Day: 03/25/2011

Rats wake up for behavioural research

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Tiny imaging device allows scans of animals while they are awake.

RatCAP
The RatCAP scanner allows researchers to study neurochemistry and behaviour at the same time.

A miniaturized positron emission tomography (PET) scanner has opened a fresh window for research into behaviour and brain function simultaneously.

The ‘wearable’ PET, known as the RatCAP, was developed by a team of researchers led by physicist Paul Vaska at Brookhaven National Laboratory in Upton, New York, and allows scans on animals that are awake and moving around. The findings are published online today in Nature Methods1.

PET uses radioactive tracers to show the metabolism of chemicals in the body in real time. It is a key tool for examining organ function, evaluating blood flow, diagnosing cancer early and researching neurological conditions from Alzheimer’s disease to epilepsy. But PET use for behavioural research in animals has been limited — whereas humans can lie still during a PET scan, enabling analysis while they are awake, it is a lot trickier to get animals to do as they’re told. That largely limits the use of PET to anaesthetized animals, ruling out simultaneous behavioural studies.

The tiny PET developed by the team attaches to the rat’s head using a bracket screwed onto the skull, has an inner diameter of 38 mm and weighs just 250 g. For a rat, that is still pretty heavy — nearly the weight of an adult male rat — so to optimize the rat’s movement while wearing the RatCAP, the team attached the device to a system of long springs and motion stabilisers fastened to the top of the observation chamber to reduce the weight and allow rat movement.

Using the portable PET, the rat can only move in a complete circle in one direction before having to turn back the other way, says Daniela Schulz, a behavioural neuroscientist at Brookhaven and first author on the study. “That creates some limitation in terms of where the animal can go,” she says, but adds that the rats can still move to all parts of the 40 x 40 cm observation chamber.

Jeff Dalley, a behavioural neuroscientist at the University of Cambridge, UK, applauds the development of the RatCAP. Other techniques to simultaneously track brain function and behaviour, such as the more invasive in vivo microdialysis, which involves inserting a probe into brain tissue, are limited to small regions of the brain. By contrast, he says, the RatCAP enables researchers to “look globally across the brain”.

Still, Dalley expresses some concern over how much the shape and weight of the device might undermine its use for certain experiments — such as those that involve nose-poking into narrow spaces in search of food rewards. “This is very exciting,” he says, but adds that, “In its present format it would be challenging to use in behaviourally demanding experiments.”

Up to the minute

For the initial RatCAP tests, the researchers assessed levels of the neurotransmitter dopamine by using a radiotracer to track receptor occupancy among D2 dopamine receptors in the brain. They chose to assess dopamine because of its association with a range of brain functions that can be reflected in behaviour, from motor control to reward processing. The team analysed receptor occupancy in different brain areas — in both the striatum, which has many D2-specific receptors, and as a control, in the cerebellum, which has none. Vaska and colleagues compared dopamine levels in anaesthetized rats using conventional PET with those in awake rats using the RatCAP, and found differences — unexpectedly in both the striatum and cerebellum. What’s more, they noted that, counterintuitively, dopamine levels in the awake rats were lower. Traditionally, more behavioural activity would be associated with higher levels of dopamine. The researchers speculate that the possible reason for the unexpected changes in tracer uptake in the cerebellum, and the inverse relationship between dopamine levels and behavioural activity in awake rats may indicate that anaesthesia influences uptake, perhaps by affecting metabolism of the tracer.

“It’s a methodological issue,” says Vaska, and one that could have implications for future PET research. “If you start to make assumptions that what you’re seeing under anaesthesia is what you’ll see awake, you may make a mistake in your interpretation.”

The researchers also noted a strong correlation between the extent of behavioural activity — such as head turns and body motion — and dopamine levels, an indication that the technique uniquely enables them to assess neurochemistry and behaviour simultaneously. What’s more, Vaska and colleagues were particularly encouraged to find that in one experiment, they were able to monitor behavioural changes and associated alterations in dopamine levels on a minute to minute basis — a significant achievement considering that currently, PET studies tend to average changes in biochemistry over the course of a half hour- to hour-long scan.

