A Structural Model for the Core Nup358-BicD2 Interface

Dynein motors facilitate the majority of minus-end-directed transport events on microtubules. The dynein adaptor Bicaudal D2 (BicD2) recruits the dynein machinery to several cellular cargo for transport, including Nup358, which facilitates a nuclear positioning pathway that is essential for the differentiation of distinct brain progenitor cells. Previously, we showed that Nup358 forms a "cargo recognition α-helix" upon binding to BicD2; however, the specifics of the BicD2-Nup358 interface are still not well understood. Here, we used AlphaFold2, complemented by two additional docking programs (HADDOCK and ClusPro) as well as mutagenesis, to show that the Nup358 cargo-recognition α-helix binds to BicD2 between residues 747 and 774 in an anti-parallel manner, forming a helical bundle. We identified two intermolecular salt bridges that are important to stabilize the interface. In addition, we uncovered a secondary interface mediated by an intrinsically disordered region of Nup358 that is directly N-terminal to the cargo-recognition α-helix and binds to BicD2 between residues 774 and 800. This is the same BicD2 domain that binds to the competing cargo adapter Rab6, which is important for the transport of Golgi-derived and secretory vesicles. Our results establish a structural basis for cargo recognition and selection by the dynein adapter BicD2, which facilitates transport pathways that are important for brain development.

Coil-to-α-helix transition at the Nup358-BicD2 interface activates BicD2 for dynein recruitment

Nup358, a protein of the nuclear pore complex, facilitates a nuclear positioning pathway that is essential for many biological processes, including neuromuscular and brain development. Nup358 interacts with the dynein adaptor Bicaudal D2 (BicD2), which in turn recruits the dynein machinery to position the nucleus. However, the molecular mechanisms of the Nup358/BicD2 interaction and the activation of transport remain poorly understood. Here for the first time, we show that a minimal Nup358 domain activates dynein/dynactin/BicD2 for processive motility on microtubules. Using nuclear magnetic resonance titration and chemical exchange saturation transfer, mutagenesis, and circular dichroism spectroscopy, a Nup358 α-helix encompassing residues 2162–2184 was identified, which transitioned from a random coil to an α-helical conformation upon BicD2 binding and formed the core of the Nup358-BicD2 interface. Mutations in this region of Nup358 decreased the Nup358/BicD2 interaction, resulting in decreased dynein recruitment and impaired motility. BicD2 thus recognizes Nup358 through a ‘cargo recognition α-helix,’ a structural feature that may stabilize BicD2 in its activated state and promote processive dynein motility.

Cargo properties play a critical role in myosin Va-driven cargo transport along actin filaments

High-resolution experiments revealed that a single myosin-Va motor can transport micron-sized cargo on actin filaments in a stepwise manner. However, intracellular cargo transport is mediated through the dense actin meshwork by a team of myosin Va motors. The mechanism of how motors interact mechanically to bring about efficient cargo transport is still poorly understood. This study describes a stochastic model where a quantitative understanding of the collective behaviors of myosin Va motors is developed based on cargo stiffness. To understand how cargo properties affect the overall cargo transport, we have designed a model in which two myosin Va motors were coupled by wormlike chain tethers with persistence length ranging from 10 to 80 nm and contour length from 100 to 200 nm, and predicted distributions of velocity, run length, and tether force. Our analysis showed that these parameters are sensitive to both the contour and persistence length of cargo. While the velocity of two couple motors is decreased compared to a single motor (from 531 ± 251 nm/s to as low as 318 ± 287 nm/s), the run length (716 ± 563 nm for a single motor) decreased for short, rigid tethers (to as low as 377 ± 187 μm) and increased for long, flexible tethers (to as high as 1.74 ± 1.50 μm). The sensitivity of processive properties to tether rigidity (persistence length) was greatest for short tethers, which caused the motors to exhibit close, yet anti-cooperative coordination. Motors coupled by longer tethers stepped more independently regardless of tether rigidity. Therefore, the properties of the cargo or linkage must play an essential role in motor-motor communication and cargo transport.

Coiled-coil registry shifts in the F684I mutant of Bicaudal D result in cargo-independent activation of dynein motility

The dynein adaptor Drosophila Bicaudal D (BicD) is auto-inhibited and activates dynein motility only after cargo is bound, but the underlying mechanism is elusive. In contrast, we show that the full-length BicD/F684I mutant activates dynein processivity even in the absence of cargo. Our X-ray structure of the C-terminal domain of the BicD/F684I mutant reveals a coiled-coil registry shift; in the N-terminal region, the two helices of the homodimer are aligned, whereas they are vertically shifted in the wild-type. One chain is partially disordered and this structural flexibility is confirmed by computations, which reveal that the mutant transitions back and forth between the two registries. We propose that a coiled-coil registry shift upon cargo-binding activates BicD for dynein recruitment. Moreover, the human homolog BicD2/F743I exhibits diminished binding of cargo adaptor Nup358, implying that a coiled-coil registry shift may be a mechanism to modulate cargo selection for BicD2-dependent transport pathways.

Agronomic, economic, and environmental performance of nitrogen rates and source in Bangladesh's coastal rice agroecosystems

Farmers in low-elevation coastal zones in South Asia face numerous food security and environmental sustainability challenges. This study evaluated the effects of nitrogen (N) rate and source on the agronomic, economic, and environmental performance of transplanted and rainfed 'aman' (monsoon-season) rice in Bangladesh's non-saline coastal areas. Fifty-one farmers participated in trials distributed across two landscape positions described as 'highlands' (on which field water inundation depth typically remains <30 cm) and 'medium-highlands' (inundation depths 30-90 cm) planted singly with varieties appropriate to each position (BRRI dhan 39 for highlands and the traditional variety Bhushiara for medium-highlands). Researcher designed but farmer-managed dispersed plots were located across three district sub-units (Barisal Sadar, Hizla, Mehendigonj) and compared N source (broadcast prilled urea or deep-placed urea super granules (USG)) at four N rates. Rice grown on medium-highlands did not respond to increasing N rates beyond 28 kg N ha^-1, indicating that little fertilization is required to maintain yields and profitability while limiting environmental externalities. In highland locations, clear trade-offs between agronomic and environmental goals were observed. To increase yields and profits for BRRI dhan 39, 50 or 75 kg N ha^-1 was often needed, although these rates were associated with declining energy and increasing greenhouse gas (GHG) efficiencies. Compared to prilled urea, USG had no impact on yield, economic, energy and GHG efficiencies in medium-highland locations. USG conversely led to 4.2-5.8% yield improvements at higher N rates on highlands, while also increasing energy efficiency. Given the observed yield, agronomic and economic benefit of USG, our preliminary results that farmers can consider use of USG at 50 kg N ha^-1 to produce yields equivalent to 75 kg N ha^-1 of prilled urea in highland landscapes, while also reducing environmental externalities. These results suggest that when assessing sustainable intensification (SI) strategies for rice in South Asia's coastal zones, N requirements should be evaluated within specific production contexts (e.g. cultivar type within landscape position) to identify options for increasing yields without negatively influencing environmental and economic indicators. Similar studies in other parts of coastal South Asia could help policy-makers prioritize investments in agriculture with the aim of improving rice productivity while also considering income generation and environmental outcomes.

