Prions and transfusion medicine

BACKGROUND AND OBJECTIVES

There is growing concern at national and international levels that blood supplies might be contaminated with Creutzfeldt-Jakob disease (CJD) agents (prions).

MATERIALS AND METHODS

This review on CJD and blood focuses on experimental and epidemiological data, available tests, factors contributed by donors and recipients, and production processes. All of this has been recently detailed in excellent reports and opinions which are summarised here.

RESULTS

Solid evidence from experimentally infected animals, and fragmentary evidence from naturally infected humans, indicates that blood may contain low levels of the infectious agent, yet blood products have never been identified as a cause of CJD in humans.

CONCLUSION

The evaluation of all relevant data leads to the opinion that transmission of CJD by blood and blood products either does not occur or does not contribute to the CJD epidemiology. Although a hazard cannot be excluded, a real risk is not recognisable. As the experience with variant CJD (vCJD) is limited, the same statement cannot be made for vCJD [1]. In consequence, it is mainly the risk of vCJD that might have relevance for transfusion medicine; this has already resulted in some precautionary donor exclusion regulations.

[Review of Creutzfeldt-Jakob disease and other prion diseases]

INTRODUCTION

Creutzfeldt-Jakob disease (CJD) is a rapidly progressive dementia syndrome which is probably caused by prions. The annual incidence of this disease is 1/1,000,000. Most cases are sporadic in type, although 10-15% are familial. The total incidence of CJD has not changed following the epidemic due to a new variant (nv-CJD); however, this has led to greater awareness of the subject.

OBJECTIVE

To review current scientific knowledge of CJD.

DEVELOPMENT

A search was made for relevant literature using MEDLINE. The criteria proposed for diagnosis of CJD include the presence of progressive dementia and at least two of the following characteristics: 1. Myoclonias, 2. Cortical blindness, 3. Pyramidal, extrapyramidal or cerebellar signs, 4. Akinetic mutism, or 5 Abnormal EEG. Laboratory and neuroimaging investigations may also help in diagnosis of CJD, although neuropathological confirmation is necessary for definite diagnosis. Two promising methods of pre mortem diagnosis of CJD are determination of 14-3-3 protein in the cerebrospinal fluid, in the case of sporadic CJD, and biopsy of the palatine tonsil in the case of nv-CJD. The physiopathology of CJD seems to be centred on the proteins forming prions, which are glycoproteins found in the plasmatic membrane and are very often expressed in the neurons, particularly at neuromuscular junctions and synapses. The pathological form resists proteolytic degradation, so that they accumulate in the CNS. The precise neurotoxic mechanism of these proteins is still not clear.

CONCLUSIONS

There is still no treatment for CJD. Further studies of the physiopathological mechanisms of prion diseases may help in the development of treatment to delay the progress of this disease.

Attenuated Creutzfeldt-Jakob Disease agents can hide more virulent infections

We previously showed that a slow infectious strain of Creutzfeldt-Jakob Disease (CJD) can dramatically suppress the expression of a fast virulent agent injected intracerebrally 80days later. While the slow SY agent eventually produced disease at approximately 400days, there was little evidence of the fast FU agent. However, two of 18superinfected mice showed a minor increase in pathologic changes. To determine if FU was partially or completely suppressed, or if FU and SY agents formed a 'chimera' with intermediate incubation properties as predicted by prion theory, we passaged representative brains. All traces of FU were obliterated in typical brains of suppressed mice. The two aberrant mice however had mixed SY and FU infections, with FU reappearing at late stages of SY disease. Thus less virulent sporadic CJD infections in older people can conceal other agents such as variant CJD, the more recently evolved and virulent agent linked to bovine spongiform encephalopathy. This powerful model of agent-induced repression also implicates targets other than prion protein (PrP) in eliminating infection.

Bovine spongiform encephalopathy: an overview

Bovine spongiform encephalopathy (BSE), widely known as "mad cow disease," is a chronic, degenerative disease affecting the central nervous system of cattle. Worldwide, there have been more than 180,000 cases since the disease was first diagnosed in 1986 in Great Britain. Bovine spongiform encephalopathy has had a substantial impact on the livestock industry in the United Kingdom. The disease has also been confirmed in native-born cattle in Belgium, Denmark, France, Ireland, Luxembourg, Liechtenstein, The Netherlands, Northern Ireland, Portugal, and Switzerland. However, over 95% of all BSE cases have occurred in the United Kingdom. Bovine spongiform encephalopathy is not known to exist in the United States.

