Multilevel meta-analysis and dose-response analysis for bisphenol A (BPA) exposure on metabolic and neurobehavioral effects

Evidence suggests that oral exposure to bisphenol A (BPA) may result in adverse metabolic and neurobehavioral effects. The aim of the present meta-analysis is to examine this association based on systematically selected laboratory rodent studies published from 2012 to 2021 and sourced from Scopus, Web of Science, EmBase, and PubMed. Articles satisfying eligibility and inclusion criteria were included for the calculation of the summary standardised mean difference (SMD). Subgroup analysis and subsequent dose-response analysis were conducted if applicable. In total, 32 studies were analysed for 6 metabolic endpoints (cholesterol, triglycerides, insulin, glucose, leptin, and adiponectin) and 6 neurobehavioral endpoints (locomotor activity, exploratory, anxiety, depression, spatial learning and memory, non-spatial learning and memory). Summary SMDs implied that no significant effects were observed in endpoints considered. The dose was not determined as a significant moderator with regards to medium or high heterogeneity; however, there was significant impairment of spatial learning and memory at health-based guidance value ('HBGV') (0.05-9 mg (kg bw)-1 day-1) and 'High' (>9 mg (kg bw)-1 day-1) dose group. As a result, an indicative toxicological reference dose value of 0.034 mg (kg bw)-1 day-1 was proposed due to large variability. Potential harm to spatial learning and memory from BPA exposure requires further investigation. This study has provided some additional information on potential adverse metabolic and neurobehavioral effects of BPA from the perspective of meta-analysis which can inform the public, regulatory authorities, and policymakers.

Risk assessment of bisphenol A (BPA) in Irish meat and meat products

Bisphenol A (BPA) is a chemical with large-scale applications in the manufacturing of industrial products. Concerns have been raised regarding human exposure to BPA and dietary consumption is the main route of exposure. BPA is recognised as an endocrine disruptor with multiple adverse effects on the reproductive, immune, and nervous systems. This study aimed to conduct a probabilistic risk assessment to evaluate the human health risk based on the raw concentration data (N = 1266) of BPA in non-canned meat and meat products purchased from supermarkets and local butchers in Dublin and the surrounding area. The mean exposure levels for BPA in non-canned meat and meat products, fresh meat, and processed meat products among children were 0.019, 0.0022, and 0.015 μg (kg bw)^-1 day^-1, respectively. Therefore, simulated human exposures to BPA were far below the EFSA recommended current temporary tolerable daily intake (t-TDI) of 4 μg (kg bw)^-1 day^-1. However recently, the EFSA has proposed a draft TDI of 0.04 ng (kg bw)^-1 day^-1 to replace the current t-TDI. Hence, our results indicated potential health concerns as the estimated exposure levels (5th-95th percentile) were below current t-TDI but above draft TDIs. Further investigation into the source of BPA contamination in processed meat products is highly recommended. The research presented here will inform the public, meat producers and processors, and policymakers on potential exposure to BPA.

Effect of different botanically-diverse diets on the fatty acid profile, tocopherol content and oxidative stability of beef

BACKGROUND

Beef from pasture-fed animals is viewed as a healthier and more welfare-friendly alternative to concentrate-fed beef. Botanically-diverse pastures consisting of numerous plant species may alter the fatty acid (FA) profile and the tocopherol content of beef, as well as the oxidative stability of the meat. In the present study, steers were assigned to one of three botanically-diverse diets: perennial ryegrass (PRG), perennial ryegrass + white clover (PRG + WC) or multi-species (MS), all with a finishing diet of the respective botanically-diverse silages plus a cereal-based concentrate, consistent with production systems in Ireland. The FA profile, tocopherol content, oxidative stability and colour of meat during storage were measured.

RESULTS

Compared to the other diets, the MS diet resulted in higher proportions of linolenic acid (C18:3n-3c), linoleic acid (C18:2n-6c) and total polyunsaturated fatty acids (PUFA), with higher PUFA:saturated fatty acid and n-6:n-3 ratios in the meat. α-Tocopherol concentrations were lowest in the meat of animals from the MS diet. In uncooked meat, lipid oxidation and colour values were affected by storage time across all diets, whereas the MS diet led to higher hue values only on day 14 of storage. When cooked, meat from animals on PRG + WC and MS diets had higher lipid oxidation on days 1 and 2 of storage than meat from animals on the PRG diet.

CONCLUSION

Feeding steers on a botanically-diverse diet consisting of six plant species can improve the n-3 FA and PUFA concentration of beef, affecting the susceptibility of cooked, but not uncooked, beef to oxidation. © 2023 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Hazard characterization of bisphenol A (BPA) based on rodent models - Multilevel meta-analysis and dose-response analysis for reproductive toxicity

Bisphenol A (BPA) is a widely used synthetic industrial compound frequently detected in food. Dietary exposure to BPA has been recognised as a potential health concern. However, there are uncertainties regarding BPA toxicity. The primary objective of this study was to summarise and analyse multiple toxicity endpoints of adverse reproductive effects caused by BPA exposure in rodent models. Therefore, a multilevel meta-analysis and subsequent dose-response analysis were conducted. Relevant articles published in English between 2012 and 2021 were collected from online databases, viz. Scopus, EmBase, Web of Science, and PubMed. In total, 41 studies were included for statistical analysis. All statistical analyses were performed using open-source RStudio packages. Summary effects indicated the statistical significance of BPA exposure on decreased sperm concentration (Hedges' g: -1.35) and motility (Hedges' g: -1.12) on average, while no significant effects were observed on the absolute and relative weight of male and female reproductive organs. The lowest mean toxicological reference dose values of 0.0011 mg (kg bw)^-1 day^-1 was proposed for BPA exposure on sperm concentration from the dose-response model. In conclusion, potential health risks from BPA exposure were shown with regards to reproductive toxicity, especially that sperm concentration and sperm motility require further attention.

A probabilistic approach to model bisphenol A (BPA) migration from packaging to meat products

Bisphenol A (BPA), a synthetic chemical which has raised concerns due to its potential toxicological effects on humans, has been widely detected in canned and non-canned meat and meat products. This study estimated BPA migration from packaging to non-canned and canned meat products by developing two probabilistic models. BPA concentration data in packaging materials were collated, including polyethylene terephthalate, polyvinyl chloride, epoxy-based coatings, and polyester-based coatings. Migration ratios were calculated from migration tests of BPA molecules moving from packaging to food simulants. The predictive model revealed that the BPA migration concentration from packaging ranges from 0.017 to 0.13 (5th-95th percentile) μg kg-1 with a simulated mean of 0.056 μg kg-1 in non-canned meat products. This is in stark contrast to the simulated mean of 134.57 (5th-95th percentile: 59.17-223.25) μg kg-1 for canned meat products. Nevertheless, plastic packaging was estimated to contribute only 3 % of BPA levels in non-canned meat products. The sensitivity analysis showed that the contact area of meat products with films is the most sensitive parameter of the plastic packaging migration model. It is concluded that plastic packaging may not be the only or dominant source of BPA in non-canned meat products.

Yeast β-Glucan Improves Insulin Sensitivity and Hepatic Lipid Metabolism in Mice Humanized with Obese Type 2 Diabetic Gut Microbiota

SCOPE

Gut microbiota alterations are associated with obesity and type 2 diabetes. Yeast β-glucans are potential modulators of the innate immune-metabolic response, by impacting glucose, lipid, and cholesterol homeostasis. The study examines whether yeast β-glucan interacts differentially with either an obese healthy or obese diabetic gut microbiome, to impact metabolic health through hepatic effects under high-fat dietary challenge.

