HER2/HER3 heterodimers and p21 expression are capable of predicting adjuvant trastuzumab response in HER2+ breast cancer

Human epidermal growth factor receptor 2 (HER2) plays an important role in breast cancer progression and provides predictive information for response to targeted therapy including trastuzumab although this is limited. Downstream pathways, such as PI3K/Akt, are associated with HER2/HER3 heterodimerization promoting survival and proliferation amongst cancer cells. Thus, patient outcome and trastuzumab therapy effectiveness might be further characterised by HER2/HER3 dimerisation and its signalling pathways. HER2/HER3 dimerisation status was assessed, using chromogenic in situ Proximity Ligation Assay, in two breast cancer series: early stage primary breast cancer, including 224 HER2+ patients that were not submitted to trastuzumab, and HER2+ breast cancer where patients were treated with adjuvant trastuzumab (n = 143). Levels of biomarkers including PI3K, pAKT, ER, PgR, HER3, BCL2, p53, PTEN and p21 were measured using immunohistochemistry. Levels of HER2/HER3 heterodimers were compared with biomarker expression and patient outcome. An association between high levels of HER2/HER3 dimerisation and absence of hormone receptors, ER and PgR, was observed. We further show for the first time the presence of HER2/HER3 heterodimers and the loss of p21 expression in HER2+ breast cancer predicts a significantly poorer outcome when submitted to adjuvant trastuzumab. Breast cancer patients that reveal high levels of HER2/HER3 dimerisation and loss of p21 are associated with poor survival prognosis in patients with HER2+ breast cancer treated with adjuvant trastuzumab. Further quantification analysis of HER dimer/ligand complexes and downstream signalling pathways will begin to unravel the complex associations with patient outcome and its relationship with sensitivity to targeted treatment.

Nottingham Prognostic Index Plus (NPI+): a modern clinical decision making tool in breast cancer

BACKGROUND

Current management of breast cancer (BC) relies on risk stratification based on well-defined clinicopathologic factors. Global gene expression profiling studies have demonstrated that BC comprises distinct molecular classes with clinical relevance. In this study, we hypothesised that molecular features of BC are a key driver of tumour behaviour and when coupled with a novel and bespoke application of established clinicopathologic prognostic variables can predict both clinical outcome and relevant therapeutic options more accurately than existing methods.

METHODS

In the current study, a comprehensive panel of biomarkers with relevance to BC was applied to a large and well-characterised series of BC, using immunohistochemistry and different multivariate clustering techniques, to identify the key molecular classes. Subsequently, each class was further stratified using a set of well-defined prognostic clinicopathologic variables. These variables were combined in formulae to prognostically stratify different molecular classes, collectively known as the Nottingham Prognostic Index Plus (NPI+). The NPI+ was then used to predict outcome in the different molecular classes.

RESULTS

Seven core molecular classes were identified using a selective panel of 10 biomarkers. Incorporation of clinicopathologic variables in a second-stage analysis resulted in identification of distinct prognostic groups within each molecular class (NPI+). Outcome analysis showed that using the bespoke NPI formulae for each biological BC class provides improved patient outcome stratification superior to the traditional NPI.

CONCLUSION

This study provides proof-of-principle evidence for the use of NPI+ in supporting improved individualised clinical decision making.

Molecular profiling of breast cancer in Nigerian women identifies an altered p53 pathway as a major mechanism underlying its poor prognosis compared with British counterpart

BACKGROUND

Advances in breast cancer (BC) research have demonstrated differences between black and white women with regarding tumour behaviour, patient outcome and response to treatment which can be explained by underlying genetic changes. The tumour suppressor gene p53 has been speculated to be involved in tumour biology of triple negative and/or basal -like BC and more commonly observed in black than caucasian women.

MATERIALS AND METHODS

In this study, the protein expression of p53 was investigated in tissue samples from a series of 308 Nigerian women, prepared as a tissue microarray (TMA), using immunohistochemistry. Clinicopathological parameters, biomarkers of functional significance in BC and patient outcome of tumours expressing p53 in Nigerian women were correlated with UK grade matched series.