[Neurovegetative diseases in dementia]

Dementia is the result of the dysfunction and death of cells in the central and peripheral nervous system. Of diverse etiology, these processes are insidious in their onset and are characterized by a progressive neural depletion resulting in a range of cognitive deficits, including a deterioration in the capacity to learn and a tendency to forget what has been learned. Neurodegenerative diseases resulting in dementia include: Alzheimer, Parkinson, Huntington, Pick, and Creutzfeld Jakob, as well as dementias with multiple etiologies. The population with the highest probability of suffering from one of these diseases are those over 50 years of age, because they have reduced circulating levels of gonadal hormones, one of several risk factors associated with the onset of dementia. Anatomical areas most commonly affected include the hippocampus, the primary motor and somatosensory areas, various limbic structures, and the parieto-temporal, frontal, and entorhinal corticies. Affliction of this last area has been suggested to account for the early olfactory dysfunction often shown by patients after the onset of Alzheimer and Parkinson, leading to the suggestion that olfactory testing could be useful in the early diagnosis of such neurodegenerative diseases.

[Prions, infections and confusions in the "transmissible" spongiform encephalopathies. The other evidence-based science. III. Review]

There are some neurological disorders with a pathological hallmark called spongiosis which include Creutzfeld-Jakob disease and its new variant, the Gertsmann-Straussler-Scheinker Syndrome and the Fatal Familial Insomnia in humans; and Scrapie and Bovine Spongiform Encephalopathy, among others, in animals. The etiological agent has been considered either transmissible or hereditary or both. Curiously, this agent has no nucleic acids, is impossible to filter, is resistant to inactivation by chemical means, has not been cultured and is unobservable at electron microscopy. All of these facts have led to some researches to claim that these agents are similar to viruses appearing in computers. However, after almost fifty years of research, is still not possible to explain why and how such elements produce the diseases commented about. On the contrary, during these years have been possible to know that these entities called slow viral infections, transmissible amyloidosis, transmissible dementia, transmissible spongiform encephalopathies or prion diseases appear in individuals with genetical predispositions exposed to several worldwide immunological stressors. The possibility that prions are the consequence and not the cause of these diseases in animals and man is day by day more reliable, and supports the suggestion that a systematic intoxication due to pesticides as well as mycotoxin ingestion, produced mainly by different molds such as Aspergillus, Penicillium or Fusarium, seem to be the true etiology of these neurodegenerative disorders.

Follicular dendritic cells in TSE pathogenesis

The pathogenesis of transmissible spongiform encephalopathies (TSEs) often includes a replication phase in lymphoid tissues before infection spreads to the central nervous system. Recent studies show that the follicular dendritic cells of the germinal centres are critical for this replication. These cells are therefore potential targets for therapy or prophylaxis in natural TSEs, such as variant Creutzfeldt-Jakob disease.

The risk of blood-borne Creutzfeldt--Jakob disease

With the increasing ability of modern medicine to transfer life-giving tissues and tissue products from one individual to another comes a parallel, often life-taking consequence of the unsuspected transfer of infectious passengers. Creutzfeldt-Jakob disease (CJD) has been transmitted by contaminated stereotactic EEG electrodes, neurosurgical instruments, dura mater allografts, and cadaveric pituitary hormone therapy. Widespread concern has been voiced about the possible risks of transmitting CJD through the administration of blood or plasma products, although no such case has so far been identified by epidemiological studies of at-risk populations. Recently completed experiments using hamsters and mice showed decreasing levels of infectivity in buffy coat, plasma, cryoprecipitate (the source of anti-haemophilic factor), and fraction I + II + III (the source of immune globulin). Preliminary results from further rodent experiments indicate that little or no infectivity is detectable in plasma during the pre-clinical phase of infection, that plasma infectivity is not reduced by either leukodepletion filtration or high speed centrifugation, and that about 5-10 times more infectivity is needed to transmit disease by the intravenous than intracerebral route. Altogether, the data from these rodent studies, especially when considered together with results from similar studies underway in primates, should provide a rational foundation for policy decisions by government agencies, plasma product manufacturers, and blood banking communities.

Creutzfeldt-Jakob disease in a patient with a lyophilized dura mater graft

A 37-year-old patient with Creutzfeldt-Jakob disease (CJD) is presented, who had received a cadaveric dura matter graft 12 year before the onset of neurologic symptoms. Initial clinical presentation included cerebellar symptoms, with dementia and myoclonus developing in later stages of the disease. EEG showed diffuse slowing with sporadic triphasic periodic activity. CT was normal in the early stage but pronounced cerebral and cerebellar atrophy with widened sulci were seen on MRI in the late stage of the disease. The prion protein (PrP) gene was homozygous for valin at the polymorphic codon 129. Cerebrospinal fluid analysis for 14-3-3 protein was positive. We believe that this patient is the first Croatian to acquire CJD by dural implant. Based on this case and a review of 66 cases from the literature, it is manifest that the awareness of iatrogenic transmission of CJD and adoption of preventive measures are the only effective way to stop the spread of CJD among surgically treated patients.