METHODS AND RESULTS

Male C57BL/6J mice are pre-inoculated with gut microbiota from obese healthy (OBH) or obese type 2 diabetic (OBD) subjects, in conjunction with a high-fat diet (HFD) with/without yeast β-glucan. OBD microbiome colonization adversely impacts metabolic health compared to OBH microbiome engraftment. OBD mice are more insulin resistant and display hepatic lipotoxicity compared to weight matched OBH mice. Yeast β-glucan supplementation resolves this adverse metabolic phenotype, coincident with increasing the abundance of health-related bacterial taxa. Hepatic proteomics demonstrates that OBD microbiome transplantation increases HFD-induced hepatic mitochondrial dysfunction, disrupts oxidative phosphorylation, and reduces protein synthesis, which are partly reverted by yeast β-glucan supplementation.

CONCLUSIONS

Hepatic metabolism is adversely affected by OBD microbiome colonization with high-fat feeding, but partially resolved by yeast β-glucan. More targeted dietary interventions that encompass the interactions between diet, gut microbiota, and host metabolism may have greater treatment efficacy.

Human health risk assessment of bisphenol A (BPA) through meat products

Meat and meat products are often consumed in our daily diet, providing essential nutrients. Contamination by chemical hazards, including bisphenol A (BPA) in meat products, is a concern and is continuously monitored. BPA is well-known for its endocrine-disrupting properties, which may cause potential toxicological effects on reproductive, nervous, and immune systems. Dietary consumption is the main route of BPA exposure, and meat products are a major contributor. BPA exposure from meat consumption is the focus of this review. This review found that BPA has been widely detected in canned and non-canned meat products. BPA in canned meat is assumed to be predominantly from migration from can coatings. Relatively low levels are observed in non-canned products, and the source of contamination in these products has yet to be definitively identified. A recent European Food Safety Authority (EFSA) draft opinion has proposed to lower the tolerable daily intake of BPA from 4 μg kg body weight (bw)^-1 day^-1 to 0.04 ng kg body weight (bw)^-1 day^-1, therefore potential health risks need to be addressed. This review has investigated potential contamination at the farm, industrial processes, and retail levels. Data gaps in the literature are also identified to improve future food safety in the meat industry. Also, a unified risk assessment strategy has been proposed. Further understanding of BPA migration in meat products is needed as a part of the exposure assessment to reduce potential risk, and more data on the dose-response relationship will help comprehend potential adverse health effects of BPA on humans. This research will inform the public, meat producers and processing industry, and policymakers on potential exposure to BPA and risk reduction measures, thus, ensuring food safety.

Bisphenol A and Metabolites in Meat and Meat Products: Occurrence, Toxicity, and Recent Development in Analytical Methods

Bisphenol A (BPA) is a commonly used compound in many industries and has versatile applications in polycarbonate plastics and epoxy resins production. BPA is classified as endocrine-disrupting chemical which can hamper fetal development during pregnancy and may have long term negative health outcomes in humans. Dietary sources, main route of BPA exposure, can be contaminated by the migration of BPA into food during processing. The global regulatory framework for using this compound in food contact materials is currently not harmonized. This review aims to outline, survey, and critically evaluate BPA contamination in meat products, including level of BPA and/or metabolites present, exposure route, and recent advancements in the analytical procedures of these compounds from meat and meat products. The contribution of meat and meat products to the total dietary exposure of BPA ranges between 10 and 50% depending on the country and exposure scenario considered. From can lining materials of meat products, BPA migrates towards the solid phase resulting higher BPA concentration in solid phase than the liquid phase of the same can. The analytical procedure is comprised of meat sample pre-treatment, followed by cleaning with solid phase extraction (SPE), and chromatographic analysis. Considering several potential sources of BPA in industrial and home culinary practices, BPA can also accumulate in non-canned or raw meat products. Very few scientific studies have been conducted to identify the amount in raw meat products. Similarly, analysis of metabolites and identification of the origin of BPA contamination in meat products is still a challenge to overcome.

Effect of Cold Plasma on Meat Cholesterol and Lipid Oxidation

Cold atmospheric plasma (CAP) is a novel non-thermal technology with potential applications in inactivating microorganisms in food products. However, its impact on food quality is not yet fully understood. The aim of this research is to study the impact of in-package plasma technology on the stability of cholesterol and total lipid in four different types of meat (beef, pork, lamb and chicken breast). Additionally, any changes in the primary or secondary lipid oxidation, which is undesirable from a health perspective, is investigated. CAP was not found to have any impact on the cholesterol or lipid content. However, higher peroxide and thiobarbituric acid reactive substances (TBARS) values were found for the treated samples, indicating that plasma can induce the acceleration of primary and secondary lipid oxidation. Finally, color was not affected by the treatment supporting the suitability of the technology for meat products.

Monitoring the effect of different microwave extraction parameters on the recovery of polyphenols from shiitake mushrooms: Comparison with hot-water and organic-solvent extractions

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MAE facilitates the extraction of phenols from mushrooms in short processing times.

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Three extraction methods were compared.

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Chlorogenic and caffeic acids were identified in the MAE extracts.

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SEM showed that all the extraction methods led to cell damage to varying extents.

The current study aimed to investigate the effect of different microwave-assisted extraction (MAE) parameters (i.e., particle size of the sample, solid-to-liquid ratio, microwave power, and extraction time) on the total phenolic content (TPC), antioxidant capacity (DPPH and CUPRAC), chlorogenic acid and caffeic acid contents of shiitake mushrooms. All the independent variables affected TPC and antioxidant capacity values. Only the sample particle size had no significant effect on phenolic acid contents. The highest TPC, DPPH, and CUPRAC values were obtained when a particle size of 1.75 mm, solid-to-liquid ratio of 1/40, microwave power of 600 W, and extraction time of 15 min were used. The extracts obtained by MAE were compared with those obtained after hot-water extraction (HWE) and organic-solvent extraction (OSE). Scanning electron microscopy (SEM) confirmed that MAE resulted in cell wall disruption which might be due to an increase in the pressure of the inner part of the cells.

Volatile and sensory analysis to discriminate meat from lambs fed different concentrate-based diets

Context Diet is one the most important pre-slaughter factors that potentially influences meat quality, but its effect on flavour quality remains equivocal. Aim The aim of the present study was to investigate the effect of diet composition on the flavour and sensory quality of meat from Texel × Scottish Blackface ram lambs. Methods Groups of 11 lambs were assigned to one of the following four dietary treatments for 54 days before slaughter: a concentrate containing barley, maize and soybean (C treatment); C supplemented with a saturated fat source (Megalac®); C supplemented with protected linseed oil; a by-product-based diet containing citrus pulp, distillers grain and soybean. Samples of cooked M. longissimus thoracis et lumborum were subjected to volatile analysis involving solid-phase microextraction followed by gas chromatography–mass spectrometry and to sensory analysis performed by a trained panel. Key results Univariate analysis of volatile data and sensory data showed few differences due to dietary treatments. However, multivariate analysis of the volatile data, and to a lesser extent the sensory profile data, showed potential to discriminate between lamb meat samples, on the basis of the different dietary treatments. Conclusions The inclusion of certain dietary ingredients in the diets of lambs to enhance the nutritional profile of lamb meat (through increasing n-3 fatty acid content) or to reduce feed-formulation costs (through the use of by-products) has minor effects on sensory quality but permits some discrimination between dietary treatments following the application of multivariate analysis. Implications The application of the findings is in allowing lamb producers to use alternative feed types without affecting the sensory quality of lamb negatively, but with the potential to discriminate lamb meat on the basis of its dietary background.

A Validated Method for Cholesterol Determination in Turkey Meat Products Using Relative Response Factors

The objective of this study was to develop a precise and accurate method to quantify cholesterol in turkey meat products using relative response factors, based on a modification of a previously published method for plant sterols determination. Validation was performed using neat solutions to determine linearity, precision, and accuracy. The method was linear in the concentration range considered (1–20 µg/mL, r² ≥ 0.991). Precision and accuracy were within the acceptability guidelines of the U.S. Food and Drug Administration (FDA) for method validation (<20% relative standard deviation (RSD) at the lower limit of quantification (LLOQ) and <15% RSD for other standards). Turkey meat was spiked with cholesterol at two levels (low = 3 µg/mL and high = 18 µg/mL), either before or after saponification, to establish the recovery and matrix effects. Recovery ranged from 94% to 105%, with a mean value of 105% at the low spike level and 95% at the high spike level. No significant matrix effects were found (90% to 112% recovery). This method is reliable for the quantification of cholesterol in turkey meat products in the range 0.4–8 mg/g.

