Predicting population responses to environmental change from individual-level mechanisms: towards a standardized mechanistic approach

Animal populations will mediate the response of global biodiversity to environmental changes. Population models are thus important tools for both understanding and predicting animal responses to uncertain future conditions. Most approaches, however, are correlative and ignore the individual-level mechanisms that give rise to population dynamics. Here, we assess several existing population modelling approaches and find limitations to both 'correlative' and 'mechanistic' models. We advocate the need for a standardized mechanistic approach for linking individual mechanisms (physiology, behaviour, and evolution) to population dynamics in spatially explicit landscapes. Such an approach is potentially more flexible and informative than current population models. Key to realizing this goal, however, is overcoming current data limitations, the development and testing of eco-evolutionary theory to represent interactions between individual mechanisms, and standardized multi-dimensional environmental change scenarios which incorporate multiple stressors. Such progress is essential in supporting environmental decisions in uncertain future conditions.

Alternative reproductive strategies in white-throated sparrows are associated with differences in parasite load following experimental infection

Immune defences often trade off with other life-history components. Within species, optimal allocation to immunity may differ between the sexes or between alternative life-history strategies. White-throated sparrows (Zonotrichia albicollis) are unusual in having two discrete plumage morphs, white-striped and tan-striped. Within each sex, white-striped individuals are more aggressive and provide less parental care than tan-striped individuals. We extended immunocompetence handicap models, which predict sex differences in immunity and parasitism, to hypothesize that infection susceptibility should be greater in white-striped than tan-striped birds. We inoculated birds of both morphs with malarial parasites. Contrary to our prediction, among birds that became infected, parasite loads were higher in tan-striped than white-striped individuals and did not differ between the sexes. Circulating androgen levels did not differ between morphs but were higher in males than females. Our findings are not consistent with androgen-mediated immunosuppression. Instead, morph differences in immunity could reflect social interactions or life-history-related differences in risk of injury, and/or genetic factors. Although plumage and behavioural morphs of white-throated sparrow may differ in disease resistance, these differences do not parallel sex differences that have been reported in animals, and do not appear to be mediated by differences in androgen levels.

The efficacy of structured assessment and analgesia provision in the paediatric emergency department

OBJECTIVES

To ascertain if the use of a structured pain assessment tool and nurse initiated oral analgesia protocols improve uptake and time to analgesia for children presenting to the emergency department with minor or moderate musculoskeletal injuries.

METHODS

Three groups of children with peripheral limb injuries were examined to identify the rates of analgesia provision and time from attendance to analgesia provision. These groups corresponded to an initial group with no pain scoring and physician initiated analgesia, a second group with pain scoring at triage then physician initiated analgesia, and a third group with pain scoring and nurse initiated analgesia.

RESULTS

The mean time to analgesia in the initial group was 138 minutes. After initiation of triage pain assessment the mean time to analgesia was 93 minutes, there was no statistical difference between these two groups. After the introduction of nurse initiated analgesia, the time to analgesia fell to a mean of 46 minutes. The rate of analgesia provision was initially 20.5% while after the initiation of triage pain assessment the provision rate was 23%. After the initiation of nurse initiated analgesia the analgesia provision rate significantly rose to 34% of attendances.

CONCLUSIONS

The use of a nurse initiated, oral analgesia protocol for treatment of children with mild to moderate injury can significantly increase analgesia provision rates and decrease time to provision of analgesia.

Modeling the action of an antitumor drug: a density functional theory study of the mechanism of tirapazamine

Density functional theory methods are employed to investigate experimentally proposed mechanisms by which the antitumor drug tirapazamine may react with a DNA sugar-C(1)' radical to give the sugar derivative deoxyribonolactone, with concomitant DNA strand breakage. For the previously proposed minor pathway, ionization of the sugar-C(1)' radical by tirapazamine, the calculated ionization energy, and the electron affinity of the models of the sugar-C(1)' radical of DNA and tirapazamine suggest that tirapazamine must be protonated to be able to oxidize the sugar-C(1)' radical. The preferred mechanism for reaction of tirapazamine with a sugar-C(1)' radical, in agreement with experimental observations, is found to proceed by direct attack of an N-oxide oxygen of tirapazamine at the sugar-C(1)' position, followed by homolytic cleavage of the N-O bond of the drug moiety. Possible alternative mechanisms are also investigated.