[Juvenile onset Creutzfeldt-Jakob disease with the history of neurosurgical operation]

Juvenile onset Creutzfeldt-Jakob disease with the history of neurosurgical operation: a case report A 15-year-old boy gradually developed gait disturbance and dementia. After three months, his condition was deteriorated and he became a state of akinetic mutism. Then, he was transferred to our hospital. He had a history of neurosurgical operation for arterio-venous malformation in his right occipital lobe at the age of five. He showed myoclonus, periodic synchronous discharges in electroencephalogram, and a high cerebrospinal fluid level of neuron-specific enolase. He also revealed progressive brain atrophy by CT examination. He was diagnosed as having Creutzfeldt-Jakob disease (CJD). We could not detect gene mutation of prion protein. As far as we know, this is the youngest case of CJD in Japan. He is too young for the sporadic form of CJD. So the possibility of new variant form of CJD or iatrogenic CJD was considered, the former having been reported in England and the neighboring countries in Europe. However, new variant form of CJD was less likely because of the presence of definite PSD in EEG and the absence of the history of his stay in England. The relationship between the CJD onset and the neurosurgical operation was suggested, but no evidence such as frozen dura matter graft was proved.

The new variant of Creutzfeldt-Jakob disease

New variant Creutzfeldt-Jakob disease (nvCJD) is a novel human transmissible spongiform encephalopathy which was first identified in 1996 in the United Kingdom (UK). Subsequent scientific studies have revealed that the strain of the transmissible agent responsible for nvCJD is identical to that of the bovine spongiform encephalopathy (BSE) agent, and the disease has been considered as 'human BSE'. By 31 December 1999, 52 cases of nvCJD had been reported (49 cases in the UK, two cases in France and one case in the Republic of Ireland). All these individuals were under 53 years of age and all those tested were methionine homozygotes at codon 129 of the prion protein gene. The number of cases of nvCJD likely to occur in the future is impossible to estimate because of multiple uncertainties, in particular the disease incubation period, the degree of exposure to the infective agent and the susceptibility of other genetic subtypes. Continued surveillance of both BSE and CJD is required in the UK and in other countries, to ensure that the scale of this potential epidemic is adequately monitored and that all possible steps are taken to prevent further human exposure to the BSE agent.

Ecosystems supporting clusters of sporadic TSEs demonstrate excesses of the radical-generating divalent cation manganese and deficiencies of antioxidant co factors Cu, Se, Fe, Zn. Does a foreign cation substitution at prion protein's Cu domain initiate TSE?

Analyses of food chains supporting isolated clusters of sporadic TSEs (CWD in N Colorado, scrapie in Iceland, CJD in Slovakia) demonstrate a consistent 2 1/2+ fold greater concentration of the pro-oxidant divalent cation, manganese (Mn), in relation to normal levels recorded in adjoining TSE-free localities. Deficiencies of the antioxidant co factors Cu/Se/Zn/Fe and Mg, P and Na were also consistently recorded in TSE foodchains. Similarities between the clinical/pathological profile of TSEs and Mn delayed psycho-neurotoxicity in miners are cited, and a novel theory generated which suggests that sporadic TSE results from early life dependence of TSE susceptible genotypes on ecosystems characterised by this specific pattern of mineral imbalance. Low Cu/Fe induces an excessive absorption of Mn in ruminants and an increased oxidation of Mn2+ into its pro oxidant species, Mn3+, which accumulates in mitochondria of CNS astrocytes in Mn SOD deficient genotypes. Deficiencies of scavenger co factors Cu/Zn/Se/Fe in the CNS permits Mn3+ initiated chain reactions of auto-oxidant mediated neuronal degeneration to proliferate, which, in turn, up-regulates the expression of the Cu-metalloprotein, prion protein (PrP). Once the rate of PrP turnover and its demand for Cu exceeds the already depleted supply of Cu within the CNS, PrP can no longer bind sufficient Cu to maintain its conformation. Mn3+ substitutes at the vacated Cu domain on PrP, thus priming up a latent capacity for lethal auto-oxidative activity to be carried along with PrP like a 'trojan horse'; where Mn 3+ serves as the integral 'infectious' transmissible component of the misfolded PrP-cation complex. The Mn overactivation of concanavalin A binding to glycoprotein and Mn-initiated autoxidation results in a diverse pathological profile involving receptor capping, aggregation/modification of CNS membrane/cytoskeletal proteins. TSE ensues. The BSE/nv CJD strain entails a 'synthetic' induction of the same CNS mineral disturbance, where 'in utero' exposure to Cu-chelating insecticides/Mn supplements accelerates the onset of a more virulent 'strain' of adolescent TSE.

