1408
which is corrected for the initial dilution. In gross hyperlipidaemia, the initial dilution produces a volume artifact leading to pseudohyponatraemia.’ The less widely available direct ionselective electrode measures sodium in the undiluted specimen, and is free from this artifact. Pseudoeuglycaemia is less well recognised as a complication of hyperlipidaemia. The mechanism may be complex. Because glucose is distributed solely in the aqueous phase, a volume artifact will occur in a similar way to that noted with the measurement of sodium concentration. In addition, as the glucose concentration is assayed by an enzymic spectrophotometric method, the opalescent plasma is likely to cause a photometric inaccuracy leading to a spuriously low measurement. We were unable to use bedside glucose monitoring (Ames Glucometer 2) to assess the effect of therapy because the whole-blood glucose concentrations were persistently low, despite the presence of increased plasma glucose measured from ultracentrifuged samples. The discrepancy was in part related to a dilutional artifact. Other possible mechanisms were coating of the enzymic pad on the test strips with chylomicra and the opalescent plasma, which would both affect the colour change. Pseudoeuglycaemia should be suspected in ketoacidosis if the clinical picture is otherwise suggestive of the diagnosis, especially if there is concurrent hyponatraemia. In such circumstances a bedside reflectance-meter measurement of glucose may give a misleadingly low result. Where bedside results are at variance with the clinical impressions, analysis is essential. Intensive Care Unit, and Department of Chemical and Medicine, Princess Alexandra Hospital, Brisbane Q4102, Australia
Pathology,
L. BALDWIN L. PRICE A. HENDERSON P. HICKMAN R. CUNBO
Masarei PE, KP, JRL. Pseudohyponatraemia. Dwyer hypercholesterolaemia and primary biliary cirrhosis. J Clin Pathol 1989; 42:
1. Hickman
167-71.
Umbilical cord blood progenitor cells for clinical transplantation SiR,—Hows et all have shown by clonogenic assays that the quality and quantity of haemopoietic "stem" cells derived from human umbilical cord (HUC) blood are better for transplantation than those of normal bone marrow. The report opens up fascinating prospects for the banking of HLA-typed HUC blood to facilitate transplantation of patients who lack a family donor. Transplantation of enriched populations of CD34 cells completely restored haemopoiesis in lethally irradiated baboons.2 We have investigated3 HUC blood cells with three-colour flow cytometry. CD34 haemopoietic progenitor cells were subdivided on the basis of the expression of CD33, CD71, and HLA-DR antigens. We identified a mean 3-49 (SD 1-8)% CD34 cells of gradientcentrifuged mononuclear HUC cells in 13 premature and 1-84 (0-8)% in 18 mature newborn babies. This concentration was as high as that from adult bone marrow mononuclear cell preparations (n = 16). Commitment of CD34 cells to the erythroid lineage is characterised by coexpression of the CD71 antigen (transferrin receptor),4 whereas commitment to the myeloid lineage is signalled by appearance of the CD33 antigen.4 The proportion of CD34 cells coexpressing the CD33 antigen in bone marrow (43[20’1]%, n= 16)
was
similar
to
that in HUC blood of 18
term
babies (40 8
[20’1]%). l1’4(5’7,n= 18)% CD34 HUC cells coexpressed CD71. Long-term culture-initiating cells can be characterised by flow cytometry, high CD34, and no or low HLA-DR expression.s Since bone marrow CD34 cells predominantly coexpress high HLA-DR,3there is a small population of these primitive cells. In HUC blood the substantial proportion of 57-1 (20-0)% of lineage-negative CD34 cells expresses no or low HLA-DR, suggesting the presence of a high fraction of long-term cultureinitiating cells. This observation may explain why, on preformed irradiated marrow stroma, both progenitor cell production and the
lifespan of cultures are significantly greater in HUC blood than in bone marrow. Departments of Paediatrics, Pathology, and Gynaecology and Obstetrics, University of Innsbruck, A-6020 Innsbruck, Austria
BERNHARD MEISTER WOLFGANG SPERL MARTIN TÖTSCH OTTO HUTER
JM, Bradley BA, Marsh JCW, et al. Growth of human umbilical-cord blood in long-term haemopoietic cultures. Lancet 1992; 340: 73-76. 2. Berenson RJ, Andrews RG, Bendinger WI, et al. Antigen CD34+ marrow cells engrafted lethally irradiated baboons. J Clin Invest 1988; 81: 951. 3. Bender JG, Unverzagt KL, Walker DE, et al. Identification and comparison of CD34-positive cells and their subpopulations from normal peripheral blood and 1. Hows
bone marrow using multicolor flow cytometry. Blood 1991; 77: 2591. 4.
