Epileptogenic Tubers Are Associated with Increased Kurtosis of Susceptibility Values: A Combined Quantitative Susceptibility Mapping and Stereoelectroencephalography Pilot Study

BACKGROUND AND PURPOSE

Prior studies have found an association between calcification and the epileptogenicity of tubers in tuberous sclerosis complex. Quantitative susceptibility mapping is a novel tool sensitive to magnetic susceptibility alterations due to tissue calcification. We assessed the utility of quantitative susceptibility mapping in identifying putative epileptogenic tubers in tuberous sclerosis complex using stereoelectroencephalography data as ground truth.

MATERIALS AND METHODS

We studied patients with tuberous sclerosis complex undergoing stereoelectroencephalography at a single center who had multiecho gradient-echo sequences available. Quantitative susceptibility mapping and R2* values were extracted for all tubers on the basis of manually drawn 3D ROIs using T1- and T2-FLAIR sequences. Characteristics of quantitative susceptibility mapping and R2* distributions from implanted tubers were compared using binary logistic generalized estimating equation models designed to identify ictal (involved in seizure onset) and interictal (persistent interictal epileptiform activity) tubers. These models were then applied to the unimplanted tubers to identify potential ictal and interictal tubers that were not sampled by stereoelectroencephalography.

RESULTS

A total of 146 tubers were identified in 10 patients, 76 of which were sampled using stereoelectroencephalography. Increased kurtosis of the tuber quantitative susceptibility mapping values was associated with epileptogenicity (P = .04 for the ictal group and P = .005 for the interictal group) by the generalized estimating equation model. Both groups had poor sensitivity (35.0% and 44.1%, respectively) but high specificity (94.6% and 78.6%, respectively).

CONCLUSIONS

Our finding of increased kurtosis of quantitative susceptibility mapping values (heavy-tailed distribution) was highly specific, suggesting that it may be a useful biomarker to identify putative epileptogenic tubers in tuberous sclerosis complex. This finding motivates the investigation of underlying tuber mineralization and other properties driving kurtosis changes in quantitative susceptibility mapping values.

Headache in children with Sturge-Weber syndrome - Prevalence, associations and impact

BACKGROUND

Sturge-Weber syndrome (SWS) is a congenital neurovascular disorder characterised by capillary-venous malformations involving the skin, brain and eye. Patients experience headache, however little is known about its characteristics or associations. We aimed to estimate prevalence, associations and the impact of headache in children with SWS.

MATERIALS AND METHODS

Case notes of all patients in a national tertiary paediatric SWS clinic were retrospectively reviewed. Patients were categorised into those with or without a history of headache, with an analysis performed of clinical stigmata of their disease and headache symptomology, associations and treatment. A multivariable logistic regression analysis was undertaken to elicit independent predictors of headache.

RESULTS

37% of patients with SWS (n = 84) reported headaches that were variably associated with seizures, a preceding blow to the head and a minority had migraine features. In those reporting headaches, headaches interfered with daily activities of a quarter of the children and 39% experienced headaches frequently (more than 1/month). Headache was associated with glaucoma and aspirin administration while children with monoplegia and hemiplegia were less likely to have headache.

CONCLUSIONS

Headache is common in children with SWS, often without classical migraine features and affects daily activities. Awareness of headache and its associations in SWS may improve management of this complex population.

Cognitive impairment in temporal lobe epilepsy: role of online and offline processing of single cell information

Cognitive impairment is a common comorbidity in temporal lobe epilepsy (TLE) and is often considered more detrimental to quality of life than seizures. While it has been previously shown that the encoding of memory during behavior is impaired in the pilocarpine model of TLE in rats, how this information is consolidated during the subsequent sleep period remains unknown. In this study, we first report marked deficits in spatial memory performance and severe cell loss in the CA1 layer of the hippocampus lower spatial coherence of firing in TLE rats. We then present the first evidence that the reactivation of behavior-driven patterns of activity of CA1 place cells in the hippocampus is intact in TLE rats. Using a template-matching method, we discovered that real-time (3-5 s) reactivation structure was intact in TLE rats. Furthermore, we estimated the entropy rate of short time scale (∼250 ms) bursting activity using block entropies and found that significant, extended temporal correlations exist in both TLE and control rats. Fitting a first-order Markov Chain model to these bursting time series, we found that long sequences derived from behavior were significantly enriched in the Markov model over corresponding models fit on randomized data confirming the presence of replay in shorter time scales. We propose that the persistent consolidation of poor spatial information in both real time and during bursting activity may contribute to memory impairments in TLE rats.

