Mechanistic insight into biopolymer induced iron oxide mineralization through quantification of molecular bonding.

Microbial production of iron (oxyhydr)oxides on polysaccharide rich biopolymers occurs on such a vast scale that it impacts the global iron cycle and has been responsible for major biogeochemical events. Yet the physiochemical controls these biopolymers exert on iron (oxyhydr)oxide formation are poorly understood. Here we used dynamic force spectroscopy to directly probe binding between complex, model and natural microbial polysaccharides and common iron (oxyhydr)oxides. Applying nucleation theory to our results demonstrates that if there is a strong attractive interaction between biopolymers and iron (oxyhydr)oxides, the biopolymers decrease the nucleation barriers, thus promoting mineral nucleation. These results are also supported by nucleation studies and density functional theory. Spectroscopic and thermogravimetric data provide insight into the subsequent growth dynamics and show that the degree and strength of water association with the polymers can explain the influence on iron (oxyhydr)oxide transformation rates. Combined, our results provide a mechanistic basis for understanding how polymer-mineral-water interactions alter iron (oxyhydr)oxides nucleation and growth dynamics and pave the way for an improved understanding of the consequences of polymer induced mineralization in natural systems.

The mechanisms of crystal growth inhibition by organic and inorganic inhibitors.

Understanding mineral growth mechanism is a key to understanding biomineralisation, fossilisation and diagenesis. The presence of trace compounds affect the growth and dissolution rates and the form of the crystals produced. Organisms use ions and organic molecules to control the growth of hard parts by inhibition and enhancement. Calcite growth in the presence of Mg2+ is a good example. Its inhibiting role in biomineralisation is well known, but the controlling mechanisms are still debated. Here, we use a microkinetic model for a series of inorganic and organic inhibitors of calcite growth. With one, single, nonempirical parameter per inhibitor, i.e. its adsorption energy, we can quantitatively reproduce the experimental data and unambiguously establish the inhibition mechanism(s) for each inhibitor. Our results provide molecular scale insight into the processes of crystal growth and biomineralisation, and open the door for logical design of mineral growth inhibitors through computational methods.

Visual field defect after ischemic stroke-impact on mortality.

OBJECTIVES: We aimed to investigate the impact of visual field defects (VFD) on mortality in ischemic stroke patients. MATERIALS AND METHODS: All patients with acute infarction and a clinically detected VFD from February 2006 to December 2013 in the NORSTROKE Registry (n = 506) were included and compared with ischemic stroke patients with normal visual fields (n = 2041). A record of patients who had died per ultimo April 2015 was obtained from the central registry at Haukeland University Hospital. RESULTS: Patients with VFD were significantly older (75.0 vs 69.8, P < .001) than patients with normal visual fields. The majority of patients with VFD was male, had higher cardiovascular morbidity prestroke, and were more likely to have shorter median time from symptom onset to admission (1.7 hours vs 2.7 hours, P < .001). Baseline National Institute of Health Stroke Scale (NIHSS) score was higher (12.7 vs 3.5, P < .001) as was modified Rankin Scale (mRS) score (3.5 vs 1.9, P < .001) and Barthel Index was lower (51.9 vs 84.8, P < .001) day 7. VFD was associated with increased mortality on Kaplan-Meier plots. Hazard ratio was significantly higher for patients with VFD after adjusting for age, sex, employment prior to infarction, married prior to infarction, institutionalization prior to infarction, prior myocardial infarction, atrial fibrillation, smoking, Barthel Index score and i.v. thrombolysis with Cox regression (hazard ratios [HR] 1.30, CI 1.07-1.56, P = .007). CONCLUSIONS: Having a visual field defect after ischemic stroke is independently associated with increased mortality. This should be addressed when selecting candidates for thrombolysis and in the rehabilitation process.

Prebiotic RNA polymerisation: energetics of nucleotide adsorption and polymerisation on clay mineral surfaces.