Shedding Light on the Trehalose-Enabled Mucopermeation of Nanoparticles with Label-Free Raman Spectroscopy

Nanoparticle-based drug delivery systems have attracted significant interest owing to their promise as tunable platforms that offer improved intracellular release of cargo therapeutics. However, significant challenges remain in maintaining the physiological stability of the mucosal matrix due to the nanoparticle-induced reduction in the matrix diffusivity and promotion of mucin aggregation. Such aggregation also adversely impacts the permeability of the nanoparticles, and thus, diminishes the efficacy of nanoparticle-based formulations. Here, an entirely complementary approach is proposed to the existing nanoparticle functionalization methods to address these challenges by using trehalose, a naturally occurring disaccharide that offers exceptional protein stabilization. Plasmon-enhanced Raman spectroscopy and far-red fluorescence emission of the plasmonic silver nanoparticulate clusters are harnessed to create a unique dual-functional, aggregating, and imaging agent that obviates the need of an additional reporter to investigate mucus-nanoparticle interactions. These spectroscopy-based density mapping tools uncover the mechanism of mucus-nanoparticle interactions and establish the protective role of trehalose microenvironment in minimizing the nanoparticle aggregation. Thus, in contrast to the prevailing belief, these results demonstrate that nonfunctionalized nanoparticles may rapidly penetrate through mucus barriers, and by leveraging the bioprotectant attributes of trehalose, an in vivo milieu for efficient mucosal drug delivery can be generated.

Fatty acid composition of young dairy bull beef as affected by breed type, production treatment, and relationship to sensory characteristics

The number of male calves from the Irish dairy herd has increased following the abolition of EU milk quotas in 2015. This is a new resource for the industry, and they can be reared economically to produce meat of acceptable eating quality with optimal fatty acid (FA) profile. The effects of breed and feeding treatment on the FA profile of the longissimus thoracis (LT) muscles of young dairy bulls (n = 69) of Holstein–Friesian and Jersey × Holstein–Friesian were evaluated. The relationship between FA composition and sensory characteristics was also investigated. Bulls were offered either 1 or 2 kg of concentrates at pasture during the first grazing season. Bulls finished on silage with 5 kg of concentrates or on ad libitum concentrates were slaughtered at 15 months of age, while bulls slaughtered at 19 months were fed either ad libitum pasture or pasture with 5 kg of concentrates during a second grazing season and finished on pasture with 5 kg of concentrates or ad libitum concentrates. Pasture-finished 19-month-old bulls had higher relative proportions of C18:0 (P &lt; 0.001), C20:5n3 (eicosapentaenoic acid; P &lt; 0.001), C18:2n6c (P &lt; 0.05), C20:4n6 (P &lt; 0.01), and total n-3 (P &lt; 0.001) and n-6 polyunsaturated FAs (P &lt; 0.05), but reduced C14:0, C16:0, C14:1, C16:1 and total monounsaturated FA (P &lt; 0.001) proportions than in other production treatments. The silage-based finishing system of 15-month-old bulls increased the relative proportions of C15:0 (P &lt; 0.01), C18:0 (P &lt; 0.001) and total saturated FA (P &lt; 0.01), but decreased the proportions of C20:3n6 (P &lt; 0.05) and total unsaturated FA (P &lt; 0.01) compared with the ad libitum-concentrate finishing system. However, the feeding system of the first or second grazing seasons had limited effects on the FA profile. Jersey × Holstein–Friesian breed type had higher relative proportions of C14:1 and C16:1 (P &lt; 0.05), but lower C15:0 (P &lt; 0.01), C17:0 (P &lt; 0.001) and C17:1 (P &lt; 0.01) proportions than did Holstein–Friesian beef. Slaughter age did not affect the FA profile. Monounsaturated FA, C14:0 and C16:0 proportions were positively (P &lt; 0.05) correlated, but polyunsaturated FA proportion was negatively (P &lt; 0.05) correlated with intramuscular fat content, sensory roast beef aroma, flavour, flavour length, juiciness, initial tenderness and ease of disintegration scores. Finishing system and slaughter weight were well discriminated on the basis of FA relative proportions by canonical discriminant analysis.

Validation of a Rapid Microwave-Assisted Extraction Method and GC-FID Quantification of Total Branched Chain Fatty Acids in Lamb Subcutaneous Adipose Tissue

A rapid microwave-assisted extraction and derivatization of three branched chain fatty acids (BCFA): 4-methyloctanoic acid (MOA), 4-ethyloctanoic acid (EOA) and 4-methylnonanoic acid (MNA) from subcutaneous adipose tissue (SAT) of lamb was developed and validated. Linearity was excellent (R² > 0.99), and the limits of detection and quantification (μg/mL) were between 0.03 to 0.05 and 0.04 to 0.06, respectively. The relative response factors were 0.9416, 1.2840, and 1.0370 determined with high precision (RSD: 5.8%, 6.7%, and 5.9%) for MOA, EOA, and MNA, respectively. The accuracy, recoveries and matrix effect were 92.5% to 108.3%, 103.1% to 103.8%, and 89.3% to 101.9%, respectively. Analysis of 24 SAT samples can be done in under 4 hr. The levels of total BCFA in SAT of lambs were in good agreement with levels found in literature using more time-consuming method. PRACTICAL APPLICATION: Microwave-assisted preparation and quantification of branched chain fatty acids (BCFA) in lamb subcutaneous adipose tissue (SAT) was developed and validated. This method requires the use of less toxic chemicals and a relatively higher number of samples can be analyzed in a short period of time in comparison to established methods of fatty acid analysis. The validated method met the internationally accepted standards, and the BCFA levels in lamb SAT were consistent with published values; consequently, the method can be used for future analyses.

Volatile Profile of Grilled Lamb as Affected by Castration and Age at Slaughter in Two Breeds

The aim of this study was to assess the effect of castration and slaughter age on the volatile profile of cooked meat from Scottish Blackface (SB) and Texel × Scottish Blackface (T × SB) lambs. M. longissimus thoracis et lumborum was sampled at slaughter and subjected to volatile analysis by SPME-GC-MS. Rams had higher relative proportions, expressed as relative abundance (RA), in lipid oxidation products while castrates had higher RA in pyrazines and benzenoid compounds. There was no consistent age effect on the RA of volatiles, although rams in November and January had a different volatile profile to castrates. There were higher proportions of free branched-chain fatty acids in muscle from SB compared to T × SB lambs. Overall, the results showed that production factors affected the volatile profile of cooked lamb meat which may explain differences in lamb flavor.

PRACTICAL APPLICATION

Lamb meat has a characteristic flavor which, according to the evidence to date, may be influenced by farm production factors like gender or slaughter age. Our results showed variations in the proportions of some flavor compounds in cooked lamb between rams and castrated lambs while an increase in slaughter age did not have a consistent effect on proportions of compounds.

Effect of castration and carcass suspension method on the quality and fatty acid profile of beef from male dairy cattle

BACKGROUND

The use of bulls rather than steers for beef production offers some considerable advantages; however, the eating quality of bull beef is an issue of marketing concern. This study assessed the physicochemical characteristics of young Holstein-Friesian (HF) bull and steer beef. Steer carcasses were suspended by the Achilles tendon (AS) and by pelvic suspension (PS).