Recruitment of two dyneins to an mRNA-dependent Bicaudal D transport complex

We investigated the role of full-length Drosophila Bicaudal D (BicD) binding partners in dynein-dynactin activation for mRNA transport on microtubules. Full-length BicD robustly activated dynein-dynactin motility only when both the mRNA binding protein Egalitarian (Egl) and K10 mRNA cargo were present, and electron microscopy showed that both Egl and mRNA were needed to disrupt a looped, auto-inhibited BicD conformation. BicD can recruit two dimeric dyneins, resulting in faster speeds and longer runs than with one dynein. Moving complexes predominantly contained two Egl molecules and one K10 mRNA. This mRNA-bound configuration makes Egl bivalent, likely enhancing its avidity for BicD and thus its ability to disrupt BicD auto-inhibition. Consistent with this idea, artificially dimerized Egl activates dynein-dynactin-BicD in the absence of mRNA. The ability of mRNA cargo to orchestrate the activation of the mRNP (messenger ribonucleotide protein) complex is an elegant way to ensure that only cargo-bound motors are motile.

Disease Pattern among Children attending Pediatric Outpatient Department in Community Based Medical College Hospital, Bangladesh

Disease pattern is based on socio-demographic characteristics, comprehensive health care services, and environmental variables like water supply, basic sanitation and housing, illness behavior like quick decision to arrive at health care facility, and treatment behavior like the modality of treatment they receive. The descriptive cross-sectional study was conducted during the period of January 2014 to December 2015. The study was carried out among 310 purposively selected children attended at Pediatric Outpatient department of Community Based Medical College Hospital, Bangladesh. Data were collected by face to face interview of the parents and clinical examination and anthropometric measurement of children using case record form. Mean age of the children was 4.11 years with a SD of 4.35 years, male-female ratio was 1.25:1 with predominance 201(64.84%) of under-five children. The common diseases were 121(39.03%) with Acute Respiratory Infections (ARI), while 43(13.87%) diarrheal diseases, 25(8.06%) each with bronchial asthma and helminthiasis. Other diseases 96(30.97%) include anemia 17(5.48%), urinary tract infection 15 (4.84%), peptic ulcer disease 9(2.90%), enteric fever, oral candidiasis, apthous ulcer of mouth, scabies and vulvovaginitis. Average number of children per family was 2.2 including 251(80.97%) children having sanitary latrine in the family, 297(95.81%) with safe drinking water facilities and 270(87.10%) were fully vaccinated under EPI. More than three fourth 76(24.52%) of the children were underweight, 114(36.77%) were from poor families and 136(43.87%) lived in Kancha house. With the improvement of safe water supply and use of sanitary latrine diseases like diarrhoeal disease and helminthiasis are showing a decreasing trend.

Cargo Transport by Two Coupled Myosin Va Motors on Actin Filaments and Bundles

Myosin Va (myoVa) is a processive, actin-based molecular motor essential for intracellular cargo transport. When a cargo is transported by an ensemble of myoVa motors, each motor faces significant physical barriers and directional challenges created by the complex actin cytoskeleton, a network of actin filaments and actin bundles. The principles that govern the interaction of multiple motors attached to the same cargo are still poorly understood. To understand the mechanical interactions between multiple motors, we developed a simple in vitro model in which two individual myoVa motors labeled with different-colored Qdots are linked via a third Qdot that acts as a cargo. The velocity of this two-motor complex was reduced by 27% as compared to a single motor, whereas run length was increased by only 37%, much less than expected from multimotor transport models. Therefore, at low ATP, which allowed us to identify individual motor steps, we investigated the intermotor dynamics within the two-motor complex. The randomness of stepping leads to a buildup of tension in the linkage between motors-which in turn slows down the leading motor-and increases the frequency of backward steps and the detachment rate. We establish a direct relationship between the velocity reduction and the distribution of intermotor distances. The analysis of run lengths and dwell times for the two-motor complex, which has only one motor engaged with the actin track, reveals that half of the runs are terminated by almost simultaneous detachment of both motors. This finding challenges the assumptions of conventional multimotor models based on consecutive motor detachment. Similar, but even more drastic, results were observed with two-motor complexes on actin bundles, which showed a run length that was even shorter than that of a single motor.

Myosin Va molecular motors manoeuvre liposome cargo through suspended actin filament intersections in vitro

Intracellular cargo transport relies on myosin Va molecular motor ensembles to travel along the cell's three-dimensional (3D) highway of actin filaments. At actin filament intersections, the intersecting filament is a structural barrier to and an alternate track for directed cargo transport. Here we use 3D super-resolution fluorescence imaging to determine the directional outcome (that is, continues straight, turns or terminates) for an ∼10 motor ensemble transporting a 350 nm lipid-bound cargo that encounters a suspended 3D actin filament intersection in vitro. Motor–cargo complexes that interact with the intersecting filament go straight through the intersection 62% of the time, nearly twice that for turning. To explain this, we develop an in silico model, supported by optical trapping data, suggesting that the motors' diffusive movements on the vesicle surface and the extent of their engagement with the two intersecting actin tracks biases the motor–cargo complex on average to go straight through the intersection.

Cellular cargo transported along actin filaments is faced with a directional choice at an intersection. Here the authors show that myosin Va-bound cargo prefers to go straight through the intersection, and propose a model to explain this by a tug-of-war between motors on the lipid cargo that engage the actin tracks.

