Deciphering Photoreceptors Through Atomistic Modeling from Light Absorption to Conformational Response

In this review, we discuss the successes and challenges of the atomistic modeling of photoreceptors. Throughout our presentation, we integrate explanations of the primary methodological approaches, ranging from quantum mechanical descriptions to classical enhanced sampling methods, all while providing illustrative examples of their practical application to specific systems. To enhance the effectiveness of our analysis, our primary focus has been directed towards the examination of applications across three distinct photoreceptors. These include an example of Blue Light-Using Flavin (BLUF) domains, a bacteriophytochrome, and the orange carotenoid protein (OCP) employed by cyanobacteria for photoprotection. Particular emphasis will be placed on the pivotal role played by the protein matrix in fine-tuning the initial photochemical event within the embedded chromophore. Furthermore, we will investigate how this localized perturbation initiates a cascade of events propagating from the binding pocket throughout the entire protein structure, thanks to the intricate network of interactions between the chromophore and the protein.

Monitoring the adsorption of per- and polyfluoroalkyl substances on carbon black by LDI-MS capable of simultaneous analysis of elemental and organic carbon

Elemental carbon (EC) and organic carbon (OC) exist ubiquitously and interact mutually in the environment. Simultaneous analysis of EC and OC will greatly advance our understanding of the behavior and fate of EC and OC, but is however still a great challenge due to the lack of suitable analytical tools. Here, we report a matrix-free laser desorption/ionization mass spectrometry (LDI-MS) method capable of simultaneous analysis of EC and OC by monitoring two independent groups of specific MS fingerprint peaks. We found that EC itself can generate carbon cluster peaks in the low mass range under laser excitation, and meanwhile it can also serve as a matrix to assist the ionization of OC in LDI-MS. By using per- and polyfluoroalkyl substances (PFASs) as a typical set of OC and carbon black (CB) as a model EC, we successfully monitored the adsorption process of PFASs on CB enabled by LDI-MS. We show that hydrophobic interaction dominates the sorption of PFASs to CB, which was affected by the functional groups and carbon chain length of PFASs. Furthermore, environmental substances in water such as humic acid (HA) and surfactants can significantly affect the adsorption of PFASs on CB probably by changing the adsorption sites of CB. Overall, we demonstrate that LDI-MS offers a versatile and high-throughput tool for simultaneous analysis of EC and OC species in real environmental samples, which makes it promising for investigating the environmental behaviors and ecological risks of pollutants.

In Vitro Methods in the Prediction of Kinetics of Drugs: Focus on Drug Metabolism

The absorption, distribution, metabolism, excretion and toxicity (ADMET) properties of a candidate drug influence its final clinical success. These properties have traditionally been evaluated by using various in vivo animal approaches, but recently, a number of in vitro and in silico methods have been introduced to determine key ADMET features. Basic events, such as absorption through the gut wall, binding to plasma proteins, active and passive transfer through the blood-brain barrier, and various metabolic parameters, can now be screened with rapid in vitro and computer modelling methods. The focus in this short review is on the basic in vitro and in silico methods that are used for studying the metabolism properties of new drug molecules.

Pharmacologic Data and Technical Feasibility of Intraperitoneal Doxorubicin Administration

Seventy intraperitoneal administrations of doxorubicin were performed in 12 patients with malignant disease in the abdominopelvic space. Peritoneal and hematologic drug levels were measured by fluorimetric assay. A first-order decline in the peritoneal level was determined (T1/2 96 ± 18 min), with a mean drug absorption of 84 % in 4 h (range 40-96 %) and a mean ratio of a peak dialysate/peak serum level of 111 (range 12-390). Gastrointestinal toxicity was common and peritoneal phlogosis occurred twice. The doxorubicin level and the time of peritoneal exposure seem to be critical factors for major local toxicity. At a moderate concentration doxorubicin can be intraperitoneally administered, but its usefullness is probably confined to patients with minimal abdominal disease.