Dexamethasone exacerbates cerebral edema and brain injury following lithium-pilocarpine induced status epilepticus

Anti-inflammatory therapies are the current most plausible drug candidates for anti-epileptogenesis and neuroprotection following prolonged seizures. Given that vasogenic edema is widely considered to be detrimental for outcome following status epilepticus, the anti-inflammatory agent dexamethasone is sometimes used in clinic for alleviating cerebral edema. In this study we perform longitudinal magnetic resonance imaging in order to assess the contribution of dexamethasone on cerebral edema and subsequent neuroprotection following status epilepticus. Lithium-pilocarpine was used to induce status epilepticus in rats. Following status epilepticus, rats were either post-treated with saline or with dexamethasone sodium phosphate (10 mg/kg or 2 mg/kg). Brain edema was assessed by means of magnetic resonance imaging (T₂ relaxometry) and hippocampal volumetry was used as a marker of neuronal injury. T₂ relaxometry was performed prior to, 48 h and 96 h following status epilepticus. Volume measurements were performed between 18 and 21 days after status epilepticus. Unexpectedly, cerebral edema was worse in rats that were treated with dexamethasone compared to controls. Furthermore, dexamethasone treated rats had lower hippocampal volumes compared to controls 3 weeks after the initial insult. The T₂ measurements at 2 days and 4 days in the hippocampus correlated with hippocampal volumes at 3 weeks. Finally, the mortality rate in the first week following status epilepticus increased from 14% in untreated rats to 33% and 46% in rats treated with 2 mg/kg and 10 mg/kg dexamethasone respectively. These findings suggest that dexamethasone can exacerbate the acute cerebral edema and brain injury associated with status epilepticus.

•

Dexamethasone given following seizures caused a worsening of edema and brain injury.

•

This finding also applied to doses dexamethasone as low as 2 mg/kg.

•

We show the use of automated hippocampal volume measurement for therapy monitoring.

Prolonged febrile seizures cause reversible reductions in white matter integrity

Prolonged febrile seizures (PFS) are the commonest cause of childhood status epilepticus and are believed to carry a risk of neuronal damage, in particular to the mesial temporal lobe. This study was designed to determine: i) the effect of prolonged febrile seizures on white matter and ii) the temporal evolution of any changes seen.

33 children were recruited 1 month following PFS and underwent diffusion tensor imaging (DTI) with repeat imaging at 6 and 12 months after the original episode of PFS. 18 age-matched healthy control subjects underwent similar investigations at a single time point. Tract-based spatial statistics (TBSS) was used to compare fractional anisotropy (FA), mean diffusivity (MD), axial diffusivity (AD) and radial diffusivity (RD) between patients and controls on a voxel-wise basis within the white matter skeleton.

Widespread reductions in FA along multiple white matter tracts were found at 1 and 6 months post-PFS, but these had resolved at 12 months. At one month post-PFS the main changes seen were reductions in AD but at 6 months these had predominantly changed to increases in RD.

These widespread white matter changes have not previously been noted following PFS. There are many possible explanations, but one plausible hypothesis is that this represents a temporary halting of normal white matter development caused by the seizure, that then resumes and normalises in the majority of children.

•

Widespread reductions in FA occur in children after prolonged febrile seizures.

•

These reductions persist up to 6 months post-PFS but resolve by 1 year.

•

This may represent a seizure-related disruption of white matter development.

Altered short-term plasticity in the prefrontal cortex after early life seizures

Seizures during development are a relatively common occurrence and are often associated with poor cognitive outcomes. Recent studies show that early life seizures alter the function of various brain structures and have long-term consequences on seizure susceptibility and behavioral regulation. While many neocortical functions could be disrupted by epileptic seizures, we have concentrated on studying the prefrontal cortex (PFC) as disturbance of PFC functions is involved in numerous co-morbid disorders associated with epilepsy. In the present work we report an alteration of short-term plasticity in the PFC in rats that have experienced early life seizures. The most robust alteration occurs in the layer II/III to layer V network of neurons. However short-term plasticity of layer V to layer V network was also affected, indicating that the PFC function is broadly influenced by early life seizures. These data strongly suggest that repetitive seizures early in development cause substantial alteration in PFC function, which may be an important component underlying cognitive deficits in individuals with a history of seizures during development.