We measured the binding energy and bonding parameters between model nucleotide functional groups and model clay mineral surfaces in solutions of acidic pH. We demonstrate that basal surfaces of clay minerals interact most strongly with nucleobases and show that the adsorption of the phosphate group to clay edges could facilitate polymerisation. Our results suggest that Al- and Fe-rich edge sites behave similarly in nucleotide polymerisation through change of the phosphodiester bond strength. We present an internally consistent set of thermodynamic parameters that represent the nucleotide-clay mineral system.

Quantifying the free energy landscape between polymers and minerals.

Higher organisms as well as medical and technological materials exploit mineral-polymer interactions, however, mechanistic understanding of these interactions is poorly constrained. Dynamic force spectroscopy can probe the free energy landscape of interacting bonds, but interpretations are challenged by the complex mechanical behavior of polymers. Here we restate the difficulties inherent to applying DFS to polymer-linked adhesion and present an approach to gain quantitative insight into polymer-mineral binding.

Controlling biomineralisation with cations.

The production of polymers for controlling calcite growth is a well-known approach in biomineralising organisms. Numerous studies have shown that polymers significantly influenced the growth rate and morphology of CaCO3 but little is known about how the polymers are actually controlled by the organisms. Here we show that cations control the effect of polysaccharides and that these processes have been in place for at least 60 million years. We studied the interaction between cleaved samples of pure calcite and ancient coccolith associated polysaccharides (aPS) that we had extracted from the samples of Cretaceous chalk, in solutions that contained one of the common seawater cations, K+, Ca2+, Mg2+ and Sr2+. With atomic and chemical force microscopy (AFM and CFM), we showed that K+, Ca2+ and Sr2+ complex aPS through a weak, outer sphere bonding, giving the aPS affinity to sites on steps and terraces. In contrast, Mg2+ enhanced the formation of stronger and longer aPS complexes, resulting in low affinity to calcite terraces and strong affinity to steps. It is known that adsorption is influenced by ionic potential and ionic strength. Our results show that cation-polysaccharide complexing can modify the effectiveness of the polymer. Thus, creating organic molecules with cation complexing ability is an effective strategy for regulating mineral growth, both now and in the past.

Less thrombolysis in posterior circulation infarction-a necessary evil?

OBJECTIVES: Patients with posterior circulation infarction (PCI) have more subtle symptoms than anterior circulation infarction (ACI) and could come too late for acute intervention. This study aimed to describe the clinical presentation, management, and outcome of PCI in the NORSTROKE registry. METHODS: All patients with PCI admitted to the Department of Neurology at Haukeland University Hospital and registered in the NORSTROKE database 2006-2013 were included (n=686). Patients with ACI (n=1758) were used for comparison. RESULTS: Patients with PCI were younger (68.2 vs 71.8, P<.001), had longer median time from symptom onset to admission (3.8 hours vs 2.2 hours, P<.001), and were less likely to arrive at hospital within 4.5 hours from symptom onset (56.2% vs 72.5%, P<.001, ictus known). Patients with PCI scored lower on baseline National Institute of Health Stroke Scale (NIHSS) total score (3.2 vs 6.3, P<.001), and lower or equally on all items of NIHSS, except for ataxia in two limbs. Patients with PCI were less likely to receive i.v. thrombolytic treatment (9.9% vs 21.5%, OR 0.66, CI 0.47-0.94). On day 7, patients with PCI scored lower on NIHSS (2.8 vs 4.9, P<.001), modified Rankin Scale (2.0 vs 2.3, P<.001), and higher on Barthel Index (84.5 vs 76.0, P<.001). CONCLUSIONS: Our study is, to our knowledge, the largest series reporting comprehensively on PCI verified by diffusion-weighted imaging. PCI patients are younger than ACI and have better outcome. PCI and ACI are equally investigated in the acute setting, but thrombolysis rates remain 50% lower in PCI.

A Microkinetic Model of Calcite Step Growth.

