Characterization of large-pore polymeric supports for use in perfusion biochromatography

Perfusion chromatography is uniquely characterized by the flow of a portion of the column eluent directly through the resin in the packed bed. The benefits of this phenomenon and some of the properties of perfusive resins have been described before, and can be summarized as enhanced mass transport to interior binding sites. Here we extend the understanding of this phenomenon by comparing resins with different pore size distributions. Resins are chosen to give approximately the same specific pore volumes (as shown in the characterization section) but the varying contribution of large pores is used to control the amount of liquid flowing through the beads. POROS R1 has the largest contribution of throughpores, and therefore the greatest intraparticle flow. POROS R2 has a lower contribution of throughpores, and a higher surface area coming from a greater population of diffusive pores, but still shows significant mass transport enhancements relative to a purely diffusive control. Oligo R3 is dominated by a high population of diffusive pores, and is used comparatively as a non-perfusive resin. Although the pore size distribution can be engineered to control mass transport rates, the resulting surface area is not the only means by which binding capacity can be controlled. Surface coatings are employed to increase binding capacity without fundamentally altering the mass transport properties. Models are used to describe the amount of flow transecting the beads, and comparisons of coated resins to uncoated (polystyrene) resins leads to the conclusion that these coatings do not obstruct the throughpore structures. This is an important conclusion since the binding capacity of the coated product, in some cases, is shown to be over 10-fold higher than the precursor polystyrene scaffold (i.e., POROS R1 or POROS R2).

Accelerated recombinant protein purification process development automated, robotics-based integration of chromatographic purification and analysis

Recovery of recombinant proteins from endogenous, host molecules can be an experimentally intensive and time-consuming task. Often the time to analyze material during development of recovery procedures is the rate-limiting step. Nowadays, modern techniques and equipment are being specifically engineered to make this effort much more efficient. We present a case study to illustrate how a new, automation tool, designed for easy, systematic methods development, can be used for very rapid process and analytical optimization. This tool uses robotics to integrate process development with rapid LC-based analysis requiring no user intervention. The methods and procedures described can be generalized to any recombinant protein recovery campaign.

Colour blindness

The physiology of colour vision is discussed; as is the way in which the human eye can detect various combinations of red, green and blue. Red-green colour blindness, with X-linked inheritance, is the most common, but other types are also considered. Methods of testing relating to the age of the child are reviewed. The use of colours in teaching is widespread, but there is controversy over the difficulties this may cause a colour blind child. A review of the literature does not reveal much information on this, and any problems that do arise are likely to be individual to the child, and to depend on such factors as overall intelligence, the attitude of the teacher, and the personality of the child. There is not doubt that it is essential to recognise colour vision defects when it comes to choosing a career, and that tests must be done during secondary schooling, but in order to avoid some affected children being disadvantaged there is enough evidence to support testing at school entry.

Episodic ataxia and channelopathies

Clinical details are given of different types of episodic ataxia: type 1, with myokymia, and attacks which usually last a few minutes, and may occur several times a day, and treatment with acetazolamide can reduce the number of attacks; type 2, with interictal nystagmus, and attacks which last for several hours to a day or more, and treatment with acetazolamide is very effective; paroxysmal choreoathetosis with episodic ataxia, with attacks lasting for about 20 min and occurring at varying intervals; and familial hemiplegic migraine, with transient hemiplegia presenting during the aura of a migraine headache, the symptoms improving on treatment with acetazolamide. Their inheritance is of dominant type; and the gene for type 1 is mapped to chromosome 12p near to a cluster of potassium channel genes, and that for type 2 and for familial hemiplegic migraine to chromosome 19p near to calcium channel genes. The differential diagnosis from other conditions with a periodic symptomatology is discussed, especially from a number of metabolic disorders. Treatment is effective for many of these, and the treatment of the episodic ataxias with acetazolamide can sometimes have a dramatic effect. The possible role of the channelopathies in the causation of some periodic neurological disorders is considered; with the expectation that further research will improve the identification of specific diseases, and lead to more effective treatment.