Statin-induced myopathy in the rat: relationship between systemic exposure, muscle exposure and myopathy

Rare instances of myopathy are associated with all statins, but cerivastatin was withdrawn from clinical use due to a greater incidence of myopathy. The mechanism of statin-induced myopathy with respect to tissue disposition was investigated by measuring the systemic, hepatic, and skeletal muscle exposure of cerivastatin, rosuvastatin, and simvastatin in rats before and after muscle damage. The development of myopathy was not associated with the accumulation of statins in skeletal muscle. For each statin exposure was equivalent in muscles irrespective of their fibre-type sensitivity to myopathy. The low amount of each statin in skeletal muscle relative to the liver does not support a significant role for transporters in the disposition of statins in skeletal muscle. Finally, the concentration of cerivastatin necessary to cause necrosis in skeletal muscle was considerably lower than rosuvastatin or simvastatin, supporting the concept cerivastatin is intrinsically more myotoxic than other statins.

Childhood convulsive status epilepticus: epidemiology, management and outcome

Convulsive status epilepticus (CSE) in childhood is a medical emergency and its aetiology and outcome mean that it should be studied separately from adult CSE. The incidence in developed countries is between 17 and 23/100,000 with a higher incidence in younger children. Febrile CSE is the commonest single group with a good prognosis in sharp distinction to CSE related to central nervous system infections which have a high mortality. The aim of treatment is to intervene at 5 min and studies indicate that intravenous (i.v.) lorazepam may be a better first-line treatment than rectal diazepam and i.v. phenytoin a better second-line treatment than rectal paraldehyde. An epidemiological study strongly supports the development of prehospital treatment with buccal midazolam becoming a widely used but unlicensed option in the community. More than two doses of benzodiazepines increase the rate of respiratory depression without obvious benefit. The 1 year recurrence rate is 17% and the hospital mortality is about 3%.

Childhood convulsive status epilepticus: epidemiology, management and outcome

Convulsive status epilepticus (CSE) in childhood is a medical emergency and its aetiology and outcome mean that it should be studied separately from adult CSE. The incidence in developed countries is between 17 and 23/100,000 with a higher incidence in younger children. Febrile CSE is the commonest single group with a good prognosis in sharp distinction to CSE related to central nervous system infections which have a high mortality. The aim of treatment is to intervene at 5 min and studies indicate that intravenous (i.v.) lorazepam may be a better first-line treatment than rectal diazepam and i.v. phenytoin a better second-line treatment than rectal paraldehyde. An epidemiological study strongly supports the development of prehospital treatment with buccal midazolam becoming a widely used but unlicensed option in the community. More than two doses of benzodiazepines increase the rate of respiratory depression without obvious benefit. The 1 year recurrence rate is 17% and the hospital mortality is about 3%.

A systematic review of the epidemiology of status epilepticus

Population-based data on the incidence, aetiology, and mortality associated with status epilepticus (SE) are required to develop preventative strategies for SE. Through a systematic review, we aimed to assess the methodological quality as well as similarities, and differences between available population based studies in order to arrive at conclusions on the epidemiology of SE. All population-based studies where primary outcome was incidence, aetiology or mortality of SE were identified through a systematic search and synthesized. Methodological quality of studies were independently rated by two examiners using a unique scoring system. Seven population-based projects on SE yielding nine published reports and five abstracts were reviewed. Quality scores were in the range of 19-34 with a possible maximum of 40 (kappa scores 0.67-1.0). The incidence of SE has a bimodal distribution with peaks in children aged less than a year and the elderly. Most SE were acute symptomatic. Short-term mortality was 7.6-22% and long-term mortality was 43%. Age and aetiology were the major determinants of mortality. There are few population-based studies on SE but most are of good quality. Most studies are primarily or exclusively based on adult populations. There is limited information on the association of ethnicity and socio-economic status and SE.

Meningitis is a common cause of convulsive status epilepticus with fever

AIMS

In children with convulsive status epilepticus (CSE) with fever, to determine the likelihood of acute bacterial meningitis (ABM), the proportion that are treated with antibiotics, and the proportion that have diagnostic CSF sampling.

METHODS

Patients with an incident episode of CSE with fever were identified as part of an ongoing prospective population based study of CSE in childhood.

RESULTS

There were 49 incident cases of CSE in the first six months. Ascertainment was 96%. Twenty four had CSE with fever, 16 had early parenteral antibiotics, nine had diagnostic CSF sampling, and four had ABM. The population risk of ABM in CSE with fever was significantly higher than that of short seizures with fever (17% v 1.2%).

