Scientists Discover Toxin That Causes Gastro Disease
Main Category: GastroIntestinal / Gastroentorology News
Article Date: 11 Oct 2006 - 21:00pm (PDT)



Australian scientists have identified a highly potent toxin that causes severe gastrointestinal illnesses, including food poisoning.

The toxin, produced by certain strains of E. coli bacteria, has been found to be responsible for an outbreak of haemolytic uraemic syndrome, a dangerous disease that causes acute kidney failure, in South Australia in 1998.

The research team was led by Dr Adrienne Paton from the University of Adelaide, and included scientists from Monash University's ARC Centre of Excellence in Structural and Functional Microbial Genomics, and the United States.

Dr Travis Beddoe from Monash University's Department of Biochemistry and Molecular Biology, is one of the investigators who discovered that the bacterial toxin, subtilase cytotoxin, deactivates an essential component of cells in the gastrointestinal tract.

"It is unique because it cuts an essential component of the cell machinery in half, therefore disabling it," he said.

As well as learning how the toxin works, the scientists have also determined its three-dimensional structure, which will aid in the development of treatments for toxin-related diseases.

"This toxin belongs to the family of toxins that cause whooping cough, a very serious bacterial infection that affects children," Dr Beddoe said.

He said the research breakthrough may also provide insights into the development of age-related and degenerative diseases such as Parkinson's disease and Alzheimer's disease, and may be used in the treatment of some cancers.

The collaborative research was supported by the National Health and Medical Research Council and the Australian Research Council. The research findings are published in the latest issue of the journal Nature.

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Nature 443, 548-552(5 October 2006) | doi:10.1038/nature05124; Received 23 May 2006; Accepted 1 August 2006
AB5 subtilase cytotoxin inactivates the endoplasmic reticulum chaperone BiP

From the article:

"AB5 toxins are produced by pathogenic bacteria and consist of enzymatic A subunits that corrupt essential eukaryotic cell functions, and pentameric B subunits that mediate uptake into the target cell. AB5 toxins include the Shiga, cholera and pertussis toxins and a recently discovered fourth family, subtilase cytotoxin, which is produced by certain Shiga toxigenic strains of Escherichia coli.

Here we show that the extreme cytotoxicity of this toxin for eukaryotic cells is due to a specific single-site cleavage of the essential endoplasmic reticulum chaperone BiP/GRP78. The A subunit is a subtilase-like serine protease; structural studies revealed an unusually deep active-site cleft, which accounts for its exquisite substrate specificity.

A single amino-acid substitution in the BiP target site prevented cleavage, and co-expression of this resistant protein protected transfected cells against the toxin. BiP is a master regulator of endoplasmic reticulum function, and its cleavage by subtilase cytotoxin represents a previously unknown trigger for cell death."


Discussion

The findings of this study indicate that SubAB is unique in two ways. Unlike other bacterial AB5 cytotoxins, it does not need to be translocated from the ER lumen into the cytosol in order to interact with its cellular target. For Ctx and Stx, this retro-translocation is achieved through subversion of the Sec61 translocon apparatus, which is normally used to transport terminally misfolded host proteins from the ER lumen into the cytosol for degradation, a process in which BiP is also involved15, 16.

Most importantly, however, no other cytotoxin has been shown to target chaperone proteins or components of the ER directly.

Defects in chaperone function, particularly those that affect ER stress responses, have been implicated in cellular senescence and a range of degenerative conditions including cataracts and Parkinson's and Alzheimer's diseases6, 17. Through its ability to rapidly and specifically abolish BiP function, SubAB provides a new tool in cell biology that enables in vitro modelling of key events in the pathogenesis of these diseases.

BiP is a highly conserved master regulator of ER function, and is essential for survival of eukaryotes from simple yeasts to higher organisms such as mammals6, 7. There is negligible sequence variation in the vicinity of the cleavage site, indicating that SubAB has the potential for toxicity against a broad spectrum of life forms. Our findings reveal a previously undescribed mechanism of inducing cell death, through the specific targeting of a protease to disable chaperone function.

wondered why measurements were made on alpha 1 antitrypsin in people with neurodegenerative diseases--it is a serine protease inhibitor (serpin). information in the article you posted helps. thanks, madelyn

http://tinyurl.com/y8x6tk

10/11/06 -- Osta Biotechnologies Inc. (TSX VENTURE:OBI.V) today announced the results of a pilot clinical study involving 81 subjects for the development of novel blood tests for Parkinson's disease (PD) and also for Alzheimer's disease (AD). Data from this clinical study showed statistically significant difference in the plasma alpha-1-antitrypsin (AAT) concentrations of patients suffering from PD compared to normal elderly controls (NEC), patients with Alzheimer's disease (AD) and those suffering from mild cognitive impairment (MCI). Additionally, the data showed that the plasma AAT concentrations in subjects with MCI and AD were higher than those in NEC and PD subjects suggesting that plasma AAT concentrations could be useful in early diagnosis of AD. These results hold promise that these blood tests provide simple and reliable diagnosis of subjects suffering from Parkinson's or early Alzheimer's disease.