Low-fluoride Dentifrice and Gastrointestinal Fluoride Absorption after Meals

A low-fluoride (F) dentifrice has been recommended to reduce the risk of dental fluorosis, but its anti-caries efficacy is questionable compared with that of conventional dentrifices (1000–1100 μg F/g). The tested hypothesis was that conventional dentifrices might be safe if used soon after meals, since food interferes with F absorption. In a crossover, double-blind study, 11 volunteers ingested a dentifrice slurry containing 0 (placebo), 550 (low F), or 1100 μg F/g in 3 gastric content situations: on fasting, or 15 min after breakfast or lunch. F was analyzed in saliva and 24-hour urine samples. The conventional dentifrice ingested after lunch resulted in only 10% higher F absorption than the low-F ingested on fasting. Analysis of the data suggests that the risk of fluorosis could be reduced by the use of either a low-F dentifrice or a conventional dentifrice, if toothbrushing occurred soon after meals.

Roles of CLCA and CFTR in Electrolyte Re-absorption from Rat Saliva

A molecular basis for Cl− re-absorption has not been well-characterized in salivary ductal cells. Previously, we found strong expression of a rat homologue proposed to be Ca2+-dependent Cl− channels (rCLCA) in the intralobular ducts of the rat submandibular gland. To address the question as to whether rCLCA and cystic fibrosis transmembrane conductance regulator (CFTR) are involved in Cl− re-absorption, we evaluated the electrolyte content of saliva from glands pre-treated with a small interfering RNA (siRNA). Retrograde injection into a given submandibular duct of an siRNA designed to knock down either rCLCA or CFTR reduced the expression of each of the proteins. rCLCA and CFTR siRNAs significantly increased Cl− concentration in the final saliva during pilocarpine stimulation. These results represent the first in vivo evidence for a physiological significance of rCLCA, along with CFTR, in transepithelial Cl− transport in the ductal system of the rat submandibular gland.

Calcium Bioavailability and Kinetics of Calcium Ascorbate and Calcium Acetate in Rats

The objective was to investigate the bioavailability and mechanism of calcium absorption of calcium ascorbate (ASC) and calcium acetate (AC). A series of studies was performed in adult Sprague-Dawley male rats. In the first study, each group of rats (n = 10/group) was assigned to one of the five test meals labeled with 45Ca: (i) 25 mg calcium as heated ASC or (ii) unheated ASC, (iii) 25 mg calcium as unheated AC, (iv) 3.6 mg Ca as unheated ASC, or (v) unheated AC. Femur uptake indicated better calcium bioavailability from ASC than AC t both calcium loads. A 5-min heat treatment partly reduced bioavailability of ASC. Kinetic studies were performed to further investigate the mechanism of superior calcium bioavailability from ASC. Two groups of rats (n = 10/group) received oral doses of 25 mg Ca as ASC or AC. Each dose contained 20 μCi 45Ca. Two additional groups of rats (n = 10/group) received an intravenous injection (iv) of 10 μCi 45Ca after receiving an unlabeled oral dose of 25 mg calcium as ASC or AC. Sequential blood samples were collected over 48 hrs. Urine and fecal samples were collected every 12 hrs for 48 hrs and were analyzed for total calcium and 45Ca content. Total calcium and 45Ca from serum, urine, and feces were fitted by a compartment kinetics model with saturable and nonsaturable absorption pathways by WinSAAM (Windows-based Simulation Analysis and Modeling). The difference in calcium bioavailability between the two salts was due to differences in saturable rather than passive intestinal absorption and not to endogenous secretion or calcium deposition rate. The higher bioavailability of calcium ascorbate was due to a longer transit time in the small intestine compared with ASC.

Comparative Absorption Profiles of Divalproex Sodium Delayed-Release Versus Extended-Release Tablets—Clinical Implications

Background:

The distinct absorption characteristics of the conventional enteric-coated, delayed-release (DR) and the novel extended-release (ER) divalproex sodium formulations are not well recognized.

Objective:

To quantitatively and qualitatively differentiate the absorption characteristics of divalproex-DR and -ER formulations.

Methods:

Healthy volunteers (N = 28) received single 1000 mg doses of divalproex-DR and divalproex-ER tablets in a crossover fashion. Noncompartmental and compartmental analyses were used to estimate valproic acid (VPA) pharmacokinetics from the plasma concentration–time profiles determined from intensive blood sampling over 48 hours.

