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Reply to the letter by reynolds and pearson (J. neurol. sci., 113 (1992) 230–231)
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.Dmrmd ~l the ,\cto~Uogt~ ~;¢ ~ ,'cH,'c~. [ i~ ! i !)U2i 232 233 ,
itJct2 l-]lsevier Science Ptihlishers B . V . A l l l'igh!~ rt ,, '!:~
JNS ~t3894
Letter to the Editor
Reply to the Letter by Reynolds and Pearson (J. Neurol. Sci., 113 (1992) 230-231) M. F l i n t B e a l a n d W a y n e R. M a t s o n Department ~f Neurolo~o,, Massachusetts General Hospital. Boston, M,4, USA (Received 15 June, 1992) (Accepted 10 July, 1992/
Dear Sir, We appreciate the correspondence of Reynolds and Pearson who have astutely found an error in Table 3 of our recent paper describing kynurenic acid concentrations in Huntington's disease cerebral cortex (Beal et al. 1992). They correctly pointed out that the values for serotonin and 5-hydroxyindoleacetic acid were exceptionally low in caudate. On review of the standard, sample and data table structure of the study we have found a file recognition error in the final table merging. In the analytical design duplicate samples were run by two methods with common analytes except for norepinephrine, serotonin, and 5-hydroxyindoleacetic acid. The wet weight corrected files for common analytes were merged and averaged and the single method analytes then merged in a separate macro to create a final report file. The headers for nine of the files (four 5HT, four 5 H I A A and one NE) were misread and imported as raw uncorrected concentrations in n g / m l . Corrected values are shown below. We apologize for missing this error. The true values accord well with those of others in the literature including those of Reynolds and Pearson. The corrected results do show increased serotonin and 5-hydroxyindoleacetic acid in the Huntington's disease samples, however only the serotonin increase in the inferior temporal cortex was significant. Our prior results in the putamen with a larger number of samples are in accord with those of Reynolds and Pearson in that we found significant increases in serotonin and 5-hydroxyindoleacetic acid (Beal et al. 1990). We are confident of the analytic validity of our results which were obtained with analyti-
Correspondence to: Dr. M. Flint Beal, D e p a r t m e n t of Neurology, M G H , Harvard Medical School, Fruit Street, Boston, M A 02114, USA.
cal protocols which carefully controlled for:the precision, reproducibility and accuracy of the measurements. Both controls and Huntington's disease samples were run at the same time to insure the validity of comparisons amongst the groups. We agree that other differences between our results and other in absolute numbers may reflect differences in age, agonal state, medications and tissue dissection. One potential difference is that the present study examined brain tissue from advanced grade patients (grade 3 and 4 of the Vonsattel classification), and it included 5 juvenile onset patients who are known to have particularly severe disease, The results of Pearson and Reynolds that 3-hydroxykynurenine is significantly increased in temporal and frontal cortex are of interest (Reynolds and Pearson 1989). The concentrations of 3-hydroxykynurenine which we measured are similar to their measurements. We did find increases in precentral gyrus and Bredmann area 9, however these changes were not significant. The only region in which we found a significant change was the inferior temporal gyrus where 3-hydroxykynurenine was reduced~ They point out that 3-hydroxykynurenine is a neurotoxin, however this resuit has only been shown with I(X) g M concentrations in vitro against a neuronal hybrid cell line (Eastman and Guilarte 1989), which are approximately 2(10 fold greater than the highest tissuc concentrations they have measured. We did not discuss changes in other neurotransmitters in detail in the present paper since the major finding was the reduction in kynurenic acid concentrations in cerebral cortex. Although it is possible that this could exacerbate an excitotoxic process in Huntington's disease, it is also possible that the reductions may reflect a more fundamental defect in energy metabolism in Huntington's disease (Beal 1992). We believe the latter possibility is more likely. We believe our results
233
do provide further valuable evidence for an abnormality in the kynurenine branch of tryptophan metabolism in Huntington's disease. Serotonin
HIAA
Frontal pole AI0 Control 16.3_+ 2.9 HD 12.5_+ 2.4
86.6_+ 8.5 93.9+ 15.4
Inferior temporal A20 Control 6.8_+ 1.4 HD 8.5_+ 2.1
128.1 _+26.5 117.9_+12.5
Middle temporal A21 Control 6.2+ 0.8 HD 9.3+ 0 . 8 " *
77.7_+ ll.5 101.5_+11.3
Caudate Control HD
372.8+40.8 465.9 _+54.2
108.1 _+ 14.2 133.4 + 28.6
** P < 0.01 by Mann-Whitney U test
NE
59.1 -+ 7.2 87.4_+ 16.5
References Beal, M.F. (1992) Does impairment of energy metabolism result in excitotoxic neuronal death in neurodegenerative illnesses? Ann. Neurol., 31: 119-150. Beal, M.F., W.R. Matson, E. Storey, P. Milbury, E.A. Ryan, T. Ogawa and E.D. Bird (1992) Kynurenic acid concentrations are reduced in Huntington's disease cerebral cortex. J. Neurol. Sci., 108: 80-87. Beak M.F., W.R. Matson, K.J. Swartz, P.H. Gamache and E.D. Bird (1990) Kynurenine pathway measurements in Huntington's disease striatum: evidence for reduced formation of kynurenic acid. J. Neurochem., 55: 1327-1339. Eastman, C.L. and T.R. Guilarte, (1989) Cytotoxicity of 3-hydroxykynurenine in a neuronal hybrid cell line. Brain Res., 495: 225231. Reynolds, G.P. and S.J. Pearson (1989) Increased brain 3-hydroxykynurenine in Huntington's disease. Lancet, ii: 979-980.