Small teams of myosin Vc motors coordinate their stepping for efficient cargo transport on actin bundles

Myosin Vc (myoVc) is unique among vertebrate class V myosin isoforms in that it requires teams of motors to move continuously on single actin filaments. Single molecules of myoVc cannot take multiple hand-over-hand steps from one actin-binding site to the next without dissociating, in stark contrast to the well studied myosin Va (myoVa) isoform. At low salt, single myoVc motors can, however, move processively on actin bundles, and at physiologic ionic strength, even teams of myoVc motors require actin bundles to sustain continuous motion. Here, we linked defined numbers of myoVc or myoVa molecules to DNA nanostructures as synthetic cargos. Using total internal reflectance fluorescence microscopy, we compared the stepping behavior of myoVc versus myoVa ensembles and myoVc stepping patterns on single actin filaments versus actin bundles. Run lengths of both myoVc and myoVa teams increased with motor number, but only multiple myoVc motors showed a run-length enhancement on actin bundles compared with actin filaments. By resolving the stepping behavior of individual myoVc motors with a quantum dot bound to the motor domain, we found that coupling of two myoVc motors significantly decreased the futile back and side steps that were frequently observed for single myoVc motors. Changes in the inter-motor distance between two coupled myoVc motors affected stepping dynamics, suggesting that mechanical tension coordinates the stepping behavior of two myoVc motors for efficient directional motion. Our study provides a molecular basis to explain how teams of myoVc motors are suited to transport cargos such as zymogen granules on actin bundles.

Surgical Outcome of Intradural Spinal Tumors

Results of 63 surgically treated intradural spinal tumors between the period of October 2003 and December 2014 at Bangabandhu Sheikh Mujib Medical University (BSMMU) and in our private settings, Dhaka, were analyzed retrospectively. There were 33 males, 30 females with an average age of 52.4 years (13-70 years) and followed up for at least a year. The preoperative symptom with duration, tumors location and intradural space occupancy and the histopathological diagnosis were analyzed. Pain was evaluated by the visual analogue scale (VAS) and the neurologic function was assessed by Nurick's grade. The tumors were located as, thoracic (n=32, 50.79%), lumbar (n=16, 25.39%), cervical (n=05, 07.93%), and junctional (n=10, 15.87%, CervicoThoracic-01, Thoracolumbar-09). The histopathological diagnosis included schwannoma (n=30, 47.7%), meningiomas (n=14, 22.3%), neurofibroma, arachnoid cyst and myxopapillary ependymoma (n=03, 04.76%) each and paraganglioma (n=01, 01.59%). Among the intramedullary tumors, ependymoma (n=03, 04.76%), astrocytoma and epidermoid cyst (n=02, 03.17%), haemangioblastoma, paraganglioma and cavernous haemangioma (n=01, 01.59%) each. The VAS score was reduced in all cases from 8.0±1.2 to 1.2±0.8 (p<0.003) and the Nurick's grade was improved in all cases from 3.0±1.3 to 1.0±0.0 (p<0.005). The preoperative neurological deficit improved within 8 postoperative weeks in most cases and within 1 postoperative year in all cases. Complications included cerebrospinal fluid leakage, parasthesia and further neurological deterioration (Astrocytoma) (n=02, 03.17%) and dependant bedsore and recurrence (Ependymoma) (n=01, 01.59%). Aggressive surgical excision potentially minimizes neurologic morbidity and improved outcome except intramedullary tumors where initial treatment consists of maximum safe surgical resection or biopsy.

Overexpression of sonic hedgehog in the triple negative breast cancer: clinicopathological characteristics of high burden breast cancer patients from Bangladesh

Dysregulation of Hedgehog (Hh) signaling pathway has been documented in mammary gland development and breast cancer (BC) progression. Despite the remarkable progress in therapeutic interventions, BC related mortality in Bangladesh increased in the last decade. Triple negative breast cancer (TNBC) still presents a critical therapeutic challenge. Thus effective targeted therapy is urgently needed. In this study, we report the clinicopathological characteristics and prognosis of BC patients from Bangladesh. Routine immunohistochemical analysis and high throughput RNA-Seq data from the TCGA library were used to analyze the expression pattern and association of high and low level of Shh expression in a collection of BC patients with a long-term follow-up. High levels of Shh were observed in a subset of BC tumors with poor prognostic pathological features. Higher level of Shh expression correlated with a significantly poorer overall survival of patients compared with patients whose tumors expressed a low level of Shh. These data support the contention that Shh could be a novel biomarker for breast cancer that is involved in mediating the aggressive phenotype of BC. We propose that BC patients exhibiting a higher level of Shh expression, representing a subset of BC patients, would be amenable to Shh targeted therapy.

Antibacterial Effect of Curcuma longa (Turmeric) Against Staphylococcus aureus and Escherichia coli

This observational study was conducted during the period from July 2010 to June 2011 in the Department of Pharmacology in the collaboration of Department of Microbiology, Mymensingh Medical College, Mymensingh to determine the profile of antibacterial effect of Crude Turmeric paste aqueous turmeric extract, and standard antibiotic Amikacin against Staphylococcus aureus and Escherichia coli. Three separate experiments were done e.g. (Expt- I) Inhibitory effect of Crude Turmeric paste incorporated into nutrient agar (NA) media, (Expt- II) Minimum inhibitory concentration of (a) Aqueous Turmeric extract and (b) Amikacin by broth dilution technique and (Expt-III) their subculture study in nutrient agar (NA) media for confirmation of respective results of previous experiments. Inhibitory effects were observed against the growth of Staph Aureus and Esch coli at 10% and 30% respectively of Crude Turmeric paste incorporated into NA media. The broth dilution technique was followed to determine the MIC of Aqueous Turmeric extract and Amikacin. The MIC of Aqueous Turmeric extract was 800 μg/ml against Staph aureus and that against Esch coli was 2000 μg/ml and the MIC of Amikacin was 10 μg/ml for both the bacteria. The MIC of Amikacin was the lowest in comparison to MIC of Aqueous Turmeric extract for complete inhibition of growth of Staph aureus and Esch coli. The subculture study showed similar results with that of previous experiments in terms of inhibitory effects of Crude Turmeric paste and MIC of Aqueous Turmeric extract and Amikacin against all of the organisms studied.

Myosin VI must dimerize and deploy its unusual lever arm in order to perform its cellular roles

It is unclear whether the reverse-direction myosin (myosin VI) functions as a monomer or dimer in cells and how it generates large movements on actin. We deleted a stable, single-α-helix (SAH) domain that has been proposed to function as part of a lever arm to amplify movements without impact on in vitro movement or in vivo functions. A myosin VI construct that used this SAH domain as part of its lever arm was able to take large steps in vitro but did not rescue in vivo functions. It was necessary for myosin VI to internally dimerize, triggering unfolding of a three-helix bundle and calmodulin binding in order to step normally in vitro and rescue endocytosis and Golgi morphology in myosin VI-null fibroblasts. A model for myosin VI emerges in which cargo binding triggers dimerization and unfolds the three-helix bundle to create a lever arm essential for in vivo functions.

