Shine a light: Under-ice light and its ecological implications in a changing Arctic Ocean

The Arctic marine ecosystem is shaped by the seasonality of the solar cycle, spanning from 24-h light at the sea surface in summer to 24-h darkness in winter. The amount of light available for under-ice ecosystems is the result of different physical and biological processes that affect its path through atmosphere, snow, sea ice and water. In this article, we review the present state of knowledge of the abiotic (clouds, sea ice, snow, suspended matter) and biotic (sea ice algae and phytoplankton) controls on the underwater light field. We focus on how the available light affects the seasonal cycle of primary production (sympagic and pelagic) and discuss the sensitivity of ecosystems to changes in the light field based on model simulations. Lastly, we discuss predicted future changes in under-ice light as a consequence of climate change and their potential ecological implications, with the aim of providing a guide for future research.

"Albedo dome": a method for measuring spectral flux-reflectance in a laboratory for media with long optical paths

A method is presented for accurate measurement of spectral flux-reflectance (albedo) in a laboratory, for media with long optical path lengths, such as snow and ice. The approach uses an acrylic hemispheric dome, which, when placed over the surface being studied, serves two functions: (i) it creates an overcast "sky" to illuminate the target surface from all directions within a hemisphere, and (ii) serves as a platform for measuring incident and backscattered spectral radiances, which can be integrated to obtain fluxes. The fluxes are relative measurements and because their ratio is used to determine flux-reflectance, no absolute radiometric calibrations are required. The dome and surface must meet minimum size requirements based on the scattering properties of the surface. This technique is suited for media with long photon path lengths since the backscattered illumination is collected over a large enough area to include photons that reemerge from the domain far from their point of entry because of multiple scattering and small absorption. Comparison between field and laboratory albedo of a portable test surface demonstrates the viability of this method.

Interim estimates of 2013/14 influenza clinical severity and vaccine effectiveness in the prevention of laboratory-confirmed influenza-related hospitalisation, Canada, February 2014

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Effects of arachidonic acid metabolites in a murine model of squamous cell carcinoma

BACKGROUND

A murine model (C3H mice) of squamous cell carcinoma (SCCVII) has been used to investigate the role of arachidonic acid (AA) metabolites in head and neck cancer. Inhibition of tumor growth by cyclooxygenase (COX) and lipoxygenase (LOX) inhibitors of AA metabolism has been associated with changes in levels of AA metabolites in tumor tissues and inflammatory cell infiltrates. To characterize this model further, the effects of exogenous AA metabolites on tumor growth in vitro and in vivo were investigated.

METHODS

Following subcutaneous inoculation with SCCVII tumor cells, control (16 mice) and treatment (24 mice) groups were injected with peritumoral vehicle or AA metabolite. Peritumoral injections of prostaglandin E2 (PGE2), leukotriene B4 (LTB4), and 12-hydroxyeicosatetraenoic acid (12-HETE) were performed for 16-21 days, and final excised tumor weights were measured. In vitro production of PGE2 and LTB4 was assayed in 2-5 day cultures of SCCVII. Exogenous PGE2 effects on tumor cell growth was assessed with the MTT assay in vitro.

RESULTS

Tumor growth was significantly inhibited (p =.03) following peritumoral injection of PGE2. Final tumor weights were not affected by LTB4 or 12-HETE. Tumor inhibition by PGE2 was associated with increased tumor tissue levels of LTB4 (p =.04). In vitro, SCCVII produced minimal amounts of PGE2 and LTB4, and PGE2 had minimal effect on growth.

CONCLUSIONS

In this model, tumor inhibition by exogenous PGE2 is primarily mediated by affecting host-tumor interactions, although there may be some direct effect on tumor cells. Changes in tumor tissue levels of LTB4 following peritumoral PGE2 administration may be attributable to negative feedback inhibition of the COX pathway with shunting into the LOX pathway. SCCVII cells are probably not a significant source of prostaglandins and leukotrienes in vivo. These data provide insight into the mechanism of action of inhibitors of AA metabolism on tumor growth.