Some influences on cognition in early life: a short review of recent opinions

Many factors can affect a child's ability to learn, and these may operate before, during, and after birth. Some of these are considered, and are hopefully important, but not necessarily the most obvious. The intrauterine environment may not be so influential as the infant's genetic endowment, but nevertheless is of considerable importance. For example, malnutrition resulting from placental insufficiency leading to small-for-date babies can impair brain development. Also a relationship between birth weight and cognitive function in early adult life has been demonstrated; and the babies' condition at birth can be a risk factor for various disabilities. Lack of stimulation in infancy, for example if postnatal depression interferes with the mother's interaction with her baby, can significantly affect the infant's learning capacity. A good paradigm is the development of language, which starts with the way mothers 'talk' to their babies; and this continues into childhood. The importance of nutrition also continues, and is one of the factors which favours breast feeding against formula foods. The whole subject has to be viewed against the background of normal development, and the great loss of neurons and synapses that occur in early life. If neural circuits are formed at this time, and these neurons and synapses are not lost, the easier it will be to exploit them. This emphasizes the importance of early education, which is not always sufficiently acknowledged.

The Landau-Kleffner syndrome: increased understanding

The Landau-Kleffner and the continuous spike and wave discharges during slow sleep (CSWS) syndromes are described and possible links between the two are discussed. They certainly overlap, with clinical and electroencephalographic features in common. Potential causes are discussed. There is seldom a definite reason for the seizures but it way well be that the spike and wave discharges seen in the EEG, whatever their origin, may disrupt the development of language and cognitive function at a critical stage. If neurons and axons are involved in this disorganized activity they surely cannot perform normally. The evidence that these discharges in the Landau-Kleffner syndrome can have a focal origin in areas important for language supports this hypothesis. Certain variations among studies quoted may be due to factors such as age of onset, the duration of the paroxysmal activity, its intensity and especially its localization. Also, if development has been distorted subsequent progress is likely to be disturbed after the primary condition has ceased to exist. The diagnosis can sometimes present difficulties, for example from deafness, psychiatric condition, post-ical dysphasia and from progressive degenerative neurological disorders. If the possible role of the epileptic activity is accepted, there are strong reasons for advocating anti-epileptic treatment, even if overt seizures are rare. The response to drugs is varied. Fits will usually stop, but not so often the spike and wave discharges, and it is justifiable to try various regimes. Subpial resection has been reported to be successful, possibly by preventing the cortex generating seizures, and their spread.

Nutrition and cognitive function

The work of the Medical Research Council Dunn Nutrition Unit, Cambridge, on the influence of early diet on the development of preterm infants is reviewed. Then further consideration is given to the implication of the findings. Malnutrition during a sensitive period may result in disease in adult life, and studies strongly suggest the development of the brain and retina can be affected. This may be due to the lack of essential fatty acids, and will particularly involve premature babies born at a time when cell membrane development is especially vulnerable. These findings must sometimes be viewed with caution, as genetic and environmental influences can be paramount. There are many reasons to favour breast feeding, rather than giving formula feeds, including improved cognition and visual function. For example breast milk contains docosahexaenoic acid and arachidonic acid, essential for normal brain development, and often absent or in short supply in formula feeds. Although the advantages in developmental status may be due, in part anyhow, to factors such as the mother's ability and education, and to the child being given greater opportunities, the evident importance of the composition of human breast milk cannot be denied. Formula feeds do contain a higher nutrient value than breast milk, which can result in improved height and weight of infants fed in this way: if it is necessary to use them the challenge for future research is to improve their composition. Although this may be of more importance for premature babies, term babies can also be affected; this has both medical and social implications.

Multidimensional chromatography coupled with mass spectrometry for target-based screening

The synthesis of structural analogs and the process of drug discovery have evolved dramatically through recent advances in solid-phase synthesis reagents and automated screening systems. As molecular diversity strategies emerge, the need for automated target-based selection of lead candidates becomes equally important. Multidimensional automated chromatographic techniques coupled to electrospray ionization mass spectrometry facilitate the selection process and provide maximum characterization information in a single screening run. The capture of tightly bound affinity leads by target biomolecules, followed by subsequent release and high-resolution separation with sensitive detection, significantly reduces the time required to identify and characterize lead compounds. This automated multidimensional chromatographic approach coupled with mass spectrometry, Selectronics, was used with several organic and natural libraries to demonstrate an automated target-based screening technique to select for high-affinity binders as potential lead compounds.