In spite of decades of research, mineral growth models based on ion attachment and detachment rates fail to predict behavior beyond a narrow range of conditions. Here we present a microkinetic model that accurately reproduces calcite growth over a very wide range of published experimental data for solution composition, saturation index, pH and impurities. We demonstrate that polynuclear complexes play a central role in mineral growth at high supersaturation and that a classical complexation model is sufficient to reproduce measured rates. Dehydration of the attaching species, not the mineral surface, is rate limiting. Density functional theory supports our conclusions. The model provides new insights into the molecular mechanisms of mineral growth that control biomineralization, mineral scaling and industrial material synthesis.

Age dependency of ischaemic stroke subtypes and vascular risk factors in western Norway: the Bergen Norwegian Stroke Cooperation Study.

OBJECTIVES: Age dependency of acute ischaemic stroke aetiology and vascular risk factors have not been adequately evaluated in stroke patients in Norway. Aims of this study were to evaluate how stroke subtypes and vascular risk factors vary with age in a western Norway stroke population. MATERIALS AND METHODS: Patients aged 15-100 years consecutively admitted to our neurovascular centre with acute ischaemic stroke between 2006 and 2012 were included. The study population was categorized as young (15-49 years), middle-aged (50-74 years) or elderly (≥ 75 years). Stroke aetiology was defined by TOAST criteria. Risk factors and history of cardiovascular disease were recorded. RESULTS: In total, 2484 patients with acute cerebral infarction were included: 1418 were males (57.3%). Mean age was 70.8 years (SD ± 14.9), 228 patients were young, 1126 middle-aged, and 1130 were elderly. The proportion of large-artery atherosclerosis and of small-vessel occlusion was highest among middle-aged patients. The proportion of cardioembolism was high at all ages, especially among the elderly. The proportion of stroke of other determined cause was highest among young patients. Some risk factors (diabetes mellitus, active smoking, angina pectoris, prior stroke and peripheral artery disease) decreased among the elderly. The proportions of several potential causes increased with age. CONCLUSION: The proportion of stroke subtypes and vascular risk factors are age dependent. Age 50-74 years constitutes the period in life where cardiovascular risk factors become manifest and stroke subtypes change.

Can the cardiovascular family history reported by our patients be trusted? The Norwegian Stroke in the Young Study.

BACKGROUND AND PURPOSE: Family history (FH) is used as a marker for inherited risk. Using FH for this purpose requires the FH to reflect true disease in the family. The aim was to analyse the concordance between young and middle-aged ischaemic stroke patients' reported FH of cardiovascular disease (CVD) with their parents' own reports. METHODS: Ischaemic stroke patients aged 15-60 years and their eligible parents were interviewed using a standardized questionnaire. Information of own CVD and FH of CVD was registered. Concordance between patients and parents was tested by kappa statistics, sensitivity, specificity, predictive values and likelihood ratios. Regression analyses were performed to identify patient characteristics associated with non-concordance of replies. RESULTS: There was no difference in response rate between fathers and mothers (P = 0.355). Both parents responded in 57 cases. Concordance between patient and parent reports was good, with kappa values ranging from 0.57 to 0.7. The patient-reported FH yielded positive predictive values of 75% or above and negative predictive values of 90% or higher. The positive likelihood ratios (LR+) were 10 or higher and negative likelihood ratios (LR-) were generally 0.5 or lower. Interpretation regarding peripheral arterial disease was limited due to low parental prevalence. Higher age was associated with impaired concordance between patient and parent reports (odds ratio 1.05; 95% confidence interval 1.01-1.09; P = 0.020). CONCLUSIONS: The FH provided by young and middle-aged stroke patients is in good concordance with parental reports. FH is an adequate proxy to assess inherited risk of CVD in young stroke patients.

Vision problems in ischaemic stroke patients: effects on life quality and disability.