Mycobacteriocidal action of exogenous nitric oxide

We tested the hypothesis that exposure of extracellular Mycobacterium tuberculosis to low concentrations (< 100 ppm) of nitric oxide (NO) for short periods (24 h or less) will result in microbial killing. We observed that NO had both dose- and time-dependent cidal effects that were very significant by two-way analysis of variance (F ratios of 13.4 [P < 0.001] and 98.1 [P < 0.0001], respectively). Conceivably, extracellular bacilli in patients with pulmonary tuberculosis might be vulnerable to exogenous NO.

Refractive-index measurements in freezing sea-ice and sodium chloride brines

Sea ice contains numerous pockets of brine and precipitated salts whose size and number distributions change dramatically with temperature. Theoretical treatment of scattering produced by these inclusions requires information on refractive-index differences among the brine, salts, and surrounding ice. Lacking specific data on refractive-index variations in the brine, we carried out laboratory measurements in freezing-equilibrium solutions between -2 and -32 °C. Index values at 589 nm increased from 1.341 to 1.397 over this temperature range, corresponding to salinities of 35 and 240 parts per thousand (ppt). Spectral data were also taken at 50-nm intervals between 400 and 700 nm in nonequilibrium solutions with salinities ranging up to 300 ppt. Spectral gradients increased slightly with salinity but showed no measurable dependence on temperature between +12 and -16 °C. The Lorentz-Lorenz equation, combined with data on density, molar refractivities, and brine composition, yielded temperature-dependent index predictions in excellent agreement with the experimental data. Similar index and density measurements in freezing sodium chloride brines yielded values nearly identical to those in the sea-ice brines. The absence of mirabilite crystals in sodium chloride ice, however, will cause it to have higher transmissivity and lower reflectivity than sea ice above -22 °C.

In vitro sensitivity of human hematopoietic progenitor cells to 4-hydroperoxycyclophosphamide

Protracted engraftment and prolonged thrombocytopenia remain problems when marrow purged with 4-hydroperoxy-cyclophosphamide (4-HC) is employed for autotransplants. Toxic effects of 4-HC on early progenitor and stem cells might play an important causative role. Surprisingly, few investigations have examined the effects of 4-HC on progenitor cells other than colony-forming units-granulocyte/macrophage (CFU-GM) and burst-forming units-erythroid (BFU-E), and only one study could be found where 4-HC exposure was carried out on cells purified beyond the buffy coat stage. Since the cellular milieu, and in particular the red blood cell count, can ameliorate 4-HC toxicity, the suppressive effect of this agent on marrow stem cells might be underestimated. We therefore investigated the relative 4-HC sensitivity of different human bone marrow progenitor cells in vitro using partially purified adherent cell- and T lymphocyte-depleted bone marrow mononuclear cells (A-T-MNC). Cells were exposed to increasing doses (10 to 200 micrograms/mL) of 4-HC using a standard purging protocol established for bone marrow buffy coat cells. Effects on mixed (CFU-Mix), erythroid (CFU-E and BFU-E), granulocyte-macrophage (CFU-GM), and stromal cell (CFU-F) progenitors were determined. In addition, we examined the 4-HC sensitivity of megakaryocyte progenitors (CFU-Meg) since, to our knowledge, this has not been reported before. As expected, increasing doses of 4-HC led to progressive inhibition of hematopoietic colony formation. CFU-F, CFU-Mix, and CFU-Meg appeared most resistant to 4-HC exposure, while CFU-E, BFU-E, and CFU-GM appeared most sensitive. At doses over 100 micrograms/mL, the usual concentration recommended for purging of buffy coat cells, hematopoietic colony formation was completely inhibited. These data suggest that if more highly purified marrow cells are employed for purging, lower 4-HC doses may need to be used. They also suggest that the thrombocytopenia that frequently accompanies 4-HC purging is not likely due to loss of CFU-Meg.