Reflex sympathetic dystrophy

Reflex sympathetic dystrophy presents with pain out of proportion to the cause, loss of function, and significant evidence of an autonomic disorder. These findings are often accompanied by psychological disturbances, which can dominate the condition. There are differences in the symptoms and signs during childhood. It is more frequent among girls than boys, and the legs are more often affected than the arms; and trophic changes may be absent. There may be no history of trauma, and the response to treatment is often satisfactory. There are a number of theories on etiology. A disorder of the sympathetic nervous system with increased activity has been suggested, but on the evidence available super-sensitivity to neurotransmitters is more likely. Also there may be a spinal, as well as a peripheral, component to the sensitivity. Other suggestions include the release of a pain substance, a disturbance of natural opioid metabolism, and an exaggerated inflammatory response. The diagnosis is mainly clinical, supported by X-ray examination, bone scans with Technetium 99m labelled diphosphonates, and a characteristic scintograph pattern. Laser Doppler flowmetry can also, be useful. The most effective preventative measure is control of pain and early mobilisation. Many treatments have been tried, but the response is variable. Drugs include analgesics, non-steroid anti-inflammatory drugs, anti-depressants, and steroids. Betablockers, with gradually increasing doses may help; as may vasodilators. Calcitonin, by intramuscular injection has been given a particularly favourable report. Physiotherapy is of prime importance. Some treatments are only likely to be considered in older children. Blocking of sympathetic pathways can be tried with paravertebral or epidural injections of local anesthetics. Regional intravenous injections of alpha adrenergic blocking agents distal to a tourniquet can relieve pain, but usually only transiently; and ketanserin may act favourably as a serotonin antagonist. Surgical sympathectomy can also be considered.

Heterotopic pregnancy after ovulation induction and assisted reproductive technologies: a literature review from 1971 to 1993

OBJECTIVE

To review and analyze records on heterotopic pregnancy occurring after ovulation induction and assisted reproductive technologies.

DATA IDENTIFICATION

Case reports in the English literature related to the topic were identified through a computerized bibliography search up to December 1993.

CONCLUSIONS

The incidence of heterotopic pregnancies increased in recent years because of the escalating use of new reproductive technologies in infertile patients and has stabilized at approximately 1:100 pregnancies with these procedures. The main reasons for development of such a condition in these patients are past tubal or pelvic disease and multiple ovulations or multiple ET. Progress has been made in diagnosis of heterotopic pregnancy during the last two decades, mainly because of development of ultrasonographic techniques, especially transvaginal ultrasonography. Treatment of heterotopic pregnancy should be prompt to avoid maternal morbidity and mortality from extensive intraperitoneal bleeding. No increased intrauterine fetal mortality due to hemoperitoneum has been proven in the present review, except in advanced cornual pregnancies. More experience is needed for application of new treatment modalities such as salpingocentesis, which are used successfully for ectopic pregnancy, in treatment of heterotopic pregnancy. With early diagnosis and skillful treatment, the outcome of the intrauterine pregnancy is favorable and its survival rate should increase in the future.

Medication misadventures resulting in emergency department visits at and HMO medical center