CONCLUSIONS

The classical symptoms and signs of ABM may be absent in CSE with fever. A high index of suspicion for ABM in the child with CSE with fever is paramount. The most appropriate management is suggested to be early parenteral antibiotics and a lumbar puncture when there are no contraindications.

Inappropriate emergency management of status epilepticus in children contributes to need for intensive care

OBJECTIVES

To characterise the clinical features, emergency pre-paediatric intensive care (PIC) treatment, and course of status epilepticus (SE) in children admitted to PIC. This may provide insight into reasons for admission to PIC and provide a framework for the development of strategies that decrease the requirement for intensive care.

DESIGN

Cross sectional, retrospective study.

SETTING

A tertiary paediatric institution's intensive care unit.

PARTICIPANTS

The admission database and all discharge summaries of each admission to a tertiary paediatric institution's PIC over a three year period were searched for children aged between 29 days and 15 years with a diagnosis of SE or related diagnoses. The case notes of potential cases of SE were systematically reviewed, and clinical and demographic data extracted using a standard data collection form.

RESULTS

Most children with SE admitted to PIC are aged less than 5 years, male to female ratio 1:1, and most (77%) will have had no previous episodes of SE. Prolonged febrile convulsions, SE related to central nervous system infection, and SE associated with epilepsy occur in similar proportions. Contrary to the Advanced Paediatric Life Support guidelines many children admitted to PIC for SE receive over two doses, or inadequate doses, of benzodiazepine. There is a risk of respiratory depression following administration of over two doses of benzodiazepine (chi2 = 3.4, p = 0.066). Children with SE admitted to PIC who had prehospital emergency treatment are more likely to receive over two doses of benzodiazepines (chi2 = 11.5, p = 0.001), and to subsequently develop respiratory insufficiency (chi2 = 6.2, p = 0.01). Mortality is low. Further study is required to determine the morbidity associated with SE in childhood requiring intensive care.

CONCLUSIONS

As the risk of respiratory depression is greater with more than two doses of benzodiazepines, clinicians should not disregard prehospital treatment of SE. As pre-PIC treatment of SE is inadequate in many cases, appropriate audit and modifications of standard guidelines are required.

Quantitative magnetic resonance characterization of mesial temporal sclerosis in childhood

OBJECTIVE

To investigate whether quantitative MR techniques can be used to distinguish between mesial temporal sclerosis in patients with a history of prolonged febrile convulsion and in patients without such a history.

METHODS

Quantitative hippocampal T2 relaxometry, hippocampal volumetry, and single voxel (1)H-MRS data were acquired from 16 children who subsequently underwent temporal lobe resections for intractable temporal lobe epilepsy and histologically were shown to have sclerosis of the horn of Ammon. Eight children had a history of prolonged febrile convulsion in early childhood and eight children had other or no associations.

RESULTS

Patients with a history of prolonged febrile convulsion had smaller hippocampi (p = 0.02) and prolonged T2 relaxation time (p = 0.03) ipsilateral to the seizure focus when compared with patients without such a history. There was also more side-to-side asymmetry of T2 relaxation time (p = 0.004) and hippocampal volume (p = 0.02) in the patients with a history of prolonged febrile convulsion than in those with other or no associations. No differences between the groups were identified using (1)H-MRS.

CONCLUSIONS

These data support the view that there are at least two types of mesial temporal sclerosis. There may be several pathogenetic pathways from initial insult to later mesial temporal sclerosis, and these pathways are, at least in part, dependent on the initial insult.

Buccal midazolam and rectal diazepam for treatment of prolonged seizures in childhood and adolescence: a randomised trial

BACKGROUND

Convulsive status epilepticus is the most common neurological medical emergency and has high morbidity and mortality. Early treatment before admission to hospital is best with an effective medication that can be administered safely. We aimed to find out whether there are differences in efficacy and adverse events between buccal administration of liquid midazolam and rectal administration of liquid diazepam in the acute treatment of seizures.

METHODS

At a residential school with on-site medical facilities 42 young people with severe epilepsy were enrolled. Continuous seizures of more than 5 min duration were randomly treated with buccal midazolam or rectal diazepam. If the seizure did not stop within 10 min additional medication chosen by the attending physician was administered. We monitored oxygen saturation and blood pressure for 30 min after treatment. The main outcome measures were efficacy, time from arrival of the nurse to drug administration, time from drug administration to end of seizure, and incidence of adverse cardiorespiratory events.