Mammalian prion proteins

The past two years have seen the extension of our knowledge on the cellular prion protein structure with new NMR data on both the hamster and human proteins. In addition, the folding dynamics of two cellular prion proteins have been elucidated. There are now several examples of recombinant prion proteins that are able to adopt different conformations in solution and recent work on the molecular basis of prion strains has done much to consolidate the protein-only hypothesis. Important advances in relating disease to structure have also been made through the identification of the minimal prion protein fragment that is capable of conferring susceptibility to and propagation of the scrapie agent.

Transgenic models of prion disease

There is growing concern that bovine spongiform encephalopathy (BSE) may have passed from cattle to humans, resulting in approximately 70 cases of an atypical, variant CJD (vCJD) in teenagers and young adults. We report here that transgenic (Tg) mice expressing full-length bovine (Bo) PrP serially propagate BSE prions and that there is no species barrier for transmission from cattle to Tg(BoPrP) mice. Surprisingly, these same mice were also highly susceptible to vCJD and natural sheep scrapie. The incubation times (approximately 250 d), neuropathology, and PrP(Sc) isoforms in Tg(BoPrP) mice inoculated with vCJD and BSE brain extracts were indistinguishable and differed dramatically from those seen in these mice injected with natural scrapie. In efforts to identify PrP sequences required for prion formation, we found that a redacted prion protein of only 106 amino acids (PrP106) containing two large deletions supported prion propagation. In Tg(PrP106) mice, an artificial transmission barrier for the passage of full-length mouse prions was diminished by the coexpression of full-length wt MoPrP(C), suggesting that wt MoPrP acts in trans to accelerate the replication of "miniprions" containing PrP(Sc)106. Following a single passage (approximately 300 d) in Tg(PrP106) mice, the miniprions efficiently transmitted disease to Tg(PrP106) mice after only approximately 66 days. Our findings with Tg(BoPrP) mice provide compelling evidence that prions from cattle with BSE have infected humans and caused fatal neurodegeneration, the unique features of miniprions offer new insights into the mechanism of prion replication, and the trans-acting effects of full-length PrP coexpression suggest a new approach to the development of even more efficient animal models for prion diseases.

The transmission of prions to humans

The identification of new-variant Creutzfeldt-Jakob disease (nvCJD) in 1996 led to the proposal that this new disease was caused by the transmission of bovine spongiform encephalopathy (BSE) to the human population. The ramifications of such a proposal have been extensive and profound, both politically and on the general public in the UK and other countries. Patients with nvCJD exhibit a consistent set of clinicopathological features, and cases of nvCJD continue to be reported almost exclusively in the UK, the country with by far the highest incidence of BSE. Laboratory studies, including transmission experiments in mice, provide strong support for the hypothesis that nvCJD is caused by BSE.

New insight into abnormal prion protein using monoclonal antibodies

Studies of abnormal prion protein (PrPres) are hindered by the lack of specific monoclonal antibodies (mAbs), and the relationships between PrPres, infectivity, and strain specificity in prion diseases are still subject to debate. We have studied PrPres with new mAbs produced against PrP in mice using various immunization strategies. PrPres was analyzed by Western blot with different prion strains in various hosts. Differences in the electrophoretic pattern of human PrPres revealed by these antibodies provide new insight into PrPres cleavage by proteases and interpretation of strain typing. This study confirms that the N-terminal extremity of PrPres is differentially sensitive to proteases. Conversely, the C-terminal extremity, which resists proteolysis, seems to be abnormally detectable by antibodies in ultrastructural studies. This work confirms the highly complex role of PrPres in prion diseases and provides new tools which will be made available to facilitate progress in qualitative and quantitative studies of PrP.