RESULTS

A significantly large proportion of BC from Nigerian women showed high p53 expression compared with UK women (p<0.001). In those tumours showing positive p53 in the Nigerian series, a significant proportion were premenopausal, diagnosed before 50 years, larger in size, with evidence of metastasis into lymphatic vessels ( all p<0.001). In addition, p53 positive expression was also significantly correlated with negative expression of ER and PgR (p<0.001, p<0.03 respectively), BRCA1, MDM2 (all p<0.001), p21 (p=0.006) and E-cadherin (p=0.001) and positively associated with P-cadherin (p=0.001), triple negative phenotype, basal cytokeratin (CK) 5/6 expression (p<0.04) and basal phenotype compared with the UK series (p<0.001). Survival analyses showed Nigerian women with BC were significantly associated with poor BC specific survival (p<0.001, but no significant association with disease free interval was observed.

CONCLUSION

In this study, protein expressions of p53 pathways are different between Nigerian and UK BC women and this may also contribute to differences in tumour biology. Therefore, targeting these p53 pathways for therapeutic usage might improve the poor outcome observed in Black Nigerian women.

Characterisation of HER heterodimers in breast cancer using in situ proximity ligation assay

HER2 plays an important role in breast cancer progression and provides predictive and prognostic information. HER2 receptor family members function through dimerisation, which can lead to impact on cell function, growth and differentiation; however, their value in breast cancer development remains to be defined. This study aims to examine the relationships of HER2 heterodimers to breast cancer characteristics in trastuzumab naïve and treated cases. HER2 protein (IHC), HER2 gene (chromogenic ISH) and HER2 heterodimerisation status [chromogenic in situ proximity ligation assay (PLA)] were assessed in two breast cancer series prepared in tissue microarray (TMA) format. A range of signals/cell for each HER2 heterodimer was detected (0-34.6 signals/cell). The vast majority of cases with HER2 heterodimers showed HER2 gene amplification and/or protein expression. There was an association between HER2 dimerisation with HER3 and HER4 and their protein expression level but no such association was found in with HER1 (EGFR). Of the HER2+ cases, 74, 66, and 58 % showed heterodimers with EGFR, HER3 and HER4, respectively. 51 % of HER2+ tumours expressed all three heterodimers whereas 23 % of the cases did not show expression of any of the three heterodimers. There was an inverse association between the presence and levels of HER2 heterodimers and hormone receptor expression in HER2+ tumours. Tumours exhibiting high levels of HER2 heterodimers demonstrated aggressive clinicopathological features and poor outcome. In the HER2+ cases, dimerisation with EGFR and HER3 but not with HER4 showed an association with aggressive features. There was no association between HER2 heterodimers with patient breast cancer-specific survival or recurrence in HER2+ breast cancer in those patients receiving trastuzumab or not. Our results demonstrate that HER2 dimerisation is a complex process that may underlie the biological heterogeneity of HER2 positive tumours and may identify patients suitable for a specific targeted therapy but does not predict patient outcome for those receiving trastuzumab. PLA proved to be a useful tool for detecting, visualising and quantifying the frequency of protein-protein interactions in archival formalin-fixed paraffin-embedded tissue samples.

Identification of key clinical phenotypes of breast cancer using a reduced panel of protein biomarkers

Background:

Breast cancer is a heterogeneous disease characterised by complex molecular alterations underlying the varied behaviour and response to therapy. However, translation of cancer genetic profiling for use in routine clinical practice remains elusive or prohibitively expensive. As an alternative, immunohistochemical analysis applied to routinely processed tissue samples could be used to identify distinct biological classes of breast cancer.

Methods:

In this study, 1073 archival breast tumours previously assessed for 25 key breast cancer biomarkers using immunohistochemistry and classified using clustering algorithms were further refined using naïve Bayes classification performance. Criteria for class membership were defined using the expression of a reduced panel of 10 proteins able to identify key molecular classes. We examined the association between these breast cancer classes with clinicopathological factors and patient outcome.

Results:

We confirm patient classification similar to established genotypic biological classes of breast cancer in addition to novel sub-divisions of luminal and basal tumours. Correlations between classes and clinicopathological parameters were in line with expectations and showed highly significant association with patient outcome. Furthermore, our novel biological class stratification provides additional prognostic information to the Nottingham Prognostic Index.

Conclusion:

This study confirms that distinct molecular phenotypes of breast cancer can be identified using robust and routinely available techniques and both the luminal and basal breast cancer phenotypes are heterogeneous and contain distinct subgroups.