Evaluation of the outcome of replacement hemiarthroplasty by uncemented bipolar prosthesis in displaced fracture neck femur

Despite continued discussion regarding the treatment of displaced femoral neck fractures, controversies continue regarding their optimal treatment, including the choice of implant and fixation method. Hemiarthroplasty is one of the option which eliminate concerns about fixation failure, nonunion, and avascular necrosis and has become the choice of surgery among the aged >60. This prospective interventional study was carried out on 28 cases at the Department of Orthopaedic Surgery, Bangabandhu Sheikh Mujib Medical University (BSMMU), from July 2009 to April 2012 to evaluate cementless, bipolar prosthesis among the active elderly patients. All subjects were evaluated with regard to postoperative clinical, functional and activity outcome (Modified Harris Hip Scoring and Hip Outcome Scoring), intra and post operative complications. One case was dropped from follow up and 22(81.48%) patients were considered to have satisfactory outcome after statistical analysis by chi-square test on at least 12 months follow up records. Although prosthetic stem valgus and periprosthetic fracture developed in 02 cases and 01 patient had sunken prosthesis, uncemented bipolar hemiarthroplasty can give significantly good functional outcomes with minimal complications for displaced intracapsular femoral neck fracture in active elderly patients.

Effect of different levels of Dhania seed (Coriandrum sativum) on the performance of broiler

A total of 72 as hatched Cobb 500 broilers were fed ad libitum on a diet with 0 %, 0.5 %, 1.0 % and 1.5 % of coriander seed meal (CSM) to assess its feeding value. Treatment group with 1.5 % of CSM significantly (p<0.05) affected live weight of broilers at the age of 28 and 35 days. Among the dietary groups there is no significant difference in feed intake and feed efficiency. Meat yield characteristics especially abdominal fat level decreased significantly (p<0.01) at 1.5 % level of CSM. Cost of production per kg live broiler decreased when dietary inclusion level was increased. Profit per kg of live broiler was significantly (p<0.05) increased with the increase levels of dietary CSM. These results suggest that the CSM could be considered as a potential natural growth promoter for poultry, and showed the best responses at a 1.5 % level of inclusion. It was concluded that the supplementation of the coriander seed meal to broiler diet had beneficial effects on body weight gain, feed conversion ratio and carcass yield.DOI: http://dx.doi.org/10.3329/bjas.v43i1.19383 Bang. J. Anim. Sci. 2014. 43 (1): 38-44

Relationship between physical work load and lumbar disc herniation

Lumbar disc herniation (LDH) is a disabling problem. This retrospective case control study was done to evaluate the possible relevance of physical work load with Lumbar Disc Herniation. We have performed this study in the Spinal Surgery Unit of Department of Orthopaedic Surgery at BSMMU, Dhaka from July 2007 to June 2010 where 200 cases with Lumbar Disc Herniation and 200 control subjects matched by age, gender and area of residence were taken and analyzed. Chi-square test was computed for sex, area of residence, type of physical work and effort at work, whereas Odds ratio was computed for physical work load, stress at work and daily working period. The highest odds ratio (OR) was with the physical work load (OR: 03.48, CI: 01.84-06.59), hard work (OR: 03.14, CI: 01.74-05.65) and working period of >8 hours (OR: 01.34, CI: 0.75-02.38). Odds ratio for heavy load carrying at work was 03.48 and less job satisfaction or stress at work was 02.45. There was a statistically significant positive association between cumulative exposure of physical work load and lumbar disc herniation indicating an increased occurrence of herniation in heavy physical work load and occupation requiring harder efforts.

A branched kinetic scheme describes the mechanochemical coupling of Myosin Va processivity in response to substrate

Myosin Va is a double-headed cargo-carrying molecular motor that moves processively along cellular actin filaments. Long processive runs are achieved through mechanical coordination between the two heads of myosin Va, which keeps their ATPase cycles out of phase, preventing both heads detaching from actin simultaneously. The biochemical kinetics underlying processivity are still uncertain. Here we attempt to define the biochemical pathways populated by myosin Va by examining the velocity, processive run-length, and individual steps of a Qdot-labeled myosin Va in various substrate conditions (i.e., changes in ATP, ADP, and P(i)) under zero load in the single-molecule total internal reflection fluorescence microscopy assay. These data were used to globally constrain a branched kinetic scheme that was necessary to fit the dependences of velocity and run-length on substrate conditions. Based on this model, myosin Va can be biased along a given pathway by changes in substrate concentrations. This has uncovered states not normally sampled by the motor, and suggests that every transition involving substrate binding and release may be strain-dependent.

Myosin VI has a one track mind versus myosin Va when moving on actin bundles or at an intersection

Myosin VI (myoVI) and myosin Va (myoVa) serve roles both as intracellular cargo transporters and tethers/anchors. In both capacities, these motors bind to and processively travel along the actin cytoskeleton, a network of intersecting actin filaments and bundles that present directional challenges to these motors. Are myoVI and myoVa inherently different in their abilities to interact and maneuver through the complexities of the actin cytoskeleton? Thus, we created an in vitro model system of intersecting actin filaments and individual unipolar (fascin-actin) or mixed polarity (α-actinin-actin) bundles. The stepping dynamics of individual Qdot-labeled myoVI and myoVa motors were determined on these actin tracks. Interestingly, myoVI prefers to stay on the actin filament it is traveling on, while myoVa switches filaments with higher probability at an intersection or between filaments in a bundle. The structural basis for this maneuverability difference was assessed by expressing a myoVI chimera in which the single myoVI IQ was replaced with the longer, six IQ myoVa lever. The mutant behaved more like myoVI at actin intersections and on bundles, suggesting that a structural element other than the lever arm dictates myoVI's preference to stay on track, which may be critical to its role as an intracellular anchor.

Quantum dot labeling strategies to characterize single-molecular motors

Recent advances in single-molecule labeling and detection techniques allow high-resolution imaging of the motion of single molecules. Molecular motors are biological machines that convert chemical energy into mechanical work. Myosin Va (MyoVa) is a well-characterized processive molecular motor, essential for cargo transport in living organisms. Quantum dots (Qdots) are fluorescent semiconductor nanocrystals that are extremely useful for single-molecule studies in biological sciences. High-resolution video microscopy and single-particle tracking of a Qdot-labeled MyoVa motor molecule allow the detection of individual steps in vitro and in live cells.