Luc Zimmer, a neuropharmacologist at the University of Lyon, France, who was not involved in the research, says that they technology should be of interest to “a broad range” of researchers. “The current results presented in this article are convincing. The researchers present a real proof of concept of their RatCAP device,” Zimmer says.

As a next step, they aim to use the RatCAP to observe changes in dopamine levels during other types of behaviour, but suggest that the technology will have broader applications for behavioural studies using a range of radiotracers to track different neurotransmitters.

“The advantage of being able to correlate behaviour and neurochemistry is far-reaching,” says Schulz. “We do lose a lot of information by looking at them separately. To be able to analyse both processes simultaneously would allow us very different insight.”

source: nature

Inspirational Chemistry

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Throughout 2011, nations are celebrating the International Year of Chemistry. This worldwide recognition of the importance of chemistry is somewhat unusual. It is true that chemistry has been called “the central science,” not only by chemists but even in Wikipedia (of course, that article may have been written by a chemist), perhaps as a metaphor for its role in connections between the fundamental concepts of physics and the practical problems of biology. Furthermore, it is the discipline that will continue to drive the discoveries that tackle today’s most vexing challenges: solving the energy problem, developing and producing new treatments for diseases, devising advanced materials for a host of applications, and many more. It seems most appropriate to talk of chemistry as overlapping, rather than bridging, other disciplines. And most certainly it is time to celebrate the creative future of chemistry, which lies in myriad directions.

source: science

Cystic Fibrosis Double Whammy

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People with cystic fibrosis (CF) suffer from life-threatening antibiotic-resistant Pseudomonas aeruginosa respiratory infections, with consequent chronic inflammation, which generates oxidative stress. P. aeruginosa expresses several multidrug efflux systems, including the MexXY-OprM pump, which drives antimicrobial resistance in CF lungs. Expression of MexXY-OprM is unexpected, because ribosome disruption, but not antibiotics such as aminoglycosides, induces its expression, yet CF isolates exhibit high degrees of resistance to aminoglycosides. It turns out that mexXY up-regulation depends on the gene PA5471, which is induced by oxidative stress. Fraud and Poole now demonstrate that exposure to inflammation-induced oxidative stress for several days produced a fourfold elevation in aminoglycoside resistance in P. aeruginosa, which was indeed mediated by PA5471. Aminoglycoside resistance did not always follow increased mexXY expression alone, which suggests that additional genes required for translation or protein synthesis may be involved. Thus, chronic inflammation, rather than antibiotics, drives the expression of MexXY-OprM, which leads to drug resistance in CF lungs.

source:Antimicrobial Agents Chemotherapy.

Targeting Tryptophan

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S-adenosylmethionine (SAM) seems like an innocuous combination of an amino acid and a nucleoside, yet it supports a wide variety of biochemical transformations whose scope remains underappreciated. Zhang et al. explore its intriguing role in the biosynthesis pathway of the antibiotic nosiheptide—a macrocyclic thiopeptide with an embedded indole. The first step is reductive cleavage of SAM to yield the 5′-deoxyadenosyl radical (5′-dA*) along with methionine. Surprisingly, 5′-dA* goes on in this case to abstract a hydrogen atom, not from the usual suspect (a carbon atom of the substrate), but from the indole nitrogen of tryptophan. This leads to a rather complicated sequence of events, with the final outcome being the release of the nitrogen atom and α-carbon (from the backbone portion of tryptophan) as ammonia and formaldehyde and the attachment of the carboxylate to the indole ring at C2; the indolic acid is then used to make nosiheptide. Having established this mechanism, the authors go on to introduce a fluorinated tryptophan derivative into the medium and show that the fluorinated indole functionality is incorporated (albeit somewhat less efficiently) into the corresponding final product, thereby broadening the structural diversity of this antibiotic class.

source: science

Alerting genetic relatives to a risk of serious inherited disease without a patient’s consent

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Every health care practitioner must respect confidentiality. Patients reasonably expect that private information offered or identified during an episode of care will not be divulged without their consent. The fundamental importance of confidentiality finds formal expression in the National Privacy Principles. Practitioners in the private sector must comply with the National Privacy Principles, which are embodied in the Privacy Act 1988 (Cwlth).1 Public sector employees are obliged to comply with the relevant legislation in each jurisdiction.

