic gonadotropin (HCG) synthesis. Under the conditions of use, these agents do not significantly depress RNA or protein synthesis. Simultaneous addition of thymidine with methotrexate or fluorodeoxyuridine and of deoxycytidine with 1-beta-D-arabinofuranosylcytosine blocks the HCG stimulation. Despite a rapid inhibition of DNA synthesis, HCG stimulation is gradual and reaches a peak after drug removal. Decline in HCG synthesis is coincident with recovery of DNA synthesis, and there is a positive correlation between the duration of inhibition of DNA synthesis and the amount of HCG increase. Although most of the methotrexate-induced stimulation of HCG synthesis occurs after methotrexate removal, preventing protein synthesis during the exposure to methotrexate abrogates the increase. The stimulation of HCG synthesis by methotrexate is more sensitive to protein synthesis inhibition during the first 12 hr of a 24-hr exposure than it is during the second 12 hr. Thus, in accord with the kinetics, specificity, dose dependence, and protein synthesis requirement, HCG synthesis seems to be stimulated as a direct consequence of inhibition of DNA synthesis, with a requirement for some other protein synthesis-dependent event(s) preceding the stimulation.

Ca+2-accumulating components in developing skeletal muscle

This ultrastructural study on the localization of Ca+2 in developing skeletal muscle indicates that the formation of calcium-accumulating components begins during embryonic development. Both oxalate and pyroantimonate techniques are used to localize Ca+2 in distinct cellular components of chick pectoral and sartorius muscles. Two major sites for Ca+2 accumulation are present in ultrathin sections of embryonic and post-embryonic muscles: the terminal cisternae of the sarcoplasmic reticulum and specific lines in the I-bands. Calcium oxalate-accumulating vesicles are present in the smallest recognizable myotubes at the twelfth day of incubation, but calcium-accumulating components are not seen at myofibrillar I-band sites until the fourteenth to seventeenth days of incubation. The fact that myofibrils first form and later in development accumulate a Ca+2-binding component suggests that this Ca+2-binding component is not necessary for the formation of myofibrils, but is added to myofibrils before hatching to serve a probable regulatory role in contraction.

Effect of incubation in human plasma on electrophoretic mobility of brain-type creatine phosphokinase

1. Electrophoretic mobility of brain-type creatine phosphokinase (CPK) from rabbit, rat and human decreased after incubation in human plasma for 3 h or 17 h but did not change after incubation in isotonic saline solution. The presence of the reducing agent mercaptoethanol during incubation in human plasma tended to reduce the rate of change of electrophoretic mobility of BB-CPK. 2. The activity of brain CPK was almost completely lost after incubation for 17 h in human plasma. The addition of mercaptoethanol after incubation of brain CPK in human plasma could only partially restore the enzyme activity. 3. The decrease in electrophoretic mobility of rat brain CPK occurred after incubation in an ultra-filtrate of human plasma which contained molecules whose molecular weight did not exceed 1000. 4. Gel chromatography indicated that incubation of brain CPK in human plasma did not markedly change the molecular size of the enzyme.

Pressure-induced depolymerization of spindle microtubules. III. Differential stability in HeLa cells

Evidence from light microscopy (principally polarization microscopy) has demonstrated that hydrostatic pressure can reversibly inhibit mitosis by rapidly depolymerizing the spindle fiber microtubules. We have confirmed this finding in ultrastructural studies of mitotic HeLa cells incubated at 37 degrees C and pressurized at 680 atm (10,000 psi). Althouth there are many spindle microtubules in the cells at atmospheric pressure, electron micographs of cells pressurized for 10 min (and fixed while under pressure in a Landau-Thibodeau chamber) show few microtubules. Pressure has a differential effect on the various types of spindle microtubules. Astral and interpolar MTs appear to be completely depolymerized in pressurized cells, but occasional groups of kinetochore fiber microtubules are seen. Surprisingly, the length and density of microtubules of the stem bodies and midbody of telophase cells appear unchanged by pressurization. In cells fixed 10 min after pressure was released, microtubules were again abundant, the density often appearing to be higher than in control cells. Reorganization seems incomplete, however, since many of the microtubules are randomly oriented. Unexpectedly, kinetochores appeared diffuse and were difficult to identify in sections of pressurized cells. Even after 10 min of recovery at atmospheric pressure, their structure was less distinct than in unpressurized cells.