Random walk of processive, quantum dot-labeled myosin Va molecules within the actin cortex of COS-7 cells

Myosin Va (myoVa) is an actin-based intracellular cargo transporter. In vitro experiments have established that a single myoVa moves processively along actin tracks, but less is known about how this motor operates within cells. Here we track the movement of a quantum dot (Qdot)-labeled myoVa HMM in COS-7 cells using total internal reflectance fluorescence microscopy. This labeling approach is unique in that it allows myoVa, instead of its cargo, to be tracked. Single-particle analysis showed short periods (</=0.5 s) of ATP-sensitive linear motion. The mean velocity of these trajectories was 604 nm/s and independent of the number of myoVa molecules attached to the Qdot. With high time (16.6 ms) and spatial (15 nm) resolution imaging, Qdot-labeled myoVa moved with sequential 75 nm steps per head, at a rate of 16 s(-1), similarly to myoVa in vitro. Monte Carlo modeling suggests that the random nature of the trajectories represents processive myoVa motors undergoing a random walk through the dense and randomly oriented cortical actin network.

Diffusive movement of processive kinesin-1 on microtubules

The processive motor kinesin-1 moves unidirectionally toward the plus end of microtubules. This process can be visualized by total internal reflection fluorescence microscopy of kinesin bound to a carboxylated quantum dot (Qdot), which acts both as cargo and label. Surprisingly, when kinesin is bound to an anti-HIS Qdot, it shows diffusive movement on microtubules, which decreased in favor of processive runs with increasing salt concentration. This observation implies that kinesin movement on microtubules is governed by its conformation, as it is well established that kinesin undergoes a salt-dependent transition from a folded (inactive) to an extended (active) molecule. A truncated kinesin lacking the last 75 amino acids (kinesin-Delta C) showed both processive and diffusive movement on microtubules. The extent of each behavior depends on the relative amounts of ADP and ATP, with purely diffusive movement occurring in ADP alone. Taken together, these data imply that folded kinesin.ADP can exist in a state that diffuses along the microtubule lattice without expending energy. This mechanism may facilitate the ability of kinesin to pick up cargo, and/or allow the kinesin/cargo complex to stay bound after encountering obstacles.

Cargo transport: molecular motors navigate a complex cytoskeleton

Intracellular cargo transport requires microtubule-based motors, kinesin and cytoplasmic dynein, and the actin-based myosin motors to maneuver through the challenges presented by the filamentous meshwork that comprises the cytoskeleton. Recent in vitro single molecule biophysical studies have begun to explore this process by characterizing what occurs as these tiny molecular motors happen upon an intersection between two cytoskeletal filaments. These studies, in combination with in vivo work, define the mechanism by which molecular motors exchange cargo while traveling between filamentous tracks and deliver it to its destination when going from the cell center to the periphery and back again.

Myosin Va maneuvers through actin intersections and diffuses along microtubules

Certain types of intracellular organelle transport to the cell periphery are thought to involve long-range movement on microtubules by kinesin with subsequent handoff to vertebrate myosin Va (myoVa) for local delivery on actin tracks. This process may involve direct interactions between these two processive motors. Here we demonstrate using single molecule in vitro techniques that myoVa is flexible enough to effectively maneuver its way through actin filament intersections and Arp2/3 branches. In addition, myoVa surprisingly undergoes a one-dimensional diffusive search along microtubules, which may allow it to scan efficiently for kinesin and/or its cargo. These features of myoVa may help ensure efficient cargo delivery from the cell center to the periphery.

Regulation of vascular nitric oxide in vitro and in vivo; a new role for endogenous hydrogen sulphide?

BACKGROUND AND PURPOSE

The aim of these experiments was to evaluate the significance of the chemical reaction between hydrogen sulphide (H2S) and nitric oxide (NO) for the control of vascular tone.

EXPERIMENTAL APPROACH

The effect of sodium hydrosulphide (NaHS; H2S donor) and a range of NO donors, such as sodium nitroprusside (SNP), either alone or together, was determined using phenylephrine (PE)-precontracted rat aortic rings and on the blood pressure of anaesthetised rats.

KEY RESULTS

Mixing NaHS with NO donors inhibited the vasorelaxant effect of NO both in vitro and in vivo. Low concentrations of NaHS or H2S gas in solution reversed the relaxant effect of acetylcholine (ACh, 400 nM) and histamine (100 microM) but not isoprenaline (400 nM). The effect of NaHS on the ACh response was antagonized by CuSO(4) (200 nM) but was unaffected by glibenclamide (10 microM). In contrast, high concentrations of NaHS (200-1600 microM) relaxed aortic rings directly, an effect reduced by glibenclamide but unaffected by CuSO4. Intravenous infusion of a low concentration of NaHS (10 micromol kg(-1) min(-1)) into the anaesthetized rat significantly increased mean arterial blood pressure. L-NAME (25 mg kg(-1), i.v.) pretreatment reduced this effect.

CONCLUSIONS AND IMPLICATIONS

These results suggest that H2S and NO react together to form a molecule (possibly a nitrosothiol) which exhibits little or no vasorelaxant activity either in vitro or in vivo. We propose that a crucial, and hitherto unappreciated, role of H2S in the vascular system is the regulation of the availability of NO.

The rotor tip inside a bearing of a thermophilic F1-ATPase is dispensable for torque generation

F(1)-ATPase is an ATP-driven rotary molecular motor in which the central gamma-subunit rotates inside a stator cylinder made of alpha(3)beta(3) subunits. To elucidate the role of rotor-stator interactions in torque generation, we truncated the gamma-subunit at its carboxyl terminus, which forms an alpha helix that penetrates deeply into the stator cylinder. We used an alpha(3)beta(3)gamma subcomplex of F(1)-ATPase derived from thermophilic Bacillus PS3 and expressed it in Escherichia coli. We could obtain purified subcomplexes in which 14, 17, or 21 amino-acid residues were deleted. The rotary characteristics of the truncated mutants, monitored by attaching a duplex of 0.49-microm beads to the gamma-subunit, did not differ greatly from those of the wild-type over the ATP concentrations of 20 nM-2 mM, the most conspicuous effect being approximately 50% reduction in torque and approximately 70% reduction in the rate of ATP binding upon deletion of 21 residues. The ATP hydrolysis activity estimated in bulk samples was more seriously affected. The 21-deletion mutant, in particular, was >10-fold less active, but this is likely due to instability of this subcomplex. For torque generation, though not for rapid catalysis, most of the rotor-stator contacts on the deeper half of the penetrating portion of the gamma-subunit are dispensable.