Knowledge of a history of disease in relatives can be crucial for making a diagnosis in a patient. Similarly, medical care of relatives may be affected by the patient’s diagnosis. For example, a family history of colorectal cancer may assist in identifying the cause of a patient’s abdominal pain, and the diagnosis of colorectal cancer in the patient would then place his or her close relatives at increased risk of the same condition.

In general, a practitioner is not obliged to inform relatives about the diagnosis of a familial disorder. There are some situations in which a practitioner may be required to advise a third party about a patient’s non-genetic diagnosis because of an immediate threat to the safety of others, as is the case with certain infections such as hepatitis A.2 These legally sanctioned breaches of confidentiality do not apply to the risk of a relative developing a familial disorder at some unspecified time in the future. Nonetheless, a practitioner cannot ignore the medical implications of a familial diagnosis for the patient’s relatives, and must inform the patient (or the patient’s authorised representative) of these implications and recommend that they seek medical advice in their own right.3

It is unusual for a patient to refuse to share such information with relatives,4 but such situations do arise and present the practitioner with a challenging dilemma.5 On the one hand, the patient has a right to make an autonomous decision about the use of personal information. On the other hand, this information has a direct bearing on the future health of relatives who may welcome the opportunity to make strategic decisions regarding their health. Whose rights should prevail?

Before 2006, the privacy legislation in Australia was unequivocal: in the absence of an immediate threat to the health or wellbeing of a third party, the patient’s right to privacy prevailed and relatives could not be informed without the patient’s consent. This situation has since changed. In response to a recommendation from the Australian Law Reform Commission,6 the federal government amended the Privacy Act in 2006 to make specific provision for this situation.7 The Privacy Legislation Amendment Act 2006 (Cwlth) allows for the disclosure and use of information without consent, provided that such disclosure is

necessary to lessen or prevent a serious threat to the life, health or safety (whether or not the threat is imminent) of an individual who is a genetic relative of the individual to whom the genetic information relates …

The significant provision is that the threat need not be imminent and may occur at an unspecified time in the future.

There are some important features of this amendment that must be borne in mind. First, the amendment applies only in the setting of managing a familial disorder in a health care setting. A medical practitioner must authorise disclosure, and there must be consultation with appropriate colleagues.

Second, the amendment does not require the practitioner to notify relatives about a familial disorder. The amendment provides a potential legal mechanism for doing so but does not create an obligation.

Third, the amendment only applies to the disclosure and use of genetic information that is necessary to lessen the risk of a familial disorder for a genetic relative. There is no provision to release other information about the patient (including the patient’s identity), or to release information to a non-genetic relative (other than the authorised representative of a genetic relative).

Finally, the Privacy Act currently applies only to practitioners in the private sector. The amendment does not apply to health care practitioners in the public sector. It is anticipated that similar provisions and processes will be developed in the local legislation of the states and territories, which would apply to practitioners in the public sector.

The potential to disclose a patient’s confidential information to a relative against the patient’s wishes represents a major departure from longstanding views on confidentiality in health care. It is appropriate that such an action be taken rarely and with great circumspection. Furthermore, the process for disclosure must recognise that many relatives do not use the genetic information provided to them.8

The National Health and Medical Research Council (NHMRC) has developed guidelines for practitioners who might use this amendment;1 the principles that form the heart of the document are summarised in the Box. Readers should refer to the full guidelines for details, and to a more general NHMRC discussion paper on genetic testing in health care.9

It is important to note that the guidelines1 are not simply recommendations regarding best practice — they are the formal mechanism for implementation of this federal legislation, and practitioners who wish to use the provisions of the Privacy Legislation Amendment Act must comply with the guidelines and requirements of the Privacy Commissioner.10

There is another important sense in which the guidelines do not reflect “best practice”. With careful and considerate communication, especially before embarking on genetic tests that might diagnose a familial disorder, it is usually possible to resolve issues of concern that a patient may have about sharing this personal, confronting, and potentially useful information with relatives. Best practice is represented by striving to avoid the need to use the provisions of this amendment. With a combination of professionalism and patience, most apparent conflicts can be resolved without recourse to disclosing private information without consent.