FINDINGS

Buccal midazolam was used to treat 40 seizures in 14 students, and rectal diazepam 39 seizures in 14 students. Midazolam stopped 30 (75%) of 40 seizures and diazepam 23 (59%) of 39 (p=0.16). The median time from arrival of the nurse to administration of medication was 2 min. Time from administration to end of seizure did not differ significantly between the two treatments. No clinically important adverse cardiorespiratory events were identified in the two groups. Buccal midazolam was universally acceptable to the nursing and care staff.

INTERPRETATION

Buccal midazolam is at least as effective as rectal diazepam in the acute treatment of seizures. Administration via the mouth is more socially acceptable and convenient and may become the preferred treatment for long seizures that occur outside hospital.

Developmental perspectives on epilepsy

This paper reviews current knowledge about epileptogenesis in the developing brain. Animal studies indicate that the maturational balance of excitatory and inhibitory neurotransmitter systems should result in an increased susceptibility to seizures. However, the reason for specific age-locked syndromes and the high rate of impairments secondary to early onset epilepsy remain mysterious. Present research activity is directed to prevention and amelioration of these severe cognitive and psychiatric impairments.

Buccal absorption of midazolam: pharmacokinetics and EEG pharmacodynamics

PURPOSE

To determine whether buccal/sublingual administration of midazolam (MDL) would lead to detectable venous concentrations and EEG changes in 10 healthy volunteers.

METHODS

The study consisted of an open-label and a double-blind phases. Subjects held 10 mg MDL in 2 ml peppermint-flavored fluid or peppermint-flavored placebo in their mouth for 5 min and then spat it out. Cardiorespiratory and EEG monitoring was performed in all subjects.

RESULTS

Venous MDL concentrations measured on 10 occasions from 5 to 600 min after administration showed a rapid increase for the first 20-30 min. However, changes in the 8- to 30-Hz frequencies identified by spectral analysis of the EEG showed changes in < or = 5-10 min in test but not in control subjects--more rapid than were expected from the venous absorption data. There were no significant adverse effects.

CONCLUSIONS

Our data provide direct evidence of the speed of cerebral effect of a drug. Our results suggest that the buccal/sublingual route of administration should be tested in emergency treatment of seizures as an alternative to the rectal route, over which it has clear practical advantages.

Automated grading of venous beading

The degree of venous beading in ocular fundus images has been shown to be a more powerful predictor of conversion to proliferative diabetic retinopathy than any other type of retinal abnormality. Further, the degree of venous beading has been shown to be well correlated with disease progression. An algorithm for automated grading of venous beading in digitized ocular fundus images is described. Thresholding is used to extract a rough silhouette of the vein. Morphological closing is used to fill any holes in the silhouette arising from either the central light reflex or noise. The silhouette is then "thinned" to find vein centerlines. Each centerline is partitioned into fixed-length segments of 32 pixels. Vein diameters are measured as a function of distance along each segment with the aid of the local centerline orientations. The resulting diameter data are then interpolated and resampled to generate diameter data at constant sampling intervals. A fast Fourier transform is performed on the resulting data to determine the magnitude spectrum of vein segment diameter. A venous beading index is calculated from the distribution of vein diameter frequency components. Performance of the new algorithm is compared to the currently accepted clinical practice of manual grading in a pilot clinical study of 51 subjects. The algorithm is seen to perform well.

Lansoprazole in the prophylaxis of acid aspiration during elective surgery

We have assessed the efficacy of a single dose of lansoprazole in increasing the pH and decreasing the volume of gastric residue at induction of anaesthesia in adult patients undergoing elective orthopaedic surgery. We studied 66 ASAI-II patients, allocated to one of three groups to receive either placebo (group 1), lansoprazole 30 mg (group 2) or lansoprazole 60 mg (group 3), 8-12 h before induction of anaesthesia. Volume and pH of gastric contents were measured after induction of anaesthesia by aspiration via a 16-French gauge gastric tube. Patients who received lansoprazole had a significantly higher pH than the placebo group (P < 0.01) but there was no difference between the two lansoprazole groups. The volume of gastric residue was significantly smaller (P < 0.01) in both lansoprazole groups compared with the placebo group: 28% of those in group 3 had a pH of gastric residue < 2.5 and volume > 25 ml compared with 30% in group 2 and 63% in group 1, respectively.