.Dmrmd ~l the ,\cto~Uogt~ ~;¢ ~ ,'cH,'c~. [ i~ ! i !)U2i 232 233 ,
itJct2 l-]lsevier Science Ptihlishers B . V . A l l l'igh!~ rt ,, '!:~
JNS ~t3894
Letter to the Editor
Reply to the Letter by Reynolds and Pearson (J. Neurol. Sci., 113 (1992) 230-231) M. F l i n t B e a l a n d W a y n e R. M a t s o n Department ~f Neurolo~o,, Massachusetts General Hospital. Boston, M,4, USA (Received 15 June, 1992) (Accepted 10 July, 1992/
Dear Sir, We appreciate the correspondence of Reynolds and Pearson who have astutely found an error in Table 3 of our recent paper describing kynurenic acid concentrations in Huntington's disease cerebral cortex (Beal et al. 1992). They correctly pointed out that the values for serotonin and 5-hydroxyindoleacetic acid were exceptionally low in caudate. On review of the standard, sample and data table structure of the study we have found a file recognition error in the final table merging. In the analytical design duplicate samples were run by two methods with common analytes except for norepinephrine, serotonin, and 5-hydroxyindoleacetic acid. The wet weight corrected files for common analytes were merged and averaged and the single method analytes then merged in a separate macro to create a final report file. The headers for nine of the files (four 5HT, four 5 H I A A and one NE) were misread and imported as raw uncorrected concentrations in n g / m l . Corrected values are shown below. We apologize for missing this error. The true values accord well with those of others in the literature including those of Reynolds and Pearson. The corrected results do show increased serotonin and 5-hydroxyindoleacetic acid in the Huntington's disease samples, however only the serotonin increase in the inferior temporal cortex was significant. Our prior results in the putamen with a larger number of samples are in accord with those of Reynolds and Pearson in that we found significant increases in serotonin and 5-hydroxyindoleacetic acid (Beal et al. 1990). We are confident of the analytic validity of our results which were obtained with analyti-
Correspondence to: Dr. M. Flint Beal, D e p a r t m e n t of Neurology, M G H , Harvard Medical School, Fruit Street, Boston, M A 02114, USA.
cal protocols which carefully controlled for:the precision, reproducibility and accuracy of the measurements. Both controls and Huntington's disease samples were run at the same time to insure the validity of comparisons amongst the groups. We agree that other differences between our results and other in absolute numbers may reflect differences in age, agonal state, medications and tissue dissection. One potential difference is that the present study examined brain tissue from advanced grade patients (grade 3 and 4 of the Vonsattel classification), and it included 5 juvenile onset patients who are known to have particularly severe disease, The results of Pearson and Reynolds that 3-hydroxykynurenine is significantly increased in temporal and frontal cortex are of interest (Reynolds and Pearson 1989). The concentrations of 3-hydroxykynurenine which we measured are similar to their measurements. We did find increases in precentral gyrus and Bredmann area 9, however these changes were not significant. The only region in which we found a significant change was the inferior temporal gyrus where 3-hydroxykynurenine was reduced~ They point out that 3-hydroxykynurenine is a neurotoxin, however this resuit has only been shown with I(X) g M concentrations in vitro against a neuronal hybrid cell line (Eastman and Guilarte 1989), which are approximately 2(10 fold greater than the highest tissuc concentrations they have measured. We did not discuss changes in other neurotransmitters in detail in the present paper since the major finding was the reduction in kynurenic acid concentrations in cerebral cortex. Although it is possible that this could exacerbate an excitotoxic process in Huntington's disease, it is also possible that the reductions may reflect a more fundamental defect in energy metabolism in Huntington's disease (Beal 1992). We believe the latter possibility is more likely. We believe our results
233
do provide further valuable evidence for an abnormality in the kynurenine branch of tryptophan metabolism in Huntington's disease. Serotonin
HIAA
Frontal pole AI0 Control 16.3_+ 2.9 HD 12.5_+ 2.4
86.6_+ 8.5 93.9+ 15.4
Inferior temporal A20 Control 6.8_+ 1.4 HD 8.5_+ 2.1
128.1 _+26.5 117.9_+12.5
Middle temporal A21 Control 6.2+ 0.8 HD 9.3+ 0 . 8 " *
77.7_+ ll.5 101.5_+11.3
Caudate Control HD
372.8+40.8 465.9 _+54.2
108.1 _+ 14.2 133.4 + 28.6
** P < 0.01 by Mann-Whitney U test
NE
59.1 -+ 7.2 87.4_+ 16.5
References Beal, M.F. (1992) Does impairment of energy metabolism result in excitotoxic neuronal death in neurodegenerative illnesses? Ann. Neurol., 31: 119-150. Beal, M.F., W.R. Matson, E. Storey, P. Milbury, E.A. Ryan, T. Ogawa and E.D. Bird (1992) Kynurenic acid concentrations are reduced in Huntington's disease cerebral cortex. J. Neurol. Sci., 108: 80-87. Beak M.F., W.R. Matson, K.J. Swartz, P.H. Gamache and E.D. Bird (1990) Kynurenine pathway measurements in Huntington's disease striatum: evidence for reduced formation of kynurenic acid. J. Neurochem., 55: 1327-1339. Eastman, C.L. and T.R. Guilarte, (1989) Cytotoxicity of 3-hydroxykynurenine in a neuronal hybrid cell line. Brain Res., 495: 225231. Reynolds, G.P. and S.J. Pearson (1989) Increased brain 3-hydroxykynurenine in Huntington's disease. Lancet, ii: 979-980.