Evolutionary aspects of lipoxygenases and genetic diversity of human leukotriene signaling

Leukotrienes are pro-inflammatory lipid mediators, which are biosynthesized via the lipoxygenase pathway of the arachidonic acid cascade. Lipoxygenases form a family of lipid peroxidizing enzymes and human lipoxygenase isoforms have been implicated in the pathogenesis of inflammatory, hyperproliferative (cancer) and neurodegenerative diseases. Lipoxygenases are not restricted to humans but also occur in a large number of pro- and eucaryotic organisms. Lipoxygenase-like sequences have been identified in the three domains of life (bacteria, archaea, eucarya) but because of lacking functional data the occurrence of catalytically active lipoxygenases in archaea still remains an open question. Although the physiological and/or pathophysiological functions of various lipoxygenase isoforms have been studied throughout the last three decades there is no unifying concept for the biological importance of these enzymes. In this review we are summarizing the current knowledge on the distribution of lipoxygenases in living single and multicellular organisms with particular emphasis to higher vertebrates and will also focus on the genetic diversity of enzymes and receptors involved in human leukotriene signaling.

Leukotriene signaling in the extinct human subspecies Homo denisovan and Homo neanderthalensis. Structural and functional comparison with Homo sapiens

Mammalian lipoxygenases (LOXs) have been implicated in cell differentiation and in the biosynthesis of pro- and anti-inflammatory lipid mediators. The initial draft sequence of the Homo neanderthalensis genome (coverage of 1.3-fold) suggested defective leukotriene signaling in this archaic human subspecies since expression of essential proteins appeared to be corrupted. Meanwhile high quality genomic sequence data became available for two extinct human subspecies (H. neanderthalensis, Homo denisovan) and completion of the human 1000 genome project provided a comprehensive database characterizing the genetic variability of the human genome. For this study we extracted the nucleotide sequences of selected eicosanoid relevant genes (ALOX5, ALOX15, ALOX12, ALOX15B, ALOX12B, ALOXE3, COX1, COX2, LTA4H, LTC4S, ALOX5AP, CYSLTR1, CYSLTR2, BLTR1, BLTR2) from the corresponding databases. Comparison of the deduced amino acid sequences in connection with site-directed mutagenesis studies and structural modeling suggested that the major enzymes and receptors of leukotriene signaling as well as the two cyclooxygenase isoforms were fully functional in these two extinct human subspecies.

Probing conformational changes in lipoxygenases upon membrane binding: fine-tuning by the active site inhibitor ETYA

Lipoxygenases (LOXs) are lipid-peroxidizing enzymes that are involved in the metabolism of polyunsaturated fatty acids. Their biological activity includes a membrane binding process whose molecular details are not completely understood. The mechanism of enzyme-membrane interactions is thought to involve conformational changes at the level of the protein tertiary structure, and the extent of such alterations depends on the degree of structural flexibility of the different LOX isoforms. In this study, we have tested the resilience properties of a plant and a mammalian LOX, by using high pressure fluorescence measurements at different temperatures. The binding of LOXs to the lipid bilayer has been characterized using both large and giant unilamellar vesicles and electron transfer particles (inner mitochondrial membranes) as model membranes. The data indicate that the degree of LOXs' flexibility is strictly dependent on the two distinct N- and C-terminal domains that characterize the 3D structure of these enzymes. Furthermore, they demonstrate that increasing the rigidity of protein scaffolding by the presence of an active site ligand impairs the membrane binding ability of LOXs. These findings provide evidence that the amphitropic nature of LOXs is finely tuned by the interaction of the substrate with the residues of the active site, suggesting new strategies for the design of enzyme inhibitors.

Lipoxygenase pathways in Homo neanderthalensis: functional comparison with Homo sapiens isoforms

Lipoxygenases (LOX) have been implicated in biosynthesis of pro- and anti-inflammatory mediators, and a previous report suggested compromised leukotriene signaling in H. neanderthalensis. To search for corresponding differences in leukotriene biosynthesis, we screened the Neandertal genome for LOX genes and found that, as modern humans, this archaic hominid contains six LOX genes (nALOX15, nALOX12, nALOX5, nALOX15B, nALOX12B, and nALOXE3) and one pseudogene. In the Neandertal genome, 60-75% of the amino acids of the different human LOX isoforms have been identified, and the degree of identity varies between 96 and 99%. Most functional amino acids (iron ligands, specificity determinants, calcium and ATP-binding sites, membrane-binding determinants, and phosphorylation sites) are well conserved in the Neandertal LOX isoforms, and expression of selected neandertalized human LOX mutants revealed no major functional defects. However, in nALOX12 and nALOXE3, two premature stop codons were found, leading to inactive enzyme species. These data suggest that ALOX15, ALOX5, ALOX15B, and ALOX12B should have been present as functional enzymes in H. neanderthalensis and that in contrast to lower nonhuman primates (M. mulatta) and other mammals (mice, rats), this ancient hominid expressed a 15-lipoxygenating ALOX15. Expression of ALOXE3 and ALOX12 was compromised, which might have caused problems in epidermal differentiation.

Dental amalgam: effects of alloy/mercury mixing ratio, uses and waste management

BACKGROUND

Silver dental amalgam is one of the oldest filling materials used in dentistry. The American Dental Association (ADA) has estimated that billions of amalgam restorations have been placed in patients in the last 150 years. Due to the presence of mercury and mishandling during the filling make it more controversial. The objective of this study was to conduct a survey of the use of different brands and to assess any deviations in practice from the hand mixing manual method of elemental mercury and alloy in a pestle/mortar and encapsulated form.