BACKGROUND AND PURPOSE: Vision problems after cerebral infarction are an increasingly acknowledged problem. Our aim was to investigate the effect on quality of life and post-stroke disability. METHODS: Patients admitted to the Stroke Unit, Department of Neurology, Haukeland University Hospital, between February 2006 and July 2008 with acute cerebral infarction were prospectively registered in the NORSTROKE Registry. Patients received a postal questionnaire at least 6 months after stroke. The questionnaire included 15D©, EuroQol 5D (EQ-5D(™) ), the Hospital Anxiety and Depression Scale (HADS), the Fatigue Severity Scale (FSS) and the Barthel Index (BI). RESULTS: Of 328 responders, 83 (25.4%) reported a vision problem. Vision problems were associated with older age (71.8 years vs. 66.5 years, P = 0.001), higher National Institutes of Health Stroke Scale score on admission (5.9 vs. 3.8, P < 0.001), higher modified Rankin Scale day 7 (2.0 vs. 1.4, P < 0.001) and lower BI day 7 (85.7 vs. 93.9, P = 0.002). Patients with vision problems had lower median EQ-5D utility score (0.62 vs. 0.80, P < 0.001), lower median 15D utility score (0.73 vs. 0.89, P < 0.001), higher median HADS score (12 vs. 5, P < 0.001), higher median FSS score (5.6 vs. 4.3, P < 0.001) and lower median BI (95 vs. 100, P < 0.001) on long-term follow-up. Patients with self-reported vision problems scored lower on all sub-scores of BI on follow-up (all P < 0.001). CONCLUSION: One in four patients reported a vision problem on follow-up after cerebral infarction. Vision problems after cerebral infarction reduce quality of life and are associated with increased disability. Thorough diagnostic evaluation and targeted rehabilitation is important.

Intricacies of redoxome function demonstrated with a simple in vitro chemiluminescence method, with special reference to vitamin B12 as antioxidant.

The homeostatic control of the redox system (the redoxome) in mammalian cells depends upon a large number of interacting molecules, which tend to buffer the electronegativity of cells against oxidants or reductants. Some of these components kill - at high concentration - microbes and by-stander normal cells, elaborated by professional phagocytes. We examined whether a simple, in vitro chemiluminescence set-up, utilizing redox components from human polymorphonuclear neutrophils (PMN) and red blood cells (RBC), could clarify some unexplained workings of the redoxome. PMN or purified myeloperoxidase (MPO) triggers formation of reactive oxygen species (ROS), quantified by light emission from oxidized luminol. Both PMN and RBC can generate abundant amounts of ROS, necessitating the presence of a high-capacity redoxome to keep the cellular electronegativity within physiological limits. We obtained proof-of-principle evidence that our assay could assess redox effects, but also demonstrated the intricacies of redox reactions. Simple dose-responses were found, as for the PMN proteins S100A9 (A9) and S100A8 (A8), and the system also revealed the reducing capacity of vitamin B12 (Cbl) and lutein. However, increased concentrations of oxidants in the assay mixture could decrease the chemiluminescence. Even more remarkable, A9 and NaOCl together stimulated the MPO response, but alone they inhibited MPO chemiluminescence. Biphasic responses were also recorded for some dose-response set-ups and are tentatively explained by a 'balance hypothesis' for the redoxome.

Infrared spectroscopy and density functional theory investigation of calcite, chalk, and coccoliths--do we observe the mineral surface?