Results:

VPA was not absorbed from divalproex-DR in the first 2 hours (absorption lag-time) after dosing. After VPA release in the intestine, approximately 63% of the dose was absorbed in less than 1 hour, that is, 2.9 hours (mean absorption time) from dosing. Maximum concentration (Cmax) was achieved approximately 4 hours after dosing. VPA absorption was complete (~93% of dose) within 3 absorption half-lives (~4.5 h) post-absorption lag-time, that is, 6–7 hours from dosing. In contrast, VPA absorption from divalproex-ER starts immediately after administration, initially at a modest rate, followed by slow and extended absorption at a constant rate for more than 20 hours; VPA concentrations at 1 and 2 hours were 28% and 40% of Cmax. Approximately 53% of the dose was absorbed within 12 hours (mean absorption time); complete absorption occurred over more than 20 hours without any dose dumping.

Conclusions:

When antihypertensive treatment options are clinically equivalent, prescribers may first consider using a verapamil SR–based strategy, especially in patients with CAD who have no history of depression. VPA absorption from enteric-coated divalproex-DR is rapid following a lag-time of approximately 2 hours and is complete within 6–7 hours of dosing. In contrast, VPA absorption from divalproex-ER starts immediately after administration, but occurs at a slow, approximately constant rate over more than 20 hours.

Stable Isotopes of Minerals as Metabolic Tracers in Human Nutrition Research

Enriched stable isotopes used as tracers have proven to be valuable in studies of the absorption and metabolism of minerals. Unlike radioisotopes, they can be used in high-risk population groups such as infants, children, and pregnant or lactating women. Estimates of mineral absorption can be made from the oral administration of a single tracer or from two tracers, one given orally and the other intravenously (IV). It is possible to determine the metabolism of the mineral with modeling based on the amount of the tracer or tracers in different biological samples. One of the key decisions in studies of this type is determining which enriched isotope and what amount to use. An example is given of calculations to estimate and compare the amounts of tracers needed for an absorption study. Methods for calculating the amounts of tracer in oral and IV doses are presented, and limits of detection and quantitation are discussed in terms of percent of enrichment and related to isotope ratio measurement precision. A general review of the use of mass spectrometric instruments for quantifying various stable isotopes is given.

Digital skeletal radiography: Reduction of absorbed dose by adaptation of exposure factors and image processing

Purpose: The possibility to reduce the absorbed dose to the patient by increase of tube potential while maintaining the same exposure to the image plate and sufficient image quality in skeletal radiography has been investigated.

Material and Methods: Image processing parameters were adjusted to account for an increase in tube potential by 20 kV. Revision of image processing parameters was based on measurements with phantoms constructed to simulate the histogram shape recorded for clinical images. Image quality was evaluated both using image quality criteria and visual grading analysis. Energy imparted was calculated from measurement of the kerma-area-product.

Results and Conclusion: Energy imparted was reduced by 20-30% using the modified technique with increased kV. All images were considered of accurate quality for diagnosis and the difference in image quality score was marginal. There was, however, a significant shift towards lower grades for the "high kV" technique using visual grading analysis.

The Advantages of the Ussing Chamber in Drug Absorption Studies

By adding high concentrations of test drugs to an Ussing chamber with rat jejunum, we established a systemthat yields very high correlations between the rat absorption percentage and the membrane permeability, and that can accurately predict the absorption percentage for rats. An advantage of this technique is that, unlike the results obtained using Caco-2, the slope of the absorption/membrane-permeability curve is gentle, which facilitates a more exact prediction of the absorption percentage. In addition, the results obtained with this technique demonstrated that it could be used to evaluate the absorption percentage of drugs with an affinity for P-glycoprotein (P-gp), which cannot be assessed using Caco-2. Thismethod also allows for cassette screening, whichwould facilitate evaluation of the contribution of P-gp to absorption in the small intestine. Cassette screening showed that absorption of fexofenadinewas unaffected by combinationwith the P-gp substrate ketoconazole. Consistent with this finding, in vivo studies showed that ketoconazole did not affect the Fa Fg for fexofenadine, a pharmacokinetic parameter that reflects absorption and bioavailability in the small intestine. This confirms the usefulness of the Ussing chamber for cassette screening and also suggests that intestinal P-gp has a minimal contribution to drug absorption.