On the importance of prereactive complexes in molecule-radical reactions: hydrogen abstraction from aldehydes by OH

In this work, the OH + formaldehyde and OH + acetaldehyde reactions have been characterized using accurate ab initio methods with large basis sets. The results clearly indicate that the reaction occurs by hydrogen abstraction, and that the OH addition channel is unfavorable. Close to zero (for formaldehyde) and negative (for acetaldehyde) activation energy values are obtained, which are in excellent agreement with the experimentally observed values. The reaction rate constants, calculated using the classical transition-state theory as applied to a complex mechanism involving the formation of a prereactive complex, reproduce very well the reported experimental results. Consideration of the prereactive complex is shown to be essential for the determination of the height of the energy barrier and thus for the correct calculation of the tunneling factor.

Hydrogen-bond mediated catalysis: the aminolysis of 6-chloropyrimidine as catalyzed by derivatives of uracil

The aminolysis of 6-chloropyrimidine and 2-amino-6-chloropyrimidine has been examined by using density functional theory. Relative to the aminolysis of 6-chloropyrimidine, the addition of an electron-donating NH(2) group to C(2) increases the barrier to aminolysis, indicating that the third hydrogen bond does not play a catalytic role but introduces additional rigidity into the system. However, the computations suggest that there is an interesting correlation between the barrier to aminolysis and the proton affinity of the species that interacts with the incoming NH(3). To extend the range of proton affinities, the aminolysis of 6-chloropyrimidine was examined by using fluoro, imine, and thioketo derivatives of the uracil-derived bases. The proton affinity of the moiety that hydrogen bonds with NH(3) is decreased by fluoro substitution, and thus the aminolysis barriers are increased. Similarly, imine substitution enhances the PA of the moiety, which is reflected in a decrease in the aminolysis barriers. The same correlation exists for the thioketo-derived bases, whose PAs are intermediate between the fluoro and imine derivatives. Thus, the aminolysis of 6-chloropryimidine and 2-amino-6-chloropyrimidine demonstrates the importance of a well-chosen proton acceptor and the catalytic possibilities associated with the formation of multiple hydrogen bonds.

Pharmacologic actions of the second-generation leukotriene B4 receptor antagonist LY293111: in vitro studies

The in vitro actions were investigated of LY293111, a potent and selective leukotriene B4 (LTB4) receptor antagonist, on human neutrophils, human blood fractions, guinea pig lung membranes, and guinea pig parenchymal and tracheal strips. The IC50 for inhibiting [3H]LTB4 binding to human neutrophils was 17.6 +/- 4.8 nM. LY293111 inhibited LTB4-induced human neutrophil aggregation (IC50 = 32 +/- 5 nM), luminol-dependent chemiluminescence (IC50 = 20 +/- 2 nM), chemotaxis (IC50 = 6.3 +/- 1.7 nM), and superoxide production by adherent cells (IC50 = 0.5 nM). Corresponding responses induced by N-formyl-L-methionyl-L-leucyl-L-phenylalanine were inhibited by 100-fold higher concentrations of LY293111. LTB4 binding to guinea pig tissues and subsequent activation were also inhibited. The Ki for inhibition of [3H]LTB4 binding to lung membranes was 7.1 +/- 0.8 nM; IC50 for preventing binding of [3H]LTB4 to spleen membranes was 65 nM. The compound inhibited LTB4-induced contraction of guinea pig lung parenchyma. At 10 nM, LY293111 caused a parallel rightward shift of the LTB4 concentration-response curve. At higher concentrations, plots were shifted in a nonparallel manner, and maximum responses were depressed. LY293111 did not prevent antigen-stimulated contraction of sensitized trachea strips. At micromolar concentrations, LY293111 inhibited production of LTB4 and thromboxane B2 by plasma-depleted human blood stimulated with N-formyl-L-methionyl-L-leucyl-L-phenylalanine and thrombin. In addition, at these higher concentrations, formation of LTB4 by A23187-activated whole blood and conversion of arachidonic acid to LTB4 by a human neutrophil cytosolic fraction were inhibited. In summary, LY293111 is a second-generation LTB4 receptor antagonist with much improved potency in a variety of functional assay systems.

The efficacy of pedicle screw/plate fixation on lumbar/lumbosacral autogenous bone graft fusion in adult patients with degenerative spondylolisthesis

A total of 18 patients with grade I or II degenerative spondylolisthesis fused three levels or fewer with autogenous bone graft were entered at three clinical sites. After 2 years, these patients were found to have a fusion rate of 89%. A statistical analysis of these results compared with those in the literature showed that patients with spondylolisthesis who underwent fusion with pedicle screw instrumentation were > 3 times more likely to fuse than comparable patients implanted without a pedicle screw/plate system. The pedicle screw/plate system used in this study was shown to be an effective method of facilitating lumbar or lumbosacral fusion with autogenous bone graft for adult patients with a primary indication of grade I or II degenerative spondylolisthesis.