5.
Terstappen LW, Huang S, Safford M, Landsdorp PM, Loken MR. Sequential generations of hematopoietic colonies derived from single nonlineage-committed CD34 + CD38- progenitor cells. Blood 1991; 77: 1218. Sutherland HJ, Eaves CJ, Eaves AC, Dragowska W, Lansdorp. Characterization and partial purification of human marrow cells capable of initiating long-term hematopoiesis in vitro. Blood 1989; 74: 1563.
Chemicals and human
cancer
SIR,—Dr Melnick (Sept 19,p 724) and DrWard(Oct31,p1104) and their colleagues clarify major misconceptions by Abelson’ about the metabolism and carcinogenicity of butadiene in animals and in man. On the basis of previous reports by Melnick et al, the US Occupational Safety and Health Administration has proposed to lower the occupational exposure standard for butadiene from 1000 ppm to 2 ppm.2 Melnick et al emphasise the importance of prediction of risk in man on the basis of evidence of chemically induced carcinogenicity in laboratory animals and that animal cancer data are very useful for setting exposure standards to protect the general public and specific groups of workers. Abelson3 has attacked the use of data in animals to estimate human risk; seven steps in this process that he claims are used by US regulatory agencies and that he criticised3are commented on here. The metabolism of species most sensitive to carcinogens is regarded as representative of that of man by default, unless there is evidence to the contrary. Differences in species metabolism can be misleading and extrapolations across species involve more than mere consideration of metabolic differences. They should also consider variations in pharmacodynamics-ie, cell and organ sensitivities in different species to the same tissue concentration. For haemopoietic tumours, Dedrick and Morrison’s’ findings indicate that for three cancer chemotherapeutic agents, human beings were significantly more sensitive than rodents on a mg/kg per day basis after correction for pharmacokinetics. Abelson is urging that risk assessments should be based on the metabolism of the animal species that is the least sensitive to the chemical. That would be poor public health policy. One-for-one extrapolation of cancer incidence to man is based on much more than cancer incidence data. Our knowledge of tissue responses is not sufficient to safely assume that man is more or less sensitive than animals. Carcinogenicity for 25-30% of substances known to be human carcinogens was first noted in animals. The pooling of benign and malignant tumour counts is essential because there is strong scientific evidence showing that most benign tumours have the potential to progress to malignant disease S The maximum tolerated dose (MTD) is applied because prediction risk to the 10-3 to 10-6 level in the human population is based on fmdings for only about 50 animals per exposure level. Nevertheless, butadiene-induced cancers arose at doses far below the MTD, and exposures at MTD and lower do not usually cause overt and extant toxicity.6 Because of our limited knowledge of cancer mechanisms, there are no proven models of chemical carcinogenesis. Models are modified routinely to accommodate relevant mechanistic information that is accepted by the scientific community. A 95% confidence limit to estimate human cancer risk is used because of the instability in the estimate of one index, and it is not a true upper limit, but is indicative of an average value once other uncertainties are taken into account, including interindividual variability in man. The upper 95% confidence limit derived from the linearised multistage model used by the Environmental