Source: Australian journal of medicine

Doctors breaching patient privacy

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Of all the ethical principles underlying medical practice, confidentiality is so fundamental that its breach is an illegal, high-order betrayal of responsibility. Disclosing personal medical information without consent profoundly violates the autonomy, beneficence and privacy that patients have always rightly expected.1 Although disclosure without consent has only rarely been necessitated by an urgent threat to life or health, two recent legal erosions of doctor–patient confidentiality illustrate how privacy-invading legislation can so easily and silently harm individuals who do not form sufficiently clamorous rights-demanding groups. In one, a state government directs that private medical records be lodged in an Orwellian sounding “Central Register” without regard for the individual’s knowledge, and risking privacy breaches by seeking consent for disclosure to third parties. The other permits disclosures of a patient’s medical information against their wishes even without any urgent threat to the life or health of another person. Both represent unreasonable intrusions on privacy and erosion of personal liberty.

Recently, the New South Wales Government made a legislative amendment, without parliamentary debate or public discussion, in the last days of their current term. This amendment to the Assisted Reproductive Technology Act 2007 (NSW)2 forces doctors to provide the identity of anonymous sperm donors to a central register when their genetic offspring submit a request for information to the Director-General of NSW Health. This transfer of identifying information can occur regardless of the sperm donor’s consent, and overrides any prior condition of strict confidentiality guaranteed at the time of sperm donation. Although it is argued that identifying information cannot be released without the donor’s consent, the Director-General’s possession of donor contact details creates a situation where a stranger to the donor might try to contact him to seek consent for disclosure. The donor, however, did not ever consent to such an approach from a government instrumentality which, in itself, is virtually certain to breach the donor’s strict confidentiality. Inevitably, once the Director-General possesses identifying information and this contact and consent process proves unworkable, the logical next step is eliminating the troublesome consent requirement. This retroactive legislation is starkly at variance with the recent Australian Senate’s report of its inquiry into donor conception in Australia,3 which recognised that all states’ legislation on donor conception respected the time-honoured principle of rejecting legislative retrospectivity.

Sperm donors have often long forgotten their altruistic act, two decades previously, motivated by a wish to help infertile couples and thought of as akin to blood donation; certainly they would not have provided sperm without the guarantee of enduring and strict confidentiality. Now, merely expecting undisturbed privacy, they do not constitute any sort of group to oppose the persistent, vocal donor-conception lobby groups demanding involuntary disclosure that overrides donors’ legal and moral rights. Sperm donors’ lives over the decades since donation could have changed in every imaginable way so that forced disclosure may be unwelcome, and damaging to some. It denies natural justice to disregard the usual requirement for their consent. We hope that a new NSW Government will show regard for consent and amend the retrospectivity of this assault on the privacy and personal liberty of well intentioned individuals.

The other legal assault on privacy is highlighted in a recent update of the National Health and Medical Research Council (NHMRC) guidelines on medical genetic testing.4 These guidelines endorse a recent amendment to Commonwealth privacy legislation that widens the legal exemption allowing disclosure of patients’ genetic information to others, even against a patient’s wishes. Rarely, the situation arises where a patient is unwilling to inform relatives of a genetic test result that, in a doctor’s opinion, should be disclosed. Such disclosure was previously only permitted to resolve an imminent danger to another person’s health. After the previous exemption for imminent medical danger created a precedent, a recent amendment has removed the requirement altogether. In effect, this now creates genetic testing without consent by proxy — a situation where the relative may be informed, against the patient’s wishes, of the patient’s genetic status without the relative soliciting the information and possibly without wishing to know.

The arbitrary nature of this new standard is illustrated by its vague boundaries — only a “serious threat to life, health or safety” extending to “third-degree relatives” is required to override the patient’s denial of consent. The NHMRC guidelines even encourage not disclosing that the original genetic testing occurred, piling dishonesty upon breach of faith. The widened loophole creates an elastic legal excuse for the well meaning (but impatient) to breach individuals’ privacy. This disavowal of patient confidentiality at a doctor’s sole discretion has the net effect of allowing one individual’s subjective, value-laden judgement, triggered by any remote threat to health or welfare, to override a patient’s refusal of consent. Inevitably, unintended perverse outcomes should be expected — bringing to mind the legal maxim “hard cases make bad law”.