Persistent back pain and sciatica in the United States: patient characteristics

Low back pain is an extremely common, seriously disabling, nonfatal public health problem worldwide. The National Low Back Pain Study was a multicenter study of a large, heterogeneous group of patients who have been referred to either a neurosurgeon or an orthopedic surgeon for the evaluation and treatment of a persistent complaint of low back pain. In this paper, we characterize persistent low back pain patients and their complaints, describe the impact of persistent low back pain on the patients' functional and psychological status, report on the patients' medical characteristics, and identify treatments that are currently prescribed for these patients. Persistent low back pain is most common among people in their mid-to-late thirties and early-to-mid forties. The patients are mostly white, well educated, and generally affluent. The majority are gainfully employed, but some quit working because of pain and those who do tend to be less educated, and more likely to be involved in litigation. The average patient has had low back pain intermittently for 10 years. The pain is usually well localized but its severity varies considerably. Besides pain, most persistent low back pain patients report a variety of motor and sensory deficits. Patients also report significant functional impairment at work, at play, and at home. The typical patient does not, however, display significant psychological distress. Most patients have consulted multiple health care providers, have received a variety of treatments, and have used a variety of medications to alleviate pain; a few have been subjected to more aggressive treatment measures including surgery, intradiscal therapy, and narcotic and psychoactive drugs. None of these treatments has been effective. Physical examinations of these patients do not provide significant clues for making a definitive diagnosis. Nonspecific abnormalities such as muscle spasm, tenderness, and trigger points are quite common, but motor weakness and sensory deficits in the lower extremities, and reflex changes in the knees and ankles, are much less common. The classic combination of reflex changes, motor weakness, and sensory deficits associated with specific protruded discs are extremely rare even though one of three patients had a diagnosis of disc herniation. Diagnostic imaging studies revealed that the majority of persistent low back pain patients have spondylotic abnormalities involving root compression or lumbar instability or both, with root compression as the primary cause of the complaint. Myofascial syndrome and lumbar instability were the next most common diagnoses. After a thorough evaluation by specialists in spinal disorders, three of five persistent low back pain patients were prescribed an additional course of conservative therapy, one of five was prescribed surgery, and the rest were prescribed no treatment. Persistent low back pain patients appear to be a distinct group of low back pain patients who are different from patients who have similar nonpersistent acute symptoms and those who have the chronic pain syndrome characterized by significant behavioral and psychological co-morbidities.

Molecular geometries of dibenzothiazepinone and dibenzoxazepinone calcium antagonists

A number of dibenzothiazepinones and dibenzoxazepinones have been designed, synthesized and evaluated as calcium antagonists. Molecular geometries of these dibenzotricyclic calcium antagonists have been studied using X-ray crystallography, molecular modeling and two-dimensional NMR spectroscopy. X-Ray diffraction reveals dibenzothiazepinone 1 and dibenzoxazepinone 2 to have, respectively, flexure angles of 108 degrees and 116.9 degrees between the two benzene rings. The molecular mechanics-optimized geometry of dibenzothiazepinone 1 shows a 7 degrees smaller flexure angle than the X-ray crystallographic result, while that of dibenzoxazepinone 2 has an angle only 2 degrees smaller than the X-ray result. AM1 and ab initio calculations show that the side chains can affect the geometry of the tricyclic nucleus and both 1 and 2 have negative electrostatic potentials around the bridged portion of the tricyclics. Two-dimensional NOESY NMR spectroscopy supports the extended geometry of the 6 carbon spacer as obtained from X-ray crystallography and molecular mechanics calculations. Vasorelaxation properties among these compounds appear to be relatively insensitive to the flexure angle and to chain length. Vasorelaxation is profoundly influenced by the nature of the basic terminal moiety.

The effect of pedicle screw/plate fixation on lumbar/lumbosacral autogenous bone graft fusions in patients with degenerative disc disease

STUDY DESIGN

A prospective, multi-center Investigational Device Exemption Study was carried out in the United States using a pedicle screw and plate system to perform a fusion in patients with degenerative disc disease or spondylolisthesis. The patients' pain function, complications, and fusion status were evaluated and compared with literature controls.