Vehicle effects on in vitro percutaneous absorption through rat and human skin

We studied the effects of three vehicles (propylene glycol, octanol and ethyl decanoate) with differing polarity on the in vitro percutaneous absorption of three chemicals (fluazifop-butyl, dimethyl phthalate and fomesafen sodium salt) with a range of physico-chemical properties. Absorption rate measurements were made from high vehicle volume (200 microliters/cm2) and low vehicle volume (< 10 microliters/cm2) applications. For the lipophilic fluazifop-butyl absorption rate was highest from the more polar vehicle propylene glycol, but this effect was only significant under high-volume conditions. There was a variable vehicle effect on absorption of the intermediate chemical dimethyl phthalate. The largest vehicle effect was seen for the more hydrophilic fomesafen sodium salt where absorption was fastest from the least polar vehicle ethyl decanoate. These results support the hypothesis that the absorption process can in part be predicted from a knowledge of solute solubility. Vehicle effects were greater from high volume applications than from those more comparable to occupational exposure conditions.

The predictive accuracy of in vitro measurements for the dermal absorption of a lipophilic penetrant (fluazifop-butyl) through rat and human skin

The predictive accuracy of in vitro measurements in estimating dermal absorption has been evaluated in rat and human skin using fluazifop-butyl (FB), a lipophilic model compound, at dosage rates of 2.5, 25, and 250 micrograms/cm2. In vitro studies used rat and human epidermal membranes mounted in static diffusion cells with radiolabeled FB and receptor fluids of 50% aqueous ethanol (Aq Et), 6% polyethylene glycol 20 oleyl ether in saline (PEG), or tissue culture medium (TCM). In vivo rat studies with radiolabeled FB were carried out to parallel previously published human volunteer studies. For rat skin, in vitro measurements with all types of receptor fluid provide an adequate prediction (generally within a factor of 3) of in vivo absorption. Absorption data for human epidermal membranes with a receptor fluid of Aq Et were adequately predictive of the in vivo absorption. In contrast, membranes with PEG or TCM significantly underestimated the in vivo absorption. The results support the conclusion that in vitro studies are useful to predict in vivo dermal absorption in rat and man, when appropriate receptor fluids are used.

A physiologically based mathematical model of dermal absorption in man

A sound understanding of the mechanisms determining percutaneous absorption is necessary for toxicological risk assessment of chemicals contacting the skin. As part of a programme investigating these mechanisms we have developed a physiologically based mathematical model. The structure of the model parallels the multi-layer structure of the skin, with separate surface, stratum corneum and viable tissue layers. It simulates the effects of partitioning and diffusive transport between the sub-layers, and metabolism in the viable epidermis. In addition the model describes removal processes on the surface of the skin, including the effects of washing and desquamation, and rubbing off onto clothing. This model is applied to data on the penetration of the herbicide fluazifop-butyl through human skin in vivo and in vitro. Part of this dataset is used to estimate unknown model parameter values and the remainder is used to provide a partial validation of the model. Only a small fraction of the applied dose was absorbed through the skin; most of it was removed by washing or onto clothing. The model provides a quantitative description of these loss processes on the skin surface.

Methods for measuring dermal penetration of pesticides

The quantitation of percutaneous absorption of pesticides is required as part of the registration, re-registration or hazard assessment process. There is a paucity of regulatory guidelines in this area. This paper presents three protocols that can be used to quantitate percutaneous absorption, primarily as a result of continuous skin exposure over a period equivalent to a working day (8 hr). A rat in vivo protocol, an in vitro protocol and a human in vivo protocol are described. None of these protocols is considered to be ideal and/or to represent a preferred method. The final choice of protocol must take into account the toxicity and physicochemical properties of the test molecule as well as cost and resource/technical ability. Nevertheless, the protocols described allow percutaneous absorption to be quantitated, and it is believed that, if adopted, they will prove useful in the regulatory and research areas for the acquisition of data under standard defined conditions.

Catheterization of posterior tibial artery leading to limb amputation

A cannula inserted into the posterior tibial artery of a preterm infant resulted in irreversible ischaemia of the foot with proximal extension to involve the lower leg. No predisposition to thrombosis was found and a below-knee amputation was ultimately required.