Poly(adenosine diphosphate-ribose) polymerase expression in BRCA-proficient ovarian high-grade serous carcinoma; association with patient survival

SUMMARY

Ovarian cancers with BRCA mutations rely on the alternative DNA repair mechanism of the poly(adenosine diphosphate-ribose) polymerases (PARP)-dependent base excision repair pathway, with a better overall survival and response to chemotherapy, than BRCA1-proficient cases. This can be enhanced further by using PARP inhibitors. Rate of PARP cleavage may have an independent role from BRCA in contributing to response to chemotherapy. We hypothesize that, regardless of BRCA profile, high expression of PARP1 is associated with poor disease outcome and could be used as a biomarker to identify cases that may have a better response to PARP inhibitors. The expressions of BRCA1, PARP1 in its intact and cleaved (C-PARP1) forms were immunohistochemically semiquantified in 174 sporadic high-grade serous carcinoma patients. Association with clinicopathologic variables and survival was analyzed. PARP1 expression was negatively associated with overall survival and progression-free survival in those patients with low BRCA1 profile (P = .04). Analysis of the combined expression of PARP1 and BRCA1 revealed that high expression of PARP1 is associated with poor survival when combined with either high or low BRCA expression. This was reinforced by multivariate analysis showing PARP1 (P = .034) as an independent prognostic factor. A trend toward worse survival was noted with low levels of C-PARP. PARP1 may have an independent role in response to chemotherapy separate from BRCA gene mutation and partly due to reduced PARP cleavage. An approach to exploit PARP expression as a beneficial biomarker to identify patients suitable for PARP inhibitor therapy is suggested.

Lack of expression of the proteins GMPR2 and PPARα are associated with the basal phenotype and patient outcome in breast cancer

Basal-like tumours (BP) are a poor prognostic class of breast cancer but remain a biologically and clinically heterogeneous group. We have previously identified two novel genes PPARα (positive) and GMPR2 (negative) whose expression was significantly associated with BP at the transcriptome level. In this study, using a large and well-characterised series of operable invasive breast carcinomas (1,043 cases) prepared as TMAs, we assessed these targets at the protein level using immunohistochemistry and investigated associations with clinicopathological variables and patient outcome.

RESULTS

Lack of PPARα and GMPR2 protein expression was associated with BP, as defined by the expression of cytokeratin (CK) 5/6 and/or CK14, (p = 0.023, p = 0.001, respectively) or as triple-negative (ER-, PR-, HER2-) phenotype (p < 0.001 for both proteins). Positive expression of both markers was associated ER and PR positive status (p < 0.05) and with the good Nottingham Prognostic Index group (p = 0.012, p < 0.001, respectively). Univariate survival analysis showed an association between lack of expression of PPARα and GMPR2 and poor outcome in terms of shorter disease-free survival and shorter breast cancer-specific survival, respectively. However, multivariate analysis showed that these associations were not independent of other prognostic variables, namely tumour size, grade, and nodal stage. In conclusion, this study demonstrates that loss of expression of GMPR2 and PPARα is associated with BP at the protein level; indicating that they may play a role in carcinogenesis of this molecularly complex and clinically important subtype. Further studies into their relevance in further classification of BP are warranted.

Pathological outcomes in kidney and brain in male Fischer rats given dietary ochratoxin A, commencing at one year of age

Malignant renal carcinoma, manifest in morbid ageing rats, is the striking component of an otherwise silent response after about nine months of exposure to ochratoxin A in the first year of life (daily intake ~100-250 µg/kg body weight). Reasons for the long latency are unclear, as is whether there would be a similar carcinogenic response if toxin exposure started at one year of age. Therefore, 24 male Fischer rats were given 100 µg ochratoxin A as a daily dietary contaminant for 35 weeks from age 50 weeks. Plasma ochratoxin A concentration reached a maximum value of ~8 µg/mL within one month of starting the toxin regimen. No renal carcinomas occurred. Four renal adenomas, two of which were only microscopic, were found among the six rats surviving for 110 weeks. The findings raise new questions about a difference between young adults and mature adults in sensitivity of male rats to the ochratoxin A-induced DNA damage necessary for renal carcinogenesis. A pilot histological study of perfuse-fixed brains of the toxin-treated rats showed no gross abnormalities, correlating with the consistent absence of behavioral or neurological disorders from chronic ochratoxin A exposure regimens in the range 100-250 µg/kg/day during the second half of life. Reasoned questioning concerning ochratoxin A as a neurotoxic mycotoxin is made.