Transient ionized hypocalcemia and secondary hyperparathyroidism accompanying acute adrenal insufficiency

OBJECTIVE

To describe the hitherto unrecognized occurrence of transient ionized hypocalcemia with acute adrenal insufficiency and its therapy.

METHODS

We present three case reports with documented longitudinal laboratory findings.

RESULTS

Transient ionized hypocalcemia of acute illness has been noted in children and adults and is associated with increased mortality. Precipitating illnesses include gram-positive and gram-negative sepsis and staphylococcal toxic shock syndrome. We encountered three patients with transient ionized hypocalcemia associated with acute adrenal insufficiency. Similar to severely ill, transiently hypocalcemic patients without adrenal insufficiency, one patient demonstrated 25-hydroxyvitamin D deficiency, a second had minimal magnesium deficiency, and a third had no identifiable underlying abnormality. All three patients exhibited a transient increase in levels of serum intact parathyroid hormone and 1,25-dihydroxyvitamin D in response to ionized hypocalcemia, indicative of temporary secondary hyperparathyroidism. Two of the three patients were treated solely with glucocorticoids and intravenous administration of fluids, whereas the third received minimal intramuscularly administered magnesium and antibiotics in addition. All ultimately demonstrated a return to normal of serum total and ionized calcium, parathyroid hormone, and 1,25-dihydroxyvitamin D with no further treatment, even though one patient remained deficient in 25-hydroxyvitamin D.

CONCLUSION

On the basis of these cases, we conclude that acute adrenal insufficiency and its treatment must be added to the disorders associated with transient ionized hypocalcemia and that transient secondary hyperparathyroidism is characteristic of at least some of the patients.

Unconstrained steps of myosin VI appear longest among known molecular motors

Myosin VI is a two-headed molecular motor that moves along an actin filament in the direction opposite to most other myosins. Previously, a single myosin VI molecule has been shown to proceed with steps that are large compared to its neck size: either it walks by somehow extending its neck or one head slides along actin for a long distance before the other head lands. To inquire into these and other possible mechanism of motility, we suspended an actin filament between two plastic beads, and let a single myosin VI molecule carrying a bead duplex move along the actin. This configuration, unlike previous studies, allows unconstrained rotation of myosin VI around the right-handed double helix of actin. Myosin VI moved almost straight or as a right-handed spiral with a pitch of several micrometers, indicating that the molecule walks with strides slightly longer than the actin helical repeat of 36 nm. The large steps without much rotation suggest kinesin-type walking with extended and flexible necks, but how to move forward with flexible necks, even under a backward load, is not clear. As an answer, we propose that a conformational change in the lifted head would facilitate landing on a forward, rather than backward, site. This mechanism may underlie stepping of all two-headed molecular motors including kinesin and myosin V.

Immunobiology and gene-based immunotherapy of hepatocellular carcinoma

PURPOSE

Hepatocellular carcinoma (HCC) is one of the major malignancies worldwide. For most patients with advanced or multifocal HCC treatment options are limited resulting in a poor prognosis. Several local ablation methods have been developed as minimally invasive strategies for HCC treatment. It is unclear, until now, whether these therapies will significantly improve the poor prognosis of patients with unresectable HCC. Novel therapeutic strategies and a better understanding of HCC imunobiology are, therefore, urgently required.

DESIGN

The scientific literature since 1970 in all languages cited in Medline was systematically reviewed.

RESULTS

Until now, a variety of specific and non-specific immunostimulatory strategies against HCC has been applied in preclinical experimental models with some promising results. The molecular characterization of HCC associated tumour antigens such as alpha-fetoprotein (AFP) and the increased understanding of the immunological pathways involved in liver and tumor immunology have paved the way for the design of promising gene-based cancer vaccines. The first phase I and II immunotherapeutic clinical trials based on dendritic cell immunotherapy and peptide vaccines are ongoing in HCC-patients. Clinical trials have, in general, demonstrated the safety of such strategies. Recently, exciting new immunological techniques and tools have been developed which allow to characterize antigen specific T cells at a single-cell level. In future, HCC specific tumor rejection antigens which can be used therapeutically have to be identified using microarray-based analysis. The different therapeutic modalities need to be compared directly resulting in optimised therapeutic approaches and the identification of sub-groups of HCC-patients responding favourably to treatment.

Ideal or actual body weight to calculate CD34+ cell doses for autologous hematopoietic stem cell transplantation?

The number of CD34+ cells infused influences the speed of hematologic recovery post-transplant. There are limited data on whether ideal (IBW) or actual (ABW) body weight should be used to calculate CD34+ cell dose. We compared the correlation between recovery to 0.5 x 10(9)/l neutrophils and the CD34+ cell dose based upon ABW as well as IBW in 87 patients autografted for cancer. ABW was >or=25% over IBW in 43% of patients. The median number of CD34+ cells administered was 3.6 x 10(6)/kg ABW and 4.2 x 10(6)/kg IBW. The time to neutrophil recovery was 8-15 days (median 10). There was a stronger inverse correlation between CD34+ cell dose/IBW and neutrophil recovery (r(2)=0.308; P<0.0001) than between CD34+ cell dose/ABW and neutrophil recovery (r(2)=0.267; P<0.0001). The median time to neutrophil recovery was comparable for those receiving >or=2 x 10(6)/kg CD34+ cells/kg IBW as well as ABW (10 days) and those receiving >or=2 x 10(6)/kg CD34+ cells/kg IBW but <2/kg ABW (10 days), but was significantly slower for those receiving <2 x 10(6)/kg CD34+ cells/kg IBW (12 days). These data show that the CD34+ cell dose based on IBW is a better predictor of neutrophil recovery after autotransplantation.

Reassessing the definition of myeloid engraftment after autotransplantation: it is not necessary to see 0.5 x 10(9)/l neutrophils on 3 consecutive days to define myeloid recovery

The time to myeloid recovery after autologous hematopoietic stem cell transplantation (HSCT) is usually defined as the first of 3 consecutive days with an absolute neutrophil count (ANC) of >or=0.5 x 10(9)/l (ANC500). Universal documentation of ANC500 for 3 consecutive days, historically required to ensure robust myeloid recovery, has become difficult with a trend towards early discharge and outpatient HSCT. We studied 90 autografted patients to see how frequently ANC declined after having reached >or=0.5 x 10(9)/l. ANC500 was documented on 2 and 3 consecutive days in 14 and 63 patients, respectively. ANC increased by a median of 213% from the 1st to the 2nd day (rise in 75 and unchanged in two), and by a median of 142% from the 2nd day to the 3rd (rise in 60, unchanged in one, and decline in two; higher than the 1st day in the latter three). The increase from the 1st to the 3rd day was 13-3433% (median, 557%). Thus, in all 63 patients, no decline below ANC500 was seen, and the first day with ANC500 was also the first of 3 consecutive days with ANC500. The remaining 13 patients had repeat counts 2-7 days after the 1st day with ANC500 documenting further increase in ANC with no evidence of failed engraftment. These data show that the first day with ANC500 is also consistently the first of 3 consecutive days with ANC500 in autografted patients. Therefore, the traditional definition of myeloid engraftment should be changed to consider the first day with ANC500 as the day of engraftment without necessarily documenting ANC500 on the subsequent 1-2 days. This simple change in definition has significant implications for how data are reported to transplant registries and how peer-review organizations such as the Foundation for the Accreditation of Hematopoietic Cell Therapy (FAHCT) define completeness of data.