We have measured infrared spectra from several types of calcite: chalk, freshly cultured coccoliths produced by three species of algae, natural calcite (Iceland Spar), and two types of synthetic calcite. The most intense infrared band, the asymmetric carbonate stretch vibration, is clearly asymmetric for the coccoliths and the synthetic calcite prepared using the carbonation method. It can be very well fitted by two peaks: a narrow Lorenzian at lower frequency and a broader Gaussian at higher frequency. These two samples both have a high specific surface area. Density functional theory for bulk calcite and several calcite surface systems allows for assignment of the infrared bands. The two peaks that make up the asymmetric carbonate stretch band come from the bulk (narrow Lorenzian) and from a combination of two effects (broad Gaussian): the surface or near surface of calcite and line broadening from macroscopic dielectric effects. We detect water adsorbed on the high surface area synthetic calcite, which permits observation of the chemistry of thin liquid films on calcite using transmission infrared spectroscopy. The combination of infrared spectroscopy and density functional theory also allowed us to quantify the amount of polysaccharides associated with the coccoliths. The amount of polysaccharides left in chalk, demonstrated to be present in other work, is below the IR detection limit, which is 0.5% by mass.

C-reactive protein triggers calcium signalling in human neutrophilic granulocytes via FcγRIIa in an allele-specific way.

C-reactive protein (CRP) binds to Fcγ-receptors, FcγRIIa (CD32) with high affinity and to FcγRIa (CD64) with low affinity. The binding to CD32 has been shown to be allele specific, that is, it binds to R/R131 but not to H/H131. Little is known about the cooperation of CRP and neutrophilic granulocytes (PMNs) in inflammatory reactions. The purpose of the present study was to examine CRP signalling in human PMNs, and whether this signalling is also allele specific. Cytosolic calcium of PMN was measured in a single-cell digital imaging system. Receptor expression and polymorphism were studied by real-time RT-PCR, flow cytometry and standard PCR. C-reactive protein induced cytosolic calcium signals in PMNs from homozygote R/R131 donors, but not in PMNs from heterozygote R/H131 donors. However, after the heterozygote PMNs had been incubated with IFN-γ (100 U/ml) for 2 h, both the proportion of cells responding and the size of the CRP-induced calcium signals increased. IFN-γ increased mRNA expression of CD64 about fivefold and surface protein expression of CD64 about fourfold. The calcium signal elicited by CRP was augmented by PMN adhesion to fibronectin, but almost totally abrogated by sphingosine kinase inhibitors. The signals were partly dependent on calcium influx. In conclusion, calcium signalling instigated by CRP in human PMN is FcγRIIa allele specific, as R/R131 responded to CRP, whereas R/H131 did not. However, increased expression of FcγRIa (CD64), stimulated by IFN-γ, can augment calcium signalling by CRP in low-responders. This suggests that the state of the PMNs, as well as the genetic origin, affect sensitivity for CRP.

Visual impairment in stroke patients--a review.

Approximately 30% of all stroke patients suffer from post-stroke visual impairment. Hemianopia is the most common symptom, but also neglect, diplopia, reduced visual acuity, ptosis, anisocoria, and nystagmus are frequent. Partial or complete recovery of visual disorders can occur, but many patients suffer permanent disability. This disability is often less evident than impairment of motor and speech functions, but is negatively correlated with rehabilitation outcome and can lead to a significant reduction in day-to-day functioning. To be visually impaired after stroke reduces quality of life and causes social isolation because of difficulties in navigating/orientating in the surroundings. A thorough diagnosis including targeted examination and later follow-up with eye examination and perimetry is essential in order to establish the extent of the visual impairment and to select the best rehabilitation strategy. Patients seem to profit from visual rehabilitation focused on coping strategies.

Diagnosis and rehabilitation of visual field defects in stroke patients: a retrospective audit.