which is corrected for the initial dilution. In gross hyperlipidaemia, the initial dilution produces a volume artifact leading to pseudohyponatraemia.’ The less widely available direct ionselective electrode measures sodium in the undiluted specimen, and is free from this artifact. Pseudoeuglycaemia is less well recognised as a complication of hyperlipidaemia. The mechanism may be complex. Because glucose is distributed solely in the aqueous phase, a volume artifact will occur in a similar way to that noted with the measurement of sodium concentration. In addition, as the glucose concentration is assayed by an enzymic spectrophotometric method, the opalescent plasma is likely to cause a photometric inaccuracy leading to a spuriously low measurement. We were unable to use bedside glucose monitoring (Ames Glucometer 2) to assess the effect of therapy because the whole-blood glucose concentrations were persistently low, despite the presence of increased plasma glucose measured from ultracentrifuged samples. The discrepancy was in part related to a dilutional artifact. Other possible mechanisms were coating of the enzymic pad on the test strips with chylomicra and the opalescent plasma, which would both affect the colour change. Pseudoeuglycaemia should be suspected in ketoacidosis if the clinical picture is otherwise suggestive of the diagnosis, especially if there is concurrent hyponatraemia. In such circumstances a bedside reflectance-meter measurement of glucose may give a misleadingly low result. Where bedside results are at variance with the clinical impressions, analysis is essential. Intensive Care Unit, and Department of Chemical and Medicine, Princess Alexandra Hospital, Brisbane Q4102, Australia
Pathology,
L. BALDWIN L. PRICE A. HENDERSON P. HICKMAN R. CUNBO
Masarei PE, KP, JRL. Pseudohyponatraemia. Dwyer hypercholesterolaemia and primary biliary cirrhosis. J Clin Pathol 1989; 42:
1. Hickman
167-71.
Umbilical cord blood progenitor cells for clinical transplantation SiR,—Hows et all have shown by clonogenic assays that the quality and quantity of haemopoietic "stem" cells derived from human umbilical cord (HUC) blood are better for transplantation than those of normal bone marrow. The report opens up fascinating prospects for the banking of HLA-typed HUC blood to facilitate transplantation of patients who lack a family donor. Transplantation of enriched populations of CD34 cells completely restored haemopoiesis in lethally irradiated baboons.2 We have investigated3 HUC blood cells with three-colour flow cytometry. CD34 haemopoietic progenitor cells were subdivided on the basis of the expression of CD33, CD71, and HLA-DR antigens. We identified a mean 3-49 (SD 1-8)% CD34 cells of gradientcentrifuged mononuclear HUC cells in 13 premature and 1-84 (0-8)% in 18 mature newborn babies. This concentration was as high as that from adult bone marrow mononuclear cell preparations (n = 16). Commitment of CD34 cells to the erythroid lineage is characterised by coexpression of the CD71 antigen (transferrin receptor),4 whereas commitment to the myeloid lineage is signalled by appearance of the CD33 antigen.4 The proportion of CD34 cells coexpressing the CD33 antigen in bone marrow (43[20’1]%, n= 16)
was
similar
to
that in HUC blood of 18
term
babies (40 8
[20’1]%). l1’4(5’7,n= 18)% CD34 HUC cells coexpressed CD71. Long-term culture-initiating cells can be characterised by flow cytometry, high CD34, and no or low HLA-DR expression.s Since bone marrow CD34 cells predominantly coexpress high HLA-DR,3there is a small population of these primitive cells. In HUC blood the substantial proportion of 57-1 (20-0)% of lineage-negative CD34 cells expresses no or low HLA-DR, suggesting the presence of a high fraction of long-term cultureinitiating cells. This observation may explain why, on preformed irradiated marrow stroma, both progenitor cell production and the
lifespan of cultures are significantly greater in HUC blood than in bone marrow. Departments of Paediatrics, Pathology, and Gynaecology and Obstetrics, University of Innsbruck, A-6020 Innsbruck, Austria
BERNHARD MEISTER WOLFGANG SPERL MARTIN TÖTSCH OTTO HUTER
JM, Bradley BA, Marsh JCW, et al. Growth of human umbilical-cord blood in long-term haemopoietic cultures. Lancet 1992; 340: 73-76. 2. Berenson RJ, Andrews RG, Bendinger WI, et al. Antigen CD34+ marrow cells engrafted lethally irradiated baboons. J Clin Invest 1988; 81: 951. 3. Bender JG, Unverzagt KL, Walker DE, et al. Identification and comparison of CD34-positive cells and their subpopulations from normal peripheral blood and 1. Hows
bone marrow using multicolor flow cytometry. Blood 1991; 77: 2591. 4.