Myosin V is a left-handed spiral motor on the right-handed actin helix

Myosin V is a two-headed, actin-based molecular motor implicated in organelle transport. Previously, a single myosin V molecule has been shown to move processively along an actin filament in discrete approximately 36 nm steps. However, 36 nm is the helical repeat length of actin, and the geometry of the previous experiments may have forced the heads to bind to, or halt at, sites on one side of actin that are separated by 36 nm. To observe unconstrained motion, we suspended an actin filament in solution and attached a single myosin V molecule carrying a bead duplex. The duplex moved as a left-handed spiral around the filament, disregarding the right-handed actin helix. Our results indicate a stepwise walking mechanism in which myosin V positions and orients the unbound head such that the head will land at the 11th or 13th actin subunit on the opposing strand of the actin double helix.

Cobe Spectra is superior to Fenwal CS 3000 Plus for collection of hematopoietic stem cells

One hundred and seventy-seven stem cell apheresis procedures performed on 91 patients using the Fenwal CS 3000 Plus cell separator and 61 procedures performed on 37 patients using the Cobe Spectra cell separator were studied to compare the CD34(+) cell collection efficiencies (CE; the proportion of the total CD34(+) cell content in the blood volumes processed that is harvested) of the two machines. The absolute peripheral blood CD34(+) cell count was comparable for the two groups (P = 0.27). A strong correlation was seen between the blood CD34(+) cell count and the total number of CD34(+) cells collected for the Spectra (r(2) = 0.59; P < 10(-6)) and for the CS 3000 Plus (r(2) = 0.60; P < 10(-6)). No significant correlation emerged between the peripheral blood CD34(+) cell count and the CE of either machine. The total number of CD34(+) cells collected per procedure was comparable (P = 0.51): median 113 x 10(6) for CS 3000 Plus and median 218 x 10(6)for Spectra. CE was significantly higher with the Spectra (median 45.7%, range 9.8-98.6%) than the CS 3000 Plus (median 30.3%, range 1.7-89.3%; P < 0.00001). We conclude that the CD34(+) cell CE of the Spectra is superior to that of the CS 3000 Plus. Therefore, under the usual clinical conditions, Cobe Spectra should be used preferentially for peripheral blood progentor cell collection to maximize the number of hematopoietic stem cells collected.

SFE-plus-C(18) lipid cleanup and selective extraction method for GC/MS quantitation of polycyclic aromatic hydrocarbons in smoked meat

In biological matrixes lipid material often poses an interference problem for determinations of nonpolar compounds, e.g., polycyclic aromatic hydrocarbons (PAHs). A newly developed supercritical fluid extraction plus adsorbent method, "SFE-plus-C(18)", offers selective extraction of PAHs in lipid-rich biological matrixes without the need for supplementary cleanup. This method eliminates the use of large volumes of toxic solvent and lengthy lipid removal procedures. This study reports the first application of the SFE-plus-C(18) method to the analysis of a genuine food product, i.e., smoked meat (beef). The procedure employs the addition of C(18) adsorbent beads to the initial sample slurry of pureed smoked meat prior to supercritical CO(2) extraction and GC/MS quantitation. During SF extraction, indigenous lipids are preferentially retained on the beads, and PAHs are selectively extracted with supercritical CO(2). In a comparison of determinations of PAHs by SFE-plus-C(18) vs the conventional SFE method, only 11-17% of the indigenous lipids observed by the conventional SFE method were co-extracted using the SFE-plus-C(18) method. The PAHs in smoked meat could thus be determined efficiently in the presence of a reduced background of co-extracted lipids. Out of 10 targeted PAHs, seven were detected with a range of 10.0-26.0 ng/g in the smoked meat sample. The other three PAHs were not present above the detection limit of the instrument (2.5-4.1 pg). The recoveries of PAHs obtained using the conventional SFE method were 63-94% lower than those achieved by SFE-plus-C(18).

Fertility of the cysts of Echinococcus granulosus in domestic herbivores from Benghazi, Libya, and the reactivity of antigens produced from them

Unilocular cysts produced by Echinococcus granulosus were recovered from 110 domestic herbivores (60 sheep, 25 cattle, 20 goats and five camels) slaughtered in Benghazi. The proportion of the cysts from the sheep found to be fertile (75%) was higher than that of the cysts from the goats (55%), camels (40%), or cattle (0%). When tested in indirect haemagglutination assays (IHA) with eight sera from human cases of cystic echinococcosis, the fluid from the cattle cysts never gave a positive reaction. Antigens in the fluids collected from sheep or goat cysts did react with the sera, with antigens from each of the two sources giving similar titres with each serum. However, crude somatic antigens (prepared from protoscolices and brood capsules collected from sheep cysts) appeared to be more sensitive for the immunodiagnosis of human cystic echinococcosis than the cyst-fluid antigens.

C. elegans KLP-11/OSM-3/KAP-1: orthologs of the sea urchin kinesin-II, and mouse KIF3A/KIFB/KAP3 kinesin complexes

Kinesins are intracellular multimeric transport motor proteins that move cellular cargo on microtubule tracks. It has been shown that the sea urchin KRP85/95 holoenzyme associates with a KAP115 non-motor protein, forming a heterotrimeric complex in vitro, called the Kinesin-II. Here we describe isolation of a cDNA clone corresponding to the klp-11 kinesin in C. elegans. Our sequence analysis of the encoded KLP-11 shows that it shares high homology with the OSM-3 kinesin. We also describe a nematode cDNA encoding KAP-1 that shares extensive homology with the sea urchin KAP115 kinesin associated protein. Sequence-based structural analysis of the OSM-3, KLP-11, and KAP-1, presented here suggests that these may form a heterotrimeric complex. We also describe the presence of a Drosophila armadillo consensus motif in CeKAP-1, first found in spKAP115, that suggests a possible role for the KAP-1 in signal transduction.