Neurochemical and oedematous changes in 1,3-dinitrobenzene-induced astroglial injury in rat brain from a 1H-nuclear magnetic resonance perspective

1,3-Dinitrobenzene (1,3-DNB), an intermediate used in the chemical industry, has toxic effects in the brain and testes. It produces focal lesions with marked astroglial necrosis in the rat brain upon repeated administration. Astrocytic death occurs in parallel with elevated local blood flow and is followed by damage to the cerebral vasculature and neurones. (1)H-nuclear magnetic resonance spectroscopic analysis before the onset of astrocytic damage, showed a global elevation of lactate, whereas choline containing compounds increased in the non-vulnerable cerebral cortex, yet decreased in the vulnerable brainstem. Similarly, glutamate increased in the cerebral cortex, cerebellum and midbrain, but decreased in the susceptible brainstem. In vivo T2-weighted NMR imaging showed high signal intensities in brain nuclei shown to develop astroglial loss by conventional neuropathology at 24 hours after completion of dosing, but not at 6-10 hours. Hence the early neurochemical changes in susceptible areas contribute to the aetiology of degeneration, and those seen elsewhere may represent adaptive responses dependent on the particular phenotype of different cell groups and underlying metabolic relationships.

Microglial activation and increased synthesis of complement component C1q precedes blood-brain barrier dysfunction in rats

A reliable way to visualise the state of microglial activation is to monitor the microglial gene expression profile. Microglia are the only CNS resident cells that synthesise C1q, the recognition sub-component of the classical complement pathway, in vivo. C1q biosynthesis in resting ramified microglia is often low, but it increases dramatically in activated microglia. In this study, the expression of C1q was used to monitor microglial activation at all stages of 3-chloropropanediol-induced neurotoxicity, a new model of blood-brain barrier (BBB) breakdown. In rats, 3-chloropropanediol produces very focused lesions in the brain, characterised by early astrocyte swelling and loss, followed by neuronal death and barrier dysfunction. Using in situ hybridisation, immunohistochemistry, and real-time RT-PCR, we found that increased C1q biosynthesis and microglial activation precede BBB dysfunction by at least 18 and peak 48 h after injection of 3-chloropropanediol, which coincides with the onset of active haemorrhage. Microglial activation is biphasic; an early phase of global activation is followed by a later phase in which microglial activation becomes increasingly focused in the lesions. During the early phase, expression of the pro-inflammatory mediators interleukin-1beta (IL1beta), tumour necrosis factor alpha (TNFalpha) and early growth response-1 (Egr-1) increased in parallel with C1q, but was restricted to the lesions. Expression of C1q (but not IL1beta, TNFalpha or Egr-1) remains high after BBB function is restored, and is accompanied by late up-regulation of the C1q-associated serine proteases, C1r and C1s, suggesting that microglial biosynthesis of the activation complex of the classical pathway may support the removal of cell debris by activation of complement.

Reversible disruption of tight junction complexes in the rat blood-brain barrier, following transitory focal astrocyte loss

Breakdown of the blood-brain barrier is a feature of acute and chronic neurodegenerative changes, yet the relationship between astrocytes and the mature barrier remains unclear. We studied this role of astrocytes in vivo using a gliotoxin and evaluated changes in three vascular tight junction markers. Male Fisher F344 rats given systemic 3-chloropropanediol showed astrocytic loss in the inferior colliculus from 12-24 h until the lesion was repopulated 8-28 days later. Within 6 h of astrocyte loss, microvessels in this area began to demonstrate a loss of the normal paracellular localization of the transmembrane proteins occludin and claudin-5 and cytoplasmic zonula occludens-1, which correlated with focal vascular leak of dextran (10 kDa) and fibrinogen. Platelet endothelial adhesion molecule-1 staining revealed that there was no loss of the endothelial lining. Between 4-8 days, severe downregulation of tight junction protein expression was observed, which subsequently returned over the same time period as astrocytes repopulated the lesion. Unexpectedly, dextran and fibrinogen leak from vessels had ceased at 6 days, well before the return of occludin and claudin-5 to appropriate paracellular domains. Control nonvulnerable cortical tissue showed no change in astrocyte morphology and tight junction expression over the same time course. Our data supports a primary role for astrocytic contact in the expression of occludin, claudin-5, and zonula occludens-1 in the mature brain vasculature in vivo. However, barrier integrity to dextran (10 kDa) and fibrinogen can be restored in the absence of astrocytes and tight junction proteins (occludin, claudin-5, and zonula occludens-1).

