Go Fly a Chitin: The Mystery of Chitin and Chitinases in Vertebrate Tissues

A controversy arose decades ago whether the DG42 gene product expressed during frog embryogenesis synthesized hyaluronan or chitin. Both sets of investigators were correct. It is now possible to understand how prescient those findings were. Synthesis of a seven to nine chitin sugar chain fragment is required before hyaluronan synthesis begins. Thus, DG42 indeed synthesizes both hyaluronan and chitin. Hyaluronan turns over rapidly in vertebrate tissues, but chitin oligomers are difficult to degrade. They accumulate and can cause pathology. Chitin is a simple beta-linked repeating sugar homopolymer found prominently in the building block structures of fungi, molluscs, arthropods, and other forms of invertebrate life. It is a highly resistant insoluble material requiring chitin synthases for production and chitinases for degradation. Mysteriously, chitins and chitinases also occur in vertebrate tissues, while it had previously been assumed that no chitins were contained therein. That assumption is now challenged based on recent biochemical evidence. Chitin does accumulate in many tissues, but may be particularly toxic to neurons. Its accumulation in the brain may account for the cognitive decline found in patients with Alzheimer's disease. The DG42 observations together with the participation of chitins and chitinases in several human diseases, among which in addition to Alzheimer's disease include Gaucher's disease, asthma, and aspects of abnormal immune recognition justify a reexamination of these topics. The purpose of this review is to summarize data in order to place chitins and their attendant enzymes in a rational framework in an attempt to create a cohesive story.

Field-stepped broadband NMR in pulsed magnets and application to SrCu2(BO3)2 at 54T

Pulsed magnets generate the highest magnetic fields as brief transients during which the observation of NMR is difficult, however, this is the only route to unique insight into material properties up to the regime of 100T. Here, it is shown how rather broad NMR spectra can be assembled in a pulsed magnet during a single field pulse by using the inherent time dependence of the field for the recording of field-stepped free induction decays that cover a broad frequency range. The technique is then applied to (11)B NMR of the spin-dimer system SrCu2(BO3)2, a magnetic insulator known to undergo a series of field-driven changes of the magnetic ground state. At peak fields of about 54T at the Dresden High Magnetic Field Laboratory, (11)B NMR spectra spanning a total of about 9MHz width are reconstructed. The results are in good accordance with a change from a high-temperature paramagnetic state to a low-temperature commensurate superstructure of field-induced spin-dimer triplets.

Hyaluronan in wound healing: rediscovering a major player

Wound healing involves a series of carefully modulated steps, from initial injury and blood clot to the final reconstituted tissue or scar. A dynamic reciprocity exists throughout between the wound, blood elements, extracellular matrix, and cells that participate in healing. Multiple cytokines and signal transduction pathways regulate these reactions. A major component throughout most of the process is hyaluronan, a straight-chain carbohydrate extracellular matrix polymer. Hyaluronan occurs in multiple forms, chain length being the only distinguishing characteristic between them. Levels of hyaluronan in its high-molecular-weight form are prominent in the earliest stages of wound repair. Progressively more fragmented forms occur in a manner not previously appreciated. We outline here steps in the wound healing cascade in which hyaluronan participates, as well as providing a review of its metabolism. Although described by necessity in a series of quantum steps, the healing process is constituted by a smooth continuum of overlapping reactions. The prevalence of hyaluronan in the wound (initially termed "hexosamine-containing mucopolysaccharide"), particularly in its early stages, was pointed out over half a century ago by the Harvard surgeon J. Engelbert Dunphy. It appears we are now returning to where we started.

Radiographic evaluation of posttraumatic osteoarthritis of the ankle: the Kellgren-Lawrence scale is reliable and correlates with clinical symptoms

OBJECTIVE

To assess reliability and construct validity of the Kellgren-Lawrence (K&L) scale in posttraumatic ankle osteoarthritis (OA); additionally evaluate the validity of including tibiotalar tilting in the scale.