Porous Poly (DL-Lactic Acid) Modified Chitosan-Gelatin Scaffolds for Tissue Engineering

Chitosan-gelatin (Cs-Gel) scaffolds are modified with poly (DL-lactic acid) (PDLLA) dichloromethane solution of different concentrations (0.1, 0.5, and 1.0%) and immersed in water after the evaporation of the solvent. The swollen scaffolds are freeze dried. The concentration of PDLLA has significant effects on both the physicomechanical properties and the cytocompatibility. Data reveal that only the 0.1% concentration could increase the tensile strength fourfold in comparison with the pristine Cs-Gel scaffold, while maintaining the human fibroblast adhesion, migration, and proliferation just like the Cs-Gel scaffold.

Effects of the Degree of Deacetylation on the Physicochemical Properties and Schwann Cell Affinity of Chitosan Films

Chitosan is a potential material for the preparation of nerve repair conduits. In order to find a better chitosan for the application in peripheral nerve regeneration, the effects of the degree of deacetylation (DD) on the physicochemical properties and Schwann cell affinity of chitosan films have been evaluated. Six kinds of chitosan samples with similar molecular weight, but various DD in a range from 70.1 to 95.6% were prepared from one stock chitosan material and fabricated into films. X-ray diffraction analysis showed that there were more crystalline regions in the higher DD chitosan films. Swelling and mechanical property measurements revealed that the swelling index of chitosan films decreased and their elastic modulus and tensile strength increased with the increase in DD. The adsorption amount of fibronectin and laminin on chitosan films was measured by means of enzyme-linked immunosorbent assay (ELISA). Culture of adult rat Schwann cells on the films showed that the chitosan films with higher DD provided better substrata for Schwann cell spreading and proliferation. In conclusion, DD of chitosan plays an important role in their physicochemical properties and affinity with Schwann cells. The results suggest that chitosan with a DD higher than 90% is considered as a promising material for application in peripheral nerve regeneration.

Effects of active sunscreen ingredient combinations on the topical penetration of the herbicide 2,4-dichlorophenoxyacetic acid

Sunscreen use can reduce the incidence of certain skin cancers. However, a number of commercially available formulations have been shown to enhance the transdermal penetration of the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D). Most of the active ingredients used in these compounds can individually act as penetration enhancers. Commercial sunscreens frequently contain multiple active ingredients in order to provide broad sunscreen protection. The purpose of this study was therefore to examine the effect of these active ingredient combinations on the transdermal absorption of 2,4-D in vitro. All six of the combinations tested resulted in increased cumulative penetration ( P <0.01) and faster lag times ( P <0.05). The 2,4-D cumulative penetration in the presence of the OFF! Deepwoods combination was significantly greater than the absorption with either the individual ingredients or their average ( P <0.05). A systematic study designed to isolate the chemicals responsible for this enhancement demonstrated that with UV absorbers DEET synergistically increased the 2,4-D penetration and that DEET’s cumulative enhancement properties correlate with its concentration. By contrast, octocrylene significantly slowed the lag time when used in combinations and was the only active ingredient that showed any antagonistic effects on 2,4-D penetration. Because none of the active ingredient combinations were able to inhibit dermal uptake of 2,4-D, it seems that proper selection of inert ingredients may be the most feasible solution for reducing penetration enhancement.

Sunscreens containing physical UV blockers can increase transdermal absorption of pesticides