Focal astrocyte loss is followed by microvascular damage, with subsequent repair of the blood-brain barrier in the apparent absence of direct astrocytic contact

Blood-brain barrier (BBB) breakdown is a feature of cerebral ischaemia, multiple sclerosis, and other neurodegenerative diseases, yet the relationship between astrocytes and the BBB integrity remains unclear. We present a simple in vivo model in which primary astrocyte loss is followed by microvascular damage, using the metabolic toxin 3-chloropropanediol (S-alpha-chlorohydrin). This model is uncomplicated by trauma, ischaemia, or primary immune involvement, permitting the study of the role of astrocytes in vascular endothelium integrity, maintenance of the BBB, and neuronal function. Male Fisher F344 rats given 3-chloropropanediol show astrocytic damage and death at 4-24 h in symmetrical brainstem and midbrain nuclear lesions, while neurons show morphological changes at 24-48 h. Fluorescent 10 kDa dextran tracers show the BBB leaking from 24 h, progressing to petechial haemorrhage after 48-72 h, with apparent repair after 6 days. BBB breakdown, but not the earlier astrocytic death, is accompanied by a delayed increase in blood flow in the inferior colliculus. An ED1 inflammatory response develops well after astrocyte loss, suggesting that inflammation may not be a factor in starting BBB breakdown. This model demonstrates that the BBB can self-repair despite the apparent absence of direct astrocytic-endothelial contact. The temporal separation of pathological events allows pharmacological intervention, and the mild reversible ataxia permits long-term survival studies of repair mechanisms.

The dynamics of blood-brain barrier breakdown in an experimental model of glial cell degeneration

This study was undertaken to investigate the dynamics of blood-brain barrier breakdown in an in vivo rat model of selective CNS vulnerability. 1,3-Dinitrobenzene was used to induce rapid glial degeneration in highly defined areas of the brainstem. Leakage of fluorescent dextran was used to demonstrate the breakdown of the blood-brain barrier, and antibodies to glial and neuronal specific proteins to assess the accompanying cell changes. Beginning 18 h after a toxic dose of dinitrobenzene and before loss of glial ensheathment, a sub-population of blood vessels became permeable to fluorescent dextrans below 500,000 mol. wt in size. By 24h most macroglial cells had been lost from within susceptible areas and vascular leakage had reached peak levels. Macrophage invasion was detected three days following dinitrobenzene. Vessels continued to leak up to four days after the lesion was formed, but by six days blood-brain barrier integrity was largely re-established. Multiple tracer injections over time demonstrated that a single sub-population of vessels was leaking during the experimental period. From these findings we conclude that blood-brain barrier breakdown in this model system is highly selective, graded in extent and molecular weight specificity and not a direct consequence of astrocyte degeneration or microglial activation. This system could be useful in modeling human CNS pathological processes with a vascular component and for understanding in vivo glial blood-brain barrier interactions.

Pharmacokinetic factors and concentration-time threshold in m-dinitrobenzene-induced neurotoxicity

m-Dinitrobenzene is a multitarget toxicant. This study presents a concentration-time threshold model in m-dinitrobenzene (m-DNB)-induced neurotoxicity in F344 rats based on pharmacokinetic modeling and variable duration infusions with neuropathological end points. Pharmacokinetic parameters for m-DNB were determined after giving a single i.v. dose of 10 mg/kg m-DNB. Time dependency of the brain lesions was studied by either giving a single bolus i.v. dose of 30 mg/kg m-DNB or infusing this dose over 6, 12, or 24 h, or 2, 4, 6, 8, or 14 days. The results show that the 6-day infusion, in which the theoretical steady-state blood concentration was 2.0 microM, caused brain damage, whereas the 8- and 14-day infusions, in which the steady-state blood concentrations were 1.5 and 0.8 microM, respectively, did not induce apparent brain damage. When this dose was infused over 6 h, the peak blood concentration of m-DNB was 35 microM and the time (T(m)) for which m-DNB exceeded the 2-microM concentration threshold was 18.8 h, but no brain damage was observed. However, when the same total dosage was infused over periods of either 12 or 24 h, or 2, 4, or 6 days, the theoretical blood concentrations were from 21.9 to 2.0 microM and the T(m) was from 22. 7 to 144 h, and brain damage was produced. Hence a T(m) of 22.7 h was considered to be the time threshold for m-DNB-induced brain damage. It is concluded that a high concentration alone does not result in m-DNB-induced neurotoxicity and that in addition to a concentration threshold, there also exists a time threshold. Both apparently need to be exceeded before neurotoxicity is seen.