Differential DNA sequence deletions from chromosomes 3, 11, 13, and 17 in squamous-cell carcinoma, large-cell carcinoma, and adenocarcinoma of the human lung

Activation of protooncogenes and inactivation of putative tumor suppressor genes are genetic lesions considered to be important in lung carcinogenesis. Fifty-four cases of non-small-cell lung cancer (23 adenocarcinomas, 23 squamous-cell carcinomas, and 8 large-cell carcinomas) were examined for loss of DNA sequences at 13 polymorphic genetic loci. Loss of heterozygosity was seen more frequently in squamous-cell carcinoma than in adenocarcinoma. The loss of DNA sequences from the short arm of chromosome 17 (D17S1 locus) was detected in 8 of 9 heterozygous cases of squamous-cell carcinoma and in only 2 of 11 heterozygous cases of adenocarcinomas. Furthermore, in 7 of these 8 squamous-cell carcinomas, loss of heterozygosity from chromosome 17 was accompanied by loss of DNA sequences from chromosome 11. The spectrum of allelic sequences lost from chromosome 11 was, however, similar in every type of carcinoma studied, and the data show two regions commonly deleted from chromosome 11 (11pter-p15.5 and 11p13-q13) that may have a role in the pathogenesis of all these types of non-small-cell bronchogenic carcinoma. Loss of DNA sequences from chromosome 3 was seen in 16 of 31 cases where the constitutive DNA was heterozygous-i.e., informative. These data included only 6 of 16 cases where loss of heterozygosity involved a chromosomal locus previously shown to be lost consistently in small-cell lung cancer (DNF15S2). Loss of heterozygosity at the chromosome 13q locus, D13S3, was seen in 9 of 21 informative cases, and in 2 cases, both adenocarcinomas, duplication of the intact DNA sequences suggested the possibility that mitotic recombination had occurred. Frequent DNA sequence deletions, including those from chromosome 17, in squamous-cell carcinomas may reflect the extensive mutagenic and clastogenic effects of tobacco smoke that may lead to inactivation of putative tumor-suppressor genes.

The effect of triethylenetetramine dihydrochloride on the in vivo susceptibility of Pseudomonas aeruginosa to gentamicin

A chelating agent, triethylenetetramine dihydrochloride (TRIEN dihydrochloride) increased the efficacy of gentamicin in vivo against a clinical isolate of P. aeruginosa, designated Ps 15. Mice which were inoculated with 10 X LD50 of Ps 15 and treated with doses of 2 approximately 16 mg of gentamicin per kg per day all died. However, treatment with 8 mg of gentamicin per kg body weight per day plus 30 mg of Trien dihydrochloride per day markedly reduced the mortality. The combined therapy also reduced the number of viable organisms that accumulated in the kidney during a 24-hour period post inoculation. When a dosage level of 8 mg of gentamicin was exceeded in the combined treatment regimen, all of the infected mice died, and a high concentration of endotoxin could be detected in the mouse sera by the limulus assay.

Effect of triethylenetetramine dihydrochloride on the antibiotic susceptibility of Pseudomonas aeruginosa

A chelating agent, triethylenetetramine dihydrochloride, interacted synergistically in vitro with both gentamicin and carbenicillin against a clinical isolate of Pseudomonas aeruginosa designated Ps 15. The minimal inhibitory concentrations of carbenicillin and gentamicin for Ps 15 in a 50% serum-Trypticase soy broth were 250 and 72.9 mug/ml, respectively. However, addition of triethylenetetramine dihydrochloride to the 50% serum-Trypticase soy broth reduced the minimal inhibitory concentration of both antibiotics approximately 10-fold. A comparison of the growth of Ps 15 in 50% serum-Trypticase soy broth containing either of the antibiotics showed that a rapid decrease in the percentage of survivors only occurred when the chelating agent was present.