METHODS

A questionnaire was sent to 250 of randomly selected dental practitioner in various localities of Karachi. Data was analysed to record the specified brands used along with their powder/liquid (P/L) ratio and the different methods for disposing off mercury in this study.

RESULTS

The most commonly used form of dispensing method was hand mixing (57%) and only 30% of the dentists followed the manufacturer instruction for hand mixing ratio.Eighty-seven percent of dental amalgam restoration was performed and 13% removed by the dentist per month and the method of disposing the amalgam wastage that 55%, 25%, and 20% dentists were used the sink, bin and other methods respectively in their dental clinics.

CONCLUSION

Amalgam restoration is still popular filling material in the posterior region of the mouth but we need to create awareness among the dentists who do not follow the ADA specifications.

Tubeless combined high-frequency jet ventilation for laryngotracheal laser surgery in paediatric anaesthesia

BACKGROUND

High-frequency jet ventilation (HFJV) is an alternative ventilatory approach in airway surgery and for facilitating gas exchange in patients with pulmonary insufficiency. We have developed a new technique of combined HFJV utilising two superimposed jet streams. In this study we describe the application of tubeless supralaryngeal HFJV during laryngotracheal laser surgery in infants and children.

METHODS

Tubeless combined HFJV characterised by the simultaneous supralaryngeal application of a low-frequency (LF) and a high-frequency (HF) jet stream was evaluated in a clinical study in 10 children undergoing elective laryngotracheal CO2 laser surgery. Additionally, pressure and flow characteristics were determined with the use of a paediatric test lung. HFJV was applied by means of a modified Kleinsasser laryngoscope with integrated metal injectors. In addition to pulse oximetry, monitoring of ECG, heart rate and blood pressure, supraglottic airway pressure was measured and arterial blood gases were analysed.

RESULTS

Tubeless combined HFJV was used in 10 infants and children (mean age 4.6 yr, range 2 months-10 years) undergoing 17 consecutive endoscopic procedures with CO2 laser microsurgery of the larynx or the trachea under general anaesthesia. The mean duration of supralaryngeal HFJV was 46 min (range 15-75 min). Mean driving pressures of the HF and the LF jet streams were 0.75 bar and 0.95 bar, respectively. Inspiratory oxygen ratios were in the range 0.4-1.0. HFJV resulted in mean PaO2 and PaCO2 values of 19.7 kPa and 6.1 kPa, respectively. No complications during HFJV were observed. In the test lung, combined HFJV applied with driving pressures of 0.7-1.0 bar and 0.9-1.2 bar for HF and LF jet ventilation, respectively, resulted in maximum peak and baseline distal airway pressures of 17.6 cm H2O and 5.4 cm H2O, respectively.

CONCLUSION

The application of the combined double frequency HFJV was effective in maintaining gas exchange in the presence of laryngeal or tracheal stenoses. It provided good visibility of anatomical structures and offered space for surgical manipulation, avoiding the use of combustible material inside the larynx or trachea.

Supralaryngeal tubeless combined high-frequency jet ventilation for laser surgery of the larynx and trachea

We have developed a new technique of combined high-frequency jet ventilation (HFJV), characterized by simultaneous application of a low-frequency (LF) and a high-frequency (HF) jet stream. Tubeless supralaryngeal jet ventilation was delivered via a modified Kleinsasser laryngoscope. We studied 44 adults undergoing 45 elective surgical procedures of the larynx and trachea using a carbon dioxide laser during HFJV. Applied inspiratory oxygen ratios ranged from 0.4 to 1.0. Mean driving pressures of the HF and LF jet streams were 1.5 bar and 1.8 bar in adults, respectively. Mean duration of HFJV was 41 (range 10-180) min. HFJV resulted in mean PaO2 and PaCO2 values of 16.6 (range 9.8-26.9) kPa and 5.7 (3.0-7.6) kPa, respectively. Tubeless supralaryngeal HFJV was safe and effective in maintaining gas exchange in the presence of laryngeal or tracheal stenoses, providing optimal visibility of anatomical structures, offering maximum space for surgical manipulation, and avoiding the use of combustible material inside the larynx or trachea.

Occupational exposure to sevoflurane during sedation of adult patients

OBJECTIVES

In a field study we evaluated the workplace pollution occurring during conscious sedation with sevoflurane in adults.

METHODS

Sevoflurane was given in 100% oxygen at a fresh gas flow rate of 3 l/min via a nasal mask. This was conducted in 25 patients scheduled for surgical procedures performed under regional anesthesia. Trace concentrations of sevoflurane were directly measured every minute in the breathing zone by means of a photoacoustic infrared spectrometer in an operating room with an air turnover of 20 changes/h.

RESULTS

The mean sedation time was 49.6+/-20.4 min. The average vaporizer setting of the anesthesia machine was 1.63+/-0.6 vol%, resulting in a patient's mean end-tidal sevoflurane concentration of 0.78+/-0.2 vol%. The 8-h time-weighted average was calculated to be 0.58 ppm sevoflurane.

CONCLUSIONS

The trace gas concentrations were low and comparable with values obtained under inhalation induction in adults and children. Although no occupational standard for sevoflurane is currently defined, the measured values are clearly under the standards recommended for enflurane (20 ppm) and isoflurane (10 ppm) by the European health authorities. We conclude that the new anesthesiologic method of conscious sedation with sevoflurane in adults using a nasal mask would not result in a violation of occupational standards, provided that the future value set for sevoflurane would be similar to those recommended for isoflurane or enflurane.