Glutathione depletion increases brain susceptibility to m-dinitrobenzene neurotoxicity

To test the hypothesis that glutathione (GSH) status in brain tissue plays an important role in the selective neurotoxicity of m-dinitrobenzene (DNB), the sensitivity to intoxication of three groups of male F344 rats were studied and correlated with brain tissue GSH levels. In Group I were young 6-8 week old rats with normal GSH levels, and in Group II were rats of the same age whose brain GSH levels had been reduced by intracerebroventricular (i.c.v.) injections of L-buthionine-[S,R]-sulfoximine (BSO), an inhibitor of gamma-glutamylcysteine synthetase. In Group III were 6 month old rats that, as a result of normal aging, show GSH levels of 16-29% below those seen in younger animals. All three groups were subjected to a 1 to 4 dose schedule of dosing with DNB (7.5 mg/kg/day i.p.) and killed 1 day after the last dose of DNB. It was found that whereas Group I animals developed ataxia and brain stem lesions after 4 doses, Group III animals showed these changes after 3 doses, while Group II animals had brain stem lesions after only 2 doses of DNB. The timing of the onset of these changes correlated closely with the degree of reduction of brain tissue levels of GSH, this being greatest in those animals infused i.c.v. with BSO. This demonstration indicates that GSH status in brain tissue is likely to be an important factor in determining regional sensitivity to gliovascular damage from this agent.

The effect of 1,3-dinitrobenzene on the functioning of the auditory pathway in the rat

1,3-Dinitrobenzene (DNB) has previously been shown to be neuropathic, causing gliovascular lesioning in the rat brainstem, with the nuclei of the auditory pathway being particularly affected. Lesion severity was shown to be dependent on functional activity, which could be markedly decreased within one pathway by monaurally reducing sensory input. The aim of this study was to characterise the changes in electrophysiological and vascular function associated with this asymmetric lesioning. Depth electrodes located in the inferior colliculi were used to measure wave II and IV of the auditory evoked response (AER) and collicular blood flow. These were measured up to eight days after DNB exposure in rats, in which preexisting reduction in sensory input in one ear was achieved by tympanic membrane rupture. Significant increases of between 14-27 dB were seen in the mean stimulus level required to generate a 50% isoamplitude response for wave IV in the intact (ie vulnerable) pathway over days 1-8 post DNB. No significant changes in this response for the other AER waves were seen over the same recording period. Significant increases in blood flow were seen in the inferior colliculi up to 24 hours after the final dose of DNB. Differences in increased flow between the colliculi were also highly significant, with peak increases of 200% and 80% seen in the intact and protected sides respectively. This difference shows that DNB enhanced blood flow appears to reflect the severity of the DNB induced functional deficit. In both cases, disturbance to normal glial function in maintaining K+ homeostasis, may underlie the neurophysiological deficit and the increase in blood flow seen at the level of the inferior colliculi. These asymmetric functional changes were also parallelled by the differential lesion severity between the protected and unprotected pathways. Hence, protection against DNB glial lesion severity by reduction in sensory input, and consequently metabolic demand, is paralleled by the early vascular response and functional neuronal deficit seen over the eight day post DNB recording period.

Neurotoxic potential of gadodiamide after injection into the lateral cerebral ventricle of rats

PURPOSE

Results of a previous report showed that, if administered by intraventricular injection to access tissue normally protected by the blood-brain barrier, gadopentetate dimeglumine produced acute excitation, persistent ataxia, and widespread brain lesions in rats at 5-micromol/g brain but not at 3.8-micromol/g brain. The present study using gadodiamide was undertaken to see whether the effects were agent-specific.

METHODS

Rats, surgically prepared with a lateral ventricular cannula, were administered a slow injection at 2 microL/min of gadodiamide into the lateral ventricle, and behavioral and neuropathologic changes were noted.