RESULTS

HF steer beef had higher redness, yellowness and chroma values, whereas bulls had higher ultimate pH and darker muscle. Warner-Bratzler shear force, cook loss at different ageing times, moisture, and insoluble and total collagen were higher for HF bull beef, whereas intramuscular fat, soluble collagen and collagen solubility were higher for steer beef. HF steer beef had a higher proportion of saturated fatty acids (SFA) and monounsaturated fatty acids (MUFA), whereas bull beef had higher proportions of polyunsaturated fatty acids (PUFA), PUFA/SFA and n-6/n-3 PUFA ratios. In comparison to AS, PS increased redness and chroma after 24 h blooming; PS improved tenderness up to 7 days of ageing and accelerated the ageing process.

CONCLUSION

For young dairy cattle, steer beef would likely have superior eating quality but a relatively less favourable nutritional fatty acid profile to bull beef. Suspension method affected the tenderness and colour intensity of dairy steer beef at different ageing times. © 2018 Society of Chemical Industry.

Nanoparticle passage through porcine jejunal mucus: Microfluidics and rheology

A micro-slide chamber was used to screen and rank sixteen functionalized fluorescent silica nanoparticles (SiNP) of different sizes (10, 50, 100 and 200 nm) and surface coatings (aminated, carboxylated, methyl-PEG₁₀₀₀ylated, and methyl-PEG₂₀₀₀ylated) according to their capacity to permeate porcine jejunal mucus. Variables investigated were influence of particle size, surface charge and methyl-PEGylation. The anionic SiNP showed higher transport through mucus whereas the cationic SiNP exhibited higher binding with lower transport. A size-dependence in transport was identified - 10 and 50 nm anionic (uncoated or methyl-PEGylated) SiNP showed higher transport compared to the larger 100 and 200 nm SiNP. The cationic SiNP of all sizes interacted with the mucus, making it more viscous and less capable of swelling. In contrast, the anionic SiNP (uncoated or methyl-PEGylated) caused minimal changes in the viscoelasticity of mucus. The data provide insights into mucus-NP interactions and suggest a rationale for designing oral nanomedicines with improved mucopermeability.

Quality of deli-style turkey enriched with plant sterols

Low-fat meat products could be excellent carriers for plant sterols, known for their cholesterol-lowering properties. In this study, we developed a protocol for the manufacture of a deli-style turkey enriched with plant sterols (S) at a level sufficient to deliver the maximum plant sterols amount recommended for cholesterol reduction by the European Food Safety Authority (3 g of plant sterols per day) in a 70 g portion. We investigated the stability of the plant sterols and the effects of their addition on the product quality. Plant sterols remained stable during the seven-day storage period. The addition of plant sterols significantly affected some texture parameters, shear force, lipid oxidation, L values and water-holding capacity compared with control (C). Sensory analysis was carried out by an untrained panel (32) using the difference-from-control test between C and S samples to evaluate first the extent of the overall sensory difference and then the extent of sensory difference on colour, texture and flavour. Results indicated that panellists considered the intensity of the difference between C and S samples to be ‘small’. Plant sterols could be used as a potential health-promoting meat ingredient with no effect on plant sterol stability but with some effects on texture and sensory characteristics.

Isotopic turnover of carbon and nitrogen in bovine blood fractions and inner organs

RATIONALE

Isotope ratio analysis of bovine tissues is a tool for inferring aspects of the dietary history of cattle. The objective of this experiment was to quantify the carbon (C) and nitrogen (N) isotopic turnover in blood (serum and residue) and inner organs (liver, kidney, heart and brain) of beef cattle.

METHODS

Growing beef cattle (n = 70 in total) were either switched from a control diet containing barley and urea to an experimental diet containing maize and (15)N-enriched urea, for various intervals prior to slaughter or maintained on the control diet for 168 days pre-slaughter. Samples of blood, liver, kidney, heart and brain were collected at 0, 14, 28, 56, 112 and 168 days and analysed using Isotope Ratio Mass Spectrometry.

RESULTS

After 168 days, C- and N-isotopic equilibrium was reached in the blood serum, liver and kidney, approached in the heart and brain, but not reached in the non-serum component of blood. The estimated C and N half-lives were 16.5 and 20.7 days for liver, 19.2 and 25.5 days for kidney, 29.2 and 35.6 days for blood serum, 37.6 and 49.9 days for heart, 53.3 and 52.2 days for brain and 113.3 and 115.0 days for the non-serum blood residue, respectively. Modelling the C and N turnover in the different tissue combinations revealed that a combined analysis of liver and heart as well as brain and kidney can provide the most accurate estimation of the timing of the diet switch.

CONCLUSIONS

Based on the difference in turnover rates, bovine soft tissues can provide isotopic information on short- and long-term dietary changes, which in turn may be linked to the geographic or production origin of beef cattle. This study also provides basic biological data on organ C and N turnover in a large herbivorous mammal.

Negative inotropic effects of tumour necrosis factor-alpha and interleukin-1beta are ameliorated by alfentanil in rat ventricular myocytes

BACKGROUND AND PURPOSE

Serum levels of tumour necrosis factor-alpha (TNF-alpha) and interleukin-1beta (IL-1beta) increase during an inflammatory response and have been reported to induce a negative inotropic effect on the myocardium. Alfentanil, an opioid analgesic often used in the critical care of patients with sepsis, has been shown to enhance ventricular contractility. This study characterised the effects of TNF-alpha and IL-1beta on contraction and the Ca(2+) transient and investigated whether depressed ventricular function was ameliorated by alfentanil.

EXPERIMENTAL APPROACH

Isolated rat ventricular myocytes were loaded with fura-2 and electrically stimulated at 1 Hz. Contraction and Ca(2+) transients were measured after 60, 120 and 180 min incubations in TNF-alpha (0.05 ng ml(-1)) and IL-1beta (2 ng ml(-1)). The effects of 10 microM alfentanil on contractility and Ca(2+) transients of TNF-alpha and IL-1beta treated cells were determined.

KEY RESULTS

After 180 min of TNF-alpha and IL-1beta treatment, the amplitude of contraction, the Ca(2+) transient and sarcoplasmic reticulum (SR) Ca(2+) content were significantly reduced. Alfentanil significantly increased contraction of TNF-alpha and IL-1beta treated cells via a small increase in the Ca(2+) transient and a larger increase in myofilament Ca(2+) sensitivity, effects that were not blocked by 10 microM naloxone, a broad spectrum opioid receptor antagonist.

CONCLUSIONS AND IMPLICATIONS

TNF-alpha and IL-1beta induce a significant negative inotropic effect on ventricular myocytes in a time dependent manner through disruption of SR Ca(2+) handling and the Ca(2+) transient. This negative inotropic effect was ameliorated by alfentanil, but this response may not be mediated via opioid receptors.

Three-dimensional growth of bovine hoof as recorded by carbon stable isotope ratios

To investigate the usefulness of bovine hooves as incremental tissues, the objective of this research was to gain a better understanding of hoof growth in three dimensions. In a controlled experiment, cattle were switched from a barley-based diet to a maize-based diet (C isotopic spacing between diets was 13.6 per thousand) and maintained on this experimental diet for 168 days. To compare growth rates along the hoof wall, three slices were sampled post-mortem from one bovine claw. In addition, one claw from each of three different animals was sampled at different depths from the surface to determine any possible time lag ('offset') in the laying down of keratin tissue layers. From each hoof as many as 41 superficial samples were taken over the first 60 mm, starting at the periople, and up to 12 samples were taken sequentially at increasing depths to a depth of 6 mm at five particular points on the surface. The growth rate of the abaxial wall of the bovine claw increased from the anterior to the posterior region of the bovine hoof. Analysis of the deep samples revealed that the deeper layers were younger than the surface layers. This offset was inversely related to the hoof growth rate, i.e. hooves with a high hoof growth rate showed a smaller offset. Observed offsets ranged between 9.2 +/- 1.8 days per mm in depth for a high and 14.0 +/- 2.8 days per mm in depth for a low hoof growth rate and were significantly different (t > or = 3.92, p < 0.0005, n = 19 or 27). The results of this study demonstrate that when sampling hooves or hoof fragments for applications such as diet reconstruction, careful consideration needs to be given to sample location.