Influence of sodium lauryl sulphate on 2,4-dinitrochlorobenzene-induced lymph node activation

The influence of the anionic surfactant sodium lauryl sulphate (SLS) on the ability of the contact allergen 2,4-dinitrochlorobenzene (DNCB) to provoke draining lymph node cell proliferative responses, a correlate of skin sensitizing potential, has been examined in mice. Topical application of 10% SLS with 0.1% DNCB caused a more vigorous proliferative response than did exposure to 0.1% DNCB alone. Lower concentrations (0.1% or 1%) of SLS were ineffective and 10% SLS failed to influence proliferative responses to higher concentrations (0.5% or 1%) of DNCB. Using an in vitro model for measurement of percutaneous absorption 10% SLS was shown not to increase the skin penetration of 0.1% DNCB. We therefore examined the influence of SLS on the accumulation of dendritic cells (DC) in lymph nodes draining the site of exposure, an important early event during the induction phase of skin sensitization. The frequency of DC in draining nodes was measured following topical application of SLS, DNCB or a combination of both. Epicutaneous exposure to 0.1% DNCB caused only a modest increase in the number of lymph node DC. However, 10% SLS or a mixture of 10% SLS with 0.1% DNCB each resulted in a significant elevation of DC numbers. It is proposed that SLS augments the skin sensitizing potential of sub-irritant concentrations of DNCB via an increase in the number of immunostimulatory DC which reach the draining nodes.

Fate of fluazifop butyl in rat and human skin in vitro

Enzyme mediated hydrolysis of fluazifop butyl has been measured with rat and human skin post-mitochondrial fractions. Rat skin had a ten times greater capacity to metabolise fluazifop butyl than human skin, but the enzyme affinities were similar. The post-mitochondrial fraction metabolism was compared to that seen during absorption in a flow through diffusion cell with viable skin. Limited hydrolysis of absorbed fluazifop butyl was seen in rat skin, but increased two fold if the stratum corneum was removed. The stratum corneum was found to retain fluazifop butyl. When the skin was pre-incubated with the esterase inhibitor bis (p-nitrophenol) phosphate (BNPP), reduced metabolism was seen. No metabolism of fluazifop butyl was seen in human skin during absorption. Retention of the compound by the stratum corneum is postulated to restrict the accessibility of the compound to the enzyme site, thus influencing the observed metabolism during the absorption process.

Pig ear skin as an in-vitro model for human skin permeability

Pig skin has been shown to have similar histological and physiological properties to human skin and has been suggested as a good model for human skin permeability. In this series of experiments, the in-vitro permeability of pig ear skin was compared with human (abdominal) skin and rat (dorsal) skin using both hydrophilic (water, mannitol, paraquat) and lipophilic (aldrin, carbaryl, fluazifop-butyl) penetrants. Pig skin was found to have a closer permeability character than rat skin to human skin, particularly for lipophilic penetrants. Electrical conductivity measurements across pig skin membranes showed that skin conductivity could be a useful method for assessing the integrity of membranes, particularly when used in conjunction with water permeability assessments.

Further validation of an in vitro method to reduce the need for in vivo studies for measuring the absorption of chemicals through rat skin

Current requirements for the registration of agrochemicals, particularly in the U.S.A., often require the provision of dermal absorption data. In this process the rat is often used and complex in vivo studies, using large numbers of animals, are performed. We have compared the data obtained from in vivo and in vitro dermal absorption studies using eight pesticides with a range of physicochemical properties. Measurements were made of the 14C-labeled pesticides which could be washed from the skin, were associated with (on/in) skin, or absorbed through the skin following dermal applications in vivo and in vitro at various time points over a 24-hr exposure period. Good agreement was found between the amounts washed from and associated with the skin in vivo and in vitro. Over the time period 4-24 hr after application the in vitro experiments predicted the in vivo absorption within a factor of 2-3. These results show that, with a range of pesticide molecules, the in vitro method accurately predicted in vivo absorption supporting the utilization of the in vitro method for risk assessment from exposure to pesticides and other chemicals.