RESULTS

Both gadodiamide and gadopentetate dimeglumine produced focal and generalized myoclonus over several hours. Gadodiamide did not produce the medium-term tremor or persistent ataxia seen after treatment with gadopentetate dimeglumine. Neuropathologic changes developed over 1 to 3 days and took three distinct forms: vacuolated thalamic lesions closely resembling those produced by gadopentetate dimeglumine; small but similar vacuolated symmetrical caudate lesions not produced by gadopentetate dimeglumine; and severe swelling and astrocytic hypertrophy and hyperplasia in the cerebellar vermis, again not produced by gadopentetate dimeglumine. Unlike gadopentetate dimeglumine, gadodiamide produced no spinal cord lesions. The cerebellar changes were seen at 1.25-micromol/g brain and above, behavioral changes at 2.5-micromol/g brain and above, and thalamic and caudate lesions at 10-micromol/g brain, the maximal dose used. Markedly reducing the rate of injecting the same volume over 28 hours prevented the acute excitation but did not reduce the severity of the morphologic effects.

CONCLUSION

The acute excitatory effects of high intraventricular doses of gadopentetate dimeglumine and gadodiamide are similar and appear to be attributable to local action at the infusion site, but differences exist between the two agents in the character and topography of the distant morphologic changes. The cerebellum was the brain area most sensitive to gadodiamide in this experimental model. It is unlikely that gadodiamide would gain access to the brain at these tissue doses when used intravenously for conventional clinical imaging, but our experimental model suggested that it had some unexpectedly specific neuropathologic potential.

Neuropathy target esterase: immunolocalization to neuronal cell bodies and axons

Determination of the molecular mechanisms involved in organophosphate-induced axonopathy may help to elucidate those involved in normal axonal maintenance and in other neurodegenerative conditions. In this study we aimed to define the cellular distribution of neuropathy target esterase, the primary target protein for neuropathic organophosphates. A synthetic peptide corresponding to the sequence of a proteolytic fragment of neuropathy target esterase purified from chicken brain was used to raise a rabbit antiserum designated R28. The antiserum was shown by immunoprecipitation and western blotting of brain extracts to react with a polypeptide of the expected molecular size (155,000 mol. wt); this reaction was blocked by preincubating the antiserum with the immunizing peptide. Prominent intracellular immunostaining by R28 was seen in neuronal cell bodies and, in some cases, proximal axon segments in frozen sections of chicken brain cortex, optic tectum, cerebellum, spinal cord, and dorsal root ganglia. Cells with glial morphology were not immunostained, neither were normal sciatic nerve or motor end plates. However, 8-12 h following sciatic nerve ligation, immunoreactive material was seen to accumulate both proximal and, to a lesser extent, distal to the ligature, indicating that neuropathy target esterase undergoes fast axonal transport. No gross qualitative or quantitative changes in the above pattern of neuropathy target esterase immunoreactivity were detected in tissue obtained from chickens one or three days following treatment with a neuropathic organophosphate. The presence of neuropathy target esterase in essentially all neurons indicates that the selective vulnerability of long axons to neuropathic organophosphates is dependent on factors additional to the presence of the target protein.

The effects of the tremorgenic mycotoxin penitrem A on the rat cerebellum

Within 10 minutes of intraperitoneal injection of penitrem A (3 mg/kg), rats develop severe generalized tremors and ataxia that persist for up to 48 hours. These are accompanied by a three- to fourfold increase in cerebellar cortical blood flow. Mitochondrial swelling occurs in cerebellar stellate and basket cells within 30 minutes of dosing and persists for more than 12 hours without leading to cell death. From 2 hours, Purkinje cell dendrites show early cytoplasmic condensation accompanied by fine vacuolation of smooth endoplasmic reticulum and enlargement of perikaryal mitochondria. From 6 hours, many Purkinje cells develop intense cytoplasmic condensation with eosinophilia that resembles "ischemic cell change," and from 12 hours, many other Purkinje cells show marked watery swelling. Astrocytes begin to swell from 0.5 hours after injection and show hypertrophy of organelles from 6 hours. Also from 6 hours onward, discrete foci of necrosis appear in the granule cell layer, while permeability of overlying meningeal vessels to horseradish peroxidase becomes evident at 8 hours. All changes are more severe in vermis and paravermis. Despite widespread loss of Purkinje cells, the animals' behavior becomes almost normal within a week. While tremor occurs with doses of 1.5 and 0.5 mg/kg, cellular damage is minimal. The tremor mechanism differs from that of harmaline since destruction of inferior olivary nuclei abolishes neither the tremor response to penitrem A nor the cellular damage. No morphological changes are found in other brain regions. The affinities of penitrem A for high-conductance calcium-dependent potassium channels and for gamma-aminobutyric acid receptors with the probability of resultant excitotoxity are considered to be important underlying factors for these changes.