Using hooves for high-resolution isotopic reconstruction of bovine dietary history

The objective of this study was to ascertain whether sequential sampling and isotopic analysis of bovine hooves could be used to reconstruct the dietary history of cattle. A controlled, on-farm experiment was conducted in which cattle were switched from a barley-based diet to an isotopically different diet incorporating maize, urea and seaweed (the isotopic spacing between diets was 13.6 per thousand for delta(13)C and 8.0 per thousand for delta(15)N) and maintained on that diet for 168 days. Postmortem sampling of the cleaned anterior wall of the lateral, left front claw was carried out on five individuals using a micro-drilling technique. From the first 60 mm of each claw, up to 41 samples with a spacing between them of less than 1 mm were collected. Bands were less than 1 mm deep and had a mean width of 1.2 mm. The hoof keratin showed a rapid increase followed by a slower increase in its delta(13)C and delta(15)N values following the diet switch, suggesting that C and N in hoof keratin originate from more than one pool. However, the response of the N isotope composition of the hoof was somewhat delayed compared with that of C. Estimated mean hoof growth rates for these cattle were 10.5 +/- 2.3 mm per month and 6.7 +/- 1.0 mm per month (+/-SD, n = 5) when receiving the barley-based transition diet and the maize-based experimental diet, respectively. These values are considerably higher than previous estimates obtained by visual methods and they suggest that diet may have a greater influence on hoof growth rates than seasonality. These results demonstrate that hooves are a suitable incremental tissue for high-resolution isotopic reconstruction of the dietary history of bovine animals.

A pinch elastometer for soft tissue

A prototype compression elastometer suited to the characterisation of soft tissue is analysed and tested by application to various elastomers. The test material is pinched between two rigid cylinders and the compression force and displacement interpreted to yield a measure of "effective" stiffness or to calibrate a simple non-linear-elastic material model (Neo-Hookean). This deformation suits the testing of bulk soft tissue since it effectively isolates the test material from boundary conditions such as other soft tissue, ligaments and bones. These can be highly variable in the body and can affect results greatly when employing other types of tests to determine the elastic nature of tissue. A simple linear-material analysis, based on established solutions to two-dimensional problems, is extended to take into account various geometrical complexities. This analysis permits immediate inversion of the readings from the device to yield the elastic properties of the material, without the need for complex numerical analysis. Finite element analysis is also employed to determine the range of reliable application of the linear-elastic model. In particular, this analysis permits the extension of the linear-elastic analysis to include simple forms of non-linear-material behaviour. The method is demonstrated using three elastomers having significantly different material properties. A viable range of application of the device is identified in which it yields results with reasonable precision and accuracy. The prototype device was able to measure the effective elastic modulus of the test materials with a maximum error of 13% for three material types (N=25). Repeatability error was less than 7% in all cases. Further refinement of the device and measuring system will reduce this uncertainty.

Halothane and sevoflurane inhibit Na/Ca exchange current in rat ventricular myocytes

BACKGROUND

The electrogenic Na+/Ca2+ exchanger (NCX) represents the main extrusion pathway for Ca2+ in ventricular muscle and therefore plays an important role in the regulation of cytosolic Ca2+ and contraction. Halothane and sevoflurane modulate cytosolic Ca2+ regulation and at steady state are negatively inotropic, however, the involvement of anaesthetic-induced changes in NCX activity in these effects requires further study.

METHODS

Ventricular myocytes were isolated using a standard collagenase/protease dispersion technique and superfused with a physiological salt solution at 30 degrees C. Whole-cell patch-clamp technique was used to control membrane voltage. I(NCX) (identified as Ni2+ sensitive current) was recorded using a ramp clamp protocol under conditions to inhibit contaminating currents.

RESULTS

With 0.6 mM sevoflurane, outward I(NCX) at positive voltages (> or = 0 mV) and inward I(NCX) at voltages negative to -60 mV was significantly reduced (P<0.05, n=13; I(NCX) reduced by 48% at +50 and 65% of control at -120 mV). Halothane (0.6 mM) inhibited outward I(NCX) at voltages positive to -10 mV and inward I(NCX) at voltages negative to -80 mV (P<0.05, n=10; I(NCX) reduced by 64% at +50 and 65% of control at -120 mV). Anaesthetic-induced inhibition of both inward and outward current was not voltage-dependent.

CONCLUSIONS

Inhibition of Ca2+ efflux via NCX (i.e. inward I(NCX)) during an exposure to halothane or sevoflurane would be expected to limit the negative inotropic effects of these agents and help maintain SR Ca2+ content.

Animal glues in mixtures of natural binding media used in artistic and historic objects: identification by capillary zone electrophoresis

Animal glues were often used in historic and artistic objects, e.g. as paint ground, as binders for pigments, or as adhesives. The sources were egg, casein, or different collagens. For restoration and conservation purposes it is important to know which kind of animal glue a museum object contains. Capillary electrophoresis can deliver such information, because it enables differentiation among the three proteinaceous glue classes according to their different amino acid patterns after hydrolysis. This work deals with the most relevant problem in practice, whether this identification is obstructed by the presence of other binders, with which they are mixed in many real samples; in particular, interference from plant gums and drying oils was investigated. Capillary electrophoresis of the hydrolysates (after reaction with 6 mol L(-1) HCl) was performed with an acidic background electrolyte consisting of chloroacetic acid (51.9 mmol L(-1)) adjusted with LiOH to pH 2.26. The underivatised analytes were detected with a contactless conductivity detector. It was found that the constituents of the plant gums (monosaccharides) or drying oils (long-chain fatty acids and short-chain dicarboxylic acids) never interfered with identification of the animal glues, as shown for artificial mixtures of the different binders even at tenfold excess over the animal glue, and for egg tempera samples. The method was used to identify the filling material from a statue from the eighteenth century.

Transient and sustained changes in myofilament sensitivity to Ca2+ contribute to the inotropic effects of sevoflurane in rat ventricle

BACKGROUND

The volatile anaesthetics isoflurane and sevoflurane induce both negative and positive inotropic effects in ventricular myocytes, the mechanisms of which are not fully understood. Previous data suggest that changes in myofilament Ca(2+) sensitivity contribute to their sustained negative inotropic effects. In this study, the role of changes in myofilament Ca(2+) sensitivity in both positive and negative inotropic effects of these agents was examined in intact ventricular myocytes.

METHODS

Contractility and cytosolic Ca(2+) (fura-2) were recorded optically in ventricular myocytes stimulated electrically (1 Hz) at 30 degrees C. Myofilament Ca(2+) sensitivity was assessed from plots of cell length against fura-2 fluorescence ratio (Fr) from individual twitches at various points before, during and after a 1 or 4 min exposure to 0.6 mM anaesthetic.

RESULTS

Isoflurane reduced mean (sd) myofilament Ca(2+) sensitivity from 10.3 (1.9) to 5.9 (1.6) microm Fr(-1) (P<0.001) throughout a 1 min exposure, which returned to control on removal. In contrast, on initial exposure to sevoflurane, Ca(2+) sensitivity was reduced from 10.8 (1.3) to 4.3 (0.9) microm Fr(-1) (P<0.001) but this recovered partially towards control over 3 min. On removal, sensitivity was increased above control (to 17.7 (2.2) microm Fr(-1); P<0.001) before preanaesthetic levels were restored.

CONCLUSIONS

These data show that both isoflurane and sevoflurane reduce apparent myofilament Ca(2+) sensitivity at steady state. However, sevoflurane (but not isoflurane) induced transient changes in apparent myofilament Ca(2+) sensitivity, which would contribute to its inotropic profile.