Decreased low-density lipoprotein receptor function and mRNA levels in lymphocytes from uremic patients

The mechanisms by which renal failure causes hyperlipoproteinemia remain unclear. To investigate the potential role of the low-density lipoprotein (LDL) receptor in lipoprotein metabolism in uremia we measured LDL receptor function in peripheral blood mononuclear cells (PBMC) from uremic patients and control subjects using a functional assay in which proliferation of lectin-stimulated PBMC in the presence of lovastatin was dependent upon internalization of exogenous cholesterol via a functional LDL receptor. The amount of LDL required to reverse 50% of lovastatin-induced inhibition of proliferation in PBMC from uremic patients was significantly greater (3.6 +/- 1.8 micrograms/ml, N = 33, P < 0.05) than controls, (1.99 +/- 0.6 micrograms/ml, N = 37). Abnormal LDL receptor function in four uremic patients normalized following renal transplantation. To investigate the molecular basis for LDL receptor dysfunction, we directly quantitated LDL receptor messenger RNA (mRNA) in PBMC from uremic patients and control subjects using a ribonuclease protection assay. LDL receptor mRNA expression in uremic patients was 0.42 +/- 0.08 (N = 10), significantly lower (P < 0.015) than in normal subjects, 0.71 +/- 0.08 (N = 14). These data suggest that an acquired defect in LDL receptor function in PBMC from uremic patients exists which may be due to decreased LDL receptor expression. These abnormalities, if present in other tissues, could contribute to the aberrant lipoprotein metabolism which is a consistent feature of uremia.

Automated detection and quantification of venous beading using Fourier analysis

Venous beading associated with diabetic retinopathy is currently assessed by means of subjective comparison to standard photographs from the modified Airlie House classification scheme. We describe a computerized grading scheme for venous beading. The algorithm, based on Fourier analysis of vessel width measurements, generates a venous beading index (VBI) for digitized colour fundus photographs. Colour photographs of local vessel segments about 1200 microns in length were evaluated by experienced graders. A comparison between the VBI and subjective grading showed good agreement. The mean VBI values across the four levels of clinical grading were significantly different (p = 0.000). Multiple comparison testing indicated that the VBI was able to significantly differentiate between all four categories except the "questionable" (grade 1) category (p < 0.05). We also found that progression of venous beading can be followed with the VBI. The results indicate that further development of automated grading of venous beading is warranted.

The influence of different strains and age on in vitro rat skin permeability to water and mannitol

Water and mannitol were used as test penetrants to study the effect of age on the skin permeability of the Wistar-derived Alderley Park (AP) rat and Sprague-Dawley (SD) rat. Whole-skin membranes were prepared from rats aged 10 to 120 days, while epidermal membranes were prepared from rats aged 24 to 32 days. The results indicated that the skin permeabilities of the two strains were very similar for either whole-skin or epidermal membranes. The influence of age on skin permeability was found to be negligible for the AP rat, and a small decrease in whole-skin permeability was observed for SD rats above 80 days of age. A statistically derived expression ("the separation efficiency factor") was used to determine the optimum age for preparing intact epidermal membranes; these were 26 days for AP rats and 28 days for SD rats. Histological examination of whole-skin membranes for both strains revealed that the stratum corneum and epidermal thickness did not alter significantly with age (10 to 120 days old). Dermal thickness, hair follicle depth, and, to a lesser extent, the surface area occupied by hair follicles all appeared to be influenced by age, although these changes had no detectable effect on skin permeability.

Percutaneous absorption and metabolism of aldrin by rat skin in diffusion cells

Using a static diffusion cell with varying receptor fluids the viability of isolated rat skin mounted as whole skin or as split thickness skin has been studied. Skin viability decreased with time with phosphate buffer or Eagles MEM and was not supported with ethanol/water as the receptor fluid. The pesticide aldrin was absorbed through the skin into ethanol/water but not the aqueous receptor fluids. With viable skin preparations aldrin was metabolised to dieldrin and absorbed aldrin and the metabolite remained in the skin. Viable skin preparations must be used to assess in vitro, the degree of metabolism of xenobiotics which occurs during percutaneous absorption.

Fate of carbaryl in rat skin

Metabolism of carbaryl by rat liver and skin post-mitochondrial fraction has been measured in the presence and absence of cofactors to promote different metabolic pathways. The metabolic capacity was compared with the metabolism of carbaryl during percutaneous absorption in a static skin diffusion system using a variety of receptor fluids. Carbaryl was metabolised by hydrolysis, and ring hydroxylation followed by conjugation to the glucuronide or sulphate with liver post-mitochondrial fraction. Using skin post-mitochondrial fraction only hydrolysis and conjugation were detected. No metabolism was seen during percutaneous absorption in vitro even with receptor fluids which maintain the skin tissue viability. Studies using post-mitochondrial fraction indicate the metabolic capacity of the tissue, whereas during absorption, rates of absorption and accessibility of substrate to the metabolising enzymes must be considered.