Medication misadventures resulting in visits to the emergency department of a health maintenance organization (HMO) were studied. The records of patients who visited the emergency department at a California HMO between August 1992 and August 1993 were evaluated for evidence of medication misadventures brought to the department. The definition of misadventure included noncompliance and inappropriate prescribing but excluded intentional overdoses and substance abuse. If it seemed probable that a misadventure occurred, a pharmacist interviewed the patient by telephone. During the 12-month study, 1,074 (1.7%) of 62,216 visits to the emergency department were due to medication misadventures. The patients who had had a misadventure were predominantly female (62%); 38% were 15-44 years of age and 33% were 65 or older. Interviews were possible with 962 patients. Only 30.6% of the patients had a good understanding of the potential adverse effects of their regimen, and only 29.0% had a good understanding of the potential interactions. Misadventures were most often due to allergies or medication underuse among patients < or = 14 years of age and to adverse effects and inappropriate dosage in elderly patients. Of the 1,074 misadventures, 152 (14.1%) resulted in hospital admission. Three areas of particular concern were identified (1) noncompliance with respiratory agents in the young, (2) nonsteroidal anti-inflammatory use leading to hospital admission, and (3) the frequency of problems in the elderly. Medication misadventures accounted for 1.7% of emergency department visits and 1.0% of hospital admissions at an HMO medical center.

Benign paroxysmal positional vertigo

Benign paroxysmal positional vertigo should be considered when a patient complains of attacks of dizziness of brief duration, that seem to occur under particular circumstances related to the position of the head. The true nature of the disorder may be missed unless examination is carried out in a certain way: the head must be positioned below the rest of the body and turned to one or other side. Diagnosis then depends on the occurrence of vertigo and on noting the transient nystagmus. There are a number of causes of benign paroxysmal positional vertigo-head injury is a relatively frequent one. It has been suggested that this disorder is due to deposits on the cupula of the precipitating posterior semicircular canal. Indeed, exercises designed to dislodge such deposits can be successful. If not, and the vertigo lasts for more than a few months, surgery can be considered.

Monoclonal B-cell population mimicking lymphoma in a patient with multiple sclerosis

BACKGROUND

Diagnosis of intraparenchymal brain lesions has usually required invasive diagnostic procedures, because too few cells are shed into cerebrospinal fluid to permit cytologic diagnosis. Polymerase chain reaction technology makes it possible to identify cell populations that are present at a much lower frequency than traditional techniques.

CASE REPORT

A young woman presented with multiple brain lesions raised the question of primary central nervous system lymphoma. Polymerase chain reaction analysis of cerebrospinal fluid showed evidence of a monoclonal B-cell population heightening suspicion of lymphoma. Brain biopsy showed acute demyelination most consistent with multiple sclerosis.

CONCLUSION

Although T-cell restriction has been demonstrated in multiple sclerosis lesions, the finding of a monoclonal B-cell population was unexpected and to our knowledge has not been previously reported. This case emphasizes that monoclonality is not always indicative of a neoplastic process, particularly in the central nervous system.

Speech, language, and the cerebellum

The cerebellum can affect speech and language in a number of ways. The most obvious is dysarthria when motor movements are deprived of the regulatory control, which is one of the main functions of the cerebellum. Less well-known is cerebellar mutism, which most often occurs after the removal of a cerebellar tumour. It is unlikely that this is simply the result of dysarthria. The most controversial aspect of cerebellar function, and the main stress of this paper, is the contribution it may make to language production. A number of studies have suggested that the cerebellum can, indeed, be involved in both cognition and language. A number of these are reviewed, in particular, the results of diffuse and focal lesions of the cerebellum, and how these can affect the function of the cerebrum; and conversely how cerebral lesions can cause changes in the cerebellum. Positron emission tomography (PET) has been essential in the assessment of these patients. During human evolution parts of the cerebellum and their connections have enlarged enormously, and it would be surprising if these parts of the brain had not taken on new roles. To regard the cerebellum as only serving motor function is too narrow a concept.

Undescended testes: screening and early operation

The prevalence of undescended testes at birth, or cryptorchidism, is about 2-3%--higher among premature babies. Associated complications include infertility and malignancy, and a number of studies have shown that UK screening programs to date--the examinations carried out by the community services, for example--have failed to identify cryptorchidism at an early age in many cases. If complications, particularly infertility, are to be avoided, operations on undescended testes should be done before the age of two; at this age, operation may also be less disturbing for the patient. The cause of maldescent of the testes is uncertain, but there are related conditions, including exposure to oestrogens in the first trimester, and low birth weight: these need to be considered as they influence management.