LPA1 receptor-deficient mice have phenotypic changes observed in psychiatric disease

Several psychiatric diseases, including schizophrenia, are thought to have a developmental aetiology, but to date no clear link has been made between psychiatric disease and a specific developmental process. LPA(1) is a G(i)-coupled seven transmembrane receptor with high affinity for lysophosphatidic acid. Although LPA(1) is expressed in several peripheral tissues, in the nervous system it shows relatively restricted temporal expression to neuroepithelia during CNS development and to myelinating glia in the adult. We report the detailed neurological and behavioural analysis of mice homozygous for a targeted deletion at the lpa(1) locus. Our observations reveal a marked deficit in prepulse inhibition, widespread changes in the levels and turnover of the neurotransmitter 5-HT, a brain region-specific alteration in levels of amino acids, and a craniofacial dysmorphism in these mice. We suggest that the loss of LPA(1) receptor generates defects resembling those found in psychiatric disease.

Effects of halothane on contraction and intracellular calcium in ventricular myocytes from streptozotocin-induced diabetic rats

BACKGROUND

Some of the cellular targets affected by volatile anaesthetics (e.g. halothane) which contribute to the negative inotropic effects of these agents are also affected during the progression of diabetic cardiomyopathy. A previous report suggested that halothane inhibited contraction to a lesser extent in papillary muscle from diabetic animals and so the aim of this study was to investigate possible mechanisms underlying this effect.

METHODS

Contractility and cytosolic calcium ion (Ca(2+)) transients were measured (fura-2) in ventricular myocytes isolated from control and streptozotocin (STZ)-induced diabetic rats in the absence and presence of halothane 0.6 mmol litre(-1) at 1 Hz stimulation. Sarcoplasmic reticulum (SR) Ca(2+) content was assessed by rapid application of caffeine. All experiments were carried out at 36-37 degrees C.

RESULTS

The amplitude of shortening, the electrically evoked Ca(2+) transient, SR Ca(2+) content and myofilament Ca(2+) sensitivity, though not altered by STZ treatment, were significantly reduced by halothane to a similar extent in control and STZ myocytes. The time course of contraction and Ca(2+) transient were prolonged in myocytes from STZ-treated rats compared with controls but this was not altered further by halothane. STZ treatment appeared to reduce Ca(2+) efflux from the cell, an effect reversed by halothane.

CONCLUSIONS

In contrast to a previous report, we could find no evidence of amelioration of the negative inotropic effect of halothane in myocytes from the STZ-induced diabetic rat. Contractility, the cytosolic Ca(2+) transient, SR Ca(2+) content and myofilament Ca(2+) sensitivity were qualitatively similar in control and STZ myocytes and were all depressed to the same extent by halothane.

Effects of halothane on action potential configuration in sub-endocardial and sub-epicardial myocytes from normotensive and hypertensive rat left ventricle

BACKGROUND

Halothane shortens ventricular action potential duration (APD), as a consequence of its inhibitory effects on a variety of membrane currents, an effect that is greater in sub-endocardial than sub-epicardial myocytes. In hypertrophied ventricle, APD is prolonged as a consequence of electrical remodelling. In this study, we compared the effects of halothane on transmural APD in myocytes from normal and hypertrophied ventricle.

METHODS

Myocytes were isolated from the sub-endocardium and sub-epicardium of the left ventricle of spontaneously hypertensive (SHR) and normotensive Wistar-Kyoto (WKY) rats. Action potentials were recorded before, during, and after a 1-min exposure to 0.6 mM halothane and APD measured from the peak of the action potential to repolarization at -50 mV (APD(-50 mV)). Data are presented as mean (SEM).

RESULTS

In WKY myocytes, halothane reduced APD(-50 mV) from 21 (2) to 18 (2) ms (P<0.001, n=15) in sub-epicardial myocytes but abbreviated APD(-50 mV) to a greater extent in sub-endocardial myocytes (37 (4) to 28 (3) ms; P<0.001, n=14). In SHR myocytes, APD(-50 mV) values were prolonged compared with WKY and APD(-50 mV) was reduced by halothane from 36 (6) to 27 (4) ms (P<0.016) and from 77 (10) to 38 (4) ms (P<0.001) in sub-epicardial and sub-endocardial myocytes, respectively.

CONCLUSIONS

In the SHR, hypertrophic remodelling was not homogeneous; APD(-50 mV) was prolonged to a greater extent in sub-endocardial than sub-epicardial cells. Halothane reduced APD to a greater extent in sub-endocardium than sub-epicardium in both WKY and SHR but this effect was larger proportionately in SHR myocytes. The transmural gradient of repolarization was reduced in WKY and effectively abolished in SHR by halothane, which might disturb normal ventricular repolarization.

Different regional effects of voluntary exercise on the mechanical and electrical properties of rat ventricular myocytes

Short-term (6 weeks) voluntary wheel running exercise in young female rats that were in an active growth phase resulted in whole-heart hypertrophy and myocyte concentric hypertrophy, when compared to sedentary controls. The cross-sectional area of ventricular myocytes from trained rats was significantly greater than for those isolated from sedentary rats, with the greatest change in morphology seen in sub-endocardial cells. There was no statistically significant effect of training on cell shortening in the absence of external mechanical loading, in [Ca2+](i) transients, or in myofilament Ca2+ sensitivity (assessed during re-lengthening following tetanic stimulation). Under the external mechanical load of carbon fibres, absolute force developed in myocytes from trained rats was significantly greater than in those from sedentary rats. This suggests that increased myocyte cross-sectional area is a major contractile adaptation to exercise in this model. Training did not alter the passive mechanical properties of myocytes or the relative distribution of titin isomers, which was exclusively of the short, N2B form. However, training did increase the steepness of the active tension-sarcomere length relationship, suggesting an exercise-induced modulation of the Frank-Starling mechanism. This effect would be expected to enhance cardiac contractility. Training lengthened the action potential duration of sub-epicardial myocytes, reducing the transmural gradient in action potential duration. This observation may be important in understanding the cellular causes of T-wave abnormalities found in the electrocardiograms of some athletes. Our study shows that voluntary exercise modulates the morphological, mechanical and electrical properties of cardiac myocytes, and that this modulation is dependent upon the regional origin of the myocytes.

Halothane inhibits contraction and action potential duration to a greater extent in subendocardial than subepicardial myocytes from the rat left ventricle

BACKGROUND

Halothane inhibits the 4-aminopyridine-sensitive transient outward K(+) current (I(to)) which in many species, including humans, plays an important role in determining action potential duration. As I(to) is greater in the ventricular subepicardium than subendocardium, halothane may have differential effects on action potential duration and, therefore, contraction in cells isolated from these two regions.

METHODS

Myocytes were isolated from the subendocardium and subepicardium of the rat left ventricle. Myocytes from each region were electrically stimulated at 1 Hz to measure contractions and action potentials and exposed to 0.6 mm halothane (approximately 2 x minimum alveolar concentration(50) for the rat) for 1 min. The time from the peak of the action potential to repolarization at 0 and -50 mV was measured to assess the effects of halothane on action potential duration.

RESULTS

Halothane inhibited contraction to a significantly (P = 0.002) greater extent in subendocardial myocytes than in subepicardial myocytes: the amplitude of contraction during control conditions was 3.6 +/- 0.4 microm and 3.2 +/- 0.7 microm in subendocardial and subepicardial cells, respectively, and this was reduced to 1.1 +/- 0.2 microm (29 +/- 2% of control, P < 0.0001, n = 10) and 1.4 +/- 0.3 microm (46 +/- 3% of control, P = 0.007, n = 7), respectively, after a 1-min exposure to 0.6 mm halothane. Control action potential duration (at -50 mV) was 67 +/- 10 and 28 +/- 4 ms in subendocardial and subepicardial myocytes, respectively, and these values were reduced to 39 +/- 6 ms (58 +/- 3% of control, P < 0.001) and 20 +/- 3 ms (73 +/- 5% of control, P = 0.009) by halothane, respectively.

CONCLUSIONS

Action potential duration was reduced to a greater extent in subendocardial than subepicardial myocytes, which would contribute to the greater negative inotropic effect of halothane in the subendocardium. Furthermore, the transmural difference in action potential duration was reduced by halothane, which could contribute to its arrhythmogenic properties.