OBJECTIVES

To study the safety and efficacy of the ISF pedicle screw/plate system. This article focuses only on those study patients with degenerative disc disease treated with autogenous bone grafts and compares the results to those of similar patients treated without instrumentation, as reported in the literature.

SUMMARY OF BACKGROUND DATA

Twenty-eight patients were in the subgroup studied--patients with degenerative disc disease who had fusions with autogenous bone graft. This study was conducted at four clinical sites with a 2-year follow-up. Patient follow-up was greater than 95% at all time points.

METHODS

To be considered a patient with degenerative disc disease, radiographs had to demonstrate a collapse of the disc, the presence of bone erosion, or the compression of the vertebrae as the primary spinal abnormality. Spinal fusion must have been the recommended surgical treatment for discogenic pain. The fusion status was evaluated by the operating surgeon and an independent reviewer.

RESULTS

After 2 years, this subset of patients (n = 28) with degenerative disc disease who had lumbar/lumbosacral fusion with autogenous bone graft was found to have a pseudarthrosis rate of 0%. Eight articles in the literature were found to be valid noninstrumented literature controls with which this subgroup could be compared. The average pseudarthrosis rate in the control group was 32%.

CONCLUSIONS

A statistical analysis showed that patients with degenerative disc disease who underwent fusion without pedicle screw instrumentation were over 24 times more likely to have a pseudarthrosis than comparable patients implanted with a pedicle screw/plate system. Regarding the most important goal in performing a spinal fusion--fusion of the spine--the pedicle screw/plate system used in this study was shown to be a safe and efficacious method of facilitating fusion with autogenous bone graft for this patient population.

Leukotriene B4 (LTB4) receptor antagonists: a series of (hydroxyphenyl)pyrazoles

A series of (hydroxyphenyl)pyrazoles was designed by molecular modeling comparison with the LTB4 structure and prepared for evaluation as LTB4 receptor antagonists, culminating in 4-ethyl-5-[[6-methyl-6-(1H-tetrazol-5-yl)heptyl]oxy]-2-(1H-pyrazol -3- yl)phenol (2). Using an assay for inhibition of specific [3H]LTB4 binding to human PMN, it was found that the pyrazole ring could be methylated at N(1) with little loss of activity while methylation at N(2) reduced activity significantly. The structure-activity relationship of the terminal acid group was investigated. Good activity was found with o- and m-phenylalkanoic acids, chromane carboxylic acid, and tetrazole groups. The best in vitro activity was realized with the pyrazole nitrogen unsubstituted and with a six-carbon chain linking the phenyl ether oxygen to the tetrazole group. Compound 2, having an IC50 of 6.4 +/- 0.8 nM in the binding assay, was selected for further preclinical evaluation.

Design, synthesis, and pharmacological evaluation of potent xanthone dicarboxylic acid leukotriene B4 receptor antagonists

In an effort to develop increasingly potent and specific leukotriene B4 (LTB4) receptor antagonists, several xanthone dicarboxylic acids were synthesized and evaluated. Two separate synthetic routes were used to construct a xanthone nucleus containing a regiospecific orientation of each carboxylic acid pharmacophore. These compounds represent the major conformationally-restricted analogues of benzophenone dicarboxylic acids previously shown to antagonize the activation of human neutrophils by LTB4. The most potent agent was compound 32, which inhibited the specific binding of [3H]LTB4 to receptors on intact human neutrophils (IC50, 6.2 +/- 0.1 nM), LTB4-induced luminol-dependent chemiluminescence (IC50, 55 +/- 11 nM), aggregation (IC50, 133 +/- 42 nM), and chemotaxis (IC50, 899 +/- 176 nM). The compound was a poor antagonist of N-formyl-L-methionyl-L-leucyl-L-phenylalanine-induced chemiluminescence (IC50, 1599 +/- 317 nM) and aggregation (IC50, 2166 +/- 432 nM), indicating specificity in the inhibition of LTB4-stimulated events. Compound 32 (LY210073), which was completely devoid of agonist activity, appears to be one of the strongest inhibitors of LTB4 receptor binding reported so far.