In practice, this loophole will encourage the taking of the lazy path of legal coercion rather than gradual persuasion and ultimate acceptance of a patient’s decision. If forced disclosure is really required, such a momentous breach of a patient’s expressed wishes in the absence of genuine life-threatening circumstances should require approval from an independent legal tribunal, a standard well established for surgery on children whose parents refuse consent, or for sterilisation operations or other major elective procedures for those unable to consent.

Both these legislative assaults on privacy reflect the fashionable belief in genetic determinism prevailing over any ethical, moral and legal constraints of everyday life. But ditching the trusted confidentiality of medical information for doctors’ convenience or to satisfy lobby groups permits arbitrary and damaging intrusion on personal liberty — the price of which remains eternal vigilance.

Source: the medical journal of Australia

 

FDG–PET–CT and whole-body MRI for triage in patients planned for radioembolisation therapy

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The purpose was to evaluate the potential of FDG–PET–CT and whole-body MRI (WB-MRI) as diagnostic triage methods for patients planned for radioembolisation of metastatic liver disease.

Materials and methods

135 patients with multifocal liver metastases were evaluated for potential palliative therapy with radioembolisation using 90-Yttrium microspheres. All patients were examined consecutively with FDG–PET–CT and WB-MRI for exclusion of relevant extra-hepatic tumor manifestations. All patients underwent 99mTc-albumine angiography followed by scintigraphy to exclude significant hepato-pulmonary shunting.

Results

Out of the 135 patients included into the pre-therapeutic diagnostic algorithm, 56% were eligible and received radioembolisation, while 44% could not be treated. In 91% the exclusion criteria was diagnosis of significant extra-hepatic metastatic disease. In 85% exclusion diagnosis was made concordantly by both FDG–PET–CT and WB-MRI, in 9% diagnosis was provided by PET–CT, in 6% by WB-MRI alone. Patient-based sensitivity for detection of extra-hepatic disease was 94% for PET–CT and 91% for WB-MRI. False-positive diagnosis of extrahepatic disease leading to exclusion for radioembolisation therapy was made in 2% of patients, in one patient by PET–CT and in one patient by WB-MRI alone. Overall, specificity for inclusion of radioembolisation therapy by combining both modalities was 99%. In 9% of patients angiographic diagnosis made radioembolisation impossible, in 7% solely the angiographic findings were decisive.

Conclusion

Both FDG–PET–CT and WB-MRI are efficient diagnostic triage methods for patients planned for radioembolisation of liver metastases. Overall, FDG–PET–CT shows a trend to higher diagnostic accuracy compared to WB-MRI and may be used as imaging method of choice as a standalone examination. In combination, both modalities exhibited high sensitivity for the diagnosis of extra-hepatic tumor manifestations and result in high specificity.

source: European Journal of Radiology

Cross-sectional imaging for diagnosis and clinical outcome prediction of acute basilar artery thrombosis

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Basilar artery occlusion is a potentially fatal condition and imaging findings can be subtle. Prompt diagnosis is vital, as recognition may lead to therapeutic recanalization that may improve functional outcome and survival. Furthermore, cross-sectional imaging signs may help predict eventual outcome and, therefore, guide which patients should be subjected to aggressive treatment. Computed tomography (CT) signs include a hyperdense basilar artery that has a high specificity, accuracy, positive and negative predictive value. Evidence regarding the prognostic significance of the hyperdense basilar artery sign is conflicting. Early magnetic resonance imaging (MRI) features include loss of flow void, seen as increased signal intensity within the basilar artery on T2-weigted images and identification of acute thrombus, seen as intermediate signal on T1-weighted images. MRI sequences are more sensitive for early detection of acute ischaemia or infarction, ideally with diffusion-weighted imaging (DWI). Both CT and MR angiography are sensitive for detection of acute thrombus, seen as a filling defect or occlusion. These are the non-invasive imaging techniques of choice to confirm diagnosis, with perhaps the speed and accessibility of CT angiography resulting in this technique being valuable in the acute setting. Several new scoring systems based on arterial segmentation rather than global volume assessment using CT angiography source images and DWI have shown early promise in the prediction of eventual clinical outcome in order to isolate those patients who may benefit from therapeutic recanalization.

source: science direct