5.
Terstappen LW, Huang S, Safford M, Landsdorp PM, Loken MR. Sequential generations of hematopoietic colonies derived from single nonlineage-committed CD34 + CD38- progenitor cells. Blood 1991; 77: 1218. Sutherland HJ, Eaves CJ, Eaves AC, Dragowska W, Lansdorp. Characterization and partial purification of human marrow cells capable of initiating long-term hematopoiesis in vitro. Blood 1989; 74: 1563.
Chemicals and human
cancer
SIR,—Dr Melnick (Sept 19,p 724) and DrWard(Oct31,p1104) and their colleagues clarify major misconceptions by Abelson’ about the metabolism and carcinogenicity of butadiene in animals and in man. On the basis of previous reports by Melnick et al, the US Occupational Safety and Health Administration has proposed to lower the occupational exposure standard for butadiene from 1000 ppm to 2 ppm.2 Melnick et al emphasise the importance of prediction of risk in man on the basis of evidence of chemically induced carcinogenicity in laboratory animals and that animal cancer data are very useful for setting exposure standards to protect the general public and specific groups of workers. Abelson3 has attacked the use of data in animals to estimate human risk; seven steps in this process that he claims are used by US regulatory agencies and that he criticised3are commented on here. The metabolism of species most sensitive to carcinogens is regarded as representative of that of man by default, unless there is evidence to the contrary. Differences in species metabolism can be misleading and extrapolations across species involve more than mere consideration of metabolic differences. They should also consider variations in pharmacodynamics-ie, cell and organ sensitivities in different species to the same tissue concentration. For haemopoietic tumours, Dedrick and Morrison’s’ findings indicate that for three cancer chemotherapeutic agents, human beings were significantly more sensitive than rodents on a mg/kg per day basis after correction for pharmacokinetics. Abelson is urging that risk assessments should be based on the metabolism of the animal species that is the least sensitive to the chemical. That would be poor public health policy. One-for-one extrapolation of cancer incidence to man is based on much more than cancer incidence data. Our knowledge of tissue responses is not sufficient to safely assume that man is more or less sensitive than animals. Carcinogenicity for 25-30% of substances known to be human carcinogens was first noted in animals. The pooling of benign and malignant tumour counts is essential because there is strong scientific evidence showing that most benign tumours have the potential to progress to malignant disease S The maximum tolerated dose (MTD) is applied because prediction risk to the 10-3 to 10-6 level in the human population is based on fmdings for only about 50 animals per exposure level. Nevertheless, butadiene-induced cancers arose at doses far below the MTD, and exposures at MTD and lower do not usually cause overt and extant toxicity.6 Because of our limited knowledge of cancer mechanisms, there are no proven models of chemical carcinogenesis. Models are modified routinely to accommodate relevant mechanistic information that is accepted by the scientific community. A 95% confidence limit to estimate human cancer risk is used because of the instability in the estimate of one index, and it is not a true upper limit, but is indicative of an average value once other uncertainties are taken into account, including interindividual variability in man. The upper 95% confidence limit derived from the linearised multistage model used by the Environmental