Transmissible spongiform encephalopathies in humans

Creutzfeldt-Jakob disease (CJD), the first transmissible spongiform encephalopathy (TSE) to be described in humans, occurs in a sporadic, familial, or iatrogenic form. Other TSEs in humans, shown to be associated with specific prion protein gene mutations, have been reported in different parts of the world. These TSEs compose a heterogeneous group of familial diseases that traditionally have been classified as familial CJD, Gerstmann-Sträussler-Scheinker syndrome, or fatal familial insomnia. In 1996, a newly recognized variant form of CJD among young patients (median age, 28 years) with unusual clinical features and a unique neuropathologic profile was reported in the United Kingdom. In the absence of known CJD risk factors or prion protein gene abnormalities, the UK government concluded that the clustering of these cases may represent transmission to humans of the agent causing bovine spongiform encephalopathy. Additional epidemiologic and recent laboratory data strongly support the UK government's conclusion.

New variant Creutzfeldt-Jakob disease

It is now recognised that new variant Creutzfeldt-Jakob disease (CJD) can present during adolescence, so it may be within the experience of any paediatrician. Some observations on prion proteins are made, and some of the features of classical CJD are reviewed. Reports of patients with new variant CJD are given. The possible links between this condition and bovine spongiform encephalopathy (BSE) are considered, especially the finding that certain people who are homozygous for methionine at codon 129 of the prion protein may be particularly susceptible to this infection. The diagnosis of new variant CJD can be difficult. Early sensory and psychiatric symptoms can be suggestive, so can the initial signs of ataxia and involuntary movements. The EEG does not help in this variety. Although not specific some serum and CSF tests may give diagnostic support. It has been claimed that tonsillar biopsy may confirm the diagnosis, but this often necessitates brain biopsy; or the diagnosis may only be made at autopsy. Beliefs about the way infections spread will have to be modified, and more must be learnt about the nature of prions, how they enter the body, and how they spread in the brain.

Is the pathogen of prion disease a microbial protein?

Though considerable circumstantial evidence suggests that the pathogen of prion disease is proteinaceous, it has not yet been conclusively identified. Epidemiological observations indicate that a microbial vector is responsible for the transmission of natural prion disease in sheep and goats and that the real causative agent may correspond to a structural protein of that microorganism. The microbial protein should resemble prion protein (PrP) and may replicate itself in the host by using mammalian DNA. A similar phenomenon was already described with a protein antigen of the ameba Naegleria gruberi. The various serotypes of the microbial protein may account for the existence of scrapie strains. It is proposed that many microbial proteins may be capable of replicating themselves in mammalian cells eliciting and sustaining thereby degenerative and/or autoimmune reactions subsequent to infections with microorganisms.

Prion protein glycotype analysis in familial and sporadic Creutzfeldt-Jakob disease patients

Creutzfeldt-Jakob disease (CJD) and other transmissible spongiform encephalopathies (TSEs) are characterised by the accumulation of a pathological conformer of PrP, named PrPsc. Molecular weight and glycosylation of the protease-resistant core of PrPsc (PrP27-30) are heterogeneous in different forms of TSEs. We analysed PrP27-30 glycotypes in a large number of TSE-affected patients: 50 sporadic CJD (sCJD), 1 iatrogenic CJD, 1 Gerstmann-Sträussler-Scheinker syndrome (GSS) with the Pro102Leu mutation of PrP, 3 familial CJD (fCJD) with the Glu200Lys mutation and, for the first time, 7 fCJD with the Val210ll3e mutation. All patients were screened for the polymorphic codon 129 of the PrP gene. PrP27-30 deglycosylation and PrPsc immunohistochemistry were performed in selected cases. We found that two PrP27-30 glycotypes (type 1A and type 2A) are produced in sCJD. Type 1A is more frequently associated with methionine than valine in position 129. Type 1A is also formed in Val210lle fCJD. In Glu200Lys fCJD and GSS patients, we found that PrP27-30 has the same mobility of type 1 but different glycosylation ratios (type 1B). Our findings indicate that the polymorphic residue 129 of PrP has a leading role in determining the proteinase degradation site of PrPsc while mutant residues 102 or 200 influence only the glycosylation pattern.

The relationship between new variant Creutzfeldt-Jakob disease and bovine spongiform encephalopathy

Creutzfeldt-Jakob disease (CJD) has been transmitted in the laboratory and also by iatrogenic accident. However, research has failed to find evidence that its most common form (sporadic CJD) is a natural infection and, in particular, that there is a causal link with scrapie. Bovine spongiform encephalopathy (BSE) probably resulted from scrapie infection in cattle food. In the wake of the BSE epidemic, a novel clinico-pathological form of CJD has been recognized: new variant CJD (nvCJD). This paper reviews the relationship between nvCJD and BSE and presents the accumulated evidence supporting the view that nvCJD resulted from BSE contamination of human food.