Numerical Analysis of the Light Modulation by the Frustule of Gomphonema parvulum: The Role of Integrated Optical Components

Siliceous diatom frustules present a huge variety of shapes and nanometric pore patterns. A better understanding of the light modulation by these frustules is required to determine whether or not they might have photobiological roles besides their possible utilization as building blocks in photonic applications. In this study, we propose a novel approach for analyzing the near-field light modulation by small pennate diatom frustules, utilizing the frustule of Gomphonema parvulum as a model. Numerical analysis was carried out for the wave propagation across selected 2D cross-sections in a statistically representative 3D model for the valve based on the finite element frequency domain method. The influences of light wavelength (vacuum wavelengths from 300 to 800 nm) and refractive index changes, as well as structural parameters, on the light modulation were investigated and compared to theoretical predictions when possible. The results showed complex interference patterns resulting from the overlay of different optical phenomena, which can be explained by the presence of a few integrated optical components in the valve. Moreover, studies on the complete frustule in an aqueous medium allow the discussion of its possible photobiological relevance. Furthermore, our results may enable the simple screening of unstudied pennate frustules for photonic applications.

Factor XII activation is essential to sustain the procoagulant effects of particulate matter

BACKGROUND

Particulate matter (PM) is a key component of ambient air pollution and has been associated with an increased risk of thrombotic events and mortality. The underlying mechanisms remain unclear.

OBJECTIVES

 To study the mechanisms of PM-driven procoagulant activity in human plasma and to investigate mainly, the coagulation driven by ultrafine particles (UFPs; < 0.1 μm) in genetically modified mice.

METHODS

Thrombin generation in response to PM of different sizes was assessed in normal human platelet-poor plasma, as well as in plasmas deficient in the intrinsic pathway proteases factors XII (FXII) or XI (FXI). In addition, UFPs were intratracheally instilled in wild-type (WT) and FXII-deficient (FXII(-/-) ) mice and plasma thrombin generation was analyzed in plasma from treated mice at 4 and 20 h post-exposure.

RESULTS

In normal human plasma, thrombin generation was enhanced in the presence of PM, whereas PM-driven thrombin formation was completely abolished in FXII- and FXI-deficient plasma. UFPs induced a transient increase in tissue factor (TF)-driven thrombin formation at 4 h post-instillation in WT mice compared with saline instillation. Intratracheal instillation of UFPs resulted in a procoagulant response in WT mice plasma at 20 h, whereas it was entirely suppressed in FXII(-/-) mice.

CONCLUSIONS

 Overall, the data suggest that PM promotes its early procoagulant actions mostly through the TF-driven extrinsic pathway of coagulation, whereas PM-driven long lasting thrombogenic effects are predominantly mediated via formation of activated FXII. Hence, FXII-driven thrombin formation may be relevant to an enhanced thrombotic susceptibility upon chronic exposure to PM in humans.

Factor XI deficiency in animal models

The blood coagulation system forms fibrin to limit blood loss from sites of injury, but also contributes to occlusive diseases such as deep vein thrombosis, myocardial infarction, and stroke. In the current model of a coagulation balance, normal hemostasis and thrombosis represent two sides of the same coin; however, data from coagulation factor XI-deficient animal models have challenged this dogma. Gene targeting of factor XI, a serine protease of the intrinsic pathway of coagulation, severely impairs arterial thrombus formation but is not associated with excessive bleeding. Mechanistically, factor XI may be activated by factor XII following contact activation or by thrombin in a feedback activation loop. This review focuses on the role of factor XI, and its deficiency states as novel target for prevention of thrombosis with low bleeding risk in animal models.