Selective damage to the cerebellar vermis in chronic alcoholism: a contribution from neurotoxicology to an old problem of selective vulnerability

The curiously consistent localization of cerebellar cortical damage in chronic alcoholism is re-evaluated in the light of selective damage, with a similar topography in the cerebellar vermal region, in superficial siderosis in man and in experimental animals exposed to certain toxic substances. Attention is drawn to the capacity for Purkinje cell dendrites and Bergmann glia to extract materials from the CSF, and to the close anatomical relationships of the susceptible lobules I-II, IX and X to the roof of the IVth ventricle and to the cistern of the great cerebral veins. This restriction of damage to vermis and paravermis may reflect some compartmentalization of CSF flow within leptomeninges, consistently increasing exposure of these cerebellar surfaces to materials circulating in the CSF. In other circumstances when this pattern of damage is encountered it raises the question as to whether other environmental agents, gaining access to the CSF, may be similarly distributed.

Increasing or decreasing nervous activity modulates the severity of the glio-vascular lesions of 1,3-dinitrobenzene in the rat: effects of the tremorgenic pyrethroid, Bifenthrin, and of anaesthesia

To test the hypothesis that altered neuronal activity may influence the extent and severity of the glio-vascular lesions produced by 1,3-dinitrobenzene (DNB), rats were either given the tremorgenic pyrethroid, Bifenthrin, or anaesthetised during various dosing schedules of DNB. When compared with controls dosed only with DNB, Bifenthrin tremor made both the ataxia and other functional effects caused by DNB more pronounced. Lesions in the brain stem were made significantly more severe and widespread across three dose levels of DNB. Centres such as facial nuclei, motor nuclei of fifth nerve, subthalamic nuclei and mamillary bodies, not damaged by DNB alone, were also affected in some animals. In contrast, general anaesthesia by either isoflurane ur urethane decreased the severity of the lesions, this being more pronounced with urethane. The character of the tissue changes, however, was not altered by these additional procedures. These findings support the suggestion that neuronal activity is one important determinant of the selective vulnerability of sensitive brain stem nuclei to glio-vascular damage from DNB intoxication.

Neurotoxic effects of gadopentetate dimeglumine: behavioral disturbance and morphology after intracerebroventricular injection in rats

PURPOSE

To determine the neurotoxic potential of gadopentetate dimeglumine in an animal model that allowed the agent to avoid the blood-brain barrier. Gadopentetate dimeglumine is known to produce functional changes when injected into the cerebrospinal fluid, and we hypothesized that such changes might be associated with morphologic damage.

METHODS

Conscious rats, surgically prepared with a lateral ventricular cannula, were given a slow injection of gadopentetate dimeglumine into the lateral ventricle, and behavioral and neuropathologic changes were noted.

RESULTS

Gadopentetate dimeglumine produced signs of acute neurotoxicity over several hours (stereotyped movements and myoclonus), medium-term signs over several days (ataxia and tremor), and neuropathologic changes over 24 hours, with reactive changes persisting for 42 days. All of the above were dose-dependent over the range of 2.5 to 15 mumol/g brain. The lowest dose producing morphologic or behavioral changes was 5 mu mol/g brain. Iso-osmotic, isovolumetric injections of sucrose produced no such effects. Focal lesions occurred within the thalamus, brain stem, and spinal cord, with necrosis of glia, loss of myelin, and, usually, sparing of neurons and nerve fibers. Persisting ataxia was always associated with brain stem or spinal cord lesions.

CONCLUSION

Intraventricular administration of contrast medium allows toxicity to be evaluated in areas such as the spinal cord that are not accessible by osmotic opening. While it is unlikely that these toxic effects would be seen at the doses used for clinical imaging by the intravenous route, gadopentetate dimeglumine clearly has some neurotoxic and neuropathologic potential. Although the acute excitation could be attributed to a transiently high local concentration of the agent at the injection site, the lesions were widely distributed through the brain and spinal cord and may reflect a region-specific neurotoxic action, possibly related to central pontine myelinolysis.