Specific inhibition of leukotriene B4-induced neutrophil activation by LY223982

LY223982, (E)-5-(3-carboxybenzoyl)-2-((6-(4-methoxyphenyl)-5- hexenyl)oxy)benzenepropanoic acid, is a newly discovered potent inhibitor of specific binding of leukotriene B4 (LTB4) to its receptor on human neutrophils. This study demonstrated that the compound is also a specific antagonist of LTB4-induced neutrophil activation under both in vitro and in vivo conditions. LY223982 was found to be 189-fold more effective in displacing [3H]LTB4 than 35S-N-formyl-L-methionyl-L-leucyl-L-phenylalanine (FMLP) from their corresponding receptors on human neutrophils. The concentration inhibiting 50% of response (IC50) for displacement of [3H]LTB4 (13.2 nM) was only 6.8-fold higher than the value for nonradioactive LTB4. The compound inhibited the aggregation of guinea pig neutrophils caused by LTB4 more strongly than FMLP or platelet-activating factor. The IC50 for inhibition of LTB4-induced responses (74 nM) was 93- and > 135-fold lower than the IC50 for inhibition of the corresponding FMLP and platelet-activating factor-induced effects. LY223982 was also a potent antagonist of the aggregation of human neutrophils by LTB4 (IC50, 100 nM). Chemotaxis of human neutrophils induced by LTB4 was only modestly inhibited by the compound (IC50 = 6 microM) but it had even less effect on cell movement caused by FMLP. LY223982 inhibited transient leukopenia induced in rabbits with LTB4 (ED50, 3 mg/kg) but not with FMLP. It had no agonist activity in any of the test systems. In summary, the results indicate that LY223982 is a potent specific antagonist of LTB4-induced neutrophil activation.

Association of parvoviruses with rheumatoid arthritis of humans

A small virus resembling parvoviruses in its morphological and physicochemical properties was derived from synovial tissue of a patient with severe rheumatoid arthritis. This virus, designated RA-1, elicits a syndrome in neonatal mice that includes neurological disturbances, permanent crippling of limbs, dwarfism, alopecia, blepharitis, "masking," and a rigid curvature of the thoracic spine. Polyclonal antibodies against RA-1 display high virus neutralizing activity and in immunoassays detect reactive antigen in synovial cells from different rheumatoid arthritis patients but not persons with osteoarthritis. Putative parvoviruses isolated from several other rheumatoid arthritis patients are only weakly pathogenic for newborn mice but can generate RA-1 virus-specific antigens in tissues of these animals. It has not been established that RA-1 and existing parvoviruses of mammalian species are related.

Safety and efficacy of chymopapain (Chymodiactin) in herniated nucleus pulposus with sciatica. Results of a randomized, double-blind study

A double-blind, randomized trial was conducted to compare the efficacy of intradiskal injection of chymopapain (Chymodiactin) with injection of placebo in patients with a herniated lumbar disk. Patients were randomly assigned to either placebo or drug regimens and followed up for six months. The primary measure of performance was agreement by patient and surgeon that further intervention was not necessary. At any time that patient and investigator agreed that treatment had failed, the patient was classified as a failure and the treatment code was broken. Of 53 placebo-treated patients, 31 failed by this criterion. Of 55 drug-treated patients, 15 failed. Placebo-treated patients who failed were allowed to receive drug treatment, and 29 (91%) of 32 were treated successfully. This study demonstrates that chymopapain is more effective than placebo for treatment of patients with a herniated lumbar disk.

The oblique view: an unnecessary component of the initial adult lumbar spine examination

A retrospective study was undertaken to determine the diagnostic contribution of oblique views in 200 consecutive lumbar spine examinations done in adults. In four cases (two percent) there was a change in the radiographic interpretation when the oblique views were used for diagnosis. Considering the low diagnostic and therapeutic yield, as well as the gonadal radiation dose, the authors feel that the oblique view should not be a routine part of the initial lumbar spine examination in adults.

Thermal and photochemical reactivity of cyclopropene derivatives: a semi-empirical molecular orbital study

The MINDO/3 semi-empirical MO method has been used to study the conversion of cyclopropene to vinyl carbene. In particular, the surfaces of the ground state and the first excited singlet and triplet states have been calculated. Additional calculations, including geometry optimization, have been carried out on vinyl substituted cyclopropenes. In general, the results are consistent with the known thermal and photochemical reactivities of cyclopropenes and the results of the few abinitio calculations on these species.

On the Bond Order between Atoms in Approximate SCF-MO Theory

The bond order between two atoms is discussed within the framework of all-valence-electron SCF-MO theories based on the Zero-Differential Overlap Approximation, and a definition of the bond order is proposed which is analogous to the procedure used to extract charge distributions from approximate SCF-MO calculations. Bond orders are calculated for a variety of small molecules and relationships similar to those found in π-electron theory between bond lengths and bond orders are observed. CNDO wave functions are used in this work, although the definition may also be used for calculations based on the INDO and NDDO approximations.