METHOD

One-hundred and fifty ankle radiographs (75 patients, unilateral malleolar fractures) evaluated at average of 18 years after surgery. American Orthopaedic Foot & Ankle Society (AOFAS) ankle-hindfoot (HF) score and pain (visual analog scale) were recorded. Grading of OA according to K&L criteria and identification of OA features was performed on standardized radiographs by four physicians. Minimal joint space width, sclerosis, and talar tilt angle were quantified by digital measurements. A modified K&L scale including talar tilting is presented. Validity of original and modified scale was evaluated and expressed as ability to (1) Identify those with clinical symptoms of ankle OA; and (2) Distinguish between different degrees of fracture severity.

RESULTS

Inter- and intra-observer reliability of OA assessment according to K&L were good (ICC 0.61 and 0.75). Original and modified K&L grades significantly increased with decreasing AOFAS ankle-HF scores and greater pain. A talar-tilt angle > 2° compared with ≤ 2° in grade 3 was associated with significantly higher pain levels (VAS pain 4.2 vs 1.4, respectively; mean difference 2.8, 95% CI 0.5-5.1). More severe fracture patterns at time of surgery were more often in patients with the highest K&L grades.

CONCLUSIONS

The K&L scale is a valid and reliable radiographic grading system for assessment of ankle OA. Inclusion of the talar tilt angle might allow for better differentiation with respect to clinical outcomes.

Absence of skin rash in Goodpasture's syndrome: the hyaluronan effect

Goodpasture's syndrome is a rare disease that involves rapidly progressive kidney failure as well as hemorrhagic lung disease. It is a form of autoimmune disorder with unusual features; marked male preponderance, in contrast with other autoimmune disease in which females are at far greater risk. The autoantibodies are directed again the carboxy-extension non-collagenous (NC1) portion of one of the basement membrane-specific collagen IV alpha 3 chains. Basal laminas throughout the body share this structure, including those in kidney, lung and skin. But curiously, skin is rarely involved in Goodpasture's syndrome. Hyaluronan is a large extracellular matrix carbohydrate polymer. Half of total body hyaluronan occurs in skin. High molecular weight hyaluronan, a potent immunosuppressive polymer, might be functioning as an immune shield for skin in Goodpasture's syndrome, and be the basis for the anomaly. A summary of this putative effect is described, including possible molecular mechanisms involved, and suggestions for testing this hypothesis.

A Novel SAT-Based Approach to Model Based Diagnosis

This paper introduces a novel encoding of Model Based Diagnosis (MBD) to Boolean Satisfaction (SAT) focusing on minimal cardinality diagnosis. The encoding is based on a combination of sophisticated MBD preprocessing algorithms and the application of a SAT compiler which optimizes the encoding to provide more succinct CNF representations than obtained with previous works. Experimental evidence indicates that our approach is superior to all published algorithms for minimal cardinality MBD. In particular, we can determine, for the first time, minimal cardinality diagnoses for the entire standard ISCAS-85 and 74XXX benchmarks. Our results open the way to improve the state-of-the-art on a range of similar MBD problems.

A comparative assessment of small-head metal-on-metal and ceramic-on-polyethylene total hip replacement

Large-head metal-on-metal (MoM) total hip replacements (THR) have given rise to concern. Comparative studies of small-head MoM THRs over a longer follow-up period are lacking. Our objective was to compare the incidence of complications such as infection, dislocation, revision, adverse local tissue reactions, mortality and radiological and clinical outcomes in small-head (28 mm) MoM and ceramic-on-polyethylene (CoP) THRs up to 12 years post-operatively. A prospective cohort study included 3341 THRs in 2714 patients. The mean age was 69.1 years (range 24 to 98) and 1848 (55.3%) were performed in women, with a mean follow-up of 115 months (18 to 201). There were 883 MoM and 2458 CoP bearings. Crude incidence rates (cases/1000 person-years) were: infection 1.3 vs 0.8; dislocation 3.3 vs 3.1 and all-cause revision 4.3 vs 2.2, respectively. There was a significantly higher revision rate after ten years (adjusted hazard ratio 9.4; 95% CI 2.6 to 33.6) in the MoM group, and ten of 26 patients presented with an adverse local tissue reaction at revision. No differences in mortality, osteolysis or clinical outcome were seen. In conclusion, we found similar results for small-head MoM and CoP bearings up to ten years post-operatively, but after ten years MoM THRs had a higher risk of all-cause revision. Furthermore, the presence of an adverse response to metal debris seen in the small-head MOM group at revision is a cause for concern.