People are encouraged to wear sunscreens because of their effectiveness at reducing the risk of skin cancer. The dermal penetration of the herbicide 2,4-D can be enhanced by commercial formulations containing chemical ultraviolet (UV) absorbers, the absorbers themselves and the insect repellent DEET. This work has been extended to determine whether commercially available sunscreens containing the physical UV absorbers titanium dioxide (TiO2) or zinc oxide (ZnO) enhance the transdermal absorption of pesticides. Hairless mouse skin was pretreated with either commercially available sunscreens or the UV absorbers themselves, dissolved in phenyl trimethicone. In vitro permeability studies were performed with the pesticides 2,4-D, paraquat, parathion or malathion. The data demonstrate that pretreatment with five of the nine sunscreens tested increased the transdermal absorption of 2,4-D ( P <0.05). Transdermal studies using paraquat, parathion and malathion pretreated with a representative sunscreen all demonstrated significant penetration enhancement when compared to controls ( P <0.05). Repeated 2,4-D and sunscreen applications resulted in either no change between pulses or an increase in absorption after the second pulse depending on the washing regimen. Examining penetration of individual UV absorbers formulated in phenyl trimethicone showed that that ZnO can impede 2,4-D penetration and TiO2 had no effect. Combining UV absorbers in the presence of trimethicone resulted in ‘sunscreens’ that could actually inhibit 2,4-D penetration. Inert ingredients therefore control the increased absorption seen in commercial sunscreen products and this enhancement can be eliminated by substituting phenyl trimethicone as the solvent. Sunscreen use must still be encouraged even with the undesirable side effect of increased penetration through the skin.

Exaggerated natri-calci-uresis and increased circulating levels of parathyroid hormone and 1,25-dihydroxyvitamin D in patients with senile hypertension

Renal handling of Na and Ca in response to physiological saline infusion (20 ml/kg i.v. for 2 h) was compared between 27 hypertensive (mean +/- SD age 79.8 +/- 9.2 years) and 44 normotensive (79.1 +/- 4.1 years) senile females. Compared to the normotensive group, the hypertensive group showed statistically significant decreases in the basal values of serum Ca and PRA, and significant increases in basal circulating levels of parathyroid hormone and 1,25(OH)2D and in urinary excretions of Na, Ca and Pi in the 2-hour urine specimens during the saline infusion. These results suggest that the excessive excretions of Ca and Pi associated with exaggerated natriuresis may participate in aberration of Ca metabolism in low-renin hypertensive seniles.

Supplemented dialysis: amino acid-based solutions in peritoneal dialysis

Peritoneal dialysis is associated with several metabolic and nutritional abnormalities, some of which are related to the use of glucose-based solutions. Furthermore, the catabolic effects of uremia per se, protein and amino acid losses into the dialysate, peritonitis and poor appetite contribute to amino acid abnormalities, negative nitrogen balance and a high prevalence of malnutrition in peritoneal dialysis patients. To overcome these problems the use of amino acid instead of glucose as an osmotic agent has been proposed. Short-term studies have shown that amino acid-based solutions in peritoneal dialysis may supplement in excess the daily losses of amino acids during dialysis with glucose-based solutions. The amino acid solutions produce similar ultrafiltration and solute transport as the standard glucose solutions although the period of effective ultrafiltration is rather short. However, it should be noted that some studies have reported that the transport of small and large solutes may increase in patients using amino acid solutions. During the early 1980s several investigators have developed and tested different amino acid solutions for peritoneal dialysis. The initial clinical experience from Toronto with amino acid solutions containing large amounts of non-essential amino acids and inadequate amount of buffer were in general discouraging. The patients, who were not always malnourished and tended to have a low energy intake, developed increased BUN levels, acidosis, no improvement in nutritional status or amino acid abnormalities and, in some cases, anorexia. In 1985 a new 1% amino acid solution, containing an increased buffer amount and amino acids (mainly essential) in proportions which take the amino acid abnormalities in uremic patients into account, became available. The use of this solution resulted in some improvement in amino acid pattern and nutritional parameters, but acidosis and increased BUN levels remained problems. The experiences from these and previous studies showed that: (1) the improvement of the composition of amino acid solutions was beneficial; (2) a further increase of the buffer amount was needed; (3) patients included should have signs of protein malnutrition combined with low dietary protein intake to benefit from intraperitoneal amino acid supply, and (4) energy intake should be sufficient to prevent amino acids to end up as energy source. For this purpose a new improved 1.1% amino acid solution has been developed containing a further increase of some essential amino acids and an increased amount of lactate (40 mmol/l). This solution has been tested in malnourished patients eating 0.8 g protein/kg/day and 25-30 kcal/kg/day.(ABSTRACT TRUNCATED AT 400 WORDS)