Regional effects of voluntary exercise on cell size and contraction-frequency responses in rat cardiac myocytes

A model of voluntary exercise, in which rats are given free access to a running wheel over a 14-week period, led to left ventricular hypertrophy. To test whether the hypertrophic response to exercise was uniformly distributed across the ventricular wall, single ventricular myocytes were isolated from the sub-epicardium (EPI) and sub-endocardium (ENDO) of exercised rats and from sedentary rats for comparison. Cellular hypertrophy (approximately 20 % greater cell volume) was seen in ENDO cells from exercised animals, but no significant changes were observed in EPI cells when compared with sedentary controls. This regional effect of exercise may be a response to transmural changes in ventricular wall stress and/or strain. Cell contraction was measured as cell shortening in ENDO and EPI cells at stimulation frequencies between 1 and 9 Hz at 37 degrees C. Exercise training had no effect on cell shortening. Positive and negative contraction-frequency relationships (CFRs) were found in both EPI and ENDO cells between 1 and 5 Hz; at higher frequencies (5–9 Hz), all myocytes displayed a negative CFR. The CFR of a myocyte was, therefore, independent of regional origin and unaffected by exercise. These results suggest that, in vivo, the rat heart displays a negative CFR. We conclude that increased cell size may be a more important adaptive response to exercise than a modification of excitation-contraction coupling.

Sp5, a new member of the Sp1 family, is dynamically expressed during development and genetically interacts with Brachyury

We describe the identification, biochemical characterisation, and mutation of a novel mouse gene: Sp5. Sp5 encodes a protein having a C-terminal C(2)H(2) zinc finger domain closely related to that of the transcription factor Sp1. In vitro, DNA binding studies show that it binds to the GC box, a DNA motif present in the promoter of a very large number of genes, including Brachyury, and recognised by members of the Sp1 family. However, outside of its DNA binding domain, Sp5 has little homology with any other member of the Sp1 family. In contrast to the ubiquitous expression of Sp1, Sp5 exhibits a remarkably dynamic pattern of expression throughout early development. This is suggestive of a role in numerous tissue patterning events, including gastrulation and axial elongation; differentiation and patterning of the neural tube, pharyngeal region, and somites; and formation of skeletal muscle in the body and limbs. Mice homozygous for a targeted mutation in Sp5 show no overt phenotype. However, the enhancement of the T/+ phenotype in compound mutant mice (Sp5(lacZ)/Sp5(lacZ), T/+) indicates a genetic interaction between Sp5 and Brachyury. These observations are consistent with a role for Sp5 in the coordination of changes in transcription required to generate pattern in the developing embryo.

Effects of isoflurane, sevoflurane, and halothane on myofilament Ca2+ sensitivity and sarcoplasmic reticulum Ca2+ release in rat ventricular myocytes

BACKGROUND

The aim of this study was to describe and compare the effects of isoflurane, sevoflurane, and halothane at selected concentrations (i.e., concentrations that led to equivalent depression of the electrically evoked Ca2+ transient) on myofilament Ca2+ sensitivity, sarcoplasmic reticulum (SR) Ca2+ content, and the fraction of SR Ca2+ released during electrical stimulation (fractional release) in rat ventricular myocytes.

METHODS

Single rat ventricular myocytes loaded with fura-2 were electrically stimulated at 1 Hz, and the Ca2+ transients and contractions were recorded optically. Cells were exposed to each anesthetic for 1 min. Changes in myofilament Ca2+ sensitivity were assessed by comparing the changes in the Ca2+ transient and contraction during exposure to anesthetic and low Ca2+. SR Ca2+ content was assessed by exposure to 20 mm caffeine.

RESULTS

Isoflurane and halothane caused a depression of myofilament Ca2+ sensitivity, unlike sevoflurane, which had no effect on myofilament Ca2+ sensitivity. All three anesthetics decreased the electrically stimulated Ca2+ transient. SR Ca2+ content was reduced by both isoflurane and halothane but was unchanged by sevoflurane. Fractional release was reduced by both isoflurane and sevoflurane, but was unchanged by halothane.

CONCLUSIONS

Depressed myofilament Ca2+ sensitivity contributes to the negative inotropic effects of isoflurane and halothane but not sevoflurane. The decrease in the Ca2+ transient is either responsible for or contributory to the negative inotropic effects of all three anesthetics and is either primarily the result of a decrease in fractional release (isoflurane and sevoflurane) or primarily the result of a decrease in SR Ca2+ content (halothane).

Levels of nerve growth factor and neurotrophin-3 are affected differentially by the presence of p75 in sympathetic neurons in vivo

The development and survival of sympathetic neurons is critically dependent on the related neurotrophic factors nerve growth factor (NGF) and neurotrophin-3 (NT3), the actions of which must be executed appropriately despite spatial and temporal overlaps in their activities. The tyrosine receptor kinases, trkA and trkC, are the cognate receptors for NGF and NT3, respectively. The p75 neurotrophin receptor has been implicated in neurotrophin binding and signaling for both NGF and NT3. In this study, the authors used mice that overexpressed NGF (NGF-OE) or NT3 (NT3-OE) in skin and mice that lacked p75 (p75(-/-)) to understand the dynamics of sympathetic neuron response to each neurotrophin and to address the role of p75. NGF and NT3 were measured in sympathetic ganglia and skin (a major target of sympathetic neurons) by using the enzyme-linked immunosorbent assay (ELISA) technique. A three- to four-fold increase in skin NT3 was seen in both NT3-OE and p75(-/-) mice. Moreover, both mouse lines exhibited a three-fold increase in ganglionic NT3. However, the increase in ganglionic NT3 was accompanied by a decrease in ganglionic NGF in p75(-/-) mice but not in NT3-OE mice. This indicated that p75 plays an important role in determining the level of NGF within sympathetic neurons. In NGF-OE mice, the overexpression of NGF was correlated with increased ganglionic NGF and increased ganglionic expression of p75 mRNA. In addition, in NGF-OE mice, ganglionic trkC expression was decreased, as was the amount of NT3 present within sympathetic ganglia. These results indicate that the level of p75 is integral in determining the level of sympathetic NGF and that NGF competes with NT3 by increasing the expression of p75 and decreasing the expression of trkC.

The concentration-dependent effects of propofol on rat ventricular myocytes

Whether propofol contributes a direct negative inotropic effect is controversial. Our principal aim in this study was to determine whether negative inotropic effects of propofol occur at clinically relevant concentrations. We constructed the concentration-response relationship for the negative inotropic effects on intact, isolated, stimulated rat ventricular myocytes. Contraction was measured as cell shortening by using an optical system. Propofol was applied as dilutions of the commercial preparation in physiological saline solution. The drug vehicle had a minimal effect on myocyte contractility. Propofol produced a concentration-dependent reduction in evoked contraction at concentrations greater than 5 microM. The maximum effect was observed at >100 microM, with the K(0.5) calculated to be 34.5 microM (95% CI, 21.8-54.7 microM). In further experiments, we investigated the relationship between changes in contractility and changes in Ca(2+) transient (measured by using fura-2 fluorescence) after the application of propofol. By using the shift in the relationship of the cell length to fura-2 fluorescence ratio in the relaxation phase of a contraction as an index of Ca(2+) response of the myofilaments, we demonstrated that some of the negative inotropic effect of propofol may be caused by a reduction in myofilament Ca(2+) sensitivity. We confirmed this by comparing the reduction in contractility in the presence of propofol with that caused by reducing the extracellular Ca(2+) concentration. We observed that, for a decrease in the fura-2 fluorescence ratio of 21%, propofol caused a 12% (95% CI, 2% to 22%) greater reduction in contractility than predicted from reducing the extracellular Ca(2+) concentration. However, the K(0.5) for the negative inotropic effect of propofol we observed is more than 80 times the 50% effective concentration value for anesthesia. The potential relevance of these findings for clinical use of propofol in humans is discussed.