OBJECTIVE: Visual field defects (VFD) after stroke can cause significant disability and reduction in quality of life. Adequate diagnosis of VFD and referral to visual rehabilitation are important to improve outcome. Our aim was to conduct a retrospective clinical audit to investigate how neurologists detect and follow up VFD in stroke patients in a university hospital in Norway. METHODS: All patients registered in the Bergen NORSTROKE Registry from February 2006 to May 2009 with (1) occipital lobe infarctions and (2) non-occipital infarction and clinically detected VFD were included in the study. Their medical records were reviewed for referral to perimetry for examination of VFD and for referral to a visual rehabilitation program within the first year after brain injury. RESULTS: Of 353 patients, 34 (9.6%) were referred to perimetry and 8 (2.3%) to visual rehabilitation. Patients referred to perimetry were younger (65.1 vs. 74.7 years, p < 0.001), had lower modified Rankin Scale scores (2.53 vs. 3.47, p = 0.003), and scored lower on the National Institutes of Health Stroke Scale upon admission (6.68 vs. 13.90, p < 0.001). Men were more often referred to perimetry than women (73.5 vs. 26.5%, p < 0.001), and those referred were younger (61.2 vs. 75.8 years, p = 0.03). CONCLUSIONS: Only few patients were referred to perimetry, and even fewer were offered visual rehabilitation. Age and gender were negative predictors for referral. Neurologists' awareness of the significant disability related to VFD must be increased. Focused diagnostics on visual impairment and early referral to a visual rehabilitation program should be mandatory in stroke unit services.

Readability of informed consent documents (1987-2007) for clinical trials: a linguistic analysis.

We investigated the readability of informed consent documents linguistically and compared old and new ICDs. Twenty ICDs (ten from 1987-1992 and ten from 2006-2007) were included. The Evaluative Linguistic Framework (ELF) was used to analyze the texts. The ELF evaluates the following items: main themes, order of themes, rhetorical functions, the relationship between reader and writer, metadiscourse, headings, expert terminology, and visual aspects. An ICD is considered readable if it achieves the goal of inviting the reader to participate and explaining the implication of participation. The new ICDs were more readable than the old ones, as they were more oriented towards research, contained instructions about how to consent, and provided clear contact information. Aspects that reduced the readability of the new ICDs were the large number of topics, details, and actors presented. The readability of the old ICDs was enhanced by fewer topics, a clear presentation of the involved actors, and brevity. However, their readability was reduced by the inclusion of a vast amount of information about the reader's diagnosis and treatment.

Binding of ethanol on calcite: the role of the OH bond and its relevance to biomineralization.

The interaction of OH-containing compounds with calcite, CaCO(3), such as is required for the processes that control biomineralization, has been investigated in a low-water solution. We used ethanol (EtOH) as a simple, model, OH-containing organic compound, and observed the strength of its adsorption on calcite relative to OH from water and the consequences of the differences in interaction on crystal growth and dissolution. A combination of atomic force microscopy (AFM) and molecular dynamics (MD) simulations showed that EtOH attachment on calcite is stronger than HOH binding and that the first adsorbed layer of ethanol is highly ordered. The strong ordering of the ethanol molecules has important implications for mineral growth and dissolution because it produces a hydrophobic layer. Ethanol ordering is disturbed along steps and at defect sites, providing a bridge from the bulk solution to the surface. The strong influence of calcite in structuring ethanol extends further into the liquid than expected from electrical double-layer theory. This suggests that in fluids where water activity is low, such as in biological systems optimized for biomineralization, organic molecules can control ion transport to and from the mineral surface, confining it to specific locations, thus providing the organism with control for biomineral morphology.

Interaction of ethanol and water with the {1014} surface of calcite.

Molecular dynamics simulations have been used to model the interaction between ethanol, water, and the {1014} surface of calcite. Our results demonstrate that a single ethanol molecule is able to form two interactions with the mineral surface (both Ca-O and O-H), resulting in a highly ordered, stable adsorption layer. In contrast, a single water molecule can only form one or other of these interactions and is thus less well bound, resulting in a more unstable adsorption layer. Consequently, when competitive adsorption is considered, ethanol dominates the adsorption layer that forms even when the starting configuration consists of a complete monolayer of water at the surface. The computational results are in good agreement with the results from atomic force microscopy experiments where it is observed that a layer of ethanol remains attached to the calcite surface, decreasing its ability to interact with water and for growth at the {1014} surface to occur. This observation, and its corresponding molecular explanation, may give some insight into the ability to control crystal form using mixtures of different organic solvents.