Enhanced Partial Expansion A*

When solving instances of problem domains that feature a large branching factor, A* may generate a large number of nodes whose cost is greater than the cost of the optimal solution. We designate such nodes as surplus. Generating surplus nodes and adding them to the OPEN list may dominate both time and memory of the search. A recently introduced variant of A* called Partial Expansion A* (PEA*) deals with the memory aspect of this problem. When expanding a node n, PEA* generates all of its children and puts into OPEN only the children with f = f (n). n is re-inserted in the OPEN list with the f -cost of the best discarded child. This guarantees that surplus nodes are not inserted into OPEN. In this paper, we present a novel variant of A* called Enhanced Partial Expansion A* (EPEA*) that advances the idea of PEA* to address the time aspect. Given a priori domain- and heuristic- specific knowledge, EPEA* generates only the nodes with f = f(n). Although EPEA* is not always applicable or practical, we study several variants of EPEA*, which make it applicable to a large number of domains and heuristics. In particular, the ideas of EPEA* are applicable to IDA* and to the domains where pattern databases are traditionally used. Experimental studies show significant improvements in run-time and memory performance for several standard benchmark applications. We provide several theoretical studies to facilitate an understanding of the new algorithm.

Angiotensin converting enzyme inhibitors and the reduced risk of Alzheimer's disease in the absence of apolipoprotein E4 allele

Our cross-sectional study showed that the interaction between apolipoprotein E4 (ApoE4) and angiotensin converting enzyme (ACE) inhibitors was associated with Alzheimer’s disease (AD). The aim of this longitudinal study was to differentiate whether ACE inhibitors accelerate or reduce the risk of AD in the context of ApoE alleles. Using the longitudinal data from the National Alzheimer’s Coordinating Center (NACC) with ApoE genotyping and documentation of ACE inhibitors use, we found that in the absence of ApoE4, subjects who had been taking central ACE inhibitor use (χ² test: 21% versus 27%, p = 0.0002) or peripheral ACE inhibitor use (χ² test: 13% versus 27%, p < 0.0001) had lower incidence of AD compared with those who had not been taking an ACE inhibitor. In contrast, in the presence of ApoE4, there was no such association between ACE inhibitor use and the risk of AD. After adjusting for the confounders, central ACE inhibitor use (OR = 0.68, 95% CI = 0.55, 0.83, p = 0.0002) or peripheral ACE inhibitor use (OR = 0.33, 95% CI = 0.33, 0.68, p < 0.0001) still remained inversely associated with a risk of developing AD in ApoE4 non-carriers. In conclusion, ACE inhibitors, especially peripherally acting ones, were associated with a reduced risk of AD in the absence of ApoE4, but had no such effect in those carrying the ApoE4 allele. A double-blind clinical trial should be considered to determine the effect of ACE inhibitors on prevention of AD in the context of ApoE genotype.

Is there any benefit in pre-operative urinary analysis before elective total joint replacement?

Whether patients with asymptomatic bacteriuria should be investigated and treated before elective hip and knee replacement is controversial, although it is a widespread practice. We conducted a prospective observational cohort study with urine analyses before surgery and three days post-operatively. Patients with symptomatic urinary infections or an indwelling catheter were excluded. Post-discharge surveillance included questionnaires to patients and general practitioners at three months. Among 510 patients (309 women and 201 men), with a median age of 69 years (16 to 97) undergoing lower limb joint replacements (290 hips and 220 knees), 182 (36%) had pre-operative asymptomatic bacteriuria, mostly due to Escherichia coli, and 181 (35%) had white cells in the urine. Most patients (95%) received a single intravenous peri-operative dose (1.5 g) of cefuroxime as prophylaxis. On the third post-operative day urinary analysis identified white cells in 99 samples (19%) and bacteriuria in 208 (41%). Pathogens in the cultures on the third post-operative day were different from those in the pre-operative samples in 260 patients (51%). Only 25 patients (5%) developed a symptomatic urinary infection during their stay or in a subsequent three-month follow-up period, and two thirds of organisms identified were unrelated to those found during the admission. All symptomatic infections were successfully treated with oral antibiotics with no perceived effect on the joint replacement.