IMPLICATIONS

By using intact, isolated rat heart ventricle cells, we investigated the mechanisms and concentration dependence of the depressant effect of propofol on contractility of the heart. We conclude that direct effects of propofol on the heart are unlikely to be of significance at the clinical dosage usually given.

Quantitative analysis of Na+-Ca2+ exchanger expression in guinea-pig heart

In previous studies, regional variations in the expression of the Na+-Ca2+ exchanger (NCX) have been examined qualitatively in human heart using the C2C12 monoclonal antibody [Wang, J., Schwinger, R.H., Frank, K., Muller-Ehmsen, J., Martin-Vasallo, P., Pressley, T.A., Xiang, A., Erdmann, E. & McDonough, A.A. (1996) J. Clin. Invest. 98, 1650-1658]. Although NCX expression was found to be significantly lower in the atria compared to the septum, no significant differences were found between atrial and ventricular tissue. NCX has been located in the general sarcolemma and t-tubules of ventricular muscle and as t-tubules are sparse in atrial tissue compared to ventricular tissue, it is surprising that NCX expression was found to be similar in both atria and ventricles [Wang et al. (1996)]. To reinvestigate this, we have used SDS/PAGE and a quantitative Western blotting technique to determine the pattern of expression of NCX in guinea-pig heart in tissue samples from left atrium, right atrium, septum, left ventricle and right ventricle. NCX protein expression was 17.5 +/- 3.9 pmol.mg-1 of protein in the left atrium and 29.2 +/- 6.1 pmol.mg-1 of protein in the right atrium, which were both significantly lower (P < 0.05) than NCX expression in the septum, left ventricle and right ventricle (64.7 +/- 15.2, 76.8 +/- 19.5 and 69.4 +/- 14.1 pmol.mg-1 of protein, respectively, n = 7). These differences in NCX expression may reflect variations in the cellular location of NCX protein in these regions. To study this, we used confocal immunofluorescence of single isolated myocytes to examine differences in the proportion of fluorescent staining on the general surface membrane compared with the interior of the cell (which presumably reflects a t-tubular location). We found that the general membrane staining was 79.0 +/- 1.2% in cells from the atria which was significantly higher (P < 0. 001) than that seen in cells from the septum, left ventricle and right ventricle, with 48.1 +/- 1.1%, 48.2 +/- 1.8% and 45.6 +/- 1.3%, respectively (n = 20). These results illustrate a similar pattern of NCX expression in guinea-pig and human, with expression in atrial tissue significantly lower than in ventricular tissue. However, the cellular location of NCX differs regionally; in atrial tissue, the majority of the NCX protein is located in the general sarcolemma whereas in ventricular and septal tissue, approximately 50% of NCX protein is located within the cell (presumably at the level of the t-tubules).

Concentration-dependent inotropic effects of halothane, isoflurane and sevoflurane on rat ventricular myocytes

We have described the concentration-dependent inotropic effects of halothane, isoflurane and sevoflurane on rat ventricular cells and investigated the role of the sarcoplasmic reticulum (SR) in these inotropic actions. Single ventricular myocytes, isolated from rat hearts, were stimulated electrically at 1 Hz and contractions recorded optically. Cells were exposed to a range of concentrations of halothane, isoflurane or sevoflurane for a period of 1 min to determine the concentration-dependency of their inotropic actions. For each anaesthetic, the peak negative inotropic action was determined early during an exposure, and sustained negative inotropic action was measured at steady-state just before wash-off. In some experiments, cells were equilibrated with ryanodine 1 mumol litre-1 to investigate the role of the SR in these intropic effects. Halothane caused a concentration-dependent initial increase in contractions (to mean 130 (SEM 28)% at 10 mmol litre-1) followed by rapid onset of a negative inotropic effect (K0.5 0.34 mmol litre-1 for peak effect; K0.5 0.46 mmol litre-1 for sustained effect). Exposure to isoflurane induced a small potentiation of contractions in some cells, followed by a concentration-dependent decrease in contraction in all cells (K0.5 0.85 mmol litre-1 for peak effect; K0.5 1.92 mmol litre-1 for sustained effect); contractions recovered partially during a 1-min exposure. On wash-off, contractions were increased transiently above control. Sevoflurane caused a large initial decrease in contraction which then returned rapidly towards control (K0.5 0.2 mmol litre-1 for peak effect; K0.5 2.57 mmol litre-1 for sustained effect). In common with isoflurane, removal of sevoflurane caused a transient increase in contractions above control. After exposure to ryanodine, the positive inotropic effects of halothane and isoflurane did not occur, and recovery of contractions during exposure to isoflurane and sevoflurane was abolished as was the transient increase in contractions seen on wash-off, indicating that these effects were mediated via the SR. Halothane had the most potent sustained negative inotropic effect but there was little difference between the negative inotropic effects of isoflurane and sevoflurane at clinically relevant concentrations. At higher concentrations, sevoflurane caused a less potent negative inotropic effect than isoflurane. The SR plays a major role in the effects of all three anaesthetics. One possible mechanism underlying the initial potentiation of contraction by halothane (and isoflurane) may be sensitization of the Ca(2+)-induced Ca(2+)-release process of the SR.

Mechanisms underlying the inotropic action of halothane on intact rat ventricular myocytes

The mechanisms contributing to the negative inotropic effect of halothane were studied in isolated rate ventricular myocytes. Contraction and intracellular Ca2+ transients were measured optically in these cells. The initial application of halothane (2% or 0.5 mmol litre-1) led to short-lived increases in the Ca2+ transient and contraction, which were abolished by ryanodine. Continued application of halothane led to a sustained decrease in contraction: this resulted from: (i) a decrease in myofilament Ca2+ sensitivity; (ii) a decrease in the Ca2+ transient; and (iii) a decrease in the Ca2+ content of the sarcoplasmic reticulum. Although halothane reduced action potential duration, the sustained negative inotropic effect was similar when action potentials or voltage clamp pulses of constant duration were used to trigger contractions. In cells exposed to nifedipine 0.5 mumol litre-1 (which decreases the L-type Ca2+ current, ICa), Ca2+ transients, sarcoplasmic reticulum Ca2+ content and fractional release (the fraction of sarcoplasmic reticulum Ca2+ content released during each stimulus) were reduced. Halothane 0.5 mmol litre-1 (which also decreases ICa) decreased Ca2+ transients to a lesser extent and reduced sarcoplasmic reticulum Ca2+ content to a greater extent than nifedipine, whereas fractional release was unchanged compared with control. These data suggest that halothane sensitizes Ca(2+)-induced Ca2+ release from the sarcoplasmic reticulum in addition to reducing ICa.

Changes in contraction, cytosolic Ca2+ and pH during metabolic inhibition and upon restoration of mitochondrial respiration in rat ventricular myocytes

Exposure of cardiac muscle to metabolic poisons reduces the availability of cellular ATP and cardiac dysfunction ensues. In this study rat ventricular myocytes were exposed to 2-deoxyglucose, iodoacetate and cyanide to induce complete metabolic blockade. Changes in contraction, cytosolic Ca2+ and pH were determined during metabolic blockade and following restoration of mitochondrial ATP production. Metabolic blockade resulted in a rapid failure of contractions and Ca2+ transients, a rise of diastolic Ca2+, a cytosolic acidosis and ultimately a rigor contracture. Washing out cyanide during the development of the rigor contracture led to a rapid relaxation of the contracture, a fall in cytosolic Ca2+ and a rapid, partial reversal of the cytosolic acidosis. The partial reversal of the cytosolic acidosis and fall of cytosolic Ca2+ were abolished in the presence of oligomycin. This suggests that the rapid partial recovery of cytosolic acidosis could result from the rephosphorylation of ADP to ATP by the mitochondrial F1,F0-ATPase (a reaction that consumes protons).