These findings represent an important milestone in Osta's plan to develop novel blood tests for neurodegenerative diseases including PD and AD and provide an important advancement towards generating sufficient clinical data in order for the company to enter into co-development/commercialization agreements with pharmaceutical/diagnostic companies world-wide.

Currently, there are no commercial blood tests with proven utility in the evaluation of patients with PD. Idiopathic Parkinson disease (PD) is a common neurodegenerative disorder that affects more than 2% of the population over 65 years of age. The current diagnosis of PD is rendered purely on clinical grounds at a relatively late stage of the disease when a significant damage to the dopaminergic neurons has already taken place and unfortunately cannot be reversed.

Moreover, currently, there are no commercial blood tests with proven utility in the evaluation of patients with sporadic (non-familial) AD. The causes of AD are not known, but major risk factors include old age and a family history of dementia. AD is the most common form of adult-onset dementia. It is estimated that between 5-10% of North Americans aged 65 and above suffer from AD. The prevalence of AD in the US is currently estimated at approximately 4 million people and, should effective therapy remain elusive, is anticipated to rise to about 14 million people by 2050.

At present, the degree of cognitive impairment is assessed by physicians using Mini-Mental State Examination (MMSE) scores, a battery of neuropsychological tests, blood tests to exclude potentially reversible causes of memory loss, and neuroimaging. However, these techniques are tedious, expensive and often inconclusive. There are several genetic markers such as Presenilin-1, Presenilin-2, and mutant APP that can identify relatively uncommon cases of familial AD, but these genetic markers have no role in the management of patients with the far more prevalent sporadic forms of the illness. Measurements of Tau and Amyloid peptides in the cerebrospinal fluid have proven to be useful biomarkers of sporadic AD, but these measurements require a relatively invasive spinal tap that is not ideal for the mass screening of patients with memory loss.

Results of the Clinical Study

The clinical study was conducted in collaboration with Dr. Hyman M. Schipper, a Professor of Neurology & Medicine at McGill University and the Director of Centre for Neurotranslational Research at the Lady Davis Institute for Medical Research of the Jewish General Hospital. The technology is based on a key protein called alpha-1-antitrypsin (AAT). In a pilot study involving a total of 81 subjects with 16 normal elderly controls (NEC), 26 MCI, 20 AD and 19 PD subjects, 13 out of 16 NEC subjects, 23 out of 26 MCI subjects and 17 out of 20 AD subjects were found to have plasma concentrations of AAT higher than 1.23 mg/mL, whereas, only 8 out of 19 subjects with PD were found to have plasma concentration of AAT higher than 1.23 mg/mL (P less than 0.025 NEC vs PD; P less than 0.001 MCI vs PD; P less than 0.01 AD vs PD, overall P less than 0.01). Moreover, the plasma AAT concentrations of MCI subjects were found to be similar to those with AD suggesting that plasma AAT concentrations could be useful in diagnosis of MCI and hence potentially providing an early diagnosis of AD as it is well known that MCI precedes AD. The mean plasma AAT concentration of PD subjects was found to be 1.18 + 0.19 mg/mL and was lower than the mean plasma AAT concentration of NEC who had a mean plasma AAT concentration of 1.33 + 0.12 mg/mL. The mean plasma AAT concentration of MCI subjects was found to be 1.44 + 0.30 mg/mL and that of the AD subjects was found to be 1.48 + 0.26 mg/mL which were both higher than those in PD and NEC subjects.

Dr. Hyman Schipper, Principal Investigator of the study commented "We are quite pleased with these results and are continuing to further scale up our clinical study to validate the AAT measurement as a novel biomarker for the diagnosis of PD, AD and prognosis of subjects with MCI. The development of a blood test for the diagnosis of PD, sporadic AD and MCI would represent an advance in the management of these devastating neurodegenerative conditions."

Osta Biotechnologies Inc.

Osta is a biopharmaceutical company listed on the TSX Venture Exchange (TSX VENTURE:OBI.V) dedicated to developing novel diagnostics and therapeutics for the aging population particularly in the areas of Alzheimer's disease, Osteoporosis, Osteoarthritis and Cancer.

Certain information in this press release is forward-looking and is subject to numerous risks and uncertainties. By their nature, such forward-looking statements involve risks and uncertainties that could cause actual results to differ materially from those contemplated by the forward-looking statements. These risks include actions of Osta's competitors, and those inherent in scientific research and development.

The TSX Venture Exchange does not accept responsibility for the adequacy or accuracy of this release.

Source: Osta Biotechnologies Inc