We conclude that testing and treating asymptomatic urinary tract colonisation before joint replacement is unnecessary.

Cite this article: Bone Joint J 2014;96-B:390–4.

Hyaluronan peroxidation is required for normal synovial function: an hypothesis

Despite widespread use of antioxidants, reactive oxygen species have important functions in normal tissues. Herein, we present an example of a physiological role for free radicals, and in particular, reactive oxygen species, that are suppressed by anti-oxidants. Free radicals catalyze the degradation of hyaluronan in synovial fluid, a tissue in which hyaluronidase activity is barely detectable. Articular cartilage requires a low oxygen environment. The process of hyaluronan peroxidation consumes significant amounts of molecular oxygen, thus keeping the tension of oxygen in the joint at a low but physiologically critical level. One concern is the change in physical activity between day and night, with periods of joint hyperemia and ischemia, respectively. Increased oxygen and the resulting oxidative stress would lead to chondrocyte dysfunction and cartilage damage. A mechanism for keeping oxygen levels low is required. We postulate that a mechanism indeed exists for the removal of excess oxygen. High-molar-mass hyaluronan turnover in synovial fluid utilizes peroxidative degradation, during which oxygen is massively consumed. The peroxidation itself may be initiated by hydrogen peroxide, which is produced by chondrocyte mitochondria, that can diffuse into the synovial fluid. The resulting decrease in available oxygen down-regulates hyaluronan peroxidation. This in turn prevents excessive oxygen consumption. It appears that free radicals and reactive oxygen species may be components of normal physiology, particularly in the synovial fluid of joints and articular cartilage. It is suggested therefore that indiscriminate use of anti-oxidants, vigorously promoted currently by health professionals and the health industry, be approached with caution.

Angiotensin converting enzyme inhibitors and Alzheimer disease in the presence of the apolipoprotein E4 allele

OBJECTIVE

The effect of angiotensin converting enzyme (ACE) inhibitors on Alzheimer disease (AD) remains unclear, with conflicting results reported. We studied the interaction of the Apolipoprotein E (ApoE) genotype and ACE inhibitors on AD.

METHODS

This was a cross-sectional study of homebound elderly with an AD diagnosis and documentation of medications taken. ApoE genotype was determined.

RESULTS

A total of 355 subjects with status on ApoE alleles and cognitive diagnoses were studied. The average age (mean ± SD) of this population was 73.3 ± 8.3 years old, and 73% were female. Cross-sectionally, there was no difference in the number of AD cases between ApoE4 carriers and ApoE4 non-carriers or between ACE inhibitor users and non-users in the homebound elderly. ApoE4 carriers treated with ACE inhibitors, however, had more diagnoses of AD compared with those who did not have the treatment (28% versus 6%, p = 0.01) or ApoE4 non-carriers treated with an ACE inhibitor (28% versus 10%, p = 0.03). ACE inhibitor use was associated with AD diagnosis only in the presence of an E4 allele. Using multivariate logistic regression analysis, we found that in diagnosed AD cases there was a significant interaction between ApoE4 and ACE inhibitor use (odds ratio: 20.85; 95% confidence interval: 3.08-140.95; p = 0.002) after adjusting for age, sex, ethnicity, and education.

CONCLUSION

The effects of ACE inhibitors on AD may be different depending on ApoE genotype. A prospective study is needed to determine whether ACE inhibitor use accelerates or poorly delays AD development in ApoE4 carriers compared with ApoE4 non-carriers.

Jahn–Teller orbital glass state in the expanded fcc Cs3C60 fulleride

Magic-angle-spinning NMR measurements on fcc Cs₃C₆₀ to cryogenic temperatures reveal freezing-out of the C₆₀^3¬ Jahn–Teller dynamics and emergence of an electronic orbital glass state guided by the C₆₀^3¬ merohedral disorder.