A novel C-terminal kinesin subfamily may be involved in chromosomal movement in caenorhabditis elegans

C-terminal kinesin motor proteins, such as the Drosophila NCD and yeast KAR3, are involved in chromosomal segregation. Previously we have described two orthologs of NCD in Caenorhabditis elegans, KLP-3 and KLP-17, which also participate in chromosome movement. Here we report cDNA cloning of klp-15 and klp-16, and the expression pattern of the genes encoding C-terminal motor kinesins including klp-15 and klp-16. Interestingly KLP-15 and KLP-16 form a unique class of C-terminal kinesins, distinct from the previously known C-terminal motors in other organisms. Using in situ hybridization and RNA interference assay, we show that although all of these motors mediate chromosome segregation, they do so in a combination of unique and overlapping manners, suggesting a complex hierarchy of kinesin motor function in metazoans.

Glossina austeni (Diptera: Glossinidae) eradicated on the island of Unguja, Zanzibar, using the sterile insect technique

An area-wide integrated tsetse eradication project was initiated in Zanzibar in 1994 by the International Atomic Energy Agency and the governments of Tanzania and Zanzibar, to eradicate Glossina austeni Newstead from Unguja Island (Zanzibar) using the sterile insect technique. Suppression of the tsetse population on Unguja was initiated in 1988 by applying residual pyrethroids as a pour-on formulation to livestock and by the deployment of insecticide impregnated screens in some of the forested areas. This was followed by sequential releases of gamma-sterilized male flies by light aircraft. The flies, packaged in carton release containers, were dispersed twice a week along specific flight lines separated by a distance of 1-2 km. More than 8.5 million sterile male flies were released by air from August 1994 to December 1997. A sterile to indigenous male ratio of >50:1 was obtained in mid-1995 and it increased to >100:1 by the end of 1995. As a consequence the proportion of sampled young females (1-2 ovulations), with an egg in utero in embryonic arrest or an uterus empty as a result of expulsion of a dead embryo, increased from <25% in the 1st quarter to >70% in the last quarter of 1995. In addition, the age structure of the female population became significantly distorted in favor of old flies (> or = 4 ovulations) by the end of 1995. The apparent density of the indigenous fly population declined rapidly in the last quarter of 1995, followed by a population crash in the beginning of 1996. The last trapped indigenous male and female flies were found in weeks 32 and 36, 1996, respectively. Time for 6 fly generations elapsed between the last catch of an indigenous fly and the end of the sterile male releases in December 1997.

cDNA cloning and expression of a C-terminus motor kinesin-like protein KLP-17, involved in chromosomal movement in Caenorhabditis elegans

Members of the kinesin protein family transport intracellular cargo to their correct cellular destination. Previously we have characterized the klp-3 gene from Caenorhabditis elegans, which encodes an ortholog of the retrograde C-terminus kinesin motors, such as Drosophila NCD, and yeast KAR3, involved in the chromosomal movement. Here we report the cloning of a full-length klp-17 cDNA in C. elegans, encoding a C-terminus kinesin of 605 amino residues. KLP-17 sequence defines a novel phylogenetic group, distinct from the NCD/KAR3 family. Interestingly, the klp-17 gene transcript is restricted to the nuclear compartment, as deduced by the RNA in situ hybridization in embryos. The klp-17::gfp-expressing transgenic animals do not display any GFP fluorescence signal, but expression of the extra chromosomal arrays cause production of abnormal males, and embryos with morphological defects and lethality in the progeny. Similarly, the klp-17 RNA interference assay results in embryonic death, arrested embryos, and polyploid cells. Thus, KLP-17 represents a new motor protein that mediates chromosome movement, essential for cell divisions during metazoan development.

Hypercalcemia associated with infection by Cryptococcus neoformans and Coccidioides immitis

BACKGROUND

Of the 13 reported cases of hypercalcemia associated with fungal infection, 1 was caused by Cryptococcus neoformans and probably mediated by increased levels of 1,25-dihydroxyvitamin D [1,25(OH)2D]. Eight others were associated with Coccidioides immitis, of which only 2 had measured 1,25(OH)2D levels; in both, they were diminished. We report a patient with human immunodeficiency virus infection and simultaneous C. immitis and C. neoformans pneumonia and C. immitis fungemia associated with hypercalcemia.

METHODS

Consecutive measurements of serum total and ionized calcium, phosphorous, blood urea nitrogen, creatinine, 25(OH)D, 1,25(OH)2D, parathyroid hormone (PTH), parathyroid hormone-related protein (PTHrp) and albumin were performed over a period of 46 months.

RESULTS

While the patient was hypercalcemic, intact serum PTH and PTHrp were undetectable, serum 25(OH)D levels were normal, and serum 1,25(OH)2D levels were in the high normal range. Successful treatment of the C. immitis and C. neoformans infections resulted in resolution of the hypercalcemia and increase of PTH and PTHrp to the normal range.

CONCLUSION

In some patients with HIV infection, coincident hypercalcemia, and severe fungal infection, the responsible factor may be 1,25(OH)2D. Although total serum levels of this compound may not be frankly elevated, they are inappropriately high for the circumstances. Free 1,25(OH)2D levels should be determined in this situation.

SFE plus C18 lipid cleanup method for selective extraction and GC/MS quantitation of polycyclic aromatic hydrocarbons in biological tissues

Lipid material represents a potential interference for determination of nonpolar compounds (e.g., polycyclic aromatic hydrocarbons) in biological tissue samples. This study reports the development of a selective extraction method using supercritical CO2 that allows the GC/MS quantitation of PAHs in the presence of a substantial lipid background. Selective extraction of PAHs relies upon addition of C18 adsorbent beads to the initial sample slurry. The dried mixture, including C18 adsorbent, is placed in the supercritical fluid extraction (SFE) chamber. During the SFE process, lipids are preferentially retained on the C18 beads. This "SFE plus C18" procedure was developed by first optimizing SFE conditions (100 degrees C, 350 bar) for recovery of PAH standards. PAHs containing added model lipid compounds (stearic acid and cholesterol) were then subjected to SFE plus C18 treatment followed by GC/MS analysis. Using this approach, a recovery of 94-100% of PAHs was obtained while only 9-17% of the lipid material present was coextracted from the same test sample. The developed method is demonstrated to permit efficient recovery and detection of PAHs spiked into crab tissue, a matrix with a high lipid content.