Review of photokeratitis: Corneal response to ultraviolet radiation (UVR) exposure*

The development of photokeratitis in response to natural solar ultraviolet radiation (UVR) is prevalent in individuals participating in outdoor recreational activities in environments with high reflective surfaces, such as beach activities, water sports and snow skiing. Eye care practitioners (ECPs) are frequently encouraged by manufacturers and researchers to recommend UVR-blocking eyewear in the form of sunglasses and contact lenses. However, little is known about the precise nature of the corneal tissue response in the development of photokeratitis. This paper reviews the mechanisms responsible for the development of photokeratitis. Clinical signs and symptoms of photokeratitis, UVR corneal threshold and action spectra, corneal cellular changes and ocular protection from corneal UVR exposure are discussed. The content of this article will be useful to ECPs in making appropriate recommendations when prescribing UVR-protec-tive eyewear. (S Afr Optom 2010 69(3) 123-131)

Influence of 8DSS Peptide on Nano-mechanical Behavior of Human Enamel

Aspartate-serine-serine (DSS) repeats are abundant in naturally occurring proteins that are critical for tooth formation. We recently developed octuplet repeats of aspartate-serine-serine (8DSS) peptides to promote the nucleation of calcium phosphate carbonate from free ions. In this paper, we report a possible role of 8DSS in promoting mineral deposition onto human enamel. Human enamel specimens were demineralized, exposed briefly to 8DSS solution, and then exposed to simulated body fluid that favors mineral deposition. At various stages of treatment, nano-mechanical behaviors, namely, hardness and elastic modulus, were determined by nano-indentation. Nano-indentation results showed that 8DSS treatment effectively improved the mechanical and elastic properties of demineralized enamel. The values of hardness and elastic modulus for the 8DSS-treated enamel were significantly higher than those of surfaces without 8DSS treatment. Furthermore, 8DSS peptides promoted the uniform deposition of nano-crystalline calcium phosphate carbonate over demineralized enamel surfaces and reduced surface roughness of demineralized enamel.

Biomonitoring of essential and toxic metals in single hair using on-line solution-based calibration in laser ablation inductively coupled plasma mass spectrometry

Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) has been established as a powerful and sensitive surface analytical technique for the determination of concentration and distribution of trace metals within biological systems at micrometer spatial resolution. LA-ICP-MS allows easy quantification procedures if suitable standard references materials (SRM) are available. In this work a new SRM-free approach of solution-based calibration method in LA-ICP-MS for element quantification in hair is described. A dual argon flow of the carrier gas and nebulizer gas is used. A dry aerosol produced by laser ablation (LA) of biological sample and a desolvated aerosol generated by pneumatic nebulization (PN) of standard solutions are carried by two different flows of argon as carrier or nebulizer gas, respectively and introduced separately in the injector tube of a special ICP torch, through two separated apertures. Both argon flows are mixed directly in the ICP torch. External calibration via defined standard solutions before analysis of single hair was employed as calibration strategy. A correction factor, calculated using hair with known analyte concentration (measured by ICP-MS), is applied to correct the different elemental sensitivities of ICP-MS and LA-ICP-MS. Calibration curves are obtained by plotting the ratio of analyte ion M(+)/(34)S(+) ion intensities measured using LA-ICP-MS in dependence of analyte concentration in calibration solutions. Matrix-matched on-line calibration in LA-ICP-MS is carried out by ablating of human hair strands (mounted on a sticky tape in the LA chamber) using a focused laser beam in parallel with conventional nebulization of calibration solutions. Calibrations curves of Li, Na, Mg, Al, K, V, Cr, Mn, Fe, Ni, Co, Cu, Zn, Sr, Mo, Ag, Cd, I, Hg, Pb, Tl, Bi and U are presented. The linear correlation coefficients (R) of calibration curves for analytes were typically between 0.97 and 0.999. The limits of detection (LODs) of Li, V, Mn, Ni, Co, Cu, Sr, Mo, Ag, Ba, Cd, I, Hg, Pb, Bi and U in a single hair strand were in the range of 0.001-0.90 μg g(-1), whereas those of Cr and Zn were 3.4 and 5.1 μg g(-1), respectively. The proposed quantification strategy using on-line solution-based calibration in LA-ICP-MS was applied for biomonitoring (the spatial resolved distribution analysis) of essential and toxic metals and iodine in human hair and mouse hair.

Transporters in the brain endothelial barrier

The blood-brain barrier (BBB) not only impedes the influx of intravascular substances from blood to brain, but also promotes transport of substances from blood to brain or from brain to blood through several transport systems such as carrier-mediated transport, active efflux transport, and receptor-mediated transport systems. The multidrug resistance transporter P-glycoprotein (P-gp) is an ATP-dependent efflux pump and contributes to efflux of undesirable substances such as amyloid-beta:(Abeta) proteins from the brain into the blood as well as many drugs such as anti-cancer drugs. The inhibition of P-gp has favorable and unfavorable effects on living bodies. P-gp deficiency at the BBB induces the increase of Abeta:deposition in the brain of an Alzheimer disease mouse model. It is also known that the Abeta:deposition is inversely correlated with P-gp expression in the brains of elderly non-demented humans. However, the transient inhibition of P-gp by antidepressants enables medicines such as anti-cancer drugs to enter the brain. Concerning Abeta:clearance in the brain, the low-density lipoprotein receptor-related protein 1 (LRP1) is a major efflux transporter for Abeta, while the receptor for advanced glycation end products (RAGE) is a major influx transporter for Abeta:across the BBB. Dysfunction of the BBB with efflux and influx transporters may contribute to the pathogenesis of some degenerative neuronal disorders. This review will focus on several transporters and discuss how medicines pass the BBB to reach the brain parenchyma.

Induction of pancreatic phenotypes in central nervous system derived pluripotential progenitor cells

Fetal rat brain stem cells (RSCs) have been induced to express pituitary properties when exposed to pituitary cells (U et al., 2002). In this study, we explored whether these RSCs could also be influenced to acquire properties characteristic of the pancreas. To this end, RSCs in culture were exposed to media conditioned by rat islet tumor cells and media containing Exendin-4 and nicotinamide since both have been shown to induce pancreatic phenotypes in embryonic stem cells. Lastly, an expression construct for pdx-1 was introduced into RSCs. The expression of pancreatic markers was analyzed using RT-PRC and immunocytochemistry. When RSCs were exposed to rat islet tumor cell conditioned media and media containing Exendin-4 and nicotinamide, the expression of pdx-1, insulin and somatostatin were observed. They also acquired a spherical shape typical of pancreatic cells in culture. Under these varied conditions, transcriptional factors essential to pancreatic development such as pdx-1 and Isl-1 were induced. The critical role of pdx-1 in stimulating certain endocrine pancreatic properties in RSCs was further confirmed upon the introduction of an expression construct for pdx-1 which markedly induced insulin and somatostatin. Taken together, these findings suggests that fetal brain stem cells are pluripotent and can be reprogrammed to acquire pancreatic properties through pathways which involved the transcription factor Pdx1.

Pharmacokinetic/pharmacodynamic model-based combination therapy approach to target antibiotic resistant populations emerged from ciprofloxacin exposure

BACKGROUND

Despite decades of antimicrobial usage, the relationship between antimicrobial drugs and the development of drug resistance has not been fully delineated. This has led to increased frequency of resistance with increased usage of antimicrobials. In recent years, new insights into the mechanisms of antibiotic resistance have been proposed, leading to a re-evaluation of novel pharmacokinetic/pharmacodynamic (PK/PD) models. We have developed a semi-mechanistic PK/PD model to describe drug-bacteria kill curve relationships using the compensatory mutation hypothesis. In addition, we explored the model-based combination therapy approach to combat the resistance population.

METHODS

In vitro kill-curves of E. coli 204 up to 48 h following initial ciprofloxacin (CIP) treatment at 0.0, 0.1, 0.2, 0.5, 1.0, 2.0, 4.0, 8.0, 16.0, 32.0 and 125 times the minimum inhibitory concentration (MIC) totaling 193 data points were obtained with an in vitro system with a simulated CIP half-life of 4 h. The proposed antibiotic resistant mechanism mimics the sequential compensatory mutation hypothesis, in which mutations that acquire drug resistant traits are associated with fitness costs. Subsequent restoration of bacterial fitness is necessary for the population to be clinically relevant. Model parameters were estimated from simultaneous fitting of eleven dose groups using Adapt II software. Standard goodness of fit criteria used to obtain the final model included model convergence, Schwartz Criterion, Akaike Information Criterion, residuals versus predicted concentrations and time, and visual inspection.

RESULTS/CONCLUSIONS

The eleven E. coli kill curves after CIP treatment were well described simultaneously by the compensatory mutation model. The emergence of bacterial population with drug resistance characteristics and bacterial fitness restored appears to dominate shortly following CIP treatment. The model suggests a subsequent dose of a different mechanisms of action should be considered for the emerged resistant population.

Translocation of protein kinase C isoforms is involved in propofol-induced endothelial nitric oxide synthase activation

BACKGROUND

Previous studies have indicated that protein kinase C (PKC) may enhance endothelial nitric oxide synthase (eNOS) activation, although the detailed mechanism(s) remains unclear. In this study, we investigated the roles of PKC isoforms in regulating propofol-induced eNOS activation in human umbilical vein endothelial cells (HUVECs).

METHODS

We applied western blot (WB) analysis to investigate the effects of propofol on Ser(1177) phosphorylation-dependent eNOS activation in HUVECs. Nitrite (NO(2)(-)) accumulation was measured using the Griess assay. The phosphatidylinositol 3-kinase/Akt (PI3K/Akt) pathway was examined by WB assay. Propofol-induced translocation of individual PKC isoforms in subcellular fractions in HUVECs was analysed using WB assay.

RESULTS

In HUVECs, protocol treatment (1-100 microM) for 10 min induced a concentration-dependent increase in phosphorylation of eNOS at Ser(1177). The NO production was also increased accordingly. PKC inhibitors, bisindolylmaleimide I (0.1-1 microM), and staurosporine (20 and 100 nM), effectively blocked propofol-induced eNOS activation and NO production. Further analyses in fractionated endothelial lysate showed that short-term propofol treatment (50 microM) led to translocation of PKC-alpha, PKC-delta, PKC-zeta, PKC-eta, and PKC-epsilon from cytosolic to membrane fractions, which could also be inhibited by both PKC inhibitors. These data revealed that the differential redistribution of these isozymes is indispensable for propofol-induced eNOS activation. In addition, Akt was not phosphorylated in response to propofol at Ser(473) or Thr(308).

CONCLUSIONS

Propofol induces the Ser(1177) phosphorylation-dependent eNOS activation through the drug-stimulated translocation of PKC isoforms to distinct intracellular sites in HUVECs, which is independent of PI3K/Akt-independent pathway.